bluuebunny/crossref_metadata_2025 huggingface dataset:
Extreme ultraviolet lithography mask flatness and electrostatic chucking analysis
Authors: Mikkelson A. , Engelstad R. , Lovell E. , Blaedel K. , Claudet A.
Published: December 2003

The Semiconductor Industry Association Roadmap for Extreme Ultraviolet Lithography (EUVL) calls for significant improvements in the quality and flatness of the substrate and patterned mask. Due to the difficulty of meeting the mask flatness specifications, an alternative strategy has been proposed to ensure that suitable substrates will be available for EUVL. A new SEMI standard for EUVL electrostatic chucks is currently being developed. If such a standard were established, then the flatness requirements for the substrate might be relaxed to permit certain types of bow that can later be flattened by the chuck. The purpose of this study is to identify which shapes can indeed be flattened by an electrostatic chuck. To support the proposed strategy, it is essential that the clamping ability of the electrostatic chuck be characterized and well-understood. The ability of the chuck to flatten the mask will depend primarily on the mechanical stiffness of the chuck and the clamping pressure. Legendre polynomials have been identified as an effective and efficient means of representing EUVL mask surface shapes. Finite element (FE) models have been developed to utilize the Legendre polynomials as input data to define the surfaces of the reticle. The FE models were then used to determine the clamping response of the various mask shapes. In particular, the maximum reticle-to-chuck gap within the flatness quality area and over the entire reticle has been tracked as a function of clamping pressure and chuck thickness for the low-order Legendre modes.
Nanoscopic magnetic field sensor based on extraordinary magnetoresistance
Authors: Solin S. A. , Hines D. R. , Rowe A. C. H. , Tsai J. S. , Pashkin Yu A.
Published: December 2003

The design, fabrication, and performance of a nanoscopic magnetic field sensor based on the newly discovered phenomenon of extraordinary magnetoresistance (EMR) are reported. It is shown that a sensor with an active volume of 35 nm length×30 nm width×20 nm height yields room temperature EMR values as high as 35% at an applied field of 0.05 T. The mesoscopic physics implications of these new results are discussed.
Development of three-dimensional pattern-generating system for focused-ion-beam chemical-vapor deposition
Authors: Hoshino T. , Watanabe K. , Kometani R. , Morita T. , Kanda K. , Haruyama Y. , Kaito T. , Fujita J. , Ishida M. , Ochiai Y. , Matsui S.
Published: December 2003

We studied the fabrication of free-designed three-dimensional (3D) structures by using focused-ion-beam chemical-vapor deposition. The 3D structures are fabricated by scanning 30 keV Ga+ ion-beam-assisted deposition in a 1×10−4 Pa phenanthrene atmosphere. The scanning pattern and blanking signal of the ion beam are generated by a 3D computer-aided-designed model using a computer pattern-generating system. This 3D pattern-generating system is able to fabricate overhang and hollow structures by setting suitable parameters (for example, plot pitch, dwell time, time interval of irradiations, and priorities of scanning). In this article, we demonstrate the performance of a 3D pattern-generating system by fabricating a 1:100 000 000 scale model of the Enterprise spaceship, a microring, a moth’s eyelike structure, and a morpho butterflylike structure with 200 nm spacing.
Fabrication of quasi-three-dimensional micro/nanomechanical components using electron beam cross-linked poly (methyl methacrylate) resist
Authors: Teh W. H. , Smith C. G.
Published: December 2003

We present a useful, flexible, and simple surface nanomachining technique which employs electron beam cross-linked poly (methyl methacrylate) (PMMA) as a high-resolution negative resist for the sacrificial layer. This technique simplifies the fabrication of quasi-three-dimensional micro/nanomechanical components without the need to pile up two-dimensional layers. The high compliance of cross-linked PMMA allows the stress relaxation of the mechanical structures to begin after the deposition of each mechanical layer. This happens prior to the stiction-free dry release step. The fact that it can be used both as an insulating layer and sacrificial layer allows the high-resolution patterning of micro/nanomechanical structures alongside unique multilayer devices. We demonstrate this technique by the characterization of PMMA as a function of electron irradiation levels and by referring to fabricated micro/nanoelectromechanical structures and devices.
Step and flash imprint lithography template characterization, from an etch perspective
Authors: Dauksher W. J. , Mancini D. P. , Nordquist K. J. , Resnick D. J. , Standfast D. L. , Convey D. , Wei Y.
Published: December 2003

As a means of studying process windows with short turnaround time while avoiding substrate-to-substrate repeatability issues, Step and Flash Imprint Lithography templates were fabricated with physical masking of quadrants during dry etching used to introduce process perturbations. For every 20 s of descum (Ar/O2 etch) time, critical dimensions (CD) were observed to change approximately 2.6 nm on sub-100 nm features. Similarly, increasing Cr overetch time by 20% resulted in a positive CD change of 3.8 nm. Line edge roughness decreased with increasing descum and Cr overetch times. Best overall performance was observed for a 20 s descum used in conjunction with a 110% Cr overetch. Of four tip types studied, sharpened silicon atomic force microscopy tips were able to accurately measure etch depth of 80 nm trenches, but geometrical considerations limited sidewall angle determination to greater than 100°. Cross-sectioning of features on 6×6×0.25 in. quartz plates was successfully accomplished using a focused ion beam technique with typical sidewall angles of about 95° observed on 150 nm features. Finally, minimal microloading was observed for the ICP-based quartz etch process. Feature sizes ranging from 70 nm up to 8 μm possessed an average etch depth of 88.8 nm with a 1.2 nm (1 sigma) variation.
Nanometer-period gratings in hydrogen silsesquioxane fabricated by electron beam lithography
Authors: Word Michael J. , Adesida Ilesanmi , Berger Paul R.
Published: December 2003

