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Tilt Angle (tilt + angle)
Kinds of Tilt Angle Selected AbstractsStudies on the structural, thermal and optical behaviour of solution grown organic NLO material: 8-hydroxyquinolineCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007N. Vijayan Abstract Single crystal of 8-hydroxyquinoline (8HQ) having chemical formula C9H7NO, an organic nonlinear optical (NLO) material has been successfully grown by slow evaporation solution growth technique at room temperature. The crystal system has been confirmed from the powder X-ray diffraction (PXRD) analysis. The crystalline perfection was evaluated by high resolution X-ray diffractometry (HRXRD). From this analysis we found that the quality of the crystal is quite good. However, a very low angle (tilt angle 14 arc sec) boundary was observed which might be due to entrapping of solvent molecules in the crystal during growth. Its optical behavior has been examined by UV-Vis. analysis, which shows the absence of absorbance between the wavelengths ranging from 400 to 1200 nm. From the thermal analysis it was observed that the material exhibits single sharp weight loss starting at 113°C without any degradation. The laser damage threshold was measured at single shot mode and the SHG behavior has been tested using Nd:YAG laser as a source. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thickness-Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films,ADVANCED FUNCTIONAL MATERIALS, Issue 17 2007H.-L. Cheng Abstract Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (,tilt) of the pentacene molecule from the c- axis toward the a- axis. We propose a growth model that rationalizes the ,tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C,C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries. [source] Photoresponsive Ferroelectric Liquid-Crystalline PolymersADVANCED FUNCTIONAL MATERIALS, Issue 1 2007P. Beyer Abstract The photoresponse of ferroelectric smectic side-chain liquid-crystalline (LC) polymers containing a photoisomerizable azobenzene derivative as a covalently linked photochromic side group is investigated. By static measurements in different photostationary states, the effect of trans,cis isomerization on the material's phase-transition temperatures and its ferroelectric properties (spontaneous electric polarization PS and director tilt angle ,) are analyzed. It turns out that the Curie temperature (transition SC* to SA) can be reversibly shifted by up to 17,°C. The molecular mechanism of this "photoferroelectric effect" is studied in detail using time-resolved measurements of the dye's optical absorbance, the director tilt angle, and the spontaneous polarization, which show a direct response of the ferroelectric parameters to the molecular isomerization. The kinetics of the thermal reisomerization of the azo dye in the LC matrix are evaluated. A comparison to the reisomerization reaction in isotropic solution (toluene) reveals a faster thermal relaxation of the dye in the LC phase. [source] Ultrahigh-Crystalline-Quality Silicon Pillars Formed by Millimeter-Wave Annealing of Amorphous Silicon on GlassADVANCED MATERIALS, Issue 29 2009Fude Liu Silicon pillars are formed by millisecond-long, single-pulse annealing of 110,GHz millimeter-wave radiation incident upon intrinsic amorphous silicon (a-Si) thin films deposited on glass by hot-wire chemical vapor deposition. The image was taken at a sample tilt angle of 52° for a better 3D view. [source] Experimental study of the combustion efficiency and formation of NOx in an industrial pulverized coal combustorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2004Li ZhengQi Abstract With horizontal bias combustion burners, experiments have been carried out on a 670 t h,1, corner-fired, pulverized-coal fired boiler burning bituminous coal. At 200 MWe load, the furnace excess O2 remains stable. The different horizontal fuel biases are obtained by changing the tilt angle of all the Louvre enrichers' regulating blades. The tilt angles of the blades are 0, 15, 24, 32°; the result is that the enriching ratios of the fuel-rich primary air increase from 2.2 to 2.6 at No. 2 corner, and from 1.2 to 4.2 at No. 3 corner. The gas temperature increases in the burner region. The application of the horizontal bias combustion burners results in a reduction in NOx formation from 545.7 mg Nm,3 (O2=6%) to 287.9 mg Nm,3, and a substantial reduction in carbon in ash content from 5.24 to 2.48%. The boiler operated stably at a load of 80 MWe without auxiliary fuel oil. Copyright © 2004 John Wiley & Sons, Ltd. [source] Comparison of energy and exergy efficiencies of an underground solar thermal storage systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2004H. Hüseyin Öztürk Abstract In this experimental study, solar energy was stored daily using the volcanic material with the sensible heat technique. The external heat collection unit consisted of 27 m2 of south-facing solar air collectors mounted at a 55° tilt angle. The dimensions of the packed-bed heat storage