Context.
The heating of the solar corona by small heating events requires an increasing number of such events at progressively smaller scales, with the bulk of the heating occurring at scales that ...are currently unresolved.
Aims.
The goal of this work is to study the smallest brightening events observed in the extreme-UV quiet Sun.
Methods.
We used commissioning data taken by the Extreme Ultraviolet Imager (EUI) on board the recently launched Solar Orbiter mission. On 30 May 2020, the EUI was situated at 0.556 AU from the Sun. Its High Resolution EUV telescope (HRI
EUV
, 17.4 nm passband) reached an exceptionally high two-pixel spatial resolution of 400 km. The size and duration of small-scale structures was determined by the HRI
EUV
data, while their height was estimated from triangulation with simultaneous images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory mission. This is the first stereoscopy of small-scale brightenings at high resolution.
Results.
We observed small localised brightenings, also known as ‘campfires’, in a quiet Sun region with length scales between 400 km and 4000 km and durations between 10 s and 200 s. The smallest and weakest of these HRI
EUV
brightenings have not been previously observed. Simultaneous observations from the EUI High-resolution Lyman-
α
telescope (HRI
Lya
) do not show localised brightening events, but the locations of the HRI
EUV
events clearly correspond to the chromospheric network. Comparisons with simultaneous AIA images shows that most events can also be identified in the 17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although they appear weaker and blurred. Our differential emission measure analysis indicated coronal temperatures peaking at log
T
≈ 6.1 − 6.15. We determined the height for a few of these campfires to be between 1000 and 5000 km above the photosphere.
Conclusions.
We find that ‘campfires’ are mostly coronal in nature and rooted in the magnetic flux concentrations of the chromospheric network. We interpret these events as a new extension to the flare-microflare-nanoflare family. Given their low height, the EUI ‘campfires’ could stand as a new element of the fine structure of the transition region-low corona, that is, as apexes of small-scale loops that undergo internal heating all the way up to coronal temperatures.
The amazing climbing ability of geckos has attracted the interest of
philosophers and scientists alike for centuries. However,
only in the past few years has progress been made in
understanding the ...mechanism behind this ability, which relies on submicrometre
keratin hairs covering the soles of geckos. Each hair produces a miniscule
force 10−7 N (due to van der Waals and/or capillary
interactions) but millions of hairs acting together create a formidable
adhesion of 10 N cm−2: sufficient to keep geckos
firmly on their feet, even when upside down on a glass ceiling. It is very
tempting to create a new type of adhesive by mimicking the
gecko mechanism. Here we report on a prototype of such 'gecko tape' made by
microfabrication of dense arrays of flexible plastic pillars, the geometry of
which is optimized to ensure their collective adhesion. Our approach shows a
way to manufacture self-cleaning, re-attachable dry adhesives, although
problems related to their durability and mass production are yet to be
resolved.
Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ...ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km s
and life-times of about 40 s. The null-point reconnection also occurs explosively but only for 4 minutes, its coupling with a mini-filament eruption generates a spiral jet. These results suggest that magnetic reconnection, at previously unresolved scales, proceeds continually in a gentle and/or explosive way to persistently transfer mass and energy to the overlying corona.
Plastic pollution is one of the most pressing environmental problems, and a huge amount of effort and money is directed towards solving it. The existing processing methods are ineffective. The main ...component of all plastic materials (CxHy) is carbon. High-purity fine titanium carbide was obtained using plastic waste (polyethylene terephthalate – C10H8O4) as a carbon raw material. Combustion processes, phase composition and structure of the obtained materials were studied. A probable mechanism for the formation of titanium carbide during the combustion of the (Ti + C10H8O4) mixture was proposed. During the synthesis, polyethylene terephthalate decomposes into carbon, hydrogen and oxygen. Carbon and oxygen react with titanium and form titanium oxycarbide. Titanium oxycarbide is saturated with carbon to form titanium carbide and carbon dioxide. The remaining hydrogen and carbon dioxide are released from the synthesis products, which leads to self-purification of the synthesis products. The obtained results will create the basis for the development of a fundamentally new, cost-effective technology for recycling plastic waste into carbides and carbide-containing materials.
Abstract
In the present study, a method for the synthesis of gelatin-stabilized copper oxide nanoparticles was developed. Synthesis was carried out by direct chemical precipitation. Copper sulfate, ...chloride, and acetate were used as precursors for the copper oxide synthesis. Gelatin was used as a stabilizer. It was found that the formation of monophase copper oxide II only occurred when copper acetate was used as a precursor. Our results showed that particles of the smallest diameter are formed in an aqueous medium (18 ± 6 nm), and those of th largest diameter—in an isobutanol medium (370 ± 131 nm). According to the photon correlation spectroscopy data, copper oxide nanoparticles synthesized in an aqueous medium were highly stable and had a monomodal size distribution with an average hydrodynamic radius of 61 nm. The study of the pH effect on the colloidal stability of copper oxide nanoparticles showed that the sample was stable in the pH range of 6.8 to 11.98. A possible mechanism for the pH influence on the stability of copper oxide nanoparticles is described. The effect of the ionic strength of the solution on the stability of the CuO nanoparticles sol was also studied, and the results showed that Ca
2+
ions had the greatest effect on the sample stability. IR spectroscopy showed that the interaction of CuO nanoparticles with gelatin occurred through the hydroxyl group. It was found that CuO nanoparticles stabilized with gelatin have a fungicidal activity at concentration equivalent 2.5 · 10
−3
mol/L and as a material for food nanopackaging can provide an increase in the shelf life of products on the example of strawberries and tomatoes. We investigated the possibility of using methylcellulose films modified with CuO nanoparticles for packaging and storage of hard cheese “Holland”. The distribution of CuO nanoparticles in the methylcellulose film was uniform. We found that methylcellulose films modified with CuO nanoparticles inhibited the growth and development of QMAFAM, coliforms, yeast and mold in experimental cheese sa mples. Our research has shown that during the cheese storage in thermostat at 35 ± 1 °C for 7 days, CuO nanoparticles migrated to the product from the film. Nevertheless, it is worth noting that the maximum change in the concentration of copper in the experimental samples was only 0.12 µg/mg, which is not a toxic concentration. In general, the small value of migration of CuO nanoparticles confirms the high stability of the developed preparation. Our results indicated that the CuO nanoparticles stabilized with gelatin have a high potential for use in food packaging – both as an independent nanofilm and as part of other packaging materials.
