Search Results - (Author, Cooperation:J. Bernhardt)

2012-05-05

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Alphaproteobacteria/enzymology/genetics/*growth & development/metabolism ; Bacterial Proteins/genetics/metabolism ; Bacteroidetes/enzymology/genetics/*growth & development/metabolism ; Diatoms/*growth & development/metabolism ; *Ecosystem ; *Eutrophication ; Gammaproteobacteria/enzymology/genetics/*growth & development/metabolism ; Glycoside Hydrolases/genetics/metabolism ; Membrane Proteins/genetics/metabolism ; Membrane Transport Proteins/genetics/metabolism ; Metagenome ; Microbial Interactions ; North Sea ; Phosphates/metabolism ; Phytoplankton/*growth & development/metabolism ; Seawater/*microbiology ; Sulfatases/genetics/metabolism

1089-7550

AIP Digital Archive

Physics

An equation developed by Le Claire is widely used to obtain a grain-boundary diffusion product, aD′, from the measured solute concentration gradients produced under conditions of constant surface concentration in grain-boundary diffusion experiments. However, a numerical assessment of the accuracy of Le Claire's equation has revealed errors as large as 70% when applied outside of its range of validity to the shallow gradients (∼102 nm) that are provided by high-resolution analytical methods. To provide a relation applicable to this region, a numerical analysis of the variation of computed values of ∂ ln C¯/∂η6/5 with β has been used to develop a new and greatly improved expression of the form aD′=D3/2t1/2[10A(−∂ ln C¯/∂η6/5)B ], where A and B are parameters whose value depends on the experimental value of ∂ ln C¯/∂η6/5. The relation is valid for the experimentally useful range of solute penetrations 6(square root of)Dt∼10(square root of)Dt and for 1≤β≤105, and has been shown to produce a grain-boundary diffusion product accurate to within 1% throughout this domain. As the accuracy of the relation does not change systematically with η or β, it avoids introduction of an error in the activation energy for boundary diffusion that would result from inappropriate use of Le Claire's equation in this region. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The preparation of hexagonal {0001} 4H and 6H silicon carbide surfaces by hydrogen plasma or etching in hydrogen flow produces highly ordered monolayers of silicon dioxide. Their structure and epitaxial relationship to the SiC substrate were analyzed by quantitative low-energy electron diffraction and Auger electron spectroscopy. The bond angles and distances retrieved agree with those of bulk SiO2. Due to the saturation of all dangling bonds the semiconductor surface is passivated and preserves its perfect order also in air. The practically ideal oxide monolayers may serve as a seed for growing epitaxial oxides with low defect density and only few structural distortions at the interface to the SiC substrate. © 1999 American Institute of Physics.

Electronic Resource

1089-7666

AIP Digital Archive

Physics

The response of the sectional side force coefficient to localized suction has been studied on a slender body placed at 55° angle of attack. A strong dependence in the behavior of the asymmetric vortex system on Reynolds number is shown, which resolves discrepancies observed by different investigators.

Electronic Resource

0006-291X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0006-291X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0301-4622

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0301-4622

Gating process ; Ion transport ; Tracer flux

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0301-4622

(Torpedo marmorata) ; Gating process ; Ion transport ; Tracer flux

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0014-5793

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

0022-5193

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

0006-291X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

1432-055X

Schlüsselwörter Gynäkologische Laparoskopien (Pelviskopien) ; PONV ; Desfluran-N2O ; Dolasetron ; Metoclopramid ; Key-words Gynaecological laparascopy ; Desflurane-N2O ; Metoclopramide

