Secondary Nuclei Research Articles

Significance of the organic aerosol driven climate feedback in the boreal area

Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Higher temperatures resulting from increased greenhouse gas levels have been suggested to lead to increased biogenic secondary organic aerosol and cloud condensation nuclei concentrations creating a negative climate feedback mechanism. Here, we present direct observations on this feedback mechanism utilizing collocated long term aerosol chemical composition measurements and remote sensing observations on aerosol and cloud properties. Summer time organic aerosol loadings showed a clear increase with temperature, with simultaneous increase in cloud condensation nuclei concentration in a boreal forest environment. Remote sensing observations revealed a change in cloud properties with an increase in cloud reflectivity in concert with increasing organic aerosol loadings in the area. The results provide direct observational evidence on the significance of this negative climate feedback mechanism.

Magnetic diffusion and interaction effects on ultrahigh energy cosmic rays: Protons and nuclei

The flux of ultrahigh energy cosmic rays reaching the Earth is affected by the interactions with the cosmic radiation backgrounds as well as with the magnetic fields that are present along their trajectories. We combine the SimProp cosmic ray propagation code with a routine that allows to account for the average effects of a turbulent magnetic field on the direction of propagation of the particles. We compute in this way the modification of the spectrum which is due to the magnetic horizon effect, both for primary nuclei as well as for the secondary nuclei resulting from the photo-disintegration of the primary ones. We also provide analytic parameterizations of the attenuation effects, as a function of the magnetic field parameters and of the density of cosmic ray sources, which make it possible to obtain the expected spectra in the presence of the magnetic fields from the spectra that would be obtained in the absence of magnetic fields. The discrete nature of the distribution of sources with finite density also affects the spectrum of cosmic rays at the highest energies where the flux is suppressed due to the interactions with the radiation backgrounds, and parameterizations of these effects are obtained.

Origin of Spectral Hardening of Secondary Cosmic-Ray Nuclei

Abstract We discuss the acceleration and escape of secondary cosmic-ray (CR) nuclei, such as lithium, beryllium, and boron, produced by spallation of primary CR nuclei like carbon, nitrogen, and oxygen accelerated at the shock in supernova remnants (SNRs) surrounded by the interstellar medium (ISM) or a circumstellar medium (CSM). We take into account the energy-dependent escape of CR particles from the SNR shocks, which is supported by gamma-ray observations of SNRs, to calculate the spectra of primary and secondary CR nuclei running away into the ambient medium. We find that if the SNR is surrounded by a CSM with a wind-like density distribution (i.e., n CSM ∝ r −2), the spectra of the escaping secondary nuclei are harder than those of the escaping primary nuclei, while if the SNR is surrounded by a uniform ISM, the spectra of the escaping secondaries are always softer than those of the escaping primaries. Using this result, we show that if there was a past supernova surrounded by a dense wind-like CSM (∼2.5 × 10−3 M ⊙ yr−1), which happened ∼1.6 × 105 yr ago at a distance of ∼1.6 kpc, we can simultaneously reproduce the spectral hardening of primary and secondary CRs above ∼200 GV that have recently been reported by AMS-02.

Unveiling the Population of Wandering Black Holes via Electromagnetic Signatures

Abstract While most galaxies appear to host a central supermassive black hole (SMBH), they are expected to also contain a substantial population of off-center “wandering” SMBHs naturally produced by the hierarchical merger-driven process of galaxy assembly. This population has been recently characterized in an analysis of the Romulus cosmological simulations, which correct for the dynamical forces on SMBHs without artificially pinning them to halo centers. Here we predict an array of electromagnetic signatures for these wanderers. The predicted wandering population of SMBHs from Romulus broadly reproduces the observed spatial offsets of a recent sample of hyperluminous X-ray sources. We predict that the sources with the most extreme offsets are likely to arise from SMBHs within satellite galaxies. These simulations also predict a significant population of secondary active galactic nuclei (AGNs) with luminosities at least 10% that of the central AGN. The majority of galaxies at z = 4 that host a central AGN with bolometric luminosity L bol > 1042 erg s−1 are predicted to host a companion off-center AGN of comparable brightness. We demonstrate that stacked X-ray observations of similar mass galaxies may reveal a halo of collective emission attributable to these wanderers. Finally, because wanderers dominate the population of SMBHs with masses of ≲107 M ⊙ in Romulus, they may dominate tidal disruption event (TDE) rates at these masses if they retain a stellar component (e.g., a nuclear star cluster). This could warrant an order of magnitude correction to current theoretically estimated TDE rates at low SMBH masses.

