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Structure of Actin Cross-Linked with α-Actinin: A Network of Bundles

Physical Review Letters 2003年第14期91卷 148102-148102页

作者： O. Pelletier E. Pokidysheva L. S. Hirst N. Bouxsein Y. Li C. R. Safinya Materials Department Physics Department Biomolecular Science and Engineering Program University of California

Three-dimensional laser scanning confocal microscopy has revealed that filamentous actin, when complexed with the cross-linking protein α-actinin, will spontaneously assemble on a micron scale into a structure comprised of a relatively rigid, frequently branching, 3D network of bundles with characteristic mesh size of the order of the persistence length of F-actin. In contrast, additional nanoscale ordering is observed, as synchrotron x-ray diffraction has revealed a disordered, distorted square lattice of actin fibers within the individual bundles.

关键词： .branching laments cytoskeleton square lattice bundling mesh size actin rods micron scale Network of Bundles Actinin

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Time-asymptotic wave propagation in collisionless plasmas

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Physical Review E 2003年第2期68卷 026406-026406页

作者： Carlo Lancellotti J. J. Dorning Engineering Physics Program University of Virginia Charlottesville Virginia 22903-2442 USA

We report the results of a new, systematic study of nonlinear longitudinal wave propagation in a collisionless plasma. Based on the decomposition of the electric field E into a transient part T and a time-asymptotic part A, we show that A is given by a finite superposition of wave modes, whose frequencies obey a Vlasov dispersion relation, and whose amplitudes satisfy a set of nonlinear algebraic equations. These time-asymptotic mode amplitudes are calculated explicitly, based on approximate solutions for the particle distribution functions obtained by linearizing only the term that contains T in the Vlasov equation for each particle species, and then integrating the resulting equation along the nonlinear characteristics associated with A, which are obtained via Hamiltonian perturbation theory. For “linearly stable” initial Vlasov equilibria, we obtain a critical initial amplitude (or threshold), separating the initial conditions that produce Landau damping to zero (A≡0) from those that lead to nonzero multiple-traveling-wave time-asymptotic states via nonlinear particle trapping (A≢0). These theoretical results have important implications about the stability of spatially uniform plasma equilibria, and they also explain why large-scale numerical simulations in some cases lead to zero-field final states whereas in others they yield nonzero multiple-traveling-wave final states.

关键词： Plasma waves

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Nanoindentation of amorphous and nanostructured polymers

Nanoindentation of amorphous and nanostructured polymers

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Mechanical Properties Derived from Nanostructuring Materials

作者： Maner, Kyle C. Begley, Matthew R. Utz, Marcel Structural and Solid Mech. Program Department of Civil Engineering University of Virginia Charlottesville VA 22904 United States Department of Physics Institute for Materials Science University of Connecticut Storrs CT 06269 United States

We present a detailed nanoindentation study of micron-scale thin films of polystyrene (PS), poly(phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), a metal-centered PMMA-Ruthenium block copolymer, and a PS-poly(ethylene-propylene) (PS-PEP) block copolymer with lamellar morphology. The results show that size-dependence is most readily noticeable for the lamellar PS-PEP film, indicating that the nanoidentation approach has sufficient sensitivity to capture scale dependence on scales in the range of tens of nanometers. The less pronounced scale-dependence (or lack thereof) in the other films is discussed in the context of identifying the physical length-scale of elementary processes of plastic deformation. The results indicate that the upper limit on the size of plastic shear zones in amorphous polymers is approximately 1200-9600 nm3 (i.e. a sphere with a diameter in the range of 20-40 nm).

关键词： Nanostructured materials

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Massive Magnetic-Field-Induced Structural Transformation in Gd5Ge4 and the Nature of the Giant Magnetocaloric Effect

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Physical Review Letters 2003年第19期91卷 197204-197204页

作者： V. K. Pecharsky A. P. Holm K. A. Gschneidner, Jr. R. Rink Materials and Engineering Physics Program Ames Laboratory Ames Iowa 50011-3020 USA Department of Materials Science and Engineering Iowa State University Ames Iowa 50011-2300 USA

A massive magnetic-field-induced structural transformation in Gd5Ge4, which occurs below 30 K, was imaged at the atomic level by uniquely coupling high-resolution x-ray powder diffraction with magnetic fields up to 35 kOe. In addition to uncovering the nature of the magnetic field induced structural transition, our data demonstrate that the giant magnetocaloric effect, observed in low magnetic fields, arises from the amplification of a conventional magnetic entropy-driven mechanism by the difference in the entropies of two phases, borne by the concomitant structural transformation.

