668 research outputs found
Promotion of protocell self-assembly from mixed amphiphiles at the origin of life
Vesicles formed from single-chain amphiphiles (SCAs) such as fatty acids probably played an important role in the origin of life. A major criticism of the hypothesis that life arose in an early ocean hydrothermal environment is that hot temperatures, large pH gradients, high salinity and abundant divalent cations should preclude vesicle formation. However, these arguments are based on model vesicles using 1â3 SCAs, even though FischerâTropsch-type synthesis under hydrothermal conditions produces a wide array of fatty acids and 1-alkanols, including abundant C10âC15 compounds. Here, we show that mixtures of these C10âC15 SCAs form vesicles in aqueous solutions between pH ~6.5 and >12 at modern seawater concentrations of NaCl, Mg2+ and Ca2+. Adding C10 isoprenoids improves vesicle stability even further. Vesicles form most readily at temperatures of ~70â°C and require salinity and strongly alkaline conditions to self-assemble. Thus, alkaline hydrothermal conditions not only permit protocell formation at the origin of life but actively favour it
Target structure independent elastic scattering at low momentum transfers
Analyzing powers and cross sections for the elastic scattering of polarized
7Li by targets of 6Li, 7Li and 12C are shown to depend only on the properties
of the projectile for momentum transfers of less than 1.0 fm-1. The result of a
detailed analysis of the experimental data within the framework of the coupled
channels model with ground state reorientation and transitions to the excited
states of the projectile and targets included in the coupling schemes are
presented. This work suggests that nuclear properties of weakly-bound nuclei
can be tested by elastic scattering experiments, independent of the target
used, if data are acquired for momentum transfers less than ~1.0 fm-1.Comment: 9 pages, 4 figures, 1 table, accepted in Phys. Lett.
Molecular characterisation of Staphylococcus aureus strains isolated from small and large ruminants reveals a host rather than tissue specificity.
International audienceStaphylococcus aureus is an important pathogen in domestic ruminants. The main objective of this study was to determine the similarity of epidemiologically unrelated S. aureus isolates from bovine, ovine, and caprine hosts regardless the locus of isolation (nares and udder). By pulsed-field gel electrophoresis, seven major pulsotypes were identified among 153 isolates recovered from 12 different regions of France as well as from Brazil, the USA and Belgium. Typing of the accessory gene regulator (agr) and capsular (cap) serotype was carried out on all the isolates and revealed the predominance of agr I and III and of cap8 regardless the ruminant host species. Screening for methicilin-resistant S. aureus (MRSA) was carried out by disk diffusion and revealed a prevalence of only 3.2% of MRSA among the strains tested. These results suggest the existence of a host rather than tissue specificity among S. aureus isolates colonising the ruminant species and suggest a limited transmission of those isolates between large (bovine) and small (ovine-caprine) ruminants. The agr class and cap types correlated with pulsotype clusters rather than with a specific host species. Antimicrobial resistance appears not to have contributed to the predominance of any given genotypes, and MRSA prevalence appears very low in ruminant isolates
Deformation of the N=Z nucleus 76Sr using beta-decay studies
A novel method of deducing the deformation of the N=Z nucleus 76Sr is
presented. It is based on the comparison of the experimental Gamow-Teller
strength distribution B(GT) from its beta decay with the results of QRPA
calculations. This method confirms previous indications of the strong prolate
deformation of this nucleus in a totally independent way. The measurement has
been carried out with a large Total Absorption gamma Spectrometer, "Lucrecia",
newly installed at CERN-ISOLDE.Comment: Accepted in Phys. Rev. Letter
Folding model analysis of elastic and inelastic proton scattering on Sulfur isotopes
The folding formalism for the nucleon-nucleus optical potential and inelastic
form factor is applied to study elastic and inelastic proton scattering on
30-40S isotopes. A recently developed realistic density dependent M3Y
interaction, well tested in the folding analysis of nucleus-nucleus elastic and
inelastic scattering, is used as effective NN interaction. The nuclear ground
state and transition densities (for the 2+ excitations in Sulfur isotopes) are
obtained in the Hartree-Fock-BCS and QRPA approaches, respectively. The best
fit ratios of transition moments Mn/Mp for the lowest 2+ states in Sulfur
isotopes are compared to those obtained earlier in the DWBA analysis of the
same data using the same structure model and inelastic form factors obtained
with the JLM effective interaction. Our folding+DWBA analysis has shown quite a
strong isovector mixing in the elastic and inelastic scattering channels for
the neutron rich 38,40S nuclei. In particular, the relative strength of the
isovector part of the transition potential required by the inelastic p+38S data
is significantly stronger than that obtained with the corresponding QRPA
transition density.Comment: 24 pages, 11 figures, accepted for publication in Nucl. Phys.
A Survey of Satisfiability Modulo Theory
Satisfiability modulo theory (SMT) consists in testing the satisfiability of
first-order formulas over linear integer or real arithmetic, or other theories.
In this survey, we explain the combination of propositional satisfiability and
decision procedures for conjunctions known as DPLL(T), and the alternative
"natural domain" approaches. We also cover quantifiers, Craig interpolants,
polynomial arithmetic, and how SMT solvers are used in automated software
analysis.Comment: Computer Algebra in Scientific Computing, Sep 2016, Bucharest,
Romania. 201
A Gromov-Hausdorff distance between von Neumann algebras and an application to free quantum fields
A distance between von Neumann algebras is introduced, depending on a further norm inducing the w*-topology on bounded sets. Such notion is related both with the GromovâHausdorff distance for quantum metric spaces of Rieffel and with the EffrosâMarĂ©chal topology on the von Neumann algebras acting on a Hilbert space. This construction is tested on the local algebras of free quantum fields endowed with norms related with the BuchholzâWichmann nuclearity condition, showing the continuity of such algebras w.r.t. the mass parameter
Determination of Matter Surface Distribution of Neutron-rich Nuclei
We demonstrate that the matter density distribution in the surface region is
determined well by the use of the relatively low-intensity beams that become
available at the upcoming radioactive beam facilities. Following the method
used in the analyses of electron scattering, we examine how well the density
distribution is determined in a model-independent way by generating pseudo data
and by carefully applying statistical and systematic error analyses. We also
study how the determination becomes deteriorated in the central region of the
density, as the quality of data decreases. Determination of the density
distributions of neutron-rich nuclei is performed by fixing parameters in the
basis functions to the neighboring stable nuclei. The procedure allows that the
knowledge of the density distributions of stable nuclei assists to strengthen
the determination of their unstable isotopes.Comment: 41 pages, latex, 27 figure
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