Showing papers by "ETH Zurich published in 1993"

Secret key agreement by public discussion from common information

Abstract: The problem of generating a shared secret key S by two parties knowing dependent random variables X and Y, respectively, but not sharing a secret key initially, is considered. An enemy who knows the random variable Z, jointly distributed with X and Y according to some probability distribution P/sub XYZ/, can also receive all messages exchanged by the two parties over a public channel. The goal of a protocol is that the enemy obtains at most a negligible amount of information about S. Upper bounds on H(S) as a function of P/sub XYZ/ are presented. Lower bounds on the rate H(S)/N (as N to infinity ) are derived for the case in which X=(X/sub 1/, . . ., X/sub N/), Y=(Y/sub 1/, . . ., Y/sub N/) and Z=(Z/sub 1/, . . ., Z/sub N/) result from N independent executions of a random experiment generating X/sub i/, Y/sub i/ and Z/sub i/ for i=1, . . ., N. It is shown that such a secret key agreement is possible for a scenario in which all three parties receive the output of a binary symmetric source over independent binary symmetric channels, even when the enemy's channel is superior to the other two channels. >

Superconductivity above 130 K in the Hg–Ba–Ca–Cu–O system

Abstract: THE recent discovery1 of superconductivity below a transition temperature (Tc) of 94 K in HgBa2CuO4+δ has extended the repertoire of high-Tc superconductors containing copper oxide planes embedded in suitably structured (layered) materials. Previous experience with similar compounds containing bismuth and thallium instead of mercury suggested that even higher transition temperatures might be achieved in mercury-based compounds with more than one CuO2 layer per unit cell. Here we provide support for this conjecture, with the discovery of superconductivity above 130 K in a material containing HgBa2Ca2Cu3O1+x (with three CuO2 layers per unit cell), HgBa2CaCu2O6+x (with two CuO2 layers) and an ordered superstructure comprising a defined sequence of the unit cells of these phases. Both magnetic and resistivity measurements confirm a maximum transition temperature of ∼ 133 K, distinctly higher than the previous established record value of 125–127 K observed in Tl2Ba2Ca2Cu3O10 (refs 2,3). The discovery in 1986 of the first copper oxide superconductor stimulated an explosion of research activity that continues to the present day. The early years of high-temperature superconductivity were characterized by the rapid discovery of many new materials with increasingly high transition temperatures. The record now stands at ~133 K, attributed to a mercury-containing compound reported by Schilling et al. in 1993, although the dream of achieving room-temperature superconductivity has yet to be fulfilled.

The LRU-K page replacement algorithm for database disk buffering

Abstract: This paper introduces a new approach to database disk buffering, called the LRU-K method The basic idea of LRU-K is to keep track of the times of the last K references to popular database pages, using this information to statistically estimate the interarrival times of references on a page by page basis Although the LRU-K approach performs optimal statistical inference under relatively standard assumptions, it is fairly simple and incurs little bookkeeping overhead As we demonstrate with simulation experiments, the LRU-K algorithm surpasses conventional buffering algorithms in discriminating between frequently and infrequently referenced pages In fact, LRU-K can approach the behavior of buffering algorithms in which page sets with known access frequencies are manually assigned to different buffer pools of specifically tuned sizes Unlike such customized buffering algorithms however, the LRU-K method is self-tuning, and does not rely on external hints about workload characteristics Furthermore, the LRU-K algorithm adapts in real time to changing patterns of access

Pseudoholomorphic curves in symplectizations with applications to the Weinstein conjecture in dimension three.

