Showing papers by "Leibniz University of Hanover published in 2000"

Optimization of entanglement witnesses

Abstract: An entanglement witness (EW) is an operator that allows the detection of entangled states. We give necessary and sufficient conditions for such operators to be optimal, i.e., to detect entangled states in an optimal way. We show how to optimize general EW, and then we particularize our results to the nondecomposable ones; the latter are those that can detect positive partial transpose entangled states (PPTES's). We also present a method to systematically construct and optimize this last class of operators based on the existence of ``edge'' PPTES's, i.e., states that violate the range separability criterion [Phys. Lett. A 232, 333 (1997)] in an extreme manner. This method also permits a systematic construction of nondecomposable positive maps (PM's). Our results lead to a sufficient condition for entanglement in terms of nondecomposable EW's and PM's. Finally, we illustrate our results by constructing optimal EW acting on $H={C}^{2}\ensuremath{\bigotimes}{C}^{4}.$ The corresponding PM's constitute examples of PM's with minimal ``qubit'' domains, or---equivalently---minimal Hermitian conjugate codomains.

Dynamics of performance measurement systems

Abstract: Begins by creating a vision for dynamic performance measurement systems and goes on to describe the background to the work. Develops a model for integrated and dynamic performance measurement systems. Provides a critical review of existing frameworks, models and techniques against the model. Identifies that current knowledge and techniques are sufficiently mature to create dynamic performance measurement systems. The use of the dynamic performance measurement system is illustrated through a case study. Concludes with a series of lessons highlighting further research and development needs.

Biocompatibility of Resin-Modified Filling Materials

Abstract: Increasing numbers of resin-based dental restorations have been placed over the past decade. During this same period, the public interest in the local and especially systemic adverse effects caused by dental materials has increased significantly. It has been found that each resin-based material releases several components into the oral environment. In particular, the comonomer, triethyleneglycol di-methacrylate (TEGDMA), and the 'hydrophilic' monomer, 2-hydroxy-ethyl-methacrylate (HEMA), are leached out from various composite resins and 'adhesive' materials (e.g., resin-modified glass-ionomer cements [GICs] and dentin adhesives) in considerable amounts during the first 24 hours after polymerization. Numerous unbound resin components may leach into saliva during the initial phase after polymerization, and later, due to degradation or erosion of the resinous restoration. Those substances may be systemically distributed and could potentially cause adverse systemic effects in patients. In addition, absorption of organic substances from unpolymerized material, through unprotected skin, due to manual contact may pose a special risk for dental personnel. This is borne out by the increasing numbers of dental nurses, technicians, and dentists who present with allergic reactions to one or more resin components, like HEMA, glutaraldehyde, ethyleneglycol di-methacrylate (EGDMA), and dibenzoyl peroxide (DPO). However, it must be emphasized that, except for conventional composite resins, data reported on the release of substances from resin-based materials are scarce. There is very little reliable information with respect to the biological interactions between resin components and various tissues. Those interactions may be either protective, like absorption to dentin, or detrimental, e.g., inflammatory reactions of soft tissues. Microbial effects have also been observed which may contribute indirectly to caries and irritation of the pulp. Therefore, it is critical, both for our patients and for the profession, that the biological effects of resin-based filling materials be clarified in the near future.

Schmidt number for density matrices

Abstract: We introduce the notion of a Schmidt number of a bipartite density matrix. We show that k-positive maps witness the Schmidt number, in the same way that positive maps witness entanglement. We determine the Schmidt number of the family of states that is made from mixing the completely mixed state and a maximally entangled state. We show that the Schmidt number does not necessarily increase when taking tensor copies of a density matrix $\ensuremath{\rho};$ we give an example of a density matrix for which the Schmidt numbers of $\ensuremath{\rho}$ and $\ensuremath{\rho}\ensuremath{\bigotimes}\ensuremath{\rho}$ are both $2.$

Genotypical Differences in Aluminum Resistance of Maize Are Expressed in the Distal Part of the Transition Zone. Is Reduced Basipetal Auxin Flow Involved in Inhibition of Root Elongation by Aluminum

