text:
# Photonic Chiral Vortical Effect [CL]

Circularly polarized photons have the Berry curvature in the semiclassical regime. Based on the kinetic equation for such chiral photons, we derive the (non)equilibrium expression of the photon current in the direction of the vorticity. We briefly discuss the relevance of this “photonic chiral vortical effect” in pulsars and rotating massive stars and its possible realization in semiconductors.

N. Yamamoto
Wed, 1 Mar 17
7/67

# The gluon condensation at high energy hadron collisions [CL]

We report that the saturation/CGC model of gluon distribution is unstable under action of the chaotic solution in a nonlinear QCD evolution equation, and it evolves to the distribution with a sharp peak at the critical momentum. We find that this gluon condensation is caused by a new kind of shadowing-antishadowing effects, and it leads to a series of unexpected effects in high energy hadron collisions including astrophysical events. For example, the extremely intense fluctuations in the transverse-momentum and rapidity distributions of the gluon jets present the gluon-jet bursts; a sudden increase of the proton-proton cross sections may fill the GZK suppression; the blocking QCD evolution will restrict the maximum available energy of the hadron-hadron colliders.

W. Zhu and J. Lan
Thu, 9 Feb 17
58/67

Comments: 45 pages, 19 figures, to be published in Nucl. Phys. B

# Neutron Stars in the Laboratory [HEAP]

Neutron stars are astrophysical laboratories of many extremes of physics. Their rich phenomenology provides insights into the state and composition of matter at densities which cannot be reached in terrestrial experiments. Since the core of a mature neutron star is expected to be dominated by superfluid and superconducting components, observations also probe the dynamics of large-scale quantum condensates. The testing and understanding of the relevant theory tends to focus on the interface between the astrophysics phenomenology and nuclear physics. The connections with low-temperature experiments tend to be ignored. However, there has been dramatic progress in understanding laboratory condensates (from the different phases of superfluid helium to the entire range of superconductors and cold atom condensates). In this review, we provide an overview of these developments, compare and contrast the mathematical descriptions of laboratory condensates and neutron stars and summarise the current experimental state-of-the-art. This discussion suggests novel ways that we may make progress in understanding neutron star physics using low-temperature laboratory experiments.

V. Graber, N. Andersson and M. Hogg
Mon, 24 Oct 16
6/53

# Detecting continuous gravitational waves with superfluid $^4$He [CL]

Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high $Q$-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For reasonable experimental parameters, we find that strain fields on the order of $h\sim 10^{-23} /\sqrt{\rm Hz}$ are detectable. We show that the proposed system can significantly improve the limits on gravitational wave strain from nearby pulsars within a few months of integration time.

S. Singh, L. Lorenzo, I. Pikovski, et. al.
Fri, 17 Jun 16
65/65

# On the Detectability of Light Dark Matter with Superfluid Helium [CL]

We show that a two-excitation process in superfluid helium, combined with sensitivity to meV energy depositions, can probe dark matter down to the ~keV warm dark matter mass limit. This mass reach is three orders of magnitude below what can be probed with ordinary nuclear recoils in helium at the same energy resolution. The kinematics of the process requires the two athermal excitations to have nearly equal and opposite momentum, potentially providing a built-in coincidence mechanism for controlling backgrounds.

K. Schutz and K. Zurek
Fri, 29 Apr 16
11/57

# Half-quantized Non-Abelian Vortices in Neutron $^3P_2$ Superfluids inside Magnetars [CL]

We point out that half-quantized non-Abelian vortices exist as the minimum energy states in rotating neutron $^3P_2$ superfluids in the inner cores of magnetars with magnetic field greater than $3 \times 10^{15}$ Gauss, while they do not in ordinary neutron stars with smaller magnetic fields. One integer vortex is split into two half-quantized vortices. The number of vortices is about $10^{19}$ and they are separated at about $\mu$m in a vortex lattice for typical parameters, while the vortex core size is about 10-100 fm. They are non-Abelian vortices characterized by non-Abelian first homotopy group, and consequently when two vortices corresponding to non-commutative elements collide, a rung vortex must be created between them, implying the formation of an entangled vortex network inside the cores of magnetars. We find the spontaneous magnetization in the vortex core showing anti-ferromagnetism whose typical magnitude is about $10^{8-9}$ Gauss that is ten times larger than that of integer vortices, when external magnetic fields are present along the vortex line.

K. Masuda and M. Nitta
Wed, 24 Feb 16
23/48

# CO2 hydrate dissociation at low temperatures – formation and annealing of ice Ic [CL]

Dissociation of gas hydrates below 240 K leads to the formation of a metastable form of water ice, so called cubic ice (Ic). Through its defective nature and small particle size the surface film composed of such material is incapable of creating any significant diffusion barrier. Above 160 K, cubic ice gradually transforms to the stable hexagonal (Ih) form on laboratory time scales. The annealing, coupled with a parallel decomposition of gas hydrates, accelerates as temperature rises but already above 190 K the first process prevails, transforming cubic stacking sequences in-to ordinary Ih ice within a few minutes. Remaining stacking faults are removed through very slow isothermal annealing or after heating up above 240 K. The role of the proportion of cubic stacking on the decomposition rate is discussed. A better understanding of the dissociation kinetics at low temperatures is particularly im-portant for the critical evaluation of existing hypotheses that consider clathrates as a potential medium that actively participate in geological processes or is able to store gases (e.g. CH4, CO2 or Xe) in environments like comets, icy moons (i. e. Titan, Europa, Enceladus) or on Mars. Here, we present kinetics studies on the dissociation of CO2 clathrates at isothermal and isobaric conditions between 170 and 190K and mean Martian surface pressure. We place special attention to the formed ice and demonstrate its influence on the dissociation rates with a combination of neutron diffraction studies (performed on D20 at ILL/Grenoble) and cryo-SEM. More detailed crystallo-graphic information has been acquired via a flexible stacking-fault model capable of revealing the time evolution of the defect structure of ice Ic in terms of stacking probabilities and crystal size.

A. Falenty, T. Hansen and W. Kuhs
Wed, 28 Oct 15
57/79

Comments: Unpublished contribution to the 7th International Conference on Gas Hydrates (ICGH-7), Edinburgh, UK, 17-21 July 2011 (was only available to the conference participants)

# A Dark Matter Superfluid [CEA]

In this talk we present a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures, which we briefly discuss. Remarkably the critical temperature and equation of state of the dark matter superfluid are similar to those of known cold atom systems. Identifying a precise cold atom analogue would give important insights on the microphysical interactions underlying DM superfluidity. Tantalizingly, it might open the possibility of simulating the properties and dynamics of galaxies in laboratory experiments.

J. Khoury
Tue, 14 Jul 15
39/64

Comments: 8 pages. To appear in the proceedings of the 2015 Rencontres de Moriond, “Gravitation: 100 years after GR”

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# Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure [CL]

We extend the solid-state nudged elastic band method to handle a non-conserved order parameter – in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volume collapse during the pressure-induced transformation in iron – from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface (yet all the atomic and cell degrees of freedom are continuous); the calculated pressure jump of 25 GPa is related to the observed 25 GPa spread in measured coexistence pressures arising from martensitic and coherency stresses in samples. Our results agree with experiments, but necessarily differ from those arising from drag and restricted parametrization methods having improperly constrained or uncontrolled degrees of freedom.

