bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi‐element analysis of tree rings by EDXRF spectrometry
Authors: Selin E. , Standzenieks P. , Boman J. , Teeyasoontranont V. 
Published: May 2005

AbstractAn EDXRF system for scanning samples in steps of 5 μm was developed. The system is based on a conventional x‐ray tube and secondary target in closest possible geometry. For tree ring analysis, which was made in steps of 200 μm, the exciting x‐ray beam was allowed to pass through a slit collimator of dimensions 0.1 × 1 mm made of pure silver. The sample holder is movable in steps of 5 μm in three orthogonal directions. The beam path of the exciting and fluorescent radiation can be adjusted in relation to the sample plane by the movable sample holder. Further adjustments can be made by a movable detector platform. All movements are driven by microcomputercontrolled step motors. The detection limits of thick samples, like tree biopsies, are of the order of parts per million for medium‐heavy elements. The system was applied to multielement analysis of healthy samples of pine, birch and spruce biopsies. Long‐term trends in some trace element concentrations could be seen in these samples, together with the possible influence of stress.
EDXRS modelling for in vivo trace element analysis by using the SHAPE code
Authors: Tartari A. , Fernandez J. E. , Casnati E. , Baraldi C. , Felsteiner J. 
Published: May 2005

AbstractThe validity of the SHAPE code, a computer package able to simulate EDXRS spectra, was tested to model the in vivo XRF determination of cadmium concentrations in the kidney by choosing the best source–measurement geometry combination. Accurate measurements were performed in order to validate the results of this code in the energy interval involved in in vivo XRF analysis. In addition, a comparison was made with Monte Carlo results including thrid‐order contributions and polarization. Very good agreement was found with the experimental and Monte Carlo results. In spite of the fact that, at present, this code does not include higher order multiple scattering, modelling results using the SHAPE code agree very well with the expensive Monte Carlo solutions and the empirical values recently predicted for this technique.
Determination of potassium and calcium in vegetables by x‐ray fluorescence spectrometry
Authors: Mittal Raj , Allawadhi K. L. , Sood B. S. , Singh N. , Kumar Anita , Kumar Parminder 
Published: May 2005

AbstractA method based on XRF was used for the determination of the total concentration of potassium and calcium, in the presence of each other and irrespective of the nature of their chemical compounds, in the roots and leaves of spinach and radish plants. The enhancement of potassium K x‐rays due to K x‐rays of calcium present in the samples was avoided by selective excitation of the sample with external conversion calcium K x‐rays in a compact triaxial double reflection geometry set‐up. The absorption of calcium and potassium K x‐rays in the samples was taken care of in terms of counts under K x‐ray peaks only. The overlapping of the calcium K x‐ray photopeak with the potassium K x‐ray photopeak due to the limited resolution of the Si(Li) spectrometer was estimated and counts under the calcium K x‐ray photopeak were corrected accordingly. The results for whole plants of spinach and radish agreed with those normally quoted in nutrition books.
Bent and flat highly oriented pyrolytic graphite crystals as small bragg angle monochromators in thin‐specimen energy‐dispersive XRF analysis
Authors: Beckhoff Burkhard , Laursen Jens 
Published: May 2005

AbstractA monochromatic high‐intensity x‐ray beam, obtained by Bragg reflection of the strongest characteristic tube line under small angles on single crystals, can be used as an EDXRF excitation source. A systematic selection procedure and search of 55 single crystals suitable as EDXRF Bragg reflectors was made and highly oriented pyrolytic graphite (HOPG) was found to be a superior candidate for the characteristic Kα line of an Mo tube within the range of low‐order reflections, yielding the highest intensities. Meridionally and sagitally curved HOPGs were studied in a flexible experimental set‐up and the reflected beam intensity and profile were compared with the corresponding data obtained from flat HOPGs with different mosaic spreads. The relationships between collimation, crystal curvature and mosaic spread were evaluated. The experimental angular beam acceptance and the secondary extinction effects dependent on the mosaic spread of the HOPG were found to be in line with theoretical expectations. Measured in similar configurations as required for realistic EDXRF applications, the sagitally bent HOPG increases the reflected beam intensity up to 77% whereas the meridionally bent HOPG yields an intensity gain of only up to 28% compared with the flat crystal with the same mosaic spread. The detection limits for the corresponding thin‐filter EDXRF analysis are presented.
Monte carlo simulation of the scattering contributions to the XRF line
Authors: JorgeSánchez Héctor , Sartori Renzo 
Published: May 2005

