Scalability in Global Mobile Information Systems (GloMo): Issues,Evaluation Methodology and Experiences

The GloMo (Global Mobile Information Systems) project¹ has focused on developing new wireless ad hoc networking technologies. These new technologies rely on a broad and varied set of techniques to help cope with the problems inherent in the wireless environment. One of the most critical design elements of all the various technologies is their applicability in large scale deployments. The main objective of our work is to develop and implement a simulation methodology to help evaluate the scalability of these new ad hoc networking technologies and gain some insight into the various aspects of ad hoc network performance scalability issues. To achieve that we have developed a scalability performance evaluation framework and plan, that spans all the various dimensions of scalability: size (number of nodes and density), traffic, operational environment (i.e. propagation models, terrain etc.), mobility. For demonstration purposes we have applied this process on a representative integrated protocol suite designed to provide communication services in mobile ad hoc wireless networks. The corresponding results of the two most critical aspects of scalability properties in tactical networks (i.e. network initialization time and traffic scalability) are also presented here, and demonstrate that a very extensive evaluation of the corresponding scalability metrics under a combination of the various scalability dimensions defined in this paper, is necessary in order to provide an in-depth analysis of the scalability properties in wireless mobile ad hoc networking environments.     

Adaptive Network Overload Controls

Network overloads can seriously degrade the quality or availability of telecommunications services if they are not effectively controlled. This paper explains why overload controls are required and how they should behave for both today's and future networks. The requirements of overload controls are presented, in terms of the conditions under which they must operate and the behaviour they should exhibit. Good design principles are proposed, which include identifying the controlled variable, the control structure, convergence and stability, and parameter configuration, while ensuring that different implementations work together. Relevant network standards are highlighted, and the paper stresses the crucial importance that these standards adequately specify the behaviour of overload controls.     

Proportional degradation services in wireless/mobile adaptive multimedia networks

Adaptive multimedia services are very attractive since resources in wireless/mobile networks are relatively scarce and widely variable, and more importantly the resource fluctuation caused by mobility and channel fading can be mitigated using adaptive services. Therefore, there are extensive research activities on Quality of Service (QoS), call admission control, as well as bandwidth degradation and adaptation for adaptive multimedia services in wireless/mobile networks in recent years. However, fairness of bandwidth degradation has largely been ignored in previous work and remains an important issue in adaptive multimedia service provisioning. In this paper, we propose and study proportional degradation service provisioning in wireless/mobile networks that offer multiple classes of adaptive multimedia services. The proposed proportional degradation fairness model guarantees the proportional bandwidth degradation among different classes of services. Two proportional degradation scenarios are studied in this paper. In the first scenario, we study the proportional degradation provisioning with two QoS parameters for adaptive multimedia: the degradation ratio (DR) and the degradation degree (DD). In the second scenario, we study the proportional degradation provisioning with a new QoS parameter for adaptive multimedia: the degradation area (DA). For each scenario, based on the QoS parameters, proportional degradation adaptation algorithms are proposed to approximate the proportional degradation model, to fairly adapt calls' degradations, to utilize the system resource efficiently, as well as to optimize QoS parameters. Performance studies show that in the first scenario, proportional DR has been achieved very well, whereas proportional DD has not been well achieved. In other words, DR outperforms DD in terms of proportional degradation. In the second scenario, proportional DA has been well achieved. Furthermore, bandwidth resources have been efficiently utilized and DA has been minimized. Copyright © 2004 John Wiley & Sons, Ltd.     

Noncentrosymmetric Tetrel Pnictides RuSi4P4 and IrSi3P3: Nonlinear Optical Materials with Outstanding Laser Damage Threshold

Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi₄P₄ and IrSi₃P₃ are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and ²⁹Si and ³¹P magic angle spinning NMR. In agreement with previous report RuSi₄P₄ crystallizes in NCS space group P1, while IrSi₃P₃ is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi₄P₄ and IrSi₃P₃ to be wide bandgap (E_g) semiconductors, E_g = 1.9 and 1.8 eV, respectively. RuSi₄P₄ and IrSi₃P₃ outperform the current state-of-the-art infrared SHG material, AgGaS₂, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi₄P₄ and IrSi₃P₃ are promising candidates for longer wavelength NLO materials.     

Tunable 3D Nanoresonators for Gas‐Sensing Applications

The detection of gas species with high sensitivity is a significant task for fundamental sciences as well as for industrial applications. Similarly, the ongoing trend for device miniaturization brings new challenges for advanced fabrication including on‐demand functionality tuning. Following this motivation, here the additive, direct‐write fabrication of freestanding 3D nanoarchitectures is introduced, which can be brought into mechanical resonance via electric AC fields. Specifically, this study focuses on the 3D nanostructure synthesis, the subsequent determination of Young's modulus, and demonstrates a postgrowth procedure, which can precisely tune the material modulus. As‐fabricated resonators reveal a Young's modulus of 9–13 GPa, which can be increased by a factor greater than 5. Next, the electric readout of the resonance behavior is demonstrated via electric current measurement as an essential element for the resonance sensor applications. Finally, the implications of gas‐physisorption and gas‐chemisorption on the resonance frequencies are studied, representing a proof‐of‐principle for sensing applications by the here presented approach.     

