28 research outputs found
Properties of Metallic Helimagnets
This dissertation investigates various aspects of helimagnets. Helimagnets are magnets with spins aligned in helical order at low temperatures. It exists in materials of crystal structure lacking the spatial inversion symmetry. The helical order is due to the Dzyaloshinskii-Moriya (DM) mechanism. Examples of helimagnets include MnSi, FeGe and Fe1-xCoxSi.
A field theory appropriate for such magnets is used to derive the phase diagram in a mean-field approximation. The helical phase, the conical phase, the columnar phase and the non-Fermi-liquid (NFL) region in the paramagnetic phase are discussed. It is shown that the orientation of the helical vector along an external magnetic field within the conical phase occurs via two distinct phase transitions. The columnar phase, believed to be a Skyrmion lattice, is found to exist as Abrikosov Skyrmions near the helimagnetic phase boundary, and the core-to-core distance is estimated.
The Goldstone modes that result from the long-range order in the various phases are determined, and their consequences for electronic properties, in particular, the specific heat, single-particle relaxation rate and the electrical conductivity, are derived.
In addition, Skyrmion gases and lattices in helimagnets are studied, and the size of a Skyrmion in various phases is estimated. For isolated Skyrmions, the long distance tail is related to the magnetization correlation functions and exhibits power-law decay if the phase spontaneously breaks a continuous symmetry, but decays exponentially otherwise. The size of a Skyrmion is found to depend on a number of length scales. These length scales are related to the strength of DM interaction, the temperature, and the external magnetic field
Generation of Innovative and Sparse Encoding Vectors for Broadcast Systems with Feedback
In the application of linear network coding to wireless broadcasting with
feedback, we prove that the problem of determining the existence of an
innovative encoding vector is NP-complete when the finite field size is two.
When the finite field size is larger than or equal to the number of users, it
is shown that we can always find an encoding vector which is both innovative
and sparse. The sparsity can be utilized in speeding up the decoding process.
An efficient algorithm to generate innovative and sparse encoding vectors is
developed. Simulations show that the delay performance of our scheme with
binary finite field outperforms a number of existing schemes in terms of
average and worst-case delay.Comment: 5 pages, 4 figures, accepted for publication in the Proc. of IEEE
ISIT 201
Linear Network Code for Erasure Broadcast Channel with Feedback: Complexity and Algorithms
Abstract-This paper investigates the construction of linear network codes for broadcasting a set of data packets to a number of users. The links from the source to the users are modeled as independent erasure channels. Users are allowed to inform the source node whether a packet is received correctly via feedback channels. In order to minimize the number of packet transmissions until all users have received all packets successfully, it is necessary that a data packet, if successfully received by a user, can increase the dimension of the vector space spanned by the encoding vectors he or she has received by one. Such an encoding vector is called innovative. To reduce decoding complexity, sparse encoding vectors are preferred, since the sparsity can be exploited when solving systems of linear equations. Generating a sparsest encoding vector with large finite field size, however, is shown to be NP-hard. An approximation algorithm is constructed. For binary field, heuristic algorithms are also proposed. Index Terms-Erasure broadcast channel, network coding, computational complexity
Expression and functional characterization of the putative protein 8b of the severe acute respiratory syndrome-associated coronavirus
AbstractSARS 8b is one of the putative accessory proteins of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) with unknown functions. In this study, the cellular localization and activity of this estimated 9.6kDa protein were examined. Confocal microscopy results indicated that SARS 8b is localized in both nucleus and cytoplasm of mammalian cells. Functional study revealed that overexpression of SARS 8b induced DNA synthesis. Coexpression of SARS 8b and SARS 6, a previously characterized SARS-CoV accessory protein, did not elicit synergistic effects on DNA synthesis
Ordered Phases of Itinerant Dzyaloshinsky-Moriya Magnets and Their Electronic Properties
A field theory appropriate for magnets that display helical order due to the
Dzyaloshinsky-Moriya mechanism, a class that includes MnSi and FeGe, is used to
derive the phase diagram in a mean-field approximation. The helical phase, the
conical phase in an external magnetic field, and recent proposals for the
structure of the A-phase and the non-Fermi-liquid region in the paramagnetic
phase are discussed. It is shown that the orientation of the helical pitch
vector along an external magnetic field within the conical phase occurs via two
distinct phase transitions. The Goldstone modes that result from the long-range
order in the various phases are determined, and their consequences for
electronic properties, in particular the specific heat, the single-particle
relaxation time, and the electrical and thermal conductivities, are derived.
