Distribution by Scientific Domains

Kinds of Proof

  • constructive proof
  • convergence proof
  • direct proof
  • elementary proof
  • mathematical proof
  • new proof
  • rigorous proof
  • short proof
  • simple proof
  • simpler proof

  • Selected Abstracts


    Annalisa Coliva
    Moore's proof of an external world is a piece of reasoning whose premises, in context, are true and warranted and whose conclusion is perfectly acceptable, and yet immediately seems flawed. I argue that neither Wright's nor Pryor's readings of the proof can explain this paradox. Rather, one must take the proof as responding to a sceptical challenge to our right to claim to have warrant for our ordinary empirical beliefs, either for any particular empirical belief we might have, or for belief in the existence of an external world itself. I show how Wright's and Pryor's positions are of interest when taken in connection with Humean scepticism, but that it is only linking it with Cartesian scepticism which can explain why the proof strikes us as an obvious failure. [source]

    Proof of principle: An HIV p24 microsphere immunoassay with potential application to HIV clinical diagnosis,

    CYTOMETRY, Issue 3 2009
    Pascale Ondoa
    Abstract The measurement of CD4 counts and viral loads on a single instrument such as an affordable flow cytometer could considerably reduce the cost related to the follow-up of antiretroviral therapy in resource-poor settings. The aim of this study was to assess whether the HIV-1 p24 antigen could be measured using a microsphere-based flow cytometric (FC) assay and the experimental conditions necessary for processing plasma samples. A commercial anti-p24 antibody pair from Biomaric was used to develop a p24 microsphere immunoassay (MIA) using HIV culture supernatant as the source of antigen. The ultrasensitive Perkin Elmer enzyme immunoassay (EIA) served as a reference assay. Quantification of HIV p24 using the heat-mediated immune complex disruption format described for plasma samples was feasible using the Biomaric MIA and applicable to a broad range of HIV-1 Group M subtypes. The inclusion of a tyramide amplification step was successful and increased the fluorescence signal up to 3 logs as compared with the MIA without amplification. The analytical sensitivity of this ultrasensitive Biomaric assay reached 1 pg/mL, whereas the ultrasensitive Perkin Elmer EIA was sensitive to less than 0.17 pg/mL. Our data indicate, for the first time, that the principle of p24 detection using the heat-denatured ultrasensitive format can be applied to FC. © 2008 Clinical Cytometry Society [source]

    Development of a Rapid Single-Drop Analysis Biosensor for Screening of Phenanthrene in Water Samples

    ELECTROANALYSIS, Issue 20 2004

    Abstract Detection techniques for biosensors often require bulky instruments or cells that are not feasible for in-field analysis. Our single-drop cell design, optimized in this work, comprised a screen-printed three-electrode (SPE), strip in horizontal position onto which a volume of 100,,L of sample or substrate solution was placed to ensure electrical contact (complete circuit). Together with optimized linear sweep voltammetry (LSV), parameters for the detection of the enzyme alkaline phosphatase (AP), the system was applied to a biosensor for the analysis of polycyclic aromatic hydrocarbons (PAHs), in environmental samples. A limit of detection (LOD), of 0.15,ppb was achieved for a model system with an IC50 value of 0.885 ppb and a linear range (LR), of 0.2,10,ppb. Application of the single drop analysis (SDA), format to a PAH biosensor gave a LOD of 1.4,ppb for detection of phenanthrene with an IC50 value of 29.3,ppb and linear range of 2,100,ppb. Proof of concept is shown with spiked sample analysis of phenanthrene in matrices such as sea, river and tap water. [source]

    Proof of an Association between Helicobacter pylori and Idiopathic Thrombocytopenic Purpura in Latin America

