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Major Difficulties (major + difficulty)
Selected AbstractsDaughters' dilemma: grief resolution in girls whose widowed fathers remarry earlyJOURNAL OF FAMILY THERAPY, Issue 4 2000Gordon Riches This paper explores how a widower's early remarriage might complicate his bereaved daughter's grief resolution. In some families the emotional and domestic responsibilities of the deceased mother may be shouldered by an elder daughter on behalf of the surviving males in the family. Utilizing some of the propositions in recent ,new models' of grief, we explore the particular problems of ,conversational remembering' among daughters whose fathers remarry soon after their wives' deaths. Major difficulties may arise over conflicting perceptions of the role of the deceased mother within the new family system. [source] Towards the high-throughput expression of metalloproteins from the Mycobacterium tuberculosis genomeJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2005John F. Hall The provision of high-quality protein in adequate quantities is a prerequisite for any structural genomics programme. A number of proteins from the Mycobacterium tuberculosis genome have been expressed and the success at each stage of the process assessed. Major difficulties have been encountered in the purification and solubilization of many of these proteins, most likely as a result of mis-folding. Some improvements have been made to the protocol but the overall success rate is still limited; however, the use of a cell-free protein expression system will circumvent some of the difficulties encountered. Alternative purification systems are also required and the properties of a mutant blue copper protein are described, that may offer a combined purification and tagging system. [source] Discovery of diagnostic serum biomarkers of gastric cancer using proteomicsPROTEOMICS - CLINICAL APPLICATIONS, Issue 2 2008Katie Wing-kei Lam Abstract Gastric cancer has significant morbidity and mortality worldwide and locally. Good prognosis relies on an early diagnosis. However, this remains a challenge due to the lack of specific and sensitive serum biomarkers for early detection. Hence, there is a constant search for these biomarkers for screening purposes. Proteomic profiling enables a new approach to the discovery of biomarkers in disease. This review presents recent attempts in search of gastric cancer serum biomarker using proteomics. Different methodologies and different types of samples were employed by different groups of researchers. Major difficulties were encountered in the discovery processes, including interference from abundant proteins and continuous changing serum proteomes from different individuals. [source] NMR diffusion measurements under chemical exchange between sites involving a large chemical shift differenceCONCEPTS IN MAGNETIC RESONANCE, Issue 2 2010S. Leclerc Abstract This study concerns the thallium-205 cation in aqueous solution in the presence of a calixarene molecule. Although the measurement of the self-diffusion coefficient of pure thallium (without calixarene in the aqueous solution) does not pose any particular problem, major difficulties are encountered with the standard method using gradient strength increment as soon as thallium is partly complexed by calixarene. With static magnetic field gradients, the NMR signal is so weak that it prevents any reliable measurement, whereas radio frequency (rf) field gradients lead to an unrealistic value of the diffusion coefficient. This failure is explained by the fact that thallium is in fast exchange between two sites (complexed and free thallium) thus exhibiting a single NMR signal although, in the course of the experiment, two signals, with an important difference in resonance frequencies (due to the large thallium chemical shift range), are effectively involved. With the objective to understand these quite unexpected observations, the theory underlying NMR diffusion experiments is first reviewed, and criteria of fast exchange are discussed for three parameters: chemical shifts, relaxation rates, and diffusion coefficients. It turns out that off-resonance effects are responsible for unwanted defocusing due to rf pulses in the static magnetic field gradient method and for time-dependent gradients in the rf field gradient method. Concerning the latter, a remedy is proposed which consists in applying the stronger gradient and incrementing the gradient pulse durations. After correction for relaxation, the expected value of the diffusion coefficient is retrieved. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 127,137, 2010. [source] Stabilization of organic matter in temperate soils: mechanisms and their relevance under different soil conditions , a reviewEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006M. v. Lützow Summary Mechanisms for C stabilization in soils have received much interest recently due to their relevance in the global C cycle. Here we review the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils: (i) selective preservation due to recalcitrance of OM, including plant litter, rhizodeposits, microbial products, humic polymers, and charred OM; (ii) spatial inaccessibility of OM against decomposer organisms due to occlusion, intercalation, hydrophobicity and encapsulation; and (iii) stabilization by interaction with mineral surfaces (Fe-, Al-, Mn-oxides, phyllosilicates) and metal ions. Our