8,087 research outputs found
A quantum-group-like structure on noncommutative 2-tori
In this paper we show that in the case of noncommutative two-tori one gets in
a natural way simple structures which have analogous formal properties as Hopf
algebra structures but with a deformed multiplication on the tensor product
Impact of nuclear vibrations on van der Waals and Casimir interactions at zero and finite temperature
Van der Waals (vdW) and Casimir interactions depend crucially on material
properties and geometry, especially at molecular scales, and temperature can
produce noticeable relative shifts in interaction characteristics. Despite
this, common treatments of these interactions ignore electromagnetic
retardation, atomism, or contributions of collective mechanical vibrations
(phonons) to the infrared response, which can interplay with temperature in
nontrivial ways. We present a theoretical framework for computing
electromagnetic interactions among molecular structures, accounting for their
geometry, electronic delocalization, short-range interatomic correlations,
dissipation, and phonons at atomic scales, along with long-range
electromagnetic interactions among themselves or in the vicinity of continuous
macroscopic bodies. We find that in carbon allotropes, particularly fullerenes,
carbyne wires, and graphene sheets, phonons can couple strongly with long-range
electromagnetic fields, especially at mesoscopic scales (nanometers), to create
delocalized phonon polaritons that significantly modify the infrared molecular
response. These polaritons especially depend on the molecular dimensionality
and dissipation, and in turn affect the vdW interaction free energies of these
bodies above a macroscopic gold surface, producing nonmonotonic power laws and
nontrivial temperature variations at nanometer separations that are within the
reach of current Casimir force experiments.Comment: 11 pages, 4 figures (3 single-column, 1 double-column), 2 appendice
Evaporant feed device facilitates flash vapor deposition process in vacuum
Mechanism using a helix sequentially feeds prescribed amounts of metal charges into an evaporation boat used for flash vapor deposition of the evaporants onto a substrate in a vacuum chamber. The helix is advanced by external manual controls extending through sealed feed- through devices into the chamber wall
Charge Order Superstructure with Integer Iron Valence in Fe2OBO3
Solution-grown single crystals of Fe2OBO3 were characterized by specific
heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific
heat at 340 K indicates the onset of charge order. Evidence for a doubling of
the unit cell at low temperature is presented. Combining structural refinement
of diffraction data and Mossbauer spectra, domains with diagonal charge order
are established. Bond-valence-sum analysis indicates integer valence states of
the Fe ions in the charge ordered phase, suggesting Fe2OBO3 is the clearest
example of ionic charge order so far.Comment: 4 pages, 5 figures. Fig. 3 is available in higher resolution from the
authors. PRL in prin
CELL-MEDIATED IMMUNE RESPONSE IN VITRO : III. THE REQUIREMENT FOR MACROPHAGES IN CYTOTOXIC REACTIONS AGAINST CELL-BOUND AND SUBCELLULAR ALLOANTIGENS
All efficient cell separation procedure and specific anti-macrophage serum were used to investigate the requirement of macrophages in the in vitro allograft response of mouse lymphoid cells. The efficiency of the macrophage-depletion procedure used and the undiminished capacity of the purified lymphocytes to respond were verified by also testing the antibody responses to sheep red cells (SRC) and dinitrophenylated polymeric flagellin (DNP POL) as well as the proliferative response to allogeneic cells. It was found that the generation of cytotoxic lymphocytes were diminished after macrophage depletion by surface adherence. The combination of anti-macrophage serum and column purification resulted in the total abolition of cytotoxic activity. The cell-mediated immune response was restored completely by addition of peritoneal macrophages, with as few as 1 macrophage to 600 lymphocytes permitting a significant restoration. Macrophages were not involved in the cytotoxic effector phase, but were essential in immune induction. A subcellular H-2 alloantigen preparation was only immunogenic in the presence of macrophages, indicating that a mere reduction in the size of the antigen from cell-bound alloantigens to membrane fragments was not the sole function of macrophages. The results suggest that macrophages collaborate with T cells in the initiation of an allograft response in vitro
Matter-Wave Decoherence due to a Gas Environment in an Atom Interferometer
Decoherence due to scattering from background gas particles is observed for
the first time in a Mach-Zehnder atom interferometer, and compared with
decoherence due to scattering photons. A single theory is shown to describe
decoherence due to scattering either atoms or photons. Predictions from this
theory are tested by experiments with different species of background gas, and
also by experiments with different collimation restrictions on an atom beam
interferometer.Comment: 4 pages, 3 figures, accepted to PR
Computer simulation of crystallization kinetics with non-Poisson distributed nuclei
The influence of non-uniform distribution of nuclei on crystallization
kinetics of amorphous materials is investigated. This case cannot be described
by the well-known Johnson-Mehl-Avrami (JMA) equation, which is only valid under
the assumption of a spatially homogeneous nucleation probability. The results
of computer simulations of crystallization kinetics with nuclei distributed
according to a cluster and a hardcore distribution are compared with JMA
kinetics. The effects of the different distributions on the so-called Avrami
exponent are shown. Furthermore, we calculate the small-angle scattering
curves of the simulated structures which can be used to distinguish
experimentally between the three nucleation models under consideration.Comment: 14 pages including 7 postscript figures, uses epsf.sty and
ioplppt.st
Incommensurate Charge Order Phase in Fe2OBO3 due to Geometrical Frustration
The temperature dependence of charge order in Fe2OBO3 was investigated by
resistivity and differential scanning calorimetry measurements, Mossbauer
spectroscopy, and synchrotron x-ray scattering, revealing an intermediate phase
between room temperature and 340 K, characterized by coexisting mobile and
immobile carriers, and by incommensurate superstructure modulations with
temperature-dependent propagation vector (1/2,0,tau). The incommensurate
modulations arise from specific anti-phase boundaries with low energy cost due
to geometrical charge frustration.Comment: 4 p., 5 fig.; v2: slightly expanded introduction + minor changes. PRL
in prin
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