Generalization Per Category: Theory And Application

The concept of Generalization Per Category (GPO is formalized. It is shown that GPC imposes lattice structures on entity types and their subtypes. A high level application oriented data definition language based on the GPC is outlined which allows the system to derive general entity types and organize their instances. Users are freed from undue efforts in the design of databases which are about entity types with rich varieties and high populations. Effective browsing of these databases and efficient execution of frequent queries against them are achieved by using the lattice structures among the entity types and their subtypes

Deterministic mechanical model of T-killer cell polarization reproduces the wandering of aim between simultaneously engaged targets

T-killer cells of the immune system eliminate virus-infected and tumorous cells through direct cell-cell interactions. Reorientation of the killing apparatus inside the T cell to the T-cell interface with the target cell ensures specificity of the immune response. The killing apparatus can also oscillate next to the cell-cell interface. When two target cells are engaged by the T cell simultaneously, the killing apparatus can oscillate between the two interface areas. This oscillation is one of the most striking examples of cell movements that give the microscopist an unmechanistic impression of the cell's fidgety indecision. We have constructed a three-dimensional, numerical biomechanical model of the molecular-motor-driven microtubule cytoskeleton that positions the killing apparatus. The model demonstrates that the cortical pulling mechanism is indeed capable of orienting the killing apparatus into the functional position under a range of conditions. The model also predicts experimentally testable limitations of this commonly hypothesized mechanism of T-cell polarization. After the reorientation, the numerical solution exhibits complex, multidirectional, multiperiodic, and sustained oscillations in the absence of any external guidance or stochasticity. These computational results demonstrate that the strikingly animate wandering of aim in T-killer cells has a purely mechanical and deterministic explanation. © 2009 Kim, Maly

Sequence Determinants of a Specific Inactive Protein Kinase Conformation

SummaryOnly a small percentage of protein kinases have been shown to adopt a distinct inactive ATP-binding site conformation, called the Asp-Phe-Gly-out (DFG-out) conformation. Given the high degree of homology within this enzyme family, we sought to understand the basis of this disparity on a sequence level. We identified two residue positions that sensitize mitogen-activated protein kinases (MAPKs) to inhibitors that stabilize the DFG-out inactive conformation. After characterizing the structure and dynamics of an inhibitor-sensitive MAPK mutant, we demonstrated the generality of this strategy by sensitizing a kinase (apoptosis signal-regulating kinase 1) not in the MAPK family to several DFG-out stabilizing ligands, using the same residue positions. The use of specific inactive conformations may aid the study of noncatalytic roles of protein kinases, such as binding partner interactions and scaffolding effects

Perceptions of Adolescent Pregnancy Among Teenage Girls in Rakai, Uganda.

The leading causes of death and disability among Ugandan female adolescents aged 15 to 19 years are pregnancy complications, unsafe abortions, and childbirth. Despite these statistics, our understanding of how girls perceive adolescent pregnancy is limited. This qualitative study explored the social and contextual factors shaping the perceptions of adolescent pregnancy and childbirth among a sample of 12 currently pregnant and 14 never pregnant girls living in the rural Rakai District of Uganda. Interviews were conducted to elicit perceived risk factors for pregnancy, associated community attitudes, and personal opinions on adolescent pregnancy. Findings indicate that notions of adolescent pregnancy are primarily influenced by perceptions of control over getting pregnant and readiness for childbearing. Premarital pregnancy was perceived as negative whereas postmarital pregnancy was regarded as positive. Greater understanding of the individual and contextual factors influencing perceptions can aid in development of salient, culturally appropriate policies and programs to mitigate unintended adolescent pregnancies