Hydrogen silsesquioxane (HSQ) is a high-resolution negative-tone inorganic resist for electron beam lithography. Investigations on the smoothness of the surfaces of thin films (less than 100 nm thick) have been conducted for nanolithography applications. It is demonstrated that films at thicknesses down to 25 nm have very low rms roughness and are defect free. Using 50 kV electron beam lithography, we demonstrate the achievement of isolated 6-nm-wide lines and 27 nm period gratings in 30 nm HSQ films on silicon substrates. These results are superior to those achieved with poly(methylmethacrylate) resist and demonstrates the versatility of HSQ for nanolithography.
Extreme expansion of proximity gap by double exposures using enlarged pattern masks for line and space pattern formation in x-ray lithography (evolution of exposure method to symmetric illumination)
Authors: Toyota E. , Washio M. , Watanabe H. , Sumitani H.
Published: December 2003

The extendibility of x-ray lithography is limited by the usable proximity gap. The gap is considered to be larger than 10 μm. Practically, a line and space (L/S) pattern of 70 nm linewidth and 140 nm pitch can be formed at a 10 μm gap using a 1:1 exposure mask (1× mask). If a double-pitch mask (2× mask), whose L/S pitch is twice as large as desired what to be printed on the wafer, is used while applying double exposures, the gap can be expanded greatly. A simulation result showed that using a 2× mask, a gap of more than 1000 μm can be used to form a L/S pattern of 200 nm pitch. An exposure test at a gap of 160 μm using the 2× mask proved sufficient to form the L/S pattern of 200 nm pitch. The principle of symmetric illumination explains this result well. The principle is also applicable to two-dimensional pattern formation, for which we propose a concept of mask design, i.e., the symmetric-illumination mask (SIM). Multidot images formed by the SIMs can produce mega- or giga-unit patterns of less than 25 nm linewidth by applying continuous writing.
Fabrication of trilayer resist using photocuring-imprint lithography
Authors: Kim Sang Hoon , Hiroshima H. , Inoue S. , Kurashima Y. , Komuro M.
Published: December 2003

We fabricated fine trilayer resist structures (photocurable polymer/spin-on-glass (SOG)/Novolak resist) with a smooth-top surface and low-edge roughness, which is useful for standard patterning for the evaluation of critical dimension-atomic-force microscopy using photocuring-imprint lithography. A very serious pattern shrinkage problem observed at the top of the photocurable polymer after etching at room temperature was greatly improved by using substrate cooling, where the temperature was decreased to −120 °C. Finally, we obtained improved pattern shrinkage of the photocurable polymer, ranging from a maximum of 23 nm to a minimum of 4 nm, at optimum etching conditions. The pattern reduction did not occur in the following etch process. From this result, we noticed that throughout the trilayer resist etch process, the pattern reduction was mainly generated in the photocurable polymer etching step. SOG was used as the hard mask. The SOG showed high etch selectivity against the bottom layer of the Novolak resist in O2-based plasmas. The SOG etched only in pure SF6 gas, but the SOG was not etched in O2-based plasmas. Novolak resist etching at room temperature showed very small pattern shrinkage, no residue, no undercut, and fine features, while the Novolak etching at −120 °C showed much residue and damaged etch profiles. It is probable that in contrast to −120 °C, at room temperature, the residue of the Novolak resist was clearly removed by the reactive species, which are activated by the increased temperature. After trilayer resist etching, removal of the SOG layer was needed for the measurement of the pattern shrinkage and the line-edge roughness (LER). In this experiment, the SOG layer was removed by using anhydrous hydrofluoric acid. This method did not cause the pattern collapse which is frequently found in wet etching removal. Furthermore, trilayer resist patterns after the removal of the SOG layer showed very fine etch profiles, and the LER variation was very small through the whole trilayer resist etching process.
Fabrication of sub-50 nm critical feature for magnetic recording device using electron-beam lithography
Authors: Yang XiaoMin , Eckert Andrew , Mountfield Keith , Gentile Harold , Seiler Carl , Brankovic Stanko , Johns Earl
Published: December 2003

We report an electron-beam lithography method for printing and plating sub-50 nm isolated trenches with a high aspect ratio (AR) for the nanofabrication of magnetic thin-film heads. To eliminate the issues of resist footing and resist residue in the narrow trench process, we coated a thin dissolution layer of polymethylglutarimide (PMGI) as an undercoat layer between a seed layer and a resist layer. The undercoat PMGI layer was easily and more quickly dissolved than the top resist layer, so it completely cleared the trench during the develop process. In addition, a vertical sidewall at the bottom of the narrow trench was achieved by controlling the processing conditions, e.g., bake temperature and thickness of the dissolution layer. All of these allowed us to facilitate plating the narrow trench with a high magnetic moment material. In this work, narrow trenches were electroplated with both 1.0 T NiFe and 1.8 T CoNiFe alloys. We demonstrated the capability of fabricating narrow electrodeposited magnetic write top pole structures with a critical dimension (CD) of 30 nm in a 0.24 μm resist (AR=8:1) and a CD of 22 nm in a 0.11 μm resist (AR=5:1).
Deterministic photon transport calculations in general geometry for external beam radiation therapy
Authors: Williams M. L. , Ilas D. , Sajo E. , Jones D. B. , Watkins K. E.
Published: December 2003

