Does the Sun shrink with increasing magnetic activity?

It has been demonstrated that frequencies of f-modes can be used to estimate the solar radius to a good accuracy. These frequencies have been used to study temporal variations in the solar radius with conflicting results. The variation in f-mode frequencies is more complicated than what is assumed in these studies. If a careful analysis is performed then it turns out that there is no evidence for any variation in the solar radius.Comment: To appear in Astrophys.

Particle-associated dissolved elemental fluxes: revising the stochiometry of mixed layer export

International audienceSinking particles carry substantial loads of dissolved elements in their interstitial spaces that contribute to the vertical transport of elements out of the euphotic zone. Elemental fluxes as traditionally measured by sediment traps underestimate total export when this particle-associated dissolved flux is not considered. The errors introduced are variable and alter both the absolute levels of flux as well as the stochiometry of export. Using samples from sediment traps in the North Atlantic and measuring excess dissolved carbon, nitrogen, phosphorus, silica and calcium in the supernatant of the collection cups, it is possible to quantitatively assess the total flux in the sample. At the base of the winter mixed layer, up to 90±6% of phosphorus fluxes are found as excess phosphate whereas for carbon and nitrogen dissolved concentrations account for between 30% and 47% of total fluxes respectively. Particle-associated dissolved silica fluxes are a mean of 61% of total flux. Little (2 sequestration by the biological pump is about 50% higher at this site when the particle-associated dissolved elemental fluxes are considered

Structure of the near-surface layers of the Sun: asphericity and time variation

We present results on the structure of the near-surface layers of the Sun obtained by inverting frequencies of high-degree solar modes from "ring diagrams". We have results for eight epochs between June 1996 and October 2003. The frequencies for each epoch were obtained from ring diagrams constructed from MDI Dopplergrams spanning complete Carrington rotations. We find that there is a substantial latitudinal variation of both sound speed and the adiabatic index Gamma_1 in the outer 2% of the Sun. We find that both the sound-speed and Gamma_1 profiles change with changes in the level of solar activity. In addition, we also study differences between the northern and southern hemispheres of the Sun and find a small asymmetry that appears to reflect the difference in magnetic activity between the two hemispheres.Comment: To appear in ApJ (January 2007

How much do helioseismological inferences depend upon the assumed reference model?

We investigate systematic uncertainties in determining the profiles of the solar sound speed, density, and adiabatic index by helioseismological techniques. We find that rms uncertainties-averaged over the sun of ~ 0.2%-0.4% are contributed to the sound speed profile by each of three sources: 1)the choice of assumed reference model, 2) the width of the inversion kernel, and 3) the measurements errors. The density profile is about an order of magnitude less well determined by the helioseismological measurements. The profile of the adiabatic index is determined to an accuracy of about 0.2% . We find that even relatively crude reference models yield reasonably accurate solar parameters.Comment: Accepted for publication in ApJ . Related material at http://www.sns.ias.edu/~jn

Relativistic Treatment of Spinless Particles Subject to the Hulthen plus Yukawa Potential with Arbitrary States

We have obtained the bound state energy eigenvalues and the corresponding wave functions of the Klein – Gordon particles for the unequal scalar and vector Hulthen plus Yukawa potential.  The generalized parametric form of Nikiforov-Uvarov (NU) method is used in the calculation.  By approximate choice of potential parameters our potential reduces to three well known potentials: Hulthen, Yukawa and Coloumb potentials and their corresponding energies are evaluated. Our results under limiting cases are consistent with those available in the literature. We have also obtained the numerical values of our results. Keywords: Klein – Gordon equation, Hulthen potential, Yukawa potential, Nikiforov-Uvarov (NU) method

Re-examining rotavirus innate immune evasion: Potential applications of the reverse genetics system

Rotaviruses represent one of the most successful pathogens in the world, with high infectivity and efficient transmission between the young of many animal species, including humans. To overcome host defenses, rotaviruses have evolved a plethora of strategies to effectively evade the innate immune response, establish initial infection in the small intestine, produce progeny, and shed into the environment. Previously, studying the roles and relative contributions of specific rotaviral factors in innate immune evasion had been challenging without a plasmid-only reverse genetics system. Although still in its infancy, current reverse genetics technology will help address important research questions regarding rotavirus innate immune evasion, host range restriction, and viral pathogenesis. In this review, we summarize the current knowledge about the antiviral host innate immune defense mechanisms, countermeasures of rotavirus-encoded factors, and strategies to better understand these interactions using the rotavirus reverse genetics system

Helioseismic analysis of the hydrogen partition function in the solar interior

The difference in the adiabatic gradient gamma_1 between inverted solar data and solar models is analyzed. To obtain deeper insight into the issues of plasma physics, the so-called ``intrinsic'' difference in gamma_1 is extracted, that is, the difference due to the change in the equation of state alone. Our method uses reference models based on two equations of state currently used in solar modeling, the Mihalas-Hummer-Dappen (MHD) equation of state, and the OPAL equation of state (developed at Livermore). Solar oscillation frequencies from the SOI/MDI instrument on board the SOHO spacecraft during its first 144 days in operation are used. Our results confirm the existence of a subtle effect of the excited states in hydrogen that was previously studied only theoretically (Nayfonov & Dappen 1998). The effect stems from internal partition function of hydrogen, as used in the MHD equation of state. Although it is a pure-hydrogen effect, it takes place in somewhat deeper layers of the Sun, where more than 90% of hydrogen is ionized, and where the second ionization zone of helium is located. Therefore, the effect will have to be taken into account in reliable helioseismic determinations of the astrophysically relevant helium-abundance of the solar convection zone.Comment: 30 pages, 4 figures, 1 table. Revised version submitted to Ap