388 research outputs found
Temporal evolution of oscillating coronal loops
Context. Transverse oscillations of coronal structures are currently
intensively studied to explore the associated magnetohydrodynamic wave physics
and perform seismology of the local medium. Aims. We make a first attempt to
measure the thermodynamic evolution of a sample of coronal loops that undergo
decaying kink oscillations in response to an eruption in the corresponding
active region. Methods. Using data from the six coronal wavelengths of SDO/AIA,
we performed a differential emission measure (DEM) analysis of 15 coronal loops
before, during, and after the eruption and oscillation. Results. We find that
the emission measure, temperature, and width of the DEM distribution undergo
significant variations on time scales relevant for the study of transverse
oscillations. There are no clear collective trends of increases or decreases
for the parameters we analysed. The strongest variations of the parameters
occur during the initial perturbation of the loops, and the influence of
background structures may also account for much of this variation. Conclusions.
The DEM analysis of oscillating coronal loops in erupting active regions shows
evidence of evolution on time scales important for the study of the
oscillations. Further work is needed to separate the various observational and
physical mechanisms that may be responsible for the variations in temperature,
DEM distribution width, and total emission measure.Comment: Accepted in A&
Packed hybrid silica nanoparticles as sorbents with thermo-switchable surface chemistry and pore size for fast extraction of environmental pollutants
Thermoresponsive poly(N-isopropylacrylamide)-grafted silica nanoparticles (SiNPs) have been synthesized and fully characterized by ATR-FTIR, TGA, HRTEM, BET and DLS analysis. Hybrid solid phase extraction (SPE) beds with tuneable pore size and switchable surface chemistry were prepared by packing the polymergrafted nanoparticles inside SPE cartridges. The cartridges were tested by checking the thermoregulated elution of model compounds, namely methylene blue, caffeine and amoxicillin. Extraction of the analytes and regeneration of the interaction sites on the sorbent surface was carried out entirely in water solution by changing the external temperature below and above the lower critical solution temperature (LCST) of the polymer. The results demonstrate that the elution of model compounds depends on the temperature-regulated size of the inter-particle voids and on the change of surface properties of the PNIPAM-grafted nanoparticles from hydrophilic to hydrophobic
SQUARE CONCRETE SECTION CONFINED BY FRP: ULTIMATE STRENGTH PREDICTION
ABSTRACT During the last ten years, several studies have been devoted to understanding the behaviour of circular concrete sections confined by FRP. Less studies have dealt with square and rectangular sections, even if the problem is equally important, given the large amount of buildings with such sections that need to be retrofitted due to poor performance under vertical and horizontal actions. A numerical model was already proposed for the prediction of the stress-strain relationship. In order to implement such model in a design code framework, a mechanics-based equation has been developed and preliminary results are presented for the prediction of the ultimate strength of square sections confined by FRP. Since the model considers the corner radius influence, circular sections are automatically included as a particular case. The simplified model has been calibrated by means of a set of experimental values available in the literature
Oscillations of cometary tails: a vortex shedding phenomenon?
