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Diamond shows unprecedented hardness. Because hardness is a measure of resistance of chemical bonds in a material to external indentation, the electronic bonding nature of diamond beyond several million atmospheres is key to understanding the origin of hardness. However, probing the electronic structures of diamond at such extreme pressure has not been experimentally possible. The measurements on the inelastic x-ray scattering spectra for diamond up to 2 million atmospheres provide data on the evolution of its electronic structures under compression. The mapping of the observed electronic density of states allows us to obtain a two-dimensional image of the bonding transitions of diamond undergoing deformation. The spectral change near edge onset is minor beyond a million atmospheres, while its electronic structure displays marked pressure-induced electron delocalization. Such electronic responses indicate that diamond’s external rigidity is supported by its ability to reconcile internal stress, providing insights into the origins of hardness in materials.

In this paper, we propose a deep reinforcement learning (DRL)-based algorithm to generate policies of Baseband Function (BBF) placement and routing. In order to explore the performance of the proposed algorithm in practical systems, the online scenario with the completely random requests is used in the simulation considering C-RAN and NG-RAN architectures. Besides, an Integer Linear Programming (ILP) model is formulated to generate the optimal solution as the benchmark. The simulation results show that DRL-based algorithm converges in a short time, and its performance closes to the optimal benchmark obtained by ILP in terms of latency and bandwidth for the online scenarios. In addition, the performance of the generated policies based on DRL is compared with a classic heuristic algorithm, i.e., first-fit algorithm. The performance of DRL-based algorithm is superior to the first-fit algorithm from above two perspectives. The fast convergence and the near-optimal performance prove that the DRL-based algorithm is a promising approach for the BBF placement and routing of RAN in 5G and Beyond.

δ-AlOOH has emerged as a promising candidate for water storage in the lower mantle and could have delivered water into the bottom of the mantle. To date, it still remains unclear how the presence of iron affects its elastic, rheological, vibrational, and transport properties, especially across the spin crossover. Here, we conducted high-pressure X-ray emission spectroscopy experiments on a δ-(Al0.85Fe0.15) OOH sample up to 53 GPa using silicone oil as the pressure transmitting medium in a diamond-anvil cell. We also carried out laser Raman measurements on δ-(Al0.85Fe0.15)OOH and δ-(Al0.52Fe0.48)OOH up to 57 and 62 GPa, respectively, using neon as the pressure-transmitting medium. Evolution of Raman spectra of δ-(Al0.85Fe0.15)OOH with pressure shows two new bands at 226 and 632 cm−1 at 6.0 GPa, in agreement with the transition from an ordered (P21nm) to a disordered hydrogen bonding structure (Pnnm) for δ-AlOOH. Similarly, the two new Raman bands at 155 and 539 cm−1 appear in δ-(Al0.52Fe0.48)OOH between 8.5 and 15.8 GPa, indicating that the incorporation of 48 mol% FeOOH could postpone the order-disorder transition upon compression. On the other hand, the satellite peak (Kβ′) intensity of δ-(Al0.85Fe0.15)OOH starts to decrease at ~30 GPa and it disappears completely at 42 GPa. That is, δ-(Al0.85Fe0.15)OOH undergoes a gradual electronic spin-pairing transition at 30–42 GPa. Furthermore, the pressure dependence of Raman shifts of δ-(Al0.85Fe0.15)OOH discontinuously decreases at 32–37 GPa, suggesting that the improved hydrostaticity by the use of neon pressure medium could lead to a relatively narrow spin crossover. Notably, the pressure dependence of Raman shifts and optical color of δ-(Al0.52Fe0.48)OOH dramatically change at 41–45 GPa, suggesting that it probably undergoes a relatively sharp spin transition in the neon pressure medium. Together with literature data on the solid solutions between δ-AlOOH and ε-FeOOH, we found that the onset pressure of the spin transition in δ-(Al,Fe)OOH increases with increasing FeOOH content. These results shed new insights into the effects of iron on the structural evolution and vibrational properties of δ-AlOOH. The presence of FeOOH in δ-AlOOH can substantially influence its high-pressure behavior and stability at the deep mantle conditions and play an important role in the deep-water cycle.

