bluuebunny/crossref_metadata_2025 huggingface dataset:
Genomewide Screen for Negative Regulators of Sirtuin Activity inSaccharomyces cerevisiaeReveals 40 Loci and Links to Metabolism
Authors: Raisner Ryan M , Madhani Hiten D
Published: August 2008

Sirtuins are conserved proteins implicated in myriad key processes including gene control, aging, cell survival, metabolism, and DNA repair. In Saccharomyces cerevisiae, the sirtuin Silent information regulator 2 (Sir2) promotes silent chromatin formation, suppresses recombination between repeats, and inhibits senescence. We performed a genomewide screen for factors that negatively regulate Sir activity at a reporter gene placed immediately outside a silenced region. After linkage analysis, assessment of Sir dependency, and knockout tag verification, 40 loci were identified, including 20 that have not been previously described to regulate Sir. In addition to chromatin-associated factors known to prevent ectopic silencing (Bdf1, SAS-I complex, Rpd3L complex, Ku), we identified the Rtt109 DNA repair-associated histone H3 lysine 56 acetyltransferase as an anti-silencing factor. Our findings indicate that Rtt109 functions independently of its proposed effectors, the Rtt101 cullin, Mms1, and Mms22, and demonstrate unexpected interplay between H3K56 and H4K16 acetylation. The screen also identified subunits of mediator (Soh1, Srb2, and Srb5) and mRNA metabolism factors (Kem1, Ssd1), thus raising the possibility that weak silencing affects some aspect of mRNA structure. Finally, several factors connected to metabolism were identified. These include the PAS-domain metabolic sensor kinase Psk2, the mitochondrial homocysteine detoxification enzyme Lap3, and the Fe-S cluster protein maturase Isa2. We speculate that PAS kinase may integrate metabolic signals to control sirtuin activity.
Molecular Cytogenetic Evidence of Rearrangements on the Y Chromosome of the Threespine Stickleback Fish
Authors: Ross Joseph A , Peichel Catherine L
Published: August 2008

To identify the processes shaping vertebrate sex chromosomes during the early stages of their evolution, it is necessary to study systems in which genetic sex determination was recently acquired. Previous cytogenetic studies suggested that threespine stickleback fish (Gasterosteus aculeatus) do not have a heteromorphic sex chromosome pair, although recent genetic studies found evidence of an XY genetic sex-determination system. Using fluorescence in situ hybridization (FISH), we report that the threespine stickleback Y chromosome is heteromorphic and has suffered both inversions and deletion. Using the FISH data, we reconstruct the rearrangements that have led to the current physical state of the threespine stickleback Y chromosome. These data demonstrate that the threespine Y is more degenerate than previously thought, suggesting that the process of sex chromosome evolution can occur rapidly following acquisition of a sex-determining region.
The Arp2/3 Activators WAVE and WASP Have Distinct Genetic Interactions With Rac GTPases inCaenorhabditis elegansAxon Guidance
Authors: Shakir M Afaq , Jiang Ke , Struckhoff Eric C , Demarco Rafael S , Patel Falshruti B , Soto Martha C , Lundquist Erik A
Published: August 2008

In the developing nervous system, axons are guided to their targets by the growth cone. Lamellipodial and filopodial protrusions from the growth cone underlie motility and guidance. Many molecules that control lamellipodia and filopodia formation, actin organization, and axon guidance have been identified, but it remains unclear how these molecules act together to control these events. Experiments are described here that indicate that, in Caenorhabditis elegans, two WH2-domain-containing activators of the Arp2/3 complex, WVE-1/WAVE and WSP-1/WASP, act redundantly in axon guidance and that GEX-2/Sra-1 and GEX-3/Kette, molecules that control WAVE activity, might act in both pathways. WAVE activity is controlled by Rac GTPases, and data are presented here that suggest WVE-1/WAVE and CED-10/Rac act in parallel to a pathway containing WSP-1/WASP and MIG-2/RhoG. Furthermore, results here show that the CED-10/WVE-1 and MIG-2/WSP-1 pathways act in parallel to two other molecules known to control lamellipodia and filopodia and actin organization, UNC-115/abLIM and UNC-34/Enabled. These results indicate that at least three actin-modulating pathways act in parallel to control actin dynamics and lamellipodia and filopodia formation during axon guidance (WASP–WAVE, UNC-115/abLIM, and UNC-34/Enabled).
Loss of Least-Loaded Class in Asexual Populations Due to Drift and Epistasis
Authors: Jain Kavita
Published: August 2008

We consider the dynamics of a nonrecombining haploid population of finite size that accumulates deleterious mutations irreversibly. This ratchet-like process occurs at a finite speed in the absence of epistasis, but it has been suggested that synergistic epistasis can halt the ratchet. Using a diffusion theory, we find explicit analytical expressions for the typical time between successive clicks of the ratchet for both nonepistatic and epistatic fitness functions. Our calculations show that the interclick time is of a scaling form that in the absence of epistasis gives a speed that is determined by size of the least-loaded class and the selection coefficient. With synergistic interactions, the ratchet speed is found to approach zero rapidly for arbitrary epistasis. Our analytical results are in good agreement with the numerical simulations.
Regulation of Apical Dominance inAspergillus nidulansHyphae by Reactive Oxygen Species
Authors: Semighini Camile P , Harris Steven D
Published: August 2008

