Row Direction Research Articles

A Subblock Matrix Approach to Data-Reduction in Gait Recognition

We propose a novel method for data reduction in gait recognition, called Subblock Complete Two Dimensional Principal Component Analysis (SbC2DPCA). GEIs were divided into smaller sub-images and redundant subblocks were adaptively removed. Complete Two Dimensional Principal Component Analysis (C2DPCA) was then applied to every sub-image directly, to acquire a set of projection sub-vectors for both row and column directions and these were synthesized into whole features for subsequent classification using nearest neighbor classifier. We evaluate the proposed gait recognition method on the CASIA gait database. The experimental results and analysis show the recognition accuracy of SbC2DPCA to be superior to C2DPCA, with C2DPCA being a special case of SbC2DPCA. The novelty of the proposed method lies in the adaptive removal of redundant data while extracting local features. This translates to data reduction with very minimal loss of information, as demonstrated by the remarkable recognition accuracy when subjects change clothing or have a backpack.

Estimating Paddy Rice Leaf Area Index with Fixed Point Continuous Observation of Near Infrared Reflectance Using a Calibrated Digital Camera

A two-band digital imaging system—one band for visible red (RED, 630–670 nm) and the other for near infrared (NIR, 820–900 nm)—was positioned 12 m above a 600-m2 rice field. The imaging system automatically logged bird’s-eye-view images at 10-min intervals from 0700 to 1700 JST daily during the 2008 paddy rice season. Radiometric corrections and midterm field validations for the pairs of two-band images utilized solar irradiance sensors and prior calibrations to calculate 0900-1500 JST daily-averaged reflectance factor (DARF). The DARF values in the RED and the NIR bands agreed with observations made with a portable spectroradiometer and showed smooth seasonal changes in terms of plant growth. During the before-heading period, NIR DARF values had a correlation coefficient (r) of 0.91 with the leaf area index (LAI). An empirically derived equation for LAI using NIR DARF values and the cosines of angles between the view and the planting row directions, and the view and the meridian directions, showed R2 values of 0.93, in estimations of LAI from the dataset (number of observations=52) acquired at four sample points centrally located within the viewing field. Validation indicated that the equation also worked well for the other six observation points spread across the viewing field, the data of which were not used in deriving the equation parameters. The DARF values observed in the NIR band calibrated with solar spectral irradiance sensors were useful for assessing rice LAI during the before-heading periods.

Regression-Based Models to Predict Rice Leaf Area Index Using Biennial Fixed Point Continuous Observations of Near Infrared Digital Images

A weatherproof digital imaging system for the near infrared band (NIR, 820–900 nm) was positioned 12 m above a 600-m2 rice field. During the 2008 and 2009 paddy rice seasons, the system automatically logged images at 10-min intervals throughout the day. Radiometric corrections for the NIR images utilized a solar irradiance sensor and prior calibrations to calculate 0900–1500 JST daily-averaged reflectance factors (DARF). Prior to heading, empirically derived equations for predicting leaf area index (LAI) using the 2008 DARF values in NIR, the cosines of angles between the view and the planting row directions, and between the view and the meridian directions were verified with the 2009 data set. Transformation of a model variable by arcsine square root function improved the performance of the LAI prediction by reducing the errors and bias at low LAI values. Adding variables to incorporate lateral angular components to the horizontal viewing angular parameters hardly affected the overall performance of the models and did not reduce variation. This was probably because the height and position of the camera system were the same in successive years. In-plot means of two or four predicted values in each plot reduced the root-mean square error 30%. These results indicate that radiometric NIR images derived using a fixed-point observation system can accurately predict LAI and the simple multiple linear regression equations developed for a given year can be used the following year without in-situ recalibration.

