18 research outputs found
The G-O Rule and Waldmeier Effect in the Variations of the Numbers of Large and Small Sunspot Groups
We have analysed the combined Greenwich and Solar Optical Observing Network
(SOON) sunspot group data during the period of 1874-2011 and determined
variations in the annual numbers (counts) of the small, large and big sunspot
groups (these classifications are made on the basis of the maximum areas of the
sunspot groups). We found that the amplitude of an even-numbered cycle of the
number of large groups is smaller than that of its immediately following
odd-numbered cycle. This is consistent with the well known Gnevyshev and Ohl
rule or G-O rule of solar cycles, generally described by using the Zurich
sunspot number (Rz). During cycles 12-21 the G-O rule holds good for the
variation in the number of small groups also, but it is violated by cycle pair
(22, 23) as in the case of Rz. This behaviour of the variations in the small
groups is largely responsible for the anomalous behaviour of Rz in cycle pair
(22, 23). It is also found that the amplitude of an odd-numbered cycle of the
number of small groups is larger than that of its immediately following
even-numbered cycle. This can be called as `reverse G-O rule'. In the case of
the number of the big groups, both cycle pairs (12, 13) and (22, 23) violated
the G-O rule. In many cycles the positions of the peaks of the small, large,
and big groups are different and considerably differ with respect to the
corresponding positions of the Rz peaks. In the case of cycle 23, the
corresponding cycles of the small and large groups are largely symmetric/less
asymmetric (Waldmeier effect is weak/absent) with their maxima taking place two
years later than that of Rz. The corresponding cycle of the big groups is more
asymmetric (strong Waldmeier effect) with its maximum epoch taking place at the
same time as that of Rz.Comment: 13 pages, 5 figures, 1 table, accepted by Solar Physic
A comparison between fine-grained and nanocrystalline electrodeposited Cu-Ni films. Insights on mechanical and corrosion performance
This is the author's version of a work that was accepted for publication in Surface & coating technology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Surface & coating technology, Vol. 205, Núm. 23-24 (Sep 2011), p. 2585-5293 DOI 10.1016/j.surfcoat.2011.05.047Cu1−x-Nix (0.43 ≤ x ≤ 1.0) films were electrodeposited from citrate-sulphate baths at different current densities onto Cu/Ti/Si (100) substrates with the addition of saccharine as a grain-refining agent. The Cu-Ni alloy films produced from saccharine-free baths were fine-grained (crystallite size of ~400 nm). The addition of saccharine to the electrolytic solution induced a dramatic decrease in crystal size (down to ~27 nm) along with a reduction in surface roughness. Although the effect of saccharine on pure Ni films was less obvious, significant changes were observed due to the presence of saccharine in the bath during the alloying of Cu with Ni. Compared to fine-grained Cu-Ni films, the nanocrystalline films exhibited lower microstrains and a larger amount of stacking faults as observed by X-ray diffraction. These features enhance the mechanical properties of the Cu-Ni alloys, making the nanocrystalline Cu-Ni films superior to both the corresponding fine-grained films and pure Ni films. In particular, hardness in fine-grained films varied from 4.2 (x=0.43) to 5.4 GPa (x=0.86), whereas hardness varied between 6.7 and 8.2 GPa for nanocrystalline films of similar composition. In addition, wear resistance and elastic recovery were enhanced. Nanostructuring did not significantly affect corrosion resistance of Cu-Ni alloys in chloride media. Although the corrosion potential shifted slightly towards more negative values, the corrosion current density decreased, thereby making the electrodeposition nanostructuring process an effective tool to improve the overall properties of the Cu-Ni system
Localized electrochemical deposition of porous Cu-Ni microcolumns: insights into the growth mechanisms and the mechanical performance
Cu-rich Cu-Ni alloy microcolumns (11-35 at% Ni) with large porosity degree were grown by localized electrochemical deposition (LECD) at voltages of 6.5 and 7.0 V. In turn, conventional electrodeposition was used to deposit fully-compact Cu-Ni films with analogous Ni/Cu ratios from a similar citrate-containing electrolytic solution. The localized supply rate of the predominant Cu(II) and Ni(II) electroactive species in the LECD microregion was calculated assuming both large and small concentration gradients. A shortage of Cu(II) at the cathode surface is mainly responsible for the development of porosity in the microcolumns, which directly affects mechanical performance, specifically nanoindentation hardness and Young's modulus. From nanoindentation experiments, a relative microcolumn density ranging between 14 and 20% was determined. These values indicate the current efficiency of the LECD process and can be used to calculate the consumption rates associated with metal cation electroreduction
