Showing papers by "Leibniz University of Hanover published in 2010"

Quantum state tomography via compressed sensing.

Abstract: We establish methods for quantum state tomography based on compressed sensing. These methods are specialized for quantum states that are fairly pure, and they offer a significant performance improvement on large quantum systems. In particular, they are able to reconstruct an unknown density matrix of dimension d and rank r using O(rdlog^2d) measurement settings, compared to standard methods that require d^2 settings. Our methods have several features that make them amenable to experimental implementation: they require only simple Pauli measurements, use fast convex optimization, are stable against noise, and can be applied to states that are only approximately low rank. The acquired data can be used to certify that the state is indeed close to pure, so no a priori assumptions are needed.

Predictions for the rates of compact binary coalescences observable by ground-based gravitational-wave detectors

Abstract: We present an up-to-date, comprehensive summary of the rates for all types of compact binary coalescence sources detectable by the initial and advanced versions of the ground-based gravitational-wave detectors LIGO and Virgo. Astrophysical estimates for compact-binary coalescence rates depend on a number of assumptions and unknown model parameters and are still uncertain. The most confident among these estimates are the rate predictions for coalescing binary neutron stars which are based on extrapolations from observed binary pulsars in our galaxy. These yield a likely coalescence rate of 100 Myr−1 per Milky Way Equivalent Galaxy (MWEG), although the rate could plausibly range from 1 Myr−1 MWEG−1 to 1000 Myr−1 MWEG−1 (Kalogera et al 2004 Astrophys. J. 601 L179; Kalogera et al 2004 Astrophys. J. 614 L137 (erratum)). We convert coalescence rates into detection rates based on data from the LIGO S5 and Virgo VSR2 science runs and projected sensitivities for our advanced detectors. Using the detector sensitivities derived from these data, we find a likely detection rate of 0.02 per year for Initial LIGO–Virgo interferometers, with a plausible range between 2 × 10−4 and 0.2 per year. The likely binary neutron–star detection rate for the Advanced LIGO–Virgo network increases to 40 events per year, with a range between 0.4 and 400 per year.

Determination of the 10Be half-life by multicollector ICP-MS and liquid scintillation counting

Abstract: A new method was designed and used for determining the half-life of the isotope 10 Be. The method is based on (1) accurate 10 Be/ 9 Be measurements of 9 Be-spiked solutions of a 10 Be-rich master solution using multicollector ICP mass spectrometry (MC-ICP-MS) and (2) liquid scintillation counting (LSC) using the CIEMAT/NIST method for determining the activity concentrations of the solutions whose 10 Be concentrations were determined by mass spectrometry. Important requirements for the success of this approach (a) was the previous coating of glass ampoules filled for counting experiments with 9 Be, thereby reducing the risk of the adsorptive loss of 10 Be; (b) the removal of Boron from solutions to be measured by MC-ICP-MS by cation chromatography without the introduction of mass fractionation and (c) the accurate determination of the mass bias of 10 Be/ 9 Be measurements by ICP-MS which are always affected by the space-charge effect. The mass bias factor was determined to be 1.1862 ± 0.071 for 10 Be/ 9 Be from careful fitting and error propagation of ratios of measured Li, B, Si, Cr, Fe, Cu, Sr, Nd, Hf, Tl and U standard solutions of known composition under the same measurement conditions. Employing this factor, an absolute 10 Be/ 9 Be ratio of 1.464 ± 0.014 was determined for a first dilution of the 10 Be-rich master solution. This solution is now available as an absolute Be ratio standard in AMS measurements. Finally, a half-life of (1.386 ± 0.016) My (standard uncertainty) was calculated. This value is much more precise than previous estimates and was derived from a fully independent set of experiments. In a parallel, fully independent study using the same master solution, Korschinek et al. [35] have determined a half-life of (1.388 ± 0.018) My. The combined half-life and uncertainty amounts to (1.387 ± 0.012) My. We suggest the use of this value in nuclear studies and in studies that make use of cosmogenic 10 Be in environmental and geologic samples.

