22,681 research outputs found
Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy
The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced
Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture
Radio-frequency spectroscopy is used to study pairing in the normal and
superfluid phases of a strongly interacting Fermi gas with imbalanced spin
populations. At high spin imbalances the system does not become superfluid even
at zero temperature. In this normal phase full pairing of the minority atoms is
observed. This demonstrates that mismatched Fermi surfaces do not prevent
pairing but can quench the superfluid state, thus realizing a system of fermion
pairs that do not condense even at the lowest temperature
Fermionic Superfluidity with Imbalanced Spin Populations and the Quantum Phase Transition to the Normal State
Whether it occurs in superconductors, helium-3 or inside a neutron star,
fermionic superfluidity requires pairing of fermions, particles with
half-integer spin. For an equal mixture of two states of fermions ("spin up"
and "spin down"), pairing can be complete and the entire system will become
superfluid. When the two populations of fermions are unequal, not every
particle can find a partner. Will the system nevertheless stay superfluid? Here
we study this intriguing question in an unequal mixture of strongly interacting
ultracold fermionic atoms. The superfluid region vs population imbalance is
mapped out by employing two complementary indicators: The presence or absence
of vortices in a rotating mixture, as well as the fraction of condensed fermion
pairs in the gas. Due to the strong interactions near a Feshbach resonance, the
superfluid state is remarkably stable in response to population imbalance. The
final breakdown of superfluidity marks a new quantum phase transition, the
Pauli limit of superfluidity.Comment: 15 pages, 5 figure
Synchronization and fault-masking in redundant real-time systems
A real time computer may fail because of massive component failures or not responding quickly enough to satisfy real time requirements. An increase in redundancy - a conventional means of improving reliability - can improve the former but can - in some cases - degrade the latter considerably due to the overhead associated with redundancy management, namely the time delay resulting from synchronization and voting/interactive consistency techniques. The implications of synchronization and voting/interactive consistency algorithms in N-modular clusters on reliability are considered. All these studies were carried out in the context of real time applications. As a demonstrative example, we have analyzed results from experiments conducted at the NASA Airlab on the Software Implemented Fault Tolerance (SIFT) computer. This analysis has indeed indicated that in most real time applications, it is better to employ hardware synchronization instead of software synchronization and not allow reconfiguration
Case History of Soil Improvement for a Large-Scale Land Reclamation
In recent years, land reclamation works have been extensively implemented along the coastal lines for a variety of purposes. This paper relates to the case history of a land reclamation project for a steel mill complex construction in Korea. Site improvement techniques used in this project include construction of sand drains and pre loading. Construction procedures of sand drains are described as well as staged loading process along with field observations. Field measurement of settlement and theoretically estimated values are compared. The results of standard penetration tests and unconfined compression tests at various depths of soil, and time intervals are presented. Finally, the methods of construction quality assurance are discussed
Case History of Soil Improvement for a Large-Scale Land Reclamation
In recent years, land reclamation works have been extensively implemented along the coastal lines for a variety of purposes. This paper relates to the case history of a land reclamation project for a steel mill complex construction in Korea. Site improvement techniques used in this project include construction of sand drains and preloading. Construction procedures of sand drains are described as well as staged loading process along with field observations. Field measurement of settlement and theoretically estimated values are compared. The results of standard penetration tests and unconfined compression tests at various depths of soil, and time intervals are presented. Finally, the methods of construction quality assurance are discussed
Tomographic RF Spectroscopy of a Trapped Fermi Gas at Unitarity
We present spatially resolved radio-frequency spectroscopy of a trapped Fermi
gas with resonant interactions and observe a spectral gap at low temperatures.
The spatial distribution of the spectral response of the trapped gas is
obtained using in situ phase-contrast imaging and 3D image reconstruction. At
the lowest temperature, the homogeneous rf spectrum shows an asymmetric
excitation line shape with a peak at 0.48(4) with respect to the
free atomic line, where is the local Fermi energy
Thermalization of quark-gluon matter by 2-to-2 and 3-to-3 elastic scatterings
Thermalization of quark-gluon matter is studied with a transport equation
that includes contributions of 2-to-2 and 3-to-3 elastic scatterings.
Thermalization time is related to the squared amplitudes for the elastic
scatterings that are calculated in perturbative QCD.Comment: LaTex, 6 pages, 3 figures, talk presented at the 19th international
conference on ultra-relativistic nucleus-nucleus collisions, Shanghai, China,
Nov. 200
Theoretical analysis for critical fluctuations of relaxation trajectory near a saddle-node bifurcation
A Langevin equation whose deterministic part undergoes a saddle-node
bifurcation is investigated theoretically. It is found that statistical
properties of relaxation trajectories in this system exhibit divergent
behaviors near a saddle-node bifurcation point in the weak-noise limit, while
the final value of the deterministic solution changes discontinuously at the
point. A systematic formulation for analyzing a path probability measure is
constructed on the basis of a singular perturbation method. In this
formulation, the critical nature turns out to originate from the neutrality of
exiting time from a saddle-point. The theoretical calculation explains results
of numerical simulations.Comment: 18pages, 17figures.The version 2, in which minor errors have been
fixed, will be published in Phys. Rev.
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