bluuebunny/crossref_metadata_2025 huggingface dataset:
β-Spectrin functions independently of Ankyrin to regulate the establishment and maintenance of axon connections in theDrosophilaembryonic CNS
Authors: Garbe David S. , Das Amlan , Dubreuil Ronald R. , Bashaw Greg J.
Published: November 2006

α- and β-Spectrin are major components of a submembrane cytoskeletal network connecting actin filaments to integral plasma membrane proteins. Besides its structural role in red blood cells, the Spectrin network is thought to function in non-erythroid cells during protein targeting and membrane domain formation. Here, we demonstrate that β-Spectrin is required in neurons for proper midline axon guidance in the Drosophila embryonic CNS. In β-spectrin mutants many axons inappropriately cross the CNS midline, suggesting a role forβ-Spectrin in midline repulsion. Surprisingly, neither the Ankyrin-binding nor the pleckstrin homology (PH) domains of β-Spectrin are required for accurate guidance decisions. α-Spectrin is dependent upon β-Spectrin for its normal subcellular localization and/or maintenance, whereas α-spectrin mutants exhibit a redistribution of β-Spectrin to the axon scaffold.β -spectrin mutants show specific dose-dependent genetic interactions with the midline repellent slit and its neuronal receptor roundabout (robo), but not with other guidance molecules. The results suggest that β-Spectrin contributes to midline repulsion through the regulation of Slit-Robo pathway components. We propose that the Spectrin network is playing a role independently of Ankyrin in the establishment and/or maintenance of specialized membrane domains containing guidance molecules that ensure the fidelity of axon repulsion at the midline.
Dynamic Compression Regulates the Expression and Synthesis of Chondrocyte-Specific Matrix Molecules in Bone Marrow Stromal Cells
Authors: Mouw Janna K. , Connelly John T. , Wilson Christopher G. , Michael Kristin E. , Levenston Marc E.
Published: November 2006

The overall objective of the present study was to investigate the mechanotransduction of bovine bone marrow stromal cells (BMSCs) through the interactions between transforming growth factor β1 (TGF-β1), dexamethasone, and dynamic compressive loading. Overall, the addition of TGF-β1 increased cell viability, extracellular matrix (ECM) gene expression, matrix synthesis, and sulfated glycosaminoglycan content over basal construct medium. The addition of dexamethasone further enhanced extracellular matrix gene expression and protein synthesis. There was little stimulation of ECM gene expression or matrix synthesis in any medium group by mechanical loading introduced on day 8. In contrast, there was significant stimulation of ECM gene expression and matrix synthesis in chondrogenic media by dynamic loading introduced on day 16. The level of stimulation was also dependent on the medium supplements, with the samples treated with basal medium being the least responsive and the samples treated with TGF-β1 and dexamethasone being the most responsive at day 16. Both collagen I and collagen II gene expressions were more responsive to dynamic loading than aggrecan gene expression. Dynamic compression upregulated Smad2/3 phosphorylation in samples treated with basal and TGF-β1 media. These findings suggest that interactions between mechanical stimuli and TGF-β signaling may be an important mechanotransduction pathway for BMSCs, and they indicate that mechanosensitivity may vary during the process of chondrogenesis.
Concise Review: Stem Cells, Myocardial Regeneration, and Methodological Artifacts
Authors: Anversa Piero , Leri Annarosa , Rota Marcello , Hosoda Toru , Bearzi Claudia , Urbanek Konrad , Kajstura Jan , Bolli Roberto
Published: November 2006

This review discusses the current controversy about the role that endogenous and exogenous progenitor cells have in cardiac homeostasis and myocardial regeneration following injury. Although great enthusiasm was created by the possibility of reconstituting the damaged heart, the opponents of this new concept of cardiac biology have interpreted most of the findings supporting this possibility as the product of technical artifacts. This article challenges this established, static view of cardiac growth and favors the notion that the mammalian heart has the inherent ability to replace its cardiomyocytes through the activation of a pool of resident primitive cells or the administration of hematopoietic stem cells.
Simplified approach for assessing seismic displacements of soil-retaining walls. Part I: Geosynthetic-reinforced modular block walls
Authors: Huang C.-C. , Wu S.-H.
Published: November 2006

Pseudo-static-based multi-wedge and Newmark sliding block analyses are performed to derive the values of critical seismic coefficient ([Formula: see text]) and horizontal seismic displacement (δh) of geosynthetic-reinforced modular block walls (GR-MBWs). It is shown that the values of [Formula: see text] can be expressed using linear functions of parameters representing the geometry and the reinforcement configuration of the wall. It is also shown that horizontal seismic displacement of GR-MBWs subjected to three recent major earthquakes, namely the 1994 Loma-Prieta, 1995 Hyogoken-Nambu and 1999 Chi-Chi earthquakes, can be estimated using the gradient of the linear relationships proposed between [Formula: see text] and log(δh), or using well-established empirical formulae in conjunction with the analytical values of [Formula: see text]. Four example walls are analysed to verify the proposed approach. Good agreement between the calculated and observed seismic displacement of the walls is obtained.
Evaluating the strength and deformation characteristics of a soil bag pile from full-scale laboratory tests
Authors: Lohani T. N. , Matsushima K. , Aqil U. , Mohri Y. , Tatsuoka F.
Published: November 2006