Abstract: Short-term Al treatment (90 μm Al at pH 4.5 for 1 h) of the distal transition zone (DTZ; 1–2 mm from the root tip), which does not contribute significantly to root elongation, inhibited root elongation in the main elongation zone (EZ; 2.5–5 mm from the root tip) to the same extent as treatment of the entire maize (Zea mays) root apex. Application of Al to the EZ had no effect on root elongation. Higher genotypical resistance to Al applied to the entire root apex, and specifically to the DTZ, was expressed by less inhibition of root elongation, Al accumulation, and Al-induced callose formation, primarily in the DTZ. A characteristic pH profile along the surface of the root apex with a maximum of pH 5.3 in the DTZ was demonstrated. Al application induced a substantial flattening of the pH profile moreso in the Al-sensitive than in the Al-resistant cultivar. Application of indole-3-acetic acid to the EZ but not to the meristematic zone significantly alleviated the inhibition of root elongation induced by the application of Al to the DTZ. Basipetal transport of exogenously applied [3H]indole-3-acetic acid to the meristematic zone was significantly inhibited by Al application to the DTZ in the Al-sensitive maize cv Lixis. Our results provide evidence that the primary mechanisms of genotypical differences in Al resistance are located within the DTZ, and suggest a signaling pathway in the root apex mediating the Al signal between the DTZ and the EZ through basipetal auxin transport.

Cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands.

Abstract: Bidendate ligands have proven important in a variety of complexes and are invaluable in a number of catalytic processes. While ligands of this type usually have two identical ligand fragments (homobidendate ligands), heterobidendate ligands allow for a differentiation of the ligands and therefore are prone to selective reactions. This is especially interesting in cases where the ligands are rather different from one another. Phosphane and cyclopentadienyl ligands are among the most commonly used in organometallic chemistry, and they are quite different in nature: Whereas a phosphane is electroneutral and often subjected to ligand exchange processes, the cyclopentadienyl ligand is normally considered to be negatively charged and rather tightly bound to a metal. Reviewing the literature in the field of cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands is timely given that the number of publications of relevance to this topic is growing exponentially as can easily be seen from the list of references in this review: the number of references since 1993 clearly exceeds that of all years before. The reason for this development may be that cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands are expected to perform chemistry different from that of usual cyclopentadienyl complexes. Indeed this has often been the case. Complexes discussed in this review facilitate the complexation of sensitive ligands, offer new aspects concerning chirality, allow novel reactions, and are beginning to be applied to transition metal catalysis. It is therefore hoped that this review will contribute to these developments by offering state of the art information for those active in the field and, even more important, for those who join in the future. This review covers the chemistry of cyclopentadienylmetal complexes, in which the cyclopentadienyl ligand bears a sidearm which includes a phosphorus, arsenic, or sulfur ligand. The pendant ligand has to be separated from the cyclopentadienyl part, that is, † Dedicated to Professor Günther Wilke on the occasion of his 75th birthday. * To whom correspondence should be addressed. Fax: +49/(0)511/ 762-4616. E-mail: holger.butenschoen@mbox.oci.uni-hannover.de. Holger Butenschön was born and raised in Hamburg, Germany. After his army service he studied chemistry at the University of Hamburg and obtained his Dr. rer. nat. degree in 1983 with Professor Armin de Meijere as a fellow of the Studienstiftung des Deutschen Volkes. From 1983 to 1984 he spent a postdoctoral year with Professor K. Peter C. Vollhardt at the University of California at Berkeley as a NATO fellow. Having returned to Germany, he joined the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr as a Liebig fellow to do preparative organometallic work in the fields of anellated arenechromium complexes and cyclopentadienyl cobalt complexes with pendant phosphane ligands. After his habilitation in 1991 (University of Hamburg), he became a Heisenberg fellow of the DFG at the University of Wuppertal from 1992 to 1993. Since 1993 he has been a professor of organic chemistry at the University of Hannover. In 1999 he was a foreign visiting professor at Kyushu University in Fukuoka, Japan. Holger Butenschön is the editor of the German translation of Peter Vollhardt’s and Neil Schore’s textbook Organic Chemistry as well as a coauthor of the Memofix OC. He currently serves as the chairman of the Hannover district of the German Chemical Society (GDCh). His spare time is occupied by the female part of his family, his wife Bettina and their four daughters Lisa, Nora, Inga, and Lara. 1527 Chem. Rev. 2000, 100, 1527−1564

Melting of isolated tin nanoparticles

Abstract: The melting of isolated neutral tin cluster distributions with mean sizes of about 500 atoms has been investigated in a molecular beam experiment by calorimetrically measuring the clusters' formation energies as a function of their internal temperature. For this purpose the possibility to adjust the temperature of the clusters' internal degrees of freedom by means of the temperature of the cluster source's nozzle was exploited. The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin. The melting behavior of the isolated tin clusters is discussed with respect to the occurrence of surface premelting.