goal is to assess the relevance of these mechanisms to the formation of soil OM during different stages of decomposition and under different soil conditions. The view that OM stabilization is dominated by the selective preservation of recalcitrant organic components that accumulate in proportion to their chemical properties can no longer be accepted. In contrast, our analysis of mechanisms shows that: (i) the soil biotic community is able to disintegrate any OM of natural origin; (ii) molecular recalcitrance of OM is relative, rather than absolute; (iii) recalcitrance is only important during early decomposition and in active surface soils; while (iv) during late decomposition and in the subsoil, the relevance of spatial inaccessibility and organo-mineral interactions for SOM stabilization increases. We conclude that major difficulties in the understanding and prediction of SOM dynamics originate from the simultaneous operation of several mechanisms. We discuss knowledge gaps and promising directions of future research. [source] EVOLUTION AND STABILITY OF THE G-MATRIX ON A LANDSCAPE WITH A MOVING OPTIMUMEVOLUTION, Issue 8 2004Adam G. Jones Abstract In quantitative genetics, the genetic architecture of traits, described in terms of variances and covariances, plays a major role in determining the trajectory of evolutionary change. Hence, the genetic variance-covariance matrix (G-matrix) is a critical component of modern quantitative genetics theory. Considerable debate has surrounded the issue of G-matrix constancy because unstable G-matrices provide major difficulties for evolutionary inference. Empirical studies and analytical theory have not resolved the debate. Here we present the results of stochastic models of G-matrix evolution in a population responding to an adaptive landscape with an optimum that moves at a constant rate. This study builds on the previous results of stochastic simulations of G-matrix stability under stabilizing selection arising from a stationary optimum. The addition of a moving optimum leads to several important new insights. First, evolution along genetic lines of least resistance increases stability of the orientation of the G-matrix relative to stabilizing selection alone. Evolution across genetic lines of least resistance decreases G-matrix stability. Second, evolution in response to a continuously changing optimum can produce persistent maladaptation for a correlated trait, even if its optimum does not change. Third, the retrospective analysis of selection performs very well when the mean G-matrix (,) is known with certainty, indicating that covariance between G and the directional selection gradient (3 is usually small enough in magnitude that it introduces only a small bias in estimates of the net selection gradient. Our results also show, however, that the contemporary ,-matrix only serves as a rough guide to ,. The most promising approach for the estimation of G is probably through comparative phylogenetic analysis. Overall, our results show that directional selection actually can increase stability of the G-matrix and that retrospective analysis of selection is inherently feasible. One ?riajor remaining challenge is to gain a sufficient understanding of the G-matrix to allow the confident estimation of ,. [source] Soft Contact Deposition onto Molecularly Modified GaAs.ADVANCED FUNCTIONAL MATERIALS, Issue 11-12 2002Electrical Effects, Thin Metal Film Flotation: Principles Abstract We describe and analyze a process to position a ,,1 nm thick molecular layer between two solid surfaces without damage to the molecules. The method is used to deposit a metal film in a soft, gentle manner on a semiconductor, yielding functional semiconductor/molecule/metal junctions. It is a combination of the lift-off procedure, known from, for example, lithography, and the bonding process, known from, for example, wafer bonding. The combined method may find application also outside the area described here. We point out its major difficulties as well as solutions to overcome them. For this we rely on concepts from the physics of liquid and solid surfaces and interfaces. Conditions are found, in terms of choice of solvents, under which the method will be effective. The efficacy of floatation as a soft contacting procedure is demonstrated by the preparation of Au and Al contacts on GaAs single crystal surfaces, modified by a self-assembled monolayer of small organic molecules. The resulting electrical properties of the contacts depend crucially on how the molecular interface with the contacting metal is formed. This type of wet contacting procedure to make dry devices may be advantageous especially if biomolecules are used. [source] Imposition of essential boundary conditions by displacement constraint equations in meshless methodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3 2001Xiong Zhang Abstract One of major difficulties in the implementation of meshless methods is the imposition of essential boundary conditions as the approximations do not pass through the nodal parameter values. As a consequence, the imposition of essential boundary conditions in meshless methods is quite awkward. In this paper, a displacement constraint equations method (DCEM) is proposed for the imposition of the essential boundary conditions, in which the essential boundary conditions is treated as a constraint to the discrete equations obtained from the Galerkin methods. Instead of using the methods