Similarity of percolation thresholds on the hcp and fcc lattices

Extensive Monte-Carlo simulations were performed in order to determine the precise values of the critical thresholds for site ($p^{hcp}_{c,S} = 0.199 255 5 \pm 0.000 001 0$) and bond ($p^{hcp}_{c,B} = 0.120 164 0 \pm 0.000 001 0$) percolation on the hcp lattice to compare with previous precise measuremens on the fcc lattice. Also, exact enumeration of the hcp and fcc lattices was performed and yielded generating functions and series for the zeroth, first, and second moments of both lattices. When these series and the values of $p_c$ are compared to those for the fcc lattice, it is apparent that the site percolation thresholds are different; however, the bond percolation thresholds are equal within error bars, and the series only differ slightly in the higher order terms, suggesting the actual values are very close to each other, if not identical.Comment: 10 pages, 4 figures, submitted to J. Stat. Phy

Sensor tip for a robotic gripper and method of manufacture

A sensor tip (10) for use in a robotic hand has a three-dimensional compliant elastomeric body (12) with an outer boundary (22) having a circular base (24) and a convex surface (26) extending therefrom. Four strain transducers (14, 16, 18, and 20) produce electrical signals indicative of the strain at various positions near the boundary of the elastomeric body (12) resulting from forces exerted upon the sensor tip (10) by an object which the robotic hand is manipulating. The transducers (14, 16, 18, and 20) are positioned about the convex surface (26) so as to produce signals that may be decoupled to determine the normal and tangential forces and the applied torque. A buffer amplifier circuit (34), one for each of the transducers (14, 16, 18, and 20), receives the signals and provides quasi-steady state force information. The circuit (34) connects the respective transducer (40) in a feedback loop around an amplifier (36) and has desirable attributes for static charge buffering. The sensor tip (10) is calibrated to determine proportionality constants for the decoupling algorithm for use of a force delivering system (60), which uses voice coils (74) to apply a force that is linearly related to the current introduced to each of the coils (74). A method of manufacture of the sensor tip (10) results in improved bonding between the transducers (14, 16, 18, and 20) and the elastomeric body (12) for better performance and longer life of the sensor tip (10)

Precise determination of the critical percolation threshold for the three-dimensional “Swiss cheese” model using a growth algorithm

Precise values for the critical threshold for the three-dimensional “Swiss cheese” continuum percolation model have been calculated using extensive Monte Carlo simulations. These simulations used a growth algorithm and memory blocking scheme similar to what we used previously in three-dimensional lattice percolation. The simulations yield a value for the critical number density nc = 0.652 960±0.000 005,nc=0.652960±0.000005, which confirms recent work but extends the precision by two significant figures. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70114/2/JCPSA6-114-8-3659-1.pd

Flux-Based Deadbeat Control of Induction-Motor Torque

An improved method and prior methods of deadbeat direct torque control involve the use of pulse-width modulation (PWM) of applied voltages. The prior methods are based on the use of stator flux and stator current as state variables, leading to mathematical solutions of control equations in forms that do not lend themselves to clear visualization of solution spaces. In contrast, the use of rotor and stator fluxes as the state variables in the present improved method lends itself to graphical representations that aid in understanding possible solutions under various operating conditions. In addition, the present improved method incorporates the superposition of high-frequency carrier signals for use in a motor-self-sensing technique for estimating the rotor shaft angle at any speed (including low or even zero speed) without need for additional shaft-angle-measuring sensors

Shape-dependent universality in percolation

The shape-dependent universality of the excess percolation cluster number and cross-configuration probability on a torus is discussed. Besides the aspect ratio of the torus, the universality class depends upon the twist in the periodic boundary conditions, which for example are generally introduced when triangular lattices are used in simulations.Comment: 11 pages, 3 figures, to be published in Physica

Excess number of percolation clusters on the surface of a sphere

Monte Carlo simulations were performed in order to determine the excess number of clusters b and the average density of clusters n_c for the two-dimensional "Swiss cheese" continuum percolation model on a planar L x L system and on the surface of a sphere. The excess number of clusters for the L x L system was confirmed to be a universal quantity with a value b = 0.8841 as previously predicted and verified only for lattice percolation. The excess number of clusters on the surface of a sphere was found to have the value b = 1.215(1) for discs with the same coverage as the flat critical system. Finally, the average critical density of clusters was calculated for continuum systems n_c = 0.0408(1).Comment: 13 pages, 2 figure