Modified sessile drop method for assessing initial soil-water contact angle of sandy soil

Abstract: Existing methods for determining the soil-water contact angle as a measure of water repellency are either indirect, cumbersome, or time-consuming. Our objective was to develop a method that is simpler than existing procedures and that still yields accurate results. The proposed method represents a modified sessile drop method for measuring the initial contact angle of powdered or granular material. The measurements are made by placing a layer of uniform soil particles onto adhesive tape, adding droplets of deionized water, and reading off the contact angle at the three-phase boundary line with a goniometerfitted microscope immediately after placing the drops on the soil sample. Sieved soil fractions <63 μm, 63 to 100 μm, and 100 to 200 pm were used to ensure particle layer uniformity. The method was tested on 10 samples from different depths of a sandy soil profile. The contact angles measured on these soil fractions were compared with the water drop penetration time (WDPT) test and the capillary-rise method. The contact angles of the fractions <63 μm and 63 to 100 μm compared reasonably well with those measured with the capillary-rise method and their rank order agreed in general with that of the WDPT test. We conclude thai the new method appears to he promising for the simple, rapid, and reproducible determination of the contact angle of sandy soils. The sessile drop method can he used in a wider range of water repellency conditions compared with either the capillary-rise or the WDPT method.

The production of cosmogenic nuclides in stony meteoroids by galactic cosmic‐ray particles

Abstract: (Received 1999 April 5; accepted in revised form 1999 October 12) ~~ ~~ Abstract-We present a purely physical model for the calculation of depth- and size-dependent production rates of cosmogenic nuclides by galactic cosmic-ray (GCR) particles. Besides the spectra of primary and secondary particles and the excitation hnctions of the underlying nuclear reactions, the model is based on only one free parameter-the integral number of GCR particles in the meteoroid orbits. We derived this value from analysis of radionuclide data in Knyahinya. We also show that the mean GCR proton spectrum in the meteoroid orbits has been constant over about the last 10 Ma. For the major target elements in stony meteoroids, we present depth- and size-dependent production rates for loBe, 14C, 26A1, 36Cl, and 53Mn as well as for the rare gas isotopes 3He, ZoNe, 21Ne, 22Ne, 36Ar, and 38Ar. The new data differ from semi- empirical estimates by up to a factor of 4 but agree within -20% with results obtained by earlier parametric or physical approaches. The depth and size dependence of the shielding parameter 22Ne/21Ne and the correlations 26AI vs. loge, 26AI vs. 53Mn, loBe/zlNe vs. 22Ne/21Ne, and 36Ar vs. 36Cl for deciphering preatmospheric sizes, shielding depths, terrestrial residence times, and exposure histories are also discussed.

Aluminium tolerance is achieved by exudation of citric acid from roots of soybean (Glycine max)

Abstract: Fourteen soybean (Glycine max [L.] Merr.) cultivars were analysed and found to differ considerably in aluminium (Al) resistance. The cultivars Suzunari (Al-resistant) and Shishio (Al-sensitive) were selected for further analysis of physiological mechanisms of Al resistance. The relative root growth of Shishio was 48% compared to 76% for Suzunari in response to 15 μM Al (24 h). Aluminium accumulation and Al-induced callose formation in root apices were 50 and 25% of that in Suzunari, respectively. Al inhibited both Suzunari and Shishio during the first 6 h of exposure. However, the root growth inhibition was further increased in Shishio but not in Suzunari, suggesting an Al-induced Al-resistant mechanism operating in Suzunari. Organic acid analysis in root exudates of both cultivars revealed that they specifically exuded citrate in response to Al. However, the citrate exudation rate was significantly higher in Suzunari during the 6 h/24 h Al treatment, which was 52/330 compared to Shishio's 26/118 (nmol [g root fresh weight] -1 [6 h] -1 ), respectively. This Al-induced citric acid exudation was found to be specific for Al, as several other metals failed to induce citrate exudation in both cultivars. Fourteen days of P deficiency did not elicit citrate excretion in both cultivars, while application of Al to P-deficient plants rapidly induced citrate exudation in both cultivars, confirming the specificity of the response of these soybean cultivars to Al. To our knowledge, this is the first report demonstrating an Al-exclusion mechanism in soybean cultivars, which is conferred by enhanced and specific Al-induced exudation of citrate.

