3,986 research outputs found
Development of a Mathematical Model for Galvanic Cells
It is possible to utilize principles of equilibrium thermodynamics to model the voltage a battery renders as it powers a load in time and discharges. Similarly, consideration of the internal chemistry inside a battery, or galvanic cell, enables modeling thereof. This paper builds upon these principles and presents a derivation of the Nernst equation that utilizes this result to model discharge curves in time for different types of batteries. The Nernst equation relates chemical activity of the reagents inside a battery to the open circuit voltage rendered by the system. By combining the Nernst equation with Faraday\u27s laws of electrolysis, it is possible to obtain realistic battery models. Such models can reproduce discharge behavior, such as voltage rendered vs. time, under a particular electrical load. The results from this work demonstrate that the model matches real battery discharge behavior rather closely and provides insights into battery operation and how to best utilize such. The use of the model will allow the development of more efficient intelligent battery chargers and for superior energy control systems to be developed, which would manage batteries utilized for energy storage. In summary, the research herein starts at first principles and builds upon itself until a model is presented capable of describing the behavior of galvanic cells, or batteries, as these operate in time. This paper then develops and applies the model aforementioned and ends by discussing future avenues for development and room for possible advancement
The History of the Mysterious Eclipses of KH 15D: Asiago Observatory, 1967-1982
We are gathering archival observations to determine the photometric history
of the unique and unexplained eclipses of the pre-main-sequence star KH 15D.
Here we present a light curve from 1967-1982, based on photographic plates from
Asiago Observatory. During this time, the system alternated periodically
between bright and faint states, as observed today. However, the bright state
was 0.9 mag brighter than the modern value, and the fractional variation
between bright and faint states (Delta I = 0.7 mag) was smaller than observed
today (3.5 mag). A possible explanation for these findings is that the system
contains a second star that was previously blended with the eclipsing star, but
is now completely obscured.Comment: Accepted to AJ. 24 pages, 10 figures, 2 tables. v2: Phase error
corrected in figures 8 and 1
Diverging volumetric trajectories following pediatric traumatic brain injury.
Traumatic brain injury (TBI) is a significant public health concern, and can be especially disruptive in children, derailing on-going neuronal maturation in periods critical for cognitive development. There is considerable heterogeneity in post-injury outcomes, only partially explained by injury severity. Understanding the time course of recovery, and what factors may delay or promote recovery, will aid clinicians in decision-making and provide avenues for future mechanism-based therapeutics. We examined regional changes in brain volume in a pediatric/adolescent moderate-severe TBI (msTBI) cohort, assessed at two time points. Children were first assessed 2-5 months post-injury, and again 12 months later. We used tensor-based morphometry (TBM) to localize longitudinal volume expansion and reduction. We studied 21 msTBI patients (5 F, 8-18 years old) and 26 well-matched healthy control children, also assessed twice over the same interval. In a prior paper, we identified a subgroup of msTBI patients, based on interhemispheric transfer time (IHTT), with significant structural disruption of the white matter (WM) at 2-5 months post injury. We investigated how this subgroup (TBI-slow, N = 11) differed in longitudinal regional volume changes from msTBI patients (TBI-normal, N = 10) with normal WM structure and function. The TBI-slow group had longitudinal decreases in brain volume in several WM clusters, including the corpus callosum and hypothalamus, while the TBI-normal group showed increased volume in WM areas. Our results show prolonged atrophy of the WM over the first 18 months post-injury in the TBI-slow group. The TBI-normal group shows a different pattern that could indicate a return to a healthy trajectory
How to Measure Galaxy Star Formation Histories. II. Nonparametric Models
Nonparametric star formation histories (SFHs) have long promised to be the
`gold standard' for galaxy spectral energy distribution (SED) modeling as they
are flexible enough to describe the full diversity of SFH shapes, whereas
parametric models rule out a significant fraction of these shapes {\it a
priori}. However, this flexibility is not fully constrained even with
high-quality observations, making it critical to choose a well-motivated prior.
Here, we use the SED-fitting code \texttt{Prospector} to explore the effect of
different nonparametric priors by fitting SFHs to mock UV-IR photometry
generated from a diverse set of input SFHs. First, we confirm that
nonparametric SFHs recover input SFHs with less bias and return more accurate
errors than do parametric SFHs. We further find that, while nonparametric SFHs
robustly recover the overall shape of the input SFH, the primary determinant of
the size and shape of the posterior star formation rate (SFR) as a function of
time is the choice of prior, rather than the photometric noise. As a practical
demonstration, we fit the UV-IR photometry of 6000 galaxies from the GAMA
survey and measure inter-prior scatters in mass (0.1 dex), SFR (0.8 dex), and mass-weighted ages (0.2 dex), with the bluest
star-forming galaxies showing the most sensitivity. An important distinguishing
characteristic for nonparametric models is the characteristic timescale for
changes in SFR(t). This difference controls whether galaxies are assembled in
bursts or in steady-state star formation, corresponding respectively to
(feedback-dominated/accretion-dominated) models of galaxy formation and to
(larger/smaller) confidence intervals derived from SED-fitting. High-quality
spectroscopy has the potential to further distinguish between these proposed
models of SFR(t).Comment: replacing with ApJ accepted versio
2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable -ray emission
We present optical photometric and spectroscopic observations of the likely
stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT)
-ray source 2FGL J0846.0+2820, selected for study based on positional
coincidences of optical variables with unassociated LAT sources. Using optical
spectroscopy from the SOAR telescope, we have identified a late-G giant in an
eccentric ( = 0.06) 8.133 day orbit with an invisible primary. Modeling the
spectroscopy and photometry together lead us to infer a heavy neutron star
primary of and a partially stripped giant secondary of . H emission is observed in some of the spectra, perhaps
consistent with the presence of a faint accretion disk. We find the
-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009,
accompanied by an increased variation in the optical brightness, and since then
it has not been detected by \emph{Fermi}. The long period and giant secondary
are reminiscent of the -ray bright binary 1FGL J1417.7--4407, which
hosts a millisecond pulsar apparently in the final stages of the pulsar
recycling process. The discovery of 2FGL J0846.0+2820 suggests the
identification of a new subclass of millisecond pulsar binaries that are the
likely progenitors of typical field millisecond pulsars.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Ap
Postexposure Treatment of Marburg Virus Infection
Rhesus monkeys are protected from disease when a recombinant vesicular stomatitis virus–based vaccine is administered 20–30 min after infection with Marburg virus. We protected 5/6 monkeys when this vaccine was given 24 h after challenge; 2/6 animals were protected when the vaccine was administered 48 h postinfection
Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk
We show that grains have grown to ~mm size (sand sized) or larger in the
terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3
Myr old binary star KH 15D. We also argue that the reflected light in the
system reaches us by back scattering off the far side of the same ring whose
near side causes the obscuration.Comment: 22 pages, 5 figures. To be published in Nature, March 13, 2008.
