Distribution by Scientific Domains

Selected Abstracts

Families of pairs of graphs with a large number of common cards

Andrew Bowler
Abstract The vertex-deleted subgraph G,v, obtained from the graph G by deleting the vertex v and all edges incident to v, is called a card of G. The deck of G is the multiset of its unlabelled vertex-deleted subgraphs. The number of common cards of G and H (or between G and H) is the cardinality of the multiset intersection of the decks of G and H. In this article, we present infinite families of pairs of graphs of order n , 4 that have at least common cards; we conjecture that these, along with a small number of other families constructed from them, are the only pairs of graphs having this many common cards, for sufficiently large n. This leads us to propose a new stronger version of the Reconstruction Conjecture. In addition, we present an infinite family of pairs of graphs with the same degree sequence that have common cards, for appropriate values of n, from which we can construct pairs having slightly fewer common cards for all other values of n,10. We also present infinite families of pairs of forests and pairs of trees with and common cards, respectively. We then present new families that have the maximum number of common cards when one graph is connected and the other disconnected. Finally, we present a family with a large number of common cards, where one graph is a tree and the other unicyclic, and discuss how many cards are required to determine whether a graph is a tree. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 146,163, 2010 [source]

On factors of 4-connected claw-free graphs,

H. J. Broersma
Abstract We consider the existence of several different kinds of factors in 4-connected claw-free graphs. This is motivated by the following two conjectures which are in fact equivalent by a recent result of the third author. Conjecture 1 (Thomassen): Every 4-connected line graph is hamiltonian, i.e., has a connected 2-factor. Conjecture 2 (Matthews and Sumner): Every 4-connected claw-free graph is hamiltonian. We first show that Conjecture 2 is true within the class of hourglass-free graphs, i.e., graphs that do not contain an induced subgraph isomorphic to two triangles meeting in exactly one vertex. Next we show that a weaker form of Conjecture 2 is true, in which the conclusion is replaced by the conclusion that there exists a connected spanning subgraph in which each vertex has degree two or four. Finally we show that Conjectures 1 and 2 are equivalent to seemingly weaker conjectures in which the conclusion is replaced by the conclusion that there exists a spanning subgraph consisting of a bounded number of paths © 2001 John Wiley & Sons, Inc. J Graph Theory 37: 125,136, 2001 [source]

On the Coates,Sinnott Conjecture

Cristian D. Popescu
Abstract In [5], Coates and Sinnott formulated a far reaching conjecture linking the values ,F/k,S(1 , n) for even integers n , 2 of an S -imprimitive, Galois-equivariant L -function ,F/k,S associated to an abelian extension F/k of totally real number fields to the annihilators over the group ring ,[G (F/k)] of the even Quillen K -groups K2n,2 (OF) associated to the ring of integers OF of the top field F. In the same paper, Coates and Sinnott essentially prove the ,, -adic étale cohomological version of their conjecture, in which K2n,2(OF) is replaced by H2et(OF [1/,, ], ,(n)), for all primes ,, > 2, under the hypothesis that k = ,. Refinements of this result for k = ,, involving Fitting ideals rather than annihilators of H2et(OF [1/,,], ,,,(n)), were obtained in particular cases by Cornacchia,Řstvaer [7] and in general by Kurihara [14]. More recently, Burns and Greither [3] proved the same type of refinements (involving Fitting ideals of étale cohomology groups) for arbitrary totally real base fields k, but working under the very strong hypothesis that the Iwasawa , -invariants ,F,,, vanish for all odd primes ,,. In this paper, we study a class of abelian extensions of an arbitrary totally real base field k including, for example, subextensions of real cyclotomic extensions of type k (,)+/k, where p is an odd prime. For this class of extensions, we prove similar refinements of the étale cohomological version of the Coates,Sinnott conjecture, under no vanishing hypotheses for the Iwasawa ,-invariants in question. Our methods of proof are different from the ones employed in [3], [14] and [7]. We build upon ideas developed by Greither in [10] and Wiles in [23] and [22], in the context of Brumer's Conjecture. If the Quillen,Lichtenbaum Conjecture is proved (and a proof seems tobe within reach), then we have canonical ,,,[G (F/k)]-module isomorphisms for all n , 2, all i = 1,2, and all primes ,, > 2, and all these results will yield proofs of the original K -theoretic version of the Coates,Sinnott Conjecture, in the cases and under the various hypotheses mentioned above (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Comparative innervation of cephalic photophores of the loosejaw dragonfishes (Teleostei: Stomiiformes: Stomiidae): Evidence for parallel evolution of long-wave bioluminescence