In fungal hyphae, apical dominance refers to the suppression of secondary polarity axes in the general vicinity of a growing hyphal tip. The mechanisms underlying apical dominance remain largely undefined, although calcium signaling may play a role. Here, we describe the localized accumulation of reactive oxygen species (ROS) in the apical region of Aspergillus nidulans hyphae. Our analysis of atmA (ATM) and prpA (PARP) mutants reveals a correlation between localized production of ROS and enforcement of apical dominance. We also provide evidence that NADPH oxidase (Nox) or related flavoproteins are responsible for the generation of ROS at hyphal tips and characterize the roles of the potential Nox regulators NoxR, Rac1, and Cdc42 in this process. Notably, our genetic analyses suggest that Rac1 activates Nox, whereas NoxR and Cdc42 may function together in a parallel pathway that regulates Nox localization. Moreover, the latter pathway may also include Bem1, which we propose represents a p40phox analog in fungi. Collectively, our results support a model whereby localized Nox activity generates a pool of ROS that defines a dominant polarity axis at hyphal tips.
Drosophila LIM-Only Is a Positive Regulator of Transcription During Thoracic Bristle Development
Authors: Zenvirt Shamir , Nevo-Caspi Yael , Rencus-Lazar Sigal , Segal Daniel
Published: August 2008

The Drosophila LIM-only (LMO) protein DLMO functions as a negative regulator of transcription during development of the fly wing. Here we report a novel role of DLMO as a positive regulator of transcription during the development of thoracic sensory bristles. We isolated new dlmo mutants, which lack some thoracic dorsocentral (DC) bristles. This phenotype is typical of malfunction of a thoracic multiprotein transcription complex, composed of CHIP, PANNIER (PNR), ACHAETE (AC), and DAUGHTERLESS (DA). Genetic interactions reveal that dlmo synergizes with pnr and ac to promote the development of thoracic DC bristles. Moreover, loss-of-function of dlmo reduces the expression of a reporter target gene of this complex in vivo. Using the GAL4-UAS system we also show that dlmo is spatially expressed where this complex is known to be active. Glutathione-S-transferase (GST)-pulldown assays showed that DLMO can physically bind CHIP and PNR through either of the two LIM domains of DLMO, suggesting that DLMO might function as part of this transcription complex in vivo. We propose that DLMO exerts its positive effect on DC bristle development by serving as a bridging molecule between components of the thoracic transcription complex.
The Y Chromosome That Lost the Male-Determining Function Behaves as an X Chromosome in the Medaka Fish,Oryzias latipes
Authors: Otake Hiroyuki , Hayashi Yusuke , Hamaguchi Satoshi , Sakaizumi Mitsuru
Published: August 2008

The medaka, Oryzias latipes, has an XX/XY sex-determination system, and a Y-linked DM-domain gene, DMY, is the sex-determining gene in this species. Since DMY appears to have arisen from a duplicated copy of the autosomal DMRT1 gene ∼10 million years ago, the medaka Y chromosome is considered to be one of the youngest male-determining chromosomes in vertebrates. In the screening process of sex-reversal mutants from wild populations, we found a population that contained a number of XY females. PCR, direct sequencing, and RT–PCR analyses revealed two different null DMY mutations in this population. One mutation caused loss of expression during the sex-determining period, while the other comprised a large deletion in putative functional domains. YY females with the mutant-type DMY genes on their Y chromosomes were fully fertile, indicating that the X and Y chromosomes were functionally the same except for the male-determining function. In addition, we investigated the frequencies of the sex chromosome types in this population over four successive generations. The Y chromosomes bearing the mutant-type DMY genes were detected every year with no significant differences in their frequencies. These results demonstrate that aberrant Y chromosomes behaving as X chromosomes have been maintained in this population.
Gene Dosage and Gene Duplicability
Authors: Qian Wenfeng , Zhang Jianzhi
Published: August 2008

The evolutionary process leading to the fixation of newly duplicated genes is not well understood. It was recently proposed that the fixation of duplicate genes is frequently driven by positive selection for increased gene dosage (i.e., the gene dosage hypothesis), because haploinsufficient genes were reported to have more paralogs than haplosufficient genes in the human genome. However, the previous analysis incorrectly assumed that the presence of dominant abnormal alleles of a human gene means that the gene is haploinsufficient, ignoring the fact that many dominant abnormal alleles arise from gain-of-function mutations. Here we show in both humans and yeast that haploinsufficient genes generally do not duplicate more frequently than haplosufficient genes. Yeast haploinsufficient genes do exhibit enhanced retention after whole-genome duplication compared to haplosufficient genes if they encode members of stable protein complexes, but the same phenomenon is absent if the genes do not encode protein complex members, suggesting that the dosage balance effect rather than the dosage effect is the underlying cause of the phenomenon. On the basis of these and other results, we conclude that selection for higher gene dosage does not play a major role in driving the fixation of duplication genes.
Synthetic Genetic Array Analysis in Saccharomyces cerevisiae Provides Evidence for an Interaction Between RAT8/DBP5 and Genes Encoding P-Body Components
Authors: Scarcelli John J , Viggiano Susan , Hodge Christine A , Heath Catherine V , Amberg David C , Cole Charles N
Published: August 2008

