"Mind the trap": mindfulness practice reduces cognitive rigidity

Two experiments examined the relation between mindfulness practice and cognitive rigidity by using a variation of the Einstellung water jar task. Participants were required to use three hypothetical jars to obtain a specific amount of water. Initial problems were solvable by the same complex formula, but in later problems ("critical" or "trap" problems) solving was possible by an additional much simpler formula. A rigidity score was compiled through perseverance of the complex formula. In Experiment 1, experienced mindfulness meditators received significantly lower rigidity scores than non-meditators who had registered for their first meditation retreat. Similar results were obtained in randomized controlled Experiment 2 comparing non-meditators who underwent an eight meeting mindfulness program with a waiting list group. The authors conclude that mindfulness meditation reduces cognitive rigidity via the tendency to be "blinded" by experience. Results are discussed in light of the benefits of mindfulness practice regarding a reduced tendency to overlook novel and adaptive ways of responding due to past experience, both in and out of the clinical setting.     

Testing and weighting characters

Published justifications for weighting characters in parsimony analyses vary tremendously. Some authors argue for weighting a posteriori, some for a priori, and especially those authors that rely on a falsificationist approach to systematics argue for non-weighting. To find a decision, while following the falsificationist approach, one first has to investigate the necessary conditions for the possibility of phylogenetic research to establish an empirical science sensu Popper. A concept of phylogenetic homology together with the criterion of identity is proposed, which refers to the genealogical relations between individual organisms. From this concept a differentiation of the terms character and character state is proposed, defining each character as a single epistemological argument for the reconstruction of a unique transformation event. Synapomorphy is distinguished from homology by referring to the relationship between species instead of individual organisms, thus the set of all synapomorphies constitutes a subset of the set of all homologies. By examining the structure of characteristics during character analysis and hypothesizing specific types of transformations responsible for having caused them, a specific degree of severity is assigned to each identity test. It thus provides a specific degree of corroboration for every hypothesis that successfully passed this test. Since the congruence criterion tests hypotheses of synapomorphy against each other on grounds of their degree of corroboration gained from the identity test, these different degrees of corroboration determine the specific weights given to characters and character state transformations before the cladistic analysis. This provides a reasonable justification for an a priori weighting scheme within a falsificationist approach to phylogeny. It also demonstrates the indispensable necessity of its application.     

Rigidity sensing at the leading edge through alphavbeta3 integrins and RPTPalpha

Cells require optimal substrate stiffness for normal function and differentiation. The mechanisms for sensing matrix rigidity and durotaxis, however, are not clear. Here we showed that control, Shp2-/-, integrin beta1-/-, and talin1-/- cell lines all spread to a threefold greater area on fibronectin (FN)-coated rigid polyacrylamide surfaces than soft. In contrast, RPTPalpha-/- cells spread to the same area irrespective of rigidity on FN surfaces but spread 3x greater on rigid collagen IV-coated surfaces than soft. RPTPalpha and alphavbeta3 integrins were shown previously to be colocalized at leading edges and antibodies to alphavbeta3 blocked FN rigidity sensing. When FN beads were held with a rigid laser trap at the leading edge, stronger bonds to the cytoskeleton formed than when held with a soft trap; whereas back from the leading edge and in RPTPalpha-/- cells, weaker bonds were formed with both rigid and soft laser traps. From the rigidity of the trap, we calculate that a force of 10 pN generated in 1 s is sufficient to activate the rigidity response. We suggest that RPTPalpha and alphavbeta3 at the leading edge are critical elements for sensing FN matrix rigidity possibly through SFK activation at the edge and downstream signaling.     

Relationships between mutation and transformation frequencies in mammalian cells treated "in vitro" with chemical carcinogens.

An analytical quantitative comparison of data from the literature about frequencies of mutations and transformations induced by mutagenic-carcinogenic compounds in mammalian cells was carried out without any selection of unfitting data. The analysis was performed for equitoxic doses and background level. Data on transformation frequency came from 105 experiments performed with 34 carcinogenic compounds: those on mutation frequency came from 66 experiments performed with 26 mutagenic compounds; 7 compounds were assayed for both these activities. The difference in frequency between structural mutations and transformations was about 10(2)-10(3) and it appears statistically extremely significant. These results seem to indicate an absolute difference between structural mutations and transformations. In the framework of other observations it is suggested that structural alterations in a single gene are perhaps only a component of the steps present in the oncogenetic process. We may regard as "epigenetic" type phenomena the other steps involved in this process.     

