Research and education in management of large- scale technical programs Semiannual progress report

Research and education in management of large scale technical programs - education and integration of interdisciplinary tea

Technology and management of large-scale programs Semiannual progress report

Technology and management of large scale program

The Starburst in the Central Kiloparsec of Markarian 231

We present VLBA observations at 0.33 and 0.61 GHz, and VLA observations between 5 and 22 GHz, of subkiloparsec scale radio emission from Mrk 231. In addition to jet components clearly associated with the AGN, we also find a smooth extended component of size 100 - 1000 pc most probably related to the purported massive star forming disk in Mrk 231. The diffuse radio emission from the disk is found to have a steep spectrum at high frequencies, characteristic of optically thin synchrotron emission. The required relativistic particle density in the disk can be produced by a star formation rate of 220 Msolar/yr in the central kiloparsec. At low frequencies the disk is absorbed, most likely by ionized gas with an emission measure of 8 x 10^5 pc cm-6. We have also identified 4 candidate radio supernovae that, if confirmed, represent direct evidence for ongoing star formation in the central kiloparsec.Comment: in press at ApJ for v. 519 July 1999, 14 page LaTeX document includes 6 postscript figure

A Foundation for the Study of IT Effects: A New Look at DeSanctis and Poole’s Concepts of Structural Features and Spirit

Gerardine DeSanctis and Marshall Scott Poole made an important contribution to the study of IT uses and effects with their insightful concepts of “structural features” and “spirit.” Unlike their concept of “appropriation,” which has found broad acceptance in the IS community, the concepts of structural features and spirit have not been widely used. Published concerns that the concepts are not consistent with basic assumptions in Giddens’ structuration theory, on which the concepts were based, could account for their neglect. However, concepts like structural features and spirit are indispensable for any program of research that attempts to show how IT artifacts can, together with other influences, contribute to the consequences of IT use. Addressing the criticisms that have been leveled against these concepts is, therefore, important. In this paper we unpack DeSanctis and Poole’s concepts and propose redefining them as three new concepts: technical objects, functional affordances, and symbolic expressions. We believe this reconceptualization addresses several concerns about the original concepts, while retaining the core insights of DeSanctis and Poole’s innovative analysis

Formation and decay of electron-hole droplets in diamond

We study the formation and decay of electron-hole droplets in diamonds at both low and high temperatures under different excitations by master equations. The calculation reveals that at low temperature the kinetics of the system behaves as in direct-gap semiconductors, whereas at high temperature it shows metastability as in traditional indirect-gap semiconductors. Our results at low temperature are consistent with the experimental findings by Nagai {\em et al.} [Phys. Rev. B {\bf 68}, 081202 (R) (2003)]. The kinetics of the e-h system in diamonds at high temperature under both low and high excitations is also predicted.Comment: 7 pages, 8 figures, revised with some modifications in physics discussion, to be published in PR

Magnetic Properties of the Second Mott Lobe in Pairing Hamiltonians

We explore the Mott insulating state of single-band bosonic pairing Hamiltonians using analytical approaches and large scale density matrix renormalization group calculations. We focus on the second Mott lobe which exhibits a magnetic quantum phase transition in the Ising universality class. We use this feature to discuss the behavior of a range of physical observables within the framework of the 1D quantum Ising model and the strongly anisotropic Heisenberg model. This includes the properties of local expectation values and correlation functions both at and away from criticality. Depending on the microscopic interactions it is possible to achieve either antiferromagnetic or ferromagnetic exchange interactions and we highlight the possibility of observing the E8 mass spectrum for the critical Ising model in a longitudinal magnetic field.Comment: 14 pages, 15 figure

Why Neurons Are Not the Right Level of Abstraction for Implementing Cognition

International audienceThe cortex accounts for 70% of the brain volume. The human cortex is made of micro-columns, arrangements of 110 cortical neurons (Mountcastle), grouped in by the thousand in so-called macro-colums (or columns) which belong to the same functional unit as exemplified by Nobel laureates Hubel and Wiesel with the orientation columns of the primary visual cortex. The cortical column activity does not exhibit the limitations of single neurons: activation can be sustained for very long periods (sec.) instead of been transient and subject to fatigue. Therefore, the cortical column has been proposed as the building block of cognition by several researchers, but to not effect – since explanations about how the cognition works at the column level were missing. Thanks to the Theory of neuronal Cognition, it is no more the case. The cortex functionality is cut into small areas: the cortical maps. Today, about 80 cortical maps are known in the primary and secondary cortex [1]. These maps form a hierarchical organization. A cortical map is a functional structure encompassing several thousands of cortical columns. The function of such maps (also known as Kohonen maps) is to build topographic (i.e., organized and localized) representations of the input stimulii (events). This organization is such that similar inputs activate either the same cortical column or neighboring columns. Also, the more frequent the stimulus, the greater the number of cortical columns involved. Each map acts as a novelty detector and a filter. Events are reported as patterns of activations on various maps, each map specialized in a specific " dimension ". Spatial and temporal coordinates of events are linked to activations within the hippo-campus and define de facto the episodic memory. Learning is achieved at neuronal level using the famous Hebb's law: " Neurons active in the same time frame window reinforce their connections ". This rule does not respect " causality ". This, plus the fact that there is at least as much feedback connections as there are feed-forward ones, explain why a high level cortical activation generates a low level cortical pattern of activations – the same one that would trigger this high level activity. Therefore, our opinion is that the true building block of the cognition is a set of feed-forward and feedback connections between at least two maps, each map a novelty detector

THE INFORMATION TECHNOLOGY INTERACTION MODEL: A CORE MODEL FOR THE MBA CORE COURSE

This paper presents a teaching model we have used successfully in the MBA core course in Information Systems at several universities. The model is referred to as the "Information Technology Interaction Model" because it maintains that the consequences of information systems in organizations follow largely from the interaction of the technology with the organization and its environment. The model serves a number of pedagogical purposes: to integrate the various course components, to provide a formal foundation for the course content, to foster practical analytical skills, and to provide a framework for case discussions and student projects. Moreover, the model is intended to acquaint students with the dynamics of information systems in organizations and to help them recognize the benefits, dangers, and limitations of these systems. The paper includes a discussion and examples of how the model can be used for proactive and reactive analyses, and it concludes with an assessment of the model's effectiveness in the core course.Information Systems Working Papers Serie

Fast algorithm for calculating two-photon absorption spectra

We report a numerical calculation of the two-photon absorption coefficient of electrons in a binding potential using the real-time real-space higher-order difference method. By introducing random vector averaging for the intermediate state, the task of evaluating the two-dimensional time integral is reduced to calculating two one-dimensional integrals. This allows the reduction of the computation load down to the same order as that for the linear response function. The relative advantage of the method compared to the straightforward multi-dimensional time integration is greater for the calculation of non-linear response functions of higher order at higher energy resolution.Comment: 4 pages, 2 figures. It will be published in Phys. Rev. E on 1, March, 199