We have deterministically created a stable topological spin texture in magnetic tunnel junctions (MTJ) by using pulsed or microwave currents. The spin texture is characterized by a field-dependent ...intermediate resistance state and a new magnetic resonance. Micromagnetic simulations show that the observations are consistent with the nucleation of a single skyrmion, facilitated by a spatially nonuniform stray field. The unique resonance spectrum is identified as the skyrmion breathing mode and a skyrmion diameter of 75 nm is estimated. This work shows the possibility to create skyrmions in MTJs without the Dzyaloshinskii-Moriya interaction and could lead to noninvasive, on-chip skyrmion measurement.
Our knowledge is still poor regarding the response of the precipitation vertical
structure to aerosols, partly due to the ignorance of precipitation occurring
at different spatial scales. A total of ...6 years of collocated ground-based PM10
and satellite-based (Tropical Rainfall Measuring Mission, TRMM) radar data, along with ERA-Interim reanalysis, are
used in this study to investigate the aerosol effects on three localized rain
regimes (shallow, stratiform, and convective rain) over the Pearl River Delta
region of China. A subjective analysis method is proposed to discriminate
between the localized and synoptic-scale precipitations based on weather
composite charts where daily averaged wind field at 850 hPa is overlaid with
the geopotential height at 500 hPa. In general, average rain rate tends to be
greater under polluted conditions than under clean conditions. But such
potential aerosol effects are regime dependent: as the atmosphere becomes
slightly polluted (PM10≤38 µg m−3), the top 1 % radar reflectivity (Z) for all regimes
initially increases, followed by continued increases and weak decreases for
convective and stratiform/shallow rain regimes, respectively. As the
atmosphere becomes much more polluted, such regime dependences of aerosol
effects are more significant. From a perspective of the vertical Z structure,
comparisons between polluted conditions (days with the highest third of
PM10 concentration) and clean conditions (days with the lowest third of
PM10 concentration) show that the convective rain regime exhibits a deeper
and stronger Z pattern, whereas a much shallower and weaker Z pattern is
observed for stratiform and shallow precipitation regimes. In particular, the
top height of the 30 dBZ rain echo increases by ∼29 %
(∼1.27 km) for the convective regime, but decreases by
∼10.8 % (∼0.47 km) for the stratiform regime.
However, no noticeable changes are observed for the shallow precipitation regime.
Impacts of meteorological factors are further studied on both rain top height
(RTH) and the center of gravity of Z, including vertical velocity, vertical wind
shear, convection available potential energy, and vertically integrated
moisture flux divergence (MFD). The possible invigoration effect on convective
precipitation seems dependent on wind shear, in good agreement with previous
findings. Overall, the observed dependence of the precipitation vertical
structure on ground-based PM10 supports the notion of aerosol
invigoration or suppression effect on cold or warm rain and adds new insights into
the nature of the complex interactions between aerosol and various localized
precipitation regimes.
The geographical shift of global anthropogenic aerosols from the developed countries to the Asian continent since the 1980s could potentially perturb the regional and global climate due to ...aerosol‐cloud‐radiation interactions. We use an atmospheric general circulation model with different aerosol scenarios to investigate the radiative and microphysical effects of anthropogenic aerosols from different regions on the radiation budget, precipitation, and large‐scale circulations. An experiment contrasting anthropogenic aerosol scenarios in 1970 and 2010 shows that the altered cloud reflectivity and solar extinction by aerosols results in regional surface temperature cooling in East and South Asia, and warming in the US and Europe, respectively. These aerosol‐induced temperature changes are consistent with the relative temperature trends from 1980 to 2010 over different regions in the reanalysis data. A reduced meridional streamfunction and zonal winds over the tropics as well as a poleward shift of the jet stream suggest weakened and expanded tropical circulations, which are induced by the redistributed aerosols through a relaxing of the meridional temperature gradient. Consequently, precipitation is suppressed in the deep tropics and enhanced in the subtropics. Our assessments of the aerosol effects over the different regions suggest that the increasing Asian pollution accounts for the weakening of the tropics circulation, while the decreasing pollution in Europe and US tends to shift the circulation systems southward. Moreover, the aerosol indirect forcing is predominant over the total aerosol forcing in magnitude, while aerosol radiative and microphysical effects jointly shape the meridional energy distributions and modulate the circulation systems.
Key Points
The emission shift contributes to the “dimming” in Asia and “brightening” in the US and Europe
Atmospheric meridional circulations are weakened by the redistributed aerosols
Aerosol effects from different regions contribute distinctively to the circulation modification
A rechargeable lithium anode requires a porous structure for a high capacity, and a stable electrode/electrolyte interface against dendrite formation and polysulfide crossover when used in a ...lithium-sulfur battery. Here, we design two simple steps of spontaneous reactions for protecting porous lithium electrodes. First, a reaction between molten lithium and sulfur-impregnated carbon nanofiber forms a fibrous network with a lithium shell and a carbon core. Second, we coat the surface of this porous lithium electrode with a composite of lithium bismuth alloys and lithium fluoride through another spontaneous reaction between lithium and bismuth trifluoride, solvated with phosphorous pentasulfide, which also polymerizes with lithium sulfide residual in the electrode to form a solid electrolyte layer. This protected porous lithium electrode enables stable operation of a lithium-sulfur battery with a sulfur loading of 10.2 mg cm
at 6.0 mA cm
for 200 cycles.
