What is the true nature of blinkers?

Aims. The aim of this work is to identify the true nature of the transient EUV brightenings, called blinkers. Methods. Co-spatial and co-temporal multi-instrument data, including imaging (EUVI/STEREO, XRT and SOT/Hinode), spectroscopic (CDS/SoHO and EIS/Hinode) and magnetogram (SOT/Hinode) data, of an isolated equatorial coronal hole were used. An automatic program for identifying transient brightenings in CDS O v 629 Å, EUVI 171 Å and XRT was applied. Results. We identified 28 blinker groups in the CDS O v 629 Å raster images. All CDS O v 629 Å blinkers showed counterparts in EUVI 171 Å and 304 Å images. We classified these blinkers into two categories, one associated with coronal counterparts and other with no coronal counterparts as seen in XRT images and EIS Fe xii 195.12 Å raster images. Around two-thirds of the blinkers show coronal counterparts and correspond to various events like EUV/X-ray jets, brightenings in coronal bright points or foot-point brightenings of larger loops. These brightenings occur repetitively and have a lifetime of around 40 min at transition region temperatures. The remaining blinker groups with no coronal counterpart in XRT and EIS Fe xii 195.12 Å appear as point-like brightenings and have chromospheric/transition region origin. They take place only once and have a lifetime of around 20 min. In general, lifetimes of blinkers are different at different wavelengths, i.e. different temperatures, decreasing from the chromosphere to the corona. Conclusions. This work shows that the term blinker covers a range of phenomena. Blinkers are the EUV response of various transient events originating at coronal, transition region and chromospheric heights. Hence, events associated with blinkers contribute to the formation and maintenance of the temperature gradient in the transition region and the corona

Stanje tvrdog i mekog periimplantnog tkiva u estetskoj regiji gornje vilice posle prezervacije alveolarnog grebena beta-trikalcijum fosfatom sa kolagenom tip I - studija sa jednogodišnjim periodom praćenja

Background/Aim. Alveolar ridge dimensional alterations following tooth extraction in the anterior maxilla often result in an inadequate bone volume for a correct implant placement. In order to obtain optimal bone volume various bone graft substitutes have become commercially available and widely used for socket grafting. The aim of this study was to examine and compare long-term clinical outcomes of dental implant therapy in the maxillary esthetic zone, after socket grafting with beta-tricalcium phosphate (TCP) combined with collagen type I, either with or without barrier membrane and flap surgery, after a 12-month follow-up. Methods. Twenty healthy patients were allocated to either C group (beta-TCP and type I collagen without mucoperiosteal flap coverage) or C+M group (beta-TCP and type I collagen barrier membrane with mucoperiosteal flap coverage). Following clinical parameters were assessed: implant stability (evaluated by a resonance frequency analysis - RFA), periimplant soft tissue stability (sulcus bleeding index - SBI, Mombelli sulcus bleeding index - MBI, periimplant sulcus depth, keratinized gingiva width, gingival level) and marginal bone level at the retroalveolar radiograms. Results. Within C+M group, RFA values significantly increased 12 weeks after implant installation compared to primary RFA values. Comparison between investigated groups showed a significantly reduced keratinized gingiva width in the C+M group compared to the C group after 3, 6, 9 and 12 months. Comparison between groups revealed significantly lower gingival level values in the C+M group at 9th and 12th month when compared to the C group. Conclusion. Implant treatment in the anterior maxilla could be effective when using a 9 months alveolar ridge preservation healing with combined treatment with beta-tricalcium phosphate and type I collagen, with regard to the peri-implant soft and hard tissue stability.Uvod/Cilj. Posle ekstrakcije zuba, dimenzionalne promene alveolarnog grebena u estetskoj regiji gornje vilice za posledicu često imaju nedovoljnu količinu kosti za ugradnju zubnih implanata. U vezi sa tim, primenjuju se različiti koštani zamenici sa ciljem očuvanja dimenzija alveolarnog grebena posle ekstrakcije zuba. Cilj rada bio je da se, posle prezervacije alveolarnog grebena beta-trikalcijum fosfatom (TCP) sa kolagenom tip 1, sa barijernom membranom i mukoperiostalnim režnjem i bez nje, ispitaju i uporede klinički ishodi zarastanja posle ugradnje zubnih implanata u estetskoj regiji gornje vilice, tokom jednogodišnjeg perioda praćenja. Metode. Dvadeset zdravih bolesnika podeljeno je u dve grupe: C (beta TCP/kolagen tip 1 bez barijerne membrane i mukoperiostalnog režnja) i C+M (beta TCP/kolagen tip 1 sa barijernom membranom i mukoperiostalnim režnjem). Praćeni su uobičajeni klinički parametri ishoda terapije: implantna stabilnost (analiza rezonantne frekvence), stanje mekih tkiva (indeks krvarenja, plak indeks, širina pripojne mukoze, recesija gingive) i nivo periimplantnog koštanog tkiva na retroalveolarnom radiogramu. Rezultati. U C+M grupi, implantna stabilnost posle 12 nedelja bila je značajno veća u odnosu na primarnu stabilnost. U C+M grupi, širina keratinizovane gingive bila je značajno manja posle 3, 6, 9 i 12 meseci u odnosu na C grupu. Recesija gingive bila je značajno veća u C+M grupi u odnosu na C grupu posle 9 i 12 meseci. Zaključak. Razmatrajući stabilnost mekog i tvrdog periimplantnog tkiva, terapija zubnim implantima može biti uspešna prilikom ugradnje u estetskoj regiji gornje vilice

