New Solution (new + solution)

Distribution by Scientific Domains

Selected Abstracts

AgJOBS: New Solution or New Problem?

Philip Martin
Over half of the workers employed on U.S. farms are not authorized to work in the United States. An historic compromise between employer and worker advocates in September 2003 would legalize some currently unauthorized workers and make it easier for farmers to obtain guest workers, but is unlikely to change the farm labor market, so that the percentage of unauthorized workers is likely to climb again. [source]

New Solutions to the C-12,13 Stereoproblem of Epothilones B and D; Synthesis of a 12,13-Diol-Acetonide Epothilone B Analog

Tanja Gaich
Abstract New approaches are described to the synthesis of epothilone B and a 12,13-diol-acetonide derivative. Specifically the (12Z) double bond is formed quantitatively by a silicon-tethered ring-closing metathesis (RCM) reaction with 85,% selectivity. Alternatively, a direct route to the 12,13-epoxide by cyclization of a 12,13-diol has been developed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

FRW minisuperspace with local N=4 supersymmetry and self-interacting scalar field

P. Vargas Moniz
Abstract A supersymmetric FRW model with a scalar supermultiplet and generic superpotential is analysed from a quantum cosmological perspective. The corresponding Lorentz and supersymmetry constraints allow to establish a system of first order partial differential equations from which solutions can be obtained. We show that this is possible when the superpotential is expanded in powers of a parameter ,,1. At order ,0 we find the general class of solutions, which include in particular quantum states reported in the current literature. New solutions are partially obtained at order ,1, where the dependence on the superpotential is manifest. These classes of solutions can be employed to find states for higher orders in ,. Our analysis further points to the following: (i) supersymmetric wave functions can only be found when the superpotential has either an exponential behaviour, an effective cosmological constant form or is zero; (ii) If the superpotential behaves differently during other periods, the wave function is trivial ( = 0, i.e., no supersymmetric states). We conclude this paper discussing how our FRW minisuperspace (with N = 4 supersymmetry and invariance under time-reparametrization) can be relevant concerning the issue of supersymmetry breaking. [source]

Twisted Intercalating Nucleic Acids , Intercalator Influence on Parallel Triplex Stabilities

Vyacheslav V. Filichev
Abstract Phosphoramidites of several new twisted intercalating nucleic acid (TINA) monomers and the previously discovered (R)-1- O -[4-(1-pyrenylethynyl)phenylmethyl]glycerol (1) were synthesized and used in DNA synthesis. Stabilization of Hoogsteen-type triplexes was observed in cases of insertion of the novel (R)-1- O -[3-(naphthalen-1-ylethynyl)phenylmethyl]glycerol (2) as a bulge into homopyrimidine oligodeoxynucleotides (ONs), whereas phenylethynyl and 4-(biphenylylethynyl) derivatives of TINAs resulted in destabilization of parallel triplexes relative to the wild-type triplex. It was concluded that TINA monomers should possess at least two fused phenyl rings attached through the triple bond at the 4-position of bulged (R)-1- O -(phenylmethyl)glycerol in homopyrimidine ONs in order to stabilize parallel triplexes. Slight destabilization of DNA/DNA Watson,Crick type duplexes (,Tm = 1.0,4.5 °C) was detected for 2 inserted as a bulge, while RNA/DNA duplexes and duplexes with other TINA analogues were considerably destabilized (,Tm > 6.0 °C). In cases of double insertion of 1 opposite to base inversions in dsDNA, the thermal stabilities of the triplexes were higher than that of the wild-type triplex, which is a new solution to overcome the problem of targeting homopurine stretches with single base pair inversions. A DNA three-way junction was considerably stabilized (,Tm in a range of 10.0,15.5 °C) upon insertion of TINA monomers in the junction point as a bulge. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Drawdown and Stream Depletion Produced by Pumping in the Vicinity of a Partially Penetrating Stream

