Search Results - (Author, Cooperation:A. Marx)

2018-08-08

American Physical Society (APS)

0031-9007

1079-7114

Physics

General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

2015-12-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-08-22

National Academy of Sciences

0027-8424

1091-6490

Biology

Medicine

Natural Sciences in General

2013-04-20

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-12-17

Italian Society of Silviculture and Forest Ecology

1971-7458

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

1089-7550

AIP Digital Archive

Physics

We have successfully fabricated superconducting nanobridges and grain-boundary junctions from epitaxial YBa2Cu3O7−δ thin films with thickness between 20 and 30 nm and width down to ∼100 nm. The patterning process turned out to severely deteriorate the transport properties resulting in structural damage, corrosion, and oxygen loss. The most crucial steps are the baking procedure used to cure the electron beam resist, the resist development, and the ion beam etching process. By optimizing these steps and applying a suitable post-treatment procedure a significant enhancement of the sample quality could be achieved. An ultraviolet light assisted oxygenation procedure after the patterning process enabled us to achieve superconducting transition temperatures between 80 and 87 K and critical current densities at 4.2 K up to 4×107 A cm−2 for the nanobridges and 5×103–2×105 A cm−2 for the grain boundary junctions. At 4.2 K junctions with width down to 100 nm corresponding to a junction area down to 2.3×10−3 μm2 showed superconductivity. © 2002 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A spectrometer for inverse photoemission in the vacuum ultraviolet range is described. A spherical grating with an acceptance of f/4 is used in normal incidence. Two position-sensitive detectors allow the registration of spectra covering the whole range of photon energies from 8 to 28 eV in parallel. The optical resolution is 18 A(ring) for the Lyman-α line of hydrogen. A space-charge-limited electron gun with an energy spread of 0.25 eV is used to excite inverse photoemission spectra. The large acceptance angle of the grating allows one to measure spectra with high efficiency and low background level.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have performed a detailed analysis of the low frequency 1/f noise in YBa2Cu3O7−δ and Bi2Sr2CaCu2O8+x grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates. The normalized fluctuation of the critical current, δIc/Ic, and the normal resistance, δRn/Rn were found to be almost independent of temperature and the misorientation angle. Furthermore, the magnitude of the fluctuations is very similar for both high-Tc cuprates. Correlation experiments showed that the fluctuations of Ic and Rn are anti-correlated. Our analysis strongly suggests that the source of 1/f noise in high-Tc bicrystal GBJs are localized defect states in an insulating grain boundary barrier with fluctuating electron occupation. The effective charge trapping time within single traps was found to decay exponentially with increasing bias voltage. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have studied the spatial distribution of the critical current density in YBa2Cu3O7−δ ramp edge Josephson junctions using low-temperature scanning electron microscopy. Applying this technique allows the imaging of the critical current density distribution with a spatial resolution of about 1 μm. Our measurements show that the geometry of the ramp-edge junction eases the trapping of magnetic flux quanta in the YBa2Cu3O7−δ layer covering the ramp edge. These trapped flux quanta result in a spatially inhomogeneous magnetic field parallel to the barrier layer, which in turn results in a spatially modulated supercurrent density and an unusual magnetic field dependence of the critical current.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Extensive studies of the low frequency 1/f noise in high-temperature superconducting (HTS) Josephson junctions of various types and materials have been performed for a wide range of operating parameters. The origin of the measured voltage fluctuations can be traced back to the trapping and release of charge carriers in trapping centers in an insulating barrier, giving rise to correlated fluctuations of the junction critical current Ic and normal-state resistance Rn. We observed a linear dependence of the normalized critical current and resistance fluctuations on Rn, which suggests a constant density of trapping centers for the HTS Josephson junctions. The scaling of the normalized fluctuations is in good agreement with the previously found scaling relation IcRn∝1/Rn and supports a junction model assuming a leaky tunnel barrier. © 1997 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have studied the electric transport properties of symmetrical [001] tilt Nd1.85Ce0.15CuO4−y (NCCO) bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates with misorientation angles of 24° and 36.8°. The superconducting properties of the NCCO GBJs are similar to those of GBJs fabricated from the hole doped high temperature superconductors (HTS). The critical current density Jc decreases strongly with increasing misorientation angle. The products of the critical current Ic and the normal resistance Rn (∼100 μV at 4.2 K) are small compared to the gap voltage and fit well to the universal scaling law IcRn∝Jc found for GBJs fabricated from the hole doped HTS. This suggests that the symmetry of the order parameter, which most likely is different for the electron and the hole doped HTS, has little influence on the characteristic properties of symmetrical [001] tilt GBJs. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We performed numerical simulations and experiments on Josephson vortex flow transistors based on parallel arrays of YBa2Cu3O7–δ grain boundary junctions with a cross gate line allowing us to operate the same devices in two different modes named the Josephson fluxon transistor (JFT) and Josephson fluxon–antifluxon transistor (JFAT). The simulations yield a general expression for the current gain versus number of junctions and normalized loop inductance and predict higher current gain for the JFAT. The experiments are in good agreement with simulations and show improved coupling between gate line and junctions for the JFAT as compared to the JFT. © 2001 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report on the preparation and characterization of the double-perovskite compound Sr2CrWO6 with a Curie temperature of 390 K. We have fabricated both Sr2CrWO6 bulk sintered polycrystalline bars and high-quality epitaxial thin films on SrTiO3 substrates by pulsed-laser deposition. The samples were characterized by thermogravimetric analysis, x-ray diffraction, electrical transport, and magnetization measurements. Polycrystalline samples containing a large number of grain boundaries show a large low-field magnetoresistance of up to 100% at 5 K. At room temperature, this effect is reduced to a few percent. Our results show that Sr2CrWO6 is an interesting candidate for room-temperature magnetoelectronic materials. © 2001 American Institute of Physics.

