Deep Minimum Research Articles

New archeomagnetic secular variation data from Central Europe, II: Intensities

Variations of the geomagnetic field during the past millennia can be obtained by investigating archeological material. The spatial distribution of the available data across Europe is rather uneven and only about 15% of the sites provide a full vector record of the geomagnetic field. Here we report 39 new reliable paleointensity data for sites from Austria, Germany and Switzerland, with ages ranging between 1500 BCE and 1900 CE. For 31 of them, directional information is available, too. Paleointensities were determined with Thellier type techniques, with the multiple-specimen domain-state corrected paleointensity protocol or with both techniques. Corrections for anisotropy of thermoremanent magnetization were carried out for the structures, showing small variations of only a few per cent in most cases. Cooling rate dependence was tested for 16 structures. Often strong alteration during the experiments was observed. Seven successful cooling rate corrections were applied, which lowered the paleointensity values by about 10%. Values obtained from the multiple-specimen technique are generally somewhat lower than those from the Thellier experiments. Rock magnetic measurements revealed magnetite-type minerals mostly in pseudo single domain range as main magnetic carrier, but also high coercive mineral components like hematite or epsilon iron oxide are present. The new data are mostly in good agreement with published paleointensities. They support the presence of strong intensity variations around 800 CE and in the millennium BCE. The new full vector data reveal that the deep paleointensity minimum observed from German data around 850 BCE is accompanied by large variations in direction with declinations up to 50°.

Weight and bias initialization routines for Sigmoidal Feedforward Network

The success of the Sigmoidal Feedforward Networks in the solution of complex learning task can be attributed to their Universal Approximation Property. These networks are trained using non-linear iterative optimization method (of first-order or second-order) to solve a learning task. The convergence rate in Sigmoidal Feedforward Network training is affected by the initial choice of weights, therefore, in this paper, we propose two new weight initialization routines (Routine-1 and Routine-2) using characteristics of input and output data and property of activation function. Routine-1 uses the linear dependency of weight update step size on derivative of activation function and thus, initialize weights and bias to activate the activation function region near zero (input), where the derivative is maximum, therefore, increasing the weight update step size, and hence, the convergence speed. The same principle is used to derive Routine-2, that initialize weights and bias to activate distinct point in the significant range of activation function (where significant range defines the non-saturated region in activation function), such that, each node evolves independently of each other, and act as distinct feature identifier. Initializing weights in significant range reduces chances of (hidden) nodes getting stuck in saturated state. The networks initialized using proposed routines has higher convergence and higher probability to achieve deeper minima. The efficiency of proposed routines is evaluated by comparing them to conventional random weight initialization routine and 11 weight initialization routines proposed in literature (4 well established routines and 7 recently proposed routines) for several benchmark problems. The proposed routine is also tested for larger networks sizes and larger datasets such as MNIST. The results show that the performance of proposed routines is better than conventional random weight initialization routine and 11 established weight initialization routines.

Radio and optical investigations of storm time evolution of post-midnight equatorial plasma bubbles (EPBs) and their drifts over Indian sector

We investigated the spatio-temporal evolution of disturbed time post mid-night Equatorial Plasma Bubbles (EPBs) using Canadian Advanced Digital Ionosonde (CADI) located at dip equatorial station, Tirunelveli (8.73°N, 77.7°E, 0.23°N Dip. Lat.), an all-sky imager (ASI) observations at low latitude station Panhala (16.48°N, 74.6°E, 11.1°N Dip. Lat.) and Gadanki Ionospheric Radar Interferometer (GIRI) at Gadanki (13.5°N, 79.2°E; 6.5°N Dip. Lat.) which is situated at few degrees towards east and south of Panhala on 02–03 February 2017 night. During this night, IMF Bz showed its periodic variation starting from 16:00 UT to 23:00 UT accompanied by decrease in SYM-H to as low as −35 nT indicating the onset of weak magnetic storm. The analyzed results suggested that cause of post-midnight EPBs could be due to manifestation of fluctuating eastward/westward electric field due to combined under-shielding/over-shielding Electric Fields and disturbance dynamo electric fields that led to rise and fall of the F-layer over dip equator. Interestingly, the EPBs over Panhala showed eastward motion initially that quickly reversed to westward later. Along with westward motion they also started growing until 21:30 UT. However, most of these EPBs disappeared with time except the one that started descending/shrinking towards southern side (i.e. towards equator). The rising and shrinking of EPBs is found to be fairly correlated with the equatorial vertical drifts. The westward drift of EPBs at Panhala and its anti-correlation with vertical drifts has been confirmed from CADI zonal/vertical drifts. Accordingly, the study also investigated the role of storm induced vertical Hall electric field as a possible cause for westward drifts and its anti-correlation with vertical drifts. However, GIRI observations do not show any significant westward drift on this night at Gadanki suggesting that there is a longitudinal gradient in the zonal drift of these EPBs. In addition to longitudinal drift reversal, the latitudinal gradient in zonal drifts also has been noticed. The present work highlights the role of storm induced disturbances in the generation and evolution of post-midnight EPBs which is believed to be triggered by weak magnetic disturbances in the deep low solar minimum.

