Showing papers by "VU University Amsterdam published in 1978"

A perturbation theory approach to relativistic calculations

Abstract: In this paper a perturbative procedure for the calculation of relativistic effects is proposed, that consistently treats all first-order terms, including relativistic changes of the electronic potential. The results of test calculations on some fifth row elements are compared with full relativistic Dirac-Fock-Slater treatments of the same systems. Both orbital energies and the first order changes in the wave functions are calculated.

Population differentiation and germination ecology in Stellaria media (L.) Vill.

Abstract: Population differentiation in Stellaria media was studied with regard to life-cycle strategy and germination ecology. Two populations were identified in the study area, growing side by side, W1 and W2. The life-span of population W1 is much shorter than that of population W2, especially under summer conditions: 1–2 months versus 4–6 months; the time to flowering differs accordingly. Germination properties of seed produced under summer, winter, and field conditions were studied. Fresh seeds produced at 20° C showed good germination (ca. 75%) over a broad range of temperatures in the case of population W1, but seeds of population W2 showed appreciable germination only at high temperatures (ca. 30%). Seeds produced at 7° C showed very little (population W2) or no germination at all (population W1). To simulate seasonal changes in temperature, a “comprehensive” germination scheme was developed which enabled the response of hydrated seeds to two temperature cycles (cold-warm-cold and warm-cold-warm) to be tested. The two populations reacted differently. At the end of the cycles, only a few seeds of population W1, but about half of the seeds of population W2, remained dormant. The data obtained were used to study the effects of differential germination ecology on the dynamics of the two populations. In a reconstruction of the courses of development, the populations were shown to possess different strategies. Population W1 builds up a uniform seed stock, and population W2 a phenotypically diverse seed reserve. The implications for population dynamics are discussed.

The fine structure of decalcified cartilage and bone: A comparison between decalcification procedures performed before and after embedding

Abstract: The ultrastructure of calcifying cartilage and bone has been examined under the electron microscope after using three different methods of decalcification. The first was carried out before embedding (by soaking specimens in EDTA or formic acid), the second after embedding (by floating ultrathin sections on formic acid), and the third after embedding (by soaking embedded specimens in EDTA or formic acid), and with later re-embedding. The first procedure invariably induces drastic changes in the fine structure of the cells and calcified matrix, probably as a results of the extraction of organic material along with extraction of mineral. The second and third procedures make it possible to preserve ultrastructural details perfectly in both cells and calcified matrix. Of the two, the third procedure is preferable because of its greater simplicity. In areas that are still calcifying, these post-embedding decalcification techniques reveal the presence of crystal-associated, filamentous organic structures which are not recognizable in specimens decalcified before embedding. These structures, which could have a key role in inducing and regulating crystal formation and growth, are less evident in fully calcified areas (but not at their borders). This may partly be due to the loss of glycan components in the matrix during calcification. The most important determinant, however, seems to be the fact that during calcification the components of the matrix, including collagen fibrils, are involved in an aggregation process which reduces the amounts of free chemical groups available for reaction with the stain solution. Because post-embedding decalcification does not disturb this state of aggregation, the stainability of the matrix and the electron microscopic evidence of its components remain very low.

Das Energieprofil des o‐Chinodimethan‐Benzocyclobuten‐Gleichgewichtes

Abstract: Durch Verbrennungskalorimetrie wird die Bildungsenthalpie des Benzocyclobutens (2) zu ΔH (g) = 199.4 kJ mol−1 (47.7 kcal mol−1) bestimmt. Aus der Kinetik der Reaktion von 2 mit Maleinsaure-anhydrid (MSA) ergeben sich fur die o-Chinodimethanbildung 2 1 Aktivierungsparameter Ea = 166.9 kJ mol−1 (39.9 kcal mol−1), A = 2.8 × 1014 s−1. Die entsprechenden Werte der Ruckreaktion 1 2 werden aus der Dimerisierungsgeschwindigkeit des Benzocyclobutens sowie der durch Blitzlichtphotolyse von 5,6-Dimethylenbicyclo[2.2.1]hept-2-en-7-on (5) ermittelten Geschwindigkeitskonstanten der o-Chinodimethandimerisierung zu Ea = 122.7 kJ mol−1 (29.3 kcal mol−1), A = 2.2 × 1013 s−1, bestimmt. Energy Profile of the o-Quinodimethane-Benzocyclobutene Equilibrium The enthalpy of formation of benzocyclobutene (2) is measured by combustion calorimetry to be ΔH (g) = 199.4 kJ mol−1 (47.7 kcal mol−1). From the kinetics of the reaction of 2 with maleic anhydride the activation parameters for the o-quinodimethane formation 2 1 are obtained: Ea = 166.9 kJ mol−1 (39.9 kcal mol−1), A = 2.8 × 1014 s−1. The corresponding values for the back reaction 1 2 are derived from the dimerisation rate of o-quinodimethane, obtained by flash photolysis of 5,6-dimethylenebicyclo[2.2.1]hept-2-en-7-one (5), and from the dimerisation of benzocyclobutene yielding Ea = 122.7 kJ mol−1 (29.3 kcal mol−1), A = 2.2 × 1013 s−1.