A deterministic method is described for performing three‐dimensional (3D) photon transport calculations of a LINAC head and phantom/patient geometry to obtain dose distributions for therapy planning. The space, energy, and directional‐dependent photon flux density is obtained by numerically solving the Boltzmann equation in general 3D geometry using the method of characteristics. The deterministic transport calculations use similar ray tracing routines as found in Monte Carlo (MC) codes. A special treatment is developed to better represent the impact of scattering from accelerator head components. Equations are presented for computing the water kerma distribution due to the uncollided and collided photon flux density field in the patient region. Kerma results obtained from the deterministic computation are compared to Monte Carlo values for a variety of source spectra and field sizes. The agreement for kerma values in the beam is usually within the MC uncertainties. It is concluded that the deterministic method is a rigorous, first‐principles approach that could provide a superior alternative to Monte Carlo calculations for some types of problems. However additional development is needed to provide capability for 3D electron transport calculations.
A comparison of TLD dosimeters: LiF:Mg,Ti and LiF:Mg,Cu,P for measurement of radiation therapy doses
Authors: Glennie Gilbert D.
Published: December 2003

TLDs (thermoLuminescent dosimeters) are used in radiation therapy to verify the radiation dose cancer patients receive. University of Virginia Radiation Oncology clinic TLD results must be fully trustworthy so physicians can confidently monitor and determine a patient's treatment. A systematic investigation of major factors affecting TLD response and accuracy was carried out. The factors investigated were dose response, energy response, and fading response for two types of TLDs. The supralinear dose response of LiF:Mg,Ti and slightly sublinear dose response of LiF:Mg,Cu,P is documented. In energy response, LiF:Mg,Ti over‐responds 46% at 33 keV while LiF:Mg,Cu,P under‐responds by 10%–20% in the kilovoltage region. Fading of LiF:Mg,Ti was measured at 9% in 63 days while the output of LiF:Mg,Cu,P enhanced by 8% 23 days after irradiation. Overall accuracy at the 95% CL is 2.18% for LiF:Mg,Ti and 4.09% for LiF:Mg,Cu,P. Confidence in UVa Radiation Oncology TLD measurements was enhanced with the use of improved procedures. The improvements include reading LiF:Mg,Cu,P with a neutral density filter in the TLD reader, labeling of TLDs with identifying numbers, and use of a circular annealing tray for cooling. LiF:Mg,Cu,P releases about 34 times more light than LiF:Mg,Ti, and a neutral density filter prevents saturation of the TLD reader. Labeled TLDs are easier to work with, resolve mix‐ups, and increase accuracy by allowing TLDs to be read always in the same orientation (although labeling slightly reduces the light output). TLDs all cool at the same rate on the circular tray, which maintains consistent TLD sensitivity between TLDs and multiple uses. The improved University of Virginia TLD procedure is documented.
Feldkamp‐based cone‐beam reconstruction for gantry‐tilted helical multislice CT
Authors: Hein Ilmar , Taguchi Katsuyuki , Silver Michael D. , Kazama Masahiro , Mori Issei
Published: December 2003

Depending on the clinical application, it is frequently necessary to tilt the gantry of an x‐ray CT system with respect to the patient and couch. For single‐slice fan–beam systems, tilting the gantry introduces no errors or artifacts. Most current systems, however, are helical multislice systems with up to 16 slices. The multislice helical reconstruction algorithms used to create CT images must be modified to account for tilting of the gantry. If they are not, the quality of reconstructed images will be poor with the presence of significant artifacts, such as smearing and double‐imaging of anatomical structures. Current CT systems employ three primary types of reconstruction algorithms: helical fan‐beam approximation, advanced single‐slice rebinning, and Feldkamp‐based algorithms. This paper presents a generalized helical cone‐beam Feldkamp‐based algorithm that is valid for both tilted and nontilted orientations of the gantry. Unlike some of the other algorithms, generalization of the Feldkamp algorithm to include gantry tilt is simple and straightforward with no significant increase in computational complexity. The effect of gantry tilt for helical Feldkamp reconstruction is to introduce a lateral shift in the isocenter of the reconstructed slice of interest, which is a function of the tilt, couch speed, and view angle. The lateral shift is easily calculated and incorporated into the helical Feldkamp backprojection algorithm. A tilt‐generalized helical Feldkamp algorithm has been developed and incorporated into Aquilion™ 16‐slice CT (Toshiba, Japan) scanners. This paper describes modifications necessary for the tilt generalization and its verification.
The “Sparking Chaotic Pendulum”: Trajectories of a Chaotic Pendulum Revealed
Authors: Cássaro Fabio Augusto Meira , da Costa Saab Sérgio , Bernardes Luiz Antônio Bastos , da Silva Jeremias Borges
Published: December 2003

A few years ago, The Physics Teacher published two very interesting papers describing experiments involving pendulums. The first article1 described an easy way to create, using magnets, a pendulum that exhibits a chaotic behavior. The second paper2 showed how a spark generator coupled to a spherical pendulum could be used to “trace” and study two-dimensional trajectories such as Lissajous patterns, ellipses, and circles. In this paper, those two ideas were joined to develop an experimental apparatus, the “chaotic sparking pendulum,” that reveals chaotic two-dimensional orbits of a pendulum sliding over a set of magnets.
Molecular Interactions of Nucleic Acid Bases. A Review of Quantum-Chemical Studies
Authors: Šponer Jiří , Hobza Pavel
Published: December 2003