Abstract: l. In t roduct ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515 1.1. The Weinstein conjecture . . . . . . . . . . . . . . . . . . . . . . . . 515 1.2. The main results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517 1.3. Sketch of the proof . . . . . . . . . . . . . . . . . . . . . . . . . . . 522 2. Local F redho lm theory . . . . . . . . . . . . . . . . . . . . . . . . . . . 525 2.1. Similar i ty principle and consequences . . . . . . . . . . . . . . . . . . . 525 2.2. N_ • M as a lmost complex manifold and local fillings . . . . . . . . . . . . . 529 2.3. Local propert ies of ho lomorphic curves . . . . . . . . . . . . . . . . . . 531 3. Bubbl ing off analysis and global Fredholm theory . . . . . . . . . . . . . . . . 533 3.l. Grad ien t bounds imply Ca -bounds . . . . . . . . . . . . . . . . . . . . 533 3.2. Bubbing off analysis of ho lomorphic planes . . . . . . . . . . . . . . . . . 534 3.3. Grad ien t bounds near the boundary . . . . . . . . . . . . . . . . . . . . 537 4. Proof of the main results . . . . . . . . . . . . . . . . . . . . . . . . . . 544 4.1. Set-up for a global Fredholm theory . . . . . . . . . . . . . . . . . . . . 544 4.2. Bishop's theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545 4.3. Proof of theorem 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . 546 4.4. Proof of theorems 8 and 11 . . . . . . . . . . . . . . . . . . . . . . . 547 4.5. Uniqueness results for foliations . . . . . . . . . . . . . . . . . . . . . 547 5. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550 5.1. Per turbing surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . 550 5.2. Ki l l ing crit ical points of hypersurfaces . . . . . . . . . . . . . . . . . . . 552 5.3. Adding a thin tube to a sphere . . . . . . . . . . . . . . . . . . . . . . 560

Adsorption of cesium on minerals: A review

Abstract: The adsorption behavior of cesium on pure minerals is reviewed. Although this field has been investigated intensively, the data are extremely variable in scope and interpretation with detailed information being available for only a few minerals. In current investigations in this field, the emphasis is on the nature of the adsorption sites and identification of these sites using spectroscopic techniques. In the first section of this review, the general mechanism of cesium adsorption is discussed and this is followed by consideration of the effect of parameters such as cesium concentration, the properties of the mineral and the characteristics of the solution phase, on cesium adsorption. Finally, interaction of cesium with some different minerals is described in some detail.

Improved myocardial tagging contrast

Abstract: Myocardial tagging is a new noninvasive MRI method that allows the study of myocardial motion with high accuracy. However, with conventional tagging techniques tagging contrast is impaired at later heart phases due to longitudinal relaxation. An improved method, called Complementary SPAtial Modulation of Magnetization (CSPAMM), which separates the component of the magnetization with the tagging information from the relaxed component by subtraction of two measurements with first a positive and then a negative tagging grid, is presented. This technique improves the grid contrast and greatly facilitates the automatic evaluation of the myocardial motion. Thus the motion assessment of the entire heart cycle becomes possible. The improvements are documented by numerical simulations and by experiments on phantoms and on human volunteers.

ATP-dependent glutathione S-conjugate export pump in the vacuolar membrane of plants

Abstract: PLANTS are exposed to many potentially phytotoxic foreign compounds, such as microbial toxins and agrochemicals (xenobiotics). Detoxification and elimination of these compounds within or from the cell is a prerequisite for their survival. Metabolism and detoxification of xenobiotics are remarkably similar in plants and animals and can generally be divided into three phases1,2. In the first phase, a foreign compound may be oxidized, reduced or hydrolysed to introduce or reveal a functional group. In a second step, the activated xenobiotic is conjugated to either glutathione, glucuronate (animals), or malonyl or glucosyl moieties (plants) by the respective transferases. In animals the third step, excretion of conjugated xenobiotics to the extracellular medium, is mediated by a specific ATPase1,3–5. In plants, instead of excretion, conjugates of xenobiotics appear to be stored in the large central vacuole6, but it is not known how they are transported into this organelle. We show here that glutathione S-conjugate uptake into the vacuole is mediated by a specific ATPase which is remarkably similar to the glutathione S-conjugate export pumps in the canalicular membrane of mammalian liver.

