bluuebunny/crossref_metadata_2025 huggingface dataset:
Passive Decomposition Approach to Formation and Maneuver Control of Multiple Rigid Bodies
Authors: Lee Dongjun , Li Perry Y.
Published: August 2007

A passive decomposition framework for the formation and maneuver controls for multiple rigid bodies is proposed. In this approach, the group dynamics of the multiple agents is decomposed into two decoupled systems: The shape system representing internal group formation shape (formation, in short), and the locked system abstracting the overall group maneuver as a whole (maneuver, in short). The decomposition is natural in that the shape and locked systems have dynamics similar to the mechanical systems, and the total energy is preserved. The shape and locked system can be decoupled without the use of net energy. The decoupled shape and locked systems can be controlled individually to achieve the desired formation and maneuver tasks. Since all agents are given equal status, the proposed scheme enforces a group coherence among the agents. By abstracting a group maneuver by its locked system whose dynamics is similar to that of a single agent, a hierarchical control structure for the multiple agents can be easily imposed in the proposed framework. A decentralized version of the controller is also proposed, which requires only undirected line communication (or sensing) graph topology.
Position and Attitude Control of Deep-Space Spacecraft Formation Flying Via Virtual Structure and θ-D Technique
Authors: Xin Ming , Balakrishnan S. N. , Pernicka H. J.
Published: August 2007

Control of deep-space spacecraft formation flying is investigated in this paper using the virtual structure approach and the θ-D suboptimal control technique. The circular restricted three-body problem with the Sun and the Earth as the two primaries is utilized as a framework for study and a two-satellite formation flying scheme is considered. The virtual structure is stationkept in a nominal orbit around the L2 libration point. A maneuver mode of formation flying is then considered. Each spacecraft is required to maneuver to a new position and the formation line of sight is required to rotate to a desired orientation to acquire new science targets. During the rotation, the formation needs to be maintained and each spacecraft’s attitude must align with the rotating formation orientation. The basic strategy is based on a “virtual structure” topology. A nonlinear model is developed that describes the relative formation dynamics. This highly nonlinear position and attitude control problem is solved by employing a recently developed nonlinear control approach, called the θ-D technique. This method is based on an approximate solution to the Hamilton-Jacobi-Bellman equation and yields a closed-form suboptimal feedback solution. The controller is designed such that the relative position error of the formation is maintained within 1cm accuracy.
Cooperative Avoidance Control for Multiagent Systems
Authors: Stipanović Dušan M. , Hokayem Peter F. , Spong Mark W. , Šiljak Dragoslav D.
Published: August 2007

The objective of this paper is to present a methodology for designing cooperative control laws for individual agents that guarantee collision avoidance in multiagent systems. The proposed avoidance control laws are easy to design and implement, and may be directly appended to the optimal control laws of the individual agents within the cooperation framework. The avoidance control laws are computed using value functions that resemble the behavior of barrier functions in the static optimization theory. The most attractive feature of the proposed optimization scheme is the fact that the avoidance laws are active only in the bounded sensing regions of each individual agent, and they do not interfere with the agents’ individual optimal control laws outside of these regions.
Recent Research in Cooperative Control of Multivehicle Systems
Authors: Murray Richard M.
Published: August 2007

This paper presents a survey of recent research in cooperative control of multivehicle systems, using a common mathematical framework to allow different methods to be described in a unified way. The survey has three primary parts: an overview of current applications of cooperative control, a summary of some of the key technical approaches that have been explored, and a description of some possible future directions for research. Specific technical areas that are discussed include formation control, cooperative tasking, spatiotemporal planning, and consensus.
Autonomous Vehicle-Target Assignment: A Game-Theoretical Formulation
Authors: Arslan Gürdal , Marden Jason R. , Shamma Jeff S.
Published: August 2007

We consider an autonomous vehicle-target assignment problem where a group of vehicles are expected to optimally assign themselves to a set of targets. We introduce a game-theoretical formulation of the problem in which the vehicles are viewed as self-interested decision makers. Thus, we seek the optimization of a global utility function through autonomous vehicles that are capable of making individually rational decisions to optimize their own utility functions. The first important aspect of the problem is to choose the utility functions of the vehicles in such a way that the objectives of the vehicles are localized to each vehicle yet aligned with a global utility function. The second important aspect of the problem is to equip the vehicles with an appropriate negotiation mechanism by which each vehicle pursues the optimization of its own utility function. We present several design procedures and accompanying caveats for vehicle utility design. We present two new negotiation mechanisms, namely, “generalized regret monitoring with fading memory and inertia” and “selective spatial adaptive play,” and provide accompanying proofs of their convergence. Finally, we present simulations that illustrate how vehicle negotiations can consistently lead to near-optimal assignments provided that the utilities of the vehicles are designed appropriately.
Differential Geometric Path Planning of Multiple UAVs
Authors: Shanmugavel Madhavan , Tsourdos Antonios , White Brian A. , Żbikowski Rafaeł
Published: August 2007

