18,886 research outputs found
TGRS Observations of Positron Annihilation in Classical Novae
The TGRS experiment on board the Wind spacecraft has many advantages as a sky
monitor --- broad field of view (~2 pi) centered on the south ecliptic pole),
long life (1994-present), and stable low background and continuous coverage due
to Wind's high altitude high eccentricity orbit. The Ge detector has sufficient
energy resolution (3-4 keV at 511 keV) to resolve a cosmic positron
annihilation line from the strong background annihilation line from beta-decays
induced by cosmic ray impacts on the instrument, if the cosmic line is
Doppler-shifted by this amount. Such lines (blueshifted) are predicted from
nucleosynthesis in classical novae. We have searched the entire TGRS database
for 1995-1997 for this line, with negative results. In principle such a search
could yield an unbiased upper limit on the highly-uncertain Galactic nova rate.
We carefully examined the times around the known nova events during this
period, also with negative results. The upper limit on the nova line flux in a
6-hr interval is typically <3.8 E-3 photon/(cm2 s) at 4.6 sigma. We performed
the same analysis for times around the outburst of Nova Vel 1999, obtaining a
worse limit due to recent degradation of the detector response caused by cosmic
ray induced damage.Comment: 5 pp. inc. 3 figs. Proc. 5th Compton Symposium (AIP Conf. Series),
ed. M. McConnell, in pres
Convergent Chaos
Chaos is widely understood as being a consequence of sensitive dependence upon initial conditions. This is the result of an instability in phase space, which separates trajectories exponentially. Here, we demonstrate that this criterion should be refined. Despite their overall intrinsic instability, trajectories may be very strongly convergent in phase space over extremely long periods, as revealed by our investigation of a simple chaotic system (a realistic model for small bodies in a turbulent flow). We establish that this strong convergence is a multi-facetted phenomenon, in which the clustering is intense, widespread and balanced by lacunarity of other regions. Power laws, indicative of scale-free features, characterize the distribution of particles in the system. We use large-deviation and extreme-value statistics to explain the effect. Our results show that the interpretation of the 'butterfly effect' needs to be carefully qualified. We argue that the combination of mixing and clustering processes makes our specific model relevant to understanding the evolution of simple organisms. Lastly, this notion of convergent chaos, which implies the existence of conditions for which uncertainties are unexpectedly small, may also be relevant to the valuation of insurance and futures contracts
Properties of the solvation force of a two-dimensional Ising strip in scaling regimes
We consider d=2 Ising strip with surface fields acting on boundary spins.
Using the properties of the transfer matrix spectrum we identify two
pseudotransition temperatures and show that they satisfy similar scaling
relations as expected for real transition temperatures in strips with d>2. The
solvation force between the boundaries of the strip is analysed as a function
of temperature, surface fields and the width of the strip. For large widths the
solvation force can be described by scaling functions in three different
regimes: in the vicinity of the critical wetting temperature of 2D
semi-infinite system, in the vicinity of the bulk critical temperature, and in
the regime of weak surface fields where the critical wetting temperature tends
towards the bulk critical temperature. The properties of the relevant scaling
functions are discussed
Ample consumption period available until use-by dates: a potential, marketing position for store brands
Traditionally store brands in Australia are viewed with suspicion in regard to their quality and are usually purchased because of the "value for money" that they offer. Australian supermarket majors are considering introducing a new suite of store brands in the higher price brackets. The danger of moving upscale however is that these store brands are relinquishing their value for money appeal and will come head to head with the manufactured brands. Store brands will now require some quality dimension to compete. This paper after studying the attitudes and behavioural response of grocery shoppers to use by dates, is proposing that that the promise of "generous" use-by dates as a surrogate for quality, could be considered as a positioning plank to promote store brands as alternatives to manufactured brands. Logit analysis is employed to explain shoppers' perception and response to use-by dates, of products that they regularly buy, and of alternative products which they have never bought before if the use-by dates of their regular items are perceived to be too shor
Maintained physical activity and physiotherapy in the management of distal upper limb pain â a protocol for a randomised controlled trial (the arm pain trial)
<b>Background</b><p></p>
