Chamber response time: A neglected issue in gas exchange measurements

When the dimensions of standard commercial chambers for measuring gas exchange cannot accommodate the object being measured, scientists construct their own chambers. The time needed to reach chamber steady state (chamber response time) depends on net system volume (e.g. chamber and tubing volume) and airflow. Unfortunately, some authors take chamber response time into consideration while others ignore it. We present the formula for calculating chamber response time.     

A net-like structure in the venous system of the late chick embryo

A net-like structure of unknown function found at the junction of the umbilical vein and the left hepatic vein of the 16-day chick embryo is described. The net consists of strands of mesenchyme tissue covered by an endothelial layer continuous with that of the blood vessels in which it is located. An unusual feature of the net is the presence, at certain points where the strands meet, of hollow spherical or ellipsoid bodies, the walls of which are formed from a layer of simple cuboidal epithelium arranged upon a well defined basal lamina. The cavity of these bodies appears to contain some non-cellular material but they have no obvious duct to their exterior. The embryological origin of the net and its possible functions are discussed.     

Input and output channels of quantum biocomputers]

It is proposed that "Quantum Molecular" computer of a neuron consists of the cell cytoskeleton serving as calculating media and input ionic channel sending a hypersound signal to observe these media. The sound spreads through the media travelling along microtubules and microfilaments and switching between those via molecular bridges which serve as elementary switches. The whole system works like a wave guiding net connecting input ionic channels (which generate different sound signals) and output ionic channels (which are controlled by the processed sound signals). Thus the output of such systems depends on the input (controlled by synaptic activity) and on the construction and state of these calculating media. We think that the sound waves spreading through different calculating media solve different physical problems. The construction of the calculating part of the cytoskeleton, according to the hypothesis, is different in different neurons. It is defined by special protein which is produced by DNA, RNA and protein molecular word processor (during brain development and, may be, education). We comment on how the existence of an extremal computer produces an impact on physics and mathematics exemplified by the optimality principle as substitution of physical relativity principle for a complex problem.     

Algorithm to estimate cell biovolume using image analyzed microscopy

This paper describes an algorithm for calculating the biovolume of cells with simple shapes, such as bacteria, flagellates, and simple ciliates, from a 2-dimensional digital image. The method can be adapted to any image analysis system which allows access to the binary cell image--(i.e., the pixels, or (x,y) points, composing the cell. The cell image is rotated to a standard orientation (horizontal), and a solid of revolution is calculated by digital integration. Verification and a critical assessment of the method are presented. The algorithm accounts for irregularities in cell shape that conventional methods based on length, width, and geometrical formulas do not.     

Comparing polynomial and cubic spline interpolation of segment angles for estimating L5/S1 net moment during symmetric lifting tasks

Simple video-based methods previously proposed for field research to estimate L5/S1 net moments during real-world manual materials handling rely on polynomial interpolation on the joint angles from key frames extracted from video recordings; however, polynomial interpolations may not converge as the number of interpolation points increases. Therefore, we compared L5/S1 net moments calculated from continuous kinematic measurements to those calculated from both polynomial and cubic spline interpolation on body segments angles during lifting tasks. For small number of interpolation points (<6) the error in the predicted moment from both the spline and polynomial fits decreased with the increase in the number of interpolation points; however, above 6 interpolation points error for the polynomial fits started to increase while the error from the spline fit continued to decrease. These results suggest that cubic spline interpolation on body segments angles provides a more robust basis for calculating L5/S1 net moment from a few key video frames.     

Hierarchical evolutive systems: A mathematical model for complex systems

The notion of an evolutive hierarchical system proposed in this paper is a mathematical model for systems, like organisms, with more or less complex objects. This model, based on category theory, retains the following characteristics of natural systems: they have an internal organization consisting of components with interrelations; they maintain their organization in time though their components are changing; their components are divided into several levels corresponding to the increasing complexity of their own organization, and the system may be studied at any of these levels (e.g. molecular, cellular...). The state of the system at a given instant is modeled by a category whose objects are its components, the state transition by a functor, a complex object by the (direct) limit of a pattern of linked objects (which describes its internal organization). The properties of limits in a category make it possible to ‘measure’ the emergence of properties for a complex object with respect to its components, and to reduce the study of a hierarchical system to that of its components of the lowest degree and their links. Categorical constructions describe the formation of a hierarchical evolutive system stepwise, by means of the operations: absorption of external objects, destruction of some components, formation of new complex objects.     