Explosive events - swirling transition region jets

In this paper, we extend our earlier work to provide additional evidence for an alternative scenario to explain the nature of so-called `explosive events'. The bi-directed, fast Doppler motion of explosive events observed spectroscopically in the transition region emission is classically interpreted as a pair of bidirectional jets moving upward and downward from a reconnection site. We discuss the problems of such a model. In our previous work, we focused basically on the discrepancy of fast Doppler motion without detectable motion in the image plane. We now suggest an alternative scenario for the explosive events, based on our observations of spectral line tilts and bifurcated structure in some events. Both features are indicative of rotational motion in narrow structures. We explain the bifurcation as the result of rotation of hollow cylindrical structures and demonstrate that such a sheath model can also be applied to explain the nature of the puzzling `explosive events'. We find that the spectral tilt, the lack of apparent motion, the bifurcation, and a rapidly growing number of direct observations support an alternative scenario of linear, spicular-sized jets with a strong spinning motion.Comment: 9 pages, 3 figures, accepted for publication in Solar Physic

How to use magnetic field information for coronal loop identification?

The structure of the solar corona is dominated by the magnetic field because the magnetic pressure is about four orders of magnitude higher than the plasma pressure. Due to the high conductivity the emitting coronal plasma (visible e.g. in SOHO/EIT) outlines the magnetic field lines. The gradient of the emitting plasma structures is significantly lower parallel to the magnetic field lines than in the perpendicular direction. Consequently information regarding the coronal magnetic field can be used for the interpretation of coronal plasma structures. We extrapolate the coronal magnetic field from photospheric magnetic field measurements into the corona. The extrapolation method depends on assumptions regarding coronal currents, e.g. potential fields (current free) or force-free fields (current parallel to magnetic field). As a next step we project the reconstructed 3D magnetic field lines on an EIT-image and compare with the emitting plasma structures. Coronal loops are identified as closed magnetic field lines with a high emissivity in EIT and a small gradient of the emissivity along the magnetic field.Comment: 14 pages, 3 figure

Magnetic field diagnostics and spatio-temporal variability of the solar transition region

Magnetic field diagnostics of the transition region from the chromosphere to the corona faces us with the problem that one has to apply extreme UV spectro-polarimetry. While for coronal diagnostic techniques already exist through infrared coronagraphy above the limb and radio observations on the disk, for the transition region one has to investigate extreme UV observations. However, so far the success of such observations has been limited, but there are various projects to get spectro-polarimetric data in the extreme UV in the near future. Therefore it is timely to study the polarimetric signals we can expect for such observations through realistic forward modeling. We employ a 3D MHD forward model of the solar corona and synthesize the Stokes I and Stokes V profiles of C IV 1548 A. A signal well above 0.001 in Stokes V can be expected, even when integrating for several minutes in order to reach the required signal-to-noise ratio, despite the fact that the intensity in the model is rapidly changing (just as in observations). Often this variability of the intensity is used as an argument against transition region magnetic diagnostics which requires exposure times of minutes. However, the magnetic field is evolving much slower than the intensity, and thus when integrating in time the degree of (circular) polarization remains rather constant. Our study shows the feasibility to measure the transition region magnetic field, if a polarimetric accuracy on the order of 0.001 can be reached, which we can expect from planned instrumentation.Comment: Accepted for publication in Solar Physics (4.Mar.2013), 19 pages, 9 figure

