Optimal load balanced clustering in homogeneous wireless sensor networks

Balancing the load among sensor nodes is a major challenge for the long run operation of wireless sensor networks. When a sensor node becomes overloaded, the likelihood of higher latency, energy loss, and congestion becomes high. In this paper, we propose an optimal load balanced clustering for hierarchical cluster‐based wireless sensor networks. We formulate the network design problem as mixed‐integer linear programming. Our contribution is 3‐fold: First, we propose an energy aware cluster head selection model for optimal cluster head selection. Then we propose a delay and energy‐aware routing model for optimal inter‐cluster communication. Finally, we propose an equal traffic for energy efficient clustering for optimal load balanced clustering. We consider the worst case scenario, where all nodes have the same capability and where there are no ways to use mobile sinks or add some powerful nodes as gateways. Thus, our models perform load balancing and maximize network lifetime with no need for special node capabilities such as mobility or heterogeneity or pre‐deployment, which would greatly simplify the problem. We show that the proposed models not only increase network lifetime but also minimize latency between sensor nodes. Numerical results show that energy consumption can be effectively balanced among sensor nodes, and stability period can be greatly extended using our models.     

An SoC with 1.3 gtexels/s 3-D graphics full pipeline for consumer applications

A high-speed three-dimensional (3-D) graphics SoC for consumer applications is presented. A 166-MHz 3-D graphics full pipeline engine with performance of 33 Mvertices/s and 1.3Gtexels/s, and 333-MHz ARM11 RISC processor, and video composition IPs are integrated together on a single chip. The geometry part of 3-D graphics IP provides full programmability in vertex and triangle level, and two-level multi-texturing with trilinear MIPMAP filtering are realized in the rasterization part. Per-pixel effects such as fog effects, alpha blending, and stencil test are also implemented in the proposed 3-D graphics IP. The rasterization architecture is designed for reducing external memory accesses to achieve the peak performance. The chip is fabricated using 0.13/spl mu/m CMOS technology and its area is 7.1/spl times/7.0mm/sup 2/.     

Self‐assembled Electroactive Phosphonic Acids on ITO: Maximizing Hole‐Injection in Polymer Light‐Emitting Diodes

In order to fulfill the promise of organic electronic devices, performance‐limiting factors, such as the energetic discontinuity of the material interfaces, must be overcome. Here, improved performance of polymer light‐emitting diodes (PLEDs) is demonstrated using self‐assembled monolayers (SAMs) of triarylamine‐based hole‐transporting molecules with phosphonic acid‐binding groups to modify the surface of the indium tin oxide (ITO) anode. The modified ITO surfaces are used in multilayer PLEDs, in which a green‐emitting polymer, poly[2,7‐(9,9‐dihexylfluorene)‐co‐4,7‐(2,1,3‐benzothiadiazole)] (PFBT5), is sandwiched between a thermally crosslinked hole‐transporting layer (HTL) and an electron‐transporting layer (ETL). All tetraphenyl‐diamine (TPD)‐based SAMs show significantly improved hole‐injection between ITO and the HTL compared to oxygen plasma‐treated ITO and simple aromatic SAMs on ITO. The device performance is consistent with the hole‐transporting properties of triarylamine groups (measured by electrochemical measurements) and improved surface energy matching with the HTL. The turn‐on voltage of the devices using SAM‐modified anodes can be lowered by up to 3 V compared to bare ITO, yielding up to 18‐fold increases in current density and up to 17‐fold increases in brightness at 10 V. Variations in hole‐injection and turn‐on voltage between the different TPD‐based molecules are attributed to the position of alkyl‐spacers within the molecules.     

Implementation of an open platform for 3D spatial information based on WebGL

VWorld is run by the Ministry of Land, Infrastructure, and Transport of South Korea and provides national spatial information, such as aerial images, digital elevation models, and 3D structural models. We propose herein an open platform for 3D spatial information based on WebGL using spatial information from VWorld. WebGL is a web‐based graphics library and has the advantage of being compatible with various web browsers. Our open platform is also compatible with various web browsers. Accordingly, it is easily accessible via the VWorld site and uses the three‐dimensional (3D) map program. In this study, we describe the proposed platform configuration, and the requests, management, and visualization approaches for VWorld spatial information data. Our aim is to establish an approach that will provide a stable rendering speed even on a low‐end personal computer without a graphics processing unit based on a quadtree structure. We expect that users will be able to visualize 3D spatial information through the VWorld open platform, and that the proposed platform will become the basis for various applications.     

