Showing papers by "Karlsruhe Institute of Technology published in 2004"
TL;DR: The measured optical spectra of the nanofabricated gold structures come very close to the theoretical expectations and additional numerical simulations show that the structures exhibit a frequency range with negative permeability for a beam configuration in which the magnetic field couples to the LC resonance.
Abstract: An array of single nonmagnetic metallic split rings can be used to implement a magnetic resonance, which arises from an inductor-capacitor circuit (LC) resonance, at 100-terahertz frequency. The excitation of the LC resonance in the normal-incidence geometry used in our experiments occurs through the coupling of the electric field of the incident light to the capacitance. The measured optical spectra of the nanofabricated gold structures come very close to the theoretical expectations. Additional numerical simulations show that our structures exhibit a frequency range with negative permeability for a beam configuration in which the magnetic field couples to the LC resonance. Together with an electric response that has negative permittivity, this can lead to materials with a negative index of refraction.
1,448 citations
TL;DR: The technical challenges that have to be met when implementing the interesting new technology of spectrum pooling are described, which represents the coexistence of two mobile radio systems within the same frequency range.
Abstract: This article describes the technical challenges that have to be met when implementing the interesting new technology of spectrum pooling. This notion represents the coexistence of two mobile radio systems within the same frequency range. It enables the secondary utilization of already licensed frequency bands as aimed at by several regulatory authorities worldwide. The goal of spectrum pooling is to enhance spectral efficiency by overlaying a new mobile radio system on an existing one without requiring any changes to the actual licensed system. Several demanding tasks originate from this idea. Some of them have been solved in recent research projects. Others are subject to ongoing investigations. Here, the state of the art in spectrum pooling is presented.
1,268 citations
TL;DR: The fabrication—through direct laser writing—and detailed characterization of high-quality large-scale f.c. c.
Abstract: The past decade has witnessed intensive research efforts related to the design and fabrication of photonic crystals1,2. These periodically structured dielectric materials can represent the optical analogue of semiconductor crystals, and provide a novel platform for the realization of integrated photonics. Despite intensive efforts, inexpensive fabrication techniques for large-scale three-dimensional photonic crystals of high enough quality, with photonic bandgaps at near-infrared frequencies, and built-in functional elements for telecommunication applications, have been elusive. Direct laser writing by multiphoton polymerization3 of a photoresist has emerged as a technique for the rapid, cheap and flexible fabrication of nanostructures for photonics. In 1999, so-called layer-by-layer4 or woodpile photonic crystals were fabricated with a fundamental stop band at 3.9 μm wavelength5. In 2002, a corresponding 1.9 μm was achieved6, but the important face-centred-cubic (f.c.c.) symmetry was abandoned. Importantly, fundamental stop bands or photonic bandgaps at telecommunication wavelengths have not been demonstrated. In this letter, we report the fabrication—through direct laser writing—and detailed characterization of high-quality large-scale f.c.c. layer-by-layer structures, with fundamental stop bands ranging from 1.3 to 1.7 μm.
1,054 citations
TL;DR: An overview on the available candidates in the quest for the least coordinating anion and a summary of new applications, available starting materials, and general strategies to introduce a WCA into a system are presented.
Abstract: A review on the available candidates in the quest for the least coordinating anion and a summary of new applications, available starting materials, and general strategies to introduce a WCA into a system. Some of the unusual properties of WCA salts such as high soly. in low dielec. media, pseudo gas-phase conditions in condensed phases, and the stabilization of weakly bound and low-charged complexes are rationalized on thermodn. grounds. Limits of the WCAs, i.e., anion coordination and decompn., are shown and a quantum chem. anal. of all types of WCAs is presented which allows the choice of a particular WCA to be based on quant. data from a wide range of different anions. [on SciFinder (R)]
929 citations
TL;DR: The random waypoint model is a commonly used mobility model for simulations of wireless communication networks and some of its fundamental stochastic properties are investigated, including the transition length and time of a mobile node between two waypoints, the spatial distribution of nodes, and the direction angle at the beginning of a movement transition.
