727 research outputs found
Disorder and interactions in quantum Hall ferromagnets: effects of disorder in Skyrmion physics
We present a Hartree-Fock study of the competition between disorder and
interactions in quantum Hall ferromagnets near . We find that the ground
state at evolves with increasing interaction strength from a
quasi-metallic paramagnet, to a partially spin-polarized ferromagnetic Anderson
insulator, and to a fully spin-polarized ferromagnet with a charge gap. Away
from , the ground state evolves from a conventional Anderson insulator,
to a conventional quasiparticle glass, and finally to a ferromagnetic Skyrmion
quasiparticle glass. These different regimes can be measured in low-temperature
transport and NMR experiments. We present calculations for the NMR spectra in
different disorder regimes.Comment: 3 pages, 3 figures, proceedings for EP2DS-14, Prague 200
Properties of the Soliton-Lattice State in Double-Layer Quantum Hall Systems
Application of a sufficiently strong parallel magnetic field produces a soliton-lattice (SL) ground state in a double-layer quantum
Hall system. We calculate the ground-state properties of the SL state as a
function of for total filling factor , and obtain the
total energy, anisotropic SL stiffness, Kosterlitz-Thouless melting
temperature, and SL magnetization. The SL magnetization might be experimentally
measurable, and the magnetic susceptibility diverges as .Comment: 4 pages LaTeX, 1 EPS figure. Proceedings of the 12th International
Conference on the Electronic Properties of Two-Dimensional Electron Systems
(EP2DS-12), to be published in Physica B (1998
Phase transition and spin-wave dispersion in quantum Hall bilayers at filling factor nu=1
We present an effective Hamiltonian for a bilayer quantum Hall system at
filling factor neglecting charge fluctuations. Our model is formulated
in terms of spin and pseudospin operators and is an exact representation of the
system within the above approximation. We analyze its low-lying excitations in
terms of spin-wave theory. Moreover we add to previous first-principle
exact-diagonalization studies concentrating on the quantum phase transition
seen in this system.Comment: Four pages, proceedings for EP2DS-14, Prague 200
Assessing gender mainstreaming in the education sector: depoliticised technique or a step towards women's rights and gender equality?
In 1995 the Beijing Conference on Women identified gender mainstreaming as a key area for action. Policies to effect gender mainstreaming have since been widely adopted. This special issue of Compare looks at research on how gender mainstreaming has been used in government education departments, schools, higher education institutions, international agencies and NGOs .1 In this introduction we first provide a brief history of the emergence of gender mainstreaming and review changing definitions of the term. In the process we outline some policy initiatives that have attempted to mainstream gender and consider some difficulties with putting ideas into practice, particularly the tensions between a technical and transformative interpretations . Much of the literature about experiences with gender mainstreaming tends to look at organizational processes and not any specificities of a particular social sector. However, in our second section, we are concerned to explore whether institutional forms and particular actions associated with education give gender mainstreaming in education sites some distinctive features. In our last section we consider some of the debates about global and local negotiations in discussions of gender policy and education and the light this throws on gender mainstreaming. In so doing, we place the articles that follow in relation to contestations over ownership, political economy, the form and content of education practice and the social complexity of gender equality
Magnetoroton instabilities and static susceptibilities in higher Landau levels
We present analytical results concerning the magneto-roton instability in
higher Landau levels evaluated in the single mode approximation. The roton gap
appears at a finite wave vector, which is approximately independent of the LL
index n, in agreement with numerical calculations in the composite-fermion
picture. However, a large maximum in the static susceptibility indicates a
charge density modulation with wave vectors , as
expected from Hartree-Fock predictions. We thus obtain a unified description of
the leading charge instabilities in all LLs.Comment: 4 pages, 5 figure
BioMiCo:A supervised Bayesian model for inference of microbial community structure
Here, we describe a novel hierarchical model for Bayesian inference of microbial communities (BioMiCo). The model takes abundance data derived from environmental DNA, and models the composition of each sample by a two-level hierarchy of mixture distributions constrained by Dirichlet priors. BioMiCo is supervised, using known features for samples and appropriate prior constraints to overcome the challenges posed by many variables, sparse data, and large numbers of rare species. The model is trained on a portion of the data, where it learns how assemblages of species are mixed to form communities and how assemblages are related to the known features of each sample. Training yields a model that can predict the features of new samples. We used BioMiCo to build models for three serially sampled datasets and tested their predictive accuracy across different time points. The first model was trained to predict both body site (hand, mouth, and gut) and individual human host. It was able to reliably distinguish these features across different time points. The second was trained on vaginal microbiomes to predict both the Nugent score and individual human host. We found that women having normal and elevated Nugent scores had distinct microbiome structures that persisted over time, with additional structure within women having elevated scores. The third was trained for the purpose of assessing seasonal transitions in a coastal bacterial community. Application of this model to a high-resolution time series permitted us to track the rate and time of community succession and accurately predict known ecosystem-level events
Effects of communication and utility-based decision making in a simple model of evacuation
We present a simple cellular automaton based model of decision making during
evacuation. Evacuees have to choose between two different exit routes,
resulting in a strategic decision making problem. Agents take their decisions
based on utility functions, these can be revised as the evacuation proceeds,
leading to complex interaction between individuals and to jamming transitions.
