Search

Highlights: [•] This paper assesses the state of the art in the use of computer models to simulate the level of safety in the traffic system. [•] This paper reviews computer models of driver and vehicle behaviour within a road context. [•] The paper explores the general data types used to develop, calibrate and validate these models. [•] The paper investigates the measures of effectiveness used by the models. It outlines the use surrogate safety measures and crash data in the models. [•] The paper explores future developments which may assist in further development of these models. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasonically aided electric propulsion (UAEP) is a new type of colloid thruster which uses ultrasonic nozzle instead of the traditional capillary or needle emitter. This paper focuses on the effects of propellant upon the performance of UAEP system. Multiple solutions, such as doped formamide, water and tributyl-phosphate were employed and tested as the propellant. The relationships between the spray current and several characteristic parameters of the propellant, such as surface tension coefficient, electrical conductivity, viscosity and doped solute, were experimentally investigated. The experimental results showed that the operation state of UAEP system was greatly influenced by the physical properties of the propellant. The solution of LiCl/tributyl phosphate was selected as the propellant for UAEP. [Copyright &y& Elsevier]

Abstract: This paper studies the star sensor low frequency error (LFE) in-flight calibration problem. The star sensor low frequency error, which is caused primarily by the periodic thermal distortion, has a great impact on the satellite attitude determination accuracy. It is formulated as a Fourier series in this paper. The low frequency error calibration is fulfilled by estimating the Fourier coefficients, which are assumed time-constant. The performance of the calibration method is evaluated through the derivation of the estimation error covariance. It is specified that the attitude determination accuracy can be improved by using the calibration method in the case that the calibration error is less than the true low frequency error parameters. The low frequency error model for numerical simulation are established based on the telemetry data from real star sensors operating under in-orbit conditions. The simulation results illustrate the efficiency of the proposed methods. [Copyright &y& Elsevier]

Abstract: Since its launch on 20 May 2004, FORMOSAT-2 (FS2) is still the unique satellite to observe the transient luminous events (TLEs) from orbit. In nearly 9 years from 4 July 2004 to 31 May 2013, the number and distribution of TLEs observed are summarized. The instrument used for the observation of TLEs is called imager of sprites and upper atmospheric lightning (ISUAL). This is the first time the observation results are presented in the International Astronautical Congress (IAC). Due to the orbital characteristics of FORMOSAT-2, unobserved gaps exist between each two orbits. Also, the ISUAL has its detection threshold. In this paper, besides the presentation of above results, globalization extension of TLEs is performed based on FORMOSAT-2׳s observation. Factors considered include number of orbits ISUAL in operations, daytime and night-time, season, non-observed areas, observability of TLEs, limb view hiding, and other factors. An estimated global occurrence rate is 24TLEs/min, but this number is still much less than the possible potential rate of 195. To enhance the results, more instruments and longer observation time are required. [Copyright &y& Elsevier]

Abstract: Space manipulator is an important tool for spacecraft to complete a variety of tasks in space. Nowadays the harmonic drive is widely used as the reducer in the space manipulator, which may influence the dynamical properties of flexible space manipulator. The analysis of dynamic reliability and parameter sensitivity of space manipulator with harmonic drive is of significant importance for space manipulator designers in the early stage of design. The trajectory precision of the manipulator determines whether the mechanism performs normally. However, it is difficult to use the existing methods to resolve reliability apportionment issues because of the data insufficiency and the uncertainty of the relations among the components in the mechanical system. This paper establishes the dynamical models of space manipulator considering the harmonic hysteresis phenomenon derived from the harmonic reducer. A new method is proposed to analyze the dynamic reliability and parameter sensitivity of space manipulator with harmonic drive. The proposed method extends the previous response surface method (RSM) and focuses on the characteristics of the output dynamical property of the space manipulator. With the result of parameter sensitivity analysis, we can prolong the fine arm or shorten the main arm to improve the motion precision reliability of space manipulator. Therefore, our revised response surface method (RRSM) is suitable for reliability apportionment of the space manipulator when the design information has not been clearly identified, particularly in early design phrase. [Copyright &y& Elsevier]