Context. During their journey to perihelion, comets may appear in the
field-of-view of space-borne optical instruments, showing in some cases a
nicely developed plasma tail extending from their coma and exhibiting an
oscillatory behaviour. Aims. The oscillations of cometary tails may be
explained in terms of vortex shedding because of the interaction of the comet
with the solar wind streams. Therefore, it is possible to exploit these
oscillations in order to infer the value of the Strouhal number , which
quantifies the vortex shedding phenomenon, and the physical properties of the
local medium. Methods. We used the Heliospheric Imager (HI) data of the Solar
TErrestrial Relations Observatory (STEREO) mission to study the oscillations of
the tails of the comets 2P/Encke and C/2012 S1 (ISON) during their perihelion
in Nov 2013, determining the Strouhal numbers from the estimates of the halo
size, the relative speed of the solar wind flow and the period of the
oscillations. Results. We found that the estimated Strouhal numbers are very
small, and the typical value of would be extrapolated for size of
the halo larger than km. Conclusions. Despite the vortex shedding
phenomenon has not been unambiguously revealed, the findings suggest that some
MHD instability process is responsible for the observed behaviour of cometary
tails, which can be exploited for probing the physical conditions of the
near-Sun region.Comment: 10 pages, 9 figures, accepted for publication in A&A, Sect. 1
Pigsâ husbandry as case study to test effects of vegetable residuesâ hydrolysates on animals
Soluble biopolymers (SBO) are research products obtained from alkaline hydrolysis of municipal and agriculture bio-residues. They contain a mix of soluble macromolecules with different C types and functional groups. These features make SBO multipurpose products for the chemical industry, agriculture and animal husbandry. As such, they may contribute to the development of bio-based circular economy by recycling renewable carbon over urban and agriculture environments. To foster production and commercialization, assessment of SBOâs compliance with countriesâ regulations is mandatory. The authors performed the present in vivo pigs study to investigate quality, safety, and efficacy of SBOâs as animal feed supplement. Total 106 male and female piglets were fed 42 days with protein-based diets containing 0.1 and 0.2 % SBO. Pigs grew from average 7.7 to 26 kg. Average mortality rate was 3.9 %. Relatively to control diets with no added SBO, the diets containing 0.1 and 0.2 % SBO evidenced no significant effects on pigsâ growth, mortality, and anatomy and pathology of dead animals. A previous rabbit study reported similar results for SBO supplemented diets. The authors discuss the economic and environmental implications of the results in relation to SBO potential marketability
Multi-instrument observations of a failed flare eruption associated with MHD waves in a loop bundle
Context. We present observations of a B7.9 class flare that occurred on January 24th, 2015, using SDO/AIA, Hinode/EIS and XRT.
The flare triggers an eruption of a dense cool plasma blob as seen in AIA 171Ă
which is unable to completely break out and remains
confined within a local bundle of active region loops. During this process, transverse oscillations of the threads are observed. The cool
plasma is then observed to descend back to the chromosphere along each loop strand. At the same time, a larger diffuse co-spatial
loop observed in the hot wavebands of SDO/AIA and Hinode/XRT is formed, exhibiting periodic intensity variations along its lenght.
Aims. The formation and evolution of magnetohydrodynamic (MHD) waves depend upon the values of the local plasma parameters
(e.g., density, temperature, magnetic field) which can hence be inferred by coronal seismology. In this study we aim to assess how the
observed MHD modes are affected by the variation of density and temperature.
Methods. We combine analysis of EUV/X-ray imaging and spectroscopy using SDO/AIA, Hinode/EIS and XRT.
Results. The transverse oscillations of the cool loop threads are interpreted in terms of vertically polarised kink oscillations. The
fitting procedure provides estimates for the period of about 3.5â4 min, and the amplitude of âź 5 Mm. The oscillations are strongly
damped showing very low quality factor (1.5â2), which is defined as the ratio of the damping time and the oscillation period. The
weak variation of the period of the kink wave, which is estimated from the fitting analysis, is in agreement with the density variations
due to the presence of the plasma blob inferred from the intensity light curve at 171Ă
. The coexisting intensity oscillations along the
hot loop are interpreted as a slow MHD wave with the period of 10 min and phase speed of about 436 km sâ1
. Comparison between
the fast and slow modes allows for the determination of the AlfvÊn speed, and consequently magnetic field values. The plasma-β
inferred from the analysis is estimated to be around 0.1â0.3.