Ab initio quantum-chemical calculations with inclusion of electron correlation significantly contributed to our understanding of molecular interactions of DNA and RNA bases. Some of the most important findings are introduced in the present overview: structures and energies of hydrogen bonded base pairs, nature of base stacking, interactions between metal cations and nucleobases, nonplanarity of isolated nucleobases and other monomer properties, tautomeric equilibria of nucleobases, out-of-plane hydrogen bonds and amino acceptor interactions. The role of selected molecular interactions in nucleic acids is discussed and representative examples where these interactions occur are given. Also, accuracy of density functional theory, semiempirical methods, distributed multipole analysis and empirical potentials is commented on. Special attention is given to our very recent reference calculations on base stacking and H-bonding. Finally, we briefly comment on the relationship between advanced ab initio quantum-chemical methods and large-scale explicit solvent molecular dynamics simulations of nucleic acids.
Van der Waals Attraction and Coalescence of Aqueous Salt Nanodroplets
Authors: Jungwirth Pavel , Buch Victoria
Published: December 2003

Collisions of aqueous salt nanodroplets at zero initial relative velocity are investigated by means of molecular dynamics simulations. The character of the van der Waals interactions, which bring the droplets together and cause coalescence, is described in detail, and the parameters of the droplet-droplet potential are extracted from the collisional trajectories. Concentration and size effects, together with implications for cloud and precipitation modeling are discussed.
Linear Scaling with Cluster Size for Calculations of NMR Properties in Liquids
Authors: Müller Markus G. , Huber Hanspeter
Published: December 2003

It is shown for liquid water that the contributions of the solvent molecules to the NMR chemical shielding of a proton in the solute molecule is approximately pair-additive. This leads to linear scaling in the computational effort with cluster size if the cluster method is applied. Alternatively, a pair chemical shielding surface, in analogy to the pair potential surface, can be calculated in advance of the simulation. Its analytical fit can be coded into the simulation program to be easily evaluated any time during the simulation, e.g. to get time correlation functions. As water is an extreme case, it is assumed that for other systems an even better additivity might be found.
The Importance of Photodissociative Trichloromethanol for Atmospheric Chemistry
Authors: Mühlhäuser Max , Schnell Melanie , Peyerimhoff Sigrid D.
Published: December 2003

Multireference configuration interaction calculations are carried out for ground and excited states of trichloromethanol to investigate two important photofragmentation processes relevant to atmospheric chemistry. For CCl3OH five low-lying excited states in the energy range between 6.1 and 7.1 eV are found to be highly repulsive for C-Cl elongation leading to Cl2COH (X2A') and Cl (X2P). Photodissociation along C-O cleavage resulting in Cl3C (X2A') and OH (X2Π) has to overcome a barrier of about 0.8 eV (13A'', 11A'') and 1.2 eV (13A') because the low-lying excited states 11A'', 13A' and 13A'' become repulsive only after elongating the C-O bond by about 0.3 Å.
Multireference Brillouin-Wigner Coupled Cluster Singles and Doubles (MRBWCCSD) and Multireference Doubles Configuration Interaction (MRD-CI) Calculations for the Bergman Cyclization Reaction
Authors: Puiggros Oscar Rey , Pittner Jiří , Čársky Petr , Stampfuss Philipp , Wenzel Wolfgang
Published: December 2003

We used the Bergman cyclization reaction of hex-3-ene-1,5-diyne to 1,4-didehydrobenzene (p-benzyne) as a benchmark system to assess the accuracy of recently developed multireference Brillouin-Wigner coupled cluster singles and doubles method (MRBWCCSD) in comparison with the multireference doubles configuration interaction (MRD-CI) calculations using the same geometry and basis set. Activation and reaction enthalpies were calculated. We found good agreement between experiment and theory at the MRCI+Q/CCSD(T) level of theory, provided a sufficiently large polarized basis set is used (cc-pVTZ). The MRBWCCSD theory gives results of a somewhat lower accuracy, presumably because of the absence of T3 clusters in the cluster expansion.
A Combined ab initio and Density Functional Study of the Electronic Structure of Thymine and 2-Thiothymine Radicals
Authors: Vianello Robert , Maksić Zvonimir B.
Published: December 2003

The electronic and energetic properties of thymine (1) and 2-thiothymine (2) and their neutral and positively charged radicals are considered by a combined ab initio and density functional theory approach. It is conclusively shown that ionization of 1 and 2 greatly facilitates deprotonation of the formed radical cations thus making the proton transfer between charged and neutral precursor species thermodynamically favourable. The adiabatic ionization potential of 1 and 2 are analysed. It appears that ADIP(1) is larger than ADIP(2) by 10 kcal/mol, because of greater stability of the highest occupied molecular orbital (HOMO) of the former. It is also shown beyond any doubt that the spin density in neutral and cationic radical of 2 is almost exclusively placed on the σ-3p AO of sulfur implying that these two systems represent rather rare sigma-radicals. In contrast, the spin density of radicals of 1 is distributed over their π-network.
Spin-Orbit Coupling in Biradicals. 4. Zero-Field Splitting in Triplet Nitrenes, Phosphinidenes, and Arsinidenes
Authors: Havlas Zdeněk , Kývala Mojmír , Michl Josef
Published: December 2003

The spin dipole-spin dipole and spin-orbit coupling contributions to the zero-field splitting parameter D of CH3-N, CH3-P, CH3-As, SiH3-N, SiH3-P, and SiH3-As have been calculated from CAS(12,11)/cc-pVTZ wave functions and the Breit-Pauli Hamiltonian at T1 B3LYP/cc-pVTZ optimized geometries. The spin-orbit coupling contributions represent a minor correction for the nitrenes, and bring the value computed for methylnitrene from 1.66 to 1.84 cm-1, in good agreement with experiment (1.72 cm-1). They dominate the spin-spin terms by an order of magnitude in phosphinidenes and by more than two orders of magnitude for arsinidenes. The properties of all these perfect axial biradicals follow expectations based on the simple algebraic 2-in-2 model of biradical structure.
Hardness and HOMO-LUMO Gap Probed by the Helium Atom Pushing the Molecular Surface of the First-Row Hydride Molecules
Authors: Małolepsza Edyta , Piela Lucjan
Published: December 2003

