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Growth Direction (growth + direction)
Kinds of Growth Direction Selected AbstractsGrowth Direction and Cross-Sectional Study of Silicon Nanowires,ADVANCED MATERIALS, Issue 7-8 2003C.-P. Li Cross-sectional samples of silicon nanowires (SiNWs) are examined using transmission electron microscopy. The cross-sections are bounded by well-defined low-index crystallographic facets of various shapes (e.g., the square section in the Figure, 50 nm edge) and characterized by shape-dependent growth directions, with ,112, and ,110, predominating. Both shape and growth direction are consistent with surface energy considerations and growth mechanisms. [source] Interdiffusion phenomena in InGaAs/GaAs superlattice structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2010B. Sar, kavak Abstract We have studied structural properties of InGaAs/GaAs superlattice sample prepared by Molecular Beam Epitaxy (MBE) using high resolution X-ray diffractometer (HRXRD). Increasing strain relaxation and defect generations are observed with the increasing Rapid Thermal Annealing (RTA) temperature up to 775 °C. The higher temperatures bring out relaxation mechanisms; interdiffusion and favored migration. The defect structure and the defects which are observed with the increasing annealing temperature were analyzed. Firstly, the in-plane and out-of-plane strains after the annealing of sample were found. Secondly, the structural defect properties such as the parallel X-ray strain, perpendicular X-ray strain, misfit, degree of relaxation, x composition, tilt angles and dislocation that are obtained from X-ray diffraction (XRD) analysis were carried out at every temperature. As a result, we observed that the asymmetric peaks especially in asymmetric (224) plane was affected more than symmetric and asymmetric planes with lower polar or inclination angles due to c-direction at low temperature. These structural properties exhibit different unfavorable behaviors for every reflection direction at the increasing temperatures. The reason is the relaxation which is caused by spatially inhomogeneous strain distribution with the increasing annealing temperature. In the InGaAs superlattice samples, this process enhances preferential migration of In atoms along the growth direction. Further increase in the annealing temperature leads to the deterioration of the abrupt interfaces in the superlattice and degradation in its structural properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Porous Porphyrin Nanoarchitectures on SurfacesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2010Rie Makiura Abstract Controlling the size and the growth direction of porous hybrid objects , metal,organic frameworks (MOFs) or porous coordination polymers (PCPs) , at the nanoscale is a critical issue for enabling their use in a number of potential applications that have arisen from the current remarkable activity in studying such porous materials. This microreview describes the recent progress in the design, growth, and characterization of multidimensional nanoarchitectures by employing porphyrin-based components. The versatility of the sequential bottom-up fabrication process, which uses multitopic molecular building units assembled by appropriately chosen linkers, is suitable to be extended to the formation of a rich variety of nanostructures endowed with pores on surfaces. [source] Advanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin filmsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2005H. OGI ABSTRACT This paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants Cij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in-plane direction, and they macroscopically show five independent elastic constants. Because all of the Cij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the Cij of the film with known density, dimensions and the Cij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the Cij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement,amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the Cij smaller than bulk values of Cij. Micromechanics calculations indicate the presence of incohesive bonded regions. [source] Prediction of crack growth direction under plane stress for mixed-mode I and II loadingFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2000Wasiluk The estimation of the plastic zone geometry ahead of a crack is fundamental to the evaluation of crack growth. Presented here is an analytical investigation for predicting crack growth direction for mixed-mode I and II loading under plane stress conditions. It is proposed that under complex loading the crack will extend in the direction where the radius of the plastic zone attains a