11,961 research outputs found
Modifications of the hydrogen bond network of liquid water in a cylindrical SiO_2 pore
We present results of molecular dynamics simulations of water confined in a
silica pore. A cylindrical cavity is created inside a vitreous silica cell with
geometry and size similar to the pores of real Vycor glass. The simulations are
performed at different hydration levels. At all hydration levels water adsorbs
strongly on the Vycor surface; a double layer structure is evident at higher
hydrations. At almost full hydration the modifications of the
confinement-induced site-site pair distribution functions are in qualitative
agreement with neutron diffraction experiment. A decrease in the number of
hydrogen bonds between water molecules is observed along the pore radius, due
to the tendency of the molecules close to the substrate to form hydrogen-bonds
with the hydrophilic pore surface. As a consequence we observe a substrate
induced distortion of the H-bond tetrahedral network of water molecules in the
regions close to the surface.Comment: Talk presented at "Physics of Liquids: Foundations, Highlights,
Challenge", Murau Sept. 1998. To appear in J. Mol. Li
Teleportation scheme implementing contextually the Universal Optimal Quantum Cloning Machine and the Universal Not Gate. Complete experimental realization
By a significant modification of the standard protocol of quantum state
Teleportation two processes ''forbidden'' by quantum mechanics in their exact
form, the Universal NOT gate and the Universal Optimal Quantum Cloning Machine,
have been implemented contextually and optimally by a fully linear method. In
particular, the first experimental demonstration of the Tele-UNOT Gate, a novel
quantum information protocol has been reported (cfr. quant-ph/0304070). A
complete experimental realization of the protocol is presented here.Comment: 11 pages, 3 figure
Geoneutrinos and reactor antineutrinos at SNO+
In the heart of the Creighton Mine near Sudbury (Canada), the SNO+ detector
is foreseen to observe almost in equal proportion electron antineutrinos
produced by U and Th in the Earth and by nuclear reactors. SNO+ will be the
first long baseline experiment to measure a reactor signal dominated by CANDU
cores (55\% of the total reactor signal), which generally burn natural
uranium. Approximately 18\% of the total geoneutrino signal is generated by the
U and Th present in the rocks of the Huronian Supergroup-Sudbury Basin: the
60\% uncertainty on the signal produced by this lithologic unit plays a crucial
role on the discrimination power on the mantle signal as well as on the
geoneutrino spectral shape reconstruction, which can in principle provide a
direct measurement of the Th/U ratio in the Earth.Comment: 7 pages including 2 figures and 1 table, in XIV International
Conference on Topics in Astroparticle and Underground Physics (TAUP 2015) IOP
Publishing , published on Journal of Physics: Conference Series 718 (2016)
06200
Alternative splicing of tropomyosin pre-mRNAs in vitro and in vivo
A single rat gene encodes both fibroblast TM-1 and skeletal muscle beta-tropomyosin by an alternative RNA-processing mechanism. The gene contains 11 exons: Exons 1-5 and exons 8 and 9 are constitutive exons common to all mRNAs expressed from this gene; exons 6 and 11 are used in fibroblasts as well as smooth muscle; exons 7 and 10 are used exclusively in skeletal muscle. We have studied the internal alternative RNA splice choice (exons 6 and 7) of the rat tropomyosin 1 gene in vitro, using nuclear extracts obtained from HeLa cells. Use of alternative splice sites in vitro is dependent on the ionic conditions of the assay, and correct splicing occurs only under well-defined salt conditions. Splicing of exon 5 to exon 6 (fibroblast-type splice) and exon 5 to exon 7 (skeletal muscle-type splice) was dependent on precursors in which exon 6 or 7 was first joined to exon 8. The same patterns of alternatively spliced RNAs were formed when similar templates were introduced in HeLa cells by transfection. Thus, there appears to be an ordered pathway of splicing in which the internal alternatively spliced exons must first be joined to the downstream constitutive exon before they can be spliced to the upstream constitutive exon. The data are consistent with a model in which the critical event in alternative splicing occurs during the joining of exon 6 to exon 8 (fibroblast-type splice) or exon 7 to exon 8 (skeletal muscle-type splice)
Influence of the Lower Hybrid Drift Instability on the onset of Magnetic Reconnection
Two-dimensional and three-dimensional kinetic simulation results reveal the
importance of the Lower-Hybrid Drift Instability LHDI to the onset of magnetic
reconnection. Both explicit and implicit kinetic simulations show that the LHDI
heats electrons anisotropically and increases the peak current density. Linear
theory predicts these modifications can increase the growth rate of the tearing
instability by almost two orders of magnitude and shift the fastest growing
modes to significantly shorter wavelengths. These predictions are confirmed by
nonlinear kinetic simulations in which the growth and coalescence of small
scale magnetic islands leads to a rapid onset of large scale reconnection
Hour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides LaSrCoO
The magnetic excitations in the cuprate superconductors might be essential
for an understanding of high-temperature superconductivity. In these cuprate
superconductors the magnetic excitation spectrum resembles an hour-glass and
certain resonant magnetic excitations within are believed to be connected to
the pairing mechanism which is corroborated by the observation of a universal
linear scaling of superconducting gap and magnetic resonance energy. So far,
charge stripes are widely believed to be involved in the physics of hour-glass
spectra. Here we study an isostructural cobaltate that also exhibits an
hour-glass magnetic spectrum. Instead of the expected charge stripe order we
observe nano phase separation and unravel a microscopically split origin of
hour-glass spectra on the nano scale pointing to a connection between the
magnetic resonance peak and the spin gap originating in islands of the
antiferromagnetic parent insulator. Our findings open new ways to theories of
magnetic excitations and superconductivity in cuprate superconductors.Comment: Nature Communications 5, 5731 (2014
Light and neutron scattering studies of the OH stretching band in liquid and supercritical water
The hydrogen projected OH stretching density of states has been determined by an inelastic neutron scattering experiment in liquid and supercritical water, The results, compared with new measurements of the isotropic Raman spectra at the same state conditions, support the interpretation of the Raman spectra in terms of superposition of the allowed nu(1) band with the overtone of the nu(2) band. (C) 1998 American Institute of Physics
Cluster derivation of Parisi's RSB solution for disordered systems
We propose a general scheme in which disordered systems are allowed to
sacrifice energy equi-partitioning and separate into a hierarchy of ergodic
sub-systems (clusters) with different characteristic time-scales and
temperatures. The details of the break-up follow from the requirement of
stationarity of the entropy of the slower cluster, at every level in the
hierarchy. We apply our ideas to the Sherrington-Kirkpatrick model, and show
how the Parisi solution can be {\it derived} quantitatively from plausible
physical principles. Our approach gives new insight into the physics behind
Parisi's solution and its relations with other theories, numerical experiments,
and short range models.Comment: 7 pages 5 figure
Electronic and magnetic nano phase separation in cobaltates LaSrCoO
The single-layer perovskite cobaltates have attracted enormous attention due
to the recent observation of hour-glass shaped magnetic excitation spectra
which resemble the ones of the famous high-temperature superconducting
cuprates. Here, we present an overview of our most recent studies of the spin
and charge correlations in floating-zone grown cobaltate single crystals. We
find that frustration and a novel kind of electronic and magnetic nano phase
separation are intimately connected to the appearance of the hour-glass shaped
spin excitation spectra. We also point out the difference between nano phase
separation and conventional phase separation.Comment: * plenary talk SUPERSTRIPES conference 201
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