Cell wall pectin content modulates aluminium sensitivity of Zea mays (L.) cells grown in suspension culture

Abstract: The pectin content of the cell walls of maize suspension cells was modified to investigate its role in the expression of aluminium (Al) toxicity. Long-term adaptation to NaCI or to the cellulose synthesis inhibitor 2,6-dichlorbenzonitirle (DCB) increased the pectin content by 31 and 86%, respectively. Subculturing salt-adapted cells for up to 3 weeks without NaCI supply or treatment of cells with pectolyase for up to 15 min reduced pectin contents by up to 46%. Such pre-cultured cells were incubated for 2 h in presence of Al. There was a close positive correlation between pectin and both total and BaCl 2 non-exchangeable Al contents. Aluminium-induced callose formation as an indicator of Al injury was closely positively correlated to the loss of cell viability. In NaCI-adapted and pectolyase-treated cells, Al-induced callose formation was reduced when compared with normal cells. However, there was a close positive relationship between pectin contents and relative callose induction (digitonin-induced callose formation, reflecting the different capabilities of cells to synthesize callose set to 100%) indicating that cells with higher pectin contents are more Al-sensitive. The results presented support our view that the binding of Al to the cell wall pectin-matrix represents an important step in the expression of Al toxicity.

Gender-related beliefs of teachers in elementary school mathematics

Abstract: In this quantitative study, questionnaire data of fifty-two third- and fourth-grade teachers were analyzed using MANOVA tools. Teachers were asked to consider boys' and girls' achievement in mathematics, giving their views on the reasons for the students' successes and failures and describing their learning characteristics. Teachers thought that their average achieving girls were less logical than equally achieving boys. The girls were thought to profit less than boys from additional effort and to exert relatively more effort to achieve the level of actual performance in mathematics. Teachers rated mathematics as more difficult for average achieving girls than for equally achieving boys. With regard to girls, teachers attributed unexpected failure more to low ability and less to lack of effort than with boys. The results increase our understanding of stereotypical teacher beliefs that might help explain gender differences in achievement and in subsequent occupational choices.

Agrobacterium mediated transformation of chickpea (Cicer arietinum L.) embryo axes.

Abstract: Embryo axes of four accessions of chickpea (Cicer arietinum L.) were treated with Agrobacterium tumefaciens strains C58C1/GV2260 carrying the plasmid p35SGUSINT and EHA101 harbouring the plasmid pIBGUS. In both vectors the GUS gene is interrupted by an intron. After inoculation shoot formation was promoted on MS medium containing 0.5 mg/l BAP under a selection pressure of 100 mg/l kanamycin or 10 mg/l phosphinothricin, depending on the construct used for transformation. Expression of the chimeric GUS gene was confirmed by histochemical localization of GUS activity in regenerated shoots. Resistant shoots were grafted onto 5-day-old dark-grown seedlings, and mature plants could be recovered. T-DNA integration was confirmed by Southern analysis by random selection of putative transformants. The analysis of 4 plantlets of the T1 progeny revealed that none of them was GUS-positive, whereas the presence of the nptII gene could be detected by polymerase chain reaction.

