Kodaikanal Digitized White-light Data Archive (1921-2011): Analysis of various solar cycle features

Long-term sunspot observations are key to understand and predict the solar activities and its effects on the space weather.Consistent observations which are crucial for long-term variations studies,are generally not available due to upgradation/modifications of observatories over the course of time. We present the data for a period of 90 years acquired from persistent observation at the Kodaikanal observatory in India. We use an advanced semi-automated algorithm to detect the sunspots form each calibrated white-light image. Area, longitude and latitude of each of the detected sunspots are derived. Implementation of a semi-automated method is very necessary in such studies as it minimizes the human bias in the detection procedure. Daily, monthly and yearly sunspot area variations obtained from the Kodaikanal, compared well with the Greenwich sunspot area data. We find an exponentially decaying distribution for the individual sunspot area for each of the solar cycles. Analyzing the histograms of the latitudinal distribution of the detected sunspots, we find Gaussian distributions, in both the hemispheres, with the centers at $\sim$15$^{\circ}$ latitude. The height of the Gaussian distributions are different for the two hemispheres for a particular cycle. Using our data, we show clear presence of Waldmeier effect which correlates the rise time with the cycle amplitude. Using the wavelet analysis, we explored different periodicities of different time scales present in the sunspot area times series.Comment: Accepted for Publication in A&

On ideal sequence covering maps

[EN] In this paper we introduce the concept of ideal sequence covering map which is a generalization of sequence covering map, and investigate some of its properties. The present article contributes to the problem of characterization to the certain images of metric spaces which posed by Y. Tanaka [22], in more general form. The entire investigation is performed in the setting of ideal convergence extending the recent results in [11,15,16].The work of N. Adhikary has been supported by UGC (Ref:1127/(CSIR-UGC NET DEC. 2017)), India.Pal, SK.; Adhikary, N.; Samanta, U. (2019). On ideal sequence covering maps. Applied General Topology. 20(2):363-377. https://doi.org/10.4995/agt.2019.11238SWORD363377202A. Arhangelskii, Some types of factor mappings and the relation between classes of topological spaces, Soviet Math. Dokl. 4 (1963), 1726-1729.J. Chaber, Mappings onto metric spaces, Topology Appl. 14 (1982), 31-42. https://doi.org/10.1016/0166-8641(82)90045-1H. Fast, Sur Ia convergence Statistique, Colloq. Math. 2 (1951), 241-244. https://doi.org/10.4064/cm-2-3-4-241-244S. P. Franklin, Spaces in which sequence suffice, Fund. Math. 57 (1965) 107-115. https://doi.org/10.4064/fm-57-1-107-115J. A. Fridy, On ststistical convergence, Analysis 5 (1985), 301-313. https://doi.org/10.1524/anly.1985.5.4.301P. Kostyrko, T. Salát and W. Wilczynski, $mathcal{I}$-convergence, Real Analysis Exchange 26, no. 2 (2000-2001), 669-686.B. K. Lahiri and P. Das, I and I*-convergence in topological spaces, Math. Bohem. 130 (2005), 153-160.S. Lin, Point-countable Covers and Sequence-covering Mappings (in Chinese), Science Press, Beijing, 2002.F. Lin and S. Lin, On sequence-covering boundary compact maps of metric spaces, Adv. Math. (China) 39, no. 1 (2010), 71-78.F. Lin and S. Lin, Sequence-covering maps on generalized metric spaces, Houston J. Math. 40, no. 3 (2014), 927-943.S. Lin and P. Yan, Sequence-covering maps of metric spaces, Topology Appl. 109 (2001), 301-314. https://doi.org/10.1016/S0166-8641(99)00163-7G. D. Maio and Lj.D.R. Kocinac, Statistical convergence in topology, Topology Appl. 156 (2008), 28-45. https://doi.org/10.1016/j.topol.2008.01.015E. Michael, A quintuple quotient quest, General Topology Appl. 2 (1972), 91-138. https://doi.org/10.1016/0016-660X(72)90040-2T. Nogura and Y. Tanaka, Spaces which contains a copy of Sω or S2 , and their applications, Topology Appl. 30 (1988), 51-62. https://doi.org/10.1016/0166-8641(88)90080-6V. Renukadevi and B. Prakash, On statistically sequentially covering maps, Filomat 31, no. 6 (2017), 1681-1686. https://doi.org/10.2298/FIL1706681RV. Renukadevi and B. Prakash, On statistically sequentially quotient maps, Korean J. Math. 25, no. 1 (2017), 61-70.T. Salát, On statistically convergent sequences of real numbers, Math. Slovaca. 30, no. 2 (1980), 139-150.M. Scheepers, Combinatorics of open covers(I): Ramsey theory, Topology Appl. 69 (1996), 31-62. https://doi.org/10.1016/0166-8641(95)00067-4I. J. Schoenberg, The integrability of certain function and related summability methods Amer. Math. Monthly 66 (1959), 361-375. https://doi.org/10.2307/2308747F. Siwiec, Sequence-covering and countably bi-quotient maps, General Topology Appl. 1 (1971), 143-154. https://doi.org/10.1016/0016-660X(71)90120-6F. Siwiec, Generalizations of the first axiom of countability, Rocky Mountain J. Math. 5 (1975), 1-60. https://doi.org/10.1216/RMJ-1975-5-1-1Y. Tanaka, Point-countable covers and k-networks, Topology Proc. 12 (1987), 327-349.J. E. Vaughan, Discrete sequences of points, Topology Proc. 3 (1978), 237-265.P. F. Yan, S. Lin and S. L. Jiang, Metrizability is preserved by closed sequence-covering maps, Acta Math. Sinica. 47 (2004), 87-90.P. F. Yan and C. Lu, Compact images of spaces with a weaker metric topology, Czech. Math. j. 58, no. 4 (2008), 921-926. https://doi.org/10.1007/s10587-008-0060-5A. Zygmund, Trigonometric Series, Cambridge Univ. Press, Cambridge, UK (1979)

