Flock Together

After stumbling upon a book of photographs depicting extinct animals, B.J. Hollars became fascinated by the creatures that are no longer with us; specifically, extinct North American birds.How, he wondered, could we preserve so beautifully on film what we’ve failed to preserve in life?And so begins his yearlong journey to find out, one that leads him from bogs to art museums, from archives to Christmas Counts, until he at last comes as close to extinct birds as he ever will during a behind-the-scenes visit at the Chicago Field Museum.Heartbroken by the birds we’ve lost, Hollars takes refuge in those that remain. Armed with binoculars, a field guide, and knowledgeable friends, he begins his transition from budding birder to environmentally conscious citizen, a first step on a longer journey toward understanding the true tragedy of a bird’s song silenced forever.Told with charm and wit, Flock Together is a remarkable memoir that shows how “knowing” the natural world—even just a small part—illuminates what it means to be a global citizen and how only by embracing our ecological responsibilities do we ever become fully human. A moving elegy to birds we’ve lost, Hollars’s exploration of what we can learn from extinct species will resonate in the minds of readers long beyond the final page

The temperature dependence of the response of 103a-0 and Tri-X at 4400 A

Temperature effects on 103a-0 and Tri-X photographic emulsion sensitivities at 4400

Experiential Learning Based Discussion vs. Lecture Based Discussion: How to Estimate the Unemployment Rate

This pedagogical method to estimate the unemployment rate is appropriate for an undergraduate course in macroeconomics. Class instructors can use the experiment to make many macroeconomic principles readily apparent to the unskilled reader. This experiment examines the dynamics of calculating the unemployment rate by means of an assessment instrument. Students can learn that the unemployment rate is calculated using estimates of the size of the labor force, which includes individuals who are both employed and unemployed. In addition, they discover that their estimated unemployment rate agrees with the estimates made by leading economic indices. Thus, by participating in the experiment, students better understand how to calculate the unemployment rate and how to understand published unemployment estimates.economic experiment, unemployment rate

Temperature Effects on Photographic Sensitivity

Temperature effects on photographic sensitivit

Preliminary results on noncollocated torque control of space robot actuators

In the Space Station era, more operations will be performed robotically in space in the areas of servicing, assembly, and experiment tending among others. These robots may have various sets of requirements for accuracy, speed, and force generation, but there will be design constraints such as size, mass, and power dissipation limits. For actuation, a leading motor candidate is a dc brushless type, and there are numerous potential drive trains each with its own advantages and disadvantages. This experiment uses a harmonic drive and addresses some inherent limitations, namely its backdriveability and low frequency structural resonances. These effects are controlled and diminished by instrumenting the actuator system with a torque transducer on the output shaft. This noncollocated loop is closed to ensure that the commanded torque is accurately delivered to the manipulator link. The actuator system is modelled and its essential parameters identified. The nonlinear model for simulations will include inertias, gearing, stiction, flexibility, and the effects of output load variations. A linear model is extracted and used for designing the noncollocated torque and position feedback loops. These loops are simulated with the structural frequency encountered in the testbed system. Simulation results are given for various commands in position. The use of torque feedback is demonstrated to yield superior performance in settling time and positioning accuracy. An experimental setup being finished consists of a bench mounted motor and harmonic drive actuator system. A torque transducer and two position encoders, each with sufficient resolution and bandwidth, will provide sensory information. Parameters of the physical system are being identified and matched to analytical predictions. Initial feedback control laws will be incorporated in the bench test equipment and various experiments run to validate the designs. The status of these experiments is given

Evaluation of thermal evaporation conditions used in coating aluminum on near-field fiber-optic probes

This is the published version, also available here: http://dx.doi.org/10.1063/1.1148836.The effects that the thermal evaporation conditions have on the roughness of aluminum-coated near-field fiber-optic probes were investigated using the high-resolution capabilities of atomic force microscopy. The coating conditions studied include the effects of background gas composition, base vacuum pressure, and aluminum evaporation rate. The effects of aging on the aluminum-coated tips were also evaluated. The results from topography measurements of the resulting aluminumfilm indicated that the most dramatic improvements in the tip coatings can be achieved using high aluminum evaporation rates at base vacuum pressures below 10−5 Torr. These results agree with other studies on thin aluminumfilms and reflect a decrease in oxide formation. For demanding applications of near-field microscopy requiring maximal resolution, the results presented here indicate that it may also be necessary to reduce oxygen and/or water from the vacuum chamber prior to coating

Probing single molecule orientations in model lipid membranes with near-field scanning optical microscopy

This is the published version, also available here: http://dx.doi.org/10.1063/1.481367.Single molecule near-field fluorescence measurements are utilized to characterize the molecular level structure in Langmuir–Blodgett monolayers of L-α-dipalmitoylphosphatidylcholine (DPPC).Monolayers incorporating 3×10−4 mol % of the fluorescent lipid analog N-(6-tetramethylrhodaminethiocarbamoyl)-1,2-dihexadecanoyl-sn- glycero-3-phosphoethanolamine, triethylammonium salt (TRITC–DHPE) are transferred onto a freshly cleaved mica surface at low (π=8 mN/m) and high (π=30 mN/m)surfacepressures. The near-field fluorescence images exhibit shapes in the single molecule images that are indicative of the lipid analog probe orientation within the films. Modeling the fluorescence patterns yields the single molecule tilt angle distribution in the monolayers which indicates that the majority of the molecules are aligned with their absorption dipole moment pointed approximately normal to the membrane plane. Histograms of the data indicate that the average orientation of the absorption dipole moment is 2.2° (σ=4.8°) in monolayers transferred at π=8 mN/m and 2.4° (σ=5.0°) for monolayers transferred at π=30 mN/m. There is no statistical difference in the mean tilt angle or distribution for the two monolayer conditions studied. The insensitivity of tilt angle to filmsurfacepressure may arise from small chromophore doped domains of trapped liquid-expanded lipid phase remaining at high surfacepressure. There is no evidence in the near-field fluorescence images for probe molecules oriented with their dipole moment aligned parallel with the membrane plane. We do, however, find a small but significant population of probe molecules (∼13%) with tilt angles greater than 16°. Comparison of the simultaneously collected near-field fluorescence and force images suggests that these large angle orientations are not the result of significant defects in the films. Instead, this small population may represent a secondary insertion geometry for the probe molecule into the lipidmonolayer

Counting constituents in molecular complexes by fluorescence photon antibunching

Modern single molecule fluorescence microscopy offers new, highly quantitative ways of studying the systems biology of cells while keeping the cells healthy and alive in their natural environment. In this context, a quantum optical technique, photon antibunching, has found a small niche in the continuously growing applications of single molecule techniques to small molecular complexes. Here, we review some of the most recent applications of photon antibunching in biophotonics, and we provide a guide for how to conduct photon antibunching experiments at the single molecule level by applying techniques borrowed from time-correlated single photon counting. We provide a number of new examples for applications of photon antibunching to the study of multichromophoric molecules and small molecular complexes