Prolate Configurations Research Articles

Aspherical ULDM collapse: variation in the core–halo mass relation

ABSTRACT Ultralight dark matter (ULDM) is an interesting alternative to the cold dark matter (CDM) paradigm. Due to the extremely low mass of the constituent particle (∼10−22 eV), ULDM can exhibit quantum effects up to kiloparsec scales. In particular, runaway collapse in the centres of ULDM haloes is prevented by quantum pressure, providing a possible resolution to the ‘core-cusp problem’ of CDM. However, the the detailed relationship between the ULDM core mass and that of the overall halo is poorly understood. We simulate the collapse of both spherical and aspherical isolated ULDM overdensities using AxioNyx, finding that the central cores of collapsed haloes undergo sustained oscillatory behaviour, which affects both their peak density and overall morphology. The asphericity of the post-collapse core fluctuates both quantitatively and qualitatively, with oblate initial overdensities generating cores, which fluctuate between prolate and oblate configurations, and more complicated dynamics arising in triaxial scenarios. Furthermore, the peak central densities are higher in spherical configurations. Consequently, astrophysically realistic haloes may exhibit substantial departures from theoretical core–halo profiles and we would expect a significant variance of the properties of haloes with the same mass.

Decay Modes and Half-Life of 265–282Ds Isotopes

The decay modes and half-lives of superheavy 265–282Ds isotopes have been investigated by using Relativistic Mean Field (RMF) model with density-dependent point-coupling and density-dependent meson-exchange functional. The potential energy surfaces as a funtion of deformation parameters ( $$\beta ,\gamma$$ ) for the considered Ds nuclei have been obtained by using a triaxially deformed RMF model calculations for the investigation of their ground-state shapes and binding energies. The computed ground-state binding energy values of given Ds isotopes have been used for calculations of Q values of the alpha ( $$\alpha$$ ), beta-plus/electron capture ( $$\beta ^{+}$$ /EC), beta-minus ( $$\beta ^{-}$$ ) and spontaneous fission (SF) decay modes. The dominant decay modes and half-lives of 265–282Ds isotopes have been predicted by using the computed Q-values and some empirical formulas. The results of the present study demonstrate that the 265–282Ds isotopes are well deformed, with prolate configuration in their ground-states. Our estimations for decay modes and half-lives are consistent with available experimental data.

Hexadecapole strength in the rare isotopes 74,76Kr

In the Ge-Sr mass region, isotopes with neutron number N≤40 are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes 74,76Kr. This work focuses on observables related to the Jπ=41+ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters β4 were determined for the Jπ=41+ states of 74,76Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive β4 solutions. These β4 values are unambiguously linked to the well deformed prolate configuration. Given the β2−β4 trend, established in this work, it appears that β4 values could provide a sensitive measure of the nuclear shell structure.

Isovector giant monopole and quadrupole resonances in a Skyrme energy density functional approach with axial symmetry

[Background] Giant resonance (GR) is a typical collective mode of vibration. The deformation splitting of the isovector (IV) giant dipole resonance is well established. However, the splitting of GRs with other multipolarities is not well understood. [Purpose] I explore the IV monopole and quadrupole excitations and attempt to obtain the generic features of IV giant resonances in deformed nuclei by investigating the neutral and charge-exchange channels simultaneously. [Method] I employ a nuclear energy-density functional (EDF) method: the Skyrme-Kohn-Sham-Bogoliubov and the quasiparticle random-phase approximation are used to describe the ground state and the transition to excited states. [Results] I find the concentration of the monopole strengths in the energy region of the isobaric analog or Gamow-Teller resonance irrespective of nuclear deformation, and the appearance of a high-energy giant resonance composed of the particle-hole configurations of $2\hbar \omega_0$ excitation. Splitting of the distribution of the strength occurs in the giant monopole and quadrupole resonances due to deformation. The lower $K$ states of quadrupole resonances appear lower in energy and possess the enhanced strengths in the prolate configuration, and vice versa in the oblate configuration, while the energy ordering depending on $K$ is not clear for the $J=1$ and $J=2$ spin-quadrupole resonances. [Conclusions] The deformation splitting occurs generously in the giant monopole and quadrupole resonances. The $K$-dependence of the quadrupole transition strengths is largely understood by the anisotropy of density distribution.