Abstract: This paper attempts to characterize failure behaviour of small satellites through statistical analysis of actual in-orbit failures. A unique Small Satellite Anomalies Database comprising empirical failure data of 222 small satellites has been developed. A nonparametric analysis of the failure data has been implemented by means of a Kaplan–Meier estimation. An innovative modelling method, i.e. Bayesian theory in combination with Markov Chain Monte Carlo (MCMC) simulations, has been proposed to model the reliability of small satellites. An extensive parametric analysis using the Bayesian/MCMC method has been performed to fit a Weibull distribution to the data. The influence of several characteristics such as the design lifetime, mass, launch year, mission type and the type of satellite developers on the reliability has been analyzed. The results clearly show the infant mortality of small satellites. Compared with the classical maximum-likelihood estimation methods, the proposed Bayesian/MCMC method results in better fitting Weibull models and is especially suitable for reliability modelling where only very limited failures are observed. [Copyright &y& Elsevier]

Abstract: This paper studies the thrust vector control problem for an upper-stage rocket with fuel slosh dynamics. The dynamics of a three-axis stabilized spacecraft with a single partially-filled fuel tank are formulated and the sloshing propellant is modeled as a multi-mass–spring system, where the oscillation frequencies of the mass–spring elements represent the prominent sloshing modes. The equations of motion are expressed in terms of the three-dimensional spacecraft translational velocity vector, the attitude, the angular velocity, and the internal coordinates representing the slosh modes. A Lyapunov-based nonlinear feedback control law is proposed to control the translational velocity vector and the attitude of the spacecraft, while attenuating the sloshing modes characterizing the internal dynamics. A simulation example is included to illustrate the effectiveness of the control law. [Copyright &y& Elsevier]

Abstract: Robotic planetary surface exploration missions are becoming much more ambitious in their science goals as they attempt to answer the bigger questions relating to the possibility of life elsewhere in our solar system. Answering these questions will require scientifically rich landing sites. Such sites are unlikely to be located in relatively flat regions that are free from hazards, therefore there is a growing need for next generation entry descent and landing systems to possess highly sophisticated navigation capabilities coupled with active hazard avoidance that can enable a pin-point landing. As a first step towards achieving these goals, a multi-source, multi-rate data fusion algorithm is presented that combines single camera recursive feature-based structure from motion (SfM) estimates with measurements from an inertial measurement unit in order to overcome the scale ambiguity problem by directly estimating the unknown scale factor. This paper focuses on accurate estimation of absolute motion parameters, as well as the estimation of sparse landing site structure to provide a starting point for hazard detection. We assume no prior knowledge of the landing site terrain structure or of the landing craft motion in order to fully assess the capabilities of the proposed algorithm to allow a pin-point landing on distant solar system bodies where accurate knowledge of the desired landing site may be limited. We present results using representative synthetic images of deliberately challenging landing scenarios, which demonstrates that the proposed method has great potential. [Copyright &y& Elsevier]

Abstract: The main limitation of gene therapy towards clinics is the lack of robust, safe and efficient gene delivery vectors. This paper describes new polycations for gene delivery based on poly(β-amino ester)s (pBAE) containing terminal oligopeptides. The authors developed oligopeptide-modified pBAE–pDNA nanoparticles that achieve better cellular viability and higher transfection efficacy than other end-modified pBAE and commercial transfection agents. Gene expression in highly permissive cell lines was remarkably high, but transfection efficiency in less-permissive cell lines was highly dependent on oligopeptide composition and nanoparticle formulation. Moreover, the use of selected oligopeptides in the pBAE formulation led to preferential intracellular localization of the particles. Particle analysis of highly efficient pBAE formulations revealed different particle sizes and charge features, which indicates chemical pseudotyping of the particle surface, related to the oligopeptide chemical nature. In conclusion, chemical modification at the termini of pBAE with amine-rich oligopeptides is a powerful strategy for developing delivery systems for future gene therapy applications. [Copyright &y& Elsevier]

