bluuebunny/crossref_metadata_2025 huggingface dataset:
FISCAL POLICY, INCREASING RETURNS, AND ENDOGENOUS FLUCTUATIONS
Authors: Guo Jang-Ting , Lansing Kevin J.
Published: May 2008

This paper examines the quantitative implications of government fiscal policy in a discrete-time one-sector growth model with a productive externality that generates social increasing returns to scale. Starting from a laissez-faire economy that exhibits local indeterminacy, we show that the introduction of a constant capital tax or subsidy can lead to various forms of endogenous fluctuations, including stable 2-, 4-, 8-, and 10-cycles, quasiperiodic orbits, and chaos. In contrast, a constant labor tax or subsidy has no effect on the qualitative nature of the model's dynamics. We show that the use of local steady-state analysis to detect the presence of multiple equilibria in this class of models can be misleading. For a plausible range of capital tax rates, the log-linearized dynamical system exhibits saddle-point stability, suggesting a unique equilibrium, whereas the true nonlinear model exhibits global indeterminacy. This result implies that stabilization policies designed to suppress sunspot fluctuations near the steady state may not prevent sunspots, cycles, or chaos in regions away from the steady state. Overall, our results highlight the importance of using a model's nonlinear equilibrium conditions to fully investigate global dynamics.
PERFECT PREDICTIONS IN ECONOMIC DYNAMICAL SYSTEMS WITH RANDOM PERTURBATIONS
Authors: Böhm Volker , Wenzelburger Jan
Published: May 2008

The paper studies multivariate non linear economic dynamical systems with an expectations feedback subjected to exogenous perturbations. In these systems, agents form expectations on future variables based on subjective transition probabilities given by a Markov kernel. The notion of a perfect Markov kernel that generates rational expectations along all orbits of the system is proposed. Conditions are provided under which perfect Markov kernels exist. Applications are given to models of the Cobweb type, to multivariate affine-linear systems, and to the stochastic OLG model of economic growth. For the latter two models, it is shown when a globally attracting random fixed point with rational expectations exists.
FURTHER INSPECTION OF THE STOCHASTIC GROWTH MODEL BY AN ANALYTICAL APPROACH
Authors: Lau Sau-Him Paul
Published: May 2008

It has been argued that a clear understanding of the stochastic growth model can best be achieved by working out an approximate analytical solution. This paper follows that idea but streamlines the presentation of the loglinear approximate solution for the neoclassical model of capital accumulation. By focusing on the partial elasticity of capital stock with respect to its lag term, this paper is able to confirm analytically some conclusions based on numerical calculations in previous papers, and to clarify why a simpler solution arises in several special cases.
STABILIZATION POLICY AS BIFURCATION SELECTION: WOULD STABILIZATION POLICY WORK IF THE ECONOMY REALLY WERE UNSTABLE?
Authors: Barnett William A. , He Yijun
Published: May 2008

Taken literally, the concept of “stabilization policy” implicitly assumes that the macroeconomy is unstable without imposition of a policy. Hence, selection of a “stabilization policy” can be viewed as selection of a policy to bifurcate the system from an unstable to a stable operating regime. The literature on dynamics of high-dimensional systems suggests that successful bifurcation selection is challenging. As an experiment to investigate this point of view, we use the continuous-time UK dynamic macroeconometric model. Under assumptions designed to be most favorable to stabilization policy, we find that policies that would produce successful bifurcation are very complicated. We also find that less complicated policies based upon reasonable economic intuition can be counterproductive, since such policies can contract the size of the stable subset of the parameter space. In fact, an economy that is dynamically stable without policy, but subject to stochastic shocks, could be bifurcated to instability with imposition of a poorly designed “stabilization” policy.
Introduction and Comments
Authors: Hochschild Jennifer L.
Published: May 2008

“I think good thoughts, whilst others write good words” (Shakespeare, Sonnet 85). Such is the life of a journal editor, as well as that of a love-sick poetical genius. I can at least hope that the good words written by others and published in this issue of Perspectives on Politics will last—if not quite as long as Shakespeare's sonnets, then well into the future.
Would the Dream of Political Equality Turn out to Be a Nightmare?
Authors: Verba Sidney
Published: May 2008

The SGML version of this article is currently unavailable.
Structures Do Not Come with an Instruction Sheet: Interests, Ideas, and Progress in Political Science
Authors: Blyth Mark
Published: May 2008

This article questions the centrality of interest-based explanation in political science. Through an examination of the “turn to ideas” undertaken in the past decade by rationalist and nonrationalist scholars in both comparative politics and international relations, it seeks to make three points. First, interests are far from the unproblematic and ever-ready explanatory instruments we assume them to be. Second, the ideational turn of historical institutionalism and constructivist international relations theory marks a substantive theoretical shift in the field precisely because it problematizes notions of action that take interest as given. Third, such scholarship emerged from, and in reaction to, the inherent limits of rationalist treatments of interests and ideas. That it did so suggests that progress in the discipline may be more dialectic—rather than linear or paradigmatic—than we realize.
Retrospective Comments
Authors: Piven Frances Fox
Published: May 2008

Poor People's Movements: Why They Succeed, How They Fail. By Frances Fox Piven and Richard A. Cloward. New York: Pantheon Books, 1977. 381 pages.
Organizing versus Mobilizing:Poor People's Movementsafter 25 Years
Authors: Block Fred
Published: May 2008

