bluuebunny/crossref_metadata_2025 huggingface dataset:
Soaking, moist-chilling, and temperature effects on germination of Acer pensylvanicum seeds
Authors: Bourgoin A , Simpson J D
Published: November 2004

The effect on germination of soaking duration, moist-chilling time, and temperature was evaluated using five seed lots of Acer pensylvanicum L. Seeds were soaked for 0, 48, 72, or 96 h, then moist chilled at 4 °C for 16, 24, or 32 weeks. Two temperature regimes were used for germination: (i) 16 h dark at 5 °C : 8 h light at 15 °C (5:15 °C) and (ii) 16 h dark at 20 °C : 8 h light at 30 °C (20:30 °C). Soaking and chilling seeds significantly increased germination. Germination was highest at 5:15 °C, but the germination speed was slow. Germination at 20:30 °C was lower, but 94%98% of ungerminated seeds appeared to be viable, suggesting that they were dormant. Overall results showed that soaking seeds for 48 h, moist chilling for 16 weeks, and germinating at 5:15 °C produced an average germination of 92%.
SIMULATION AND MODELING OF COMPOUND SEMICONDUCTOR DEVICES
Authors: FJELDLY TOR A. , SHUR MICHAEL S.
Published: November 2004

We review the simulation and modeling techniques used for popular compound semiconductor devices such as the Heterostructure Field Effect Transistor (HFET), the Metal Semiconductor Field Effect Transistor (MESFET), and the Heterostructure Bipolar Transistor (HBT). Starting with the basic transport theory and the numerical simulation techniques based on this theory, we proceed to give examples of Monte Carlo simulations and of 2D balance equation simulations for investigating fundamental device properties and for exploring new design concepts. Next, we present analytical HFET and MESFET models suitable for circuit simulations. These models are based on the so-called universal FET modeling concept, and accurately reproduce FET I-V and C-V characteristics. Finally, we review basic simulation and modeling issues for HBTs.
A NETWORK CHARGE-ORIENTED MOS TRANSISTOR MODEL
Authors: KATZENELSON JACOB , UNIKOVSKI AHARON
Published: November 2004

The MOS transistor physical model as described in Ref. 3 is presented here as a network model. The goal is to obtain an accurate model, suitable for simulation, free from certain problems reported in the literature,13 and conceptually as simple as possible. To achieve this goal the original model had to be extended and modified. The paper presents the derivation of the network model from physical equations, including the corrections which are required for simulation and which compensate for simplifications introduced in the original physical model.

Our intrinsic MOS model consists of three nonlinear voltage-controlled capacitors and a dependent current source. The charges of the capacitors and the current of the current source are functions of the voltages Vgs, Vbs, and Vds. The complete model consists of the intrinsic model plus the parasitics. The apparent simplicity of the model is a result of hiding information in the characteristics of the nonlinear components.

The resulted network model has been checked by simulation and analysis. It is shown that the network model is suitable for simulation: It is defined for any value of the voltages; the functions involved are continuous and satisfy the Lipschitz conditions with no jumps at region boundaries; Derivatives have been computed symbolically and are available for use by the Newton-Raphson method. The model’s functions can be measured from the terminals. It is also shown that small channel effects can be included in the model. Higher frequency effects can be modeled by using a network consisting of several sections of the basic lumped model.

Future plans include a detailed comparison of the network model with models such as SPICE level 3 and a comparison of the multi-section higher frequency model with experiments.
AN OVERVIEW OF PLACEMENT AND ROUTING ALGORITHMS FOR MULTI-CHIP MODULES
Authors: CHATTOPADHYAY SUBHOMOY , BOULDIN DONALD W. , DEHKORDI PEYMAN H.
Published: November 2004

Multi-chip modules are now required to achieve higher system speed and greater density than the traditional single chip packages mounted on printed circuit boards. Algorithms for placement of bare dies and and routing of their interconnections on MCM substrates are reviewed in this paper. Comparisons are given to point out the strengths and weaknesses of each approach. This information can assist researchers in identifying those areas which need improvement and application designers in selecting the most appropriate algorithm for a specific application.
PIN REDISTRIBUTION PROBLEM FOR MULTI-CHIP MODULES: ALGORITHMS AND COMPLEXITY
Authors: CHANG DOUGLAS , GONZALEZ TEOFILO F.
Published: November 2004

We investigate the pin redistribution problem (PRP) for multi-chip modules. We transform the PRP to the max-flow problem and obtain an efficient algorithm for finding a 2-layer solution, whenever one exists. A greedy heuristic to find a k-layer solution is described. Our approach can also construct a minimum layer solution for two variants; nets can be routed on more than one layer, and terminals (source and target) are drilled through all layers. Our algorithms take O(min{|S|, mk1/2}m2k) time, except for the heuristic procedure which takes O(km4 log 2 m) time, where S is the set of source terminals, m is the number of rows and columns in the grid, and k is the number of layers required. Several variations of the PRP when generalized to graphs can also be solved efficiently by our algorithms, whereas other variations are shown to be NP-complete.
A NEW LAYOUT DESIGN SYSTEM FOR MULTICHIP MODULES
Authors: RIESS BERNHARD M. , SCHOENE ANDREAS A.
Published: November 2004