unit were 6 × 2 × 0.6 m deep. The packed-bed heat storage unit was built under the soil. The heat storage unit was filled with 6480 kg of volcanic material. Energy and exergy analyses were applied in order to evaluate the system efficiency. During the charging periods, the average daily rates of thermal energy and exergy stored in the heat storage unit were 1242 and 36.33 W, respectively. Since the rate of exergy depends on the temperature of the heat transfer fluid and surrounding, the rate of exergy increased as the difference between the inlet and outlet temperatures of the heat transfer fluid increased during the charging periods. It was found that the average daily net energy and exergy efficiencies in the charging periods were 39.7 and 2.03%, respectively. The average daily net energy efficiency of the heat storage system remained nearly constant during the charging periods. The maximum energy and exergy efficiencies of the heat storage system were 52.9 and 4.9%, respectively. Copyright © 2004 John Wiley & Sons, Ltd. [source] Modelling of diffraction from fibre texture gradients in thin polycrystalline filmsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2007M. Birkholz Crystallographic textures in thin polycrystalline films typically exhibit a rotational symmetry, i.e. they occur as a fibre texture with the texture pole being orientated in the direction of the substrate normal. As a further characteristic of thin-film textures, it was often observed that the degree of preferred orientation increases with increasing thickness. It is shown in this work how a fibre texture gradient may be modelled in kinematical X-ray diffraction and which effects it has on the intensity mapping of the IHKL reflection, when the HKL pole is the fibre axis. A general expression for IHKL is derived for a depth-dependent fibre texture that is based on the finite Laplace transform of the texture distribution. The concept is outlined for the cosn, function to model the tilt-angle dependence of intensity, with the parameter n denoting the degree of texture. It is found that the measured intensity distribution sensitively depends on the ratio of texture gradient over X-ray attenuation coefficient. For particular cases, it is found that the maximum intensity may occur for non-zero tilt angles and thus arise at a different tilt angle from the pole of the fibre texture. [source] Direct Scanning Electron Microscopy Imaging of Ferroelectric Domains After Ion MillingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Daniel Grüner A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O3. Stable high-resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain- and defect-free surface generated by gentle ion milling, pronounced orientation contrast is observed. [source] A simple method for simultaneous measurement of the tilt angle and temperatureMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2007Jinhua Yan Abstract A simple and compact sensor for simultaneous measurement of the tilt angle and temperature is presented. The sensor is composed of a fiber taper and a fiber Bragg grating. The tilt angle is measured by monitoring the tilt-induced loss of the taper. The grating is used for enhancing the tilt angle sensitivity as well as monitoring the wavelength shift induced by the temperature variation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2248,2250, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22701 [source] Anatomical information is needed in ultrasound imaging of muscle to avoid potentially substantial errors in measurement of muscle geometryMUSCLE AND NERVE, Issue 5 2009Menno R. Bénard MSc Abstract This study validates two-dimensional (2D) ultrasound measurements of muscle geometry of the human medial gastrocnemius (GM) and investigates effects of probe orientation on errors in these measurements. Ultrasound scans of GM muscle belly were made both on human cadavers (n = 4) and on subjects in vivo (n = 5). For half of the cadavers, ultrasound scans obtained according to commonly applied criteria of probe orientation deviated 15° from the true fascicle plane. This resulted in errors of fascicle length and fascicle angle up to 14% and 23%, respectively. Fascicle-like structures were detectable over a wide range of probe tilt and rotation angles, but they did not always represent true fascicles. Errors of measurement were either linear or quadratic functions of tilt angle. Similar results were found in vivo. Therefore, we conclude that similar errors are likely to occur for in vivo measurements. For all cadavers, at the distal end of GM, the true fascicle plane was shown to be perpendicular to the distal aponeurosis. Using transverse images of GM to detect the curvature of the deep aponeurosis at the distal end of the muscle belly is a simple strategy to help identify the fascicle plane. For subsequent longitudinal imaging, probe alignment within this plane will help minimize measurement errors of fascicle length, fascicle angle, and muscle thickness. Muscle Nerve, 2009 [source] Temperature dependence