Rm Ra Research Articles

Discovery of a split stellar stream in the periphery of the Small Magellanic Cloud

ABSTRACT I report the discovery of a stellar stream (Sutlej) using Gaia DR3 (third data release) proper motions and XP metallicities located $\sim$15° north of the Small Magellanic Cloud (SMC). The stream is composed of two parallel linear components (‘branches’) approximately $\sim$8° × 0.6° in size and separated by 2.5°. The stars have a mean proper motion of ($\mu _{\rm RA},\mu _{\rm Dec.}$) = (+0.08 mas yr−1, −1.41 mas yr−1), which is quite similar to the proper motion of stars on the western side of the SMC. The colour–magnitude diagram of the stream stars has a clear red giant branch, horizontal branch, and main-sequence turn-off that are well matched by a parsec isochrone of 10 Gyr, [Fe/H] = −1.8 at 32 kpc, and a total stellar mass of $\sim$33 000 M$_{\odot }$. The stream is spread out over an area of 9.6 deg2 and has a surface brightness of 32.5 mag arcsec−2. The metallicity of the stream stars from Gaia XP spectra extends over $-2.5$$\le$ [M/H] $\le$$-1.0$ with a median of [M/H] = −1.8. The tangential velocity of the stream stars is 214 km s−1 compared to the values of 448 km s−1 for the Large Magellanic Cloud and 428 km s−1 for the SMC. While the radial velocity of the stream is not yet known, a comparison of the space velocities using a range of assumed radial velocities shows that the stream is unlikely to be associated with the Magellanic Clouds. The tangential velocity vector is misaligned with the stream by nearly 90°, which might indicate an important gravitational influence from the nearby Magellanic Clouds.

Doping and gap size dependence of high-harmonic generation in graphene: Importance of consistent formulation of light-matter coupling

High-harmonic generation (HHG) in solids is a fundamental nonlinear phenomenon, which can be efficiently controlled by modifying system parameters such as doping-level and temperature. In order to correctly predict the dependence of HHG on these parameters, consistent theoretical formulation of the light-matter coupling is crucial. Recently, contributions to the current that are often missing in the HHG analysis based on the semiconductor Bloch equations have been pointed out [J. Wilhelm, et.al. PRB 103 125419 (2021)]. In this paper, by systematically analyzing the doping and gap-size dependence of HHG in gapped graphene, we discuss the practical impact of such terms. In particular, we focus on the role of the current $J_{\rm ra}^{(2)}$, which originates from the change of the intraband dipole via interband transition. When the gap is small and the system is close to half filling, intraband and interband currents mostly cancel, thus suppressing the HHG signal - an important property that is broken when neglecting $J_{\rm ra}^{(2)}$. Furthermore, without $J_{\rm ra}^{(2)}$, the doping and gap-size dependence of HHG becomes qualitatively different from the full evaluation. Our results demonstrate the importance of the consistent expression of the current to study the parameter dependence of HHG for the small gap systems.

Reservoir computing model of two-dimensional turbulent convection

Reservoir computing is applied to model the large-scale evolution and the resulting low-order turbulence statistics of a two-dimensional turbulent Rayleigh-B\'{e}nard convection flow at a Rayleigh number ${\rm Ra}=10^7$ and a Prandtl number ${\rm Pr}=7$ in an extended domain with an aspect ratio of 6. Our data-driven approach which is based on a long-term direct numerical simulation of the convection flow comprises a two-step procedure. (1) Reduction of the original simulation data by a Proper Orthogonal Decomposition (POD) snapshot analysis and subsequent truncation to the first 150 POD modes which are associated with the largest total energy amplitudes. (2) Setup and optimization of a reservoir computing model to describe the dynamical evolution of these 150 degrees of freedom and thus the large-scale evolution of the convection flow. The quality of the prediction of the reservoir computing model is comprehensively tested. At the core of the model is the reservoir, a very large sparse random network charcterized by the spectral radius of the corresponding adjacency matrix and a few further hyperparameters which are varied to investigate the quality of the prediction. Our work demonstrates that the reservoir computing model is capable to model the large-scale structure and low-order statistics of turbulent convection which can open new avenues for modeling mesoscale convection processes in larger circulation models.

