Techniques for High Contrast Imaging in Multi-Star Systems II: Multi-Star Wavefront Control

Direct imaging of exoplanets represents a challenge for astronomical instrumentation due to the high-contrast ratio and small angular separation between the host star and the faint planet. Multi-star systems pose additional challenges for coronagraphic instruments because of the diffraction and aberration leakage introduced by the additional stars, and as a result are not planned to be on direct imaging target lists. Multi-star wavefront control (MSWC) is a technique that uses a coronagraphic instrument's deformable mirror (DM) to create high-contrast regions in the focal plane in the presence of multiple stars. Our previous paper introduced the Super-Nyquist Wavefront Control (SNWC) technique that uses a diffraction grating to enable the DM to generate high-contrast regions beyond the nominal controllable region. These two techniques can be combined to generate high-contrast regions for multi-star systems at any angular separations. As a case study, a high-contrast wavefront control (WC) simulation that applies these techniques shows that the habitable region of the Alpha Centauri system can be imaged reaching 8 times 10(exp -9) mean contrast in 10 percent broadband light in one-sided dark holes from 1.6-5.5 lambda (wavelength) divided by D (distance)

COHESION, CONSENSUS AND EXTREME INFORMATION IN OPINION DYNAMICS

Opinion formation is an important element of social dynamics. It has been widely studied in the last years with tools from physics, mathematics and computer science. Here, a continuous model of opinion dynamics for multiple possible choices is analysed. Its main features are the inclusion of disagreement and possibility of modulating external information/media effects, both from one and multiple sources. The interest is in identifying the effect of the initial cohesion of the population, the interplay between cohesion and media extremism, and the effect of using multiple external sources of information that can influence the system. Final consensus, especially with the external message, depends highly on these factors, as numerical simulations show. When no external input is present, consensus or segregation is determined by the initial cohesion of the population. Interestingly, when only one external source of information is present, consensus can be obtained, in general, only when this is extremely neutral, i.e., there is not a single opinion strongly promoted, or in the special case of a large initial cohesion and low exposure to the external message. On the contrary, when multiple external sources are allowed, consensus can emerge with one of them even when this is not extremely neutral, i.e., it carries a strong message, for a large range of initial conditions

BiDAl: Big Data Analyzer for Cluster Traces

Modern data centers that provide Internet-scale services are stadium-size structures housing tens of thousands of heterogeneous devices (server clusters, networking equipment, power and cooling infrastructures) that must operate continuously and reliably. As part of their operation, these devices produce large amounts of data in the form of event and error logs that are essential not only for identifying problems but also for improving data center efficiency and management. These activities employ data analytics and often exploit hidden statistical patterns and correlations among different factors present in the data. Uncovering these patterns and correlations is challenging due to the sheer volume of data to be analyzed. This paper presents BiDAl, a prototype “log-data analysis framework” that incorporates various Big Data technologies to simplify the analysis of data traces from large clusters. BiDAl is written in Java with a modular and extensible architecture so that different storage backends (currently, HDFS and SQLite are supported), as well as different analysis languages (current implementation supports SQL, R and Hadoop MapReduce) can be easily selected as appropriate. We present the design of BiDAl and describe our experience using it to analyze several public traces of Google data clusters for building a simulation model capable of reproducing observed behavior

A public dataset of 24-H multi-levels psycho-physiological responses in young healthy adults

Wearable devices now make it possible to record large quantities of physiological data, which can be used to obtain a clearer view of a person’s health status and behavior. However, to the best of our knowledge, there are no open datasets in the literature that provide psycho-physiological data. The Multilevel Monitoring of Activity and Sleep in Healthy people (MMASH) dataset presented in this paper provides 24 h of continuous psycho-physiological data, that is, inter-beat intervals data, heart rate data, wrist accelerometry data, sleep quality index, physical activity (i.e., number of steps per second), psychological characteristics (e.g., anxiety status, stressful events, and emotion declaration), and sleep hormone levels for 22 participants. The MMASH dataset will enable the investigation of possible relationships between the physical and psychological characteristics of people in daily life. Data were validated through different analyses that showed their compatibility with the literature

Few-mode metal-free perovskite optical fiber with second-order optical nonlinearity