    HELICOBACTER, Issue 3 2007
    Germán Campuzano-Maya
    Abstract Background:, Association between Helicobacter pylori and idiopathic thrombocytopenic purpura (ITP) has been found in Japan and in some European countries. It has also been shown that eradication of H. pylori can increase platelet counts in patients with ITP. The aims of this study were to determine the prevalence of H. pylori infection in patients with ITP in Colombia, and the effect of bacterial eradication on their platelet counts. Materials and methods:, Between December 1998 and April 2006, a total of 32 patients diagnosed with ITP were included in the study. Controls were age and sex matched. Results:,H. pylori infection in patients with ITP was significantly higher (p = .00006) than in control individuals (90.6% and 43.8%, respectively), as determined by 13C-urea breath test. A significant association between H. pylori infection and ITP was found (p < .0003), with an odds ratio (OR) of 13.15 (95%CI: 3.24,53.29). Multivariate analysis for the association between H. pylori and ITP showed an OR of 20.44 (95%CI: 3.88,107.49) for women and 19.28 (95%CI: 2.03,183.42) for individuals over 50 years. All 29 H. pylori -positive patients with ITP received eradication treatment. After a median follow up of 12.2 months, 80.8% had a recovery in platelet counts. Conclusions:, According to these results and others from different countries where H. pylori infection rates are high, patients with ITP should be initially tested for H. pylori status, and if present, infection should be eradicated before initiating a drastic conventional ITP treatment. An algorithm for the study and management of patients with ITP in the post- Helicobacter era is presented. [source]

    Productive Asymmetric Styrene Epoxidation Based on a Next Generation Electroenzymatic Methodology

    Reto Ruinatscha
    Abstract We have established a novel and scalable methodology for the productive coupling of redox enzymes to reductive electrochemical cofactor regeneration relying on efficient mass transfer of the cofactor to the electron-delivering cathode. Proof of concept is provided by styrene monooxygenase (StyA) catalyzing the asymmetric (S)-epoxidation of styrene with high enantiomeric excess, space-time yields, and current efficiencies. Highly porous reticulated vitreous carbon electrodes, maximized in volumetric surface area, were employed in a flow-through mode to rapidly regenerate the consumed FADH2 cofactor required for StyA activity. A systematic investigation of the parameters determining cofactor mass transfer revealed that low FAD concentrations and high flow rates enabled the continuous synthesis of the product (S)-styrene oxide at high rates, while at the same time the accumulation of the side-products acetophenone and phenylacetaldehyde was minimized. At 10,,M FAD and a flow rate of 150,mL,min,1, an average space-time yield of 0.35,g,L,1,h,1 could be achieved during 2,h with a final (S)-styrene oxide yield of 75.2%. At two-fold lower aeration rates, the electroenzymatic reaction could be sustained for 12,h, albeit at the expense of lower (59%) overall space-time yields. Under these conditions, as much as 20.5% of the utilized current could be channeled into (S)-styrene oxide formation. In comparison with state-of-the-art electroenzymatic methodologies for the same conversion, (S)-styrene oxide synthesis could be improved up to 150-fold with respect to both reaction time and space-time yield. These productivities constitute the most efficient reaction reported for asymmetric in vitro epoxidations of styrene. [source]

    Proof of a conjecture on fractional Ramsey numbers

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

    Proof of Mader's conjecture on k -critical n -connected graphs

    Su Jianji
    Abstract Mader conjectured that every k -critical n -connected noncomplete graph G has 2k,+,2 pairwise disjoint fragments. The author in 9 proved that the conjecture holds if the order of G is greater than (k,+,2)n. Now we settle this conjecture completely. © 2004 Wiley Periodicals, Inc. J Graph Theory 45: 281,297, 2004 [source]

    Near-Infrared Spectroscopy for Plaque Characterization

    A near-infrared (NIR) spectroscopy catheter-based system has been developed for intracoronary detection of lipid-rich plaques, capable of scanning an artery through blood and during cardiac motion. The lipid-rich plaque chemometric algorithm was validated in an ex vivo study using coronary artery specimens from autopsy hearts. A parallel clinical study was performed to demonstrate safety of the system in patients and the similarity of spectra acquired in vivo to data from the ex vivo study. Proof of spectral similarity between data obtained in patients and data from autopsy specimens is required to demonstrate the applicability of the algorithm to patients, in whom tissue for analysis is not available. A preliminary analysis in an unblinded cohort of patients from the clinical study reported promising results. The final results of the clinical study will be submitted for publication. The potential clinical value of this NIR spectroscopy device is discussed. [source]

