802 research outputs found
Energy and Economic Losses due to Soiling on Utility Scale PV Systems to Guide Timing of Cost Effective Cleaning
The energy and associated economic losses due to soiling on both residential and utility scale PV (photovoltaic) systems can be both significant and avoidable. Losses from 1.2% up to 6% have been reported, which is of interest to system operators [1]. Modules may be cleaned to reduce losses, but this comes with an offsetting economic cost. A quantification of energy losses, and the corresponding economic loss, will allow a determination of a closer to optimal cleaning schedule depending on the level of soiling and corresponding energy loss. Two methods are proposed and compared. Method 1 uses an ARES Soiling Measurement Station to perform irradiance and short circuit current measurements to calculate a soiling rate [2]. Method 2 uses direct measurement of energy production from recorded inverter data. A soiling rate will be determined by measuring energy production in control modules and modules with varying levels of soiling. This data was used to create a program to estimate the profitability of cleaning the PV installation at any given time
Equilibrating temperature-like variables in jammed granular subsystems
Although jammed granular systems are athermal, several thermodynamic-like
descriptions have been proposed which make quantitative predictions about the
distribution of volume and stress within a system and provide a corresponding
temperature-like variable. We perform experiments with an apparatus designed to
generate a large number of independent, jammed, two-dimensional configurations.
Each configuration consists of a single layer of photoelastic disks supported
by a gentle layer of air. New configurations are generated by alternately
dilating and re-compacting the system through a series of boundary
displacements. Within each configuration, a bath of particles surrounds a
smaller subsystem of particles with a different inter-particle friction
coefficient than the bath. The use of photoelastic particles permits us to find
all particle positions as well as the vector forces at each inter-particle
contact. By comparing the temperature-like quantities in both systems, we find
compactivity (conjugate to the volume) does not equilibrate between the
systems, while the angoricity (conjugate to the stress) does. Both independent
components of the angoricity are linearly dependent on the hydrostatic
pressure, in agreement with predictions of the stress ensemble
Recent Decisions
Comments on recent decisions by Frank P. Maggio, Paul Driscoll, Richard H. Puckett, John F. Costello, Harold E. McKee, and Edmund John Adams
Failure Assessment Diagram for Titanium Brazed Joints
The interaction equation was used to predict failure in Ti-4V-6Al joints brazed with Al 1100 filler metal. The joints used in this study were geometrically similar to the joints in the brazed beryllium metering structure considered for the ATLAS telescope. This study confirmed that the interaction equation R(sub sigma) + R(sub Tau) = 1, where R(sub sigma) and R(sub Tau)are normal and shear stress ratios, can be used as conservative lower bound estimate of the failure criterion in ATLAS brazed joints as well as for construction of the Failure Assessment Diagram (FAD)
Cryogenic Durability of a Carbon Fiber Reinforced Cyanate Ester Composite: Degree-of-Cure Effect
The James Webb Space Telescope (JWST) will be located approximately 1.5 million kilometers from Earth, producing extremely cold temperatures on the optical portion of the observatory. Specifically, the Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM) will operate at approximately -240 C. Construction of the structural components of the OTE and ISIM require bonding dissimilar materials together, e.g. Invar-36 (an iron-nickel alloy) to a carbon fiber reinforced cyanate ester composite (CFRCE) with an epoxy adhesive. While these materials enable the cryogenic stability required for optical performance, their joint strength at these extreme conditions presents a unique design challenge. Therefore, the current study presents a detailed investigation into the optimization of cryogenic composite durability. It is demonstrated that by controlling the degree-of-cure of a laminate, one can achieve an enhanced resistance to microcracking and an improved residual strength following cryogenic cycling to -253 C
Modulation of NF-κB-dependent gene transcription using programmable DNA minor groove binders
Nuclear factor κB (NF-κB) is a transcription factor that regulates various aspects of immune response, cell death, and differentiation as well as cancer. In this study we introduce the Py-Im polyamide 1 that binds preferentially to the sequences 5′-WGGWWW-3′ and 5′GGGWWW-3′. The compound is capable of binding to κB sites and reducing the expression of various NF-κB–driven genes including IL6 and IL8 by qRT-PCR. Chromatin immunoprecipitation experiments demonstrate a reduction of p65 occupancy within the proximal promoters of those genes. Genome-wide expression analysis by RNA-seq compares the DNA-binding polyamide with the well-characterized NF-κB inhibitor PS1145, identifies overlaps and differences in affected gene groups, and shows that both affect comparable numbers of TNF-α–inducible genes. Inhibition of NF-κB DNA binding via direct displacement of the transcription factor is a potential alternative to the existing antagonists
Chandra Observations of Type Ia Supernovae: Upper Limits to the X-ray Flux of SN 2002bo, SN 2002ic, SN 2005gj, and SN 2005ke
We set sensitive upper limits to the X-ray emission of four Type Ia
supernovae (SNe Ia) using the Chandra X-ray Observatory. SN 2002bo, a normal,