The compressive strength of a soil bag pile when compressed vertically and the shear strength when sheared laterally were evaluated by performing a series of full-scale loading tests. The effects of soil bag material, backfill soil type, number of soil bags in a pile and associated effects of the end restraint at the top and bottom ends of a soil bag pile were evaluated. The results of vertical compression tests showed that initial compaction of the backfill in the soil bags is effective in increasing the initial stiffness at small deformation, and that preloading is even more effective in increasing the overall stiffness and decreasing the creep deformation. The shear strength of a soil bag pile subjected to lateral shear is substantially smaller as compared with a high compressive strength when compressed vertically. It was found that the shear strength of well-graded granular backfill was partially mobilised in vertical compression tests but the mobilisation was even lower in the lateral shear tests. The soil bag pile showed highly anisotropic strength characteristics, resulting from no or negligible complementary shear stresses acting at the vertical interface between the horizontally adjacent soil bags and highly anisotropic reinforcing effects of geosynthetic cover sheets of soil bags.
2D and 3D numerical modelling of flow through composite liners involving partially saturated GCLs
Authors: Saidi F. , Touze-Foltz N. , Goblet P.
Published: November 2006

A numerical study was performed in order to investigate the influence on the flow rate of the presence of defects in the geomembrane of a composite liner involving GCLs. In the approach presented in this paper, porous media in the composite liner, i.e. the interface, the GCL and the underlying soil liner, which is a CCL, are partially saturated in the numerical modelling performed. The first aim of the paper is to evaluate the impact of this partial saturation on the flow rates and the lateral extension of the wetted area for circular defects and defects of infinite length in the geomembrane through 2D numerical modelling. Results from existing analytical solutions are used as a reference. Results obtained in terms of flow rates and wetted areas reveal that: (i) a good agreement is obtained as regards flow rates between numerical modelling and analytical solutions; and (ii) larger differences between numerical and analytical results were observed for the wetted area, attributed to the difference in saturation state in both cases. The second aim of the paper is to check the impact of the shape of the ends of defects of finite length – circle or square – and to test the impact of 2D and 3D modelling of this end on the resulting flow rates. Results obtained show that the impact on the flow rate of the shape of the ends is negligible. However, 2D and 3D modelling can lead to significantly different results depending on the defect length, especially as regards the evolution of the flow rate with the hydraulic head.
Strong normalisation for applied lambda calculi
Authors: Berger Ulrich
Published: November 2006

We consider the untyped lambda calculus with constructors and recursively defined constants. We construct a domain-theoretic model such that any term not denoting bottom is strongly normalising provided all its `stratified approximations' are. From this we derive a general normalisation theorem for applied typed lambda-calculi: If all constants have a total value, then all typeable terms are strongly normalising. We apply this result to extensions of G\"odel's system T and system F extended by various forms of bar recursion for which strong normalisation was hitherto unknown.
Comparing hierarchies of total functionals
Authors: Normann Dag
Published: November 2006

In this paper we consider two hierarchies of hereditarily total and continuous functionals over the reals based on one extensional and one intensional representation of real numbers, and we discuss under which asumptions these hierarchies coincide. This coincidense problem is equivalent to a statement about the topology of the Kleene-Kreisel continuous functionals. As a tool of independent interest, we show that the Kleene-Kreisel functionals may be embedded into both these hierarchies.
An Operational Foundation for Delimited Continuations in the CPS Hierarchy
Authors: Biernacka Malgorzata , Biernacki Dariusz , Danvy Olivier
Published: November 2006

We present an abstract machine and a reduction semantics for the lambda-calculus extended with control operators that give access to delimited continuations in the CPS hierarchy. The abstract machine is derived from an evaluator in continuation-passing style (CPS); the reduction semantics (i.e., a small-step operational semantics with an explicit representation of evaluation contexts) is constructed from the abstract machine; and the control operators are the shift and reset family. We also present new applications of delimited continuations in the CPS hierarchy: finding list prefixes and normalization by evaluation for a hierarchical language of units and products.
Deciding Quantifier-Free Presburger Formulas Using Parameterized Solution Bounds
Authors: Seshia Sanjit A. , Bryant Randal E.
Published: November 2006

Given a formula in quantifier-free Presburger arithmetic, if it has a satisfying solution, there is one whose size, measured in bits, is polynomially bounded in the size of the formula. In this paper, we consider a special class of quantifier-free Presburger formulas in which most linear constraints are difference (separation) constraints, and the non-difference constraints are sparse. This class has been observed to commonly occur in software verification. We derive a new solution bound in terms of parameters characterizing the sparseness of linear constraints and the number of non-difference constraints, in addition to traditional measures of formula size. In particular, we show that the number of bits needed per integer variable is linear in the number of non-difference constraints and logarithmic in the number and size of non-zero coefficients in them, but is otherwise independent of the total number of linear constraints in the formula. The derived bound can be used in a decision procedure based on instantiating integer variables over a finite domain and translating the input quantifier-free Presburger formula to an equi-satisfiable Boolean formula, which is then checked using a Boolean satisfiability solver. In addition to our main theoretical result, we discuss several optimizations for deriving tighter bounds in practice. Empirical evidence indicates that our decision procedure can greatly outperform other decision procedures.
Probabilistic Algorithmic Knowledge
Authors: Halpern Joseph Y. , Pucella Riccardo
Published: November 2006

