Circular Window Research Articles

Study on growing correlation length prior to the earthquakes occurred in Gansu Province and its nearby area

The growing correlation length prior to the moderate-great earthquakes occurred in Gansu Province and its nearby area since 1986 has been studied using the method of single-link cluster analysis (SLC). According to different conditions in the source area, the circular spatial window centered in the epicenter and the parallelgrammic spatial window along the fault belt have been selected. The results show that the phenomena of growing correlation length have been observed before the earthquakes studied in the paper.

Fusion of Small-Footprint Lidar and Multispectral Data to Estimate Plot- Level Volume and Biomass in Deciduous and Pine Forests in Virginia, USA

Abstract The principal study objective was to explore the feasibility of using small-footprint lidar data and multispectral imagery to estimate forest volume and biomass on small (0.017-ha) plots. In addition, the spatial dependency of residuals between ground-measured and lidar-estimated variables was investigated. The lidar data set was acquired over deciduous and pine stands in the southeastern United States. Individual trees were identified on the lidar-derived canopy height model by local maximum focal filtering with both square and circular windows of variable size. The size of the dynamically varying window was based on the height of the canopy and the taxonomic group as derived from coregistered multispectral optical data. Lidar-measured parameters at an individual tree level (height, crown diameter) were used with regression models and cross validation to estimate plot-level field inventory data, including volume, biomass, basal area, and diameter at breast height (dbh). Maximum R2 values for estimating biomass were 0.32 for deciduous trees (RMSE 44 Mg/ha) and 0.82 for pines (RMSE 29 Mg/ha). When estimating volume, maximum R2 values for deciduous trees were 0.39 (RMSE 52.84 m3/ha) and 0.83 for pines (RMSE 47.9 m3/ha). Calculation of Moran's I coefficient for each regression model revealed a lack of significant autocorellation of the residuals at 0.05 level. Both model fit and prediction for volume and biomass models for deciduous and pine plots indicated that the circular window shape is more appropriate to locate individual trees with lidar. Using the fused data set, lidar and optical imagery, as opposed to using lidar data alone, always improved biomass and volume estimates for pines and in some cases for deciduous plots as well. FOR. SCI. 50(4):551–565.

Growth and optical properties of Ge/Si quantum dots formed on patterned [formula omitted] substrates

Single and stacked layers of Ge/Si quantum dots were grown in SiO 2 windows patterned by electron-beam lithography on oxidized Si (0 0 1) substrates. The growth of a silicon buffer layer prior to Ge deposition is found to be an additional parameter for adjusting the Ge-dot nucleation process. We show that the silicon buffer layer evolves towards [1 1 3] -faceted pyramids, which reduces the area of the topmost (0 0 1) surface available for Ge nucleation. By controlling the top facet area of the Si buffer layers, only one dot per circular window and a high cooperative arrangement of dots on a striped window can be achieved. In stacked layers, the dot homogeneity can be improved through the adjustment of the Ge deposited amount in the upper layers. The optical properties of these structures measured by photoluminescence spectroscopy are also reported. In comparison with self-assembled quantum dots, we observed, both in single and stacked layers, the absence of the wetting-layer component and an energy blue shift, confirming therefore the dot formation by selective growth.

Seeing the Trees in the Forest

The main study objective was to develop robust processing and analysis techniques to facilitate the use of small-footprint lidar data for estimating plot-level tree height by measuring individual trees identifiable on the three-dimensional lidar surface. Lidar processing techniques included data fusion with multispectral optical data and local filtering with both square and circular windows of variable size. The lidar system used for this study produced an average footprint of 0.65 m and an average distance between laser shots of 0.7 m. The lidar data set was acquired over deciduous and coniferous stands with settings typical of the southeastern United States. The lidar-derived tree measurements were used with regression models and cross-validation to estimate tree height on 0.017-ha plots. For the pine plots, lidar measurements explained 97 percent of the variance associated with the mean height of dominant trees. For deciduous plots, regression models explained 79 percent of the mean height variance for dominant trees. Filtering for local maximum with circular windows gave better fitting models for pines, while for deciduous trees, filtering with square windows provided a slightly better model fit. Using lidar and optical data fusion to differentiate between forest types provided better results for estimating average plot height for pines. Estimating tree height for deciduous plots gave superior results without calibrating the search window size based on forest type.

