9,136 research outputs found
Hydrazine monitoring in spacecraft
Hydrazine (HZ) and monomethyl hydrazine (MMH) are highly toxic compounds used as fuels in the Space Shuttle Orbiter Main Engines and in its maneuvering and reaction control system. Satellite refueling during a mission may also result in release of hydrazines. During extravehicular activities, the potential exists for hydrazines to contaminate the suit and to be brought into the internal atmosphere inadvertantly. Because of the high toxicity of hydrazines, a very sensitive, reliable, interference-free, and real-time method of measurement is required. A portable ion mobility spectrometer (IMS) has exhibited a low ppb detection limit for hydrazines suggesting a promising technology for the detection of hydrazines in spacecraft air. The Hydrazine Monitor is a modified airborne vapor monitor (AVM) with a custom-built datalogger. This off-the-shelf IMS was developed for the detection of chemical warfare agents on the battlefield. After early evaluations of the AVM for hydrazine measurements showed a serious interference from ammonia, the AVM was modified to measure HZ and MMH in the ppb concentration range without interference from ammonia in the low ppm range. A description of the Hydrazine Monitor and how it functions is presented
Memory in paediatric temporal lobe epilepsy: effects of lesion type and side.
This study investigated the role of underlying pathology on memory function of children with temporal lobe epilepsy (TLE). Memory was assessed in 44 children with TLE resulting from hippocampal sclerosis (HS) or dysembryoplastic neuroepithelial tumours (DNT), and 22 control children. Delayed story and paired associate recall performance was significantly more impaired in children with HS compared to those with DNT, irrespective of the affected side. Semantic memory was impaired in both HS groups, and also in the left DNT group. These results suggest a role for type, and to a lesser extent, side of pathology in the memory profile of children with TLE
The local electronic structure of alpha-Li3N
New theoretical and experimental investigation of the occupied and unoccupied
local electronic density of states (DOS) are reported for alpha-Li3N. Band
structure and density functional theory calculations confirm the absence of
covalent bonding character. However, real-space full-multiple-scattering
(RSFMS) calculations of the occupied local DOS finds less extreme nominal
valences than have previously been proposed. Nonresonant inelastic x-ray
scattering (NRIXS), RSFMS calculations, and calculations based on the
Bethe-Salpeter equation are used to characterize the unoccupied electronic
final states local to both the Li and N sites. There is good agreement between
experiment and theory. Throughout the Li 1s near-edge region, both experiment
and theory find strong similarities in the s- and p-type components of the
unoccupied local final density of states projected onto an orbital angular
momentum basis (l-DOS). An unexpected, significant correspondence exists
between the near-edge spectra for the Li 1s and N 1s initial states. We argue
that both spectra are sampling essentially the same final density of states due
to the combination of long core-hole lifetimes, long photoelectron lifetimes,
and the fact that orbital angular momentum is the same for all relevant initial
states. Such considerations may be generically applicable for low atomic number
compounds.Comment: 34 pages, 7 figures, 1 tabl
A temperature-controlled device for volumetric measurements of Helium adsorption in porous media
We describe a set-up for studying adsorption of helium in silica aerogels,
where the adsorbed amount is easily and precisely controlled by varying the
temperature of a gas reservoir between 80 K and 180 K. We present validation
experiments and a first application to aerogels. This device is well adapted to
study hysteresis, relaxation, and metastable states in the adsorption and
desorption of fluids in porous media
Effects of Experimental Releases of Oil and Dispersed Oil on Arctic Nearshore Macrobenthos. III. Macroalgae
An experimental subsurface release of chemically dispersed oil at Cape Hatt, northern Baffin Island, resulted in short-term relatively high oil concentrations in the water of two adjacent bays. Untreated oil released onto the surface of the third bay could not be detected in the water below a depth of 1 m. Both releases, however, resulted in measurable contamination of sediments in shallow water. Macroalgae at 3 m depth were sampled by a diver-operated airlift sampler in three treatment bays and in a fourth (reference) bay during the open water seasons of 1980-83 (two pre-spill and four post-spill sampling periods). Biomass, number of species and reproductive condition of the dominant understory algae at 3 m depth did not seem to be adversely affected wither by oil in subtidal sediments or by chemically dispersed oil in the water column. No oil effects were detected in data on the biomasses of total algae or of two of the three species analyzed (Stictyosiphon tortilis and Pilayella littoralis). In the third species, Dictyosiphon foeniculaceus, growth increased in the year following the oil release, either stimulated by low levels of oil in sediments or through natural annual variability. The lack of major effects on macroalgae may have been partly attributable to the lack of effects on herbivores and the vegetative mode of reproduction in the dominant macroalgal species.Key words: arctic macroalgae, oil effects, dispersed oil effects, experimental oil releases, Baffin Island, macrobenthos, Stictyosiphon tortilis, Pilayella littoralis, Dictyosiphon foeniculaceusMots clés: macro-algues arctiques, effets dus au pétrole, effets dus au pétrole dispersé, déversements expérimentaux de pétrole, île Baffin, macrobenthos, Stictyosiphon tortilis, Pilayella littoralis, Dictyosiphon foeniculaceu
Dynamics of Multiferroic Domain Wall in Spin-Cycloidal Ferroelectric DyMnO
We report the dielectric dispersion of the giant magnetocapacitance (GMC) in
multiferroic DyMnO over a wide frequency range. The GMC is found to be
attributable not to the softened electromagnon but to the electric-field-driven
motion of multiferroic domain wall (DW). In contrast to conventional
ferroelectric DWs, the present multiferroic DW motion holds extremely high
relaxation rate of s even at low temperatures. This
mobile nature as well as the model simulation suggests that the multiferroic DW
is not atomically thin as in ferroelectrics but thick, reflecting its magnetic
origin.Comment: 4 pages, 4 figure
Enhanced tracer transport by the spiral defect chaos state of a convecting fluid
To understand how spatiotemporal chaos may modify material transport, we use
direct numerical simulations of the three-dimensional Boussinesq equations and
of an advection-diffusion equation to study the transport of a passive tracer
by the spiral defect chaos state of a convecting fluid. The simulations show
that the transport is diffusive and is enhanced by the spatiotemporal chaos.