A new layout design system for multichip modules (MCMs) consisting of three components is described. It includes a k-way partitioning approach, an algorithm for pin assignment, and a placement package. For partitioning, we propose an analytical technique combined with a problem-specific multi-way ratio cut method. This method considers fixed module-level pad positions and assigns the cells to regularly arranged chips on the MCM substrate. In the subsequent pin assignment step the chip-level pads resulting from cut nets are positioned on the chip borders. Pin assignment is performed by an efficient algorithm, which profits from the cell coordinates generated by the analytical technique. Global and final placement for each chip is computed by the state-of-the-art placement tools GORDIANL and DOMINO. For the first time, results for MCM layout designs of benchmark circuits with up to 100,000 cells are presented. They show a small number of required chip-level pads, which is the most restricted resource in MCM design, and short total wire lengths.
BOARD LEVEL PARTITIONING FOR IMPROVED PARTIAL SCAN
Authors: TRAGOUDAS SPYROS
Published: November 2004

We present a two phase board level partitioning scheme for improved partial scan on the resulting Integrated Circuits (ICs). The first phase clusters the nodes of the synchronous sequential PCB system into sets of bounded capacity. Each set represents an IC. The main objective function is to minimize the maximum number of inputs to a set. This considerably affects the test generation and response verification phases while testing the ICs. The second phase repositions the flip-flops so that we minimize the partial scan related hardware overhead for each IC, maintain a small sequential depth for all chips, and minimize the period of the global clock. We present an efficient iterative improvement heuristic for the partitioning problem of the first phase whose performance is tested on benchmarks. We also employ provably good algorithms for the second phase which result to reduced hardware overhead for partial scan. The proposed tool may also be applied to the system level partitioning problem where we partition the input circuit into Printed Circuit Boards or Multi-Chip Modules.
THREE-DIMENSIONAL PACKAGING FOR HIGH-PERFORMANCE INTERCONNECT IN LARGE-SCALE VLSI SYSTEMS
Authors: DEHON ANDRÉ , DRENCKHAHN FRED , KNIGHT THOMAS , MINSKY HENRY
Published: November 2004

The transit time through the interconnect between VLSI components can be a significant fraction of the latency in a large VLSI system. In this paper we describe a scheme for dense, three-dimensional packaging of VLSI components which reduces chip-to-chip transit latencies by reducing interconnect distances. Our packaging scheme sandwiches layers of conventional printed-circuit boards between layers of packaged components to efficiently utilize all three spatial dimensions for interconnect. We introduce the key components of our stack packaging scheme and show how they combine to provide efficient housing for a large range of large-scale VLSI systems.
A SEPARATION BETWEEN RECONFIGURABLE MESH MODELS
Authors: MACKENZIE PHILIP D.
Published: November 2004

We prove a separation between two models of the reconfigurable mesh (rmesh), the cross-over model and the non-cross-over model. Specifically, for any constant k ≥ 1, we show that in the non-cross-over model, a k × n rmesh requires Ω( log n) time to compute the parity of n bits stored one per column, while in the cross-over model, when k ≥ 3, a k × n rmesh can compute the parity in constant time. This is the first separation demonstrated between the cross-over and non-cross-over model. The lower bound does not rely on the bandwidth constraints of the mesh and does not restrict the instruction sets of the processors. Moreover, it is the first lower bound for the rmesh which requires only binary inputs.
THE RECONFIGURABLE RING OF PROCESSORS: EFFICIENT ALGORITHMS VIA HYPERCUBE SIMULATION
Authors: ROSENBERG ARNOLD L. , SCARANO VITTORIO , SITARAMAN RAMESH K.
Published: November 2004

We propose a design for, and investigate the computational power of a dynamically reconfigurable parallel computer that we call the Reconfigurable Ring of Processors ([Formula: see text], for short). The [Formula: see text] is a ring of identical processing elements (PEs) that are interconnected via a flexible multi-line reconfigurable bus, each of whose lines has one-packet width and can be configured, independently of the other lines, to establish an arbitrary PE-to-PE connection. A novel aspect of our design is a communication protocol we call COMET — for Cooperative MEssage Transmission — which allows PEs of an [Formula: see text] to exchange one-packet messages with latency that is logarithmic in the number of PEs the message passes over in transit.

The main contribution of this paper is an algorithm that allows an N-PE, N-line [Formula: see text] to simulate an N-PE hypercube executing a normal algorithm, with slowdown less than 4 log log N, provided that the local state of a hypercube PE can be encoded and transmitted using a single packet. This simulation provides a rich class of efficient algorithms for the [Formula: see text], including algorithms for matrix multiplication, sorting, and the Fast Fourer Transform (often using fewer than N buslines). The resulting algorithms for the [Formula: see text] are often within a small constant factor of optimal.
PERMUTATION ROUTING AND SORTING ON MESHES WITH ROW AND COLUMN BUSES
Authors: SUEL TORSTEN
Published: November 2004

We study the problems of permutation routing and sorting on several models of meshes with fixed and reconfigurable row and column buses. We describe two fast and fairly simple deterministic algorithms for permutation routing on two-dimensional networks, and a more complicated algorithm for multi-dimensional networks. The algorithms are obtained by converting two known off-line routing schemes into deterministic routing algorithms, and they can be implemented on a variety of different models of meshes with buses. We also give a deterministic algorithm for 1–1 sorting whose running time matches that for permutation routing, and another algorithm that matches the bisection lower bound on reconfigurable networks of arbitrary constant dimension.
PERFORMANCE STUDY OF LU FACTORIZATION WITH LOW COMMUNICATION OVERHEAD ON MULTIPROCESSORS
Authors: DESPREZ F. , DONGARRA J. J. , TOURANCHEAU B.
Published: November 2004

