Showing papers by "University of Stuttgart published in 1976"
TL;DR: In this paper, a single integral constitutive equation is presented, which gives a reasonable description of the non-linear shear and elongational behavior of a low-density branched polyethylene melt at constant strain rate observed by Meissner.
Abstract: A single integral constitutive equation is presented, which gives a reasonable description of the non-linear shear and elongational behavior of a low-density branched polyethylene melt at constant strain rate observed byMeissner. The memory function of this integral equation is a product of the memory function of Lodge's rubber like-liquid theory and a damping functionh = exp [ —n\(h = \exp [ - n\sqrt {I_2 - 3} ]\)], whereI2 is the second invariant of the Finger tensor. Stress- and normal stress overshoot are described as well as shear rate dependence of the transient shear viscosity and the first normal stress coefficient. Tensil stress overshoot and a finite, rate-dependent steady-state elongational viscosity is predicted in simple elongational flow.
336 citations
TL;DR: In this paper, the stability of boundary-layer flows on a semi-infinite flat plate and the growth of disturbances in such flows are investigated by numerical integration of the complete Navier-Stokes equations for laminar two-dimensional flows.
Abstract: The stability of incompressible boundary-layer flows on a semi-infinite flat plate and the growth of disturbances in such flows are investigated by numerical integration of the complete Navier–;Stokes equations for laminar two-dimensional flows. Forced time-dependent disturbances are introduced into the flow field and the reaction of the flow to such disturbances is studied by directly solving the Navier–Stokes equations using a finite-difference method. An implicit finitedifference scheme was developed for the calculation of the extremely unsteady flow fields which arose from the forced time-dependent disturbances. The problem of the numerical stability of the method called for special attention in order to avoid possible distortions of the results caused by the interaction of unstable numerical oscillations with physically meaningful perturbations. A demonstration of the suitability of the numerical method for the investigation of stability and the initial growth of disturbances is presented for small periodic perturbations. For this particular case the numerical results can be compared with linear stability theory and experimental measurements. In this paper a number of numerical calculations for small periodic disturbances are discussed in detail. The results are generally in fairly close agreement with linear stability theory or experimental measurements.
262 citations
TL;DR: In this paper, the photoisomerism following selective excitation with a dye laser into the S 1←S 0 transition of either of the two forms, for H2P and D2P (two inner hydrogens replaced by deuterium), was investigated.
Abstract: It is known that the porphyrin free base (H2P) can be incorporated in an n-octane Shpol'skii matrix. In slowly grown crystals the solute molecules occur in two orientations, which are co-planar and have their N-H … H-N axes at right angles; in the S 1↔S 0 ‘quasi-line’ absorption and fluorescence spectra they can be distinguished by a relative shift of 65 cm-1 of their spectral features. By irradiation with light the two species are transformed into one another via a shift of the two inner protons. Here a study is presented of the photoisomerism following selective excitation with a dye laser into the 0-0 band of the S 1←S 0 transition of either of the two forms, for H2P and D2P (two inner hydrogens replaced by deuterium). At 4·2 K the reaction proceeds in both directions; for H2P the reaction in one direction appears to be 10 per cent faster than in the other, for D2P the absolute rates are nearly ten times lower than for H2P and not measurably different in the two directions. The reactions are not signif...
180 citations
TL;DR: In this paper, an anomalous behaviour of the density was observed on melts in the binary chalcogenide system SexTe1−x up to a temperature of 950°C.
Abstract: Density measurements have been performed on melts in the binary chalcogenide system SexTe1−x up to a temperature of 950°C. Anomalous behaviour of the density was observed. At higher temperatures the density increased on raising the temperature up to a maximum whose position shifts to lower temperatures with increasing concentration of tellurium. This anomalous density behaviour clearly shows an increase of the average coordination number of atoms in the melt. This increase of CN is caused by a change of the bonding system because of the tendency of Te to form pσ bondings. It was assumed that there exist two distinct structures in thermodynamical equilibrium at each temperature according to a law of mass action, for which cooperation effects have to be taken in account. At low temperatures Te atoms easily accept a loosely packed structure I with the aid of selenium. At high temperatures even Se atoms develop a more densely packed structure II with the aid of Te.