Space radiation electrostatic shielding scaling laws: Beam-like and isotropic angular distributions

Passive radiation shielding alone cannot provide adequate protection for astronauts on long-term, deep-space missions. High atomic number and energy (HZE) ions, and/or their secondaries, can penetrate any realistic mass shielding for long-term deep-space missions and cause damage to cells via direct energy deposition and/or through the production of secondary particles and fragmented nuclei. Active shielding, or the use of electromagnetic fields to deflect or stop incoming ions before reaching the spacecraft, has gained substantial attention over the last decade as a way to augment passive shielding. Recently, a mathematical relationship between a dimensionless scaling parameter characterizing the active shield and the incoming ion and a protected area formed on a downstream detector due to the deflection of HZE ions by the applied field was validated in Earth-based laboratory conditions. In the present work, the mathematical formulation is extended to relate electrostatic shielding efficacy with the ability to deflect positively charged ions with parameters relevant to space applications. Additionally, a modified scaling parameter is formulated to characterize the shielding efficacy of a “family” of electrostatic active shielding configurations for reducing flux density for a space-relevant isotropic source of energetic protons. The results of this study demonstrate a strong correlation among dimensionless scaling parameters and shielding efficacy metrics for space radiation-relevant HZE ions in beam and isotropic angular distributions. Furthermore, it establishes a framework for optimizing design of three-dimensional electrostatic shielding configurations to improve space radiation protection for astronauts on exploration-class missions.

Transneuronal delivery of designer cytokines: perspectives for spinal cord injury.

Transneuronal delivery of designer cytokines: perspectives for spinal cord injury.

Effects of sintering temperature on microstructure and properties of low‐grade bauxite‐based ceramic proppant

AbstractLow density and high strength ceramic proppant was prepared by sintering high aluminium type low‐grade bauxite and high iron type low‐grade bauxite at the temperature range from 1300℃ to 1360℃. The phase composition and micromorphology of ceramic proppant were, respectively, characterized by X‐ray diffraction (XRD) and scanning electron microscope (SEM). The bulk density, apparent density, and breakage ratio of ceramic proppant were tested using standard methods. The results show that mullite crystal and corundum crystal are fully developed, the spatial network structure of rod‐shaped mullite is formed, and corundum crystal is evenly distributed in the sample when the sintering temperature is 1340℃. At this temperature, the bulk density of the sample is 1.42 g/cm3, the apparent density is 2.67 g/cm3, and the breakage ratio is 5.1% under the closure pressure of 52 MPa. Then, the growth mechanism of mullite crystal in ceramic proppant was explored. The results reveal that the mullite crystal in ceramic proppant conforms to the layer growth theory. The secondary crystal nucleus is formed in the growth process and shows a step growth mechanism. With the increase in sintering temperature, the preferred orientation growth of mullite crystal finally forms needle‐like morphology.

Neuroanatomical organization of methionine-enkephalinergic system in the brain of the Mozambique tilapia Oreochromis mossambicus

