Junior Recital

List of performers and performances

Link communities reveal multiscale complexity in networks

Networks have become a key approach to understanding systems of interacting objects, unifying the study of diverse phenomena including biological organisms and human society. One crucial step when studying the structure and dynamics of networks is to identify communities: groups of related nodes that correspond to functional subunits such as protein complexes or social spheres. Communities in networks often overlap such that nodes simultaneously belong to several groups. Meanwhile, many networks are known to possess hierarchical organization, where communities are recursively grouped into a hierarchical structure. However, the fact that many real networks have communities with pervasive overlap, where each and every node belongs to more than one group, has the consequence that a global hierarchy of nodes cannot capture the relationships between overlapping groups. Here we reinvent communities as groups of links rather than nodes and show that this unorthodox approach successfully reconciles the antagonistic organizing principles of overlapping communities and hierarchy. In contrast to the existing literature, which has entirely focused on grouping nodes, link communities naturally incorporate overlap while revealing hierarchical organization. We find relevant link communities in many networks, including major biological networks such as protein-protein interaction and metabolic networks, and show that a large social network contains hierarchically organized community structures spanning inner-city to regional scales while maintaining pervasive overlap. Our results imply that link communities are fundamental building blocks that reveal overlap and hierarchical organization in networks to be two aspects of the same phenomenon.Comment: Main text and supplementary informatio

Robustness and modular structure in networks

Complex networks have recently attracted much interest due to their prevalence in nature and our daily lives [1, 2]. A critical property of a network is its resilience to random breakdown and failure [3-6], typically studied as a percolation problem [7-9] or by modeling cascading failures [10-12]. Many complex systems, from power grids and the Internet to the brain and society [13-15], can be modeled using modular networks comprised of small, densely connected groups of nodes [16, 17]. These modules often overlap, with network elements belonging to multiple modules [18, 19]. Yet existing work on robustness has not considered the role of overlapping, modular structure. Here we study the robustness of these systems to the failure of elements. We show analytically and empirically that it is possible for the modules themselves to become uncoupled or non-overlapping well before the network disintegrates. If overlapping modular organization plays a role in overall functionality, networks may be far more vulnerable than predicted by conventional percolation theory.Comment: 14 pages, 9 figure

Protein-Tyrosine Phosphatase in Normal and Malignant Melanocytes

We embarked on a study to define the role of protein-tyrosine phosphatases (PTPases) in both normal melanocytes and melanoma cells, searching for specific differences that might provide clues to the malignant transformation process in these cells and to the role of PTPases as possible tumor suppressor genes. We used Northern blotting and RNase protection assays to measure mRNA expression levels, immunoprecipitation and immunoblotting to measure protein expression, and a bioassay to measure protein PTPase activity in normal melanocyte and melanoma cell lines. Our experiments showed that all major PTPases are equally expressed at both mRNA and protein levels, except for HPTPase O, which is expressed in two out of four melanoma cell lines tested, but not in normal melanocytes. In addition, basal levels of PTPase activity were detected in cell extracts of both normal and transformed melanocytes, and the major cytosolic PTPase, PTPlB, was identified at the protein level. PTPlB expression in both normal and malignant melanocytes was not altered by the addition of mast cell growth factor (MGF), except in the melanoma cell line 888, in which PTPlB was expressed after, but not before, MGF stimulation. In undertaking studies of PTPase activity, we found that in a specific melanoma cell line, YU-ZAZ, stimulation by vascular endothelial growth factor increased overall PTPase activity compared to basal levels. Furthermore, specificity of PTPase activity in these whole cell extracts was demonstrated to be equal towards both reduced carboxamidomethylated and maleylated lysozyme (RCML) and myelin basic protein (MBP) phosphorylated substrates. These studies are the first to characterize the role of PTPases in normal melanocytes and melanoma cells, and may help to clarify the mode of transformation in these cells and elucidate the physiological role of PTPases in regulation of cell growth