In this paper, we make efficient use of asynchronous communications on the LU decomposition algorithm with pivoting and a column-scattered data decomposition to derive precise computational complexities. We then compare these results with experiments on the Intel iPSC/860 and Paragon machines and show that very good performances can be obtained on a ring with asynchronous communications.
EFFICIENT ALGORITHMS FOR THE EUCLIDEAN DISTANCE TRANSFORM
Authors: PAVEL SANDY , AKL SELIM G.
Published: November 2004

The Euclidean Distance Transform is an important computational tool for the processing of binary images, with applications in many areas such as computer vision, pattern recognition and robotics. We investigate the properties of this transform and describe an O(n2) time optimal sequential algorithm. A deterministic EREW-PRAM parallel algorithm which runs in O( log n) time using O(n2) processors and O(n2) space is also derived. Further, a cost optimal randomized parallel algorithm which runs within the same time bounds with high probability, is given.
EFFICIENT BROADCAST ON HYPERCUBES WITH WORMHOLE AND E-CUBE ROUTINGS
Authors: HO CHING-TIEN , KAO MING-YANG
Published: November 2004

We consider the problem of broadcasting on an n-dimensional hypercube with wormhole e-cube routing, intermediate reception capability, and one-port communication. We give an algorithm, optimal to within a multiplicative constant, that broadcasts in this model in Θ(n/ log 2(n+1)) routing steps. We also give routing algorithms that achieve tight time bounds for n-cubes where n ≤ 6.
FAST PARALLEL ALGORITHMS FOR MINIMUM AND RELATED PROBLEMS WITH SMALL INTEGER INPUTS
Authors: BERKMAN OMER , MATIAS YOSSI
Published: November 2004

The fundamental problem of minimum computation has several well-studied generalizations such as prefix minima, range minima, and all nearest smaller values computations. Recent papers introduced parallel algorithms for these problems when the n input elements are given from an integer domain [1..s], obtaining O( lglglg s) running time and linear work for s ≥ n. However, most of these algorithms have the running time of O( lglglg n) (rather than O( lglglg s)) for all values of s ≤ n, except for the case of s = O(1) in which case the running time is O(α(n)). In this paper we focus on the range s ≤ n and provide linear-work algorithms whose running time O( lglglg s + f(n)) is for all s ≥ 0, where f(n) is either one of the slow growing functions lg *n or α(n). We show how to generalize our algorithms to the case that the domain size s is unknown, with the same complexities. (All previous algorithms work only under the assumption that the domain size s is known.) Moreover, we make our algorithms output-sensitive with the lglglgs term replaced by lglglg M, where M is the maximum input value. In fact, for the minimum computation problem the running time is O( lglglg m) for all s ≥ 0, where m is the minimum input value.
A PARALLEL FAST MULTIPOLE METHOD FOR THE HELMHOLTZ EQUATION
Authors: STALZER MARK A.
Published: November 2004

Presented is a parallel algorithm based on the fast multipole method (FMM) for the Helmholtz equation. This variant of the FMM is useful for computing radar cross sections and antenna radiation patterns. The FMM decomposes the impedance matrix into sparse components, reducing the operation count of the matrix-vector multiplication in iterative solvers to O(N3/2) (where N is the number of unknowns). The parallel algorithm divides the problem into groups and assigns the computation involved with each group to a processor node. Careful consideration is given to the communications costs. A time complexity analysis of the algorithm is presented and compared with empirical results from a Paragon XP/S running the lightweight Sandia/University of New Mexico operating system (SUNMOS). For a 90,000 unknown problem running on 60 nodes, the sparse representation fits in memory and the algorithm computes the matrix-vector product in 1.26 seconds. It sustains an aggregate rate of 1.4 Gflop/s. The corresponding dense matrix would occupy over 100 Gbytes and, assuming that I/O is free, would require on the order of 50 seconds to form the matrix-vector product.
ON OPTIMAL OROW-PRAM ALGORITHMS FOR COMPUTING RECURSIVELY DEFINED FUNCTIONS
Authors: NIEDERMEIER ROLF , ROSSMANITH PETER
Published: November 2004

We investigate parallel algorithms to compute recursively defined functions. Our computational model are parallel random access machines (PRAM's). We preferably make use of the OROW-PRAM (owner read, owner write), a model supposed to be even weaker and more realistic than the EREW-PRAM (exclusive read, exclusive write) and that still provides the opportunities of a completely connected processor network. For OROW-PRAM's we show that our parallel algorithms are work-optimal.
TIGHT BOUNDS ON THE NUMBER OF l-NODES IN A FAULTY HYPERCUBE
Authors: WU JIE
Published: November 2004

The spanning binomial tree is one of most frequently used spanning tree structures to implement various parallel applications in multiprocessor systems, such as hypercubes. In this paper, we define an l-node as a root node of an incomplete spanning binomial tree of a hypercube, which is defined as a connected subtree of a spanning binomial tree with the same root node that connects all the nonfaulty nodes in the hypercube. We show that in an n-dimensional hypercube with m faulty nodes there are at least 2n − 2ml-nodes. This implies that at least half of the nodes of the hypercube are l-nodes if the number of faulty nodes is less than the dimension of the hypercube.
LINEAR ELECTION IN HYPERCUBES
Authors: TEL GERARD
Published: November 2004

