Showing papers by "DSM published in 1993"

Evidence for general instability of past climate from a 250-kyr ice-core record

Abstract: RECENT results1,2 from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper3) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record4, in agreement with other land-based observations5,6. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.

Correlations between climate records from North Atlantic sediments and Greenland ice

Abstract: OXYGEN isotope measurements in Greenland ice demonstrate that a series of rapid warm-cold oscillations—called Dansgaard–Oeschger events—punctuated the last glaciation1. Here we present records of sea surface temperature from North Atlantic sediments spanning the past 90 kyr which contain a series of rapid temperature oscillations closely matching those in the ice-core record, confirming predictions that the ocean must bear the imprint of the Dansgaard–Oeschger events2,3. Moreover, we show that between 20 and 80 kyr ago, the shifts in ocean-atmosphere temperature are bundled into cooling cycles, lasting on average 10 to 15 kyr, with asymmetrical saw-tooth shapes. Each cycle culminated in an enormous discharge of icebergs into the North Atlantic (a 'Hein-rich event'4,5), followed by an abrupt shift to a warmer climate. These cycles document a previously unrecognized link between ice sheet behaviour and ocean–atmosphere temperature changes. An important question that remains to be resolved is whether the cycles are driven by external factors, such as orbital forcing, or by inter-nal ice-sheet dynamics.

Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores

Abstract: RECENT results1,2 from the Greenland Ice-core Project (GRIP) Summit ice core suggest that the climate in Greenland has been remarkably stable during the Holocene, but was extremely unstable for the time period represented by the rest of the core, spanning the last two glaciations and the intervening Eemian inter-glacial. Here we present the complete oxygen isotope record for the Greenland Ice Sheet Project 2 (GISP2) core, drilled 28 km west of the GRIP core. We observe large, rapid climate fluctuations throughout the last glacial period, which closely match those reported for the GRIP core. However, in the bottom 10% of the cores, spanning the Eemian interglacial and the previous glacia-tion, there are significant differences between the two records. It is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores. Considerable further work will be necessary to evaluate the likelihood of this, and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores.

Poly(propylene imine) Dendrimers: Large‐Scale Synthesis by Hetereogeneously Catalyzed Hydrogenations

Abstract: In kilogram quantities; pure poly(propylene imine) dendrimers can be prepared in an extremely simple reaction sequence comprising Michael addition (primary amines to acrylonitrile) and heterogeneous hydrogenation with a Raney cobalt catalyst. Both steps proceed quantitatively and selectively and can be employed with many core and end groups.

Extending the Vostok ice-core record of palaeoclimate to the penultimate glacial period

Abstract: The ice-core record of local temperature, dust accumulation and air composition at Vostok station, Antarctica, now extends back to the penultimate glacial period (∼140–200 kyr ago) and the end of the preceding interglacial. This yields a new glaciological timescale for the whole record, which is consistent with ocean records. Temperatures at Vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one. Concentrations of CO2 and CH4 correlate well with temperature throughout the record.

Structures of peptides from alpha-amino acids methylated at the alpha-carbon.

Abstract: The structural preferences of peptides (and depsipeptides) from the achiral MeAib and Hib residues, and the chiral Iva, (alpha Me) Val, (alpha Me) Leu, and (alpha Me) Phe residues, as determined by conformational energy computations, x-ray diffraction analyses, and 1H-nmr and spectroscopic studies, are reviewed and compared with literature data on Aib-containing peptides. The results obtained indicate that helical structures are preferentially adopted by peptides rich in these alpha-amino acids methylated at the alpha-carbon. Intriguing experimental findings on the impact of the chirality of Iva, (alpha Me) Val, and (alpha Me) Phe residues on helix screw sense are illustrated.

