Showing papers by "Virginia Tech published in 2001"

A New Heuristic Optimization Algorithm: Harmony Search

Abstract: Many optimization problems in various fields have been solved using diverse optimization al gorithms. Traditional optimization techniques such as linear programming (LP), non-linear programming (NL...

Academic Tribes and Territories: Intellectual Enquiry and the Cultures of Disciplines

Abstract: Points of departure academic disciplines overlaps, boundaries and specialisms aspects of community life patterns of communication academic careers the wider context implications for theory and practice. Appendix: research issues.

Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology

Abstract: The role of flavonoids as the major red, blue, and purple pigments in plants has gained these secondary products a great deal of attention over the years. From the first description of acid and base effects on plant pigments by Robert Boyle in 1664 to the characterization of structural and

Empirically Supported Psychological Interventions: Controversies and Evidence

Abstract: ▪ Abstract Efforts to increase the practice of evidence-based psychotherapy in the United States have led to the formation of task forces to define, identify, and disseminate information about empirically supported psychological interventions. The work of several such task forces and other groups reviewing empirically supported treatments (ESTs) in the United States, United Kingdom, and elsewhere is summarized here, along with the lists of treatments that have been identified as ESTs. Also reviewed is the controversy surrounding EST identification and dissemination, including concerns abou research methodology, external validity, and utility of EST research, as well as the reliability and transparency of the EST review process.

Switched reluctance motor drives : modeling, simulation, analysis, design, and applications

Abstract: PRINCIPLE OF OPERATION OF THE SWITCH RELUCTANCE MOTOR (SRM) Introduction Background Elementary Operation of the Switch Reluctance Motor Principle of Operation of the Switched Reluctance Motor Derivation of the Relationship Between Inductance and Rotor Position Equivalent Circuit SRM Configurations Linear Switched Reluctance Machines References DERIVATION OF SRM CHARACTERISTICS Introduction Data for Performance Computation Analytic Method for the Computation of Machine Characteristics Computation of Unaligned Inductance Computation of Aligned Inductance Computation of Inductance vs. Rotor Position vs. Excitation Current Comparison of Measured, Analytic and Finite Element Results References DESIGN OF SRM Introduction Derivation of Output Equation Selection of Dimensions Design Verification Operational Limit Selection of Number of Phases Selection of Poles Ratio of Pole-Arc to Pole-Pitch Selection of Pole Base Selection of Pole-Arcs Measurement of Inductance Calculation of Torque Design of Linear Switched Reluctance Machine (LSRM) References CHAPTER 4: CONVERTERS FOR SRM DRIVES Converter Configurations Asymmetric Bridge Converter Asymmetric Converter Variation Single Switch per Phase Converters m Switches and 2m Diodes m Switches and 2m Diodes with Independent Phase Current Control (m+1) Switch and Diode Configurations One Common Switch Configuration Minimum Switch Topology With Variable DC Link Variable DC Link Voltage with Buck Boost Converter Topology 1.5m Switches and Diodes Configuration Comparison of Some Power Converters Two Stage Power Converter Resonant Converter Circuits for Switched Reluctance Motor Drives References CONTROL OF SRM DRIVE Introduction Control Principle Closed Loop Speed Controlled SRM Drive Design of Current Controllers Flux Linkage Controller Torque Control Design of the Speed Controller References MODELING AND SIMULATION OF SRM DRIVE SYSTEM Introduction Modeling Simulation References ACOUSTIC NOISE AND ITS CONTROL IN SRM Introduction Sources of Acoustic Noise in Electrical Machines Noise Sources Noise Mitigation Qualitative Design Measures to Reduce Noise Measurement of Acoustic Noise and Vibrations Future Directions Appendix-1: Derivation of First Mode Frequency of SRM References SENSORLESS OPERATION OF SRM DRIVES Introduction Current Sensing Rotor Position Measurement Methods Rotor Position Estimation References APPLICATION CONSIDERATIONS AND APPLICATIONS Introduction Review of SRM Drive Features for Application Consideration Applications Emerging applications References

Control of nitrogen export from watersheds by headwater streams

Abstract: A comparative 15 N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.

Cooperative Networks and Competitive Dynamics: a Structural Embeddedness Perspective

Abstract: Firms are embedded in networks of cooperative relationships that influence the flow of resources among them. Dynamic resource flows and differentiated structural positions lead to asymmetries and influence firms' competitive behavior toward others in the network. We develop a multilevel conceptual model relating key network properties to competitive action and response. A structural embeddedness perspective with a focus on simultaneous cooperation and competition advances our understanding of competitive dynamics and provides intriguing possibilities for future research.