The framework of algorithmic knowledge assumes that agents use deterministic knowledge algorithms to compute the facts they explicitly know. We extend the framework to allow for randomized knowledge algorithms. We then characterize the information provided by a randomized knowledge algorithm when its answers have some probability of being incorrect. We formalize this information in terms of evidence; a randomized knowledge algorithm returning ``Yes'' to a query about a fact \phi provides evidence for \phi being true. Finally, we discuss the extent to which this evidence can be used as a basis for decisions.
Security Policies as Membranes in Systems for Global Computing
Authors: Gorla Daniele , Hennessy Matthew , Sassone Vladimiro
Published: November 2006

We propose a simple global computing framework, whose main concern is code migration. Systems are structured in sites, and each site is divided into two parts: a computing body, and a membrane, which regulates the interactions between the computing body and the external environment. More precisely, membranes are filters which control access to the associated site, and they also rely on the well-established notion of trust between sites. We develop a basic theory to express and enforce security policies via membranes. Initially, these only control the actions incoming agents intend to perform locally. We then adapt the basic theory to encompass more sophisticated policies, where the number of actions an agent wants to perform, and also their order, are considered.
Modularizing the Elimination of r=0 in Kleene Algebra
Authors: Hardin Christopher
Published: November 2006

Given a universal Horn formula of Kleene algebra with hypotheses of the form
r = 0, it is already known that we can efficiently construct an equation which
is valid if and only if the Horn formula is valid. This is an example of
elimination of hypotheses, which is useful because the equational theory
of Kleene algebra is decidable while the universal Horn theory is not. We show
that hypotheses of the form r = 0 can still be eliminated in the presence of
other hypotheses. This lets us extend any technique for eliminating hypotheses
to include hypotheses of the form r = 0.
Computably Based Locally Compact Spaces
Authors: Taylor Paul
Published: November 2006

ASD (Abstract Stone Duality) is a re-axiomatisation of general topology in which the topology on a space is treated, not as an infinitary lattice, but as an exponential object of the same category as the original space, with an associated lambda-calculus. In this paper, this is shown to be equivalent to a notion of computable basis for locally compact sober spaces or locales, involving a family of open subspaces and accompanying family of compact ones. This generalises Smyth's effectively given domains and Jung's strong proximity lattices. Part of the data for a basis is the inclusion relation of compact subspaces within open ones, which is formulated in locale theory as the way-below relation on a continuous lattice. The finitary properties of this relation are characterised here, including the Wilker condition for the cover of a compact space by two open ones. The real line is used as a running example, being closely related to Scott's domain of intervals. ASD does not use the category of sets, but the full subcategory of overt discrete objects plays this role; it is an arithmetic universe (pretopos with lists). In particular, we use this subcategory to translate computable bases for classical spaces into objects in the ASD calculus.
Model Checking Probabilistic Pushdown Automata
Authors: Esparza Javier , Kucera Antonin , Mayr Richard
Published: November 2006

We consider the model checking problem for probabilistic pushdown automata (pPDA) and properties expressible in various probabilistic logics. We start with properties that can be formulated as instances of a generalized random walk problem. We prove that both qualitative and quantitative model checking for this class of properties and pPDA is decidable. Then we show that model checking for the qualitative fragment of the logic PCTL and pPDA is also decidable. Moreover, we develop an error-tolerant model checking algorithm for PCTL and the subclass of stateless pPDA. Finally, we consider the class of omega-regular properties and show that both qualitative and quantitative model checking for pPDA is decidable.
Approximate reasoning for real-time probabilistic processes
Authors: Gupta Vineet , Jagadeesan Radha , Panangaden Prakash
Published: November 2006

We develop a pseudo-metric analogue of bisimulation for generalized semi-Markov processes. The kernel of this pseudo-metric corresponds to bisimulation; thus we have extended bisimulation for continuous-time probabilistic processes to a much broader class of distributions than exponential distributions. This pseudo-metric gives a useful handle on approximate reasoning in the presence of numerical information -- such as probabilities and time -- in the model. We give a fixed point characterization of the pseudo-metric. This makes available coinductive reasoning principles for reasoning about distances. We demonstrate that our approach is insensitive to potentially ad hoc articulations of distance by showing that it is intrinsic to an underlying uniformity. We provide a logical characterization of this uniformity using a real-valued modal logic. We show that several quantitative properties of interest are continuous with respect to the pseudo-metric. Thus, if two processes are metrically close, then observable quantitative properties of interest are indeed close.
Algorithmic correspondence and completeness in modal logic. I. The core algorithm SQEMA
Authors: Conradie Willem , Goranko Valentin , Vakarelov Dimiter
Published: November 2006

