3,539 research outputs found
An Introduction to Programming for Bioscientists: A Python-based Primer
Computing has revolutionized the biological sciences over the past several
decades, such that virtually all contemporary research in the biosciences
utilizes computer programs. The computational advances have come on many
fronts, spurred by fundamental developments in hardware, software, and
algorithms. These advances have influenced, and even engendered, a phenomenal
array of bioscience fields, including molecular evolution and bioinformatics;
genome-, proteome-, transcriptome- and metabolome-wide experimental studies;
structural genomics; and atomistic simulations of cellular-scale molecular
assemblies as large as ribosomes and intact viruses. In short, much of
post-genomic biology is increasingly becoming a form of computational biology.
The ability to design and write computer programs is among the most
indispensable skills that a modern researcher can cultivate. Python has become
a popular programming language in the biosciences, largely because (i) its
straightforward semantics and clean syntax make it a readily accessible first
language; (ii) it is expressive and well-suited to object-oriented programming,
as well as other modern paradigms; and (iii) the many available libraries and
third-party toolkits extend the functionality of the core language into
virtually every biological domain (sequence and structure analyses,
phylogenomics, workflow management systems, etc.). This primer offers a basic
introduction to coding, via Python, and it includes concrete examples and
exercises to illustrate the language's usage and capabilities; the main text
culminates with a final project in structural bioinformatics. A suite of
Supplemental Chapters is also provided. Starting with basic concepts, such as
that of a 'variable', the Chapters methodically advance the reader to the point
of writing a graphical user interface to compute the Hamming distance between
two DNA sequences.Comment: 65 pages total, including 45 pages text, 3 figures, 4 tables,
numerous exercises, and 19 pages of Supporting Information; currently in
press at PLOS Computational Biolog
Multi-Instantons and Exact Results II: Specific Cases, Higher-Order Effects, and Numerical Calculations
In this second part of the treatment of instantons in quantum mechanics, the
focus is on specific calculations related to a number of quantum mechanical
potentials with degenerate minima. We calculate the leading multi-instanton
constributions to the partition function, using the formalism introduced in the
first part of the treatise [J. Zinn-Justin and U. D. Jentschura, e-print
quant-ph/0501136]. The following potentials are considered: (i) asymmetric
potentials with degenerate minima, (ii) the periodic cosine potential, (iii)
anharmonic oscillators with radial symmetry, and (iv) a specific potential
which bears an analogy with the Fokker-Planck equation. The latter potential
has the peculiar property that the perturbation series for the ground-state
energy vanishes to all orders and is thus formally convergent (the ground-state
energy, however, is nonzero and positive). For the potentials (ii), (iii), and
(iv), we calculate the perturbative B-function as well as the instanton
A-function to fourth order in g. We also consider the double-well potential in
detail, and present some higher-order analytic as well as numerical
calculations to verify explicitly the related conjectures up to the order of
three instantons. Strategies analogous to those outlined here could result in
new conjectures for problems where our present understanding is more limited.Comment: 55 pages, LaTeX; refs. to part I preprint update
Typology of goat feeding systems in Benin
Feeding is one of the limiting factors of productivity in goat production in developing countries. That’s why this study was carried out to characterize the feeding systems used in goat farming in Benin. Accordingly, a semi-structured survey was conducted among 533 goat farmers in 6 agro-ecological zones in Benin. Data were collected on socio-demographic characteristics, breeding practices and feeding methods. A typology of goat feeding systems was developed using a factorial analysis of mixed data followed by an ascending hierarchical classification. The results of the study revealed three main types of feeding systems. These are feeding systems based on the use of: (i) natural pasture in a free-grazing system, (ii) natural pasture, crop residues and concentrates in a semi-controlled breeding system, and (iii) natural pasture, crop residues and concentrates in a controlled breeding system. The implementation of a programme to improve goat feeding and management systems will contribute significantly to increasing goat productivity. It will also contribute to food security in the rural community.
Keywords: Benin, Capra hircus, feeding practices, management practice
Efficient Color-Dressed Calculation of Virtual Corrections
With the advent of generalized unitarity and parametric integration
techniques, the construction of a generic Next-to-Leading Order Monte Carlo
becomes feasible. Such a generator will entail the treatment of QCD color in
the amplitudes. We extend the concept of color dressing to one-loop amplitudes,
resulting in the formulation of an explicit algorithmic solution for the
calculation of arbitrary scattering processes at Next-to-Leading order. The
resulting algorithm is of exponential complexity, that is the numerical
evaluation time of the virtual corrections grows by a constant multiplicative
factor as the number of external partons is increased. To study the properties
of the method, we calculate the virtual corrections to -gluon scattering.Comment: 48 pages, 23 figure
Bell numbers and Kurepa’s conjecture
We prove under a mild condition that Kurepa's conjecture holds for the set of prime numbers such that (\frac{p-1}{2})! = {2 \overwithdelims () p\;} in
Visible and near infrared spectroscopy in soil science
This chapter provides a review on the state of soil visible–near infrared (vis–NIR) spectroscopy. Our intention is for the review to serve as a source of up-to date information on the past and current role of vis–NIR spectroscopy in soil science. It should also provide critical discussion on issues surrounding the use of vis–NIR for soil analysis and on future directions. To this end, we describe the fundamentals of visible and infrared diffuse reflectance spectroscopy and spectroscopic multivariate calibrations. A review of the past and current role of vis–NIR spectroscopy in soil analysis is provided, focusing on important soil attributes such as soil organic matter (SOM), minerals, texture, nutrients, water, pH, and heavy metals. We then discuss the performance and generalization capacity of vis–NIR calibrations, with particular attention on sample pre-tratments, co-variations in data sets, and mathematical data preprocessing. Field analyses and strategies for the practical use of vis–NIR are considered. We conclude that the technique is useful to measure soil water and mineral composition and to derive robust calibrations for SOM and clay content. Many studies show that we also can predict properties such as pH and nutrients, although their robustness may be questioned. For future work we recommend that research should focus on: (i) moving forward with more theoretical calibrations, (ii) better understanding of the complexity of soil and the physical basis for soil reflection, and (iii) applications and the use of spectra for soil mapping and monitoring, and for making inferences about soils quality, fertility and function. To do this, research in soil spectroscopy needs to be more collaborative and strategic. The development of the Global Soil Spectral Library might be a step in the right direction
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