475 research outputs found
Capillary waves at the liquid-vapor interface and the surface tension of water models
Capillary waves occurring at the liquid-vapor interface of water are studied
using molecular dynamics simulations. In addition, the surface tension,
determined thermodynamically from the difference in the normal and tangential
pressure at the liquid-vapor interface, is compared for a number of standard
three- and four-point water models. We study four three-point models (SPC/E,
TIP3P, TIP3P-CHARMM, and TIP3P-Ew) and two four-point models (TIP4P and
TIP4P-Ew). All of the models examined underestimate the surface tension; the
TIP4P-Ew model comes closest to reproducing the experimental data. The surface
tension can also be determined from the amplitude of capillary waves at the
liquid-vapor interface by varying the surface area of the interface. The
surface tensions determined from the amplitude of the logarithmic divergence of
the capillary interfacial width and from the traditional thermodynamic method
agree only if the density profile is fitted to an error function instead of a
hyperbolic tangent function.Comment: 11 pages, 8 figures, 7 tables. Accepted for publication in J. Chem.
Phys. [v2: Added references, corrected minor errors
Assessment of the occlusion technique as a means for evaluating the distraction potential of driver support systems
Driver distraction is a safety-critical issue that has been bought to greater public attention with the recent developments of more advanced driver support systems (DSS),
such as navigation and collision warning. Tasks performed with such systems have the
potential to distract drivers significantly from the primary task of controlling their
vehicle, and this may result in an accident. Designers of DSS need to be able to assess
this distraction potential in the early stages of design. In this respect, the occlusion
technique and its associated measures are claimed to be reliable indicators of potential
visual distraction. In particular, it has been argued that the technique provides more
information concerning the likely visual demand of a system than other economical
methods based on static task time, such as the 15-second rule. To investigate these
assertions, a study compared results from an occlusion assessment and a road-based
assessment. Sixteen experienced drivers carried out a range of tasks using two
alternative user-interfaces under three conditions: statically, with full vision, statically,
with restricted vision (occlusion), and whilst driving on a dual carriageway road within
the UK. It was found that occlusion measures provided more information regarding the
prospective visual demand of a DSS than did static task times. In particular, the
resumability ratio assessed how far a task can be progressed whilst in periods with
vision and without vision. It is concluded that the technique offers advantages over
other methods, but requires a robust prototype for use as part of a driver-centred design process
Построение индивидуальных траекторий обучения и создание индивидуального плана развития студента на основе портрета компетенций выбранной специализации
В данной работе проводится анализ соответствия компетенций студента целевому портрету компетенций вы бранной специализации и на основе этого реализовано создание индивидуального плана развития студента до вышеописанного портрета.In this work, analyzes the correspondence of the student's competencies to the target portrait of the competencies of the chosen specialization and, on the basis of this, the creation of an individual student development plan to the above portrait is realized
Light-Evoked Calcium Responses of Isolated Melanopsin- Expressing Retinal Ganglion Cells
A small number (\u3c2%) of mammalian retinal ganglion cells express the photopigment melanopsin and are intrinsically photosensitive (ipRGCs). Light depolarizes ipRGCs and increases intracellular calcium levels ( [Ca2+]i ) but the signaling cascades underlying these responses have yet to be elucidated. To facilitate physiological studies on these rare photoreceptors, highly enriched ipRGC cultures from neonatal rats were generated using anti-melanopsin-mediated plate adhesion (immunopanning). This novel approach enabled experiments on isolated ipRGCs, eliminating the potential confounding influence of rod/cone-driven input. Light induced a rise in [Ca2+]i (monitored using fura-2 imaging) in the immunopanned ipRGCs and the source of this Ca2+ signal was investigated. The Ca2+ responses were inhibited by 2-aminoethoxydiphenyl borate, SKF-96365 (1–2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl-1H-imidazole), flufenamic acid, lanthanum, and gadolinium, consistent with the involvement of canonical transient receptor potential (TRP) channels in ipRGC phototransduction. However, the contribution of direct Ca2+ flux through a putative TRP channel to ipRGC [Ca2+]i was relatively small, as most (~90%) of the light-induced Ca2+ responses could be blocked by preventing action potential firing with tetrodotoxin. The L-type voltage-gated Ca2+ channel (VGCC) blockers verapamil and (+)-cis-diltiazem significantly reduced the light-evoked Ca2+ responses, while the internal Ca2+ stores depleting agent thapsigargin had negligible effect. These results indicate that Ca2+ influx through VGCCs, activated after action potential firing, was the primary source for light-evoked elevations in ipRGC [Ca2+]i. Furthermore, concurrent Ca2+ imaging and cell-attached electrophysiological recordings demonstrated that the Ca2+ responses were highly correlated to spike frequency, thereby establishing a direct link between action potential firing and somatic [Ca2+]i in lightstimulated ipRGCs
