Showing papers by "University of Texas at Dallas published in 2004"
TL;DR: By introducing twist during spinning of multiwalled carbon nanotubes from nanotube forests to make multi-ply, torque-stabilized yarns, this work achieves yarn strengths greater than 460 megapascals, nearly as tough as fibers used for bulletproof vests.
Abstract: By introducing twist during spinning of multiwalled carbon nanotubes from nanotube forests to make multi-ply, torque-stabilized yarns, we achieve yarn strengths greater than 460 megapascals. These yarns deform hysteretically over large strain ranges, reversibly providing up to 48% energy damping, and are nearly as tough as fibers used for bulletproof vests. Unlike ordinary fibers and yarns, these nanotube yarns are not degraded in strength by overhand knotting. They also retain their strength and flexibility after heating in air at 450°C for an hour or when immersed in liquid nitrogen. High creep resistance and high electrical conductivity are observed and are retained after polymer infiltration, which substantially increases yarn strength.
1,653 citations
TL;DR: This paper presents two extensions to the coded cooperation framework, which increase the diversity of coded cooperation in the fast-fading scenario via ideas borrowed from space-time codes and investigates the application of turbo codes to this framework.
Abstract: When mobiles cannot support multiple antennas due to size or other constraints, conventional space-time coding cannot be used to provide uplink transmit diversity. To address this limitation, the concept of cooperation diversity has been introduced, where mobiles achieve uplink transmit diversity by relaying each other's messages. A particularly powerful variation of this principle is coded cooperation. Instead of a simple repetition relay, coded cooperation partitions the codewords of each mobile and transmits portions of each codeword through independent fading channels. This paper presents two extensions to the coded cooperation framework. First, we increase the diversity of coded cooperation in the fast-fading scenario via ideas borrowed from space-time codes. We calculate bounds for the bit- and block-error rates to demonstrate the resulting gains. Second, since cooperative coding contains two code components, it is natural to apply turbo codes to this framework. We investigate the application of turbo codes in coded cooperation and demonstrate the resulting gains via error bounds and simulations.
956 citations
TL;DR: This article found that teacher mobility is much more strongly related to characteristics of the students, particularly race and achievement, than to salary, although salary exerts a modest impact once compensating differentials are taken into account.
Abstract: Many school districts experience difficulties attracting and retaining teachers, and the impending retirement of a substantial fraction of public school teachers raises the specter of severe shortages in some public schools. Schools in urban areas serving economically disadvantaged and minority students appear particularly vulnerable. This paper investigates those factors that affect the probabilities that teachers switch schools or exit the public schools entirely. The results indicate that teacher mobility is much more strongly related to characteristics of the students, particularly race and achievement, than to salary, although salary exerts a modest impact once compensating differentials are taken into account.
943 citations
TL;DR: Extending previous theorizing on cultural diversity's organizational effects by integrating value-in-diversity and social identity perspectives with the framework of Blau's (1977) theory of heterog...
Abstract: Extending previous theorizing on cultural diversity's organizational effects by integrating value-in-diversity and social identity perspectives with the framework of Blau's (1977) theory of heterog...
734 citations
TL;DR: A review of electrochromic (EC) polymers and their applications in absorption/transmission, reflective, and patterned ECDs is presented in this article, where fundamental properties of EC materials such as optical contrast, coloration efficiency, switching speed, and stability are described along with the commonly used characterization methods.
Abstract: A review of electrochromic (EC) polymers and their applications in absorption/transmission, reflective, and patterned electrochromic devices (ECDs) is presented. Fundamental properties of EC materials such as optical contrast, coloration efficiency, switching speed, and stability are described along with the commonly used characterization methods. The origin of electrochromism in conjugated polymers is explained in terms of the electronic structure changes in the backbone upon doping/dedoping. The ability to tailor the EC properties of conjugated polymers and tune their color states via modification of the polymer structure is demonstrated. Multicolor electrochromic materials can be obtained by substitution of a parent polymer and controlled polymerization of comonomers and with blends and laminates of homopolymers. Absorption/transmission-type ECDs from complementarily colored polymers and reflective-type ECDs on metalized substrates are illustrated with several examples from the literature. Finally, sev...
732 citations
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TL;DR: The authors showed that accountability systems introduced during the 1990s had a clear positive impact on student achievement, but this single policy instrument did not lead to any narrowing in the black-white achievement gap (though it did narrow the Hispanic white achievement gap).