Modal formulae express monadic second-order properties on Kripke frames, but
in many important cases these have first-order equivalents. Computing such
equivalents is important for both logical and computational reasons. On the
other hand, canonicity of modal formulae is important, too, because it implies
frame-completeness of logics axiomatized with canonical formulae.
Computing a first-order equivalent of a modal formula amounts to elimination
of second-order quantifiers. Two algorithms have been developed for
second-order quantifier elimination: SCAN, based on constraint resolution, and
DLS, based on a logical equivalence established by Ackermann.
In this paper we introduce a new algorithm, SQEMA, for computing first-order
equivalents (using a modal version of Ackermann's lemma) and, moreover, for
proving canonicity of modal formulae. Unlike SCAN and DLS, it works directly on
modal formulae, thus avoiding Skolemization and the subsequent problem of
unskolemization. We present the core algorithm and illustrate it with some
examples. We then prove its correctness and the canonicity of all formulae on
which the algorithm succeeds. We show that it succeeds not only on all
Sahlqvist formulae, but also on the larger class of inductive formulae,
introduced in our earlier papers. Thus, we develop a purely algorithmic
approach to proving canonical completeness in modal logic and, in particular,
establish one of the most general completeness results in modal logic so far.
On the Expressiveness of the Ambient Logic
Authors: Hirschkoff Daniel , Lozes Etienne , Sangiorgi Davide
Published: November 2006

The Ambient Logic (AL) has been proposed for expressing properties of process mobility in the calculus of Mobile Ambients (MA), and as a basis for query languages on semistructured data. In this paper, we study the expressiveness of AL. We define formulas for capabilities and for communication in MA. We also derive some formulas that capture finitess of a term, name occurrences and persistence. We study extensions of the calculus involving more complex forms of communications, and we define characteristic formulas for the equivalence induced by the logic on a subcalculus of MA. This subcalculus is defined by imposing an image-finiteness condition on the reducts of a MA process.
A System of Interaction and Structure II: The Need for Deep Inference
Authors: Tiu Alwen
Published: November 2006

This paper studies properties of the logic BV, which is an extension of
multiplicative linear logic (MLL) with a self-dual non-commutative operator. BV
is presented in the calculus of structures, a proof theoretic formalism that
supports deep inference, in which inference rules can be applied anywhere
inside logical expressions. The use of deep inference results in a simple
logical system for MLL extended with the self-dual non-commutative operator,
which has been to date not known to be expressible in sequent calculus. In this
paper, deep inference is shown to be crucial for the logic BV, that is, any
restriction on the ``depth'' of the inference rules of BV would result in a
strictly less expressive logical system.
Context-Sensitive Languages, Rational Graphs and Determinism
Authors: Carayol Arnaud , Meyer Antoine
Published: November 2006

We investigate families of infinite automata for context-sensitive languages. An infinite automaton is an infinite labeled graph with two sets of initial and final vertices. Its language is the set of all words labelling a path from an initial vertex to a final vertex. In 2001, Morvan and Stirling proved that rational graphs accept the context-sensitive languages between rational sets of initial and final vertices. This result was later extended to sub-families of rational graphs defined by more restricted classes of transducers. languages.

 Our contribution is to provide syntactical and self-contained proofs of the above results, when earlier constructions relied on a non-trivial normal form of context-sensitive grammars defined by Penttonen in the 1970's. These new proof techniques enable us to summarize and refine these results by considering several sub-families defined by restrictions on the type of transducers, the degree of the graph or the size of the set of initial vertices.
On the complexity of XPath containment in the presence of disjunction, DTDs, and variables
Authors: Neven Frank , Schwentick Thomas
Published: November 2006

XPath is a simple language for navigating an XML-tree and returning a set of
answer nodes. The focus in this paper is on the complexity of the containment
problem for various fragments of XPath. We restrict attention to the most
common XPath expressions which navigate along the child and/or descendant axis.
In addition to basic expressions using only node tests and simple predicates,
we also consider disjunction and variables (ranging over nodes). Further, we
investigate the containment problem relative to a given DTD. With respect to
variables we study two semantics, (1) the original semantics of XPath, where
the values of variables are given by an outer context, and (2) an existential
semantics introduced by Deutsch and Tannen, in which the values of variables
are existentially quantified. In this framework, we establish an exact
classification of the complexity of the containment problem for many XPath
fragments.
Logics for Unranked Trees: An Overview
Authors: Libkin Leonid
Published: November 2006

Labeled unranked trees are used as a model of XML documents, and logical
languages for them have been studied actively over the past several years. Such
logics have different purposes: some are better suited for extracting data,
some for expressing navigational properties, and some make it easy to relate
complex properties of trees to the existence of tree automata for those
properties. Furthermore, logics differ significantly in their model-checking
properties, their automata models, and their behavior on ordered and unordered
trees. In this paper we present a survey of logics for unranked trees.
Relational Parametricity and Control
Authors: Hasegawa Masahito
Published: November 2006

