bluuebunny/crossref_metadata_2025 huggingface dataset:
Equity Volatility and Corporate Bond Yields
Authors: Campbell John Y. , Taksler Glen B.
Published: November 2003

This paper explores the effect of equity volatility on corporate bond yields. Panel data for the late 1990s show that idiosyncratic firm‐level volatility can explain as much cross‐sectional variation in yields as can credit ratings. This finding, together with the upward trend in idiosyncratic equity volatility documented by Campbell, Lettau, Malkiel, and Xu (2001), helps to explain recent increases in corporate bond yields.
Institutional Investors and Executive Compensation
Authors: Hartzell Jay C. , Starks Laura T.
Published: November 2003

We find that institutional ownership concentration is positively related to the pay‐for‐performance sensitivity of executive compensation and negatively related to the level of compensation, even after controlling for firm size, industry, investment opportunities, and performance. These results suggest that the institutions serve a monitoring role in mitigating the agency problem between shareholders and managers. Additionally, we find that clientele effects exist among institutions for firms with certain compensation structures, suggesting that institutions also influence compensation structures through their preferences.
Intraday Price Formation in U.S. Equity Index Markets
Authors: Hasbrouck Joel
Published: November 2003

The market for U.S. equity indexes presently comprises floor‐traded index futures contracts, exchange‐traded funds (ETFs), electronically traded, small‐denomination futures contracts (E‐minis), and sector ETFs that decompose the S&P 500 index into component industry portfolios. This paper empirically investigates price discovery in this environment. For the S&P 500 and Nasdaq‐100 indexes, most of the price discovery occurs in the E‐mini market. For the S&P 400 MidCap index, price discovery is shared between the regular futures contract and the ETF. The S&P 500 ETF contributes markedly to price discovery in the sector ETFs, but there are only minor effects in the reverse direction.
Financial Development, Property Rights, and Growth
Authors: Claessens Stijn , Laeven Luc
Published: November 2003

In countries with more secure property rights, firms might allocate resources better and consequentially grow faster as the returns on different types of assets are more protected against competitors' actions. Using data on sectoral value added for a large number of countries, we find evidence consistent with better property rights leading to higher growth through improved asset allocation. Quantitatively, the growth effect is as large as that of improved access to financing due to greater financial development. Our results are robust using various samples and specifications, including controlling for growth opportunities.
The Behavior of Bid‐Ask Spreads and Volume in Options Markets during the Competition for Listings in 1999
Authors: De Fontnouvelle Patrick , Fishe Raymond P. H. , Harris Jeffrey H.
Published: November 2003

In August 1999, U.S. exchanges began to compete directly for order flow in many options that had been exclusively listed on another exchange, shifting 37% of option volume to multiple‐listing status by the end of September. Effective and quoted bid–ask spreads decrease significantly after multiple listings with spreads generally maintaining their initial lower levels 1 year later. These results hold for both time series and pooled regressions and are robust. We reject that economies of scale in market making cause the decrease in spreads and support the view that interexchange competition reduces option transaction costs.
Model Misspecification and Underdiversification
Authors: Uppal Raman , Wang Tan
Published: November 2003

In this paper, we study intertemporal portfolio choice when an investor accounts explicitly for model misspecification. We develop a framework that allows for ambiguity about not just the joint distribution of returns for all stocks in the portfolio, but also for different levels of ambiguity for the marginal distribution of returns for any subset of these stocks. We find that when the overall ambiguity about the joint distribution of returns is high, then small differences in ambiguity for the marginal return distribution will result in a portfolio that is significantly underdiversified relative to the standard mean‐variance portfolio.
Momentum Investing and Business Cycle Risk: Evidence from Pole to Pole
Authors: Griffin John M. , Ji Xiuqing , Martin J. Spencer
Published: November 2003

We examine whether macroeconomic risk can explain momentum profits internationally. Neither an unconditional model based on the Chen, Roll, and Ross (1986) factors nor a conditional forecasting model based on lagged instruments provides any evidence that macroeconomic risk variables can explain momentum. In addition, momentum profits around the world are economically large and statistically reliable in both good and bad economic states. Further, these momentum profits reverse over 1‐ to 5‐year horizons, an action inconsistent with existing risk‐based explanations of momentum.
Equilibrium “Anomalies”
Authors: Ferguson Michael F. , Shockley Richard L.
Published: November 2003

Many empirical “anomalies” are actually consistent with the single beta capital asset pricing model if the empiricist utilizes an equity‐only proxy for the true market portfolio. Equity betas estimated against this particular inefficient proxy will be understated, with the error increasing with the firm's leverage. Thus, firm‐specific variables that correlate with leverage (such as book‐to‐market and size) will appear to explain returns after controlling for proxy beta simply because they capture the missing beta risk. Loadings on portfolios formed on relative leverage and relative distress completely subsume the powers of the Fama and French (1993) returns to small minus big market capitalization (SMB) portfolios and returns to high minus low book‐to‐market (HML) portfolios factors in explaining cross‐sectional returns.
Capital Structure and Financial Risk: Evidence from Foreign Debt Use in East Asia
Authors: Allayannis George , Brown Gregory W. , Klapper Leora F.
Published: November 2003

