Factors Contributing to the Catastrophe in Mexico City During the Earthquake of September 19, 1985

The extensive damage to high‐rise buildings in Mexico City during the September 19, 1985 earthquake is primarily due to the intensity of the ground shaking exceeding what was previously considered credible for the city by Mexican engineers. There were two major factors contributing to the catastrophe, resonance in the sediments of an ancient lake that once existed in the Valley of Mexico, and the long duration of shaking compared with other coastal earthquakes in the last 50 years. Both of these factors would be operative again if the Guerrero seismic gap ruptured in a single earthquake

Ultrasensitive detections in atomic and molecular physics: demonstration in molecular overtone spectroscopy

We consider several highly sensitive techniques commonly used in detection of atomic and molecular absorptions. Their basic operating principles and corresponding performances are summarized and compared. We then present our latest results on the ultrasensitive detection of molecular overtone transitions to illustrate the principle and application of the cavity-enhanced frequency-modulation (FM) spectroscopy. An external cavity is used to enhance the molecular response to the light field, and an FM technique is applied for shot-noise-limited signal recovery. A perfect match between the FM sideband frequency and the cavity free spectral range makes the detection process insensitive to the laser-frequency noise relative to the cavity, and, at the same time, overcomes the cavity bandwidth limit. Working with a 1.064-µm Nd:YAG laser, we obtained sub-Doppler overtone resonances of C2HD, C2H2, and CO2 molecules. A detection sensitivity of 5 x 10^-13 of integrated absorption (1 x 10^-14/cm) over 1-s averaging time has been achieved

Nobel Lecture: Defining and Measuring Optical Frequencies

Four long-running currents in laser technology met and merged in 1999–2000. Two of these were the quest toward a stable repetitive sequence of ever-shorter optical pulses and, on the other hand, the quest for the most time-stable, unvarying optical frequency possible. The marriage of UltraFast and UltraStable lasers was brokered mainly by two international teams and became exciting when a special “designer” microstructure optical fiber was shown to be nonlinear enough to produce “white light” from the femtosecond laser pulses, such that the output spectrum embraced a full optical octave. Then, for the first time, one could realize an optical frequency interval equal to the comb’s lowest frequency, and count out this interval as a multiple of the repetition rate of the femtosecond pulse laser. This “gear-box” connection between the radio frequency standard and any/all optical frequency standards came just as Sensitivity-Enhancing ideas were maturing. The four-way Union empowered an explosion of accurate frequency measurement results in the standards field and prepares the way for refined tests of some of our cherished physical principles, such as the time-stability of some of the basic numbers in physics (e.g., the “fine-structure” constant, the speed of light, certain atomic mass ratios etc.), and the equivalence of time-keeping by clocks based on different physics. The stable laser technology also allows time-synchronization between two independent femtosecond lasers so exact they can be made to appear as if the source were a single laser. By improving pump/probe experiments, one important application will be in bond-specific spatial scanning of biological samples. This next decade in optical physics should be a blast

Identity in multicultural societies: who do we think we are?

This paper examines identity issues in multicultural Australia. In its extreme, negative form, assumptions that certain characteristics apply to all members of an ethnic group can be attributed to racism. However, the belief that individuals who share the same ethnic background have similar needs, interests and perceptions is also reflected in business, government policy and academic research. Often, ethnic groupings used for research and policy formulation are very broad and fail to take into account within-group differences. The criteria used to assess an individuals membership of an ethnic group can be problematic. Criteria based purely on objective measures such as country of birth or ethnic ancestry do not take into account acculturation processes or the degree to which individuals consider themselves to be \u27ethnic \u27. These objective measures are complicated further as individuals may have ethnic roots from multiple countries depending on their family composition over several generations. This theory-focused paper proposes that ethnic identity should be viewed as a subjective phenomenon where individuals are likely to align themselves with the ethnic background to which they most identify. This has implications for research and policy making in multicultural societies.<br /

Arts marketing challenges in multicultural societies

With an increasingly diverse, multicultural society in many countries, it is timely to look more closely at the current literature on arts marketing, ethnic identity and segmentation issues. The growth of diverse, multicultural societies in many countries warrants a closer examination of arts marketing and the use of ethnicity as a basis for segmentation, as these issues have implications for attracting and retaining arts audiences and other consumers of arts related activities. Researchers in the arts industry have stressed the importance of understanding the fundamentals of audience development and the ability to focus on satisfying the needs and wants of their audiences. The focus on marketing activities comes at a time when there is greater pressure on arts organisations to move beyond their traditional role as subsidized non-profit organisations in order to become more self-supporting. Internationally, audience development in the arts industry has focused on segmentation dimensions such as youth, mature aged individuals, geographic location (rural), individuals with disabilities, low income earners, and individuals with culturally diverse backgrounds. Most of these potential segments are under represented in the population of arts consumers in Australia, the United Kingdom, Singapore, and North America. Of those dimensions, segmentation of arts markets by cultural differences such as ethnic identity appears to be a somewhat under researched area. Hofstede\u27s (1980) model of national cultural differences continues to be widely used as a basis for strategic and marketing decisions in international business. However, the cultural characteristics attributed to individuals in their country of birth are likely to change through immigration to another country. In this situation, the ability to predict the consumption behaviour of various ethnic groups is complicated by acculturation processes in which arrivals attempt to adapt to their new environment. Over time, this process has resulted in the emergence of bicultural individuals who are able to switch, at will, between their ethnic identity and an identity aligned with their host country, or a combination of both at any time. Ethnic identity and affiliation with ethnic groups can also change over time, suggesting challenges for arts marketing approaches, and the application of market segmentation theory in particular.<br /

Cavity Ringdown Heterodyne Spectroscopy: High Sensitivity with Microwatt Light Power

We present an ac heterodyne technique in cavity ringdown spectroscopy that permits 1×10−10 absorption sensitivity with microwatt-level light power. Two cavity modes, one probing the empty cavity and the other probing intracavity absorption, are excited simultaneously but with their intensities temporally out of phase, with one mode decaying and the other rising. Heterodyne detection between the two modes reveals the dynamic time constants associated with the empty cavity and the additional intracavity gas absorption. The method offers a quick comparison between the on- and off-resonance information, a prerequisite to reaching the fundamental shot-noise limit. This simple and yet important improvement of cavity ringdown spectroscopy should lead to the enhanced performance of a wide range of applications

Analysis/Reduction of Residual Amplitude Modulation in Phase/Frequency Modulation by an EOM

Summary form only given. Frequency modulation (FM) is a powerful tool for sensitive spectroscopy and laser frequency stabilization. The high potential modulation frequency and FM format makes it easier to achieve shot-noise limit detection. Usually the laser frequency is modulated by an external frequency modulator such as an electrooptic modulator (EOM). However to obtain a pure FM signal is not easy because of residual amplitude modulation (RAM) arising by several effects: 1) etalon effects by light scattering within and at surfaces of the EOM crystal; 2) piezo-electric response of the EOM crystal, leading to beam steering and/or spatial position dither; 3) spatial inhomogeneity of modulation field in EOM crystal, leading to angular deviation of the beam and/or impure FM when part of the beam is selected; 4) and temperature dependence of the RAM associated with changes of the EOM crystal\u27s optical path and birefringence. RAM can easily be in the percent domain, and degrades the sensitivity in the FM spectroscopy, and also gives undesirable frequency offsets from the frequency reference. To solve the RAM problem, we measured and analyzed the RAM experimentally. A new active RAM suppression system is suggested