Poly(hydroxyalkanoates): A Fifth Class of Physiologically Important Organic Biopolymers?†

Abstract: Along with polyisoprenoids, polypeptides, polysaccharides, and polynucleotides, Nature contains a further group of biopolymers, the poly(hydroxyalkanoates). The commonest member of this group, poly[(R)-3-hydroxybutyrate] P(3-HB), had been identified by Lemoigne as early as the 1920s, as a storage substance in the microorganism Bacillus megaterium made up of more than 12000 (3-HB) units. However, the widespread distribution and significance of these biopolymers has only become clear recently. The work of Reusch, in particular, has shown that low molecular weight P(3-HB) (100–200 3-HB units) occurs in the cell membranes of prokaryotic and eukaryotic organisms. The function of P(3-HB) in the latter sources is largely unknown; it has been proposed that a complex of P(3-HB) and calcium polyphosphate acts as an ion channel through the membrane. Indeed, it has even been speculated that P(3-HB) plays a role in transport of DNA through the cell wall. In the present article, the following subjects will be discussed: metabolism of P(3-HB) and analogous polyesters in the synthesis and degradation of storage materials; P(3-HB) as a starting material for chiral synthetic building blocks; synthesis of cyclic oligomers (oligolides) of up to ten 3-HB units, and their crystal structure; high molecular weight bio-copolymers of hydroxybutyrate and hydroxyvalerate (BIOPOL) as biologically degradable plastics; nonbiological production of polyhydroxyalkanoates from 3-hydroxy carboxylic acids and the corresponding β-lactones; specific synthesis of linear oligomers with a narrow molecular weight distribution, consisting of about 100 (R)-3-hydroxybutyrate units, by using an exponential coupling procedure; structure of the polyesters, and a comparison with other polymers; the experimental results which led to the postulation of a P(3-HB) ion channel through the cell wall; modeling of P(3-HB) helices of various diameters, by using the parameters obtained from the crystal structures of oligolides; formation of a crown ester complex and ion transport experiments with the triolide of 3-HB. The article describes one example of the contributions that synthetic organic chemists can make to important biological problems in an interdisciplinary framework.

The importance of blueschist → eclogite dehydration reactions in subducting oceanic crust

Abstract: The metamorphic evolution and dehydration of subducting oceanic crust may be predicted by combining calculated pressure-temperature ( P-T ) paths with a model of metabasalt phase equilibria. In steady-state subduction zones with high rates of shear heating, the upper parts of the subducting oceanic crust progress through the greenschist → amphibolite → granulite → eclogite facies, whereas lower parts of the subducting oceanic crust progress through the blueschist → eclogite facies. In steady-state subduction zones with moderate rates of shear heating, most of the subducting oceanic crust passes through the blueschist → eclogite transition. In steady-state subduction zones with low rates of shear heating, the entire subducting oceanic crust lies within the blueschist facies to depths greater than 70 km. For oceanic crust containing 1-2 wt% H 2 O, dehydration will not begin until the onset of eclogite- or amphibolite-facies metamorphism, depending on the P-T path. For many subduction zones, the most important dehydration reactions in the subducting oceanic crust occur at the blueschist → eclogite facies transition associated with the breakdown of lawsonite (or clinozoisite), glaucophane, and chlorite. Large amounts of H 2 O released by blueschist → eclogite dehydration reactions could trigger partial melting in the overlying mantle wedge and may play a crucial role in the generation of arc magmas.

Genes for a microaerobically induced oxidase complex in Bradyrhizobium japonicum are essential for a nitrogen-fixing endosymbiosis.

