Home About us Contact
|
Home About us Contact | ||
|
|
||
One Used (one + used)
Selected AbstractsAdaptive state- dependent importance sampling simulation of markovian queueing networksEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2002Pieter-Tjerk De Boer In this paper, a method is presented for the efficient estimation of rare-event (buffer overflow) probabilities in queueing networks using importance sampling. Unlike previously proposed change of measures, the one used here is not static, i.e., it depends on the buffer contents at each of the network nodes. The ,optimal' state-dependent change of measure is determined adaptively during the simulation, using the cross-entropy method. The adaptive state-dependent importance sampling algorithm proposed in this paper yields asymptotically efficient simulation of models for which it is shown (formally or otherwise) that no effective static change of measure exists. Simulation results for queueing models of communication systems are presented to demonstrate the effectiveness of the method. [source] Surface waves in a general anisotropic poroelastic solid half-spaceGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2004M. D. Sharma SUMMARY A method is introduced for studying surface waves in a general anisotropic poroelastic medium. The method is analogous to the one used for isotropic media and derives a complex secular equation to represent the propagation of surface waves at the stress-free plane surface of a non-dissipative porous medium. The point of importance is that the derived equation is, analytically, separable into real and imaginary parts and hence can be solved by iterative numerical methods. A root of this secular equation represents the existence of surface waves and calculates the apparent phase velocity along a given direction on the surface. Numerical work is carried out for the model of a crustal rock. The propagation of surface waves is studied numerically for the top three anisotropies (i.e. triclinic, monoclinic, orthorhombic). [source] Context-dependent effects of hippocampal damage on memory in the shock-probe testHIPPOCAMPUS, Issue 1 2005Hugo Lehmann Abstract We assessed the role of the hippocampus in anterograde memory, using the shock-probe test. Rats with sham or neurotoxic lesions of the hippocampus were given a shock-probe acquisition session during which each time they contacted a probe they received a shock; 24 h later, the rats were given a second shock-probe session to test their retention, but in this instance the probe was not electrified. Rats were tested in either the same context as the one used during acquisition or in a different context. The hippocampal lesions impaired avoidance of the probe and burying on the retention test, suggesting that the lesions induced anterograde amnesia. However, the impairment was context dependent. The hippocampal lesions impaired avoidance only when the rats were tested in the context in which they received the conditioning. The results of the shock-probe test suggest that the anterograde amnesia following hippocampal lesions is due mainly to an inability to associate the context with the shock more than to an inability to associate the probe with shock. © 2004 Wiley-Liss, Inc. [source] Improved four-node Hellinger,Reissner elements based on skew coordinatesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2008K. Wisniewski Abstract Mixed four-node elements based on the Hellinger,Reissner (HR) functional are developed for stress representations in various coordinates, including the skew, natural and Cartesian ones. The two-field HR functional is used in the classical form and in the incremental form suitable for non-linear materials. We argue that the skew coordinates, not the natural ones, should be associated with the natural basis at the element's center. If 5- and 7-parameter stress representations are assumed in these coordinates, then, for a linear elastic case, the homogenous equilibrium equations and the stress form of compatibility equation are satisfied point-wise. Two mixed four-node elements are developed and tested: 1.An assumed stress element (HR5-S) is developed from the non-enhanced HR functional, for a 5-parameter representation of stresses, formally identical as the one used, for example, in Pian and Sumihara [Int. J. Numer. Meth. Engng 1984; 20:1685,1695], but in terms of skew coordinates. This element is very simple and uses a smaller number of parameters, but is equally accurate as the elements by Yuan et al. [Int. J. Numer. Meth. Engng 1993; 36:1747,1763] and by Piltner and Taylor [Int. J. Numer. Meth. Engng 1995; 38:1783,1808]. 