bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic scale friction of nanoscale clusters
Authors: Ohno Keita , Nitta Toshihiro , Nakamura Jun , Natori Akiko
Published: August 2004

We study both the activation energy for diffusion and dynamics of nanoscale clusters of a Frenkel–Kontrova chain subject to the microscopic friction, in connection with atomic friction phenomena. We clarify the atomistic mechanism for the presence of a magic size for diffusion and show how the magic size effects appear in the friction. When a cluster is pulled by a constant driving force, the critical force strength of depinning depends crucially on the cluster size, and it is smallest at the magic size. When a cluster is pulled by a spring at a constant velocity below the critical value, clusters show a stick-and-slip motion, and the maximum force of a spring also becomes smallest at the magic size.
Low-temperature growth of carbon nanotube by thermal chemical vapor deposition with FeZrN catalyst
Authors: Shiroishi Tetsuya , Sawada Takao , Hosono Akihiko , Nakata Shuhei , Kanazawa Yasunori , Takai Mikio
Published: August 2004

Recently the direct growth of carbon nanotubes (CNT) on glass substrates by thermal chemical-vapor deposition at low temperatures has been researched for the fabrication of field-emission displays. We have achieved synthesis of CNT on soda lime glass with a catalyst: FeZrN at low temperature (500–550 °C). The FeZrN film deposited by sputtering is amorphous. However, this film changes into a crystalloid to separate out Fe fine particles by thermal treatment. This characteristic has been successfully applied to make the precursor of CNT. There is a possibility that the density and diameter of CNT can be controlled by varying the composition ratio of FeZrN. The emission from CNT has also been obtained. The turn-on electric field has been ∼2.5–3 V/μm. We have fabricated a microtriode structure and the emission has been also recognized.
Growth kinetics and modeling of selective molecular beam epitaxial growth of GaAs ridge quantum wires on pre-patterned nonplanar substrates
Authors: Sato Taketomo , Tamai Isao , Hasegawa Hideki
Published: August 2004

The growth kinetics involved in the selective molecular beam epitaxial growth of GaAs ridge QWRs is investigated in detail experimentally and an attempt is made to model the growth theoretically. For this purpose, detailed experiments were carried out on the growth of 〈1̄10〉-oriented AlGaAs–GaAs ridge quantum wires on mesa-patterned (001) GaAs substrates. A phenomenological modeling was done based on the continuum approximation including parameters such as group III adatom lifetime, diffusion constant and migration length. Computer simulation using the resultant model well reproduces the experimentally observed growth features such as the cross-sectional structure of the ridge wire and its temporal evolution, its temperature dependence and evolution of facet boundary planes. The simple phenomenological model developed here seems to be very useful for design and precise control of the growth process.
Real-time microscopic observation of emission fluctuation on Mo-tip field emitter array caused by introduced gas
Authors: Minami K. , Yamane K. , Nakane H. , Adachi H.
Published: August 2004

Emission behaviors of Spindt type molybdenum microtip field emitter arrays (Mo-tip FEA) are observed by use of a field-emission electron microscope (FEEM). Individual active micro-tips are separated as bright spots on a phosphor screen. Changes of both total-emission current and emission image are examined by introducing gases, which are nitrogen, hydrogen, methane, and ethylene, respectively. The number rates of active microtips behave differently from the total-emission current. The total-emission current increases during gas introduction, and then gradually decreases after the gas is evacuated. The final current levels are different from gas to gas. Among the gases, ethylene gives the largest final current and the largest number of active microtips. On the contrary, methane decreases in both the final current and the number of active microtips. The emission behaviors for hydrocarbon are different from the nonorganic gases.
Effect of sidewall roughness on the bottom etch properties of an SiO2 trench produced in a CF4 plasma
Authors: Hwang Sung-Wook , Lee Gyeo-Re , Min Jae-Ho , Moon Sang Heup
Published: August 2004

The effect of sidewall roughness on the bottom etch profile and the etch rate of an SiO2 trench produced in a CF4 plasma were examined using a specially designed apparatus that involved a Faraday cage, which permits the observation of microfeatures on an enlarged scale under practical processing conditions. A microtrench was produced on the bottom of a trench-shaped structure with a low aspect ratio when its sidewalls were smooth because ions reflected from the sidewall enhanced the bottom etch rate near the sidewall. However, the microtrench was not produced in a trench-shaped structure with a high aspect ratio and smooth sidewalls because the effects of ions reflected from two sidewalls were overlapped, nor in step-shaped and trench-shaped structures with rough sidewalls because the contribution of reflected ions to the bottom etch rate was negligible. The overlap in ion reflection effects in a trench having a high aspect ratio and smooth sidewalls was responsible for the inverse reactive ion etching lag phenomenon observed in this study.
Characterization of GaAs grown by molecular beam epitaxy on vicinal Ge(100) substrates
Authors: Wan A. , Menon V. , Forrest S. R. , Wasserman D. , Lyon S. A. , Kahn A.
Published: August 2004

In this article we investigate the growth of GaAs on two different vicinal surfaces of Ge (100), cut 6° off the (100) plane toward the (110) plane or toward the (111) plane. Both substrates exhibit evidence of a regular array of double steps. Ge substrates and GaAs films are characterized with low energy electron diffraction, low temperature photoluminescence, scanning tunneling microscopy, electron channeling, and scanning electron microscopy. GaAs grown on wafers cut toward the (111) plane exhibits high quality as compared to reference GaAs samples, whereas GaAs grown on wafers cut toward the (110) plane displays clear evidence of three-dimensional growth and low crystallinity.
Metallic nanostructures on Co/GaAs(001)(4×2) surfaces
Authors: Lüdge K. , Vogt P. , Richter W. , Fimland B.-O. , Braun W. , Esser N.
Published: August 2004