Abstract: We report the discovery of a Bradyrhizobium japonicum gene cluster (fixNOQP) in which mutations resulted in defective soybean root-nodule bacteroid development and symbiotic nitrogen fixation. The predicted, DNA-derived protein sequences suggested that FixN is a heme b and copper-binding oxidase subunit, FixO a monoheme cytochrome c, FixQ a polypeptide of 54 amino acids, and FixP a diheme cytochrome c and that they are all membrane-bound. The isolation and analysis of membrane proteins from B. japonicum wild-type and mutant cells revealed two c-type cytochromes of 28 and 32 kDa as the likely products of the fixO and fixP genes and showed that both were synthesized only under oxygen-limited growth conditions. Furthermore, fixN insertion and fixNO deletion mutants grown microaerobically or anaerobically (with nitrate) exhibited a strong decrease in whole-cell oxidase activity as compared with the wild type. The data suggest that the fixNOQP gene products are induced at low oxygen concentrations and constitute a member of the bacterial heme/copper cytochrome oxidase superfamily. The described features are compatible with the postulate that this oxidase complex is specifically required to support bacterial respiration in endosymbiosis.

Supervisory control of a rapid thermal multiprocessor

Abstract: An application of supervisory control theory to a piece of semiconductor manufacturing equipment is presented. The approach allows the flexible design and reliable update of processing recipes to accommodate frequently changing manufacturing requirements. An input-output interpretation of supervisory control theory is given. This interpretation leads to a generic implementation scheme for manufacturing systems. A synthesis fixpoint algorithm implementation using binary decision diagrams enables the design of supervisors of realistic size. A sample synthesis for an oxide growth recipe is performed on a state space of the order of 10/sup 6/ states. The actual implementation of the logic sequencing control software for the application under investigation is described. >

Scale-invariant motion in intermittent chaotic systems

Abstract: We investigate the dynamics generated from iterated maps and analyze the motion in terms of the probabilistic continuous-time random-walk (CTRW) approach. Two different CTRW models are considered: (i) Particles jump between sites (turning points) or (ii) particles move at a constant velocity between sites and choose a new direction at random. For both models we study the mean-squared displacement 〈${\mathit{r}}^{2}$(t)〉 and the propagator P(r,t), the probability to be at location r at time t having started at the origin at t=0. Iterated maps are used to generate both dispersive and enhanced diffusion and the results are analyzed using the CTRW framework and scaling arguments. For the case of dispersive motion we discuss the problem of the stationary state and point out its relevance.

C‐O‐H‐S fluid composition and oxygen fugacity in graphitic metapelites

Abstract: C-0-H fluid produced by the equilibration of HzO and excess graphite must maintain the atomic H/O ratio of water, 2: 1. This constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric-isothermal conditions. The O,, H20 and CO, fugacities (J& fHto and fC%) of such fluids have been estimated from equations of state and fit as a function of pressure and temperature. These fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration, e.g. pelitic lithologies. Because there are no compositional degrees of freedom for graphite-saturated fluids produced entirely by dehydration, the variance of the dehydration process is not increased in comparison with that in non-graphitic systems. Thus, compositional 'buffering' of C-0-H fluids by dehydration equilibria, a common petrological model, requires that redox reactions, decarbonation reactions or external, H/O#2, fluid sources perturb the evolution of the metamorphic system. Such perturbations are not likely to be significant in metapelitic environments, but their tendency will be to increase the fo, of the fluid phase. At high metamorphic grades, pyrite desulphidation reactions may cause a substantial reduction of fHz0 and slight increases info, and fcs relative to sulphur-free fluid. At low metamorphic grade, sulphur solubility in H/O =s 2 fluids is so low that pyrite decomposition must occur by sulphurconserving reactions that cause iron depletion in silicates, a common feature of sulphidic pelites. With increasing temperature and sulphur solubility, pyrite desulphidation may be driven by dehydration reactions or infiltration of H,O-rich fluids. The absence of magnetite and the assemblages carbonate + aluminosilicate or pyrite + pyrrhotite + ilmenite from most graphitic metapelites is consistent with an H/O = 2 model for GCOH(S) fluid. For graphitic rocks in which such a model is inapplicable, a phase diagram variable that defines the H/O ratio of GCOH(S) fluid is more useful than the conventional

