bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural derivation and crystal chemistry of apatites
Authors: White T. J. , ZhiLi Dong
Published: January 2003

The crystal structures of the [A(1)2][A(2)3](BO4)3
X apatites and the related compounds [A(1)2][A(2)3](BO5)3
X and [A(1)2][A(2)3](BO3)3
X are collated and reviewed. The structural aristotype for this family is Mn5Si3 (D88 type, P63/mcm symmetry), whose cation array approximates that of all derivatives and from which related structures arise through the systematic insertion of anions into tetrahedral, triangular or linear interstices. The construction of a hierarchy of space-groups leads to three apatite families whose high-symmetry members are P63/m, Cmcm and P63
cm. Alternatively, systematic crystallographic changes in apatite solid-solution series may be practically described as deviations from regular anion nets, with particular focus on the O(1)—A(1)—O(2) twist angle φ projected on (001) of the A(1)O6 metaprism. For apatites that contain the same A cation, it is shown that φ decreases linearly as a function of increasing average ionic radius of the formula unit. Large deviations from this simple relationship may indicate departures from P63/m symmetry or cation ordering. The inclusion of A(1)O6 metaprisms in structure drawings is useful for comparing apatites and condensed-apatites such as Sr5(BO3)3Br. The most common symmetry for the 74 chemically distinct [A(1)2][A(2)3](BO4)3
X apatites that were surveyed was P63/m (57%), with progressively more complex chemistries adopting P63 (21%), P\bar 3 (9%), P\bar 6 (4.3%), P21/m (4.3%) and P21 (4.3%). In chemically complex apatites, charge balance is usually maintained through charge-coupled cation substitutions, or through appropriate mixing of monovalent and divalent X anions or X-site vacancies. More rarely, charge compensation is achieved through insertion/removal of oxygen to produce BO5 square pyramidal units (as in ReO5) or BO3 triangular coordination (as in AsO3). Polysomatism arises through the ordered filling of [001] BO4 tetrahedral strings to generate the apatite–nasonite family of structures.
Salts of maleic and fumaric acids with organic polyamines: comparison of isomeric acids as building blocks in supramolecular chemistry
Authors: Bowes Katharine F. , Ferguson George , Lough Alan J. , Glidewell Christopher
Published: January 2003

Maleic acid and fumaric acid both readily form adducts with organic diamines: maleic acid usually forms 2:1 adducts with bases, while fumaric acid usually forms 1:1 adducts, and the supramolecular stuctures within the two series are not simply related. The 1:2 adducts formed by 1,2-bis(4-pyridyl)ethane and by 4,4′-bipyridyl, respectively, with maleic acid, compounds (1) and (2), are salts [{(diamine)H2}2+]·[(C4H3O4)−]2 in which the cations lie across a centre of inversion and a twofold rotation axis, respectively. The ions are linked by N—H...O hydrogen bonds into three-ion aggregates, which are further linked by C—H...O hydrogen bonds into two- and three-dimensional arrays, respectively. In the fumarate salts formed by 2,2′-dipyridylamine (1:1) and 1,4-diazabicyclo[2.2.2]octane (1:2), compounds (3) and (4), the ionic components are linked into molecular ladders. The 1:1 adduct of 4,4′-bipyridyl and fumaric acid, compound (5), contains two neutral components, both of which lie across centres of inversion; these components are linked into chains by a single O—H...N hydrogen bond and thence into sheets by C—H...O hydrogen bonds. The corresponding adduct formed by 1,4-diazabicyclo[2.2.2]octane, compound (6), is a salt that again contains chains linked into sheets by C—H...O hydrogen bonds. In the 1:1 adducts, compounds (7), (8) and (10), that are formed between 1,2-bis(4-pyridyl)ethane, 4,4′-trimethylenedipyridine and hexamethylenetetramine, respectively, with fumaric acid, and in the 1:2 adduct, compound (9), of 2,2′-dipyridylamine and maleic acid, the chains that are generated by the hard hydrogen bonds are linked by C—H...O hydrogen bonds to form, in each case, a single three-dimensional framework. In the 1:1 adduct, compound (11), of 2,2′-bipyridyl and fumaric acid the hydrogen bonds generate two interwoven three-dimensional frameworks.
The incommensurate structure of K3In(PO4)2
Authors: Arakcheeva Alla , Chapuis Gervais , Petříček Vaclav , Dušek Michal , Schönleber Andreas
Published: January 2003

The incommensurately modulated structure of K3In(PO4)2 has been solved and refined. The origin of the modulation relates to the ordering of K cations within the hexagonal close packing of the PO4 anions. The driving forces for the modulation of the other cations are In—P and K—P interactions. The modulation of O atoms of rigid PO4 units follows the cations in order to stabilize the InO6 octahedron. It is shown that the previously published three-dimensional structure refined from powder diffraction data obtained at room temperature is an average structure. Therefore the incommensurately modulated phase of K3In(PO4)2 is the only one that has been unequivocally identified at room temperature. The origin of the modulation is discussed in comparison with the structures of Na3InP2, α- and β-Na3In(PO4)2, Na3Fe(PO4)2 and Rb3In(PO4)2.
The modulated structure of Ba0.39Sr0.61Nb2O6. I. Harmonic solution
Authors: Woike Theo , Petříček Václav , Dušek Michal , Hansen Niels K. , Fertey Pierre , Lecomte Claude , Arakcheeva Alla , Chapuis Gervais , Imlau Mirco , Pankrath Rainer
Published: January 2003