176 citations
TL;DR: In this paper, the experimental results on dislocation relaxation processes in b.c. metals are compared with the theoretical findings reviewed in the earlier parts and it is shown that the so-called γ-relaxation process should be attributed to the formation of kink pairs on screw dislocations.
Abstract: This paper consists of three parts. In the first part the properties of dislocations and kinds in b.c.c. metals are studied in some detail, with special emphasis on screw dislocations. The unusual features associated with 〈111〉screw dislocations in b.c.c metals («polarity», asymmetry of glide, unusually large Peierls energies) are derived partly from geometry and partly from the results of computer calculations, and are compared with the properties of dislocations in f.c.c. metals and in the diamond structure. The second part reviews the theory of the relaxation processes associated with the migration of kinks along dislocation lines, with the formation of kink pairs and with the trapping and detrapping of kinks at point defects. In the third part the experimental results on dislocation relaxation processes in b.c.c. metals are compared with the theoretical findings reviewed in the earlier parts. It is shown that the so-called γ-relaxation process should be attributed to the formation of kink pairs on screw dislocations, as proposed earlier. The experimental evidence on the α and α′ maxima appears to be in favour of a suggestion of Igataet al., who interpreted the α-peak as due to kink pair formation on nonscrew dislocations and the α′-peak (observed in some metals) as due to the migration of kinks on screw dislocations. The β-relaxation processes appear to be of a nonintrinsic nature. According to Kuke, Kronmuller and Schultz, a further intrinsic dislocation relaxation process, namely the nonconservative movement of jogs in screw dislocations, is responsible for the high-temperature magnetic after-effect in iron.
151 citations
TL;DR: A concept is presented of the molecular involvement of sialo-glyco-macromolecules in the processes of synaptic transmission and memory formation, under the assumption that by complexation between lipid-bound negative charged sialic acid and Ca 2+ -ions the synaptic membrane is “closed”, while dissociation of these complexes will cause an “opening” of presynaptic regions.
148 citations
Book•
01 Jan 1976114 citations
TL;DR: T1 and T2 dispersion measurements of proton spin relaxation on aqueous solutions of bovine serum albumin as a function of both protein concentration and temperature will be presented as a most conclusive test for a three-phase fast-exchange relaxation model.
87 citations
TL;DR: In this article, the path integral solution of a stochastic process described by a generalized Langevin equation with coordinate-dependent fluctuating forces and white spectrum was determined, and the exponent of the exponential function occurring in that solution was interpreted as generalization of the Onsager-Machlup function.
Abstract: We determine the path integral solution of a stochastic process described by a generalized Langevin equation with coordinate-dependent fluctuating forces and white spectrum. Since such equations do not permit a unique determination of the distribution function but require the Ito or Stratonovich prescription, we first pass over to the corresponding Fokker-Planck equation adopting such a prescription. By means of the one-dimensional case we show that the path integral solutions are not uniquely determined in form but allow for a class of equivalent representations. Adopting an especially suitable representation we then present the path integral solution of the multi-dimensional Fokker-Planck equation. The exponent of the exponential function occurring in that solution can be interpreted as generalization of the Onsager-Machlup function. Finally we give a path-integral solution of the master equation. In the “Fokker-Planck limit” again a generalized Onsager-Machlup function is obtained.
82 citations
TL;DR: In this article, an improved expression for the effective interaction radius was derived for the general case of energy transfer accompanied by diffusion, and the donor fluorescence decay of pyrene/perylene in 1:1 paraffin oil/1-methylnaphthalene supports the theory.
74 citations
TL;DR: Using generalized Ginzburg-Landau equations derived recently, the authors solved the laser equations analytically for the case of spontaneous ultra-short laser pulses and compared their results with previous computer solutions by Risken and Nummedal.
TL;DR: In this article, the ESR signal of poly-[1,2-bis-(p -tolysulfonyloxymethylen)-I-buten-3-inylen] (PTS) triplet ESR signals are observed with the following zero field splitting parameters: D/hc = +(0.2731 ± 0.0005) cm −1 and E/Hc = −( 0.0048 −0.000 5) cm−1.
TL;DR: In this paper, density measurements were performed on melts of the binary chalcogenide system GexSe1−x (0.5) up to 1000°C and the anomalous density behaviour of the melts clearly showed a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system.
