17,762 research outputs found
Self-similar structure and experimental signatures of suprathermal ion distribution in inertial confinement fusion implosions
The distribution function of suprathermal ions is found to be self-similar
under conditions relevant to inertial confinement fusion hot-spots. By
utilizing this feature, interference between the hydro-instabilities and
kinetic effects is for the first time assessed quantitatively to find that the
instabilities substantially aggravate the fusion reactivity reduction. The ion
tail depletion is also shown to lower the experimentally inferred ion
temperature, a novel kinetic effect that may explain the discrepancy between
the exploding pusher experiments and rad-hydro simulations and contribute to
the observation that temperature inferred from DD reaction products is lower
than from DT at National Ignition Facility.Comment: Revised version accepted for publication in PRL. "Copyright (2015) by
the American Physical Society.
Principal infinity-bundles - General theory
The theory of principal bundles makes sense in any infinity-topos, such as
that of topological, of smooth, or of otherwise geometric
infinity-groupoids/infinity-stacks, and more generally in slices of these. It
provides a natural geometric model for structured higher nonabelian cohomology
and controls general fiber bundles in terms of associated bundles. For suitable
choices of structure infinity-group G these G-principal infinity-bundles
reproduce the theories of ordinary principal bundles, of bundle
gerbes/principal 2-bundles and of bundle 2-gerbes and generalize these to their
further higher and equivariant analogs. The induced associated infinity-bundles
subsume the notions of gerbes and higher gerbes in the literature.
We discuss here this general theory of principal infinity-bundles, intimately
related to the axioms of Giraud, Toen-Vezzosi, Rezk and Lurie that characterize
infinity-toposes. We show a natural equivalence between principal
infinity-bundles and intrinsic nonabelian cocycles, implying the classification
of principal infinity-bundles by nonabelian sheaf hyper-cohomology. We observe
that the theory of geometric fiber infinity-bundles associated to principal
infinity-bundles subsumes a theory of infinity-gerbes and of twisted
infinity-bundles, with twists deriving from local coefficient infinity-bundles,
which we define, relate to extensions of principal infinity-bundles and show to
be classified by a corresponding notion of twisted cohomology, identified with
the cohomology of a corresponding slice infinity-topos.
In a companion article [NSSb] we discuss explicit presentations of this
theory in categories of simplicial (pre)sheaves by hyper-Cech cohomology and by
simplicial weakly-principal bundles; and in [NSSc] we discuss various examples
and applications of the theory.Comment: 46 pages, published versio
Software Process Assessment (SPA)
NASA's environment mirrors the changes taking place in the nation at large, i.e. workers are being asked to do more work with fewer resources. For software developers at NASA's Goddard Space Flight Center (GSFC), the effects of this change are that we must continue to produce quality code that is maintainable and reusable, but we must learn to produce it more efficiently and less expensively. To accomplish this goal, the Data Systems Technology Division (DSTD) at GSFC is trying a variety of both proven and state-of-the-art techniques for software development (e.g., object-oriented design, prototyping, designing for reuse, etc.). In order to evaluate the effectiveness of these techniques, the Software Process Assessment (SPA) program was initiated. SPA was begun under the assumption that the effects of different software development processes, techniques, and tools, on the resulting product must be evaluated in an objective manner in order to assess any benefits that may have accrued. SPA involves the collection and analysis of software product and process data. These data include metrics such as effort, code changes, size, complexity, and code readability. This paper describes the SPA data collection and analysis methodology and presents examples of benefits realized thus far by DSTD's software developers and managers
Optical Guidance System /OGS/ for rendezvous and docking Final report
Optical guidance system for Apollo rendezvous and dockin
Coherent states for Hopf algebras
Families of Perelomov coherent states are defined axiomatically in the
context of unitary representations of Hopf algebras possessing a Haar integral.
