Showing papers by "North Carolina State University published in 1995"

Firm Performance and Mechanisms to Control Agency Problems between Managers and Shareholders

Abstract: This paper examines the use of seven mechanisms to control agency problems between managers and shareholders. These mechanisms are: shareholdings of insiders, institutions, and large blockholders; use of outside directors; debt policy; the managerial labor market; and the market for corporate control. We present direct empirical evidence of interdependence among these mechanisms in a large sample of firms. This finding suggests that cross-sectional OLS regressions of firm performance on single mechanisms may be misleading. Indeed, we find relations between firm performance and four of the mechanisms when each is included in a separate OLS regression. These are insider shareholdings, outside directors, debt, and corporate control activity. Importantly, the effect of insider shareholdings disappears when all of the mechanisms are included in a single OLS regression, and the effects of debt and corporate control activity also disappear when estimations are made in a simultaneous systems framework. Together, these findings are consistent with optimal use of each control mechanism except outside directors.

The silica balance in the world ocean: a reestimate.

Abstract: The net inputs of silicic acid (dissolved silica) to the world ocean have been revised to 6.1 +/- 2.0 teramoles of silicon per year (1 teramole = 10(12) moles). The major contribution (about 80 percent) comes from rivers, whose world average silicic acid concentration is 150 micromolar. These inputs are reasonably balanced by the net ouputs of biogenic silica of 7.1 +/- 1.8 teramoles of silicon per year in modern marine sediments. The gross production of biogenic silica (the transformation of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 +/- 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross production in surface waters) averages 3 percent. In the world ocean the residence time of silicon, relative to total biological uptake in surface waters, is about 400 years.

Path Dependence, Lock-In, and History

Abstract: Do economies and markets make remediable errors in the choice of products? Does the economy "lock-in" to these incorrect choices even when the knowledge that these choices are incorrect is readily available? The literature of path dependence may be understood to argue that these lock-ins and errors occur, even in a world characterized by voluntary decisions and individually maximizing behavior. In this paper we examine path dependence and illustrate three different forms of the term, each having a different implication regarding market errors and lock-in. Two of these meanings are common in the economy but provide no support for the claims that remediable errors occur. The third meaning, which does imply irremediable error, we show to be based on restrictive assumptions that are likely to be overcome in the real world. The analysis is illustrated by examining the market's choice of videorecorder formats.

Path Dependence, Lock-In, and History

Abstract: Do economies and markets make remediable errors in the choice of products? Does the economy "lock-in" to these incorrect choices even when the knowledge that these choices are incorrect is readily available? The literature of path dependence may be understood to argue that these lock-ins and errors occur, even in a world characterized by voluntary decisions and individually maximizing behavior. In this article, we examine path dependence and illustrate three different forms of the term, each having a different implication regarding market errors and lock-in. Two of these meanings are common in the economy but provide no support for the claims that remediable errors occur. The third meaning, which does imply irremediable error, we show to be based on highly restrictive and implausible assumptions. The analysis is illustrated by examining the market's choice of video-recorder formats. Path dependence has been offered as an alternative analytical perspective for economics, a revolutionary reformulation of the neoclassical paradigm. Brian Arthur, a leading figure in this literature, distinguishes between "conventional economics," which largely avoids increasing returns or path dependence, and the new "positive feedback economics," which embraces them (Arthur, 1990: 99). Before we stroll too far along the path dependence path, however, it makes sense to stop, take stock, and figure out where that path is leading us. The claim for path dependence is that a minor or fleeting advantage or a seemingly inconsequential lead for some technology, product, or standard can have important and irreversible influences on the ultimate market allocation of resources, even in a world characterized by voluntary decisions and individually maximizing behavior. The path dependence literature comes to us accompanied and motivated by amathematical literature of nonlinear dynamic models, known as chaos or complexity models, for which a key finding is "sensitive dependence

The image processing handbook (2nd ed.)

Abstract: A device for injecting medicament without the use of a needle is disclosed wherein medicament is expelled from the device at high pressure, caused to break the skin of a patient, and appropriately forced into the patient's body. A preferred embodiment of the present invention is a jet injector having a piston slidably movable within a medicament chamber to selectively change the volume of the medicament chamber and a mechanism for advancing the piston including releasably held springs which may be compressed by a winding mechanism or pressurized fluid. Medicament is provided to the medicament chamber from a medicament container mounted on the injector by a container holder assembly including flexible fingers that can be caused to grasp the pierceable cap of the medicament container. Medicament is then selectively directed from the medicament container to the medicament chamber by valving which, in a first position, interacts with a safety to provide air to the medicament container during the filling of the medicament chamber and, in a second position, allows injection into the patient while the safety prevents movement of the valve member from the second position during injection and simultaneously blocks air communication to the medicament container.

