The effect of cubic damping on a base excited isolator: an experimental study for harmonic excitation

An experimental study has been conducted to validate theoretical solutions for the response of a base excited single degree-of-freedom isolation system possessing pure cubic damping. The cubic damping characteristic was implemented using an electromagnetic shaker with a simple non-linear velocity feedback control. The rig and practical implementation of the active damping are described. The base excitation was harmonic at a set of discrete frequencies with constant displacement amplitude. Consistent with theoretical predictions, the isolation performance at high excitation frequencies is shown to be worse than either the undamped or linear viscously damped isolation system with the displacement transmissibility tending to unity. This is contrary to the case of force excitation reported in the literature where cubic damping offers improved performance. The physical causes of the distinct behaviours and the consequences for isolator design are discusse

Carboniferous geology of Northern England

The British Geological Survey (BGS) has produced a wholesale rationalisation of Carboniferous lithostratigraphical nomenclature. This presentation describes the Carboniferous stratigraphy of northern England, illustrated with research carried out as part of recent BGS mapping projects. During the Tournaisian and Visean a phase of north–south rifting resulted in the development of grabens and half-grabens, separated by platforms and tilt-block highs. Visean marine transgressions resulted in the establishment of platform carbonates, which gradually onlapped raised horst and tilt-block highs. The evolution of one such tilt-block high, the Askrigg block, and associated Great Scar Limestone Group, is described in detail. During late Visean times a cyclic succession of fluvio-deltaic clastics, marine reworked sandstones and shallow-shelf marine carbonates (Yoredale Group) dominated across northern England, terminating deposition of the platform carbonates. To the south of the Craven fault system, which defines the southern margin of the Askrigg Block, the block and basin structures persisted, though generally the high subsidence rates created a province dominated by hemipelagic mudstones and carbonate/siliciclastic turbidites (Craven Group). Cessation of rifting during the late Visean in the area between the Southern Uplands and the Wales–Brabant High resulted in a period dominated by thermally induced regional subsidence during Namurian and Westphalian times, with formation of the Pennine Basin. During early Namurian times fluvio-deltaic systems started to feed siliciclastic sediment into the northern margin of the basin (Millstone Grit Group). Initial deposition in the basinal areas is marked by the formation of thick turbidity-fronted delta successions. By late Namurian times, the southern part of the basin began to be infilled by fluvio-deltaic systems entering the basin from the east and south-east, but ultimately still sourced from the north. Three case studies are described in detail: the Kinderscout Grit, Ashover Grit and Chatsworth Grit. The development of these sand bodies occurred within a regime of regular and marked sea level changes. Evidence will be provided for the duration of this cyclicity. From early in the Westphalian, a coal-forming delta-top environment, associated with formation of the Pennine Coal Measures Group became established across the Pennine Basin. There was gradual waning of the influence of marine flooding events in the basin. The sediment influx into the Pennine Basin progressively changed from a dominantly northern provenance, comparable to the Millstone Grit Group, to initially a western source and subsequently to a southern one, later in the Westphalian

Policy and Practice Brief 4: The Obligation of Schools to Provide Information to Multilingual Families in a Language They Can Understand

Research shows that strong relationships between families and schools are key to student success. By providing information and communication in languages and formats that multilingual parents and guardians can access and understand, schools can strengthen relationships with these families. This policy and practice brief provides research and resources on this topic

Teachers\u27 Perceptions of the Broad Validity of a High Stakes English Language Proficiency Test

The No Child Left Behind Act of 2001 mandated that the English acquisition of all students identified as English learners be assessed annually using high-stakes standardized English language proficiency tests, and the Every Student Succeeds Act of 2015 continues this testing mandate. The WIDA ACCESS for ELLs® has been used for this and other purposes since 2005, and has been adopted by 40 State Education Agencies, including the Virginia Department of Education. However, despite the long-standing and widespread use of this assessment, no comprehensive independent evaluations of the test have been conducted. This mixed-methods study is a conceptual replication of a previous study evaluating the validity of a similar high-stakes standardized English language proficiency test. Using a Broad Validity Framework that considered the test’s reliability, criterion validity, and consequential validity, the study surveyed and interviewed Virginia teachers of English as a second language on their perspectives on the test. Findings suggest that while some teachers believe some sort of test is warranted for accountability and informing decisions, there are many threats to the validity of decisions based on test scores, including potential sources of construct-irrelevant variance, issues with technology associated with the online version of the test, the lapse of time between test administration and the receipt of scores, and questions regarding student motivation and test-taking effort. Furthermore, the study suggests the test has unintended consequences, including negative emotional impacts for teachers and students and a loss of instructional time. Because of questions raised regarding the reliability and validity of the test, study findings suggest the use of multiple measures in high-stakes decision-making for English learners. Furthermore, findings affirm the value of a consideration of teacher input in test evaluations