Abstract: The random waypoint model is a commonly used mobility model for simulations of wireless communication networks. By giving a formal description of this model in terms of a discrete-time stochastic process, we investigate some of its fundamental stochastic properties with respect to: (a) the transition length and time of a mobile node between two waypoints, (b) the spatial distribution of nodes, (c) the direction angle at the beginning of a movement transition, and (d) the cell change rate if the model is used in a cellular-structured system area.
The results of this paper are of practical value for performance analysis of mobile networks and give a deeper understanding of the behavior of this mobility model. Such understanding is necessary to avoid misinterpretation of simulation results. The movement duration and the cell change rate enable us to make a statement about the "degree of mobility" of a certain simulation scenario. Knowledge of the spatial node distribution is essential for all investigations in which the relative location of the mobile nodes is important. Finally, the direction distribution explains in an analytical manner the effect that nodes tend to move back to the middle of the system area.
888 citations
01 May 2004
TL;DR: The first phase of the Pierre Auger Observatory has been completed and all of the sub-systems that will be used in the full instrument to be tested under field conditions as discussed by the authors.
Abstract: Construction of the first stage of the Pierre Auger Observatory has begun. The aim of the Observatory is to collect unprecedented information about cosmic rays above 1018 eV. The first phase of the project, the construction and operation of a prototype system, known as the engineering array, has now been completed. It has allowed all of the sub-systems that will be used in the full instrument to be tested under field conditions. In this paper, the properties and performance of these sub-systems are described and their success illustrated with descriptions of some of the events recorded thus far. © 2003 Elsevier B.V. All rights reserved.
775 citations
17 May 2004
TL;DR: A quantitative comparison of both approaches to spectrum pooling aims at enabling public access to these spectral ranges without sacrificing the transmission quality of the actual license owners, and it is obvious that both approaches sacrifice bandwidth of the rental system.
Abstract: The public mobile radio spectrum has become a scarce resource while wide spectral ranges are only rarely used. Here, the new strategy called spectrum pooling is considered. It aims at enabling public access to these spectral ranges without sacrificing the transmission quality of the actual license owners. Unfortunately, using OFDM modulation in a spectrum pooling system has some drawbacks. There is an interaction between the licensed system and the OFDM based rental system due to the non-orthogonality of their respective transmit signals. This interaction is described mathematically, providing a quantitative evaluation of the mutual interference that leads to an SNR loss in both systems. However, this interference can be mitigated by windowing the OFDM signal in the time domain or by the adaptive deactivation of adjacent subcarriers providing flexible guard bands between licensed and rental system. It is obvious that both approaches sacrifice bandwidth of the rental system. A quantitative comparison of both approaches is given as a tradeoff between interference reduction and throughput in the rental system.
642 citations
TL;DR: Induction of DSBs could be used as a means for the controlled manipulation of plant genomes in an analogous way for the use of marker gene excision and site-specific integration.
Abstract: The efficient repair of double-strand breaks (DSBs) in genomic DNA is important for the survival of all organisms. In recent years, basic mechanisms of DSB repair in somatic plant cells have been elucidated. DSBs are mainly repaired by non-homologous end-joining (NHEJ). The repair can be associated with deletions, but also insertions due to copying genomic sequences from elsewhere into the break. Species-specific differences of NHEJ have been reported and an inverse correlation of deletion size to genome size has been postulated, indicating that NHEJ might contribute significantly to evolution of genome size. DSB repair by homologous recombination (HR) might also influence genome organization. Whereas homology present in an allelic or an ectopic position is hardly used for repair, the use of homologous sequences in close proximity to the break is frequent. A 'single-strand annealing' mechanism that leads to sequence deletions between direct repeats is particularly efficient. This might explain the accumulation of single long terminal repeats of retroelements in cereal genomes. The conservative 'synthesis-dependent strand annealing' mechanism, resulting in conversions without crossovers is also prominent and seems to be significant for the evolution of tandemly arranged gene families such as resistance genes. Induction of DSBs could be used as a means for the controlled manipulation of plant genomes in an analogous way for the use of marker gene excision and site-specific integration.
