Showing papers by "University of Hamburg published in 1980"
TL;DR: In this article, the authors discuss the scope of Ziegler catalysis, stereoselectivity, kinetics, and mechanism of homogeneous Natta catalysts; and side reactions in homogeneous catalysts.
Abstract: Publisher Summary This chapter discusses the scope of Ziegler catalysis; stereoselectivity, kinetics, and mechanism of Ziegler catalysis; homogeneous Ziegler–Natta catalysts; and side reactions in homogeneous catalysts. Ziegler catalysis involves rapid polymerization of ethylene and α-ole-fins with the aid of catalysts based on transition-element compounds, normally formed by the reaction of a transition-element halide or alkoxide or alkyl or aryl derivative with a main-group element alkyl or alkyl halide. There are thousands of patents involving every combination of pure or mixed main-group alkyls with transition-element compounds, each claiming advantages. The result of the early work led to the development of “second-generation” Ziegler catalysts. Polymers produced with unmodified Ziegler catalysts showed extremely high molecular weight and broad distribution, and in some cases, there was evidence for “living polymer.” All homogeneous catalyst systems for ethylene polymerization become heterogeneous when polyethylene is formed. On using vanadium-based homogeneous catalysts, polymers consisting of syndiotactic stereo blocks and stereo-irregular blocks are obtained. Very high stereoselectivity is observed for racemic 4-methyl- 1-hexene and racemic 3,7-dimethyl-1-octene, where the asymmetric carbon atom is in the α-position relative to the double bond. Stereoselectivity is caused by the chirality of the catalytically active center, and not by chiral atoms in the growing chain. It must be concluded from the results that reactions take place, which change the number of active sites present, due to the different behavior of the polymers in solution. Study of these new catalysts is intensive. After a short induction period, the activity of polymerization increases as a function of the monomer concentration.
810 citations
TL;DR: In this article, a well-defined, reparametrization invariant expression for the next to leading term in the small ħ expansion of the euclidean loop Green functional ψ(C ) was derived.
519 citations
TL;DR: In this article, the results of the Joint North Sea Wave Project (JNWP) were reported from a series of measurements made by the meteorological buoy of the University of Hamburg and a pitch-and-roll buoy from the Institute of Oceanographic Sciences.
Abstract: Estimates of the directional wave spectrum obtained from the meteorological buoy of the University of Hamburg and a pitch-and-roll buoy of the Institute of Oceanographic Sciences are reported from a series of measurements made within the framework of the Joint North Sea Wave Project during September 1973. Three main aspects were considered. First, the properties and parameterization of the directional spectrum were studied when the waves were generated by steady winds without any significant swell contribution. The results do not support the parameterization proposed by Mitsuyasu et al. (1975) and are in agreement with a parameterization in which the peak frequency is the relevant scale parameter. Second, comparisons are made between two independent methods of fitting the data exactly by means of a maximum likelihood technique (Long and Hasselmann, 1979) and a least-squares technique. The two methods give very similar fits to the observed data. Finally, the response of the directional wave spectr...
494 citations
TL;DR: In this article, for the n → m amplitude in the multi-Regge limit, the first corrections beyond the leading logarithmic approximation were obtained. But this was for the case where the mass of the vector particle is taken to zero, not only for the approximation of the present paper but also for higher order corrections.
348 citations
TL;DR: Aphidicolin is a more useful reagent than hydroxyurea and thymidine because it does not affect cell viability or "S" phase duration and does not interfere with the synthesis of dNTPs or DNA polymerases.
Abstract: Both the inhibitory effect of aphidicolin on the replicative alpha-polymerase and the reversibility of its action in vivo (Pedrali-Noy & Spadari, 1979, Biochem. Biophys. Res. Commun. 88, 1194-2002) allow the synchronization of cells in culture. Aphidicolin prevents G1 cells from entering the DNA synthetic period, blocks cells in "S" phase, allows G2, M and G1 cells to continue the cell cycle and to accumulate at the G1/S border. Aphidicolin is a more useful reagent than hydroxyurea and thymidine because it does not affect cell viability or "S" phase duration and does not interfere with the synthesis of dNTPs or DNA polymerases. In fact cells exposed to the drug continue to synthesize all three DNA polymerases alpha, beta and gamma as well as all dNTPs which, when the block is removed, are present at levels optimal for DNA initiation and replication. The technique is simple and can be applied to cells growing in suspension or monolayers and allows one to harvest large quantities of synchronized cells.
