Motion perception and motion estimation by total-least squares

A computational model of motion perception is proposed. The model, which is gradient-based, adheres to the neural constraint that transmitted signals are positive-valued functions by posing the estimation of image motion as a quadratic programming problem combined with total-least squares: a model that assumes that image signals are contaminated by noise in both the spatial and temporal dimensions. By shrinking motion estimates with a regularizer whose subtractive effect introduces a contrast dependent speed threshold into motion computations, it is shown that the total-least squares model when posed as a quadratic programming problem, is capable of explaining both increases and decreases in perceived speed as these effects were reported by Thompson (1982) to vary as a function of image contrast and temporal frequency. The correlation that exists between the model's contrast speed response and results reported from visual psychophysics is consistent with the view that the visual system assumes that image signals may be contaminated by noise in both the spatial and the temporal domain, and that visual motion is influenced by the consequence of these assumptions.     

Quantitative description of cell cycle kinetics under chemotherapy utilizing flow cytometry.

A discrete time cell cycle kinetics model is developed to account for the effects of cytotoxic chemotherapy, particularly including the existence of cells destined to die. A model structure is determined from related experiments, leaving key parameter values undetermined. These values are found by determining the best least squares fit of the predicted to the observed DNA distribution data at a series of time intervals. The numerical methods include separable least squares, linear inequality constrained least squares and the Gauss--Newton method. This approach is applied to an experiment in which the Ehrlich ascites tumour was given a single dose of bleomycin. The results include several different parameters, including the age response function and a time series of cell age and DNA distributions, which can be used as a basis for further treatment.     

Quantitative Description of Cell Cycle Kinetics Under Chemotherapy Utilizing Flow Cytometry

A discrete time cell cycle kinetics model is developed to account for the effects of cytotoxic chemotherapy, particularly including the existence of cells destined to die. A model structure is determined from related experiments, leaving key parameter values undetermined. These values are found by determining the best least squares fit of the predicted to the observed DNA distribution data at a series of time intervals. the numerical methods include separable least squares, linear inequality constrained least squares and the Gauss-Newton method. This approach is applied to an experiment in which the Ehrlich ascites tumour was given a single dose of bleomycin. the results include several different parameters, including the age response function and a time series of cell age and DNA distributions, which can be used as a basis for further treatment.     

The impact of giant panda foraging on bamboo dynamics in an isolated environment

Wildlife species are threatened by massive habitat destruction worldwide. Habitat fragmentation and isolation spatially constrain animals and in turn cause non-sustainable rates of animal foraging on plant populations. However, little empirical research has been done in large controlled settings to investigate foraging impacts. We conducted an experiment to characterize the impact of panda foraging on the sustainability of its food resource, bamboo, in an enclosed area of natural habitat (approximately 19 ha). We monitored bamboo density, age, and percent cover throughout the enclosure across a 3-year period. We documented marked declines in bamboo density and percent cover as a result of panda foraging, particularly in younger bamboo age classes. We constructed simultaneous autoregressive models to explain bamboo loss to panda foraging and subsequent bamboo recovery as a function of habitat conditions. Areas with high initial bamboo cover not only were prone to high rates of bamboo percent cover loss but also experienced high rates of subsequent bamboo recovery, as bamboo cover loss opened up the understory for new growth. Variograms of ordinary least squares model residuals revealed that the range of spatial autocorrelation in bamboo loss increased over time as available bamboo forage declined. The results have implications for understanding the impact of animal foraging on vegetation and also highlight the importance of preventing further habitat fragmentation and isolation.     

Fractal texture features based on optical density surface area. Use in image analysis of cervical cells

The spatial distribution of the optical density of an image of a cell nucleus can be imagined to resemble a rugged surface in a three-dimensional space. The area of this surface can be measured using different unit-sized squares, yielding different values for the total area depending on the unit size. A fractal dimension can be calculated from the relationship between the unit size and the overall area measured; this fractal dimension is characteristic of the surface measured. This technique was applied to extract three new nuclear features from stained cervical cells. These new features were useful for the computer discrimination of normal and premalignant cervical cells. The features are defined, and their discriminating power is compared to that of some other nuclear features.     

高原鼠兔洞穴区次生斑块面积的测定方法

利用数码相机快速获得高原鼠兔挖掘活动形成的次生斑块图像,运用地理信息系统软件（Arcview） 计算其面积。运用该方法对草地内高原鼠兔洞穴区次生斑块的面积进行了实地测量,结果显示该方法可以快速、准确测量出不同形状次生斑块的面积,具有良好的实用性和可操作性。     

The taxonomic distribution of rare and common species among families in the vascular plant flora of Fennoscandia

Many plant traits are not randomly distributed among families. The question considered here is ‘are rarity and commonness of vascular plants in Fennoscandia randomly distributed among families?’ If more rare or more common species are found within a family, this may give some initial indications about which traits may predict rarity and commonness of species. A species was defined as rare or common based on its abundance and on the number of grid squares it occupies. 1521 naturally occurring species in 229 75×75 km grid squares were used. Permutation tests were performed to assess statistically if rarity and commonness are randomly distributed among families. Several families can be identified as having more rare or more common species than would be expected under a random allocation model. However, there are little deviations from what would be expected if rarity and commonness were randomly distributed among families in the whole Fennoscandian flora. It is proposed that the arbitrary geographical limits of the study area may account for the lack of any clear patterns of rarity and commonness among and between families.     