minimum value. There is good agreement between the predicted results which are computed on the basis of this criterion and experimental data published in the literature. [source] Topotactic Conversion Route to Mesoporous Quasi-Single-Crystalline Co3O4 Nanobelts with Optimizable Electrochemical PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Li Tian Abstract The growth of mesoporous quasi-single-crystalline Co3O4 nanobelts by topotactic chemical transformation from , -Co(OH)2 nanobelts is realized. During the topotactic transformation process, the primary , -Co(OH)2 nanobelt frameworks can be preserved. The phases, crystal structures, morphologies, and growth behavior of both the precursory and resultant products are characterized by powder X-ray diffraction (XRD), electron microscopy,scanning electron (SEM) and transmission electron (TEM) microscopy, and selected area electron diffraction (SAED). Detailed investigation of the formation mechanism of the porous Co3O4 nanobelts indicates topotactic nucleation and oriented growth of textured spinel Co3O4 nanowalls (nanoparticles) inside the nanobelts. Co3O4 nanocrystals prefer [0001] epitaxial growth direction of hexagonal , -Co(OH)2 nanobelts due to the structural matching of [0001] , -Co(OH)2//[111] Co3O4. The surface-areas and pore sizes of the spinel Co3O4 products can be tuned through heat treatment of , -Co(OH)2 precursors at different temperatures. The galvanostatic cycling measurement of the Co3O4 products indicates that their charge,discharge performance can be optimized. In the voltage range of 0.0,3.0,V versus Li+/Li at 40,mA g,1, reversible capacities of a sample consisting of mesoporous quasi-single-crystalline Co3O4 nanobelts can reach up to 1400,mA h g,1, much larger than the theoretical capacity of bulk Co3O4 (892,mA h g,1). [source] A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by CrystallizationADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Yeo-Wan Chiang Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source] Synthesis and Lasing Properties of Highly Ordered CdS Nanowire Arrays,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2007L. Cao Abstract Highly ordered large-area arrays of wurtzite CdS nanowires are synthesized on Cd-foil substrates via a simple liquid reaction route using thiosemicarbazide and Cd foil as the starting materials. The CdS nanowires are single crystals growing along the [001],direction and are perpendicular to the surface of the substrate. The characteristic Raman peaks of CdS are red-shifted and show asymmetric broadening, which is ascribed to phonon confinement effects arising from the nanoscale dimensions of the nanowires. Significantly, the uniform CdS nanowire arrays can act as laser cavities in the visible-light range, leading to bandgap lasing at ca.,515,nm with obvious modes. The high density of nuclei and the preferential growth direction induce the formation of aligned CdS nanowires on the metal substrate. [source] Well-Aligned ZnO Nanowire Arrays Fabricated on Silicon Substrates ,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2004C. Geng Abstract Arrays of well-aligned single-crystal zinc oxide (ZnO) nanowires of uniform diameter and length have been synthesized on a (100) silicon substrate via a simple horizontal double-tube system using chemical vapor transport and condensation method. X-ray diffraction and transmission electron microscopy (TEM) characterizations showed that the as-grown nanowires had the single-crystal hexagonal wurtzite structure with detectable defects and a <0002> growth direction. Raman spectra revealed phonon confinement effect when compared with those of ZnO bulk powder, nanoribbons, and nanoparticles. Photoluminescence exhibited strong ultraviolet emission at 3.29,eV under 355,nm excitation and green emission at 2.21,eV under 514.5,nm excitation. No catalyst particles were found at the tip of the nanowires, suggesting that the growth mechanism followed a self-catalyzed and saturated vapor,liquid,solid (VLS) model. Self-alignment of nanowires was attributed to the local balance and steady state of vapor flow at the substrate. The growth technique would be of particular interest for direct integration in the current silicon-technology-based optoelectronic devices. [source] Self-Assembled Quantum Dot MoleculesADVANCED MATERIALS, Issue 25-26 2009Lijuan Wang Abstract Semiconductor quantum dot molecules (QDMs) are systems composed of two or more closely spaced and interacting QDs. QDMs are receiving much attention both as playground for studying coupling and energy transfer processes between "artificial atoms" and as new systems, which substantially extend the range of possible applications of QDs. QDMs can be conveniently fabricated