In this paper, we study the physical-layer security in a 3-D multiuser visible light communication (VLC) network. The locations of access points (APs) and mobile users are modeled as two 2-D, ...independent and homogeneous Poisson point processes at distinct heights. Using mathematical tools from stochastic geometry, we provide a new analytical framework to characterize the secrecy performance in multiuser VLC networks. Closed-form results for the outage probability and the ergodic secrecy rate are derived for networks without AP cooperation. Considering the cooperation among APs, we give tight lower and upper bounds on the secrecy outage probability and the ergodic secrecy rate. To further enhance the secrecy performance at the legitimate user, a disk-shaped secrecy protected zone is implemented in the vicinity of the transmit AP. Based on the obtained results, it is shown that cooperating neighboring APs in a multiuser VLC network can bring performance gains on the secrecy rate, but only to a limited extent. We also show that building an eavesdropper-free protected zone around the AP significantly improves the secrecy performance of legitimate users, which appears to be a promising solution for the design of multiuser VLC networks with high security requirements.
Lithium–sulfur (Li–S) batteries with high sulfur loading are urgently required in order to take advantage of their high theoretical energy density. Ether‐based Li–S batteries involve sophisticated ...multistep solid–liquid–solid–solid electrochemical reaction mechanisms. Recently, studies on Li–S batteries have widely focused on the initial solid (sulfur)–liquid (soluble polysulfide)–solid (Li2S2) conversion reactions, which contribute to the first 50% of the theoretical capacity of the Li–S batteries. Nonetheless, the sluggish kinetics of the solid–solid conversion from solid‐state intermediate product Li2S2 to the final discharge product Li2S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge, resulting in low discharge capacity output and low sulfur utilization. To tackle the aforementioned issue, a catalyst of amorphous cobalt sulfide (CoS3) is proposed to decrease the dissociation energy of Li2S2 and propel the electrochemical transformation of Li2S2 to Li2S. The CoS3 catalyst plays a critical role in improving the sulfur utilization, especially in high‐loading sulfur cathodes (3–10 mg cm−2). Accordingly, the Li2S/Li2S2 ratio in the discharge products increased to 5.60/1 from 1/1.63 with CoS3 catalyst, resulting in a sulfur utilization increase of 20% (335 mAh g−1) compared to the counterpart sulfur electrode without CoS3.
Amorphous CoS3
are developed to promote the solid–solid conversion from solid‐state intermediate product Li2S2 to the final discharge product Li2S, which significantly increased the sulfur utilizations for over 20% for high loading electrodes.
Lysophosphatidylcholine (LPC) is increasingly recognized as a key marker/factor positively associated with cardiovascular and neurodegenerative diseases. However, findings from recent clinical ...lipidomic studies of LPC have been controversial. A key issue is the complexity of the enzymatic cascade involved in LPC metabolism. Here, we address the coordination of these enzymes and the derangement that may disrupt LPC homeostasis, leading to metabolic disorders. LPC is mainly derived from the turnover of phosphatidylcholine (PC) in the circulation by phospholipase A₂ (PLA₂). In the presence of Acyl-CoA, lysophosphatidylcholine acyltransferase (LPCAT) converts LPC to PC, which rapidly gets recycled by the Lands cycle. However, overexpression or enhanced activity of PLA₂ increases the LPC content in modified low-density lipoprotein (LDL) and oxidized LDL, which play significant roles in the development of atherosclerotic plaques and endothelial dysfunction. The intracellular enzyme LPCAT cannot directly remove LPC from circulation. Hydrolysis of LPC by autotaxin, an enzyme with lysophospholipase D activity, generates lysophosphatidic acid, which is highly associated with cancers. Although enzymes with lysophospholipase A₁ activity could theoretically degrade LPC into harmless metabolites, they have not been found in the circulation. In conclusion, understanding enzyme kinetics and LPC metabolism may help identify novel therapeutic targets in LPC-associated diseases.