Various aspects of the ferromagnetic limit, and qualitative differences between
the transport properties of helimagnets and ferromagnets, are also discussed.Comment: 22pp, 8 eps fig
Vortex Formation in Two-Dimensional Bose Gas
We discuss the stability of a homogeneous two-dimensional Bose gas at finite
temperature against formation of isolated vortices. We consider a patch of
several healing lengths in size and compute its free energy using the Euclidean
formalism. Since we deal with an open system, which is able to exchange
particles and angular momentum with the rest of the condensate, we use the
symmetry-breaking (as opposed to the particle number conserving) formalism, and
include configurations with all values of angular momenta in the partition
function. At finite temperature, there appear sphaleron configurations
associated to isolated vortices. The contribution from these configurations to
the free energy is computed in the dilute gas approximation. We show that the
Euclidean action of linearized perturbations of a vortex is not positive
definite. As a consequence the free energy of the 2D Bose gas acquires an
imaginary part. This signals the instability of the gas. This instability may
be identified with the Berezinskii, Kosterlitz and Thouless (BKT) transition.Comment: RevTeX, 13 pages, 3 figure
Hsa-miRNA-765 as a key mediator for inhibiting growth, migration and invasion in fulvestrant-treated prostate cancer
Fulvestrant (ICI-182,780) has recently been shown to effectively suppress prostate cancer cell growth in vitro and in vivo. But it is unclear whether microRNAs play a role in regulating oncogene expression in fulvestrant-treated prostate cancer. Here, this study reports hsa-miR-765 as the first fulvestrant-driven, ERβ-regulated miRNA exhibiting significant tumor suppressor activities like fulvestrant, against prostate cancer cell growth via blockage of cell-cycle progression at the G2/M transition, and cell migration and invasion possibly via reduction of filopodia/intense stress-fiber formation. Fulvestrant was shown to upregulate hsa-miR-765 expression through recruitment of ERβ to the 5′-regulatory-region of hsa-miR-765. HMGA1, an oncogenic protein in prostate cancer, was identified as a downstream target of hsa-miR-765 and fulvestrant in cell-based experiments and a clinical study. Both the antiestrogen and the hsa-miR-765 mimic suppressed HMGA1 protein expression. In a neo-adjuvant study, levels of hsa-miR-765 were increased and HMGA1 expression was almost completely lost in prostate cancer specimens from patients treated with a single dose (250 mg) of fulvestrant 28 days before prostatectomy. These findings reveal a novel fulvestrant signaling cascade involving ERβ-mediated transcriptional upregulation of hsa-miR-765 that suppresses HMGA1 protein expression as part of the mechanism underlying the tumor suppressor action of fulvestrant in prostate cancer. © 2014 Leung et al
Towards a global partnership model in interprofessional education for cross-sector problem-solving
Objectives
A partnership model in interprofessional education (IPE) is important in promoting a sense of global citizenship while preparing students for cross-sector problem-solving. However, the literature remains scant in providing useful guidance for the development of an IPE programme co-implemented by external partners. In this pioneering study, we describe the processes of forging global partnerships in co-implementing IPE and evaluate the programme in light of the preliminary data available.
Methods
This study is generally quantitative. We collected data from a total of 747 health and social care students from four higher education institutions. We utilized a descriptive narrative format and a quantitative design to present our experiences of running IPE with external partners and performed independent t-tests and analysis of variance to examine pretest and posttest mean differences in students’ data.
Results
We identified factors in establishing a cross-institutional IPE programme. These factors include complementarity of expertise, mutual benefits, internet connectivity, interactivity of design, and time difference. We found significant pretest–posttest differences in students’ readiness for interprofessional learning (teamwork and collaboration, positive professional identity, roles, and responsibilities). We also found a significant decrease in students’ social interaction anxiety after the IPE simulation.
Conclusions
The narrative of our experiences described in this manuscript could be considered by higher education institutions seeking to forge meaningful external partnerships in their effort to establish interprofessional global health education