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Search Results: 1 - 10 of 156270 matches for " Dr. H. Mangalam "
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Efficient FPGA implementation of AES 128 bit for IEEE 802.16e mobile WiMax standards  [PDF]
P. Rajasekar, Dr. H. Mangalam
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.74032
Abstract: In an advancement of communication field, wireless technology plays a predominant role in data transmission. In the timeline of wireless domain, Wi-Fi, Bluetooth, zigbee etc are some of the standards, which are being used in today’s wireless medium. In addition, the WiMax is introduced by IEEE in IEEE 802.16 for long distance communication, specifically 802.16e standard for mobile WiMax. It is an acronym of Worldwide Interoperability for Microwave Access. It is to be deliver wireless transmission with high quality of service in a secured environment. Since, security becomes dominant design aspect of every communication, a new technique has been proposed in wireless environment. Privacy across the network and access control management is the goal in the predominant aspects in the WiMax protocol. Especially, MAC sub layer should be evaluated in the security architecture. It has been proposed on cryptography algorithm AES that require high cost. Under this scenario, we present the optimized AES 128 bit counter mode security algorithm for MAC layer of 802.16e standards. To design a efficient MAC layer, we adopt the modification of security layers data handling process. As per the efficient design strategy, the power and speed are the dominant factors in mobile device. Since we concentrate mobile WiMax, efficient design is needed for MAC Security layer. Our proposed model incorporates the modification of AES algorithm. The design has been implemented in Xilinx virtex5 device and power has been analyzed using XPower analyzer. This proposed system consumes 41% less power compare to existing system.
A Modified PFD Based PLL with Frequency Dividers in 0.18-μm CMOS Technology  [PDF]
N. K. Anushkannan, H. Mangalam
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.713343
Abstract: This paper introduces a modified design of CMOS dynamic Phase Frequency Detector (PFD). The proposed PFD circuit (PPFD) is designed, simulated and the results obtained are analyzed. In order to reduce dead zone, internal signal routing is used in the PPFD circuit. To extend, Phase Locked Loop (PLL) is designed and it is verified with two different Frequency Divider (FD) circuits. There is a decrease in area of the PPFD circuit with 16 transistors and dissipates power of 40.8 pW for 1.2 V power supply. The pre-layout simulation result shows that the PPFD circuit has an elimination of a dead zone. Further, it works with the high speed and reduced power operated in the reference frequency of 50 MHz and the feedback frequency up to 4 GHz.
Physics of Supermassive Disks: Formation and Collapse
A. Mangalam
Physics , 2003,
Abstract: Supermassive disks are thought to be precursors of supermassive black holes that are believed to power quasars and exist at centers of galaxies. Formation scenarios of such disks are reviewed and it is argued that gas dynamical schemes are favourable compared to stellar dynamical schemes which could however be important feeding mechanisms for the growth of the black hole. A new self-similar model of a collapse of a self-gravitating disk due to radiation induced stresses applicable to two different situations of radiative viscosity and Compton drag is presented. The collapse timescale purely due to radiative viscosity is found to be a fraction of Hubble time, $\tau_\gamma \sim{\sigma_T c/ (m_p G)} ({L_{edd}/ L}) \simeq 6 \times 10^9$yrs is slow and probably magnetic fields play an important role before general relativistic effects take over. A model of self-gravitating disk collapsing due to Compton drag by the Cosmic Microwave Background is also presented which is found to be effective at redshifts $1400>z\gsim 300$. It is proposed that the small $\lsim 10^5 \Msun$ objects that form by this mechanism by $z \sim 20$ can merge and coalesce by dynamical friction to form the high redshift quasars seen. Supermassive stars which are systems (and could be end products of a supermassive disk phase) en route to the final collapse are also briefly reviewed.
Formation of a Proto-Quasar from Accretion Flows in a Halo
A. Mangalam
Physics , 2001, DOI: 10.1051/0004-6361:20011405
Abstract: We present a detailed model for the formation of massive objects at the centers of galaxies. The effects of supernovae heating and the conditions of gas loss are revisited. The escape time of the gas is compared with the cooling time, which provides an additional condition not previously considered. Its consequences for the allowed mass range of the halo is calculated. It is shown that sufficient gas is retained to form massive dark objects and quasars even for moderately massive halos but a decline is expected at low redshifts. Subsequently, a gaseous disk forms with a radial extent of a ~kpc, spun up by tidal torques and magnetized by supernovae fields with fields strengths of $10-100 \mu G$. In a model of a self-similar accretion flow in an initially dominant halo, it is shown that for typical halo parameters, about $10^8 M_\odot$ accretes via small magnetic stresses (or alternatively by self-gravity induced instability or by alpha viscosity) in $10^8$ years into a compact region. A model of a self-gravitating evolution of a compact magnetized disk, which is relevant when a significant fraction of the disk mass falls in, is presented, and it has a rapid collapse time scale of a million years. The two disk solutions, one for accretion in an imposed halo potential and the other for self-gravitating disk, obtained here, have general utility and can be adapted to other contexts like protostellar disks as well.