The structure of a crystal of Sr0.61Ba0.39Nb2O6 has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P4bm(\,pp1/2,p - p1/2), unit-cell parameters a = 12.4566 (9), c = 7.8698 (6) Å, modulation vectors q
1 = 0.3075 (6) (a* + b*), q
2 = 0.3075 (6) (a* − b*). The data collection was performed on a KUMA-CCD diffractometer and allowed the integration of weak first-order satellite reflections. The structure was refined from 2569 reflections to a final value of R = 0.0479. The modulation affects mainly the positions of the O atoms, which are displaced by as much as 0.5 Å, and the site 4c that is occupied by Sr and Ba atoms. Only a simplified model, in which this atomic position is occupied by an effective atom Sr/Ba, could be refined from the data set. The modulation of displacement parameters has been used to account for the modulated distribution of Sr and Ba. The whole refinement uses only first-order modulation waves, but there are strong indications that for a complete solution the use of higher-order satellites and a more complicated model is necessary.
Influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals
Authors: Wunschel Markus , Dinnebier Robert E. , Carlson Stefan , Bernatowicz Piotr , van Smaalen Sander
Published: January 2003

The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH_3)_3]_1[Si(CH_3)_3]_3 (Bu1), and di-tert-butyl-bis(trimethylsilyl)silane, Si[C(CH_3)_3]_2[Si(CH_3)_3]_2 (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm\bar{3}m symmetry (Z = 4) with a = 13.2645 (2) Å, V = 2333.87 (4) Å3 for Bu1 and a = 12.9673 (1) Å, V = 2180.46 (3) Å3 for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at temperatures T_c = 230 (5) K (Bu1) and T_c = 250 (5) K (Bu2) into monoclinic structures with space group P2_1/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) Å, \gamma = 109.477 (4)°, V = 4172.7 (8) Å3 and Z = 8 for Bu1and a = 17.0089 (9), b = 15.3159 (8), c = 15.9325 (8) Å, \gamma = 110.343 (3)°, V = 3891.7 (5) Å3 and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13–0.28 GPa for Bu1 and 0.20–0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependencies of the lattice parameters were observed. These anomalies are explained as additional disorder–order phase transitions.
Hydrogen bonding in enantiomeric versus racemic mono-carboxylic acids; a case study of 2-phenoxypropionic acid
Authors: Sørensen Henning Osholm , Larsen Sine
Published: January 2003

The structural and thermodynamic backgrounds for the crystallization behaviour of racemates have been investigated using 2-phenoxypropionic acid (PPA) as an example. The racemate of PPA behaves normally and forms a racemic compound that has a higher melting point and is denser than the enantiomer. Low-temperature crystal structures of the pure enantiomer, the enantiomer cocrystallized with n-alkanes and the racemic acid showed that hydrogen-bonded dimers that form over crystallographic symmetry elements exist in all but the structure of the pure enantiomer. A database search for optically pure chiral mono-carboxylic acids revealed that the hydrogen-bonded cyclic dimer is the most prevalent hydrogen-bond motif in chiral mono-carboxylic acids. The conformation of PPA depends on the hydrogen-bond motif; the antiplanar conformation relative to the ether group is associated with a catemer hydrogen-bonding motif, whereas the more abundant synplanar conformation is found in crystals that contain cyclic dimers. Other intermolecular interactions that involve the substituent of the carboxylic group were identified in the crystals that contain the cyclic dimer. This result shows how important the nature of the substituent is for the crystal packing. The differences in crystal packing have been related to differences in melting enthalpy and entropy between the racemic and enantiomeric acids. In a comparison with the equivalent 2-(4-chlorophenoxy)-propionic acids, the differences between the crystal structures of the chloro and the unsubstituted acid have been identified and related to thermodynamic data.
Urotropin azelate: a rather unwilling co-crystal
Authors: Bonin Michel , Welberry T. Richard , Hostettler Marc , Gardon Manuel , Birkedal Henrik , Chapuis Gervais , Möckli Pedro , Ogle Craig A. , Schenk Kurt J.
Published: January 2003