In this article, the growth of cobalt at 150 °C on the Ga-rich (4×2) reconstructed GaAs(001) surface is studied, emphasizing particularly submonolayer coverage. The surfaces were analyzed using scanning tunneling microscopy, soft x-ray photoemission spectroscopy (SXPS), low-energy electron diffraction, and reflection anisotropy spectroscopy (RAS). Co deposition above 1 monolayer thickness leads to a highly reacted interface consisting of CoGa and CoAs compounds, as evidenced by SXPS. At submonolayer coverage, however, Co atoms are incorporated in the row-like structure of the clean, Ga-rich (4×2) surface, forming one-dimensional, ordered chains in the [110] direction. Scanning tunneling spectroscopy and RAS demonstrate that these rows act as one-dimensional metallic nanowires.
Charge writing on the nanoscale: From nanopatterning to molecular docking
Authors: Wilks S. P. , Maffeïs T. G. G. , Owen G. T. , Teng K. S. , Penny M. W. , Ferkel H.
Published: August 2004

The drive towards nanotechnology has highlighted the need to engineer the properties of surfaces in unprecedented detail. Here, we report the modification of nanocrystalline SnO2 surfaces using the tip of a scanning tunneling microscope (STM) to inject electrons into individual 8 nm SnO2 nanocrystals. The surface displays a characteristic consistent with charge retention within the grains producing dramatic enhancements in the effective height of the nanoparticles, as observed by STM imaging. This allows the production of modified surfaces where patterns can be written onto a surface with a spatial resolution limited by the size of tip and the nanoparticles, 8 nm in this case. It is also possible to selectively erase the features on the surface using the STM tip under reverse bias. The pattern remains for up to three weeks and therefore opens the door to applications such as patterned nanoscale catalysis, molecular docking, and even ultrahigh density analog data storage.
Near-edge absorption fine structure and UV photoemission spectroscopy studies of aligned single-walled carbon nanotubes on Si(100) substrates
Authors: Fleming L. , Ulrich M. D. , Efimenko K. , Genzer J. , Chan A. S. Y. , Madey T. E. , Oh S.-J. , Zhou O. , Rowe J. E.
Published: August 2004

We report near-edge absorption fine structure (NEXAFS) and UV photoemission spectroscopy (UPS) studies of aligned single-walled carbon nanotube films on Si(100) substrates. Orientation of the films was detected in the NEXAFS spectra, with the intensity of the π* core exciton at 284.4 eV showing a strong dependence on nanotube alignment with respect to the polarization of the incident radiation. At lower angles of incidence, the intensity of the π* peak was higher for all orientations, which we attribute to the greater accessibility of the π* orbitals. UPS spectra of the films showed little angular dependence and included features consistent with the total density of states of graphite. As a result of the nanotube curvature and the distribution of nanotube chiralities, the UPS spectra are similar to angle-integrated graphite spectra.
Deposition of silicon carbide films using a high vacuum metalorganic chemical vapor deposition method with a single source precursor: Study of their structural properties
Authors: Jeong S. H. , Lim D. C. , Jee H.-G. , Moon O. M. , Jung C.-K. , Moon J. S. , Kim S. K. , Lee S.-B. , Boo J.-H.
Published: August 2004

Silicon carbide (SiC) thin films were prepared on Si(100) substrates by high vacuum metalorganic chemical vapor deposition using a single-source precursor at various growth temperatures in the range of 700–1000 °C. The precursor is diethylmethylsilane, and is used without carrier gas. The effects of substrate temperature as well as deposition time on the crystal growth were investigated. The optimum temperature for the formation of high quality polycrystalline SiC thin films was found to be 900 °C on the basis of x-ray diffraction and transmission electron diffraction results. X-ray photoemission spectroscopy shows that SiC films grown at 900 °C have slightly carbon-rich compositions (Si:C=1:1.2) in the surface region, but stoichiometric composition in the bulk. Scanning and transmission electron microscope images show the influence of substrate temperature on the grain size and crystallinity of the films. Large grain sizes and high quality crystallinity can be obtained below 900 °C.
Epitaxial growth of InGaAsSb/AlGaAsSb heterostructures for mid-infrared lasers based on strain engineering
Authors: Héroux J. B. , Pei C. W. , Wang W. I.
Published: August 2004

An approach based on strain engineering to fabricate GaSb-based type I InGaAsSb/AlGaAsSb mid-infrared laser diodes emitting at long wavelengths is presented. By incorporating a high arsenic fraction (above 2.1%) in the AlGaAsSb barriers, a tensile strain is created to compensate the compressive strain in the InGaAsSb wells. Calculations are presented to show how, while maintaining a low average strain in the active region, a low well bandgap energy and an increased valence band offset resulting in a better hole confinement can be obtained. Strain compensation is investigated experimentally by x-ray diffraction and photoluminescence. Double quantum well laser diodes were grown on GaSb by molecular-beam epitaxy. Stable room temperature pulsed lasing emission at 2.89 μm, the longest wavelength ever reported for this type of structure, was observed along with a threshold current density of 920 A/cm2.
In situ investigation of MnAs/GaAs(001) growth and interface structure using synchrotron x-ray diffraction
Authors: Satapathy D. K. , Jenichen B. , Kaganer V. M. , Braun W. , Däweritz L. , Ploog K. H.
Published: August 2004

