Different real-time degradation scenarios of functionalized poly(ε-caprolactone) for biomedical applications

Anterior cruciate ligament (ACL) ruptures are a much-commented injury as it can end the season or even career of professional athletes. However, the recovery of a patient from the general population is no less painful during the long period required by current treatments. Artificial ligaments could improve this healing, yet, orthopedic surgeons are still cautious about permanent ACL implants. Therefore, combining biodegradation and bioactivity could be a key feature for the popularization of these devices. This study aim at evaluating the real-time degradation of poly(ε-caprolactone) (PCL) grafted with the bioactive polymer sodium polystyrene sulfonate in different scenarios. PCL physical–chemical properties were evaluated before and after degradation. In addition, in vitro experiments were realized to confirm the long term influence of the grafting on cell response. Altogether, we were able to show different degradations scenarios, enabling to study the impact of degradation environment on degradation mode and rate of functionalized PCL.     

Effect of climatic factors on farm income of rain-fed and irrigated farming households in Vietnam

The paper provides new evidence of the effect of temperature and precipitation on crop profit of farmers applying different farming systems across different seasons as well as geographical regions in Vietnam for the period 2004–2016. The result finds that the effect of fluctuation in temperature and rainfall on the crop profit of farmers is not uniform across the three regions (North, Central and South) and also considerable variation across rain-fed and irrigated farms. For the rain-fed farming system, (i) rainfall in the dry season has a nonlinearly (⋂) association with the profit, but rainfall in the rainy season has no effect, and (ii) dry season temperature and rainy season temperature have, respectively, ⋂-shaped and U-shaped relationship with the profit. For the irrigated farming systems, the temperatures in the dry season and rainy season have a U-shaped relationship with the profit. The findings show that the irrigated farming systems have been effective in the long term in the face of climate change. Therefore, in preparation for adaptation to climate change, the Vietnamese agricultural sector needs a complete irrigation system at both farm and regional levels.     

Energy-efficient transceiver designs for multiuser MIMO cognitive radio networks via interference alignment

This paper studies the transceiver design for multiuser multiple-input multiple-output cognitive radio networks. Different from the conventional methods which aim at maximizing the spectral efficiency, this paper focuses on maximizing the energy efficiency (EE) of the network. First, we formulate the precoding and decoding matrix designs as optimization problems which maximize the EE of the network subject to per-user power and interference constraints. With a higher priority in accessing the spectrum, the primary users (PUs) can design their transmission strategies without awareness of the secondary user (SU) performance. Thus, we apply a full interference alignment technique to eliminate interference between the PUs. Then, the EE maximization problem for the primary network can be reformulated as a tractable concave-convex fractional program which can be solved by the Dinkelbach method. On the other hand, the uncoordinated interference from the PUs to the SUs cannot be completely eliminated due to a limited coordination between the PUs with the SUs. The secondary transceivers are designed to optimize the EE while enforcing zero-interference to the PUs. Since the EE maximization for the secondary network is an intractable fractional programming problem, we develop an iterative algorithm with provable convergence by invoking the difference of convex functions programming along with the Dinkelbach method. In addition, we also derive closed-form expressions for the solutions in each iteration to gain insights into the structures of the optimal transceivers. The simulation results demonstrate that our proposed method outperforms the conventional approaches in terms of the EE.     

Enhanced hot-carrier cooling and ultrafast spectral diffusion in strongly coupled PbSe quantum-dot solids

PbSe quantum-dot solids are of great interest for low cost and efficient photodetectors and solar cells. We have prepared PbSe quantum-dot solids with high charge carrier mobilities using layer-by-layer dip-coating with 1,2-ethanediamine as substitute capping ligands. Here we present a time and energy resolved transient absorption spectroscopy study on the kinetics of photogenerated charge carriers, focusing on 0-5 ps after photoexcitation. We compare the observed carrier kinetics to those for quantum dots in dispersion and show that the intraband carrier cooling is significantly faster in quantum-dot solids. In addition we find that carriers diffuse from higher to lower energy sites in the quantum-dot solid within several picoseconds.     