Abstract: The leading school reform policy in the United States revolves around strong accountability of schools with consequences for performance. The federal government's involvement through the No Child Left Behind Act of 2001 reinforces the prior movement of many states toward policies based on measured student achievement. Analysis of state achievement growth as measured by the National Assessment of Educational progress shows that accountability systems introduced during the 1990s had a clear positive impact on student achievement. This single policy instrument did not, however, also lead to any narrowing in the black-white achievement gap (though it did narrow the Hispanic-white achievement gap). Moreover, the balck-white gap appears to have been harmed over the decade by increasing minority concentrations in the schools. An additional issue surrounding stronger accountability has been a concern about unintended consequences related to such things as higher exclusion rates from testing, increased drop-out rates, and the like. Our analysis of special education placement rates, a frequently identified area of concern, does not show any responsiveness to the introduction of accountability systems.
723 citations
TL;DR: The association between the initial tidal volume and the development of acute lung injury suggests that ventilator-associated lung injury may be an important cause of this syndrome.
Abstract: Objective:Although ventilation with small tidal volumes is recommended in patients with established acute lung injury, most others receive highly variable tidal volume aimed in part at normalizing arterial blood gas values. We tested the hypothesis that acute lung injury, which develops after the in
700 citations
TL;DR: Evidence is presented that TRAF6 ubiquitin ligase and TAK1 protein kinase mediate IKK activation by BCL10 and MALT1, and a small fraction of these proteins form high molecular weight oligomers, which culminates in NF-kappaB activation in T lymphocytes.
686 citations
TL;DR: Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nan ofibers.
Abstract: Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials.
648 citations
TL;DR: In this article, the authors used market valuations to assess the impact of security breaches on the market value of breached firms and found that the security developers in the sample realized an average abnormal return of 1.36 percent during the two-day period after the announcement.
Abstract: Assessing the value of information technology (IT) security is challenging because of the difficulty of measuring the cost of security breaches. An event-study analysis, using market valuations, was used to assess the impact of security breaches on the market value of breached firms. The information-transfer effect of security breaches (i.e., their effect on the market value of firms that develop security technology) was also studied. The results show that announcing an Internet security breach is negatively associated with the market value of the announcing firm. The breached firms in the sample lost, on average, 2.1 percent of their market value within two days of the announcement--an average loss in market capitalization of $1.65 billion per breach. Firm type, firm size, and the year the breach occurred help explain the cross-sectional variations in abnormal returns produced by security breaches. The effects of security breaches are not restricted to the breached firms. The market value of security developers is positively associated with the disclosure of security breaches by other firms. The security developers in the sample realized an average abnormal return of 1.36 percent during the two-day period after the announcement--an average gain of $1.06 billion in two days. The study suggests that the cost of poor security is very high for investors. rity, information technology security management, Internet security, security breach an-
628 citations
TL;DR: Using Monte Carlo simulations it is shown that estimation algorithms can come close to attaining the limit given in the expression and explicit quantitative results are provided to show how the limit of the localization accuracy is reduced by factors such as pixelation of the detector and noise sources in the detection system.
TL;DR: In this paper, surface oxidation of a carbon black commonly used in proton exchange membrane (PEM) fuel cells was studied following potentiostatic treatments up to 120 h at potentials from 0.6 to 1.2 V at room temperature and 65°C.
Abstract: Electrochemical surface oxidation of Vulcan XC-72, a carbon black commonly used in proton exchange membrane (PEM) fuel cells, was studied following potentiostatic treatments up to 120 h at potentials from 0.6 to 1.2 V at room temperature and 65°C. Surface oxidation was followed using cyclic voltammetry (CV), thermal gravimetric analysis coupled to on-line mass spectrum-etry (TGA-MS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The analytical techniques all indicate significant surface oxidation occurred during the first 16 h of 1.2 V potential holds at room temperature and a slow increase in surface oxide formation thereafter. An identification of ether, carbonyl, and carboxyl surface oxide species was made by deconvolution of XPS spectra and assigning these functional groups to the observed TGA-MS CO 2 evolution peaks (150-750°C). An increase in CO evolution (>800°C) determined by TGA-MS was consistent with electrochemical CV data, which detected electroactive hydroquinone/quinone species; these electrochemically detected species were a minor fraction of the electrochemically generated surface oxides. Potential holds at 1.0 V at room temperature only resulted in slight oxidation of Vulcan XC-72. However, experiments at 65°C showed clear signs of surface oxidation after only 16 h at potentials ≥0.8 V, verifying that surface oxides can be generated under simulated PEM fuel cell conditions. Overall, these results suggest that changes in component hydrophobicity, driven by carbon surface oxidation, are an important factor in determining long-term PEM performance instability and decay.
TL;DR: In this article, two general mechanisms are recognized: induced and spontaneous nucleation of subduction zones, i.e., induced nucleation (INSZ) responds to continuing plate convergence following jamming of a subduction zone by buoyant crust.
