Nuclear Species Research Articles

Observations of mixed-species bird flocks at Kichwa Tembo Camp, Kenya

Mixed-species foraging flocks were studied at Kichwa Tembo Camp on the edge of the Masai Mara National Reserve in Kenya between July and September 2004. Observations were made on 29 mixed-species flocks, in which 24 species participated. African Paradise-Flycatcher Terpsiphone viridis, Black-backed Puffback Dryoscopus cubla, Grey-backed Camaroptera Camaroptera brachyura, Collared Sunbird Hedydipna collars and Cabanis's Greenbul Phyllastrephus cabanisi were the most common participants in mixed-species flocks, as well as among the most frequently encountered bird species overall. The Black-backed Puffback was identified as the nuclear species in flocks due to their abundance and frequency with which they were followed by other species. Mixed-species flocks represent another niche dimension in this diverse bird community, but few of these species could be described as flock specialists; most of the birds observed in mixed-species flocks in this study were opportunistic attendant species, including the African Pygmy-Kingfisher Ispidina picta, not previously described as joining mixed-species flocks.

Evolution and nucleosynthesis of extremely metal-poor and metal-free low- and intermediate-mass stars

Models of primordial and hyper-metal-poor stars with masses similar to the Sun experience an ingestion of protons into the hot core during the core helium flash phase at the end of their red giant branch evolution. This produces a concurrent secondary flash powered by hydrogen burning that gives rise to further nucleosynthesis in the core. We perform post-process nucleosynthesis calculations on a one-dimensional stellar evolution calculation of a star of 1 solar mass and metallicity [Fe/H] = -6.5 that suffers a proton ingestion episode. Our network includes 320 nuclear species and 2,366 reactions and treats mixing and burning simultaneously. The mixing and burning of protons into the hot convective core leads to the production of 13C, which then burns via the 13C(alpha,n)16O reaction releasing a large number of free neutrons. During the first two years of neutron production the neutron poison 14N abundance is low, allowing the prodigious production of heavy elements such as strontium, barium, and lead via slow neutron captures (the s process). These nucleosynthetic products are later mixed to the stellar surface and ejected via stellar winds. We compare our results with observations of the hyper-metal-poor halo star HE 1327-2326, which shows a strong Sr overabundance. Our model provides the possibility of self-consistently explaining the Sr overabundance in HE 1327-2326 together with its C, N, and O overabundances (all within a factor of ~4) if the material were heavily diluted, for example, via mass transfer in a wide binary system. The model produces at least 18 times too much Ba than observed, but this may be within the large modelling uncertainties. In this scenario, binary systems of low mass must have formed in the early Universe. If true then this puts constraints on the primordial initial mass function.

Non-linear diffusive acceleration of heavy nuclei in supernova remnant shocks

We describe a semi-analytical approach to non-linear diffusive shock acceleration in the case in which nuclei other than protons are also accelerated. The structure of the shock is determined by the complex interplay of all nuclei, and in turn this shock structure determines the spectra of all components. The magnetic field amplification upstream is described as due to streaming instability of all nuclear species. The amplified magnetic field is then taken into account for its dynamical feedback on the shock structure as well as in terms of the induced modification of the velocity of the scattering centers that enters the particle transport equation. The spectra of accelerated particles are steep enough to be compared with observed cosmic ray spectra only if the magnetic field is sufficiently amplified and the scattering centers have high speed in the frame of the background plasma. We discuss the implications of this generalized approach on the structure of the knee in the all-particle cosmic ray spectrum, which we interpret as due to an increasingly heavier chemical composition above 10 15 eV. The effects of a non trivial chemical composition at the sources on the gamma ray emission from a supernova remnant when gamma rays are of hadronic origin are also discussed.