A molecular surface defined as an isosurface of the valence repulsion energy may be hard or soft with respect to probe penetration. As a probe, the helium atom has been chosen. In addition, the Pauli exclusion principle makes the electronic structure change when the probe pushes the molecule (at a fixed positions of its nuclei). This results in a HOMO-LUMO gap dependence on the probe site on the isosurface. A smaller gap at a given probe position reflects a larger reactivity of the site with respect to the ionic dissociation.
Theoretical Study of Solvent Effect on π-EDA Complexation I. SCF and DFT Calculations Within Polarized Continuum Model on TCNE-Benzene Complex
Authors: Kyseľ Ondrej , Juhász György , Mach Pavel
Published: December 2003

SCF, MP2, DFT(B3LYP) and the polarizable continuum model (PCM) were used to study geometry, charge distribution and energetics of the π-EDA complex formation between tetracyanoethene (TCNE) and benzene both in gas phase and in various polar solvents (cyclohexane, dichloromethane and water). MP2/6-31G*, MP2/6-31+G*, MP2/6-31G*(0.25) calculations have shown that geometry of the complex is planparallel with interplane distance of 3.05 × 10-10 m on the MP2/6-31G* level and the complexation energy is equal to -6.8 to -8.95 kcal/mol, while dominant contributions to the complexation energy come from intermolecular correlation and energy. The PCM continuum model of polar solvents describes well both the Gibbs energy of solvation of individual solutes and the difference between the complex and its constituents and also agrees with the experimental finding that the polar solvent effect decreases the complexation constant of the π-EDA complex formation by a factor of 2-4 when chloroform is replaced by more polar dichloromethane, and by a factor of 9, when tetrachlormethane is replaced by dichloromethane. It seems that the solvation Gibbs energy of the π-EDA complex formation always prefers stability of solvated constituents to that of the solvated complex. The electrostatic polarization Gibbs energy of solvation is responsible for the tendency of complexation constants to decrease with increasing solvent polarity; however, non-electrostatic terms contribute as well. While the enthalpy of complexation between benzene and TCNE in gas phase is about -10.0 kcal/mol due to the negative complexation entropy ∆(∆S) = -22.56 cal/mol K, the ∆G of complexation is -3.8 kcal/mol. The solvation part of the complexation Gibbs energy in dichloromethane is +5.14 kcal/mol (PCM-SCF/6-31G* calculation) so that complexation constant K = 0.1 dm3/mol in this solvent was found.
On the Stability of Hydroxo-Dilead(II) Complex Cations
Authors: Breza Martin , Biskupič Stanislav
Published: December 2003

Using Hartree-Fock, B3LYP and MP2 treatments, the optimal geometries and corresponding electronic structures of various isomers of [Pb2(OH)n]q complex cations with total charges q = 4 - n, n = 1, 2, 3, are investigated. [Pb(μ-OH)Pb]3+ seems to be the most stable whereas [Pb(μ-OH)Pb(OH)]2+ and [Pb(μ-OH)Pb(OH)2]+ are unstable (because additional non-bridging hydroxyl weakens the neighboring Pb-Oμ and Oμ-Hμ bonds). Direct Pb-Pb and Oμ-Oμ interactions are weakly antibonding in all the systems under study. The clusters are held together exclusively by relatively weak Pb-O bonds. Non-measurable concentrations of [Pb(μ-OH)Pb]3+ in aqueous solutions might be explained by its reaction with OH- yielding preferably unstable [Pb(μ-OH)Pb(OH)]2+ species.
EFFICIENT QUANTUM KEY DISTRIBUTION SCHEME USING THE BELL STATE MEASUREMENT
Authors: LI XIAOYU
Published: December 2003

In this paper we provide a quantum key distribution (QKD) scheme based on the correlations of Einstein–Podolsky–Rosen (EPR) pairs. The scheme uses an auxiliary qubit to interact with the EPR pair and does the Bell state measurement to get the key. It is proved to be secure. All EPR pairs are used in distributing the key except some error-checking bits. So it is efficient. On the other hand there are less classical communications needed in the scheme.
INFLUENCE OF ENTANGLEMENT DEGREE ON SQUEEZING AND PHOTON ANTIBUNCHING IN THE TWO-PHOTON JAYNES–CUMMINGS MODEL
Authors: ZHANG GUO-FENG , JIA XIN-JUAN , LIANG JIU-QING
Published: December 2003

We study the interaction of two entangled two-energy-level atoms interacts with a single-mode and two-photon cavity field. The atom state is detected after exiting the cavity, and it is found that the nonclassical properties of the field states depend strongly on the entanglement degree between the two atoms. Meanwhile it is shown that squeezing of field and photon antibunching can be greatly enhanced via selective atomic measurements.
SPECIATION EFFECT IN THE PENNA AGING MODEL
Authors: ŁASZKIEWICZ A. , SZYMCZAK SZ. , CEBRAT S.
Published: December 2003

