58,748 research outputs found
The SA-2239/WLQ-4(V) Cutty Sark distribution system
A redundant frequency and time distribution system provides a multiplicity of isolated outputs, all of which are derived from three atomic frequency standards. The distribution system monitors input parameters of the signals coming from the Cesium Standards and selects one to be the primary standard, phase locks an internal oscillator which has excellent aging characteristics in the open loop mode and acts as a filter to provide phase noise improvement, and generates 1 megahertz and 100 kHz by direct synthesis. Additionally, the system distributes RF and timing signals consisting of 5 MHz, 1 MHz, 100 kHz, BCD Time-of-Day, 1 pps and 1 ppm
Momentum Analysis in Strong-field Double Ionization
We provide a basis for the laser intensity dependence of the momentum
distributions of electrons and ions arising from strong-field non-sequential
double ionization (NSDI) at intensities in the range . To do this we use a completely classical method introduced previously
\cite{ho-etal05}. Our calculated results reproduce the features of experimental
observations at different laser intensities and depend on just two distinct
categories of electon trajectories.Comment: 5 pages, 7 figure
Intermediate-mass Black Holes in Galactic Nuclei
We present the first homogeneous sample of intermediate-mass black hole
candidates in active galactic nuclei. Starting with broad-line active nuclei
from the Sloan Digital Sky Survey, we use the linewidth-luminosity-mass scaling
relation to select a sample of 19 galaxies in the mass range M_BH ~ 8 x 10^4 -
10^6 solar masses. In contrast to the local active galaxy population, the host
galaxies are ~1 mag fainter than M* and thus are probably late-type systems.
The active nuclei are also faint, with M_g ~ -15 to -18 mag, while the
bolometric luminosities are close to the Eddington limit. The spectral
properties of the sample are compared to the related class of objects known as
narrow-line Seyfert 1 galaxies. We discuss the importance of our sample as
observational analogues of primordial black holes, contributors to the
integrated signal for future gravitational wave experiments, and as a valuable
tool in the calibration of the M-sigma relation.Comment: 4 pages, 4 figures. To appear in "The Interplay among Black Holes,
Stars and ISM in Galactic Nuclei," Proc. IAU 222 (Gramado, Brazil), eds Th.
Storchi Bergmann, L.C. Ho, H.R. Schmit
Spin-glass-like state in GdCu: role of phase separation and magnetic frustration
We report investigations on the ground state magnetic properties of
intermetallic compound GdCu through dc magnetization measurements. GdCu
undergoes first order martensitic type structural transition over a wide
temperature window of coexisting phases. The high temperature cubic and the low
temperature orthorhombic phases have different magnetic character and they show
antiferromagnetic and helimagnetic orderings below 145 K and 45 K respectively.
We observe clear signature of a glassy magnetic phase below the helimagnetic
ordering temperature, which is marked by thermomagnetic irreversibility, aging
and memory effects. The glassy magnetic phase in GdCu is found to be rather
intriguing with its origin lies in the interfacial frustration due to distinct
magnetic character of the coexisting phases.Comment: Physical Review B 83, 134427 (2011
Nondestructive measurement of capillary tube internal diameter
Technique provides nondestructive method of making quick, accurate determination by measuring electrical resistance of capillary tube when it is filled with electrolyte of known conductivity. Apparatus consists of conductivity cell and equipment for measuring resistance and for monitoring and controlling temperature
Trees of Unusual Size: Biased Inference of Early Bursts from Large Molecular Phylogenies
An early burst of speciation followed by a subsequent slowdown in the rate of
diversification is commonly inferred from molecular phylogenies. This pattern
is consistent with some verbal theory of ecological opportunity and adaptive
radiations. One often-overlooked source of bias in these studies is that of
sampling at the level of whole clades, as researchers tend to choose large,
speciose clades to study. In this paper, we investigate the performance of
common methods across the distribution of clade sizes that can be generated by
a constant-rate birth-death process. Clades which are larger than expected for
a given constant-rate branching process tend to show a pattern of an early
burst even when both speciation and extinction rates are constant through time.
All methods evaluated were susceptible to detecting this false signature when
extinction was low. Under moderate extinction, both the gamma-statistic and
diversity-dependent models did not detect such a slowdown but only because the
signature of a slowdown was masked by subsequent extinction. Some models which
estimate time-varying speciation rates are able to detect early bursts under
higher extinction rates, but are extremely prone to sampling bias. We suggest
that examining clades in isolation may result in spurious inferences that rates
of diversification have changed through time.Comment: 17 pages, 5 figure
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SLS Processing Studies of Nylon 11 Nanocomposites
Selective Laser Sintering (SLS) is widely used for rapid prototyping/manufacturing of
nylon 11 and nylon 12 parts. This processing technique has not been explored for
nylon nanocomposites. This study investigates the technicalities of processing nylon
11-clay and nylon-carbon nanofiber nanocomposites with SLS. Microstructural
analyses of the SLS powders and parts were conducted under SEM. Results suggest
that SLS processing is possible with the new nylon 11 nanocomposites. Yet the SLS
parts built have inferior properties relative to those of injection molding, suggesting
that more fine tuning for the processing is required.Mechanical Engineerin
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