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 $XXX$ 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 $XXX$ 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 $nth$ energy band is a linear superposition of Mathieu's functions $ce_{n-1}$ and $se_n$; and the Bloch wave in the $nth$ band gap is a linear superposition of $ce_n$ and $se_n$. 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%–95% 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 worldwide—Google, Yahoo and Bing—and used lay search terms, “period pain” and “menstrual cramps.” 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 Flesch–Kincaid Reading Ease and Flesch–Kincaid 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 Flesch–Kincaid 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 user‐driven content production; 8% of web pages referenced evidence‐based guidelines, 32% of web pages had accurate content, and 4% of web pages recommended shared decision‐making. 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 evidence‐based information and developing a decision aid to support shared decision‐making. 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 ¹²C/¹³C and ¹⁴N/¹⁵N ratios and the mystery of ¹⁵N

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 ¹²C/¹³C and ¹⁴N/¹⁵N 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 ¹³C and ¹⁵N. The short-lived radionuclides ²²Na and ²⁶Al are increased by orders of magnitude. The production of radiogenic ²²Ne from the decay of ²²Na 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 ¹⁴N/¹⁵N 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 ¹⁴N and ¹⁵N in the Galaxy, helping to produce the ¹⁴N/¹⁵N ratio in the solar system