121956644
A fast voltage preamplifier for use with MWPCs
Abstract We report the development of a voltage preamplifier for use with ionizing particles detection. It has been designed to match the requirements of a test station for muon Multiwire Proportional Chambers (MWPC) of the LHCb experiment at CERN. Simulation results and bench test measurements are presented, which exhibit the main circuit features: gain close to 500, rise time below 20 ns, bandwidth exceeding 30 MHz, input noise lower than 10 nV / Hz . Other results that demonstrate the applicability of the device in other contexts, specially with X-Ray imaging systems based on position sensitive detectors and proportional counters, are presented.
347666
Novel considerations about the non-equilibrium regime of the tricritical point in a metamagnetic model: Localization and tricritical exponents
a b s t r a c t We have investigated the time-dependent regime of a two-dimensional metamagnetic model at its tri- critical point via Monte Carlo simulations. First, we obtained the temperature and magnetic field corre- sponding to the tricritical point of the model by using a refinement process based on optimization of the coefficient of determination in the log-log fit of magnetization decay as a function of time. With these es- timates in hand, we obtained the dynamic tricritical exponents θ and z and the static tricritical exponents ν and β by using the universal power-law scaling relations for the staggered magnetization and its mo- ments at an early stage of the dynamic evolution. Our results at the tricritical point confirm that this model belongs to the two-dimensional Blume-Capel model universality class for both static and dynamic behav- iors, and they also corroborate the conjecture of Janssen and Oerding for the dynamics of tricritical points.
118072730
Construction and test of the prototype chamber for region 1 of the LHCb muon station 2
A four gapMWPC prototypefor region 1 of the muonstation2, with non-staggered wires,wasbuilt andtested.Theconstructiondetailsandthetestresultsarepresented. 1 Intr oduction TheLHCb muonsystem[1] will useMulti-Wire ProportionalChambers(MWPC) for thefour regionsof stations2 and3, for regions3 and4 of station1 andfor regions1 and2 of stations4 and5. Thechambersvary in sizefor thedifferentstationsandregionsandthey have different readoutpadsizesin thoseregions(see[2] for moredetails). In this note,theconstructionof a MWPC prototypefor region 1 of station2 is described.The prototypeis an exact realization of a chamberfor this region. It hasfour symmetricgasgapsandthe characteristicslisted in table1. Table1: Somechamberparametersandoperationconditions. GasGapsize(mm) 5 Anode-Cathodespacing(mm) 2.5 Wire Diameter( m) 30 Sensiti vearea(mm ) 300 250 Wire pitch (mm) 1.5 Wire padsize(mm ) 6.3 250 Wire length(mm) 257 Cathodepadsize(mm ) 37.5 31.3 Wire Tension(gf) 60 10 NominalGasmixture (40%50%10%) Wire nominalpotential(V) 3150 The chamberhasa combinedreadoutof wire andcathodepadsasa consequenceof the requiredgranularity. 2 Chamber Construction The prototypewasbuilt in Rio (CEFET-RJ andLAPE/IF-UFRJ)with PCB-honeycomb-PCB panelsas describedin the Muon SystemTDR [1]. The panels’flatnesswas measured(INMETRO1 andBargoa2) to be within m, which is betterthanthe requiredspecifications (see[3]). Thewire fixation barswerealsomeasuredandgluedto thecathodepanels.Theanodeto cathodedistancewasinsuredbymeansof aprecisesteelspacerfixedto thosebars,during thegluing of thewires. For thepresentprototypethewire fixation barswerenot machinedto have a noseon theedgeswhich wasdonefor thepreviousprototypesto avoid dischar ges[3]. The resultsfor the dark currentandthe sparklimit show that this noseis not necessary . The darkcurrentmeasuredwasof theorderof thenA andthesparklimit wasof about3.45kV. The wiring wasdonein a latheasshown in thepictureof figure1. The wire tensionwas guaranteedusinga calibrateddevice asshown in figure 2. This device hasa DC motor that keepsthewire undertensionby applyinga torqueon thereel. TheDC voltageappliedto the motorwascalibratedwith a60gf weight. 1InstitutoNacionaldeMetrologia,Normalizaç̃aoe QualidadeIndustrial,Rio deJaneiro 2BargoaConectores, Rio deJaneiro
118557560
STOCHASTIC STAR FORMATION AND A (NEARLY) UNIFORM STELLAR INITIAL MASS FUNCTION
Recent observations indicate a lower H{alpha} to FUV ratio in dwarf galaxies than in brighter systems, a trend that could be explained by a truncated and/or steeper initial mass function (IMF) in small galaxies. However, at low star formation rates (SFRs), the H{alpha} to FUV ratio can vary due to stochastic sampling even for a universal IMF, a hypothesis that has, prior to this work, received limited investigation. Using SLUG, a fully stochastic code for synthetic photometry in star clusters and galaxies, we compare the H{alpha} and FUV luminosity in a sample of {approx}450 nearby galaxies with models drawn from a universal Kroupa IMF and a modified IMF, the integrated galactic initial mass function (IGIMF). Once random sampling and time evolution are included, a Kroupa IMF convolved with the cluster mass function (CMF) reproduces the observed H{alpha} distribution at all FUV luminosities, while a truncated IMF as implemented in current IGIMF models underpredicts the H{alpha} luminosity by more than an order of magnitude at the lowest SFRs. We conclude that the observed luminosity is the result of the joint probability distribution function of the SFR, CMF, and a universal IMF, consistent with parts of the IGIMF theory, but that amore » truncation in the IMF in clusters is inconsistent with the observations. Future work will examine stochastic star formation and its time dependence in detail to study whether random sampling can explain other observations that suggest a varying IMF.« less