Recent Results on the Biology of Hodgkin and Reed-Sternberg cells: II. Continuous Cell Lines

Abstract: The relative scarcity of Hodgkin (H) and Reed-Sternberg (RS) cells within biopsies from cases with Hodgkin's disease (HD) is an impediment to the analysis of the nature and function of these cells. Continuous cell lines as uniform and permanently available sources of cells provide a valid alternative. Development of HD cell lines has proven to be rather difficult when compared with the results on leukemia and Non-Hodgkin lymphoma cells. Only a few cell lines containing cells that resemble in-vivo H-RS cells have been established. Because the in-vitro culture conditions favor the self-propagation of residual normal cells, e.g. Epstein-Barr virus transformed B-lymphoblastoid cells or monocyte/macrophage monolayers, early attempts at culturing HD tissue resulted mainly in the generation of such cell lines. Even for the bona fide HD cell lines it is difficult to prove that the immortalized cells originated from an H-RS cell. These 13 HD cell lines have been extensively characterized in a large variety of aspects. These data have resulted in widely varying conclusions about the nature of the cell lines. It is apparent that all HD cell lines are unique among hematopoietic cell lines and are also different from one another. No conclusive evidence towards the origin of the cells has been obtained for some cell lines, while others could be operationally, albeit not always unequivocally, assigned to the T- or B-cell or monocyte-macrophage lineages. The overall phenotypes are often not concordant with those of normal hematopoietic cells; some cell lines show clearly mixed lineage attributes. The artifactual expansion of non-HRS cells in culture and the acquisition or loss of certain properties during the adaptation to culture systems cannot be excluded. There was also a bias for the establishment of cell lines from cases with advanced clinical stages, nodular sclerosing subtype and pleural effusions. The extensive analysis of a few cell lines has provided a wealth of information useful for the understanding of the biology of H-RS cells. The striking heterogeneity could be reflective of a biologically heterogeneous disease.

The Pearson product‐moment correlation coefficient is better suited for identification of DNA fingerprint profiles than band matching algorithms

Abstract: A database of DNA fingerprint profiles from permanently established human and animal cell lines was prepared with a computer program originally designed for numerical taxonomy of bacteria. Identifications of cell line DNA profiles were performed, both by the Pearson product-moment correlation coefficient and by band matching. Under the conditions used the Pearson product-moment correlation coefficient was consistently more reliable.

Dendritic macromolecule and the preparation thereof

Abstract: The invention relates to a dendritic macromolecule, comprising a core and branches emanating from the core, characterised in that the branches are prepared from vinyl cyanide units. The invention also relates to a process with which the dendritic macromolecule according to the invention can be prepared. The dendritic macromolecules according to the invention are not sensitive to degradation through hydrolysis reactions and are also very stable at a high temperature. The process is very suitable for use on a large scale and the synthesized intermediates do not have to be isolated.

Acute myeloid leukemias expressing lymphoid-associated antigens: diagnostic incidence and prognostic significance.

Abstract: A portion of patients with acute myeloid leukemia also display surface antigens associated with lymphoid development (Ly+AML). The incidence of Ly+AML varies considerably between independent studies, both overall and with regard to individual antigens. On average, lymphoid-associated antigen expression is relatively low in AML. The reasons for some striking differences between conflicting reports are not clear, but are most probably due to various technical aspects including several arbitrary parameters. The data accumulated from the literature lead to the following conclusions: (i) use of different reagents against the CD surface antigens, different positive/negative cut-off levels, analysis of fresh or frozen cell material and variable sensitivities of the analytical instruments (expression of lymphoid-associated antigens was commonly weaker than myeloid-associated markers) seriously influence the results; (ii) most antigens (CD1, CD2, CD3, CD5, CD8, CD10, CD19, CD20, CD21, CD22) were expressed on less than 10% of AML cases; (iii) the CD4 and CD7 antigens, also found on normal monocytic and immature myeloid progenitor cells, were detected in 24% and 15% of AML cases, and their expression correlated with FAB M4/M5 and M1/M2 morphology, respectively; (iv) differences between pediatric and adult Ly+AML were restricted to CD4 and CD19 expression being detected more often in childhood cases; (v) there is no cytogenetic anomaly specific for Ly+AML; anomalies exclusively associated with lymphoid malignancies were not seen; aberrations involving 11q23, 14q32, and the 9;22 translocation seem to be increased; (vi) in most studies, expression of lymphoid-associated antigens (with the exception of CD7) on AML blasts lacked prognostic significance; CD7+AML appears to be a particular subset of malignant myeloid progenitors. In summary, these findings suggest that in general, Ly+AML may not represent a biologically distinct form of leukemia as these cases have similar clinical features and respond to therapy in a comparable manner.

