The effect of strontium oxide in glass–ionomer cements

The reaction of strontium oxide powder with poly(acrylic acid) has been studied both alone and within glass–ionomer cements. Reaction was found to be slow and the strontium-carboxylate structure was found to be partially covalent in character, as determined by Fourier transform infrared spectroscopy (FTIR). These are similar to the structures formed by calcium in glass–ionomer cements, but are different from typical monomeric strontium carboxylates, which tend to be purely ionic. Strontium oxide powder introduced in two types of glass–ionomer cements, slowed down the setting reaction at both 21 °C and 37 °C, but at low levels (5 wt %), increased the compressive strength in both cement formulations studied. However, at higher levels, it was found to decrease the compressive strength. This study confirms the view that strontium is a cement-forming ion; but concludes that, except at very low levels, strontium oxide powder does not improve the properties of glass–ionomer cements.     

Optical model methods of predicting nuclide production cross sections from heavy ion fragmentation

Quantum mechanical optical potential methods for calculating inclusive isotope and element production cross sections from the fragmenting of heavy nuclei by intermediate- and high-energy protons and heavy ions are presented based upon a modified abrasion-ablation-FSI (frictional spectator interaction) collision model. The abrasion stage is treated as a quantum mechanical knockout process that leaves the residual prefragment in an excited state. Prefragment excitation energies are estimated using a combined liquid drop and FSI method. In ablation the prefragment deexcites by particle and photon emission to produce the final fragment. Contributions from electromagnetic dissociation to single nucleon removal cross sections are incorporated using a Weiszacker-Williams theory that includes electric dipole and electric quadrupole interactions. Estimates of elemental and isotopic production cross sections are in good agreement with published cross section measurements for a variety of projectile-target-beam energy combinations.     

The design of a simulated forcible entry test for fire fighters

This study investigated the physiological responses and performances for 20 fire fighters when completing simulated forcible entry tests. The purpose was to establish the validity of using a tire striking test and to examine the effects of varying the test parameters. The tests consisted of striking a reinforced structure and a weighted truck tire on a plywood covered table with either a 4.54 or a 5.60 kg sledge hammer. The results indicate that the simulated forcible entry tests are short in duration (range = 8.0-17.6 s), but are also physically demanding in terms of cardiovascular response (range = 86.5-97.2 for a percentage of heart rate reserve). The differences in striking a reinforced structure versus hitting a tire were insignificant according to most of the measures taken. The parameters for the simulated forcible entry test that were determined to be most appropriate were to move the tire 30 cm and use the 4.54 kg sledge hammer.     

Traffic fatalities, Peltzman's model, and directed graphs

We show how statistical methods based on directed graphs may be useful in modeling traffic fatalities by comparing models specified using directed graphs to a model originally developed by Peltzman. The comparison uses Peltzman's original data, as well as up-dated data (and coefficients) through 1993. Out-of-sample forecasts of traffic fatalities from Peltzman's model are compared with those from a model constructed using directed graphs over data for the more recent period. The directed graphs model outperforms Peltzman's model in root mean squared forecast error.     

Luminol/H2O2 chemiluminescence detector for the analysis of nitric oxide in exhaled breath

A new instrument for the detection of nitric oxide has been developed and applied to the analysis of exhaled breath. The instrument is based on conversion of NO to NO2, using the oxidant chromium trioxide, followed by detection of chemiluminescence in the reaction of NO2 with an alkaline luminol/H2O2 solution. The presence of H2O2 is found to enhance the sensitivity of NO2 detection by a factor of approximately 20. A bundle of porous polypropylene hollow fiber membranes is used to bring the gaseous sample into contact with the luminol solution. Chemiluminescence occurring within the translucent hollow fibers is detected using a miniature photomultiplier tube. The limit of detection for NO is 0.3 ppbv for S/N = 3, and the 1/e response time is 2 s. A large interference resulting from the 4-6% CO2 concentration in exhaled breath is removed by use of an ascarite scrubber in the air stream. Breath measurements of NO were made using a sampling technique developed by Sensor Medics (Yorba Linda, CA) with simultaneous detection using the luminol/H2O2 and NO + O3 chemiluminescence techniques. The two instruments were found to be in excellent agreement. Nitric oxide levels were in the range 6.0-22.0 ppbv for healthy individuals and 40.0-80.0 ppbv for individuals with asthma or a respiratory infection. This new detector offers the advantages of compact size, low cost, and a simple configuration compared to NO detectors based on NO + O3 chemiluminescence.     