Using grazing-incidence synchrotron x-ray diffraction, we have quantitatively studied the strain evolution of epitaxial MnAs films in situ during growth by molecular-beam epitaxy. We find that the MnAs layer grows in four distinct stages, being compressively strained at the beginning of growth and relaxing as the thickness increases. The evolution of the in-plane grain size is determined as a function of layer thickness. We find a one-dimensional ordered array of periodic misfit dislocations at the interface, having a periodicity of 4.9±0.05 nm along GaAs[110]. An annealing of the film increases the grain size as well as improves the ordering of dislocation array.
Nitrogen incorporation engineering and electrical properties of high-k gate dielectric (HfO2 and Al2O3) films on Si (100) substrate
Authors: Lee Chihoon , Choi Jihoon , Cho Moonju , Park Jahoo , Hwang Cheol Seong , Kim Hyeong Joon , Jeong Jaehack
Published: August 2004

Pt/HfO 2 ,  HfO2–Al2O3, or Al2O3–HfO2–Al2O3/p-type Si (100) metal oxide semiconductor capacitors, which were fabricated using an atomic-layer-deposition technique, were post-deposition annealed under a NH3 atmosphere in order to investigate the nitrogen incorporation behavior along with their influences on the electrical properties. X-ray photoelectron spectroscopy showed that the binding energy of Hf 4f peak shifts to the lower values with increasing PDA temperature due to the formation of Hf–N bonds. An amorphous Al2O3 interface layer suppressed N diffusion into the Si substrate. The rapid thermally annealed HfO2–Al2O3 film at 800 °C for 30 s, which contained approximately 20 at. % N in the HfO2 layer, showed a flat-band voltage shift of ∼30 mV (corresponding to a negative fixed charge ∼1.6×1011 cm−2), a leakage current density of −4.7×10−10 A/cm2 at −1 V, a hysteresis voltage <20 mV, excellent charge-to-breakdown characteristics and the lowest surface roughness. The single layer HfO2 film did not demonstrate good electrical properties due to excessive N diffusion into the Si substrate. A thin Al2O3 capping layer deteriorates the surface morphology and electrical properties of the HfO2–Al2O3 bilayer.
Line edge roughness and critical dimension variation: Fractal characterization and comparison using model functions
Authors: Constantoudis V. , Patsis G. P. , Leunissen L. H. A. , Gogolides E.
Published: August 2004

Line edge (or width) roughness (LER or LWR) of photoresists lines constitutes a serious issue in shrinking the critical dimensions (CD) of the gates to dimensions of a few tens of nanometers. In this article, we address the problem of the reliable LER characterization as well as the association of LWR with the CD variations. The complete LER characterization requires more parameters than the rms value σ since the latter neglects the spatial aspects of LER and does not predict the dependence on the length of the measured line. The further spatial LER descriptors may be the correlation length ξ and the roughness exponent α, which can be estimated through various methods. One aim of the present work is to perform a systematic comparative study of these methods using model edges generated by a roughness algorithm, in order to show their advantages and disadvantages for a reliable and accurate determination of the spatial LER parameters. In particular, we compare the results from (a) the study of the height–height correlation function (HHCF), (b) the Fourier [or power spectrum (PS)] analysis, and (c) the variation of rms value σ with measured line edge L [σ(L) curve]. It is found that the HHCF can be considered approximately a rescaled version of σ(L) and that the value of σ becomes almost independent of the measured edge length for lengths larger than ten times the correlation length. As regards the PS, it is shown that the finite length of the edge may harmfully affect the reliable estimation of α and ξ. Finally, we confirm theoretically and generalize an experimental observation [Leunissen et al., Microelectron. Eng. (to be published)] regarding the relationship between LWR and the σ of the CD variations within a die of a wafer. It is shown that they behave in a complimentary way as line length increases so that the sum of their squares remains constant and equal to the square of the LWR σ of the infinite line.
Bias-temperature stressing analysis on the stability of an ultrathin Ta diffusion barrier
Authors: Lim Boon Kiat , Park Hun Sub , Chin Lian Kon , Woo Sun Woong , See Alex K. H. , Seet Chim Seng , Lee Tae-Jong , Yakovlev Nikolai L.
Published: August 2004

Proper electrical functionality of devices is dependent on the proper insulation between active/passive areas and metal interconnect. Although low-k materials are gradually replacing SiO2 to achieve lower parasitic capacitance, they are still SiO2-based. With the introduction of Cu as back-end metallization, the need for a barrier between insulator and metal arises, regardless of insulating materials. Ta has been established as a mainstream diffusion barrier in Cu interconnects. As device feature size shrinks, thickness of the Ta barrier also decreases. This raises a big concern on the effectiveness of thin, columnar Ta barriers in stopping the diffusion of Cu into SiO2, especially under simultaneous application of bias and thermal stresses. As the integrity of SiO2 is reliant on Ta to prevent Cu diffusion, bias-temperature stressing (BTS) would be a very suitable test to indirectly evaluate the Ta barrier through SiO2 integrity. In this study, the stability of a 5 nm Ta barrier is investigated under various bias and thermal stressing conditions through BTS analysis. Stressed samples are analyzed with high frequency C–V curves, and time-of-flight secondary ion mass spectrometry depth profiles. From the results, the 5 nm Ta barrier is proved to be stable in the Cu interconnect system.
Numerical Cognition Without Words: Evidence from Amazonia
Authors: Gordon Peter
Published: August 2004

Members of the Pirahã tribe use a “one-two-many” system of counting. I ask whether speakers of this innumerate language can appreciate larger numerosities without the benefit of words to encode them. This addresses the classic Whorfian question about whether language can determine thought. Results of numerical tasks with varying cognitive demands show that numerical cognition is clearly affected by the lack of a counting system in the language. Performance with quantities greater than three was remarkably poor, but showed a constant coefficient of variation, which is suggestive of an analog estimation process.
Local Nanomechanical Motion of the Cell Wall of
Saccharomyces cerevisiae
Authors: Pelling Andrew E. , Sehati Sadaf , Gralla Edith B. , Valentine Joan S. , Gimzewski James K.
Published: August 2004

We demonstrate that the cell wall of living
Saccharomyces cerevisiae
(baker's yeast) exhibits local temperature-dependent nanomechanical motion at characteristic frequencies. The periodic motions in the range of 0.8 to 1.6 kHz with amplitudes of ∼3 nm were measured using the cantilever of an atomic force microscope (AFM). Exposure of the cells to a metabolic inhibitor causes the periodic motion to cease. From the strong frequency dependence on temperature, we derive an activation energy of 58 kJ/mol, which is consistent with the cell's metabolism involving molecular motors such as kinesin, dynein, and myosin. The magnitude of the forces observed (∼10 nN) suggests concerted nanomechanical activity is operative in the cell.
Uracil DNA Glycosylase Activity Is Dispensable for Immunoglobulin Class Switch
Authors: Begum Nasim A. , Kinoshita Kazuo , Kakazu Naoki , Muramatsu Masamichi , Nagaoka Hitoshi , Shinkura Reiko , Biniszkiewicz Detlev , Boyer Laurie A. , Jaenisch Rudolf , Honjo Tasuku
Published: August 2004

Activation-induced cytidine deaminase (AID) is required for the DNA cleavage step in immunoglobulin class switch recombination (CSR). AID is proposed to deaminate cytosine to generate uracil (U) in either mRNA or DNA. In the second instance, DNA cleavage depends on uracil DNA glycosylase (UNG) for removal of U. Using phosphorylated histone γ-H2AX focus formation as a marker of DNA cleavage, we found that the UNG inhibitor Ugi did not inhibit DNA cleavage in immunoglobulin heavy chain (IgH) locus during CSR, even though Ugi blocked UNG binding to DNA and strongly inhibited CSR. Strikingly, UNG mutants that had lost the capability of removing U rescued CSR in UNG
–/–
B cells. These results indicate that UNG is involved in the repair step of CSRyet by an unknown mechanism. The dispensability of U removal in the DNA cleavage step of CSR requires a reconsideration of the model of DNA deamination by AID.
Intercontinental Spread of Pyrimethamine-Resistant Malaria
Authors: Roper Cally , Pearce Richard , Nair Shalini , Sharp Brian , Nosten François , Anderson Tim
Published: August 2004

Here we present molecular evidence demonstrating that malaria parasites bearing high-level pyrimethamine resistance originally arrived in Africa from southeast Asia. The resistance alleles carried by these migrants are now spreading across Africa at an alarming rate, signaling the end of affordable malaria treatment and presenting sub-Saharan Africa with a public health crisis.
Enhanced Dendritic Cell Antigen Capture via Toll-Like Receptor-Induced Actin Remodeling
Authors: West Michele A. , Wallin Robert P. A. , Matthews Stephen P. , Svensson Henrik G. , Zaru Rossana , Ljunggren Hans-Gustaf , Prescott Alan R. , Watts Colin
Published: August 2004

Microbial products are sensed through Toll-like receptors (TLRs) and trigger a program of dendritic cell (DC) maturation that enables DCs to activate T cells. Although an accepted hallmark of this response is eventual down-regulation of DC endocytic capacity, we show that TLR ligands first acutely stimulate antigen macropinocytosis, leading to enhanced presentation on class I and class II major histocompatibility complex molecules. Simultaneously, actin-rich podosomes disappear, which suggests a coordinated redeployment of actin to fuel endocytosis. These reciprocal changes are transient and require p38 and extracellular signal–regulated kinase activation. Thus, the DC actin cytoskeleton can be rapidly mobilized in response to innate immune stimuli to enhance antigen capture and presentation.
Requirement of Rac1 and Rac2 Expression by Mature Dendritic Cells for T Cell Priming
Authors: Benvenuti Federica , Hugues Stephanie , Walmsley Marita , Ruf Sandra , Fetler Luc , Popoff Michel , Tybulewicz Victor L. J. , Amigorena Sebastian
Published: August 2004

Upon maturation, dendritic cells (DCs) acquire the unique ability to activate naïve T cells. We used time-lapse video microscopy and two-photon imaging of intact lymph nodes to showthat after establishing initial contact between their dendrites and naïve T lymphocytes, mature DCs migrate toward the contacted lymphocytes. Subsequently, the DCs tightly entrap the T cells within a complex net of membrane extensions. The Rho family guanosine triphosphatases Rac1 and Rac2 but not Rho itself control the formation of dendrites in mature DCs, their polarized short-range migration toward T cells, and T cell priming.
Molecular Topographies
Authors: Clary David C.
Published: August 2004

Energy Landscapes
Applications to Clusters, Biomolecules and Glasses. David J. Wales. Cambridge University Press, Cambridge, 2004. 691 pp. $85, £55. ISBN 0-521-81415-4.

