Characteristic Width Research Articles

Broadening of divertor heat flux profile with increasing number of ELM filaments in NSTX

Edge localized modes (ELMs) represent a challenge to future fusion devices, owing to cyclical high peak heat fluxes on divertor plasma facing surfaces. One ameliorating factor has been that the heat flux characteristic profile width has been observed to broaden with the size of the ELM, as compared with the inter-ELM heat flux profile. In contrast, the heat flux profile has been observed to narrow during ELMs under certain conditions in NSTX. Here we show that the ELM heat flux profile width increases with the number of filamentary striations observed, i.e. profile narrowing is observed with zero or very few striations. Because NSTX often lies on the long wavelength current-driven mode side of ideal MHD instabilities, few filamentary structures can be expected under many conditions. ITER is also projected to lie on the current driven low-n stability boundary, and therefore detailed projections of the unstable modes expected in ITER and the heat flux driven in ensuing filamentary structures is needed.

Image understanding based on histogram of contrast

An image descriptor based on the orientation of contrasts is proposed to facilitate image understanding. A mathematical function that satisfies the heat equation is proposed to model the parameters of an ideal edge, including the width, contrast, offset, position, and orientation. A simple method can compute the contrast and width of canny edge features. Inspired by the histogram of oriented gradients method, an image representation is proposed based on a histogram of contrasts. The proposed method encodes the weighted orientation in a sub-window. The weighting is based on the contrast instead of the gradient magnitude. Our experiments showed that the new representation was more robust against noise compared with several state-of-the-art methods. Several sub-window resolutions were also considered, which resulted in a pyramid that incorporated the global and local context. A method based on Bayes’ theorem and empirical cumulative distribution function is proposed to predict the probability of correctness for the nearest neighbor classification. The annotation and class label of an image were retrieved using a nearest neighbor method or a support vector machine classifier. This method was tested using several benchmark datasets and toolboxes, which showed that it is suitable for image understanding tasks.

Scaling of divertor power footprint width in RF-heated type-III ELMy H-mode on the EAST superconducting tokamak

Dedicated experiments for the scaling of divertor power footprint width have been performed in the ITER-relevant radio-frequency (RF)-heated H-mode scheme under the lower single null, double null and upper single null divertor configurations in the Experimental Advanced Superconducting Tokamak (EAST) under lithium wall coating conditioning. A strong inverse scaling of the edge localized mode (ELM)-averaged power fall-off width with the plasma current (equivalently the poloidal field) has been demonstrated for the attached type-III ELMy H-mode as by various heat flux diagnostics including the divertor Langmuir probes (LPs), infra-red (IR) thermograph and reciprocating LPs on the low-field side. The IR camera and divertor LP measurements show that , in good agreement with the multi-machine scaling trend during the inter-ELM phase between type-I ELMs or ELM-free enhanced Dα (EDA). H-mode. However, the magnitude is nearly doubled, which may be attributed to the different operation scenarios or heating schemes in EAST, i.e., dominated by electron heating. It is also shown that the type-III ELMs only broaden the power fall-off width slightly, and the ELM-averaged width is representative for the inter-ELM period. Furthermore, the inverse Ip (Bp) scaling appears to be independent of the divertor configurations in EAST. The divertor power footprint integral width, fall-off width and dissipation width derived from EAST IR camera measurements follow the relation, λint ≅ λq + 1.64S, yielding . Detailed analysis of these three characteristic widths was carried out to shed more light on their extrapolation to ITER.

First measurements of D(α) spectrum produced by anisotropic fast ions in the gas dynamic trap.

