189 research outputs found
Comparison of History Effects in Magnetization in Weakly pinned Crystals of high- and low-T Superconductors
A comparison of the history effects in weakly pinned single crystals of a
high YBaCuO (for H c) and a low
CaRhSn, which show anomalous variations in critical current
density are presented via tracings of the minor magnetization
hysteresis loops using a vibrating sample magnetometer. The sample histories
focussed are, (i) the field cooled (FC), (ii) the zero field cooled (ZFC) and
(iii) an isothermal reversal of field from the normal state. An understanding
of the results in terms of the modulation in the plastic deformation of the
elastic vortex solid and supercooling across order-disorder transition is
sought.Comment: Presented in IWCC-200
Health worker views on pre-treatment loss to follow-up in adults with pulmonary TB in Western Kenya
SETTING:
County referral hospital in Western Kenya.
OBJECTIVES:
To explore factors contributing to pre-treatment loss to follow-up (PTLFU) in adults with pulmonary TB and propose solutions to address PTLFU from healthcare worker (HCW) perspectives.
DESIGN:
This was an exploratory qualitative study using thematic analysis.
RESULTS:
We conducted 19 key informant interviews with HCWs representing laboratory, clinical care, management and the community. Participant age ranged from 26 to 62 years; 14 (74%) were females; and most (74%) had worked in TB care for 5 years. They reported that patients experienced stigma and had misconceptions about TB that contributed to PTLFU. HCWs were hesitant to work in the TB clinic, which contributed to suboptimal patient care, leading to PTLFU. Unclear linkage between laboratory and clinician, and limited financial resources to track patients were among the healthcare system factors that led to PTLFU. HCWs suggested having proper patient preparation, assigning resources to track patients and holding regular interdisciplinary meetings as practical solutions to address PTLFU.
CONCLUSION: HCWs reported multiple factors that may influence PTLFU and recommended various solutions to address these. Knowledge of TB management, patient preparation, resources to track patients and multidisciplinary meetings will be central to addressing PTLFU
Stable and Metastable vortex states and the first order transition across the peak effect region in weakly pinned 2H-NbSe_2
The peak effect in weakly pinned superconductors is accompanied by metastable
vortex states. Each metastable vortex configuration is characterized by a
different critical current density J_c, which mainly depends on the past
thermomagnetic history of the superconductor. A recent model [G. Ravikumar, et
al, Phys. Rev. B 61, R6479 (2000)] proposed to explain the history dependent
J_c postulates a stable state of vortex lattice with a critical current density
J_c^{st}, determined uniquely by the field and temperature. In this paper, we
present evidence for the existence of the stable state of the vortex lattice in
the peak effect region of 2H-NbSe_2. It is shown that this stable state can be
reached from any metastable vortex state by cycling the applied field by a
small amplitude. The minor magnetization loops obtained by repeated field
cycling allow us to determine the pinning and "equilibrium" properties of the
stable state of the vortex lattice at a given field and temperature
unambiguously. The data imply the occurence of a first order phase transition
from an ordered phase to a disordered vortex phase across the peak effect.Comment: 20 pages, 10 figures. Corresponding author: S. Ramakrishna
Disordered Type-II Superconductors: A Universal Phase Diagram for Low-T Systems
A universal phase diagram for weakly pinned low-T type-II superconductors
is revisited and extended with new proposals. The low-temperature ``Bragg
glass'' phase is argued to transform first into a disordered, glassy phase upon
heating. This glassy phase, a continuation of the high-field equilibrium vortex
glass phase, then melts at higher temperatures into a liquid. This proposal
provides an explanation for the anomalies observed in the peak effect regime of
2H-NbSe and several other low-T materials which is independent of the
microscopic mechanisms of superconductivity in these systems.Comment: 23 pages, 9 figure
Effect of pinning and driving force on the metastability effects in weakly pinned superconductors and the determination of spinodal line pertaining to order-disorder transition
We explore the effect of varying drive on metastability features exhibited by
the vortex matter in single crystals of 2H-NbSe and CeRu with varying
degree of random pinning. An optimal balance between the pinning and driving
force is needed to view the metastability effects in typically weakly pinned
specimen of low temperature superconductors. As one uses samples with larger
pinning in order to differentiate the response of different metastable vortex
states, one encounters a new phenomena, viz., the second magnetization peak
(SMP) anomaly prior to the PE. Interplay between the path dependence in the
critical current density and the non-linearity in the electromagnetic response
determine the metastability effects seen in first and the third harmonic
response of the ac susceptibility across the temperature regions of the SMP and
the PE. The limiting temperature above which metastability effects cease can be
conveniently located in the third harmonic data, and the observed behavior can
be rationalized within the Beans Critical State model. A vortex phase diagram
showing the different vortex phases for a typically weakly pinned specimen has
been constructed via the ac susceptibility data in a crystal of 2H-NbSe
which shows the SMP and the PE anomalies. The phase space of coexisting weaker
and stronger pinned regions has been identified. It can be bifurcated into two
parts, where the order and disorder dominate, respectively. The former part
continuously connects to the reentrant disordered vortex phase pertaining to
the small bundle pinning regime, where the vortices are far apart, interaction
effects are weak and the polycrystalline form of flux line lattice prevails.Comment: Submitted to the Special Volume on Vortex State Studies, Pramana J.
