Measurement of instantaneous temperature in shock-loaded nonmetallic solids

The feasibility of direct measurement of temperature in shock-loaded, nonmetallic solids within microseconds using a foil thermocouple of 200 Å thickness has been studied over a range of pressure from 0.5 to 4 GPa. The foil thermocouple and thermopile (200 Å thickness) were designed and used to measure the temperature rise in shock-compressed polymethylmethacrylate (PMMA). The method used to manufacture the gauges is spelled out in detail in this paper. The results agree with calculated PMMA temperatures when the shock pressure is below 2.2 GPa. Above this pressure the measured temperature rise is far higher than the calculated values. This result appears to be very similar to that obtained earlier by Bloomquist and Sheffield.

Simultaneous measurement of temperature, density and velocity in gas-flows by modulated photoluminescence

A novel possibility to determine the temperature, density and velocity simultaneously in gas flows by measuring the average value, amplitude of modulation and phase shift of the photoluminescence excited by a temporally or spatially modulated light source is investigated. Time-dependent equations taking the flow, diffusion, excitation and decay into account are solved analytically. Different experimental arrangements are proposed. Measurements of velocity with two components, and temporal and spatial resolutions in the measurements are investigated. Numerical examples are given for N z with biacetyl as the seed gas. Practical considerations for the measurements and the relation between this method and some existing methods of lifetime measurement are discussed.

Measurement of high-voltage pulses employing a quartz pockels cell

A high-voltage measuring system, employing a quartz Pockels cell, is described. The system is capable of a large voltage range, a fast response time (ns), a high SNR, an excellent accuracy, a good linearity, and high reliability. Furthermore, the Pockels cell can be isolated from ground potential. Equally important, the detection system can be isolated from sources of electrical noise present in, for example, fast discharges.

Optimal Correction for Guessing in Multiple-Choice Tests

Building on Item Response Theory we introduce students’ optimal behavior in multiple-choice tests. Our simulations indicate that the optimal penalty is relatively high, because although correction for guessing discriminates against risk-averse subjects, this effect is small compared with the measurement error that the penalty prevents. This result obtains when knowledge is binary or partial, under different normalizations of the score, when risk aversion is related to knowledge and when there is a pass-fail break point. We also find that the mean degree of difficulty should be close to the mean level of knowledge and that the variance of difficulty should be high.