784 research outputs found
Dissecting an intermediate-mass (IM) protostar: Chemical differentiation in IC1396N
We have carried out high-angular resolution (1.4") observations in the
continuum at 3.1mm and in the N2H+ 1-0, CH3CN 5_k-4_k and 13CS 2-1 lines using
the Plateau de Bure Interferometer (PdBI) towards the intermediate mass (IM)
protostar IRAS21391+5802 (IC1396N). In addition, we have merged the PdBI images
with previous BIMA (continuum data at 1.2mm and 3.1mm) and single-dish (N2H+
1-0) data to have a comprehensive description of the region. The combination of
our data with BIMA and 30m data show that the bipolar outflow associated has
completely eroded the initial molecular globule. The 1.2mm and 3.1mm continuum
emissions are extended along the outflow axis tracing the warm walls of the
biconical cavity. Most of the molecular gas, however, is located in an
elongated feature in the direction perpendicular to the outflow. A strong
chemical differentiation is detected across the molecular toroid, with the N2H+
1-0 emission absent in the inner region.This chemical differentiation can be
understood in terms of the different gas kinetic temperature. The
[CH3CN]/[N2H+] ratio increases by 5 orders of magnitude with gas temperature,
for temperatures between 20K and 100K. The CH3CN abundance towards IRAM 2A, the
most massive protostellar core, is similar to that found in hot corinos and
lower than that expected towards IM and high mass hot cores. This could
indicate that IRAM 2A is a low mass or at most Herbig Ae star (IRAM 2A) instead
of the precursor of a massive Be star. Alternatively, the low CH3CN abundance
could also be the consequence of IRAM 2A being a Class 0/I transition object
which has already formed a small photodissociation region (PDR).Comment: accepted A&
Measuring the evolution of contemporary western popular music
Popular music is a key cultural expression that has captured listeners'
attention for ages. Many of the structural regularities underlying musical
discourse are yet to be discovered and, accordingly, their historical evolution
remains formally unknown. Here we unveil a number of patterns and metrics
characterizing the generic usage of primary musical facets such as pitch,
timbre, and loudness in contemporary western popular music. Many of these
patterns and metrics have been consistently stable for a period of more than
fifty years, thus pointing towards a great degree of conventionalism.
Nonetheless, we prove important changes or trends related to the restriction of
pitch transitions, the homogenization of the timbral palette, and the growing
loudness levels. This suggests that our perception of the new would be rooted
on these changing characteristics. Hence, an old tune could perfectly sound
novel and fashionable, provided that it consisted of common harmonic
progressions, changed the instrumentation, and increased the average loudness.Comment: Supplementary materials not included. Please see the journal
reference or contact the author
Valorization of brewer’s spent grain by furfural recovery/removal from subcritical water hydrolysates by pervaporation
This work is focused on the development of a sustainable process for the valorisation of the main by-product
generated in the brewing industry, the brewer’s spent grain (BSG). A two-step process combining subcritical
water treatment and pervaporation (PV) was proposed to hydrolyse the hemicelluloses fraction of this lignocellulosic biomass and further removal/recovery of some of the degradation products of sugars by using two
different organophilic membranes, polydimethylsiloxane (PDMS) and polyoctilmethylsiloxane (POMS) membranes. Specifically, furfural is the dehydration product of pentoses and it is one of the top biomass-based
chemicals being an important platform chemical. For synthetic binary mixtures, lower total permeation flux
but higher enrichment factors for furfural were determined for POMS. When dealing with subW hydrolysates,
POMS membranes yielded the highest furfural recovery, 94.1 %, with permeate concentrations as high as 40 g⋅L1
. Furthermore, it was assessed that PV is a suitable detoxification method that yielded a retentate nearly free of
furfural allowing its use as growth media in the opposite to the subW hydrolysate with inhibitory furfural
concentrations for microbial bioprocesses.publishe
Excitation Spectrum and Superexchange Pathways in the Spin Dimer VODPO_4 . 1/2 D_2O
Magnetic excitations have been investigated in the spin dimer material
VODPO_4 \cdot 1/2 D_2O using inelastic neutron scattering. A dispersionless
magnetic mode was observed at an energy of 7.81(4) meV. The wavevector
dependence of the scattering intensityfrom this mode is consistent with the
excitation of isolated V^{4+} spin dimers with a V-V separation of 4.43(7) \AA.