An empirical investigation of the relationship between change in corporate social performance and financial performance: A stakeholder theory perspective

Abstract: Stakeholder theory provides a framework for investigating the relationship between corporate social performance (CSP) and corporate financial performance. This relationship is investigated by examining how change in CSP is related to change in financial accounting measures. The findings provide some support for a tenet in stakeholder theory which asserts that the dominant stakeholder group, shareholders, financially benefit when management meets the demands of multiple stakeholders. Specifically, change in CSP was positively associated with growth in sales for the current and subsequent year. This indicates that there are short-term benefits from improving CSP. Return on sales was significantly positively related to change in CSP for the third financial period, indicating that long-term financial benefits may exist when CSP is improved.

Using Internet Technology to Deliver a Behavioral Weight Loss Program

Abstract: ContextRapid increases in access to the Internet have made it a viable mode for public health intervention. No controlled studies have evaluated this resource for weight loss.ObjectiveTo determine whether a structured Internet behavioral weight loss program produces greater initial weight loss and changes in waist circumference than a weight loss education Web site.DesignRandomized, controlled trial conducted from April to December 1999.Setting and ParticipantsNinety-one healthy, overweight adult hospital employees aged 18 to 60 years with a body mass index of 25 to 36 kg/m2. Analyses were performed for the 65 who had complete follow-up data.InterventionsParticipants were randomly assigned to a 6-month weight loss program of either Internet education (education; n = 32 with complete data) or Internet behavior therapy (behavior therapy; n = 33 with complete data). All participants were given 1 face-to-face group weight loss session and access to a Web site with organized links to Internet weight loss resources. Participants in the behavior therapy group received additional behavioral procedures, including a sequence of 24 weekly behavioral lessons via e-mail, weekly online submission of self-monitoring diaries with individualized therapist feedback via e-mail, and an online bulletin board.Main Outcome MeasuresBody weight and waist circumference, measured at 0, 3, and 6 months, compared the 2 intervention groups.ResultsRepeated-measures analyses showed that the behavior therapy group lost more weight than the education group (P = .005). The behavior therapy group lost a mean (SD) of 4.0 (2.8) kg by 3 months and 4.1 (4.5) kg by 6 months. Weight loss in the education group was 1.7 (2.7) kg at 3 months and 1.6 (3.3) kg by 6 months. More participants in the behavior therapy than education group achieved the 5% weight loss goal (45% vs 22%; P = .05) by 6 months. Changes in waist circumference were also greater in the behavior therapy group than in the education group at both 3 months (P = .001) and 6 months (P = .005).ConclusionsParticipants who were given a structured behavioral treatment program with weekly contact and individualized feedback had better weight loss compared with those given links to educational Web sites. Thus, the Internet and e-mail appear to be viable methods for delivery of structured behavioral weight loss programs.

A New Measure of Quality of Work Life (QWL) Based on Need Satisfaction and Spillover Theories

Abstract: A new measure of QWL was developed based on need satisfaction and spillover theories The measure was designed to capture the extent to which the work environment, job requirements, supervisory behavior, and ancillary programs in an organization are perceived to meet the needs of an employee We identified seven major needs, each having several dimensions These are: (a) health and safety needs (protection from ill health and injury at work and outside of work, and enhancement of good health), (b) economic and family needs (pay, job security, and other family needs), (c) social needs (collegiality at work and leisure time off work), (d) esteem needs (recognition and appreciation of work within the organization and outside the organization), (e) actualization needs (realization of one's potential within the organization and as a professional), (f) knowledge needs (learning to enhance job and professional skills), and (g) aesthetic needs (creativity at work as well as personal creativity and general aesthetics) The measure's convergent and discriminant validities were tested and the data provided support to the construct validity of the QWL measure Furthermore, the measure's nomological (predictive) validity was tested through hypotheses deduced from spillover theory Three studies were conducted – two studies using university employees and the third using accounting firms The results from the pooled sample provided support for the hypotheses and thus lent some support to the nomological validity to the new measure

The Developmental Psychopathology of Anxiety

Abstract: Anxiety is one of the basic human emotions (Plutchik, 1980) and is present in all persons at some time, often on a daily basis to some degree. Concerns about taking a test or being late for an appointment often indicate anxiety in everyday life. Anxiety has a well-defined progression that is recognizable in infancy and progresses through childhood as an indicator of developmental progress. Anxiety and fear are related and often are used interchangeably. Arguably, anxiety has been described as reflecting concerns about subjective, anticipatory events, while fear has been considered to be in response to objective threatening events. Gray and McNaughton (2000) suggested that fear is a defensive response to a real threat, while anxiety is a defensive response to a perceived threat. This chapter will focus primarily on anxiety as a subjective experience of future events, although it is well known that children may have fears of specific stimuli, such as large animals, loud sounds, and unfamiliar people.