Safe and simultaneous arrival of constant speed, constant altitude unmanned air vehicles (UAVs) on target is solved by design of paths of equal lengths. The starting point for our solution is the well-known Dubins path, which is composed of circular arc and line segments, thus requiring only one simple maneuver—constant rate turn. An explicit bound can be imposed on the rate during the design and the resulting paths are the minimum time solution of the problem. However, transition between arc and line segments entails discontinuous changes in lateral acceleration (latax), making this approach impractical for real fixed wing UAVs. Therefore, we replace the Dubins solution with a novel one, based on quintic Pythagorean hodograph (PH) curves, whose latax demand is continuous. The PH paths are designed to have lengths close to the lengths of the Dubins paths to stay close to the minimum time solution. To derive the PH paths, the Dubins solution is first interpreted in terms of differential geometry of curves using the path length and curvature as the key parameters. The curvature of a Dubins path is a piecewise constant and discontinuous function of its path length, which is a differential geometric expression of the discontinuous latax demand involved in transitions between the arc and the line segment. By contrast, the curvature of the PH path is a fifth order polynomial of its path length. This is not only continuous but also has enough design parameters (polynomial coefficients) to meet the latax (curvature) constraints (bounds) and make the PH solution close to the minimum time one. The solution involves the design of paths meeting the curvature constraint and is followed by producing multiple paths of equal length by increasing the lengths of the shorter paths to match the longest one. The safety constraint, intercollision avoidance is achieved by satisfying two conditions: minimum separation distance and nonintersection at equal distance. The offset curves of the PH path are used to design a safety region along each path.
Formation of a Group of Vehicles With Full Information Using Constraint Forces
Authors: Zou Yunfei , Pagilla Prabhakar R. , Misawa Eduardo
Published: August 2007

We consider the problem of controlling a group of vehicles to a formation. The approach mimics the development of dynamics of a system of particles subject to constraints. In particular, we use the notion of constraint forces to achieve and maintain a given formation. As opposed to the potential function approach used in the literature, the proposed constraint force approach directly compensates for only those parts of the applied forces, which act against the constraints. We develop a stable control algorithm that will achieve the formation while ensuring navigation of the group based on the desired trajectories, which are consistent with the constraints. Simulation results on an example are shown to corroborate the proposed method.
Imidazolium-Tagged Ferrocene Ligands
Authors: Šebesta Radovan , Mečiarová Mária , Poláčková Viera , Veverková Eva , Kmentová Iveta , Gajdošíková Eva , Cvengroš Ján , Buffa Radovan , Gajda Vladimír
Published: August 2007

New chiral imidazolium-tagged ferrocene ligands were prepared. Diastereoselective ortho-lithiation of the Ugi amine was employed in the synthesis of planar chiral P/P, P/N and Se/N ligands. These compounds were attached through six-carbon spacers to an imidazolium moiety. Pd-complexes of these ligands were successfully used as catalysts for asymmetric allylic substitution in ionic liquids.
Synthesis and Study of Novel Benzothiazole Derivatives with Potential Nonlinear Optical Properties
Authors: Sigmundová Ivica , Zahradník Pavol , Loos Dušan
Published: August 2007

The synthesis of new benzothiazole push-pull systems as candidates for NLO-phores is described. Spectral (UV/VIS and solvatochromic) and theoretical studies (electronic properties based on semiempirical AM1 and PM3 methods) of the prepared compounds were carried out. The structure and physico-chemical parameters affecting the push-pull character and intramolecular charge transfer (ICT) of the studied compounds have been investigated and compounds with enhanced hyperpolarizability β have been predicted. The benzothiazolium salts were found to be much more effective NLO-phores in comparison with the corresponding neutral benzothiazoles. The 4-NPh2 group is the most effective donor. The extension of conjugated bridge improves the studied NLO characteristics. An additional acceptor group bonded to the heterocycle causes a red shift of λmax but does not increase hyperpolarizability.
In Search of New Approaches to Asymmetric Conjugate Addition: Screening Studies on the Use of [Zn(bpy*)X(R)] Reagents and α,β-Unsaturated Amide Michael Acceptors
Authors: Blake Alexander J. , Giunta Daniela , Shannon Jonathan , Solinas Maurizio , Walzer Francesca , Woodward Simon
Published: August 2007

Conjugate additions of [Zn(bpy*)Cl(Et)] (bpy* = 4,4'-di-tert-butyl-2,2'-bipyridine) to cyclohex-2-en-1-one are promoted by ZnMe2 in 88% ee but in moderate yield under CuI phosphoramidite catalysis. In the absence of ZnMe2 the [Zn(bpy*)Cl(Et)] is inactive indicating a Schlenk-type equilibrium. Other derivatives of [Zn(bpy*)Cl(R)] (R = Bu, 4-methylbenzyl), prepared in situ from [ZnCl(R)] and the bipyridine give low yields due to competing chloride abstraction. 13C NMR studies indicate facile organo-ligand exchange between [Zn(bpy*)(Et)2] and [Zn(bpy*)Cl2] complexes. In the presence of the bipyridine, [ZnBr(allyl)] disproportionates into [Zn(bpy*)Br2] and [Zn(bpy*)(allyl)2] species. In separate studies, simple (E)-MeCH=CHCONMeR (R = Me, OMe) α,β-unsaturated amides undergo asymmetric 1,4-addition of EtMgBr in 75-99% yield and 48-79% ee in the presence of the diphosphines JosiPhos or MeDuPhos and copper(I) sources.
Chiral Binaphthalenes Bearing Two Pyridine Ligands Attached Via Acetylene Spacers. Synthesis and Coordination Study
Authors: Kasák Peter , Brath Henrich , Krascsenicsová-Poláková Katarína , Kicková Anna , Moldovan Natalia , Putala Martin
Published: August 2007