This result is unexpected since the V-V pair previously thought to constitute
themagnetic dimer has a separation of 3.09 \AA. We identify an alternative V-V
pair as the likely magnetic dimer, which involves superexchange pathways
through a covalently bonded PO_4 group. This surprising result casts doubt on
the interpretation of (VO)_2P_2O_7 as a spin ladder.Comment: 4 pages, 4 postscript figures - identical to previous paper but
figure 2 and 3 hopefully more compatible .p
Chirality in Bare and Passivated Gold Nanoclusters
Chiral structures have been found as the lowest-energy isomers of bare
(Au and Au_{28}(SCH_{16}_{38}(SCH_{3})_{24}) gold nanoclusters. The degree of chirality existing in
the chiral clusters was calculated using the Hausdorff chirality measure. We
found that the index of chirality is higher in the passivated clusters and
decreases with the cluster size. These results are consistent with the observed
chiroptical activity recently reported for glutahione-passivated gold
nanoclusters, and provide theoretical support for the existence of chirality in
these novel compounds.Comment: 5 pages, 1 figure. Submitted to PR
Synthesis and Structure of Trinuclear W3S4 Clusters Bearing Aminophosphine Ligands and Their Reactivity toward Halides and Pseudohalides
The aminophosphine ligand (2-aminoethyl)- diphenylphosphine (edpp) has been coordinated to the W3(μ-
S)(μ-S)3 cluster unit to afford trimetallic complex [W3S4Br3(edpp)3]+ (1+) in a one-step synthesis process with high yields. Related [W3S4X3(edpp)3]+ clusters (X = F−, Cl−, NCS−; 2+−4+) have been isolated by treating 1+ with the
corresponding halide or pseudohalide salt. The structure of complexes 1+ to 4+ contains an incomplete W3S4 cubane-type cluster unit, and only one of the possible isomers is formed: the one with the phosphorus atoms trans to the capping sulfur and the amino groups trans to the bridging sulphurs. The remaining coordination position on each metal is occupied by X. Detailed studies using stopped-flow, 31P{1H} NMR, and ESI-MS have been carried out in order to understand the solution behavior and the kinetics of interconversion among species 1+, 2+, 3+, and 4+ in solution. Density functional theory (DFT) calculations have been also carried out on the reactions of cluster 1+ with the different anions. The whole set of experimental and theoretical data indicate that the actual mechanism of substitutions in these clusters is strongly dependent on the nature of the leaving and entering anions. The interaction between an entering F− and the amino group coordinated to the adjacent metal have also been found to be especially relevant to the kinetics of these reactions
Near- and Far-Infrared Counterparts of Millimeter Dust Cores in the Vela Molecular Ridge Cloud D
The aim of this paper is to identify the young protostellar counterparts
associated to dust millimeter cores of the Vela Molecular Ridge Cloud D through
new IR observations (H_2 narrow-band at 2.12 micron and N broad band at 10.4
micron) along with an investigation performed on the existing IR catalogues.
The association of mm continuum emission with infrared sources from catalogues
(IRAS, MSX, 2MASS), JHK data from the literature and new observations, has been
established according to spatial coincidence, infrared colours and spectral
energy distributions. Only 7 out of 29 resolved mm cores (and 16 out of the 26
unresolved ones) do not exhibit signposts of star formation activity. The other
ones are clearly associated with: far-IR sources, H_2 jets or near-IR objects
showing a high intrinsic colour excess. The distribution of the spectral
indices pertaining to the associated sources is peaked at values typical of
Class I objects, while three objects are signalled as candidates Class 0
sources. We remark the high detection rate (30%) of H_2 jets driven by sources
located inside the mm-cores. They appear not driven by the most luminous
objects in the field, but rather by less luminous objects in young clusters,
testifying the co-existence of both low- and intermediate-mass star formation.
The presented results reliably describe the young population of VMR-D. However,
the statistical evaluation of activity vs inactivity of the investigated cores,
even in good agreement with results found for other star forming regions, seems
to reflect the limiting sensitivity of the available facilities rather than any
property intrinsic to the mm-condensations.Comment: 38 pages. To be published to Astronomy & Astrophysic
Dark Matter from Minimal Flavor Violation
We consider theories of flavored dark matter, in which the dark matter
particle is part of a multiplet transforming nontrivially under the flavor
group of the Standard Model in a manner consistent with the principle of
Minimal Flavor Violation (MFV). MFV automatically leads to the stability of the
lightest state for a large number of flavor multiplets. If neutral, this
particle is an excellent dark matter candidate. Furthermore, MFV implies
specific patterns of mass splittings among the flavors of dark matter and
governs the structure of the couplings between dark matter and ordinary
particles, leading to a rich and predictive cosmology and phenomenology. We
present an illustrative phenomenological study of an effective theory of a
flavor SU(3)_Q triplet, gauge singlet scalar.Comment: 10 pages, 2 figures; v2: references added, minor changes to collider
analysis, conclusions unchange
Complex organic molecules in protostellar environments in the SKA era
Molecular complexity builds up at each step of the Sun-like star formation
process, starting from simple molecules and ending up in large polyatomic
species. Complex organic molecules (COMs; such as methyl formate, HCOOCH,
dymethyl ether, CHOCH, formamide, NHCHO, or glycoaldehyde,
HCOCHOH) are formed in all the components of the star formation recipe
(e.g. pre-stellar cores, hot-corinos, circumstellar disks, shocks induced by
fast jets), due to ice grain mantle sublimation or sputtering as well as
gas-phase reactions. Understanding in great detail the involved processes is
likely the only way to predict the ultimate molecular complexity reached in the
ISM, as the detection of large molecules is increasingly more difficult with
the increase of the number of atoms constituting them.
Thanks to the recent spectacular progress of astronomical observations, due
to the Herschel (sub-mm and IR), IRAM and SMA (mm and sub-mm), and NRAO (cm)
telescopes, an enormous activity is being developed in the field of
Astrochemistry, extending from astronomical observatories to chemical
laboratories. We are involved in several observational projects providing
unbiased spectral surveys (in the 80-300 and 500-2000 GHz ranges) with
unprecedented sensitivity of templates of dense cores and protostars. Forests
of COM lines have been detected. In this chapter we will focus on the chemistry
of both cold prestellar cores and hot shocked regions, (i) reviewing results
and open questions provided by mm-FIR observations, and (ii) showing the need
of carrying on the observations of COMs at lower frequencies, where SKA will
operate. We will also emphasize the importance of analysing the spectra by the
light of the experimental studies performed by our team, who is investigating
the chemical effects induced by ionising radiation bombarding astrophysically
relevant ices.Comment: 18 pages, 8 figure
Olfactory function and viral recovery in COVID-19
Olfactory and taste disorders were reported in up to 30%-80% of COVID-19 patients. The purpose of our study was to objectively assess smell impairment in COVID-19 patients and to correlate olfactory function with viral recovery
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