Ferroptosis is a new type of cell death that was discovered in recent years and is usually accompanied by a large amount of iron accumulation and lipid peroxidation during the cell death process; the ...occurrence of ferroptosis is iron-dependent. Ferroptosis-inducing factors can directly or indirectly affect glutathione peroxidase through different pathways, resulting in a decrease in antioxidant capacity and accumulation of lipid reactive oxygen species (ROS) in cells, ultimately leading to oxidative cell death. Recent studies have shown that ferroptosis is closely related to the pathophysiological processes of many diseases, such as tumors, nervous system diseases, ischemia-reperfusion injury, kidney injury, and blood diseases. How to intervene in the occurrence and development of related diseases by regulating cell ferroptosis has become a hotspot and focus of etiological research and treatment, but the functional changes and specific molecular mechanisms of ferroptosis still need to be further explored. This paper systematically summarizes the latest progress in ferroptosis research, with a focus on providing references for further understanding of its pathogenesis and for proposing new targets for the treatment of related diseases.
Boron‐doped LiNi0.90Co0.05Mn0.05O2 cathodes are synthesized by adding B2O3 during the lithiation of the hydroxide precursor. Density functional theory confirms that boron doping at a level as low as ...1 mol% alters the surface energies to produce a highly textured microstructure that can partially relieve the intrinsic internal strain generated during the deep charging of LiNi0.90Co0.05Mn0.05O2. The 1 mol% B‐LiNi0.90Co0.05Mn0.05O2 cathode thus delivers a discharge capacity of 237 mAh g−1 at 4.3 V, with an outstanding capacity retention of 91% after 100 cycles at 55 °C, which is 15% higher than that of the undoped LiNi0.90Co0.05Mn0.05O2 cathode. This proposed synthesis strategy demonstrates that an optimal microstructure exists for extending the cycle life of Ni‐rich LiNi1‐x‐yCoxMnyO2 cathodes that have an inadequate cycling stability in electric vehicle applications and indicates that an optimal microstructure can be achieved through surface energy modification.
Boron doping produces a highly textured microstructure of LiNi0.90Co0.05Mn0.05O2 (NCM90) cathode, thus relieving the internal strain generated during charge and discharge cycling. Due to the unique morphology of the B‐doped NCM90, microcracking and electrolyte penetration are hindered, and formation of the NiO‐like impurity phase is confined. B‐doped NCM90 exhibits high capacity and excellent cycle life, especially at 55 °C.
Na metal anode attracts increasing attention as a promising candidate for Na metal batteries (NMBs) due to the high specific capacity and low potential. However, similar to issues faced with the use ...of Li metal anode, crucial problems for metallic Na anode remain, including serious moss‐like and dendritic Na growth, unstable solid electrolyte interphase formation, and large infinite volume changes. Here, the rational design of carbon paper (CP) with N‐doped carbon nanotubes (NCNTs) as a 3D host to obtain Na@CP‐NCNTs composites electrodes for NMBs is demonstrated. In this design, 3D carbon paper plays a role as a skeleton for Na metal anode while vertical N‐doped carbon nanotubes can effectively decrease the contact angle between CP and liquid metal Na, which is termed as being “Na‐philic.” In addition, the cross‐conductive network characteristic of CP and NCNTs can decrease the effective local current density, resulting in uniform Na nucleation. Therefore, the as‐prepared Na@CP‐NCNT exhibits stable electrochemical plating/stripping performance in symmetrical cells even when using a high capacity of 3 mAh cm−2 at high current density. Furthermore, the 3D skeleton structure is observed to be intact following electrochemical cycling with minimum volume change and is dendrite‐free in nature.
Carbon paper (CP) with N‐doped carbon nanotubes (NCNTs) is rationally designed as a 3D host for Na metal anode. The contact angle between the CP and liquid metal Na is effectively reduced with the vertical N‐doped carbon nanotubes. As‐prepared Na@CP‐NCNTs exhibit stable electrochemical plating/stripping performance in symmetrical cells operated at high current density and high capacity.
What is LiFi? Haas, Harald; Liang Yin; Yunlu Wang ...
Journal of lightwave technology,
03/2016, Volume:
34, Issue:
6
Journal Article
Peer reviewed
This paper attempts to clarify the difference between visible light communication (VLC) and light-fidelity (LiFi). In particular, it will show how LiFi takes VLC further by using light emitting ...diodes (LEDs) to realise fully networked wireless systems. Synergies are harnessed as luminaries become LiFi attocells resulting in enhanced wireless capacity providing the necessary connectivity to realise the Internet-of-Things, and contributing to the key performance indicators for the fifth generation of cellular systems (5G) and beyond. It covers all of the key research areas from LiFi components to hybrid LiFi/wireless fidelity (WiFi) networks to illustrate that LiFi attocells are not a theoretical concept any more, but at the point of real-world deployment.