of Lagrange multipliers and the penalty method, a procedure is proposed in which unknowns are partitioned into two subvectors, one consisting of unknowns on boundary ,u, and one consisting of the remaining unknowns. A simplified displacement constraint equations method (SDCEM) is also proposed, which results in a efficient scheme with sufficient accuracy for the imposition of the essential boundary conditions in meshless methods. The present method results in a symmetric, positive and banded stiffness matrix. Numerical results show that the accuracy of the present method is higher than that of the modified variational principles. The present method is a exact method for imposing essential boundary conditions in meshless methods, and can be used in Galerkin-based meshless method, such as element-free Galerkin methods, reproducing kernel particle method, meshless local Petrov,Galerkin method. Copyright © 2001 John Wiley & Sons, Ltd. [source] A rational elasto-plastic spatially curved thin-walled beam elementINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2007Yong-Lin Pi Abstract Torsion is one of the primary actions in members curved in space, and so an accurate spatially curved-beam element needs to be able to predict the elasto-plastic torsional behaviour of such members correctly. However, there are two major difficulties in most existing finite thin-walled beam elements, such as in ABAQUS and ANSYS, which may lead to incorrect predictions of the elasto-plastic behaviour of members curved in space. Firstly, the integration sample point scheme cannot capture the shear strain and stress information resulting from uniform torsion. Secondly, the higher-order twists are ignored which leads to loss of the significant effects of Wagner moments on the large twist torsional behaviour. In addition, the initial geometric imperfections and residual stresses are significant for the elasto-plastic behaviour of members curved in space. Many existing finite thin-walled beam element models do not provide facilities to deal with initial geometric imperfections. Although ABAQUS and ANSYS have facilities for the input of residual stresses as initial stresses, they cannot describe the complicated distribution patterns of residual stresses in thin-walled members. Furthermore, external loads and elastic restraints may be applied remote from shear centres or centroids. The effects of the load (and restraint) positions are important, but are not considered in many beam elements. This paper presents an elasto-plastic spatially curved element with arbitrary thin-walled cross-sections that can correctly capture the uniform shear strain and stress information for integration, and includes initial geometric imperfections, residual stresses and the effects of the load and restraint positions. The element also includes elastic restraints and supports, which have to be modelled separately as spring elements in some other finite thin-walled beam elements. Comparisons with existing experimental and analytical results show that the elasto-plastic spatially curved-beam element is accurate and efficient. Copyright © 2006 John Wiley & Sons, Ltd. [source] Finite-element/level-set/operator-splitting (FELSOS) approach for computing two-fluid unsteady flows with free moving interfacesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2005Anton Smolianski Abstract The present work is devoted to the study on unsteady flows of two immiscible viscous fluids separated by free moving interface. Our goal is to elaborate a unified strategy for numerical modelling of two-fluid interfacial flows, having in mind possible interface topology changes (like merger or break-up) and realistically wide ranges for physical parameters of the problem. The proposed computational approach essentially relies on three basic components: the finite element method for spatial approximation, the operator-splitting for temporal discretization and the level-set method for interface representation. We show that the finite element implementation of the level-set approach brings some additional benefits as compared to the standard, finite difference level-set realizations. In particular, the use of finite elements permits to localize the interface precisely, without introducing any artificial parameters like the interface thickness; it also allows to maintain the second-order accuracy of the interface normal, curvature and mass conservation. The operator-splitting makes it possible to separate all major difficulties of the problem and enables us to implement the equal-order interpolation for the velocity and pressure. Diverse numerical examples including simulations of bubble dynamics, bifurcating jet flow and Rayleigh,Taylor instability are presented to validate the computational method. Copyright © 2004 John Wiley & Sons, Ltd. [source] An integrated routing and admission control mechanism for real-time multicast connection establishmentINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2001Xiaohua Jia Abstract There are two major difficulties in real-time multicast connection setup. One is the design of an efficient distributed routing algorithm which optimizes the network cost of routing trees under the real-time constraints. The other is the integration of routing with admission control into one single phase of operations. This paper presents a real-time multicast connection setup mechanism, which integrates multicast routing with real-time admission