Bound states in coupled guides. II. Three dimensions

We compute bound-state energies in two three-dimensional coupled waveguides, each obtained from the two-dimensional configuration considered in paper I [J. Math. Phys. 45, 1359–1379 (2004)] by rotating the geometry about a different axis. The first geometry consists of two concentric circular cylindrical waveguides coupled by a finite length gap along the axis of the inner cylinder, and the second is a pair of planar layers coupled laterally by a circular hole. We have also extended the theory for this latter case to include the possibility of multiple circular windows. Both problems are formulated using a mode-matching technique, and in the cylindrical guide case the same residue calculus theory as used in paper I is employed to find the bound-state energies. For the coupled planar layers we proceed differently, computing the zeros of a matrix derived from the matching analysis directly.

Formation and optical properties of Ge quantum dots selectively grown on patterned Si(001) substrates

Single and stacked layers of Ge/Si quantum dots (QDs) were grown in windows patterned by electron-beam lithography on oxidized Si(001) substrates. A Si buffer layer was selectively deposited in the windows prior to Ge growth, that plays an important role for nucleation of Ge dots. The Si buffer layer evolves towards [113] faceted pyramids, which reduces the area of the topmost (001) surface available for Ge nucleation. By controlling the top facet area of the Si buffer layers, only one dot per circular window and a high cooperative arrangement of dots on a stripe can be observed. In stacked layers, the dot homogeneity can be improved through the adjustment of the Ge deposited amount in the upper layers. The optical properties of these structures measured by photoluminescence spectroscopy are also reported. In comparison with self-assembled QDs, we observed, both in single and stacked layers, the absence of the wetting-layer contribution and an energy blue shift, confirming therefore the dot formation by selective growth. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Measuring individual tree crown diameter with lidar and assessing its influence on estimating forest volume and biomass

The main objective of this study was to develop reliable processing and analysis techniques to facilitate the use of small-footprint lidar data for estimating tree crown diameter by measuring individual trees identifiable on the three-dimensional lidar surface. In addition, the study explored the importance of the lidar-derived crown diameter for estimating tree volume and biomass. The lidar dataset was acquired over deciduous, coniferous, and mixed stands of varying age classes and settings typical of the southeastern United States. For identifying individual trees, lidar processing techniques used data fusion with multispectral optical data and local filtering with both square and circular windows of variable size. The crown diameter was calculated as the average of two values measured along two perpendicular directions from the location of each tree top by fitting a fourth-degree polynomial on both profiles. The lidar-derived tree measurements were used with regression models and cross-validation to estimate plot level field-measured crown diameter. Linear regression was also used to compare plot level tree volume and biomass estimation with and without lidar-derived crown diameter measures from individual trees. Results for estimating crown diameter were similar for both pines and deciduous trees, with R2 values of 0.62‐0.63 for the dominant trees (root mean square error (RMSE) 1.36 to 1.41 m). Lidar-measured crown diameter improved R2 values for volume and biomass estimation by up to 0.25 for both pines and deciduous plots (RMSE improved by up to 8 m3/ha for volume and 7 Mg/ha for biomass). For the pine plots, average crown diameter alone explained 78% of the variance associated with biomass (RMSE 31.28 Mg/ha) and 83% of the variance for volume (RMSE 47.90 m3/ha).

The aperture problems in the Pulfrich effect.

