2,123 research outputs found

    Anisotropic diffusion in square lattice potentials: giant enhancement and control

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    The unbiased thermal diffusion of an overdamped Brownian particle in a square lattice potential is considered in the presence of an externally applied ac driving. The resulting diffusion matrix exhibits two orthogonal eigenvectors with eigenvalues D1>D2>0D_1>D_2>0, indicating anisotropic diffusion along a "fast" and a "slow principal axis". For sufficiently small temperatures, D1D_1 may become arbitrarily large and at the same time D2D_2 arbitrarily small. The principal diffusion axis can be made to point into (almost) any direction by varying either the driving amplitude or the coupling of the particle to the potential, without changing any other property of the system or the driving.Comment: 7 pages, 7 figure

    Exploiting lattice potentials for sorting chiral particles

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    Several ways are demonstrated of how periodic potentials can be exploited for sorting molecules or other small objects which only differ by their chirality. With the help of a static bias force, the two chiral partners can be made to move along orthogonal directions. Time-periodic external forces even lead to motion into exactly opposite directions.Comment: 4 pages, 4 figure

    Location of the Lee-Yang zeros and absence of phase transitions in some Ising spin systems

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    We consider a class of Ising spin systems on a set \Lambda of sites. The sites are grouped into units with the property that each site belongs to either one or two units, and the total internal energy of the system is the sum of the energies of the individual units, which in turn depend only on the number of up spins in the unit. We show that under suitable conditions on these interactions none of the |\Lambda| Lee-Yang zeros in the complex z = exp{2\beta h} plane, where \beta is the inverse temperature and h the uniform magnetic field, touch the positive real axis, at least for large values of \beta. In some cases one obtains, in an appropriately taken \beta to infinity limit, a gas of hard objects on a set \Lambda'; the fugacity for the limiting system is a rescaling of z and the Lee-Yang zeros of the new partition function also avoid the positive real axis. For certain forms of the energies of the individual units the Lee-Yang zeros of both the finite- and zero-temperature systems lie on the negative real axis for all \beta. One zero-temperature limit of this type, for example, is a monomer-dimer system; our results thus generalize, to finite \beta, a well-known result of Heilmann and Lieb that the Lee-Yang zeros of monomer-dimer systems are real and negative.Comment: Plain TeX. Seventeen pages, five figures from .eps files. Version 2 corrects minor errors in version

    Beach changes at Nauset Inlet, Cape Cod, Massachusetts, 1670-1981

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    A historical study of barrier beach and inlet changes for the Nauset Inlet region, Cape Cod, Massachusetts, was performed to document patterns of beach and inlet change as a preliminary to designing and carrying out ffeld studies of inlet sediment transport. 120 historical charts from 1670 and 125 sets of aerial photographs from 1938 formed the basis for this study. Specific aspects of barrier beach and inlet change addressed include onshore barrier beach movement, longshore tidal inlet migration, and longshore sand bypassing past the inlet. In an effort to correlate forcing events with barrier changes, an exhaustive study of the local storm climate was performed. Detailed treatment of the specific mechanisms responsible for Nauset Inlet migration episodes in a direction opposite the dominant littoral drift are treated in a companion paper by Aubrey, Speer, and Ruder (1982). Documentation of the data base available for the Nauset Area is presented herein as appendices.Prepared for NOAA, 0ffice of Sea Gnant under Grant NA 80-AA-D- 00077 (R/B-21) and for the U.S. Army Research 0ffice under Grant DAAG29-81-K-0004

    Hydrodynamical Modeling of a Multiple‐Inlet Estuary/Barrier System: Insight Into Tidal Inlet Formation and Stability

