Showing papers by "ETH Zurich published in 1997"
TL;DR: The X-ray crystal structure of the nucleosome core particle of chromatin shows in atomic detail how the histone protein octamer is assembled and how 146 base pairs of DNA are organized into a superhelix around it.
Abstract: The X-ray crystal structure of the nucleosome core particle of chromatin shows in atomic detail how the histone protein octamer is assembled and how 146 base pairs of DNA are organized into a superhelix around it. Both histone/histone and histone/DNA interactions depend on the histone fold domains and additional, well ordered structure elements extending from this motif. Histone amino-terminal tails pass over and between the gyres of the DNA superhelix to contact neighbouring particles. The lack of uniformity between multiple histone/DNA-binding sites causes the DNA to deviate from ideal superhelix geometry.
7,841 citations
Book•
02 Jun 1997TL;DR: In this article, an approach to Extremes via Point Processes is presented, and statistical methods for Extremal Events are presented. But the approach is limited to time series analysis for heavy-tailed processes.
Abstract: Reader Guidelines.- Risk Theory.- Fluctuations of Sums.- Fluctuations of Maxima.- Fluctuations of Upper Order Statistics.- An Approach to Extremes via Point Processes.- Statistical Methods for Extremal Events.- Time Series Analysis for Heavy-Tailed Processes.- Special Topics.
3,577 citations
TL;DR: Test calculations starting from conformers with random torsion angle values showed that DYANA is capable of efficient calculation of high-quality protein structures with up to 400 amino acid residues, and of nucleic acid structures.
2,768 citations
TL;DR: In this article, a new finite element method is presented that features the ability to include in the finite element space knowledge about the partial differential equation being solved, which can therefore be more efficient than the usual finite element methods.
Abstract: A new finite element method is presented that features the ability to include in the finite element space knowledge about the partial differential equation being solved This new method can therefore be more efficient than the usual finite element methods An additional feature of the partition-of-unity method is that finite element spaces of any desired regularity can be constructed very easily This paper includes a convergence proof of this method and illustrates its efficiency by an application to the Helmholtz equation for high wave numbers The basic estimates for a posteriori error estimation for this new method are also proved © 1997 by John Wiley & Sons, Ltd
2,387 citations
TL;DR: The TROSY principle should benefit a variety of multidimensional solution NMR experiments, especially with future use of yet somewhat higher polarizing magnetic fields than are presently available, and thus largely eliminate one of the key factors that limit work with larger molecules.
Abstract: Fast transverse relaxation of 1H, 15N, and 13C by dipole-dipole coupling (DD) and chemical shift anisotropy (CSA) modulated by rotational molecular motions has a dominant impact on the size limit for biomacromolecular structures that can be studied by NMR spectroscopy in solution. Transverse relaxation-optimized spectroscopy (TROSY) is an approach for suppression of transverse relaxation in multidimensional NMR experiments, which is based on constructive use of interference between DD coupling and CSA. For example, a TROSY-type two-dimensional 1H,15N-correlation experiment with a uniformly 15N-labeled protein in a DNA complex of molecular mass 17 kDa at a 1H frequency of 750 MHz showed that 15N relaxation during 15N chemical shift evolution and 1HN relaxation during signal acquisition both are significantly reduced by mutual compensation of the DD and CSA interactions. The reduction of the linewidths when compared with a conventional two-dimensional 1H,15N-correlation experiment was 60% and 40%, respectively, and the residual linewidths were 5 Hz for 15N and 15 Hz for 1HN at 4°C. Because the ratio of the DD and CSA relaxation rates is nearly independent of the molecular size, a similar percentagewise reduction of the overall transverse relaxation rates is expected for larger proteins. For a 15N-labeled protein of 150 kDa at 750 MHz and 20°C one predicts residual linewidths of 10 Hz for 15N and 45 Hz for 1HN, and for the corresponding uniformly 15N,2H-labeled protein the residual linewidths are predicted to be smaller than 5 Hz and 15 Hz, respectively. The TROSY principle should benefit a variety of multidimensional solution NMR experiments, especially with future use of yet somewhat higher polarizing magnetic fields than are presently available, and thus largely eliminate one of the key factors that limit work with larger molecules.
2,262 citations
2,105 citations
01 Oct 1997
TL;DR: This paper describes a new algorithm for best matching prefix using binary search on hash tables organized by prefix lengths that scales very well as address and routing table sizes increase and introduces Mutating Binary Search and other optimizations that considerably reduce the average number of hashes to less than 2.
