23,586 research outputs found
“One More for Luck”: The Destruction of U971 by HMCS Haida and HMS Eskimo, 24 June 1944
On the evening of 23 June 1944, HMCS Haida and HMS Eskimo set out from Plymouth, operational base of the 10th Destroyer Flotilla (10th DF), to conduct a sweep of the Western Approaches to the English Channel. Their role was to assist in securing these waters for the ongoing delivery of supplies and reinforcements to the Normandy bridgehead. Across the Channel to the southest, American, British and Canadian forces were now in their third week of fighting across the fields and hedgerows of Normandy. Operation OVERLORD had been the largest amphibious invasion in history and, dependent as it was on the unimpeded use of the sea, required an intensive concentration of air and naval forces to protect Allied supply convoys. This naval counterpart of OVERLORD was Operation NEPTUNE, and it was as part of this massive undertaken that Haida and Eskimo now steamed out of Plymouth
Computer program TRACK performs transient and/or steady state thermal analysis with coupled fluid flow and heat conduction
Computer program called TRACK was developed by combining a transient fluid flow computer code and the existing modified TOSS heat conduction code to perform the computation
On the thermal buffering of naturally ventilated buildings through internal thermal mass
In this paper we examine the role of thermal mass in buffering the interior temperature of a naturally ventilated building from the diurnal fluctuations in the environment. First, we show that the effective thermal mass which is in good thermal contact with the air is limited by the diffusion distance into the thermal mass over one diurnal temperature cycle. We also show that this effective thermal mass may be modelled as an isothermal mass. Temperature fluctuations in the effective thermal mass are attenuated and phase-shifted from those of the interior air, and therefore heat is exchanged with the interior air. The evolution of the interior air temperature is then controlled by the relative magnitudes of (i) the time for the heat exchange between the effective thermal mass and the air; (ii) the time for the natural ventilation to replace the air in the space with air from the environment; and (iii) the period of the diurnal oscillations of the environment. Through analysis and numerical solution of the governing equations, we characterize a number of different limiting cases. If the ventilation rate is very small, then the thermal mass buffers the interior air temperature from fluctuations in the environment, creating a near-isothermal interior. If the ventilation rate increases, so that there are many air changes over the course of a day, but if there is little heat exchange between the thermal mass and interior air, then the interior air temperature locks on to the environment temperature. If there is rapid thermal equilibration of the thermal mass and interior air, and a high ventilation rate, then both the thermal mass and the interior air temperatures lock on to the environment temperature. However, in many buildings, the more usual case is that in which the time for thermal equilibration is comparable to the period of diurnal fluctuations, and in which ventilation rates are moderate. In this case, the fluctuations of the temperature of the thermal mass lag those of the interior air, which in turn lag those of the environment. We consider the implications of these results for the use of thermal mass in naturally ventilated buildings
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Abductive reasoning in neural-symbolic learning systems
Abduction is or subsumes a process of inference. It entertains possible hypotheses and it chooses hypotheses for further scrutiny. There is a large literature on various aspects of non-symbolic, subconscious abduction. There is also a very active research community working on the symbolic (logical) characterisation of abduction, which typically treats it as a form of hypothetico-deductive reasoning. In this paper we start to bridge the gap between the symbolic and sub-symbolic approaches to abduction. We are interested in benefiting from developments made by each community. In particular, we are interested in the ability of non-symbolic systems (neural networks) to learn from experience using efficient algorithms and to perform massively parallel computations of alternative abductive explanations. At the same time, we would like to benefit from the rigour and semantic clarity of symbolic logic. We present two approaches to dealing with abduction in neural networks. One of them uses Connectionist Modal Logic and a translation of Horn clauses into modal clauses to come up with a neural network ensemble that computes abductive explanations in a top-down fashion. The other combines neural-symbolic systems and abductive logic programming and proposes a neural architecture which performs a more systematic, bottom-up computation of alternative abductive explanations. Both approaches employ standard neural network architectures which are already known to be highly effective in practical learning applications. Differently from previous work in the area, our aim is to promote the integration of reasoning and learning in a way that the neural network provides the machinery for cognitive computation, inductive learning and hypothetical reasoning, while logic provides the rigour and explanation capability to the systems, facilitating the interaction with the outside world. Although it is left as future work to determine whether the structure of one of the proposed approaches is more amenable to learning than the other, we hope to have contributed to the development of the area by approaching it from the perspective of symbolic and sub-symbolic integration
Upper limits on the luminosity of the progenitor of type Ia supernova SN2014J
We analysed archival data of Chandra pre-explosion observations of the
position of SN2014J in M82. No X-ray source at this position was detected in
the data, and we calculated upper limits on the luminosities of the progenitor.
