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Statistically, the cool loop's footpoints are diagnosed using Si  iv resonance lines observations provided by Interface Region Imaging Spectrograph (IRIS). The intensity and full width at half-maximum (FWHM) of the loop's footpoints in β–γ active regions (ARs) are higher than the corresponding parameters of footpoints in β ARs. However, the Doppler velocity of footpoints in both ARs are almost similar to each other. The intensities of footpoints from β–γ AR is found to be around nine times that of β AR when both ARs are observed nearly at the same time. The same intensity difference reduces nearly to half (four times) when considering all ARs observed over 9 yr. Hence, the instrument degradation affects comparative intensity analysis. We find that Doppler velocity and FWHM are well correlated while peak intensity is neither correlated with Doppler velocity nor FWHM. The loop's footpoints in β–γ ARs have around four times more complex Si  iv spectral profiles than that of β ARs. The intensity ratios (Si  iv 1393.78 Å/1402.77 Å) of the significant locations of footpoints differ, marginally, (i.e. either less than 1.9 or greater than 2.10) from the theoretical ratio of 2, i.e. 52 per cent (55 per cent) locations in β (β–γ) ARs significantly deviate from 2. Hence, we say that more than half of the footpoint locations are either affected by the opacity or resonance scattering. We conclude that the nature and attributes of the footpoints of the cool loops in β–γ ARs are significantly different from those in β ARs. [ABSTRACT FROM AUTHOR]

Submolecular charge distribution significantly affects the physical-chemical properties of molecules and their mutual interaction. One example is the presence of a π-electron-deficient cavity in halogen-substituted polyaromatic hydrocarbon compounds, the so-called π-holes, the existence of which was predicted theoretically, but the direct experimental observation is still missing. Here we present the resolution of the π-hole on a single molecule using the Kelvin probe force microscopy, which supports the theoretical prediction of its existence. In addition, experimental measurements supported by theoretical calculations show the importance of π-holes in the process of adsorption of molecules on solid-state surfaces. This study expands our understanding of the π-hole systems and, at the same time, opens up possibilities for studying the influence of submolecular charge distribution on the chemical properties of molecules and their mutual interaction. A π-electron-deficient cavity in halogen-substituted polyaromatic hydrocarbon compounds, the so-called π-holes, have been predicted theoretically. Here authors present an experimental resolution of the πhole on a single molecule using the Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

We study the dynamics of shock waves observed in the umbra of a sunspot using the spectroscopic observations from the Interface Region Imaging Spectrograph. The presence of a shock significantly deforms the shape of the spectral lines of Mg ii , C ii , and Si iv. We found that C ii 1335.71 Å and Si iv 1393.75 Å show double-peaked profiles that change to a single peak later on. However, the Mg ii h 2803.53 Å line first shows flat-top profiles that change into double peaks followed by the single peak. To study the shock dynamics, we isolate the shock component from the spectra by fitting two Gaussians. We find that the lifetime of the shock is largest in the Mg ii h 2803.53 Å line. Moreover, the plasma motion shows both the acceleration and deceleration phases of the shock. Yet, in C ii 1335.71 Å and Si iv 1393.75 Å, only the deceleration phase is observed. We observe a strong correlation between the largest blueshift of the shock and deceleration for all three spectral lines. We find a positive (negative) correlation between intensities contributed by the shocks in Mg ii and C ii (Si iv). This suggests that the shocks are first amplified in C ii , followed by a decline in the height range corresponding to Si iv. These results may indicate the dissipation of shocks above the formation height of C ii , and the shocks may have important roles in the dynamics of the upper chromosphere and transition region above sunspots. [ABSTRACT FROM AUTHOR]