568 citations
07 Nov 2004
TL;DR: In this paper, Quick Ontology Mapping (QOM) is proposed as a way to trade off between effectiveness and efficiency of the mapping generation algorithm, which has lower run-time complexity than existing prominent approaches.
Abstract: (Semi-)automatic mapping - also called (semi-) automatic alignment - of ontologies is a core task to achieve interoperability when two agents or services use different ontologies In the existing literature, the focus has so far been on improving the quality of mapping results We here consider QOM, Quick Ontology Mapping, as a way to trade off between effectiveness (ie quality) and efficiency of the mapping generation algorithms We show that QOM has lower run-time complexity than existing prominent approaches Then, we show in experiments that this theoretical investigation translates into practical benefits While QOM gives up some of the possibilities for producing high-quality results in favor of efficiency, our experiments show that this loss of quality is marginal
484 citations
TL;DR: An approach to integrate various similarity methods is presented, which determines similarity through rules which have been encoded by ontology experts and are then combined for one overall result.
Abstract: Ontology mapping is important when working with more than one ontology Typically similarity considerations are the basis for this In this paper an approach to integrate various similarity methods is presented In brief, we determine similarity through rules which have been encoded by ontology experts These rules are then combined for one overall result Several boosting small actions are added All this is thoroughly evaluated with very promising results
473 citations
TL;DR: In this article, the authors explore the hypothesis that the primary fluctuations responsible for the non-Fermi liquid physics are those associated with the destruction of the large Fermi surface of the Fermani liquid.
Abstract: This paper is concerned with the weak-moment magnetism in heavy-fermion materials and its relation to the non-Fermi liquid physics observed near the transition to the Fermi liquid. We explore the hypothesis that the primary fluctuations responsible for the non-Fermi liquid physics are those associated with the destruction of the large Fermi surface of the Fermi liquid. Magnetism is suggested to be a low-energy instability of the resulting small Fermi surface state. A concrete realization of this picture is provided by a fractionalized Fermi liquid state which has a small Fermi surface of conduction electrons, but also has other exotic excitations with interactions described by a gauge theory in its deconfined phase. Of particular interest is a three-dimensional fractionalized Fermi liquid with a spinon Fermi surface and a U(1) gauge structure. A direct second-order transition from this state to the conventional Fermi liquid is possible and involves a jump in the electron Fermi surface volume. The critical point displays non-Fermi liquid behavior. A magnetic phase may develop from a spin density wave instability of the spinon Fermi surface. This exotic magnetic metal may have a weak ordered moment although the local moments do not participate in the Fermi surface. Experimental signatures of this phase and implications for heavy-fermion systems are discussed.
TL;DR: In this article, large-eddy simulations of an industrial gas turbine burner are carried out for both nonreacting and reacting flow using a compressible unstructured solver, and results demonstrate the capacity of the LES to predict the mean flow, with and without combustion, as well as its main unstable modes: it is shown, for example, that the PVC mode is very strong for the cold flow but disappears with combustion.
TL;DR: In this paper, the authors reported the observation of a state consistent with X(3872) decaying into J/ψπ+π-decomposition, where the observed width was consistent with the detector resolution and the results were found to be converging well with the measurements by the Belle Collaboration using b± decays.
Abstract: The observation of a state consistent with X(3872) decaying into J/ψπ+π- was reported. The X(3872) mass was measured to be 3871.3±0.7(stat)±0.4(syst)MeV/c2 from a sample of 730±90 candidates. The observed width was consistent with the detector resolution. The results were found to be converging well with the measurements by the Belle Collaboration using b± decays.