Past Accumulation rates derived from observed annual layers in the GRIP ice core from Summit, Central Greenland

Abstract: Based on dated reference horizons down to 1623 m an ice flow model has been developed. The model is used to reconstruct past accumulation rates from the sequences of detected annual layers in the upper 2321 m of the 3029 m deep GRIP ice core. Comparison of these past time accumulation rates with the corresponding δ 18O values show a strong correlation. This relationship can be used in a non steady state flow model, in which past accumulation rates, deduced from the continuous δ 18O record, are used to model a time scale. The hereby determined time scale and the modelled annual layers compare well with the observed data.

Enzymatic resolution of α,α-disubstituted α-amino acid esters and amides

Abstract: The scope and limitations of the enzymatic resolution of α,α-disubstituted α-amino acid amides by an amino acid amidase from Mycobacterium neoaurum and of the corresponding ethyl esteis with Pig liver estetase (PLE) have been studied. Moderate enantiomeric excesses were obtained with PLE, with only a narrow substrate specificity. Mycobacterium neoaurum on the contrary yields a broad range of S-α,α-disubstituted α-amino acids 1 and the corresponding R-amides 2.

Indenyl compounds and catalyst components for the polymerization of olefins.

Abstract: The invention relates to an indenyl compound of the general formula: R'Ind-M-(Cp)Qk in which the symbols have the following meanings: Ind: an indenyl group, R': a substituent, other than hydrogen, to the Ind group, Cp: a cyclopendadienyl group, M: a transition metal from group 3, 4, 5 or 6 of the Periodic System of Elements, Q: a ligand to M and k is an integer linked to the valence of M The invention is characterized in that the R' group is bound to the Ind group at the 2-position The indenyl compound is a catalyst component for the polymerization of olefins The invention also relates to polymers obtainable with such indenyl compounds

Critical Behaviour of Lyotropic Liquid Crystals

Abstract: The occurrence of a critical point in lyotropic smectic liquid crystal is experimentally evidenced by neutron and X-ray small-angle scattering experiments. In the vicinity of the critical point in the (c-T) phase diagram of a true binary system, we observe: 1) broadening of the Bragg peak of the coexisting lamellar phases; 2) strong scattering at small angle where the concentration and periodicity difference between the two phases (Lα) in equilibrium vanishes. First approximate values of the critical exponents are given.

Lignin peroxidase L3 from Phlebia radiata. Pre-steady-state and steady-state studies with veratryl alcohol and a non-phenolic lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol.

Abstract: The catalytic cycle of lignin peroxidase (LiP, ligninase) isozyme L3 from the white-rot fungus Phlebia radiata was investigated using stopped-flow techniques. Veratryl (3,4-dimethoxybenzyl) alchol and a lignin model compound, non-phenolic β-O-4 dimer 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol, were used as electron donors. This is the first report on the detailed kinetic analysis of a LiP-catalysed Cα-Cβ bond cleavage of the dimer, representing the major depolymerisation reaction in the lignin polymer. The native enzxyme showed a typical heme peroxidase absorbance spectrum with a Soret maximum at 407 nm. Following the reaction with H2O2, the Soret band decreased in absorbance, shifted to 403 nm and then to 421 nm, demonstrating the formation of compound I followed by the formation of compound II, respectively. Similar results have been reported for the LiP from Phanerochaete chrysosporium upon reaction with H2O2. However, compound I of L3 was more stable in the absence of additional electron donors. thesecond-order rate constant of compound I formation by H2O2was determined to be 6X105 M−1 s−1 and was the same at pH 3.0 and 6.0. Compound I was rapidly reduced to compound II and further to native enzyme when either veratryl alcohol or the β-O-4 dimer was supplied as electron donor and in both cases veratraldehyde appeared as the major product. At pH 6.0, the second-order rate constant for compound II formation was similar with either veratryl alcohol or the β-O-4 dimer (6.7 × 103 and 6.5 × 103 M−1 s−1, respectively). At pH 3.0 formation of compound II with either reductant proceeded so rapidly that determination of the respective rate constants was not possible. The results point to identical catalytic cycles of L3 with veratryl alcohol or the β-O-4 dimer involing both compounds I and II as intermediates and participation of the same veratryl alcohol radical as the most appropriate reductant for compound II. Chemical evidence of such a radical, formed after the initial LiP-catalysed one-electron oxidation of β-O-4 dimeric lignin models, is presented in a separate article [Lundell, T., Schoemaker, H., Hatakka, A & Brunow, G. (1993) Holzforschung, in the press]. The catalytic redox-cycle and the oxidation mechanism presented here reconcile seemingly contradictory results obtaind in previous studies on LiP kinetics during the last decade.