We perform numerical simulations of impulsively generated magnetic swirls in an isolated flux tube that is rooted in the solar photosphere. These swirls are triggered by an initial pulse in a horizontal component of the velocity. The initial pulse is launched either (a) centrally, within the localized magnetic flux tube or (b) off-central, in the ambient medium. The evolution and dynamics of the flux tube are described by three-dimensional, ideal magnetohydrodynamic equations. These equations are numerically solved to reveal that in case (a) dipole-like swirls associated with the fast magnetoacoustic kink and m = 1 Alfvén waves are generated. In case (b), the fast magnetoacoustic kink and m = 0 Alfvén modes are excited. In both these cases, the excited fast magnetoacoustic kink and Alfvén waves consist of a similar flow pattern and magnetic shells are also generated with clockwise and counter-clockwise rotating plasma within them, which can be the proxy of dipole-shaped chromospheric swirls. The complex dynamics of vortices and wave perturbations reveals the channelling of sufficient amount of energy to fulfil energy losses in the chromosphere (~104 Wm-1) and in the corona (~10² W m-1). Some of these numerical findings are reminiscent of signatures in recent observational data. [ABSTRACT FROM AUTHOR]

Solar flare emission is detected in all EM bands and variations in flux density of solar energetic particles. Often the EM radiation generated in solar and stellar flares shows a pronounced oscillatory pattern, with characteristic periods ranging from a fraction of a second to several minutes. These oscillations are referred to as quasi-periodic pulsations (QPPs), to emphasise that they often contain apparent amplitude and period modulation. We review the current understanding of quasi-periodic pulsations in solar and stellar flares. In particular, we focus on the possible physical mechanisms, with an emphasis on the underlying physics that generates the resultant range of periodicities. These physical mechanisms include MHD oscillations, self-oscillatory mechanisms, oscillatory reconnection/reconnection reversal, wave-driven reconnection, two loop coalescence, MHD flow over-stability, the equivalent LCR-contour mechanism, and thermal-dynamical cycles. We also provide a histogram of all QPP events published in the literature at this time. The occurrence of QPPs puts additional constraints on the interpretation and understanding of the fundamental processes operating in flares, e.g. magnetic energy liberation and particle acceleration. Therefore, a full understanding of QPPs is essential in order to work towards an integrated model of solar and stellar flares. [ABSTRACT FROM AUTHOR]

Aims. During the impulsive flare phase, the plasma at the flare loop footpoints is rapidly heated by particle beams. In the present paper, we study processes that occur after this sudden heating in a two-dimensional magnetic loop. Methods. We adopt a 2D magnetohydrodynamic (MHD) model, in which we solve a full set of the ideal time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method. Periods in the processes are estimated by the wavelet analysis technique. Results. We consider a model of the solar atmosphere with a symmetric magnetic loop. The length of this loop in the corona is approximately 21.5 Mm. At both loop footpoints, at the transition region, we initiate the Gaussian temperature (pressure) perturbation with the maximum temperature 14, 7, or 3.5 times higher than the unperturbed temperature. In the corona, the perturbations produce supersonic blast shocks with the Mach number of about 1.1, but well below Alfvén velocities. We consider cases with the same perturbations at both footpoints (symmetric case) and one with different perturbations (asymmetric case). In the symmetric case, the shocks move along both loop legs upwards to the top of the loop, where they interact and form a transient compressed region. Then they continue in their motion to the transition region at the opposite side of the loop, where they are reflected upwards, and so on. At the top of the loop, the shock appears periodically with the period of about 170 s. In the loop legs during this period, a double peak of the plasma parameters, which is connected with two arrivals of shocks, is detected: firstly, when the shock moves up and then when the shock, propagating from the opposite loop leg, moves down. Increasing the distance of the detection point in the loop leg from the top of the loop, the time interval between these shock arrivals increases. Thus, at these detection points, the processes with shorter periods can be detected. After ~500 s the process with the periodically interacting shocks slowly changes to slow mode magnetosonic free oscillation. Furthermore, we detected quasi-periodic processes, even in the chromosphere under the location of the pressure perturbation. These processes can be observed in intensities and Doppler shifts of optical chromospheric lines. In the case with the asymmetric perturbations, we found that the processes are even more complex. [ABSTRACT FROM AUTHOR]

Magnetohydrodynamic (MHD) oscillatory processes in different plasma systems, such as the corona of the Sun and the Earth's magnetosphere, show interesting similarities and differences, which so far received little attention and remain under-exploited. The successful commissioning within the past ten years of THEMIS, Hinode, STEREO and SDO spacecraft, in combination with matured analysis of data from earlier spacecraft (Wind, SOHO, ACE, Cluster, TRACE and RHESSI) makes it very timely to survey the breadth of observations giving evidence for MHD oscillatory processes in solar and space plasmas, and state-of-the-art theoretical modelling. The paper reviews several important topics, such as Alfvénic resonances and mode conversion; MHD waveguides, such as the magnetotail, coronal loops, coronal streamers; mechanisms for periodicities produced in energy releases during substorms and solar flares, possibility of Alfvénic resonators along open field lines; possible drivers of MHD waves; diagnostics of plasmas with MHD waves; interaction of MHD waves with partly-ionised boundaries (ionosphere and chromosphere). The review is mainly oriented to specialists in magnetospheric physics and solar physics, but not familiar with specifics of the adjacent research fields. [ABSTRACT FROM AUTHOR]

A number of technologies is developed that substitute simple metal cores in the high-pressure casting technology. Soluble cores, namely on the salt basis, represent the highest prospect. The contribution gives the results of the production of salt cores by high-pressure squeezing and shooting with using a binder. Special attention is paid to the shape of NaCl salt crystals with additives and the influence on strength properties of cores. A technology of bonding the salt cores is developing. Salinity of circulating water is studied and it is checked with the aid of electrical conductance. [ABSTRACT FROM AUTHOR]

Copyright of Archives of Metallurgy & Materials is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Archives of Metallurgy & Materials is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Archives of Metallurgy & Materials is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Development of salt cores prepared by high-pressure squeezing and shooting with inorganic binders has shown a high potential of the given technology even for high-pressure casting of castings. Strength, surface quality of achieved castings, and solubility in water become a decisive criterion. The shape and quality of grain surface particularly of NaCl - cooking salts that can be well applied without anticaking additives has shown to be an important criterion. Thus the salt cores technology can cover increasingly growing demands for casting complexity especially for the automobile industry. [ABSTRACT FROM AUTHOR]

Aims. We present a model for dm-fiber bursts that is based on assuming fast sausage magnetoacoustic wave trains that propagate along a dense vertical filament or current sheet. Methods. Eight groups of dm-fiber bursts that were observed during solar flares were selected and analyzed by the wavelet analysis method. To model these fiber bursts we built a semi-empirical model. We also did magnetohydrodynamic simulations of a propagation of the magnetoacoustic wave train in a vertical and gravitationally stratified current sheet. Results. In the wavelet spectra of the fiber bursts computed at different radio frequencies we found the wavelet tadpoles, whose head maxima have the same frequency drift as the drift of fiber bursts. It indicates that the drift of these fiber bursts can be explained by the propagating fast sausage magnetoacoustic wave train. Using new semi-empirical and magnetohydrodynamic models with a simple radio emission model we generated the artificial radio spectra of the fiber bursts, which are similar to the observed ones. [ABSTRACT FROM AUTHOR]

Aims. To obtain diagnostics tools for solar flare current sheets, we numerically studied impulsively generated magnetoacoustic waves in the Harris current sheet. Methods. We used two-dimensional (2-D) magnetohydrodynamic (MHD) and wave dispersion models. Tests of these models were performed for waves in the density slab, where analytical solutions are known. In the MHD model, we solved the full set of ideal MHD equations by means of the modified two-step Lax-Wendroff algorithm. The initial perturbation was chosen to generate preferentially the fast sausage magnetoacoustic waves. To determine the dispersion characteristics of MHD waves in the Harris current sheet, we numerically solved the equation of plasma motions by means of the Runge-Kutta fourth order method together with the bisection iteration one. To establish some diagnostics of these waves and their corresponding flare current sheets, we used the wavelet analysis method. Results. We find that the results of tests of our 2-D MHD and wave dispersion models for the density slab are in good agreement with analytical results. We analyze the magnetoacoustic waves in the current sheet and compare them with those in the density slab. In both cases, for similar geometrical and plasma parameters, we find that wave trains were generated and propagated in a similar way. Their signals registered at selected locations of the Harris current sheet and density slab are also similar. Nevertheless, a dependence of the period of the magnetoacoustic waves on the width of the Harris current sheet differs from that for the density slab. The form of the wave front inside the current sheet similarly differs from that in the density slab. We find that the wavelet spectra of the signals of incoming magnetoacoustic waves at selected locations in the current sheet have the form of wavelet tadpoles. We distinguish that the form of these wavelet tadpoles becomes longer and the heads of the wavelet tadpoles are detected later in time as the distance of the detection point from that of the initial wave perturbation increases. We also find that the wavelet tadpole period depends on the plasma beta parameter. The results are discussed from the point of view of their use as diagnostics of the flare current sheets or flare loops. [ABSTRACT FROM AUTHOR]

