Reciprocity theorem to compute the static deformation due to a point dislocation buried in a spherically symmetric earth

Intriguing reciprocity relations exist between the static deformation excited by a point dislocation in a SNREI earth and those generated by external forces, such as tidal force, surface loading and surface shear forces. Coseismic deformations can be rewritten as follows: (1) potential change in terms of the tide deformation field, (2) radial displacement in terms of the load and tidal deformation fields, and (3) tangential displacement in terms of shear and torsional deformation fields. The relations greatly reduce the effort to compute the coseismic crustal deformation in a spherically symmetric earth.     

Comments to a polar bear population model

Larsen, T. & Ugland, K. I. (Polar Research 2 n.s., 117–118) note correctly that a Leslie matrix model treats cubs and females as independent units which is not the case lor polar bears. Population projections using the Leslie model with hunting mortalities added are instructive first approximations in evaluations of field data, however, and are recommended as exercises also for polar bear biologists. An APL programme for such projections is available.     

Tidal asymmetry in a coastal lagoon subject to a mixed tidal regime

Tidal asymmetry is a key factor in the geomorphology of many coastal lagoons. Whilst tidal asymmetry in semi-diurnal tidal regimes has been extensively studied, its occurrence in mixed tidal regimes is less well understood, and has a number of unique causes and characteristics. Tidal phase duration analysis and least squares harmonic analysis have been used to study the temporal and spatial nature of asymmetry in both offshore and coastal lagoon tides at the Murray Mouth in south-eastern Australia. GIS analysis of bathymetric survey data has been used to study the roles of lagoon bathymetry on tidal distortion.Tidal asymmetry in the Murray Mouth coastal lagoon results from frequency relationships between major astronomical driving tides as well as bathymetry-induced tidal transformations. The frequency difference between the K₁ and S₂ tides produces an important 6-monthly ebb/flood-dominant asymmetry cycle in the incoming oceanic tides, whilst phase relationships between the K₁ and K₂ tides contribute to persistent asymmetry. The use of standard relationships between the M₂ and M₄ tides as asymmetry indicators is shown to be invalid for this mixed tidal regime. In this shallow, microtidal system, the impacts of bathymetry on tidal asymmetry within the lagoon are profound, with inlet and channel configurations identified as the most important controlling factors.The results of this study may inform the strategic management of tidal inlets in mixed tidal regimes, such as the Murray Mouth, that are subject to intermittent or long-term constriction.     

建设校园人工湿地 开发湿地文化资源

广雅小学在开展绿色科技教育,推进"为了环境可持续发展的科技"教育的基础上,借鉴国内外湿地建设的成功经验,结合时代特点、地域特色、以及当前的人才需求,应用人工湿地这一种以生态处理水污染为主的科学技术,侧重其湿地的科技功能与文化功能,即在校园内建设人工湿地科普园,还原湿地生态景观,使湿地的天然景观和原始野趣与校园建筑相得益彰、完美结合,使湿地科普园成为融生态环保、地貌气象、科技教育的特殊"课堂",为学生开展实践活动提供广阔空间。     

Learning to See Landscape Through a Flexible Lens

Abstract

Students' established conclusions about the world can often hinder a teacher's efforts to suggest new ideas and new ways to pursue alternative explanations. Flexible thinking helps students practice the value that one's present conclusions should remain tentative and subject to re-evaluation. Meinig's ten alternative perspectives for seeing a landscape were used successfully as a pedagogical rubric to teach students experientially how to observe more attentively and think more flexibly about place.     

Public housing as a barrier to long-distance migration

The relationship between migration and housing tenure in Britain is explored, with particular reference to those living in subsidized housing provided by local councils. "In this study, data have been extracted from the 1991 Sample of Anonymised Records to assess the impacts of tenure on long-distance migration compared with short-distance migration. Logit models are used to control for the effects of a wide range of socio-economic variables, allowing the independent impact of tenure to be identified. It is shown that long-distance migrants are less likely to move into council housing than other tenures, but it is argued that this does not support the assumption that the sale of council housing will necessarily increase labour mobility."     

