Resonant difference-frequency atomic force ultrasonic microscope

A scanning probe microscope and methodology called resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), employs an ultrasonic wave launched from the bottom of a sample while the cantilever of an atomic force microscope, driven at a frequency differing from the ultrasonic frequency by one of the contact resonance frequencies of the cantilever, engages the sample top surface. The nonlinear mixing of the oscillating cantilever and the ultrasonic wave in the region defined by the cantilever tip-sample surface interaction force generates difference-frequency oscillations at the cantilever contact resonance. The resonance-enhanced difference-frequency signals are used to create images of nanoscale near-surface and subsurface features

Nonlinear Dynamics of Cantilever Tip-Sample Surface Interactions in Atomic Force Microscopy

The interaction of the cantilever tip of an atomic force microscope (AFM) with the sample surface is obtained by treating the cantilever and sample as independent systems coupled by a nonlinear force acting between the cantilever tip and a volume element of the sample surface. The volume element is subjected to a restoring force from the remainder of the sample that provides dynamical equilibrium for the combined systems. The model accounts for the positions on the cantilever of the cantilever tip, laser probe, and excitation force (if any) via a basis set of set of orthogonal functions that may be generalized to account for arbitrary cantilever shapes. The basis set is extended to include nonlinear cantilever modes. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a matrix iteration procedure. The effects of oscillatory excitation forces applied either to the cantilever or to the sample surface (or to both) are obtained from the solution set and applied to the to the assessment of phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) modalities. The influence of bistable cantilever modes of on AFM signal generation is discussed. The effects on the cantilever-sample surface dynamics of subsurface features embedded in the sample that are perturbed by surface-generated oscillatory excitation forces and carried to the cantilever via wave propagation are accounted by the Bolef-Miller propagating wave model. Expressions pertaining to signal generation and image contrast in A-AFM are obtained and applied to amplitude modulation (intermittent contact) atomic force microscopy and resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM). The influence of phase accumulation in A-AFM on image contrast is discussed, as is the effect of hard contact and maximum nonlinearity regimes of A-AFM operation

Factors Affecting the Spread of a Bioterrorist Agent Throughout a Building

Bioterrorism has become a greater concern for Americans since the 2001 anthrax letters. Recent studies have explored the possibilities of biological attacks, and most deal with possible large-scale attacks. However, there is reason to believe that small-scale attacks are more likely. Even though there have been investigations of the postal delivery system and the spread of bioagents through mail, few if any studies have looked at attack on a single building and the resultant spread form room to room. One particular method of attacking a building would be a single-even release of an aerosol bioagent in the building. This paper describes the development of a method for studying the spread of an aerosol throughout a building in order to determine what factors most affect the time between release and the lethal exposure of an occupant in various locations. A multi-zone airflow model, CONTAM, was used to simulate and compare the effects of the air handling system operation door position, building level, predominant wind direction and other factors. It was found that the air handling system, building floor level, and door position changed the exposure ties ranged from 5 seconds to nearly 15 minutes, and the air handling system was found to have the greatest effect on a contaminant’s spread through a building

Technical Note: Review of methods for linear least-squares fitting of data and application to atmospheric chemistry problems

International audienceThe representation of data, whether geophysical observations, numerical model output or laboratory results, by a best fit straight line is a routine practice in the geosciences and other fields. While the literature is full of detailed analyses of procedures for fitting straight lines to values with uncertainties, a surprising number of scientists blindly use the standard least squares method, such as found on calculators and in spreadsheet programs, that assumes no uncertainties in the x values. Here, the available procedures for estimating the best fit straight line to data, including those applicable to situations for uncertainties present in both the x and y variables, are reviewed. Representative methods that are presented in the literature for bivariate weighted fits are compared using several sample data sets, and guidance is presented as to when the somewhat more involved iterative methods are required, or when the standard least-squares procedure would be expected to be satisfactory. A spreadsheet-based template is made available that employs one method for bivariate fitting

Analytical Model of the Nonlinear Dynamics of Cantilever Tip-Sample Surface Interactions for Various Acoustic-Atomic Force Microscopies

