The change in mean-square nuclear charge radii δ⟨r^{2}⟩ along the even-A tin isotopic chain ^{108-134}Sn has been investigated by means of collinear laser spectroscopy at ISOLDE/CERN using the atomic ...transitions 5p^{2} ^{1}S_{0}→5p6 s^{1}P_{1} and 5p^{2} ^{3}P_{0}→5p6s ^{3}P_{1}. With the determination of the charge radius of ^{134}Sn and corrected values for some of the neutron-rich isotopes, the evolution of the charge radii across the N=82 shell closure is established. A clear kink at the doubly magic ^{132}Sn is revealed, similar to what has been observed at N=82 in other isotopic chains with larger proton numbers, and at the N=126 shell closure in doubly magic ^{208}Pb. While most standard nuclear density functional calculations struggle with a consistent explanation of these discontinuities, we demonstrate that a recently developed Fayans energy density functional provides a coherent description of the kinks at both doubly magic nuclei, ^{132}Sn and ^{208}Pb, without sacrificing the overall performance. A multiple correlation analysis leads to the conclusion that both kinks are related to pairing and surface effects.
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Abstract
Nuclear charge radii globally scale with atomic mass number
A
as
A
1∕3
, and isotopes with an odd number of neutrons are usually slightly smaller in size than their even-neutron neighbours. ...This odd–even staggering, ubiquitous throughout the nuclear landscape
1
, varies with the number of protons and neutrons, and poses a substantial challenge for nuclear theory
2–4
. Here, we report measurements of the charge radii of short-lived copper isotopes up to the very exotic
78
Cu (with proton number
Z
= 29 and neutron number
N
= 49), produced at only 20 ions s
–1
, using the collinear resonance ionization spectroscopy method at the Isotope Mass Separator On-Line Device facility (ISOLDE) at CERN. We observe an unexpected reduction in the odd–even staggering for isotopes approaching the
N
= 50 shell gap. To describe the data, we applied models based on nuclear density functional theory
5,6
and
A
-body valence-space in-medium similarity renormalization group theory
7,8
. Through these comparisons, we demonstrate a relation between the global behaviour of charge radii and the saturation density of nuclear matter, and show that the local charge radii variations, which reflect the many-body polarization effects, naturally emerge from
A
-body calculations fitted to properties of
A
≤ 4 nuclei.
Abstract
Nuclear charge radii are sensitive probes of different aspects of the nucleon–nucleon interaction and the bulk properties of nuclear matter, providing a stringent test and challenge for ...nuclear theory. Experimental evidence suggested a new magic neutron number at
N
= 32 (refs.
1–3
) in the calcium region, whereas the unexpectedly large increases in the charge radii
4,5
open new questions about the evolution of nuclear size in neutron-rich systems. By combining the collinear resonance ionization spectroscopy method with β-decay detection, we were able to extend charge radii measurements of potassium isotopes beyond
N
= 32. Here we provide a charge radius measurement of
52
K. It does not show a signature of magic behaviour at
N
= 32 in potassium. The results are interpreted with two state-of-the-art nuclear theories. The coupled cluster theory reproduces the odd–even variations in charge radii but not the notable increase beyond
N
= 28. This rise is well captured by Fayans nuclear density functional theory, which, however, overestimates the odd–even staggering effect in charge radii. These findings highlight our limited understanding of the nuclear size of neutron-rich systems, and expose problems that are present in some of the best current models of nuclear theory.
•Analyze the thermal damage behavior of granite by optical microscopic observation.•Investigate the effect of temperature on the strength and deformation parameters of granite.•Explore the acoustic ...emission behavior of granite subjected to various high temperature treatment.•Discuss the internal crack mechanism of deformed granite specimens by X-ray micro CT system.
A detailed understanding of the thermal damage and failure mechanical behavior of granite at elevated temperatures is a key concern in nuclear waste disposal engineering, underground coal gasification, and heat mining in enhanced geothermal energy. In this research, uniaxial compression tests were first carried out to evaluate the effect of high temperature treatments (200, 300, 400, 500, 600, 700 and 800°C) on the crack damage, strength and deformation failure behavior of a granite. The results demonstrated that, in all cases, the crack damage threshold, the strength and static elastic modulus of granite were increased at 300°C, before decreasing up to our maximum temperature of 800°C. However, the static Poisson’s ratio of granite first decreased at 600°C, and then increased rapidly with the temperature. The crack damage and peak axial strain always showed an increase when the temperature was increased. However, the dynamic elastic modulus decreased with the temperature, whereas the dynamic Poisson’s ratio did not depend on the temperature. The gradual increase of temperature results in a more ductile failure of granite. Next, the thermal damage mechanism of uncompressed granite was analyzed by optical microscopic observation. At T=25–300°C, the mechanisms were favored by the thermal expansion of mineral grains but no microcracks were observed; at T=400–600°C, the mechanisms were contributed by boundary cracks and transgranular cracks in feldspar and quartz grains; and at T=700–800°C, the mechanisms were associated with the coalescence of boundary cracks and transgranular cracks. The internal crack evolution process was then monitored during deformation using acoustic emission (AE) monitoring. The results showed that the cracking process of granite depended on the heat treatment temperature. Finally, the deformation mechanism of failed granite at various temperatures was analyzed using X-ray micro CT. During loading, the uniaxial compression stress direction dominated the more brittle fracture process of granite at T=25–600°C, which led to splitting tensile main cracks induced along the axial stress, and thermal damage determined the larger ductile fracture process of granite at T=700–800°C, which resulted in a more ductile deformation after the peak strength.
