Showing papers by "University of Delaware published in 2005"

Advantages of the mean absolute error (MAE) over the root mean square error (RMSE) in assessing average model performance

Abstract: The relative abilities of 2, dimensioned statistics — the root-mean-square error (RMSE) and the mean absolute error (MAE) — to describe average model-performance error are examined The RMSE is of special interest because it is widely reported in the climatic and environmental liter- ature; nevertheless, it is an inappropriate and misinterpreted measure of average error RMSE is inappropriate because it is a function of 3 characteristics of a set of errors, rather than of one (the average error) RMSE varies with the variability within the distribution of error magnitudes and with the square root of the number of errors (n 1/2 ), as well as with the average-error magnitude (MAE) Our findings indicate that MAE is a more natural measure of average error, and (unlike RMSE) is unambiguous Dimensioned evaluations and inter-comparisons of average model-performance error, therefore, should be based on MAE

Trends in the exchange current for hydrogen evolution

Abstract: Department of Physics, Technical University Munich, D-85748 Garching, GermanyA density functional theory database of hydrogen chemisorption energies on close packed surfaces of a number of transition andnoble metals is presented. The bond energies are used to understand the trends in the exchange current for hydrogen evolution. Avolcano curve is obtained when measured exchange currents are plotted as a function of the calculated hydrogen adsorptionenergies and a simple kinetic model is developed to understand the origin of the volcano. The volcano curve is also consistent withPt being the most efficient electrocatalyst for hydrogen evolution.© 2005 The Electrochemical Society. @DOI: 10.1149/1.1856988# All rights reserved.Manuscript submitted May 10, 2004; revised manuscript received August 12, 2004. Available electronically January 24, 2005.

Diabetic neuropathies: a statement by the American Diabetes Association.

Abstract: The diabetic neuropathies are heterogeneous, affecting different parts of the nervous system that present with diverse clinical manifestations. They may be focal or diffuse. Most common among the neuropathies are chronic sensorimotor distal symmetric polyneuropathy (DPN) and the autonomic neuropathies. DPN is a diagnosis of exclusion. The early recognition and appropriate management of neuropathy in the patient with diabetes is important for a number of reasons. 1 ) Nondiabetic neuropathies may be present in patients with diabetes. 2 ) A number of treatment options exist for symptomatic diabetic neuropathy. 3 ) Up to 50% of DPN may be asymptomatic, and patients are at risk of insensate injury to their feet. As >80% of amputations follow a foot ulcer or injury, early recognition of at-risk individuals, provision of education, and appropriate foot care may result in a reduced incidence of ulceration and consequently amputation. 4 ) Autonomic neuropathy may involve every system in the body. 5 ) Autonomic neuropathy causes substantial morbidity and increased mortality, particularly if cardiovascular autonomic neuropathy (CAN) is present. Treatment should be directed at underlying pathogenesis. Effective symptomatic treatments are available for the manifestations of DPN and autonomic neuropathy. This statement is based on two recent technical reviews (1,2), to which the reader is referred for detailed discussion and relevant references to the literature. An internationally agreed simple definition of DPN for clinical practice is “the presence of symptoms and/or signs of peripheral nerve dysfunction in people with diabetes after the exclusion of other causes” (3). However, the diagnosis cannot be made without a careful clinical examination of the lower limbs, as absence of symptoms should never be assumed to indicate an absence of signs. This definition conveys the important message that not all patients with peripheral nerve dysfunction have a neuropathy caused by diabetes. Confirmation can be established with …

Potential Problems in the Statistical Control of Variables in Organizational Research: A Qualitative Analysis With Recommendations

Abstract: The author examines statistical control in a random sample of 60 articles published in four top journals during 2000 to 2002. Authors’bases for including control variables, clarity regarding measur...