Poor People's Movements: Why They Succeed, How They Fail. By Frances Fox Piven and Richard A. Cloward. New York: Pantheon Books, 1977. 381 pages.
School Reform and Equal Opportunity in America's Geography of Inequality
Authors: Macedo Stephen
Published: May 2008

How can the American educational system be improved for all? What can and should be done about substandard inner-city schooling that leaves large numbers of poor and overwhelmingly minority children incapable of effective civic participation and ineligible for good jobs? These perennial issues of politics and public policy implicate fundamental principles of justice. Educational choices involve, among other things, choices about a future in which children's life chances will take shape either under the sway of inherited privilege or on the basis of equal citizenship and opportunity. In the midst of America's vast and growing inequalities of income and wealth, which continue to be associated with race, how can we clothe ourselves in comforting myths of equal opportunity if we fail to provide good schools for everyone?
A New View on the MMN and Attention Debate
Authors: Sussman Elyse S.
Published: May 2008

The question of whether the mismatch negativity (MMN) is modulated by attention has been debated for over a decade. Although the MMN is widely regarded as reflecting a preattentive auditory process, many studies have shown attention effects on MMN. So, what does preattentive mean if attention can modulate the MMN? To understand the function of MMN in auditory processing, we need to shed new light on the “MMN and attention” debate. This review will discuss the apparent paradox that MMN can be modulated by attention and still be considered an attention-independent process, and provide a new framework for viewing the MMN system. The new model proposes that the principal factor governing MMN is the sound context. MMN generation relies on multiple processing mechanisms that are part of a larger system of auditory scene analysis.
The Frontal Generator of the Mismatch Negativity Revisited
Authors: Deouell Leon Y.
Published: May 2008

The mismatch negativity (MMN) is an event-related brain potential elicited by the occurrence of a rare event (deviance) in an otherwise regular acoustic environment, and is assumed to reflect a preattentive mechanism for change detection. A widely adopted model holds that MMN has main generators in the superior temporal planes bilaterally, which are responsible for the sensory memory part of change detection, as well as frontal lobe sources responsible for triggering an attention shift upon change detection. Whereas the temporal sources have been documented in numerous studies across species and methodologies, much less is known about the frontal sources. The present review examines the current state of the evidence for their existence, location, and possible function. It confirms that the frontal generator is still a less consistent finding in MMN research than the temporal generator. There is clear evidence from scalp EEG and, especially, current source density studies for the existence of an MMN generator that is functionally distinct from the main supratemporal generator of the MMN. Evidence from fMRI, PET, optical imaging, EEG source imaging, and lesion studies implicates mainly the inferior frontal and possibly also the medial frontal cortex. However, these results should be taken with caution because of the paucity of support from more direct measures like intracranial recordings and MEG, and the negative findings from several fMRI and PET, as well as EEG source imaging studies. Recent studies also raise questions about the exact role of the frontal generator in triggering an attention shift. Delineating the exact cortical locations of frontal MMN generators, the conditions under which they are activated and, consequently, their function, remains an acute challenge.
ERP Repetition Effects and Mismatch Negativity Generation
Authors: Baldeweg Torsten
Published: May 2008

Neuronal adaptation is a ubiquitous property of the cortex. This review presents evidence from MMN studies that show ERP components with similar adaptive properties. Specifically, I consider the empirical evidence from the perspective of a predictive coding model of perceptual learning and inference. Within this framework, ERP and neuronal repetition effects (repetition suppression) are seen as reductions in prediction error, a process that requires synaptic modifications. Repetition positivity is a human auditory ERP component, which shows similar properties to stimulus-specific adaptation of auditory cortex neurons; a candidate mechanism for auditory trace formation.
Mismatch Negativity and Stimulus-Specific Adaptation in Animal Models
Authors: Nelken Israel , Ulanovsky Nachum
Published: May 2008

Animal models of MMN may serve both to further our understanding of neural processing beyond pure sensory coding and for unraveling the neural and pharmacological processes involved in the generation of MMN. We start this review by discussing the methodological issues that are especially important when pursuing a single-neuron correlate of MMN. Correlates of MMN have been studied in mice, rats, cats, and primates. Whereas essentially all of these studies demonstrated the presence of stimulus-specific adaptation, in the sense that responses to deviant tones are larger than the responses to standard tones, the presence of real MMN has been established only in a few. We argue for the use of more and better controls in order to clarify the situation. Finally, we discuss in detail the relationships between stimulus-specific adaptation of single-neuron responses, as established in the cat auditory cortex, and MMN. We argue that this is currently the only fully established correlate of true change detection, and hypothesize that it precedes and probably induces the neural activity that is eventually measured as MMN.
Role of Mismatch Negativity and Novelty-P3 in Involuntary Auditory Attention
Authors: Escera Carles , Corral M.J.
Published: May 2008

It has been proposed that the functional role of the mismatch negativity (MMN) generating process is to issue a call for focal attention toward any auditory change violating the preceding acoustic regularity. This paper reviews the evidence supporting such a functional role and outlines a model of how the attentional system controls the flow of bottom-up auditory information with regard to ongoing-task demands to organize goal-oriented behavior. Specifically, the data obtained in auditory-auditory and auditory-visual distraction paradigms demonstrated that the unexpected occurrence of deviant auditory stimuli or novel sounds captures attention involuntarily, as they distract current task performance. These data indicate that such a process of distraction takes place in three successive stages associated, respectively, to MMN, P3a/novelty-P3, and reorienting negativity (RON), and that the latter two are modulated by the demands of the task at hand.
Solar forcing and planetary ion escape from Mars
Authors: Lundin R. , Barabash S. , Fedorov A. , Holmström M. , Nilsson H. , Sauvaud J.‐A. , Yamauchi M.
Published: May 2008