Studies on Transformations of Hemophilus influenzae : IV. Linked and unlinked transformations

Unlinked transformations were demonstrated to occur by varying the multiplicity of DNA molecules taken up by competent cells. The number of doubles was directly proportional to the product of the frequency of singles for varying concentrations of cells. The kinetics of transformation to doubles and the effect of DNA concentration on double transformations were consistent with the concept that the cell must take up two molecules of DNA in order to be doubly transformed. Linked markers, on the other hand, were a constant fraction of the single transformation for variations in DNA or cell concentration, or time. The kinetics of transformation of linked markers was the same as for the kinetics of single transforming factors. It was, therefore, concluded that linked transformations involve interaction between the cell and a molecule of DNA carrying both markers. The frequency of transformation was found to be the same from resistance to sensitivity as from sensitivity to resistance for the markers streptomycin (S) and cathomycin (C). Purified DNAs, in general, show lower levels of linkage than crude DNA preparations, and for some crude preparations all the S markers were linked to C, suggesting that some dispersion, at least, was a result of DNA preparation. The inactivation of linked markers by heat, ultraviolet, and DNAase was studied.     

Transformations that preserve detailed balance in Markov models.

Aggregated Markov processes related by similarity transformation are equivalent in that they cannot be distinguished by steady-state experiments. We derive an explicit formula for the set of all detailed-balance preserving similarity transformations between such continuous time Markov chains with N states. The matrices that define the allowed similarity transformations are found to be a simple non-linear function applied to almost any element of the special orthogonal group in N dimensions. Since a model is identifiable only if there is no similarity transformations to an equivalent model, we expect this result to prove useful in the theory of identification of aggregated Markov chains, an enterprise of growing importance as more and more single molecules yield to observation.     

Shape equations and curvature bifurcations induced by inhomogeneous rigidities in cell membranes

This article aims at two objectives: one is the shape equation for the equilibrium configurations of biomembranes with heterogeneous rigidities; another is the possible mechanism for curvature bifurcations in various biomembranes such as human red blood cells (RBC). The shape equation is established by treating the inhomogeneous biomembrane as a lipid bilayer vesicle containing inclusions or impurities. After careful investigation of the equation, the rigidity gradient is found to be an initial "driving force" that may destabilize the biomembrane and stimulate shape transitions, and the concept (or mechanism) termed "curvature bifurcations induced by rigidity gradients" is suggested. Various post-bifurcation modes recording the new equilibrium configurations are disclosed. A few post-bifurcation modes are found to coincide well with some practical shape transitions in cells such as the cup-like shape (stomatocyte) transition and spiculated shape (echinocyte) transition in RBC.     

Membrane protein phosphorylation during stomatocyte-echinocyte transformation of human erythrocytes

The normal, discoid shape of red blood cells represents an equilibrium between two opposing factors, i.e., stomatocytic and echinocytic transformations. Most stomatocytic agents were found to be inhibitors of calmodulin, a regulator of the phosphorylation of membrane proteins. We determined whether red cell shape transformations could be caused by changes in phosphorylation of membrane proteins, specifically the cAMP-dependent phosphorylation of ankyrin and band 4.1. Red blood cells were incubated with 32P and 100 microM chlorpromazine (stomatocytic transformation) or 30 mM sodium salicylate (echinocytic transformation) for various time intervals. Ghost membrane proteins were examined by polyacrylamide gel electrophoresis and autoradiography. Spectrin (beta-chain), ankyrin, band 3, band 4.1 and 4.9 were phosphorylated. No change was found in the degree and pattern of phosphorylation after stomatocytic transformation. Salicylate caused a reversible inhibition of transmembranous phosphate transport in both directions. The results indicate that the stomatocytic transformation induced by chlorpromazine and the echinocytic transformation induced by salicylate do not involve a change in phosphorylation, but that the echinocytic transformation induced by salicylate is associated with an inhibition of transmembranous transport of phosphate. Studies with salicylate suggest that the phosphorylation sites of band 3 are found mainly on the endofacial side of the membrane.     

