664 research outputs found
Superconducting magnesium diboride films on Silicon with Tc0 about 24K grown via vacuum annealing from stoichiometric precursors
Superconducting magnesium diboride films with Tc0 ~ 24 K and sharp transition
\~ 1 K were successfully prepared on silicon substrates by pulsed laser
deposition from a stoichiometric MgB2 target. Contrary to previous reports,
anneals at 630 degree and a background of 2x10^(-4) torr Ar/4%H2 were performed
without the requirement of Mg vapor or an Mg cap layer. This integration of
superconducting MgB2 films on silicon may thus prove enabling in
superconductor-semiconductor device applications. Images of surface morphology
and cross-section profiles by scanning electron microscopy (SEM) show that the
films have a uniform surface morphology and thickness. Energy dispersive
spectroscopy (EDS) reveals these films were contaminated with oxygen,
originating either from the growth environment or from sample exposure to air.
The oxygen contamination may account for the low Tc for those in-situ annealed
films, while the use of Si as the substrate does not result in a decrease in Tc
as compared to other substrates.Comment: 5 pages, 4 figures, 15 references; due to file size limit, images
were blure
Validation of Computational Models of Auxiliary Ventilation Systems with Experimental Data
This paper reports the interim findings of a research program whose objective is to determine whether Computational Fluid Dynamic (CFD) models can be employed to accurately predict the airflow patterns within rapid development headings. In particular, the project aims to investigate the optimum set back distances for the ducts in order to adequately ventilate the face of the drivage. To validate the accuracy of the CFD model simulations measurements were obtained from a series of experiments performed on both scale models and within a full-scale surface gallery. The experimental scale-modeling program included making a series of pressure measurements across the face of the model for equivalent forcing duct setback distances of 5, 10 and 15 m (16, 33 and 50 ft). This pressure data was then plotted as contour plots and compared with the corresponding CFD predictions. A series of full-scale auxiliary ventilation trials were performed within a modified surface gallery. Three-dimensional velocity measurements were taken across a number of cross-sections using an ultrasonic anemometer. Velocity measurements were obtained for three forcing duct setback distances and for a typical force-exhaust overlap configuration
Design and test of optical payload for polarization encoded QKD for Nanosatellites
Satellite based Quantum Key Distribution (QKD) in Low Earth Orbit (LEO) is
currently the only viable technology to span thousands of kilometres. Since the
typical overhead pass of a satellite lasts for a few minutes, it is crucial to
increase the the signal rate to maximise the secret key length. For the QUARC
CubeSat mission due to be launched within two years, we are designing a dual
wavelength, weak-coherent-pulse decoy-state Bennett-Brassard '84 (WCP DS BB84)
QKD source. The optical payload is designed in a
bespoke aluminium casing. The Discrete Variable QKD Source consists of two
symmetric sources operating at 785 nm and 808 nm. The laser diodes are fixed to
produce Horizontal,Vertical, Diagonal, and Anti-diagonal (H,V,D,A) polarisation
respectively, which are combined and attenuated to a mean photon number of 0.3
and 0.5 photons/pulse. We ensure that the source is secure against most side
channel attacks by spatially mode filtering the output beam and characterising
their spectral and temporal characterstics. The extinction ratio of the source
contributes to the intrinsic Qubit Error Rate(QBER) with .