Corporate Governance and Acquirer Returns

Abstract: We examine whether corporate governance mechanisms, especially the market for corporate control, affect the profitability of firm acquisitions. We find that acquirers with more anti-takeover provisions experience significantly lower announcement-period stock returns than other acquirers. We also find that acquiring firms operating in more competitive industries or separating the positions of CEO and chairman of the board experience higher abnormal announcement returns. Our results support the hypothesis that managers protected by more anti-takeover provisions face weaker discipline from the market for corporate control and thus, are more likely to indulge in empire-building acquisitions that destroy shareholder value. They provide a partial explanation for why anti-takeover provision indices of Gompers, Ishii and Metrick and others are negatively correlated with shareholder value.

Evidence and implications of recent climate change in northern Alaska and other arctic regions.

Abstract: The Arctic climate is changing. Permafrost is warming, hydrological processes are chang- ing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates con- vincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and pro- cesses influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show

Synthesis and antibacterial properties of silver nanoparticles.

Abstract: Nanometer sized silver particles were synthesized by inert gas condensation and co-condensation techniques. Both techniques are based on the evaporation of a metal into an inert atmosphere with the subsequent cooling for the nucleation and growth of the nanoparticles. The antibacterial efficiency of the nanoparticles was investigated by introducing the particles into a media containing Escherichia coli. The antibacterial investigations were performed in solution and on petri dishes. The silver nanoparticles were found to exhibit antibacterial effects at low concentrations. The antibacterial properties were related to the total surface area of the nanoparticles. Smaller particles with a larger surface to volume ratio provided a more efficient means for antibacterial activity. The nanoparticles were found to be completely cytotoxic to E. coli for surface concentrations as low as 8 microg of Ag/cm2.

Early Identification and Interventions for Students With Mathematics Difficulties

Abstract: This article highlights key findings from the small body of research on mathematics difficulties (MD) relevant to early identification and early intervention. The research demonstrates that (a) for many children, mathematics difficulties are not stable over time; (b) the presence of reading difficulties seems related to slower progress in many aspects of mathematics; (c) almost all students with MD demonstrate problems with accurate and automatic retrieval of basic arithmetic combinations, such as 6 + 3. The following measures appear to be valid and reliable indicators of potential MD in kindergartners: (a) magnitude comparison (i.e., knowing which digit in a pair is larger), (b) sophistication of counting strategies, (c) fluent identification of numbers, and (d) working memory (as evidenced by reverse digit span). These are discussed in terms of the components of number sense. Implications for early intervention strategies are explored.

Elucidation of the small RNA component of the transcriptome.

Abstract: Small RNAs play important regulatory roles in most eukaryotes, but only a small proportion of these molecules have been identified. We sequenced more than two million small RNAs from seedlings and the inflorescence of the model plant Arabidopsis thaliana. Known and new microRNAs (miRNAs) were among the most abundant of the nonredundant set of more than 75,000 sequences, whereas more than half represented lower abundance small interfering RNAs (siRNAs) that match repetitive sequences, intergenic regions, and genes. Individual or clusters of highly regulated small RNAs were readily observed. Targets of antisense RNA or miRNA did not appear to be preferentially associated with siRNAs. Many genomic regions previously considered featureless were found to be sites of numerous small RNAs.

An optimized kinetic model of H2/CO combustion

Abstract: We propose a H2–CO kinetic model which incorporates the recent thermodynamic, kinetic, and species transport updates relevant to high-temperature H2 and CO oxidation. Attention has been placed on obtaining a comprehensive and kinetically accurate model able to predict a wide variety of H2–CO combustion data. The model was subject to systematic optimization and validation tests against reliable H2–CO combustion data, from global combustion properties (shock-tube ignition delays, laminar flame speeds, and extinction strain rates) to detailed species profiles during H2 and CO oxidation in flow reactor and in laminar premixed flames.

