4,694 research outputs found
Dynamic Server Allocation over Time Varying Channels with Switchover Delay
We consider a dynamic server allocation problem over parallel queues with
randomly varying connectivity and server switchover delay between the queues.
At each time slot the server decides either to stay with the current queue or
switch to another queue based on the current connectivity and the queue length
information. Switchover delay occurs in many telecommunications applications
and is a new modeling component of this problem that has not been previously
addressed. We show that the simultaneous presence of randomly varying
connectivity and switchover delay changes the system stability region and the
structure of optimal policies. In the first part of the paper, we consider a
system of two parallel queues, and develop a novel approach to explicitly
characterize the stability region of the system using state-action frequencies
which are stationary solutions to a Markov Decision Process (MDP) formulation.
We then develop a frame-based dynamic control (FBDC) policy, based on the
state-action frequencies, and show that it is throughput-optimal asymptotically
in the frame length. The FBDC policy is applicable to a broad class of network
control systems and provides a new framework for developing throughput-optimal
network control policies using state-action frequencies. Furthermore, we
develop simple Myopic policies that provably achieve more than 90% of the
stability region. In the second part of the paper, we extend our results to
systems with an arbitrary but finite number of queues.Comment: 38 Pages, 18 figures. arXiv admin note: substantial text overlap with
arXiv:1008.234
Recommended from our members
Empire and nation in the city : Christians, Muslims and Jews in Ottoman and Post-Ottoman Ruse, 1864-1885
My dissertation explores how people of various ethnic and religious backgrounds experienced the transition from Ottoman rule to Bulgarian nation state in the city of Ruse, in present-day northern Bulgaria. It examines the transformative effects of the Ottoman Tanzimat reforms (1864-1876), the Russo-Ottoman War of 1877-8, the Russian provisional government and the early years of a Bulgarian national government. It argues Bulgarian nationalism was not a uniform and deterministic ideology but was rather a complex and contested phenomenon that left room for multiple loyalties and self-definitions. Through various reform programs, the Ottoman Empire also put together its own alternative to Bulgarian nationalism—secular Ottomanism—, which was progressive and open to different perspectives and integrated Bulgarian Christians into the Ottoman political system. After Ottoman withdrawal, the transfer of power to Bulgarian Christians and the marginalization and disenfranchisement of Muslims was not drastic or immediate, but rather a gradual process. Residents of Ruse’s diverse urban environment responded to these political changes through a complex interplay of urban dynamics, political and religious loyalties, and self-interest, rather than inflexible nationalist or imperial ideology.Histor
Interactions mechanism of commonly used drugs for the treatment of Covid-19
In this study conformation analysis of seven drugs commonly used in the treatment of COVID-19 was performed. The most stable conformers of the drug molecules were used as initial data for docking analysis. Using the Cavityplus program, the probable most active binding sites of both apo and holo forms of COVID-19 main protease enzyme (Mpro) and spike glycoprotein of SARSCoV-2 receptors were determined. The interaction mechanisms of the 7 FDA approved drugs (arbidol, colchicine, dexamethasone, favipiravir, galidesivir, hydroxychloroquine, remdesivir) were examined using the AutoDock Vina program. The six of the seven drugs were found to be more stable in binding to apo form of COVID-19 Mpro and spike glycoprotein. Moreover, a set of molecular mechanics (MM) Poisson-Boltzmann (PB) surface area (SA) calculations on the investigated drugs-protein systems were performed and the estimated binding free energy of remdesivir and the apo form of Mpro system was found to be the best. The interaction results of FDA drugs with the apo form of COVID-19 Mpro and spike glycoprotein can play an important role for the treatment of COVID-19.
KEY WORDS: COVID-19, Drugs, Molecular modelling, Conformational analysis, Molecular docking
Bull. Chem. Soc. Ethiop. 2020, 34(3), 613-623.