N. Zarkevich and D. Johnson
Fri, 5 Jun 15
26/63

# Oscillatory superfluid Ekman pumping in Helium II and neutron stars [CL]

The linear response of a superfluid, rotating uniformly in a cylindrical container and threaded with a large number of vortex lines, to an impulsive increase in the angular velocity of the container is investigated. At zero temperature and with perfect pinning of vortices to the top and bottom of the container, we demonstrate that the system oscillates persistently with a frequency proportional to the vortex line tension parameter to the quarter power. This low-frequency mode is generated by a secondary flow analogous to classical Ekman pumping that is periodically reversed by the vortex tension in the boundary layers. We compare analytic solutions to the two-fluid equations of Chandler & Baym (1986) with the spin-up experiments of Tsakadze & Tsakadze (1980) in helium II and find the frequency agrees within a factor of four, although the experiment is not perfectly suited to the application of the linear theory. We argue that this oscillatory Ekman pumping mode, and not Tkachenko modes provide a natural explanation for the observed oscillation. In neutron stars, the oscillation period depends on the pinning interaction between neutron vortices and flux tubes in the outer core. Using a simplified pinning model, we demonstrate that strong pinning can accommodate modes with periods of days, which are only weakly damped by mutual friction over a timescale of months.

C. Eysden
Tue, 5 May 15
7/51

Comments: 25 pages, 6 figures, submitted to Journal of Fluid Mechanics

# Thermal conductivity of the neutron star crust: A reappraisal [HEAP]

We use classical and quantum Monte Carlo techniques to study the static structure function $S(q)$ of a one-component ion lattice and use it to calculate the thermal conductivity $\kappa$ of high-density solid matter expected in the neutron star crust. We also calculate the phonon spectrum using the dynamic-matrix method and use it to obtain $\kappa$ in the one-phonon approximation. We compare the results obtained with these methods and assess the validity of some commonly used approximations in the literature. We find that quantum effects became relevant for the calculation of $\kappa$ when the temperature $T\lesssim 0.3~\Omega_\mathrm{P}$, where $\Omega_\mathrm{P}$ is the ion plasma frequency. Dynamical information beyond the static structure becomes relevant when $T\lesssim 0.1~\Omega_\mathrm{P}$. We discuss the implications of these findings for calculations of $\kappa$ in multi-component systems and identify strategies for using Monte Carlo techniques in future work.

S. Abbar, J. Carlson, H. Duan, et. al.
Fri, 6 Mar 15
17/51

# Cubic wavefunction deformation of compressed atoms [CL]

We hypothesize that in a non-metallic crystalline structure under extreme pressures, atomic wavefunctions deform to adopt a reduced rotational symmetry consistent with minimizing interstitial space in the crystal. We exemplify with a simple numeric variational calculation that yields the energy cost of this deformation for Helium to 25%. Balancing this with the free energy gained by tighter packing we obtain the pressures required to effect such deformation. The consequent modification of the structure suggests a decrease in the resistance to tangential stress, and an associated decrease of the crystal’s shear modulus. The atomic form factor is also modified. We also compare with neutron matter in the interior of compact stars.

Fri, 13 Feb 15
27/63

Comments: 6 pages, 13 figure files

# The Leading Correction to the Thomas-Fermi Model at Finite Temperature [CL]

The semi-classical approach leading to the Thomas-Fermi (TF) model provides a simple universal thermodynamic description of the electronic cloud surrounding the nucleus in an atom. This model is known to be exact at the limit of $Z\rightarrow\infty$, i.e., infinite nuclear charge, at finite density and temperature. Motivated by the zero-temperature case, we show in the current letter that the correction to TF due to quantum treatment of the strongly bound inner-most electrons, for which the semi-classical approximation breaks, scales as $Z^{-1/3}$, with respect to the TF solution. As such, it is more dominant than the quantum corrections to the kinetic energy, as well as exchange and correlation, which are known to be suppressed by $Z^{-2/3}$. We conjecture that this is the leading correction for this model. In addition, we present a different free energy functional for the TF model, and a successive functional that includes the strongly bound electrons correction. We use this corrected functional to derive a self-consistent potential and the electron density in the atom, and to calculate the corrected energy. At this stage, our model has a built-in validity limit, breaking as the L shell ionizes.

E. Segev and D. Gazit
Tue, 9 Dec 14
55/64

Comments: 5 pages, 4 figures, 1 table

# Iron under pressure: bcc-hcp equilibrium coexistence revisited [CL]

We revisit results from decades of pressure experiments on the bcc – hcp transformations in iron, which are sensitive to non-hydrostatic conditions and sample size. We emphasize the role of martensitic stress in the observed pressure hysteresis and address the large spread in values for onset pressures of the nucleating phase. From electronic-structure calculations, we find a bcc – hcp equilibrium coexistence pressure of 8.4 GPa. Accounting for non-hydrostatic martensitic stress and a stress-dependent transition barrier, we suggest a pressure inequality for better comparison to experiment and observed hysteresis. We construct the equation of state for bcc and hcp phases under hydrostatic pressure, and compare to experiments and previous calculations.

N. Zarkevich and D. Johnson
Mon, 8 Dec 14
20/61

Comments: 9 pages, 1 figure, 199 citations

# Bose-Einstein Condensate strings [CL]

We consider the possible existence of gravitationally bound general relativistic strings consisting of Bose-Einstein Condensate (BEC) matter which is described, in the Newtonian limit, by the zero temperature time-dependent nonlinear Schr{\”}odinger equation (the Gross-Pitaevskii equation), with repulsive inter-particle interactions. In the Madelung representation of the wave function, the quantum dynamics of the condensate can be formulated in terms of the classical continuity equation and the hydrodynamic Euler equations. In the case of a condensate with quartic nonlinearity, the condensates can be described as a gas with two pressure terms, the interaction pressure, which is proportional to the square of the matter density, and the quantum pressure, which is without any classical analogue though, when the number of particles in the system is high enough, the latter may be neglected. By assuming cylindrical symmetry, we analyze the physical properties of the BEC strings in both the interaction pressure and quantum pressure dominated limits, by numerically integrating the gravitational field equations. In this way we obtain a large class of stable string-like astrophysical objects, whose basic parameters (mass density and radius) depend sensitively on the mass and scattering length of the condensate particle, as well as on the quantum pressure of the Bose-Einstein gas.

T. Harko and M. Lake
Tue, 28 Oct 14
56/67

Comments: 18 pages, 16 figures. arXiv admin note: text overlap with arXiv:hep-ph/0504083 by other authors

# Astrophysical Bose-Einstein Condensates and Superradiance [CL]

We investigate gravitational analogue models to describe slowly rotating objects (e.g., dark-matter halos, or boson stars) in terms of Bose-Einstein condensates, trapped in their own gravitational potentials. We begin with a modified Gross-Pitaevskii equation, and show that the resulting background equations of motion are stable, as long as the rotational component is treated as a small perturbation. The dynamics of the fluctuations of the velocity potential are effectively governed by the Klein-Gordon equation of a “Eulerian metric”, where we derive the latter by the use of a relativistic Lagrangian extrapolation. Superradiant scattering on such objects is studied. We derive conditions for its occurence and estimate its strength. Our investigations might give an observational handle to phenomenologically constrain Bose-Einstein condensates.