272 citations
TL;DR: In this article, the possibility of a $p$-wave "equal-spin-pairing" superconducting state is predicted in itinerant ferromagnets, where the pairing interaction is mediated by the exchange of longitudinal spin fluctuations, and the resulting state is analogous to the $A1$ phase of superfluid $^{3}He$.
Abstract: The possibility of a $p$-wave "equal-spin-pairing" superconducting state is predicted in itinerant ferromagnets. The pairing interaction is mediated by the exchange of longitudinal spin fluctuations, and the resulting state is analogous to the $A1$ phase of superfluid $^{3}\mathrm{He}$. We describe the system in terms of a Hubbard-type exchange interaction constant $\overline{I}$ and a Stoner enhancement factor $S={(1\ensuremath{-}\overline{I})}^{\ensuremath{-}1}$. As $\overline{I}$ is varied and the ferromagnetic transition is approached from either the ferromagnetic or paramagnetic side, the $p$-state transition temperature goes through a maximum and then falls to zero. Rough calculations of the transition temperature indicate that this state should be observable in very clean samples of weak itinerant ferromagnets at currently attainable temperatures. Applications to Zr${\mathrm{Zn}}_{2}$ and Ni are discussed.
254 citations
TL;DR: In this paper, the authors analyzed two hundred and seventy five cases of cystadenolymphomas (CAL) from the files of the Salivary Glands Register of the Institute of Pathology, University of Hamburg (1965-1979).
Abstract: Cystadenolymphomas (CAL) of the parotid gland are variable in their epithelial differentiation and the ratio of the epithelial tumor component to lymphoid stroma. Two hundred and seventy five cases of CAL from the files of the Salivary Glands Register of the Institute of Pathology, University of Hamburg (1965-1979) were analysed. Their pathogenesis from parenchyma included in regional lymph nodes is discussed. The following subclassification was established. 1. Depending on to the ratio of epithelial tumor component to lymphoid stroma, three subtypes were distinguished. Subtype 1, "typical CAL" with an epithelial tumor component of 50%, amounted to 77% of all cases of CAL studied. Oncocytic differentiation and focal metaplasia to goblet cells or squamous epithelium was also found. 13.5% of CAL were classified as subtype 2, "stroma-poor CAL" with an epithelial tumor component of 70 to 80%. The tumor structure was similar to that of an oncocytoma in places. Two per cent of the CAL were in subtype 3, "stroma-rich CAL" with an epithelial tumor component of only 20 to 30%. Subtype 3 was found solely in men. The average age at presentation (61 years) was slightly lower than that of all the cases studied (65 years). 2. In 7.5% of the cases large areas of squamous cell metaplasia and regressive changes was found within a CAL. These cases were classified as subtype 4 ("metaplastic CAL"). The average age was 67 years. The case histories showed that 20% of these metaplastic CAL had previously been irradiated. 3. Bilateral CAL was found in 7.5% of the cases. In 4% multifocal CAL occurred in the parotid gland unilaterally. Recurrences were observed in 2% of all CAL. 4. Carcinoma in CAL is rare (we found two cases in our own material). In 50% of all cases reported radiotherapy was mentioned in the case histories. 5. Malignant tumors coincident with CAL were recorded in 3% of the cases. 6. The lymphoid stroma showed reaction patterns similar to those of the regional lymph nodes. These included granulomatous changes (foreign body granuloma with cholesterol deposits, tuberculosis) and tumor metastases. In the neighborhood of oncocytic tumor epithelium focal accumulations plasma cells forming IgA and IgG were found. Metaplasia to squamous epithelium is believed to be caused by circulatory disturbances, irradiation, and other noxae. In the differential diagnosis of the stroma-poor subtype 2, oncocytoma and cystic sialadenoma must be excluded, and in the differential diagnosis of subtype 4 (the metaplastic CAL), sebaceous adenoma, mucepidermoid tumor, squamous cell carcinoma, lymphoepithelioma, and other non-tumorous lesions of the parotid gland (lymphoepithelial cysts, myoepithelial parotitis) must be ruled out. Our findings suggest that CAL develops from parenchyma included in parotid lymph nodes with the oncocytic ductal epithelium representing the neoplastic component.