TL;DR: In this paper, the authors present a single-chip fully compliant Bluetooth radio fabricated in a digital 130-nm CMOS process, which is compatible with digital deep-submicron CMOS processes and can be readily integrated with a digital baseband and application processor.
Abstract: We present a single-chip fully compliant Bluetooth radio fabricated in a digital 130-nm CMOS process. The transceiver is architectured from the ground up to be compatible with digital deep-submicron CMOS processes and be readily integrated with a digital baseband and application processor. The conventional RF frequency synthesizer architecture, based on the voltage-controlled oscillator and the phase/frequency detector and charge-pump combination, has been replaced with a digitally controlled oscillator and a time-to-digital converter, respectively. The transmitter architecture takes advantage of the wideband frequency modulation capability of the all-digital phase-locked loop with built-in automatic compensation to ensure modulation accuracy. The receiver employs a discrete-time architecture in which the RF signal is directly sampled and processed using analog and digital signal processing techniques. The complete chip also integrates power management functions and a digital baseband processor. Application of the presented ideas has resulted in significant area and power savings while producing structures that are amenable to migration to more advanced deep-submicron processes, as they become available. The entire IC occupies 10 mm/sup 2/ and consumes 28 mA during transmit and 41 mA during receive at 1.5-V supply.
08 Nov 2004
TL;DR: The disposable plastic biochip incorporating smart passive microfluidics with embedded on-chip power sources and integrated biosensor array for applications in clinical diagnostics and point-of-care testing and a handheld analyzer capable of multiparameter detection of clinically relevant parameters is developed.
Abstract: This paper presents the development of a disposable plastic biochip incorporating smart passive microfluidics with embedded on-chip power sources and integrated biosensor array for applications in clinical diagnostics and point-of-care testing. The fully integrated disposable biochip is capable of precise volume control with smart microfluidic manipulation without costly on-chip microfluidic components. The biochip has a unique power source using on-chip pressurized air reservoirs, for microfluidic manipulation, avoiding the need for complex microfluidic pumps. In addition, the disposable plastic biochip has successfully been tested for the measurements of partial oxygen concentration, glucose, and lactate level in human blood using an integrated biosensor array. This paper presents details of the smart passive microfluidic system, the on-chip power source, and the biosensor array together with a detailed discussion of the plastic micromachining techniques used for chip fabrication. A handheld analyzer capable of multiparameter detection of clinically relevant parameters has also been developed to detect the signals from the cartridge type disposable biochip. The handheld analyzer developed in this work is currently the smallest analyzer capable of multiparameter detection for point-of-care testing.
TL;DR: Statistical test results indicate that performance evaluations are influenced by strategically linked measures more than non‐linked measures only when evaluators are provided detailed information about business unit strategies.
Abstract: The balanced scorecard provides a framework for selecting multiple performance measures that supplement traditional financial measures with operating measures of customer satisfaction, internal processes, and learning and growth activities. An essential aspect of the balanced scorecard lies in its articulation of the linkage between performance measures and business strategy. This study conducts an experiment to assess how individuals' evaluations of the performance of business unit managers depend on strategically linked performance measures of a balanced scorecard. Statistical test results indicate that performance evaluations are influenced by strategically linked measures more than non‐linked measures only when evaluators are provided detailed information about business unit strategies. The results also confirm Lipe and Salterio's (2000) finding that evaluators rely more on common measures than on unique measures. Evaluators rely more on strategically linked measures than on common measures when they ...
TL;DR: In this paper, a variation of the CAPM model is derived to capture this observation as well as to draw testable implications, finding that idiosyncratic volatility is useful in explaining cross-sectional expected returns.
Abstract: The traditional CAPM approach argues that only market risk should be incorporated into asset prices and command a risk premium. This result may not hold, however, if some investors can not hold the market portfolio. For example, if one group of investors fails to hold the market portfolio for exogenous reasons, the remaining investors will also be unable to hold the market portfolio. Therefore, idiosyncratic risk could also be priced to compensate rational investors for an inability to hold the market portfolio. A variation of the CAPM model is derived to capture this observation as well as to draw testable implications. Under both the Fama and MacBeth (1973) and Fama and French (1992) testing frameworks, we find that idiosyncratic volatility is useful in explaining cross-sectional expected returns. We also discover that returns from constructed portfolios directly co-vary with idiosyncratic risk hedging portfolio returns.
TL;DR: This commentary on the Bass Model shall discuss some background and history of the development of the paper, the reasons why the model has been influential, some important extensions of the model, some Examples of applications, and some examples of the frontiers of research involving the Bass model.
