This paper investigates and analyzes the number of reflecting elements for guaranteed energy- and spectral-efficient intelligent reflecting surface (IRS)-assisted communication systems. As opposed to ...previous works where the energy efficiency (EE)/the spectral efficiency (SE) maximization or the EE-SE tradeoff was considered, our goal is to minimize the number of reflecting elements in the IRS-assisted system. Besides, both the EE and the SE constraints are considered in the number minimization problem, which has not been addressed in existing works. However, both the EE and the SE performance do not admit exact closed-form expressions due to the non-convexity incurred by joint beamforming and phase shift design. In order to make the optimization problem tractable, we resort to their performance bounds for problem reformulation. By decomposing the problem into two sub-problems, we are able to derive closed-form expressions for the minimum number of reflecting elements, and both the coherent phase shift (CPS)-oriented solution and the random phase shift (RPS)-oriented solution are proposed for comparison. In order to shed light on the practical design, the relationship between the derived number of reflecting elements is established for both schemes, and the upper bounds on both the EE and the SE thresholds and the placement of the IRS to achieve only one reflecting element are obtained. Simulation results confirm the validity of our analysis on the minimum number of reflecting elements and effectiveness of both schemes.
A new triterpene, javablumine A (1) along with six known ones were isolated from the aerial parts of Sambucus javanica Blume. They were identified as ...3β,23-dihydroxy-11α,12α-epoxy-urs-20(30)-en-28,13β-olide (1), ursolic acid (2), pomolic acid (3), oleanic acid (4), 2α-hydroxy-oleanolic acid (5), α-amyrin (6), and lupeol palmitate (7), respectively. Compounds 1 and 3 exhibited inhibitory effect against nitric oxide (NO) production in lipopolysaccharide (LPS)-activated RAW264.7 macrophage cell lines with IC
50
values of 17.4 and 26.2 μM, respectively.
Separation is an important industrial step with critical roles in the chemical, petrochemical, pharmaceutical, and nuclear industries, as well as in many other fields. Although much progress has been ...made, the development of better separation technologies, especially through the discovery of high‐performance separation materials, continues to attract increasing interest due to concerns over factors such as efficiency, health and environmental impacts, and the cost of existing methods. Metal–organic frameworks (MOFs), a rapidly expanding family of crystalline porous materials, have shown great promise to address various separation challenges due to their well‐defined pore size and unprecedented tunability in both composition and pore geometry. In the past decade, extensive research is performed on applications of MOF materials, including separation and capture of many gases and vapors, and liquid‐phase separation involving both liquid mixtures and solutions. MOFs also bring new opportunities in enantioselective separation and are amenable to morphological control such as fabrication of membranes for enhanced separation outcomes. Here, some of the latest progress in the applications of MOFs for several key separation issues, with emphasis on newly synthesized MOF materials and the impact of their compositional and structural features on separation properties, are reviewed and highlighted.
The development of advanced separation materials is central to address challenging separation tasks in a number of essential industrial processes in the petrochemical, pharmaceutical, and nuclear industries. The emerging class of metal–organic frameworks (MOFs) has shown a great promise. The latest advances in MOF materials used for such applications are reviewed.