Phy
Challenges of rapid reviews for diagnostic test accuracy questions: a protocol for an international survey and expert consultation
Background: Assessment of diagnostic tests, broadly defined as any element that aids in the collection of additional information for further clarification of a patient’s health status, has increasingly become a critical issue in health policy and decision-making. Diagnostic evidence, including the accuracy of a medical test for a target condition, is commonly appraised using standard systematic review methodology. Owing to the considerable time and resources required to conduct these, rapid reviews have emerged as a pragmatic alternative by tailoring methods according to the decision maker’s circumstances. However, it is not known if streamlining methodological aspects has an impact on the validity of evidence synthesis. Furthermore, due to the particular nature and complexity of the appraisal of diagnostic accuracy, there is need for detailed guidance on how to conduct rapid reviews of diagnostic tests. In this study, we aim to identify the methods currently used by rapid review developers to synthesize evidence on diagnostic test accuracy, as well as to analyze potential shortcomings and challenges related to these methods. Methods: We will carry out a two-fold approach: (1) an international survey of professionals working in organizations that develop rapid reviews of diagnostic tests, in terms of the methods and resources used by these agencies when conducting rapid reviews, and (2) semi-structured interviews with senior-level individuals to further explore and validate the findings from the survey and to identify challenges in conducting rapid reviews. We will use STATA 15.0 for quantitative analyses and framework analysis for qualitative analyses. We will ensure protection of data during all stages.
Discussion: The main result of this research will be a map of methods and resources currently used for conducting rapid reviews of diagnostic test accuracy, as well as methodological shortcomings and potential solutions in diagnostic knowledge synthesis that require further research
Data and Image Transfer Using Mobile Phones to Strengthen Microscopy-Based Diagnostic Services in Low and Middle Income Country Laboratories
Background: The emerging market of mobile phone technology and its use in the health sector is rapidly expanding and connecting even the most remote areas of world. Distributing diagnostic images over the mobile network for knowledge sharing, feedback or quality control is a logical innovation. Objective: To determine the feasibility of using mobile phones for capturing microscopy images and transferring these to a central database for assessment, feedback and educational purposes. Methods: A feasibility study was carried out in Uganda. Images of microscopy samples were taken using a prototype connector that could fix a variety of mobile phones to a microscope. An Information Technology (IT) platform was set up for data transfer from a mobile phone to a website, including feedback by text messaging to the end user. Results: Clear images were captured using mobile phone cameras of 2 megapixels (MP) up to 5MP. Images were sent by mobile Internet to a website where they were visualized and feedback could be provided to the sender by means of text message. Conclusion: The process of capturing microscopy images on mobile phones, relaying them to a central review website and feeding back to the sender is feasible and of potential benefit in resource poor settings. Even though the system needs furthe
Are current case-finding methods under-diagnosing tuberculosis among women in Myanmar? An analysis of operational data from Yangon and the nationwide prevalence survey
Modeling the impact of novel diagnostic tests on pediatric and extrapulmonary tuberculosis
HP1 Recruits Activity-Dependent Neuroprotective Protein to H3K9me3 Marked Pericentromeric Heterochromatin for Silencing of Major Satellite Repeats
H3 lysine 9 trimethylation (H3K9me3) is a histone posttranslational modification (PTM) that has emerged as hallmark of pericentromeric heterochromatin. This constitutive chromatin domain is composed of repetitive DNA elements, whose transcription is differentially regulated. Mammalian cells contain three HP1 proteins, HP1α, HP1β and HP1γ These have been shown to bind to H3K9me3 and are thought to mediate the effects of this histone PTM. However, the mechanisms of HP1 chromatin regulation and the exact functional role at pericentromeric heterochromatin are still unclear. Here, we identify activity-dependent neuroprotective protein (ADNP) as an H3K9me3 associated factor. We show that ADNP does not bind H3K9me3 directly, but that interaction is mediated by all three HP1 isoforms in vitro. However, in cells ADNP localization to areas of pericentromeric heterochromatin is only dependent on HP1α and HP1β. Besides a PGVLL sequence patch we uncovered an ARKS motif within the ADNP homeodomain involved in HP1 dependent H3K9me3 association and localization to pericentromeric heterochromatin. While knockdown of ADNP had no effect on HP1 distribution and heterochromatic histone and DNA modifications, we found ADNP silencing major satellite repeats. Our results identify a novel factor in the translation of H3K9me3 at pericentromeric heterochromatin that regulates transcription
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