Low-Field MR Coils: Comparison between Strip and Wire Conductors

This work describes how the cross-sectional shape of radio-frequency coil conductors affects coils performance. This is of particular importance at low Larmor frequencies such as those of low-field magnetic resonance imaging systems where conductor and capacitor losses are the dominant power dissipation mechanisms. We demonstrate that conductors having a circular cross section allow the coil to achieve significantly better performance than the one built using flat strips. The change in coil quality factor due to conductor geometry was verified to be due only to changes in the conductors’ resistance and not their inductance. The results are not limited to low-field proton imaging but they are equally applicable to other situations where the Larmor frequency is in the megahertz range, including nuclear magnetic resonance of other nuclear species at intermediate fields.

Variational Approach to Nuclear Matter

We calculated the energies of asymmetric nuclear matter at zero and finite temperatures with the cluster variational method. At zero temperature, the expectation value of the two-body Hamiltonian composed of the kinetic energies and the AV18 two-bo dy forces is calculated with the Jastrow wave function in the two-body cluster approximation. The obtained two-body energy is in good agreement with the result with the Fermi Hypernetted Chain (FHNC) calculation by Akmal et al. The energy caused by the UI X three-body forces is treated somewhat phenomenologically so that the total energy reproduces the empirical saturation point. Furthermore, the parameters included in the three-body energy are readjusted so that the Thomas-Fermi (TF) calculations with use of the obtained energy of nuclear matter reproduce the gross feature of the experimental data on atomic nuclei. The nuclear species in the neutron star crust obtained by the TF calculation are reasonable. The free energies of asymmetric nuclear matter at finite temperatures are calculated with an extension of the method proposed by Schmidt and Pandharipande. The obtained free energies are in good agreement with those with the FHNC method, and it is also found that the present variational method is self-c onsistent. It is remarkable that the symmetry free energy is not proportional to (1 - 2x)(2), where x is the proton fraction. With use of the obtained thermodynamic quantities, we are constructing a new nuclear equation of state for supernova simulations.

The nuclear question: rethinking species importance in multi‐species animal groups

1. Animals group for various benefits, and may form either simple single-species groups, or more complex multi-species associations. Multi-species groups are thought to provide anti-predator and foraging benefits to participant individuals. 2. Despite detailed studies on multi-species animal groups, the importance of species in group initiation and maintenance is still rated qualitatively as 'nuclear' (maintaining groups) or 'attendant' (species following nuclear species) based on species-specific traits. This overly simplifies and limits understanding of inherently complex associations, and is biologically unrealistic, because species roles in multi-species groups are: (i) likely to be context-specific and not simply a fixed species property, and (ii) much more variable than this dichotomy indicates. 3. We propose a new view of species importance (measured as number of inter-species associations), along a continuum from 'most nuclear' to 'least nuclear'. Using mixed-species bird flocks from a tropical rainforest in India as an example, we derive inter-species association measures from randomizations on bird species abundance data (which takes into account species 'availability') and data on 86 mixed-species flocks from two different flock types. Our results show that the number and average strength of inter-species associations covary positively, and we argue that species with many, strong associations are the most nuclear. 4. From our data, group size and foraging method are ecological and behavioural traits of species that best explain nuclearity in mixed-species bird flocks. Parallels have been observed in multi-species fish shoals, in which group size and foraging method, as well as diet, have been shown to correlate with nuclearity. Further, the context in which multi-species groups occur, in conjunction with species-specific traits, influences the role played by a species in a multi-species group, and this highlights the importance of extrinsic factors in shaping species importance. 5. Our view of nuclearity provides predictive power in examining species roles in a variety of situations (e.g. predicting leadership in differently composed communities), and can be applied to examine a broad range of ecological and evolutionary questions pertinent to multi-species groups in general.

