2,724 research outputs found
Dynamical Structure Factor in Cu Benzoate and other spin-1/2 antiferromagnetic chains
Recent experiments of the quasi-one-dimensional spin-1/2 antiferromagnet
Copper Benzoate established the existence of a magnetic field induced gap. The
observed neutron scattering intensity exhibits resolution limited peaks at both
the antiferromagnetic wave number and at incommensurate wave numbers related to
the applied magnetic field. We determine the ratio of spectral weights of these
peaks within the framework of a low-energy effective field theory description
of the problem.Comment: 5 pages, 3figure
Synthesis and characterization of a pyrochlore solid solution in the Na2OâBi2O3âTiO2 system
The compositional limits of a previously reported (J. Am. Ceram. Soc., 61, 5â8. (1978)) but relatively unstudied sodiumâbismuth titanate pyrochlore solid solution are revised and their electrical properties presented. The pyrochlore solid solution we report forms via a different mechanism to that originally reported and occurs in a different location within the Na2OâBi2O3âTiO2 ternary system. In both cases, relatively large amounts of vacancies are required on the Aâsites and on the oxygen sites, similar to that reported for undoped âBi2Ti2O7â pyrochlore. In contrast to âBi2Ti2O7â, this ternary pyrochlore solid solution can be prepared and ceramics sintered using conventional solidâstate methods; however, the processing requires several challenges to be overcome to obtain dense ceramics. This cubic pyrochlore series has low electrical conductivity (and does not exhibit any evidence of oxideâion conduction) and exhibits relaxor ferroelectric behavior with a broad permittivity maximum of ~100 near room temperature. Variable temperature neutron diffraction data do not provide any conclusive evidence for a phase transition in the pyrochlore solid solution between ~4 and 873 K
Kosterlitz-Thouless Transition Line for the Two Dimensional Coulomb Gas
With a rigorous renormalization group approach, we study the pressure of the
two dimensional Coulomb Gas along a small piece of the Kosterlitz-Thouless
transition line, i.e. the boundary of the dipole region in the
activity-temperature phase-space.Comment: 61 pages, 2 figure
Numerical Study of the Spin-Flop Transition in Anisotropic Spin-1/2 Antiferromagnets
Magnetization processes of the spin-1/2 antiferromagnetic model in two
and three spatial dimensions are studied using quantum Monte Carlo method based
on stochastic series expansions. Recently developed operator-loop algorithm
enables us to show a clear evidence of the first-order phase transition in the
presence of an external magnetic field. Phase diagrams of closely related
systems, hard core bosons with nearest-neighbor repulsions, are also discussed
focusing on possibilities of phase-separated and supersolid phases.Comment: 4 pages, Revtex version 4, with 4 figures embedded, To appear in
Phys. Rev.
Molecular evidence of the haploid origin in wheat (Triticum aestivum L.) with Aegilops kotschyi cytoplasm and whole genome expression profiling after haploidization
Aegiolops kotschyi cytoplasmic male sterile system often results in part of haploid plants in wheat (Triticum aestivum L.). To elucidate the origin of haploid, 235 wheat microsatellite (SSR) primers were randomly selected and screened for polymorphism between haploid (2n = 3x = 21 ABD) and its parents, male-sterile line YM21 (2n = 6x = 42 AABBDD) and male fertile restorer YM2 (2n = 6x = 42 AABBDD). About 200 SSR markers yielded clear bands from denatured PAGE, of which 180 markers have identifiable amplification patterns, and 20 markers (around 8%) resulted in different amplification products between the haploid and the restorer, YM2. There were no SSR markers that were found to be distinguishable between the haploid and the male sterile line YM21. In addition, different distribution of HMW-GS between endosperm and seedlings from the same seeds further confirmed that the haploid genomes were inherited from the maternal parent. After haploidization, 1.7% and 0.91% of total sites were up- and down-regulated exceeding twofold in the shoot and the root of haploid, respectively, and most of the differentially expressed loci were up/down-regulated about twofold. Out of the sensitive loci in haploid, 94 loci in the shoot, 72 loci in the root can be classified into three functional subdivisions: biological process, cellular component and molecular function, respectively
Competing interactions in the XYZ model
We study the interplay between a XY anisotropy , exchange modulations
and an external magnetic field along the z direction in the XYZ chain using
bosonization and Lanczos diagonalization techniques. We find an Ising critical
line in the space of couplings which occur due to competing relevant
perturbations which are present. More general situations are also discussed.Comment: 6 pages, 6 figure
Two-spinon dynamic structure factor of the one-dimensional S=1/2 Heisenberg antiferromagnet
The exact expression derived by Bougourzi, Couture, and Kacir for the
2-spinon contribution to the dynamic spin structure factor
of he one-dimensional =1/2 Heisenberg antiferromagnet at is evaluated
for direct comparison with finite-chain transition rates () and an
approximate analytical result previously inferred from finite- data, sum
rules, and Bethe-ansatz calculations. The 2-spinon excitations account for
72.89% of the total intensity in . The singularity structure
of the exact result is determined analytically and its spectral-weight
distribution evaluated numerically over the entire range of the 2-spinon
continuum. The leading singularities of the frequency-dependent spin
autocorrelation function, static spin structure factor, and -dependent
susceptibility are determined via sum rules.Comment: 6 pages (RevTex) and 5 figures (Postscript
Dual paths node-disjoint routing for data salvation in mobile ad hoc
The operational patterns of multifarious backup strategies on AODV-based (Ad-hoc On-Demand Vector) routing protocols are elaborated in this article. To have a broader picture on relevant routing protocols together, variants of AODV-based backup routing protocols are formulated by corresponding algorithms, and also each of them are simulated to obtain the necessary performance metrics for comparisons in terms of packet delivery ratio, average latency delay, and the normalized routing load. Then to make the process of data salvation more efficiently in case of link failure, we explore the possibility of combining the AODV backup routing strategy and on-demand node-disjoint multipath routing protocols. This article proposes an improved approach named DPNR (Dual Paths Node-disjoint Routing) for data salvation, a routing protocol that maintains the only two shortest backup paths in the source and destination nodes. The DPNR scheme can alleviate the redundancy-frames overhead during the process of data salvation by the neighboring intermediate nodes. Our simulation results have demonstrated that DPNR scheme delivers good data delivery performance while restricting the impacts of transmission collision and channel contention. The mathematical rationale for our proposed approach is stated as well
Recommended from our members
Analysis of gaseous-phase stable and radioactive isotopes in the unsaturated zone, Yucca Mountain, Nevada
The Nevada Nuclear Waste Storage Investigations Project of the US Department of Energy provides that agency with data for evaluating volcanic tuff beneath Yucca Mountain, Nevada, to determine its suitability for a potential repository of high-level radioactive waste. Thickness of the unsaturated zone, which consists of fractured, welded and nonwelded tuff, is about 1640 to 2460 feet (500 to 750 meters). One question to be resolved is an estimate of minimum ground-water traveltime from the disturbed zone of the potentail repository to the accessible environment. Another issue is the potential for diffusive or convective gaseous transport of radionuclides from an underground facility in the unsaturated zone to the accessible environment. Gas samples were collected at intervals to a depth of 1200 feet from the unsaturated zone at Yucca Mountain, Nevada. Samples were analyzed for major atmospheric gases; carbon dioxide in the samples was analyzed for carbon-14 activity and for {delta}2!{sup 3}C; water vapor in the samples was analyzed for deuterium and oxygen-18. These data could provide insight into the nature of unsaturated zone transport processes. 15 refs., 4 figs., 4 tabs
- âŠ