Formation of chiral morphologies through selective binding of amino acids to calcite surface steps

Abstract: Many living organisms contain biominerals and composites with finely tuned properties, reflecting a remarkable level of control over the nucleation, growth and shape of the constituent crystals. Peptides and proteins play an important role in achieving this control. But the general view that organic molecules affect mineralization through stereochemical recognition, where geometrical and chemical constraints dictate their binding to a mineral, seems difficult to reconcile with a mechanistic understanding, where crystallization is controlled by thermodynamic and kinetic factors. Indeed, traditional crystal growth models emphasize the inhibiting effect of so-called 'modifiers' on surface-step growth, rather than stereochemical matching to newly expressed crystal facets. Here we report in situ atomic force microscope observations and molecular modelling studies of calcite growth in the presence of chiral amino acids that reconcile these two seemingly divergent views. We find that enantiomer-specific binding of the amino acids to those surface-step edges that offer the best geometric and chemical fit changes the step-edge free energies, which in turn results in macroscopic crystal shape modifications. Our results emphasize that the mechanism underlying crystal modification through organic molecules is best understood by considering both stereochemical recognition and the effects of binding on the interfacial energies of the growing crystal.

Performance improvements of interleaving VRMs with coupling inductors

Abstract: The multichannel interleaving buck converter with small inductance has proved to be suitable for voltage regulator modules (VRMs) with low voltages, high currents, and fast transients. Integrated magnetic components are used to reduce the size of the converter and improve efficiency. However, the structure of the integrated magnetic requires precise adjustment and is not mechanical stable. This paper proposes integrated coupling inductors between the channels to solve these problems. With the proper design, coupling inductors can improve both the steady-state and dynamic performances of VRMs with easier manufacturing.

Network dynamics and cell physiology

Abstract: Complex assemblies of interacting proteins carry out most of the interesting jobs in a cell, such as metabolism, DNA synthesis, movement and information processing. These physiological properties play out as a subtle molecular dance, choreographed by underlying regulatory networks. To understand this dance, a new breed of theoretical molecular biologists reproduces these networks in computers and in the mathematical language of dynamical systems.

Relationships between land use, spatial scale and stream macroinvertebrate communities

Abstract: 1. The structure of lotic macroinvertebrate communities may be strongly influenced by land-use practices within catchments. However, the relative magnitude of influence on the benthos may depend upon the spatial arrangement of different land uses in the catchment. 2. We examined the influence of land-cover patterns on in-stream physico-chemical features and macroinvertebrate assemblages in nine southern Appalachian headwater basins characterized by a mixture of land-use practices. Using a geographical information system (GIS)/remote sensing approach, we quantified land-cover at five spatial scales; the entire catchment, the riparian corridor, and three riparian ‘sub-corridors’ extending 200, 1000 and 2000 m upstream of sampling reaches. 3. Stream water chemistry was generally related to features at the catchment scale. Conversely, stream temperature and substratum characteristics were strongly influenced by land-cover patterns at the riparian corridor and sub-corridor scales. 4. Macroinvertebrate assemblage structure was quantified using the slope of rank-abundance plots, and further described using diversity and evenness indices. Taxon richness ranged from 24 to 54 among sites, and the analysis of rank-abundance curves defined three distinct groups with high, medium and low diversity. In general, other macroinvertebrate indices were in accord with rank-abundance groups, with richness and evenness decreasing among sites with maximum stream temperature. 5. Macroinvertebrate indices were most closely related to land-cover patterns evaluated at the 200 m sub-corridor scale, suggesting that local, streamside development effectively alters assemblage structure. 6. Results suggest that differences in macroinvertebrate assemblage structure can be explained by land-cover patterns when appropriate spatial scales are employed. In addition, the influence of riparian forest patches on in-stream habitat features (e.g. the thermal regime) may be critical to the distribution of many taxa in headwater streams draining catchments with mixed land-use practices.

