On the red coloration of saltern crystallizer ponds   总被引：3，自引：0，他引：3  

Aharon Oren  Noga Stambler  Zvy Dubinsky 《International Journal of Salt Lake Research》1992,1(2):77-89

To assess, respectively, the contribution of red bacteria of theHalobacterium-Haloferax-Haloarcula group and of the β-carotene-rich green algaDunaliella salina to the red colour of saltern crystallizer ponds, we studied the optical properties of the brines of NaCl-saturated saltern ponds in Eilat, Israel, and quantified the pigments present in their biota. The absorption spectrum of the brines, as measured using the opal glass method to reduce the interference by scattering, or using an integrating sphere, nearly corresponded to thein vivo absorption spectrum of bacterioruberin-containing red archaeobacteria. However, extracts of the microbial community in organic solvents were dominated by β-carotene, a pigment occurring in high concentrations in theDunaliella cells present, and bacterioruberin contributed only between 13 and 28 per cent of the total visible light absorption by the extracts. The apparent discrepancy between these results can be explained by the very small in vivo optical cross-section of β-carotene, which is densely packed in globules inside theD. salina cells.  相似文献   

Species differences in stomatal control of water loss at the canopy scale in a mature bottomland deciduous forest   总被引：2，自引：0，他引：2  

D. E. Pataki  R. Oren   《Advances in water resources》2003,26(12):1267

In order to evaluate factors controlling transpiration of six common eastern deciduous species in North America, a model describing responses of canopy stomatal conductance (G_S) to net radiation (R_N), vapor pressure deficit (D) and relative extractable soil water (REW) was parameterized from sap flux data. Sap flux was measured in 24 mature trees consisting of the species Carya tomentosa, Quercus alba, Q. rubra, Fraxinus americana, Liriodendron tulipifera, and Liquidambar styraciflua in a bottomland oak-hickory forest in the Duke Forest, NC. Species differences in model coefficients were found during the 1997 growing season. All species showed a reduction in G_S with increasing D. R_N influenced G_S in the overstory shade intolerant L. styraciflua to a larger extent than the other species measured. In addition, despite a severe drought during the study period, only L. tulipifera showed a decline in G_S with decreasing REW. The primary effect of the drought for the other species appeared to be early autumn leaf senescence and abscission. As a result, despite the drought in this bottomland forest accustomed to ample water supply, maximum daily transpiration (1.6 mm) and growing season transpiration (264 mm) were similar to a nearby upland forest measured during a year of above average precipitation. These results may aid in assessing differences in water use and the ability of bottomland deciduous species to tolerate alterations in the frequency or amount of precipitation. Results also suggest little variation in water use among forests of similar composition and structure growing in different positions in the landscape and subjected to large interannual variation in water supply.  相似文献   

Design of passive systems for control of inelastic structures     

Gian Paolo Cimellaro  Oren Lavan  Andrei M. Reinhorn 《地震工程与结构动力学》2009,38(6):783-804

A design strategy for control of buildings experiencing inelastic deformations during seismic response is formulated. The strategy is using weakened, and/or softened, elements in a structural system while adding passive energy dissipation devices (e.g. viscous fluid devices, etc.) in order to control simultaneously accelerations and deformations response during seismic events. A design methodology is developed to determine the locations and the magnitude of weakening and/or softening of structural elements and the added damping while insuring structural stability. A two‐stage design procedure is suggested: (i) first using a nonlinear active control algorithm, to determine the new structural parameters while insuring stability, then (ii) determine the properties of equivalent structural parameters of passive system, which can be implemented by removing or weakening some structural elements, or connections, and by addition of energy dissipation systems. Passive dampers and weakened elements are designed using an optimization algorithm to obtain a response as close as possible to an actively controlled system. A case study of a five‐story building subjected to El Centro ground motion, as well as to an ensemble of simulated ground motions, is presented to illustrate the procedure. The results show that following the design strategy, a control of both peak inter‐story drifts and total accelerations can be obtained. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Recovery rates of microbiotic crusts within a dune ecosystem in the Negev Desert   总被引：1，自引：0，他引：1  

Giora J. Kidron  Ahuva Vonshak  Aharon Abeliovich   《Geomorphology》2008,100(3-4):444-452

Despite the important role played by microbiotic crusts in desert ecosystems, data concerning their recovery rates are scarce and are mainly based on estimates that fluctuate between several years to a few hundred years. In order to study the recovery rates of microbiotic crusts inhabiting sand dunes in the western Negev Desert, Israel, annual measurements of chlorophyll, protein, carbohydrates and moss counts were carried out during 1990–1995. Measurements were taken in two pairs of plots (1.5–6.3 m²) established in each north- and south-facing aspect from which the upper 10 cm surface from one plot of each pair was removed. Recovery of the crusts was fast with surface-removed plots showing a complete recovery of chlorophyll a within 6–7 years, of protein within 6–8 years and of carbohydrates within 8–9 years. Recovery of the mosses was slightly longer at 17–22 years. The data are higher than the lower estimates of recovery but much lower than the higher estimates proposed in the literature. The data also suggest that upon prohibition of goat and sheep grazing (and consequently trampling) a relatively rapid stabilization process may take place in the north-eastern Sinai dune field.  相似文献   

Earthquake engineering research needs in light of lessons learned from the 2011 Tohoku earthquake     

Masayoshi Nakashima  Oren Lavan  Masahiro Kurata  Yunbiao Luo 《地震工程与工程振动(英文版)》2014,(Z1)

