1,140 research outputs found
F-8C digital CCV flight control laws
A set of digital flight control laws were designed for the NASA F-8C digital fly-by-wire aircraft. The control laws emphasize Control Configured Vehicle (CCV) benefits. Specific pitch axis objectives were improved handling qualities, angle-of-attack limiting, gust alleviation, drag reduction in steady and maneuvering flight, and a capability to fly with reduced static stability. The lateral-directional design objectives were improved Dutch roll damping and turn coordination over a wide range in angle-of-attack. An overall program objective was to explore the use of modern control design methodilogy to achieve these specific CCV benefits. Tests for verifying system integrity, an experimental design for handling qualities evaluation, and recommended flight test investigations were specified
Matrix isolation as a tool for studying interstellar chemical reactions
Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques
Number-of-Particle Fluctuations and Stability of Bose-Condensed Systems
In this paper we show that a normal total number-of-particle fluctuation can
be obtained consistently from the static thermodynamic relation and dynamic
compressibility sum rule. In models using the broken U(1) gauge symmetry, in
order to keep the consistency between statics and dynamics, it is important to
identify the equilibrium state of the system with which the density response
function is calculated, so that the condensate particle number , the
number of thermal depletion particles , and the number of
non-condensate particles can be unambiguously defined. We also show
that the chemical potential determined from the Hugenholtz-Pines theorem should
be consistent with that determined from the equilibrium equation of state. The
anomalous fluctuation of the number of non-condensate particles is an
intrinsic feature of the broken U(1) gauge symmetry. However, this anomalous
fluctuation does not imply the instability of the system. Using the random
phase approximation, which preserves the U(1) gauge symmetry, such an anomalous
fluctuation of the number of non-condensate particles is completely absentComment: 9 pages, submitted to PR
Considerations on the Adoption of Named Data Networking (NDN) in Tactical Environments
Mobile military networks are uniquely challenging to build and maintain, because of their wireless nature and the unfriendliness of the environment, resulting in unreliable and capacity limited performance. Currently, most tactical networks implement TCP/IP, which was designed for fairly stable, infrastructure-based environments, and requires sophisticated and often application-specific extensions to address the challenges of the communication scenario. Information Centric Networking (ICN) is a clean slate networking approach that does not depend on stable connections to retrieve information and naturally provides support for node mobility and delay/disruption tolerant communications - as a result it is particularly interesting for tactical applications. However, despite ICN seems to offer some structural benefits for tactical environments over TCP/IP, a number of challenges including naming, security, performance tuning, etc., still need to be addressed for practical adoption. This document, prepared within NATO IST-161 RTG, evaluates the effectiveness of Named Data Networking (NDN), the de facto standard implementation of ICN, in the context of tactical edge networks and its potential for adoption
Low rank positive partial transpose states and their relation to product vectors
It is known that entangled mixed states that are positive under partial
transposition (PPT states) must have rank at least four. In a previous paper we
presented a classification of rank four entangled PPT states which we believe
to be complete. In the present paper we continue our investigations of the low
rank entangled PPT states. We use perturbation theory in order to construct
rank five entangled PPT states close to the known rank four states, and in
order to compute dimensions and study the geometry of surfaces of low rank PPT
states. We exploit the close connection between low rank PPT states and product
vectors. In particular, we show how to reconstruct a PPT state from a
sufficient number of product vectors in its kernel. It may seem surprising that
the number of product vectors needed may be smaller than the dimension of the
kernel.Comment: 29 pages, 4 figure
Collective Antenna Effects in the Terahertz and Infrared Response of Highly Aligned Carbon Nanotube Arrays
We study macroscopically-aligned single-wall carbon nanotube arrays with
uniform lengths via polarization-dependent terahertz and infrared transmission
spectroscopy. Polarization anisotropy is extreme at frequencies less than
3 THz with no sign of attenuation when the polarization is perpendicular
to the alignment direction. The attenuation for both parallel and perpendicular
polarizations increases with increasing frequency, exhibiting a pronounced and
broad peak around 10 THz in the parallel case. We model the electromagnetic
response of the sample by taking into account both radiative scattering and
absorption losses. We show that our sample acts as an effective antenna due to
the high degree of alignment, exhibiting much larger radiative scattering than
absorption in the mid/far-infrared range. Our calculated attenuation spectrum
clearly shows a non-Drude peak at 10 THz in agreement with the
experiment.Comment: 5 pages, 5 figure
Screening properties and phase transitions in unconventional plasmas for Ising-type quantum Hall states
Utilizing large-scale Monte-Carlo simulations, we investigate an
unconventional two-component classical plasma in two dimensions which controls
the behavior of the norms and overlaps of the quantum-mechanical wavefunctions
of Ising-type quantum Hall states. The plasma differs fundamentally from that
which is associated with the two-dimensional XY model and Abelian fractional
quantum Hall states. We find that this unconventional plasma undergoes a
Berezinskii-Kosterlitz-Thouless phase transition from an insulator to a metal.
The parameter values corresponding to Ising-type quantum Hall states lie on the
metallic side of this transition. This result verifies the required properties
of the unconventional plasma used to demonstrate that Ising-type quantum Hall
states possess quasiparticles with non-Abelian braiding statistics.Comment: 16 pages, 14 figures. Submitted to Physical Review
Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas
We report the direct observation of sub-Poissonian number fluctuation for a
degenerate Bose gas confined in an optical trap. Reduction of number
fluctuations below the Poissonian limit is observed for average numbers that
range from 300 to 60 atoms.Comment: 5 pages, 4 figure
Polarization dependence of coherent phonon generation and detection in highly-aligned single-walled carbon nanotubes
We have investigated the polarization dependence of the generation and
detection of radial breathing mode (RBM) coherent phonons (CP) in
highly-aligned single-walled carbon nanotubes. Using polarization-dependent
pump-probe differential-transmission spectroscopy, we measured RBM CPs as a
function of angle for two different geometries. In Type I geometry, the pump
and probe polarizations were fixed, and the sample orientation was rotated,
whereas, in Type II geometry, the probe polarization and sample orientation
were fixed, and the pump polarization was rotated. In both geometries, we
observed a very nearly complete quenching of the RBM CPs when the pump
polarization was perpendicular to the nanotubes. For both Type I and II
geometries, we have developed a microscopic theoretical model to simulate CP
generation and detection as a function of polarization angle and found that the
CP signal decreases as the angle goes from 0 degrees (parallel to the tube) to
90 degrees (perpendicular to the tube). We compare theory with experiment in
detail for RBM CPs created by pumping at the E44 optical transition in an
ensemble of single-walled carbon nanotubes with a diameter distribution
centered around 3 nm, taking into account realistic band structure and
imperfect nanotube alignment in the sample
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