1,799 research outputs found
Design of a Thermal and Micrometeorite Protection System for an Unmanned Lunar Cargo Lander
The first vehicles to land on the lunar surface during the establishment phase of a lunar base will be unmanned lunar cargo landers. These landers will need to be protected against the hostile lunar environment for six to twelve months until the next manned mission arrives. The lunar environment is characterized by large temperature changes and periodic micrometeorite impacts. An automatically deployable and reconfigurable thermal and micrometeorite protection system was designed for an unmanned lunar cargo lander. The protection system is a lightweight multilayered material consisting of alternating layers of thermal and micrometeorite protection material. The protection system is packaged and stored above the lander common module. After landing, the system is deployed to cover the lander using a system of inflatable struts that are inflated using residual fuel (liquid oxygen) from the fuel tanks. Once the lander is unloaded and the protection system is no longer needed, the protection system is reconfigured as a regolith support blanket for the purpose of burying and protecting the common module, or as a lunar surface garage that can be used to sort and store lunar surface vehicles and equipment. A model showing deployment and reconfiguration of the protection system was also constructed
Entropic Lattice Boltzmann Simulation of the Flow Past Square Cylinder
Minimal Boltzmann kinetic models, such as lattice Boltzmann, are often used
as an alternative to the discretization of the Navier-Stokes equations for
hydrodynamic simulations.
Recently, it was argued that modeling sub-grid scale phenomena at the kinetic
level might provide an efficient tool for large scale simulations. Indeed, a
particular variant of this approach, known as the entropic lattice Boltzmann
method (ELBM), has shown that an efficient coarse-grained simulation of
decaying turbulence is possible using these approaches.
The present work investigates the efficiency of the entropic lattice
Boltzmann in describing flows of engineering interest. In order to do so, we
have chosen the flow past a square cylinder, which is a simple model of such
flows. We will show that ELBM can quantitatively capture the variation of
vortex shedding frequency as a function of Reynolds number in the low as well
as the high Reynolds number regime, without any need for explicit sub-grid
scale modeling. This extends the previous studies for this set-up, where
experimental behavior ranging from to were
predicted by a single simulation algorithm.Comment: 12 pages, 5 figures, to appear in Int. J. Mod. Phys.
Ketamine as an adjuvant in sympathetic blocks for management of central sensitization following peripheral nerve injury
Proliferation of NMDA receptors and role of glutamate in producing central sensitization and 'wind up' phenomena in CRPS [complex regional pain syndrome] forms a strong basis for the use of Ketamine to block the cellular mechanisms that initiate and maintain these changes. In this case series, we describe 3 patients of CRPS Type II with debilitating central sensitization, heat/mechano allodynia and cognitive symptoms that we termed 'vicarious pain'. Each of these patients had dramatic relief with addition of Ketamine as an adjuvant to the sympathetic blocks after conventional therapy failed
Noncommutative Dynamics of Random Operators
We continue our program of unifying general relativity and quantum mechanics
in terms of a noncommutative algebra on a transformation groupoid
where is the total space of a principal fibre bundle
over spacetime, and a suitable group acting on . We show that
every defines a random operator, and we study the dynamics of
such operators. In the noncommutative regime, there is no usual time but, on
the strength of the Tomita-Takesaki theorem, there exists a one-parameter group
of automorphisms of the algebra which can be used to define a state
dependent dynamics; i.e., the pair , where is a state
on , is a ``dynamic object''. Only if certain additional conditions
are satisfied, the Connes-Nikodym-Radon theorem can be applied and the
dependence on disappears. In these cases, the usual unitary quantum
mechanical evolution is recovered. We also notice that the same pair defines the so-called free probability calculus, as developed by
Voiculescu and others, with the state playing the role of the
noncommutative probability measure. This shows that in the noncommutative
regime dynamics and probability are unified. This also explains probabilistic
properties of the usual quantum mechanics.Comment: 13 pages, LaTe
Earnings Announcement Premia and the Limits to Arbitrage
We document that earnings announcement-day premia persist beyond the sample period of earlier studies, over different disclosure environments and remain robust to the refinement of using the expected announcement day rather than the actual announcement
day. A portfolio of announcing firms yields returns in excess of the corresponding risk.
