Constraints on neutrino and dark radiation interactions using cosmological observations

Observations of the cosmic microwave background (CMB) and large-scale structure (LSS) provide a unique opportunity to explore the fundamental properties of the constituents that compose the cosmic dark radiation background (CDRB), of which the three standard neutrinos are thought to be the dominant component. We report on the first constraint to the CDRB rest-frame sound speed, ceff^2, using the most recent CMB and LSS data. Additionally, we report improved constraints to the CDRB viscosity parameter, cvis^2. For a non-interacting species, these parameters both equal 1/3. Using current data we find that a standard CDRB, composed entirely of three non-interacting neutrino species, is ruled out at the 99% confidence level (C.L.) with ceff^2 = 0.30 +0.027 -0.026 and cvis^2 = 0.44 +0.27 -0.21 (95% C.L.). We also discuss how constraints to these parameters from current and future observations (such as the Planck satellite) allow us to explore the fundamental properties of any anomalous radiative energy density beyond the standard three neutrinos.Comment: 6 pages, 3 figures, comments welcome; v2: updated with SPT data, corrected minor typos; v3: version accepted for publication in PR

Computation of outflow rates from accretion disks around black holes

We self-consistently estimate the outflow rate from the accretion rates of an accretion disk around a black hole in which both the Keplerian and the sub-Keplerian matter flows simultaneously. While Keplerian matter supplies soft-photons, hot sub-Keplerian matter supplies thermal electrons. The temperature of the hot electrons is decided by the degree of inverse Comptonization of the soft photons. If we consider only thermally-driven flows from the centrifugal pressure-supported boundary layer around a black hole, we find that when the thermal electrons are cooled down, either because of the absence of the boundary layer (low compression ratio), or when the surface of the boundary layer is formed very far away, the outflow rate is negligible. For an intermediate size of this boundary layer the outflow rate is maximal. Since the temperature of the thermal electrons also decides the spectral state of a black hole, we predict that the outflow rate should be directly related to the spectral state.Comment: 9 pages, 5 figure

Topological phases in a two-dimensional lattice: Magnetic field versus spin-orbit coupling

In this work, we explore the rich variety of topological states that arise in two-dimensional systems, by considering the competing effects of spin-orbit couplings and a perpendicular magnetic field on a honeycomb lattice. Unlike earlier approaches, we investigate minimal models in order to clarify the effects of the intrinsic and Rashba spin-orbit couplings, and also of the Zeeman splitting, on the quantum Hall states generated by the magnetic field. In this sense, our work provides an interesting path connecting quantum Hall and quantum spin Hall physics. First, we consider the properties of each term individually and we analyze their similarities and differences. Secondly, we investigate the subtle competitions that arise when these effects are combined. We finally explore the various possible experimental realizations of our model.Comment: 19 pages, 15 figure

The Interplay of Landau Level Broadening and Temperature on Two-Dimensional Electron Systems

This work investigates the influence of low temperature and broadened Landau levels on the thermodynamic properties of two-dimensional electron systems. The interplay between these two physical parameters on the magnetic field dependence of the chemical potential, the specific heat and the magnetization is calculated. In the absence of a complete theory that explains the Landau level broadening, experimental and theoretical studies in literature perform different model calculations of this parameter. Here it is presented that different broadening parameters of Gaussian-shaped Landau levels cause width variations in their contributions to interlevel and intralevel excitations. Below a characteristic temperature, the interlevel excitations become negligible. Likewise, at this temperature range, the effect of the Landau level broadening vanishes.Comment: 5 pages, 5 figures, submitted to Solid State Communication

Seasonal variation of arsenic concentrations in tubewells in west Bengal, India.