Urotropin (U) and azelaic acid (AA) form 1:1 co-crystals (UA) that give rise to a rather complex diffraction pattern, the main features of which are diffuse rods and bands in addition to the Bragg reflections. UA is characterized by solvent inclusions, parasite phases, and high vacancy and dislocation densities. These defects compounded with the pronounced tendency of U to escape from the crystal edifice lead to at least seven exotic phase transitions (many of which barely manifest themselves in a differential scanning calorimetry trace). These involve different incommensurate phases and a peritectoid reaction in the recrystallization regime (T_{h}\, \gt \,0.6). The system may be understood as an OD (order–disorder) structure based on a layer with layer group P(c)c2 and cell a_{o} ≃ 4.7, b ≃ 26.1 and c ≃ 14.4 Å. At 338 K the layer stacking is random, but with decreasing temperature the build-up of an orthorhombic MDO (maximal degree of order) structure with cell a_1 = 2a_{o}, b_1 = b, c_1 = c and space group Pcc2 is begun (at ∼301 K). The superposition structure of the OD system at T = 286 (1) K with space group Bmmb and cell \widehat{\bf a} = 2{\bf a}_{o}, \widehat{\bf b} = {\bf b} and {\widehat{\bf c}} = {\bf c}/2 owes its cohesion to van der Waals interactions between the AA chains and to three types of hydrogen bonds of varied strength between U—U and U—AA. Before reaching completion, this MDO structure is transformed, at 282 K, into a monoclinic one with cell a_{m} = −a_{o} + {}c/4, b_{m} = b, c_{m} = −2({\bf a}_{o} + {c}/2), space group P{{2_1}/{c}}, spontaneous deformation ∼2°, and ferroelastic domains. This transformation is achieved in two steps: first a furtive triggering transition, which is not yet fully understood, and second an improper ferroelastic transition. At ∼233 K, the system reaches its ground state (cell {\bf a}_{M} = {\bf a}_{m}, {\bf b}_{M} = {\bf b}, {\bf c}_{M} = {\bf c}_{m} and space group P{{2_1}/{c}}) via an irreversible transition. The phase transitions below 338 K are described by a model based on the interaction of two thermally activated slip systems. The OD structure is described in terms of a three-dimensional Monte Carlo model that involves first- and second-neighbour interactions along the a axis and first-neighbour interactions along the b and c axes. This model includes random shifts of the chains along their axes and satisfactorily accounts for most features that are seen in the observed diffraction pattern.
(1R,3S)-Camphoric acid as a building block in supramolecular chemistry: adducts with organic polyamines
Authors: Zakaria Choudhury M. , Ferguson George , Lough Alan J. , Glidewell Christopher
Published: January 2003

(1R,3S)-Camphoric acid [(1R,3S)-1,2,2,-trimethylcyclopentane-1,3-dicarboxylic acid, C10H16O4] forms adducts with a range of amines in which the acid component may be the neutral molecule, the mono-anion (C10H15O4)− or the di-anion (C10H14O4)2−. The structures generated by the hard hydrogen bonds take the form of chains in the 1:1 adducts (II) and (III) formed with 4,4′-bipyridyl and 1,2-bis(4-pyridyl)ethane. There are single sheets in the hydrated 1:1 adduct (IV) formed with 1,4-diazabicyclo[2.2.2]octane, and pairwise-interwoven sheets in the 2:1 adduct (V) formed with hexamethylenetetramine. Three-dimensional frameworks are present in the salt-like 1:1 adduct (VI) formed with piperazine and in the hydrated 3:1 adduct (VII) formed with N,N′-dimethylpiperazine. This latter adduct contains both neutral C10H16O4 and anionic (C10H15O4)− units. In (II), (III) and (IV), the chain and sheet substructures are linked by C—H...O hydrogen bonds to form three-dimensional frameworks. The monoclinic polymorph of camphoric acid itself (I) has been reinvestigated.
An X-ray diffraction study of partially ordered electron density in clathrates of Dianin's compound that include simple carboxylic acids
Authors: Small Ronald W. H.
Published: January 2003

The nature of the inclusions in ten clathrate complexes of Dianin's compound have been investigated by the use of electron-density difference maps. The guest species are the first eight straight-chain carboxylic acids, formic to octanoic, a branched-chain acid (dimethylacetic acid) and trifluoroacetic acid. The point-group symmetry of the clathrate cavity, \bar 3, is satisfied by partial occupation of symmetry-related sites by two included molecules in the case of formic, acetic and trifluoroacetic acids and by a single molecule in the remainder. Hydrogen-bonding requirements in the case of formic and acetic acids are satisfied by dimer formation; in the trifluoroacetic acid complex the two acid molecules form hydrogen bonds to framework O atoms at either end of the cavity. The adoption of gauche conformations in heptanoic and octanoic acid chains shortens them sufficiently that they fit the cavity with only slight distortion.
22 Space-group changes
Authors: Clemente Dore Augusto , Marzotto Armando
Published: January 2003

This paper reports 22 examples of space-group changes from low to higher symmetry. The revisions involve 15 crystal structures that were originally described in space group P21, six in P\bar 1 and one in P1. The relevance of higher-symmetry elements is discussed in connection with the crystallography, the molecular dimensions and, when possible, the spectroscopic properties.
Single-crystal-to-single-crystal photodimerization of 4-chlorocinnamoyl-O,O'-dimethyldopamine
Authors: Ohba Shigeru , Ito Yoshikatsu
Published: January 2003

[2+2]Photodimerization of the title compound, C19H20ClNO3, has been observed in situ by single-crystal X-ray diffraction. Pairs of monomers related by centers of symmetry have parallel C=C bonds at a C...C distance of 4.155 (17) Å. Irradiation of a single crystal with a mercury lamp achieves 100% conversion to the dimer. Redetermination of the structure during the course of the reaction revealed a linear correlation between the percent conversion to the dimer and the decrease in the cell volume. The displacement parameters for the pure dimer structure are substantially smaller than those for the pure monomer structure. The dimerization reaction is also induced by irradiation with X-rays, the induction being stronger with Cu Kα than with Mo Kα radiation.
Determination of the crystal structure of the π-AlFeMgSi phase using symmetry- and site-sensitive electron microscope techniques
Authors: Foss S. , Olsen A. , Simensen C. J. , Taftø J.
Published: January 2003

