bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linear placement algorithms and applications to VLSI design
Authors: Cheng Chung‐Kuan 
Published: May 2007

AbstractA linear placement technique that uses an objective function of the sum of wiring lengths is proposed. The method evolves from well‐known concepts in job sequencing and network flow. The relation between a job sequencing problem and this linear placement problem was demonstrated by Lawler. Also, Sidney proposed decomposition algorithms for job sequencing problems. Building on Lawler's and Sidney's work, we first develop a polynomial‐time algorithm to obtain optimal solutions for the special case of parallel graphs. Adolphson and Hu applied the max‐flow min‐cut method of the network flow problem to the partitioning of general placement problems. However, when the cut operation creates the cut of the same configuration as the previous cut operations, no additional partitioning information is obtained. We devise an optimal graph modification that tries to change the configuration of the cut for further partitioning of the problem, and achieve the maximum partitioning of the problem. Finally, a heuristic algorithm is derived to solve some Very Large Scale Integrated Circuits (VLSI) design linear placement problems. A comparison with published papers shows that our VLSI placement method produces better results.
Minimum augmentation of a tree to a K‐edge‐connected graph
Authors: Ueno Shuichi , Kajitani Yoji , Wada Hajime 
Published: May 2007

AbstractThis paper solves the minimum augmentation problem for a given tree and positive integer k, that is, to make a tree k‐edge‐connected by adding the minimum number of edges. It is shown that the minimum number of edges is the least integer not less than a half of the deficiency of the tree which is defined as the sum of k‐(degree) over all the vertices whose degrees are less than k. The proof is constructive and gives a polynomial‐time algorithm for constructing such an augmentation.
Generalized de Bruijn digraphs
Authors: Du D. Z. , Hwang F. K. 
Published: May 2007

AbstractWe show that the digraphs proposed independently by Imase and Itoh, and Reddy, Pradhan and Kuhl to minimize diameters essentially retain all the nice properties of de Bruijn digraphs and yet are applicable to any number of nodes. In particular we give results on the number of loops, the link connectivities and connectivities, the embedding properties and the self‐routing properties for these digraphs.
The minimax multistop location problem on a tree
Authors: Berman O. , Simchi‐Levi D. , Tamir A. 
Published: May 2007

AbstractIn many services (e.g., delivery, or customer pickup vehicles) the service unit usually visits a number of demand points on a single multistop tour. Typically, at a specific time of the day, the unit receives the list of waiting calls and immediately starts a tour of the network that includes all waiting customers. The multistop location problem is to find the home location for the service unit. We focus on the minimax criterion for the multistop problem defined on a tree network. Each potential list of customers is associated with the length of its respective tour and with some weight. We seek for the home location of the unit that minimizes the maximum weighted tour length over all feasible customer lists. We consider several weight functions and obtain results that reveal additional properties of the classical absolute center of the tree.
The tolerance approach to sensitivity analysis in network linear programming
Authors: Ravi N. , Wendell Richard E. 
Published: May 2007

AbstractThe tolerance approach to sensitivity analysis, in contrast to classical sensitivity analysis, allows for simultaneous and independent perturbations of objective function coefficients and of right‐hand‐side terms from their original values. Here we specialize this approach to network problems. The specialization yields streamlined results in that the computations can be performed directly on a network.
New lower bounds for the Capacitated Arc Routing Problem
Authors: Pearn Wen Lea 
Published: May 2007

AbstractThe Capacitated Arc Routing Problem (CARP), a generalization of the arc routing problems such as the Chinese Postman Problem (CPP), is a very practical distribution management problem which has many real‐world applications. This paper briefly reviews two existing lower bounding procedures—the Matching Lower Bound and the Node Scanning Lower Bound, then introduces a new bounding technique to provide tighter lower bounds on the problem solutions.
Data transfers in networks with transceivers
Authors: Choi Hyeong‐Ah , Louis Hakimi S. 
Published: May 2007