Angled injection of eight deuterium beams in gas dynamic trap (GDT) plasmas builds up the population of fast ions with the distribution function, which conserves a high degree of initial anisotropy in space, energy, and pitch angle. Unlike the Maxwellian distribution case, the fast ion plasma component in GDT cannot be exhaustively characterized by the temperature and density. The instrumentation complex to study of fast ions is comprised of motional Stark effect diagnostic, analyzers of charge exchange atoms, and others. The set of numerical codes using for equilibrium modeling is also an important tool of analysis. In the recent campaign of summer 2014, we recorded first signals from the new fast ion D-alpha diagnostic on GDT. This paper presents the diagnostic description and results of pilot measurements. The diagnostic has four lines of sight, distributed across the radius of an axially symmetric plasma column in GDT. In the present setup, a line-integrated optical signal is measured in each channel. In the transverse direction, the spatial resolution is 18 mm. Collected light comes to the grating spectrometer with the low-noise detector based on a charge-coupled device matrix. In the regime of four spectra stacked vertically on the sensor, the effective spectral resolution of measurements is approximately 0.015 nm. Exposure timing is provided by the fast optical ferroelectric crystal shutter, allowing frames of duration down to 70 μs. This number represents the time resolution of measurements. A large dynamic range of the camera permits for a measurement of relatively small light signals produced by fast ions on top of the bright background emission from the bulk plasma. The fast ion emission has a non-Gaussian spectrum featuring the characteristic width of approximately 4 nm, which can be separated from relatively narrow Gaussian lines of D-alpha and H-alpha coming from the plasma periphery, and diagnostic beam emission. The signal to noise ratio varies from approximately ten for the central channel to approximately five for the outermost channel. We used the special set of Monte Carlo codes to fit the measured spectra. The shape of model fit shows a good agreement with the experimental fast ion D-alpha spectrum.

Experimental Demonstration of Reduced Light Absorption by Intracavity Metallic Layers in Tamm Plasmon-based Microcavity

We demonstrate experimentally a microcavity based on SiO2/TiO2 with two gold layers directly attached to the central base of the microcavity. The design of optical modes based on the peculiarities of Tamm plasmons provides reduced absorption due to the fixing of the node of the electric field of optical mode to metallic layers. Experimentally measured reflection and transmission spectra exhibits three features, corresponding to three hybrid modes of the microcavity. The widths of spectral features confirm that absorption of light by metallic layers is vanishing for optimized mode. The latter is confirmed by resonant transmission of light through the structure. In case of the laser structure, two intracavity metallic layers could serve as contacts for electrical pumping.

Three Dimensional Micro Detection Scheme of Fatigue Cracks in Steel Box Girder with HIROX Testing System

In practical steel box girder, the fatigue cracks are inevitably existed in steel bridges after they are burdened with the overloading vehicles and larger numbers of automobiles. How to efficiently detect the fatigue cracks, especially the initial fatigue cracks, become one of the most important question to be solved for the steel box girder. HIROX testing system is based on three dimensional micro detection technique, which was successfully used into the domains of aeronautics and astronautics. Three dimensional micro detection scheme of fatigue cracks in steel box girder with HIROX testing system is studied in this paper. Through the data from the testing design, the important characteristic width and length of the fatigue crack can be achieved, which can be used for the grasping of the mechanism of the steel box girder.

Micro-scale and meso-scale architectural cues cooperate and compete to direct aligned tissue formation

Tissue and biomaterial microenvironments provide architectural cues that direct important cell behaviors including cell shape, alignment, migration, and resulting tissue formation. These architectural features may be presented to cells across multiple length scales, from nanometers to millimeters in size. In this study, we examined how architectural cues at two distinctly different length scales, “micro-scale” cues on the order of ∼1–2 μm, and “meso-scale” cues several orders of magnitude larger (>100 μm), interact to direct aligned neo-tissue formation. Utilizing a micro-photopatterning (μPP) model system to precisely arrange cell-adhesive patterns, we examined the effects of substrate architecture at these length scales on human mesenchymal stem cell (hMSC) organization, gene expression, and fibrillar collagen deposition. Both micro- and meso-scale architectures directed cell alignment and resulting tissue organization, and when combined, meso cues could enhance or compete against micro-scale cues. As meso boundary aspect ratios were increased, meso-scale cues overrode micro-scale cues and controlled tissue alignment, with a characteristic critical width (∼500 μm) similar to boundary dimensions that exist in vivo in highly aligned tissues. Meso-scale cues acted via both lateral confinement (in a cell-density-dependent manner) and by permitting end-to-end cell arrangements that yielded greater fibrillar collagen deposition. Despite large differences in fibrillar collagen content and organization between μPP architectural conditions, these changes did not correspond with changes in gene expression of key matrix or tendon-related genes. These findings highlight the complex interplay between geometric cues at multiple length scales and may have implications for tissue engineering strategies, where scaffold designs that incorporate cues at multiple length scales could improve neo-tissue organization and resulting functional outcomes.