Tailoring the physical properties of electrodeposited CoNiReP alloys with large Re content by direct, pulse, and reverse pulse current techniques
This is the author's version of a work that was accepted for publication in Electrochimica acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Electrochimica acta, [96,(2013)] DOI10.1016/j.electacta.2013.02.077)The composition, surface morphology and structure of CoNiReP alloy films with large Re content (up to 27 at%), obtained in a citrate-glycine based electrolyte have been studied as a function of the electrodeposition technique. Direct current (DC), pulse plating (PP) and reverse pulse plating (RPP) were considered with cathodic current densities from −50 mA cm−2 to −250 mA cm−2. The mechanical and magnetic properties have been analyzed and the data obtained has been correlated with composition and crystallographic structure. For values of j (DC), jon (PP) and jc (RPP) below −100 mA cm−2, Co-rich, P-containing deposits are obtained. Beyond these current densities, both the quantities of Ni and Re increase simultaneously at the expense of Co and P, the latter virtually falling to zero. The highest Re percentage (25-27 at%) was achieved in both PP and RPP conditions at a cathodic pulse of −250 mA cm−2. All the films were either entirely nanocrystalline in nature or partially amorphous. Hardness values as high as 9.2 GPa have been found in PP plated Co64Ni18Re18 deposits. Besides the large hardness, the incorporation of Re in the films leads to high elastic recovery values. The magnetic character of the deposits ranges from soft to semi-hard ferromagneti
A Comparison of Solar Cycle Variations in the Equatorial Rotation Rates of the Sun's Subsurface, Surface, Corona, and Sunspot Groups
Using the Solar Optical Observing Network (SOON) sunspot-group data for the
period 1985-2010, the variations in the annual mean equatorial-rotation rates
of the sunspot groups are determined and compared with the known variations in
the solar equatorial-rotation rates determined from the following data: i) the
plasma rotation rates at 0.94Rsun, 0.95Rsun,...,1.0Rsun measured by Global
Oscillation Network Group (GONG) during the period 1995-2010, ii) the data on
the soft X-ray corona determined from Yohkoh/SXT full disk images for the years
1992-2001, iii) the data on small bright coronal structures (SBCS) which were
traced in Solar and Heliospheric Observatory (SOHO)/EIT images during the
period 1998-2006, and iv) the Mount Wilson Doppler-velocity measurements during
the period 1986-2007. A large portion (up to approximate 30 deg latitude) of
the mean differential-rotation profile of the sunspot groups lies between those
of the internal differential-rotation rates at 0.94Rsun and 0.98Rsun.The
variation in the yearly mean equatorial-rotation rate of the sunspot groups
seems to be lagging that of the equatorial-rotation rate determined from the
GONG measurements by one to two years.The amplitude of the latter is very
small.The solar-cycle variation in the equatorial-rotation rate of the solar
corona closely matches that determined from the sunspot-group data.The
variation in the equatorial-rotation rate determined from the Mount Wilson
Doppler-velocity data closely resembles the corresponding variation in the
equatorial-rotation rate determined from the sunspot-group data that included
the values of the abnormal angular motions (> 3 deg per day) of the sunspot
groups. Implications of these results are pointed out.Comment: 22 pages, 10 figures, accepted by Solar Physic
Grain boundary segregation and interdiffusion effects in nickel-copper alloys : an effective means to improve the thermal stability of nanocrystalline nickel
Nanocrystalline (nc) Ni films show pronounced grain growth and suffer from concomitant deterioration of their mechanical and magnetic properties after annealing at relatively low temperatures (T(ANN) ≥ 475 K). This constitutes a drawback for their applicability as coatings or in components of miniaturized devices. This work reveals that the thermal stability of nc Ni is significantly improved by controllably alloying Ni with Cu, by means of electrodeposition, to form a Ni(1-x)Cu(x) solid solution. To tune the composition of such nc alloys, Ni(1-x)Cu(x) films are deposited galvanostatically using an electrolytic bath containing Ni and Cu sulfate salts as electroactive species, saccharine as grain-refining agent, and applying current densities ranging from -10 to -40 mA cm(-2). The enhanced thermal stability is ascribed to segregation of a Cu-rich phase at the Ni(1-x)Cu(x) grain boundaries, which acts as a shielding layer against grain growth. As a result, high values of hardness (in excess of 6 GPa) remain in nc Ni(1-x)Cu(x) for x ≥ 0.3, even after annealing at T(ANN) ≥ 575 K. From a magnetic point of view, Ni(1-x)Cu(x) films possess lower coercivity values than pure nc Ni films, both in the as-prepared and annealed states, thus offering potential advantages for certain soft magnetic applications
