Extremum Properties of the Regular Polyhedra

1950 ◽  
Vol 2 ◽  
pp. 22-31 ◽  
Author(s):  
Lâszlό Fejes Tόth
Keyword(s):  
Regular Polygons ◽  
Surface Areas ◽  
Extremum Problems ◽  
Regular Polyhedra ◽  
Historical Remarks

1. Historical remarks. In this paper we extend some well-known extremum properties of the regular polygons to the regular polyhedra. We start by mentioning some known results in this direction.First, let us briefly consider the problem which has received the greatest attention among all the extremum problems for polyhedra. It is the determination of the polyhedron of greatest volume F of a class of polyhedra of equal surface areas F, i.e., the isepiphan problem.

Studies on the surface area of zeolites, as determined by physical adsorption and X-ray crystallography

1968 ◽  
Vol 46 (10) ◽  
pp. 1695-1701 ◽  
Author(s):  
D. J. C. Yates
Keyword(s):  
Surface Area ◽  
Physical Adsorption ◽  
Independent Method ◽  
Linear Portion ◽  
Adsorbed Molecules ◽  
X Ray ◽  
X Ray Crystallography ◽  
Surface Areas

The determination of the surface areas of zeolites is discussed. It is shown that it is incorrect to use the multilayer isotherm method of Brunauer, Emmett, and Teller for solids where only little more than one monolayer can be adsorbed, in cavities little larger than the adsorbed molecules. The areas of such materials can, however, be determined from the beginning of the linear portion of their isotherms (point B). In addition, X-ray spectra can provide an independent method of measuring changes in the surface areas of zeolites.

scholarly journals Monitoring of snow surface near-infrared bidirectional reflectance factors with added light-absorbing particles

2019 ◽  
Vol 13 (6) ◽  
pp. 1753-1766 ◽  
Author(s):  
Adam Schneider ◽  
Mark Flanner ◽  
Roger De Roo ◽  
Alden Adolph
Keyword(s):  
Near Infrared ◽  
Bidirectional Reflectance ◽  
Nondestructive Technique ◽  
Snow Albedo ◽  
Considerable Uncertainty ◽  
Clear Sky ◽  
Surface Areas ◽  
Microphysical Properties ◽  
Sky Conditions

Abstract. Broadband snow albedo can range from 0.3 to 0.9 depending on microphysical properties and light-absorbing particle (LAP) concentrations. Beyond the widely observed direct and visibly apparent effect of darkening snow, it is still unclear how LAPs influence snow albedo feedbacks. To investigate LAPs' indirect effect on snow albedo feedbacks, we developed and calibrated the Near-Infrared Emitting and Reflectance-Monitoring Dome (NERD) and monitored bidirectional reflectance factors (BRFs) hourly after depositing dust and black carbon (BC) particles onto experimental snow surfaces. After comparing snow infrared BRFs to snow specific surface areas (SSAs), we found that both measured and modeled snow infrared BRFs are correlated with snow SSA. These results, however, demonstrate a considerable uncertainty of ±10 m2 kg−1 in the determination of snow SSA from our BRF measurements. The nondestructive technique for snow SSA retrieval that we present here can be further developed for science applications that require rapid in situ snow SSA measurements. After adding large amounts of dust and BC to snow, we found more rapid decreasing of snow BRFs and SSAs in snow with added LAPs compared to natural (clean) snow but only during clear-sky conditions. These results suggest that deposition of LAPs onto snow can accelerate snow metamorphism via a net positive snow grain-size feedback.

Determination of metallic surface areas of platinum - rhenium catalysts

1981 ◽  
Vol 1 (1-2) ◽  
pp. 71-80 ◽  
Author(s):  
Jacques Barbier ◽  
Henri Charcosset ◽  
Gladys de Periera ◽  
Jacques Riviere
Keyword(s):  
Metallic Surface ◽  
Surface Areas

scholarly journals Development and Validation of a High-Performance Thin-Layer Chromatographic Method for Determination of Ofloxacin Residues on Pharmaceutical Equipment Surfaces

2011 ◽  
Vol 94 (3) ◽  
pp. 735-742 ◽  
Author(s):  
Irena Vovk ◽  
Breda Simonovska
Keyword(s):  
Stainless Steel ◽  
High Performance ◽  
Water Solution ◽  
Liquid Paraffin ◽  
Stainless Steel Surface ◽  
Surface Areas ◽  
Quantitation Limit ◽  
Absolute Detection Limit ◽  
Development And Validation

Abstract An HPTLC method with densitometric quantification using fluorescence at 313 nm was developed and validated for the determination of ofloxacin residue in controlling pharmaceutical equipment cleanliness. Simulated samples at a residue level of 1 mg/m2 were prepared by spreading the calculated amount of ofloxacin solution on 1, 5, and 10 dm2 stainless steel surfaces. After evaporation of the solvent, the residue was removed by two ethanol wetted cotton swabs, which were thereafter extracted with the mixture of ethanol and Na2EDTA–water solution at pH 11 for 15 min with sonication. The extract and standards were applied on HPTLC silica gel 60 plates and then developed in a horizontal developing chamber from both sides using ethanol-conc. ammonia (4 + 1, v/v) as the mobile phase. The mean recovery (n = 6) at 1 mg/m2 from 1, 5, and 10 dm2 was 95.3, 88.6, and 89.7% with the CV values 3.78, 4.41, and 4.97%, respectively. The absolute detection limit was 0.6 ng and the quantitation limit was 2 ng, but it was shown that these can be improved by immersion of the developed plate into a solution of liquid paraffin–n-hexane (1 + 2, v/v) to approximately 0.25 and 0.9 ng, respectively. The LOD of the method using detection without paraffin–n-hexane was 3, 0.6, and 0.3 μg/m2 by swabbing 1, 5, and 10 dm2, respectively. The method can be applied to routine control of pharmaceutical equipment cleanliness by sampling from stainless steel surface areas of 1 to 10 dm2 with acceptable residue limit/surface of 1 mg/m2.

Parallelized N2O Frontal Chromatography for the Fast Determination of Copper Surface Areas

2008 ◽  
Vol 10 (3) ◽  
pp. 387-390 ◽  
Author(s):  
Stefan Olejnik ◽  
Christian Baltes ◽  
Martin Muhler ◽  
Ferdi Schüth
Keyword(s):  
Copper Surface ◽  
Fast Determination ◽  
Surface Areas ◽  
Determination Of Copper ◽  
Frontal Chromatography

scholarly journals II. Micro-chemical researches on the digestion of starch and amylaceous foods

1856 ◽  
Vol 7 ◽  
pp. 225-232
Keyword(s):  
Chemical Analysis ◽  
Alimentary Canal ◽  
Intestinal Canal ◽  
Definite Structure ◽  
Historical Remarks

After some general historical remarks on the methods hitherto employed in the investigation of the complicated phenomena of the process of digestion, the comparatively small results obtained by chemical analysis of the contents of the stomach, intestinal canal, and of the evacuations, by Tiedemann and Gmelin, Berzelius, and others, the author proceeded to demonstrate the necessity of a minute examination of the contents of the alimentary canal by the microscope, and such chemical tests as we possess for the determination of the changes of such articles of food as exhibit definite structure.

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