Gauge invariance and current algebra in nonrelativistic many-body theory

Abstract: The main purpose of this paper is to further our theoretical understanding of the fractional quantum Hall effect, in particular of spin effects, in two-dimensional incompressible electron fluids subject to a strong, transverse magnetic field. As a prerequisite for an analysis of the quantum Hall effect, the authors develop a general formulation of the many-body theory of spinning particles coupled to external electromagnetic fields and moving through a general, geometrically nontrivial background. Their formulation is based on a Lagrangian path-integral quantization and is valid in arbitrary coordinates, including coordinates moving according to a volume-preserving flow. It is found that nonrelativistic quantum theory exhibits a fundamental, local U(1)\ifmmode\times\else\texttimes\fi{}SU(2) gauge invariance, and the corresponding gauge fields are identified with physical, external fields. To illustrate the usefulness of their formalism, the authors prove a general form of the quantum-mechanical Larmor theorem and discuss some well-known effects, including the Barnett-Einstein-de Haas effect and superconductivity, emphasizing the implications of U(1)\ifmmode\times\else\texttimes\fi{}SU(2) gauge invariance. They then consider two-dimensional, incompressible quantum fluids in more detail. Exploiting U(1)\ifmmode\times\else\texttimes\fi{}SU(2) gauge invariance, they calculate the leading terms in the effective actions of such systems as functionals of the U(1) and SU(2) gauge fields, on large-distance and low-frequency scales. Among the applications of these results are a simple proof of the Goldstone theorem for spin waves and the linearresponse theory of two-dimensional, incompressible Hall fluids, including a Hall effect for spin currents and sum rules for the response coefficients. For two-dimensional, incompressible systems with broken parity and time-reversal symmetry, a particularly significant implication of U(1)\ifmmode\times\else\texttimes\fi{}SU(2) gauge invariance is a duality between the physics inside the bulk of the system and the physics of gapless, chiral modes propagating along the boundary of the system. These modes form chiral $\stackrel{^}{\mathrm{u}}(1)$ and $\mathrm{s}\stackrel{^}{\mathrm{u}}(2)$ current algebras. The representation theory of these current algebras, combined with natural physical constraints, permits one to derive the quantization of the response coefficients, such as the Hall conductivity. A classification of incompressible Hall fluids is outlined, and many examples, including one concerning a superfluid $^{3}\mathrm{He}$-$\frac{A}{B}$ interface, are discussed.

Enzymatic recognition of the base pair between isocytidine and isoguanosine.

Abstract: The ability of various polymerases to catalyze the template-directed formation of a base pair between isoguanine (iso-G) and isocytosine (iso-C) in duplex oligonucleotides has been investigated. A new procedure was developed for preparing derivatives of deoxyisoguanosine suitable for incorporation into DNA using an automated DNA synthesizer. T7 RNA polymerase, AMV reverse transcriptase, and the Klenow fragment of DNA polymerase all incorporated iso-G opposite iso-C in a template. T4 DNA polymerase did not. Several polymerases also incorporated iso-G opposite T, presumably through pairing with a minor tautomeric form of iso-G complementary to T. In a template, iso-G directs the incorporation of both iso-C and T when Klenow fragment is the catalyst and only U when T7 RNA polymerase is the catalyst. Further, derivatives of iso-C were found to undergo significant amounts of deamination under alkaline conditions used for base deprotection after automated oligonucleotide synthesis. Both the deamination reaction of iso-C and the ambivalent tautomeric forms of iso-G make it unlikely that the (iso-C).(iso-G) base pair was a part of information storage molecules also containing the A-T and G*C base pairs found in primitive forms of life that emerged on planet earth several billion years ago. Nevertheless, the extra letters in the genetic alphabet can serve useful roles in a contemporary laboratory setting. The interaction between two complementary oligonucleotide strands remains one of the most remarkable examples of molecular recognition known to chemistry, especially because several features of nucleic acids appear a priori to suit them poorly for this process. Because oligonucleotides are flexible unidimensional polymers, duplex formation involves substan- tial loss of conformational entropy. Specificity is mediated by hydrogen bonds, problematic in an aqueous environment. Heterocyclic rings bearing exocyclic heteroatomic substituents form the hydrogen bonds. Yet such heterocycles often have accessible tautomeric forms that create hydrogen-bonding ambiguities (Elgureo et al., 1976), a fact that has generated much confusion in the history of oligonucleotide research (Watson & Crick, 1953a). Despite these features, nucleic acids perform superbly for the storage and transmission of encoded information. The fidelity of recognition between nucleic acids is extremely high, especially when assisted by enzymes. Most polymerases catalyze the replication of nucleic acids with fewer than one error per million. Only with this level of precision is life as we know it possible.

