Showing papers by "University of California, Santa Barbara published in 1995"
TL;DR: In this paper, the carrier collection efficiency and energy conversion efficiency of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C60 or its functionalized derivatives.
Abstract: The carrier collection efficiency (ηc) and energy conversion efficiency (ηe) of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C60 or its functionalized derivatives. Composite films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and fullerenes exhibit ηc of about 29 percent of electrons per photon and ηe of about 2.9 percent, efficiencies that are better by more than two orders of magnitude than those that have been achieved with devices made with pure MEH-PPV. The efficient charge separation results from photoinduced electron transfer from the MEH-PPV (as donor) to C60 (as acceptor); the high collection efficiency results from a bicontinuous network of internal donor-acceptor heterojunctions.
9,611 citations
TL;DR: It is shown that D-branes, extended objects defined by mixed Dirichlet-Neumann boundary conditions, break half the supersymmetries of the type II superstring and carry a complete set of electric and magnetic Ramond-Ramond charges.
Abstract: We show that D-branes, extended objects defined by mixed Dirichlet-Neumann boundary conditions, break half the supersymmetries of the type II superstring and carry a complete set of electric and magnetic Ramond-Ramond charges. The product of the electric and magnetic charges is a single Dirac unit, and the quantum of charge is that required by string duality. This is strong evidence that D-branes are intrinsic to type II string theory and are the Ramond-Ramond sources needed for string duality. Also, we find in the IIa string a 9-form potential, which gives an effective cosmological constant.
3,151 citations
TL;DR: In this article, an image fusion scheme based on the wavelet transform is presented, where wavelet transforms of the input images are appropriately combined, and the new image is obtained by taking the inverse wavelet transformation of the fused wavelet coefficients.
1,532 citations
TL;DR: In this paper, an understanding of the molecular mechanisms of tribology in thin films and at surfaces has been presented, which is of fundamental importance in many pure and applied sciences, such as computer simulations.
Abstract: Friction, wear and lubrication between materials in contact are of fundamental importance in many pure and applied sciences. Owing to the development of experimental and computer-simulation techniques for studying these phenomena at the atomic scale, an understanding is beginning to emerge of the molecular mechanisms of tribology in thin films and at surfaces.
1,393 citations
TL;DR: This article found that there is a home bias in national investment portfolios despite the potential gains from international diversification, and that the composition of the portfolio of foreign securities seems to reflect factors other than diversification of risk, such as cross-border capital flows and the high turnover rate on foreign equity investments relative to turnover on domestic equity markets.
1,329 citations
TL;DR: In this paper, the authors measured the hardness of a thin epitaxial gold film embedded in the silver layers and found that the deformation was primarily restricted to the sharp edges of the indentation.
Abstract: The hardness of thick, high-purity, epitaxially grown silver on sodium chloride is found to be dependent on the size of the indentation for sizes below ≃10 μm. The measurement of the size effect has been made in two ways. In one, the hardness has been calculated from the load-displacement curve obtained from an instrumented microhardness testing machine and assuming a geometric self-similarity in the indenter shape. In the other measurement, the hardness was obtained from the load exerted by the microhardness tester divided by the indentation impression area as measured by atomic force microscopy. The observed variation in microhardness with indentation size is consistent with a simplified strain gradient plasticity model in which the densities of the geometrically necessary and statistically stored dislocations are fitting parameters. An equally good fit can also be made with a simple geometric scaling relationship. Transmission electron microscopy observations of a thin (≃50 nm) epitaxial gold film embedded in the silver layers revealed that the deformation was primarily restricted to the sharp edges of the indentation. In addition, deformation twinning within the indentation impression was observed on the {1H} planes.
1,259 citations
TL;DR: It is shown that extremal magnetic black hole solutions of N=2 supergravity coupled to vector multiplets with a generic holomorphic prepotential F can be described as supersymmetric solitons which interpolate between maximally symmetric limiting solutions at spatial infinity and the horizon.