We study the equational theory of Parigot's second-order
λμ-calculus in connection with a call-by-name continuation-passing
style (CPS) translation into a fragment of the second-order λ-calculus.
It is observed that the relational parametricity on the target calculus induces
a natural notion of equivalence on the λμ-terms. On the other hand,
the unconstrained relational parametricity on the λμ-calculus turns
out to be inconsistent with this CPS semantics. Following these facts, we
propose to formulate the relational parametricity on the λμ-calculus
in a constrained way, which might be called ``focal parametricity''.
Resource Usage Analysis for the Pi-Calculus
Authors: Kobayashi Naoki , Suenaga Kohei , Wischik Lucian
Published: November 2006

We propose a type-based resource usage analysis for the π-calculus
extended with resource creation/access primitives. The goal of the resource
usage analysis is to statically check that a program accesses resources such as
files and memory in a valid manner. Our type system is an extension of previous
behavioral type systems for the π-calculus, and can guarantee the safety
property that no invalid access is performed, as well as the property that
necessary accesses (such as the close operation for a file) are eventually
performed unless the program diverges. A sound type inference algorithm for the
type system is also developed to free the programmer from the burden of writing
complex type annotations. Based on the algorithm, we have implemented a
prototype resource usage analyzer for the π-calculus. To the authors'
knowledge, ours is the first type-based resource usage analysis that deals with
an expressive concurrent language like the pi-calculus.
Generalized Majority-Minority Operations are Tractable
Authors: Dalmau Victor
Published: November 2006

Generalized majority-minority (GMM) operations are introduced as a common
generalization of near unanimity operations and Mal'tsev operations on finite
sets. We show that every instance of the constraint satisfaction problem (CSP),
where all constraint relations are invariant under a (fixed) GMM operation, is
solvable in polynomial time. This constitutes one of the largest tractable
cases of the CSP.
A State-Based Regression Formulation for Domains with Sensing Actions and Incomplete Information
Authors: Tuan Le-Chi , Baral Chitta , Son Tran Cao
Published: November 2006

We present a state-based regression function for planning domains where an
agent does not have complete information and may have sensing actions. We
consider binary domains and employ a three-valued characterization of domains
with sensing actions to define the regression function. We prove the soundness
and completeness of our regression formulation with respect to the definition
of progression. More specifically, we show that (i) a plan obtained through
regression for a planning problem is indeed a progression solution of that
planning problem, and that (ii) for each plan found through progression, using
regression one obtains that plan or an equivalent one.
Positional Determinacy of Games with Infinitely Many Priorities
Authors: Graedel Erich , Walukiewicz Igor
Published: November 2006

We study two-player games of infinite duration that are played on finite or
infinite game graphs. A winning strategy for such a game is positional if it
only depends on the current position, and not on the history of the play. A
game is positionally determined if, from each position, one of the two players
has a positional winning strategy.
The theory of such games is well studied for winning conditions that are
defined in terms of a mapping that assigns to each position a priority from a
finite set. Specifically, in Muller games the winner of a play is determined by
the set of those priorities that have been seen infinitely often; an important
special case are parity games where the least (or greatest) priority occurring
infinitely often determines the winner. It is well-known that parity games are
positionally determined whereas Muller games are determined via finite-memory
strategies.
In this paper, we extend this theory to the case of games with infinitely
many priorities. Such games arise in several application areas, for instance in
pushdown games with winning conditions depending on stack contents.
For parity games there are several generalisations to the case of infinitely
many priorities. While max-parity games over omega or min-parity games over
larger ordinals than omega require strategies with infinite memory, we can
prove that min-parity games with priorities in omega are positionally
determined. Indeed, it turns out that the min-parity condition over omega is
the only infinitary Muller condition that guarantees positional determinacy on
all game graphs.
The Completeness of Propositional Resolution: A Simple and Constructive Proof
Authors: Gallier Jean
Published: November 2006

It is well known that the resolution method (for propositional logic) is
complete. However, completeness proofs found in the literature use an argument
by contradiction showing that if a set of clauses is unsatisfiable, then it
must have a resolution refutation. As a consequence, none of these proofs
actually gives an algorithm for producing a resolution refutation from an
unsatisfiable set of clauses. In this note, we give a simple and constructive
proof of the completeness of propositional resolution which consists of an
algorithm together with a proof of its correctness.
Elgot Algebras
Authors: Adamek Jiri , Milius Stefan , Velebil Jiri
Published: November 2006

Denotational semantics can be based on algebras with additional structure
(order, metric, etc.) which makes it possible to interpret recursive
specifications. It was the idea of Elgot to base denotational semantics on
iterative theories instead, i.e., theories in which abstract recursive
specifications are required to have unique solutions. Later Bloom and Esik
studied iteration theories and iteration algebras in which a specified solution
has to obey certain axioms. We propose so-called Elgot algebras as a convenient
structure for semantics in the present paper. An Elgot algebra is an algebra
with a specified solution for every system of flat recursive equations. That
specification satisfies two simple and well motivated axioms: functoriality
(stating that solutions are stable under renaming of recursion variables) and
compositionality (stating how to perform simultaneous recursion). These two
axioms stem canonically from Elgot's iterative theories: We prove that the
category of Elgot algebras is the Eilenberg-Moore category of the monad given
by a free iterative theory.
Commodity or Gift: Teotihuacan Obsidian in the Maya Region
Authors: Spence Michael W.
Published: November 2006

