Mitigating the gateway bottleneck via transparent cooperative caching in wireless mesh networks

Wireless mesh networks (WMNs) have been proposed to provide cheap, easily deployable and robust Internet access. The dominant Internet-access traffic from clients causes a congestion bottleneck around the gateway, which can significantly limit the throughput of the WMN clients in accessing the Internet. In this paper, we present MeshCache, a transparent caching system for WMNs that exploits the locality in client Internet-access traffic to mitigate the bottleneck effect at the gateway, thereby improving client-perceived performance. MeshCache leverages the fact that a WMN typically spans a small geographic area and hence mesh routers are easily over-provisioned with CPU, memory, and disk storage, and extends the individual wireless mesh routers in a WMN with built-in content caching functionality. It then performs cooperative caching among the wireless mesh routers.We explore two architecture designs for MeshCache: (1) caching at every client access mesh router upon file download, and (2) caching at each mesh router along the route the Internet-access traffic travels, which requires breaking a single end-to-end transport connection into multiple single-hop transport connections along the route. We also leverage the abundant research results from cooperative web caching in the Internet in designing cache selection protocols for efficiently locating caches containing data objects for these two architectures. We further compare these two MeshCache designs with caching at the gateway router only.Through extensive simulations and evaluations using a prototype implementation on a testbed, we find that MeshCache can significantly improve the performance of client nodes in WMNs. In particular, our experiments with a Squid-based MeshCache implementation deployed on the MAP mesh network testbed with 15 routers show that compared to caching at the gateway only, the MeshCache architecture with hop-by-hop caching reduces the load at the gateway by 38%, improves the average client throughput by 170%, and increases the number of transfers that achieve a throughput greater than 1 Mbps by a factor of 3.     

Mechanism of O2-anneal induced Vfb shifts of Ru gated stacks

A systematic study of the flat-band voltage (V_fb) shift of Ru gated metal-oxide-semiconductor (MOS) capacitors subjected to thermal treatment in O₂ has been performed. The dependence of the V_fb shift on the thickness of Ru, anneal temperature and time is studied. The V_fb shift is ascribed to the shift of metal gates’ work function (WF), and is not significantly dependent on the type of dielectric (HfO₂ or SiO₂). From time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement, it was found that after thermal treatment in ¹⁸O₂, ¹⁸O penetrated through Ru and was incorporated in the Ru/dielectric interface region. We believe that the formation of the thin interfacial RuO_x layer is responsible for the V_fb shift.     

Resistance Compression Networks for Radio-Frequency Power Conversion

A limitation of many high-frequency resonant inverter topologies is their high sensitivity to loading conditions. This paper introduces a new class of matching networks that greatly reduces the load sensitivity of resonant inverters and radio frequency (RF) power amplifiers. These networks, which we term resistance compression networks, serve to substantially decrease the variation in effective resistance seen by a tuned RF inverter as loading conditions change. We explore the operation, performance characteristics, and design of these networks, and present experimental results demonstrating their performance. Their combination with rectifiers to form RF-to-dc converters having narrow-range resistive input characteristics is also treated. The application of resistance compression in resonant power conversion is demonstrated in a dc-dc power converter operating at 100MHz     

SrCaO Protective Layer for High-Efficiency PDPs

The sustain pulse voltage of the panel for 66-kPa Ne + Xe (5%-30%) is 20%-40% lower with a Sr_0.62Ca_0.38O protective layer than with a MgO protective layer. At a normal sustain voltage of 160-200 V, the luminous efficiency of the panel with the Sr_0.62 Ca_0.38O protective layer for Xe (30%) is about twice as high as with the MgO protective layer for Xe (10%). The luminances of these panels are almost the same. This high efficiency at normal sustain pulse voltage and normal luminance is obtained through the combined use of the Sr_0.62Ca_0.38O protective layer and high Xe content. With regard to ion bombardment, the Sr_0.62Ca_0.38O film has a 4.5 times longer life than SrO film and nearly 80% of the life of MgO film. We also calculated the values of theoretical secondary electron emission yield gamma_imin of MgO, SrO, and CaO without energy bands in the band gap for rare gas ions and found that [ gamma_imin of MgO] les [gamma_imin of CaO] < [gamma_imin of SrO] except for the one case with He. The breakdown voltage decreases with higher gamma_imin values. As expected, the discharge voltage of the panel is much lower with the SrO protective layer than with the MgO protective layer. The discharge voltages of the panels with Sr_0.62Ca_0.38O and SrO protective layers are almost the same. These findings show that the life of the SrO protective layer can be made 4.5 times longer without any increase in the discharge voltage by adding CaO (40 at.%)     

The Interaction Force Between a Permanent Magnet and a Superconducting Ring

The interaction force between a small magnet and a superconducting ring in assumptions of the Meissner state was analyzed using the dipole-dipole interaction model. Two configurations were evaluated: the vertical configuration when the magnetic moment lies parallel to the symmetry axis of the ring and the horizontal when it is perpendicular. The levitation force on the magnet increases by decreasing the distance from the center of the ring up to a maximum value and then decreases down to zero when the magnet is exactly at the center of the ring. The levitation force when the magnet is in the horizontal configuration is mostly higher than that when it is in the vertical configuration. Simulation results were compared with experimental results reported in literature.     

