759 research outputs found
Effective meson masses, effective meson-nucleon couplings and neutron star radii
Using the generalized mean field theory, we have studied the relation among
the effective meson masses, the effective meson-nucleon couplings and the
equation of state (EOS) in asymmetric nuclear matter. If the effective
omega-meson mass becomes smaller at high density, the EOS becomes stiffer.
However, if we require that the omega-meson mean field is proportional to the
baryon density, the effective omega-nucleon coupling automatically becomes
smaller at the same time as the effective omega-meson mass becomes smaller.
Consequently, the EOS becomes softer. A similar relation is found for the
effective rho-meson mass and the effective rho-nucleon coupling. We have also
studied the relation among the effective meson masses, the effective
meson-nucleon couplings and a radius R of a neutron star. The R depends
somewhat on the value of the effective omega-meson mass and the effective
omega-nucleon coupling.Comment: 29pages, 24 figure
"Gtool5": a Fortran90 library of input/output interfaces for self-descriptive multi-dimensional numerical data
A Fortran90 input/output library, "gtool5", is developed for use with numerical simulation models in the fields of Earth and planetary sciences. The use of this library will simplify implementation of input/output operations into program code in a consolidated form independent of the size and complexity of the software and data. The library also enables simple specification of the metadata needed for post-processing and visualization of the data. These aspects improve the readability of simulation code, which facilitates the simultaneous performance of multiple numerical experiments with different software and efficiency in examining and comparing the numerical results. The library is expected to provide a common software platform to reinforce research on, for instance, the atmosphere and ocean, where a close combination of multiple simulation models with a wide variety of complexity of physics implementations from massive climate models to simple geophysical fluid dynamics models is required
Characterisation of an Escherichia coli line that completely lacks ribonucleotide reduction yields insights into the evolution of parasitism and endosymbiosis
Life requires ribonucleotide reduction for de novo synthesis of deoxyribonucleotides. As ribonucleotide reduction has on occasion been lost in parasites and endosymbionts, which are instead dependent on their host for deoxyribonucleotide synthesis, it should in principle be possible to knock this process out if growth media are supplemented with deoxyribonucleosides. We report the creation of a strain of Escherichia coli where all three ribonucleotide reductase operons have been deleted following introduction of a broad spectrum deoxyribonucleoside kinase from Mycoplasma mycoides. Our strain shows slowed but substantial growth in the presence of deoxyribonucleosides. Under limiting deoxyribonucleoside levels, we observe a distinctive filamentous cell morphology, where cells grow but do not appear to divide regularly. Finally, we examined whether our lines can adapt to limited supplies of deoxyribonucleosides, as might occur in the switch from de novo synthesis to dependence on host production during the evolution of parasitism or endosymbiosis. Over the course of an evolution experiment, we observe a 25-fold reduction in the minimum concentration of exogenous deoxyribonucleosides necessary for growth. Genome analysis reveals that several replicate lines carry mutations in deoB and cdd. deoB codes for phosphopentomutase, a key part of the deoxyriboaldolase pathway, which has been hypothesised as an alternative to ribonucleotide reduction for deoxyribonucleotide synthesis. Rather than complementing the loss of ribonucleotide reduction, our experiments reveal that mutations appear that reduce or eliminate the capacity for this pathway to catabolise deoxyribonucleotides, thus preventing their loss via central metabolism. Mutational inactivation of both deoB and cdd is also observed in a number of obligate intracellular bacteria that have lost ribonucleotide reduction. We conclude that our experiments recapitulate key evolutionary steps in the adaptation to life without ribonucleotide reduction
The Venus' Cloud Discontinuity in 2022
First identified in 2016 by JAXA's Akatsuki mission, the
discontinuity/disruption is a recurrent wave observed to propagate during
decades at the deeper clouds of Venus (47--56 km above the surface), while its
absence at the clouds' top (70 km) suggests that it dissipates at the
upper clouds and contributes in the maintenance of the puzzling atmospheric
superrotation of Venus through wave-mean flow interaction. Taking advantage of
the campaign of ground-based observations undertaken in coordination with the
Akatsuki mission since December 2021 until July 2022, we aimed to undertake the
longest uninterrupted monitoring of the cloud discontinuity up to date to
obtain a pioneering long-term characterization of its main properties and
better constrain its recurrence and lifetime.
The dayside upper, middle and nightside lower clouds were studied with images
with suitable filters acquired by Akatsuki/UVI, amateur observers and NASA's
IRTF/SpeX, respectively. Hundreds of images were inspected in search of
manifestations of the discontinuity events and to measure key properties like
its dimensions, orientation or rotation period. We succeeded in tracking the
discontinuity at the middle clouds during 109 days without interruption. The
discontinuity exhibited properties nearly identical to measurements in 2016 and
2020, with an orientation of , length/width of
/ km and a rotation period of days.
Ultraviolet images during 13-14 June 2022 suggest that the discontinuity may
have manifested at the top of the clouds during 21 hours as a result of
an altitude change in the critical level for this wave due to slower zonal
winds.Comment: 8 pages, 4 figures, 2 animated figures, 1 tabl
RELAY, Ramucirumab Plus Erlotinib Versus Placebo Plus Erlotinib in Patients with Untreated, Epidermal Growth Factor Receptor Mutation-Positive, Metastatic Non-Small-Cell Lung Cancer: Safety Profile and Manageability
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