    The allergen Bet v 1 in fractions of ambient air deviates from birch pollen counts

    ALLERGY, Issue 7 2010
    J. T. M. Buters
    To cite this article: Buters JTM, Weichenmeier I, Ochs S, Pusch G, Kreyling W, Boere AJF, Schober W, Behrendt H. The allergen Bet v 1 in fractions of ambient air deviates from birch pollen counts. Allergy 2010; 65: 850,858. Abstract Background:, Proof is lacking that pollen count is representative for allergen exposure, also because allergens were found in nonpollen-bearing fractions of ambient air. Objective:, We monitored simultaneously birch pollen and the major birch pollen allergen Bet v 1 in different size fractions of ambient air from 2004 till 2007 in Munich, Germany. Methods:, Air was sampled with a ChemVol® high-volume cascade impactor equipped with stages for particulate matter (PM)>10 ,m, 10 ,m>PM>2.5 ,m, and 2.5 ,m>PM>0.12 ,m. Allergen was determined with a Bet v 1-specific ELISA. Pollen count was assessed with a Burkard pollen trap. We also measured the development of allergen in pollen during ripening. Results:, About 93 ± 3% of Bet v 1 was found in the PM,>,10 ,m fraction, the fraction containing birch pollen. We did not measure any Bet v 1 in 2.5 ,m,>,PM,>,0.12 ,m. Either in Munich no allergen was in this fraction or the allergen was absorbed to diesel soot particles that also deposit in this fraction. Pollen released 115% more Bet v 1 in 2007 than in 2004. Also within 1 year, the release of allergen from the same amount of pollen varied more than 10-fold between different days. This difference was explained by a rapidly increasing expression of Bet v 1 in pollen in the week just before pollination. Depending on the day the pollen is released during ripening, its potency varies. Conclusion:, In general, pollen count and allergen in ambient air follow the same temporal trends. However, because a 10-fold difference can exist in allergen potency of birch pollen, symptoms might be difficult to correlate with pollen counts, but perhaps better with allergen exposure. [source]


    METAPHILOSOPHY, Issue 2 2009
    Abstract: Some seventy years ago, G. E. Moore invoked his own sensory experience (as of a hand before him in the right circumstances), added some philosophical analysis about externality, and took himself to have offered his "Proof" of the existence of an external world. Current neo-Mooreans either reject completely the standard negative assessment of the Proof or qualify it substantially. For Sosa, the Proof can be persuasive, but only when read literally as offering reasons for the conclusion that there is at least one external object,rather than that the prover is justified in believing, or even knowing, that there is at least one external object. Sosa, then, is a neo-Moorean,though not of the sort we might expect in light of the ongoing debate about the Proof. I argue that Sosa needs to say more about the circularity often thought to vitiate the Proof before we can accept his view. [source]

    Proof or Consequences: Who Shall Pay for the Evidence in Pain Medicine?

    PAIN MEDICINE, Issue 1 2010
    FFPM(ANZCA), Nikolai Bogduk MD
    No abstract is available for this article. [source]

    Spinoza's Proof of Necessitarianism

    This paper consists of four sections. The first section considers what the proof of necessitarianism in Spinoza's system requires. Also in the first section, Jonathan Bennett's (1984) reading of lpl6 as involving a commitment to necessitarianism is presented and accepted. The second section evaluates Bennett's suggestion how Spinoza might have been led to conclude necessitarianism from his basic assumptions. The third section of the paper is devoted to Don Garrett's (1991) interpretation of Spinoza's proof. I argue that Bennett's and Garrett's interpretations of Spinoza's necessitarianism have shortcomings which justify an attempt to offer an alternative proof. In the proof given in the fourth section, it is argued that Spinoza derived necessitarianism from the conjunction of the following principles: (i) necessary existence of the substances; (ii) substance-property ontology; (iii) superessentialism; and (iv) the ,no shared attribute'thesis. [source]