Multiuser detection for CDMA systems

Abstract: Spread spectrum-based code division multiple access (CDMA), has taken on a significant role in cellular and personal communications. We concentrate on direct sequence CDMA (DS/CDMA). We show that there is a natural modification of the present systems that is potentially capable of significant capacity increases. By "natural modification" we mean a modification that can be made conceptually clear, not that it is easy to implement. Indeed, the optimal multiuser detector is much too complex and most of the present research addresses the problem of simplifying multiuser detection for implementation. The objective of the article is to make the basic idea intuitive and then show how investigators are trying to reduce the idea to practice. We also indicate multiuser receiver structures with potentially acceptable levels of complexity and address potential obstacles for achieving theoretically predicted performance in practice. As a result of these investigations, an answer to the following question is expected. Is there a suboptimal multiuser detector that is cost effective to build with significant enough performance advantage over present day systems? A definitive answer is not yet available. >

The Small Nucleolar RNAs

Abstract: The present review summarizes key progress made in characterizing the small nucleolar RNAs (snoRNAs) of eukaryotic cells. Recent studies have shown snoRNA populations to be substantially more complex than anticipated initially. Many newly discovered snoRNAs are synthesized by an intron-processing pathway, which provides a potential mechanism for coordinating nuclear RNA synthesis. Several snoRNAs and snoRNP proteins are known to be needed for processing of ribosomal RNA, but precise functions remain to be defined. In principle, snoRNAs could have several roles in ribosome synthesis including: folding of pre-rRNA, formation of rRNP substrates, catalyzing RNA cleavages, base modification, assembly of pre-ribosomal subunits, and export of product rRNP particles.

Strongly homotopy Lie algebras

Abstract: (1995). Strongly homotopy lie algebras. Communications in Algebra: Vol. 23, No. 6, pp. 2147-2161.

Integration of chemical and biological oxidation processes for water treatment: Review and recommendations

Abstract: The literature of studies which used a combination of chemical and biological degradation (usually oxidative) of organic contaminants in water is reviewed. Beneficial effects of such two-step treatments are commonly reported; these results, primarily from laboratory studies, suggest potential advantages for water treatment via process integration rather than single technology processing. Four wastewater contaminant types are identified which can benefit from combined processes: 1.) recalcitrant compounds 2.) biodegradable wastes with small amounts of recalcitrant compounds 3.) inhibitory compounds and 4.) intermediate dead-end products. The design key for such two-step systems lies in choosing processes that complement each other and lead to a synergistic effect. Predicting this performance outcome requires knowledge of the physical, chemical and biological properties of the major reaction intermediates and their susceptibility to degradation by each process. Economic, physical and technological limitations of the individual processes should be recognized for design of more effective and economical integrated processes. The ultimate treatment goal, whether specific pollutant removal or reduction of a global parameter such as TOC, must be known so that appropriate and complementary processes can be utilized. More work is needed concerning the degradation kinetics within the combined process, from initial attack of the primary compound through dynamics of intermediates and on to total mineralization.

Learning and Teaching Styles In Foreign and Second Language Education

Abstract: The ways in which an individual characteristically acquires, retains, and retrieves information are collectively termed the individual's learning style. Mismatches often occur be- tween the learning styles of students in a language class and the teaching style of the instructor, with unfortunate effects on the quality of the students' learning and on their attitudes toward the class and the subject. This paper defines several dimensions of learning style thought to be particularly relevant to foreign and second language education, outlines ways in which certain learning styles are favored by the teaching styles of most language instructors, and suggests steps to address the educational needs of all students in foreign language classes. Students learn in many ways—by seeing and hearing; reflecting and acting; reasoning logi- cally and intuitively; memorizing and visualiz- ing. Teaching methods also vary. Some instructors lecture, others demonstrate or dis- cuss; some focus on rules and others on ex- amples; some emphasize memory and others understanding. How much a given student learns in a class is governed in part by that stu- dent's native ability and prior preparation but also by the compatibility of his or her charac- teristic approach to learning and the instructor's characteristic approach to teaching. The ways in which an individual character- istically acquires, retains, and retrieves infor- mation are collectively termed the individual's learning style. Learning styles have been extensively discussed in the educational psychology literature (Claxton & Murrell 1987; Schmeck 1988) and specifically in the context

