Nuclear Species Research Articles

Nucleus-acoustic waves: Excitation, propagation, and stability

The propagatory excitation dynamics of the collective nucleus-acoustic waves supported in a strongly coupled self-gravitating degenerate quantum dusty plasma (QDP) system, widely realizable as the constitutive matter for white dwarfs and other compact astro-objects, is semi-analytically studied. The spherically symmetric QDP is composed of strongly coupled non-degenerate heavy nuclei, weakly coupled degenerate light nuclei, and non-relativistically and ultra-relativistically degenerate lighter electrons. A standard normal spherical mode analysis is applied to derive a complex generalized dispersion relation. A numerical illustrative calculation is executed in the ultra-low frequency approximation to see the dependency of various sensible parameters on the instability evolution. It is seen that the relative nuclear charge-mass coupling parameter (β) acts as a destabilizing and stabilizing agents in the non-relativistic (NR) and ultra-relativistic (UR) limits, respectively. The ratio of the charge density of heavy-to-light nuclear species (μ) acts as a destabilizer (stabilizer) in the NR (UR) limits, to the instability. The quantum parameter (H′) interestingly acts as a stabilizing agency in both the NR-UR limits.

The involvement of tau in nucleolar transcription and the stress response

Tau is known for its pathological role in neurodegenerative diseases, including Alzheimer’s disease (AD) and other tauopathies. Tau is found in many subcellular compartments such as the cytosol and the nucleus. Although its normal role in microtubule binding is well established, its nuclear role is still unclear. Here, we reveal that tau localises to the nucleolus in undifferentiated and differentiated neuroblastoma cells (SHSY5Y), where it associates with TIP5, a key player in heterochromatin stability and ribosomal DNA (rDNA) transcriptional repression. Immunogold labelling on human brain sample confirms the physiological relevance of this finding by showing tau within the nucleolus colocalises with TIP5. Depletion of tau results in an increase in rDNA transcription with an associated decrease in heterochromatin and DNA methylation, suggesting that under normal conditions tau is involved in silencing of the rDNA. Cellular stress induced by glutamate causes nucleolar stress associated with the redistribution of nucleolar non-phosphorylated tau, in a similar manner to fibrillarin, and nuclear upsurge of phosphorylated tau (Thr231) which doesn’t colocalise with fibrillarin or nucleolar tau. This suggests that stress may impact on different nuclear tau species. In addition to involvement in rDNA transcription, nucleolar non-phosphorylated tau also undergoes stress-induced redistribution similar to many nucleolar proteins.

The conservation implications of mixed-species flocking in terrestrial birds, a globally-distributed species interaction network

Conservation biologists now view species interaction networks as systems that should be targets of conservation, but there are few actual cases in which networks have formed the basis for management strategies. Terrestrial mixed-species bird flocks (hereafter, TMSF) represent one such potential system: they form throughout the world, and in most cases have an asymmetric organization in which one or a few species play ‘nuclear’ roles, being particularly important for flock formation or maintenance. A quantitative study on the distribution of TMSF and how they respond to anthropogenic disturbance (AD) is still, however, needed. We surveyed 201 publications on terrestrial TMSF worldwide, finding that 19% of the world's bird species participate in them, including 158 threatened species, with tropical species dominating these lists. Of 31 TMSF studies that investigated AD, 22 showed significant declines in some metric, with TMSF in more impacted areas including 1/4 fewer species, and 1/3 fewer individuals. In 13/15 studies, TMSF were more sensitive to AD than the overall bird community. We conceptualize the reasons behind this response: first, AD directly influences drivers of flocking (predation, foraging), and second, AD produces changes in community composition that affect TMSF, such as when the extirpation or reduction of nuclear species affects other species' participation. We rank nuclear species globally by their consistency of leadership and number of followers, suggesting that these species' interactive roles be considered as part of their conservation value, and further that conserving TMSF provides an efficient mechanism to ensure the protection of many species simultaneously.

