22,766 research outputs found
OGY Control of Haken Like Systems on Different Poincare Sections
The Chua system, the Lorenz system, the Chen system and The L\"u system are
chaotic systems that their state space equations is very similar to Haken
system which is a nonlinear model of a optical slow-fast system. These
Haken-Like Sys-tems have very similar properties. All have two slow but
unstable eigenvalues and one fastest but stable eigenvalue. This lets that an
approximation of slow manifold be equivalent with unstable manifold of the
system. In other hand, control of discreet model of the system on a defined
manifold (Poincare map) is main essence of some important control methods of
chaotic systems for example OGY method. Here, by using different methods of
defining slow manifold of the H-L systems the efficiency of the OGY control for
stabilizing problem investigated.Comment: 4 page
A theoretical study of microwave beam absorption by a rectenna
The rectenna's microwave power beam absorption limit was theoretically confirmed by two mathematical models descriptive of the microwave absorption process; first one model was based on the current sheet equivalency of a large planar array above a reflector and the second model, which was based on the properties of a waveguide with special imaging characteristics, quantified the electromagnetic modes (field configurations) in the immediate vicinity of a Rectenna element spacing which permit total power beam absorption by preventing unwanted modes from propagating (scattering) were derived using these models. Several factors causing unwanted scattering are discussed
Studies of Stellar Collapse and Black Hole Formation with the Open-Source Code GR1D
We discuss results from simulations of black hole formation in failing core-collapse supernovae performed with the code GR1D, a new open-source Eulerian spherically-symmetric general-relativistic hydrodynamics code. GR1D includes rotation in an approximate way (1.5D) comes with multiple finite-temperature nuclear equations of state (EOS), and treats neutrinos in the post-core-bounce phase via a 3-flavor leakage scheme and a heating prescription. We chose the favored K_0 = 220 MeV-variant of the Lattimer & Swesty (1990) EOS and present collapse calculations using the progenitor models of Limongi & Chieffi (2006). We show that there is no direct (or “prompt”) black hole formation in the collapse of ordinary massive stars (8M_☉ ≲ M_(ZAMS) ≲ 100 M_☉) present first results from black hole formation simulations that include rotation
Workshop on Spaceflight Alterations in Host-Microorganism Interactions
On June 11, 2009, a workshop that included internal and external experts was convened to determine the risk of changes in microorganisms that could alter host-microorganism interactions during a mission. The evidence is based in part on multiple flight experiments which indicate altered virulence in Salmonella typhimurium when cultured in flight. The workshop participants were tasked to determine if adequate information was available to initiate changes in NASA's current approach to infectious disease risk assessment and medical operations. The consensus of the participants is that the current evidence was not adequate to provide direction for operational changes; however, the evidence is compelling and clearly indicates that changes to microorganisms were occurring during spaceflight and further research is required
Infrared Spectra of Meteoritic SiC Grains
We present here the first infrared spectra of meteoritic SiC grains. The
mid-infrared transmission spectra of meteoritic SiC grains isolated from the
Murchison meteorite were measured in the wavelength range 2.5--16.5 micron, in
order to make available the optical properties of presolar SiC grains. These
grains are most likely stellar condensates with an origin predominately in
carbon stars. Measurements were performed on two different extractions of
presolar SiC from the Murchison meteorite. The two samples show very different
spectral appearance due to different grain size distributions. The spectral
feature of the smaller meteoritic SiC grains is a relatively broad absorption
band found between the longitudinal and transverse lattice vibration modes
around 11.3 micron, supporting the current interpretation about the presence of
SiC grains in carbon stars. In contrast to this, the spectral feature of the
large (> 5 micron) grains has an extinction minimum around 10 micron. The
obtained spectra are compared with commercially available SiC grains and the
differences are discussed. This comparison shows that the crystal structure
(e.g., beta-SiC versus alpha-SiC) of SiC grains plays a minor role on the
optical signature of SiC grains compared to e.g. grain size.Comment: 7 pages, 6 figures. To appear in A&
Culture-Based Environmental Microbiology Monitoring of Crop-Based Space Food Systems (veggie Monitoring)
Crewmembers live and work in a closed environment that is monitored to ensure their health and safety. Quarterly monitoring of the microorganisms in the International Space Station (ISS) environment supports crew safety and contributes to a large set of microbial concentration and diversity data from air, surfaces and water samples. This study leverages quarterly operational Environmental Health System (EHS) sampling by collecting additional microbial samples from the surface of the stations Veggie plant production system. Longer exploration missions may require spaceflight-based systems for growth of plants, and this investigation is expected to provide additional data to help establish requirements to protect these systems, plants, and crew, mitigating adverse microbial exposure
Auctions as a vehicle to reduce airport delays and achieve value capture
Congestion at airports imposes large costs on airlines and their passengers. A key reason for congestion is that an airline schedules its flights without regard to the costs imposed on other airlines and their passengers. As a result, during some time intervals, airlines schedule more flights to and from an airport than that airport can accommodate and flights are delayed. This paper explores how a specific market-based proposal by the Federal Aviation Administration (FAA), which includes the use of auctions to determine the right to arrive or depart in a specific time interval at airports in the New York City area, might be used as part of a strategy to mitigate delays and congestion. By explaining the underlying economic theory and key arguments with minimal technical jargon, the paper allows those with little formal training in economics to understand the fundamental issues associated with the FAA's controversial proposal. Moreover, the basics of the proposed auction process, known as a combinatorial auction, and value capture are also explained.Airlines ; Airports
Microelectromagnets for Trapping and Manipulating Ultracold Atomic Quantum Gases
We describe the production and characterization of microelectromagnets made
for trapping and manipulating atomic ensembles. The devices consist of 7
fabricated parallel copper conductors 3 micrometer thick, 25mm long, with
widths ranging from 3 to 30 micrometer, and are produced by electroplating a
sapphire substrate. Maximum current densities in the wires up to 6.5 * 10^6 A /
cm^2 are achieved in continuous mode operation. The device operates
successfully at a base pressure of 10^-11 mbar. The microstructures permit the
realization of a variety of magnetic field configurations, and hence provide
enormous flexibility for controlling the motion and the shape of Bose-Einstein
condensates.Comment: 4 pages, 3 figure
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