This article proposes an election algorithm for the hypercube; it exchanges less than [Formula: see text] messages and uses O( log 2 N) time (where N is the size of the cube). A randomized version of the algorithm achieves the same (expected) asymptotic message and time bounds, but uses messages of only O( log log N) bits and can be used in anonymous hypercubes.
ON THE EFFECTIVENESS OF SYNCHRONOUS PARALLEL BRANCH-AND-BOUND ALGORITHMS
Authors: CORRÊA RICARDO , FERREIRA AFONSO
Published: November 2004

We theoretically compare the efficiency of two versions, sequential and parallel (synchronous), of the method called branch-and-bound used for searching for an optimal solution in the scope of combinatorial optimization. The sequential version consists of successive decompositions of the original problem in smaller disjoint subproblems and its parallel version consists of a high level parallelization that assumes a shared memory model of parallel computation. Its principle consists of decomposing several subproblems in parallel at each iteration in a synchronous way, and its efficiency is usually defined with respect to its sequential counterpart. In this paper, we redefine the notion of efficiency in such a way that the usefulness of the work done by each processor will be taken into account. The knapsack problem is used as an application and some simulation results are presented to validate and illustrate the use of the new efficiency measures.
A CONSTANT TIME SORTING ALGORITHM FOR A THREE DIMENSIONAL RECONFIGURABLE MESH AND RECONFIGURABLE NETWORK
Authors: MERRY MARK S. , BAKER JOHNNIE
Published: November 2004

Sorting techniques have numerous applications in computer science. Current real number and integer sorting techniques for the reconfigurable mesh operate in constant time using a reconfigurable mesh of size n × n to sort n numbers. This paper presents a constant time algorithm to sort n items on a reconfigurable network with [Formula: see text] switches and [Formula: see text] processors. Also, new constant time selection and compression algorithms are given. All results may also be implemented on the 3-D reconfigurable mesh.
BIPARTITE EXPANDER MATCHING IS IN NC
Authors: HAGLIN DAVID J.
Published: November 2004

A work-efficient deterministic [Formula: see text] algorithm is presented for finding a maximum matching in a bipartite expander graph with any expansion factor β > 1. This improves upon a recently presented deterministic [Formula: see text] maximum matching algorithm which is restricted to those bipartite expanders with large expansion factors (β ≥ Δ∊, ∊ > 0), and is not work-efficient [1].
A COST-EFFECTIVE STREAMLINING OF THE DIOGENES DESIGN METHODOLOGY
Authors: PICQUENDAR MARC , ROSENBERG ARNOLD L. , SCARANO VITTORIO
Published: November 2004

The original DIOGENES design methodology produces fault-tolerant layouts of VLSI processor arrays by designing an array's interconnection network as a (possibly large) number of (re)configurable bundles of wires, each bundle being organized as either a stack or a queue. The benefits of DIOGENES often come only at high cost, in terms of both configuration hardware and algorithmic cost of configuration. In this paper, we improve the original methodology in a way that simultaneously: streamlines the design process; produces more cost-effective layouts; can be augmented to allow efficient dynamic reconfigurability.

Our new version of DIOGENES replaces the wire-stacks and/or -queues of the original methodology by a single generalized deletion stack (GDS for short), independent of the topology of the array. The new methodology has three major benefits:

1. A GDS-network can be configured in time linear in the size of the graph being realized. (Optimal network configuration is superlinear for the queue-based version and NPcomplete for the stack-based version of the original methodology.)

2. A GDS-network can realize any linearization of any graph, subject only to the constraints of the implemented node-degree and cutwidth. (The original methodology demands a priori commitment to a fixed number of stacks or queues of fixed sizes, hence limits one to a restricted set of array topologies.)

3. A GDS-network usually requires dramatically less configuration hardware than a stack- or queue-based network would (albeit with larger switches).

We end with suggested enhancements to this new, flexible, version of DIOGENES.
SIMULTANEOUS ALLOCATION AND SCHEDULING USING CONVEX PROGRAMMING TECHNIQUES
Authors: RAMASWAMY SHANKAR , BANERJEE PRITHVIRAJ
Published: November 2004

Simultaneous exploitation of task and data parallelism provides significant benefits for many applications. The basic approach for exploiting task and data parallelism is to use a task graph representation (Macro Dataflow Graph) for programs to decide on the degree of data parallelism to be used for each task (allocation) and an execution order for the tasks (scheduling). Previously, we presented a two step approach for allocation and scheduling by considering the two steps to be independent of each other. In this paper, we present a new simultaneous approach which uses constraints to model the scheduler during allocation. The new simultaneous approach provides significant benefits over our earlier approach for the benchmark task graphs that we have considered.
AN EFFECTIVE TWO-DIMENSIONAL MESH PARTITIONING STRATEGY
Authors: CHU YUNG-KANG , ROVER DIANE T.
Published: November 2004

Mesh-connected parallel architectures have become increasingly popular in the design of multiprocessor systems in recent years. Many partitionable two-dimensional (2D) mesh systems have been built or are currently being developed. To allow the best usage of these systems, an effective mesh partitioning/submesh allocation strategy is desirable. In this paper, we report on a new best-fit processor allocation strategy for 2D mesh systems. An efficient implementation of this strategy is presented that keeps the searching overhead low. Extensive simulations have been performed to compare the performance of this strategy with existing ones. The results show that it outperforms existing strategies in terms of mean response time under all load conditions and different job characteristics.
PARALLEL INCREMENTAL SCHEDULING
Authors: WU MIN-YOU
Published: November 2004

