bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulating the dynamics of genes and environment in development
Authors: Turkheimer Eric , Gottesman Irving I.
Published: March 2009

Biometric analyses of variability in behavioral phenotypes have demonstrated that genotype plays a significant role in all behavioral development, but the developmental significance of the environment has remained obscure. Behavior genetic analyses typically show the effect of shared family environment to be very small, although considerable variability remains to be explained after genetic factors have been accounted for. Behavior geneticists have suggested, contrary to intuition, that almost all of the important effects of the environment serve to make family members more different from each other. Environmentalists of several persuasions have pointed to the crucial importance of the environment in the initiation and regulation of all developmental processes. In this article, we present a series of simulations to suggest that some of the difficulty of identifying environmental effects in biometric models is methodological. Adding simple dynamic parameters to models of development leads to systems in which environment produces substantial variability that can be detected in the context of a particular genotype, but vanishes when genotype is allowed to vary.
Boys' externalizing problems at elementary school age: Pathways from early behavior problems, maternal control, and family stress
Authors: Campbell Susan B. , Pierce Elizabeth W. , Moore Ginger , Marakovitz Susan , Newby Kristin
Published: March 2009

Hard-to-manage preschool boys and comparison boys were studied at age 4 years and followed at ages 6 and 9 years. Externalizing problems at ages 4 and 9 were associated with concurrent family stress, but this relationship was partially mediated by negative maternal control. Cross-lagged regressions indicated that despite the high stability in children's problem ratings, observed negative maternal control at age 4 and self-reported negative discipline at age 9 predicted externalizing problems at age 9 years, controlling for earlier levels of symptoms. Hierarchical regression analyses revealed that problems were more likely to persist in the context of chronic family stress, defined as negative life events, marital dissatisfaction, and maternal depressive symptoms. When problem boys who met diagnostic criteria for Oppositional Disorder and/or Attention Deficit Disorder were compared with boys who were improved by age 9 years, family stress and earlier symptom levels, as well as maternal control differentiated between them. Teacher ratings suggested that these boys were on a clear pathway to persistent problems by age 6 years. A small sample of comparison boys with emerging problems also were living in more dysfunctional families and their mothers reported using more negative discipline at age 9 years.
Longitudinal stability and change in consumption among female twins: Contributions of genetics
Authors: Prescott Carol A. , Kendler Kenneth S.
Published: March 2009

Problem alcohol use among women is increasingly recognized as an important public health and mental health issue. Younger women appear to be at increased risk for heavy drinking and alcohol-related problems compared to women from earlier cohorts. Understanding the sources for inter- and intra-individual differences in alcohol consumption is an important first step in addressing these trends. We studied the sources underlying variation in alcohol consumption in a sample of 2,163 female twins born in Virginia between 1934 and 1970. Measures of past-year alcohol consumption quantity and frequency were obtained on two occasions across a 5-year interval. Quantity and frequency of consumption declined over age, both cross-sectionally and longitudinally. Intra-individual correlations over the interval were substantial for frequency of drinking (r= .62) and quantity consumed per drinking occasion (r= .56) but lower for quantity consumed weekly (r= .22). There was significant intrapair resemblance for all measures, with the drinking behavior of identical twin pairs being more similar than that of fraternal pairs. Twin analyses of patterns of change in consumption over a 5-year interval revealed little within-pair similarity in rate of change, with correlations ranging from .06 to .18, suggesting that among young adult to middle-aged women, determinants of changing alcohol consumption are largely individual-specific. There was some evidence for significant age interactions, with the role of individual-specific sources increasing over age.
Self and personality in old and very old age: A sample case of resilience?
Authors: Staudinger U. M. , Fleeson W.
Published: March 2009

Characteristics and processes linked to self and personality functioning are considered as illustrations of resilience in old and very old age. Two self-related processes—coping styles and personal life investment—are investigated as examples of internal resources that the aging person may bring to bear when dealing with the risks of old age. Beyond chronological age as a rough approximation of such risks, this article specifically explores the relationship between physical risks, self-related processes, and level of adaptation in a representative sample of 70- to 103-year-olds. The central hypothesis is that self-related processes may buffer age-related risks, and may to a certain degree preserve or avoid large drops in levels of adaptation. Working on a correlational level of analysis, results indicated that well into old age, the self is able to maintain a relatively high level of adaptation. Also, under conditions of a high degree of physical constraints: (a) both coping styles and personal life investment were associated with resilience; (b) beyond particular coping styles, a selective flexibility in coping was associated with resilience. The degree of physical constraints moderated (c) the adaptiveness of several coping styles and of personal life investment; and (d) extreme physical constraints appeared to limit the possibilities of resilience. The effect of physical constraints on level of adaptation in turn was moderated by age. Consistent with a life-span theory of development, results are interpreted as an example of evidence for the resilience of the aging self and its limits.
Algebra of constructions II: an algebraic approach to Martin-Löf type theory and the calculus of constructions
Authors: Obtułowicz Adam
Published: March 2009

