Showing papers by "ETH Zurich published in 1976"

Timing Recovery in Digital Synchronous Data Receivers

Abstract: A new class of fast-converging timing recovery methods for synchronous digital data receivers is investigated. Starting with a worst-case timing offset, convergence with random binary data will typically occur within 10-20 symbols. The input signal is sampled at the baud rate; these samples are then processed to derive a suitable control signal to adjust the timing phase. A general method is outlined to obtain near-minimum-variance estimates of the timing offset with respect to a given steady-state sampling criterion. Although we make certain independence assumptions between successive samples and postulate ideal decisions to obtain convenient analytical results, our simulations with a decision-directed reference and baud-to-baud adjustments yield very similar results. Convergence is exponential, and for small loop gains the residual jitter is proportional and convergence time is inversely proportional to the loop gain. The proposed algorithms are simple and economic to implement. They apply to binary or multilevel PAM signals as well as to partial response signals.

Characteristics of the amino acids as components of a peptide hormone sequence

Abstract: In the living organism the polypeptide chains of proteins are used for the most diverse purposes: structural support and protection, catalysis of a wide range of chemical reactions, energy transduction, food storage, transport, and—among many others—regulation and co-ordination by information transfer (including humoral transmission by hormones). Molecules with the varied properties required for these multifarious functions are built up of a mere 20 units: the protein-constituent amino acids, connected primarily in a single structural mode (a linear sequence) but finally arranged in space in intricate ways to molecules of the required size, shape and properties. Although the peptide hormones fulfil such a highly specialised role, there is nothing to distinguish, a priori, their sequences from other polypeptide or protein sequences with different biological functions, or no function at all.

Titanium (III) citrate as a nontoxic oxidation-reduction buffering system for the culture of obligate anaerobes

Abstract: An oxidation-reduction buffering system based on titanium(III) citrate eliminates any traces of oxygen in a culture medium, serves as an indicator for low oxidation-reduction potentials, and prevents the growth of facultative anaerobes, which frequently contaminate anaerobic cultures.

Interaction of Pb2+ with hydrous γ-Al2O3☆

Abstract: Significant adsorption of Pb(II) on to hydrous γ-Al2O3 from dilute solutions is observed even at pH values far below the zero point of charge. The specific binding of Pb2+ on hydrous γ-Al2O3 in dilute electrolyte is interpreted as surface complex formation. The amphoteric properties of the coordinating surface are characterized in 0.1 M NaC1O4 in terms of a two-protic acid-base system (pHZPC = 8.3). The extent of Pb2+ interaction with the Al2O3 surface was determined both from measurements of residual [Pb2+] with a Pb2+ electrode and from the displacement of alkalimetric titration curves by the presence of Pb(II). The complex forming properties of the surface coordination reaction can be quantified by the equilibria: ≡ AlOH + Pb2+ ⇄ ≡ AlOPb+ + H+; 2 ≡ AlOH +Pb2+ ⇄ (≡ AlO)2Pb + 2H+. Hydrolysis need not be invoked to describe the interaction.

Photoemission of spin-polarized electrons from GaAs

Abstract: The spin polarization of electrons photoemitted from (110) GaAs by irradiating with circularly polarized light of energy 1.5 & heu & 3.6 eU was measured by Mott scattering. The GaAs surface was treated with cesium and oxygen to obtain a negative electron af6nity (NEA), The spectrum of spin polarization P(hem) exhibits a peak (P = 40%) at threshold arising from transitions at I, and positive (P = 8%) and negative (P = —8%) peaks at 3.0 and 3.2 eV, respectively, arising from transitions at L (A). Anomalous behavior, consisting of a depolarization at threshold and an increase and shift in the peak polarization to 54% at 1.7 eV, is attributed to a small positive electron a%nity (PEA) characteristic of some samples. Restriction of the photoelectron emission angle by the PEA leads directly to the anomalously high P. Results of calculations show that P cannot be increased above 50% for emission arising from transitions at I in NEA GaAs. Our detailed interpretation of the spectra indicates how spin-polarized photoemission can be used to study the spin-

The X-Pro peptide bond as an nmr probe for conformational studies of flexible linear peptides.