Algorithm for soot sheet quantification in a piloted turbulent jet non-premixed natural gas flame

A novel method to quantify soot sheets from planar images of soot volume fraction is presented and demonstrated in a well-characterised turbulent, non-premixed flame, known as the ‘Delft-Adelaide Flame’. The image processing algorithm presented is based on the adaption and combination of two existing computational methodologies that were presented in the literature. The algorithm starts by identifying the longest line spanning the object. The line is subsequently segmented repetitively to generate ‘anchor points’ that are forced to lie along the centreline of the object. The length of the soot sheet is obtained by fitting straight lines to the anchor points, whilst the average characteristic width of the sheet is determined from the mean thickness of the ellipses that are fitted to the segmented soot sheet. The algorithm employed in this method, which has an uncertainty of \(\sim \)11 %, is found to be well suited to extract the characteristic dimension and position information of soot sheet with bend, irregular shape and random orientation. Statistical assessments of these dimensions in this flame reveal that: (1) the characteristic width and length of the soot sheets range from \(\sim \)6 to \(\sim \)10 mm, and \(\sim \)30 to \(\sim \)50 mm, respectively, (2) a strong correlation exists between the soot characteristic width and length, and (3) the soot sheets display high sensitivity to local flow dynamics, with measured normalised interaction lengths ranging from 3.4 to 3.9, for the present flame.

Mapping Layers of Clay in a Vertical Geological Surface Using Hyperspectral Imagery: Variability in Parameters of SWIR Absorption Features under Different Conditions of Illumination

Hyperspectral imagery of a vertical mine face acquired from a field-based platform is used to evaluate the effects of different conditions of illumination on absorption feature parameters wavelength position, depth and width. Imagery was acquired at different times of the day under direct solar illumination and under diffuse illumination imposed by cloud cover. Imagery acquired under direct solar illumination did not show large amounts of variability in any absorption feature parameter; however, imagery acquired under cloud caused changes in absorption feature parameters. These included the introduction of a spurious absorption feature at wavelengths > 2250 nm and a shifting of the wavelength position of specific clay absorption features to longer or shorter wavelengths. Absorption feature depth increased. The spatial patterns of clay absorption in imagery acquired under similar conditions of direct illumination were preserved but not in imagery acquired under cloud. Kaolinite, ferruginous smectite and nontronite were identified and mapped on the mine face. Results were validated by comparing them with predictions from x-ray diffraction and laboratory hyperspectral imagery of samples acquired from the mine face. These results have implications for the collection of hyperspectral data from field-based platforms.

INFRARED SPECTRA AND PHOTOMETRY OF COMPLETE SAMPLES OF PALOMAR-GREEN AND TWO MICRON ALL SKY SURVEY QUASARS

As a step toward a comprehensive overview of the infrared diagnostics of the central engines and host galaxies of quasars at low redshift, we present Spitzer Space Telescope spectroscopic (5-40 {\mu}m) and photometric (24, 70 and 160 {\mu}m) measurements of all Palomar-Green (PG) quasars at z < 0.5 and 2MASS quasars at z < 0.3. We supplement these data with Herschel measurements at 160 {\mu}m. The sample is composed of 87 optically selected PG quasars and 52 near-IR selected 2MASS quasars. Here we present the data, measure the prominent spectral features, and separate emission due to star formation from that emitted by the dusty circumnuclear torus. We find that the mid-IR (5-30 {\mu}m) spectral shape for the torus is largely independent of quasar IR luminosity with scatter in the SED shape of ~ 0.2 dex. Except for the silicate features, no large difference is observed between PG (unobscured - silicate emission) and 2MASS (obscured - silicate absorption) quasars. Only mild silicate features are observed in both cases. When in emission, the peak wavelength of the silicate feature tends to be longer than 9.7 {\mu}m, possibly indicating effects on grain properties near the AGN. The IR color is shown to correlate with the equivalent width of the aromatic features, indicating that the slope of the quasar mid- to far-IR SED is to first order driven by the fraction of radiation from star formation in the IR bands.