Lagrangian coherent sets in turbulent Rayleigh-Bénard convection.

Coherent circulation rolls and their relevance for the turbulent heat transfer in a two-dimensional Rayleigh-Bénard convection model are analyzed. The flow is in a closed cell of aspect ratio four at a Rayleigh number Ra=10^{6} and at a Prandtl number Pr=10. Three different Lagrangian analysis techniques based on graph Laplacians (distance spectral trajectory clustering, time-averaged diffusion maps, and finite-element based dynamic Laplacian discretization) are used to monitor the turbulent fields along trajectories of massless Lagrangian particles in the evolving turbulent convection flow. The three methods are compared to each other and the obtained coherent sets are related to results from an analysis in the Eulerian frame of reference. We show that the results of these methods agree with each other and that Lagrangian and Eulerian coherent sets form basically a disjoint union of the flow domain. Additionally, a windowed time averaging of variable interval length is performed to study the degree of coherence as a function of this additional coarse graining which removes small-scale fluctuations that cause trajectories to disperse quickly. Finally, the coherent set framework is extended to study heat transport.

Thermal convection in rotating spherical shells: Temperature-dependent internal heat generation using the example of triple- α burning in neutron stars

We present an extensive study of Boussinesq thermal convection including a temperature-dependent internal heating source, based on numerical three-dimensional simulations. The temperature dependence mimics triple-$\alpha$ nuclear reactions and the fluid geometry is a rotating spherical shell. These are key ingredients for the study of convective accreting neutron star oceans. A dimensionless parameter ${{\rm Ra}}_n$, measuring the relevance of nuclear heating, is defined. We explore how flow characteristics change with increasing ${{\rm Ra}}_n$ and give an astrophysical motivation. The onset of convection is investigated with respect to this parameter and periodic, quasiperiodic, chaotic flows with coherent structures, and fully turbulent flows are exhibited as ${{\rm Ra}}_n$ is varied. Several regime transitions are identified and compared with previous results on differentially heated convection. Finally, we explore (tentatively) the potential applicability of our results to the evolution of thermonuclear bursts in accreting neutron star oceans.

Transition to turbulence scaling in Rayleigh-Bénard convection

If a fluid flow is driven by a weak Gaussian random force, the nonlinearity in the Navier-Stokes equations is negligibly small and the resulting velocity field obeys Gaussian statistics. Nonlinear effects become important as the driving becomes stronger and a transition occurs to turbulence with anomalous scaling of velocity increments and derivatives. This process has been described by V. Yakhot and D. A. Donzis, Phys. Rev. Lett. 119, 044501 (2017) for homogeneous and isotropic turbulence (HIT). In more realistic flows driven by complex physical phenomena, such as instabilities and nonlocal forces, the initial state itself, and the transition to turbulence from that initial state, are much more complex. In this paper, we discuss the Reynolds-number-dependence of moments of the kinetic energy dissipation rate of orders 2 and 3 obtained in the bulk of thermal convection in the Rayleigh-B\'{e}nard system. The data are obtained from three-dimensional spectral element direct numerical simulations in a cell with square cross section and aspect ratio 25 by A. Pandey et al., Nat. Commun. 9, 2118 (2018). Different Reynolds numbers $1 \lesssim {\rm Re}_{\ell} \lesssim 1000$ which are based on the thickness of the bulk region $\ell$ and the corresponding root-mean-square velocity are obtained by varying the Prandtl number Pr from 0.005 to 100 at a fixed Rayleigh number ${\rm Ra}=10^5$. A few specific features of the data agree with the theory but the normalized moments of the kinetic energy dissipation rate, ${\cal E}_n$, show a non-monotonic dependence for small Reynolds numbers before obeying the algebraic scaling prediction for the turbulent state. Implications and reasons for this behavior are discussed.

