Expanding Ring Research Articles

Assimilating an expanded tree ring dataset to reconstruct the millennial air temperature fields for the Northern Hemisphere

AbstractThe spatiotemporal variations of the climate of the last millennium provide the context for understanding the recent climate. However, there are few 1000‐year‐long spatiotemporally continuous climate reconstructions at hemispheric to global scales. Here, a millennial, spatiotemporally continuous and annually resolved air temperature dataset for the Northern Hemisphere (NH) was reconstructed using paleoclimate data assimilation (PDA) approach based on an expanded tree ring proxy dataset and artificial neural network‐based proxy system models. Verifications show the PDA‐based reconstruction agrees well with instrumental temperature, previous proxy‐based reconstructions and the Last Millennium Climate Reanalysis version 2 (LMRv2) dataset in space and time domains. Since the PDA‐based reconstruction is spatiotemporally continuous fields without missing value over the whole NH, which is a distinct advantage of the PDA‐based reconstruction over other proxy‐based NH‐averaged temperature reconstructions, we focussed on analysing the spatial variations of the NH temperature during the last millennium, for example, the primary modes of temperature variabilities and the spatial variabilities of the NH temperature in three typical climatic epochs of the millennium. Results show that the first‐leading mode (explained variance of 72.50%) of the NH temperature variability is a spatially consistent mode, while the second‐leading mode (explained variance of 10.60%) exhibits a different pattern that is different from the first‐leading empirical orthogonal function mode, particularly in the Arctic, which shows a dipole structure anomaly. The 20th century was the warmest, with 94.17% of the NH displaying positive anomalies. The 11th century was the second warmest century in the record, with 70.26% of the NH showing a positive anomaly. The 19th century was the coldest, with negative anomalies covering 86.97% of the NH. Northwest North America and the Northern Europe‐Barents Sea are two distinctly anomalous centres during these three centuries. Overall, the reconstructed air temperatures provide a new and reliable dataset for studying the millennial NH temperature variations.

Expanded Ring NHC Silver Carboxylate Complexes as Efficient and Reusable Catalysts for the Carboxylative Cyclization of Unsubstituted Propargylic Derivatives.

Stabilized by a bulky N‐heterocyclic carbene [BPDPr, 1,3‐bis(2,6‐diisopropylphenyl)‐1,3‐diazonine‐2‐ylidene] ligand, new silver carboxylate complexes of the form BPDPrAgO2C‐R (R=Me, Ph) have been synthesized and fully characterized in solution and in the solid state and implemented as sole catalysts (base‐, additive‐, and, in some cases, solvent‐free) in the challenging fixation of carbon dioxide to unsubstituted propargylic derivatives for the synthesis of oxazolidinones and α‐methylene cyclic carbonates. Derived from X‐ray diffraction studies, the molecular geometry and the concept of buried volume were employed to describe the structural and steric features of these silver complexes. Their stability and efficiency as catalysts have been demonstrated by the synthesis of 29 carboxylation products (72–98 % yield) at low catalyst loadings (0.01–1.5 mol%). Characteristics are high turnover numbers (up to 9400), catalyst recyclability (up to 96 % yield after the 7th cycle with no decomposition of the silver complex), and the possibility to scale‐up the reaction.

Novel AODV based service discovery protocol for MANETS

Service discovery is an inevitable process in most of the network. Mobile AdHoc network (MANET) being self-sustained and resource constrained, sharing of resources and service discovery is very essential. A service discovery protocol designed for a fixed network is not suitable for AdHoc network because of the constraint in the resources, mobility of nodes and the lack of centralized infrastructure. Therefore there arises a need to design protocols specific to MANET. A protocol designed for service discovery at the application layer in Mobile AdHoc Network would generate the same amount of control messages during service discovery as would a routing protocol during route discovery. To ease the network congestion it would be beneficial to integrate service discovery with route discovery. This would discover the services and route simultaneously. Therefore the AdHoc On-demand Distance Vector (AODV) routing protocol being a reactive routing protocol was modified to include service discovery so that as the services are discovered, a route to the service provider is also available. During service discovery if multiple servers are offering the same service, there arises a need to select the best one. We propose a ranking mechanism that selects an optimal server by considering the route and server specific metrics. We also propose an algorithm that performs service discovery by taking care of Expanding Ring Search of AODV protocol so as to be able to discover multiple servers. The proposed approach has been evaluated, and it was observed that the storage overhead is reduced by 50%, average Service Discovery Latency was reduced and the Service Discovery Ratio was improved by 16%.

