249 research outputs found
New spectrum of negative-parity doubly charmed baryons: Possibility of two quasistable states
The discovery of by the LHCb Collaboration triggers
predictions of more doubly charmed baryons. By taking into account both the
-wave excitations between the two charm quarks and the scattering of light
pseudoscalar mesons off the ground state doubly charmed baryons, a set of
negative-parity spin-1/2 doubly charmed baryons are predicted already from a
unitarized version of leading order chiral perturbation theory. Moreover,
employing heavy antiquark-diquark symmetry the relevant low-energy constants in
the next-to-leading order are connected with those describing light
pseudoscalar mesons scattering off charmed mesons, which have been well
determined from lattice calculations and experimental data. Our calculations
result in a spectrum richer than that of heavy mesons. We find two very narrow
, which very likely decay into
breaking isospin symmetry. In the isospin-1/2 sector, three states
are predicted to exist below 4.2~GeV with the lowest one being narrow and the
other two rather broad. We suggest to search for the states in
the mode. Searching for them and their analogues are
helpful to establish the hadron spectrum.Comment: 6 pages, 3 figures; accepted for publication as a Rapid Communication
in Physical Review
Suppression of electron-electron repulsion and superconductivity in Ultra Small Carbon Nanotubes
Recently, ultra-small-diameter Single Wall Nano Tubes with diameter of have been produced and many unusual properties were observed, such as
superconductivity, leading to a transition temperature , much
larger than that observed in the bundles of larger diameter tubes.
By a comparison between two different approaches, we discuss the issue
whether a superconducting behavior in these carbon nanotubes can arise by a
purely electronic mechanism. The first approach is based on the Luttinger Model
while the second one, which emphasizes the role of the lattice and short range
interaction, is developed starting from the Hubbard Hamiltonian. By using the
latter model we predict a transition temperature of the same order of magnitude
as the measured one.Comment: 7 pages, 3 figures, to appear in J. Phys.-Cond. Ma
Premartensitic transition driven by magnetoelastic interaction in bcc ferromagnetic
We show that the magnetoelastic coupling between the magnetization and the
amplitude of a short wavelength phonon enables the existence of a first order
premartensitic transition from a bcc to a micromodulated phase in .
Such a magnetoelastic coupling has been experimentally evidenced by AC
susceptibility and ultrasonic measurements under applied magnetic field. A
latent heat around 9 J/mol has been measured using a highly sensitive
calorimeter. This value is in very good agreement with the value predicted by a
proposed model.Comment: 4 pages RevTex, 3 Postscript figures, to be published in Physical
Review Letter
Stabilizing single atom contacts by molecular bridge formation
Gold-molecule-gold junctions can be formed by carefully breaking a gold wire
in a solution containing dithiolated molecules. Surprisingly, there is little
understanding on the mechanical details of the bridge formation process and
specifically on the role that the dithiol molecules play themselves. We propose
that alkanedithiol molecules have already formed bridges between the gold
electrodes before the atomic gold-gold junction is broken. This leads to
stabilization of the single atomic gold junction, as observed experimentally.
Our data can be understood within a simple spring model.Comment: 14 pages, 3 figures, 1 tabl
Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy
Magnetic, transport, and x-ray diffraction measurements of ferromagnetic
shape memory alloy NiMnGa revealed that this alloy undergoes
an intermartensitic transition upon cooling, whereas no such a transition is
observed upon subsequent heating. The difference in the modulation of the
martensite forming upon cooling from the high-temperature austenitic state
[5-layered (5M) martensite], and the martensite forming upon the
intermartensitic transition [7-layered (7M) martensite] strongly affects the
magnetic and transport properties of the alloy and results in a large thermal
hysteresis of the resistivity and magnetization . The
intermartensitic transition has an especially marked influence on the transport
properties, as is evident from a large difference in the resistivity of the 5M
and 7M martensite, , which is larger than the jump of resistivity at
the martensitic transition from the cubic austenitic phase to the monoclinic 5M
martensitic phase. We assume that this significant difference in between
the martensitic phases is accounted for by nesting features of the Fermi
surface. It is also suggested that the nesting hypothesis can explain the
uncommon behavior of the resistivity at the martensitic transition, observed in
stoichiometric and near-stoichiometric Ni-Mn-Ga alloys.Comment: 7 pages, 6 figures, REVTEX
Khuri-Treiman analysis of
We study the decay within the framework of
the Khuri-Treiman equations. We find that the BESIII experimental di-pion mass
distribution in the -region is well reproduced with a
once-subtracted -wave amplitude. Furthermore, we show that -wave
contributions to the amplitude improve the description of the data in the
mass region around 1.5 GeV. We also present predictions for the
transition form factor.Comment: 20 pages, 9 figure
Galaxies and Cladistics
The Hubble tuning fork diagram, based on morphology and established in the
1930s, has always been the preferred scheme for classification of galaxies.
