bluuebunny/crossref_metadata_2025 huggingface dataset:
C and Si codoping method for p-type AlN
Authors: Wu Honglei , Zheng Ruisheng , Liu Wen , Meng Shu , Huang Junyi
Published: September 2010

Aluminum Nitride (AlN), the largest direct band gap material (6.2 eV) in the III-nitride semiconductors, is emerging as an important semiconductor due to its promising applications in the development of solid-state ultraviolet light sources in the form of light-emitting diodes and laser diodes. However, the applications have been limited by absence of p-type AlN. In view of the extremely low ∼1010 cm−3 hole concentration in p-type AlN reported up to date, we proposes a method of C:Si codoping in AlN. We have performed ab initio density functional pseudopotential calculations to investigate the energies of separated C acceptor binding to Cn–Si (n=0, 1, 2, and 3, respectively) complexes in wurtzite AlN. The results show that the Cn+1–Si complexes are favorable and stable. In N-rich growth condition, the formation level of C2–Si complex is −0.24 eV, suggesting high doping concentration can be formed. The calculated activation energy for C2–Si is only 0.19 eV, which is 0.28 eV lower than that for a single C acceptor. The results suggest the codoping of C:Si is an effective p-type doping method in AlN.
Disentangling fluxes of energy and matter in plasma-surface interactions: Effect of process parameters
Authors: Wolter M. , Levchenko I. , Kersten H. , Kumar S. , Ostrikov K.
Published: September 2010

The possibility to discriminate between the relative importance of the fluxes of energy and matter in plasma-surface interaction is demonstrated by the energy flux measurements in low-temperature plasmas ignited by the radio frequency discharge (power and pressure ranges 50–250 W and 8–11.5 Pa) in Ar, Ar+H2, and Ar+H2+CH4 gas mixtures typically used in nanoscale synthesis and processing of silicon- and carbon-based nanostructures. It is shown that by varying the gas composition and pressure, the discharge power, and the surface bias one can effectively control the surface temperature and the matter supply rates. The experimental findings are explained in terms of the plasma-specific reactions in the plasma bulk and on the surface.
Communication: Are hydrodynamic models suited for describing the reorientational dynamics of ions in ionic liquids? A case study of methylimidazolium tetra(hexafluoroisopropoxy)aluminates
Authors: Huang Mian-Mian , Bulut Safak , Krossing Ingo , Weingärtner Hermann
Published: September 2010

We report on dielectric relaxation spectra of six homologous ionic liquids (ILs) with tetra(hexafluoroisopropoxy)aluminate ([Al(hfip)4]−) as a common anion. The dominating mode on the time scale of several 100 ps mainly results from cation reorientation. Because the viscosities are low and cation modification does not substantially change the viscosity, these ILs are interesting candidates for testing hydrodynamic models of rotational dynamics. The calculated hydrodynamic volumes are extraordinarily low, and roughly agree with values calculated from literature data for ILs with the same cations, but different anions. Comparison with magnetic relaxation data shows that the peculiarities are founded in the rotational dynamics and are not special to dielectric relaxation. Collectively, the observations make a strong case against the applicability of hydrodynamic approaches to the orientational dynamics of ions.
High field vortex matching effects in superconducting Nb thin films with a nanometer-sized square array of antidots
Authors: Sabatino P. , Cirillo C. , Carapella G. , Trezza M. , Attanasio C.
Published: September 2010

Nb thin films containing a regular square array of antidots with 17 nm diameter and 50 nm spacing have been fabricated using a relatively simple lithographic process. The critical current density jc(H) curves, obtained here by electric transport measurements, exhibit commensurability effects with pronounced maxima just above the expected μ0H1=0.830 T and μ0H1/2=0.415 T matching fields, down to temperatures as low as 2.3 K. The behavior of jc(H) as well as the position of the maxima are consistent with the ones calculated in the framework of the time dependent Ginzburg–Landau model.
A scaling theory for the hydrodynamic interaction between a pair of vesicles or capsules
Authors: Ramachandran Arun , Leal Gary
Published: September 2010

We present a scaling theory based on the analysis of A. K. Chesters [Chem. Eng. Res. Des. 69, 259 (1991)] that describes the time required to drain the thin, suspending fluid film that forms between two deformable capsules or vesicles as they are pushed toward each other by a constant force. Capsules and vesicles show a decrease in the drainage time with the pushing force, which results in the prediction that in a shear flow, the number of doublet formation events increases with the shear rate. Both trends are exactly opposite to what is expected and observed for deformable drops.
Full spin-coated multilayer structure hybrid light-emitting devices
Authors: Cheng Gang , Mazzeo Marco , Carallo Sonia , Wang Huiping , Ma Yuguang , Gigli Giuseppe
Published: September 2010

We report on a multilayer structure hybrid light-emitting device (HLED) using a water/alcohol-soluble polymer poly(9,9-bis{30-[(N,N-dimethyl)-N-ethylammonium}-propyl]-2,7-fluorene dibromide) as an electron-transporting layer and a close-packed quantum dot-layer (QD-layer) as an emitting layer. The device was realized by full spin-coating technology without thermal evaporation process for the deposition of organic layers. The QD-layer was a mixture of QDs with two different sizes, in which large size QD-emitters were dispersed in small size QDs to weaken the concentration quenching. The device achieved a maximum power efficiency of 0.58 lm/W, which nearly quadrupled that of the HLED with a plain large size QD-EML.
Polarization mode preservation in elliptical index tailored optical fibers for apertureless scanning near-field optical microscopy
Authors: Zeh Christoph , Spittel Ron , Unger Sonja , Opitz Jörg , Köhler Bernd , Kirchhof Johannes , Bartelt Hartmut , Eng Lukas M.
Published: September 2010

