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61.
I. Ben-Israel T. Piran Aharon Eviatar J. Weinstock 《Astrophysics and Space Science》1975,38(1):125-155
A statistical theory, previously developed for electrostatic waves is extended to the case of electromagnetic waves in the presence of a constant magnetic field. The theory is nonlinear and contains the effects of mode-mode coupling. The extension is not straightforward as assumed previously by many authors and involves calculation of perturbed trajectories in both velocity and configuration space. A diffusion equation is derived for the average particle distribution function, the associated diffusion tensor is calculated and a nonlinear wave dispersion relation is found. All these results contain the usual quasilinear theory as the lowest order approximation. 相似文献
62.
Experimental data describing the effect of the South Atlantic anomaly on E? 280 keV electron flux at L = 2 and high B values, are compared to the numerical solution of a pitch-angle diffusion equation with a varying loss cone. The diffusion coefficient needed to explain replenishment of the electrons lost over the anomaly is found to be 3.2 × 10?2 sec?1 Calculation of the diffusion coefficient due to cyclotron resonant interaction with VLF electro-magnetic waves leads to the conclusion that the observed wave spectral density can yield the needed diffusion coefficient. 相似文献
63.
Oren Yiftachel Dr. 《GeoJournal》1992,28(3):319-332
The paper compares and contrasts three cases of plural democracies in the Middle East: Lebanon (1943–1975), Cyprus (1960–1974) and Israel (1948–1992). It begins with a classification and review of two bodies of theories: the role of the state in maintaining democratic stability in plural (deeply divided) societies; and the links between ethnic spatial structures and political stability. The role of the state and the geography of ethnicity in the three cases are then analysed in the light of these theories.The comparison highlights four key points: (a) the importance of interethnic proportionality; (b) the importance of ethnic spatial separation; (c) the irreversibility of the consociational process in plural democracies; and (d) the need to integrate both theories of state and theories of spatial relations for explanation of democratic instability in plural societies. 相似文献
64.
Dr. Aharon Kellerman 《GeoJournal》1987,15(1):31-38
The paper examines organizational and spatial responses of metropolitan retail trade in Israel to increases in demand. Since
the late 1960s until 1984 Israel enjoyed continuous increases in incomes, rates of car ownership and dwelling sizes. These
coincided with a suburbanization of population in the metropolitan areas of Tel-Aviv and Haifa. Consequently, there developed
four new forms of retailing, namely ribbons in industrial areas, factory retail outlets, hypermarkets and shopping malls.
Locational and other characteristics of these forms of commerce are discussed. Special criticism is pointed at an undifferentiated
evolution of ribbons and outlets.
I wish to thank Ms. Naomi Elad and Mr. Moshe Schmerler for field work in metropolitan Haifa and Tel-Aviv respectively. 相似文献
65.
Bacterial activities in the Dead Sea, 1980-1991: survival at the upper limit of salinity 总被引:2,自引:0,他引:2
Aharon Oren 《International Journal of Salt Lake Research》1992,1(1):7-20
Since the mass development of halophilic bacteria in 1980 and the subsequent decline of the community in 1982, no new mass
development of bacteria has occurred in the Dead Sea, and bacterial numbers have remained extremely low. The lake’s salinity,
and more specifically the divalent cation concentration, have increased greatly during the last ten years. To quantitate the
activity of the community of heterotrophic bacteria in the Dead Sea water column, rates of incorporation of amino acids, glycerol,
and acetate were measured, both during the 1980–1981 bloom and in recent years. With the development of the bloom, rates of
incorporation amino acids, glycerol and acetate increased. Concomitant with the decline in bacterial numbers, the incorporation
rates of amino acids and acetate decreased at the end of 1980-beginning of 1981, while glycerol incorporation rates remained
high for one more year. Measurements in 1989 and in 1991 showed very low but significant incorporation rates (three to four
orders of magnitude lower than during the 1980–1981 bloom). By the use of specific inhibitors, it was shown that the remaining
activity was due to halophilic archaeobacteria. The mechanism of the long-term survival of a small active bacterial community
in the Dead Sea in the absence of primary producers and other obvious sources of organic carbon, and at divalent cation concentrations
greatly exceeding those enabling growth, is still unknown. 相似文献
66.
Aharon Kellerman 《GeoJournal》2016,81(4):503-517
This article aims, first, at the exposition of image space and a scalar model differentiating among its four visual classes: virtual space (visual presentations of real space and material artifacts), cyberspace (digital communications and information media), the Internet (digital communications and informational spaces), and Internet screen-space (ISS) (users’ visual interface with the Internet), thus leading from the wider to the specific. This differentiation is followed by discussions of cyberspace and Internet screen-space geography. Cyberspace has been spatially defined as artificial reality, interactivity, and conceptual and metaphorical spaces. As a spatial experience, cyberspace involves co-presence, low cognitive mapping, and egalitarian and global communications. The article aims further at the development of interpretations for ISSs and their uses along dimensions originally developed for real-space geography. These include: real space parameters (ground; distance; places; scale/regions; boundaries; and flows); user spatial parameters (speed; directionality; circularity; distanciation); and user socio-spatial parameters (proximity; networking; time–space compression). 相似文献
67.
