12,444 research outputs found
Paramagnon dispersion in -FeSe observed by Fe -edge resonant inelastic x-ray scattering
We report an Fe -edge resonant inelastic x-ray scattering (RIXS) study of
the unusual superconductor -FeSe. The high energy resolution of this
RIXS experiment (55meV FWHM) made it possible to resolve
low-energy excitations of the Fe manifold. These include a broad peak
which shows dispersive trends between 100-200meV along the and
directions of the one-Fe square reciprocal lattice, and which can
be attributed to paramagnon excitations. The multi-band valence state of FeSe
is among the most metallic in which such excitations have been discerned by
soft x-ray RIXS
The Emergence of the Thick Disk in a CDM Universe II: Colors and Abundance Patterns
The recently emerging conviction that thick disks are prevalent in disk
galaxies, and their seemingly ubiquitous old ages, means that the formation of
the thick disk, perhaps more than any other component, holds the key to
unravelling the evolution of the Milky Way, and indeed all disk galaxies. In
Paper I, we proposed that the thick disk was formed in an epoch of gas rich
mergers, at high redshift. This hypothesis was based on comparing N-body/SPH
simulations to a variety of Galactic and extragalactic observations, including
stellar kinematics, ages and chemical properties.Here examine our thick disk
formation scenario in light of the most recent observations of extragalactic
thick disks. In agreement, our simulted thick disks are old and relatively
metal rich, with V-I colors that do not vary significantly with distance from
the plane. Further, we show that our proposal results in an enhancement of
alpha-elements in thick disk stars as compared with thin disk stars, consistent
with observations of the relevant populations of the Milky Way. We also find
that our scenario naturally leads to the formation of an old metal weak stellar
halo population with high alpha-element abundances.Comment: submitted to Ap
Further Evidence for a Merger Origin for the Thick Disk: Galactic Stars Along Lines-of-sight to Dwarf Spheroidal Galaxies
The history of the Milky Way Galaxy is written in the properties of its
stellar populations. Here we analyse stars observed as part of surveys of local
dwarf spheroidal galaxies, but which from their kinematics are highly probable
to be non-members. The selection function -- designed to target metal-poor
giants in the dwarf galaxies, at distances of ~100kpc -- includes F-M dwarfs in
the Milky Way, at distances of up to several kpc. Thestars whose motions are
analysed here lie in the cardinal directions of Galactic longitude l ~ 270 and
l ~ 90, where the radial velocity is sensitive to the orbital rotational
velocity. We demonstrate that the faint F/G stars contain a significant
population with V_phi ~ 100km/s, similar to that found by a targeted, but
limited in areal coverage, survey of thick-disk/halo stars by Gilmore, Wyse &
Norris (2002). This value of mean orbital rotation does not match either the
canonical thick disk or the stellar halo. We argue that this population,
detected at both l ~ 270 and l ~ 90, has the expected properties of `satellite
debris' in the thick-disk/halo interface, which we interpret as remnants of the
merger that heated a pre-existing thin disk to form the thick disk.Comment: Accepted, Astrophysical Journal Letter
Two-neutron separation energies, binding energies and phase transitions in the interacting boson model
In the framework of the interacting boson model the three transitional
regions (rotational-vibrational, rotational--unstable and,
vibrational--unstable transitions) are reanalyzed. A new kind of plot
is presented for studying phase transitions in finite systems such as atomic
nuclei. The importance of analyzing binding energies and not only energy
spectra and electromagnetic transitions, describing transitional regions is
emphasized. We finally discuss a number of realistic examples.Comment: 34 pages, TeX (ReVTeX). 12 ps figures. 3 tables. Submitted to Nucl.
Phys.
Remote participation during glycosylation reactions of galactose building blocks: Direct evidence from cryogenic vibrational spectroscopy
The stereoselective formation of 1,2âcisâglycosidic bonds is challenging. However, 1,2âcisâselectivity can be induced by remote participation of C4 or C6 ester groups. Reactions involving remote participation are believed to proceed via a key ionic intermediate, the glycosyl cation. Although mechanistic pathways were postulated many years ago, the structure of the reaction intermediates remained elusive owing to their shortâlived nature. Herein, we unravel the structure of glycosyl cations involved in remote participation reactions via cryogenic vibrational spectroscopy and first principles theory. Acetyl groups at C4 ensure αâselective galactosylations by forming a covalent bond to the anomeric carbon in dioxoleniumâtype ions. Unexpectedly, also benzyl ether protecting groups can engage in remote participation and promote the stereoselective formation of 1,2âcisâglycosidic bonds
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