    Proof of a tiling conjecture of Komlós

    Ali Shokoufandeh
    Abstract A conjecture of Komlós states that for every graph H, there is a constant K such that if G is any n -vertex graph of minimum degree at least (1 , (1/,cr(H)))n, where ,cr(H) denotes the critical chromatic number of H, then G contains an H -matching that covers all but at most K vertices of G. In this paper we prove that the conjecture holds for all sufficiently large values of n. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 180,205, 2003 [source]

    Hereditary inclusion body myopathy: single patient response to GNE gene Lipoplex therapy

    Gregory Nemunaitis
    Abstract Background Hereditary inclusion body myopathy (HIBM) is an autosomal recessive adult onset myopathy. It is characterized by mutations of the GNE (UDP- N -acetylglucosamine 2-epimerase/N -acetylmannosamine kinase) gene. Afflicted patients have no therapeutic options. In preclinical testing, we have previously demonstrated the ability to correct GNE gene function and the safety of delivery of wild type GNE gene using a liposomal delivery vehicle. Methods A single patient (subject #001) with severe HIBM treated by compassionate investigational new drug received four doses of GNE gene Lipoplex via intramuscular injection. GNE transgene expression, downstream induction of sialic acid, safety and muscle function were evaluated. Results Significant durable improvement in locoregional skeletal muscle function was observed in the injected left extensor carpi radialis longus of #001 in correlation with GNE transgene upregulation and local induction of sialic acid. Other than transient low grade fever and pain at the injection site, no significant toxicity was observed. Conclusions Proof of principle for manufacturing of ,clinical grade' GNE gene Lipoplex, clinical safety and activity are demonstrated with GNE gene Lipoplex. Further assessment will involve intravenous administration and subsequent phase I trial involving additional but less severely afflicted HIBM patients. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Proof of a decomposition theorem for symmetric tensors on spaces with constant curvature

    ANNALEN DER PHYSIK, Issue 8 2008
    N. Straumann
    Abstract In cosmological perturbation theory a first major step consists in the decomposition of the various perturbation amplitudes into scalar, vector and tensor perturbations, which mutually decouple. In performing this decomposition one uses , beside the Hodge decomposition for one-forms , an analogous decomposition of symmetric tensor fields of second rank on Riemannian manifolds with constant curvature. While the uniqueness of such a decomposition follows from Gauss' theorem, a rigorous existence proof is not obvious. In this note we establish this for smooth tensor fields, by making use of some important results for linear elliptic differential equations. [source]

    Proof of perturbative gauge invariance for tree diagrams to all orders

    ANNALEN DER PHYSIK, Issue 7 2005
    M. Dütsch
    Abstract It is proved that classical BRS-invariance of the Lagrangian implies perturbative gauge invariance for tree diagrams to all orders. The proof applies in particular to the Einstein Hilbert Lagrangian of gravity. [source]


    ARCHAEOMETRY, Issue 2 2010
    A. DURAN
    The employment of synchrotron techniques complemented by conventional laboratory systems has allowed us to deepen and improve our knowledge of Roman wall painting procedures. The palette identified in wall paintings from Pompeii and Herculaneum from the second century bc includes goethite, hematite, cinnabar, glauconite, Egyptian blue, and other components such as calcite and aragonite. Proof of the use of organic binders is provided by FTIR and PY,GC/MS. Therefore, the possibility of the use of ,a secco' techniques cannot be ruled out. Pigments in wall paintings are usually found in small percentages and conventional X-ray diffractometers do not detect them. Synchrotron radiation , high-resolution X-ray powder diffraction has allowed identification with only a few micrograms of sample. [source]

    Clinical benefit of joint distraction in the treatment of severe osteoarthritis of the ankle: Proof of concept in an open prospective study and in a randomized controlled study