A stabilization technique to avoid hourglassing in finite elasticity

Abstract: Enhanced strain element formulations are known to show an outstanding performance in many applications. The stability of these elements, however, cannot be guaranteed for general deformation states and arbitrarily shaped elements. In order to overcome this deficiency, we develop an innovative control technique based on a modal analysis on element level. The control is completely automatic in the sense that no artificial factors are introduced. The computational effort is negligible. The key to the approach is the split of the element tangent matrix into constant and hourglass parts which is not possible for the classical enhanced strain concept in general. This motivates the use of a recently developed reduced integration method, which, since its stabilization part is derived on the basis of the enhanced strain method, shows the same performance and retains the crucial split. Using this formulation in combination with the new control technique, leads to a “smart” element which is free of hourglass instabilities and generally applicable, also for strongly distorted meshes. Copyright © 2000 John Wiley & Sons, Ltd.

Pectin methylesterase modulates aluminium sensitivity in Zea mays and Solanum tuberosum

Abstract: Cell suspension cultures of Zea mays L. were adapted to grow under conditions of NaCl stress, which increased the cell-wall pectin content of these cells by 31% compared with unadapted cells (controls). Both cultures were treated for 5 or 10 min with pectin methylesterase (PME) and afterwards incubated in the presence of Al for 2 h. The different capabilities of the cells to synthesise callose due to pre-treatment were taken into account by calculating relative Al-induced callose induction (digitonin = 100%). Only in salt-adapted cells with a degree of methylation of cell-wall pectin (DM) decreasing from 34% (control) to 13%, did PME treatment enhance total and BaCl 2 -non-exchangeable Al contents and Al sensitivity as indicated by increased callose formation. In a further step, a wider variation in DM was achieved by subculturing the NaCI-adapted cells for up to 3 weeks without NaCI supply and adapting them to the cellulose-synthesis inhibitor 2,6-dichlorbenzonitrile (DCB). This reduced DM to 26%, while short-term treatment with pectolyase resulted in the lowest DM (12%). After the 2 h Al treatment, there was a close negative relationship between DM and relative callose formation of Al contents, with the exception of pectolyase-treated cells. In addition, intact plants of Solanum tuberosum L. genotypes were characterised for their Al sensitivity in hydroponics using root elongation, Al-induced callose formation and Al contents of root tips as parameters. Based on all three parameters, the transgenic potato mutant overexpressing PME proved to be more Al-sensitive than the wild type, the Al-resistant and even the Al-sensitive potato cultivar. Especially in the root tips (1 cm), Al treatment (2 h, 50 μM) increased the activity of PME more in the Al-sensitive than in the Al-resistant genotypes. The presented data emphasise the importance of the DM of the pectin matrix and the activity of PME for the expression of Al toxicity and Al resistance.

Relationship Marketing — Some Reflections on the State-of-the-Art of the Relational Concept

Abstract: With the concept of relationship marketing approaching a stage of maturity, the authors give a comprehensive overview of the main research findings in the field of relationship marketing theory. They use this review to draw out some proposals for future resource allocation in relationship marketing research.

Nanocrystalline versus Microcrystalline Li 2 O:B 2 O 3 Composites: Anomalous Ionic Conductivities and Percolation Theory

Abstract: We study ionic transport in nano- and microcrystalline (1-x)Li(2)O:xB(2)O3 composites using standard impedance spectroscopy. In the nanocrystalline samples (average grain size of about 20 nm), the ionic conductivity sigma(dc) increases with increasing content x of B2O3 up to a maximum at x approximately 0.5. Above x approximately 0.92, sigma(dc) vanishes. By contrast, in the microcrystalline samples (grain size about 10 mm), sigma(dc) decreases monotonically with x and vanishes above x approximately 0. 55. We can explain this strikingly different behavior by a percolation model that assumes an enhanced conductivity at the interfaces between insulating and conducting phases in both materials and explicitly takes into account the different grain sizes.