Total absorption gamma-ray spectroscopy study of the β-decay of 186Hg

The Gamow-Teller strength distribution of the decay of 186Hg into 186Au has been determined for the first time using the total absorption gamma spectroscopy technique and has been compared with theoretical QRPA calculations using the SLy4 Skyrme force. The measured Gamow-Teller strength distribution and the half-life are described by mixing oblate and prolate configurations independently in the parent and daughter nuclei. In this theoretical framework the best description of the experimental beta strength is obtained with dominantly prolate components for both parent 186Hg and daughter 186Au. The approach also allowed us to determine an upper limit of the oblate component in the parent state. The complexity of the analysis required the development of a new approach in the analysis of the X-ray gated total absorption spectrum.

Origin of stellar prolate rotation in a cosmologically simulated faint dwarf galaxy

ABSTRACT Stellar prolate rotation in dwarf galaxies is rather uncommon, with only two known galaxies in the Local Group showing such feature (Phoenix and And II). Cosmological simulations show that in massive early-type galaxies prolate rotation likely arises from major mergers. However, the origin of such kinematics in the dwarf galaxies regime has only been explored using idealized simulations. Here, we made use of hydrodynamical cosmological simulations of dwarfs galaxies with stellar mass between 3 × 105 and 5 × 108 M⊙ to explore the formation of prolate rotators. Out of 27 dwarfs, only one system showed clear rotation around the major axis, whose culprit is a major merger at $z$ = 1.64, which caused the transition from an oblate to a prolate configuration. Interestingly, this galaxy displays a steep metallicity gradient, reminiscent of the one measured in Phoenix and And II: this is the outcome of the merger event that dynamically heats old, metal-poor stars, and of the centrally concentrated residual star formation. Major mergers in dwarf galaxies offer a viable explanation for the formation of such peculiar systems, characterized by steep metallicity gradients and prolate rotation.

All–Anisotropic Spheroidal Photonic Antennas: Theory and Modeling

We introduce the concept of all-anisotropic spheroidal photonic antennas, where the nanoantenna is formed by a uniaxial anisotropic crystal, and study their modeling and optimization. For this purpose, we develop, for the first time, a rigorous theory for the electromagnetic (EM) scattering by anisotropic spheroids, using a full-wave method which features spheroidal eigenvectors with a set of discrete wavenumbers for the expansion of the fields in the region of anisotropy. We fully validate our theory by comparisons with the commercial HFSS software, as well as with a general purpose discrete dipole approximation method. Our implementation turns out to be fast, and serves as an efficient tool for modeling the resonant properties of spheroidal photonic antennas. In this context, we show that geometrical tailoring, by employing high-aspect ratio prolate and oblate spheroids, allows for optimizing the nanoantenna and achieving maximal forward-to-back scattering or maximal forward-scattering with reduced back-scattering. In addition, we demonstrate how the use of anisotropic materials enables us to set this optimum state at smaller wavelengths, even close to ultraviolet (UV), as compared to isotropic dielectrics, and we reveal the key role of the incident field's polarization in achieving optimized operation for both prolate and oblate configurations.

Nonlinear dynamics of Josephson vortices in merging superfluid rings

We consider merger of two parallel toroidal atomic Bose-Einstein condensates with different vorticities in a three-dimensional (3D) trap. In the tunnel-coupling regime, Josephson vortices (rotational fluxons) emerge in the barrier between the superflows. When the barrier is gradually eliminated, we observe essentially three-dimensional evolution of quantum vortices, which may include the development of the Kelvin-Helmholtz instability at the interface between the rings, in the framework of a weakly dissipative Gross-Pitaevskii equation. An initially more populated ring, carrying a persistent current, can drag an initially non-rotating less populated one into the same vortex state. The final state of the condensate crucially depends on an initial population imbalance in the double-ring set, as well as on the shape of the 3D trapping potential, oblate or prolate. In the prolate (axially elongated) configuration, robust 3D hybrid structures may appear as a result of the merger of persistent currents corresponding to different vorticities.

