Explicit Picture Research Articles

Traveling Waves and Patches in Dendritic Actin Nucleation

The dynamics of cell edges are closely related to those of F-actin. Recent fluorescence imaging studies have shown that F-actin can spontaneously form traveling waves or moving patches at low actin concentrations. I investigate possible mechanisms for such phenomena by numerically simulating the “dendritic nucleation” model of actin network growth. The simulations treat actin network growth on a 3 by 3 micron piece of membrane. They store information about actin filaments subunit by subunit, giving an explicit three-dimensional picture of the actin network. The calculations include filament growth, capping, branching, severing, and random thermal motion. The dynamics of nucleation-promoting factors (NPFs) in the membrane are also included: they diffuse in the membrane, and detach/inactivate in the presence of F-actin. The simulations show three types of behavior which are “tuned” by the actin concentration: 1) traveling waves, 2) coherently moving patches, and 3) random fluctuations with occasional moving patches. Wave formation is favored by a long recovery time for NPFs which have been inactivated, and by weakness of the attractive interaction between filaments and the membrane. Low G-actin concentrations cause waves to break up into patches which, however, move coherently. Similar effects are seen with increasing capping-protein concentration. Diffusion of NPFs slows the waves, and, if fast enough, stops them completely, resulting in the formation of a static spot.

Mixed-mode singularity and temperature effects on dislocation nucleation in strained interconnects

Dislocations can be nucleated from sharp geometric features in strained interconnects due to the thermal expansion coefficient mismatch, lattice mismatch, or stresses that arise during material processing. The asymptotic stress fields near the edge root can be described by mixed-mode singularities, which depend on the dihedral angle and material properties, and a transverse T-stress, which depends on how residual stress is realized in the interconnects. The critical condition for stress nucleation can be determined when an appropriate measure of the stress intensity factors (SIFs) reaches a critical value. This method, however, does not offer an explicit picture of the dislocation nucleation process so that it has difficulties in studying complicated structures, mode mixity effects, and more importantly the temperature effects. Using the Peierls concept, a dislocation can be described by a continuous slip field, and the dislocation nucleation occurs when the total potential energy reaches a stationary state. Through implementing this ad hoc interface model into a finite element framework, it is found that dislocation nucleation becomes more difficult with the increase of mode mixity, or the decrease of the T-stress, or the decrease of the length-to-height ratio of the surface pad, while the shape of the surface pad, being a square or a long line, plays a less important role. The Peierls dislocation model also allows us to determine the activation energy, which is the energy needed for the thermally activated, mechanically assisted dislocation nucleation when the applied load is lower than the athermal critical value. The calculated saddle point configuration agrees well with the molecular simulations in literature. Suggestions on making immortal strained interconnects are made.

Unifying treatment of nonequilibrium and unstable dynamics of cold bosonic atom system with time-dependent order parameter in Thermo Field Dynamics

The coupled equations which describe the temporal evolution of the Bose–Einstein condensed system are derived in the framework of nonequilibrium Thermo Field Dynamics. The key element is that they are not the naive assemblages of assumed equations, but are the self-consistent ones derived by appropriate renormalization conditions. While the order parameter is time-dependent, an explicit quasiparticle picture is constructed by a time-dependent expansion. Our formulation is valid even for the system with a unstable condensate, and describes the condensate decay caused by the Landau instability as well as by the dynamical one.

The origins of lactase persistence in Europe.

Lactase persistence (LP) is common among people of European ancestry, but with the exception of some African, Middle Eastern and southern Asian groups, is rare or absent elsewhere in the world. Lactase gene haplotype conservation around a polymorphism strongly associated with LP in Europeans (−13,910 C/T) indicates that the derived allele is recent in origin and has been subject to strong positive selection. Furthermore, ancient DNA work has shown that the −13,910*T (derived) allele was very rare or absent in early Neolithic central Europeans. It is unlikely that LP would provide a selective advantage without a supply of fresh milk, and this has lead to a gene-culture coevolutionary model where lactase persistence is only favoured in cultures practicing dairying, and dairying is more favoured in lactase persistent populations. We have developed a flexible demic computer simulation model to explore the spread of lactase persistence, dairying, other subsistence practices and unlinked genetic markers in Europe and western Asia's geographic space. Using data on −13,910*T allele frequency and farming arrival dates across Europe, and approximate Bayesian computation to estimate parameters of interest, we infer that the −13,910*T allele first underwent selection among dairying farmers around 7,500 years ago in a region between the central Balkans and central Europe, possibly in association with the dissemination of the Neolithic Linearbandkeramik culture over Central Europe. Furthermore, our results suggest that natural selection favouring a lactase persistence allele was not higher in northern latitudes through an increased requirement for dietary vitamin D. Our results provide a coherent and spatially explicit picture of the coevolution of lactase persistence and dairying in Europe.

