Showing papers by "Lehigh University published in 1994"

Corporate Divestiture Intensity in Restructuring Firms: Effects of Governance, Strategy, and Performance

Abstract: Both inadequate governance and inappropriate strategy have been proposed as antecedents of the divestment activity of restructuring firms in the 1980s. We combined both views in a structural equati...

ADHD in the Schools: Assessment and Intervention Strategies

Abstract: Overview of ADHD. Assessment of ADHD in School Settings. ADHD and Learning Difficulties: What Is the Connection? Early Screening, Identification, and Intervention. School-Based Intervention Strategies. Medication Therapy. Adjunctive Interventions for ADHD. Communication with Parents, Professionals, and Students. Conclusions and Future Directions.

Robustness measures and robust scheduling for job shops

Abstract: A robust schedule is defined as a schedule that is insensitive to unforeseen shop floor disturbances given an assumed control policy. In this paper, a definition of schedule robustness is developed which comprises two components: post-disturbance make-span and post-disturbance makespan variability. We have developed robustness measures and robust scheduling methods for the case where a “right-shift” control policy is used. On occurrence of a disruption, the right-shift policy maintains the scheduling sequence while delaying the unfinished jobs as much as necessary to accommodate the disruption. An exact measure of schedule robustness is derived for the case in which only a single disruption occurs within the planning horizon. A surrogate measure is developed for the more complex case in which multiple disruptions may occur. This surrogate measure is then embedded in a genetic algorithm to generate robust schedules for job-shops. Experimental results show that robust schedules significantly outper...

Resilient early school-age children from maltreating homes: Outcomes in late adolescence.

Abstract: The interaction of individual and environmental characteristics over time in children from maltreating families is examined in order to explore the origins, scope, and stability of resilience in children from abusive and neglectful home environments. Response to supportive influences in the extended family and wider community, as well as determination to be different from abusive parents, is emphasized as crucial to resilient behavior and is illustrated by a case study.

XMAP from Xenopus eggs promotes rapid plus end assembly of microtubules and rapid microtubule polymer turnover.

Abstract: We have used video-enhanced DIC microscopy to examine the effects of XMAP, a Mr 215,000 microtubule-associated protein from Xenopus eggs (Gard, D.L., and M. W. Kirschner. 1987. J. Cell Biol. 105:2203-2215), on the dynamic instability of microtubules nucleated from axoneme fragments in vitro. Our results indicate that XMAP substantially alters the parameters of microtubule assembly at plus ends. Specifically, addition of 0.2 microM XMAP resulted in (a) 7-10-fold increase in elongation velocity, (b) approximately threefold increase in shortening velocity, and (c) near elimination of rescue (the switch from rapid shortening to elongation). Thus, addition of XMAP resulted in the assembly of longer, but more dynamic, microtubules from the plus ends of axonemes which upon catastrophe disassembled back to the axoneme nucleation site. In agreement with previous observations (Gard, D.L., and M. W. Kirschner. 1987. J. Cell Biol. 105:2203-2215), the effects of XMAP on the minus end were much less dramatic, with only a 1.5-3-fold increase in elongation velocity. These results indicate that XMAP, unlike brain MAPs, promotes both polymer assembly and turnover, and suggests that the interaction of XMAP with tubulin and the function of XMAP in vivo may differ from previously characterized MAPs.

Dispersion polymerization of methyl methacrylate: Mechanism of particle formation

Abstract: The mechanism for the formation of micron-size polymer particles in the dispersion polymerization of methyl methacrylate was investigated by applying dynamic light scattering to monitor the evolution of the average particle size in the early stages of the polymerization. In addition, the contributions of physically adsorbed stabilizer and graft copolymer were evaluated by measuring the bound, unbound (adsorbed), and free stabilizer, and by determining the amount of added stabilizer required in seeded dispersion polymerizations. Twenty nanometer particles (termed nuclei) were the smallest particles detected and are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. Aggregation of these nuclei with themselves and their aggregates continues until mature and stable particles are formed. This occurs when sufficient stabilizer occupies the particle surface which includes both the polymeric stabilizer [poly(vinylpyrrolidone)] and its graft copolymer which is created in situ. The effects of process variables are discussed based on this mechanistic picture of the dispersion polymerization process. © 1994 John Wiley & Sons, Inc.

