27,495 research outputs found
Extremal Graph Theory for Metric Dimension and Diameter
A set of vertices \emph{resolves} a connected graph if every vertex
is uniquely determined by its vector of distances to the vertices in . The
\emph{metric dimension} of is the minimum cardinality of a resolving set of
. Let be the set of graphs with metric dimension
and diameter . It is well-known that the minimum order of a graph in
is exactly . The first contribution of this
paper is to characterise the graphs in with order
for all values of and . Such a characterisation was
previously only known for or . The second contribution is
to determine the maximum order of a graph in for all
values of and . Only a weak upper bound was previously known
Assessing carbon-based anodes for lithium-ion batteries: A universal description of charge-transfer binding
Many key performance characteristics of carbon-based lithium-ion battery
anodes are largely determined by the strength of binding between lithium (Li)
and sp2 carbon (C), which can vary significantly with subtle changes in
substrate structure, chemistry, and morphology. Here, we use density functional
theory calculations to investigate the interactions of Li with a wide variety
of sp2 C substrates, including pristine, defective, and strained graphene;
planar C clusters; nanotubes; C edges; and multilayer stacks. In almost all
cases, we find a universal linear relation between the Li-C binding energy and
the work required to fill previously unoccupied electronic states within the
substrate. This suggests that Li capacity is predominantly determined by two
key factors -- namely, intrinsic quantum capacitance limitations and the
absolute placement of the Fermi level. This simple descriptor allows for
straightforward prediction of the Li-C binding energy and related battery
characteristics in candidate C materials based solely on the substrate
electronic structure. It further suggests specific guidelines for designing
more effective C-based anodes. The method should be broadly applicable to
charge-transfer adsorption on planar substrates, and provides a
phenomenological connection to established principles in supercapacitor and
catalyst design.Comment: accepted by Physical Review Letter
Short-Chained Oligo(Ethylene Oxide)-Functionalized Gold Nanoparticles: Realization Of Significant Protein Resistance
Protein corona formed on nanomaterial surfaces play an important role in the bioavailability and cellular uptake of nanomaterials. Modification of surfaces with oligoethylene glycols (OEG) are a common way to improve the resistivity of nanomaterials to protein adsorption. Short-chain ethylene oxide (EO) oligomers have been shown to improve the protein resistance of planar Au surfaces. We describe the application of these EO oligomers for improved protein resistance of 30 nm spherical gold nanoparticles (AuNPs). Functionalized AuNPs were characterized using UV-Vis spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. Capillary electrophoresis (CE) was used for separation and quantitation of AuNPs and AuNP-protein mixtures. Specifically, nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was employed for the determination of equilibrium and rate constants for binding between citrate-stabilized AuNPs and two model proteins, lysozyme and fibrinogen. Semi-quantitative CE analysis was carried out for mixtures of EO-functionalized AuNPs and proteins, and results demonstrated a 2.5-fold to 10-fold increase in protein binding resistance to lysozyme depending on the AuNP surface functionalization and a 15-fold increase in protein binding resistance to fibrinogen for both EO oligomers examined in this study
Spectropolarimetry of the H-alpha line in Herbig Ae/Be stars
Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS
telescope, we have obtained a large number of high precision spectropolarimetrc
observations (284) of Herbig AeBe stars collected over 53 nights totaling more
than 300 hours of observing. Our sample of five HAeBe stars: AB Aurigae,
MWC480, MWC120, MWC158 and HD58647, all show systematic variations in the
linear polarization amplitude and direction as a function of time and
wavelength near the H-alpha line. In all our stars, the H-alpha line profiles
show evidence of an intervening disk or outflowing wind, evidenced by strong
emission with an absorptive component. The linear polarization varies by 0.2%
to 1.5% with the change typically centered in the absorptive part of the line
profile. These observations are inconsistent with a simple disk-scattering
model or a depolarization model which produce polarization changes centered on
the emmissive core. We speculate that polarized absorption via optical pumping
of the intervening gas may be the cause.Comment: Accepted for publication in ApJ Letter
Application of Phase Change Materials to Domestic Refrigerators
The paper investigates the performance improvement provided by a phase change material associated with the evaporator in a domestic refrigerator. The heat release and storage rate of encapsulated ice, used as the thermal energy storage material, has been investigated numerically. The mathematical model for phase change is based on the enthalpy method and the governing equations were discretized on a fixed grid using the finite difference method.
The influence of PCM thickness (2, 3 and 4 × 10-3 m slabs), ambient temperature (20°C, 25°C, 30°C and 43°C) and evaporating temperature (-15°C and -10°C) have been investigated. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 47% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C. Overall, the model provides a useful tool for evaluating the design and operation of a thermal storage refrigerator
Do Employees From Less-Healthy Communities Use More Care and Cost More? Seeking to Establish a Business Case for Investment in Community Health.
INTRODUCTION: Few studies have examined the impact of community health on employers. We explored whether employed adults and their adult dependents living in less-healthy communities in the greater Philadelphia region used more care and incurred higher costs to employers than employees from healthier communities.
