2,375 research outputs found
HPMC Hydrogel Formation Mechanisms Unveiled by the Evaluation of the Activation Energy
Aqueous solutions of hydroxypropyl methylcellulose (HPMC) show inverse thermoreversible gelation, i.e., they respond to small temperature variations exhibiting solâgel transition during heating, and reversibly gelâsol transition during cooling. According to the pertinent literature on HPMC aqueous systems, at room temperature, the loss modulus (Gâ) is higher than the storage modulus (Gâ). During the heating ramp, the viscoelastic response follows a peculiar path: initially, Gâ and Gâ smoothly decrease, then drop to a minimum and finally increase. Eventually, Gâ overcomes Gâ, indicating the gel formation. A recent explanation of this behaviour considers a twoâstep mechanism: first, phase separation occurs, then fibrils form from a polymer-rich phase and entangle, leading to a threeâdimensional network. Based on this, our research focuses on the rheological analysis of the different steps of the solâgel transition of an HPMC aqueous solution. We perform different viscoelastic tests: thermal ramps, time sweeps, and frequency sweeps at selected characteristic temperatures. We couple classical analysis of the SAOS experiments with an innovative approach based on the evaluation of the activation energy (Ea), made possible by the instrument intrinsic temperature oscillations around the target value. Results show that Ea can be a valid tool that contributes to further clarifying the peculiar microstructural evolution occurring in this kind of thermoreversible gel
An extreme proto-cluster of luminous dusty starbursts in the early Universe
We report the identification of an extreme proto-cluster of galaxies in the
early Universe whose core (nicknamed Distant Red Core, DRC) is formed by at
least ten dusty star-forming galaxies (DSFGs), confirmed to lie at via detection of [CI](1-0), CO(6-5), CO(4-3),
CO(2-1) and emission lines, detected
using ALMA and ATCA. The spectroscopically-confirmed components of the
proto-cluster are distributed over a region
and have a collective obscured star-formation rate (SFR) of , considerably higher than has been seen before in any
proto-cluster of galaxies or over-densities of DSFGs at . Most of
the star formation is taking place in luminous DSFGs since no Ly
emitters are detected in the proto-cluster core, apart from a Ly blob
located next to one of the DRC dusty components and extending over . The total obscured SFR of the proto-cluster could rise to if all the members of an over-density
of bright DSFGs discovered around DRC in a wide-field LABOCA 870-m image
are part of the same structure. The total halo mass of DRC could be as high as
and could be the progenitor of a Coma-like
cluster at . The relatively short gas-depletion times of the DRC
components suggest either the presence of a mechanism able to trigger extreme
star formation simultaneously in galaxies spread over a few hundred kpc or the
presence of gas flows from the cosmic web able to sustain star formation over
several hundred million years.Comment: Submitted to ApJ. Minor updates added, including a change of the
source name. Comments welcom
A graceful multiversal link of particle physics to cosmology
In this paper we work out a multiverse scenario whose physical
characteristics enable us to advance the following the conjecture that whereas
the physics of particles and fields is confined to live in the realm of the
whole multiverse formed by finite-time single universes, that for our
observable universe must be confined just in one of the infinite number of
universes of the multiverse when such a universe is consistently referred to an
infinite cosmic time. If this conjecture is adopted then some current
fundamental problems that appear when one tries to make compatible particle
physics and cosmology- such as that for the cosmological constant, the arrow of
time and the existence of a finite proper size of the event horizon- can be
solved.Comment: 10 pages, LaTe
280 one-opposition near-Earth asteroids recovered by the EURONEAR with the <i>Isaac Newton</i> Telescope
Context. One-opposition near-Earth asteroids (NEAs) are growing in number, and they must be recovered to prevent loss and mismatch risk, and to improve their orbits, as they are likely to be too faint for detection in shallow surveys at future apparitions.
Aims. We aimed to recover more than half of the one-opposition NEAs recommended for observations by the Minor Planet Center (MPC) using the Isaac Newton Telescope (INT) in soft-override mode and some fractions of available D-nights. During about 130 h in total between 2013 and 2016, we targeted 368 NEAs, among which 56 potentially hazardous asteroids (PHAs), observing 437 INT Wide Field Camera (WFC) fields and recovering 280 NEAs (76% of all targets).
Methods. Engaging a core team of about ten students and amateurs, we used the THELI, Astrometrica, and the Find_Orb software to identify all moving objects using the blink and track-and-stack method for the faintest targets and plotting the positional uncertainty ellipse from NEODyS.
Results. Most targets and recovered objects had apparent magnitudes centered around V ~ 22.8 mag, with some becoming as faint as V ~ 24 mag. One hundred and three objects (representing 28% of all targets) were recovered by EURONEAR alone by Aug. 2017. Orbital arcs were prolonged typically from a few weeks to a few years; our oldest recoveries reach 16 years. The OâC residuals for our 1854 NEA astrometric positions show that most measurements cluster closely around the origin. In addition to the recovered NEAs, 22â000 positions of about 3500 known minor planets and another 10â000 observations of about 1500 unknown objects (mostly main-belt objects) were promptly reported to the MPC by our team. Four new NEAs were discovered serendipitously in the analyzed fields and were promptly secured with the INT and other telescopes, while two more NEAs were lost due to extremely fast motion and lack of rapid follow-up time. They increase the counting to nine NEAs discovered by the EURONEAR in 2014 and 2015.
Conclusions. Targeted projects to recover one-opposition NEAs are efficient in override access, especially using at least two-meter class and preferably larger field telescopes located in good sites, which appear even more efficient than the existing surveys
Characterization of the n-TOF EAR-2 neutron beam
The experimental area 2 (EAR-2) at CERNs neutron time-of-flight facility (n-TOF), which is operational since 2014, is designed and built as a short-distance complement to the experimental area 1 (EAR-1). The Parallel Plate Avalanche Counter (PPAC) monitor experiment was performed to characterize the beam prole and the shape of the neutron 'ux at EAR-2. The prompt Îł-flash which is used for calibrating the time-of-flight at EAR-1 is not seen by PPAC at EAR-2, shedding light on the physical origin of this Îł-flash
Measurement of the 240Pu(n,f) cross-section at the CERN n-TOF facility : First results from experimental area II (EAR-2)
The accurate knowledge of the neutron-induced fission cross-sections of actinides and other isotopes involved in the nuclear fuel cycle is essential for the design of advanced nuclear systems, such as Generation-IV nuclear reactors. Such experimental data can also provide the necessary feedback for the adjustment of nuclear model parameters used in the evaluation process, resulting in the further development of nuclear fission models. In the present work, the 240Pu(n,f) cross-section was measured at CERN's n-TOF facility relative to the well-known 235U(n,f) cross section, over a wide range of neutron energies, from meV to almost MeV, using the time-of-flight technique and a set-up based on Micromegas detectors. This measurement was the first experiment to be performed at n-TOF's new experimental area (EAR-2), which offers a significantly higher neutron flux compared to the already existing experimental area (EAR-1). Preliminary results as well as the experimental procedure, including a description of the facility and the data handling and analysis, are presented
Measurement of 73 Ge(n,Îł) cross sections and implications for stellar nucleosynthesis
© 2019 The Author(s). Published by Elsevier B.V.73 Ge(n,γ) cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the stellar cross section at kT=30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of 73 Ge produced in stars, which would explain the low isotopic abundance of 73 Ge in the solar system.Peer reviewe
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