Beyond the headlines: changing patterns in international student enrollment in the United States     

Heike C. Alberts 《GeoJournal》2007,68(2-3):141-153

In the aftermath of the terrorist attacks of September 11, 2001, newspapers and magazines reported a dramatic decline in the enrollment of international students at US universities. Many of these articles blamed this decrease on the difficulties of getting a visa to the US and expressed concern about the potential impact on the US education system and economy. A look beyond the headlines, however, reveals that this decline cannot be attributed exclusively to the heightened security measures, as student numbers from some countries had already begun to decline before 2001 or continue to increase despite the changed regulations. Therefore, other factors also play a role in explaining the diverse migration patterns—most notably increasing competition from other host countries and changing economic and educational conditions in sending countries. Since international students often stay in their host countries after the completion of their degrees, the United States has a strong interest in continuing to attract international students as potential highly skilled immigrants. In order to achieve this, changes need to be implemented at the government level as well as at individual universities.  相似文献   

A bridge over troubled waters? Systems theory and dialogue in geography     

Heike Egner  Kirsten von Elverfeldt 《Area》2009,41(3):319-328

In physical geography, systems are seen as a unity of parts and relationships, whereas human geographers using a second-order sociological systems approach define systems in terms of the difference between system and environment. Starting from this, dialogue between physical and human geographers using terms derived from systems theory is mostly in vain. This article explores some of the consequences that follow for dialogue in geography: the differences in defining systems, in the understanding of processes, the problem of system borders, the inconsistent understanding of the 'environment' itself as well as the different epistemology that comes with it (or leads to it). The article tries to bring systems theory back into geography with the decisive aim of enhancing the potentials for interaction between human and physical geographers and, therefore, to explore the possibility of connecting the social with the physical world – deviating from systems theory.  相似文献   

Utilisation of terrestrial carbon by osmotrophic algae     

Jörg Tittel  Ines Wiehle  Nicola Wannicke  Heike Kampe  Juergen Poerschmann  Jutta Meier  Norbert Kamjunke 《Aquatic Sciences - Research Across Boundaries》2009,71(1):46-54

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Transition from symmetry to asymmetry during continental rifting: an example from the Bight Basin–Terre Adélie (Australian and Antarctic conjugate margins)     

Nicolas Espurt  Jean‐Paul Callot  François Roure  Jennifer M. Totterdell  Heike I. M. Struckmeyer  Roland Vially 《地学学报》2012,24(3):167-180

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Fate of microbial biomass-derived amino acids in soil and their contribution to soil organic matter   总被引：2，自引：0，他引：2  

Anja Miltner  Reimo Kindler  Heike Knicker  Hans-Hermann Richnow  Matthias Kstner 《Organic Geochemistry》2009,40(9):978-985

Soil organic matter (SOM) is important for soil fertility and for the global C cycle. Previous studies have shown that during SOM formation no new compound classes are formed and that it consists basically of plant- and microorganism-derived materials. However, little data on the contribution from microbial sources are available. Therefore, we investigated previously in a model study the fate of C from ¹³C-labelled Gram-negative bacteria in soil (Kindler, R., Miltner, A. Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil – mineralization and contribution to SOM. Soil Biology and Biochemistry 38, 2860–2870) and showed that 44% of the bulk ¹³C remained in the soil. Here we present the corresponding data on the fate of amino acids hydrolysed from proteins, which are the most abundant components of microbial biomass. After 224 days incubation, the label in the total amino acids in the soil amended with ¹³C-labelled cells decreased only to >95%. The total amino acids therefore clearly showed a lower turnover than the bulk ¹³C and a surprisingly stable concentration. Proteins therefore have to be considered as being stabilised in soil in dead, non-extractable biomass or cell fragments by known general stabilisation mechanisms. The label in the amino acids in a fraction highly enriched in living microbial biomass decreased to a greater extent, i.e. to 25% of the initially added amount. The amino acids removed from this fraction were redistributed via the microbial food web to non-living SOM. All amino acids in the microbial biomass were degraded at similar rates without a change in isotopic signature. The nuclear magnetic resonance (NMR) spectra of the soils were very similar and indicate that the residues of the degraded microbial biomass were very similar to those of the SOM and are a significant source for the formation of the SOM.  相似文献   

Wetland soil organic matter composition in a Mediterranean semiarid wetland (Las Tablas de Daimiel, Central Spain): Insight into different carbon sequestration pathways   总被引：3，自引：0，他引：3  

J.C. Rodríguez-Murillo  G. AlmendrosH. Knicker 《Organic Geochemistry》2011,42(7):762-773

Wetland soils from a Mediterranean semiarid wetland (Las Tablas de Daimiel, Central Spain) were studied to characterize the organic matter (OM) and determine its origin and transformation. Cross polarization magic angle spinning (CPMAS) ¹³C nuclear magnetic resonance (NMR) spectroscopy and mathematical molecular mixing allowed analysis of the organic fraction in terms of six generic components (carbohydrate, protein, lignin, lipid, char and “carbonyl”). Las Tablas is an active carbon sink, with total organic carbon (TOC) content independent of soil OM quality; the TOC content of the upper sediment is 10.0 ± 7.8%. The inorganic carbon content is also high (5.4 ± 3.3%) and is associated mainly with OM of aliphatic character. The OM composition is variable; samples predominantly aliphatic (carbohydrate, lipid and protein) are characteristic of the northern sector, whereas predominantly aromatic samples are typical of the southern Tablas. A strong negative relationship between protein content and lignin content was found, interpreted as a consequence of different proportions of vascular vs. non-vascular (mostly charophyte) litter input. The effect of perturbation is apparent in the extended presence of char, particularly abundant in fire-prone areas. OM quantity and quality do not seem to depend on hydrology (although seasonal flooding is associated with lower TOC wetland soils) or soil characteristics. Dominant vegetation and fire are the main drivers of OM content and composition. Structural carbohydrate, protein and lipid (>60% of total organic fraction) dominate. Widespread anaerobic conditions and the recent character of the sediments could explain the preservation of different fractions of the original detritus composition (due to different vegetation and presence of microbes).  相似文献   