Abstract: The equilibrium between the cis and trans forms of X-Pro peptide bonds can readily be measured in the 13C nmr spectra. In the present paper we investigate how observation of this equilibrium could be used as an nmr probe for conformational studies of flexible polypeptide chains. The experiments include studies by 13C nmr of a series of linear oligopeptides containing different X-L-Pro peptide bonds, with X = Gly, L-Ala, L-Leu, L-Phe, D-Ala, D-Leu, and D-Phe. Overall the study confirms that X-Pro peptide bonds can generally be useful as 13C nmr probes reporting the formation of nonrandom conformation in flexible polypeptide chains. It was found that the cis–trans equilibrium of X-Pro is greatly affected by the side chain of X and the configuration of the α-carbon atom of X. On the basis of these observations some general rules are suggested for a practical applications of the X-Pro nmr probes in conformational studies of polypeptide chains.

Dynamics of the aromatic amino acid residues in the globular conformation of the basic pancreatic trypsin inhibitor (BPTI). I. 1H NMR studies

Abstract: The basic pancreatic trypsin inhibitor (BPTI) was investigated by high resolution 1H NMR techniques at 360 MHz. Observation of the amide proton resonances of the polypeptide backbone showed that the globular conformation of BPTI determined by X-ray studies in single crystals is maintained in aqueous solution over the temperature range from 4 degrees to 87 degrees. NMR studies over this temperature range of the aromatic amino acid residues of BPTI. i.e. 4 tyrosines and 4 phenylalanines, led to complete assignments of all the aromatic spin systems in the protein. From this, information was obtained on the rotational motions about the C beta--Cv bond axis of the aromatic rings in the globular form of PBTI. At 25 degrees, two tyrosine rings and one phenylalanine ring are rotating rapidly on the NMR time scale. For the other rings the transitions from slow to rapid rotational motions were investigated at variable temperatures and energy barriers for these intramolecular rate processes determined. The studies of the tyrosine resonances had been described in detail in a previous publication. The present paper describes the identification of the phenylalanine resonances and comments on some technical aspects which might be of quite general interest for the analysis of highly resolved 1H NMR spectra of proteins. Data for the tyrosines and the phenylalanines are compiled in three tables, i.e. the pK alpha-values for the tyrosines, the NMR parameters for all eight aromatics, and the parameters delta G not equal to, and, where available, delta H not equal to and delta S not equal to for the rotational motions of the rings.

MODULA: a language for modular multiprogramming

Abstract: This paper defines a language called Modula, which is intended primarily for programming dedicated computer systems, including process control systems on smaller machines. The language is largely based on Pascal, but in addition to conventional block structure it introduces a so-called module structure. A module is a set of procedures, data types and variables, where the programmer has precise control over the names that are imported from and exported to the environment. Modula includes general multiprocessing facilities, namely processes, interface modules and signals. It also allows the specification of facilities that represent a computer's specific peripheral devices. Those given in this paper pertain to the PDP-11.

Rotational diffusion of band 3 proteins in the human erythrocyte membrane

Abstract: Band 3 proteins rotate in the human erythrocyte membrane; rotation is almost certainly confined to an axis normal to the plane of the membrane and is characterised by a diffusion coefficient of the order of 1,000 s−1. Spectrin does not restrict rotational motion of band 3 proteins.

Radioactive heat production in rocks and its relation to other petrophysical parameters

Abstract: Radioactive heat productionA is a scalar and isotropic petrophysical property independent of in situ temperature and pressure. Its value is usually expressed in HGU units (1 HGU=10−13 cal/cm3 sec) and depends on the amounts of uranium, thorium and potassium.A varies with rock type over several orders of magnitude and reflects the geochemical conditions during rock formation (magmatic differentiation, sedimentation or metamorphism).

Nmr studies of the molecular conformations in the linear oligopeptides H-(L-Ala)n-L-Pro-OH.