Abstract: Density measurements were performed on melts of the binary chalcogenide system GexSe1−x (0 ⩽ x ⩽ 0.5) up to 1000°C. The isotherm of molar volumes Vm at 750°C shows a relative maximum near GeSe2. Molar volumes of the system behave linearly between GeSe and Se at 1000°C. Vm's of melts between x = 0.30 and x = 0.35 decrease at high temperatures on heating. The anomalous density behaviour of the melts clearly shows a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system. Within the composition range 0 ⩽ x ⩽ 1 3 the short-range order at lower temperatures is determined mainly by GeSe 4 2 tetrahedra linked directly corner-to-corner or via Se atoms. At higher temperatures pσ bonds arise more and more, even in melts rich in selenium. Within the composition range 1 3 ⩽ x ⩽ 0.5 the short-range order is mainly determined by a distorted octahedral configuration, even at lower temperatures. From the short-range orders of melts and from crystalline structures of GeSe2 and GeSe, the tendency of glass formation from the melt is discussed in detail.
TL;DR: In this paper, a two-constants memory function is presented, which gives a qualitative description of the non-linear elongational behavior of a low-density polyethylene melt at constant elongation rate observed by Meissner.
Abstract: Based onLodge's theory of rubberlike liquids, a two-constants memory function is presented, which gives a qualitative description of the non-linear elongational behavior of a low-density polyethylene melt at constant elongation rate observed byMeissner. The two material constants necessary for the description are the steady-state zero-shear viscosity and a characteristic time constant, which can be determined from experiments in the linear viscoelastic region.
TL;DR: In this paper, the energies of the free exciton and of four excitons bound to neutral acceptors (A°, X) were determined by either reflection, absorption, or emission with high purity p-type GaSb.
Abstract: The energies of the free exciton and of four excitons bound to neutral acceptors (A°, X) are determined by either reflection, absorption, or emission with high purity p-type GaSb. The data give evidence that bound excitons may be described alternatively as an electron bound by a donor-like A+-centre. For one particular deep A+-centre, transitions from neutral donor states to that A+-centre are observed besides the bound exciton decay. p-GaSb is especially favourable for observing deep A+-centres, because of the position of the Fermilevel. Conditions under which they may be observable for other III–V compounds are discussed.
Die Energien des freien Exzitons und von vier an neutrale Akzeptoren gebundenen Exzitonen (A°, X) wurden aus Reflexions-, Absorptions- und Emissionsspektren von hochreinem p-leitendem GaSb bestimmt. Die Mesergebnisse deuten darauf hin, das gebundene Exzitonen als Donator-ahnliche A+-Zentren mit einem gebundenen Elektron beschrieben werden konnen. Bei einem bestimmten, tiefen A+-Zentrum wurden neben dem Zerfall des gebundenen Exzitons die Rekombination von Elektronen von neutralen Donatorzustanden mit dem Loch dieses A+-Zentrums beobachtet. p-GaSb ist wegen der Lage des. Ferminiveaus fur die Beobachtung tiefer A+-Zustande besonders geeignet. Es werden Bedingungen diskutiert, unter denen auoh in anderen III-V-Halbleitern A+-Zustande beobachtbar sein sollten.
TL;DR: In spite of the fact that some proteins from one or another kind of messenger ribonucleoprotein, have apparently the same molecular weight, the majority of proteins differ.
TL;DR: A finite difference method with non-equidistant space steps, based upon the Crank—Nicolson technique, which proves to be well suited for the solution of all kinds of diffusion type models, especially if steep gradients or moving profiles occur, and can be used even on moderate size process computers.