We report on the development of elliptical, index tailored optical fibers for higher-order mode preservation for fiber-based, apertureless, internally illuminated scanning near-field optical microscopy (ai-SNOM). The fiber structure is simulated by the finite element method, showing large spreads of the effective indices for neighboring first higher-order modes. We demonstrate experimentally that due to this spread, the first higher-order modes do not couple, hence, the polarization is maintained, when the fiber is bent down to 1 cm radius. Further, we discuss the implications for ai-SNOM applications.
Controllability of ferromagnetism in graphene
Authors: Ma Tianxing , Hu Feiming , Huang Zhongbing , Lin Hai-Qing
Published: September 2010

We systematically study magnetic correlations in graphene within Hubbard model on a honeycomb lattice by using quantum Monte Carlo simulations. In the filling region below the Van Hove singularity, the system shows a short-range ferromagnetic correlation, which is slightly strengthened by the on-site Coulomb interaction and markedly by the next-nearest-neighbor hopping integral. The ferromagnetic properties depend on the electron filling strongly, which may be manipulated by the electric gate. Due to its resultant controllability of ferromagnetism, graphene-based samples may facilitate the development of many applications.
Atomically smooth surfaces through thermoplastic forming of metallic glass
Authors: Kumar Golden , Staffier Peter A. , Blawzdziewicz Jerzy , Schwarz Udo D. , Schroers Jan
Published: September 2010

We demonstrate that atomically smooth surfaces can be generated by thermoplastic forming of metallic glasses. This is enabled by the flow associated with the contact-line motion which removes rough surface layer from the advancing metallic glass-air interface. The thermoplastically formed surface is two orders of magnitude smoother than a polished surface of the same alloy. This process is capable of generating atomically smooth surfaces and replicating nanoscale features in a single processing step, providing a versatile toolbox for nanofabrication.
An analytical model for pulse shape and electrothermal stability in two-body transition-edge sensor microcalorimeters
Authors: Bennett D. A. , Horansky R. D. , Hoover A. S. , Hoteling N. J. , Rabin M. W. , Schmidt D. R. , Swetz D. S. , Vale L. R. , Ullom J. N.
Published: September 2010

High-resolution superconducting gamma-ray sensors show potential for the more accurate analysis of nuclear material. These devices are part of a larger class of microcalorimeters and bolometers based on transition edge sensors (TESs) that have two distinct thermal bodies. We derive the time domain behavior of the current and temperature for compound TES devices in the small signal limit and demonstrate the utility of these equations for device design and characterization. In particular, we use the model to fit pulses from our gamma-ray microcalorimeters and demonstrate how critical damping and electrothermal stability can be predicted.
Full spin switch effect for the superconducting current in a superconductor/ferromagnet thin film heterostructure
Authors: Leksin P. V. , Garif’yanov N. N. , Garifullin I. A. , Schumann J. , Vinzelberg H. , Kataev V. , Klingeler R. , Schmidt O. G. , Büchner B.
Published: September 2010

Using the spin switch design F1/F2/S theoretically proposed by Oh et al., [Appl. Phys. Lett. 71, 2376 (1997)], that comprises a ferromagnetic bilayer as a ferromagnetic component, and an ordinary superconductor as the second interface component, we have realized a full spin switch effect for the superconducting current. An experimental realization of this spin switch construction was achieved for the CoOx/Fe1/Cu/Fe2/In multilayer.
Melting and freezing lines for a mixture of charged colloidal spheres with spindle-type phase diagram
Authors: Lorenz Nina J. , Palberg Thomas
Published: September 2010

We have measured the phase behavior of a binary mixture of like-charged colloidal spheres with a size ratio of Γ=0.9 and a charge ratio of Λ=0.96 as a function of particle number density n and composition p. Under exhaustively deionized conditions, the aqueous suspension forms solid solutions of body centered cubic structure for all compositions. The freezing and melting lines as a function of composition show opposite behavior and open a wide, spindle shaped coexistence region. Lacking more sophisticated treatments, we model the interaction in our mixtures as an effective one-component pair energy accounting for number weighted effective charge and screening constant. Using this description, we find that within experimental error the location of the experimental melting points meets the range of melting points predicted for monodisperse, one-component Yukawa systems made in several theoretical approaches. We further discuss that a detailed understanding of the exact phase diagram shape including the composition dependent width of the coexistence region will need an extended theoretical treatment.
Cathodoluminescence of GaInN quantum wells grown on nonpolar a plane GaN: Intense emission from pit facets
Authors: Fujan K. J. , Feneberg M. , Neuschl B. , Meisch T. , Tischer I. , Thonke K. , Schwaiger S. , Izadi I. , Scholz F. , Lechner L. , Biskupek J. , Kaiser U.
Published: September 2010

