Coronal loop transverse oscillations excited by different driver frequencies

We analyse transverse oscillations of a coronal loop excited by continuous monoperiodic motions of the loop footpoint at different frequencies in the presence of gravity. Using the MPI-AMRVAC code, we perform three-dimensional numerical magnetohydrodynamic simulations, considering the loop as a magnetic flux tube filled in with denser, hotter, and gravitationally stratified plasma. We show the resonant response of the loop to its external excitation and analyse the development of the Kelvin-Helmholtz instability at different heights. We also study the spatial distribution of plasma heating due to transverse oscillations along the loop. The positions of the maximum heating are in total agreement with those for the intensity of the Kelvin-Helmholtz instability, and correspond to the standing wave anti-nodes in the resonant cases. The initial temperature configuration and plasma mixing effect appear to play a significant role in plasma heating by transverse footpoint motions. In particular, the development of the Kelvin-Helmholtz instability in a hotter loop results in the enhancement of the mean plasma temperature in the domain.Comment: Published in Ap

Petrography, lithology, geochemistry and geochronology of the Takanen greenstone belt, eastern Finland

Archean cratons hold information of the early crustal development of the Earth, in conditions much different than the ones that exist today. Archean cratons consist of felsic plutonic rocks and greenstone belts. These belts are a useful tool for the understanding of the development of the early geological processes that shaped the Earth. There has been a variety of suggestions regarding the origin and geodynamic conditions that formed the Archean greenstone belts and there are several possible geotectonic scenarios that could form them. This thesis focuses on the Takanen greenstone belt found in the Karelia province in the Fennoscandian shield. The main objective of this study is to constrain the age of the greenstone belt, as well as to classify and group the formations found in it and compare it with its neighbouring, and much larger, Suomussalmi-Kuhmo-Tipasjärvi greenstone belt system - the biggest complex of its kind in the Karelian craton. A diamond drilling profile across the Takanen belt has been sampled. The various rocks found in the belt are divided into 5 groups based on their thin-section petrography and major and trace element geochemistry, outlining the general stratigraphy of the belt. There are also whole rock analyses that help to obtain major and trace element geochemical data for multiple samples from different locations throughout the belt. There are 3 calc-alkaline units (CALC1, CALC2, CALC3, named after their predominantly calc-alkaline nature) that include felsic, to intermediate volcanic/volcanosedimentary rocks and 2 units that consist of channelized komatiitic lavas and tholeiitic basalts (KOMBAS, named after the komatiites and basalts of the unit), olivine/olivine-pyroxene cumulates and high-Mg to tholeiitic basalts (OLIAD, named after the abundance of olivine adcumulates). The CALC1 unit is found lowest in the stratigraphy of the area and bares the oldest age of 2.95 Ga, while CALC3, which is the youngest formation of the belt, gives an age of 2.7 Ga. There is a direct correlation with the lowest CALC1 unit and the Luoma group in the Suomussalmi greenstone belt in terms of petrography, geochemistry and age, indicating that Takanen is the continuation of the Suomussalmi-Kuhmo-Tipasjärvi system to the north. Based on the initial Lu-Hf isotope composition of the dated samples, and the stratigraphic layering of Takanen, the oldest units in the belt originate from a process of continental rifting, while the youngest ones were most likely formed by a combination of continental rifting and some interaction of the continental crust with oceanic lithosphere. The Takanen greenstone belt lies on top of a large positive gravimetric and magnetic anomaly in the Koillismaa area called the ‘‘hidden dyke’’, composed of mafic-ultramafic cumulates and hypothesized to be related to the Paleoproterozoic Koillismaa-Näränkävaara Layered Intrusion Complex. The dyke and Takanen may not be genetically related, yet their overlapping existence points to a large crustal structure that served as a magma pathway throughout the Archean and the Paleoproterozoic. The potential of an economic orthomagmatic nickel deposit related to Takanen should not be completely overlooked, as there are some favorable indications in the geochemistry of the komatiitic units, as well as their possible interaction of these units with older sulphur rich units of the belt

That\u27s Not My Bag, Baby: The Seventh Circuit Tackles Fourth Amendment Standing in \u3cem\u3eUnited States v. Carlisle\u3c/em\u3e

In its recent decision in United States v. Carlisle, the Seventh Circuit made clear that challenging the constitutionality of a search is no easy task. Although the Fourth Amendment protects individuals from unreasonable government intrusion, defendants seeking to suppress evidence must first prove a reasonable expectation of privacy. This Note will use Carlisle as a basis of exploring the law of Fourth Amendment standing. This Note will argue that the Seventh Circuit applied a flawed test in evaluating a defendant\u27s subjective expectation of privacy, but nevertheless arrived at a result supported by existing precedent. Finally, this Note will examine the policy concerns surrounding Fourth Amendment standing