18 Sep 2004
TL;DR: In this article, a modified multi-objective evolutionary algorithm is introduced to focus search on these knee regions, resulting in a smaller set of solutions which are likely to be more relevant to the decision maker.
Abstract: Many real-world optimization problems have several, usually conflicting objectives. Evolutionary multi-objective optimization usually solves this predicament by searching for the whole Pareto-optimal front of solutions, and relies on a decision maker to finally select a single solution. However, in particular if the number of objectives is large, the number of Pareto-optimal solutions may be huge, and it may be very difficult to pick one “best” solution out of this large set of alternatives. As we argue in this paper, the most interesting solutions of the Pareto-optimal front are solutions where a small improvement in one objective would lead to a large deterioration in at least one other objective. These solutions are sometimes also called “knees”. We then introduce a new modified multi-objective evolutionary algorithm which is able to focus search on these knee regions, resulting in a smaller set of solutions which are likely to be more relevant to the decision maker.
01 Jan 2004
TL;DR: In this paper, the authors report on recent breakthroughs in the functional analytic approach to maximal regularity for parabolic evolution equations, which set off a wave of activity in the last years and allowed to establish maximal L p -regularity for large classes of classical partial differential operators and systems.
Abstract: In these lecture notes we report on recent breakthroughs in the functional analytic approach to maximal regularity for parabolic evolution equations, which set off a wave of activity in the last years and allowed to establish maximal L p -regularity for large classes of classical partial differential operators and systems.
01 Oct 2004
TL;DR: The results indicate that the proper design of repetition or multi-hop retransmission strategies represents an important aspect of future work for robustness and network stability of vehicular ad hoc networks.
Abstract: One key usage of VANET is to support vehicle safety applications. This use case is characterized by the prominence of broadcasts in scaled settings. In this context, we try to answer the following questions: i) what is the probability of reception of a broadcast message by another car depending on its distance to the sender, ii) how to give priority access and an improved reception rate for important warnings, e.g., sent out in an emergency situation, and iii) how are the above two results affected by signal strength fluctuations caused by radio channel fading? We quantify via simulation the probability of reception for the two-ray-ground propagation model as well as for the Nakagami distribution in saturated environments. By making use of some IEEE 802.11e EDCA mechanisms for priority access, we do not only quantify how channel access times can be reduced but also demonstrate how improved reception rates can be achieved. Our results show that the mechanisms for priority access are successful under the two-way-ground model. However, with a non-deterministic radio propagation model like Nakagami's distribution the benefit is still obvious but the general level of probability of reception is much smaller compared to two-ray-ground model. The results indicate that -- particularly for safety-critical and sensor network type of applications -- the proper design of repetition or multi-hop retransmission strategies represents an important aspect of future work for robustness and network stability of vehicular ad hoc networks.
01 Jan 2004
TL;DR: In this article, a modified multi-objective evolutionary algorithm is introduced to focus search on these knee regions, resulting in a smaller set of solutions which are likely to be more relevant to the decision maker.
Abstract: Many real-world optimization problems have several, usually conflicting objectives. Evolutionary multi-objective optimization usually solves this predicament by searching for the whole Pareto-optimal front of solutions, and relies on a decision maker to finally select a single solution. However, in particular if the number of objectives is large, the number of Pareto-optimal solutions may be huge, and it may be very difficult to pick one “best” solution out of this large set of alternatives. As we argue in this paper, the most interesting solutions of the Pareto-optimal front are solutions where a small improvement in one objective would lead to a large deterioration in at least one other objective. These solutions are sometimes also called “knees”. We then introduce a new modified multi-objective evolutionary algorithm which is able to focus search on these knee regions, resulting in a smaller set of solutions which are likely to be more relevant to the decision maker.
TL;DR: The performance and long-term stability of the single cell is significantly increased by the use of suitable materials, a proper design of the cell and an optimized microstructure at the electrode/electrolyte interfaces as discussed by the authors.
