1,609 research outputs found
Conductivity landscape of highly oriented pyrolytic graphite surface containing ribbons and edges
We present an extensive study on electrical spectroscopy of graphene ribbons
and edges of highly oriented pyrolytic graphite (HOPG) using atomic force
microscope (AFM). We have addressed in the present study two main issues, (1)
How does the electrical property of the graphite (graphene) sheet change when
the graphite layer is displaced by shear forces? and (2) How does the
electrical property of the graphite sheet change across a step edge? While
addressing these two issues we observed, (1) variation of conductance among the
graphite ribbons on the surface of HOPG. The top layer always exhibits more
conductance than the lower layers, (2) two different monolayer ribbons on the
same sheet of graphite shows different conductance, (3) certain ribbon/sheet
edges show sharp rise in current, (4) certain ribbons/sheets on the same edge
shows both presence and absense of the sharp rise in the current, (5) some
lower layers at the interface near a step edge shows a strange dip in the
current/conductance (depletion of charge). We discuss possible reasons for such
rich conducting landscape on the surface of graphite.Comment: 13 pages, 9 figures. For better quality figures please contact autho
The application of active controls technology to a generic hypersonic aircraft configuration
Analytical methods are described for the prediction of aerothermoelastic stability of hypersonic aircraft including active control systems. Thermal loads due to aerodynamic heating were applied to the finite element model of the aircraft structure and the thermal effects on flutter were determined. An iterative static aeroelastic trim analysis procedure was developed including thermal effects. And active control technology was assessed for flutter suppression, ride quality improvement, and gust load alleviation to overcome any potential adverse aeroelastic stability or response problems due to aerodynamic heating. A generic hypersonic aircraft configuration was selected which incorporates wing flaps, ailerons, and all moveable fins to be used for active control purposes. The active control system would use onboard sensors in a feedback loop through the aircraft flight control computers to move the surfaces for improved structural dynamic response as the aircraft encounters atmospheric turbulence
Screening and interlayer coupling in multilayer graphene field-effect transistors
With the motivation of improving the performance and reliability of
aggressively scaled nano-patterned graphene field-effect transistors, we
present the first systematic experimental study on charge and current
distribution in multilayer graphene field-effect transistors. We find a very
particular thickness dependence for Ion, Ioff, and the Ion/Ioff ratio, and
propose a resistor network model including screening and interlayer coupling to
explain the experimental findings. In particular, our model does not invoke
modification of the linear energy-band structure of graphene for the multilayer
case. Noise reduction in nano-scale few-layer graphene transistors is
experimentally demonstrated and can be understood within this model as well.Comment: 13 pages, 4 figures, 20 reference
The Hydration Status of Female Collegiate Soccer Players Over Consecutive Training and Match Days
Purpose: Hydration has been shown to play a pivotal role in sport. Soccer is a team sport in which the integrity of all players is vital for team performance; thus, individual player hydration status is important. The primary aim of this study was to investigate the hydration status of female collegiate soccer players during regular season.
Methods: Sixteen collegiate female soccer players (age: 20.4 ± 0.8 years; height: 163.6 ± 6.9 cm; weight: 65.3 ± 12 kg) provided urine over 9 days to monitor their hydration status. Hydration was determined by urine specific gravity (Usg). Usg was analyzed in the morning (AM) and in the afternoon before practice/game (PM).
Results: All 16 players were at least minimally hypohydrated (Usg \u3e 1.010) in the AM on 5 of the 9 days tested. Players had significantly higher Usg values in the AM as compared to PM (F(1,250) = 23.09; p \u3c 0.0001); however, there was no significant time*day interaction (F(1,250) = 1.98; p = 0.16).
Conclusion: Data show a high prevalence of hypohydration occurring in this specific population. This sub-optimal hydration status could be a cause for concern in terms of overall performance. Efforts should be made to integrate hydration interventions and daily monitoring to minimize hypohydration in players
The Hydration Status of Female Collegiate Soccer Players Over Consecutive Training and Match Days
Purpose: Hydration has been shown to play a pivotal role in sport. Soccer is a team sport in which the integrity of all players is vital for team performance; thus, individual player hydration status is important. The primary aim of this study was to investigate the hydration status of female collegiate soccer players during regular season.
Methods: Sixteen collegiate female soccer players (age: 20.4 ± 0.8 years; height: 163.6 ± 6.9 cm; weight: 65.3 ± 12 kg) provided urine over 9 days to monitor their hydration status. Hydration was determined by urine specific gravity (Usg). Usg was analyzed in the morning (AM) and in the afternoon before practice/game (PM).