Enkephalins are a class of opioid peptides implicated in several physiological and neuroendocrine responses in vertebrates. In this study, using immunocytochemical or immunofluorescence technique, we examined the neuroanatomical distribution of methionine enkephalin (M-ENK) immunoreactivity in the central nervous system (CNS) of the cichlid fish Oreochromis mossambicus. In the telencephalon, no M-ENK-like-immunoreactive (M-ENK-L-ir) perikarya, but sparsely distributed fibres were detected in the glomerular layer and the granule cell layer of the olfactory bulb. Although intensely labeled M-ENK-L-ir cells and fibres were found in the pallium, no M-ENK immunoreactivity was observed in the subpallium. The preoptic area showed a few M-ENK-L-ir somata and dense innervations of fibres. In the hypothalamic area, M-ENK-L-ir cells and fibres were located in magnocellular and parvocellular subdivisions of the nucleus preopticus, and medial and lateral subdivisions of the nucleus lateralis tuberis. Surrounding the recessus lateralis of the third ventricle, several intensely stained and packed M-ENK-L-ir cells and fibres were seen in dorsal, lateral and ventral subdivisions of the nucleus recessus lateralis. In the diencephalon, M-ENK immunoreactivity was restricted to the habenula, the thalamus, the pretectal area and the nucleus posterior tuberis. Dense aggregations of M-ENK-L-ir fibres were seen in the mesencephalic subdivisions, the optic tectum and the torus semicircularis, whereas a few fusiform M-ENK-L-ir cells and fibres were scattered in the midbrain tegmentum. In the rhombencephalon, different populations of ovoid or spindle shaped M-ENK-L-ir cells were observed in the secondary gustatory nucleus, the sensory trigeminal nerve nucleus, the nucleus reticularis medialis and the vagal motor nucleus, whereas bands of fibres were seen in the rostral spinal cord. Collectively, the widespread distribution of M-ENK immunoreactivity in the CNS suggests a role for this opioid peptide in regulation of neuroendocrine control of reproduction and modulation of sensorimotor functions in fish.

Features of the Energy Spectra of Primary and Secondary Nuclei of Cosmic Rays: A Consistent Astrophysical Interpretation

Features of the Energy Spectra of Primary and Secondary Nuclei of Cosmic Rays: A Consistent Astrophysical Interpretation

Fresh insights on properties of particle fluxes in cosmic rays measured with the Alpha Magnetic Spectrometer on the international space station

The Alpha Magnetic Spectrometer is a particle physics detector focusing on the search for dark matter, the existence of antimatter, the origin and composition of cosmic rays from primordial sources in the universe and the exploration of new physics in space. Important features of the elementary particle (proton, antiproton, positron and election) fluxes in cosmic rays are presented: (1) The proton spectrum has a smooth hardening from 200 GeV; (2) antiproton and positron spectra show excess from traditional physics background; (3) in particular, the positron flux shows a source term with a cutoff energy of 810 GeV, which raises the question of its source; (4) the origin of the energetic electrons is different from that of positrons and (5) the identical momentum dependence of primary and secondary cosmic ray nuclei fluxes are also reviewed.

Implications of current nuclear cross sections on secondary cosmic rays with the upcoming DRAGON2 code

Current measurements of cosmic-ray fluxes have reached unprecedented accuracy thanks to the new generation of experiments, and in particular the AMS-02 mission. At the same time, significant progress has been made in the propagation models of galactic cosmic rays. These models include several propagation parameters, which are usually inferred from the ratios of secondary to primary cosmic rays, and which depend on the cross sections describing the collisions among the various species of cosmic-ray nuclei. At present, our knowledge of these cross sections in the energy range where cosmic-ray interactions occur is limited, and this is a source of uncertainties in the predicted fluxes of secondary cosmic-ray nuclei. In this work we study the impact of the cross section uncertainties on the fluxes of light secondary nuclei (Li, Be, B) using a preliminary version of the upcoming DRAGON2 code. We first present a detailed comparison of the secondary fluxes computed by implementing different parameterizations for the network of spallation cross sections. Then, we discuss the use of secondary-over-secondary cosmic-ray flux ratios as a tool to improve the consistency of cross sections parameterizations and give insight of the overall uncertainties coming from the cross sections parametrisations. We show that the uncertainties inferred from the cross section data are enough to explain the discrepancies in the Be and Li fluxes with respect to the AMS-02 data, with no need of a primary component in their spectra. In addition, we show that the fluxes of B, Be and Li can be simultaneously reproduced by rescaling their cross sections within the experimental uncertainty. Finally, we also revisit the diffusive estimation of the halo size, obtaining good agreement with previous works and a best fit value of 6.8 ± 1 kpc from the most updated cross sections parametrisations.