Using a data set of East Asian nonfinancial companies, we examine a firm's choice between local, foreign, and synthetic local currency (hedged foreign currency) debt. We find evidence of unique as well as common factors that determine each debt type's use, indicating the importance of examining debt at a disaggregated level. We exploit the Asian financial crisis as a natural experiment to investigate the role of debt type in firm performance. Surprisingly, we find that the use of synthetic local currency debt is associated with the biggest drop in market value, possibly due to currency derivative market illiquidity during the crisis.
Shareholder Taxes in Acquisition Premiums: The Effect of Capital Gains Taxation
Authors: Ayers Benjamin C. , Lefanowicz Craig E. , Robinson John R.
Published: November 2003

We exploit cross‐temporal differences in capital gains tax rates to test whether shareholder‐level capital gains taxes are associated with higher acquisition premiums for taxable acquisitions. We model acquisition premiums as a function of proxies for the capital gains taxes of target shareholders, taxability of the acquisition, and tax status of the price‐setting shareholder as represented by the level of target institutional ownership. Consistent with a lock‐in effect for acquisition premiums, results suggest a unique positive association between shareholder capital gains taxes for individual investors and acquisition premiums for taxable acquisitions, which is mitigated by target institutional ownership.
Mapping and Characterization of the Dominant Black Colour Locus in Sheep
Authors: Våge Dag Inge , Fleet Malcolm R. , Ponz Ricardo , Olsen Ranveig T. , Monteagudo Luis V. , Tejedor Maria Teresa , Arruga Maria Victoria , Gagliardi Rosa , Postiglioni Alicia , Nattrass Greg S. , Klungland Helge
Published: November 2003

Dominant black pigment synthesis in sheep is caused by alterations of the melanocortin‐1 receptor (MC1‐R) coding sequence. Using five bovine microsatellite markers we have mapped the sheep MC1‐R gene to chromosome 14, corresponding to the location in other mammalian species. The existence of two independent mutations, both causing an amino acid substitution, in distantly related breeds of sheep, support the hypothesis that the observed black pigment synthesis is caused by a mutual effect of the two mutations. As similar mutations are found separately at both locations in dominant black variants of other animal species, it is also possible that any of the two mutations could be sufficient for a partial pigment switch.
Changes in the Proliferation and Differentiation of Neonatal Mouse Pink‐Eyed Dilution Melanocytes in the Presence of Excess Tyrosine
Authors: Hirobe Tomohisa , Wakamatsu Kazumasa , Ito Shosuke
Published: November 2003

Changes in the proliferation and differentiation of epidermal melanocytes derived from newborn mice wild‐type at the pink‐eyed dilution (p) locus (P/P) and from congenic mice mutant at that locus (p/p) were investigated in serum‐free primary culture, with or without the addition of L‐Tyr. Incubation with added L‐Tyr inhibited the proliferation of P/P melanocytes in a concentration‐dependent manner and inhibition was gradually augmented as the donor mice aged. In contrast, L‐Tyr stimulated the proliferation of p/p melanoblasts–melanocytes derived from 0.5‐day‐old mice, but inhibited their proliferation when derived from 3.5‐ or 7.5‐day‐old mice. L‐Tyr stimulated the differentiation of P/P melanocytes. However, almost all cells were undifferentiated melanoblasts in control cultures derived from 0.5‐, 3.5‐ and 7.5‐day‐old p/p mice, but L‐Tyr induced their differentiation as the age of the donor mice advanced. The content of the eumelanin marker, pyrrole‐2,3,5‐tricarboxylic acid as well as the pheomelanin marker, 4‐amino‐3‐hydroxyphenylalanine in p/p melanocytes was greatly reduced compared with P/P melanocytes. However, the contents of eumelanin and its precursor, 5,6‐dihydroxyindole‐2‐carboxylic acid, as well as the contents of pheomelanin and its precursor, 5‐S‐cysteinyldopa in culture media from p/p melanocytes were similar to those of P/P melanocytes at all ages tested. L‐Tyr increased the content of eumelanin and pheomelanin two‐ to threefold in cultured cells and media derived from 0.5‐, 3.5‐ and 7.5‐day‐old mice. These results suggest that the proliferation of p/p melanoblasts–melanocytes is stimulated by L‐Tyr, and that the differentiation of melanocytes is induced by L‐Tyr as the age of the donor mice advanced, although eumelanin and pheomelanin fail to accumulate in p/p melanocytes and are released from them at all ages of skin development.
Lightening Effect on Ultraviolet‐Induced Pigmentation of Guinea Pig Skin by Oral Administration of a Proanthocyanidin‐Rich Extract from Grape Seeds
Authors: Yamakoshi Jun , Otsuka Fujio , Sano Atsushi , Tokutake Shoichi , Saito Makoto , Kikuchi Mamoru , Kubota Yoshiro
Published: November 2003

