10,265 research outputs found
Advanced powder metallurgy aluminum alloys via rapid solidification technology, phase 2
Marko's rapid solidification technology was applied to processing high strength aluminum alloys. Four classes of alloys, namely, Al-Li based (class 1), 2124 type (class 2), high temperature Al-Fe-Mo (class 3), and PM X7091 type (class 4) alloy, were produced as melt-spun ribbons. The ribbons were pulverized, cold compacted, hot-degassed, and consolidated through single or double stage extrusion. The mechanical properties of all four classes of alloys were measured at room and elevated temperatures and their microstructures were investigated optically and through electron microscopy. The microstructure of class 1 Al-Li-Mg alloy was predominantly unrecrystallized due to Zr addition. Yield strengths to the order of 50 Ksi were obtained, but tensile elongation in most cases remained below 2 percent. The class 2 alloys were modified composition of 2124 aluminum alloy, through addition of 0.6 weight percent Zr and 1 weight percent Ni. Nickel addition gave rise to a fine dispersion of intermetallic particles resisting coarsening during elevated temperature exposure. The class 2 alloy showed good combination of tensile strength and ductility and retained high strength after 1000 hour exposure at 177 C. The class 3 Al-Fe-Mo alloy showed high strength and good ductility both at room and high temperatures. The yield and tensile strength of class 4 alloy exceeded those of the commercial 7075 aluminum alloy
A Note on the Lower Bound of Black Hole Area Change in Tunneling Formalism
In the framework of tunneling mechanism and employing Bekenstein's general
expression for the variation of the black hole area, we determine the area
quantum up to a constant. Depending on the value of this constant one can get
either Bekenstein's lower bound or Hod's one for the change in the black hole
area.Comment: 4 pages, LaTeX, no figures; v2: 6 pages, clarifications and
references added, no changes in physics and results, to appear in EP
Quantum tunneling and black hole spectroscopy
The entropy-area spectrum of a black hole has been a long-standing and
unsolved problem. Based on a recent methodology introduced by two of the
authors, for the black hole radiation (Hawking effect) as tunneling effect, we
obtain the entropy spectrum of a black hole. In Einstein's gravity, we show
that both entropy and area spectrum are evenly spaced. But in more general
theories (like Einstein-Gauss-Bonnet gravity), although the entropy spectrum is
equispaced, the corresponding area spectrum is not.Comment: 10 pages, LaTeX, no figures; v2: 9 pages, now, title changed, minor
changes to match published version in Phys. Lett.
-SELC: Optimization by sequential elimination of level combinations using genetic algorithms and Gaussian processes
Identifying promising compounds from a vast collection of feasible compounds
is an important and yet challenging problem in the pharmaceutical industry. An
efficient solution to this problem will help reduce the expenditure at the
early stages of drug discovery. In an attempt to solve this problem, Mandal, Wu
and Johnson [Technometrics 48 (2006) 273--283] proposed the SELC algorithm.
Although powerful, it fails to extract substantial information from the data to
guide the search efficiently, as this methodology is not based on any
statistical modeling. The proposed approach uses Gaussian Process (GP) modeling
to improve upon SELC, and hence named -SELC. The performance of
the proposed methodology is illustrated using four and five dimensional test
functions. Finally, we implement the new algorithm on a real pharmaceutical
data set for finding a group of chemical compounds with optimal properties.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS199 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Anisotropic generalization of well-known solutions describing relativistic self-gravitating fluid systems: An algorithm
We present an algorithm to generalize a plethora of well-known solutions to
Einstein field equations describing spherically symmetric relativistic fluid
spheres by relaxing the pressure isotropy condition on the system. By suitably
fixing the model parameters in our formulation, we generate closed-form
solutions which may be treated as anisotropic generalization of a large class
of solutions describing isotropic fluid spheres. From the resultant solutions,
a particular solution is taken up to show its physical acceptability. Making
use of the current estimate of mass and radius of a known pulsar, the effects
of anisotropic stress on the gross physical behaviour of a relativistic compact
star is also highlighted.Comment: To appear in Eur. Phys. J.
Measurements of a Quantum Dot with an Impedance-Matching On-Chip LC Resonator at GHz Frequencies
We report the realization of a bonded-bridge on-chip superconducting coil and
its use in impedance-matching a highly ohmic quantum dot (QD) to a
measurement setup. The coil, modeled as a lumped-element resonator, is
more compact and has a wider bandwidth than resonators based on coplanar
transmission lines (e.g. impedance transformers and stub tuners) at
potentially better signal-to-noise ratios. In particular for measurements of
radiation emitted by the device, such as shot noise, the 50 larger
bandwidth reduces the time to acquire the spectral density. The resonance
frequency, close to 3.25 GHz, is three times higher than that of the one
previously reported wire-bonded coil. As a proof of principle, we fabricated an
circuit that achieves impedance-matching to a load
and validate it with a load defined by a carbon nanotube QD of which we measure
the shot noise in the Coulomb blockade regime.Comment: 7 pages, 6 figure
Connecting anomaly and tunneling methods for Hawking effect through chirality
The role of chirality is discussed in unifying the anomaly and the tunneling
formalisms for deriving the Hawking effect. Using the chirality condition and
starting from the familiar form of the trace anomaly, the chiral
(gravitational) anomaly, manifested as a nonconservation of the stress tensor,
near the horizon of a black hole, is derived. Solution of this equation yields
the stress tensor whose asymptotic infinity limit gives the Hawking flux.
Finally, use of the same chirality condition in the tunneling formalism gives
the Hawking temperature that is compatible with the flux obtained by anomaly
method.Comment: LaTex, 8 pages, no figures, reformulation of tunneling mechanism, to
appear in Phys. Rev.
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