Abstract: This paper presents an understanding of how initial molecular weight and initial monomer fraction affect the degradation of bioresorbable polymers in terms of the underlying hydrolysis mechanisms. A mathematical model was used to analyse the effects of initial molecular weight for various hydrolysis mechanisms including noncatalytic random scission, autocatalytic random scission, noncatalytic end scission or autocatalytic end scission. Different behaviours were identified to relate initial molecular weight to the molecular weight half-life and to the time until the onset of mass loss. The behaviours were validated by fitting the model to experimental data for molecular weight reduction and mass loss of samples with different initial molecular weights. Several publications that consider initial molecular weight were reviewed. The effect of residual monomer on degradation was also analysed, and shown to accelerate the reduction of molecular weight and mass loss. An inverse square root law relationship was found between molecular weight half-life and initial monomer fraction for autocatalytic hydrolysis. The relationship was tested by fitting the model to experimental data with various residual monomer contents. [Copyright &y& Elsevier]

The grain structure, especially the grain orientation, number and type of grain boundaries, influences many of the properties of multicrystalline (mc) silicon (Si) wafers used for manufacturing solar cells. In order to increase the efficiency of silicon solar cells, the relation between material defects, such as dislocations, impurities and precipitates, and the grain structure must be understood. Currently no measurement system exists that can determine the grain orientation on a full mc Si wafer with an area of 156×156mm2. The most widely used measuring method is electron backscatter diffraction (EBSD). However, it is only possible to measure small sample sizes by EBSD depending on the scanning electron microscopy stage, and moreover a time-consuming surface preparation is needed. In this paper an innovative fast characterization method is presented that allows the orientation measurement of as-cut and polished Si samples up to 380×400mm2. This method, known as the Laue scanner, is based on X-ray diffraction. Experimental and theoretical considerations, limits of the system and example results of possible tasks are shown and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical strengthening by grain refinement is a method whereby a material’s strength and hardness can be increased by decreasing the average crystallite grain size. The empirical Hall–Petch relationship mathematically describes grain boundary strengthening and provides guidance for a straightforward way to produce stronger materials. While the phenomenon has been widely explored in nanocrystalline metals, the difficulty associated with fabricating high-quality dense nanocrystalline ceramics has left unanswered the question of the validity and extent of the relationship in ceramics. Prior studies suggest the occurrence of an inverse Hall–Petch response in ceramics with grain sizes <100nm. This paper demonstrates a novel integrated approach, comprised of nanopowder processing and high-pressure, low-temperature sintering to fabricate bulk, fully dense and high-purity nanocrystalline ceramics with unprecedentedly small nanometer-sized grains. Using magnesium aluminate spinel as an archetypal hard ceramic, the hardness of this transparent ceramic armor is shown to rigorously follow the Hall–Petch relationship down to grain sizes of 28nm. Consequentially, the nanocrystalline spinel ceramics are shown to exhibit a 50% increase in hardness over a corresponding order of magnitude reduction in grain size without a decline in density or fracture resistance. Additionally, the produced nanocrystalline ceramics have an optical transparency near theoretical. Reaching an exceptional hardness of 20.2GPa at 28nm, the behavior shows no evidence supporting an inverse Hall–Petch effect. [Copyright &y& Elsevier]