Molecular Sieve Membrane: Supported Metal–Organic Framework with High Hydrogen Selectivity

Abstract: Microporous membranes with pore apertures below the nanolevel can exhibit size selectivity by serving as a molecular sieve, which is promising for overcoming Robeson s “upperbound” limits in membrane-based gas separation. Zeolites, polymers of intrinsic microporosity (PIMs), metal oxides, and active carbon are the typical materials used for this purpose. Metal–organic frameworks (MOFs) have attracted much research interest in recent years, and are emerging as a new family of molecular sieves. MOFs are novel porous crystalline materials consisting of metal ions or clusters interconnected by a variety of organic linkers. In addition to promising applications in adsorptive gas separation and storage or in catalysis, their unique properties, such as their highly diversified structures, large range in pore sizes, very high surface areas, and specific adsorption affinities, make MOFs excellent candidates for use in the construction of molecular sieve membranes with superior performance. The preparation of MOF membranes for gas separation is rapidly becoming a research focus. A number of attempts have been made to prepare supported-MOF membranes; however, progress is very limited and so far there are only very few reports of continuous MOF films on porous supports being used as separating membranes. Recently, Guo et al. reported a copper-net-supported HKUST-1 (Cu3(BTC)2; BTC= benzene-1,3,5-tricarboxylate) membrane exhibiting a H2/N2 selectivity of 7 [13] (separation factor of H2 over N2 is calculated as the permeate-to-retentate composition ratio of H2, divided by the same ratio for N2 as proposed by IUPAC) ; this is the first MOF membrane to show gasseparation performance beyond Knudsen diffusion behavior. Very recently, Ranjan and Tsapatsis prepared a microporous metal–organic framework [MMOF, Cu(hfipbb)(H2hfipbb)0.5; hfipbb= 4,4’-(hexafluoroisopropylidene)bis(benzoic acid)] membrane by seeded growth on an alumina support. The ideal selectivity for H2/N2, based on single permeation tests, was 23 at 190 8C. This higher selectivity, compared to the report from Guo et al., might be a result of the smaller effective pore size (ca. 0.32 nm of MMOF versus 0.9 nm of HKUTS-1), which results in a relatively low H2 permeance of this MMOF membrane (10 9 molm 2 s Pa 1 at 190 8C). The authors attributed this finding to the blockage of the onedimensional (1D) straight-pore channels in the membrane. Therefore, with regard to H2 separation, small-pore MOFs having three-dimensional (3D) channel structures are considered to be ideal membrane materials. Zeolitic imidazolate frameworks (ZIFs), a subfamily of MOFs, consist of transition metals (Zn, Co) and imidazolate linkers which form 3D tetrahedral frameworks and frequently resemble zeolite topologies. A number of ZIFs exhibit exceptional thermal and chemical stability. Another important feature of ZIFs is their hydrophobic surfaces, which give ZIF membranes certain advantages over zeolite membranes and sol–gel-derived silica membranes in the separation of H2 in the presence of steam. Very recently we reported the first result from permeation measurements on a ZIF-8 membrane. The ZIF-8 membrane showed a H2/CH4 separation factor greater than 10. Whereas the ZIF-8 pores (0.34 nm) are slightly larger than the kinetic diameter of CO2 (0.33 nm), and are very flexible, the H2/CO2 separation on this ZIF-8 membrane showed Knudsen selectivity. In the current work, we therefore chose ZIF-7 as a promising candidate for the development of a H2-selective membrane to satisfy the above requirements. ZIF-7 (Zn(bim)2) is formed by bridging benzimidazolate (bim) anions and zinc cations with soladite (SOD) topology. The pore size of ZIF-7 (the hexagonal window size in the SOD cage) estimated from crystallographic data is about 0.3 nm, which is just in between the size of H2 (0.29 nm) and CO2 (0.33 nm). We could therefore expect a ZIF-7 membrane to achieve a high selectivity of H2 over CO2 and other gases through a molecular sieving effect. In many cases, it was reported that the heterogeneous nucleation density of MOF crystals on ceramic supports is very low, 14] which makes it extremely difficult to prepare supported-MOF membranes by an in situ synthesis route. Chemical modifications of substrate surfaces have been proposed to direct the nucleation and orientation of the deposited MOF layers. Based on our knowledge in the development of zeolite membranes, we adopted a seeded secondary growth method for the ZIF-7 membrane prepara[*] Prof. Dr. Y.-S. Li, F.-Y. Liang, H. Bux, A. Feldhoff, Prof. Dr. J. Caro Institute of Physical Chemistry and Electrochemistry and the Laboratory for Nano and Quantum Engineering (LNQE) in cooperation with the Center for Solid State Research and New Materials, Leibniz Universit t Hannover Callinstrasse 3A, 30167 Hannover (Germany) Fax: (+49)511-762-19121 E-mail: yanshuo.li@pci.uni-hannover.de juergen.caro@pci.uni-hannover.de

