True Width Research Articles

Off-axis electron holography of pseudo-spin-valve thin-film magnetic elements

Magnetic remanent states in a rectangular array of 75×280-nm2NiFe∕Cu∕Co thin-film pseudo-spin-valve elements are studied using off-axis electron holography in the transmission electron microscope (TEM). An approach based on focused ion-beam milling is used to minimize damage to the magnetic properties of the elements during preparation for TEM examination in plan-view geometry. Experimental electron holographic phase images are used to measure the switching fields of the Co and NiFe layers in each of three adjacent elements separately, and comparisons with micromagnetic simulations are used to infer the true magnetic thicknesses and widths of the layers. Demagnetizing fields are included in the discussion of the results, and the possibility that the conclusions may be affected by the procedure used to analyze the holograms is discussed.

Effects of along- and cross-radar-beam winds on Doppler radar spectrum

Abstract. Beam broadening effects on the Doppler radar spectrum induced by along- and cross-radar-beam winds are theoretically investigated in this article. Analytical expression of beam broadening spectrum for a vertical beam subject to a constant vertical wind in the absence of horizontal wind is derived first. We find that the resultant beam broadening spectral shape is in an exponential form, rather than a Gaussian shape. The peak of the exponential spectrum corresponds to the true vertical wind velocity, and the spectral width σ is a function of vertical wind velocity w and the half-power beam width θ1/2 of the radar beam, in accordance with the expression σ=0.09wθ1/22. The beam broadening spectrum for a vertical radar beam subject to both vertical and horizontal winds is numerically studied, and the result shows that the spectral shape is distorted from the Gaussian form. The estimated vertical wind velocity of the distorted spectrum is very close to the true vertical wind velocity with a difference of less than 0.6% for a typical case. However, its spectral width is substantially greater than that of the conventional Gaussian spectrum broadened by horizontal wind only. The difference of the spectral widths Δσ (in unit of percentage) in the two, as a function of the half-power beam width and the ratio of vertical to horizontal wind velocities, can be well approximated by a parabolic equation. With this equation and the conventional Gaussian beam broadening spectral width caused by horizontal wind, the true width of the distorted beam broadening spectrum induced by vertical and horizontal winds can be inferred without complicated numerical computation. Through a transformation of wind velocity from vertical and horizontal winds into along- and cross-radar-beam winds defined on the cross section of an oblique radar beam, the results obtained from the case of vertical radar beam can be directly applied to the case of the oblique beam. We show that in some special cases the beam broadening spectral widths of an oblique beam subject to both vertical and horizontal winds will be exceedingly narrower than those estimated by the existing formula, irrespective of the presence of strong horizontal wind velocity.

Comparison of Radio Observations and Numerical Simulations of the Radio Lobes of Cygnus A

We present a comparison of radio observations of the powerful archetypal radio galaxy Cyg A and two-dimensional numerical hydrodynamic simulations. We characterize some global trends in the observed radio properties and compare them with the properties of a simulated radio source. The observational results are the following. The width of the observed surface brightness distribution perpendicular to the source axis can be well characterized by a Gaussian over most of the length of the source. The ratio of the Gaussian FWHM to the second moment is fairly constant along the source, with an average value of about 2.5, indicating that they give roughly consistent measurements of the source width. The average observed surface brightness, estimated pressure, and estimated minimum-energy B-field decrease with distance from the hot spots. We find evidence for significant structure in the estimated cross-sectional slices of the emissivity. The numerical results are the following. Jets propagating in a constant-density atmosphere decelerate with time. Thus, the estimated dynamical age of the source is greater than the actual age of the source. For a source similar to Cyg A, the difference is about a factor of 2. The second moment gives an accurate representation of the width of the simulated source. The Gaussian FWHM tends to be about 40% larger than the true width and can be systematically in error if the surface brightness exhibits multiple peaks. We suggest that the ratio of the Gaussian FWHM to the second moment may be a diagnostic of the emissivity profile in the lobes. The simulations can qualitatively reproduce the overall observed morphology, the behavior of the cross sections in surface brightness, the decline in surface brightness with distance from the hot spots, and the width of the lobes. This suggests that the two-dimensional simulations give a reasonable representation of the properties of Cyg A.