We numerically investigated standing slow acoustic waves impulsively excited in a solar coronal loop by gas pressure and mass density perturbations in one-dimensional space. The corresponding computer model is described by the hydrodynamic equations that are solved numerically by means of the so-called flux limiters methods on uniformly structured mesh. We discuss the fundamental mode and the first harmonic mode which are generated in dependence on position of the initial perturbation in the numerical box. We show how the standing slow acoustic waves are generated in the corona, where they are trapped in space between two dense layers as in the resonator, and how their energy leaks from the corona to the dense layers. We found that this leakage increases with the decrease of the density jump at the transition region. We also studied the case when the perturbation is initiated at the transition region. We found that even in this case the standing wave is formed, but their energetics is influenced by the evaporation of the plasma from the transition region into the corona. [ABSTRACT FROM AUTHOR]

This paper is focused on the study of the electrical charging process of micron-sized particles immersed into low-temperature argon plasma by the methods of computer modelling. The hybrid computer simulations are performed for a set of particles with the radius up to $20~{\rm \mu m}$ in order to determine the dependence of the electric charge on the surface of the particulate on its radius. This dependence seems to be linear. The distribution of the electric potential in the vicinity of the particulate is obtained from the fluid model. Afterwards, the non self-consistent particle simulation is performed in order to determine both the reaction rates and the electric charge on the surface of the particulate. The most important collision processes of charged particles in plasma and the appropriate dependence of the collision cross-section on the particle energy are considered (elastic scattering of electrons on neutrals, excitation of neutrals into all important energetic states, ionisation of Argon atoms by fast electrons, elastic scattering of positively charged ions etc.). The presented algorithm provides an effective way, how the key quantity in dusty plasma physics – electric charge on the surface of the particulate – can be determined. [ABSTRACT FROM AUTHOR]

A method for improving the electronic spectrum of standard Density-Functional Theory (DFT) calculations (i.e., LDA or GGA approximations) is presented, and its application is discussed for the case of the copper phthalocyanine (CuPc) molecule. The method is based on a treatment of exchange and correlation in a many-body Hamiltonian, and it leads to easy-to-evaluate corrections to the DFT eigenvalues. Self-interaction is largely corrected, so that the modified energy levels do not suffer from spurious crossings, as often encountered for CuPc in DFT, and they remedy the standard underestimation of the gap. As a specific example we study the sequence and position of the CuPc molecular orbitals, which are wrongly calculated by standard DFT, and show that they are correctly reproduced after our corrections are included. The suggested method is fast and simple and, while not as accurate as hybrid or semiempirical functionals for molecular levels, it can be easily applied to any local-orbital DFT approach, improving on several important limitations of standard DFT methods. [ABSTRACT FROM AUTHOR]

The article discusses transoesophageal echocardiography showing a thrombosis of the aortic valve mechanical replacement before and after thrombolytic treatment. The technique is illustrated through the case of a 75 year old female patient with a four year history of aortic valve replacement with mechanical prosthesis, and a one month history of progressing dyspnoea and coughing episodes. The patient denied having chest pain. Electrocardiography showed signs of hypertrophy and overload of the left ventricle.