210 research outputs found
A virtual world of paleontology
Computer-aided visualization and analysis of fossils has revolutionized the study of extinct organisms. Novel techniques allow fossils to be characterized in three dimensions and in unprecedented detail. This has enabled paleontologists to gain important insights into their anatomy, development, and preservation. New protocols allow more objective reconstructions of fossil organisms, including soft tissues, from incomplete remains. The resulting digital reconstructions can be used in functional analyses, rigorously testing long-standing hypotheses regarding the paleobiology of extinct organisms. These approaches are transforming our understanding of long-studied fossil groups, and of the narratives of organismal and ecological evolution that have been built upon them
Classical Physics and Quantum Loops
The standard picture of the loop expansion associates a factor of h-bar with
each loop, suggesting that the tree diagrams are to be associated with
classical physics, while loop effects are quantum mechanical in nature. We
discuss examples wherein classical effects arise from loop contributions and
display the relationship between the classical terms and the long range effects
of massless particles.Comment: 15 pages, 3 figure
Measuring transversity densities in singly polarized hadron-hadron and lepton-hadron collisions
We show how the transverse polarization of a quark initiating a jet can be
probed by the azimuthal distribution of two hadrons (of large ) in the jet.
This permits a twist 2 asymmetry in hard processes when only one of the initial
particles is polarized transversely. Applications to hadron-hadron and
lepton-hadron scattering are discussed.Comment: 16 pages, LaTeX + EPSF, 2 postscript figures. PSU/TH/10
The identification of mitochondrial DNA variants in glioblastoma multiforme
Background:
Mitochondrial DNA (mtDNA) encodes key proteins of the electron transfer chain (ETC), which produces ATP through oxidative phosphorylation (OXPHOS) and is essential for cells to perform specialised functions. Tumor-initiating cells use aerobic glycolysis, a combination of glycolysis and low levels of OXPHOS, to promote rapid cell proliferation and tumor growth. Glioblastoma multiforme (GBM) is an aggressively malignant brain tumor and mitochondria have been proposed to play a vital role in GBM tumorigenesis.
Results:
Using next generation sequencing and high resolution melt analysis, we identified a large number of mtDNA variants within coding and non-coding regions of GBM cell lines and predicted their disease-causing potential through in silico modeling. The frequency of variants was greatest in the D-loop and origin of light strand replication in non-coding regions. ND6 was the most susceptible coding gene to mutation whilst ND4 had the highest frequency of mutation. Both genes encode subunits of complex I of the ETC. These variants were not detected in unaffected brain samples and many have not been previously reported. Depletion of HSR-GBM1 cells to varying degrees of their mtDNA followed by transplantation into immunedeficient mice resulted in the repopulation of the same variants during tumorigenesis. Likewise, de novo variants identified in other GBM cell lines were also incorporated. Nevertheless, ND4 and ND6 were still the most affected genes. We confirmed the presence of these variants in high grade gliomas.
Conclusions:
These novel variants contribute to GBM by rendering the ETC. partially dysfunctional. This restricts metabolism to anaerobic glycolysis and promotes cell proliferation
The weight for random quark masses
In theories in which the parameters of the low energy theory are not unique,
perhaps having different values in different domains of the universe as is
possible in some inflationary models, the fermion masses would be distributed
with respect to some weight. In such a situation the specifics of the fermion
masses do not have a unique explanation, yet the weight provides the visible
remnant of the structure of the underlying theory. This paper introduces this
concept of a weight for the distribution of masses and provides a quantitative
estimate of it from the observed quarks and leptons. The weight favors light
quark masses and appears roughly scale invariant (rho ~ 1/m). Some relevant
issues, such as the running of the weight with scale and the possible effects
of anthropic constraints, are also discussed.Comment: 35pages, 19 figure
The Electromagnetic Mass Differences of Pions and Kaons
We use the Cottingham method to calculate the pion and kaon electromagnetic
mass differences with as few model dependent inputs as possible. The
constraints of chiral symmetry at low energy, QCD at high energy and
experimental data in between are used in the dispersion relation. We find
excellent agreement with experiment for the pion mass difference. The kaon mass
difference exhibits a strong violation of the lowest order prediction of
Dashen's theorem, in qualitative agreement with several other recent
calculations.Comment: 40 pages, Latex, needs axodraw. and psfig. macros, 4 figure
- …