199 citations
TL;DR: In this paper, the topological distribution of charged and neutral hadrons from the reaction e+e− → multihadrons is studied at √s of about 30 GeV, and an excess of planar events is observed at a rate which cannot be explained by statistical fluctuations in the standard two-jet process.
173 citations
TL;DR: The astrocytes in the eye of the monkey and the cat may be considered as a special glia for the axons of ganglion cells because of their intimate morphological relationship to axon bundles of the nerve fibre layer and the intraocular portion of the optic nerve.
Abstract: The neuroglia in the retina and the intraocular portion of the optic nerve of the monkey and cat has been examined by light and electron microscopy. In the retina two types of macroglial cells can be distinguished: 1) Muller cells, and 2) astrocytes. The bipolar radial glial cells of Muller penetrate the entire thickness of the retina and their basal processes align in the nerve fibre layer to form septa that fasciculate the axons of the ganglion cells. In contrast to the Muller cells, the retinal astrocytes are not homogeneously distributed throughout the retina; their number correlates with the thickness of the nerve fibre layer. The processes of the astrocytes are confined to the ganglion cell layer and to the nerve fibre layer. In the latter, the astrocytic processes run parallel to and between the axons of a given nerve fibre bundle. According to cytological criteria, the retinal astrocytes are protoplasmic. In the intraocular portion of the optic nerve, however, the astrocytes are fibrous and their processes run perpendicular to the axon bundles of the prelaminar portion of the optic nerve. Thus, because of their intimate morphological relationship to axons of the nerve fibre layer and the intraocular portion of the optic nerve, the astrocytes in the eye of the monkey and the cat may be considered as a special glia for the axons of ganglion cells.
159 citations
TL;DR: The results indicate that the most important parameter determining the "target tropism" of Moloney leukemia virus infection and expression is the stage of embryogenesis and cellular differentiation at which virus infection takes place and may also lead to cellular dysfunctions other than leukemic transformation.
151 citations
TL;DR: Four major ALDH isozymes have been identified in human tissues using starch gel electrophoresis and isoelectric focusing andKinetic characteristics of ALDH I and II were found to be quite similar to ALDH enzyme 2 and enzyme 1 described earlier by Greenfield and Pietruszko.
TL;DR: It is concluded that papillary epithelial hyperplasia is probably only indicative of early duct obstruction and/or a general neoplastic stimulus, intraductal epithelial proliferation with atypia is a true precursor of duct carcinoma, and chronic pancreatitis lacks atypical duct lesions.
Abstract: In 21 patients who had undergone total pancreatectomy for pancreatic head carcinoma, the uninvolved pancreas was examined with regard to the type, incidence and regional distribution of duct epithelial proliferation. The results were compared with those in 37 operative specimens from patients with chronic pancreatitis, in 46 normal pancreases from autopsies and with findings in experimental pancreatic carcinogenesis. While the incidence of squamous metaplasia and non-papillary epithelial hypertrophy varied little in the different groups, papillary epithelial hyperplasia was found three times more often in cases of carcinoma, with associated mild duct obstruction. Atypical epithelial proliferation was only detected in the vicinity of carcinomas. Unequivocal transition from papillary hyperplasia to atypical proliferation was not observed. In hamsters treated with dihydroxy-di-n-propylnitrosamine (DHPN) for induction of pancreatic duct carcinomas, the early duct lesions closely resembled atypical epithelial proliferation of human pancreas. It is concluded that (1) papillary epithelial hyperplasia is probably only indicative of early duct obstruction and/or a general neoplastic stimulus, (2) intraductal epithelial proliferation with atypia is a true precursor of duct carcinoma, and (3) chronic pancreatitis lacks atypical duct lesions.
TL;DR: In this paper, a large number of seawater and sediment pore water samples from a wide variety of environments and locations were analyzed using electrodialysis and two forms of liquid chromatography.
TL;DR: There were important differences in the distribution of these keratin antigens in altered epithelia which may be of value in the differential diagnosis of inflammatory, premalignant and malignant lesions of the skin and oral mucosa.