Loss of Cystic Fibrosis Transmembrane Conductance Regulator Function Enhances Activation of p38 and ERK MAPKs, Increasing Interleukin-6 Synthesis in Airway Epithelial Cells Exposed to Pseudomonas aeruginosa

In cystic fibrosis (CF), the absence of functional cystic fibrosis transmembrane conductance regulator (CFTR) translates into chronic bacterial infection, excessive inflammation, tissue damage, impaired lung function and eventual death. Understanding the mechanisms underlying this vicious circle of inflammation is important to design better therapies for CF. We found in CF lung biopsies increased immunoreactivity for p38 MAPK activity markers. Moreover, when compared with their non-CF counterpart, airway epithelial cells expressing the most common mutation in CF (CFTRDeltaF508) were more potent at inducing neutrophil chemotaxis through increased interleukin (IL)-6 synthesis when challenged with Pseudomonas aeruginosa diffusible material. We then discovered that in CFTRDeltaF508 cells, the p38 and ERK MAPKs are hyperactivated in response to P. aeruginosa diffusible material, leading to increased IL-6 mRNA expression and stability. Moreover, although TLR5 contributes to p38 MAPK activation upon P. aeruginosa challenge, it only played a weak role in IL-6 synthesis. Instead, we found that the production of reactive oxygen species is essential for IL-6 synthesis in response to P. aeruginosa diffusible material. Finally, we uncovered that in CFTRDeltaF508 cells, the extracellular glutathione levels are decreased, leading to a greater sensitivity to reactive oxygen species, providing an explanation for the hyperactivation of the p38 and ERK MAPKs and increased IL-6 synthesis. Taken together, our study has characterized a mechanism whereby the CFTRDeltaF508 mutation in airway epithelial cells contributes to increase inflammation of the airways.

Statistical approach for supernova matter

We formulate a statistical approach for description of nuclear composition and equation of state of stellar matter at subnuclear densities and temperature up to 20 MeV, which are expected during the collapse and explosion of massive stars. The model includes nuclear, electromagnetic and weak reactions between all constituents of matter, under condition of statistical equilibrium. We construct a realistic ensemble of nuclear species, and demonstrate the differences from the models employing a single-nucleus approximation for heavy nuclei. Thermodynamical characteristics, isentropic trajectories, EOS, and nuclear composition of supernova matter are calculated for different values of the lepton fraction. Special attention is paid to a possible in-medium reduction of the nuclear symmetry energy, as suggested by nuclear multifragmentation experiments. We demonstrate that this effect may lead to significant modifications of the nuclear composition and electron capture rates, which are important for stellar dynamics and nucleosynthesis.

Inhibition of NEDD8-activating enzyme: a novel approach for the treatment of acute myeloid leukemia

AbstractNEDD8 activating enzyme (NAE) has been identified as an essential regulator of the NEDD8 conjugation pathway, which controls the degradation of many proteins with important roles in cell-cycle progression, DNA damage, and stress responses. Here we report that MLN4924, a novel inhibitor of NAE, has potent activity in acute myeloid leukemia (AML) models. MLN4924 induced cell death in AML cell lines and primary patient specimens independent of Fms-like tyrosine kinase 3 expression and stromal-mediated survival signaling and led to the stabilization of key NAE targets, inhibition of nuclear factor-κB activity, DNA damage, and reactive oxygen species generation. Disruption of cellular redox status was shown to be a key event in MLN4924-induced apoptosis. Administration of MLN4924 to mice bearing AML xenografts led to stable disease regression and inhibition of NEDDylated cullins. Our findings indicate that MLN4924 is a highly promising novel agent that has advanced into clinical trials for the treatment of AML.

Free-induction decay and envelope modulations in a narrowed nuclear spin bath

We evaluate free-induction decay for the transverse components of a localized electron spin coupled to a bath of nuclear spins via the Fermi-contact hyperfine interaction. Our perturbative treatment is valid for special (narrowed) bath initial conditions and when the Zeeman energy of the electron $b$ exceeds the total hyperfine coupling constant $A$: $b>A$. Using one unified and systematic method, we recover previous results reported at short and long times using different techniques. We find an unexpected modulation of the free-induction-decay envelope, which is present even for a purely isotropic hyperfine interaction without spin echoes and for a single nuclear species. We give subleading corrections to the decoherence rate, and show that, in general, the decoherence rate has a nonmonotonic dependence on electron Zeeman splitting, leading to a pronounced maximum. These results illustrate the limitations of methods that make use of leading-order effective Hamiltonians and re-exponentiation of short-time expansions for a strongly interacting system with non-Markovian (history-dependent) dynamics.

