Connectivity properties of large-scale sensor networks

In wireless sensor networks, both nodes and links are prone to failures. In this paper we study connectivity properties of large-scale wireless sensor networks and discuss their implicit effect on routing algorithms and network reliability. We assume a network model of n sensors which are distributed randomly over a field based on a given distribution function. The sensors may be unreliable with a probability distribution, which possibly depends on n and the location of sensors. Two active sensor nodes are connected with probability p _e (n) if they are within communication range of each other. We prove a general result relating unreliable sensor networks to reliable networks. We investigate different graph theoretic properties of sensor networks such as k-connectivity and the existence of the giant component. While connectivity (i.e. k = 1) insures that all nodes can communicate with each other, k-connectivity for k > 1 is required for multi-path routing. We analyze the average shortest path of the k paths from a node in the sensing field back to a base station. It is found that the lengths of these multiple paths in a k-connected network are all close to the shortest path. These results are shown through graph theoretical derivations and are also verified through simulations.     

Sol-gel processed silica/titania/ÿ-Glycidoxypropyltrimethoxysilane composite materials for photonic applications

Silica/titania/?-Glycidoxypropyltrimethoxysilane composite materials processed by the sol-gel technique were studied for photonic applications. Waveguide thin films with thickness more than 1.7 μm were prepared by the sol-gel spin coating technique and low temperature heat treatment from this high titanium content composite materials. The films were analyzed by atomic force microscopy (AFM), ellipsometry, differential thermal analysis (DTA), thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-VIS), and Fourier transform infrared (FT-IR) spectroscopy. It was observed that the film becomes thinner as the titanium contents increase. A change of the refractive index through the range 1.52–1.61 at the optical wavelength of 633 nm was achieved by varying the molar ratio between silica and titanium. A dense, low absorption, and high transparency in the visible range waveguide films could be obtained at a low temperature. It was also noted that organic compounds in the film would decompose in the temperature range from 200°C to 480°C. Accordingly, purely inorganic silica-titania films with a thickness of about 0.7 μm could also be obtained by a single-coating process, when the film was baked at a temperature of 500°C or higher. The waveguides properties and photonic applications of the composite material solgel films were also investigated.     

Passive alignment optical subassemblies for military/aerospacefiber-optic transmitter/receiver modules

Under the DARPA sponsored Avionics Optoelectronic Module Technology program, new passive alignment carrier (PAC) optical subassemblies (LED-PAC and PIN-PAC) ruggedized for military/aerospace avionics fiber-optic transmitter and receiver applications have been developed, LED-PAC and PIN-PAC silicon micro-optical bench substrates were fabricated together on a 5 in diameter silicon wafer via multistage photolithography, thin-film, and substrate processing. Alignment v-grooves designed for passive optical alignment of 100/140 μm multimode optical fiber to the optoelectronic devices were terminated by solder locking the fiber to the silicon PAC substrates. The LED-PAC comprising a surface emitting LED die-bonded onto a novel precision molded AM submount passively mounted onto the silicon microbench achieves the required high coupling efficiency to 100/140 μm multimode optical fiber to meet stringent avionics transmitter output power requirements. The 100/130 μm multimode optical fiber-pigtailed PIN-PAC with a refractive lens etched into the p-i-n photodiode backside surface exhibited responsivities greater than 0.8 A/W at 1.3 μm wavelength. The LED-PAC and PIN-PAC optical subassemblies integrated with Boeing ARINC 636 (FDDI) transmitter and receiver thick film multichip (MCM-C) circuitry are capable of meeting both ARINC 636 and FDDI physical layer requirements     

A Genetic Fuzzy Controller for Vehicle Automatic Steering Control

This paper presents the design and experimental implementation of a genetic fuzzy controller for automatic steering of a small-scaled vehicle. We first derive a dynamic model of the vehicle via system identification and show that the model exhibits similar characteristics to full-sized vehicles. Subsequently, a stable fuzzy proportional-derivative controller is designed and optimized by genetic algorithms. The control system is transformed into a Lureacute system, and Lyapunov's direct method is used to guarantee the stability of the control system. Experimental studies suggest that the control system is insensitive to parametric uncertainty, load, and disturbances. The performance of the proposed controller is also compared against a conventional proportional derivative (PD) controller. Experimental results confirm that it outperforms the conventional PD controller, particularly in terms of robustness     