Conclusions. We show that the evolution of the detected waves is determined by the temporal variations of the local plasma parameters,
caused by the flare heating and the consequent cooling. We apply coronal seismology to both waves obtaining estimations of the
background plasma parameter
Bell inequalities as constraints on unmeasurable correlations
The interpretation of the violation of Bell-Clauser-Horne inequalities is
revisited, in relation with the notion of extension of QM predictions to
unmeasurable correlations. Such extensions are compatible with QM predictions
in many cases, in particular for observables with compatibility relations
described by tree graphs. This implies classical representability of any set of
correlations , , , and the equivalence of the
Bell-Clauser-Horne inequalities to a non void intersection between the ranges
of values for the unmeasurable correlation associated to different
choices for B. The same analysis applies to the Hardy model and to the "perfect
correlations" discussed by Greenberger, Horne, Shimony and Zeilinger. In all
the cases, the dependence of an unmeasurable correlation on a set of variables
allowing for a classical representation is the only basis for arguments about
violations of locality and causality.Comment: Some modifications have been done in order to improve clarity of
presentation and comparison with other approache
Dissolved organic carbon retention by coprecipitation during the oxidation of ferrous iron (EGU2018-3906)
Although the importance of Fe (hydr)oxides for soil organic matter (OM) stabilization and C retention by surface adsorption is well known, only recently has coprecipitation been recognized as an important process responsible for C storage in hydromorphic soils, such as rice paddy soils. Under periodic fluctuations in redox conditions the interaction between dissolved organic carbon (DOC) and Fe (hydr)oxides may not only involve organic coatings
on mineral surfaces, but also Fe-DOC coprecipitates that form during the oxidation of soil solutions containing important amounts of DOC and Fe2+.
The aim of this work was to provide new insights into the mechanisms involved, and the amount and selectivity of C retained during the coprecipitation process. A series of Fe-OM associations with increasing C loading was synthesized at pH 6 by surface adsorption or coprecipitation (oxidation of ferrous iron) utilizing rice-straw derived dissolved organic matter. The kinetics of Fe2+ oxidation and complexation, and the total and selective retention of DOC during the coprecipitation process were evaluated. Moreover, synthesized associations, as well as a field coprecipitate collected in situ from a paddy soil, were studied by X-ray diffraction, N2 gas adsorption-desorption isotherms, electrophoretic mobility measurements and thermogravimetric analyses. Coprecipitation resulted in higher organic C contents (49-213 mg g-1) with respect to adsorbed systems (18-47 mg g-1), and favoured the inclusion of OM within highly aggregated associations having particularly low BET specific surface areas. Coprecipitates sampled in situ also showed a similar retention of organic C confirming that this process may contribute significantly to the OM stabilization in paddy topsoils. The mechanisms involved in the retention of straw-derived DOM during coprecipitation were shown to be strongly dependent on C/Fe ratio of the solution. Although the overall coprecipitation process was highly selective for aromatic constituents, initial complexation of Fe2+ and precipitation as C-rich metal salts involved the selective interaction with aliphatic carboxylic constituents. The contribution of the latter mechanism to total C retention during coprecipitation was shown to increase with increasing solution C/Fe ratios. These aliphatic complexes formed during coprecipitation may play an important, though often underestimated, role in C stabilization in hydromorphic. The process-related selectivity of specific constituents of DOM during coprecipitation highlights the involvement of specific mechanisms, i.e. complexation, adsorption, salt precipitation, while ruling out non-selective, physical occlusion of OM within the forming coprecipitat
Observing the corona and inner heliosphere with Parker Solar Probe
The recently launched Parker Solar Probe (PSP) mission is expected to provide unprecedented views of the solar corona and inner heliosphere. In addition to instruments devoted to taking measurements of the local solar wind, the spacecraft carries a visible imager: the Wide-ďŹeld Imager for Solar PRobe (WISPR). WISPR will take advantage of the proximity of the spacecraft to the Sun to perform local imaging of the near-Sun environment. WISPR will observe coronal structures at high spatial and time resolutions, although the observed plane-of-sky will rapidly change because of the fast transit at the perihelia. We present a concise description of the PSP mission, with particular regard to the WISPR instrument, discussing its main scientiďŹc goals, targets of observations, and outlining the possible synergies with current and upcoming space missions
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