Integration of Density Multiplication in the Formation of Device‐Oriented Structures by Directed Assembly of Block Copolymer–Homopolymer Blends

Non‐regular, device‐oriented structures can be directed to assemble on chemically nanopatterned surfaces such that the density of features in the assembled pattern is multiplied by a factor of two or more compared to the chemical pattern. By blending the block copolymers with homopolymers and designing the chemical pattern rationally, complicated structures such as bends, jogs, junctions, terminations, and combined structures are fabricated. Previously, directed assembly of block copolymers has been shown to enhance the resolution of lithographic processes for hexagonal arrays of spots and parallel lines, corresponding to the bulk morphologies of block copolymer systems, but this is the first demonstration of enhanced resolution for more complicated, device‐oriented features. This fundamental knowledge broadens the range of technologies that can be served by the directed assembly of block copolymers.     

Extracting Graphics Information for Better Video Compression

Cloud gaming services are heavily dependent on the efficiency of real‐time video streaming technology owing to the limited bandwidths of wire or wireless networks through which consecutive frame images are delivered to gamers. Video compression algorithms typically take advantage of similarities among video frame images or in a single video frame image. This paper presents a method for computing and extracting both graphics information and an object's boundary from consecutive frame images of a game application. The method will allow video compression algorithms to determine the positions and sizes of similar image blocks, which in turn, will help achieve better video compression ratios. The proposed method can be easily implemented using function call interception, a programmable graphics pipeline, and off‐screen rendering. It is implemented using the most widely used Direct3D API and applied to a well‐known sample application to verify its feasibility and analyze its performance. The proposed method computes various kinds of graphics information with minimal overhead.     

On‐Demand Liquid Transportation Using Bioinspired Omniphobic Lubricated Surfaces Based on Self‐Organized Honeycomb and Pincushion Films

In this work, on‐demand control of liquids is realized by using elastic, patterned omniphobic surfaces. This paves the way for novel microfluidics, as well as liquid harvesting, transportation, and manipulation technologies. Inspired by the lubricating properties of pitcher plants, microstructured 1,2‐polybutadiene honeycomb and pincushion films obtained by self‐organization are fluorinated by the ene‐thiol reaction and infused with fluorinated lubricant to obtain omniphobic liquid‐repellent surfaces. Unlike conventional bioinspired omniphobic surfaces, the liquid repellency of the fabricated surface can be programmed by changing the surface microstructures via patterning of the film. Furthermore, the elasticity of the omniphobic film is suitable for controlling the repellency through external stimuli. The method presented here for the fabrication of lubricant‐infused omniphobic microstructured surfaces is also simple, cost‐effective, and can be scaled for large area fabrication.     

High-frequency RCS of complex radar targets in real-time

This paper presents a new and original approach for computing the high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. The aircraft is modeled with I-DEAS solid modeling software using a parametric surface approach. High-frequency RCS is obtained through physical optics (PO), method of equivalent currents (MEC), physical theory of diffraction (PTD), and impedance boundary condition (IBC). This method is based on a new and original implementation of high-frequency techniques which the authors have called graphical electromagnetic computing (GRECO). A graphical processing approach of an image of the target at the workstation screen is used to identify the surfaces of the target visible from the radar viewpoint and obtain the unit normal at each point. High-frequency approximations to RCS prediction are then easily computed from the knowledge of the unit normal at the illuminated surfaces of the target. The image of the target at the workstation screen (to be processed by GRECO) can be potentially obtained in real time from the I-DEAS geometric model using the 3-D graphics hardware accelerator of the workstation. Therefore, CPU time for RCS prediction is spent only on the electromagnetic part of the computation, while the more time-consuming geometric model manipulations are left to the graphics hardware. This hybrid graphic-electromagnetic computing (GRECO) results in real-time RCS prediction for complex radar targets     

Controlled Folding of 2D Au–Polymer Brush Composites into 3D Microstructures

Microscale, quasi‐2D Au–polymer brush composite objects are fabricated by a versatile, controllable process based on microcontact printing followed by brush growth and etching of the substrate. These objects fold into 3D microstructures in response to a stimulus: crosslinked poly(glycidyl methacrylate) (PGMA) brushes fold on immersion in MeOH, and poly(methacryloxyethyl trimethylammonium chloride) (PMETAC) brushes fold on addition of salt. Microcages and microcontainers are fabricated. A multistep microcontact printing process is also used to create sheets of Au–PGMA bilayer lines linked by a PGMA film, which fold into cylindrical tubes. The bending of these objects can be predicted, and hence predefined during the synthesis process by controlling the parameters of the gold layer, and of the polymer brush.     

