Temperature dependent refractive index of silicon and germanium

Silicon and germanium are perhaps the two most well-understood semiconductor materials in the context of solid state device technologies and more recently micromachining and nanotechnology. Meanwhile, these two materials are also important in the field of infrared lens design. Optical instruments designed for the wavelength range where these two materials are transmissive achieve best performance when cooled to cryogenic temperatures to enhance signal from the scene over instrument background radiation. In order to enable high quality lens designs using silicon and germanium at cryogenic temperatures, we have measured the absolute refractive index of multiple prisms of these two materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA Goddard Space Flight Center, as a function of both wavelength and temperature. For silicon, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 20 to 300 K at wavelengths from 1.1 to 5.6 microns, while for germanium, we cover temperatures ranging from 20 to 300 K and wavelengths from 1.9 to 5.5 microns. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. Citing the wide variety of values for the refractive indices of these two materials found in the literature, we reiterate the importance of measuring the refractive index of a sample from the same batch of raw material from which final optical components are cut when absolute accuracy greater than +/-5 x 10^-3 is desired.Comment: 10 pages, 8 figures, to be published in the Proc. of SPIE 6273 (Orlando

Mass transfer enhancement produced by laser induced cavitation

A microelectrode is used to measure the mass transfer perturbation and characteristics during the growth and subsequent collapse of a single bubble (which, following its initial expansion, achieved a maximum radius, Rm, of not, vert, similar500–1000 ?m). This mass transfer enhancement was associated with the forced convection, driven by bubble motion, as the result of a single cavitation event generated by a laser pulse beneath a 25 ?m diameter Au microelectrode. Evidence for bubble growth and rebound is gained from the electrochemical and acoustic measurements. This is supported with high-speed video footage of the events generated. A threshold for the formation of large cavitation bubbles in electrolyte solutions is suggested

Digging Digitally: Creating a More Dynamic Archaeological Field Journal Archive

As the daily record of observations, the field journal always has been central to the archaeological process. Yet in recent decades, these important texts have been ignored in the rush to create digital artifact archives. This project, which builds upon software designed to manage the field books at the Ohio State University Excavations at Isthmia, will correct this oversight by enabling a community of scholars to use scans of the hand written texts to link electronically the disparate forms of evidence that make up the archaeological record. Also, this project will determine the best equipment and practices to allow archaeologists to utilize a digital notebook archive in their research. The result will be an inexpensive, multi-platform, and open source system that can be adapted by other scholars to simplify and enhance research in any field of humanities research that depends upon hand written documents as a primary source of evidence

Temperature-dependent Refractive Index of CaF2 and Infrasil 301

In order to enable high quality lens designs using calcium fluoride (CaF2) and Heraeus Infrasil 301 (Infrasil) for cryogenic operating temperatures, we have measured the absolute refractive index of these two materials as a function of both wavelength and temperature using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center. For CaF2, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 25 to 300 K at wavelengths from 0.4 to 5.6 pm, while for Infrasil, we cover temperatures ranging from 35 to 300 K and wavelengths from 0.4 to 3.6 pm. For CaF2, we compare our index measurements to measurements of other investigators. For Infrasil, we compare our measurements to the mate~al manufacturer's data at room temperature and to cryogenic measurements for fused silica from previous investigations including one of our own. Finally, we provide temperature-dependent Sellmeier coefficients based on our measured data to allow accurate interpolation of index to other wavelengths and temperatures

Cryogenic Temperature-dependent Refractive Index Measurements of N-BK7, BaLKN3, and SF15 for NOTES PDI

In order to enable high quality lens designs using N-BK7, BaLKN3, and SF15 at cryogenic temperatures, we have measured the absolute refractive index of prisms of these three materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For N-BK7, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 50 to 300 K at wavelengths from 0.45 to 2.7 micrometers; for BaLKN3 we cover temperatures ranging from 40 to 300 K and wavelengths from 0.4 to 2.6 micrometers; for SF15 we cover temperatures ranging from 50 to 300 K and wavelengths from 0.45 to 2.6 micrometers. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. While we generally find good agreement (plus or minus 2 x 10(exp -4) for N-BK7, less than 1 x 10(exp -4) for the other materials) at room temperature between our measured values and those provided by the vendor, there is some variation between the datasheets provided with the prisms we measured and the catalog values published by the vendor. This underlines the importance of measuring the absolute refractive index of the material when precise knowledge of the refractive index is required