A comparison between fine-grained and nanocrystalline electrodeposited Cu-Ni films. Insights on mechanical and corrosion performance
This is the author's version of a work that was accepted for publication in Surface & coating technology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Surface & coating technology, Vol. 205, Núm. 23-24 (Sep 2011), p. 2585-5293 DOI 10.1016/j.surfcoat.2011.05.047Cu1−x-Nix (0.43 ≤ x ≤ 1.0) films were electrodeposited from citrate-sulphate baths at different current densities onto Cu/Ti/Si (100) substrates with the addition of saccharine as a grain-refining agent. The Cu-Ni alloy films produced from saccharine-free baths were fine-grained (crystallite size of ~400 nm). The addition of saccharine to the electrolytic solution induced a dramatic decrease in crystal size (down to ~27 nm) along with a reduction in surface roughness. Although the effect of saccharine on pure Ni films was less obvious, significant changes were observed due to the presence of saccharine in the bath during the alloying of Cu with Ni. Compared to fine-grained Cu-Ni films, the nanocrystalline films exhibited lower microstrains and a larger amount of stacking faults as observed by X-ray diffraction. These features enhance the mechanical properties of the Cu-Ni alloys, making the nanocrystalline Cu-Ni films superior to both the corresponding fine-grained films and pure Ni films. In particular, hardness in fine-grained films varied from 4.2 (x=0.43) to 5.4 GPa (x=0.86), whereas hardness varied between 6.7 and 8.2 GPa for nanocrystalline films of similar composition. In addition, wear resistance and elastic recovery were enhanced. Nanostructuring did not significantly affect corrosion resistance of Cu-Ni alloys in chloride media. Although the corrosion potential shifted slightly towards more negative values, the corrosion current density decreased, thereby making the electrodeposition nanostructuring process an effective tool to improve the overall properties of the Cu-Ni system
Grain boundary segregation and interdiffusion effects in nickel-copper alloys : an effective means to improve the thermal stability of nanocrystalline nickel
Nanocrystalline (nc) Ni films show pronounced grain growth and suffer from concomitant deterioration of their mechanical and magnetic properties after annealing at relatively low temperatures (T(ANN) ≥ 475 K). This constitutes a drawback for their applicability as coatings or in components of miniaturized devices. This work reveals that the thermal stability of nc Ni is significantly improved by controllably alloying Ni with Cu, by means of electrodeposition, to form a Ni(1-x)Cu(x) solid solution. To tune the composition of such nc alloys, Ni(1-x)Cu(x) films are deposited galvanostatically using an electrolytic bath containing Ni and Cu sulfate salts as electroactive species, saccharine as grain-refining agent, and applying current densities ranging from -10 to -40 mA cm(-2). The enhanced thermal stability is ascribed to segregation of a Cu-rich phase at the Ni(1-x)Cu(x) grain boundaries, which acts as a shielding layer against grain growth. As a result, high values of hardness (in excess of 6 GPa) remain in nc Ni(1-x)Cu(x) for x ≥ 0.3, even after annealing at T(ANN) ≥ 575 K. From a magnetic point of view, Ni(1-x)Cu(x) films possess lower coercivity values than pure nc Ni films, both in the as-prepared and annealed states, thus offering potential advantages for certain soft magnetic applications
Tailoring the physical properties of electrodeposited CoNiReP alloys with large Re content by direct, pulse, and reverse pulse current techniques
This is the author's version of a work that was accepted for publication in Electrochimica acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Electrochimica acta, [96,(2013)] DOI10.1016/j.electacta.2013.02.077)The composition, surface morphology and structure of CoNiReP alloy films with large Re content (up to 27 at%), obtained in a citrate-glycine based electrolyte have been studied as a function of the electrodeposition technique. Direct current (DC), pulse plating (PP) and reverse pulse plating (RPP) were considered with cathodic current densities from −50 mA cm−2 to −250 mA cm−2. The mechanical and magnetic properties have been analyzed and the data obtained has been correlated with composition and crystallographic structure. For values of j (DC), jon (PP) and jc (RPP) below −100 mA cm−2, Co-rich, P-containing deposits are obtained. Beyond these current densities, both the quantities of Ni and Re increase simultaneously at the expense of Co and P, the latter virtually falling to zero. The highest Re percentage (25-27 at%) was achieved in both PP and RPP conditions at a cathodic pulse of −250 mA cm−2. All the films were either entirely nanocrystalline in nature or partially amorphous. Hardness values as high as 9.2 GPa have been found in PP plated Co64Ni18Re18 deposits. Besides the large hardness, the incorporation of Re in the films leads to high elastic recovery values. The magnetic character of the deposits ranges from soft to semi-hard ferromagneti