A unified description of anti-dynamo conditions for incompressible flows
A. Mangalam
Physics , 2005,
Abstract: A general type of mathematical argument is described, which applies to all the cases in which dynamo maintenance of a steady magnetic field by motion in a uniform density is known to be impossible. Previous work has demonstrated that magnetic field decay is unavoidable under conditions of axisymmetry and in spherical or planar incompressible flows. These known results are encompassed by a calculation for flows described in terms of a generalized poloidal-toroidal representation of the magnetic field with respect to an arbitrary two dimensional surface. We show that when the velocity field is two dimensional, the dynamo growth, if any, that results, is linear in one of the projections of the field while the other projections remain constant. We also obtain criteria for the existence of and classification into two and three dimensional velocity results which are satisfied by a restricted set of geometries. In addition, we discuss the forms of spatial variation of the density and the resistivity that are allowed so that field decay still occurs for this set of geometries.
tacg – a grep for DNA
Harry J Mangalam
BMC Bioinformatics , 2002, DOI: 10.1186/1471-2105-3-8
Abstract: I describe a small application which allows searching for all the above pattern types individually, which further allows these atomic motifs to be assembled into logical rules for more sophisticated analysis.tacg is small, portable, faster and more capable than most alternatives, relatively easy to modify, and freely available in source code.String searching is a well-developed field of computer science, with highly optimized algorithms implemented in a variety of applications to efficiently search large collections of text [12,15]. Many of these algorithms are intuitive; some of them are beautiful, the best of them are quite extraordinarily efficient [1,3,6]. Many of these algorithms have been applied to the field of searching genomic sequences and associated databases, either for exact [2,17,18] or probablistic [11,4] matches, but it is striking that many useful algorithms in combinatorial pattern matching have not made their way into tools designed explicitly for bioinformaticists.Most of the tools that have been developed for pattern matching in molecular biology have been prototyped on Unix systems but there has been a perplexing deficit of free bioinformatics tools (comparable to the GNU text utilities [9]) for this platform. Recently, however, the EMBOSS suite of about 100 tools [20] has approached the commercial GCG application suite for breadth of utility. There are other good tools (ie. SEALS [24]) that can be coerced into providing searching capability although often at the cost of non-standard interfaces, large installation or maintenance overhead, or that provide considerable utility but at the cost of building the application yourself, such as the Bio* toolkits [5].A useful utility would be a grep[13] for DNA, a command line program requiring a short learning curve and few resources, but providing sophisticated search abilities as well as being easily extensible. tacg was developed to provide this functionality. For example, tacg -pName, pattern, err#
Flexibility in Food Extraction Techniques in Urban Free-Ranging Bonnet Macaques, Macaca radiata
Madhur Mangalam, Mewa Singh
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0085497
Abstract: Non-human primate populations, other than responding appropriately to naturally occurring challenges, also need to cope with anthropogenic factors such as environmental pollution, resource depletion, and habitat destruction. Populations and individuals are likely to show?considerable?variations in food extraction abilities, with some populations and individuals more efficient than others at exploiting a set of resources. In this study, we examined among urban free-ranging bonnet macaques, Macaca radiata (a) local differences in food extraction abilities, (b) between-individual variation and within-individual consistency in problem-solving success and the underlying problem-solving characteristics, and (c) behavioral patterns associated with higher efficiency in food extraction. When presented with novel food extraction tasks, the urban macaques having more frequent exposure to novel physical objects in their surroundings, extracted food material from PET bottles and also solved another food extraction task (i.e., extracting an orange from a wire mesh box), more often than those living under more natural conditions. Adults solved the tasks more frequently than juveniles, and females more frequently than males. Both solution-technique and problem-solving characteristics varied across individuals but remained consistent within each individual across the successive presentations of PET bottles. The macaques that solved the tasks showed lesser within-individual variation in their food extraction behavior as compared to those that failed to solve the tasks. A few macaques appropriately modified their problem-solving behavior in accordance with the task requirements and solved the modified versions of the tasks without trial-and-error learning. These observations are ecologically relevant – they demonstrate considerable local differences in food extraction abilities, between-individual variation and within-individual consistency in food extraction techniques among free-ranging bonnet macaques, possibly affecting the species’ local adaptability and resilience to environmental changes.
