“Software,Jobs Go Begging,Threatening Technology Boom”: Computer Services Employment in U.S. Metropolitan Areas, 1982 and 1993     

Samuel Nunn  Robert Warren  Joseph B. Rubleske 《The Professional geographer》1998,50(3):358-372

The campaign to promote the networking of America underscores the importance of information infrastructures that can support regional competitiveness. One crucial element of a regional information infrastructure is a computer services (CS) industry that supports computer systems, provides backward and forward linkages among all sectors of the economy, serves as engines for economic growth, enhances production efficiency, and encourages innovation. But research on metropolitan CS has been limited, and where CS are analyzed directly, spatial units of analysis vary and CS are rarely disaggregated. This paper situates CS employment within spatial analyses of producer services, outlines infrastructural characteristics, analyzes CS distribution across metropolitan areas in 1982 and 1993, and considers the implications of the findings. The data suggest that while large metropolitan areas are most likely to have a diverse base of specializations in multiple CS types, many smaller metropolitan areas possess CS specializations. We conclude that ranking in the urban CS hierarchy is more likely to be a function of local economic structure than metropolitan population. The uneven dispersion of CS capacity across metropolitan areas potentially has negative ramifications for implementation of national policy and development of underserved regional economies.  相似文献   

Prototype LAAS Architecture Design Considerations     

Boris S. Pervan  Samuel P. Pullen  David G. Lawrence  Konstantin Gromov  Jock Christie  Guttorm Opshaug  Vicky Lu  Ping-Ya Ko  Per Enge  Bradford W. Parkinson 《GPS Solutions》1998,2(1):49-61

  相似文献   

Vertical profiles of Volcanic Aerosol and Polar Stratospheric Clouds Above Kiruna, Sweden: Winters 1993 and 1995     

Terry Deshler  Samuel J. Oltmans 《Journal of Atmospheric Chemistry》1998,30(1):11-23

Vertical profiles of aerosol were measured in February 1993, and January - March 1995 using balloon-borne particle counters released from Kiruna, Sweden. Condensation nuclei (CN) and aerosol with radii 0.15 - 10.0 µm were measured in 8-12 size classes. The three flights in 1993 were within the polar vortex. Temperatures were below polar stratospheric cloud (PSC) threshold temperatures on one flight and a thin PSC was observed. The volcanic aerosol in the 1993 vortex was similar to that in 1992. In 1993, surface areas were 10 - 20 µm2 cm-3 and volumes 1 - 3 µm3 cm-3. In 1995 three of five flights were within the polar vortex. The volcanic aerosol had decreased to 3 - 7 µm2 cm-3 and 0.1 - 0.4 µm3 cm-3. The top of the volcanic aerosol layer in both years was near 500 K potential temperature (~20 km). A thick nitric acid and water PSC was observed in January 1995. In the thickest region of this PSC nearly all CN were observed to be activated, and surface areas of 5 - 10 µm2 cm-3 were calculated. The volumes observed in this PSC were closer to what would be expected for particles composed of nitric acid trihydrate than for ternary solution droplets. In 1993 the opposite was observed, the volumes in the thin PSC were closer to what would be expected for ternary solution droplets.  相似文献   

Lake victoria: The water hyacinth (Eichhornia crassipes [Mart.] Solms), its socio-economic effects, control measures and resurgence in the Winam gulf     

George Ogueno Opande  John Charles Onyango  Samuel Otieno Wagai 《Limnologica》2004,34(1-2):105

The aquatic weed Eichhornia crassipes [Mart.]Solms was introduced in Lake Victoria from Rwanda via the Kagera River by the activities of man. After originally infesting Lake Victoria (Uganda), it eventually spread into the Winam gulf, where its proliferation was spectacular, resulting in an enormous public outcry. The aim of this study was to find out how a beach/bay covered by a weed carpet affected the life of a lakeshore community, if there were any seasonal changes in carpet sizes and to establish if the water hyacinth is a friend or an enemy. Surveys were conducted in selected beaches between June 1995 and November 1999. When surveys were complete, it became clear that this weed is nomadic, except in lagoons and beaches that had little external interference. The open waters remained generally clear due to constant wave action. Interviews conducted on selected beaches/bays indicated that weed carpets impacted both positively and negatively, i.e. they disrupted fishing activities, transport, irrigation, water treatment, enhanced breeding grounds for vectors of human diseases, impacted on biodiversity and had become a source of raw materials for making furniture, paper and artefacts. After successful biological control by the Kenya Agricultural Research Institute (KARI), resurgence and succession were observed. The impact of water hyacinth on the life of the lakeshore communities in the Winam gulf is serious and needs to be quantified. Further research is necessary to establish whether this weed is an enemy or a friend of the lakeshore communities.  相似文献   