Light-induced heat-conducting micro/nano spheroidal particles and their thermoosmotic velocity fields

A micro/nano spheroidal conducting particle embedded in a fluid of a uniform ambient temperature is considered for its temperature and the induced velocity fields due to thermoosmosis. The particle is assumed to be uniformly heated using for example continuous light irradiation by a conventional laser. This is a model problem of thermoplasmonics, where nano or micro particles are used for heat storage and release as in medical therapy and imaging purposes. The temperature field is governed by the Poisson heat diffusion equation and the self-induced thermoosmotic flow (STOF) field is taken as a Stokes type. Analytical closed solutions are derived for both the temperature distributions (inside and outside the particle) as well as for the STOF in the solute for both prolate and oblate configurations. They are based on using spheroidal harmonics expressed in terms of Legendre functions, where owing to orthogonality only a few terms are needed to fully prescribe the entire field. The analytical solutions thus obtained are also numerically verified for few selected cases.Results for conducting spheroidal particles with inner thermal conductivities lower or higher than the outer medium’s conductivity are analysed. It is shown that the surface temperature of the particle is always highest at the tip nearest to the spheroid's centre. However, the location of the peak of the surface heat flux depends on the precise ratio between the inner and outer thermal conductivities, where it peaks at the nearest tip for a low inner thermal conductivity and at the farthest tip for a high inner thermal conductivity. Plots of temperature and heat flux distributions over the surface of both prolate and oblate spheroidal particles as well as the thermoosmotic (Soret) induced velocity, vorticity and stream-function in the liquid phase are given and analysed.

Total absorption γ -ray spectroscopy of niobium isomers

The $\beta$ intensity distributions of the decays of $^{100\text{gs},100\text{m}}$Nb and $^{102\text{gs},102\text{m}}$Nb have been determined using the Total Absorption $\gamma$-Ray Spectroscopy technique. The JYFLTRAP double Penning trap system was employed to disentangle the isomeric states involved, lying very close in energy, in a campaign of challenging measurements performed with the Decay Total Absorption $\gamma$-ray Spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyv\"askyl\"a. The low-spin isomeric state of each niobium case was populated through the decay of the zirconium parent, that was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained $\beta$ intensity distributions for these zirconium decays. The $\beta$-strength distributions evaluated with these results were compared with calculations in quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of $^{100,102}$Zr. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The $\beta$-intensities of the decay of $^{102\text{m}}$Nb were obtained for the first time. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported and here we detail the significant impact on decay heat calculations.

First observation of γ -soft and triaxial bands in Zr isotopes

New results obtained in this work from measurements of $\ensuremath{\gamma}$ radiation following fission of $^{248}\mathrm{Cm}$ and $^{252}\mathrm{Cf}$, performed using Eurogam2 and Gammasphere arrays, respectively, reveal excitations corresponding to $\ensuremath{\gamma}$ vibrations and triaxial deformation present in $^{100}\mathrm{Zr}$ and $^{102}\mathrm{Zr}$ nuclei. This is the first observation of nonaxial bands in Zr isotopes. Such excitations probably occur due to competing prolate and oblate configurations, identified recently in these nuclei. Evolution of $\ensuremath{\gamma}$ softness and triaxiality in Zr isotopes is observed in the function of the neutron number.

Cosmic Censorship Upheld in Spheroidal Collapse of Collisionless Matter.

We study the collapse of spheroidal configurations of collisionless particles in full general relativity. This setup was originally considered by Shapiro and Teukolsky, where it was found that prolate configurations with a sufficiently large semimajor axis gave rise to diverging curvature, but no apparent horizon. This was taken as evidence for the formation of a naked singularity, in violation of cosmic censorship. We revisit such configurations using different coordinates and slicing, and considering a range of values for the semimajor axis and eccentricity of the initial matter distribution, and find that the final state in all cases studied is a black hole plus gravitational radiation. Though initially distorted, the proper circumferences of the apparent horizons that are found do not significantly exceed the hoop conjecture bound. Configurations with a larger semimajor axis can produce strong gravitational radiation, with luminosities up to P_{GW}∼2×10^{-3}c^{5}/G.

Validation method for the systematization of results based on a similarity concept