To accommodate ever-growing mobile data and heterogeneous 5G services, considerable challenges have emerged to stimulate new design principles on radio access networks (RAN). Advanced functional splits are then introduced to divide baseband unit (BBU) into two new entities, i.e., distributed unit (DU) and central unit (CU), that DU-CU can be co-located or separated into different processing pools (PP) honoring service requirements. Then, the optical transport network evolves towards a more flexible architecture to support agile DU-CU deployment (i.e., alterable DU-CU locations). However, this agile DU-CU deployment without an effective management strategy may lead to the activation of many unnecessary PPs and lightpaths in the network infrastructure that results in low energy efficiency. Moreover, this problem will be continuously amplified with network scale expansion, which becomes one of the operator's major concerns for OPEX reduction. Thus, in this paper, we are dedicated to solving this problem through turning network devices from “always on” to “on-demand on” pattern to support energy-efficient DU-CU deployment and lightpath provisioning. To this end, we propose a mixed-integer linear programming (MILP) model and auxiliary graph-based heuristic to minimize the power consumption of reconfigurable add/drop multiplexer, Ethernet switch, optical transponder, PP, and DU-CU processor. We analyze the power consumption under different 5G services (i.e., eMBB, URLLC, and mMTC) from a latency perspective in both small-scale and large-scale networks. Moreover, our strategies can also be applied with adjustable deployment that adapts to time-varying user traffics, which reduces power by over 14% compared to conventional static deployment. Our analyses can help provide insights into the modeling and designing of energy-efficient DU-CU deployment and lightpath provisioning in 5G.

Volume collapse under high pressure is an intriguing phenomenon involving subtle interplay between lattice, spin, and charge. The two most important causes of volume collapse are lattice collapse (low-density to high-density) and magnetic collapse (high-spin to low-spin). Herein we report the pressure-driven sequential volume collapses in partially intercalated FexNbS2 (x = 1/4, 1/3, 1/2, 2/3). Because of the distinct interlayer atomic occupancy, the low-iron-content samples exhibit both lattice and magnetic collapses under compression, whereas the high-iron-content samples exhibit only one magnetic collapse. Theoretical calculations indicate that the low-pressure volume collapses for x = 1/4 and x = 1/3 are lattice collapses, and the high-pressure volume collapses for all four samples are magnetic collapses. The magnetic collapse involving the high-spin to low-spin crossover of Fe2+ has also been verified by in situ X-ray emission measurements. Integrating two distinct volume collapses into one material provides a rare playground of lattice, spin, and charge.

This paper investigates the effectiveness of online reviews on addressing price endogeneity issue in an application to consumer demand for smartphone. We consider review variables as the substitutes of unobserved product quality in terms of a scalar variable as seen in previous methods. An aspect-based sentiment classification technique is designed to construct feature-related review variables from millions of review contents. We discuss the performance of review variables both in a hedonic pricing model and a conditional logit discrete choice model. Our results demonstrate that review variables show a good performance either as instruments for price or as explicit control variables in demand models. In detail, the pricing prediction accuracy increases 3.4%, which is considered as a significant improvement in the practice of forecasting. In the discrete choice model, the estimated price coefficient is biased in the positive direction without endogeneity correction. It is adjusted in the expected way after including review variables. The findings indicate that online reviews provide alternative sources of information in dealing with endogeneity in discrete choice models. We also analyze the differences in the preferences and needs of individual consumers to provide some practical implications of marketing.