Creep of duplex microstructures

Abstract: The tensile creep behavior of two ceramic composite systems exhibiting duplex microstructures was studied relative to their single-phase constituents in the temperature and stress ranges of 1,100--1,350 C and 35--75 MPa. The equi-volumetric compositions in the Al[sub 2]O[sub 3]:c-ZrO[sub 2] (8 mol% Y[sub 2]O[sub 3]) and Al[sub 2]O[sub 3]:Y[sub 3]Al[sub 5]O[sub 12] systems both exhibit lower creep rates than either of their single-phase constituents. This effect is attributed to Y[sup 3+] (and possibly Zr[sup 4+]) present in the Al[sub 2]O[sub 3] as a segregant which lowers the creep rate by [approximately]2 orders of magnitude. It is believed that the segregation of Y[sup 3+] to the Al[sub 2]O[sub 3] grain boundaries hinders the interface reaction believed to control the creep. If one of the single-phase constituents is taken to be the Y[sup 3+]-doped Al[sub 2]O[sub 3], the creep of the duplex microstructures can be modeled using standard composite theory applied to flow.

Theory and application of charge pumping for the characterization of Si-SiO/sub 2/ interface and near-interface oxide traps

Abstract: A generalized charge pumping model has been developed which extends the use of charge pumping from a study of traps at the Si-SiO/sub 2/ interface to a study of traps in the oxide. The analytical model, based on tunneling theory, allows the spatial distribution of near-interface oxide traps to be determined from variable frequency charge pumping data. Profiling of near-interface oxide traps in irradiated MOSFET's as well as SONOS nonvolatile memory devices is presented. >

The generation and regeneration of single hairpin vortices

Abstract: The generation and growth of single hairpin vortices created by controlled surface fluid injection were examined experimentally within a laminar boundary layer over a range of Reynolds numbers. Flow visualization, using both dye and hydrogen bubbles, was employed in conjunction with hot-film anemometry to investigate the growth characteristics and evolution of these single hairpin vortices. Hydrogen-bubble visualization results reveal that the passage of a hairpin vortex can give rise to a low-speed streak pattern adjacent to the surface, and a turbulent pocket-like pattern farther removed from the surface. When the displacement and injection Reynolds numbers exceed critical levels, regeneration processes occur, which result in the development of new hairpin-like vortices by both (i) lateral deformation of the vortex lines comprising the initial hairpin vortex and (ii) a process of vortex-surface interaction, which causes the ejection of surface fluid and subsequent hairpin formation by viscous-inviscid interactions. The combination of these processes results in both lateral and streamwise growth of the initial hairpin-vortex structure, yielding a symmetric turbulent-spot type of behaviour.

Response of Children with ADHD to Methylphenidate: Interaction with Internalizing Symptoms

Abstract: Objective The purpose of this study was to examine differences in methylphenidate (MPH) response between groups of children with attention-deficit hyperactivity disorder (ADHD) who exhibited varying degrees of internalizing symptoms. Method A sample of 40 children with ADHD was subdivided into three groups based on the severity of comorbid internalizing symptoms. Differential effects of three doses of MPH (5 mg, 10 mg, 15 mg) were evaluated in a double-blind, placebo-controlled fashion using multiple outcome measures across home, school, and clinic settings. Results Children with ADHD and comorbid internalizing symptoms were significantly less likely to respond positively to MPH than were their noninternalizing counterparts according to teacher ratings and behavioral observations during a clinic-based academic task. Conclusions Children who exhibit comorbid symptoms of ADHD and internalizing disorder are less likely to respond to MPH in classroom settings and on academic tasks. A significant minority of children with comorbid conditions may be at a higher risk for an adverse medication response relative to patients with ADHD who are not exhibiting internalizing symptoms. Further research is necessary to delineate the characteristics of possible adverse responders.

Vibrational study of the role of trivalent ions in sodium trisilicate glass

Abstract: The structure of glasses in the system Na 2 O · x R 2 O 3 · (3 − 2 x )SiO 2 (RAl, B) has been studied by employing Raman and infrared reflectance spectroscopies. These particular glass compositions were chosen for elucidating the role of aluminum and boron substitution on glass structure and properties while keeping the Na/(Si + R) ratio fixed. In the presence of aluminum, the equilibrium 2Q 3 ⇔ Q 4 + Q 2 shifts to the left. The role of boron was found to be the opposite, since it induces the destruction of the Q 3 species and the creation of the highly charged Q 2 and Q 1 species, as well as the fully polymerized Q 4 silicate units. The combined far-infrared and XPS results on the same glasses suggest that the average charge density of sites populated by sodium ions is smaller in aluminosilicate than in borosilicate glasses.

Satisfaction with hospital care and interventions after pregnancy loss.

Abstract: Hospital practices after pregnancy loss have changed considerably over the past decade, yet they have not been well evaluated. In a longitudinal study of 194 women and men who experienced miscarriage, ectopic pregnancy, stillbirth, or newborn death, the recommended interventions at the time of loss are examined. In most cases, parents were more satisfied if they had experienced an intervention than if they had not, but having experienced more total interventions was not associated with her grief or greater satisfaction with overall care; the latter was related more to the attentiveness and sensitivity of health care personnel. Three groups identified as in need of greater attention are clinic patients, who were significantly less satisfied and more griefstricken than the patients of private physicians, those who had spontaneous abortions or ectopic pregnancies, and those who had early fetal losses.