IDENTIFICATION OF TREATED-COLOR FRESHWATER CULTURED PEARLS

Ta τελευταία 30 χρόνια η ζήτηση των χρωματιστών μαργαριταριών (όπου είναι σπανιότερα από τα λευκά) έχει ανέβει κατακόρυφα. Αποτέλεσμα αυτού είναι η εισροή στην αγορά μαργαριταριών με τεχνητό χρώμα, η αναγνώριση των οποίων απασχολεί έντονα τους γεμμολόγους. Για την αναγνώριση, τα μαργαριτάρια εξετάζονται μακροσκοπικά και μικροσκοπικά, γίνονται μετρήσεις φθορισμού σε ακτίνες-Χ (EDXRF) και τέλος μελετώνται οι ακτινογραφίες τους. Με τη χρήση ωστόσο των παραπάνω μεθόδων δεν καθίσταται, πάντα, εφικτή η αναγνώριση των τεχνητά χρωματισμένων μαργαριταριών. Παλαιότερες έρευνες έδειξαν ότι η φασματοσκοπία Raman είναι χρήσιμη στην αναγνώριση των χρωστικών ουσιών των μαργαριταριών γλυκού νερού. Στη παρούσα εργασία παρουσιάζονται μετρήσεις του φαινομένου Raman, με τη χρήση πράσινου laser, σε 35 φυσικά και 15 τεχνητά χρωματισμένα δείγματα. Όλα τα φάσματα Raman των φυσικά χρωματισμένων δειγμάτων παρουσιάζουν δύο κορυφές, όπου είναι χαρακτηριστικές για τις πολυακετυλενικές χρωστικές ουσίες. Αυτές οι κορυφές είναι παρούσες, ανεξαρτήτως του χρώματος των δειγμάτων, και οφείλονται στη δόνηση τάσης (stretching) των μορίων του των διπλών δεσμών άνθρακα (C—C) -στα 1530(±25) cm'1- και των μονών δεσμών άνθρακα (CC) -στα 1130(±10) cm'1- των χρωστικών ουσιών. Στη παρούσα εργασία προτείνεται ότι  η πιθανή απουσία των παραπάνω κορυφών Raman σε ένα χρωματιστό μαργαριτάρι γλυκού νερού αποτελεί απόδειξη ότι το χρώμα του μαργαριταριού αυτού είναι τεχνητό.Demand for colored pearls has grown during the last thirty years. Colored pearls are rarer than white ones. Thus treated-color pearls have entered the marketplace and their identification became a challenge for the gemologists. With only the help of visual observation, EDXRF and X-radiography, methods that are used today for pearls identification, it is not always easy to identify them. Previous studies, have established that Raman scattering is useful to detect pigments in cultured freshwater pearls. The present study is based on the measurement of the Raman spectroscopy of 35 natural colored freshwater pearls and 15 treated-color freshwater pearls, covering a wide range of typical colors for this material, with green excitation. All natural- color pearls show the two major Raman resonance features of polacetyenic pigments assigned to C=C stretching-at about 1530(±25) cm'1- and C-C stretching - at about 1130(±10) cm' -, regardless of their specific hue. In this paper it is proposed that the absence of these Raman features prove the artificial origin of pigments in a colored freshwater cultured pearl

Heating by transverse waves in simulated coronal loops

K.K. was funded by GOA-2015-014 (KU Leuven). T.V.D was supported by the IAP P7/08 CHARM (Belspo) and the GOA-2015-014 (KU Leuven). P.A. acknowledges funding from the UK Science and Technology Facilities Council and the European Union Horizon 2020 research and innovation programme (grant agreement No. 647214).Context.  Recent numerical studies of oscillating flux tubes have established the significance of resonant absorption in the damping of propagating transverse oscillations in coronal loops. The nonlinear nature of the mechanism has been examined alongside the Kelvin-Helmholtz instability,which is expected to manifest in the resonant layers at the edges of the flux tubes. While these two processes have been hypothesized to heat coronal loops through the dissipation of wave energy into smaller scales, the occurring mixing with the hotter surroundings can potentially hide this effect. Aims.  We aim to study the effects of wave heating from driven and standing kink waves in a coronal loop. Methods.  Using the MPI-AMRVAC code, we perform ideal, three dimensional magnetohydrodynamic (MHD) simulations of both (a) footpoint driven and (b) free standing oscillations in a straight coronal flux tube, in the presence of numerical resistivity. Results.  We have observed the development of Kelvin-Helmholtz eddies at the loop boundary layer of all three models considered here, as well as an increase of the volume averaged temperature inside the loop. The main heating mechanism in our setups was Ohmic dissipation, as indicated by the higher values for the temperatures and current densities located near the footpoints. The introduction of a temperature gradient between the inner tube and the surrounding plasma, suggests that the mixing of the two regions, in the case of hotter environment, greatly increases the temperature of the tube at the site of the strongest turbulence, beyond the contribution of the aforementioned wave heating mechanism.PostprintPeer reviewe

Wave heating in gravitationally stratified coronal loops in the presence of resistivity and viscosity

In recent years, coronal loops have been the focus of studies related to the damping of different magnetohydrodynamic (MHD) surface waves and their connection with coronal seismology and wave heating. For a better understanding of wave heating, we need to take into account the effects of different dissipation coefficients such as resistivity and viscosity, the importance of the loop physical characteristics, and the ways gravity can factor into the evolution of these phenomena. We aim to map the sites of energy dissipation from transverse waves in coronal loops in the presence and absence of gravitational stratification and to compare ideal, resistive, and viscous MHD. Using the PLUTO code, we performed 3D MHD simulations of kink waves in single, straight, density-enhanced coronal flux tubes of multiple temperatures. We see the creation of spatially expanded Kelvin-Helmholtz eddies along the loop, which deform the initial monolithic loop profile. For the case of driven oscillations, the Kelvin-Helmholtz instability develops despite physical dissipation, unless very high values of shear viscosity are used. Energy dissipation gets its highest values near the apex, but is present all along the loop. We observe an increased efficiency of wave heating once the kinetic energy saturates at the later stages of the simulation and a turbulent density profile has developed. The inclusion of gravity greatly alters the dynamic evolution of our systems and should not be ignored in future studies. Stronger physical dissipation leads to stronger wave heating in our set-ups. Finally, once the kinetic energy of the oscillating loop starts saturating, all the excess input energy turns into internal energy, resulting in more efficient wave heating.Comment: 15 pages, 13 figures. Accepted for publication in Astronomy and Astrophysics (A&A