Personal Exposure in Displacement Ventilated Rooms

Personal exposure in a displacement ventilated room is examined. The stratified flow and the considerable concentration gradients necessitate an improvement of the widely used fully mixing compartmental approach. The exposure of a seated and a standing person in proportion to the stratification height is examined by means of full-scale measurements. A breathing thermal manikin is used to simulate a person. It is found that the flow in the boundary layer around a person is able to a great extent to entrain and transport air from below the breathing zone. In the case of non-passive, heated contaminant sources, this entrainment improves the indoor air quality. Measurements of exposure due to a passive contaminant source show a significant dependence on the flow field as well as on the contaminant source location. Poor system performance is found in the case of a passive contaminant released in the lower part of the room close to the occupant. A personal exposure model for displacement ventilated rooms is proposed. The model takes the influence of gradients and the human thermal boundary layer into account. Two new quantities describing the interaction between a person and the ventilation are defined.     

German Materials Science: A self-portrait

An influential and refreshingly frank report on the state of health of non-university materials research in Germany has recently been published. National Research Centers, Max Planck Institutes, and Fraunhofer Institutes are among the organizations covered. Recommendations are made on the basis of materials type, and on the performances of the individual institutes. The conclusions of this self-portrait, painted by representatives of the organizations themselves along with participants from the universities, industry, and state, will provide food for thought for both German materials scientists and those in other European countries concerned with the future development of this crucial economic sector.     

Ti3+ ion concentration and Ti:sapphire laser performance

The pulsed and CW laser performance of a range of titanium sapphire laser crystals is reported. Titanium ion concentration in the crystals ranged from 0.07 at.% to 0.25 and 0.41 at.% for some recently developed heavily doped crystals. Values of the crystal figure of merit lay between 30 and 220. Threshold, slope efficiency, tunability, and temporal response are assessed. Comparisons are made with the predictions of a simple rate equation model     

LD泵浦的声光调Q腔内倍频激光器

研制成用ＬＤ泵浦的声光调Ｑ的Ｎｄ：ＹＶＯ４－ＫＴＰ腔内倍频激光器，得到了ＴＥＭ００模、频率高达１００ｋＨｚ的稳定的５３２ｕｍ绿激光脉冲系列输出，阈值泵浦功率为２７ｍＷ；在连续５７０ｍＷ的泵浦功率下，绿激光脉冲的峰值功率达１１００Ｗ，脉宽为４．６ｕｓ；输出功率稳定，在±５℃的工作温度变化下，输出功率变化小于±２％。此种器件可望得到广泛的应用。     

Resistance measurements and vortex fluctuations in two-dimensional superconducting films

Recently theories of vortex fluctuations in two-dimensional superconducting films have been compared to the experimentally determined power law dependence of voltage on current and to the temperature-dependent resistance in small applied fields. Here an alternative interpretation of the power law and a practical difficulty of flux pinning for measurements in small fields are pointed out. To illustrate these points, experimental examples are presented for very homogeneous granular aluminum films.     

Bending and torsional fatigue of nylon 66 monofilaments

Using newly developed test equipment, the fatigue behavior of nylon 66 monofilaments was studied under two loading conditions, pure bending or simple torsion. For each mode, results are expressed in terms of the measured decay in stiffness with numbers of cycles over a range of maximum applied strain levels. Fatigue lifetimes are presented in S–N format where the log number of cycles of fatigue for a 40% decay in stiffness (N) is plotted as a function of applied strain (S). The failure mechanism for these fibers in each fatigue mode reflects the morphology of semicrystalline-oriented synthetic fibers. In torsion, many longitudinal cracks form around the perimeter of a fiber as the result of cleavage of the relatively weak interfibrillar bonds in nylon 66. In bending, cracks form within kink band boundaries and grow at an oblique angle to the fiber axis. © 1992 John Wiley & Sons, Inc.