Christopher P. Kenaley
Abstract Four genera of the teleost family Stomiidae, the loosejaw dragonfishes, possess accessory cephalic photophores (AOs). Species of three genera, Aristostomias, Malacosteus, and Pachystomias, are capable of producing far-red, long-wave emissions (>650nm) from their AOs, a character unique among vertebrates. Aristostomias and Malacosteus posses a single far-red AO, while Pachystomias possesses anterior and posterior far-red AOs, each with smaller separate photophores positioned in their ventral margins. The purpose of this study was to establish the primary homology of the loosejaw AOs based on topological similarity of cranial nerve innervation, and subject these homology conjectures to tests of congruence under a phylogenetic hypothesis for the loosejaw dragonfishes. On the basis of whole-mount, triple-stained specimens, innervation of the loosejaw AOs is described. The AO of Aristostomias and the anterior AO of Pachystomias are innervated by the profundal ramus of the trigeminal (Tpr), while the far-red AO of Malacosteus and a small ventral AO of Pachystomias are innervated by the maxillary ramus of the trigeminal (Tmx). The largest far-red AO of Pachystomias, positioned directly below the orbit, and the short-wave AO of Photostomias are innervated by a branch of the mandibular ramus of the trigeminal nerve. Conjectures of primary homology drawn from these neuroanatomical similarities were subjected to tests of congruence on a phylogeny of the loosejaws inferred from a reanalysis of a previously published morphological dataset. Optimized for accelerated transformation, the AO innervated by the Tpr appears as a single transformation on the new topology, thereby establishing secondary homology. The AOs innervated by the Tmd found in Pachystomias and Photostomias appear as two transformations in a reconstruction on the new topology, a result that rejects secondary homology of this structure. The secondary homology of AOs innervated by the Tmx found in Malacosteus and Pachystomias is rejected on the same grounds. Two short-wave cephalic photophores present in all four genera, the suborbital (SO) and the postorbital (PO), positioned in the posteroventral margin of the orbit and directly posterior to the orbit, respectively, are innervated by separate divisions of the Tmd. The primary homologies of the loosejaw PO and SO across loosejaw taxa are proposed on the basis of similar innervation patterns. Because of dissimilar innervation of the loosejaw SO and SO of basal stomiiforms, primary homology of these photophores cannot be established. Because of similar function and position, the PO of all other stomiid taxa is likely homologous with the loosejaw PO. Nonhomology of loosejaw long-wave photophores is corroborated by previously published histological evidence. The totality of evidence suggests that the only known far-red bioluminescent system in vertebrates has evolved as many as three times in a closely related group of deep-sea fishes. J. Morphol., 2010. © 2009 Wiley-Liss, Inc. [source]

Sacred Conjectures: the Context and Legacy of Robert Lowth and Jean Astruc , Edited by John Jarick

Tyler Mayfield
No abstract is available for this article. [source]

Palaeomorphology: fossils and the inference of cladistic relationships

ACTA ZOOLOGICA, Issue 1 2010
Gregory D. Edgecombe
Abstract Edgecombe, G.D. 2010. Palaeomorphology: fossils and the inference of cladistic relationships. ,Acta Zoologica (Stockholm) 91: 72,80 Twenty years have passed since it was empirically demonstrated that inclusion of extinct taxa could overturn a phylogenetic hypothesis formulated upon extant taxa alone, challenging Colin Patterson's bold conjecture that this phenomenon ,may be non-existent'. Suppositions and misconceptions about missing data, often couched in terms of ,wildcard taxa' and ,the missing data problem', continue to cloud the literature on the topic of fossils and phylogenetics. Comparisons of real data sets show that no a priori (or indeed a posteriori) decisions can be made about amounts of missing data and most properties of cladograms, and both simulated and real data sets demonstrate that even highly incomplete taxa can impact on relationships. The exclusion of fossils from phylogenetic analyses is neither theoretically nor empirically defensible. [source]

Inter-sexual combat and resource allocation into body parts in the spider, Stegodyphus lineatus