Abstract: Internet address lookup is a challenging problem because of increasing routing table sizes, increased traffic, higher speed links, and the migration to 128 bit IPv6 addresses. IP routing lookup requires computing the best matching prefix, for which standard solutions like hashing were believed to be inapplicable. The best existing solution we know of, BSD radix tries, scales badly as IP moves to 128 bit addresses. Our paper describes a new algorithm for best matching prefix using binary search on hash tables organized by prefix lengths. Our scheme scales very well as address and routing table sizes increase: independent of the table size, it requires a worst case time of log2(address bits) hash lookups. Thus only 5 hash lookups are needed for IPv4 and 7 for IPv6. We also introduce Mutating Binary Search and other optimizations that, for a typical IPv4 backbone router with over 33,000 entries, considerably reduce the average number of hashes to less than 2, of which one hash can be simplified to an indexed array access. We expect similar average case behavior for IPv6.
928 citations
TL;DR: In this article, the GENERIC is formulated as a general equation for the nonequilibrium reversible-irreversible coupling (abbreviated as GIC) and its solutions are derived.
Abstract: We recognize some universal features of macroscopic dynamics describing the approach of a well-established level of description (that is, successfully tested by experimental observations) to equilibrium. The universal features are collected in a general equation for the nonequilibrium reversible-irreversible coupling (abbreviated as GENERIC). In this paper we formulate a GENERIC, derive properties of its solutions, and discuss their physical interpretation. The relation of the GENERIC with thermodynamics is most clearly displayed in a formulation that uses contact structures. The GENERIC is also discussed in the presence of noise. In applications we either search for new governing equations expressing our insight into a particular complex fluid or take well-established governing equations and cast them into the form of a GENERIC. In the former case we obtain the governing equations as particular realizations of the GENERIC structure; in the latter case we justify the universality of the GENERIC and derive some properties of solutions. Both types of applications are discussed mainly in the following paper [Phys. Rev. E 56, 6633 (1997)].
915 citations
TL;DR: This paper shows that complementary CMOS is the logic style of choice for the implementation of arbitrary combinational circuits if low voltage, low power, and small power-delay products are of concern.
Abstract: Recently reported logic style comparisons based on full-adder circuits claimed complementary pass-transistor logic (CPL) to be much more power-efficient than complementary CMOS. However, new comparisons performed on more efficient CMOS circuit realizations and a wider range of different logic cells, as well as the use of realistic circuit arrangements demonstrate CMOS to be superior to CPL in most cases with respect to speed, area, power dissipation, and power-delay products. An implemented 32-b adder using complementary CMOS has a power-delay product of less than half that of the CPL version. Robustness with respect to voltage scaling and transistor sizing, as well as generality and ease-of-use, are additional advantages of CMOS logic gates, especially when cell-based design and logic synthesis are targeted. This paper shows that complementary CMOS is the logic style of choice for the implementation of arbitrary combinational circuits if low voltage, low power, and small power-delay products are of concern.
911 citations
17 Aug 1997
TL;DR: These novel compounds are produced by allowing Ln2(CO3)3.mH2O and boric acid to react with each other at a molar ratio of 1:2 under a practically air-tight condition in a container, with the CO2 gas removed continuously as it is formed in the course of the reaction.
Abstract: A group signature scheme allows members of a group to sign messages on the group's behalf such that the resulting signature does not reveal their identity Only a designated group manager is able to identify the group member who issued a given signature Previously proposed realizations of group signature schemes have the undesirable property that the length of the public key is linear in the size of the group In this paper we propose the first group signature scheme whose public key and signatures have length independent of the number of group members and which can therefore also be used for large groups Furthermore, the scheme allows the group manager to add new members to the group without modifying the public key The realization is based on methods for proving the knowledge of signatures
881 citations
TL;DR: This article showed that covalently bound fluorine hardly ever acts as a hydrogen-bond acceptor, which is in accord with results of other physicochemical studies and with the physical properties of fluorinated organic compounds.
Abstract: Statistical analysis of structural data and detailed inspection of individual crystal structures culled from the Cambridge Structural Database and the Brookhaven Protein Data Bank show that covalently bound fluorine (in contrast to anionic fluoride) hardly ever acts as a hydrogen-bond acceptor. The weakness of covalently bound fluorine as hydrogen-bond acceptor is backed by results of new molecular orbital calculations on model systems using ab initio intermolecular perturbation theory (IMPT), and is in accord with results of other physicochemical studies and with the physical properties of fluorinated organic compounds. Factors influencing the strength of hydrogen bonding in extended systems are discussed.
