Larger Total Area Research Articles

Amazon diversity in light of the paleoecological record

Disjunct distributions of Amazonian species have been explained previously by a refugial theory which postulates that Amazonian rain forest was preserved in large highland regions throughout the Pleistocene. No direct, radiocarbon dated evidence exists for the last glacial maximum with which to test this theory. The only radiocarbon dates of Pleistocene age from the Amazon basin are of fossiliferous deposits in the proposed Napo refugium of the West, where both pollen assemblages and wood samples indicate that forest with cool Andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation, implying a temperature depression of at least 4°C in the Amazon lowlands. Under modern climatic conditions, lateral erosion by river meander, together with surface erosion, serves as a rejuvenating mechanism for the rain forests of Peru and Ecuador. The instability of late Holocene Amazonian climates is demonstrated by documenting a precipitation event in the eastern Andean cordillera that caused widespread flooding of western Amazonian forests 800–1300 BP. Late Holocene pollen histories from widely dispersed parts of central Amazonia distinguish between vegetation histories in the drainage of northern, south-western and western watersheds, but all show histories of fluctuating intensities of dry seasons. Radiocarbon dating of charcoal layers in soils of Venezuelan Amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka. The high species richness of Amazonia is a result of numerous opportunities for vicariance because of a very large total area, wide variety of habitats and intermediate levels of disturbance, particularly by hydrological processes, that has varied on timescales from years to millennia. Amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times.

Amazon Diversity in Light of the Paleoecological Record

Disjunct distributions of Amazonian species have been explained previously by a refugial theory which postulates that Amazonian rain forest was preserved in large highland regions throughout the Pleistocene. No direct, radiocarbon dated evidence exists for the last glacial maximum with which to test this theory. The only radiocarbon dates of Pleistocene age from the Amazon basin are of fossiliferous deposits in the proposed Napo refugium of the West, where both pollen assemblages and wood samples indicate that forest with cool Andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation, implying a temperature depression of at least 4°C in the Amazon lowlands. Under modern climatic conditions, lateral erosion by river meander, together with surface erosion, serves as a rejuvenating mechanism for the rain forests of Peru and Ecuador. The instability of late Holocene Amazonian climates is demonstrated by documenting a precipitation event in the eastern Andean cordillera that caused widespread flooding of western Amazonian forests 800–1300 BP. Late Holocene pollen histories from widely dispersed parts of central Amazonia distinguish between vegetation histories in the drainage of northern, south-western and western watersheds, but all show histories of fluctuating intensities of dry seasons. Radiocarbon dating of charcoal layers in soils of Venezuelan Amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka. The high species richness of Amazonia is a result of numerous opportunities for vicariance because of a very large total area, wide variety of habitats and intermediate levels of disturbance, particularly by hydrological processes, that has varied on timescales from years to millennia. Amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times.

A NOTE ON THE MINIMUM NUMBER OF UNITS FOR HEAT EXCHANGER NETWORK SYNTHESIS

Although graph theory shows that the minimum number of exchangers (Umin) in a network is usually one less than the number of streams (N - 1), examples have been published, which demonstrate that this limiting case cannot always be achieved. Some of these examples contain a pinch point, for which it is advocated that the ‘N - 1 target’ should be applied on both sides of the pinch. However, by using a novel arrangement of stream splitting, mixing and by-passes, some of the literature examples can be designed to conform to the N - 1 target. For networks with similar total areas, those having fewer units will usually be cheaper, so Umin networks often have lower capital costs. Although the networks discussed here have somewhat larger total areas, possible applications are discussed where they may be economically attractive.

Effect of Bit Hydraulic Horsepower on the Drilling Rate of a Polycrystalline Diamond Compact Bit

Summary A laboratory drilling program was conducted to measure the effect of bit hydraulic horsepower on the drilling rate obtained with a polycrystalline diamond compact (PDC) bit. Drilling tests were conducted under simulated downhole conditions with an 8 1/2-in. [21.59-cm] diameter PDC bit fitted with four sets of five equal-sized nozzles. PDC bit fitted with four sets of five equal-sized nozzles. Mancos shale, Pierre shale, and Berea sandstone were drilled with both water- and oil-based drilling fluids to determine the interactions among bit hydraulics, rock characteristics, and the drilling fluid. For the range of drilling conditions and rocks examined, the results indicated that bit hydraulic horsepower had a significant influence on the drilling rate. The degree to which drilling rate was affected by bit hydraulic horsepower was dependent on the rock/drilling-fluid combination. Introduction Proper hydraulic design for effective cleaning and Proper hydraulic design for effective cleaning and cooling of PDC bits has been recognized as a major factor in their successful application since these bits were introduced. Historically, there have been two approaches to the hydraulic design of PDC bits:natural diamond-bit flow-distribution systems (water courses with large total flow areas) andhigh-velocity jet nozzles. Both types have been used with varying degrees of success but often for unrecognized reasons. The water-course-type hydraulic designs were characteristic of most early matrix-bodied PDC bits. Nozzled bits evolved from the steel-bodied bits with stud-mounted cutters, although matrix-bodied bits are now available with jet nozzles. An increasing number of commercial PDC bits are becoming available with interchangeable nozzles, providing the flexibility of rig-site hydraulics optimization, providing the flexibility of rig-site hydraulics optimization, With these interchangeable nozzles, the hydraulic energy (or power) of the drilling fluid that is dissipated across the bit face can be adjusted to match that portion of the rig's hydraulic power that is available for the bit after other system losses have been considered. Unfortunately, the benefit in increased drilling rate that can be expected by an optimization of bit hydraulic horsepower has yet to be adequately defined quantitatively for PDC bits. The objective of our work was to determine experimentally the effect of bit hydraulic horsepower on the drilling rate achieved with a jet-nozzled PDC bit while three rock types were drilled with both oil- and water-based drilling fluids. PDC Bit Hydraulics-Background PDC Bit Hydraulics- JPT p. 2110