We have simulated the evolution of diploid, sexually reproducing populations using the Penna model of aging. We have noted that diminishing the recombination frequency during the gamete production generates a specific diversity of genomes in the populations. When two populations independently evolving for some time were mixed in one environmental niche of the limited size and crossbreeding between them was allowed, the average lifespan of hybrids was significantly shorter than the lifespan of the individuals of parental lines. Another effect of higher hybrid mortality is the faster elimination of one parental line from the shared environment. The two populations living in one environment co-exist much longer if they are genetically separated — they compete as two species instead of crossbreeding. This effect can be considered as the first step to speciation — any barrier eliminating crossbreeding between these populations, leading to speciation, would favor the populations.
EFFICIENCY OF GENETIC ALGORITHM AND DETERMINATION OF GROUND STATE ENERGY OF IMPURITY IN A SPHERICAL QUANTUM DOT
Authors: SAFAK HALUK , SAHIN MEHMET , GÜLVEREN BERNA , TOMAK MEHMET
Published: December 2003

In the present work, genetic algorithm method (GA) is applied to the problem of impurity at the center of a spherical quantum dot for infinite confining potential case. For this purpose, any trial variational wave function is considered for the ground state and energy values are calculated. In applying the GA to the problem under investigation, two different approaches were followed. Furthermore, a standard variational procedure is also performed to determine the energy eigenvalues. The results obtained by all methods are found in satisfactory agreement with each other and also with the exact values in literature. But, it is found that the values obtained by genetic algorithm based upon wavefunction optimization are closer to the exact values than standard variational and also than genetic algorithm based on parameter optimization methods.
AN AXISYMMETRIC LATTICE BOLTZMANN MODEL FOR SIMULATION OF TAYLOR–COUETTE FLOWS BETWEEN TWO CONCENTRIC CYLINDERS
Authors: NIU X. D. , SHU C. , CHEW Y. T.
Published: December 2003

Recently, Halliday et al. presented an idea by inserting the "source" terms into the two-dimensional (2D) lattice Boltzmann equation (LBE) so that the emergent dynamics of the lattice fluid can be transformed into the cylindrical polar system. This paper further extends the idea of Halliday et al. to include the effect of azimuthal rotation. The terms related to the azimuthal effect are considered as inertia forces. By using our recently developed Taylor-series-expansion and least-square-based lattice Boltzmann method (TLLBM) for the transformed LBE and a second order explicit finite difference method for the azimuthal moment equation, Taylor–Couette flows between two concentric cylinders with the inner cylinder rotating were simulated. To show the performance of the proposed model, the same problem was also simulated by the three-dimensional (3D) LBM. Numerical results showed that the present axisymmetric model is much more efficient than the 3D model for an axisymmetric flow problem.
INFORMATION STORAGE IN NANOSCOPIC MAGNETIC ARRAYS
Authors: KACZANOWSKI A. , KUŁAKOWSKI K.
Published: December 2003

Magnetostatic interaction between elements of nanomagnetic arrays leads to flips of magnetic moments in the magnetic posts. Such flips are equivalent to errors of information stored in an array. We prove that antiferromagnetic-like modulation strongly reduces the probability of errors, with relatively small reduction in the density of the stored information. We also show that some magnetic configurations of the array generate errors more likely than the others. Elimination of these configurations leads to a substantial improvement of the storage quality.
DAMAGE SPREADING IN THE BAK–SNEPPEN MODEL: SENSITIVITY TO THE INITIAL CONDITIONS AND EQUILIBRATION DYNAMICS
Authors: TIRNAKLI UGUR , LYRA MARCELO L.
Published: December 2003

The short-time and long-time dynamics of the Bak–Sneppen model of biological evolution are investigated using the damage spreading technique. By defining a proper Hamming distance measure, we are able to make it exhibit an initial power-law growth which, for finite size systems, is followed by a decay towards equilibrium. In this sense, the dynamics of self-organized critical states is shown to be similar to the one observed at the usual critical point of continuous phase transitions and at the onset of chaos of nonlinear low-dimensional dynamical maps. The transient, pre-asymptotic and asymptotic exponential relaxation of the Hamming distance between two initially uncorrelated equilibrium configurations is also shown to be fit within a single mathematical framework.
A LINUX PC CLUSTER FOR LATTICE QCD WITH EXACT CHIRAL SYMMETRY
Authors: CHIU TING-WAI , HSIEH TUNG-HAN , HUANG CHAO-HSI , HUANG TSUNG-REN
Published: December 2003

A computational system for lattice QCD with overlap Dirac quarks is described. The platform is a home-made Linux PC cluster, built with off-the-shelf components. At present the system constitutes of 64 nodes, with each node consisting of one Pentium 4 processor (1.6/2.0/2.5 GHz), one Gbyte of PC800/1066 RDRAM, one 40/80/120 Gbyte hard disk, and a network card. The computationally intensive parts of our program are written in SSE2 codes. The speed of our system is estimated to be 70 Gflops, and its price/performance ratio is better than $1.0/Mflops for 64-bit (double precision) computations in quenched QCD. We discuss how to optimize its hardware and software for computing propagators of overlap Dirac quarks.
STUDY OF THE UNEQUAL SPHERES PACKING PROBLEM: AN APPLICATION TO RADIOSURGERY TREATMENT
Authors: LI S. P. , NG KA-LOK
Published: December 2003

We employ the Monte Carlo method to study a constrained optimization problem — packing hard spheres with unequal radii (r2 > r1) into a 3D bounded region and discuss its connection with the Gamma Knife radiosurgery treatment planning. Selection of the best fit solution is based on the Boltzmann factor, e-ΔE/T, which allows us to search for the global optimal solution. As an illustration we determined the least number (≤15) of packed spheres that will occupy the largest volume for three different hypothetical tumor sizes (4115, 10 000 and 36 000 voxels). For the bounded regions and the sizes of the packed spheres that we studied here, the optimal volume packing ratio ranges from 41.3 to 48.7%. From our study, using a lower r2/r1 ratio is more desirable due to the ≤15 radiation shots constraint. The optimal volume packing ratio can be obtained within a relative short CPU computing time and could provide a good starting point for the radiosurgery treatment planning.
PHASE TRANSITIONS IN SOME EPIDEMIC MODELS DEFINED ON SMALL-WORLD NETWORKS
Authors: AGIZA H. N. , ELGAZZAR A. S. , YOUSSEF S. A.
Published: December 2003