Nuclear lipid mediators: Role of nuclear sphingolipids and sphingosine-1-phosphate signaling in epigenetic regulation of inflammation and gene expression.

Phospholipids, sphingolipids, and cholesterol are integral components of eukaryotic cell organelles, including the nucleus. Recent evidence shows characteristic features of nuclear lipid composition and signaling, which are distinct from that of the cytoplasm and plasma membrane. While the nuclear phosphoinositol lipid signaling in cell cycle regulation and differentiation has been well described, there is a paucity on the role of nuclear sphingolipids and sphingolipid signaling in different physiological and pathophysiological human conditions. In this prospective, we describe the role of sphingolipids and specifically focus on the sphingoid bases, such as sphingosine, ceramide, and sphingosine-1-phosphate (S1P) generation and catabolism in nuclear signaling and function. Particularly, S1P generated in the nucleus by phosphorylation of SPHK2 modulates HDAC activity either by direct binding or through activation of nuclear reactive oxygen species and regulates cell cycle and pro-inflammatory gene expression. Potential implication of association of SPHK2 with the co-repressor complexes and generation of S1P in the nucleus on chromatin remodeling under normal and pathological conditions is discussed. A better understanding of sphingolipid signaling in the nucleus will facilitate the design and development of new and novel therapeutic approaches to modulate expression of pro-inflammatory and cell cycle dependent genes in human pathologies such as cancer, bacterial lung infection, neurodegeneration, and cystic fibrosis.

From America to Eurasia: a multigenomes history of the genus Abies

The origin of conifer genera, the main components of mountain temperate and boreal forests, was deemed to arise in the Mesozoic, although paleontological records and molecular data point to a recent diversification, presumably related to Neogene cooling. The geographical area(s) where the modern lines of conifers emerged remains uncertain, as is the sequence of events leading to their present distribution. To gain further insights into the biogeography of firs (Abies), we conducted phylogenetic analyses of chloroplast, mitochondrial and nuclear markers. The species tree, generated from ten single-copy nuclear genes, yielded probably the best phylogenetic hypothesis available for Abies. The tree obtained from five regions of chloroplast DNA largely corresponded to the nuclear species tree. Ancestral area reconstructions based on fossil calibrated chloroplast DNA and nuclear DNA trees pointed to repeated intercontinental migrations. The mitochondrial DNA haplotype tree, however, disagreed with nuclear and chloroplast DNA trees. It consisted of two clusters: one included mainly American haplotypes, while the other was composed of only Eurasian haplotypes. Presumably, this conflict is due to inter-continental migrations and introgressive hybridization, accompanied by the capture of the mitotypes from aboriginal species by the invading firs. Given that several species inhabiting Northeastern Asia carry American mitotypes and mutations typical for the American cluster, whereas no Asian mitotypes were detected within the American species, we hypothesize that Abies migrated from America to Eurasia, but not in the opposite direction. The direction and age of intercontinental migrations in firs are congruent with other conifers, such as spruces and pines of subsection Strobus, suggesting that these events had the same cause.

Nuclear species in Peruvian Amazonian mixed-species flocks are differentially attractive to transient species and to each other

ABSTRACT In resident Amazonian mixed-species flocks, the pattern of attraction of transient species to nuclear Dusky-throated Antshrikes (Thamnomanes ardesiacus) and Long-winged Antwrens (Myrmotherula longipennis) and the pattern of heterospecific attraction between the nuclear species are undocumented. Patterns of attraction can help elucidate the nature of interspecific relationships (i.e., whether they are mutualistic, commensal, or parasitic). We played Dusky-throated Antshrike and Long-winged Antwren vocalizations to flocks and recorded how many transient species approached the playbacks, whether the antshrikes and antwrens were attracted to each other's playbacks, and how strongly they responded to the playbacks. More transient species were attracted to the antshrike vocalizations than antwren vocalizations, and more transient species were attracted to antwren than control vocalizations. Dusky-throated Antshrikes and Long-winged Antwrens approached each other's playback significantly more often than...