control. The proposed mechanism performs the real-time admission tests on a cost optimal tree (COT) and a shortest path tree (SPT) in parallel, aiming at optimizing network cost of the routing tree under real-time constraints. It has the following important features: (1) it is fully distributed; (2) it achieves sub-optimal network cost of routing trees; (3) it takes less time and less network messages for a connection setup. Copyright © 2001 John Wiley & Sons, Ltd. [source] On the fast search algorithms for vector quantization encodingINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 5 2002Wen-Shiung Chen Abstract One of the major difficulties arising in vector quantization (VQ) is high encoding time complexity. Based on the well-known partial distance search (PDS) method and a special order of codewords in VQ codebook, two simple and efficient methods are introduced in fast full search vector quantization to reduce encoding time complexity. The exploitation of the "move-to-front" method, which may get a smaller distortion as early as possible, combined with the PDS algorithm, is shown to improve the encoding efficiency of the PDS method. Because of the feature of energy compaction in DCT domain, search in DCT domain codebook may be further speeded up. The experimental results show that our fast algorithms may significantly reduce search time of VQ encoding. © 2003 Wiley Periodicals, Inc. Int J Imaging Syst Technol 12, 204,210, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10030 [source] Pondering the Sinlessness of Jesus Christ: Moral Christologies and the Witness of ScriptureINTERNATIONAL JOURNAL OF SYSTEMATIC THEOLOGY, Issue 4 2008IVOR J. DAVIDSON The models that typically emerge in modernity face major difficulties. This article seeks to reorient the discussion of sinlessness in biblical terms, and suggests that scripture's witness points toward an account of the moral character of Jesus as grounded specifically in inner-divine relations rather than in any sort of idealism. Such a trinitarian account also raises questions about some conventional approaches to the metaphysics of sinlessness. [source] The use of chronosequences in studies of ecological succession and soil developmentJOURNAL OF ECOLOGY, Issue 4 2010Lawrence R. Walker Summary 1.,Chronosequences and associated space-for-time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time-scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development. 2.,Chronosequences are appropriate to study plant succession at decadal to millennial time-scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time-scales of centuries to millennia, sometimes independently of their application to shorter-term plant and soil biological communities. 3.,Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach. 4.,Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species-rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages. 5.,Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences. [source] Elastic image registration of 2-D gels for differential and repeatability studiesPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 1 2008Carlos O. S. Sorzano Dr. Abstract One of the main applications of electrophoretic 2-D gels is the analysis of differential responses between different conditions. For this reason, specific spots are present in one of the images, but not in the other. In some other occasions, the same experiment is repeated between 2 and 12 times in order to increase statistical significance. In both situations, one of the major difficulties of these analysis is that 2-D gels are affected by spatial distortions due to run-time differences and dye-front deformations, resulting in images that are significantly dissimilar not only because of their content, but also because of their geometry. In this technical brief, we show how to use free, state-of-the-art image registration and fusion algorithms developed by us for solving the problem of comparing differential expression profiles, or computing an "average" image from a series of virtually identical gels. [source] Mining biomarkers in human sera using proteomic toolsPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 1 2004Rulin Zhang Abstract One of the major difficulties in mining low abundance biomarkers from serum or plasma is due to the fact that a small number of proteins such as albumin, ,2-macroglobulin, transferrin, and immunoglobulins, may represent as much as 80% of the total serum protein. The large quantity of these proteins makes it difficult to identify low abundance proteins in serum using traditional 2-dimensional electrophoresis. We recently used a combination of multidimensional liquid chromatography and gel electrophoresis coupled to matrix-assisted laser desorption/ionization-quadrupole-time of flight and Ion Trap liquid chromatography-tandem mass spectrometry to identify protein markers in sera of Alzheimer's disease (AD), insulin resistance/type-2 diabetes (IR/D2), and congestive heart failure (CHF) patients. We identified 8 proteins that exhibit higher levels in control sera and 36 proteins that exhibit higher levels in disease sera. For example, haptoglobin and hemoglobin are elevated in sera of AD, IR/D2, and CHF patients. The levels of several other proteins including fibrinogen and its fragments, alpha 2-macroglobulin, transthyretin, pro-platelet basic protein, protease inhibitors clade A and C, as well as proteins involved in the classical complement