Ga x In 1 − x N quantum wells grown by metal organic vapor phase epitaxy on a plane GaN grown on r plane sapphire substrate typically show relatively large surface pits. We show by correlation of low temperature photoluminescence, cathodoluminescence, scanning and transmission electron microscopy that the different semipolar side facets of these pits dominate the overall luminescence signal of such layers.
Detection of bio-organism simulants using random binding on a defect-free photonic crystal
Authors: Baker Sarah E. , Pocha Michael D. , Chang Allan S. P. , Sirbuly Donald J. , Cabrini Stefano , Dhuey Scott D. , Bond Tiziana C. , Létant Sonia E.
Published: September 2010

The defect-free photonic crystal (PC) slab geometry was explored for size-selective detection of bio-organism simulants. Through feedback between finite-difference time-domain simulations and experiments, we generated a conservative limit of detection estimate for randomized pore filling of a two-dimensional PC slab, and predict that random binding affords the label-free PC-based optical detection of low numbers (of the order of 10) of biological particles.
Optical nonlinearities of fine exciton states in a CdSe quantum dot
Authors: Je Koo-Chul , Shin In-Chul , Kim Jihoon , Kyhm Kwangseuk
Published: September 2010

Optical nonlinearities near the band edge exciton states in a CdSe quantum dot have been investigated. The photoinduced changes in the real and imaginary parts of the refractive index have been calculated for an injected pulse area and occupancy on the basis of the size-dependence of the fine exciton states by using semiconductor Bloch equations. We found that the optical nonlinearities are dominant in ±1L. However, the gain for ±1L is compensated by absorption at the other bright exciton states (±1U and 0U) for a resonantly exciting femtosecond pulse. These results were in good agreement with those obtained for a cocircularly polarized degenerate pump-probe experiment.
Pair-correlation properties and momentum distribution of finite number of interacting trapped bosons in three dimensions
Authors: Biswas Anindya , Chakrabarti Barnali , Das Tapan Kumar
Published: September 2010

We study the ground state pair-correlation properties of a weakly interacting trapped Bose gas in three dimensions by using a correlated many-body method. The use of the van der Waals interaction potential and an external trapping potential shows realistic features. We also test the validity of shape-independent approximation in the calculation of correlation properties.
Size correlated long and short range order of ternary Co2FeGa Heusler nanoparticles
Authors: Wang C. H. , Guo Y. Z. , Casper F. , Balke B. , Fecher G. H. , Felser C. , Hwu Y.
Published: September 2010

The long and short range order of chemically prepared Co2FeGa Heusler nanoparticles with various sizes are determined by x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) spectroscopy. Specifically, EXAFS fittings reveal the size dependent crystal structure and short range order of the Heusler type Co2FeGa nanoparticles. With decreasing particle size, the degree of L21 order in the nanoparticles decreases and the probability of B2 disorder increases simultaneously. The consequences of antisite disorder on the size correlated structure of Co2FeGa nanoparticles are also discussed.
Optical transitions between Landau levels: AA-stacked bilayer graphene
Authors: Ho Yen-Hung , Wu Jhao-Ying , Chen Rong-Bin , Chiu Yu-Huang , Lin Ming-Fa
Published: September 2010

The magneto-optical absorption spectra of AA-stacked bilayer graphene (AABG) exhibit two kinds of absorption peaks resulting from two groups of Landau levels (LLs). Only intragroup excitations that follow a single selection rule take place. The excitation channels are altered as the field strength approaches a critical strength. These optical properties can be comprehended by the characteristics of the LL wave functions. A comparison of AABG and AB-stacked bilayer graphene (BBG) demonstrates that the optical properties are dominated by the stacking symmetry. The presented results could offer a way to distinguish AABG from BBG and monolayer graphene.
The influence of sputtering power and O2/Ar flow ratio on the performance and stability of Hf–In–Zn–O thin film transistors under illumination
Authors: Kim Hyun-Suk , Park Kyung-Bae , Son Kyoung Seok , Park Joon Seok , Maeng Wan-Joo , Kim Tae Sang , Lee Kwang-Hee , Kim Eok Su , Lee Jiyoul , Suh Joonki , Seon Jong-Baek , Ryu Myung Kwan , Lee Sang Yoon , Lee Kimoon , Im Seongil
Published: September 2010

The performance and stability of amorphous HfInZnO thin film transistors under visible light illumination were studied. The extent of device degradation upon negative bias stress with the presence of visible light is found to be strongly sensitive to the extent of photoelectric effect in the oxide semiconductor. Highly stable devices were fabricated by optimizing the deposition conditions of HfInZnO films, where the combination of high sputtering power and high O2/Ar gas flow ratio was found to result in the highest stability under bias stress experiments.
Modelling wafer bow in silicon–polycrystalline CVD diamond substrates for GaN-based devices
Authors: Edwards M J , Bowen C R , Allsopp D W E , Dent A C E
Published: September 2010

Composite silicon–polycrystalline chemical vapour deposition (CVD) diamond wafers are potential substrates for GaN-based devices for use in harsh environments due to their high thermal conductivity and chemical stability. When cooled from a typical diamond deposition temperature of approximately 800 to 25 °C wafer bowing arises from a mismatch in the coefficients of thermal expansion of silicon and polycrystalline diamond. In this paper 100 mm diameter silicon–polycrystalline diamond wafers have been modelled using ANSYS finite element software to investigate their bowing behaviour as a function of temperature and geometry. The maximum bow of a wafer occurred where the thicknesses of both the silicon and polycrystalline diamond layers was almost identical; this has been confirmed using analytical methods. Strategies are discussed for reducing wafer bow.
Theoretical Study on Stereodynamics of Reactions of N(2D)+H2 → NH+H and N(2D)+D2 → ND+D
Authors: Yue Xian-fang , Cheng Jie , Feng Hai-ran , Li Hong , L. Wu Emilia
Published: September 2010