Antioxidants such as vitamins C and E have been reported to inhibit the progression of ultraviolet (UV) radiation‐induced pigmentation in the skin of hairless mice. However, little is known of the lightening effect of proanthocyanidin, a powerful polyphenolic antioxidant, on UV‐induced pigmentation of the skin. We investigated the lightening effect of oral administration of a proanthocyanidin‐rich grape seed extract (GSE) using guinea pigs with UV‐induced pigmentation. These pigmented guinea pigs were fed diets containing 1% GSE or 1% vitamin C (w/w) for 8 weeks. GSE‐feeding had an apparent lightening effect on the guinea pigs’ pigmented skin. Histologic evaluation demonstrated a decrease in the number of 3,4‐dihydroxyphenylalanine (DOPA)‐positive melanocytes as well as 8‐hydroxy‐2′‐deoxyguanosine (8‐OHdG)‐positive, Ki‐67‐positive, proliferating cell nuclear antigen (PCNA)‐positive melanin‐containing cells in the basal epidermal layer of the UV‐irradiated skin in GSE‐fed guinea pigs. In contrast, these parameters did not change in the skin of vitamin C‐fed or control guinea pigs. GSE inhibited the activity of mushroom tyrosinase and also inhibited melanogenesis without inhibiting the growth of cultured B16 mouse melanoma cells. In conclusion, we demonstrated that oral administration of GSE is effective in lightening the UV‐induced pigmentation of guinea pig skin. This effect may be related to the inhibition of melanin synthesis by tyrosinase in melanocytes and the reactive oxygen species (ROS)‐related proliferation of melanocytes.
Identification of Protein Kinase C (PKC) Isoforms in Teleostean, Amphibian and Avian Pigment Cells
Authors: Isoldi Mauro César , Matioli Sergio Russo , Castrucci Ana Maria de Lauro , Lima Leonardo Henrique Ribeiro Graciani de , Visconti Maria Aparecida , Rebouças Nancy Amaral
Published: November 2003

The beta isoform of protein kinase C (PKC) has been described as the main isoform involved in the stimulation of melanogenesis in mammalian skin melanocytes. Little is known about PKC isoforms in non‐mammalian pigment cells. In neopterigian fish (holostei and teleostei), PKC is associated with pigment granule aggregation within the pigment cells (skin lightening), whereas in elasmobranchs and tetrapods, the activation of PKC leads to pigment granule dispersion (skin darkening). In an attempt to a better understanding of this distinct functional behavior upon PKC activation, we decided to investigate the PKC isoforms expressed in pigment cell lines of teleost fish, amphibians and birds, using RT‐PCR followed by cloning and sequencing. Our results demonstrate the presence of messenger RNA (mRNA) for the following PKC isoforms: beta 1, lambda and iota in GEM‐81 cells (Carassius auratus erythrophoroma), beta 1, beta 2 and zeta in Xenopus laevis (amphibian) melanophores; beta 1 and lambda in Gallus gallus (chicken) primary melanocytes. Beta 1 PKC seems to be conserved throughout phylogeny, but the diversity of the other isoforms in the different groups may account for the functional differences after PKC activation, which are observed between teleost and tetrapod pigment cells.
The Bh (Black at Hatch) Gene that Causes Abnormal Feather Pigmentation Maps to Chromosome 1 of the Japanese Quail
Authors: Niwa Tohru , Shibusawa Mami , Matsuda Yoichi , Terashima Akira , Nakamura Akira , Shiojiri Nobuyoshi
Published: November 2003

Japanese quail embryos normally have longitudinal black and brown stripes formed by colored feather buds on their back whereas an autosomal dominant mutation, black at hatch (Bh), disrupts this pigmentation pattern by causing overall black and brown coating in heterozygotes and homozygotes, respectively. These phenotypes of the Bh mutant embryos suggest that the Bh locus plays an important role in the pigment pattern formation of plumage, but its genetic origin, including cloning of the responsible gene, has been insufficiently studied. In this study, we adapted genetically directed representational difference analysis with elimination of excessive clones (GDRDA‐WEEC) to Bh quails and isolated two genetic markers linked to the Bh locus as DNA fragments. Cytogenetic study by fluorescence in situ hybridization (FISH) of the DNA fragments used as probes demonstrated that the marker loci were located in the same region on the long arm of chromosome 1. Close genetic linkage between the Bh and the marker loci, and the chromosomal location of the latter suggested that the Bh locus is located on the long‐arm of chromosome 1 of the Japanese quail.
Identification and Functional Validation of a 5′ Upstream Regulatory Sequence in the Human Tyrosinase Gene Homologous to the Locus Control Region of the Mouse Tyrosinase Gene
Authors: Regales Lucía , Giraldo Patricia , García‐DÍaz Ángel , Lavado Alfonso , Montoliu Lluís
Published: November 2003

Comparison analysis of the sequences of the mouse and human genomes has proven a powerful approach in identifying functional regulatory elements within the non‐coding regions that are conserved through evolution between homologous mammalian loci. Here, we applied computational analysis to identify regions of homology in the 5′ upstream sequences of the human tyrosinase gene, similar to the locus control region (LCR) of the mouse tyrosinase gene, located at −15 kb. We detected several stretches of homology within the first 30 kb 5′ tyrosinase gene upstream sequences of both species that include the proximal promoter sequences, the genomic region surrounding the mouse LCR, and further upstream segments. We cloned and sequenced a 5′ upstream regulatory sequence found between −8 and −10 kb of the human tyrosinase locus (termed h5′URS) homologous to the mouse LCR sequences, and confirmed the presence of putative binding sites at −9 kb, homologous to those described in the mouse tyrosinase LCR core. Finally, we functionally validated the presence of a tissue‐specific enhancer in the h5′URS by transient transfection analysis in human and mouse cells, as compared with homologous DNA sequences from the mouse tyrosinase locus. Future experiments in cells and transgenic animals will help us to understand the in vivo relevance of this newly described h5′URS sequence as a potentially important regulatory element for the correct expression of the human tyrosinase gene.
Who should fund and control the direction of human behavior genetics? Review of Nuffield Council on Bioethics 2002 Report, Genetics and Human Behaviour: the Ethical Context
Authors: Hay D. A.
Published: November 2003