Fast optimal frictionless atom cooling in harmonic traps: shortcut to adiabaticity.

Abstract: A method is proposed to cool down atoms in a harmonic trap without phase-space compression as in a perfectly slow adiabatic expansion, i.e., keeping the same populations of instantaneous levels in the initial and final traps, but in a much shorter time. This may require that the harmonic trap become transiently an expulsive parabolic potential. The cooling times achieved are shorter than those obtained using optimal-control bang-bang methods and real frequencies.

Efficient quantum state tomography

Abstract: Quantum state tomography--deducing quantum states from measured data--is the gold standard for verification and benchmarking of quantum devices. It has been realized in systems with few components, but for larger systems it becomes unfeasible because the number of measurements and the amount of computation required to process them grows exponentially in the system size. Here, we present two tomography schemes that scale much more favourably than direct tomography with system size. One of them requires unitary operations on a constant number of subsystems, whereas the other requires only local measurements together with more elaborate post-processing. Both rely only on a linear number of experimental operations and post-processing that is polynomial in the system size. These schemes can be applied to a wide range of quantum states, in particular those that are well approximated by matrix product states. The accuracy of the reconstructed states can be rigorously certified without any a priori assumptions.

Shortcut to adiabatic passage in two- and three-level atoms.

Abstract: We propose a method to speed up adiabatic passage techniques in two-level and three-level atoms extending to the short-time domain their robustness with respect to parameter variations It supplements or substitutes the standard laser beam setups with auxiliary pulses that steer the system along the adiabatic path Compared to other strategies, such as composite pulses or the original adiabatic techniques, it provides a fast and robust approach to population control

Boilerplate detection using shallow text features

Abstract: In addition to the actual content Web pages consist of navigational elements, templates, and advertisements. This boilerplate text typically is not related to the main content, may deteriorate search precision and thus needs to be detected properly. In this paper, we analyze a small set of shallow text features for classifying the individual text elements in a Web page. We compare the approach to complex, state-of-the-art techniques and show that competitive accuracy can be achieved, at almost no cost. Moreover, we derive a simple and plausible stochastic model for describing the boilerplate creation process. With the help of our model, we also quantify the impact of boilerplate removal to retrieval performance and show significant improvements over the baseline. Finally, we extend the principled approach by straight-forward heuristics, achieving a remarkable detection accuracy.

Selecting skyline services for QoS-based web service composition

Abstract: Web service composition enables seamless and dynamic integration of business applications on the web. The performance of the composed application is determined by the performance of the involved web services. Therefore, non-functional, quality of service aspects are crucial for selecting the web services to take part in the composition. Identifying the best candidate web services from a set of functionally-equivalent services is a multi-criteria decision making problem. The selected services should optimize the overall QoS of the composed application, while satisfying all the constraints specified by the client on individual QoS parameters. In this paper, we propose an approach based on the notion of skyline to effectively and efficiently select services for composition, reducing the number of candidate services to be considered. We also discuss how a provider can improve its service to become more competitive and increase its potential of being included in composite applications. We evaluate our approach experimentally using both real and synthetically generated datasets.