Adaptive Expanding Ring Search Based Per Hop Behavior Rendition of Routing in MANETs

Routing protocols in Mobile Ad Hoc Networks (MANETs) operate with Expanding Ring Search (ERS) mechanism to avoid flooding in the network while tracing step. ERS mechanism searches the network with discerning Time to Live (TTL) values described by respective routing protocol that save both energy and time. This work exploits the relation between the TTL value of a packet, traffic on a node and ERS mechanism for routing in MANETs and achieves an Adaptive ERS based Per Hop Behavior (AERSPHB) rendition of requests handling. Each search request is classified based on ERS attributes and then processed for routing while monitoring the node traffic. Two algorithms are designed and examined for performance under exhaustive parametric setup and employed on adaptive premises to enhance the performance of the network. The network is tested under congestion scenario that is based on buffer utilization at node level and link utilization via back-off stage of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). Both the link and node level congestion is handled through retransmission and rerouting the packets based on ERS parameters. The aim is to drop the packets that are exhausting the network energy whereas forward the packets nearer to the destination with priority. Extensive simulations are carried out for network scalability, node speed and network terrain size. Our results show that the proposed models attain evident performance enhancement.

Minimizing Delay Using Dynamic Blocking Expanding Ring Search Technique for Ad Hoc Networks

Minimizing Delay Using Dynamic Blocking Expanding Ring Search Technique for Ad Hoc Networks

Catalyst-free, direct electrochemical synthesis of annulated medium-sized lactams through C–C bond cleavage

Expanding ring under green electricity: The electrosynthetic approach enabled atom-economical synthesis of challenging medium-sized lactams through a unique remote amidyl migration under exceedingly mild, transition metal- and oxidant-free conditions.

On Modeling Optimizations and Enhancing Routing Protocols for Wireless Multihop Networks

The contribution of this paper is two fold. It first analyses the flooding strategies for the Wireless Multihop Networks (WMNs) then it enhances the reactive and proactive routing protocols. For analysis purpose, we select four widely used flooding techniques for routing: i. traditional flooding, ii. Time-To-Live based Expanding Ring Search (TTL-based ERS) flooding scheme, iii. TTL-based Scope Routing (SR) flooding and iv. Multi-Point Relays (MPR) flooding. These techniques play a vital role and act as a backbone for routing protocols. Therefore, we compare efficiency of these techniques for six widely used routing protocols: Ad-hoc On-demand Distance Vector (AODV), Destination Sequenced Distance Vector (DSDV), Dynamic Source Routing (DSR), DYnamic MANET On-demand (DYMO), Fish-eye Scope Routing (FSR) and Optimized Link State Routing (OLSR). DSDV uses traditional flooding, AODV, DSR and DYMO use TTL-based ERS flooding, FSR uses TTL-based SR flooding and OLSR uses MPR flooding. This paper also presents mathematical models for flooding techniques and studies the affects of these techniques on their respective protocols in terms of energy and time consumption. This is done to measure the cost incurred by the routing protocols in the form of routing overhead and latencies. A novel contribution of this work is the enhancement in search set values and intervals of routing algorithms to improve the efficiency of selected existing protocols. A detailed comparison analysis of selected protocols with their default and enhanced routing algorithms in NS-2 is also a part of this work.