We present an algebraic approach to the syntax and semantics of Martin-Löf type theory and the calculus of constructions developed by T. Coquand and G. Huet. In our approach, models of this theory and this calculus are treated as three-sorted partial algebras, called ITSΠ-structures, described by essentially algebraic theories. We give a proof that derived statements of Martin-Löf type theory hold in appropriate ITSΠ-structures. In this proof, a formal translation from the language of terms and types into the language of terms of an appropriate essentially algebraic theory of ITSΠ-structures is used. A straightforward set-theoretic construction of ITSΠ-structures that are models of Martin-Löf type theory is demonstrated. We present a construction of a recursive ITSΠ-structure(i.e. its partial and total operations are recursive functions over some alphabet) that is a model of the calculus of constructions and demonstrates the decidability of this calculus.
The theory of semi-functors
Authors: Hoofman Raymond
Published: March 2009

The notion ofsemi-functorwas introduced in Hayashi (1985) in order to make possible a category-theoretical characterization of models of the non-extensional typed lambda calculus. Motivated by the further use of semi-functors in Martini (1987), Jacobs (1991) and Hoofman (1992a), (1992b) and (1992c), we consider the general theory of semi-functors in this paper. It turns out that the notion ofsemi natural transformationplays an important part in this theory, and that various categorical notions involving semi-functors can be viewed as 2-categorical notions in the 2-category of categories, semi-functors and semi natural transformations. In particular, we find that the notion ofnormal semi-adjunctionas defined in Hayashi (1985) is the canonical generalization of the notion of adjunction to the world of semi-functors. Further topics covered in this paper are the relation between semi-functors and splittings, the Karoubi envelope construction, semi-comonads, and a semi-adjoint functor theorem.
Quantales, observational logic and process semantics
Authors: Abramsky Samson , Vickers Steven
Published: March 2009

Various notions of observing and testing processes are placed in a uniform algebraic framework in which observations are taken as constituting a quantale. General completeness criteria are stated, and proved in our applications.
An application of PER models to program extraction
Authors: Berardi Stefano
Published: March 2009

Type theory allows us to extract from a constructive proof that a specification is satisfiable a program that satisfies the specification. Algorithms for optimization of such programs are currently the object of research.

In this paper we consider one such algorithm, which was described in Beeson (1985) and which we will call ‘Harrop’. This algorithm greatly simplifies programs extracted from proofs in the Pure Construction Calculus. We use a Partial Equivalence Relation model for higher order lambda calculus, to check that t and Harrop(t) return the same outputs from the same inputs, i.e. that they are extensionally equal.

As a corollary, we show that it is correct (and, of course, useful) to replace a program t with Harrop(t). Such a correctness result has already been proved by Möhring (Möhring 1989a, 1989b) using realizability semantics, but we obtain it as a corollary of a new result, the extensional equality between t and Harrop(t). Also the semantic method we use is interesting in its own right.
A model for syntactic control of interference
Authors: O'Hearn P. W.
Published: March 2009

Two imperative programming language phrases interfere when one writes to a storage variable that the other reads from or writes to. Reynolds has described an elegant linguistic approach to controlling interference in which a refinement of typed λ-calculus is used to limit sharing of storage variables; in particular, different identifiers are required never to interfere. This paper examines semantic foundations of the approach.

We describe a category that has (an abstraction of) interference information built into all objects and maps. This information is used to define a ‘tensor’ product whose components are required never to interfere. Environments are defined using the tensor, and procedure types are obtained via a suitable adjunction. The category is a model of intuitionistic linear logic. Reynolds' concept of passive type - i.e. types for phrases that do not write to any storage variables - is shown to be closely related, in this model, to Girard's ‘of course’ modality.
Recognizable sets of graphs: equivalent definitions and closure properties
Authors: Courcelle Bruno
Published: March 2009

The notion of a recognizable set of words, trees or graphs is relative to an algebraic structure on the set of words, trees or graphs respectively. We establish that several algebraic structures yield the same notion of a recognizable set of graphs. This notion is equivalent to that of a fully cutset-regular set of graphs introduced by Fellows and Abrahamson. We also establish that the class of recognizable sets of graphs is closed under the operations considered in these various equivalent definitions. This fact is not a standard consequence of the definition of recognizability.
A remark on the theory of semi-functors
Authors: Hoofman R. , Moerdijk I.
Published: March 2009

By establishing an appropriate equivalence, we observe that the theory of semi-functors can be fully embedded in the theory of (ordinary) functors. As a result, standard properties and constructions on functors extend automatically to semi-functors.
Equivalence and difference between institutions: simulating Horn Clause Logic with based algebras
Authors: Kreowski Hans-Jörg , Mossakowski Till
Published: March 2009

In this paper, we investigate several logical frameworks whose expressiveness lies between Conditional Equational Logic and Horn Clause Logic. The main result deals with thePART-construction, which interprets total based algebras as partial algebras. This construction can be viewed as a simulation of Horn Clause Theories by means of Conditional Equational Theories. Other constructions in other frameworks are extendable to simulations in a similar way. The notion of categorical retractive simulation captures some essential properties of these, which allows us to measure the equivalence and difference between institutions.
Strong normalization with non-structural subtyping
Authors: Wand Mitchell , O'Keefe Patrick , Palsberg Jens
Published: March 2009