Archaeologists have long noted the presence of green obsidian artifacts in a number of Maya sites and have recognized that they were manufactured from the obsidian of the Pachuca source in central Mexico. Viewed as evidence of Teotihuacán influence, these finds were initially explained in economic terms as commodities in an exchange of goods that had a substantial impact on the economies of the Maya and on the development of the obsidian industry in Teotihuacán. However, when the contexts of the finds are examined it becomes clear that the significance of the artifacts was more symbolic than economic. The forms include prismatic blades, bifacially worked points and knives, needles, sequins, and some eccentrics. These are often recovered from ritual contexts, in association with other evidence of Teotihuacán influence. They apparently served to express a variety of relationships with Teotihuacán, ranging from actual Teotihuacanos proclaiming their identity to the attempts of Maya elite to forge some social affiliation with the city. Although most of the finds of green obsidian consist of only one or a few pieces, some contexts, such as the tombs of mounds A and B at Kaminaljuyú, produced more substantial amounts. Nevertheless, despite these occasional impressive finds, green obsidian does not seem to have been a major import, and it is clear that the Teotihuacán obsidian industry had largely attained its Classic-period structure before the Maya demand developed. Although the flow of central Mexican obsidian to the Maya region was not negligible, it could not in itself have had a major effect on either economic system.
Mid-Holocene Cultural Interaction between the North Coast of Peru and Ecuador
Authors: Sandweiss Daniel H.
Published: November 2006

Incised pebbles found at the mid-Holocene, Middle Preceramic period Ostra Base Camp site on the Peruvian north coast demonstrate long-distance links to coastal Ecuador, 700 km to the north. The artifacts belong to a northwestern Andean pebble-figurine tradition associated with the tropical coast. Environmental indicators at the Ostra site show a warm-water lagoonal environment, unlike the modern cold-water conditions of northwestern Peru but similar to modern Ecuador. The Ostra site dates between ca. 5500 and 6250 B.P. (3550 and 4300 B.C.), during a hiatus in the coastal Ecuadorian record, so the link to Ecuador provides the earliest evidence of long-distance cultural interaction between these regions. Until contemporary sites are found in Ecuador, the Ostra Base Camp site provides our only example for this time of tropical coastal cultures of the northwestern Andean interaction sphere.
A Mathematical Projection of Population Growth in the Copan Valley, Honduras, A.D. 400-800
Authors: Paine Richard R. , Freter AnnCorinne , Webster David L.
Published: November 2006

Demographers use mathematical projections to estimate both future and past population in areas where they lack quality data. Such projections may be very useful in archaeological situations. In this analysis, we mathematically project population growth rates from Classic Maya settlement in the Copán Valley, Honduras, from A.D. 650-800 backward to A.D. 450 to estimate valley population levels during the Middle Classic. Projections based on the growth rate (r = .0098) that best describes Late Classic growth yield population estimates that are from 40 to 100 percent higher than the unsmoothed estimates for the Middle Classic calculated by Webster et al. (1992:189). However, they still indicate that Middle Classic Copán was a relatively small polity, with a population of approximately 2,400 by A.D. 550 and 6,400 by A.D. 650. The fact that population growth at Copán from the period A.D. 400-800 conforms well to exponential growth indicates that population growth in the valley was relatively unaffected by episodic events. Each of the three growth rates considered would have been sustainable in a preindustrial agrarian society.
Extending the Calakmul Dynasty Back in Time: A New Stela from a Maya Capital in Campeche, Mexico
Authors: Pincemin Sophia , Marcus Joyce , Folan Lynda Florey , Folan William J. , Carrasco María del Rosario Domínguez , López Abel Morales
Published: November 2006

The 200-year period from A.D. 230 to 430 witnessed the transition from chiefdom to state in the Maya Lowlands and the founding of several early political dynasties. Considerable information on that era is known for major cities like Tikal and Copán, but we knew less about the Calakmul area until recently. Previously, Calakmul's earliest dated monument was Stela 43, carved at A.D. 514. On the other hand, Tikal's earliest text dated to A.D. 292, and its ruling dynasty claimed that its founding date was A.D. 230. The ruling dynasties of most other cities that eventually became Maya regional capitals were evidently founded later, between A.D. 330 and 430.