This study was conducted to monitor the changes in arsenic concentration during different seasons in a one-year period during 2002-2003 in selected tubewells in an arsenic-affected area in the district of South 24 Parganas in West Bengal, India, and to map the location of the wells. Seasonal variations in concentrations of arsenic in water were measured from 74 selected tubewells, ranging in depth from 40 to 500 feet. Water samples were collected from these wells during winter, summer, monsoon, and the following winter in 2002-2003. A global positioning system was used for locating the tubewells, and a geographic information system was used for mapping. There was evidence of seasonal variation in concentrations of arsenic in water (p=0.02) with the minimum average concentration occurring in the summer season (694 microg/L) and the maximum in the monsoon season (906 microg/L). From the winter of 2002 to the winter of 2003, arsenic concentrations increased, irrespective of the depth of the tubewells, from an average of 464 microg/L to 820 microg/L (p<0.001). This extent of variation in arsenic concentration, if confirmed, has important implications for both epidemiological research and mitigation programmes

The so-called two dimensional metal-insulator transition

We provide a critical perspective on the collection of low-temperature transport phenomena in low-density two-dimensional semiconductor systems often referred to as the 2D metal-insulator transition. We discuss the physical mechanisms underlying the anomalous behavior of the two-dimensional effective metallic phase and the metal-insulator transition itself. We argue that a key feature of the 2D MIT physics is the long-range bare Coulombic disorder arising from the random distribution of charged impurities in the low-density 2D semiconductor structures.Comment: 12 pages, 4 figures; Revised final version with additional references and some modifications in the tex

Predictors of ophthalmology career success (POCS) study

OBJECTIVE: Ophthalmology is the busiest outpatient specialty with demand predicted to rise over 40% in the next 20 years. A significant increase in the number of trainee ophthalmologists is required to fill currently vacant consultant posts and meet the UK’s workforce demands by 2038. Our aim was to understand what determines success in ophthalmology training, in order to inform future ophthalmologists, refine recruitment and facilitate workforce planning. METHODS AND ANALYSIS: This was a retrospective longitudinal cohort study using routinely collected data available from UK Medical Education Database (UKMED) (https://www.ukmed.ac.uk/). Data were analysed on 1350 candidates who had applied for ophthalmology specialty training (OST) between 2012 and 2018, as well as 495 candidates who had attempted Fellow of the Royal College of Ophthalmologists (FRCOphth) Part 1 between 2013 and 2018. Participants who had not obtained their primary medical qualification from the UK medical schools were excluded. Primary outcome measures included gaining a place on the OST programme and passing the FRCOphth Part 1 examination on first attempt. RESULTS: Higher education performance measure decile scores at medical school are strongly predictive in securing an OST post and passing the part 1 examination first time (p<0.001). Candidates who attempt FRCOphth Part 1 prior to their ST1 application are more likely to get a place on OST on first attempt. Socioeconomic factors, gender and ethnicity do not influence success in OST entry. Male trainees are more likely to pass FRCOphth Part 1 on their first attempt. CONCLUSION: This study is the first quantitative assessment of the factors that determine success in OST recruitment and ophthalmology postgraduate examinations in the UK. Similar studies should be undertaken in all other medical and surgical specialties to understand what factors predict success

Dark Before Light: Testing the Cosmic Expansion History through the Cosmic Microwave Background

The cosmic expansion history proceeds in broad terms from a radiation dominated epoch to matter domination to an accelerated, dark energy dominated epoch. We investigate whether intermittent periods of acceleration are possible in the early universe -- between Big Bang nucleosynthesis (BBN) and recombination and beyond. We establish that the standard picture is remarkably robust: observations of anisotropies in the cosmic microwave background exclude any extra period of accelerated expansion between 1 \leq z \lesssim 10^5 (corresponding to 5\times10^{-4}\ {\rm eV} \leq T \lesssim 25\ {\rm eV}).Comment: 7 pages, 5 figure

Digital Risk Considerations Across Generative AI-Based Mental Health Apps

Mental health platforms on online mobile applications are increasingly adopting generative AI algorithms, however, studies point to the digital risks involved in this adoption. Ethical dilemmas, misinterpretation of complex medical cases, compromised patient privacy, and potential legal liabilities deter generative AI integration with online mobile applications. This study examines 1 million user-generated review comments from 54 applications on various mobile platforms such as Google Store and App Store which use generative AI to provide mental health assistance. The review comments are studied using text-mining approaches to identify the potential digital risks posed to users across these mental healthcare apps. Results from our study aim to guide regulatory frameworks in healthcare in the future