A level-set approach to image blending

This paper presents a novel method for blending images. Image blending refers to the process of creating a set of discrete samples of a continuous, one-parameter family of images that connects a pair of input images. Image blending has uses in a variety of computer graphics and image processing applications. In particular, it ran be used for image morphing, which is a method for creating video streams that depict transformations of objects in scenes based solely on pairs of images and sets of user-defined fiducial points. Image blending also has applications for video compression and image-based rendering. The proposed method for image blending relies on the progressive minimization of a difference metric which compares the level sets between two images. This strategy results in an image blend which is the solution of a pair of coupled, nonlinear, first-order partial differential equations that model multidimensional level-set propagations. When compared to interpolation this method produces more natural appearances of motion because it manipulates the shapes of image contours rather than simply interpolating intensity values. This strategy results in a process that has the qualitative property of deforming greyscale objects in images rather than producing a simple fade from one object to another. This paper presents the mathematics that underlie this new method, a numerical implementation, and results on real images that demonstrate its effectiveness.     

Adhesion Selectivity Using Rippled Surfaces

Highly selective adhesion can be achieved between surfaces by patterning them with ripples. Materials with such surfaces are fabricated by successive molding of an elastomer, poly(dimethylsiloxane) (PDMS), against a master with a surface rippled by instability of a residually stressed surface thin film. Adhesion of interfaces between both complementary and non‐complementary rippled surfaces was measured. Complementary surfaces showed significantly enhanced interfacial adhesion with increasing ripple amplitude. In contrast, interfaces with mismatched amplitudes had nearly negligible adhesion. Rate‐dependence of adhesion in these surfaces was also studied. For complementary surfaces with low amplitudes we found a multiplicative coupling between the structure and rate enhancement of adhesion. A quantitative model developed for adhesion between complementary surfaces explains these observations.     

Phase and Composition Tuning of 1D Platinum‐Nickel Nanostructures for Highly Efficient Electrocatalysis

Among various platinum (Pt)‐based nanostructures, porous or hollow ones are of great importance because they exhibit fantastic oxygen reduction reaction (ORR) enhancements and maximize atomic utilization by exposing both exterior and interior surfaces. Here, a new class of porous Pt₃Ni nanowires (NWs) with 1D architecture, an ultrathin Pt‐rich shell, high index facets, and a highly open structure is designed via a selective etching strategy by using the phase and composition segregated Pt‐Ni NWs as the starting material. The porous feature of Pt₃Ni NWs can be readily fulfilled by changing the Pt/Ni atomic ratio of the starting Pt‐Ni NWs. Such porous Pt₃Ni NWs show extraordinary activity and stability enhancements toward methanol oxidation reaction and ORR. The porous Pt₃Ni NWs can deliver ORR mass activity of 5.60 A mg^?1, which is 37.3‐fold higher than that of the Pt/C. They also show outstanding stability with negligible activity loss after 20 000 cycles. This study offers a unique approach for the design of complex nanostructures as efficient catalysts through precisely tailoring.     

Registration of 3-D head surfaces using multiple landmarks

A mathematical procedure based on Newton's method is described that enables surface measurements to be registered, or normalized, with respect to spatial position, orientation, and, optionally, scale in three dimensions. An operator is required to identify homologous landmarks on the computer graphics images of surfaces to be registered. In this application, where the method is used to measure changes in facial shape, these landmarks are restricted to parts of the surface that have remained unchanged between the surfaces to be registered. Error in the registration of landmarks is minimized in a least-squares sense; hence multiple landmarks are favored to minimize the effect of individual errors produced by the measuring system and the operator. Examples are presented using measurements of the head taken with an optical surface scanner and a conventional X-ray computed tomography scanner.     

Decorating Liquid Crystal Surfaces with Proteins for Real‐Time Detection of Specific Protein–Protein Binding

Here, a novel method of immobilizing proteins with well‐defined orientation directly on liquid crystal surfaces that allow subsequent real‐time imaging of specific protein–protein binding events on these surfaces is reported. Self‐assembly of nitrilotriacetic acid terminated amphiphiles loaded with Ni²⁺ ions at aqueous‐liquid crystal interface creates a surface capable of immobilizing histidine‐tagged ubiquitin through complex formation between Ni²⁺ and histidine. When these surfaces containing immobilized histidine‐tagged ubiquitin are exposed to anti‐ubiquitin antibody, the spatial and temporal of specific protein–protein binding events trigger orientational transitions of liquid crystals. As a result, sharp liquid crystal optical switching from dark to bright can readily be observed under polarized lighting. The protein–protein binding can be observed within seconds and only requires nanogram quantities of proteins. This work demonstrates a simple strategy to immobilize proteins with well‐defined orientation on liquid crystal surfaces for real‐time and label‐free detection of specific protein–protein binding events, which may find use in biomedical diagnostics.     