Fluency: Bridge Between Decoding and Reading Comprehension

Abstract: A deep, developmental construct and definition of fluency, in which fluency and reading comprehension have a reciprocal relationship, is explicated and contrasted with superficial approaches to that construct. The historical development of fluency is outlined, along with conclusions of the U.S. National Reading Panel, to explore why fluency has moved from being “the neglected aspect of reading” to a popular topic in the field. A practical, developmental instructional program based largely on the theoretical framework and research findings of Linnea Ehri is delineated. The nine essential components of that program include building the graphophonic foundations for fluency; building and extending vocabulary and oral language skills; providing expert instruction and practice in the recognition of high-frequency vocabulary; teaching common word parts and spelling patterns; teaching, modeling, and providing practice in the application of a decoding strategy; using appropriate texts to coach strategic behaviors and to build reading speed; using repeated reading procedures as an intervention approach for struggling readers; extending growing fluency through wide independent reading; and monitoring fluency development through appropriate assessment procedures. The position is taken throughout that teaching, developing, and assessing fluency must always be done in the context of reading comprehension.

Core stability and its relationship to lower extremity function and injury.

Abstract: Core stability may provide several benefits to the musculoskeletal system, from maintaining low back health to preventing knee ligament injury. As a result, the acquisition and maintenance of core stability is of great interest to physical therapists, athletic trainers, and musculoskeletal researchers. Core stability is the ability of the lumbopelvic hip complex to prevent buckling and to return to equilibrium after perturbation. Although static elements (bone and soft tissue) contribute to some degree, core stability is predominantly maintained by the dynamic function of muscular elements. There is a clear relationship between trunk muscle activity and lower extremity movement. Current evidence suggests that decreased core stability may predispose to injury and that appropriate training may reduce injury. Core stability can be tested using isometric, isokinetic, and isoinertial methods. Appropriate intervention may result in decreased rates of back and lower extremity injury.

Velocity and position control of a wheeled inverted pendulum by partial feedback linearization

Abstract: In this paper, the dynamic model of a wheeled inverted pendulum (eg, Segway, Quasimoro, and Joe) is analyzed from a controllability and feedback linearizability point of view First, a dynamic model of this underactuated system is derived with respect to the wheel motor torques as inputs while taking the nonholonomic no-slip constraints into considerations This model is compared with the previous models derived for similar systems The strong accessibility condition is checked and the maximum relative degree of the system is found Based on this result, a partial feedback linearization of the system is obtained and the internal dynamics equations are isolated The resulting equations are then used to design two novel controllers The first one is a two-level velocity controller for tracking vehicle orientation and heading speed set-points, while controlling the vehicle pitch (pendulum angle from the vertical) within a specified range The second controller is also a two-level controller which stabilizes the vehicle's position to the desired point, while again keeping the pitch bounded between specified limits Simulation results are provided to show the efficacy of the controllers using realistic data

On the ERN and the significance of errors.

Abstract: The error-related negativity (ERN) is an event-related brain potential observed when subjects commit errors. To examine whether the ERN is sensitive to the value of errors, the motivational significance of errors was manipulated in two experiments. In Experiment 1, low and high monetary value errors were compared to evaluate the effect of trial value on the ERN. In Experiment 2, subjects performed a flanker task both while their performance was being evaluated and during a control condition. Consistent with the notion that the error-detection system is sensitive to the significance of errors, the ERN was significantly larger on high-value trials in Experiment 1 and during evaluation in Experiment 2. There were no corresponding effects on the correct response negativity, and no behavioral differences between conditions were evident in either experiment. These results are discussed in terms of the functional role of the ERN in response monitoring. Descriptors: Motivation, Event-related potentials (ERPs), Error-related negativity (ERN), Ne, Value, Affect

Three-month-olds, but not newborns, prefer own-race faces

Abstract: Adults are sensitive to the physical differences that define ethnic groups. However, the age at which we become sensitive to ethnic differences is currently unclear. Our study aimed to clarify this by testing newborns and young infants for sensitivity to ethnicity using a visual preference (VP) paradigm. While newborn infants demonstrated no spontaneous preference for faces from either their own- or other-ethnic groups, 3-month-old infants demonstrated a significant preference for faces from their own-ethnic group. These results suggest that preferential selectivity based on ethnic differences is not present in the first days of life, but is learned within the first 3 months of life. The findings imply that adults’ perceptions of ethnic differences are learned and derived from differences in exposure to own- versus other-race faces during early development.