Parallel incremental scheduling is a new approach for load balancing. In parallel scheduling, all processors cooperate together to balance the workload. Parallel scheduling accurately balances the load by using global load information. In incremental scheduling, the system scheduling activity alternates with the underlying computation work. This paper provides an overview of parallel incremental scheduling. Different categories of parallel incremental scheduling are discussed.
GROUND STATE PROPERTIES OF A DISSIPATIVE TWO STATE SYSTEM COUPLED TO PHONONS
Authors: PAREEK T.P. , JAYANNAVAR A.M.
Published: November 2004

We present a systematic analysis of the ground state properties of a tunneling system coupled to an Ohmic bath. The nonadiabatic effects induced by coupling with tunneling particle, on the ground state properties of phonons are taken into account. For this we have considered both displacement and deformation of phonons via a variational treatment. The symmetry breaking transition, or the delocalization-localization transition, of the tunneling particle is presented and is compared with earlier known results. We also show that in the critical regime a gap will be opened near the zero momentum in the spectrum of the phonons. The modified phonon spectrum along with the phonon displacement field correlation functions have been calculated. It is shown that in the critical regime the tunneling system stabilizes the lattice against long wavelength fluctuations.
LOCALIZED SPACE-CHARGE WAVES IN SPACE-CHARGE DOMINATED BEAMS
Authors: WANG J.G. , REISER M.
Published: November 2004

The physics of space-charge waves in space-charge dominated beams is presented. This includes the generation and propagation of such waves in coasting beams, and the end effect on space-charge waves in bunched beams. It is shown for the first time in experiments that a single space-charge wave can be generated, that the geometry factor g can be measured with localized space-charge waves, and that both reflection and transmission take place at the ends of an initially rectangular bunch. The experimental results are supported by theoretical analyses. The application of localized space-charge waves as a new technique for beam diagnostics is also described.
ON EXACT BOSONIZATION OF THE CALOGERO-SUTHERLAND MODEL
Authors: KHVESHCHENKO D.V.
Published: November 2004

We elaborate on an algebraic method of a momentum space bosonization of exactly solvable one-dimensional models in the framework of the Calogero-Sutherland model. The approach provides an exact representation of the local field operator of the Calogero-Sutherland model in terms of quasiparticle eigenstate’s creation-annihilation operators and furnishes a simple method to compute exact correlation functions.
STABILITY OF A SPIRAL ARRAY OF MAGNETIC DIPOLES: A PHYSICAL SELF-ORGANIZED GROWTH PROCESS
Authors: FAN X.D. , BURSILL L.A.
Published: November 2004

In Douady and Couder’s experiment [Phys. Rev. Lett. 68, 2098, (1992)], spiral phyllotactic-like patterns were formed by magnetic dipoles dropped sequentially into a vertical magnetic field. The dipoles move radially with constant velocity limited by frictional forces in a silicone oil. This paper presents an analysis of the stability of this self-organized growth process using a second nearest neighbor (SNN) interaction approximation. A recurrence formula is written for the divergence angle; i.e. the angle defined by successive radial vectors. Further analysis of the dynamics reveals conditions for convergence of the recurrence formula. The limit of the divergence angle sequence includes a fractional part of 2π which is the ratio of pairs of Fibonacci numbers. It also includes a term which varies linearly with a growth parameter µ, defined in the text. The system is stable within the SNN approximation. Even richer dynamical behaviors, including that observed experimentally, require higher order approximations.
THE OPTICAL PROPERTIES OF CHIRAL LIQUID CRYSTALS
Authors: SURESH K.A.
Published: November 2004

In recent times, optical diffraction and reflection from periodically twisted liquid crystalline media have attracted a lot of attention. The important developments in this area have been considered here.
RHEOLOGY AND RHEO-OPTICS OF POLYMER LIQUID CRYSTALS
Authors: SRINIVASARAO MOHAN
Published: November 2004

The rheological and rheo-optical properties of nematic solutions of rodlike polymers are discussed. Magnetic field induced instability in the twist geometry is discussed in terms of the flow properties of these solutions. The rheological properties of these nematic solutions are compared to isotropic solutions of the same polymer. The behavior in shear flow of nematic solutions is discussed in terms of the Ericksen-Leslie equations. Deviations from those solutions are also discussed in context to polymeric nematics.
The ${\mathbb K}{\rm d}{\mathbb V}$ and ℝLW Sets
Authors: TARASOV V.F.
Published: November 2004

It is shown that the well-known (1+1)-dimension equations of Korteweg-de Vries (KdV), Boussinesq (BSQ) and regulated long waves (RLW) have a “latent structure”, the latter connected with the [Formula: see text] and ℝLW sets. The elements of these sets are solition-like equations of the KdV(τ, α) and RLW(τ, α) type, where τ≥1 is the order of higher derivative with respect to t and the parameter α>0 defines the “modification” of the above input equations. For example, KdV (1, 1)= KdV , KdV (1, 1/2)= mKdV ,…, KdV (2, 1)= BSQ , KdV (2, 1/2)= mBSQ ,…; RLW (1,1)= RLW , RLW (1,1/2)= mRLW , etc.
NOVEL FLUX INDUCED RESONANT TUNNELING IN THE MESOSCOPIC RING CONFINED BETWEEN POTENTIAL BARRIERS
Authors: SADREEV ALMAS F. , VID’MANOV VALERY A.
Published: November 2004