Valence transition could induce structural, insulator-metal, nonmagnetic-magnetic and superconducting transitions in rare-earth metals and compounds, while the underlying physics remains unclear due to the complex interaction of localized 4f electrons as well as their coupling with itinerant electrons. The valence transition in the elemental metal europium (Eu) still has remained as a matter of debate. Using resonant x-ray emission scattering and x-ray diffraction, we pressurize the states of 4f electrons in Eu and study its valence and structure transitions up to 160 GPa. We provide compelling evidence for a valence transition around 80 GPa, which coincides with a structural transition from a monoclinic (C2/c) to an orthorhombic phase (Pnma). We show that the valence transition occurs when the pressure-dependent energy gap between 4f and 5d electrons approaches the Coulomb interaction. Our discovery is critical for understanding the electrodynamics of Eu, including magnetism and high-pressure superconductivity.

Eu(Fe

The isotopic compositions of iron in major mantle minerals may record chemical exchange between deep-Earth reservoirs as a result of early differentiation and ongoing plate tectonics processes. Bridgmanite (Bdg), the most abundant mineral in the Earth’s lower mantle, can incorporate not only Al but also Fe with different oxidation states and spin states, which in turn can influence the distribution of Fe isotopes between Bdg and ferropericlase (Fp) and between the lower mantle and the core. In this study, we combined first-principles calculations with high-pressure nuclear resonant inelastic X-ray scattering measurements to evaluate the effects of Fe site occupancy, valence, and spin states at lower-mantle conditions on the reduced Fe partition function ratio (β-factor) of Bdg. Our results show that the spin transition of octahedral-site (B-site) Fe3+ in Bdg under mid-lower-mantle conditions generates a +0.09‰ increase in its β-factor, which is the most significant effect compared to Fe site occupancy and valence. Fe2+-bearing Bdg varieties have smaller β-factors relative to Fe3+-bearing varieties, especially those containing B-site Fe3+. Our models suggest that Fe isotopic fractionation between Bdg and Fp is only significant in the lowermost mantle due to the occurrence of low-spin Fe2+ in Fp. Assuming early segregation of an iron core from a deep magma ocean, we find that neither core formation nor magma ocean crystallization would have resulted in resolvable Fe isotope fractionation. In contrast, Fe isotopic fractionation between low-spin Fe3+-bearing Bdg/Fe2+-bearing Fp and metallic iron at the core-mantle boundary may have enriched the lowermost mantle in heavy Fe isotopes by up to +0.20‰.

The centralized radio access network (C-RAN) is an effective architecture to promote CAPEX/OPEX reduction and cell cooperation derived from its centralized baseband processing. However, there is a contradiction between centralization gain and transport resource saving, which hinders the vision of a resource-efficient and cost-effective RAN deployment. Advanced RAN architectures with functional splits are then introduced to cope with this challenge. Distinguished with other studies, we are intended to investigate whether a fine-grained functional split architecture could benefit to the RAN evolution, and how it impacts on the converged optical-wireless access networks. To this end, we establish a quantitative model to analyze the performance of this architecture. With the fine-grained split, baseband unit (BBU) is divided into a set of fine-grained units (FU) to be placed in desired processing pools (PP) as a service chain. To analyze the placement performance, we propose a mixed-integer linear programming model (MILP) considering the PP selection, routing, wavelength and bandwidth assignment, as well as latency control to minimize the number of PPs, bandwidth, latency, and functions deployment cost. We compare its performance with other two coarse-grained split architectures, i.e., SBBU (adopt low-PHY split like BBU in 4G) and recently emerged DU-CU in both small-scale and large-scale network scenarios. Our analyses provide insights into the modeling and design of efficient converged optical-wireless access networks in 5G and beyond.

High-Pressure Collaborative Access Team (HPCAT) is a synchrotron-based facility located at the Advanced Photon Source (APS). With four online experimental stations and various offline capabilities, HPCAT is focused on providing synchrotron x-ray capabilities for high pressure and temperature research and supporting a broad user community. Overall, the array of online/offline capabilities is described, including some of the recent developments for remote user support and the concomitant impact of the current pandemic. General overview of work done at HPCAT and with a focus on some of the minerals relevant work and supporting capabilities is also discussed. With the impending APS-Upgrade (APS-U), there is a considerable effort within HPCAT to improve and add capabilities. These are summarized briefly for each of the end-stations.

