Leveraging 802.11n frame aggregation to enhance QoS and power consumption in Wi-Fi networks

The Wi-Fi technology, driven by its tremendous success, is expanding into a wide variety of devices and applications. However, many of these new devices, like handheld devices, pose new challenges in terms of QoS and energy efficiency. In order to address these challenges, in this paper we study how the novel MAC aggregation mechanisms developed in the 802.11n standard can be used to enhance the current 802.11 QoS and power saving protocols. Our contribution is twofold. First, we present a simulation study that illustrates the interactions between 802.11n and the current 802.11 QoS and power saving protocols. This study reveals that the 802.11n MAC aggregation mechanisms perform better when combined with the power save mode included in the original 802.11 standard than with the 802.11e U-APSD protocol. Second, we design CA-DFA, an algorithm that, using only information available at layer two, adapts the amount of 802.11n aggregation used by a Wi-Fi station according to the level of congestion in the network. A detailed performance evaluation demonstrates the benefits of CA-DFA in terms of QoS, energy efficiency and network capacity with respect to state of the art alternatives.     

Crawl through Neighbors: A Simple Curve Reconstruction Algorithm

Given a planar point set sampled from an object boundary, the process of approximating the original shape is called curve reconstruction. In this paper, a novel non‐parametric curve reconstruction algorithm based on Delaunay triangulation has been proposed and it has been theoretically proved that the proposed method reconstructs the original curve under ε‐sampling. Starting from an initial Delaunay seed edge, the algorithm proceeds by finding an appropriate neighbouring point and adding an edge between them. Experimental results show that the proposed algorithm is capable of reconstructing curves with different features like sharp corners, outliers, multiple objects, objects with holes, etc. The proposed method also works for open curves. Based on a study by a few users, the paper also discusses an application of the proposed algorithm for reconstructing hand drawn skip stroke sketches, which will be useful in various sketch based interfaces.     

On the Corrosion Performance of Monel 400 in Molten LiCl-Li2O-Li at 923 K

Metallurgical and Materials Transactions A - The corrosion resistance of a Ni-Cu alloy, Monel 400, in molten LiCl-Li2O-Li at 923 K (650 °C) was investigated. Exposure testing...     

Postnatal survival and growth of mouse irradiated in utero with low dose

In order to investigate radiation risks associated with low dose and low dose-rates, pregnant Swiss albino mice were exposed to gamma rays, 0.80 Gy from a cobalt-60 source at two different dose-rates (0.0795 and 0.0012 Gy/min) on 18 day post conception. In females exposed to lower dose-rate (0.0012 Gy/min), litter size was found to be decreased, while those exposed to higher dose-rate (0.0795 Gy/min), it remained unaltered. In both groups, appearance of fur and development of complete fur were delayed, whereas gait was delayed only in higher dose-rate group. Male offspring exhibited a biphasic mode of weight loss, while female offspring after an initial weight loss at 1 week, displayed a continuous recovery, but could not attain the normal weight till 12 weeks of age. It appears that higher dose-rate is more effective in delaying the appearance of physiological markers and weight loss, while in terms of litter size lower dose-rate (0.0012 Gy/min) is more effective.     

The yields of extracted leaf protein from lucerne (Medicago sativa L.)

The effects of fertilisers, frequency of cutting, row spacing and simazine on the yields of dry matter and extractable protein from lucerne (Medicago sativa L.) were studied using the laboratory-scale pulper and press. Between 40 and 65% protein nitrogen was extractable; extractability was not affected by the various treatments but altered with season. Lucerne responded with increased yields of dry matter and extractable protein to fertilisers, simazine (35 g/ha) and rows spaced at 30.5 cm. Six or 8 harvests were found to give greater yields than 5 harvests in 180 days. The annual yields of extractable protein reached 3100 kg/ha and it is felt that better control of pests could lead to even greater yields.     

