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PubMed2004

Noise, delays, robustness, canalization and all that.

A biological system such as a developing embryo can withstand many perturbations. What is the basis of this robustness both against noise and mutation? Recent advances in modeling may throw new light on this old problem. First, recent theoretical and experimental work clearly demonstrates the importance of noise and time delays for the proper functioning of genetic networks: noise and delays are simply part of the normal operating constraints. By contrast, sweeping statements have been made recently about a so-called 'robustness' of biological processes, based on work that neglects noise and delays completely. I submit that studying the stability of complex biological systems with such omissions is an unnecessary, inadequate and potentially disastrous simplification. I review the existing alternatives and propose using them to construct a modeling framework that overcomes all serious limitations.

Computational Biology↗
PubMed1979

Syntactic and phonological influences on children's articulation.

The effects of syntactic and phonological structure on the consonant articulations of children with phonological deficits were investigated. Three structural variables were studied: syntactic structure (noun phrase, declarative sentence and passive sentence), work structure (monosyllable and disyllable) and word position (initial and final). Syntactic structure and word structure significantly affected the accuracy of articulation and the degree of word simplification. Structural complexity may contribute to overall hierarchial complexity, in turn causing children to simplify their speech.

Articulation Disorders↗
PubMed1996

Acknowledging mixed-sex people.

This article calls attention to the importance of more carefully defining femaleness and maleness and more fully acknowledging the existence of mixed-sex people. Mixed-sex people are defined as people with at least one female and one male characteristic, where female or male characteristics are defined as characteristics that are possessed by no more than roughly half the population (the distribution criterion) and either play a clear role in reproduction (the reproduction criterion) or are very highly correlated across all cultures with characteristics that meet both the distribution and reproduction criteria (the correlation criterion). Among other recommendations, those who work in the field of human sexuality are urged, on the basis of these more careful definitions and on ethical grounds, to use the term sex-simplification rather than sex-change in describing surgical/hormonal treatments for transsexuals and to radically alter their use of the terms heterosexual and homosexual.

Female↗
PubMed1980

Cholinergic neuronotrophic factors: fractionation properties of an extract from selected chick embryonic eye tissues.

An aqueous extract derived from selected intraocular tissues of 15-day chick embryos contains a soluble macromolecular agent which is capable of ensuring the survival of 8-day chick embryonic ciliary ganglionic neurons in monolayer culture. When this ciliary neuronotrophic factor (CNTF) was concentrated using ultrafiltration and subjected to Sephadex G100 and G200 chromatography, activity was detected in most of the eluted fractions. A peak of the most active fractions was eluted in a region corresponding to a molecular weight of 35-40 X 10(3) and contained about 20-30% of the applied protein. CNTF activity bound readily to DE-52 cellulose resin at neutral pH and was eluted with NaCl in a narrow region containing about 20-40% of the applied protein. Gel electrophoretic staining profiles of the active DE52 fraction indicated considerable (but still only partial) simplification in protein composition. While significant CNTF activity losses were incurred in response to each of the above treatments, an active material could be conveniently generated in one working day in milligram amounts having a specific activity of 60,000 trophic units/mg protein. This trophic activity is in the same range as that of the only other known neuronotrophic factor, Nerve Growth Factor.

Animals↗
PubMed1994

DNA polymerase III of Mycoplasma pulmonis: isolation and characterization of the enzyme and its structural gene, polC.

Mycoplasmas have originated from Gram-positive bacteria via rapid degenerative evolution. The results of previous investigations of mycoplasmal DNA polymerases suggest that the process of evolution has wrought a major simplification of the typical Gram-positive bacterial DNA polymerase profile, reducing it from three exonuclease (exo)-positive enzymes to a single exo-negative species. The objective of this work was to rigorously investigate this suggestion, focusing on the evolutionary fate of DNA polymerase III (Pol III), the enzyme which Gram-positive bacteria specifically require for replicative DNA synthesis. The approach used Mycoplasma pulmonis as the model organism and exploited structural gene cloning, enzymology, and Pol III-specific inhibitors of the HPUra class as investigative tools. Our results indicate that M. pulmonis has strongly conserved a single copy of a structural gene homologous to polC, the Gram-positive bacterial gene encoding Pol III. M. pulmonis was found to possess a DNA polymerase that displays the size, primary structure, exonuclease activity, and level of HPUra sensitivity expected of a prototypical Gram-positive Pol III. The high level of sensitivity of M. pulmonis growth to Gram-positive Pol III-selective inhibitors of the HPUra type strongly suggests that Mycoplasma has conserved not only the basic structure of Pol III, but also its essential replicative function. Evidence for a second, HPUra-resistant polymerase activity in M. pulmonis is also described, indicating that the DNA polymerase composition of Mycoplasma is complex and closer to that of Gram-positive bacteria than previously thought.