FIER: Software for analytical modeling of delayed gamma-ray spectra

A new software package, the Fission Induced Electromagnetic Response (FIER) code, has been developed to analytically predict delayed γ-ray spectra following fission. FIER uses evaluated nuclear data and solutions to the Bateman equations to calculate the time-dependent populations of fission products and their decay daughters resulting from irradiation of a fissionable isotope. These populations are then used in the calculation of γ-ray emission rates to obtain the corresponding delayed γ-ray spectra. FIER output was compared to experimental data obtained by irradiation of a 235U sample in the Godiva critical assembly. This investigation illuminated discrepancies in the input nuclear data libraries, showcasing the usefulness of FIER as a tool to address nuclear data deficiencies through comparison with experimental data. FIER provides traceability between γ-ray emissions and their contributing nuclear species, decay chains, and parent fission fragments, yielding a new capability for the nuclear science community.

COMPASS—A COMPAct decay spectroscopy set-up

A compact silicon detector array with high spatial granularity and fast, fully digital data recording has been developed and commissioned for the investigation of heavy and superheavy nuclear species. The detector array can be combined in close geometry with large volume germanium detectors. It offers comprehensive particle and photon coincidence and correlation spectroscopy by highly efficient evaporation residue, α, γ, conversion electron and X-ray detection supported by the high granularity of the implantation chip. Access to fast decay events in the sub-microsecond region is made possible by the fast timing properties of the digital signal processing. A novel Si-chip support design allows direct cooling of the Si-chips and short signal transport. The compact and modular mechanical design equipped with a standard flange facilitates its transport and connection to different separators at different ion beam facilities. After initial tests, first α-γ coincidence spectroscopy experiments have been performed at the LISE separator of GANIL in Caen, France, in FULIS (velocity filter) mode and at the velocity filter SHIP of GSI in Darmstadt, Germany.

Proton and Carbon-13 Dynamic Nuclear Polarization of Methylated β-Cyclodextrins.

1H and 13C dynamic nuclear polarizations have been studied in 13C-enriched β-cyclodextrins doped with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl free radical. 1H and 13C polarizations raised above 7.5 and 7%, respectively, and for both nuclear species, the transfer of polarization from the electron spins appears to be consistent with a thermal mixing scenario for a concentration of 9 13C nuclei per molecule. When the concentration is increased to 21 13C nuclei per molecule, a decrease in the spin-lattice relaxation and polarization buildup rates is observed. This reduction is associated with the bottleneck effect induced by the decrease in the number of electron spins per nucleus when both the nuclear spin-lattice relaxation and the polarization occur through the electron non-Zeeman reservoir. 13C nuclear spin-lattice relaxation has been studied in the 1.8-340 K range, and the effects of internal molecular motions and of the free radicals on the relaxation are discussed. 13C hyperpolarization performances and room-temperature spin-lattice relaxation times show that these are promising materials for future biomedical applications.

