64,339 research outputs found
Leaching of nitroso rubber material removes uncured polymer
New leaching process removes uncured polymer from nitroso rubber, elastomer used in presence of nitrogen tetroxide. Uncured portion is removed by controlled soaking of polymer slab in Freon TF. Leaching with Freon TF prevents nitroso rubber from adhering to adjoining surfaces and limiting its usefulness in either static or dynamic applications
Two and three electrons in a quantum dot: 1/|J| - expansion
We consider systems of two and three electrons in a two-dimensional parabolic
quantum dot. A magnetic field is applied perpendicularly to the electron plane
of motion. We show that the energy levels corresponding to states with high
angular momentum, J, and a low number of vibrational quanta may be
systematically computed as power series in 1/|J|. These states are relevant in
the high-B limit.Comment: LaTeX, 15 pages,6 postscript figure
Tracing the Dynamics of Disk Galaxies with Optical and IR Surface Photometry: Color Gradients in M99
We present optical and IR surface photometry of M99 (NGC 4254) at g, r_S i, J
and K'. We also present a K' image of M51 (NGC 5194) for comparison. Fourier
decomposition of the disk light reveals that the radial distribution of power
depends on wavelength, which in turn implies that the spiral structure traced
in the visual (i.e. young population I and dust) is different from the one
detected at 2 microns (i.e. old stellar disk). We observe radial modulation of
the power and a dependency of power with wavelength that are consistent with
modal theory of spiral structure.
A central motivation for our research is the fundamental idea of density wave
theory that the passage of a spiral density wave triggers star formation. We
have found a stellar population age gradient consistent with this scenario in a
reddening-free, red supergiant-sensitive, Q-like photometric parameter at 6 kpc
galactocentric distance across one of the arms of M99. We rule out that the
change in this parameter, Q(r_SJgi), across the arm is mainly due to dust. The
difference in Q(r_SJgi) going from the interarm regions to the arms also
indicates that arms cannot be due exclusively to crowding of stellar orbits.
We present the first measurement of Omega_p, the angular speed of the spiral
pattern, and of the location of the corotation radius, derived from the drift
velocity of the young stars away from their birth site. The measured Q(r_SJgi)
implies a star formation rate for M99 within the range of 10-20 M_odot/yr; a
disk stellar mass surface density of ~80 M_odot/pc^2; and a maximum
contribution of ~20 percent from red supergiants to the K' light in a small
region, and much smaller on average. We measure a K' arm--interarm contrast of
2-3, too high for M99 to be a truly isolated galaxy.Comment: 25 pages of uuencoded, compressed Postscript (text only). To appear
in 1 April 1996 issue of The Astrophysical Journal. Also available, together
with 2 uuencoded, compressed PostScript files with 10 figures each, at
http://astro.berkeley.edu/preprints.htm
Reporting ethics committee approval and patient consent by study design in five general medical journals.
BACKGROUND: Authors are required to describe in their manuscripts ethical approval from an appropriate committee and how consent was obtained from participants when research involves human participants. OBJECTIVE: To assess the reporting of these protections for several study designs in general medical journals. DESIGN: A consecutive series of research papers published in the Annals of Internal Medicine, BMJ, JAMA, Lancet and The New England Journal of Medicine between February and May 2003 were reviewed for the reporting of ethical approval and patient consent. Ethical approval, name of approving committee, type of consent, data source and whether the study used data collected as part of a study reported elsewhere were recorded. Differences in failure to report approval and consent by study design, journal and vulnerable study population were evaluated using multivariable logistic regression. RESULTS: Ethical approval and consent were not mentioned in 31% and 47% of manuscripts, respectively. 88 (27%) papers failed to report both approval and consent. Failure to mention ethical approval or consent was significantly more likely in all study designs (except case-control and qualitative studies) than in randomised controlled trials (RCTs). Failure to mention approval was most common in the BMJ and was significantly more likely than in The New England Journal of Medicine. Failure to mention consent was most common in the BMJ and was significantly more likely than in all other journals. No significant differences in approval or consent were found when comparing studies of vulnerable and non-vulnerable participants. CONCLUSION: The reporting of ethical approval and consent in RCTs has improved, but journals are less good at reporting this information for other study designs. Journals should publish this information for all research on human participants
Collisionless reconnection: The sub-microscale mechanism of magnetic field line interaction
Magnetic field lines are quantum objects carrying one quantum