The variability of planetary ion escape from Mars is studied using data from the Ion Mass Analyzer, IMA, on Mars Express (MEX). 42 orbits were selected during 17 months for different solar wind conditions, focusing on the low energy (≈30 – 800 eV) heavy ion (e.g. O+, O2+ and CO2+) outflow. A strong correlation is found between solar wind forcing of the obstacle, the cross‐sectional area enclosing the ion outflow from Mars and the total heavy ion escape flux. The at least one order of magnitude changes of the ion outflow on the short term (hours, days), is directly connected with the variability of solar wind, solar soft x‐ray and solar EUV (XEUV). The latter was first inferred from an analysis of how the obstacle size changes with changing solar wind and solar XEUV forcing. The 17‐month trend of decreasing ion outflow with EUV during a declining phase of solar cycle 23, the EUV determined from the Neutral Particle Imager (NPI) on MEX, illustrates the influence of solar EUV forcing. On the basis of this we conclude that changes in solar wind‐ and solar XEUV forcing governs the variable ion escape from Mars. Both forcing terms appear to be equally important for the escape rate. Considering the difference in travel time for XEUV and the solar wind to Mars, the XEUV effect will precede the solar wind effect by several (3–9) days.
Reconnection at the dayside magnetopause: Comparisons of global MHD simulation results with Cluster and Double Star observations
Authors: Berchem J. , Marchaudon A. , Dunlop M. , Escoubet C. P. , Bosqued J. M. , Reme H. , Dandouras I. , Balogh A. , Lucek E. , Carr C. , Pu Z.
Published: May 2008

This study uses two conjunctions between Cluster and Double Star TC‐1 spacecraft together with global magnetohydrodynamic (MHD) simulations to investigate the large‐scale configuration of magnetic reconnection at the dayside magnetopause. Both events involve southward interplanetary magnetic fields with significant By components. The first event occurred on 8 May 2004, while both spacecraft were exploring the dawn flank of the magnetosphere; TC‐1 was skimming the magnetopause whereas Cluster was exploring higher latitudes. Results from a global MHD simulation show the formation of an equatorial merging line in the morning sector and suggest that the three‐dimensional geometry of the merging region is mostly a radial juxtaposition of planes displaying X‐type reconnection geometries. The second conjunction was on 6 April 2004. During this event, Cluster was located at high latitudes and close to the noon‐midnight meridian, while TC‐1 was exploring the dawnside at low latitudes. Analysis of the simulation reveals that both antiparallel and component merging occurred simultaneously. Three‐dimensional rendering of the parallel electric field indicates that component merging initiated in the subsolar magnetopause. Simulation runs carried out using different parameters in the model suggest that the spread of the merging region depends on the local resistivity. The subsolar‐merging region grows with increasing resistivity values and becomes patchy when a resistivity threshold is used. However, the region of component merging appears to remain spatially constrained to the subsolar region where stronger parallel electric fields occur and no clear connection with the antiparallel‐merging regions is found for the range of parameters surveyed.
Veneers, rinds, and fracture fills: Relatively late alteration of sedimentary rocks at Meridiani Planum, Mars
Authors: Knoll Andrew H. , Jolliff Brad L. , Farrand William H. , Bell James F. , Clark Benton C. , Gellert Ralf , Golombek M. P. , Grotzinger John P. , Herkenhoff Kenneth E. , Johnson Jeffrey R. , McLennan Scott M. , Morris Richard , Squyres Steven W. , Sullivan Robert , Tosca Nicholas J. , Yen Albert , Learner Zoe
Published: May 2008

Veneers and thicker rinds that coat outcrop surfaces and partially cemented fracture fills formed perpendicular to bedding document relatively late stage alteration of ancient sedimentary rocks at Meridiani Planum, Mars. The chemistry of submillimeter thick, buff‐colored veneers reflects multiple processes at work since the establishment of the current plains surface. Veneer composition is dominated by the mixing of silicate‐rich dust and sulfate‐rich outcrop surface, but it has also been influenced by mineral precipitation, including NaCl, and possibly by limited physical or chemical weathering of sulfate minerals. Competing processes of chemical alteration (perhaps mediated by thin films of water or water vapor beneath blanketing soils) and sandblasting of exposed outcrop surfaces determine the current distribution of veneers. Dark‐toned rinds several millimeters thick reflect more extensive surface alteration but also indicate combined dust admixture, halite precipitation, and possible minor sulfate removal. Cemented fracture fills that are differentially resistant to erosion occur along the margins of linear fracture systems possibly related to impact. These appear to reflect limited groundwater activity along the margins of fractures, cementing mechanically introduced fill derived principally from outcrop rocks. The limited thickness and spatial distribution of these three features suggest that aqueous activity has been rare and transient or has operated at exceedingly low rates during the protracted interval since outcropping Meridiani strata were exposed on the plains surface.
Validation of the space weather modeling framework using ground‐based magnetometers
Authors: Yu Yiqun , Ridley Aaron J.
Published: May 2008

