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21.
Gilbert V. Levin 《Icarus》2002,159(1):266-267
Tsapin et al. (2000, Icarus147, 68-78) propose the strong oxidant ferrate(VI) to explain the Viking Labeled Release Mars life detection results. However, their data do not support that theory. Further, sensitive IR searches for oxidants on Mars found none, and Viking produced physical evidence against an oxidizing surface. Finally, Tsapin et al. (2000, Icarus147, 68-78) report no precautions to prevent microbial contamination from confounding their results. 相似文献
22.
23.
McKay CP Grunthaner FJ Lane AL Herring M Bartman RK Ksendzov A Manning CM Lamb JL Williams RM Ricco AJ Butler MA Murray BC Quinn RC Zent AP Klein HP Levin GV 《Planetary and Space Science》1998,46(6-7):769-777
The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants. 相似文献
24.
By the use of the model of approaching drops (Arbel and Levin, 1977) the coalescence efficiencies of drops are computed. It is found that for interactions of drops at their terminal velocities the coalescence depends both on the size of the large drop and on the size ratio of the interacting drops in agreement with the experimental results of Whelpdale and List (1971) and Levin and Machnes (1977).The results were found to be sensitive to the assumption of the drops deformation and to the critical separation distance. This distance is defined as the distance at which the drops begin to merge. The variations of the coalescence efficiency with these parameters is discussed.Appendix: List of symbols
D
distance between the deformed surfaces of the drops
-
D
o
initial value ofD
-
D
s
stop distance, the distance at which the impact velocity vanishes
-
D
c
critical coalescence distance
-
E
collection efficiency
-
E
1
collision efficiency
-
E
2
coalescence efficiency
-
E
2R
coalescence efficiency for collisions with stationary targets
-
F
c
centrifugal force
-
p
ratio of the radii of the interacting drops
-
r
o
initial distance between drops' centers
-
R
L
radius of larger drop
-
R
s
radius of smaller drop
-
R
D
radius of deformation
-
v
approach velocity of two deformed surfaces
-
v
o
initial value ofv
-
V
i
impact velocity (given negative sign when drops approach each other)
-
V
c
critical impact velocity
-
W
i
velocity of the smaller drop at infinity for it to reachD
o with velocityv
o
-
x
i
impact distance, the distance between the trajectories of the two drops
-
x
c
critical impact distance for coalescence
-
average critical impact distance for coalescence
-
X
c
critical impact distance for collisions
-
coefficient of deformation given in equation 1
-
i
impact angle defined byWhelpdale andList (1971) given also inArbel andLevin (1977)
-
coefficient of deformation given in equation 2
-
viscosity of air
-
i
impact angle used inArbel andLevin (1977) and here
-
c
critical angle for coalescence
-
average critical angle for coalescence
On sabbatical leave (1976–77) from the Department of Geophysics and Planetary Sciences, Tel Aviv University, Ramat Aviv, Israel.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
25.
Yu. P. Dikov E. I. Debolsky Yu. N. Romashenko S. P. Dolin A. A. Levin 《Physics and Chemistry of Minerals》1977,1(1):27-41
The Si, Al LII, III and OKα emission and quantum yield spectra were obtained for 24 silicates. It was found that in minerals of a homogeneous anion composition the Si LII, III line has double-humped structure, and when in addition to SiO 4 4? ions of other composition (BeO 4 6? , AlO 4 5? etc.) are present it has triple-humped structure. The process of crystal-glass transition was studied by X-ray spectroscopy. The result is that in spite of the original form of the Si LII, III line of the mineral this line changes its structure in glass and exhibits a typical double-humped structure. The CNDO/2 approach was used to calculate the electronic structure of basic structural groups of silicates from SiO 4 4? to Si5O 16 12? by replacing one or two of the Si atoms by Be, B, Al and P. A qualitative interpretation of the X-ray spectra is presented. 相似文献
26.