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource

1365-2559

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Aims : To determine whether chorioamnionitis has an impact on the extent of apoptosis and proliferation in fetal lungs. Fetuses exposed to chorioamnionitis have an increased risk of aquiring lung tissue damage in utero.Methods and results : Lung tissue sections from 35 stillborn fetuses were used in this study. Chorioamnionitis-exposed fetuses were subdivided depending on whether pneumonia was diagnosed (n = 13) or not (n = 10); 12 unaffected fetuses served as controls. Apoptotic and proliferating cells were determined by in-situ terminal deoxytransferase-mediated dUTP nick end labelling (TUNEL) assay and by anti-Ki67 immunohistochemistry, and quantified. The median apoptotic index in lungs of chorioamnionitis-exposed fetuses increased 2.4-fold compared with chorioamnionitis-negative stillborn controls (P = 0.043) and rose 21.6-fold when chorioamnionitis-exposed fetuses additionally developed pneumonia (P 〈 0.001). Compared with the proliferation index of the control group (PI =2.3), the median percentage of proliferating cells in the lungs of chorioamnionitis-exposed fetuses decreased (PI = 1.4) (P = 0.036), but increased 1.8-fold (P = 0.036) in fetal lungs of the chorioamnionitis/pneumonia group. By double labellings combining the TUNEL assay or the Ki67 antigen with cell marker proteins, we identified distal airway epithelial cells as the cell type undergoing apoptosis in chorioamnionitis-exposed fetal lungs, while epithelial, endothelial and smooth muscle cells proliferated. Immunolabellings of cleaved caspases -8 and -9 revealed that apoptosis is mediated via initiator caspase-8.Conclusion : Chorioamnionitis induces apoptosis of distal airway epithelial cells via the caspase-8 pathway and interferes with the normal proliferative activity of epithelial, endothelial, and smooth muscle cells in fetal lungs. Thus, apoptosis and proliferation are an important feature of chorioamnionitis-associated lung injury in utero.

Electronic Resource

1365-2559

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

A multifocal lymphoepithelioma-like carcinoma and a low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT-type) were found simultaneously in the stomach of a 65-year-old patient. Carcinoma and lymphoma were intimately associated forming complexes resembling lymphoepithelial lesions at the primary gastric site and in lymph node metastases. The two tumours had developed on a background of severe chronic-atrophic gastritis of the mucosa of antrum and fundus. Autoantibodies to normal gastric glandular tissue could be demonstrated in the patient’s sera. Using non-radioactive in situ hybridization (ISH), Epstein-Barr virus (EBV) sequences were detected in virtually all carcinoma cells but neither in the non-neoplastic mucosa nor in the lymphoma. These findings suggest that a focal EBV infection occurred early in the development of the carcinoma followed by a subsequent clonal expansion of the EBV-containing tumour cells. A neoplastic transformation in MALT-type lymphoma is not EBV-related but might be triggered by altered immune mechanisms.

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource

1365-2559

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Aims:  To investigate whether degrading proteases can be found in patent calvarial sutures. Sutural growth and fusion means replacement of the sutural connective tissue, rich in fibronectin and collagen type V, by expanding calvarial bone. Proliferation of one tissue into the border area of another implies the presence of enzymes able to degrade extracellular matrix (ECM). An important family of proteases is the matrix metalloproteinases (MMPs), as is the plasminogen/plasmin system.Methods and results:  Expression of two MMPs with substrate specifity for fibronectin and collagen type V and of the plasminogen activator system was studied by immunohistochemistry in samples of human fetal calvariae (age range weeks 19–35 of gestation). In all cases, intense staining for MMPs, urokinase, and urokinase receptor was found in the sutural connective tissue and along the outer and inner borders of calvarial bone.Conclusions:  Our findings suggest that degradation of sutural connective tissue takes place during sutural growth. This might facilitate proliferation of calvarial bone. Recently, it was shown that an important regulatory mechanism of sutural growth is apoptosis of osteoblasts in the osteogenic front. Intact fibronectin is known to prevent apoptosis of proliferating osteoblasts while fibronectin degradation induces their apoptosis.

Electronic Resource

1365-2559

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Five cases of a characteristic low-grade thymic epithelial tumour are described that we suggest calling metaplastic carcinoma of the thymus.〈section xml:id="abs1-2"〉〈title type="main"〉Methods and resultsThe patients' ages ranged from 44 to 71 (mean 56.2) years. Four of the patients were male. Three of five tumours showed invasion into mediastinal fat or pleura but, otherwise, all were well circumscribed. No metastases were present. Histologically, the tumours showed a biphasic pattern with solid carcinomatous areas merging gradually with a spindle cell component. Lymphocytes were rare. Cytological atypia and mitotic activity were variable in the solid areas, but slight or absent in the spindle cell component. On immunohistochemistry, the tumours showed expression of cytokeratin, vimentin and/or epithelial membrane antigen, both in the carcinomatous and spindle cell components. In two cases, actin expression was also present in both components. In one case, chromogranin, S100 protein, glial fibrillary acidic protein and neuron-specific enolase were expressed in at least some cells of both components. None of the patients had myasthenia gravis. All patients are alive without evidence of recurrence or metastasis.〈section xml:id="abs1-3"〉〈title type="main"〉ConclusionMetaplastic carcinoma of the thymus is a distinct clinicopathological entity that should be distinguished from the usually benign medullary thymomas and from the clinically aggressive carcinosarcomas and sarcomatoid carcinomas.

Electronic Resource

0030-5383

Linguistics and Literary Studies

Ethnic Sciences

History

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