Correlation Between the Behavior of $${\alpha}$$-Decay Half-Life Time and $$\boldsymbol{Q}$$ Values with Neutron Number Variation of Daughter Nuclei

$$\alpha$$ decay of 2000 parent heavy and superheavy nuclei, with atomic numbers in the range $$Z=80$$ to $$Z=122$$ , is considered. We calculated the half-life time, $$T_{\alpha}$$ , of each nucleus using the density-dependent cluster model with M3Y-effective nucleon–nucleon interaction. The $$Q_{\alpha}$$ values needed for calculation of $$T_{\alpha}$$ were extracted from four different mass tables used frequently in $$\alpha$$ -decay calculation. These tables are WS4, WS3, FRDM(2012), and DZ tables. The present study shows to what extent the behavior and value of $$T_{\alpha}$$ , as the nucleon number varies, depends on choosing the mass table used to extract $$Q_{\alpha}$$ values. For this purpose, we studied the variation of log $$T_{\alpha}$$ and the corresponding $$1/Q_{\alpha}$$ with the neutron number of the daughter nucleus, $$N_{d}$$ , using the four different mass tables. The results show that the log $$T_{\alpha}$$ variation follows the corresponding $$1/Q_{\alpha}$$ variation. The two mass tables WS3 and WS4 predict almost the same log $$T_{\alpha}$$ variation and agree in the magic and semi-magic numbers. For FRDM(2012) and DZ tables the variation of log $$T_{\alpha}$$ with $$N_{d}$$ follows the same $$1/Q_{\alpha}$$ variation but the magic numbers deduced from these two tables do not agree with each other and almost differ from those predicted from WS3 and WS4. FRDM(2012) tables predict the main deep minimum at $$N_{d}=128$$ instead of the magic neutron number $$N_{d}=126$$ .

Variation of bottom-side profile parameters (B0, B1) over Multan and their comparisons with IRI-2016 during deep solar minimum of solar cycles 23/24

The present study reports the variations in bottom-side thickness (B0) and shape (B1) parameters from ionospheric measurements of Digisonde Portable Sounder, DPS-4 installed at Multan (geog coord 30.18°N, 71.48°E, dip 47.4°) during the deep solar minimum between solar cycles 23/24 i.e., 2008–09 as a continuation to our previous work (Ameen et al., 2018). We have found that B0 has peak values during daytime whereas, B1 exhibits nighttime peaks, with both parameters showing a diurnal pattern. Seasonally, B0 showed annual trend with maximum values during summer and the least values in winter. B1 has the converse seasonal behaviour with respect to B0. These electron density profile parameters have been compared with International Reference Ionosphere (IRI-2016) to check the performance of three available options namely, ‘Gul-1987’, ‘Bil-2000’ and ‘ABT-2009’. The least Root Mean Square Error (RMSE) values with respect to the three options show that ABT-2009 estimated seasonal B0 and B1 with greater confidence as compared to other two options. For day and nighttime values of the parameters, no specific model may be declared the best predicting B0 and B1 for the period under study. Much of the factors that influenced the behaviour of hmF2 over Multan (Ameen et al., 2018) seem to be affecting the magnitude of B0 including the post-sunset peak in winter. The present study may be helpful in updating sub-model ABT-2009 of IRI for better reconstruction of bottom-side profile over Multan.

