Molecular Dynamics Investigation of the Structural and Mechanical Properties of Off-Stoichiometric Epoxy Resins

We carried out molecular dynamics (MD) simulations to measure the mechanical properties of various off-stoichiometric polymers regarding amine to epoxy ratios (r) and to understand the stiffness of the polymers in terms of their structures. The aerospace-grade API-60 epoxy resin is used as an adhesive bond for assembling large-scale composite structures via the co-curing-ply bonding method. This method will produce a reliable and certifiable composite joint without additional fasteners. Calculated Young's modulus was measured from the uniaxial tension simulation with several high strain rates, and the experimental modulus was estimated by extrapolating the simulation results. We found that the stiffness was associated with molecular packing caused by chemical cross-linking. We also found that the number of network clusters gradually decreased as the ratio approached r = 1.0, which made the tighter cluster and the system much stiffer with an increase in the molecular weight and the degree of cross-linking. Structural properties such as Rg, MSD were measured to figure out the degree of stiffness with respect to the r

A new phase for screening redundant broadcast nodes in source-independent broadcasting protocols

Following the distributed approach, source-independent broadcasting protocols select a subset of nodes in a network as broadcasting nodes to cover the entire network. The selection of broadcasting nodes is performed prior to actual message transmission. These broadcasting nodes collectively form a connected dominating set or CDS. Aiming at finding a minimum CDS, existing source-independent broadcasting protocols consist of two phases. In this paper, we propose to add a third phase to eliminate unnecessary nodes in a CDS while ensuring all remaining nodes are still connected. We call it the redundant node screening phase. This paper shows that this new phase is a very important element that has been ignored by existing source-independent broadcasting protocols. When applying the new phase on existing broadcasting protocols, the savings in terms of number of nodes in the CDS could be as high as 21% in a 1000m x 1000m network of 20 nodes. © 2011 IEEE.published_or_final_versionThe 2011 IEEE International Conference on Communications (ICC 2011), Kyoto, Japan, 5-9 June 2011. In Proceedings of the IEEE ICC, 2011, p. 1-

Self-pruning broadcasting for mobile ad hoc networks

The IEEE Global Telecommunications Conference (GLOBECOM 2009), Honolulu, HI., 30 November-4 December 2009, p. 1-6Broadcasting is a process of delivering a message to all nodes in a network. While it is important to ensure that all nodes get a copy of the broadcast message, minimizing the number of sending nodes is equally important especially in resource-constrained wireless networks. Existing broadcasting protocols based on self-pruning are ineffective in achieving these objectives. Therefore this paper proposes two protocols based on simple timer mechanisms to prioritize broadcasting of messages such that node with most uncovered neighbors rebroadcast first. Additionally a timer suppression mechanism is proposed to further enhance the effectiveness of the broadcasting protocol. Compared with an existing protocol, extensive simulation experiments confirm that the proposed protocols achieve better performance.published_or_final_versio

Enhanced termination condition for deterministic broadcasting protocols in mobile ad hoc networks

Deterministic approach to broadcasting in Mobile Ad Hoc Networks (MANETs) is effective in reducing redundant broadcasting. In this approach, a transmitting node selects a subset of its immediate or 1-hop neighbors to rebroadcast the message such that all its 2-hop neighbors will receive the message, or being covered. In order to reduce redundant broadcasting, the set of 1-hop neighbors to be covered should be reduced as much as possible. Another important aspect that affects the effectiveness of a deterministic broadcasting protocol is the termination condition that inhibits a node from transmitting a particular message unnecessarily. However, existing termination conditions are not optimized. We propose a new covered/uncovered termination condition where each node is assigned with covered/uncovered status. In this paper, we show that our covered/uncovered termination condition ensures full network coverage, does not incur any control message overhead, and yet requires the least number of rebroadcasting nodes. When we apply the termination condition to some existing deterministic broadcasting protocols, the saving in the number of broadcasting nodes can be as significant as 45% when there are 100 nodes randomly distributed in an area of 1000 x 1000 m2. ©2010 IEEE.published_or_final_versionThe 72nd IEEE Vehicular Technology Conference (VTC 2010-Fall), Ottawa, ON., 6-9 September 2010. In Proceedings of the IEEE-VTS Vehicular Technology Conference, 2010, p. 1-