Geomagnetically induced currents (GICs) can disrupt power grid operations, causing significant interference for many people; therefore, predictions of ground‐based magnetic perturbations and their time derivatives are quite important. This study quantifies how well the University of Michigan's Global MHD code predicts approximately 150 ground‐based magnetometer traces for a number of storm‐time intervals. It is found that in order to accurately represent the magnetic perturbation, Biot‐Savart integrals over the entire hemisphere are needed, especially when calculating the vertical component. The 4 May 1998 storm is examined in detail. The code compares well with some stations, quantified by a normalized root mean squared error and cross correlation, while missing even the general trends for other stations. When multiple magnetometer station perturbations are averaged together, the model does an adequate job in the north and vertical components but reverses the trends in the eastward component. The code does significantly better when comparing an AL‐like index but does not have as strong a variation as the actual data. Comparison of dB/dt in a wide window rather than simultaneously shows better model performance in capturing events but worse in yielding false alarms. It is further found that the MHD code models the magnetic perturbations better in the summer hemisphere than in the winter hemisphere.
Modeling benzene plume elongation mechanisms exerted by ethanol using RT3D with a general substrate interaction module
Authors: Gomez Diego E. , de Blanc Phillip C. , Rixey William G. , Bedient Phillip B. , Alvarez Pedro J. J.
Published: May 2008

A mathematical model was developed to evaluate the effect of the common fuel additive ethanol on benzene fate and transport in fuel‐contaminated groundwater and to discern the most influential benzene plume elongation mechanisms. The model, developed as a module for the Reactive Transport in 3 Dimensions (RT3D) model, includes commonly considered fate and transport processes (advection, dispersion, adsorption, biodegradation, and depletion of molecular oxygen during biodegradation) and substrate interactions previously not considered (e.g., a decrease in the specific benzene utilization rate due to metabolic flux dilution and/or catabolite repression) as well as microbial population shifts. Benzene plume elongation predictions, based on literature model parameters, were on the order of 40% for a constant source of E10 gasoline (10% vol/vol ethanol), which compares favorably to field observations. For low benzene concentrations (<1 mg/L), oxygen depletion during ethanol degradation was the principal mechanism hindering benzene natural attenuation. For higher benzene concentrations (exerting an oxygen demand higher than the available dissolved oxygen), metabolic flux dilution was the dominant plume elongation process. If oxygen were not limiting, as might be the case in zones undergoing aerobic biostimulation, model simulations showed that microbial growth on ethanol could offset negative substrate interactions and enhance benzene degradation, resulting in shorter plumes than baseline conditions without ethanol.
Contribution of Yap1 towards Saccharomyces cerevisiae adaptation to arsenic-mediated oxidative stress
Authors: Menezes Regina A. , Amaral Catarina , Batista-Nascimento Liliana , Santos Claudia , Ferreira Ricardo Boavida , Devaux Fréderic , Eleutherio Elis C. A. , Rodrigues-Pousada Claudina
Published: May 2008

In the budding yeast Saccharomyces cerevisiae, arsenic detoxification involves the activation of Yap8, a member of the Yap (yeast AP-1-like) family of transcription factors, which in turn regulates ACR2 and ACR3, genes encoding an arsenate reductase and a plasma-membrane arsenite-efflux protein respectively. In addition, Yap1 is involved in the arsenic adaptation process through regulation of the expression of the vacuolar pump encoded by YCF1 (yeast cadmium factor 1 gene) and also contributing to the regulation of ACR genes. Here we show that Yap1 is also involved in the removal of ROS (reactive oxygen species) generated by arsenic compounds. Data on lipid peroxidation and intracellular oxidation indicate that deletion of YAP1 and YAP8 triggers cellular oxidation mediated by inorganic arsenic. In spite of the increased amounts of As(III) absorbed by the yap8 mutant, the enhanced transcriptional activation of the antioxidant genes such as GSH1 (γ- glutamylcysteine synthetase gene), SOD1 (superoxide dismutase 1 gene) and TRX2 (thioredoxin 2 gene) may prevent protein oxidation. In contrast, the yap1 mutant exhibits high contents of protein carbonyl groups and the GSSG/GSH ratio is severely disturbed on exposure to arsenic compounds in these cells. These results point to an additional level of Yap1 contribution to arsenic stress responses by preventing oxidative damage in cells exposed to these compounds. Transcriptional profiling revealed that genes of the functional categories related to sulphur and methionine metabolism and to the maintenance of cell redox homoeostasis are activated to mediate adaptation of the wild-type strain to 2 mM arsenate treatment.
Heat shock and ethanol stress provoke distinctly different responses in 3′-processing and nuclear export of HSP mRNA in Saccharomyces cerevisiae
Authors: Izawa Shingo , Kita Takeomi , Ikeda Kayo , Inoue Yoshiharu
Published: May 2008

