Selective toxicity of hydroxyl-rich carbon nanodots for cancer research

Nano Research - The toxicity of nanoparticles in a biological system is an integration of effects arising from surface functionality, particle size, ionic dissolution, etc. This complexity suggests...     

Failure analysis of unidirectional polymeric matrix composites with two serial pin loaded-holes

The objective of this study is to investigate the effects of geometrical and physical parameters on failure modes and failure loads in unidirectional polymeric matrix composites with two serial pin loaded holes, analytically and experimentally. It is assumed that all of unidirectional fibers in the laminate lie in one direction while loaded by a load p ₀ at infinity, parallel to the direction of the fibers. To derive equilibrium equations based on a Shear-Lag theory, a rectangular arrangement of fibers is considered and with the proper use of boundary and boundness conditions, stress and displacement fields are computed within the laminate, along with the surrounding pinholes. Finally by using the Hashin criterion failure modes and failure loads are estimated. To validate analytical results based on shear-lag theory, an experimental program is carried out. A very good agreement is observed between two procedures. Based on results, in small sizes of two pins, the dominant failure mode is bearing and with the increasing of hole sizes, failure modes are changed to tension and shear modes.     

Cleaning method of InSb [111] B of n-InSb [111] A/B for the growth of epitaxial layers by liquid phase epitaxy

The crystal structure of InSb[111]A/B surfaces shows that this structure is polarized.This means that the surfaces of InSb[111]A and InSb[111]B contain two different crystallized directions and they have different physical and chemical properties.Experiments were carried out on the InSb[111]A/B surfaces,showing that tartaric acid etchant could create a very smooth surface on the InSb[111]B without any traces of oxides and etch pit but simultaneously create etch pit on InSb[111]A surfaces.After lapping and polishing,some particles remained on the InSb[111]B surface,they could not be removed easily by standard cleaning process and if these particles remain on the surface of the substrate,the growth layer was not uniform and some island-like regions were observed.The purpose of this work is to remove these particles on the InSb[111]B surface.Some morphology images of both surfaces,InSb[111]A/B,will be presented.     

Rapid Biofabrication of Printable Dense Collagen Bioinks of Tunable Properties

Recent convergence of the 3D printing of tissue‐like bioinks and regenerative medicine offers promise in the high‐throughput engineering of in vitro tissue models and organoids for drug screening and discovery research, and of potentially implantable neo‐tissues with tailored structural, biological, and mechanical properties. However, the current printing approaches are not compatible with collagen, the native scaffolding material. Herein, a unique biofabrication approach that uses automated gel aspiration‐ejection (GAE) is reported to potentially overcome these challenges. Automated‐GAE generates highly defined, aligned, dense collagen gel bioinks of various geometries (i.e., cylindrical, quadrangular, and tubular), dimensions, as well as tunable microstructural and mechanical properties that modulate seeded cellular responses. By densifying initial naturally derived reconstituted collagen hydrogels incorporating cells, automated‐GAE generates mini‐tissue building blocks with tailored protein fibril density and alignment, as well as cell loading, density and orientation according to the intended use. Surprisingly, a simple mathematical relationship defining the bioink compaction factor is found to be highly effective in predicting the initial and temporal properties of the bioinks in culture. Therefore, automated‐GAE will potentially also enable a fourth dimension to biofabrication, where cell–cell communications and cell‐extracellular matrix interactions as a function of time in culture can be predicted and modeled.     

A Framework on the Performance Analysis of Cooperative Wireless Body Area Networks

Wireless body area networks (WBANs) are deal with wireless networks in the human body. We describe the performance analysis of dual-hop cooperative relaying systems employing amplify-and-forward (AF) technique in WBANs over independent and nonnecessary identically distributed Gamma fading channels. More specifically, we present closed-form derivations of the outage probabilities (OP), symbol error probabilities (SEP) and ergodic capacity (EC) for fixed gain and channel state information (CSI)-assisted relaying techniques at arbitrary signal-to-noise-ratios (SNRs). We also deduce novel expressions in the high SNR region. By doing so, we can quantify the performance of system by the diversity and coding gains. Using the derived expressions as a starting point and for the case of Exponential fading, we consider three practical optimization scenarios. They are optimal relay position with fixed power allocation, power allocation under the fixed location of the relay and joint optimization of power allocation and relay position under a transmit power constraint. The Monte Carlo simulations are used to validate the accuracy of our derivations, where it is demonstrated that the proposed adaptive allocation method significantly outperforms the fixed allocation method.