The crystal structure of the complex π-AlFeMgSi phase, which was previously thought to have the composition Al8FeMg3Si6, has been investigated. Microprobe analysis revealed that the phase has a different composition, Al9FeMg3Si5. The space group was determined and confirmed to be P\bar 62m with the use of parallel-beam electron diffraction (SAD) and convergent-beam electron diffraction (CBED). Owing to symmetry considerations the elements within the unit cell had to be rearranged. The rearrangement was confirmed using electron channelling. The z parameters of the elements were refined by examining the intensities from high-angle convergent-beam electron diffraction. Finally, the x parameters were adjusted slightly to arrive at acceptable interatomic distances.
Twinning in natural melilite simulating a fivefold superstructure
Authors: Bindi Luca , Rees Leigh H. , Bonazzi Paola
Published: January 2003

Additional reflections seemingly leading to a tetragonal fivefold supercell have been observed in a number of melilites. A careful examination of the collected intensity data reveals that this feature is due to the coexistence of two twin domains related by a (1\bar20) twin plane. Reflections of the first domain (I) with h_{\rm b}^2+k_{\rm b}^2=5n overlap those of the second domain (II) when both the following additional conditions are verified: −h
b + 2k
b = 5n and 2h
b + k
b = 5n. Indices of the superimposed reflections are h
b,I k
b,I l
b,I for the first domain, and h
b,II = \textstyle{3\over5}\,h
b,I + \textstyle{4\over5}\,k
b,I, k
b,II = \textstyle{4\over5}\,h
b,I − \textstyle{3\over5}\,k
b,I, l
b,II = l
b,I for the second domain. The non-crystallographic pseudosymmetry in the melilite structure is discussed.
Electron density study of 2H-chromene-2-thione
Authors: Munshi Parthapratim , Guru Row T. N.
Published: January 2003

Owing to a printers' error in the paper by Munshi & Guru Row [ Acta Cryst. (2002), B58, 1011–1017], Figs. 4(a) and 4(b) on page 1015 were transposed. Revised PDF versions of these pages are available in the online version of this erratum, which is available through Crystallography Journals Online.
Influence of the electro‐magnetic stirring on the boundary layer of a molten steel pool
Authors: Fabbri Massimo , Galante Francesco , Negrini Francesco , Takeuchi Eiichi , Toh Takehiko
Published: January 2003

Electro‐magnetic stirrers, applied to the mold of a continuous caster, induces electromagnetic forces that influence the steel flow pattern modifying the casting parameters. The steel quality has been highly improved by the application of this magneto‐hydro‐dynamic (MHD) technique. Anyway, the complexity of the MHD interaction made difficult the complete comprehension of the factors that contribute to eliminate the defects due to the inclusions in the cast products. The optimization of the MHD techniques is still the object of a large research effort, which utilizes both experimental activity and numerical simulation. In this paper, the numerical simulation of the 2D flow pattern of the molten steel in a mold for billets has been done. The attention is focused on the gradient of the velocity of the molten steel near the wall and on the effects that the gradient change determines on the inclusions, which are present in the metallic pool. Actually the increase of the velocity gradient corresponds to the increase of the forces that can clean the solidifying shell from the inclusions.
Dynamic load impedance matching for induction heater systems
Authors: Sewell H.I. , Stone D.A. , Bingham C.M.
Published: January 2003

It is not normally possible to heat a static steel work‐piece past the Curie temperature without incurring reduced inverter utilisation. Since the inverter cost increases with rated power, reduced utilisation implies an increase in investment costs for a given performance. The paper shows that third‐order resonant work‐head circuits can intrinsically allow better utilisation of the inverter for variable‐load heating operations. A further refinement is then shown to allow control of the load impedance, thereby allowing the utilisation to approach 100 percent over the heating cycles.
Turbulent flow dynamics, heat transfer and mass exchange in the melt of induction furnaces
Authors: Baake E. , Nacke B. , Umbrashko A. , Jakovics A.
Published: January 2003

Experimental investigations of the turbulent flow velocities measured in the melt of experimental induction furnaces show, that beside the intensive local turbulence pulsations, macroscopic low‐frequency oscillations of the recirculated toroidal main flow eddies play an important role in the heat and mass exchange processes. Traditional numerical calculations of the flow and transfer processes, based on wide spread commercial codes using various modifications of the k‐ε turbulence model show that these models do not take into account the low‐frequency oscillations of the melt flow and the calculated temperature and concentration distributions in the melt essentially differs from experimental results. Therefore, the melt flow dynamics in an induction crucible furnace was numerically simulated with help of transient three‐dimensional calculations using the large eddy simulation turbulence model. This leads to a good agreement between calculated and measured periods of low‐frequency oscillations and heat and mass transfer between the toroidal flow eddies.
Computer simulation of induction heating system with series inverter
Authors: Zgraja Jerzy , Bereza Jerzy
Published: January 2003