Abstract: It is shown that extremal magnetic black hole solutions of N=2 supergravity coupled to vector multiplets ${\mathit{X}}^{\mathrm{\ensuremath{\Lambda}}}$ with a generic holomorphic prepotential F(${\mathit{X}}^{\mathrm{\ensuremath{\Lambda}}}$) can be described as supersymmetric solitons which interpolate between maximally symmetric limiting solutions at spatial infinity and the horizon. A simple exact solution is found for the special case that the ratios of the ${\mathit{X}}^{\mathrm{\ensuremath{\Lambda}}}$ are real, and it is seen that the logarithm of the conformal factor of the spatial metric equals the K\"ahler potential on the vector multiplet moduli space. Several examples are discussed in detail.
1,248 citations
TL;DR: This model can explain a number of elastic properties of cross-linked gels and sterically entangled solutions of semiflexible biopolymers such as F-actin in vitro, including the concentration dependence of the storage modulus and yield strain.
Abstract: We develop a model for cross-linked gels and sterically entangled solutions of semiflexible biopolymers such as F-actin. Such networks play a crucial structural role in the cytoskeleton of cells. We show that the rheologic properties of these networks can result from nonclassical rubber elasticity. This model can explain a number of elastic properties of such networks in vitro, including the concentration dependence of the storage modulus and yield strain.
988 citations
TL;DR: In this article, nonperturbative instanton corrections to the moduli space geometry of type IIA string theory compactified on a Calabi-Yau space are derived and found to contain order e − 1/g s contributions, where g s is the string coupling.
963 citations
TL;DR: In this paper, it was shown that low-energy effective field theories arising from Calabi-Yau string compactifications are generically inconsistent or ill-defined at the classical level because of conifold singularities in the moduli space.
896 citations
TL;DR: The paper presents a new approach to representing and detecting computer penetrations in real time, called state transition analysis, which models penetrations as a series of state changes that lead from an initial secure state to a target compromised state.
Abstract: The paper presents a new approach to representing and detecting computer penetrations in real time. The approach, called state transition analysis, models penetrations as a series of state changes that lead from an initial secure state to a target compromised state. State transition diagrams, the graphical representation of penetrations, identify precisely the requirements for and the compromise of a penetration and present only the critical events that must occur for the successful completion of the penetration. State transition diagrams are written to correspond to the states of an actual computer system, and these diagrams form the basis of a rule based expert system for detecting penetrations, called the state transition analysis tool (STAT). The design and implementation of a Unix specific prototype of this expert system, called USTAT, is also presented. This prototype provides a further illustration of the overall design and functionality of this intrusion detection approach. Lastly, STAT is compared to the functionality of comparable intrusion detection tools. >
TL;DR: A model that makes use of the cooperative organization of inorganic and organic molecular species into three dimensionally structured arrays is generalized for the synthesis of nanocomposite materials to separate the effects of self-assembly from the kinetics of silicate polymerization.
Abstract: A model that makes use of the cooperative organization of inorganic and organic molecular species into three dimensionally structured arrays is generalized for the synthesis of nanocomposite materials. In this model, the properties and structure of a system are determined by dynamic interplay among ion-pair inorganic and organic species, so that different phases can be readily obtained through small variations of controllable synthesis parameters, including mixture composition and temperature. Nucleation, growth, and phase transitions may be directed by the charge density, coordination, and steric requirements of the inorganic and organic species at the interface and not necessarily by a preformed structure. A specific example is presented in which organic molecules in the presence of multiply charged silicate oligomers self-assemble into silicatropic liquid crystals. The organization of these silicate-surfactant mesophases is investigated with and without interfacial silicate condensation to separate the effects of self-assembly from the kinetics of silicate polymerization.
TL;DR: In this article, the authors examined the possibility that the superconducting state of these materials is characterized by d x 2 − y 2 pairing and showed that this type of pairing might be favored in a strongly correlated system with a short-range Coulomb interaction.
TL;DR: In this article, a quantization of diffeomorphism invariant theories of connections is studied and the quantum diffeomorphicism constraint is solved and the space of solutions is equipped with an inner product that is shown to satisfy the physical reality conditions.
