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Understanding the structure of the diffusion region of magnetic reconnection is crucial to pinpoint the mechanism of energy conversion from magnetic field to plasma. Characteristics of a diffusion region with guide field (i.e., component reconnection) may be significantly different from those of a diffusion region without guide field (i.e., antiparallel reconnection). In this study, we attempt to understand the structure of a diffusion region with guide field by studying the density cavity along separatrix. We present an event in which a density cavity was detected by the Cluster spacecraft in a diffusion region in the presence of guide field. The cavity was located around the separatrix region on the southern hemisphere of the neutral sheet and earthward of the X‐line and was coincident with strong magnetic field compression. The width of the cavity was on the ion inertial scale. This cavity contained a relatively strong antiparallel current, which was mainly contributed by parallel streaming electrons with energy of 1–10 keV. Enhancements of lower hybrid wave and electromagnetic whistler wave were observed inside the cavity. These waves are probably excited by parallel streaming electrons along separatrix via electron beam instability. Two‐dimensional electromagnetic particle‐in‐cell simulation was employed to study the structure of the density cavity. The location and scale of the cavity and the signature of electric current and electron velocity are consistent with our observations. It is found that there was displacement between the position of electron density minimum and out‐of‐plane magnetic field maximum in reconnection with guide field. However, this displacement is much less than that in reconnection without guide field. There was no significant acceleration for electrons to reach energy larger than 30 keV at the cavity. Key Points Reveal the microphysics of density cavity in diffusion region with guide field Study the wave‐particle interaction that occurred inside the density cavity Kinetic simulations reproduce most features of the observed depletion layer

We compared growth performance and survival of three hybrid poplar clones (Walker, Northwest and Okanese) planted as cuttings into five different Styroblock ® containers (412A, 415D, 512A, 515A, 615A) with increasing cavity volume and decreasing cavity density under commercial growing conditions at two nurseries in central Alberta, Canada. After 175 days of growth, our results showed considerable variation in growth traits among container types while survival was generally high with an overall average of 89 %. Initial cutting diameter appeared to be an important predictor of survival and our results showed that a cutting diameter of ≥7.5 mm increased survival rates of the tested hybrid poplar planting stock. Furthermore, containers with larger cavity volume and lower cavity density had a strong positive influence on growth and survival across nurseries ( R 2  = 0.96). Growth trait interactions with container type showed that container 512A (cavity volume: 220 ml; cavity depth: 12 cm) resulted in more diameter growth across clones. Cavities with a depth of 15 cm (415D, 515A, 615A) resulted in higher root:shoot ratios than cavities with a depth of only 12 cm (412A, 512A), irrespective of cavity volume or cavity density. Lastly, our study identified Okanese as a well-rounded clone with great growth potential both above and below ground. From an operational standpoint, we found container types 512A and 515A the most cost-effective choices under the assumption that nursery space and budgets are limiting factors.

Tree cavities are a critical resource for many animals, especially as nesting sites for birds. Patterns of cavity distribution in temperate forests are well studied, yet little is known of cavities in tropical forests, despite a hypothesized decrease in cavity availability with decreasing latitude. We studied cavity density and distribution in a wet lowland tropical forest in Costa Rica and compared our results with estimates from forests around the world. Cavities at our site were common, occurred frequently in living trees, and were often formed by damage or decay rather than by woodpeckers. Most cavities had small openings, and woodpecker-created cavities were nonrandomly oriented. Contrary to prediction, cavity density appears to increase from the poles to the tropics. We suggest potential mechanisms to explain these patterns.