of structural parameters in the perovskite Na0.74WO3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2005C. N. W. Darlington Abstract NaxWO3 undergoes three phase transitions involving tilting of the oxygen octahedra about ,100, pseudocubic directions. We have measured the temperature dependence of the lattice parameters between 200 and 750 K , a temperature range that spans the three transitions , and determined the evolution of the structure within each phase as temperature changes. The experiments were performed on the high-resolution powder diffractometer HRPD, Rutherford Appleton Laboratory, UK, using time-of-flight neutron diffraction. The critical exponent that describes the temperature dependence of the total tilt angle has been evaluated. An unexpected change in the thermal expansion coefficient in the cubic phase is not understood: an argument based on Landau's theory of phase transitions is used to demonstrate that the change is not the result of co-existence of two phases. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] MOCVD n-InAs thin layers compared with MBE samples , far infrared magnetophotoconductivityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2003Z. Romanowski Abstract A comparison of the properties of n-InAs thin layers grown by the MOCVD method and, reported elsewhere, similar samples obtained by MBE processing is presented. The measured photoconductivity spectra exhibit a variety of peaks, among them , very narrow peaks (with the halfwidths of ,20 mT) due to cyclotron resonance (CR) and impurity cyclotron resonance (ICR) transitions. Measurements with tilted magnetic field allowed to correlate peaks with the CR or ICR transitions in the different sample regions: with 2D and 3D electron gas. The detailed analysis shows, that we observe peaks with positions more strongly dependent on the magnitude of the tilt angle than the standard 1/cos,, (, is a sample tilt angle) dependence. These lines were not observed in MBE samples. Results are discussed in terms of a correspondence between the distribution of carriers and the spatial structure of the sample. As a result one can state, that the MOCVD samples seem to have the same quality as samples obtained by the MBE method. [source] Conformational changes induced by a single amino acid substitution in the trans -membrane domain of Vpu: Implications for HIV-1 susceptibility to channel blocking drugsPROTEIN SCIENCE, Issue 10 2007Sang Ho Park Abstract The channel-forming trans -membrane domain of Vpu (Vpu TM) from HIV-1 is known to enhance virion release from the infected cells and is a potential target for ion-channel blockers. The substitution of alanine at position 18 by a histidine (A18H) has been shown to render HIV-1 infections susceptible to rimantadine, a channel blocker of M2 protein from the influenza virus. In order to describe the influence of the mutation on the structure and rimantadine susceptibility of Vpu, we determined the structure of A18H Vpu TM, and compared it to those of wild-type Vpu TM and M2 TM. Both isotropic and orientationally dependent NMR frequencies of the backbone amide resonance of His18 were perturbed by rimantadine, and those of Ile15 and Trp22 were also affected, suggesting that His18 is the key residue for rimantadine binding and that residues located on the same face of the TM helix are also involved. A18H Vpu TM has an ideal, straight ,-helix spanning residues 6,27 with an average tilt angle of 41° in C14 phospholipid bicelles, indicating that the tilt angle is increased by 11° compared to that of wild-type Vpu TM. The longer helix formed by the A18H mutation has a larger tilt angle to compensate for the hydrophobic mismatch with the length of the phospholipids in the bilayer. These results demonstrate that the local change of the primary structure plays an important role in secondary and tertiary structures of Vpu TM in lipid bilayers and affects its ability to interact with channel blockers. [source] On the determination of fiber tilt angles in fiber diffractionACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009Norbert Stribeck The common digital method that is used to eliminate the effect of fiber tilt from fiber diffraction patterns is based on an approximation given by Franklin & Gosling [Acta Cryst. (1953), 6, 678,685]. The estimate of the tilt angle is iteratively optimized in the so-called `Fraser correction'. Building on the fundamental work of Polanyi [Z. Phys. (1921), 7, 149,180], the exact solution is presented. [source] Association between Attributes of a Cyclist and Bicycle Seat PressureTHE JOURNAL OF SEXUAL MEDICINE, Issue 10 2010Eadric Bressel PhD ABSTRACT Introduction., Bicycle seat pressure is thought to be the principal risk factor for bicycle seat injuries such as erectile dysfunction; however there is a lack of understanding regarding the characteristics of a cyclist that predict bicycle seat pressure. Aim., The purpose of this study was to determine if select attributes of a cyclist are associated with seat pressure during stationary bicycling. A secondary