77 research outputs found
Recommended from our members
Measurement of RT amplitudes and wavelengths of laser driven plates
A laser drive plate, that is a dense solid plate drive by a laser heated, lower density plasma, is inherently Raleigh-Taylor (R-T) unstable, We have previously indicated that observed surface perturbation on the plate are probably R-T instabilities, initiated by the mode structure of the driving laser beam. Using a semi- transparent impact target viewed with a polarized Epi-Illuminated Confocal Streak Microscope, has allowed us to measure the amplitude and growth of the instability
Recommended from our members
High speed imaging of Raleigh-Taylor instabilities in laser driven plates
Recent improvements and modifications of the imaging techniques have identified and provided measurements of Raleigh-Taylor (R-T) instabilities that occur in these events. The microscope system in the LLNL Micro Detonics Facility, was converted to an epi-illuminated polarization configuration. A double pulse nanosecond illuminator and a second independently focusable frame camera were also added to the system. A laser driven plate, that is a dense solid driven by a laser heated, lower density plasma, is inherently R-T unstable. The plates are aluminum, deposited on the ends of optical fibers. They are launched by a YAG Laser pulse traveling down the fiber. Plate velocities are several kilometers per second and characteristic dimensions of the instabilities are a few to tens of microns. Several techniques were used to examine the plates, the most successful being specularly reflecting polarization microscopy looking directly at the plate as it flies toward the camera. These images gave data on the spatial frequencies of the instabilities but could not give the amplitudes. To measure the amplitude of the instability a semi- transparent witness plate was placed a known distance from the plate. As above, the plate was observed using the polarization microscope but using the streak camera as the detector. Both the launch of the plate and its impact into the witness plate are observed on the streak record. Knowing the plate velocity function from earlier velocimetry measurements and observing the variations in the arrival time across the plate, the amplitude of the instability can be calculated
Correlation dynamics of three spin under a classical dephasing environment
By starting from the stochastic Hamiltonian of the three correlated spins and
modeling their frequency fluctuations as caused by dephasing noisy environments
described by Ornstein-Uhlenbeck processes, we study the dynamics of quantum
correlations, including entanglement and quantum discord. We prepared initially
our open system with Greenberger-Horne-Zeilinger or W state and present the
exact solutions for evolution dynamics of entanglement and quantum discord
between three spins under both Markovian and non-Markovian regime of this
classical noise. By comparison the dynamics of entanglement with that of
quantum discord we find that entanglement can be more robust than quantum
discord against this noise. It is shown that by considering non-Markovian
extensions the survival time of correlations prolong.Comment: 13 pages, 4 figure
A Taxonomy of Causality-Based Biological Properties
We formally characterize a set of causality-based properties of metabolic
networks. This set of properties aims at making precise several notions on the
production of metabolites, which are familiar in the biologists' terminology.
From a theoretical point of view, biochemical reactions are abstractly
represented as causal implications and the produced metabolites as causal
consequences of the implication representing the corresponding reaction. The
fact that a reactant is produced is represented by means of the chain of
reactions that have made it exist. Such representation abstracts away from
quantities, stoichiometric and thermodynamic parameters and constitutes the
basis for the characterization of our properties. Moreover, we propose an
effective method for verifying our properties based on an abstract model of
system dynamics. This consists of a new abstract semantics for the system seen
as a concurrent network and expressed using the Chemical Ground Form calculus.
We illustrate an application of this framework to a portion of a real
metabolic pathway
Quantifying evolvability in small biological networks
We introduce a quantitative measure of the capacity of a small biological
network to evolve. We apply our measure to a stochastic description of the
experimental setup of Guet et al. (Science 296:1466, 2002), treating chemical
inducers as functional inputs to biochemical networks and the expression of a
reporter gene as the functional output. We take an information-theoretic
approach, allowing the system to set parameters that optimize signal processing
ability, thus enumerating each network's highest-fidelity functions. We find
that all networks studied are highly evolvable by our measure, meaning that
change in function has little dependence on change in parameters. Moreover, we
find that each network's functions are connected by paths in the parameter
space along which information is not significantly lowered, meaning a network
may continuously change its functionality without losing it along the way. This
property further underscores the evolvability of the networks.Comment: 8 pages, 3 figure
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Optimizing design of research to evaluate antibiotic stewardship interventions: consensus recommendations of a multinational working group.
BACKGROUND: Antimicrobial stewardship interventions and programmes aim to ensure effective treatment while minimizing antimicrobial-associated harms including resistance. Practice in this vital area is undermined by the poor quality of research addressing both what specific antimicrobial use interventions are effective and how antimicrobial use improvement strategies can be implemented into practice. In 2016 we established a working party to identify the key design features that limit translation of existing research into practice and then to make recommendations for how future studies in this field should be optimally designed. The first part of this work has been published as a systematic review. Here we present the working group's final recommendations. METHODS: An international working group for design of antimicrobial stewardship intervention evaluations was convened in response to the fourth call for leading expert network proposals by the Joint Programming Initiative on Antimicrobial Resistance (JPIAMR). The group comprised clinical and academic specialists in antimicrobial stewardship and clinical trial design from six European countries. Group members completed a structured questionnaire to establish the scope of work and key issues to develop ahead of a first face-to-face meeting that (a) identified the need for a comprehensive systematic review of study designs in the literature and (b) prioritized key areas where research design considerations restrict translation of findings into practice. The working group's initial outputs were reviewed by independent advisors and additional expertise was sought in specific clinical areas. At a second face-to-face meeting the working group developed a theoretical framework and specific recommendations to support optimal study design. These were finalized by the working group co-ordinators and agreed by all working group members. RESULTS: We propose a theoretical framework in which consideration of the intervention rationale the intervention setting, intervention features and the intervention aims inform selection and prioritization of outcome measures, whether the research sets out to determine superiority or non-inferiority of the intervention measured by its primary outcome(s), the most appropriate study design (e.g. experimental or quasi- experimental) and the detailed design features. We make 18 specific recommendation in three domains: outcomes, objectives and study design. CONCLUSIONS: Researchers, funders and practitioners will be able to draw on our recommendations to most efficiently evaluate antimicrobial stewardship interventions
- …