Transport properties of mesoscopic rings confined between potential barriers are considered. Also considered is the double barrier structure with barriers fabricated of rings connected by a one-dimensional wire. Such structures we define as Aharonov-Bohm diodes with resonant tunneling (ABDRT) because for zero external magnetic flux their transport properties are quite similar to diodes with resonant tunneling (DRT). However, application of external magnetic flux gives rise to new resonant peaks of transmission determined by the quantization condition of the rings. Positions and widths of these novel flux induced resonant peaks extremely depend on the flux.
ORBITAL PARAMAGNETISM IN METALLIC SYSTEMS WITH LARGE ANGULAR MOMENTA
Authors: HJELM ANDERS , TRYGG JOAKIM , ERIKSSON OLLE , JOHANSSON BÖRJE , WILLS JOHN M.
Published: November 2004

We demonstrate that the field induced spin and orbital moments in paramagnetic metals in general are parallel, since the Zeeman energy overcomes the spin-orbit energy that is in favor of an antiparallel arrangement when the electronic shell is less than half-filled. In the early actinides, however, the spin-orbit energy becomes sufficiently strong to approach the border where the moments can couple antiparallel. This results in peculiar magnetic states for α-Pu and some uranium compounds, where the spin moments are antiparallel to the applied field and the magnetic response dominated by the orbital character, and consequently these systems display unusual spin densities and magnetic form factors.
TOPOLOGICAL EXCITATIONS, SPIN WAVES AND THE ORIGIN OF MASS
Authors: GOSWAMI GAUTAM
Published: November 2004

Topological aspects of low energy excitations in the form of spin-waves in ferromagnetic systems are studied here. It is pointed out that the generation of spin-waves in three-dimensional Ising fermions can be visualized through the change in chirality. The characteristic features of spin-waves in both the phases of a continuous symmetric XY model are also studied. It is argued that the mass generation of these low energy excitations has a topological origin.
RESONANT TUNNELING IN DOUBLE BARRIER SEMICONDUCTOR NANO-STRUCTURES
Authors: ROY DILIP K. , SINGH AJIT
Published: November 2004

The principles of operation of a double barrier resonant tunneling diode (DBRTD) giving rise to negative differential conductivity effect are first reviewed. Next, the physics of resonant tunneling based on (i) the time-independent conventional approach and (ii) the time-dependent quantum measurement approach, as applied to a DBRTD, is discussed. Expressions for the resonant tunneling current densities through the barriers are then derived on the ideas of quantum measurement. Through the well the current, however, flows by the conventional mechanism. The three current density magnitudes are found to be identical under resonant conditions. Finally, an expression for the resonant tunneling current density due to a group of incident electrons is derived.
A NUMERICAL STUDY OF THE QUANTUM OSCILLATIONS IN MULTIPLE DANGLING RINGS
Authors: GU B.Y. , BASU CHAITALI
Published: November 2004

We present the quantum mechanical calculations on the conductance of the quantum waveguide topology containing multiply connected dangling mesoscopic rings with the transfer matrix approach. The profiles of the conductance as functions of the Fermi wave number of electrons depend on the number of rings and also on the geometric configuration of the system. The conductance spectrum of this system for disordered lengths in the ring circumferences, dangling links, ballistic leads connecting consecutive dangling rings is examined in detail. We find that there exist two kinds of mini-bands, one originating from the eigenstates of the rings, i.e. the intrinsic mini-bands, and the extra mini-bands. Some of these extra minibands are associated with the dangling links connecting the rings to the main quantum wire, while others are from the standing wave modes associated with the ballistic leads connecting adjacent dangling rings. These different kinds of mini-bands have completely different properties and respond differently to the geometric parameter fluctuations. Unlike the system of potential scatterers, this system of geometric scatterers shows complete band formations at all energies even for finite number of scatterers present. There is a preferential decay of the energy states, depending upon the type of disorder introduced. By controling the geometric parameters, the conductance band structure of such a model can be artificially tailored.
FERROMAGNETIC MONOLAYERS
Authors: ELMERS HANS-JOACHIM
Published: November 2004

The ferromagnetic properties of ultrathin films grown on non-magnetic substrates provide interesting new insights into the physics of magnetism. In this report we review experiments in the very low coverage regime (Θ < 2 atomic layers). The Fe monolayer on W plays an outstanding role, because it forms a ferromagnetic and thermodynamically stable monolayer. Ferromagnetic Fe monolayers on W can be prepared with a high degree of perfection. We therefore focus on ultrathin Fe films on W(110) and W(100) substrates. Experimental results for these in-plane magnetized films, prepared as close as possible to 2-dimensional structures of perfect translational symmetry, are compared with appropriate theoretical models, We also discuss experimental results for the perpendicularly magnetized Co monolayer on Cu(111). The symmetry of the magnetic anisotropy is found to play an important role for the understanding of the magnetic phase transition in 2 dimensions.