GROUND WATER, Issue 5 2001
James J. Butler Jr.
Commonly used analytical approaches for estimation of pumping-induced drawdown and stream depletion are based on a series of idealistic assumptions about the stream-aquifer system. A new solution has been developed for estimation of drawdown and stream depletion under conditions that are more representative of those in natural systems (finite width stream of shallow penetration adjoining an aquifer of limited lateral extent). This solution shows that the conventional assumption of a fully penetrating stream will lead to a significant overestimation of stream depletion (> 100%) in many practical applications. The degree of overestimation will depend on the value of the stream leakance parameter and the distance from the pumping well to the stream. Although leakance will increase with stream width, a very wide stream will not necessarily be well represented by a model of a fully penetrating stream. The impact of lateral boundaries depends upon the distance from the pumping well to the stream and the stream leakance parameter. In most cases, aquifer width must be on the order of hundreds of stream widths before the assumption of a laterally infinite aquifer is appropriate for stream-depletion calculations. An important assumption underlying this solution is that stream-channel penetration is negligible relative to aquifer thickness. However, an approximate extension to the case of nonnegligible penetration provides reasonable results for the range of relative penetrations found in most natural systems (up to 85%). Since this solution allows consideration of a much wider range of conditions than existing analytical approaches, it could prove to be a valuable new tool for water management design and water rights adjudication purposes. [source]

A new solution for a partially penetrating constant-rate pumping well with a finite-thickness skin

Pin-Yuan Chiu
Abstract A mathematical model describing the constant pumping is developed for a partially penetrating well in a heterogeneous aquifer system. The Laplace-domain solution for the model is derived by applying the Laplace transforms with respect to time and the finite Fourier cosine transforms with respect to vertical co-ordinates. This solution is used to produce the curves of dimensionless drawdown versus dimensionless time to investigate the influences of the patch zone and well partial penetration on the drawdown distributions. The results show that the dimensionless drawdown depends on the hydraulic properties of the patch and formation zones. The effect of a partially penetrating well on the drawdown with a negative patch zone is larger than that with a positive patch zone. For a single-zone aquifer case, neglecting the effect of a well radius will give significant error in estimating dimensionless drawdown, especially when dimensionless distance is small. The dimensionless drawdown curves for cases with and without considering the well radius approach the Hantush equation (Advances in Hydroscience. Academic Press: New York, 1964) at large time and/or large distance away from a test well. Copyright © 2007 John Wiley & Sons, Ltd. [source]

An efficient pursuit automata approach for estimating stable all-pairs shortest paths in stochastic network environments,

Sudip Misra
Abstract This paper presents a new solution to the dynamic all-pairs shortest-path routing problem using a fast-converging pursuit automata learning approach. The particular instance of the problem that we have investigated concerns finding the all-pairs shortest paths in a stochastic graph, where there are continuous probabilistically based updates in edge-weights. We present the details of the algorithm with an illustrative example. The algorithm can be used to find the all-pairs shortest paths for the ,statistical' average graph, and the solution converges irrespective of whether there are new changes in edge-weights or not. On the other hand, the existing popular algorithms will fail to exhibit such a behavior and would recalculate the affected all-pairs shortest paths after each edge-weight update. There are two important contributions of the proposed algorithm. The first contribution is that not all the edges in a stochastic graph are probed and, even if they are, they are not all probed equally often. Indeed, the algorithm attempts to almost always probe only those edges that will be included in the final list involving all pairs of nodes in the graph, while probing the other edges minimally. This increases the performance of the proposed algorithm. The second contribution is designing a data structure, the elements of which represent the probability that a particular edge in the graph lies in the shortest path between a pair of nodes in the graph. All the algorithms were tested in environments where edge-weights change stochastically, and where the graph topologies undergo multiple simultaneous edge-weight updates. Its superiority in terms of the average number of processed nodes, scanned edges and the time per update operation, when compared with the existing algorithms, was experimentally established. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Shopping for E-Learning

Craig Hannas
Corporate training for employees and executives is vital in today's quickly changing market. However, it can be very expensive. But a new solution is revolutionizing corporate training and slashing costs: online training, or e-learning. The author explains how it works and gives advice on how to shop for an e-learning provider. © 2001 John Wiley & Sons, Inc. [source]