Springer Online Journal Archives 1860-2000

Medicine

Abstract Background: Gynaecological surgery including laparoscopy is frequently associated with PONV. Therefore, choosing an anaesthetic with only little side effects in operations eligible for outpatient surgery is at least as important as applying anaesthetics that enable fast-tracking. Study goal: To assess the incidence and severity of PONV after balanced desflurane-N2O-anaesthesia and to compare the antiemetic efficacy of dolasetron or metoclopramide versus placebo. Methods: 120 ASA physical status I and II women aged 18 to 55 scheduled for elective laparoscopic surgery were enrolled . Anaesthesia was standardized: fentanyl (2 µg/kg), etomidate (0.25 mg/kg) and succinylcholine (1 mg/kg) for induction and desflurane 3–5% et along with 30% O2 in N2O, fentanyl (max. 0.1 mg/h) and cis-atracurium for maintenance. Patients were randomly allocated to receive one of the following: dolasetron 12.5 mg (group-D), metoclopramide 10 mg (group-M) or placebo (group-P). Results: Within the first 24 h, postoperative nausea (PON) and postoperative vomiting (POV) were reduced significantly in group D (38%/19%) and group M (36%/27%) compared to group P (69%/56%). Furthermore, PON and POV proved to be less intense in groups D and -M compared to group P: Episodes of severe nausea were recorded 17 times in 10 patients (17/10) in group P, compared to 5/4 in group M and 5/3 in group D, episodes of repeated vomiting 13 times in 8 patients (13/8) in group P, compared to 2/2 in group M and 2/1 in group D. Conclusions: Our results confirm the increased incidence of PONV after gynaecological laparoscopic surgery under balanced anaesthesia compared to the predicted rates. Both dolasetron and metoclopramide proved to be effective prophylactic measures. Given a PONV-incidence of 38% in group D and 39% in group M, it is doubtful, whether the anaesthetic technique chosen in this study is the most suitable regimen for ambulatory gynaecological laparoscopies.

Zusammenfassung Fragestellung: Gynäkologische Laparoskopien (Pelviskopien) sind mit einer hohen Inzidenz an PONV (postoperative nausea and vomiting) belastet. Daher sollte der prophylaktische antiemetische Effekt von Dolasetron (Gruppe D) oder Metoclopramid (Gruppe M) versus Plazebo (Gruppe P) unter Desflurananästhesie überprüft werden. Methodik: 120 Patientinnen (ASA I–II) wurden prospektiv, randomisiert und doppelblind untersucht: Einleitung der Anästhesie mit Fentanyl (2 µg/kg), Etomidat (0,25 mg/kg) und Succinylcholin (1 mg/kg) und Aufrechterhaltung mittels Desfluran (3–5et Vol.-%), N2O/O2, Fentanyl (max. 0,1 mg/h) und Cis-Atracurium. Die Gabe der Prüfsubstanz (D: 12,5 mg, M: 10 mg, P: 1 ml NaCl 0,9%) erfolgte 20 min vor OP-Ende. Ergebnisse: Jeweils 32 Patientinnen der Gruppen D und P sowie 33 der Gruppe M konnten ausgewertet werden. Postoperatives Erbrechen trat in den ersten 24 h in Gruppe D (19%) und Gruppe M (27%) signifikant seltener auf als in Gruppe P (56%). Auch PONV war in Gruppe D (38%) und in Gruppe M (39%) signifikant seltener als in Gruppe P (69%), (p〈0,05). Diskussion: Sowohl durch Dolasetron als auch durch Metoclopramid konnten die Inzidenz und Intensität von PONV signifikant gegenüber Plazebo reduziert werden. Trotz antiemetischer Prophylaxe lag aber die PONV-Inzidenz bei dem gewählten Narkoseverfahren noch auf einem unbefriedigend hohen Niveau.

Electronic Resource

1432-1084

Key words: Diagnostic radiology (Germany) ; Annual frequency of examinations ; Effective doses ; Collective doses ; Radiation risk for patients

Springer Online Journal Archives 1860-2000

Medicine

Abstract. The exposure of the German population to man-made radiation results mainly from diagnostic X-ray and nuclear medical examinations. Data are presented about the annual frequency and the average dose of the various examination types for West Germany in the years 1990–1992. According to these data a yearly average of approximately 1550 diagnostic examinations using ionizing radiation were performed per 1000 inhabitants resulting in an annual per caput effective dose of 1.9 mSv. Despite the frequent use of alternative examination techniques, such as sonography, nuclear magnetic resonance and endoscopy, the frequency of X-ray and nuclear medical examinations is still increasing. If collective risk assessments are done using the per caput effective dose, at least the age distribution of the patients must be considered. This leads to a “risk-modifying factor“ of 0.6–0.7 for patients to be applied to the ICRP risk coefficient of 5 % per Sv valid for the general population. However, radiation risk must always be viewed in context with disease- and therapy-related risks and balanced against the benefit of the diagnostic examination, which should always exceed the risk for a well-indicated procedure.