Ultra-high-energy cosmic rays from radio galaxies

Radio galaxies are intensively discussed as the sources of cosmic rays observed above about 3 × 1018 eV, called ultra-high energy cosmic rays (UHECRs). We present a first, systematic approach that takes the individual characteristics of these sources into account, as well as the impact of the extragalactic magnetic-field structures up to a distance of 120 Mpc. We use a mixed simulation setup, based on 3D simulations of UHECRs ejected by observed, individual radio galaxies taken out to a distance of 120 Mpc, and on 1D simulations over a continuous source distribution contributing from beyond 120 Mpc. Additionally, we include the ultra-luminous radio galaxy Cygnus A at a distance of about 250 Mpc, as its contribution is so strong that it must be considered as an individual point source. The implementation of the UHECR ejection in our simulation setup, both that of individual radio galaxies and the continuous source function, is based on a detailed consideration of the physics of radio jets and standard first-order Fermi acceleration. This allows to derive the spectrum of ejected UHECR as a function of radio luminosity, and at the same time provides an absolute normalization of the problem involving only a small set of parameters adjustable within narrow constraints. We show that the average contribution of radio galaxies taken over a very large volume cannot explain the observed features of UHECRs measured at Earth. However, we obtain excellent agreement with the spectrum, composition, and arrival-direction distribution of UHECRs measured by the Pierre Auger Observatory, if we assume that most UHECRs observed arise from only two sources: the ultra-luminous radio galaxy Cygnus A, providing a mostly light composition of nuclear species dominating up to about 6 × 1019 eV, and the nearest radio galaxy Centaurus A, providing a heavy composition dominating above 6 × 1019 eV . Here we have to assume that extragalactic magnetic fields out to 250 Mpc, which we did not include in the simulation, are able to isotropize the UHECR events {at about 8 EeV} arriving from Cygnus A. Even in this case, significant anisotropy correlated with Cygnus A and Centaurus A could be present at higher energies, and thus allow for differences in UHECR spectrum and composition between the northern and southern hemispheres. If this scenario can be confirmed, it would also imply that the UHECR flux in our local cosmic environment is significantly above the average throughout the universe.

Ab initio potential and rotational spectra of the CO-N2 complex.

Ab initio calculations of the intermolecular potential energy surface (PES) of CO-N2 have been carried out using the closed-shell single- and double-excitation coupled cluster approach with a non-iterative perturbative treatment of triple excitations method and the augmented correlation-consistent quadruple-zeta (aug-cc-pVQZ) basis set supplemented with midbond functions. The global minimum (De = 117.35 cm-1) of the four-dimensional PES corresponds to an approximately T-shaped structure with the N2 subunit forming the leg and CO the top. The bound rovibrational levels of the CO-N2 complex were calculated for total angular momenta J = 0-8 on this intermolecular potential surface. The calculated dissociation energies D0 are 75.60 and 76.79 cm-1 for the ortho-N2 (A-symmetry) and para-N2 (B-symmetry) nuclear spin modifications of CO-N2, respectively. Guided by these bound state calculations, a new millimeter-wave survey for the CO-N2 complex in the frequency range of 110-145 GHz was performed using the intracavity OROTRON jet spectrometer. Transitions not previously observed were detected and assigned to the subbands connecting the K = 0 and 1, (jCO, jN2 ) = (1, 0) states with a new K = 1, (jCO, jN2 ) = (2, 0) state. Finally, the measured rotational energy levels of the CO-N2 complex were compared to the theoretical bound state results, thus providing a critical test of the quality of the PES presented. The computed rovibrational wave functions were analyzed to characterize the nature of the different bound states observed for the two nuclear spin species of CO-N2.

Follower fish of the goldspotted eel Myrichthys ocellatus with a review on anguilliform fish as nuclear species

In a nuclear-follower fish foraging association, the follower benefits from food uncovered or flushed out when the nuclear fish disturbs the bottom, while nuclear species generally do not seem to be benefiting. Among nuclear species, eels (anguilliform fish) are known to be one of the most represented groups. Here we investigated the frequency and time duration of foraging associations among the goldspotted eel Myrichthys ocellatus and reef fish in a subtropical marginal reef. In addition, we reviewed nuclear eel species and their followers described in the literature. From a total of 211 goldspotted eels observed, seven follower species were recorded in 19% of the samples. The average time of the following associations per species ranged from 40 to 190 s. Four species were reported for the first time as M. ocellatus followers (Bodianus rufus, B. pulchellus, Stephanolepis hispidus, and Serranus baldwini) and three of them have never been reported in the literature as eel followers (B. pulchellus, S. hispidus, and S. baldwini). The literature describes 13 eel species acting as nuclear for 66 fish species, represented mainly by groupers and sea basses. The size of the eel was not correlated with the size of its follower and neither with the number of described follower species. The nuclear role of eels is likely to be an important component of the trophic ecology of small and medium-sized macrocarnivore fish.

