1,881 research outputs found
Low-noise top-gate graphene transistors
We report results of experimental investigation of the low-frequency noise in
the top-gate graphene transistors. The back-gate graphene devices were modified
via addition of the top gate separated by 20 nm of HfO2 from the single-layer
graphene channels. The measurements revealed low flicker noise levels with the
normalized noise spectral density close to 1/f (f is the frequency) and Hooge
parameter below 2 x 10^-3. The analysis of the noise spectral density
dependence on the top and bottom gate biases helped us to elucidate the noise
sources in these devices and develop a strategy for the electronic noise
reduction. The obtained results are important for all proposed graphene
applications in electronics and sensors.Comment: 9 pages, 4 figure
Management of wet grassland habitat to reduce the impact of predation on breeding waders: Phase 1. Final report
Terahertz Response of Field-Effect Transistors in Saturation Regime
We report on the broadband THz response of InGaAs/GaAs HEMTs operating at
1.63 THz and room temperature deep in the saturation regime. We demonstrate
that responses show linear increase with drain-to-source voltage (or drain bias
current) and reach very high values up to 170V/W. We also develop a
phenomenological theory valid both in the ohmic and in the saturation regimes.Comment: 11 pages, 3 figure
The incidence of pica in a sample of dialysis patients
End Stage Renal Disease (ESRD) occurs when the kidneys are no longer able to function at a level necessary for day to day life. Pica refers to the persistent, compulsive craving for and ingestion of nonfood items and certain food items. ESRD may constitute a potent stress and stimulus for pica, especially in those patients with an underlying cultural predisposition. The occurrence of pica in a South Florida dialysis unit was studied via a carefully designed a pica questionnaire aimed towards creating a human connection. A significantly greater proportion of subjects endorsing pica practices were found in the dialysis group (38.3%) as compared to the control group (16%). Dialysis patients endorsing pica behaviors were significantly younger than those who denied pica behavior. Additionally there was a significantly greater proportion of females endorsing pica behaviors. Odds ratios analyses revealed greater odds of engaging in pica behaviors for Black participants than Hispanics or Whites. Pagophagia (ice pica) was the most frequently reported type of pica practice. The incidence of pica in this study was considerably higher than that which had been found in past studies. This likely resulted from the unique manner in which the information was educed. Implications and suggestions for future research directions are discussed
Epigenetic Chromatin Silencing: Bistability and Front Propagation
The role of post-translational modification of histones in eukaryotic gene
regulation is well recognized. Epigenetic silencing of genes via heritable
chromatin modifications plays a major role in cell fate specification in higher
organisms. We formulate a coarse-grained model of chromatin silencing in yeast
and study the conditions under which the system becomes bistable, allowing for
different epigenetic states. We also study the dynamics of the boundary between
the two locally stable states of chromatin: silenced and unsilenced. The model
could be of use in guiding the discussion on chromatin silencing in general. In
the context of silencing in budding yeast, it helps us understand the phenotype
of various mutants, some of which may be non-trivial to see without the help of
a mathematical model. One such example is a mutation that reduces the rate of
background acetylation of particular histone side-chains that competes with the
deacetylation by Sir2p. The resulting negative feedback due to a Sir protein
depletion effect gives rise to interesting counter-intuitive consequences. Our
mathematical analysis brings forth the different dynamical behaviors possible
within the same molecular model and guides the formulation of more refined
hypotheses that could be addressed experimentally.Comment: 19 pages, 5 figure
Predicting effects of environmental change on a migratory herbivore
Changes in climate, food abundance and disturbance from humans threaten the ability of species to successfully use stopover sites and migrate between non-breeding and breeding areas. To devise successful conservation strategies for migratory species we need to be able to predict how such changes will affect both individuals and populations. Such predictions should ideally be process-based, focusing on the mechanisms through which changes alter individual physiological state and behavior. In this study we use a process-based model to evaluate how Black Brant (Branta bernicla nigricans) foraging on common eelgrass (Zostera marina) at a stopover site (Humboldt Bay, USA), may be affected by changes in sea level, food abundance and disturbance. The model is individual-based, with empirically based parameters, and incorporates the immigration of birds into the site, tidal changes in availability of eelgrass, seasonal and depth-related changes in eelgrass biomass, foraging behavior and energetics of the birds, and their mass- dependent decisions to emigrate. The model is validated by comparing predictions to observations across a range of system properties including the time birds spent foraging, probability of birds emigrating, mean stopover duration, peak bird numbers, rates of mass gain and distribution of birds within the site: all 11 predictions were within 35% of the observed value, and 8 within 20%. The model predicted that the eelgrass within the site could potentially support up to five times as many birds as currently use the site. Future predictions indicated that the rate of mass gain and mean stopover duration were relatively insensitive to sea level rise over the next 100 years, primarily because eelgrass habitat could redistribute shoreward into intertidal mudflats within the site to compensate for higher sea levels. In contrast, the rate of mass gain and mean stopover duration were sensitive to changes in total eelgrass biomass and the percentage of time for which birds were disturbed. We discuss the consequences of these predictions for Black Brant conservation. A wide range of migratory species responses are expected in response to environmental change. Process-based models are potential tools to predict such responses and understand the mechanisms which underpin them
Relative Humidity on Mars: New Results From the Phoenix TECP Sensor
