Thiophene-based molecular and polymeric semiconductors for organic field effect transistors and organic thin film transistors

Organic electronics has been a popular field for the last two decades, due to its potential to commercialize cheap-price and large-area flexible electronics. The devices based on organic compounds heavily rely on organic semiconductors (OSs). Primary challenge for materials chemist is the new OSs construction that has ameliorated attainment in organic thin film transistors (OTFTs) and organic field effect transistors (OFETs). The construction of air-stable (stable in air) n-channel OSs (electron-conducting materials) is particularly needed with capability comparable to that of p-channel materials (hole-conducting materials). In the last 10 years, there have been significant advancements in thiophene-based OSs. Thiophene-mediated molecules have a prominent role in the advancement of OSs. The main significance in thiophene-based molecules is their cheap-price (in comparison to silicon), processability at low temperature, structural flexibility, ability to be applied on flexible substrates, and high charge transport characteristics. In this paper, we review the progress in the performance of thiophene-based OSs that has been reported in the last 18 years, with a major emphasis on the last 10 years. This approach provides a crisp introduction to organic devices and catalogs progress toward the fabrication of thiophene containing p, n and ambipolar channel OSs, and discusses their characteristics. Finally, review discusses current challenges and future research directions for thiophene based OSs. This review would be beneficial for further developments in the technological performance. Moreover, this review will serve to accelerate knowledge and lays the foundation for improved applications. Hopefully, this struggle pushes the reader’s mind to consider new perspectives, think differently and forge new connections.     

Study of Hydrology and Drought in the Flood Region of Sudan

ABSTRACT

An attempt is made to thoroughly investigate the important hydrological features ofhe flood region that is located in the southern part of Sudan. The hydrologic data that were used in the study include temperature, precipitation, sunshine duration. radiation, humidity, wind speed, and evaporation. The investigation also includes the stream flow records of the Nile River in the region. In this region, a huge amount of the Nile water is lost by evaporation and overspilling. The hydrological data of Malakal meteorological station, taken as the index station, and the long-term flow data of the White Nile and its principal tributary, the Sobat, have been analyzed. The effect of changes in the behavior of the hydrological factors on the degree of aridity is also assessed. The study clearly indicates significant changes in the hydrological behavior of the region characterized by an increase in temperature levels and a substantial reduction in rainfall and river flows.     

A joint resource optimization and adaptive modulation framework for uplink single‐carrier frequency‐division multiple access systems

In this paper, we study joint resource allocation and adaptive modulation in single‐carrier frequency‐division multiple access systems, which is adopted as the multiple access scheme for the uplink in the 3GPP Long Term Evolution standard. We formulate an adaptive modulation and sum‐cost minimization (JAMSCmin) problem. Unlike orthogonal frequency‐division multiple access, in addition to the restriction of allocating a subchannel to one user at most, the multiple subchannels allocated to a user in single‐carrier frequency‐division multiple access systems should be consecutive as well. This renders the resource allocation problem prohibitively difficult and the standard optimization tools (e.g., Lagrange dual approach widely used for orthogonal frequency‐division multiple access, etc.) cannot help towards its optimal solution. We propose a novel optimization framework for the solution of this problem that is inspired from the recently developed canonical duality theory. We first formulate the optimization problem as binary‐integer programming (BIP) problem and then transform this BIP problem into continuous space canonical dual problem that is the concave maximization problem. Based on the solution of the canonical dual problem, we derive joint resource allocation and adaptive modulation algorithm, which has polynomial time complexity. We provide conditions under which the proposed algorithm is optimal. We compare the proposed algorithm with the existing algorithms in the literature. The results show a tremendous performance gain. Copyright © 2013 John Wiley & Sons, Ltd.     

Measuring elastic constants of Hevea brasiliensis using compression and Iosipescu shear test

The increasing demand and widespread utility of wood composite products necessitate the knowledge of the orthotropic engineering and strength properties of the raw wood used for its safe design and effective performance. This research study aimed at finding the orthotropic elastic parameters of a sustainable timber in India, namely rubber wood (Hevea brasiliensis) with respect to the material axes longitudinal (L), radial (R) and tangential (T), which is a potential raw material for laminated products as verified. This study evaluated the three Young’s moduli, the three shear moduli and the six Poisson’s ratios of the wood species, unavailable in literature. Compression test in rectangular prism was used for the determination of the Young’s moduli and Poisson’s ratios. Shear characterization in the three material planes was done using the Iosipescu test. The highest value of normal stiffness of the material in compression was obtained in the longitudinal direction followed by radial stiffness and tangential stiffness. The shear stiffness was largest in the LR plane followed by LT and RT planes. RT plane exhibited the highest Poisson’s ratio and TL plane the lowest. Significant difference was noted in the shear strength of LR planes between block shear test and Iosipescu test but not with the LT planes.     