We study a type system with a notion of subtyping that involves a largest type ⊤, a smallest type ⊥, atomic coercions between base types, and the usual ordering of function types. We prove that any λ-term typable in this system is strongly normalizing, which solves an open problem of Thatte. We also prove that the fragment without ⊥ types has strictly fewer terms. This demonstrates that ⊥ adds power to a type system.
A categorical approach to the semantics of argumentation
Authors: Ambler Simon
Published: March 2009

Argumentation is a proof theoretic paradigm for reasoning under uncertainty. Whereas a ‘proof’ establishes its conclusion outright, an ‘argument’ can only lend a measure of support. Thus, the process of argumentation consists of identifying all the arguments for a particular hypothesis φ, and then calculating the support for φ from the weight attached to these individual arguments. Argumentation has been incorporated as the inference mechanism of a large scale medical expert system, the ‘Oxford System of Medicine’ (OSM), and it is therefore important to demonstrate that the approach is theoretically justified. This paper provides a formal semantics for the notion of argument embodied in the OSM. We present a categorical account in which arguments are the arrows of a semilattice enriched category. The axioms of a cartesian closed category are modified to give the notion of an ‘evidential closed category’, and we show that this provides the correct enriched setting in which to model the connectives of conjunction (&) and implication (⇒).

Finally, we develop a theory of ‘confidence measures’ over such categories, and relate this to the Dempster-Shafer theory of evidence.
Hopf algebras and linear logic
Authors: Blute Richard F.
Published: March 2009

It has recently become evident that categories of representations ofHopf algebrasprovide fundamental examples of monoidal categories. In this expository paper, we examine such categories as models of (multiplicative) linear logic. By varying the Hopf algebra, it is possible to model several variants of linear logic. We present models of the original commutative logic, the noncommutative logic of Lambek and Abrusci, the braided variant due to the author, and the cyclic logic of Yetter. Hopf algebras provide a unifying framework for the analysis of these variants. While these categories are monoidal closed, they lack sufficient structure to model the involutive negation of classical linear logic. We recall work of Lefschetz and Barr in which vector spaces are endowed with an additional topological structure, calledlinear topology. The resulting category has a large class of reflexive objects, which form a *-autonomous category, and so model the involutive negation. We show that the monoidal closed structure of the category of representations of a Hopf algebra can be extended to this topological category in a natural and simple manner. The models we obtain have the advantage of being nondegenerate in the sense that the two multiplicative connectives, tensor and par, are not equated. It has been recently shown by Barr that this category of topological vector spaces can be viewed as a subcategory of a certain Chu category. In an Appendix, Barr uses this equivalence to analyze the structure of its tensor product.
Interpolation and compactness in categories of pre-institutions
Authors: Salibra Antonino , Scollo Giuseppe
Published: March 2009

An analysis of relationships between Craig-style interpolation, compactness, and other related model-theoretic properties is carried out in the softer framework of categories of pre-institutions. While the equivalence between sentence interpolation and the Robinson property under compactness and Boolean closure is well known, a similar result under different assumptions (not involving compactness) is newly established for presentation interpolation. The standard concept of naturality of model transformation is enriched by a new property, termed restriction adequacy, which proves useful for the reduction of interpolation along pre-institution transformations. A distinct reduction theorem for the Robinson property is presented as well. A variant of the ultraproduct concept is further introduced, and the related closure property for pre-institutions is shown to be equivalent to compactness
Functional completeness of the free locally Cartesian closed category and interpretations of Martin-Löf's theory of dependent types
Authors: Preller A. , Simonet G.
Published: March 2009

We establish functional completeness of Locally Cartesian Closed Categories by axiomatising the theory of LCCC's in a constructive style. As a consequence we show that there is essentially only one interpretation of Martin-Löf's theory of types with extensional equality in the theory of LCCC's.
A formalism for the specification of essentially-algebraic structures in 2-categories
Authors: Power A. J. , Wells Charles
Published: March 2009

A type of higher-order two-dimensional sketch is defined which has models in suitable 2-categories. It has as special cases the ordinary sketches of Ehresmann and certain previously defined generalizations of one-dimensional sketches. These sketches allow the specification of constructions in 2-categories such as weighted limits, as well as higher-order constructions such as exponential objects and subobject classifiers, that cannot be sketched by limits and colimits. These sketches are designed to be the basis of a category-based methodology for the description of functional programming languages, complete with rewrite rules giving the operational semantics, that is independent of the usual specification methods based on formal languages and symbolic logic. A definition of ‘path grammar’, generalizing the usual notion of grammar, is given as a step towards this goal.
Girard quantaloids
Authors: Rosenthal Kimmo I.
Published: March 2009