2.An assumed stress/enhanced strain element (HR9) is developed from the enhanced HR functional, for a 7-parameter representation of stress and a 2-parameter enhanced assumed displacement gradient or enhanced assumed strain enhancement. Various forms of 7-parameter representations appearing in the literature are reviewed, and we prove that they are linked by a linear onto transformation. The choice of coordinates for the stress and the enhancement turns out to be the crucial factor, and four combinations of coordinates for which the element performs the best are identified. Both elements are based on the Green strain, and several numerical tests show their good accuracy, in particular, their robustness to shape distortions for coarse meshes. Two update schemes for the multipliers of modes and the incremental constitutive procedure accounting for the plane stress condition for non-linear materials are tested for large deformation problems. Copyright © 2008 John Wiley & Sons, Ltd. [source] Severe Hemorrhagic Complication Due to Acquired Factor V Inhibitor After Single Exposure to Bovine Thrombin ProductJOURNAL OF CARDIAC SURGERY, Issue 6 2000Michio Kajitani M.D., Ph.D. Our patient underwent emergency repair of acute aortic dissection and coronary artery bypass grafting. The patient developed leg wound infection at the saphenous vein harvest site, which was debrided and left open. Attempt to reclose the leg wound 1 month later was complicated by a life-threatening hemorrhage with markedly elevated activated partial thromboplatin time. There was no evidence of infection or disseminated intravascular coagulation, and further study identified low factor V level with positive factor V inhibitor. Treatment with plasmapheresis and steroid successfully reversed the coagulopathy. Detailed case review failed to reveal exposure to any thrombin products other than the one used for the aortic dissection repair. This case was unusual because only a single exposure to this product resulted in severe hemorrhagic complication 1 month after surgery. [source] Self-evaluation and peer review , an example of action research in promoting self-determination of patients with rheumatoid arthritisJOURNAL OF CLINICAL NURSING, Issue 3a 2007LicNSc, Päivi Löfman RN Aims and objectives., The aim of this paper was to describe the areas that have been performed well and the areas in need of further development of rheumatoid arthritis patients. Background., Nurses' self-evaluation and peer review are important methods for ascertaining the changes and success in the development of nursing practice. To date, there has been minimal research regarding the use of those evaluation methods in nursing practice. Design., The findings of self-evaluation and peer review of nurses are described in a participatory action research study aimed at promotion of self-determination for patients with rheumatoid arthritis. Methods., In self-evaluation, the collection of data was accomplished using a self-evaluation instrument with the permanent nursing staff (n = 18), then analysed through quantitative methods. For peer review, the data were gathered through focus groups (n = 21) using a tool similar to the one used for self-evaluation. The participants included many of the same nurses as in self-evaluation. The data were analysed using qualitative content analysis. Results., Well-performed areas in nursing of rheumatoid arthritis patients were found to be promoting patient participation, supporting self-determination, performing patient-centred nursing and raising patient self-respect. The areas in need of development were connected to the nursing staff themselves: increasing collaboration of nursing staff, decreasing authoritarianism in nursing care and developing nursing practice with colleagues. Conclusions., Self-evaluation and peer review are complementary and support one another, especially since nurses were found to be more critical in their self-evaluations than in peer review. Relevance to clinical practice., Both evaluation tools proved to be useful methods in the evaluation phase of the action research process as a means of professional development. Also assisting in the development of clinical nursing practice. [source] ABSINTH: A new continuum solvation model for simulations of polypeptides in aqueous solutionsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2009Andreas Vitalis Abstract A new implicit solvation model for use in Monte Carlo simulations of polypeptides is introduced. The model is termed ABSINTH for self- Assembly of Biomolecules Studied by an Implicit, Novel, and Tunable Hamiltonian. It is designed primarily for simulating conformational equilibria and oligomerization reactions of intrinsically disordered proteins in aqueous solutions. The paradigm for ABSINTH is conceptually similar to the EEF1 model of Lazaridis and Karplus (Proteins 1999, 35, 133). In ABSINTH, the transfer of a polypeptide solute from the gas phase into a continuum solvent is the sum of a