Fungal weathering of basaltic rocks in a cold oceanic environment (Iceland): comparison between experimental and field observations     

Samuel Etienne  Joëlle Dupont 《地球表面变化过程与地形》2002,27(7):737-748

This paper presents evidence for strong biochemical weathering of basaltic outcrops induced by fungal communities in a cold environment. Weathering rind formation is considered to be a consequence of the biological activity. Comparisons between in vitro experiments and in situ observations allow a characterization of fungal effects on rocks and help to define the place of these micro‐organisms in the cold environment weathering chain. It is concluded that biological weathering is chronologically the first process of weathering, probably leading to the subsequent expression of cryogenic processes. Information presented here suggests the need for reconsideration of the traditional frost‐driven morphogenetic system normally considered for subpolar areas. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The effect of iteration frequency on a numerical model of near-surface ice segregation     

Samuel I. Outcalt 《Engineering Geology》1979,13(1-4):111-124

It is possible to construct numerical models of the ice segregation process. However, the model is a discrete approximation of a nonlinear continuous process and thus is subject to somewhat more pronounced effects of node geometry and calculation frequency than linear models. The model more closely simulates natural frozen soil structure when vapor phase transport is included in the model structure. An iteration frequency of 10 s appeared sufficient to yield realistic results with the exponentially spaced node geometry employed in these tests.  相似文献   

Textural evolution and metamorphism of pillow basalts from the Franciscan Complex,western Marin County,California     

Samuel E. Swanson  Peter Schiffman 《Contributions to Mineralogy and Petrology》1979,69(3):291-299

Petrogenesis of Franciscan pillow basalts from the Franciscan Complex of western Marin County California entails both dynamic crystallization of tholeiitic magma and subsequent low-temperature metamorphism. Brittle deformation during tectonic emplacement of pillow basalts into a chert greywacke terrain is manifested by the shearing of interpillow matrix and polishing of pillow rims, but the igneous textures within pillows are well preserved.The cooling history of pillow basalts can be understood through analysis of morphologic variations of primary olivine and plagioclase from rim to core of the pillow. Crystal sizes and plagioclase dendrite spacings are consisted with a cooling rate which generally decreases inward. Some pillows show a marked asymmetry in plagioclase and olivine morphology suggesting lower cooling rates caused by asymmetric cooling of the pillows. Olivine morphologies, primarily hopper and chain forms, are consistent with cooling rates of 2–10 °C/h for pillow cores and 50–75 °C/h for pillow rims.Low temperature hydrothermal alteration has produced secondary minerals indicative of zeolite facies conditions. Pillow matrix is either chloritic or zeolitic (in part laumontized). Pillow rims display incomplete replacement of calcic palagonite by pumpellyite (Fe₂O₃=9–21 wt%), prehnite (Fe₂O₃=5–7 wt%), sphene and quartz. Metamorphism of pillow interiors, manifested by: (1) veins of quartz, pumpellyite, calcite, or harmotome (BaO=15 wt%); (2) amygdules containing analcime, chlorite or quartz; and (3) replacement of olivine by pumpellyite or smectite/illite, of plagioclase by albite (An3)+sericite, and of glassy groundmass by fine-grained chlorite. Primary augite (Wo3₃₉En₁₃Fs₄₈) was not altered. The described paragenesis may be attributed to oceanfloor and/or Franciscan-type metamorphism.  相似文献   

Climatic implications of D/H ratios of meteoric water over North America (9500–22,000 B.P.) as inferred from ancient wood cellulose CH hydrogen     

Crayton J. Yapp  Samuel Epstein 《Earth and Planetary Science Letters》1977,34(3):333-350