The vector correlations between products and reagents for the title reactions have been calculated by the quasi-classical trajectory method at a collision energy of 21.32 kJ/mol on an accurate potential energy surface of Ho et al. (J. Chem. Phys. 119, 3063 (2003)). The peaks of the product angular distribution are found to be in both backward and forward directions for the two title reactions. The product rotational angular momentum is not only aligned, but also oriented along the negative direction of y-axis. These theoretical results are in good agreement with recent experimental findings for the two title reactions. The isotopic effect is also revealed and primarily attributed to the difference of the mass factor in the two title reactions.
Large Scale Homogeneous Growth Mechanics of Microcrystalline Silicon Films on Rough Surface
Authors: Zhao Wen-feng , Chen Jun-fang , Wang Yan , Meng Ran , Zhao Yi-ran , Shao Shi-yun , Li Ji-yun , Zhang Yun
Published: September 2010

Large scale homogenous growth of microcrystalline silicon (μc-Si:H) on cheap substrates by inductively coupled plasma (ICP) of Ar diluted SiH4 has been studied. From XRD and Raman spectrum, we find that substrates can greatly affect the crystalline orientation, and the μc-Si:H films are comprised of small particles. Thickness detection by surface profilometry shows that the thin μc-Si:H films are homogenous in large scale. Distributions of both ion density and electron temperature are found to be uniform in the vicinity of substrate by means of diagnosis of Langmuir probe. Based on these experimental results, it can be proposed that rough surfaces play important roles in the crystalline network formation and Ar can affect the reaction process and improve the characteristics of μc-Si:H films. Also, ICP reactor can deposit the thin film in large scale.
Production of Hydrogen from Bio-oil Using Low-temperature Electrochemical Catalytic Reforming Approach over CoZnAl Catalyst
Authors: Lin Shao-bin , Ye Tong-qi , Yuan Li-xia , Hou Tao , Li Quan-xin
Published: September 2010

High-efficient production of hydrogen from bio-oil was performed by electrochemical catalytic reforming method over the CoZnAl catalyst. The influence of current on the hydrogen yield, carbon conversion, and products distribution were investigated. Both the hydrogen yield and carbon conversion were remarkably enhanced by the current through the catalyst, reaching hydrogen yield of 70% and carbon conversion of 85% at a lower reforming temperature of 500°C. The influence of current on the properties of the CoZnAl catalyst was also characterized by X-ray diffraction, X-ray photoelectron spectroscopy, thermal gravimetric analysis, and Brunauer-Emmett-Teller measurements. The thermal electrons would play an important role in promoting the reforming reactions of the oxygenated-organic compounds in the bio-oil.
PubDNA Finder: a web database linking full-text articles to sequences of nucleic acids
Authors: García-Remesal Miguel , Cuevas Alejandro , Pérez-Rey David , Martín Luis , Anguita Alberto , de la Iglesia Diana , de la Calle Guillermo , Crespo José , Maojo Víctor
Published: September 2010

Summary: PubDNA Finder is an online repository that we have created to link PubMed Central manuscripts to the sequences of nucleic acids appearing in them. It extends the search capabilities provided by PubMed Central by enabling researchers to perform advanced searches involving sequences of nucleic acids. This includes, among other features (i) searching for papers mentioning one or more specific sequences of nucleic acids and (ii) retrieving the genetic sequences appearing in different articles. These additional query capabilities are provided by a searchable index that we created by using the full text of the 176 672 papers available at PubMed Central at the time of writing and the sequences of nucleic acids appearing in them. To automatically extract the genetic sequences occurring in each paper, we used an original method we have developed. The database is updated monthly by automatically connecting to the PubMed Central FTP site to retrieve and index new manuscripts. Users can query the database via the web interface provided.

Availability: PubDNA Finder can be freely accessed at http://servet.dia.fi.upm.es:8080/pubdnafinder

Contact:  mgarcia@infomed.dia.fi.upm.es
Characterization of Lagenaria mild mosaic virus, a NewPotexvirusfrom Bottle Gourd in Myanmar
Authors: Kim Ok-Kyung , Mizutani Tadasuke , Soe Khin , Lee Key-Woon , Natsuaki Keiko T.
Published: September 2010

A putative Potexvirus was detected from bottle gourd (Lagenaria siceraria) showing mosaic and mottle symptoms in Myanmar in 2007. The virus was designated Lagenaria mild mosaic virus (LaMMoV) and was further characterized. In artificial inoculation tests, infectivity of LaMMoV was limited to two families: Chenopodiaceae and Cucurbitaceae. The host range of LaMMoV differs from those of the two cucurbit-infecting potexviruses, Alternanthera mosaic virus (AltMV) and Papaya mosaic virus (PapMV). Sequence analyses of LaMMoV showed that the C-terminal 3,859 nucleotides, excluding the poly-A tail, includes the C-terminal region of an RNA-dependent RNA polymerase (RdRp), a triple gene block (TGB), a coat protein (CP), and a 3′ untranslated region (UTR), all of which are typical of potexviruses. Although LaMMoV is related closely to AltMV and PapMV, its nucleotide sequences differ from those of other previously reported potexviruses. Therefore, we report LaMMoV as a new species of the genus Potexvirus that occurs in the cucurbit bottle gourd.
A quadruple-enterotoxin-deficient mutant of Bacillus thuringiensis remains insecticidal
Authors: Klimowicz Amy K. , Benson Terry A. , Handelsman Jo
Published: September 2010