by self-assembly either through chemical synthesis or epitaxial growth. Although QDMs relying on the random occurrence of nearby QDs can be used for fundamental studies, special fabrication protocols must be used to create QDMs with well-defined properties. In this article, we focus on self-assembled QDMs obtained by epitaxial growth and embedded in a semiconductor matrix, which are appealing for the possible realization of quantum gates based on two-level systems defined in QDs. We provide a comprehensive overview of the development and current stage of the research on QDMs composed of vertically (in the growth direction) or laterally (in the growth plane) aligned QDs. The review highlights some recent milestone works and points out the challenges and future directions in the field. [source] Cover Picture: Direction-Dependent Homoepitaxial Growth of GaN Nanowires (Adv. Mater.ADVANCED MATERIALS, Issue 2 20062/2006) Abstract GaN nanowires with vastly different morphologies depending upon their growth direction can be produced by direct nitridation and vapor transport of Ga in disassociated ammonia, report Sunkara and co-workers on p.,216. Nanowires grown along the c -direction develop hexagonal-prism island morphologies, while wires grown along the a -direction form uniform, belt-shaped morphologies. A "ballistic" phenomenon involving the 1D transport of adatoms on the non-polar surfaces of <0001> GaN nanowires is proposed to explain the prismatic island morphologies. [source] Direction-Dependent Homoepitaxial Growth of GaN Nanowires,ADVANCED MATERIALS, Issue 2 2006H. Li GaN nanowires with vastly different morphologies depending upon the growth direction are produced by direct nitridation and vapor transport of Ga in disassociated ammonia. Nanowires grown homoepitaxially along the c -direction develop hexagonal-prism island morphologies (see Figure, left, and Cover), while wires grown along the a -direction form uniform, belt-shaped morphologies (Figure, right). A "ballistic" transport phenomenon for adatoms is proposed to explain the observed prismatic island morphologies. [source] Routes to Grow Well-Aligned Arrays of ZnSe Nanowires and Nanorods,ADVANCED MATERIALS, Issue 11 2005X. Zhang Well-aligned ZnSe nanowires and nanorods can be grown on ZnSe epilayers on different GaAs substrates, with and without catalyst, by metal,organic chemical vapor deposition. Gold particles affect the number density, growth direction, and the morphology of the resulting nanostructures. In the absence of the gold catalyst, hexagonal nanorods grow along the <111> directions (see Figure). Growth defects on the epilayers may be the nucleation sites of the nanorods. [source] Size-Dependent Periodically Twinned ZnSe Nanowires,ADVANCED MATERIALS, Issue 16 2004Q. Li Cubic ZnSe nanowires with periodically alternating twins along the wire growth direction (see Figure) have been synthesized using thermal evaporation with a Au catalyst. The periodicity of the alternating twins has a linear dependence on the diameter of the nanowires. Sharp excitonic peaks dominating the low-temperature photoluminescence spectrum of the nanowires reveal the high quality of their electronic structure despite the large unpassivated surface and interface associated with the twinned nanowire configuration. [source] Growth Direction and Cross-Sectional Study of Silicon Nanowires,ADVANCED MATERIALS, Issue 7-8 2003C.-P. Li Cross-sectional samples of silicon nanowires (SiNWs) are examined using transmission electron microscopy. The cross-sections are bounded by well-defined low-index crystallographic facets of various shapes (e.g., the square section in the Figure, 50 nm edge) and characterized by shape-dependent growth directions, with ,112, and ,110, predominating. Both shape and growth direction are consistent with surface energy considerations and growth mechanisms. [source] Oxide-Assisted Growth of Semiconducting Nanowires,ADVANCED MATERIALS, Issue 7-8 2003R.-Q. Zhang Abstract In this contribution, we outline oxide-assisted growth (OAG) (distinct from the conventional metal-catalytic vapor,liquid,solid (VLS) process) for the growth of nanostructured materials. This synthesis technique, in which oxides instead of metals play an important role in inducing the nucleation and growth of nanowires, is capable of producing large quantities of high-purity silicon nanowires with a preferential growth direction, uniform size, and long length, without the need for a metal catalyst. The OAG 1D nanomaterials synthesis is complementary to, and coexistent with, the conventional metal-catalyst VLS approach, and can be utilized to produce nanowires from a host of materials other than Si including Ge nanowires, carbon nanowires, silicon and SnO2 