247 research outputs found
Investigation of cycling-induced microstructural degradation in silicon-based electrodes in lithium-ion batteries using X-ray nanotomography
The microstructural degradation of a composite silicon electrode at different stages in its cycle life was investigated in 3D using X-ray nano-computed tomography. A reconstructed volume of 36 μm × 27 μm × 26 μm from the composite electrode was imaged in its pristine state and after 1, 10 and 100 cycles. Particle fracturing and phase transformation was observed within the electrode with increased cycling. In addition, a distinct, lower X-ray attenuating phase was clearly resolved, which can be associated with surface film formation resulting from electrolyte breakdown and with silicon particle phase transformation. Changes in quantified microstructural properties such as phase volume fraction and particle specific surface area were tracked. Electrode performance loss is associated with loss of active silicon. These imaging results further highlight the capability of high resolution X-ray tomography to investigate the role of electrode microstructure in battery degradation and failure
Thermal Adaptation of Dihydrofolate Reductase from the Moderate ThermophileGeobacillus stearothermophilus
The thermal melting temperature of dihydrofolate reductase from Geobacillus stearothermophilus (BsDHFR) is 30 °C higher than that of its homologue from the psychrophile Moritella profunda. Additional proline residues in the loop regions of BsDHFR have been proposed to enhance the thermostability of BsDHFR, but site-directed mutagenesis studies reveal that these proline residues contribute only minimally. Instead, the high thermal stability of BsDHFR is partly due to removal of water-accessible thermolabile residues such as glutamine and methionine, which are prone to hydrolysis or oxidation at high temperatures. The extra thermostability of BsDHFR can be obtained by ligand binding, or in the presence of salts or cosolvents such as glycerol and sucrose. The sum of all these incremental factors allows BsDHFR to function efficiently in the natural habitat of G. stearothermophilus, which is characterized by temperatures that can reach 75 °C
Loop Interactions during Catalysis by Dihydrofolate Reductase fromMoritella profunda
Dihydrofolate reductase (DHFR) is often used as a model system to
study the relation between protein dynamics and catalysis. We have studied a
number of variants of the cold-adapted DHFR from Moritella profunda
(MpDHFR), in which the catalytically important M20 and FG loops have been
altered, and present a comparison with the corresponding variants of the wellstudied
DHFR from Escherichia coli (EcDHFR). Mutations in the M20 loop do not
affect the actual chemical step of transfer of hydride from reduced nicotinamide
adenine dinucleotide phosphate to the substrate 7,8-dihydrofolate in the catalytic
cycle in either enzyme; they affect the steady state turnover rate in EcDHFR but
not in MpDHFR. Mutations in the FG loop also have different effects on catalysis
by the two DHFRs. Despite the two enzymes most likely sharing a common catalytic cycle at pH 7, motions of these loops,
known to be important for progression through the catalytic cycle in EcDHFR, appear not to play a significant role in MpDHFR
A Very Intense Neutrino Super Beam Experiment for Leptonic CP Violation Discovery based on the European Spallation Source Linac: A Snowmass 2013 White Paper
Very intense neutrino beams and large neutrino detectors will be needed in
order to enable the discovery of CP violation in the leptonic sector. We
propose to use the proton linac of the European Spallation Source currently
under construction in Lund, Sweden to deliver, in parallel with the spallation
neutron production, a very intense, cost effective and high performance
neutrino beam. The baseline program for the European Spallation Source linac is
that it will be fully operational at 5 MW average power by 2022, producing 2
GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade
the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron
production and 14 pulses/s for neutrino production. Furthermore, because of the
high current required in the pulsed neutrino horn, the length of the pulses
used for neutrino production needs to be compressed to a few s with the
aid of an accumulator ring. A long baseline experiment using this Super Beam
and a megaton underground Water Cherenkov detector located in existing mines
300-600 km from Lund will make it possible to discover leptonic CP violation at
5 significance level in up to 50% of the leptonic Dirac CP-violating
phase range. This experiment could also determine the neutrino mass hierarchy
at a significance level of more than 3 if this issue will not already
have been settled by other experiments by then. The mass hierarchy performance
could be increased by combining the neutrino beam results with those obtained
from atmospheric neutrinos detected by the same large volume detector. This
detector will also be used to measure the proton lifetime, detect cosmological
neutrinos and neutrinos from supernova explosions. Results on the sensitivity
to leptonic CP violation and the neutrino mass hierarchy are presented.Comment: 28 page
Gravitational-wave astronomy: the high-frequency window
This contribution is divided in two parts. The first part provides a
text-book level introduction to gravitational radiation. The key concepts
required for a discussion of gravitational-wave physics are introduced. In
particular, the quadrupole formula is applied to the anticipated
``bread-and-butter'' source for detectors like LIGO, GEO600, EGO and TAMA300:
inspiralling compact binaries. The second part provides a brief review of high
frequency gravitational waves. In the frequency range above (say) 100Hz,
gravitational collapse, rotational instabilities and oscillations of the
remnant compact objects are potentially important sources of gravitational
waves. Significant and unique information concerning the various stages of
collapse, the evolution of protoneutron stars and the details of the
supranuclear equation of state of such objects can be drawn from careful study
of the gravitational-wave signal. As the amount of exciting physics one may be
able to study via the detections of gravitational waves from these sources is
truly inspiring, there is strong motivation for the development of future
generations of ground based detectors sensitive in the range from hundreds of
Hz to several kHz.Comment: 21 pages, 5 figures, Lectures presented at the 2nd Aegean Summer
School on the Early Universe, Syros, Greece, September 200
Success Factors of European Syndromic Surveillance Systems: A Worked Example of Applying Qualitative Comparative Analysis
Introduction: Syndromic surveillance aims at augmenting traditional public health surveillance with timely information. To gain a head start, it mainly analyses existing data such as from web searches or patient records. Despite the setup of many syndromic surveillance systems, there is still much doubt about the benefit of the approach. There are diverse interactions between performance indicators such as timeliness and various system characteristics. This makes the performance assessment of syndromic surveillance systems a complex endeavour. We assessed if the comparison of several syndromic surveillance systems through Qualitative Comparative Analysis helps to evaluate performance and identify key success factors.
