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1. Acceleration and Spectral Redistribution of Cosmic Rays in Radio-jet Shear Flows

   https://doi.org/10.3847/1538-4357/acfda9  

   Webb, G. M. ; Xu, Y. ; Biermann, P. L. ; Al-Nussirat, S. ; Mostafavi, P. ; Li, G. ; Barghouty, A. F. ; Zank, G. P. ( November 2023 , The Astrophysical Journal)

   A steady-state, semi-analytical model of energetic particle acceleration in radio-jet shear flows due to cosmic-ray viscosity obtained by Webb et al. is generalized to take into account more general cosmic-ray boundary spectra. This involves solving a mixed Dirichlet–Von Neumann boundary value problem at the edge of the jet. The energetic particle distribution functionf₀(r,p) at cylindrical radiusrfrom the jet axis (assumed to lie along thez-axis) is given by convolving the particle momentum spectrum$f_0(\infty ,p\prime )$with the Green’s function$G(r,p;p\prime )$, which describes the monoenergetic spectrum solution in which$f_0\to \delta (p-p\prime )$asr→ ∞ . Previous work by Webb et al. studied only the Green’s function solution for$G(r,p;p\prime )$. In this paper, we explore for the first time, solutions for more general and realistic forms for$f_0(\infty ,p\prime )$. The flow velocityu=u(r)e_zis along the axis of the jet (thez-axis).uis independent ofz, andu(r) is a monotonic decreasing function ofr. The scattering time$\tau {(r,p)={\tau }_0(p/p_0)}^{\alpha }$in the shear flow region 0 <r<r₂, and$\tau {(r,p)={\tau }_0(p/p_0)}^{\alpha }{(r/r_2)}^s$, wheres> 0 in the regionr>r₂is outside the jet. Other original aspects of the analysis are (i) the use of cosmic ray flow lines in (r,p) space to clarify the particle spatial transport and momentum changes and (ii) the determination of the probability distribution${\psi }_p(r,p;p\prime )$that particles observed at (r,p) originated fromr→ ∞ with momentum$p\prime$. The acceleration of ultrahigh-energy cosmic rays in active galactic nuclei jet sources is discussed. Leaky box models for electron acceleration are described.

    

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2. (Digital Presentation) Oxide Memristors Based on SiO 2 with Cu/Ag Alloy Metallization for Neuromorphic Computing

   https://doi.org/10.1149/MA2022-0215808mtgabs  

   Qin, Fei ; Song, Han Wook ; Qin, Fei ( October 2022 , ECS Meeting Abstracts)

   By mimicking biomimetic synaptic processes, the success of artificial intelligence (AI) has been astounding with various applications such as driving automation, big data analysis, and natural-language processing.[1-4] Due to a large quantity of data transmission between the separated memory unit and the logic unit, the classical computing system with von Neumann architecture consumes excessive energy and has a significant processing delay.[5] Furthermore, the speed difference between the two units also causes extra delay, which is referred to as the memory wall.[6, 7] To keep pace with the rapid growth of AI applications, enhanced hardware systems that particularly feature an energy-efficient and high-speed hardware system need to be secured. The novel neuromorphic computing system, an in-memory architecture with low power consumption, has been suggested as an alternative to the conventional system. Memristors with analog-type resistive switching behavior are a promising candidate for implementing the neuromorphic computing system since the devices can modulate the conductance with cycles that act as synaptic weights to process input signals and store information.[8, 9]

   The memristor has sparked tremendous interest due to its simple two-terminal structure, including top electrode (TE), bottom electrode (BE), and an intermediate resistive switching (RS) layer. Many oxide materials, including HfO₂, Ta₂O₅, and IGZO, have extensively been studied as an RS layer of memristors. Silicon dioxide (SiO₂) features 3D structural conformity with the conventional CMOS technology and high wafer-scale homogeneity, which has benefited modern microelectronic devices as dielectric and/or passivation layers. Therefore, the use of SiO₂as a memristor RS layer for neuromorphic computing is expected to be compatible with current Si technology with minimal processing and material-related complexities.

   In this work, we proposed SiO₂-based memristor and investigated switching behaviors metallized with different reduction potentials by applying pure Cu and Ag, and their alloys with varied ratios. Heavily doped p-type silicon was chosen as BE in order to exclude any effects of the BE ions on the memristor performance. We previously reported that the selection of TE is crucial for achieving a high memory window and stable switching performance. According to the study which compares the roles of Cu (switching stabilizer) and Ag (large switching window performer) TEs for oxide memristors, we have selected the TE materials and their alloys to engineer the SiO₂-based memristor characteristics. The Ag TE leads to a larger memory window of the SiO₂memristor, but the device shows relatively large variation and less reliability. On the other hand, the Cu TE device presents uniform gradual switching behavior which is in line with our previous report that Cu can be served as a stabilizer, but with small on/off ratio.[9] These distinct performances with Cu and Ag metallization leads us to utilize a Cu/Ag alloy as the TE. Various compositions of Cu/Ag were examined for the optimization of the memristor TEs. With a Cu/Ag alloying TE with optimized ratio, our SiO₂based memristor demonstrates uniform switching behavior and memory window for analog switching applications. Also, it shows ideal potentiation and depression synaptic behavior under the positive/negative spikes (pulse train).