An effective methodology has been developed for the synthesis of enantiopure 2,2'-dialkynylated 1,1'-binaphthalene derivatives. Enantiopure 2,2'-diiodo-1,1'-binaphthalene (10) provided 2,2'-diethynyl-1,1'-binaphthalene (16) in the Negishi alkynylation supported by microwave irradiation in a very good yield with conservation of stereochemical information. The Stephen-Castro alkynylation of 10 afforded products in lower yields; however, in stereoconservative manner as well. Terminal diacetylene 16 served as precursor in the Sonogashira cross-coupling reaction to give new bispyridine derivatives 7-9 as potential ligands in moderate to high yields. Coordination of bispyridines with Zn2+ and Ag+ ions was observed by NMR and CD spectroscopy. The coordination ability of bis(2-pyridylethynyl) derivative 7 to palladium cation was determined by X-ray structure analysis.
COMPUTING EPITAXIAL GROWTH IN A TILTED MOCVD REACTOR BY A FINITE ELEMENT MULTIGRID METHOD
Authors: DUQUE JAIRO
Published: August 2007

A multigrid (MG) numerical solution procedure for a mathematical model for epitaxial growth in metalorganic chemical vapor deposition reactors is developed. The model is governed by the full compressible Navier–Stokes equations for two-dimensional (plane and axisymmetric) laminar flows extended by transport equations for the chemical species, the energy equations and the equation of state, together with boundary conditions providing information on the reactor geometry and experimental conditions. The MG numerical solution is implemented in a finite element procedure that uses the same linear finite elements to discretize both convection and diffusion fluxes by adding to the model a stabilizing term, resulting in easy implementation of the procedure. A deposition process for a model of GaAs growth is calculated with our procedure showing consistency with experimental data.
A LATTICE BOLTZMANN MODEL FOR GROUNDWATER FLOWS
Authors: ZHOU JIAN GUO
Published: August 2007

A novel lattice Boltzmann model is proposed for groundwater isotropic flows (LABGIF). It solves the isotropic groundwater equation. This is generally suitable for both steady and unsteady groundwater problems. Only a 5-speed square lattice is required for 2D and 7-speed cubic for 3D cases in the model. The Dirichlet and Neumann conditions associated with the common boundary conditions encountered in the groundwater modeling are treated with a simple procedure. The stability conditions for the model are described. The model is verified by being applied to steady and unsteady groundwater flows. There are excellent agreements between numerical predictions and exact/analytical solutions. This indicates that the scheme is simple, accurate, and robust.
A LATTICE BOLTZMANN STUDY ON THE LARGE DEFORMATION OF RED BLOOD CELLS IN SHEAR FLOW
Authors: SUI Y. , CHEW Y. T. , LOW H. T.
Published: August 2007

The transient deformation of a liquid-filled elastic capsule, simulating a red blood cell, was studied in simple shear flow. The simulation is based on a hybrid method which introduces the immersed boundary concept in the framework of the multi-block lattice Boltzmann model. The method was validated by the study on deformation of an initially circular capsule with Hooke's membrane. Also studied were capsules with Skalak membrane of initially elliptical and biconcave shapes, which are more representative of a red blood cell. Membrane tank treading motion is observed. As the ratio between membrane dilation modulus and shear modulus increases, the capsule shows asymptotic behavior. For an initially elliptical capsule, it is found that the steady shape is independent of initial inclination angle. For an initially biconcave capsule, the tank treading frequency from two-dimensional modeling is comparable to that of real cells. Another interesting finding is that the tank treading velocity has not attained steady state when the capsule shape becomes steady; and at this state there is the internal vortex pair. The treading velocity continues to decrease and reaches a steady value when the internal vortex pair has developed into a single vortex.
INTERPLAY BETWEEN HIV/AIDS EPIDEMICS AND DEMOGRAPHIC STRUCTURES BASED ON SEXUAL CONTACT NETWORKS
Authors: BAI WEN-JIE , ZHOU TAO , WANG BING-HONG
Published: August 2007

In this article, we propose a network spreading model for HIV epidemics, wherein each individual is represented by a node of the transmission network and the edges are the connections between individuals along which the infection may spread. The sexual activity of each individual, measured by its degree, is not homogeneous but obeys a power-law distribution. Due to the heterogeneity of activity, the infection can persistently exist at a very low prevalence, which has been observed in the real data but cannot be illuminated by previous models with homogeneous mixing hypothesis. The model displays a clear picture of hierarchical spread: In the early stage the infection is adhered to these high-risk persons, and then, diffuses toward low-risk population. Furthermore, we find that to reduce the risky behaviors is much more effective in the fight against HIV/AIDS rather than the antiretroviral drug therapies. The prediction results show that the development of epidemics can be roughly categorized into three patterns for different countries, and the pattern of a given country is mainly determined by the average sex-activity and transmission probability per sexual partner. In most cases, the effect of HIV epidemics on demographic structure is very small. However, for some extremely countries, like Botswana, the number of sex-active people can be depressed to nearly a half by AIDS.
BIHAM–MIDDLETON–LEVINE TRAFFIC MODEL WITH ORIGIN-DESTINATION TRIPS
Authors: MOUSSA NAJEM
Published: August 2007

We extended the Biham–Middleton–Levine model to incorporate the origin and destination effect of drivers trips on the traffic in cities. The destination sites are randomly chosen from some origin-destination distances probability distribution "ODDPD." We use three different distributions: exponential, uniform, and power-law. We found that the traffic dynamics of the model are greatly influenced by the ODDPD. Moreover, it is found that we can adjust the ODDPD to enhance the road capacity of the city and to minimize the arrival times of drivers.
FORMATION OF LANGUAGES: EQUALITY, HIERARCHY AND TEACHERS
Authors: TUNCAY ÇAĞLAR
Published: August 2007