Amino Acid Sequence↗
PubMed2005

Critical viscosity exponent for classical fluids.

A self-consistent mode-coupling calculation of the critical viscosity exponent z(eta) for classical fluids is performed by including the memory effect and the vertex corrections. The incorporation of the memory effect is through a self-consistency procedure that evaluates the order parameter and shear momentum relaxation rates at nonzero frequencies, thereby taking their frequency dependence into account. This approach offers considerable simplification and efficiency in the calculation. The vertex corrections are also demonstrated to have significant effects on the numerical value for the critical viscosity exponent, in contrast to some previous theoretical work which indicated that the vertex corrections tend to cancel out from the final result. By carrying out all of the integrations analytically, we have succeeded in tracing the origin of this discrepancy to an error in earlier work. We provide a thorough treatment of the two-term epsilon expansion, as well as a complete three-dimensional analysis of the fluctuating order-parameter and transverse hydrodynamic modes. The study of the interactions of these modes is carried out to high order so as to arrive at z(eta) = 0.0679+/-0.0007 for comparison with the experimentally observed value, 0.0690+/-0.0006 .

Journal Article↗
PubMed2000

Evolutionary malignant resistance of cells to damaging factors as common biological defence mechanism in neoplastic development. Review of conception.

Cells have some inborn resistance to harmful factors, which could be called physiological or natural resistance. The mechanisms of multixenobiotic resistance (MXR) and multidrug resistance (MDR) have common features in the formation of acquired resistance in microorganisms, carcinogenesis, tumour metastases and chemotherapy or irradiation. ATP-dependent membrane P-glycoprotein, as an MDR efflux pump, glutathione S-transferases and other products of evolutionary resistance-related genes arised for exportation and detoxification of cytotoxic xenobiotics and drugs are transmitted from bacteria to man. On the one hand, this evolutionary MXR as a common biological defence mechanism is a "driving" power to conserve homeostasis of cells, tissues and organs. On the other hand, mutation, selection and simplification of properties are the causes of functional and morphological changes in tumour cells which regress to a more primitive mode of existence (atavism) for adaptation to survival. In the present work are presented data on the forms of E. coli resistant to antibiotics and of sarcoma 45 resistant to alkylic preparations. They may be helpful in revealing the causes of resistance and acquired accelerated growth of cells. The development of tumours as fibromas 14-15 years following injection of a vital dye trypan blue into human skin supports our conception that neoplastic growth is a particular case of the evolutionary resistance of cells adapted to the damaging factors. So, tumour cells adopting the enhancement mechanisms of general biological persistent resistance, i. e. undergoing repeated cycles of malignancy enhancement, adapt themselves to survive under the changed unfavourable conditions.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Human nutrition--paradoxes of drugs and diet.

Complex historical and other reasons account for public confusion concerning optimal nutritional practice. The mass media are not alone in presenting results of scientific work in non-scientific form. Health professionals, scientists, and people from industry have all contributed to the confusion concerning diet and the public good. Extrapolation from one situation to another, simplification of issues, and biased presentation of data, have intensified the problems. The limited perspective of many experts is frequently coupled with over-enthusiastic promotion of what are really hypotheses rather than established truths. The public good is not being served by the present confusing pattern of paradoxes. There is an urgent need for health professionals to review their presentations to the public such that emerging scientific knowledge is presented effectively in terms of a broad perspective.

Adolescent↗
PubMed1991

SV-40 transformation: effect on GM2 ganglioside in cultured cell lines.