Volume collapse under high pressure is an intriguing phenomenon involving subtle interplay between lattice, spin, and charge. The two most important causes of volume collapse are lattice collapse (low-density to high-density) and magnetic collapse (high-spin to low-spin). Herein we report the pressure-driven sequential volume collapses in partially intercalated Fe

To establish the microscopic P-T phase diagram of recent 112-type iron-pnictides $\mathrm{Eu}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}){\mathrm{As}}_{2}$ (x = 0, 0.04), high-pressure synchrotron M\"ossbauer spectroscopy experiments in $^{151}\mathrm{Eu}$ and $^{57}\mathrm{Fe}$ have been performed. In ${\mathrm{EuFeAs}}_{2}$ application of pressure completely suppresses the itinerant electron magnetism from the Fe sublattice and the local-moment magnetism in Eu ions at $\ensuremath{\sim}10\phantom{\rule{0.16em}{0ex}}$ and $\ensuremath{\sim}11.6\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, respectively. High-pressure x-ray diffraction experiments in ${\mathrm{EuFeAs}}_{2}$ reveal an anomalous change in the lattice parameters and a discontinuity in volume around 10 GPa, suggesting an isostructural transition at this pressure. With Ni-doping (x = 0.04), a collapse of local magnetic order occurs at $\ensuremath{\sim}8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, a lower critical pressure compared with the parent compound. In both systems, the suppression of local-moment magnetism is associated with a significant increase of mean valence in Eu ions.

Massive MIMO (mMIMO) is a technology with high potential in future 5G radio access networks (RAN). As a crucial feature in mMIMO, beam-forming provides a remarkable enhancement for the wireless transmission. However, beam-forming introduces extra wireless resource and fronthaul bandwidth consumption for utilizing multiple antennas to transmit the same data. Moreover, this problem will be highlighted in the multicast-service beam-forming because more identical data will be transmitted in networks. In this paper, we focus on the entire resource consumption of a single cell for the multicast-service beam-forming in next-generation RAN and propose a flexible wavelength-division-multiplexing-based fronthaul to support the high-capacity and resilient transport. A mixed-integer nonlinear programming formulation and two heuristic algorithms are developed to minimize the utilized optical bandwidth, radio resource blocks and antennas. Simulation comparisons are performed among different resource allocation strategies. Numerical results demonstrate that our strategies can efficiently reduce the total resource consumption.

Massive multiple input multiple output (mMIMO) enabled beamforming is a promising technology in the next generation of mobile communication. It allows multiple antennas transmit the same data to a user to improve the signal strength and quality. However, beamforming may incur redundant data transmission over fronthaul in the centralized radio access networks. When accommodating a set of beam requests, a key problem is how to coordinate radio and optical resources to maximize the beamforming throughput and minimize the fronthaul bandwidth. In this paper, we study on the joint wavelength, antenna, radio resource block allocation (WARA) in a time and wavelength division multiplexed passive optical network, which is an economic fronthaul solution for the mMIMO. We formulate the WARA into an integer linear programming (ILP) model. Three heuristic algorithms are proposed to optimize fronthaul bandwidth, radio resource block (RB) utilization, and both. We compare ILP with the proposed algorithms under different sizes of antenna arrays. A tradeoff is shown to exist between fronthaul bandwidth and radio RB utilization. Also, we find that the optimization goal depends on the number of antennas in an optical network unit.