Abstract: Quantization of diffeomorphism invariant theories of connections is studied and the quantum diffeomorphism constraint is solved. The space of solutions is equipped with an inner product that is shown to satisfy the physical reality conditions. This provides, in particular, a quantization of the Husain–Kuchař model. The main results also pave the way to quantization of other diffeomorphism invariant theories such as general relativity. In the Riemannian case (i.e., signature ++++), the approach appears to contain all the necessary ingredients already. In the Lorentzian case, it will have to be combined in an appropriate fashion with a coherent state transform to incorporate complex connections.
TL;DR: Gemini surfactants, with two quaternary ammonium head groups separated by a methylene chain of variable length, can be used to control organic charge sitting relative to the bivariable hydrophobic tail configurations, leading to a mesophase (SBA-2) that has three-dimensional hexagonal (P63/mmc) symmetry, regular supercages that can be dimensionally tailored, and a large inner surface area.
Abstract: At low temperatures, liquid crystal-like arrays made up of inorganic-cluster and organic molecular units readily undergo reversible lyotropic transformations. Gemini surfactants, with two quaternary ammonium head groups separated by a methylene chain of variable length and with each head group attached to a hydrophobic tail, can be used to control organic charge sitting relative to the bivariable hydrophobic tail configurations. This approach has led to the synthesis of a mesophase (SBA-2) that has three-dimensional hexagonal (P6(3)/mmc) symmetry, regular supercages that can be dimensionally tailored, and a large inner surface area. This mesostructure analog of a zeolite cage structure does not appear to have a lyotropic surfactant or lipid liquid crystal mesophase counterpart. Through the modification of gemini charge separation and each of the two organic tails, these syntheses can be used to optimize templating effects, including the synthesis of MCM-48 at room temperature.
TL;DR: In this article, lead lanthanum zirconate titanate (PLZT) was loaded with compressive stress parallel to the polarization and the stress vs strain curve was recorded.
Abstract: Ferroelectric and ferroelastic switching cause ferroelectric ceramics to depolarize and deform when subjected to excessive electric field or stress. Switching is the source of the classic butterfly shaped strain vs electric field curves and the corresponding electric displacement vs electric field loops [1]. It is also the source of a stress—strain curve with linear elastic behavior at low stress, non-linear switching strain at intermediate stress, and linear elastic behavior at high stress [2, 3]. In this work, ceramic lead lanthanum zirconate titanate (PLZT) is polarized by loading with a strong electric field. The resulting strain and polarization hysteresis loops are recorded. The polarized sample is then loaded with compressive stress parallel to the polarization and the stress vs strain curve is recorded. The experimental results are modeled with a computer simulation of the ceramic microstructure. The polarization and strain for an individual grain are predicted from the imposed electric field and stress through a Preisach hysteresis model. The response of the bulk ceramic to applied loads is predicted by averaging the response of individual grains that are considered to be statistically random in orientation. The observed strain and electric displacement hysteresis loops and the nonlinear stress—strain curve for the polycrystalline ceramic are reproduced by the simulation.
TL;DR: Examination of the preferences of female guppies from 11 localities in Trinidad shows that females are on average more attracted to males from their own population than from alien populations, and populations appear to vary in the criteria used in female choice.
Abstract: We examined the preferences of female guppies (Poecilia reticulata) from 11 localities in Trinidad with respect to male color-pattern elements, body shape and size, and overall color and brightness contrast. Females are on average more attracted to males from their own population than from alien populations, and populations appear to vary in the criteria used in female choice. Multiple-regression analysis suggests that mate-preference criteria vary among localities in intensity, sign, and the number of traits used. Although preference estimators and color-pattern parameters are unique to each population, only orange, black, and color contrast showed a correlation between degree of male trait and degree of preference for that trait. There is a clear effect of water color and a possible effect of predation intensity. The results are discussed in light of various models of sexual selection and the early stages of speciation.