Some modified versions of susceptible-infected-recovered-susceptible (SIRS) model are defined on small-world networks. Latency, incubation and variable susceptibility are separately included. Phase transitions in these models are studied. Then inhomogeneous models are introduced. In some cases, the application of the models to small-world networks is shown to increase the epidemic region.
ACCELERATED LATTICE BGK METHOD FOR UNSTEADY SIMULATIONS THROUGH MACH NUMBER ANNEALING
Authors: ARTOLI A. M. , HOEKSTRA A. G. , SLOOT P. M. A.
Published: December 2003

We present an adaptation of the lattice BGK method for fast convergence of simulations of laminar time-dependent flows. The technique is an extension to the recent accelerated procedures for steady flow computations. Being based on Mach number annealing, the present technique substantially improves the accuracy and computational efficiency of the standard lattice BGK method for such unsteady flows.
POLYNOMIAL MAP FACTORIZATION OF SYMPLECTIC MAPS
Authors: RANGARAJAN GOVINDAN
Published: December 2003

Long-term stability studies of nonlinear Hamiltonian systems require symplectic integration algorithms which are both fast and accurate. In this paper, we study a symplectic integration method wherein the symplectic map representing the Hamiltonian system is refactorized using polynomial symplectic maps. This method is analyzed for the three degree of freedom case. Finally, we apply this algorithm to study a large particle storage ring.
REVIEW OF THE PROPERTIES OF THE W BOSON AT LEP, AND THE PRECISION DETERMINATION OF ITS MASS
Authors: STRÖHMER RAIMUND
Published: December 2003

We review the precision measurement of the mass and couplings of the W boson at LEP. The total and differential W+W-cross section is used to extract the WWZ and WWγ couplings. We discuss the techniques used by the four LEP experiments to determine the W mass in different decay channels, and present the details of methods used to evaluate the sources of systematic uncertainty.
SYMMETRY PRINCIPLE PRESERVING AND INFINITY FREE REGULARIZATION AND RENORMALIZATION OF QUANTUM FIELD THEORIES AND THE MASS GAP
Authors: WU YUE-LIANG
Published: December 2003

Through defining irreducible loop integrals (ILI's), a set of consistency conditions for the regularized (quadratically and logarithmically) divergent ILI's are obtained to maintain the generalized Ward identities of gauge invariance in non-Abelian gauge theories. The ILI's of arbitrary loop graphs can be evaluated from the corresponding Feynman loop integrals by adopting an ultraviolet (UV) divergence preserving parameter method. Overlapping UV divergences are explicitly shown to be factorizable in the ILI's and be harmless via suitable subtractions. A new regularization and renormalization method is presented in the initial space–time dimension of the theory. The procedure respects unitarity and causality. Of interest, the method leads to an infinity free renormalization and meanwhile maintains the symmetry principles of the original theory except the intrinsic mass scale caused conformal scaling symmetry breaking and the anomaly induced symmetry breaking. Tadpole graphs of Yang–Mills gauge fields are found to play an essential role for maintaining manifest gauge invariance via cancellations of quadratically divergent ILI's. Quantum field theories (QFT's) regularized through the new method are well defined and governed by a physically meaningful characteristic energy scale (CES) Mc and a physically interesting sliding energy scale (SES) μs which can run from μs ~ Mc to a dynamically generated mass gap μs = μc or to μs = 0 in the absence of mass gap and infrared (IR) problem. For Mc → ∞, the initial UV divergent properties of QFT's are recovered and well-defined. In fact, the CES Mc and SES at μs = μc play the role of UV and IR cutoff energy scales respectively. It is strongly indicated that the conformal scaling symmetry and its breaking mechanism play an important role for understanding the mass gap and quark confinement. The new method is developed to be applicable for both underlying renormalizable QFT's and effective QFT's. It also leads to a set of conjectures on mathematically interesting numbers and functional limits which may provide deep insights in mathematics.
ℤ3-GRADED SYMMETRIES IN QUANTUM MECHANICS
Authors: SAMANI KEIVAN AGHABABAEI , POOLADSAZ DAVOOD
Published: December 2003

In this paper we consider ℤ3-graded topological symmetries (TS's)2,3 in one-dimensional quantum mechanics. We give a classification of one-dimensional quantum systems possessing these symmetries and show that different classes correspond to a positive integer N.
D-BRANE CATEGORIES
Authors: LAZAROIU C. I.
Published: December 2003

This is an exposition of recent progress in the categorical approach to D-brane physics. I discuss the physical underpinnings of the appearance of homotopy categories and triangulated categories of D-branes from a string field theoretic perspective, and with a focus on applications to homological mirror symmetry.
THE TRANSVERSITY FUNCTION AND DOUBLE SPIN AZIMUTHAL ASYMMETRY IN SEMI-INCLUSIVE PION LEPTOPRODUCTION
Authors: DI SALVO ELVIO
Published: December 2003

