The gravitational attraction of any polygonally shaped vertical prism with inclined top and bottom faces

 A closed formula for computing the gravitational attraction of a general vertical prism with N+2 faces (N faces are vertical planes, the other two are the inclined top and bottom planes) in Cartesian coordinates is presented. In addition, the special case of a triangular prism is discussed. Algebraic differences and overlooked singularity conditions of a previously published formula of this computation (which was only for the triangular special case) were identified and are also presented. Received: 22 March 1999 / Accepted: 2 February 2000     

Genesis Conditions for Thunderstorm Growth and the Development of a Squall Line in the Northern Alpine Foreland

Summary  Two numerical models are used to investigate aspects of thunderstorm dynamics and thunderstorm initiation in the northern Alpine foreland. The first, an isentropic model of airflow over and around the Alps, is used to investigate flow patterns favourable for the initiation of deep convection in the region. It is found that a stably-stratified southerly flow towards the Alps leads to a southwesterly flow in the Alpine foreland, a situation most often found during thunderstorm periods, and to the formation of a gravity wave in the lee of the Alps. This wave is accompanied by raised isentropes which, in reality, would lead to a reduction in static stability and convective inhibition as well as an increase in convective available potential energy. The second model, a cloud model, is used to study the development of an observed squall line over southern Bavaria. The model is initialized with wind, temperature and moisture profiles from a radiosonde sounding ahead of the squall line and the squall line is initiated by an array of thermal bubbles. The model simulation is used to interpret the evolution of the squall line. Received March 9, 1999/Revised July 10, 1999     

Polar patches observed by ESR and their possible origin in the cusp region

Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF B_z southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.     

弹塑性有限元模拟分析影响基坑位移的因素

分析影响基坑支护破坏因素对于防止基坑事故的发生,优化基坑支护设计有重要意义。本文用弹塑性有限元方法模拟基坑破坏过程,分析了影响基坑支护破坏的因素。分析结果表明,土体和桩墙的弹性模量都对基坑的位移有一定影响,但土体弹性模量的影响比桩墙弹性模量的影响更大。根据这些结果,推论出传统基坑设计方法与弹性地基梁法的不足之处。另外,分析结果还表明,基坑坑顶水平位移与土体弹性模量的关系无固定规律,而坑底最大位移与弹性模量呈非线性的关系。由此推论出基坑坑顶水平位移监测方法的不可靠性。      

Photosynthetic responses of Larrea tridentata to a step-increase in atmospheric CO2at the Nevada Desert FACE Facility

Of all terrestrial ecosystems, the productivity of deserts has been suggested to be the most responsive to increasing atmospheric CO₂. The extent to which this prediction holds will depend in part on plant responses to elevated CO₂under the highly variable conditions characteristic of arid regions. The photosynthetic responses ofLarrea tridentata , an evergreen shrub, to a step-increase in atmospheric CO₂(to 550 μmolmol⁻¹) were examined in the field using Free-Air CO₂Enrichment (FACE) under seasonally varying moisture conditions. Elevated CO₂substantially increased net assimilation rate (A_net) in Larrea during both moist and dry periods of the potential growing season, while stomatal conductance (g_s) did not differ between elevated and ambient CO₂treatments. Seasonal and diurnal gas exchange dynamics in elevated CO₂mirrored patterns in ambient CO₂, indicating that elevated CO₂did not extend photosynthetic activity longer into the dry season or during more stressful times of the day. Net assimilation vs. internal CO₂(A/C_i) responses showed no evidence of photosynthetic down-regulation during the dry season. In contrast, after significant autumn rains, A_max(the CO₂saturated rate of photosynthesis) and CE (carboxylation efficiency) were lower in Larrea under elevated CO₂. In situ chlorophyll fluorescence estimation ofLarrea Photosystem II efficiency (F_v/F_m) responded more to water limitation than to elevated CO₂. These findings suggest that predictions regarding desert plant responses to elevated CO₂should account for seasonal patterns of photosynthetic regulatory responses, which may vary across species and plant functional types.     

Distribution and inducibility of P-glycoprotein in the catfish: immunohistochemical detection using the mammalian C-219 monoclonal.

Mounting evidence suggests that the P-glycoprotein (pgp) efflux pump may be a modulator of bioavailability and a mode of excretion for xenobiotics. Immunohistochemistry was utilized to examine the distribution and inducibility of a pgp like protein in catfish. Immunoreactivity to the MDR C-219 monoclonal antibody was noted primarily in bile canaliculi or bile preductules of the liver, discrete areas of the extratubular region of the kidney and the columnar epithelia of the intestine. Regional differences in pgp content were noted in the intestine with the distal region containing greater pgp levels than the proximal intestine. Dietary administration of vincristine, a prototypic pgp inducer and beta-naphthoflavone an Ah agonist resulted in induction of the C-219 immunoreactivity in the liver and the distal intestine. These results are consistent in location and inducibility with pgp like proteins and support a possible relationship to xenobiotic absorption and/or excretion in the catfish.     

