A deterministic approach to throughput scaling in wireless networks

We address the problem of how throughput in a wireless network scales as the number of users grows. Following the model of Gupta and Kumar, we consider n identical nodes placed in a fixed area. Pairs of transmitters and receivers wish to communicate but are subject to interference from other nodes. Throughput is measured in bit-meters per second. We provide a very elementary deterministic approach that gives achievability results in terms of three key properties of the node locations. As a special case, we obtain /spl Omega/(/spl radic/n) throughput for a general class of network configurations in a fixed area. Results for random node locations in a fixed area can also be derived as special cases of the general result by verifying the growth rate of three parameters. For example, as a simple corollary of our result we obtain a stronger (almost sure) version of the /spl radic/n//spl radic/(logn) throughput for random node locations in a fixed area obtained by Gupta and Kumar. Results for some other interesting non-independent and identically distributed (i.i.d.) node distributions are also provided.     

Disordered Topography Mediates Filopodial Extension and Morphology of Cells on Stiff Materials

In cell–material interactions, cells use filopodia to sense external biochemical and mechanical cues, and subsequently dictate their survival. In an effort toward understanding how disordered topography of stiff materials influences filopodial recognition, diamond films with grain sizes varying from nano‐ to micrometers are fabricated for the investigation of osteoblast filopodial extension. Interestingly, straight filopodia with pronounced cell–substrate adhesion are observed on a nanocrystalline diamond (NCD) region, whereas filopodia on a microcrystalline diamond (MCD) surface only adhere to, and get deflected by, large diamond grains. More importantly, filopodia on NCD keep propagating with a constant velocity, whereas the same process takes place in a slow and intermittent manner on MCD. A theoretical model is also developed and it suggests that the contact between the disordered topography and the filopodial tip plays a key role in altering filopodial growth dynamics. In particular, it is predicted that large surface asperities can block the movement of the filopodial tip, delay its extension, and cause bending of the structure, in quantitative agreement with experimental observations. These findings reveal previously underappreciated effects of random, stiff topographies on the response of cells, and hence can provide new insights for the design of future implant biomaterials.     

The Capacity Region of the Degraded Multiple-Input Multiple-Output Compound Broadcast Channel

The capacity region of a compound multiple-antenna broadcast channel is characterized when the users exhibit a certain degradedness order. The channel under consideration has two users, each user has a finite set of possible realizations. The transmitter transmits two messages, one for each user, in such a manner that regardless of the actual realizations, both users will be able to decode their messages correctly. An alternative view of this channel is that of a broadcast channel with two common messages, each common message is intended to a different set of users. The degradedness order between the two sets of realizations/users is defined through an additional, fictitious, user whose channel is degraded with respect to all realizations/users from one set while all realizations/users from the other set are degraded with respect to him.     

Exploring mesh and tree-based multicast. Routing protocols for MANETs

Recently, it became apparent that group-oriented services are one of the primary application classes targeted by MANETs. As a result, several MANET-specific multicast routing protocols have been proposed. Although these protocols perform well under specific mobility scenarios, traffic loads, and network conditions, no single protocol has been shown to be optimal in all scenarios. The goal of this paper is to characterize the performance of multicast protocols over a wide range of MANET scenarios. To this end, we evaluate the performance of mesh and tree-based multicast routing schemes relative to flooding and recommend protocols most suitable for specific MANET scenarios. Based on the analysis and simulation results, we also propose two variations of flooding, scoped flooding and hyper flooding, as a means to reduce overhead and increase reliability, respectively. Another contribution of the paper is a simulation-based comparative study of the proposed flooding variations against plain flooding, mesh, and tree-based MANET routing. In our simulations, in addition to "synthetic" scenarios, we also used more realistic MANET settings, such as conferencing and emergency response.     

Density and viscosity of vegetable oils

A generalized method was developed to estimate the liquid density of vegetable oils and fatty acids. The correlation for vegetable oils was based on fatty acid critical properties and composition of the oil. The correlations predicted the density of vegetable oils and fatty acids with an average absolute deviation of 0.21 and 0.77%, respectively. The present method is slightly more accurate in predicting vegetable oil density and simpler than the method of Halvorsen et al. Also, a method is introduced that predicts viscosity from density data, thus relating two key properties of vegetable oils.     

Anthranilamide-pyrazolo[1,5-a]pyrimidine conjugates as p53 activators in cervical cancer cells

A library of new anthranilamide-pyrazolo[1,5-a]pyrimidine conjugates were designed, synthesized, and evaluated for their anticancer activity in cervical cancer cells such as HeLa and SiHa that possess low levels of p53. All 24 conjugates showed antiproliferative activity, while some of them exhibit significant cytotoxicity. In assays related to cell-cycle distribution, these conjugates induced G(2) /M arrest in HeLa cells and G(1) cell-cycle arrest in SiHa cells. Immunocytochemistry assays revealed that these compounds cause nuclear translocation of p53, thereby indicating the activation of p53. In cervical cancer cells, the p53 protein is degraded by E6 oncoprotein. Immunoblot and RT-PCR analyses proved the presence of mitochondria-mediated apoptosis with involvement p53 target genes such as BAX, Bcl2, and p21 (CDKI). Moreover, these compounds increased the phosphorylated forms of p53 and provide signals for apoptosis induction. Interestingly, one of the conjugates, (2-phenyl-7-(3,4,5-trimethoxyphenyl)pyrazolo[1,5-a]pyrimidin-5-yl)(4-(2-(thiophen-2-ylmethylamino)benzoyl)piperazin-1-yl)methanone, is the most promising candidate in this series and has the potential to be taken up for further detailed studies.     