Semiconductor core optical fibers are highly desirable for fiber-based photonic and optoelectronic applications as they can combine strong optical nonlinearities, tight light confinement, wide transmission bands, and electronic functionality within a single platform. Perovskites have emerged as particularly exciting materials for semiconductor photonics as they have strong optical nonlinearities and tunable optoelectronic bandgaps. However, lead-based perovskites contain toxic elements and are, therefore, not environmentally friendly. Furthermore, in fiber form, their core-size is prohibitively large, making them unsuitable for nonlinear optics and applications that require single-mode guidance, such as telecommunications. Here, we report a metal-free perovskite core optical fiber where lead has been substituted for an ammonium cation in the perovskite structure. The core material has a wide bandgap greater than 5 eV, a high laser damage threshold, and a core diameter that can be produced as small as 5 \ub5m. At this core size, the fiber supports just six modes, and the fundamental mode can readily be excited and isolated. Moreover, the metal-free perovskite has a second-order susceptibility that is absent in the archetypal lead-based perovskites and many other semiconductor core materials, such as silicon and germanium. The second-order susceptibility is important for many nonlinear optics applications, such as second-harmonic generation and quantum optics

Untangling free carrier and exciton dynamics in layered hybrid perovskites using ultrafast optical and terahertz spectroscopy

\ua9 2024 The Author(s). Published by IOP Publishing Ltd.Layered hybrid perovskites (LPKs) are promising as alternatives or additives to 3D metal halide perovskites for optoelectronic applications including photovoltaic cells, LEDs and lasers due to their increased stability. However, high exciton binding energies in these materials mean that excitons are the majority species under the operating conditions of many devices. Although the efficiency of devices that incorporate LPKs has been increasing, much is still unknown about the interplay of excitons and free charge-carriers in these materials, which is vital information for understanding how optoelectronic properties dictate device efficiency. In this work, we employ optical pump/THz probe spectroscopy (OPTP) and visible transient absorption spectroscopy (TAS) to analyse the optoelectronic properties and charge-carrier dynamics of phenylethylammonium lead iodide (PEA)2PbI4. By combining these techniques, we are able to disentangle the contributions from excitons and free charge-carriers. We observe fast cooling of free charge-carriers and exciton formation on a timescale of ∼400 fs followed by slower bimolecular recombination of residual free charge-carriers with a rate constant k 2 ∼ 109 cm3s−1. Excitons recombine via two monomolecular processes with lifetimes t 1 ∼ 11 ps and t2 ∼ 83 ps. Furthermore, we detect signatures of exciton-phonon coupling in the transient absorption kinetic traces. These findings provide new insight into the interplay between free charge-carriers and excitons as well as a possible mechanism to further understand the charge-carrier dynamics in LPKs

A comparative study of rehabilitation methods of patients with edentulous arches associated with insufficient bone volume

Ilarion Postolachi Department of Prosthodontics, Nicolae Testemitsanu State University of Medicine and Pharmacy, Chisinau, the Republic of MoldovaBackground: The rehabilitation of patients with insufficient bone support may be difficult because of multiple disturbances from stomatognathic system and the necessity to reestablish the lost bone volume. Material and methods: In this study were included 24 patients who were treated with conventional prosthesis (15 patients) and fixed implanting supported prosthesis (9 patients). Results: Implant-prosthetic rehabilitation with preliminary bone augmentation has esthetic, functional and biomechanical advantages over conventional prosthesis but it is more costly, traumatic and requires a long rehabilitation period with multiple surgical procedures. However, because of their disadvantages and hard conditions these prostheses are not always functional may not fully restore the lost functions of stomatognathic system. The necessity of additional surgical procedures, a higher cost and a longer rehabilitation time limit the applicability of this method. Conclusions: Implant supported prostheses provide a psychological comfort and prevent the progression of bone atrophy. Rehabilitation with conventional prostheses permits to restore the lost soft and hard tissue volume and patients’ integration into the society. Bone grafting allows restoring of lost soft and hard tissue volume which allows inserting of implants of standard size and manufacture of functional and aesthetical restorations. The questionnaire analysis has shown that patients that wore conventional prostheses for many years are usually unsatisfied by their performance and require implant prosthetic rehabilitation with fixed restorations. The last ones are well tolerated by patients and provide a psychological comfort that cannot be achieved with conventional prostheses