Under conditions of heat shock at 42 °C, mRNAs of HSP (heat shock protein) genes are exported out of the nucleus, whereas bulk poly(A)+ (polyadenylated) mRNA shows a nuclear accumulation in Saccharomyces cerevisiae. Such a selective mRNA export seems an efficacious strategy of yeast cells to adapt rapidly to stress. Although ethanol stress (10%, v/v) as well as heat shock blocks the export of bulk poly(A)+ mRNA, the differences and/or similarity between heat shock and ethanol stress in the mechanisms of selective mRNA export still remain to be clarified. We found that ethanol stress induced transcriptional activation of a subset of yeast HSP genes; however, intriguingly, most such transcripts remained in the nucleus in a hyperadenylated state and, as a consequence, were not translated into HSPs. Elimination of ethanol resulted in a rapid shortening of the poly(A) tails of HSP mRNAs, loss of their nuclear retention, and the coincidental synthesis of the respective HSPs. Since HSP mRNAs are selectively exported from the nucleus in heat-shocked cells, yeast cells respond differently to ethanol stress and heat shock in the 3′-processing and transport of HSP mRNAs. Furthermore, these results also suggest that hyperadenylation and nuclear retention of mRNAs might be used as a means to control eukaryotic gene expression under stressed conditions.
S-nitrosylation of syntaxin 1 at Cys145 is a regulatory switch controlling Munc18-1 binding
Authors: Palmer Zoë J. , Duncan Rory R. , Johnson James R. , Lian Lu-Yun , Mello Luciane V. , Booth David , Barclay Jeff W. , Graham Margaret E. , Burgoyne Robert D. , Prior Ian A. , Morgan Alan
Published: May 2008

Exocytosis is regulated by NO in many cell types, including neurons. In the present study we show that syntaxin 1a is a substrate for S-nitrosylation and that NO disrupts the binding of Munc18-1 to the closed conformation of syntaxin 1a in vitro. In contrast, NO does not inhibit SNARE {SNAP [soluble NSF (N-ethylmaleimide-sensitive fusion protein) attachment protein] receptor} complex formation or binding of Munc18-1 to the SNARE complex. Cys145 of syntaxin 1a is the target of NO, as a non-nitrosylatable C145S mutant is resistant to NO and novel nitrosomimetic Cys145 mutants mimic the effect of NO on Munc18-1 binding in vitro. Furthermore, expression of nitrosomimetic syntaxin 1a in living cells affects Munc18-1 localization and alters exocytosis release kinetics and quantal size. Molecular dynamic simulations suggest that NO regulates the syntaxin–Munc18 interaction by local rearrangement of the syntaxin linker and H3c regions. Thus S-nitrosylation of Cys145 may be a molecular switch to disrupt Munc18-1 binding to the closed conformation of syntaxin 1a, thereby facilitating its engagement with the membrane fusion machinery.
SOX9 transduction increases chondroitin sulfate synthesis in cultured human articular chondrocytes without altering glycosyltransferase and sulfotransferase transcription
Authors: Tew Simon R. , Pothacharoen Peraphan , Katopodi Theoni , Hardingham Timothy E.
Published: May 2008

The transcription factor SOX9 (Sry-type high-mobility-group box 9) is expressed in all chondrocytes and is essential for the expression of aggrecan, which during biosynthesis is substituted with more than 10 times its weight of CS (chondroitin sulfate) and is secreted by chondrocytes to form the characteristic GAG (glycosaminoglycan)-rich ECM (extracellular matrix) of cartilage. SOX9 expression rapidly falls during monolayer culture of isolated chondrocytes and this turns off aggrecan and associated CS synthesis. We therefore investigated whether SOX9 transduction of cultured human articular chondrocytes had any effect on the gene expression of the glycosyltransferases and sulfotransferases necessary for GAG biosynthesis. Retroviral SOX9 transduction of passaged chondrocytes increased the endogenous rate of GAG synthesis and the total capacity for GAG synthesis assessed in monolayer culture with β-xyloside. Both the endogenous rate and the total capacity of GAG biosynthesis were increased further in chondrogenic cell aggregate cultures. The GAG synthesized was predominantly CS and the hydrodynamic size of the newly synthesized chains was unchanged by SOX9 transduction. Aggrecan gene expression was increased in the SOX9-transduced chondrocytes and increased further in chondrogenic culture, but no comparable effects were found in SOX9 transduced dermal fibroblasts. However, the expression of CS glycosyltransferase and sulfotransferase genes in chondrocytes was unaffected by SOX9 transduction. Therefore SOX9 transduction in chondrocytes increased their CS synthetic capacity, but this was not accompanied by changes in the transcription of the CS biosynthetic enzymes and must occur by indirect regulation of enzyme activity through control of enzyme protein translation or enzyme organization.
Identification of essential amino acid residues in a sterol 8,7-isomerase from Zea mays reveals functional homology and diversity with the isomerases of animal and fungal origin
Authors: Rahier Alain , Pierre Sylvain , Riveill Geneviève , Karst Francis
Published: May 2008