Abstract 1.,Sexual conflict, which results from the divergence of genetic interests between males and females, is predicted to affect multiple behavioural, physiological, and morphological traits. 2.,Sexual conflict over mating may interact with population density to produce predictable changes in resource allocation into inter-sexual armament. 3.,In the spider Stegodyphus lineatus, males fight with females over re-mating. The outcome of the fight is influenced by the cephalothorax size of the contestants. The investment in armament , the cephalothorax, may be traded-off against investment in abdomen, which is a trait that affects survival and fecundity. Pay-offs may depend on population density. Both sexes are expected to adjust resource allocation into different body parts accordingly. 4.,Males had increased cephalothorax/body size ratio in low densities where probability of finding another receptive female is low and females had increased cephalothorax/body size ratio in high densities where cumulative costs of multiple mating are high. 5.,The results support the theoretical conjecture that population density affects resource allocation into inter-sexual armament and call for further research on the interaction between sexual selection and population density. [source]

Emission trading regimes and incentives to participate in international climate agreements

Barbara Buchner
This paper analyses whether different emission trading regimes provide different incentives to participate in a cooperative climate agreement. Different incentive structures are discussed for those countries, namely the US, Russia and China, that are most important in the climate negotiation process. Our analysis confirms the conjecture that, by appropriately designing the emission trading regime, it is possible to enhance the incentives to participate in a climate agreement. Therefore, participation and optimal policy should be jointly analysed. Moreover, our results show that the US, Russia and China have different most preferred climate coalitions and therefore adopt conflicting negotiation strategies. Copyright © 2004 John Wiley & Sons, Ltd and ERP Environment. [source]

Native and subunit molecular mass and quarternary structure of the hemoglobin from the primitive branchiopod crustacean Triops cancriformis

FEBS JOURNAL, Issue 17 2006
Morgane Rousselot
Many branchiopod crustaceans are endowed with extracellular, high-molecular-weight hemoglobins whose exact structural characteristics have remained a matter of conjecture. By using a broad spectrum of techniques, we provide precise and coherent information on the hemoglobin of one of the phylogenetically ,oldest' extant branchiopods, the tadpole shrimp Triops cancriformis. The hemoglobin dissociated under reducing conditions into two subunits, designated TcHbA and TcHbB, with masses of 35 775 ± 4 and 36 055 ± 4 Da, respectively, determined by ESI-MS. Nonreducing conditions showed only two disulfide-bridged dimers, a homodimer of TcHbA, designated D1 (71 548 ± 5 Da), and the heterodimer D2 (71 828 ± 5 Da). Carbamidomethylation of free SH groups revealed the presence of three cysteines per subunit and indicated one intrasubunit and one intersubunit disulfide bridge. Ultracentrifugation and light-scattering experiments under nondenaturating conditions yielded mass estimates that suggested an uneven number of 17 subunits forming the native hemoglobin. This unrealistic number resulted from the presence of two size classes (16-mer and 18-mer), which were recognized by native PAGE and Ferguson plot analysis. ESI-MS revealed three hemoglobin isoforms with masses of 588.1 kDa, 662.0 kDa, and 665.0 kDa. The 16-mer and the smaller 18-mer species are supposed to be composed of TcHbA only, given the dominance of this subunit type in SDS/PAGE. Transmission electron microscopy of negatively stained specimens showed a population of compact molecules with geometrical extensions of 14, 16 and 9 nm. The proposed stoichiometric model of quarternary structure provides the missing link to achieve a mechanistic understanding of the structure,function relationships among the multimeric arthropodan hemoglobins. [source]

Is high strength concrete more susceptible to explosive spalling than normal strength concrete in fire?

Faris Ali
There is a belief, within the fire research community, that high strength concrete is more susceptible to explosive spalling than normal strength concrete. This impression is based on studying concrete properties and collecting experimental data from different research sources. But there are still doubts about the credibility of this conjecture due to the lack of integrated experimental research, particularly designed to address this issue. This paper represents the outcomes of experimental study involving normal and high strength concrete columns tested under fire. The columns were subjected to a constant load and to different values of axial restraint. The paper attempts to address the question of the susceptibility of normal and high strength concrete to explosive spalling under fire. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Free fermions violate the area law for entanglement entropy

R.C. Helling
Abstract We show that the entanglement entropy associated to a region grows faster than the area of its boundary surface. This is done by proving a special case of a conjecture due to Widom that yields a surprisingly simple expression for the leading behaviour of the entanglement entropy. [source]