Operator algebras and conformal field theory

Abstract: We define and study two-dimensional, chiral conformal field theory by the methods of algebraic field theory. We start by characterizing the vacuum sectors of such theories and show that, under very general hypotheses, their algebras of local observables are isomorphic to the unique hyperfinite type III1 factor. The conformal net determined by the algebras of local observables is proven to satisfy Haag duality. The representation of the Moebius group (and presumably of the entire Virasoro algebra) on the vacuum sector of a conformal field theory is uniquely determined by the Tomita-Takesaki modular operators associated with its vacuum state and its conformal net. We then develop the theory of Moebius covariant representations of a conformal net, using methods of Doplicher, Haag and Roberts. We apply our results to the representation theory of loop groups. Our analysis is motivated by the desire to find a “background-independent” formulation of conformal field theories.

X-ray/microwave relation of different types of active stars

Abstract: Coronal active stars of seven classes between spectral types F and M, single and double, are compared in their quiescent radio and X-ray luminosities L(R) and L(X). We find, largely independent of stellar class, log L(X) is less than about log L(R) + 15.5. This general relation points to an intimate connection between the nonthermal, energetic electrons causing the radio emission and the bulk plasma of the corona responsible for thermal X-rays. The relation, observed over six orders of magnitude, suggests that the heating mechanism necessarily involves particle acceleration. We derive requirements for simple models based on optically thin gyrosynchrotron emission of mildly relativistic electrons and thermal X-rays from the bulk plasma. We discuss the possibility that a portion of the accelerated particles heats the ambient plasma by collisions. More likely, plasma heating and particle acceleration may occur in parallel and in the same process, but at a fixed ratio.

Systematics, distribution, and host specificity of grass endophytes

Abstract: Clavicipitaceous endophytes (Ascomycetes) are distributed worldwide in many grasses and sedges forming a perennial and often mutualistic association with their hosts. Most endophytes appear to produce alkaloid toxins in infected plants. The high frequency of infection in many grasses and in certain grassland communities may indicate a selective advantage of infected over non-infected host plants due to their toxic effects on grazing animals and insects. Field observations and artificial inoculations of seedlings have demonstrated a high degree of specificity of most endophytes to their host plant, particularly in asexual, seed-borne endophytes. Specific isozyme genotypes found on several host species suggest that host-specific physiological races may occur. Knowledge of host range and host specificity is vital for potential applications of endophytes in pest control.

Cosmological theory without singularities

Abstract: A theory of gravitation is constructed in which all homogeneous and isotropic solutions are nonsingular, and in which all curvature invariants are bounded All solutions for which curvature invariants approach their limiting values approach de Sitter space The action for this theory is obtained by a higher-derivative modification of Einstein's theory We expect that our model can easily be generalized to solve the singularity problem also for anisotropic cosmologies

The fourth immunoglobulin-like domain of NCAM contains a carbohydrate recognition domain for oligomannosidic glycans implicated in association with L1 and neurite outgrowth.