A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials

We present the successful application of a concerted approach for the investigation of the local environment in ordered and disordered phases in the solid state. In this approach we combined isotope labeling with computational methods and different solid-state NMR techniques. We chose triphenylphosphite (TPP) as an interesting example of our investigations because TPP exhibits two crystalline modifications and two different amorphous phases one of which is highly correlated. In particular we analyzed the conformational distribution in three of these phases. A sample of triply labeled 1-[13C]TPP was prepared and 1D MAS as well as wide-line 13C NMR spectra were measured. Furthermore we acquired 2D 13C wide-line exchange spectra and used this method to derive highly detailed information about the phenyl orientation in the investigated TPP phases. For linkage with a structure model a DFT analysis of the TPP molecule and its immediate environment was carried out. The ab initio calculations of the 13C chemical shift tensor in three- and six-spin systems served as a base for the calculation of 1D and 2D spectra. By comparing these simulations to the experiment an explicit picture of all phases could be drawn on a molecular level. Our results therefore reveal the high potential of the presented approach for detailed studies of the mesoscopic environment even in the challenging case of amorphous materials.

Thermal distinction of HEU-type mineral phases contained in Greek zeolite-rich volcaniclastic tuffs

Ten zeolite-bearing rocks rich in HEU-type zeolites from Evros District and Samos island were studied. The samples were heated at 450°C for 8 h and the reductions in the intensity and the peak area of the (020) reflection was measured. Electron microscope and thermal analyses were used, as well. The results of the above methods gave an explicit picture for the HEU-type phases that exist in each sample and they led to their regrouping in three different groups: group I where the main phase of deter- mined HEU-type zeolite was clinoptilolite, group II, presenting mediate characteristics between groups I and III, where the contained main phase of HEU-type zeolite is intermediate heulandite, and group III, where heulandite is the main HEU-type zeolite phase. The combined study of the XRD results in initial and thermally treated samples, compared with the SEM-EDS results and the thermal study of the mass recovery during the cooling stage of the thermal analysis constitute a useful tool for the classification of the HEU-type zeolites in their different phases.

Collaborating to Conserve Large Mammals in Southeast Asia

Depressed mammal densities characterize the interior of many Southeast Asian protected areas, and are the result of commercial and subsistence hunting. Local people are part of this problem but can participate in solutions through improved partnerships that incorporate local knowledge into problem diagnosis. The process of involving local people helps build a constituency that is more aware of its role (positive and negative) in a protected area and generates site-specific conservation assessments for management planning. We illustrate the practical details of initiating such a partnership through our work in a Thai wildlife sanctuary. Many protected areas in Southeast Asia present similar opportunities. In local workshops, village woodsmen were led through ranking exercises to develop a spatially explicit picture of 20-year trends in the abundance of 31 mammal species and to compare species-specific causes for declines. Within five taxonomic groups, leaf monkeys (primates), porcupines (rodents), tigers (large carnivores), civets (small carnivores), and elephants (ungulates) had declined most severely (37-74%). Commercial hunting contributed heavily to extensive population declines for most species, and subsistence hunting was locally significant for some small carnivores, leaf monkeys, and deer. Workshops thus clarified which species were at highest risk of local extinction, where the most threatened populations were, and causes for these patterns. Most important, they advanced a shared problem definition, thereby unlocking opportunities for collaboration. As a result, local people and sanctuary managers have increased communication, initiated joint monitoring and patrolling, and established wildlife recovery zones. Using local knowledge has limitations, but the process of engaging local people promotes collaborative action that large mammals in Southeast Asia need.