Flux compactification of M-theory on compact manifolds with Spin(7) holonomy,

D. Constantin
At the leading order, M-theory admits minimal supersymmetric compactifications if the internal manifold has exceptional holonomy. The inclusion of non-vanishing fluxes in M-theory and string theory compactifications induce a superpotential in the lower dimensional theory, which depends on the fluxes. In this work, we check the conjectured form of this superpotential in the case of warped M-theory compactifications on Spin(7) holonomy manifolds. We perform a Kaluza-Klein reduction of the eleven-dimensional supersymmetry transformation for the gravitino and we find by direct comparison the superpotential expression. We check the conjecture for the heterotic string compactified on a Calabi-Yau three-fold as well. The conjecture can be checked indirectly by inspecting the scalar potential obtained after the compactification of M-theory on Spin(7) holonomy manifolds with non-vanishing fluxes. The scalar potential can be written in terms of the superpotential and we show that this potential stabilizes all the moduli fields describing deformations of the metric except for the radial modulus. All the above analyses require the knowledge of the minimal supergravity action in three dimensions. Therefore we calculate the most general causal ,, =1 three-dimensional, gauge invariant action coupled to matter in superspace and derive its component form using Ectoplasmic integration theory. We also show that the three-dimensional theory which results from the compactification is in agreement with the more general supergravity construction. The compactification procedure takes into account higher order quantum correction terms in the low energy effective action. We analyze the properties of these terms on a Spin(7) background. We derive a perturbative set of solutions which emerges from a warped compactification on a Spin(7) holonomy manifold with non-vanishing flux for the M-theory field strength and we show that in general the Ricci flatness of the internal manifold is lost, which means that the supergravity vacua are deformed away from the exceptional holonomy. Using the superpotential form we identify the supersymmetric vacua out of this general set of solutions. [source]

Flux vacua statistics for two-parameter Calabi-Yau's

A. Misra
Abstract We study the number of flux vacua for type IIB string theory on an orientifold of the Calabi-Yau expressed as a hypersurface in WCP4[1,1,2,2,6] by evaluating a suitable integral over the complex-structure moduli space as per the conjecture of Douglas and Ashok. We show that away from the singular conifold locus, one gets a power law, and that the (neighborhood) of the conifold locus indeed acts as an attractor in the (complex structure) moduli space. In the process, we evaluate the periods near the conifold locus. We also study (non)supersymmetric solutions near the conifold locus, and show that supersymmetric solutions near the conifold locus do not support fluxes. [source]

Nonlocal quantum gravity and the size of the universe

M. Reuter
Motivated by the conjecture that the cosmological constant problem is solved by strong quantum effects in the infrared we use the exact flow equation of Quantum Einstein Gravity to determine the renormalization group behavior of a class of nonlocal effective actions. They consist of the Einstein-Hilbert term and a general nonlinear function Fk(V) of the Euclidean spacetime volume V. For the V + V ln V -invariant the renormalization group running enormously suppresses the value of the renormalized curvature which results from Planck-size parameters specified at the Planck scale. One obtains very large, i.e., almost flat universes without finetuning the cosmological constant. A critical infrared fixed point is found where gravity is scale invariant. [source]

Field theory on a non-commutative plane: a non-perturbative study

F. Hofheinz
Abstract The 2d gauge theory on the lattice is equivalent to the twisted Eguchi,Kawai model, which we simulated at N ranging from 25 to 515. We observe a clear large N scaling for the 1- and 2-point function of Wilson loops, as well as the 2-point function of Polyakov lines. The 2-point functions agree with a universal wave function renormalization. The large N double scaling limit corresponds to the continuum limit of non-commutative gauge theory, so the observed large N scaling demonstrates the non-perturbative renormalizability of this non-commutative field theory. The area law for the Wilson loops holds at small physical area as in commutative 2d planar gauge theory, but at large areas we find an oscillating behavior instead. In that regime the phase of the Wilson loop grows linearly with the area. This agrees with the Aharonov-Bohm effect in the presence of a constant magnetic field, identified with the inverse non-commutativity parameter. Next we investigate the 3d ,,4 model with two non-commutative coordinates and explore its phase diagram. Our results agree with a conjecture by Gubser and Sondhi in d = 4, who predicted that the ordered regime splits into a uniform phase and a phase dominated by stripe patterns. We further present results for the correlators and the dispersion relation. In non-commutative field theory the Lorentz invariance is explicitly broken, which leads to a deformation of the dispersion relation. In one loop perturbation theory this deformation involves an additional infrared divergent term. Our data agree with this perturbative result. We also confirm the recent observation by Ambjř rn and Catterall that stripes occur even in d = 2, although they imply the spontaneous breaking of the translation symmetry. [source]