The paper presents the results of computer simulation of the process of induction heating with series transistor inverter. In the simulation of induction heating system the coupled harmonic electromagnetic and transient thermal fields were combined with the simulated real energy source. As a source, the transistor bridge inverter with series resonant circuit was applied. The source parameters (inductor voltage and frequency) depend on the load parameters obtained by numerical calculations of the coupled fields. As the examples, the induction heating before hardening of stationary cylindrical workpiece and of the moving flat workpiece were considered. The simulation results were compared with these obtained in the simulation at constant inductor voltage and frequency.
Removal of SiC inclusions in molten aluminium using a 12 T static magnetic field
Authors: Colli Fabrizio , Fabbri Massimo , Negrini Francesco , Asai Shigeo , Sassa Kensuke
Published: January 2003

The analysis of particles trajectories in a vertical cylindrical coil shows that the magnetization force acting on paramagnetic particles has predominantly axial component which aims upwards and opposite to the gravitational force. In case of superconducting coil and depending on the value of the particle susceptibility, the axial force component can exceed several times the force of gravity. As a result, a motion of the particles in vertical upward direction appears. This effect was utilized to realize a magnetic separator, the main advantage of which is the high effectivity of separation process. A NbTi SC coil generates the magnetization force with a flux density field up to 12 T. Experiments with SiC inclusions in molten Aluminium have been performed to confirm the feasibility of this segregation concept.
Modelling of induction heating and consequent hardening of long prismatic bodies
Authors: Dolezel I. , Barglik J. , Sajdak C. , Skopek M. , Ulrych B.
Published: January 2003

The paper deals with the problem of induction hardening of long prismatic ferromagnetic bodies. The body is first heated to the austenitizing temperature typically in a cylindrical inductor fed from a source of harmonic current and then merged into a cooling medium. In specific cases, equalisation of temperatures within the body before its cooling may also be required. The mathematical model of the induction heating consists of two non‐linear second order differential equations of the parabolic type describing the distribution of the electromagnetic and non‐stationary temperature fields while the cooling is described by the heat equation and a theoretically empirical algorithm for mapping the process of hardening. The suggested methodology partially takes into account the temperature dependencies of all material parameters. The theoretical analysis is supplemented with an illustrative example and discussion of the results. Computations have been performed by means of professional codes and single‐purpose user programs developed by the authors.
Experimental and numerical investigations of the temperature field and melt flow in the induction furnace with cold crucible
Authors: Baake E. , Nacke B. , Bernier F. , Vogt M. , Mühlbauer A. , Blum M.
Published: January 2003

Comprehensive knowledge of the complicated physical behavior of the induction furnace with cold crucible (IFCC) is required to utilize the advantages of this melting aggregate in melting and casting chemically high‐reactive materials, like titanium‐aluminides (TiAl). Practical experiences show that the overheating temperature of the melt is decisive for the quality of the cast products. Therefore, a systematic analysis of the electromagnetic and in particular, the hydrodynamic and thermal behavior of the IFCC is carried out. The examinations of the influence of the construction elements as well as the process parameters on the temperature field and finally the overheating temperature in the IFCC are performed using specifically developed numerical models. The evaluation of the numerical results is done by experimental investigations, where aluminum serves as a model melt for the experimental determination of the thermal and hydrodynamic field of the melt. The analysis of the influence of construction‐elements on the overheating temperature is focused on the design of the crucible wall and the crucible bottom, on the height‐diameter ratio of the crucible and on the axial inductor position. The inductor current, the operation frequency and the crucible filling level are found to be very important for reaching a high overheating temperature.
Transverse flux induction heating: comparison between numerical models and experimental validation
Authors: Fireteanu V. , Tudorache T. , Geri A. , Veca G.M.
Published: January 2003

This paper presents two numerical methods, which will be able to predict the temperature distribution in the thin moving conducting sheet, which is caused by the eddy‐current losses in transverse flux inductive heating devices (TFIH). The first method is based on a finite element calculation, while the second one is based on a circuit approach. The main aim of this paper is the validation of the circuit model by comparison with the more accurate and sophisticate finite element model. In addition, the results of both numerical models have also been compared with those obtained by experimental measurements.
Optimal shape design of devices and systems for induction‐heating: methodologies and applications
Authors: Di Barba P. , Savini A. , Dughiero F. , Lupi S.
Published: January 2003

The paper reports recent experiences of the authors in the automated optimal design of devices and systems for induction heating. The results presented have been obtained in the frame of a long‐lasting cooperation between Laboratory of Electroheat, University of Padova and Electromagnetic Devices CAD Laboratory, University of Pavia. In particular, two case studies are discussed; in both cases, the shape design of the inductor is carried out in a systematic way, by minimizing user‐defined objective functions depending on design variables and subject to bounds and constraints. When the design problem is characterized by many objectives which are in mutual conflict, the non‐dominated set of solutions is identified.
TFH – transverse flux induction heating of non‐ferrous and precious metal strips
Authors: Dughiero F. , Lupi S. , Mühlbauer A. , Nikanorov A.
Published: January 2003