化选矿硫酸浸出稀土工艺研究

化选矿经硫酸浸出,在合适的酸度、温度、反应时间条件下,稀土浸出率为90%。     

Effect of milling on the anisotropic grain growth in a sintered Ba5Nb4O15 specimen and its effect on microwave dielectric properties

In this study, relationships between the processing, microstructure, and properties of barium niobate (Ba₅Nb₄O₁₅) are investigated. The milling of a Ba₅Nb₄O₁₅ powder in water is effective with respect to size reduction. However, after milling in water, BaCO₃ is formed within the slurry. With the increase in the amount of BaCO₃ formed, the aspect ratio of the elongated Ba₅Nb₄O₁₅ grains increases. The formation of the elongated Ba₅Nb₄O₁₅ grains prohibits the densification. Hence, the microwave dielectric properties, including permittivity and quality factor, are poor because of the low density. In addition, milling in ethanol is carried out for comparison: A lower amount of BaCO₃ is formed after milling in ethanol; the extent of anisotropic grain growth is thus reduced.     

Two‐Terminal Multibit Optical Memory via van der Waals Heterostructure

2D van der Waals (vdWs) heterostructures exhibit intriguing optoelectronic properties in photodetectors, solar cells, and light‐emitting diodes. In addition, these materials have the potential to be further extended to optical memories with promising broadband applications for image sensing, logic gates, and synaptic devices for neuromorphic computing. In particular, high programming voltage, high off‐power consumption, and circuital complexity in integration are primary concerns in the development of three‐terminal optical memory devices. This study describes a multilevel nonvolatile optical memory device with a two‐terminal floating‐gate field‐effect transistor with a MoS₂/hexagonal boron nitride/graphene heterostructure. The device exhibits an extremely low off‐current of ≈10^?14 A and high optical switching on/off current ratio of over ≈10⁶, allowing 18 distinct current levels corresponding to more than four‐bit information storage. Furthermore, it demonstrates an extended endurance of over ≈10⁴ program–erase cycles and a long retention time exceeding 3.6 × 10⁴ s with a low programming voltage of ?10 V. This device paves the way for miniaturization and high‐density integration of future optical memories with vdWs heterostructures.     

Anomalous independence of multiple exciton generation on different group IV-VI quantum dot architectures

Multiple exciton generation (MEG) in PbSe quantum dots (QDs), PbSe(x)S(1-x) alloy QDs, PbSe/PbS core/shell QDs, and PbSe/PbSe(y)S(1-y) core/alloy-shell QDs was studied with time-resolved optical pump and probe spectroscopy. The optical absorption exhibits a red-shift upon the introduction of a shell around a PbSe core, which increases with the thickness of the shell. According to electronic structure calculations this can be attributed to charge delocalization into the shell. Remarkably, the measured quantum yield of MEG, the hot exciton cooling rate, and the Auger recombination rate of biexcitons are similar for pure PbSe QDs and core/shell QDs with the same core size and varying shell thickness. The higher density of states in the alloy and core/shell QDs provide a faster exciton cooling channel that likely competes with the fast MEG process due to a higher biexciton density of states. Calculations reveal only a minor asymmetric delocalization of holes and electrons over the entire core/shell volume, which may partially explain why the Auger recombination rate does not depend on the presence of a shell.     

Creep fracture behaviour of SUS304H steel with vanadium addition based on small punch creep testing

The high-temperature creep fracture behaviour and creep strength of SUS 304H containing a minor addition of V were investigated in this study. A series of small punch (SP) creep and uniaxial creep tests were performed at 700 °C. The load and punch displacement rates obtained from the SP creep tests were used to derive conversion equations to determine the equivalent stress and creep strain rates. A converting equation is suggested in this study so that Norton’s secondary power law creep constants obtained from the SP creep testing can be in agreement with those obtained from the uniaxial tensile creep tests. The creep strength of the modified SUS 304H steel containing V was shown to be superior to that without V based on the current results and other available results for type 304H steel.