Subsurface Drip Irrigation Placement and Cotton Irrigation Water Requirement in the Tennessee Valley

Fluctuations in dryland cotton yield in the Tennessee Valley region of northern Alabama are common and are usually related to irregular drought periods during the growing season. Subsurface drip irrigation (SDI) has gained popularity as a water delivery system for small, irregular-shaped cotton fields. A seven-year study was conducted with the objective to determine the response of seed cotton yield to SDI tape orientation relative to crop row direction and different irrigation rates under dryland conditions of the Tennessee Valley. Seven treatments were tested in a randomized incomplete block design which consisted of three irrigation treatments (33%, 66%, and 99% pan evaporation), two SDI tape orientations (parallel and perpendicular), and a dryland control. All SDI treatments produced yields significantly higher than non-irrigated, dryland cotton in four out of seven years. Maximum yield was obtained at a median pan evaporation water replacement value of 74%. No statistical differences were observed between SDI tape orientations on seed cotton yield in all years except in 1999 when parallel out yielded perpendicular at lower irrigation rates. Results confirm the long-term efficacy of supplemental irrigation to increase seed cotton yield irrespective of SDI tape placement during sporadic periods of drought. These results are applicable only for fields with the same soil type or with similar water movement characteristics.

Face recognition by generalized two-dimensional FLD method and multi-class support vector machines

This paper presents a novel scheme for feature extraction, namely, the generalized two-dimensional Fisher's linear discriminant (G-2DFLD) method and its use for face recognition using multi-class support vector machines as classifier. The G-2DFLD method is an extension of the 2DFLD method for feature extraction. Like 2DFLD method, G-2DFLD method is also based on the original 2D image matrix. However, unlike 2DFLD method, which maximizes class separability either from row or column direction, the G-2DFLD method maximizes class separability from both the row and column directions simultaneously. To realize this, two alternative Fisher's criteria have been defined corresponding to row and column-wise projection directions. Unlike 2DFLD method, the principal components extracted from an image matrix in G-2DFLD method are scalars; yielding much smaller image feature matrix. The proposed G-2DFLD method was evaluated on two popular face recognition databases, the AT&T (formerly ORL) and the UMIST face databases. The experimental results using different experimental strategies show that the new G-2DFLD scheme outperforms the PCA, 2DPCA, FLD and 2DFLD schemes, not only in terms of computation times, but also for the task of face recognition using multi-class support vector machines (SVM) as classifier. The proposed method also outperforms some of the neural networks and other SVM-based methods for face recognition reported in the literature.

Color face recognition based on quaternion matrix representation

There are several methods to recognize and reconstruct a human face image. The principal component analysis (PCA) is a successful approach because of its effective extraction of the global feature and excellent reconstruction of face image. However, the crucial shortcomings of PCA are its low recognition rate and overfitting of feature extraction which leads to the dependence of training data on training samples. In this paper, a modified two-dimension principal component analysis (2DPCA) and bidirectional principal component analysis (BDPCA) methods based on quaternion matrix are proposed to recognize and reconstruct a color face image. In these methods, the spatial distribution information of color images is used to represent a color face, and the 2DPCA or BDPCA feature of color face image is extracted by reducing the dimensionality in both column and row directions. A method obtaining orthogonal eigenvector set of quaternion matrix is proposed. Numerous experiments show that the present approach based on quaternion matrix can effectively smooth the overfitting issue and substantially enhance the recognition rate.

Proporção e tamanho de sedimentos e teor de carbono orgânico na enxurrada e no solo para dois cultivos e duas formas de semeadura