Chromosome Oscillations in Mitosis

Successful cell division requires a tight regulation of chromosome motion via the activity of molecular motors. Many of the key players at the origin of the forces generating the movement have been identified, but their spatial and temporal organization remains elusive. The protein complex Kinetochore on the chromosome associates with microtubules emanating from one of the spindle poles and drives the chromosome toward the pole. Chromokinesin motors on the chromosome arms also interact with microtubules, ejecting the chromosome away from the pole. In animal cells, a monooriented chromosome (associated to a single pole) periodically switches between phases of poleward and away from the pole movement[, a behavior tentatively explained so far by the existence of a complex switching mechanism within the kinetochore itself. Here we show that the interplay between the morphology of the mitotic spindle and the collective kinetics of chromokinesins can account for the highly non-linear periodic chromosome motion. Our analysis provides a natural explanation for the origin of chromosome directional instability and for the mechanism by which chromosomes feel their position in space.Comment: http://hogarth.pct.espci.fr/~pierre

Methods of Nature: Landscapes from the Gettysburg College Collection

Methods of Nature: Landscapes from the Gettysburg College Collection is the third annual exhibition curated by students enrolled in the Art History Methods course. The exhibition is an exciting academic endeavor and incredible opportunity for engaged learning, research, and curatorial experience. The five student curators are Molly Chason ’17, Leah Falk ’18, Shannon Gross ’17, Bailey Harper ’19 and Laura Waters ’19. The selection of artworks in this exhibition includes the depiction of landscape in the nineteenth- and twentieth-century French, American and East Asian cultural traditions in various art forms from traditional media of paintings and prints to utilitarian artifacts of porcelain and a paper folding fan. Landscape paintings in this exhibition are inspired by nature, specific locales and literature. Each object carries a distinctive characteristic, a mood, and an ambience. Collectively, they present a multifaceted view of the landscape in the heart and mind of the artists and intended viewers. [excerpt]https://cupola.gettysburg.edu/artcatalogs/1020/thumbnail.jp

A Merged Satellite Infrared and Manually Digitized Radar Product

This paper describes an automated technique which uses digital data from a geosynchronous environmental satellite and conventional meteorological data mapped to the satellite\u27s viewing projection. The technique produces a cloud-top height display with coincident manually digitized radar

Inbreeding in the White Leghorn Fowl

A study, extending over a 10-year period, has been made of the effect of inbreeding in the White Leghorn breed of domestic fowl. The major object of this investigation was to study the effect of various intensities of inbreeding on the following characters: Fertility, hatchability, viability, days to first egg, egg production, egg size and body size. In the present investigation the degree of inbreeding was, in general, less intense than that from brother and sister or parent and offspring matings. One intensely inbred family, however, with the equivalent of brother and sister mating, was maintained successfully for nine generations. Six more or less distinct families, each with a somewhat different type and intensity of inbreeding but with a similar foundation ancestry, were developed. All individuals were selected primarily on the basis of high hatchability of their eggs, upon general vigor of the individual bird and of the offspring of each pair of birds. Other characters besides vigor and hatchability also were considered whenever practical. The ancestry of all the birds in the present generation of these 6 families may be traced to four males and seven females. One of the four original males (No. 823), however, has a greater degree o£ relationship to the present generation than any of the other foundation birds. This relationship still averages approximately 55 percent, with the lowest degree of relationship being 29 percent and the highest 61 percent. The relationship of the present generation to the other three foundation males does not exceed 5 percent. The relationship between brothers and sisters in the present generation chicks of the separate families ranges from 74 to 94 percent. The average inter-se relationship between the present chicks which are not sibs is above 50 percent. The inbreeding coefficients of the present birds range from 41 percent for the least inbred to 82 percent for the most intensely inbred family. There was no general decrease in percent of eggs fertile as the degree of inbreeding increased ; in fact some inbred families have shown an increase in percent of eggs fertile. There was a slow but gradual decline in the average percent hatchability of fertile eggs set for all inbreds as the inbreeding increased. The average hatchability for all inbreds, however, was in most cases well above 60 percent. In six of the families studied there was no general decrease in hatchability, which demonstrates that it is possible to maintain a reasonably safe level of hatchability under a system of intense inbreeding. There was a significant decrease in the number of days to first egg. The most intensely inbred birds on the average matured sexually 16 days earlier than the birds of the original non-inbred foundation stock. There was a general but not a consistent decrease in number of eggs laid during a given period as the inbreeding increased. An exception was observed for the 70 percent inbred group which compared favorably with the original non-inbred foundation birds in egg production. There was no marked decrease in 200-day egg production for anyone of the six separate families as a result of the inbreeding. The data on egg weight suggest no general decrease or increase in average egg weight as a result of the inbreeding. The results indicate that intensive inbreeding did not decrease materially the growth rate or adult body weight of the birds used in this experiment. With the exception of the 80 percent group, there was no increase in mortality in any of the groups up to 24 weeks of age. The pullet year mortality, however, showed a marked rise for the more intensely inbred birds with the exception of that group of birds having an inbreeding coefficient of 70 percent