Role of nuclear reactions on stellar evolution of intermediate-mass stars

The evolution of intermediate-mass stars (8 - 12 solar masses) represents one of the most challenging subjects in nuclear astrophysics. Their final fate is highly uncertain and strongly model dependent. They can become white dwarfs, they can undergo electron-capture or core-collapse supernovae or they might even proceed towards explosive oxygen burning and a subsequent thermonuclear explosion. We believe that an accurate description of nuclear reactions is crucial for the determination of the pre-supernova structure of these stars. We argue that due to the possible development of an oxygen-deflagration, a hydrodynamic description has to be used. We implement a nuclear reaction network with ∼200 nuclear species into the implicit hydrodynamic code AGILE. The reaction network considers all relevant nuclear electron captures and beta-decays. For selected relevant nuclear species, we include a set of updated reaction rates, for which we discuss the role for the evolution of the stellar core, at the example of selected stellar models. We find that the final fate of these intermediate-mass stars depends sensitively on the density threshold for weak processes that deleptonize the core.

Super Heavy Elements - experimental developments

With his theoretical work Walter Greiner, our mentor, pioneered super heavy element research and motivated us young scientists. He actively shaped the profile of GSI. We are happy that still during his lifetime we could prove some of his predictions: Fusion with magic nuclei paving the way to super heavy elements and the proof of the prediction of the nuclear species existing only by shell stabilization, super heavy elements. With the discovery of oganesson, Z=118, the heaviest element known today, we have come to the end of this era. New experimental developments will be discussed.

Experimental study of materials radiation resistance in reactor mixed fields for the construction of the SPES facility at LNL

The Selective Production of Exotic Species (SPES) facility, now under construction at Legnaro National Laboratories of INFN, is a second-generation accelerator for the production of neutron-rich ion beams. The radioactive nuclear species are produced by fission of a [Formula: see text]U target, on which a 200[Formula: see text][Formula: see text]A primary proton beam of 40[Formula: see text]MeV energy impinges. Materials and components constituting the Target and Ion Source assembly and the Front-End supporting structure are subjected to serious radioactive damage due to intense neutron and photon fields present under operating conditions. In the framework of the SPES project, experimental campaigns aimed at testing the radiation hardness of critical materials and components of potential use in the construction were started. Irradiations were conducted in a reactor mixed field of neutrons and photons in order to reproduce, as close as possible, the actual environmental service conditions. Results obtained for different types of elastomeric materials used for construction of vacuum O-rings, as well as preliminary results obtained for lubricating oils and greases, are presented. Materials under consideration are both conventional ones as well as materials specifically developed for applications in the presence of ionizing radiation. The latter materials were previously tested mainly in gamma radiation fields.

Relativistic analogue of the Newtonian fluid energy equation with nucleosynthesis

In Newtonian fluid dynamics simulations in which composition has been tracked by a nuclear reaction network, energy generation due to composition changes has generally been handled as a separate source term in the energy equation. A relativistic equation in conservative form for total fluid energy, obtained from the spacetime divergence of the stress-energy tensor, in principle encompasses such energy generation; but it is not explicitly manifest. An alternative relativistic energy equation in conservative form---in which the nuclear energy generation appears explicitly, and that reduces directly to the Newtonian $\text{internal}+\text{kinetic energy}\text{ }$ in the appropriate limit---emerges naturally and self-consistently from the difference of the equation for total fluid energy and the equation for baryon number conservation multiplied by the average baryon mass $m$, when $m$ is expressed in terms of contributions from the nuclear species in the fluid, and allowed to be mutable.

