2,777 research outputs found
A Study of Evaporation Heat Transfer Coefficient Correlations at Low Heat and Mass Fluxes for Pure Refrigerants and Refrigerant Mixtures
An average R12 refrigerant correlation has been developed for the mass flux range of 25-100
kg/m2-s and the heat flux range of 2-10 kW/m2. Refrigerant mixtures of 80% R22/lO% R141b and 65%
R22/35% R123 have also been tested over asjrniJar range of conditions. Mixture heat transfer
coefficients have been detennined and correlations for each mixture pair are presented. The R221R141b
average correlation may have a strong dependence on changes in surface tension. The heat transfer
coefficient of R22JR141b compares well with that of R12. The heat transfer coefficient of R22/R123
severely under performs R12.Air Conditioning and Refrigeration Center Project 0
Radix-2n serialâserial multipliers
All serialâserial multiplication structures previously reported in the literature have been
confined to bit serialâserial multipliers. An architecture for digit serialâserial multipliers is presented. A set of designs are derived from the radix-2n design procedure, which was first reported by the authors for the design of bit level pipelined digit serialâparallel structures. One significant aspect of the new designs is that they can be pipelined to the bit level and give the designer the flexibility to obtain the best trade-off between throughput rate and hardware cost by varying the digit size and the number of pipelining levels. Also, an area-efficient digit serialâserial multiplier is proposed which provides a 50% reduction in hardware without degrading the speed performance.
This is achieved by exploiting the fact that some cells are idle for most of the multiplication
operation. In the new design, the computations of these cells are remapped to other cells, which
make them redundant. The new designs have been implemented on the S40BG256 device from the
SPARTAN family to prove functionality and assess performance
Thermal conductivity enhancement of laser induced graphene foam upon P3HT infiltration
Significant research has been dedicated to the exploration of high thermal conductivity polymer composite materials with conductive filler particles for use in heat transfer applications. However, poor particle dispersibility and interfacial phonon scattering have limited the effective composite thermal conductivity. Three-dimensional foams with high ligament thermal conductivity offer a potential solution to the two aforementioned problems but are traditionally fabricated through expensive and/or complex manufacturing methods. Here, laser induced graphene foams, fabricated through a simple and cost effective laser ablation method, are infiltrated with poly(3-hexylthiophene) in a step-wise fashion to demonstrate the impact of polymer on the thermal conductivity of the composite system. Surprisingly, the addition of polymer results in a drastic (250%) improvement in material thermal conductivity, enhancing the graphene foam's thermal conductivity from 0.68âW/m-K to 1.72âW/m-K for the fully infiltrated composite material. Graphene foam density measurements and theoretical models are utilized to estimate the effective ribbon thermal conductivity as a function of polymer filling. Here, it is proposed that the polymer solution acts as a binding material, which draws graphene ligaments together through elastocapillary coalescence and bonds these ligaments upon drying, resulting in greatly reduced contact resistance within the foam and an effective thermal conductivity improvement greater than what would be expected from the addition of polymer alone
The Ahupua'a concept: relearning coastal resource management from ancient Hawaiians
Coastal zone management, Resource conservation, Hawaii,
Asymptotic information leakage under one-try attacks
We study the asymptotic behaviour of (a) information leakage and (b) adversaryâs error probability in information hiding systems modelled as noisy channels. Specifically, we assume the attacker can make a single guess after observing n independent executions of the system, throughout which the secret information is kept fixed. We show that the asymptotic behaviour of quantities (a) and (b) can be determined in a simple way from the channel matrix. Moreover, simple and tight bounds on them as functions of n show that the convergence is exponential. We also discuss feasible methods to evaluate the rate of convergence. Our results cover both the Bayesian case, where a prior probability distribution on the secrets is assumed known to the attacker, and the maximum-likelihood case, where the attacker does not know such distribution. In the Bayesian case, we identify the distributions that maximize the leakage. We consider both the min-entropy setting studied by Smith and the additive form recently proposed by Braun et al., and show the two forms do agree asymptotically. Next, we extend these results to a more sophisticated eavesdropping scenario, where the attacker can perform a (noisy) observation at each state of the computation and the systems are modelled as hidden Markov models