Abstract: The molecular conformations of the linear oligopeptides H-(L-Ala)n-L-Pro-OH, with n = 1,2 and 3, have been investigated. 13C nmr observation of the equilibrium between the cis and trans forms of the Ala-Pro peptide bond indicated the occurrence of nonrandom conformations in solutions of these flexible peptides. The formation of the nonrandom species containing the cis form of the Ala-Pro bond was found to depend on the deprotonation of the carboxylic acid group of proline, the solvent, and the ionic strength in aqueous solution. The influence of intramolecular hydrogen bonding on the relative conformational energies of the species containing the cis and trans Ala-Pro peptide bond was studied by comparison of the peptides H-(Ala)n-Pro-OH with analogous molecules where hydrogen bond formation was excluded by the covalent structure. In earlier work a hydrogen bond between the protonated terminal carboxylic acid group and the carbonyl oxygen of the penultimate amino acid residue had been suggested to stabilize conformations including trans proline. For the systems described here this hypothesis can be ruled out, since the cis:trans ratio is identical for molecules with methyl ester protected and free protonated terminal carboxylic acid groups of proline. Direct evidence for hydrogen bond formation between the deprotonated terminal carboxylic acid group and the amide proton of the penultimate amino acid residue in the molecular species containing cis proline was obtained from 1H nmr studies. However, the cis:trans ratio of the Ala-Pro bond was not affected by N-methylation of the penultimate amino acid residue, which prevents formation of this hydrogen bond. Overall the experimental observations lead to the conclusion that the relative energies of the peptide conformations including cis or trans proline are mainly determined by intramolecular electrostatic interactions, whereas in the molecules considered, intramolecular hydrogen bonding is a consequence of specific peptide backbone conformations rather than a cause for the occurrence of energetically favored species. Independent support for this conclusion was obtained from model consideration which indicated that electrostatic interactions between the terminal carboxylic acid group and the carbonyl oxygen of the penultimate amino acid residue could indeed account for the observed relative conformational energies of the species containing cis and trans proline, respectively.

Measurements of Density Underflows from Walensee, Switzerland

Abstract: Speed and direction of bottom currents induced by density underflow of two sediment-laden rivers were measured by oceanographic current meters in the Walensee (= Lake of Walenstadt), Switzerland. The apparently shooting flow of currents (up to 30 cm/s in this study) is suggested as an explanation for laminations in turbidite sequences. The current speed apparently stabilizes on slopes around 2°; this angle seems to correspond to the critical slope where the flow of the measured currents becomes steady. Current direction is controlled by bottom topography and direction of river inflow. Reversal of current direction observed at two sites is probably due to the underflow-induced backward motion of the overlying lake water. Underflow activity in Walensee is correlative with density peaks of the river water input. The currents are compared to Lake Mead (Southwestern U.S.) underflows and sporadic currents in some submarine canyons.

Electronic structure of Sm monochalcogenides

Abstract: The optical reflectivity of single crystals of semiconducting SmS, SmSe, and SmTe as well as of the metallic, high-pressure phase of SmS has been investigated in the photon energy range between 0.03 and 12 eV, for metallic SmS also between 4.2 and 300 K. The dielectric functions have been derived by means of a Kramers-Kronig analysis and been interpreted by interband and intraband transitions. In addition, semiconducting evaporated films of SmS have been prepared and the absorption in function of temperature (4.2-300 K) and pressure (0-1.5 kbar) has been investigated. It can be shown that the electronic structure of the semiconducting Sm monochalcognides can be obtained from the corresponding one of the Eu monochalcogenides by a simple uniform shift in the energy of the $4f$ electronic state. Valence fluctuations in single crystalline, metallic SmS are present to a much lower degree than assumed so far.

Effects of nicotine on the exploratory locomotion patterns of female Roman high- and low-avoidance rats.

Abstract: Utilizing an automated, Dashiell-type hexagonal maze, it was demonstrated that RHA rats: 1) were more active, 2) reversed direction more often, 3) entered radial (blind) alleys less often, and 4) displayed shorter latencies than did RLA rats. Direction reversals (U-turns) tended to increase from day to day with the RHA rats, whereas the opposite was true for the RLA rats. Nicotine injections (0.2 mg/kg) increased activity and the number of U-turns, shortened the latencies and lessened the likelihood of entering radial alleys for both strains. The RHA rats were more sensitive to nicotine than were the RLA rats in all of these measurements, which varied, depending upon alley length and structural complexity, among the maze configurations.

U-Pb zircon and Rb-Sr whole-rock dating of low-grade metasediments example: Montagne Noire (Southern France)

Abstract: Three detrital, Proterozoic zircon suites extracted from siltstones progressively metamorphosed between chlorite- and staurolite-grade independently date the major Caledonian metamorphism within the gneiss dome of the Montagne Noire (Southern France). From this, the following conclusions concerning U-Pb systematics of zircons in low-, medium- and highgrade metamorphic rocks can be drawn: 1) Temperatures of at most 350–400 °C are sufficient to open U-Pb systems of metamict zircons or domains within zircons. 2) The observed open U-Pb system behaviour during metamorphism of the host rocks was found to be due to a low-temperature recrystallisation of highly radiation damaged zircon lattices, probably enhanced by high concentrations of fluid phases in the dehydrating rock volumes. 3) Recrystallisation of metamict zircons under low temperatures causes maximum U-Pb ages for the thermal climax of metamorphism of medium-and high-grade metamorphic rocks, as annealing and accompaning closing of U-Pb systems took place before the maximum temperatures of metamorphism were reached. 4) Low-temperature recrystallisation of old — generally Proterozoic—zircons can readily help to explain the fact that the numerous zircon suites from ancient shield areas yield “lower intercept ages” which are not correlated to any known geological event. Thus, either a weak thermal pulse, not necessarily registered by the mineral assemblage of the host rock, and/or elevated temperatures during burial in the crust might supply enough energy for a structural reordering and simultaneous lead loss of at least the most disordered lattice domains.

