Detection of Clostridium botulinum types C and D toxin by ELISA

An ELISA to detect Clostridium botulinum type D toxin was developed using polyclonal antibodies to a semi-purified toxic complex of the neurotoxin. Sensitivity of the ELISA for detecting type C and type D toxin compared with mouse inoculation was 70% and specificity 96% on samples from animals with botulism diagnosed on clinical signs and herd history. However, both mouse inoculation and the ELISA failed to detect toxin in many animals with a presumptive diagnosis of botulism. Some cross-reaction was seen with Clostridium novyi type A, but not with other clostridial species. While the ELISA described here cannot replace mouse inoculation for the diagnosis of botulism, it is a useful additional test.     

Desflurane vapor pressure depression

Due to its high vapor pressure and low boiling point, desflurane requires a specially designed, electronically controlled, temperature and pressure compensated vaporizer to regulate agent delivery to the anesthetic circuit. However, if the vapor pressure and boiling point were decreased, desflurane could be used in any conventional variable bypass vaporizer. Raoult's Law states that the vapor pressure of a liquid is proportional to its molar fraction in a solution. Accordingly, propylene glycol was used as a solvent for desflurane, and the physical characteristics of this mixture were evaluated at various molar concentrations and temperatures. Desflurane boiling point increased and vapor pressure decreased as a nonlinear function of dilution, but these changes were less than predicted by Raoult's Law. Using a circle system with a breathing bag attached at the patient end and a mechanical ventilator to simulate respiration, an in‐circuit, nonprecision vaporizer containing 40% desflurane and 60% propylene glycol achieved a 11.5 ± 1.0% (mean ± SD) circuit desflurane concentration with a 5.2 ± 0.4 (0 = off, 10 = maximum) vaporizer setting. This experiment was repeated with a dog attached to the breathing circuit under spontaneous ventilation with a fresh gas flow of 0.5 L min^–1. Anesthesia was maintained for over two hours at a mean vaporizer setting of 6.2 ± 0.4, yielding mean inspired and end‐tidal desflurane concentrations of 8.7 ± 0.5% and 7.9 ± 0.7%, respectively. Within 5 minutes after cessation of anesthesia, the dog was awake, extubated and standing. In clinical practice, propylene glycol may not prove an ideal solvent for desflurane due to its instability in solution and substantial positive deviation from Raoult's Law. However, rather than alter the vaporizer to suit physical properties of anesthetic agents, this study demonstrates that it may also be possible to alter anesthetic agents to suit physical properties of the vaporizer.     

Earthquakes on dipping faults: the effects of broken symmetry

Dynamic simulations of earthquakes on dipping faults show asymmetric near-source ground motion caused by the asymmetric geometry of such faults. The ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more, given identical initial stress magnitudes. The motion of the hanging wall is larger than that of the footwall in both thrust (reverse) and normal earthquakes. The asymmetry between normal and thrust (reverse) faults results from time-dependent normal stress caused by the interaction of the earthquake-generated stress field with Earth's free surface. The asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault.     

The radio-frequency single-electron transistor (RF-SET): A fast and ultrasensitive electrometer

A new type of electrometer is described that uses a single-electron transistor (SET) and that allows large operating speeds and extremely high charge sensitivity. The SET readout was accomplished by measuring the damping of a 1.7-gigahertz resonant circuit in which the device is embedded, and in some ways is the electrostatic "dual" of the well-known radio-frequency superconducting quantum interference device. The device is more than two orders of magnitude faster than previous single-electron devices, with a constant gain from dc to greater than 100 megahertz. For a still-unoptimized device, a charge sensitivity of 1.2 x 10(-5) e/hertz was obtained at a frequency of 1.1 megahertz, which is about an order of magnitude better than a typical, 1/f-noise-limited SET, and corresponds to an energy sensitivity (in joules per hertz) of about 41 Planck's over 2pi.     

不同水分条件下施用稻草对土壤有机酸和有效磷的影响

稻草在分解过程中产生有机酸。高浓度的有机酸一方面对水稻生长产生毒害作用，另一方面，有机酸可通过酸溶、螯合和竞争吸附等机制活化土壤难溶态磷，提高磷的生物有效性。所以，研究稻草分解过程中有机酸和有效磷的动态变化，对于评价稻草还田在水稻营养中的作用，指导秸秆管理具有十分重要的意义。