Steam-stable zeolitic imidazolate framework ZIF-90 membrane with hydrogen selectivity through covalent functionalization.

Abstract: A novel covalent functionalization strategy was developed to prepare reproducible ZIF-90 molecular sieve membranes by using 3-aminopropyltriethoxysilane as a covalent linker between the ZIF-90 layer and Al(2)O(3) support via imines condensation. The ZIF-90 membranes show high thermal and hydrothermal stabilities, and they allow the separation of hydrogen from larger gases by molecular sieving.

Crowdsourcing geospatial data

Abstract: In this paper we review recent developments of crowdsourcing geospatial data. While traditional mapping is nearly exclusively coordinated and often also carried out by large organisations, crowdsourcing geospatial data refers to generating a map using informal social networks and web 2.0 technology. Key differences are the fact that users lacking formal training in map making create the geospatial data themselves rather than relying on professional services; that potentially very large user groups collaborate voluntarily and often without financial compensation with the result that at a very low monetary cost open datasets become available and that mapping and change detection occur in real time. This situation is similar to that found in the Open Source software environment. We shortly explain the basic technology needed for crowdsourcing geospatial data, discuss the underlying concepts including quality issues and give some examples for this novel way of generating geospatial data. We also point at applications where alternatives do not exist such as life traffic information systems. Finally we explore the future of crowdsourcing geospatial data and give some concluding remarks.

Biofortification and localization of zinc in wheat grain.

Abstract: Zinc (Zn) deficiency associated with low dietary intake is a well-documented public health problem, resulting in serious health and socioeconomic problems. Field experiments were conducted with wheat to test the role of both soil and foliar application of ZnSO4 in Zn concentration of whole grain and grain fractions (e.g., bran, embryo and endosperm) in 3 locations. Foliar application of ZnSO4 was realized at different growth stages (e.g., stem elongation, boot, milk, dough stages) to study the effect of timing of foliar Zn application on grain Zn concentration. The rate of foliar Zn application at each growth stage was 4 kg of ZnSO4·7H2O ha−1. Laser ablation (LA)-ICP-MS was used to follow the localization of Zn within grain. Soil Zn application at a rate of 50 kg of ZnSO4·7H2O ha−1 was effective in increasing grain Zn concentration in the Zn-deficient location, but not in the locations without soil Zn deficiency. In all locations, foliar application of Zn significantly increased Zn concentration in whole ...

Tailored Titanium Dioxide Nanomaterials: Anatase Nanoparticles and Brookite Nanorods as Highly Active Photocatalysts

Abstract: High quality brookite TiO2 nanorods have been obtained by the thermal hydrolysis of commercially available aqueous solutions of titanium bis(ammonium lactate) dihydroxide in the presence of high concentrations of urea (≥6.0 M) as an in situ OH− source. Biphasial anatase/brookite mixtures are obtained at lower urea concentrations. The ratios between anatase and brookite can readily be tailored by the control of the urea concentration. The obtained powders have been characterized by X-ray diffraction, Raman spectroscopy, field emission-scanning electron microscopy, high-resolution transmission electron microscopy, UV−vis diffuse reflectance spectra, and nitrogen adsorption. The photocatalytic activity of pure anatase nanoparticles, of anatase/brookite mixtures, and of pure brookite nanorods has been assessed by hydrogen evolution from aqueous methanol solution as well as by the degradation of dichloroacetic acid (DCA) in aqueous solution. The results indicate that the photocatalytic hydrogen evolution activ...