Wireless Sensor Network Quality of Service Improvement on Flooding Attack Condition

There are two methods of building communication using wireless media. The first method is building a base infrastructure as an intermediary between users. Problems that arise on this type of network infrastructure is limited space to build any network physical infrastructure and also the cost factor. The second method is to build an ad hoc network between users who will communicate. On ad hoc network, each user must be willing to send data from source to destination for the occurrence of a communication. One of network protocol in Ad Hoc, Ad hoc on demand Distance Vector (AODV), has the smallest overhead value, easier to adapt to dynamic network and has small control message. One AODV protocol’s drawback is route finding process’ security for sending the data. In this research, AODV protocol is optimized by determining Expanding Ring Search (ERS) best value. Random topology is used with variation in the number of nodes: 25, 50, 75, 100, 125 and 150 with node’s speed of 10m/s in the area of 1000m x 1000m on flooding network condition. Parameters measured are Throughput, Packet Delivery Ratio, Average Delay and Normalized Routing Load. From the test results of AODV protocol optimization with best value of Expanding Ring Search (ERS), throughput increased by 5.67%, packet delivery ratio increased by 5.73%, and as for Normalized Routing Load decreased by 4.66%. ERS optimal value for each node’s condition depending on the number of nodes on the network.

Experimental Technique for Dynamic Fragmentation of Liquid-Driving Expanding Ring

Expanding ring experiment is an important method for dynamic fragmentation of solid under 1D tensile loading. Based on the split Hokinson pressure bar (SHPB), a liquid-driving experimental technology was developed for conducting expanding ring tests. The loading fixture includes a hydraulic cylinder filled with water, which is pushed by a piston connected to the input bar. As the water is driven, it expands the metallic ring specimen in the radial direction. The approximately incompressible property of the water makes it possible to drive the specimen in very high radial velocity by low velocity movement of piston, according to the large sectional area ratio of the cylinder to specimen. Using liquid-driving expanding ring device, 1060 aluminum rings (ductile materials)/PMMA rings (brittle materials) were fragmented and the fragments were recovered. Impact deformation of free-flying fragments was avoided through the use of “sample soft-capture” technology. The fragmentation process was observable by high speed camera through modifying the driving direction of the water. From the observations of the fracture morphology and the residual internal cracks of the recovered fragments, it is concluded that the fracture of the rings is caused by the circumferential tensile stress.

New Mitral Annuloplasty Ring Enables Oversizing of Transcatheter Heart Valve and Prevents Central or Paravalvular Leakage.

Background Transcatheter valve-in-ring strategies have been developed to treat recurrent mitral regurgitation (MR) after failing surgical annuloplasty. However, suboptimal THV expansion with consecutive paravalvular leakage (PVL) is a procedure-immanent issue. Methods A rigid, saddle-shaped ring was cut at four locations. The segments were reconnected with pull-springs, rearranged to the original shape, and covered with a sewing cuff. The length of the annuloplasty ring construct, including extended pull-springs, was defined by the perimeter of an appropriate THV. We deployed a Sapien XT within the new ring, expanded it to its maximum extent, and investigated the geometrical changes. Results Fluoroscopy confirmed oval, saddle-shaped ring before dilation. After THV implantation, the ring segments spread apart and pull-springs were stretched. The extended ring changed its configuration from "oval" to "round" and anchored the THV leaving no paravalvular or central gaps as potential source for PVL. Conclusion We developed an expandable annuloplasty ring that is perfectly concerted to THV implantation. This proof-of-concept study revealed no PVL and good oversizing ability that might impact future annuloplasty ring design. Further studies have to evaluate durability and device safety.

Expanding Ring Search Energy Analysis and Optimization for Wireless Sensor Networks

Expanding Ring Search (ERS) is an advanced flooding technique exploring for targets progressively. It is widely used to locate destinations or information in wireless sensor networks. In this paper, a fundamental problem concerning the best ERS strategy to minimize energy cost in wireless sensor networks is addressed. We propose a model for estimating the average energy cost of ERS strategies, and a model for comparing the energy cost of an ERS strategy with pure flooding. The second model is then used to prove that incremental ERS strategies are inefficient in large-scale wireless sensor networks. Furthermore, we propose an ERS strategy optimization algorithm SSetOpt, which can be applied to both dense wireless sensor networks and sparse ones. The simulation results show that the strategy obtained by SSetOpt can cost 5% less energy than prior works when the network is sparse, say, the average degree is less than 30..