F. Kuhnel and C. Rampf
Tue, 5 Aug 14
52/61

# Giant Planets [EPA]

We review the interior structure and evolution of Jupiter, Saturn, Uranus and Neptune, and giant exoplanets with particular emphasis on constraining their global composition. Compared to the first edition of this review, we provide a new discussion of the atmospheric compositions of the solar system giant planets, we discuss the discovery of oscillations of Jupiter and Saturn, the significant improvements in our understanding of the behavior of material at high pressures and the consequences for interior and evolution models. We place the giant planets in our Solar System in context with the trends seen for exoplanets.

T. Guillot and D. Gautier
Fri, 16 May 14
32/55

Comments: This chapter has been finished in February 2014 for publication in the second edition of the Treatise on Geophysics. 42 pages, 16 figures

# Rotating analogue black holes: Quasinormal modes and tails, superresonance, and sonic bombs and plants in the draining bathtub acoustic hole [CL]

The analogy between sound wave propagation and light waves led to the study of acoustic holes, the acoustic analogues of black holes. Many black hole features have their counterparts in acoustic holes. The Kerr metric, the rotating metric for black holes in general relativity, has as analogue the draining bathtub metric, a metric for a rotating acoustic hole. Here we report on the progress that has been made in the understanding of features, such as quasinormal modes and tails, superresonance, and instabilities when the hole is surrounded by a reflected mirror, in the draining bathtub metric. Given then the right settings one can build up from these instabilities an apparatus that stores energy in the form of amplified sound waves. This can be put to wicked purposes as in a bomb, or to good profit as in a sonic plant.

Tue, 31 Dec 13
20/49


text:
VASP: TiO₂ surface relaxation¶

This tutorial will teach you how to:

• construct a slab for rutile TiO2(001)
• set up a geometry optimization job with constraints
• set up a DFT+U VASP job to be run via the AMS driver

Step 1: Check the VASP installation¶

Important

VASP is not distributed together with the Amsterdam Modeling Suite, but needs to be obtained and installed separately.

Verify that you have access to a working installation of VASP 5, on either your local or a remote machine. If you want to run on a remote machine or computer cluster, check that you have set up a working AMSjobs queue for that system.

Check that you can run VASP, for example using one of the following commands:

vasp
mpirun -np 4 vasp #parallelize over 4 cores

Step 2: Locate the POTCAR library¶

VASP requires the use of pseudopotentials or PAW potentials for each element. These are distributed with VASP in files called POTCAR or POTCAR.Z.

In this tutorial, you will use the Projector Augmented Wave (PAW) potentials for Ti and O constructed for the PBE density functional. You should have obtained those PAW potentials with VASP.

On your local machine (the machine running AMSinput), locate the needed POTCAR files. If you do not have them, you can download them from the VASP website.

For example, if the needed POTCAR or POTCAR.Z files are at

/some/path/PAW_PBE/Ti/POTCAR
/some/path/PAW_PBE/O/POTCAR

then the path /some/path/PAW_PBE/ would be the POTCAR Library that you need to specify in one of the following steps.

Step 3: Set up the system - a TiO2(001) slab¶

1. Start AMSinput
2. Switch to VASP:
3. In the menu bar, select Edit → Crystal → Tetragonal → Rutile
4. Click OK to get the experimental rutile TiO2 crystal structure unit cell (a = 4.59 Å, c = 2.96 Å).
5. Click Yes when asked whether to map the atoms to the unit cell.

Note

In production calculations, one would normally perform a lattice optimization of the bulk structure before creating a slab. In this tutorial, we will just use the experimental lattice parameters.

Now create a 2-layer (001) slab (because the crystal unit cell contains 2 layers of atoms at different positions along c, the resulting slab will actually be 4 atomic layers thick).

6. Select Edit → Crystal → Generate slab
7. Enter 0 0 1 as the Miller indices.
8. Set the number of layers to 2.
9. Click “Generate slab”.

This should create a 2-layer slab in the 3D area on the left. Select View → View Direction → Along X from the menu bar, or rotate the system so that the z-axis (shown as a blue line) is roughly displayed vertically, giving you a side view of the slab. The slab is 2c = 5.92 Å thick.

Note

• It may happen that bonds are drawn between adjacent Ti ions. These bonds do not affect the VASP calculation and can safely be ignored. If you prefer, you can remove them by clicking on them and pressing Backspace.
• In production calculations, one would normally use a much thicker slab.

All VASP calculations are performed under 3D periodic boundary conditions. Therefore, slabs are necessarily separated by a vacuum gap in the surface normal direction.

10. Click on the Periodic View Tool to visualize a few periodically repeated images of the central cell.

Note that the vacuum gap is very large. Because VASP uses a planewave basis set, a larger vacuum gap will increase the computational cost. Therefore, it is a good idea to use a smaller vacuum gap, but the vacuum gap should not be so small that one side of the slab interacts with the other side through the vacuum gap. Here, we will set a rather small vacuum gap of about 8 Å.

Note

In production calculations, the vacuum gap should be systematically varied for the particular system at hand, and be large enough such that any calculated quantity (surface energy, adsorption energy, work function, etc.) is converged.

11. In the panel bar, select Model → Lattice.
12. Set the components of the c lattice vector to 0.0 0.0 14.0. (Note: this c lattice vector now refers to the slab system including the vacuum gap, and no longer to the original unit cell of the crystal).
13. Click on one of the Ti atoms in the center of the slab to select it. Then, in the menu bar select Edit → Crystal → Set (0.5, 0.5, 0.5). This moves the slab to the center of the vacuum gap, which typically makes visualization easier.
14. Click again on the Periodic View Tool so that only a single periodic image is displayed.
15. In the menu bar, select Edit → Crystal → Map atoms to (0..1). This places all of the atoms inside the displayed unit cell.

Step 4: Set the VASP settings¶

1. In the panel bar, select Main.
2. In Command to execute VASP enter the command to execute VASP (from Step 1).
3. In POTCAR library enter the path to the PBE PAW POTCAR library (from Step 2). This path will be remembered the next time you start AMSinput.

Tip

In the panel bar, select Details → Pseudopotentials to see and/or change exactly which POTCAR files that will be used in the calculation.

4. In the main panel, set the Type of k-point grid to Monkhorst-Pack (default).
5. Set the k-point grid dimensions to 3 3 1.
6. Set the XC Functional to PBE.
7. Set the Planewave energy cutoff to 400 eV (default).
8. Set the Type of smearing to Gaussian (default).
9. Set the Smearing width to 0.1 eV.

Note

In production calculations, the k-point grid dimensions and planewave energy cutoff need to be converged by means of convergence tests.

10. In the panel bar, select Model → Hubbard U.
11. Check the Use DFT+U checkbox.
12. Set Hubbard U-type to 2 (default, the method by Dudarev et al.)
13. Set LMAXMIX to 4.
14. For Ti, set U to 3.0 eV, and l to d (default).
15. For O, set l to Disable.