Phase transitions and magnetocaloric and transport properties in off-stoichiometric GdNi2Mnx

The structural, magnetic, magnetocaloric, transport, and magnetoresistance properties of the rare-earth intermetallic compounds GdNi2Mnx (0.5 ≤ x ≤ 1.5) have been studied. The compounds with x = 0.5 and 0.6 crystallize in the cubic MgCu2 type phase, whereas samples with x ≥ 0.8 form a mixed MgCu2 and rhombohedral PuNi3 phase. A second order magnetic phase transition from a ferromagnetic to paramagnetic state was observed near the Curie temperature (TC). The GdNi2Mnx (0.5 ≤ x ≤ 1.5) compounds order in a ferrimagnetic structure in the ground state. The largest observed values of magnetic entropy changes (at TC for ΔH = 5T) were 3.9, 3.5, and 3.1 J/kg K for x = 0.5, 0.6, and 0.8, respectively. The respective relative values of the cooling power were 395, 483, and 220 J/kg. These values are greater than some well-known prototype magnetocaloric materials such as Gd (400 J/kg) and Gd5Si2Ge2 (240 J/kg). Analysis of the resistivity data showed a T2 dependence at low temperatures, suggesting strong electron-phonon interactions, whereas at higher temperatures s-d scattering was dominated by the electron-phonon contribution, resulting in a slow increase in resistivity. Magnetoresistance values of ∼-1.1% were found for x = 0.5 near TC, and -7% for x = 1.5 near T = 80 K

Magnetostructural phase transitions and magnetocaloric effects in as-cast Mn1-xAlxCoGe compounds

The structural and magnetic properties of as-cast Mn1-xAlxCoGe (0 ≤ x ≤ 0.05) have been studied by X-ray diffraction, differential scanning calorimetry, and magnetization measurements. The partial substitution of Al for Mn in Mn1-xAlxCoGe results in a decrease in the martensitic transition temperature TM. For the concentration range 0 ≤ x ≤ 0.01, TM was found to coincide with ferromagnetic transition temperature (TC) resulting in a first-order magnetostructural transition (MST). A further increase in aluminum concentration resulted in a splitting of the phase transition temperatures, which included a drastic decrease in the martensitic temperature. The compounds with x \u3e 0.02 showed a single transition at TC. The maximum values of the magnetic entropy changes (-ΔSM) were ∼18 J/kgK, 12 J/kgK, and 7 J/kgK for ΔH = 5T at 313 K (x = 0.00), 286 K (x = 0.01), and 220 K (x = 0.02), respectively. The maximum value of the relative cooling power (RCP) was found to be 303 J/kg for x = 0.01 at T = 286 K for ΔH = 5T. It has been established that as-cast samples of this system show large value of MCE near room temperature making this system a promising material for magnetic cooling technologies

Comparing magnetostructural transitions in Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys

The crystal structure, magnetic and transport properties, including resistivity and thermopower, of Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys were studied in the (10-400) K temperature interval. We show that their physical properties are remarkably different, thereby pointing to different origin of their magnetostructural transition (MST). A Seebeck coefficient (S) was found to pass minimum of about -20 μV/K in respect of temperature for both compounds. It was shown that MST observed for both compounds results in jump-like changes in S for Ga-based compound and jump in resistivity of about 20 and 200 μΩ cm for Ga and In -based compounds, respectively. The combined analyzes of the present results with that from literature show that the density of states at the Fermi level does not change strongly at the MST in the case of Ni-Mn-In alloys as compared to that of Ni-Mn-Ga

Multifunctional properties related to magnetostructural transitions in ternary and quaternary Heusler alloys

In this report, the results of a study on the effects of compositional variations induced by the small changes in concentrations of the parent components and/or by the substitution of Ni, Mn, or In by an extra element Z, on the phase transitions, and phenomena related to the magnetostructural transitions in off-stoichiometric Ni-Mn-In based Heusler alloys are summarized. The crystal structures, phase transitions temperatures, and magnetic and magnetocaloric properties were analyzed for representative samples of the following systems (all near 15 at% indium concentration): Ni-Mn-In, Ni-Mn-In-Si, Ni-Mn-In-B, Ni-Mn-In-Cu, Ni-Mn-In-Cu-B, Ni-Mn-In-Fe, Ni-Mn-In-Ag, and Ni-Mn-In-Al