although reddened, nearby SN Ia, was observed 9.3 days after explosion. For an
absorbed, high temperature bremsstrahlung model the flux limits are 3.2E-16
ergs/cm^2/s (0.5-2 keV band) and 4.1E-15 ergs/cm^2/s (2-10 keV band). Using
conservative model assumptions and a 10 km/s wind speed, we derive a mass loss
rate of \dot{M} ~ 2E-5 M_\odot/yr, which is comparable to limits set by the
non-detection of Halpha lines from other SNe Ia. Two other objects, SN 2002ic
and SN 2005gj, observed 260 and 80 days after explosion, respectively, are the
only SNe Ia showing evidence for circumstellar interaction. The SN 2002ic X-ray
flux upper limits are ~4 times below predictions of the interaction model
currently favored to explain the bright optical emission. To resolve this
discrepancy we invoke the mixing of cool dense ejecta fragments into the
forward shock region, which produces increased X-ray absorption. A modest
amount of mixing allows us to accommodate the Chandra upper limit. SN 2005gj is
less well studied at this time. Assuming the same circumstellar environment as
for SN 2002i, the X-ray flux upper limits for SN 2005gj are ~4 times below the
predictions, suggesting that mixing of cool ejecta into the forward shock has
also occurred here. Our reanalysis of Swift and Chandra data on SN 2005ke does
not confirm a previously reported X-ray detection. The host galaxies NGC 3190
(SN 2002bo) and NGC 1371 (SN 2005ke) each harbor a low luminosity (L_X ~ 3-4E40
ergs/s) active nucleus in addition to wide-spread diffuse soft X-ray emission.Comment: 16 pages, to appear in ApJ (20 Nov 2007
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Proteomic analyses of primary human villous trophoblasts exposed to flame retardant BDE-47 using SWATH-MS
Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants and recognized developmental toxicants that are detectable in placental tissues. Higher levels of in utero PBDE exposure have been associated with an increased risk of adverse birth outcomes. During pregnancy, cytotrophoblasts (CTBs) from the placenta play critical roles in the formation of the maternal-fetal interface via uterine invasion and vascular remodeling. The differentiation of these cells towards an invasive phenotype is crucial for proper placental development. We previously have shown that BDE-47 can impact CTB viability and hinder the ability of these cells to migrate and invade. To expand on potential toxicological mechanisms, we utilized quantitative proteomic approaches to identify changes in the global proteome of mid-gestation primary human CTBs after exposure to BDE-47. Using sequential window acquisition of all theoretical fragment-ion spectra (SWATH), we identified 3024 proteins in our CTB model of differentiation/invasion. Over 200 proteins were impacted as a function of BDE-47 exposure (1 μM and 5 μM) across the treatment period (15, 24, and 39 h). The differentially expressed molecules displayed time- and concentration-dependent changes in expression and were enriched in pathways associated with aggregatory and adhesive processes. Network analysis identified CYFIP1, a molecule previously unexplored in a placental context, to be dysregulated at BDE-47 concentrations previously seen to impact CTB migration/invasion. Our SWATH-MS dataset thus demonstrates BDE-47 impacts the global proteome of differentiating CTBs and serves as a valuable resource for further understanding of the relationship between environmental chemical exposures and placental development and function. AVAILABILITY OF DATA AND MATERIAL: Raw chromatograms are deposited on the MassIVE proteomic database (https://massive.ucsd.edu) under accession number MSV000087870. Normalized relative abundances are also available as Table S1
Final analysis of proton form factor ratio data at Q(2)=4.0, 4.8, and 5.6 GeV2
Precise measurements of the proton electromagnetic form factor ratio R = mu(p)G(E)(p)/G(M)(p) using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of R with momentum transfer Q(2) for Q(2) greater than or similar to 1 GeV2, in strong disagreement with previous extractions of R from cross-section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab\u27s Hall A measured R at four Q(2) values in the range 3.5 GeV2 \u3c = Q(2) \u3c = 5.6 GeV2. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher Q(2) motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus, and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for R, improving the consistency of the polarization transfer data in the high-Q(2) region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis
Late-Time Spectroscopy of SN 2002cx: The Prototype of a New Subclass of Type Ia Supernovae
We present Keck optical spectra of SN 2002cx, the most peculiar known Type Ia
supernova (SN Ia), taken 227 and 277 days past maximum light. Astonishingly,
the spectra are not dominated by the forbidden emission lines of iron that are
a hallmark of thermonuclear supernovae in the nebular phase. Instead, we
identify numerous P-Cygni profiles of Fe II at very low expansion velocities of
about 700 km/s, which are without precedent in SNe Ia. We also report the
tentative identification of low-velocity O I in these spectra, suggesting the
presence of unburned material near the center of the exploding white dwarf. SN
2002cx is the prototype of a new subclass of SNe Ia, with spectral
characteristics that may be consistent with recent pure deflagration models of
Chandrasekhar-mass thermonuclear supernovae. These are distinct from the
majority of SNe Ia, for which an alternative explosion mechanism, such as a
delayed detonation, may be required.Comment: 18 pages, 5 figures, to appear in The Astronomical Journal; minor
revisions to match accepted versio
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