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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 110 (1988), S. 2323-2324 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 66 (1994), S. 1610-1619 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 14 (1977), S. 141-147 
    ISSN: 1432-0630
    Keywords: 82.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We have determined by direct molecular beam velocity measurements that translational energy accommodation of O2 molecules scattered from a hot polycrystalline tungsten target is inefficient at high surface temperatures. Translational energy accommodation is inefficient whether the surface is clean or covered with oxygen to a varying extent, even though in the latter case the scattering is diffuse. On a clean tungsten surface the scattering of the O2 was approximately specular and the reaction probability of O2 was constant and greater than 90% over the temperature range 1000K to 2800 K. It was shown by simultaneous helium scattering that atomic surface roughness of an oxygen chemilayer, rather than trapping, is a major cause of the observed diffuse scattering of oxygen. At the lowest surface temperature of 1000 K, with an oxygen chemilayer present, the velocity of the most probable number density of the scattered O2 was lower than in the incoming beam or than that expected for complete equilibration with the surface.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0630
    Keywords: 72.20.−i ; 72.80.Ey ; 78.70.Gq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We report the contactless determination of the conductivity, the mobility and the carrier concentration of II–VI semiconductors by means of the technique of the partially filled waveguide at a microwave frequency of 9 GHz. The samples are CdHgTe epitaxial layers, grown on CdZnTe substrates by molecular beam epitaxy. The conductivity is determined from the transmission coefficient of the sample in the partially filled waveguide. For the analysis of the experimental data, the complex transmission coefficient is calculated by a rigorous multi-mode matching procedure. By varying the conductivity of the sample, we obtain an optimum fit of the calculated data to the experimental results. Comparison with conductivity data determined by the van der Pauw method shows that our method allows to measure the conductivity with good accuracy. The behaviour of the transmission coefficient of the sample is discussed in dependence on the layer conductivity, the layer thickness and the dielectric constant of the substrate. The calculations require to consider in detail the distribution of the electromagnetic fields in the sample region. The usual assumption of a hardly disturbed TE10 mode cannot be used in our case. By applying a magnetic field in extraordinary Voigt configuration, galvanomagnetic measurements have been carried out which yield the mobility and thus the carrier concentration. These results are also in good agreement with van der Pauw transport measurements.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-1084
    Keywords: Key words: Heart neoplasm – Heart valves – Magnetic resonance imaging – Tomography, X-ray computed, echocardiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. We describe the findings from various cross-sectional imaging modalities in patients with cardiac valve adherent masses. The techniques are discussed, and imaging findings are compared with the results of cardiac surgery. All three patients had neurological symptoms and/or cardiac murmurs. Transthoracic and/or transesophageal echocardiography revealed the cardiac mass in all three. For differentiation of thrombus and cardiac neoplasm magnetic resonance imaging (MRI) was also performed in all three patients and electron-beam computed tomography (EBCT) in two. Fast segmented cine gradient-echo MRI techniques provided mass depiction in all patients, while T1-weighted spin-echo imaging failed in mass detection in one patient. None of the patients showed evidence of valve regurgitation or stenosis in flow sensitive cine MRI. EBCT excluded mass calcifications in both patients and reliably demonstrated the valve attached lesions. Although echocardiography is the modality of choice in evaluating cardiac masses and especially valve attached masses, MRI and EBCT provide additional information about tissue characteristics and allows an excellent overview of the cardiac and paracardiac morphology. Fast segmented cine gradient-echo MRI is especially able to depict even small tumors attached to rapidly moving cardiac valves, and valve competence can be easily assessed within the same examination.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1084
    Keywords: Key words: X-ray CT ; Aorta ; Stenosis ; Obstruction ; Computer-assisted image processing ; Thoracic aorta ; Collateral circulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The objective of this study was to assess the reliability of spiral CT angiography (CTA) and 3D reconstruction in patients with aortic coarctation (CoA). Eighteen patients with suspected or surgically proven coarctation were examined by spiral CT. In addition to the axial slices, 3D reconstructions, such as shaded surface display (SSD) and maximum intensity projection (MIP), were used to determine the diameters of the CoA and the pre- and poststenotic aorta and to visualise the collateral vessels. Diameters derived from cardiac catheterization were compared with those from CTA in 8 patients. The degree of aortic stenosis was correlated with blood pressure gradients (BPG) in 12 patients. The difference between the diameters of the CoA and the pre- and poststenotic aorta derived from MIP and angiography was not statistically significant (p = 0.69). With SSD the internal thoracic artery was detected in 16 and the posterior intercostal artery in 13 cases. The degree of aortic stenosis correlated poorly with the BPG (r = 0.51, r 2 = 0.26). CTA with 3D reconstruction represents a reliable noninvasive technique for the assessment of the degree of CoA and the visualisation of collateral vessels. It may serve as a follow-up investigation after intervention or surgical treatment.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1084
    Keywords: Key words: CT ; Gastrointestinal tract ; Pancreas ; Adrenal glands ; Kidneys ; Trauma State-of-the-art reviews