The partially ordered models of linear logic, a logical system developed by J. Y. Girard, turn out to be a class of quantales called Girard quantales. The notion of a quantaloid is a natural categorical generalization of a quantale and is one possible way of keeping track of types. In this paper, Girard quantales are generalized to Girard quantaloids. The general theory is developed and several key examples are studied. Turning our attention to the theory of categories enriched in a bicategory, it is then shown that if G is a Girard quantaloid, then the quantaloids Bim(G), Matr(G), and Mon(G), consisting of G-bimodules, G-matrices and G-monads respectively, are also Girard quantaloids.
Pre-adjunctions in order enriched categories
Authors: Martin C. E. , Hoare C. A. R. , Jifeng He
Published: March 2009

Category theory offers a unified mathematical framework for the study of specifications and programs in a variety of styles, such as procedural, functional and concurrent. One way that these different languages may be treated uniformly is by generalising the definitions of some standard categorical concepts. In this paper we reproduce in the generalised theory analogues of some standard theorems on isomorphism, and outline their applications to programming languages.
*-Autonomous categories and linear logic
Authors: Barr Michael
Published: March 2009

The subject of linear logic has recently become very important in theoretical computer science. It is apparent that the *-autonomous categories studied at length in by Barr (1979) are a model for a large fragment of linear logic, although not quite for the whole thing. Since the main reference is out of print and since large parts of that volume are devoted to results highly peripheral to the matter at hand, it seemed reasonable to provide a short introduction to the subject.
Parallelism and concurrency in high-level replacement systems
Authors: Ehrig Hartmut , Habel Annegret , Kreowski Hans-Jörg , Parisi-Presicce Francesco
Published: March 2009

High-level replacement systems are formulated in an axiomatic algebraic framework based on categories pushouts. This approach generalizes the well-known algebraic approach to graph grammars and several other types of replacement systems, especially the replacement of algebraic specifications which was recently introduced for a rule-based approach to modular system design.

in this paper basic notions like productions, derivations, parellel and sequential independence are introduced for high-level replacement syetms leading to Church-Rosser, Parallelism and concurrency Theorems previously shown in the literature for special cases only. In the general case of high-level replacement systems specific conditions, called HLR1- and HLR2-conditions, are formulated in order to obtain these results.

Several examples of high-level replacement systems are discussed and classified w.r.t. HLR1- and HLR2-conditions showing which of the results are valid in each case.
Provable isomorphisms of types
Authors: Bruce Kim B. , Di Cosmo Roberto , Longo Giuseppe
Published: March 2009

A constructive characterization is given of the isomorphisms which must hold in all models of the typed lambda calculus with surjective pairing. Using the close relation between closed Cartesian categories and models of these calculi, we also produce a characterization of those isomorphisms which hold in all CCC's. Using the correspondence between these calculi and proofs in intuitionistic positive propositional logic, we thus provide a characterization of equivalent formulae of this logic, where the definition of equivalence of terms depends on having “invertible” proofs between the two terms. Work of Rittri (1989), on types as search keys in program libraries, provides an interesting example of use of these characterizations.
An imperative language based on distributive categories
Authors: Walters R. F. C.
Published: March 2009

It is the contention of the author that there is a preferred categorical structure appropriate for the analysis of imperative programming languages, namely the existence of finite sums and products and a distributive law of products over sums. An imperative language based on these operations is described.
From operational semantics to abstract machines
Authors: Hannan John , Miller Dale
Published: March 2009

We consider the problem of mechanically constructing abstract machines from operational semantics, producing intermediate-level specifications of evaluators guaranteed to be correct with respect to the operational semantics. We construct these machines by repeatedly applying correctness-preserving transformations to operational semantics until the resulting specifications have the form of abstract machines. Though not automatable in general, this approach to constructing machine implementations can be mechanized, providing machine-verified correctness proofs. As examples, we present the transformation of specifications for both call-by-name and call-by-value evaluation of the untyped λ-calculus into abstract machines that implement such evaluation strategies. We also present extensions to the call-by-value machine for a language containing constructs for recursion, conditionals, concrete data types, and built-in functions. In all cases, the correctness of the derived abstract machines follows from the (generally transparent) correctness of the initial operational semantic specification and the correctness of the transformations applied.
Reactivation of ancient rift systems triggers devastating intraplate earthquakes
Authors: Kato Aitaro , Kurashimo Eiji , Igarashi Toshihiro , Sakai Shinichi , Iidaka Takashi , Shinohara Masanao , Kanazawa Toshihiko , Yamada Tomoaki , Hirata Naoshi , Iwasaki Takaya
Published: March 2009

Large historical and recent intraplate earthquakes have been concentrated along a contractional zone at the eastern margin of the Japan Sea back‐arc basin. Here we present high‐resolution three‐dimensional tomographic imaging of seismic velocities in this zone using data from a dense seismograph deployment. We discover that stepwise and tilted block structures of the basement, which are geophysical evidence of a Miocene rift system, are widely distributed beneath the thick sedimentary basin. Most aftershocks following recent intraplate earthquakes align roughly along the tilted block boundaries and are controlled by weaknesses associated with buried rift systems. Furthermore, slow anomalies are localized beneath the seismogenic zones, suggesting that fluids may have locally weakened the strength of the lower crust. We propose that stress loading through ductile creeping of the weak lower crust reactivates pre‐existing weak faults within ancient rift systems, leading to devastating intraplate earthquakes.
Chemical nonlinearities in relating intercontinental ozone pollution to anthropogenic emissions
Authors: Wu Shiliang , Duncan Bryan N. , Jacob Daniel J. , Fiore Arlene M. , Wild Oliver
Published: March 2009

