This paper presents an in-chip thermal-isolation technique for a micro-ovenized microelectromechanical-system resonator. Resonators with a microoven can be used for high-precision feedback control of temperature to compensate for the temperature dependence of resonator frequency over a wide temperature range. However, ovenization requires power consumption for heating, and the thermal time constant must be minimized for effective temperature control. This paper demonstrates an efficient local-thermal-isolation mechanism, which can reduce the power requirement to a few milliwatts and the thermal time constant to a few milliseconds. In this method, the mechanical suspension of the resonator is modified to provide thermal isolation and include an integrated resistive heater. This combination provides mechanical suspension, electrical heating, and thermal isolation in a compact structure that requires low heating power and has a small thermal time constant. A power consumption of approximately 12 mW for a 125degC temperature rise and a thermal time constant ranging from 7 to 10 ms is reported in this paper, which is orders of magnitude lower than that of commercially available ovenized quartz resonators. A CMOS-compatible wafer-scale encapsulation process is used to fabricate this device, and the thermal-isolation design is achieved without any modification to the existing resonator fabrication process. 相似文献
If r?1, and m and n are each a multiple of (r+1)2+r2, then each isomorphic component of Cm×Cn admits of a vertex partition into (r+1)2+r2 perfect r-dominating sets. The result induces a dense packing of Cm×Cn by means of vertex-disjoint subgraphs, each isomorphic to a diagonal array. Areas of applications include efficient resource placement in a diagonal mesh and error-correcting codes. 相似文献
In this article, a new polynomial-time approximation algorithm called Service Path Local Optimization (SPLO) is proposed for the online restoration problem. SPLO is shown to perform competitively with existing offline heuristics algorithm in terms of spare capacity. SPLO is designed for online computation where only one request is computed at any one time, and the decision making does not depend on future requests. The polynomial-time and online nature of the algorithm makes SPLO suitable for use in real-time on-demand path request applications. SPLO can be combined with a non-polynomial post-processing component that re-optimizes the backup paths. Significant reductions in spare capacity requirements are achievable at the expense of higher computation time. Further, the potential for SPLO as an algorithm in traffic engineering applications is investigated by looking at the performance impact when source-destination-based traffic aggregation is applied. We also introduce a new concept called path intermix where the service path?s allocated bandwidth can be used by the backup paths protecting that particular service path. 相似文献
Friction Stir Welding (FSW) of Cu-0.80Cr-0.10Zr (in wt pct) alloy under aged condition was performed to study the effects of process parameters on microstructure and properties of the joint. FSW was performed over a wide range of process parameters, like tool-rotation speed (from 800 to 1200 rpm) and tool-travel speed (from 40 to 100 mm/min), and the resulting thermal cycles were recorded on both sides (advancing and retreating) of the joint. The joints were characterized for their microstructure and tensile properties. The welding process resulted in a sound and defect-free weld joint, over the entire range of the process
parameters used in this study. Microstructure of the stir zone showed fine and equiaxed grains, the scale of which varied with FSW process parameters. Grain size in the stir zone showed direct correlation with tool rotation and inverse correlation with tool-travel speed. Tensile strength of the weld joints was ranging from 225 to 260 MPa, which is substantially lower than that of the parent metal under aged condition (~ 400 MPa), but superior to that of the parent material under annealed condition (~ 220 MPa). Lower strength of the FSW joint than that of the parent material under aged condition can be attributed to dissolution of the precipitates in the stir zone and TMAZ. These results are presented and discussed in this paper.
In this paper, the relationship between the number of unit-cells used in the design of a frequency selective surface (FSS) and its expected directivity is established. The relationship between the number of FSS unit-cells and the directivity is based on the planer microstrip patch array antenna design concept where the unit-cell is treated as the superstrate illuminated by the source. To validate the proposed technique, the analytical value of the directivity has been compared with that of ray-tracing method. The directivity of antenna is calculated for two different planar array configurations at 600 GHz. The results of numerical analysis are compared to that of the full-wave electromagnetic simulator CST Microwave Studio and results are comparable. Further, the directivity computed by this proposed technique has also been compared with that of the reported in literatures. 相似文献
Invert traps have been successfully used to collect sediments at convenient locations within the sewer network, where large volumes of solids can be stored. In the present study, experiments have been performed in 15 cm wide and 5 m long channel for the measurement of retention ratios of five different invert trap configurations (namely, rectangular, trapezoidal with one side vertical, trapezoidal, trapezoidal with rectangular base, rectangular with trapezoidal base) having top width of 32 cm and depth of 28 cm with slots of three different sizes (namely, 5, 9 and 15 cm) for the flow of seven different sediment types (namely, two types of sand, glass beads and four types of plastic beads) at different flow rates for each trap. The flow rates selected in present study cover entire range of flow rate expected in channels during dry weather flow and monsoon. Flow field and retention ratio predictions for each invert trap configuration have been carried out using CFD modeling with the help of FLUENT software using Renormalization Group (RNG) k–ε along with Discrete Phase Model (DPM). The simulation results are capable of showing particle trajectories, the effect of flow rate and trap geometry on the flow patterns, developed within the trap. Based on CFD modeling and experimental measurements, it is concluded that the invert trap having rectangular shape with trapezoidal base is the most efficient trap configuration with highest sediment retention ratio. 相似文献
A series of densely grafted poly(n-butyl acrylate) (PBA) molecular brushes with four different grafting densities were synthesized by the “grafting-from” approach using atom transfer radical polymerization (ATRP). A novel monomer, isopropylidene-2,2-Bis(methoxy)propionic hydroxyethylmethacrylate (IMPHMA), was synthesized and copolymerized with methyl methacrylate (MMA) under different monomer feed ratios to yield a series of linear poly(methyl methacrylate-stat-IMAPA), [PMMA-s-(PIMPHMA)]. The resulting copolymers were deprotected and transformed to macroinitiators, [PMMA-s-(PHEMA-IMPHMA-Br)]. n-Butyl acrylate (BA) was grafted from these macroinitiators to yield a series of molecular brushes, [PMMA-s-{(PIMPHMA)-g-PBA}], with various side chain lengths. Molecular brushes were characterized by gel permeation chromatography (GPC) and 1H NMR. PBA side chains were cleaved by acid hydrolysis, and the resulting linear PBA polymers were characterized by GPC to study initiation efficiency during the synthesis of molecular brushes. The initiation efficiency increased with polymerization time and decreased with macroinitiators that had more initiation sites. Atomic force microscopy (AFM) measurements demonstrated the characteristic molecular structure by resolving individual brush molecules. 相似文献
Thin films of YBCO and YBCO:BaZrO3 (BZO) nanocomposite have been deposited using the pulsed laser deposition technique. Substantial increase in critical current
density (JC) and pinning force density (Fp) of the nanocomposite thin films was observed. The possible pinning mechanism in YBCO:BZO nanocomposite thin films has been
explored and compared with the pinning mechanism in pure YBCO thin film by studying the variation of JC with magnetic field (B) and temperature. In the intermediate field regime (0.1–1 T), JC follows B−α with nearly similar values of α for YBCO and YBCO:BZO nanocomposite thin films indicating similar pinning mechanism in both thin films. The variation of
JC with reduced temperature (t=T/TC) has been studied for both the films and it was observed that the mechanism of pinning in both YBCO and YBCO:BZO thin films
is similar (δTC pinning). The observed enhanced values of JC and Fp of the nanocomposite thin film is attributed to the presence of BZO nanoparticles, which induces more defects due to lattice
mismatch between YBCO and BZO leading to improved flux pinning properties of the nanocomposite thin film. 相似文献