Betelgeuse Fainter in the Submillimeter Too: An Analysis of JCMT and APEX Monitoring during the Recent Optical Minimum

Abstract Betelgeuse, the nearest red supergiant star to Earth, underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimeter observations taken by the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 yr including the optical dimming. We find that Betelgeuse has also dimmed by ∼20% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust, as was previously suggested in the literature.

Difficulties of Popular Density Functionals to Describe the Conformational Isomerism in Iodoacetic Acid.

Matrix isolation studies in solid argon and neon at 4.2 K reveal that iodoacetic acid initially only exists as its ground state (c,x) conformer with an almost perpendicular I-C-C═O dihedral angle, but UV irradiation in the 240-255 nm range leads to population of the 0.8 kcal mol-1 less stable (c,c) isomer. The latter structure exhibits a close 3.23 Å contact of the iodine and carbonyl oxygen atoms decidedly below the sum of their van der Waals radii (3.50 Å). Increasing the matrix temperature by only a few Kelvin triggers the thermal back reaction of (c,c) to (c,x) and leads to an estimated upper limit of 0.38 kcal mol-1 for the associated torsional barrier. While wave function methods including completely uncorrelated Hartree-Fock theory have no problem to identify (c,c) as a proper minimum, many popular density functionals fail to describe the C-C torsional potential in cis-iodoacetic acid qualitatively correct. We assessed the performance of 12 density functionals of different levels of sophistication, namely, the BLYP, PBE, TPSS, B3LYP, BHandHLYP, PBE0, M06-2X, CAM-B3LYP, ωB97X-D3, B2-PLYP, B2GP-PLYP, and DSD-PBEP86 methods, against accurate extrapolated CCSD(T)/CBS(T-Q)//MP2/def2-TZVPP energies and found that almost all of them yield acceptable relative energies. Still, even some of the best performers fail to find a reasonably deep minimum in the region of the (c,c) conformer, and addition of the empirical D3-dispersion correction does not remedy the qualitative shortcoming. Instead, inclusion of a sufficient amount of (long-range) exact exchange and likely a proper treatment of medium-range correlation effects all along the torsional coordinate play an important role in the proper description of the sub-van der Waals iodine-oxygen contact. More modern, recommended functionals do not suffer from the described shortcoming.

Long term variations of galactic cosmic radiation on board the International Space Station, on the Moon and on the surface of Mars

<div class="abstract"> <p> <div><div class="abstract"> <div><p>The radiation environment in free space and the related radiation exposure is seen as one of the main health detriments for future long-duration human exploration missions beyond Low Earth Orbit (LEO). The steady flux of energetic particles in the galactic cosmic radiation (GCR) produces  a low dose-rate radiation exposure, which is heavily influenced by several factors including the solar cycle, the presence of an atmosphere, relevant magnetic fields (as on Earth) and of course by the relevant spacecraft shielding. Investigations of the GCR variations over the course of a solar cycle provide valuable data for exploration mission planning and for the determination of the radiation load received due to the GCR environment. Within the current work these investigations have been performed applying three datasets generated on board the International Space Station (ISS) with the DOSTEL instruments in the frame of the DOSIS and DOSIS-3D projects, with the CRaTER instrument in a Moon orbit and with the MSL-RAD instrument on the way to and on the surface of Mars. To derive GCR dose contributions on board the ISS two procedures have been developed separating the contributions from GCR from passing’s through the South Atlantic Anomaly (SAA), as well as ways to extrapolate the GCR dose measured on board the ISS to free space based on various ranges of the McIlwain <em>L</em>-shell parameter. At the end we provide a dataset spanning the timeframe for GCR measurements on the ISS (2009 – 2011 & 2012 – 2019), Moon (2009 – 2019) and Mars (2012 – 2019), thereby covering the time span from the deep minimum of solar cycle 23, the ascending phase and maximum of solar cycle 24, and the descending phase of cycle 24, which is ongoing at the time of this writing.</p> </div> </div></div> </p> </div>