David Clary reviews Energy Landscapes by David Wales, an overview of the use of landscape-like diagrams for quantitative description of the energy of interaction between molecules.
NOBOX Deficiency Disrupts Early Folliculogenesis and Oocyte-Specific Gene Expression
Authors: Rajkovic Aleksandar , Pangas Stephanie A. , Ballow Daniel , Suzumori Nobuhiro , Matzuk Martin M.
Published: August 2004

Primordial ovarian follicles in mice form when somatic cells surround individual oocytes. We show that lack of
Nobox
, an oocyte-specific homeobox gene, accelerates postnatal oocyte loss and abolishes the transition from primordial to growing follicles in mice. Follicles are replaced by fibrous tissue in female mice lacking
Nobox
in a manner similar to nonsyndromic ovarian failure in women. Genes preferentially expressed in oocytes, including
Oct4
and
Gdf9
, are down-regulated in
Nobox
–/–
mice, whereas ubiquitous genes such as
Bmp4, Kit
, and
Bax
remain unaffected. Therefore,
Nobox
is critical for specifying an oocyte-restricted gene expression pattern essential for postnatal follicle development.
Jupiter's Atmospheric Composition from the Cassini Thermal Infrared Spectroscopy Experiment
Authors: Kunde V. G. , Flasar F. M. , Jennings D. E. , Bézard B. , Strobel D. F. , Conrath B. J. , Nixon C. A. , Bjoraker G. L. , Romani P. N. , Achterberg R. K. , Simon-Miller A. A. , Irwin P. , Brasunas J. C. , Pearl J. C. , Smith M. D. , Orton G. S. , Gierasch P. J. , Spilker L. J. , Carlson R. C. , Mamoutkine A. A. , Calcutt S. B. , Read P. L. , Taylor F. W. , Fouchet T. , Parrish P. , Barucci A. , Courtin R. , Coustenis A. , Gautier D. , Lellouch E. , Marten A. , Prangé R. , Biraud Y. , Ferrari C. , Owen T. C. , Abbas M. M. , Samuelson R. E. , Raulin F. , Ade P. , Césarsky C. J. , Grossman K. U. , Coradini A.
Published: August 2004

The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of acetylene and ethane, the latter a tracer of atmospheric motion; observations of unexpected spatial distributions of carbon dioxide and hydrogen cyanide, both considered to be products of comet Shoemaker-Levy 9 impacts; characterization of the morphology of the auroral infrared hot spot acetylene emission; and a new evaluation of the energetics of the northern auroral infrared hot spot.
Intracellular Acidosis Enhances the Excitability of Working Muscle
Authors: Pedersen Thomas H. , Nielsen Ole B. , Lamb Graham D. , Stephenson D. George
Published: August 2004

Intracellular acidification of skeletal muscles is commonly thought to contribute to muscle fatigue. However, intracellular acidosis also acts to preserve muscle excitability when muscles become depolarized, which occurs with working muscles. Here, we show that this process may be mediated by decreased chloride permeability, which enables action potentials to still be propagated along the internal network of tubules in a muscle fiber (the T system) despite muscle depolarization. These results implicate chloride ion channels in muscle function and emphasize that intracellular acidosis of muscle has protective effects during muscle fatigue.
Decamethyldizincocene, a Stable Compound of Zn(I) with a Zn-Zn Bond
Authors: Resa Irene , Carmona Ernesto , Gutierrez-Puebla Enrique , Monge Angeles
Published: August 2004

Unlike mercury, which has an extensive +1 oxidation state chemistry, zinc usually adopts the +2 oxidation state. Decamethyldizincocene, Zn
2
(η
5
-C
5
Me
5
)
2
, an organometallic compound of Zn(I) formally derived from the dimetallic [Zn–Zn]
2+
unit, has been isolated from the low-temperature (–10°C) reaction of Zn(C
5
Me
5
)
2
and Zn(C
2
H
5
)
2
in diethyl ether. X-ray studies show that it contains two eclipsed Zn(η
5
-C
5
Me
5
) fragments with a Zn–Zn distance (± standard deviation) of 2.305(±3) angstroms, indicative of a metal-metal bonding interaction.
Sudden Onset of Pitting Corrosion on Stainless Steel as a Critical Phenomenon
Authors: Punckt C. , Bölscher M. , Rotermund H. H. , Mikhailov A. S. , Organ L. , Budiansky N. , Scully J. R. , Hudson J. L.
Published: August 2004

Stainless steels undergo a sharp rise in pitting corrosion rate as the potential, solution concentration, or temperature is changed only slightly. We report experiments using real-time microscopic in situ visualizations that resolve the nucleation and evolution of individual pits during the transition. They suggest that the sudden onset of corrosion is explained by an explosive autocatalytic growth in the number of metastable pits and that stabilization of individual pits takes place only later. This finding agrees with a theoretical approach treating the onset of pitting corrosion as a cooperative critical phenomenon resulting from interactions among metastable pits, and it extends perspectives on the control and prevention of corrosion onset.
Nota Bene: Education Can Be Fun
Authors: Smith Orla
Published: August 2004

Marian Koshland Science Museum of the National Academy of Sciences
. 6th and E Streets NW, Washington, DC.
www.koshland-science-museum.org
.