TiO2 for water treatment: Parameters affecting the kinetics and mechanisms of photocatalysis

Abstract: The photocatalytic activity of TiO2 is the result of an interplay between a considerable number of parameters, e.g., phase composition, electronic structure, particle size, exposed surface area, degree of aggregation, mobility of charge carriers, presence of impurities, amount and kind of defects, adsorption of molecules from gas or aqueous phase, lateral interactions between adsorbed species, nature of solvent, etc. Furthermore, these parameters can be broadly subdivided into those that are intrinsic to the photocatalytic material, and those that are extrinsic being influenced by the surrounding environment and conditions. The specific function and influence of a given feature for the photocatalytic performance of a TiO2 sample is difficult to characterize since many of the before-mentioned parameters are strongly coupled. For example, while the degree of aggregation could be inherent to a given material, it is also simultaneously influenced by pH. The degree of aggregation can then influence adsorption of molecules, light scattering and photon adsorption, charge carrier dynamics etc. The plurality of variables driving the nature of the photocatalytic activity, presents a challenge when trying to understand the kinetics and mechanisms underlying photocatalytic processes. It is of primary importance to develop a method to understand and control these properties (or at least some of them). In this paper, we also discuss the relevance of quantum-integrated systems in which the local environment where the molecule is adsorbed is different from the “lonely” photocatalyst or the molecule in solution, and could be treated as a whole.

Controllable Synthesis of Metal-Organic Frameworks: From MOF Nanorods to Oriented MOF Membranes

Abstract: Tailoring of the crystal size and morphology of metal-organic framework (mof) materials and manipulation of mof films is possible by the solvothermal synthesis route introduced here. a c-out-of-plane zif-7 membrane (see figure) is obtained through evolutionary selection in a van der drift-type growth originating from randomly oriented seed layers. highly oriented mof thin films are important as molecular sieve membranes.

REVIEW: PART OF A HIGHLIGHT SECTION ON PLANT -SOIL INTERACTIONS AT LOW PH The role of the root apoplast in aluminium-induced inhibition of root elongation and in aluminium resistance of plants: a review

Abstract: †Background Aluminium (Al) toxicity is the most important soil constraint for plant growth and development inacid soils. The mechanism of Al-induced inhibition of root elongation is still not well understood, and it is amatter of debate whether the primary lesions of Al toxicity are apoplastic or symplastic.†Scope The present review focuses on the role of the apoplast in Al toxicity and resistance, summarizing evi-dence from our own experimental work and other evidence published since 1995.†Conclusions The binding of Al in the cell wall particularly to the pectic matrix and to the apoplastic face of theplasma membrane in the most Al-sensitive root zone of the root apex thus impairing apoplastic and symplasticcell functions is a major factor leading to Al-induced inhibition of root elongation. Although symplastic lesionsof Al toxicity cannot be excluded, the protection of the root apoplast appears to be a prerequisite for Al resistancein both Al-tolerant and Al-accumulating plant species. In many plant species the release of organic acid anionscomplexing Al, thus protecting the root apoplast from Al binding, is a most important Al resistance mechanism.However, there is increasing physiological, biochemical and, most recently also, molecular evidence showing thatthe modification of the binding properties of the root apoplast contributes to Al resistance. A further in-depthcharacterization of the Al-induced apoplastic reaction in the most Al-sensitive zone of the root apex is urgentlyrequired, particularly to understand the Al resistance of the most Al-resistant plant species.Key words: Aluminium, aluminum, resistance, apoplast, cell wall, pectin, root elongation.

Quantum metrology for gravitational wave astronomy

Abstract: Einstein's general theory of relativity predicts that accelerating mass distributions produce gravitational radiation, analogous to electromagnetic radiation from accelerating charges. These gravitational waves (GWs) have not been directly detected to date, but are expected to open a new window to the Universe once the detectors, kilometre-scale laser interferometers measuring the distance between quasi-free-falling mirrors, have achieved adequate sensitivity. Recent advances in quantum metrology may now contribute to provide the required sensitivity boost. The so-called squeezed light is able to quantum entangle the high-power laser fields in the interferometer arms, and could have a key role in the realization of GW astronomy.

