8 research outputs found
Algebraic properties of ordinary differential equations.
Thesis (Ph.D.)-University of Natal, 1995.In Chapter One the theoretical basis for infinitesimal transformations is
presented with particular emphasis on the central theme of this thesis which
is the invariance of ordinary differential equations, and their first integrals,
under infinitesimal transformations. The differential operators associated with
these infinitesimal transformations constitute an algebra under the operation
of taking the Lie Bracket. Some of the major results of Lie's work are recalled.
The way to use the generators of symmetries to reduce the order of a differential
equation and/or to find its first integrals is explained. The chapter concludes
with a summary of the state of the art in the mid-seventies just before the
work described here was initiated.
Chapter Two describes the growing awareness of the algebraic properties of
the paradigms of differential equations. This essentially ad hoc period demonstrated
that there was value in studying the Lie method of extended groups
for finding first integrals and so solutions of equations and systems of equations.
This value was emphasised by the application of the method to a class of
nonautonomous anharmonic equations which did not belong to the then pantheon
of paradigms. The generalised Emden-Fowler equation provided a route
to major development in the area of the theory of the conditions for the linearisation
of second order equations. This was in addition to its own interest.
The stage was now set to establish broad theoretical results and retreat from
the particularism of the seventies.
Chapters Three and Four deal with the linearisation theorems for second
order equations and the classification of intrinsically nonlinear equations according
to their algebras. The rather meagre results for systems of second
order equations are recorded.
In the fifth chapter the investigation is extended to higher order equations
for which there are some major departures away from the pattern established
at the second order level and reinforced by the central role played by these
equations in a world still dominated by Newton. The classification of third
order equations by their algebras is presented, but it must be admitted that
the story of higher order equations is still very much incomplete.
In the sixth chapter the relationships between first integrals and their algebras
is explored for both first order integrals and those of higher orders. Again
the peculiar position of second order equations is revealed.
In the seventh chapter the generalised Emden-Fowler equation is given a
more modern and complete treatment.
The final chapter looks at one of the fundamental algebras associated with
ordinary differential equations, the three element 8£(2, R), which is found in all
higher order equations of maximal symmetry, is a fundamental feature of the
Pinney equation which has played so prominent a role in the study of nonautonomous
Hamiltonian systems in Physics and is the signature of Ermakov
systems and their generalisations
SIMILARITY SOLUTIONS AND CONSERVATION LAWS FOR THE BEAM EQUATIONS: A COMPLETE STUDY
We study the similarity solutions and we determine the conservation laws of various forms of beam equations, such as Euler-Bernoulli, Rayleigh and Timoshenko-Prescott. The travelling-wave reduction leads to solvable fourth-order odes for all the forms. In addition, the reduction based on the scaling symmetry for the Euler-Bernoulli form leads to certain odes for which there exists zero symmetries. Therefore, we conduct the singularity analysis to ascertain the integrability. We study two reduced odes of second and third orders. The reduced second-order ode is a perturbed form of Painlevé-Ince equation, which is integrable and the third-order ode falls into the category of equations studied by Chazy, Bureau and Cosgrove. Moreover, we derived the symmetries and its corresponding reductions and conservation laws for the forced form of the abovementioned beam forms. The Lie Algebra is mentioned explicitly for all the cases
New genetic loci link adipose and insulin biology to body fat distribution.
Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms
Genetic associations at 53 loci highlight cell types and biological pathways relevant for kidney function
Reduced glomerular filtration rate defines chronic kidney disease and is associated with cardiovascular and all-cause mortality. We conducted a meta-analysis of genome-wide association studies for estimated glomerular filtration rate (eGFR), combining data across 133,413 individuals with replication in up to 42,166 individuals. We identify 24 new and confirm 29 previously identified loci. Of these 53 loci, 19 associate with eGFR among individuals with diabetes. Using bioinformatics, we show that identified genes at eGFR loci are enriched for expression in kidney tissues and in pathways relevant for kidney development and transmembrane transporter activity, kidney structure, and regulation of glucose metabolism. Chromatin state mapping and DNase I hypersensitivity analyses across adult tissues demonstrate preferential mapping of associated variants to regulatory regions in kidney but not extra-renal tissues. These findings suggest that genetic determinants of eGFR are mediated largely through direct effects within the kidney and highlight important cell types and biological pathways
Genome-wide association study identifies loci influencing concentrations of liver enzymes in plasma.
Concentrations of liver enzymes in plasma are widely used as indicators of liver disease. We carried out a genome-wide association study in 61,089 individuals, identifying 42 loci associated with concentrations of liver enzymes in plasma, of which 32 are new associations (P = 10(-8) to P = 10(-190)). We used functional genomic approaches including metabonomic profiling and gene expression analyses to identify probable candidate genes at these regions. We identified 69 candidate genes, including genes involved in biliary transport (ATP8B1 and ABCB11), glucose, carbohydrate and lipid metabolism (FADS1, FADS2, GCKR, JMJD1C, HNF1A, MLXIPL, PNPLA3, PPP1R3B, SLC2A2 and TRIB1), glycoprotein biosynthesis and cell surface glycobiology (ABO, ASGR1, FUT2, GPLD1 and ST3GAL4), inflammation and immunity (CD276, CDH6, GCKR, HNF1A, HPR, ITGA1, RORA and STAT4) and glutathione metabolism (GSTT1, GSTT2 and GGT), as well as several genes of uncertain or unknown function (including ABHD12, EFHD1, EFNA1, EPHA2, MICAL3 and ZNF827). Our results provide new insight into genetic mechanisms and pathways influencing markers of liver function