This paper presents the results from a numerical study of the effects of multiple ion species on the development of small‐scale, intense electromagnetic waves and density structures that are frequently observed in the auroral ionosphere in the vicinity of discrete auroral arcs. The study is based on a multifluid MHD model describing nonlinear coupling between shear and slow ultra‐low‐frequency MHD waves in cold, low‐altitude plasma containing several ion species. Simulations reveal that these waves can be generated by the ionospheric feedback instability in the downward current channels adjacent to the upward currents, causing aurora, when heavy ionospheric ions (in particular, O2+) provide the “matching impedance” condition between the ionosphere and the magnetosphere. The ponderomotive force associated with these waves moves ions along the ambient magnetic field from the ionosphere. Different ion species exhibit different dynamics, depending on their masses and initial distributions. The strongest variations in density of −14% and +23% of the background values occur in the F region and are produced by the dynamics of O+ ions. These density variations can be detected by ground radars and low‐orbiting satellites in the auroral zone. Key Points Realistic multi‐fluid MHD model for MI coupling The model describes coupling between plasma density and ULF waves The results explain large number of observations at high latitudes

In this manuscript, we study the localization and density cavitations using inertial Alfvén wave (AW) and fast AW in the auroral ionosphere. We first develop a system of equations semi-analytically for both wave modes by using two-fluid model and then solve the model equations numerically using two-dimensional pseudo-spectral approach to analyze the localized structures and cavity formation at different instant of time. The ponderomotive force associated with the pump wave changes the background density and as the inertial AWs propagate through the modified density channel it gets localized. Therefore, the inertial AW splits up into filamentary/localized structures. A low frequency fast AW traveling through these complex structures created by inertial AW, is intensified having its own filamentary structures. The filamentary structures grow with time until the instability acquires steady state. We notice that the density cavities are also accompanied by the high amplitude magnetic fields. The amplitude of the strongest density cavity is estimated as ∼0.26 n 0 ( n 0 is unperturbed plasma number density). We also discuss the implications of the present study in the context of auroral ionosphere.

Strong light–matter coupling provides a promising path for the control of quantum matter where the latter is routinely described from first principles. However, combining the quantized nature of light with this ab initio tool set is challenging and merely developing as the coupled light–matter Hilbert space is conceptually different and computational cost quickly becomes overwhelming. In this work, we provide a nonperturbative photon-free formulation of quantum electrodynamics (QED) in the long-wavelength limit, which is formulated solely on the matter Hilbert space and can serve as an accurate starting point for such ab initio methods. The present formulation is an extension of quantum mechanics that recovers the exact results of QED for the zero- and infinite-coupling limit and the infinite-frequency as well as the homogeneous limit, and we can constructively increase its accuracy. We show how this formulation can be used to devise approximations for quantum-electrodynamical density-functional theory (QEDFT), which in turn also allows us to extend the ansatz to the full minimal-coupling problem and to nonadiabatic situations. Finally, we provide a simple local density–type functional that takes the strong coupling to the transverse photon degrees of freedom into account and includes the correct frequency and polarization dependence. This QEDFT functional accounts for the quantized nature of light while remaining computationally simple enough to allow its application to a large range of systems. All approximations allow the seamless application to periodic systems.

Deep neural networks (DNNs) are reshaping the field of information processing. With the exponential growth of these DNNs challenging existing computing hardware, optical neural networks (ONNs) have recently emerged to process DNN tasks with high clock rates, parallelism and low-loss data transmission. However, existing challenges for ONNs are high energy consumption due to their low electro-optic conversion efficiency, low compute density due to large device footprints and channel crosstalk, and long latency due to the lack of inline nonlinearity. Here we experimentally demonstrate a spatial-temporal-multiplexed ONN system that simultaneously overcomes all these challenges. We exploit neuron encoding with volume-manufactured micrometre-scale vertical-cavity surface-emitting laser (VCSEL) arrays that exhibit efficient electro-optic conversion (<5 attojoules per symbol with a π-phase-shift voltage of Vπ = 4 mV) and compact footprint (<0.01 mm2 per device). Homodyne photoelectric multiplication allows matrix operations at the quantum-noise limit and detection-based optical nonlinearity with instantaneous response. With three-dimensional neural connectivity, our system can reach an energy efficiency of 7 femtojoules per operation (OP) with a compute density of 6 teraOP mm−2 s−1, representing 100-fold and 20-fold improvements, respectively, over state-of-the-art digital processors. Near-term development could improve these metrics by two more orders of magnitude. Our optoelectronic processor opens new avenues to accelerate machine learning tasks from data centres to decentralized devices.Energy consumption and compute density are challenges for computing systems. Here researchers show an optical computing architecture using micrometre-scale VCSEL transmitter arrays enabling 7 fJ energy per operation and a potential compute density of 6 tera-operations mm−2 s−1.