The main VASP input file, INCAR, allows the user to set an enormous number of settings and have great control over the resulting calculation. AMSinput does not have dedicated panels for all of the settings. Instead, it is possible for you to set arbitrary settings by simply typing them in. In this example, you will change the self-consistent-field algorithm.

16. In the panel bar, select Details → Expert VASP.
17. Type ALGO = Fast in the Additional INCAR options text box.

Tip

On the Details → Expert VASP panel, consider checking the Only preprocess box. When you submit your calculation, VASP will then not be executed, but all of the input files that VASP would have seen will be left on disk for you to inspect. This way, you can double-check that the input to VASP is correct before actually running the calculation.

Step 5: Set the AMS settings¶

1. In the main panel, select Task → Geometry Optimization.
2. Click the button, or in the menu bar select Details → Geometry Optimization.
3. Inspect, but do not change, the convergence criteria.
4. Click the next to Constraints, or in the menu bar select Model → Geometry Constraints and PES Scan.
5. In the molecule drawing area, select the six atoms (2 Ti and 4 O) in the center of the slab, by first clicking on one of them, and subsequently clicking the others while holding Shift.
6. Click the button next to selected atoms (fix positions).
7. In the menu bar, select File → Save, and save your job with the name VASP_PBE_U_TiO2_slab.ams.

Note

When running VASP via the AMS driver, the geometry optimization settings and constraints are set for the AMS driver and not for VASP. This means that VASP’s internal geometry convergence criteria, like the EDIFFG setting in INCAR, should not be set. You also do not need to enable VASP’s “Selective optimization” to keep some atoms fixed. Instead, all geometry optimization settings are handled by the AMS driver.

format: plain


text:
If you open up your copy of ASHRAE Fundamentals, in the chapter on psychrometrics, you’ll see a formula for the total enthalpy of moist air, $$h$$, that takes dry bulb temperature, $$t$$, and the specific humidity ratio, $$W$$ as inputs. The complete formula, in traditional IP units (°F and BTU/lb d.a.), you will see is

$h = 0.24 t + W \left( 1061 + 0.445 t \right)$

When I first came across this, a few question arose in my mind.

1. Where did 0.24, 0.445, and 1061 come from?

2. Why does the term related to water vapor have to have the constant, but the term for the dry air doesn’t?

Let’s first take one step back and look at the previous formula before this one. That formula, plus a few more for clarification, was

$H_{\text{total}} = H_{\text{da}} + H_{ \text{v} }$ $H_{\text{total}} = m_{da} h_{\text{da}} + m_{v} h_{ \text{v} }$

Divide both sides by the mass of the dry air, not total mass, and you get

$h_{\text{total, per lb da}} = h_{\text{da}} + \frac{m_{v}}{m_{da}} h_{\text{v} } = h_{\text{da}} + W h_{\text{v} }$

I’ll have to do another post to explain why we normalize to the mass of the dry air portion only and not the total mass, but you’ll just have to take my word for now that this is a smart thing to do.

So now we can do some pattern matching and know that the $$0.24 t$$ is the $$h_{da}$$ and the $$W \left( 1061 + 0.445 t \right)$$ term is the $$W h_{v}$$ term.

## Dry air portion

Under conditions that HVAC engineers will face, air can be considered as an ideal gas, and in my career, I’ve never faced a situation in which this wasn’t a good assumption. If you went through a thermodynamics course, one consequence of this is that the enthalpy is solely a function of temperature. You also should have learned that enthalpy is not an absolute property, that it requires some datum or reference. It’s analogous to potential energy, where it is the height difference that is important, not some arbitrary absolute height value.

One way to calculate a difference in enthalpy is to use the specific heat, $$c_p$$. For our case, the enthalpy is just a function of temperature only, so

$c_{p} = \frac{ \partial h }{\partial t } = \frac{ \text{d}h }{\text{d} t}$

and

$h_2 - h_1 = \int c_p \; \text{d}t$

It would be awesome if $$c_p$$ would be constant, so that this integral would just be $$c_p$$ multiplied by the change in temperature. So lets check out the actual $$c_p$$ values in our reference text and see what we find:

The values that we are interested in are the three in the upper left hand corner, the $$c_p$$ values for air at 40, 100, and 200°F. Those values are 0.240, 0.240, and 0.241. So we are justified in taking the $$c_p$$ value to be constant in the normal range of temperatures encountered in HVAC.

Cool. We also know that we can set our reference enthalpy to be whatever we’d like. So obviously, we want our calculations with dry bulb temperature in °F to be as easy as possible, so we’ll make the enthalpy 0 at 0°F, so now we have a formula for enthalpy for the dry air portion.

$h_{da} = c_p t = 0.24 t$

## Water vapor portion

Let’s now look at the $$W \left( 1061 + 0.445 t \right)$$ portion.

Based on the dry air portion, it should follow that the 0.445 corresponds to the $$c_p$$ value for water vapor. And from a table in my reference book, this is true.

The $$c_p$$ values of interest are in the third column from the right. The $$t$$ values are in units of °F and the $$c_p$$ values are in units of BTU/lbm-°F, so we are all good there. This table is more granular than the table I posted for air and you can see that there is more variability over the range of 32-200°F than for air, but it’s still a valid assumption to take the $$c_p$$ value to be constant (it ranges from 0.4439 to 0.4506). So the authors decided that they would take a reasonable value for the corresponding temperature, and the value 0.445 was taken. This is the value for a temperature somewhere between 70-80°F, which is a pretty good value to take.

That wasn’t too hard. Now the question that bothered me after this was,

Why can’t we just do the same thing we did for air and make the enthalpy 0 at 0°F and not bring in the constant 1061 term, the formulas that are derived from this would be much simpler.

The short answer to this is that you certainly could, but you are going to quickly run into an issue when you start trying to do energy balances with real life problems.

The difference between the air portion and the water vapor portion is that for air, we are never going to have a phase change, and we are always going to be assuming it behaves as an ideal gas. But for the water portion, we normally are not going to be injecting pure, low-pressure, water vapor into air streams, but rather we are going to be taking out or putting in liquid water. This is a big difference.

Say for example, you are analyzing a cooling coil in which you are condensing liquid water out of the thermodynamic system. You will need to determine an enthalpy for that liquid water flow. How are you going to get this value? You no longer can just use the $$c_p \Delta t$$ formulation because obviously liquid water isn’t an ideal gas, and you have a phase change happening.

So you will turn to your steam tables to look these values up for the liquid water or high pressure steam that no longer can be considered an ideal gas.

What reference state are those enthalpy values taken at? Well, nearly all the references I’ve come across use 32°F or 0°C of saturated liquid water to set the specific internal energy $$u$$ to 0. All enthalpy values are determined from that state.

So, as a warning, if you actually come across a table that doesn’t use this as a reference state, you are going have big problems using this shorthand formula.

We are finally ready to then answer where the 1061 comes from. We want our enthalpy formula to match with the reference state given in most texts. Look at the first row of the steam table posted above for water, and check out the fifth column. The value of $$h$$ in units of BTU/lbm-°F is 1075.5.

So we want a linear relationship, using our $$c_p$$ from before, that makes the enthalpy value equal 1075.5 at 32°F. In mathematical form we are looking for a constant value $$C$$ that makes this relationship true.