Synthese des (R)‐trans‐11‐Hydroxy‐8‐dodecensäure‐lactons (Recieifeiolid)

Abstract: Synthesis of Recifeiolide The synthesis of the mould metabolite recifeiolide (VIII), a 12-membered ring lactone, is described. 1,3-Butandiol was resolved with (−)-camphanic acid via (R)-1-iodo-3-butanol (II) into (R)-3-hydroxybutyl triphenyl phosphonium iodide (III). Wittig condensation of the phosphorane derived from III with methyl 8-oxo-octanoate (V) led to the methyl trans-11-hydroxy-8-dodecenoate (VI). The corresponding hydroxy acid VII was transformed into the S-(2-pyridyl) carbothioate which cyclizes under the influence of silver ion to the lactone VIII. With (−)-(R)-1,3-butandiol (I) as starting material the naturally occurring (+)-(R)-recifeiolide (VIII) is produced in 70% yield from VII.

Spin-Polarized Photoelectrons from Nickel Single Crystals

Abstract: Photoelectrons emitted from nickel single-crystal surfaces defined by low-energy-electron diffraction and Auger-electron-spectroscopy analysis exhibit negative electron-spin polarization at threshold. The abrupt change from negative to positive polarization occurs at $h\ensuremath{\omega}\ensuremath{\simeq}\ensuremath{\Phi}+0.05$ eV, where $\ensuremath{\Phi}$ is the work function. This excludes an interpretation based on a simple band theory of magnetism and also explains why the negative electron-spin polarization has not been observed in earlier experiments on polycrystalline films.

Differences in neutral amino acid and glucose transport between brush border and basolateral plasma membrane of intestinal epithelial cells

Abstract: A comparison of L-valine and D-glucose transport was carried out with vesicles of plasma membrane isolated either from the luminal (brush border) or from the contra-luminal (basolateral) region of small intestinal epithelial cells. The existence of transport systems for both non-electrolytes was demonstrated by stereospecificity and saturability of uptake, as well as tracer coupling. Transport of L-valine and D-glucose differs markedly in the two types of plasma membrane with respect to stimulation by Na+. The presence of Na+ stimulated initial L-valine and D-glucose uptake in brush border, but not in basolateral membrane. Moreover, an electro-chemical Na+ gradient, oriented with the lower potential on the inside, supported accumulation of the non-electrolytes above medium concentration only in the brush border membrane. L-Valine and D-glucose transport also were saturated at lower concentrations in brush border (10-20 mM) than in basolateral plasma membranes (30-50 mM). A third difference between the two membranes was found in the effectiveness of known inhibitors of D-glucose transport. In brush border membranes phlorizin was more potent than phloretin and 2', 3', 4'-trihydroxy-4-methoxy chalcone and cytochalasin B did not inhibit at all. In contrast, with the basolateral plasma membranes the order of potency was changed to phloretin = 2',3',4'-trihydroxy-4-methoxy chalcone greater than cytochalasin B greater than phlorizin. These results indicate the presence of different types of transport systems for monosaccharides and neutral amino acids in the luminal and contra-luminal region of the plasma membrane. Active transepithelial transport can be explained on the basis of the different properties of the non-electrolyte transport systems in the two cellular regions and an electro-chemical Na+ gradient that is dependent on cellular metabolism.

Final-state effects in the 3d photoelectron spectrum of Fe 3 O 4 and comparison with Fe x O.

