5,202 research outputs found

    Enhancing Water Quality and Dredged Material for the Port of Harlingen (Phase I)

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    The Arroyo Colorado is located in the Lower Rio Grande Valley of South Texas and flows through the middle of Hidalgo and Cameron counties. The lower 16 miles of the Arroyo Colorado form the boundary between Cameron and Willacy Counties, but the lower 26 miles form the tidally influenced segment. This tidal segment is periodically dredged to accommodate barge traffic to the Port of Harlingen and is characterized by steep eroding slopes with bank heights up to 50 feet. The steep banks are partially the result of the placement of dredged spoil material on the banks of the stream. In the upper portions of the tidal segment, the steep banks are thought to occasionally impede the flow of air across the surface of the stream, which can reduce aeration and vertical mixing, factors that contribute to the low levels of dissolved oxygen (DO) observed in this portion of the stream. The average width of the tidal segment of the Arroyo Colorado is about 200 feet and the average depth is 13 feet. Being tidally influenced, it is brackish to saline (slightly salty to very salty) and usually stratifies under warm weather conditions, forming layers of warmer, fresher water on the surface and cooler, more saline water near the bottom. For most of its course, the tidal segment of the Arroyo Colorado has a significant degree of natural sinuosity. However, sinuosity in the tidal segment of the Arroyo Colorado severely diminishes in the final four miles of the stream as the Arroyo Colorado flows into a man-made channel that leads to the Intracoastal Waterway (GIWW) and the Lower Laguna Madre

    Transportation and development: insights from the U.S., 1840-1860

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    We study the effects of large transportation costs on economic development. We argue that the Midwest and the Northeast of the U.S. is a natural case because starting from 1840 decent data is available showing that the two regions shared key characteristics with today’s developing countries and that transportation costs were large and then came way down. To disentangle the effects of the large reduction in transportation costs from those of other changes that happened during 1840?1860, we build a model that speaks to the distribution of people across regions and across the sectors of production. We find that the large reduction in transportation costs was a quantitatively important force behind the settlement of the Midwest and the regional specialization that concentrated agriculture in the Midwest and industry in the Northeast. Moreover, we find that it led to the convergence of the regional per capita incomes measured in current regional prices and that it increased real GDP per capita. However, the increase in real GDP per capita is considerably smaller than that resulting from the productivity growth in the nontransportation sectors.Transportation ; Middle West ; Developing countries

    Oxidation of an oil rich in docosahexaenoic acid compared to linoleic acid in lactating women

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    Background: We studied the oxidation of an oil rich in docosahexaenoic acid (DHA; DHASCO(R)) in lactating mothers receiving a dietary DHA supplement or a placebo. The results were compared with the oxidation of linoleic acid. Methods: Breast-feeding mothers received a dietary supplement (DHASCO; 200 mg DHA/day, n = 5) or a placebo (n = 5) for 14 days. Six weeks post partum all 10 mothers received a single dose of 2 mg/kg body weight uniformly C-13-labeled DHASCO. In a previously reported study 6 mothers received 1 mg/kg body weight uniformly C-13-labeled linoleic acid. Breath samples were collected over 48 h after tracer application. The total CO2 production was measured by indirect calorimetry and the C-13 isotopic enrichment of labeled CO2 by isotopic ratio mass spectrometry. Results: The oxidation of C-13-labeled DHASCO in the supplemented and placebo groups was similar. Maximal C-13 enrichment was reached earlier in the group receiving C-13-DHASCO (median 1.0 vs. 3.0 h in the linoleic acid group). The cumulative C-13 recovery in breath was higher in the DHASCO versus the linoleic acid group until 10 h after tracer application and comparable thereafter. Conclusions: The difference in oxidation of DHASCO versus linoleic acid after tracer ingestion might be partly due to a faster absorption and oxidation of shorter chain saturated fatty acids contained in DHASCO. The cumulative oxidation of DHASCO and linoleic acid 24 and 48 h after tracer ingestion is similar. Copyright (C) 2000 S. Karger AG, Basel

    ΛNN\Lambda NN and ΣNN\Sigma NN systems at threshold: II. The effect of D waves

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    Using the two-body interactions obtained from a chiral constituent quark model we study all ΛNN\Lambda NN and ΣNN\Sigma NN states with I=0,1,2 and J=1/2,3/2 at threshold, taking into account all three-body configurations with S and D wave components. We constrain further the limits for the ΛN\Lambda N spin-triplet scattering length a_{1/2,1}. Using the hypertriton binding energy we find a narrow interval for the possible values of the ΛN\Lambda N spin-singlet scattering length a_{1/2,0}. We found that the ΣNN\Sigma NN system has a quasibound state in the (I,J) = (1,1/2) channel very near threshold with a width of about 2.1 MeV.Comment: 19 pages, 4 tables, 6 figures. Accepted for publication in Phys. Rev.

    How well can you know the edge of a quantum pyramid?

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    We consider a symmetric quantum communication scenario in which the signal states are edges of a quantum pyramid of arbitrary dimension and arbitrary shape, and all edge states are transmitted with the same probability. The receiver could employ different decoding strategies: he could minimize the error probability, or discriminate without ambiguity, or extract the accessible information. We state the optimal measurement scheme for each strategy. For large parameter ranges, the standard square-root measurement does not extract the information optimally.Comment: 13 pages, 5 figures, 1 tabl

    Coherent Eavesdropping Attacks in Quantum Cryptography: Nonequivalence of Quantum and Classical Key Distillation

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    The security of a cryptographic key that is generated by communication through a noisy quantum channel relies on the ability to distill a shorter secure key sequence from a longer insecure one. We show that -- for protocols that use quantum channels of any dimension and completely characterize them by state tomography -- the noise threshold for classical advantage distillation is substantially lower than the threshold for quantum entanglement distillation because the eavesdropper can perform powerful coherent attacks. The earlier claims that the two noise thresholds are identical, which were based on analyzing incoherent attacks only, are therefore invalid.Comment: 4 pages, 1 figure; this is the detailed account for the results Reported in quant-ph/031015