4,735 research outputs found
The advanced solar cell orbital test
The motivation for advanced solar cell flight experiments is discussed and the Advanced Solar Cell Orbital Test (ASCOT) flight experiment is described. Details of the types of solar cells included in the test and the kinds of data to be collected are given. The orbit will expose the cells to a sufficiently high radiation dose that useful degradation data will be obtained in the first year
The re-emission spectrum of digital hardware subjected to EMI
The emission spectrum of digital hardware under the influence of external electromagnetic interference is shown to contain information about the interaction of the incident energy with the digital circuits in the system. The generation mechanism of the re-emission spectrum is reviewed, describing how nonlinear effects may be a precursor to the failure of the equipment under test. Measurements on a simple circuit are used to demonstrate how the characteristics of the re-emission spectrum may be correlated with changes to the digital waveform within the circuit. The technique is also applied to a piece of complex digital hardware where Similar, though more subtle, effects can be measured. It is shown that the re-emission spectrum can be used to detect the interaction of the interference with the digital devices at a level well below that which is able to cause static failures in the circuits. The utility of the technique as a diagnostic tool for immunity testing of digital hardware, by identifying which subsystems are being affected by external interference, is also demonstrated
Quarks, Gluons and Frustrated Antiferromagnets
The Contractor Renormalization Group method (CORE) is used to establish the
equivalence of various Hamiltonian free fermion theories and a class of
generalized frustrated antiferromagnets. In particular, after a detailed
discussion of a simple example, it is argued that a generalized frustrated
SU(3) antiferromagnet whose single-site states have the quantum numbers of
mesons and baryons is equivalent to a theory of free massless quarks.
Furthermore, it is argued that for slight modification of the couplings which
define the frustrated antiferromagnet Hamiltonian, the theory becomes a theory
of quarks interacting with color gauge-fields.Comment: 21 pages, Late
Assessment of Buffet Forcing Function Development Process Using Unsteady Pressure Sensitive Paint
A wind tunnel test was conducted at the Ames Unitary Plan Wind Tunnel to characterize the transonic buffet environment of a generic launch vehicle forebody. The test examined a highly instrumented version of the Coe and Nute Model 11 test article first tested in the 1960s. One of the measurement techniques used during this test was unsteady pressure sensitive paint (uPSP) developed at the Arnold Engineering Development Complex. This optical measurement technique measured fluctuating pressures at over 300,000 locations on the surface of the model. The high spatial density of these measurements provided an opportunity to examine in depth the assumptions underpinning the development of buffet forcing functions (BFFs) used in the development of the Space Launch System vehicle. The comparison of discrete-measurement-based BFFs to BFFs developed by continuous surface pressure integration indicates that the current BFF development approach under predicts low frequency content of the BFFs while over predicting high frequency content. Coherence-based adjustments employed to reduce over prediction in the surface integration of discrete pressure measurements contribute to the inaccuracy of the BFFs and their implementation should be reevaluated
On Unitary Evolution of a Massless Scalar Field In A Schwarzschild Background: Hawking Radiation and the Information Paradox
We develop a Hamiltonian formalism which can be used to discuss the physics
of a massless scalar field in a gravitational background of a Schwarzschild
black hole. Using this formalism we show that the time evolution of the system
is unitary and yet all known results such as the existence of Hawking radiation
can be readily understood. We then point out that the Hamiltonian formalism
leads to interesting observations about black hole entropy and the information
paradox.Comment: 45 pages, revte
CORE and the Haldane Conjecture
The Contractor Renormalization group formalism (CORE) is a real-space
renormalization group method which is the Hamiltonian analogue of the Wilson
exact renormalization group equations. In an earlier paper\cite{QGAF} I showed
that the Contractor Renormalization group (CORE) method could be used to map a
theory of free quarks, and quarks interacting with gluons, into a generalized
frustrated Heisenberg antiferromagnet (HAF) and proposed using CORE methods to
study these theories. Since generalizations of HAF's exhibit all sorts of
subtle behavior which, from a continuum point of view, are related to
topological properties of the theory, it is important to know that CORE can be
used to extract this physics. In this paper I show that despite the folklore
which asserts that all real-space renormalization group schemes are necessarily
inaccurate, simple Contractor Renormalization group (CORE) computations can
give highly accurate results even if one only keeps a small number of states
per block and a few terms in the cluster expansion. In addition I argue that
even very simple CORE computations give a much better qualitative understanding
of the physics than naive renormalization group methods. In particular I show
that the simplest CORE computation yields a first principles understanding of
how the famous Haldane conjecture works for the case of the spin-1/2 and spin-1
HAF.Comment: 36 pages, 4 figures, 5 tables, latex; extensive additions to conten
Spin squeezing of high-spin, spatially extended quantum fields
Investigations of spin squeezing in ensembles of quantum particles have been
limited primarily to a subspace of spin fluctuations and a single spatial mode
in high-spin and spatially extended ensembles. Here, we show that a wider range
of spin-squeezing is attainable in ensembles of high-spin atoms, characterized
by sub-quantum-limited fluctuations in several independent planes of
spin-fluctuation observables. Further, considering the quantum dynamics of an
ferromagnetic spinor Bose-Einstein condensate, we demonstrate
theoretically that a high degree of spin squeezing is attained in multiple
spatial modes of a spatially extended quantum field, and that such squeezing
can be extracted from spatially resolved measurements of magnetization and
nematicity, i.e.\ the vector and quadrupole magnetic moments, of the quantum
gas. Taking into account several experimental limitations, we predict that the
variance of the atomic magnetization and nematicity may be reduced as far as 20
dB below the standard quantum limits.Comment: 18 pages, 5 figure
High-Performance Atomically-Thin Room-Temperature NO2 Sensor.
The development of room-temperature sensing devices for detecting small concentrations of molecular species is imperative for a wide range of low-power sensor applications. We demonstrate a room-temperature, highly sensitive, selective, stable, and reversible chemical sensor based on a monolayer of the transition-metal dichalcogenide Re0.5Nb0.5S2. The sensing device exhibits a thickness-dependent carrier type, and upon exposure to NO2 molecules, its electrical resistance considerably increases or decreases depending on the layer number. The sensor is selective to NO2 with only minimal response to other gases such as NH3, CH2O, and CO2. In the presence of humidity, not only are the sensing properties not deteriorated but also the monolayer sensor shows complete reversibility with fast recovery at room temperature. We present a theoretical analysis of the sensing platform and identify the atomically sensitive transduction mechanism
- …