Showing papers by "ETH Zurich published in 1990"
TL;DR: In this article, a modification of this method is proposed as a more powerful analytical technique, where different coercivity fractions of IRM are remagnetized in successively smaller fields along three orthogonal directions.
Abstract: The common ferromagnetic minerals have distinctive, characteristic coercivities and thermomagnetic properties. The analysis of the acquisition curve of isothermal remanent magnetization (IRM) is a useful but often ambiguous diagnostic technique. For a more conclusive interpretation, IRM acquisition must be combined with subsequent thermal demagnetization of the IRM. A modification of this method is proposed as a more powerful analytical technique. Different coercivity fractions of IRM are remagnetized in successively smaller fields along three orthogonal directions. The thermal demagnetization of each orthogonal component of the composite IRM is then plotted separately. This method often gives a clearer interpretation of the ferromagnetic mineral content of a rock. Examples are described for limestone and sandstone samples.
1,434 citations
TL;DR: A new Watson-Crick base pair, with a hydrogen bonding pattern different from that in the A·T and G·C base pairs, is incorporated into duplex DNA and RNA byDNA and RNA polymerases and expands the genetic alphabet from 4 to 6 letters.
Abstract: A new Watson-Crick base pair, with a hydrogen bonding pattern different from that in the A.T and G.C base pairs, is incorporated into duplex DNA and RNA by DNA and RNA polymerases and expands the genetic alphabet from 4 to 6 letters. This expansion could lead to RNAs with greater diversity in functional groups and greater catalytic potential.
639 citations
TL;DR: In this paper, a simple cascode with the gate voltage of the cascode transistor being controlled by a feedback amplifier called a regulated cascode is presented, where the minimum output voltage is lower by 30 to 60% while the output conductance and the feedback capacitance are lower by about 100 times.
Abstract: A simple cascode with the gate voltage of the cascode transistor being controlled by a feedback amplifier called a regulated cascode is presented. In comparison to the standard cascode circuit, the minimum output voltage is lower by about 30 to 60% while the output conductance and the feedback capacitance are lower by about 100 times. An analytical large-signal, small-signal, and noise analysis is carried out. Some applications like current mirrors and voltage amplifiers are discussed. Experimental results confirming the theory are presented. >
553 citations
01 Apr 1990-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The L3 experiment as discussed by the authors is one of the six large detectors designed for the new generation of electron-positron accelerators, which is the only detector that concentrates its efforts on limited goals of measuring electrons, muons and photons.
Abstract: The L3 experiment is one of the six large detectors designed for the new generation of electron-positron accelerators. It is the only detector that concentrates its efforts on limited goals of measuring electrons, muons and photons. By not attempting to identify hadrons, L3 has been able to provide an order of magnitude better resolution for electrons, muons and photons. Vertices and hadron jets are also studied. The construction of L3 has involved much state of the art technology in new principles of vertex detection and in new crystals for large scale electromagnetic shower detection and ultraprecise muon detection. This paper presents a summary of the construction of L3.
505 citations
TL;DR: For a review of the major developments in organic synthesis during the past 25 years, and to project them into the future, see, e.g., the authors, for instance, the authors of this article.
Abstract: This review article is an attempt to sketch the important developments in organic synthesis during the past 25 years, and to project them into the future.—The primary motivations that once induced chemists to undertake natural product syntheses no longer exist. Instead of target structures themselves, molecular function and activity now occupy center stage. Thus, inhibitors with an affinity for all the important natural enzymes and receptors have moved to the fore as potential synthetic targets.—New synthetic methods are most likely to be encountered in the fields of biological and organometallic chemistry. Enzymes, whole organisms, and cell cultures for enan-tioselective synthesis of specific substances have already been incorporated into the synthetic arsenals of both research laboratories and industry. In addition, designing appropriate analogues to transition states and intermediates should soon make it possible, with the aid of the mammalian immune system and gene technology, to prepare catalytically active monoclonal antibodies for almost any reaction; perhaps, more important, such processes will increasingly come to be applied on an industrial scale.-The discovery of truly new reactions is likely to be limited to the realm of transition-metal organic chemistry, which will almost certainly provide us with additional “miracle reagents” in the years to come. As regards main group elements (“organoelemental chemistry”), we can surely anticipate further stepwise improvements in experimental procedures and the broader application of special techniques, leading to undreamed of efficiency and selectivity with respect to known procedures. The primary center of attention for all synthetic methods will continue to shift toward catalytic and enantioselective variants; indeed, it will not be long before such modifications will be available with every standard reaction for converting achiral educts into chiral products. Analysis, spectroscopy, structure determination, theory, and electronic data processing have all become indispensable in organic synthesis. Only with the aid of these “tools” will the methods of organic chemistry permit selective syntheses of ever larger and more complex systems on both the molecular and supramolecular levels.—Examples have been introduced throughout this discourse to illustrate its many themes, and a very comprehensive bibliography should help the interested reader become more familiar with important keywords and authors.[1 ]—This article will have served its intended purpose if it changes the minds of some of those who claim organic chemistry is a mature science, and if it causes students to discover the vitality and forcefulness with which organic synthesis is meeting new challenges and attempting to fulfill old dreams.