The Pulfrich effect yields a perceived depth for horizontally moving objects but not for vertically moving ones. In this study the Pulfrich effect was measured by translating oblique lines seen through a circular window, which made motion direction ambiguous. Overlaying random dots that moved horizontally, vertically, or diagonally controlled the perceptual motion direction of the lines. In experiment 1, when the lines were seen to move horizontally, the effect was strongest in spite of the same physical motion of the lines. Experiment 2 was performed to test the above conditions again, excluding the Pulfrich effect of the dots on the depth of the lines. The overlaid dots were presented to one eye only. The result showed that the Pulfrich effect of the lines was persistently strong in spite of the perceptual changes in motion direction. Experiment 3 also showed that the Pulfrich depth was independent of the perceived horizontal speed in a plaid display. The Pulfrich effect was determined by measuring the horizontal disparity component, independently of the perceived motion direction. These results demonstrate that the aperture problems in motion and stereopsis in the Pulfrich effect are solved independently.

Classification of Voronoi and Delone tiles of quasicrystals: II. Circular acceptance window of arbitrary size

In this paper we describe all the Voronoi and Delone tiles arising in tilings of point sets ?(?) ('quasicrystals') built by the standard projection of the root lattice of type A4 onto a two-dimensional plane spanned by the roots of the Coxeter group H2 (dihedral group of order 10). The acceptance window ? for ?(?) is a disc of any radius 0 < r < ?. There are 22 distinct sets VTj (j = 1, ..., 22) of Voronoi tiles and eight sets DTk (k = 1, ..., 8) of Delone tiles, up to a uniform scaling by a factor ?n where ? = 1/2(1 + ?5) is the golden ratio and n .

Classification of Voronoi and Delone tiles in quasicrystals: I. General method

A new general method is presented which allows one to find all distinct Voronoi and Delone tiles in any quasicrystal from a large family. This includes the tiles which may be present with arbitrarily low density >0. At all stages, the method requires only consideration of a (possibly large) finite number of cases. Our method is applicable, in principle, to quasicrystals in any dimension and with any irrationality. This is the first of three papers where the Voronoi and Delone tilings are studied. Two-dimensional point sets, 'quasicrystals', arising from the A4-root lattice by means of the standard projection to a two-dimensional plane with the irrationality τ = 1/2(1 + √5), are considered. In general, we require that the acceptance window be bounded with non-empty interior. Specific results are provided here for rhombic acceptance windows of any size oriented along the direction of simple roots of the Coxeter group H2. Within one quasicrystal the tiles are distinguished by their shape, size and orientation. The rhombic window case is indispensable for subsequent classification of Voronoi and Delone tiles in quasicrystals with general shape of the acceptance window. Voronoi and Delone tiles of quasicrystals with circular and decagonal windows of any size are given in subsequent papers. Let VT denote the set of distinct Voronoi tiles making up a quasicrystal with a given acceptance window. There are three VT sets of the 'generic' type and three of the 'singular' type. The latter occur for one precise value of the size of the acceptance window. Any other VT set is a uniform scaling of the tiles listed here. Similar results, differing in detail, are provided for the sets of distinct Delone tiles DT. Altogether there are four different sets DT of Delone tiles.

Elgin Cathedral: The Western Rose Window Reconstructed

The remarkable survival of considerable elements of a large rose window at Elgin Cathedral allows an accurate reconstruction of its form. The design can be shown to be from the mainstream of rose window tracery patterns in northern Britain and can be related to the pre-1390 west front of the cathedral. When reconstructed the design of the front shows close affinities with the west front of Arbroath Abbey which also featured a large circular window. Certain elements of the tracery also show similarities with the eastern rose window reconstructed at Fountains Abbey and indicate strong links with sources in northern England.

Elgin Cathedral: The Western Rose Window Reconstructed

The remarkable survival of considerable elements of a large rose window at Elgin Cathedral allows an accurate reconstruction of its form. The design can be shown to be from the mainstream of rose window tracery patterns in northern Britain and can be related to the pre-1390 west front of the cathedral. When reconstructed the design of the front shows close affinities with the west front of Arbroath Abbey which also featured a large circular window. Certain elements of the tracery also show similarities with the eastern rose window reconstructed at Fountains Abbey and indicate strong links with sources in northern England.

Calculation of the average solid angle subtended by a detector to source in a parallel plane by a Monte Carlo method.

