6,811 research outputs found
CRASH3: cosmological radiative transfer through metals
Here we introduce CRASH3, the latest release of the 3D radiative transfer
code CRASH. In its current implementation CRASH3 integrates into the reference
algorithm the code Cloudy to evaluate the ionisation states of metals,
self-consistently with the radiative transfer through H and He. The feedback of
the heavy elements on the calculation of the gas temperature is also taken into
account, making of CRASH3 the first 3D code for cosmological applications which
treats self-consistently the radiative transfer through an inhomogeneous
distribution of metal enriched gas with an arbitrary number of point sources
and/or a background radiation. The code has been tested in idealized
configurations, as well as in a more realistic case of multiple sources
embedded in a polluted cosmic web. Through these validation tests the new
method has been proven to be numerically stable and convergent. We have studied
the dependence of the results on a number of physical quantities such as the
source characteristics (spectral range and shape, intensity), the metal
composition, the gas number density and metallicity.Comment: accepted for publication in MNRA
UV background fluctuations traced by metal ions at
Here we investigate how LyC-opaque systems present in the intergalactic
medium at can distort the spectral shape of a uniform UV background
(UVB) through radiative transfer (RT) effects. With this aim in mind, we
perform a multi-frequency RT simulation through a cosmic volume of
~cMpc scale polluted by metals, and self-consistently derive the ions
of all the species. The UVB spatial fluctuations are traced by the ratio of
He and H column density,
, and the ratio of C and Si optical depths, . We find that: (i)
spatially fluctuates through over-dense systems () with statistically
significant deviations \% in 18\% of the volume ; (ii) same
fluctuations in are also present in \% of the enriched domain (only
8\% of the total volume) and derive from a combination of RT induced effects
and in-homogeneous metal enrichment, both effective in systems with .Comment: Accepted for pub. in MNRAS after very minor re
On the validity of the adiabatic approximation in compact binary inspirals
Using a semi-analytical approach recently developed to model the tidal
deformations of neutron stars in inspiralling compact binaries, we study the
dynamical evolution of the tidal tensor, which we explicitly derive at second
post-Newtonian order, and of the quadrupole tensor. Since we do not assume a
priori that the quadrupole tensor is proportional to the tidal tensor, i.e. the
so called "adiabatic approximation", our approach enables us to establish to
which extent such approximation is reliable. We find that the ratio between the
quadrupole and tidal tensors (i.e., the Love number) increases as the inspiral
progresses, but this phenomenon only marginally affects the emitted
gravitational waveform. We estimate the frequency range in which the tidal
component of the gravitational signal is well described using the stationary
phase approximation at next-to-leading post-Newtonian order, comparing
different contributions to the tidal phase. We also derive a semi-analytical
expression for the Love number, which reproduces within a few percentage points
the results obtained so far by numerical integrations of the relativistic
equations of stellar perturbations.Comment: 13 pages, 1 table, 2 figures. Minor changes to match the version
appearing on Phys. Rev.
Galaxy formation with radiative and chemical feedback
Here we introduce GAMESH, a novel pipeline which implements self-consistent
radiative and chemical feedback in a computational model of galaxy formation.
By combining the cosmological chemical-evolution model GAMETE with the
radiative transfer code CRASH, GAMESH can post process realistic outputs of a
N-body simulation describing the redshift evolution of the forming galaxy.
After introducing the GAMESH implementation and its features, we apply the code
to a low-resolution N-body simulation of the Milky Way formation and we
investigate the combined effects of self-consistent radiative and chemical
feedback. Many physical properties, which can be directly compared with
observations in the Galaxy and its surrounding satellites, are predicted by the
code along the merger-tree assembly. The resulting redshift evolution of the
Local Group star formation rates, reionisation and metal enrichment along with
the predicted Metallicity Distribution Function of halo stars are critically
compared with observations. We discuss the merits and limitations of the first
release of GAMESH, also opening new directions to a full implementation of
feedback processes in galaxy formation models by combining semi-analytic and
numerical methods.Comment: This version has coloured figures not present in the printed version.
Submitted to MNRAS, minor revision
Effect of Mn substitution by Ga on the optical properties of a metallic manganite
In a metallic manganite like La(2/3)Sr(1/3)MnO(3), the substitution of Mn(+3)
by Ga(+3) dilutes the ferromagnetic order and locally cancels the Jahn-Teller
distortion, without heavily affecting the crystal structure. One can thus
follow the changes in the charge dynamics induced by Ga, until the
ferro-metallic manganite is turned into an insulator. Here this phenomenon is
studied in detail through the infrared reflectivity of five samples of
La(2/3)Sr(1/3)Mn(1-x)Ga(x)O(3), with x increasing from 0 to 0.30 and for 50 < T
< 320 K. A simple model which links the measured optical parameters to the
magnetization M(x, T) well describes the behavior of the plasma frequency, the
scattering rate, and the mid-infrared absorption along the metal-to-insulator
transition.Comment: 8 pages including 7 figure
Sea floor bedforms and their influence on slope accommodation (2019)
We sincerely thank Petroleum Geo-Services (PGS) Investigação Petrolífera Limitada, and specifically David Hajovsky and Scott Opdyke, that kindly provided the dataset and allowed us to show these results. We would also like to thank Schlumberger for providing academic licenses of their software (Petrel). We are grateful to Associate Editor Kei Ogata for his support, and we sincerely thank reviewers Daniele Casalbore and Kamaldeen Omosanya for their comments and suggestions that significantly improved the quality of the manuscript.Peer reviewedPostprin
Design methodology for the development of variable stiffness devices based on layer jamming transition
Variable stiffness mechanisms as Jamming Transition draw huge attention recently in Soft Robotics. This paper proposes a comprehensive design methodology for developing variable stiffness devices based on layer jamming. Starting from pre-existing modelling, we highlight the design parameters that should be considered, extracting them from literature and our direct experience with the phenomenon. Then we validated the methodology applying the design process to previous layer jamming cases presented in literature. The comparison between the results obtained from our methodology and those presented in the analyzed previous works highlights a good predictive capability, demonstrating that this methodology can be used as a valid tool to design variable stiffness devices based on layer jamming transition. Finally, in order to provide the scientific community with an easily usable tool to design variable stiffness structures based on layer jamming transition, we have elaborated a Matlab script that guides the user through the main design parameters implementing the proposed methodology in an interactive process
Tidal modulation of river-flood deposits: How low can you go?
Quantification of the interaction between river discharge and tides is vital to characterize fluvio-deltaic systems, to identify diagnostic elements of tidal signatures in the rock record, and to reconstruct paleogeographies. In modern systems, even microtides can significantly influence delta morphodynamics; yet, many fundamental processes, particularly in prodeltaic settings, remain elusive. Here, by combining a unique process-product data set acquired during a flood event of the Po River (Italy) with numerical modeling, we show that tidal signatures are recorded in the open-water prodelta zone of a microtidal system. Based on the analyses of box-cores collected before and after a flood off the main distributary channel, we interpreted storm beds, tide-modulated flood strata of alternating normal and inverse graded beds, and rapid bioturbation. Modeling of the river discharge indicates that, at the peak of the flood, the steepening of the water-surface profile forced by 0.15 m lowering of sea level during low tides generated an 8% increase in river flow velocity. The alternation of profile steepness and associated cyclicity in flow strength during consecutive tidal cycles controlled the sediment load of the plume and, consequently, led to the deposition of tidal-modulated strata. Formation of microtidal signals appears to be enhanced in fluvio-deltaic successions characterized by multiple distributaries and in basins where river floods are out of phase with storm-wave activity. Bioturbation of sediment, which can start during the waning stage of the flow, and erosion by storm waves hamper the preservation of tidal signals, unless rapid burial occurs. The recognition of tidal-modulated strata in river-dominated settings may facilitate the characterization of mudstone reservoirs and reconstruction of paleogeographic conditions during deposition
Prevalence and incidence of low back pain among runners: A systematic review
Background: Running is one of the most popular sports worldwide. Despite low back pain (LBP) represents the most common musculoskeletal disorder in population and in sports, there is currently sparse evidence about prevalence, incidence and risk factors for LBP among runners. The aims of this systematic review were to investigate among runners: prevalence and incidence of LBP and specific risk factors for the onset of LBP. Methods: A systematic review has been conducted according to the guidelines of the PRISMA statement. The research was conducted in the following databases from their inception to 31st of July 2019: PubMed; CINAHL; Google Scholar; Ovid; PsycINFO; PSYNDEX; Embase; SPORTDiscus; Scientific Electronic Library Online; Cochrane Library and Web of Science. The checklists of The Joanna Briggs Institute Critical Appraisal tools were used to investigate the risk of bias of the included studies. Results: Nineteen studies were included and the interrater agreement for full-text selection was good (K = 0.78; 0.61-0.80 IC 95%). Overall, low values of prevalence (0.7-20.2%) and incidence (0.3-22%) of LBP among runners were reported. Most reported risk factors were: running for more than 6 years; body mass index > 24; higher physical height; not performing traditional aerobics activity weekly; restricted range of motion of hip flexion; difference between leg-length; poor hamstrings and back flexibility. Conclusions: Prevalence and incidence of LBP among runners are low compared to the others running related injuries and to general, or specific population of athletes. View the low level of incidence and prevalence of LBP, running could be interpreted as a protective factor against the onset of LBP. Systematic review registration: PROSPERO CRD42018102001
Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil)
Circular to elliptical topographic depressions, isolated or organized in trails, have been observed on the modern seabed in different contexts and water depths. Such features have been alternatively interpreted as pockmarks generated by fluid flow, as sediment waves generated by turbidity currents, or as a combination of both processes. In the latter case, the dip of the slope has been hypothesized to control the formation of trails of downslope migrating pockmarks. In this study, we use high-quality 3D seismic data from the offshore Ceará Basin (Equatorial Brazil) to examine vertically stacked and upslope-migrating trails of depressions visible at the seabed and in the subsurface. Seismic reflection terminations and stratal architecture indicate that these features are formed by cyclic steps generated by turbidity currents, while internal amplitude anomalies point to the presence of fluid migration. Amplitude Versus Offset analysis (AVO) performed on partial stacks shows that the investigated anomalies do not represent hydrocarbon indicators. Previous studies have suggested that the accumulation of permeable and porous sediments in the troughs of vertically stacked cyclic steps may create vertical pathways for fluid migration, and we propose that this may have facilitated the upward migration of saline pore water due to fluid buoyancy. The results of this study highlight the importance of gravity-driven processes in shaping the morphology of the Ceará Basin slope and show how non-hydrocarbon fluids may interact with vertically stacked cyclic steps
- …