Er zeigt uns so in seinem wissenschaftlichen Leben, das die Chemie nicht von einer Theorie, nicht von einer Methode aus zu erschopfen ist, und das Erkenntnis und Nutzen in ihr untrennbar verwoben sind.1
R. Koch, writing about Louis Pasteur
456 citations
TL;DR: The 1:1 complex of the mutant Antp(C39––S) homeodomain with a 14 bp DNA fragment corresponding to the BS2 binding site was studied by nuclear magnetic resonance (NMR) spectroscopy in aqueous solution to enable a unique docking of the protein on the DNA.
Abstract: The 1:1 complex of the mutant Antp(C39----S) homeodomain with a 14 bp DNA fragment corresponding to the BS2 binding site was studied by nuclear magnetic resonance (NMR) spectroscopy in aqueous solution. The complex has a molecular weight of 17,800 and its lifetime is long compared with the NMR chemical shift time scale. Investigations of the three-dimensional structure were based on the use of the fully 15N-labelled protein, two-dimensional homonuclear proton NOESY with 15N(omega 2) half-filter, and heteronuclear three-dimensional NMR experiments. Based on nearly complete sequence-specific resonance assignments, both the protein and the DNA were found to have similar conformations in the free form and in the complex. A sufficient number of intermolecular 1H-1H Overhauser effects (NOE) could be identified to enable a unique docking of the protein on the DNA, which was achieved with the use of an ellipsoid algorithm. In the complex there are intermolecular NOEs between the elongated second helix in the helix-turn-helix motif of the homeodomain and the major groove of the DNA. Additional NOE contacts with the DNA involve the polypeptide loop immediately preceding the helix-turn-helix segment, and Arg5. This latter contact is of special interest, both because Arg5 reaches into the minor groove and because in the free Antp(C39----S) homeodomain no defined spatial structure could be found for the apparently flexible N-terminal segment comprising residues 0-6.
420 citations
TL;DR: In this paper, the authors show that 10Be concentrations in polar ice can be used to study variations in the solar activity, particularly the 11-year cycle, in time periods pre-dating historical records.
Abstract: A DETAILED knowledge of the history of solar magnetic activity is important in several respects. From satellite data there is increasing evidence that solar magnetic activity and solar irradiance are positively correlated, a conclusion with important implications for climatology1. Because of the complexity of variations in solar activity, a long record is necessary for understanding the mechanisms responsible for heliomagnetic cyclicity2. Here we show that 10Be concentrations in polar ice can be used to study variations in the solar activity—particularly the 11-year cycle—in time periods pre-dating historical records.
353 citations
TL;DR: The use of heteronuclear filters in two-dimensional (2D) [ 1 H, 1 H]-NMR experiments is focused on and the selection of the material covered was primarily motivated by its impact on the practice of protein structure determination in solution, and on NMR studies of intermolecular interactions with biological macromolecules.