$h = C + c_p t$

At 32°F,

$1075.5 = C + 0.445 (32)$ $C = 1075.5 - 0.445 (32) = 1061.3 \approx 1061$

There we have it, the 1061 appears.

Not understanding every part of this bothered me for a while, and I hope this post brings to light why these formulas were created the way they were.


text:
# modules that are both injective projective

• January 5th 2012, 03:58 AM
ymar
modules that are both injective projective
Vector spaces are both projective and injective if the axiom of choice holds. Are there any other modules with this property? Do they have a good characterization?
• January 5th 2012, 11:38 PM
NonCommAlg
Re: modules that are both injective projective
Quote:

Originally Posted by ymar
Vector spaces are both projective and injective if the axiom of choice holds. Are there any other modules with this property? Do they have a good characterization?

there's a characterization of rings over which every module is both projective and injective. these rings are called semisimple and they are in the form $\bigoplus_{i=1}^k M_{n_i}(D_i),$ where $k \geq 1$ is any integer, each $D_i$ is a division ring and $M_{n_i}(D_i)$ is the ring of $n_i \times n_i$ matrices with entries in $D_i.$


text:
# How nice can sets of reals be under $\mathsf{ZF} + \mathsf{BPI}$?

It's well known that the full axiom of choice is not needed to prove the existence of non-measurable subsets of $$\mathbb{R}$$. In particular, the Boolean prime ideal theorem ($$\mathsf{BPI}$$) is sufficient, since non-principle ultrafilters on $$\omega$$, coded as a subset of $$2^\omega$$, are not Lebesgue measurable. They also necessarily fail to be Baire measurable.

That said, they can satisfy a weaker regularity condition. I've convinced myself that under $$\mathsf{ZFC}+\mathsf{CH}$$ if $$\mathcal{F}_0 \subset 2^\omega$$ is a proper filter generated by an $$F_\sigma$$ subset of $$2^\omega$$, then $$\mathcal{F}_0$$ can be extended to an ultrafilter $$\mathcal{F}$$ with the property that for every Borel set $$B \subseteq 2^\omega$$, both $$B \cap \mathcal{F}$$ and $$B \setminus \mathcal{F}$$ have the perfect set property (i.e., are either finite, countable, or have a non-empty perfect subset). I'm not sure about filters generated by Borel sets in general, and I do not know what $$\mathsf{ZFC}$$ entails regarding the question of whether every ultrafilter on $$\omega$$ has this property.

This has lead me to the following question.

Question. Is $$\mathsf{ZF}+\mathsf{BPI}+\text{“Every set of reals has the perfect set property."}$$ consistent?

Looking through Consequences of the Axiom of Choice by Howard and Rubin, it seems like this was open 24 years ago at the very least.


text:
# Does the Labor Theory of Value hold in the long term in competitive markets?

Most criticisms of the Labor Theory of Value I have come across go something like this quote from Carl Menger:

There is no necessary and direct connection between the value of a good and whether, or in what quantities, labor and other goods of higher order were applied to its production. A non-economic good (a quantity of timber in a virgin forest, for example) does not attain value for men since large quantities of labor or other economic goods were not applied to its production. Whether a diamond was found accidentally or was obtained from a diamond pit with the employment of a thousand days of labor is completely irrelevant for its value.

This is perfectly obvious and Marx even mentions this:

A commodity, such as iron, corn, or a diamond, is therefore, so far as it is a material thing, a use value, something useful. This property of a commodity is independent of the amount of labour required to appropriate its useful qualities.

But putting aside the natural resource example for a moment, in the long term in a competitive market isn't it the case that if there is a situation where someone is able to sell something for more than the cost of the labor that went into it, someone else should be able to step in and sell that thing for a lower price? Eventually prices will go down until they are stopped by another constraint. That constraint being the cost of all the labor required to produce the product.

In situations where this doesn't happen isn't it an indication of some anti-competitive force? Monopoly of a natural resource, monopoly of a technology through a patent, externalities that result in a small number of large companies, cooperation between large companies to set prices, etc...

So is it fair to say that in the long term in competitive markets the labor theory of value holds?

If the theory is "at any point in time a commodity is worth as much as the cost of labor that went into it" then it is obviously wrong and I can't imagine any classical economist would have believed it. But if the theory is "over time the cost of a good will tend towards the cost of the amount of labor that went into it assuming the market is competitive" then it still seems plausible.

• Adam Smith: "The value of any commodity ... is equal to the quantity of labour which it enables him to purchase or command. Labour, therefore, is the real measure of the exchangeable value of all commodities. "The real price of every thing, what every thing really costs to the man who wants to acquire it, is the toil and trouble of acquiring it. What every thing is really worth to the man who has acquired it, and who wants to dispose of it or exchange it for something else, is the toil and trouble which it can save to himself, and – user18 Dec 23 '20 at 2:33
• which it can impose upon other people. What is bought with money or with goods is purchased by labor as much as what we acquire by the toil of our own body. That money or those goods indeed save us this toil. They contain the value of a certain quantity of labor which we exchange for what is supposed at the time to contain the value of an equal quantity. Labor was the first price, the original purchase-money that was paid for all things. It was not by gold or by silver, but by labor, that all the wealth of the world was originally purchased; and its value to those – user18 Dec 23 '20 at 2:33
• who possess it and who want to exchange it for some new productions, is precisely equal to the quantity of labor which it can enable them to purchase or command." – user18 Dec 23 '20 at 2:33
• Smith would add many qualifications (sometimes somewhat contradictory). But Smith, Ricardo, Marx, and other classical economists all believed in some version of the LTV. They were certainly confused (as are you) and this confusion was not fully cleared up until the 1870s. – user18 Dec 23 '20 at 2:35
• What happened 1870? Léon Walras and his pioneering 1874 work Elements of Pure Economics – Jesper Hybel Dec 23 '20 at 2:40

No it does not for several reasons. Labor theory of value (LTV) central tenant is that there is some intrinsic component to value determined objectively by labor (see Brue and Grant History of Economic Thought 7ed). This implies that there exist some unit of labor in which every value could be measured. In addition, it means that the value ($$V$$) is some sort of function labor $$L$$ i.e. $$V=f(L)$$. As stated by Adam Smith in Wealth of Nations who first developed the LTV (and as mentioned in the comments as well):

"The value of any commodity ... is equal to the quantity of labour which it enables him to purchase or command. Labour, therefore, is the real measure of the exchangeable value of all commodities.

Hence, at the core of labor theory of value is proposition that all value can be somehow objectively measured by labor, and that it should depend on labor.

Well there are several problems with that proposition:

1. What about things that require great labor inputs but are worthless (which is situation that can and empirically does arise even in competitive markets as preferences and tastes change and something that was once desired might be trash today)?

The LTV actually has no good answer for that. Adam Smith tried to answer this objection by distinguishing between value in use and value in exchange. As Smith further writes in his Wealth of Nations:

The word value, it is to be observed, has two different meanings, and sometimes expresses the utility of some particular object, and sometimes the power of purchasing other goods which the possession of that object conveys. The one may be called "value in use"; the other, "value in exchange." The things which have the greatest value in use have frequently little or no value in exchange; and, on the contrary, those which have the greatest value in exchange have frequently little or no value in use. Nothing is more useful than water: but it will purchase scarce anything; scarce anything can be had in exchange for it. A diamond, on the contrary, has scarce any value in use; but a very great quantity of other goods may frequently be had in exchange for it.