Development of an infrared hollow waveguide as a sensing device for detection of organic compounds in aqueous solutions

In this paper, a new detection method based on an infrared hollow waveguide is developed to detect semivolatile to nonvolatile organic compounds in aqueous solutions. The hollow waveguide is produced by chemical deposition of silver on the inner surface of a polyethylene tube. The surface of the silver layer is further coated with a hydrophobic film to attract organic compounds in aqueous solution. Samples were pumped through this hollow waveguide sampler and organic compounds were attracted onto the hydrophobic film. After removal of the residual water molecules in the hollow waveguide sampler, organic compounds can be sensed by conventional Fourier transform infrared (FT-IR) spectrometry. Theoretical aspects of this type of sampler are also presented. The derived analytical equations for this type of sampler were consistent with experimental data. Under the condition of constant hydrophobic film volume, high linearity (R(2) equal to 0.9993) between the concentration of analyte and the detected signal was obtained for concentrations in the range from 2.5 ppm to 50 ppb. By co-adding 100 scans with 4 cm(-)(1) resolution, the typical detection limit in this type of sensing method can be lower than 10 ppb. Several factors such as sampling flow rate, sampling time, and hydrophobic film volume were also investigated in this work.     

Straightness measurements by use of a reflection confocal optical system

Straightness measurement is a very important technique in the field of mechanical engineering. A particular application for straightness measurement is high-accuracy machining on a diamond-turning lathe. We propose a novel, to our knowledge, optical method for measuring the straightness of motion, and its mathematical analysis is outlined. The technique is based on measurement of the lateral displacement of point images by use of reflection confocal optical systems. The advantages of this method are that (i) the lateral displacements in the direction of the two axes perpendicular to the optical axis can be measured, (ii) the rotation angles around all three axes can be measured, and (iii) reflection optical systems are more compact in length than are transmission optical systems.     

Water at the ice point: a useful quasi-blackbody infrared calibration source

Water at the ice point makes a good calibration source in the 4- to 13-mum spectral region because of its high emissivity, small skin depth, and the ease with which an ice-point bath may be prepared and used. In a simple ice bath the emissivity is slightly less than unity, and we have calculated corrections that allow one to predict the apparent radiation temperature of the equivalent blackbody. We propose an alternate configuration that uses an auxiliary mirror. This configuration should provide an emissivity extremely close to unity.     

Measurement of the linewidth of a continuous-wave laser with a cavity-length modulation technique

We introduce a Fabry-Perot cavity-length modulation technique for measuring the linewidth of a continuous wave (cw) laser. We calculate the peak intensity of a cw laser transmitted through a Fabry-Perot cavity as a function of mirror speed. By fitting the experimental data to the results of the calculation, we determine the linewidth of a frequency-stabilized cw laser. The linewidth of a cw ring dye laser measured in the 570-590-nm wavelength range is approximately 170 +/- 20 kHz. We also demonstrate the use of this technique to measure the reflectivity of a high-reflectance mirror.     

地震荷载作用下钢筋混凝土框架柱斜截面抗剪强度计算方法的探讨

本文收集了近年来日本、美国和我国所进行的钢筋混凝土框架柱抗震试验中、产生剪切破坏的35个短柱试验资料。根据这些资料对目前国内外提出的6个抗剪强度计算公式进行了验证,并进一步分析了构件极限抗剪强度与主要参数的关系。最后,经数理统计分析提出了一个较为符合实际情况的经验公式。