Coordination of the multiple steps of mRNA biogenesis helps to ensure proper regulation of gene expression. The Saccharomyces cerevisiae DEAD-box protein Rat8p/Dbp5p is an essential mRNA export factor that functions at the nuclear pore complex (NPC) where it is thought to remodel mRNA/protein complexes during mRNA export. Rat8p also functions in translation termination and has been implicated in functioning during early transcription. We conducted a synthetic genetic array analysis (SGA) using a strain harboring the temperature-sensitive rat8-2 allele. Although RAT8 had been shown to interact genetically with >15 other genes, we identified >40 additional genes whose disruption in a rat8-2 background causes synthetic lethality or dramatically reduced growth. Included were five that encode components of P-bodies, sites of cytoplasmic mRNA turnover and storage. Wild-type Rat8p localizes to NPCs and diffusely throughout the cell but rat8-2p localized to cytoplasmic granules at nonpermissive temperature that are distinct from P-bodies. In some genetic backgrounds, these granules also contain poly(A)-binding protein, Pab1p, and additional mRNA export factors. Although these foci are distinct from P-bodies, the two merge under heat-stress conditions. We suggest that these granules reflect defective mRNP remodeling during mRNA export and during cytoplasmic mRNA metabolism.
Maternal Phosphatase Inhibitor-2 Is Required for Proper Chromosome Segregation and Mitotic Synchrony During Drosophila Embryogenesis
Authors: Wang Weiping , Cronmiller Claire , Brautigan David L
Published: August 2008

Protein phosphatase-1 (PP1) is a major Ser/Thr phosphatase conserved among all eukaryotes, present as the essential GLC7 gene in yeast. Inhibitor-2 (I-2) is an ancient PP1 regulator, named GLC8 in yeast, but its in vivo function is unknown. Unlike mammals with multiple I-2 genes, in Drosophila there is a single I-2 gene, and here we describe its maternally derived expression and required function during embryogenesis. During oogenesis, germline expression of I-2 results in the accumulation of RNA and abundant protein in unfertilized eggs; in embryos, the endogenous I-2 protein concentrates around condensed chromosomes during mitosis and also surrounds interphase nuclei. An I-2 loss-of-function genotype is associated with a maternal-effect phenotype that results in drastically reduced progeny viability, as measured by reduced embryonic hatch rates and larval lethality. Embryos derived from I-2 mutant mothers show faulty chromosome segregation and loss of mitotic synchrony in cleavage-stage embryos, patchy loss of nuclei in syncytial blastoderms, and cuticular pattern defects in late-stage embryos. Transgenic expression of wild-type I-2 in mutant mothers gives dose-dependent rescue of the maternal effect on embryo hatch rate. We propose that I-2 is required for proper chromosome segregation during Drosophila embryogenesis through the coordinated regulation of PP1 and Aurora B.
Discrete thermodynamics of chemical equilibria and classical limit in thermodynamic simulation
Authors: Zilbergleyt Boris
Published: August 2008

This article sets forth comprehensive basic concepts of the discrete thermodynamics of chemical equilibrium as balance between internal and external thermodynamic forces. Conditions of chemical equilibrium in the open chemical system are obtained in the form of a logistic map, containing only one new parameter that defines the chemical system's resistance to external impact and its deviation from thermodynamic equilibrium. Solutions to the basic map are bifurcation diagrams that have quite traditional shape but the diagram areas feature specific meanings for chemical systems and constitute the system's domain of states. The article is focused on two such areas: the area of “true” thermodynamic equilibrium and the area of open chemical equilibrium. The border between them represents the classical limit, a transition point between the classical and newly formulated equilibrium conditions. This limit also separates regions of the system ideality, typical for isolated classical systems, and non‐ideality due to the limitations imposed on the open system from outside. Numerical examples illustrating the difference between results of classical and discrete thermodynamic simulation methods are presented. The article offers an analytical formula to find the classical limit, compares analytical results with these obtained by simulation, and shows the classical limit dependence upon the chemical reaction stoichiometry and robustness.
A mathematical model of powder components oxidation during thermal spray process
Authors: Kossenko Alexey , Lugovskoy Alex , Zinigrad Michael
Published: August 2008

A model developed on the basis of kinetic principles of mass transfer allows performing computer simulation of the oxidation of powder materials during the thermal spray process. Such simulation enables one to determine the oxidation degree of the powder. The calculation is based on determining quasi‐stationary oxygen diffusion flow on a flying particle. Calculations performed for various spray powders and various flammable gases demonstrate a significant decrease of the oxidation degree with the growth of the particle diameter and density of a spray powder. The calculation results were confirmed by experiments.
Computer simulation of internal oxidation and its application to heating‐up experiments for determination of oxygen diffusivities metals—palladium as an example
Authors: Gegner Jürgen
Published: August 2008