Nearby groups of galaxies in the Hercules–Bootes constellations

We consider a sample of 412 galaxies with radial velocities $V_{\rm LG} < 2500$ km s$^{-1}$ situated in the sky region of ${\rm RA}=13^h\hspace{-0.4em}.\,0$ ... $19^h\hspace{-0.4em}.\,0$, ${\rm Dec}=+10^{\circ}$ ... $+40^{\circ}$ between the Local Void and the Supergalactic plane. One hundred and eighty-one of them have individual distance estimates. Peculiar velocities of the galaxies as a function of Supergalactic latitude SGB show signs of Virgocentric infall at $SGB < 10^{\circ}$ and motion from the Local Void at $SGB > 60^{\circ}$. A half of the Hercules-Bootes galaxies belong to 17 groups and 29 pairs, with the richest group around NGC5353. A typical group is characterized by the velocity dispersion of $67$ km s$^{-1}$, the harmonic radius of $182$ kpc, the stellar mass of $4.3 \times10^{10} M_{\odot}$ and the virial-to-stellar mass ratio of $32$. The binary galaxies have the mean radial velocity difference of $37$ km s$^{-1}$, the projected separation of $96$ kpc, the mean integral stellar mass of $2.6\times 10^9 M_{\odot}$ and the mean virial-to-stellar mass ratio of about $8$. The total dark-matter-to-stellar mass ratio in the considered sky region amounts to $37$ being almost the same as that in the Local Volume.

Discovery of the VHE gamma-ray source HESS J1832-093 in the vicinity of SNR G22.7-0.2

The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the H.E.S.S. Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HESS J1832-093, at the position $\rm RA=18^h 32^m 50^s \pm 3^s_{stat} \pm 2^s_{syst}, \rm Dec=-9^\circ 22' 36'' \pm 32''_{stat} \pm 20''_{syst} (J2000)$, spatially coincident with a part of the radio shell of the neighboring remnant G22.7-0.2. The photon spectrum is well described by a power-law of index $\Gamma = 2.6 \pm 0.3_{\rm stat} \pm 0.1_{\rm syst}$ and a normalization at 1 TeV of $\Phi_0=(4.8 \pm 0.8_{\rm stat}\pm 1.0_{\rm syst})\,\times\,10^{-13}\,\rm{cm} ^{-2}\,s^{-1}\,TeV^{-1}$. The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic-rays illuminating a nearby molecular cloud. Then a dedicated XMM-Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832-093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multi-wavelength observations will help to shed new light on this intriguing VHE source.

Computational Analysis of Three-Dimensional Unsteady Natural Convection and Entropy Generation in a Cubical Enclosure Filled with Water-Al2O3 Nanofluid

Effects of Rayleigh number, solid volume fraction and entropy generation on the natural convection heat transfer and fluid flow inside a three-dimensional cubical enclosure filled with water-Al2O3 nanofluid have been investigated numerically using the control volume finite difference method. The enclosure left sidewall is maintained at isothermal hot temperature, while the right one is maintained at isothermal cold temperature. The other enclosure walls are considered adiabatic. The second law of thermodynamics is applied to predict the nature of irreversibility in terms of entropy generation rate. Numerical computations are carried out for Rayleigh numbers from $${(10^{3} \leq {\rm Ra} \leq 10^{6})}$$ , solid volume fraction from $${(0\% \leq \varphi\, \leq 20\%)}$$ , while the Prandtl number of water is considered constant as (Pr = 6.2). Streamlines, isothermal lines, counters of local and total entropy generation and the variation of Bejan number, local and average Nusselt numbers are presented and discussed in detail. The results explain that the average Nusselt number increases when the solid volume fraction of nanoparticles and the Rayleigh number increase. Also, the Bejan and average Nusselt numbers have a reverse behavior to each other for the same range of Rayleigh number and solid volume fraction. In addition, the results show that the entropy generation rate due to heat transfer, friction and the total entropy generation increase as the solid volume fraction increases, while it increases highly when the Rayleigh number increases especially near the hot left sidewall.

