1,403 research outputs found
Three-body monopole corrections to the realistic interactions
It is shown that a very simple three-body monopole term can solve practically
all the spectroscopic problems--in the , and shells--that were
hitherto assumed to need drastic revisions of the realistic potentials.Comment: 4 pages, 5figure
Isobaric multiplet yrast energies and isospin non-conserving forces
The isovector and isotensor energy differences between yrast states of
isobaric multiplets in the lower half of the region are quantitatively
reproduced in a shell model context. The isospin non-conserving nuclear
interactions are found to be at least as important as the Coulomb potential.
Their isovector and isotensor channels are dominated by J=2 and J=0 pairing
terms, respectively. The results are sensitive to the radii of the states,
whose evolution along the yrast band can be accurately followed.Comment: 4 pages, 4 figures. Superseeds second part of nucl-th/010404
RNA denaturation: excluded volume, pseudoknots and transition scenarios
A lattice model of RNA denaturation which fully accounts for the excluded
volume effects among nucleotides is proposed. A numerical study shows that
interactions forming pseudoknots must be included in order to get a sharp
continuous transition. Otherwise a smooth crossover occurs from the swollen
linear polymer behavior to highly ramified, almost compact conformations with
secondary structures. In the latter scenario, which is appropriate when these
structures are much more stable than pseudoknot links, probability
distributions for the lengths of both loops and main branches obey scaling with
nonclassical exponents.Comment: 4 pages 3 figure
Calculated corrections to superallowed Fermi beta decay: New evaluation of the nuclear-structure-dependent terms
The measured -values for superallowed nuclear
-decay can be used to obtain the value of the vector coupling constant
and thus to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. An
essential requirement for this test is accurate calculations for the radiative
and isospin symmetry-breaking corrections that must be applied to the
experimental data. We present a new and consistent set of calculations for the
nuclear-structure-dependent components of these corrections. These new results
do not alter the current status of the unitarity test -- it still fails by more
than two standard deviations -- but they provide calculated corrections for
eleven new superallowed transitions that are likely to become accessible to
precise measurements in the future. The reliability of all calculated
corrections is explored and an experimental method indicated by which the
structure-dependent corrections can be tested and, if necessary, improved.Comment: Revtex4, one figur
Glassy transition in a disordered model for the RNA secondary structure
We numerically study a disordered model for the RNA secondary structure and
we find that it undergoes a phase transition, with a breaking of the replica
symmetry in the low temperature region (like in spin glasses). Our results are
based on the exact evaluation of the partition function.Comment: 4 pages, 3 figure
Freiburg RNA Tools: a web server integrating IntaRNA, ExpaRNA and LocARNA
The Freiburg RNA tools web server integrates three tools for the advanced analysis of RNA in a common web-based user interface. The tools IntaRNA, ExpaRNA and LocARNA support the prediction of RNA–RNA interaction, exact RNA matching and alignment of RNA, respectively. The Freiburg RNA tools web server and the software packages of the stand-alone tools are freely accessible at http://rna.informatik.uni-freiburg.de
RNA secondary structure formation: a solvable model of heteropolymer folding
The statistical mechanics of heteropolymer structure formation is studied in
the context of RNA secondary structures. A designed RNA sequence biased
energetically towards a particular native structure (a hairpin) is used to
study the transition between the native and molten phase of the RNA as a
function of temperature. The transition is driven by a competition between the
energy gained from the polymer's overlap with the native structure and the
entropic gain of forming random contacts. A simplified Go-like model is
proposed and solved exactly. The predicted critical behavior is verified via
exact numerical enumeration of a large ensemble of similarly designed
sequences.Comment: 4 pages including 2 figure
Sorting live stem cells based on Sox2 mRNA expression.
PMCID: PMC3507951This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.While cell sorting usually relies on cell-surface protein markers, molecular beacons (MBs) offer the potential to sort cells based on the presence of any expressed mRNA and in principle could be extremely useful to sort rare cell populations from primary isolates. We show here how stem cells can be purified from mixed cell populations by sorting based on MBs. Specifically, we designed molecular beacons targeting Sox2, a well-known stem cell marker for murine embryonic (mES) and neural stem cells (NSC). One of our designed molecular beacons displayed an increase in fluorescence compared to a nonspecific molecular beacon both in vitro and in vivo when tested in mES and NSCs. We sorted Sox2-MB(+)SSEA1(+) cells from a mixed population of 4-day retinoic acid-treated mES cells and effectively isolated live undifferentiated stem cells. Additionally, Sox2-MB(+) cells isolated from primary mouse brains were sorted and generated neurospheres with higher efficiency than Sox2-MB(-) cells. These results demonstrate the utility of MBs for stem cell sorting in an mRNA-specific manner
Correlation between nucleotide composition and folding energy of coding sequences with special attention to wobble bases
Background: The secondary structure and complexity of mRNA influences its
accessibility to regulatory molecules (proteins, micro-RNAs), its stability and
its level of expression. The mobile elements of the RNA sequence, the wobble
bases, are expected to regulate the formation of structures encompassing coding
sequences.
Results: The sequence/folding energy (FE) relationship was studied by
statistical, bioinformatic methods in 90 CDS containing 26,370 codons. I found
that the FE (dG) associated with coding sequences is significant and negative
(407 kcal/1000 bases, mean +/- S.E.M.) indicating that these sequences are able
to form structures. However, the FE has only a small free component, less than
10% of the total. The contribution of the 1st and 3rd codon bases to the FE is
larger than the contribution of the 2nd (central) bases. It is possible to
achieve a ~ 4-fold change in FE by altering the wobble bases in synonymous
codons. The sequence/FE relationship can be described with a simple algorithm,
and the total FE can be predicted solely from the sequence composition of the
nucleic acid. The contributions of different synonymous codons to the FE are
additive and one codon cannot replace another. The accumulated contributions of
synonymous codons of an amino acid to the total folding energy of an mRNA is
strongly correlated to the relative amount of that amino acid in the translated
protein.
Conclusion: Synonymous codons are not interchangable with regard to their
role in determining the mRNA FE and the relative amounts of amino acids in the
translated protein, even if they are indistinguishable in respect of amino acid
coding.Comment: 14 pages including 6 figures and 1 tabl
Missing and Quenched Gamow Teller Strength
Gamow-Teller strength functions in full spaces are calculated with
sufficient accuracy to ensure that all the states in the resonance region have
been populated. Many of the resulting peaks are weak enough to become
unobservable. The quenching factor necessary to bring into agreement the low
lying observed states with shell model predictions is shown to be due to
nuclear correlations. To within experimental uncertainties it is the same that
is found in one particle transfer and (e,e') reactions. Perfect consistency
between the observed peaks and the calculation is
achieved by assuming an observation threshold of 0.75\% of the total strength,
a value that seems typical in several experimentsComment: 11 pages, 6 figures avalaible upon request, RevTeX, FTUAM-94/0
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