AbstractA Monte Carlo program to simulate the scattering contributions to the x‐ray fluorescent line was developed. Simulations were carried out on three pure samples (Z = 14, 28 and 40) in several geometrical situations (incident and take‐off directions of the photons). The results show that the scattering effects do not exceed 4% for the analysed elements in the X‐ray regime. Good agreement between normal incidence simulations and theoretical results was found. The vanishing of second‐order interactions inside the sample when the propagation plane approximates π/2 was also verified.
Determination of fractal dimension in cement gels by PIXE
Authors: Potiriadis C. , Bakopoulos Y. 
Published: May 2005

AbstractTwo samples of ordinary Portland cement, one consisting of dry powder and the other of hydrated paste 28 days old, were bombarded with protons, resulting in proton‐induced X‐ray emission (PIXE). The X‐ray yield was measured as a function of the exit angle and the differences between the two samples were interpreted by the hypothesis that the pores of the hydrated cement gel form a fractal. The fractal dimension that was calculated is in good agreement with the values found by small‐angle neutron scattering and nuclear magnetic resonance.
Determination of the mean size of submicron particles by electron probe microanalysis
Authors: Berner A. , Levin I. , Klinger L. , Brandon D. G. 
Published: May 2005

AbstractA method for the determination of the mean size of submicron particles randomly distributed in a matrix by electron probe x‐ray microanalysis (EPMA) is described. The method is based on an analysis of variance of the characteristic x‐ray intensity from an element contained only in the particle. Analytical expressions relating this variance to the mean size of the particles were derived and the method was validated using test samples. The present technique can be used with a conventional x‐ray microanalyser for the rapid determination of the mean size of submicron particles.
Detailed ray‐tracing code for capillary optics
Authors: Vincze L. , Janssens K. , Adams F. , Rindby A. 
Published: May 2005

AbstractA description of a detailed ray‐tracing code for capillary optics is given and a number of examples of the use of the program are discussed. The model uses numerically defined capillary shapes and is able to simulate the behaviour of devices having shape distortions of various nature, including bending of the capillary. Comparisons are made with previously published capillary calculation models and with experimental results described in the literature. The use of the code is also demonstrated for the optimization of conical capillary dimensions assuming extended x‐ray sources. With respect to the modelling of realistic capillary shapes, the beam transmission properties of an ellipsoidal device are calculated, using the experimentally determined capillary profile.
Determination of thickness maps of thin coatings by EDS EPMA
Authors: Benhayoune H. , Jbara O. , Thomas X. , Cazaux J. 
Published: May 2005

AbstractA new experimental procedure for the measurement of the thickness fo thin coatings on substrates is presented. Based on the experimental determination of the electron backscattering coefficient η (via the measurement of the electric current of the correctly polarized specimen holder), the number of reference specimens to be used for the calibration during measurements can be reduced. Thickness maps free of artifacts associated with local changes in the substrate composition illustrate the proposed methods.
EDXRF procedure for quantitative analysis matching theoretically generated reference spectra to measured spectra
Authors: Fernández J. E. , Tartari A. 
Published: May 2005