高性能LCoS虚拟显示器的光学特性

本文叙述一种用于LCoS双瞳虚拟显示器的新型光路结构,它首次达到或超过了pSi(多晶硅)头戴装置的性能36°的视场,801的对比度,无需IPD调节(12mm出射光瞳),并且整个电-光模件的封装配合并不比奥林巴斯EyeTrek和索尼Glasstron的工业标准更复杂.     

迈向纳米级芯片技术的IMEC研发——先进封装技术部分

近期、芯片制造工艺发展到了纳米时代(栅极宽度<100nm),IM E C发起并联合了全球七家主要半导体芯片制造商和几乎所有主要设备制造商,在刚建立起来的φ300m m硅片尺寸工艺中试线上,共同展开了45nm和32nm的芯片制造工艺的研究工作。虽然芯片封装技术也在快速发展,但其速度赶不上芯片制造工艺的迅猛发展。在先进的芯片制造技术和最新的PCB技术之间所谓的“互连技术壕沟”在不断扩大。而且,不断增加的工作频率,以及由于集成电路复杂程度提高而导致I O管脚的增加,都要求封装技术产生重大的技术变革,以保证在将纳米级的芯片与毫米级的系统相连…     

Role of PbSe Structural Stabilization in Photovoltaic Cells

Semiconductor nanocrystals are promising materials for printed optoelectronic devices, but their high surface areas are susceptible to forming defects that hinder charge carrier transport. Furthermore, correlation of chalcogenide nanocrystal (NC) material properties with solar cell operation is not straightforward due to the disorder often induced into NC films during processing. Here, an improvement in long‐range ordering of PbSe NCs symmetry that results from halide surface passivation is described, and the effects on chemical, optical, and photovoltaic device properties are investigated. Notably, this passivation method leads to a nanometer‐scale rearrangement of PbSe NCs during ligand exchange, improving the long‐range ordering of nanocrystal symmetry entirely with inorganic surface chemistry. Solar cells constructed with a variety of architectures show varying improvement and suggest that triplet formation and ionization, rather than carrier transport, is the limiting factor in singlet fission solar cells. Compared to existing protocols, our synthesis leads to PbSe nanocrystals with surface‐bound chloride ions, reduced sub‐bandgap absorption and robust materials and devices that retain performance characteristics many hours longer than their unpassivated counterparts.     

New sources of resistance to Acanthoscelides obtectus (Say) and Zabrotes subfasciatus Boheman (Coleoptera: Bruchidae) in mature seeds of five species of Phaseolus

The importance of carefully applied bioassay techniques is highlighted for identifying resistance of Phaseolus spp to the bruchids Acanthoscelides obtectus (Say) and Zabrotes subfasciatus Boheman. Two potential sources of resistance are identified amongst the varieties of P. vulgaris screened. In one the presence of a lectin-like protein (LLP) was identified, which has previously been associated with resistance, while in the other, resistance may be linked to the presence of a novel protein, similar to but not the same as LLP. The use of anti-LLP antibodies are suggested as a useful tool for distinguishing between resistant and susceptible varieties. Five varieties of P. lunatus and six of P. acutifolius are shown to be resistant to A. obtectus, and the potential is recognized for transferring resistant genes to P. vulgaris via interspecific crosses.     

Enhanced Electron Mobility Due to Dopant‐Defect Pairing in Conductive ZnMgO

The increase of the band gap in Zn_1‐xMg_xO alloys with added Mg facilitates tunable control of the conduction band alignment and the Fermi‐level position in oxide‐heterostructures. However, the maximal conductivity achievable by doping decreases considerably at higher Mg compositions, which limits practical application as a wide‐gap transparent conductive oxide. In this work, first‐principles calculations and material synthesis and characterization are combined to show that the leading cause of the conductivity decrease is the increased formation of acceptor‐like compensating intrinsic defects, such as zinc vacancies (V_Zn), which reduce the free electron concentration and decrease the mobility through ionized impurity scattering. Following the expectation that non‐equilibrium deposition techniques should create a more random distribution of oppositely charged dopants and defects compared to the thermodynamic limit, the paring between dopant Ga_Zn and intrinsic defects V_Zn is studied as a means to reduce the ionized impurity scattering. Indeed, the post‐deposition annealing of Ga‐doped Zn_0.7Mg_0.3O films grown by pulsed laser deposition increases the mobility by 50% resulting in a conductivity as high as σ = 475 S cm^‐1.