Bacillus thuringiensis is the leading biopesticide used to control insect pests worldwide. Although they have a long record of safe use, under certain conditions commercial strains of B. thuringiensis have the ability to produce numerous putative enterotoxins that have been associated with food poisoning attributed to Bacillus cereus. Therefore, we designed a strategy to delete the genes encoding these toxins. B. thuringiensis strain VBTS 2477 contained genes encoding NHE, CytK-2 and three homologues of haemolysin BL (HBL, HBLa1 and HBLa2). This is the first report, to our knowledge, of a strain of B. cereus or B. thuringiensis containing three sets of hbl operons. The genes encoding HBLa1 and HBLa2 were 96–97 % identical to each other and 76–84 % identical to those encoding HBL. The hbla2
operon was detected by PCR amplification only after hbla1
was deleted. We used sequential gene replacement to replace the wild-type copies of the NHE and three HBL operons with copies that contained internal deletions that span the three genes in each operon. The insecticidal activity of the quadruple-enterotoxin-deficient mutant was similar to that of the wild-type strain against larvae of Trichoplusia ni, Spodoptera exigua and Plutella xylostella. This demonstrates that the genes for enterotoxins can be deleted, eliminating the possibility of enterotoxin production without compromising the insecticidal efficacy of a strain of B. thuringiensis.
Twenty-eight divergent polysaccharide loci specifying within- and amongst-strain capsule diversity in three strains of Bacteroides fragilis
Authors: Patrick Sheila , Blakely Garry W. , Houston Simon , Moore Jane , Abratt Valerie R. , Bertalan Marcelo , Cerdeño-Tárraga Ana M. , Quail Michael A. , Corton Nicola , Corton Craig , Bignell Alexandra , Barron Andrew , Clark Louise , Bentley Stephen D. , Parkhill Julian
Published: September 2010

Comparison of the complete genome sequence ofBacteroides fragilis638R, originally isolated in the USA, was made with two previously sequenced strains isolated in the UK (NCTC 9343) and Japan (YCH46). The presence of 10 loci containing genes associated with polysaccharide (PS) biosynthesis, each including a putative Wzx flippase and Wzy polymerase, was confirmed in all three strains, despite a lack of cross-reactivity between NCTC 9343 and 638R surface PS-specific antibodies by immunolabelling and microscopy. Genomic comparisons revealed an exceptional level of PS biosynthesis locus diversity. Of the 10 divergent PS-associated loci apparent in each strain, none is similar between NCTC 9343 and 638R. YCH46 shares one locus with NCTC 9343, confirmed by mAb labelling, and a second different locus with 638R, making a total of 28 divergent PS biosynthesis loci amongst the three strains. The lack of expression of the phase-variable large capsule (LC) in strain 638R, observed in NCTC 9343, is likely to be due to a point mutation that generates a stop codon within a putative initiating glycosyltransferase, necessary for the expression of the LC in NCTC 9343. Other major sequence differences were observed to arise from different numbers and variety of inserted extra-chromosomal elements, in particular prophages. Extensive horizontal gene transfer has occurred within these strains, despite the presence of a significant number of divergent DNA restriction and modification systems that act to prevent acquisition of foreign DNA. The level of amongst-strain diversity in PS biosynthesis loci is unprecedented.
Minimization of absorption contrast for accurate amorphous phase quantification: application to ZrO2nanoparticles
Authors: Suzuki-Muresan T. , Deniard P. , Gautron E. , Petříček V. , Jobic S. , Grambow B.
Published: September 2010

Monoclinic and tetragonal zirconia samples were characterized by X-ray diffraction, pycnometry, thermogravimetric analysis (TGA), Fourier transform (FT) IR and mass (MS) spectroscopies, and scanning and transmission electron (TEM) microscopies. The results show, for the particular case of a tetragonal zirconia sample, an X-ray-undetected subproduct identified as an amorphous organic phase by FTIR–ATR (attenuated total reflection) and TGA–MS. The observations by TEM allowed this amorphous phase to be localized on the surface as a shell coating the nanoparticles. Moreover, this amorphous phase was quantified by Rietveld refinementviathe addition of an internal silicon standard. Because zirconia and silicon have different linear absorption coefficients, the microabsorption effect was minimized by using small particle sizes. The amorphous phase was calculated to constitute 11.4 (30)% of the initial mass before Brindley correction and 10.6 (30)% of the initial mass after Brindley correction. The closeness of these values shows that the contribution of the Brindley correction can be neglected if precautions are taken on the microabsorption effect. This work has also highlighted the importance of thoroughly characterizing commercial products, which are not necessarily pure. Indeed, the presence of impurities could become a non-negligible parameter for physical and chemical properties studies related to commercial materials.
Ambiguities in the structure determination of antimony tellurides arising from almost homometric structure models and stacking disorder
Authors: Schneider Matthias N. , Seibald Markus , Lagally Patrick , Oeckler Oliver
Published: September 2010