Trust in Crowds: probabilistic behaviour in anonymity protocols
The existing analysis of the Crowds anonymity protocol assumes that a participating member is either âhonestâ or âcorruptedâ. This paper generalises this analysis so that each member is assumed to maliciously disclose the identity of other nodes with a probability determined by her vulnerability to corruption. Within this model, the trust in a principal is defined to be the probability that she behaves honestly. We investigate the effect of such a probabilistic behaviour on the anonymity of the principals participating in the protocol, and formulate the necessary conditions to achieve âprobable innocenceâ. Using these conditions, we propose a generalised Crowds-Trust protocol which uses trust information to achieves âprobable innocenceâ for principals exhibiting probabilistic behaviour
Universality classes in nonequilibrium lattice systems
This work is designed to overview our present knowledge about universality
classes occurring in nonequilibrium systems defined on regular lattices. In the
first section I summarize the most important critical exponents, relations and
the field theoretical formalism used in the text. In the second section I
briefly address the question of scaling behavior at first order phase
transitions. In section three I review dynamical extensions of basic static
classes, show the effect of mixing dynamics and the percolation behavior. The
main body of this work is given in section four where genuine, dynamical
universality classes specific to nonequilibrium systems are introduced. In
section five I continue overviewing such nonequilibrium classes but in coupled,
multi-component systems. Most of the known nonequilibrium transition classes
are explored in low dimensions between active and absorbing states of
reaction-diffusion type of systems. However by mapping they can be related to
universal behavior of interface growth models, which I overview in section six.
Finally in section seven I summarize families of absorbing state system
classes, mean-field classes and give an outlook for further directions of
research.Comment: Updated comprehensive review, 62 pages (two column), 29 figs
included. Scheduled for publication in Reviews of Modern Physics in April
200
Measurement of the 58Ni(α, γ) 62Zn reaction and its astrophysical impact
Funding Details: PHY 08-22648, NSF, National Science Foundation; PHY 0969058, NSF, National Science Foundation; PHY 1102511, NSF, National Science FoundationCross section measurements of the 58Ni(α,γ)62Zn reaction were performed in the energy range Eα=5.5to9.5 MeV at the Nuclear Science Laboratory of the University of Notre Dame, using the NSCL Summing NaI(Tl) detector and the γ-summing technique. The measurements are compared to predictions in the statistical Hauser-Feshbach model of nuclear reactions using the SMARAGD code. It is found that the energy dependence of the cross section is reproduced well but the absolute value is overestimated by the prediction. This can be remedied by rescaling the α width by a factor of 0.45. Stellar reactivities were calculated with the rescaled α width and their impact on nucleosynthesis in type Ia supernovae has been studied. It is found that the resulting abundances change by up to 5% when using the new reactivities. © 2014 American Physical Society.Peer reviewe
Co, Ni-free ultrathick free-standing dry electrodes for sustainable lithium-ion batteries
The conventional method of manufacturing lithium-ion battery electrodes employs a complex slurry casting process with solvents that are not environmentally friendly and process parameters that are often difficult to control. This study explores a solvent-free dry electrode fabrication process of Co- and Ni-free LiMn2O4 (LMO) cathodes using a fibrillated polymer, polytetrafluoroethylene (PTFE). A thick, dry electrode (265-368 ÎŒm, 30-64 mg cm-2) of LMO cathode was prepared successfully for the first time. Altering the conductive additives in the LMO dry electrode revealed multiwalled carbon nanotubes (CNTs) as the best conducting agent for dry electrode formulation in terms of conductivity and rate performance. Additionally, an all-dry electrode full cell consisting of both a dry electrode cathode (LMO) and an anode (LTO) delivered a stable cycling performance with a capacity retention of 82.8% after 200 cycles, demonstrating the scope for all-dry electrode full cells for future applications
- âŠ