Dense and Sharp Resonance Peaks in Stretched Moir\'e Waveguides

In this article, we demonstrate dense resonant peaks in the transmission spectra of a rectangular waveguide inscribed with a stretched moir\'e pattern. We investigated an array of silicon waveguides with sinusoidally modulated cladding of varying depth of modulation. The investigation reveals a critical depth of modulation that splits the geometries into weakly scattering and strongly scattering regimes. Geometries in the weakly scattering regime resemble Bragg waveguides with shallow cladding modulation, whereas in the strongly scattering regime, the geometries resemble chains of isolated dielectric particles. The guided mode photonic bandgap for geometries in the strongly scattering regime is much larger than that of the weakly scattering regime. By inscribing stretched moir\'e patterns in the strongly scattering regime, we show that a large number of sharp peaks can be created in the transmission spectra of the waveguide. All periodic stretched moir\'e patterns can be identified with an R parameter. The R parameter indicates the ratio of the supercell period of the stretched system to the unstretched system. Our empirical study shows that the density of peaks linearly increases with R. The multiple resonance peaks evolve along well-defined trajectories with quality factor defined by exponential functions of R

Bilayer Metasurface: Induced Transparency and Fabry Perot Resonance

A Fabry-Perot resonator utilizes two solid, non-resonating, reflecting mirrors to form resonant patterns when the separation between the mirrors satisfies the resonance conditions. The resonant mode concentrates at the middle of the cavity. In this study, we constructed a Fabry-Perot cavity with nanostructured resonant metasurfaces as meta-mirrors. The individual metasurfaces exhibit resonant transmission dips with a minimum transmission and a quality factor of t0 and Qs, respectively. The coherent interference between the two metasurfaces changes the behavior of the entire resonant system, generating an induced transparency in the original spectrum. The sharpness of the induced transparency peak is linearly related to the group delay of the single metasurface. Assuming a Lorentzian lineshape, we show that for small t0, the quality factor of the induced transparency peak is Qs/t0^3. The field confines to the meta-mirrors region rather than at the middle of the Fabry-Perot cavity. We provide examples of practical metasurfaces made from dielectric scatters composed of silicon thin nanodisks and demonstrate high quality factors and phase dispersion that are unattainable by any nano or microscale flat optics systems

Optimizing global health experiences in emergency medicine residency programs: A consensus statement from the Council of Emergency Medicine Residency Directors 2011 Academic Assembly global health specialty track

BACKGROUND: An increasing number of emergency medicine (EM) residency training programs have residents interested in participating in clinical rotations in other countries. However, the policies that each individual training program applies to this process are different. To our knowledge, little has been done in the standardization of these experiences to help EM residency programs with the evaluation, administration and implementation of a successful global health clinical elective experience. The objective of this project was to assess the current status of EM global health electives at residency training programs and to establish recommendations from educators in EM on the best methodology to implement successful global health electives. METHODS: During the 2011 Council of Emergency Medicine Residency Directors (CORD) Academic Assembly, participants met to address this issue in a mediated discussion session and working group. Session participants examined data previously obtained via the CORD online listserve, discussed best practices in global health applications, evaluations and partnerships, and explored possible solutions to some of the challenges. In addition a survey was sent to CORD members prior to the 2011 Academic Assembly to evaluate the resources and processes for EM residents’ global experiences. RESULTS: Recommendations included creating a global health working group within the organization, optimizing a clearinghouse of elective opportunities for residents and standardizing elective application materials, site evaluations and resident assessment/feedback methods. The survey showed that 71.4% of respondents have global health partnerships and electives. However, only 36.7% of programs require pre-departure training, and only 20% have formal competency requirements for these global health electives. CONCLUSIONS: A large number of EM training programs have global health experiences available, but these electives and the trainees may benefit from additional institutional support and formalized structure

Derivation of Pre-X Inactivation Human Embryonic Stem Cells under Physiological Oxygen Concentrations

The presence of two active X chromosomes (XaXa) is a hallmark of the ground state of pluripotency specific to murine embryonic stem cells (ESCs). Human ESCs (hESCs) invariably exhibit signs of X chromosome inactivation (XCI) and are considered developmentally more advanced than their murine counterparts. We describe the establishment of XaXa hESCs derived under physiological oxygen concentrations. Using these cell lines, we demonstrate that (1) differentiation of hESCs induces random XCI in a manner similar to murine ESCs, (2) chronic exposure to atmospheric oxygen is sufficient to induce irreversible XCI with minor changes of the transcriptome, (3) the Xa exhibits heavy methylation of the XIST promoter region, and (4) XCI is associated with demethylation and transcriptional activation of XIST along with H3K27-me3 deposition across the Xi. These findings indicate that the human blastocyst contains pre-X-inactivation cells and that this state is preserved in vitro through culture under physiological oxygen.Susan WhiteheadHillel and Liliana Bachrac

Seroepidemiology of Varicella and value of self-reported history of Varicella infection in Iranian medical students

Objectives: We conducted this study to assess the seroprevalence of Varicella zoster virus (VZV) antibodies in a group of Iranian medical sciences students that were at risk of Varicella and the value of self-reported history as a predictor of immunity. Material and Methods: 255 medical, nursing and obstetrics students who had not entered as a student or worked in a hospital from 3 different schools were enrolled in the study in 2012 (Qazvin province, Iran). Demographics and other information as well as the history of Varicella were obtained through a self-administered questionnaire. Blood samples were collected to determine the Varicella IgG levels via an enzyme-linked immunosorbent assay. A statistical analysis was performed by calculating prevalences and their 95% confidence intervals. Sensitivity, specificity, positive and negative predictive values, Cohen's kappa and positive and negative likelihood ratios of recalled history were determined. p < 0.05 was considered statistically significant. Results: The mean age of participants was 21.3±4.3 years. Seropositivity rate was 74.5%. The relationships between marital status, number of family members, and acquired VZV history with immunity against the virus were statistically significant. The overall rate of reported history was 57%. The positive and negative predictive values of self-reported history of Varicella were 91% and 47.3%, respectively. Conclusions: Immunization of students of Iranian medical sciences seems logical in the near future. Also, they should be tested for Varicella immunity regardless of the history of previous infection

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability