8,980 research outputs found
One-pot synthesis of 2,3,4,5,6-pentasubstituted tetrahydropyrans using lithiation-borylation, allylation and Prins cyclisation reactions
Stacking boundaries and transport in bilayer graphene
Pristine bilayer graphene behaves in some instances as an insulator with a
transport gap of a few meV. This behaviour has been interpreted as the result
of an intrinsic electronic instability induced by many-body correlations.
Intriguingly, however, some samples of similar mobility exhibit good metallic
properties, with a minimal conductivity of the order of . Here we
propose an explanation for this dichotomy, which is unrelated to electron
interactions and based instead on the reversible formation of boundaries
between stacking domains (`solitons'). We argue, using a numerical analysis,
that the hallmark features of the previously inferred many-body insulating
state can be explained by scattering on boundaries between domains with
different stacking order (AB and BA). We furthermore present experimental
evidence, reinforcing our interpretation, of reversible switching between a
metallic and an insulating regime in suspended bilayers when subjected to
thermal cycling or high current annealing.Comment: 13 pages, 15 figures. Published version (Nano Letters
Low-mass young stellar population and star formation history of the cluster IC 1805 in the W4 H{\sc ii} region
W4 is a giant H{\sc ii} region ionized by the OB stars of the cluster
IC~1805. The H{\sc ii} region/cluster complex has been a subject of numerous
investigations as it is an excellent laboratory for studying the feedback
effect of massive stars on the surrounding region. However, the low-mass
stellar content of the cluster IC~1805 remains poorly studied till now. With
the aim to unravel the low-mass stellar population of the cluster, we present
the results of a multiwavelength study based on deep optical data obtained with
the Canada-France-Hawaii Telescope, infrared data from 2MASS, Space
Telescope and X-ray data from Space Telescope. The present optical
dataset is complete enough to detect stars down to 0.2~M, which is the
deepest optical observations so far for the cluster. We identified 384
candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within
the cluster using various colour-colour and colour-magnitude diagrams. We
inferred the mean age of the identified YSOs to be 2.5 Myr and mass in
the range 0.3 - 2.5 M. The mass function of our YSO sample has a power
law index of -1.23 0.23, close to the Salpeter value (-1.35), and
consistent with those of other star-forming complexes. We explored the disk
evolution of the cluster members and found that the diskless sources are
relatively older compared to the disk bearing YSO candidates. We examined the
effect of high-mass stars on the circumstellar disks and found that within
uncertainties, the influence of massive stars on the disk fraction seems to be
insignificant. We also studied the spatial correlation of the YSOs with the
distribution of gas and dust of the complex to conclude that IC 1805 would have
formed in a large filamentary cloud.Comment: Accepted for publication in MNRAS; 34 pages, 10 figure
Young Stellar Population of the Bright-Rimmed Clouds BRC 5, BRC 7 and BRC 39
Bright-rimmed clouds (BRCs), illuminated and shaped by nearby OB stars, are
potential sites of recent/ongoing star formation. Here we present an optical
and infrared photometric study of three BRCs: BRC 5, BRC 7 and BRC 39 to obtain
a census of the young stellar population, thereby inferring the star formation
scenario, in these regions. In each BRC, the Class I sources are found to be
located mostly near the bright rim or inside the cloud, whereas the Class II
sources are preferentially outside, with younger sources closer to the rim.
This provides strong support to sequential star formation triggered by
radiation driven implosion due to the UV radiation. Moreover, each BRC contains
a small group of young stars being revealed at its head, as the next-generation
stars. In particular, the young stars at the heads of BRC 5 and BRC 7 are found
to be intermediate/high mass stars, which, under proper conditions, may
themselves trigger further star birth, thereby propagating star formation out
to long distances.Comment: 30 pages, 7 Figures, 6 Tables, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Heavy-ion Fusion Cross Sections of 32S on 90,96Zr Targets Using Coulomb and Proximity Potential
The fusion excitation functions for the fusion of 32S on 90,96Zr have been calculated larger value, while using one-dimensional barrier penetration model, taking scattering potential as the sum of Coulomb and proximity potential and the calculated values are compared with experimental data with considerations to shape degrees of freedom. At and above the barrier the computed cross sections match well with the experimental data, whereas below the barrier, calculations with nuclear surface tension coefficient improved by Reisdorf in the proximity potential with considerations to shape degrees of freedom give an approximate fit. Reduced reaction cross sections for the systems 32S on 90,96Zr have also been described
Probable Projectile-Target Combinations for the Synthesis of Super Heavy Nucleus 286112
The fusion cross sections for the reactions of all the projectile-target combinations found in the cold valleys of 286112 have been studied using scattering potential as the sum of Coulomb and proximity potential, so as to predict the most probable projectile-target combinations in heavy ion fusion reactions for the synthesis of super heavy nucleus 286112. While considering the nature of potential pockets and half lives of the colliding nuclei, the systems 82Ge + 204Hg, 80Ge + 206Hg and 78Zn + 208Pb found in the deep cold valley region and the systems 48Ca+238U, 38S+248Cm and 44Ar+242Pu in the cold valleys are predicted to be the better optimal projectile-target combinations for the synthesis of super heavy nucleus 286112
- …