Anisotropic magnetocaloric properties of the ludwigite single crystal Cu2MnBO5

We report upon the specific heat and magnetocaloric properties of Cu2MnBO5 over a temperature range of 60–350 K and in magnetic fields up to 18 kOe. It is found that at temperatures below the Curie temperature (TC ∼ 92 K), CP(T)/T possesses a linear temperature-dependent behavior, which is associated with the predominance of two-dimensional antiferromagnetic interactions of magnons. The temperature independence of CP/T = f(T) is observed in the temperature range of 95–160 K, which can be attributed to the excitation of the Wigner glass phase. The magnetocaloric effect [i.e., the adiabatic temperature change, ΔTad (T,H)] is assessed through a direct measurement or an indirect method using the CP(T,H) data. Owing to its strong magnetocrystalline anisotropy, an anisotropic magnetocaloric effect (MCE) or the rotating MCE [ΔTadrot (T)] is observed in Cu2MnBO5. A deep minimum in the ΔTadrot (T) near the TC is observed and ascribed to the anisotropy of the paramagnetic susceptibility.

Evidence of nodal superconductivity in LaFeSiH

Unconventional superconductivity has recently been discovered in the first iron-based superconducting silicide LaFeSiH. By using the complementary techniques of muon spin rotation, tunneling diode oscillator and density functional theory, we investigate the magnetic penetration depth and thereby the superconducting gap of this novel high-temperature superconductor. We find that the magnetic penetration depth displays a sub-$T^2$ behavior in the low-temperature regime below $T_c/3$, which evidences a nodal structure of the gap (or a gap with very deep minima). Even if the topology of the computed Fermi surface is compatible with the $s_\pm$-wave case with accidental nodes, its nesting and orbital-content features may eventually result in a $d$-wave state, more unusual for high-temperature superconductors of this class.

Deep Minima in the Triply Differential Cross Section for Ionization of Atomic Hydrogen by Electron and Positron Impact

We investigate ionization of atomic hydrogen by electron- and positron-impact. We apply the Coulomb–Born (CB1) approximation, various modified CB1 approximations, the three body distorted wave (3DW) approximation, and the time-dependent close-coupling (TDCC) method to electron-impact ionization of hydrogen. For electron-impact ionization of hydrogen for an incident energy of approximately 76.45 eV, we obtain a deep minimum in the CB1 triply differential cross section (TDCS). However, the TDCC for 74.45 eV and the 3DW for 74.46 eV gave a dip in the TDCS. For positron-hydrogen ionization (breakup) we apply the CB1 approximation and a modified CB1 approximation. We obtain a deep minimum in the TDCS and a zero in the CB1 transition matrix element for an incident energy of 100 eV with a gun angle of 56.13 ° . Corresponding to a zero in the CB1 transition matrix element, there is a vortex in the velocity field associated with this element. For both electron- and positron-impact ionization of hydrogen the velocity field rotates in the same direction, which is anticlockwise. All calculations are performed for a doubly symmetric geometry; the electron-impact ionization is in-plane and the positron-impact ionization is out-of-plane.

Cooperative band-stop filters

We analyze light transmission both through a 1D waveguide that has a regular array of atoms inside, and through a stack of equally-spaced partially reflecting mirrors. We view the atoms and mirrors as linear filters. As such, they have two inputs, light coming in from both sides, and two outputs, light going out to both sides. The example systems formally have the individual filters chained so that inputs and outputs of successive filters are cross-coupled, whereupon the filters act cooperatively. Such an arrangement may form a band-stop filter with sharp edges and a deep minimum of transmission.

Daily dust variation from the PFS MEx observations

We collected over 7 Martian years (MY) of data observed by the Planetary Fourier Spectrometer (PFS) to present a daily variation of dust content in the Martian atmosphere. We found three typical behaviors of dust opacities with LT (local time). The most peculiar variation was observed when global dust storms (MYs 28 and 34) or particularly strong regional storms (MY 29) occurred on Mars. Here, large dust opacities were measured at 10 LT (MY 34) and 11 LT (MY 28). Then, relatively small values of dust opacities were found in the evening (20 LT). The non-dusty season, particularly near northern summer solstice, was characterized by a deep minimum of the total dust opacity at late night/early morning, while small variations around the mean value were observed during daytime. The clear trend of dust was observed over both hemispheres during early morning. We noted elevated dust opacities in the second half of the year compared to the non-dusty season in all Martian years without global dust storms. The daily variation of three types of storms occurring in moderately dusty conditions was also investigated. Dust in A storms was present in the atmosphere at all LTs and was mostly confined to the southern hemisphere. The maximum of dust opacities in B storms was found at 15–17 LT, close to the South Pole. C storms were mainly constrained to southern latitudes and occurred from the late morning to midday.

