Low Net Density Research Articles

Meteorological Alleviation by a Windbreak Net at Reclaimed Land of Isahaya Bay

The reclaimed land in Isahaya Bay is approximately 816 ha in area, including the central area (706 ha) and the Oe area (110 ha). The reclamation will be complete in 2007. It will be necessary to perform continued meteorological research on the lands, which are intended for agricultural usage after the completion of reclamation. These lands are not protected against the wind, and strong winds do frequently blow across this wide and horizontal area. In order to use this area as arable land, it will be necessary to introduce many windbreaks for the protection of these open fields. A windbreak net of 2.4 m height with an open space of 0.4 m between the bottom of the net and the ground was constructed on the open field and its length was 100 m. The windbreak net was made of blue polyethylene Russell net with 6 mm mesh. The wind speed was measured from a distance of -20H windward to 25H leeward and at heights of 6, 3, 2, 1 and 0.5 m, where H represents the height of the net on the ground, and the numerals the multiple distances from the net, and negative signs denote the windward side and positive signs the leeward. Wind speed, air temperature, relative humidity, and surface soil and leaf temperatures were measured from Nov. 2003 to Feb. 2004. Variations of horizontal, vertical and isopleths of the wind speed under conditions of both weak and strong winds were obtained. Wind speed decreased about 16% in the immediate leeward side, as compared with the standard wind speed at -20H at each height due to the low net density of 15%; however, the effective decrease was continued over a long distance. Air, surface leaf and surface soil temperatures with right-angle wind increased significantly in the leeward side under conditions of weak wind, and this increase continued for more than 25H. The temperatures increased and relative humidity decreased during the daytime for 20H in the leeward side. Temperature increase is useful for growth and development of crops, vegetables and other vegetation. However, the harmful decrease of temperatures by surface inversion was measured from the night to early morning under conditions of a fine or clear day with weak wind. As the net density was low and not sufficiently effective, it will be necessary to introduce considerably higher windbreak net and to reduce the open space under the net. Moreover it will be necessary to obtain accurate data using different windbreak nets in the open field.

The evolution of andesite volcano structures: new evidence from gravity studies in Costa Rica

Published gravity data on active volcanoes generally reflect either the low density scoriaceous/pumiceous deposits that are localized within ring-fracture collapse depressions, such as the calderas of mature silicic volcanoes, or the high density frozen magma conduits that occur beneath basaltic shields and cones. The intensive gravity surveys reported here over three complex andesite volcanoes reveal features of both types. Their multi-component gravity fields have crater-centred positive anomalies (1–2 km diameter) surrounded by broader zones of negative gravity with similar amplitudes but greater width (5–10 km). The former are thought to reflect sub-crater magma pipes of normal density (ca. 2.5–2.6 Mg m −3) surrounded by pyroclastic scoria, ashes and occasional lava flows of much lower net density (1.8–2.4 Mg m −3) which, in turn, account for the negative anomalous zones because the deeper, more consolidated and older parts of these andesite volcano edifices have more normal densities (2.3–2.6 Mg m −3). The low density materials are particularly interesting because they appear to have filled topographic depressions to depths of several hundred metres, especially where old caldera-like structures have been postulated from the steep gravity gradients over perimeter ring faults. A model is developed whereby short periods of caldera collapse, associated with intermittent, large high level magma bodies, are interspersed by normal crater-like activity with narrow sub-surface magma pipes. Dominantly pyroclastic activity from summit craters generates the materials that gradually fill earlier-formed topographic depressions. This study demonstrates the unique value of detailed gravity surveys, combined with surface geological information, for modelling and understanding the evolution of active volcano summit regions.

Evidence for a B-cell -like helper function in mixed lymphocyte culture between immunocompetent thymus cells.

The immunocompetent subpopulation by mouse thymus cell (TH-2) was isolated by buoyant density centrifugation and by hydrocortisone pretreatment. TH-2 cells undergo a proliferative one-way or two-way mixed lymphocyte culture (MLC) response only when cultured with allogeneic or congenic peripheral lymphoid cells. However, mixtures of allogeneic TH-2 cells alone do not proliferate in either one-way or two-way MLC reactions. Such MLC mixtures are proliferative only if mitomycin-blocked peripheral lymphoid cells are also present in the mixture. The peripheral helper cell has been found to be of low net density, non-adherent, insensitive to anti-thy-1 serum cytotoxicity, but sensitive to the cytotoxic effets of anti-immunoglobulin serume plus complement. The helper effect does not depend on proliferation nor does it appear to involve demonstrable soluble mediators. The nature of failure of MLC between TH-2 subpopulations appears to be dependent on the exppression of some product of the K, I regions of the H-2 locus. Possible mechanisms by which a B-cell-like helper cell triggers TH-2 proliferation are discussed terms of the present knowledge of specific alloantigen receptor on T and B cells, and the immunoglobulin Fc region receptors on T cells.