We study the problem of disseminating data of time-constrained services through multiple broadcast channels. By time-constrained services, we mean those services whose data must reach clients before a certain constrained time. Otherwise, the data would become useless or substantially less valuable to the clients. We first explore the difficulties of solving the problem and derive the theoretical minimum number of channels required for the task. Then, we propose a transformation-based data allocation (TDA) algorithm that guarantees to fulfill the task (i.e., all requested data reach the clients within the constrained time) by using the minimum number of channels. Finally, we analyze the computation complexity and prove the validity and optimality of the TDA algorithm. 相似文献
A new method is studied for preparing nano-ceria by acid leaching MgO from CeO2−MgO mixed powder made by calcining a gel. The MgO in the mixed powder can be leached completely with acetic acid solution at room temperature, but the CeO2 remains unaffected. The surface area (Sg) of the resulting CeO2 increases with Mg/Ce ratio, but approaches constant after the ratio is larger than a given value which is higher for the higher gel calcining temperature. When Mg/Ce is 8 (molar ratio) and the calcining temperature is 1253 K, the Sg of the resulting ceria remains 25.1 m2/g even after annealed at 1253 K for 4 h. In comparison with the conventional methods, CeO2 from the new method shows higher surface area and higher thermal stability. 相似文献
We investigate in detail the process of CO2-laser writing of long-period fiber gratings (LPFGs) in unannealed and annealed boron-doped fiber samples by using repeated scanning of CO2-laser pulses. We find that the writing dynamics depends strongly on the CO2-laser energy density and the annealing temperature of the fiber. Our results from analyzing the writing dynamics reveal the relative importance of various physical effects arising from glass structure changes due to different writing conditions and thus provide a better understanding of the formation and the properties of CO2-laser written LPFGs. 相似文献
A novel automatic-gain-control (AGC) architecture utilizing wideband current feedback is proposed for the baseband circuit of a wireless endoscope capsule. The baseband circuit consists of a fast-settling wideband AGC loop and an amplitude-shift-keying demodulator. Additional integrators in the reverse signal path provide negative feedback, bandpass-filtering effect, attenuating low-frequency noises, and dc offset from the radio-frequency front end. The baseband circuit fabricated in a 180-nm complementary metal-oxide-semiconductor process achieves a wide-intermediate-frequency (IF) carrier frequency in the range of 0.5-40 MHz, a measured settling time of 2 mus, and an input sensitivity of -57 dBm. The entire baseband demodulator dissipates only 5 mA, with a 1.8-V supply at a data rate of 1.37 Mb/s and an IF carrier frequency of 10 MHz. 相似文献
The channel rectilinear Steiner tree problem is to construct an optimal rectilinear Steiner tree interconnecting n terminals on the upper shore and the lower shore of a channel without crossing any obstacles inside the channel. However, intersecting boundaries of obstacles is allowed. We present an algorithm that computes an optimal channel rectilinear Steiner tree in O(F1(k)n + F2(k)) time, where k is the number of obstacles inside the channel and F1 and F2 are exponential functions of k. For any constant k the proposed algorithm runs in O(n) time. 相似文献
A microscopic three-dimensional (3-D) shape measurement system based on digital fringe projection has been developed and experimentally investigated. A Digital Micromirror Device along with its illumination optics is integrated into a stereomicroscope, which projects computer-generated fringe patterns with a sinusoidal intensity profile through the microscope objective onto the object surface being measured. The fringe patterns deformed by the object surface are recorded by a CCD camera. The microscopic 3-D shape of the object surface is measured and reconstructed by use of a phase-shifting technique. We discuss design considerations and error analysis of the system. Experimental results successfully demonstrate the capability of this technique for surface profile measurement of rough surfaces at the micrometer level. 相似文献
This paper presents a novel micro-fabricated formaldehyde gas sensor with enhanced sensitivity and detection resolution capabilities. The device comprises a quartz substrate with Pt heaters as a micro-hotplate and deposited formaldehyde-sensing layer on it. A sputtered NiO thin film is used as the formaldehyde-sensing layer. A specific orientation of NiO becomes more apparent as the substrate temperature increases in the sputtering process, which helps the formation of NiO material with a correct stoichiometric ratio. The gas sensor incorporates Pt heating resistors integrated with a micro-hotplate to provide a heating function and utilizes Au inter-digitated electrodes. When formaldehyde is present in the atmosphere, oxydation happens near the sensing layer with a high temperature caused by the micro-hotplate and causes a change in the electrical conductivity of the NiO film. Therefore, the measured resistance between the inter-digitated electrodes changes correspondingly. The application of a voltage to the Pt heaters causes the temperature of the micro-hotplate to increase, which in turn enhances the sensitivity of the sensor. The nanometer scale grain size of the sputtered oxide thin film is conducive to improving the sensitivity of the gas sensor. The experimental results indicate that the developed device has a high stability (0.23%), a low hysteresis value (0.18%), a quick response time (13.0 s), a high degree of sensitivity (0.14 Ω ppm−1), and a detection capability of less than 1.2 ppm.
Reactor coolant system (RCS) injection using accumulator is an important strategy for both emergency operating procedure (EOP) and severe accident management guideline (SAMG) of pressurized water reactor (PWR) nuclear power plant. Once accumulator injection starts, the operator is requested to close the accumulator isolation valve to avoid nitrogen gas flow into RCS as the water level is low. Current accumulator water level indication system is not designed for this purpose. In emergency operating procedure, it relies on the steam generator pressure to close the accumulator isolation valve.The purpose of this paper is to develop a computational aid for estimating RCS injection volume of accumulator. First of all, simple accumulator model is verified using the plant data during a station blackout incident of Maanshan nuclear power plant. An isentropic expansion model is found better than adiabatic expansion model. Then, a computational aid is developed based on this model. Using this computational aid, the accumulator water level can be judged directly from the accumulator pressure. This computational aid can be applied for typical PWR nuclear power plants in both emergency operating procedure and severe accident management guideline. 相似文献
This paper presents the design of a robust face detector that can detect arbitrarily tilted human faces in color images. This detector locates face regions by identifying mouth corners and eyes. The novel techniques included in the proposed detector are: (1) a method for compensating the colors of the input images, (2) a method for deskewing tilted faces, (3) a method for locating mouth corners, and (4) a discriminant function for positioning eyes. According to the performance evaluation on three test databases which contain 1791 faces on 1580 images, the proposed method achieves a precision rate of 94.62% and a recall rate of 92.24% in average at the detection speed of 1.6 faces per second. The performance of the proposed detector also slightly outperforms a detector from CMU. 相似文献
The formation of Ag3Sn plates in the Sn-Ag-Cu lead-free solder joints for two different Ag content solder balls was investigated in wafer level
chip scale packages (WLCSPs). After an appropriate surface mount technology reflow process on a printed circuit board, samples
were subjected to 150°C high-temperature storage (HTS), 1,000 h aging, or 1,000 cycles thermal cycling test (TCT). Sequentially,
the cross-sectional analysis was scrutinized using a scanning electron microscope/energy dispersive spectrometer (SEM/EDX)
to observe the metallurgical evolution of the amount of the Ag3Sn plates at the interface and the solder bulk itself. Pull and shear tests were also performed on samples. It was found that
the interfacial intermetallic compound (IMC) thickness, the overall IMC area, and the numbers of Ag3Sn plates increase with increasing HTS and TCT cycles. The amount of large Ag3Sn plates found in the Sn-4.0Ag-0.5 Cu solder balls is much greater than that found in the Sn-2.6Ag-0.5Cu solder balls; however,
no significant difference was found in the joint strength between two different Ag content solder joints. 相似文献