Characterizations of Almost Periodic Strongly Continuous Groups and Semigroups

Abstract: The set of all e-periods for f is denoted by J ( f e). We say that f is almost periodic, written a.p., if for every e >0, the set J(J~e) is relatively dense in ,I1. A subset V of $ is called relatively dense (in $) if there exists an l > 0 such that every subinterval of $ of length I meets V. We call f weakly almost periodic, written w.a.p., if for each x' in the conjugate space X', the function x' of, mapping $ into the complex plane ~, is almost periodic. Continuous a.p. and continuous w.a.p, functions are treated in [1]. Let ~ be a family of functions mapping $ into X. We say that ~ is uniformly

Human serum galactosyltransferase: distinction, separation and product identification of two galactosyltransferase activities.

Abstract: Two different galactosyltransferase activities have been found in normal sera from A and O donors. Galactosyltransferase A incorporated galactose from UDP-Gal into sialic-acid-free ovine submaxillary mucin (asialo-mucin), whereas galactosyltransferase B transferred galactose from UDP-Gal to free N-acetylglucosamine or N-acetylglucosamine-glycoproteins. Specificity, kinetic and stability differences permitted the distinction of the activity of galactosyltransferase A from that of galactosyltransferase B; the only substrate found for galactosyltransferase A was asialo-mucin, whereas galactosyltransferase B showed only low activity towards asialo-mucin and free N-acetyl-galactosamine, but had a main specificity for either free N-acetylglucosamine or N-acetylglucosamine-protein. Galactosyltransferase B was more stable on heat inactivation than galactosyltransferase A; galactosyltransferase B could be separated from galactosyltransferase A by affinity chromatography on N-acetylglucosamine-derivatized agarose. The products of both enzyme activities have been analyzed. The galactosyltransferase A product was cleaved from asialo-mucin by alkaline-borohydride treatment. The acceptor used to identify the galactosyltransferase B product was free N-acetylglucosamine. Periodate oxidation studies performed on the reduced disaccharides indicated the linkage type of the products. The anomeric configuration of the respective galactosyltransferase products were determined with specific galactosidases. Using these methods, galactosyltransferase A was found to form a Galbeta (1 leads to 3)GalNAc-protein linkage and galactosyltransferase B was found to form a Galbeta(1 leads to 4)GlcNAc-linkage.

Optimal Procedures for Estimation of Factor Scores

Abstract: This study identifies three different applications of factor scores which lead to three different sets of criteria for optimal estimation procedures. The regression method and the Bartlett method best satisfy the first two sets of criteria, and a generalized Anderson and Rubin procedure is optimal for the third set of criteria. The differences between the methods have been illustrated by an example.

Quantitative analysis of the protein composition of yeast ribosomes.

Abstract: The molecular weights of the individual yeast ribosomal proteins were determined. The ribosomal proteins from the 40-S subunit have molecular weights ranging from 11 800 to 31 000 (average molecular weight = 21 300). The molecular weights of the 60-S subunit proteins range from 10 000 to 48 400 (average molecular weight = 21 800). Stoichiometric measurements, performed by densitometric scanning on ribosomal proteins extracted from high-salt dissociated subunits revealed that isolated ribosomal subunits contain, besides some protein species occurring in submolar amounts, a number of protein species which are present in multiple copies: S13, S27, L22, L31, L33, L34 and L39. The mass fractions of the ribosomal proteins which were found to be present on isolated ribosomes in non-unimolar amounts, were re-examined by using an isotope dilution technique. Applying this method to proteins extracted from mildely isolated 80-S ribosomes, we found that some protein species such as S32, S34 and L43 still are present in submolar amounts. On the other hand, however, we conclude that some other ribosomal proteins, in particular the strongly acidic proteins L44 and L45 get partially lost during ribosome dissociation. Proteins L44/L45 appears to be present on 80-S ribosomes in three copies.

Occlusive phlebitis, a diagnostic feature in Riedel's thyroiditis

Abstract: Five cases of Riedel's invasive fibrous thyroiditis are presented.-Clinically and histopathologically all cases fulfilled the criteria for this lesion. In both small and large veins there were inflammatory changes and obliteration of the lumen, followed by sclerosis. These changes were found in each operative specimen, and seemed to be a diagnostic feature of invasive fibrous thyroiditis. We consider this change to be an occlusive phlebitis, and have noted that it occurs in association with multifocal fibrosclerosis. Three stages can be recognised: infiltrative, occlusive and sclerotic. In other thyroid lesions such as Hashimoto's thyroiditis, granulomatous thyroiditis of the Quervain type and adenomatous goitre these peculiar changes in the veins were not found.