Abstract: The use of heteronuclear filters enables the editing of complex 1H nuclear magnetic resonance (NMR) spectra into simplified subspectra containing a lesser number of resonance lines, which are then more easily amenable to detailed spectral analysis. This editing is based on the creation of heteronuclear two-spin or multiple-spin coherence and discrimination between protons that do or do not participate in these heteronuclear coherences. In principle, heteronuclear editing can be used in conjunction with one-dimensional or multidimensional 1H-NMR experiments for studies of a wide variety of low-molecular-weight compounds or macromolecular systems, and is implicitely applied in a wide range of heteronuclear NMR experiments with proton detection (e.g. Bax et al. 1983; Griffey & Redfield, 1987). In the present article we shall focus on the use of heteronuclear filters in two-dimensional (2D) [1H, 1H]-NMR experiments. The selection of the material covered was primarily motivated by its impact on the practice of protein structure determination in solution, and on NMR studies of intermolecular interactions with biological macromolecules. Section 2 surveys potential applications of heteronuclear filters in this area. The remainder of the article is devoted to an introduction of the theoretical principles used in heteronuclear filters, and to a detailed description of the experimental implementation of these measurements. In writing the review we tried to minimize redundancy with the recent article in Quarterly Review of Biophysics by Griffey & Redfield (1987) and to concentrate on experiments that were introduced during the period 1986–9.
348 citations
TL;DR: The NMR method provides data that are in many ways complementary to those obtained from x-ray crystallography and thus promises to widen the view of protein molecules, giving a clearer insight into the relation between structure and function.
329 citations
TL;DR: Special attention is given to areas where solubility limitations pose major problems, as in the preparation of highly concentrated solutions of recombinant proteins for structural determination with NMR and X-ray crystallography, refolding of inclusion body proteins, studies of membrane protein dynamics, and the formulation of proteins for pharmaceutical use.
Abstract: This review deals with ways of stabilizing proteins against aggregation and with methods to determine, predict, and increase solubility. Solvent additives (osmolytes) that stabilize proteins are listed with a description of their effects on proteins and on the solvation properties of water. Special attention is given to areas where solubility limitations pose major problems, as in the preparation of highly concentrated solutions of recombinant proteins for structural determination with NMR and X-ray crystallography, refolding of inclusion body proteins, studies of membrane protein dynamics, and in the formulation of proteins for pharmaceutical use. Structural factors relating to solubility and possibilities for protein engineering are analyzed.
303 citations
TL;DR: In this paper, a new formulation of Toda theories is proposed by showing that they can be regarded as certain gauged Wess-Zumino-Novikov-Witten (WZNW) models.
TL;DR: In this paper, the structure of the Fock modules over A1(1) introduced by Wakimoto was investigated and it was shown that irreducible highest weight modules arise as degree zero cohomology groups in a BRST-like complex of Fock module.
Abstract: We investigate the structure of the Fock modules overA1(1) introduced by Wakimoto. We show that irreducible highest weight modules arise as degree zero cohomology groups in a BRST-like complex of Fock modules. Chiral primary fields are constructed as BRST invariant operators acting on Fock modules. As a result, we obtain a free field representation of correlation functions of theSU(2) WZW model on the plane and on the torus. We also consider representations of fractional level arising in Polyakov's 2D quantum gravity. Finally, we give a geometrical, Borel-Weil-like interpretation of the Wakimoto construction.
TL;DR: Key enzymes of the degradation of lignin substructures have been identified recently and recombinant DNA techniques have been successfully applied to elucidate the structure and regulation of the corresponding genes.
TL;DR: Modulation of DNA repair occurs in a simple yeast minichromosome and correlates with gene expression, nucleosome stability, and (possibly) control of replication.
TL;DR: In this article, boundary scavenging plays a major role in the removal of 10Be from the Pacific Ocean, and the residence time of the 10Be with respect to chemical scavenging varies regionally from > 1000 years at red-clay sites in the deep central Pacific to ∼ 100 years at the margin sites.
TL;DR: In this article, the concentrations of dissolved iron in fog droplets were measured and it was found that a large fraction of the total Fe is present as dissolved Fe(II) in fog water.
Abstract: ALTHOUGH liquid water is a minor component of the troposphere, the chemical reactions that occur in water droplets (clouds, fog or rain) affect the composition of the atmosphere and the atmos-pheric input to terrestrial and aquatic ecosystems. Iron (Fe(II) and Fe(III)) is involved in many of these processes, particularly redox and radical chain reactions1–6. Here we report measurements of Fe(II) concentration (up to 200 μ?) in fog water (pH 3–7). We find that a large fraction of the total Fe is present as dissolved Fe(II). The concentrations of Fe(II) increase both with exposure to light and with decreasing pH. The concentrations of dissolved iron in fog droplets are much higher than those measured in oxic surface waters and so atmospheric deposition may be a source of dissolved Fe(II) to surface waters, thereby increasing the availabil-ity of iron to aquatic biota.