    ARTHRITIS & RHEUMATISM, Issue 11 2002
    Anne C. A. Marijnissen
    Objective Osteoarthritis (OA) is a degenerative, disabling joint disease that affects >10% of the adult population. No effective disease-modifying treatment is available. In the present study, we used joint distraction, a relatively new treatment in which mechanical contact between the articular surfaces is avoided while intraarticular intermittent fluid pressure is maintained, to treat patients with severe OA of the ankle. Methods Patients with severe ankle OA (n = 57) who were being considered for joint fusion (arthrodesis) were treated with joint distraction in an open prospective study. In addition, a randomized trial was performed in 17 patients to determine whether joint distraction had a better outcome than debridement. A standardized evaluation protocol (physical examination, assessment of pain, mobility, and functional ability) was used, and changes in radiographic joint space width and subchondral sclerosis were measured. Thirty-eight patients in the open study have been followed up for >1 year, with up to 5 years of followup in 7 of them (mean ± SD followup 2.8 ± 0.3 years). Patients in the randomized study have been followed up for 1 year. Results Significant clinical benefit was found in three-fourths of the 57 patients in the open prospective study. Most interestingly, the improvement increased over time. Radiographic evaluation showed increased joint space width and decreased subchondral sclerosis. Moreover, joint distraction showed significantly better results than debridement. Conclusion The clinical benefit of joint distraction in the treatment of severe OA is proof of the concept. Although the followup remains relatively short and effects over time remain unpredictable, our study creates possibilities for the treatment of severe OA in general. Considering the high prevalence of OA and the lack of a cure for it, joint distraction as a treatment of severe OA may have great medical, social, and economic impact. [source]

    In situ magnetic separation for extracellular protein production

    Tobias Käppler
    Abstract A new approach for in situ product removal from bioreactors is presented in which high-gradient magnetic separation is used. This separation process was used for the adsorptive removal of proteases secreted by Bacillus licheniformis. Small, non-porous bacitracin linked magnetic adsorbents were employed directly in the broth during the fermentation, followed by in situ magnetic separation. Proof of the concept was first demonstrated in shake flask culture, then scaled up and applied during a fed batch cultivation in a 3.7 L bioreactor. It could be demonstrated that growth of B. licheniformis was not influenced by the in situ product removal step. Protease production also remained the same after the separation step. Furthermore, degradation of the protease, which followed first order kinetics, was reduced by using the method. Using a theoretical modeling approach, we could show that protease yield in total was enhanced by using in situ magnetic separation. The process described here is a promising technique to improve overall yield in bio production processes which are often limited due to weak downstream operations. Potential limitations encountered during a bioprocess can be overcome such as product inhibition or degradation. We also discuss the key points where research is needed to implement in situ magnetic separation in industrial production. Biotechnol. Bioeng. 2009;102: 535,545. © 2008 Wiley Periodicals, Inc. [source]

    Using ColE1-derived RNA I for suppression of a bacterially encoded gene: implication for a novel plasmid addiction system

    Irene Pfaffenzeller
    Abstract The use of plasmid DNA for gene therapeutical purposes is a novel technology with advantages and drawbacks. One of the required improvements is to avoid antibiotic resistance genes or other additional sequences for selection within the plasmid. Here, we describe an alternative approach to equip a ColE1 plasmid with a regulatory function within the cell, which could be used for selection of plasmid carrying cells. No additional sequences are required, since the mechanism is based on RNA/RNA antisense interaction involving the naturally occurring RNA I derived from the plasmid's origin of replication. The plasmid replicational regulatory network was linked to the transcriptional regulatory network of an engineered target gene, present on the bacterial chromosome. Thus, gene suppression of a reporter could be achieved by mere presence of the ColE1-type plasmid pBR322. Proof of this concept was shown in shaker-flask experiments and fed-batch fermentation processes. The strategy of regulating gene expression by plasmid replication implicates a novel strategy for plasmid selection, as the gene to be suppressed could be toxic or growth hampering, providing advantage to plasmid carrying host cells. [source]

    Oscillations in growth of multicellular tumour spheroids: a revisited quantitative analysis