The development of a functional methodological approach is presented here, to clarify a globally valid way of evaluating the precision of mathematical modeling of physical and/or chemical processes. Starting from the description of the system, a phenomenon accompanied by a disclaiming hypothesis is investigated, against which the knowledge is accumulated with time. Moreover, the possibility of the evolution of any phenomenon being interrupted when a parameter overpasses a critical threshold, after which the hypothesis is not any more valid, is introduced. This possibility should be obtained through the dependence of a selected macroscopic quantity (marker) on a specific parameter. To apply this methodology, the problem of Stokes flow through a granular medium of spheroidal grains has been selected as an indicative case study. The prolate spheroidal configuration is considered, since the results for the oblate spheroid can be recovered via a simple transformation. Therein, the three‐dimensional flow fields are initially constructed analytically via the Papkovich‐Neuber differential representation, which provides the velocity and pressure fields in terms of harmonic spheroidal eigenfunctions. Next, under the Kuwabara‐type spheroidal 2D unit cell concept, the above expressions degenerate to the axisymmetric case, and the full solution is then obtained, keeping the leading terms of the series, which are adequate for most engineering applications for specific aspect ratio of the spheroids. In the sequel, the aforementioned problem is solved numerically for a 3D extension of the same model, where this numerical solution has been achieved by using the finite volumes method, while the resulting linear systems were approximated by applying the well‐known successful over‐relaxation concept. Finally, outcomes by both models have been compared via the above methodology, resulting to objective and reliable accuracy criteria.

Localizing the Shape Transition in Neutron-Deficient Selenium.

Neutron-deficient selenium isotopes are thought to undergo a rapid shape change from a prolate deformation near the line of beta stability towards oblate deformation around the line of N=Z. The point at which this shape change occurs is unknown, with inconsistent predictions from available theoretical models. A common feature in the models is the delicate nature of the point of transition, with the introduction of even a modest spin to the system sufficient to change the ordering of the prolate and oblate configurations. We present a measurement of the quadrupole moment of the first-excited state in radioactive ^{72}Se-a potential point of transition-by safe Coulomb excitation. This is the first low-energy Coulomb excitation to be performed with a rare-isotope beam at the reaccelerated beam facility at the National Superconducting Cyclotron Laboratory. By demonstrating a negative spectroscopic quadrupole moment for the first-excited 2^{+} state, it is found that any low-spin shape change in neutron-deficient selenium does not occur until ^{70}Se.

Aqueous solvation of Mg(ii) and Ca(ii): A Born-Oppenheimer molecular dynamics study of microhydrated gas phase clusters.

The hydration features of [Mg(H2O)n]2+ and [Ca(H2O)n]2+ clusters with n = 3-6, 8, 18, and 27 were studied by means of Born-Oppenheimer molecular dynamics simulations at the B3LYP/6-31+G** level of theory. For both ions, it is energetically more favorable to have all water molecules in the first hydration shell when n ≤ 6, but stable lower coordination average structures with one water molecule not directly interacting with the ion were found for Mg2+ at room temperature, showing signatures of proton transfer events for the smaller cation but not for the larger one. A more rigid octahedral-type structure for Mg2+ than for Ca2+ was observed in all simulations, with no exchange of water molecules to the second hydration shell. Significant thermal effects on the average structure of clusters were found: while static optimizations lead to compact, spherically symmetric hydration geometries, the effects introduced by finite-temperature dynamics yield more prolate configurations. The calculated vibrational spectra are in agreement with infrared spectroscopy results. Previous studies proposed an increase in the coordination number (CN) from six to eight water molecules for [Ca(H2O)n]2+ clusters when n ≥ 12; however, in agreement with recent measurements of binding energies, no transition to a larger CN was found when n > 8. Moreover, the excellent agreement found between the calculated extended X-ray absorption fine structure spectroscopy spectra for the larger cluster and the experimental data of the aqueous solution supports a CN of six for Ca2+.

Dimensional analysis of the endometrial cavity: how many dimensions should the ideal intrauterine device or system have?

BackgroundThe geometrical shape of the human uterus most closely approximates that of a prolate ellipsoid. The endometrial cavity itself is more likely to also have the shape of a prolate ellipsoid especially when the extension of the cervix is omitted. Using this information and known endometrial cavity volumes and lateral and vertical dimensions, it is possible to calculate the anteroposterior (AP) dimensions and get a complete evaluation of all possible dimensions of the endometrial cavity. These are singular observations and not part of any other study.MethodsThe AP dimensions of the endometrial cavity of the uterus were calculated using the formula for the volume of the prolate ellipsoid to complete a three-dimensional picture of the endometrial cavity.ResultsCalculations confirm ultrasound imaging which shows large variations in cavity size and shape. Known cavity volumes and length and breadth measurements indicate that the AP diameter may vary from 6.29 to 38.2 mm. These measurements confirm the difficulty of getting a fixed-frame intrauterine device (IUD) to accommodate to a space of highly variable dimensions. This is especially true of three-dimension IUDs. A one-dimensional frameless IUD is most likely to be able to conform to this highly variable space and shape.ConclusionThe endometrial cavity may assume many varied prolate ellipsoid configurations where one or more measurements may be too small to accommodate standard IUDs. A one-dimensional device is most likely to be able to be accommodated by most uterine cavities as compared to two- and three-dimensional devices.