nanoribbons, and Group III,V and II,VI compound semiconductor nanowires. [source] Collagen orientation in periosteum and perichondrium is aligned with preferential directions of tissue growthJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 9 2008Jasper Foolen Abstract A feedback mechanism between different tissues in a growing bone is thought to determine the bone's morphogenesis. Cartilage growth strains the surrounding tissues, eliciting alterations of its matrix, which in turn, creates anisotropic stresses, guiding directionality of cartilage growth. The purpose of this study was to evaluate this hypothesis by determining whether collagen fiber directions in the perichondrium and periosteum align with the preferential directions of long bone growth. Tibiotarsi from chicken embryos across developmental stages were scanned using optical projection tomography (OPT) to assess preferential directions of growth at characteristic sites in perichondrium and periosteum. Quantified morphometric data were compared with two-photon laser-scanning microscopy images of the three-dimensional collagen network in these fibrous tissues. The diaphyseal periosteum contained longitudinally oriented collagen fibers that aligned with the preferential growth direction. Longitudinal growth at both metaphyses was twice the circumferential growth. This concurred with well-developed circumferential fibers, which covered and were partly interwoven with a dominant network of longitudinally oriented fibers in the outer layer of the perichondrium/periosteum at the metaphysis. Toward both articulations, the collagen network of the epiphyseal surface was randomly oriented, and growth was approximately biaxial. These findings support the hypothesis that the anisotropic architecture of the collagen network, detected in periosteum and perichondrium, concurs with the assessed growth directions. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1263,1268, 2008 [source] Modulation of vertebral and tibial growth by compression loading: Diurnal versus full-time loadingJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2005Ian A. Stokes Abstract Purpose: This study was designed to determine whether the amount of endochondral growth response to mechanical compression and the underlying growth mechanism differed with night-time or day-time loading, relative to full-time loading. Methods: Mechanical compression (nominally 0.1 MPa stress) was applied across tibial and tail vertebral growth plates of growing Sprague,Dawley rats. Four groups of animals (five per group) were used: 24/24 h (full-time loading); 12/24 h (day-loading); 12/24 h (night-loading); and 0/24 h (sham instrumented). Contralateral tibiae and adjacent vertebrae served as within-animal controls. The animals were euthanized after eight days. Growth plates were processed for quantitative histology to measure 24-h growth, total and BrdU-positive proliferative zone chondrocyte counts, and hypertrophic chondrocytic enlargement in the growth direction. Results: Growth as a percentage of within-animal control averaged 82% (full-time); 93% (day-loading); 90% (night-loading); 100% (sham) for vertebrae. For proximal tibiae it averaged 70% (full-time); 84% (day-loading); 86% (night-loading); 89% (sham). Reduced amount of hypertrophic chondrocytic enlargement explained about half of this effect in full-time loaded growth plates, but was not significantly altered in half-time loaded growth plates. The remaining variation in growth was apparently explained by reduced total numbers of proliferative zone chondrocytes. These findings indicate that sustained compression loading suppressed growth more than intermittent loading at both anatomical locations. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] TEM/STEM Observation of ZrC Coating Layer for Advanced High-Temperature Gas-Cooled Reactor Fuel, Part IIJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009Jun Aihara The Japan Atomic Energy Agency (JAEA) has started to study and develop zirconium carbide (ZrC)-coated fuel particles for advanced high-temperature gas-cooled reactors. The ZrC coating layer has been fabricated at JAEA by chemical vapor deposition using a pyrolytic reaction of zirconium bromide. The microstructures of the ZrC layers, whose nominal deposition temperatures could be measured and controlled during the deposition process, were characterized by means of TEM and STEM. In the present study, three batches were prepared and compared with each other as well as the previous batches. The crystallographic orientation of ZrC with regard to the growth direction in the ZrC layers deposited at a constant temperature of 1630 K was different from that deposited at varying temperatures in the 1493,1823 K range. A