Arbitrary Reference Point Research Articles

Two-dimensional stochastic analysis of flow in leaky confined aquifers subject to spatial and periodic leakage

This paper addresses the issue of flow in heterogeneous leaky confined aquifers subject to leakage. The leakage into the confined aquifer is driven by spatial and periodic fluctuations of water table in an overlying phreatic aquifer. The introduction of leakage leads to non-uniformity in the mean head gradient and results in nonstationarity in hydraulic head and velocity fields. Therefore, a nonstationary spectral approach based on Fourier–Stieltjes representations for the perturbed quantities is adopted to account for the spatial variability of nonstationary head fields. Closed-form expressions for the variances of hydraulic head and specific discharge are developed in terms of statistical properties of hydraulic parameters. The results indicate that the spatiotemporal variations in leakage leads to enhanced variability of the hydraulic head and of the specific discharge, which increase with distance from any arbitrary reference point. The coefficient of leakage and the spatial structure of log transmissivity field and of the amplitude of water table fluctuation are critical in quantifying the variability of the hydraulic head and of the specific discharge.

Endowment effect in capuchin monkeys

In humans, the capacity for economically rational choice is constrained by a variety of preference biases: humans evaluate gambles relative to arbitrary reference points; weigh losses heavier than equally sized gains; and demand a higher price for owned goods than for equally preferred goods that are not yet owned. To date, however, fewer studies have examined the origins of these biases. Here, we review previous work demonstrating that human economic biases such as loss aversion and reference dependence are shared with an ancestrally related New World primate, the capuchin monkey (Cebus apella). We then examine whether capuchins display an endowment effect in a token-trading task. We identified pairs of treats (fruit discs versus cereal chunks) that were equally preferred by each monkey. When given a chance to trade away their owned fruit discs to obtain the equally valued cereal chunks (or vice versa), however, monkeys required a far greater compensation than the equally preferred treat. We show that these effects are not due to transaction costs or timing issues. These data suggest that biased preferences rely on cognitive systems that are more evolutionarily ancient than previously thought—and that common evolutionary ancestry shared by humans and capuchins may account for the occurrence of the endowment effect in both species.

What can we learn about the scene structure from three orthogonal vanishing points in images

The problem of 3D Euclidean reconstruction of structured scenes from uncalibrated images based on the property of vanishing points is studied in this paper. Under the assumption of three-parameter-camera model with varying parameters, we prove that under an arbitrary preassigned world coordinate system, the camera projection matrix of an image can be uniquely determined from three mutually orthogonal vanishing points obtained from the image. When multiple images of the object are present, it is proved that the global consistent projection matrices can be recovered if an arbitrary reference point in space is observed across the views. For the scenario with multiple objects, we may reconstruct each object individually by the proposed method, then register and align them together via the technique of visual metrology so as to obtain the 3D structure of the entire scene. Compared with previous stereovision techniques, the proposed method avoids the bottleneck problem of feature matching and is easy to implement, therefore, more accurate, robust and realistic results are expected. Extensive experiments on synthetic and real world images validate the effectiveness of the proposed method.

Central venous pressure: A useful but not so simple measurement

To review the clinical use of central venous pressure measurements. The Medline database, biographies of selected articles, and the author's personal database. Four basic principles must be considered. Pressure measurements with fluid-filled systems are made relative to an arbitrary reference point. The pressure that is important for preload of the heart is the transmural pressure, whereas the pressure relative to atmosphere still affects other vascular beds outside the thorax. The central venous pressure is dependent upon the interaction of cardiac function and return function. There is a plateau to the cardiac function curve, and once it is reached, further volume loading will not increase cardiac output. If careful attention is paid to proper measurement techniques, central venous pressure can be very useful clinically. However, the physiologic or pathophysiological significance of the central venous pressure should be considered only with a corresponding measurement of cardiac output or at least a surrogate measure of cardiac output.

Method of analyzing tire pitch sequence based on lug stiffness variations

A method of comparing tire noise pitch sequences based on the tire noise generated by tire tread lug stiffness variations provides a secondary examination technique used to evaluate tire noise pitch sequences that have been selected by traditional evaluation techniques. The method includes the steps of defining the tire noise pitch sequence and the pitch lengths, calculating the differential between the arc length from an arbitrary fixed reference point to the end of each pitch length in the pitch sequence and the arc length of the mean pitch length of the number of pitches from that arbitrary reference point, and analyzing the differential to identify desirable and undesirable tire noise characteristics.

Exact distribution of Poisson shot noise with constant marks under power-law attenuation

Considered is a wireless network where nodes transmitting simultaneously at some common power are located at the points of a Poisson process in the infinite plane. In the case of a pure power-law path loss model, the probability distribution of the interference power sum at an arbitrary reference point is evaluated exactly. In particular, when the attenuation exponent equals 4, the distribution in closed form is obtained.