     

Estimating the scattering distribution of the received signals in multipath fading channels

This paper presents a novel approach for estimating the distribution of the incoming waves at the mobile unit antenna, i.e. the scattering distribution, in a typical micro-cellular system. This estimate is vital in determining many system parameters of interest as well as designing unbiased estimators for the velocity of mobile units in micro-cellular systems. The proposed approach deploys the zero-crossing rates of the quadrature components and the instantaneous frequency of the received signal at the mobile unit to estimate the scattering distribution. We also propose a new model for simulating multipath fading channels with non-isotropic scattering. We use the channel simulator to evaluate the performance of the proposed estimator for the scattering distribution. Simulation results show that proposed estimator exhibits small bias and root mean square error.     

An evolutionary game theory–based security model in vehicular ad hoc networks

The word population is growing on a daily basis; consequently, the growth of commute and transport, developing efficient and intelligent transportation systems (ITS), has become one of the most popular requirements and the most significant attempts in modern urban areas containing large population. A key component of intelligent transportation systems is a vehicular ad hoc network. Devising internet‐based practical programs such as awareness of climatic conditions, geographical location, practical programs like on‐line payment services in the vehicular ad hoc network has led to safer driving, prevention of deadly accidents, transportation improvement, more welfare and convenience for passengers, and even offering more commercial opportunities. The special features of vehicular ad hoc network, such as intense activity, constantly‐changing topology, the vehicles' high speed, etc, will lead to challenges in gaining security. Therefore, providing vehicular ad hoc networks with security is of extreme importance in terms of users' anonymity, identification, and data privacy. In this paper, a security model is presented using a method based on evolutionary games. This method, in every vehicle, is applied as a node in the network while interacting with other vehicles; it aims at distinguishing some common attacks and defending against attackers. In this method, defending (honest) vehicles and attacking vehicles take part in an asymmetrical game; each vehicle aims at gaining the most utility and achieving its goals. The proposed method is simulated using various scenarios. The simulation results reveal that the proposed method is efficient and it reaches equilibrium and convergence at the end of the game in each scenario.     

Bounds on capacity and minimum energy-per-bit for AWGN relay channels

Upper and lower bounds on the capacity and minimum energy-per-bit for general additive white Gaussian noise (AWGN) and frequency-division AWGN (FD-AWGN) relay channel models are established. First, the max-flow min-cut bound and the generalized block-Markov coding scheme are used to derive upper and lower bounds on capacity. These bounds are never tight for the general AWGN model and are tight only under certain conditions for the FD-AWGN model. Two coding schemes that do not require the relay to decode any part of the message are then investigated. First, it is shown that the "side-information coding scheme" can outperform the block-Markov coding scheme. It is also shown that the achievable rate of the side-information coding scheme can be improved via time sharing. In the second scheme, the relaying functions are restricted to be linear. The problem is reduced to a "single-letter" nonconvex optimization problem for the FD-AWGN model. The paper also establishes a relationship between the minimum energy-per-bit and capacity of the AWGN relay channel. This relationship together with the lower and upper bounds on capacity are used to establish corresponding lower and upper bounds on the minimum energy-per-bit that do not differ by more than a factor of 1.45 for the FD-AWGN relay channel model and 1.7 for the general AWGN model.     

Information properties of order statistics and spacings

We explore properties of the entropy, Kullback-Leibler information, and mutual information for order statistics. The probability integral transformation plays a pivotal role in developing our results. We provide bounds for the entropy of order statistics and some results that relate entropy ordering of order statistics to other well-known orderings of random variables. We show that the discrimination information between order statistics and data distribution, the discrimination information among the order statistics, and the mutual information between order statistics are all distribution free and are computable using the distributions of the order statistics of the samples from the uniform distribution. We also discuss information properties of spacings for uniform and exponential samples and provide a large sample distribution-free result on the entropy of spacings. The results show interesting symmetries of information orderings among order statistics.     

Analytical comparison of various fiber-optic CDMA receiverstructures

We study the performance of optical code-division multiple access (CDMA) systems using various receivers structures. Two general classes of receivers based on required electronic bandwidth are studied. Optical orthogonal codes (OOCs) are utilized as signature sequences and the performance studied in this paper takes into account the effect of all major noise sources, i.e., quantum shot-noise, dark current noise, and Gaussian circuit noise. Furthermore, this paper introduces a generalized method of analyzing the performance of various optical CDMA receiver structures. Required mean number of photon count per chip time for reliable transmission of data bits for various receiver structures is investigated. Finally, the advantages and disadvantages of various receiver structures are discussed