TL;DR: In this paper, a linear large-signal MOS transconductor with the gain adjustable linearly by a voltage is described, and a perfect linear transfer characteristic is obtained by two cross-coupled differential transistor pairs operating in saturation pairwise at unequal bias, offering offset-free operation, with both differential or singleended input and differential output.
Abstract: A linear large-signal MOS transconductor with the gain adjustable linearly by a voltage is described. A perfect linear transfer characteristic is obtained by two cross-coupled differential transistor pairs operating in saturation pairwise at unequal bias, offering offset-free operation, with both differential or single-ended input and differential output. Single-ended output is achievable by use of a current mirror. The nonlinearity caused by mobility reduction, channel-length modulation, mismatch, etc. is discussed. A test circuit with transconductance of 6.25 mu mho has been built with 3- mu m MOS components, and a linearity error of less than +or-1% was measured for an input voltage range from -4 to 4 V. >
TL;DR: In this paper, the selection of coherence-transfer pathways in EPR pulse experiments to suppress artifacts and undesired echoes is discussed, exemplified by four-pulse spin-echo experiments.
TL;DR: In this paper, the probem of central configurations of the N-body problem has been studied in the context of celestial mechanics and has since taken on a life of its own.
Abstract: This paper concerns an old problem which arose in celestial mechanics and has since taken on a life of its own: the probem of central configurations of the N-body problem
TL;DR: The physico-chemical properties of these organogels were characterized using a variety of techniques such as NMR, DSC, dynamic shear viscosity measurements, and light scattering, and based on these measurements, preliminary models for the structure of these novel systems were developed.
Abstract: A new family of organogels is described. They originate from water-in-oil microemulsions, from which the name microemulsion gels or microemulsion-based gels is derived. Two different types of such gels are presented here, referred to asgelatine gels andlecithin gels, respectively. In the case of gelatine gels, the initial ternary system typically consists of isooctane, AOT (bis 2-ethylhexyl sodiumsuccinate) and water; gelation is induced by solubilization of gelatine in the water microphase above a critical concentration. In the case of lecithin gels no polymeric material is needed. Starting from a reverse micellar solution of lecithin (50–200 mM) in an organic solvent, gelation is induced by the addition of a small amount of water. The molar ratio of water to lecithin typically varies between 1 and 12 for the 50 different solvents investigated to date. These gels are isotropic, thermoreversible and optically transparent. For both microemulsion gels the influence of the concentration of the components on gelation is presented in the form of preliminary phase diagrams. The physico-chemical properties of these organogels were characterized using a variety of techniques such as NMR, DSC, dynamic shear viscosity measurements, and light scattering. Based on these measurements, preliminary models for the structure of these novel systems were developed. It is possible to co-solubilize a variety of reactive molecules in these gels. Therefore, it may be possible to use these organogels for a number of chemical, pharmaceutical, and cosmetic applications.
TL;DR: The structure of the phycobiliprotein phycoerythrocyanin from the thermophilic cyanobacterium Mastigocladus laminosus has been determined at 2.7 A resolution by X-ray diffraction methods on the basis of the molecular model of C-phycocyanin, and the two structures are very similar.
TL;DR: In this article, a transresistor realized with only two MOS devices using the same technique is presented, achieving linearity error of less than ± 0-5% for the output swing from supply voltage Vss to VDD.
Abstract: Square-difference is a new and very attractive linearisation technique. It has been successfully used to implement large-signal MOS transconductors. A transresistor realised with only two MOS devices using the same technique is presented. A linearity error of less than ±0–5% for the output swing from supply voltage Vss to VDD is achieved.
TL;DR: In this article, an alternative geometrical proof of asymptotic completeness for an arbitrary number of quantum particles interacting through shortrange pair potentials is given, which relies on an estimate showing that the intercluster motion concentrates on classical trajectories.
Abstract: We give an alternative geometrical proof of asymptotic completeness for an arbitrary number of quantum particles interacting through shortrange pair potentials. It relies on an estimate showing that the intercluster motion concentrates asymptotically on classical trajectories.