O tipo de cultura e a orientação de semeadura em relação ao declive do terreno podem modificar a proporção e o tamanho dos sedimentos transportados na enxurrada, além da relação do teor de C orgânico nos sedimentos e no solo erodido. Este trabalho teve o objetivo de determinar a proporção e o tamanho dos sedimentos transportados pela enxurrada sob taxa constante desta e o teor de C orgânico contido nos sedimentos e no solo erodido, sob duas formas de semeadura das culturas de aveia e ervilhaca. Quatro testes de chuva simulada foram aplicados entre março e novembro de 2006, durante o ciclo vegetativo das culturas, com intensidade constante de 64 mm h-1 e 1 h de duração de cada teste, em Lages, SC, num Cambissolo Húmico com declividade média de 11,9 cm m-1. Os tratamentos eram formados pela combinação de duas culturas e duas orientações de semeadura em relação ao declive. As culturas utilizadas foram aveia (Avena strigosa) e ervilhaca (Vicia sativa); as formas de semeadura eram: mecanizada em linhas em contorno ao declive e mecanizada em linhas paralelas ao declive (morro abaixo). As amostras de enxurrada para a coleta dos sedimentos foram obtidas sob taxa constante de enxurrada, aos 50 min de duração de cada teste de chuva. A aveia reduziu a quantidade de sedimentos na enxurrada em 46 % em relação à ervilhaca, e a semeadura em contorno, em 56 % em relação à semeadura morro abaixo. A proporção de sedimentos na enxurrada foi diminuída em 63 % entre o início e o final do ciclo das culturas. Na classe de menor tamanho dos sedimentos (< 0,038 mm), a aveia aumentou sua proporção em 17 % em relação à ervilhaca, e o contorno os aumentou em 10 % em relação à semeadura morro abaixo. O índice D50 dos sedimentos presentes na enxurrada foi de 0,043 mm na aveia e 0,119 mm na ervilhaca, e de 0,047 mm na semeadura em contorno e 0,117 mm na semeadura morro abaixo. A razão entre o teor de C orgânico dos sedimentos transportados pela enxurrada e o teor de C do solo na camada de 0-2,5 cm foi de 1,39 na aveia e 1,21 na ervilhaca, e de 1,43 na semeadura em contorno e 1,17 na semeadura morro abaixo.

Movement behaviour within and beyond perceptual ranges in three small mammals: effects of matrix type and body mass

1. For animal species inhabiting heterogeneous landscapes, the tortuosity of the dispersal path is a key determinant of the success in locating habitat patches. Path tortuosity within and beyond perceptual range must differ, and may be differently affected by intrinsic attributes of individuals and extrinsic environmental factors. Understanding how these factors interact to determine path tortuosity allows more accurate inference of successful movements between habitat patches. 2. We experimentally determined the effects of intrinsic (body mass and species identity) and extrinsic factors (distance to nearest forest fragment and matrix type) on the tortuosity of movements of three forest-dwelling didelphid marsupials, in a fragmented landscape of the Atlantic Forest, Brazil. 3. A total of 202 individuals were captured in forest fragments and released in three unsuitable matrix types (mowed pasture, abandoned pasture and manioc plantation), carrying spool-and-line devices. 4. Twenty-four models were formulated representing a priori hypotheses of major determinants of path tortuosity, grouped in three scenarios (only intrinsic factors, only extrinsic factors and models with combinations of both), and compared using a model selection approach. Models were tested separately for individuals released within the perceptual range of the species, and for individuals released beyond the perceptual range. 5. Matrix type strongly affected path tortuosity, with more obstructed matrix types hampering displacement of animals. Body mass was more important than species identity to determine path tortuosity, with larger animals moving more linearly. Increased distance to the fragment resulted in more tortuous paths, but actually reflects a threshold in perceptual range: linear paths within perceptual range, tortuous paths beyond. 6. The variables tested explained successfully path tortuosity, but only for animals released within the perceptual range. Other factors, such as wind intensity and direction of plantation rows, may be more important for individuals beyond their perceptual range. 7. Simplistic scenarios considering only intrinsic or extrinsic factors are inadequate to predict path tortuosity, and to infer dispersal success in heterogeneous landscapes. Perceptual range represents a fundamental threshold where the effects of matrix type, body mass and individual behaviour change drastically.

