Viscoelastic characterization of thin-film polymers exposed to low Earth orbit

The materials made available through the Long Duration Exposure Facility (LDEF) satellite provide a set of specimens that can be well characterized and have a known exposure history with reference to atomic oxygen and ultraviolet radiation exposure. Mechanical characteristics measured from control samples and exposed samples provide a data base for predicting the behavior of polymers in low earth orbit. Samples of 1.0 mil thick low density polyethylene were exposed to the low earth orbit environment for a period of six years. These materials were not directly exposed to ram atomic oxygen and offer a unique opportunity for measuring the effect of atomic oxygen and UV radiation on mechanical properties with little concern to the effect of erosion. The viscoelastic characteristics of these materials were measured and compared to the viscoelastic characteristics of control samples. To aid in differentiating the effects of changes in crystallinity resulting from thermal cycling, from the effects of changes in chemical structure resulting from atomic oxygen/UV attack to the polymer, a second set of control specimens, annealed to increase crystallinity, were measured as well. The resulting characterization of these materials will offer insight into the impact of atomic oxygen/UV on the mechanical properties of polymeric materials. The viscoelastic properties measured for the control, annealed, and exposed specimens were the storage and loss modulus as a function of frequency and temperature. From these datum is calculated the viscoelastic master curve derived using the principle of time/temperature superposition. Using the master curve, the relaxation modulus is calculated using the method of Ninomiya and Ferry. The viscoelastic master curve and the stress relaxation modulus provide a direct measure of the changes in the chemical or morphological structure. In addition, the effect of these changes on long-term and short-term mechanical properties is known directly. It should be noted that the dependence on directionality for the polymer films was considered since these films were manufactured by a blown-film process

Impeller-Induced Rotor-Dynamic Forces

The flow through and around the rotor of a turbomachine exerts a force on the rotor and, hence, rotor shaft and bearing system. In some circumstances this force may lead to excitation of shaft whirl in the direction of impeller rotation. Recent international research of this phenomenon is briefly reviewed; these findings suggest that turbomachines intended to operate well above the first critical speed should take the effect into account

A MORE OBJECTIVE PROCEDURE FOR DETERMINING ECONOMIC SUBREGIONS: CLUSTER ANALYSIS

Research Methods/ Statistical Methods,

Siphonaptera Records and Host Associations From the Central and Eastern Upper Peninsula of Michigan

Fleas were collected from birds and mammals over a five year period in four upper peninsula counties. Identified specimens were compared to published records of distribution for the parasite species and its host species, and only those records which are new county distributions for host or parasite are listed. Four new host records for Michigan, four new flea distribution records for the upper peninsula, and 26 new county records are listed

A Microphone to the People: The Recordings of the Mobile Unit of the New Zealand Broadcasting Service, 1946-1948

The Mobile Recording Unit, an initiative of the New Zealand Broadcasting Service began work in 1946 with the intention covering small towns and rural districts of North and South Islands but it only recorded in three districts during its three year span. These contributions provide a significant archive of the post-war years

Forces on Centrifugal Pump Impellers

Forces are exerted on a centrifugal pump impeller, due to the asymmetry of the flow caused by the volute of diffuser, and to the motion of the center of the impeller whenever the shaft whirls. Recent work in the measurement of these forces as a function of the whirl speed to shaft speed ratio, and the influence of the volute, is reviewed. These forces may be decomposed into a steady force, a static stiffness matrix, a damping matrix and an inertia matrix. It is shown that for centrifugal pumps of the moderate specific speed typical of boiler feed stages, there is a region of potential shaft vibration excitation from the hydrodynamic forces if the operating speed is well above the first flexural critical speed

A postcritical poetics? Transtemporal encounters in defunct Soviet barracks in works by Ulrike Almut Sandig and Clemens Meyer

This article argues that Ulrike Almut Sandig’s poetry models what might be termed a ‘postcritical poetics’, expanding on Rita Felski’s idea of ‘postcritical reading’ to reveal strategies for a postcritical writing. In Sandig’s earlier poems, particularly ‘russenwald’ and ‘gardinen’ (2007), she evokes encounters on and around former Soviet military installations. The poems assume a postcritical stance to the past and in turn prompt a postcritical reading. Using theories by Felski and José Esteban Muñoz, I argue that Sandig stages fleeting interpersonal encounters based on openness and fascination, which work against the backdrop of past and present violence in both works. Sandig’s encounters suggest how everyday interactions can articulate dissatisfaction with a difficult present and look towards possible ethical relations in the future. Sandig’s writing further suggests productive ways of reading other contemporary writing, which I demonstrate using Clemens Meyer’s short narrative ‘Glasscherben im Objekt 95’ (2017), which also depicts a transtemporal encounter on a defunct Soviet military installation.PostprintPeer reviewe