purpose was to determine which of the associated attributes were the best predictors of seat pressure and if they were consistent between two different seats. Methods., There were two data collection phases to this correlational study in which 40 males between the ages 20 and 50 years volunteered. For the first phase, select attributes of the cyclist (age, weight, flexibility, experience level, and ischial tuberosity width) were measured. The second phase required participants to ride a stationary cycle ergometer while pelvic tilt angles and seat pressures were measured on two different traditional seats. Main Outcome Measure., The main outcome is the mean and peak bicycle seat interface pressure over the anterior and total seat. Results., Body weight explained up to 50% of the variance in mean total seat pressure (P = 0.001). Regarding peak total pressure, pelvic tilt angle and flexibility explained 43% and 17% of the variance, respectively, for the two seats tested (P = 0.01). Conclusion., These results indicate that predictors of mean seat pressure are not the same for peak pressure. Body weight alone accounted for the most variance in mean pressure whereas pelvic tilt and flexibility accounted for the most variance in peak pressure. These variables related to seat pressure may give some guidance to cyclists and clinicians who intend to prevent or alleviate the symptoms associated with bicycle seat injuries that include erectile dysfunction. Bressel E, Nash D, and Dolny D. Association between attributes of a cyclist and bicycle seat pressure. J Sex Med 2010;7:3424,3433. [source] Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn,Teller transitions in ABX3 perovskites.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009The structural evolution of selected perovskites containing Jahn,Teller cations has been investigated in the light of a formal analysis of symmetry hierarchies for phase transitions driven by octahedral tilting and Jahn,Teller cooperative distortions. General expressions derived from the strain/order-parameter coupling relationships allowed by symmetry are combined with observed changes in lattice parameters to reveal details of order-parameter evolution and coupling. LuVO3, YbVO3, YVO3 and CeVO3 are representative of systems which develop Jahn,Teller ordering schemes associated with irreducible representations and of the space group . Tilting of their octahedra is associated with and . The Pnma ( tilting) ,P21/a ( tilting, Jahn,Teller order) transition below room temperature is close to second order in character. Shear strains which depend primarily on tilt angles show little variation, implying that there is only weak coupling between the tilting and Jahn,Teller order parameters. The subsequent P21/a,Pnma ( tilting, Jahn,Teller order) is first order in character, and involves either a reduction in the tilt angle or a change in the strength of tilt/Jahn,Teller order-parameter coupling. In LaMnO3, the isosymmetric Pnma ( tilting) ,Pnma ( tilting, Jahn,Teller order) transition can be described in terms of a classical first-order transition conforming to a 246 Landau expansion with negative fourth-order coefficients. Strain evolution in Ba-doped samples suggests that the transition becomes second order in character and reveals a new strain relaxation mechanism in LaMnO3 which might be understood in terms of local strain heterogeneities due to the disordering of distorted MnO6 octahedra. Transitions in PrAlO3 and La0.5Ba0.5CoO3 illustrate the transformation behaviour of systems in which the Jahn,Teller ordering scheme is associated with the irreducible representation . Overall, coupled tilting + Jahn,Teller phase transitions in perovskites conform to mean-field behaviour, consistent with the underlying role of strain in promoting long interaction lengths. [source] Magnetoresistance in dilute p-Si/SiGe in parallel and tilted magnetic fieldsANNALEN DER PHYSIK, Issue 12 2009I.L. Drichko Abstract We report the results of an experimental study of the magnetoresistance ,xx and ,xy in two samples of p-Si/SiGe with low carrier concentrations p = 8.2 × 1010 cm -2 and p = 2 × 1011 cm -2. The research was performed in the temperature range of 0.3,2 K and in the magnetic fields of up to 18 T, parallel or tilted with respect to the two-dimensional (2D) channel plane. The large in-plane magnetoresistance can be explained by the influence of the in-plane magnetic field on the orbital motion of the charge carriers in the quasi-2D system. The measurements of ,xx and ,xy in the tilted magnetic field showed that the anomaly in ,xx, observed at filling factor , = 3/2 is practically nonexistent in the conductivity ,xx. The anomaly in ,xx at , = 2 might be explained by overlapping of the levels with different spins 0 , and 1 , when the tilt angle of the applied magnetic field is changed. The dependence of g-factor g*(,)/g*(00) on the tilt angle , was determined. [source] Determination of grave locations in Dedemezari Necropolis (Western Turkey) using magnetic field derivativesARCHAEOLOGICAL