关键词： Gadolinium compounds

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Lamellar Phase of Stacked Two-Dimensional Rafts of Actin Filaments

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Physical Review Letters 2003年第1期91卷 018103-018103页

作者： Gerard C. L. Wong Alison Lin Jay X. Tang Youli Li Paul A. Janmey Cyrus R. Safinya Materials Department Physics Department Biomolecular Science and Engineering Program University of California Santa Barbara California 93106 USA Physics Department Brown University Providence Rhode Island 02912 USA Institute for Medicine and Engineering University of Pennsylvania Philadelphia Pennsylvania 19104 USA

We examined liquid crystalline phases of the cytoskeletal polyelectrolyte filamentous (F-)actin in the presence of multivalent counterions. As a function of increasing ion concentration, the F-actin rods in either an isotropic or a nematic phase will transform into a new and unexpected lamellar phase of cross-linked rafts (LXR phase), before condensing into a bundled phase of parallel, close-packed rods. This behavior is generic for alkali earth divalent ions Mg2+, Ca2+, Sr2+, and Ba2+, and the structural transitions are achieved without any architecture-specific actin-binding linker proteins.

关键词： .lamellar liquid crystalline VOLUME NUMBER week ion concentration counterions rafts divalent multivalent actin rods LXR bundled phase

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Ordered structures in Ba(Cd1/3Ta2/3)O3 microwave ceramics: A transmission electron microscopy study

Ordered structures in Ba(Cd1/3Ta2/3)O3 microwave ceramics: A...

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Materials, Integration and Packaging Issues for High - Frequency Devices

作者： Sun, J. Liu, S.J. Newman, N. Smith, David J. Center for Solid State Science Arizona State University Tempe AZ 85287 United States Department of Chemical Engineering Materials and Engineering Program Arizona State University Tempe AZ 85287 United States Department of Physics Arizona State University Tempe AZ 85287 United States Sch. of Mat. Science and Engineering Shanghai Jiao-Tong University Shanghai 20003 China

Ordered structures of Ba(Cd1/3Ta1/2)O3 ceramics with and without boron additive were investigated systemically by electron diffraction and high resolution transmission electron microscopy. The results showed a well-ordered structure of 1:2 with hexagonal symmetry for Ba(Cd1/3Ta1/2)O3 with boron additive. No significant changes in ordered structures were observed after long-period annealing. The 1:2 ordered domain structures (average domain size ∼ 18 nm) and high-density domain boundaries induced by ordering were observed for Ba(Cd1/3Ta1/2)O3 without boron additive sintered at relatively high temperature. The sintering process has a profound influence on the microstructure of Ba(Cd1/3Ta2/3)O 3 ceramics.

关键词： Barium compounds

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Intersubband Transitions in InxGa1-xAs/AlGaAs Multiple Quantum Wells for Long Wavelength Infrared Detection

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MRS Online Proceedings Library 2003年第1期744卷 1-6页

作者： Workman, Clayton L. Wang, Zhiming Ma, Wenquan George, Christi E. Panneer Selvam, R. Salamo, Gregory J. Zhou, Qiaoying Omar Manasreh, M. Center for Semiconductor Physics in Nanostructures (C-SPIN) and the Microelectronics-Photonics Program University of Arkansas Fayetteville USA Department of Electrical and Computer Engineering University of New Mexico Albuquerque USA

We report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.

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Structural polymorphism of DNA-dendrimer complexes

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Physical Review Letters 2003年第7期91卷 075501-075501页

作者： Heather M. Evans A. Ahmad K. Ewert T. Pfohl A. Martin-Herranz R. F. Bruinsma C. R. Safinya Materials Department Physics Department and Biomolecular Science and Engineering Program University of California Santa Barbara California 93106 USA Department of Physics and Astronomy University of California Los Angeles California 90095 USA and Instituut-Lorentz/LION Universiteit Leiden 2300 RA Leiden The Netherlands

DNA condensation in vivo relies on electrostatic complexation with small cations or large histones. We report a synchrotron x-ray study of the phase behavior of DNA complexed with synthetic cationic dendrimers of intermediate size and charge. We encounter unexpected structural transitions between columnar mesophases with in-plane square and hexagonal symmetries, as well as liquidlike disorder. The isoelectric point is a locus of structural instability. A simple model is proposed based on competing long-range electrostatic interactions and short-range entropic adhesion by counterion release.