An Electrochemical Cell for the Efficient Turn Around of Wafer Working Electrodes

We present a new design for an electrochemical cell for use with wafer working electrodes. The key feature of the design is the use of half turn thumb screws to form a liquid-tight seal between an o-ring and the sample surface. The assembly or disassembly of the cell requires a half turn of each thumb screw, which facilitates the quick turn around of wafer samples. The electrochemical performance of the cell is demonstrated by cyclic voltammetry and double step chronoamperometry measurements of the ferricyanide/ferrocyanide couple

Taking the focus away from the self: low individualism mediates the effect of oxytocin on creativity

Recently, it has been shown that the hormone oxytocin can enable creative cognition. The aim of this investigation was to examine the psychological mechanism via which oxytocin influences creativity. Two opposing explanatory approaches suggested by previous research were investigated: It was predicted that the effect of oxytocin on creativity would be determined by low versus high individualism, especially in people with low levels of anxiety. Participants filled out an anxiety questionnaire and intranasally administered oxytocin or a placebo. After a 40-min waiting period, they performed a creativity task and indicated their level of individualism. Participants with low levels of anxiety showed heightened creative potential under oxytocin, and this relationship was mediated by low individualism. The results could not be explained by changes in the participants’ affective state. The findings underscore the moderating role of dispositional factors and reveal an important factor to understand the role of oxytocin in human behavior

Elliptic curves, modular forms, and sums of Hurwitz class numbers

Let H(N) denote the Hurwitz class number. It is known that if $p$ is a prime, then {equation*} \sum_{|r|<2\sqrt p}H(4p-r^2) = 2p. {equation*} In this paper, we investigate the behavior of this sum with the additional condition $r\equiv c\pmod m$. Three different methods will be explored for determining the values of such sums. First, we will count isomorphism classes of elliptic curves over finite fields. Second, we will express the sums as coefficients of modular forms. Third, we will manipulate the Eichler-Selberg trace for ula for Hecke operators to obtain Hurwitz class number relations. The cases $m=2,3$ and 4 are treated in full. Partial results, as well as several conjectures, are given for $m=5$ and 7.Comment: Preprint of an old pape

NCLB technology and a rural school: A case study

The requirements of the No Child Left Behind Act of 2001 (NCLB) have presented special challenges and opportunities for rural schools (Reeves, 2003). Researchers have suggested that one way rural schools may be able to overcome these challenges is through an increase in the level of technology integration in their school (Collins & Dewees, 2001). This case study reports on one school’s attempt to use grant resources funded through NCLB to integrate specific instructional technologies to facilitate increased student achievement. Through interviews and observations, the roles, attitudes, and difficulties of teachers and administrators in implementing a technology initiative in a rural middle school were observed, examined and discussed. Emerging themes included issues related to teacher ownership of the technology, teacher feelings of power and participation, differing goals of teachers and administrators, technical difficulties, school wide support, and changes in school culture

NCLB Technology and a Rural School: A Case Study

The requirements of the No Child Left Behind Act of 2001 (NCLB) have presented special challenges and opportunities for rural schools (Reeves, 2003). Researchers have suggested that one way rural schools may be able to overcome these challenges is through an increase in the level of technology integration in their school (Collins & Dewees, 2001). This case study reports on one school’s attempt to use grant resources funded through NCLB to integrate specific instructional technologies to facilitate increased student achievement. Through interviews and observations, the roles, attitudes, and difficulties of teachers and administrators in implementing a technology initiative in a rural middle school were observed, examined and discussed. Emerging themes included issues related to teacher ownership of the technology, teacher feelings of power and participation, differing goals of teachers and administrators, technical difficulties, school wide support, and changes in school culture