δD and δ¹³C values have been measured for the unexchangeable hydrogen and the total carbon of cellulose extracted from 40 North American¹⁴C-dated trees that range in age from 9500 to 22,000 years B.P.Meteoric waters which precipitated over ice-free regions of North America in the interval 14,000–22,000 B.P. had more positive δD values than corresponding modern waters by an average of 19‰. Lower ocean temperatures and smaller temperature gradients than exist at present between ocean and ice-free North America are indicated for the late Wisconsin glacial maximum. This is compatible with warmer winters and cooler summers for this glacial period. The δD value of the North American ice sheet during the Late Wisconsin maximum was approximately ?100‰ as determined from the inferred δD values of the waters of proglacial lakes Agassiz and Whittlesey. From this figure the increase in δ¹⁸O of the oceans during the glacial maximum can be calculated to have been +0.8‰. At the point where they began to move over the ice, air masses supplying moisture to the North American ice sheet contained a little more than 50% of their original moisture content, which is a much greater percentage than exists in air masses supplying the modern Greenland and Antarctic ice sheets. This relatively vapor-rich air coupled with lower summer temperatures, which reduced ablation, probably contributed to the maintenance and growth of the ice sheet.The transition from glacial to interglacial conditions on North America was rapid and occurred within a 2000–3000-year interval. However, the transition may not have been synchronous over North America.A 40-year δD record in a spruce branch from the Two Creeks (Wisconsin) forest (～11,800 B.P.) shows large variations which suggest an unusual hydrologic environment in the area of the tree.Cellulose δ¹³C values range between ?20.8 and ?25.9‰, but do not correlate with δD variations for the samples analyzed in this work. Thus, climatic significance of δ¹³C variations cannot be resolved from these data.  相似文献   

Low-Cost Apparatus for On-Site Monitoring of Methane in Ground Water     

Samuel S. Harrison 《Ground Water Monitoring & Remediation》1986,6(2):73-76

An upsurge in oil- and gas-well drilling in northwestern Pennsylvania and western New York has been accompanied by several incidents of contamination of ground water by methane. Determining which well is causing the contamination is extremely difficult if more than one gas or oil well is present in the area.
The fact that the solubility of methane decreases as the pressure on ground water decreases provides a quantitative basis for monitoring changes in the amount of methane in the ground water. Quantitative measurements of the volume of methane given off by ground water pumped from a well as the water enters atmospheric pressure permit detection of temporal changes in the gas content which are too subtle to be detected visually. These gas volume changes may, in some cases, be correlated with variations in the pressure of methane in the annulus of nearby individual gas/oil wells and thus may provide a means of pinpointing the gas/oil well that is causing the methane contamination.
The basic principle of the gas-volume monitoring apparatus (GVMA) described in this paper is that as a measured amount of ground water enters atmospheric pressure the gas which comes out of solution is trapped and measured. The GVMA can be constructed of materials costing less than $100 and requires no special skills to assemble or operate. In a recent study conducted in a western New York village, four homeowners were able to collect quantitative gas-volume data from their household water wells daily in about one-half hour. Unlike laboratory analyses for dissolved methane, there is no cost involved in monitoring with the GVMA beyond the initial instrument cost and operator time. Another advantage is that the data are available immediately.  相似文献   

The determination of the D/H ratio of non-exchangeable hydrogen in cellulose extracted from aquatic and land plants     

Samuel Epstein  Crayton J. Yapp  John H. Hall 《Earth and Planetary Science Letters》1976,30(2):241-251

A method has been developed for the analysis of D/H ratios of non-exchangeable hydrogen in plant cellulose. Plant samples are nitrated at low temperature and pure cellulose nitrate is extracted by acetone dissolution. Tests of this nitrated product have demonstrated that the nitration-extraction procedure eliminates the OH hydrogen and does not alter the D/H ratio of the cellulose carbon-bound hydrogen. Significant differences exist between δD values of plant total hydrogen and δD values of cellulose nitrate hydrogen. This difference is due to the effect of chemical heterogeneity of the δD value of plant material. Plant-extracted cellulose nitrate D/H ratios are systematically related to the D/H ratios of the associated environmental water. The overall relationship is linear with slope of one and intercept of ?22%. Five aquatic plants which grew at 16–17°C are related isotopically to the water by a linear curve with a slope of 1 and intercept of ?36%. Three plants which grew at 28–29°C have an intercept of ?11%. The general dependence of plant cellulose non-exchangeable hydrogen D/H ratios on the D/H ratios of the associated environmental water suggests that variations of the extracted cellulose nitrate δD values of plants can be used as indicators of climatic change.  相似文献