CLASSIFICATION, AUTOMORPHISM GROUPS AND CATEGORICAL STRUCTURE OF THE TWO-DIMENSIONAL REAL DIVISION ALGEBRAS

The category of all 2-dimensional real division algebras is shown to split into four full subcategories, each of which is given by the natural action of a Coxeter group of type 𝔸1 or 𝔸2 on the set of all pairs of ellipses in ℝ2, which are centred in the origin and have reciprocal axis lengths. Cross-sections for the orbit sets of these group actions are being determined. They yield a classification of all 2-dimensional real division algebras. Moreover all morphisms between the objects in this classifying list are described, and thus an explicit and geometric picture of the category of all 2-dimensional real division algebras is obtained. This elementary and self-contained exposition extends Darpö and Dieterich's recent description [14] of the category of all 2-dimensional commutative real division algebras, which in turn is based on Benkart, Britten and Osborn's investigation [4] of the isotopes of ℂ. It also supplements earlier contributions of Althoen and Kugler [2], Burdujan [9], Gottschling [25], Petersson [33], Hübner and Petersson [29], and Doković and Zhao [23] to the problem of classifying all 2-dimensional real division algebras.

A Simplified Formulation of Linear and Nonlinear Spectroscopy of Ordered Molecular Systems

A simplified formulation for treating the linear and nonlinear spectroscopy of ordered molecular systems is presented, in order to help experimentalists to have an explicit physical picture and quantitative tool on using linear and nonlinear spectroscopy to study molecules in ordered molecular systems. this formulation is expended from our recent quantitative orientational and polarization treatment on second-order nonlinear spectroscopic techniques in interface studies, namely, the second harmonic generation (shg) and sum frequency generation-vibrational polarization spectroscopy (sfg-vps). the key to this formulation is to simplify the effective linear or nonlinear molecular susceptibility and construct the general orientational functional with a clear approach to calculate the orientational and intensity parameters from the experimental parameters, which deter-mines the orientational and polarization behavior of the general orientational functional in a particular experimental configuration. also discussed are the advantages of coherent spectroscopic techniques over incoherent ones for the accurate measurement of orientation and ordering of ordered molecular system.

NEOTECTONIC DEFORMATION OF NORTH PARNIS

The morphotectonic analysis in the eastern part of Biotic Asopos river catchment, results to an explicit picture of a new drainage network with individual abnormalities that are focused mainly in phenomena of "piracy" and abrupt knick points. Topographic sections along the main streams and correlation between rose diagrams of faults and stream network reveal an influence of the drainage network (E-W and N-S direction) from the active tectonic structure of E-W to WNW-ESE direction, which is accompanied by phenomena of intense depth erosion transversely to the main active tectonic faults. The important dextral slip component of the main active fault zones (Sfendali-Avlona and Milesi Oropos) has influenced the alpine tectonic structure, determining the current NE-SW spread of Upper Cretaceous limestones and changing the direction of flysch axes from NNE-SSW in mountainous Parnis area to ENE-WSW in the flat area of Malakasa. The distribution of planation surfaces in combination with the presence of en echelon oblique slip faults of WNW-ESE direction, reveal a complex kinematic evolution, with main characteristics the progressive rotation of tectonic blocks to the WNW for the mountainous south area and to the SSW for the NE area of low relief.

Competitive edge: A strategic management model

To assess a firm's strategic position, its managers must collect and interpret data regarding the firm itself, its competitors, its stakeholders, and the industry. Having implement a strategy based on that information, the managers further must measure that strategy's effect. The “competitive-edge model” presented in this article provides a series of questions to guide the strategic decision-making and data-collection process so that managers gain an explicit picture of what is happening with their firm, their competitors, and the industry. Equipped with the requisite information, managers can develop marker and non-marker strategies by matching internal resources with external opportunities. Market-based strategies seek to provide an advantage for the firm over its competitors by appealing to specific customer attributes. Non-market strategies take into account aspects of the environment not directly related to customers, including the actions of government, shareholders, and special interest groups.

Topological analysis of electrostatic potential in SrTiO 3

The topological analysis of the electrostatic potential distribution of SrTiO 3 calculated from the experimental and theoretical electron densities was performed. It was found that the electrostatic potential and the electron density fields in SrTiO 3 had different sets of the critical points. The topological features of the electrostatic potential lead to the explicit picture of Coulomb force field, showing that the Coulomb interactions are transmitted through a crystal in the form of the ‘atom–atom interactions’, a network of which is a specific property of each compound.