Elastic energy of curvature-driven bump formation on red blood cell membrane.

Model calculations were performed to explore quantitative aspects of the discocyte-echinocyte shape transformation in red blood cells. The shape transformation was assumed to be driven by changes in the preferred curvature of the membrane bilayer and opposed by the elastic shear rigidity of the membrane skeleton. The energy required for echinocyte bump formation was calculated for a range of bump shapes for different preferred curvatures. Energy minima corresponding to nonzero bump heights were found when the stress-free area difference between the membrane leaflets or the spontaneous curvature of the membrane became sufficiently large, but the calculations predict that the membrane can tolerate significant differences in the resting areas of the inner and outer leaflets or significant spontaneous curvature without visible changes in shape. Thus, if the cell is near the threshold for bump formation, the calculations predict that small changes in membrane properties would produce large changes in cellular geometry. These results provide a rational framework for interpreting observations of shape transformations in red cells and for understanding the mechanism by which small changes in membrane elastic properties might lead to significant changes in geometry.     

Elucidating quantitative stability/flexibility relationships within thioredoxin and its fragments using a distance constraint model

Numerous quantitative stability/flexibility relationships, within Escherichia coli thioredoxin (Trx) and its fragments are determined using a minimal distance constraint model (DCM). A one-dimensional free energy landscape as a function of global flexibility reveals Trx to fold in a low-barrier two-state process, with a voluminous transition state. Near the folding transition temperature, the native free energy basin is markedly skewed to allow partial unfolded forms. Under native conditions the skewed shape is lost, and the protein forms a compact structure with some flexibility. Predictions on ten Trx fragments are generally consistent with experimental observations that they are disordered, and that complementary fragments reconstitute. A hierarchical unfolding pathway is uncovered using an exhaustive computational procedure of breaking interfacial cross-linking hydrogen bonds that span over a series of fragment dissociations. The unfolding pathway leads to a stable core structure (residues 22-90), predicted to act as a kinetic trap. Direct connection between degree of rigidity within molecular structure and non-additivity of free energy is demonstrated using a thermodynamic cycle involving fragments and their hierarchical unfolding pathway. Additionally, the model provides insight about molecular cooperativity within Trx in its native state, and about intermediate states populating the folding/unfolding pathways. Native state cooperativity correlation plots highlight several flexibly correlated regions, giving insight into the catalytic mechanism that facilitates access to the active site disulfide bond. Residual native cooperativity correlations are present in the core substructure, suggesting that Trx can function when it is partly unfolded. This natively disordered kinetic trap, interpreted as a molten globule, has a wide temperature range of metastability, and it is identified as the "slow intermediate state" observed in kinetic experiments. These computational results are found to be in overall agreement with a large array of experimental data.     

CELLULAR INHERITANCE AND TRANSFORMATION

1. The article summarizes the empirical evidence relating to the production of inherited character differences between cells that generate cell lineages by asexual fission.
2. The modes of cellular transformation are classified under three headings: adaptive transformations , including antibody formation and some forms of bacterial adaptation; infective transformations , including those secured by viruses, some cellular transformations of micro-organisms, and a colour transformation of mammalian skin; and inductive transformations , mainly exemplified by carcinogenesis and embryonic evocation.
3. Selective transformations of populations of cells are considered only as they may qualify the interpretation of the other types.
4. Adaptive transformations are defined as initially reversible and progressively induced particulate changes in cellular heredity that are functionally dependent in degree and kind upon the nature of the transforming stimulus.
5. Infective transformations are defined as heritable and serially propagable cellular transformations, not normally reversible and not progressively induced, in which the continued presence of the transforming agent or a replica of it is a necessary condition for the maintenance of the transformed state.
6. Inductive transformations are defined as heritable cellular transformations, normally irreversible, not serially propagable, and not progressively induced, in which the maintenance of the transformed state after its initiation does not depend on the continued presence of the inductive stimulus.
7. The inherited character differences between cells are particulate and combinatorial in nature, and there is ground for supposing that they are mediated by cytoplasmic entities that behave as discrete self-reproducing particles.     

Comparison of traps for the control of sheep blowfly in the U.K.