Room‐Temperature Self‐Organizing Characteristics of Soluble Acene Field‐Effect Transistors

We report on the room‐temperature self‐organizing characteristics of thin films of the organic small‐molecule semiconductor triethylsilylethynyl‐anthradithiophene (TES‐ADT) and its effect on the electrical properties of TES‐ADT‐based field‐effect transistors (FETs). The morphology of TES‐ADT films changed dramatically with time, and the field‐effect mobility of FETs based on these films increased about 100‐fold after seven days as a result of the change in molecular orientation from a tilted structure in the as‐prepared film to a well‐oriented structure in the final film. We found that the molecular movement is large enough to induce a conformational change to an energetically stable state in spin‐coated TES‐ADT films, because TES‐ADT has a low glass‐transition temperature (around room temperature). Our findings demonstrate that organic small‐molecule semiconductors that exhibit a low crystallinity immediately after spin‐coating can be changed into highly crystalline structures by spontaneous self‐organization of the molecules at room temperature, which results in improved electrical properties of FETs based on these semiconductors.     

Reconfigurable Surfaces Based on Photocontrolled Dynamic Bonds

Photocontrolled surfaces have attracted increasing interest because of their potential applications in lithography, photopatterning, biointerfaces, and microfluidics. Light provides high spatiotemporal resolution to control functions of such surfaces without getting into direct contact. However, conventional photocontrolled surfaces can only be switched between two states (on and off). The development of photocontrolled reconfigurable surfaces that can be switched among multiple states is highly desirable because these surfaces can adapt to rapid environmental changes or different applications. Herein, recent developments of photocontrolled reconfigurable surfaces are reviewed. Specially, reconfigurable surfaces based on photocontrolled reversible reactions including thiol‐quinone methide, disulfide exchange, thiol‐disulfide interconversion, diselenide exchange, and photosubstitution of Ru complexes are highlighted. As a perspective, other photocontrolled dynamic bonds that can be used to construct reconfigurable surfaces are summarized. Remaining challenges in this field are discussed.     

Microtribology of Aqueous Carbon Nanotube Dispersions

The tribological behavior of carbon nanotubes (CNTs) in aqueous humic acid (HA) solutions was studied using a surface forces apparatus (SFA) and shows promising lubricant additive properties. Adding CNTs to the solution changes the friction forces between two mica surfaces from “adhesion controlled” to “load controlled” friction. The coefficient of friction with either single‐walled (SW) or multi‐walled (MW) CNT dispersions is in the range 0.30–0.55 and is independent of the load and sliding velocity. More importantly, lateral sliding promotes a redistribution or accumulation, rather than squeezing out, of nanotubes between the surfaces. This accumulation reduced the adhesion between the surfaces (which generally causes wear/damage of the surfaces), and no wear or damage was observed during continuous shearing experiments that lasted several hours even under high loads (pressures ～10 MPa). The frictional properties can be understood in terms of the Cobblestone Model where the friction force is related to the fraction of the adhesion energy dissipated during impacts of the nanoparticles. We also develop a simple generic model based on the van der Waals interactions between particles and surfaces to determine the relation between the dimensions of nanoparticles and their tribological properties when used as additives in oil‐ or water‐based lubricants.     

Length‐Scale Mediated Differential Adhesion of Mammalian Cells and Microbes

Surfaces of implantable biomedical devices are increasingly engineered to promote their interactions with tissue. However, surfaces that stimulate desirable mammalian cell adhesion, spreading, and proliferation also enable microbial colonization. The biomaterials‐associated infection that can result is now a critical clinical problem. We have identified an important mechanism to create a surface that can simultaneously promote healing while reducing the probability of infection. Surfaces are created with submicrometer‐sized, non‐adhesive microgels patterned on an otherwise cell‐adhesive surface. Quantitative force measurements between a staphylococcus and a patterned surface show that the adhesion strength decreases significantly at inter‐gel spacings comparable to bacterial dimensions. Time‐resolved flow‐chamber measurements show that the microbial deposition rate dramatically decreases at these same spacings. Importantly, the adhesion and spreading of osteoblast‐like cells is preserved despite the sub‐cellular non‐adhesive surface features. Since such length‐scale‐mediated differential interactions do not rely on antibiotics, this mechanism can be particularly significant in mitigating biomaterials‐associated infection by antibiotic‐resistant bacteria such as MRSA.     

A novel silicon texturization method based on etching through a silicon nitride mask

We present a new texturing technique applicable to silicon solar cells. The technique is based on the isotropic etching of silicon through a very thin layer of silicon nitride, deposited by low‐pressure chemical vapor deposition. Spectrophotometry measurements show that the resulting surface texture displays low reflectivity after encapsulation behind glass, and nearly ideal light‐trapping behaviour. The surfaces can also be well passivated using standard passivation techniques. Emitter dark saturation currents in the range 4–5 × 10⁻¹⁴ A/cm² have been measured by quasi‐steady‐state photoconductance following the growth of a thermal oxide. Copyright © 2005 John Wiley & Sons, Ltd.