AbstractThe scheduling of data transfers in networks, where the schedule does not permit interruption and each communication module can be used as a transmitter and as a receiver (i.e., as a transceiver) was studied by Coffman et al. The same problem when interruption in the schedule is permitted and the transmitting and receiving modules are distinct was studied by Choi and Hakimi among others. Hajek and Sasaki studied another interesting variation of the problem where interruption is permitted but each communication module is a transmitter and a receiver. This paper presents certain generalizations and improvements of Hajek and Sasaki's results.
Spherulitic structures of poly [tetrafluoroethylene‐co‐(perfluoroalkyl vinyl ether)]
Authors: Fujimori Atsuhiro , Hasegawa Masahiro , Masuko Toru 
Published: May 2007

AbstractSpherulitic textures of poly[tetrafluoroethylene‐co‐(perfluoropropyl vinyl ether)] (PFA) were examined in detail using polarized optical microscopy. The PFA consisting of random comonomer units among the tetrafluoroethylene units crystallizes as spherulites composed of lamellae, although polytetrafluoroethylene usually forms extended‐chain crystals because of the rigid nature of 13/6 helices. The spherulites obtained exhibit positive birefringence since the polymer crystal has a larger refractive index in the direction normal to the chain than that along it. These fluorocopolymers exhibit a thicker long period of at least 30 nm in small‐angle X‐ray scattering profiles than is generally the case for hydrogenated crystalline polymers. In these copolymers, we consider the formation of a switchboard‐type lamellae model according to P. J. Flory's suggestion. In addition, we find the overlooked reflections near 2θ = 8.5° based on the superlattice in wide‐angle X‐ray diffraction profiles of fluorocopolymers with high reproducibility. From this result, it was found that the lattice constant that was previously proposed is required to be refined to twice the value on the a‐ and b‐axes of the reciprocal lattice to assign all the reflection indices. Copyright © 2007 Society of Chemical Industry
Proteomic analysis of high‐molecular‐weight protein polymers in a doxorubicin‐resistant breast‐cancer cell line
Authors: Park Sung‐Soo , Kim Dae‐Seok , Park Kang‐Seo , Song Hye‐Jin , Kim Soo‐Youl 
Published: May 2007

AbstractWe recently reported that increased transglutaminase 2 (TGase 2) expression correlates with increased resistance to the cancer drug doxorubicin in breast‐cancer cell lines. Interestingly, high‐molecular‐weight (HMW) proteins also increased with increased TGase 2 expression in the drug‐resistant cell lines. TGase 2 is likely to be responsible for the formation of HMW proteins, because TGase 2 catalyzes cross‐linking between proteins. Although the role of the HMW proteins is unclear, we demonstrated that TGase 2 inhibition increases drug sensitivity in breast‐cancer cells. Herein we find that TGase 2 inhibition by cystamine dramatically reduces the level of HMW proteins. Identification of the HMW proteins may suggest the mechanism of cancer drug resistance associated with aberrant TGase 2 function. To explore the identities of HMW proteins, we performed in‐gel tryptic digestions of unresolved HMW proteins and analyzed the resulting peptides using LC‐MALDI‐MS/MS. Most of the identified proteins were associated with gene regulation, such as polyadenylate‐binding proteins, translation initiation factors, and ribonucleoproteins. This finding suggests that TGase 2 may participate in gene regulation, in addition to its role in cell adhesion.
Metastable supersymmetry breaking and gauge/gravity duality
Authors: Argurio R. , Bertolini M. , Franco S. , Kachru S. 
Published: May 2007

AbstractWe discuss metastable supersymmetry breaking states in gauge theories and in their gravity duals. We then engineer a quiver gauge theory with several interesting features by studying D‐branes at a simple Calabi‐Yau singularity. At weak 't Hooft coupling we argue using field theory techniques that it admits, besides the supersymmetric vacua, also metastable non‐supersymmetric vacua, though the arguments indicating the existence of the latter are not decisive. At strong 't Hooft coupling we present a simple candidate gravity dual description for both sets of vacua.
BPS preons in M‐theory and supergravity
Authors: Bandos I.A. , de Azcárraga J.A. 
Published: May 2007