We experimentally study the stability of a bosonic Mott insulator against the formation of a density wave induced by long-range interactions and characterize the intrinsic dynamics between these two states. The Mott insulator is created in a quantum degenerate gas of 87-Rubidium atoms, trapped in a 3D optical lattice. The gas is located inside and globally coupled to an optical cavity. This causes interactions of global range, mediated by photons dispersively scattered between a transverse lattice and the cavity. The scattering comes with an atomic density modulation, which is measured by the photon flux leaking from the cavity. We initialize the system in a Mott-insulating state and then rapidly increase the global coupling strength. We observe that the system falls into either of two distinct final states. One is characterized by a low photon flux, signaling a Mott insulator, and the other is characterized by a high photon flux, which we associate with a density wave. Ramping the global coupling slowly, we observe a hysteresis loop between the two states—a further signature of metastability. A comparison with a theoretical model confirms that the metastability originates in the competition between short- and global-range interactions. From the increasing photon flux monitored during the switching process, we find that several thousand atoms tunnel to a neighboring site on the timescale of the single-particle dynamics. We argue that a density modulation, initially forming in the compressible surface of the trapped gas, triggers an avalanche tunneling process in the Mott-insulating region.

Background Jaw-bone defects caused by various diseases lead to aesthetic and functional complications, which can seriously affect the life quality of patients. Current treatments cannot fully meet the needs of reconstruction of jaw-bone defects. Thus, the research and application of bone tissue engineering are a “hot topic.” As seed cells for engineering of jaw-bone tissue, oral cavity-derived stem cells have been explored and used widely. Models of jaw-bone defect are excellent tools for the study of bone defect repair in vivo. Different types of bone defect repair require different stem cells and bone defect models. This review aimed to better understand the research status of oral and maxillofacial bone regeneration. Main text Data were gathered from PubMed searches and references from relevant studies using the search phrases “bone” AND (“PDLSC” OR “DPSC” OR “SCAP” OR “GMSC” OR “SHED” OR “DFSC” OR “ABMSC” OR “TGPC”); (“jaw” OR “alveolar”) AND “bone defect.” We screened studies that focus on “bone formation of oral cavity-derived stem cells” and “jaw bone defect models,” and reviewed the advantages and disadvantages of oral cavity-derived stem cells and preclinical model of jaw-bone defect models. Conclusion The type of cell and animal model should be selected according to the specific research purpose and disease type. This review can provide a foundation for the selection of oral cavity-derived stem cells and defect models in tissue engineering of the jaw bone.

Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging applications in quantum and nonlinear optics as well as opportunities for modifying material-related properties. Exploration of these phenomena is theoretically demanding, as polaritons exist at the intersection between quantum optics, solid state physics, and quantum chemistry. Fortunately, nanoscale polaritons can be realized in small plasmon-molecule systems, enabling treatment with ab initio methods. Here, we show that time-dependent density-functional theory calculations access the physics of nanoscale plasmon-molecule hybrids and predict vacuum Rabi splitting. By considering a system comprising a few-hundred-atom aluminum nanoparticle interacting with benzene molecules, we show that cavity quantum electrodynamics holds down to resonators of a few cubic nanometers in size, yielding a single-molecule coupling strength exceeding 200 meV due to a massive vacuum field of 4.5 V · nm −1 . In a broader perspective, ab initio methods enable parameter-free in-depth studies of polaritonic systems for emerging applications. Light-matter interaction is described by many different approaches and approximations depending on the coupling strength. Here the authors model a plasmonic system of aluminum nanoparticle interacting with benzene molecules using TDDFT and show its validity to a strong plasmon-molecule coupling regime.