The effect of water content on proton transport in polymer electrolyte membranes

FUEL CELLS, Issue 3-4 2002
P. Commer
Abstract We investigate proton transport in a polymer electrolyte membrane using continuum theory and molecular dynamics (MD) computer simulations. Specifically our goal is to understand the possible molecular origin of the effect of water content on the activation energy (AE) and pre-exponential factor of proton conductivity, in comparison with experimental observations reported for Nafion, where a decrease of AE with increasing water content has been observed. We study proton diffusion in a single pore, using a slab-like model. We find that although the average proton diffusion coefficient is several times smaller in a narrow pore than in a wide water-rich pore, its AE is almost unaffected by the pore width. This contradicts an earlier proposed conjecture that the sizable Coulomb potential energy barriers near the lattice of immobile point-like SO3, groups increase the AE in a narrow pore. Here we show that these barriers become smeared out by thermal motion of SO3, groups and by the spatial charge distribution over their atoms. This effect strongly diminishes the variation of the AE with pore width, which is also found in MD simulations. The pre-exponential factor for the diffusion process, however, decreases, indicating a limited number of pathways for proton transfer and the freezing out of degrees of freedom that contribute to the effective frequency of transfer. Decreasing the pore size diminishes bulk-like water regions in the pore, with only less mobile surface water molecules remaining. This hampers proton transfer. The increase of AE takes place only if the thermal motion of the SO3, head groups freezes out simultaneously with decreasing water content, but the effect is not profound. The stronger effect observed experimentally may thus be associated with some other rate-determining consecutive process, concerned with polymer dynamics, such as opening and closing of connections (bridges) between aqueous domains in the membrane under low water content. [source]

Cost savings in migraine associated with less chest pain on new triptan therapy.

HEADACHE, Issue 3 2003
JT Wang
Am J Manag Care. 2002 Feb;8(3 Suppl):S102-S107 Objectives: This article constructs an economic model to estimate cost of chest-pain-related care in migraine patients receiving almotriptan 12.5 mg compared with those receiving sumatriptan 50 mg. Study Design: This population-based, retrospective cohort study used data from the MEDSTAT Marketscan database (Ann Arbor, Michigan) to quantify incidence and costs of chest-pain-related diagnoses and procedures. After a 6-month exclusion period, the study used a pre-post design, with baseline and treatment periods defined, respectively, as 5 months before and after receiving sumatriptan therapy. An economic model was constructed to estimate annual cost savings per 1,000 patients receiving almotriptan instead of sumatriptan as a function of differing rates of chest pain. Annual direct medical cost avoided was calculated for a hypothetical health plan covering 1 million lives. Results: Among a cohort of 1,390 patients, the incidence of chest-pain-related diagnoses increased significantly (43.6%) with sumatriptan, from 110 during the baseline period to 158 during the treatment period (P = .003). Aggregate costs for chest-pain-related diagnoses and procedures increased 33.1%, from $22,713 to $30,234. Payments for inpatient hospital services rose 10-fold; costs for primary care visits and outpatient hospital visits rose 53.1% and 14.4%, respectively. Payments for angiography increased from $0 to $462, and costs for chest radiographs and electrocardiograms increased 58.7% and 31.2%, respectively. Sumatriptan treatment was associated with a 3-fold increase in payments for services for painful respiration and other chest pain. The model predicted $11,215 in direct medical cost savings annually per 1000 patients treated with almotriptan instead of sumatriptan. Annual direct medical costs avoided for the health plan totaled $195,913. Conclusion: Using almotriptan instead of sumatriptan will likely reduce the cost of chest-pain-related care for patients with migraine headaches. Comment: In my view, this study takes conjecture a step too far. The lower reported chest adverse events (AEs) reported in clinical trials where all AEs are scrutinized will not necessarily lead to lower reporting in the clinic. This hypothesis remains to be proven in a well-designed post-marketing surveillance program, untarnished by commercial sponsorship. Until such an independent prospective study is carried out, the extrapolations described here and in similar papers are pure conjecture and should be classed as the lowest grade of evidence on a par with uncorroborated clinical opinion. DSM [source]

Enhancement of temporal and spatial synchronization of entorhinal gamma activity by phase reset