METHODS: We used a multi-employer database to identify adult employees and dependents with continuous employment and mapped them to 31 zip code regions. We calculated community health scores at the regional level, by using metrics similar to the Robert Wood Johnson Foundation (RWJF) County Health Rankings but with local data. We used descriptive analyses and multilevel linear modeling to explore relationships between community health and 3 outcome variables: emergency department (ED) use, hospital use, and paid claims. Business leaders reviewed findings and offered insights on preparedness to invest in community health improvement.
RESULTS: Poorer community health was associated with high use of ED services, after controlling for age and sex. After including a summary measure of racial composition at the zip code region level, the relationship between community health and ED use became nonsignificant. No significant relationships between community health and hospitalizations or paid claims were identified. Business leaders expressed interest in further understanding health needs of communities where their employees live.
CONCLUSION: The health of communities in which adult employees and dependents live was associated with ED use, but similar relationships were not seen for hospitalizations or paid claims. This finding suggests a need for more primary care access. Despite limited quantitative evidence, business leaders expressed interest in guidance on investing in community health improvement
Modelling of a thermal storage refrigerator
The paper investigates the effect of adding a phase change material in thermal contact with the evaporator in a natural convection domestic refrigerator. The enthalpy method has been applied to investigate the heat release and storage rate of encapsulated ice. The effect of three parameters was investigated by the numerical method: PCM thickness, ambient temperature and evaporating temperature. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 48% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C.
A CFD simulation of the airflow and temperature distribution in the natural convection refrigerator was carried out to evaluate the most effective position to place the PCM (top or back wall). The predicted airflow patterns and temperature profiles were considerably different for the two PCM orientations. The predicted air temperature was above 5ºC, thus a eutectic PCM may be required to reduce the temperature in the refrigerator compartment
Hydrodynamics of the stream-disk impact in interacting binaries
We use hydrodynamic simulations to provide quantitative estimates of the
effects of the impact of the accretion stream on disks in interacting binaries.
For low accretion rates, efficient radiative cooling of the hotspot region can
occur, and the primary consequence of the stream impact is stream overflow
toward smaller disk radii. The stream is well described by a ballistic
trajectory, but larger masses of gas are swept up and overflow at smaller, but
still highly supersonic, velocities. If cooling is inefficient, overflow still
occurs, but there is no coherent stream inward of the disk rim. Qualitatively,
the resulting structure appears as a bulge extending downstream along the disk
rim. We calculate the mass fraction and velocity of the overflowing component
as a function of the important system parameters, and discuss the implications
of the results for X-ray observations and doppler tomography of cataclysmic
variables, low-mass X-ray binaries and supersoft X-ray sources.Comment: 16 pages, including 8 figures. 1 color figure as a jpeg. ApJ, in
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Effects of augmented exercise therapy time after stroke: a meta-analysis
<p><b>Background and Purpose:</b> To present a systematic review of studies that addresses the effects of intensity of augmented exercise therapy time (AETT) on activities of daily living (ADL), walking, and dexterity in patients with stroke.</p>
<p><b>Summary of Review:</b> A database of articles published from 1966 to November 2003 was compiled from MEDLINE, CINAHL, Cochrane Central Register of Controlled Trials, PEDro, DARE, and PiCarta using combinations of the following key words: stroke, cerebrovascular disorders, physical therapy, physiotherapy, occupational therapy, exercise therapy, rehabilitation, intensity, dose–response relationship, effectiveness, and randomized controlled trial. References presented in relevant publications were examined as well as abstracts in proceedings. Studies that satisfied the following selection criteria were included: (1) patients had a diagnosis of stroke; (2) effects of intensity of exercise training were investigated; and (3) design of the study was a randomized controlled trial (RCT). For each outcome measure, the estimated effect size (ES) and the summary effect size (SES) expressed in standard deviation units (SDU) were calculated for ADL, walking speed, and dexterity using fixed and random effect models. Correlation coefficients were calculated between observed individual effect sizes on ADL of each study, additional time spent on exercise training, and methodological quality. Cumulative meta-analyses (random effects model) adjusted for the difference in treatment intensity in each study was used for the trials evaluating the effects of AETT provided. Twenty of the 31 candidate studies, involving 2686 stroke patients, were included in the synthesis. The methodological quality ranged from 2 to 10 out of the maximum score of 14 points. The meta-analysis resulted in a small but statistically significant SES with regard to ADL measured at the end of the intervention phase. Further analysis showed a significant homogeneous SES for 17 studies that investigated effects of increased exercise intensity within the first 6 months after stroke. No significant SES was observed for the 3 studies conducted in the chronic phase. Cumulative meta-analysis strongly suggests that at least a 16-hour difference in treatment time between experimental and control groups provided in the first 6 months after stroke is needed to obtain significant differences in ADL. A significant SES supporting a higher intensity was also observed for instrumental ADL and walking speed, whereas no significant SES was found for dexterity.</p>
<p><b>Conclusion:</b> The results of the present research synthesis support the hypothesis that augmented exercise therapy has a small but favorable effect on ADL, particularly if therapy input is augmented at least 16 hours within the first 6 months after stroke. This meta-analysis also suggests that clinically relevant treatment effects may be achieved on instrumental ADL and gait speed.</p>
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