Internal oxidation of metal alloys is of great applicational significance as an effective dispersion‐hardening technique, e.g., for Ag, Cu, or Ni alloys, as well as having undesirable side effects to many heat treatment technologies of steels. Wagner's kinetics theory comprises three practically important restrictions: (1) homogeneous initial concentration distribution of the alloying metal M, (2) isobaric, and (3) isothermal processes. The presented new computer model, which is based on an iterative solution of Fick's 2nd law for the inward diffusion of oxygen with internal reaction, overcomes these limitations. Illustrative processes are simulated. Considering the restrictions of Wagner's theory, incomplete isothermal isobaric internal oxidation of dilute homogeneous binary alloys represents an established experimental method for determining the diffusion coefficient of oxygen in the matrix metal: the sought Arrhenius equation is derived by carrying out annealing series at several constant temperatures. The modified simulation‐aided measuring technique of incomplete nonisothermal isobaric internal oxidation, introduced in the present work, reduces the necessary experimental time considerably. Also, as a test of the new computer model, the mathematical evaluation of the data obtained by microscopic analysis of polished cross‐sections is performed by means of this tool. To demonstrate the applicability of the novel experimental technique of temperature‐programmed internal oxidation, the diffusivity of oxygen in palladium is exemplarily measured this way in a Pd‐9.19 at.% Fe alloy and, expressed in cm2/s, found to be DO = 5.32·10−1 · exp(‐18728.27/T). Here, the temperature T ranges from 1073 to 1473 K. This result is compared with literature sources and agrees well with previously published reliable data.
The features of ribbon‐like polymers in thin films
Authors: Arinstein Arkadii
Published: August 2008

The features of ribbon‐like polymers in thin film, which are anisotro‐pic in cross section, are considered using a lattice model of oriented self‐correlated walks (OSCW). The local properties of the ribbon‐like chain are assumed to be strongly anisotropic: bending is possible only in the plane of the ribbon (the orientation of this plane can change due to molecule twist). On the basis of this model, the phase transition of the ribbon‐like polymers possessing certain bending and twist rigidity into the rotator phase is described in the mean‐field approximation. The dimension reducing of the polymer system results in an increase of phase transition temperature. Moreover, spontaneous polarization arises in a non‐orientated system and that is the most interesting phenomenon caused by confinement of polymer macromolecules.
Thermodynamic modeling of iron oxide reduction by hydrogen from the B2O3‐CaO‐FeO melt in bubbled layer
Authors: Dmitriev Andrey N. , Vusikhis Alexander S. , Sitnikov Vladimir A. , Leontiev Leopold I. , Kudinov Dmitriy Z.
Published: August 2008

Study of the gas interaction process with the multicomponent oxide melt during barbotage with the purpose of testing the selective extraction possibility, is of interest from scientific and practical points of view. The solution of this problem within the scope of the complex decisions of the problem of rational resource development is of especial interest for the Urals, and for the Sverdlovsk region in particular.

The processes mentioned above are heterogeneous ones and go through a number of sequential stages. Each stage can be limiting and can influence the overall process. However, despite the mechanism of the reaction its rate depends on the chemical composition of the gas contained in the bubbles that move in the melt. If the bubbles are in the melt for a long enough time, equilibrium is reached inside it and the process of gas interaction with melt is stopped. A model giving a qualitative description of the process of kinetics on the basis of thermodynamic equilibrium calculations has been developed by the authors. This model has been used for describing interaction between hydrogen and B2O3‐CaO‐FeO melt at various temperatures. This model has allowed us to analyze the process course and to consider temperature influence on such characteristics as melt component concentrations and their changes during process, the final gas composition, and other characteristics without any experiments.
Capillarity‐induced patterning of thin polymer films and related regular dewetting structures
Authors: Suh Kahp Y.
Published: August 2008

When a thin polymer film is spin‐coated on a solid substrate and heated above its glass transition temperature (Tg) while in conformal contact with a patterned polydimethylsiloxane (PDMS) mold, capillarity forces the polymer melt to fill up the void space of the mold, thereby forming a negative replica of the polymer after mold removal. In this study, particular emphasis is given to the nodal dewetting phenomenon in a thin, laterally confined polymer film that sticks to a substrate. When heated above the glass transition temperature, the film dewets from the substrate through the generation of nodal waves, with the PDMS wall acting as a node. Various superposed waves were observed depending on the intrinsic period of dewetting and the confining width of the cavity.
The influence of Ag and Si additions on the electrochemical behavior in extruded Mg‐Zn alloys
Authors: Ben‐Hamu Guy , Eliezer Amir
Published: August 2008

Development of new wrought magnesium alloys for the automotive industry has increased in recent years, due to their high potential as structural materials for low density and high strength/weight ratio demands. However, the poor mechanical properties and low corrosion resistance of the magnesium alloys have led to a search for new kinds of magnesium alloys, for better strength, ductility, and high corrosion resistance. The main objective of this research is to investigate the corrosion behavior of new magnesium alloys: Mg‐Zn‐Ag (ZQ) and Mg‐Zn‐Si (ZS). The ZQ6X and ZS6X alloys were prepared using the hot extrusion method. AC and DC polarization tests were carried out on the extruded rods, which contain different amounts of silver or silicon.

The microstructure was examined using optical and electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that the silver addition decreased corrosion resistance. The addition of silicon also affected corrosion behavior. These results can be explained by the effects of alloying elements on the microstructure of Mg‐Zn alloys, such as grain size and precipitates caused by the change in precipitation, and by recrystallization behavior.
An attempt to improve the evaluation of mechanical material properties from the Axisymmetric Tensile Test
Authors: Gromada Magdalena , Mishuris Gennady , Öchsner Andreas
Published: August 2008

