481 research outputs found
Topology of multiple log transforms of 4-manifolds
Given a 4-manifold X and an imbedding of T^{2} x B^2 into X, we describe an
algorithm X --> X_{p,q} for drawing the handlebody of the 4-manifold obtained
from X by (p,q)-logarithmic transforms along the parallel tori. By using this
algorithm, we obtain a simple handle picture of the Dolgachev surface
E(1)_{p,q}, from that we deduce that the exotic copy E(1)_{p,q} # 5(-CP^2) of
E(1) # 5(-CP^2) differs from the original one by a codimension zero simply
connected Stein submanifold M_{p,q}, which are therefore examples of infinitely
many Stein manifolds that are exotic copies of each other (rel boundaries).
Furthermore, by a similar method we produce infinitely many simply connected
Stein submanifolds Z_{p} of E(1)_{p,2} # 2(-CP^2)$ with the same boundary and
the second Betti number 2, which are (absolutely) exotic copies of each other;
this provides an alternative proof of a recent theorem of the author and Yasui
[AY4]. Also, by using the description of S^2 x S^2 as a union of two cusps
glued along their boundaries, and by using this algorithm, we show that
multiple log transforms along the tori in these cusps do not change smooth
structure of S^2 x S^2.Comment: Updated, with 17 pages 21 figure
Quantum Monte Carlo Simulation of the Trellis Lattice Heisenberg Model for SrCuO and CaVO
We study the spin-1/2 trellis lattice Heisenberg model, a coupled spin ladder
system, both by perturbation around the dimer limit and by quantum Monte Carlo
simulations. We discuss the influence of the inter-ladder coupling on the spin
gap and the dispersion, and present results for the temperature dependence of
the uniform susceptibility. The latter was found to be parameterized well by a
mean-field type scaling ansatz. Finally we discuss fits of experimental
measurements on SrCuO and CaVO to our results.Comment: 7 pages, 8 figure
Production of Sodium Borohydride by Using Dynamic Behaviors of Protide at the Extreme Surface of Magnesium Particles
Abstract An advanced process for the production of sodium borohydride (NaBH 4 ) as a hydrogen storage material was developed, which applied the dynamic hydriding and dehydriding behaviors of protide (H − ) in Mg-H system under transitional temperature conditions. An abundant natural resource named borax (Na 2 B 4 O 7 ·10H 2 O) and the anhydrous sodium metaborate (NaBO 2 ) recovered from the "spent fuel" as NaBO 2 ·4H 2 O were used as the starting material in the present process. Powder-state Mg played an important role in the transitional hydriding and dehydriding process where the gaseous hydrogen was converted to protide at the extreme surface of Mg to form NaBH 4 in exchange with the simultaneous transition of oxygen in NaBO 2 to form MgO. In the present process, the protide as the most reactive state among the four states of hydrogen is applied for the synthesis of NaBH 4 , which can exist in metal-hydrogen complexes, such as NaAlH 4 and NaBH 4 . The NaBH 4 yield was reached higher than 90% by a single batch process but was found to be largely dependent on the rate of temperature change and the particle size, i.e., the specific surface area of Mg particles
Infrared and Raman spectra of LiV2O5 single crystals
The phonon dynamics of LiV2O5 single crystals is studied using infrared and
Raman spectroscopy techniques. The infrared-active phonon frequencies and
dielectric constants are obtained by oscillator fitting procedure of the
reflectivity data measured at room temperature. The Raman scattering spectra
are measured at room temperature and at T=10 K in all nonequivalent polarized
configurations. The assignment of the phonons is done by comparing the infrared
and Raman spectra of LiV2O5 and NaV2O5. The factor-group-analysis of the LiV2O5
crystal symmetry and of its constituent layers is performed to explain the
symmetry properties of the observed modes. We concluded that layer symmetry
dominates in the vibrational properties of this compound.Comment: 10 pages, 5 figure
Diffuse Neutron Scattering Study of a Disordered Complex Perovskite Pb(Zn1/3Nb2/3)O3 Crystal
Diffuse scattering around the (110) reciprocal lattice point has been
investigated by elastic neutron scattering in the paraelectric and the relaxor
phases of the disordered complex perovskite crystal-Pb(Zn1/3Nb2/3)O3(PZN). The
appearance of a diffuse intensity peak indicates the formation of polar
nanoregions at temperature T*, approximately 40K above Tc=413K. The analysis of
this diffuse scattering indicates that these regions are in the shape of
ellipsoids, more extended in the direction than in the direction.