Vulnerability : a view from different disciplines

Abstract: Practitioners from different disciplines use different meanings and concepts of vulnerability, which, in turn, have led to diverse methods of measuring it This paper presents a selective review of the literature from several disciplines to examine how they define and measure vulnerability The disciplines include economics, sociology/anthropology, disaster management, environmental science, and health/nutrition Differences between the disciplines can be explained by their tendency to focus on different components of risk, household responses to risk and welfare outcomes In general, they focus either on the risks (at one extreme) or the underlying conditions (or outcomes) at the other Trade-offs exist between simple measurement schemes and rich conceptual understanding

Factors Influencing Numbers of Mycobacterium avium, Mycobacterium intracellulare, and Other Mycobacteria in Drinking Water Distribution Systems

Abstract: Eight water distribution systems were sampled over an 18-month period (528 water and 55 biofilm samples) to measure the frequency of recovery and number of mycobacteria, particularly Mycobacterium avium and Mycobacterium intracellulare, in raw source waters before and after treatment and within the distribution system. The systems were chosen to assess the influence of source water, treatment, and assimilable organic carbon levels on mycobacterial numbers. Overall, mycobacterial recovery from the systems was low (15% of samples). Numbers of mycobacteria ranged from 10 to 700,000 CFU liter(-1). The number of M. avium in raw waters was correlated with turbidity. Water treatment substantially reduced the number of mycobacteria in raw waters by 2 to 4 log units. Mycobacterial numbers were substantially higher in the distribution system samples (average, 25,000-fold) than in those collected immediately downstream from the treatment facilities, indicating that mycobacteria grow in the distribution system. The increase in mycobacterial numbers was correlated with assimilable organic carbon and biodegradable organic carbon levels (r(2) = 0.65, P = 0.03). Although M. intracellulare was seldom recovered from water samples, it was frequently recovered (six of eight systems) in high numbers from biofilms (average, 600 CFU/cm(2)). Evidently, the ecological niches of M. avium and M. intracellulare are distinct.

Spatial, polarization, and pattern diversity for wireless handheld terminals

Abstract: This paper examines the antenna diversity configurations that improve the performance in handheld radios. Experiments using spatial, polarization, and pattern diversity were conducted for both line-of-sight (LOS) and obstructed outdoor and indoor multipath channels that experienced Ricean fading. Antenna separation, polarization, and pattern were varied independently to the extent possible. Envelope correlation, power imbalance, and diversity gain were calculated from the measurements. Diversity performance is measured by diversity gain, which is the difference in signal-to-noise ratio (SNR) between the output of a diversity combiner and the signal on a single branch, measured at a given probability level. Diversity gain increases with decreasing envelope correlation between the antenna diversity branches. However, diversity gain decreases as the power imbalance between diversity branches increases because a branch that has a weak signal has only a small contribution to the combined signal. Diversity gain values of 7-9 dB at the 99% reliability level were achieved in non-line-of-sight (NLOS) channels for all diversity configurations even with very small antenna spacings. The use of polarization diversity reduced polarization mismatches, improving SNR by up to 12 dB even in LOS channels.

Packaging communication: attentional effects of product imagery

Abstract: This article provides a theoretical framework for understanding the communicative effects of product imagery on attention to the brand, specifically, the attentional effects of incorporating a picture or illustration of the product on the packaging of the product. Empirical results from a virtual reality simulation show that package pictures increase shoppers’ attention to the brand. However this effect is contingent, occurring only for low familiarity brands (private‐label brands) within product categories that offer a relatively high level of experiential benefits. These results suggest that package pictures may be especially useful for private label brands and/or lesser tier national brands whose strategic objectives are to improve consumers’ perceptions of the brand and enter the consideration set.

Effects of sampling standardization on estimates of Phanerozoic marine diversification

Abstract: Global diversity curves reflect more than just the number of taxa that have existed through time: they also mirror variation in the nature of the fossil record and the way the record is reported. These sampling effects are best quantified by assembling and analyzing large numbers of locality-specific biotic inventories. Here, we introduce a new database of this kind for the Phanerozoic fossil record of marine invertebrates. We apply four substantially distinct analytical methods that estimate taxonomic diversity by quantifying and correcting for variation through time in the number and nature of inventories. Variation introduced by the use of two dramatically different counting protocols also is explored. We present sampling-standardized diversity estimates for two long intervals that sum to 300 Myr (Middle Ordovician-Carboniferous; Late Jurassic-Paleogene). Our new curves differ considerably from traditional, synoptic curves. For example, some of them imply unexpectedly low late Cretaceous and early Tertiary diversity levels. However, such factors as the current emphasis in the database on North America and Europe still obscure our view of the global history of marine biodiversity. These limitations will be addressed as the database and methods are refined.

