Dynamic variations in the expression of type I collagen and its molecular chaperone Hsp47 in cells of the mouse dental follicle during tooth eruption

Tooth eruption is a precisely timed and sequenced event that brings the tooth from within bone into a functional position in the mouth. Every part of the developing tooth has been theoretically implicated as a primary factor in this process, but it now appears that eruption is multifactorial, with the dental follicle and type I collagen playing an important part. Immunological probes were used here to investigate in vivo and in vitro the temporal and spatial expression of type I collagen and its molecular chaperone Hsp47 in the dental follicle during eruption. Mandibles were dissected from 2-, 5-, 9- and 11-day-old neonatal mice and fixed in 95% ethanol overnight. Sections of 7 microns were obtained and reacted with antibodies directed against type I collagen. Dental follicles were isolated from 2-, 5-, 9- and 11-day-old neonates and cells were grown in culture for 8 days. Slides were then reacted with antibodies directed against type I collagen and Hsp47. The production of type I collagen and Hsp47 in the follicle varied with the stage of dental development and eruption. There was a progressive decrease of type I collagen in the coronal part of the follicle, leading to an arrest of its production in these areas. These findings support the notion that cells of the coronal portion of the dental follicle stop producing type I collagen as a prerequisite to the initiation of tooth eruption and that this phenotype persists in vitro.     

Correlation between steady state flow curve and molecular weight distribution for polyethylene melts

This article uses Graessley's theory of viscosity to predict the flow curve for several high-density and low-density polyethylene melts using the molecular weight distribution data obtained from the gel permeation chromatograph. The agreement with the experimental flow curve obtained from the Weissenberg rheogoniometer and the Instron rheometer was not quantitative for many high-density polyethylenes studied here. For the low-density polyethylenes, it was shown that the agreement between the theory and the experiment was good even though the molecular weight distribution data were not corrected for long-chain branching. For these samples, the experimental relaxation time τ₀ obtained by superposition of the data with the theoretical master curve was of the order of the Rouse relaxation time τ_R. The systematic increase in the ratio τ_R/τ₀ was ascribed to the increase in the molecular weight or to the increased number of long-chain branches.     

Modelling VBR video over networks end-to-end using deterministic smoothing at the source

Video traffic is expected to become increasingly important with the large scale deployment of broadband ISDN. In the literature, it is suggested that smoothing variable bit rate (VBR) video traffic^1,2 before transmitting it onto the network would help reduce the probability of cell loss. In this paper we show why deterministic smoothing at the source approximates the minimum achievable loss over the network end-to-end of all possible smoothing schemes. Furthermore, we develop a powerful yet simple analytical technique that can efficiently calculate the loss probability at any point in a network carrying video traffic. We validate our analytical results using traces of actual video segments. The results can be used for admission control and traffic management. We find that in the case of highly correlated traffic such as motion JPEG video, the way to control loss is to ensure that the fraction of time the arrival process exceeds the service process is small. We also find that for such sources increasing the buffer size only marginally decreases the loss.     

Delay and Capacity Trade-Offs in Mobile Ad Hoc Networks: A Global Perspective

Since the original work of Grossglauser and Tse, which showed that mobility can increase the capacity of an ad hoc network, there has been a lot of interest in characterizing the delay-capacity relationship in ad hoc networks. Various mobility models have been studied in the literature, and the delay-capacity relationships under those models have been characterized. The results indicate that there are trade-offs between the delay and capacity, and that the nature of these trade-offs is strongly influenced by the choice of the mobility model. Some questions that arise are: (i) How representative are these mobility models studied in the literature? (ii) Can the delay-capacity relationship be significantly different under some other "reasonable" mobility model? (iii) What sort of delay-capacity trade-off are we likely to see in a real world scenario? In this paper, we take the first step toward answering some of these questions. In particular, we analyze, among others, the mobility models studied in recent related works, under a unified framework. We relate the nature of delay-capacity trade-off to the nature of node motion, thereby providing a better understanding of the delay-capacity relationship in ad hoc networks in comparison to earlier works.     