In this (Nuffield Council on Bioethics 2002), the third in its series on ethics and related issues in genetics (see alsoNuffield Council on Bioethics 1993 andNuffield Council on Bioethics 1998), the Nuffield Council has focused on four ‘normal’ behaviors; intelligence, personality, antisocial behavior and sexual orientation. This is a narrow range of behaviors and one where their discussion of the potential impact of predictive genetic testing is probably inappropriate. They also take an unduly narrow view of the purposes of behavior genetics in the 21st century. It is not simply to estimate heritability but to understand more about the structure of behavior and the processes which underlie it. Their narrow focus and their negative approach to the history and achievements of genetics is reflected in their less than positive support for future behavior genetic research. Behavior geneticists need to do more to publicize what their field has achieved in order to counter the very extensive antibehavior genetics initiatives which are almost unique in science. At the same time, organizations such as the Nuffield Council need to consider carefully the impact their deliberations may have on research funding.
Functional neuroimaging of genetic variation in serotonergic neurotransmission
Authors: Hariri A. R. , Weinberger D. R.
Published: November 2003

Serotonin (5‐hydroxytryptamine; 5‐HT) is a potent modulator of the physiology and behavior involved in generating appropriate responses to environmental cues such as danger or threat. Furthermore, genetic variation in 5‐HT subsystem genes can impact upon several dimensions of emotional behavior including neuroticism and psychopathology, but especially anxiety traits. Recently, functional neuroimaging has provided a dramatic illustration of how a promoter polymorphism in the human 5‐HT transporter (5‐HTT) gene, which has been weakly related to these behaviors, is strongly related to the engagement of neural systems, namely the amygdala, subserving emotional processes. In this commentary, we discuss how functional neuroimaging can be used to characterize the effects of polymorphisms in 5‐HT subsystem genes on the response of neural circuits underlying the generation and regulation of mood and temperament as well as susceptibility to affective illness. We argue that in time, such knowledge will allow us to not only transcend phenomenological diagnosis and represent mechanisms of disease, but also identify at‐risk individuals and biological pathways for the development of new treatments.
Abnormal anxiety‐related behavior in serotonin transporter null mutant mice: the influence of genetic background
Authors: Holmes A. , Li Q. , Murphy D. L. , Gold E. , Crawley J. N.
Published: November 2003

Serotonin transporter (5‐HTT) null mutant mice provide a model system to study the role genetic variation in the 5‐HTT plays in the regulation of emotion. Anxiety‐like behaviors were assessed in 5‐HTT null mutants with the mutation placed on either a B6 congenic or a 129S6 congenic background. Replicating previous findings, B6 congenic 5‐HTT null mutants exhibited increased anxiety‐like behavior and reduced exploratory locomotion on the light ↔ dark exploration and elevated plus‐maze tests. In contrast, 129S6 congenic 5‐HTT null mutant mice showed no phenotypic abnormalities on either test. 5‐HTT null mutants on the 129S6 background showed reduced 5‐HT1A receptor binding (as measured by quantitative autoradiography) and reduced 5‐HT1A receptor function (as measured by 8‐OH‐DPAT‐indcued hypothermia). These data confirm that the 5‐HTT null mutation produced alterations in brain 5‐HT function in mice on the 129S6 background, thereby discounting the possibility that the absence of an abnormal anxiety‐like phenotype in these mice was due to a suppression of the mutation by 129 modifier genes. Anxiety‐like behaviors in the light ↔ dark exploration and elevated plus‐maze tests were significantly higher in 129S6 congenic +/+ mice as compared to B6 congenic +/+ mice. This suggests that high baseline anxiety‐like behavior in the 129S6 strain might have precluded detection of the anxiety‐like effects of the 5‐HTT null mutation on this background. Present findings provide further evidence linking genetic variation in the 5‐HTT to abnormalities in mood and anxiety. Furthermore, these data highlight the utility of conducting behavioral phenotyping of mutant mice on multiple genetic backgrounds.
Topological instability along filamented invariant surfaces
Authors: Carreras B. A. , Lynch V. E. , Garcia L. , Edelman M. , Zaslavsky G. M.
Published: November 2003

In dynamical systems with a zero Lyapunov exponent, weak mixing can be governed by a specific topological structure of some surfaces that are invariant with respect to particle dynamics. In particular, when the genus of the invariant surfaces is more than one, they may have weak mixing and the corresponding fractional kinetics. This possibility is demonstrated by using a typical example from plasma physics, a three-dimensional resistive pressure-gradient-driven turbulence model. In a toroidal geometry and with a low-pressure gradient, this model shows the emergence of quasicoherent structures. In this situation, the isosurfaces of the velocity stream function have a web structure with filamentary surfaces emerging from the outer region of the torus and covering the inner region. The filamentary surfaces can result in stochastic jets of particles that cause a “topological instability.” In such a situation, particle transport along the surfaces is of the anomalous superdiffusion type.
Self-emergence of chaos in the identification of irregular periodic behavior
Authors: De Feo Oscar
Published: November 2003