Model studies typically estimate intercontinental influence on surface ozone by perturbing emissions from a source continent and diagnosing the ozone response in the receptor continent. Since the response to perturbations is non‐linear due to chemistry, conclusions drawn from different studies may depend on the magnitude of the applied perturbation. We investigate this issue for intercontinental transport between North America, Europe, and Asia with sensitivity simulations in three global chemical transport models. In each region, we decrease anthropogenic emissions of NOx and nonmethane volatile organic compounds (NMVOCs) by 20% and 100%. We find strong nonlinearity in the response to NOx perturbations outside summer, reflecting transitions in the chemical regime for ozone production. In contrast, we find no significant nonlinearity to NOx perturbations in summer or to NMVOC perturbations year‐round. The relative benefit of decreasing NOx vs. NMVOC from current levels to abate intercontinental pollution increases with the magnitude of emission reductions.
High‐CO2 cloud radiative forcing feedback over both land and ocean in a global climate model
Authors: Abbot Dorian S. , Huber Matthew , Bousquet Gabriel , Walker Chris C.
Published: March 2009

A positive feedback on high‐latitude winter marine climate change involving convective clouds has recently been proposed using simple models. This feedback could help explain data from equable climates, e.g., the Eocene, and might be relevant for future climate. Here this convective cloud feedback is shown to be active in an atmospheric GCM in modern configuration (CAM) at CO2 = 2240 ppm and in a coupled GCM in Eocene configuration (CCSM) at CO2 = 560 ppm. Changes in boundary conditions that increase surface temperature have a similar effect as increases in CO2 concentration. It is also found that the high‐latitude winter cloud radiative forcing over land increases with increases in surface temperature due to either increased CO2 or changes in boundary conditions, which could represent an important part of the explanation for warm continental interior winter surface temperatures during equable climates. This is due to increased low‐level layered clouds caused by increased relative humidity.
Real‐time earthquake detection and hazard assessment by ElarmS across California
Authors: Allen Richard M. , Brown Holly , Hellweg Margaret , Khainovski Oleg , Lombard Peter , Neuhauser Douglas
Published: March 2009

ElarmS is a network‐based methodology for rapid earthquake detection, location and hazard assessment in the form of magnitude estimation and peak ground motion prediction. The methodology is currently being tested as part of the real‐time seismic system in California leveraging the resources of the California Integrated Seismic Network (CISN) and the Advanced National Seismic System. A total of 603 velocity and acceleration sensors at 383 sites across the state stream waveform data to ElarmS processing modules at three network processing centers where waveforms are reduced to a few parameters. These parameters are then collected and processed at UC Berkeley to provide a single statewide prediction of future ground shaking that is updated every second. The system successfully detected the Mw 5.4 Alum Rock earthquake in northern California for which it generated an accurate hazard prediction before peak shaking began in San Francisco. It also detected the Mw 5.4 Chino Hills earthquake in southern California. The median system latency is currently 11.8 sec; the median waveform data latency is 6.5 sec.
Selective absorption mechanism for the maintenance of blocking
Authors: Yamazaki Akira , Itoh Hisanori
Published: March 2009

A new maintenance mechanism of blocking is proposed; a blocking high, which is characterized by low potential vorticity, selectively absorbs synoptic highs, thereby maintaining its own low potential vorticity. It is shown that the effectiveness of the new mechanism is verified by two case studies of blocking events and simple numerical experiments.
Terminal versus transient cumulus congestus: A CloudSat perspective
Authors: Luo Zhengzhao , Liu G. Y. , Stephens Graeme L. , Johnson Richard H.
Published: March 2009

While cumulus congestus as an important mode of tropical convection has been established, many of the previous studies that rely on radar observations usually capture them as snapshots. A logical question to consider is: are the statistics gathered from snapshot observations of cumulus congestus really reflective of this mode of convection that ceases its growth at these intermediate levels (terminal cumulus congestus), or will the convection being observed continue to ascend to greater altitudes to become deep convection at a later time (transient cumulus congestus)? This short article strives to answer this question by analyzing simultaneous, independent measurements of CTH and CTT from CloudSat and MODIS, together with CloudSat radar profile and collocated ECMWF analysis. It is found, based on analysis of one year of data, that a significant fraction (∼30–40%) of the tropical cumulus congestus observed by the snapshot views are in transient mode that will ascend to greater altitude at a later time. The analysis concept used in this study, which gives “static” snapshot observations some “dynamic” context, can be applied to analyze convection of all types.
Field‐aligned currents of postnoon auroral arcs
Authors: Kozlovsky Alexander , Turunen Tauno , Massetti Stefano
Published: March 2009

