Frequency-dependent (ac) Conduction in Disordered Composites: a Percolative Study

In a recent paper [Phys. Rev. B{\bf57}, 3375 (1998)], we examined in detail the nonlinear (electrical) dc response of a random resistor cum tunneling bond network ($RRTN$, introduced by us elsewhere to explain nonlinear response of metal-insulator type mixtures). In this work which is a sequel to that paper, we consider the ac response of the $RRTN$-based correlated $RC$ ($CRC$) model. Numerical solutions of the Kirchoff's laws for the $CRC$ model give a power-law exponent (= 0.7 near $p = p_c$) of the modulus of the complex ac conductance at moderately low frequencies, in conformity with experiments on various types of disordered systems. But, at very low frequencies, it gives a simple quadratic or linear dependence on the frequency depending upon whether the system is percolating or not. We do also discuss the effective medium approximation ($EMA$) of our $CRC$ and the traditional random $RC$ network model, and discuss their comparative successes and shortcomings.Comment: Revised and reduced version with 17 LaTeX pages plus 8 JPEG figure

Scheduling and efficient energy utilization in cloud system

Cloud computing is an emerging topic on software and distributed computing based on Internet, which means users can access storages and applications from remote servers by web browsers or other fixed or mobile terminals. In a cloud framework different services such as servers, storage in the form of data as well as Big data, resources etc are given to a management's computers and different devices on interest through the Internet. Multiple clients want to run their jobs or cloudlets in the cloud at a particular instant of time. The tasks are executed depending on the number of processors available and the scheduling policy of the cloud. In a cloud simulation software such as CloudSim a two level scheduling in the form of Space-shared and Time-shared can be used in collaboration with First Come First Serve(FCFS). An efficient way of job scheduling in cloud is to assign weightage or priority to the various parameters coming along with the job also taking into consideration the priority value set by the client to the task. In this thesis an attempt has been made to develop an efficient priority algorithm for the jobs running in the cloud. Also an attempt has been made to reduce the energy consumption at a particular over utilized node as well as switching idle nodes to the sleep mode thereby optimizing resource usage and reducing energy consumption

Cosmology with decaying tachyon matter

We investigate the case of a homogeneous tachyon field coupled to gravity in a spatially flat Friedman-Robertson-Walker spacetime. Assuming the field evolution to be exponentially decaying with time we solve the field equations and show that, under certain conditions, the scale factor represents an accelerating universe, following a phase of decelerated expansion. We make use of a model of dark energy (with p=-\rho) and dark matter (p=0) where a single scalar field (tachyon) governs the dynamics of both the dark components. We show that this model fits the current supernova data as well as the canonical \LambdaCDM model. We give the bounds on the parameters allowed by the current data.Comment: 14 pages, 6 figures, v2, Discussions and references addede

Study of Hematological Parameters in Patients of Different Subtypes of Panduroga

Introduction: Diagnosis in Ayurveda depends on history and clinical examination of the patient. Application of technological advancements and diagnostics tin Ayurveda may increase its acceptability globally and add objectivity to it. This research is advancement in the same direction to observe and analyze the haematological profile in patients of Panduroga (anemia) after categorizing them into Pandu roga subtypes and report the findings.Material and Methods: A prospective non – interventional observational exploratory study was conducted for a period of 18 months on hundred newly diagnosed adult and pediatric cases of anemia presenting to department of pediatrics and general medicine. Patients were categorized into Panduroga subtypes after examining them in detail with history, physical examination, hematological and other relevant investigations and with their due written informed consent. The data was then put to statistical analysis.Results: Differences were observed in the values of hematological parameters for the different subtypes of Panduroga which were statistically significant for Hemoglobin, Total Red blood cell count (TRBC), Hematocrit (HCT), Mean corpuscular volume (MCV), Mean corpuscular hemoglobin (MCH), Mean corpuscular hemoglobin concentration (MCHC) and Red cell distribution width (RDW).Conclusion: The differences in the objective profile as uncovered in the study reveals that the subtypes of Panduroga correlate to some extent to the different stages and pathology of anemia. However, the application of this study to the management of different types of anemia will require further confirmatory study with larger sample size in each subgroup

Nonlinear DC-response in Composites: a Percolative Study

The DC-response, namely the $I$-$V$ and $G$-$V$ charateristics, of a variety of composite materials are in general found to be nonlinear. We attempt to understand the generic nature of the response charactersistics and study the peculiarities associated with them. Our approach is based on a simple and minimal model bond percolative network. We do simulate the resistor network with appropritate linear and nonlinear bonds and obtain macroscopic nonlinear response characteristics. We discuss the associated physics. An effective medium approximation (EMA) of the corresponding resistor network is also given.Comment: Text written in RevTEX, 15 pages (20 postscript figures included), submitted to Phys. Rev. E. Some minor corrections made in the text, corrected one reference, the format changed (from 32 pages preprint to 15 pages

Wigner delay time from a random passive and active medium

We consider the scattering of electron by a one-dimensional random potential (both passive and active medium) and numerically obtain the probability distribution of Wigner delay time ($\tau$). We show that in a passive medium our probability distribution agrees with the earlier analytical results based on random phase approximation. We have extended our study to the strong disorder limit, where random phase approximation breaks down. The delay time distribution exhibits the long time tail ($1/\tau^2$) due to resonant states, which is independent of the nature of disorder indicating the universality of the tail of the delay time distribution. In the presence of coherent absorption (active medium) we show that the long time tail is suppressed exponentially due to the fact that the particles whose trajectories traverse long distances in the medium are absorbed and are unlikely to be reflected.Comment: 13 pages RevTex, 5 EPS figures included, communicated to PR

Study of transmission and reflection from a disordered lasing medium

A numerical study of the statistics of transmission ($t$) and reflection ($r$) of quasi-particles from a one-dimensional disordered lasing or amplifying medium is presented. The amplification is introduced via a uniform imaginary part in the site energies in the disordered segment of the single-band tight binding model. It is shown that $t$ is a non-self-averaging quantity. The cross-over length scale above which the amplification suppresses the transmittance is studied as a function of amplification strength. A new cross-over length scale is introduced in the regime of strong disorder and weak amplification. The stationary distribution of the backscattered reflection coefficient is shown to differ qualitatively from the earlier analytical results obtained within the random phase approximation.Comment: 5 pages RevTex (twocolumn format), 5 EPS figures, considerably modifie

Comparison between the two models of dephasing in mesoscopic systems

In mesoscopic systems to study the role of inelastic scattering on the phase coherent motion of electrons two phenomenological models have been proposed. In the first one, due to B\"uttiker, one adds a voltage probe into the system (or in the scattering matrix). The second model invokes the complex (or optical) potential in the system Hamiltonian. Studying a simple geometry of a metallic loop in the presence of Aharonov-Bohm magnetic flux, we show that the two probe conductance is symmetric in the reversal of the magnetic field in B\"uttiker's approach. Whereas the two probe conductance within the complex potential model is asymmetric in the magnetic flux reversal contrary to the expected behavior.Comment: 11 pages RevTex, 4 figures inculded, Communicated to PR