Abstract: The paper that I authored and that was published in Management Science in 1969 (Bass 1969) has become widely known as the "Bass Model" (see Morrison and Raju 2004). The model of the diffusion of new products and technologies developed in the paper is one of the most widely applied models in management science. It was especially gratifying for me to learn that INFORMS members have voted the "Bass Model" paper as one of the Top 10 Most Influential Papers published in the 50-year history of Management Science in connection with the 50th anniversary of the journal. In this commentary on the paper I shall discuss some background and history of the development of the paper, the reasons why the model has been influential, some important extensions of the model, some examples of applications, and some examples of the frontiers of research involving the Bass Model. In the current period, in which there is much discussion about the marketing of applications of management science methods and practice, I hope that this commentary will be useful in providing insights about some of the properties of models that will be applied.
TL;DR: It is concluded that one renal manifestation of insulin resistance may be low urinary ammonium and pH, which can result in increased risk of uric acid precipitation despite normouricosuria.
TL;DR: In this article, the authors examined the effects of subjective bonuses on employee pay satisfaction and firm performance using data from a sample of 526 department managers in 250 car dealerships and found that subjective bonuses are used to complement perceived weaknesses in quantitative performance measures and to provide employees insurance against downside risk in their pay.
Abstract: This study examines two questions: When do firms make greater use of subjectivity in awarding bonuses? What are the effects of subjectivity on employee pay satisfaction and firm performance? We examine these questions using data from a sample of 526 department managers in 250 car dealerships. First, the findings suggest that subjective bonuses are used to complement perceived weaknesses in quantitative performance measures and to provide employees insurance against downside risk in their pay. Specifically, use of subjective bonuses is positively related to: (1) the extent of long‐term investments in intangibles; (2) the extent of organizational interdependencies; (3) the extent to which the achievability of the formula bonus target is both difficult and leads to significant consequences if not met; and (4) the presence of an operating loss. Second, we find that the effects of subjective bonuses on pay satisfaction, productivity, and profitability are larger the greater the manager's tenure, consistent wit...
TL;DR: This article applied the three-factor model to A-shares in Chinese equity market, one of the fastest growing markets ever, and found that size was found to explain the cross-sectional differences in returns, but contrary to findings for the U.S. market, the book to market ratio was not helpful.
Abstract: This study applied the three-factor model to A-shares in the Chinese equity market, one of the fastest growing markets ever. The sample period is July 1996 through June 2002. Size was found to explain the cross-sectional differences in returns, but contrary to findings for the U.S. market, the book-to-market ratio was not helpful. As in the U.S. experience, beta did not account for return differences among individual stocks. Because of the speculative nature of Chinese capital markets, the large proportion of government-owned shares, and the low quality of the companies' accounting information, the free float (that is, the ratio of shares in a public company that are freely available to the investing public to total company shares) was added to the study to serve as a proxy for company fundamentals. The three-factor model that included proxies for size and free float significantly increased the explanatory power of the market model—from 81 percent to 90 percent.
TL;DR: The simple techniques involoved in obtaining films of single-walled carbon nanotubes (SWNT) bundles could help facilitate the rapid fabrication of transparent, flexible electronic devices, heralding what promises to be a new approach towards the development of next-generation optoelectronic devices.
Abstract: A convenient method to obtain patterns of films of single-walled carbon nanotubes (SWNT) bundles on flexible plastic is described Using the Line Patterning method SWNT films of thickness ranging from ∼300−1500 nm can be obtained from aqueous surfactant-supported dispersions of chemically purified SWNT bundles synthesized by the pulsed-laser ablation method These films are strongly adherent and are competitive in performance with commercially available films of indium-tin-oxide (ITO) on plastics For example, an ∼1500 thick film of SWNT on poly(ethylene terephthalate) (PET) shows a surface resisitvity of ∼80 Ω/sq, optical transparency >80%, and robust flexibility Unlike ITO/PET, films of SWNT/PET can be folded and bent to a crease without cracking The simple techniques involoved in obtaining these films (ie, those without requiring lithography or ink-jet printing) could help facilitate the rapid fabrication of transparent, flexible electronic devices, heralding what promises to be a new approach towa
TL;DR: This paper found that by 36 months of age, large net social class and Black-White vocabulary knowledge knowledge gaps have already emerged, and these widened until 60 months and then cease widening.
TL;DR: While calculating ROSI seems taxing, increasing possibility and scope of IT security breaches due to increasing interconnectivity makes it imperative, as the number of security breaches increases exponentially according to the CERT, so does their cost.