On 9 January 2008, postnoon (at about 15–16 magnetic local time [MLT]) poleward moving auroral arcs were observed over Svalbard during slightly negative interplanetary magnetic field (IMF) Bz and the IMF By gradually changing from near zero to about −3 nT. The arcs appeared from the western (dayside) horizon and developed toward the east coming to the postnoon sector. The steerable 32‐m antenna of the European Incoherent Scatter (EISCAT) radar was directed at an elevation angle of 45° to the north‐west at about 45° to geomagnetic west, allowing for measurement of azimuthal (along east‐west) plasma flow in a range of latitudes. On the basis of this radar configuration, a new method has been developed and applied for calculating the field‐aligned currents (FACs) in the vicinity of the arcs. The arcs were located in the region of the postnoon convection reversal, and the background upward FAC had a density of about 1 μA/m2. The optical arcs were of the order of 30–40 km wide and coincided with peaks of upward FAC. The return downward FAC and the southward electric field were observed poleward of the arcs. Equatorward of the arcs, secondary weaker arcs were detected so that the postnoon arcs appear to have a double structure. These features are surprisingly similar to the electric field and current patterns of morning Sun‐aligned arcs. We suggest that the double arc structure can be explained by the nonlinear ionospheric feedback that results in splitting of the elongated magnetospheric plasma structures associated with the arcs.
Nickel-Carbon Bonds in Acetyl-Coenzyme A Synthases/Carbon Monoxide Dehydrogenases
Authors: Lindahl Paul A.
Published: March 2009

Acetyl-coenzyme A synthases/carbon monoxide dehydrogenases are bifunctional enzymes that catalyze the synthesis of acetyl-CoA and the reversible reduction of CO2 to CO. The active site for the first reaction, called the A-cluster, consists of a [Fe4S4] cubane bridged to a dinuclear nickel subcomponent. The active site for the second reaction, the C-cluster, consists of a [Fe3S4] subsite linked to a Ni-Fe dinuclear site. There is evidence for the formation of five Ni-C bonds, involving methyl, acetyl, carbonyl, and carboxylate groups. In this review, the current evidence for each of these bonds is described. The mechanism of catalysis is discussed, highlighting the role of these species. The unique coordination environments of nickel that may facilitate the formation of organometallic species is discussed. Current puzzles in the field and future research directions that might resolve them are outlined.
Structure and Function of [NiFe]-Hydrogenases
Authors: Fontecilla-Camps Juan C.
Published: March 2009

[NiFe(Se)]-hydrogenases are hetero-dimeric enzymes present in many microorganisms where they catalyze the oxidation of molecular hydrogen or the reduction of protons. Like the other two types of hydrogen-metabolizing enzymes, the [FeFe]- and [Fe]-hydrogenases, [NiFe]-hydrogenases have a Fe(CO)x unit in their active sites that is most likely involved in hydride binding. Because of their complexity, hydrogenases require a maturation machinery that involves several gene products. They include nickel and iron transport, synthesis of CN− (and maybe CO), formation and insertion of a FeCO(CN−)2 unit in the apo form, insertion of nickel and proteolytic cleavage of a C-terminal stretch, a step that ends the maturation process. Because the active site is buried in the structure, electron and proton transfer are required between this site and the molecular surface. The former is mediated by either three or one Fe/S cluster(s) depending on the enzyme. When exposed to oxidizing conditions, such as the presence of O2, [NiFe]-hydrogenases are inactivated. Depending on the redox state of the enzyme, exposure to oxygen results in either a partially reduced oxo species probably a (hydro)peroxo ligand between nickel and iron or a more reduced OH– ligand instead. Under some conditions the thiolates that coordinate the NiFe center can be modified to sulfenates. Understanding this process is of biotechnological interest for H2 production by photosynthetic organisms.
Carbon Monoxide and Cyanide Ligands in the Active Site of [FeFe]-Hydrogenases
Authors: Peters John W.
Published: March 2009

The [FeFe]-hydrogenases, although share common features when compared to other metal containing hydrogenases, clearly have independent evolutionary origins. Examples of [FeFe]-hydrogenases have been characterized in detail by biochemical and spectroscopic approaches and the high resolution structures of two examples have been determined. The active site H-cluster is a complex bridged metal assembly in which a [4Fe-4S] cubane is bridged to a 2Fe subcluster with unique non-protein ligands including carbon monoxide, cyanide, and a five carbon dithiolate. Carbon monoxide and cyanide ligands as a component of a native active metal center is a property unique to the metal containing hydrogenases and there has been considerable attention to the characterization of the H-cluster at the level of electronic structure and mechanism as well as to defining the biological means to synthesize such a unique metal cluster. The chapter describes the structural architecture of [FeFe]-hydrogenases and key spectroscopic observations that have afforded the field with a fundamental basis for understanding the relationship between structure and reactivity of the H-cluster. In addition, the results and ideas concerning the topic of H-cluster biosynthesis as an emerging and fascinating area of research, effectively reinforcing the potential linkage between iron-sulfur biochemistry to the role of iron-sulfur minerals in prebiotic chemistry and the origin of life.
The Evolution of Diagnosing Benign Vocal Fold Lesions: From Vague to Specific
Authors: Gartner-Schmidt Jackie L. , Rosen Clark A.
Published: March 2009

