Field Response Research Articles

Vibration and stability control of robotic manipulator systems consisting of a thin‐walled beam and a spinning tip rotor

AbstractVibration and stability feedback control of a robotic manipulator modeled as a cantilevered thin‐walled beam carrying a spinning rotor at its tip is investigated. The control is achieved via incorporation of adaptive capabilities that are provided by a system of piezoactuators, bonded or embedded into the host structure. Based on converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied voltage, and as a result, an adaptive change of vibrational and stability response characteristics is obtained. A feedback control law relating the piezoelectrically induced bending moments at the beam tip with the appropriately selected kinematical response quantities is used, and the beneficial effects of this control methodology upon the closed‐loop eigenvibration characteristics and stability boundaries are highlighted. The cantilevered structure modeled as a thin‐walled beam, and built from a composite material, encompasses non‐classical features, such as anisotropy, transverse shear, and secondary warping, and in this context, a special ply‐angle configuration inducing a structural coupling between flapping‐lagging and transverse shear is implemented. It is also shown that the directionality property of the material of the host structure used in conjunction with piezoelectric strain actuation capability, yields a dramatic enhancement of both the vibrational and stability behavior of the considered structural system. © 2002 Wiley Periodicals, Inc.

Moving beyond the Written Comment: Narrowing the Gap between Response Practice and Research

While our field's response practices have changed dramatically over the past two decades to involve more student comments on their own texts, empirical studies have lagged far behind classroom practices, focusing almost exclusively on teachers' written comments as texts. By broadening our notion of response-and acknowledging the many and varied ways that teachers respond to student writing as well as the many and varied ways that students influence and interpret those responses-we will be able to narrow the gap between our teaching practices and our research questions.

Neural basis of a perceptual decision in the parietal cortex (area LIP) of the rhesus monkey.

We recorded the activity of single neurons in the posterior parietal cortex (area LIP) of two rhesus monkeys while they discriminated the direction of motion in random-dot visual stimuli. The visual task was similar to a motion discrimination task that has been used in previous investigations of motion-sensitive regions of the extrastriate cortex. The monkeys were trained to decide whether the direction of motion was toward one of two choice targets that appeared on either side of the random-dot stimulus. At the end of the trial, the monkeys reported their direction judgment by making an eye movement to the appropriate target. We studied neurons in LIP that exhibited spatially selective persistent activity during delayed saccadic eye movement tasks. These neurons are thought to carry high-level signals appropriate for identifying salient visual targets and for guiding saccadic eye movements. We arranged the motion discrimination task so that one of the choice targets was in the LIP neuron's response field (RF) while the other target was positioned well away from the RF. During motion viewing, neurons in LIP altered their firing rate in a manner that predicted the saccadic eye movement that the monkey would make at the end of the trial. The activity thus predicted the monkey's judgment of motion direction. This predictive activity began early in the motion-viewing period and became increasingly reliable as the monkey viewed the random-dot motion. The neural activity predicted the monkey's direction judgment on both easy and difficult trials (strong and weak motion), whether or not the judgment was correct. In addition, the timing and magnitude of the response was affected by the strength of the motion signal in the stimulus. When the direction of motion was toward the RF, stronger motion led to larger neural responses earlier in the motion-viewing period. When motion was away from the RF, stronger motion led to greater suppression of ongoing activity. Thus the activity of single neurons in area LIP reflects both the direction of an impending gaze shift and the quality of the sensory information that instructs such a response. The time course of the neural response suggests that LIP accumulates sensory signals relevant to the selection of a target for an eye movement.

Reading Old English Texts (review)

