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M Angst

Publications and source records attributed to M Angst.

10 recordsLinked to original sources
PubMed2002

Magneto-optical study of the superconducting gap of MgB(2) single crystals.

We present magneto-optical reflectivity results in the basal plane of the hexagonal MgB(2). The data were collected on a mosaic of MgB(2) single crystals with T(c)=38 K from the ultraviolet down to the far infrared as a function of temperature and magnetic field oriented along the c axis. In the far infrared, there is a clear signature of the superconducting gap with a gap ratio 2 Delta/k(B)T(c) approximately 1.2, well below the weak-coupling value. The gap is suppressed in an external magnetic field, which is a function of temperature. We extract the upper critical field H(c2) along the c axis. The temperature dependence of H(c2) is compatible with the Helfand-Werthamer behavior.

Journal Article↗
PubMed2002

Temperature and field dependence of the anisotropy of MgB2.

The anisotropy gamma of the superconducting state of high quality single crystals of MgB2 was determined, using torque magnetometry with two different methods. The anisotropy of the upper critical field was found to be temperature dependent, decreasing from gamma approximately 6 at 15 K to 2.8 at 35 K. Reversible torque data near T(c) reveal a field dependent anisotropy, increasing nearly linearly from gamma approximately equal to 2 in zero field to 3.7 in 10 kOe. The unusual temperature dependence is a true bulk property and can be explained by nonlocal effects of anisotropic pairing and/or the k--> dependence of the effective mass tensor.

Journal Article↗
PubMed2001

Chemistry and biology of thiamethoxam: a second generation neonicotinoid.

Thiamethoxam is the first commercial neonicotinoid insecticide from the thianicotinyl subclass. It was discovered in the course of our optimisation program on neonicotinoids started in 1985. Novel variations of the nitroimino-heterocycle of imidacloprid led to 4-nitroimino-1,3,5-oxadiazinanes exhibiting high insecticidal activity. Among these, thiamethoxam (CGA 293433) was identified as the best compound and selected for worldwide development. The compound can be synthesised in only a few steps and high yield from easily accessible starting materials. Thiamethoxam acts by binding to nicotinic acetylcholine receptors. It exhibits exceptional systemic characteristics and provides excellent control of a broad range of commercially important pests, such as aphids, jassids, whiteflies, thrips, rice hoppers, Colorado potato beetle, flea beetles and wireworms, as well as some lepidopteran species. In addition, a strong preventative effect on some virus transmissions has been demonstrated. Thiamethoxam is developed both for foliar/soil applications and as a seed treatment for use in most agricultural crops all over the world. Low use rates, flexible application methods, excellent efficacy, long-lasting residual activity and favourable safety profile make this new insecticide well-suited for modern integrated pest management programmes in many cropping systems.

Animals↗
PubMed2001

Painless electrodiagnostic current perception threshold and pain tolerance threshold values in CRPS subjects and healthy controls: a multicenter study.

The purpose of this study is to evaluate both painless and painful sensory transmission in patients with Complex Regional Pain Syndrome (CRPS) using the automated electrodiagnostic sensory Nerve Conduction Threshold (sNCT) test. This test generates reliable, painless Current Perception Threshold (CPT) and atraumatic Pain Tolerance Threshold (PTT) measures. Standardized CPT and PTT measures using constant alternating current sinusoid waveform stimulus at 3 different frequencies 5 Hz, 250 Hz, and 2 kHz (Neurometer CPT/C Neurotron, Inc. Baltimore, MD) were obtained from CRPS subjects at a distal phalange of the affected extremity and at an ipsilateral asymptomatic control site. Matched sites were tested on healthy subjects. Detection sensitivities for an abnormal PTT and CPT test were calculated based on specificity of 90% as determined from data obtained from healthy controls. A Spearman rank correlation was used to test for a significant association between presence of allodynia and an abnormal PTT or CPT at any frequency tested. Thirty-six CRPS subjects and 57 healthy controls were tested. The highest detection sensitivity of the PTT test from symptomatic test sites was 63% for the finger and 71% for the toe. PTT abnormalities were also detected, to a lesser degree, at the asymptomatic control site (41% finger control site, 16% toe control site). The highest CPT detection sensitivity at the symptomatic site was 37% for the finger site and 53% for the toe site. CPT abnormalities were also detected at the asymptomatic control site (29% finger control site, 37% toe control site). Eighty-six percent of the CRPS subjects had either a PTT or CPT abnormality at any frequency at the symptomatic site. There was a significant correlation between presence of allodynia and presence of an abnormal CPT and PTT, respectively (P < .01). The correlation coefficient was lower for CPT than for PTT, ie, 0.34 versus 0.6 for the finger and 0.48 versus 0.67 for the toe, respectively. In studied CRPS patients an abnormal PTT was detected with higher sensitivity than an abnormal CPT. Assessing PTT may become a useful electrodiagnostic quantitative sensory test for diagnosing and following the course of neuropathic pain conditions.

Journal Article↗
PubMed2001

The relationship between tracheal width and left bronchial width: Implications for left-sided double-lumen tube selection.

OBJECTIVE: To determine if there is a relationship between tracheal width (TW) and left bronchial width (LBW). DESIGN: Three-dimensional chest computed tomography (CT) scans were used to reconstruct major airways for measurement of TW and LBW. SETTING: Stanford University Medical Center, Stanford, California. PARTICIPANTS: Thirty-one adult patients undergoing chest CT scans. INTERVENTIONS: Cursors were used to directly measure internal diameter from coronal images of the trachea at midclavicular level and the left main bronchus at a level 1 cm below the carina. MEASUREMENTS AND MAIN RESULTS: TW and LBW, but not the LBW-to-TW ratio, were significantly larger in men than in women. The LBW-to-TW ratio was consistent for men (0.75 +/- 0.09) and women (0.77 +/- 0.10). CONCLUSIONS: LBW is proportional to TW. If LBW cannot be measured directly but TW can, the ratio of LBW to TW can be used to predict LBW. An appropriate-sized left double-lumen tube can then be selected for the patient.