Electromagnetically Driven Expanding Ring Test for the Strength Study of the Zylon/Epoxy Composite

An improved electromagnetically launched method for driving specimens of composite materials is developed. The electromagnetic expansion ring device consists of a solenoid and sample rings. The solenoid is made up of eight layers of copper wire reinforced with Zylon fiber, which can produce magnetic field up to 35 T. The sample ring is composed of a high-conductivity driver (6061-T6 aluminum ring) and a layer of Zylon/epoxy composite that is directly wound on the driver. The solenoid driven by a 100-kJ (25 kV, 320 $\mu\text{F}$) capacitor bank is designed for inducing a pulsed current in the aluminum driver. Consequently, the induced current interacts with the axial magnetic field at the center plane of the solenoid to produce a large, uniform, and outward electromagnetic force. The Zylon/epoxy composite specimen is thus pushed outward by the aluminum driver. By adjusting the charging voltage of the capacitor bank, the force can be adjusted, and thus, the strength of the sample can be easily found by exploding the rings. Different thickness values of the sample rings with an aluminum driver have been tested. The strength is calculated to be around 5.2 GPa by means of finite element analysis.

New expandable mitral annuloplasty ring facilitates transcatheter mitral valve implantation: proof of concept.

Transcatheter mitral valve-in-ring (TMVIR) implantation with transcatheter heart valve (THV) prostheses can be performed in patients with recurrent mitral regurgitation (MR) following annuloplasty. However, an oval configuration and sometimes the rigidity of surgical rings can often lead to suboptimal THV expansion, resulting in considerable paravalvular or central leakage. Therefore, our aim was to develop an annuloplasty ring that fully adjusts to THV implantation. A three-dimensional annuloplasty ring was separated into four pieces at defined locations, the sections were reconnected with heat-shrinkable tubing and rearranged into the original shape. A non-tear stainless steel circular cord of defined length was inserted into the ring's sewing cuff to serve as a limiting structure for THV expansion. We implanted this ring in the mitral position into an isolated pig heart, deployed a THV into the ring, and investigated its function. Fluoroscopy showed that, upon THV deployment, the four breaking points of the ring separated as expected, and the ring expanded in a circular fashion to full expansion of the limiting cord. It securely anchored the THV to the ring, leaving no paravalvular gaps. We developed an expandable mitral ring to which the THV attached without leakage. This may impact on the future design of annuloplasty rings. Further studies should evaluate the safety of increasing the perimeter of a mitral ring and its durability.

Expanded ring N-heterocyclic carbene adducts of group 15 element trichlorides: synthesis and reduction studies.

Reactions of the expanded ring N-heterocyclic carbene, 6-Dip (:C{N(Dip)CH2}2CH2, Dip = 2,6-diisopropylphenyl), with group 15 element trichlorides have yielded the monomeric complexes, [(6-Dip)ECl3] (E = P, As or Sb), two examples of which (E = P and Sb) have been crystallographically characterised. Reduction of [(6-Dip)PCl3] with KC8 yielded the unusual tetraphosphorus dicationic complex, [(6-Dip)2(μ-P4)]Cl2, the X-ray crystal structure of which shows it to be an ion-separate salt. The compound can also be prepared from the direct reaction of excess 6-Dip with PCl3. Treatment of the cyclic amidinium salt, [6-MesH]Br (6-MesH = [HC{N(Mes)CH2}2CH2](+), Mes = mesityl) with KC8, leads to reductive coupling of the heterocycle and formation of the hindered bis(hexahydropyrimidine), (6-MesH)2. An X-ray crystallographic analysis of (6-MesH)2 shows the compound to have a long central C-C bond, while an electrochemical analysis reveals it to undergo an irreversible two-electron oxidation in dichloromethane solutions.