This is basically the argument that Marx repeats (although he had different name for it), as mentioned above (indeed I am always surprised that Marx is often quoted regarding LTV given he did not do virtually any original work on the LTV and just took it from Ricardo and Smith).

The problem with this is that it is already quite scientifically undesirable as it is essentially a cop-out. Labor is the source of value, well, except in cases where it isn't because the object is not useful. So already LTV from the get go admits it is not a theory that can explain all value, which is scientifically undesirable as we want to generalize as much as possible. Now, if we would not have alternative theories of value this could be forgiven but given we do have them and they can explain more this in itself is argument for ditching LTV (e.g. we can safely ditch Newtons theory of gravity in favor of relativity as the latter is more general, but even though theory of relativity can't explain everything we cannot ditch because there is no other competing theory that can).

With regards to your main question, already this point 1 proves that in competitive markets LTV does not need to hold as it is completely valid outcome under perfect competition that value of produced good will be 0 (or indeed even negative like with oil futures).

1. How to measure value in labor (the problem of transformation)?

One of the central tenets of labor theory of value as mentioned above is that labor must be some sort of real measure of value of all commodities. However, due to the problem mentioned in point 1 it is also necessary to argue that value of labor will not correspond exactly to the price.

Hence, this gives raise to the question how to actually establish some correspondence between prices and labor which is also known as the problem of transformation (see Samuelson; 1971). This was in fact a problem that Ricardo devoted considerable amount of time to solve, although he was ultimately unsuccessful. Samuelson argues there is no general solution to the problem, and although there are some scholars claiming to solve it there are no generally accepted solutions.

In regards to your question, assuming competitive market does not provide solution to the above problem and without the above being possible it is very hard to sustain claim that value can be somehow objectively measured by labor.

1. Empirically value seems to be orthogonal on labor inputs and this hold regardless of how competitive industry is.

There simply does not seem to be any relationship between value and labor inputs. Relative prices fluctuate widely even when labor inputs stay same. This can occur both in theoretical models of perfect competition (e.g. consider two perfectly sectors two goods model with some idiosyncratic demand shocks), and frequently occurs in reality.

Now even if there would be a discrepancy between price and the value of labor that went into producing the product, if there is any objective value determined by labor then you would at the very least expect relative prices to depend on relative labor inputs but they do not and there is no indication that they start doing so in competitive industries. Hence $$V \perp L$$.

This also connects to the previous point, but for LTV to hold it is simply not enough to just show that something that was produced with labor is happens to have value - the value of it should depend on labor input and ultimately be measurable. What even more it should be the measuring stick of the value. But this is clearly inconsistent with observation that relative prices change and fluctuate widely even when labor inputs do not.

• Does point 3 mean there is no direct relation or also no indirect relation? Because to me it sounds logical that the amount of labor input is part of the supply and thus indirectly contributes to the value. Like if there is a demand for something and it takes 1 day to make something more people will try to make it then if it takes 1 year to make it. Thus labor input will influence the supply and thus the price. Maybe I'm missing the definition of value, but I thought it would be price in modern economic theories. – Hakaishin Dec 23 '20 at 10:16
• @Hakaishin 1. As the point 3 is not enough to show that labor in some cases influences price. Under LTV there labor must be able to serve as some sort of unit of value and so for example something that takes 2h to make should be twice as valuable than something that takes 1h to make - we do not observe that empirically. 2. Yes value should be closely related to price (although does not need to be exactly equivalent in all cases) - this is already failure of LTV and why modern economics uses subjective theory of value instead - LTV always needs some hot fixes because price does not have any – 1muflon1 Dec 23 '20 at 10:29
• discernible relationship with labor inputs. For example, labor inputs of firms are relatively stable - companies usually do not fire employees at a whim on hourly basis. Yet prices can fluctuate even hourly at commodity markets for example. Even in general markets again usually when people are fired hired it is long process yet stores change prices sometimes daily. So the question is why they do that if labor component of the goods is same. LTV does not have any good answer for that save for saying that they fluctuate due to the value of usefulness- which is already half abandoning the LTV – 1muflon1 Dec 23 '20 at 10:35
• In addition to prices fluctuating relative prices fluctuate as well. The last nail to the coffin is that it seems it is even impossible to solve the transformation problem generally (hence labor cannot serve as measurement of value). Now subjective theory of value that states that value depends on people’s subjective judgments and preferences (marginal utility) can explain everything what LTV does and even things that LTV cannot, hence there really is no use for LTV anymore. – 1muflon1 Dec 23 '20 at 10:41


text:
rivet is hosted by Hepforge, IPPP Durham

## Rivet analyses reference

### LHCB_2018_I1665223

Measurement of $pp$ inelastic cross-section at 13 TeV using prompt, long-lived particles in the LHCb fiducial phase-space
Experiment: LHCB (LHC)
Inspire ID: 1665223
Status: VALIDATED
Authors:
• Michael Schmelling
• Alex Grecu
References:
• JHEP 1806 (2018) 100
• DOI:10.1007/JHEP06(2018)100
• arXiv: 1803.10974
• LHCb-PAPER-2018-003, CERN-EP-2018-044
Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
• Proton-proton interactions at 13 TeV centre-of-mass energy. LHCb minimum bias, inelastic events.

LHCb measurement of the inelastic interaction cross-section in proton-proton collisions at $\sqrt{s}=13$ TeV. Events are selected if they contain at least one prompt long-lived charged particle with momentum $p > 2$ GeV$/c$ and pseudorapidity ($\eta$) in the range $2 < \eta < 5$. A particle is long-lived if its proper (mean) lifetime is larger than $0.3 \times 10^{-10}$ s, (proper $c\tau > 9$ mm) and it is prompt if it is produced directly in the $pp$ collision or if none of its ancestors is long-lived. This definition is recommended by the LHC Minimum Bias and Underlying Event working group. Prompt long-lived charged hadrons should be used themselves in vetoeing events rather than their charged decay products (e.g. Sigma +/-, Xi and Omega decays are blocked).