Corporate Governance, Idiosyncratic Risk, and Information Flow

Abstract: We study the relationship of corporate governance policy and idiosyncratic risk in stock returns. Firms with fewer anti-takeover provisions display higher levels of idiosyncratic risk, trading activity, private information flow, and more information about future earnings in stock prices. Trading interest by institutions, especially those active in merger arbitrage, strengthens the relationship of governance to idiosyncratic risk. Our results indicate that openness to the market for corporate control leads to more informative stock prices by encouraging collection of and trading on private information. Consistent with an information-flow interpretation, the component of volatility unrelated to governance is associated with the efficiency of corporate investment.

Interlimb Coordination During Locomotion: What Can be Adapted and Stored?

Abstract: Interlimb coordination is critically important during bipedal locomotion and often must be adapted to account for varying environmental circumstances. Here we studied adaptation of human interlimb coordination using a split-belt treadmill, where the legs can be made to move at different speeds. Human adults, infants, and spinal cats can alter walking patterns on a split-belt treadmill by prolonging stance and shortening swing on the slower limb and vice versa on the faster limb. It is not known whether other locomotor parameters change or if there is a capacity for storage of a new motor pattern after training. We asked whether adults adapt both intra- and interlimb gait parameters during split-belt walking and show aftereffects from training. Healthy subjects were tested walking with belts tied (baseline), then belts split (adaptation), and again tied (postadaptation). Walking parameters that directly relate to the interlimb relationship changed slowly during adaptation and showed robust aftereffects during postadaptation. These changes paralleled subjective impressions of limping versus no limping. In contrast, parameters calculated from an individual leg changed rapidly to accommodate split-belts and showed no aftereffects. These results suggest some independence of neural control of intra- versus interlimb parameters during walking. They also show that the adult nervous system can adapt and store new interlimb patterns after short bouts of training. The differences in intra- versus interlimb control may be related to the varying complexity of the parameters, task demands, and/or the level of neural control necessary for their adaptation.

A Social Skill Account of Problematic Internet Use

Abstract: This study integrates research on social skill and self-presentation into the recently introduced cognitive-behavioral theory of generalized problematic Internet use. The model proposed and tested here predicted that individuals who lack self-presentational skill are especially likely to prefer online social interaction over face-to-face communication. Further, the model predicted that a preference for online social interaction fosters compulsive Internet use, which results in negative outcomes. Participants in this study completed measures of social skill, preference for online social interaction, compulsive Internet use, and negative outcomes associated with Internet use. Structural equation modeling analysis techniques tested the proposed model. The analysis indicated a good fit between the hypothesized model and the current data.

Global Distribution of Methane Hydrate in Ocean Sediment

Abstract: In this paper, we present an equilibrium thermodynamic model to accurately predict the maximum depth of hydrate stability in the seafloor, including the effects of water salinity, hydrate confinement in pores, and the distribution of pore sizes in natural sediments. This model uses sediment type, geothermal gradient, and seafloor depth as input to predict the thickness of the hydrate zone. Using this hydrate model and a mass-transfer description for hydrate formation, we have also developed a predictive method for the occurrence of methane hydrates in the ocean. Based on this information, a prediction for the distribution of methane hydrate in ocean sediment is presented on a 1° latitude by 1° longitude (1° × 1°) global grid. From this detailed prediction, we estimate that there is a total volume of 1.2 × 1017 m3 of methane gas (expanded to atmospheric conditions), or, equivalently, 74 400 Gt of CH4 in ocean hydrates, which is 3 orders of magnitude larger than worldwide conventional natural gas reserves. ...