Abstract: Immune sera against total keratin and keratin polypeptide subunits were induced in guinea pigs, using the different bands of SDS polyacrylamide gel electrophoresis of fibrous proteins of stratum corneum, derived from normal human epidermis. The distribution of the different polypeptides was studied in numerous human biopsies of normal epidermis, normal oral mucosa and epidermal and mucosal inflammatory, premalignant and malignant lesions using the indirect immunoperoxidase method. Antisera against total keratin (TK) and against the keratin polypeptide of M.W. 55,000 dalton (55K) labelled all keratinocytes in normal and pathological conditions. These antisera may be useful for the histodifferentiation in diagnostic pathology. Atisera against the keratin polypeptides of M.W. 67,000 (67K) and 62,000 dalton (62K) identified only keratin antigens in the spinous, granular and keratinized layer of normal epidermis and oral mucosa. No labelling of the basal layer was achieved with these immune sera. However, there were important differences in the distribution of these keratin antigens in altered epithelia which may be of value in the differential diagnosis of inflammatory, premalignant and malignant lesions of the skin and oral mucosa.
TL;DR: In this article, the authors analyse the recent high energy e+e− data from PETRA in the context of QCD, taking into account single and double gluon bremsstrahlung, the weak decays of the bottom and charm quarks, and the Q2-dependence of the fragmentation functions in the spirit of qCD.
TL;DR: Evidence is presented that apparently identical viral genomes show differences in spontaneous virus activation and that defective viral genomes can be carried in the germ line of mice.
Abstract: Endogenous avian1–3 and murine4–9 C-type viruses are genetic elements which are transmitted at several distinct chromosomal loci. Different patterns of virus activation have been observed in a variety of different mouse strains10–12. However, because there are multiple copies of closely related endogenous viruses in every mouse strain, the genetic basis of the differential expression of these genes is poorly understood. A new substrain of mice, BALB/Mo, was derived previously13 carrying the exogenous Moloney leukaemia virus (M-MuLV) genome on chromosome 6 (ref. 14). Virus activation occurs in lymphatic tissues of all BALB/Mo mice soon after birth12. We report here the derivation of three new substrains of mice each carrying a single M-MuLV genome on different chromosomal integration sites. Each locus was associated with a distinct phenotype of virus expression. Evidence is presented that apparently identical viral genomes show differences in spontaneous virus activation and that defective viral genomes can be carried in the germ line of mice.
TL;DR: In this paper, multilayer mirrors have been fabricated for various angles of incidence throughout the wavelength range λ=1.5-160 A. Reflectivity increases by more than a factor 103 over the best single-film reflectors have been obtained.
Abstract: Multilayer mirrors have been fabricated for various angles of incidence throughout the wavelength range λ=1.5–160 A. Reflectivity increases by more than a factor 103 over the best single‐film reflectors have been obtained. Measured reflectivities are around 10% near normal incidence in the λ=45–160‐A wavelength region and above 50% near grazing incidence (grazing angle 1°–2°) for λ=1.54 A. The required thickness control has been achieved by monitoring the reflectivity of the films in situ during the deposition.
TL;DR: In this paper, a sufficient condition for confinement of static quarks by a vortex condensation mechanism was derived, which admits vortices that are thick at all times at the cost of constraining them to a finite volume Γ i whose complement is not simply connected.
TL;DR: The thickness of the ventricular layer (in the lateral part of neocortex) decreases dramatically from ED 16 on, and at the same time the cortical plate starts to form, the significance of these developmental features with regard to neocortical histogenesis is discussed.
Abstract: The formation and transformation of embryonic neocortical cell layers has been studied by means of autoradiographic and morphometric methods in the light of the concept of a dual origin of mammalian neocortex (Marin-Padilla, 1978; Raedler and Raedler, 1978) A primordial plexiform layer begins to form on ED 13, when the first postmitotic preneurons enter the area between ventricular layer and pial basement membrane Before this stage the area was occupied by single fibres and processes of the ventricular cells only The further development of the primordial plexiform layer is characterized by a linear increase in width, mainly due to the addition of migrating preneurons and ingrowing fibre bundles The older preneurons of the primordial plexiform layer are situated outermost in the layer, the younger ones at its inner circumference The differentiation accordingly follows an outside — inside gradient The preneurons of this layer are designed to become either the Cajal-Retzius cells of Layer I or subcortical neurons (Layer VII) (Rickmann et al, 1977) While the mitotic activity of cells in the ventricular layer decreases only gradually during the course of neurogenesis, the thickness of the ventricular layer (in the lateral part of neocortex) decreases dramatically from ED 16 on At the same time the cortical plate starts to form This is brought about by a translocation of ultrastructurally rather undifferentiated ventricular daughter cells from the inner to the outer circumference of the cerebral wall The width of the cortical plate grows almost exponentially, especially its medial part Its development is characterized by the addition of preneurons on its outer circumference while maturation takes place at its inner border The significance of these developmental features with regard to neocortical histogenesis is discussed
TL;DR: The main results were mean Tn, DHTn, E2n and SHBG remained on a constant level until the age of 65 yr, and the age dependent increase of SHBG in Group II can be best explained by the respective alterations of the E 2n/DHTn ratio.