Since their inception, micro-size light emitting diode (µLED) arrays based on III-nitride semiconductors have emerged as a promising technology for a range of applications. This paper provides an ...overview on a decade progresses on realizing III-nitride µLED based high voltage single-chip AC/DC-LEDs without power converters to address the key compatibility issue between LEDs and AC power grid infrastructure; and high-resolution solid-state self-emissive microdisplays operating in an active driving scheme to address the need of high brightness, efficiency and robustness of microdisplays. These devices utilize the photonic integration approach by integrating µLED arrays on-chip. Other applications of nitride µLED arrays are also discussed.
Biocomposites consisting of hydroxyapatite (HAp) and natural polymers such as collagen, chitosan, chitin, and gelatin have been extensively investigated. However, studies on the combination of HAp ...with bacterial cellulose (BC) have not been conducted yet. In this work, our latest results concerning the biomimetic synthesis and characterization of HAp-BC nanocomposites with a 3-dimensional (3-D) network are reported. The present research focuses on characterizing the structure of this novel class of nanocomposites. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy (FTIR) were employed to characterize the HAp-BC nanocomposites. It is found that HAp crystals are formed when the phosphorylated and CaCl
2-treated BC fibers are soaked in a 1.5 simulated body fluid (SBF). XRD reveals that the crystallite sizes of the HAp crystals are nano-sized and their crystallinities are low. The FTIR results show that the HAp crystals are partially substituted with carbonate, resembling natural bones. The nanocomposites containing HAp with structural features close to those of biological apatites are attractive for applications as artificial bones and scaffolds for tissue engineering.
Convective clouds produce a significant proportion of the global precipitation and play an important role in the energy and water cycles. We quantify changes of the convective cloud ice mass-weighted ...altitude centroid (Z
) as a function of aerosol optical thickness (AOT). Analyses are conducted in smoke, dust and polluted continental aerosol environments over South America, Central Africa and Southeast Asia, using the latest measurements from the CloudSat and CALIPSO satellites. We find aerosols can inhibit or invigorate convection, depending on aerosol type and concentration. On average, smoke tends to suppress convection and results in lower Z
than clean clouds. Polluted continental aerosol tends to invigorate convection and promote higher Z
. The dust aerosol effects are regionally dependent and their signs differ from place to place. Moreover, we find that the aerosol inhibition or invigoration effects do not vary monotonically with AOT and the variations depend strongly on aerosol type. Our observational findings indicate that aerosol type is one of the key factors in determining the aerosol effects on convective clouds.
► γ-Fe2O3/SiO2/chitosan composite was prepared by water-in-oil emulsification method. ► Adsorption process followed the pseudo-second-order kinetic model. ► The intraparticle diffusion was related to ...the adsorption but not as a sole rate-controlling step. ► The equilibrium adsorption data was well described by Freundlich isotherm model. ► The adsorption process was feasible, spontaneous and exothermic in nature.
A γ-Fe2O3/SiO2/chitosan composite was prepared by water-in-oil emulsification, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Effects of various factors, including adsorbent dosage, initial dye concentration, solution pH, and competing anions, on the adsorption of methyl orange from aqueous solutions by the resulting composite were studied by batch adsorption experiments. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, and intraparticle diffusion was related to the adsorption, but not as a sole rate-controlling step. The equilibrium adsorption data were well described by the Freundlich isotherm model. Evaluation of the thermodynamic parameters ΔG°, ΔH°, and ΔS° revealed that the adsorption process was naturally feasible, spontaneous, and exothermic. The composite was proven to be efficient, suitable and promising for the removal of methyl orange from aqueous solutions since it has a relatively higher adsorption capacity than other low-cost adsorbents.
We have proposed a novel numerical method to calculate accurately physical quantities of the ground state using the tensor network wave function in two dimensions. The tensor network wave function is ...determined by an iterative projection approach which uses the Trotter-Suzuki decomposition formula of quantum operators and the singular value decomposition of matrix. The norm of the wave function and the expectation value of a physical observable are evaluated by a coarse-grain tensor renormalization group approach. Our method allows a tensor network wave function with a high bond degree of freedom (such as D=8) to be handled accurately and efficiently in the thermodynamic limit. For the Heisenberg model on a honeycomb lattice, our results for the ground state energy and the staggered magnetization agree well with those obtained by the quantum Monte Carlo and other approaches.
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