In the years 1999 and 2000 the Universities of Hannover and Padua and four industrial partners from Italy and Germany have developed a common research project on TFH financed by the EU (Project JOE3‐CT98‐7023). In this paper, the main results obtained are shortly described.
Electromagnetic phenomena in resistance heating of curvilinear cylindrical work pieces
Authors: Lupi S. , Aliferov A.
Published: January 2003

Distribution of alternating current density and internal power sources in the cross‐section of curvilinear hollow work pieces under resistance heating are presented in this paper. The calculation is based on an analytical model. The results of analytical calculations are compared with experimental data. The received expression was investigated in a wide range of geometrical parameters.
Mathematical modelling of the industrial growth of large silicon crystals by CZ and FZ process
Authors: Mühlbauer Alfred , Muiznieks Andris , Ratnieks Gundars , Krauze Armands , Raming Georg , Wetzel Thomas
Published: January 2003

The present paper gives an overview of the complex mathematical modelling of industrial Czochralski (CZ) and floating‐zone (FZ) processes for the growth of large silicon single crystals from melt. Extensive numerical investigations of turbulent Si‐melt flows in large diameter CZ crucibles, global thermal calculations in growth facilities and analysis of the influence of various electromagnetic fields on CZ process are presented. For FZ process, a complex system of coupled 2D and 3D mathematical models is presented to show the possibilities of modelling from the calculation of the molten zone shape till the resistivity distribution in the grown crystal. A special developed program code is presented that is used to calculate the temperature field in the crystal including radiation exchange with reflectors, stress field due to thermal expansion and shape of the dislocated zone in the case of dislocation generation. Besides the macroscopic modelling of crystal growth processes, the crystallisation model on the atomistic level in the mean field approximation is also presented.
Computer simulation for fundamental study and practical solutions to induction heating problems
Authors: Nemkov Valentin , Goldstein Robert
Published: January 2003

This presentation is a continuation of the presentation made at IHS 98. The topics remain the same; however, the content is updated to reflect the improvements in both computer software and hardware and some new studies made by Centre for Induction Technology, Inc. (CIT). Several examples are presented that show the results of computer simulation studies and their verification by means of empirical studies. These examples include 1‐D, 2‐D and 3‐D computer simulation of various induction heating systems. Special attention is paid to 3‐D electromagnetic simulation, including a fundamental study of the end and edge effects for induction heating of slabs and the historical perspective of this case.
Accessibility of Web‐based information resources for people with disabilities (part two): introduction
Authors: Schmetzke Axel
Published: January 2003

The previous special‐theme issue of Library Hi Tech (Vol. 20 No. 2) focused mainly on a variety of specific information resources commonly provided by libraries: online catalogs, electronic indexes and databases, e‐journals and online references works. This issue deals with accessibility issues, as they emerge in the library and education environment, which are not specifically tied to particular vendor‐supplied information products.
Web access and the law: a public policy framework
Authors: Noble Steve
Published: January 2003

This article details the public policy framework that establishes the legal foundation for requiring access to Web‐based information resources for people with disabilities. Particular areas of focus include: the application of the fair use doctrine to an understanding of disability access to digital information; the application of the Americans with Disabilities Act and Section 504 of the Rehabilitation Act to Web‐based services; and the application of Section 508 of the Rehabilitation Act to Federal Web‐based resources and the extent to which Section 508 may be applicable to states through linkage under the Assistive Technology Act.
Web accessibility and the law: recommendations for implementation
Authors: Yu Holly
Published: January 2003

The proliferation of information in electronic format does not guarantee its accessibility. The fact that many Web sites are not accessible to large segments of the disabled community has created a “digital divide”. The accessibility barriers are systemic. In recent years, there has been a growing body of significant laws and standards concerning Web accessibility that impact people with disabilities. Ways of breaking down these barriers to a fuller accessibility implementation do exist, including education to raise awareness of Web accessibility, nationwide policy and guidelines for accessibility, and Web‐based applications and tools to facilitate Web accessibility, to name a few.
Distance learning: the library’s role in ensuring access to everyone
Authors: Burgstahler Sheryl
Published: January 2003

Federal legislation and increasing support for the full inclusion of all students in precollege education have resulted in higher expectations and increased participation of students with disabilities in academic programs that have prepared them for college studies. As a result, greater numbers of people with disabilities are attending postsecondary academic institutions and participating in distance learning offerings. This article focuses on the role that libraries can play in assuring that all distance learning students and instructors have access to the electronic resources they offer. It can be used to help libraries develop policies, guidelines, and procedures for making their electronic resources accessible to people with disabilities.
Access to online learning: the role of the courseware authoring tool developer
Authors: Harrison Laurie
Published: January 2003

Implementation of recommended design strategies can potentially allow any Web‐based learning program to be made accessible to learners who use adaptive technologies. However, one of the greatest barriers to achieving this goal is the lack of authoring tools that support course content developers in adhering to existing accessibility guidelines. In order to ensure universal access, attention must be given to Web pages generated automatically by courseware programs, as well as those uploaded from an external source. Courseware authoring environments could easily include utilities to support developers in making their online resources accessible. This paper will review products recently available on the market using the guidelines published by the World Wide Web Consortium’s Web Accessibility Initiative as a framework for analysis.
An evaluation of accessibility in online learning management systems
Authors: Johnson AnnMarie , Ruppert Sean
Published: January 2003