Application of a nondestructive method to evaluate the active layer in a cold region

To provide a safe transportation system in an extremely cold region,evaluation needs to be conducted of the thickness and the volumetric water content of the active layer,as they significantly affect frost heave.The objective of this study was to evaluate the dielectric constant(κ)of the active layer using ground-penetrating radar(GPR)and a dynamic cone penetrometer(DCP);this evaluation was then used to estimate the thickness and the volumetric water content of the active layer.A field located in midwest Alaska was selected as the study site.A GPR survey and two DCP tests were conducted on the surface of the ground,and the ground temperature was measured.From the GPR survey,travel times of the electromagnetic wave in the active layer were obtained.In addition,the thickness of the active layer was determined by using the dynamic cone penetration index(DCPI)and ground temperature.By using the travel time and travel distance of the electromagnetic wave in the active layer,dielectric constants were calculated as 26.3 and 26.4 for two DCP points.From the mean dielectric constant,the volumetric water content was estimated to be 40%~43%,and the thickness of the active layer was evaluated along the GPR survey line.The spatial-scaled GPR image showed that the thickness of the active layer varied from 520 mm to 700 mm due to the presence of a puddle,which accelerated the heat exchange.The results show that evaluation of the dielectric constant using the GPR survey and the DCP test can be effectively used to estimate the thickness and the volumetric water content of the active layer.     

Access to locally-oriented television broadcasting in a digital era

Defined as the connection between media and communities, localism has been a cornerstone of U.S. broadcasting policy since the late 1920s. Among other ways, the principle of localism has been advanced through Federal Communication Commission licensing rules favoring small radio and television stations that carry local news, sports, and other programming serving community needs and values. However, in recent years changes in federal policy coupled with the emergence of new broadcasting technologies such as enhanced cable and satellite-based television have profoundly altered the relationship between broadcasting and local communities. Increasingly, community-centered television content has been replaced with syndicated programming targeting a national audience. In this paper we examine socioeconomic factors most closely associated with over-the-air, pay-to-view cable, and satellite television broadcasting with the objective of uncovering how access to community-based programming can be characterized on the basis of socioeconomic factors and geographic location. Using the Nielsen Corporation's Designated Market Areas (DMAs), we identify hot and cold spots of reception by reception type and then use hierarchical clustering to identify geographic regions based on the relationship between select socioeconomic traits and the primary method used within households for receiving television signals.     

Time and Practice: Learning to Become a Geographer

Abstract

Illustrated Dictionary of Place Names: United States and Canada. By Kelsie B. Harder. New York: Van Nostrand, 1976. Pp. xiv + 631, $18.95.

Middle America: Its Lands and Peoples. 2nd ed. By Robert C. West and John P. Augelli. Englewood Cliffs, N.J.: Prentice-Hall, 1976. Pp. xvii + 494, $14.95.

Contemporary Africa: Geography and Change. Edited by C. Gregory Knight and James L. Newman. Englewood Cliffs, N.J.: Prentice-Hall, 1976. Pp. xiv + 546, $14.95.

Atlas of Mexico. By Stanley A. Arbingast et al. 2nd ed. Austin, Tex.: Bureau of Business Research, University of Texas, 1975. Pp. ix + 165, $15.00.

Readings in Social Geography. Edited by Emrys Jones. London: Oxford University Press, 1975. Pp. 328, $18.50 and $6.95.

California: Patterns on the Land. 5th ed. By Robert Durrenberger and Robert Johnson. A California Council for Geographic Education Publication. Palo Alto, Calif.: Mayfield Publishing, 1976. Pp. viii + 134, $6.95.

Studying China in Elementary and Secondary Schools, Studying India in Elementary and Secondary Schools, and Studying Japan in Elementary and Secondary Schools. By Leonard S. Ken-worthy. World Affairs Guides. New York: Teachers College Press, 1975. Pp. 68, iii + 67, and iii + 65, $2.75 each.

World Regional Geography: A Question of Place. By Paul Ward English and James Andrew Miller. Harper &; Row Series in Geography. New York: Harper &; Row, 1977. Pp. xiii + 591, $15.95.