Materials and Methods: We compiled case-based, mixed data on performance and characteristics of 19 syndromic surveillance systems in Europe from scientific and grey literature and from site visits. We identified success factors by applying crisp-set Qualitative Comparative Analysis. We focused on two main areas of syndromic surveillance application: seasonal influenza surveillance and situational awareness during different types of potentially health threatening events.
Results: We found that syndromic surveillance systems might detect the onset or peak of seasonal influenza earlier if they analyse non-clinical data sources. Timely situational awareness during different types of events is supported by an automated syndromic surveillance system capable of analysing multiple syndromes. To our surprise, the analysis of multiple data sources was no key success factor for situational awareness.
Conclusions: We suggest to consider these key success factors when designing or further developing syndromic surveillance systems. Qualitative Comparative Analysis helped interpreting complex, mixed data on small-N cases and resulted in concrete and practically relevant findings
Recommended from our members
The MERIT (nTOF-11) High Intensity Liquid Mercury Target Experiment at the CERN PS
The MERIT(nTOF-11) experiment is a proof-of-principle test of a target system for a high power proton beam to be used as front-end for a neutrino factory or a muon collider. The experiment took data in autumn 2007 with the fast-extracted beam from the CERN Proton Synchrotron (PS) to a maximum intensity of 30 x 10{sup 12} per pulse. The target system, based on a free mercury jet, is capable of intercepting a 4-MW proton beam inside a 15-T magnetic field required to capture the low energy secondary pions as the source for intense muon beams. Particle detectors installed around the target setup measure the secondary particle flux out of the target and can probe cavitation effects in the mercury jet when excited by an intense proton beam.Preliminary results of the data analysis will be presented here
Recommended from our members
The Merit(nTOF-11) High Intensity Liquid Mercury Target Experiment at the CERN PS
The MERIT(nTOF-11) experiment is a proof-ofprinciple test of a target system for a high power proton beam to be used as front-end for a neutrino factory or a muon collider. The experiment took data in autumn 2007 with the fast-extracted beam from the CERN Proton Synchrotron (PS) to a maximum intensity of per pulse. The target system, based on a free mercury jet, is capable of intercepting a 4-MW proton beam inside a 15-T magnetic field required to capture the low energy secondary pions as the source for intense muon beams. Partice detectors installed around the target setup measure the secondary particle flux out of the target and can probe cavitation effects in the mercury jet when excited by an intense proton beam.Preliminary results of the data analysis will be presented here
Post-common envelope binaries from SDSS - XVI. Long orbital period systems and the energy budget of CE evolution
Virtually all close compact binary stars are formed through common-envelope
(CE) evolution. It is generally accepted that during this crucial evolutionary
phase a fraction of the orbital energy is used to expel the envelope. However,
it is unclear whether additional sources of energy, such as the recombination
energy of the envelope, play an important role. Here we report the discovery of
the second and third longest orbital period post-common envelope binaries
(PCEBs) containing white dwarf (WD) primaries, i.e. SDSSJ121130.94-024954.4
(Porb = 7.818 +- 0.002 days) and SDSSJ222108.45+002927.7 (Porb = 9.588 +- 0.002
days), reconstruct their evolutionary history, and discuss the implications for
the energy budget of CE evolution. We find that, despite their long orbital
periods, the evolution of both systems can still be understood without
incorporating recombination energy, although at least small contributions of
this additional energy seem to be likely. If recombination energy significantly
contributes to the ejection of the envelope, more PCEBs with relatively long
orbital periods (Porb >~ 1-3 day) harboring massive WDs (Mwd >~ 0.8 Msun)
should exist.Comment: Accepted for publication in MNRAS. 8 pages, 6 figures and 4 table
Time Structure of Particle Production in the Merit High-Power Target Experiment
The MERIT experiment is a proof-of-principle test of a target system for high power proton beam to be used as front-end for a neutrino factory complex or amuon collider. The experiment took data in autumn 2007 with the fast extracted beam from the CERN Proton Synchrotron (PS) to a maximum intensity of about 30 × 1012 protons per pulse. We report results from the portion of the MERIT experiment in which separated beam pulses were delivered to a free mercury jet target with time intervals between pulses varying from 2 to 700 μs. The analysis is based on the responses of particle detectors placed along side and downstream of the target
- …