Causes of the reconstructed cross appearing in lensless Fourier transform digital holography

Causes of the bright cross appearing in the reconstructed field of lensless Fourier transform digital hologram (LFDH) are presented. Firstly, as LFDH's reconstruction was directly performed by Fourier transform algorithm, the intensity distribution of reconstructed image plane was just LFDH's spectrum, and three parts of the reconstructed field are imaged in the spectral plane. Meanwhile their intensities were almost the same. Hence, the ratio of signal to noise of the reconstructed image was obviously lower than that of the conventional digital hologram. Further, non-uniformity of the background intensity and random noises usually existed in a practical LFDH. Meanwhile their spectra spread through the central and the edge areas; this also led to decrease in the ratio of signal to noise of the reconstructed image. Specially, as the two-dimensional Fourier transform algorithm was performed row by row, and then column by column, the low-frequency spectrum induced by the non-uniformity of the background and random noises along the directions of rows and columns would concentrate on the central column and row, respectively, and what is gotten looked like a cross. Therefore, the cross appearing in LFDH's reconstructed field should be attributed to the combination of the background and the Fourier transform algorithm itself.

A Low Vth SRAM Reducing Mismatch of Cell-Stability with an Elevated Cell Biasing Scheme

A lower-threshold-voltage (LVth) SRAM cell with an elevated cell biasing scheme, which enables to reduce the random threshold-voltage (Vth) variation and to alleviate the stability-degradation caused by word-line (WL) and cell power line (VDDM) disturbed accesses in row and column directions, has been proposed. The random Vth variation (σVth) is suppressed by the proposed LVth cell. As a result, the LVth cell reduces the variation of static noise margin (SNM) for the data retention, which enables to maintain a higher SNM over a larger memory size, compared with a conventionally being used higher Vth (HVth) cell. An elevated cell biasing scheme cancels the substantial trade-off relationship between SNM and the write margin (WRTM) in an SRAM cell. Obtained simulation results with a 45-㎚ CMOS technology model demonstrate that the proposed techniques allow sufficient stability margins to be maintained up to 6σ level with a 0.5-V data retention voltage and a 0.7-V logic bias voltage.

Morphological and histological changes of dermal scales during the fish-to-tetrapod transition

Witzmann F. (2011). Morphological and histological changes of dermal scales during the fish-to-tetrapod transition. —Acta Zoologica (Stockholm) 92: 281–302. The gastral scales of limbed tetrapodomorphs evolved from the ‘elpistostegid’-type of scale by an enlargement and differentiation of the articulation facets and a shortening and broadening of the keel. These changes caused a tighter connection between gastral scales within a scale row and a greater overlap between the rows. Dorsal round scales of limbed tetrapodomorphs developed from a gastral scale-type by an alteration of the ontogenetic pathway. The posterolateral direction of scale rows in ‘elpistostegids’ was retained in the gastral scalation of most limbed tetrapodomorphs, whereas the arrangement of round dorsal scales is modified to a transverse orientation. Both gastral and dorsal scales of limbed tetrapodomorphs consist solely of parallel-fibred bone with circumferential growth marks. The proportionally larger overlap surfaces of gastral scales and their mode of articulation in the ventral midline indicate that the body of limbed tetrapodomorphs might have been more flexible than that of their finned relatives. The alteration of dermal scales was one of the most rapid morphological changes during the fish-to-tetrapod transition. Once established, gastral and dorsal scales were retained as a conservative character in different lineages of basal tetrapods, in both the amphibian and the amniote lineages.

State-resolved reactivity of CH4 on Pt(110)-(1×2): The role of surface orientation and impact site