Synthesis and Characterization of Hybrid Metal Zeolitic Imidazolate Framework Membrane for Efficient H2/CO2 Gas Separation

In this paper, we propose mixed metal ions in the node of the zeolitic imidazolate framework (ZIF) structure. The hybrid metal ZIF is formed for the gas separation of hydrogen and carbon dioxide. In the first stage, the nanoparticles were prepared as a coating on a substrate, and acting as secondary growing nuclei. The hybrid metal ZIF structures were characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). N2 adsorption–desorption isotherms determined surface area, and scanning electron microscopy (SEM) was used to observe the microstructure and surface morphology. The hybrid metal ZIF-8-67 powder had the largest surface area (1260.40 m2 g−1), and the nanoparticles (100 nm) could be fully dense-coated on the substrate to benefit the subsequent membrane growth. In the second stage, we prepared the hybrid metal ZIF-8-67 membrane on the pre-seeding substrate with mixed metal nanoparticles of cobalt and zinc, by the microwave hydrothermal method. Cobalt ions were identified in the tetrahedral coordination through UV–Vis, and the membrane structure and morphology were determined by XRD and SEM. Finally, a gas permeation analyzer (GPA) was used to determine the gas separation performance of the hybrid metal ZIF-8-67 membrane. We successfully introduced zinc ions and cobalt ions into the ZIF structure, where cobalt had a strong interaction with CO2. Therefore, GPA analysis showed an excellent H2/CO2 separation factor due to lower CO2 permeability. The CO2 permeance was ~0.65 × 10−8 mol m−2 s−1 Pa−1, and the separation factors for H2/CO2 and H2/N2 were 9.2 and 2.9, respectively. Our results demonstrate that the hybrid metal ZIF-8-67 membrane has a superior H2/CO2 separation factor, which can be attributed to its very high specific surface area and structure. Based on the above, hybrid metal ZIF-8-67 membranes are expected to be applied in hydrogen or carbon dioxide gas separation and purification.

Secondary cosmic-ray nucleus spectra disfavor particle transport in the Galaxy without reacceleration

The precise observations of Galactic cosmic ray fluxes of the secondary family, such as Li, Be, B, are expected to have significant implications on our understanding of the cosmic ray origin and propagation. Here we employ the recent very precise measurements of those species by the Alpha Magnetic Spectrometer on the International Space Station, together with their parent species (C and O), as well as the data collected by the Voyager-1 spacecraft outside the heliosphere and the Advanced Composition Explorer, to investigate the propagation of cosmic rays in the Milky Way. We consider the diffusion of cosmic rays plus reacceleration or convection effect during the propagation, and find that the reacceleration model can fit the data significantly better than the convection model. We further find that for the reacceleration model, the spectral hardenings of both the primary and secondary particles can be well described by the injection hardening without including additional propagation hardening. This is due to that the reacceleration effect results in a steeper secondary-to-primary ratio at low energies, and can thus naturally reproduce the fact that the secondary spectra harden more than the primary spectra found by AMS-02.

Severe Acute Respiratory Syndrome Coronavirus 2 Attachment Receptor Angiotensin-Converting Enzyme 2 Is Decreased in Crohn’s Disease and Regulated By Microbial and Inflammatory Signaling

Severe Acute Respiratory Syndrome Coronavirus 2 Attachment Receptor Angiotensin-Converting Enzyme 2 Is Decreased in Crohn’s Disease and Regulated By Microbial and Inflammatory Signaling

Expected Impacts of Mixing European Beech with Silver Fir on Regional Air Quality and Radiation Balance

The anticipated climate change during the next decades is posing crucial challenges to ecosystems. In order to decrease the vulnerability of forests, introducing tree species’ mixtures are a viable strategy, with deep-rooting native Silver fir (Abies alba) being a primary candidate for admixture into current pure stands of European beech (Fagus sylvatica) especially in mountainous areas. Such a change in forest structure also has effects on the regional scale, which, however, have been seldomly quantified. Therefore, we measured and modeled radiative balance and air chemistry impacts of admixing Silver fir to European beech stands, including changes in biogenic volatile organic compound emissions. An increased fraction of Silver fir caused a smaller albedo and a (simulated) larger evapotranspiration, leading to a dryer and warmer forest. While isoprene emission was negligible for both species, sesquiterpene and monoterpene emissions were larger for fir than for beech. From these differences, we derived that ozone concentration as well as secondary organic aerosols and cloud condensation nuclei would increase regionally. Overall, we demonstrated that even a relatively mild scenario of tree species change will alter the energy balance and air quality in a way that could potentially influence the climate on a landscape scale.