TL;DR: It is shown that the multi-swarm optimizer significantly outperforms single population PSO on this problem, and that multi-quantum swarms are superior to multi-charged swarms and SOS.
Abstract: Many real-world problems are dynamic, requiring an optimization algorithm which is able to continuously track a changing optimum over time. In this paper, we present new variants of Particle Swarm Optimization (PSO) specifically designed to work well in dynamic environments. The main idea is to extend the single population PSO and Charged Particle Swarm Optimization (CPSO) methods by constructing interacting multi-swarms. In addition, a new algorithmic variant, which broadens the implicit atomic analogy of CPSO to a quantum model, is introduced. The multi-swarm algorithms are tested on a multi-modal dynamic function – the moving peaks benchmark – and results are compared to the single population approach of PSO and CPSO, and to results obtained by a state-of-the-art evolutionary algorithm, namely self-organizing scouts (SOS). We show that our multi-swarm optimizer significantly outperforms single population PSO on this problem, and that multi-quantum swarms are superior to multi-charged swarms and SOS.
TL;DR: In this paper, the authors present appropriate power line channel models, which form the basis for the design of a channel emulator, which turns out to be extremely helpful for various tests and comparison of performance of different communication systems.
Abstract: The development of power line communication systems requires detailed knowledge of the channel properties, such as transfer function, interference scenario, and channel capacity in order to choose suitable transmission methods. This article presents appropriate power line channel models, which form the basis for the design of a channel emulator. Such a device turns out to be extremely helpful for various tests and the comparison of performance of different communication systems. A basic estimation of the power line channel capacity clearly demonstrates their enormous potential for high-speed communication purposes. Eventually, an evaluation of different modulation schemes is carried to optimize PLC system design.
17 May 2004
TL;DR: PANKOW (Pattern-based Annotation through Knowledge on theWeb), a method which employs an unsupervised, pattern-based approach to categorize instances with regard to an ontology, is proposed.
Abstract: The success of the Semantic Web depends on the availability of ontologies as well as on the proliferation of web pages annotated with metadata conforming to these ontologies. Thus, a crucial question is where to acquire these metadata from. In this paper wepropose PANKOW (Pattern-based Annotation through Knowledge on theWeb), a method which employs an unsupervised, pattern-based approach to categorize instances with regard to an ontology. The approach is evaluated against the manual annotations of two human subjects. The approach is implemented in OntoMat, an annotation tool for the Semantic Web and shows very promising results.
TL;DR: Although the authors are just at the very beginning of an extremely important field of interdisciplinary research, the fast-growing number of papers obliges this state-of-the-art summary.
07 Nov 2004
TL;DR: It is shown thatquery answering in such a combined logic is decidable, and an algorithm for query answering in SHIQ(D) extended with DL-safe rules based on the reduction to disjunctive datalog is presented.
Abstract: Both OWL-DL and function-free Horn rules are decidable logics with interesting, yet orthogonal expressive power: from the rules perspective, OWL-DL is restricted to tree-like rules, but provides both existentially and universally quantified variables and full, monotonic negation From the description logic perspective, rules are restricted to universal quantification, but allow for the interaction of variables in arbitrary ways Clearly, a combination of OWL-DL and rules is desirable for building Semantic Web ontologies, and several such combinations have already been discussed However, such a combination might easily lead to the undecidability of interesting reasoning problems Here, we present a decidable such combination which is, to the best of our knowledge, more general than similar decidable combinations proposed so far Decidability is obtained by restricting rules to so-called DL-safe ones, requiring each variable in a rule to occur in a non-DL-atom in the rule body We show that query answering in such a combined logic is decidable, and we discuss its expressive power by means of a non-trivial example Finally, we present an algorithm for query answering in SHIQ(D) extended with DL-safe rules based on the reduction to disjunctive datalog
TL;DR: In this paper, an efficient implementation of second order analytical derivatives (force constants) within density functional theory which applies to non-hybrid functionals has been presented, which results in pronounced reductions of computational work and implies insignificant losses in accuracy as is shown by extensive tests.
