Search Results

You are looking at 1 - 6 of 6 items for

  • Author or Editor: M. Walter x
Clear All Modify Search
Thermal stability of the β″ phase in the ZrO2-Zr3N4 system
Authors: D. Walter, M. Lerch and W. Laqua

Annealing of ZrO2 in a nitrogen atmosphere leads to a nitrogen containing phase called Β″ phase having a trigonally distorted fluorite structure with ordered anion vacancies. DTA/TG investigations indicated that the Β″ phase decomposes intom-ZrO2 above 500‡C releasing nitrogen during the reaction with oxygen. Prevention of oxygen uptake by use of closed tantalum tubes instead of open platinum crucibles enabled the detection of a new reversible phase transition at ∼965‡C. The thermoanalytical results have been confirmed by high temperature-X-ray investigation.

Full access
The transitions in phases II–III–IV in high purity ammonium nitrate
Authors: R. R. Sowell, M. M. Karnowsky and L. C. Walters

The phase changes in high-purity ammonium nitrate were studied by a differential thermal analysis (DTA) apparatus designed for constant heating and cooling rates and continuous cycling for ∼3-gram samples. On the basis of DTA and X-ray diffraction data very consistent behavior is observed. Phase IV → III transformation on heating in the range 43‡ to 51‡ and Phase II → IV transformation on cooling in the range 49‡ to 53‡ are demonstrated. The III → II transition at about 86→ is seen with repeated temperature cycling. This repeatable behavior not consistently seen by investigators using other techniques is believed to be due to the high purity material and constant heating and cooling rates.

Full access
Chromatographic and spectroscopic analysis of the fluorescent compounds derived from monosaccharides on HPTLC-NH 2 plates
Authors: G. Grygierczyk, Walter Fischer, M. Sajewicz, P. Kuś, R. Wrzalik, M. Czaja, M. Dziadek and Teresa Kowalska

In this paper we present results from recent studies focusing on elucidation of the mechanism of visualization of simple sugars (e.g. d -(+)-glucose, d -(+)-galactose, and d -(−)-fructose) developed on glass TLC plates precoated with 3-aminopropyl chemically bonded stationary phase and then heated at elevated temperatures, a method originally developed, then recommended commercially, by Merck.Detection of the sugars under UV illumination is possible because of their substantial fluorescence; this suggests that during heating the analytes probably undergo a process which results in their structural transformation. We postulated a possible analogy with the Maillard reaction, omnipresent in innumerable living organisms.To verify our assumption we performed analysis with high-performance thin-layer chromatography (HPTLC), high-performance liquid chromatography (HPLC), and IR, UV, and fluorescence spectroscopy. All the results obtained seem to confirm the analogy between the Maillard reaction and the reaction of simple carbohydrates after development on the amino stationary phase.

Full access
Facility for non-destructive analysis for major and trace elements using neutron-capture gamma-ray spectrometry
Authors: D. Anderson, M. Failey, W. Zoller, W. Walters, G. Gordon and R. Lindstrom

Abstract  

A facility for neutron-capture γ-ray spectroscopy for analytical purposes has been developed and tested at the National Bureau of Standards reactor. The system consists of an internal beam tube with collimators, an external beam tube and irradiation station, a Compton-suppressed Ge(Li) γ-ray detection system, and a minicomputer-based data-collection and-analysis system. Detection limits have been established for many elements and errors arising from neutron self shielding, γ-ray peak overlap, neutron beam variations, and sample matrix evaluated.

Full access
Small-scale patterns in community structure of Sarracenia purpurea inquilines
Authors: H.L. Buckley, J.H. Burns, J.M. Kneitel, E.L. Walters, P. Munguia and E. Miller

We examined the environmental factors associated with community structure in the inquiline communities of the purple pitcher plant (Sarracenia purpurea L.). We sampled all 141 communities in a 10- x 20-m grid and recorded their spatial relationships to determine the relative influence of environmental and spatial factors on community structure. Environmental and spatial factors contributed equally to the variance in community composition (species identity and abundance) among pitchers.  The species richness of communities was influenced by both spatial and environmental variables, particularly environmental variables related to community size. In addition, our study suggests a number of hypotheses about factors influencing community structure (e.g. predation) that could be tested experimentally.

Full access
Liquid and dry swabs for culture- and PCR-based detection of colonization with methicillin-resistant Staphylococcus aureus during admission screening
Authors: N. von Allmen, K. Gorzelniak, O. Liesenfeld, M. Njoya, J. Duncan, E. M. Marlowe, T. Hartel, A. Knaust, B. Hoppe and M. Walter

Rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) colonization status facilitates isolation and decolonization and reduces MRSA infections. Liquid but not dry swabs allow fully automated detection methods. However, the accuracy of culture and polymerase chain reaction (PCR) using liquid and dry swabs has not been analyzed. We compared different swab collection systems for routine nasal–throat MRSA screening in patients admitted to a tertiary care trauma center in Germany. Over 3 consecutive months, dry swabs (month 1), ESwabs (month 2), or MSwabs (month 3) were processed using Cepheid GeneXpert, Roche cobas and BD-MAX™ MRSA tests compared to chromogenic culture. Among 1680 subjects, the MRSA detection rate using PCR methods did not differ significantly between dry swabs, ESwab, and MSwab (6.0%, 6.2%, and 5.3%, respectively). Detection rates using chromogenic culture were 2.9%, 3.9%, and 1.9%, using dry, ESwab, and MSwab, respectively. Using chromogenic culture as the “gold standard”, negative predictive values for the PCR tests ranged from 99.2–100%, and positive predictive values from 33.3–54.8%. Thus, efficient and accurate MRSA screening can be achieved using dry, as well as liquid E- or MSwab, collection systems. Specimen collection using ESwab or MSwab facilitates efficient processing for chromogenic culture in full laboratory automation while also allowing molecular testing in automated PCR systems.

Open access