Various forms of chaotic synchronization have been proposed as ways of realizing associative memories and/or pattern recognizers. To exploit this kind of synchronization phenomena in temporal pattern recognition, a chaotic dynamical system representing the class of signals that are to be recognized must be established. This system can be determined by means of identification techniques. The fulfillment of the chaotic condition could be imposed as a constraint. However, it is shown here that, even for a very simple identification algorithm, chaos emerges by itself, allowing us to model the diversity of nearly periodic signals.
An adjustable aperiodic model class of genomic interactions using continuous time Boolean networks (Boolean delay equations)
Authors: Öktem Hakan , Pearson Ronald , Egiazarian Karen
Published: November 2003

Following the complete sequencing of several genomes, interest has grown in the construction of genetic regulatory networks, which attempt to describe how different genes work together in both normal and abnormal cells. This interest has led to significant research in the behavior of abstract network models, with Boolean networks emerging as one particularly popular type. An important limitation of these networks is that their time evolution is necessarily periodic, motivating our interest in alternatives that are capable of a wider range of dynamic behavior. In this paper we examine one such class, that of continuous-time Boolean networks, a special case of the class of Boolean delay equations (BDEs) proposed for climatic and seismological modeling. In particular, we incorporate a biologically motivated refractory period into the dynamic behavior of these networks, which exhibit binary values like traditional Boolean networks, but which, unlike Boolean networks, evolve in continuous time. In this way, we are able to overcome both computational and theoretical limitations of the general class of BDEs while still achieving dynamics that are either aperiodic or effectively so, with periods many orders of magnitude longer than those of even large discrete time Boolean networks.
InAs/GaAs square nanomesas: Multimillion-atom molecular dynamics simulations on parallel computers
Authors: Su Xiaotao , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya , Madhukar Anupam
Published: November 2003

A model potential for GaAs(100) and InAs(100) surface atoms is developed and surface reconstructions on GaAs(100) and InAs(100) are studied with the conjugate gradient (CG) method. Not only does this model reproduce well surface energies for the (100) orientation, it also yields (1×2) dimer lengths in accordance with ab initio calculations. Large-scale molecular dynamics (MD) simulations are performed to investigate mechanical stresses in InAs/GaAs nanomesas with {101}-type sidewalls. The in-plane lattice constant of InAs layers parallel to the InAs/GaAs(001) interface are found to exceed the InAs bulk value at the twelfth monolayer (ML) and the hydrostatic stresses in InAs layers become tensile above 12 ML. Hence, it is energetically unfavorable for InAs overlayers to exceed 12 ML. This may explain the experimental finding that the growth of flat InAs overlayers is self-limiting to ∼11 ML on GaAs nanomesas. MD simulations are also used to investigate the lateral size effects on the stress distribution and morphology of InAs/GaAs square nanomesas. Two nanomesas with the same vertical size but different lateral sizes are simulated. While a single stress domain is observed in the InAs overlayer of the smaller mesa, two stress domains are found in the larger mesa. This indicates the existence of a critical lateral size for stress domain formation in accordance with recent experimental findings. It is found that the InAs overlayer in the larger mesa is laterally constrained to the GaAs bulk lattice constant at the interface but vertically relaxed to the InAs bulk lattice constant. Surface energies of GaAs and InAs for the (110) and (111) orientations are also calculated with the MD and CG methods.
Invariant manifolds of an autonomous ordinary differential equation from its generalized normal forms
Authors: Palacián Jesús
Published: November 2003

A method to approximate some invariant sets of dynamical systems defined through an autonomous m-dimensional ordinary differential equation is presented. Our technique is based on the calculation of formal symmetries and generalized normal forms associated with the system of equations, making use of Lie transformations for smooth vector fields. Once a symmetry is determined up to a certain order, a reduction map allows us to pass from the equation in normal form to a related equation in a certain reduced space, the so-called reduced system of dimension s<m. Now, under certain regularity conditions, a nondegenerate p-dimensional invariant set of the reduced system is formally transformed into a (p+m−s)-dimensional invariant set of the original equation. Moreover, the existence of some actual (p+m−s)-dimensional invariant manifolds of the initial equations related to the ones determined through our analysis can be proven under certain hypotheses that we make explicit. The procedure is illustrated by characterizing the set of all periodic orbits sufficiently close to the origin of the Hamiltonian vector field defined by the Hénon and Heiles family.
A three-dimensional concurrent atomistic/continuum analysis of an epitaxially strained island
Authors: Liu P. , Zhang Y. W. , Lu C.
Published: November 2003

A three-dimensional concurrent atomistic/continuum analysis is performed to study the stress distributions in an epitaxial island. The island and the adjacent substrate are modeled by the molecular dynamics method, and the surrounding zone is modeled by the finite element method in which the nonlinear elasticity is governed by the atomic potential. An overlapping zone is defined to be the location where the atomistic and continuum models exchange necessary material information. It is found that the nonlinear elasticity based on the atomic potential is required for a smooth stress transition in the overlapping zone, and that the linear elasticity assumption significantly overestimates the stress levels at moderate and high loading levels. The implications of the present results on surface roughening driven by strain energy are discussed.
Increase in ferromagnetic/antiferromagnetic exchange bias due to a reduction of the interfacial exchange interaction
Authors: Ernult F. , Dieny B. , Billard L. , Lançon F. , Regnard J. R.
Published: November 2003

