1,663 research outputs found
Patterns of Activity Expressed by Juvenile Horseshoe Crabs
Adult American horseshoe crabs, Limulus polyphemus, possess endogenous circadian and circatidal clocks controlling visual sensitivity and locomotion, respectively. The goal of this study was to determine the types of activity rhythms expressed by juvenile horseshoe crabs (n = 24) when exposed to a 14:10 light/dark cycle (LD) for 10 days, followed by 10 days of constant darkness (DD). Horseshoe crab activity was recorded with a digital time-lapse video system that used an infrared-sensitive camera so animals could be monitored at night. In LD, 15 animals expressed daily patterns of activity, 6 displayed a circatidal pattern, and the remaining 3 were arrhythmic. Of the 15 animals with daily patterns of locomotion, 7 had a significant preference (P \u3c 0.05) for diurnal activity and 3 for nocturnal activity; the remainder did not express a significant preference for day or night activity. In DD, 13 horseshoe crabs expressed circatidal rhythms and 8 maintained a pattern of about 24 h. Although these results suggest the presence of a circadian clock influencing circatidal patterns of locomotion, these apparent circadian rhythms may actually represent the expression of just one of the two bouts of activity driven by the putative circalunidian clocks that control their tidal rhythms. Overall, these results indicate that, like adults, juvenile horseshoe crabs express both daily and tidal patterns of activity and that at least one, and maybe both, of these patterns is driven by endogenous clocks
Quantitative brain electrical activity in the initial screening of mild traumatic brain injuries
Introduction: The incidence of emergency department (ED) visits for Traumatic Brain Injury (TBI) in the United States exceeds 1,000,000 cases/year with the vast majority classified as mild (mTBI). Using existing computed tomography (CT) decision rules for selecting patients to be referred for CT, such as the New Orleans Criteria (NOC), approximately 70% of those scanned are found to have a negative CT. This study investigates the use of quantified brain electrical activity to assess its possible role in the initial screening of ED mTBI patients as compared to NOC.Methods: We studied 119 patients who reported to the ED with mTBI and received a CT. Using a hand-held electroencephalogram (EEG) acquisition device, we collected data from frontal leads to determine the likelihood of a positive CT. The brain electrical activity was processed off-line to generate an index (TBI-Index, biomarker). This index was previously derived using an independent population, and the value found to be sensitive for significant brain dysfunction in TBI patients. We compared this performance of the TBI-Index to the NOC for accuracy in prediction of positive CT findings.Results: Both the brain electrical activity TBI-Index and the NOC had sensitivities, at 94.7% and 92.1% respectively. The specificity of the TBI-Index was more than twice that of NOC, 49.4% and 23.5% respectively. The positive predictive value, negative predictive value and the positive likelihood ratio were better with the TBI-Index. When either the TBI-Index or the NOC are positive (combining both indices) the sensitivity to detect a positive CT increases to 97%.Conclusion: The hand-held EEG device with a limited frontal montage is applicable to the ED environment and its performance was superior to that obtained using the New Orleans criteria. This study suggests a possible role for an index of brain function based on EEG to aid in the acute assessment of mTBI patients. [West J Emerg Med. 2012;13(5):394-400.
Demonstrating the model nature of the high-temperature superconductor HgBaCuO
The compound HgBaCuO (Hg1201) exhibits a simple tetragonal
crystal structure and the highest superconducting transition temperature
(T) among all single Cu-O layer cuprates, with T = 97 K (onset) at
optimal doping. Due to a lack of sizable single crystals, experimental work on
this very attractive system has been significantly limited. Thanks to a recent
breakthrough in crystal growth, such crystals have now become available. Here,
we demonstrate that it is possible to identify suitable heat treatment
conditions to systematically and uniformly tune the hole concentration of
Hg1201 crystals over a wide range, from very underdoped (T = 47 K, hole
concentration p ~ 0.08) to overdoped (T = 64 K, p ~ 0.22). We then present
quantitative magnetic susceptibility and DC charge transport results that
reveal the very high-quality nature of the studied crystals. Using XPS on
cleaved samples, we furthermore demonstrate that it is possible to obtain large
surfaces of good quality. These characterization measurements demonstrate that
Hg1201 should be viewed as a model high-temperature superconductor, and they
provide the foundation for extensive future experimental work.Comment: 15 pages, 6 Figure
Charge-Transfer Excitations in the Model Superconductor HgBaCuO
We report a Cu -edge resonant inelastic x-ray scattering (RIXS) study of
charge-transfer excitations in the 2-8 eV range in the structurally simple
compound HgBaCuO at optimal doping ( K).