Mitonuclear discordance as a confounding factor in the DNA taxonomy of monogonont rotifers

Discordance between mitochondrial and nuclear phylogenies is being increasingly recognized in animals and may confound DNA‐based taxonomy. This is especially relevant for taxa whose microscopic size often challenges any effort to distinguish between cryptic species without the assistance of molecular data. Regarding mitonuclear discordance, two strikingly contrasting scenarios have been recently demonstrated in the monogonont rotifers of the genus Brachionus. While strict mitonuclear concordance was observed in the marine B. plicatilis species complex, widespread hybridization‐driven mitonuclear discordance was revealed in the freshwater B. calyciflorus species complex. Here, we investigated the frequency of occurrence and the potential drivers of mitonuclear discordance in three additional freshwater monogonont rotifer taxa, and assessed its potential impact on the reliability of DNA taxonomy results based on commonly used single markers. We studied the cryptic species complexes of Keratella cochlearis, Polyarthra dolichoptera and Synchaeta pectinata. Phylogenetic reconstructions were based on the mitochondrial barcoding marker cytochrome c oxidase subunit I gene and the nuclear internal transcribed spacer 1 locus, which currently represent the two most typical genetic markers used in rotifer DNA taxonomy. Species were delimited according to each marker separately using a combination of tree‐based coalescent, distance‐based and allele‐sharing‐based approaches. Mitonuclear discordance was observed in all species complexes with incomplete lineage sorting and unresolved phylogenetic reconstructions recognized as the likely drivers. Evidence from additional sources, such as morphology and ecology, is thus advisable for deciding between often contrasting mitochondrial and nuclear species scenarios in these organisms.

SkyNet: A Modular Nuclear Reaction Network Library

Almost all of the elements heavier than hydrogen that are present in our solar system were produced by nuclear burning processes either in the early universe or at some point in the life cycle of stars. In all of these environments, there are dozens to thousands of nuclear species that interact with each other to produce successively heavier elements. In this paper, we present SkyNet, a new general-purpose nuclear reaction network that evolves the abundances of nuclear species under the influence of nuclear reactions. SkyNet can be used to compute the nucleosynthesis evolution in all astrophysical scenarios where nucleosynthesis occurs. SkyNet is free and open-source and aims to be easy to use and flexible. Any list of isotopes can be evolved and SkyNet supports various different types of nuclear reactions. SkyNet is modular so that new or existing physics, like nuclear reactions or equations of state, can easily be added or modified. Here, we present in detail the physics implemented in SkyNet with a focus on a self-consistent transition to and from nuclear statistical equilibrium (NSE) to non-equilibrium nuclear burning, our implementation of electron screening, and coupling of the network to an equation of state. We also present comprehensive code tests and comparisons with existing nuclear reaction networks. We find that SkyNet agrees with published results and other codes to an accuracy of a few percent. Discrepancies, where they exist, can be traced to differences in the physics implementations.

Binary and ternary ionic compounds in the outer crust of accreted neutron stars

The outer crust of an accreted neutron star is thought to contain a large distribution of different nuclear species resulting from the burying of ashes of X-ray bursts and superbursts. By analysing the stability of multicomponent Coulomb crystals against phase separation, it is found that various binary and ternary ionic compounds could be formed.

Planar and non-planar nucleus-acoustic shock structures in self-gravitating degenerate quantum plasma systems

The basic properties of planar and non-planar (spherical and cylindrical) nucleus-acoustic (NA) shock structures (SSs) in a strongly coupled self-gravitating degenerate quantum plasma system (containing strongly coupled non-relativistically degenerate heavy nuclear species, weakly coupled non-relativistically degenerate light nuclear species, and inertialess non-/ultra-relativistically degenerate electrons) have been investigated. The generalized quantum hydrodynamic model and the reductive perturbation method have been used to derive the modified Burgers equation. It is shown that the strong correlation among heavy nuclear species acts as the source of dissipation and is responsible for the formation of the NA SSs with positive (negative) electrostatic (self-gravitational) potential. It is also observed that the effects of non-/ultra-relativistically degenerate electron pressure, dynamics of non-relativistically degenerate light nuclear species, spherical geometry, etc., significantly modify the basic features of the NA SSs. The applications of our results in astrophysical compact objects like white dwarfs and neutron stars are briefly discussed.