    CELL PROLIFERATION, Issue 4 2010
    A. S. Gliozzi
    Objectives:, Multicellular tumour spheroids (MTS) provide an important tool for study of the microscopic properties of solid tumours and their responses to therapy. Thus, observation of large-scale volume oscillations in MTS, reported several years ago by two independent groups (1,2), in our opinion represent a remarkable discovery, particularly if this could promote careful investigation of the possible occurrence of volume oscillations of tumours ,in vivo'. Materials and methods:, Because of high background noise, quantitative analysis of properties of observed oscillations has not been possible in previous studies. Such an analysis can be now performed, thanks to a recently proposed approach, based on formalism of phenomenological universalities (PUN). Results:, Results have provided unambiguous confirmation of the existence of MTS volume oscillations, and quantitative evaluation of their properties, for two tumour cell lines. Proof is based not only on quality of fitting of the experimental datasets, but also on determination of well-defined values of frequency and amplitude of the oscillations for each line investigated, which would not be consistent with random fluctuation. Conclusions:, Biological mechanisms, which can be directly responsible for observed oscillations, are proposed, which relates also to recent work on related topics. Further investigations, both at experimental and at modelling levels, are also suggested. Finally, from a methodological point of view, results obtained represent further confirmation of applicability and usefulness of the PUN approach. [source]

    ChemInform Abstract: The Fluorine,Iminium Ion Gauche Effect: Proof of Principle and Application to Asymmetric Organocatalysis.

    CHEMINFORM, Issue 34 2009
    Christof Sparr
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Enyne Metathesis,Oxidation Sequence for the Synthesis of 2-Phosphono Pyrroles: Proof of the "Yne-then-Ene" Pathway.

    CHEMINFORM, Issue 16 2007
    Nicolai Dieltiens
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

    ChemInform Abstract: cine-Substitution of Nitro Group in 1-Aryl-2-methyl-4-nitroimidazoles by Thiols; X-Ray Diffraction Proof for the Product Structure.

    CHEMINFORM, Issue 32 2001
    J. Suwinski
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    The Presence of B-type Natriuretic Peptide in Burns and the Responsiveness of Fibroblasts to BNP: Proof of Principle

    Adam J. Singer MD
    Background:B-type natriuretic peptide (BNP) released from cardiac myocytes plays an important role in cardiac homeostasis through cyclic guanosine monophosphate (cGMP) activation. BNP also reduces cardiac remodeling and fibrosis. The antifibrotic effects of BNP are mediated in part by blocking the effects of transforming growth factor ,, a profibrotic cytokine that plays a significant role in cutaneous wound healing. It is unclear if BNP plays any role in cutaneous wound healing.ObjectivesTo investigate if BNP levels would be elevated in thermally injured human skin and if human-derived fibroblasts would respond to BNP exposure by increasing levels of cGMP.MethodsThis was an in vitro analysis of human skin. Skin samples and cells were collected from patients with and without thermal injury. The authors stained three skin samples from normal skin (taken at the time of elective cosmetic surgery) with antibodies to BNP and compared these with three tissue samples obtained from burned human skin taken during tangential excision of deep burns. Normal human-derived fibroblasts and keratinocytes were exposed in triplicate to BNP in vitro, and cGMP accumulation was evaluated. Levels of cGMP were quantified and compared with analysis of variance.ResultsBNP was present in all specimens of thermally injured skin (especially around collagen, epithelial cells, and endothelial cells) but not in any uninjured skin samples (p = 0.05, single-tailed Fisher's exact test). In vitro grown fibroblasts showed significant increases of cGMP levels with increasing levels of BNP exposure (mean [±SD]: 0.6 [±0.3], 1.2 [±0.2], 4.6 [±0.1], and 5.0 [±0.9] pmol/mL with BNP concentrations of 0, 10, 500, and 1,000 nmol/L, respectively; p < 0.001). The effect of BNP on keratinocytes was minimal and below the level of quantification.Conclusions:These findings demonstrate proof of principle that human fibroblasts are responsive to the effects of BNP in vitro and that BNP is present in injured skin, suggesting that BNP may play a role in cutaneous wound healing. [source]

    Proofs of the Coexistence of Two Magnetic Contributions in Pure and Doped CaCu3Ti4O12 Giant Dielectric Constant Ceramics