An investigation of tourists’ destination loyalty and preferences

Abstract: Investigates the relationship between tourists’ destination loyalty and their preferences as to destination. Destination loyalty is operationally defined as the level of tourists’ perceptions of a destination as a recommendable place. On‐site surveys of Korean outbound travellers were conducted at the Seoul International Airport, South Korea, in March 1997. Of 285 questionnaires collected from Korean outbound travellers, 265 useful questionnaires are analyzed. Multiple regression analysis reveals that three destination preferences, including different culture experiences, safety, and convenient transportation, have a positive relationship with tourist’s loyalty to the destination. Results from a path analysis show that past trip experience affects tourists’ destination preference. The implications and limitations of the study are discussed in the conclusion.

Inter‐biome comparison of factors controlling stream metabolism

Abstract: 'SUMMARY 1. We studied whole-ecosystem metabolism in eight streams from several biomes in North America to identify controls on the rate of stream metabolism over a large geographic range. The streams studied had climates ranging from tropical to cool-temperate and from humid to arid and were all relatively uninfluenced by human disturbances. 2. Rates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) were determined using the open-system, two-station diurnal oxygen change method. 3. Three general patterns in metabolism were evident among streams: (1) relatively high GPP with positive NEP (i.e. net oxygen production) in early afternoon, (2) moderate primary production with a distinct peak in GPP during daylight but negative NEP at all times and (3) little or no evidence of GPP during daylight and a relatively constant and negative NEP over the entire day. ', 4. Gross primary production was most strongly correlated with photosynthetically active radiation (PAR). A multiple regression model that included log PAR and stream water soluble reactive phosphorus (SRP) concentration explained 90% of the variation in log GPP. 5. Ecosystem respiration was significantly correlated with SRP concentration and size of the transient storage zone and, together, these factors,explained 73% of the variation in R. The rate of R was poorly correlated with the rate of GPP. 6. Net ecosystem production was significantly correlated only with PAR, with 53% of the variation in log NEP explained by log PAR. Only Sycamore Creek, a desert stream in Arizona, had positive NEP (GPP: R > I), supporting the idea that streams are generally net sinks rather than net sources of organic matter.

Chivalry and Solidarity in Ultimatum Games

Abstract: We report the results of ultimatum game experiments designed to test for differences in the behavior of women and men. Women's proposals are on average more generous than men's, regardless of the sex of the partner, and women respondents are more likely to accept an offer of a given amount. A given offer is more likely to be accepted if it comes from a woman; we term this result chivalry. Women paired with women almost never failed to reach an agreement; we term this result solidarity. Age, earnings, and race also significantly affect proposals and the rates of rejection.

Branching fraction and photon energy spectrum for b→sγ

Abstract: We have measured the branching fraction and photon energy spectrum for the radiative penguin process b-->s gamma. We find Beta(b-->s gamma) = (3.21+/-0.43+/-0.27(+0.18)(-0.10))x10(-4), where the errors are statistical, systematic, and from theory corrections. We obtain first and second moments of the photon energy spectrum above 2.0 GeV, = 2.346+/-0.032+/-0.011 GeV, and - (2) = 0.0226+/-0.0066+/-0.0020 GeV(2), where the errors are statistical and systematic. From the first moment, we obtain (in the modified minimal subtraction renormalization scheme, to order 1/M(3)(B) and beta(0)alpha(2)(s)) the heavy quark effective theory parameter Lambda = 0.35+/-0.08+/-0.10 GeV.

Bacterial Recognition of Mineral Surfaces: Nanoscale Interactions Between Shewanella and α-FeOOH

Abstract: Force microscopy has been used to quantitatively measure the infinitesimal forces that characterize interactions between Shewanella oneidensis (a dissimilatory metal-reducing bacterium) and goethite (alpha-FeOOH), both commonly found in Earth near-surface environments. Force measurements with subnanonewton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, between a cell and the mineral surface. Energy values [in attojoules (10(-18) joules)] derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions in which electron transfer from bacterium to mineral is expected. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process.