Catastrophic hurricane history revealed by organic geochemical proxies in coastal lake sediments: a case study of Lake Shelby,Alabama (USA) 总被引:2,自引:0,他引:2
We developed a new method for reconstructing millennia-long hurricane records from coastal environments that uses Organic
Geochemical Proxies (OGPs) of organic carbon and nitrogen concentrations and their δ13C and δ15N compositions. The new method is independent of presence/absence of sand layers and improves significantly the severe-storm
history resolution. The subject of this investigation is a 1.5 m long sediment core raised at 2.8 m water depth from the center
of Lake Shelby, Alabama, a freshwater lake located approximately 250 m from the Gulf of Mexico, from which an overwash sand-layer
based record was previously derived. The core contains two distinct sediment units; an upper 62 cm thick, fine-grained, organic-rich
lacustrine sapropel (gyttja) that shows no visible structures except one sand lamina at 23.7 cm depth, and an underlying 90 cm
thick, organic-poor lagoon/estuary clay unit. The sapropel unit was deposited over a 682 ± 30 cal year time interval (1320–2002 A.D.)
with a mean sedimentation rate of 0.79 ± 0.04 mm/year. Lake Shelby’s water column exhibits two contrasting states based on
water chemistry surveys (i) an “isolated”, stratified, mode under calm weather conditions with a relatively low trophic state,
and (ii) a “flooded” mode occurring during storm surges when nutrient-rich seawater floods the lake. Statistically significant
δ13C and δ15N positive excursions in organic matter, up to maximum values of −25 (‰ PDB) and 4 (‰ Air N2), respectively, are interpreted as geochemical responses to the marine intrusions that fertilize the lake, increase light
availability, and cause eutrophication spikes. Detailed OGPs analyses crossing a sand layer that offers visual evidence of
a catastrophic hurricane overwash event at 1717 A.D. exhibit large δ13C and δ15N positive shifts bounded by rapid returns to base values, thus confirming the validity of the hurricane identification by
the OGPs model. Our data indicate that 11 catastrophic hurricanes hit the Alabama coast over the past 682 years with a rough
recurrence interval of one in 62 years. 相似文献
68.
Oren Lavan 《地震工程与结构动力学》2012,41(12):1673-1692
This paper rigorously assesses the efficiency of viscous dampers connecting two walls to result in “viscously coupled shear walls”. This assessment also holds for viscous dampers in wall structures as they are mounted on frames parallel to the walls leading to “wall-viscous frame” systems. A continuum approach is adopted to model the structure so as to enable non-dimensional formulation of the governing equations. Those equations reveal that, under the approximations considered, the system damping ratio (defined here by 0.5 sqrt(c^2/(m*EI))) is a convenient compact single parameter controlling the response reduction w.r.t. the response of the corresponding undamped system. In contrast to coupled shear walls, this controlling parameter does not depend on the height of the building; therefore, the viscously damped system is efficient for low-rise buildings as well. The continuum approach also allows a semi-analytical solution of the eigenproblem in the complex domain followed by a complex modal spectral analysis. Those solutions reveal the efficiency of the added damping in reducing not only the displacements, inter-story drifts, and wall moments but also the absolute accelerations, wall shear, total shear, and total overturning moments. The results of the analyses and the non-dimensional tables and graphs developed for important response parameters lead to a simple method that could easily be implemented in practice for the purpose of initial design. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
69.
Minimal‐disturbance seismic rehabilitation of steel moment‐resisting frames using light‐weight steel elements 下载免费PDF全文
Masahiro Kurata Miho Sato Lei Zhang Oren Lavan Tracy Becker Masayoshi Nakashima 《地震工程与结构动力学》2016,45(3):383-400
This paper presents a rehabilitation technique developed under a design and construction scheme, termed minimal‐disturbance seismic rehabilitation. This scheme pursues enhancing the seismic performance of buildings with the intention of improving the continuity of business while minimizing obstruction of the visual and physical space of building users and the use of heavy construction equipment and hot work (welding/cutting). The developed rehabilitation technique consists of light‐weight steel elements and aims to decrease demands to beam‐ends of steel moment‐resisting frames. The behavior of the baseline model was verified through numerical analysis and proof‐of‐concept testing. Furthermore, the effectiveness of rehabilitation is studied through retrofitting a four‐story steel moment‐resisting frame originally designed with Japanese design guidelines. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
70.
This paper presents an effective approach for achieving minimum cost designs for seismic retrofitting using viscous fluid dampers. A new and realistic retrofitting cost function is formulated and minimized subject to constraints on inter-story drifts at the peripheries of frame structures. The components of the new cost function are related to both the topology and to the sizes of the dampers. This constitutes an important step forward towards a realistic definition of the optimal retrofitting problem. The optimization problem is first posed and solved as a mixed-integer problem. To improve the efficiency of the solution scheme, the problem is then re-formulated and solved by nonlinear programming using only continuous variables. Material interpolation techniques, that have been successfully applied in topology optimization and in multi-material optimization, play a key role in achieving practical final design solutions with a reasonable computational effort. Promising results attained for 3-D irregular frames are presented and compared with those achieved using genetic algorithms. 相似文献