Contains a Supplemen
G-Quadruplex Dynamics Contribute To Regulation Of Mitochondrial Gene Expression
Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). Mitochondrial DNA (mtDNA) sequences that are predicted to form G4 are enriched on the heavy-strand and have been associated with formation of deletion breakpoints. Increasing evidence supports the ability of mtDNA to form G4 in cancer cells; however, the functional roles of G4 structures in regulating mitochondrial nucleic acid homeostasis in non-cancerous cells remain unclear. Here, we demonstrate by live cell imaging that the G4-ligand RHPS4 localizes primarily to mitochondria at low doses. We find that low doses of RHPS4 do not induce a nuclear DNA damage response but do cause an acute inhibition of mitochondrial transcript elongation, leading to respiratory complex depletion. We also observe that RHPS4 interferes with mtDNA levels or synthesis both in cells and isolated mitochondria. Importantly, a mtDNA variant that increases G4 stability and anti-parallel G4-forming character shows a stronger respiratory defect in response to RHPS4, supporting the conclusion that mitochondrial sensitivity to RHPS4 is G4-mediated. Taken together, our results indicate a direct role for G4 perturbation in mitochondrial genome replication, transcription processivity, and respiratory function in normal cells
Differences in outpatient care and treatment utilization for patients with HIV/HCV coinfection, HIV, and HCV monoinfection, a cross-sectional study
Background Few studies have explored how utilization of outpatient services differ for HIV/HCV coinfected patients compared to HIV or HCV monoinfected patients. The objectives of this study were to (1) compare annual outpatient clinic visit rates between coinfected and monoinfected patients, (2) to compare utilization of HIV and HCV therapies between coinfected and monoinfected patients, and (3) to identify factors associated with therapy utilization. Methods Data were from the 2005–2010 U.S. National Hospital Ambulatory Medical Care Surveys. Clinic visits with a primary or secondary ICD-9-CM codes for HIV or HCV were included. Coinfection included visits with codes for both HIV and HCV. Monoinfection only included codes for HIV or HCV, exclusively. Patients <15 years of age at time of visit were excluded. Predictors of HIV and HCV therapy were determined by logistic regressions. Visits were computed using survey weights. Results 3,021 visits (11,352,000 weighted visits) met study criteria for patients with HIV/HCV (8%), HIV (70%), or HCV (22%). The HCV subgroup was older in age and had the highest proportion of females and whites as compared to the HIV/HCV and HIV subgroups. Comorbidities varied significantly across the three subgroups (HIV/HCV, HIV, HCV): current tobacco use (40%, 27%, 30%), depression (32%, 23%, 24%), diabetes (9%, 10%, 17%), and chronic renal failure (<1%, 3%, 5%), (p < 0.001 for all variables). Annual visit rates were highest in those with HIV, followed by HIV/HCV, but consistently lower in those with HCV. HIV therapy utilization increased for both HIV/HCV and HIV subgroups. HCV therapy utilization remained low for both HIV/HCV and HCV subgroups for all years. Coinfection was an independent predictor of HIV therapy, but not of HCV therapy. Conclusion There is a critical need for system-level interventions that reduce barriers to outpatient care and improve uptake of HCV therapy for patients with HIV/HCV coinfection
Inter- and Intra-Individual Differences in EMG and MMG during Maximal, Bilateral, Dynamic Leg Extensions
The purpose of this study was to compare the composite, inter-individual, and intra-individual differences in the patterns of responses for electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) during fatiguing, maximal, bilateral, and isokinetic leg extension muscle actions. Thirteen recreationally active men (age = 21.7 2.6 years; body mass = 79.8 11.5 kg; height = 174.2 12.7 cm) performed maximal, bilateral leg extensions at 1801 until the torque values dropped to 50% of peak torque for two consecutive repetitions. The EMG and MMG signals from the vastus lateralis (VL) muscles of both limbs were recorded. Four 2(Leg) 19(time) repeated measures ANOVAs were conducted to examine mean differences for EMG AMP, EMG MPF, MMG AMP, and MMG MPF between limbs, and polynomial regression analyses were performed to identify the patterns of neuromuscular responses. The results indicated no significant differences between limbs for EMG AMP (p = 0.44), EMG MPF (p = 0.33), MMG AMP (p = 0.89), or MMG MPF (p = 0.52). Polynomial regression analyses demonstrated substantial inter-individual variability. Inferences made regarding the patterns of neuromuscular responses to fatiguing and bilateral muscle actions should be considered on a subject-by-subject basis
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