AbstractThe diversity of processes that contribute to an x‐ray fluorescence spectrum make it difficult to obtain an accurate estimate of the line intensities needed to determine the sample composition in XRF analysis. The radiative contributions forming the spectrum are produced by the interactions that x‐ray photons undergo with the atoms of the sample. Many multiple scattering terms contribute to the continuous portions of spectrum that overlap the lines of interest. The lines themselves are formed by the overlap of many narrow (discrete) contributions and some continuous ones: one ‘primary intensity’ plus several enhancement terms. The lines can also interfere with other neighbouring lines produced in the sample. The resulting spectrum, sufficiently complicated at this stage, is still modified in a complex way by the influence of the detector response and successive digitalization by the multi‐channel analyser. The difficulties that such spectral complexity introduces in the process of extracting the ‘primary fluorescence intensity’ from the experimental spectrum can be overcome by using a theoretical spectrum of reference that, in this paper, was calculated using the code SHAPE. Such a theoretical spectrum has the property that all the single contributions are well known, and therefore can be used to estimate correctly the fraction of ‘primary fluorescence intensity’ under any experimental line of interest in the real spectrum enclosed between two given energy channels. Since the theoretical spectrum can be computed only for a known composition, the calculated fraction can be initially obtained by feeding SHAPE with an arbitrary composition. The fraction estimated with the theoretical spectrum is used to correct the corresponding peak area in the experimental measured spectrum, which in turn is used to obtain a new calculated composition. This result is used to feed a new spectrum computation, defining an iterative method that converges to the unknown composition. The theoretical details of this iterative method are described and some experimental examples of EDXRF analysis using this technique are given. The advantages of the method for treating some paradigmatic cases of analysis are also illustrated.
Partial restoration of meiosis in an apomictic strain of Saccharomyces cerevisiae: A model system for investigation of nucleomitochondrial interactions during sporulation
Authors: Marmiroli Nelson , Bilinski Carl A. 
Published: May 2005

AbstractIn an apomitic strain of Saccharomyces cerevisiae (ATCC 4117‐H2) which undergoes a single nuclear division during sporulation and consequently forms asci containing two uninucleate diploid spores, a study was undertaken to investigate the effects of cultivation in three presporulation media (YPA; YNB; SMM) on nuclear division and ascoporogenesis in sporulation medium. Comparison of effects of presporulation culture in these media on the number of spores formed per ascus showed that a marked induction (30 ± 4·3 per cent) of three‐ and four‐spored asci could occur in sporulation medium following cultivation in a defined YNB medium supplemented with a 1 per cent solution of vitamins and containing decreased ammonium sulphate and increased glucose levels. Experiments in which the concentrations of glucose and of ammonium sulphate were varied simultaneously indicated that the initial presporulation carbon to nitrogen source ratio is an important factor in determining tetrad formation in sporulation medium. Nuclear staining demonstrated two classes of asci: binucleate (one‐ and two‐spored) and tetranucleate (three‐ and four‐spored). Genetic evidence and data concerning effects of inclusion in sporulation medium of a meiotic inhibitor (glucose) indicated spores in tetrads were haploid rather than diploid. This ability to condition a significant number of cells for meiotic rather than apomictic differentiation made possible investigation of effects of mitochondrial inhibitors on both developmental processes simultaneously. It was found possible to selectively inhibit meiotic development by inclusion in sporulation medium of appropriate concentrations of specific inhibitors. Moreover, the data suggest meiotic sporulation is more strictly dependent than apomictic sporulation on mitochondrial function.
Yeast/E. coli shuttle vectors with multiple unique restriction sites
Authors: Hill John E. , Myers Alan M. , Koerner T. J. , Tzagoloff Alexander 
Published: May 2005

AbstractTwo yeast/E. coli shuttle vectors have been constructed. The two vectors, YEp351 and YEp352, have the following properties: (1) they can replicate autonomuosly in Saccharomyces cerevisiae and in E. coli; (2) they contain the β‐lactamase gene and confer ampicillin resistance to E. coli; (3) they contain the entire sequence of pUC18; (4) all ten restriction sites of the multiple cloning region of pUC18 including EcoRI, SacI, KpnI, SmaI, BamH1, XbaI, SbaI, SalI, PstI, SphI and HindIII are unique in YEp352; these sites are also unique in YEp351 except for EcoRI and KpnI, which occur twice; (5) recombinant plasmids with DNA inserts in the multiple cloning region of YEp351 and YEp352 can be recognised by loss of β‐galactosidase function in appropriate E. coli hosts; (6) YEp351 and YEp352 contain the yeast LEU2 and URA3 genes, respectively, allowing for selection of these grown under non‐selective conditions indicative of high plasmid copy number. The above properties make the shuttle vectors suitable for constructions of yeast genomic libraries and for cloning of DNA fragments defined by a large number of different restriction sites.The two vectors have been further modified by deletion of the sequences necessary for antunomous replication in yeast. The derivative plasmids YIp651 and YIp352 can therefore be used ti integrate specific sequences into yeast chromosomal DNA.
Cell division age dependency of meiosis in an apomictic variant of Saccharomyces cerevisiae
Authors: Bilinski Carl A. , Marmiroli Nelson , Miller John J. 
Published: May 2005