‘Window’ effect in the analysis of frequency dependence of ionic conductivity

Abstract: Usually the frequency dependence of ionic conductivity of solids in analyzed in the form of a power law or as the deviation of imaginary part of electric modulus from ideal Debye peak. The power law formalism is shown to be sensitive to the choice of frequency window employs in the analysis. The results demonstrate the inadequacies of either formalism and a method is suggested of combining the two formalisms for parameterizing non-ideal electric response in the vicinity of the electrical conductivity relaxation time.

Light-scattering study of the liquid-glass transition in propylene carbonate

Abstract: Depolarized light-scattering spectra of propylene carbonate were obtained in the frequency range 0.2 GHz--4 THz at temperatures from 350 to 135 K. Analysis of the resulting susceptibility spectra revealed reasonable agreement with the predictions of the idealized mode coupling theory, yielding critical exponents a=0.29, b=0.50, and an exponent parameter \ensuremath{\lambda}=0.78\ifmmode\pm\else\textpm\fi{}0.05. A scaling analysis demonstrated critical slowing down of the scaling frequencies from both above and below ${\mathit{T}}_{\mathit{C}}$, with the scaling frequency extrapolating to zero at ${\mathit{T}}_{\mathit{C}}$=187\ifmmode\pm\else\textpm\fi{}5 K. The \ensuremath{\alpha}-relaxation peak was fit to a Kohlrausch function, which gave \ensuremath{\beta}=0.77\ifmmode\pm\else\textpm\fi{}0.05 for 210\ensuremath{\le}T\ensuremath{\le}350 K with no sign of systematic temperature dependence. An extended mode coupling theory analysis was also carried out which corroborated the results obtained with the idealized version. Polarized Brillouin spectra were also obtained, and were analyzed with a generalized hydrodynamics approach using low-frequency sound velocity values determined separately in an ultrasonics experiment. The results indicate that the Cole-Davidson function is not an adequate model for the structural relaxation due to the neglect of \ensuremath{\beta}-relaxation processes, so that this analysis cannot provide a meaningful estimate of ${\mathit{T}}_{\mathit{C}}$. Furthermore, the \ensuremath{\alpha}-relaxation time associated with Brillouin scattering was found to be about five times shorter than that probed by depolarized light scattering.

Control of emulsion polymerization reactors

Abstract: The interest in emulsion polymerization is strong because it offers the possibility of producing products with special properties not easily produced by other types of polymerization processes. Because the main reaction medium is water, not an organic solvent, its importance is steadily increasing with efforts to design environmentally benign processes. The control of emulsion polymerization is a challenging problem due to major limitations encountered in its modeling and on-line monitoring. Although emulsion polymerization has been studied and used for several decades, progress has been slow. Industrial practice relies heavily on experience while several controversial issues are still being studied. The literature related to this issue is vast and sometimes contradictory, and most deals with experimental investigation of specific emulsion polymerization systems to improve the process understanding and develop a process model. However, universally accepted conclusions are scarce. This article reviews the major issues related to control of emulsion polymerization. The latest contributions in process understanding, mathematical modeling, sensor technology, and process control techniques for emulsion polymerization are discussed. Emphasis is on contributions, which are important in resolving the control of emulsion polymerization processes.

Materiality judgments and audit firm culture: Social-behavioral and political perspectives

Abstract: Researchers have traditionally interpreted the formation of auditor judgments as either a technical or a cognitive phenomenon. Their research has, therefore, focused mainly on refining empirical techniques designed to reveal the mental processes used to form judgments interior to the individual. This theoretical and empirical analysis opens this conceptualization on three levels. On the first level, the authors interpret auditor judgment formation as a social-behavioral phenomenon in which the social context of the audit firm vis-a-vis its audit philosophy influences materiality judgments. On the second level, rather than interpreting the firm's philosophy as merely one form of “variable” administrative partners may manipulate to achieve desired ends, the authors treat it as determining of and being determined by the social structure of the audit firm and in turn its culture. Accordingly, they hypothesize that (1) a firm's audit culture, expressed in terms of mechanistic versus organic orientations, systematically influences its members' materiality judgments, which are characterized as “rational comprehensive” or “satisficing”, respectively; and (2) the level of experience of audit firm members, expressed in terms of hierarchical ranks, amplifies the effect of firm culture. On the third level, the authors interpret the formation of materiality judgments vis-a-vis culture as forming an implicit tension with political interests in which the practitioner and administrative components of audit firms contend with one another over the “location” of decision-making discretion and autonomy. Results obtained from an experimental simulation involving the participation of 212 partners, managers and seniors from the former Big 8 firms strongly support both audit firm culture hypotheses. Finally, the authors explore implications using empirical results as well as insights gathered during interviews with firms members directed at probing the political forces influencing the location of decision-making discretion.