This paper deals with new analytical modeling of the classical tensile test with an axisymmetric sample and determining the yield stress of elasto‐plastic materials under the neck formation. Known for many years, classical Bridgman and Siebel‐Davidenkov‐Spiridonova's formulas provide certain errors, especially visible in the case of weakly hardening or ideal‐plastic materials. Accurate numerical simulations of the process allowed verification of the analytical results. Based on the numerical simulations, some modifications of the analytical models and their derivation have been proposed which enabled the elimination of the two most questionable classic assumptions. Comparison of new results with well‐known formulas shows that some progress is reached for small plastic deformations; however, for greater strain level further improvement is still advisable.
Excess oxygen at metal‐oxide interfaces—a review of the segregation process based on the current state of knowledge
Authors: Gegner Jürgen
Published: August 2008

Accumulation or depletion of excess oxygen atoms at metal‐oxide interfaces, which can handily be controlled by adjusting the oxygen activity, leads to modifications of the atomic structure and chemical composition of the heterophase boundaries. The established atomistic model, which also explains changes of the macroscopic material behavior, interprets the process as interfacial oxygen segregation. Structurally necessary vacancies at terminating close‐packed oxide lattice planes serve as oxygen traps. These point defects are reversibly refillable with excess atoms. Experimental findings on oxygen‐controlled alterations of metal‐oxide interfaces obtained by electron energy loss spectroscopy, quantitative gas volume measurement,18O‐16O isotope exchange experiments, and the electrochemical hydrogen probe are compiled and valued with regard to the basic modeling assumptions. Thermodynamics data derived from volumetrically determined oxygen isotherms show that the chemisorption segregation process is energetically comparable with the formation of a two‐dimensional oxide layer of the metal component at the phase boundary. Subsequent hydrogen accumulation occurs by the development of hydroxide bonds. For palladium‐based nano‐oxide dispersion microstructures under practical process conditions, diffusion of bulk‐dissolved oxygen to the precipitates represents the rate‐controlling substep of interfacial segregation, which can thus be suppressed by shock quenching. The spatial arrangement of the embedded particles is characterized by quantitative transmission electron image analysis. For these palladium‐oxide materials, an adapted model of the kinetics of interfacial oxygen segregation is established. The simulations are compared with results of electrochemical measurements and cooling curves determined contactlessly by infrared pyrometry.
Creation of Shock‐Abrasion Resistance Build‐up Metal Using a Physicochemical Model of High‐Temperature Processes
Authors: Borodianskiy Konstantin , Mazurovsky Vladimir , Zinigrad Michael , Gedanken Aharon
Published: August 2008

Build‐up metal for shock‐abrasion resistance was the focus of this work, where the mathematical model of physicochemical high‐temperature processes developed by the authors in their previous works was used. A computer program based on the model permitted forecasting of the required chemical composition and structure of the build‐up metal.

Flux‐cored wires were fabricated from a cold‐rolled ribbon (1008 steel) and filled with a powder mixture. Low carbon steel (A 516) was used as the base metal.

The specimens were prepared by 3‐layered build‐up. The prepared specimens were tested using light microscopy, scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDS), hardness measurements, and shock‐abrasion resistance measurements.

The results of the above‐mentioned tests confirmed the correct calculation of the model and the good shock‐abrasion resistance of the suggested build‐up metal.
Pressure Dependence of Exchange Parameters and Neel Temperature in La2CuO4
Authors: Fishman Anatolii Ya. , Mitrofanov Valentin Ya.
Published: August 2008

Microscopic mechanisms responsible for the observed pressure dependencies of the Neel temperature TN and parameters of isotropic and anisotropic exchange interaction in the orthorhombic antiferromagnet La2CuO4 are investigated. Within the framework of the Anderson microscopic theory of superexchange interaction, the expressions establishing interrelation between parameters of isotropic and anisotropic (both symmetric and antisymmetric) exchange interactions and by the structural parameters describing the Cu‐O‐Cu bonding angle and the Cu‐O bond length in La2CuO4 are obtained. Experimentally determined pressure dependencies of structural parameters by H. Takahashi et al., allow one to present pressure dependencies of exchange parameters and TN in an apparent form.
Simulation of Ni3Al‐based Alloy and Investment Casting Process of its Thin Wall Castings
Authors: Zhang Xi‐e , Li Shi‐qiong , Cao He‐li Luo, Xu , Feng Di , Li Shang‐ping
Published: August 2008

It is very difficult to produce thin wall complex castings of the Ni3Al‐based alloy by investment casting. Defects such as incomplete mold filling and hot tears appear commonly. In this paper, physical parameters of Ni3Al‐based alloy are obtained by experiments and simulations using JmatPro software. The calculation results of physical parameters are credible by comparing with test results and can be used in the pre‐processing of casting simulaton software ProCAST of thin wall castings. Gating and feeding system is optimized to decrease hot tearing tendentiousness and ensure filling ability according to casting simulation results.
Thermodynamic Modeling of Phase Equilibria in the WO3‐Zn System
Authors: Shubin Alexey B. , Shunyaev Konstantin Yu.
Published: August 2008

There are no alloys in the W‐Zn binary system. The combustion process in the WO3‐Zn powder mixture gives mainly metallic tungsten and zinc oxide. The ZnO in the product can be easily leached (e.g., with HCl), so that from stoichiometric quantities of reagents, one can obtain W powder of good purity.

Here we investigated the phase equilibria for the WO3‐Zn system in the temperature range of 900‐1500 K. The inert component (Ar) was introduced into the system to change the pressure within the range of 0.1‐0.5 MPa.