Egg capsule hatch rate and incubation duration of the California market squid,Doryteuthis (= Loligo) opalescens: insights from laboratory manipulations     

Louis D. Zeidberg  George Isaac  Chad L. Widmer  Heike Neumeister  William F. Gilly 《Marine Ecology》2011,32(4):468-479

Egg capsules of the squid Doryteuthis (= Loligo) opalescens were reared in the laboratory to assess the dependence of time‐to‐hatching (incubation time) and hatching success rate on temperature and light regime. Both incubation time and hatch duration were found to be inversely related to temperature. More than 96% of paralarvae hatch from eggs reared at temperatures between 9 and 14 °C. Hatch rate drops below 90% in warmer and colder water. No eggs hatch below 7 °C, and the upper limit of viability is near 25 °C. The vast majority (91%) of hatchlings emerged during the dark phase of the photoperiod. Egg capsules reared at 13.4 °C with a supposedly commensal polychaete, Capitella ovincola, had a slightly higher hatch rate than those without the annelid. Because eggs are naturally laid closely together, crowding was hypothesized to cause decreased ventilation and a lower hatch rate. Crowding was tested by placing two capsules (rather than one) into the small incubation chambers (50 ml). This treatment did not result in a lower hatch rate at 13.4 °C, but at 21.4 °C it decreased the hatch rate by 20%. Brood incubation duration is related to temperature by the equation: Incubation (days) = 14.97 + 177.40 × exp(?0.119 × Temperature –°C) (χ² = 282.5, P = 0.001). Stable isotope analysis confirmed that C. ovincola worms eat the capsule matrix, not the paralarvae. These polychaetes had a δ¹⁵N value of 12.79‰versus 12.06‰ for squid paralarvae, and 10.54‰ for the gelatinous matrix of egg capsules. This fractionation factor ε of 2.25‰ is consistent with marine food webs. Provision of nutrients and shelter for the annelids and increased hatch rate for the squid embryos suggests a symbiotic relationship between these organisms.  相似文献   

Marine benthic invertebrates from the Upper Jurassic of northern Ethiopia and their biogeographic affinities     

Wolfgang Kiessling  Dhirendra Kumar Pandey  Mena Schemm-Gregory  Heike Mewis  Martin Aberhan 《Journal of African Earth Sciences》2011,59(2-3):195-214

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Large-Scale Differences in Community Structure and Ecosystem Services of Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) Beds Across Three Regions in Eastern Canada     

Mizuho Namba  Heike K. Lotze  Allison L. Schmidt 《Estuaries and Coasts》2018,41(1):177-192

Eelgrass (Zostera marina) forms extensive beds in temperate coastal and estuarine environments worldwide and provides important ecosystem services, including habitat for a wide range of species as well as nutrient cycling and carbon storage. However, little is known about how eelgrass ecosystem structure and services differ naturally among regions. Using large-scale field surveys, we examined differences in eelgrass bed structure, carbon and nitrogen storage, community composition, and habitat services across three distinct regions in Eastern Canada. We focused on eelgrass beds with low anthropogenic impacts to compare natural differences. In addition, we analyzed the relationships of eelgrass bed structure with environmental conditions, and species composition with bed structure and environmental conditions, to elucidate potential drivers of observed differences. Our results indicate that regional differences in eelgrass bed structure were weakly correlated with water column properties, whereas differences in carbon and nitrogen storage were mainly driven by differences in eelgrass biomass. There were distinct regional differences in species composition and diversity, which were particularly linked to temperature, as well as eelgrass bed structure indicating differences in habitat provision. Our results highlight natural regional differences in ecosystem structure and services which could inform spatial management and conservation strategies for eelgrass beds.  相似文献   

Whose neighbourhood is it? Ethnic diversity in urban spaces in Germany     

Heike Hanhörster 《GeoJournal》2000,51(4):329-338

This article focuses on the reciprocal effects that exist between the physical environment and the social interactions between ethno-cultural groups in disadvantaged neighbourhoods. Biographical narrative interviews and mental map analyses were carried out with German and Turkish residents in two disadvantaged neighbourhoods in Germany to define the resident's own experience of their physical surroundings.The findings of the research verify that the changes in the environment were not only physical and structural changes: they also led to changing identities having a symbolic meaning for the established German residents. As the Turkish residents work to create a sense of identity, the established residents view these changes more as a threat than as an enrichment. They do not so much feel threatened by the cultural differences between the groups, but they sense that their own `old-time' German socio-cultural position could be affected by the establishment of Turkisch residences and institutions in `their' neighbourhood. The empirical research revealed differences in the ethno-cultural perceptions between Duisburgh-Marxloh where there is a pronounced small-scale segregation between the groups, whereas there is a small-scale mix of different ethnic groups even at the block level in the other area investigated in Wuppertal-Osterbaum. Although both areas have a high percentage of ethnic minorities the small-scale mix in Wuppertal-Ostersbaum seems to have prevented a polarisation in the population.  相似文献