Earthquake engineering research and development have received much attention since the first half of the twentieth century. This valuable research presented a huge step forward in understanding earthquake hazard mitigation,which resulted in appreciable reduction of the effects of past earthquakes. Nevertheless,the 2011 Tohoku earthquake and the subsequent tsunami resulted in major damage. This paper presents the timeline of earthquake mitigation and recovery,as seen by the authors. Possible research directions where the authors think that many open questions still remain are identified. These are primarily based on the important lessons learned from the 2011 Tohoku earthquake.  相似文献   

Minimum‐cost optimization of nonlinear fluid viscous dampers and their supporting members for seismic retrofitting          下载免费PDF全文

Nicolò Pollini  Oren Lavan  Oded Amir 《地震工程与结构动力学》2017,46(12):1941-1961

This paper presents an effective approach for achieving minimum‐cost designs for seismic retrofitting using nonlinear fluid viscous dampers. The damping coefficients of the dampers and the stiffness coefficients of the supporting braces are designed by an optimization algorithm. A realistic retrofitting cost function is minimized subject to constraints on inter‐story drifts at the peripheries of frame structures. The cost function accounts for costs related to both the topology and the sizes of the dampers. The behavior of each damper‐brace element is defined by the Maxwell model, where the force–velocity relation of the nonlinear dampers is formulated with a fractional power law. The optimization problem is first posed and solved as a mixed integer problem. For the reduction of the computational effort required in the optimization, the problem is then reformulated with continuous variables only and solved with a gradient‐based algorithm. Material interpolation techniques, which 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 discussed. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Hydrocarbon-derived carbonate buildups of the northern Gulf of Mexico continental slope: A review of submersible investigations   总被引：15，自引：3，他引：15  

Harry H. Roberts  Paul Aharon 《Geo-Marine Letters》1994,14(2-3):135-148

Hydrocarbon-derived and microbially mediated authigenic carbonates occur over the entire depth range of the northern Gulf of Mexico slope. These carbonates consist of nodules and incipient nodules in surface sediments, hardgrounds and isolated slabs, and moundlike buildups of up to 10–20 m relief above the surrounding seafloor. The authigenic carbonates are characterized by ¹³C negative values in the range –18 to –55 (PDB) suggesting mixing of seawater carbon with¹³C-depleted carbon sources ranging from crude oil to biogenic methane. Near the shelf edge, carbonates are diluted with biogenic material produced by reefs—bioherms developed at low sea level stands. Fossil-poor carbonates over salt diapirs of the upper and middle slope formed in the shallow subsurface and have been exhumed by the combined processes of uplift and physical erosion. Middle and lower slope carbonates are generally rich in fossil shells of chemosynthetic organisms. Mg calcite pelloidal matrix and acicular to botryoidal aragonitic void-filling cements are common petrographic features of these hydrocarbonderived carbonates. At two sites carbonates are mixed with barite.  相似文献   

Oxygen and hydrogen isotopes of rainfall and dripwater at DeSoto Caverns (Alabama, USA): Key to understanding past variability of moisture transport from the Gulf of Mexico     

W. Joe Lambert  Paul Aharon 《Geochimica et cosmochimica acta》2010,74(3):846-695

The Southeast and the US Gulf Coast in particular are notably lacking isotope data in the water cycle despite the fact that moisture transport from the Gulf of Mexico (GOM) has a considerable influence on both regional and continental rainfall patterns. This study reports time-series of oxygen and hydrogen isotopes acquired over a 3-year period (2005-2008) from GOM-derived rainfall, cave dripwater and shallow groundwaters, and offers valuable insights on the links between factors controlling regional rainfall and the ubiquitous karst hydrology.Amount-weighted mean monthly rainwater δ¹⁸O and δD values in Tuscaloosa, Alabama range from −1.5 to −8.3‰ and −1.2 to −49.5‰, respectively, and show mean seasonal amplitudes of ∼4‰ (δ¹⁸O) and ∼25‰ (δD). In comparison d-excess values display large seasonal amplitudes of 10-20‰ resulting from differences in the degree of evaporation from falling raindrops between summer and winter months, and correlate well with the coeval air temperature (r² = 0.59; p < 0.05). Deviations of the Gulf Coast Meteoric Water Line (GCMWL) slope and d-excess from the global meteoric water line (GMWL) are attributed to different rates of evaporation after condensation, and to humidity contrast between the cloud boundary layer and the surrounding atmosphere in the vapor source region, respectively. Rainfall amounts declined during the study interval from an excessive “wet” year, ascribed to six tropical storms incursions during an unusually active hurricane season in 2005, to an onset of a regional drought during 2007-2008 with monthly rainfall amounts substantially below normal values (30-year monthly means). An interannual trend of ¹⁸O and ²H enrichments is discerned from 2005 to 2008 (1.4‰ and 11.6‰, respectively) coeval with the decline in rainfall amounts.Dripwater samples from nearby DeSoto Caverns show weak δ¹⁸O and δD seasonal variations and record only 20% and 51% of the ¹⁸O and ²H enrichments, respectively, discerned in the rainwater 3-year time-trends. The seasonal and interannual amplitude attenuations in the dripwaters are attributed to a relatively thick overlying bedrock (∼30-40 m) and a relatively large, well-mixed, epikarst-storage reservoir. Residence time of water in the cave’s epikarst is estimated to be 1-3 months based on high-resolution flow-rate data.Our investigation suggests that global atmospheric circulation patterns (ENSO and Bermuda High) likely govern the interannual δ¹⁸O and δD isotope trends discerned in the water cycle compartments but much longer time-series are required to confirm our conjectures. The results of this study form a solid basis for future acquisition and interpretation of climate proxy records from regional speleothems.  相似文献   

The apparent size of gamma-ray burst afterglows as a test of the fireball model     

Yonatan Oren  Ehud Nakar  Tsvi Piran 《Monthly notices of the Royal Astronomical Society》2004,353(4):L35-L40

  相似文献   

Image spaces and the geography of Internet screen-space     

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