The National Academy of Science's new science museum is intended to highlight research on questions relevant to the general public in their everyday lives.
HYPER SENSITIVITY ANALYSIS OF PORTFOLIO OPTIMIZATION PROBLEMS
Authors: CHURILOV LEONID , BOMZE IMMANUEL M. , SNIEDOVICH MOSHE , RALPH DANIEL
Published: August 2004

Hyper Sensitivity Analysis (HSA) is an intuitive generalization of conventional sensitivity analysis, where the term "hyper" indicates that the sensitivity analysis is conducted with respect to functions rather than numeric values. In this paper Composite Concave Programming is used to perform HSA in the area of Portfolio Optimization Problems. The concept of HSA is suited for situations where several candidates for the function quantifying the utility of (mean, variance) pairs are available. We discuss the applications of HSA to two types of mean–variance portfolio optimization problems: the classical one and a discrete knapsack-type portfolio selection problem. It is explained why in both cases the methodology can be applied to full size problems.
AN EFFICIENT APPROACH FOR THE THREE-DIMENSIONAL CONTAINER PACKING PROBLEM WITH PRACTICAL CONSTRAINTS
Authors: JIN ZHIHONG , OHNO KATSUHISA , DU JIALI
Published: August 2004

This paper deals with the three-dimensional container packing problem (3DCPP), which is to pack a number of items orthogonally onto a rectangular container so that the utilization rate of the container space or the total value of loaded items is maximized. Besides the above objectives, some other practical constraints, such as loading stability, the rotation of items around the height axis, and the fixed loading (unloading) orders, must be considered for the real-life 3DCPP. In this paper, a sub-volume based simulated annealing meta-heuristic algorithm is proposed, which aims at generating flexible and efficient packing patterns and providing a high degree of inherent stability at the same time. Computational experiments on benchmark problems show its efficiency.
THE ASSIGNMENT OF INDIVIDUAL RENEWABLE RESOURCES IN SCHEDULING
Authors: BURDETT ROBERT L. , KOZAN ERHAN
Published: August 2004

Resource constrained scheduling problems are concerned with the allocation of limited resources to tasks over time. The solution to these problems is often a sequence, resource allocation, and schedule. When human workers are incorporated as a renewable resource, the allocation is defined as the number of workers assigned to perform each task. In practice, however, this solution does not adequately address how individual workers are to be assigned to tasks. This paper, therefore, provides mathematical models and heuristic techniques for solving this multi-period precedence constrained assignment problem. Results of a significant numerical investigation are also presented.
EXISTENCE, UNIQUENESS, AND DETERMINACY OF A NONNEGATIVE EQUILIBRIUM PRICE VECTOR IN ASSET MARKETS WITH GENERAL UTILITY FUNCTIONS AND AN ELLIPTICAL DISTRIBUTION
Authors: CHEN ZHIPING
Published: August 2004

For the asset market with finite numbers of investors whose utility functions are general concave functions, we derive a necessary and sufficient condition for the existence and uniqueness of the nonnegative equilibrium price vector that clears the asset market, through considering the expected utility maximization problem under the assumption that the joint distribution of risky assets' returns is an elliptical distribution. An explicit formula for the equilibrium price is given. We also discuss the economic implication of the given condition and demonstrate that our necessary and sufficient condition can be regarded as a necessary condition to maintain the stability of the asset market. These results extend some results about the equilibrium analysis of the asset market.
ITERATED KLEINIAN EQUATIONS
Authors: BOLLINI C. G. , ROCCA M. C.
Published: August 2004

A higher order field has different forms of excitation. Some of them have negative energies. The signs of the quantization rules depend on the signs of the energies. An abnormal sign implies a negative sign of the residue at the on-shell pole of the propagator, leading to a clash with unitarity.

To change these signs we can change the identification of the creation and annihilation operators. But then the energy has no lower bound. The way out is found by adopting a symmetric vacuum state. The corresponding propagator is a half retarded and half advanced Green function. It has a zero residue at the on-shell pole. There is no associated free particle. The abnormal modes act only as mediators of interactions.
DUAL GENERALIZATIONS OF SINE–GORDON FIELD THEORY AND INTEGRABILITY SUBMANIFOLDS IN PARAMETER SPACE
Authors: BASEILHAC P. , REYNAUD D.
Published: August 2004

The dual relationship between two n-1 parameter families of quantum field theories based on extended complex numbers is investigated in two dimensions. The nonlocal conserved charges approach is used. The lowest rank affine Toda field theories are generated and identified as integrability submanifolds in parameter space. A truncation of the model leads to a conformal field theory in extended complex space. Depending on the projection over the usual complex space chosen, a parametrized central charge is calculated.
PERFECT SCALARS ON THE LATTICE
Authors: BIETENHOLZ W.
Published: August 2004

We perform renormalization group transformations to construct optimally local perfect lattice actions for free scalar fields of any mass. Their couplings decay exponentially. The spectrum is identical to the continuum spectrum, while thermodynamic quantities have tiny lattice artifacts. To make such actions applicable in simulations, we truncate the couplings to a unit hypercube and observe that spectrum and thermodynamics are still drastically improved compared to the standard lattice action. We show how preconditioning techniques can be applied successfully to this type of action. We also consider a number of variants of the perfect lattice action, such as the use of an anisotropic or triangular lattice, and modifications of the renormalization group transformations motivated by wavelets. Along the way we illuminate the consistent treatment of gauge fields, and we find a new fermionic fixed point action with attractive properties.
TYPE I ON (GENERALIZED) VOISIN–BORCEA ORBIFOLDS AND NONPERTURBATIVE ORIENTIFOLDS
Authors: KAKUSHADZE ZURAB
Published: August 2004

We consider nonperturbative four-dimensional [Formula: see text] space–time supersymmetric orientifolds corresponding to Type I compactifications on (generalized) Voisin–Borcea orbifolds. Some states in such compactifications arise in "twisted" open string sectors which lack world sheet description in terms of D-branes. Using Type I-heterotic duality as well as the map between Type IIB orientifolds and F theory we are able to obtain the massless spectra of such orientifolds. The four-dimensional compactifications we discuss in this context are examples of chiral [Formula: see text] supersymmetric string vacua which are nonperturbative from both orientifold and heterotic points of view. In particular, they contain both D9- and D5-branes as well as nonperturbative "twisted" open string sector states. We also explain the origins of various inconsistencies arising in such compactifications for certain choices of the gauge bundle.
A SCREENING MECHANISM FOR EXTRA W AND Z GAUGE BOSONS
Authors: MATIAS JOAQUIM , VICINI ALESSANDRO
Published: August 2004