In previous work, we observed the presence of substantially elevated levels of GM2 after Simian Virus 40 (SV-40) transformation of human fetal brain cells. This elevated level of GM2 contrasted with the reports of many other investigators who had often observed decreased levels of GM2 and a simplification of ganglioside pattern in various non-neural rodent cell lines. In order to determine if the increase in GM2 in the transformed human brain cells would also be found in transformed rodent brain cells, we analyzed ganglioside changes after transformation in mouse brain cell lines and observed the increase in GM3 and low levels or lack of GM2 usually noted in rodent SV-40 transformed cell lines. In addition, we analyzed changes after SV-40 transformation in three human fibroblast lines and found that all three lines contained substantially elevated levels of GM2 after SV-40 transformation. As a result of this study, our earlier work on SV-40 transformed human brain cells, and occasional other reports of high levels of GM2 in human SV-40 transformed cell lines, elevated levels of GM2 may be considered a marker for SV-40 transformed human cells of both fibroblastic and neural origin.

Animals↗
PubMed1985

[Test report on the system components for film processing by the middle-format technology].

Industrially developed accessories for use with medium-format equipment, which have been tested in a-clinical settery, were evaluated separately. The automatic mounting system (Delcadro) with the plastic mount (Cadrix) was accepted by all of our colleagues, and was rated as an advantage, with hardly any reservations. A slight modification is needed in the design of the mounts. This equipment would be a desirable addition to our own equipment for routine work. The daylight system (camera magazine and feeder) is, in principle, certainly a step in the right direction. Handling of the magazine proved to be too complicated and it was prone to malfunctions. Simplification, especially of the loading mechanism, would be desirable. The film feeder is designed for use with conventional roll processing machines. In our opinion, a feeder will always be put to full use if the films processed in this machine are mainly or exclusively of middle format; the darkroom is not permanently staffed and/or adaptation to an existing daylight system (large formats) has already been effected and/or depending on availability, both large and medium size-formats can be processed fully automatically as quickly as possible. However, if films of various formats are processed by an assistant in a darkroom, it is possible to deal with the total quantity of films faster than with a feeder by inserting 3 or 4 medium-format films (or 2 or 3 large-format films) simultaneously. The Heliomat film viewer offers impressive reproductions of 100 mm film on a glare-free glass screen.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation Studies as Topic↗
PubMed1994

An analytical solution for the dynamic control of multileaf collimators.

All current optimization techniques in radiation therapy benefit from the use of strongly non-uniform radiation beams. The most flexible way of generating these fields under real time control is by elementary beam scanning and/or dynamic multileaf collimation. In this work general analytical expressions are derived for the required motion of the collimator leaves to achieve a desired energy fluence distribution or collimator opening density in the patient in the shortest possible time. By simplification of the general expressions the equations of motion have been derived for both the shrinking field and the curtain shutter techniques with the associated approximations clearly quantified. The mechanical limitations on leaf motion, caused by the finite velocity and acceleration, are taken into account. It is shown that almost any desired energy fluence distribution can be created even when the limitations on velocity and acceleration are considered. The basic rule with the curtain shutter technique is that when the energy fluence gradient along the direction of motion of the leaves is positive, the leading leaf should move at maximum speed and the lagging leaf should modulate the field. In regions where the gradient is negative the lagging leaf should instead move at full speed and the leading leaf should modulate the field. The overall treatment time is then proportional to the total increment in energy fluence or opening density between consecutive minima and maxima. For energy fluence profiles with numerous high peaks the treatment time may therefore increase considerably over that for conventional uniform dose delivery. However, in general the treatment time is prolonged by a factor of about two compared to a traditional uniform treatment. Obviously the method developed here for multileaf collimators is also suitable for simple block collimators since it can be used to deliver arbitrary regular or irregular 'dynamic wedge' profiles along the direction of motion of the collimator blocks.

Humans↗
PubMed1990

Reduction syringe liposculpturing.

The use of the syringe has been an advance in reduction and incremental liposculpturing. A real democratization in the medicosurgical group has been possible due to the simplification of the equipment. The shock-absorbing action of the syringe makes the operation safer and allows more fat to be removed and better results to be obtained because one does perfectly symmetrical work. The syringe is a unit of measurement in this surgery of volume.

Adipose Tissue↗
PubMed1983

[Hypnosis and cancer: a working hypothesis. Initial notes].

