3,398 research outputs found
A study of aircraft fire hazards related to natural electrical phenomena Final report, Jun. 1966 - Jul. 1967
Natural electrical phenomena as aircraft fire hazards, with study of flame propagation in fuel vent system
Neutrino spin relaxation in medium with stochastic characteristics
The helicity evolution of a neutrino interacting with randomly moving and
polarized matter is studied. We derive the equation for the averaged neutrino
helicity. The type of the neutrino interaction with background fermions is not
fixed. In the particular case of a tau-neutrino interacting with
ultrarelativistic electron-positron plasma we obtain the expression for the
neutrino helicity relaxation rate in the explicit form. We study the neutrino
spin relaxation in the relativistic primordial plasma. Supposing that the
conversion of left-handed neutrinos into right-handed ones is suppressed at the
early stages of the Universe evolution we get the upper limit on the
tau-neutrino mass.Comment: 6 pages, RevTeX4; 2 references added; more detailed discussion of
correlation functions and cosmological neutrinos is presented; version to be
published in Int. J. Mod. Phys.
Field Redefinition Invariance in Quantum Field Theory
The issue of field redefinition invariance of path integrals in quantum field
theory is reexamined. A ``paradox'' is presented involving the reduction to an
effective quantum-mechanical theory of a -dimensional free scalar field
in a Minkowskian spacetime with compactified spatial coordinates. The
implementation of field redefinitions both before and after the reduction
suggests that operator-ordering issues in quantum field theory should not be
ignored.Comment: 7 page
Communications Biophysics
Contains research objectives and reports on one research project.U. S. Air Force under Contract AF19(604)-411
Developmental separation of V(D)J recombinase expression and initiation of IgH recombination in B lineage progenitors in vivo
In B lineage progenitors, V(D)J recombination occurs only during distinct stages of development and is restricted to immunoglobulin loci. This process is thought to be controlled by both regulated expression of the V(D)J recombinase and by limited accessibility of target loci to the recombinase complex. However, it is unknown whether these two processes occur concomitantly in developing B lineage progenitors or whether these events are temporally distinct and, therefore, potentially independently regulated. To distinguish between these possibilities, we developed a transgenic V(D)J recombination substrate that is not governed by the same chromatin remodeling constraints as endogenous immunoglobulin heavy chain (IgH) loci and examined the requirements for V(D)J recombination to initiate in early B lineage progenitors. We find that single B lineage precursors express an active V(D)J recombinase in vivo before the stage when IgH rearrangements are frequently detectable. Our results indicate that the onset of recombinase activity and the initiation of IgH recombination are developmentally distinct events in the B lineage
Bootstrap tomography of high-precision pulses for quantum control
Long-time dynamical decoupling and quantum control of qubits require
high-precision control pulses. Full characterization (quantum tomography) of
imperfect pulses presents a bootstrap problem: tomography requires initial
states of a qubit which can not be prepared without imperfect pulses. We
present a protocol for pulse error analysis, specifically tailored for a wide
range of the single solid-state electron spins. Using a single electron spin of
a nitrogen-vacancy (NV) center in diamond, we experimentally verify the
correctness of the protocol, and demonstrate its usefulness for quantum control
tasks
The role of the slope of `realistic' potential barriers in preventing relativistic tunnelling in the Klein zone
The transmission of fermions of mass m and energy E through an electrostatic
potential barrier of rectangular shape (i.e. supporting an infinite electric
field), of height U> E + m - due to the many-body nature of the Dirac equation
evidentiated by the Klein paradox - has been widely studied. We exploit here
the analytical solution, given by Sauter for the linearly rising potential
step, to show that the tunnelling rate through a more realistic trapezoidal
barrier is exponentially depressed, as soon as the length of the regions
supporting a finite electric field exceeds the Compton wavelenght of the
particle - the latter circumstance being hardly escapable in most realistic
cases
Scaling laws of human interaction activity
Even though people in our contemporary, technological society are depending
on communication, our understanding of the underlying laws of human
communicational behavior continues to be poorly understood. Here we investigate
the communication patterns in two social Internet communities in search of
statistical laws in human interaction activity. This research reveals that
human communication networks dynamically follow scaling laws that may also
explain the observed trends in economic growth. Specifically, we identify a
generalized version of Gibrat's law of social activity expressed as a scaling
law between the fluctuations in the number of messages sent by members and
their level of activity. Gibrat's law has been essential in understanding
economic growth patterns, yet without an underlying general principle for its
origin. We attribute this scaling law to long-term correlation patterns in
human activity, which surprisingly span from days to the entire period of the
available data of more than one year. Further, we provide a mathematical
framework that relates the generalized version of Gibrat's law to the long-term
correlated dynamics, which suggests that the same underlying mechanism could be
the source of Gibrat's law in economics, ranging from large firms, research and
development expenditures, gross domestic product of countries, to city
population growth. These findings are also of importance for designing
communication networks and for the understanding of the dynamics of social
systems in which communication plays a role, such as economic markets and
political systems.Comment: 20+7 pages, 4+2 figure
A Study of Aircraft Fire Hazards Related to Natural Electrical Phenomena
The problems of natural electrical phenomena as a fire hazard to aircraft are evaluated. Assessment of the hazard is made over the range of low level electrical discharges, such as static sparks, to high level discharges, such as lightning strikes to aircraft. In addition, some fundamental work is presented on the problem of flame propagation in aircraft fuel vent systems. This study consists of a laboratory investigation in five parts: (1) a study of the ignition energies and flame propagation rates of kerosene-air and JP-6-air foams, (2) a study of the rate of flame propagation of n-heptane, n-octane, n-nonane, and n-decane in aircraft vent ducts, (3) a study of the damage to aluminum, titanium, and stainless steel aircraft skin materials by lightning strikes, (4) a study of fuel ignition by lightning strikes to aircraft skins, and (5) a study of lightning induced flame propagation in an aircraft vent system
The CRIT framework for identifying cross patterns in systems biology and application to chemogenomics
Biological data is often tabular but finding statistically valid connections between entities in a sequence of tables can be problematic - for example, connecting particular entities in a drug property table to gene properties in a second table, using a third table associating genes with drugs. Here we present an approach (CRIT) to find connections such as these and show how it can be applied in a variety of genomic contexts including chemogenomics data
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