Nachweis der allgemeinen Gültigkeit des Gefrierkernspektrums     

Dr. Walter Rau 《Pure and Applied Geophysics》1953,26(1):75-87

Zusammenfassung Durch weitere experimentelle Untersuchungen wird festgestellt, dass das an destillierten Wassertropfen ermittelte Gefrierkernspektrum von speziellen Versuchsbedingungen unabhängig ist und auch für Wasserarten mit verschiedenen natürlichen oder künstlichen Verunreinigungen gilt. Es kann ausserdem in allen bisher im Laboratorium und in der Atmosphäre durchgeführten Untersuchungen über die Eiskeimbildung nachgewiesen werden. Dieser Befund stützt als notwendige Bedingung die Deutung des Gefrierkernspektrums durch Strukturänderungen des Wassers und besagt, dass im Laboratorium und in der Atmosphäre dieselben Gefrierkerne vorhanden sind und dass bei der atmosphärischen Eiskeimbildung auch nur die aus Untersuchungen im Laboratorium bekannten Besonderheiten des Gefrieveorgangs (im unterkühlten Wasser) vorliegen.

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Summary Further experimental investigations demonstrate the «Gefrierkernspektrum», which was found for droplets from destilled water, to be independent from special experimental conditions and valid for sorts of water containing natural or artificial impurities, too. Furthermore it can be pointed out from all existing investigations on ice-nucleation, made in laboratory and in the atmosphere. This result supports, as a necessary condition, the interpretation of the «Gefrierkernspektrum» by means of changes in the structure of water itself and proves, that there are the same freezing nuclei both in the laboratory and the fre atmosphere and that ice-nucleation in the atmosphere holds but the same peculiarities of freezing (of supercooled water), known from laboratory work.

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Eine neue Methode der Kondensationskernzählung     

Walter Wieland 《Pure and Applied Geophysics》1955,30(1):137-143

Zusammenfassung In der vorliegenden Arbeit wird eine Methode beschrieben, die es gestattet, mit Hilfe lackierter Glasplatten Kondensationskerntröpfchen oder andere Tröpfchen mit einem Durchmesser von 5 zu fixieren und dann elektronisch auszuzählen. Vorversuche, bei denen diese Methode angewendet wurde, machen es wahrscheinlich, dass bei Kondensationskernzählern, die nach dem Expansionsprinzip arbeiten, ein Teil der Kerne wegen ihrer Aktivität schon vor der Expansion als Wassertröpfchen ausfällt und damit der Zählung entgeht.

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Summary In the present paper a method is described, which allows to fix droplets of condensation nucleus or other droplets (diameter 5 ) by means of varnished plates of glass and count them afterwards electronically. Preliminary experiments with this method show up the probability, that in the nucleus counter, working on the principle of expansion, some of the very active nucleus drops out before the expansion chamber is dilated and thus escapes registration.

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Riassunto Nella presente ricerca si descrive un metodo il quale consente di fissare goccioline provenienti da nuclei di condensazione, o altre goccioline (diam. 5 ), su dischi di vetro verniciati, e in seguito di contarle elettronicamente. Prove eseguite con questo metodo rendono probabile che, in contatori di nuclei di condensazione che lavorano secondo il principio dell'espansione, una parte dei nuclei, in seguito alla loro stessa attività, cada sotto forma di goccioline d'acqua già prima dell'espansione e che quindi sfugga al conteggio.

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Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign     

Josef Gochermann  Walter F. Wargau  Claus Tappert  Theodor Schmidt-Kaler  Robert S. Stobie  Fred Marang  Greg Roberts  Francois G. van Wyk  Peter Rucks 《Experimental Astronomy》1999,9(1):1-15

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.  相似文献   

On the gradient line of the moon's zonal gravitational potential field     

Walter Köhnlein 《Earth, Moon, and Planets》1973,6(3-4):384-397

The analytical expression of the gradient line, i.e. the perpendicular to the Moon's zonal equipotential surfaces is derived. Being a sensitive indicator of the geometric structure of the gravitational field, the shape of the trajectory, its direction field and curvature, the points of inflection, etc., are computed at elevations 0 km, 250 km, 1000 km and 10000 km above the Moon's surface. The numerical results were derived from the coefficients of Liu and Laing (1971) and are compared- whenever suitable - with the results obtained from the coefficients of Michaelet al. (1969).  相似文献   

Surveillance for previously unmonitored organic contaminants in the San Francisco Estuary     

Oros DR  Jarman WM  Lowe T  David N  Lowe S  Davis JA 《Marine pollution bulletin》2003,46(9):1102-1110

The San Francisco Estuary Regional Monitoring Program initiated surveillance monitoring to identify previously unmonitored synthetic organic contaminants in the San Francisco Estuary. Organic extracts of water samples were analyzed using gas chromatography-mass spectrometry in full scan mode. The major contaminant classes identified in the samples were fire retardants, pesticides, personal care product ingredients, and plasticizers. Evidence from the literature suggests that some of these contaminants can persist in the environment, induce toxicity, and accumulate in marine biota and in higher food chain consumers. The major sources of these contaminants into the marine environment are the discharge of municipal and industrial wastewater effluents, urban stormwater, and agricultural runoff. As a proactive effort, it is suggested that surveillance studies be used routinely in monitoring programs to identify and prevent potential problem contaminants from harming the marine environment.  相似文献   

The capture efficiency map: the capture zone under time-varying flow   总被引：3，自引：0，他引：3  