关键词： .short-range complexation columnar counterion mesophases DNA condensation spermidine histones

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Real-time embedded system support for the BTeV level 1 muon trigger

Real-time embedded system support for the BTeV level 1 muon ...

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2003 IEEE Nuclear Science Symposium Conference Record - Nuclear Science Symposium, Medical Imaging Conference

作者： Haney, Michael J. Beauregard, D. Iyer, R. Kalbarczyk, Z. Liu, Q. Wang, L. Haney, M. Selen, M. Mosse, D. Shigiltchoff, O. Chopade, R. Hovey, L. Jung, M. Messie, D. Oh, J. Stone, S. Bapty, T. Neema, S. Nordstrom, S. Shetty, S. Vashishtha, S. Yao, D. Sheldon, P. Vaandering, E. Butler, J. Gottschalk, E. Kowalkowski, J. Votava, M. Appel, J. University of Illinois Urbana IL 61801 United States Des./Validation Reliable N.S.R.G. University of Illinois High Energy Physics Group Department of Physics University of Illinois Department of Computer Science Coll. in High Sch. Educ. Program University of Pittsburgh Department of Electrical Engineering Syracuse University High Energy Physics Group Department of Physics Syracuse University Inst. for Software Intgd. Systems Vanderbilt University Department of Physics BTeV Group Vanderbilt University BTeV Collaboration Particle Physics Division Fermi Natl. Accelerator Laboratory Computing Division Fermi Natl. Accelerator Laboratory Fermilab Education Office Fermi Natl. Accelerator Laboratory

The Level 1 Muon Trigger subsystem for BTeV will be implemented using the same architectural building blocks as the BTeV Level 1 Pixel Trigger: pipelined field programmable gate arrays feeding a farm of dedicated processing elements. The muon trigger algorithm identifies candidate tracks, and is sensitive to the muon charge (sign);candidate dimuon events are identified by complementary charge track-pairs. To insure that the trigger is operating effectively, the trigger development team is actively collaborating in an independent multi-university research program for reliable, self-aware, fault adaptive behavior in real-time embedded systems (RTES). Key elements of the architecture, algorithm, performance, and engineered reliability are presented.

关键词： Embedded systems

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A course in micro- and nanoscale mechanics

A course in micro- and nanoscale mechanics

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2003 ASEE Annual Conference and Exposition: Staying in Tune with engineering Education

作者： Crone, Wendy C. Carpick, Robert W. Lux, Kenneth W. Johnson, Buck D. Department of Engineering Physics University of Wisconsin-Madison Madison WI 53706 United States Engineering Mechanics Program University of Wisconsin-Madison Madison WI 53706 United States Department of Biomedical Engineering University of Wisconsin-Madison Madison WI 53706 United States Mat. Res. Sci./Eng. Ctr. N.M./I. University of Wisconsin-Madison Madison WI 53706 United States

At small scales, mechanics enters a new regime where the role of surfaces, interfaces, defects, material property variations, and quantum effects play more dominant roles. A new course in nanoscale mechanics for engineering students was recently taught at the University of Wisconsin - Madison. This course provided an introduction to nanoscale engineering with a direct focus on the critical role that mechanics needs to play in this developing area. The limits of continuum mechanics were presented as well as newly developed mechanics theories and experiments tailored to study and describe micro- and nano-scale phenomena. Numerous demonstrations and experiments were used throughout the course, including synthesis and fabrication techniques for creating nanostructured materials, bubble raft models to demonstrate size scale effects in thin film structures, and a laboratory project to construct a nanofilter device. A primary focus of this paper is the laboratory content of this course, which includes an integrated series of laboratory modules utilizing atomic force microscopy, self-assembled monolayer deposition, and microfluidic technology.

关键词： Quantum theory

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