TL;DR: The two erythrocyte Ca2+ pumps display high sequence divergence in a few localized regions that may determine isoform-specific functional specializations; for example, the putative extracellular loop separating transmembrane domains 1 and 2, the highly negatively charged region previously suggested to be involved in Ca2- binding, and the site of cAMP-dependent protein kinase phosphorylation.
TL;DR: The characteristics of a nodulation-gene region of B. japonicum that contributes only marginally to the bacterium's ability to nodulate soybean but is essential for the nodulation of the three alternative hosts are reported.
Abstract: Bradyrhizobium japonicum is the root nodule endosymbiont of soybean (Glycine max), mung bean (Vigna radiata), cowpea (Vigna unguiculata), and Siratro (Macroptilium atropurpureum). We report the characteristics of a nodulation-gene region of B. japonicum that contributes only marginally to the bacterium's ability to nodulate soybean but is essential for the nodulation of the three alternative hosts. This DNA region consists of two open reading frames designated nodV and nodW. The predicted amino acid sequences of the NodV and NodW proteins suggest that they are members of the family of two-component regulatory systems, which supports the hypothesis that NodV responds to an environmental stimulus and, after signal transduction, NodW may be required to positively regulate the transcription of one or several unknown genes involved in the nodulation process. It seems likely that all host plants produce the necessary signal, whereas host specificity may be brought about by the product(s) of the gene(s) activated by NodW.
TL;DR: The nuclear magnetic resonance data present no evidence for a preferred relative orientation of the two domains of human metallothionein-2, and the polypeptide conformations in the three proteins are also closely similar.
TL;DR: A retrospective of the Darmstadt database system project, also known as DASDBS, is presented, aimed at providing data management support for advanced applications, such as geo-scientific information systems and office automation.
Abstract: A retrospective of the Darmstadt database system project, also known as DASDBS, is presented. The project is aimed at providing data management support for advanced applications, such as geo-scientific information systems and office automation. Similar to the dichotomy of RSS and RDS in System R, a layered architectural approach was pursued: a storage management kernel serves as the lowest common denominator of the requirements of the various applications classes, and a family of application-oriented front-ends provides semantically richer functions on top of the kernel. The lessons that were learned from building the DASDBS system are discussed. Particular emphasis is placed on the following issues: the role of nested relations, the experiences with using object buffers for coupling the system with the programming-language environment and the learning process in implementing multilevel transactions. >
TL;DR: The results show that transgenic rabbits may represent a convenient and economic system for the rapid production of biologically active protein in milk.
Abstract: To test the potential usefulness of transgenic rabbits as production systems for human proteins of pharmaceutical value, we cloned the rabbit beta-casein promoter and fused it to the genomic sequence of the human interleukin-2 (hIL2) gene. Four transgenic female rabbits were tested for expression and biological activity of the foreign protein in their milk. The milk of all four females proved to contain biologically active hIL2. The results show that transgenic rabbits may represent a convenient and economic system for the rapid production of biologically active protein in milk.
TL;DR: The results clearly demonstrate that the thalli of fruticose lichens harbor a great variety of filamentous fungi, and it can be assumed that many of the observed fungi are in some way associated with their hosts and are not only passive random colonizers.
Abstract: The colonization by filamentous fungi of seventeen samples of fruticose lichens belonging to the genera Cladonia and Sterocaulon collected at one site in the southern Black Forest, FRG, has been studied. A total of 506 fungal strain types were isolated: 166 of them were isolated more than once and 62 of these sporulated and were identified to genus or species. The isolates can be assigned to three ecological groups: soil and litter fungi, symbionts or pathogens of higher plants, and apparently specific lichen-inhabiting taxa. Community ordination was done by cluster and principal component analysis using the taxa that accounted for at least 3% of the isolates in at least one sample. The results clearly demonstrate that the thalli of fruticose lichens harbor a great variety of filamentous fungi. They do not appear to be very specific to one host or confined to only one microhabitat. It can be assumed, however, that many of the observed fungi are in some way associated with their hosts and are not only passive random colonizers.
TL;DR: In this paper, electron-spin transient nutation is exploited to simplify complicated solid state ESR spectra, making use of the dependence of the nutation frequencies on the transition matrix element of the excited ESR line.