The US Southern Ocean Joint Global Ocean Flux Study: an introduction to AESOPS

The United States Southern Ocean Joint Global Ocean Flux Study (JGOFS), also known as AESOPS (Antarctic Environment and Southern Ocean Process Study), focused on two distinct regions. The first was the Ross-Sea continental shelf, where a series of six cruises collected a variety of data from October 1996 through February 1998. The second area was the southwest Pacific sector of the Southern Ocean, spanning the Antarctic Circumpolar Current (ACC) at 170°W. Data were collected within this region during five cruises from September 1996 through March 1998, as well as during selected transits between New Zealand and the Ross Sea. The first results of these cruses are described in this issue. The Ross-Sea investigation extensively sampled the area along 76°30′S to elucidate the temporal patterns and processes that contribute to making this one of the Antarctic's most productive seas. Hydrographic distributions confirm that stratification is initiated early in October within the polynya, generating an environment that is favorable for phytoplankton growth. Significant spatial variations in mixed-layer depths, the timing of the onset of stratification, and the strength of the stratification existed throughout the growing season. Nutrient concentrations reflected phytoplankton uptake, and reached their seasonal minimal in early February. Chlorophyll concentrations were maximal in early January, whereas productivity was maximal in late November, which reflects the temporal uncoupling between growth and biomass accumulation in the region. Independent estimates of biogenic export suggest that majority of the flux occurred in late summer and was strongly uncoupled from phytoplankton growth. The ACC region exhibited seasonal changes that in some cases were greater than those observed in the Ross Sea. Sea ice covered much of the region south of the Polar Front in winter, and retreated rapidly in late spring and early summer. Mixed layers throughout the region shoaled in summer due to surface heating, while the addition of freshwater from melting sea ice enhanced stratification in the Seasonal Ice Zone, creating conditions favorable for phytoplankton growth. For example, silicic acid concentrations decreased from initial values as high as 65 to less than 2 μM within approximately 100 km (from 65.7 to 64.8°S). Fluorescence values, however, showed less than a two-fold variation over the same distance. The vertical flux of carbon in the Polar Front area is substantial, and marked variations in the composition of exported material exited over the region. The results provide a means whereby the controls of phytoplankton growth and organic matter flux and remineralization can be analyzed in great detail. Additional results of the AESOPS project are discussed.     

Nutrient and carbon removal ratios and fluxes in the Ross Sea, Antarctica

Net community production (NCP) and nutrient deficits (Def(X)) were calculated using decreases in dissolved CO₂ and nutrient concentrations due to biological removal in the upper 200 m of the water column during four cruises in the Ross Sea, Antarctica along 76°30′S in 1996 and 1997. A comparison to excess dissolved and particulate organic carbon showed close agreement between surplus total organic carbon (TOC) and NCP during bloom initiation and productivity maximum; however, when TOC values had returned to low wintertime values NCP was still significantly above zero. This seasonal NCP, 3.9±1 mol C m⁻², must be equivalent to the particle export to depths greater than 200 m over the whole productive season. We estimate that the annual export was 55±22% of the seasonal maximum in NCP. The fraction of the seasonal maximum NCP that is exported through 200 m is significantly higher than that measured by moored sediment traps at a depth of 206 m. The removal of carbon, nitrate and phosphate (based on nutrient disappearance since early spring) and their ratios showed significant differences between regions dominated by diatoms and regions dominated by the haptophyte Phaeocystis antarctica. While the ΔC/ΔN removal ratio was similar (7.8±0.2 for diatoms and 7.2±0.1 for P. antarctica), the ΔN/ΔP and ΔC/ΔP removal ratios for diatoms (10.1±0.3 and 80.5±2.3) were significantly smaller than those of P. antarctica (18.6±0.4 and 134.0±4.7). The similarity in ΔC/ΔN removal ratios of the two assemblages suggests that preferential uptake of phosphate by diatoms caused the dramatic differences in ΔC/ΔP and ΔN/ΔP removal ratios. In contrast to low ΔC/ΔP and ΔN/ΔP removal ratio in diatom-dominated areas early in the growing season, deficit N/P and C/P ratios in late autumn indicate that the elemental stochiometry of exported organic matter did not deviate significantly from traditional Redfield ratios. Changes in biologically utilized nutrient and carbon ratios over the course of the growing season indicated either a substantial remineralization of phosphate or a decrease in phosphate removal relative to carbon and total inorganic nitrogen over the bloom period. The species dependence in C/P ratios, and the relative constancy in the C/N ratios, makes N a better proxy of biological utilization of CO₂.