Pd–PEPPSI-Type Expanded Ring N-Heterocyclic Carbene Complexes: Synthesis, Characterization, and Catalytic Activity in Suzuki–Miyaura Cross Coupling

The synthesis and characterization of the new six- and seven-membered Pd–PEPPSI-type N-heterocyclic carbene (NHC) complexes 3 and 4 is described. Complexes of the general formula [Pd(NHC)(3ClPy)Cl2] (NHC = 6- or 7-Mes, 3ClPy = 3-chloropyridine) are accessed via the oxidation of the well-defined parent palladium(0) complexes 1 and 2. Complexes 3 and 4 have been employed in Suzuki–Miyaura cross-coupling and catalytic dehalogenation of a range of aryl halide substrates.

Reactivity of (NHC)2FeX2Complexes toward Arylborane Lewis Acids and Arylboronates

(NHC)2FeCl2 complexes undergo methoxide transfer in preference to aryl transfer from [(Aryl)B(OR)3]−, while addition of ArylBY2 (Y = Cl, OR) to (NHC)Fe–methoxide compounds leads only to formation of (NHC)BY2Aryl. The addition of PhBCl2 to (NHC)2FeX2 compounds is introduced as a method for probing NHC dissociation from iron. Two expanded ring NHCs also undergo dissociation from iron in the respective (NHC)2FeCl2 complexes.

Improving time-efficiency in blocking expanding ring search for mobile ad hoc networks

We propose a new strategy for reducing the amount of latency and energy consumption in Blocking Expanding Ring Search (BERS) and enhanced Blocking Expanding Ring Search (BERS*) for mobile ad hoc networks (MANETs). BERS and BERS* are respectively energy and energy–time efficient route discovery protocols for MANETs as compared to conventional Expanding Ring Search (ERS). In this study, we identify unnecessary waiting time caused by a STOP/END instruction in BERS/BERS* and explore the potential of further improvement of their time efficiency. This leads to tBERS and tBERS*, the improved BERS and BERS* respectively. In tBERS/tBERS*, a route node may also issue the STOP/END instruction to terminate flooding. We implement this idea in algorithms, conduct analysis, and achieve further latency reduction in both tBERS and tBERS* as well as the energy saving in tBERS*.

ChemInform Abstract: Recent Developments of Expanded Ring N‐Heterocyclic Carbenes

ChemInform Abstract: Recent Developments of Expanded Ring N‐Heterocyclic Carbenes

Numerical investigations of the structural behavior of a balloon expandable stent design using finite element method

This paper discusses some issues regarding the structural behavior of a Balloon-Expandable (BE) stent made of stainless steel material (AISI316L). BE stent is a tubular, often mesh-like, structure which is expanded inside a diseased (stenosed) artery segment to restore blood flow and keep the vessel open following angioplasty. Most of BE stent designs have two fundamental constituents: expandable ring elements, and connecting elements “bridges” which connect adjacent rings together. The stent design is a major factor which determines its reliability during insertion into the blocked artery and throughout the long term in vivo service. The objective of this paper is to study the structural behavior of the stent in order to show the effect of the stent design, especially the geometry of the “bridges” in terms of flexibility, torsion and expansion. The numerical investigation is based on Finite Element Analysis (FEA) using Abaqus© finite element code. It has been demonstrated by FEA that the geometry of the connecting elements “bridges” has a significant impact on the structural behavior of the stent.

Expanded ring diaminocarbene palladium complexes: synthesis, structure, and Suzuki–Miyaura cross-coupling of heteroaryl chlorides in water

A series of new 6- and 7-membered N-heterocyclic carbene (NHC) complexes of palladium (NHC)Pd(cinn)Cl (cinn = cinnamyl = 3-phenylallyl) were synthesized and characterized structurally in the solid state. The influence of ring size (5, 6 or 7) and bulkiness of N-aryl substituents (Mes = 2,4,6-trimethylphenyl, or Dipp = 2,6-diisopropylphenyl) in carbenes on palladium catalysed Suzuki-Miyaura cross-coupling was revealed. Due to the unique stereoelectronic properties of expanded ring NHCs, a versatile, highly efficient green protocol of coupling of heteroaromatic chlorides and bromides with boronic acids has been developed. High quantitative yields of biaryls were achieved with water as solvent, under air, using low catalyst and phase transfer agent loadings, and with mild and environmentally benign base NaHCO3.