Latitudinal and longitudinal dependence of the cosmic ray diurnal anisotropy during 2001-2014

Abstract. The diurnal anisotropy of cosmic ray intensity for the time period 2001 to 2014 is studied, covering the maximum and the descending phase of solar cycle 23, the minimum between solar cycles 23 and 24, and the ascending phase and maximum of solar cycle 24. Cosmic ray intensity data from 11 neutron monitor stations located at different places around the Northern Hemisphere obtained from the high-resolution Neutron Monitor Database (NMDB) were used. Special software was developed for the calculations of the amplitude and the phase of the diurnal anisotropy vectors on annual and monthly basis using Fourier analysis and for the creation of the harmonic dial diagrams. The geomagnetic bending for each station was taken into account in our calculations determined from the asymptotic cones of each station via the Tsyganenko96 (Tsyganenko and Stern, 1996) magnetospheric model. From our analysis, it was resulted that there is a different behavior of the diurnal anisotropy vectors during the different phases of the solar cycles depending on the solar magnetic field polarity. The latitudinal and longitudinal distribution of the cosmic ray diurnal anisotropy was also examined by grouping the stations according to their geographic coordinates, and it was shown that diurnal variation is modulated not only by the latitude but also by the longitude of the stations. The diurnal anisotropy during strong events of solar and/or cosmic ray activity is discussed

Geometric flow description of minimal surfaces

We introduce a description of a minimal surface in a space with boundary, as the world hypersurface that the entangling surface traces. It does so by evolving from the boundary to the interior of the bulk under an appropriate geometric flow, whose parameter is the holographic coordinate. We specify this geometric flow for arbitrary bulk geometry. In the case of pure AdS spaces, we implement a perturbative approach for the solution of the flow equation around the boundary. We systematically study both the form of the perturbative solution as well as its dependence on the boundary conditions. This expansion is sufficient for the determination of all the divergent terms of the holographic entanglement entropy, including the logarithmic universal terms in odd spacetime bulk dimensions, for an arbitrary entangling surface, in terms of the extrinsic geometry of the latter. © 2020 author

Salient features of dressed elliptic string solutions on R× S 2

We study several physical aspects of the dressed elliptic strings propagating on R× S 2 and of their counterparts in the Pohlmeyer reduced theory, i.e. the sine-Gordon equation. The solutions are divided into two wide classes; kinks which propagate on top of elliptic backgrounds and non-localised periodic disturbances of the latter. The former class of solutions obey a specific equation of state that is in principle experimentally verifiable in systems which realize the sine-Gordon equation. Among both of these classes, there appears to be a particular class of interest the closed dressed strings. They in turn form four distinct subclasses of solutions. One of those realizes instabilities of the seed elliptic solutions. The existence of such solutions depends on whether a superluminal kink with a specific velocity can propagate on the corresponding elliptic sine-Gordon solution. Unlike the elliptic strings, the dressed ones exhibit interactions among their spikes. These interactions preserve an appropriately defined turning number, which can be associated to the topological charge of the sine-Gordon counterpart. Finally, the dispersion relations of the dressed strings are studied. A qualitative difference between the two wide classes of dressed strings is discovered. © 2019, The Author(s)

Dressed minimal surfaces in AdS4

We apply an arbitrary number of dressing transformations to a static minimal surface in AdS4. Interestingly, a single dressing transformation, with the simplest dressing factor, interrelates the latter to solutions of the Euclidean non linear sigma model in dS3. We present an expression for the area element of the dressed minimal surface in terms of that of the initial one and comment on the boundary region of the dressed surface. Finally, we apply the above formalism to the elliptic minimal surfaces and obtain new ones. © 2020, The Author(s)

The dressing method as non linear superposition in sigma models

We apply the dressing method on the Non Linear Sigma Model (NLSM), which describes the propagation of strings on ℝ × S2, for an arbitrary seed. We obtain a formal solution of the corresponding auxiliary system, which is expressed in terms of the solutions of the NLSM that have the same Pohlmeyer counterpart as the seed. Accordingly, we show that the dressing method can be applied without solving any differential equations. In this context a superposition principle emerges: the dressed solution is expressed as a non-linear superposition of the seed with solutions of the NLSM with the same Pohlmeyer counterpart as the seed. © 2021, The Author(s)

Elliptic string solutions on R× S 2 and their pohlmeyer reduction

We study classical string solutions on R× S 2 that correspond to elliptic solutions of the sine-Gordon equation. In this work, these solutions are systematically derived by inverting the Pohlmeyer reduction. A mapping of the physical properties of the string solutions to those of their Pohlmeyer counterparts is established. An interesting element of this mapping is the association of the number of spikes of the string to the topological charge in the sine-Gordon theory. Finally, the adopted parametrization of the solutions facilitates the identification of a dense subset of the moduli space of solutions, where the dispersion relation can be expressed in a closed form, arbitrarily far from the infinite size limit. © 2018, The Author(s)

Translation and validation of the dizziness handicap inventory in Greek language

Objective: The aim of the study was to test the reliability and validity of the Dizziness Handicap Inventory in the Greek language (DHI). Design: This study was performed in a university tertiary centre. Internal consistency was estimated using Cronbach’s alpha for the DHI, physical (DHI-P), functional (DHI-F) and emotional (DHI-E) subscale scores. Correlation between DHI (total and subscales) and the SOT (sensory organisation test) as well as correlation between the DHI and FGA (functional gait assessment) was tested using Spearman’s correlation coefficient. Test–retest reliability was tested using ICC (Intraclass Correlation Coefficient). Sample size: Ninety (90) patients were included in the study. Results: Internal consistency was excellent for the total score and very good for the physical functional and emotional subscale scores. No statistically significant correlation was found between SOT and DHI. There was a moderate correlation between FGA and total DHI scores (r = −0.472; p < 0.0001) and poor to moderate between FGA and DHI subscale scores (DHI-E r1 = −0.342; p1 = 0.001, DHI-F r2 = −0.448 p2 < 0.0001, DHI-P r3 = −0.472 p3 < 0.0001). Test–retest reliability was excellent. Conclusion: Greek version of DHI is recommended as a valid measure for patients with vestibular disorders. © 2017 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society