An Analytical Model to Quantify Decay Chain Disequilibrium–Application to the Thorium Decay Chain

An emissivity model, generalized to disequilibrium states of radioactive decay chains, is used to study the effects of thorium decay chain disequilibrium on alpha emissivity. The results show that even if the alpha emissivity produced by the thorium decay chain is initially acceptable, it can increase significantly during the device lifetime. Three radionuclides in the thorium chain are responsible for the increase: ${}^{232}{\rm Th}$ , ${}^{228}{\rm Th}$ , and ${}^{228}{\rm Ra}$ . Their initial concentrations determine the evolution of the emissivity during the device lifetime.

Multipolar Approach for Description of Bremsstrahlung During α -Decay and Unified Formula of the Bremsstrahlung Probability

Model of angular bremsstrahlung of photons emitted during $\alpha$-decay is presented. A special emphasis is given on development of unified formalism of matrix elements in the dipole and multipolar approaches. A probability of the emission of photons calculated on the basis of the multipole model without any normalization on experimental data (i. e. in absolute scale) is found at $90^{\circ}$ of the angle $\vartheta_{\alpha\gamma}$ between directions of motion of the $\alpha$-particle (with its tunneling under barrier) and emission of photons to be in a good agreement with the newest experimental data for the $^{210}{\rm Po}$, $^{214}{\rm Po}$, and $^{226}{\rm Ra}$ nuclei. The spectrum for $^{244}{\rm Cm}$ is found at $\vartheta_{\alpha\gamma} = 25^{\circ}$ to be in satisfactory agreement with high limit of errors of experimental data of Japanese group. A comparative analysis for the spectra calculated for $^{210}{\rm Po}$ by the multipole and dipole approaches in the absolute scale and with normalization on experimental data is performed. The emission of photons from the internal well in the dipole approach is found to be not small while the multipolar approach does not show such a strong dependence. Distribution of the bremsstrahlung probability on the numbers of protons and nucleons of the $\alpha$-decaying nucleus in selected region close to $^{210}{\rm Po}$ is obtained. An unified formula of the bremsstrahlung probability during the $\alpha$-decay of arbitrary nucleus expressed directly through the $Q_{\alpha}$-value and numbers $A_{p}$, $Z_{p}$ of nucleons and protons of this nucleus is proposed.

Passive models of neurons in the deep cerebellar nuclei: the effect of reconstruction errors

The goal of this study was to determine how the fit of passive parameters in a compartmental model varies depending on the precise morphological reconstruction of the neuron. We performed whole-cell recordings of deep cerebellar nucleus neurons in brain slices, reconstructed the neuronal morphologies and converted them into detailed compartmental models. A genetic algorithm was used to find the best fit of specific capacitance CM, membrane resistance RM and axial resistivity RA of the model with recordings from the same cell. We then introduced morphological alterations that represented the likely consequence of shrinkage artefacts and reconstruction errors. We found that the optimal fits of passive parameters change as much as 173% with such morphological alterations. In addition, dendrites cut during slicing could affect the value of RM, but not CM or RA.

The 2dF Galaxy Redshift Survey: the population of nearby radio galaxies at the 1-mJy level

