Cryoplanation Terrace Orientation in Alaska   总被引：2，自引：0，他引：2  

Frederick E. Nelson 《Geografiska Annaler: Series A, Physical Geography》1998,80(2):135-151

Exploratory analysis of the orientation of 303 cryoplanation terraces in interior and western Alaska lends tentative support to the hypothesis that these landforms develop through localized erosion related to spatial patterns of snow accumulation and ablation. Cryoplanation terraces exhibit orientation patterns similar to those of cirques in several regions of Alaska. In climatically continental east-central Alaska, cryoplanation terraces are developed preferentially on north-facing slopes and the frequency distribution of terrace orientation is similar to but less concentrated than that of glacial cirques. In south-central Alaska, both cirques and terraces have bimodal frequency distributions corresponding to generalized wind patterns that predominated during Pleistocene glaciations. In western Alaska, terraces and cirques have relatively diffuse patterns without preferred orientation. No clear relation is apparent between the orientation of cryoplanation terraces and their size or elevation, although this may be an artifact of the current inability to differentiate terraces by age. Data from the Eagle Summit/Mastodon Dome area in interior Alaska indicate a possible relation between snowline elevation and the concentration of terrace orientation.  相似文献   

Genus statistics of the Virgo N-body simulations and the 1.2-Jy redshift survey     

Volker Springel  Simon D. M. White  Jo¨rg M. Colberg  Hugh M. P. Couchman  George P. Efstathiou  Carlos S. Frenk  Adrian R. Jenkins  Frazer R. Pearce  Alistair H. Nelson  John A. Peacock  & Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》1998,298(4):1169-1188

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Comet plasma densities deduced from refraction of occulted radio sources     

C.S. Wright  G.J. Nelson 《Icarus》1979,38(1):123-135

Eighty MHz observations of the occultation of the radio source Culgoora-1 0300 + 16 by the plasma tail of Comet Kohoutek (1973f) were made in February/March 1974 with the Culgoora radioheliograph. No detectable source broadening or change in flux density was observed, but the results showed a 2' arc anomaly in the observed position. This is greater than can be attributed to ionospheric refraction or experimental error. We suggest that it arose from refraction in the plasma tail of the comet. Similar observations of the occulation of the radio source Culgoora-1 2313-14 by the plasma tail of Comet West (1975n) were made at Culgoora in February 1976. These results were inconclusive but did suggest that the cometary plasma may have had some influence on the observed source position. The results are used to derive, from simple models, the distribution of electron density in comet tails. Peak electron densities of approximately 2 to 5 × 10⁴ cm^?3 and density gradients of ～0.05 cm^?3 km^?1 are indicated.  相似文献   

Search for color changes and brightening of Io upon eclipse reappearance     

Robert M. Nelson 《Icarus》1977,32(2):225-228

Medium-resolution spectra were made of Io as it emerged from two eclipses in December 1975. In the wavelength range 4000–5800 Å, no spectral changes greater than the standard deviations were observed when the spectrum of Io just after reappearance was divided by the spectrum of Io 20 min later. No substantial increase in total brightness was observed over the same time interval. These observations were made at a time when the sub-Earth point was in Io's northern hemisphere; therefore, prediction of positive posteclipse brightening in this circumstance is not confirmed.  相似文献   

POLAR 5—an electron accelerator experiment within an aurora. 3. Evidence for significant spacecraft charging by an electron accelerator at ionospheric altitudes     

Tore A. Jacobsen  Nelson C. Maynard 《Planetary and Space Science》1980,28(3):291-307

The POLAR 5 rocket experiment carried an electron accelerator on a “daughter” payload which injected a 0,1 A beam of 10 keV electrons in a pulsed mode every 410ms. With spin and precession, injections were made over a wide range of pitch angles. Measurements from a double probe electric field instrument and from particle detectors on the “mother” payload and from a crude R.P.A. on the “daughter” payload are interpreted to indicate that the “daughter” charges to a potential between several hundred volts and 1 kV. The neutralizing return current to the “daughter” is shown to be assymetrically distributed with the majority being collected from the direction of the beam. The additional electrons necessary to neutralize the daughter are thought to be produced and heated through beam-plasma interactions postulated by Maehlum et al. (1980b) and Grandal et al. (1980) to explain the particle and optical measurements. Significant electric fields emanating from the charged “daughter” and the beam are seen at distances exceeding 100 m at the “mother” payload.  相似文献   