Source code: LHCB_2018_I1665223.cc
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 // -*- C++ -*- #include "Rivet/Analysis.hh" #include "Rivet/Projections/ChargedFinalState.hh" namespace Rivet { /// @brief Inelastic xsection in pp collisions at 13 TeV for charged particles in LHCb acceptance class LHCB_2018_I1665223 : public Analysis { public: /// Constructor DEFAULT_RIVET_ANALYSIS_CTOR(LHCB_2018_I1665223); /// @name Analysis methods //@{ /// Book histograms and initialise projections before the run void init() { // Register projection declare(ChargedFinalState(Cuts::etaIn(ETAMIN, ETAMAX)), "lbCFS"); // Book histogram book(_h_ppInel, 1, 1, 1); } /// Perform the per-event analysis void analyze(const Event& event) { // Eliminate non-inelastic events and empty events in LHCb const ChargedFinalState& cfs = apply(event, "lbCFS"); if (cfs.particles().size() == 0) vetoEvent; for (const Particle& myp : cfs.particles()) { if (hasLongLivedParent(myp)) continue; if (!isLongLivedParticle(myp)) continue; // Only particles with p > 2 GeV measured if (myp.momentum().p() < PMIN) continue; // Histo gets filled only for inelastic events (at least one prompt charged particle) _h_ppInel->fill(sqrtS()); break; } } /// Normalise histograms etc., after the run void finalize() { scale(_h_ppInel, crossSection()/millibarn/sumOfWeights()); // norm to cross section (one-sided LHCb) } //@} bool isLongLivedParticle(const Particle& p) { // Stable long-lived final-state charged particles in LHCb static const int stablePids[9] = {11,13,211,321,2212,3112,3222,3312,3334}; for (int stablePid : stablePids) { if (p.abspid() == stablePid) return true; } return false; } bool hasLongLivedParent(const Particle& p) { // List of PDG IDs for particle with lifetimes higher than 0.03 ns (3.E-11 s) - long lived particles according to LHC MB&UE WG static const int longLivedPids[20] = {3334,3322,3312,3222,3122,3112,2212,2112,321,310,130,211,20022,480000000,11,12,13,14,16,22}; for (int longLivedPid : longLivedPids) { if (p.hasParentWith(Cuts::abspid == longLivedPid)) return true; } return false; } /// @name Histogram Histo1DPtr _h_ppInel; /// Cut constants const double ETAMIN = 2.0, ETAMAX = 5.0, PMIN = 2.0*GeV; }; DECLARE_RIVET_PLUGIN(LHCB_2018_I1665223); }


text:
# Steps to scratch build a VW

Discussion in 'Hangar Flying' started by Little Scrapper, Aug 13, 2019.

### Help Support HomeBuiltAirplanes Forum by donating:

1. Aug 22, 2019

### Little Scrapper

#### Well-Known MemberHBA Supporter

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Lot's of posts! Excellent.

I have an idea, how about an interactive VW engine build. I'll flip the bill, everyone makes comments and suggestions, some will learn and some will teach, we all seem to get along and are mature because we all have the same goal.

If someone is able we can create a timeline list and just work through the list. I'll take the list and produce a 2 min movie per list item. In the end we have a motor that runs on a stand and everyone has skin in the game even if the only thing you do is watch.

If we're luck we may even help aviation. Like I said, I'll spend what it takes. Let's have fun.

On vacation this week I've been doing some reflection and decided to shut down a part of my business that will bring me from 70 hours a week to about 40/50.

I'm a 100% in on this. Life is too short not to do it.

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2. Aug 22, 2019

### karmarepair

#### Active Member

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Back to heads. http://vwparts.aircooled.net/OEM-VW-35-x-32mm-Dual-Port-Cylinder-Head-EACH-p/oem-cylinder-head.htm is what I've got for my un-completed engine. ASSUME you'll have to take care of the casting flash your own self. Drag racers need big head to run big displacement engines at HIGH RPM. At the LOW RPM we run at, we do not need that, even with big jugs and big strokes. Big valves are usually single piece stainless steel, and unless they are VERY high quality and cost, they tend to stretch and open up and burn. I'm not aware of a source for NEW single port heads.

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3. Aug 22, 2019

### Vigilant1

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Little Scrapper,
That sounds great, but ambitious! And, I expect some ruffled feathers along the way.
The GPAS engine build manual might be a convenient starting point for a framework of the order of processes, I think. Discussion here would result in variations from that, and it would be good to make each choice explicit so it is easy to understand what was done and why.
As we know, the VW engine is very adaptable, suitable for everything from 40HP to 75 HP, can turn a prop from either end, can have a starter and electrical system or none. all kinds of ignition and fuel induction options, etc. Every choice made will be wrong/non-optimum for some other users, so the videos will be useful to some people and not others.

Last edited: Aug 22, 2019
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4. Aug 22, 2019

### Little Scrapper

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Sounds good to me.

5. Aug 22, 2019

#### Well-Known MemberHBA Supporter

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Pops likes this.
6. Aug 22, 2019

### blane.c

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7. Aug 22, 2019

### Vigilant1

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Wow, 360% of the price of Mahle pistons. They must be very special.

Maybe a glob of JB Weld on the top of a flat-topped piston would do the trick

8. Aug 22, 2019

### blane.c

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Food in the trough.

9. Aug 22, 2019

### Pops

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Removing part of the bellhousing when using a flywheel drive VW engine. Removed 1/2 pound of metal. Left a smaller flange for strength.
Notice that the case is welded behind #3 cylinder and bored for 94's or heavy wall 92 mm cylinders. The case has been clearanced for a stroker crank if wanted. Used the powered hacksaw for 95% of the cutting and the rest with the handheld hacksaw. Then cleaned up with a air grinder with a drum bit.

#### Attached Files:

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• ###### DSCF0038.JPG
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10. Aug 23, 2019

### blane.c

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The "squish" pistons will allow the use of longer rods or reduce the compression ratio, which may be advantageous to some and depending on what combinations you are putting together could be less expensive than other options.

11. Aug 23, 2019

### Vigilant1

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Sorry, I was just being a wisacre. I'm sure some folks might like to have them. $650 for a set of pistons is a lot when folks are used to paying$180 for a set of good pistons. \$470 extra isn't much in the airplane world, but it is a lot in the VW airplane engine world.

Last edited: Aug 23, 2019
12. Aug 23, 2019

### blane.c

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The shop Pops uses? http://keithsautoparts.com/

Interesting variety of build options http://onex-svingenb.blogspot.com/p/vw-engines.html

Accessory weights http://www.greatplainsas.com/scaccesslbs.html

Hoovers blog page on the oil system modifications and other things towards bottom of page http://bobhooversblog.blogspot.com/...-max=2007-06-01T00:00:00-07:00&max-results=10

I balanced engines in the back of this shop the summer of 1976, if you got your HD or Triumph balanced in Northern California back then I did it cause this was the shop everyone sent there stuff to. But mostly I balanced small block V-8". https://www.yelp.com/biz/horse-power-by-gerolamy-carmichael

Drilled for oil magnesium engine case https://www.scatvw.com/engine-cases/as41-dual-relief/ Split Port Heads https://www.scatvw.com/cylinder-heads/split-port/ Case Savers and Case Studs https://www.scatvw.com/engine-cases/accessories/ Dry/Wet sump https://www.scatvw.com/engine-cases/drywet-sump-accessories/

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13. Aug 23, 2019

### Little Scrapper

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Because I'm close to MOFOCO it probably would be smart to use them or buy parts from them because of shipping. I'm in Milwaukee once every two weeks at a minimum because of a wholesale supplier I use for my plumbing business so stopping at MOFOCO would be effortless.