HIPPOCAMPUS, Issue 4 2002
Clayton T. Dickson
Abstract The synchronization of cortical gamma oscillatory activity (25,80 Hz) is thought to coordinate neuronal assemblies in the processing and storage of information. The mechanism by which independently oscillating and distantly located cortical zones become synchronized is presumed to involve activity in corticocortical connections, although evidence supporting this conjecture has only been indirect. In the present study, we show that activation of synaptic inputs within and to the medial entorhinal cortex (mEC) of the in vitro isolated guinea pig brain preparation resets the phase of ongoing gamma activity induced by muscarinic receptor agonism with carbachol (frequency: 24 ± 2 Hz at 32°C). Phase reset was associated with a transient enhancement of the synchronization of gamma activity recorded at distant (>1 mm) mEC sites, across which low coherence (>0.75) was observed before stimulation. This increase in synchronization, as measured by cross-correlation analysis, was restricted to a maximal period of 200 ms after either local mEC or CA1 afferent stimulation. The results provide direct evidence that synaptic activation can enhance the rhythmic synchronization of spatially remote, independently oscillating neuronal assemblies in the mEC through a mechanism of synaptically evoked phase reset. Dynamic functional grouping of oscillatory discharges across long distances in the mEC may underlie coding processes involved in the integration and storage of incoming information and thus may be important for the role of this region in memory processes. Hippocampus 2002;12:447,456. © 2002 Wiley-Liss, Inc. [source]

Verbal memory performance improved via an acute administration of D -amphetamine

Inge Zeeuws
Abstract Background An improved long-term retention of verbal memory was observed after an acute D -amphetamine administration. It was proposed that D -amphetamine modulates consolidation, but a possible drug effect on retrieval could not be rejected. Objectives We want to provide additional support for the consolidation hypothesis, and investigate whether an influence on intervening retrieval can be refuted. Methods Thirty-six male paid volunteers participated in a double blind, counterbalanced, placebo-controlled design in which the number of intermediate free recall tests was manipulated. Results A significant D -amphetamine facilitation effect on recall performance emerged 1 h and 1 day after list learning. In line with the consolidation hypothesis, no effect was found on immediate tests. Importantly, the number of intermediate retrievals did not affect the magnitude of the drug effect, suggesting that the D -amphetamine facilitation effect is independent of retrieval. Conclusion The D -amphetamine facilitation effect on verbal memory does not involve a modulation of the initial encoding or short-term memory (STM) processes. Moreover, the drug does not enhance long-term retention by acting on intervening retrieval processes. The current findings are in line with the conjecture of an involvement of the consolidation process in the D -amphetamine facilitation effect on verbal memory in healthy humans. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Edward J. Green
We investigate the efficiency property of a monetary economy with spot trade. We prove a conjecture that is essentially due to Bewley (Models of Monetary Economics (1980); Econometrica 51 (1983), 1485,504). The gist is that monetary spot trading is nearly efficient ex ante in an environment where very patient agents can accumulate large enough money stocks to be completely self-insured. We also study examples where a nonmonetary mechanism is preferred ex ante to any monetary mechanism in a stationary environment, and where an inflationary monetary mechanism is preferred ex ante to a laissez-faire or deflationary monetary mechanism in an environment with impatient agents. [source]

How many-body perturbation theory (MBPT) has changed quantum chemistry

Werner KutzelniggArticle first published online: 26 AUG 200
Abstract The history of many-body perturbation theory (MBPT) and its impact on Quantum Chemistry is reviewed, starting with Brueckner's conjecture of a linked-cluster expansion and the time-dependent derivation by Goldstone of such an expansion. A central part of this article is the time-independent formulation of quantum chemistry in Fock space and its diagrammatic representation including the particle-hole picture and the inversion of a commutator. The results of the time-independent derivation of MBPT are compared with those of Goldstone. It is analyzed which ingredients of Goldstone's approach are decisive. The connected diagram theorem is derived both in a constructive way based on a Lie-algebraic formulation and a nonconstructive way making use of the separation theorem. It is discussed why the Goldstone derivation starting from a unitary time-evolution operator, ends up with a wave operator in intermediate normalization. The Mřller,Plesset perturbation expansions of Bartlett and Pople are compared. Examples of complete summations of certain classes of diagrams are discussed, for example, that which leads to the Bethe-Goldstone expansion. MBPT for energy differences is analyzed. The paper ends with recent developments and challenges, such as the generalization of normal ordering to arbitrary reference states, contracted Schrödinger k -particle equations and Brillouin conditions, and finally the Nakatsuji theorem and the Nooijen conjecture. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

Can the Discretionary Nature of Certain Criteria Lead to Differential Prediction Across Cultural Groups?

