Showing papers by "Karlsruhe Institute of Technology published in 2001"

Quantum-state engineering with Josephson-junction devices

Abstract: Quantum-state engineering, i.e., active control over the coherent dynamics of suitable quantum-mechanical systems, has become a fascinating prospect of modern physics. With concepts developed in atomic and molecular physics and in the context of NMR, the field has been stimulated further by the perspectives of quantum computation and communication. Low-capacitance Josephson tunneling junctions offer a promising way to realize quantum bits (qubits) for quantum information processing. The article reviews the properties of these devices and the practical and fundamental obstacles to their use. Two kinds of device have been proposed, based on either charge or phase (flux) degrees of freedom. Single- and two-qubit quantum manipulations can be controlled by gate voltages in one case and by magnetic fields in the other case. Both kinds of device can be fabricated with present technology. In flux qubit devices, an important milestone, the observation of superpositions of different flux states in the system eigenstates, has been achieved. The Josephson charge qubit has even demonstrated coherent superpositions of states readable in the time domain. There are two major problems that must be solved before these devices can be used for quantum information processing. One must have a long phase coherence time, which requires that external sources of dephasing be minimized. The review discusses relevant parameters and provides estimates of the decoherence time. Another problem is in the readout of the final state of the system. This issue is illustrated with a possible realization by a single-electron transistor capacitively coupled to the Josephson device, but general properties of measuring devices are also discussed. Finally, the review describes how the basic physical manipulations on an ideal device can be combined to perform useful operations.

Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities

Abstract: There is increased recognition by the world’s scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth’s atmosphere, particularly CO_2, are increasing. For example, recent studies of Antarctic ice cores to depths of over 3600 m, spanning over 420 000 years, indicate an 80 ppm increase in atmospheric CO_2 in the past 200 years (with most of this increase occurring in the past 50 years) compared to the previous 80 ppm increase that required 10 000 years.2 The 160 nation Framework Convention for Climate Change (FCCC) in Kyoto focused world attention on possible links between CO2 and future climate change and active discussion of these issues continues.3 In the United States, the PCAST report4 “Federal Energy Research and Development for the Challenges of the Twenty First Century” focused attention on the growing worldwide demand for energy and the need to move away from current fossil fuel utilization. According to the U.S. DOE Energy Information Administration,5 carbon emission from the transportation (air, ground, sea), industrial (heavy manufacturing, agriculture, construction, mining, chemicals, petroleum), buildings (internal heating, cooling, lighting), and electrical (power generation) sectors of the World economy amounted to ca. 1823 million metric tons (MMT) in 1990, with an estimated increase to 2466 MMT in 2008-2012 (Table 1).

Knowledge processes and ontologies

Abstract: In this article, we present an approach for ontology-based knowledge management (KM) that includes a tool suite and a methodology for developing ontology-based KM systems. It builds on the distinction between knowledge processes and knowledge metaprocesses, and is illustrated by CHAR (Corporate History AnalyzeR), a KM system for corporate history analysis.

Operator–valued Fourier multiplier theorems and maximal $L_p$-regularity

Abstract: We prove a Mihlin–type multiplier theorem for operator–valued multiplier functions on UMD–spaces. The essential assumption is R–boundedness of the multiplier function. As an application we give a characterization of maximal \(L_p\)–regularity for the generator of an analytic semigroup \(T_t\) in terms of the R–boundedness of the resolvent of A or the semigroup \(T_t\).

FCA-MERGE: bottom-up merging of ontologies

Abstract: Ontologies have been established for knowledge sharing and are widely used as a means for conceptually structuring domains of interest. With the growing usage of ontologies, the problem of overlapping knowledge in a common domain becomes critical. We propose the new method FCA-MERGE for merging ontologies following a bottom-up approach which offers a structural description of the merging process. The method is guided by application-specific instances of the given source ontologies, that are to be merged. We apply techniques from natural language processing and formal concept analysis to derive a lattice of concepts as a structural result of FCA-MERGE. The generated result is then explored and transformed into the merged ontology with human interaction.