   In conclusion, the SiO₂memristors with different metallization were established. To tune the property of RS layer, the sputtering conditions of RS were varied. To investigate the influence of TE selections on switching performance of memristor, we integrated Cu, Ag and Cu/Ag alloy as TEs and compared the switch characteristics. Our encouraging results clearly demonstrate that SiO₂with Cu/Ag is a promising memristor device with synaptic switching behavior in neuromorphic computing applications.

   Acknowledgement

   This work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 22011044) by KRISS.

   References

   [1] Younget al.,IEEE Computational Intelligence Magazine,vol. 13, no. 3, pp. 55-75, 2018.

   [2] Hadsellet al.,Journal of Field Robotics,vol. 26, no. 2, pp. 120-144, 2009.

   [3] Najafabadiet al.,Journal of Big Data,vol. 2, no. 1, p. 1, 2015.

   [4] Zhaoet al.,Applied Physics Reviews,vol. 7, no. 1, 2020.

   [5] Zidanet al.,Nature Electronics,vol. 1, no. 1, pp. 22-29, 2018.

   [6] Wulfet al.,SIGARCH Comput. Archit. News,vol. 23, no. 1, pp. 20–24, 1995.

   [7] Wilkes,SIGARCH Comput. Archit. News,vol. 23, no. 4, pp. 4–6, 1995.

   [8] Ielminiet al.,Nature Electronics,vol. 1, no. 6, pp. 333-343, 2018.

   [9] Changet al.,Nano Letters,vol. 10, no. 4, pp. 1297-1301, 2010.

   [10] Qinet al., Physica Status Solidi (RRL) - Rapid Research Letters, pssr.202200075R1, In press, 2022.

    

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3. Thermal property values of a central Iowa soil as functions of soil water content and bulk density or of soil air content

   https://doi.org/10.1111/ejss.12856  

   Tong, Bing ; Kool, Dilia ; Heitman, Joshua L. ; Sauer, Thomas J. ; Gao, Zhiqiu ; Horton, Robert ( July 2019 , European Journal of Soil Science)

   Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content (θ) and bulk density (ρ_b). Bothθandρ_bchange with time, particularly in recently tilled soil. However, few studies have addressed the full extent of soil thermal property changes withθandρ_b. The objective of this study is to examine how changes inρ_bwith time after tillage impact soil thermal properties (volumetric heat capacity,C_v, thermal diffusivity,k, and thermal conductivity,λ). The study provides thermal property values as functions ofθandρ_band of air content (n_air) on undisturbed soil cores obtained at selected times following tillage. Heat pulse probe measurements of thermal properties were obtained on each soil core at saturated, partially saturated (θat pressure head of −50 kPa) and oven‐dry conditions. Generally,kandλincreased with increasingρ_bat the three water conditions. TheC_vincreased asρ_bincreased in the oven‐dry and unsaturated conditions and decreased asρ_bincreased in the saturated condition. For a givenθ, a largerρ_bwas associated with larger thermal property values, especially forλ. The figures ofC_v,kandλversusθandρ_b, as well asC_v,kandλversusn_air, represented the range of soil conditions following tillage. Trends in the relationships of thermal property values withθandρ_bwere described by 3‐D surfaces, whereas each thermal property had a linear relationship withn_air. Clearly, recently tilled soil thermal property values were quite dynamic temporally due to varyingθandρ_b. The dynamic soil thermal property values should be considered in soil heat and mass transfer models either as 3‐D functions ofθandρ_bor as linear functions ofn_air.

   Thermal property values for a range ofθandρ_bwere measured on undisturbed soil cores.

   Freshly tilled soil thermal property values were quite dynamic temporally.

   The thermal property values of a tilled soil were described as 3‐D surfaces withθandρ_b.

   The thermal property values of a tilled soil varied linearly withn_air.