The evaluation and treatment process for dysphonia due to benign vocal fold lesions (BVFL) can often be a complex and confusing process for clinicians as well as patients. There is no one perfect method, and there are many different approaches to this problem. It is our goal to share our multidisciplinary team evaluation process, decision-making approach, and treatment for patients with these types of voice fold lesions. Our goal is to highlight the teamwork and cross disciplinary cooperation that optimizes patient evaluation and care.
Spin-dependent tunneling through NiFe nanoparticles
Authors: Dempsey K. J. , Hindmarch A. T. , Marrows C. H. , Wei H.-X. , Qin Q.-H. , Wen Z.-C. , Han X.-F.
Published: March 2009

Double magnetic tunnel junctions (DMTJs) have been fabricated using alumina barriers with NiFe particles (∼1.8 nm) embedded within. The junctions exhibit spin-dependent transport properties and Coulomb blockade effects. We study differences between control samples and the DMTJs; specifically I-V characteristics and tunnel magnetoresistance (TMR) versus bias voltage characteristics. Clear differences in the systems are evident: the DMTJ with NiFe particles shows a marked peak in TMR at low bias, whereas the dependence of TMR on bias is much weaker for the control MTJ without embedded particles. Hence the TMR at low bias is enhanced by the Coulomb blockade effects.
Magnetic and reversible magnetocaloric properties of (Gd1−xDyx)4Co3 ferrimagnets
Authors: Zhang Q. , Li B. , Zhao X. G. , Zhang Z. D.
Published: March 2009

Magnetic properties and magnetocaloric effect of the ferrimagnetic compounds Gd4Co3 and (Gd0.9Dy0.1)4Co3 have been studied. In Gd4Co3, two successive magnetic-entropy changes occur due to a spin-reorientation transition at TSR=163 K and a ferrimagnetic-magnetic ordering transition at TC=220 K. For a field change from 0 to 5 T, −ΔSMmax at TC is 5.74 J/kg K, the full width at half maximum (δTFWHM) of the −ΔSM versus T curve has a high value of 131 K, and the refrigerant capacity is as high as 575 J/kg. TC can easily be tuned by Dy substitution for Gd and the magnetic-entropy change is increased simultaneously. −ΔSMmax of (Gd0.9Dy0.1)4Co3 at TC=145 K for the same field change has increased to 8.47 J/kg K. Our studies suggest that the successive magnetic transitions could enlarge the temperature interval, which makes this type of material meaningful for magnetic refrigeration in wider temperature regions than conventional materials.
Color control of multilayer stacked white polymer light-emitting diodes using a quantum dot as an interlayer
Authors: Jeon Soon Ok , Joo Chul Woong , Yook Kyungsoo , Lee Jun Yeob
Published: March 2009

Color tunable multilayer stacked white polymer light-emitting diodes (WPLEDs) have been developed using a quantum dot as an interlayer. Multilayer WPLEDs were fabricated by a stamp transfer printing method and the charge transport of WPLEDs could be controlled by the quantum dot interlayer. The use of the quantum dot as the interlayer shifted the color coordinate of blue/yellow stacked WPLEDs from (0.34, 0.41) to (0.41, 0.48). The electron trapping effect of the quantum dot was responsible for the color shift in the multilayer stacked WPLEDs.
Jump transformations and an embedding of O∞ into O2
Authors: Kawamura Katsunori , Lascu Dan , Coltescu Ion
Published: March 2009

A measurable map F on a measure space induces a representation ΠF of a Cuntz algebra ON when F satisfies a certain condition. For such two maps F and G and representations ΠF and ΠG associated with them, we show that ΠG is the restriction of ΠF when G is a jump transformation of F. Especially, the Gauss map τ1 and the Farey map σ1 induce representations Πτ1 of O∞ and that Πσ1 of O2, respectively, and Πτ1=Πσ1∣O∞ with respect to a certain embedding of O∞ into O2.
Elastic buckling of AlN ribbons on elastomeric substrate
Authors: Seo Hui-Chan , Petrov Ivan , Jeong Hyejin , Chapman Patrick , Kim Kyekyoon
Published: March 2009

For optoelectronic applications requiring unconventional substrates, use of flexible forms of semiconductors may be inevitable. We have fabricated a flexible form of single crystalline AlN ribbons with periodic and wavelike structures on an elastomeric substrate. Single crystalline AlN films were grown on Si (111) substrate using high vacuum unbalanced magnetron sputtering. Crystallinity of the AlN films was confirmed with x-ray diffraction and pole figure. The AlN ribbons were transferred to a prestrained (3.1%) elastomeric substrate and the resulting “wavy” ribbons on the substrate were flexible up to 30% strain without any crack formation on the surface. As the film thickness changed from 300 to 900 nm, the periods of the waves varied from 95 to 277 μm, which were within a 10% error of the calculated values. When we applied more than 30% strain, mechanical instability, such as the failure of AlN ribbons due to the cracks on the surface and the merged ribbons, was observed.
Internal effective field sources for spin torque nanopillar oscillators
Authors: Hrkac Gino , Schrefl Thomas , Dean Julian , Goncharov Alexander , Bance Simon , Suess Dieter , Fidler Josef
Published: March 2009