An Efficient and Scalable Routing for MANETs

Recently, Distributed-Hash-Table (DHT)-based routing protocols have been proposed for large scale mobile ad hoc networks (MANETs). The motive behind using DHT is to avoid/reduce network wide flooding in MANETs in route discovery phase leading to achieve more scalable network. The challenge of deploying DHT at network layer for routing purpose in MANETs is to achieve more matching between logical and physical networks. The paper describes that existing DHT-based routing protocols for MANETs lack this feature. The paper presents a new DHT based scheme [called an efficient and scalable routing for MANETs (ESR)] which reduces the ill-matching between logical and physical networks. This is achieved be distributing the logical identifier (LID) space of DHT structure among the nodes such that the physical neighbors have consecutive LID space portions, i.e. all physical neighbors of a node are also the logical neighbors of the node. Therefore the logical ID space portion of a node may be non-contiguous. Based on this logical structure, a node builds up binary-search-tree (BST) using both logical ID space portion of itself and its neighbors. This BST at the node is traversed to find the next hop for a query/message. Through simulation, the paper shows the proposed approach (ESR) performs better than the existing one in term of routing overhead, average end-to-end delay, path-stretch values and false-negative ratio.     

Growth on poly(l-lactic acid) porous scaffold preserves CD73 and CD90 immunophenotype markers of rat bone marrow mesenchymal stromal cells

Few data are available on the effect of biomaterials on surface antigens of mammalian bone marrow-derived, adult mesenchymal stromal cells (MSCs). Since poly(l-lactic acid) or PLLA is largely used in tissue engineering of human bones, and we are developing a reverse engineering program to prototype with biomaterials the vascular architecture of bones for their bioartificial reconstruction, both in humans and animal models, we have studied the effect of porous, flat and smooth PLLA scaffolds on the immunophenotype of in vitro grown, rat MSCs in the absence of any coating, co-polymeric enrichment, and differentiation stimuli. Similar to controls on plastic, we show that our PLLA scaffold does not modify the distribution of some surface markers in rat MSCs. In particular, the maintained expression of CD73 and CD90 on two different subpopulations (small and large cells) is consistent with their adhesion to the PLLA scaffold through specialized appendages, and to their prominent content in actin. In addition, our PLLA scaffold favours retention of the intermediate filament desmin, believed a putative marker of undifferentiated state. Finally, it preserves all rat MSCs morphotypes, and allows for their survival, adhesion to the substrate, and replication. Remarkably, a subpopulation of rat MSCs grown on our PLLA scaffold exhibited formation of membrane protrusions of uncertain significance, although in a size range and morphology compatible with either motility blebs or shedding vesicles. In summary, our PLLA scaffold has no detrimental effect on a number of features of rat MSCs, primarily the expression of CD73 and CD90.     

Zinc-Blende MnTe Under Pressure: Structural,Mechanical, and Optical Properties from Ab Initio Calculation

We present first-principles studies of structural, mechanical, and optical properties of zinc blende MnTe using the pseudopotential plane-wave method within the local density approximation. The effect of hydrostatic pressure on investigated properties has been examined and discussed. At zero pressure, our results are found to agree reasonably well with those reported in the literature. The generalized elastic stability criteria showed that the material of interest is mechanically stable in all the studied pressure ranges. Applied pressure is found to shift all optical spectra under consideration, giving new optical parameters.     

Automatic rule installation in case of policy change in software defined networks

Software Defined Networking (SDN) has emerged recently as a new network architecture. It implements both control and management planes at centralized controller and data plane at forwarding devices. Therefore, SDN helps to simplify network management and improves network programmability. Changes in network policies occur frequently by making modifications at controller. However, in existing approaches, the rules installed at switches before policy change at controller are not modified. This can cause violation of network policy by packets. To address this problem, this paper presents a new approach that stores the rules generated at controller. After detecting the change in policy, the proposed approach finds the rules that will be affected by policy change by examining stored rules at controller. Then the affected rules are removed from the forwarding devices. Simulation results reveal that our proposed approach provides less packets violation ratio and normalized traffic overhead as compared to existing approach. Therefore, the proposed approach increases network performance and efficiency.