High‐resolution NMR correlation experiments in a single measurement (HR‐PANACEA)

Three important NMR pulse sequences, INADEQUATE, HSQC and three-dimensional HMBC have been combined into a single entity called high-resolution Parallel Acquisition NMR: an All-in-one Combination of Experimental Applications (HR-PANACEA) to provide reliable structural information about a small molecule in a single measurement. This exploits a recent instrumental development that permits simultaneous acquisition of signals from several nuclear species, using multiple receivers. Where high-precision values of the long-range heteronuclear splittings are important, selected regions of a large experimental data matrix are extracted and examined with the highest possible resolution. The J-doubling technique is then applied to derive precise values for these couplings. As proof of principle, the method is applied to the molecule of methyl salicylate, confirming the expected conformation of the C-O-H moiety.

Double-Λ Hypernuclei via the [formula omitted] Hyperon Capture at Rest Reaction in a Hybrid Emulsion

We have obtained nearly one thousand events of the Ξ − hyperon captured at rest in nuclear emulsion. Among them, production and decay of double-Λ hypernuclei was successfully found and analyzed for five events which correspond to five nuclear species with double strangeness. Preliminary results are discussed for the binding energy and interaction energy of two Λ hyperons. By comparison with older data, the excitation energy of the Be Λ Λ 10 nucleus is also discussed. A new experiment,which is expected to provide 10 times more double-strangeness events than before, is introduced.

The radiation environment in the ISS-USLab measured by ALTEA: Spectra and relative nuclear abundances in the polar, equatorial and SAA regions

We present here the energy spectra relative to different geomagnetic regions as measured by the ALTEA (Anomalous Long Term Effects on Astronauts) detector in the International Space Station – USLab from August 2006 to July 2007. ALTEA is an active detector composed by six silicon telescopes and it is able to follow the dynamics of the radiation flux, with the capability to discriminate impinging nuclei from Boron to Molybdenum. We divided each orbit in three regions (polar, equatorial and South Atlantic Anomaly), according to the values of the geomagnetic coordinates, and show the relative energy spectra. Finally we calculated the relative nuclear abundances compared to the ones of the total data. As expected all nuclear species are similarly modulated by the geomagnetic cutoff.

The possible effects of magnetic fields on laser experiments of Rayleigh–Taylor instabilities

The interaction of a blast wave generated in a supernova explosion with a composition discontinuity in the star's envelope produces crossed density and pressure gradients that are unstable to the growth of Rayleigh–Taylor modes. This instability is thought to be responsible for mixing of nuclear species in the ejecta and to produce observable effects in the light curve and spectrum of the explosion. Blast-wave-driven instabilities of this type have been studied extensively by numerical simulation as well as experimentally using the Omega Laser at the University of Rochester. Initial comparisons between the numerical simulations and the experiments show poor agreement. The simulations show the bubble and spike morphology of the classic Rayleigh–Taylor instability, with well-developed mushroom caps at the tips of the spikes. However, the mushroom caps seem to be completely absent from experiments with three-dimensional initial seed perturbations and are smaller than expected in two-dimensional experiments. Also, some experiments show mass extending beyond the spikes and penetrating almost to the shock front. This effect is completely absent from the numerical simulations. This paper discusses the possibility that the morphology of the instability is significantly altered by the generation of very strong magnetic fields during the laser experiments.

The Birth Environment of the Solar System

This review examines our current understanding of the possible birth environments of our Solar System. Because most stars form within groups and clusters, the question becomes one of determining the nature of the birth aggregate of the Sun. This discussion starts by reviewing Solar System properties that provide constraints on our environmental history. We then outline the range of star-forming environments that are available in the Galaxy and discuss how they affect star and planet formation. The nature of the solar birth cluster is constrained by many physical considerations, including radiation fields provided by the background environment, dynamical scattering interactions, and by the necessity of producing the short-lived radioactive nuclear species inferred from meteoritic measurements. Working scenarios for the solar birth aggregate can be constructed, as discussed herein, although significant uncertainties remain.

