We present the design and analysis of a nearly-linear work parallel algorithm for solving symmetric diagonally dominant (SDD) linear systems. On input an SDD n-by-n matrix A with m nonzero entries and a vector b, our algorithm computes a vector \(\tilde{x}\) such that \(\|\tilde{x} - A^{+}b\|_{A} \leq\varepsilon\cdot\|{A^{+}b}\|_{A}\) in \(O(m\log^{O(1)}{n}\log {\frac{1}{\varepsilon}})\) work and \(O(m^{1/3+\theta}\log\frac{1}{\varepsilon})\) depth for any θ>0, where A+ denotes the Moore-Penrose pseudoinverse of A. The algorithm relies on a parallel algorithm for generating low-stretch spanning trees or spanning subgraphs. To this end, we first develop a parallel decomposition algorithm that in O(mlogO(1)n) work and polylogarithmic depth, partitions a graph with n nodes and m edges into components with polylogarithmic diameter such that only a small fraction of the original edges are between the components. This can be used to generate low-stretch spanning trees with average stretch O(nα) in O(mlogO(1)n) work and O(nα) depth for any α>0. Alternatively, it can be used to generate spanning subgraphs with polylogarithmic average stretch in O(mlogO(1)n) work and polylogarithmic depth. We apply this subgraph construction to derive a parallel linear solver. By using this solver in known applications, our results imply improved parallel randomized algorithms for several problems, including single-source shortest paths, maximum flow, minimum-cost flow, and approximate maximum flow. 相似文献
This paper presents the design of a highly sensitive surface acoustic wave (SAW)-based sensor with novel structure for the longitudinal strain measurement. The sensor utilizes thin lithium niobate (LiNbO3) diaphragm as the sensing element rather than the bulk substrate. The application of the diaphragm effectively decreases the cross-sectional area of the strain sensitive element, and meanwhile reduces the resistance between the sensor and the specimen. The newly designed strain sensor is to operate around a frequency of 50 MHz. The insertion loss of − 12 dB and quality factor of 63 are obtained analytically from impulse-response model. The sensor performance with tensile testing of the steel beam is predicted by the finite element method. The prestressed eigenfrequency analysis is conducted with the COMSOL commercial software. The simulation shows the resonance frequency of the sensor shifts linearly with the strain induced in the testing beam. For the SAW sensor with traditional configuration applying 1 mm thick substrate, the strain sensitivity is obtained as 0.41 ppm/με. For the sensor with the novel design employing thin diaphragm with the thickness of 200 μm, the strain sensitivity is increased to 0.83 ppm/με. With the availability of the bulk micromachining of LiNbO3, the application of the piezoelectric diaphragm as sensing element in SAW strain sensor can be an alternative way to enhance the sensor sensitivity.
There are large gaps in energy consumption data and consequently in the estimates of CO2 emissions from fuel combustion in Kazakhstan. This study provides the first comprehensive review of energy consumption trends in Kazakhstan, discusses several important discrepancies in energy statistics and presents an improved versions of Energy Balances, developed using additional data. The results indicate that Kazakhstan’s energy intensity of gross domestic product (GDP) declined by 30% from 1.14 to 0.8 toe/thousand 2005USD between 2000 and 2014. To understand factors influencing this decline, the change in energy intensity of GDP was decomposed using the Logarithmic Mean Divisia Index I method. The upstream sector (mainly oil and gas) played the most important role in the observed GDP energy intensity change. Although the share of this sector in total GDP increased, causing an increase in energy intensity due to inter-sectoral structural effects, the consequences were counteracted by a twofold decline in the sector’s energy intensity, resulting in a net decrease. On the contrary, the power and heat, transport and household sectors saw an increase in energy intensity between 2000 and 2014. The results clearly demonstrate that there is an urgent need for policies and measures to be put in place in the power and heat, household and transport sectors, to support renewable energy development, increase buildings’ energy efficiencies, replace inefficient stoves and improve heating systems and encourage changes in public transportation systems. Furthermore, improving energy statistics and setting appropriate sectoral energy intensity reduction targets are crucial for achieving real efficiency improvements in the economy. 相似文献
Restoration of the iconic Golden Horn Estuary in Istanbul, Turkey was a substantial political, logistical, ecological, and social challenge. Forty years of uncontrolled industrial and urban growth resulted in thick layers of anoxic sediment, toxic bacteria, strong hydrogen sulfide odor, and ecologically unlivable conditions. The major components of restoration, spanning two decades, have included (1) demolition and relocation of industries and homes along the shore, (2) creation of wastewater infrastructure, (3) removal of anoxic sludge from the estuary, (4) removal of a floating bridge that impeded circulation, and (5) creation of cultural and social facilities. Although Turkey is not known as an environmental leader in pollution control, the sum of these efforts was largely successful in revitalizing the area through dramatic water quality improvement. Consequently, the estuary is once again inhabitable for aquatic life as well as amenable to local resource users and foreign visitors, and Istanbul has regained a lost sense of cultural identity. This paper focuses on literature review and personal interviews to discuss the causes of degradation, solutions employed to rehabilitate the estuary, and subsequent physicochemical, ecological, and social changes. 相似文献