Spectroscopic remote sensing of plant stress at leaf and canopy levels using the chlorophyll 680 nm absorption feature with continuum removal

This paper explores the use of spectral feature analysis to detect plant stress in visible/near infrared wavelengths. A time series of close range leaf and canopy reflectance data of two plant species grown in hydrocarbon-contaminated soil was acquired with a portable spectrometer. The ProSpecTIR-VS airborne imaging spectrometer was used to obtain far range hyperspectral remote sensing data over the field experiment. Parameters describing the chlorophyll 680nm absorption feature (depth, width, and area) were derived using continuum removal applied to the spectra. A new index, the Plant Stress Detection Index (PSDI), was calculated using continuum-removed values near the chlorophyll feature centre (680nm) and on the green-edge (560 and 575nm). Chlorophyll feature’s depth, width and area, the PSDI and a narrow-band normalised difference vegetation index were evaluated for their ability to detect stressed plants. The objective was to analyse how the parameters/indices were affected by increasing degrees of plant stress and to examine their utility as plant stress indicators at the remote sensing level (e.g. airborne sensor). For leaf data, PSDI and the chlorophyll feature area revealed the highest percentage (67–70%) of stressed plants. The PSDI also proved to be the best constraint for detecting the stress in hydrocarbon-impacted plants with field canopy spectra and airborne imaging spectroscopy data. This was particularly true using thresholds based on the ASD canopy data and considering the combination of higher percentage of stressed plants detected (across the thresholds) and fewer false-positives.

Evidence for longitudinal variability of ethane ice on the surface of Pluto

We present the results of an investigation using near-infrared spectra of Pluto taken on 72 separate nights using SpeX/IRTF. These data were obtained between 2001 and 2013 at various sub-observer longitudes. The aim of this work was to confirm the presence of ethane ice and to determine any longitudinal trends on the surface of Pluto. We computed models of the continuum near the 2.405μm band using Hapke theory and calculated an equivalent width of the ethane absorption feature for six evenly-spaced longitude bins and a grand average spectrum. The 2.405μm band on Pluto was detected at the 7.5-σ level from the grand average spectrum. Additionally, the band was found to vary longitudinally with the highest absorption occurring in the N2-rich region and the lowest absorption occurring in the visibly dark region. The longitudinal variability of 12CO does not match that of the 2.405μm band, suggesting a minimal contribution to the band by 13CO. We argue for ethane production in the atmosphere and present a theory of volatile transport to explain the observed longitudinal trend.

Growth and dissipation of typhoon-forced solitary continental shelf waves in the northern South China Sea

This study aims to gain insight into the sea level response to typhoon in the northern South China Sea using typhoon records from 1978 to 1997, simultaneous tidal gauge records and satellite altimeter along-track sea level data. We find that the ocean sea level response signatures in the deep water agree well with a single sea level soliton, of which the average soliton amplitude is (34 ± 6) cm and the average characteristic half width is (115 ± 12) km. Evolution of the single soliton as propagating across a shoaling bottom topography obeys solutions of the perturbed Korteweg and de Vries equation. The solutions reveal that forced by the hyperbolic-tangent-shaped topography, the single soliton evolves to a solitary wave packet consisting of a large leading soliton and smaller following waves in an oscillatory tail as approaching the shallow water. This phenomenon is verified by observed sea level signatures of 19 storm surges. The correlation coefficient between theoretical solution and observations is as high as 0.91. Meanwhile, the soliton amplitude grows with a soliton amplitude growth ratio (SAGR), which depends on the deep water and shallow water depths. However, without consideration of viscous effects, the SAGR model overestimates the soliton amplitude growth. Thus the vorticity equation for viscous fluid is adopted to solve this issue. The results indicate that turbulent viscosities are responsible to soliton amplitude decay concurring with the growth and causes dependence of the storm surge amplitude on the typhoon incident angle.