AbstractAfter introducing the notion of BPS preons as the basic constituents of M‐theory, we discuss the recent negative results in the search for solutions of the D = 10 and D = 11 supergravity equations preserving 31/32 supersymmetries i.e., of preonic solutions. The absence of these supergravity preonic solutions may point out to a pure quantum nature of BPS preons, manifesting itself in the need of incorporating quantum (stringy/M‐theoretic) corrections to the supergravity equations.
Twistor string as tensionless superstring
Authors: Bandos I.A. , de Azcárraga J.A. , Miquel‐Espanya C. 
Published: May 2007

AbstractWe give a brief review of the twistor string approach to supersymmetric Yang‐Mills theories with an emphasis on the different formulations of (super)string models in supertwistor space and their superspace form. We discuss the classical equivalence among the Siegel closed twistor string and the Lorentz harmonics formulation of the (N = 4) tensionless superstring, and notice the possible relation of the twistor string to the D = 10 Green‐Schwarz superstring action, as well as to models in the enlarged, tensorial superspaces that are relevant in higher spin theories.
Instanton calculus with R‐R background and topological strings
Authors: Billó M. 
Published: May 2007

AbstractThe non‐perturbative low energy effective action of N = 2 SYM is studied within a microscopic string realization via D3/D‐instanton systems. The localization deformation of instanton moduli space which has allowed the exact computation of multi‐instanton contributions is, in this setting, due to a RR graviphoton background. The relation of deformed instanton contributions to topological string amplitudes on CY, argued by Nekrasov, appears quite natural in this framework. Based on Billo, et al., J. High Energy Phys. 0611, 012 (2006) [arXiv:hep‐th/0606013].
Meson decays from string splitting
Authors: Bigazzi F. , Cotrone A.L. , Martucci L. , Troost W. 
Published: May 2007

AbstractWe discuss exclusive decays of large spin mesons into mesons in models of large Nc quenched QCD at strong coupling using string theory. The rate of the processes are calculated by studying the splitting of a macroscopic string on the relevant dual gravity backgrounds. We study analytic formulas for the decay rates of mesons made up of very heavy or very light quarks.
Calibrations on spaces with G × G‐structure
Authors: Gmeiner F. , Witt F. 
Published: May 2007

AbstractIn these notes we give an introduction to the concept of spaces with G × G‐structure and their structured submanifolds. These objects generalise the classical notion of a calibrated submanifold. Therefore, they are interesting from a string theory viewpoint as they are relevant to describe D‐branes in string compactifications on backgrounds with fluxes. This article is based on a talk given by the first author at the RTN Workshop “Constituents, Fundamental Forces and Symmetries of the Universe”, Naples, Italy, 9–13 Oct 2006.
Evidence for new seven‐branes
Authors: Bergshoeff E.A. , Hartong J. , Ortín T. , Roest D. 
Published: May 2007

AbstractIn order to construct globally well‐defined 7‐brane solutions we postulate the existence of a new type of 7‐brane. We show that these new 7‐branes play an important role in understanding both the existing F‐theory 7‐brane configurations as well as more general 7‐brane configurations.
pp‐wave matrix models from point‐like gravitons
Authors: Lozano Y. , Rodríguez‐Gómez D. 
Published: May 2007

AbstractThe BFSS Matrix model can be regarded as a theory of coincident M‐theory gravitons. In this spirit, we summarize how using the action for coincident gravitons proposed in hep‐th/0207199 it is possible to go beyond the linear order approximation of Kabat and Taylor, and to provide a satisfactory microscopical description of giant gravitons in AdSm × Sn backgrounds. We then show that in the M‐theory maximally supersymmetric pp‐wave background, the action for coincident gravitons, besides reproducing the BMN Matrix model, predicts a new quadrupolar coupling to the M‐theory 6‐form potential, which supports the so far elusive fuzzy 5‐sphere giant graviton solution. Finally, we discuss similar Matrix models that can be derived in Type II string theories using dualities.
BPS solutions in AdS/CFT
Authors: Milanesi G. , Gava E. , Narain K.S. , O'Loughlin M. 
Published: May 2007