Occupational eczema from garlic and onion.

Abstract: B.Z., a woman aged 58 years with no allergy history in her family, started to work as a coil winder for telephone exchanges in 1961, where she had contact with hardened epoxy resins. The premises where she worked were adjacent to the place where epoxy resin was hardened with triethylenetetramine. After 3 years in these conditions she developed dermatitis simultaneously on the hands, face and legs. There were many recurrences. The patient does not remember their duration; she stated only that she was more often ill than well. On patch testing in January 1977 she was positive to Epidian 5 (Polish epoxy resin of bisphenol type) and to triethylenetetramine. Although she ceased working in April 1977, the dermatitis did not subside. It was found that the patient was taking aminophylline in various forms since March, mainly as suppositories because of bronchial spasm. All Polish aminophylline preparations contain ethylenediamine (van Hecke 1975, Rudzki & Krajewska 1976). The patient was positive to ethylenediamine (1 % pet.). When she was seen 1 month after discontinuing the aminophylline and 3 months after changing her work, the improvement was considerable, although a mild dermatitis still persisted on the dorsum of her right hand.

Stable factorizations of monic matrix polynomials and stable invariant subspaces

Abstract: The stable factorizations of a monic matrix polynomial are characterized in terms of spectral properties. Proofs are based on the divisibility theory developed by I. Gohberg, P. Lancaster and L. Rodman. A large part of the paper is devoted to a detailed analysis of stable invariant subspaces of a matrix. The results are also used to describe all stable solutions of the operator Riccati equation.

The Amino‐Acid Sequence of Kangaroo Pancreatic Ribonuclease

Abstract: Red kangaroo (Macropus rufus) ribonuclease was isolated from pancreatic tissue by affinity chromatography. The amino acid sequence was determined by automatic sequencing of overlapping large fragments and by analysis of shorter peptides obtained by digestion with a number of proteolytic enzymes. The polypeptide chain consists of 122 amino acid residues. Compared to other ribonucleases, the N-terminal residue and residue 114 are deleted. In other pancreatic ribonucleases position 114 is occupied by a cis proline residue in an external loop at the surface of the molecule. Other remarkable substitutions are the presence of a tyrosine residue at position 123 instead of a serine which forms a hydrogen bond with the pyrimidine ring of a nucleotide substrate, and a number of hydrophobic-hydrophilic interchanges in the sequence 51–55, which forms part of an α-helix in bovine ribonuclease and exhibits few substitutions in the placental mammals. Kangaroo ribonuclease contains no carbohydrate, although the enzyme possesses a recognition site for carbohydrate attachment in the sequence Asn-Val-Thr (62–64). The enzyme differs at about 35–40% of the positions from all other mammalian pancreatic ribonucleases sequenced to date, which is in agreement with the early divergence between the marsupials and the placental mammals. From fragmentary data a tentative sequence of red-necked wallaby (Macropus rufogriseus) pancreatic ribonuclease has been derived. Eight differences with the kangaroo sequence were found.

Pulse compression inside an actively AM mode-locked ND:YAG laser using a liquid Kerr cell

Abstract: A mode-locked Nd:YAG laser capable of generating pulses substantially shorter than the present limit of 30-50 ps, while retaining the stability of active mode locking, would be a useful development. We present here a simplified theoretical analysis and a preliminary experimental verification of the use of an optical Kerr cell as a passive lossless pulse compressor inside a Q -switched and actively mode-locked YAG laser. The theoretical model indicates possible compression to as short as ∼5 ps in a typical low-power Nd:YAG laser. The preliminary experimental results show substantial pulse compression via the predicted mechanism, though still not below ∼30 ps. The technique appears capable, however, of pulse compression to substantially shorter values without the instabilities, statistical fluctuations, or energy losses associated with saturable-absorber mode locking.

Alkali-labile sites and post-irradiation effects in single-stranded DNA induced by H radicals.

Abstract: Single-stranded phiX174 DNA in aqueous solutions has been irradiated in the absence of oxygen, under conditions in which only H radicals react with the DNA. It was shown that H radical reactions result in breaks, which contribute approximately 10 per cent inactivation. Further, two types of alkali-labile sites are formed. One is lethal and gives rise to single-strand breaks by alkali and is most probably identical with post-irradiation heat damage and contributes about 33 per cent to the inactivation mentioned above. The other consists of non-lethal damage, partly dihydropyrimidine derivatives, and is converted to lethal damage by alkali. This follows from experiments in which the DNA was treated with osmium-tetroxide, which oxidizes thymine to 5,6-dihydroxy-dihydrothymine. Treatment with alkali of this DNA gives the same temperature dependence as found for the non-lethal alkali-labile sites in irradiated DNA. A similar temperature dependence is found for dihydrothymine and irradiated pyrimidines with alkali.