1,317 research outputs found
Large variation in the boundary-condition slippage for a rarefied gas flowing between two surfaces
We study the slippage of a gas along mobile rigid walls in the sphere-plane
confined geometry and find that it varies considerably with pressure. The
classical no-slip boundary condition valid at ambient pressure changes
continuously to an almost perfect slip condition in a primary vacuum. Our study
emphasizes the key role played by the mean free-path of the gas molecules on
the interaction between a confined fluid and solid surfaces and further
demonstrates that the macroscopic hydrodynamics approach can be used with
confidence even in a primary vacuum environment where it is intuitively
expected to fail
Casimir force measurements in Au-Au and Au-Si cavities at low temperature
We report on measurements of the Casimir force in a sphere-plane geometry
using a cryogenic force microscope to move the force probe in situ over
different materials. We show how the electrostatic environment of the
interacting surfaces plays an important role in weak force measurements and can
overcome the Casimir force at large distance. After minimizing these parasitic
forces, we measure the Casimir force between a gold-coated sphere and either a
gold-coated or a heavily doped silicon surface in the 100-400 nm distance
range. We compare the experimental data with theoretical predictions and
discuss the consequence of a systematic error in the scanner calibration on the
agreement between experiment and theory. The relative force over the two
surfaces compares favorably with theory at short distance, showing that this
Casimir force experiment is sensitive to the dielectric properties of the
interacting surfaces.Comment: accepted for publication in Physical Review
Discrepancy in Grain Size Estimation of HO Ice in the Outer Solar System and the Interstellar Medium
Widespread detection of amorphous and crystalline water (HO) ice in
the outer solar system bodies and the interstellar medium has been confirmed
over the past decades. Radiative transfer models (RTMs) are used to estimate
the grain sizes of HO ice from near-infrared (NIR) wavelengths. Wide
discrepancies in the estimation of HO ice grain size on the Saturnian
moons (Hansen, 2009), as well as nitrogen (N) and methane (CH)
ices on Kuiper belt objects have been reported owing to different scattering
models used (Emran and Chevrier, 2022). We assess the discrepancy in the grain
size estimation of HO ice at a temperature of 15, 40, 60, and 80 K
(amorphous) and 20, 40, 60, and 80 K (crystalline) - relevant to the outer
solar system and beyond. We compare the single scattering albedos of HO
ice phases using the Mie theory (Mie, 1908) and Hapke approximation models
(Hapke, 1993) from the optical constant at NIR wavelengths (1 - 5 m). This
study reveals that the Hapke approximation models - Hapke slab and internal
scattering model (ISM) - predict grain size of the crystalline phase, overall,
much better compared to the amorphous phase at temperatures of 15 - 80 K.
However, the Hapke slab model estimates much approximate grain sizes, in
general, to that of the Mie model's prediction while ISM exhibits a higher
uncertainty. We recommend using the Mie model for unknown spectra of outer
solar system bodies and beyond in estimating HO ice grain sizes. While
choosing the approximation model for employing RTMs, we recommend using a Hapke
slab approximation model over the internal scattering model.Comment: 15 pages, 4 figures, 2 table
Experimental observation of nanoscale radiative heat flow due to surface plasmons in graphene and doped silicon
Owing to its two dimensional electronic structure, graphene exhibits many
unique properties. One of them is a wave vector and temperature dependent
plasmon in the infrared range. Theory predicts that due to these plasmons,
graphene can be used as a universal material to enhance nanoscale radiative
heat exchange for any dielectric substrate. Here we report on radiative heat
transfer experiments between SiC and a SiO2 sphere which have non matching
phonon polariton frequencies, and thus only weakly exchange heat in near field.
We observed that the heat flux contribution of graphene epitaxially grown on
SiC dominates at short distances. The influence of plasmons on radiative heat
transfer is further supported with measurements for doped silicon. These
results highlight graphenes strong potential in photonic nearfield and energy
conversion devices.Comment: 4 pages, 3 figure
In utero and childhood polybrominated diphenyl ether (PBDE) exposures and neurodevelopment in the CHAMACOS study.