We experimentally investigated the influence of the location of nonmagnetic impurities (Au) inserted in the NiO layer of NiO/Co bilayers on the exchange bias. The inserted Au layer actually consists of a discontinuous plane of Au islands leading to local disruption of the exchange interactions within the NiO layer or at the Co/NiO interface. When the Au layer is introduced at the Co/NiO interface, this results in a significant initial increase in the exchange bias field. If the Au layer is moved deeper within the NiO layer, the exchange bias progressively decreases towards its value without Au. Our experiments are interpreted in terms of a reduced dragging of the NiO magnetization during Co magnetization reversal due to the reduced interfacial interaction. This interpretation is supported by numerical simulations which also predict the formation and annihilation of bubble-like domain walls.
Some properties of two-dimensional stochastic regimes of double-diffusive convection in plane layer
Authors: Sibgatullin I. N. , Gertsenstein S. Ja. , Sibgatullin N. R.
Published: November 2003

The existence of a two-dimensional attracting manifold is established for trajectories emanating from the vicinity of static solution. The structure of this manifold is studied with the help of succession map of points in intersection of trajectories with some coordinate plane. The structure of the attracting manifold varies depending on Rayleigh numbers of heat and salinity. With growth of Rayleigh numbers of heat and salinity the structure of one-dimensional curve becomes more irregular and sophisticated. The convergence of Bubnov–Galerkin approximation with a large number of basic functions was demonstrated in norms of kinetic energy, dissipation function, and directly by norm evaluation of the residual (noncompensated terms in substitution of Bubnov–Galerkin approximation to the initial double-diffusive convection system).
Time-resolved x-ray diffraction study of the relaxation process of electric-field-induced strain in KD2PO4
Authors: van Reeuwijk S. J. , Puig-Molina A. , Mathon O. , Tucoulou R. , Graafsma H.
Published: November 2003

In this article, we report on measurements of the strain relaxation process in KD2PO4. The application of a static electric field to a piezoelectric crystal generates stresses, which are released by the introduction of strain. Time-resolved x-ray diffraction experiments on square platelike samples indicated that the strain relaxation process strongly depends on the rise time of the electric field. In the case of an instantaneously applied electric field (rise time 30 ns, i.e., much shorter than the response time of the crystal), the induced strain waves were only weakly damped and still present 400 μs after activating the external electric field (which corresponds to roughly 50 round trips of the strain wave). The strain waves can be suppressed completely by employing a rise time equivalent to the intrinsic response time of the crystal. Measurements on a bar-shaped crystal indicated that the strain waves are generated at the edges of the crystal and propagate along the length of the crystal at the speed of sound. This was concluded from the time of arrival of the strain waves, as well as from the measured vibration frequency.
Growth model of CuGaSe2 grains in a Cu-rich/Cu-poor bilayer process
Authors: Nishiwaki S. , Siebentritt S. , Giersig M. , Ch. Lux-Steiner M.
Published: November 2003

Cu-rich Cu–Ga–Se films were prepared on a Mo coated soda-lime glass substrate by thermal codeposition and the microstructures were characterized. An increase in the grain size of CuGaSe2 (CGS) as the Cu-rich composition approached stoichiometry was observed. In the Cu-rich film, precipitated Cu–Se grains were located between the CGS grains and were connected to the film surface, which suppressed the lateral growth of the CGS grains. On the film surface, a quasi-epitaxial growth of Cu2−xSe grains was found. In order to investigate the development of the microstructure together with the phase change from Cu–Se to CGS, a small amount of Ga and Se were deposited onto Cu-rich Cu–Ga–Se films. By transmission electron microscopy, Cu1.8Se and Cu1.5Se grains were identified in the Cu-rich film. A coherent lattice structure from the CGS into the Cu1.5Se grains was found. The microstructural development of the Cu-rich Cu–Ga–Se film is discussed and models of the growth mechanism are proposed.
Surface evolution of nanostructured CrN and Si3N4 films
Authors: Xu Junhua , Yu Lihua , Kojima Isao
Published: November 2003

Comparative surface evolution of nanocrystalline (nc)-CrN and amorphous (a)-Si3N4 monolithic films and their alternative multilayer films has been studied in relation to film thickness in monolithic films, as well as to modulation periods in multilayers. Structural analysis was carried out using atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The scaling behaviors of the AFM topographical profiles were analyzed using the one-dimensional power spectral density method (1DPSD). It is interesting to note that the growth exponents (β) of both CrN and Si3N4 films can be divided into two regions of β1=0.22±0.08 and β2=0.87±0.1 for CrN films and β1=0.09±0.01 and β2=0.24±0.03 for Si3N4 films. The critical transition thickness, where the roughness jumps, is about 16.0 for CrN films and 168.0 nm for Si3N4 films. The 1DPSD analysis showed that the dependence at high frequency can be fitted to f−4.3 and f−4.2 power law decays, since the film thickness is less than 16.0 for CrN films and 168.0 nm for Si3N4 films. However, a region with an intermediate slope of −2 appeared as the film thickness exceeded 37.0 for CrN films and 222.0 nm for Si3N4 films. For CrN/Si3N4 multilayers, the roughness increases with increased modulation periods, and is much smaller than that of monolithic Si3N4 films at small modulation periods. Cross-sectional HRTEM analysis of the films revealed that the highly diffusive surface a-Si3N4 films are responsible for very smooth surfaces, while the oriented grain growth of nc-CrN films is a determining factor in the surface roughening of multilayers. The resulting parameters are discussed in terms of three competitive factors: surface diffusion, shadowing, and oriented growth, and are compared with the results of previous experimental and theoretical studies.
Effect of thermal annealing on the microstructural and optical properties of vertically stacked InAs/GaAs quantum dots embedded in modulation-doped heterostructures
Authors: Lee H. S. , Lee J. Y. , Kim T. W. , Kim M. D.
Published: November 2003