A DCM‐Type Red‐Fluorescent Dopant for High‐Performance Organic Electroluminescent Devices

2‐(2‐tert‐Butyl‐6‐((E)‐2‐(2,6,6‐trimethyl‐2,4,5,6‐tetrahydro‐1H‐pyrrolo[3,2,1‐ij]quinolin‐8‐yl)vinyl)‐4H‐pyran‐4‐ylidene)malononitrile (DCQTB) is designed and synthesized in high yield for application as the red‐light‐emitting dopant in organic light‐emitting diodes (OLEDs). Compared with 4‐(dicyanomethylene)‐2‐tert‐butyl‐6‐(1,1,7,7,‐tetramethyljulolidyl‐9‐enyl)‐4H‐pyran (DCJTB), one of the most efficient red‐emitting dopants, DCQTB exhibits red‐shifted fluorescence but blue‐shifted absorption. The unique characteristics of DCQTB with respect to DCJTB are utilized to achieve a red OLED with improved color purity and luminous efficiency. As a result, the device that uses DCQTB as dopant, with the configuration: indium tin oxide (ITO)/N,N′‐bis(1‐naphthyl)‐N,N′‐diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB; 60 nm)/tris(8‐quinolinolato) aluminum (Alq₃):dopant (2.3 wt %) (7 nm)/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP; 12 nm)/Alq₃(45 nm)/LiF(0.3 nm):Al (300 nm), shows a larger maximum luminance (L_max = 6021 cd m^–2 at 17 V), higher maximum efficiency (η_max = 4.41 cd A^–1 at 11.5 V (235.5 cd m^–2)), and better chromaticity coordinates (Commission Internationale de l'Eclairage, CIE, (x,y) = (0.65,0.35)) than a DCJTB‐based device with the same structure (L_max = 3453 cd m^–2 at 15.5 V, η_max = 3.01 cd A^–1 at 10 V (17.69 cd m^–2), and CIE (x,y) = (0.62,0.38)). The possible reasons for the red‐shifted emission but blue‐shifted absorption of DCQTB relative to DCJTB are also discussed.     

Highly Ordered Mesoporous Silicon Carbide Ceramics with Large Surface Areas and High Stability

Highly ordered mesoporous silicon carbide ceramics have been successfully synthesized with yields higher than 75 % via a one‐step nanocasting process using commercial polycarbosilane (PCS) as a precursor and mesoporous silica as hard templates. Mesoporous SiC nanowires in two‐dimensional (2D) hexagonal arrays (p6m) can be easily replicated from a mesoporous silica SBA‐15 template. Small‐angle X‐ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images show that the SiC nanowires have long‐range regularity over large areas because of the interwire pillar connections. A three‐dimensional (3D) bicontinuous cubic mesoporous SiC structure (Ia3d) can be fabricated using mesoporous silica KIT‐6 as the mother template. The structure shows higher thermal stability than the 2D hexagonal mesoporous SiC, mostly because of the 3D network connections. The major constituent of the products is SiC, with 12 % excess carbon and 14 % oxygen measured by elemental analysis. The obtained mesoporous SiC ceramics are amorphous below 1200 °C and are mainly composed of randomly oriented β‐SiC crystallites after treatment at 1400 °C. N₂‐sorption isotherms reveal that these ordered mesoporous SiC ceramics have high Brunauer–Emmett–Teller (BET) specific surface areas (up to 720 m² g^–1), large pore volumes (～ 0.8 cm³ g^–1), and narrow pore‐size distributions (mean values of 2.0–3.7 nm), even upon calcination at temperatures as high as 1400 °C. The rough surface and high order of the nanowire arrays result from the strong interconnections of the SiC products and are the main reasons for such high surface areas. XRD, N₂‐sorption, and TEM measurements show that the mesoporous SiC ceramics have ultrahigh stability even after re‐treatment at 1400 °C under a N₂ atmosphere. Compared with 2D hexagonal SiC nanowire arrays, 3D cubic mesoporous SiC shows superior thermal stability, as well as higher surface areas (590 m² g^–1) and larger pore volumes (～ 0.71 cm³ g^–1).     

Electrotunable Non‐reciprocal Laser Emission from a Liquid‐Crystal Photonic Device

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.     

Use of linear programming for dynamic subcarrier and bit allocation in multiuser OFDM

An adaptive subcarrier allocation and an adaptive modulation for multiuser orthogonal frequency-division multiplexing (OFDM) are considered. The optimal subcarrier and bit allocation problems, which are previously formulated as nonlinear optimizations, are reformulated into and solved by integer programming (IP). A suboptimal approach that performs subcarrier allocation and bit loading separately is proposed. It is shown that the subcarrier allocation in this approach can be optimized by the linear-programming (LP) relaxation of IP, while the bit loading can be performed in a manner similar to a single-user OFDM. In addition, a heuristic method for solving the LP problem is presented. The LP-based suboptimal and heuristic algorithms are considerably simpler to implement than the optimal IP, plus their performances are close to those of the optimal approach.     

Development of a standing style transfer system "ABLE" for disabled lower limbs

We have developed a standing style transfer system, or "ABLE," for a person with disabled legs. It allows travel in a standing posture even on uneven ground, a standing up motion from a chair, and allows the stairs. ABLE consists of three modules: a pair of telescopic crutches, a powered lower extremity orthosis, and a pair of mobile platforms. We present here the conceptual design of ABLE and the motion of each module. Cooperative operations using the three modules are discussed through simulations. The standing up motion from a chair and ascending the stairs, however, have problems with adaptability to the environment and safety, because it executes the movement that has till now relied on telescopic crutches. To solve these problems, we propose a new motion technique and compare it with the previous one. In this paper, some experimental results are also presented.