Abstract: This paper examines the idea that reversible hysteresis in MAX phases is caused by the formation, growth and collapse of unstable, or incipient, kink bands. In situ X-ray diffraction of polycrystalline Ti3SiC2 in compression showed that residual elastic lattice strains developed during the first loading cycle and remained approximately constant afterwards. These residual strains were compressive in grains with a low Schmid factor and tensile in grains with a high Schmid factor, consistent with previous observations of plastically deformed hexagonal metals. In contrast, incipient kink bands would be expected to collapse completely, without any residual strain. Elastoplastic self-consistent simulations showed that reversible hysteresis is predicted if some grains yield by slip on the basal plane, while others remain predominantly elastic, giving both the experimentally observed magnitude of the work dissipated and its dependence on the maximum applied stress. The reversible hysteresis in single crystals was studied by cyclically indenting thin films of Ti3SiC2 and Ti3SiC2/TiC multilayers on Al2O3 substrates. The work dissipated in the multilayer films was greater than in Ti3SiC2 alone, despite the reduction in volume fraction of Ti3SiC2. Reversible hysteresis was also observed during indentation of single-crystal cubic MgO, demonstrating that this behaviour can occur if there are insufficient slip systems to accommodate the strain around the indentation. These results show that reversible hysteresis is associated with conventional dislocation flow, without the need for unstable kinking. [Copyright &y& Elsevier]

Abstract: An additional length scale is introduced which is not considered by the existing Taylor or viscoplastic self-consistent (VPSC) models. In these models, a macroscopic deformation is imposed on a representative volume element (RVE) of the macroscopic length scale (∼1000 grains). Each grain constitutes a RVE at what will be called the “mesoscopic-1” length scale. Here an additional intermediate length scale is introduced, called “mesoscopic-2”. Its RVE is a “cluster” of several grains. Within each cluster, the algorithm of the Neffect-VPSC model is employed to treat grain interactions. The average deformation of each cluster is the macroscopic deformation. This model gives texture predictions as good as, or better than, the Neffect-VPSC or the ALAMEL models for several tested materials and kinds of tests. The Taylor, VPSC and the ALAMEL models can be seen as special versions of such cluster-type model. The Taylor and the VPSC models were then tested to give two bounds of the predicted total slip rate in the aggregate for rolling. The total slip rate is proportional to the predicted von Mises equivalent stress of the aggregate. The difference among these model predictions was studied statistically by plotting the x-value distribution as defined and discussed in this paper. It seems that according to a cluster model simulation for rolling, statistically the strain rates of the hard grains defined in this paper tend to reduce less than the increase in the strain rate of soft grains in the direction of the imposed strain rate; gradually this diminution/increase reduces for both hard and soft grains as deformation increases. We call these diminution/increase “relaxations”. Relaxations projected on the five bases in the 5-D plastic strain rate space for rolling indicate that different numbers of grains in each cluster correspond to different levels of relaxations. [Copyright &y& Elsevier]

Abstract: Many of the most useful structural steels have dislocated lath martensitic structures. The microstructures of these steels are complex since each prior austenite grain contains as many as 24 different crystallographic variants of the γ(fcc)–α′(bcc) transformation. Recent research, using electron backscatter diffraction (EBSD), has significantly clarified the “block-and-packet” structure of lath martensite in low-carbon steel. The blocks are bivariant composites of two transformation variants, with the three distinct blocks stacked so that all six of the possible variants of the packet are used. The present work was undertaken to complete the description of this structure and identify its underlying causes. We address these issues in two steps. First, we present an EBSD characterization of lath martensite in low-carbon 9Ni steel. The results show that all packets have the bivariant block structure, and, with the proper notation, the full hierarchical structure has a simple pattern that is easily described and visualized. The results are readily explained on the basis of two assumptions: (i) the bivariant block, in contrast to a single-variant block, has an α′–γ invariant plane very near {011}α″||{111}γ, which permits the plate-shaped blocks to stack without significant strain to form a packet; (ii) the transformation goes to completion, with the consequence that the net strain in the prior austenite grain is a simple dilatation, and polygranular bodies can transform martensitically without significant residual stress. In a companion paper we use an appropriate modification of the crystallographic theory of lath martensite to validate the first of these assumptions. [Copyright &y& Elsevier]