direct mean field interaction (DMFI), and a term to model the screening of polar interactions. Polypeptide solutes are decomposed into a set of distinct solvation groups. The DMFI is a sum of contributions from each of the solvation groups, which are analogs of model compounds. Continuum-mediated screening of electrostatic interactions is achieved using a framework similar to the one used for the DMFI. Promising results are shown for a set of test cases. These include the calculation of NMR coupling constants for short peptides, the assessment of the thermal stability of two small proteins, reversible folding of both an ,-helix and a ,-hairpin forming peptide, and the polymeric properties of intrinsically disordered polyglutamine peptides of varying lengths. The tests reveal that the computational expense for simulations with the ABSINTH implicit solvation model increase by a factor that is in the range of 2.5,5.0 with respect to gas-phase calculations. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Inclusion of Blended Lipid Solutions as Functional Ingredients to Alter the Fatty Acid Profile of Beef PattiesJOURNAL OF FOOD SCIENCE, Issue 7 2010A.C. Lowder Abstract:, Beef patties formulated to contain beef fat, plant oil, and a rosemary extract to increase unsaturated fatty acid content and maintain desirable sensory attributes were compared to control beef patties formulated without plant oils. Treatment patties were formulated to a fat content of 10% or 20% by combining beef trimmings (6% fat) with 4% or 14% addition of a lipid blend. Blends contained 57% beef tallow, 0.3% rosemary extract, and 43% of high oleic safflower oil (SO), olive oil (OO), or corn oil (CO). Lipid oxidation, as measured by TBA values, of treatment patties were similar to control patties after 0 and 3 d of refrigerated (2 °C) storage and up to 56 d of frozen (,10 °C) storage. Cooked lipid blend patties having a fat content of 10% or 20% were similar to or higher than control patties for juiciness and were no different for other sensory attributes evaluated. At fat levels of 10% or 20%, oleic acid (18: 1) in cooked SO patties (46.1% and 50.3%, respectively) and OO patties (43.8% and 48.1%, respectively) was higher than the control (37.3% and 37.6%, respectively). Unsaturated to saturated fatty acid ratios at the 10% or 20% fat levels were higher in SO (1.37 and 1.60, respectively) and CO (1.40 and 1.48, respectively) patties than the control (0.97 and 0.94, respectively). Beef patties manufactured with varying lipid blends increased unsaturated fatty acid content and were similar in physical characteristics and sensory attributes of all beef patties formulated without lipid blends. Practical Application:, The development of healthier beef products that will be more appealing to consumers has long been an industry goal. The authors believe that lipid blends such as the one used in this study could be used to create such products, not only in the form of beef patties, but any number of processed meat products. Because the materials and equipment used to create the lipid blends in this study are widely available, their incorporation into meat products would represent a small capital investment. This is an important factor in bringing a reasonably priced, healthier product to consumers. [source] Quantifier elimination for the theory of algebraically closed valued fields with analytic structureMLQ- MATHEMATICAL LOGIC QUARTERLY, Issue 3 2007n F. Çelikler Abstract The theory of algebraically closed non-Archimedean valued fields is proved to eliminate quantifiers in an analytic language similar to the one used by Cluckers, Lipshitz, and Robinson. The proof makes use of a uniform parameterized normalization theorem which is also proved in this paper. This theorem also has other consequences in the geometry of definable sets. The method of proving quantifier elimination in this paper for an analytic language does not require the algebraic quantifier elimination theorem of Weispfenning, unlike the customary method of proof used in similar earlier analytic quantifier elimination theorems. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Robust parameter-free algebraic multilevel preconditioningNUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 6-7 2002Y. Notay Abstract To precondition large sparse linear systems resulting from the discretization of second-order elliptic partial differential equations, many recent works focus on the so-called algebraic multilevel methods. These are based on a block incomplete factorization process applied to the system matrix partitioned in hierarchical form. They have been shown to be both robust and efficient in several circumstances, leading to iterative solution schemes of optimal order of computational complexity. Now, despite the procedure is essentially algebraic, previous works focus generally on a specific context and consider schemes that use classical grid hierarchies with characteristic mesh sizes h,2h,4h, etc. Therefore, these methods require some extra information besides the matrix of the linear system and lack of robustness in some situations where semi-coarsening would be desirable. In this paper, we develop a general method that can be applied in a black box fashion to a wide class of problems, ranging from 2D model Poisson problems to 3D singularly perturbed convection,diffusion equations. It is based on an automatic coarsening process similar to the one used in the AMG method, and on coarse grid matrices computed according to a simple and cheap aggregation principle. Numerical experiments illustrate the efficiency and the robustness of the proposed approach. Copyright © 2002 John Wiley & Sons, Ltd. [source] Selective floating gate non-volatile paper memory transistorPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 9 2009Rodrigo Martins Abstract Here we report the performance of a selective floating gate (VGS) n-type non-volatile memory paper field-effect transistor. The paper dielectric exhibits a spontaneous polarization of about 1 mCm,2 and GIZO and IZO amorphous oxides are used respectively as the channel and the gate layers. The drain and source regions are based in continuous conductive thin films that promote the integration of fibres coated with the active semiconductor. The floating memory transistor writes, reads and erases the stored information with retention times above 14500 h, and is selective (for VGS > 5 ± 0.1 V). That is, to erase stored information a symmetric pulse to the one used to write must be utilized, allowing to store in the same space different information. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modulation by phytochrome of the blue light-induced extracellular acidification by leaf epidermal cells of pea (Pisum sativum L.): a kinetic analysisTHE PLANT JOURNAL, Issue 5 2000J. Theo M. Elzenga Summary Blue light induces extracellular acidification, a prerequisite of cell expansion, in epidermis cells of young pea leaves, by stimulation of the proton pumping-ATPase activity in the plasma membrane. A transient acidification, reaching a maximum 2.5,5 min after the start of the pulse, could be induced by pulses as short as 30 msec. A pulse of more than 3000 ,mol m,2 saturated this response. Responsiveness to a second light pulse was recovered with a time constant of about 7 min. The fluence rate-dependent lag time and sigmoidal increase of the acidification suggested the involvement of several reactions between light perception and activation of the ATPase. In wild-type pea plants, the fluence response relation for short light pulses was biphasic, with a component that saturates at low fluence and one that saturates at high fluence. The phytochrome-deficient mutant pcd2 showed a selective loss of the high-fluence component, suggesting that the high-fluence component is phytochrome-dependent and the low-fluence component is phytochrome-independent. Treatment with the calmodulin inhibitor W7 also led to the elimination of the phytochrome-dependent high-fluence component. Simple models adapted from the one used to simulate blue light-induced guard cell opening failed to explain one or more elements of the experimental data. The hypothesis that phytochrome and a blue light receptor interact in a short-term photoresponse is endorsed by model calculations based upon a three-step signal transduction cascade, of which one component can be modulated by phytochrome. [source] Optimal fed-batch cultivation when mass transfer becomes limitingBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2007John Villadsen Abstract In the design of an aerobic fed-batch process to produce, for example, a pharmaceutical protein, the volumetric production rate will eventually become limited by mass transfer when the biomass concentration exceeds a certain upper limit x*. It appears to be common practice to switch from exponential feed of substrate to a constant feed rate when x* is reached. This is done to avoid oxygen starvation with a potential risk of undesired stress responses. But with a constant feed rate the carbon source (glucose) concentration may decrease to a low level with a resulting loss of viability and an undesired production of endotoxins. It is shown that an exponential feeding strategy may be continued, but with a smaller exponent than the one used before oxygen limitation occurs. This will diminish the potential detrimental effects on the culture due to low glucose concentration, and the total time to reach a given final biomass concentration will be reduced. Biotechnol. Bioeng. 2007;98: 706,710. © 2007 Wiley Periodicals, Inc. [source] | |||||||||||||||||||