DOI: https://dx.doi.org/10.4314/bcse.v34i3.1
Cavitation phenomena in a stagnation point flow
Cavitation phenomena inherently occur in regions with low pressure. Consequently, it seems unlikely that cavitation would develop near the stagnation point of a blunt body flow. However, in recent experiments involving a high-speed bubbly jet impinging on a blunt body, we have observed substantial rapid growth and stretching of bubbles near the stagnation point over a wide range of flow parameters. Using a highspeed camera we observe that bubbles with initial diameters of tens of microns located very close to the blunt body are being stretched into long strings that are generally aligned parallel to the body surface. In-line Digital Holographic Microscopy (DHM) measurements show that the bubble strings are located far from the walls. High resolution 3-D holographic Particle Image Velocimetry (DHM-PIV) is performed to quantify the 3-D flow field near the leading edge of the blunt body. Instantaneous data show vortices being stretched by the local strain field close to the blunt body in an orientation consistent with the appearance of cavitation. These vortices are originated from the turbulent jet upstream. An estimate based on the measured vortex strength and strain field shows that stretching rapidly decreases the pressure in the vortex core below the vapor pressure, explaining the occurrence of cavitation.http://deepblue.lib.umich.edu/bitstream/2027.42/84222/1/CAV2009-final179.pd
Multicanonical Study of the 3D Ising Spin Glass
We simulated the Edwards-Anderson Ising spin glass model in three dimensions
via the recently proposed multicanonical ensemble. Physical quantities such as
energy density, specific heat and entropy are evaluated at all temperatures. We
studied their finite size scaling, as well as the zero temperature limit to
explore the ground state properties.Comment: FSU-SCRI-92-121; 7 pages; sorry, no figures include
A Reduced Order Model for the Design of Oxy-Coal Combustion Systems
Oxy-coal combustion is one of the more promising technologies currently under development for addressing the issues associated with greenhouse gas emissions from coal-fired power plants. Oxy-coal combustion involves combusting the coal fuel in mixtures of pure oxygen and recycled flue gas (RFG) consisting of mainly carbon dioxide (CO2). As a consequence, many researchers and power plant designers have turned to CFD simulations for the study and design of new oxy-coal combustion power plants, as well as refitting existing air-coal combustion facilities to oxy-coal combustion operations. While CFD is a powerful tool that can provide a vast amount of information, the simulations themselves can be quite expensive in terms of computational resources and time investment. As a remedy, a reduced order model (ROM) for oxy-coal combustion has been developed to supplement the CFD simulations. With this model, it is possible to quickly estimate the average outlet temperature of combustion flue gases given a known set of mass flow rates of fuel and oxidant entering the power plant boiler as well as determine the required reactor inlet mass flow rates for a desired outlet temperature. Several cases have been examined with this model. The results compare quite favorably to full CFD simulation results
Radiation Testing of Electronics for the CMS Endcap Muon System
The electronics used in the data readout and triggering system for the
Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC)
particle accelerator at CERN are exposed to high radiation levels. This
radiation can cause permanent damage to the electronic circuitry, as well as
temporary effects such as data corruption induced by Single Event Upsets. Once
the High Luminosity LHC (HL-LHC) accelerator upgrades are completed it will
have five times higher instantaneous luminosity than LHC, allowing for
detection of rare physics processes, new particles and interactions. Tests have
been performed to determine the effects of radiation on the electronic
components to be used for the Endcap Muon electronics project currently being
designed for installation in the CMS experiment in 2013. During these tests the
digital components on the test boards were operating with active data readout
while being irradiated with 55 MeV protons. In reactor tests, components were
exposed to 30 years equivalent levels of neutron radiation expected at the
HL-LHC. The highest total ionizing dose (TID) for the muon system is expected
at the inner-most portion of the CMS detector, with 8900 rad over ten years.
Our results show that Commercial Off-The-Shelf (COTS) components selected for
the new electronics will operate reliably in the CMS radiation environment
Fluid Flows of Mixed Regimes in Porous Media
In porous media, there are three known regimes of fluid flows, namely,
pre-Darcy, Darcy and post-Darcy. Because of their different natures, these are
usually treated separately in literature. To study complex flows when all three
regimes may be present in different portions of a same domain, we use a single
equation of motion to unify them. Several scenarios and models are then
considered for slightly compressible fluids. A nonlinear parabolic equation for
the pressure is derived, which is degenerate when the pressure gradient is
either small or large. We estimate the pressure and its gradient for all time
in terms of initial and boundary data. We also obtain their particular bounds
for large time which depend on the asymptotic behavior of the boundary data but
not on the initial one. Moreover, the continuous dependence of the solutions on
initial and boundary data, and the structural stability for the equation are
established.Comment: 33 page
- …