Novel poly(N‐isopropylacrylamide)‐clay (PNIPAM‐clay) nanocomposite (NC) hydrogels with both excellent responsive bending and elastic properties are developed as temperature‐controlled manipulators. ...The PNIPAM‐clay NC structure provides the hydrogel with excellent mechanical property, and the thermoresponsive bending property of the PNIPAM‐clay NC hydrogel is achieved by designing an asymmetrical distribution of nanoclays across the hydrogel thickness. The hydrogel is simply fabricated by a two‐step photo polymerization. The thermoresponsive bending property of the PNIPAM‐clay NC hydrogel is resulted from the unequal forces generated by the thermoinduced asynchronous shrinkage of hydrogel layers with different clay contents. The thermoresponsive bending direction and degree of the PNIPAM‐clay NC hydrogel can be adjusted by controlling the thickness ratio of the hydrogel layers with different clay contents. The prepared PNIPAM‐clay NC hydrogels exhibit rapid, reversible, and repeatable thermoresponsive bending/unbending characteristics upon heating and cooling. The proposed PNIPAM‐clay NC hydrogels with excellent responsive bending property are demonstrated as temperature‐controlled manipulators for various applications including encapsulation, capture, and transportation of targeted objects. They are highly attractive material candidates for stimuli‐responsive “smart” soft robots in myriad fields such as manipulators, grippers, and cantilever sensors.
Poly(N‐isopropylacrylamide)‐clay nanocomposite hydrogels with responsive bending property are successfully developed as temperature‐controlled manipulators by designing an asymmetrical distribution of nanoclays across the hydrogel thickness. The hydrogels show rapid, reversible, and repeatable thermoresponsive bending characteristics, and are demonstrated as temperature‐controlled soft manipulators for applications of encapsulating, grapping, and transporting target objects in aqueous environments.
Smart polymeric materials with dynamically tunable physico‐chemical characteristics in response to changes of environmental stimuli, have received considerable attention in myriad fields. The diverse ...combination of their micro‐/nano‐structural and molecular designs creates promising and exciting opportunities for exploiting advanced smart polymeric materials. Engineering micro‐/nano‐structures into smart polymeric materials with elaborate molecular design enables intricate coordination between their structures and molecular‐level response to cooperatively realize smart functions for practical applications. In this review, recent progresses of smart polymeric materials that combine micro‐/nano‐structures and molecular design to achieve designed advanced functions are highlighted. Smart hydrogels, gating membranes, gratings, milli‐particles, micro‐particles and microvalves are employed as typical examples to introduce their design and fabrication strategies. Meanwhile, the key roles of interplay between their micro‐/nano‐structures and responsive properties to realize the desired functions for their applications are emphasized. Finally, perspectives on the current challenges and opportunities of micro‐/nano‐structured smart polymeric materials for their future development are presented.
Smart polymeric materials with elaborate micro‐/nano‐structural and molecular designs to achieve designed functions for myriad applications are summarized. The smart materials, including responsive hydrogels, gating membranes, gratings, milli‐particles, micro‐particles and microvalves, can achieve intricate coordination between their micro‐/nano‐structures and responsive properties to cooperatively achieve desired functions.
In this paper, the performance of non-orthogonal multiple access (NOMA) is characterized in a downlink visible light communication system for two separate cases. In the case of guaranteed quality of ...service (QoS) provisioning, we derive an analytical expression of the system coverage probability and show the existence of optimal power allocation coefficients on two-user paired NOMA. In the case of opportunistic best-effort service provisioning, we formulate a closed-form expression of the ergodic sum rate, which is applicable for arbitrary power allocation strategies. The probability that NOMA achieves higher individual rates than OMA is derived. Also, we give an upper bound of the sum rate gain of NOMA over OMA in the high signal-to-noise ratio regime. Both the theoretical and simulation results prove that the performance gain of NOMA over OMA can be further enlarged by pairing users with distinctive channel conditions. We also find out that the choice of light emitting diodes (LEDs) have a significant impact on the system performance. In the case of guaranteed QoS provisioning, the LEDs with larger semi-angles have better performance; while in the case of opportunistic best-effort service provisioning, the LEDs with 35° semi-angle give nearly optimal performance.
PDF