Adult↗
PubMed1993

Fixation of transforaminal sacrum fractures: a biomechanical study.

A transforaminal fracture of the sacrum usually represents the posterior part of an unstable pelvic ring fracture and is associated with a high rate of neurological complications. Nerve root decompression combined with open reduction and internal fixation (ORIF) can be beneficial. Present fixation methods have the disadvantage of extensive bilateral posterior approaches and fixation across the sacroiliac joint. Three methods of internal fixation of the sacrum were compared in a biomechanical study using six fresh pelvic specimens. A fracture model consisting of a transforaminal osteotomy combined with a symphysis disruption in a single-leg stance was used. Standard Harrington sacral bars, an internal fixator, and a newly developed stabilization technique using adapted standard AO/ASIF small-fragment implants ("local osteosynthesis") were compared. Three-dimensional measurement of the fragment movement (goniometer system) showed a maximum displacement of 4.0-4.5 mm after maximal loading (990-1,181 N) and no differences among the implants. The failure load related to body weight was 85% for sacral bars, 74% for the local osteosynthesis, and 58% for the internal fixator. Major displacement under loading was observed in the direction of the foramen axis. The new osteosynthesis technique showed strength comparable to the clinically successfully applied method of stabilization with sacral bars. It adds the theoretical advantage of a minimized approach, without fixation and thus without involvement of the SI joints.

Biomechanical Phenomena↗
PubMed1992

[Biomechanical studies of the spine. Their significance for the development of rational treatment techniques].

A treatment is rational when the goal of restoring form and function can be achieved safely and with the least possible technical input and iatrogenic damage. In the field of spinal surgery a number of techniques have recently been developed than can be termed rational. Biomechanical investigations have made a decisive contribution to the progress achieved. Forces acting on the spine and their cyclic frequency are determined from (1) calculations based on models of the human body, (2) measurement of physical parameters, e.g. intradiscal pressure, and (3) loads acting on implants. Selection of the size and form of implants and investigation of their mechanical properties are based on the values recorded for forces and cycles. In vitro examinations on deformation of bone-implant complexes exposed to predetermined loads lead to improvements in form and dimensions of implants. Finally, comparative in vitro studies with different techniques can help in answering the question as to what technique is best suited to solve a given clinical problem.

Biomechanical Phenomena↗
PubMed1988

Corticosteroid-induced stimulation of atrial natriuretic peptide in man.

UNLABELLED: Previously, we reported elevated plasma immunoreactive ANP (irANP) levels from the 2nd to the 9th day of administering either prednisone, 50 mg/day, or 9 alpha-fludrocortisone acetate (9 alpha F), 0.6 mg/day, to normal humans. To investigate the course of plasma irANP levels during the first 48 h of corticosteroid administration, 9 healthy men (mean age +/- SEM, 24 +/- 1 years) received in randomised sequence A) a 4-h iv infusion of prednisolone sodium tetrahydrophthalate followed by oral administration of prednisone for 2 days; or B) a 4-h infusion of aldosterone followed by oral administration of 9 alpha F for 2 days. Basal supine plasma irANP levels averaged 32 +/- 5 ng/l in study A and 30 +/- 6 ng/l in study B; they were unchanged or even deceased up to 24 h of glucocorticoid or mineralocorticoid administration, but rose (P less than 0.01) to 56 +/- 9 and 62 +/- 12 ng/l at 48 h, respectively, of the two interventions. During glucocorticoid treatment, blood pressure (BP) and indices of the sodium-fluid volume state were unchanged after 48 h. During 9 alpha F administration, body weight increased (1.1 +/- 0.3%, P less than 0.001), whereas urinary sodium excretion (63 +/- 7%, P less than 0.001), hematocrit (4.1 +/- 1.1%, P less than 0.001), and plasma renin activity (38 +/- 4%, P less than 0.001) decreased. CONCLUSIONS: The increase in circulating irANP at 48 h of administration of either a glucocorticoid or a mineralocorticoid demonstrates a distinct but slow response of the ANP system to these corticosteroids in normal humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

[Increasing bone screw anchoring in the femur head by cement administration via the implant--a biomechanical study].

PURPOSE: Osteoporosis reveals a higher risk of fractures. Due to the lack of possibilities to anchor fixation elements, fracture treatment often turns out to be complicated. An experimental study served to investigate the extent to which the application of bone cement through a modified gliding screw (Dynamic Hip Screw DHS) would improve the screw anchoring in osteoporotic femoral heads. METHODS: Quasi-static compressive and torsional load tests were used to assess the desired improvement of the screw anchoring. Cadaver femur pairs served to compare the cement augmentation to the uncemented contralateral control. RESULTS: The improvement of the holding strength of the screw under static compressive and torsional load depended on the cement flow into the adjacent bone tissue. The filling with additional cement was only successful after having created a small hollow space at the screw tip with a special instrument. Consequently, under compression as well as torsion, the cement application yielded improvements from 17% up to several times as much. CONCLUSION: In the application of gliding screws in osteoporotic femoral heads, the locally limited cement application through the implant has been shown to be a biomechanical possibility to improve screw fixation.

Absorptiometry, Photon↗