Nonenzymatic Glycation Impairs the Antiinflammatory Properties of Apolipoprotein A-I

The goal of this study was to investigate the effects of nonenzymatic glycation on the antiinflammatory properties of apolipoprotein (apo) A-I. Rabbits were infused with saline, lipid-free apoA-I from normal subjects (apoA-I(N)), lipid-free apoA-I nonenzymatically glycated by incubation with methylglyoxal (apoA-I(Glyc in vitro)), nonenzymatically glycated lipid-free apoA-I from subjects with diabetes (apoA-I(Glyc in vivo)), discoidal reconstituted high-density lipoproteins (rHDL) containing phosphatidylcholine and apoA-I(N), (A-I(N))rHDL, or apoA-I(Glyc in vitro), (A-I(Glyc in vitro))rHDL. At 24 hours postinfusion, acute vascular inflammation was induced by inserting a nonocclusive, periarterial carotid collar. The animals were euthanized 24 hours after the insertion of the collar. The collars caused intima/media neutrophil infiltration and increased endothelial expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). ApoA-I(N) infusion decreased neutrophil infiltration and VCAM-1 and ICAM-1 expression by 89%, 90%, and 66%, respectively. The apoA-I(Glyc in vitro) infusion decreased neutrophil infiltration by 53% but did not reduce VCAM-1 or ICAM-1 expression. ApoA-I(Glyc in vivo) did not inhibit neutrophil infiltration or adhesion molecule expression. (A-I(Glyc in vitro))rHDL also inhibited vascular inflammation less effectively than (A-I(N))rHDL. The reduced antiinflammatory properties of nonenzymatically glycated apoA-I were attributed to a reduced ability to inhibit nuclear factor-kappaB activation and reactive oxygen species formation. Nonenzymatic glycation impairs the antiinflammatory properties of apoA-I.

The relationship between leadership and gregariousness in mixed‐species bird flocks

Among the various species that form mixed‐species bird flocks, “nuclear species” are thought to be important in flock formation and maintaining flock cohesion. Such nuclear species have been noted to occur in large groups on their own and to lead flocks, but the relationship between leadership and intraspecific group size has not been quantitatively tested at a large scale. Using a dataset of descriptive studies of terrestrial flock systems collected over 75 y, we found that intraspecific group size was significantly larger in flock leaders than in species that attend the same flocks but do not lead. The relationship held in a reduced dataset with phylogenetically‐independent flock systems. We discuss a framework for explaining the connection between leadership and intraspecific group size, contrasting between those hypotheses that emphasize that gregariousness serves to attract the attention of other species, and those hypotheses that suggest that gregariousness leads to kin‐selected behavior from which other species can also benefit.