AbstractWe study a class of exact supersymmetric solutions of type IIB Supergravity. They have an SO(4) SU(2) × U(1) isometry and preserve generically 4 of the 32 supersymmetries of the theory. Asymptotically AdS5 × S5 solutions in this class are dual to 1/8 BPS chiral operators which preserve the same symmetries in the 𝒩 = 4 SYM theory. They are parametrized by a set of four functions that satisfy certain differential equations. We analyze the solutions to these equations in a large radius asymptotic expansion: they carry charges with respect to two U(1) KK gauge fields and their mass saturates the expected BPS bound. We show how the same formalism is suitable for the description of excitations of the AdS5 × Yp,q geometries.
Higher genus superstring amplitudes and the measure on the moduli space
Authors: Volpato R. 
Published: May 2007

AbstractRecent derivations of completely gauge‐invariant two‐loop superstring amplitudes renewed the interest in the possible form of higher genus contributions. In this respect, two main points are discussed: a. At genus greater than 3, the Schottky problem actually represents a formidable obstruction for the explicit expression of the integration measure on the moduli space in terms of Riemann period matrices. As a first step toward such a construction, a modular invariant measure for all genera is derived, corresponding to the restriction to the Schottky locus of the Siegel metric on the upper half‐space. b. A class of natural generalizations of the 2 loop D'Hoker and Phong formula is discussed for the higher genus contributions to the 4‐gravitons amplitude in type II theories. Such expressions also satisfy the non‐trivial requirements of modular invariance and gauge slice independence.
Quasinormal modes and meson decay rates
Authors: Hoyos C. , Landsteiner K. , Montero S. 
Published: May 2007

AbstractWe model meson melting in a hot plasma by the quasinormal modes of D7‐brane fluctuations of embeddings that fall into the horizon of a black hole in Ads5 × S5 geometry. The inverse of the imaginary part of the quasinormal frequency gives the lifetime of the meson in the plasma. We briefly comment on the possible application of our model to quarkonium suppression.
Supersymmetric black holes in string theory
Authors: Mohaupt T. 
Published: May 2007

AbstractWe review recent developments concerning supersymmetric black holes in string theory. After a general introduction to the laws of black hole mechanics and to black hole entropy in string theory, we discuss black hole solutions in N = 2 supergravity, special geometry, the black hole attractor equations and the underlying variational principle. Special attention is payed to the crucial role of higher derivative corrections. Finally we discuss black hole partition functions and their relation with the topological string, mainly from the supergravity perspective. We try to summarize the state of art and discuss various open questions and problems.
Gauge theory and knot homologies
Authors: Gukov S. 
Published: May 2007

AbstractTopological gauge theories in four dimensions which admit surface operators provide a natural framework for realizing homological knot invariants. Every such theory leads to an action of the braid group on branes on the corresponding moduli space. This action plays a key role in the construction of homological knot invariants. We illustrate the general construction with a simple example based on surface operators in 𝒩 = 4 twisted gauge theory which lead to a categorification of a variant of the Casson invariant.
High breakdown field of pnp GaN/InGaN/AlGaN DHBTs with AlGaN collector
Authors: Kumakura Kazuhide , Nishikawa Atsushi , Makimoto Toshiki 
Published: May 2007

AbstractWe have investigated the characteristics of pnp GaN/InGaN/(Al)GaN double heterojunction bipolar transistors (DHBTs) grown by metalorganic vapour phase epitaxy. In GaN‐collector DHBTs, the collector–base breakdown voltage under the open‐emitter condition increased with increasing collector thickness. By fitting the experimental results to the theoretical model of the punch‐through diode, we obtained the breakdown field of 3.1 MV/cm and the residual carrier concentration of 8.5 × 1016 cm–3 for the GaN collector layer. On the other hand, in a 500 nm thick AlGaN collector, the breakdown voltage was 190 V. Assuming that the bias was uniformly applied in the AlGaN collector, the corresponding breakdown field was calculated to be 3.8 MV/cm. The results indicate that the use of an AlGaN collector in HBTs is a promising way to increase the breakdown voltage without increasing the collector thickness. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison between optical gain spectra of InxGa1–xN/In0.02Ga0.98N laser diodes emitting at 404 nm and 470 nm
Authors: Kojima K. , Funato M. , Kawakami Y. , Braun H. , Schwarz U. T. , Nagahama S. , Mukai T. 
Published: May 2007