Are Broker Quotes Too Optimistic? Korean Evidence

We examine the behavior of broker quotes in Korean housing markets by comparing the Kookmin Bank apartment (a condominium in a high- rise residential building) price index, a broker quote based apartment price index, and a repeat sales apartment price index that we built using transaction prices, which have become available since January 2006. Broker quotes may differ from actual prices depending on the housing market conditions. Specifically, we test the hypotheses: (1) price increases shown by the broker quote based apartment price index are greater than those shown by the repeat sales apartment price index in an up market; and (2) the broker quote based price index shows a far less price reduction than the repeat sales price index in a down market. We find that indeed in a down market, the broker quote based price index shows far less price reduction than the repeat sales price index (5.75%-8.07%). However, the broker quote based price index does not distort the prices in an up market, where trading volumes are high. It appears that the price inflation in the broker quotes rises as the transaction volume drops. While broker quotes are substantially higher than transaction prices in a down market, the broker sentiment, which is a qualitative assessment of market conditions, appears to be more in line with transaction prices. We have also documented that the broker quote based index reaches its peak about two months after the peak of the repeat sales based index. Finally, broker quotes are smooth in comparison to transaction prices and they are smoothed more in a down market than an up market. Our results suggest that an optimistic view of broker quotes is problematic only in down markets where trading volumes are limited. The price inflation in broker quotes is a risk to the financial system in a market with only a broker quote based index in that it overstates the collateral values underlying mortgage loans in a down market.Broker quotes; Broker quote based apartment price index; Repeat sales apartment price index; House price cycle; Broker sentiment; Korean housing markets

Variable power broadcasting based on local information for source-dependent broadcasting protocols

A typical broadcasting protocol for wireless network usually involves fixed transmission power that covers, for example an area within 250 meters (m). However, it is often unnecessary to broadcast using fixed power because a node that needs to be covered may just be 100m away. By reducing the transmission power enough to cover this node, energy expenditure would be reduced, thus, prolonging the lifetime of battery-powered wireless networks such as Mobile Ad Hoc Networks (MANETs) and Wireless Sensor Networks (WSNs). Existing source-dependent broadcasting protocols do not have any mechanisms for adjusting the transmission power of nodes. Therefore, this paper proposes some effective mechanisms based on local neighborhood knowledge, while ensuring the overall network is still covered. Results of extensive simulations confirm the effectiveness of the proposed protocols in reducing energy consumption. © 2011 IEEE.published_or_final_versionThe 2011 IEEE Wireless Communications and Networking Conference (WCNC), Cancun, Mexico, 28-31 March 2011. In Proceedings of IEEE WCNC, 2011, p. 796-80

Enhanced variable power broadcasting based on local information in mobile ad hoc networks

Broadcasting in mobile ad hoc networks (MANETs) usually involve fixed transmission power that covers, for example an area within 250 meters. However, it is often unnecessary to broadcast using fixed power because a node that needs to be covered may just be 100 meters away. By reducing the transmission power enough to cover this node, energy expenditure would be reduced, thus, prolonging the lifetime of a battery-powered MANET. Existing works on variable power broadcasting based on local information are effective in achieving this objective. However, they are not optimized and can be improved by dynamically adjusting the transmission power based on where a broadcast message comes from. This paper proposes simple mechanisms based on local knowledge to adjust the transmission power dynamically and incorporates a timer suppression mechanism to further enhance the effectiveness of the protocols in reducing energy expenditure. Results of simulation studies confirm the effectiveness of the proposed enhancements. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of IEEE-WCNC, 2010, p. 1-

Novel Features for Brain-Computer Interfaces

While conventional approaches of BCI feature extraction are based on the power spectrum, we have tried using nonlinear features for classifying BCI data. In this paper, we report our test results and findings, which indicate that the proposed method is a potentially useful addition to current feature extraction techniques

The Management of “Coats' Response” in a Patient with X-Linked Retinitis Pigmentosa—A Case Report

The management of exudative retinal detachment in Coats disease can be very difficult with variable results. A case is presented of a 12 year old boy who was diagnosed with X-linked retinitis pigmentosa with an associated “Coat's Response”. The patient had a marked reduction in his left visual acuity due to intragel and subhyaloid haemorrhage as well as exudative retinal detachment. This was managed successfully with vitrectomy and endolaser, resulting in clearance of the haemorrhage and flattening of the retina. In our experience endolaser should be considered as viable therapeutic option in the management of this condition

Silica grain catalysis of methanol formation

The specific catalytic effect of a silica grain on the formation of methanol via the sequential addition of H atoms to CO adsorbed on the surface is investigated. A negatively charged defect on a siliceous edingtonite surface is found to reduce the gas phase barriers for the H + COads and H + H2C=O-ads reactions by 770 and 399 K, respectively, when compared to the same reactions in the gas phase. The catalytic effect of negatively charged surface sites could also be applicable to the hydrogenation of other adsorbed unsaturated species. However, the activation energies on the surface defect are still too large (1150 and 2230 K) for CH3OH to form efficiently at 10-20 K in the interstellar medium via a classical mechanism. It is therefore suggested that quantum mechanical tunnelling through the activation barrier is required for these hydrogen addition reactions to proceed at such temperatures. The calculations show that because the adsorption energies of CO and H2C=O on the negatively charged defect are substantial, CH3OH may form efficiently during the warm-up period in star-forming regions