Na zelenom putu inovacija – vodonik iz laserski potpomognute alkalne elektrolize

The dominant problem that needs to be solved today is the issue of energy sources and how to use them, which must be ecological and sustainable - in a word, green. As the best candidate for a global solution to this problem, hydrogen produced electrolytically stood out as a green fuel with no carbon footprint. However, for a hydrogen-based economy to have a realistic and sustainable perspective in the future, it largely depends on its efficient and economically viable production that would meet the market's needs. Special attention in this paper is devoted to the influence of laser radiation on the possibility of improving the process of alkaline electrolysis for obtaining hydrogen, as well as on increasing the amount of separated hydrogen when the electrolytic cell is directly irradiated with a laser beam during the electrolysis process itself. After the experiments, it was determined that the application of direct irradiation of the electrolyte with a green laser at 532 nm wavelength significantly increases the amount of hydrogen produced and reduces the voltage of the electrolytic process, which is directly related to the increase in the energy efficiency of the overall hydrogen production process.Dominantan problem koji danas treba rešiti je pitanje energenata i načina njihove upotrebe koji moraju biti ekološki i održivi – jednom rečju zeleni. Kao najbolji kandidat za globalno rešenje ovog problema istakao se vodonik proizveden elektolitičkim putem, kao zeleno gorivo bez ugljeničnih otisaka. Da bi ekonomija zasnovana na vodoniku imala realnu i održivu perspektivu u budućnosti, u velikoj meri zavisi od njegove efikasne i ekonomski podobne proizvodnje koja bi zadovoljila potrebe tržišta. Posebna pažnja u ovom radu posvećena je uticaju laserskog zračenja na mogućnost poboljšanja procesa alkalne elektrolize za dobijanje vodonika, kao i na povećanje količine izdvojenog vodonika pri direktnom ozračivanju elektrolitičke ćelije laserskim snopom tokom samog procesa elektrolize. Nakon izvršenih eksperimenata utvrđeno je da se primenom direktnog ozračivanja elektrolita zelenim laserom talasne dužine 532 nm u značajnoj meri povećava količina proizvedenog vodonika i smanjuje napon elektrolitičkog procesa, što je u direktnoj vezi sa povećanjem energetske efikasnosti ukupnog procesa dobijanja vodonika

Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots

We analyse 3-min oscillations of microwave and EUV emission generated at different heights of a sunspot atmosphere, studying the amplitude and frequency modulation of the oscillations, and its relationship with the variation of the spatial structure of the oscillations. High-resolution data obtained with the Nobeyama Radioheliograph, TRACE and SDO/AIA are analysed with the use of the Pixelised Wavelet Filtering and wavelet skeleton techniques. 3-min oscillations in sunspots appear in the form of repetitive trains of the duration 8-20 min (13 min in average). The typical interval between the trains is 30-50 min. The oscillation trains are transient in frequency and power. We detected a repetitive frequency drifts of 3-min oscillations during the development of individual trains. Wavelet analysis shows three types of the frequency drift: positive, negative and fluctuations without drift. The start and end of the drifts coincide with the start time and end of the train. The comparative study of 3-min oscillations in the sequences of microwave and EUV images show the appearance of new sources of the oscillations in sunspots during the development of the trains. These structures can be interpreted as waveguides that channel upward propagating waves, responsible for 3-min oscillations. A possible explanation of the observed properties is the operation of two simultaneous factors: dispersive evolution of the upwardly-propagating wave pulses and the non-uniformity of the distribution of the oscillation power over the sunspot umbra with different wave sources corresponding to different magnetic flux tubes with different physical conditions and line-of-sight angles.Comment: 12 pages, 11 figures, submitted to A&A, 201