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Nitroarylurea-terminated supramolecular polymers that exhibit facile thermal repair and aqueous swelling-induced sealing of defects
Bi- and tri-armed polyethylene glycol units endcapped with nitroaryl urea units have been synthesised. These endcapped polymers are able to self-assemble via complementary supramolecular interactions, specifically urea-urea and nitro-urea hydrogen bonding, to afford materials with dramatically increased mechanical and thermal properties when compared to those of the uncapped polyethylene glycol precursors. Thin films of the capped polymeric systems are able to self-repair following defect creation. Control over the mechanical and thermal characteristics (in terms of bulk viscosity) of the self-assembled networks was achieved by varying the proportion of tri-armed to bi-armed self-assembly units included in the polymer. These systems demonstrate water absorption and swelling capabilities that are also controllable by varying the ratio of the two types of unit. These physical properties have been optimised to realise a secondary pathway to puncture-repair as a result of swelling on water contact
Phase Coexistence of a Stockmayer Fluid in an Applied Field
We examine two aspects of Stockmayer fluids which consists of point dipoles
that additionally interact via an attractive Lennard-Jones potential. We
perform Monte Carlo simulations to examine the effect of an applied field on
the liquid-gas phase coexistence and show that a magnetic fluid phase does
exist in the absence of an applied field. As part of the search for the
magnetic fluid phase, we perform Gibbs ensemble simulations to determine phase
coexistence curves at large dipole moments, . The critical temperature is
found to depend linearly on for intermediate values of beyond the
initial nonlinear behavior near and less than the where no
liquid-gas phase coexistence has been found. For phase coexistence in an
applied field, the critical temperatures as a function of the applied field for
two different are mapped onto a single curve. The critical densities
hardly change as a function of applied field. We also verify that in an applied
field the liquid droplets within the two phase coexistence region become
elongated in the direction of the field.Comment: 23 pages, ReVTeX, 7 figure
Diagnosing childhood pulmonary tuberculosis using a single sputum specimen on Xpert MTB/RIF at point of care
Background. The GeneXpertMTB/RIF (Cepheid, USA) (Xpert) has proved successful for pulmonary tuberculosis (TB) diagnosis on decontaminated/concentrated induced sputum specimens from children. Capacity to perform induction in many settings is limited.Objective. To assess: (i) volumes of ‘routinely obtained’ sputum in a district-level academic hospital; (ii) whether sputum specimens not meeting Xpert-required testing volumes could still be tested; and (iii) performance of Xpert on a single paediatric sputum specimen at point of care (POC).Methods. Two sputa were collected from paediatric TB suspects (£14 years) at Rahima Moosa Mother and Child Hospital, Johannesburg, South Africa. One specimen was weighed at POC; if the volume was ≥0.1 mL but <0.5 mL, it was increased to 0.5 mL using saline. On-site Xpert testing (G3 cartridge) was performed by a dedicated laboratory technician. The second specimen was referred for TB smear microscopy and culture as per standard of care (SOC). Results. A total of 484 patients presumed to have TB (median age 24 months) were eligible for this study, performed between June 2011 and May 2012. Xpert could not be used on 4.1% of specimens because of volumes <0.1 mL, and 62.8% required addition of saline prior to Xpert testing. Xpert generated a 2.2% error and 3.7% invalid rate, compared with the SOC that rejected 2.3% because of insufficient volume and 2.3% that were contaminated. The diagnostic performance compared with culture was 62.5% (95% confidence interval (CI) 24.7 - 91) and 99.1% (95% CI 97.4 - 99.8) sensitivity and specificity, respectively, for Xpert (n=345) and 33.3% (7.9 - 69.9) and 99.5% (98.1 - 99.9) sensitivity and specificity, respectively, for smear microscopy (n=374).Conclusions. Up to 67% of ‘routinely obtained’ sputum specimens from children (£14 years) are below the required volume for Xpert testing but can be ‘topped up’ with saline. XpertMTB/RIF performed better than microscopy and generated clinically relevant, timeous results, but sensitivity did not reach the same levels as culture in children
Turbulence Transport Modeling and First Orbit Parker Solar Probe (PSP) Observations
Parker Solar Probe (PSP) achieved its first orbit perihelion on November 6,
2018, reaching a heliocentric distance of about 0.165 au (35.55 R).