Ambiguities in the interpretation of both single-crystal and powder diffraction data can lead to wrong conclusions concerning the structure analysis of layered chalcogenides with interesting physical properties and potential applications. This is illustrated for binary and Pb-doped phases of the homologous series (Sb2)k(Sb2Te3)m. Almost homometric structure models for 39R-Sb10Te3[R\bar 3m,a = 4.2874 (6),c = 64.300 (16) Å,R1 = 0.0298] have been derived from initial structure solutions and crystal chemical considerations. The variation of the electron density on certain positions may further reduce the differences between the calculated diffraction patterns of non-congruent structure models as exemplified by the new compound 33R-[Sb0.978(3)Pb0.022(3)]8Te3[R\bar 3m,a = 4.2890 (10),c = 75.51 (2) Å,R1 = 0.0615]. Both compounds are long-range ordered, and in either case both `almost homometric' models can be refined equally well on experimental data sets. The models can only be distinguished by chemical analysis, as reasonable atom assignments lead to different compositions for each model. Interestingly, all structure solution attempts led to the wrong models in both cases. In addition, it is shown that stacking disorder of characteristic layers may lead to powder diffraction patterns that can be misinterpreted in terms of three-dimensional randomly disordered almost isotropic structures with a simple α-Hg-type basic structure.
Experimental and predicted crystal structures of Pigment Red 168 and other dihalogenated anthanthrones
Authors: Schmidt Martin U. , Paulus Erich F. , Rademacher Nadine , Day Graeme M.
Published: September 2010

The crystal structures of 4,10-dibromo-anthanthrone (Pigment Red 168; 4,10-dibromo-dibenzo[def,mno]chrysene-6,12-dione), 4,10-dichloro- and 4,10-diiodo-anthanthrone have been determined by single-crystal X-ray analyses. The dibromo and diiodo derivatives crystallize inP21/c,Z= 2, the dichloro derivative in P\bar 1,Z= 1. The molecular structures are almost identical and the unit-cell parameters show some similarities for all three compounds, but the crystal structures are neither isotypic to another nor to the unsubstituted anthanthrone, which crystallizes inP21/c,Z= 8. In order to explain why the four anthanthrone derivatives have four different crystal structures, lattice-energy minimizations were performed using anisotropic atom–atom model potentials as well as using the semi-classical density sums (SCDS-Pixel) approach. The calculations showed the crystal structures of the dichloro and the diiodo derivatives to be the most stable ones for the corresponding compound; whereas for dibromo-anthanthrone the calculations suggest that the dichloro and diiodo structure types should be more stable than the experimentally observed structure. An experimental search for new polymorphs of dibromo-anthanthrone was carried out, but the experiments were hampered by the remarkable insolubility of the compound. A metastable nanocrystalline second polymorph of the dibromo derivative does exist, but it is not isostructural to the dichloro or diiodo compound. In order to determine the crystal structure of this phase, crystal structure predictions were performed in various space groups, using anisotropic atom–atom potentials. For all low-energy structures, X-ray powder patterns were calculated and compared with the experimental diagram, which consisted of a few broad lines only. It turned out that the crystallinity of this phase was not sufficient to determine which of the calculated structures corresponds to the actual structure of this nanocrystalline polymorph.
Conformational polymorphism in a Schiff-base macrocyclic organic ligand: an experimental and theoretical study
Authors: Lo Presti Leonardo , Soave Raffaella , Longhi Mariangela , Ortoleva Emanuele
Published: September 2010

Polymorphism in the highly flexible organic Schiff-base macrocycle ligand 3,6,9,17,20,23-hexa-azapentacyclo(23.3.1.111,15.02,6.016,20)triaconta-1(29),9,11,13,15(30),23,25,27-octaene (DIEN, C24H30N6) has been studied by single-crystal X-ray diffraction and both solid-state and gas-phase density functional theory (DFT) calculations. In the literature, only solvated structures of the title compound are known. Two new polymorphs and a new solvated form of DIEN, all obtained from the same solvent with different crystallization conditions, are presented for the first time. They all have P\bar 1 symmetry, with the macrocycle positioned on inversion centres. The two unsolvated polymorphic forms differ in the number of molecules in the asymmetric unitZ′, density and cohesive energy. Theoretical results confirm that the most stable form is (II°), withZ′ = 1.5. Two distinct molecular conformations have been found, named `endo' or `exo' according to the orientation of the imine N atoms, which can be directed towards the interior or the exterior of the macrocycle. Theendoarrangement is ubiquitous in the solid state and is shared by two independent molecules which constitute an invariant supramolecular synthon in all the known crystal forms of DIEN. It is also the most stable arrangement in the gas phase. Theexoform, on the other hand, appears only in phase (II°), which contains both the conformers. Similarities and differences among the occurring packing motifs, as well as solvent effects, are discussed with the aid of Hirshfeld surface fingerprint plots and correlated to the results of the energy analysis. A possible interconversion path in the gas phase between theendoand theexoconformers has been found by DFT calculations; it consists of a two-step mechanism with activation energies of the order of 30–40 kJ mol−1. These findings have been related to the empirical evidence that the most stable phase (II°) is also the last appearing one, in accordance with Ostwald's rule.
Validation of experimental molecular crystal structures with dispersion-corrected density functional theory calculations
Authors: van de Streek Jacco , Neumann Marcus A.
Published: September 2010

