2,105 research outputs found
Density of states in graphene with vacancies: midgap power law and frozen multifractality
The density of states (DoS), , of graphene is investigated
numerically and within the self-consistent T-matrix approximation (SCTMA) in
the presence of vacancies within the tight binding model. The focus is on
compensated disorder, where the concentration of vacancies, and
, in both sub-lattices is the same. Formally, this model belongs to
the chiral symmetry class BDI. The prediction of the non-linear sigma-model for
this class is a Gade-type singularity . Our numerical data is compatible with this
result in a preasymptotic regime that gives way, however, at even lower
energies to , . We take this finding as an evidence that similar to the case
of dirty d-wave superconductors, also generic bipartite random hopping models
may exhibit unconventional (strong-coupling) fixed points for certain kinds of
randomly placed scatterers if these are strong enough. Our research suggests
that graphene with (effective) vacancy disorder is a physical representative of
such systems.Comment: References updated onl
Impact of Gene-Gender Effects of Adrenergic Polymorphisms on Hypothalamic-Pituitary-Adrenal Axis Activity in Depressed Patients
Objective: There is overwhelming evidence that activation of the hypothalamic-pituitary-adrenal (HPA) system plays a major role in depression and cardiovascular disease in genetically susceptible individuals. We hypothesized that due to the multiple interactions between the sympathetic and the HPA systems via adrenoceptors, polymorphisms in these genes could have an impact on HPA axis activity in major depression. Methods: Using the dexamethasone/corticotrophin-releasing hormone (DEX/CRH) test, we investigated the association of alpha 2-adrenoceptor (ADRA2A -1291C -> G) and the beta 2-adrenoceptor gene (ADRB2 Arg16Gly) in 189 patients with major depression during the acute state of the disease and after remission. Results: Male ADRA2A -1291G allele homozygotes showed significant pretreatment HPA axis hyperactivity, with increased adrenocorticotropin (ACTH; F = 4.9, d.f. = 2, p = 0.009) and cortisol responses (F = 6.4, d.f. = 2, p = 0.003). In contrast, female ADRB2 Arg/Arg homozygotes had increased pretreatment ACTH (F = 7.17, d.f. = 2, p = 0.001) and cortisol (F = 8.95, d.f. = 2, p = 0.000) levels. Interestingly, in the respective genotypes, the stress hormones remained elevated in the second DEX/CRH test, despite a reduction in depressive symptoms. Conclusions: This study provides evidence that, depending on gender and polymorphisms, there is continuous HPA axis overdrive in a proportion of patients irrespective of the status of depression. Considering the importance of stress hormones for cardiovascular disorders, our data might suggest that these patients are at high risk of comorbidity between depression and cardiovascular disorders. Copyright (c) 2008 S. Karger AG, Base
A Spreading Layer Origin for Dwarf Nova Oscillations
Dwarf nova outbursts often show coherent () sinusoidal
oscillations with the largest pulsed fraction in the extreme ultraviolet.
Called dwarf nova oscillations (DNOs), they have periods of and scale with luminosity as with
. We propose that DNOs may be produced by nonradial
oscillations in a thin hydrostatic layer of freshly accreted material, the
``spreading layer'' (SL), at the white dwarf (WD) equator. This would naturally
explain a number of key properties of DNOs, including their frequency range,
sinusoidal nature, sensitivity to accretion rate, and why they are only seen
during outburst. In support of this hypothesis we construct a simple model that
treats the SL as a cavity containing shallow surface waves, each with the same
radial structure, but split into three different modes denoted by their
azimuthal wavenumber, . The latitudinally propagating mode best
matches the periods and scalings associated with most DNOs, and DNOs with
periods shorter than the WD Keplerian period are explained by the
prograde mode. We also predict a third set of oscillations, produced by the
retrograde mode, and show its expected dependence on accretion rate.Comment: Accepted for publication in Astrophysical Journal Letters, 4 pages, 2
figure
Experimental Verification of PCH-EM Algorithm for Characterizing DSERN Image Sensors
The Photon Counting Histogram Expectation Maximization (PCH-EM) algorithm has
recently been reported as a candidate method for the characterization of Deep
Sub-Electron Read Noise (DSERN) image sensors. This work describes a
comprehensive demonstration of the PCH-EM algorithm applied to a DSERN capable
quanta image sensor. The results show that PCH-EM is able to characterize DSERN
pixels for a large span of quanta exposure and read noise values. The per-pixel
characterization results of the sensor are combined with the proposed Photon
Counting Distribution (PCD) model to demonstrate the ability of PCH-EM to
predict the ensemble distribution of the device. The agreement between
experimental observations and model predictions demonstrates both the
applicability of the PCD model in the DSERN regime as well as the ability of
the PCH-EM algorithm to accurately estimate the underlying model parameters.Comment: 8 pages, 9 figure
Summary of FY 2010 Iodine Capture Studies at the INL