Quantitative anatomical and morphological classification of the iliac vessels anterior to the lumbosacral vertebrae

Anterior surgical approaches to the lumbosacral disc spaces are being undertaken with increasing frequency. This increase and the use of minimally invasive techniques themselves have the potential to raise the incidence of major vessel injuries. The purpose of this study was to determine the variability of the vascular anatomy anterior to the lumbosacral spine and to draw conclusions regarding surgical accessibility of the L5-S1 disc space. Thirty-five cadavers (age range at the time of death 31-87 years) were obtained to evaluate the anatomical features of iliac vessels with respect to the anterior approach to the lumbosacral spine. Direct measurement and morphological classification regarding the relations of these great vessels to the four arbitrary reference points of the lumbosacral disc space were performed. The mean width and height of the L5-S1 disc were 56.4 mm (range 41.6-65.4 mm) and 18.8 mm (range 10-24 mm), repectively. According to the authors' morphological classification, nine specimens (26%) were found to be Type A (standard), 12 (34%) Type B (narrow), two (6%) Type C (ajar), and 12 (34%) Type D (obstacle). The authors have noted quite a variation in the venous vascular anatomy anterior to the lumbosacral disc. During surgical planning for the anterior approach to the lumbosacral spine when using any technique, it is vital to assess carefully radiographic and neuroimaging studies to minimize potentially disastrous vascular complications.

Finger arterial compliance as determined by transmission of light during mental stress and reactive hyperaemia.

A near-infrared finger photoplethysmogram adopting a wavelength of 810 nm provides data pertaining to the pulsatile a.c. component of finger blood flow (delta I) superimposed on the transmitted d.c. components in a normal ( I: tissue plus blood) and an ischaemic circulatory state ( I(t): tissue only). Simultaneous recording of finger blood pressure provides data pertaining to the distending pulse (PP) and mean blood pressure. Based on the Lambert-Beer law, indices of the arterial compliance (CI=delta I/ I/PP) and distensibility [DI=delta I/ I/ln( I(t)/ I)/PP] are advocated for assessing finger vasculature. The functional relationships between transmural pressure and CI and DI were examined using finger occlusion while performing an arithmetic test (i.e. a mental stress) in 16 females, and during reactive hyperaemia in 5. Gradual occlusion of the finger was conducted at 20-s intervals and the beat-by-beat transmural pressure was determined by calculating mean blood pressure minus the occluding cuff pressure. Logarithmically transformed CI and DI data were linearly associated with the transmural pressure; thus, the estimates obtained at a transmural pressure of 40 mmHg were chosen as an arbitrary reference point (CI40 and DI40). The results indicated that CI40 and DI40 were reduced while performing an arithmetic test, and increased during reactive hyperaemia. Responses were larger for CI40 than for DI40. In conclusion, noninvasive finger occlusion allowed the measurement of the compliance/distending pressure relationship, and CI40 could be utilised to evaluate changes in finger vascular tone.

Automatic inversion of magnetic anomalies of faults

An automatic inversion scheme and the related computer program in FORTRAN 77 to invert the magnetic anomalies of faults magnetized in an unknown direction are presented. The inversion scheme finds the initial values of the model parameters and improves them iteratively using Marquardt's optimization technique. The program is generalized in the sense that it can be used for any component of the magnetic anomaly, viz., total, horizontal and vertical. The positions of the dominant minimum and maximum anomaly values are used to estimate the initial values of the depths to top and bottom of the fault model, while the ratio of their anomaly values is used to initialize the value of the direction of magnetization. The position of the fault is located at the point where the anomaly equals to the sum of the maximum and minimum anomaly values. The input to the inversion program consists of the anomalies measured at given distances from an arbitrary reference point on the profile, besides the geological strike of the body and the direction of measurement. The output consists of observed and calculated anomalies, the model parameters, besides the location of the origin of the fault measured from the chosen reference point and the coefficients of linear regional anomaly that may be present in the data.

Extension of the universal equation of state for solids in high-pressure phases

The defects in applying the universal equation of state (UEOS) presented by Vinet et al. to the analysis of the experimental isothermal compression data of solids in high-pressure phases are that the fitting parameters have actually little physical meaning and have been increased from the original two to three. In this paper, assuming the isothermal bulk modulus varies linearly with pressure we derive the UEOS with an arbitrary reference point from the UEOS presented by Vinet et al. that will eliminate the defects mentioned above. The test on the isothermal compression of ten metal halides as well as cerium shows that the UEOS in the form given by the paper describes the isothermal behavior of solids in high-pressure phases very well.