TL;DR: For a number of well-known time-evolution equations for nonequilibrium systems, the authors extract a common structure from these equations, referred to as a general equation for the reversible-irreversible coupling (GENERIC).
Abstract: For a number of well-known time-evolution equations for nonequilibrium systems we extract a common structure from these equations, referred to as a general equation for the nonequilibrium reversible-irreversible coupling (GENERIC). This fundamental structure is determined by four building blocks, two ``potentials'' (total energy and entropy) and two ``matrices.'' We illustrate for various examples how three of the four building blocks can be determined in a rather straightforward manner so that, within our GENERIC approach to nonequilibrium dynamics, understanding of a given nonequilibrium system is reduced to determining a single ``metric matrix,'' or friction matrix, either empirically or by more microscopic considerations. In formulating nonisothermal polymer kinetic theories, we show how the general structure provides a clear distinction between spring potentials of energetic and entropic origins in the various time-evolution equations.
TL;DR: The recombinant murine prion protein, mPrP(23-231), was expressed in E. coli with uniform 15N-labeling and NMR experiments showed that the previously determined globular three-dimensional structure of the C-terminal domain mPrp(121-231) is preserved in the intact protein, and that the Nterminal polypeptide segment 23-120 is flexibly disordered as mentioned in this paper, based on nearly complete sequence-specific assignments for the backbone amide nitrogens, amide protons and alpha-protols of
TL;DR: A Lagrangian-based method of analysis is introduced to examine the space-time structure and dynamics of extratropical cyclogenesis and can provide a qualitative depiction of, quantitative information about, and dynamical insight into, key features of mid-latitude cyclones.
Abstract: A Lagrangian-based method of analysis is introduced to examine the space-time structure and dynamics of extratropical cyclogenesis. the three-step method involves the calculation of extensive ensembles of trajectories, the evaluation of the Lagrangian time-trace of physical variables along these paths, and the application of objective selection criteria to identify significant Lagrangian structures. the approach can provide a qualitative depiction of, quantitative information about, and dynamical insight into, key features of mid-latitude cyclones. In this, the first of a two-part study, examples are given of the application of the method. A case-study approach has been adopted and used to identify coherent ensembles of trajectories (CETs) whose dynamics are seminal to an event of Atlantic cyclogenesis, to trace the origin of subsynoptic potential vorticity anomalies, and to analyse stratosphere-troposphere exchange accompanying extratropical cyclogenesis. In addition, a statistical investigation has been made of the climatology of CETs in the northern hemisphere for one particular winter month. Some consideration has been given to the shortcomings and potential of the method, and its complementarity with other approaches.
TL;DR: A monoclonal antibody is described, 15B3, that can discriminate between the normal and disease-specific forms of PrP, suggesting that it recognizes an epitope common to prions from different species.
Abstract: Prions are infectious particles causing transmissible spongiform encephalopathies (TSEs). They consist, at least in part, of an isoform (PrPSc) of the ubiquitous cellular prion protein (PrPC). Conformational differences between PrPC and PrPSc are evident from increased beta-sheet content and protease resistance in PrPSc. Here we describe a monoclonal antibody, 15B3, that can discriminate between the normal and disease-specific forms of PrP. Such an antibody has been long sought as it should be invaluable for characterizing the infectious particle as well as for diagnosis of TSEs such as bovine spongiform encephalopathy (BSE) or Creutzfeldt-Jakob disease (CJD) in humans. 15B3 specifically precipitates bovine, murine or human PrPSc, but not PrPC, suggesting that it recognizes an epitope common to prions from different species. Using immobilized synthetic peptides, we mapped three polypeptide segments in PrP as the 15B3 epitope. In the NMR structure of recombinant mouse PrP, segments 2 and 3 of the 15B3 epitope are near neighbours in space, and segment 1 is located in a different part of the molecule. We discuss models for the PrPSc-specific epitope that ensure close spatial proximity of all three 15B3 segments, either by intermolecular contacts in oligomeric forms of the prion protein or by intramolecular rearrangement.
Book•
13 Oct 1997TL;DR: The most popular undergraduate textbook for geophysics is the Geophysics: A Coursebook for Undergraduates as mentioned in this paper, which contains twelve chapters covering the same breadth of topics as earlier editions, but in a substantially modernized fashion to facilitate classroom teaching.