The enhancement in tracer diffusivity follows two regimes. For large Peclet
numbers (that is, small molecular diffusivities of the tracer), we find that
the enhancement is proportional to the Peclet number. For small Peclet numbers,
the enhancement is proportional to the square root of the Peclet number. We
explain the presence of these two regimes in terms of how the local transport
depends on the local wave numbers of the convection rolls. For large Peclet
numbers, we further find that defects cause the tracer diffusivity to be
enhanced locally in the direction orthogonal to the local wave vector but
suppressed in the direction of the local wave vector.Comment: 11 pages, 12 figure
Total hydrocarbon analysis by ion mobility spectrometry
Astronauts must be alerted quickly to chemical leaks that compromise their health and the success of their missions. An ideal leak detector would be equally sensitive to all compounds that might constitute a hazard and insensitive to nontoxic compounds. No ideal sensor exists; thus, selection of a methodology is a series of compromises. The commonly used methods are either insensitive at the low exposure levels set by OSHA, NASA, and other organizations or are selectively insensitive to important classes of chemicals such as Freons. After extensive study and experience, the Toxicology Group at JSC has selected ion mobility spectrometry (IMS) for development into a broad range, sensitive detector. In addition to the sensing method, signal processing is important leak detection because a background signal can be expected at all times. The leak-detecting instrument must be programmed to discriminate between authentic leaks and background fluctuations caused by routine operations. The results of an evaluation of the prototype THA is presented in terms related to spacecraft operations. The evaluation included determination of instrumental parameters such as stability and response times. We also included responses to some common components of spacecraft atmospheres in pure form and in binary and ternary mixtures. The output of the four algorithms to the mixtures was found to be noticeably different. These responses are compared on the basis of their utility for signaling a chemical leak. As a means of evaluating its resistance to a falsely positive response, the THA was challenged with carbon dioxide and methane, compounds whose concentrations normally increase in spacecraft air during human habitation. The instrument showed virtually no response to these interferences. Although the prototype THA is designed for space flight, this detector is expected to be useful for field screening at chemical waste dumps and other environmentally sensitive locations
Mass spectrometers and atomic oxygen
The likely role of atmospheric atomic oxygen in the recession of spacecraft surfaces and in the shuttle glow has revived interest in the accurate measurement of atomic oxygen densities in the upper atmosphere. The Air Force Geophysics Laboratory is supplying a quadrupole mass spectrometer for a materials interactions flight experiment being planned by the Johnson Space Center. The mass spectrometer will measure the flux of oxygen on test materials and will also identify the products of surface reactions. The instrument will be calibrated at a new facility for producing high energy beams of atomic oxygen at the Los Alamos National Laboratory. The plans for these calibration experiments are summarized
Randomised controlled trial and economic evaluation of a chest pain observation unit compared with routine care
Objectives To measure the effectiveness and cost effectiveness
of providing care in a chest pain observation unit compared
with routine care for patients with acute, undifferentiated chest
pain.
Design Cluster randomised controlled trial, with 442 days
randomised to the chest pain observation unit or routine care,
and cost effectiveness analysis from a health service costing
perspective.
Setting The emergency department at the Northern General
Hospital, Sheffield, United Kingdom.
Participants 972 patients with acute, undifferentiated chest
pain (479 attending on days when care was delivered in the
chest pain observation unit, 493 on days of routine care)
followed up until six months after initial attendance.
Main outcome measures The proportion of participants
admitted to hospital, the proportion with acute coronary
syndrome sent home inappropriately, major adverse cardiac
events over six months, health utility, hospital reattendance and
readmission, and costs per patient to the health service.
Results Use of a chest pain observation unit reduced the
proportion of patients admitted from 54% to 37% (difference
17%, odds ratio 0.50, 95% confidence interval 0.39 to 0.65,
P < 0.001) and the proportion discharged with acute coronary
syndrome from 14% to 6% (8%, –7% to 23%, P = 0.264). Rates
of cardiac event were unchanged. Care in the chest pain
observation unit was associated with improved health utility
during follow up (0.0137 quality adjusted life years gained, 95%
confidence interval 0.0030 to 0.0254, P = 0.022) and a saving of
£78 per patient (–£56 to £210, P = 0.252).
Conclusions Care in a chest pain observation unit can improve
outcomes and may reduce costs to the health service. It seems
to be more effective and more cost effective than routine care
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