We use redshift determinations and spectral analysis of galaxies in the 2dF Galaxy Redshift Survey to study the properties of local radio sources with $S\ge 1$ mJy. 557 objects drawn from the FIRST survey, corresponding to 2.3 per cent of the total radio sample, are found in the 2dFGRS cataloge within the area $9^h 48^m \simlt {\rm RA}({\rm 2000}) \simlt 14^h 32^m$ and $-2.77^\circ \simlt {\rm dec}({\rm 2000}) \simlt 2.25^\circ$, down to a magnitude limit $b_J= 19.45$. The excellent quality of 2dF spectra allows us to divide these sources into classes, according to their optical spectra. Radio galaxies (i.e. absorption systems, mainly belonging to the class of FR I sources, whose spectra may or may not show emission lines due to AGN activity) make up 63 per cent of the spectroscopic sample; they are characterized by relatively high radio-to-optical ratios, red colours and luminosities $10^{21}\simlt P_{1.4{\rm GHz}} W Hz^${-1}$ sr$^{-1}$ \simlt 10^{24}$. Actively star-forming galaxies instead contribute with 30 per cent to the total sample. These objects -- principally found at low redshifts ($z \simlt 0.1$) -- in general show low radio-to-optical ratios, blue colours and low radio luminosities. We also found 18 Seyfert 2 galaxies and 4 Seyfert 1's. Analysis of the local radio luminosity function shows that radio galaxies are well described by models that assume pure luminosity evolution, at least down to radio powers $P_{1.4{\rm GHz}}\simlt 10^{20.5} W Hz$^{-1}$ sr$^{-1}$ Late-type galaxies, whose relative contribution to the RLF is found to be lower than was predicted by previous work, present a luminosity function which is compatible with the IRAS galaxy LF, and therefore plausibly constitute the radio counterpart of the dusty spirals and starbursts that dominate the counts at 60 $\mu$m.

Control of chromosomal DNA replication in the early Xenopus embryo.

In order for the genome to be faithfully maintained, chromosomal DNA must be precisely replicated and segregated in each cell cycle. Over the last decade an enormous amount has been learned about how this is achieved. Much of the progress has come from genetic analysis in yeast. However, biochemical analysis of cell cycle events using extracts prepared from eggs of the South African clawed toad Xenopus laevis has also played an important role. Although there are differences in the detailed regulation of the yeast and frog cell cycles, the basic cell cycle machinery appears to have been conserved throughout evolution. The results obtained in these model organisms, therefore, seem likely to be generally applicable to the cell cycles of all eukaryotes. ### Xenopus eggs and egg extracts The fertilized Xenopus egg undergoes 12 synchronous rounds of cell division in ∼8 h. These cell divisions take place in the absence of growth, subdividing the large (∼1 mm diameter) single‐celled egg into ∼4000 smaller cells. Transcription does not occur during these early embryonic divisions, although translation of pre‐existing maternal mRNA continues. Most of the proteins required for cell cycle progression are pre‐formed in the egg, and the continuing translation of a single protein (cyclin B) can support passage through the whole cell cycle (Murray and Kirschner, 1989). The stockpile of cell cycle proteins present in the Xenopus egg became exploitable by biochemical means following the development of cell‐free extracts that support all the nuclear events of the early embryonic cell division cycle (Lohka and Masui, 1983). Gentle lysis associated with minimal dilution of the cytoplasm yields a ‘low speed supernatant’ that maintains all the cell cycle activities present in the intact egg. These ‘low speed supernatants’ support precise rounds of DNA replication on exogenously added DNA templates, and like the intact egg, only re‐replicate DNA after passage through …

Plutonium-Induced Osteosarcomas in the St. Bernard

Fourteen osteosarcomas were observed among the eight St. Bernards that died following the injection of239 Pu. Early data tentatively indicate that the St. Bernard is about 5 times more sensitive than the beagle and about 130 times more sensitive than the average person is estimated to be to ${}^{239}{\rm Pu}\text{-induced}$ bone sarcomas. Thus the St. Bernard may be an excellent model in which to study the pathogenesis of bone cancer induction, to evaluate the relationship between spontaneous susceptibility and radiosensitivity, and to determine whether radiosensitivity significantly affects the toxicity ratio of ${}^{239}{\rm Pu}/{}^{226}{\rm Ra}$ .

Lifetime Studies of 226 Ra and 90 Sr Toxicity in Beagles: A Status Report

Beagles at the University of California at Davis injected with226 Ra or fed90 Sr have been under lifetime study for over 18 years. This report summarizes the dose-response observations to June 30, 1978, based upon the temporal average dose rate (rad/day) to the skeleton from initiation of exposure to death. Bone marrow dyscrasias were more numerous than bone cancers from90 Sr (in equilibrium with ${}^{90}{\rm Y}$ ) at dose rates to bone of about 2 to 20 rad/day, while bone cancers have been the dominating effect of ${}^{226}{\rm Ra}n$ (and associated progeny) at dose rates of from 0.5 to about 20 rad/day. No radiogenic effects are yet apparent for skeletal doses below 0.05 rad/day. Results to date indicate that although bone cancer continues to be the important endpoint for226 Ra, other cancer types appear to be more important for90 Sr (such as soft-tissue cancers adjacent to bone), particularly at late times from lower skeletal dose rates. Continued study of the 3...