A quantitative method is suggested, where meanings of words, and grammatic rules about these, of a vocabulary are represented by real numbers. People meet randomly, and average their vocabularies if they are equal; otherwise they either copy from higher hierarchy or stay idle. The presence of teachers broadcasting the same (but arbitrarily chosen) vocabulary leads the language formations to converge more quickly.
A GEOMETRICAL APPROACH TOWARDS ENTANGLEMENT
Authors: BASU B. , BANDYOPADHYAY P.
Published: August 2007

We have studied the concurrence of two-site entanglement and have shown that it is related to the geometric phase accumulated due to a complete rotation of the entangled state. The geometric phase and hence the concurrence is evaluated for transverse Ising model and antiferromagnetic chain which is found to be in good agreement with that obtained by other methods.
RELATIVITY GROUPOID INSTEAD OF RELATIVITY GROUP
Authors: OZIEWICZ ZBIGNIEW
Published: August 2007

In 1908, Minkowski [13] used space-like binary velocity-field of a medium, relative to an observer. In 1974, Hestenes introduced, within a Clifford algebra, an axiomatic binary relative velocity as a Minkowski bivector [7, 8]. We propose to consider binary relative velocity as a traceless nilpotent endomorphism in an operator algebra. Any concept of a binary axiomatic relative velocity made possible the replacement of the Lorentz relativity group by the relativity groupoid. The relativity groupoid is a category of massive bodies in mutual relative motions, where a binary relative velocity is interpreted as a categorical morphism with the associative addition. This associative addition is to be contrasted with non-associative addition of (ternary) relative velocities in isometric special relativity (loop structure).

We consider an algebra of many time-plus-space splits, as an operator algebra generated by idempotents. The kinematics of relativity groupoid is ruled by associative Frobenius operator algebra, whereas the dynamics of categorical relativity needs the non-associative Frölicher–Richardson operator algebra.

The Lorentz covariance is the cornerstone of physical theory. Observer-dependence within relativity groupoid, and the Lorentz-covariance within the Lorentz relativity group, are different concepts. Laws of Physics could be observer-free, rather than Lorentz-invariant.
PSEUDO-RIEMANNIAN JACOBI–VIDEV MANIFOLDS
Authors: GILKEY P. , NIKČEVIĆ S.
Published: August 2007

We exhibit several families of Jacobi–Videv pseudo-Riemannian manifolds which are not Einstein. We also exhibit Jacobi–Videv algebraic curvature tensors where the Ricci operator defines an almost complex structure.
SMOOTH CHANGES OF FRAME AND PROLONGATIONS OF VECTOR FIELDS
Authors: GAETA GIUSEPPE
Published: August 2007

We discuss how prolongations of vector fields, and hence symmetries of differential equations, are affected by changes of the reference frame in the dependent variables space depending on independent variables. We devise a relation with the recently developed theory of μ-prolongations of vector fields and μ-symmetries of differential equations.
TENSORIAL CURVATURE AND D-DIFFERENTIATION PART I: "COMMUTATIVE" KIND
Authors: HURLEY D. J. , VANDYCK M. A.
Published: August 2007

A special class of operators of D-differentiation is introduced, called the "commutative" kind. It is closely related to the family of D-differentiation operators, the curvature of which is a tensor (as opposed to a non-linear operator), and to that of the D-differentiation operators admitting a scalar curvature. It is found that all commutative D-differentiation operators admit a scalar curvature, but that only a proper subset of them (which is explicitly characterized) has a curvature operator that is a tensor. It is also established that all commutative D-differentiation operators can be expressed in terms of covariant differentiation and a tensor field. This generalizes the well-known result about the difference of two sets of connection coefficients yielding a tensor field.

In a companion article, a cognate class of operators is defined, which contains the commutative type as a special case. It enables one to construct a unified framework for the Einstein–Maxwell theory through D-differentiation.
The early hydration and the set of Portland cements:In situX-ray powder diffraction studies
Authors: Merlini M. , Artioli G. , Meneghini C. , Cerulli T. , Bravo A. , Cella F.
Published: August 2007

The hydration of ordinary Portland cements (OPC) was investigated with X-ray powder diffraction (XRPD) technique, mainly using synchrotron radiation.In situexperiments were performed during the first hours of hydration to study the evolution of the crystalline phases in the system. The hydration was carried out with pure water and in the presence of additives such as superplasticizers and setting accelerating agents. As soon as water is added to the cement, ettringite crystallizes. Its evolution appears to be very complex, and lattice parameters change as a function of setting time, indicating a possible chemical evolution of ettringite with time and as a function ofpH. CSH (Ca-Si-hydrate) forms after a few hours from the beginning of hydration. CSH can be indirectly quantified and its evolution studied.
Crystal structure of Nd2−xMxRu2O7−y (M=Cu, Ag) pyrochlores by X-ray powder diffraction
Authors: Kimmel G. , On H. , Itzhak D. , Hormadaly J.
Published: August 2007

The crystal structures of ruthenium oxides with the general formula
Nd2−xMxRu2O7−y, where M is Cu or Ag, 0≤x≤0.25, were investigated. All compounds that were prepared exhibit the pyrochlore structure with a cubic unit cell. The compounds were characterized by X-ray powder diffraction, and single-phase structures were found for
Nd2−xCuxRu2O7−y, x=0.1, 0.2, 0.25, and for
Nd2−xAgxRu2O7−y, x=0.1, 0.15, 0.2. The relative metal concentrations were verified by EDS. The cell parameters were determined by advanced peak-position analysis and calibrated by a Si internal standard. Atomic positions and oxygen occupancies where refined by the Rietveld method. It was found that the cell-size modifications agree with the relations between ionic sizes.
High-resolution X-ray diffraction analysis of InN films grown by metalorganic vapor phase epitaxy
Authors: Wang W. J. , Sugita K. , Nagai Y. , Houchin Y. , Hashimoto A. , Yamamoto A.
Published: August 2007