    

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4. Dipole Response of Millennial Variability in Tropical South American Precipitation and δ18Op during the Last Deglaciation. Part II: δ18Op Response

   https://doi.org/10.1175/JCLI-D-22-0289.1  

   Bao, Yuntao ; Liu, Zhengyu ; He, Chengfei ( July 2023 , Journal of Climate)

   Understanding the hydroclimate representations of precipitationδ¹⁸O (δ¹⁸O_p) in tropical South America (TSA) is crucial for climate reconstruction from available speleothem caves. Our preceding study (Part I) highlights a heterogeneous response in millennial hydroclimate over the TSA during the last deglaciation (20–11 ka before present), characterized by a northwest–southeast (NW–SE) dipole in both rainfall andδ¹⁸O_p, with opposite signs between central-western Amazon and eastern Brazil. Mechanisms of suchδ¹⁸O_pdipole response are further investigated in this study with the aid of moisture tagging simulations. In response to increased meltwater discharge, the intertropical convergence zone (ITCZ) migrates southward, causing a moisture source location shift and depleting the isotopic value of the vapor transported into eastern Brazil, which almost entirely contributes to theδ¹⁸O_pdepletion in eastern Brazil (SE pole). In contrast, the moisture source location change and local condensation change (due to the lowering convergence level and increased rain reevaporation in unsaturated subcloud layers) contribute nearly equally to theδ¹⁸O_penrichment in the central-western Amazon (NW pole). Therefore, although a clear inverse relationship betweenδ¹⁸O_pand rainfall in both dipole regions seems to support the “amount effect,” we argue that the local rainfall amount only partially interprets the millennialδ¹⁸O_pchange in the central-western Amazon, whileδ¹⁸O_pdoes not document local rainfall change in eastern Brazil. Thus, the paleoclimate community should be cautious when usingδ¹⁸O_pas a proxy for past local precipitation in the TSA region. Finally, we discuss the discrepancy between the model and speleothem proxies on capturing the millennialδ¹⁸O_pdipole response and pose a challenge in reconciling the discrepancy.

   We want to comprehensively understand the hydroclimate footprints ofδ¹⁸O_pand the mechanisms of the millennial variability ofδ¹⁸O_pover tropical South America with the help of water tagging experiments performed by the isotope-enabled Community Earth System Model (iCESM). We argue that the millennialδ¹⁸O_pchange in eastern Brazil mainly documents the moisture source location change associated with ITCZ migration and the change of the isotopic value of the incoming water vapor, instead of the local rainfall amount. In contrast, the central-western Amazon partially documents the moisture source location shift and local precipitation change. Our study cautions that one should not simply resort to the isotopic “amount effect” to reconstruct past precipitation in tropical regions without studying the mechanisms behind it.

    

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5. Relationship between local-scale topography and vegetation on the invasive C 4 perennial bunchgrass buffelgrass ( Pennisetum ciliare ) size and reproduction

   https://doi.org/10.1017/inp.2023.9  

   Hovanes, Katherine A. ; Lien, Aaron M. ; Baldwin, Elizabeth ; Li, Yue M. ; Franklin, Kim ; Gornish, Elise S. ( March 2023 , Invasive Plant Science and Management)

   Buffelgrass [Pennisetum ciliare(L.) Link] is an invasive C₄perennial bunchgrass that is a threat to biodiversity in aridlands in the Americas and Australia. Topography influencesP. ciliareoccurrence at large spatial scales, but further investigation into the relationship between local-scale topography andP. ciliaregrowth and reproduction would be beneficial. Further, density-dependent effects onP. ciliaregrowth and reproduction have been demonstrated in greenhouse experiments, but the extent to which density dependence influencesP. ciliarein natural populations warrants further investigation. Here we present a study on the relationships between local-scale topography (aspect and slope gradient) and vegetation characteristics (shrub cover,P. ciliarecover, andP. ciliaredensity) and their interactions on individualP. ciliareplant size and reproduction. We measured slope gradient, aspect, shrub cover,P. ciliarecover,P. ciliaredensity, and the total number of live culms and reproductive culms of 10P. ciliareplants in 33 4 by 4 m plots located in 11 transects at the Desert Laboratory at Tumamoc Hill, Tucson, AZ, USA. We modeled the relationships at the local scale of (1)P. ciliarecover and density with aspect and slope gradient and (2)P. ciliaresize and reproduction with abiotic (slope gradient and aspect) and biotic (P. ciliarecover and density and native shrub and cacti cover) characteristics. Aspect and slope gradient were poor predictors ofP. ciliarecover and density in already invaded sites at the scale of our plots. However, aspect had a significant relationship withP. ciliareplant size and reproduction.Pennisetum ciliareplants on south-facing aspects were larger and produced more reproductive culms than plants on other aspects. Further, we found no relationship betweenP. ciliaredensity andP. ciliareplant size and reproduction. Shrub cover was positively correlated withP. ciliarereproduction. South-facing aspects are likely most vulnerable to fast spread and infilling by newP. ciliareintroductions.

    

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