Abstract: This enduringly popular undergraduate textbook has been thoroughly reworked and updated, and now comprises twelve chapters covering the same breadth of topics as earlier editions, but in a substantially modernized fashion to facilitate classroom teaching. Covering both theoretical and applied aspects of geophysics, clear explanations of the physical principles are blended with step-by-step derivations of the key equations and over 400 explanatory figures to explain the internal structure and properties of the planet, including its petroleum and mineral resources. New topics include the latest data acquisition technologies, such as satellite geophysics, planetary landers, ocean bottom seismometers, and fibre optic methods, as well as recent research developments in ambient noise interferometry, seismic hazard analysis, rheology, and numerical modelling - all illustrated with examples from the scientific literature. Student-friendly features include separate text boxes with auxiliary explanations and advanced topics of interest; reading lists of foundational, alternative, or more detailed resources; end-of-chapter review questions and an increased number of quantitative exercises. Completely new to this edition is the addition of computational exercises in Python, designed to help students acquire important programming skills and develop a more profound understanding of geophysics.
TL;DR: In this article, the authors combine global distributions of aerosol loading resulting from transport models for soil dust, sulfate, sea salt, and carbonaceous aerosol, and estimate optical thicknesses.
Abstract: We combine global distributions of aerosol loading resulting from transport models for soil dust, sulfate, sea salt, and carbonaceous aerosol. From the aerosol distributions we estimate optical thicknesses and compare them with Sun photometer measurements and satellite retrievals, thereby revealing problems with both model results and comparisons with such measurements. Globally, sulfate, dust, and carbonaceous particles appear to contribute equally to the total aerosol optical thickness. Owing to the different optical properties of different aerosol types, aerosol composition should be taken into consideration for estimating the aerosol climate effect as well as for aerosol retrievals from satellite measurements.
Book•
01 Feb 1997TL;DR: In this article, a clear and thorough explanation of the mechanical properties and fracture processes of concrete is given, followed by an evaluation of test methods for assessing both experimental and numerical models.
Abstract: This book begins with a clear and thorough explanation of the mechanical properties and fracture processes of concrete, followed by an evaluation of test methods for assessing both experimental and numerical models. The book then presents different types of fracture models available to design experiments and analyze their accuracy. Numerous examples are included to support key concepts, and hundreds of photographs, diagrams, and tables further illuminate the text.
TL;DR: In this paper, the authors proposed a new actualistic model for dolomite formation in Lagoa Vermelha, a shallow-water isolated coastal lagoon east of Rio de Janeiro, Brazil.
Abstract: Dolomite, despite its thermodynamic stability and abundance in the ancient rock record, is rarely found forming in Holocene environments. This enigma is frequently called the Dolomite Problem. The recent discovery of modern dolomite formation in Lagoa Vermelha, a shallow-water isolated coastal lagoon east of Rio de Janeiro, Brazil, provides a new environment to investigate the factors promoting dolomite precipitation under earth surface conditions. Lagoa Vermelha serves as a natural laboratory in which the dolomite formation process was studied using an integrated hydrologic, geochemical, and sedimentological approach. The results of this study indicate that Ca-dolomite precipitation occurs under anoxic hypersaline conditions within a black sludge layer directly overlying the water/se iment interface. With deposition, the dolomite undergoes an "ageing" process, whereby increased ordering of the crystal structure occurs. Both the initial precipitation and subsequent early diagenesis are strongly mediated by microbial activity. In fact, using sulfate-reducing bacteria cultured from Lagoa Vermelha samples, a highly ordered dolomite has been produced in the laboratory at low temperatures. These experimental results combined with the study of the natural environment mandate that a microbial factor be added to the list of factors capable of causing dolomite precipitation. Considering the Lagoa Vermelha system, we propose a new actualistic model for dolomite formation, which we call the microbial dolomite model.
TL;DR: Nucleosome core particles containing native and mutant histones made in bacteria have facilitated its X-ray structure determination at 2.8 A resolution.
TL;DR: A summary of the scientific work performed on the system during the last 6 years is presented in this paper, with special emphasis on the relationship between the structural and the physical properties, and possible mechanisms responsible for the metal-insulator transition, which is the major open question for perovskites, are also discussed.