Simulation of a forced-air-twin-chamber for measuring heat treatment uniformity in harvested tomatoes

A heat transfer simulation model combining convection and conduction was developed to predict accurately the temperatures of air and produce (tomatoes) placed within a custom designed experimental set-up used for the measurement of the uniformity of hot air treatment. The thermal conductivity of the produce and air humidity have significant effects on the uniformity of heat treatment, particularly on the temperature gradients generated in the design. Tomato position, signifying the length of tunnel, is another factor to be considered when designing such experimental device. While air velocity is a factor affecting heat treatment uniformity, the tomato orientation did not show any significant effect. The simulation was experimentally validated and found to be accurate. This method could also be used for other fruits.     

Fuzzy Reliability Assessment of Distribution System with Wind Farms and Plug-in Electric Vehicles

Abstract

The equipment failures are highly uncertain in nature and simple average failure rate will not reflect this uncertainty. The uncertainty level further increases in reliability evaluation due to the integration of wind farm (WF) because of the intermittent nature of wind speed and random charging patterns of plug-in electric vehicles (PEVs). In this work, the uncertain variables in the distribution system (failure rate, repair time, WF output, PEVs charging and system load factor) are represented as fuzzy numbers to handle the uncertainty. The available uncertain data are used to find the probability distribution function (PDF) of that parameter and is converted into fuzzy membership function using transformation techniques. Failure rate of equipment is converted into failure probability using Monte Carlo simulation (MCS) method. Sampling method is applied to create the PDF of a variable which has average value. Fuzzy severity index (FSI) is proposed to find the importance of an equipment on reliability and is evaluated by measuring the fuzzy distance between the fuzzy reliability indices. The proposed assessment method is validated on modified RBTS bus 2 by comparing with analytical and MCS methods. The proposed method has been tested with integration of WFs and PEVs.     

An alternate method for using a visual discrimination model (VDM) to optimize soft-copy display image quality

Researchers have developed visual discrimination models (VDMs) that can predict a human observer's ability to detect a target object superposed on an image. These models incorporate sophisticated knowledge of the properties of the human visual system. In the predictive approach, termed conventional VDM usage, two input images with and without a target are analyzed by an algorithm that calculates a just-noticeable-difference (JND) index, which is a taken as a measure of the detectability of the target. A new method of using the VDM is described, termed channelized VDM, which involves finding the linear combination of the VDM-generated channels (which are not used in conventional VDM analysis) that has optimal classification ability between normal and abnormal images. The classification ability can be measured using receiver operating characteristic (ROC) or two alternative forced choice (2AFC) experiments, and in special cases they can also be predicted by signal detection theory (SDT) based model-observer methods. In this study simulated background and nodule containing regions were used to validate the new method. It was found that the channelized VDM predictions were in excellent qualitative agreement with human-observer validated SDT predictions. Either VDM method (conventional or channelized) has potential applicability to soft-copy display optimization. An advantage of any VDM-based approach is that complex effects, such as visual masking, are automatically accounted for, which effects are usually not included in SDT-based methods.     

Implementations of a four-level mechanical architecture for fault-tolerant robots

This paper describes a fault tolerant mechanical architecture with four levels devised and implemented in concert with NASA (Tesar, D. & Sreevijayan, D., Four-level fault tolerance in manipulator design for space operations. In First Int. Symp. Measurement and Control in Robotics (ISMCR '90), Houston, Texas, 20–22 June 1990.) Subsequent work has clarified and revised the architecture. The four levels proceed from fault tolerance at the actuator level, to fault tolerance via in-parallel chains, to fault tolerance using serial kinematic redundancy, and finally to the fault tolerance multiple arm systems provide. This is a subsumptive architecture because each successive layer can incorporate the fault tolerance provided by all layers beneath. For instance a serially-redundant robot can incorporate dual fault-tolerant actuators. Redundant systems provide the fault tolerance, but the guiding principle of this architecture is that functional redundancies actively increase the performance of the system. Redundancies do not simply remain dormant until needed. This paper includes specific examples of hardware and/or software implementation at all four levels.