Abstract: A ssessing the return on investment has always been a sticking point for technology investments. Similar to IT productivity paradox [1], Return on Security Investment (ROSI) has become a controversial topic due to immense growth of e-businesses. Defining the value of security investments is challenging. However, it is clear that “security consumers will need to understand the variables that define ROSI and endure the discomfort of assigning dollar values to quantities that currently are extremely ill-defined” [12]. While calculating ROSI seems taxing, increasing possibility and scope of IT security breaches due to increasing interconnectivity makes it imperative. As the number of security breaches increases exponentially according to the CERT (see Table 1) so does their cost. The 2003 CSI/FBI Computer Crime and Security Survey revealed that 56% of respondents detected security breaches. Information Week and PricewaterhouseCoopers LLP estimated that computer viruses and hacking took a $1.6 trillion toll on the worldwide economy and $266 billion in the U.S. [5]. Security breaches have a significant impact on the market values of firms too. We have estimated that compromised firms, on average, lost approximately 2.1% of their market values within two days surrounding security breaches [3]. This translates to an average loss of $1.65 billion in market capitalization per incident. Moitra and Konda [10] found that as investment in security increases the survivability of firms from security breaches increases rapidly at first and then more slowly at higher levels of investment. Undoubtedly these figures point to the importance of more studies on the economics and management of IT security investments. Fear, uncertainty, and doubt (FUD) strategy has been used for years to sell investments in security [1]. However, according to Earthlink security experts Lisa Ekman and Lisa Hoyt, “Crying wolf may get the first firewall, but over the long run, you need a more well-rounded perspective” [12]. Since diverse security techA Model for Evaluating IT Security Investments
TL;DR: The authors disentangles the disruption effects of moves from changes in SQ and identifies the negative externality movers impose on other students, and shows that student turnover is associated with a substantial cost for movers and non-movers alike.
TL;DR: Return to scale (RTS) in data envelopment analysis (DEA) for each of the presently available types of models is discussed for each type of model and relations between the results for the different models are established.
TL;DR: In this paper, the authors investigate learning-by-doing in the newsvendor inventory problem and find that this kind of hands-on learning is more effective than providing newsvendors with an upfront statistical analysis that includes the expected profitability of orders.
Abstract: We investigate learning-by-doing in the newsvendor inventory problem. An earlier study observed that decision makers tend to anchor orders away from the expected profit maximizing order. We study enhancements to the learning environment suggested by the behavioral literature. Extended experience improves performance some but feedback enhancements do little. A manipulation with a strong positive effect constrains inventory policy to a standing order for multiple periods, precluding responses to short term fluctuations in demand. With experience, our newsvendors collectively achieve over 90% of expected profit potential. It turns out that this kind of hands-on learning is more effective than providing newsvendors with an upfront statistical analysis that includes the expected profitability of orders. The results speak to the kinds of training and decision support that might improve the performance of inventory decision makers.
TL;DR: In this article, the authors considered the current drivers of the observed ion and electron drifts in the low and middle latitudes of the ionosphere and provided an overall understanding of the governing principles.
TL;DR: In this paper, the authors quantified the impact of civil wars on economic growth at home and in nearby countries, using three alternative measures of nearness (contiguity, length of contiguous borders, and distance of closest approach) to capture the spatial dispersion of civil war consequences.
Abstract: This article quantifies the impact of civil wars on economic growth at home and in nearby countries. Three alternative measures of nearness—contiguity, length of contiguous borders, and distance of closest approach—are used to capture the spatial dispersion of civil war consequences. We present short-run panel estimates (at five-year intervals) and long-run (1961‐95) panel estimates for the world. Generally, the distance measures, novel to this study, and not contiguity provides the most accurate measure of the diffusion of the negative economic consequences of civil wars on other countries. Unlike earlier studies, we also investigate the temporal influence of civil wars on growth at home and in nearby countries. Both the duration and the timing of civil wars have an economic impact.
TL;DR: One of the best-established molecular mechanisms of addiction is upregulation of the cAMP second messenger pathway, which occurs in many neuronal cell types in response to chronic administration of opiates or other drugs of abuse as discussed by the authors.
Abstract: Addiction can be viewed as a form of drug-induced neural plasticity. One of the best-established molecular mechanisms of addiction is upregulation of the cAMP second messenger pathway, which occurs in many neuronal cell types in response to chronic administration of opiates or other drugs of abuse. This upregulation and the resulting activation of the transcription factor CREB appear to mediate aspects of tolerance and dependence. In contrast, induction of another transcription factor, termed DeltaFosB, exerts the opposite effect and may contribute to sensitized responses to drug exposure. Knowledge of these mechanisms could lead to more effective treatments for addictive disorders.