The reactivity of methane (CH(4)) on Pt(110)-(1 x 2) has been studied by quantum state-resolved surface reactivity measurements. Ground state reaction probabilities, S(0)(v=0) congruent with S(0)(laser-off), as well as state-resolved reaction probabilities S(0)(2nu(3)), for CH(4) excited to the first overtone of the antisymmetric C-H stretch (2nu(3)) have been measured at incident translational energies in the range of 4-64 kJ/mol. We observe S(0)(2nu(3)) to be up to three orders of magnitude higher than S(0)(v=0), demonstrating significant vibrational activation of CH(4) dissociation on Pt(110)-(1 x 2) by 2nu(3) excitation. Furthermore, we explored the azimuthal and polar incident angle dependence of S(0)(2nu(3)) and S(0)(v=0) for a fixed incident translational energy E(t)=32 kJ/mol. For incidence perpendicular to the missing row direction on Pt(110)-(1 x 2) and polar angles theta>40 degrees, shadowing effects prevent the incident CH(4) molecules from impinging into the trough sites. Comparison of this polar angle dependence with reactivity data for incidence parallel to the missing rows yields state-resolved site specific reactivity information consistent with a Pt(110)-(1 x 2) reactivity that is dominated by top layer Pt atoms located at the ridge sites. A comparison of S(0)(v=0) measured on Pt(110)-(1 x 2) and Pt(111) yields a lower average barrier for Pt(110)-(1 x 2) by 13.7+/-2.0 kJ/mol.

얼굴 인식을 위한 쌍대각 2DLDA 방법

본 논문에서는 얼굴을 인식하기 위한 쌍대각 2차원 LDA를 제안하였다. 기존의 Dia2DPCA와 Dia2DLDA가 대각 방향 영상들의 행 변화량과 열 변화량 사이의 상관을 제한하기 위하여 제안되어지고 있다. 그러나 이러한 방법들은 영상들의 행방향으로 동작한다. 제한 방법에 있어서 행방향의 투영 행렬은 기존 방법과 전혀 다르게 대각 방향 얼굴 영상들의 열 변화량을 고려한 클래스 간의 공분산 행렬과 클래스 내의 공분산 행렬을 이용함으로써 얻어진다. 그리고 열방향의 투영 행렬은 대각방향 얼굴 영상들의 행 변화량을 고려한 클래스 간의 공분산 행렬과 클래스 내의 공분산 행렬을 이용함으로써 얻어진다. 좌우 양측의 투영 방법은 투영 행렬들을 좌우로 곱함으로써 적용된다. 그 결과로 특징 행렬의 차원과 계산 시간이 감소된다. ORL 얼굴 데이터베이스에서 수행된 실험들은 Frobenius, Yang, AMD와 같은 3가지 거리 척도를 사용하여 2DPCA, B2DPCA, 2DLDA 등과 같은 다른 얼굴 인식 방법들보다 제안된 방법의 인식률이 높음을 보여준다. In this paper, a method called bilateral diagonal 2DLDA is proposed for face recognition. Two methods called Dia2DPCA and Dia2DLDA were suggested to reserve the correlations between the variations in the rows and columns of diagonal images. However, these methods work in the row direction of these images. A row-directional projection matrix can be obtained by calculating the between-class and within-class covariance matrices making an allowance for the column variation of alternative diagonal face images. In addition, column-directional projection matrix can be obtained by calculating the between-class and within-class covariance matrices making an allowance for the row variation in diagonal images. A bilateral projection scheme was applied using left and right multiplying projection matrices. As a result, the dimension of the feature matrix and computation time can be reduced. Experiments carried out on an ORL face database show that the proposed method with three different distance measures, namely, Frobenius, Yang and AMD, is more accurate than some methods, such as 2DPCA, B2DPCA, 2DLDA, etc.

Ab initiostudy of subsurface diffusion of Cu on the H-passivated Si(001) surface

In this paper we use density-functional theory calculations to analyze both the stability and diffusion of Cu adatoms near and on the H-passivated Si(001) surface. Two different Cu sources are considered: depositing Cu from vacuum, and contaminating Cu outdiffusing from bulk Si. Deposited Cu from vacuum quickly moves subsurface to an interstitial site in the third Si layer (T2). Once there, Cu adatoms enter a subsurface zigzag migration route between T2 and another subsurface site, $\text{T}2\ensuremath{\rightarrow}\text{HSL}\ensuremath{\rightarrow}\text{T}2$, along the dimer row direction. Contaminating Cu outdiffusing from bulk is found to be a fast diffuser along both parallel and perpendicular directions to the dimer row when far from the surface. It is attracted to the layers close to the surface and becomes trapped at an interstitial site located at the sixth Si layer (T3). As the outdiffusing Cu atoms get closer to the surface, a channeling zigzag diffusion along the dimer row direction, similar to that one followed by deposited Cu from vacuum, is favoured over diffusion along the perpendicular direction. These results are consistent with previous experimental work done on similar systems and will motivate further experiments on the interesting interaction between Cu and Si surfaces.