Influence of 226 Ra on Bone Marrow Stem Cells in Mice: Effect of Radium Decorporation by a Long-Term Treatment with Na-Alginate on Stem-Cell Damage

Three-month-old male BALB/c mice were injected intraperitoneally with ${}^{226}{\rm RaCl}{}_{2}$ at dose levels of 4.5, 6.9, 9.0, and $13.5 \mu {\rm Ci} {}^{226}{\rm Ra}/{\rm kg}$ body wt. At the two highest doses, the number of multipotential bone marrow stem cells was severely depressed 8 weeks after the injection. By 30 weeks no depression was observed compared to controls. The number of peripheral red blood cells was never altered, while the number of white blood cells was slightly depressed after 8 weeks of contamination. Mice fed every other week with standard pellets and on alternate weeks with a diet containing 6% Na-alginate (first given 12 days after the injection of ${}^{226}{\rm RaCl}{}_{2}$ ) showed a significant reduction of stem-cell depression 8 and 12 weeks after contamination in three of the six treatment groups with manifest radiation effects on the stem cells.

Assessment of the 220 Rn Franction Retained in Mice after a Single Injection of 224 Ra

The time course of ${}^{224}{\rm Ra}$, ${}^{212}{\rm Pb}$, and212 Bi retention and220 Rn exhalation was measured in two groups of mice after a single intraperitoneal administration of ${}^{224}{\rm Ra}$. The retained220 Rn fraction was calculated using two approaches: (1) From measured activity of220 Rn in exhaled air and from ${}^{224}{\rm Ra}$ retention data. (2) From the measured ${}^{212}{\rm Pb}$ or212 Bi retention and using a theoretical time course of the retention of these radionuclides; it was assumed in this case that the retained220 Rn fraction is constant within the duration of the experiment, i.e., during the first 3 wk after ${}^{224}{\rm Ra}$ administration. The retained fractions found using the two approaches are in good agreement equaling 60-70% in both groups of mice; thus the fraction exhaled amounts to 30-40%.

Methods of Assay of the Relative Toxicity of Certain Bone-Seeking Radionuclides

Four methods of handling the dose-response relation in the data from the long-term experiment on the effects of certain radioisotopes administered intravenously to dogs at the University of Utah are presented and discussed. The results are cast in terms of the relative biological effectiveness of five radionuclides: ${}^{226}{\rm Ra},{}^{239}{\rm Pu},{}^{90}{\rm Sr},{}^{228}{\rm Ra}$, and228 Th for the production of bone cancers. One of the methods is based on quantal response (deaths from osteosarcomas), two are based on survival times, and the fourth is a modification of that proposed by Blair (which takes account of the induction period between dosage and the beginning of oncogenesis). There is evidence that Blair's approach has most merit.

Retention of Radium in Man

While a recent injection of ${}^{223}{\rm Ra}$ was retained as $t^{-0.50}$ , a long-term burden of226 Ra in the same man decreased as $t^{-1.7}$ . This dramatic difference in the rate of change of retention is predicted by the modified power function model with an observed rate of excretory plasma clearance of 126 liters/day. From the ${}^{223}{\rm Ra}$ data, the model predicts that the226 Ra burden should have reached transient equilibrium within the body ( $t_{{\rm y}}=6.7$ years) so that its retention today can be described by a final exponential. With a somewhat lower average rate of plasma clearance (72 liters/day, $t_{{\rm y}}=20$ years) the model would be consistent with the retention functions of Norris et al., Miller and Finkel, and the halftime for retention reported by Keane and Evans. Accordingly, it would be most interesting to measure the rates of plasma clearance in the...