A new aspect is provided by finite size effects resulting from the morphology of magnetic ultrathin films. Microscopy with atomic resolution allows a systematic approach to the understanding of these finite size effects. Starting from the well-known magnetic properties of the extended Fe monolayer on W(110), we focus on ultrathin Fe films on W(110) deviating from the nearly perfect structure.
DISSIPATIVE 2D ELECTRON ON A TORUS IN EXTERNAL MAGNETIC FIELD: TRANSPORT PROPERTIES AND MAGNETIC TRANSLATIONS
Authors: CRISTOFANO G. , GIULIANO D. , MAIELLA G. , VALENTE L.
Published: November 2004

The effect of dissipation on the electron ground state wave function on a torus in the presence of an external transverse magnetic field is analyzed on large time scales [Formula: see text]. Its extension to the multiparticle center of the mass wave function is also given. The novel transport properties of the system are then studied by applying Laughlin gauge argument with the use of the magnetic translation operators.
DOUBLE EXCITATION IN PROTON–HELIUM COLLISIONS
Authors: SCHULZ M.
Published: November 2004

Theoretical and experimental studies on double excitation in proton–helium collisions are reviewed. Two theoretical approaches, which are common in the treatment of atomic collision processes, are described: perturbative approaches and the close coupling method. Experimentally, double excitation has mainly been studied by spectroscopy of the autoionized electrons emitted by the decay of the doubly excited states and by projectile energy-loss spectroscopy. The results emerging from the theoretical and experimental studies include the following points: first, the coupling of the doubly excited states to the continuum is very important in the electron spectra leading to pronounced interference effects. Second, double excitation mechanisms involving the electron–electron interaction are dominant except for low projectile energies. Third, interference effects between various double excitation mechanisms appear to be insignificant in the cross-sections differential in the electron emission angle, but might be important under certain conditions in the cross-sections differential in the projectile scattering angle.
NUCLEATION AT FIRST-ORDER WETTING TRANSITIONS
Authors: BLOSSEY R.
Published: November 2004

A brief review is given of the status of both theory and experiments of nucleation phenomena at first-order wetting transitions, focusing on the early stages of the decay of metastable thin and thick wetting films. Generally, the decay of metastable films is initiated by the formation of critical nuclei, which for a metastable thin film are droplets on the wall of the system, and holes in the wetting layer for a metastable thick film. The shapes of critical droplets and critical holes are characterized in the various regions of the wetting phase diagram. The nucleation rate of critical nuclei is determined, which is a measure of the lifetime of the metastable states. The connection of the theoretical results with recent experiments on nucleated wetting layers is discussed. An outlook on open problems concludes the review.
SYNTHESIS OF CARBON NITRIDE
Authors: MARTON D. , BOYD K. J. , RABALAIS J. W
Published: November 2004

In 1990, Liu and Cohen presented a pseudopotential study of the structural and electronic properties of β- C 3 N 4, a hypothetical compound. The calculated properties of β- C 3 N 4, including bulk modulus and velocity of sound, were found to be comparable to that of diamond suggesting high values for hardness and for thermal conductivity. In this paper, the field of experimental efforts to produce carbon nitride is reviewed. Synthesis of β- C 3 N 4 has been claimed on the basis of diffraction data. However, the overall composition of the materials obtained in these as in most other experiments is not stoichiometric; the N-to-C concentration ratio attained in most cases is [ N ]/[ C ] < 1. The likely reasons for this and the dependence of the nitrogen content and bonding on deposition conditions are discussed. The determination of the carbon and nitrogen contents and, more importantly, their contents in specific bonding states is a complex problem to which a significant part of this paper is devoted. Most of the experimental work to date, including those claiming success, applied deposition methods using energetic particles. Among these methods, ion beam deposition (IBD) stands out for its ability to control deposition conditions. We discuss in particular detail our work based on IBD. On the basis of results from electron spectroscopies and computer simulations, a film growth model that includes surface deposition, subplantation and preferential sputtering of nitrogen has been developed. Some future possibilities for the deposition of C-N films are discussed on the basis of this model.
OPTICAL SPECTROSCOPY STUDY OF PULSED EXCIMER LASER GENERATED PLASMA FROM CuO
Authors: ADHI K. P. , KALE SHILPA , PADHYE YOGESH , LIMAYE A. V. , OGALE S. B.
Published: November 2004

Optical emissions from pulsed excimer laser induced plasma emanating from CuO target are studied by an Optical Multichannel Analyzer system in the context of its implications for thin film growth by Pulsed Laser Deposition. The plasma is generated in four different ambients viz. hydrogen, helium, oxygen (pressure of 100 mTorr in each case) and vacuum (2 × 10−5 Torr ) at different energy densities from 1 to 3.5 J/cm 2. The plasma constituents and their evolution in the growth space (i.e. at a distance of 1.5cm from the target) has been studied. Various transitions corresponding to Cu(I), H(I), Cu(II) and O(II) are observed. The observation of strong transitions due to O(II) in the plasma formed in vacuum, hydrogen and helium suggests significant degree of ionization of atoms via molecular splitting and inverse Bremsstrahlung process during early plasma formation. The persistence of ionicity in the plasma can be attributed to long recombination lifetimes for the specific conditions used. In the case of ablation in oxygen ambient a very significant and remarkably selective enhancement of the copper vapor lasing transition at 510.5 nm is observed which brings out the role of oxygen molecules in sustaining the radiation trapping condition. The changes in the concentrations of neutrals and ions as a function of the laser energy density are also examined. It is argued that impingement of ions/atoms in an excited state on the growing surface can potentially lead to localized energy deposition via non-radiative deexcitation resulting into enhancement of film quality and density.
HALL-MEISSNER EFFECT IN CHARGED ANYON FLUID AT T → 0
Authors: FERRER E. J. , DE LA INCERA V.
Published: November 2004