Pattern formation in associative neural networks with weak lateral interaction

A model is proposed for the formation of singularities in the director field of orientation-selective cells in the visual cortex. The model consists of a two-layer associative neural net. The forward connections converge to a continuum of steady states. The degeneracy is removed by lateral interactions. It is shown that in many cases the director field contains critical points which are identified as the vortex locations. Received: 1 January 1993/Accepted in revised form: 8 September 1993     

Analysis of object clustering

Objects of a given type lie on a plane or in a thin layer. In the analysis of the arrangement of such objects, the question may arise as to whether these objects form clusters or whether they are randomly distributed. This question can be answered by the calculation of the coefficient of dispersion (CD) of the objects. Some statistical properties of this coefficient, i.e., its sensitivity and its chi-square approximation, are analyzed in this paper. The proposed approach for calculating sensitivity is a mathematical simulation that is not generally applicable but is valid in various biologic applications. Assuming that the objects are much smaller than the expected clusters and that no knowledge exists about interactions among the objects or between the objects and their surroundings, the objects can be assumed to be distributed randomly on the plane. Such situations may occur in various fields, i.e., biology, sociology, archaeology and ecology. The authors have applied this approach successfully in investigating the densities of T-cell lymphocytes in renal transplants treated with Cyclosporin A or conventional immunosuppressive therapy.     

Crossmodal Discrimination of 2 vs. 4 Objects across Touch and Vision in 5-Month-Old Infants

Infants are known to possess two different cognitive systems to encode numerical information. The first system encodes approximate numerosities, has no known upper limit and is functional from birth on. The second system relies on infants’ ability to track up to 3 objects in parallel, and enables them to represent exact numerosity for such small sets. It is unclear, however, whether infants may be able to represent numerosities from all ranges in a common format. In various studies, infants failed to discriminate a small vs. a large numerosity (e.g., 2 vs. 4, 3 vs. 6), although more recent studies presented evidence that infants can succeed at these discriminations in some situations. Here, we used a transfer paradigm between the tactile and visual modalities in 5-month-olds, assuming that such cross-modal paradigm may promote access to abstract representations of numerosities, continuous across the small and large ranges. Infants were first familiarized with 2 to 4 objects in the tactile modality, and subsequently tested for their preference between 2 vs. 4, or 3 vs. 6 visual objects. Results were mixed, with only partial evidence that infants may have transferred numerical information across modalities. Implications on 5-month-old infants’ ability to represent small and large numerosities in a single or in separate formats are discussed.     

Height and cognitive achievement among Indian children

Taller children perform better on average on tests of cognitive achievement, in part because of differences in early-life health and net nutrition. Recent research documenting this height-achievement slope has primarily focused on rich countries. Using the India Human Development Survey, a representative sample of 40,000 households which matches anthropometric data to learning tests, this paper documents a height-achievement slope among Indian children. The height-achievement slope in India is more than twice as steep as in the U.S. An earlier survey interviewed some IHDS children's households eleven years before. Including matched early-life control variables reduces the apparent effect of height, but does not eliminate it; water, sanitation, and hygiene may be particularly important for children's outcomes. Being one standard deviation taller is associated with being 5 percentage points more likely to be able to write, a slope that falls only to 3.4 percentage points controlling for a long list of contemporary and early-life conditions.     

Neuronal processing delays are compensated in the sensorimotor branch of the visual system

Moving objects change their position until signals from the photoreceptors arrive in the visual cortex. Nonetheless, motor responses to moving objects are accurate and do not lag behind the real-world position. The questions are how and where neural delays are compensated for. It was suggested that compensation is achieved within the visual system by extrapolating the position of moving objects. A visual illusion supports this idea: when a briefly flashed object is presented in the same position as a moving object, it appears to lag behind. However, moving objects do not appear ahead of their final or reversal points. We investigated a situation where participants localized the final position of a moving stimulus. Visual perception and short-term memory of the final target position were accurate, but reaching movements were directed toward future positions of the target beyond the vanishing point. Our results show that neuronal latencies are not compensated for at early stages of visual processing, but at a late stage when retinotopic information is transformed into egocentric space used for motor responses. The sensorimotor system extrapolates the position of moving targets to allow for precise localization of moving targets despite neuronal latencies.     

A novel connectionist framework for computation of an approximate convex-hull of a set of planar points, circles and ellipses

We propose a two layer neural network for computation of an approximate convex-hull of a set of points or a set of circles/ellipses of different sizes. The algorithm is based on a very elegant concept - shrinking of a rubber band surrounding the set of planar objects. Logically, a set of neurons is placed on a circle (rubber band) surrounding the objects. Each neuron has a parameter vector associated with it. This may be viewed as the current position of the neuron. The given set of points/objects exerts a force of attraction on every neuron, which determines how its current position will be updated (as if, the force determines the direction of movement of the neuron lying on the rubber band). As the network evolves, the neurons (parameter vectors) approximate the convex-hull more and more accurately. The scheme can be applied to find the convex-hull of a planar set of circles or ellipses or a mixture of the two. Some properties related to the evolution of the algorithm are also presented.     