The ability of three commercially available trap types to catch Lucilia (Diptera: Calliphoridae) blowflies was assessed on three sheep farms in southwest England in 2008. The aim was to evaluate their relative value for the control of ovine cutaneous myiasis (sheep blowfly strike) on farms. There was a highly significant difference between the total number of female Lucilia caught per day by the traps, with an Agrilure Trap (Agrimin Ltd, Brigg, U.K.) catching more than the other trap types (Rescue Disposable Fly Trap, Sterling International, Spokane, U.S.A.; Redtop Trap, Miller Methods, Johannesburg, South Africa). However, there was no significant difference between the traps in the numbers of female Lucilia sericata (Meigen) caught. Nevertheless, consideration of the rate at which female L. sericata were caught over time showed that the Agrilure trap did not begin catching until about 30 days after its initial deployment. It subsequently caught L. sericata at a faster rate than the other two traps. The data suggest that the freeze‐dried liver bait used in the Agrilure trap required a period of about 30 days to become fully rehydrated and decompose to the degree required to attract and catch L. sericata. Once the bait was attractive, however, the trap outperformed the other two traps in terms of the rate of L. sericata capture. The Agrilure trap would appear to be the most effective of the designs tested for use against sheep blowfly and blowfly strike in the U.K., but care would be needed to ensure that the traps were deployed in advance of the blowfly season so that the bait was suitably aged when trapping was required.     

Data transformation as a scaling operation in ordination of plankton

Data transformation is seen here as an aspect of scaling such that we are less interested in the quirks and properties of each transformation but are more concerned with the general scaling properties and trends of suites of transformations.Over two years of daily phytoplankton abundance data for 30 species from a temperate lake (Llyn Maelog, North Wales) were subjected to a series of scale-ordered transformations. Two major classes of transformation were systematically varied: binary and smoothing. Binary transformation scaled the cutoff threshold between presence and absence of a species to various levels of abundance.With successively smaller universes and smoothing windows and successive species exclusion, ordinations of sample dates revealed smaller scaled structures in the order: annual cycles of species turnover, seasonal areas of attraction and uniqueness of individual sample dates. Gradual increases in the length of the smoothing window resulted in gradual shifts in the positions of points in sample data ordination, but not necessarily in the species ordinations. Thus sample data structures are more stable with change in scale than are species data structures. These differences in stability are discussed in the context of filtering characteristics of data collection and data analysis. Transformations producing similar species statistics (means, variances and skews) did not generally give similar ordination results, while some transformations giving similar ordinations differed in species statistical parameters.Acknowledgement: The present research was supported by a grant from the National Science foundation (NSF DEB 78-07546) to the first author.     

Transformation of the rice blast fungus Magnaporthe grisea to benomyl resistance

A transformation method based on a dominant selectable marker (benomyl resistance) was developed for the rice blast fungus Magnaporthe grisea. The heterologous gene for -tubulin from Neurospora crassa (pBT3) was used to obtain benomyl-resistant M. grisea transformants at a frequency of 20 to 30/g of DNA. Control transformations carried out with a plasmid conferring hygromycin resistance or a derivative of pBT3 containing a repetitive DNA sequence, yielded the same frequency of transformation as that of pBT3. Molecular analysis of the transformants indicated multiple integration of the vector DNA.     

Spatiotemporal analysis of cell response to a rigidity gradient: a quantitative study using multiple optical tweezers

We investigate the dynamic response of single cells to weak and local rigidities, applied at controlled adhesion sites. Using multiple latex beads functionalized with fibronectin, and each trapped in its own optical trap, we study the reaction in real time of single 3T3 fibroblast cells to asymmetrical tensions in the tens of pN · μm⁻¹ range. We show that the cell feels a rigidity gradient even at this low range of tension, and over time develops an adapted change in the force exerted on each adhesion site. The rate at which force increases is proportional to trap stiffness. Actomyosin recruitment is regulated in space and time along the rigidity gradient, resulting in a linear relationship between the amount of recruited actin and the force developed independently in trap stiffness. This time-regulated actomyosin behavior sustains a constant and rigidity-independent velocity of beads inside the traps. Our results show that the strengthening of extracellular matrix-cytoskeleton linkages along a rigidity gradient is regulated by controlling adhesion area and actomyosin recruitment, to maintain a constant deformation of the extracellular matrix.     