The superconducting behavior of the charged anyon fluid at finite density (µ ≠ 0) and in the zero temperature statistical limit (T → 0) is investigated in a self-consistent way. It is found that total magnetic screening appears only in the presence of a transverse electric field. This electric field is interpreted as a way to simulate, in the linear effective theory, the Hall potential associated with the vortex structure of the charged anyon system. The London penetration depth of the superconducting phase is found to be dependent on the filling factor.
LASER ABLATION PROCESS FOR FABRICATION OF Y1Ba2Cu3Ox THIN FILM
Authors: FUKUSHIMA KENSUKE
Published: November 2004

For understanding the laser ablation process, the interaction between the laser beam and the target, the motion of plasma species under the various conditions, and the correlation between the film properties and the behavior of plasma species are investigated. It is suggested that by laser irradiation an energetic plasma is formed above a target and an expansion of the plasma species continuously occurs converting thermal energy to translational energy. Plasma species expand forward, colliding with ambient oxygen and lead to a formation of a shock front far from the target. Plasma temperature and the density are drastically increased due to the shock front formation. These phenomena affect film properties such as film growth orientation and surface morphology. Preferential orientation of thin films can be related with the kinetic energy of species impinging the substrate and it is found that the nucleation of outgrowths on film surfaces increases at higher oxygen pressures at which the shock front is generated above the target.
THE INFLUENCE OF SINTERING AND Sb CONTENT ON THE FORMATION OF HIGH TEMPERATURE SUPERCONDUCTING PHASE IN Bi(Pb)-Sr-Ca-Cu-O SYSTEM
Authors: SIDDIQI S. A. , AKHTAR BILQUEES , MAQSOOD A.
Published: November 2004

Six different compositions in ( Bi 1.5 Pb 0.5−x Sb x) Sr 2 Ca 2 Cu 3 O y (with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by the solid state reaction method. Sintering at different temperatures (between 800–860° C) and time periods has been carried out in order to study its effect on T c values. The samples have been characterized by x ray powder diffraction (XRD), Scanning Electron Microscopy (SEM) and measurement of resistance at various temperatures. The study reveals that the incorporation of Sb up to x = 0.2 promotes the formation of a high-T c 2223 phase and large sintering time helps in reducing the number of unwanted phases. Compositions with x ≥ 0.3 result in the formation of a new monoclinic "4441 phase" (along with 2223 and 2212 minor phases) which is non-superconducting down to 77 K. Sintering time at 860°C for samples with x = 0.0, 0.1, 0.2 and 0.3 affects the respective T c values and the maximum values observed are 94 K, 96 K, 100 K and 87 K, respectively. The samples with x = 0.4 and 0.5 do not superconduct up to 77 K.
DENSITY-DEPENDENT PHONORITON STATES IN HIGHLY EXCITED SEMICONDUCTORS
Authors: QUANG NGUYEN HONG , KHUE NGUYEN MINH
Published: November 2004

The dynamical aspects of the phonoriton state in highly-photoexcited semiconductors is studied theoretically. The effect of the exciton–exciton interaction and nonbosonic character of high-density excitons are taken into account. Using Green's function method and within the Random Phase Approximation it is shown that the phonoriton dispersion and damping are very sensitive to the exciton density, characterizing the excitation degree of semiconductors.
MOTION PLANNING OF LEGGED ROBOTS: THE SPIDER ROBOT PROBLEM
Authors: BOISSONNAT JEAN-DANIEL , DEVILLERS OLIVIER , DONATI LEONBATTISTA , PREPARATA FRANCO P.
Published: November 2004

We consider the problem of planning motions of a simple legged robot called the spider robot. The robot is modelled as a point where all its legs are attached, and the footholds where the robot can securely place its feet consist of a set of n points in the plane. We show that the space F of admissible and stable placements of such robots has size Θ(n2) and can be constructed in O(n2 log n) time and O(n2) space. Once F has been constructed, we can efficiently solve several problems related to motion planning.
FINDING k FARTHEST PAIRS AND k CLOSEST/FARTHEST BICHROMATIC PAIRS FOR POINTS IN THE PLANE
Authors: KATOH NAOKI , IWANO KAZUO
Published: November 2004

We study the problem of enumerating k farthest pairs for n points in the plane and the problem of enumerating k closest/farthest bichromatic pairs of n red and n blue points in the plane. We propose a new technique for geometric enumeration problems which iteratively reduces the search space by a half and provides efficient algorithms. As applications of this technique, we develop algorithms, using higher order Voronoi diagrams, for the above problems, which run in O(min{n2, n log n+k4/3log n/log1/3 k}) time and O(n+k4/3/log1/3 k+k log n) space for general Lp metric with p≠2, and O(min{n2, n log n+k4/3}) time and O(n+k4/3+k log n) space for L2 metric. For the problem of enumerating k closest/farthest bichromatic pairs, we shall also discuss the case where we have different numbers of red and blue points. To the authors’ knowledge, no nontrivial algorithms have been known for these problems and our algorithms are faster than trivial ones when k=o(n3/2).
MANHATTONIAN PROXIMITY IN A SIMPLE POLYGON
Authors: KLEIN ROLF , LINGAS ANDRZEJ
Published: November 2004

Let P be a simple planar polygon. We present a linear time algorithm for constructing the bounded Voronoi diagram of P in the Manhattan metric, where each point z in P belongs to the region of the closest vertex of P that is visible from z. Among other consequences, the minimum spanning tree of the vertices in the Manhattan metric that is contained in P can be computed within optimal linear time. The same results hold for the L∞-metric.α