Distal upper limb pain (pain affecting the elbow, forearm, wrist, or hand) can be non-specific, or can arise from specific musculoskeletal disorders. It is clinically important and costly, the best approach to clinical management is unclear. Physiotherapy is the standard treatment and, while awaiting treatment, advice is often given to rest and avoid strenuous activities, but there is no evidence base to support these strategies. This paper describes the protocol of a randomised controlled trial to determine, among patients awaiting physiotherapy for distal arm pain, (a) whether advice to remain active and maintain usual activities results in a long-term reduction in arm pain and disability, compared with advice to rest; and (b) whether immediate physiotherapy results in a long-term reduction in arm pain and disability, compared with physiotherapy delivered after a seven week waiting list period.<p></p>
<b>Methods/Design</b><p></p>
Between January 2012 and January 2014, new referrals to 14 out-patient physiotherapy departments were screened for potential eligibility. Eligible and consenting patients were randomly allocated to one of the following three groups in equal numbers: 1) advice to remain active, 2) advice to rest, 3) immediate physiotherapy. Patients were and followed up at 6, 13, and 26 weeks post-randomisation by self-complete postal questionnaire and, at six weeks, patients who had not received physiotherapy were offered it at this time. The primary outcome is the proportion of patients free of disability at 26 weeks, as determined by the modified DASH (Disabilities of the Arm, Shoulder and Hand) questionnaire.<p></p>
We hypothesise (a) that advice to maintain usual activities while awaiting physiotherapy will be superior than advice to rest the arm; and (b) that fast-track physiotherapy will be superior to normal (waiting list) physiotherapy. These hypotheses will be examined using an intention-to-treat analysis.<p></p>
<b>Discussion</b><p></p>
Results from this trial will contribute to the evidence base underpinning the clinical management of patients with distal upper limb pain, and in particular, will provide guidance on whether they should be advised to rest the arm or remain active within the limits imposed by their symptoms
Wide Range Thin-FIlm Ceramic Metal-Alloy Thermometers with Low Magnetoresistance
Many thermal measurements in high magnetic fields require thermometers that
are sensitive over a wide temperature range, are low mass, have a rapid thermal
response, and have a minimal, easily correctable magnetoresistance. Here we
report the development of a new granular-metal oxide ceramic composite (cermet)
for this purpose formed by co-sputtering of the metallic alloy nichrome
NiCr and the insulator silcon dioxide SiO. The resulting
thin films are sensitive enough to be used from room temperature down to below
100 mK in magnetic fields up to at least 35 tesla
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Design and measurement considerations for WBG switching circuits
Wide Band Gap (WBG) transistors using materials such as Gallium Nitride (GaN) and Silicon Carbide (SiC) offer superior electrical and thermal properties, as well as fast switching capability. However, the high dv/dt and high di/dt may cause ringing with the parasitic inductances and capacitances in the switching loop, increasing overshoot voltages and reducing confidence in the design. Also, making accurate measurements of the switching behaviour without unduly loading the circuit under test is challenging and further impedes the development of WBG applications. This paper presents a prototype WBG Development Platform, built around a half-bridge switched inductive load test circuit. Additional circuits are integrated on to the main PCB for test and measurement purposes: These include a high bandwidth linear current gate-drive circuit and a high bandwidth on-board measurement system. These sub-circuits are described in detail in this paper, together with the switching waveforms that have been achieved during tests with SiC MOSFETs. The authors demonstrate a practical implementation for high frequency WBG power circuits
Confirmation of the \eps -- \eiso (Amati) relation from the X-ray flash XRF 050416A observed by Swift/BAT
We report Swift Burst Alert Telescope (BAT) observations of the X-ray Flash
(XRF) XRF 050416A. The fluence ratio between the 15-25 keV and 25-50 keV energy
bands of this event is 1.5, thus making it the softest gamma-ray burst (GRB)
observed by BAT so far. The spectrum is well fitted by the Band function with
E^{\rm obs}_{\rm peak} of 15.0_{-2.7}^{+2.3} keV. Assuming the redshift of the
host galaxy (z = 0.6535), the isotropic-equivalent radiated energy E_{\rm iso}
and the peak energy at the GRB rest frame (E^{\rm src}_{\rm peak}) of XRF
050416A are not only consistent with the correlation found by Amati et al. and
extended to XRFs by Sakamoto et al., but also fill-in the gap of this relation
around the 30 - 80 keV range of E^{\rm src}_{\rm peak}. This result tightens
the validity of the E^{\rm src}_{\rm peak} - E_{\rm iso} relation from XRFs to
GRBs.
We also find that the jet break time estimated using the empirical relation
between E^{\rm src}_{\rm peak} and the collimation corrected energy E_{\gamma}
is inconsistent with the afterglow observation by Swift X-ray Telescope. This
could be due to the extra external shock emission overlaid around the jet break
time or to the non existence of a jet break feature for XRF, which might be a
further challenging for GRB jet emission, models and XRF/GRB unification
scenarios.Comment: 16 pages, 4 figures; accepted for publication in ApJ
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