The model also includes the possibility to communicate and exchange information
with distant agents, information received may affect the decision of agents. We
show that under a wider range of evacuation scenarios performance of the model
system as a whole is optimal at an intermediate fraction of evacuees with
access to communication.Comment: 9 pages, 9 figure
Rotational and vibrational spectra of quantum rings
One can confine the two-dimensional electron gas in semiconductor
heterostructures electrostatically or by etching techniques such that a small
electron island is formed. These man-made ``artificial atoms'' provide the
experimental realization of a text-book example of many-particle physics: a
finite number of quantum particles in a trap. Much effort was spent on making
such "quantum dots" smaller and going from the mesoscopic to the quantum
regime. Far-reaching analogies to the physics of atoms, nuclei or metal
clusters were obvious from the very beginning: The concepts of shell structure
and Hund's rules were found to apply -- just as in real atoms! In this Letter,
we report the discovery that electrons confined in ring-shaped quantum dots
form rather rigid molecules with antiferromagnetic order in the ground state.
This can be seen best from an analysis of the rotational and vibrational
excitations
Critical Currents of Ideal Quantum Hall Superfluids
Filling factor bilayer electron systems in the quantum Hall regime
have an excitonic-condensate superfluid ground state when the layer separation
is less than a critical value . On a quantum Hall plateau current
injected and removed through one of the two layers drives a dissipationless
edge current that carries parallel currents, and a dissipationless bulk
supercurrent that carries opposing currents in the two layers. In this paper we
discuss the theory of finite supercurrent bilayer states, both in the presence
and in the absence of symmetry breaking inter-layer hybridization. Solutions to
the microscopic mean-field equations exist at all condensate phase winding
rates for zero and sufficiently weak hybridization strengths. We find, however,
that collective instabilities occur when the supercurrent exceeds a critical
value determined primarily by a competition between direct and exchange
inter-layer Coulomb interactions. The critical current is estimated using a
local stability criterion and varies as when approaches
from below. For large inter-layer hybridization, we find that the
critical current is limited by a soliton instability of microscopic origin.Comment: 18 RevTeX pgs, 21 eps figure
Majority of Fortune 500 Companies in 2018 Did Not Recognize Risk of Epidemics Such as COVID-19
Infectious disease threats, like the 2002 severe acute respiratory syndrome coronavirus (SARS-CoV) disease, 2009 pandemic influenza A (H1N1), and the current coronavirus disease 2019 (COVID-19), pose multisectoral risk with the potential for wide-ranging socioeconomic disruption. In our globally intertwined economy, the impact of such events can elicit economic shock waves that reach far beyond the country of origin. Review of the 2018 Fortune 500 company 10-K filings shows the majority did not document perceived risks associated with epidemics, outbreaks, or pandemics. Enhanced engagement and investment of the public and private sectors in advancing global health security is needed to effectively prevent, detect, and respond to infectious disease events and ensure U.S. economic security
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