Probing of Higher Excited States of Merocyanine Derivatives of Azaazulene and Indandione by Fluorescence Excitation Anisotropy Spectra

This paper is dedicated to the spectral and quantum-chemical studies of higher excited states of merocyanine derivatives of azaazulene and indandione. A particular attention is paid to the analysis of fluorescence excitation anisotropy spectra of the mentioned compounds. The long-wave shift by ≈ 50 nm of a deep clear minimum in the fluorescence excitation anisotropy spectrum due to an elongation of the polymethine dye chromophore is established. Such shift is close in a value to the bathochromic shift of the first minimum in the anisotropy spectrum of symmetric ionic polymethine dyes, in which this minimum corresponds to the second electronic transition. The parallel spectral study and quantum-chemical calculations allowed us to correctly interpret the fluorescence excitation anisotropy spectra of merocyanines and relate the first clear minimum with the seventh electronic transition. The last resembles the second electronic transition between delocalized molecular orbitals (MO) in polymethine dyes.

Magnetite Hydrosols with Positive and Negative Surface Charge of Nanoparticles: Stability and Effect on the Lifespan of Drosophila melanogaster.

This paper presents sols of uncoated and citric acid-coated Fe3O4 nanoparticles obtained by a combination of coprecipitation and sonochemistry methods. A stable concentrated CA-Fe3O4 sol synthesized by a combination of coprecipitation with an inconvenient Fe2+/Fe3+ ratio, modification with citric acid and US treatment was obtained for the first time. A comparative analysis of the composition and morphology of nanoparticles was performed. The sols are oppositely charged and behave as a typical ferrofluid. The citric acid-modified sol is aggregatively stable over wider ranges of pH and electrolyte concentration, but it becomes less stable with the temperature increase. DLVO calculations showed that steric repulsion forces are a vital factor contributing to increased aggregative stability in a modified Fe3O4 sol. The experiments have revealed the magneto-optical effect in a modified Fe3O4 sol with an electrolyte concentration of 0.025-0.075 M caused by a high potential barrier and a deep secondary minimum in pairwise interaction curves. The "pK spectroscopy" mathematical model to describe the potentiometric curves of synthesized magnetite sols was used for the first time. According to potentiometric titration, the ions of the electrolyte practically do not contribute to formation of a surface charge in modified Fe3O4 with a change in pH due to blocking the magnetite surface by citric acid molecules. Drosophila melanogaster was used as a model to show that Fe3O4 in chronic exposure has a low toxic effect.

Deep minima in the Coulomb-Born triply differential cross sections for ionization of helium by electron and positron impact

Previously, a deep minimum in the measurements of the triply differential cross section (TDCS) for electron-helium ionization at an incident energy of 64.6 eV was interpreted in terms of a vortex. We apply the Coulomb-Born (CB1) and modified CB1 approximations to this process at the same incident energy and obtain a deep minimum whose position is in reasonable accord with time-dependent close-coupling results and experimental data. We also obtain the deep minimum in the TDCS that was measured for an energy of 74.6 eV. For both incident energies, but at slightly different gun angles to those used experimentally, we obtain a very deep minimum in the TDCS that is related to a vortex in the velocity field associated with the CB1 transition matrix element. We determine for energies of 44.6 eV–79.6 eV the gun and polar angles for a deep minimum in the CB1 TDCS. We apply both approximations to positron-helium ionization. For an incident energy of 205.25 eV we find a deep minimum in the TDCS that is related to a vortex in the velocity field associated with the CB1 transition matrix element.

Mobility of Cellulose Nanocrystals in Porous Media: Effects of Ionic Strength, Iron Oxides, and Soil Colloids.

