36285154
Microcantilever actuation via periodic internal heating.
This paper reports electrothermal actuation of silicon microcantilevers having integrated resistive heaters. Periodic electrical excitation induced periodic resistive heating in the cantilever, while the cantilever deflection was monitored with a photodetector. Excitation was either at the cantilever resonant frequency, f(0), f(0)/2, or f(0)/3. When the time averaged maximum cantilever temperature was 174 degrees C, the cantilever out-of-plane actuation amplitude was 484 nm near the cantilever resonance frequency of 24.9 kHz. This actuation was sufficiently large to operate the cantilever in intermittent contact mode and scan a calibration grating of height of 20 nm.
21814270
Electrical and thermal coupling to a single-wall carbon nanotube device using an electrothermal nanoprobe.
We utilize a multifunctional atomic force microscope (AFM) cantilever applying highly localized temperature and electric fields to interrogate transport in single-wall carbon nanotube field-effect transistors (CNTFETs). The probe can be operated either in contact with the CNT, in intermittent contact, or as a Kelvin probe, and can independently control the electric field, mechanical force, and temperature applied to the CNT. We modulate current flow in the CNT with tip-applied electric field, and find this field-effect depends upon both cantilever heating and CNT self-heating. CNT transport is also investigated with AFM tip temperature up to 1170 degrees C. Tip-CNT thermal resistance is estimated at 1.6 x 10(7) K/W and decreases with increasing temperature. Threshold force (<100 nN) for reliable contact mode imaging is extracted and used to determine set points for nanotube manipulation, such as displacement or cutting. The ability to measure thermal coupling to a single-molecule electronic device could offer new insights into nanoelectronic devices.
23509495
FgVelB globally regulates sexual reproduction, mycotoxin production and pathogenicity in the cereal pathogen Fusarium graminearum.
The velvet genes are conserved in ascomycetous fungi and function as global regulators of differentiation and secondary metabolism. Here, we characterized one of the velvet genes, designated FgVelB, in the plant-pathogenic fungus Fusarium graminearum, which causes fusarium head blight in cereals and produces mycotoxins within plants. FgVelB-deleted (ΔFgVelB) strains produced fewer aerial mycelia with less pigmentation than those of the wild-type (WT) during vegetative growth. Under sexual development conditions, the ΔFgVelB strains produced no fruiting bodies but retained male fertility, and conidiation was threefold higher compared with the WT strain. Production of trichothecene and zearalenone was dramatically reduced compared with the WT strain. In addition, the ΔFgVelB strains were incapable of colonizing host plant tissues. Transcript analyses revealed that FgVelB was highly expressed during the sexual development stage, and may be regulated by a mitogen-activated protein kinase cascade. Microarray analysis showed that FgVelB affects regulatory pathways mediated by the mating-type loci and a G-protein alpha subunit, as well as primary and secondary metabolism. These results suggest that FgVelB has diverse biological functions, probably by acting as a member of a possible velvet protein complex, although identification of the FgVelB-FgVeA complex and the determination of its roles require further investigation.
31281743
Respiration-induced B0 field fluctuation compensation in balanced SSFP: real-time approach for transition-band SSFP fMRI.
In functional MRI (fMRI) the resonance frequency shift induced from respiration is a major source of physiological noise. In transition-band SSFP fMRI the respiration-induced resonance offset not only increases noise interference, it also shifts the activation band. This leads to a reduction in the contrast-to-noise ratio (CNR) and the potential for varying contrast levels during the experiment. A novel real-time method that compensates for the respiration-induced resonance offset frequency is presented. This method utilizes free induction decay (FID) phase information to measure the resonance offset. For compensation, one can update the resonant frequency in real time by changing the transmit RF pulse and receiver phases to track the measured offset. The results show decreased signal power in the respiration frequency band and increased numbers of activated voxels with higher Z-scores compared to uncompensated experiments.
24325594
Population structure of and mycotoxin production by Fusarium graminearum from maize in South Korea.
Fusarium graminearum (Gibberella zeae) is an important pathogen of wheat, maize, barley, and rice in South Korea, and harvested grain often is contaminated with trichothecenes such as deoxynivalenol and nivalenol. In this study, we examined 568 isolates of F. graminearum collected from maize at eight locations in South Korea. We used amplified fragment length polymorphisms (AFLPs) to identify four lineages (2, 3, 6, and 7); lineage 7 was the most common (75%), followed by lineage 6 (12%), lineage 3 (12%), and lineage 2 (1%). The genetic identity among populations was high (>0.98), and the effective migration rate between locations was higher than that between lineages. Female fertility varied by lineage: all lineage 7 isolates were fertile, while 70%, 26%, and 14% of the isolates in lineages 6, 3, and 2, respectively, were fertile. All lineage 3 and lineage 7 isolates produced deoxynivalenol, whereas most lineage 2 and 6 isolates produced nivalenol. Genotypic diversity in lineage 3 and lineage 6 populations is similar to that found in previously described Korean rice populations, but genotypic diversity in lineage 7 is much lower, even though similar levels of gene flow occur between lineage 7 populations. We conclude that lineage 7 was relatively recently introduced into South Korea, perhaps accompanying imported maize seeds.
7202726
Improved shim method based on the minimization of the maximum off-resonance frequency for balanced steady-state free precession (bSSFP).
In this work, a shim method that minimizes the maximum off-resonance frequency (min-max shim) in balanced steady-state free precession (bSSFP) is tested for brain imaging at 3T with constant and linear shim terms. The method demonstrates improvement of spatial coverage and banding artifact reduction over standard least-squares shimming. In addition, a new method (modified min-max shim) is introduced. This method reduces boundary band regions where the artifact is inevitable due to the excessive off-resonance frequency distribution. In comparison to standard least-squares shimming, the min-max based shim method either eliminates or reduces the size of banding artifacts. The method can be used to increase the signal-to-noise ratio (SNR) in bSSFP imaging or to increase the functional contrast in bSSFP functional MRI (fMRI) by allowing a longer usable repetition time (TR).
20668920
Dynamic light scattering optical coherence tomography.
We introduce an integration of dynamic light scattering (DLS) and optical coherence tomography (OCT) for high-resolution 3D imaging of heterogeneous diffusion and flow. DLS analyzes fluctuations in light scattered by particles to measure diffusion or flow of the particles, and OCT uses coherence gating to collect light only scattered from a small volume for high-resolution structural imaging. Therefore, the integration of DLS and OCT enables high-resolution 3D imaging of diffusion and flow. We derived a theory under the assumption that static and moving particles are mixed within the OCT resolution volume and the moving particles can exhibit either diffusive or translational motion. Based on this theory, we developed a fitting algorithm to estimate dynamic parameters including the axial and transverse velocities and the diffusion coefficient. We validated DLS-OCT measurements of diffusion and flow through numerical simulations and phantom experiments. As an example application, we performed DLS-OCT imaging of the living animal brain, resulting in 3D maps of the absolute and axial velocities, the diffusion coefficient, and the coefficient of determination.