Collision induced spatial organization of microtubules

The dynamic behavior of microtubules in solution can be strongly modified by interactions with walls or other structures. We examine here a microtubule growth model where the increase in size of the plus-end is perturbed by collisions with other microtubules. We show that such a simple mechanism of constrained growth can induce ordered structures and patterns from an initially isotropic and homogeneous suspension. First, microtubules self-organize locally in randomly oriented domains that grow and compete with each other. By imposing even a weak orientation bias, external forces like gravity or cellular boundaries may bias the domain distribution eventually leading to a macroscopic sample orientation.Comment: Submitted to Biophysical Journa

Pseudogap effects induced by resonant pair scattering

We demonstrate how resonant pair scattering of correlated electrons above T_c can give rise to pseudogap behavior. This resonance in the scattering T-matrix appears for superconducting interactions of intermediate strength, within the framework of a simple fermionic model. It is associated with a splitting of the single peak in the spectral function into a pair of peaks separated by an energy gap. Our physical picture is contrasted with that derived from other T-matrix schemes, with superconducting fluctuation effects, and with preformed pair (boson-fermion) models. Implications for photoemission and tunneling experiments in the cuprates are discussed.Comment: REVTeX3.0; 4 pages, 4 EPS figures (included

Simultaneous 2D-Single Shot Imaging of OH Concentrations and Temperature Fields in a SI Engine Simulator

Two-dimensional (2D) temperature measurements in engines are required for the detailed understanding of the combustion process. Because of the unsteady and turbulent nature of engine combustion, these measurements must be performed on a single-shot basis to obtain cycle-resolved results. Details of the flame front structure are also important to know for the numerical modeling of internal combustion processes. Simultaneous measurements of temperature and hydroxyl radical distributions provide such data sets. The combustion of methane in a fully transparent square piston engine was studied with a combination of 2D laser-induced fluorescence of hydroxyl radicals and 2D Rayleigh scattering. A tunable KrF excimer laser at 248 nm was used for the measurementsThe wavelength of the laser was tuned to excite the P2(8) transition in the OH (3,0) band of the A-X system. Spectral filtering of the resulting fluorescence to detect solely the fluorescence from the (3,2) band significantly reduces the effect of collisional quenching imposed to the fluorescence to the predissociating v_=3 level by vibrational energy transfer (VET) to lower vibrational levels. Using a second camera, which only records the Rayleigh signals after appropriate filtering, allows the simultaneous measurement of temperature fields with a single laser. The analysis of corresponding OH and temperature images allowed the decision that the combustion conditions are in a regime where the flamelet approach for modeling is appropriate. Good agreement with model predictions has been achieved for the peak temperatures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86753/1/Sick49.pd

The pseudogap state in superconductors: Extended Hartree approach to time-dependent Ginzburg-Landau Theory

It is well known that conventional pairing fluctuation theory at the Hartree level leads to a normal state pseudogap in the fermionic spectrum. Our goal is to extend this Hartree approximated scheme to arrive at a generalized mean field theory of pseudogapped superconductors for all temperatures $T$. While an equivalent approach to the pseudogap has been derived elsewhere using a more formal Green's function decoupling scheme, in this paper we re-interpret this mean field theory and BCS theory as well, and demonstrate how they naturally relate to ideal Bose gas condensation. Here we recast the Hartree approximated Ginzburg-Landau self consistent equations in a T-matrix form. This recasting makes it possible to consider arbitrarily strong attractive coupling, where bosonic degrees of freedom appear at $T^*$ considerably above $T_c$. The implications for transport both above and below $T_c$ are discussed. Below $T_c$ we find two types of contributions. Those associated with fermionic excitations have the usual BCS functional form. That they depend on the magnitude of the excitation gap, nevertheless, leads to rather atypical transport properties in the strong coupling limit, where this gap (as distinct from the order parameter) is virtually $T$-independent. In addition, there are bosonic terms arising from non-condensed pairs whose transport properties are shown here to be reasonably well described by an effective time-dependent Ginzburg-Landau theory.Comment: 14 pages, 5 figures, REVTeX4, submitted to PRB; clarification of the diagrammatic technique added, one figure update