5,193 research outputs found
Boundary and impurity effects on entanglement of Heisenberg chains
We study entanglement of a pair of qubits and the bipartite entanglement
between the pair and the rest within open-ended Heisenberg and XY models.
The open boundary condition leads to strong oscillations of entanglements with
a two-site period, and the two kinds of entanglements are 180 degree out of
phase with each other. The mean pairwise entanglement and ground-state energy
per site in the model are found to be proportional to each other. We
study the effects of a single bulk impurity on entanglement, and find that
there exists threshold values of the relative coupling strength between the
impurity and its nearest neighbours, after which the impurity becomes pairwise
entangled with its nearest neighbours.Comment: 6 pages and 6 figure
Localized gap soliton trains of Bose-Einstein condensates in an optical lattice
We develop a systematic analytical approach to study the linear and nonlinear
solitary excitations of quasi-one-dimensional Bose-Einstein condensates trapped
in an optical lattice. For the linear case, the Bloch wave in the energy
band is a linear superposition of Mathieu's functions and ;
and the Bloch wave in the band gap is a linear superposition of
and . For the nonlinear case, only solitons inside the band gaps are
likely to be generated and there are two types of solitons -- fundamental
solitons (which is a localized and stable state) and sub-fundamental solitons
(which is a lacalized but unstable state). In addition, we find that the
pinning position and the amplitude of the fundamental soliton in the lattice
can be controlled by adjusting both the lattice depth and spacing. Our
numerical results on fundamental solitons are in quantitative agreement with
those of the experimental observation [Phys. Rev. Lett. {\bf92}, 230401
(2004)]. Furthermore, we predict that a localized gap soliton train consisting
of several fundamental solitons can be realized by increasing the length of the
condensate in currently experimental conditions.Comment: 9 pages, 6 figures, accepted for publicaiton in PR
Gaming the no-choice system? School choice and persistent educational inequality in China
The admission policy for public compulsory schools in China is neighbourhood enrolment which entitles children to attend their assigned local school free of charge, and this policy has been rigorously implemented in recent years to prevent school choice. However, driven by disparities in education provision, parents still find ways to make choices in an officially no-choice public educational system. Inspired by a Bourdieusian framework, this study uses the China Family Panel Studies (CFPS) to explore the relationships between family capital, school choice, and the quality of the school pupils attend. We seek to offer a lens to explore the prevalence and patterns of school choice, and its impact on constructing educational stratification. Findings suggest persistent inequality in the no-choice policy context and that children from more privileged families are more likely to study in higher performing schools
Determination and optimization of mode matching into optical cavities by heterodyne detection
We report on a novel high-sensitivity method to characterize and improve mode matching into optical cavities. This method is based on heterodyne detection of cylindrical transverse cavity modes. A specially designed annular-segmented photodiode is used to measure the amplitude of nonresonant modes reflected by the cavity. Our measurements allow us to optimize cavity mode matching to nearly 99.98% and will play an important diagnostic role in gravitational-wave detectors
Assisting interruption recovery in mission control operations
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 105-108).Frequent interruptions are commonplace in modem work environments. The negative impacts of interruptions are well documented and include increased task completion and error rates in individual task activities, as well as interference with team coordination in team-based activities. The ramifications of an interruption in mission control operations, such as military command and control and emergency response, can be particularly costly due to the time and life-critical nature of these operations. The negative impacts of interruptions have motivated recent developments in software tools, called interruption recovery tools, which help mitigate the effects of interruptions in a variety of task environments. However, mission control operations introduce particular challenges for the design of these tools due to the dynamic and highly collaborative nature of these environments. To address this issue, this thesis investigates methods of reducing the negative consequences of interruptions in complex, mission control operations. In particular, this thesis focuses on supporting interruption recovery for team supervisors in these environments, as the research has shown that supervisors are particularly susceptible to frequent interruptions. Based on the results of a requirements analysis, which involved a cognitive task analysis of a representative mission control task scenario, a new interruption recovery tool, named the Interruption Recovery Assistance (IRA) tool, was developed. In particular, the IRA tool was designed to support a military mission commander overseeing a team of unmanned aerial vehicle (UAV) operators performing ground force protection operations. The IRA tool provides the mission commander a visual summary of mission changes, in the form of an event bookmark timeline. It also provides interactive capabilities to enable the commander to view additional information on the primary task displays when further detail about a particular mission event is needed. The thesis also presents the findings from a user study that was conducted to evaluate the effectiveness of the IRA tool on interruption recovery during collaborative UAV mission operations. The study produced mixed results regarding the effectiveness of the IRA tool. The statistical analysis indicated a negative impact on recovery time, while indicating a positive impact on decision accuracy, especially in complex task situations. The study also indicated that the effect of the IRA tool varied across differ user populations. In particular, the IRA tool tended to provide greater benefits to participants without military experience, compared to military participants involved in the study. The qualitative findings from the study provided key insights into the impact and utility of the IRA tool. These insights were used to identify several future research and design directions related to interruption recovery in mission control operations.by Jordan Wan.M.Eng
The radiating part of circular sources
An analysis is developed linking the form of the sound field from a circular
source to the radial structure of the source, without recourse to far-field or
other approximations. It is found that the information radiated into the field
is limited, with the limit fixed by the wavenumber of source multiplied by the
source radius (Helmholtz number). The acoustic field is found in terms of the
elementary fields generated by a set of line sources whose form is given by
Chebyshev polynomials of the second kind, and whose amplitude is found to be
given by weighted integrals of the radial source term. The analysis is
developed for tonal sources, such as rotors, and, for Helmholtz number less
than two, for random disk sources. In this case, the analysis yields the
cross-spectrum between two points in the acoustic field. The analysis is
applied to the problems of tonal radiation, random source radiation as a model
problem for jet noise, and to noise cancellation, as in active control of noise
from rotors. It is found that the approach gives an accurate model for the
radiation problem and explicitly identifies those parts of a source which
radiate.Comment: Submitted to Journal of the Acoustical Society of Americ
Online Information on Dysmenorrhea: An Evaluation of Readability, Credibility, Quality, and Usability
Aims and objectives
To evaluate online information on dysmenorrhoea, including readability, credibility, quality and usability.
Background
Menstrual pain impacts 45%ā95% of women of reproductive age globally and is the leading cause of school and work absences among women. Women often seek online information on dysmenorrhoea; however, little is known about the information quality.
Design
This was a descriptive study to evaluate online information on dysmenorrhoea.
Methods
We imitated search strategies of the general public. Specifically, we employed the three most popular search engines worldwideāGoogle, Yahoo and Bingāand used lay search terms, āperiod painā and āmenstrual cramps.ā We screened 60 web pages. Following removal of duplicates and irrelevant web pages, 25 met the eligibility criteria. Two team members independently evaluated the included web pages using standardised tools. Readability was evaluated with the FleschāKincaid Reading Ease and FleschāKincaid Grade formulas; credibility, quality and usability were evaluated with established tools. We followed the STROBE checklist for reporting this study.
Results
For readability, the mean FleschāKincaid level was 10th grade. For credibility, 8% of web pages referenced scientific literature and 28% stated the author's name and qualifications. For quality, no web page employed userādriven content production; 8% of web pages referenced evidenceābased guidelines, 32% of web pages had accurate content, and 4% of web pages recommended shared decisionāmaking. Most web pages were interactive and included nontextual information. Some nontextual information was inaccurate.
Conclusion
Online information on dysmenorrhoea has generally low readability, mixed credibility and variable quality.
Relevance to clinical practice
Strategies to improve health information on dysmenorrhoea include avoiding complex terms, incorporating visual aids, presenting evidenceābased information and developing a decision aid to support shared decisionāmaking. Healthcare providers should be aware of the problematic health information that individuals are exposed to and provide education about how to navigate online health information
Carbon-rich presolar grains from massive stars : subsolar Ā¹Ā²C/Ā¹Ā³C and Ā¹ā“N/Ā¹āµN ratios and the mystery of Ā¹āµN
Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C and low-density (LD) graphites condensed in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing Ā¹Ā²C/Ā¹Ā³C and Ā¹ā“N/Ā¹āµN ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. Different explosion energies and H concentrations are considered. If the supernova shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of Ā¹Ā³C and Ā¹āµN. The short-lived radionuclides Ā²Ā²Na and Ā²ā¶Al are increased by orders of magnitude. The production of radiogenic Ā²Ā²Ne from the decay of Ā²Ā²Na in the He shell might solve the puzzle of the Ne-E(L) component in LD graphite grains. This scenario is attractive for the SiC grains of type AB with Ā¹ā“N/Ā¹āµN ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of Ā¹ā“N and Ā¹āµN in the Galaxy, helping to produce the Ā¹ā“N/Ā¹āµN ratio in the solar system
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