Validating multiple-period density-forecasting models

Kevin Dowd
Abstract This paper examines the problem of how to validate multiple-period density forecasting models. Such models are more difficult to validate than their single-period equivalents, because consecutive observations are subject to common shocks that undermine i.i.d. The paper examines various solutions to this problem, and proposes a new solution based on the application of standard tests to a resample that is constructed to be i.i.d. It suggests that this solution is superior to alternatives, and presents results indicating that tests based on the i.i.d. resample approach have good power.,,Copyright © 2007 John Wiley & Sons, Ltd. [source]

Internal loading: A new solution to an old problem in aquatic sciences

Lars Håkanson
Abstract Internal loading has long been regarded as an ,Achilles heel' in aquatic science and management. Internal loading is of fundamental importance in large and shallow lakes, where even low wind velocities can cause a considerable resuspension of matter deposited on the lake bed. The resuspended matter, and the chemical substances bound to the resuspended matter, will influence almost all processes in the aquatic ecosystem, such as water clarity and depth of the photic zone, and hence, primary and secondary production. If the sediments are contaminated, it will increase the concentrations of harmful substances in water and sediments and the potential ecosystem effects related to such concentrations. This paper presents an overview of the processes regulating bottom dynamic conditions in lakes (erosion, transport, accumulation), provides examples on the role of internal loading within the context of limnology and water management, and presents a new, general approach to quantify internal loading from sediments in lakes. The new approach has been critically tested, being a key factor behind the increase in predictive power of a new generation of lake models meant to be used for practical water management. Internal loading of any water pollutant depends on sedimentation. Sedimentation in this approach is presented as a function of two substance-specific variables, including the fall velocity of the carrier-particles and the particulate fraction (which, by definition, is the only fraction of a water pollutant that can settle out on the lake bed), and three generic variables, including mean depth, suspended particulate matter and ET-areas (areas of erosion and transport). On ET-areas there is, by definition, a discontinuous sedimentation of materials that settles according to Stokes' law. Basically, internal loading is the sum of advective (resuspension) and diffusive transport from the sediments. Resuspension from ET-areas is given as a function of the lake form (a new algorithm based on the volume development) and the age of ET-sediments. [source]

New anisotropic models from isotropic solutions

S. D. Maharaj
Abstract We establish an algorithm that produces a new solution to the Einstein field equations, with an anisotropic matter distribution, from a given seed isotropic solution. The new solution is expressed in terms of integrals of known functions, and the integration can be completed in principle. The applicability of this technique is demonstrated by generating anisotropic isothermal spheres and anisotropic constant density Schwarzschild spheres. Both of these solutions are expressed in closed form in terms of elementary functions, and this facilitates physical analysis. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Direct Reference, Psychological Explanation, and Frege Cases

MIND & LANGUAGE, Issue 4 2005
Susan Schneider
I offer a new solution to the problem of Frege Cases. Frege Cases involve agents who are unaware that certain expressions co-refer (e.g. that ,Cicero' and ,Tully' co-refer), where such knowledge is relevant to the success of their behavior, leading to cases in which the agents fail to behave as the intentional laws predict. It is generally agreed that Frege Cases are a major problem, if not the major problem, that this sort of theory faces. In this essay, I hope to show that the theory can surmount the Frege Cases. [source]


RATIO, Issue 1 2005
Frank Hofmann
Hugh Mellor has proposed what appears to be a new solution to the problem of intrinsic change (Mellor 1998). Assuming endurantism and a B-theoretic, nonpresentist view of time, facts are supposed to have only enduring things and atemporal properties (or relations) as constituents, but no times. The having of properties and relations is not relativised to times. Instead, the whole of a fact is conceived of as temporally localised. It will be argued that this interesting and novel proposal does not succeed as an account of change in the intrinsic properties of things. The basic difficulty is that the view still leads into contradiction, since it makes it incomprehensible how one and the same thing can have both a property and some incompatible property. The having of these incompatible properties is treated as two facts. But to add that these facts have certain temporal locations is of no help for avoiding the contradiction. [source]

Modified Two-Layer Preservation Method (M-Kyoto/PFC) Improves Islet Yields in Islet Isolation

