306 research outputs found
Imbibition in mesoporous silica: rheological concepts and experiments on water and a liquid crystal
We present, along with some fundamental concepts regarding imbibition of
liquids in porous hosts, an experimental, gravimetric study on the
capillarity-driven invasion dynamics of water and of the rod-like liquid
crystal octyloxycyanobiphenyl (8OCB) in networks of pores a few nanometers
across in monolithic silica glass (Vycor). We observe, in agreement with
theoretical predictions, square root of time invasion dynamics and a sticky
velocity boundary condition for both liquids investigated.
Temperature-dependent spontaneous imbibition experiments on 8OCB reveal the
existence of a paranematic phase due to the molecular alignment induced by the
pore walls even at temperatures well beyond the clearing point. The ever
present velocity gradient in the pores is likely to further enhance this
ordering phenomenon and prevent any layering in molecular stacks, eventually
resulting in a suppression of the smectic phase in favor of the nematic phase.Comment: 18 pages, 8 figure
Observation of charge-density-wave excitations in manganites
In the optical conductivity of four different manganites with commensurate
charge order (CO), strong peaks appear in the meV range below the ordering
temperature T_{CO}. They are similar to those reported for one-dimensional
charge density waves (CDW) and are assigned to pinned phasons. The peaks and
their overtones allow one to obtain, for La{1-n/8}Ca{n/8}$MnO{3} with n = 5, 6,
the electron-phonon coupling, the effective mass of the CO system, and its
contribution to the dielectric constant. These results support a description of
the CO in La-Ca manganites in terms of moderately weak-coupling and of the CDW
theory.Comment: To be published on Phys. Rev. Let
NASA Desert RATS 2011 Education Pilot Project and Classroom Activities
The National Aeronautics and Space Administration's (NASA's) Desert Research and Technology Studies (Desert RATS) is a multi-year series of tests of hardware and operations carried out annually in the high desert of Arizona, as an analog to future exploration activities beyond low Earth orbit [1]. For the past several years, these tests have occurred in the San Francisco Volcanic Field, north of Flagstaff. For the 2011 Desert RATS season, the Exploration Systems Mission Directorate (ESMD) at NASA headquarters provided support to develop an education pilot project that would include student activities to parallel the Desert RATS mission planning and exploration activities in the classroom, and educator training sessions. The development of the pilot project was a joint effort between the NASA Johnson Space Center (JSC) Astromaterials Research and Exploration Science (ARES) Directorate and the Aerospace Education Services Project (AESP), managed at Penn State University
Recurrence of hepatitis C virus during leucocytopenia and spontaneous clearance after recovery from cytopenia: a case report
<p>Abstract</p> <p>Introduction</p> <p>There is little information about the risk of HCV recurrence in immunosuppressed patients. Although the presence of antibodies to HCV and the absence of HCV-RNA is usually considered to indicate viral elimination, the virus may not be completely eliminated but may be under control of an effective immune response.</p> <p>Case presentation</p> <p>A 69 year old man presented with jaundice, elevated ALT, AST, lipase and concomitant abdominal pain. He was found to be positive for HCV-RNA (genotype 3a) and was diagnosed with acute hepatitis C. Six weeks later no HCV-RNA was detected, and the patient was diagnosed with hyperthyreosis and started on propylthiouracil. After 4 weeks of propylthiouracil treatment, the patient developed leucocytopenia, followed by liver function deterioration and reappearance of HCV-RNA. Propylthiouracil was discontinued and his leukocyte counts increased. Twenty-eight weeks after onset of acute hepatitis C, no HCV-RNA was detected.</p> <p>Conclusion</p> <p>This case history shows the risk of recurrence of HCV during leucocytopenia. These findings indicate that patients who are anti-HCV positive but HCV-RNA negative may be at risk of cytopenia-induced HCV reactivation.</p
A Compact Approximate Solution to the Friedel-Anderson Impuriy Problem
An approximate groundstate of the Anderson-Friedel impurity problem is
presented in a very compact form. It requires solely the optimization of two
localized electron states and consists of four Slater states (Slater
determinants). The resulting singlet ground state energy lies far below the
Anderson mean field solution and agrees well with the numerical results by
Gunnarsson and Schoenhammer, who used an extensive 1/N_{f}-expansion for a spin
1/2 impurity with double occupancy of the impurity level.
PACS: 85.20.Hr, 72.15.R
Gas damping force noise on a macroscopic test body in an infinite gas reservoir
We present a simple analysis of the force noise associated with the
mechanical damping of the motion of a test body surrounded by a large volume of
rarefied gas. The calculation is performed considering the momentum imparted by
inelastic collisions against the sides of a cubic test mass, and for other
geometries for which the force noise could be an experimental limitation. In
addition to arriving at an accurated estimate, by two alternative methods, we
discuss the limits of the applicability of this analysis to realistic
experimental configurations in which a test body is surrounded by residual gas
inside an enclosure that is only slightly larger than the test body itself.Comment: 8 pages. updated with correct translational damping coefficient for
cylinder on axis. added cylinder orthogonal to symmetry axis, force and
torque. slightly edited throughou
Fermi surface nesting in several transition metal dichalcogenides
By means of high-resolution angle resolved photoelectron spectroscopy (ARPES)
we have studied the fermiology of 2H transition metal dichalcogenide polytypes
TaSe2, NbSe2, and Cu0.2NbS2. The tight-binding model of the electronic
structure, extracted from ARPES spectra for all three compounds, was used to
calculate the Lindhard function (bare spin susceptibility), which reflects the
propensity to charge density wave (CDW) instabilities observed in TaSe2 and
NbSe2. We show that though the Fermi surfaces of all three compounds possess an
incommensurate nesting vector in the close vicinity of the CDW wave vector, the
nesting and ordering wave vectors do not exactly coincide, and there is no
direct relationship between the magnitude of the susceptibility at the nesting
vector and the CDW transition temperature. The nesting vector persists across
the incommensurate CDW transition in TaSe2 as a function of temperature despite
the observable variations of the Fermi surface geometry in this temperature
range. In Cu0.2NbS2 the nesting vector is present despite different doping
level, which lets us expect a possible enhancement of the CDW instability with
Cu-intercalation in the CuxNbS2 family of materials.Comment: Accepted to New J. Phy
Synthesis and extraction properties of preorganized host molecules based on tetraamides of thiacalix[4]arene
Template effect of alkali metal ions was employed to prepare three isomers of tetraamide of p-tert-butylthiacalix[4]arene: cone, partial cone and 1,3-alternate. It was demonstrated that pre-organization of four amide fragments attached to the calix[4]arene platform has a strong macrocyclic cooperative effect on the extraction ability of the title hosts. © 2005 Springer Science+Business Media, Inc
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