Native defects in gallium nitride

Abstract: The results of an extensive theoretical study of native defects in hexagonal GaN are presented. We have considered cation and anion vacancies, antisites, and interstitials. The computations were carried out using ab initio molecular dynamics in supercells containing 72 atoms. N vacancy introduces a shallow donor level, and may be responsible for the n-type character of as-grown GaN. Due to the wide gap of nitrides, self-compensation effects strongly reduce both n-type and p-type doping efficiencies due to the formation of gallium vacancy and interstitial Ga, respectively.

Chaos in a noisy world: new methods and evidence from time-series analysis

Abstract: Chaos is usually regarded as a distinct alternative to random effects such as environmental fluctuations or external disturbances. We argue that strict separation between chaotic and stochastic dynamics in ecological systems is unnecessary and misleading, and we present a more comprehensive approach for systems subject to stochastic perturbations. The defining property of chaos is sensitive dependence on initial conditions. Chaotic systems are "noise amplifiers" that magnify perturbations; nonchaotic systems are "noise mufflers" that dampen perturbations. We also present statistical methods for detecting chaos in time-series data, based on using nonlinear time-series modeling to estimate the Lyapunov exponent λ, which gives the average rate at which perturbation effects grow (λ > 0) or decay (λ < 0). These methods allow for dynamic noise and can detect low-dimensional chaos with realistic amounts of data. Results for natural and laboratory populations span the entire range from noise-dominated and strongl...

Dust as a standard of space and time in canonical quantum gravity.

Abstract: The coupling of the metric to an incoherent dust introduces into spacetime a privileged dynamical reference frame and time foliation. The comoving coordinates of the dust particles and the proper time along the dust worldlines become canonical coordinates in the phase space of the system. The Hamiltonian constraint can be resolved with respect to the momentum that is canonically conjugate to the dust time. Formal imposition of the resolved constraint as an operator restriction on the quantum states yields a functional Schr\"odinger equation. The ensuing Hamiltonian density has an extraordinary feature: it depends only on the geometric variables, not on the dust coordinates or time. This has three important consequences. First, the functional Schr\"odinger equation can be solved by separating the dust time from the geometric variables. Second, disregarding the standard factor-ordering difficulties, the Hamiltonian densities strongly commute and therefore can be simultaneously defined by spectral analysis. Third, the standard constraint system of vacuum gravity is cast into a form in which it generates a true Lie algebra. The particles of dust introduce into space a privileged system of coordinates that allows the supermomentum constraint to be solved explicitly. The Schr\"odinger equation yields a formally conserved inner product that can be written in terms of either the instantaneous state functionals or the solutions of constraints. Gravitational observables admit a similar dual representation. Examples of observables are given, though neither the intrinsic metric nor the extrinsic curvature are observables. This comes as close as one can reasonably expect to a satisfactory phenomenological quantization scheme that is free of most of the problems of time.

A critical review of ohmic and rectifying contacts for silicon carbide

Abstract: For more than three decades, SiC has been investigated as a wide band gap semiconductor. This paper reviews ohmic and rectifying metal contacts on n- and p-type α- and β-SiC reported throughout that time period. Electrical characteristics, Schottky barrier heights (SBHs), thermal stability, and chemical reactions are discussed. Most metals formed very good rectifying contacts in the as-deposited condition on both n- and p-type 6H-SiC with Schottky barrier heights ⪖ 1 eV. Low ideality factors (n 1100 V) have been displayed in this material. The electrical properties of contacts on 3C-SiC have been more dependent on the quality of the 3C-SiC films, which have been plagued by higher defect densities than 6H-SiC. In general, a partial pinning of the Fermi level has been evidenced by positive correlations, which are less than 1 (≈ 0.2–0.6), between the SBHs and the metal work functions. Ohmic contacts with low contact resistivities (⪕ 10−5 Ω cm2), especially important for high power applications, on any of the SiC polytypes have been exceptionally difficult to achieve. Most of the ohmic contacts have relied on high doping concentrations in combination with annealing at temperatures between 800 and 1300 °C. Annealed Ni and Al have primarily been used in ohmic contact metallizations for n- and p-type SiC, respectively. The tendency of SiC to react with metals to form carbides and/or silicides at potential device operating temperatures ( ∼ 600 °C) can be a problem for potential long term applications at high temperature. These critical issues are discussed along with future perspectives for research approaches.