A global geometric picture involving locally trivial noncommutative fibre
bundles is involved in the construction. A noncommutative resolution of
identity formula is proved in that setup. Examples come from quantum groups.Comment: 19 pages, uses kluwer.cls; the exposition much improved; an example
of deriving the resolution of identity via coherent states for SUq(2) added;
the result differs from the proposals in literatur
Efficient Phase-Encoding Quantum Key Generation with Narrow-Band Single Photons
We propose an efficient phase-encoding quantum secret key generation scheme
with heralded narrow-band single photons. The key information is carried by the
phase modulation directly on the single-photon temporal waveform without using
any passive beam splitters or optical switches. We show that, when the
technique is applied to the conventional fiber-based phase-encoding BB84 and
differential phase shift (DPS) quantum key distribution schemes, the key
generation efficiencies can be improved by a factor of 2 and 3, respectively.
For N(>3)-period DPS systems, the key generation efficiency can be improved by
a factor of N. The technique is suitable for quantum memory-based long-distance
fiber communication system.Comment: 5 pages, 5 figure
Estimation of Arterial Carbon Dioxide Based on End-Tidal Gas Pressure and Oxygen Saturation
Arterial blood gas (ABG) analysis is the traditional method for measuring the partial pressure of carbon dioxide. In mechanically ventilated patients a continuous noninvasive monitoring of carbon dioxide would obviously be attractive. In the current study, we present a novel formula for noninvasive estimation of arterial carbon dioxide. Eighty-one datasets were collected from 19 anesthetized and mechanically ventilated pigs. Eleven animals were mechanically ventilated without interventions. In the remaining eight pigs the partial pressure of carbon dioxide was manipulated. The new formula (Formula 1) is PaCO2 = PETCO2 + k(PETO2 - PaO2) where PaO2 was calculated from the oxygen saturation. We tested the agreements of this novel formula and compared it to a traditional method using the baseline PaCO2 - ETCO2 gap added to subsequently measured, end-tidal carbon dioxide levels (Formula 2). The mean difference between PaCO2 and calculated carbon dioxide (Formula 1) was 0.16 kPa (+/- SE 1.17). The mean difference between PaCO2 and carbon dioxide with Formula 2 was 0.66 kPa (+/- SE 0.18). With a mixed linear model excluding cases with cardiorespiratory collapse, there was a significant difference between formulae (p <0.001), as well as significant interaction between formulae and time (p <0.001). In this preliminary animal study, this novel formula appears to have a reasonable agreement with PaCO2 values measured with ABG analysis, but needs further validation in human patients.Peer reviewe
Anisotropy and non-universality in scaling laws of the large scale energy spectrum in rotating turbulence
Rapidly rotating turbulent flow is characterized by the emergence of columnar
structures that are representative of quasi-two dimensional behavior of the
flow. It is known that when energy is injected into the fluid at an
intermediate scale , it cascades towards smaller as well as larger scales.
In this paper we analyze the flow in the \textit{inverse cascade} range at a
small but fixed Rossby number, {}. Several
{numerical simulations with} helical and non-helical forcing functions are
considered in periodic boxes with unit aspect ratio. In order to resolve the
inverse cascade range with {reasonably} large Reynolds number, the analysis is
based on large eddy simulations which include the effect of helicity on eddy
viscosity and eddy noise. Thus, we model the small scales and resolve
explicitly the large scales. We show that the large-scale energy spectrum has
at least two solutions: one that is consistent with
Kolmogorov-Kraichnan-Batchelor-Leith phenomenology for the inverse cascade of
energy in two-dimensional (2D) turbulence with a {}
scaling, and the other that corresponds to a steeper {}
spectrum in which the three-dimensional (3D) modes release a substantial
fraction of their energy per unit time to 2D modes. {The spectrum that} emerges
{depends on} the anisotropy of the forcing function{,} the former solution
prevailing for forcings in which more energy is injected into 2D modes while
the latter prevails for isotropic forcing. {In the case of anisotropic forcing,
whence the energy} goes from the 2D to the 3D modes at low wavenumbers,
large-scale shear is created resulting in another time scale ,
associated with shear, {thereby producing} a spectrum for the
{total energy} with the 2D modes still following a {}
scaling
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
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