Reviews 253 disassociation. If at the end Napier appears to be concerned with 'the so-called loss of self (p. 196), there is no question that his text is focused formally on what m a y be called Western culture's 'memories...dynamic events out of which "new things" are created'. Thus thematically read, his text is a key to a cluster of linked ideas: the early Greek creation of a feared Other; classical dramatists' and artists' productions of the person or the individual; Christian environments symbolic of 'animated memory'; the continuum of xenophobic ideas; and the dangers of millennial thought. Napier's writing isrich,insightful and provocative, as is his daringly intermeshed bibliography. While his 'maps' are boldly limned they can and do provide wise directions, and his whole text constitutes one of the most brilliant, if modestly claimed, cases for both classical and Renaissance studies in the post-modern university and general society. Napier's post is one in 'Anthropology and Art' and it is both exciting and deeply satisfying to find this field's response to both Greek and Renaissance history, and to art and literature, as well as to savour its insights into the movement of, and limitations to, Western culture. J . S. Ryan School of English, Communication and Theatre University of N e w England O'Keeffe, Katherine O'Brien, ed., Reading Old English Texts, Cambridge Cambridge University Press, 1997; paper; pp. xii, 231; R.R.P. AUS$29.95. Reading Old English Texts is eminently suitable for use in advanced undergraduate and graduate Old English classes. Katherine O'Brien O'Keeffe has assembled a team of nine expert contributors, each of w h o m provides a chapter explaining and illustrating a particular critical method for reading and analysing Old English. Literary texts and literary analysis predominate as the objects of discourse, but essay after essay raises important questions about what constitutes a text, what texts qualify as 'literature', h o w w e gain access to texts, and h o w w e interpret them. The volume is clear, accessible and coherent. O'Keeffe's introduction 254 Reviews provides a critical map, charting the overlapping phases of Old English studies from linguistic and humanistic philology, to formalism ('New Criticism'), historicism (exemplified by Augustinian exegetical criticism), and the post-structuralist challenges to earlier modes of criticism. The introduction usefully synopsises the different chapters and highlights links between them. Each chapter conforms to a plan in providing a brief historical background to and explanation of the critical approach i t describes, a survey of significant scholarship, and a practical demonstration of the method at work, focused upon one or more texts typically taught in Old English classes. A n appendix provides suggestions for further reading in each area. Chapter One, Michael Lapidge's T h e Comparative Approach', outlines the long history of this critical mode. Alongside recent scholarship it commends classic studies like H. M . and N. K. Chadwick's The Growth of Literature, and W. P. Ker's Epic and Romance and The Dark Ages. This chapter should inspire students to range widely in their reading and to make informed comparisons drawn from the European heritage (where the possibilities of derivation and influence m a y exist) and from world literatures, in order to appreciate some possible 'universals' of literature. As a practical application of the comparative method Lapidge examines the psychological realism of the Beowulf-poet's inspired shift in narrative perspective from Beowulf to Grendel, w h e n the monster experiences intense terror as he feels the hero's hand-grip (lines 750-55). This shift parallels that which is found in Vergil's Aeneid (XII. 908-17) where Turnus's mental perceptions are similarly revealed as he confronts his nemesis in Aeneas. A s a further illustration Lapidge compares the evocation of m o o d through landscape in The Wife's Lament with that in Tennyson's 'Mariana'. The comparative method is further defined by contrast with 'Source Study', the subject of the chapter by D. G. Scragg, w h o as editor of the Pontes Anglo-Saxonici project is well-qualified to trace the history ofsource studies...

Spectral-ripple representation of steady-state vowels in primary auditory cortex.

Responses to various steady-state vowels were recorded in single units in the primary auditory cortex (AI) of the barbiturate-anaesthetized ferret. Six vowels were presented (/a/, /epsilon/, 2 different /i/'s, and 2 different /u/'s) in a natural voiced and a synthetic unvoiced mode. In addition, the responses to broadband stimuli with a sinusoidally shaped spectral envelope (called ripple stimuli) were recorded in each cell, and the response field (RF), which consists of both excitatory and inhibitory regions, was derived from the ripple transfer function. We examined whether the vowel responses could be predicted using a linear ripple analysis method [Shamma et al., Auditory Neurosci. 1, 233-254 (1995)], i.e., by cross correlating the RF of the single unit, and the smoothed spectral envelope of the vowel. We found that for most AI cells (71%) the relative responses to natural vowels could be predicted on the basis of this method. Responses and prediction results for unvoiced and voiced vowels were very similar, suggesting that the spectral fine structure may not play a significant role in the neuron's response to the vowels. Predictions on the basis of the entire RF were significantly better than based solely on best frequency (BF) (or "place"). These findings confirm the ripple analysis method as a valid method to characterize AI responses to broadband sounds as we proposed in a previous paper using synthesized spectra [Shamma and Versnel, Auditory Neurosci. 1, 255-270 (1995)].

Interior Design Visionaries’ Explorations of Emerging Trends

Objectives A two–phase project is underway to identify salient social, technological, and global trends and anticipate their impact on interior design. A group of recognized visionaries from interior design education, practice, and industry was brought together to consider a menu of over 100 societal and global trends. Two objectives determined both the gathering of data and its analysis: (a) to identify trends deemed important by the participants, and (b) to amplify and clarify what these trends mean for the future of interior design. Research Design Phase I employed a focus group methodology to structure a carefully planned discussion. Sixteen Roundtable participants selected trends and discussed the expected impacts important to the interior design profession. Analysis Voting procedures within the focus group facilitated the selection of a few trends considered most important to the future of interior design. Audio tape recordings were made of all discussions and then transcribed for qualitative data analysis. Key Findings Future designers will need a broad–based liberal arts education complemented with specialized expertise to prepare them for new roles and responsibilities in an emerging global market. The importance of teamwork among divisions within the field and with other disciplines was highlighted. Calls were issued for strategic planning that will guide the field's response to new design problems to be solved, new knowledge to be acquired, research to be undertaken, and new design and business skills and methods to be developed. Conclusions Participants expressed optimism about opportunities for the profession and roles for future designers. A remarkable level of agreement evolved among educators, practitioners, and industry participants regarding ideals for the discipline.