Electronic Resource

1432-2099

Springer Online Journal Archives 1860-2000

Biology

Physics

Summary Particles with a nonconducting membrane, oriented in an alternating electrical field, will show the behaviour of electrical dipoles. Across the membranes there will be generated alternating electrical potential differences, which may be calculated for confocal ellipsoidal cells by solving Laplace's equation. We have evaluated a formula valid generally for single confocal ellipsoidal cells under physiological conditions, the cells being placed with one of their semi-axes parallel to an external electrical field. The values of the generated potential difference, considered at the position of their maximum values, are dependent on the shape and size of the cells, on their orientation to the electrical field and on the frequency and strength of the field. The relaxation frequency depends also on cell shape, size and orientation, but furthermore on the membrane properties and on the conductivities inside and outside the cells. For simple cases like spheres and cylinders perpendicular to the electrical field, our formula will correspond to known expressions. Values for the generated potential differences, form-factors and relaxation frequencies are given for different types of spheroids and at different orientations. Of some practical importance are long prolate spheroids with their long semi-axes parallel to the external field, because only small field strengths are necessary in order to generate large potential differences which may evoke action potentialse.g. in muscle or nerve cells. The significance of this mechanism concerning the determination of protection and safeguard standards for the exposure to low-frequency electrical fields is discussed.

Electronic Resource

1432-2099

Springer Online Journal Archives 1860-2000

Biology

Physics

Summary By using several biophysical approximations and considering man as free space model limiting order-of-magnitude values for external electric and magnetic field strengths which may be hazardous for human beings were calculated. Danger may occur by excitation processes below 30 kHz for field strengths exceeding these limiting values; for frequencies larger than 30 kHz, thermal effects are predominant before excitation occurs. The external electric field strength necessary for causing action potentials in the central nervous system exceeds by far the corona forming level. But excitation is possible by strong alternating magnetic fields. Furthermore, by comparing the electrically and magnetically induced currents with the naturally flowing currents in man caused by the brain's and heart's electrical activity, a “lower boundary-line” was estimated. Regarding electric or magnetic field strengths undercutting this boundary-line, direct effects on the central nervous system may be excluded. Other mechanisms should be responsible for demonstrated biological effects.

Electronic Resource

1432-2099

Springer Online Journal Archives 1860-2000

Biology

Physics

Summary The biophysical model described in this paper has been used as basis for the preparation of the German standards which determine and define limits of exposure to electric or magnetic fields below several MHz, including 50/60 Hz. The electric field strength within the tissue is considered decisive for the biological effect in the low frequency range. Threshold values of field strengths and current densities including biological effects are compared. It is possible to establish “safe”, “dangerous” and “hazardous” current density curves as a function of frequency. To define exposure limits, the field strength or current density causing injury should be reduced by a factor exceeding 100 in order to avoid well established biological effects. The electric and magnetic field strengths in the human environment are correlated with the corresponding electric current density induced in the human body. This enables “safe”, “dangerous” and “hazardous” levels of current density in the human body to be correlated with the external electric or magnetic field strength. Additionally to the direct field effects indirect effects must be considered. In the second part of this paper data on touch voltages and currents are summarized and evaluated with regard to their health risk. Furthermore, as an example for indirect effects the interference of electric and magnetic fields with pacemakers is considered.

Electronic Resource

1432-2099

Springer Online Journal Archives 1860-2000

Biology

Physics

Summary The paper deals with the measurement of the passive electrical properties ofNitellopsis obtusa cells by means of intracellular electrodes. TheNitellopsis cell is placed into a special sample holder and surrounded by isotonic solution of artificial pond water and saccharose. A platinum wire is inserted into the vacuole without destroying the membranes or disturbing the cytoplasmic motion. The electrode arrangement consists of a coaxial cylinder condenser with guard-rings. The guard-rings guarantees a well-defined and strictly cylinder-symmetric field with a direction of current lines independent of frequency. A special three-terminal bridge with inductively coupled ratio arms was constructed to measure between 20 Hz and 500 kHz the conductance and the capacitance of the sample with an accuracy better than 1 % without falsification by additional guard-ring currents. The measured values are shown as circular arcs with slightly depressed centres in the complex conductance plane as well as in the complex capacitance plane. The results were analysed using the theory of heterogeneous dielectrics. In accordance with the structure of the cell it is shown that a model with frequency-independent electrical properties is sufficient to explain the data. Because of the well-defined experimental arrangement the analysis leads to the conclusion that the membrane capacitance exhibits no frequency dependence. The passive electrical properties of the membranes are: 18.5 kΩ cm2 and 0.7 µF/cm2 for the plasma membrane, and 0.25 kΩ cm2 and 2.1 µF/cm2 for the tonoplast. Since the contribution of the tonoplast to the overall dispersion is much smaller than of the plasma membrane, the tonoplast data show larger errors than the data of the plasma membrane.