TL;DR: In the developing cerebellum, the form of the Purkinje cell (PC) is largely under the control of the “environment,” Genes may specify the positions and biophysical properties of adhesive sites and postsynaptic thickenings.
Abstract: Publisher Summary The geometry of dendritic trees often characterizes the morphology of neurons into sets. Dendritic growth cones and filopodia are involved in the dynamics of the growth of trees and that ingrowing axons might be capable of influencing development by an effect on filopodia/growth cone mechanisms. Research efforts have better defined the morphology of dendritic growth cones and their interaction with axons in the developing neuropil. Manipulation of the environment and the use of cerebellar mutants are helping to clarify the role of genes in development while the introduction of new quantitative morphometric techniques for dendritic fields has improved the definition of tree structure. In the developing cerebellum, the form of the Purkinje cell (PC) is largely under the control of the “environment.” Genes may specify the positions and biophysical properties of adhesive sites and postsynaptic thickenings. The spatial interaction of these specialized areas of membrane with particular groups of axons ramifying about the growing tree may be sufficient to shape the characteristic geometry of the PC.
TL;DR: In this article, the four-jet production processes e+e−→qqgg and e−e−∆→qqqq were compared to the non-perturbative acoplanarity distributions at maximum PETRA and PEP energies.
TL;DR: The sensory innervation of primate sinus hairs has been studied by light and electron microscopy and Merkel cell‐neurite complexes and Ruffini corpuscles are slowly adapting receptors; lanceolate terminals and simple Corpuscles are rapidly adapting receptors.
Abstract: The sensory innervation of primate sinus hairs has been studied by light and electron microscopy. For light microscopy paraffin sections as well as thick frozen sections were impregnated with silver and compared with serial semi-thin sections of tissue prepared for electron microscopy. One type of sensory terminal is present in the epidermis surrounding the hair follicle, and four specific nerve terminals have been identified within the blood sinus. An epidermal rete ridge collar encircles the hair shaft and contains approximately 200 Merkel cell-neurite complexes. Numerous other Merkel cell-neurite complexes are present in the external root sheath of the hair follicle beneath a thick glassy membrane innervated by approximately 65 nerve fibers. At this level 10-15 lanceolate or palisade terminals are situated in the connective tissue. Up to 10 simple encapsulated corpuscles can be identified above the level of lanceolate endings and Merkel cell terminals. Ruffini corpuscles are closely applied to the glassy membrane below the lanceolate and Merkel terminals at the level where nerve fibers penetrate the capsule of the sinus. All of these terminals are supplied by 80-100 large diameter myelinated fibers distributed approximately as follows: 65 innervate Merkel cell-neurite complexes, 15 to lanceolate, 10 to simple corpuscles, and 10 to Ruffini corpuscles. The innervation of the rete ridge collar is independent of that of the sinus consisting of 10-12 fibers derived from the superficial dermal network. Each of these sensory terminals can be correlated with specific functional parameters as described in numerous neurophysiologic studies. Merkel cell-neurite complexes and Ruffini corpuscles ae slowly adapting receptors; lanceolate terminals and simple corpuscles are rapidly adapting receptors.
TL;DR: In this paper, the extinction ratios up to 14 dB between orthogonal polarisations have been realized, by grinding off the cladding on one side of a singlemode fiber and evaporating metal onto the polished surface.
Abstract: A polariser is formed by grinding off the cladding on one side of a single-mode fibre and evaporating metal onto the polished surface. Extinction ratios up to 14 dB between orthogonal polarisations have been realised.