The effect of thermal annealing on multiple stacked InAs/GaAs quantum dots (QDs) embedded in an Al0.25Ga0.75As/GaAs heterostructure has been investigated by transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images show that the size of the InAs/GaAs QDs decreased slightly with an increase in growth temperature and that InAs/GaAs QDs annealed at 800 °C contained many dislocations due to annealing. Temperature-dependent PL spectra showed that peaks corresponding to the interband transitions of the InAs QDs shifted slightly towards the low-energy side and that the full width at half maximum of the peak decreased with an increase in annealing temperature. The integrated PL intensity decreased with an increase in temperature due to nonradiative defects resulting from the existence of dislocations. These results can help improve understanding of the thermal annealing effect on the microstructural and the optical properties of multiply stacked InAs/GaAs QDs embedded in modulation-doped heterostructures.
Strained Si–O–Si bonds in amorphous SiO2 materials: A family member of active centers in radio, photo, and chemical responses
Authors: Awazu Koichi , Kawazoe Hiroshi
Published: November 2003

Amorphous SiO2 (a-SiO2), such as bulk silica glasses and thin films has been one of the key materials in modern optoelectronic industries. These materials are currently used in communication technologies as optical fibers, thin films for electrical insulation in dynamic random access memories (DRAM), and optical lenses for excimer laser lithography, for example. The property essential for these applications is the wide band gap amounting to ∼9 eV. However, bulk silica glasses commercially available and silica thin films show photoresponses to subband gap lights in the vicinity of 5 eV and unexpected trapping of charges, and the behavior has a strong dependency on the preparation history. A number of studies were carried out to clarify the relationship between the properties and structural imperfections in the materials and the formation mechanisms of the defects. There are two categories of the imperfections: one is dopant- or impurity-related imperfections and the other is nonstoichiometry related defects. These defects constitute gap states in a-SiO2. The structural identification was usually performed by absorption and emission spectroscopy in the visible–ultraviolet (UV) region and electron spin resonance (ESR). The experimentally proposed models were compared with the predictions by theoretical calculations of energy levels. Recent development of the excimer laser lithography technique led us to recognize that a latent member, which has been unnoticed because of no response to the optical absorption or emission in the visible-UV range and ESR absorption, exists in the family of active centers in a-SiO2, that is a strained Si–O–Si bond originating from the planar three membered ring. In contrast, the puckered four membered ring is unstrained. Although it has been pointed out that there was a wide distribution in Si–O–Si bond angle from 90° to 180° by x-ray analysis or Si29 solid state nuclear magnetic resonance, the physical, and chemical responses of the Si–O–Si bonds with a particular bond angle could not be differentiated. Very recently it was clarified that a strained Si–O–Si bond, in other words chemically excited bonds, has an optical absorption locating on the band edge. The chemically excited bond can be scavenged by fluorine doping, because it is chemically reactive. In the present review we show that the unresolved optical and electric responses of silica glasses can be comprehensively understood by taking the presence of the strained bonds into consideration.
Structure of low dielectric constant to extreme low dielectric constant SiCOH films: Fourier transform infrared spectroscopy characterization
Authors: Grill Alfred , Neumayer Deborah A.
Published: November 2003

Carbon doped oxide dielectrics comprised of Si, C, O, and H (SiCOH) have been prepared by plasma enhanced chemical vapor deposition (PECVD) from mixtures of tetramethylcyclotetrasiloxane (TMCTS) and an organic precursor. The films have been analyzed by determining their elemental composition and by Fourier transform infrared spectroscopy with deconvolution of the absorption peaks. The analysis has shown that PECVD of TMCTS produces a highly crosslinked networked SiCOH film. Dissociation of TMCTS appears to dominate the deposition chemistry as evidenced by the multitude of bonding environments and formation of linear chains and branches. Extensive crosslinking of TMCTS rings occurs through Si–Si, Si–CH2–Si, Si–O–Si, and Si–CH2–O–Si moieties. The films deposited from mixtures of TMCTS and organic precursor incorporate hydrocarbon fragments into the films. This incorporation occurs most probably through the reaction of the organic precursor and the Si–H bonds of TMCTS. Annealing the SiCOH films deposited from TMCTS and organic precursor results in a large loss of carbon and hydrogen from the films resulting from the fragmentation and loss of the incorporated organic component. The deconvolution of the Si–O–Si asymmetric stretching band of the annealed films shows the existence of a larger fraction of a cage structure and a correspondingly smaller fraction of a networked (highly crosslinked) structure in the SiCOH films deposited from mixtures of TMCTS with organic precursor relative to the films deposited from TMCTS only. The evolution of the volatile hydrocarbon fragments during annealing results in the formation of nanopores and subsequent reduction of the dielectric constants of the films to extreme low-k values.
Structural characteristics of carbon nanorods and nanotubes grown using electron cyclotron resonance chemical vapor deposition
Authors: Woo Yun Sung , Jeon Duk Young , Han In Taek , Park Young Jun , Kim Ha Jin , Jung Jae Eun , Kim Jong Min , Lee Nae Sung
Published: November 2003