A putative 8,7SI (sterol 8,7-isomerase) from Zea mays, termed Zm8,7SI, has been isolated from an EST (expressed sequence tag) library and subcloned into the yeast erg2 mutant lacking 8,7SI activity. Zm8,7SI restored endogenous ergosterol synthesis. An in vitro enzymatic assay in the corresponding yeast microsomal extract indicated that the preferred Δ8-sterol substrate possesses a single C4α methyl group, in contrast with 8,7SIs from animals and fungi, thus reflecting the diversity in the structure of their active site in relation to the distinct sterol biosynthetic pathways. In accordance with the proposed catalytic mechanism, a series of lipophilic ammonium-ion-containing derivatives possessing a variety of structures and biological properties, potently inhibited the Zm8,7SI in vitro. To evaluate the importance of a series of conserved acidic and tryptophan residues which could be involved in the Zm8,7SI catalytic mechanism, 20 mutants of Zm8,7SI were constructed as well as a number of corresponding mutants of the Saccharomyces cerevisiae 8,7SI. The mutated isomerases were assayed in vivo by sterol analysis and quantification of Δ5,7-sterols and directly in vitro by examination of the activities of the recombinant Zm8,7SI mutants. These studies have identified His74, Glu78, Asp107, Glu121, Trp66 and Trp193 that are required for Zm8,7SI activity and show that binding of the enzyme–substrate complex is impaired in the mutant T124I. They underline the functional homology between the plant and animal 8,7SIs on one hand, in contrast with the yeast 8,7SI on the other hand, in accordance with their molecular diversity and distinct mechanisms.
Prevalence of GSTT1, GSTM1 and NQO1 (609C>T) in Filipino children with ALL (acute lymphoblastic leukaemia)
Authors: Rimando Marilyn G. , Chua Mary N. , Yuson Ernesto d'J. , de Castro-Bernas Gloria , Okamoto Takashi
Published: May 2008

In the present paper, we examined the incidence of polymorphic genes involved with the detoxification of exogenous chemicals, including carcinogens, namely GSTT1 (glutathione transferase θ1), GSTM1 (glutathione transferase μ1) and NQO1 (NAD(P)H:quinone oxidoreductase 1) in 60 Filipino children with ALL (acute lymphoblastic leukaemia). We found a significantly high incidence of the GSTM1 null genotype in ALL children (71.7%) compared with 51.7% in the control group of children (P<0.05). The GSTT1 null genotype was observed in 35.0% and 33.3% of the ALL cases and the control subjects respectively, with no significant difference. Screening for NQO1 (609C>T) mutant alleles showed a high incidence of the NQO1 C/C genotype (NQO1 homozygous wild-type allele genotype) in 60.0% of ALL cases and was significantly higher than in the control group (23.3%) (P<0.01). These GSTM1 null and NQO1 wild-type genotypes are independently associated with the risk of ALL in Filipino patients. When these two genotypes, GSTM1 null and NQO1 C/C, were combined, the hazard rate for childhood leukaemia was significantly increased (P<0.001). We also noticed that the incidences of GSTM1 null mutations and the NQO1 C/C genotype were significantly higher among Filipinos. These findings suggest a possible role of the GSTM1 null and NQO1 C/C genotypes in the susceptibility of paediatric ALL cases in the Philippines.
Structural characteristics of GeTe-rich GeTe–Sb2Te3 pseudobinary metastable crystals
Authors: Matsunaga T. , Morita H. , Kojima R. , Yamada N. , Kifune K. , Kubota Y. , Tabata Y. , Kim J.-J. , Kobata M. , Ikenaga E. , Kobayashi K.
Published: May 2008

The (GeTe)1−γ–(Sb2Te3)γ pseudobinary system has, over almost its entire composition range, two kinds of crystalline phase: one is a metastable phase with a NaCl-type structure and the other is a spectrum of stable phases with homologous structures. In the metastable phase, Ge/Sb atoms and intrinsic vacancies occupy the Na sites; on the other hand, Te atoms are located at the Cl sites. These vacancies are produced by following γ/1+2γ to ensure the stoichiometry of the metastable pseudobinary compound. This metastable phase obstinately holds its NaCl-type structure and resists transformation to stable homologous structures, even at high temperatures on the GeTe-rich side of the system. In GeTe (γ=0), the NaCl-type atomic configuration itself is the stable structure. GeTe has, as is well known, a high-temperature cubic phase and a low-temperature rhombohedral phase. This GeTe and the pseudobinary compounds containing a small quantity of Sb2Te3 have their single-phase regions not on the GeTe–Sb2Te3 tie line but at Ge-poor sides off the line: in other words, the Na sites of these off-stoichiometric compounds have some excess vacancies besides the intrinsic vacancies. As Sb2Te3 is further added to GeTe, however, the structural transformation temperature continuously falls and the single-phase region converges on the tie line as the excess vacancies at the Na site disappear, which change its electrical property from metallic to semiconducting conductivity. The low-temperature rhombohedral phase is present up to near γ=0.14. The NaCl-type metastable phase becomes unstable with increased Sb2Te3; after subjecting the compound Ge8Sb2Te11 (γ=0.11) to heat treatment for 15 days at 773 K, a stable homologous structure appeared.
Transparent behavior of aluminum nanoparticle compacts at microwave frequencies
Authors: Matsumura K. , Kagawa Y.
Published: May 2008

Aluminum nanoparticles are formed into compacts, and electromagnetic wave reflectance and transmittance of the compacts are measured in a microwave frequency range. The dielectriclike behavior of the compact, which transmits an electromagnetic wave with quite a small loss, is observed. This dielectric behavior originates from electrically isolated nanoparticles by an oxide layer of a few nanometers formed at the surface.
Investigation of the dielectric properties of MnO-additive Pb(Fe2∕3W1∕3)–PbTiO3 relaxors using the spin-glass model
Authors: Hong Cheng-Shong , Chu Sheng-Yuan , Li Bing-Jing , Su Wen-Chang , Chang Ren-Chuan , Nien Hsiau-Hsian , Juang Yung-Der
Published: May 2008