An accurate and effective FMM-based approach for freehand 3D ultrasound reconstruction

Freehand three-dimensional ultrasound imaging is a highly attractive research area because it is capable of volumetric visualization and analysis of tissues and organs. The reconstruction algorithm plays a key role to the construction of three-dimensional ultrasound volume data with higher image quality and faster reconstruction speed. However, a systematic approach to such problem is still missing. A new fast marching method (FMM) for three-dimensional ultrasound volume reconstruction using the tracked and hand-held probe is proposed in this paper. Our reconstruction approach consists of two stages: bin-filling stage and hole-filling stage. Each pixel in the B-scan images is traversed and its intensity value is assigned to its nearest voxel in the bin-filling stage. For the efficient and accurate reconstruction, we present a new hole-filling algorithm based on the fast marching method. Our algorithm advances the interpolation boundary along its normal direction and fills the area closest to known voxel points in first, which ensure that the structural details of image can be preserved. Experimental results on both ultrasonic abdominal phantom and in vivo urinary bladder of human subject and comparisons with some popular algorithms are used to demonstrate its improvement in both reconstruction accuracy and efficiency.     

Robust framework for PET image reconstruction incorporating system and measurement uncertainties

In Positron Emission Tomography (PET), an optimal estimate of the radioactivity concentration is obtained from the measured emission data under certain criteria. So far, all the well-known statistical reconstruction algorithms require exactly known system probability matrix a priori, and the quality of such system model largely determines the quality of the reconstructed images. In this paper, we propose an algorithm for PET image reconstruction for the real world case where the PET system model is subject to uncertainties. The method counts PET reconstruction as a regularization problem and the image estimation is achieved by means of an uncertainty weighted least squares framework. The performance of our work is evaluated with the Shepp-Logan simulated and real phantom data, which demonstrates significant improvements in image quality over the least squares reconstruction efforts.     

A neglected facet of island biogeography: The role of internal spatial dynamics in area effects

The classical theory of island biogeography has as its basic variable the presence or absence of species on entire islands, and as its basic processes colonization and extinction rates on entire islands as functions of island area, distance, and so forth. Yet for many organisms with limited dispersal abilities, it may be more reasonable to consider larger islands as comprised of an ensemble of local populations coupled by within-island dispersal. Conceptual arguments and a simple patch occupancy model are used to examine the potential relevance of such internal spatial dynamics in explaining area effects, expressed via the probability that a species is present per unit area as a function of total island area. The model suggests that strong area effects depend on a rather fine balance between local colonization and extinction rates. A fruitful direction of future research should be the application of patch dynamic theory to classic island biogeographic questions and systems.     

Scaling of organ subunits in adult mammals and birds: A model

Members of one class of organs—including kidney and lung—consist chiefly of repeating units, or subunits, similar in size and shape. Across species, both the number and size of repeating units may increase with increasing organ size. A simple model is proposed, relating the scaling of unit-size and unit-number to that of organ volume. The model makes three structural assumptions, the crucial one, biologically speaking, being that the numerical density of repeating units scales as does organ surface-to-volume ratio. Data were collected from the literature bearing on the number, diameter, total surface area and total volume of such repeating units (i.e., alveoli, air capillaries, renal tubules and glomeruli), for avian and mammalian lung and for mammalian kidney, each as a function of organ size. These data, after log-log transformation, were submitted to standard linear least squares regression analysis. The resultant slopes for nine different regression lines are in good agreement with the model predictions. This finding suggests, surprisingly, that organ scale-up, at least for selected organs, expressed in terms of repeating units, as a function of organ volume, in mammals and birds, and conceivably in other phyla, may be based on a small number of elementary structural principles.     

