1,736 research outputs found

    On the number of signals in multivariate time series

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    We assume a second-order source separation model where the observed multivariate time series is a linear mixture of latent, temporally uncorrelated time series with some components pure white noise. To avoid the modelling of noise, we extract the non-noise latent components using some standard method, allowing the modelling of the extracted univariate time series individually. An important question is the determination of which of the latent components are of interest in modelling and which can be considered as noise. Bootstrap-based methods have recently been used in determining the latent dimension in various methods of unsupervised and supervised dimension reduction and we propose a set of similar estimation strategies for second-order stationary time series. Simulation studies and a sound wave example are used to show the method's effectiveness

    Precise determination of the hyperfine parameters of europium in multifluorite perovskites by 151Eu Mössbauer spectroscopy

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    The hyperfine interactions at the europium lattice sites in samples of the homologous (Fe,Cu)Sr2(Eu,Ce)nCu2O4+2n+z (n=2,3) series were studied by Eu151 Mössbauer spectroscopy. The work was motivated by the search for new superconducting phases. This homologous series is based on the YBa2Cu3O7−δ (1:2:3) structure. The samples used in the Mössbauer measurements consisted of crystallites with random orientation and grain oriented crystallites. The texture of oriented samples was analyzed by x-ray diffraction. The complete quadrupole Hamiltonian of the 21.5-keV γ-transition of Eu151 was successfully applied in the analyses of all the Mössbauer spectra. In samples having n≤2 the europium atoms occupy a single lattice site, whereas the spectra of the n=3 samples exhibit hyperfine interactions of the two different europium sites. Analyzing the hyperfine parameters of the latter samples was made possible by simultaneous fitting of three spectra, corresponding to three different crystal orientations of the same specimen. This fitting scheme also enables more precise determination of the hyperfine parameters in the n=2 samples. In these samples an electric field gradient (EFG), with a large negative-valued main component (Vzz) parallel with the crystal c axis, was found. In the n=3 samples, the two EFG’s of the europium sites were found to have Vzz components of opposite signs. The negative Vzz value was attributed to the rare-earth site adjacent to the CuO layer. This site, found in all samples of the series, corresponds to the rare-earth site of the 1:2:3 system.Peer reviewe

    Towards an unified description of total and diffractive structure functions at HERA in the QCD dipole picture

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    It is argued that the QCD dipole picture allows to build an unified theoretical description -based on BFKL dynamics- of the total and diffractive nucleon structure functions. This description is in qualitative agreement with the present collection of data obtained by the H1 collaboration. More precise theoretical estimates, in particular the determination of the normalizations and proton transverse momentum behaviour of the diffractive components, are shown to be required in order to reach definite conclusions.Comment: latex file with 5 encapsulated figures, 19 page

    Interaction of small size wave packet with hadron target

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    We calculate in QCD the cross section for the scattering of an energetic small-size wave packet off a hadron target. We use our results to study the small-σ\sigma behaviour of Pπ(σ)P_{\pi}(\sigma), the distribution over cross section for the pion, in the leading αs\alpha_{s}-order.Comment: Revised version of the report CEBAF-TH-96-0

    A large gastrointestinal stromal tumor of the duodenum: a case report

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    <p>Abstract</p> <p>Introduction</p> <p>Gastrointestinal stromal tumors of the duodenum are uncommon. They can reach a large size. Diagnosis can be elusive and managing them can be difficult. Our case report aims to increase awareness and highlight some issues related to the diagnosis and management of duodenal gastrointestinal stromal tumors.</p> <p>Case presentation</p> <p>We present the case of a 38-year-old Middle Eastern woman with a large, slowly-growing gastrointestinal stromal tumor of the duodenum. Her complaints were minor epigastric discomfort and swelling. A pancreaticoduodenectomy with complete tumor excision was performed. She was doing very well with no evidence of disease recurrence when she was last seen 34 months after her operation.</p> <p>Conclusion</p> <p>Gastrointestinal stromal tumors of the duodenum should be suspected in any patient with a duodenal wall mass. Extramural growth and central ulceration with or without bleeding should alert the endoscopist to the possibility of a duodenal gastrointestinal stromal tumor diagnosis. There is more than one surgical approach available; however, complete surgical excision, with negative margins, is the absolute requirement. Preoperative imatinib mesylate can be considered in unresectable or borderline resectable cases.</p

    Disruption of Toxoplasma gondii Parasitophorous Vacuoles by the Mouse p47-Resistance GTPases

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    The p47 GTPases are essential for interferon-γ-induced cell-autonomous immunity against the protozoan parasite, Toxoplasma gondii, in mice, but the mechanism of resistance is poorly understood. We show that the p47 GTPases, including IIGP1, accumulate at vacuoles containing T. gondii. The accumulation is GTP-dependent and requires live parasites. Vacuolar IIGP1 accumulations undergo a maturation-like process accompanied by vesiculation of the parasitophorous vacuole membrane. This culminates in disruption of the parasitophorous vacuole and finally of the parasite itself. Over-expression of IIGP1 leads to accelerated vacuolar disruption whereas a dominant negative form of IIGP1 interferes with interferon-γ-mediated killing of intracellular parasites. Targeted deletion of the IIGP1 gene results in partial loss of the IFN-γ-mediated T. gondii growth restriction in mouse astrocytes

    Thick calcification from a GIST of the stomach penetrating into pericolic soft tissue - report of a case

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    Thick calcification is a rare presentation of gastrointestinal stromal tumor (GIST). Penetration into gastric mucosa and pericolic soft tissue has never been reported. We report a case of gastric GIST with cystic degeneration and thick calcification in an 81-year old female, who presented with hematemesis and severe abdominal pain. Thick calcification of this tumor penetrating into pericolic soft tissue was noted and successfully treated by distal gastrectomy and partial colectomy. For gastrointestinal tumors with thick calcification, even with benign behavior, surgical intervention should be considered for both oncological considerations and prevention of catastrophes like perforation or penetration into surrounding soft tissue
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