When the pressure is constant, the quantity of tungsten dioxide in the equilibrium mixture of components increases with rise in temperature, while the fraction of the zinc oxide decreases. The fraction of metallic tungsten in the mixture also decreases with temperature increase and becomes near zero at 1500 K and 0.1 MPa.

Up to 1100 K, the output of tungsten is close to the limiting (stoichiometric) value in the whole considered pressure range (0.1‐0.5 MPa).
On the Mechanisms of Colloidal Particle and Vapor Bubble Aggregation in Liquid Flows
Authors: Bormashenko Edward , Pogreb Roman
Published: August 2008

Mechanisms of aggregation of micrometrically scaled colloidal particles and vapor bubbles are discussed. It is shown that when particles move in reference to the liquid, the attractive force induced by the flow may be greater than the capillary interaction. Such a situation is realized when capillary interaction is gravity driven, and particles float. For partial (weak) wetting situations, flow‐induced and capillary attractive forces may be comparable. If the wetting is good, it will play a decisive role in the realistically achievable values of the flow velocities. Hydrody‐namic interaction between particles may be of primary importance for sedimentation and fast dip‐coating‐induced aggregation.
The Theoretical Challenge Posed by Low‐Voltage Membrane Electroporation, Viewed from the Perspective of Continuum and Molecular‐Level Models
Authors: Partenskii Michael B. , Miloshevsky Gennady V. , Jordan Peter C.
Published: August 2008

The effect of applied voltage (V) or a membrane‐bound charge (q) on local thickness fluctuations (LTFs) in lipid bilayers is examined using the continuum approach. Ponderomotive forces, calculated from the linearized Poisson‐Boltzmann equation, reduce the electroelastic energy of LTFs quadratically with V and q. Combined with a significant increase in the apex field gradient and perturbation of lipid packing at large amplitude LTFs, this creates a driving force for instability resulting in water penetration, formation of pores, and membrane rupture. The estimated critical voltages for membrane electroporation are compared with the classical Crowley prediction and recent molecular dynamics (MD) simulations. Unsolved questions impeding a full understanding of low‐voltage breakdown are critically examined. Possible connections between MD results and the issue of negative capacitance and related instabilities at electrified interfaces are outlined.
Magnetization of Manganese Perovskites
Authors: Karpenko Boris V. , Falkovskaya Lyubov D. , Kuznetsov Alexandr V.
Published: August 2008

Temperature dependence of spontaneous magnetization at a separate site in the compounds La1‐xCaxMnO3 (0 ⩽ x ⩽ 1) is investigated in the molecular field approximation using a homogeneous model for the magnetic sub‐lattice with allowance for the Heisenberg superexchange and double exchange between nearest neighbors. Unlike with the usual magnets having one type of magnetic ions, in this case there appears a system of equations with two unknowns, mean spins of ions Mn3+ and Mn4+. In the vicinity of the ordering temperature, this system can be solved analytically and the expression for the ordering temperature can be obtained as well. To find the temperature dependence of magnetization in the whole temperature range, we used the exact expression for the double exchange operator containing spin operators under the square root. The numerical solutions were found in this case.
Fabrication of Thin Oriented Organic Layers and Micropatterns by Zone Casting
Authors: Tracz Adam , Masirek Sylwia , Klos Marcin
Published: August 2008

Zone casting—a special solution processing method for obtaining highly ordered continuous layers of soluble organic materials—can also be applied for fabricating patterned layers. In this method, solution is continuously supplied onto a substrate that is withdrawn at a controlled rate, and the solvent evaporates from the surface of a meniscus formed between a flat nozzle and the substrate. Due to the gradient of a solute concentration, its solidification proceeds within the narrow zone localized in the meniscus. In this way solute molecules can be self‐assembled at surfaces into different anisotropic nanostructures (columns, rods, lamellae, or microcrystals) uniaxially aligned parallel to the substrate. Under some conditions various phenomena like dewetting, fingering instability, stick‐slip motion, etc., come into play, leading to various periodic perturbations in the film deposition. Examples of continuous and patterned layers of different materials such as low molecular weight (semi)conductors, chromophores, discotic molecules, and block copolymers, which can successfully be processed using this technique, are shown. Typical layers obtained through this method are shown to have good properties as active layers in field effect transistors.
Electrochemical Determination of Diffusion Coefficients of Iron (II) Ions in Chloride Melts at 700‐750°C
Authors: Lugovskoy Alex , Zinigrad Michael , Aurbach Doron
Published: August 2008

The diffusion coefficients of iron (II) ions depositing on solid tungsten electrodes in a molten chloride systems at about 700°C have been determined by electrochemical techniques. The deposition process occurs under diffusion control for all the iron concentrations and temperatures studied. Conventional cyclic voltammetry and convolution cyclic voltammetry methods were used. Diffusion coefficients of iron (II) were calculated according to Randles‐Sevcik and Berzins‐Delahay equations for the conventional cyclic voltammetry and also by the limiting convoluted current for the convolution cyclic voltammetry. Convolution cyclic voltammetry is believed to be superior to conventional cyclic voltammetry for the quantitative evaluation of diffusion coefficients. The values of the diffusion coefficients lay in the range 1‐40‐10−5 cm2/s for the temperature range of 700‐750°C. The Arrhenius temperature dependence of the diffusion coefficients is characterized by the value of Ea = 31.2 kJ/mol.
Deformation Behavior of Intermetallics: Models and Experiments
Authors: Greenberg Bella A. , Ivanov Michail A. , Antonova Olga V. , Patselov Alexander M. , Plotnikov Alex V.
Published: August 2008