pathway such as complement C3, C4, and C1 inhibitor, were found to differ between IR/D2 and control sera. The sera levels of proteins, such as the 10 kDa subunit of vitronectin, alpha 1-acid glycoprotein, apolipoprotein B100, fragment of factor H, and histidine-rich glycoprotein were observed to be different between AD and controls. The differences observed in these biomarker candidates were confirmed by Western blot and the enzyme-linked immunosorbent assay. The biological meaning of the proteomic changes in the disease states and the potential use of these changes as diagnostic tools or for therapeutic intervention will be discussed. [source] On the Relation between Form and Substance in LawRATIO JURIS, Issue 1 2007PHILIP SOPER In particular, he concentrates on the hazy relationship between form and substance in Summers' theory. In order to analyze some major difficulties entailed in the thesis that form and substance are different and independent things, the author discusses three specific questions: (1) the difference between form and substance; (2) the possibility of a form meant to be value-neutral; (3) how to distinguish a form-centered approach from a formalistic approach when one has to interpret a statute. This last question is dealt with through examples taken from two legal decisions.* [source] Operational Optimization of Ideal Internal Thermally Coupled Distillation ColumnsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2001Xing-Gao Liu Lack of the optimal operation parameters in operation is one of major difficulties associated with the use of advanced energy saving distillation methods. In this paper, the operational optimization of the ideal Internal Thermally Coupled Distillation Column (ITCDIC) is considered. An optimization model and the related simulation algorithm are proposed. An optimization and the related result analysis are carried out, which pave the way for further design studies and its practical application. [source] School experiences after treatment for a brain tumourCHILD: CARE, HEALTH AND DEVELOPMENT, Issue 1 2006P. Upton Abstract Background Children surviving a brain tumour face major difficulties including learning problems, lengthy school absences and psychosocial problems, all of which can impact on school functioning. Our aims were to provide information for parents and teachers about the skills and resources of this group. Specifically, we aimed to: ,,describe the special educational needs of these children; ,,document the impact of diagnosis and treatment on school attendance; ,,compare parent and teacher assessments of social, emotional and behavioural difficulties. Methods Forty families agreed to participate (response rate = 58.82%). The children (19 males and 21 females) were aged from 6 to 16 years and had completed treatment at least 2 years previously (range = 2 years,12 years 5 months). Questionnaires (Strengths and Difficulties and school experience) were completed by mothers and teachers. Results Survivors were experiencing a wide range of physical, learning and interpersonal difficulties, according to parent and teacher reports. Almost half the children (n = 19) had ongoing neurological problems that were significant enough to require special help at school. Literacy and numeracy were the most common learning difficulties. Parents also rated brain tumour survivors as having more behavioural and emotional problems than would be expected from population norms. For example, survivors were rated as having more Total Difficulties (t = 6.86, P < 0.001), Emotional Symptoms (t = 8.82, P < 0.001), Hyperactivity (t = 2.25, P = 0.03), Peer Relationship Problems (t = 7.58, P < 0.001) and poorer Pro-social Behaviour (t = ,3.34, P = 0.002) than would be expected from population norms. These problems were also seen to be having a significant impact on the child's functioning (t = 3.95, P < 0.001). Teachers rated these problems as less serious than parents. Conclusion These children experience significant problems in school some time after diagnosis and when they are considered medically cured. Closer school,hospital liaison is essential to maximize integration and achievement in these children. [source] Synthesis, chiroptical properties, and their theoretical simulation of some highly rotating benzotricamphor derivatives,,CHIRALITY, Issue 1E 2009Giuseppe Mazzeo Abstract The large molecules 1,3 (69, 90, and 102 atoms, respectively), prepared by cyclotrimerization of enantiomerically pure derivatives of (,)-bornyl acetate, show intense ECD spectra, high optical rotation (OR) values (200,1300, in absolute value) dominated in sign and order of magnitude by the lowest-energy Cotton effects, that is, they are the ideal candidates to test the reliability of our "approximate" (TDDFT/B3LYP/6-31G* or smaller basis set) approach to the calculation of chiroptical properties. As a matter of fact, a correct simulation of the OR values and ECD spectra of 1 and 2 can be obtained even using STO-3G basis set and semiempirical or molecular mechanics input geometries: for 1, at the TDDFT/B3LYP/STO-3G level, the OR values are of the order of 500,550, versus an experimental value ranging between 660 and 690, depending on the solvent. On the contrary, the case of 3 (exp. OR between ,1330 and ,1500) is really complex (for instance, the OR values range between ,3216 and ,729 (TDDFT/B3LYP/6-31G* calculations) or ,1824 and ,444 (TDDFT/B3LYP/STO-3G calculations)), making the