Possibility of measuring the width of narrow Fe II astrophysical laser lines in the vicinity of η Carinae by means of Brown–Twiss–Townes heterodyne correlation interferometry

We consider the possibility of measuring the true width of the narrow Fe II optical lines observed in spectra of the Weigelt blobs in the vicinity of η Carinae. The lines originate as a result of stimulated amplification of spontaneous emission of radiation in quantum transitions between energy levels showing inverted population [Johansson, S., Letokhov, V., 2002. JETP Lett. 75 (10) 495; Johansson, S., Letokhov, V., 2003. Phys. Rev. Lett. 90 (1) 01110-1; Johansson, S., Letokhov, V., 2004. A&A 428,497]. The lines should have a subDoppler spectral width of 30–100MHz, depending on the geometry of the lasing volume. To make measurements with a spectral resolution of R>107 and an angular resolution better than 0.1″, we suggest the use of the Brown–Twiss–Townes optical heterodyne intensity correlation interferometry. The estimates made of the S/N ratio for the optical heterodyne astrophysical laser experiment imply that it is feasible.

Raman line shape of the A1 longitudinal optical phonon in GaN

High-resolution Raman measurements of the A1 longitudinal optical (LO) phonon in GaN reveal a complex line shape that can be explained in terms of the angular dispersion of LO phonons in this material. A simple geometrical model of the line shape makes it possible to extract the true anharmonic full width at half maximum 2Γ of the A1(LO) mode. The value of this parameter, 2Γ=2.4 cm−1 at 20 K, is in much better agreement with time-domain measurements by Tsen and co-workers [Appl. Phys. Lett. 72, 2132 (1998)] than any previous frequency-domain measurement. The results indicate that angular dispersion effects must be carefully considered in any analysis of Raman spectra from noncubic crystals.

Asymptotic theory for bent-cable regression—the basic case

We use what we call the bent-cable model to describe potential change-point phenomena. The class of bent cables includes the commonly used broken stick (a bent cable without a bend segment). Theory for least-squares (LS) estimation is developed for the basic bent cable, whose incoming and outgoing linear phases have slopes 0 and 1, respectively, and are joined smoothly by a quadratic bend. Conditions on the design are given to ensure regularity of the estimation problem, despite non-differentiability of the model's first partial derivatives (with respect to the covariate and model parameters). Under such conditions, we show that the LS estimators (i) are consistent, regardless of a zero or positive true bend width; and (ii) asymptotically follow a bivariate normal distribution, if the underlying cable has all three segments. In the latter case, we show that the deviance statistic has an asymptotic chi-squared distribution with two degrees of freedom.

Resonance states of hydrogen nuclei 4H and 5H obtained in transfer reactions with exotic beams

Experimental search for 4H and 5H has been performed in the reactions 3H(t,p) 5H, 2H( 6He, 3He) 5H and 2H(t,p) 4H. A resonance state situated at 1.8±0.1 MeV above the t+n+n decay threshold is obtained in the missing mass energy spectrum of the 5H nucleus. Also, there is an indication that another resonance located at 2.7±0.1 MeV presents in this spectrum. Visible peak widths are governed mostly by the instrumental resolution, which came to about 0.4 MeV. We set an upper limit of 0.5 MeV on the true width of any of the two states. The resonance state of 4H with E res = 3.3 ± 0.2 MeV and Γ res = 4.1 ± 0.3 Mev was obtained in the 2H(t,p) 4H reaction.

Dissociating perception and action in Kanizsa's compression illusion.

When a horizontally elongated surface is occluded in the middle by a larger surface, it appears narrower than its true width (Kanizsa's compression illusion). We report that a similar compression effect occurs for closed-loop visuomotor matches of size, but not for otherwise comparable open-loop "mimed" reaching or size-matching visuomotor responses. Our study is the first in which a comparison of size perception in personal space with bilateral actions performed with both hands (instead of precision grips employing the thumb and the index finger) is used to investigate motor responses to Kanizsa's compression illusion. Implications for the current debate on the existence of dissociations between spatial perception and visually controlled actions in personal space are discussed.