Sidewall Functionalization of Carbon Nanotubes This work was supported by the European Union under the 5th Framework Research Training Network 1999, HPRNT 1999-00011 FUNCARS.

Abstract: The addition of nitrenes, nucleophilic carbenes, and radicals affords soluble, individual single-walled nanotubes (shown here is a carbene-functionalized adduct) by covalent sidewall functionalization. The characterization, a fundamental problem in nanotube chemistry, is simple to carry out.

Smart-Its Friends: A Technique for Users to Easily Establish Connections between Smart Artefacts

Abstract: Ubiquitous computing is associated with a vision of everything being connected to everything. However, for successful applications to emerge, it will not be the quantity but the quality and usefulness of connections that will matter. Our concern is how qualitative relations and more selective connections can be established between smart artefacts, and how users can retain control over artefact interconnection. We propose context proximity for selective artefact communication, using the context of artefacts for matchmaking. We further suggest to empower users with simple but effective means to impose the same context on a number of artefacts. To prove our point we have implemented Smart-Its Friends, small embedded devices that become connected when a user holds them together and shakes them.

Role of magnesium in genomic stability.

Abstract: In cellular systems, magnesium is the second most abundant element and is involved in basically all metabolic pathways. At physiologically relevant concentrations, magnesium itself is not genotoxic, but is highly required to maintain genomic stability. Besides its stabilizing effect on DNA and chromatin structure, magnesium is an essential cofactor in almost all enzymatic systems involved in DNA processing. Most obvious in studies on DNA replication, its function is not only charge-related, but very specific with respect to the high fidelity of DNA synthesis. Furthermore, as essential cofactor in nucleotide excision repair, base excision repair and mismatch repair magnesium is required for the removal of DNA damage generated by environmental mutagens, endogenous processes, and DNA replication. Intracellular magnesium concentrations are highly regulated and magnesium acts as an intracellular regulator of cell cycle control and apoptosis. As evident from animal experiments and epidemiological studies, magnesium deficiency may decrease membrane integrity and membrane function and increase the susceptibility to oxidative stress, cardiovascular heart diseases as well as accelerated aging. The relationship to tumor formation is more complex; magnesium appears to be protective at early stages but promotes the growth of existing tumors. With respect to the magnesium status in humans, the daily intake in most industrialized countries does not reach the current recommended daily dietary allowances (RDA) values, and thus marginal magnesium deficiencies are very common.

Solubility and hydrolysis of tetravalent actinides

Abstract: Summary. The solubility and hydrolysis of Th(IV), U(IV), Np(IV), and Pu(IV) are critically reviewed and a comprehenpresented. The hydrolysis constants are selected preferentially from experimental studies at actinide trace concentrations, where the interference of colloid formation can be excluded. Unknown formation constants of mononuclear complexes An(OH)n 42n are estimated by applying a semi-empirical electrostatic model and an empirical correlation with the known constants of other actinide ions. Based on the known and estimated hydrolysis constants, the solubility products of An(OH)4(am) or AnO2 2 imental solubility data available in the literature. The SIT is used for ionic strength corrections. The solubilities of U(IV), Np(IV), and Pu(IV) hydroxides or hydrous oxides can be calculated by accounting only for mononuclear hydrolysis species. The considerably higher solubilities of amorphous Th(IV) precipitates at pH , 5 include major contributions of polynuclear species. The solubility data in acidic solutions depend strongly on the preparation and crystallinity of the solid phase. In neutral and alkaline solutions, where An(OH)4(aq) are the predominant aqueous species, the solubilities of AnO 2(cr) become equal to those of the amorphous solids. This indicates that the crystalline dioxides are covered by amorphous hydroxide layers.