Overview of Secondary Nucleation: From Fundamentals to Application

Secondary nucleation can bring the crystallization process into a more easily controlled state, and it is playing an important role in controlling crystal size distribution, polymorphism, and chirality of the crystal products, no matter whether in a batch or continuous crystallizer. Therefore, in this review, we revisit the research of secondary nucleation in the past 30 years to understand the fundamentals and application of secondary nucleation. First, we summarize the sources of secondary nuclei, that is, how secondary nucleation occurs. Then, we discuss the secondary nucleation threshold from the perspective of the metastable zone widths which are associated with the nucleation mechanism. Furthermore, we discuss how to employ secondary nucleation to regulate the properties of crystalline products (particle size distribution, crystal polymorphism, chirality, etc.). More importantly, we also discuss how polymorphism and chirality can act as a probe to explore the origin of secondary nucleation. Finally, we give conclusions and outlooks, mainly on the molecular nucleation mechanism and crystal growth dead zone of the current topic of secondary nucleation.

Universal properties of primary and secondary cosmic ray energy spectra

Atomic nuclei appearing in cosmic rays (CRs) are typically classified as primary or secondary. However, a better understanding of their origin and propagation properties is still necessary. We analyse the flux of primary (He, C, O) and secondary nuclei (Li, Be, B) detected with rigidity (momentum/charge) between 2 GV and 3 TV by the alpha magnetic spectrometer on the International Space Station. We show that q-exponential distribution functions, as motivated by generalized versions of statistical mechanics with temperature fluctuations, provide excellent fits for the measured flux of all nuclei considered. Primary and secondary fluxes reveal a universal dependence on kinetic energy per nucleon for which the underlying energy distribution functions are solely distinguished by their effective degrees of freedom. All given spectra are characterized by a universal mean temperature parameter ∼200 MeV which agrees with the Hagedorn temperature. Our analysis suggests that QCD scattering processes together with nonequilibrium temperature fluctuations imprint universally onto the measured CR spectra, and produce a similar shape of energy spectra as high energy collider experiments on the Earth.

Secondary Nuclei from Peripheral and Ultraperipheral Collisions of Relativistic Heavy Ions

Secondary Nuclei from Peripheral and Ultraperipheral Collisions of Relativistic Heavy Ions

Study on Formation of Microstructure in Rheo-Diecastings of Semi-Solid A380 Aluminum Alloy Slurry

The formation of the microstructure in the rheo-diecastings were studied by the experiment of rheo-diecasting with semi-solid A380 Aluminum alloy slurry. The results show that the grain diameter and shape factor of primary α-Al grains decreased and increased along the rheo-diecasting direction, respectively, making the primary α-Al grains gradually distributing uniformly. The combination of injection pressure and narrow gate of the runner and ingate was the main reason for the evolution of the primary α-Al grains, moreover, the collision and friction among primary α-Al grains during the filling were helpful for the refinement and spheroidization of the primary α-Al grains. The residual liquid solidified into the secondary solidification microstructure accompanied by the evolution of the primary α-Al grains. The accumulation of the fragments of the primary α-Al grains, the secondary α2-Al nuclei or grains which formed in previous positions, the effective nucleation rate of the residual liquid, and the collision and fraction among the secondary α2-Al grains and between the secondary α2-Al grain and the primary α-Al grains made the secondary solidification microstructure of the residual liquid present multiplex and complicate characteristics. In this paper, the formation of the microstructure in the rheo-diecastings were studied by the experiment of rheo-diecasting. During the rheo-diecasting, the grain diameter and shape factor of primary α-Al grains decreased and increased, respectively along the rheo-diecasting direction, which made the primary α-Al grains gradually distribute uniformly. The drifting of the fragments of the primary α-Al grains and secondary α2-Al nucleus, and the effective nucleation rate of the residual liquid played an important effect on the morphology of the secondary solidification structure.

Estimation of the Size of Critical Secondary Nuclei of Melt-Grown Poly(l-lactide) Lamellar Crystals

Recently, we proposed a simple method to derive the size of critical secondary nuclei formed on the growth front of lamellar crystals via the nucleation kinetics of random copolymers and polymer bl...