3,284 research outputs found
Anderson impurity in pseudo-gap Fermi systems
We use the numerical renormalization group method to study an Anderson
impurity in a conduction band with the density of states varying as rho(omega)
\propto |omega|^r with r>0. We find two different fixed points: a local-moment
fixed point with the impurity effectively decoupled from the band and a
strong-coupling fixed point with a partially screened impurity spin. The
specific heat and the spin-susceptibility show powerlaw behaviour with
different exponents in strong-coupling and local-moment regime. We also
calculate the impurity spectral function which diverges (vanishes) with
|omega|^{-r} (|\omega|^r) in the strong-coupling (local moment) regime.Comment: 8 pages, LaTeX, 4 figures includes as eps-file
Measuring Interaction Design before Building the System: a Model-Based Approach
Early prototyping of user interfaces is an established good practice in interactive system development. However, prototypes cover only some usage scenarios, and questions dealing with number of required steps, possible interaction paths or impact of possible user errors can be answered only for the specific scenarios and only after tedious manual inspection. We present a tool (MIGTool) that transforms models of the behavior of a user interface into a graph, upon which usage scenarios can be easily specified, and used by MIGTool to compute possible interaction paths. Metrics based on possible paths, with or without user navigation errors, can then be computed. For example, when analyzing four mail applications, we show that Gmail has 3 times more shortest routes, has twice more routes that include a single user error, has routes with 13\ufewer steps, but has also optimal routes with the smallest probability to be chosen. Without MIGTool, this kind of analysis could only be done after building some prototype of the system, and then only for specific scenarios by manually tracing user actions and relative changes to the screens. With MIGTool the exploration of suitability of a design with respect to different scenarios, or comparison of different design alternatives against a single scenario, can be done with just a partial specification of the user interface behavior. This is made possible by the ability to associate scenarios steps to required user actions as defined in the model, by an efficient strategy to identify complete execution traces that users can follow, and by computing a range of diverse metrics on these results
The impact of an operation and management intervention on toilet usability in schools in the Philippines:A cluster randomised controlled trial
Adequacy of a pre-participation examination form: a study of Hawaii physicians.
Many states currently require a medical screening prior to participation in organized sports. The purpose of this study was to examine the adequacy of the existing pre-participation examination form in Hawaii. One hundred forty-eight physicians who perform school health/pre-participation physical examinations were surveyed. The results indirectly suggest that these physicians agreed that the form should be modified and improved (p, .001)
Lessons from the evaluation of the UK's NHS R&D Implementation Methods Programme
Background: Concern about the effective use of research was a major factor behind the creation
of the NHS R&D Programme in 1991. In 1994, an advisory group was established to identify
research priorities in research implementation. The Implementation Methods Programme (IMP)
flowed from this, and its commissioning group funded 36 projects. In 2000 responsibility for the
programme passed to the National Co-ordinating Centre for NHS Service Delivery and
Organisation R&D, which asked the Health Economics Research Group (HERG), Brunel University,
to conduct an evaluation in 2002. By then most projects had been completed. This evaluation was
intended to cover: the quality of outputs, lessons to be learnt about the communication strategy
and the commissioning process, and the benefits from the projects.
Methods: We adopted a wide range of quantitative and qualitative methods. They included:
documentary analysis, interviews with key actors, questionnaires to the funded lead researchers,
questionnaires to potential users, and desk analysis.
Results: Quantitative assessment of outputs and dissemination revealed that the IMP funded useful
research projects, some of which had considerable impact against the various categories in the
HERG payback model, such as publications, further research, research training, impact on health
policy, and clinical practice.
Qualitative findings from interviews with advisory and commissioning group members indicated
that when the IMP was established, implementation research was a relatively unexplored field. This
was reflected in the understanding brought to their roles by members of the advisory and
commissioning groups, in the way priorities for research were chosen and developed, and in how
the research projects were commissioned. The ideological and methodological debates associated
with these decisions have continued among those working in this field. The need for an effective
communication strategy for the programme as a whole was particularly important. However, such
a strategy was never developed, making it difficult to establish the general influence of the IMP as a
programme.
