110 research outputs found
Nonequilibrium spin injection in monolayer black phosphorus
Monolayer black phosphorus (MBP) is an interesting emerging electronic
material with a direct band gap and relatively high carrier mobility. In this
work we report a theoretical investigation of nonequilibrium spin injection and
spin-polarized quantum transport in MBP from ferromagnetic Ni contacts, in
two-dimensional magnetic tunneling structures. We investigate physical
properties such as the spin injection efficiency, the tunnel magnetoresistance
ratio, spin-polarized currents, charge currents and transmission coefficients
as a function of external bias voltage, for two different device contact
structures where MBP is contacted by Ni(111) and by Ni(100). While both
structures are predicted to give respectable spin-polarized quantum transport,
the Ni(100)/MBP/Ni(100) trilayer has the superior properties where the spin
injection and magnetoresistance ratio maintains almost a constant value against
the bias voltage. The nonequilibrium quantum transport phenomenon is understood
by analyzing the transmission spectrum at nonequilibrium.Comment: 6 pages, 6 figure
Why People Search for Images using Web Search Engines
What are the intents or goals behind human interactions with image search
engines? Knowing why people search for images is of major concern to Web image
search engines because user satisfaction may vary as intent varies. Previous
analyses of image search behavior have mostly been query-based, focusing on
what images people search for, rather than intent-based, that is, why people
search for images. To date, there is no thorough investigation of how different
image search intents affect users' search behavior.
In this paper, we address the following questions: (1)Why do people search
for images in text-based Web image search systems? (2)How does image search
behavior change with user intent? (3)Can we predict user intent effectively
from interactions during the early stages of a search session? To this end, we
conduct both a lab-based user study and a commercial search log analysis.
We show that user intents in image search can be grouped into three classes:
Explore/Learn, Entertain, and Locate/Acquire. Our lab-based user study reveals
different user behavior patterns under these three intents, such as first click
time, query reformulation, dwell time and mouse movement on the result page.
Based on user interaction features during the early stages of an image search
session, that is, before mouse scroll, we develop an intent classifier that is
able to achieve promising results for classifying intents into our three intent
classes. Given that all features can be obtained online and unobtrusively, the
predicted intents can provide guidance for choosing ranking methods immediately
after scrolling
STORM-GAN: Spatio-Temporal Meta-GAN for Cross-City Estimation of Human Mobility Responses to COVID-19
Human mobility estimation is crucial during the COVID-19 pandemic due to its
significant guidance for policymakers to make non-pharmaceutical interventions.
While deep learning approaches outperform conventional estimation techniques on
tasks with abundant training data, the continuously evolving pandemic poses a
significant challenge to solving this problem due to data nonstationarity,
limited observations, and complex social contexts. Prior works on mobility
estimation either focus on a single city or lack the ability to model the
spatio-temporal dependencies across cities and time periods. To address these
issues, we make the first attempt to tackle the cross-city human mobility
estimation problem through a deep meta-generative framework. We propose a
Spatio-Temporal Meta-Generative Adversarial Network (STORM-GAN) model that
estimates dynamic human mobility responses under a set of social and policy
conditions related to COVID-19. Facilitated by a novel spatio-temporal
task-based graph (STTG) embedding, STORM-GAN is capable of learning shared
knowledge from a spatio-temporal distribution of estimation tasks and quickly
adapting to new cities and time periods with limited training samples. The STTG
embedding component is designed to capture the similarities among cities to
mitigate cross-task heterogeneity. Experimental results on real-world data show
that the proposed approach can greatly improve estimation performance and
out-perform baselines.Comment: Accepted at the 22nd IEEE International Conference on Data Mining
(ICDM 2022) Full Pape
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