Efficient Utilization of Satellite Transponders via Time-Division Multibeam Scanning

The space segment of a satellite system is proposed wherein a fixed number of identical transponders are shared among a larger number of spot beam regions which completely span a large total service area. Time-division multiple-access techniques are employed, and each transponder is rapidly scanned over appropriately defined group pairs of spot beam regions, thereby establishing full coverage and full interconnectivity. The service is matched to the nonuniform traffic requirements exhibited among the various spot beam regions, reliability can be optimized since all transponders are identical, and each transponder is utilized with an efficiency of 100 percent. A mathematical proof is presented which shows that the traffic can always be assigned on a nonconflicting basis, and an efficient assignment technique is described.

Elevated Temperature Stability of a Lamellar Al-CuAl2 Eutectic Composite

Since the two phases of a directionally solidified binary eutectic composite are essentially in chemical equilibrium, the microstructure should be stable at elevated temperatures. This effect has been demonstrated in a number of alloys. However, eutectic composites are characterized by physicochemical instability due to the large total interfacial area. The total interfacial energy per unit volume can be reduced by coarsening of the structure, by the growth of existing lower-energy interfaces at the expense of existing higher-energy interfaces, or by the formation of new lower-energy interfaces at the expense of existing interfaces. The present study was made in order to examine these possibilities in a fine-scale lamellar Al-CuAl2 eutectic.Composites with an interlamellar spacing ≲2 μ were grown at a speed of 11 cm per hour in high-purity graphite crucibles. Exposure temperatures of 490°C, 510°C and 530°C were chosen with time at temperature ranging from 10 to 100 hours.

配分電盤の経済的配置に関する研究

To keep the cost of the wiring of electrical equipments in a building economical, we have hitherto considered it is fundamental that substations, switchboards, and panel boards required should be installed close by load centers concerned. There has been a sharp accentuation of interest in and effort on, economical planning of interior wiring, i.e. to keep electrical equipment installation to load centers in close layout which would minimize the wiring costs. But our practical experiences show that it is very difficult to keep layout of electrical equipments close by load centers in a building as satisfactorily as electrical engineers desire by so many troubles. In some case, close layout is difficult to be carried out as planned by electrical engineers being change of planning necessary for close layout impossible in due time of construction schedule, nothing left except best alternative wiring to be planned. In another case, having time enough to plan close layout and to propose economical layout of switchboads and panel boards to an architect in charge of the building design, and very often no approval from an architect, because of no numerical values specified for close layout as measuring indices in evaluating close layout characteristics. Accordingly, unsatisfactory layout of electrical equipments and rather not economical wiring are carried out in a building, and very often in such cases, electrical engineers are allowed only to seek out the best layout within the limited conditions of the building plan given by an architect. In case of small total floor area, cost-up of wiring according to the unfit layout of electrical equipments to the load center, amounts not to so much as compared with the optimum wiring. But in case of large total floor area, cost-up brought by unfit layout amounts to so much as not negligible. If we can express cost-up rates in numerical terms according to off-distances from the load center considered desirable, we can have measuring indices in numerical terms sufficient to evaluate, and we can change some parts of building plan by positive recommendation effective to carry out general coordination between electrical engineers and an architect. And we can have economical layout of switchboards and panel boards. We must assign quantitative numbers to all the significant factors relative to the economical layout of switchboards and panel boards.

Photosynthesis in leaf disks as a measure of photosynthetic capacity in crop plants

In a previous communication (Bartoš, Kubín andŠetlík 1960) a method was reported, which makes it possible to measure the average rate of photosynthesis in a representative sample of a large number of leaves. The sampling is made by cutting out disks of leaf tissue, following a definite pattern. Isolated leaf disks are then illuminated under controlled conditions and the rate of photosynthesis is estimated by weighing the increment of dry matter in a given time interval. Data published in the present paper demonstrate that this method can be successfully used for a characterisation of photosynthetic capacity (specific rate of photosynthesis, seeBartoš, Kubín andŠetlík 1960). Both specific values for individual plants and average values for homogenous plant populations may be estimated with very good accuracy. One of the chief factors which render this possible is obviously the surprising homogeneity of the photosynthetic tissue of leaves. Samples of very small size may serve as representative of a large total leaf area, e.g. of a population under field conditions. Preliminary results of comparative investigations suggest that, with the plant varieties examined, differences in photosynthetic capacity are not very great, both between and within populations of diverse varieties. Differences as large as 50% have been encountered so far solely between values of photosynthetic capacity estimated for individual plants in a population. On the other hand, values of average photosynthetic capacity in populations of crop plant varieties within one species or genus are, as a rule, not very distinct and quite often no statistically significant difference can be demonstrated in such cases. Even if the varieties belong to different genera, differences in photosynthetic capacity in their populations greater than some 50% have been found only as an exception. In considering all these results one important fact must be taken into account, i.e. the intensity of illumination in the apparatus. Contrary to what was intended and awaited, the radiation intensity used was not high enough to saturate photosynthesis in leaf disks. The light dependence of photosynthesis in isolated portions of leaf tissue apparently has a somewhat different character from that usually assumed for intact leaves of higher plants.