14. Aug 23, 2019

### don january

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Talking about steps to home build VW Engine for flight I noticed most if not all is of the type 1-2 focused much on the 1600 conversion to 1835 cc. There is info about the type 3-4 on the net for aircraft use. First step for me was to look around the neighborhood and see were there was some engines laying around such as a Melro spray coupe or a wrecked Beetle. 2nd step was to get one home and take it totally apart. I looked over the condition of the stock jugs /rods/ pistons/heads. In my case I asked just how far do I want to go with new parts and of what supplier. After many hours of reading info I believe that "stock" parts was the way for me. The first engine I did with Bob Hoover mods for cooling and balancing rods and pistons was tested in my trike and two years later still going strong. I guess the point I'm trying to make is see whats close by and think hard on how far you want to take the build. I'm glad I just started with a plain Jane 1600cc and got my hands dirty. Once you do one I think confidence level goes up ten fold for the next. FWIW

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15. Aug 23, 2019

#### Well-Known MemberHBA Supporter

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It sounds like you would be in pretty good hands there. They should be able to get you everything you need except the aviation-specific bits.

16. Aug 23, 2019

### 12notes

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If you want to trade some money for weight, a 7ah LiFePO4 battery weights a little over two pounds, and LiFePO4 doesn't catch on fire like lithium ion, and can be charged with a standard lead acid battery charger.

https://www.ebay.com/itm/12-V-7-Ah-...y-SLA-Replacement-Dakota-Lithium/222615221794

17. Aug 23, 2019

### Vigilant1

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Mofoco sold heads to Sonex, so they know their equipment has sometimes been used for aircraft. Still, they take steps to protect themselves legally (e.g. I'm not sure, but I don't think the Mofoco heads sold through Sonex still said "Mofoco" on them). So, if you have discussions with them,you may need to sneak up on this topic ("I have this friend . . ." or "I'm building an airboat . . ."). Some companies flat out will not sell directly to consumers who are using their products for aircraft.
I'm not a Mofoco fan based on the casting quality of the heads in my plane, but maybe things have changed. Kinda doubt it, though.

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18. Aug 23, 2019

### karmarepair

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19. Aug 23, 2019

### dmar836

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I cant speak for the OP but he is building a V-Witt. I can speak for myself as I am too. Doesn’t need a starter, alternator, electric avionics, or a battery. If I may very loosely paraphrase Tony Bingelis, “Cumulative ‘upgrades’ is how turds get built.”
Dave

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20. Aug 23, 2019

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text:
auctex
[Top][All Lists]

## Re: [AUCTeX] How to use tex--prettify-symbols-alist?

 From: Marcin Borkowski Subject: Re: [AUCTeX] How to use tex--prettify-symbols-alist? Date: Sat, 27 Feb 2016 19:22:40 +0100 User-agent: mu4e 0.9.13; emacs 25.1.50.4

On 2016-02-27, at 19:18, Marcin Borkowski <address@hidden> wrote:

> Hi folks,
>
> I did (setq prettify-symbols-alist tex--prettify-symbols-alist), and
> enabled prettify-symbols-mode.  However, things do not look as well as
> I would like them to.
>
> 1. Math between $...$ doesn't get prettified; $$...$$ and other
> constructs work.  Also, symbols outside math mode /do/ work!  Why?
>
> 2. $$\infty$$ does not get prettified; $$\infty$$ does.  Why?  Is that
> because prettify-symbols-mode surrounds the regex with the "symbol"
> delimiters?
>
> 3. I tried adding this to prettify-symbols-alist:
>    ("\\mathbb{R}" . 8477).  It didn't work, though.  Why is that so?

OK, this one /did/ work; I was a bit impatient and had a glance into the
code, and it turns out that disabling and enabling the mode helped.

The other questions are still a bit of a mystery for me, though.

Best,

--
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science


text:
I got involved in a discussion about using subdomains vs subfolders.

Say I want to create a new section on my website, dedicated to selling honey.

I don’t produce nor sell honey, it’s just an example. Although one of my friends has bees and produces his own honey and it’s delicious 😋

The honey part of the website would be pretty big, with its own application to manage the e-commerce.

I could add this on my website in two ways. The first is by using a subfolder, like this: flaviocopes.com/honey.

The second is by using a subdomain, for example honey.flaviocopes.com.

There is a third option, which is using its own domain name, like flaviohoney.com. But let’s focusing on keeping our original domain.

A subdomain makes things easier to manage: you have your own completely separate app or CMS or anything, you store it separately in its Git repository if that’s what you use for CI/CD, and you can also host it separately on its own hosting.

I think it’s the ideal solution when you are using an external service like Shopify or anything, as they let you use a subdomain.

A subfolder on the other hand is a bit more complicated because unless you come up with creative ways on the server side (which implies you need to manage your own server), the code must all be put under the original code that manages the main domain.

There is a huge advantage, however, that moves the bar toward the subfolder approach: SEO.

Google does not officially confirm it, but it considers subdomains as completely different sites from the main domain.

honey.flaviocopes.com would not inherit the SEO “juice” that flaviocopes.com might have. Having many subdomains will dilute the domain authority over multiple subdomains rather than centralizing it in the main domain.

This reason alone could justify using flaviocopes.com/honey.

From the branding standpoint, I don’t personally think there are differences. It’s much better to have a separate domain, logo and design for a big project. But if it’s just an idea or something you want to test-drive for example, without investing time and effort into having a separate domain, then both subfolder or subdomain approaches will work fine.

⭐ Join the waiting list for the JavaScript Masterclass ⭐


text:
Math Help - Group proof

1. Group proof

G is a group and $x,y\in G$.

Prove that $xy=yx$ iff $y^{-1}xy=x$ iff $x^{-1}y^{-1}xy=1$.

How can I break this statement up to prove. With iff proofs, I know we go both directions but how is it broken up when another iff is embedded in it?

2. Re: Group proof

If we have to show that we have i) iff ii) iff iii), then just prove that $i)\Rightarrow ii)$, $ii)\Rightarrow iii)$ and $iii)\Rightarrow i)$.


text:
5

# Question 7 (1 point) What partial pressure of hydrogen, Hz, is required above an aqueous solulion order t0 ensure Inat (he concenh7 D 00 mmol dm-3? The Henry'...

## Question

###### Question 7 (1 point) What partial pressure of hydrogen, Hz, is required above an aqueous solulion order t0 ensure Inat (he concenh7 D 00 mmol dm-3? The Henry' law conslant for hydrogen is 7.78 X10-J molm JAPe-] of hydrogen in the solulion is129 MPa129 kPa129 Pa12.9 kPaQuestion 8 (1 point)Ioluene, CoHsCH} and 136 2 g o butan-1-0l CAHgOH at 25 "C The An ideal solulion prepared by mixing 15 Calculate the partlal pressure butan-1-ol In the Vanoum pressure of pure butan-I-ol 885 Pa at thi

Question 7 (1 point) What partial pressure of hydrogen, Hz, is required above an aqueous solulion order t0 ensure Inat (he concenh7 D 00 mmol dm-3? The Henry' law conslant for hydrogen is 7.78 X10-J molm JAPe-] of hydrogen in the solulion is 129 MPa 129 kPa 129 Pa 12.9 kPa Question 8 (1 point) Ioluene, CoHsCH} and 136 2 g o butan-1-0l CAHgOH at 25 "C The An ideal solulion prepared by mixing 15 Calculate the partlal pressure butan-1-ol In the Vanoum pressure of pure butan-I-ol 885 Pa at this temperature vapoui above the mixlure speed your calculaticn note Ihai the molar maes toluene 9215 RInal - that of butan" T-ol 92 [5 Rtol -! 811 Pa 90.9 Pa 074.6 Pa 885 Pa

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