Here, we study the evolution of fully developed turbulence associated with the
slow solar wind along the PSP trajectory between 35.55 R and 131.64
R in the outbound direction, comparing observations to a theoretical
turbulence transport model. Several turbulent quantities, such as the
fluctuating kinetic energy and the corresponding correlation length, the
variance of density fluctuations, and the solar wind proton temperature are
determined from the PSP SWEAP plasma data along its trajectory between 35.55
R and 131.64 R. The evolution of the PSP derived turbulent
quantities are compared to the numerical solutions of the nearly incompressible
magnetohydrodynamic (NI MHD) turbulence transport model recently developed by
Zank et al. (2017). We find reasonable agreement between the theoretical and
observed results. On the basis of these comparisons, we derive other
theoretical turbulent quantities, such as the energy in forward and backward
propagating modes, the total turbulent energy, the normalized residual energy
and cross-helicity, the fluctuating magnetic energy, and the correlation
lengths corresponding to forward and backward propagating modes, the residual
energy, and the fluctuating magnetic energy
Variable-Speed Power-Turbine Research at Glenn Research Center
The main rotors of the NASA Large Civil Tilt-Rotor (LCTR) notional vehicle operate over a wide speed-range, from 100 percent at takeoff to 54 percent at cruise. The variable-speed power turbine (VSPT) offers one approach by which to effect this speed variation. VSPT aerodynamics challenges include high work factors at cruise, wide (40 to 60 ) incidence-angle variations in blade and vane rows over the speed range, and operation at low Reynolds numbers. Rotordynamics challenges include potential responsiveness to shaft modes within the 50 percent VSPT speed-range. A research effort underway at NASA Glenn Research Center, intended to address these key aerodynamic and rotordynamic challenges, is described. Conceptual design and 3-D multistage RANS and URANS analyses, conducted internally and under contract, provide expected VSPT sizing, stage-count, performance and operability information, and maps for system studies. Initial steps toward experimental testing of incidence-tolerant blading in a transonic linear cascade are described, and progress toward development/improvement of a simulation capability for multistage turbines with low Reynolds number transitional flow is summarized. Preliminary rotordynamics analyses indicate that viable concept engines with 50 percent VSPT shaft-speed range. Assessments of potential paths toward VSPT component-level testing are summarized
Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
Large-scale molecular simulations are performed to investigate tensile
failure of polymer interfaces as a function of welding time . Changes in the
tensile stress, mode of failure and interfacial fracture energy are
correlated to changes in the interfacial entanglements as determined from
Primitive Path Analysis. Bulk polymers fail through craze formation, followed
by craze breakdown through chain scission. At small welded interfaces are
not strong enough to support craze formation and fail at small strains through
chain pullout at the interface. Once chains have formed an average of about one
entanglement across the interface, a stable craze is formed throughout the
sample. The failure stress of the craze rises with welding time and the mode of
craze breakdown changes from chain pullout to chain scission as the interface
approaches bulk strength. The interfacial fracture energy is calculated
by coupling the simulation results to a continuum fracture mechanics model. As
in experiment, increases as before saturating at the average
bulk fracture energy . As in previous simulations of shear strength,
saturation coincides with the recovery of the bulk entanglement density. Before
saturation, is proportional to the areal density of interfacial
entanglements. Immiscibiltiy limits interdiffusion and thus suppresses
entanglements at the interface. Even small degrees of immisciblity reduce
interfacial entanglements enough that failure occurs by chain pullout and
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