The growth temperature dependence of the
InN
film’s crystalline quality is reported.
InN
films are grown on sapphire substrates from 570 to 650 °C with low-temperature
GaN
buffers by metalorganic vapor phase epitaxy (MOVPE). The X-ray rocking curves and reciprocal space mappings of the symmetric reflection (0 0 0 2) and asymmetric reflection (1 0 1 2) are measured with high resolution X-ray diffraction. The results indicate that the crystallinity is sensitive to the growth temperature for MOVPE
InN. At growth temperature 580 °C, highly crystalline
InN
film has been obtained, for which the full-width-at-half-maxima of (0 0 0 2) and (1 0 1 2) rocking curves are 24 and 28 arcmin, respectively. The crystalline quality deteriorates drastically when the growth temperature exceeds 600 °C. Combined with the carrier concentration and mobility, the approach to improve the quality of
InN
film by MOVPE is discussed.
Crystal structures of room- and low-temperature phases in oxyfluoride (NH4)2KWO3F3
Authors: Molokeev M. S. , Vasiliev A. D. , Kocharova A. G.
Published: August 2007

Crystal structures of
(NH4)2KWO3F3 at 298 K and 113 K were solved from X-ray powder diffraction data and refined by the Rietveld technique. The compound is isostructural with elpasolite
K2NaAlF6 at room temperature with space group Fm-3m, a=8.95850(5) Å, V=718.961(7) Å3, Z=4, Dx=3.363 g/cm3, and MW=364.02. The structure was refined over 18 parameters to Rwp=12.6%, Rp=10.9%, Rexp=5.03%, and RB=3.27% from 40 independent reflections. (NH4)2KWO3F3 was transformed upon cooling to a ferroelastic monoclinic phase with space group P21/n, a′=6.3072(3) Å, b′=6.3028(3) Å, c′=8.9882(3) Å, β′=90.242(2)°, V=357.30(3) Å3, Z=2, and Dx=3.383 g/cm3. The low-temperature structure at 113 K was refined over 28 parameters to Rwp=20.9%, Rp=21.3%, Rexp=12.5%, and RB=6.93% from 453 independent reflections.
Crystal and molecular structures of the organometallic species [Rh2(bim)2(cod)2]Cl2∙2H2O [bim=bis-(1-imidazolyl)methane; cod=1, 5-cyclooctadiene]
Authors: Masciocchi Norberto , Figini Albisetti Alessandro , Sironi Angelo , Pettinari Claudio , Marinelli Alessandro
Published: August 2007

The synthesis and X-ray powder diffraction data for the organometallic [Rh2(bim)2(cod)2]Cl2∙2H2O species are reported. Its crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. [Rh2(bim)2(cod)2]Cl2∙2H2O was found to crystallize in the orthorhombic Cmca space group. The lattice parameters were determined to be a=21.3574(6), b=10.7764(3), c=14.2795(4) Å, V=3286.5(2) Å3, for Z=4. The crystal structure was found to contain dimeric [Rh2(bim)2(cod)2]2+
cations, in which the bim ligands bridge Rh(cod) fragments with an intermetallic separation of ca. 8.90 Å. The crystal structure is completed by chloride ions and hydrogen-bonded water molecules, situated in the small cavities of the large cation substructure. The conformation of the bim ligand, lying on a crystallographic mirror plane, is rigorously Cs.
Crystal-structure refinement of τ3-Cr4(Al, Si)11 by full-profile Rietveld analysis
Authors: Weitzer Franz , Chen Hailin , Schuster Julius C.
Published: August 2007

Crystal structure of the triclinic ternary phase
Cr4(Al, Si)11 was investigated by full-profile Rietveld analysis of powder diffraction data. Four hundred eighty-four reflections were refined to a final RBragg value of 5.00%.
Cr4(Al, Si)11 is isostructural to
Mn4Al11. Silicon atoms enter into the structure by partially replacing aluminium on the
Al(1) and
Al(2) sites.
Powder diffraction investigations of some derivatives of benzophenone: Monomers for synthesis of new polyurethanes
Authors: Olszewska E. , Pikus S. , Kultys A. , Wolski P.
Published: August 2007

Four aliphatic-aromatic diols with ether linkages [4, 4′-Bis(2-hydroxyethoxy)benzophenone, 4, 4′-Bis(3-hydroxypropoxy)benzophenone, 4, 4′-Bis(6-hydroxyhexyloxy)benzophenone, 4, 4′-Bis(11-hydroxyundecyloxy)benzophenone] and two aliphatic-aromatic diols with sulfur linkages [4, 4′-Bis[(2-hydroxyethyl)thio]benzophenone, 4, 4′-Bis[(3-hydroxypropyl)thio]benzophenone] have been characterized by X-ray powder diffraction. These diols can be used for synthesis of thermoplastic nonsegmented polyurethanes. Experimental 2θpeaks positions, relative peak intensities, values ofd, and Miller indices as well as unit-cell parameters are presented.
Effect of partial substitution of Cr or Mn for Ga or Fe on crystal-structure and microstructures of GaFeO3
Authors: Heiba Z. K. , Abo-Shama Ali , Bakr M. , El-Sayed Karimat
Published: August 2007