However, the current large amount of multiwavelength data, most often spectra,
for objects up to very high distances, asks for more sophisticated statistical
approaches. Interpreting formation and evolution of galaxies as a ?transmission
with modification' process, we have shown that the concepts and tools of
phylogenetic systematics can be heuristically transposed to the case of
galaxies. This approach, which we call ?astrocladistics', has successfully been
applied on several samples. Many difficulties still remain, some of them being
specific to the nature of both galaxies and their diversification processes,
some others being classical in cladistics, like the pertinence of the
descriptors in conveying any useful evolutionary information.Comment: Talk given at the "12th Evolutionary Biology Meeting" held in
Marseille, France, Sept. 24-26, 200
Nucleosynthesis from massive stars 50 years after B2FH
We review some important observed properties of massive stars. Then we
discuss how mass loss and rotation affect their evolution and help in giving
better fits to observational constraints. Consequences for nucleosynthesis at
different metallicities are discussed. Mass loss appear to be the key feature
at high metallicity, while rotation is likely dominant at low and very low
metallicities. We discuss various indications supporting the view that very
metal poor stars had their evolution strongly affected by rotational mixing.
Many features, like the origin of primary nitrogen at low metallicity, that of
the C-rich extremely metal poor halo stars, of He-rich stars in massive
globular clusters, of the O-Na anticorrelation in globular clusters may be
related to the existence of a population of very fast rotating metal poor stars
that we tentatively call the {\it spinstars}. A fraction of these {\it
spinstars} may also be the progenitors of GRB in very metal poor regions. They
may avoid pair instability explosion due to the heavy mass loss undergone
during their early evolutionary phases and be, dependent on their frequency,
important sources of ionising photons in the early Universe.Comment: 46 pages, 17 figures, in Stellar Nucleosynthesis: 50 years after
B2FH, C. Charbonnel and J.P. Zahn (Eds.), EAS publications Serie
Frequency and phenotypic spectrum of KMT2B dystonia in childhood: A singleâcenter cohort study
Background: Childhood-onset dystonia is often genetically determined. Recently, KMT2B variants have been recognized as an important cause of childhood-onset dystonia.
Objective: To define the frequency of KMT2B mutations in a cohort of dystonic patients aged less than 18 years at onset, the associated clinical and radiological phenotype, and the natural history of disease.
Methods: Whole-exome sequencing or customized gene panels were used to screen a cohort of sixty-five patients who had previously tested negative for all other known dystonia-associated genes.
Results: We identified fourteen patients (21.5%) carrying KMT2B variants, of which one was classified as a Variant of Unknown Significance (VUS). We also identified two additional patients carrying pathogenic mutations in GNAO1 and ATM. Overall, we established a definitive genetic diagnosis in 23% of cases. We observed a spectrum of clinical manifestations in KMT2B variant carriers, ranging from generalized dystonia to short stature or intellectual disability alone, even within the same family. In 78.5% of cases, dystonia involved the lower limbs at onset, with later caudo-cranial generalization. Eight patients underwent pallidal Deep Brain Stimulation with a median decrease of BFMDRS-M score of 38.5% in the long term. We also report four asymptomatic carriers, suggesting that some KMT2B mutations may be associated with incomplete disease penetrance.
Conclusions: KMT2B mutations are frequent in childhood-onset dystonia and cause a complex neurodevelopmental syndrome often featuring growth retardation and intellectual disability as additional phenotypic features. A dramatic and long-lasting response to Deep Brain Stimulation is characteristic of DYT-KMT2B dystonia
- âŠ