2,392 research outputs found
New directions for hydrogen storage: Sulphur destabilised sodium aluminium hydride
Aluminium sulphide (Al2S3) is predicted to effectively destabilise sodium aluminium hydride (NaAlH4) in a single-step endothermic hydrogen release reaction. The experimental results show unexpectedly complex desorption processes and a range of new sulphur containing hydrogen storage materials have been observed. The NaAlH4-Al 2S3 system releases a total of 4.9 wt% of H2 that begins below 100°C without the need for a catalyst. Characterisation via temperature programmed desorption, in situ synchrotron powder X-ray diffraction, ex situ x-ray diffraction, ex situ Fourier transform infrared spectroscopy and hydrogen sorption measurements reveal complex decomposition processes that involve multiple new sulphur-containing hydride compounds. The system shows partial H2 reversibility, without the need for a catalyst, with a stable H2 capacity of ~1.6 wt% over 15 cycles in the temperature range of 200°C to 300°C. This absorption capacity is limited by the need for high H2 pressures (>280 bar) to drive the absorption process at the high temperatures required for reasonable absorption kinetics. The large number of new phases discovered in this system suggests that destabilisation of complex hydrides with metal sulphides is a novel but unexplored research avenue for hydrogen storage materials
Magnetic local timeâresolved examination of radiation belt dynamics during high speed solar wind speedtTriggered substorm clusters
Particle observations from low Earth orbiting satellites are used to undertake superposed epoch analysis around clusters of substorms, in order to investigate radiation belt dynamical responses to mild geomagnetic disturbances. Medium energy electrons and protons have drift periods long enough to discriminate between processes occurring at different MLT, such as magnetopause shadowing, plasma wave activity, and substorm injections. Analysis shows that magnetopause shadowing produces clear loss in proton and electron populations over a wide range of Lâshells, initially on the dayside, which interact with nightside substormâgenerated flux enhancements following chargeâdependent drift directions. Inner magnetospheric injections recently identified as an important source of 10's to 100's keV electrons at low L (L<3), occurring during similar solar windâdriving conditions as recurrent substorms, show similar but more enhanced geomagnetic AUâindex signatures. Twoâfold increases in substorm occurrence at the time of the sudden particle enhancements at low L shells (SPELLS), suggests a common linkage
HIV/AIDS and Serious Mental Illness: A Risky Conclusion
Letter to the Editor of the journal Psychiatric Services about the conclusions of the October 2012 article "Serious mental illness and risk of new HIV/AIDS diagnoses: an analysis of Medicaid beneficiaries in eight states" published in the journal
Compromised vertebral structural and mechanical properties associated with progressive kidney disease and the effects of traditional pharmacological interventions
BACKGROUND/AIMS:
Patients with chronic kidney disease mineral and bone disorder (CKD-MBD) have a significantly higher vertebral and non-vertebral fracture risk than the general population. Several preclinical models have documented altered skeletal properties in long bones, but few data exist for vertebral bone. The goal of this study was to examine the effects of progressive CKD on vertebral bone structure and mechanics and to determine the effects of treatment with either bisphosphonates or anti-sclerostin antibody in groups of animals with high or low PTH.
METHODS:
Animals with progressive kidney disease were left untreated, treated with calcium to lower PTH, zoledronic acid to lower remodeling without affecting PTH, anti-sclerostin antibody, or anti-sclerostin antibody plus calcium. Non-diseased, untreated littermates served as controls. Vertebral bone morphology (trabecular and cortical) and mechanical properties (structural and material-level) were assessed at 35 weeks of age by microCT and mechanical testing, respectively.
RESULTS:
CKD with high PTH resulted in 6-fold higher bone formation rate, significant reductions in the amount of trabecular and cortical bone, and compromised whole bone mechanical properties in the vertebra compared to normal animals. Treatments that reduced bone remodeling were effective in normalizing vertebral structure and mechanical properties only if the treatment reduced serum PTH. Similarly, treatment with anti-sclerostin antibody was effective in enhancing bone mass and mechanical properties but only if combined with PTH-suppressive treatment.
