3,918 research outputs found
Universality in the Crossover between Edge Channel and Bulk Transport in the Quantum Hall Regime
We present a new theoretical approach for the integer quantum Hall effect,
which is able to describe the inter-plateau transitions as well as the
transition to the Hall insulator. We find two regimes (metallic and insulator
like) of the top Landau level, in which the dissipative bulk current appears in
different directions. The regimes are separated by a temperature invariant
point.Comment: 4 page, 2 eps figures included, submitte
Relationship between hippocampal structure and memory function in elderly humans
With progressing age, the ability to recollect personal events declines, whereas familiarity-based memory remains relatively intact. It has been hypothesized that age-related hippocampal atrophy may contribute to this pattern because of its critical role for recollection in younger humans and after acute injury. Here, we show that hippocampal volume loss in healthy older persons correlates with gray matter loss (estimated with voxel-based morphometry) of the entire limbic system and shows no correlation with an electrophysiological (event-related potential [ERP]) index of recollection. Instead, it covaries with more substantial and less specific electrophysiological changes of stimulus processing. Age-related changes in another complementary structural measure, hippocampal diffusion, on the other hand, seemed to be more regionally selective and showed the expected correlation with the ERP index of recollection. Thus, hippocampal atrophy in older persons accompanies limbic atrophy, and its functional impact on memory is more fundamental than merely affecting recollection
Theory and computation of directional nematic phase ordering
A computational study of morphological instabilities of a two-dimensional
nematic front under directional growth was performed using a Landau-de Gennes
type quadrupolar tensor order parameter model for the first-order
isotropic/nematic transition of 5CB (pentyl-cyanobiphenyl). A previously
derived energy balance, taking anisotropy into account, was utilized to account
for latent heat and an imposed morphological gradient in the time-dependent
model. Simulations were performed using an initially homeotropic
isotropic/nematic interface. Thermal instabilities in both the linear and
non-linear regimes were observed and compared to past experimental and
theoretical observations. A sharp-interface model for the study of linear
morphological instabilities, taking into account additional complexity
resulting from liquid crystalline order, was derived. Results from the
sharp-interface model were compared to those from full two-dimensional
simulation identifying the specific limitations of simplified sharp-interface
models for this liquid crystal system. In the nonlinear regime, secondary
instabilities were observed to result in the formation of defects, interfacial
heterogeneities, and bulk texture dynamics.Comment: first revisio
Supramolecular hair dyes : a new application of cocrystallization
The manuscript presents the first report of hair dyes of various colors formed by the cocrystallization reactions. Unlike the most popular oxidative hair dye (OHD) products, these dyes are NH3 free and do not require H2O2 as a color developer. The importance of these new hair dyes products is further enhanced by recent reports which indicate that some of the OHDs may be carcinogeni
Time-dependent Hamiltonian estimation for Doppler velocimetry of trapped ions
The time evolution of a closed quantum system is connected to its Hamiltonian
through Schroedinger's equation. The ability to estimate the Hamiltonian is
critical to our understanding of quantum systems, and allows optimization of
control. Though spectroscopic methods allow time-independent Hamiltonians to be
recovered, for time-dependent Hamiltonians this task is more challenging. Here,
using a single trapped ion, we experimentally demonstrate a method for
estimating a time-dependent Hamiltonian of a single qubit. The method involves
measuring the time evolution of the qubit in a fixed basis as a function of a
time-independent offset term added to the Hamiltonian. In our system the
initially unknown Hamiltonian arises from transporting an ion through a static,
near-resonant laser beam. Hamiltonian estimation allows us to estimate the
spatial dependence of the laser beam intensity and the ion's velocity as a
function of time. This work is of direct value in optimizing transport
operations and transport-based gates in scalable trapped ion quantum
information processing, while the estimation technique is general enough that
it can be applied to other quantum systems, aiding the pursuit of high
operational fidelities in quantum control.Comment: 10 pages, 8 figure
A spatial theory for emergent multiple predator-prey interactions in food webs
Predator-prey interaction is inherently spatial because animals move through landscapes to search for and consume food resources and to avoid being consumed by other species. The spatial nature of species interactions necessitates integrating spatial processes into food web theory and evaluating how predators combine to impact their prey. Here, we present a spatial modeling approach that examines emergent multiple predator effects on prey within landscapes. The modeling is inspired by the habitat domain concept derived from empirical synthesis of spatial movement and interactions studies. Because these principles are motivated by synthesis of short-term experiments, it remains uncertain whether spatial contingency principles hold in dynamical systems. We address this uncertainty by formulating dynamical systems models, guided by core habitat domain principles, to examine long-term multiple predator-prey spatial dynamics. To describe habitat domains we use classical niche concepts describing resource utilization distributions, and assume species interactions emerge from the degree of overlap between species. The analytical results generally align with those from empirical synthesis and present a theoretical framework capable of demonstrating multiple predator effects that does not depend on the small spatial or temporal scales typical of mesocosm experiments, and help bridge between empirical experiments and long-term dynamics in natural systems
Sensing Subjective Well-being from Social Media
Subjective Well-being(SWB), which refers to how people experience the quality
of their lives, is of great use to public policy-makers as well as economic,
sociological research, etc. Traditionally, the measurement of SWB relies on
time-consuming and costly self-report questionnaires. Nowadays, people are
motivated to share their experiences and feelings on social media, so we
propose to sense SWB from the vast user generated data on social media. By
utilizing 1785 users' social media data with SWB labels, we train machine
learning models that are able to "sense" individual SWB from users' social
media. Our model, which attains the state-by-art prediction accuracy, can then
be used to identify SWB of large population of social media users in time with
very low cost.Comment: 12 pages, 1 figures, 2 tables, 10th International Conference, AMT
2014, Warsaw, Poland, August 11-14, 2014. Proceeding
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