H. Noguchi
Islet allotransplantation can achieve insulin independence in patients with type I diabetes. Recent reports show that the two-layer method (TLM), which employs oxygenated perfluorochemical (PFC) and UW solution, is superior to simple cold storage in UW for pancreas preservation in islet transplantation. However, UW solution has several disadvantages, including the inhibition of Liberase activity. In this study, we investigated the features of a new solution, designated M-Kyoto solution. M-Kyoto solution contains trehalose and ulinastatin as distinct components. Trehalose has a cytoprotective effect against stress, and ulinastatin inhibits trypsin. In porcine islet isolation, islet yield was significantly higher in the M-Kyoto/PFC group compared with the UW/PFC group. There was no significant difference in ATP content in the pancreas between the two groups, suggesting that different islet yields are not due to their differences as energy sources. Compared with UW solution, M-Kyoto solution significantly inhibited trypsin activity in the digestion step; moreover, M-Kyoto solution inhibited collagenase digestion less than UW solution. In conclusion, the advantages of M-Kyoto solution are trypsin inhibition and less collagenase inhibition. Based on these data, we now use M-Kyoto solution for clinical islet transplantation from nonheart-beating donor pancreata. [source]

Dual- and triple-mode matrix approximation and regression modelling

Stan Lipovetsky
Abstract We propose a dual- and triple-mode least squares for matrix approximation. This technique applied to the singular value decomposition produces the classical solution with a new interpretation. Applied to regression modelling, this approach corresponds to a regularized objective and yields a new solution with properties of a ridge regression. The results for regression are robust and suggest a convenient tool for the analysis and interpretation of the model coefficients. Numerical results are given for a marketing research data set. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Concomitant repeated intravesical injections of botulinum toxin-type A and laparoscopic antegrade continence enema; a new solution for an old problem

AbdolMohammad Kajbafzadeh
OBJECTIVE To report our experience of treating bladder and bowel dysfunction in children with myelomeningocele, with simultaneous laparoscopic antegrade continence enema (LACE) and repeated intravesical injection of botulinum toxin-type A (BTX-A). PATIENTS AND METHODS Six girls and 14 boys (mean age, 8.7 years) with myelomeningocele were included in this study. All patients had received one or two intravesical injection(s) of BTX-A, but had persistent fecal incontinence or constipation despite improved urinary symptoms. We performed a two-port laparoscopic appendicostomy, immediately after repeated intravesical injection of BTX-A, through a V-shaped skin flap at McBurney's point. The stoma was finally covered by a quadrilateral skin flap, using the ,VQ' technique. The degree of urinary incontinence and bowel dysfunction were determined in each patient, and conventional urodynamic studies were performed 4 months after each injection. RESULTS All patients were followed-up for a mean (range) of 19.1 (14,33) months. Urinary continence improved significantly after the first injection, and remained constant after repeat injections. The maximum detrusor pressure, bladder compliance and capacity improved significantly (P < 0.001) compared with baseline. Interestingly, the simultaneous intravesical BTX-A injection/LACE procedure significantly improved all urodynamic variables compared with the values obtained after the last BTX-A injection alone. The laparoscopic procedure was well tolerated, and 19 (95%) children were nappy-free at the final follow-up. Only two patients had stoma stenosis, and one patient had minor stoma leakage. CONCLUSION Concomitant repeat intravesical injection of BTX-A and LACE can effectively manage bladder and bowel dysfunction in children with myelomeningocele. The procedure may further contribute to improve bladder urodynamic function, as effective evacuation of the bowel provides more room for bladder distension. [source]


Fang Wang
Peer-to-peer (P2P) systems provide a new solution to distributed information and resource sharing because of its outstanding properties in decentralization, dynamics, flexibility, autonomy, and cooperation, summarized as DDFAC in this paper. After a detailed analysis of the current P2P literature, this paper suggests to better exploit peer social relationships and peer autonomy to achieve efficient P2P structure design. Accordingly, this paper proposes Self-organizing peer-to-peer social networks (SoPPSoNs) to self-organize distributed peers in a decentralized way, in which neuron-like agents following extended Hebbian rules found in the brain activity represent peers to discover useful peer connections. The self-organized networks capture social associations of peers in resource sharing, and hence are called P2P social networks. SoPPSoNs have improved search speed and success rate as peer social networks are correctly formed. This has been verified through tests on real data collected from the Gnutella system. Analysis on the Gnutella data has verified that social associations of peers in reality are directed, asymmetric and weighted, validating the design of SoPPSoN. The tests presented in this paper have also evaluated the scalability of SoPPSoN, its performance under varied initial network connectivity and the effects of different learning rules. [source]

High-Quality Adaptive Soft Shadow Mapping

Gaël Guennebaud
Abstract The recent soft shadow mapping technique [GBP06] allows the rendering in real-time of convincing soft shadows on complex and dynamic scenes using a single shadow map. While attractive, this method suffers from shadow overestimation and becomes both expensive and approximate when dealing with large penumbrae. This paper proposes new solutions removing these limitations and hence providing an efficient and practical technique for soft shadow generation. First, we propose a new visibility computation procedure based on the detection of occluder contours, that is more accurate and faster while reducing aliasing. Secondly, we present a shadow map multi-resolution strategy keeping the computation complexity almost independent on the light size while maintaining high-quality rendering. Finally, we propose a view-dependent adaptive strategy, that automatically reduces the screen resolution in the region of large penumbrae, thus allowing us to keep very high frame rates in any situation. [source]

Optimal Thermal Unit Commitment Integrated with Renewable Energy Sources Using Advanced Particle Swarm Optimization

Shantanu Chakraborty Student member
Abstract This paper presents a methodology for solving generation planning problem for thermal units integrated with wind and solar energy systems. The renewable energy sources are included in this model due to their low electricity cost and positive effect on environment. The generation planning problem also known by unit commitment problem is solved by a genetic algorithm operated improved binary particle swarm optimization (PSO) algorithm. Unlike trivial PSO, this algorithm runs the refinement process through the solutions within multiple populations. Some genetic algorithm operators such as crossover, elitism, and mutation are stochastically applied within the higher potential solutions to generate new solutions for next population. The PSO includes a new variable for updating velocity in accordance with population best along with conventional particle best and global best. The algorithm performs effectively in various sized thermal power system with equivalent solar and wind energy system and is able to produce high quality (minimized production cost) solutions. The solution model is also beneficial for reconstructed deregulated power system. The simulation results show the effectiveness of this algorithm by comparing the outcome with several established methods. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Issues in pension system design

Maria Augusztinovics
External conditions for pension system design and demographic and labour market trends are briefly considered and the latter found decisive. Basic concepts, e.g. social assistance and insurance, redistribution and actuarial fairness, are then introduced. Then it is argued that the "public PAYG versus private funded" dichotomy has attracted an unduly large share of attention in recent pension reform debates, as such institutional changes do not really address the basic problems, while quantitative aspects, the relationship between contribution and replacement rates, have been improperly neglected or shielded by the paradigmatic controversy. The next, crucial point is that traditional, employment-based, earnings-related forms of pension insurance are endangered by new trends on the labour market; hence, new solutions will have to be sought to ensure pension coverage for the entire population. A brief plea for more, relevant and comparative information on pension issues follows. The paper concludes with a concise summary and by contemplating what could and should be expected from the Second World Assembly on Ageing. [source]

Recent modelling of sedimentation of suspended particles: a survey,

P. Boogerd
modélisation de la sédimentation; dépostition granulaire; transport sédimentaire Abstract Recent literature on modelling of sedimentation was studied. Attention was paid to hydrodynamics, numerical simulation, settling velocity models, sediment and velocity distribution functions, and sediment transport equations. Many popular theories, e.g. those regarding stratification and preferential sweeping, are under discussion. The traditional view that large-scale, energy-containing fluid motions dominate the transport of particles is found to be under attack, as is the modification of the von Karman coefficient to account for the presence of sediment. It is unclear which model for hindered settling should be used under what circumstances, and the effect of particle distribution cannot yet be calculated. Even the most basic problems, such as settling of multiple and/or non-spherical particles in a quiescent liquid, still require research. In the field of sediment distribution functions new solutions are still not entirely satisfactory. Furthermore, the predictive value of transport rate models is still rather low, and several popular sediment transport functions consistently allow more degradation than aggradation. Copyright © 2001 John Wiley & Sons, Ltd. Ce document est une étude de la littérature récente de la modélisation de la sédimentation, en prêtant attention à la hydrodynamique, les simulations numériques, les modèles de la vitesse de déposer, les fonctions de la répartition du sédiment et de la vitesse, et les équations du transport sédimentaire. Beaucoup de théories modernes, celles concernant la stratification et l'entraînage préférentiel par exemple, sont en cours de discussion. L'idée traditionnelle que les mouvements fluides au champ extensif et contenant de l'energie dominent le transport granulaire est attaquée, ainsi que la modification du coefficient von Karman pour tenir compte de la présence du sédiment. Quel modèle à user pour la déposition gênée, et en quelle situation, n'est pas évident, et l'effet de la répartition granulométrique est incalculable. Même les problèmes les plus fondamentaux, comme la déposition d'e multiples granules ou des granules non-sphériques dans un liquide quiescent, ont besoin de recherche. Dans le domaine des fonctions de la répartition du sédiment, les nouvelles solutions ne sont pas encore entièrement satisfaisantes. En outre la valeur prédictionnaire des modèles de la vitesse de transport est encore assez basse, et plusieurs fonctions de transport populaires permettent constamment plus de dégradation que d'accroissement. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Mothering in Public: A Meta-Synthesis of Homeless Women With Children Living in Shelters

MPHArticle first published online: 24 AUG 200, Mikki Meadows-Oliver MSN
ISSUES AND PURPOSE The purpose of this paper is to synthesize the current qualitative literature on homeless women with children living in shelters. METHODS Eighteen qualitative studies on homeless women with children living in shelters were included in the synthesis. The meta-synthesis was conducted using the meta-ethnographic approach of Noblit and Hare (1988). RESULTS Six reciprocal translations (themes) of homeless mothers caring for their children in shelters emerged: On becoming homeless, protective mothering, loss, stressed and depressed, survival strategies, and strategies for resolution. PRACTICE IMPLICATIONS The results may be used by healthcare workers as a framework for developing intervention strategies directed toward helping mothers find new solutions to dealing with shelter living and innovative ways to resolve their homelessness. [source]

Skin and oral mucosa equivalents: construction and performance

J Liu
To cite this article: Liu J, Bian Z, Kuijpers-Jagtman AM, Von den Hoff JW: Skin and oral mucosa equivalents: construction and performance Orthod Craniofac Res 2010;13:11,20 Abstract Authors,,, Liu J, Bian Z, Kuijpers-Jagtman AM, Von den Hoff JW The skin and the oral mucosa act as a barrier against the external environment. Loss of this barrier function causes dehydration and a high risk of infection. For the treatment of extensive skin wounds such as in severe burns, autologous skin for transplantation is often not available in sufficient amounts. Reconstructions in the oral cavity, as required after tumor resections or cleft palate repair, are often complicated by similar problems. In the last two decades, the field of tissue engineering has provided new solutions to these problems. Techniques have been developed for the culture of epithelial grafts, dermal substitutes, and the combination of these two to a ,functional' skin or mucosa equivalent. The present review focuses on developments in the field of tissue engineering of skin and oral mucosa. The performance of different types of engineered grafts in animal models and clinical studies is discussed. Recent developments such as the use of epithelial stem cells, and gene therapy with transduced skin grafts are also discussed. [source]

Israeli arab-jewish sandtray group work: creating a world together

Ariel KatzArticle first published online: 27 MAY 2010
Abstract Jewish and Arab Israeli group facilitator trainees participated in an experiential sandtray workshop. Recapitulating the basic Israeli conflict over contested lands, Arab-Jewish dyads were given a contained piece of land (a sand tray) in which to create their ,shared' world using miniatures. The container was just large enough to hold a standard ream of paper, and was half-filled with sand. As the method involves tactile play and giving the unconscious a voice, we could observe the interactional process and products. Would the unconscious provide new solutions where dialogue had become stuck in anger and alienation? The observed outcome of the group work was three distinct styles of coping with the difficult and sometimes painful task of sharing: conflict, domination and co-existence. This paper examines how participants negotiated sharing a limited piece of ,land' with the hope that this concrete task can provide new ways of understanding the unspoken and unconscious aspects of the conflict as well as suggesting new possibilities and a way toward constructive and respectful solutions. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Non-Volkov solutions for a charge in a plane wave