TL;DR: Simulations show that the use of the adaptive hysteresis inverse leads to major improvements of system performance.
Abstract: For a system with hysteresis, the authors present a parameterized hysteresis model and develop a hysteresis inverse. The authors then design adaptive controllers with an adaptive hysteresis inverse for plants with unknown hysteresis. A new adaptive controller structure is introduced which is capable of achieving a linear parameterization and a linear error model in the presence of a hysteresis nonlinearity. A robust adaptive law is used to update the controller parameters and hysteresis inverse parameters, which ensures the global boundedness of the closed-loop signals for a wide class of of hysteresis models. Simulations show that the use of the adaptive hysteresis inverse leads to major improvements of system performance. >
TL;DR: A simple, semiquantitative method to determine the concentration of TEP colorimetrically, which shows that TEP are not generated as an artifact of filtration and compares well with parallel light microscope counts.
Abstract: Large transparent exopolymer particles (TEP) are found abundantly in the ocean and play an important role in many fields of marine ecology. Quantification of TEP by light microscopy, however, is labor-intensive and slow. Here we introduce a simple, semiquantitative method to determine the concentration of TEP colorimetrically. In this method TEP are first stained with alcian blue. The dye complexed with TEP is then redissolved and measured spectrophotometrically. Several independent tests of the method show that the concentration of TEP measured spectrophotometrically compares well with parallel light microscope counts. Fractionation experiments confirm that TEP are not generated as an artifact of filtration. Field data show that the concentration of TEP in different oceanic environments ranges from 10 to 500 μg liter -1 xanthan equivalent depending on season, depth, and plankton community composition.
TL;DR: A network of interactions among the traits' functions could bias the direction of evolution in characteristic ways, and suggests how intraspecific variation may give rise to interspecific variation.
Abstract: Guppies show geographical variation in many different kinds of traits. Traits covary with each other, with predation and with other environmental factors. Phenotypic correlations are often assumed to result from genetic correlations, but may also result from covariation among different sources of natural selection and interactions among the traits' functions. This network of interactions could bias the direction of evolution in characteristic ways, and suggests how intraspecific variation may give rise to interspecific variation.
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TL;DR: In this article, it was shown that many of the $p$-branes of type II string theory and $d=11$ supergravity can have boundaries on other$p$branes and the rules for when and cannot occur are derived from charge conservation.
Abstract: It is shown that many of the $p$-branes of type II string theory and $d=11$ supergravity can have boundaries on other $p$-branes. The rules for when this can and cannot occur are derived from charge conservation. For example it is found that membranes in $d=11$ supergravity and IIA string theory can have boundaries on fivebranes. The boundary dynamics are governed by the self-dual $d=6$ string. A collection of $N$ parallel fivebranes contains $\half N(N-1)$ self-dual strings which become tensionless as the fivebranes approach one another.
20 Jul 1995
TL;DR: This paper presents a new model of parallel computation---the LogGP model---and uses it to analyze a number of algorithms, most notably, the single node scatter (one-to-all personalized broadcast), examining the all- to-all remap, FFT, and radix sort.
Abstract: We present a new model of parallel computation---the LogGP model---and use it to analyze a number of algorithms, most notably, the single node scatter (one-to-all personalized broadcast). The LogGP model is an extension of the LogP model for parallel computation which abstracts the communication of fixed-sized short messages through the use of four parameters: the communication latency (L), overhead (o), bandwidth (g), and the number of processors (P). As evidenced by experimental data, the LogP model can accurately predict communication performance when only short messages are sent (as on the CM-5). However, many existing parallel machines have special support for long messages and achieve a much higher bandwidth for long messages compared to short messages (e.g., IBM SP-2, Paragon, Meiko CS-2, Ncube/2). We extend the basic LogP model with a linear model for long messages. This combination, which we call the LogGP model of parallel computation, has one additional parameter, G, which captures the bandwidth obtained for long messages. Experimental data collected on the Meiko CS-2 shows that this simple extension of the LogP model can quite accurately predict communication performance for both short and long messages. This paper discusses algorithm design and analysis under the new model, examining the all-to-all remap, FFT, and radix sort. We also examine, in more detail, the single node scatter problem. We derive solutions for this problem and prove their optimality under the LogGP model. These solutions are qualitatively different from those obtained under the simpler LogP model, reflecting the importance of capturing long messages in a model.