Millions of computer users in the USA have a disability making it difficult to use the Web. The University of Wisconsin System recently required that all System Web pages meet Priority 1 accessibility guidelines as set by the World Wide Web Consortium’s Web Accessibility Initiative (W3C/WAI). Class materials available in online learning management systems should also be accessible to students with disabilities. Four systems, Blackboard 4 and 5, Prometheus 3, and WebCT 3, were assessed against theW3C/WAI guidelines for a numerical statistic of accessibility. Practical accessibility was tested with Lynx, IBM Homepage Reader, and JAWS. Validation was performed with A‐Prompt and the W3C/WAI checklist.
Virtually accessible: empowering students to advocate for accessibility and support universal design
Authors: Oravec Jo Ann
Published: January 2003

Students’ professional training often focuses on narrow technical considerations that exclude accessibility concerns and universal design perspectives. This can make them ill‐equipped to understand the importance of accessibility approaches let alone become advocates for them. This article explores how students who design Web sites and work with computer end users in support capacities can be introduced to accessibility approaches and empowered to promote them in organizational contexts. The issues involved can also be used as springboards for examination of larger matters concerning universal design perspectives and humanistic approaches to management.
Taking FLITE: how new libraries are visioning their way into the future
Authors: Boone Morell D.
Published: January 2003

The author takes on the assertion posed in recent educational articles that technology is driving down book circulation and contributing to the decline of reading‐center learning. In his interview with Richard Cochran, Dean of the Ferris State University Library for Information, Technology, and Education, the two discuss the importance of incorporating technology to support all types of learning, and using faculty buy‐in to insure that as many media as possible are integrated into the final building design.
Comparing the means of two groups – the t‐test
Authors: Janes Joseph
Published: January 2003

This column continues a series on topics in research methodology, statistics and data analysis techniques for the library and information sciences. It discusses the t‐test for the differences in means between two independent groups.
Copyright in a networked world: permissions services
Authors: Seadle Michael
Published: January 2003

What happens when “fair use”, “fair dealing”, face‐to‐face teaching guidelines and other copyright exceptions do not apply? Only three choices remain: give up plans to use the protected work, make a risk‐assessment about the likelihood of a lawsuit, or seek a permission from the rights holder. This column examines both public and internal library‐based permissions services.
Mechanism of Reduced T-Cell Effector Functions and Class-Switched Antibody Responses to Herpes Simplex Virus Type 2 in the Absence of B7 Costimulation
Authors: Thebeau Lydia G. , Morrison Lynda A.
Published: January 2003

T-cell costimulation molecules B7-1 and B7-2 play an important role in activation of T cells to cytolytic effector function and production of cytokines. Interaction with B7 also causes T cells to upregulate surface molecules, such as CD40L, that effectively stimulate antibody responses in conjunction with cytokines. We have shown that mice lacking both B7-1 and B7-2 (B7KO mice), when infected intravaginally with virulent herpes simplex virus type 2 (HSV-2), developed more severe disease and higher mortality than their wild-type counterparts. We have now investigated the effects of B7 costimulation deficiency on induction of immune responses to HSV-2 infection of the genital tract. Fewer gamma interferon (IFN-γ)-producing T cells were present in the genital lymph nodes of B7KO mice compared to wild-type mice, either acutely after primary infection or in recall responses. Less IFN-γ and especially interleukin-10 were produced by B7KO mice, and cytolytic T-lymphocyte activity was also attenuated. Reduced expression of CD25 on CD4+T cells after infection of B7KO mice was consistent with deficits in T-cell activation to effector functions. Although HSV-specific immunoglobulin M (IgM) titers were comparable for both B7KO mice and wild-type mice, B7KO mice had significant deficits in HSV-specific serum IgG responses, with markedly reduced levels of IgG2a and IgG1. In addition, significantly less IgG was detected in the vaginal secretions of B7KO mice than in those from wild-type mice. CD4+T-cell expression of CD40L was depressed in B7KO mice in vivo and in vitro. Together with reduced cytokine production, these results suggest a mechanism for decreased IgG class switching or production. Thus, in the absence of B7 costimulation, naïve T cells fail to undergo proper activation in response to HSV-2, which limits T-cell cytokine production, cytotoxic T lymphocyte activity, and provision of help for class-switched antibody responses.
Structure and Mechanism of a Coreceptor for Infection by a Pathogenic Feline Retrovirus
Authors: Barnett Anna L. , Wensel David L. , Li Weihua , Fass Deborah , Cunningham James M.
Published: January 2003