Different types of carbonaceous materials were synthesized by electron cyclotron resonance chemical vapor deposition on Ni-coated glass substrates with radio-frequency (rf) self-biasing using a gas mixture of CH4 and Ar. Vertically aligned carbon nanorods and multiwalled carbon nanotubes (MWNTs) were obtained at the rf bias voltages of −100 and −200 V, respectively. High-resolution transmission electron microscopy indicated that the distance between two graphene layers of carbon nanorods is much larger than that of well-graphitized MWNTs having a typical value of graphite. Structural characteristics of carbon nanorods and well-graphitized MWNTs were investigated by electron-energy-loss spectra, in which the energy of π+σ plasmon peak obtained from carbon nanorods shifts to a lower value of 23.8 eV, compared to 25.5 eV from well-graphitized MWNT. Low-energy loss plasmon due to π electrons at 6 eV was not observed in carbon nanorods, but clearly defined for well-graphitized MWNTs. In addition, x-ray photoelectron spectroscopy showed that the delocalization of π electrons becomes more pronounced as the structure of carbonaceous films evolves into more crystalline phase from carbon nanowalls to well-graphitized MWNTs with increasing rf bias voltages. These results can suggest that ionic bombardment energy at high rf bias voltages provides sufficient internal energy for dehydrogenation from hydrocarbon molecules, and thus well-graphitized MWNTs can be synthesized even at low temperatures.
Effect of precursor concentration in atomic layer deposition of Al2O3
Authors: Kuse Ronald , Kundu Manisha , Yasuda Tetsuji , Miyata Noriyuki , Toriumi Akira
Published: November 2003

The effect of precursor gas-phase concentration in atomic layer deposition (ALD) of Al2O3 on Si(001) using Al(CH3)3 and H2O was investigated. Film growth rate was found to vary with Al(CH3)3 and H2O partial pressure, indicating that the process operates in a regime where complete conversion of surface sites is not reached when reactions self-extinguish. Higher precursor concentrations lead to higher conversion of surface sites as evidenced by faster film growth per ALD cycle. However, higher H2O concentrations also result in increasing amounts of aluminum silicate at the Al2O3/Si(001) interface. In addition to lower dielectric constants, flatband voltages increase by 0.5–0.6 V. Flatband voltage did not depend on the thickness of the interfacial layer as films with comparable capacitance equivalent thickness and interfacial thicknesses ranging from 2.2 to 11.1 Å yielded identical flatband voltages. Interfacial silicate could be eliminated completely by reducing the gas-phase concentration of H2O, permitting Al2O3 to form an abrupt interface with Si(001).
Surface instability of soft films with coupled tension-shear interactions
Authors: Shenoy Vijay , Sharma Ashutosh
Published: November 2003

The surface roughening instability in a soft thin film, induced by interactions with a contactor is investigated accounting for both tension and shear effects in the interaction potential. A key finding of this study is that, in the presence of coupled tension–shear interactions, the instability mode will depend on whether the contactor is brought towards the film (contact mode) or the contactor is retracted from a fully sticking configuration (peeling mode). In the contact mode, the wavelength of the roughening is about three times the film thickness, in agreement with previous works, while in the peeling mode it is about four times the film thickness. Although the analysis indicates a rich and complex dependence on the parameters of the interaction, the wavelength of the instability is essentially independent of the interactions for physically reasonable values of interaction parameters. The results are in agreement with available experiments. The results of the present study are useful in providing insights into the physics of friction and cavitation at soft interfaces.
Nanoferroelectric domains in ultrathin BaTiO3 films
Authors: Drezner Y. , Berger S.
Published: November 2003

The microstructure and electrical properties of ultrathin BaTiO3 films (2–7 nm thick) have been studied. Multidomain structures having 180° domains and 90° domain boundaries were observed by high resolution transmission electron microscopy. The domains, which have a width as small as one unit cell, are mostly oriented in parallel to the film plane. The film exhibits ferroelectric behavior characterized by polarization hysteresis loops and Curie temperature. The leakage current, switching time, and fatigue characteristics of the films are also reported.
Transmission electron microscopy study of damaged layer on GaAs surface induced by low-energy ion irradiation
Authors: Kato J. , Nagatomi T. , Takai Y.
Published: November 2003

A damaged layer on a GaAs surface induced by low-energy Ar+ ion irradiation was investigated using a transmission electron microscope. Ar+ ions with primary energies of 200, 100, and 50 eV were irradiated onto the GaAs surface at incident angles of 90°, 60°, and 30° from the sample surface. The results revealed that the thickness of the damaged layer of ∼4.3 nm formed by 200 eV Ar+ ion irradiation at 90° was reduced to ∼1.5 nm with 50 eV Ar+ ion irradiation at 30°. The results confirmed that lowering the primary energy of ions to 50 eV and employing glancing incidence are very effective for achieving higher depth resolution in sputter depth profiling.