Kinematics of and emission from helically orbiting blobs in a relativistic magnetized jet
P. Mohan,A. Mangalam
Physics , 2015, DOI: 10.1088/0004-637X/805/2/91
Abstract: We present a general relativistic (GR) model of jet variability in active galactic nuclei due to orbiting blobs in helical motion along a funnel or cone shaped magnetic surface anchored to the accretion disk near the black hole. Considering a radiation pressure driven flow in the inner region, we find that it stabilizes the flow, yielding Lorentz factors ranging between 1.1 and 7 at small radii for reasonable initial conditions. Assuming these as inputs, simulated light curves (LCs) for the funnel model include Doppler and gravitational shifts, aberration, light bending, and time delay. These LCs are studied for quasi-periodic oscillations (QPOs) and the power spectral density (PSD) shape and yield an increased amplitude ($\sim$ 12 %); a beamed portion and a systematic phase shift with respect to that from a previous special relativistic model. The results strongly justify implementing a realistic magnetic surface geometry in Schwarzschild geometry to describe effects on emission from orbital features in the jet close to the horizon radius. A power law shaped PSD with a typical slope of $-2$ and QPOs with timescales in the range of $(1.37 - 130.7)$ days consistent with optical variability in Blazars, emerges from the simulations for black hole masses $M_{\bullet} = (0.5 - 5) \times 10^8 M_{\odot}$ and initial Lorentz factors $\gamma_{jet,i} = 2 - 10$. The models presented here can be applied to explain radio, optical, and X-ray variability from a range of jetted sources including active galactic nuclei, X-ray binaries and neutron stars.
X-Ray Variability and the Inner Region in Active Galactic Nuclei
P. Mohan,A. Mangalam
Physics , 2014, DOI: 10.1088/0004-637X/791/2/74
Abstract: We present theoretical models of X-ray variability attributable to orbital signatures from an accretion disk including emission region size, quasi-periodic oscillations (QPOs) and its quality factor $Q$, and the emergence of a break frequency in the power spectral density shape. We find a fractional variability amplitude of $F_{var}\propto M^{-0.4}_{\bullet}$. We conduct a time series analysis on X-ray light curves ($0.3-10$ keV) of a sample of active galactic nuclei (AGNs). A statistically significant bend frequency is inferred in 9 of 58 light curves (16 %) from 3 AGNs for which the break timescale is consistent with the reported BH spin but not with the reported BH mass. Upper limits of $2.85 \times 10^7 M_\odot$ in NGC 4051, $8.02 \times 10^7 M_\odot$ in MRK 766 and $4.68 \times 10^7 M_\odot$ in MCG-6-30-15 are inferred for maximally spinning BHs. For REJ 1034+396, where a QPO at 3733 s was reported, we obtain an emission region size of $(6 - 6.5) M$ and a BH spin $a\lesssim$ 0.08. The relativistic inner region of a thin disk, dominated by radiation pressure and electron scattering is likely to host the orbital features as the simulated $Q$ ranges from $6.3 \times 10^{-2}$ to $4.25 \times 10^6$, containing the observed $Q$. The derived value of $Q \sim$ 32 for REJ 1034+396 therefore suggests that the AGN hosts a thin disk.
Stellar and gas dynamical model for tidal disruption events in a quiescent galaxy
T. Mageshwaran,A. Mangalam
Physics , 2015, DOI: 10.1088/0004-637X/814/2/141
Abstract: A detailed model of the tidal disruption events (TDEs) has been constructed using stellar dynamical and gas dynamical inputs that include black hole (BH) mass $M_{\bullet}$, specific orbital energy $E$ and angular momentum $J$, star mass $M_{\star}$ and radius $R_{\star}$, and the pericenter of the star orbit $r_{p}(E,\hspace{1mm}J,\hspace{1mm}M_{\bullet})$. We solved the steady state Fokker--Planck equation using the standard loss cone theory for the galactic density profile $\rho (r) \propto r^{-\gamma}$ and stellar mass function $\xi(m) $ where $m=M_{\star}/M_{\odot}$ and obtained the feeding rate of stars to the BH integrated over the phase space as $\dot{N}_{t} \propto M_{\bullet}^\beta$, where $\beta= -0.3\pm 0.01$ for $M_{\bullet}>10^7 M_{\odot}$ and $\sim 6.8 \hspace{1mm} \times 10^{-5}$ Yr$^{-1}$ for $\gamma=0.7$. We use this to model the in-fall rate of the disrupted debris, $\dot{M}(E,\hspace{1mm}J,\hspace{1mm}m,\hspace{1mm}t)$, and discuss the conditions for the disk formation, finding that the accretion disk is almost always formed for the fiduciary range of the physical parameters. We also find the conditions under which the disk formed from the tidal debris of a given star with a super Eddington accretion phase. We have simulated the light curve profiles in the relevant optical g band and soft X-rays for both super and sub-Eddington accretion disks as a function of $\dot{M}(E,\hspace{1mm}J,\hspace{1mm}t)$. Using this, standard cosmological parameters, and mission instrument details, we predict the detectable TDE rates for various forthcoming surveys finally as a function of $\gamma$.
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