TL;DR: The solvolysis of phenyl triflate (3), phenyl non-aflate (4), o-methylphenyl nonaflate, o-methoxyphenyl (M), 2,6-dimethoxymythoxymethylphenyl (S), 2.6-diisopropylphenyl iflate (2.6), 3,5-dimethylcyclopropyl (3.5-dicyclopyropyl)phenyl triferlate, 2.4-6-triisophropyl
Abstract: The solvolysis of phenyl triflate (3), phenyl nonaflate (4), o-methylphenyl nonaflate (5), o-cyclopropylphenyl nonaflate (6), o-methoxyphenyl triflate (7), 2,6-dimethoxyphenyl triflate (S), 2,6-diisopropylphenyl triflate (9), 33- dimethoxyphenyl triflate (lo), 3,5-dicyclopropylphenyl triflate (11), 3,5-di(2-methylcyclopropyl)phenyl triflate (12), 2,4,6-tricyclopropylphenyltr iflate (13), and 2,4,6-triisopropylphenytlr iflate (14) were examined in great detail under a wide variety of conditions. In highly polar nonnucleophilic solvents no reaction was observed and the unreacted triflates were recovered quantitatively. In the presence of nucleophiles or nucleophilic solvents the sole products observed were the corresponding phenols. Careful labeling and product studies showed that these phenols arose by nucleophilic attack on sulfur and S-0 bond cleavage. We have not been able to find any evidence for aryl cation intermediates.
TL;DR: For a series of cyclopentadienyl derivatives of Group IA, IIA and IIIB elements, δc, 1J(CH) and 2,3J(cH) values are reported in this paper.
TL;DR: The wavelength of the rhodamine B lactone fluorescence is strongly dependent on solvent polarity, indicating an increase in dipole moment of about 25 debye on excitation as mentioned in this paper.
TL;DR: In this paper, the biaxial testing of fabrics were examined and a suitable specimen shape was designed which allowed the measurement of the true biaaxial breaking strength. But the results showed that the bao-ial strength is equal to the uniaxia-linear strength, and the stress-strain relations were given and compared with the uniao-linear case.
Abstract: In applying coated fabrics as roofing material for lightweight structures like tents, air-inflated structures and convertible roofs, the material is stressed in two dimensions. The different possibilities for biaxial testing of fabrics were examined and a suitable specimen shape was designed which allows the measurement of the true biaxial breaking strength. Experimental results showed that the biaxial strength is equal to the uniaxial strength. Stress-strain relations are given and compared with the uniaxial case.
TL;DR: The polymeric modification of the silicon dioxides effects changed properties, such as a hydrophobic character and a different sedimentation behaviour as discussed by the authors, and the amount of polymer coverage depends on the molecular weight of the macromolecules, on the reaction parameters (time, temperature, solvent, concentration of silicon dioxide and polymers).
Abstract: Chlorsilanmodifizierte Polymere wie Polystyrol und Polymethylmethacrylat mit Chlorsilanendgruppen, reagieren mit oberflachenstandigen Hydroxylgruppen von Siliciumdioxiden unter Ausbildung von Siloxanbindungen und kovalenter Verknupfung der Makromolekulemit der Feststoffoberflache. Die reaktiven Polymeren werden durch Ubertragung bei der radikalischen Polymerisation der Monomeren und durch Abbruch anionisch lebender Polymerer mit Chlorsilanen (Siliciumtetrachlorid, Trichlormethylsilan, Dichlordimethylsilan) dargestellt. Die Menge des an die Siliciumdioxidoberflache kovalent gebundenen Polymeren betragt, abhangig vom Molekulargewicht der Makromolekule, von den Reaktionsparametern Zeit, Temperatur, Losungsmittel, Konzentration an Festkorper und Polymeren sowie von der spezifischen Oberflache der Siliciumdioxide, bis zu 500 mg Polymeres pro Gramm Siliciumdioxid. Durch einfache Adsorption und anschliesende Desorption werden maximal 30 mg Polymeres pro Gramm Siliciumdioxid irreversibel adsorptiv gebunden.
Die mit Polystyrol oder Polymethylmethacrylat modifizierten Siliciumdioxide sind hydrophob und zeigen ein gegenuber unmodifiziertem Siliciumdioxid verandertes Sedimentationsverhalten.
Polymers with chlorosilane endgroups, such as polystyrene and polymethyl methacrylate, react with superficial hydroxyl groups of silicon dioxides by formation of siloxane bonds and covalent binding of the macromolecules to the surface. The active polymers are prepared either by a radical polymerisation of the monomers in presence of chlorosilanes or by a terminating reaction of the anionically living polymers with chlorosilanes (tetrachlorosilane, trichloro methylsilane, dichloro dimethylsilane). The amount of polymer coverage depends on the molecular weight of the macromolecules, on the reaction parameters (time, temperature, solvent, concentration of silicon dioxide and polymers) and on the specific surface of the silicon dioxides. According to varying reaction conditions, the amount of polymer coverage ranges up to 500mg of polymer per gram of silicon dioxide, whereas only 30 mg of polymer per gram of silicon dioxide is bonded irreversibly by adsorption of the polymer from solution and subsequent desorption.