A short computer program is described for a PC which uses a Monte Carlo method to calculate the average solid angle subtended by a rectangular or circular detector window to a coaxial or non-coaxial rectangular, circular or point source. The advantage of the Monte Carlo method is that it allows the calculation of average solid angle for source-detector geometries that are difficult to analyse by analytical methods. The values of solid angle are calculated to accuracies of typically better than 0.1%. The calculated values from the Monte Carlo method agree closely with those produced by polygon approximation and numerical integration by Gardner and Verghese, and others.

Precise [100] crystal orientation determination on ⟨110⟩-oriented silicon wafers

In this paper we propose a novel pre-etch method to determine the [100] direction on the surface of ⟨110⟩ silicon wafers with a diameter of 100 mm for precise bulk etching. A series of circular windows is arranged in an arc with a radius of 48.9 mm, and bulk etched to form hexagonal shapes for the indication of crystal orientation. The hexagons, which have two angles of 109° and four other angles of 125.5°, are surrounded by four {111} vertical planes and two {111} planes inclined 35.5° to the wafer surface. The corners of the hexagons are used as an alignment reference to indicate the [100] direction on the ⟨110⟩ silicon wafers. Using a calculation from the relationship between the circular windows with different diameters of 153, 74 and 35 μm and the circle center distances of 192, 96 and 48 μm, the alignment accuracy can be determined as ±0.11°, ±0.06° and ±0.03° to the projected [100] orientation, respectively. Experimental results also demonstrate the feasibility of accurately aligning long etching slots along the ⟨111⟩ direction. The misalignment has been determined to be 0.02° from 20 experimental samples, much less than the estimated value of ±0.03° on a 100 mm ⟨110⟩ wafer. This simple, accurate and fast alignment technique is applicable to long slot fabrication on ⟨110⟩ wafers with tight geometry tolerance.

Estimating fracture trace intensity, density, and mean length using circular scan lines and windows

Fracture characterization protocols that reduce sampling bias are likely to yield higher quality input for exploration and development decisions when dealing with naturally fractured reservoirs. A new set of estimators for fracture density, intensity, and mean trace length corrects for sampling biases and provides a useful integrated description for bulk aspects of a fracture network. These estimators are based on counts of intersections between fracture traces and circular scan lines and of trace terminations in circular windows. Application to synthetic fracture patterns with known parameters validates the use of the new estimators, which are then applied to natural fault trace maps from seismic volumes and joint trace maps from rock pavements. The new estimators are distribution independent and eliminate the effects of orientation, censoring, and length biases, which limit the effectiveness of other sampling techniques. Estimator accuracy improves as sample size increases, particularly for larger circles that exceed a fracture-defined block size. Estimator accuracy for mean trace length improves when the sample exceeds threshold count values for fracture terminations based on guidance from the analysis of similar synthetic patterns. These new estimators also provide both inputs and independent checks of predictions for fracture-generator programs used to model fracture populations in a rock volume.

Inigo Jones and the Hatfield Riding House

Among Inigo Jones’s earliest surviving drawings is one that is generally described as being an elevation for a stable (Fig. 1). This pen and ink drawing, executed in a loose, curvaceous hand, shows a tall, rusticated archway, flanked at an upper level by a pair of windows. Above is a low pediment, with a cartouche and flanking figures, supporting three elegant statues. On either side of this central range are lower, single-storey balustraded bays, each with a large window. Beyond these are lower, lean-to ranges, with a single door flanked by a pair of small, circular windows. The design is not entirely happy and reveals Inigo Jones’s immaturity as an architect. The windows flanking the arch are cramped. The clash between the size of the quoins on the central block and those on the flanking bays is uncomfortable. The sudden jump of scale from the three central elements to the lean-tos is not convincing. The line of the lean-to roofs cuts uncomfortably close to the architraves of the doors. Nevertheless, as one of Jones’s first designs for a freestanding building the design is of great interest.