Effect of Composition on Thermoelectric Properties in PbTe-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Composites

The solidification of alloys in the Bi₂Te₃-PbTe pseudobinary system at off- and near-eutectic compositions was investigated for their microstructure and thermoelectric properties. Dendritic and lamellar structures were clearly observed due to the phase separation and the existence of a metastable ternary phase. In this system, three phases with different compositions were observed: binary Bi₂Te₃, PbTe, and metastable PbBi₂Te₄. The Seebeck coefficient, electrical resistivity, and thermal conductivity of ternary alloys as well as binary compounds were measured. The phonon thermal conductivities of Pb-Bi-Te alloys were lower than those in binary PbTe and Bi₂Te₃, which could have resulted from the increased interfacial area between phases due to the existence of the metastable ternary phase and the resultant phase separation.     

Investigation of the source/drain asymmetric effects due to gate misalignment in planar double-gate MOSFETs

A planar double-gate SOI MOSFET (DG-SOI) with thin channel and thick source/drain (S/D) was successfully fabricated. Using both experimental data and simulation results, the S/D asymmetric effect induced by gate misalignment was studied. For a misaligned DG-SOI, there is gate nonoverlapped region on one side and extra gate overlapped region on the other side. The nonoverlapped region introduces extra series resistance and weakly controlled channel, while the extra overlapped region introduces additional overlap capacitance and gate leakage current. We compared two cases: bottom gate shift to source side (DG/spl I.bar/S) and bottom gate shift to drain side (DG/spl I.bar/D). At the same gate misalignment value, DG/spl I.bar/S resulted in a larger drain-induced barrier lowering effect and smaller overlap capacitance at drain side than DG/spl I.bar/D. Because of reduced drain-side capacitance, the speed of three-stage ring oscillator of DG/spl I.bar/S, with 20% gate misalignment length (L/sub mis/) over gate length (L/sub g/), or L/sub mis//L/sub g/=20%, was faster than that of two-gate aligned DG-SOI.     

COF结构中键合力损伤芯片Al层的研究

运用实验和有限元模拟相结合的方法，研究了非导电膜和金金共金工艺中键合力对芯片Al压焊块内应力分布的影响，并分析了样品的失效部位和失效原因．挠性基板上印制线宽度不同时键合力对芯片损伤情况的研究表明，小印制线宽度在相同单位面积键合力情况下对Al压焊块损伤较轻．讨论了印制线宽度对键合偏移容差的要求．     

Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications

The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly.     

Visual Cryptography Based on an Interferometric Encryption Technique

This paper presents a new method for a visual cryptography scheme that uses phase masks and an interferometer. To encrypt a binary image, we divided it into an arbitrary number of slides and encrypted them using an XOR process with a random key or keys. The phase mask for each encrypted image was fabricated under the proposed phase‐assignment rule. For decryption, phase masks were placed on any path of the Mach‐Zehnder interferometer. Through optical experiments, we confirmed that a secret binary image that was sliced could be recovered by the proposed method.     

Design and Validation of an Efficient Authentication Scheme with Anonymity for Roaming Service in Global Mobility Networks

Designing a user authentication protocol with anonymity for the global mobility network (GLOMONET) is a difficult task because wireless networks are susceptible to attacks and each mobile user has limited power, processing and storage resources. In this paper, a secure and lightweight user authentication protocol with anonymity for roaming service in the GLOMONET is proposed. Compared with other related approaches, our proposal has many advantages. Firstly, it uses low-cost functions such as one-way hash functions and exclusive-OR operations to achieve security goals. Having this feature, it is more suitable for battery-powered mobile devices. Secondly, it uses nonces instead of timestamps to avoid the clock synchronization problem. Therefore, an additional clock synchronization mechanism is not needed. Thirdly, it only requires four message exchanges between the user, foreign agent and home agent. Further, the security properties of our protocol are formally validated by a model checking tool called AVISPA. We also demonstrate that this protocol enjoys important security attributes including prevention of various attacks, single registration, user anonymity, no password table, and high efficiency in password authentication. Security and performance analyses show that compared with other related authentication schemes, the proposed scheme is more secure and efficient.