Quadriceps Strength and the Time Course of Functional Recovery After Total Knee Arthroplasty

Abstract: Study Design Prospective study with repeated measures. Objectives The overall goal of this investigation was to describe the time course of recovery of impairments and function after total knee arthroplasty (TKA), as well as to provide direction for rehabilitation efforts. We hypothesized that quadriceps strength would be more strongly correlated with functional performance than knee flexion range of motion (ROM) or pain at all time periods studied before and after TKA. Background TKA is a very common surgery, but very little is known regarding the influence of impairments on functional limitations in this population. Methods and Measures Forty subjects who underwent unilateral TKA followed by rehabilitation, including 6 weeks of outpatient physical therapy, were studied. Testing occurred at 5 time periods: preoperatively, and at 1, 2, 3, and 6 months after surgery. Test measures included quadriceps strength, knee ROM, timed up-and-go test, timed stair-climbing test, bodily pain, and general health and kn...

Brain potentials associated with expected and unexpected good and bad outcomes.

Abstract: The error-related negativity (ERN) is an event-related brain potential observed when subjects receive feedback indicating errors or monetary losses. Evidence suggests that the ERN is larger for unexpected negative feedback. The P300 has also been shown to be enhanced for unexpected feedback, but does not appear to be sensitive to feedback valence. The present study evaluated the role of expectations on the ERN and P300 in two experiments that manipulated the probability of negative feedback (25%, 50%, or 75%) on a trial-by-trial basis in experiment 1, and by varying the frequency of positive and negative feedback across blocks of trials in experiment 2. In both experiments, P300 amplitude was larger for unexpected feedback; however, the ERN was equally large for expected and unexpected negative feedback. These results are discussed in terms of the potential role of expectations in processing errors and negative feedback.

Intermolecular potentials based on symmetry-adapted perturbation theory with dispersion energies from time-dependent density-functional calculations.

Abstract: Recently, three of us have proposed a method [Phys. Rev. Lett. 91, 33201 (2003)] for an accurate calculation of the dispersion energy utilizing frequency-dependent density susceptibilities of monomers obtained from time-dependent density-functional theory (DFT). In the present paper, we report numerical calculations for the helium, neon, water, and carbon dioxide dimers and show that for a wide range of intermonomer separations, including the van der Waals and short-range repulsion regions, the method provides dispersion energies with accuracies comparable to those that can be achieved using the current most sophisticated wave-function methods. If the dispersion energy is combined with (i) the electrostatic and first-order exchange interaction energies as defined in symmetry-adapted perturbation theory (SAPT) but computed using monomer Kohn-Sham (KS) determinants, and (ii) the induction energy computed using the coupled KS static response theory, (iii) the exchange-induction and exchange-dispersion energies computed using KS orbitals and orbital energies, the resulting method, denoted by SAPT(DFT), produces very accurate total interaction potentials. For the helium dimer, the only system with nearly exact benchmark values, SAPT(DFT) reproduces the interaction energy to within about 2% at the minimum and to a similar accuracy for all other distances ranging from the strongly repulsive to the asymptotic region. For the remaining systems investigated by us, the quality of the SAPT(DFT) interaction energies is so high that these energies may actually be more accurate than the best available results obtained with wave-function techniques. At the same time, SAPT(DFT) is much more computationally efficient than any method previously used for calculating the dispersion and other interaction energy components at this level of accuracy.

How dynamics, management, and governance of resource deployments influence firm‐level performance

Abstract: To help understand how firms develop and maintain dynamic capabilities, we examine the effects of the dynamics, management, and governance of R & D and marketing resource deployments on firm-level economic performance. In a sample of technology-based entrepreneurial firms, we find that a history of increased investments in marketing is an enduring source of competitive advantage. We also find that managers' firm-specific experience positively moderates the relationship between R & D deployment intensity and economic returns. In addition, institutional ownership boosts economic returns from marketing deployments by subjecting these deployments to increased scrutiny and by sending positive signals to the market about the firm. Copyright © 2005 John Wiley & Sons, Ltd.

Relaxed Averaged Alternating Reflections for Diffraction Imaging

Abstract: We report on progress in algorithms for iterative phase retrieval. The theory of convex optimization is used to develop and to gain insight into counterparts for the nonconvex problem of phase retrieval. We propose a relaxation of averaged alternating reflectors and determine the fixed-point set of the related operator in the convex case. A numerical study supports our theoretical observations and demonstrates the effectiveness of the algorithm compared to the current state of the art.