The NF2 tumor suppressor gene product, merlin, mediates contact inhibition of growth through interactions with CD44

Abstract: The neurofibromatosis-2 (NF2) gene encodes merlin, an ezrin-radixin-moesin-(ERM)-related protein that functions as a tumor suppressor. We found that merlin mediates contact inhibition of growth through signals from the extracellular matrix. At high cell density, merlin becomes hypo-phosphorylated and inhibits cell growth in response to hyaluronate (HA), a mucopolysaccharide that surrounds cells. Merlin’s growth-inhibitoryactivitydepends on specific interaction with the cy toplasmic tail of CD44, a transmembrane HA receptor. At low cell density, merlin is phosphorylated, growth permissive, and exists in a complex with ezrin, moesin, and CD44. These data indicate that merlin and CD44 form a molecular switch that specifies cell growth arrest or proliferation.

Materials and technologies for SOFC-components

Abstract: Solid oxide fuel cells are a forward looking technology for a highly efficient, environmental friendly power generation. A SOFC is a multilayer structure consisting of ceramic and metallic materials with different electrical transport properties. All components have to show a well adjusted thermal expansion behavior, chemical compatibility of material interfaces and chemical stability in the prevailing atmospheres. The performance of SOFC single cells is not only determined by intrinsic material properties. There is a significant influence due to the fabrication technology respectively the microstructure at the electrode/electrolyte-interfaces. The performance of cells can only be improved by the application of elevated materials using appropriate technologies.

Glucocorticoids inhibit MAP kinase via increased expression and decreased degradation of MKP-1.

Abstract: Glucocorticoids inhibit the proinflammatory activities of transcription factors such as AP-1 and NF-κB as well as that of diverse cellular signaling molecules. One of these signaling molecules is the extracellular signal-regulated kinase (Erk-1/2) that controls the release of allergic mediators and the induction of proinflammatory cytokine gene expression in mast cells. The mechanism of inhibition of Erk-1/2 activity by glucocorticoids is unknown. Here we report a novel dual action of glucocorticoids for this inhibition. Glucocorticoids increase the expression of the MAP kinase phosphatase-1 (MKP-1) gene at the promoter level, and attenuate proteasomal degradation of MKP-1, which we report to be triggered by activation of mast cells. Both induction of MKP-1 expression and inhibition of its degradation are necessary for glucocorticoid-mediated inhibition of Erk-1/2 activation. In NIH-3T3 fibroblasts, although glucocorticoids up-regulate the MKP-1 level, they do not attenuate the proteasomal degradation of this protein and consequently they are unable to inhibit Erk-1/2 activity. These results identify MKP-1 as essential for glucocorticoid-mediated control of Erk-1/2 activation and unravel a novel regulatory mechanism for this anti-inflammatory drug.

Generation of 5-fs pulses and octave-spanning spectra directly from a Ti:sapphire laser

Abstract: Spectra extending from 600 to 1200 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser producing 5-fs pulses. Specially designed double-chirped mirror pairs provide broadband controlled dispersion, and a second intracavity focus in a glass plate provides additional spectral broadening. These spectra are to our knowledge the broadest ever generated directly from a laser oscillator.

Repression of inflammatory responses in the absence of DNA binding by the glucocorticoid receptor.

Abstract: The glucocorticoid receptor (GR) acts both as a transcription factor itself on genes carrying GR response elements (GREs) and as a modulator of other transcription factors. Using mice with a mutation in the GR, which cannot activate GRE promoters, we examine whether the important anti-inflammatory and immune suppressive functions of glucocorticoids (GCs) can be established in this in vivo animal model. We find that most actions are indeed exerted in the absence of the DNA-binding ability of the GR: inhibition of the inflammatory response of locally irritated skin and of the systemic response to lipopolysaccharides. GCs repress the expression and release of numerous cytokines both in vivo and in isolated primary macrophages, thymocytes and CD4(+) splenocytes. A transgenic reporter gene controlled by NF-kappa B exclusively is also repressed, suggesting that protein- protein interaction with other transcription factors such as NF-kappa B forms the basis of the anti-inflammatory activity of GR. The only defect of immune suppression detected so far concerns the induced apoptosis of thymocytes and T lymphocytes.