With the 1994 discovery of Stela 114 at Calakmul, we can now push Calakmul's written record back to A.D. 431. The oldest stela in Calakmul’s realm was erected in A.D. 406 at Balakbal, to document the reign of a Balakbal ruler who was a contemporary of the Tikal ruler Curl Snout. Some 25 years later, Calakmul erected Stela 114 to commemorate a Calakmul ruler who was a contemporary of the Tikal ruler Stormy Sky. Even though we had expected Calakmul's dynasty to have greater time depth than A.D. 514, it was not until the discovery of Stela 114 that we were able to confirm that point.
Las Tumbas de tiro de El Piñon, en el Cañon de Bolaños, Jalisco, Mexico
Authors: G. Ma. Teresa Cabrero , Cruz Carlos López
Published: November 2006

Las tumbas de tiro son bien conocidas en el registro arqueológico del Occidente de México. Empero, se sabía muy poco de estos entierros y los rituales mortuorios asociados porque la mayoría de estos monumentos funerarios han sido saqueados. En este artículo presentamos nuevos datos procedentes de tres tumbas de tiro selladas, fechadas en los primeros siglos d.C., las cuales fueron recientemente descubiertas y excavadas sistemáticamente en el norte de Jalisco. Los artefactos recuperados de las tumbas muestran afiliaciones estilísticas con materiales culturales provenientes de otras regiones de Jalisco y partes de Nayarit.
Preceramic Connections between Yucatan and the Caribbean
Authors: Wilson Samuel M. , Iceland Harry B. , Hester Thomas R.
Published: November 2006

Archaeologists have long noted similarities between the lithic artifacts of the first colonists of the Greater Antilles (ca. 3500-2000 B.C.) and those from the eastern Yucatán Peninsula. Recent archaeological work in northern Belize has provided additional archaeological information on the characteristics and dating of the mainland assemblages. New findings by Caribbean archaeologists also have contributed to a clearer picture of the circumstances surrounding the first human migration to the Greater Antilles. A Yucatecan origin for the first Caribbean migrants is now considered probable.
Interpreting Intrasource Variation in the Composition of Obsidian: The Geoarchaeology of San Martin Jilotepeque, Guatemala
Authors: Braswell Geoffrey E. , Glascock Michael D.
Published: November 2006

Compositional analyses have long been used to assign obsidian artifacts to particular source areas. In most cases, the chemical “fingerprint” of a particular source area has been determined through the assay of only a few geological specimens from one or two outcrops. As a result, the full range of intrasource compositional variation has rarely been noted, and its spatial patterning frequently has not been studied. This report describes the results of geoarchaeological survey at the important Guatemalan source area of San Martín Jilotepeque. Neutron activation analysis demonstrates the presence of seven distinct chemical “fingerprints” corresponding to spatially discrete subsources within the region. Ancient procurement and production are associated with only three of these subsources. Statistical procedures that can be used to assign artifacts to particular quarries or quarry systems are presented. Several minor Guatemalan source areas also are examined, and one (Media Cuesta) also can be characterized as consisting of two distinct subsources.
Influence of complexation on the composition of equilibrium phases in the system of Ce2(SO4)3-La2(SO4)3
Authors: Milanova Maria , Todorovsky Dimitar , Balarew Christo , Minkova Natalia , Ivanova Katya
Published: November 2006

The cocrystallization of Ce2(SO4)3 and La2(SO4)3 is studied in aqueous and H2SO4 (150 g/dm3) solutions at 25 °C and 64 °C. The effect of the formation of inner sphere sulfate complexes of the type LnSO 4+ in determining the composition of the equilibrium phases is revealed.
The effect of doping by IV-family elements on the electronic structure and electrical characteristics of Sb2O5
Authors: Du Juan , Ji Zhenguo , Wang Chao
Published: November 2006

The electronic structures of doped Sb2O5 by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results showed that the substituted IV-family elements act as acceptors in Sb2O5. Partial DOSs indicates that by substituting Ge(GeSb) or Sn(SnSb), there may be a larger contribution to the total DOSs near EF than by substituting Si, which suggests that doping Ge or Sn in Sb2O5 produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely to exist in the substituted position rather than in the interstitial position in Sb2O5, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb2O5. Ionization energy results show that GeSb or SnSb, two among the three impurities considered, act as shallow acceptors in Sb2O5, thus producing a higher concentration of holes.
The oscillatory galvanomagnetic size-effect in multilayered structures
Authors: Dekhtyaruk Leonid
Published: November 2006

Within the framework of the modified semi-classical Fuchs-Sondheimer model, we investigated theoretically the electrical resistivity of multilayered structures (MLS) consisting of alternating metallic layers (of different purity and different thicknesses) in a transverse magnetic field as functions of the ratio of the adjacent layer thicknesses and the magnetic field value. We have derived both a general formula (valid at arbitrary values of layer thicknesses) and asymptotic expressions that are valid when metallic layers are thick or thin compared with the electron mean free path. We found a non-monotonic behavior in the resistivity vs. the value of an applied magnetic field. As we demonstrated, this behavior is sensitive to the characteristics of the electron scattering in the interlayer interfaces in low magnetic fields. Moreover, the MLS resistivity oscillates in high magnetic fields with the field value (or with the layer thicknesses). The oscillation includes the harmonics that correspond both to the each layer thicknesses and the total thickness. The intensity of the oscillation is determined by the diffusive electron scattering in the interfaces, and the oscillation amplitude is proportional to the coefficient of the electron transmission through the interlayer interfaces. We have calculated numerically the resistivity in a wide range of fields and layer thicknesses at various values of the parameters of the interface and bulk electron scattering.
Electronic transport mechanism in polydiacetylene crystals — variable range hopping or phonon-assisted tunnelling
Authors: Pipinys Povilas , Kiveris Antanas
Published: November 2006