Infection of T lymphocytes by the cytopathic retrovirus feline leukemia virus subgroup T (FeLV-T) requires FeLIX, a cellular coreceptor that is encoded by an endogenous provirus and closely resembles the receptor-binding domain (RBD) of feline leukemia virus subgroup B (FeLV-B). We determined the structure of FeLV-B RBD, which has FeLIX activity, to a 2.5-Å resolution by X-ray crystallography. The structure of the receptor-specific subdomain of this glycoprotein differs dramatically from that of Friend murine leukemia virus (Fr-MLV), which binds a different cell surface receptor. Remarkably, we find that Fr-MLV RBD also activates FeLV-T infection of cells expressing the Fr-MLV receptor and that FeLV-B RBD is a competitive inhibitor of infection under these conditions. These studies suggest that FeLV-T infection relies on the following property of mammalian leukemia virus RBDs: the ability to couple interaction with one of a variety of receptors to the activation of a conserved membrane fusion mechanism. A comparison of the FeLV-B and Fr-MLV RBD structures illustrates how receptor-specific regions are linked to conserved elements critical for postbinding events in virus entry.
Leaf photosynthetic characteristics and net primary production of the polar willow (Salix polaris) in a high arctic polar semi-desert, Ny-Ålesund, Svalbard
Authors: Muraoka Hiroyuki , Uchida Masaki , Mishio Masako , Nakatsubo Takayuki , Kanda Hiroshi , Koizumi Hiroshi
Published: February 2003

Photosynthetic characteristics and their leaf-age dependence were examined to estimate ecophysiological effects on net primary production (NPP) of a polar willow (Salix polaris), a dominant dwarf shrub species in a polar semi-desert area of Ny-Ålesund, Svalbard. Leaves of S. polaris emerged just after snowmelt in early July in 2000; flowers were initiated within 1 week, and fruits in late July. Light-saturated rate of photosynthesis and stomatal conductance to water vapor increased rapidly to their maximum values within 1 week after leaf emergence and then decreased gradually. Depending on the leaf age, photosynthetic rates saturated at photosynthetically active photon flux density (PPFD) of 200400 µmol·m2·s1, which is the light level usually available in the natural habitat. Optimum leaf temperature of photosynthesis ranged from 10 to 18°C, while air temperature in the habitat ranged from 8 to 20°C. These light and temperature responses of photosynthesis of S. polaris would be suitable for efficient carbon gain in the natural habitat characterized by highly variable light and temperature conditions. Using the photosynthetic and respiratory characteristics, biomass distribution, and meteorological data, NPP of S. polaris in the current year was estimated to be 26.1 g C·m2. A model simulation of rising temperature conditions predicted a reduction of NPP because of a large increase in respiration. It was suggested that temperature condition and leaf phenological aspects strongly influence the carbon fixation by plants in the high arctic area studied.Key words: arctic semi-desert, climate change, net ecosystem production (NEP), net primary production (NPP), Salix polaris, photosynthesis.
Strength and dilatancy of a silt stabilized by a cement and fly ash mixture
Authors: Lo S R , Wardani S PR
Published: February 2003

The mechanical behaviour of a weakly cemented silt was studied experimentally. The cementing agent was a cement and fly ash slurry, and the samples so formed were slightly cemented. In triaxial testing, both drained and undrained tests on saturated samples were conducted. Special zero effective stress tests were conducted to measure, directly, the contribution of bonding between grains to the enhanced strength and stiffness. The cemented soils were initially less dilatant than their respective parent soils but eventually became more dilatant than the parent soils. The shear strength data followed a curved failure surface that merged back, at high stress, into that of the parent soil. This feature can be captured by a failure function that models the contribution of cementing agent to strength as two parts, true bonding and increase in dilatancy rate at failure. Both parts degrade with an increase in confining stress, but at different rates.Key words: bonding, cemented soil, dilatancy, strength, triaxial testing.
A crack-induced stress approach to describe the tensile strength of transversely isotropic rocks
Authors: Li Li , Aubertin Michel
Published: February 2003

Rocks are generally more or less anisotropic, depending on their structure at the scale of interest. In engineering applications, the magnitude of such anisotropy must often be determined for compressive as well as tensile loading conditions. In this paper, the authors present the results of an investigation on tensile failure of transversely isotropic rocks, based on Inglis' analytical solution for the stress at the boundary of an elliptical flaw. The strength of transversely isotropic rocks is assumed to be controlled by the maximum tensile local stress along the crack boundary. Equations are developed and compared with tensile test data taken from the literature. The results show that the proposed formulations represent well the direct and indirect tensile strength of anisotropic rocks as a function of bedding plane orientation. It is also shown that the proposed physical model correlates well with the results obtained from more empirical formulations.Key words: rock mechanics, anisotropy, transverse isotropy, tensile strength, Brazilian test, crack.
Geotechnical properties of transparent silica
Authors: Sadek Samer , Iskander Magued G , Liu Jinyuan
Published: February 2003

This paper discusses the geotechnical properties of two families of transparent silica, which can be used to model soil structure interaction and flow problems in transparent soil models. The fundamental premise of this research is that these materials can be used in model tests to study three-dimensional deformation and flow problems, using nonintrusive optical visualization techniques. Triaxial, direct shear, consolidation, and permeability tests conducted in this study indicate that transparent silica gels and amorphous silica have macroscopic geotechnical properties consistent with those of sands and clays, respectively. The materials used in this research have the same refractive index, which permits combining both families in a stratified transparent soil model. The transparent soils described in this paper represent the only system of transparent materials capable of resembling soils that have a wide range of grain sizes including sand and clay using the same pore fluid.Key words : imaging, optical, silica gel, amorphous silica, clay, sand, modeling.