Contribution to X-ray analysis of carbo-nitrided steel layers

The non-destructive X-ray diffraction method is used to analyse carbo-nitrided steel layers after wear testing. These measurements are carried out on the two major phases of the material,i.e.the martensite and the retained austenite. Such measurements are particularly difficult for three reasons. First, strong gradients exist across the wear track. Second, the diffraction peaks obtained for the martensite are broadened, as a result of the overlap of different reflections of the tetragonal structure. Third, the studied material is multiphase. Its major phases are martensite and austenite, but it also contains carbide and nitride clusters, which lead to incoherent scattering of X-rays. A new quantitative phase analysis method is thus proposed to define the volume fractions of these different constituents of the material. This method accounts for the evolution of the background level during wear. A micro-mechanical model is then developed to process the diffraction peak positions obtained for the martensite and the retained austenite. This model defines the `true' stress and carbon content of both phases. It also allows separation of the reflections of the martensite. The true widths of the diffraction peaks, which characterize the plastic deformation, can thus be quantified. Results for wear-test specimens show a strong plastic deformation of the retained austenite during contact fatigue. This leads to a partial transformation of this phase into martensite. In the martensite, on the contrary, the plastic deformation remains low but the carbon content decreases. This is caused by a stress-induced precipitation of carbides.

Possible Local Spiral Galaxy Counterparts to Compact Blue Galaxies at Intermediate Redshift

We identify nearby disk galaxies with optical structural parameters similar to those of intermediate-redshift compact blue galaxies. By comparing H I and optical emission line widths, we show that the optical widths substantially underestimate the true kinematic widths of the local galaxies. By analogy, optical emission line widths may underrepresent the masses of intermediate-z compact objects. For the nearby galaxies, the compact blue morphology is the result of tidally triggered central star formation; we argue that interactions and minor mergers may cause apparently compact morphology at higher redshift.

Hierarchical structures in mesoscopic fibers that are self-organized by monolayer nano-clusters

Hierarchical structures in fibrous assemblies self-organized from nanometre-sized monolayer clusters are elucidated. Langmuir monolayers of a short chain carboxyazobenzene derivative feature mesoscopic fibrous structures, a monolayer thick, 80 nm apparent width, and over 100 μm long when transferred onto mica from the air–water interface. The effects of pH and salts on the large-scale morphology are followed by atomic force microscopy (AFM) and those of molecular-scale orientation are probed by UV-vis spectroscopy. The large morphological changes, despite no evidence of molecular reorientation, indicate that a small monolayer cluster, rather than a single molecule, is the relevant unit making up a fiber. Furthermore, detailed statistical analyses of the images reveal that nearly all fibers actually consist of a pair of strands, each strand 29 nm wide, that are imaged by the AFM tip, having an effective apex size of 21 nm. The results suggest the following hierarchical structure. Molecules aggregate into a monolayer cluster 29 nm wide. These clusters associate one-dimensionally to form a long monolayer strand. Finally, two strands join together to result in a fiber with a true width of 58 nm.

Diffusion and cluster formation in supersaturated solutions of ammonium sulfate at 298 K

Diffusion coefficients of supersaturated aqueous solutions of ammonium sulfate have been measured at 298°C using Gouy interferometry and were observed to rapidly decrease with increasing concentration in the supersaturated region. Water activities in the supersaturated region were measured by electrodynamic levitation of single solution droplets. The number average cluster size, critical cluster size, degree of association and spinodal concentration were calculated employing these data. These results show that the true metastable zone width is much wider than previously thought with a calculated valve of the spinodal concentration at 69.63 molal.

Nano-indentation of polymer–glass interfaces Part I. Experimental and mechanical analysis

The interface region in polymer/glass composite materials was investigated by means of the nano-indentation and the nano-scratch techniques. The nano-indentation test involved indentations as small as 30 nm in depth in order to detect the material properties in the transition region between the fibre and the matrix. A line of nano indents was produced along the 14 μm path starting from the matrix and ending on the fibre. The distinct properties of the transition zone were revealed by 2–3 indents. The nano-scratch test involves moving a sample while being in contact with a diamond tip. The coefficient of friction, defined as the ratio of the tangential force from the tip–sample contact to the normal force, also indicated a transition zone of different width. Analysis of the results allowed elimination of effects due to: (i) indenter width and its geometry; (ii) stress field and plastic zone interactions, to arrive at true interphase width as a material characteristic. These two techniques proved to be useful tools in the investigation of the size and the character of the interphase region in the fibrous polymer/glass composite materials.

