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

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.&nbsp

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

A natural bijection for contiguous pattern avoidance in words

Two words $p$ and $q$ are avoided by the same number of length-$n$ words, for all $n$, precisely when $p$ and $q$ have the same set of border lengths. Previous proofs of this theorem use generating functions but do not provide an explicit bijection. We give a bijective proof for all pairs $p, q$ that have the same set of proper borders, establishing a natural bijection from the set of words avoiding $p$ to the set of words avoiding $q$.Comment: This version is our accepted manuscript. The most important changes from the previous version are as follows. The proof of the main theorem is streamlined, the introduction is updated, and section 4 is omitted. (12 pages, 8 figures

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