Efficient recruitment and angiogenesis of endothelial progenitor cells (EPCs) are critical during a thrombus event. However, the details of EPC recruitment and the regulation of angiogenesis have not ...been fully determined. The aim of this study was to determine the role of the long noncoding (lnc)RNA Wilms tumor 1 associated protein pseudogene 1 (WTAPP1) in regulation of the migration and angiogenesis of EPCs. EPCs were isolated from human peripheral blood and characterized by flow cytometry, after which lentivirus‐mediated lncRNA WTAPP1 overexpression and knockdown were performed. Scratch assay, Transwell assay, and in vitro and in vivo tube formation assays were performed to measure cell migration, invasion, and angiogenic abilities, respectively. Moreover, a microarray screen, bioinformatic prediction, and quantitative PCR and Western blot of miRNAs interacting with lncRNA WTAPP1 were conducted. Western blot was carried out to elucidate the relationship among WTAPP1, miR‐3120‐5P, and MMP‐1 in the autophagy pathway. WTAPP1 positively regulated migration, invasion, and in vitro and in vivo tube formation in EPCs by increasing MMP‐1 expression and activating PI3K/Akt/mTOR signaling. Furthermore, WTAPP1 contains a putative miR‐3120‐5P binding site. Suppression of WTAPP1 by miR‐3120‐5P decreased the level of MMP‐1. In addition, we demonstrated that suppression of the autophagy pathway is involved in the effects of WTAPP1 on EPC migration and angiogenesis. The lncRNA WTAPP1, a molecular decoy for miR‐3120‐5p, regulates MMP‐1 expression via the PI3K/Akt and autophagy pathways, thereby mediating cell migration and angiogenesis in EPCs. Acting as a potential therapeutic target, the lncRNA WTAPP1 may play an important role in the pathogenesis of DVT. Stem Cells 2018;36:1863–12
The long noncoding RNA Wilms tumor 1 associated protein pseudogene 1, a molecular decoy for miR‐3120‐5p, regulates MMP‐1 expression via the PI3K/Akt and autophagy pathways, thereby mediating cell migration and angiogenesis in endothelial progenitor cells.
Seeking new, highly effective thermoelectrics Xiao, Yu; Zhao, Li-Dong
Science (American Association for the Advancement of Science),
03/2020, Volume:
367, Issue:
6483
Journal Article
Peer reviewed
Operating across a wide temperature range is a priority for thermoelectric materials
Thermoelectric technology can directly and reversibly convert heat to electrical energy. Although thermoelectric ...energy conversion will never be as efficient as a steam engine (
1
), improving thermoelectric performance can potentially make a technology commercially competitive. Thermoelectric conversion efficiency is estimated by the so-called dimensionless figure of merit,
ZT = S
2
σ
T
/κ, where
S
, σ,
T
, and κ denote the Seebeck coefficient, electrical conductivity, working temperature, and thermal conductivity, respectfully . These parameters are strongly coupled, and improving the final
ZT
is challenging as a result. Strategies for boosting thermoelectric performance include nanostructuring, band engineering, nanomagnetic compositing, high-throughput screening, and others (
2
). Many of these strategies create a high
ZT
in a narrow range of temperatures, limiting the overall energy conversion. Finding materials with wider operating temperature ranges may require rethinking development strategies.
Given that more than two thirds of all energy is lost, mostly as waste heat, in utilization processes worldwide, thermoelectric materials, which can directly convert waste heat to electricity, ...provide an alternative option for optimizing energy utilization processes. After the prediction that superlattices may show high thermoelectric performance, various methods based on quantum effects and superlattice theory have been adopted to analyze bulk materials, leading to the rapid development of thermoelectric materials. Bulk materials with two‐dimensional (2D) structures show outstanding properties, and their high performance originates from both their low thermal conductivity and high Seebeck coefficient due to their strong anisotropic features. Here, the advantages of superlattices for enhancing the thermoelectric performance, the transport mechanism in bulk materials with 2D structures, and optimization methods are discussed. The phenomenological transport mechanism in these materials indicates that thermal conductivities are reduced in 2D materials with intrinsically short mean free paths. Recent progress in the transport mechanisms of Bi2Te3‐, SnSe‐, and BiCuSeO‐based systems is summarized. Finally, possible research directions to enhance the thermoelectric performance of bulk materials with 2D structures are briefly considered.
Thermoelectric bulk materials with 2D structures possess natural structures similar to artificial superlattices, hence enabling the utilization of enhancement methods for superlattices. General optimization methods for Bi2Te3 are reviewed; meanwhile, the progress of advanced research into SnSe and BiCuSeO as promising thermoelectric materials is summarized.