A sufficiently general thermally activated mechanism for extension of dislocations in some preferential direction was proposed. This mechanism comprises a necessary step of dislocation transformations that lead to blocking. The reasons for blocking of different types of dislocations in different materials are diverse. A new concept was developed concerning the possibility of thermally activated blocking of superdislocations in the absence of external stresses. Some experiments with single crystals of Ni3(Al, Nb) were performed. They included no‐load heating after preliminary low‐ or high‐temperature deformation. It was found that the initial dislocation structure, which included curvilinear dislocations, transformed to a set of long rectilinear blocked superdislocations after no‐load heating. The experimental results confirmed theoretical assumptions on the possibility of thermally activated transformations of superdislocations to indestructible barriers in the absence of external stresses.
Hydrogeological Relationships of Sandy Deposits: Modeling of Two‐Dimensional Unsaturated Water and Pesticide Transport
Authors: Iversen Bo V. , van der Keur Peter , Vosgerau Henrik
Published: August 2008

Prediction of the movement of water and solutes in the vadose zone requires information on the distribution of spatial trends and heterogeneities in porous media. The present study describes different lithofacies origination mainly from glaciofluvial deposits. Among different lithofacies, hydrological relationships were investigated. By means of a two‐dimensional hydrological model it was evaluated how the flow of water and leaching of metribuzin (4‐amino‐6‐tert‐butyl‐4,5‐dihydro‐3‐methylthio‐1,2,4‐triazin‐5‐one) was affected. Two selected large outcrop sections consisting of glacial outwash deposits were used in the modeling study. Eleven different lithofacies were distinguished and described in terms of texture distribution, sorting, bedding style, and external boundaries based on excavated soil profiles from 27 locations representing seven predominantly sandy landforms in Denmark. Undisturbed soil columns were sampled from each of the lithofacies and brought to the laboratory to be analyzed. With respect to their soil hydraulic properties, the different lithofacies formed four different hydrofacies having relatively homogeneous, hydrogeological properties. Two large outcrop sections from one of the locations (a gravel pit) located near the terminal moraine of the former Weichsel glacier were used for the HYDRUS‐2D modeling. Modeling results revealed that the spatial distribution of sedimentary bodies affected water flow and the leaching of metribuzin.
Field‐Scale Variation in Microbial Activity and Soil Properties in Relation to Mineralization and Sorption of Pesticides in a Sandy Soil
Authors: Vinther F. P. , Brinch U. C. , Elsgaard L. , Fredslund L. , Iversen B.V. , Torp S. , Jacobsen C. S.
Published: August 2008

Pesticides applied to agricultural soils are subject to environmental concerns because leaching to groundwater reservoirs and aquatic habitats may occur. Knowledge of field variation of pesticide‐related parameters is required to evaluate the vulnerability of pesticide leaching. The mineralization and sorption of the pesticides glyphosate and metribuzin and the pesticide degradation product triazinamin in a field were measured and compared with the field‐scale variation of geochemical and microbiological parameters. We focused on the soil parameters clay and organic carbon (C) content and on soil respiratory and enzymatic processes and microbial biomass. These parameters were measured in soil samples taken at two depths (Ap and Bs horizon) in 51 sampling points from a 4‐ha agricultural fine sandy soil field. The results indicated that the spatial variation of the soil parameters, and in particular the content of organic C, had a major influence on the variability of the microbial parameters and on sorption and pesticide mineralization in the soil. For glyphosate, with a co‐metabolic pathway for degradation, the mineralization was increased in soils with high microbial activity. The spatial variability, expressed as the CV, was about five times higher in the Bs horizon than in the Ap horizon, and the local‐scale variation within 100 m2 areas were two to three times lower than the field‐scale variation within the entire field of about 4 ha.
Spatial Variation in 2‐Methyl‐4‐chlorophenoxyacetic Acid Mineralization and Sorption in a Sandy Soil at Field Level
Authors: Fredslund L. , Vinther F. P. , Brinch U. C. , Elsgaard L. , Rosenberg P. , Jacobsen C. S.
Published: August 2008

The phenoxyacetic acid herbicide MCPA (2‐methyl‐4‐chlorophenoxyacetic acid) is frequently detected in groundwater beneath Danish agricultural fields. We investigated spatial variation in microbial MCPA mineralization potential in a flat agricultural field of fine sandy soil (USDA classification: Humic Dystrudept) located on the Yoldia plains of Northern Jutland, Denmark. Samples for determination of MCPA mineralization and sorption were collected from the Ap and Bs horizons at 51 sampling sites located in a 200 × 220 m grid. Spatial variation in sorption was low in both horizons (distribution coefficient, 0.36–4.16 L kg−1). Sorption correlated strongly with soil organic carbon content in both horizons (CV, 93 and 83%, respectively) and negatively with soil pH. [Ring‐14C]‐MCPA mineralized readily in the Ap horizon, with 49 to 62% of the 14C‐MCPA being converted to 14CO2 during the 67‐d incubation period. With the subsoil, mineralization of 14C‐MCPA varied considerably between samples (0.5–72.8%). At neither depth was there correlation between 14C‐MCPA mineralization and sorption, soil pH, organic carbon content, clay content, number of colony‐forming units (CFU), pseudomonad CFU, or any of the four microbial activity parameters measured. The presence of microbial genes encoding for the TfdA enzyme was quantified using real‐time polymerase chain reaction. No correlation was found between MCPA mineralization potential and the natural background number of tfdA genes present in the soil samples. The degradation kinetics suggests that the high 14C‐MCPA mineralization rate detected in soil samples was linked to growth of the MCPA‐degrading soil microbial community.
Impact of Basic Soil Parameters on Pesticide Disappearance Investigated by Multivariate Partial Least Square Regression and Statistics
Authors: Juhler R. K. , Henriksen T. H. , Ernstsen V. , Vinther F. P. , Rosenberg P.
Published: August 2008