Mixed convection flow in a lid-driven inclined square enclosure filled with a nanofluid

Abstract: This work is focused on the numerical modeling of steady laminar mixed convection flow in a lid-driven inclined square enclosure filled with water–Al2O3 nanofluid. The left and right walls of the enclosure are kept insulated while the bottom and top walls are maintained at constant temperatures with the top surface being the hot wall and moving at a constant speed. The developed equations are given in terms of the stream function–vorticity formulation and are non-dimensionalized and then solved numerically subject to appropriate boundary conditions by a second-order accurate finite-volume method. Comparisons with previously published work are performed and found to be in good agreement. A parametric study is conducted and a set of graphical results is presented and discussed to illustrate the effects of the presence of nanoparticles and enclosure inclination angle on the flow and heat transfer characteristics. It is found that significant heat transfer enhancement can be obtained due to the presence of nanoparticles and that this is accentuated by inclination of the enclosure at moderate and large Richardson numbers.

Significance of long-chain polyunsaturated fatty acids (PUFAs) for the development and behaviour of children.

Abstract: ω-6 and ω-3 polyunsaturated fatty acids (PUFAs) play a central role in the normal development and functioning of the brain and central nervous system. Long-chain PUFAs (LC-PUFAs) such as eicosapentaenoic acid (EPA, C20:5ω-3), docosahexaenoic acid (DHA, C22:6ω-3) and arachidonic acid (AA, C20:4ω-6), in particular, are involved in numerous neuronal processes, ranging from effects on membrane fluidity to gene expression regulation. Deficiencies and imbalances of these nutrients, not only during the developmental phase but throughout the whole life span, have significant effects on brain function. Numerous observational studies have shown a link between childhood developmental disorders and ω-6:ω-3 fatty acid imbalances. For instance, neurocognitive disorders such as attention-deficit hyperactivity disorder (ADHD), dyslexia, dyspraxia and autism spectrum disorders are often associated with a relative lack of ω-3 fatty acids. In addition to a high ω-6 fatty acid intake and, in many cases, an insufficient supply of ω-3 fatty acids among the population, evidence is increasing to suggest that PUFA metabolism can be impaired in individuals with ADHD. In this context, PUFA imbalances are being discussed as potential risk factors for neurodevelopmental disorders. Another focus is whether the nutritive PUFA requirements—especially long-chain ω-3 fatty acid requirements—are higher among some individuals. Meanwhile, several controlled studies investigated the clinical benefits of LC-PUFA supplementation in affected children and adolescents, with occasionally conflicting results.

Bose-Einstein Condensation in Microgravity

Abstract: Albert Einstein's insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.

Dynamic capacitated lot-sizing problems: a classification and review of solution approaches

Abstract: This paper presents a review of four decades of research on dynamic lot-sizing with capacity constraints. We discuss both different modeling approaches to the optimization problems and different algorithmic solution approaches. The focus is on research that separates the lot-sizing problem from the detailed sequencing and scheduling problem. Our conceptional point of reference is the multi-level capacitated lot-sizing problem (MLCLSP). We show how different streams of research emerged over time. One result is that many practically important problems are still far from being solved in the sense that they could routinely be solved close to optimality in industrial practice. Our review also shows that currently mathematical programing and the use of metaheuristics are particularly popular among researchers in a vivid and flourishing field of research.

The use of technical analysis by fund managers: International evidence

Abstract: The use of technical analysis by financial market professionals is not well understood. This paper thus analyzes survey evidence from 692 fund managers in five countries, the vast majority of whom rely on technical analysis. At a forecasting horizon of weeks, technical analysis is the most important form of analysis and up to this horizon it is thus more important than fundamental analysis. Technicians are as experienced, as educated, as successful in their career and largely just as overconfident in decision-making as others. However, technical analysis is somewhat more popular in smaller asset management firms. What we find most significant is the relation of technical analysis with the view that prices are heavily determined by psychological influences. Consequently, technicians apply trend-following behavior.