TL;DR: Two contour-based methods which use region boundaries and other strong edges as matching primitives are presented, which have outperformed manual registration in terms of root mean square error at the control points.
Abstract: Image registration is concerned with the establishment of correspondence between images of the same scene. One challenging problem in this area is the registration of multispectral/multisensor images. In general, such images have different gray level characteristics, and simple techniques such as those based on area correlations cannot be applied directly. On the other hand, contours representing region boundaries are preserved in most cases. The authors present two contour-based methods which use region boundaries and other strong edges as matching primitives. The first contour matching algorithm is based on the chain-code correlation and other shape similarity criteria such as invariant moments. Closed contours and the salient segments along the open contours are matched separately. This method works well for image pairs in which the contour information is well preserved, such as the optical images from Landsat and Spot satellites. For the registration of the optical images with synthetic aperture radar (SAR) images, the authors propose an elastic contour matching scheme based on the active contour model. Using the contours from the optical image as the initial condition, accurate contour locations in the SAR image are obtained by applying the active contour model. Both contour matching methods are automatic and computationally quite efficient. Experimental results with various kinds of image data have verified the robustness of the algorithms, which have outperformed manual registration in terms of root mean square error at the control points. >
TL;DR: In this paper, it is shown that the azafullerene dimer is formed upon in situ reduction of the highly reactive azafulleronium ion, which opens a viable route for the preparation of other heterofullerenes in solution.
Abstract: The heterofullerene ion C59N+ is formed efficiently in the gas phase during fast atom bombardment mass spectroscopy of a cluster-opened N-MEM (N-methoxyethoxy methyl) ketolactam. This transformation is shown to occur also in solution in the presence of strong acid, affording biazafullerenyl (C59N)2 in good yield. It is proposed that the azafullerene dimer is formed upon in situ reduction of the highly reactive azafulleronium ion. The isolation and characterization of biazafullerenyl opens a viable route for the preparation of other heterofullerenes in solution.
TL;DR: The results establish that K88 encodes an IFN-inducible ds RNA-specific adenosine deaminase and suggest that at least two forms of dsRNA-specificAdenosineDeaminase occur in human cells.
Abstract: A 6,474-nucleotide human cDNA clone designated K88, which encodes double-stranded RNA (dsRNA)-specific adenosine deaminase, was isolated in a screen for interferon (IFN)-regulated cDNAs. Northern (RNA) blot analysis revealed that the K88 cDNA hybridized to a single major transcript of approximately 6.7 kb in human cells which was increased about fivefold by IFN treatment. Polyclonal antisera prepared against K88 cDNA products expressed in Escherichia coli as glutathione S-transferase (GST) fusion proteins recognized two proteins by Western (immunoblot) analysis. An IFN-induced 150-kDa protein and a constitutively expressed 110-kDa protein whose level was not altered by IFN treatment were detected in human amnion U and neuroblastoma SH-SY5Y cell lines. Only the 150-kDa protein was detected in mouse fibroblasts with antiserum raised against the recombinant human protein; the mouse 150-kDa protein was IFN inducible. Immunofluorescence microscopy and cell fractionation analyses showed that the 110-kDa protein was exclusively nuclear, whereas the 150-kDa protein was present in both the cytoplasm and nucleus of human cells. The amino acid sequence deduced from the K88 cDNA includes three copies of the highly conserved R motif commonly found in dsRNA-binding proteins. Both the 150-kDa and the 110-kDa proteins prepared from human nuclear extracts bound to double-stranded but not to single-stranded RNA affinity columns. Furthermore, E. coli-expressed GST-K88 fusion proteins that included the R motif possessed dsRNA-binding activity. Extracts prepared either from K88 cDNA-transfected cells or from IFN-treated cells contained increased dsRNA-specific adenosine deaminase enzyme activity. These results establish that K88 encodes an IFN-inducible dsRNA-specific adenosine deaminase and suggest that at least two forms of dsRNA-specific adenosine deaminase occur in human cells.