These upper limits allow us to firmly rule out an unobscured supersoft X-ray
source progenitor with a photospheric radius comparable to the radius of white
dwarf near the Chandrasekhar mass (~1.38 M_sun) and mass accretion rate in the
interval where stable nuclear burning can occur. However, due to a relatively
large hydrogen column density implied by optical observations of the supernova,
we cannot exclude a supersoft source with lower temperatures, kT < 80 eV. We
find that the supernova is located in the centre of a large structure of soft
diffuse emission, about 200 pc across. The mass, ~3x10^4 M_sun and short
cooling time of the gas, tau_cool ~ 8 Myrs, suggest that it is a
supernova-inflated super-bubble, associated with the region of recent star
formation. If SN2014J is indeed located inside the bubble, it likely belongs to
the prompt population of type Ia supernovae, with a delay time as short as ~ 50
Myrs. Finally, we analysed the one existing post-supernova Chandra observation
and placed upper limit of ~ (1-2) 10^37 erg/s on the X-ray luminosity of the
supernova itself.Comment: 8 pages, 6 figure
Estimating the Economic Viability of a New Crop Alternative for the U.S. Organic Market: Edamame - A Vegetable Soybean
whole farm modeling, edamame, Farm Management, Production Economics,
Karak syndrome: a novel degenerative disorder of the basal ganglia and cerebellum
Two brothers are reported with early onset progressive
cerebellar ataxia, dystonia, spasticity, and intellectual
decline.
• Neuroradiology showed cerebellar atrophy and features
compatible with iron deposition in the putamen
(including the “eye of the tiger sign”) and substantia
nigra.
• Diagnosis was compatible with pantothenate kinase
associated neuropathy resulting from pantothenate
kinase 2 mutation (PKAN due to PANK2) but linkage to
PNAK2 was eliminated suggesting Karak syndrome to
be a novel disorder.
• The “eye of the tiger” sign has previously only been
reported to occur in PKAN due to PKAN
The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005
On 2004 December 27, a highly-energetic giant flare was recorded from the
magnetar candidate SGR 1806-20. In the months preceding this flare, the
persistent X-ray emission from this object began to undergo significant
changes. Here, we report on the evolution of key spectral and temporal
parameters prior to and following this giant flare. Using the Rossi X-ray
Timing Explorer, we track the pulse frequency of SGR 1806-20 and find that the
spin-down rate of this SGR varied erratically in the months before and after
the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for
a discrete jump in spin frequency at the time of the December 27th flare
(|dnu/nu| < 5 X 10^-6). In the months surrounding the flare, we find a strong
correlation between pulsed flux and torque consistent with the model for
magnetar magnetosphere electrodynamics proposed by Thompson, Lyutikov &
Kulkarni (2002). As with the flare in SGR 1900+14, the pulse morphology of SGR
1806-20 changes drastically following the flare. Using the Chandra X-ray
Observatory and other publicly available imaging X-ray detector observations,
we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual
magnetar persistent emission spectral model of a power-law plus a blackbody
provides an excellent fit to the data. We confirm the earlier finding by
Mereghetti et al. (2005) of increasing spectral hardness of SGR 1806-20 between
1993 and 2004. Contrary to the direct correlation between torque and spectral
hardness proposed by Mereghetti et al., we find evidence for a sudden torque
change that triggered a gradual hardening of the energy spectrum on a timescale
of years. Interestingly, the spectral hardness, spin-down rate, pulsed, and
phase-averaged of SGR 1806-20 all peak months before the flare epoch.Comment: 37 pages, 8 figures, 8 tables. Accepted for publication in ApJ. To
appear in the Oct 20 2006 editio
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