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Computed tomography plays an important role in the detection and management of blunt visceral injuries in adults. Current standard examination techniques enable detection of the majority of perforating or devascularizing bowel injuries, although diagnostic findings are often subtle and meticulous inspection is required. Computed tomography may demonstrate pancreatic contusions and lacerations and help in distinguishing minor traumatic lesions without involvement of the pancreatic duct (organ injury scale, grades I and II) from deep lacerations with ductal involvement (grades III and V). Computed tomography enables distinguishing renal contusions and minor cortical lacerations that can usually be managed conservatively (injuries of grades I–III) from corticomedullary lacerations and injuries of the major renal vessels (grades IV and V) that have a less favorable prognosis and more commonly require surgical repair. In addition, CT is well suited for the detection of active renal hemorrhage and guidance of transcatheter embolization treatment and delineation of preexisting benign or malignant pathologies that may predispose to posttraumatic hemorrhage. The radiologist's awareness of the diagnostic CT findings of abdominal visceral injuries as well as their clinical and surgical implications are important prerequisites for optimal patient management.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-1084
    Keywords: Key words: Inferior vena cava ; interventional procedure ; Pulmonary embolism ; prophylaxis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The aim of this study was to evaluate the clinical efficacy, mechanical stability, and safety of the Simon nitinol inferior vena cava filter (SNF). The SNF was inserted in 114 consecutive patients at two institutions for prophylaxis of pulmonary embolism (PE). Clinical follow-up data were obtained retrospectively on all patients, and 38 patients underwent a dedicated radiologic follow-up protocol consisting of abdominal radiography, Doppler sonography, and CT. There was no immediate complication following filter insertion. Fifty patients died, on average, 5.6 (1–23) months after filter insertion, and 64 patients were alive, on average, 27 (3–62) months after filter insertion. Recurrent pulmonary embolism was documented in 5 patients (4.4 %) but originated distal to the filter in 1 patient. Deep venous thrombosis (DVT) was documented in 5.3 %, thrombosis at the access site in 3.5 %, and thrombosis of the inferior vena cava in 3.5 %. The rate of thromboembolic complications was similar in patients who did receive long-term anticoagulation and in those who did not. Radiologic follow-up showed no filter migration after, on average, 32 (5–62) months. A CT examination showed that struts of the SNF had penetrated the vena cava in 95 %, and were in contact with adjacent organs in 76 %; however, there were no clinical symptoms attributable to the filter. Filters were in an eccentric position in 63 % and partial filter disruption was found in 16 %; however, this did not affect filter function. The rate of recurrent pulmonary embolism after insertion of the SNF is 2.4 % per patient per year. Regardless of long-term anticoagulation, the rate of caval thrombosis is acceptably low. Except for occasional access-site thrombosis, no other filter-related morbidity was observed.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1084
    Keywords: Key words: Tomography, X-ray computed – Coronary disease – Coronary atherosclerosis – Multirow-detector computed tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. This contribution reviews the pathology and morphology of coronary calcifications. It summarizes the indications for investigation of the coronary arteries. The standard protocols for scan acquisition using electron beam and conventional computed tomography are described as well as various methods for evaluation such as the traditional Agatston scoring method and the newer three-dimensional scoring algorithms. Guidelines for interpreting scores are also reviewed. Major limitations of the reproducibility of the calcium score measurement are summarized. Future aspects of multirow-detector spiral computed tomography with retrospective electrocardiographic triggering for quantifying coronary calcium are discussed.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-1084
    Keywords: Key words: MR ; Bile ducts ; Pancreatic duct
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The objective of this article is to review technical aspects, discuss potential clinical indications for MR cholangiopancreatography (MRCP) and demonstrate the spectrum of diagnostic findings in benign, postoperative, and malignant conditions. We describe our current imaging protocol in comparison with other available techniques. Using a non-breath-hold, heavily T2-weighted fast-spin-echo (FSE) sequence with or without respiratory gating we obtained coronal and axial source images and maximum intensity projections (MIPs) in 102 patients with suspected abnormalities of the biliary or pancreatic ducts. Based on this series we demonstrate the diagnostic appearance of a variety of benign, postoperative, and malignant conditions of the biliary and pancreatic ducts and discuss potential clinical indications for MRCP. The non-breath-hold FSE technique enables a consistent image quality even in patients who cannot cooperate well. Respiratory gating increased the rate of diagnostic examinations from 79 to 95 %. Acquisition of coronal and axial source images enables detection of bile duct stones as small as 2 mm, although calculi that are impacted and not surrounded by hyperintense bile may sometimes be difficult to detect. The MIP reconstructions help to determine the level of obstruction in malignant jaundice, delineate anatomical variants and malformations, and to diagnose inflammatory conditions, e. g., sclerosing cholangitis, the Mirizzi syndrome and inflammatory changes in the main pancreatic duct. The MRCP technique also correctly demonstrates the morphology of bilio-enteric or bilio-biliary anastomoses. Because MRCP provides sufficient diagnostic information in a wide range of benign and malignant biliary and pancreatic disorders, it could obviate diagnostic endoscopic retrograde cholangiopancreatography (ERCP) in many clinical settings. The ERCP technique may be increasingly reserved for patients in whom nonsurgical interventional procedures are anticipated.
    Type of Medium: Electronic Resource
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