AbstractWe investigate the gain formation properties of Inx Ga1–x N laser diodes emitting at 404 nm and 470 nm (sample A and B, respectively). Employing the Hakki–Paoli method, their optical gain spectra were measured at 298 K and 333 K. Since spatial fluctuations of the well width and In composition are considerable for long‐wavelength laser diodes, broadening of the optical gain and luminescence spectra are clearly enhanced in sample B when compared with sample A. Moreover, population inversion occurs in at least two discrete energy levels for the gain spectra of sample B. It was found that only the modal gain of the higher gain peak can overcome the mirror loss, therefore the lower one does not contribute to lasing action. We also estimate internal loss of A and B to be 25 cm–1 and 30 cm–1, respectively. The maximum gain value of A increases linearly with increasing injected current even at 333 K, while that of B grows sub‐linearly. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
UV LED arrays at 280 and 340 nm for spectroscopic biosensing
Authors: Davitt K. , Song Y.‐K. , Patterson W. , Nurmikko A. V. , Ren Z. , Sun Q. , Han J. 
Published: May 2007

AbstractWe demonstrate the application of linear arrays of ultraviolet light emitting diodes (UV LEDs) at the wavelengths of 280 nm and 340 nm to the acquisition of fluorescence spectra from single particles in real‐time. A compact optical system and custom electronics are employed to produce a compact, standalone biosensor. The detection sensitivity of the UV LED system is established using the biofluorophores tryptophan and NADH, and the capability of the sensor to sort particles based on weak spectra is demonstrated using micron‐sized polystyrene latex (PSL) spheres. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Trends in electrospinning of natural nanofibers
Authors: Haghi A. K. , Akbari M. 
Published: May 2007

AbstractNanotechnology has become in recent years a topic of great interest to scientists and engineers, and is now established as prioritized research area in many countries. The reduction of the size to the nanometer range brings an array of new possibilities in terms of material properties, in particular with respect to achievable surface to volume ratios. Electrospinning of natural fibers is a novel process for producing superfine fibers by forcing a solution through a spinneret with an electric field. An experimental study on this technique has been made in this paper and the effect of systematic parameters on electrospun nanofibers were critically analyzed. Based on this study, the key process parameters have been identified according to our experimental observations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis of carbon nanotubes, nanofibers and encapsulated nanoparticles by decomposition of acetylene on Ge modified Pd catalysts
Authors: Segura Rodrigo A. , Tello Alejandra , Häberle Patricio 
Published: May 2007

AbstractDifferent carbon nanostructures were synthesized by decomposition of acetylene over alumina supported palladium–germanium catalysts. The addition of small amounts of Ge to the Pd(1%)/γ‐Al2O3 catalyst increases the yield of carbon nanotubes among other carbon products, in the decomposition of acetylene. The use of a higher Ge concentration (0.3%) in the catalyst induces the formation of carbon nanofibers. For larger Ge concentrations (0.5%) the bimetallic catalyst particles become encapsulated in a graphitic structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐frequency performance of multiple‐channel carbon nanotube transistors
Authors: Narita Kaoru , Hongo Hiroo , Ishida Masahiko , Nihey Fumiyuki 
Published: May 2007

AbstractWe have measured the high‐frequency characteristics of carbon nanotube field effect transistors (CNTFETs) and obtained a cut‐off frequency of 10.3 GHz and maximum oscillation frequency of 3.5 GHz. These values are among the highest ever published. We achieved them by developing a high‐density multiple‐channel CNTFET structure whose output impedance is much lower than conventional single channel CNTFETs, and by accurately measuring S‐parameters, e.g., using the de‐embedding procedure that removes existing errors in measured S‐parameters of small‐signal devices. We also described an equivalent circuit RF model consistent with the experimental results. Detailed analysis revealed that decreasing parasitic capacitances of electrodes and resistances of carbon nanotube extensions greatly improve the high‐frequency performance of CNTFETs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)