Integrated heterostructures of Group III-V nitride semiconductor materials including epitaxial ohmic contact, non-nitride buffer layer and methods of fabricating same

Abstract: An integrated heterostructure of Group III-V nitride compound semiconductors is formed on a multicomponent platform which includes a substrate of monocrystalline silicon carbide and a non-nitride buffer layer of monocrystalline zinc oxide. The zinc oxide may be formed by molecular beam epitaxy (MBE) using an MBE effusion cell containing zinc, and a source of atomic oxygen, such as an MBE-compatible oxygen plasma source which converts molecular oxygen into atomic oxygen. An ohmic contact for a semiconductor device formed of Group III-V nitride compound semiconductor materials including a layer of aluminum nitride or aluminum gallium nitride, includes a continuously graded layer of aluminum gallium nitride and a layer of gallium nitride or an alloy thereof on the continuously graded layer. The continuously graded layer eliminates conduction or valence band offsets. A multiple quantum well may also be used instead of the continuously graded layer where the thickness of the layers of gallium nitride increase across the multiple quantum well. The ohmic contacts may be used for Group III-V nitride laser diodes, light emitting diodes, electron emitters, bipolar transistors and field effect transistors.

A Longitudinal Study of Engineering Student Performance and Retention. III. Gender Differences in Student Performance and Attitudes

Abstract: In a continuing study under way at North Carolina State University, a cohort of students took five chemical engineering courses taught by the same instructor in five consecutive semesters. This report examines gender differences in the students’ academic performance, persistence in chemical engineering, and attitudes toward their education and themselves. The women in the study on average entered chemical engineering with credentials equal to or better than those of the men, but exhibited erosion relative to the men in both academic performance and confidence as they progressed through the curriculum. Possible causes of the observed disparities are suggested and remedial measures are proposed.

A likelihood-based approach to capture-recapture estimation of demographic parameters under the robust design.

Abstract: The Jolly-Seber method has been the traditional approach to the estimation of demographic parameters in long-term capture-recapture studies of wildlife and fish species. This method involves restrictive assumptions about capture probabilities that can lead to biased estimates, especially of population size and recruitment. Pollock (1982, Journal of Wildlife Management 46, 752-757) proposed a sampling scheme in which a series of closely spaced samples were separated by longer intervals such as a year. For this "robust design," Pollock suggested a flexible ad hoc approach that combines the Jolly-Seber estimators with closed population estimators, to reduce bias caused by unequal catchability, and to provide estimates for parameters that are unidentifiable by the Jolly-Seber method alone. In this paper we provide a formal modelling framework for analysis of data obtained using the robust design. We develop likelihood functions for the complete data structure under a variety of models and examine the relationship among the models. We compute maximum likelihood estimates for the parameters by applying a conditional argument, and compare their performance against those of ad hoc and Jolly-Seber approaches using simulation.

A branch-current-based state estimation method for distribution systems

Abstract: A branch-current-based three-phase state estimation (SE) method is proposed for distribution systems. The method is tailored for distribution feeders with a few loops. The method is computationally more efficient than the conventional node voltage-based SE methods. To further improve the computational efficiency, it is shown that distribution systems can be reduced without much loss of accuracy in SE. >

Geodetic observations of very rapid convergence and back-arc extension at the Tonga arc

Abstract: THE Earth's most active zone of mantle seismicity arises from the subduction of the Pacific plate at the Tonga trench1. It is not known why this slab generates so many more earthquakes than other subducting slabs worldwide. Above the subduction zone the active Tofua (Tonga) volcanic arc is separated by the V-shaped Lau basin from a remnant arc, the Lau ridge, located at the eastern edge of the Australian plate2. The irregular and discontinuous magnetic lineations within the basin have proven difficult to interpret3,4, and so the regional kinematic framework has been obscure. We report geodetic measurements of crustal motion within the Tonga-Lau system, which reveal the fastest crustal motions yet observed. The Lau basin is opening at a rate which increases northwards to a maximum of ∼160 mm yr−1 No straining is observed within the northern Tonga ridge, suggesting that it comprises part of a rigid microplate. Convergence rates across the Tonga trench increase northwards to a maximum of ∼240 mm yr−1. The extraordinary seismic activity of the subducting slab is probably related to this unusually rapid subduction.