Oleksandr S. Chernyshenko
We examined the conjecture that relations between constructs across cultures may be susceptible to cultural moderation where the performance of the criterion construct is discretionary. This hypothesis was investigated using the relationship between personality and three performance constructs, with samples from the United States and New Zealand, two ideologically distinct cultures with respect to achievement orientation. All hypotheses were supported by results of hierarchical moderated regression analyses using bias free measures, suggesting that considering whether construct behaviors are discretionary is important when considering the merit of generalizing research findings across cultures. [source]

Debt Covenants and Accounting Conservatism

ABSTRACT Using a sample of over 5,000 debt issues, I test whether firms with more extensive use of covenants in their public debt contracts exhibit timelier recognition of economic losses in accounting earnings. Covenants govern the transfer of decision-making and control rights from shareholders to bondholders when a company approaches financial distress and thereby limit managers' abilities to expropriate bondholder wealth. Covenants are expected to constrain managerial opportunism, however, only if the accounting system recognizes economic losses in earnings in a timely fashion. Thus, the demand for timely loss recognition should increase with a contract's reliance on covenants. Consistent with this conjecture, I find evidence that reliance on covenants in public debt contracts is positively associated with the degree of timely loss recognition. I also find evidence that the presence of prior private debt mitigates this relationship. [source]

Shifted factor analysis,Part II: Algorithms

Sungjin Hong
Abstract We previously proposed a family of models that deal with the problem of factor position shift in sequential data. We conjectured that the added information provided by fitting the shifts would make the model parameters identifiable, even for two-way data. We now derive methods of parameter estimation and give the results of experiments with synthetic data. The alternating least squares (ALS) approach is not fully suitable for estimation, because factor position shifts destroy the multilinearity of the latent structure. Therefore an alternative ,quasi-ALS' approach is developed, some of its practical and theoretical properties are dealt with and several versions of the quasi-ALS algorithm are described in detail. These procedures are quite computation-intensive, but analysis of synthetic data demonstrates that the algorithms can recover shifting latent factor structure and, in the situations tested, are robust against high error levels. The results of these experiments also provide strong empirical support for our conjecture that the two-way shifted factor model has unique solutions in at least some circumstances. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The tyranny of the positive attitude in America: Observation and speculation

Barbara S. Held
According to both popular and professional indicators, the push for the positive attitude in America is on the rise. After considering the popular culture zeitgeist, I compare and contrast two recent professional psychology movements,those of positive psychology and postmodern therapy,both of which rest on a foundation of optimism and positive thinking despite their opposing views about a proper philosophy of science. I then present cross-cultural empirical research that calls into question the typical (North American) assumption that a positive attitude is necessary for (a sense of) well-being. I also consider findings in health psychology, clinical/counseling psychology, and organizational behavioral science, findings which call into question the assumption that accentuating the positive (and eliminating the negative) is necessarily beneficial in terms of physical and mental health. The clinical/therapeutic implications of this analysis are addressed, as I put forth my conjecture about the existence of what I call the "tyranny of the positive attitude" in the form of a question: If there indeed now exists unprecedented pressure to accentuate the positive, could it then be that the pressure itself to be happy and optimistic contributes to at least some forms of unhappiness? © 2002 Wiley Periodicals, Inc. J Clin Psychol 58: 965,991, 2002. [source]

Empirical test of bullies' status goals: assessing direct goals, aggression, and prestige

Jelle J. Sijtsema
Abstract The literature suggests that status goals are one of the driving motivations behind bullying behavior, yet this conjecture has rarely if ever been examined empirically. This study assessed status goals in three ways, using dyadic network analysis to analyze the relations and goals among 10,11 and 14,15 year olds in 22 school classes (N boys=225; N girls=277). As a validation bullies were contrasted with victims. Bullies had direct status goals (measured with the Interpersonal Goal Inventory for Children) and showed dominance as measured with proactive aggression. Moreover, as predicted from a goal perspective, bullying behavior was related to prestige in terms of perceived popularity. In contrast, victims lacked status goals, were only reactively aggressive, and low on prestige. That being popular is not the same as being liked could be shown by the fact that bullies were just as rejected as victims by their classmates. Eighth-grade bullies had more direct status goals than fourth-grade bullies, possibly indicating that striving for the popularity component of status increases in early adolescence. Aggr. Behav. 35:57,67, 2009. © 2008 Wiley-Liss, Inc. [source]