comparison between calculated and experimental values more difficult. The behavior of 3 is due to its molecular flexibility, whereas 1 is a really rigid molecules and 2 behaves (vide infra) as it were a rigid system. These observations strongly indicate that the conformational freedom constitutes one of the major difficulties for a correct but simple simulation of the chiroptical properties. Chirality 21:E86,E97, 2009. © 2009 Wiley-Liss, Inc. [source] "In-gel patch electrophoresis:" A,new method for environmental DNA purificationELECTROPHORESIS, Issue 16 2005Changhyun Roh Abstract Most of the microorganism species are largely untapped and could represent an interesting reservoir of genes useful for biotechnological applications. Unfortunately, a major difficulty associated with the methods used to isolate environmental DNA is related to the contamination of the extracted material with humic substances. These polyphenolic compounds inhibit the DNA processing reactions and severely impede cloning procedures. In this work, we describe a rapid, simple, and efficient method for the purification of genomic DNA from environmental samples: we added a chromatography step directly embedded into an agarose gel electrophoresis. This strategy enabled the DNA extraction from various environmental samples and it appeared that the purity grade was compatible with digestion by restriction enzymes and polymerase chain reaction (PCR) amplifications. [source] Linking flux network measurements to continental scale simulations: ecosystem carbon dioxide exchange capacity under non-water-stressed conditionsGLOBAL CHANGE BIOLOGY, Issue 4 2007KATHERINE E. OWEN Abstract This paper examines long-term eddy covariance data from 18 European and 17 North American and Asian forest, wetland, tundra, grassland, and cropland sites under non-water-stressed conditions with an empirical rectangular hyperbolic light response model and a single layer two light-class carboxylase-based model. Relationships according to ecosystem functional type are demonstrated between empirical and physiological parameters, suggesting linkages between easily estimated parameters and those with greater potential for process interpretation. Relatively sparse documentation of leaf area index dynamics at flux tower sites is found to be a major difficulty in model inversion and flux interpretation. Therefore, a simplification of the physiological model is carried out for a subset of European network sites with extensive ancillary data. The results from these selected sites are used to derive a new parameter and means for comparing empirical and physiologically based methods across all sites, regardless of ancillary data. The results from the European analysis are then compared with results from the other Northern Hemisphere sites and similar relationships for the simplified process-based parameter were found to hold for European, North American, and Asian temperate and boreal climate zones. This parameter is useful for bridging between flux network observations and continental scale spatial simulations of vegetation/atmosphere carbon dioxide exchange. [source] A moving-mesh finite-volume method to solve free-surface seepage problem in arbitrary geometriesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007M. Darbandi Abstract The main objective of this work is to develop a novel moving-mesh finite-volume method capable of solving the seepage problem in domains with arbitrary geometries. One major difficulty in analysing the seepage problem is the position of phreatic boundary which is unknown at the beginning of solution. In the current algorithm, we first choose an arbitrary solution domain with a hypothetical phreatic boundary and distribute the finite volumes therein. Then, we derive the conservative statement on a curvilinear co-ordinate system for each cell and implement the known boundary conditions all over the solution domain. Defining a consistency factor, the inconsistency between the hypothesis boundary and the known boundary conditions is measured at the phreatic boundary. Subsequently, the preceding mesh is suitably deformed so that its upper boundary matches the new location of the phreatic surface. This tactic results in a moving-mesh procedure which is continued until the nonlinear boundary conditions are fully satisfied at the phreatic boundary. To validate the developed algorithm, a number of seepage models, which have been previously targeted by the other investigators, are solved. Comparisons between the current results and those of other numerical methods as well as the experimental data show that the current moving-grid finite-volume method is highly robust and it provides sufficient accuracy and reliability. Copyright © 2007 John Wiley & Sons, Ltd. [source] The Transparency of MetaphorMIND & LANGUAGE, Issue 3 2006SAMUEL GUTTENPLAN In the second and longest section, I explore a major difficulty for certain of these accounts, namely the need to explain what I describe as the ,transparency' of metaphor. In the third section, I describe two accounts which can overcome the difficulty. The first is loosely based on Davidson's treatment of metaphor, and, finding this to be inadequate for reasons having nothing to do with transparency, it will be used solely to show the way. The second is my own, and, without attempting to defend it at length, I will content myself with suggesting how it can cope with the difficulty discussed in this paper in a way which mimics the Davidsonian proposal. Finally, in the fourth section, I shall briefly mention several considerations independent of transparency for adopting my account. [source] Adaptive finite element procedures for elastoplastic problems at finite strainsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003A. Koch Dipl.