Simultaneous investigation of the T=1(Jπ=0+) and T=0(Jπ=9+) β decays in Br70

The $\beta$ decay of the odd-odd nucleus $^{70}$Br has been investigated with the BigRIPS and EURICA setups at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center. The $T=0$ ($J^{\pi}=9^+$) and $T=1$ ($J^{\pi}=0^+$) isomers have both been produced in in-flight fragmentation of $^{78}$Kr with ratios of 41.6(8)\% and 58.4(8)\%, respectively. A half-life of $t_{1/2}=2157^{+53}_{-49}$ ms has been measured for the $J^{\pi}=9^+$ isomer from $\gamma$-ray time decay analysis. Based on this result, we provide a new value of the half-life for the $J^{\pi}=0^+$ ground state of $^{70}$Br, $t_{1/2}=78.42\pm0.51$ ms, which is slightly more precise, and in excellent agreement, with the best measurement reported hitherto in the literature. For this decay, we provide the first estimate of the total branching fraction decaying through the $2^+_1$ state in the daughter nucleus $^{70}$Se, $R(2^+_1)=1.3\pm1.1\%$. We also report four new low-intensity $\gamma$-ray transitions at 661, 1103, 1561, and 1749 keV following the $\beta$ decay of the $J^{\pi}=9^+$ isomer. Based on their coincidence relationships, we tentatively propose two new excited states at 3945 and 4752 keV in $^{70}$Se with most probable spins and parities of $J^{\pi}=(6^+)$ and $(8^+)$, respectively. The observed structure is interpreted with the help of shell-model calculations, which predict a complex interplay between oblate and prolate configurations at low excitation energies.

Structural and decay properties of Z = 132, 138 superheavy nuclei

In this paper, we analyze the structural properties of Z = 132 and Z = 138 superheavy nuclei within the ambit of axially deformed relativistic mean-field framework with NL3 * parametrization and calculate the total binding energies, radii, quadrupole deformation parameter, separation energies, density distributions. We also investigate the phenomenon of shape coexistence by performing the calculations for prolate, oblate and spherical configurations. For clear presentation of nucleon distributions, the two-dimensional contour representation of individual nucleon density and total matter density has been made. Further, a competition between possible decay modes such as $\alpha$ -decay, $\beta$ -decay and spontaneous fission of the isotopic chain of superheavy nuclei with Z = 132 within the range $ 312 \le A \le 392$ and $318 \le A \le 398$ for Z = 138 is systematically analyzed within self-consistent relativistic mean-field model. From our analysis, we inferred that the $\alpha$ -decay and spontaneous fission are the principal modes of decay in majority of the isotopes of superheavy nuclei under investigation apart from $\beta$ -decay as dominant mode of decay in 318-322138 isotopes.

Spectroscopic Quadrupole Moments in {96,98}Sr: Evidence for Shape Coexistence in Neutron-Rich Strontium Isotopes at N=60.

Neutron-rich {96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.

Interpreting the AXP 1E 2259+586 antiglitch as a change in internal magnetization

The sudden spin-down event ('anti-glitch') observed in AXP 1E 2259+586 on 2012 April 21 was arguably caused by a decay of its internal toroidal magnetic field component, which turns a stable prolate configuration into an unstable one. We refine previous models of this process by modelling the star's magnetic field self-consistently as a 'twisted torus' configuration in non-barotropic equilibrium (which allows us to explore a greater range of equilibrium configurations). It is shown that, if the star's magnetic field is purely dipolar, the change in the toroidal field strength required to produce an anti-glitch of the observed size can be ~ 10 times larger than previously calculated. If the star has a quadrupolar magnetic field component, then an anti-glitch of similar magnitude can be produced via a decay of the quadrupole component, in addition to a decay of the toroidal component. We show that, if the quadrupole component decays, the minimum initial toroidal field strength and the change in toroidal field strength needed to produce the observed anti-glitch are lower than in the pure dipole twisted torus. In addition, we predict the maximum anti-glitch sizes, assuming that they are caused by a change in ellipticity, in four glitching magnetars and discuss the implications for energetics of accompanying X-ray bursts.