TL;DR: In this paper, a quantenchemische analyzes der WCA-Typen werden vorgestellt, der Entscheidung fur ein spezielles WCA auf der Basis von harten quantitativen Daten aus einer Vielzahl von Anionen zu grunden.
Abstract: Gibt es so etwas wie ein wirklich nichtkoordinierendes Anion? Ware es nicht grosartig, jede verruckte, schone oder einfach nur nutzliche kationische Spezies herstellen zu konnen, sei es, weil sie einen gerade interessiert oder weil man sie vielleicht schon einmal im Massenspektrum entdeckt hat? Um dieses Ziel in kondensierter Phase zu erreichen, mussen die Zielkationen mit einem geeigneten Gegenion versehen werden – dies ist der Moment, bei dem haufig Schwierigkeiten auftreten und viele gute Ideen wegen einer Koordination oder Zersetzung des Anions im Abguss enden. Zur Losung des Problems bietet sich womoglich eines der neuen schwach koordinierenden Anionen (WCAs) an, die Gegenstand dieses Aufsatzes sind. Vorgestellt werden neue Entwicklungen, Anwendungen, Ausgangsmaterialien und allgemeine Strategien zur Einfuhrung von WCAs in ein System. Einige der ungewohnlichen Eigenschaften von WCA-Salzen wie hohe Loslichkeit in unpolaren Medien, Pseudo-Gasphasenbedingungen in der kondensierten Phase oder die Stabilisierung von schwach gebundenen und niedrig geladenen Komplexen werden anhand thermodynamischer Betrachtungen plausibel gemacht. Die Grenzen bei der Verwendung von WCAs – durch Koordination und Zersetzung – werden aufgezeigt, und eine quantenchemische Analyse der WCA-Typen wird vorgestellt. Dies ermoglicht es, die Entscheidung fur ein spezielles WCA auf der Basis von harten quantitativen Daten aus einer Vielzahl von Anionen zu grunden.
TL;DR: An approach for teaching a humanoid robot is presented that will enable the robot to learn typical tasks required in everyday household environments and the main focus is on the knowledge representation in order to be able to abstract the problem solution strategies and to transfer them onto the robot system.
TL;DR: In this article, the photolysis of liquid H2O by vacuum-ultraviolet (VUV) photo-lysis, and in particular by the radiation emitted by Xe-excimer sources (172nm) is reviewed, and the impact of the primary radicals (hydroxyl (HO ), hydrogen (H ) and hydroperoxyl(HO2 )) on dissolved organic and inorganic substrates described.
Abstract: The photolysis of liquid H2O by vacuum-ultraviolet (VUV) photolysis, and in particular by the radiation emitted by Xe-excimer sources (172 nm) is reviewed, and the impact of the primary radicals (hydroxyl (HO ), hydrogen (H ) and hydroperoxyl (HO2 )) on dissolved organic and inorganic substrates described. Mechanisms of oxidative and reductive reaction manifolds are reported, interpreted and developed, in particular for nitrogen containing substrates. At the present state of research, at least semi-quantitative predictions on primary reaction paths and rate effects can be made, and oversimplified qualitative interpretations belong definitely to the past. Nevertheless, the review demonstrates clearly the lack of data concerning the reactivity of radical species, generated by inorganic anion oxidation, and their interaction with organic compounds and with the radicals derived from them.
TL;DR: In this article, it has been suggested that non-Fermi-liquid phases of metals may exist in some heavy-fermion compounds and oxide materials, but the discovery of a characteristic microscopic signature of such phases presents a major challenge.