Gallium iron oxide
GaFeO3 and the substituted
GaFeO3 with Cr and Mn, i.e., Ga(Fe0.95Me0.05)O3, and
(Ga0.95Me0.05)FeO3; Me=Cr and Mn, have been synthesized and investigated by X-ray powder diffraction. The refined structural parameters of the considered samples using the Rietveld technique showed a considerable distortion in the polyhedron around different cations, which may have an effect on the piezoelectricity of the studied samples. There are also changes in the interatomic distances between different cations, which may have a direct influence on the ferromagnetic properties of the samples. Crystallite size and microstrain are anisotropic and the largest along the b axis, which may be responsible for the piezoelectricity. The correlations between all these changeable parameters will be discussed.
Crystal structure of magnesium chromium vanadate Mg2CrV3O11, a member of the A2BV3O11 vanadate family
Authors: Worsztynowicz A. , Kaczmarek S. M. , Paszkowicz W. , Minikayev R.
Published: August 2007

The crystal structure of recently discovered chromium (III) dimagnesium trivanadate (V) Mg2CrV3O11 was refined using the Rietveld method. The crystal system of Mg2CrV3O11 is triclinic with space group P1− (Mg1.7Zn0.3GaV3O11 type) and lattice parameters a=6.4057(1) Å, b=6.8111(1) Å, c=10.0640(2) Å, α=97.523(1)°, β=103.351(1)°, γ=101.750(1)°, and Z=2. The characteristic feature of compounds in the A2BV3O11 (A=Mg, Zn and B=Ga, Fe, Cr) family is a strong tendency to share the octahedral M(1) and M(2) sites by both divalent A and trivalent B atoms, and the bipyramidal M(3) sites occupied by divalent A ions. In the present refinement, the only constraint assuming full occupancy of the M(1), M(2), and M(3) sites leads to the following Cr/(Cr+Mg) ratios: 0.70(2) at M(1), 0.24(2) at M(2), and 0.03(2) at M(3). These occupancies are discussed and compared to those of isotypic compounds. The values of interatomic distances are found to be comparable with those reported by R. D. Shannon in 1976. Electron paramagnetic resonance has been also analyzed. Two absorption lines with g≈2.0 (type I) and g≈1.98 (type II) have been recorded in the EPR spectra, and attributed to V4+ ions and Cr3+–Cr3+ ion pairs, respectively. The exchange constant J between Cr3+ ions has been calculated.
Chemical reasonableness in Rietveld analysis: Inorganics
Authors: Kaduk James A.
Published: August 2007

Besides statistical and graphical measures, many structural features can be used to assess the quality of a Rietveld refinement. These include the metric symmetry of the lattice (which can assist in determining the true symmetry and in identifying isostructural compounds), bond distances and angles (which should fall within normal ranges), displacement coefficients, refined stoichiometry, the absolute values of the standard uncertainties of the fractional coordinates, the hydrogen bonding pattern, the presence of approximate symmetry, the presence of unindexed peaks in the pattern, and whether the refinement converges at all. Chemical knowledge can be built into a Rietveld refinement though the use of restraints and rigid bodies. A knowledge of chemical reasonableness proved important in refining the correct structures of [Fe(H2O)6](BF4)2, (Ba1.5Sr0.5)TiO4, and (Ba1.25Sr0.75)TiO4.
Synthesis and crystal-structure determination of fibrillar methylammonium trimolybdate hydrate
Authors: Włodarczyk-Gajda B. , Rafalska-Łasocha A. , Łasocha W.
Published: August 2007

A novel synthesis method of fibrillar trimolybdates with the use of
Ag2Mo3O10∙2H2O as a precursor has been used successfully to synthesize methylammonium trimolybdate, (CH3NH3)2Mo3O10∙H2O. The crystal structure of this compound was determined by X-ray powder diffraction method and refined by the Rietveld method. The compound is orthorhombic, space group Pnma (62), with a=11.241(3), b=7.585(1), and c=15.516(4) Å. The redetermined crystal structure of the precursor and the structure of the title compound are compared and discussed.
Epidemiology and Risk Factors in Urolithiasis
Authors: Bartoletti R. , Cai T. , Mondaini N. , Melone F. , Travaglini F. , Carini M. , Rizzo M.
Published: August 2007

Stone formation in the urinary tract affects about 5–10% of the population in industrialized countries, although it is very rare in other countries such as Greenland or Japan. The high incidence and recurrence rate contribute to making the urolithiasis a serious social problem. Nowadays, urolithiasis must be considered a ‘disease in evolution’ for several reasons, such as epidemiological changes, evolution of the methods used for diagnosis, and the treatment and prophylaxis of the population considered ‘at risk’ of stone disease. Some features of stone disease have changed over the last few years due to many social, economical and cultural factors that are described here. The increased prevalence of small urinary calculi has brought about a change in clinical symptoms, with frequent episodes of renal-ureteral colic, persistent pain and hydronephrosis. Similarly, the presence of residual fragments after extracorporeal shock wave lithotripsy has induced a radical change in the management of small calculi through the use of mini-invasive surgical techniques.
Lithiasis and Risk Factors
Authors: Ferrari P. , Piazza R. , Ghidini N. , Bisi M. , Galizia G. , Ferrari G.
Published: August 2007

Nephrolithiasis is a worldwide disease with high clinical and economic costs. The increasing incidence in industrialized countries seems to be related to several risk factors, which are partly inherited and partly acquired. Although risk factors in urolithiasis are still under discussion, their identification would provide a notable gain for the patient in terms of stone episodes, and for the health service in terms of costs. This article presents an easy classification of risk factors based on clinical background.
Laboratory Assessment
Authors: Prezioso Domenico , Di Martino Mario , Galasso Raffaele , Iapicca Gennaro
Published: August 2007