The increasing severity of droughts/floods and worsening air quality from increasing aerosols in Asia monsoon regions are the two gravest threats facing over 60% of the world population living in ...Asian monsoon regions. These dual threats have fueled a large body of research in the last decade on the roles of aerosols in impacting Asian monsoon weather and climate. This paper provides a comprehensive review of studies on Asian aerosols, monsoons, and their interactions. The Asian monsoon region is a primary source of emissions of diverse species of aerosols from both anthropogenic and natural origins. The distributions of aerosol loading are strongly influenced by distinct weather and climatic regimes, which are, in turn, modulated by aerosol effects. On a continental scale, aerosols reduce surface insolation and weaken the land‐ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulations. The atmospheric thermodynamic state, which determines the formation of clouds, convection, and precipitation, may also be altered by aerosols serving as cloud condensation nuclei or ice nuclei. Absorbing aerosols such as black carbon and desert dust in Asian monsoon regions may also induce dynamical feedback processes, leading to a strengthening of the early monsoon and affecting the subsequent evolution of the monsoon. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of different monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol‐monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol‐monsoon climate system, subject to external forcing of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol‐monsoon interactions calls for an integrated approach and international collaborations based on long‐term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.
Key Points
The fast‐developing Asia has suffered severe air pollution problem
Aerosol affects the Asian monsoon
Aerosol‐monsoon interactions dictate the climate change in the region
The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow ...relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli-arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.
Abstract
Mid-infrared (mid-IR) observations are powerful in identifying heavily obscured active galactic nuclei (AGN) that have weak emission in other wavelengths. Data from the Mid-Infrared ...Instrument (MIRI) on board the James Webb Space Telescope provides an excellent opportunity to perform such studies. We take advantage of the MIRI imaging data from the Cosmic Evolution Early Release Science Survey to investigate the AGN population in the distant universe. We estimate the source properties of MIRI-selected objects by utilizing spectral energy distribution (SED) modeling, and classify them into star-forming galaxies (SFs), SF-AGN mixed objects, and AGN. The source numbers of these types are 433, 102, and 25, respectively, from four MIRI pointings covering ∼9 arcmin
2
. The sample spans a redshift range of ≈0–5. We derive the median SEDs for all three source types, respectively, and publicly release them. The median MIRI SED of AGN is similar to the typical SEDs of hot dust-obscured galaxies and Seyfert 2s, for which the mid-IR SEDs are dominated by emission from AGN-heated hot dust. Based on our SED-fit results, we estimate the black hole accretion density (BHAD; i.e., total BH growth rate per comoving volume) as a function of redshift. At
z
< 3, the resulting BHAD agrees with the X-ray measurements in general. At
z
> 3, we identify a total of 27 AGN and SF-AGN mixed objects, leading to that our high-
z
BHAD is substantially higher than the X-ray results (∼0.5 dex at
z
≈ 3–5). This difference indicates MIRI can identify a large population of heavily obscured AGN missed by X-ray surveys at high redshifts.
High-Speed and Low-Energy Nitride Memristors Choi, Byung Joon; Torrezan, Antonio C.; Strachan, John Paul ...
Advanced functional materials,
August 2, 2016, Volume:
26, Issue:
29
Journal Article
Peer reviewed
Open access
High‐performance memristors based on AlN films have been demonstrated, which exhibit ultrafast ON/OFF switching times (≈85 ps for microdevices with waveguide) and relatively low switching current ...(≈15 μA for 50 nm devices). Physical characterizations are carried out to understand the device switching mechanism, and rationalize speed and energy performance. The formation of an Al‐rich conduction channel through the AlN layer is revealed. The motion of positively charged nitrogen vacancies is likely responsible for the observed switching.
Ultrafast switching of an AlN memristor: ON switching is acheived using an 85 ps positive voltage pulse, and OFF switching using an 85 ps negative voltage pulse on the Al electrode of a Pt/AlN/Al memristor stack. A relatively low switching current (≈15 μA for 50 nm devices) has also been demonstrated in these memristors based on AlN films. The formation of an Al‐rich conduction channel through the AlN layer is revealed.
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