Structure and energetics ofSi(111)−(5×2)-Au

We propose a new structural model for the Si(111)-(5x2)-Au reconstruction. The model incorporates a new experimental value of 0.6 monolayer for the coverage of gold atoms, equivalent to six gold atoms per 5x2 cell. Five main theoretical results, obtained from first-principles total-energy calculations, support the model. (1) In the presence of silicon adatoms the periodicity of the gold rows spontaneously doubles, in agreement with experiment. (2) The dependence of the surface energy on the adatom coverage indicates that a uniformly covered phase is unstable and will phase-separate into empty and covered regions, as observed experimentally. (3) Theoretical scanning tunneling microscopy images are in excellent agreement with experiment. (4) The calculated band structure is consistent with angle-resolved photoemission spectra; analysis of their correspondence allows the straightforward assignment of observed surface states to specific atoms. (5) The calculated activation barrier for diffusion of silicon adatoms along the row direction is in excellent agreement with the experimentally measured barrier.

Segmentation of unevenly illuminated line scanned images

PurposeThough many segmentation methods have been published, few of them are developed especially for line scanned images. An ill‐illuminated line scanned (IILS) image tends to have a uniform intensity distribution in column direction while non‐uniform intensity distribution in the row direction. So, it is improper to segment IILS images using either a pixed threshold or threshold surface. In view of this, the purpose of this paper is to develop a segmentation method that is suitable for segmented IILS images.Design/methodology/approachTo obtain satisfactory segmentation results, the illumination variation across the column of a line scanned image was taken into account and a column‐based segmentation method was developed. The method first calculates each column's standard deviation. Then a threshold value is automatically assigned to each column based on the derived values. Finally, by assembling each columns threshold value, a so‐called threshold line is formed. The method is threshold‐line segmentation method based on standard deviation (TLSTD).FindingsThe developed threshold‐line‐based segmentation method is compared with Otsu's fixed threshold segmentation method and Niblack's threshold‐surface‐based segmentation method. The results show that the threshold‐line‐based segmentation method is more suitable for segmenting IILS images.Research limitations/implicationsDespite TLSTD outperforming Otsu's and Nilblack's segmentation methods, there are some limitations to it. The most obvious one is that the predetermined allowable deviation has influences on the integrality of the extracted flaws. Besides, since the proposed method is designed specifically for segmenting images captured by line scan cameras with a slant line light source, it is suitable for segmenting the kind of images only. In other words, the method shows no advantages in segment area scanned images.Practical implicationsGenerally, the approach is useful in automated visual inspection where line scan cameras are employed.Originality/valueThe merit of the proposed method is that the slant of the line light source is now allowed. In other words, even if a grabbed line scanned image is unevenly illuminated, the proposed segmentation method is still able to successfully detect desired flaws.

Relevance-Weighted (2D)2LDA Image Projection Technique for Face Recognition

In this paper, a novel image projection technique for face recognition application is proposed which is based on linear discriminant analysis (LDA) combined with the relevance-weighted (RW) method. The projection is performed through 2 - directional and 2-dimensional LDA, or (2D) 2 LDA, which simultaneously works in row and column directions to solve the small sample size problem. Moreover, a weighted discriminant hyperplane is used in the between-class scatter matrix, and an RW method is used in the within-class scatter matrix to weigh the information to resolve confusable data in these classes. This technique is called the relevance-weighted (2D) 2 LDA, or RW(2D) 2 LDA, which is used for a more accurate discriminant decision than that produced by the conventional LDA or 2DLDA. The proposed technique has been successfully tested on four face databases. Experimental results indicate that the proposed RW(2D) 2 LDA algorithm is more computationally efficient than the conventional algorithms because it has fewer features and faster times. It can also improve performance and has a maximum recognition rate of over 97%.