This paper describes the validation of a dispersion-corrected density functional theory (d-DFT) method for the purpose of assessing the correctness of experimental organic crystal structures and enhancing the information content of purely experimental data. 241 experimental organic crystal structures from the August 2008 issue ofActa Cryst.Section E were energy-minimized in full, including unit-cell parameters. The differences between the experimental and the minimized crystal structures were subjected to statistical analysis. The r.m.s. Cartesian displacement excluding H atoms upon energy minimization with flexible unit-cell parameters is selected as a pertinent indicator of the correctness of a crystal structure. All 241 experimental crystal structures are reproduced very well: the average r.m.s. Cartesian displacement for the 241 crystal structures, including 16 disordered structures, is only 0.095 Å (0.084 Å for the 225 ordered structures). R.m.s. Cartesian displacements above 0.25 Å either indicate incorrect experimental crystal structures or reveal interesting structural features such as exceptionally large temperature effects, incorrectly modelled disorder or symmetry breaking H atoms. After validation, the method is applied to nine examples that are known to be ambiguous or subtly incorrect.
Deformable Surface Techniques for Field Visualization
Authors: Sadarjoen I. , Post Frits H.
Published: September 2010

Surface extraction from data fields is often used in scientific visualization, as surfaces can represent meaningful information and they are well suited for display. This paper describes a general method for localized surface extraction from scalar and vector fields. An initial polygonal surface is placed within the field, and the shape of the surface is adapted to the field by iterative displacement of surface nodes according to a displacement criterion. To achieve a good approximation of a smooth surface, the polygon mesh can be locally refined during iteration. The type of surface extracted depends on the displacement criterion, which can be any function of the available field variables. Techniques for displacement and mesh refinement are discussed in detail. The results we show are generation of a local isosurface and extraction of a vortex tube. Finally, we will draw conclusions and discuss some issues for further development.
Building Telepresence Systems: Translating Science Fiction Ideas into Reality
Authors: Fuchs Henry
Published: September 2010

Many people feel that at some time in the distant future it will be possible to see and interact with remote individuals so realistically that they will appear to be standing next to us, that it will also be possible for physicians to look inside their patients and see organs and tumors, as if they possessed Superman’s X‐ray vision.

Although we are far from the realization of such dreams, we are witnessing some encouraging progress toward them. For example, we understand that two aspects common to these systems are a) the acquisition and synthesis of complex 3D information (whether from cameras at a distant scene or medical imaging devices inside a patient), and b) reconstruction and presentation of the 3D information to the observer (whether a distant collaborator or a nearby physician). Early results from several institutions are encouraging.

It is now possible to walk around distant scenes, although the visual data still needs to be preprocessed, the scene still needs to be static and the reconstruction still has gaps. It is possible to look inside patients, although with crude ultrasound imaging and with very limited visualization, or not naturally from the physician’s own point of view. It is not yet possible to view any of this kind of information with high degree of immersive 3D realism without wearing cumbersome visualization aids. Truly compelling realization of these long‐held dreams will take careful analysis of the remaining problems, creative thinking about new approaches, and innovative and sustained development of the required acquisition and display technologies.
Selective Pixel Transmission for Navigating in Remote Virtual Environments
Authors: Mann Yair , Cohen‐Or Daniel
Published: September 2010

This paper presents a technique to improve the performance of a walkthrough in remote virtual environments, where a scene is rendered jointly by the server and the client, in order to reduce the network requirements as much as possible. The client generates novel views by extrapolating a reference view based on the locally available geometric model, while the server transmits data necessary to prevent an accumulation of errors. Within this concept, we show that by transmitting only a selected subset of pixels, the quality of the extrapolated views can be improved while requiring less bandwidth. We focus on the selection process in which the visibility gaps between the reference view and novel view are detected, packed and transmitted compressed to the client.
Painting‐like Image Emphasis based on Human Vision Systems
Authors: Tanaka Toshimitsu , Ohnishi Noboru
Published: September 2010

Regional image emphasis is often evident in paintings and illustrations. This technique increases local contrast while reducing global contrast by amplifying image intensity on shadowed surfaces, reducing intensity on illuminated surfaces, and then expanding contrast at intensity edges. The effects are assumed to result from the visual processing needed to interpolate the real world onto canvas. Therefore, we propose an intensity emphasis method based on human vision. This method simulates the adaptation of photoreceptor cells and the lateral inhibition of receptive fields. These attributes of a vision system are realized by computation of relative intensity and differential intensity in small areas.

The proposed method can successfully generate painting‐like artifacts, which greatly improves the perception of visual elements displayed in an image. Since the method efficiently reduces the dynamic range of images, it can be used for displaying highlighted images on standard graphic monitors. Experiments on a computer‐generated image and a photograph confirm the advantages of our method.
Bounded Radiosity – Illumination on General Surfaces and Clusters
Authors: Stamminger Marc , Slusallek Philipp , Seidel Hans‐Peter
Published: September 2010

Traditionally, Radiosity algorithms have been restricted to scenes made from planar patches. Most algorithms for computing form factors and the subdivision criterion for hierarchical methods implicitly assume planar patches. In this paper, we present a new radiosity algorithm that is solely based on simple geometric information about surface elements, namely their bounding boxes and cone of normals. Using this information allows to compute efficient error bounds that can be used for the subdivision oracle and for computing the energy transfer. Due to the simple interface to geometric objects, our algorithm not only allows for computing illumination on general curved surfaces, but it can also be directly applied to a hieararchy of clusters. Several examples demonstrate the advantages of the new approach.
A Million Polygons, a Million Pixels: Which is Heavier?
Authors: Sillion François X.
Published: September 2010

The impressive progress of rendering software and hardware over the last two decades often leads to the – too rapid – conclusion that high‐quality 3D imagery can now be incorporated in all sorts of applications. Interestingly, these advances allow more and more complex applications to be envisioned: however, an increase in processing power is not necessarily used to treat the same problem faster, but also creates a desire to attack larger problems. In many ways the models for visual simulation or engineering applications grow faster than the graphics systems! recent work on image‐based rendering and modeling shows a growing awareness that traditional 3D methods may not scale well for the current and coming complexity levels.