BackgroundCalifornia children's exposures to polybrominated diphenyl ether flame retardants (PBDEs) are among the highest worldwide. PBDEs are known endocrine disruptors and neurotoxicants in animals.ObjectiveHere we investigate the relation of in utero and child PBDE exposure to neurobehavioral development among participants in CHAMACOS (Center for the Health Assessment of Mothers and Children of Salinas), a California birth cohort.MethodsWe measured PBDEs in maternal prenatal and child serum samples and examined the association of PBDE concentrations with children's attention, motor functioning, and cognition at 5 (n = 310) and 7 years of age (n = 323).ResultsMaternal prenatal PBDE concentrations were associated with impaired attention as measured by a continuous performance task at 5 years and maternal report at 5 and 7 years of age, with poorer fine motor coordination-particularly in the nondominant-at both age points, and with decrements in Verbal and Full-Scale IQ at 7 years. PBDE concentrations in children 7 years of age were significantly or marginally associated with concurrent teacher reports of attention problems and decrements in Processing Speed, Perceptual Reasoning, Verbal Comprehension, and Full-Scale IQ. These associations were not altered by adjustment for birth weight, gestational age, or maternal thyroid hormone levels.ConclusionsBoth prenatal and childhood PBDE exposures were associated with poorer attention, fine motor coordination, and cognition in the CHAMACOS cohort of school-age children. This study, the largest to date, contributes to growing evidence suggesting that PBDEs have adverse impacts on child neurobehavioral development
490 DEXAMETHASONE INHIBITS GELATINASE ACTIVITY DURING IN VITRO OSTEOGENESIS OF HUMAN BONE MARROW STROMAL CELLS
Imaging Electron Wave Functions Inside Open Quantum Rings
Combining Scanning Gate Microscopy (SGM) experiments and simulations, we
demonstrate low temperature imaging of electron probability density
in embedded mesoscopic quantum rings (QRs). The tip-induced
conductance modulations share the same temperature dependence as the
Aharonov-Bohm effect, indicating that they originate from electron wavefunction
interferences. Simulations of both and SGM conductance maps
reproduce the main experimental observations and link fringes in SGM images to
.Comment: new titl
Negative Backaction Noise in Interferometric Detection of a Microlever
Interferometric detection of mirror displacements is intrinsically limited by
laser shot noise. In practice, however, it is often limited by thermal noise.
Here we report on an experiment performed at the liquid helium temperature to
overcome the thermal noise limitation and investigate the effect of classical
laser noise on a microlever that forms a Fabry-Perot cavity with an optical
fiber. The spectral noise densities show a region of negative contribution of
the backaction noise close to the resonance frequency. We interpret this noise
reduction as a coherent coupling of the microlever to the laser intensity
noise. This optomechanical effect could be used to improve the detection
sensitivity as discussed in proposals going beyond the Standard Quantum Limit.Comment: accepted for publication in Physical Review Letter
Temperature measurements on ES steel sheets subjected to perforation by hemispherical projectiles
In this paper is reported a study on the behaviour of ES mild steel sheets subjected to perforation by hemispherical projectiles. Experiments have been conducted using a pneumatic cannon within the range of impact velocities 5m/s<=V0<=60m/s. The experimental setup allowed evaluating initial velocity, failure mode and post-mortem deflection of the plates. The tests have been recorded using high speed infrared camera. It made possible to obtain temperature contours of the specimen during impact. Thus, special attention is focussed on the thermal softening of the material which is responsible for instabilities and failure. Assuming adiabatic conditions of deformation, the increase of temperature may be related to the plastic deformation. The critical strain leading to target-failure is evaluated coupling temperature measurements with numerical simulations and with analytical predictions obtained by means of the Rusinek-Klepaczko constitutive relation [Rusinek, A., Klepaczko, J.R. Shear testing of sheet steel at wide range of strain rates and a constitutive relation with strain rate and temperature dependence of the flow stress. Int J Plasticity. 2001; 17, 87-115]. It has been estimated that the process of localization of plastic deformation which leads to target-failure involves local values close to for the boundary value problem approached. Subsequently, this failure strain level has been applied to simulate the perforation process and the numerical results obtained show satisfactory agreement with the experiments in terms of ballistic limit, temperature increase and failure mode of the target.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG08 UC3M/MAT 4464) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008 06408)Publicad
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