Results: All 16 players were at least minimally hypohydrated (Usg \u3e 1.010) in the AM on 5 of the 9 days tested. Players had significantly higher Usg values in the AM as compared to PM (F(1,250) = 23.09; p \u3c 0.0001); however, there was no significant time*day interaction (F(1,250) = 1.98; p = 0.16).
Conclusion: Data show a high prevalence of hypohydration occurring in this specific population. This sub-optimal hydration status could be a cause for concern in terms of overall performance. Efforts should be made to integrate hydration interventions and daily monitoring to minimize hypohydration in players
Disentangling the climatic and biotic factors driving changes in the dynamics of Quercus suber populations across the species’ latitudinal range
We thank A.J. Muñoz‐Pajares, L. Rodríguez and G. Rutten for their
help and logistic support during field sampling and M.E. Sánchez,
M. Serrano and M.A. Romero for pathogen analyses and interest‐
ing discussions.Data will be available from the Dryad Digital Repository upon
acceptance.Aim: Impacts of different global change drivers are altering the performance of plant
species worldwide. However, these pressures usually differ across the species’ distri‐
bution range. To properly assess the combined effect of global change at species
level, we need to evaluate its consequences across their complete distribution. We
focused on recent decline in Cork oak (Quercus suber L.) populations given its high
ecological and economic relevance.
Location: We selected 10 different sites (and two populations per site) separated
about one degree in latitude across the core distribution of Q. suber, following a
transcontinental aridity gradient.
Methods: To evaluate the current trends in population dynamics across the species’
distribution and the factors implied on population decline, we evaluated the effect of
latitude, aridity, pathogens (Phytophthora cinnamomi), stand density and tree size on
seed and crop size, demographic structure, dominance of recruitment bank, defolia‐
tion and mortality.
Results: We found an increase in seed weight as latitude decreased, with a homogene‐
ous low crop size across the complete distribution. Demographic structure was deter‐
mined by latitude, precipitation and pathogen abundance. We detected a trend towards
reduced sapling densities towards the southern edge of the distribution, with a demo‐
graphic structure dominated by old trees. The low sapling density at the southern edge
translates into a loss of dominance with respect to other woody species, suggesting an
alteration of community structure in the mid‐term future. Tree density, precipitation
and pathogen abundance determined tree mortality across the species distribution,
with a higher abundance of pathogens in central‐latitude populations.
Main conclusions: Our results allow the early detection of declining trends and the
evaluation of the main risks for species’ conservation, suggesting potential for range
displacement of the species driven by the recruitment failure at the southern edge of
the distribution and a likely range expansion at northern populations.This research was funded by the Large Research
Grant (6007210) awarded from the British Ecological Society to L.M.
L.G.A. acknowledges support from the MICINN project INTERCAPA
(CGL‐2014‐56739‐R) and European FEDER Fund
Compressibility of and (M = Rh, Ir and Co) Compounds
The lattice parameters of the tetragonal compounds CeIn and
CeIn(Rh, Ir and Co) have been studied as a function of
pressure up to 15 GPa using a diamond anvil cell under both hydrostatic and
quasihydrostatic conditions at room temperature. The addition of In
layers to the parent CeIn compound is found to stiffen the lattice as the
2-layer systems (average of bulk modulus values is 70.4 GPa) have a
larger than CeIn (67 GPa), while the 1-layer systems with the are
even stiffer (average of is 81.4 GPa). Estimating the hybridization
using parameters from tight binding calculations shows that the dominant
hybridization is in nature between the Ce and In atoms. The values of
at the pressure where the superconducting transition temperature
reaches a maximum is the same for all CeIn compounds. By
plotting the maximum values of the superconducting transition temperature
versus for the studied compounds and Pu-based superconductors, we
find a universal versus behavior when these quantities are
normalized appropriately. These results are consistent with magnetically
mediated superconductivity.Comment: Updated version resubmitted to Phys. Rev.
Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating
We model the photoelectric emission from and charging of interstellar dust
and obtain photoelectric gas heating efficiencies as a function of grain size
and the relevant ambient conditions. Using realistic grain size distributions,
we evaluate the net gas heating rate for various interstellar environments, and
find less heating for dense regions characterized by R_V=5.5 than for diffuse
regions with R_V=3.1. We provide fitting functions which reproduce our
numerical results for photoelectric heating and recombination cooling for a
wide range of interstellar conditions. In a separate paper we will examine the
implications of these results for the thermal structure of the interstellar
medium. Finally, we investigate the potential importance of photoelectric
heating in H II regions, including the warm ionized medium. We find that
photoelectric heating could be comparable to or exceed heating due to
photoionization of H for high ratios of the radiation intensity to the gas
density. We also find that photoelectric heating by dust can account for the
observed variation of temperature with distance from the galactic midplane in
the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field
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