Festger AD  Walter GR 《Ground water》2002,40(6):619-628

The capture zone or contributing area of a ground water extraction well can be defined as that portion of the aquifer from which the well draws its water. Accurate delineation of capture zones is important in many ground water remediation applications and in the definition of wellhead protection areas. Their mathematical delineation is often simplified by using quasi-steady-state models based on time-weighted average pumping rates and background hydraulic gradients. We present a new semianalytic approach for the definition of capture zones under transient-flow conditions. We then use this approach to evaluate the effects of time variations in the direction of the background hydraulic gradient on capture. Results are presented in the form of capture efficiency maps (CEMs). Although the area contributing to a given well is found to generally expand relative to the steady-state average capture zone when the gradient direction varies, the zone of 100% capture may expand or contract depending on site-specific conditions. We illustrate our CEM approach by applying it to the design of a plume containment system.  相似文献   

Spatio-temporal changes in the abundance of the populations of the gastrotrich community in a shallow lake of tropical Africa     

Serge H. Zbaz Togouet  Thomas Njine  Norbert Kemka  Moise Nola  Samuel Foto Menbohan  Walter Koste  Claude Boutin  Rick Hochberg 《Limnologica》2007,37(4):311-322

Studies on the biodiversity and population dynamics of freshwater planktonic Gastrotricha have been carried out in conjunction with a physical–chemical analysis of the water in the Yaounde Municipal Lake (Cameroon, Central Africa) over a 14 months period (November 1996–December 1997). The results obtained allow to consider the Yaounde Municipal Lake as an eutrophic lake. It harbours eight species of Gastrotricha belonging to four genera (Chaetonotus, Dasydytes, Neogossea and Polymerurus) of the order Chaetonotida. This community was characterized by high abundances of populations, and was dominated by the genus Neogossea and Chaetonotusreaching up to 2000 ind. L⁻¹. Polymerurus was mostly abundant at the almost anoxic bottom layers. The highest abundances were found mostly during the rainy season, when there is an important sedimentation process of organic matter, and were influenced by several different environmental factors such as dissolved oxygen, temperature and pH of the water.

Finally this community which may play an important role in the water bodies, is a potential water quality indicator.  相似文献   

Alternative Validation of a LC-MS/MS-Multi-Method for Pesticides in Drinking Water     

Alexander Müller  Dirk Flottmann  Wolfgang Schulz  Wolfram Seitz  Walter H. Weber 《洁净——土壤、空气、水》2007,35(4):329-338

The development of instrumental analytics such as the LC-MS/MS has made it possible to quickly determine many component concentrations in a single chromatogram. However, the validation of such multi-methods needs new strategies for robustness and optimization. Statistical execution of analytical tests is one tool that can be utilized to meet this requirement. A Central Composite Design (CCD) was utilized for the validation of an LC-MS/MS multi-method for 84 analytes. The experimental design includes six design variables and two non-design variables (response variables). Concentration, ionization temperature, dwell time, gradient, flow (of eluent), and spraying/curtain gas (continuous design variables) were varied on five different levels; the whole design encompassed 91 runs. To investigate the robustness of a LC-MS/MS method both peak sensitivity and chromatographic separation had to be verified. Therefore, two non-design variables were necessary. The distribution of the peaks over analysis time was applied to describe the quality of the chromatographic separation. The sensitivity was described with the signal to noise ratio (S/N). The evaluation of the measured data was accomplished with the Analysis of Variance (ANOVA) and the Response Surface Methodology (RSM). Three main effects (concentration, ionization temperature, dwell time) and no significant interaction effect were found for the response variable “S/N”. The variables of concentration, ionization temperature, and dwell time had no significant effects for the response variable “S/N”. The ANOVA of the response variable chromatographic separation abandoned no significant effects as well. Therefore, robustness of the method can be guaranteed for all non significant design variables.  相似文献   

The Bayesian approach to an internally consistent thermodynamic database: theory, database, and generation of phase diagrams     

Niranjan D. Chatterjee  Ralf Krüger  Gerd Haller  Walter Olbricht 《Contributions to Mineralogy and Petrology》1998,133(1-2):149-168

An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity, bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data, culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper. It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows calculation of P-T, T-X _CO2, P-X _CO2, and T-f _O2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate the quality of the data and the capabilities of the software. Received: 11 March 1998 / Accepted: 11 June 1998  相似文献   

Mass models of the Milky Way     

Walter Dehnen  & James Binney 《Monthly notices of the Royal Astronomical Society》1998,294(3):429-438

A parametrized model of the mass distribution within the Milky Way is fitted to the available observational constraints. The most important single parameter is the ratio of the scalelength R _d* of the stellar disc to R ₀. The disc and bulge dominate v _c( R ) at R ≲ R ₀ only for R _d,*/ R ₀≲0.3. Since the only knowledge we have of the halo derives from studies like the present one, we allow it to contribute to the density at all radii. When allowed this freedom, however, the halo causes changes in assumptions relating to R  ≪  R ₀ to affect profoundly the structure of the best-fitting model at R  ≫  R ₀. For example, changing the disc slightly from an exponential surface-density profile significantly changes the form of v _c( R ) at R  ≫  R ₀, where the disc makes a negligible contribution to v _c. Moreover, minor changes in the constraints can cause the halo to develop a deep hole at its centre that is not physically plausible. These problems call into question the proposition that flat rotation curves arise because galaxies have physically distinct haloes rather than outwards-increasing mass-to-light ratios.   The mass distribution of the Galaxy and the relative importance of its various components will remain very uncertain until more observational data can be used to constrain mass models. Data that constrain the Galactic force field at z ≳ R and at R  >  R ₀ are especially important.  相似文献