PROSPECTION, Issue 4 2008A. Büyüksaraç Abstract The location of the study area for this research of a Middle Bronze Age Necropolis is situated in the west of Turkey near Afyonkarahisar. Magnetic surveying was carried out in two adjacent areas (Areas 4 and 5). Four trenches have been excavated so far and graves were located in positions interpreted from a magnetic survey carried out in 2005. Initial excavations have shown that cist, pithos and simple graves were placed randomly and it is suggested that Dedemezari Necropolis is similar to the well known necropoleis of Gordion and Sariket. This paper compares the results of some phase-based filters which show improved performance as edge detectors in different ways. The filters are demonstrated on synthetic magnetic data and magnetic field data from Dedemezari Necropolis. Magnetic field derivatives, both vertical and horizontal, are common and useful tools for interpretation of the magnetic anomalies. Interpretation of magnetic field derivatives, separately or together, provide images of shallow bodies from magnetic data. The horizontal derivatives of the total magnetic field were computed in the space domain by means of finite-difference relationships, and the vertical derivative was computed in the frequency domain by using fast Fourier transform filtering. Derivatives of the magnetic anomalies have been used for detection of causative bodies. The analytic signal (AS), the enhanced horizontal derivative (EHD), tilt derivative (TD), theta map, hyperbolic tilt angle (HTA) and total horizontal derivative (THDR) methods were applied not only to synthetic anomalies but also to the measured magnetic anomalies of Areas 4 and 5. However, AS and EHD produced the best results as the other methods created edge effects. Copyright © 2008 John Wiley & Sons, Ltd. [source] Antibody-immobilized column for quick cell separation based on cell rollingBIOTECHNOLOGY PROGRESS, Issue 2 2010Atsushi Mahara Abstract Cell separation using methodological standards that ensure high purity is a very important step in cell transplantation for regenerative medicine and for stem cell research. A separation protocol using magnetic beads has been widely used for cell separation to isolate negative and positive cells. However, not only the surface marker pattern, e.g., negative or positive, but also the density of a cell depends on its developmental stage and differentiation ability. Rapid and label-free separation procedures based on surface marker density are the focus of our interest. In this study, we have successfully developed an antiCD34 antibody-immobilized cell-rolling column, that can separate cells depending on the CD34 density of the cell surfaces. Various conditions for the cell-rolling column were optimized including graft copolymerization, and adjustment of the column tilt angle, and medium flow rate. Using CD34-positive and -negative cell lines, the cell separation potential of the column was established. We observed a difference in the rolling velocities between CD34-positive and CD34-negative cells on antibody-immobilized microfluidic device. Cell separation was achieved by tilting the surface 20 degrees and the increasing medium flow. Surface marker characteristics of the isolated cells in each fraction were analyzed using a cell-sorting system, and it was found that populations containing high density of CD34 were eluted in the delayed fractions. These results demonstrate that cells with a given surface marker density can be continuously separated using the cell rolling column. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Synthesis of ansa- [n]Silacyclopentadienyl,Cycloheptatrienyl,Chromium Complexes (n = 1, 2): Novel Precursors for Polymers Bearing Chromium in the BackboneCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2006Alexandra Bartole-Scott Abstract Reaction of [(,5 -C5H4Li)(,7 -C7H6Li)Cr],tmeda with a variety of dialkyl(dichloro)silanes in aliphatic solvents afforded the corresponding [1]silatrochrocenophanes. Structural characterization by X-ray diffraction analysis of the [1]silatrochrocenophanes bearing Me2Si, (iPr)2Si, and silacyclobutane bridges revealed tilt angles , of 15.56(12)°, 15.8(1)°, and 16.33(17)°, respectively. Analogously, a [2]silatrochrocenophane (6) was prepared in excellent yield by reaction of [(,5 -C5H4Li)(,7 -C7H6Li)Cr],tmeda with 1,2-dichloro-1,1,2,2-tetramethyldisilane. This complex also was characterized structurally and exhibited a tilt angle , of 2.60(15)°. The [1]silatrochrocenophane bearing the Me2Si bridge underwent facile and regioselective carbon,silicon bond cleavage with [Pt(PEt3)4] to give a very high yield of an oxidative addition product. The ring-opening polymerization of these novel [1]silatrochrocenophanes afforded ring-opened chromium-based polymers. [source] Systematic Variation of Length Ratio and the Formation of Smectic A and Smectic C PhasesCHEMPHYSCHEM, Issue 10 2010Nadia Kapernaum Abstract The phase diagrams of four binary mixtures of chemically similar smectogenic mesogens differing only in molecular