Abstract: Photoelectron-spin-polarization measurements with photon energies up to 11 eV on ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ and energy distribution curves in the photon energy range $5lh\ensuremath{ u}l90$ eV on magnetite ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ and wustite (FeO) are interpreted in terms of the atomic theory of the single-ion-in-a-crystal-field model. The combination of the two different experiments yields the shapes and positions of the filled oxygen $2p$ bands and the $3{d}^{n\ensuremath{-}1}$ final states of Fe ions with a reliability previously not attained. The $3{d}^{n\ensuremath{-}1}$-multiplet structure of ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ can be explained with the following set of parameters: $10Dq=1.75$ eV and the Racah parameter $B=645$ ${\mathrm{cm}}^{\ensuremath{-}1}$ for ${\mathrm{Fe}}^{3+}$ left behind in $B$ lattice sites; $10Dq=1.55$ eV for ${\mathrm{Fe}}^{4+}$ in $A$ sites. The difference in threshold for photoionization of ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ in $B$ sites is 1.0 eV. The oxygen $2p$ emission is found to be centered at 7.3 eV below the Fermi level with a full width of 3 eV at half-maximum. The $3d$-multiplet structure of ${\mathrm{Fe}}_{x}\mathrm{O}$ can be explained with $10Dq=1.7\ifmmode\pm\else\textpm\fi{}0.1$ eV and $B=800$ ${\mathrm{cm}}^{\ensuremath{-}1}$.

Thermally driven acoustic oscillations, part IV: Tubes with variable cross-section

Abstract: The problem of thermally driven acoustic oscillations is treated for tubes with variable cross-section, with particular emphasis on the possible reduction of the necessary temperature ratio for excitation. Tubes with optimal conditions in the vicinity of the temperature jump, and with big cross-sections in parts with constant temperature are found to give the best performance in this respect. Included in the family of devices which were treated is the classical Sondhauss-tube. Experiments which give a striking confirmation of the theory are reported.

Dynamics of the aromatic amino acid residues in the globular conformation of the basic pancreatic trypsin inhibitor (BPTI). II. Semi-empirical energy calculations.

Abstract: The molecular conformation of the basic pancreatic trypsin inhibitor (BPTI) is known in considerable detail from both X-ray studies in single crystals and NMR studies in solution. The NMR experiments showed that the aromatic rings of the phenylalanyl and tyrosyl residues can undergo rapid rotational motions about the C beta--Cv bond. The present paper describes a model investigation of the mechanistic aspects of these intramolecular rotational motions. From calculations of the conformational energies for molecular species derived from the X-ray structure by rotations of individual aromatic rings, it was apparent that the rotational motions of the aromatics could only be understood in a flexible structure. Flexibility was simulated by allowing the protein to relax to an energetically favorable conformation for each of the different rotation states of the aromatic rings. It was then of particular interest to investigate how the perturbations caused by different rotation states of the aromatic rings were propagated in the protein structure. It was found that the rotation axes C beta--Cv were only slightly affected (delta X1 approximately less than 20 degrees. The most sizeable perturbations are caused by through space interactions with nearby atoms, which move away from the ring center and thus release the steric hindrance opposing the rotational motions. The values for the energy barriers obtained from the energy minimization are of the same order of magnitude as those measured by NMR.

L-o-carboranylalanine, a boron analogue of phenylalanine.

Abstract: The synthesis of a new, boron-containing analogue of phenylalanine is described. Carboranylalanine (Car) carries a 1,2-carborane cage in place of the benzene ring of phenylalanine. It is obtained by the reaction of derivatives of propargylglycine with decaborane. Possibilities of practical application derive from the facile neutron activation of boron nuclei with mass number 10.

Neutron diffraction study of USb: The ordered state

Abstract: The elastic magnetic neutron cross section from a single crystal of USb has been measured in the antiferromagnetic state (type-I ordering, T/sub N/ = 241.2 K) for all Bragg reflections with sintheta/lambda = kappa/4..pi.. < 0.811 A/sup -1/. By using the tensor-operator method, we have calculated the theoretical cross sections from a number of possible ground-state configurations and compared them with experiment. Excellent agreement is obtained for one model only; a 5f/sup 3/ ionic state (U/sup 3 +/) with a GAMMA/sup 1/8 crystal-field ground state. Such a crystal-field ground state implies that the fourth-order crystal-field potential V/sub 4/ is negative, which is the opposite sign to that found in the analogous 4f/sup 3/ neodymium compounds. By measuring the temperature dependence of the magnetic scattering as a function of kappa-arrow-right, the scattering vector, we have been able to estimate the magnitude of the crystal-field parameters as V/sub 4/ approx. = - 300 K, and V/sub 6/ - 15 K. The implications of this first unambiguous identification of the electronic ground state in a metallic actinide compound are discussed. (AIP)

Bitter peptides, occurrence and structure

Abstract: The bitter taste of many protein rich foods resides in the peptide fraction. 61 bitter tasting peptides, isolated from natural systems, and 145 bitter tasting synthetic peptides are reviewed. The relationships between average hydrophobicity and bitter taste are then discussed.