Performance Review of Tapered Submergible Pumps in the Three Bar Field

When lifting gaseous fluids with high-volume electric submergible pumps, compensation for compressibility and varying fluid volumes is required for the pump design. This paper describes the successful design and use of the tapered submergible pump for handling dynamic fluids in the Three Bar Field of Texas. Introduction The Three Bar (Devonian) Field waterflood project in Andrews County, TX, currently comprises 37 producing wells and 28 water injection wells. A total of 43 submergible pumps have been installed in 15 Three Bar Unit wells. Thirteen of the wells have used a total of 30 tapered pumps. This paper reviews the design, operation, and performance of these submergible pumps, with emphasis on the tapered submergible pump. Submergible electric centrifugal pumps are used widely as a high-volume artificial lift method. There are many different sizes and types of pumps designed to handle specific volume ranges. A tapered submergible pump is any multistage centrifugal pump that is designed pump is any multistage centrifugal pump that is designed to handle a volume differential between pump intake and discharge, while remaining within optimum efficiency ranges. A single-pump type can handle a limited fluid volume differential. When a required volume differential exceeds the single-type pump's efficiency range, then two or more different stages may be incorporated into one pump. The pumps are assembled with the larger-capacity pump. The pumps are assembled with the larger-capacity stages on the bottom, or the intake, and the smaller-capacity stages stacked above. Although single-type pumps may handle differential volumes, for our purposes only pumps using two or more types in the design hereafter will be designated "tapered" pumps. Fig. 1 illustrates a complete down-hole configuration of this type. On April 23, 1971, the first submergible pump, a tapered pump, was installed in the Three Bar Unit. Since then, submergible pumps have been responsible for recovering an incremental 1.84 million bbl oil more than the replaced rod-pumping equipment. About 66% of this volume was lifted by tapered submergibles. If this highvolume lift had not been introduced and operated successfully, many of these incremental reserves could have been lost because of failure to produce efficiently the volumes of fluid necessary to capitalize on the field's response to waterflooding. Special emphasis on handling substantial quantities of gas with the high-volume lift equipment created the need to apply the tapered submergible pump design. A computer program was used to design the pumps at the Three Bar Unit. program was used to design the pumps at the Three Bar Unit. Although both the tapered concept and the computer-designed procedure are used widely and generally are accepted, this procedure are used widely and generally are accepted, this performance review of the pumps at the Three Bar Unit evaluates performance review of the pumps at the Three Bar Unit evaluates each type in practice. Operating Conditions The Three Bar Unit has experienced excellent waterflooding response, while producing from a Devonian limestone at an average depth of 8,200 ft. The reservoir has two pay zones with a total net thickness of about 70 ft. Both zones are highly fractured and each displays an average porosity of 20%. The crude oil is sweet with a gravity of 41 degrees API, viscosity of 0.371 cp, and bottom-hole temperature of 130 degrees F. The typical Three Bar Unit well under primary recovery was a flowing, high-GOR producer. JPT P. 1781

Study of The Field Application of Sandstone Acidizing (includes associated papers 6507 and 6555 )