length are investigated. In these bidisperse systems the length ratio varies systematically. The phase diagrams show the stabilization of the smectic A and the destabilization of the smectic C phase with increasing length ratio as a general trend. Detailed small-angle X-ray diffraction and electro-optic measurements revealed a decrease in smectic translational order and a continuous reduction of the tilt angle with increasing length difference. These surprising results are of general interest for the understanding of the structure and dynamics of smectic phases. The remarkably strong impact of the length difference on the smectic layer structure and the phase behavior is discussed from a mechanistic point of view taking into account sterical interactions. For the observed structural changes in these bidisperse smectics we propose pronounced out-of-layer fluctuations with increasing length difference as driving force, causing neighboring molecules within nearest layer into a smectic A-like packing. [source] Electron Tunneling through Molecular Media: A Density Functional Study of Au/Dithiol/Au SystemsCHEMPHYSCHEM, Issue 9 2005Qiang Sun Dr. Abstract We report a density functional theory study of the electronic properties of n -alkanedithiols (CnS2, with n=4, 8 and 12) sandwiched between two Au(111) infinite slab electrodes. We investigate the influence of the distance between the two electrodes and of the molecular chain length, tilt angle, and coverage on the local density of states (LDOS) at the Fermi energy (Ef). We find that the (small) value of the LDOS at Efnear the center of the molecular wires,a quantity that is related to the tunneling current,is mainly determined by the length n of the alkane chains: it originates from the tails of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) which are broadened by the interaction with the electrodes, and decays exponentially with the length of the molecular wire. This opens a nonresonance tunneling channel for charge transport at small bias voltages. While the length of the hydrocarbon chain appears to be the determining factor, the tilt angle of the molecular wires with respect to the electrode surfaces, and therefore the distance between these, has a small influence on the LDOS at the center of the molecule, while the effect of coverage can be ignored. The picture which emerges from these calculations is totally consistent with a through-bond tunneling mechanism. [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] Application of sandy bed solar collector system for water extraction from airINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2006A. E. KabeelArticle first published online: 13 JAN 200 Abstract Extracting water from air by using sandy bed solar collector system is explored in the current paper. The system is studied theoretically and experimentally to evaluate the performance of the sandy bed impregnated with 30% concentration CaCl2 to produce water from moist air. In addition, the system was investigated at three different tilt angles: 15°, 20° and 25°. The theoretical model was constructed to study the effect of various parameters including solution concentration, and solar radiation intensity on the amount of collected water. Results show that sandy bed is effective for collecting water from moist air. The system can provide up to about 1.2-l fresh water per square meter of glass cover per day. A reasonable agreement between theoretical results and experimental measurements is achieved. Results show also that a slight increase in the system productivity can be generated for 25° inclination angle. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modelling of diffraction from fibre texture gradients in thin polycrystalline filmsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2007M. Birkholz Crystallographic textures in thin polycrystalline films typically exhibit a rotational symmetry, i.e. they occur as a fibre texture with the texture pole being orientated in the direction of the substrate normal. As a further characteristic of thin-film textures, it was often observed that the degree of preferred orientation increases with increasing thickness. It is shown in this work how a fibre texture gradient may be modelled in kinematical X-ray diffraction and which effects it has on the intensity mapping of the IHKL reflection, when the HKL pole is the fibre axis. A general expression for IHKL is derived for a depth-dependent fibre texture that is based on the finite Laplace transform of the texture distribution. The concept is outlined for the cosn, function to model the tilt-angle dependence of intensity, with the parameter n denoting the degree of texture. It is found that the measured intensity distribution sensitively depends on the ratio of texture gradient over X-ray attenuation coefficient. For particular cases, it is found that the maximum intensity may occur for non-zero tilt angles and thus arise at a different tilt angle from the pole of the fibre texture. [source] Two-dimensional small-angle X-ray scattering of