Cosmic Rays and Particle Physics

Abstract: The study of high energy cosmic rays is a diversified field of observational and phenomenological physics addressing questions ranging from shock acceleration of charged particles in various astrophysical objects, via transport properties through galactic and extragalactic space, to questions of dark matter, and even to those of particle physics beyond the Standard Model including processes taking place in the earliest moments of our Universe. After decades of mostly independent evolution of nuclear-, particle- and high energy cosmic ray physics we find ourselves entering a symbiotic era of these fields of research. Some examples of interrelations will be given from the perspective of modern Particle-Astrophysics and new major experiments will briefly be sketched.

Radiation hard silicon detectors—developments by the RD48 (ROSE) collaboration

Abstract: The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×1017 O/cm3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×1014 cm−2 (1 MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.

The Facile Preparation of Weakly Coordinating Anions: Structure and Characterisation of Silverpolyfluoroalkoxyaluminates AgAl(ORF)4, Calculation of the Alkoxide Ion Affinity

Abstract: Purified LiAlH4 reacts with fluorinated alcs. HORF to give LiAl(ORF)4 (RF = -CH(CF3)2, 2a; -CMe(CF3)2, 2b; -C(CF3)3, 2c) in 77-90% yield. The crude Li aluminates LiAl(ORF)4 react metathetically with AgF to give the silver aluminates AgAl(ORF)4 (RF = -CH(CF3)2, 3a; -CMe(CF3)2, 3b; -C(CF3)3, 3c) in almost quant. yield. The solid-state structures of solvated 3a-c showed that the Ag cation is only weakly coordinated (CN(Ag) = 6-10; CN = coordination no.) by the solvent and/or weak cation-anion contacts Ag-X (X = O, F, Cl, C). The strength of the Ag-X contacts of 3a-c was analyzed by Brown's bond-valence method and then compared with other Ag salts of weakly coordinating anions (WCAs), for example [CB11H6Cl6]- and [M(OTeF5)n]- (M = B, Sb, n = 4, 6). Based on this quant. picture the Al{OC(CF3)3}4- anion is one of the most weakly coordinating anions known. Also, the AgAl(ORF)4 species are certainly the easiest WCAs to access preparatively (20 g in two days), addnl. at low cost. The Al-O bond length of Al(ORF)4- is shortest in the sterically congested Al{OC(CF3)3}4- anion-which is stable in H2O and aq. HNO3 (35%), and indicates a strong and highly polar Al-O bond that is resistant towards heterolytic alkoxide ion abstraction. This observation was supported by HF-DFT calcns. of OR-, Al(OR)3 and Al(OR)4- at the MPW1PW91 and B3LYP levels (R = CH3, CF3, C(CF3)3). The alkoxide ion affinity (AIA) is highest for R = CF3 (AIA = 384 +- 9 kJ mol-1) and R = C(CF3)3 (AIA = 390 +- 3 kJ mol-1), but lowest for R = CH3 (AIA = 363 +- 7 kJ mol-1). The gaseous Al(ORF)4- anions are stable against the action of the strong Lewis acid AlF3(g) by 88.5 +- 2.5 (RF = CF3) and 63 +- 12 kJ mol-1 (RF = C(CF3)3), while Al(OCH3)4- decomps. with -91 +- 2 kJ mol-1. Therefore, the presented fluorinated aluminates Al(ORF)4- appear to be ideal candidates when large and resistant WCAs are needed, for example, in cationic homogeneous catalysis, for highly electrophilic cations or for weak cationic Lewis acid/base complexes. [on SciFinder (R)]

Coexistence of superconductivity and ferromagnetism in the d-band metal ZrZn2.