AbstractThe cell division age dependency of sporulation was investigated in a diploid strain of Saccharomyces cerevisiae (19el) which undergoes a single equational nuclear division during sporulation with consequent formation of asci containing two uninucleate diploid spores (apomictic dyads). Under modified nutritional conditions which partially restore meiosis and hence normal tetrad formation, newly formed (age 0) daughter cells were observed to be capable of formation of apomictic dyads but not of meiotic tetrads. Even under conditions in which only apomictic dyads developed, approximately 20% of the asci resulted from differentiation of newborn ‘inexperienced’ cells. Thus, the data indicated production of at least one bud to be a prerequisite for meiosis but not for apomixis; however, occurrence of at least one complete mitotic cell division cycle was evidently insufficient for the morphogenetic switch from diploid to haploid spore formation, since older cells bearing several bud scars often underwent apomictic dyad development, and some produced no spores.
Sterility (ste) genes of Schizosaccharomyces pombe
Authors: Michael Holger , Gutz Herbert 
Published: May 2005

AbstractIn previous experiments of Girgsdies (1982), eight sterile (ste) mutants of Schizosaccharomyces pombe did not sporulate when fused with h+ or h− protoplasts. We succeeded in achieving sporulation with these mutants. Two hitherto unknown ste genes, ste7 and ste8, were found.
Biochemical estimation of hepatitis B surface antigen in recombinant yeast
Authors: Wingfield Paul T. , Graber Pierre , Payton Mark A. 
Published: May 2005

AbstractPurified recombinant hepatitis B surface antigen separated on polyacrylamide gels in the presence of sodium dodecyl sulphate has a very low staining index with Coomassie blue relative to a number of standard proteins. In contrast the protein stains better than average with silver nitrate. This property has been used to develop a semi‐quantitative method of estimation of recombinant surface antigen in extracts of Saccharomyces cerevisiae producing this protein. The method can be used to follow purification protocols. It is quick, simple and since it measures the surface antigen biochemically, is independent of the aggregation state or conformation of the protein, a factor which can affect enzyme‐linked immunoassays which rely on antigen–antibody interactions.
Artifactual immunofluorescent labelling in yeast, demonstrated by affinity purification of antibody
Authors: Lillie S. H. , Brown S. S. 
Published: May 2005

AbstractIn the course of making antibodies against various yeast (S. cerevisiae) proteins, we have noted that it is common to observe reactivity of rabbit sera with a number of extraneous bands on Western transfers of yeast proteins. The pattern of reactive bands can change within a period of weeks, even when the rabbit has not been injected with antigen. A simple method of affinity purification, using antigen bound to nitrocellulose, is employed to remove the reactivity with these extraneous bands from immune sera. The importance of affinity purification is demonstrated by our attempts to immunolocalize a 55 kd yeast protein (p55). Immune serum stains yeast cells to give a striking pattern of spots and blotches not seen with preimmune serum. However, affinity purification of anti‐p55 antibody shows that this pattern is not due to staining by anti‐p55 antibody; rather the pattern is due to staining left in the serum depleted of anti‐p55 antibody.
Specificity of DNA uptake during whole cell transformation of S. cerevisiae
Authors: Bruschi Carlo V. , Comer Allen R. , Howe Gregg A. 
Published: May 2005