Is angular impulse always equal to the change of angular momentum in collisions between rigid bodies?

The relationships between angular impulse and angular momentum have been derived in the particular case of collisions between rigid bodies. It is shown that the change in absolute angular momentum about an arbitrary reference point is always equal to the angular impulse. However, the change in relative angular momentum is equal to the angular impulse only when it is calculated about particular points. We illustrate with two examples the differences between both equations. Laburpena: Bultzada angeluarraren eta momentu angeluarraren arteko erlazioak partikularizatuta solido zurrunaren talken kasurako aztertu dira. Momentu angeluar absolutoaren aldaketa edozein puntutan kalkulatuta beti dela bultzada angeluarra frogatzen da. Baina momentu angeluar erlatiboaren aldaketa da bultzada angeluarra puntu berezietan kalkulatzen bada. Ekuazioen arteko ezberdintasunak bi adibideren laguntzarekin erakusten ditugu.

Paraperspective ? affine

It is shown that the set of all paraperspective images with arbitrary reference point and the set of affine images of a 3-D object are identical. Consequently, all uncalibrated paraperspective images of an object can be constructed from a 3-D model of the object by applying an affine transformation to the model and every affine image of the object represents some uncalibrated paraperspective image of the object. It follows that the paraperspective images of an object can be expressed as linear combinations of any two non-degenerate images of the object. When the image position of the reference point is given the parameters of the affine transformation (and, likewise, the coefficients of the linear combinations) satisfy two quadratic constraints. Conversely, when the values of parameters are given the image position of the reference point is determined by solving a bi-quadratic equation.

Reference point approximation method for the solution of bicriterial nonlinear optimization problems

This paper presents a reference point approximation algorithm which can be used for the interactive solution of bicriterial nonlinear optimization problems with inequality and equality constraints. The advantage of this method is that the decision maker may choose arbitrary reference points in the criteria space. Moreover, a special tunneling technique is given for the computation of global solutions of certain subproblems. Finally, the proposed method is applied to a mathematical example and a problem in mechanical engineering.

Regional localization of the hepatocyte growth factor (HGF) gene to human chromosome 7 band q21.1

Hepatocyte growth factor (HGF) is a polypeptide involved in liver regeneration. Its amino acid sequence and gene structure are similar to those of coagulation-related serine proteases. We have used a cDNA clone of HGF and flow-sorted human chromosomes to assign this gene to chromosome 7. Fluorescence in situ hybridization of the HGF genomic clones to human metaphase chromosome spreads showed the localization of this gene to 7q21. Estimation of fluorescent signals relative to arbitrary reference points (ARPs) allowed further localization to 7q21.1.

Resting metabolic rate of the critically ill patient: measured versus predicted.

Critically ill patients requiring mechanical ventilation are particularly susceptible to malnutrition. A knowledge of the energy requirements of these patients is essential in designing nutritional regimens. This study examines 45 resting energy-expenditure measurements performed in a group (n = 40) of postoperative, critically ill patients who were hemodynamically stable, noncomatose, and receiving mechanical ventilation. It examines in particular to what degree the resting energy expenditure of such patients can be predicted using the Harris-Benedict and Aub-Dubois formulae. Resting energy expenditure was measured using indirect calorimetry. There was only a moderate correlation between measured resting energy expenditure and that predicted using the Harris-Benedict (r = 0.57) and Aub-Dubois (r = 0.59) formulae. There was little correlation between the ratio of the measured to the predicted (Harris-Benedict) resting energy expenditure and age, or the ratio of actual to ideal body weight and body weight. The measured resting energy expenditure differed widely (70-140%) from predicted, reflecting the many complex factors that influence these patients' metabolic rate. The role of standard predictive formulae in such patients is as an arbitrary reference point to be used to define hypermetabolism (measured greater than predicted) and hypometabolism (predicted greater than measured).

Analysis of gravity anomalies over an inclined fault with quadratic density function

An attempt is made to interpret the gravity anomalies over an inclined fault with variable density contrast. The decrease of density contrast with depth in sedimentary rocks is approximated by a quadratic function. The anomaly equation of an inclined fault is derived with the quadratic density function. The constantsa0,a1 anda2 of the quadratic density function can be found from the known density-depth values. A synthetic anomaly profile of the fault model is interpreted by the non-linear optimisation technique using the Marquardt algorithm. The distances are measured from an arbitrary reference point and thus the origin of the fault model is also treated as an unknown parameter. For the assumed values of the constantsa0,a1 anda2, the various parameters of the fault model are found by the non-linear optimisation technique. The convergence of the method is shown by plotting the values of the objective function, lamda, and the parameters of the fault model with respect to iteration number. The two parameters inclination and origin are found to be correlated. The same program is used to interpret the gravity anomalies with different density contrasts. Finally, the use of modelling with the quadratic density function is discussed.

