42,494 research outputs found
Entanglement and purity of single- and two-photon states
Whereas single- and two-photon wave packets are usually treated as pure
states, in practice they will be mixed. We study how entanglement created with
mixed photon wave packets is degraded. We find in particular that the
entanglement of a delocalized single-photon state of the electro-magnetic field
is determined simply by its purity. We also discuss entanglement for two-photon
mixed states, as well as the influence of a vacuum component.Comment: 11 pages, 10 figures, 1 debuting autho
Incentivizing High Quality Crowdwork
We study the causal effects of financial incentives on the quality of
crowdwork. We focus on performance-based payments (PBPs), bonus payments
awarded to workers for producing high quality work. We design and run
randomized behavioral experiments on the popular crowdsourcing platform Amazon
Mechanical Turk with the goal of understanding when, where, and why PBPs help,
identifying properties of the payment, payment structure, and the task itself
that make them most effective. We provide examples of tasks for which PBPs do
improve quality. For such tasks, the effectiveness of PBPs is not too sensitive
to the threshold for quality required to receive the bonus, while the magnitude
of the bonus must be large enough to make the reward salient. We also present
examples of tasks for which PBPs do not improve quality. Our results suggest
that for PBPs to improve quality, the task must be effort-responsive: the task
must allow workers to produce higher quality work by exerting more effort. We
also give a simple method to determine if a task is effort-responsive a priori.
Furthermore, our experiments suggest that all payments on Mechanical Turk are,
to some degree, implicitly performance-based in that workers believe their work
may be rejected if their performance is sufficiently poor. Finally, we propose
a new model of worker behavior that extends the standard principal-agent model
from economics to include a worker's subjective beliefs about his likelihood of
being paid, and show that the predictions of this model are in line with our
experimental findings. This model may be useful as a foundation for theoretical
studies of incentives in crowdsourcing markets.Comment: This is a preprint of an Article accepted for publication in WWW
\c{opyright} 2015 International World Wide Web Conference Committe
Environment-Mediated Quantum State Transfer
We propose a scheme for quantum state transfer(QST) between two qubits which
is based on their individual interaction with a common boson environment. The
corresponding single mode spin-boson Hamiltonian is solved by mapping it onto a
wave propagation problem in a semi-infinite ladder and the fidelity is
obtained. High fidelity occurs when the qubits are equally coupled to the boson
while the fidelity becomes smaller for nonsymmetric couplings. The complete
phase diagram for such an arbitrary QST mediated by bosons is discussed.Comment: 6 pages and 5 figure
DRS: Dynamic Resource Scheduling for Real-Time Analytics over Fast Streams
In a data stream management system (DSMS), users register continuous queries,
and receive result updates as data arrive and expire. We focus on applications
with real-time constraints, in which the user must receive each result update
within a given period after the update occurs. To handle fast data, the DSMS is
commonly placed on top of a cloud infrastructure. Because stream properties
such as arrival rates can fluctuate unpredictably, cloud resources must be
dynamically provisioned and scheduled accordingly to ensure real-time response.
It is quite essential, for the existing systems or future developments, to
possess the ability of scheduling resources dynamically according to the
current workload, in order to avoid wasting resources, or failing in delivering
correct results on time. Motivated by this, we propose DRS, a novel dynamic
resource scheduler for cloud-based DSMSs. DRS overcomes three fundamental
challenges: (a) how to model the relationship between the provisioned resources
and query response time (b) where to best place resources; and (c) how to
measure system load with minimal overhead. In particular, DRS includes an
accurate performance model based on the theory of \emph{Jackson open queueing
networks} and is capable of handling \emph{arbitrary} operator topologies,
possibly with loops, splits and joins. Extensive experiments with real data
confirm that DRS achieves real-time response with close to optimal resource
consumption.Comment: This is the our latest version with certain modificatio
Understanding the introduction and use of a mobile device-supported health information system in Nigeria
Copyright @ 2014 The Authors.This paper presents an in-depth analysis of efforts to introduce a mobile health information system in Nigeria as part of a development initiative aimed at improving maternal and child health. Specifically, it examines the use of mobile devices to facilitate maternal health information accessibility and exchange among health practitioners in order to reducing maternal, newborn and child mortality. Further, it also looks at the challenges raised while introducing mobile devices into work practices in the healthcare sector.
The study adopts a case study approach, relying on semi-structured interviews and document analysis as its main methods for collecting data. The specific case examined is a mobile phone-based information system introduced to support a national government effort in Nigeria, known as the midwives service scheme. The findings of this study show that this integrated approach of using mobile phones to support (health) information systems has vast potential; for instance increasing the timeliness of (health) data available to stakeholders for monitoring and planning purposes. However, we also find that over time, attaining the potential of development efforts such as this remains difficult as initiatives involving the use of mobile devices is not just about getting the technical aspect right. It is equally dependent on deep seated social-cultural influences such as poor political and financial commitment. These two mutually reinforcing influences have been identified in this study as significant impediments to efforts of this kind. Therefore, this paper argues for, first a strong political commitment across all levels of government whereby their words are backed with action. Second it is important that the government maintains financial integrity by releasing the funds budgeted to support the smooth running of these efforts, for such initiatives to thrive and ultimately contribute to development
Response of internal solitary waves to tropical storm Washi in the northwestern South China Sea
Based on in-situ time series data from an array of temperature sensors and
an acoustic Doppler current profiler on the continental shelf of the
northwestern South China Sea, a sequence of internal solitary waves (ISWs)
were observed during the passage of tropical storm Washi in the summer of
2005, which provided a unique opportunity to investigate the ISW response to
the tropical cyclone. The passing tropical storm is found to play an
important role in affecting the stratification structure of the water
column, and consequently leading to significant variability in the propagating features
of the ISWs, such as the polarity reversal and amplitude variations of the
waves. The response of the ISWs to Washi can be divided into two stages,
direct forcing by the strong wind (during the arrival of Washi) and remote
forcing via the near-inertial internal waves induced by the tropical storm
(after the passage of Washi). The field observations as well as a
theoretical analysis suggest that the variations of the ISWs closely
coincide with the changing stratification structure and shear currents in
accompanied by the typhoon wind and near-inertial waves. This study presents
the first observations and analysis of the ISW response to the tropical
cyclone in the South China Sea
Carbon-doped ZnO: A New Class of Room Temperature Dilute Magnetic Semiconductor
We report magnetism in carbon doped ZnO. Our first-principles calculations
based on density functional theory predicted that carbon substitution for
oxygen in ZnO results in a magnetic moment of 1.78 per carbon. The
theoretical prediction was confirmed experimentally. C-doped ZnO films
deposited by pulsed laser deposition with various carbon concentrations showed
ferromagnetism with Curie temperatures higher than 400 K, and the measured
magnetic moment based on the content of carbide in the films (
per carbon) is in agreement with the theoretical prediction. The magnetism is
due to bonding coupling between Zn ions and doped C atoms. Results of
magneto-resistance and abnormal Hall effect show that the doped films are
-type semiconductors with intrinsic ferromagnetism. The carbon doped ZnO
could be a promising room temperature dilute magnetic semiconductor (DMS) and
our work demonstrates possiblity of produing DMS with non-metal doping.Comment: REVtex source with 4 figures in eps forma
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