Microstructural characterization of M250 grade maraging steel using nonlinear ultrasonic technique

Nonlinear ultrasonic (NLU) technique is used for characterization of microstructures in M250 grade maraging steel subjected to solution annealing at 1093 K for 1 h followed by ageing at 755 K for various ageing durations in the range from 0.25 to 100 h. Using pulse inversion technique, feeble second harmonic is extracted to determine nonlinear ultrasonic parameter, β, and the relative β parameter (RBP) which is the ratio of β parameter of the precipitation hardened specimen to that of the solution annealed specimen. Normalized mean square strain, volume fraction of reverted austenite and hardness have been measured and transmission electron microscopy (TEM) has been carried out to understand the microstructural changes that occur during ageing and to study the correlation between these measured parameters. Hardness and normalized mean square strain are found to increase during initial stages of ageing due to precipitation of intermetallics and decrease at longer durations due to formation of reverted austenite and coarsening of precipitates. This study establishes that NLU technique can be used for non-destructive characterization of ageing behaviour of M250 grade maraging steel.     

Production inventory with service time and interruptions

This paper considers an (s,S) production inventory system with positive service time, with time for producing each item following Erlang distribution. Customers arrive according to a Poisson process. A customer who arrives when there is no inventory in the system is considered lost. On the other hand, a customer who finds a busy server with at least one inventory in the system joins a queue of infinite capacity. When the inventory level falls to s, production process is switched on, and it is switched off when the inventory level reaches back to S. Service time to each customer also follows an Erlang distribution. The service of a customer may be interrupted, where the time for such a phenomenon follows an exponential distribution, whenever it occurs. An interrupted service, after repair, resumes from where it was stopped. The correction/repair time follows an exponential distribution. We assume that the service of a single customer may encounter any number of interruptions and that the customer being served waits there until his service is completed. Moreover, at a time the server is subject to at most one interruption. We also assume that no inventory is lost due to a service interruption. Like the service process, the production process also is subject to interruptions, where the duration to an interruption follows an exponential distribution. However, in contrast to the service interruption, in the case of interruption to production process, we assume that the item being processed is lost because of interruption. That is, the production process, on being interrupted, restarts from the beginning, after repair. The repair time of an interrupted production process follows exponential distribution. Few of the last service phases are assumed to be protected in the sense that the service will not be interrupted while being in these phases. The same is assumed for the production process also.

The model is analysed as a level-independent quasi-birth–death process. We apply a novel method to obtain an explicit expression for the necessary and sufficient condition for the stability of the system under study. This method works even if we assume general phase-type distributions for the production as well as the service processes, and hence can be used to characterise the stability of inventory systems where the assumption of disallowing the customers to join the system, when there is a shortage of inventory has been made. Under stability, we apply matrix analytic methods to compute the system state distribution. In consequence to that, several system performance measures have been derived, and their dependence on the system parameters has been studied numerically.     

Frequency dependent stiffness and damping coefficients of orifice compensated multi-recess hydrostatic journal bearings

Frequency dependent stiffness and damping characteristics of an orifice compensated multi-recess hydrostatic journal bearing has been presented incorporating recess volume fluid compressibility effects into it. The theory is based on linearising the Reynolds' equation for finite bearings and the recess flow continuity equation using first order perturbations. A new dimensionless recess volume fluid compressibility parameter (γ) has been introduced. Results for stiffness and damping characteristics have been presented for various frequency of vibration or squeeze parameters (σ) and recess volume parameters (γ) in addition to the usual bearing design parameters.     

Dispersion of chitosan on perlite for enhancement of copper(II) adsorption capacity

Chitosan coated perlite beads were prepared by drop-wise addition of slurry, made of chitosan dissolved in oxalic acid and perlite, to an alkaline bath (0.7 M NaOH). The beads that contained 32% chitosan enhanced the accessibility of OH and amine groups present in chitosan for adsorption of copper ions. The experiments using Cu(II) ions were carried out in the concentration range of 50-4100 mg/L (0.78-64.1 mmol/L). Adsorption capacity for Cu(II) was pH dependent and a maximum uptake of 104 mg/g of beads (325 mg/g of chitosan) was obtained at pH 4.5 when its equilibrium concentration in the solution was 812.5 mg/L at 298 K. The XPS and TEM data suggested that copper was mainly adsorbed as Cu(II) and was attached to amine groups. The adsorption data could be fitted to one-site Langmuir adsorption model. Anions in the solution had minimal effect on Cu(II) adsorption by chitosan coated perlite beads. EDTA was used effectively for the regeneration of the bed. The diffusion coefficient of Cu(II) onto chitosan coated beads was calculated from the breakthrough curve and was found to be 2.02 x 10(-8) cm(2)/s.