Vibration–rotation-tunneling states of the benzene dimer: an ab initio study

An improved intermolecular potential surface for the benzene dimer is constructed from interaction energies computed by symmetry-adapted perturbation theory, SAPT(DFT), with the inclusion of third-order contributions. Twelve characteristic points on the surface have been investigated also using the coupled-cluster method with single, double, and perturbative triple excitations, CCSD(T), and triple-zeta quality basis sets with midbond functions. The SAPT and CCSD(T) results are in close agreement and provide the best representation of these points to date. The potential was used in calculations of vibration-rotation-tunneling (VRT) levels of the dimer by a method appropriate for large amplitude intermolecular motions and tunneling between multiple equivalent minima in the potential. The resulting VRT levels were analyzed with the use of the permutation-inversion full cluster tunneling (FCT) group G(576) and a chain of subgroups that starts from the molecular symmetry group C(s)(M) of the rigid dimer at its equilibrium C(s) geometry and leads to G(576) if all possible intermolecular tunneling mechanisms are feasible. Further information was extracted from the calculated wave functions. It was found, in agreement with the experimental data, that for all of the 54 G(576) symmetry species (with different nuclear spin statistical weights) the lower VRT states have a tilted T-shape (TT) structure; states with the parallel-displaced structure are higher in energy than the ground state of A symmetry by at least 30 cm(-1). The dissociation energy D(0) equals 870 cm(-1), while the depth D(e) of the TT minimum in the potential is 975 cm(-1). Hindered rotation of the cap in the TT structure and tilt tunneling lead to level splittings on the order of 1 cm(-1). Also intermolecular vibrations with excitation energies starting at a few cm(-1) were identified. A further small, but probably significant, level splitting was assigned to cap turnover, although in scans of the potential surface we could not find a plausible 'reaction path' for this process. Rotational constants were extracted from energy levels calculated for total angular momentum J = 0 and 1, and from expectation values of the inertia tensor. Although the end-over-end rotational constant B + C agrees well with the measured microwave spectra, there is disagreement with the measurements concerning the (a)symmetric rotor character of the benzene dimer. It is concluded from calculations for the 54 nuclear spin species that the microwave spectrum should show overlapping contributions from many different species. Another interesting conclusion regards the role of the quantum number K, for a prolate near-symmetric rotor the projection of the total angular momentum on the prolate axis. For the benzene dimer, K has a substantial effect on the energy levels associated with the intermolecular motions of the complex.

Nerve growth factor increases the sensitivity to zinc toxicity and induces cell cycle arrest in PC12 cells

Zinc is a basic trace element that plays important roles in brain and, consequently, its homeostasis needs to be critically controlled. High zinc concentrations in the interneuron synaptic space may induce neuronal death through mechanisms still partially solved. Undifferentiated pheochromocytoma (PC12) cells have been used to study zinc toxicity. As these cells can be differentiated into neuronal-like cells, the results obtained from differentiated cultures are more useful to understand zinc toxicity in neurons. In this paper, we show by flow cytometry that nerve growth factor (NGF) induces PC12 cells differentiation characterized by cell cycle arrest in the G1/G0 phase, similarly to that observed in serum-deprived cultures. Zinc induces cell death in NGF-differentiated PC12 cultures with an EC 50 value of 143 ± 14 μM, which reveals a higher sensitivity with respect to undifferentiated PC12 cultures (EC 50, 308 ± 32 μM) and a similar response to that obtained in hippocampal neurons (134 ± 12 μM). Thus, the differentiation process appeared responsible for such increase in sensitivity. To further support this tenet, when the NGF differentiation was impaired in presence of 10 μM MK-801, a selective blocker of the N-methyl- d-aspartate (NMDA) receptor that plays a role in the differentiation process, the higher sensitivity to zinc was reverted to an EC 50 value of 241 ± 26 μM. Flow cytometry experiments showed that NGF-differentiated PC12 cells in presence of zinc were positive for propidium iodide but not for annexin-V labeling. These results, together with data from fluorescent labeling of nuclear fragmentation, caspase-3 activation, and reactive oxygen species generation, support the view that zinc toxicity in NGF-differentiated PC12 cells takes place mainly through a necrotic process.

Estimation of the fractions of different nuclear iron species in uniformly metal-exchanged Fe-ZSM-5 samples based on a Poisson distribution

A simple calculation method is presented which allows for estimation of the fractions of different iron species in Fe-ZSM-5 based on statistical considerations. Under the assumption of uniformly distributed iron, the probability with which Fe–O–Fe bridged and higher nuclear Fe-species are formed in a Fe-ZSM-5 sample may be calculated based on a simple Poisson distribution. The results of these calculations were compared with DR-UV/vis and DRIFT spectroscopy measurements on a variety of Fe-ZSM-5 samples with different Fe/Al ratios. Moreover, the calculated concentration profiles were checked with literature data from other studies. It is shown that the fractions of different iron species in Fe-ZSM-5 can be estimated by this calculation method with satisfactory accuracy, provided that the metal-exchange process resulted in a uniform distribution of iron in the zeolite. The method may be useful for verifying of analytical results, understanding of observed activity patterns and may facilitate the identification of activity–structure relationships.