Electronic Resource

1432-2099

Springer Online Journal Archives 1860-2000

Biology

Physics

Summary The capacitance-conductance bridge described here has been developed particularly for dielectric measurements of biological materials where well defined flux lines for a large range of frequencies are desired, which are produced by electrode arrangements with guard-rings. The bridge is a symmetrical Wheatstone network with inductively coupled ratio arms. It is important that the current density and phase shift of the guard-ring circuit can be of the same order as that of the sample circuit. A particular range of admittances exists, dependent on the frequency and ratio arms used, where the bridge is able to measure conductance as well as capacitance of the sample with an accuracy of better than 1 %. The method of testing the ratio arms used and of determining their range of sample admittances is described. This range covers approximately two to three decades ofC/G values of the sample, and phase angles between 0.2 and 80 degrees in the frequency range from 20 Hz to 500 kHz, The maximum value ofC/G of this range is about 5×10−2 sec at 20 Hz, the minimum value 5×10−9 sec at 500 kHz. The decades used in the standard arm of the bridge are 1 Ω−1 to 0.9 μΩ−1 in the conductance range and 0.1 pF to 90 nF in the capacitance range. The bridge described is particularly suitable for measurements on biological materials with high dielectric constants and high conductivity. As matching the ratio arms is readily possible, the range of admittances can be changed if necessary by the procedure described.

Electronic Resource

1432-2102

Schlüsselwörter Kernspintomographie ; Grenzwerte ; Statisches Magnetfeld ; Gradientenfeld ; Hochfrequenzfeld ; Key words Magnetic resonance imaging ; Limits ; Static magnetic field ; Gradient field ; Radio-frequency field

Springer Online Journal Archives 1860-2000

Medicine

Summary Magnetic resonance imaging is used routinely with much success for various problems in different medical disciplines. However, the patient is exposed to static as well as to time-dependent magnetic fields and radio-frequency electromagnetic fields. In 1997 the Strahlenschutzkommission, the German Radiological Protection Commission, passed a recommendation on the use of magnetic resonance in medical diagnostics. In this recommendation basic values related to thresholds for physiological effects and limits for restricted and unrestricted use are given. In the following the aim and applicability of this recommendation are discussed, as well as the thresholds and different limits for the static magnetic fields, the gradient fields and the radio-frequency fields. Additionally, advice is given for the protection of high-risk patients, personnel, and the general public, together with further safety advice as well as recommendations for users and manufacturers.

Zusammenfassung Für viele Fragestellungen unterschiedlicher medizinischer Fachgebiete wird die Bildgebung mit magnetischen Resonanzverfahren heute routinemäßig mit großem Erfolg eingesetzt. Diese Art der Bildgebung bedingt, daß der Patient statischen und zeitlich veränderlichen Magnetfeldern sowie hochfrequenten elektromagnetischen Feldern ausgesetzt wird. Die Strahlenschutzkommission hat zur Anwendung magnetischer Resonanzverfahren in der medizinischen Diagnostik Ende letzten Jahres eine Empfehlung verabschiedet. In ihr sind sowohl Basiswerte angegeben, die auf Schwellenwerten für physiologische Wirkungen beruhen, als auch daraus abgeleitete Richt- und Grenzwerte. Im folgenden wird sowohl auf den Zweck und den Anwendungsbereich dieser Anwendung eingegangen, als auch im Einzelnen auf die Schwellen-, Richt- und Grenzwerte der bei Magnetresonanzverfahren zur Verwendung kommenden statischen Magnetfelder, Gradientenfelder und Hochfrequenzfelder. Außerdem werden die Empfehlungen zum Schutz von Risikopatienten, des Personals, der allgemeinen Öffentlichkeit und weitere Sicherheitshinweise angesprochen, sowie Anforderungen an den Hersteller und an die Betreiber.

Electronic Resource