118803404
Homogeneous photospheric parameters and C abundances in G and K nearby stars with and without planets
Aims. We present a determination of photospheric parameters and carbon abundances for a sample of 172 G and K dwarf, subgiant, and giant stars with and without detected planets in the solar ne ighbourhood. The analysis was based on high signal-to-noise ratio and high resolution spectra observed with the ELODIE spectrograph (Haute Provence Observatory, France) and for which the observational data was publicly available. We intend to contribute precise and homogeneous C abundances in studies that compare the behaviour of light elements in stars, hosting planets or not. This will br ing new arguments to the discussion of possible anomalies that have been suggested and will contribute to a better understanding of different planetary formation process. Methods. The photospheric parameters were computed through the excitation potential, equivalent widths, and ionisation equil ibrium of iron lines selected in the spectra. Carbon abundances were derived from spectral synthesis applied to prominent molecular head bands of C2 Swan (� 5128 and� 5165) and to a C atomic line (� 5380.3). Careful attention was drawn to carry out such a homogeneous procedure and to compute the internal uncertainties. Results. The distribution of [C/Fe] as a function of [Fe/H] shows no difference in the behaviour of planet-host stars in comparison with stars for which no planet was detected, for both dwarf and giant subsamples. This result is in agreement with the hypothesis of primordial origin for the chemical abundances presently observed instead of self-enrichment during the planetary system formation and evolution. Additionally, giant stars are clearly deple ted in [C/Fe] (by about 0.14 dex) when compared with dwarfs, which is probably related to evolution-induced mixing of H-burning products in the envelope of evolved stars. Subgiant stars, a lthough in small number, seems to follow the same C abundance distribution as dwarfs. We also analysed the kinematics of the sample stars that, in majority, are members of the Galaxy’s thin disc. Finally, comparisons with other analogue studies were performed and, within the uncertainties, showed good agreement.
33202267
Generalized field theoretical approach to general relativity and conserved quantities in anti–de Sitter spacetimes
A new prescription to calculate the total energies and angular momenta of asymptotically $(d+1)$-dimensional anti\char21{}de Sitter spacetimes is proposed. The method is based on an extension of the field theoretical approach to general relativity to the case where there is an effective cosmological constant. A $(d\ensuremath{-}1)$ form $\ensuremath{\Omega}$ is exhibited which, when integrated on asymptotic $(d\ensuremath{-}1)$-dimensional boundary surfaces, yields the values of those conserved quantities. The calculations are gauge independent once asymptotic conditions are not violated. Total energies and angular momenta of some known solutions in four and five dimensions are calculated agreeing with standard results.
118174601
SLUG: A new way to Stochastically Light Up Galaxies
We present SLUG, a new code to "Stochastically Light Up Galaxies". SLUG populates star clusters by randomly drawing stars from an initial mass function (IMF) and then following their time evolution with stellar models and an observationally-motivated prescription for cluster disruption. For a choice of star formation history, metallicity, and IMF, SLUG outputs synthetic photometry for clusters and field stars with a proper treatment of stochastic star formation. SLUG generates realistic distributions of star clusters, demonstrating the range of properties that result from finite sampling of an IMF and a random distribution of ages. The simulated data sets provide a quantitative means to address open problems in studies of star formation in galaxies and clusters, such as a test for IMF variations that are suggested by the systematic deficiency in the H-alpha/UV ratio in outer disks or in dwarf galaxies. SLUG will be made publicly available through the website this http URL
62806505
Two semi-automated computational approaches for spectroscopic analysis of stellar photospheres: detailed characterization at high resolution and abundance determination at medium resolution
We report on two distinct computational approaches to self-consistently measure photospheric properties of large samples of stars. Both procedures consist of a set of several semi-integrated tasks based on shell and Python scripts, which efficiently run either our own codes or open source software commonly adopted by the astronomical community. One approach aims to derive the main stellar photospheric parameters and abundances of a few elements by analysing high-resolution spectra from a given public library homogeneously constructed. The other one is applied to recover the abundance of a single element in stars with known photospheric parameters by using mid-resolution spectra from another open homogeneous database and calibrating derived abundances. Both semi-automated computational approaches provide homogeneity and objectivity to every step of the process and represent a fast way to reach partial and final results as well as to estimate measurement errors, making possible to systematically evaluate and improve the distinct steps.