Development and maintenance of the gut-associated lymphoid tissue (GALT): the roles of enteric bacteria and viruses

Hydrogen peroxide (H2O2) is considered to be a mediator of apoptotic cell death but the mechanism by which it induces apoptosis is unclear. Here, we show that cells undergoing apoptosis from exposure to H2O2 display a significant decrease in intracellular concentration of superoxide (O2-) which is associated with a reduction of the intracellular milieu, as measured by an increase in the GSH/GSSG ratio and a decrease in intracellular pH. The notion that a decrease in intracellular O2- concentration triggers apoptosis is supported by the observation that H2O2-mediated apoptosis could be retarded in cells in which the intracellular O2- concentration is maintained at or above the cellular baseline level by inhibition of the major O2- scavenger superoxide dismutase (Cu/Zn SOD). Taken together, our observations indicate that a decrease in the intracellular O2- concentration, reduction and acidification of the intracellular milieu constitute a signal for H2O2-mediated apoptosis, thereby inducing a reductive as opposed to an oxidative stress.     

Opportunistic transmission scheduling with resource-sharingconstraints in wireless networks

We present an “opportunistic” transmission scheduling policy that exploits time-varying channel conditions and maximizes the system performance stochastically under a certain resource allocation constraint. We establish the optimality of the scheduling scheme and also that every user experiences a performance improvement over any nonopportunistic scheduling policy when users have independent performance values. We demonstrate via simulation results that the scheme is robust to estimation errors and also works well for nonstationary scenarios, resulting in performance improvements of 20%-150% compared with a scheduling scheme that does not take into account channel conditions. Last, we discuss an extension of our opportunistic scheduling scheme to improve “short-term” performance     

Correlation of blown film optical properties with resin properties

The optical properties of conventional, free-radical polymerized low density polyethylene (LDPE) blown films are due essentially to surface irregularities that develop during fabrication. Past studies have shown that the extent to which these irregularities occur (and therefore optical properties) correlates well with the melt elasticity of the resin. Specifically, it has been shown that resins with higher melt elasticity result in films with poorer optical properties. However, it was recently reported that the optical properties of film blown from a Sci of three generically similar LDPE resins were found to correlate with the crystallization kinetics of the resins. Specifically, it was reported that the resins that exhibited faster crystallization rates produced films with better optical properties. This present work shows, however, that this apparent correlation is only coincidental. It has been shown that resins exhibiting faster crystallization rates do not necessarily result in films with better optical properties. On the other hand, it has been shown that resins with higher melt elasticity consistently result in films with poorer optical properties.     

An Optimization-Based Approach for QoS Routing in High-Bandwidth Networks

In this paper, we propose an optimization-based approach for Quality of Service (QoS) routing in high-bandwidth networks. We view a network that employs QoS routing as an entity that distributively optimizes some global utility function. By solving the optimization problem, the network is driven to an efficient operating point. In earlier work, it has been shown that when the capacity of the network is large, this optimization takes on a simple form, and once the solution to this optimization problem is found, simple proportional QoS routing schemes will suffice. However, this optimization problem requires global information. We develop a distributed and adaptive algorithm that can efficiently solve the optimization online. Compared with existing QoS routing schemes, the proposed optimization-based approach has the following advantages: 1) the computation and communication overhead can be greatly reduced without sacrificing performance; 2) the operating characteristics of the network can be analytically studied; and 3) the desired operating point can be tuned by choosing appropriate utility functions     

A predictive flow control scheme for efficient network utilization and QoS

In this paper, we develop a new predictive flow control scheme and analyze its performance. This scheme controls the nonreal-time (controllable) traffic based on predicting the real-time (uncontrollable) traffic. The goal of the work is to operate the network in a low congestion, high throughput regime. We provide a rigorous analysis of the performance of our flow control method and show that the algorithm has attractive and useful properties. From our analysis we obtain an explicit condition that gives us design guidelines on how to choose a predictor. We learn that it is especially important to take the queueing effect into account in developing the predictor. We also provide numerical results comparing different predictors that use varying degrees of information from the network.     

Novel modified tripeptide inhibitors of alpha 4 beta 7 mediated lymphoid cell adhesion to MAdCAM-1

MAdCAM-1 specifically binds the lymphocyte integrin alpha 4 beta 7 and participates in the homing of leukocytes to intestinal mucosal sites. The LDT sequence located on the CD loop of MAdCAM-1 is an important binding site for MAdCAM-1/alpha 4 beta 7 interactions. N-Terminus acylation of the LDT motif and modification of the C-terminus carboxamide with amines led to low micromolar MAdCAM-1 inhibitors.