22 New compounds and structures in the solid state

The discovery of new compds. and structures in the solid state has continued to fluorish during 2002. One particular highlight involves the use of CaH2 as a high temp. reducing agent for ternary transition metal oxides to prep. LaSrCoO3H0.7 that adopts an unprecedented structure contg. oxide chains that are bridged by hydride anions to form a 2-dimensional extended network. Another highlight, found within the area of microporous materials, includes the synthesis of the new zeolite ITQ-21 (Si0.66Ge0.34O2) that has a 3-dimensional pore network contg. 11.8 .ANG. wide cavities, each of which is accessible through six 7.4 .ANG. diam. circular 12-ring windows. As in last years report, and those by previous reviewers, this review will provide an overview of the most significant developments reported over the last year and focus on new compds., mainly with novel structure types, contg. extended inorg. lattices. [on SciFinder (R)]

Modeling corticofugal feedback and the sensitivity of lateral geniculate neurons to orientation discontinuity

We model feedback from primary visual cortex to the dorsal lateral geniculate nucleus (dLGN). This feedback makes dLGN neurons sensitive to orientation discontinuity (Sillito et al., 1993; Cudeiro & Sillito, 1996). In the model, each dLGN neuron receives retinotopic input driven by layer 6 cortical neurons in a full set of orientation columns. Excitation is monosynaptic, while inhibition is through perigeniculate neurons and dLGN interneurons. The stimulus consists of drifting gratings,k one within and the other outside a circular region centered over the receptive field of the model dLGN relay neuron we study. They appear as a single grating when they are aligned with equal contrast. The model reproduces experimental results showing an increasing inhibitory effect of feedback on the firing rate of dLGN neurons as the two gratings move towards the aligned position. Moreover, enhancement of dLGN cell center-surround antagonism by feedback is revealed by measuring the responses to drifting gratings inside a circular window, as a function of window radius. This effect is related to the observed length tuning of dLGN cells. Sensitivity to orientation discontinuity could be mediated in the model by feedback from either simple or complex cells. The model puts constraints on the feedback synaptic footprint and shows that its elongated shape does not play a crucial role in sensitivity to orientation discontinuity. The inhibitory component of feedback must predominate overall, but the feedback signal from a cortical neuron to a dLGN neuron with the same or nearby receptive-field center can be dominated by excitation. Predictions of the model include (1) robust stimuli for layer 6 cortical neurons give pronounced nonlinearities in the responses of dLGN neurons; (2) the sensitivity to orientation discontinuity at low contrast is twice that at high contrast.

Local epitaxy and lateral epitaxial overgrowth of SiC

Selective epitaxial growth and lateral overgrowth of SiC using a graphite mask is reported in this paper. Selective area SiC growth is accomplished using physical vapor transport (PVT) epitaxy. The growth was carried out on 4 H and 6H-SiC wafers on- and 8° off-oriented from the basal plane in the 〈1 1 2 ̄ 0〉 direction. A graphite mask, consisting of rows and columns of uniformly spaced open circles of 75-μm in diameter was used for the selective nucleation of SiC mesa structures. Using PVT epitaxy, selective area hexagonal-shaped structures were successfully grown. There was essentially no direct growth of SiC on the graphite film observed. A lateral/vertical growth rate ratio of 6 was achieved. Optical and scanning microscope images show perfectly formed hexagonal islands, which are located over the open circular windows. The results suggest that the selective area epitaxial growth of SiC is a promising technique for obtaining high quality, locally grown mesa structures for SiC device applications.

Selective area growth of GaN microstructures on patterned (1 1 1) and (0 0 1) Si substrates

Selective MOVPE growth of GaN microstructure on silicon substrates has been investigated using SiO 2 mask having circular or stripe window. In case of (0 0 1)substrate, grooves with (1 1 1) facets at the sides were made by using the etching anisotropy of a KOH solution. On the (1 1 1) facets of patterned silicon substrate (or on the as opened window region of (1 1 1) substrate), growth of wurtzite GaN was performed, of which the c-axis is oriented along the 〈1 1 1〉 axis of silicon. The photoluminescence and X-ray diffraction analysis were performed to characterize the single crystal to reveal the effect of the growth conditions of the intermediated layer and the microstructure.