•The heat transfer coefficient increases many times upon boiling on a capillary-porous coating.•Heat transfer on a cоating is lower than on a smooth surface during evaporation.•Pressure determines ...the mechanism of crises during evaporation and boiling on a coating.•The CHF increases significantly on the microstructured surface produced by a 3D laser printer.
Heat transfer was experimentally studied under evaporation/boiling conditions in thin horizontal layers of n-dodecane at low relative pressures. A capillary-porous coating from a stainless steel powder with a sinusoidal 2D modulated profile was applied using a 3D laser printer. The selective laser sintering (SLS) additive technique was applied in the study. The dependence of a heat transfer coefficient on the heat flux under different pressures was studied for liquid layers various heights. The resulting experimental data were compared with the values obtained during evaporation/boiling on a smooth surface under the same conditions. A rise in the relative pressure results in an increase of the heat transfer coefficient at bubble boiling. The study demonstrates that the use of a capillary-porous coating leads to a 3.5-fold increase of the heat transfer coefficient in the regimes of bubble boiling. The heat transfer coefficient on the capillary-porous coating was lower compared to a smooth surface in heat transfer regimes with evaporation at low relative pressures. The critical heat fluxes (CHF) on the capillary-porous coating increase with the increasing height of the liquid layer.
The magnetic anisotropy of Fe‐rich, thin, amorphous wires is tailored by stress annealing (SA). In particular, the effect of conventional annealing (CA) and SA on the magnetic properties of ...Fe74B13Si11C2 glass‐coated microwires is studied. CA treatment does not significantly change the character of the hysteresis loop. Under certain SA conditions (annealing temperature, Tann > 300 °C; applied stress, σ > 400 MPa), a transverse magnetic anisotropy is induced: a rectangular hysteresis loop transforms into an inclined one at magnetic‐anisotropy fields above 1000 A m–1. Under tensile stress, the rectangular hysteresis loop of microwires annealed using SA is recovered. Samples subjected to SA show noticeable magnetoimpedance and stress‐impedance effects, despite their large magnetostriction. The samples obtained exhibit a high stress sensitivity of their giant magnetoimpedance (GMI) effect and hysteretic properties, allowing the use of the obtained samples in magnetoelastic sensors, and for designing stress‐sensitive, tunable composite materials. By varying the time and temperature of such SA, we are able to tailor both the magnetic properties and the GMI of Fe‐rich microwires.
The magnetic anisotropy of Fe‐rich, thin, amorphous wires (see Figure) is tailored by stress annealing, allowing the induction of transverse magnetic anisotropy and a considerable stress‐sensitive giant magnetoimpedance effect in microwires with a positive magnetostriction constant. Such samples are suitable for magnetoelastic sensors and stress‐sensitive, tunable composite materials.
The application of foamed polymers as one of the components of insulating coatings allows to solve the problems of energy saving and creation of optimal operating conditions for constructions. The ...systems of application of energy-efficient heat-insulating materials must consider both the particularities of the insulating materials and the functional orientation of the constructions. The implementation of the concept of seamless insulating coatings implies the achievement of thermal effect and reduction in air permeability both by means of the application of thermal insulation with low thermal conductivity and the minimization of junctions between separate elements of the insulating coating, which is achieved using elastic foamed polymers and, first of all, polyethylene foam. Construction of seamless insulating coatings creates practically impermeable heat, vapor, and water barriers along the outer perimeter of the insulated object. Multilayer products based on polyethylene foam represent a relatively new material—a fact that requires examination of their properties, as well as under various operating conditions, and development of a methodology for evaluation of the operational resistance of these materials in structures of different purposes, including cold conservation. The performed tests have shown that the compressive strength at 10% deformation is determined by the function of load application area and varies from 70 kPa during the test of cube samples of 10 × 10 × 10 in size to 260 kPa for areas exceeding 100 m2. The longitudinal tensile strength amounts to 80–92 kPa, and the strength of the weld seam is equal to 29–32 kPa. It has been established that the values of thermal conductivity of polyethylene foam with an average density of 18–20 kg/m3 amounts to 0.032–0.034 W/(m·K), diffusion moisture absorption is equal to 0.44 kg/m2 without a metallized coating and 0.37 kg/m2 with a metallized coating; water absorption after partial immersion in water for 24 h amounts to 0.013 kg/m2; water absorption by volume after complete water immersion for 28 days is equal to 0.96%. The material does not practically change its properties under conditions of long-term temperature alteration from −60 to +70 °C. The developed and implemented insulation systems for protective surfaces of framed construction objects, rubbhalls and frameless structures, floating floors, indoor ice rinks, and snow conservation systems are presented.
Electronic excitations have a profound impact on molecular motion induced by femtosecond laser pulses and play a large role in catalytic reactions as well as in spin transport within bulk metals, ...across interfaces, and at surfaces. Chulkov et al present a study of the decay mechanisms of electron excitations on surfaces in which several experimental and theoretical methods were used including photoelectron spectroscopy, inverse photoemission, and self-energy formalism of many-body theory.
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