self-assembled nanocomposite films with oriented arrays of spheres: determination of lattice type, preferred orientation, deformation and imperfectionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007Bernd M. Smarsly Mesostructured oxide films were prepared by dip-coating from colloidal solutions on ultrathin Si wafers and solidified by heating at various temperatures. Two-dimensional small-angle X-ray scattering measurements were carried out in transmission under selected tilt angles and evaluated by comparison with analytical expressions. The films are composed of oriented mesophases, the structures of which are defined in terms of lattice type, preferred orientation, deformation and imperfection, notably stacking faults. [source] Rapid determination of stress factors and absolute residual stresses in thin filmsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2006E. Eiper A methodology is presented that allows the determination of experimental stress factors in thin films on the basis of static diffraction measurements. The approach relies on the characterization of thin films deposited on a monocrystalline substrate serving as a mechanical sensor. Rocking-curve measurements of the symmetrical reflections of the substrate are used to determine the substrate curvature and subsequently the macroscopic stress imposed on the film. The elastic strain in the film is determined by lattice-spacing measurement at different sample tilt angles. The calculated experimental stress factors are applied to thin films deposited on other types of substrates and are used to determine the absolute magnitude of the residual stress. The approach is applied to nanocrystalline TiN and CrN thin films deposited on Si(100) and steel substrates, characterized using a laboratory-type ,/, goniometer. [source] On the determination of fiber tilt angles in fiber diffractionACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009Norbert Stribeck The common digital method that is used to eliminate the effect of fiber tilt from fiber diffraction patterns is based on an approximation given by Franklin & Gosling [Acta Cryst. (1953), 6, 678,685]. The estimate of the tilt angle is iteratively optimized in the so-called `Fraser correction'. Building on the fundamental work of Polanyi [Z. Phys. (1921), 7, 149,180], the exact solution is presented. [source] Association between Attributes of a Cyclist and Bicycle Seat PressureTHE JOURNAL OF SEXUAL MEDICINE, Issue 10 2010Eadric Bressel PhD ABSTRACT Introduction., Bicycle seat pressure is thought to be the principal risk factor for bicycle seat injuries such as erectile dysfunction; however there is a lack of understanding regarding the characteristics of a cyclist that predict bicycle seat pressure. Aim., The purpose of this study was to determine if select attributes of a cyclist are associated with seat pressure during stationary bicycling. A secondary purpose was to determine which of the associated attributes were the best predictors of seat pressure and if they were consistent between two different seats. Methods., There were two data collection phases to this correlational study in which 40 males between the ages 20 and 50 years volunteered. For the first phase, select attributes of the cyclist (age, weight, flexibility, experience level, and ischial tuberosity width) were measured. The second phase required participants to ride a stationary cycle ergometer while pelvic tilt angles and seat pressures were measured on two different traditional seats. Main Outcome Measure., The main outcome is the mean and peak bicycle seat interface pressure over the anterior and total seat. Results., Body weight explained up to 50% of the variance in mean total seat pressure (P = 0.001). Regarding peak total pressure, pelvic tilt angle and flexibility explained 43% and 17% of the variance, respectively, for the two seats tested (P = 0.01). Conclusion., These results indicate that predictors of mean seat pressure are not the same for peak pressure. Body weight alone accounted for the most variance in mean pressure whereas pelvic tilt and flexibility accounted for the most variance in peak pressure. These variables related to seat pressure may give some guidance to cyclists and clinicians who intend to prevent or alleviate the symptoms associated with bicycle seat injuries that include erectile dysfunction. Bressel E, Nash D, and Dolny D. Association between attributes of a cyclist and bicycle seat pressure. J Sex Med 2010;7:3424,3433. [source] Octahedral tilt twinning and compositional modulation in NaLaMgWO6ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009Graham King A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9,Å, which corresponds to a 12ap× 2ap× 2ap superstructure of the simple perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a,a,c0 with tilt angles of ,,8° about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6ap. Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A -site cations is necessary to explain the experimental images. [source] | |||||||||||||||||||||||||