Abstract: Only a few metallic phases have been identified in pure crystalline materials. These include normal, ferromagnetic and antiferromagnetic metals, systems with spin and charge density wave order, and superconductors. Fermi-liquid theory provides a basis for the description of all of these phases. It has been suggested that non-Fermi-liquid phases of metals may exist in some heavy-fermion compounds and oxide materials, but the discovery of a characteristic microscopic signature of such phases presents a major challenge. The transition-metal compound MnSi above a certain pressure (p(c) = 14.6 kbar) provides what may be the cleanest example of an extended non-Fermi-liquid phase in a three-dimensional metal. The bulk properties of MnSi suggest that long-range magnetic order is suppressed at p(c) (refs 7-12). Here we report neutron diffraction measurements of MnSi, revealing that sizeable quasi-static magnetic moments survive far into the non-Fermi-liquid phase. These moments are organized in an unusual pattern with partial long-range order. Our observation supports the existence of novel metallic phases with partial ordering of the conduction electrons (reminiscent of liquid crystals), as proposed for the high-temperature superconductors and heavy-fermion compounds.
TL;DR: In this paper, an integral model for the conservation of mass, momentum, buoyancy and scalar quantities in the turbulent jet flow is proposed, which employs an entrainment closure approach that distinguishes between the separate contributions of transverse shear (leading to jet, plume, or wake internal flow dynamics) and of azimuthal shear mechanisms, respectively.
Abstract: The mechanics of buoyant jet flows issuing with a general three-dimensional geometry into an unbounded ambient environment with uniform density or stable density stratification and under stagnant or steady sheared current conditions is investigated. An integral model is formulated for the conservation of mass, momentum, buoyancy and scalar quantities in the turbulent jet flow. The model employs an entrainment closure approach that distinguishes between the separate contributions of transverse shear (leading to jet, plume, or wake internal flow dynamics) and of azimuthal shear mechanisms (leading to advected momentum puff or thermal flow dynamics), respectively. Furthermore, it contains a quadratic law turbulent drag force mechanism as suggested by a number of recent detailed experimental investigations on the dynamics of transverse jets into crossflow. The model is validated in several stages: First, comparison with basic experimental data for the five asymptotic, self-similar stages of buoyant jet flows, i.e., the pure jet, the pure plume, the pure wake, the advected line puff, and the advected line thermal, support the choice and magnitude of the turbulent closure coefficients contained in the entrainment formulation. Second, comparison with many types of non-equilibrium flows support the proposed transition function within the entrainment relationship, and also the role of the drag force in the jet deflection dynamics. Third, a number of spatial limits of applicability have been proposed beyond which the integral model necessarily becomes invalid due to its parabolic formulation. These conditions, often related to the breakdown of the boundary layer nature of the flow, describe features such as terminal layer formation in stratification, upstream penetration in jets opposing a current, or transition to passive diffusion in a turbulent ambient shear flow. Based on all these comparisons, that include parameters such as trajectories, centerline velocities, concentrations and dilutions, the model appears to provide an accurate and reliable representation of buoyant jet physics under highly general flow conditions.
Proceedings Article•
06 Dec 2004TL;DR: By allowing distinct device drivers to reside in separate virtual machines, this technique isolates faults caused by defective or malicious drivers, thus improving a system's dependability, and enables extensive reuse of existing and unmodified drivers.
Abstract: We propose a method to reuse unmodified device drivers and to improve system dependability using virtual machines. We run the unmodified device driver, with its original operating system, in a virtual machine. This approach enables extensive reuse of existing and unmodified drivers, independent of the OS or device vendor, significantly reducing the barrier to building new OS endeavors. By allowing distinct device drivers to reside in separate virtual machines, this technique isolates faults caused by defective or malicious drivers, thus improving a system's dependability.
We show that our technique requires minimal support infrastructure and provides strong fault isolation. Our prototype's network performance is within 3-8% of a native Linux system. Each additional virtual machine increases the CPU utilization by about 0.12%. We have successfully reused a wide variety of unmodified Linux network, disk, and PCI device drivers.