Abstract: It has generally been believed that, within the context of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, the conduction electrons in a metal cannot be both ferromagnetically ordered and superconducting. Even when the superconductivity has been interpreted as arising from magnetic mediation of the paired electrons, it was thought that the superconducting state occurs in the paramagnetic phase. Here we report the observation of superconductivity in the ferromagnetically ordered phase of the d-electron compound ZrZn2. The specific heat anomaly associated with the superconducting transition in this material appears to be absent, and the superconducting state is very sensitive to defects, occurring only in very pure samples. Under hydrostatic pressure superconductivity and ferromagnetism disappear at the same pressure, so the ferromagnetic state appears to be a prerequisite for superconductivity. When combined with the recent observation of superconductivity in UGe2 (ref. 4), our results suggest that metallic ferromagnets may universally become superconducting when the magnetization is small.

The H ∞ −calculus and sums of closed operators

Abstract: We develop a very general operator-valued functional calcu- lus for operators with an H 1 −calculus. We then apply this to the joint functional calculus of two commuting sectorial operators when one has an H 1 calculus. Using this we prove theorem of Dore-Venni type on sums of commuting sectorial operators and apply our results to the problem of Lp−maximal regularity. Our main assumption is the R-boundedness of certain sets of operators, and therefore methods from the geometry of Ba- nach spaces are essential here. In the final section we exploit the special Banach space structure of L1−spaces and C(K)−spaces, to obtain some more detailed results in this setting.

Non-Fermi-liquid nature of the normal state of itinerant-electron ferromagnets

Abstract: A century of research on magnetic phenomena had led to the view that the normal state of itinerant-electron ferromagnets such as Fe, Ni and Co could be described in terms of the standard model of the metallic state or its extension known as the nearly ferromagnetic Fermi liquid theory. In recent years, however, a large body of observations has accumulated from various complex intermetallic systems that raises the possibility that this assumption might be wrong. Here we examine this issue by means of high-precision measurements of the electrical transport and magnetic properties of pure ferromagnets-in particular, MnSi-in which the Curie temperature is tuned towards absolute zero by the application of hydrostatic pressure. With this method, it is possible for us to study the normal state over an extraordinarily large range of temperature of up to five orders of magnitude above the Curie temperature. Our results using MnSi reveal a particularly striking combination of properties-most notably a T3/2 power law for the resistivity-showing clearly that the normal state of this itinerant-electron ferromagnet cannot be described in terms of the standard model of metals.

Silicon‐Based Photonic Crystals

Abstract: In semiconductors electrons propagate in a periodic poten-tial, which originates from the atomic lattice. This modifiesthe dispersion relation of free electrons and a band structurewith a bandgap occurs in the case of semiconductors. Theincorporation of electrically active defects allows the manipu-lation of the electronic properties, which gave birth to a largevariety of electronic devices. There are distinct electrical andelectro-optical properties of the different semiconductormaterials, the dominant and most studied semiconductorbeing silicon.For more than ten years, the optical analogues to electronicsemiconductors, the so-called photonic crystals, have been thesubject of intense international research efforts. Photoniccrystals are materials with a periodically varying index ofrefraction. This allows the control of the propagation of elec-tromagnetic waves, similar to electrons in a semiconductorcrystal. By analogy with semiconductors, the periodicity of theunderlying lattice structure is of the same order of magnitudeas the wavelength of the electromagnetic radiation.Despite the far-reaching analogies between electronicwaves in semiconductors and electromagnetic waves in pho-tonic crystals, there are pronounced differences between thetwo as is noticeable from the corresponding equations of mo-tion. Electrons are described by a scalar wavefield. In con-trast, the electromagnetic field is vectorial by nature. Further-more, the time-independent Schrodinger equation allowssolutions with negative energy eigenvalues, whereas the corre-sponding wave equation in electrodynamics contains only thesquare of the eigenfrequencies, hence negative eigenvaluesare excluded from the outset. It may be inferred from the fewphotonic crystals that appear in nature, in contrast to ubiqui-tous semiconductor materials, that these differences have adisadvantageous effect on the likelihood of the formation ofphotonic bandgaps. From the multitude of the optical phe-nomena only, for example, the colorful speckles of opals, somecrystallites on the wings of butterflies and the spine of the sea-mouse