保护区的分类系统与标准

保护区是一个泛称,根据建立的目的和本身的特点可以划分不同的类型,以利于管理工作的开展。每一个国家都应制订一个与本国资源和要求相适应的保护区分类系统。本文着重讨论按保护对象和保护区性质划分的保护区类型,以供判断每一个保护区的归属和管理重点。     

On estimating the total number of genes of a given kind in the genome and similar problems

From a collection of objects identified by a common characteristic such as mutations of a given phenotype or DNA sequences with a given property, it is possible to estimate the total number of classes these objects may belong to from the number of such classes represented in the sample. An estimation procedure is presented here complementing earlier work by Lewontin and Prout (1956). The precision and bias of the astimate can also be calculated.     

Mapping of dihydrofolate-reductase receptor site by correlation with minimal topological (steric) differences

A procedure for obtaining the shape of (or part of the shape of) a receptor site cavity based on structures of molecules with known activities is outlined and applied to dihydrofolate reductase inhibitors. The procedure consists of determining the optimal standard for calculating the minimal topological (steric) differences (MTD, number of unsuperposable atoms when a molecule is superimposed over the standard). For a series of 15 diaminopyrimidines, substituted in position 5 with aliphatic, cyclo-aliphatic or arylic groups, the correlation of inhibitory power with MTD and π-Hansch hydrophobicity gives a coefficient r = 0.981, while correlating with π only, r = 0.767 is obtained. This procedure may be useful in obtaining quantitative structure-activity correlations for series of non-congeneric molecules, if there are no marked changes in polar groups.     

Metabolic pathways in three dimensions

MOTIVATION: Currently a substantial research effort is devoted to automated representation of metabolic and gene networks. Automatic visualization plays a significant role in such efforts, and becomes an important problem on its own. Graphical visualization of metabolic pathways has to be information dense and not 'overloaded', recognizable and unified, close to traditional and algebraically consistent. The use of three-dimensional 'virtual reality' visualizations may help to understand better the intricate topology of metabolic and regulatory networks. RESULTS: A system of visualizing metabolic networks as graphs in three-dimensional space by means of Virtual Reality Modeling Language (VRML) is presented. The system is based on an XML-compliant MNV ('Metabolic Network Visualizer') language, and comprises MNV language standard and parser, MNV to VRML translator, and interactive pathway constructor, all unified by the HTML graphic user interface. AVAILABILITY: The MNV can be accessed in viewer mode at http://www.patronov.net/sciencevr/mnv/indexview.html or in constructor mode at http://www.patronov.net/sciencevr/mnv/indexmake.html SUPPLEMENTARY INFORMATION: The figures for the paper as well as the Appendices may be found at http://www.patronov.net/sciencevr/mnv/screenshots.html     

A theoretical treatment of damped oscillations in the transient state kinetics of single-enzyme reactions

An extension of the available kinetic theory for reactions in the transient state is presented which establishes that single-enzyme reactions may exhibit damped oscillations under the conditions of standard kinetic experiments performed by stopped-flow techniques. Such oscillations may occur for reasonable magnitudes of rate constants in the enzymic reaction mechanism and at physiological concentrations of enzyme and substrate. In the simplest reaction systems, the oscillations will be strongly damped and lead to progress curves resembling those of a reaction governed by standard exponential transients; statistical regression methods may then have to be applied for their detection and characterization. The observation that single-enzyme reactions may exhibit oscillatory behaviour points to a previously unrecognized possible source of the damped oscillations observed in metabolic systems such as the pathways of glycolysis or photosynthesis.     

A representative pond net sample: Fiction or reality?

The occurrence of chironomids in a standard pond net sample was studied. The standard pond net sample is quite biased; its qualitative to semi-quantitive character should always be taken into account. It is advised to transform abundances (log-normal) of chironomids when collected with the standard pond net. Despite disadvantages the pond net can be used in water quality surveys because of their general objectives.     

The association of oribatid mites with lichens

Oribatei (Acari, Cryptostigmata) are found in a variety of terrestrial habitats, and many are associated with lichens; the relationship ranges from casual to highly dependent. Eighty-three species associated with lichens have been surveyed, and a tentative classification, based on their ecological requirements, is presented: Group A consists of species restricted to lichens as a biotope, though occasionally occurring as accidentals in other habitats; Group B consists of species which while preferring lichens as a habitat and feeding source are also adapted to existence on other plants (though in some cases their immatures may be lichen-restricted); Group C consists of species which, though frequently found on lichens, are equally common in other biotopes, particularly mosses, and must be regarded as much more generalized in their feeding habits. Certain aspects of oribatid-lichen specificity are discussed. The importance of oribatid-lichen associations from the point of view of soil fertility and energetics is emphasized.