thin layer of turbostratic carbon was observed at the boundary between pyrolytic carbon and ZrC in particles deposited at the highest temperature among those used in this study (the nominal temperature was 1769 K); no such structure was found in a batch deposited at a lower temperature (the nominal temperature was 1632 K). Therefore, precise control of temperature is shown to be critical to the formation of good ZrC coatings. [source] Synthesis of Porous Silicon Nitride with Unidirectionally Aligned Channels Using Freeze-Drying ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002Takayuki Fukasawa Porous silicon nitride with macroscopically aligned channels was synthesized using a freeze-drying process. Freezing of a water-based slurry of silicon nitride was done while unidirectionally controlling the growth direction of the ice. Pores were generated subsequently by sublimation of the columnar ice during freeze-drying. By sintering this green body, a porous silicon nitride with high porosity (over 50%) was obtained and its porosity was controllable by the slurry concentration. The porous Si3N4 had a unique microstructure, where macroscopically aligned open pores contained fibrous grains protruding from the internal walls of the Si3N4 matrix. It is hypothesized that vapor/solid phase reactions were important to the formation mechanism of the fibrous grains. [source] Crack Growth in Soda,Lime,Silicate Glass near the Static Fatigue LimitJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2002Sheldon M. Wiederhorn The atomic force microscope (AFM) was used to explore the nature of features formed on the surfaces of cracks in soda,lime,silicate glass that were held at stress intensity factors below the crack growth threshold. All studies were conducted in water. Cracks were first propagated at a stress intensity factor above the crack growth threshold and then arrested for 16 h at a stress intensity factor below the threshold. The stress intensity factor was then raised to reinitiate crack growth. The cycle was repeated multiple times, varying the hold stress intensity factor, the hold time, and the propagation stress intensity factor. Examination of the fracture surface by optical microscopy showed surface features that marked the points of crack arrest during the hold time. These features were identical to those reported earlier by Michalske in a similar study of crack arrest. A study with the AFM showed these features to be a consequence of a bifurcation of the crack surface. During the hold period, waviness developed along the crack front so that parts of the front propagated out of the original fracture plane, while other parts propagated into the plane. Crack growth changed from the original flat plane to a bifurcated surface with directions of as much as 3° to 5° to the original plane. This modification of crack growth behavior cannot be explained by a variation in the far-field stresses applied to the crack. Nor can the crack growth features be explained by chemical fluctuations within the glass. We speculate that changes in crack growth direction are a consequence of an enhancement in the corrosion rate on the flank of the crack at stresses below the apparent crack growth threshold in a manner described recently by Chuang and Fuller. [source] Preparation and Growth Mechanism of Molybdenum Trioxide WhiskerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002Jianqiang Li A new whisker, ,-MoO3, was fabricated via molybdenum thread oxidation at 973, 1023, and 1173 K. Various morphologies of the whiskers, such as flakelike, platelike, and needlelike, were observed under different fabrication conditions. The lateral surfaces of the whiskers were close-packed (010) plane, and the growth direction was (001), which related to the unique layered structure of the ,-MoO3 crystal. Growth of the MoO3 whiskers was attributed to a vapor-liquid-solid (VLS) mechanism at 1023 and 1173 K, whereas, at 973 K, growth was attributed to a vapor-liquid (VL) mechanism. [source] Fracture Strength of Plate and Tubular Forms of Monolithic Silicon Carbide Produced by Chemical Vapor DepositionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Brian Vern Cockeram The fracture strength of silicon carbide (SiC) plate deposits produced by chemical vapor deposition (CVD) was determined from room temperature to 1500°C using a standard 4-point flexural test method (ASTM C1161). CVD SiC materials produced by two different manufacturers are shown to have only slightly different flexural strength values, which appear to result from differences in microstructure. Although CVD deposition of SiC results in a textured grain structure, the flexural strength was shown to be independent of the CVD growth direction. The