4,990 research outputs found
Phase diagram for a Bose-Einstein condensate moving in an optical lattice
The stability of superfluid currents in a system of ultracold bosons was
studied using a moving optical lattice. Superfluid currents in a very weak
lattice become unstable when their momentum exceeds 0.5 recoil momentum.
Superfluidity vanishes already for zero momentum as the lattice deep reaches
the Mott insulator(MI) phase transition. We study the phase diagram for the
disappearance of superfluidity as a function of momentum and lattice depth
between these two limits. Our phase boundary extrapolates to the critical
lattice depth for the superfluid-to-MI transition with 2% precision. When a
one-dimensional gas was loaded into a moving optical lattice a sudden
broadening of the transition between stable and unstable phases was observed.Comment: 4 figure
Performance Metrics for the Objective Assessment of Capacitive Deionization Systems
In the growing field of capacitive deionization (CDI), a number of
performance metrics have emerged to describe the desalination process.
Unfortunately, the separation conditions under which these metrics are measured
are often not specified, resulting in optimal performance at minimal removal.
Here we outline a system of performance metrics and reporting conditions that
resolves this issue. Our proposed system is based on volumetric energy
consumption (Wh/m) and throughput productivity (L/h/m) reported for a
specific average concentration reduction, water recovery, and feed salinity. To
facilitate and rationalize comparisons between devices, materials, and
operation modes, we propose a nominal standard testing condition of removing 5
mM from a 20 mM NaCl feed solution at 50% water recovery for CDI research.
Using this separation, we compare the desalination performance of a
flow-through electrode (fte-CDI) cell and a flow between membrane (fb-MCDI)
device, showing how significantly different systems can be compared in terms of
generally desirable desalination characteristics. In general, we find that
performance analysis must be considered carefully so to not allow for ambiguous
separation conditions or the maximization of one metric at the expense of
another. Additionally, for context we discuss a number of important underlying
performance indicators and cell characteristics that are not performance
measures in and of themselves but can be examined to better understand
differences in performance
The Stability of Double White Dwarf Binaries Undergoing Direct Impact Accretion
We present numerical simulations of dynamically unstable mass transfer in a
double white dwarf binary with initial mass ratio, q = 0.4. The binary
components are approximated as polytropes of index n = 3/2 and the initially
synchronously rotating, semi-detached equilibrium binary is evolved
hydrodynamically with the gravitational potential being computed through the
solution of Poisson's equation. Upon initiating deep contact in our baseline
simulation, the mass transfer rate grows by more than an order of magnitude
over approximately ten orbits, as would be expected for dynamically unstable
mass transfer. However, the mass transfer rate then reaches a peak value, the
binary expands and the mass transfer event subsides. The binary must therefore
have crossed the critical mass ratio for stability against dynamical mass
transfer. Despite the initial loss of orbital angular momentum into the spin of
the accreting star, we find that the accretor's spin saturates and angular
momentum is returned to the orbit more efficiently than has been previously
suspected for binaries in the direct impact accretion mode. To explore this
surprising result, we directly measure the critical mass ratio for stability by
imposing artificial angular momentum loss at various rates to drive the binary
to an equilibrium mass transfer rate. For one of these driven evolutions, we
attain equilibrium mass transfer and deduce that effectively q_crit has evolved
to approximately 2/3. Despite the absence of a fully developed disk, tidal
interactions appear effective in returning excess spin angular momentum to the
orbit.Comment: 27 pages, 6 figures. Please see
http://www.phys.lsu.edu/faculty/tohline/astroph/mftd07/ for animations and
full resolution figures. Accepted for publication in the Astrophysical
Journa
The impact of prior physical conditioning in initial recruit training success: A systematic review
Aim: To determine whether recruits who underwent a physical conditioning program prior to initial tactical training had increased rates of success.Design: Systematic ReviewMethod: A systematic search, following the PRISMA protocol and registered in the Open Science Framework, was conducted to identify relevant studies. Keywords, derived from three themes (physical conditioning, tactical, and recruits), were employed in the search of database CINAHL, ProQuest, PubMed, Scopus, SportDiscus, and Web of Science. Studies were screened against inclusion/exclusion criteria with data extracted and analyzed. The Joanna Briggs Institute critical appraisal tools were used to assess methodological quality of included studies by two authors independently with a Kappa analysis to determine inter-rater agreement.Results: Of 14,411 identified articles, 13 studies informed the review. The mean quality of studies was considered ‘good’ with a Kappa of 0.81 between raters. Seven studies identified that an increase in physical fitness, through use of preconditioning programs, resulted in lower rates of injury. Three studies attributed increased basic training pass rates to physical conditioning programs. However, three studies failed to find a change in attrition rates following the programs.Conclusion: The volume of evidence suggests that programs aimed at increasing muscular conditioning and aerobic endurance prior to tactical training would result in fewer injuries and increased pass rates although reductions in absolute attrition may not change.Key Practice Points:• Recruits are less likely to be injured if they are fitter and / or have completed additional training prior to completing training for a tactical occupation
Perceptions of Discrimination Among Persons With Serious Mental Illness