Nephrolithiasis has a multifactorial origin, and several disorders may coexist in the same patient. We made a basic and a specific laboratory evaluation. The complete metabolic evaluation consisted of a serum chemistry panel: blood sugar level, complete hemogram, serum electrolytes, GOT, GPT, calcium, phosphate, uric acid, and creatinine levels and RIA dosage of PTH, vitamin D3, cAMP, FT4, FT3 and TSH. The complete analyses of random urinalysis and culture are: (1) dip-stick test: pH, leukocytes/bacteria and Brand’s test, and (2) 24-hour urine collection: calcium, magnesium, oxalate, phosphate, citrate, urea, urate, sodium, creatinine, choride, potassium. It is possible with these tests to identify secondary causes of nephrolithiasis and uncover coexisting problems that may have an impact on patient management. The future for diagnosis, prevention and therapy will be the identification of genetic alterations and related specific dosage.
Stones and Urinary Tract Infections
Authors: Miano Roberto , Germani Stefano , Vespasiani Giuseppe
Published: August 2007

The term infection stones refers to calculi that occur following urinary tract infections (UTIs) caused by urease-producing gram-negative organisms. They consist of magnesium ammonium phosphate, carbonate apatite and monoammonium urate. Alkaline urine is most favorable to their formation. Urinary tract obstruction, neurogenic bladder, voiding dysfunction, temporary or indwelling urinary catheters, distal renal tubular acidosis and medullary sponge kidney are considered the main risk factors for developing infection stones. Urinalysis and urine culture are essential for diagnosis. A typical finding on imaging is a moderately radiopaque, staghorn or branched stone. Curative treatment is possible only by eliminating all of the stone fragments and by eradicating UTI. A variety of operative and pharmaceutical approaches is available. Metaphylactic treatment is mandatory to prevent recurrences. The relationship between urinary stones and UTIs is well known and shows two different clinical pictures: (1) stones that develop following UTIs (infection stones) which play a key role in stone pathogenesis, and (2) stones complicated by UTIs (stones with infection) which are metabolic stones that passively trap bacteria from coexistent UTIs and may consist of calcium or non-calcium. This article presents an overview of infection stones, analyzing the epidemiology, composition, pathogenesis, diagnosis, treatment and prevention of this type of calculi.
Prevention of Stone Disease
Authors: Porena M. , Guiggi P. , Micheli C.
Published: August 2007

In recent years stone disease has become more widespread in developed countries. At present the prevalence is 5.2 and 15% of men and 6% of women are affected. The increase is linked to changes in lifestyle, eating patterns and obesity which has become very common. The ‘metabolic syndrome’ includes all the diseases, e.g. hypertension, lipid imbalances, type 2 diabetes mellitus, gout and cardiovascular disease, which are concomitant in the majority of stone formers. Dietary patterns, besides leading to stone formation, also determine stone chemistry. With a diet that is rich in oxalates, calcium oxalate will constitute 75% of stones, struvite 10–20%, uric acid 5–6% and cystine 1%. As approximately 50% of patients with stones suffer recurrences, metabolic and/or pharmacological prophylaxis is recommended.
Metaphylaxis of Nephrolithiasis
Authors: Jacobellis Ulrico
Published: August 2007

The introduction of extracorporeal shockwave lithotripsy (ESWL), with its noninvasive removal of stones and considerable reduction in the morbidity of stone disease, has revolutionized the therapy of urolithiasis. Unfortunately the propensity for stone recurrence is not altered by removal of stones with ESWL and stone recurrence is still about 50%. Progress in medical treatment has shown how different therapies can prevent the stone recurrence, even though it is often difficult to predict which patient will go on to become a recurrent stone former. With the right evaluation, however, the cause of calculi formation can be treated in 97% of the patients. Primary prevention of urolithiasis includes general prophylaxis in a no-risk population that has never been affected by urinary tract stones, is without familial predisposition, metabolic or genetic alterations, or urinary tract abnormalities or infections and who live in a geographical area that is at risk. Secondary prevention or metaphylaxis of stone disease is aimed at the population at risk, that is patients already affected by the stone disease, with familial predisposition, with urinary tract alterations, with metabolic or genetic alterations (gout, bone or bowel diseases) and urinary infection.
The Impact of Statin Treatment on Presentation Mode and Early Outcomes in Acute Coronary Syndromes
Authors: Cuculi F. , Radovanovic D. , Eberli F.R. , Stauffer J.C. , Bertel O. , Erne P.
Published: August 2007

Objectives: The role of statin use in the treatment of acute coronary syndromes (ACS) is not clear. The aim of our study was to evaluate the role of statins in ACS. Methods: Using data from the Acute Myocardial Infarction in Switzerland (AMIS Plus) Project, we compared the effects of chronic statin use, statin therapy after admission and no statin therapy on presentation mode and outcomes in ACS. Results: Available data from the period 2001–2006 including 11,603 patients were analyzed. Major cardiac event rates and in-hospital mortality were more common in statin-naive patients compared to patients who received statins. Conclusions: Our results support the importance of statin treatment in ACS. Chronic statin therapy seems to alter the initial presentation of ACS but it is questionable whether it provides an additional effect on early outcomes compared to the establishment of statin therapy after admission in statin-naive patients.
Pre-Discharge Exercise Test for Evaluation of Patients with Complete or Incomplete Revascularization following Primary Percutaneous Coronary Intervention: A DANAMI-2 Sub-Study
Authors: Valeur Nana , Clemmensen Peter , Grande Peer , Wachtell Kristian , Saunamäki Kari
Published: August 2007