orientation of machining marks was shown to have the most significant influence on flexural strength, as expected. The fracture strength of tubular forms of SiC produced by CVD deposition directly onto a mandrel was comparable to flexural bars machined from a plate deposit. The tubular (O-ring) specimens were much smaller in volume than the flexural bars, and higher strength values are predicted based on Weibull statistical theory for the O-ring specimens. Differences in microstructure between the plate deposits and deposits made on a mandrel result in different flaw distributions and comparable strength values for the flexural bar and O-ring specimens. These results indicate that compression testing of O-rings provides a more accurate strength measurement for tubular product forms of SiC due to more representative flaw distributions. [source] Thermal Stability of Lanthanum Zirconate Plasma-Sprayed CoatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001X. Q. Cao Lanthanum zirconate (La2Zr2O7, LZ) is a newly proposed material for thermal barrier coatings (TBCs). The thermal stability of LZ coating was studied in this work by long-term annealing and thermal cycling. After long-term annealing at 1400°C or thermal cycling, both LZ powder and plasma-sprayed coating still kept the pyrochlore structure, and a preferred crystal growth direction in the coating was observed by X-ray diffraction. A considerable amount of La2O3 in the powder was evaporated in the plasma flame, resulting in a nonstoichiometric coating. Additionally, compared with the standard TBC material yttria-stabilized zirconia (YSZ), LZ coating has a lower thermal expansion coefficient, which leads to higher stress levels in a TBC system. [source] Effects of repeated low-dose UVB irradiation on the hyphal growth of Candida albicansMYCOSES, Issue 1 2006J. Brasch Summary Ultraviolet B light (UVB) can have negative phototropic effects on fungi. Candida albicans is often found on human skin exposed to UVB. Therefore, it is of medical interest to know whether a negative phototropic response to UVB irradiation can support an invasive growth of this potentially dangerous agent. In our study we investigated how repeated irradiation with low doses of UVB can influence the hyphal growth of C. albicans. Six randomly chosen strains of C. albicans were tested. Formation of hyphae was induced and maintained within transparent agar plates. The fungi were exposed to UVB three times daily for 7 days from either the obverse or the reverse side during incubation. The wavelength spectrum was in the range of 310,315 nm, single doses were between 0.0018 and 0.432 J cm,2. After 7 days the morphology and growth direction of C. albicans cells were determined microscopically. All six strains showed a common and dose-dependent response to UVB irradiation: the progression of hyphal growth was inhibited, no phototropic effects were seen and as a new finding an increased formation of blastospores was observed. We conclude that an irradiation of human skin colonized by C. albicans with doses of UVB that can occur under natural or artificial conditions is unlikely to trigger skin invasion by C. albicans. [source] Cephalometric evaluation of condylar and mandibular growth modification: a reviewORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 1 2006G Shen Structured Abstract Authors ,, Shen G, Darendeliler MA Objective ,, Based on a wealth of orthodontic archives, this work aims to review the cephalometric analysis systems that can identify the changes in condylar and mandibular position as well as growth direction in response to bite jumping therapy. Design ,, Numerous cephalometric approaches were screened to testify their feasibility and reliability in accurately depicting the growth modification of the condyle and the mandible. The critical assessment of the working mechanisms of these cephalometric methods was elaborated to help build up the rationale and justification for their clinical use. Results ,, 1) The changes in condylar and mandibular size, position and growth direction can be identified by using lateral cephalograms with closed-mouth or open-mouth posture. 2) With superimposition methods where the anatomical structures for superimposition registration must be stable and reproducible, the growth modification of the condyle and the mandible between two time-points is qualitatively demonstrated in a diagram if reference lines are not constructed. The growth modification can be quantitatively identified if the reference lines are created. 