AbstractWe have studied the mechanism of DNA transformation of whole yeast cells in Saccharomyces cerevisiae with particular emphasis on the role of the cell wall complex in DNA uptake. Two new aspects of the process have been investigated in order to evaluated its specificity. Such aspects are: (i) effect of monovalent vs. divalent cations during incubation with the transforming DNA and (ii) timing of DNA adsorption and uptake. We found that the specificity for cation requirement is a strain‐dependent characteristic influenced by the presence of transforming DNA in the cell suspension. This finding is supported by reports from several laboratories that some yeast strains show mutually exclusive transformability with monovalent vs. divalent cations. While irreversible adsorption of plasmid DNA molecules is induced by both heat shock and polyethylene‐glycol(PEG), DNA uptake seems to occur only after the removal of PEG. In the course of this study we have developed a new, alternative method of whole cell DNA transformation with CaCl2 able to transform strains that do not respond to other methods.
Expression of two Trichoderma reesei endoglucanases in the yeast Saccharomyces cerevisiae
Authors: Panttilä Merja E. , André Lars , Saloheimo Markku , Lehtovaara Päivi , Knowles Jonathan K. C. 
Published: May 2005

AbstractThe cDNA copies of the two endo‐β‐1,4‐glucanase genes, egl1 and egl3, from the filamentous fungus Trichoderma reesei were expressed in yeast Saccharomyces cerevisiae under the control of the yeast phosphoglycerate kinase gene promoter. Active EGI and EGIII enzyme was produced and secreted by yeast into the growth medium. The recombinant EGI enzyme was larger and more heterogeneous in size than the native enzyme secreted by Trichoderma, due to differences in the extent of N‐glycosylation between these two organisms. The morphology of the yeast cells producing EGI or EGIII was clearly different from control strain.
Purification of isocitrate lyase from Saccharomyces cerevisiae
Authors: Lopez‐Boado Yolanda S. , Herrero Pilar , Fernandez Maria‐Teresa , Fernandez Rose , Moreno Fernando 
Published: May 2005

AbstractIsocitrate lyase purified to homogeneity from Saccharomyces cerevisiae was composed of four identical subunits with a molecular mass 75 K Da. The enzyme was most active at pH 7.0 in the presence of 5 mM‐Mg2+. The Km value for threo‐Ds‐isocitrate was 1.4 mM. Isocitrate lyase was shown to be thermostable at 50°C for 60 min at a high salt concentration, but rapidly lost activity at −20°C or by dialysis.
Physiological and biochemical analysis of cytochrome P‐450 in the yeast Schizosaccharomyces pombe
Authors: Bligh H. F. J. , Kelly S. L. 
Published: May 2005

AbstractThe yeast Schizosacchromyces pombe has been shown to contain a microsomal cytochrome P‐450 (cyt. P‐450) inducible under conditions of glucose repression. Under these conditions the enzyme has maximal expression of 0.43 nmol g−1 wet wt at the end of the exponential phase of growth. Substrate and inhibitor affinity was examined using studies of spectral changes on binding and revealed a type II spectrum with ketoconazole (Ks = 23 μM) and a type I spectrum with benzo(a)pyrene (Ks = 77 μM). A Km of 112 μM was found in the aryl hydrocarbon hydroxylas assay. These properties show broad comparability with the cyt. P‐450 of Saccharomyces cerevisiae.
Metabolism of 2,3‐butanediol in yeasts
Authors: Verduyn Cornelis , Breedveld Guido J. , Scheffers W. Alexander , Van Dijken Hohannes P. 
Published: May 2005

AbstractThe biochemistry and physiology of 2,3‐butanediol metabolism has been studied in a number of selected yeast species. Candida utilis CBS 621 exhibited diauxic growth on 2,3‐butanediol. The first phase was characterized bu the utilization of the two optically active stereoisomers and associated accumulatoin. In the second phase of growth the meso‐form of 2,3‐butanediol was utilized together with acetoin. An attempt is made to explain these phenomena on the basis of the substrate specificity of the two enzymes which oxidize 2,3‐butanediol in C. utilis. Although whole cells oxidized acetoin and diacetyl at high rates, attempts to identify the enzymes responsible for these oxidations were unsuccessful. In C. utilis and other yeasts metabolism of 2,3‐butanediol probably involves a cleavage of the substrate into C2‐units which are assimilated by the glyoxylate cycle. In the few yeasts which have been found to grow on 2,3‐butanediol differences may be encountered with respect to the substrate specificity for the three stereoisomers of 2,3‐butanediol. For example, Candida salmanticensis CBS 5121 showed no diauxis growth and utilized only two of three stereomers.