A family of multiuser decision-feedback detectors for asynchronous code-division multiple-access channels

Abstract: It is important to identify simple and reliable interference rejection methods for code-division multiple-access (CDMA) channels, since the conventional matched filter receiver has high error rates, and the optimal detector is too complex. We introduce decision-feedback and partial feedback detectors for asynchronous CDMA channels. Two-stage detectors with decision-feedback in the second stage are also studied. The derivation of the decision-feedback detector is based on spectral factorization which leads to a white-noise channel model. We also describe two implementations of the maximum-likelihood detector for this model. Comparisons among the proposed detectors, the conventional detector, and the linear decorrelating detector are undertaken for several asynchronous CDMA channels. In these examples, high bandwidth efficiency systems are explored, and user energies are varied form being similar to being very different. We find that decision-feedback detectors compare favorably with more complex two-stage methods and maintain good performance under diverse channel conditions. >

Physiological implications of sterol biosynthesis in yeast.

Abstract: Fungi are among the most primitive organisms that synthesize sterols. The fungal sterol, ergosterol, is similar to animal sterol, cholesterol, but with significant structural differences. The genetics and biochemistry for most of the steps in sterol biosynthesis have been studied in the yeast, Saccharomyces cerevisiae. Yet, little is known of the precise physiological roles that sterols play in the cell. Work with strains that are auxotrophic for ergosterol has led to the prediction of at least four growth-dependent functions for sterols. Most of the antifungal compounds in medical and agricultural use affect some aspect of sterol synthesis or function. Extensive studies on the modes of action of those substances and research on the effects of altering sterol metabolism by sterol mutants are providing new insights into sterol functions in the cells. In addition, questioning why fungi require ergosterol rather than the simpler cholesterol provides heuristic impetus for further experimentation.

Self-expressiveness within the family context: psychometric support for a new measure

Abstract: The family appears to be an important setting for learning about emotions and how to express them within a social context. Because of the need for reliable and valid measures of emotional expressiveness in the family, the Self-Expressiveness in the Family Questionnaire (SEFQ) is introduced and evaluated in four studies with 499 mothers and 362 fathers. Factor analyses indicate highly consistent patterns of loadings for a two-factor solution across the four studies. The resulting positive and negative scales are highly internally consistent and stable over time. Evidence of good convergent, discriminant, and construct validity was obtained, and a preliminary short form with good internal consistency and construct validity was also identified. Ideas for future research on marital and parent-child issues are suggested

Simulation-Extrapolation: The Measurement Error Jackknife

Abstract: This article provides theoretical support for our simulation-based estimation procedure, SIMEX, for measurement error models. We do so by establishing a strong relationship between SIMEX estimation and jackknife estimation. A result of our investigation is the identification of a variance estimation method for SIMEX that parallels jackknife variance estimation. Data from the Framingham Heart Study are used to illustrate the variance estimation procedure in logistic regression measurement error models.

Vertical field effect transistors having improved breakdown voltage capability and low on-state resistance

Abstract: A power transistor having high breakdown voltage and low on-state resistance includes a vertical field effect transistor in a semiconductor substrate having a plurality of source, channel, drift and drain regions therein. A trench having a bottom in the drift region and opposing sidewalls which extend adjacent the drift, channel and source regions is also provided in the substrate, at a face thereof. The trench preferably includes an insulated gate electrode therein for modulating the conductivity of the channel and drift regions in response to the application of a turn-on gate bias. The insulated gate electrode includes an electrically conductive gate in the trench and an insulating region which lines a sidewall of the trench adjacent the channel and drift regions. The insulating region has a nonuniform cross-sectional area between the trench sidewall and the gate which enhances the forward voltage blocking capability of the transistor by inhibiting the occurrence of high electric field crowding at the bottom of the trench. The thickness of the insulating region is preferably greater than 1500 Å along the portion of the sidewall which extends adjacent the drift region and less than 750 Å along the portion of the sidewall which extends adjacent the channel region. To provide low on-state resistance, the drift region is also nonuniformly doped to have a linearly graded doping profile which decreases from greater than about 1×10 17 cm -3 to less than about 5×10 -16 cm -3 in a direction from the drain region to the channel region.