TL;DR: The triphenylmethyl group can be removed from 5-trityl 2-deoxynucleosides (and their N-acyl derivatives) under aprotic neutral conditions without causing any side reactions as mentioned in this paper.
TL;DR: In this paper, an enhanced rate is observed in the reaction of iodotrimethylsilane with acetates and with cyclohexyl esters, which is particularly valuable for the synthesis of 2-deoxyglycosyl iodides.
Abstract: Bei Umsetzungen einfacher Modellverbindungen mit Iodtrimethylsilan zeigen sich hohere Reaktionsraten bei Acetaten und bei Cyclohexylestern. Bei Einsatz primarer und sekundarer Saccharid-Acetoxyderivate wird dagegen die ausschliesliche Bildung der Glycosyliodide festgestellt. Pentaacetylhexopyranosen reagieren mit Iodtrimethylsilan in hohen Ausbeuten zu den entsprechenden Tetraacetylglycosyliodiden. Auch Methylglycoside lassen sich umsetzen; beim Lactoseoctaacetat zeigt sich, das unter α-Heptaacetyllactosyliodid-Bildung die interglycosidische Bindung intakt bleibt. Besonders wertvoll ist das Verfahren zur Gewinnung der 2 Desoxyglycosyliodide. Entsprechende Umsetzungen mit Bromtrimethylsilan werden erfolgreich vorgenommen. Epoxidoffnungen mit Iodtrimethylsilan verlaufen bei sterischer Fixierung des Saccharid-Oxirans zu den trans-diaxialen bzw. bei sterisch beweglichen Derivaten uberwiegend zu den trans-diaquatorialen Iodhydrinen.
Synthetic Application of Iodo- and Bromotrimethylsilane in Saccharide Chemistry
In simple model compounds an enhanced rate is observed in the reaction of iodotrimethylsilane with acetates and with cyclohexyl esters. Primary and secondary acetoxy-substituted saccharides show an exclusive formation of glycosyl iodides. Accordingly, pentaacetyl hexopyranoses and iodotrimethylsilane give in high yields the corresponding glycosyl iodides. Methyl glycosides can be transformed similarly, and with lactose octaacetate the formation of α-heptaacetyllactosyl iodide proceeds smoothly without rupture of the interglycosidic linkage. This procedure is particularly valuable for the synthesis of 2-deoxyglycosyl iodides. Corresponding reactions with bromotrimethylsilane are achieved in a similar way. By opening of epoxides with iodotrimethylsilane in the case of sterically fixed saccharide oxiranes the trans-diaxial, and with more flexible derivatives predominantly the trans-diequatorial iodohydrines are obtained.
TL;DR: In this paper, the authors studied the effect of e+e- annihilation on particle multiplicity at high energy than at lower energies and found that the multiplicity grows faster at high energies than lower energies.
TL;DR: In this paper, the quadratic response formalism is used to derive a general expression for the Auger electron current in the limit of high energies of both photo-and Auger electrons.
Abstract: The quadratic response formalism is used to derive a general expression for the Auger electron current in the limit of high energies of both photo- and Auger electrons The Auger decay of the initial core hole is treated to all orders in the decay rate General formulas for the first and second moments of the Auger spectra are derived, and simple results are obtained for limiting cases We show that the center of gravity of the spectra depends strongly on the lifetime of the initial core hole The competition between different Auger processes can cause dramatic changes in the position and shape of the peaks in the spectra It is also shown that the Auger decay can lead to a broadening of the photoelectron spectra that cannot be represented by a Lorentzian convolution We discuss the validity of the two-step model for which the Auger decay is assumed to be decoupled from the creation of the initial core hole
TL;DR: Upon exposure to the vapours of oleoresin from 8 conifers, bark beetlesIps typographus andI.
Abstract: Upon exposure to the vapours of oleoresin from 8 conifers, bark beetlesIps typographus andI. amitinus produced verbenol, a terpene alcohol, in a predictable pattern. Apparently, this pattern changed in relation to the varied enantiomeric composition of the α-pinene contained in the resin of the various coniferous species. For calibration, defined mixtures of (+)-and (−)-α-pinene were used to establish the different levels of beetle response in the production of cis-and trans-verbenol. Methodical and ecological implications of the phenomenon are discussed.