13CO filaments in the Taurus molecular cloud

We have carried out a search for filamentary structures in the Taurus molecular cloud using $\rm^{13}CO$ line emission data from the FCRAO survey of $\rm \sim100 \, deg^2$. We have used the topological analysis tool, DisPerSe, and post-processed its results to include a more strict definition of filaments that requires an aspect ratio of at least 3:1 and cross section intensity profiles peaked on the spine of the filament. In the velocity-integrated intensity map only 10 of the hundreds of filamentary structures identified by DisPerSe comply with our criteria. Unlike Herschel analyses, which find a characteristic width for filaments of $\rm \sim0.1 \, pc$, we find a much broader distribution of profile widths in our structures, with a peak at 0.4 pc. Furthermore, even if the identified filaments are cylindrical objects, their complicated velocity structure and velocity dispersions imply that they are probably gravitationally unbound. Analysis of velocity channel maps reveals the existence of hundreds of `velocity-coherent' filaments. The distribution of their widths is peaked at lower values (0.2 pc) while the fluctuation of their peak intensities is indicative of stochastic origin. These filaments are suppressed in the integrated intensity map due to the blending of diffuse emission from different velocities. Conversely, integration over velocities can cause filamentary structures to appear. Such apparent filaments can also be traced, using the same methodology, in simple simulated maps consisting of randomly placed cores. They have profile shapes similar to observed filaments and contain most of the simulated cores.

Influence of mineral particle size and choice of suitable parameters for ore sorting using near infrared sensors

Near infrared sensor-based sorting is an emerging preconcentration technology which holds promise for many mineral processing applications, such as elimination of calcite and clay waste from ore. Preconcentration serves to increase the processing efficiency as well as to reduce the total processing cost through the rejection of unwanted gangue. Given small-scale heterogeneity in complex ores, i.e. assorted minerals occurring side-by-side inside an area of measurement, the total mineral composition may not be easily discerned from a near infrared spectrum. Hence, mineral identification and subsequent classification involves the analysis of absorption features in terms of feature depth, width, position, and level of spectral reflectance. This research investigates the near infrared spectral characteristics of minerals as a function of particle size fraction, specifically for individual minerals commonly found in malachite-rich copper ores. Samples of pure minerals are crushed and sieved into different size fractions and scanned with a near infrared line scanner. It was found that the presence of characteristic absorption features and their wavelength position were a better identification parameter than the reflectance level. The implication for preconcentrating a typical malachite-rich copper ore through near-infrared based sorting is discussed.

Fabrication of silicon molds with multi-level, non-planar, micro- and nano-scale features

A method for single-step fabrication of arbitrary, complex, three-dimensional (3D) silicon structures from the nano- to millimeter-scale at multiple levels on non-planar, curved, or domed surfaces is reported. The fabrication is based on focused or masked ion beam irradiation of p-type silicon followed by electrochemical anodization. The process allows fabrication of a wide range of surface features at multiple heights and with arbitrary orientations by varying the irradiated feature width, ion type, energy fluence, and subsequent anodization conditions. The technology has achieved depth resolution of 10 nm as step heights and is capable of creating lateral features down to 7 nm at high aspect ratios of up to 40, with surface roughness down to 1 nm scaled up to full wafer areas. The single-step ability has seamlessly interfaced a network of complex, integrated micro- to nano-structures in 3D orientations with no alignment required. The final template has been converted to a master copy for nano-imprinting lithography of 3D fluidic structures and optical components.

Dispersal and air entrainment in unconfined dilute pyroclastic density currents

Unconfined scaled laboratory experiments show that 3D structures control the behavior of dilute pyroclastic density currents (PDCs) during and after liftoff. Experiments comprise heated and ambient temperature 20 μm talc powder turbulently suspended in air to form density currents within an unobstructed 8.5 × 6 × 2.6-m chamber. Comparisons of Richardson, thermal Richardson, Froude, Stokes, and settling numbers and buoyant thermal to kinetic energy densities show good agreement between experimental currents and dilute PDCs. The experimental Reynolds numbers are lower than those of PDCs, but the experiments are fully turbulent; thus, the large-scale dynamics are similar between the two systems. High-frequency, simultaneous observation in three orthogonal planes shows that the currents behave very differently than previous 2D (i.e., confined) currents. Specifically, whereas ambient temperature currents show radial dispersal patterns, buoyancy reversal, and liftoff of heated currents focuses dispersal along narrow axes beneath the rising plumes. The aspect ratios, defined as the current length divided by a characteristic width, are typically 2.5–3.5 in heated currents and 1.5–2.5 in ambient temperature currents, reflecting differences in dispersal between the two types of currents. Mechanisms of air entrainment differ greatly between the two currents: entrainment occurs primarily behind the heads and through the upper margins of ambient temperature currents, but heated currents entrain air through their lateral margins. That lateral entrainment is much more efficient than the vertical entrainment, >0.5 compared to ∼0.1, where entrainment is defined as the ratio of cross-stream to streamwise velocity. These experiments suggest that generation of coignimbrite plumes should focus PDCs along narrow transport axes, resulting in elongate rather than radial deposits.