TL;DR: Upper and lower limits on the branching ratio, each at 95% C.L., are {ital B}({ital b}{r_arrow}{ital s}{gamma}){gt}1.0{times}10{sup {minus}4}.
Abstract: We have measured the inclusive {ital b}{r_arrow}{ital s}{gamma} branching ratio to be (2.32{plus_minus}0.57{plus_minus}0.35){times}10{sup {minus}4}, where the first error is statistical and the second is systematic. Upper and lower limits on the branching ratio, each at 95% C.L., are {ital B}({ital b}{r_arrow}{ital s}{gamma}){lt}4.2{times}10{sup {minus}4} and {ital B}({ital b}{r_arrow}{ital s}{gamma}){gt}1.0{times}10{sup {minus}4}. These limits restrict the parameters of extensions of the standard model.
TL;DR: The ability of multifrequency SAR to quantify in near realtime the extent of inundation on forested floodplains, and its potential application for timely monitoring of flood events is demonstrated.
Abstract: Floodplain inundation and vegetation along the Negro and Amazon rivers near Manaus, Brazil were accurately delineated using multi-frequency, polarimetric synthetic aperture radar (SAR) data from the April and October 1994 SIR-C missions. A decision-tree model was used to formulate rules for a supervised classification into five categories: water, clearing (pasture), aquatic macrophyte (floating meadow), nonflooded forest, and flooded forest. Classified images were produced and tested within three days of SIR-C data acquisition. Both C-band (5.7 cm) and L-band (24 cm) wavelengths were necessary to distinguish the cover types. HH polarization was most useful for distinguishing flooded from nonflooded vegetation (C-HH for macrophyte versus pasture, and L-HH for flooded versus nonflooded forest), and cross-polarized L-band data provided the best separation between woody and nonwoody vegetation. Between the April and October missions, the Amazon River level fell about 3.6 m and the portion of the study area covered by flooded forest decreased from 23% to 12%. This study demonstrates the ability of multifrequency SAR to quantify in near realtime the extent of inundation on forested floodplains, and its potential application for timely monitoring of flood events. >
TL;DR: In this paper, the authors estimate the effect of arrests on the employment and earnings of arrestees, using a large longitudinal data set constructed by merging police records with UI earnings data, finding that the effects of arrests are moderate in magnitude and rather short-lived.
Abstract: Many young men commit crime, and many are arrested. I estimate the effect of arrests on the employment and earnings of arrestees, using a large longitudinal data set constructed by merging police records with UI earnings data. I find that the effects of arrests are moderate in magnitude and rather short-lived.
TL;DR: In this paper, the principles of fail-safe thermomechanical design, based on the damage mechanisms known to occur in these systems, are discussed, including delamination and crazing of brittle layers.
Abstract: Thin films and multilayers comprised of different classes of material are often used for various functional requirements. As these become relatively large in section and geometrically more complex, thermomechanical integrity is a major concern. It influences performance, yield and reliability. A methodology for thermomechanical design is needed that complements procedures used for circuit design. This article elaborates the principles of fail-safe thermomechanical design, based on the damage mechanisms known to occur in these systems. Among the important mechanisms are delamination and crazing of brittle layers. thermomechanical fatigue of metallic constituents and interface decohesion. The damage mechanisms are generally activated by residual stress, both thermal and ‘intrinsic’. The origins of these stresses are discussed, as well as stress redistribution effects that arise because of bending, discontinuities, etc. Emphasis is given to measurement methods which provide those data needed for implementation of the fail-safe design methodology.
TL;DR: In this article, it was shown that black hole condensation can occur at conifold singularities in the moduli space of type II Calabi-Yau string vacua.