We generalize a previous construction of a fermiophobic model to the case of more than one extra W and Z gauge bosons. We focus in particular on the existence of screening configurations and their implication on the gauge boson mass spectrum. One of these configurations allows for the existence of a set of relatively light new gauge bosons, without violation of the quite restrictive bounds coming from the ρ NC parameter. The links with Bess and degenerate Bess models are also discussed. Also the signal given here by this more traditional gauge extension of the SM could help to disentangle it from the towers of Kaluza–Klein states over W and Z gauge bosons in extra dimensions.
PERTURBATIVE RENORMALIZATION FACTORS OF BARYON NUMBER VIOLATING OPERATORS FOR IMPROVED QUARK AND GAUGE ACTIONS IN LATTICE QCD
Authors: AOKI SINYA , KURAMASHI YOSHINOBU , ONOGI TETSUYA , TSUTSUI NAOTO
Published: August 2004

We calculate one-loop renormalization factors of three-quark operators, which appear in the low energy effective Lagrangian of the nucleon decay, for O(a)-improved quark action and gauge action including six-link loops. This calculation is required to predict the hadronic nucleon decay matrix elements in the continuum regularization scheme using lattice QCD. We present detailed numerical results of the one-loop coefficients for general values of the clover coefficients employing the several improved gauge actions in the Symanzik approach and in Wilson's renormalization group approach. The magnitudes of the one-loop coefficients for the improved gauge actions show sizable reduction compared to those for the plaquette action.
SCHWINGER'S RESULT ON PARTICLE PRODUCTION FROM COMPLEX PATHS WKB APPROXIMATION
Authors: BISWAS S. , SHAW A. , MODAK B.
Published: August 2004

This paper presents the derivation of Schwinger's gauge-invariant result of Im ℒ eff up to one loop approximation, for particle production in an uniform electric field through the method of complex trajectory WKB approximation (CWKB). The CWKB proposed by one of the authors1 looks upon particle production as being due to the motion of a particle in complex space–time plane, thereby requiring tunneling paths both in space and time. Recently2,3 there have been some efforts to calculate the reflection and the transmission coefficients for particle production in an uniform electric field that differ from our expressions for the same. In this paper we clarify the confusion in this regard and establish the correctness of CWKB.
QUANTUM FIELD THEORY IN A SYMMETRIC CURVED SPACE FROM A SECOND QUANTIZATION ON A GROUP
Authors: CALIXTO M. , ALDAYA V. , NAVARRO M.
Published: August 2004

In this paper we propose a "second quantization" scheme especially suitable for dealing with nontrivial, highly symmetric phase spaces, implemented within a more general group approach to quantization, which recovers the standard quantum field theory (QFT) for ordinary relativistic linear fields. We emphasize, among its main virtues, greater suitability in characterizing vacuum states in a QFT on a highly symmetric curved space–time and the absence of the usual requirement of global hyperbolicity. This can be achieved in the special case of the Anti-de Sitter universe, on which we explicitly construct a QFT.
BETHE ANSATZ SOLUTIONS FOR TEMPERLEY–LIEB QUANTUM SPIN CHAINS
Authors: GHIOTTO R. C. T. , MALVEZZI A. L.
Published: August 2004

We solve the spectrum of quantum spin chains based on representations of the Temperley–Lieb algebra associated with the quantum groups [Formula: see text] for Xn=A1, Bn, Cn and Dn. The tool is a modified version of the coordinate Bethe ansatz through a suitable choice of the Bethe states which give to all models the same status relative to their diagonalization. All these models have equivalent spectra up to degeneracies and the spectra of the lower-dimensional representations are contained in the higher-dimensional ones. Periodic boundary conditions, free boundary conditions and closed nonlocal boundary conditions are considered. Periodic boundary conditions, unlike free boundary conditions, break quantum group invariance. For closed nonlocal cases the models are quantum group invariant as well as periodic in a certain sense.
CYCLIC COSET ORBIFOLDS
Authors: EVSLIN J. , HALPERN M. B. , WANG J. E.
Published: August 2004

We apply the new orbifold duality transformations to discuss the special case of cyclic coset orbifolds in further detail. We focus in particular on the case of the interacting cyclic coset orbifolds, whose untwisted sectors are ℤλ(permutation)-invariant g/h coset constructions which are not λ copies of coset constructions. Because λ copies are not involved, the action of ℤλ(permutation) in the interacting cyclic coset orbifolds can be quite intricate. The stress tensors and ground state conformal weights of all the sectors of a large class of these orbifolds are given explicitly and special emphasis is placed on the twisted h subalgebras which are generated by the twisted (0, 0) operators of these orbifolds. We also discuss the systematics of twisted (0, 0) operators in general coset orbifolds.
MODIFIED FORM OF VECTOR MESON COUPLING TO STUDY NUCLEAR MATTER AND ITS PHASE TRANSITION TO QUARK MATTER
Authors: MALAKAR BINAY
Published: August 2004