Conclusion: Our findings about the impact of the work funded, and the difficulties faced by those
developing the IMP, have implications for the development of strategic programmes of research in
general, as well as for the development of more effective research in this field
Multi-Wavelength Coverage of State Transitions in the New Black Hole X-Ray Binary Swift J1910.2-0546
Understanding how black holes accrete and supply feedback to their
environment is one of the outstanding challenges of modern astrophysics. Swift
J1910.2-0546 is a candidate black hole low-mass X-ray binary that was
discovered in 2012 when it entered an accretion outburst. To investigate the
binary configuration and the accretion morphology we monitored the evolution of
the outburst for ~3 months at X-ray, UV, optical (B,V,R,I), and near-infrared
(J,H,K) wavelengths using Swift and SMARTS. The source evolved from a hard to a
soft X-ray spectral state with a relatively cold accretion disk that peaked at
~0.5 keV. A Chandra/HETG spectrum obtained during this soft state did not
reveal signatures of an ionized disk wind. Both the low disk temperature and
the absence of a detectable wind could indicate that the system is viewed at
relatively low inclination. The multi-wavelength light curves revealed two
notable features that appear to be related to X-ray state changes. Firstly, a
prominent flux decrease was observed in all wavebands ~1-2 weeks before the
source entered the soft state. This dip occurred in (0.6-10 keV) X-rays ~6 days
later than at longer wavelengths, which could possibly reflect the viscous time
scale of the disk. Secondly, about two weeks after the source transitioned back
into the hard state, the UV emission significantly increased while the X-rays
steadily decayed. We discuss how these observations may reflect changes in the
accretion flow morphology, perhaps related to the quenching/launch of a jet or
the collapse/recovery of a hot flow.Comment: 8 pages, 5 figures, 1 table. To be published in Ap
Local quantum phase transition in the pseudogap Anderson model: scales, scaling and quantum critical dynamics
The pseudogap Anderson impurity model provides a paradigm for understanding
local quantum phase transitions, in this case between generalised fermi liquid
and degenerate local moment phases. Here we develop a non-perturbative local
moment approach to the generic asymmetric model, encompassing all energy scales
and interaction strengths and leading thereby to a rich description of the
problem. We investigate in particular underlying phase boundaries, the critical
behaviour of relevant low-energy scales, and single-particle dynamics embodied
in the local spectrum. Particular attention is given to the resultant universal
scaling behaviour of dynamics close to the transition in both the GFL and LM
phases, the scale-free physics characteristic of the quantum critical point
itself, and the relation between the two.Comment: 39 pages, 19 figure
X-Ray Observations of V4641 SGR (= SAX J1819.3-2525) During the Brief and Violent Outburst of 2003
We present the results of detailed analysis of pointed X-ray observations by
RXTE PCA/HEXTE of the black hole X-ray binary (BHXRB) system V4641 Sgr (= SAX
J1819.3-2525) during its outburst of August 2003. Soft X-ray (3-20 keV) flux
variations by factors of 10 or more on timescales of minutes or shorter were
seen. The rapid and strong variability of this source sets it apart from
typical XRBs. In spite of large luminosity fluctuations, the spectral state of
the source did not change significantly during the dwells which suggests that
the physical emission processes did not change much during the observations.
The energy spectra during the dwells were dominated by a hard Comptonized
powerlaw component, indicative of the canonical low/hard state observed in
other BHXRBs. No soft thermal component was found in three out of the four RXTE
pointings. However spectral deconvolution of the observation with largest
average luminosity suggests an obscured, hot accretion disk. During one of the
observations we detected a short term (about 100s) soft X-ray dropout which is
apparently due to variability in the observed column density. Strong Fe
K fluorescent emisssion line near 6.5 keV was detected with large
equivalent widths in the range of 700 - 1000eV. In the temporal domain, the
Fourier power spectra were dominated by red noise below a few Hz. Poisson noise
dominated at higher frequencies and no high frequency features were detected.
The strong Comptonized spectra, broad iron emission line, absence of disk
component in the spectra, absence of any timing variability above few Hz and
occasional large changes in the column density along the line-of-sight, all
support an enshrouded black hole with occasional outflow and a very dynamic
environment.Comment: 27 pages, 10 figures (1 color figure), accepted for publication in
the Astrophysical Journal. It is tentatively scheduled for the ApJ 01
February 2006, v637, 2 issu
Specific heat of Ce_{0.8}La_{0.2}Al_{3} in magnetic fields: a test of the anisotropic Kondo picture
The specific heat C of Ce_{0.8}La_{0.2}Al_{3} has been measured as a function
of temperature T in magnetic fields up to 14 T. A large peak in C at 2.3 K has
recently been ascribed to an anisotropic Kondo effect in this compound. A 14-T
field depresses the temperature of the peak by only 0.2 K, but strongly reduces
its height. The corresponding peak in C/T shifts from 2.1 K at zero field to
1.7 K at 14 T. The extrapolated specific heat coefficient C/T(T->0) increases
with field over the range studied. We show that these trends are inconsistent
with the anisotropic Kondo model.Comment: 4 pages, 5 figures, ReVTeX + eps
- âŠ