Excluding announcers from a well-diversified portfolio, while reducing the standard
deviation of that portfolio, also reduces its Sharpe ratio, indicating that this strategy
results in a less favorable risk-return trade-off. Finally, we provide evidence that the premia are dramatically reduced when the announcement risk is reduced through preannouncements. In addition, we document that the continued presence of this premia is
likely to result from limits to arbitrage. These findings are consistent with the view that the announcement period returns are likely to represent compensation for announcement risk
Broadband spectral and temporal study of Ton 599 during the brightest January 2023 flare
In this work, we provide a detailed analysis of the broadband temporal and
spectral properties of the blazar Ton\,599 by using the observations from
\emph{Fermi}-LAT and \emph{Swift}-XRT/UVOT telescopes, during its brightest
-ray flaring. The one-day bin -ray light curve exhibits
multiple substructures with asymmetric and symmetric profiles. Notably, the
-ray light curve shows a maximum flux of on MJD\,59954.50, which is the highest flux ever observed
from this source. The correlation between the -ray flux and
-ray spectral indices suggests a moderate harder when the brighter
trend. Taking -ray light curve as the reference, a strong correlation
is observed with X-ray, optical, and UV energies. Additionally, the
-rays and optical/UV emissions exhibit higher variability compared to
X-rays. To understand the parameter variation during the active state of the
source, we conducted a statistical broadband spectral modelling of the source
in 10 flux intervals of equal duration. A one-zone leptonic model involving
synchrotron, synchrotron-self-Compton, and external-Compton processes
successfully reproduces the broadband SED in each of these flux intervals. We
observed that the flux variation during the active state is mainly associated
with the variation in the magnetic field and the particle spectral indices.Comment: 9 pages, 5 figure
Calcitonin concentrations in patients with chronic kidney disease and medullary thyroid carcinoma or c-cell hyperplasia
It is currently not known which level of pentagastrin-stimulated calcitonin serum concentration indicates medullary thyroid carcinoma in patients with chronic kidney disease (CKD). We examined CKD stage 3–5 patients who had total thyroidectomy because of a pentagastrin-stimulated calcitonin concentration greater than 100pg/ml, and tested the diagnostic performance of basal and pentagastrin-stimulated calcitonin levels for differentiating medullary thyroid carcinoma and C-cell hyperplasia in this patient population. A total of 180 CKD patients presented with an elevated calcitonin level and had a pentagastrin stimulation test. Forty patients showed a maximum pentagastrin-stimulated calcitonin concentration greater than 100pg/ml, and 22 patients had a total thyroidectomy. Seven of these 22 patients presented with a medullary thyroid carcinoma, all other patients showed C-cell hyperplasia. Patients with medullary thyroid carcinoma showed higher unstimulated (212pg/ml (36–577) vs 42pg/ml (17–150); P<0.001) and higher maximum pentagastrin-stimulated calcitonin concentrations (862pg/ml (431–2423) vs 141pg/ml (102–471); P<0.001) as compared to patients with C-cell hyperplasia. The sensitivity (100%) and specificity (93%) estimates suggested that a maximum pentagastrin-stimulated calcitonin concentration greater than 400pg/ml indicates the presence of medullary thyroid carcinoma in patients with CKD. Receiver-operating characteristic (ROC) analysis revealed an area under the ROC plot of 0.99 for maximum pentagastrin-stimulated calcitonin concentrations. A maximum pentagastrin-stimulated calcitonin concentration greater than 400pg/ml appears to be a clinically meaningful threshold for thyroidectomy
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