Objectives: It is unclear whether the completeness of revascularization impacts on the prognostic value of an exercise test after primary percutaneous coronary intervention (PCI). Methods: The DANAMI-2 trial included patients with ST elevation acute myocardial infarction randomized to primary PCI or fibrinolysis. Of the 790 patients randomized to primary PCI, 572 performed an exercise test. Prospectively, 310 patients were classified as having complete and 216 as having incomplete revascularization. Primary endpoint was a composite of reinfarction and/or death. Results: Patients with incomplete revascularization had lower exercise capacity [6.5 (95% CI: 1.9–12.8) vs. 7.0 (95% CI: 2.1–14.0) METs, p = 0.004] and more frequently ST depression [43 (20%) vs. 39 (13%), p = 0.02] compared to patients with complete revascularization. ST depression was not predictive of outcome in either groups, while multivariable analyses showed that exercise capacity was predictive of reinfarction and/or death in patients with incomplete revascularization [hazard ratio = 0.71 (95% CI: 0.54–0.93), p = 0.012] or of death alone [hazard ratio = 0.56 (95% CI: 0.41–0.77), p = 0.0003], which was not found in patients with complete revascularization. Conclusions: Exercise capacity was prognostic of reinfarction and/or death in patients with incomplete revascularization, but not in completely revascularized patients. ST segment depression alone did not predict residual coronary stenosis or dismal prognosis.
Successful Pregnancy in a Patient with Severe 11-Beta-Hydroxylase Deficiency and Novel Mutations in CYP11B1 Gene
Authors: Simm Peter J. , Zacharin Margaret R.
Published: August 2007

11β-Hydroxylase deficiency is a rare form of congenital adrenal hyperplasia, resulting in virilization, glucocorticoid deficiency and hypertension. There have been no previous reports in the literature of a successful pregnancy in a severely affected female. We report the first successful pregnancy resulting in a live birth for a female with 11β-hydroxylase deficiency and outline management issues from preconception to successful birth. We also report 2 novel mutations in the CYP11B1 gene leading to 11β-hydroxylase deficiency.
Defective Platelet Aggregation in Myelodysplastic Syndromes
Authors: Girtovitis Fotios I. , Ntaios George , Papadopoulos Athanasios , Ioannidis Georgios , Makris Pantelis E.
Published: August 2007

Introduction: Hemorrhagic tendency in patients with myelodysplastic syndrome (MDS) is mainly attributed to thrombocytopenia. However, platelet function in these patients has not been thoroughly investigated. Aim: The aim of our study is to evaluate platelet function in patients with primary MDS. Methods: Platelet function was studied with aggregometry in response to ristocetin, collagen, ADP and adrenaline in 26 MDS patients and 15 healthy individuals. Results: Aggregation was defective in 21 patients (80.7%). Adrenaline was the agonist with the most profound defect (45.9%), followed by ADP (58.7%), whereas aggregation with ristocetin and collagen was at the borderline. Abnormal aggregation to all four agonists was detected in 6 patients (23%). On the contrary, aggregation results were normal in only 5 patients (19.2%). RAEB-t (refractory anemia with excess blasts in transformation) patients were most seriously affected. Conclusions: MDS patients have impaired platelet aggregation in response to one or more stimulants. Platelet aggregation was not statistically different between MDS patients at early stages of the disease (<12 months) and those at later stages (>12 months). Defective platelet aggregation is strongly related to MDS of worse prognosis. None of our patients was detected to have hyperfunctional platelets, defined as platelets aggregating spontaneously. Functional defects in MDS do not elicit hemorrhagic tendency.
Inhibition of Phosphodiesterase Type 4 Decreases Stress-Induced Defecation in Rats and Mice
Authors: Barone Frank C. , Barton Matthew E. , White Ray F. , Legos Jeffrey J. , Kikkawa Hideo , Shimamura Midori , Kuratani Kazuyoshi , Kinoshita Mine
Published: August 2007

Background/Aims: Phosphodiesterase type 4 (PDE4) has been previously shown to regulate colonic contractile activity in vitro. In this study, the effects of PDE4 inhibition were assessed in a model of stress-induced defecation previously demonstrated to be due to increased colonic transit/evacuation. Methods: Rats were individually placed in a mild restraint cage and placed into a 12°C environment (cold-restraint stress) for 60 min. Mice received restraint (only) stress at room temperature for 30 min. Loperamide (positive control compound) or two different PDE4 inhibitors (rolipram and roflumilast) were administered orally at several doses to the rodents 1 h before stress began. Vehicle alone was administered for comparison. The number of fecal pellets expelled during stress (fecal pellet output), total fecal pellet wet weight and total fecal water content were measured. Results: Loperamide produced a dose-related decrease (ID50s in mg/kg) in fecal pellet output (rat = 7.4, mouse = 0.7) and significantly decreased fecal wet weight (72.9%) and decreased fecal percent water content (9.4%). The two PDE4 inhibitors produced a similar dose-related inhibition of fecal pellet output. Rolipram exhibited ID50s in rat and mouse of 14.1 and 27.1, respectively. Rolipram significantly decreased fecal wet weight (58.8%) but increased fecal percent water content (15.0%). For roflumilast, ID50s were 24.2 mg/kg and 12.4 in the rat and mouse, respectively. Although roflumilast also significantly (p < 0.05) decreased fecal wet weight (47.2%), it did not significantly increase fecal percent water content. Conclusions: These data indicate that PDE4 inhibition is effective in reducing rodent stress-induced defecation, provides the first functional data on a potential role for PDE4 activity in the colonic evacuation response to stress, and indicates the potential utility of PDE4 inhibitors in functional bowel disease such as irritable bowel syndrome requires further evaluation.