In this paper we numerically conduct micromagnetic modeling with an expended micromagnetic model that includes the spin torque term and an impedance model to investigate methods to replace external field sources with internal ones and to investigate its tuneability on nanopillar geometries. We present results for three methods: interlayer coupling, large perpendicular anisotropy, and magnetostatic coupling. The internal field sources are evaluated as function of frequency shift with current, its dependency on temperature, and are tested against analytical predictions.
Evolution of mechanical properties in ErT2 thin films
Authors: Knapp J. A. , Browning J. F. , Bond G. M.
Published: March 2009

The mechanical properties of rare earth tritide films evolve as tritium decays into H3e, which forms bubbles that influence long-term film stability in applications such as neutron generators. Ultralow load nanoindentation, combined with finite-element modeling to separate the mechanical properties of the thin films from their substrates, has been used to follow the mechanical properties of model ErT2 films as they aged. The size of the growing H3e bubbles was followed with transmission electron microscopy, while ion beam analysis was used to monitor total T and H3e content. The observed behavior is divided into two regimes: a substantial increase in layer hardness but elasticity changed little over ∼18 months, followed by a decrease in elastic stiffness and a modest decease in hardness over the final 24 months. We show that the evolution of properties is explained by a combination of dislocation pinning by the bubbles, elastic softening as the bubbles occupy an increasing fraction of the material, and details of bubble growth modes.
Model of a magnetic field in poloidal divertor tokamaks affected by resonant magnetic perturbations
Authors: Abdullaev S. S.
Published: March 2009

A generic analytical model for the description of magnetic field lines in poloidal divertor tokamaks in the presence of external resonant magnetic perturbations is proposed. It is based on the Hamiltonian description of magnetic field lines in tokamaks. The safety factor and the spectra of magnetic perturbations are chosen by the requirement to satisfy their generic behavior near the magnetic separatrix and at the magnetic axis. The field line equations of the model are integrated using symplectic efficient mappings of field lines. The analytical formulas for the quasilinear diffusion and convection coefficients of field lines are obtained. The latter describes the outwardly directed transport of field lines at the plasma edge. It was shown that they are in a good agreement with the corresponding numerically calculated coefficients.
Simulation and demonstration of magnetohydrodynamic energy conversion in a high-temperature inert gas
Authors: Murakami Tomoyuki , Okuno Yoshihiro
Published: March 2009

The present paper describes high-density magnetohydrodynamic (MHD) energy conversion in a high-temperature seed-free argon plasma, for which a quasi-three-dimensional numerical simulation and a single-pulse shock-tunnel-based demonstration are conducted. The numerical model simulates the two-dimensional profiles of both the electron and the heavy-particle system of the supersonic argon plasma flow, of which the total inflow temperature is 8000 K. The MHD power-generating experiment clarifies the relationship between the plasma quality and the energy conversion efficiency as functions of the total inflow temperature (7600–9600 K) and the applied magnetic flux density (up to 4.0 T). The increase in the total inflow temperature from 7600 to 9400 K and the application of magnetic flux with density of 0.5–1.2 T change the plasma state; unstable behavior accompanied by an inhomogeneous structure is transformed to a homogeneous and stable state, which results in the significant improvement of the power generation performance. Even in low-density magnetic flux, the attained generator performance is comparable or superior to previous results obtained using a conventional low-temperature seeded gas.
Excitation of the l=3 diocotron mode in a pure electron plasma by means of a rotating electric field
Authors: Bettega G. , Paroli B. , Pozzoli R. , Romé M.
Published: March 2009

The l=3 diocotron mode in an electron plasma confined in a Malmberg–Penning trap has been resonantly excited by means of a rotating electric field applied on an azimuthally four-sectored electrode. The experimental observations are interpreted with a theory based on the linearization of the drift-Poisson equations and by means of two-dimensional particle-in-cell simulations. The experimental technique presented in this paper is able to selectively excite different diocotron perturbations and can be efficiently used for electron or positron plasma control and manipulation.
Controlling of the surface energy of the gate dielectric in organic field-effect transistors by polymer blend
Authors: Gao Jia , Asadi Kamal , Xu Jian Bin , An Jin
Published: March 2009

In this letter, we demonstrate that by blending insulating polymers, one can fabricate an insulating layer with controllable surface energy for organic field-effect transistors. As a model system, we used copper phthalocyanine evaporated on layers of polymethyl metacrylate blended with polystyrene with different blending ratios and measured the field-effect mobility in transistors. We show that the highest field-effect mobility is achieved for identical surface energies of the dielectric and the semiconductor. This simple technique demonstrates the viability of using the blends of insulating polymers to systematically control the surface energy of the gate dielectric toward achieving better performances.