Foams: Theory: Measurements: Applications

Abstract: Thin liquid film physics structure, drainage and coalescence of foams and concentrated emulsions foam rheology - the theory and role of interfacial rheological properties experimental results on foam rheology experimental techniques for the characterization of foams fundamental methods for measuring foam stability nonaqueous foams additives for foams foam wet processing in the textile industry foams in personal care products foams in enhanced oil recovery foams for firefighting foams in mineral flotation and separation processes science and technology of silicone antifoams.

Transfer of bovine embryos produced in vivo or in vitro: survival and fetal development.

Abstract: The objectives of the present experiment were to compare survival after transfer of bovine embryos produced in vivo with those produced in vitro and to examine the physical characteristics of fetuses produced from these transfers. Embryos produced in vivo (Holstein x Angus) were recovered from uterine flushings of superovulated heifers 7 days after first artificial insemination, and embryos produced in vitro (Holstein x beef breeds) were collected 7 days after insemination. Embryos were paired by source (in vivo, in vitro), stage (compact morula, blastocyst), and quality grade (excellent = 1, good = 2), and transferred nonsurgically to recipient heifers on Day 7 (+/- 1 day) of the estrous cycle. Pregnancy status was monitored by determination of serum progesterone concentrations, ultrasonography, and palpation through 7 mo of gestation, at which time fetuses were recovered. In comparison with grade 1 embryos produced in vivo, the risk of embryonic death after transfer was similar for grade 2 embryos produced in vivo (p = 0.56) and for grade 1 embryos produced in vitro (p = 0.88). By contrast, grade 2 embryos produced in vitro were at greater (p = 0.04) risk of embryonic death. Embryo loss was associated (p = 0.01) with increased serum concentrations of progesterone in recipients at the time of transfer. At 7 mo of gestation, fetuses from embryos produced in vitro were heavier (p = 0.02) than fetuses from embryos produced in vivo and had skeletal measurements that were disproportionate (p < or = 0.04) to body weight.

Universal assay of vitellogenin as a biomarker for environmental estrogens.

Abstract: Vitellogenin (VTG), the serum phospholipoglycoprotein precursor to egg yolk, is potentially an ideal biomarker for environmental estrogens. This study was undertaken to develop antibodies against conserved regions on the VTG molecule that could form the basis for establishing bioassays to detect estrogen exposure in any oviparous vertebrate. We developed monoclonal antibodies (mAbs) generated against purified rainbow trout (Oncorhynchus mykiss) VTG and selected for the property of specifically recognizing VTG purified from two phylogenetically distant vertebrates, trout and striped bass (Morone saxatilis). Results of enzyme-linked immunosorbent assay and Western blotting indicated that these mAbs specifically recognize purified VTG and VTG or other estrogen-inducible proteins in plasma or serum from representative species of four vertebrate classes (fish, amphibians, reptiles, and birds). All of the mAbs generated were IgM class. A polyclonal antiserum was raised against a synthetic consensus peptide representing the conserved N-terminal amino acid sequence of VTG. The results of Western blotting indicate that this antiserum specifically recognizes VTG in plasma or serum from teleost fish of diverse families. It was used to detect VTG in Western blots of serum from brown bullhead (Ameiurus nebulosus) with cancer (hepatocellular and cholangio-carcinoma) collected from a contaminated industrial site outside of their normal vitellogenic season. Our results indicate that it is feasible to generate antibodies capable of recognizing VTG without regard to species and that development of a universal VTG assay is an achievable goal.

The index of general nonlinear DAEs

Abstract: In the last few years there has been considerable research on differential algebraic equations (DAEs) $F(t, y, y') = 0$ where $F_{y'}$ is identically singular. Much of the mathematical effort has focused on computing a solution that is assumed to exist. More recently there has been some discussion of solvability of DAEs. There has historically been some imprecision in the use of the two key concepts of solvability and index for DAEs. The index is also important in control and systems theory but with different terminology. The consideration of increasingly complex nonlinear DAEs makes a clear and correct development necessary. This paper will try to clarify several points concerning the index. After establishing some new and more precise terminology that we need, some inaccuracies in the literature will be corrected. The two types of indices most frequently used, the differentiation index and the perturbation index, are defined with respect to solutions of unperturbed problems. Examples are given to show that these indices can be very different for the same problem. We define new "maximum indices," which are the maxima of earlier indices in a neighborhood of the solution over a set of perturbations and show that these indices are simply related to each other. These indices are also related to an index defined in terms of Jacobians.