Method for the preparation of feed pellets

Abstract: The present invention discloses a method for obtaining feed pellets. The method comprises the addition of active ingredients to feed pellets after the pellets have been extruded. The method further comprises the addition of a solution or suspension of the desired feed or ingredient in a water or oil phase to the pellets under reduced pressure and subsequently increasing the pressure. The method results in pellets with a high degree of loading and in which the active ingredients are homogeneously distributed.

Terminal deoxynucleotidyl transferase (TdT) expression in acute myeloid leukemia.

Abstract: Terminal deoxynucleotidyl transferase (TdT) was initially considered as a marker of immature lymphoid cells, but many studies have since provided conclusive evidence for the existence of TdT+ cases of acute myeloid leukemia (AML). The reported incidence of TdT+ AML cases varies largely (from 0% to 55%, average of combined data of the literature 18%, children 19%, and adults 21%) suggesting interlaboratory differences in the types of AML examined, the sensitivity of the method used, and the percentage of positive blasts taken as cut-off value. Significantly higher frequencies of TdT+ AML were reported in studies employing immunocytochemical staining (alkaline phosphatase anti-alkaline phosphatase or immunoperoxidase) than in series using immunofluorescence microscopy or biochemical assays. Statistical analysis of various cut-off levels demonstrates an inverse correlation between cut-off point and incidence. The combined data show that TdT-positivity is more common in the immature cell types (M0, M1), with no correlation with age or sex. Except for contested suggestions of an association with t(6;9) and t(8;21), no clear relationship between karyotype and TdT status has been documented. Although an association between T-cell receptor or immunoglobulin gene rearrangements and expression of TdT in AML was postulated, subsequent studies could not demonstrate this correlation. There was no significant relationship with other immunophenotypic markers except for CD34 positivity suggesting that the TdT+ cells represent an immature population. The percentage of positive cells was usually lower in AML than in ALL; in most cases only a subpopulation of the AML cells was TdT+. Thus, TdT could be viewed as a marker of hematopoietic immaturity. In about one-half of the studies on adults, TdT expression was reported to indicate a poor prognosis; others did not find any prognostic difference between TdT+ and TdT- AML cases. No correlation between TdT-positivity and prognosis was found in childhood AML.

Introduction of amine groups on poly(ethylene) by plasma immobilization of a preadsorbed layer of decylamine hydrochloride

Abstract: In order to introduce amine groups on poly(ethylene) (PE) surfaces, PE surfaces were preadsorbed with decylamine hydrochloride (DA.HCl) and subsequently treated with an argon plasma. It was shown by XPS (X-ray Photoelectron Spectroscopy), that approximately half of the preadsorbed (mono)layer was immobilized and that a substantial part (60-70%) of the incorporated nitrogen containing groups were amine groups. The availability of the surface amine groups for reactions was investigated by applying a gas phase reaction with 4-trifluoromethylbenzaldehyde and by a reductive methylation reaction in aqueous solution with 14C formaldehyde. A maximal number of reactive amine groups was found after a plasma treatment time of 2 s. The reductive methylation reaction was used to estimate the surface concentration of amine groups resulting in a typical surface concentration of 1 x 10-6 mol/m2 after a plasma treatment time of 2 s.

Atomic-force microscopy of gel-drawn ultrahigh-molecular-weight polyethylene

Abstract: Gel-drawn ultrahigh molecular weight polyethylene was studied by atomic force microscopy (AFM). Three-dimensional surface profiles were recorded for tapes drawn to different extents. AFM images allowed the discrimination of different well-defined levels of the fibrillar morphology: (i) bundles of microfibrils with a diameter between 4 and 7 μm strongly depending on the elongation; (ii) microfibrils with a diameter between 0.2 and 1.2 nm which also decreased with increasing draw ratio; (iii) nanofibrils which form the elementary fibrillar building blocks; and (iv) regular chain patterns on the molecular level which correspond to the crystalline packing of polyethylene chains at the surface of the nanofibrils. The nanofibrils were formed during the initial conversion of lamellae to fibrillar crystallites and did not change considerably in diameter up to draw ratios of λ = 70.