This source operates at 200MHz, which is enough to provide secure key rates of
a few kilo bits per second despite 40 dB of estimated loss in the free space
channe
Effective Vortex Pinning in MgB2 thin films
We discuss pinning properties of MgB2 thin films grown by pulsed-laser
deposition (PLD) and by electron-beam (EB) evaporation. Two mechanisms are
identified that contribute most effectively to the pinning of vortices in
randomly oriented films. The EB process produces low defected crystallites with
small grain size providing enhanced pinning at grain boundaries without
degradation of Tc. The PLD process produces films with structural disorder on a
scale less that the coherence length that further improves pinning, but also
depresses Tc
Developing a framework for the analysis of power through depotentia
Stakeholder participation in tourism policy-making is usually perceived as providing a means of empowerment. However participatory processes drawing upon stakeholders from traditionally empowered backgrounds may provide the means of removing empowerment from stakeholders. Such an outcome would be in contradiction to the claims that participatory processes improve both inclusivity and sustainability. In order to form an understanding of the sources through which empowerment may be removed, an analytical perspective has been developed deriving from Lukes�s views of power dating from 1974. This perspective considers the concept of depotentia as the removal of �power to� without speculating upon the underlying intent and also provides for the multidimensionality of power to be examined within a single study. The application of this analytical perspective has been tested upon findings of the government-commissioned report of the Countryside and Community Research Unit in 2005. The survey and report investigated the progress of Local Access Forums in England created in response to the Countryside and Rights of Way Act 2000. Consideration of the data from this perspective permits the classification of individual sources of depotentia which can each be addressed and potentially enable stakeholder groups to reverse loss of empowerment where it has occurred
Task analysis method for procedural training curriculum development
A central venous catheter (CVC) is an important medical tool used in critical care and emergent situations. Integral to proper care in many circumstances, insertion of a CVC introduces the risk of central line-associated blood stream infections and mechanical adverse events; proper training is important for safe CVC insertion. Cognitive task analysis (CTA) methods have been successfully implemented in the medical field to improve the training of postgraduate medical trainees, but can be very time-consuming to complete and require a significant time commitment from many subject matter experts (SMEs). Many medical procedures such as CVC insertion are linear processes with well-documented procedural steps. These linear procedures may not require a traditional CTA to gather the information necessary to create a training curriculum. Accordingly, a novel, streamlined CTA method designed primarily to collect cognitive cues for linear procedures was developed to be used by medical professionals with minimal CTA training. This new CTA methodology required fewer trained personnel, fewer interview sessions, and less time commitment from SMEs than a traditional CTA. Based on this study, a streamlined CTA methodology can be used to efficiently gather cognitive information on linear medical procedures for the creation of resident training curricula and procedural skills assessments
Spatial and temporal changes in cumulative human impacts on the world's ocean
Human pressures on the ocean are thought to be increasing globally, yet we know little about their patterns of cumulative change, which pressures are most responsible for change, and which places are experiencing the greatest increases. Managers and policymakers require such information to make strategic decisions and monitor progress towards management objectives. Here we calculate and map recent change over 5 years in cumulative impacts to marine ecosystems globally from fishing, climate change, and ocean- and land-based stressors. Nearly 66% of the ocean and 77% of national jurisdictions show increased human impact, driven mostly by climate change pressures. Five percent of the ocean is heavily impacted with increasing pressures, requiring management attention. Ten percent has very low impact with decreasing pressures. Our results provide large-scale guidance about where to prioritize management efforts and affirm the importance of addressing climate change to maintain and improve the condition of marine ecosystems
Prospects for local co-governance
British local authorities and their partners are increasingly developing new ways of working together with local communities. The nature of this co-working, however, is complex, multi-faceted and little understood. This article argues for greater clarity of thinking on the topic, by analysing this co-working as a form of political co-governance, and drawing attention in particular to issues of scale and democracy. Using evidence from a study of 43 local authority areas, 16 authorities are identified where co-governance is practised, following three main types of approach: service-influencing, service-delivering and parish council developing. It is concluded that strengthening political co-governance is essential for a healthy democracy
Growth mechanism of superconducting MgB2 films prepared by various methods
The growth mechanisms of MgB2 films obtained by different methods on various
substrates are compared via a detailed cross-sectional scanning electron
microscopy (SEM) study. The analyzed films include (a) samples obtained by an
ex-situ post-anneal at 900 degree of e-beam evaporated boron in the presence of
an Mg vapor (exhibiting bulk-like Tc0 about 38.8 K), (b) samples obtained by
the same ex-situ 900 degree anneal of pulsed laser deposition (PLD)-grown Mg+B
precursors (exhibiting Tc0 ~ 25 K), and (c) films obtained by a low-temperature
(600 - 630 degree) in-situ anneal of PLD-grown Mg+B precursors (with Tc0 about
24 K). A significant oxygen contamination was also present in films obtained
from a PLD-grown precursors. On the other hand, it is clearly observed that the
films obtained by the high-temperature reaction of e-beam evaporated B with Mg
vapor are formed by the nucleation of independent MgB2 grains at the film
surface, indicating that this approach may not be suitable to obtain smooth and
(possibly) epitaxial films.Comment: 1 table, 4 figures, 17 references, 16 pages PDF fil
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