Statistical PT-symmetric lasing in an optical fiber network

PT-symmetry in optics is a condition whereby the real and imaginary parts of the refractive index across a photonic structure are deliberately balanced. This balance can lead to a host of novel optical phenomena, such as unidirectional invisibility, loss-induced lasing, single-mode lasing from multimode resonators, and non-reciprocal effects in conjunction with nonlinearities. Because PT-symmetry has been thought of as fragile, experimental realizations to date have been usually restricted to on-chip micro-devices. Here, we demonstrate that certain features of PT-symmetry are sufficiently robust to survive the statistical fluctuations associated with a macroscopic optical cavity. We construct optical-fiber-based coupled-cavities in excess of a kilometer in length (the free spectral range is less than 0.8 fm) with balanced gain and loss in two sub-cavities and examine the lasing dynamics. In such a macroscopic system, fluctuations can lead to a cavity-detuning exceeding the free spectral range. Nevertheless, by varying the gain-loss contrast, we observe that both the lasing threshold and the growth of the laser power follow the predicted behavior of a stable PT-symmetric structure. Furthermore, a statistical symmetry-breaking point is observed upon varying the cavity loss. These findings indicate that PT-symmetry is a more robust optical phenomenon than previously expected, and points to potential applications in optical fiber networks and fiber lasers.Comment: Submitted to Nature Communications, Pages 1-19: Main manuscript; Pages 20-38: Supplementary material

Event-based media monitoring methodology for Human Rights Watch

Executive Summary This report, prepared by a team of researchers from the University of Minnesota for Human Rights Watch (HRW), investigates the use of event-based media monitoring (EMM) to review its application, identify its strengths and weaknesses, and offer suggestions on how HRW can better utilize EMM in its own work. Media monitoring systems include both human-operated (manual) and automated systems, both of which we review throughout the report. The process begins with the selection of news sources, proceeds to the development of a coding manual (for manual searches) or “dictionary” (for automated searches), continues with gathering data, and concludes with the coding of news stories. EMM enables the near real-time tracking of events reported by the media, allowing researchers to get a sense of the scope of and trends in an event, but there are limits to what EMM can accomplish on its own. The media will only cover a portion of a given event, so information will always be missing from EMM data. EMM also introduces research biases of various kinds; mitigating these biases requires careful selection of media sources and clearly defined coding manuals or dictionaries. In manual EMM, coding the gathered data requires human researchers to apply codebook rules in order to collect consistent data from each story they read. In automated EMM, computers apply the dictionary directly to the news stories, automatically picking up the desired information. There are trade-offs in each system. Automated EMM can code stories far more quickly, but the software may incorrectly code stories, requiring manual corrections. Conversely, manual EMM allows for a more nuanced analysis, but the investment of time and effort may diminish the tool’s utility. We believe that both manual and automated EMM, when deployed correctly, can effectively support human rights research and advocacy

Integrable nonlinear parity-time symmetric optical oscillator

The nonlinear dynamics of a balanced parity-time symmetric optical microring arrangement are analytically investigated. By considering gain and loss saturation effects, the pertinent conservation laws are explicitly obtained in the Stokes domain-thus establishing integrability. Our analysis indicates the existence of two regimes of oscillatory dynamics and frequency locking, both of which are analogous to those expected in linear parity-time symmetric systems. Unlike other saturable parity time symmetric systems considered before, the model studied in this work first operates in the symmetric regime and then enters the broken parity-time phase.Comment: 6 pages, 5 figures, accepted for publicatio

Investment in Water-saving Irrigation Options under Uncertainties - A Comparative Analysis

The agricultural sector of Pakistan consumes 96 percent of the country's available fresh water resources. With a population of 187 million and increasing at an annual growth rate of 1.57 percent, the fresh water resources of the country will face severe stresses in the coming years, affecting its food security. At the same time, there is uncertainty prevailing in the region about climate change, timing and intensity of rainfall, flood and drought events, coupled with glacial melt and unresolved issues pertaining to trans-boundary water resource management. Under these circumstances, investment in agricultural practices that ensure crop productivity and water conservation are critical to Pakistan's food security. This study focuses on a sub-region of Punjab in Pakistan, where wheat is grown using flood irrigation. It examines whether an investment into water-saving irrigation options, such as canal lining, dredging, water saving irrigation technologies, and on farm water storage are feasible options to improve profits of the farmers. Irrigation in Pakistan is supplemented with low quality groundwater, which at times leads to very low yields per unit of water. By comparing the discounted cash flows under each of these options, this study investigates the best investment decisions on the part of the farmer and policy makers. This study also looks at the benefits of crop diversification and water markets, to examine whether these options would lead to higher profitability, hedging of risks and productivity in the study area. The economic analysis is complemented with real options analysis, and where applicable, sensitivity analysis to determine the minimum yield increases required to break even

Nonlinear reversal of PT symmetric phase transition in a system of coupled semiconductor micro-ring resonators

A system of two coupled semiconductor-based resonators is studied when lasing around an exceptional point. We show that the presence of nonlinear saturation effects can have important ramifications on the transition behavior of this system. In sharp contrast with linear PT-symmetric configurations, nonlinear processes are capable of reversing the order in which the symmetry breaking occurs. Yet, even in the nonlinear regime, the resulting non-Hermitian states still retain the structural form of the corresponding linear eigenvectors expected above and below the phase transition point. The conclusions of our analysis are in agreement with experimental data.Comment: 9 pages, 8 figure

Do axillary sentinel lymph node micrometastases predict involvement of the non-sentinel lymph nodes in breast cancer?

Palazuelo, PabloLlibre obert fet amb planxes d'acer inoxidable. Fet en motiu del 150è aniversari del naixement de mossèn Jacint Verdaguer. Ubicada davant la finca Vil·la Joana, on el mossèn va morir. N'hi ha un altre al poble de Folgueroles