-Ing. A major difficulty in the context of adaptive analysis of geometrically nonlinear problems is to provide a robust remeshing procedure that accounts both for the error caused by the spatial discretization and for the error due to the time discretization. For stability problems, such as strain localization and necking, it is essential to provide a step,size control in order to get a robust algorithm for the solution of the boundary value problem. For this purpose we developed an easy to implement step,size control algorithm. In addition we will consider possible a posteriori error indicators for the spatial error distribution of elastoplastic problems at finite strains. This indicator is adopted for a density,function,based adaptive remeshing procedure. Both error indicators are combined for the adaptive analysis in time and space. The performance of the proposed method is documented by means of representative numerical examples. [source] Close Neighbours Matter: Neighbourhood Effects on Early Performance at School,THE ECONOMIC JOURNAL, Issue 523 2007Dominique Goux Children's outcomes are strongly correlated with those of their neighbours. The extent to which this is causal is the subject of an extensive literature. There is an identification problem because people with similar characteristics are observed to live in close proximity. Another major difficulty is that neighbourhoods measured in available data are often considerably larger than those which matter for outcomes (i.e. close neighbours). Several institutional features of France enable us to address these problems. We find that an adolescent's outcomes at the end of junior high-school are strongly influenced by the performance of other adolescents in the neighbourhood. [source] Flexural properties of glass fibre reinforced acrylic resin polymersAUSTRALIAN DENTAL JOURNAL, Issue 1 2006IH Tacir Abstract Background: In recent years, glass fibres have been used to strengthen denture base resins. A major difficulty in using reinforcing fibres with multiphase acrylic resins, such as powder liquid resins, is inadequate impregnation of the fibres with the resin. Methods: This investigation examined the reinforcing effect of glass fibres on the fracture resistance and flexural strength of acrylic denture base resins. Eighty identical specimens were formed in specially designed moulds in accordance with the manufacturer's recommendations. The four experimental groups were prepared and these consisted of conventional acrylic resin and the same resin reinforced with glass fibres. Ten specimens were fabricated in a standardized fashion for each experimental group. Flexural strength was tested using a 3-point universal testing machine. Results: In this study, statistically significant differences were found in the flexural strength of the specimens (P<0.05). The injection-moulded, fibre-reinforced group had significantly lower flexural strength than the injection-moulded group (P<0.001), and the microwave-moulded, fibre-reinforced group had lower flexural strength than the microwave-moulded group. The fracture resistance was significantly higher in the injection-moulded, fibre-reinforced group than in the injection-moulded group (P<0.05), and the fracture resistance was significantly higher in the microwave-moulded, fibre-reinforced group than in the microwave-moulded group. Conclusion: Within the limitations of this study, the flexural strength of heat-polymerized PMMA denture resin was improved after reinforcement with glass fibres. It may be possible to apply these results to distal extension partial and complete denture bases. [source] No sign of harm: issues for disabled children communicating about abuseCHILD ABUSE REVIEW, Issue 4 2001Rebecca Oosterhoorn Abstract While all children may be the victims of abuse, disabled children are particularly vulnerable. This paper explores the views of professionals working with children using alternative/augmented communication systems on the issues relating to communication about abuse. Interviews were carried out with 20 staff from eight establishments for disabled children across Scotland. It describes the range of alternative/augmented communication systems used and the barriers to communication about abuse. Staff generally accepted the importance of providing the appropriate vocabulary in augmented communication systems, but systems that provide such vocabulary were not widely used. Staff considered that a major difficulty concerned the level of understanding disabled children might have about concepts of abuse. They were unsure how the appropriate vocabulary could be introduced in a natural way and how links could be made between the signs and their meanings. Staff saw themselves as those most able to protect the children, but it was felt that discovery of abuse was more likely to come from them noticing physical signs, behaviour or mood changes than from the child communicating explicitly about abuse. The need for appropriate training and increased coordination between social work, health and education is highlighted. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||