Landauer formula for phonon heat conduction: relation between energy transmittance and transmission coefficient

The heat current across a quantum harmonic system connected to reservoirs at different temperatures is given by the Landauer formula, in terms of an integral over phonon frequencies \omega, of the energy transmittance T(\omega). There are several different ways to derive this formula, for example using the Keldysh approach or the Langevin equation approach. The energy transmittance T({\omega}) is usually expressed in terms of nonequilibrium phonon Green's function and it is expected that it is related to the transmission coefficient {\tau}({\omega}) of plane waves across the system. In this paper, for a one-dimensional set-up of a finite harmonic chain connected to reservoirs which are also semi-infinite harmonic chains, we present a simple and direct demonstration of the relation between T({\omega}) and {\tau}({\omega}). Our approach is easily extendable to the case where both system and reservoirs are in higher dimensions and have arbitrary geometries, in which case the meaning of {\tau} and its relation to T are more non-trivial.Comment: 17 pages, 1 figur

Heat conduction in the \alpha-\beta -Fermi-Pasta-Ulam chain

Recent simulation results on heat conduction in a one-dimensional chain with an asymmetric inter-particle interaction potential and no onsite potential found non-anomalous heat transport in accordance to Fourier's law. This is a surprising result since it was long believed that heat conduction in one-dimensional systems is in general anomalous in the sense that the thermal conductivity diverges as the system size goes to infinity. In this paper we report on detailed numerical simulations of this problem to investigate the possibility of a finite temperature phase transition in this system. Our results indicate that the unexpected results for asymmetric potentials is a result of insufficient chain length, and does not represent the asymptotic behavior.Comment: 14 pages, 6 figure

Flow diagnosis in a domestic radiator

In UK, domestic heating contributes to about 40% of annual energy consumption. Effective and efficient heating systems are essential to drive the cost of heating down. Although there are several types of heating systems, radiators are the most popular heat emitters. Head loss in a radiator depends on various design parameters based on fluid flow path conditions and design of the radiator. In the present study, a computational fluid dynamics (CFD) code has been used to analyse flow distribution within a domestic radiator. For this study a radiator with dimensions of 300mm by 600mm with 18 columns has been considered. The study has been carried out on a radiator with BBOE and BTOE configuration at various flow rates. In this paper results are presented from a series of analysis in which flow structure within the radiator has been diagnosed

Sequence sensitivity of breathing dynamics in heteropolymer DNA

We study the fluctuation dynamics of localized denaturation bubbles in heteropolymer DNA with a master equation and complementary stochastic simulation based on novel DNA stability data. A significant dependence of opening probability and waiting time between bubble events on the local DNA sequence is revealed and quantified for a biological sequence of the T7 bacteriophage. Quantitative agreement with data from fluorescence correlation spectroscopy (FCS) is demonstrated.Comment: 4 pages, 5 figures, to appear in Physical Review Letter

Oscillation dynamics of embolic microspheres in flows with red blood cell suspensions

Dynamic nature of particle motion in blood flow is an important determinant of embolization based cancer therapy. Yet, the manner in which the presence of high volume fraction of red blood cells influences the particle dynamics remains unknown. Here, by investigating the motions of embolic microspheres in pressure-driven flows of red blood cell suspensions through capillaries, we illustrate unique oscillatory trends in particle trajectories, which are not observable in Newtonian fluid flows. Our investigation reveals that such oscillatory behavior essentially manifests when three simultaneous conditions, namely, the Reynolds number beyond a threshold limit, degree of confinement beyond a critical limit, and high hematocrit level, are fulfilled simultaneously. Given that these conditions are extremely relevant to fluid dynamics of blood or polymer flow, the observations reported here bear significant implications on embolization based cancer treatment as well as for complex multiphase fluidics involving particle

Universal power law in the orientational relaxation in thermotropic liquid crystals

We observe a surprisingly general power law decay at short to intermediate times in orientational relaxation in a variety of model systems (both calamitic and discotic, and also discrete) for thermotropic liquid crystals. As all these systems transit across the isotropic-nematic phase boundary, two power law relaxation regimes, separated by a plateau, emerge giving rise to a step-like feature (well-known in glassy liquids) in the single-particle second-rank orientational time correlation function. In contrast to its probable dynamical origin in supercooled liquids, we show that the power law here can originate from the thermodynamic fluctuations of the orientational order parameter, driven by the rapid growth in the second-rank orientational correlation length.Comment: Submitted to Physical Review Letter

Dark Energy Constraints from Galaxy Cluster Peculiar Velocities

Future multifrequency microwave background experiments with arcminute resolution and micro-Kelvin temperature sensitivity will be able to detect the kinetic Sunyaev-Zeldovich (kSZ) effect, providing a way to measure radial peculiar velocities of massive galaxy clusters. We show that cluster peculiar velocities have the potential to constrain several dark energy parameters. We compare three velocity statistics (the distribution of radial velocities, the mean pairwise streaming velocity, and the velocity correlation function) and analyze the relative merits of these statistics in constraining dark energy parameters. Of the three statistics, mean pairwise streaming velocity provides constraints that are least sensitive to velocity errors: the constraints on parameters degrades only by a factor of two when the random error is increased from 100 to 500 km/s. We also compare cluster velocities with other dark energy probes proposed in the Dark Energy Task Force report. For cluster velocity measurements with realistic priors, the eventual constraints on the dark energy density, the dark energy equation of state and its evolution are comparable to constraints from supernovae measurements, and better than cluster counts and baryon acoustic oscillations; adding velocity to other dark energy probes improves constraints on the figure of merit by more than a factor of two. For upcoming Sunyaev-Zeldovich galaxy cluster surveys, even velocity measurements with errors as large as 1000 km/s will substantially improve the cosmological constraints compared to using the cluster number density alone.Comment: 25 pages, 10 figures. Results and conclusions unchanged. Minor changes to match the accepted version in Physical Review

Implementing Provable Security and Group Key Agreement for Conbe Scheme

encoding is used during a communication system to secure data within the transmitted messages from anyone apart from the well intended receiver. To perform the encryption and decryption the transmitter and receiver should have matching encoding and decryption keys. For causing safeguard data to group required broadcast encoding (BE). BE permits a sender to securely broadcast to any set of members and need a trusted party to distribute decryption keys. Group key agreement (GKA) protocol permits variety of users to determine a common secret channel via open networks. Observing that a significant goal of GKA for many applications is to make a confidential channel among group members, however a sender cannot omit any explicit member from decrypting the cipher texts. By bridging BE and GKA notion with a hybrid primitive said as contributory broadcast encoding (CBE). With these primitives, a bunch of members move through a standard public encoding key whereas every member having their secret writing key; A sender seeing the general public cluster encoding key will limit the secret writing to set of members of sender‘s selection. An easy way to generate these keys is to use the general public key distribution system invented by Diffie and Hellman. That system, however, pass only 1 combine of communication stations to share a specific combine of encoding and secret writing keys. Key distribution sets are used to generate keys and Elliptic Curve Cryptography (ECC) is used for the encoding and decryption of documents; and this tends to give the protection for the documents over group communication