Scattering of thermal He beams by crossed atomic and molecular beams. I. Sensitivity of the elastic differential cross section to the interatomic potential

The ability of diffraction oscillations in atomic beam scattering experiments to uniquely determine interatomic potentials for highly quantal systems is examined. Assumed but realistic potentials are used to generate, by scattering calculations and incorporation of random errors, differential cross sections which are then treated as if they were ’’experimental’’ data. From these, attempts are made to recover the initial potential by varying the parameters of assumed mathematical forms different from the original one, until a best fit to the "experimental" results is obtained. It is found that the region of the interaction potential around the van der Waals minimum is accurately determined by the "measured" differential cross sections over a range of interatomic separations significantly wider than would be expected classically. It is also found, for collision energies at which the weakly repulsive wall is appreciably sampled, that the SPF–Dunham and double Morse–van der Waals types of potentials lead to accurate determinations of the interatomic potential, whereas many other mathematical forms do not. Analytical parameterizations most appropriate for obtaining accurate interatomic potentials from thermal DCS experiments, for a given highly quantal system, may depend on the collision energy used

Scattering of thermal He beams by crossed atomic and molecular beams. II. The He-Ar van der Waals potential

Differential cross sections for He–Ar scattering at room temperature have been measured. The experimental consistency of these measurements with others performed in different laboratories is demonstrated. Despite this consistency, the present van der Waals well depth of 1.78 meV, accurate to 10%, is smaller by 20% to 50% than the experimental values obtained previously. These discrepancies are caused by differences between the assumed mathematical forms or between the assumed dispersion coefficients of the potentials used in the present paper and those of previous studies. Independent investigations have shown that the previous assumptions are inappropriate for providing accurate potentials from fits to experimental differential cross section data for He–Ar. We use two forms free of this inadequacy in the present analysis: a modified version of the Simons–Parr–Finlan–Dunham (SPFD) potential, and a double Morse–van der Waals (M^2SV) type of parameterization. The resulting He–Ar potentials are shown to be equal to with experimental error, throughout the range of interatomic distances to which the scattering data are sensitive. The SPFD or M^2SV potentials are combined with a repulsive potential previously determined exclusively from fits to gas phase bulk properties. The resulting potentials, valid over the extended range of interatomic distances r≳2.4 Å, are able to reproduce all these bulk properties quite well, without adversely affecting the quality of the fits to the DC

Scattering of thermal He beams by crossed atomic and molecular beams. IV. Spherically symmetric intermolecular potentials for He+ CH_4, NH_3, H_2O, SF_6

Differential scattering cross sections are measured for He+CH_4, NH_3, H_2O, and SF_6, using the crossed molecular beams technique. These data, which are sensitive to the van der Waals attractive minima and adjacent regions of the intermolecular potential, are interpreted in terms of central‐field models. No evidence is found for quenching of the observed diffraction oscillations. The interactions of the isoelectronic hydrides CH_4, NH_3, H_2O with He are found to have decreasing van der Waals radii in this sequence, and their attractive wells all have similar depths. However, the He+SF_6 attractive well is found to be anomalously deep, and provides a counter example to the supposition that only the polarizability of the least polarizable of the interacting partners (atoms or molecules) correlates with the van der Waals well depth. Simple combination rules for predicting unlike‐pair potential parameters from the corresponding like‐pair ones are tested and found inadequate

Robust spatial coherence 5 μ\,\mum from a room-temperature atom chip

We study spatial coherence near a classical environment by loading a Bose-Einstein condensate into a magnetic lattice potential and observing diffraction. Even very close to a surface (5$\,\mu$m), and even when the surface is at room temperature, spatial coherence persists for a relatively long time ($\ge$500$\,$ms). In addition, the observed spatial coherence extends over several lattice sites, a significantly greater distance than the atom-surface separation. This opens the door for atomic circuits, and may help elucidate the interplay between spatial dephasing, inter-atomic interactions, and external noise.Comment: 15 pages, 14 figures, revised for final publication. This manuscript includes in-depth analysis of the data presented in arXiv:1502.0160