    José Francisco Fernández
    Fe3+ - or Nb5+ -doped CaCu3Ti4O12 (CCTO) ceramics show higher values of both room-temperature (RT) grain conductivity and dielectric constant than undoped ceramics. Microstructural and structural characterization combined with magnetic properties reveal the coexistence of two components that seem relevant for the dielectric behavior of the material. The grain possesses a nanostructure characterized by layered domains with thicknesses <80 nm. The formation of the layered domains is associated with the evidence of different chemical states as Cu2+/Cu+ and Ti4+/Ti3+ that are present in the material. The magnetic contribution is related to two coupled effects: the antiferromagnetic (AFM) response with TN=25 K ascribed to Cu2+, and a paramagnetic-like contribution attributed to Ti3+ cations. The coexistence of two coupled magnetic contributions could explain the proposed unusual coupling of the AFM Cu2+ superexchange interaction through the nonmagnetic Ti4+ rather than via the usual oxygen coupling. The lower the paramagnetic-like contribution at RT, the larger the conductivity and the dielectric constant of the material are. Below 150 K, the increase of the paramagnetic-like contribution is correlated with the low transition temperature of the CCTO. [source]

    Fast Filtering and Smoothing for Multivariate State Space Models

    S. J. Koopman
    This paper investigates a new approach to diffuse filtering and smoothing for multivariate state space models. The standard approach treats the observations as vectors, while our approach treats each element of the observational vector individually. This strategy leads to computationally efficient methods for multivariate filtering and smoothing. Also, the treatment of the diffuse initial state vector in multivariate models is much simpler than in existing methods. The paper presents details of relevant algorithms for filtering, prediction and smoothing. Proofs are provided. Three examples of multivariate models in statistics and economics are presented for which the new approach is particularly relevant. [source]

    Models for the Logic of Possible Proofs

    Leon Horsten
    First page of article [source]

    The origins and present status of the radio wave controversy in NMR

    D.I. Hoult
    Abstract The origins, history, and present status of the controversy surrounding a quantum description of the NMR signal as being due to radio waves are traced. With the Principle of Relativity and Coulomb's Law as formal starting points and the minimum of mathematics needed for understanding, the derivation of a classical electromagnetic theory of signal reception is first given. The agreement between that classical theory and a recent NMR experiment is then presented, leading to proof that, except for the highest field imaging experiments, there is no significant contribution of radio waves to the signal. Attention is drawn to the very different properties of the near and far energy, momenta, and fields inherent in the derivation. The role of the Correspondence Principle in formulating a quantum description is then emphasized and it is shown that the standard NMR interpretation of Dicke's theory of coherent spontaneous emission,that the latter is responsible for the NMR signal,cannot be correct. Finally, the author speculates on some of the intriguing relationships found in the classical electrodynamics of NMR signal reception and attempts to relate them to a common quantum electrodynamic precept of near field interaction: that the free induction decay voltage present at the terminals of an open-circuit receiving coil is based on an exchange of virtual photons between the nuclei in a sample and the free electrons in a receiving coil. © 2009 Crown in the right of Canada. Concepts Magn Reson Part A 34A: 193,216, 2009. [source]

    A new piezoelectric single crystal obtained by Ge doping in the SiO2 structure

    M. Miclau
    Abstract The interest of Si1,xGexO2 single crystals with alpha-quartz structure is connected to improvement of electromechanical coefficients and rise of , , , phase transition of quartz one. Growth of an ,-SixGe1,xO2 crystal was realized by a hydrothermal method of temperature gradient in autoclaves, made from Cr,Ni alloys. Nutrient material was prepared from synthetic quartz as crashed rods and placed in the bottom of autoclaves. There was loaded GeO2 powder additive in proportions to quartz nutrient. Single crystals were investigated by electron microprobe analysis, X-ray diffraction and atomic force microscopy. The most important result, which was obtained during the investigations, is an experimental proof of growth of ,-SixGe1,xO2 single crystals under the hydrothermal conditions. The present results thus open the possibility to tune the piezoelectric properties of these materials by varying the chemical composition. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]