Line broadening and localization mechanisms in CdSe/ZnSe quantum dots

We analyze the line-broadening mechanisms of single CdSe quantum dot (QD) emission lines. A jitter in the emission energy of individual CdSe QDs is reported for the first time. The jitter is caused by the quantum-confined Stark effect induced by the randomly fluctuating charges of defects in the vicinity of the QDs. These random processes lead to a broadening of the emission lines and usually inhibit the determination of a true homogeneous line width. On the other hand, identical jitter allows the unambiguous assignment of groups of emission lines to single QDs. A strong thermal broadening of the QD emission lines is observed. From our observations, parameters of the phase relaxation due to acoustic and LO phonon scattering, which is the main line broadening mechanism, are derived.

Accuracy limits for the determination of cortical width and density: the influence of object size and CT imaging parameters

In this study we analysed the accuracy of computed tomography (CT) measurements in assessing cortical bone. We determined the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods. As a secondary goal, we assessed the ability of CT to reflect small changes in cortical thickness. Two different bone-mimicking phantoms with varying cortical thickness were scanned with single-slice CT on a Somatom Plus 4 scanner. Images were reconstructed with both a standard and a high-resolution convolution kernel. Two special operator-independent segmentation methods were used to automatically detect the edges of the cortical shell. We measured cortical thickness and density and compared the phantom measurements with theoretical computations by simulating a cross-sectional shape of the cortical shell. Based on the simulations, we calculated CT's power to detect small changes in cortical thickness. Simulations and phantom measurements were in very good agreement. Cortical thickness could be measured with an error of less than 10% if the true thickness was larger than 0.9 (0.7) mm for the standard (high-resolution) kernel which is close to the full width at half maximum (FWHM) of the point spread functions for these kernels and our scanner. Density measurements yielded errors of less than 10% for true cortical thickness values above two to three times the FWHM corresponding to 2.5 (2) mm in our case. The simulations showed that a 10% change in cortical width would not be detected with satisfying probability in bones with a cortical shell thinner than 1.2 mm. An accurate determination of the cortical thickness is limited to bones with a thickness higher than the FWHM of the scanner's point spread function. Therefore, the use of a high-resolution reconstruction kernel is crucial. Cortical bone mineral density can only be measured accurately in bones two to three times thicker than this number. In thinner bones, the measured density becomes dependent on the thickness. Changes in cortical thickness can only be assessed if the change is rather large or if the measured bone has sufficient thickness. Therefore, assessing density or thickness of the vertebral shell by CT should be treated with caution.

Tip Characterization from AFM Images of Nanometric Spherical Particles

Since atomic force microscopy (AFM) images are a composite of probe and sample geometry, accurate size determinations are problematic. A relatively straightforward mathematical procedure for determining tip radius of curvature (RT) for an asymmetrical tip was recently developed by Garcia et al. (Probe Microsc. 1997, 1, 107). This study represents an experimental test of that procedure for both silica (∼150 nm) and polystyrene (∼50 nm) nanospheres. The procedure can be summarized by two steps: (1) tip characterization assuming that the observed AFM height is a true measure of a spherical particle's diameter and (2) use of the tip shape to extract a calculated width. To ensure that AFM heights were equivalent to the true width, a direct comparison of individual particle sizes determined by transmission electron microscopy (TEM) and AFM was conducted. Heights measured from AFM images of polystyrene nanospheres differed, on average, less than 5% from widths measured by TEM. The quality of RT values was there...

Investigation of the melt interface between polyethylene and polystyrene using neutron reflectivity

The characteristics of the interface between immiscible polymers, semicrystalline polyethylene (PE) and amorphous deuterated polystyrene (dPS), were determined in the melt state, using the neutron reflectivity technique. The neutron reflectivity profiles of PE-dPS bilayer samples were measured in situ at 150°C in the melt regime giving a melt interfacial roughness, σ 12, of 1.18 ± 0.33 nm. The measured interfacial width consists of a true interfacial width, l t, convoluted with a width, l 0. The latter has been variously described by a number of authors as a capillary wave interfacial width or an initial width. From the true interfacial width the Flory-Huggins-Stavermann interaction parameter, χ, was calculated. The calculated values of χ were shown to differ by almost an order of magnitude from each other depending on the definition of l 0 used. These values are compared with other values of χ obtained via theoretical interpretations of interfacial tension measurements and solubility parameter determination. It is shown that neither definition of l 0 is totally satisfactory.