This talk will examine some of the challenges lying ahead for the development of future graphics applications. Specifically, when is it better to use pixels than polygons? when is a 3D model required? how can we mix and match competing approaches? can image‐based approaches help for different applications such as lighting simulations? some issues related to network applications will also be discussed.
Polyhedral Surface Modeling with a Diffusion System
Authors: Kuriyama Shigeru , Tachibana Keihachiro
Published: September 2010

This paper presents a method of generating polyhedral surfaces by using a diffusion system that calculates the positional and normal vectors on their vertices. The system generates smooth shapes that satisfy the minimum norm property, and can be extended to imitate the shape controls of curvature continuous surfaces with bias and tension parameters. The shape of a surface is determined by the stable state of nonlinear and local calculations between vertices, and is easily controlled by adding constraints on arbitrary vertices. Such bottom‐up calculation of surfaces enhances flexibility in the interactive design of complicated free‐form shapes.
EVOLUTION OF THE HELIORNITHIDAE: RECIPROCAL ILLUMINATION BY MORPHOLOGY, BIOGEOGRAPHY AND DNA HYBRIDIZATION (AVES: GRUIFORMES)
Authors: Houde Peter
Published: September 2010

Abstract— Finfoots (Heliornithidae) were chosen to test the possibility that there has been a dramatic reversal in a suite of morphological characters, intimated by an earlier phylogenetic reconstruction of Gruiformes based on DNA hybridization. There are three nodes where unstudied finfoots could stem from the existing reconstruction. The resulting alternate trees have largely exclusive implications for morphological character suite polarity, biogeography and fossil identifications. A new DNA hybridization study that includes all relevant taxa was intended to form the basis for independent evaluation of the trees, but it produced results that conflict with the earlier DNA study. So, instead, DNA trees were evaluated by their reproducibility and consensus with most‐parsimonious trees, biogeography, paleontology and traditional classifications, I concur with traditional classifications that finfoots are monophyletic, and that Limpkin (Gruiformes: Aramidae) is the sister of cranes (Gruiformes: Gruidae). Limpkin is not supported as the sister of the Sungrebe (Heliornis fulica) or as a member of the Heliornithidae, as reported in the earlier DNA study. It is alarming that the gross lack of consensus with traditional characters and concomitant implications for character suite polarity in this case went unquestioned.
Convergence and parallelism: is a new life ahead of old concepts?
Authors: Desutter‐Grandcolas Laure , Legendre Frédéric , Grandcolas Philippe , Robillard Tony , Murienne Jérôme
Published: September 2010

In comparative biology, character observations initially separate similar and dissimilar characters. Only similar characters are considered for phylogeny reconstruction; their homology is attested in a two‐step process, firstly a priori of phylogeny reconstruction by accurate similarity statements, and secondly a posteriori of phylogeny analysis by congruence with other characters. Any pattern of non‐homology is then a homoplasy, commonly, but vaguely, associated with “convergence”. In this logical scheme, there is no way to analyze characters which look similar, but cannot meet usual criteria for homology statements, i.e., false similarity detected a priori of phylogenetic analysis, even though such characters may represent evolutionarily significant patterns of character transformations. Because phylogenies are not only patterns of taxa relationships but also references for evolutionary studies, we propose to redefine the traditional concepts of parallelism and convergence to associate patterns of non‐homology with explicit theoretical contexts: homoplasy is restricted to non‐similarity detected a posteriori of phylogeny analysis and related to parallelism; non‐similarity detected a priori of phylogenetic analysis and necessarily described by different characters would then correspond to a convergence event s. str. We propose to characterize these characters as heterologous (heterology). Heterology and homoplasy correspond to different non‐similarity patterns and processes; they are also associated with different patterns of taxa relationships: homoplasy can occur only in non‐sister group taxa; no such limit exists for heterology. The usefulness of these terms and concepts is illustrated with patterns of acoustic evolution in ensiferan insects.

© The Willi Hennig Society 2005.
Can taxon‐sampling effects be minimized by using branch supports?
Authors: Hovenkamp P.
Published: September 2010

Rydin and Källersjö (2002) found that taxon‐sampling effects were a strongly disturbing factor in a high‐level phylogenetic analysis. I have reanalyzed some of their data to assess whether bootstrap frequencies can be used to predict the stability of clades to taxon sampling, and to compare it with the performance of a stability measure based on taxon resampling (“taxon jackknifing”). High bootstrap frequencies correctly identify a small number of stable clades, but miss many other equally stable clades. When the total error rate is considered, no cut‐off level based on bootstrap frequencies performs better than using all clades in the strict consensus, whereas a slight improvement was observed when cut‐off levels based on taxon jackknifing frequencies are used.

© The Willi Hennig Society 2006.