A comprehensive analytical model of the interaction of the cantilever tip of the atomic force microscope (AFM) with the sample surface is developed that accounts for the nonlinearity of the tip-surface interaction force. The interaction is modeled as a nonlinear spring coupled at opposite ends to linear springs representing cantilever and sample surface oscillators. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a standard iteration procedure. Solutions are obtained for the phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) techniques including force modulation microscopy, atomic force acoustic microscopy, ultrasonic force microscopy, heterodyne force microscopy, resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), and the commonly used intermittent contact mode (TappingMode) generally available on AFMs. The solutions are used to obtain a quantitative measure of image contrast resulting from variations in the Young modulus of the sample for the amplitude and phase images generated by the A-AFM techniques. Application of the model to RDF-AFUM and intermittent soft contact phase images of LaRC-cp2 polyimide polymer is discussed. The model predicts variations in the Young modulus of the material of 24 percent from the RDF-AFUM image and 18 percent from the intermittent soft contact image. Both predictions are in good agreement with the literature value of 21 percent obtained from independent, macroscopic measurements of sheet polymer material

No Angel: An Analysis of Media Coverage of Nadja Benaissa in the U.K., U.S. and Germany

The media’s portrayal of HIV has taken a number of different forms since the disease was first discovered over three decades ago. HIV has been portrayed as an epidemic and a disease affecting homosexuals and immigrants. Its transmission has also been portrayed as a criminal offense. In August 2010, the German singer Nadja Benaissa was arrested for passing on HIV to a former partner and exposing two other men. Media constructions of this story draw upon HIV stereotypes because of her drug-using past, her immigrant status and her criminal actions. This media study points to a new discourse centered on the shared responsibility of safe sex. While Benaissa was mostly blamed for transmission, the media at times suggested that safe sex concerning HIV was not entirely dependent upon HIV-positive individuals

Palamedes

This thesis offers a syncretic, synoptic account of Palamedes from the Trojan War. It delineates three interpretive modes: (1) that Palamedes was present all along; (2) that later poets inserted him into the Trojan narrative, either as an archetypal intellectual figure, or as Odysseus’s double; (3) that Palamedes was present only as Odysseus’s imaginary Doppelgänger. The thesis accounts for Palamedes’s scarce attention in classical texts by way of Lacanian and—via Otto Rank—Freudian psychoanalytic theory, as well as by Slavoj Žižek’s adoption of the “vanishing mediator.” After tracing a potential textual genealogy from Palamedes to Malory’s Palomydes, the thesis concludes with a reading of Palamedes’s implied presence in Inferno 26

The Anglican Church of Rwanda: Domestic Agendas and International Linkages

The article analyses the relationship between the Anglican Church of Rwanda and evangelical Episcopalians in the United States. In 2000, the archbishop of Rwanda, Emmanuel Kolini, in a move that gained great support for Rwanda\u27s post-genocide recovery, ordained several bishops to preside over congregations of orthodox, evangelical Americans who had severed their relationship with the Episcopalian Church of the United States over issues such as the blessing of same- sex marriages and the ordination of openly gay clergy. The result was the creation of the Anglican Mission in the Americas, a missionary province in the United States that acknowledges Kolini as its archbishop. Such actions have made Rwanda the current cause celebre not only of AMIA but the wider evangelical community. While the relationship offers great support for Rwanda\u27s recovery, the Anglican Church has presented to American evangelicals a misleading narrative of Rwanda\u27s past and present political situation

United States Air Force Security Forces Merger and Career Satisfaction Relating to Retention

The relationship between the Air Force merger of Law Enforcement personnel, Security Police personnel, and Combat Arms Training and Maintenance personnel into the Air Force Security Forces Career Field; and job retention was investigated among 209 Air Force Security Forces Enlisted Personnel at five different Air Force bases (Columbus Air Force Base (AFB), MS, Keesler AFB, MS, Eglin AFB, FL, Hurlburt Field Air Base, FL, and Moody AFB, GA). Participants completed a 91-item survey designed to measure merger satisfaction, career and job satisfaction, life satisfaction, job involvement, job stress, turnover intentions and demographic data. The results showed only four items significantly related to job retention. In a simple regression analysis, satisfaction with the merger was significantly associated with retention but was not the best predictor. Career satisfaction was also a significant predictor of job retention and a stronger one. Merger satisfaction was also significantly related to career satisfaction. In a simple multiple regression analysis, however, merger satisfaction was not significantly related to retention. The results in this population of Air Force Personnel indicated that retention was significantly related to whether the major satisfaction in one’s life came from the job, the level of satisfaction with the career field, and the amount of time off from work