Characterising the extent of volcanism at the Galapagos Spreading Centre using Deep Tow sediment profiler records

Volcanism at the Galapagos Spreading Centre consists of sheet flows and other distributed extrusives. The surficial volcanics in the axial region should therefore be generally young over a finite area and those on the ridge flanks should be younger, on average, than would be predicted from simple seafloor spreading. A method for determining an upper bound on the mean age anomaly of the flanks, which is interpreted as equivalent to the mean extent of volcanism, is demonstrated using sediment thicknesses digitised from Deep Tow profiler records of the Galapagos Spreading Centre. As found previously, the sediments thicken linearly with distance from the ridge, reflecting simple seafloor spreading up to ∼ 1 Ma. Deviations from the linear trend are due to sediment redistribution (short-wavelength fluctuations) and the age distribution of extrusives, in particular due to large volcanic flows revealed by regions of uniform thickness. The full width of the extrusion zone is obtained by regressing sediment thickness on across-axis distance for both flanks and observing the separation of the two regression lines where they cross zero thickness. Since the method is quantitative and provides an average value for the length of the profile, it is more representative than estimating the width from morphological observations of the spreading axis. Due to scattering from the basement, which obscures sediment in depressions, sediment thickness is generally under-estimated and the measured axial width is an upper bound (10–12 km for the Galapagos Spreading Centre). The mean sediment thickness bias is calculated from high-resolution topography data of lava flows and is ∼ 1.5 m, suggesting that the true mean width of the extrusion zone is 8–10 km. Using this corrected value, the surface of the crust is younger than predicted by seafloor spreading by ∼ 120–150 kyr, on average. This large value implies that the flanks of the Galapagos Spreading Centre are covered with a series of large overlapping volcanic flows.

Cleft Width and Secondary Alveolar Bone Graft Success

Fifty-six cleft sites were reviewed prior to alveolar bone grafting and subsequently evaluated for graft success using study models, periapical and occlusal radiographs from the Lancaster Cleft Palate Clinic. All patients in this sample had presurgical orthodontics to expand and align the maxillary arch prior to alveolar bone grafting. Ninety-five percent of the grafts were done using iliac crest, the remaining 5% were cranial grafts. The alveolar bone grafting technique used was as described by Boyne and Sands (1972, 1976). Cleft width was measured on a radiograph taken no more than 1 month preoperatively, following the completion of all orthodontic expansion. Cleft width was determined by inspection at its narrowest point. A distortion correction was attempted by determining the ratio of the radiographic width of the maxillary central incisor adjacent to the cleft compared with the actual width of this tooth measured on study models. The radiographic cleft width was then multiplied by this factor to approximate true cleft width. Alveolar contour was measured at least 6 months postoperatively using ratios of actual bone heights measured at the mesial, middle, and distal margin of the previous cleft compared with root length of adjacent teeth. This was to eliminate the radiographic distortion factors of foreshortening and elongation. Regression analysis was carried out to see if there was a correlation between preoperative cleft width and eventual success of the graft as measured on postsurgical radiographs. The success rate for achieving a bony bridge across the cleft was 91%.(ABSTRACT TRUNCATED AT 250 WORDS)

Surface seismic and electrical methods to detect fluids related to faulting

In the absence of drilling, surface‐based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths. These in situ physical properties can then be used to infer the presence and distribution of fluids along faults, although such observations are by nature indirect and become less exact with greater depth. Multiple observations of a range of such geophysical properties as compressional and shear seismic velocity (Vp and Vs), Vp/V5 ratio (related to Poisson's ratio), resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry, fluids in the fault zone, and fluid reservoirs in the surrounding crust. For simple geometries, fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide. To address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid/rock ratios, we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry, large changes in material properties, and numerous earthquakes within the fault zone. A synthetic 0.5‐km wide fault zone with 20% velocity reduction is well imaged using local earthquake tomography. When sequential velocity inversions are done, the true fault width is found, even to 9 km depth, although the calculated amplitude of the velocity reduction is lower than the actual amplitude. Vp/Vs is as well determined as Vp. Magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km. Further, a narrow (1 km) very low resistivity (3 ohm m) fault core can be imaged within a broad (5 km) low resistivity (10 ohm m) fault zone, illustrating that regions of a fault containing large quantities of interconnected fluids within a broader, conductive fault zone should be detectable. Thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade‐off with other factors, such as intrinsic variations in porosity, mineralogy, and pore geometry. The best approach is combined modeling of varied seismic and electrical data.