Microwave excitation of argon ion and helium-krypton ion lasers

Pulsed microwave excitation of noble gas ion lasers at frequencies between 3 and 17 GHz is investigated. The advantages of using microwaves instead of conventional DC sources to pump a laser are explained. These include the lower electrode and discharge tube wear due to the oscillating nature of a microwave electric field. The propagation of microwave radiation in an ionised gas is examined. At the frequencies used, the skin depth of an Argon ion laser discharge is shown to be approximately 1 mm, indicating good microwave power absorption. The dependence of the microwave power absorption on the frequency is shown to be weak. Microwave transmission at a dielectric/gas-discharge boundary, similar to those in the laser coupling structures used, is found to be around 1% of the incident power. It is suggested that for maximum laser efficiency, microwave power should be introduced directly into the gas discharge. Two microwave coupling structure designs for supplying microwave power to the laser discharges are described. The first of these, a waveguide coupler device based on the 3dB branch guide coupler, produces a transverse electric field across the laser tube. The procedure used to design a branch guide coupler using a Chebyshev impedance taper and T- junction discontinuity corrections is outlined, and a description of the entire laser coupling structure is given. The second design comprises a helix wrapped round the laser tube and produces an axial electric field. The electric field distribution around a helix is calculated as a function of helix parameters and the effects of surrounding objects are considered. The best helix dimensions are found for optimum laser operation. The characteristics of conventional Argon ion and Helium-Krypton ion lasers are given. No significant differences between conventional noble gas ion lasers and the microwave excited lasers reported here are observed. At the input powers used (~100 kW peak, 1 uS pulses, 1000 pps), 100 mW, 1 uS and 30 mW, 5 uS laser pulses are observed from Argon and Helium-Krypton gas mixtures, respectively. The transverse and axially excited lasers perform equally well

Low-Frequency Spectral Energy Distributions of Radio Pulsars Detected with the Murchison Widefield Array

We present low-frequency spectral energy distributions of 60 known radio pulsars observed with the Murchison Widefield Array telescope. We searched the GaLactic and Extragalactic All-sky Murchison Widefield Array survey images for 200-MHz continuum radio emission at the position of all pulsars in the Australia Telescope National Facility (ATNF) pulsar catalogue. For the 60 confirmed detections, we have measured flux densities in 20 × 8 MHz bands between 72 and 231 MHz. We compare our results to existing measurements and show that the Murchison Widefield Array flux densities are in good agreement

The Distressed Brain: A Group Blind Source Separation Analysis on Tinnitus

Background: Tinnitus, the perception of a sound without an external sound source, can lead to variable amounts of distress. Methodology: In a group of tinnitus patients with variable amounts of tinnitus related distress, as measured by the Tinnitus Questionnaire (TQ), an electroencephalography (EEG) is performed, evaluating the patients ’ resting state electrical brain activity. This resting state electrical activity is compared with a control group and between patients with low (N = 30) and high distress (N = 25). The groups are homogeneous for tinnitus type, tinnitus duration or tinnitus laterality. A group blind source separation (BSS) analysis is performed using a large normative sample (N = 84), generating seven normative components to which high and low tinnitus patients are compared. A correlation analysis of the obtained normative components ’ relative power and distress is performed. Furthermore, the functional connectivity as reflected by lagged phase synchronization is analyzed between the brain areas defined by the components. Finally, a group BSS analysis on the Tinnitus group as a whole is performed. Conclusions: Tinnitus can be characterized by at least four BSS components, two of which are posterior cingulate based, one based on the subgenual anterior cingulate and one based on the parahippocampus. Only the subgenual component correlates with distress. When performed on a normative sample, group BSS reveals that distress is characterized by two anterior cingulate based components. Spectral analysis of these components demonstrates that distress in tinnitus is relate

Occupational Noise, Smoking, and a High Body Mass Index are Risk Factors for Age-related Hearing Impairment and Moderate Alcohol Consumption is Protective: A European Population-based Multicenter Study

A multicenter study was set up to elucidate the environmental and medical risk factors contributing to age-related hearing impairment (ARHI). Nine subsamples, collected by nine audiological centers across Europe, added up to a total of 4,083 subjects between 53 and 67 years. Audiometric data (pure-tone average [PTA]) were collected and the participants filled out a questionnaire on environmental risk factors and medical history. People with a history of disease that could affect hearing were excluded. PTAs were adjusted for age and sex and tested for association with exposure to risk factors. Noise exposure was associated with a significant loss of hearing at high sound frequencies (>1 kHz). Smoking significantly increased high-frequency hearing loss, and the effect was dose-dependent. The effect of smoking remained significant when accounting for cardiovascular disease events. Taller people had better hearing on average with a more pronounced effect at low sound frequencies (<2 kHz). A high body mass index (BMI) correlated with hearing loss across the frequency range tested. Moderate alcohol consumption was inversely correlated with hearing loss. Significant associations were found in the high as well as in the low frequencies. The results suggest that a healthy lifestyle can protect against age-related hearing impairment

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

SARS-CoV-2 Omicron is an immune escape variant with an altered cell entry pathway