We report here pressure induced nanocrystal coalescence of ordered lead chalcogenide nanocrystal arrays into one-dimensional (1D) and 2D nanostructures. In particular, atomic crystal phase transitions and mesoscale coalescence of PbS and PbSe nanocrystals have been observed and monitored in situ respectively by wide- and small-angle synchrotron X-ray scattering techniques. At the atomic scale, both nanocrystals underwent reversible structural transformations from cubic to orthorhombic at significantly higher pressures than those for the corresponding bulk materials. At the mesoscale, PbS nanocrystal arrays displayed a superlattice transformation from face-centered cubic to lamellar structures, while no clear mesoscale lattice transformation was observed for PbSe nanocrystal arrays. Intriguingly, transmission electron microscopy showed that the applied pressure forced both spherical nanocrystals to coalesce into single crystalline 2D nanosheets and 1D nanorods. Our results confirm that pressure can be used as a straightforward approach to manipulate the interparticle spacing and engineer nanostructures with specific morphologies and, therefore, provide insights into the design and functioning of new semiconductor nanocrystal structures under high-pressure conditions.

We propose a topology-level protection scheme (TLPS) tailored to differential reliability demands for 5G/B5G network slicing. The cases of reliable slicing are numerically evaluated that TLPS shows its superiority in redundancy resources saving.

Mobile/multi-access edge computing (MEC) takes advantage of its proximity to end-users, which greatly reduces the transmission delay of task offloading compared to mobile cloud computing (MCC). Offloading computing tasks to edge servers with a certain amount of computing ability can also reduce the computing delay. Meanwhile, device-to-device (D2D) cooperation can help to process small-scale delay-sensitive tasks to further decrease the delay of tasks. But where to offload the computing tasks is a critical issue. In this article, we integrate MEC and D2D cooperation techniques to optimize the offloading decisions and resource allocation problem in D2D-enabled three-tier MEC networks for Internet of Things (IoT). Mobile devices (MDs), edge clouds, and central cloud data center (DC) make up these three-tier MEC networks. They cooperate with each other to finish the offloading tasks. Each task can be processed by MD itself or its neighboring MDs at device tier, by edge servers at edge tier, or by remote cloud servers at cloud tier. Under the maximum energy cost constraints, we formulate the cooperative offloading problem into a mixed-integer nonlinear problem aiming to minimize the total delay of tasks. We utilize the alternating direction method of multipliers (ADMM) to speed up the computing process. The proposed scheme decomposes the complicated problem into 3 smaller subproblems, which are solved in a parallel fashion. Finally, we compare our proposal with D2D and MEC networks in simulations. Numerical results validate that the proposed D2D-enabled MEC networks for IoT can significantly enhance the computing abilities and reduce the total delay of tasks.

Metallization of hydrogen as a key problem in modern physics is the pressure-induced evolution of the hydrogen electronic band from a wide-gap insulator to a closed gap metal. However, due to its remarkably high energy, the electronic band gap of insulating hydrogen has never before been directly observed under pressure. Using high-brilliance, high-energy synchrotron radiation, we developed an inelastic x-ray probe to yield the hydrogen electronic band information in situ under high pressures in a diamond-anvil cell. The dynamic structure factor of hydrogen was measured over a large energy range of 45 eV. The electronic band gap was found to decrease linearly from 10.9 to 6.57 eV, with an 8.6 times densification ($\ensuremath{\rho}/{\ensuremath{\rho}}_{0}\ensuremath{\sim}8.6$) from zero pressure up to 90 GPa.

We have performed an extensive pressure-dependent structural, spectroscopic, and electrical transport study of LaCrSb$_3$. The ferromagnetic phase (T$_C$ = 120 K at p = 0 GPa) is fully suppressed by p = 26.5 GPa and the Cr-moment decreases steadily with increasing pressure. The unit cell volume decreases smoothly up to p = 55 GPa. We find that the bulk modulus and suppression of the magnetism are in good agreement with theoretical predictions, but the Cr-moment decreases smoothly with pressure, in contrast to steplike drops predicted by theory. The ferromagnetic ordering temperature appears to be driven by the Cr-moment., Comment: 8 pages, 8 figures