The spectra exhibit a significant dependence on the incident photon energy
which we carefully utilize to resolve a multiplet of weakly-dispersive ( eV) electron-hole excitations, including a mode at 2 eV. The observation
of this 2 eV excitation suggests the existence of a charge-transfer pseudogap
deep in the superconducting phase. Quite generally, our data demonstrate the
importance of exploring the incident photon energy dependence of the RIXS cross
section.Comment: 5 pages, 3 figure
Unraveling the Nature of Charge Excitations in LaCuO with Momentum-Resolved Cu -edge Resonant Inelastic X-ray Scattering
Results of model calculations using exact diagonalization reveal the orbital
character of states associated with different Raman loss peaks in Cu -edge
resonant inelastic X-ray scattering (RIXS) from LaCuO. The model
includes electronic orbitals necessary to highlight non-local Zhang-Rice
singlet, charge transfer and - excitations, as well as states with apical
oxygen 2 character. The dispersion of these excitations is discussed with
prospects for resonant final state wave-function mapping. A good agreement with
experiments emphasizes the substantial multi-orbital character of RIXS profiles
in the energy transfer range 1-6 eV.Comment: Original: 4.5 pages. Replaced: 4 pages and 4 figures with updated
content and reference
Using Dust from Asteroids as Regolith Microsamples
Meteorite science is rich with compositional indicators by which we classify parent bodies, but few sample groups are definitively linked with asteroid spectra. More robust links need to be forged between meteorites and their parent bodies to understand the composition, diversity and distribution. A major link can be sample analysis of the parent body material and comparison with meteorite data. Hayabusa, the first sample return mission of the Japanese Aerospace Exploration Agency (JAXA), was developed to rendezvous with and collect samples from asteroid Itokawa and return them to Earth. Thousands of sub-100 micron particles were recovered, apparently introduced during the spacecraft impact into the surface of the asteroid, linking the asteroid Itokawa to LL chondrites [1]. Upcoming missions Hayabusa 2 and OSIRIS-REx will collect more significant sample masses from asteroids. In all these cases, the samples are or will be a collection of regolith particles. Sample return to earth is not the only method for regolith particle analysis. Dust is present around all airless bodies, generated by micrometeorite impact into their airless surfaces, which in turn lofts regolith particles into a "cloud" around the body. The composition, flux, and size-frequency distribution of dust particles can provide significant insight into the geological evolution of airless bodies [2]. For example, the Cassini Cosmic Dust Analyzer (CDA) detected salts in Enceladus' icy plume material, providing evidence for a subsurface ocean in contact with a silicate seafloor [3]. Similar instruments have flown on the Rosetta, LADEE, and Stardust missions. Such an instrument may be of great use in obtaining the elemental, isotopic and mineralogical composition measurement of dust particles originating from asteroids without returning the samples to terrestrial laboratories. We investigated the ability of a limited sample analysis capability using a dust instrument to forge links between asteroid regolith particles and known meteorite groups. We further set limits on the number of individual particles statistically needed to robustly reproduce a bulk composition
Fast-neutron induced background in LaBr3:Ce detectors
The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce
crystal to incident neutrons has been measured in the energy range En = 2-12
MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6
MeV with pulsed proton beams. Using the time-of-flight information between
target and detector, energy spectra of the LaBr3:Ce detector resulting from
fast neutron interactions have been obtained at 4 different neutron energies.
Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured
in a nearby Ge detector at the lowest proton beam energy. In addition, we
obtained data for neutron irradiation of a large-volume high-purity Ge detector
and of a NE-213 liquid scintillator detector, both serving as monitor detectors
in the experiment. Monte-Carlo type simulations for neutron interactions in the
liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and
compared with measured data. Good agreement being obtained with the data, we
present the results of simulations to predict the response of LaBr3:Ce
detectors for a range of crystal sizes to neutron irradiation in the energy
range En = 0.5-10 MeVComment: 28 pages, 10 figures, 4 Table
[(IMes)2Pt(H)(ClBC5H4SiMe3)] : a BorabenzeneâPlatinum Adduct with an Unusual PtâClâB Interaction
A PtâClâB interaction is observed when a borabenzene derivative reacts with a platinum(0) precursor with bulky Nâheterocyclic carbene ligands. The resulting platinum(II) complex (see picture; Ptâ
red, Nâ
blue, Clâ
green, Bâ
pink, Siâ
yellow) involves a new bonding mode for borabenzene, which usually binds in an η6 fashion to transition metals
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