Collective dynamics of off-center ions in K1-xLixTaO3: A model of relaxor behavior.

Abstract: The relaxor behavior is characteristic of the class of disordered ferroelectrics. These systems possess a high dielectric constant with a broad relaxation peak and a low frequency dispersion. Because of their complexity, there exist various explanations for their dielectric and polarization behavior, but no unifying model. In the present paper we show that the simpler system, ${\mathrm{K}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}\mathrm{Ta}{\mathrm{O}}_{3}$, is also a relaxor and a generic one at that. We describe its dynamical behavior with a general microscopic model and show that the relaxor behavior is intrinsically due to the dipolar interaction between randomly distributed off-center ions mediated by a highly polarizable lattice.

Compression, self-bending, and collapse of Gaussian beams in photorefractive crystals

Abstract: By means of an exact solution, we demonstrate that a Gaussian beam can undergo spatial compression when it traverses a photorefractive medium. This is possible provided that the external bias field exceeds the critical value necessary to establish photorefractive spatial solitons. In this regime and under paraxial assumptions our analysis indicates that a Gaussian beam tends to exhibit self-focusing collapse. Beam self-deflection effects that arise from the pi/2-phase-shifted component of the photorefractive grating are also considered in our study.

The effects of choice and task preference on the work performance of adults with severe disabilities.

Abstract: We evaluated the effects of choice versus the assignment of tasks of varying preferences on the work engagement of adults with severe disabilities. The combined results of two experiments suggests that the relative preference for a task may be an important variable in the effectiveness of choice for some individuals.

Probability approach for prediction of corrosion and corrosion fatigue life

Abstract: A probability approach for life prediction is developed and illustrated through a simplified model for the pitting corrosion and corrosion fatigue crack growth in aluminum alloys in aqueous environments. A method for estimation of the cumulative distribution function (CDF) for the lifetime is demonstrated by using an assumed CDF for each key random variable (RV). The basic aim of this approach is to make predictions for the lifetime, reliability, and durability beyond the range of typical data by integrating the CDFs of the individual RVs into a mechanistically based model. The contribution of each key RV is considered, and its significance is assessed. Thus, the usefulness of probability-based modeling is demonstrated. It is noted that physically realistic parameters were assumed for the illustrations. As such, the results from analysis of the model qualitatively agree quite well with experimental observations. However, these results should not be construed to represent behavior in actual systems. Because of these assumptions, confidence levels for the predictions are not addressed. 9 refs.

Microtubule assembly and kinetochore directional instability in vertebrate monopolar spindles: implications for the mechanism of chromosome congression

Abstract: We have proposed previously a kinetochore motor-polar ejection model for chromosome congression to the metaphase plate where forces generated at the kinetochore are antagonized by away-from-the pole forces generated within each half-spindle on the chromosome arms. This model was based in large part on observations of the behavior of chromosomes on monopolar spindles. In these cells chromosomes typically become attached to the pole by only one kinetochore fiber. These mono-oriented chromosomes move to positions away from the pole even though they are pulled poleward at their kinetochores. Their arms are also ejected away from the pole when severed from the centromere. Here we have characterized further the properties of monopolar spindles in newt lung epithelial cells to determine the similarities between monopolar and bipolar spindles. We found no significant differences between monopolar and bipolar spindles over the parameters examined, which included: microtubule dynamics as measured by fluorescence redistribution after photobleaching; the ability of polar microtubule arrays to push chromosome arms away from the pole; the dependence of chromosome position relative to the pole on microtubule assembly; the number of kinetochore microtubules per kinetochore; and the directional instability of kinetochore motion during chromosome oscillations poleward and away-from-the-pole. As in bipolar spindles, kinetochore directional instability is characterized by abrupt switching between constant velocity phases of poleward and away-from-the-pole motion. From these data we conclude that the mechanism(s) responsible for chromosome positioning in monopolar spindles are fundamentally the same as those in bipolar spindles; only the geometry of the two spindle forms and the interplay between sister kinetochore directional instabilities are different. We also found no correlation in the kinetochore-to-pole distance with kinetochore microtubule number in monopolar spindles, but a strong qualitative correlation with microtubule density. This finding indicates that oscillations of mono-oriented chromosomes in both monopolar and bipolar spindles occur because chromosomes persist in poleward motion until they reach a density of polar microtubules sufficiently high to promote switching to away-from-the-pole motion. As the kinetochore and chromosome arms move away-from-the-pole, microtubule density decreases and the kinetochore switches to poleward motion, pulling the chromosome arms back into regions of higher microtubule density. The mechanism regulating kinetochore switching between poleward and away-from-the-pole motion is poorly understood, but may depend on tension at the kinetochore generated by pushing forces on the chromosome arms produced by the polar microtubule arrays.