Abstract: We have previously shown that the neural adhesion molecules L1 and NCAM interact with each other to form a complex which binds more avidly to L1 than L1 to L1 alone (Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990a. J. Cell Biol. 110:193-208). This cis-association between L1 and NCAM is carbohydrate-dependent (Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990b. J. Cell Biol. 110:209-218). In the present study, we report that L1 and NCAM bind to each other via oligomannosidic carbohydrates expressed by L1, but not by NCAM, as shown in several experiments: (a) complex formation between L1 and NCAM is inhibited by a mAb to oligomannosidic carbohydrates and by the oligosaccharides themselves; (b) NCAM binds to oligomannosidic carbohydrates; (c) within the L1/NCAM complex, the oligomannosidic carbohydrates are hidden from accessibility to a mAb against oligomannosidic carbohydrates; (d) the recombinant protein fragment of NCAM containing the immunoglobulin-like domains and not the fragment containing the fibronectin type III homologous repeats binds to oligomannosidic glycans. Furthermore, the fourth immunoglobulin-like domain of NCAM shows sequence homology with carbohydrate recognition domains of animal C-type lectins and, surprisingly, also with plant lectins. A peptide comprising part of the C-type lectin consensus sequence in the fourth immunoglobulin-like domain of NCAM interferes with the association between L1 and NCAM. The functional importance of oligomannosidic glycans at the cell surface was shown for neurite outgrowth in vitro. When neurons from early postnatal mouse cerebellum were maintained on laminin or poly-L-lysine, neurite outgrowth was inhibited by oligomannosidic glycans, by glycopeptides, glycoproteins, or neoglycolipids containing oligomannosidic glycans, but not by nonrelated oligosaccharides or oligosaccharide derivates. Neurite outgrowth was also inhibited by the peptide comprising part of the C-type lectin consensus sequence in the fourth immunoglobulin-like domain of NCAM. The combined results suggest that carbohydrate-mediated cis-associations between adhesion molecules at the cell surface modulate their functional properties.

Boron isotope variations in nature: a synthesis

Abstract: The large relative mass difference between the two stable isotopes of boron, 10B and 11B, and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes. Published δ11B values (relative to the NBS SRM-951 standard) span a wide range of ≈ 90‰. The lowest δ11B values around — 30‰ are reported for non-marine evaporite minerals and certain tourmalines. The most 11B-enriched reservoir known to date are brines from Australian salt lakes and the Dead Sea of Israel with δ11B values up to +59‰. Dissolved boron in present-day seawater has a constant world-wide δ11B value of + 39.5‰. In this paper, available δ11B data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects, including possible tracer applications of boron-isotope geochemistry, are summarized.

Review of New Experimental Techniques for Investigating Random Sequential Adsorption

Abstract: Burgeoning interest in random sequential adsorption (RSA) processes has led to a surge of theoretical results, but experimental work is lagging behind, due to a dearth of suitable techniques. This article reviews integrated-optical techniques for investigating the kinetics of RSA and related processes. The basic idea is to measure the phase shifts of guided waves, due to the adsorption of particles at the surface of a planar waveguide. The technique is very well suited to investigating 2-dimensional RSA, and can yield high-quality kinetic adsorption data, precise enough for rigorously testing theoretical predictions. The current state of the art allow adsorbed mass to be measured quasicontinuously with a precision of at least 1 ng/cm2.

Turbulence close to a rough urban surface part I: Reynolds stress

Abstract: The Reynolds stress field of the urban roughness sublayer is studied experimentally at a site in the centre of Zurich (Switzerland). Turbulence observations at various heights within and above a street canyon are used together with profiles of mean variables to determine an average profile of Reynolds stress for the lowest few tens of meters of an urban roughness sublayer.