Objectives: The authors sought to gain further perspective on discrimination experienced by persons with mental illness by comparing self-reports of discrimination due to mental illness to self-reports of discrimination due to other group characteristics, such as race, gender, and sexual orientation. Methods: A total of 1,824 persons with serious mental illness who participated in a baseline interview for a multistate study on consumer-operated services completed a two-part discrimination questionnaire. The first part of the questionnaire assessed participants\u27 perceptions about discrimination due to mental illness as well as more than half a dozen other group characteristics. The second part of the questionnaire asked participants who reported some experience with discrimination to identify areas in which this discrimination occurred, such as employment, education, and housing. Results: More than half of the study participants (949 participants, or 53 percent) reported some experience with discrimination. The most frequent. sources of this discrimination were mental disability, race, sexual orientation, and physical disability. Areas in which discrimination frequently occurred included employment, housing, and interactions with law enforcement. Areas in which discrimination was experienced did not significantly differ among groups of study participants characterized by mental disability, race, gender, sexual orientation, or physical disability. Conclusions: Discrimination based on group characteristics other than mental illness does not diminish the impact of stigma associated with mental illness. Antistigma programs need to target not only discrimination related to mental illness but also that associated with other group characteristics, such as race, gender, sexual orientation, and physical disability
Nanographene Aerogels: Size Effect of the Precursor Graphene Oxide on Gelation Process and Electrochemical Properties
Improving the electrochemical properties of graphene aerogels (GAs) without doping or making composites is an attractive synthetic strategy. In this work we report on the effects of graphene sheet dimensions on GAs. Nanographene aerogels (nG-AGs) were synthesized using nanographene oxide (nGO) powder with a mean platelet diameter of 90 nm. In-situ Fourier transform infrared spectroscopy (FTIR) during gelation revealed a longer fast gelation regime for nG-AGs than for stdG-AGs. The surface-area-normalized capacitance of nG-AGs calculated from cyclic voltammetry is 16% higher than that of stdG-AGs, and the onset of hydrogen evolution is observed at a lower over-potential. These observations can be attributed to increased edge sites and defects in nanographene sheets. Our results imply that the diameter of the precursor graphene sheets can be used as a parameter to optimize the electrochemical properties of graphene AGs depending on the application
Nanographene Aerogels: Size Effect of the Precursor Graphene Oxide on Gelation Process and Electrochemical Properties
Improving the electrochemical properties of graphene aerogels (GAs) without doping or making composites is an attractive synthetic strategy. In this work we report on the effects of graphene sheet dimensions on GAs. Nanographene aerogels (nG-AGs) were synthesized using nanographene oxide (nGO) powder with a mean platelet diameter of 90 nm. In-situ Fourier transform infrared spectroscopy (FTIR) during gelation revealed a longer fast gelation regime for nG-AGs than for stdG-AGs. The surface-area-normalized capacitance of nG-AGs calculated from cyclic voltammetry is 16% higher than that of stdG-AGs, and the onset of hydrogen evolution is observed at a lower over-potential. These observations can be attributed to increased edge sites and defects in nanographene sheets. Our results imply that the diameter of the precursor graphene sheets can be used as a parameter to optimize the electrochemical properties of graphene AGs depending on the application
Internal derangement of the knee in physically demanding occupations: A rapid review
Aim: To identify and review studies reporting on occupational risk factors for the occurrence of internal derangement of the knee (IDK) in physically demanding occupations.Design: Systematic review of the literature.Method: This review was guided by the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. A comprehensive search of seven databases was performed using terms derived from three concepts: ‘risk’, ‘paid occupations’, and ‘IDK’.Results: One article met the eligibility criteria. Findings revealed that male Turkish military personnel with IDK that was secondary to anterior cruciate ligament (ACL) ruptures, managed without reconstruction, and who continued their regular military duties following ACL rupture, had a high prevalence of additional intra- articular lesions. A moderate positive correlation was found between the time from the initial ACL rupture and the presence of at least one additional intra-articular lesion (rs = 0.574; p = 0.0001). Additionally, individuals aged 30 years and older were at slightly greater risk than their younger peers.Conclusion: These findings suggest that the occupational demands to which Turkish military personnel are exposed are associated with IDK developing and worsening over time after ACL rupture as military duties continue.</div
The incidence and risk factors for the development of fractures in military recruits and qualified personnel: A rapid review
Aim: To identify and synthesise findings from studies reporting on the incidence of, and risk factors for, traumatic fractures in military personnel.Design: Rapid reviewMethods: Following the PRISMA guidelines, PubMed, EBSCO, CINAHL and ProQuest databases were systematically searched using key terms derived from the following concepts: ‘fractures’, ‘work’ and ‘risk’. Key findings from the included studies were extracted and tabulated, including risk factors, incidence and risk ratios.Results: Twenty-eight studies were included, with four studies reporting on recruit/trainees and 24 reporting on qualified military personnel. Recruit incidence ranged from 7.7 – 29.5 cases per 1,000 person-years, while incidence in qualified personnel ranged from 1.9 – 57.6 cases per 1,000 person-years. Enlisted personnel, younger service members (18 – 29 years), and personnel of Army and Marines Corp branches were at increased risk. Fractures predominantly occurred in the lower extremities, although the hands were often a site of traumatic fracture. Risk factors and mechanisms identified for traumatic fractures included NSAID use, sports, physical training, motor vehicle accidents, collisions, blasts from improvised explosive devices, and gunshots, often in combat settings.Conclusion: The findings highlight the incidence of fractures in recruits and qualified military personnel, and identify a range of risk factors in military environments
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