Three breakthrough runs using silver mordenite sorbents were conducted and a dynamic sorption capacity estimated based on MeI analysis from a 2" bed. However, it is now believed the data for the first 2 runs is incomplete because the contributions from elemental iodine were not included. Although the only source of iodine was MeI, elemental iodine was generated within the sorbent bed, presumably from a recombination reaction likely catalyzed by silver mordenite. On-line effluent analysis with a GC was only capable of analyzing MeI, not I2. Scrub samples drawn during Run #3, which are specific for I2, show significant levels of I2 being emitted from a partially spent Ag-mordenite bed. By combining MeI and I2 analyses, a well defined total iodine breakthrough curve can be generated for Run #3. At the conclusion of Run #3 (IONEX Ag-900 was the sorbent) the effluent level from Bed 2 was approaching 70% of the feed concentration. The leading bed (Bed 1) had an estimated average loading of 66 mg I/g sorbent, Bed 2's was 52 mg I/g. The corresponding silver utilizations (assuming formation of AgI) were about 59% and 46%, respectively. The spent sorbents are being sent to Sandia National Laboratories for confirmatory analysis of iodine and silver utilization as well as source material for waste form development
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Treatability Studies and Large-Scale Treatment of Aqueous Mixed Waste Containing Heavy Metals
Wastes have accumulated at the Idaho National Engineering Laboratory through routine laboratory practices, experimental engineering operations, and decommissioning and decontamination of nuclear reactor facilities. A storage tank at the Test Area North held approximately 129,000 L of acidic wastewater and contained prohibited levels of lead and mercury. Radioactive constituents were also present; the most predominant being radiocesium Cs-137 and radiocobalt Co-60. Bench-scale studio were undertaken to evaluate ion exchange as a means of removing the contaminants. A set of breakthrough curves was obtained and identified capacity constraints, selectivities, and operating requirements of candidate resins. Treatment studies indicated that Purolite S-920 resin could effectively remove mercury, while Rohm and Haas` Amberlite 200-CH was used for lead and radionuclide removal. Based on these laboratory tests a full-scale facility, using multiple ion exchange columns, was designed and operated in the spring of 1994. The liquid effluents were discharged to an onsite evaporation pond and met RCRA disposal limits for hazardous metals and self-imposed radionuclide limits. All secondary wastes and residues were sampled and subjected to the to)dc characteristic leaching procedure. The resulting leachate concentrations were below RCRA discharge limits and, therefore, these will be disposed of at the onsite low-level disposal facility. After concluding the tank wastewater operations, enough reserve resin capacity was available to treat three additional mixed wastes residing onsite. These totaled about 1,900 L (500 gal) and contained prohibited levels of chromium, cadmium, and barium. Laboratory studies demonstrated that these heavy metals could also be removed by the existing resins. Treatment was performed at the full-scale facility with the effluents discharged to the evaporation pond
Information Exchange in Global Production Networks: Increasing Transparency by Simulation, Statistical Experiments and Selection of Digitalization Activities
Today, companies of all industries are part of global production networks. They have a variety of performance relationships with suppliers and customers. Digitalization offers the potential to exchange more information between the partners of global production networks. This may improve operational performance. Especially within the three business processes order management, quality problem solving and engineering change management, a targeted increase in transparency promises a better handling of disruptions and an increase in robustness. This paper presents a simulation-based methodology for modeling production and business processes as well as information exchange in global production networks. Following the principles of Design of Experiment (DoE), screening test plans first carve out the impact of disruptions and information exchange on the performance of the production network. This is followed by the determination of the disruption-robust information exchange using Taguchi-experiments. Starting from the actual state of information exchange, digitalization activities to increase transparency are finally determined. The activities consist of the implementation of digitalization technologies and the stronger linkage of information systems. The paper ends with an application of the methodology to a global production network for plastic-metal components in the automotive supplier industry
Detection of a period decrease in NN Ser with ULTRACAM: evidence for strong magnetic braking or an unseen companion?
We present results of high time resolution photometry of the eclipsing
pre-cataclysmic variable NN Ser. We observed 13 primary eclipses of NN Ser
using the high-speed CCD camera ULTRACAM and derived times of mid-eclipse, from
fitting of light curve models, with uncertainties as low as 0.06 s. The
observed rates of period change appear difficult to reconcile with any models
of orbital period change. If the observed period change reflects an angular
momentum loss, the average loss rate is consistent with the loss rates (via
magnetic stellar wind braking) used in standard models of close binary
evolution, which were derived from observations of much more massive cool
stars. Observations of low-mass stars such as NN Ser's secondary predict rates
of ~100 times lower than we observe. We show that magnetic activity-driven
changes in the quadrupole moment of the secondary star (Applegate, 1992) fail
to explain the period change by an order of magnitude on energetic grounds, but
that a light travel time effect caused by the presence of a third body in a
long (~ decades) orbit around the binary could account for the observed changes
in the timings of NN Ser's mid-eclipses. We conclude that we have either
observed a genuine angular momentum loss for NN Ser, in which case our
observations pose serious difficulties for the theory of close binary
evolution, or we have detected a previously unseen low-mass companion to the
binary.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
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