3) With non-superimposition methods, the size and position of the condyle and the mandible are separately identified for each time-pint by relating them to the stable reference structures. The growth modification between two time-pints is evaluated by comparing the two separate measurements. Conclusion ,, The application of a standardized and well designed cephalometric evaluation system may reduce the bias that attribute to the arbitrariness of the clinical effects of bite jumping functional appliances. [source] X-ray investigation of CdSe nanowiresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2009Özgül Kurtulu Abstract CdSe nanowires (NWs) have been prepared by a solution,liquid,solid (SLS) approach using Bi nanocatalysts. Structural characterization has been performed by X-ray powder diffraction providing an admixture of wurtzite and zinc-blende (ZB) structure units separated by different types of stacking faults. The relative contributions of ZB type stacking units within the NWs were determined to be in the order of 3,6% from a set of ratios of reflection intensities appearing in only wurtzite structure to those appearing in both ZB and wurtzite (W) structure. In addition, the anisotropy of domain size within the NWs was evaluated from the evolution of peak broadening for increasing scattering length. The coherence lengths along the growth direction are found to be changing between 16 and 21,nm, smaller than the results obtained from TEM measurement, while the NW diameters are determined to be between 5 and 8,nm which is in good agreement with TEM inspection. [source] Structural anisotropy of InGaAs/GaAs(001) quantum dot chains structuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2007V. P. Kladko Abstract We have studied the structural properties of ordered InGaAs/GaAs(001) quantum dot chains multilayer by high-resolution X-ray diffraction. Two systems of lateral satellites, one of which being inclined with respect to the sample surface normal, i.e. the growth direction [001], were observed. The measured inclination of 30.0° ± 2.5° does not affect the diffraction profile from planar superlattice (SL), i.e. SL peaks are not inclined with respect to the GaAs substrate peak. We identify the splitting of coherent SL satellites for all orders as well as for two perpendicular directions. This splitting most likely indicates that two discrete periods exist in SL structure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] X-ray diffraction and Raman study of nanogranular BaTiO3,CoFe2O4 thin films deposited by laser ablation on Si/Pt substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007J. Barbosa Abstract Nanocomposite thin films composed by (BaTiO3)1,x,(CoFe2O4)x with different cobalt ferrite concentrations (x) have been deposited by pulsed laser ablation on platinum covered Si(001) substrates. The films structure was studied by X-ray diffraction and Raman spectroscopy. It was found that the CoFe2O4 phase unit cell was compressed along the growth direction of the films, and it relaxed with increasing x. The opposite behavior was observed in the BaTiO3 phase where the lattice parameters obtained from the X-ray measurements presented a progressive distortion of its unit cell with increasing x. The presence of the strain in the films induced a blueshift of the Raman peaks of CoFe2O4 that decreased with increasing CoFe2O4 concentration. Cation disorder in the cobalt ferrite was observed for lower x, where the nanograins are more isolated and subjected to more strain, which was progressively decreased for higher CoFe2O4 content in the films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and photoluminescence properties of silicon nanowires treated by high-pressure water vapor annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007B. Salhi Abstract This paper reports on silicon nanowires (SiNWs) growth on porous silicon (PS) template using vapor-liquid-solid (VLS) technique and the effect of high-pressure water vapor annealing (HWA) on their optical properties. Gold nanoparticles (Au NPs) with average mean diameter of 50 and 20 nm were used as catalysts. The SiNWs were obtained by thermal decomposition of silane gas (SiH4) at high temperature (540 °C) catalyzed by the Au NPs. The resulting nanostructures display comparable diameter to the initial gold catalysts and are few microns long without a preferential growth direction. We have next examined the optical properties of the 20 nm diameter SiNWs. As-prepared SiNWs display a weak photoluminescence (PL), which is related to the recombination emissions from defect centers. High-pressure water vapor annealing (HWA) at 260 °C and 2.6 MPa of the SiNWs led to an increase of the PL by a factor 10 without significant changes in the emission band. TEM analysis of the HWA-treated SiNWs showed a crystalline silicon core surrounded by an amorphous oxide layer. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||