Effects of lateral tip control in CD-AFM width metrology

Critical dimension atomic force microscopes (CD-AFMs) use flared tips and two-dimensional sensing and position control of the tip-sample interaction to enable scanning of features with near-vertical or reentrant sidewalls. Sidewall sensing usually involves lateral dither of the tip, which was the case in the first two generations of CD-AFM. Current, third-generation instruments also have a fast dither tube actuation (FDTA) mode where a control algorithm and fast response piezo actuator are used to position the tip in a manner that resembles touch-triggering of coordinate measuring machines (CMMs). All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. When lateral dithering is involved, this effect is readily understood as the addition of a dither envelope to the geometrical tip width.The effective tip width is a key correction parameter for accurate feature width measurements and is typically estimated using a tip calibration procedure. However, the possibility exists of small errors in the estimated tip width due to variations and dependencies of the effective width on tip, tool, material, and environmental parameters. We are investigating this possibility through a systematic study of the dependence of the apparent width on measurement mode, dither amplitude, tip type, and sample composition. While we believe that there are potential effects that should be considered carefully, we also conclude, particularly for silicon features, that most potential biases can be removed by performing the calibration and measurement exercises under the same conditions.

Suggested continued heat-treatment method for investigating static and dynamic mechanical properties of cement-based materials

Thermo-induced damage affects the structural and material safety of civil engineering structures; the damage can induce direct or indirect extensive structural collapse.An innovative continued heat-treatment method to obtain several specimen pieces in a single cylinder of mortar was described in this paper; the intended purpose of the method was to predict the effects of heat treatment on the static and dynamic mechanical properties and characteristic width of process zones.All of the results can be regressed by a continuous equation; therefore, the regression equations obtained from the results of continued heat-damaged specimen pieces represented more accurate prediction equations. Moreover, using the Log–Log method resulted in a critical damage temperature of approximately 547.5°C. For a temperature range between room temperature and approximately 547.5°C; the variation of all of the mechanical properties decreased by approximately 10–11% per 100°C, but they decreased by approximately 29–31% per 100°C between 547.5°C and the highest temperature used in the tests. Finally, the fracture characteristics and the width of the process zones could be investigated using the acoustic emission technique; the width was wider at lower temperatures than at higher temperatures.

Adsorption of multiple spherical particles onto sinusoidally corrugated substrates.

We utilize a Monte Carlo simulation scheme based on the bond fluctuation model to simulate settlement of adhesive particles onto sinusoidally corrugated substrates. The particles are composed of a hard inner core with either an effective potential shell or a "soft" adhesive shell made of flexible arms attached to the particle surface. These chains adhere via either the effective potential shell or the sticky chain ends to the surface via pairwise nonspecific interactions. This simulation model allows for multiple particles to settle onto each tested substrate to elucidate the behavior of the collective adhesive layer featuring multiparticle assembly. Particles move within a 3D lattice space and settle on the substrate due to attractive particle/substrate interactions. Once a single particle adheres to the substrate, a new particle is introduced into the lattice to begin a new settlement. Through this multiparticle settlement mode, we explore the interplay among the characteristics of the particles (i.e., size, interaction shell) and the substrates (i.e., wavelength and periodicity) as well as interparticle interactions. We report that the adhesion of particles with an effective interaction shell to the substrates is reduced dramatically when the particle size is smaller than the feature width of the periodic substrate. The settlement of particles with flexible hair on the sinusoidally corrugated substrates is more complex. Specifically, the presence of flexible polymeric hairs makes the particle settlement more likely to occur on nearly all substrates studied irrespective of the characteristics of the substrate.