The low-field dielectric responses of pure and 0.15wt.% MnO-added (1−x)Pb(Fe2∕3W1∕3)O3–xPbTiO3 [(1−x)PFW–xPT] were investigated with the empirical model, the Curie–Weiss law and the spin-glass model. According to the experimental data and the fitting results, we conclude that (1) the lattice structure is changed and the electron compensation is induced with MnO addition. (2) The dielectric behaviors obey the Curie–Weiss law as the temperature is much far above Tm for all samples. (3) TCW, the temperature at which the dielectric behaviors deviate from the Curie–Weiss law, is higher and the diffuse phase characteristic is more obvious as decreasing PbTiO3 content or adding MnO. (4) The tailed temperature-dependent local order parameters, which are derived from the spin-glass model and the experimental results, for more diffuse phase transition relaxors show higher thermal stability in the spontaneous polarization microregions. (5) The temperature-dependent local ordering parameters change from a long-range-ordered ferroelectric state to a short-range-ordered relaxor with decreasing the PbTiO3 content or adding MnO.
Chaotic scattering in solitary wave interactions: A singular iterated-map description
Authors: Goodman Roy H.
Published: May 2008

We derive a family of singular iterated maps—closely related to Poincaré maps—that describe chaotic interactions between colliding solitary waves. The chaotic behavior of such solitary-wave collisions depends on the transfer of energy to a secondary mode of oscillation, often an internal mode of the pulse. This map allows us to go beyond previous analyses and to understand the interactions in the case when this mode is excited prior to the first collision. The map is derived using Melnikov integrals and matched asymptotic expansions and generalizes a “multipulse” Melnikov integral. It allows one to find not only multipulse heteroclinic orbits, but exotic periodic orbits. The maps exhibit singular behavior, including regions of infinite winding. These maps are shown to be singular versions of the conservative Ikeda map from laser physics and connections are made with problems from celestial mechanics and fluid mechanics.
Quantized acoustoelectric current in an InGaAs quantum well
Authors: Astley M. R. , Kataoka M. , Ford C. J. B. , Barnes C. H. W. , Godfrey M. D. , Farrer I. , Ritchie D. A. , Anderson D. , Jones G. A. C. , Pepper M. , Holmes S. N.
Published: May 2008

We have measured the acoustoelectric current generated in a GaAs∕Al0.33Ga0.67As heterostructure incorporating an In0.1Ga0.9As layer at the heterointerface. This wafer is designed to give a two-dimensional electron gas with a high electron g factor. We demonstrate that this wafer is of sufficient quality to produce quantized acoustoelectric current plateaus and has potential for future spintronic and quantum information technology applications.
On the impact testing of cyclotrimethylene trinitramine crystals with different internal qualities
Authors: Bouma R. H. B. , Boluijt A. G. , Verbeek H. J. , van der Heijden A. E. D. M.
Published: May 2008

Impact testing of various cyclotrimethylene trinitramine (RDX) samples has been carried out with the Ballistic Impact Chamber (BIC). Numerical simulations have been performed to guide its experimental design and explain the phenomena that are observed in the measured pressure evolution. The experimental results obtained with the BIC are compared to the RDX crystal quality observed by optical and scanning electron microscopies. The reactivity of RDX in the impact testing with the BIC correlates with the crystal quality and this opens up the possibility of achieving a quantitative determination of the crystal quality.
Parametric polarization pulse shaping demonstrated for optimal control of NaK
Authors: Weber Stefan M. , Plewicki Mateusz , Weise Fabian , Lindinger Albrecht
Published: May 2008

We present a routine for calculating and producing customized/parametric femtosecond laser pulses for investigating molecular processes involving the polarization. It is applied on the ionization of NaK molecules by feedback-loop optimization using the recently introduced double-pass “serial setup” that is capable of phase, amplitude, and polarization modulation. The temporal subpulse encoding uses the parameters distance, intensity, zero order spectral phase, and polarization state.
Design of fast state observers using a backstepping-like approach with application to synchronization of chaotic systems
Authors: Zaher Ashraf A.
Published: May 2008

A simple technique is introduced to build fast state observers for chaotic systems when only a scalar time series of the output is available. This technique relies on using a backstepping-like approach via introducing new virtual states that can be observed using the drive-response synchronization mechanism. The proposed dynamic structure of the virtual states allows for employing control parameters that can adjust the convergence rate of the observed states. In addition, these control parameters can be used to improve the transient performance of the response system to accommodate small and large variations of the initial conditions, thus achieving superior performance to conventional synchronization techniques. Simple Lyapunov functions are used to estimate the range of the control parameters that guarantees stable operation of the proposed technique. Three benchmark chaotic systems are considered for illustration; namely, the Lorenz, Chua, and Rössler systems. The conflict between stability and agility of the states observer is analyzed and a simple tuning mechanism is introduced. Implementation of the proposed technique in both analog and digital forms is also addressed and experimental results are reported ensuring feasibility and real-time applicability. Finally, advantages and limitations are discussed and a comparison with conventional synchronization methods is investigated.
Discontinuity breakdown on shock wave interaction with nanosecond discharge
Authors: Znamenskaya I. A. , Koroteev D. A. , Lutsky A. E.
Published: May 2008