Feature extraction based on Laplacian bidirectional maximum margin criterion

Maximum margin criterion (MMC) based feature extraction is more efficient than linear discriminant analysis (LDA) for calculating the discriminant vectors since it does not need to calculate the inverse within-class scatter matrix. However, MMC ignores the discriminative information within the local structures of samples and the structural information embedding in the images. In this paper, we develop a novel criterion, namely Laplacian bidirectional maximum margin criterion (LBMMC), to address the issue. We formulate the image total Laplacian matrix, image within-class Laplacian matrix and image between-class Laplacian matrix using the sample similar weight that is widely used in machine learning. The proposed LBMMC based feature extraction computes the discriminant vectors by maximizing the difference between image between-class Laplacian matrix and image within-class Laplacian matrix in both row and column directions. Experiments on the FERET and Yale face databases show the effectiveness of the proposed LBMMC based feature extraction method.

Theoretical Study of Dispersion Binding of Hydrocarbon Molecules to Hydrogen-Terminated Silicon(100)-2×1

Noncovalent interactions between organic molecules and hydrogen-terminated silicon(100)-2×1 influence surface chemistry and diffusion. To develop our understanding of these interactions, we studied the dispersion binding of two model hydrocarbons, methane and benzene, on hydrogen-terminated silicon(100)-2×1 using a density-functional theory (DFT) technique incorporating dispersion corrections. The corrections were implemented using previously developed carbon-centered potentials (DiLabio, G. A. Chem. Phys. Lett. 2008, 455, 348−353.) and newly developed silicon-centered potentials, designed to correct the well-known erroneous long-range behavior of DFT methods. Our calculations predict that the preferred position for methane binding to the surface occurs over the area between two dimer rows (the “gulley”) and between two sets of dimers (binding energy (BE) = 2.2 kcal/mol). When the methane is positioned over a dimer row, BE = 1.9 kcal/mol. Diffusion of methane along the dimer row direction was calculated to be only marginally more facile than diffusion across rows. In the case of benzene, the preferred binding position is over the dimer row with the benzene roughly parallel to the surface and centered over one surface hydrogen (BE = 5.6 kcal/mol). The complex in which the benzene is over the gulley is less strongly bound (BE = 5.3 kcal/mol). Additional higher energy structures were also found. A detailed potential energy surface map reveals that diffusion of benzene in the row direction is more facile than diffusion across dimer rows. The calculated, room-temperature rate constant associated with diffusion along the row is calculated to be 1.7 times larger than that for diffusion in the perpendicular-to-row direction. Our findings show that surface anisotropy and molecule shape contribute to a directional preference for diffusion.

Discrimination of Chiral Adsorption Configurations: Styrene on Germanium(100)

We investigated the adsorption geometries and desorption temperatures of styrene on a Ge surface using scanning tunneling microscopy (STM), temperature programmed desorption (TPD), and ab initio density functional theory (DFT) calculations. Our STM results show that styrene molecules attach via the vinyl group in two adsorption configurations: (i) on the top of single Ge dimers by forming di-σ bonds (OT) and (ii) in a paired end-bridge between two adjacent Ge dimers within the same dimer row (PEB). Moreover, the PEB configurations are divided into two types of adsorption configurations depending on the arrangement of the phenyl rings of the two styrene molecules: either the axis running through the two phenyl rings is diagonal to the dimer row direction (trans-PEB) or perpendicular to the dimer row direction (cis-PEB). STM images can discriminate the OT configurations with (S) and (R) chiralities, as well as the PEB configurations with diastereomeric (R,S) and enantiomeric (R,R) and (S,S) chiralities at t...