Abstract: perovskites (R = rare earth) provide a remarkable opportunity to study the relationship between structural and physical properties since, by moving along the 4f rare earth series, the evolution of several transport and magnetic properties can be nicely correlated to the steric effects associated with the lanthanide contraction. The most appealing example is probably the metal - insulator transition discovered for the compounds with , whose critical temperature increases with decreasing size of the rare earth ion. On the other hand, several experimental results show that in perovskites the degree of Ni 3d - O 2p hybridization is extremely high. The purely ionic configuration, first suggested by neutron diffraction experiments, has been then substituted by a ground state where the and configurations are strongly mixed. In this paper, a summary of the scientific work performed on the system during the last 6 years is presented. The results of the different experimental techniques are successively reviewed, with special emphasis on the relationship between the structural and the physical properties. The possible mechanisms responsible for the metal - insulator transition, which is the major open question for perovskites, are also discussed.
TL;DR: 13C Enrichment and 13C13C coupling patterns showed conclusively that 1-deoxy-D-xylulose and not mevalonate is the predominant isoprenoid precursor of phytol, beta-carotene, and lutein.
Abstract: The incorporation of [1-13C]- and [2,3,4,5-13C4]1-deoxy-d-xylulose into β-carotene, lutein, phytol, and sitosterol in a cell culture of Catharanthus roseus was analyzed by NMR spectroscopy. The labeling patterns of the isoprene precursors, isopentenyl pyrophosphate and dimethylallyl pyrophosphate, were obtained from the terpenes by a retrobiosynthetic approach. 13C Enrichment and 13C13C coupling patterns showed conclusively that 1-deoxy-d-xylulose and not mevalonate is the predominant isoprenoid precursor of phytol, β-carotene, and lutein. Label from 1-deoxyxylulose was also diverted to phytosterols to a minor extent (6% relative to carotene and phytol formation). The data demonstrate that the formation of isopentenyl pyrophosphate from pentulose occurs strictly by an intramolecular rearrangement process.
TL;DR: In this article, the authors used a nested regional climate model with a doubled CO2 experiment over the Alpine region and found that the simulated temperature change signal shows a substantial elevation dependency, mostly during the winter and spring seasons, resulting in more pronounced warming at high elevations than low elevations.
Abstract: Results are presented from a present-day and a doubled CO2 experiment over the Alpine region with a nested regional climate model. The simulated temperature change signal shows a substantial elevation dependency, mostly during the winter and spring seasons, resulting in more pronounced warming at high elevations than low elevations. This is caused by a depletion of snowpack in doubled CO2 conditions and further enhanced by the snow–albedo feedback. This result is consistent with some observed temperature trends for anomalously warm years over the Alpine region and suggests that high elevation temperature changes could be used as an early detection tool for global warming. Changes in precipitation, as well as other components of the surface energy and water budgets, also show an elevation signal, which may have important implications for impact assessments in high elevation regions.
TL;DR: In this paper, a general formalism based upon the subtraction method for the calculation of next-to-leading order QCD cross sections for any number of jets in any type of hard collisions is presented.
TL;DR: The oncofetal fibronectin (B-FN) isoform is present in vessels of neoplastic tissues during angiogenesis but not in mature vessels and could provide a target for diagnostic imaging and therapy of cancer.
Abstract: The oncofetal fibronectin (B-FN) isoform is present in vessels of neoplastic tissues during angiogenesis but not in mature vessels. B-FN could therefore provide a target for diagnostic imaging and therapy of cancer. Phage display libraries have been used to isolate human antibody fragments with pan-species recognition of this isoform. We describe the use of these fragments in nude mice to target an aggressive tumor (grafted F9 murine teratocarcinoma). Imaging in real time was done by infrared photodetection of a chemically coupled fluorophore. The targeting was improved by use of affinity-matured fragments with low kinetic dissociation rates (koff = 1.5 x 10(-4) s-1) and also by engineering dimeric fragments via a C-terminal amphipathic helix.
TL;DR: The genetic characterization and the putative biochemical functions of cytochrome c-specific maturation proteins suggest that they may be organized in a membrane-bound maturase complex, and models for linear maturation pathways are proposed wherever possible.