In a study to determine what factors most influence sandstone acidizing andproduction response infield treatments, it was found that the mostcritical factors are mud-acid volume and treating pressure. The optimumresponse was obtained with mud-acid volumes of 125 to 200 gal/ft; the poorest treatment response occurred when acid was injectedat pressures in excess of fracturing pressure. Introduction Much of the improvement in stimulation proceduresduring recent years has come about as a result of closelyexamining field experience. Exxon Co., U.S.A., periodically examines the success of stimulation treatments as afunction of treatment design parameters and reservoircharacteristics. Such an examination was made recentlyconcerning experience gained from April through Sept.1973. Although the original survey covered acidizing, fracturing, and surfactant methods of well stimulationand involved the treatment of both sandstone andcarbonate formations, this paper describes only the resultsfound for sandstone acidizing. As the study developed, more data were examined than were available during the6-month survey period cited. In some cases, field resultsfrom Jan. 1968 through May 1974 were examined. Overall, 222 treatments from the Texas-Louisiana Gulf Coast, West Coast, and Mid-Continent areas were examined.Test data from the Mid-Continent area were too few tojustify a separate analysis. The most detailed data wereavailable for treatments along the Texas Gulf Coast -an area where the acid-mutual solvent method isextensively used. Success of sandstone acidizing was related tothe design and execution parameters of the treatment andto reservoir characteristics thought to be significant. The outcome of a treatment was judged first on apurely economic basis. A treatment was called successfulif the increase in oil production provided payout of the jobcosts within a 3-month period. This payout was based onpre-embargo oil prices and involved an oil value of$2.20/bbl after federal income tax. This criterion is morestringent than current economic conditions wouldwarrant, and some jobs ruled unsuccessful in this studywould be ruled successful if re-evaluated. The data gathered on each job in the study are shown inTable 1. The factors of most interest were the size andcomposition of each of the three phases of a standardacid-mutual solvent treatment, the manner of executionof the treatment in the field, and several reservoirparameters. The last category comprised the porosity andpermeability of the formation, the length of theperforated interval, and the depth, bottom-hole pressure, andtemperature of the formation. No effort was made toperform a detailed mineralogical analysis of theformations treated because of the time and expense involved.Manipulation of the data acquired was accomplished by aMark IV computer program. The range of the study and the names of the formationstreated are shown in Table 2. A wide range of geologicages and a broad spectrum of formation depths, temperatures, porosities, and permeabilities were considered. Depth ranged from 1,010 to 13,358 ft, formationtemperature from 95 degrees to 275 degrees F, porosity fromless than 7 to 36 percent, and formation permeabilityfrom 1 to 2,350 md. JPT P. 1289^

The Use of Numerical Simulation To Design a Carbon Dioxide Miscible Displacement Project

The prediction of a single-layered, two-dimensional areal model was compared with results from cross-sectional, two-dimensional vertical models. Effects of gravity segregation and existing reservoir heterogeneity were not significant enough to justify use of a three-dimensional model for predicting field behavior of the North Cross (Devonian) Unit CO2 miscible displacement project in West Texas. project in West Texas. Summary A numerical simulation method was used to design a carbon dioxide (CO2) miscible displacement project in a low-permeability carbonate reservoir. A field history match was obtained as a check on the model's validity. Two-dimensional, vertical (cross-section) models were used to determine the potential effects of a high gas saturation at the top of the formation on CO2 injection profiles and to evaluate the effect of reservoir heterogeneity on sweep efficiency. A twodimensional areal model was used to describe the field's response to CO2 injection. Using an areal model, various CO2 injection patterns were simulated and compared, and an inverted patterns were simulated and compared, and an inverted nine-spot was found to be the optimum pattern for this field. Further simulation predictions were conducted to evaluate various schemes of handling produced CO2-contaminated gas after CO2 breakthrough. produced CO2-contaminated gas after CO2 breakthrough. It was found that direct reinjection of the contaminated gas was preferable to separating the CO2 from the gas or venting the contaminated gas. The project - the North Cross (Devonian) Unit in West Texas - is unlike the classical miscible project in that continuous injection of CO2 and residue project in that continuous injection of CO2 and residue gas is planned rather than injection of miscible slugs followed by or alternating with water or dry gas. Injection of CO2 commenced in April 1972. Actual project performance to date has been encouraging. project performance to date has been encouraging. Reservoir Description The Crossett field is located at the southern edge of the central basin platform of West Texas. The reservoir is a chalky, siliceous carbonate having 21 percent porosity and 3 md permeability. Fig. 1 shows percent porosity and 3 md permeability. Fig. 1 shows the gross Devonian reservoir thickness above the water-oil contact. There is no significant water drive present, so the primary recovery mechanism is solution gas drive. The reservoir is limited on the west by truncation caused by the post-Devonian unconformity. The eastern limit of the reservoir is provided by a water-oil contact, and the north and provided by a water-oil contact, and the north and south boundaries are defined by permeability and porosity deterioration. The reservoir is unusually uniform for a carbonate. Fig. 2 shows a plot of core permeability and porosity vs well depth. Properties of the reservoir fluid are listed in Table 1. The field contained 53 million STB of oil in place when discovered in 1944. The Crossett field was unitized in 1964 and renamed the North Cross (Devonian) Unit. The purpose of unitization was to implement a gas-injection purpose of unitization was to implement a gas-injection pressure maintenance project. All residue casinghead pressure maintenance project. All residue casinghead gas was injected into the three updip gas injection wells shown on Fig. 1. Fig. 3 shows the Unit's production history since unitization. production history since unitization. Residue gas injection would only increase the field's recovery to 19 percent from the expected primary efficiency of 13 percent. With so much oil being left in the reservoir, further supplemental recovery schemes were considered. P. 1327