We show that the transverse momentum dependent transversity function is proportional to the longitudinal polarization of a quark in a transversely polarized proton. This result suggests an alternative, convenient method for determining transversity, without knowing unusual fragmentation functions. The method consists of measuring the double spin azimuthal asymmetry in semi-inclusive pion leptoproduction by a transversely polarized proton target. The asymmetry, which is twist 3, is estimated to be more than 10% under the most favorable conditions. The experiment we suggest is feasible in facilities like DESY and CERN.
SEARCH FOR A "GRAVITOID" THEORY
Authors: NIETO J. A. , MARÍN M. C.
Published: December 2003

By combining the concepts of graviton and matroid, we outline a new gravitational theory which we call gravitoid theory. The idea of this theory emerged as an attempt to link the mathematical structure of matroid theory with M theory. Our observations are essentially based on the formulation of matroid bundle due to MacPherson and Anderson–Davis. Also, by considering the oriented matroid theory, we add new observations about the link between the Fano matroid and D=11 supergravity which was discussed in some of our recent papers. In particular we find a connection between the affine matroid AG(3, 2) and the G2-symmetry of D=11 supergravity.
WARD IDENTITY IN NONCOMMUTATIVE QED
Authors: MARIZ T. , PIRES C. A. DE S. , RIBEIRO R. F.
Published: December 2003

Although noncommutative QED presents a non-Abelian structure, it does not present structure constants. In view of this we investigate how Ward identity is satisfied in pair annihilation process and γγ → γγ scattering in noncommutative QED.
CARTAN CALCULUS VIA PAULI MATRICES
Authors: MAURO D.
Published: December 2003

In this paper we will provide a new operatorial counterpart of the path-integral formalism of classical mechanics developed in recent years. We call it new because the Jacobi fields and forms will be realized via finite dimensional matrices. As a byproduct of this we will prove that all the operations of the Cartan calculus, such as the exterior derivative, the interior contraction with a vector field, the Lie derivative and so on, can be realized by means of suitable tensor products of Pauli and identity matrices.
ON THE VARIABLE FINE STRUCTURE CONSTANT, STRINGS AND MAXIMAL-ACCELERATION PHASE SPACE RELATIVITY
Authors: CASTRO CARLOS
Published: December 2003

We present a new physical model that links the maximum speed of light with the minimal Planck scale into a maximal-acceleration relativity principle in the space–time tangent bundle and in phase spaces (cotangent bundle). The maximal proper-acceleration bound is a = c2/Λ in full agreement with the old predictions of Caianiello, the Finslerian geometry point of view of Brandt and more recent results in the literature. The group transformation laws of this maximal-acceleration phase space relativity theory under velocity and acceleration boosts are analyzed in full detail. For pure acceleration boosts it is shown why the minimal Planck-areas (maximal string tension) are universal invariant quantities in any frame of reference. Inspired by the maximal-acceleration corrections to the Lamb shifts of one-electron atoms by Lambiase, Papini and Scarpetta, we derive the exact integral equation that governs the renormalization-group-like scaling dependence of the fractional change of the fine structure constant as a function of the cosmological redshift factor and a cutoff scale Lc, where the maximal acceleration relativistic effects are dominant. A particular physical model exists dominated entirely by the vacuum energy, when the cutoff scale is the Planck scale, with ΩΛ = 1. The cosmological implications of this extreme case scenario are studied.
A GENERAL APPROACH OF QUASI-EXACTLY SOLVABLE SCHRÖDINGER EQUATIONS WITH THREE KNOWN EIGENSTATES
Authors: DEBERGH N. , VAN DEN BOSSCHE B. , NDIMUBANDI J.
Published: December 2003

We propose a general method for constructing quasi-exactly solvable potentials with three analytic eigenstates. These potentials can be real or complex functions but the spectrum is real. A comparison with other methods is also performed.
FRACTALITY IN ELEMENTARY COLLISIONS
Authors: WU YUANFANG , LIU LIANSHOU
Published: December 2003

Different fractality in hadron–hadron and e+e-collisions and its experimental observation are reviewed. The discussions on related underlying dynamics are presented.
SOME STRONG MIXING PROPERTIES OF A SEQUENCE OF RANDOM VARIABLES ARISING FROM α-CONTINUED FRACTIONS
Authors: NAKADA HITOSHI , NATSUI RIE
Published: December 2003

It is well known that the sequence of digits of regular continued fractions with the Gauss measure is ψ-mixing. In this paper we consider a class of semiregular continued fractions which are called α-continued fractions for α, 1/2≤α≤1. We show that the sequence of digits of α-continued fractions with the absolutely continuous invariant measure is absolutely regular for every α, 1/2≤α≤1, on the other hand, it is not φ-mixing for almost every α, 1/2≤α≤1.
LYAPUNOV FUNCTIONALS IN SINGULAR LIMITS FOR PERTURBED QUASILINEAR DEGENERATE PARABOLIC EQUATIONS
Authors: CHAVES MANUELA , GALAKTIONOV VICTOR A.
Published: December 2003

As a key example, we study the asymptotic behaviour near finite focusing time t=T of radial solutions of the porous medium equation with absorption [Formula: see text] with bounded compactly supported initial data u(x,0)=u0(|x|), and exponents m>1 and p>pc, where pc=pc(m,N)∈(-m,0) is a critical exponent. We show that under certain assumptions, the behaviour of the solution as t→T- near the origin is described by self-similar Graveleau solutions of the porous medium equation ut=Δum. In the rescaled variables, we deal with an exponential non-autonomous perturbation of a quasilinear parabolic equation, which is shown to admit an approximate Lyapunov functional. The result is optimal, and in the critical case p=pc an extra ln (T-t) scaling of the Graveleau asymptotics is shown to occur. Other types of self-similar and non self-similar focusing patterns are discussed.