The Estonian Self-Concept Clarity Scale: psychometric properties and personality correlates

Abstract The goals of this study were twofold: our first aim concerned generalizability of the Self-Concept Clarity Scale (SCCS; Campbell, J. D., Trapnell, P. D., Heine, S. J., Katz, I. M., Lavallee, L. F., & Lehman, D. R. (1996). Self-concept clarity: Measurement, personality correlates, and cultural boundaries. Journal of Personality and Social Psychology, 70, 141–156) across different languages and cultures. Second, we aimed to give a more explicit picture of the relations between self-concept clarity and other personality constructs (i.e., general self-esteem, Five-Factor Model of personality and self-consciousness) than reported in previous studies (cf. Campbell et al., 1996 ). To accomplish these two goals, we set off with an adaptation of the SCCS to the Estonian language, which, in general, turned out to be successful. On the one hand, our research provided further evidence of the generalizability of the self-concept clarity construct across different languages and cultures, at least within the boundaries of the Western cultural space. On the other hand, the results reported in this study suggested that although a considerable proportion of the variability of self-concept clarity can be predicted from personality measures, the clarity does not seem to be invariably related simply to a single specific personality trait or to their combination: a pattern of associations between the Estonian version of the SCCS and other personality variables emerging in the correlation and regression analyses was fairly unstable and largely influenced by the intercorrelations of the other measures.

Theoretical investigation of water formation on Rh and Pt Surfaces

Catalytic water formation from adsorbed H and O adatoms is a fundamental reaction step in a variety of technologically important reactions involving organic molecules. In particular, the water-formation rate determines the selectivity of the catalytic partial oxidation of methane to syngas. In this report we present a theoretical investigation of the potential-energy diagram for water formation from adsorbed O and H species on Rh(111) and Pt(111) surfaces. The study is based on accurate first-principles calculations applying density-functional theory. Our results are compared to the potential-energy diagram for this reaction inferred from experimental data by Hickman and Schmidt [AIChE. J. 39, 1164 (1993)]. The calculations essentially reproduce the scheme of Hickman and Schmidt for water formation on Rh(111) with the important difference that the OH molecule is significantly more stable than assumed by Hickman and Schmidt. On Pt(111) surfaces, however, the calculations predict a barrier to OH formation very similar to that found on Rh(111). In particular, the calculated barrier to OH formation of about 20 kcal/mol seems to contradict the small 2.5 kcal/mol barrier assumed in the Hickman–Schmidt scheme and the observed large rate of water formation on Pt. A possible explanation for the apparent discrepancy between the large calculated barrier for OH formation on Pt and the experimentally observed rapid formation of water even at low temperatures is that the active sites for water formation on Pt are at “defect” sites and not on the ideally flat terraces. A similar conclusion has been reached by Verheij and co-workers [Surf. Sci. 371, 100 (1997); Chem. Phys. Lett. 174, 449 (1990); Surf. Sci. 272, 276 (1991)], who did detailed experimental work on water formation on Pt surfaces. Analyzing our results, we develop an explicit picture of the interaction processes governing the formation of OH groups. This picture rationalizes the calculated weak dependence of OH formation on substrate material. An important conclusion from this work is that “good” catalysts for the partial oxidation of hydrocarbons should resist defect formation at their surfaces.

Domain walls of D=5 supergravity and fixed points of N=1 super-Yang–Mills

Employing the AdS/CFT correspondence, we give an explicit supergravity picture for the renormalization group flow of couplings 4-d super-Yang–Mills with four supercharges. The solution represents a domain wall of 5-d, N=2 supergravity, that interpolates between two (different) AdS 5 vacua and is obtained by gauging a U(1) subgroup of the SU(2) R-symmetry. On the supergravity side the domain wall couples only to scalar fields from vector multiplets, but not to scalars from hypermultiplets. We discuss the c-theorem, the β-functions and consider two examples: one is the sugra solution related to Z k orbifolds (corresponding to N=2 SYM) and the other is an orientifold construction for an elliptically fibered CY with F 1 basis (corresponding to N=1 SYM).

