1,446 research outputs found
The effect of reinsuring a deductible on pharmaceutical spending:A Dutch case study on low-income people
Dual Requirement for Yeast hnRNP Nab2p in mRNA poly(A) Tail Length Control and Nuclear Export
Recent studies of mRNA export factors have provided additional evidence for a mechanistic link between mRNA 3âČâend formation and nuclear export. Here, we identify Nab2p as a nuclear poly(A)âbinding protein required for both poly(A) tail length control and nuclear export of mRNA. Loss of NAB2 expression leads to hyperadenylation and nuclear accumulation of poly(A)+ RNA but, in contrast to mRNA export mutants, these defects can be uncoupled in a nab2 mutant strain. Previous studies have implicated the cytoplasmic poly(A) tailâbinding protein Pab1p in poly(A) tail length control during polyadenylation. Although cells are viable in the absence of NAB2 expression when PAB1 is overexpressed, Pab1p fails to resolve the nab2Î hyperadenylation defect even when Pab1p is tagged with a nuclear localization sequence and targeted to the nucleus. These results indicate that Nab2p is essential for poly(A) tail length control in vivo, and we demonstrate that Nab2p activates polyadenylation, while inhibiting hyperadenylation, in the absence of Pab1p in vitro. We propose that Nab2p provides an important link between the termination of mRNA polyadenylation and nuclear export
Reconstructing seasonality through stable-isotope and trace-element analyses of the Proserpine stalagmite, Han-sur-Lesse cave, Belgium : indications for climate-driven changes during the last 400 years
Fast-growing speleothems allow for the reconstruction of palaeoclimate down to a seasonal scale. Additionally, annual lamination in some of these speleothems yields highly accurate age models for these palaeoclimate records, making these speleothems valuable archives for terrestrial climate. In this study, an annually laminated stalagmite from the Han-sur-Lesse cave (Belgium) is used to study the expression of the seasonal cycle in northwestern Europe during the Little Ice Age. More specifically, two historical 12-year-long growth periods (ca. 1593-1605 CE and 1635-1646 CE) and one modern growth period (1960-2010 CE) are analysed on a sub-annual scale for their stable-isotope ratios (delta C-13 and delta O-18) and trace-element (Mg, Sr, Ba, Zn, Y, Pb, U) contents. Seasonal variability in these proxies is confirmed with frequency analysis. Zn, Y and Pb show distinct annual peaks in all three investigated periods related to annual flushing of the soil during winter. A strong seasonal in-phase relationship between Mg, Sr and Ba in the modern growth period reflects a substantial influence of enhanced prior calcite precipitation (PCP). In particular, PCP occurs during summers when recharge of the epikarst is low. This is also evidenced by earlier observations of increased delta C-13 values during summer. In the 17th century intervals, there is a distinct antiphase relationship between Mg, Sr and Ba, suggesting that processes other than PCP, i.e. varying degrees of incongruent dissolution of dolomite, eventually related to changes in soil activity and/or land-use change are more dominant. The processes controlling seasonal variations in Mg, Sr and Ba in the speleothem appear to change between the 17th century and 1960-2010 CE. The Zn, Y, Pb, and U concentration profiles; stable-isotope ratios; and morphology of the speleothem laminae all point towards increased seasonal amplitude in cave hydrology. Higher seasonal peaks in soil-derived elements (e.g. Zn and Y) and lower concentrations of host-rock-derived elements (e.g. Mg, Sr, Ba) point towards lower residence times in the epikarst and higher flushing rates during the 17th century. These observations reflect an increase in water excess above the cave and recharge of the epikarst, due to a combination of lower summer temperatures and increased winter precipitation during the 17th century. This study indicates that the transfer function controlling Mg, Sr and Ba seasonal variability varies over time. Which process is dominant - either PCP, soil activity or dolomite dissolution - is clearly climate driven and can itself be used as a palaeoenvironment proxy
Quasi-exactly solvable quartic potential
A new two-parameter family of quasi-exactly solvable quartic polynomial
potentials is introduced. Until now,
it was believed that the lowest-degree one-dimensional quasi-exactly solvable
polynomial potential is sextic. This belief is based on the assumption that the
Hamiltonian must be Hermitian. However, it has recently been discovered that
there are huge classes of non-Hermitian, -symmetric Hamiltonians
whose spectra are real, discrete, and bounded below [physics/9712001].
Replacing Hermiticity by the weaker condition of symmetry allows
for new kinds of quasi-exactly solvable theories. The spectra of this family of
quartic potentials discussed here are also real, discrete, and bounded below,
and the quasi-exact portion of the spectra consists of the lowest
eigenvalues. These eigenvalues are the roots of a th-degree polynomial.Comment: 3 Pages, RevTex, 1 Figure, encapsulated postscrip
Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures
The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes (Î47) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Î47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/CaâÎ47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca-Î47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Î47 yield concordant results, and can be used to infer the past ÎŽ18O of seawater (ÎŽ18Osw) for paleoclimate studies
Quotient Categories and Phases
We study properties of a category after quotienting out a suitable chosen
group of isomorphisms on each object. Coproducts in the original category are
described in its quotient by our new weaker notion of a 'phased coproduct'. We
examine these and show that any suitable category with them arises as such a
quotient of a category with coproducts. Motivation comes from projective
geometry, and also quantum theory where they describe superpositions in the
category of Hilbert spaces and continuous linear maps up to global phase. The
quotients we consider also generalise those induced by categorical isotropy in
the sense of Funk et al.Comment: Fixed typos, added discussion of isotropy, expanded introductio
Spin Structures on Kleinian Manifolds
We derive the topological obstruction to spin-Klein cobordism. This result
has implications for signature change in general relativity, and for the
superstring.Comment: 8 page
The Precautionary Principle: Radiofrequency Exposures from Mobile Telephones and Base Stations
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