Experimental results on the current-voltage characteristics of polydiacetylene (PDA) single crystals reported by Aleshin et al [Phys. Rev. Vol. B 69, (2004) art. 214203] are reinterpreted in terms of the phonon-assisted electron tunnelling model. It is shown that the experimental results, measured in the temperature range from 1.8 K to 300 K are consistent with the tunnelling rate dependence on field strength, computed for the same range of temperatures. An advantage of this model over that of Aleshin et al, using the variable range hopping (VRH) model, is the possibility of describing the behaviour of I — V data measured at both high and low temperatures with the same set of parameters characterizing this material. This assertion is confirmed by comparison of the temperature-dependent current-voltage data extracted from Aleshin et al’s work with tunnelling rate dependence on temperature, computed using two different expressions of the phonon-assisted tunnelling theory. The temperature dependence of the conductivity of an ion implanted PDA crystals [B. S. Elman et al, Appl. Phys. Lett., Vol. 46, (1985) p. 100] and polypyrrole [P. Dutta et al, Synth. Met., Vol. 139 (2003) p. 201] are also explained on the basis of this model.
Amplification of solitary optical waves in fibers with positive group velocity dispersion
Authors: Arabadzhiev Todor , Uzunov Ivan
Published: November 2006

Solitary optical waves with characteristic red frequency shift have been numerically identified in fibers with positive group velocity dispersion in the presence of amplification by semiconductor amplifiers. Influence of the Henry factor, the net gain, gain saturation characteristics, and frequency modulation on the frequency shift of the observed solitary optical waves has been examined. Normalized pulse energy as a function of the gain saturation characteristics has been studied.
Spectroscopic studies of D-α-tocopherol concentration-induced transformation in egg phosphatidylcholne vesicles
Authors: Dwiecki Krzysztof , Górnas Paweł , Wilk Agnieszka , Nogala-Kałucka Małgorzata , Polewski Krzysztof
Published: November 2006

The effects of embedding up to 60 mol% of α-tocopherol (α-Toc) on the morphology and structure of the egg phosphatidylcholine (PC) membrane were studied using spectroscopic techniques. The resulting vesicles were subjected to turbidometric and dynamic light scattering measurements to evaluate their size distribution. The α-Toc intrinsic fluorescence and its quenching was used to estimate the tocopherol position in the membrane. Optical microscopy was used to visualize morphological changes in the vesicles during the inclusion of tocopherol into the 2 mg/ml PC membrane. The incorporation of up to 15 mol% of tocopherol molecules into PC vesicles is accompanied by a linear increase in the fluorescence intensity and the simultaneous formation of larger, multilamellar vesicles. Increasing the tocopherol concentration above 20 mol% induced structural and morphological changes leading to the disappearance of micrometer-sized vesicles and the formation of small unilamellar vesicles of size ranging from 30 to 120 nm, mixed micelles and non-lamellar structures.
Deformation of Top‐Down and Bottom‐Up Silver Nanowires
Authors: Leach A. M. , McDowell M. , Gall K.
Published: November 2006

Atomistic simulations are employed to probe the deformation behavior of experimentally observed top‐down and bottom‐up face‐centered cubic silver nanowires. Stable, <110> oriented nanowires with a rhombic and truncated‐rhombic cross section are considered, representative of top‐down geometries, as well as the multiply twinned pentagonal nanowire that is commonly fabricated in a bottom‐up approach. The tensile deformation of a stable, experimentally observed structure is simulated to failure for each nanowire structure. A detailed, mechanistic explanation of the initial defect nucleation is provided for each nanowire. The three geometries are shown to exhibit different levels of strength and to deform by a range of mechanisms depending on the nanowire structure. In particular, the deformation behavior of top‐down and bottom‐up nanowires is shown to be fundamentally different. The yield strength of nanowires ranging from 1 to 25 nm in diameter is provided and reveals that in addition to cross‐sectional diameter, the strength of the nanowires is strongly tied to the structure. This study demonstrates that nanowire structure and size may be tailored for specific mechanical requirements in nanometer‐scale devices.
People who judge people
Authors: Weiss David J. , Shanteau James , Harries Priscilla
Published: November 2006

Experts who judge people usually provide opinions. It can be challenging to evaluate the professional performance of those experts, because for many domains there is no applicable external standard against which to verify the opinions. We review traditional methods for assessment and propose the purely empirical CWS approach as an alternative. Expert judgment entails discriminating among the various stimuli within the domain as well as being consistent when judging similar stimuli. We combine observed measures of these two components to form a ratio that we call the CWS index of expertise. We demonstrate the value of the index in an analysis of prioritization judgments made by occupational therapy students before and after they received specific training. The students' CWS scores improved considerably after training. The promise of the index as a selection tool is supported by the positive correlation of pre‐training scores with both post‐training scores and with course grades. Copyright © 2006 John Wiley & Sons, Ltd.