Discontinuity breakdown conditions were experimentally realized by instant energy input in front of a plane shock wave. A shock tube and a special type of transversal nanosecond electric discharge with plasma electrodes were used for this research. A two-dimensional (2D) numerical simulation under experimental conditions has been undertaken. The pressure, density, temperature, and velocity fields have been examined. A comparison of numerical data and shadow images of a 2D flow after shock wave interaction with the discharge area was conducted. The geometry of the disturbed flowfield was found to be in good correspondence with one from numerical calculations. The results of the investigation also showed that, by using the described experimental setup, it is possible to achieve a special type of Richtmyer–Meshkov instability without applying an additional curved diaphragm.
Dependence of plasmon polaritons on the thickness of indium tin oxide thin films
Authors: Rhodes C. , Cerruti M. , Efremenko A. , Losego M. , Aspnes D. E. , Maria J.-P. , Franzen S.
Published: May 2008

The evolution of polariton features with increasing thickness in p-polarized (TM) reflectance spectra of indium tin oxide (ITO) thin films deposited on BK7 glass reveals the nature of plasmons in conducting thin films without interference from band-to-band transitions or the tendency of very thin films to form islands, both of which are complicating factors with the noble metals Au and Ag. Although the dependence on energy, film thickness, and angle of incidence is complex, these features are accurately described by the three-phase (substrate/overlayer/ambient) Fresnel model using only the Drude free-electron representation for the dielectric function of the ITO film. For film thicknesses less than 80nm the relevant excitation is a one-dimensional screened-bulk plasmon (SBP) that corresponds to charge transfer across the entire film. The associated SBP polariton (SBPP) occurs at the energy of the SBP and is relatively independent of the angle of incidence. For film thicknesses greater than 120nm, the relevant excitation is the surface plasmons (SP). The associated surface plasmon polariton (SPP) exhibits the usual strong dependence of energy on the angle of incidence. For larger thicknesses this structure gradually weakens, in agreement with theory. No other collective excitations are observed. The optimum thicknesses for the SPP in ITO is 160nm, whereas the SBPP is observed only when the film thickness is less than 70nm. The SBPP exhibits many of the features that make the SPP attractive for both science and technology, but has not been observed previously. Our results show that ITO films, in particular, and conducting-metal-oxide films in general provide new opportunities for investigating plasmons in conductors and obtaining new insights into plasmons, plasmon polaritons, and related optical phenomena.
Determination of carrier mobility in phenylamine by time-of-flight, dark-injection, and thin film transistor techniques
Authors: Cheung C. H. , Kwok K. C. , Tse S. C. , So S. K.
Published: May 2008

The hole transport property of a phenylamine-based compound, 4, 4′,4″-tris(n- (2-naphthyl)-n-phenyl-amino)-triphenylamine, was independently studied by time-of-flight (TOF), dark-injection space-charged-limited-current (DI-SCLC), and thin film transistor (TFT) techniques. With UV-ozone treated gold as the injecting anode, clear DI-SCLC transient peaks were observed over a wide range of electric fields. The hole mobilities evaluated by DI-SCLC experiment were in excellent agreement with the mobilities obtained from the TOF technique. The injection contact was demonstrated to be Ohmic by an independent current-voltage (J-V) experiment. However, with the same injecting electrode, the mobility deduced from the TFT method was found to be 9.8×10−7 cm2/V s, which was about one order of magnitude smaller than the TOF mobility (∼1.2 ×10−5 cm2/V s). The origin of the discrepancy is discussed.
Single-pulse excimer laser nanostructuring of silicon: A heat transfer problem and surface morphology
Authors: Eizenkop Julia , Avrutsky Ivan , Georgiev Daniel G. , Chaudchary Vipin
Published: May 2008

We present computer modeling along with experimental data on the formation of sharp conical tips on silicon-based three-layer structures that consist of a single-crystal Si layer on a 1 μm layer of silica on a bulk Si substrate. The upper Si layers with thicknesses in the range of 0.8−4.1 μm were irradiated by single pulses from a KrF excimer laser focused onto a spot several micrometers in diameter. The computer simulation includes two-dimensional time-dependent heat transfer and phase transformations in Si films that result from the laser irradiation (the Stefan problem). After the laser pulse, the molten material self-cools and resolidifies, forming a sharp conical structure, the height of which can exceed 1 μm depending on the irradiation conditions. We also performed computer simulations for experiments involving single-pulse irradiation of bulk silicon, reported by other groups. We discuss conditions under which different types of structures (cones versus hollows) emerge. We confirm a correlation between the presence of the lateral resolidification condition after the laser pulse and the presence of conical structures on a solidified surface.
Wave propagation in double-walled carbon nanotubes conveying fluid
Authors: Natsuki Toshiaki , Ni Qing-Qing , Hayashi Takuya , Endo Morinobu
Published: May 2008

Carbon nanotubes may hold scientific promise in nanotechnology as nanopipes conveying fluid. In this paper, the wave propagation in double-walled carbon nanotubes (DWCNTs) conveying fluid is studied based on the Euler–Bernoulli beam theory. The influences of internal moving fluids, such as flow velocity and mass density of fluids, on the sound wave propagation of DWCNTs or the DWCNTs embedded in an elastic matrix are investigated in detail. The DWCNTs are considered as a two-shell model coupled together through the van der Waals interaction between two adjacent nanotubes. According to the proposed theoretical approach, the results indicate that fluid flow through carbon nanotubes affects the wave speed and the critical frequency in the carbon nanotubes. The amplitude ratios of the inner to outer nanotubes are largely affected by the fluid velocity and density when the vibrational frequency in nanotubes is larger than 1.5 Hz. The theoretical investigation may give a useful reference for potential application and design of nanoelectronics and nanodevices.