The quantitative analysis provides an estimate of the correlation length, \xi,
or size of the regions and shows that \xi ~1.2\xi , consistent with
the primary or dominant displacement of Pb leading to the low temperature
rhombohedral phase. Both the appearance of the polar regions at T*and the
structural transition at Tc are marked by kinks in the \xi curve but not
in the \xi one, also indicating that the primary changes take place in a
direction at both temperatures.Comment: REVTeX file. 4 pages, 3 figures embedded, New version after referee
cond-mat/010605
Electronic structure and exchange interactions of the ladder vanadates CaV2O5 and MgV2O5
We have performed ab-initio calculations of the electronic structure and
exchange couplings in the layered vanadates CaV2O5 and MgV2O5. Based on our
results we provide a possible explanation of the unusual magnetic properties of
these materials, in particular the large difference in the spin gap between
CaV2O5 and MgV2O5
DNA methylation analysis at distal and proximal promoter regions of the oestrogen receptor gene in breast cancers
Universal Static and Dynamic Properties of the Structural Transition in Pb(Zn1/3Nb2/3)O3
The relaxors Pb(ZnNb)O (PZN) and
Pb(MgNb)O (PMN) have very similar properties based on the
dielectric response around the critical temperature (defined by the
structural transition under the application of an electric field). It has been
widely believed that these materials are quite different below with the
unit cell of PMN remaining cubic while in PZN the low temperature unit cell is
rhombohedral in shape. However, this has been clarified by recent high-energy
x-ray studies which have shown that PZN is rhombohedral only in the skin while
the shape of the unit cell in the bulk is nearly cubic. In this study we have
performed both neutron elastic and inelastic scattering to show that the
temperature dependence of both the diffuse and phonon scattering in PZN and PMN
is very similar. Both compounds show a nearly identical recovery of the soft
optic mode and a broadening of the acoustic mode below . The diffuse
scattering in PZN is suggestive of an onset at the high temperature Burns
temperature similar to that in PMN. In contrast to PMN, we observe a broadening
of the Bragg peaks in both the longitudinal and transverse directions below
. We reconcile this additional broadening, not observed in PMN, in terms
of structural inhomogeneity in PZN. Based on the strong similarities between
PMN and PZN, we suggest that both materials belong to the same universality
class and discuss the relaxor transition in terms of the three-dimensional
Heisenberg model with cubic anisotropy in a random field.Comment: 11 pages, 10 figures. Updated version after helpful referee comment
Identification of Nuclear Relaxation Processes in a Gapped Quantum Magnet: Proton NMR in the S=1/2 Heisenberg Ladder Cu2(C5H12N2)2Cl4
The proton hyperfine shift K and NMR relaxation rate have been
measured as a function of temperature in the S=1/2 Heisenberg antiferromagnetic
ladder Cu2(C5H12N2)2Cl4. The presence of a spin gap in this strongly coupled ladder ()
is supported by the K and results. By comparing at two
different proton sites, we infer the evolution of the spectral functions
and . When the gap is significantly
reduced by the magnetic field, two different channels of nuclear relaxation,
specific to gapped antiferromagnets, are identified and are in agreement with
theoretical predictions.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Letter
Single-hole dynamics in dimerized and frustrated spin-chains
We present a unified account for the coupled single-hole- and spin-dynamics
in the spin-gap phase of dimerized and frustrated spin-chains and two-leg spin
ladders. Based on the strong dimer-limit of a one-dimensional
--model a diagrammatic approach is presented which employs a
mapping of the spin-Hamiltonian onto a pseudo-fermion bond-boson model. Results
for the single-hole spectrum are detailed. A finite quasi-particle weight is
observed and studied for a variety of system parameters. A comparison with
existing exact diagonalization data is performed and good agreement is found.Comment: 10 pages, 12 figure
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