of magnetic flux and have finite radius . Here
we argue that they possess a very specific dynamical interaction. Parallel
field lines reject each other. When confined to a certain area they form
two-dimensional lattices of hexagonal structure. We estimate the filling factor
of such an area. Antiparallel field lines, on the other hand, attract each
other. We identify the physical mechanism as being due to the action of the
gauge potential field which we determine quantum mechanically for two parallel
and two antiparallel field lines. The distortion of the quantum electrodynamic
vacuum causes a cloud of virtual pairs. We calculate the virtual pair
production rate from quantum electrodynamics and estimate the virtual pair
cloud density, pair current and Lorentz force density acting on the field lines
via the pair cloud. These properties of field line dynamics become important in
collisionless reconnection, consistently explaining why and how reconnection
can spontaneously set on in the field-free centre of a current sheet below the
electron-inertial scale.Comment: 13 journal pages, 6 figures, submitted to Ann. Geophy
Free Cooling Phase-Diagram of Hard-Spheres with Short- and Long-Range Interactions
We study the stability, the clustering and the phase-diagram of free cooling
granular gases. The systems consist of mono-disperse particles with additional
non-contact (long-range) interactions, and are simulated here by the
event-driven molecular dynamics algorithm with discrete (short-range shoulders
or wells) potentials (in both 2D and 3D). Astonishingly good agreement is found
with a mean field theory, where only the energy dissipation term is modified to
account for both repulsive or attractive non-contact interactions. Attractive
potentials enhance cooling and structure formation (clustering), whereas
repulsive potentials reduce it, as intuition suggests. The system evolution is
controlled by a single parameter: the non-contact potential strength scaled by
the fluctuation kinetic energy (granular temperature). When this is small, as
expected, the classical homogeneous cooling state is found. However, if the
effective dissipation is strong enough, structure formation proceeds, before
(in the repulsive case) non-contact forces get strong enough to undo the
clustering (due to the ongoing dissipation of granular temperature). For both
repulsive and attractive potentials, in the homogeneous regime, the cooling
shows a universal behaviour when the (inverse) control parameter is used as
evolution variable instead of time. The transition to a non-homogeneous regime,
as predicted by stability analysis, is affected by both dissipation and
potential strength. This can be cast into a phase diagram where the system
changes with time, which leaves open many challenges for future research.Comment: 22 pages, 15 figure
The origin of the supersoft X-ray--optical/UV flux anticorrelation in the symbiotic binary AG Draconis
AG Draconis produces a strong supersoft X-ray emission.The X-ray and
optical/UV fluxes are in a strict anticorrelation throughout the active and
quiescent phases. The aim of this contribution is to identify the source of the
X-ray emission and reveal the nature of the observed flux anticorrelation. For
this purpose we model the X-ray and UV observations with XMM-Newton, far-UV
spectroscopy from FUSE, low- and high-resolution IUE spectra and
optical/near-IR spectroscopic and/or photometric observations. Our analysis
showed that the supersoft X-ray emission is produced by the white dwarf
photosphere. The X-ray and far-UV fluxes make it possible to determine its
temperature unambiguously. The supersoft X-ray--optical/UV flux anticorrelation
is caused by the variable wind from the hot star. The enhanced hot star wind
gives rise to the optical bursts by reprocessing high-energy photons from the
Lyman continuum to the optical/UV.Comment: 9 pages, 2 figures, 3 tables. Submitted to AA on 25/11/2008, revised
on 27/05/200
Design and implementation of fuzzy logic controllers
The main objectives of our research are to present a self-contained overview of fuzzy sets and fuzzy logic, develop a methodology for control system design using fuzzy logic controllers, and to design and implement a fuzzy logic controller for a real system. We first present the fundamental concepts of fuzzy sets and fuzzy logic. Fuzzy sets and basic fuzzy operations are defined. In addition, for control systems, it is important to understand the concepts of linguistic values, term sets, fuzzy rule base, inference methods, and defuzzification methods. Second, we introduce a four-step fuzzy logic control system design procedure. The design procedure is illustrated via four examples, showing the capabilities and robustness of fuzzy logic control systems. This is followed by a tuning procedure that we developed from our design experience. Third, we present two Lyapunov based techniques for stability analysis. Finally, we present our design and implementation of a fuzzy logic controller for a linear actuator to be used to control the direction of the Free Flight Rotorcraft Research Vehicle at LaRC
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