Census Data: Geographic Significance and Classroom Utility. Edited by Borden D. Dent. Tualatin, Oreg.: Geographic and Area Study Publications, 1976. Pp. ix + 277.

The Middle East: A Geographical Study. By Peter Beaumont, Gerald H. Blake, and Malcolm J. Wagstaff. London: John Wiley &; Sons, 1976. Pp. xvii + 572, $25.50 and $14.95.

Man's Economic Environment. By Edgar C. Conklingand Maurice Yeates. New York: McGraw-Hill Book Co., 1976. Pp. xi + 308, $11.95.

Applied Climatology: An Introduction. 2nd ed. By John F. Griffiths. New York/London: Oxford University Press, 1976. Pp. xiii + 136, $9.00.

Man and the Environment: Regional Perspectives. Edited by J. H. Holmes. Hawthorn, Victoria: Longman Australia Pty Limited, 1976. Pp. vi + 261, $7.95.

Introduction to Cultural Geography. 5th ed. By Henry M. Kendall, Robert M. Glendinning, Clifford H. MacFadden, and Craig H. MacFadden. New York: Harcourt Brace Jovanovich, 1976. Pp. xx + 449, $12.95.

Interpretation of Aerial Photographs. 3rd ed. By Thomas Eugene Avery. Minneapolis, Minn.: Burgess Publishing Company, 1977. Pp. xi + 392, $14.95.

Geography of the U.S.S.R. 3rd ed. By Paul Lydolph. New York: John Wiley &; Sons, 1977. Pp. xi + 495, $18.95.     

Geomorphic response of a headwater channel to augmented flow

Since 1974, flow releases from Long Draw Reservoir have increased annual peak flows on La Poudre Pass Creek, Colorado, from ~ 5.6 m³/s to > 8.4 m³/s. The creek drains 61 km² and channel morphology varies from step-pool to pool-riffle. Comparison of five channel reaches along the creek to channel reaches along neighboring rivers without flow regulation indicates that channel width has increased by as much as a factor of three along La Poudre Pass Creek. Width-to-depth ratio has also increased, the bed material in step-pool channel reaches has coarsened, and residual pool volumes have increased in pool-riffle channel reaches. Pool-riffle channel reaches have undergone the greatest change in response to flow augmentation. Although discharge has increased consistently for all five channel reaches, morphologic response varies in relation to gradient and channel morphology, making it impractical to precisely predict a priori the magnitude of channel response to flow augmentation.     

Image analysis as a method to quantify sediment components

Varved lake sediments, with their annual to seasonal resolution, have a high potential for inferring past environmental and climatic conditions. To fully utilize the information present in varved records, high-resolution analyses, which often are time-consuming and difficult to perform, are desirable. The investigation reported here aims at (i) developing image analysis as a method for estimating annual accumulation rates of sediment components such as minerogenic matter, organic matter and biogenic silica, and (ii) assessing the relative importance of these components for changes in varve thickness. Image analysis was used to digitize the grey-scale variations and to measure the varve thickness of 540 varves (476-1015 AD) from Lake Kassjön in northern Sweden. From the 35 cm long digitized sediment sequence, 108 consecutive five-year samples were cut out quantitatively, and relationships between grey-scale variations and sediment dry mass and individual sediment components were assessed. There is a strong correlation between corrected grey-scale (i.e. the product of grey-scale and varve thickness) and the dry mass accumulation rate (r = 0.90, p < 0.001). With a stepwise multiple regression a significant model (R² = 0.81) between corrected grey-scale and the accumulation rates of minerogenic matter (r = 0.90, p < 0.001) and biogenic silica (r 0.26, p < 0.012) was obtained. Considering the minor contribution and weak significance of biogenic silica, image analysis can be used as a fast and non-destructive method to infer past annual accumulation rates of dry mass and minerogenic matter in Kassibn. The model of the relationship between changes in varve thickness, and water content and accumulation rates of sediment components has little predictive power (R² = 0.45). The result shows that the varve thickness in Kassjön, at least during the period 476-1015 AD, is not determined by a single sediment component but partly depends on interactions between the major sediment components.