Integralni pristup sustavima energetske elektronike

Today\u27s power electronics systems are typically manufactured using non-standard parts, resulting in labor-intensive manufacturing processes, increased cost and poor reliability. As a possible way to overcome these problems, this paper discusses an integrated approach to design and manufacture power electronics systems to improve performance, reliability and cost effectiveness. Addressed in the paper are the technologies being developed for integration of both power supplies and motor drives. These technologies include the planar metalization to eliminate bonding wires, the integration of power passives, the integration of current sensors, the development of power devices to facilitate integration as well as to improve performance, and the integration of necessary CAD tools to address the multidisciplinary aspects of integrated systems. The development of Integrated Power Electronics Modules (IPEMs) is demonstrated for two applications: (1) 1 kW asymmetrical half-bridge DC-DC converter and (2) 1–3 kW motor drive for heating, ventilation and air conditioning (HVAC). Electrical and thermal design tradeoffs of IPEMs and related enabling technologies are described in the paper.Današnji sustavi energetske elektronike se obično proizvode iz nestandardnih dijelova. Posljedica toga je laboratorijska proizvodnja elektroničkih učinskih pretvarača, povećani troškovi i smanjena pouzdanost. Jedan od mogućih načina prevladavanja ovih poteškoća jest integralni pristup projektiranju i proizvodnji sustava energetske elektronike. Posebice se razmatraju tehnologije razvijene za integraciju učinskih krugova i motora. Ove tehnologije uključuju postupke planarne metalizacije za izbjegavanje žičanih vodova, integraciju pasivnih dijelova učinskih krugova, integraciju strujnih senzora, te razvoj takvih poluvodičkih komponenata koje olakšavaju integraciju i poboljšavaju karakteristike uređaja. Pri projektiranju, zbog multidisciplinarnih aspekata integriranih sustava, treba primijeniti nužne CAD alate. Razvoj integriranih modula elektroničkih učinskih pretvarača (engl. integrated power electronics modules, IPEM) ilustriran je na dvije primjene: (1) istosmjerni pretvarač snage 1 kW u asimetričnom polumosnom spoju i (2) elektromotorni pogon snage 1 . . . 3 kW za grijanje, ventilaciju i klimatizaciju (engl. heating, ventilation and air conditioning, HVAC). Na IPEM-u objašnjeni su projektantski i tehnološki kompromisi električkog i toplinskog projekta

Universality of the excess number of clusters and the crossing probability function in three-dimensional percolation

Extensive Monte-Carlo simulations were performed to evaluate the excess number of clusters and the crossing probability function for three-dimensional percolation on the simple cubic (s.c.), face-centered cubic (f.c.c.), and body-centered cubic (b.c.c.) lattices. Systems L x L x L' with L' >> L were studied for both bond (s.c., f.c.c., b.c.c.) and site (f.c.c.) percolation. The excess number of clusters $\tilde {b}$ per unit length was confirmed to be a universal quantity with a value $\tilde {b} \approx 0.412$. Likewise, the critical crossing probability in the L' direction, with periodic boundary conditions in the L x L plane, was found to follow a universal exponential decay as a function of r = L'/L for large r. Simulations were also carried out to find new precise values of the critical thresholds for site percolation on the f.c.c. and b.c.c. lattices, yielding $p_c(f.c.c.)= 0.199 236 5 \pm 0.000 001 0$, $p_c(b.c.c.)= 0.245 961 5\pm 0.000 001 0$.Comment: 14 pages, 7 figures, LaTeX, submitted to J. Phys. A: Math. Gen, added references, corrected typo

Development of a fluorescence-based method for monitoring glucose catabolism and its potential use in a biomass hydrolysis assay

<p>Abstract</p> <p>Background</p> <p>The availability and low cost of lignocellulosic biomass has caused tremendous interest in the bioconversion of this feedstock into liquid fuels. One measure of the economic viability of the bioconversion process is the ease with which a particular feedstock is hydrolyzed and fermented. Because monitoring the analytes in hydrolysis and fermentation experiments is time consuming, the objective of this study was to develop a rapid fluorescence-based method to monitor sugar production during biomass hydrolysis, and to demonstrate its application in monitoring corn stover hydrolysis.</p> <p>Results</p> <p>Hydrolytic enzymes were used in conjunction with <it>Escherichia coli </it>strain CA8404 (a hexose and pentose-consuming strain), modified to produce green fluorescent protein (GFP). The combination of hydrolytic enzymes and a sugar-consuming organism minimizes feedback inhibition of the hydrolytic enzymes. We observed that culture growth rate as measured by change in culture turbidity is proportional to GFP fluorescence and total growth and growth rate depends upon how much sugar is present at inoculation. Furthermore, it was possible to monitor the course of enzymatic hydrolysis in near real-time, though there are instrumentation challenges in doing this.</p> <p>Conclusion</p> <p>We found that instantaneous fluorescence is proportional to the bacterial growth rate. As growth rate is limited by the availability of sugar, the integral of fluorescence is proportional to the amount of sugar consumed by the microbe. We demonstrate that corn stover varieties can be differentiated based on sugar yields in enzymatic hydrolysis reactions using post-hydrolysis fluorescence measurements. Also, it may be possible to monitor fluorescence in real-time during hydrolysis to compare different hydrolysis protocols.</p

Percolation Threshold, Fisher Exponent, and Shortest Path Exponent for 4 and 5 Dimensions

We develop a method of constructing percolation clusters that allows us to build very large clusters using very little computer memory by limiting the maximum number of sites for which we maintain state information to a number of the order of the number of sites in the largest chemical shell of the cluster being created. The memory required to grow a cluster of mass s is of the order of $s^\theta$ bytes where $\theta$ ranges from 0.4 for 2-dimensional lattices to 0.5 for 6- (or higher)-dimensional lattices. We use this method to estimate $d_{\scriptsize min}$, the exponent relating the minimum path $\ell$ to the Euclidean distance r, for 4D and 5D hypercubic lattices. Analyzing both site and bond percolation, we find $d_{\scriptsize min}=1.607\pm 0.005$ (4D) and $d_{\scriptsize min}=1.812\pm 0.006$ (5D). In order to determine $d_{\scriptsize min}$ to high precision, and without bias, it was necessary to first find precise values for the percolation threshold, $p_c$: $p_c=0.196889\pm 0.000003$ (4D) and $p_c=0.14081\pm 0.00001$ (5D) for site and $p_c=0.160130\pm 0.000003$ (4D) and $p_c=0.118174\pm 0.000004$ (5D) for bond percolation. We also calculate the Fisher exponent, $\tau$, determined in the course of calculating the values of $p_c$: $\tau=2.313\pm 0.003$ (4D) and $\tau=2.412\pm 0.004$ (5D)