Understanding the dispersivity and migration of cellulose nanocrystals (CNCs) in porous media is important for exploring their potential for soil and water remediation. In this study, a series of saturated column experiments were conducted to investigate the coupled effects of ionic strength, iron oxides (hematite), and soil colloids on the transport of CNCs through quartz sand and natural soils (red earth and brown earth). Results showed that CNCs had high mobility in oxide-free sand and that iron oxide coating reduced the mobility of CNCs. An analysis of Derjaguin-Landau-Verwey-Overbeek interactions indicated that CNCs exhibited a deep primary minimum, nonexistent maximum repulsion and secondary minimum on hematite-coated sand, favorable for the attachment of CNCs. The maximum effluent percentage of CNCs was 96% in natural soils at 5 mM, but this value decreased to 4% at 50 mM. Soil colloids facilitated the transport of CNCs in brown earth with larger effect at higher ionic strength. The ionic strength effect was larger in natural soils than sand and in red earth than brown earth. The study showed that CNCs can travel 0.2 m to 72 m in porous media, depending on soil properties, solution chemistry, and soil colloids.

Electroweak vacuum stability and the Higgs field relaxation via gravitational effects

The measured values of the standard model parameters favors a shallow metastable electroweak vacuum and a deep global minimum. The Higgs relaxation in its present local minimum can only be explained via a large degree of fine-tuning. In this paper, irrespective of new physics beyond the SM, we study the universal effect of gravity on the Higgs dynamics in the early universe. We consider a two-parameter framework in which the Higgs is non-minimally coupled to a higher-curvature gravity. In the Einstein frame there are genuine couplings between the Higgs field and the Weyl field with interesting predictions. In a broad region in the parameter space and for large field values, the effective Higgs mass is large and thus it initially takes over the dynamics by its coherent oscillations. Finally, the Weyl (inflaton) field with its plateau-like potential dominates and derives cosmic inflation. In this framework, the Higgs self-coupling in the electroweak vacuum is modified by contributions from gravity sector.

Application of Synoptic Magnetograms to Global Solar Activity Forecast

Abstract Synoptic magnetograms provide us with knowledge about the evolution of magnetic fields on the solar surface and present important information for forecasting future solar activity. In this work, poloidal and toroidal magnetic field components derived from synoptic magnetograms are assimilated, using the Ensemble Kalman Filter method, into a mean-field dynamo model based on Parker’s migratory dynamo theory complemented by magnetic helicity conservation. It was found that the predicted toroidal field is in good agreement with observations for almost the entire following solar cycle. However, poloidal field predictions agree with observations only for the first 2–3 yr of the predicted cycle. The results indicate that the upcoming Solar Maximum of Cycle 25 (SC25) is expected to be weaker than the current Cycle 24. The model results show that a deep extended solar activity minimum is expected during 2019–2021, and that the next solar maximum will occur in 2024–2025. The sunspot number at the maximum will be about 50 with an error estimate of 15%–30%. The maximum will likely have a double peak or show extended periods (for 2–2.5 yr) of high activity. According to the hemispheric prediction results, SC25 will start in 2020 in the southern hemisphere, and will have a maximum in 2024 with a sunspot number of about 28. In the northern hemisphere the cycle will be delayed for about 1 yr (with an error of ±0.5 yr), and reach a maximum in 2025 with a sunspot number of about 23.

Magnetic Domains without Domain Walls: A Unique Effect of He^{+} Ion Bombardment in Ferrimagnetic Tb/Co Films.

We show that it is possible to engineer magnetic multidomain configurations without domain walls in a prototypical rare-earth-transition-metal ferrimagnet using keV He^{+} ion bombardment. We additionally show that these patterns display a particularly stable magnetic configuration due to a deep minimum in the energy of the system caused by flux closure and a corresponding reduction of the magnetostatic energy without an increase in energy by exchange and anisotropy terms across the walls. This occurs because light-ion bombardment affects an element's relative contribution to the properties of the ferrimagnet differently. Therefore, it is possible to control the relative contribution from each magnetic subsystem. The selection of material and the use of light-ion bombardment allow us to engineer domain patterns in continuous magnetic films, which open a way to fabricate them in a much smaller scale than currently possible. Our Letter emphasizes that the right criterion to determine the presence or absence of a domain wall is whether there is a rotation of the spin for each sublattice and that changes of the direction of effective magnetization alone do not constitute an appropriate criterion.