Reported herein are two new polymorphic Co‐MOFs (CTGU‐5 and ‐6) that can be selectively crystallized into the pure 2D or 3D net using an anionic or neutral surfactant, respectively. Each polymorph ...contains a H2O molecule, but differs dramatically in its bonding to the framework, which in turn affects the crystal structure and electrocatalytic performance for hydrogen evolution reaction (HER). Both experimental and computational studies find that 2D CTGU‐5 which has coordinates water and more open access to the cobalt site has higher electrocatalytic activity than CTGU‐6 with the lattice water. The integration with co‐catalysts, such as acetylene black (AB) leads to a composite material, AB&CTGU‐5 (1:4) with very efficient HER catalytic properties among reported MOFs. It exhibits superior HER properties including a very positive onset potential of 18 mV, low Tafel slope of 45 mV dec−1, higher exchange current density of 8.6×10−4 A cm−2, and long‐term stability.
HER choice of surfactants: Two new Co‐MOFs phase‐selected by anionic and neutral surfactants exhibit differential affinity for entrapped water molecules, leading to a difference in the spatial accessibility of active metal sites. A composite material made from such Co‐MOFs shows impressive performance in electrocatalytic hydrogen evolution reaction (HER) as well as long‐term stability.
Skin photoaging (SP) is a premature skin-aging damage after repeated exposure to ultraviolet (UV) radiation, mainly characterized by oxidative stress and inflammatory disequilibrium, which makes skin ...show the typical symptoms of photoaging such as coarse wrinkling, dryness, irregular pigmentation and laxity. Chitosan oligosaccharide (COS), a natural polysaccharide with good humectant property, is the depolymerized product of chitosan with various biological activities, among which the antioxidant and anti-inflammatory effects have been frequently reported in recent years. However, no existing invivo study indicates whether COS has direct protective effect on UV-induced SP. In the current research, we investigated the potential preventive effect of COS against UV-caused damage in hairless mouse dorsal skin. The data showed that COS, by topical application after each UV-radiation for 10weeks, effectively inhibited the undesirable changes on the skin induced by UV. To be specific, COS obviously alleviated the macroscopic and histopathological damages of mice skin, via mitigating the disrupted collagenous fibers, as well as improving the relative content of type I collagen and the amount of total collagen. Furthermore, COS effectively inhibited the levels of pro-inflammatory cytokines such as TNF-α, IL-1β and IL-6, and markedly improved the activities of antioxidant enzymes (SOD, GSH-Px, CAT), as well as the content of skin hydroxyproline and moisture. These findings demonstrated that this natural polysaccharide attenuated UV-induced SP, at least in part, by virtue of favorable regulation of antioxidant and anti-inflammatory status, which presumably worked in concert to maintain the morphology and level of dermal collagen.
•Topical application of COS contributes to prevention in UV-induced skin aging.•COS attenuates skin collagen degradation and wrinkle formation, caused by UV, to some extent by its antioxidative and anti-inflammatory properties•The above properties presumably work in concert to inhibit the overproduction of MMPs.•COS may serve as a ponderable agent for preventing skin photoaging
Recently, sensors that can imitate human skin have received extensive attention. Capacitive sensors have a simple structure, low loss, no temperature drift, and other excellent properties, and can be ...applied in the fields of robotics, human–machine interactions, medical care, and health monitoring. Polymer matrices are commonly employed in flexible capacitive sensors because of their high flexibility. However, their volume is almost unchanged when pressure is applied, and they are inherently viscoelastic. These shortcomings severely lead to high hysteresis and limit the improvement in sensitivity. Therefore, considerable efforts have been applied to improve the sensing performance by designing different microstructures of materials. Herein, two types of sensors based on the applied forces are discussed, including pressure sensors and strain sensors. Currently, five types of microstructures are commonly used in pressure sensors, while four are used in strain sensors. The advantages, disadvantages, and practical values of the different structures are systematically elaborated. Finally, future perspectives of microstructures for capacitive sensors are discussed, with the aim of providing a guide for designing advanced flexible and stretchable capacitive sensors via ingenious human‐made microstructures.
The advantages, disadvantages, and practical applications of several popular microstructures that are widely employed in capacitive sensors are summarized. A microstructured dielectric layer or electrode can improve sensor sensitivity, reduce hysteresis, and endow the rigid electronic device with excellent elastic stretchability, which is an essential part of next‐generation wearable devices and soft robots.
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