In the proposed field theoretic model to study nuclear matter and its phase transition to quark matter, vector mesons (ωμ) have the usual coupling to fermionic currents and also scalar type coupling involving ωμωμ with fermionic fields and scalar mesons. The effect of this modified vector meson interaction for cold symmetric nuclear matter is investigated using relativistic mean-field theory. One of the striking features of the model is that at extremely high density part of the energy density due to vector mesons is proportional to the density ρ (instead of ρ2 as in Walecka model, Boguta model etc.) where Fermi gas energy density varies as ρ4/3.
SCALING BEHAVIOR OF MULTIPLICITY DIFFERENCE CORRELATORS IN FIRST-ORDER QGP PHASE TRANSITION
Authors: YAN W. B. , YANG C. B. , CAI X.
Published: August 2004

Within the extended Ginzburg–Landau model, multiplicity difference correlators in first-order quark–gluon plasma phase transition are investigated for two well-separated bins with nonidentical mean multiplicities. For very small bin width, a kind of scaling behavior and a universal exponent index γ, which are independent of the parameters of model, are found.
ISENTROPIC QUARK HADRON PHASE BOUNDARY AND STRANGENESS ENHANCEMENT
Authors: PATRA B. K. , SINGH C. P. , KHANNA F. C.
Published: August 2004

We develop a phenomenological equation of state for the quark–gluon plasma containing nf flavors when the entropy per baryon ratio remains continuous across the phase boundary and thus derive a generalized expression for the temperature and baryon chemical potential dependent bag constant. The phase boundaries are obtained for an isentropic quark–hadron phase transition after using Gibbs' criteria and the transition to an ideal QGP from the solution of the condition B(μ,T)=0. The variation of critical temperature Tc with nf and the temperature variation of the quantity (ε-4P)/T4 which measures the interaction present in QGP are obtained and compared with the results from lattice calculations. Finally we obtain the strange particle ratios on the two phase boundaries which will be useful in identifying deconfined and/or ideal QGP formation in the heavy-ion experiments.
A THEOREM ON FIRST-ORDER INTERACTION VERTICES FOR FREE p-FORM GAUGE FIELDS
Authors: HENNEAUX MARC , KNAEPEN BERNARD
Published: August 2004

The complete proof of a theorem announced in Ref. 1 on the consistent interactions for (nonchiral) exterior form gauge fields is given. The theorem can be easily generalized to the analysis of anomalies. Its proof amounts to computing the local BRST cohomology H0(s|d) in the space of local n-forms depending on the fields, the ghosts, the antifields and their derivatives.
STRUCTURE, FRAGMENTATION AND FRACTURE FUNCTIONS
Authors: GARCIA CANAL CARLOS A. , SASSOT RODOLFO
Published: August 2004

We address the partonic description of the proton, the photon and the "color singlet," as seen in inclusive and semi-inclusive DIS, in e+e-collisions, and in diffractive processes, respectively. Their formal treatment using structure, fragmentation, and fracture functions is outlined giving an insight into the perturbative QCD framework for these functions. Examples and comparisons with experimental data from LEP, HERA, and Tevatron are also covered.
TIME IN QUANTUM GEOMETRODYNAMICS
Authors: KHEYFETS ARKADY , MILLER WARNER A.
Published: August 2004

We revisit the issue of time in quantum geometrodynamics and suggest a quantization procedure on the space of true dynamic variables. This procedure separates the issue of quantization from enforcing the constraints caused by the general covariance symmetries. The resulting theory, unlike the standard approach, takes into account the states that are off shell with respect to the constraints, and thus avoids the problems of time. In this approach, quantum geometrodynamics, general covariance, and the interpretation of time emerge together as parts of the solution of the total problem of geometrodynamic evolution.
RESONANT FINAL-STATE INTERACTIONS IN $D^0\rightarrow{\bar K}^0\eta,~{\bar K}^0\eta^\prime$ DECAYS
Authors: EL AAOUD EL HASSAN , KAMAL A. N.
Published: August 2004

We have investigated the effect of the isospin ½, JP=0+ resonant state [Formula: see text] on the decays [Formula: see text] and [Formula: see text] as a function of the branching ratio sum [Formula: see text] and coupling constants [Formula: see text]. We have used a factorized input for [Formula: see text] weak transition through a πK loop. We estimated both on- and off-shell contributions from the loop. Our calculation shows that the off-shell effects are significant. For r≥30% a fit to the decay amplitude [Formula: see text] was possible, but the amplitude [Formula: see text] remained at its factorized value. For small values of r, r≤18%, we were able to fit [Formula: see text], and despite the fact that [Formula: see text] could be raised by almost 100% over its factorized value, it still falls short of its experimental value. A simultaneous fit to both amplitudes [Formula: see text] and [Formula: see text] was not possible. We have also determined the strong phase of the resonant amplitudes for both decays.
PATH INTEGRAL AND PSEUDOCLASSICAL ACTION FOR SPINNING PARTICLE IN EXTERNAL ELECTROMAGNETIC AND TORSION FIELDS
Authors: GEYER BODO , GITMAN DMITRY , SHAPIRO ILYA L.
Published: August 2004

Starting from the Dirac equation in external electromagnetic and torsion fields we derive a path integral representation for the corresponding propagator. An effective action, which appears in the representation, is interpreted as a pseudoclassical action for a spinning particle. It is just a generalization of Berezin–Marinov action to the background under consideration. Pseudoclassical equations of motion in the nonrelativistic limit reproduce exactly the classical limit of the Pauli quantum mechanics in the same case. Quantization of the action appears to be nontrivial due to an ordering problem, which needs to be solved to construct operators of first-class constraints, and to select the physical sector. Finally the quantization reproduces the Dirac equation in the given background and, thus, justifies the interpretation of the action.