1,071 research outputs found
Universal Quantum Viscosity in a Unitary Fermi Gas
A Fermi gas of atoms with resonant interactions is predicted to obey
universal hydrodynamics, where the shear viscosity and other transport
coefficients are universal functions of the density and temperature. At low
temperatures, the viscosity has a universal quantum scale where
is the density, while at high temperatures the natural scale is
where is the thermal momentum. We employ breathing mode damping to
measure the shear viscosity at low temperature. At high temperature , we
employ anisotropic expansion of the cloud to find the viscosity, which exhibits
precise scaling. In both experiments, universal hydrodynamic
equations including friction and heating are used to extract the viscosity. We
estimate the ratio of the shear viscosity to the entropy density and compare to
that of a perfect fluid.Comment: 13 pages, 3 figure
Investigations of Metastable Ca\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e Epitaxial Thin-Films: Systematic Comparison with Sr\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e and Ba\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e
We have synthesized thermodynamically metastable Ca2IrO4 thin-films on YAlO3 (110) substrates by pulsed laser deposition. The epitaxial Ca2IrO4 thin-films are of K2NiF4-type tetragonal structure. Transport and optical spectroscopy measurements indicate that the electronic structure of the Ca2IrO4 thin-films is similar to that of Jeff = 1/2 spin-orbit-coupled Mott insulator Sr2IrO4 and Ba2IrO4, with the exception of an increased gap energy. The gap increase is to be expected in Ca2IrO4 due to its increased octahedral rotation and tilting, which results in enhanced electron-correlation, U/W. Our results suggest that the epitaxial stabilization growth of metastable-phase thin-films can be used effectively for investigating layered iridates and various complex-oxide systems
Translocation of single-stranded DNA through single-walled carbon nanotubes
We report the fabrication of devices in which one single-walled carbon nanotube spans a barrier between two fluid reservoirs, enabling direct electrical measurement of ion transport through the tube. A fraction of the tubes pass anomalously high ionic currents. Electrophoretic transport of small single-stranded DNA oligomers through these tubes is marked by large transient increases in ion current and was confirmed by polymerase chain reaction analysis. Each current pulse contains about 10 7 charges, an enormous amplification of the translocated charge. Carbon nanotubes simplify the construction of nanopores, permit new types of electrical measurements, and may open avenues for control of DNA translocation.published_or_final_versio
Major Merger Galaxy Pairs at z = 0: Dust Properties and Companion Morphology
We present an analysis of dust properties of a sample of close major-merger galaxy pairs selected by K_s magnitude and redshift. The pairs represent the two populations of spiral–spiral (S+S) and mixed morphology spiral–elliptical (S+E). The Code Investigating GALaxy Emission software is used to fit dust models to the Two Micron All Sky Survey, Wide-Field Infrared Survey Explorer, and Herschel flux density measurements, and to derive the parameters describing the polycyclic aromatic hydrocarbons contribution, interstellar radiation field, and photodissociation regions. Model fits verify our previous Spitzer Space Telescope analysis that S+S and S+E pairs do not have the same level of enhancement of star formation and differ in dust composition. The spirals of mixed-morphology galaxy pairs do not exhibit the enhancements in interstellar radiation field and therefore dust temperature for spirals in S+S pairs in contrast to what would be expected according to standard models of gas redistribution due to encounter torques. This suggests the importance of the companion environment/morphology in determining the dust properties of a spiral galaxy in a close major-merger pair
Doping and temperature dependence of electron spectrum and quasiparticle dispersion in doped bilayer cuprates
Within the t-t'-J model, the electron spectrum and quasiparticle dispersion
in doped bilayer cuprates in the normal state are discussed by considering the
bilayer interaction. It is shown that the bilayer interaction splits the
electron spectrum of doped bilayer cuprates into the bonding and antibonding
components around the point. The differentiation between the bonding
and antibonding components is essential, which leads to two main flat bands
around the point below the Fermi energy. In analogy to the doped
single layer cuprates, the lowest energy states in doped bilayer cuprates are
located at the point. Our results also show that the striking
behavior of the electronic structure in doped bilayer cuprates is intriguingly
related to the bilayer interaction together with strong coupling between the
electron quasiparticles and collective magnetic excitations.Comment: 9 pages, 4 figures, updated references, added figures and
discussions, accepted for publication in Phys. Rev.
Fibrin regulates neutrophil migration in response to interleukin 8, leukotriene B4, tumor necrosis factor, and formyl-methionyl-leucyl-phenylalanine
We have examined the capacity of four different chemoattractants/cytokines to promote directed migration of polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of extracellular matrix proteins. About 20% of PMN migrated through fibrin gels and plasma clots in response to a gradient of interleukin 8 (IL-8) or leukotriene B4 (LTB4). In contrast, < 0.3% of PMN migrated through fibrin gels in response to a gradient of tumor necrosis factor alpha (TNF) or formyl-methionyl-leucyl-phenylalanine (FMLP). All four chemoattractants stimulated PMN to migrate through gels composed of collagen IV or of basement membrane proteins (Matrigel), or through filters to which fibronectin or fibrinogen had been adsorbed. PMN stimulated with TNF or FMLP adhered and formed zones of close apposition to fibrin, as measured by the exclusion of a 10-kD rhodamine-polyethylene glycol probe from the contact zones between PMN and the underlying fibrin gel. By this measure, IL-8- or LTB4-treated PMN adhered loosely to fibrin, since 10 kD rhodamine-polyethylene glycol permeated into the contact zones between these cells and the underlying fibrin gel. PMN stimulated with FMLP and IL-8, or FMLP and LTB4, exhibited very little migration through fibrin gels, and three times as many of these cells excluded 10 kD rhodamine-polyethylene glycol from their zones of contact with fibrin as PMN stimulated with IL-8 or LTB4 alone. These results show that PMN chemotaxis is regulated by both the nature of the chemoattractant and the composition of the extracellular matrix; they suggest that certain combinations of chemoattractants and matrix proteins may limit leukocyte movements and promote their localization in specific tissues in vivo
How to make your research jump off the page: Co-creation to broaden public engagement in medical research.
Nina Finley and co-authors discuss public involvement in planning and reporting medical research
Revealing the electroweak properties of a new scalar resonance
One or more new heavy resonances may be discovered in experiments at the CERN
Large Hadron Collider. In order to determine if such a resonance is the
long-awaited Higgs boson, it is essential to pin down its spin, CP, and
electroweak quantum numbers. Here we describe how to determine what role a
newly-discovered neutral CP-even scalar plays in electroweak symmetry breaking,
by measuring its relative decay rates into pairs of electroweak vector bosons:
WW, ZZ, \gamma\gamma, and Z\gamma. With the data-driven assumption that
electroweak symmetry breaking respects a remnant custodial symmetry, we perform
a general analysis with operators up to dimension five. Remarkably, only three
pure cases and one nontrivial mixed case need to be disambiguated, which can
always be done if all four decay modes to electroweak vector bosons can be
observed or constrained. We exhibit interesting special cases of Higgs
look-alikes with nonstandard decay patterns, including a very suppressed
branching to WW or very enhanced branchings to \gamma\gamma and Z\gamma. Even
if two vector boson branching fractions conform to Standard Model expectations
for a Higgs doublet, measurements of the other two decay modes could unmask a
Higgs imposter.Comment: 23 pages, two figures; v2: minor revision and version to appear in
JHE
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