In situ measurements of relative humidity (RH) on Mars have only been performed by the Phoenix (PHX) and Mars Science Laboratory (MSL) missions. Here we present results of our recalibration of the PHX thermal and electrical conductivity probe (TECP) RH sensor. This recalibration was conducted using a TECP engineering model subjected to the full range of environmental conditions at the PHX landing site in the Michigan Mars Environmental Chamber. The experiments focused on the warmest and driest conditions (daytime) because they were not covered in the original calibration (Zent et al., 2010, https://doi.org/10.1029/2009JE003420) and previous recalibration (Zent et al., 2016, https://doi.org/10.1002/2015JE004933). In nighttime conditions, our results are in excellent agreement with the previous 2016 recalibration, while in daytime conditions, our results show larger water vapor pressure values. We obtain vapor pressure values in the range ~0.005â1.4Â Pa, while Zent et al. (2016, https://doi.org/10.1002/2015JE004933) obtain values in the range ~0.004â0.4Â Pa. Our higher daytime values are in better agreement with independent estimates from the ground by the PHX Surface Stereo Imager instrument and from orbit by Compact Reconnaissance Imaging Spectrometer for Mars. Our results imply larger dayâtoânight ratios of water vapor pressure at PHX compared to MSL, suggesting a stronger atmosphereâregolith interchange in the Martian arctic than at lower latitudes. Further, they indicate that brine formation at the PHX landing site via deliquescence can be achieved only temporarily between midnight and 6Â a.m. on a few sols. The results from our recalibration are important because they shed light on the nearâsurface humidity environment on Mars.Key PointsWe have recalibrated the relative humidity sensor of the Mars Phoenix landerWe obtain water vapor pressure values in the range ~0.005â1.4Â Pa, while in previous recalibrations, values in the range ~0.004â0.4Â PaOur results show a twoâorderâofâmagnitude diurnal variation of water vapor pressure, suggesting a strong atmosphereâregolith interchangePlain Language SummaryWe present our recalibration of Phoenixâs humidity sensor. This recalibration was conducted with a copy of the sensor subjected to the environmental conditions at the Phoenix landing site. Our experiments focus on the warmest and driest conditions because they were not covered in previous calibrations. Our recalibration shows daytime water content values one order of magnitude larger than those in the previous calibration. At nighttime conditions, our results are in excellent agreement with the previous calibration. Our higher daytime values are in better agreement with independent estimates from the ground, and from orbit. Our results imply larger diurnal variations of water content at Phoenix compared to Curiosity, suggesting a stronger atmosphereâsoil interchange in the Martian arctic than at lower latitudes. Further, they indicate that environmental conditions favorable for the formation of saline solutions (brine) are only achieved temporarily between midnight and 6Â a.m. on a few Martian days. The results from our recalibration are important because measurements of humidity on the Martian surface are needed to shed light on the local and global water cycle of Mars, and so far, only the Phoenix mission in the arctic region and the Curiosity rover at equatorial latitudes have performed such measurements.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153252/1/jgre21230.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153252/2/jgre21230_am.pd
Electrical and Noise Characteristics of Graphene Field-Effect Transistors: Ambient Effects and Noise Sources
We fabricated a large number of single and bilayer graphene transistors and
carried out a systematic experimental study of their low-frequency noise
characteristics. A special attention was given to determining the dominant
noise sources in these devices and the effect of aging on the current-voltage
and noise characteristics. The analysis of the noise spectral density
dependence on the area of graphene channel showed that the dominant
contributions to the low-frequency electronic noise come from the graphene
layer itself rather than from the contacts. Aging of graphene transistors due
to exposure to ambient for over a month resulted in substantially increased
noise attributed to the decreasing mobility of graphene and increasing contact
resistance. The noise spectral density in both single and bilayer graphene
transistors either increased with deviation from the charge neutrality point or
depended weakly on the gate bias. This observation confirms that the
low-frequency noise characteristics of graphene transistors are qualitatively
different from those of conventional silicon metal-oxide-semiconductor
field-effect transistors.Comment: 26 pages with 8 figure
Coded Parity Packet Transmission Method for Two Group Resource Allocation
Gap value control is investigated when the number of source and parity packets
is adjusted in a concatenated coding scheme whilst keeping the overall coding
rate fixed. Packet-based outer codes which are generated from bit-wise XOR
combinations of the source packets are used to adjust the number of both source
packets. Having the source packets, the number of parity packets, which are the
bit-wise XOR combinations of the source packets can be adjusted such that the
gap value, which measures the gap between the theoretical and the required
signal-to-noise ratio (SNR), is controlled without changing the actual coding
rate. Consequently, the required SNR reduces, yielding a lower required energy
to realize the transmission data rate. Integrating this coding technique with
a two-group resource allocation scheme renders efficient utilization of the total
energy to further improve the data rates. With a relatively small-sized set of
discrete data rates, the system throughput achieved by the proposed two-group
loading scheme is observed to be approximately equal to that of the existing
loading scheme, which is operated with a much larger set of discrete data rates.
The gain obtained by the proposed scheme over the existing equal rate and
equal energy loading scheme is approximately 5 dB. Furthermore, a successive
interference cancellation scheme is also integrated with this coding technique,
which can be used to decode and provide consecutive symbols for inter-symbol
interference (ISI) and multiple access interference (MAI) mitigation. With this
integrated scheme, the computational complexity is signi cantly reduced by
eliminating matrix inversions. In the same manner, the proposed coding scheme
is also incorporated into a novel fixed energy loading, which distributes packets
over parallel channels, to control the gap value of the data rates although the
SNR of each code channel varies from each other
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