Doctoral Recital

List of performers and performances

A novel robust predictive control system over imperfect networks

This paper aims to study on feedback control for a networked system with both uncertain delays, packet dropouts and disturbances. Here, a so-called robust predictive control (RPC) approach is designed as follows: 1- delays and packet dropouts are accurately detected online by a network problem detector (NPD); 2- a so-called PI-based neural network grey model (PINNGM) is developed in a general form for a capable of forecasting accurately in advance the network problems and the effects of disturbances on the system performance; 3- using the PINNGM outputs, a small adaptive buffer (SAB) is optimally generated on the remote side to deal with the large delays and/or packet dropouts and, therefore, simplify the control design; 4- based on the PINNGM and SAB, an adaptive sampling-based integral state feedback controller (ASISFC) is simply constructed to compensate the small delays and disturbances. Thus, the steady-state control performance is achieved with fast response, high adaptability and robustness. Case studies are finally provided to evaluate the effectiveness of the proposed approach

Implications of the Partial Width Z->bb for Supersymmetry Searches and Model-Building

Assuming that the actual values of the top quark mass at FNAL and of the ratio of partial widths Z->bb/Z->hadrons at LEP are within their current one-sigma reported ranges, we present a No-Lose Theorem for superpartner searches at LEP II and an upgraded Tevatron. We impose only two theoretical assumptions: the Lagrangian is that of the Minimal Supersymmetric Standard Model with arbitrary soft-breaking terms, and all couplings remain perturbative up to scales of order 10^16 GeV; there are no assumptions about the soft SUSY breaking parameters, proton decay, cosmology, etc. In particular, if the LEP and FNAL values hold up and supersymmetry is responsible for the discrepancy with the SM prediction of the partial width of Z->bb, then we must have charginos and/or top squarks observable at the upgraded machines. Furthermore, little deviation from the SM is predicted within "super-unified" SUSY. Finally, it appears to be extremely difficult to find any unified MSSM model, regardless of the form of soft SUSY breaking, that can explain the partial width for large tan(beta); in particular, no model with top-bottom-tau Yukawa coupling unification appears to be consistent with the experiments.Comment: 15 pages, University of Michigan preprint UM-TH-94-23. LaTeX file with 4 uuencoded figures sent separately. Compressed PS file (114Kb) available by anonymous FTP from 141.211.96.66 in /pub/preprints/UM-TH-94-23.ps.

Wafer bonding and layer transfer processes for 4-junction high efficiency solar cells

A four-junction cell design consisting of InGaAs, InGeAsP, GaAs, and Ga0.5In0.5P subcells could reach 1 x AMO efficiencies of 35.4%. but relies on the integration of non-lattice-matched materials. Wafer bonding and layer transfer processes show promise in the fabrication of InP/Si epitaxial templates for growth of the bottom InGaAs and InGaAsP subcells on a Si support substrate. Subsequent wafer bonding and layer transfer of a thin Ge layer onto the lower subcell stack can serve as an epitaxial template for GaAs and Ga0.5In0.5P subcelis. Present results indicate that optically active III/V compound semiconductors can be grown on both Ge/Si and InP/Si heterostructures. Current-voltage electrical characterization of the interfaces of these structures indicates that both InP/Si and Ge/Si interfaces have specific resistances lower than 0.1 Ωcm^2 for heavily doped wafer bonded interfaces, enabling back surface power extraction from the finished cell structure

An Advocacy Approach for More Effective Program Delivery And Coordination: A Case Study of Maine\u27s Housing Rehab Techs

A detailed case analysis of the Maine Housing Rehabilitation Project provides an exploratory observation of the innovative use of human resources at the federal, state and regional levels through an evolutionary development process of housing rehabilitation technicians. Functioning largely as advocate planners and human service delivery administrators through self-expanded roles, these individuals were able to promote change in the context of this intergovernmental environment. The analysis presented here reveals findings of intrastate regional differences between the urban and rural areas. Low income citizens appear to be the main beneficiaries of a proactive style of leadership that was performed by the most productive rehab techs. The autonomy of their roles afforded all technicians a degree of freedom to produce different results through experimentation

Structural characterization and electrochemical properties of Co3O4 anode materials synthesized by a hydrothermal method

Cobalt oxide [Co3O4] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co3O4 powder was also studied. Physical characterizations of Co3O4 are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m2/g, 76.1 m2/g, and 55.2 m2/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co3O4 particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li+ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co3O4 prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles