3,886 research outputs found
Catalytic RNA and synthesis of the peptide bond
We are studying whether the L-19 IVS ribozyme from Tetrahymena thermophila can catalyze the formation of the peptide bond when it is supplied with synthetic aminoacyl oligonucleotides. If this reaction works, it could give us some insight into the mechanism of peptide bond formation and the origin of coded protein synthesis. Two short oligoribonucleotides, CCCCC and a protected form of CCCCU were prepared; the former was made by the controlled hydrolysis of Poly(C), and the later by multistep chemical synthesis from the protected monomers. The homopentamer was then aminocylated using C-14 labelled Boc-protected glycine imidazolide. This aminoacylated oligo-nucleotide has now been shown to enter the active site of the L-19 IVS, and aminoacyl transfer, and peptide bond formation reactions are being sought. Our synthesis of CCCCU made us aware of the inadequacy of many of the 2'- hydroxyl protecting groups that are in use today and we therefore designed a new 2'- protecting group that is presently being tested
Form factor approach to dynamical correlation functions in critical models
We develop a form factor approach to the study of dynamical correlation
functions of quantum integrable models in the critical regime. As an example,
we consider the quantum non-linear Schr\"odinger model. We derive
long-distance/long-time asymptotic behavior of various two-point functions of
this model. We also compute edge exponents and amplitudes characterizing the
power-law behavior of dynamical response functions on the particle/hole
excitation thresholds. These last results confirm predictions based on the
non-linear Luttinger liquid method. Our results rely on a first principles
derivation, based on the microscopic analysis of the model, without invoking,
at any stage, some correspondence with a continuous field theory. Furthermore,
our approach only makes use of certain general properties of the model, so that
it should be applicable, with possibly minor modifications, to a wide class of
(not necessarily integrable) gapless one dimensional Hamiltonians.Comment: 33 page
Mini Max Wallpaper
Mini Max company formulated a problem for the automatic calculation of the number of wallpaper rolls necessary for decorating a room with wallpaper. The final goal is the development of a web-based calculator open for use to both Mini Max staff and the general public. We propose an approach for reducing the studied problem to the one-dimensional cutting-stock problem. We show this in details for the case of plain wallpapers as well as for the case of patterned wallpapers with straight match. The one-dimensional cutting-stock problem can be formulated as a linear integer programming problem. We develop an approach for calculating the needed number of wallpapers for relatively small problems, create an algorithm in a suitable graphical interface and make different tests. The tests show the efficiency of the proposed approach compared with the existent (available) wallpapersâ calculators
âToxicâ Schools? How School Exposures During Adolescence Influence Trajectories of Health Through Young Adulthood
© 2020 The Author(s) A large body of research identifies the critical role of early-life social contexts such as neighborhoods and households in shaping life course trajectories of health. Less is known about whether and how school characteristics affect individual health and contribute to population health inequality. However, recent scholarship argues that some school environments are so stressful due to high levels of violence, disorder, and poverty that they may be âtoxicâ to student health, but this hypothesis has not been tested using population data. Integrating insights from the life course perspective and stress process model, we use rich longitudinal data from the National Longitudinal Study of Adolescent to Adult Health (n = 11,382), diverse markers of physiological functioning and psychological well-being, and multilevel regression models to examine whether and how school characteristics shape trajectories of physiological dysregulation and depressive risk from adolescence through early adulthood. Findings reveal that, across multiple measures of physiological functioning and psychological well-being, the social and structural characteristics of schools play an essential role in shaping health risk from adolescence through young adulthoodâlong after students left school. In particular, indicators of school-level violence and perceptions of safety and school social disconnectedness had especially strong associations with health risk in both the short- and long-term. School socioeconomic composition was also strongly associated with physiological dysregulation in young adulthood, net of individual and neighborhood socioeconomic exposures. Together, findings from this study suggest that school environments can serve as early-life stressors in the lives of young people that unequally shape health trajectories and contribute to broader patterns of health inequality
Dysplazja kregosĆupowo-przynasadowa : Kozlowski
Background: Kozlowski type spondylo-metaphyseal dysplasia is the most frequent form among spondylometaphyseal dysplasias. Case report: The first cases of such dysplasia among Gypsies - a father and two sons - have been described. Conclusions: Radiographic examination is the only means by which to diagnose Kozlowski type spondylometaphyseal dysplasia with certainty. Correct diagnosis is not only prognostic for the course of the disease and its complications, but also excludes the necessity of further, often expensive, investigations
Statics and dynamics of an Ashkin-Teller neural network with low loading
An Ashkin-Teller neural network, allowing for two types of neurons is
considered in the case of low loading as a function of the strength of the
respective couplings between these neurons. The storage and retrieval of
embedded patterns built from the two types of neurons, with different degrees
of (in)dependence is studied. In particular, thermodynamic properties including
the existence and stability of Mattis states are discussed. Furthermore, the
dynamic behaviour is examined by deriving flow equations for the macroscopic
overlap. It is found that for linked patterns the model shows better retrieval
properties than a corresponding Hopfield model.Comment: 20 pages, 6 figures, Latex with postscript figures in one tar.gz fil
Forest resource information system, phase 3
There are no author-identified significant results in this report
Probing of mortality rate by staying alive : the growthâreproduction tradeâoff in a spatially heterogeneous environment
1. In many annual plants, mollusks, crustaceans and ectothermic vertebrates, growth accompanies reproduction. The growth curves of these organisms often exhibit a complex shape, with episodic cessations or accelerations of growth occurring long after maturation. The mixed allocation to growth and reproduction has poorly understood adaptive consequences, and the lifeâhistory theory does not explain if complex growth in shortâlived organisms can be adaptive. 2. We model the tradeâoff between growth and reproduction in a shortâlived organism evolving in a metapopulation. Individuals occupy risky or safe sites throughout their lives, but are uncertain regarding the risk of death. Modelled organisms are allowed to grow and produce offspring at specified time points (moults), although we also consider scenarios that approximate continuous growth and reproduction. 3. Certain combinations of risky to safe sites select for strategies with mixed allocation to growth and reproduction that betâhedge offspring production in safe and risky sites. Our model shows that spatially heterogeneous environments select for mixed allocation only if safe sites do not become the prevailing source of recruits, for example, when risky sites are frequent. In certain conditions, growth curves are multiâphasic, with allocation to growth that stops, remains constant or accelerates during adult life. The resulting complex growth curves are more likely to evolve in shortâlived organisms that moult several times per adult life. 4. Our work shows that spatial heterogeneity can select for growth that accompanies reproduction and provides insights into the adaptive significance of complex growth curves. Shortâlived crustaceans are particularly predisposed to exhibit complex growth patterns as an adaptive response to spatially heterogeneous environments. Our results suggest that standard statistical growth models assuming adult growth rate to only decelerate over life are not well suited to approximate growth curves of shortâlived crustaceans
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