Assessing the potential range expansion of the exotic monk parakeet in Spain

In this study we determine favourable areas for the monk parakeet, Myiopsitta monachus , in peninsular Spain to account for its current distribution and predict its future course according to its potential range. We applied a favourability function based on generalized linear models using the presence/absence of breeding colonies of the species and the values of a set of variables on the 5167 UTM 10 × 10 km squares comprising the study area. We calculated the factor of distribution change in presences predicted by the model, and grouped the variables into explanatory factors performing a variation partitioning to assess the explanatory power of each factor. Our model included six predictors to explain the presence and absence of the species. These predictors were grouped into three factors: human activity, climate, and topography. Purely human influences accounted for 63.8% of the variation of the final model, while topographical variables explained 15.2% and climate only 5.7%. We obtained a high distribution change factor in which the presences of the species were predicted to increase between two- and sevenfold. Taking into account highly favourable squares, we conclude that the species is still absent in more than 72% of potential settlement areas, and thus we expect a continuous increase in the distribution of the species. Human activity is the main force moulding the distribution of the species, and lies behind its fast expansion, which is not only active, but is also passive via releases and escapes. We identified the areas of likely future expansion of the exotic monk parakeet in Spain. The pest status of the species in its native range, together to its distribution trend, should be taken into account by wildlife agencies to consider options for management.     

Use and abuse of variance models in regression

In (nonlinear) regression with heteroscedastic errors, introduction of a variance model can be useful to obtain good estimators of the regression parameter. For example, the variance model can be used to obtain the optimal weights in weighted least squares. Methodology of this kind is often used in the analysis of assay data in clinical chemistry, pharmacokinetics, and toxicology. In a series of papers in the pharmacological literature, Sheiner and Beal and others advocate the extended least squares (ELS) methodology that combines regression and variance model into a single objective function based on normal-theory maximum likelihood. The inadequacy of this method is folklore in the (mathematical) statistical literature. In this article it is pointed out that this methodology may lead to inconsistent estimators in practically relevant situations. A review is given of other methods that may be preferable to ELS.     

Shoot Extension in Picea sitchensis I. Seasonal Variation Within a Forest Canopy

The seasonal variation of the daily increment of the shootsof 20-year-old Picea sitchensis is described. Data collectedfor leading shoots and those on the five topmost whorls of branchesare compared qualitatively with seasonal trends in weather.Moving averages are used to describe the seasonal trend in dailyextension rate and systematic variation through the canopy isnoted in this trend. The fitting of Richards' growth functionsto cumulative increment is described. The fitted growth curvedescribed the seasonal trend of cumulative increment well onthe basis of residual sums of squares, but systematic variationwith time was noted in the residuals. Relative growth rate didnot decline as a simple mathematical function of increasingsize attained thus suggesting that simple determinate growthcurves may not be appropriate in describing the growth of foresttrees. Picea sitchensis, Sitka spruce, seasonal growth trends, Richards' growth functions, plant growth model     

A likelihood ratio test for a patterned covariance matrix in a multivariate growth-curve model

In a multivariate growth-curve model, the estimator of the parameter matrix is a function of the matrix of the sums of squares and of the cross-products due to error. However, if the assumption of a patterned covariance matrix is valid, then the parameter estimator does not depend on the error matrix. A likelihood ratio test of this patterned covariance matrix is constructed and its distribution is discussed. A numerical example is provided in which the design consists of two treatment groups, with three repeated measures being taken of the three response variables.     

Catalytic activity of Ntau-carboxymethylhistidine-12 ribonuclease: pH dependence.

The pH-dependence of RNAase A and of Ntau-carboxymethylhistidine-12-RNAase (ribonucleate 3'-pyrimidino-oligonucleotidohydrolase) catalysis was studied. Apparent acid dissociation constants were obtained by least squares analysis of the kinetics data. These dissociation constants were compared with pKa values of model imidazole compounds, and with pKa values of histidine residues 12 and 119 on the protein. The shapes of the kcat versus pH profiles for RNAase A and its carboxymethyl derivative are very similar, from which it is concluded that the mechanism of catalysis is closely similar in the two proteins. Apparent pKa values obtained from the kinetic data are higher for the carboxymethylated protein than for RNAase A, as are the pKa values of residues 12 and 119. The similar shifts are consistent with the conclusions that both these residues are functionally significant in native and modified enzyme, and that an unblocked tau-nitrogen on histidine-12 is not essential for activity. From the enzyme's catalytic dependence on pH, and the NMR determined pKa values we propose that histidine 12 and 119 function catalytically in their basic and acidic forms respectively.     

马尾松直径生长与气候的非线性响应函数

 在Fritts响应函数基础上,提出一种树木生长对各气候变量的非线性响应函数。该响应函数把气候变量的交互作用(各气候变量乘积)之和进行合并,不仅防止了自由度的显著下降,而且还有助于了解各气候变量交互作用对树木生长的平均效应。一组马尾松芯样(15株树,30个芯样,位于马尾松分布带北端)经定年和除趋势后得到的年轮年表与各月平均气温、降水量的关系,经该非线性响应函数分析,表明所取马尾松对前1年11月、当年2、5、8、9、11月的降水量的平方有显著正响应;对前1年12月、当年3、8、12月的平均气温之平方有显著正响应,而对当年2月的平均气温的平方有显著负响应。