Abstract: Biogenesis of respiratory cytochromes is defined as consisting of the posttranslational processes that are necessary to assemble apoprotein, heme, and sometimes additional cofactors into mature enzyme complexes with electron transfer functions. Different biochemical reactions take place during maturation: (i) targeting of the apoprotein to or through the cytoplasmic membrane to its subcellular destination; (ii) proteolytic processing of precursor forms; (iii) assembly of subunits in the membrane and oligomerization; (iv) translocation and/or modification of heme and covalent or noncovalent binding to the protein moiety; (v) transport, processing, and incorporation of other cofactors; and (vi) folding and stabilization of the protein. These steps are discussed for the maturation of different oxidoreductase complexes, and they are arranged in a linear pathway to best account for experimental findings from studies concerning cytochrome biogenesis. The example of the best-studied case, i.e., maturation of cytochrome c, appears to consist of a pathway that requires at least nine specific genes and more general cellular functions such as protein secretion or the control of the redox state in the periplasm. Covalent attachment of heme appears to be enzyme catalyzed and takes place in the periplasm after translocation of the precursor through the membrane. The genetic characterization and the putative biochemical functions of cytochrome c-specific maturation proteins suggest that they may be organized in a membrane-bound maturase complex. Formation of the multisubunit cytochrome bc, complex and several terminal oxidases of the bo3, bd, aa3, and cbb3 types is discussed in detail, and models for linear maturation pathways are proposed wherever possible.
TL;DR: It is shown that filament growth in freshly prepared Sup35pN solutions can be induced by seeding with a dilute suspension of preformed filaments, suggesting that seeding might be responsible for the maintenance of the [PSI] element in vivo.
Abstract: The yeast non-Mendelian genetic factor [PSI], which enhances the efficiency of tRNA-mediated nonsense suppression in Saccharomyces cerevisiae, is thought to be an abnormal cellular isoform of the Sup35 protein. Genetic studies have established that the N-terminal part of the Sup35 protein is sufficient for the genesis as well as the maintenance of [PSI]. Here we demonstrate that the N-terminal polypeptide fragment consisting of residues 2–114 of Sup35p, Sup35pN, spontaneously aggregates to form thin filaments in vitro. The filaments show a β-sheet-type circular dichroism spectrum, exhibit increased protease resistance, and show amyloid-like optical properties. It is further shown that filament growth in freshly prepared Sup35pN solutions can be induced by seeding with a dilute suspension of preformed filaments. These results suggest that the abnormal cellular isoform of Sup35p is an amyloid-like aggregate and further indicate that seeding might be responsible for the maintenance of the [PSI] element in vivo.
TL;DR: Results provide unequivocal proof that PAL and tyrosine ammonia-lyase activities reside in the same polypeptide and imply that maize can produce p-coumaric acid from both phenylalanine and tyosine.
Abstract: A full-length cDNA encoding phenylalanine ammonia-lyase (PAL) from Zea mays L. was isolated and the coding region was expressed in Escherichia coli as a C-terminal fusion to glutathione S-transferase. After purification by glutathione-Sepharose chromatography, the glutathione S-transferase moiety was cleaved off and the resulting PAL enzyme analyzed. In contrast to PAL from dicots, this maize PAL isozyme catalyzed the deamination of both L-phenylalanine (PAL activity) and L-tyrosine (tyrosine ammonialyase activity). These results provide unequivocal proof that PAL and tyrosine ammonia-lyase activities reside in the same polypeptide. In spite of large differences in the Michaelis constant and turnover number of the two activities, their catalytic efficiencies are very similar. Also, both activities have the same pH and temperature optima. These results imply that maize can produce p-coumaric acid from both phenylalanine and tyrosine.
TL;DR: In this paper, the authors derived the effective energy-momentum tensor for cosmological perturbations and proved its gauge-invariance and applied it to study the influence of perturbation on the behavior of the Friedmann background in inflationary universe scenarios.
Abstract: We derive the effective energy-momentum tensor for cosmological perturbations and prove its gauge-invariance. The result is applied to study the influence of perturbations on the behaviour of the Friedmann background in inflationary Universe scenarios. We found that the back reaction of cosmological perturbations on the background can become important already at energies below the self-reproduction scale.
TL;DR: In this article, the effective energy-momentum tensor (EMT) for cosmological perturbations and the back-reaction problem were formulated in a gauge-invariant manner.
Abstract: We study the effective energy-momentum tensor (EMT) for cosmological perturbations and formulate the gravitational back-reaction problem in a gauge-invariant manner. We analyze the explicit expressions for the EMT in the cases of scalar metric fluctuations and of gravitational waves and derive the resulting equations of state. The formalism is applied to investigate the back-reaction effects in chaotic inflation. We find that for long wavelength scalar and tensor perturbations, the effective energy density is negative and thus counteracts any preexisting cosmological constant. For scalar perturbations during an epoch of inflation, the equation of state is de Sitter-like.