V. Bagrov
Abstract As it is known, a set of solutions of the Klein-Gordon and Dirac equations with a plane-wave field was found for the first time by Volkov. We construct new solutions of these equations different from the Volkov ones. In particular, the new solutions are characterized by quantum numbers different from Volkov solutions. In fact, our result is based on the demonstration that the transversal charge motion in a plane wave can be mapped by a special quantum transformation to transversal free particle motion. Similarly, we find new sets of solutions of the Klein-Gordon and Dirac equations with the combined electromagnetic field. [source]

Xylem heterochrony: an unappreciated key to angiosperm origin and diversifications

All angiosperms can be arranged along a spectrum from a preponderance of juvenile traits (cambial activity lost) to one of nearly all adult characters (cambium maximally active, mature patterns realized rapidly early in ontogeny). Angiosperms are unique among seed plants in the width of this spectrum. Xylem patterns are considered here to be indicative of contemporary function, not relictual. Nevertheless, most families of early-divergent angiosperms exhibit paedomorphic xylem structure, a circumstance that is most plausibly explained by the concept that early angiosperms had sympodial growth forms featuring limited accumulation of secondary xylem. Sympodial habits have been retained in various ways not only in early-divergent angiosperms, but also among eudicots in Ranunculales. The early angiosperm vessel, relatively marginal in conductive abilities, was improved in various ways, with concurrent redesign of parenchyma and fibre systems to enhance conductive, storage and mechanical capabilities. Flexibility in degree of cambial activity and kinds of juvenile/adult expressions has been basic to diversification in eudicots as a whole. Sympodial growth that lacks cambium, such as in monocots, provides advantages by various features, such as organographic compartmentalization of tracheid and vessel types. Woody monopodial eudicots were able to diversify as a result of production of new solutions to embolism prevention and conductive efficiency, particularly in vessel design, but also in parenchyma histology. Criteria for paedomorphosis in wood include slow decrease in length of fusiform cambial initials, predominance of procumbent ray cells and lesser degrees of cambial activity. Retention of ancestral features in primary xylem (the ,refugium' effect) is, in effect, a sort of inverse evidence of acceleration of adult patterns in later formed xylem. Xylem heterochrony is analysed not only for all key groups of angiosperms (including monocots), but also for different growth forms, such as lianas, annuals, various types of perennials, rosette trees and stem succulents. Xylary phenomena that potentially could be confused with heterochrony are discussed. Heterochronous xylem features seem at least as important as other often cited factors (pollination biology) because various degrees of paedomorphic xylem are found in so many growth forms that relate in xylary terms to ecological sites. Xylem heterochrony can probably be accessed during evolution by relatively simple gene changes in a wide range of angiosperms and thus represents a current as well as a past source of variation upon which diversification was based. Results discussed here are compatible with both current molecular-based phylogenetic analyses and all recent physiological work on conduction in xylem and thus represent an integration of these fields. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 26,65. [source]

The Cognitive and Behavioral Characteristics of Children With Low Working Memory

Tracy Packiam Alloway
This study explored the cognitive and behavioral profiles of children with working memory impairments. In an initial screening of 3,189 five- to eleven-year-olds, 308 were identified as having very low working memory scores. Cognitive skills (IQ, vocabulary, reading, and math), classroom behavior, and self-esteem were assessed. The majority of the children struggled in the learning measures and verbal ability. They also obtained atypically high ratings of cognitive problems/inattentive symptoms and were judged to have short attention spans, high levels of distractibility, problems in monitoring the quality of their work, and difficulties in generating new solutions to problems. These data provide rich new information on the cognitive and behavioral profiles that characterize children with low working memory. [source]