Comparison between Analytical and Vectorial Methods of the Synthesis of Equations of Motion

In this paper the advantages and weak points of the analytical and vectorial methods of the derivation of equations of motion for discrete systems are considered. The analytical method is discussed especially with respect to Boltzmann-Hamel equations, as generalized Lagrange equations. The vectorial method is analysed with respect to the momentum equation and to the generalized angular momentum equation about an arbitrary reference point, moving in an arbitrary manner. It is concluded that, for the systems with complicated geometry of motion and a large number of degrees of freedom, the vectorial method can be more effective than the analytical method. The combination of the analytical and vectorial methods helps to verify the equations of motion and to avoid errors, especially in the case of systems with rather complicated geometry.

Difficulties of Interpreting Multi-Slope Analysis of Covariance from Statistical Computer Packages

Many statistical computing packages can be used to obtain analyses of covariance fitting different regression slopes for each group. However, the output from most packages easily can be misinterpreted. Least squares means, differences among them, and analysis of covariance vary according to the reference point for the covariate. Because the analysis of covariance and least squares means provided by many packages are based on different reference points, namely, the intercept and the overall mean of the covariate, respectively, the two sets of statistics need not correspond. In fact, significance tests for group differences based on them may suggest contradictory conclusions. Furthermore, these two reference points may be of little interest in a specific application. In some packages such as LSML76, the user can specify the reference points directly. In others, it is possible by a shift in the covariate to obtain the analysis of covariance for any reference point directly and least squares means with simple calculations. Some computer packages require the user to generate extra covariates when fitting the different slope model, a procedure that leads to incorrect least squares means. It is our view that, when the regression slopes vary, the researcher generally should avoid drawing inference based on an arbitrary reference point but instead refer to the regression lines as a whole. However, where a specific point is of interest, care should be taken that both analysis of covariance and least squares means relate to this point.

Stochastic Geometry: An Introduction and Reading-List

This informal review is aimed at nonspecialist readers in the hope of making the literature and methods of stochastic geometry more widely accessible. It develops around one elementary example and is combined with a selected reading list, including some references to early history. The review can serve as a complement to detailed surveys which have recently appeared (see ? 4 for references). Here I simply set down a few essential themes, stressing the continuity of methods applied to widely different problems. The selection is subjective, and viewpoints expressed are often rhetorical or unqualified. Stochastic geometry, or geometrical probability, is a rather broad heading for probability problems which incorporate geometrical figures as the 'outcomes' or 'data'. Examples are to be found in the earliest probability theories. Although the physical realities of coin-tossing, dice and roulette can usually be ignored, this is not true of certain games which depend on the final position of a thrown coin. Random positions of a geometrical figure are the centre of the classical theory. The recreational flavour (or stigma) once associated with these ideas is less noticeable in the presence of applications ranging from astronomy to cell biology and materials science. Additionally the probabilistic foundations are connected to other branches of pure mathematics. Scientific problems may have a geometrical content in the data, in sampling, in theoretical models, or in all three. Examples of geometrical data are: maps of trees, of meteorite finds, or of petty crimes; linear tracks made by subatomic particles; vegetation patterns; images of microscopic structure in minerals or ceramics; linear fractures in rock; thin sections of biological tissues. Here even the question of summarizing data is nontrivial. Secondly, many experimental sampling techniques can be described as geometrical. Spatial variation of vegetation patterns or bird-nest sites might be sampled along a linear transect, inside an arbitrary grid square or within a fixed radius of an arbitrary reference point. Solid structures like minerals and biological tissues are frequently studied by taking thin sections for microscopic examination. Here the deep problem of relating solid geometry to plane sections is compounded with questions of sampling variability, bias, choice of sampling design and inference. The multidisciplinary science of stereology

Geometrical effects on oxide scale integrity

The strains developed during oxidation on curved surfaces depend on the rate at which the bulk of the already formed scale is being displaced from an arbitrary reference point well within the metal substrate. A scale displacement vector is defined in terms of certain variables of scale formation and the strains arising can then be related to scale growth. Strain energy storage within the scale can be calculated for various oxidation kinetics and allowance made for stress relaxation due to oxide creep. Integrity limits for oxide scales growing on curved surfaces are then defined in terms of a critical strain energy criterion for oxide scale failure. The anodizing of aluminium and the growth of oxide scales on iron are considered as examples. It is also shown that the scale displacement vector as defined in this paper may have wider significance in areas where mechanical factors influence oxidation and where oxidation processes exert mechanical effects on their surroundings.