Application of machine learning techniques to the analysis of soil ecological data bases: relationships between habitat features and Collembolan community characteristics

We applied novel modelling techniques (neural networks, tree-based models) to relate total abundance and species number of Collembola as well as abundances of dominant species to habitat characteristics and compared their predictive power with simple statistical models (multiple regression, linear regression, land-use-specific means). The data used consisted of soil biological, chemical and physical measurements in soil cores taken at 396 points distributed over a 50×50 m sampling grid in an agricultural landscape in southern Germany. Neural networks appeared to be most efficient in reflecting the nonlinearities of the habitat–Collembola relationships. The underlying functional relations, however, are hidden within the network connections and cannot be analyzed easily. Model trees — next in predictive power to neural networks — are much more transparent and give an explicit picture of the functional relationships. Both modelling approaches perform significantly better than traditional statistical models and decrease the mean absolute error between prediction and observation by about 16–38%. Total carbon content and measurements highly correlated with it (e.g. total nitrogen content, microbial biomass and respiration) were the most important factors influencing the Collembolan community. This is in broad agreement with existing knowledge. Apparent limitations to predicting Collembolan abundance and species number by habitat quality alone are discussed.

Strong coupling model for string breaking on the lattice.

A model for SU( n) string breaking on the lattice is formulated using strong coupling ideas. It gives an explicit picture of string breaking, in the presence of dynamical quarks, as a mixing process between a string state and a two-meson state. An analysis of the Wilson loop shows that the evolution of the mixing angle as a function of separation may obscure the expected crossover effect. If a sufficiently extensive mixing region exists then an appropriate combination of transition amplitudes may help to reveal the effect. The sensitivity of the mixing region to the values of the meson energy and the dynamical quark mass is explored.

Strong coupling model for string breaking on the lattice

A model for SU( n) string breaking on the lattice is formulated using strong coupling ideas. Although necessarily rather crude, the model gives an explicit picture of string breaking in the presence of dynamical quarks as a mixing phenomenon that involves the string state and a two-meson state. A careful analysis, within the model, of the Wilson loop shows that the evolution of the mixing angle as a function of separation may obscure the expected crossover effect. If a sufficiently extensive mixing region exists then an appropriate combination of transition amplitudes can help in revealing the effect. The sensitivity of the mixing region to the values of the meson energy and the dynamical quark mass is explored and an assessment made of the detectibility of string breaking in a practical lattice simulation.

Solar cycle variation in the heliosphere

Variations in interplanetary plasma and magnetic field parameters over the course of a solar cycle affect a broad range of physical phenomena, such as planetary magnetospheres, cosmic ray modulation, and the interaction of the solar wind with the local interstellar medium. For more than 3 decades a succession of spacecraft have provided in situ measurements of these parameters. These measurements span a range of heliocentric distances from 0.3 to 61 AU and provide an explicit picture of the three‐dimensional structure of the inner and outer heliosphere in the vicinity of the ecliptic plane. In addition, ground‐based interplanetary scintillation measurements and observations from the Ulysses spacecraft have extended our knowledge to smaller heliocentric distances and higher heliographic latitudes. The structure of the heliosphere varies dramatically over the course of a solar cycle. Much of this variation can be related to the changes in the structure and inclination of the coronal magnetic field. The coronal neutral line, which separates the Sun's magnetic hemispheres, is associated with a belt of low‐speed and high‐density solar wind. Its inclination varies over the course of a solar cycle, from a low value near solar minimum to a high value near solar maximum. When the inclination of the coronal neutral line is low, its signature is evident in observations near the solar equator. When the inclination of the coronal neutral line is high, the heliosphere at moderate heliographic latitudes is swept by a succession of high‐ and low‐speed streams and is shaped by their interactions.

The role of political competition and bargaining in Russian foreign policy: The case of Russian policy toward Moldova

Recent discussions about Russian foreign policy have generally concentrated on its shift to the right. Along with numerous Western observers, who interpret Russian international behavior as a single-player activity, the Russian foreign minister Andrei Kozyrev has himself attempted to portray his policy in terms of realist theory. Answering numerous accusations on “embracing some policies that [he] once spoke out against” (Rafael et al., 1994), Kozyrev paints an explicit picture of a strategic response by his ministry to objective world conditions. However, analysis shows that world conditions played a very small role in shaping Russian foreign policy.