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    Two specific questions are addressed concerning the role of tidal hydrodynamics in determining the long‐term morphologic evolution of the Nauset Beach‐Monomoy Island barrier system and the Chatham Harbor‐Pleasant Bay tidal estuary, Massachusetts: (1) why do the barrier and estuary exhibit a long‐term (∌150 yr) cycle of new inlet formation, and (2) once a new inlet forms, why is the resulting multiple inlet system unstable? To address these questions, a branched 1‐d numerical model is used to recreate the basic flow patterns in the tidal estuary at ten‐year intervals during the last half century and also to recreate flow conditions shortly before and shortly after the formation of the new inlet. Results suggest that an inlet will form through Nauset Beach once southerly elongation of the barrier has led to a critical head across the barrier at high tide. If this critical head (enhanced by storm surge and wave set‐up) exists at high tide during consecutive tidal cycles, flood currents can deepen the overwash channel sufficiently to enable the stronger ebb currents to complete the formation process. Once a new inlet has formed, the surface gradient and tidal discharge are drastically reduced along the pre‐existing channel to the south of the inlet. This reduction eliminates the tidal scouring action needed to keep the channel open. Rapid shoaling within the channel to the south of the new inlet completes the hydrodynamic decoupling of the northern and southern sections of the estuary.https://scholarworks.wm.edu/vimsbooks/1037/thumbnail.jp

    Austenite Formation and Manganese Partitioning during Double Soaking of an Ultralow Carbon Medium-Manganese Steel

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    Double soaking (DS) is a thermal processing route intended to produce austenite–martensite microstructures in steels containing austenite-stabilizing additions and consists of intercritical annealing (primary soaking), followed by heating and brief isothermal holding at an increased temperature (secondary soaking), and quenching. Herein, experimental dilatometry during DS of a medium-manganese (Mn) steel with nominally 7 wt% Mn and an ultralow residual carbon concentration, in combination with phase-field simulations of austenite formation during secondary soaking, is presented. The feasibility of maintaining heterogeneous Mn distributions during DS is demonstrated and insight is provided on the effects of the secondary soaking temperature and prior Mn distribution on the ferrite-to-austenite phase transformation during the secondary soaking portion of the DS treatment

    Simulation of Heavily Irradiated Silicon Pixel Sensors and Comparison with Test Beam Measurements

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    Charge collection measurements performed on heavily irradiated p-spray DOFZ pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes signal trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in the ISE TCAD software can be tuned to produce a doubly-peaked electric field which describes the data reasonably well. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of charge trapping observed in the data.Comment: 8 pages, 11 figures. Talk presented at the 2004 IEEE Nuclear Science Symposium, October 18-21, Rome, Italy. Submitted to IEEE Transactions on Nuclear Scienc

    A Case Study of a Co-Instructed Multidisciplinary Senior Capstone Project in Sustainability

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    As societal challenges involving sustainable development increase, the need to effectively integrate this inherently multidisciplinary topic into existing curricula becomes more pressing. Multidisciplinary, team-taught, project-based instruction has shown effectiveness in teaching teamwork, communication, and life-long learning skills, and appreciation for other disciplines. Unfortunately, this instruction mode has not been widely adopted, largely due to its resource-intensiveness. Our proposed co-instruction model of multidisciplinary senior project administration was tested to see if it could effectively teach sustainability topics and duplicate the known benefits of team-taught instruction, while overcoming its resource-intensiveness. A case study of a co-instructed senior project was undertaken with students and faculty from electrical and mechanical engineering, business, political science, and industrial design. The participating students were compared to the control group, i.e. students who chose to complete a traditional disciplinary senior project instead. Extensive assessment was performed with pre/post quizzes, online surveys, focus groups, and course deliverables. The multidisciplinary projects outperformed traditional senior projects in 4 out of the 5 participating courses. However, the students in the multidisciplinary project rated their satisfaction with the experience lower on average than the control group. A strong, positive correlation between students’ project satisfaction and rating of other instruction aspects (0.50 \u3c r \u3c 0.7, p \u3c 0.01) was discovered, which has implications for all project-based instruction. Participating faculty generally found the process illuminating and engaged in scholarship and creative endeavors as a result
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