Akkur V. Raman Rayaroth Damodaran Lisa A. Levin Thiruchitrambalam Ganesh Yannamani K. V. Rao Sateesh Nanduri Rakhesh Madhusoodhanan 《Marine Ecology》2015,36(3):679-700
The Bay of Bengal remains one of the least studied of the world's oxygen minimum zones (OMZs). Here we offer a detailed investigation of the macrobenthos relative to oxygen minimum zone [OMZ – DO (dissolved oxygen), concentration <0.5 ml·1?1] at 110 stations off the North East Indian margin (160 and 200 N) featuring coastal, shelf and slope settings (10–1004 m). Macrobenthos (>0.5 mm) composition, abundance and diversity were studied in relation to variations in depth, dissolved oxygen, sediment texture and organic carbon. Using multivariate procedures powered by SIMPROF analysis we identified distinct OMZ core sites (depth 150–280 m; DO 0.37 ml·1?1) that exhibited dense populations of surface‐feeding polychaetes (mean 2188 ind. m?2) represented by spionids and cossurids (96%). Molluscs and crustaceans were poorly represented except for ampeliscid amphipods. The lower OMZ sites (DO > 0.55 ml·l?1) supported a different assemblage of polychaetes (cirratulids, amphinomids, eunicids, orbinids, paraonids), crustaceans and molluscs, albeit with low population densities (mean 343 ind. m?2). Species richness [E(S100)], diversity (Margalef d; H’) and evenness (J’) were lower and dominance was higher within the OMZ core region. Multiple regression analysis showed that a combination of sand, clay, organic carbon, and dissolved oxygen explained 62–78% of the observed variance in macrobenthos species richness and diversity: E(S100) and H’. For polychaetes, clay and oxygen proved important. At low oxygen sites (DO <1 ml·l?1), depth accounted for most variance. Residual analysis (after removing depth effects) revealed that dissolved oxygen and sediment organic matter influenced 50–62% of residual variation in E(S100), H’ and d for total macrofauna. Of this, oxygen alone influenced up to ~50–62%. When only polychaetes were evaluated, oxygen and organic matter explained up to 58–63%. For low oxygen sites, organic matter alone had the explanatory power when dominance among polychaetes was considered. Overall, macrobenthic patterns in the Bay of Bengal were consistent with those reported for other upwelling margins. However, the compression of faunal gradients at shallower depths was most similar to the Chile/Peru margin, and different from the Arabian Sea, where the depth range of the OMZ is two times greater. The Bay of Bengal patterns may take on added significance as OMZs shoal globally. 相似文献
27.
Both spatial and spatiotemporal distributions of the sources of tsunamigenic earthquakes of tectonic origin over the last 112 years have been analyzed. This analysis has been made using tsunami databases published by the Institute of Computational Mathematics and Mathematical Geophysics (Siberian Branch, Russian Academy of Sciences) and the National Aeronautics and Space Administration (United States), as well as earthquake catalogs published by the National Earthquake Information Center (United States). It has been found that the pronounced activation of seismic processes and an increase in the total energy of tsunamigenic earthquakes were observed at the beginning of both the 20th (1905–1920) and 21st (2004–2011) centuries. Studying the spatiotemporal periodicity of such events on the basis of an analysis of the two-dimensional distributions of the sources of tectonic tsunamis has made it possible to determine localized latitudinal zones with a total lack of such events (90°?75° N, 45°–90° S, and 35°?25° N) and regions with a periodic occurrence of tsunamis mainly within the middle (65°?35° N and 25°–40° S) and subequatorial (15° N–20° S) latitudes of the Northern and Southern hemispheres. The objective of this work is to analyze the spatiotemporal distributions of sources of tsunamigenic earthquakes and the effect of the periodic occurrence of such events on the basis of data taken from global tsunami catalogs. 相似文献
28.
Safronov's statement that relative velocities of planetesimals are on the order of the escape velocity of the largest body of the population is shown to be correct only when a major part of the total mass resides in several large bodies. In the first stage of accumulation, runaway accretion produces large bodies separated by mass form the remaining population. At this stage, relative velocities of planetesimals are much smaller than those adopted earlier. This requires a modification of Schmidt's scheme of accumulation of the Earth and other terrestrial planets from material in their feeding zones. This also leads to removal of the author's arguments (Levin 1972c) in favor of a protoplanetary nebula with an extended, massive periphery.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978. 相似文献
29.
Iris Levin 《The Australian geographer》2012,43(3):303-320
Meanings behind the choice of the migrant house are explored through an examination of 12 houses of migrants who emigrated from mainland China to Melbourne during the 1990s and 2000s. A qualitative investigation shows that there are three interconnected meanings behind the choice of houses in Melbourne: a desire to counter past experiences of housing in China, a desire to improve future opportunities through housing, and the wish to blend into Australian society. While much of the literature claims that migrant housing represents the ethnic character of their owners through architectural features, these Chinese houses do not resemble past houses in China in any physical way. The location of the house in a ‘good’ suburb was the most important factor when choosing the house. The house should be located near good educational, transport and shopping services before the built form becomes important. Chinese migrants wish to assimilate into Australian society through their choice of ordinary houses that do not communicate their ethnic identity through their external façades, while also adopting Australian ways of living that are focused on gardens and backyards. 相似文献
30.
The Relationship between Global Volcanic Activity and Variations in the Velocity of Earth’s Rotation
Levin B. W. Sasorova E. V. Gurianov V. B. Yarmolyuk V. V. 《Doklady Earth Sciences》2019,484(2):146-150
Doklady Earth Sciences - Analysis of observations of the Earth’s rotational velocity and volcanic activity of the planet from 1720 until 2015 suggests that higher volcanic activity temporally... 相似文献