湿地生态系统服务价值评估的空间尺度转换研究进展

湿地生态系统服务取决于一定空间尺度中的生态系统结构和生态过程,而人类从湿地生态系统获得利益的大小也与其空间尺度有着密切联系。同时,湿地生态系统服务价值评估的空间尺度转换问题也一直是整个湿地生态学研究中的热点和难点之一。在分析湿地生态系统服务空间尺度特征的基础上,提出了湿地生态系统服务价值评估研究中空间尺度转换的概念,即是指通过一个已经有的、与被估算湿地生态系统相似的更大空间范围的或更小空间范围的另一湿地生态系统的价值来估算该湿地生态系统的价值量的过程。介绍了常用的空间尺度转换的方法,主要包括成果参照法和空间模型分析两种方法,成果参照法又包括数值直接外推法和调整函数参照法(Meta分析法)。对目前空间尺度转换研究中存在问题进行总结,并对未来的研究进行了展望。     

家庭生态农场的氮素营养生产分析

引言土地的沙漠化也许是人类文明进程所付出的最沉重代价。我国北方干旱地区是一个巨大的潜在“沙漠化温床”,巳沙化土地达3.34×     

Homoeosis in Drosophila. II. a Genetic Analysis of Polycomb

Three dominant mutant alleles of the Polycomb locus of Drosophila melanogaster are associated with homoeotic transformations of meso- and metathoracic to prothoracic legs, a homoeotic transformation of antennae to legs, and abnormalities of wings and some thoracic bristles. Puro and Nygrén (1975) localized Polycomb in the proximal left arm of chromosome 3 within salivary gland chromosome interval 77E,F-80. In the present study, the location and dosage relationships of this locus were examined, using translocation-generated segmental aneuploidy. The results indicate that Polycomb lies within interval 78C,D-79D, and that the locus is haplo-insufficient. Males hypoploid for this interval show meso- and metathoracic leg transformations, and both males and females show wing abnormalities. In addition, the legs of hypoploids of both sexes are shorter than those of wild-type flies, and show aberrancies of segmentation, chaetal number and distribution, and other morphological characteristics. Hypoploid flies do not express a homoeotic antennal-leg transformation, but the deficiency is associated with a Minute phenotype that is known to suppress this transformation in Polycomb flies; thus it cannot be ascertained whether the antennal-leg transformation is a haplo-insufficient phenotype. It is suggested that the expression of non-homoeotic pleiotropic effects provides a criterion for identifying homoeotic mutations that do not function directly in the establishment of determined states, but rather cause homoeosis indirectly. Polycomb is interpreted in this fashion, and it is suggested that the mutant syndrome may result from localized cell death.     

Dynamic excitations in membranes induced by optical tweezers.

We present the phenomenology of transformations in lipid bilayers that are excited by laser tweezers. A variety of dynamic instabilities and shape transformations are observed, including the pearling instability, expulsion of vesicles, and more exotic ones, such as the formation of passages. Our physical picture of the laser-membrane interaction is based on the generation of tension in the bilayer and loss of surface area. Although tension is the origin of the pearling instability, it does not suffice to explain expulsion of vesicles, where we observe opening of giant pores and creeping motion of bilayers. We present a quantitative theoretical framework to understand most of the observed phenomenology. The main hypothesis is that lipid is pulled into the optical trap by the familiar dielectric effect, is disrupted, and finally is repackaged into an optically unresolvable suspension of colloidal particles. This suspension, in turn, can produce osmotic pressure and depletion forces, driving the observed transformations.     

Homeotic transformations of murine vertebrae and concomitant alteration of Hox codes induced by retinoic acid.

Exposure of murine embryos to teratogenic doses of retinoic acid (RA) induced homeotic transformations of vertebrae. Posterior transformations occurred along the complete body axis after RA administration on day 7 of gestation and were accompanied by anterior shifts of Hox gene expression domains in embryos. Anterior transformations of vertebrae in the caudal half of the vertebral column were induced on day 8.5. We suggest that the identity of a vertebral segment is specified by a combination of functionally active Hox genes, a "Hox code." In this concept the sequential activation of Hox genes defines sequentially more posterior axial levels, while mesodermal cells leave the primitive streak. Exogenous RA interferes with the normal establishment of Hox codes and thus with axial specification.