Complete graph conjecture for inner-core electrons: Homogeneous index case

Lionello Pogliani
Abstract The complete graph conjecture that encodes the inner-core electrons of atoms with principal quantum number n , 2 with complete graphs, and especially with odd complete graphs, is discussed. This conjecture is used to derive new values for the molecular connectivity and pseudoconnectivity basis indices of hydrogen-suppressed chemical pseudographs. For atoms with n = 2 the new values derived with this conjecture are coincident with the old ones. The modeling ability of the new homogeneous basis indices, and of the higher-order terms, is tested and compared with previous modeling studies, which are centered on basis indices that are either based on quantum concepts or partially based on this new conjecture for the inner-core electrons. Two similar algorithms have been proposed with this conjecture, and they parallel the two "quantum" algorithms put forward by molecular connectivity for atoms with n > 2. Nine properties of five classes of compounds have been tested: the molecular polarizabilities of a class of organic compounds, the dipole moment, molar refraction, boiling points, ionization energies, and parachor of a series of halomethanes, the lattice enthalpy of metal halides, the rates of hydrogen abstraction of chlorofluorocarbons, and the pED50 of phenylalkylamines. The two tested algorithms based on the odd complete graph conjecture give rise to a highly interesting model of the nine properties, and three of them can even be modeled by the same set of basis indices. Interesting is the role of some basis indices all along the model. © 2003 Wiley Periodicals, Inc. J Comput Chem 9: 1097,1109, 2003 [source]

Multi-coloring the Mycielskian of graphs

Wensong Lin
Abstract A k -fold coloring of a graph is a function that assigns to each vertex a set of k colors, so that the color sets assigned to adjacent vertices are disjoint. The kth chromatic number of a graph G, denoted by ,k(G), is the minimum total number of colors used in a k -fold coloring of G. Let µ(G) denote the Mycielskian of G. For any positive integer k, it holds that ,k(G) + 1,,k(µ(G)),,k(G) + k (W. Lin, Disc. Math., 308 (2008), 3565,3573). Although both bounds are attainable, it was proved in (Z. Pan, X. Zhu, Multiple coloring of cone graphs, manuscript, 2006) that if k,2 and ,k(G),3k,2, then the upper bound can be reduced by 1, i.e., ,k(µ(G)),,k(G) + k,1. We conjecture that for any n,3k,1, there is a graph G with ,k(G)=n and ,k(µ(G))=n+ k. This is equivalent to conjecturing that the equality ,k(µ(K(n, k)))=n+k holds for Kneser graphs K(n, k) with n,3k,1. We confirm this conjecture for k=2, 3, or when n is a multiple of k or n,3k2/ln k. Moreover, we determine the values of ,k(µ(C2q+1)) for 1,k,q. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 311,323, 2010 [source]

Balanced judicious bipartitions of graphs

Baogang Xu
Abstract A bipartition of the vertex set of a graph is called balanced if the sizes of the sets in the bipartition differ by at most one. B. Bollobás and A. D. Scott, Random Struct Alg 21 (2002), 414,430 conjectured that if G is a graph with minimum degree of at least 2 then V(G) admits a balanced bipartition V1, V2 such that for each i, G has at most |E(G)|/3 edges with both ends in Vi. The minimum degree condition is necessary, and a result of B. Bollobás and A. D. Scott, J. Graph Theory 46 (2004), 131,143 shows that this conjecture holds for regular graphs G(i.e., when ,(G)=,(G)). We prove this conjecture for graphs G with ; hence, it holds for graphs ]ensuremathG with . © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 210,225, 2010 [source]

Proof of a conjecture on fractional Ramsey numbers

Jason Brown
Abstract Jacobson, Levin, and Scheinerman introduced the fractional Ramsey function rf (a1, a2, ,, ak) as an extension of the classical definition for Ramsey numbers. They determined an exact formula for the fractional Ramsey function for the case k=2. In this article, we answer an open problem by determining an explicit formula for the general case k>2 by constructing an infinite family of circulant graphs for which the independence numbers can be computed explicitly. This construction gives us two further results: a new (infinite) family of star extremal graphs which are a superset of many of the families currently known in the literature, and a broad generalization of known results on the chromatic number of integer distance graphs. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 164,178, 2010 [source]