Dissipation time is a key parameter when studying and modeling the environmental fate of pesticides. This study was conducted to characterize the variability of pesticide disappearance in soil and to identify possible controlling parameters related to intrinsic soil properties and microbiology. Multivariate data analysis was used to study spatial variability in three horizons from 24 sandy soil profiles. The time for 50% disappearance (DT50) was characterized for two herbicides, metribuzin (MBZ) and MCPA, and methyltriazine amine (MTA; transformation product of metsulfuron‐methyl, tribenuron‐methyl, thifensulfuron‐methyl, and chlorsulfuron). Normal and log‐normal distributions were compared for DT50 and soil properties and descriptive statistics were calculated. Conformity with log‐transformed distributions was observed and assuming normality of the DT50 data would cause 5 to 35% overestimation. Mean DT50 were: MCPA 9.5, MBZ 168, and MTA 127. Significant effect of soil depth on DT50 was shown for MCPA and MBZ, with low values in deeper horizons. Simple linear correlation for combinations of MCPA, MTA, pH, and total organic carbon (TOC) was observed. Using partial least squares regression (PLS) 71 to 85% of the total DT50 variance was explained. A specific predictor variable could not be identified as the controlling components differed within horizons and compounds. For MCPA the overall important predictor variables were microbiology and TOC, whereas for MTA and MBZ it was inorganic variables (Al, Fe, cation exchange capacity, base saturation percent, and pH) and microbiology. The study indicates that PLS generated input data can improve pesticide fate modeling and reduce the uncertainty in dissipation estimation.
Efficacy of Natural Wetlands to Retain Nutrient, Sediment and Microbial Pollutants
Authors: Knox A. K. , Dahlgren R. A. , Tate K. W. , Atwill E. R.
Published: August 2008

Wetlands can improve water quality through natural processes including sedimentation, nutrient transformations, and microbial and plant uptake. Tailwater from irrigated pastures may contribute to nonpoint source water pollution in the form of sediments, nutrients, and pathogens that degrade downstream water quality. We examined benefits to water quality provided by a natural, flow‐through wetland and a degraded, channelized wetland situated within the flood‐irrigation agricultural landscape of the Sierra Nevada foothills of Northern California. The non‐degraded, reference wetland significantly improved water quality by reducing loads of total suspended sediments, nitrate, and Escherichia coli on average by 77, 60, and 68%, respectively. Retention of total N, total P, and soluble reactive P (SRP) was between 35 and 42% of loads entering the reference wetland. Retention of pollutant loads by the channelized wetland was significantly lower than by the reference wetland for all pollutants except SRP. A net export of sediment and nitrate was observed from the channelized wetland. Decreased irrigation inflow rates significantly improved retention efficiencies for nitrate, E. coli, and sediments in the reference wetland. We suggest that maintenance of these natural wetlands and regulation of inflow rates can be important aspects of a best management plan to improve water quality as water runs off of irrigated pastures.
Lichens as Biomonitors of Air Quality around a Diamond Mine, Northwest Territories, Canada
Authors: Naeth M. A. , Wilkinson S. R.
Published: August 2008

Lichens are known to be bioaccumulators of atmospheric pollutants and are abundant in the Canadian arctic. Mining in this region may negatively impact the tundra communities and these impacts may be detected by increased accumulation of heavy metals, greenhouse gas constituents, and organic compounds in lichen tissue. The effect of sampling direction and distance from a diamond mine on bioaccumulation in three lichen species, Flavocetraria nivalis, Flavocetraria cucullata, and Cladina arbuscula, was investigated. Eight sample sites were located immediately adjacent to a diamond mine, one in each cardinal and ordinal direction, and six sample sites each were located 30 and 60 km from the mine (cardinal, NE, and SE). Thirty‐three major and trace elements, sulfate (SO4), nitrate (NO3), ammonium (NH4), polycyclic aromatic hydrocarbons (PAH), and phthalates were analyzed in lichen tissue and soil. A significant interaction occurred between distance and direction from the mine. Highest concentrations of Al, Cr, Cu, Fe, Ni, Ti, and V in lichen were at the mine site regardless of direction. Highest concentrations for all other elements were at the mine in at least two directions. Although present in lichen tissue, there was no significant difference among sites for Hg, Mn, S, and three phthalates. PAHs were below detection limits in lichen tissue. The effect of direction was dependent on element and species, although concentrations of most elements were greatest east or southeast of the mine site. At distance from the mine, direction had less of an effect on concentrations. Elevated concentrations in tissue did not negatively impact lichen or plant cover or lichen richness. This research strongly suggests selection of sample sites and species can impact results and interpretation of data from air quality monitoring programs that use lichens as biomonitors.