Vaccines based on the spike protein of SARS-CoV-2 are a cornerstone of the public health response to COVID-19. The emergence of hypermutated, increasingly transmissible variants of concern (VOCs) threaten this strategy. Omicron (B.1.1.529), the fifth VOC to be described, harbours multiple amino acid mutations in spike, half of which lie within the receptor-binding domain. Here we demonstrate substantial evasion of neutralization by Omicron BA.1 and BA.2 variants in vitro using sera from individuals vaccinated with ChAdOx1, BNT162b2 and mRNA-1273. These data were mirrored by a substantial reduction in real-world vaccine effectiveness that was partially restored by booster vaccination. The Omicron variants BA.1 and BA.2 did not induce cell syncytia in vitro and favoured a TMPRSS2-independent endosomal entry pathway, these phenotypes mapping to distinct regions of the spike protein. Impaired cell fusion was determined by the receptor-binding domain, while endosomal entry mapped to the S2 domain. Such marked changes in antigenicity and replicative biology may underlie the rapid global spread and altered pathogenicity of the Omicron variant

Investigation of hospital discharge cases and SARS-CoV-2 introduction into Lothian care homes

Background The first epidemic wave of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in Scotland resulted in high case numbers and mortality in care homes. In Lothian, over one-third of care homes reported an outbreak, while there was limited testing of hospital patients discharged to care homes. Aim To investigate patients discharged from hospitals as a source of SARS-CoV-2 introduction into care homes during the first epidemic wave. Methods A clinical review was performed for all patients discharges from hospitals to care homes from 1st March 2020 to 31st May 2020. Episodes were ruled out based on coronavirus disease 2019 (COVID-19) test history, clinical assessment at discharge, whole-genome sequencing (WGS) data and an infectious period of 14 days. Clinical samples were processed for WGS, and consensus genomes generated were used for analysis using Cluster Investigation and Virus Epidemiological Tool software. Patient timelines were obtained using electronic hospital records. Findings In total, 787 patients discharged from hospitals to care homes were identified. Of these, 776 (99%) were ruled out for subsequent introduction of SARS-CoV-2 into care homes. However, for 10 episodes, the results were inconclusive as there was low genomic diversity in consensus genomes or no sequencing data were available. Only one discharge episode had a genomic, time and location link to positive cases during hospital admission, leading to 10 positive cases in their care home. Conclusion The majority of patients discharged from hospitals were ruled out for introduction of SARS-CoV-2 into care homes, highlighting the importance of screening all new admissions when faced with a novel emerging virus and no available vaccine

MAVIS 2: A New Approach to Content and Concept Based Navigation

One of the most active areas of multimedia research is into content based retrieval (CBR) of multimedia information. Using tools from the disparate disciplines of image processing, audio processing, video processing and others, approaches to CBR for the different media are being produced and integrated into multimedia systems, quite frequently in an ad hoc way. Also, traditional hypertext systems allow textual information to be arbitrarily linked so that users can navigate between related parts of the information in a system. Many of these systems can use multimedia information such as images, sounds and video clips that can also be linked. In such hypermedia systems the links are usually created using specific locations in particular documents. Some systems, such as Microcosm, also allow links to be created by specifying the text that forms one anchor of the link. These links are created once and can be followed from any location where the text occurs. To achieve this, the system has to examine documents currently being viewed by the user and look for matches between text in the documents and text that forms anchors of links within the system. Where matches occur the system can highlight the text as a source anchor for a link. This is a form of content based navigation(CBN). Navigational links are dynamically created by matching the content of currently viewed documents with the content of previously created link anchors. For textual documents this is relatively easy to implement since comparing text strings is often straightforward. Content based navigation for multimedia documents also involves comparing and matching selections of images, video and sound with each other. Our MAVIS 1 project addressed the problem of integrated content based retrieval and navigation from non-text media but there are many limitations associated with such systems. This paper will describe some of the reasons for these limitations and present an overview of MAVIS 2, a new architecture for multimedia content based retrieval and navigation. The architecture not only presents a consistent cross media approach to CBR and CBN but also includes the integration of a multimedia thesaurus which can substantially improve the flexibility and versatility of the multimedia information system, enhancing the capabilities of both content based retrieval and content based navigation. MAVIS stands for Multimedia Architecture for Video, Image and Sound and the MAVIS 2 architecture also includes integration of intelligent agents which support navigation by utilising both the media content and semantic concepts in the multimedia thesaurus to develop rapid paths from media based features to semantic concepts or to generate pseudo thesaurus groupings by feature clustering when no semantic relations are available. MAVIS 2 is currently being implemented and the paper will not only present details of the architecture but also show examples of retrieval and navigation with the prototype system

A Flexible Architecture for Content and Concept Based Multimedia Information Exploration

Traditional hypermedia systems can be extended to allow content based matching to give more flexibility for user navigation, but this approach is still limited by the capabilities of multimedia matching technology. The addition of a multimedia thesaurus can overcome some of these limitations by allowing multimedia representations of concepts to act like synonyms in the query process. In addition, relationships between concepts allow navigation within the context of a semantic scope. The use of agents that independently examine the information in the system can also provide alternative methods for query evaluation. This paper presents a flexible architecture that supports such a system and describes initial work on implementation