Criteria For Evaluating Usability Evaluation Methods

Abstract: The current variety of alternative approaches to usability evaluation methods (UEMs) designed to assess and improve usability in software systems is offset by a general lack of understanding of the capabilities and limitations of each. Practitioners need to know which methods are more effective and in what ways and for what purposes. However, UEMs cannot be evaluated and compared reliably because of the lack of standard criteria for comparison. In this article, we present a practical discussion of factors, comparison criteria, and UEM performance measures useful in studies comparing UEMs. In demonstrating the importance of developing appropriate UEM evaluation criteria, we offer operational definitions and possible measures of UEM performance. We highlight specific challenges that researchers and practitioners face in comparing UEMs and provide a point of departure for further discussion and refinement of the principles and techniques used to approach UEM evaluation and comparison.

Effects of nonplastic fines on the liquefaction resistance of sands

Abstract: A laboratory parametric study utilizing cyclic triaxial tests was performed to clarify the effects of nonplastic fines on the liquefaction susceptibility of sands. Studies previously published in the literature have reported what appear to be conflicting results as to the effects of silt content on the liquefaction susceptibility of sandy soils. The current study has shown that if the soil structure is composed of silt particles contained within a sand matrix, the resistance to liquefaction of the soil is controlled by the relative density of the soil and is independent of the silt content of the soil. For soils whose structure is composed of sand particles suspended within a silt matrix, the resistance to liquefaction is again controlled by the relative density of the soil, but is lower than for soils with sand-dominated matrices at similar relative densities. In this case, the resistance to liquefaction is essentially independent of the amount and type of sand. These findings suggest the need for further evaluation of the effects of nonplastic fines content upon penetration resistance, and the manner in which this relationship affects the simplified methods currently used in engineering practice to evaluate the liquefaction resistance of silty soils.

Chivalry and solidarity in ultimatum games

Abstract: PHILIP J. GROSSMAN [*] We report the results of ultimatum game experiments designed to test for differences in the behavior of women and men. Women's proposals are on average more generous than men's, regardless of the sex of the partner, and women respondents are more likely to accept an offer of a given amount. A given offer is more likely to be accepted if it comes from a woman; we term this result chivalry. Women paired with women almost never fail to reach an agreement; we term this result solidarity. Age, earnings, and race also significantly affect proposals and the rates of rejection. (JEL C78, C92, J16) Economics has done very badly [explaining] large differences among ethnic groups. This is important ... also for gender differences. Some of this can be due to individual differences, but some of it clearly must be social. Ken Arrow [1] I. INTRODUCTION A question that has occupied social psychologists for many years, and one that economists recently have come to address, is whether the decision-making calculus of individuals differs according to their sex. Evidence from social psychology suggests that, whether by nature or nurture, women behave differently from men in many arenas. [2] While economists naturally tend to focus their attention on economic parameters, economic models of behavior potentially could be expanded to incorporate systematic effects of such characteristics as sex or race. If these characteristics are associated (on average) with differences in the decision-making calculus of individuals, then simpler models that abstract from them will describe and predict less accurately. We consider differences between women and men in bargaining behavior and address two questions: (1) Does the strategy adopted or the offer made or accepted differ systematically by the sex of the decision-maker? (2) Does the sex of the opponent influence a player's strategy choice? In a study of race and gender discrimination in bargaining for a new car, Ayres and Siegelman (1995) address the first question and find significantly different negotiated prices, depending on the gender of the bargainers. They note, "Dealers quoted significantly lower prices to white males than to black or female test buyers using scripted bargaining strategies" (304). Although they find no significant gender-pair effects, in an earlier study Ayres (1991) reports that women receive worse deals from women sellers. Our laboratory study differs from field studies of bargaining behavior in three significant ways. First, the bargaining environment is much simpler: The available bargaining strategies are limited, and the heterogeneity of the bargainers is reduced. This enables us to more clearly observe the strategies chosen by each pair. Second, we can test directly for the effect of gender pairing; a given subject faces all decision environments. Finally, we observe rejection behavior by the bargainers. This allows us to distinguish between payoff-maximizing differences in offers that anticipate rejection rates and costly discrimination. We study the simplest of bargaining games, the ultimatum game, in which two players split a fixed amount of money according to specific rules [3]. The advantage of the ultimatum game over other simple decision environments, such as a prisoners' dilemma or a public good game, is that the ultimatum game allows us to study gender differences from two perspectives. First, the proposer stage of the game is a strategic environment; subjects' payoffs are interdependent, and an unequal proposal carries the risk of rejection. Second, the second (accept-or-reject) stage of the game is a nonstrategic, riskless environment. Our results indicate differences in the behavior of men and women, but the differences are subtle and complex. Our research also provides some preliminary evidence on the effect of other cultural correlates. II. BACKGROUND The conclusion of much psychological research on sex differences is that men tend to be more competitive while women are more cooperative. …