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1.
Consider the robust network design problem of finding a minimum cost network with enough capacity to route all traffic demand
matrices in a given polytope. We investigate the impact of different routing models in this robust setting: in particular,
we compare oblivious routing, where the routing between each terminal pair must be fixed in advance, to dynamic routing, where routings may depend arbitrarily on the current demand. Our main result is a construction that shows that the
optimal cost of such a network based on oblivious routing (fractional or integral) may be a factor of Ω(log n) more than the cost required when using dynamic routing. This is true even in the important special case of the asymmetric
hose model. This answers a question in (Chekuri, SIGACT News 38(3):106–128, 2007), and is tight up to constant factors. Our proof technique builds on a connection between expander graphs and robust design
for single-sink traffic patterns (Chekuri et al., Networks 50(1):50–54, 2007). 相似文献
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Ecofriendly materials are becoming a need of the day. We have severe setback when there is lot of use of agro wastes in plastics. To reduce pure plastic use in agriculture, this study has been made to find some remedial measure. In the process, we sought the effect of addition of rice husk (RH) in polyvinylchloride (PVC) on the dielectric properties at different frequency and temperature has been studied. Measurements have been performed in the frequency range from 1 to 10 kHz and temperature range of 32–80°C. The experimental results show that dielectric constant (ε′) increases with the addition of RH in PVC. Dielectric constant (ε′) decreases with increasing frequency, which indicates that the major contribution to the polarization comes from orientation polarization. Dielectric constant (ε′) increases with increasing temperature due to greater freedom of movement of dipoles within PVC at higher temperatures. A theoretical model for dielectric constant with temperature and frequency dependent is proposed. Experimental results are in good agreement with the proposed theoretical model. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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NMR imaging of low pressure,gas‐phase transport in packed beds using hyperpolarized xenon‐129 下载免费PDF全文
Galina Pavlovskaya Joseph Six Thomas Meersman Navin Gopinathan Sean P. Rigby 《American Institute of Chemical Engineers》2015,61(11):4013-4019
Gas‐phase magnetic resonance imaging (MRI) has been used to investigate heterogeneity in mass transport in a packed bed of commercial, alumina, catalyst supports. Hyperpolarized 129Xe MRI enables study of transient diffusion for microscopic porous systems using xenon chemical shift to selectively image gas within the pores, and, thence, permits study of low‐density, gas‐phase mass‐transport, such that diffusion can be studied in the Knudsen regime, and not just the molecular regime, which is the limitation with other current techniques. Knudsen‐regime diffusion is common in many industrial, catalytic processes. Significantly, larger spatial variability in mass transport rates across the packed bed was found compared to techniques using only molecular diffusion. It has thus been found that that these heterogeneities arise over length‐scales much larger than ~100 µm. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4013–4019, 2015 相似文献
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Shyam Ramkrishna Garud Belagola Shivakumar Priyanka Navin Kumar Rastogi Maya Prakash 《臭氧:科学与工程》2018,40(3):198-208
Thermal processing is the most widely adopted technology for preservation of juices; however, it is associated with significant changes in nutritional quality and flavor. Combination of nonthermal hurdles (ozone 1.2 g/h, 10 min, and lactic acid 0.5%) reduced total bacterial count of sugarcane juice by 4.3 log and controlled enzymatic activity to a moderate level (reduction of 60% and 72% activity of polyphenol oxidase and peroxidase, respectively). Combined treatment was comparable to thermal treatment in maintaining microbial and sensory quality of sugarcane juice during 1-month storage under refrigerated conditions; however, additional hurdles may be required for extended storage. 相似文献
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Preliminary analysis was performed to assess contamination levels in roadside soils, distribution behavior and human exposure with Polycyclic Aromatic Hydrocarbons (PAHs) during summer, winter, rainy, and autumn during 2013 in one of the developing cities of northern India. The concentration of PAHs was measured at ten different locations (at 1, 2, and 3 m) from roadside soil. Recovery range was 30% and 80% with lower value corresponding to the lower molecular weight PAHs compound. Identification and quantification of PAHs was done by GC-FID. Average PAHs concentration (city average) was found to be 16.53, 4.04, 17.49, and 7.82 μg g?1, during summer, winter, autumn, and the rainy seasons, respectively. Average concentration of low and high carcinogenic PAHs during summer, winter, autumn, and rainy was 5.1 and 31.29, 2.1 and 6.4, 4.74 and 35.08, 3.97 and 12.77μg g?1, respectively. The average ratio of low and high carcinogenic PAHs was found to be 1:6, 1:3, 1:7.6, and 1:3.21 during summer, winter, autumn, and the rainy seasons at most intercepts. Dib(ah)A and B(a)P were the two individual PAHs found in highest concentration during summer, winter, and the rainy seasons, whereas B(a)P and IP were individual PAHs found in highest concentration during autumn. It was also analyzed that high carcinogenic PAHs concentration was quite higher (around 85%) in comparison to low carcinogenic PAHs (around 15%) at most intercepts. This article also deals with the behavior of PAHs at places of average/high population and traffic density intercepts. Five-ringed PAHs were in highest concentration at all intercepts and seasons. Two-tailed T test was applied for authenticity of the data and results. Toxic equivalency factor of B(a)P and Dib(ah)A was maximum as compared to other PAHs. 相似文献
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Journal of Materials Science Letters - 相似文献