LABORATORY STUDIES OF IS FAILURE AS ESCALATING COMMITMENT TO A FAILING COURSE OF ACTION: OVERCOMING THE OBSTACLES

Runaway information technology (IT) projects- projects lhat exhibit significant overruns in project schedule and/or budget - represent a type of IT failure that can cost firms millions of dollars. While such projects have been frequently reported in the press (Betts 1992; Kindel 1992; Rothfeder 1988), this phenomenon has received relatively little attention from information systems researchers. Even though most runaway IT projects are eventually tenninated (or significantly scaled down in order to bring them under control), there are anecdotal data suggesting that managers allow thesc projects to continue for too long before taking corrective aclion. Many runaway IT projects appear to represent what can be described as escalating commiunent to a failing course of action (Brockner 1992) and we believe that a large number of IT failures can be described in such terms. Escalating commitment to a failing course of action occurs when a decision maker, who receives significant negative feedback concerning a project, continues to allocate resources to the project when a rational decision maker would make the choice to abandon (Brockner 1992; Staw and Ross 1987). Several theories have been offered to explain this phenomenon including self-justification theory and the so-called sunk cost effect which can be explained by prospect theory. In order to gain a better understanding of runaway IT projects, we have developed a broad-based research program that includes both field-based and laboratory-based studies that are grounded in escalation theory. Here, we focus on the results of a series of controlled experiments that have been conducted to test whether escalation can be observed within an IT context and to learn more about the factors that may promote or impede this phenomenon. Preliminary results indicate that both the level of sunk cost and the presence or absence of an alternative course of action can affect subjects\u27 willingness to continue with an IT project In the spirit of what Van Maanen (1988) refers to as a \u27confessional tale, we will discuss the challenges that were encountered in conducting these experiments

Managing IT Projects for Success: Reengineering or Better Project Management?

IT projects can fail for any number of reasons and in some cases can result in considerable financial losses for the organizations that undertake them. The strategic importance that IT now plays coupled with the burgeoning costs of developing infomation systems has raised the stakes associated with project failure. While it is difficult to obtain statistics on the actual frequency of information systems failures, various sources suggest that at least half of all IS projects are not as successful as one would like them to be (Gladden 1982; Lyytinen and Hirschheim 1987). Numerous articles in the popular press seem to provide anecdotal evidence of this (Betts 1992; Kindel 1992; McPartlin 1992; Mehler 1991; Rothfeder 1988). The relatively high prevalence of failures in this field suggests the need to reexamine the way in which projects are managed

Identifying and Preventing IS Project Escalation:A Survey of IS Auditors

Tradesurveys have estimated that from 30% to 65% of IS development projects become \u27runaways\u27 --projects that 1) fail to produce an acceptable system, 2) grossly exceed initial budget/time estimates and, 3) seem to take on a life of their own. iven that the United States spends over $250 billion annually on IS development [Johnson, 1995], it is important to ask why runaway projects occur. In this research study, we focus on why such poorly performing projects are allowed to continue for so long. Based on datafrom several specific cases of runaway projects, we believe runaways are a form of organizational decision making failure. Consider this scenario: a development project encounters some problems which may be serious enough to cause the project to fail. Thedecision maker(s) responsible for the project have two choices: continue the project or abandon it (either terminate it or radically redirect it). If the decision maker consciously chooses to continue committing resources to the project or never consciously considers abandonment, the behavior represents an escalation of commitment or escalation, for short. Runaway projects result from many such decision points. Eventually these continuation (escalation) decisions take the project beyond its initial time/cost targets. Each subsequent escalation decision leaves these targets further and further behind until there is a feeling that \u27the project is out of control\u27. Runaway projects, therefore, come from project escalation --the continued allocation of resources to projects despite negative feedback relating to project performance and the likelihood of succes

The Challenges of Redressing the Digital Divide: A Tale of Two Cities

This paper presents a study that was designed to examine efforts undertaken by two citiesóAtlanta and LaGrange, Georgiaóto redress the digital divide. Atlantaís initiative has taken the form of community technology centers where citizens can come to get exposure to information technology and to learn something about computers and their applications. LaGrange has taken a very different approach, providing free Internet access to the home via a digital cable set-top box. This research is designed to examine the strengths and limitations of the two initiatives, with the goal of understanding why neither effort has had the impact that policy makers had hoped for with respect to solving the digital divide problem. Our findings indicate that the relationship between access and use of IT is not deterministic. Social processes that exist at both the institutional and individual levels of analysis complicate this relationship. From the institutional perspective, a persistent divide exists even when cities are giving away a theoretically ìfree goodî or service. Free goods often took the form of a training course that delivered little more than basic IT literacy and computer hardware of inferior quality and capabilities. From the individual perspective, we found that economic capital explains gaps in physical access to IT, but social capital and cultural capital explain gaps in the ability to use IT as well as disparities in the benefits that one derives from IT use. Therefore, as IT access continues to proliferate to nontraditional communities of users, sustainability of these digital divide initiatives should not continue to be measured in purely economic and technological terms. We must also consider the sustainability of the innovative elements: the participants