CONCLUSIONS:
CKD significantly altered both cortical and trabecular bone properties in the vertebra resulting in compromised mechanical properties and these changes can be normalized by interventions that involve reductions in PTH levels
Genomics reveals historic and contemporary transmission dynamics of a bacterial disease among wildlife and livestock
Whole-genome sequencing has provided fundamental insights into infectious disease epidemiology, but has rarely been used for examining transmission dynamics of a bacterial pathogen in wildlife. In the Greater Yellowstone Ecosystem (GYE), outbreaks of brucellosis have increased in cattle along with rising seroprevalence in elk. Here we use a genomic approach to examine Brucella abortus evolution, cross-species transmission and spatial spread in the GYE. We find that brucellosis was introduced into wildlife in this region at least five times. The diffusion rate varies among Brucella lineages (âŒ3 to 8âkm per year) and over time. We also estimate 12 host transitions from bison to elk, and 5 from elk to bison. Our results support the notion that free-ranging elk are currently a self-sustaining brucellosis reservoir and the source of livestock infections, and that control measures in bison are unlikely to affect the dynamics of unrelated strains circulating in nearby elk populations
Momentum flow in black-hole binaries: II. Numerical simulations of equal-mass, head-on mergers with antiparallel spins
Research on extracting science from binary-black-hole (BBH) simulations has
often adopted a "scattering matrix" perspective: given the binary's initial
parameters, what are the final hole's parameters and the emitted gravitational
waveform? In contrast, we are using BBH simulations to explore the nonlinear
dynamics of curved spacetime. Focusing on the head-on plunge, merger, and
ringdown of a BBH with transverse, antiparallel spins, we explore numerically
the momentum flow between the holes and the surrounding spacetime. We use the
Landau-Lifshitz field-theory-in-flat-spacetime formulation of general
relativity to define and compute the density of field energy and field momentum
outside horizons and the energy and momentum contained within horizons, and we
define the effective velocity of each apparent and event horizon as the ratio
of its enclosed momentum to its enclosed mass-energy. We find surprisingly good
agreement between the horizons' effective and coordinate velocities. To
investigate the gauge dependence of our results, we compare pseudospectral and
moving-puncture evolutions of physically similar initial data; although
spectral and puncture simulations use different gauge conditions, we find
remarkably good agreement for our results in these two cases. We also compare
our simulations with the post-Newtonian trajectories and near-field
energy-momentum. [Abstract abbreviated; full abstract also mentions additional
results.]Comment: Submitted to Phys. Rev.
Tantalum versus Titanium Acetabular Shells in Young Active THR Patients: A Radiostereometric Analysis (RSA) Study
Introduction: In the active THR (total hip replacement) population, acetabular component stability is crucial for preventing implant failure. Titanium fiber metal coating is the most common material used in cementless THR. Trabecular metal, composed of porous tantalum, is designed to improve tissue infiltration and limit migration. It is unknown if tantalum offers an advantage over titanium in the biologic fixation of porous-coated acetabular shells. Radiostereometric analysis (RSA) provides highly precise measurements of micromotion that are otherwise not detectable by routine radiographs.
Methods: In this IRB approved, prospective, randomized, blinded study, 46 patients received a primary THR by a single surgeon. Each patient was randomized to receive a titanium (23) or tantalum (23) uncemented cup. Tantalum RSA markers were implanted around the polyethylene liner and into the patientâs femur and periacetabular bone. Also, patients received either a highly cross-linked (n=25) or a conventional liner (n=21). RSA examinations, Harris Hip, UCLA, WOMAC, SF-12 scores were obtained at 10 days, 6 months, and annually through 5 years.
Results: The randomized groups had comparable mean age, preoperative activity, and average BMI. The tantalum shells demonstrated less median translation than the titanium shells at each time-point, but there was no statistical difference between the two shells. At 6 months median translation of tantalum and titanium was -0.01mm and 0.04mm and remained stable with median translation of -0.02mm and 0.04mm at four years. Mean UCLA, WOMAC, Harris Hip, and SF-12 PCS and MCS scores improved similarly in both groups.
Conclusions: After THR, both patient cohorts had excellent clinical outcomes with statistically significant improvements in function and pain relief. Although tantalum porous-coated acetabular shells demonstrated less y-translation and y-rotation at all time points, there was no statistically significant difference in shell migration and both shells demonstrated excellent stability with minimal micromotion at four years
Improving marine disease surveillance through sea temperature monitoring, outlooks and projections
International audienceTo forecast marine disease outbreaks as oceans warm requires new environmental surveillance tools. We describe an iterative process for developing these tools that combines research, development and deployment for suitable systems. The first step is to identify candidate hostâpathogen systems. The 24 candidate systems we identified include sponges, corals, oysters, crustaceans, sea stars, fishes and sea grasses (among others). To illustrate the other steps, we present a case study of epizootic shell disease (ESD) in the American lobster. Increasing prevalence of ESD is a contributing factor to lobster fishery collapse in southern New England (SNE), raising concerns that disease prevalence will increase in the northern Gulf of Maine under climate change. The lowest maximum bottom temperature associated with ESD prevalence in SNE is 128C. Our seasonal outlook for 2015 and long-term projections show bottom temperatures greater than or equal to 128C may occur in this and coming years in the coastal bays of Maine. The tools presented will allow managers to target efforts to monitor the effects of ESD on fishery sustainability and will be iteratively refined. The approach and case example highlight that temperature-based surveillance tools can inform research, monitoring and management of emerging and continuing marine disease threats
Astrometry with the Keck-Interferometer: the ASTRA project and its science
The sensitivity and astrometry upgrade ASTRA of the Keck Interferometer is
introduced. After a brief overview of the underlying interferometric
principles, the technology and concepts of the upgrade are presented. The
interferometric dual-field technology of ASTRA will provide the KI with the
means to observe two objects simultaneously, and measure the distance between
them with a precision eventually better than 100 uas. This astrometric
functionality of ASTRA will add a unique observing tool to fields of
astrophysical research as diverse as exo-planetary kinematics, binary
astrometry, and the investigation of stars accelerated by the massive black
hole in the center of the Milky Way as discussed in this contribution.Comment: 22 pages, 10 figures (low resolution), contribution to the
summerschool "Astrometry and Imaging with the Very Large Telescope
Interferometer", 2 - 13 June, 2008, Keszthely, Hungary, corrected authorlis
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