The Effects of Streamers on the Shape of the K-Coronal Spectrum     

Nelson?L.?ReginaldEmail author  Joseph?M.?Davila  O.?C.?St.?Cyr 《Solar physics》2004,225(2):249-265

We conducted an experiment in conjunction with the total solar eclipse of 21 June 2001 in Lusaka, Zambia, to obtain the K-coronal spectrum simultaneously from multiple locations on the solar corona. Then we matched the observed K-coronal spectra with the modeled K-coronal spectra to determine the coronal electron temperature and its bulk flow speed. Here the models assumed a symmetric and isothermal corona with the coronal electron flowing away from the Sun at a constant flow speed. We were able to make remarkable matches between the observations and the models. In this paper we will try to explain how the anomalies in the matches could be accounted for with the introduction of streamers in the K-coronal spectral models.  相似文献   

The Astoria Fan: An elongate type fan     

C. Hans Nelson 《Geo-Marine Letters》1984,3(2-4):65-70

The Astoria Fan, a modern system, is located on a subducting oceanic crust and fills a north-south-trending trench along the Oregon continental margin. Well-developed channels cross the entire fan length; they display classic inner-fan leveed profiles but evolve into distributaries in the midfan area where the gradient decreases sharply. During periods of low sea level, inner- and middle-fan channels funnel sand to distal depositional sites in the outer-fan area where the sand/shale ratios are highest. This pattern of sand displacement and efficiency of transport appears to be characteristic of elongate fans fed by a major river and submarine canyon. Margin setting represents fan and/or source area  相似文献   

On the variability of 18 Degree Water formation as observed from moored instruments at 55°W     

Birgit Klein  Nelson Hogg 《Deep Sea Research Part I: Oceanographic Research Papers》1996,43(11-12)

The analysis of hydrographic time series from moored sensors from the eastern end of the Sargasso Sea has shown that in the late 1980s the Subtropical Mode Water was dominated by high temperatures. The 18 Degree Water observed during this period was warmer and saltier than the definition given by Worthington, with an increase in values over the observation period. Although severe winter conditions in 1988 led to the formation of colder types of 18 Degree Water at the eastern part of the Sargasso Sea, they were not incorporated in the subtropical gyre. Simultaneous current meter measurements indicated eastward flow within the “southern recirculation gyre” during spring that might have been responsible for the fact that these cold Mode Water types have not been entrained into the gyre. The meteorological forcing fields show considerable interannual variability that is, in part, mimicked by changes in the 18 Degree Water properties. Due to the strong influence of the advection field on the 18 Degree Water properties, the relationship between the surface forcing and 18 Degree Water properties remains qualitative. The continuing influence of further mild winters after 1989, however, is manifested in rising temperatures within the Mode Water range.  相似文献   

Density-dependent linkage between juveniles and recruitment for pink shrimp (Farfantepenaeus duorarum) in southern florida     

Ehrhardt  Nelson M.; Legault  Christopher M.; Restrepo  Victor R. 《ICES Journal of Marine Science》2001,58(5):1100-1105

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Membrane mimetic electrochemistry in the marine sciences     

A. Nelson 《Marine environmental research》1985,17(2-4)

In marine pollution studies it is generally considered that the biological availability of a particular contaminant depends to some extent on its chemical speciation.¹ Little is known, however, about the actual mechanism of transport of the toxic species into the organism. We consider the biomembrane transport of toxicants as the critical link between biological availability and chemical speciation. A study has thus been instigated into the transport of simple species across phospholipid monolayers as model membranes. In this paper we describe a novel technique whereby phospholipid monolayers are spread on a hanging mercury drop electrode (HMDE) and subsequently held within the bulk phase chloride electrolyte. In addition, we report preliminary electrochemical observations on: (i) the form and behaviour of the monolayers in response to applied electric field and (ii) the interaction of marine pollutants, polynuclear aromatic hydrocarbons (PAHs) with the lipid films.  相似文献