The polymeric modification of the silicon dioxides effects changed properties, such as a hydrophobic character and a different sedimentation behaviour.
TL;DR: In this article, the temperature dependence of sensitized delayed fluorescence in naphthalene-anthracene mixed crystals has been analyzed, and a direct trap to trap energy transfer already at relatively low concentrations is observed.
TL;DR: In this article, the authors investigated the Stage I fracture propagation in an age-hardened Al-Zn-Mg alloy with notched single crystal specimens and found that the plastic relaxation at the crack tip increases with increasing velocities.
Abstract: Fatigue crack propagation in Stage I in an age-hardened Al-Zn-Mg alloy was investigated using notched single crystal specimens. In a dry nitrogen gas environment, propagation occurs almost exclusively in the primary slip plane and preferentially along favorably oriented crystallographic slip directions. The resulting fracture surfaces show increasing roughness with increasing propagation velocities; at small velocities (about 70A/cycle) they appear like cleavage surfaces, whereas at large velocities (about 2000A/cycle) they are associated with much more ductility and show a dimpled structure. These observations indicate that the plastic relaxation at Stage I crack tip increases with increasing velocities. In the presence of moisture in the test environment crack growth occurs at larger velocities giving rise to more reflective fracture surfaces. The moisture in the environment seems to be responsible also for the inter crystalline Stage I crack propagation observed in polycrystalline samples. Low stacking fault energy materials deforming by planar slip do not show a similar tendency to fracture in macroscopic slip bands.
TL;DR: In this article, single picosecond laser pulses in the second positive band of nitrogen were observed from high pressure gas discharges with traveling wave excitation, operating in pure nitrogen and without preionization.
Abstract: Single picosecond laser pulses in the second positive band of nitrogen are observed from high‐pressure gas discharges with traveling‐wave excitation. The gas discharge is operated in pure nitrogen and without preionization. The pulse duration decreases from 300 psec at 1 atm to 50 psec at 6 atm.
TL;DR: In this article, almost split sequences for integral group rings and orders are presented, where almost split sequence for integral groups and orders is used to define the order of the integral group ring.
Abstract: (1976). Almost split sequences for integral group rings and orders. Communications in Algebra: Vol. 4, No. 10, pp. 893-917.
TL;DR: In this paper, the authors derived a probe absorption coefficient specialized to homogeneous and inhomogeneous broadening limits and illustrated as the dipole lifetime is increased from 0 to values comparable to the level lifetimes.
Abstract: The general probe absorption coefficient derived in Part I is specialized to homogeneous- and inhomogeneous-broadening limits and illustrated as the dipole lifetime is increased from 0 to values comparable to the level lifetimes. This progression reveals the relation between pulsation dips of the short-dipole lifetime limit and the dynamic Stark effect in general. Interpretations of the coherent interactions involved are given in terms of modulator and Raman effects and of dressed atoms. The single-probe unidirectional pulsation dip is shown to be a special case of the grating dip in which the fringe spacing becomes infinite. Analogies with three-level systems are given in which both two and three-level cases are seen to obey an “equal-area theorem”, and to involve level crossing. Some comparison is made with corresponding spectroscopy in which spontaneous emission provides the probe radiation.
TL;DR: In this paper, a Verbundverfahren for bestimmung von ng-Mengen Beryllium in biologischen Matrices (z.B.B., Blut, Muskelgewebe) durch flammenlose Atomabsorptionsspektrometrie is described.
TL;DR: In this article, the authors report the splitting of three sharp emission line series in silicon which are associated with the neutral impurities phosphorus, lithium, or boron, and show that all lines belonging to one series are identical except for thermalization effects.
Abstract: We report Zeeman spectra and the stress-induced splitting of the three novel sharp emission line series in silicon which are associated with the neutral impurities phosphorus, lithium, or boron. The splitting of all lines belonging to one series is identical except for thermalization effects. This result cannot be explained by the model of bound multiple-exciton complexes but rather suggests the radiative decay of single bound excitons as the origin of the lines. A detailed new model is not evident.