Retinoic Acid Reduces Glomerular Injury in a Rat Model of Glomerular Damage

Abstract: .: In the reaction of kidneys to injury, cytokine-driven proliferation plays an important role and precedes the development of glomerulosclerosis. There is great interest in agents that may interfere with such proliferation. Therefore, a rat model of mesangioproliferative glomerulonephritis (induced by anti-Thy1.1) was studied, and the effects of all-trans-retinoic acid (all-trans-RA) and isotretinoin, powerful antiproliferative and anti-inflammatory substances, on glomerular damage and cell proliferation were examined. Vehicle-injected control rats were compared with rats treated with daily subcutaneous injections of 10 mg/kg body wt all-trans-RA or 40 mg/kg body wt isotretinoin (n = 9 to 11 per group), using either a pretreatment (days -2 through 8) or posttreatment (days +3 through +8) protocol, i.e., starting before or after the induction of anti-Thy1.1 nephritis, respectively. All-trans-RA prevented the BP increase evoked by anti-Thy1.1 (anti-Thy1.1/vehicle, 112.2 +/- 4.8 mmHg; anti-Thy1.1/RA, 87.5 +/- 2. 5 mmHg; P < 0.001). Treatment with all-trans-RA or isotretinoin produced a 70% decrease in the urinary albumin excretion rate (P < 0. 02). Periodic acid-Schiff staining of saline-perfused kidneys (day 8) revealed significantly fewer glomerular cells in RA-treated nephritic rats (anti-Thy1.1/vehicle, 97 +/- 3.1 cells/glomerulus; anti-Thy1.1/RA, 80 +/- 4.4; P < 0.02; control/vehicle, 69 +/- 1.2). No difference was observed between all-trans-RA and isotretinoin treatment. The capillary occlusion scores were significantly lower for the anti-Thy1.1/RA-treated group (1.9 +/- 0.1) than for the anti-Thy1.1/vehicle-treated group (2.9 +/- 0.5, P < 0.001). In the anti-Thy1.1/vehicle-treated group, 11.9 +/- 1.1 glomerular cells were proliferating cell nuclear antigen-positive; however, in the anti-Thy1.1/RA-treated group, only 5.3 +/- 0.8 cells were proliferating cell nuclear antigen-positive (P < 0.002; control, 2.2 +/- 0.2). Glomerular mitoses were reduced by 67% in the anti-Thy1. 1/RA-treated group, compared with the anti-Thy1.1/control group (P < 0.002). Glomerular staining for platelet-derived growth factor B-chain was significantly reduced in anti-Thy1.1-treated nephritic rats in the presence of isotretinoin or all-trans-RA, compared with the vehicle-treated group (P < 0.001). It is concluded that all-trans-RA limits glomerular proliferation, glomerular lesions, and albuminuria in an established model of renal damage. The findings point to retinoids as potential novel modulators of glomerular injury.

Development, Processing and Applications Range of Magnesium Lithium Alloys

Abstract: Among the light metal alloys, magnesium is the lightest structural material with a density of 1.74 g/cm 3 and many attractive physical and mechanical properties combined with processing advantages. Therefore, it represents a very attractive material for a large amount of applications from main user automotive industry up to other industry fields like sport, robotic and electronic industry. But the usage of magnesium alloys in more complex applications is limited by insufficient properties regarding the ductility, corrosion and creep resistance. Additionally, the high reactivity of magnesium alloys leads to an increased tendency of contamination. In this regard, the paper deals with some general aspects of magnesium alloy development and casting as well as some other production technologies for magnesium alloys with improved properties and for several applications. An emphasis is put on new magnesium-lithium alloy systems with lower density, improved ductility and corrosion resistance. The basic component of metallurgical processing is a magnesium-suitable furnace system which is designed modularly with universal, adaptable components and automatic pressure metering technology. It is used in a wide range of casting processes like chill casting, cold chamber die casting, continuous casting and break-mould casting. Further applications are methods of rapid solidification technology. In the powder metallurgy and spray casting a microstructure with fine and homogenous phase distribution is generated. Based on the represented processing technology new magnesium alloy systems with lower density, improved ductility and corrosion resistance will be shown. A special peculiarity of magnesium alloys is their application in the medicine sector where they are used as implant materials for surgery.

Why Customers Build Relationships with Companies — and Why Not

Abstract: Although relationship marketing has received much attention in recent years, most of the literature focuses on benefits the firm receives from developing relationships with customers. A comprehensive model explicitly considering both the benefits and barriers of such relationships from the customer’s perspective has not been proposed. To address this gap in the literature, this chapter develops an integrative theory of customers’ motivations to participate in relationships with companies. In particular, the authors review the existing literature on customers’ relational motivations for participating in business exchanges and subsequently present an integrative model of both benefits and barriers to such relationships from a customer perspective. They then report the results of a study examining a portion of the relational benefit side of the model. Finally, implications for the management of relationships with customers are discussed.