Hypnosis has been used to resolve stress and anxiety following profound psychological-behavioural changes occurring in the cancer sufferer from the moment of diagnosis. It is stated that hypnosis is useful in improving sick persons' quality of life through the control of stress reactions, simplification of treatment and facilitation of rehabilitation, both within the family and socially. Through deep seated psycosomatic interconnections, psychological attitude can affect organic reaction to all disease, cancer included.

Humans↗
PubMed2000

The development of inhibitory control in preschool children: effects of "executive skills" training.

As one of several processes involved in the executive functioning of the cognitive system, inhibitory control plays a significant role in determining how various mental processes work together in the successful performance of a task. Studies of response inhibition have shown that although 3-year-old children have the cognitive capacity to learn the rules required for response control, indicated by the correct verbal response, developmental constraints prevent them from withholding the correct response (Bell & Livesey, 1985; Livesey & Morgan, 1991). Some argue that these abulic dissociations are relative to children's ability to reflect on the rules required for response control (Zelazo, Reznick, & Pinon, 1995). The current study showed that repeated exposure to tasks facilitating the acquisition of increasingly complex rule structures could improve inhibitory control (as measured by a go/no-go discrimination learning task), even in children aged 3 years. These tasks included a variant of Diamond and Boyer's (1989) modified version of the Wisconsin Card Sort Task and a simplification of the change paradigm (Logan & Burkell, 1986). It is argued that experience with these tasks increased the acquisition of complex rules by placing demands on executive processes. This includes response control and other executive functions, such as representational flexibility, the ability to maintain information in working memory, the selective control of attention, and proficiency at error correction. The role of experiential variables in the development of inhibitory control is discussed in terms of the interaction between neural development and appropriate executive task experience in the early years.

Attention↗
PubMed1989

[Fertilization in vitro and embryo transfer (FIVET) and endometriosis. Uncertainties and issues].

The progressive improvements in the results and extra simplification of the recent techniques for in vitro fertilisation and embryo transfer (IVFET) have contributed to broadening the indications for this method of assisted reproduction. Endometriosis has not escaped this evolution and more and more works referring to the use of IVFET for this indication. All the same, there are many questions which have not been clearly answered. The possible variety of causes for this condition, the number of factors that may be causing the infertility, make it difficult to assess completely the method of therapy, and require that controlled studies should carried out. These are not always easy to perform. IVFET is no exception to these difficulties. The relationships between endometriosis and infertility are complex and very often difficult to assess. All the same, very many hypotheses have been put out to explain the deleterious effect of this abnormality. Certain mechanisms have been suggested (such as troubles with maturation of the follicle and of the oocyte and the production of a hostile environment for the gametes and for the embryo). These are logical arguments for IVFET which initially produces follicular maturation and takes the gametes and the embryo away from the peritoneal and tubal environment. In spite of certain hypotheses which would be unfavourable in cases of endometriosis (oocytes being less likely to be fertilised, poorer quality of the embryos, defective implantation...) the results that have been obtained after IVFET are overall very favourable and certainly can compare with those obtained when it has been used for, for instance, tubal indication.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryo Transfer↗
PubMed2004

Detection of transposable elements in Drosophila salivary gland polytene chromosomes by in situ hybridization.

In situ hybridization is particularly appropriate for mapping specific DNA sequences on polytene chromosomes of Drosophila and other dipterans. This technique is based on the recognition and binding of one labeled sequence (the probe) to homologous sequences on chromosomes fixed on a microscope slide. The probes are labeled with biotin or other nonradioactive products, and the probe signal can be detected as a thin line on the chromosomes, following the shape of the classical Giemsa-stained chromosome bands, thus allowing the detection of TE insertions within the range of 50 to 200 kb. In our laboratory we work on many individuals from natural populations, and as a result we process high numbers of slides hybridized with various DNA probes of transposable elements every day. Therefore, the in situ hybridization technique we use is a simplification of earlier published protocols. This chapter presents our simplified standard in situ hybridization protocol for labeling polytene chromosomes of Drosophila with biotin and a fluorescence stain (FISH).

Animals↗
PubMed1975

[The importance of afterloading technics for radiation protection].

The importance of afterloading techniques for the improvement in radiological protection is shown. Simplifications of the constructional and operational provisions of radiation protection resulting therefrom are discussed. In this connection, the possibility is accentuated of completely giving up under certain conditions the measurement of the individual exposure doses to personnel working in the irradiation room, using long-term and short-term dosimeters.

Female↗