Abstract: In the pursuit of higher operating temperatures and better durability of thermal barrier coating (TBC) materials, the currently used air-plasma-sprayed (APS) 8wt.% yttria-stabilized zirconia (8YSZ) ceramic is faced with a phase degradation problem regarding its initial metastable T prime (T′) phase, which results in residual stress and cracks during long-term operations. In this study, we focus on the relationship between the long-term phase transformation and mechanical properties, which facilitates the simulation and prediction of properties under operating conditions. Field-assisted sintering specimens of the pure T′ phase were annealed at 1300°C for different periods of time to obtain various phase compositions. A nano/micro hybrid structure was observed as the phase transformation developed. The Vickers hardness of the materials increased by 8% due to the precipitation of fine T phase grains. On the other hand, the bending strength decreased by more than 60% when the T′ phase decomposed from 70 to 20vol.%. A noteworthy reduction in the fracture toughness, along with a decrease in the volume percentage of the T′ phase, was also observed during long-term degradation. Effects of the T′ phase decomposition on mechanical properties are discussed in this paper. This systematic research on the mechanical properties and phase degradation of YSZ is of significant importance in predicting and evaluating the performance evolvement of TBCs. [Copyright &y& Elsevier]

Abstract: The order in which information is received alters the evaluation of causal hypotheses. Specifically, research suggests that the last piece of information oftentimes has the greatest impact on the evaluation and that the difference in subjective value between two pieces of information is an important factor influencing the magnitude of this recency effect. The present paper extends this line of work by exploring individual differences in this phenomenon via one's degree of handedness. Two hundred and five participants were given two hypothetical scenarios and related causal hypotheses accompanied by two pieces of additional information and asked to revise their belief in each hypothesis as information accumulated. Results confirmed predictions that 1) inconsistent/mixed-handers (those who use their non-dominant hand for at least some activities) show a larger effect with two pieces of inconsistent weak or strong information, and 2) neither mixed-handers nor consistent/strong-handers (those who use their dominant hand for almost all activities) show an effect with strong and weak pieces of consistent information. Mixed-handers' susceptibility to persuasive arguments and Ramachandran’s (1995; Ramachandran and Blakeslee, 1998) belief-updating theory centered around communication between the two halves of the brain and functional access to the right hemisphere are used to account for these data. [Copyright &y& Elsevier]

Abstract: One of the main design challenges in Wireless Sensor Networks (WSN) is to prolong the system lifetime, while achieving acceptable quality of service for applications. In WSN, each sensor node is battery powered and it is not convenient to recharge or replace the batteries in many cases, especially in remote and hostile environments. Due to the limited capabilities of sensor nodes, it is usually desirable that a WSN should be deployed with high density and thus redundancy can be exploited to increase the network’s lifetime. In this paper, we introduce an efficient lifetime optimization and self-stabilizing algorithm to enhance the lifetime of wireless sensor networks especially when the reliabilities of sensor nodes are expected to decrease due to use and wear-out effects. Our algorithm seeks to build resiliency by maintaining a necessary set of working nodes and replacing failed ones when needed. We provide some theoretical and simulation results, that fully demonstrate the usefulness of the proposed algorithm. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a novel routing protocol, PRO, for profile-based routing in pocket switched networks. Differing from previous routing protocols, PRO treats node encounters as periodic patterns and uses them to predict the times of future encounters. Exploiting the regularity of human mobility profiles, PRO achieves fast (low-delivery-latency) and efficient (low-message-overhead) routing in intermittently connected pocket switched networks. PRO is self-learning, completely decentralized, and local to the nodes. Despite being simple, PRO forms a general framework, that can be easily instantiated to solve searching and querying problems in adhoc smartphone networks. We validate the performance of PRO on real world traces and compare its performance with that of previous approaches. [Copyright &y& Elsevier]

Abstract: Assessing the trustworthiness of sensor data and transmitters of this data is critical for quality assurance. Trust evaluation frameworks utilize data provenance along with the sensed data values to compute the trustworthiness of each data item. However, in a sizeable multi-hop sensor network, provenance information requires a large and variable number of bits in each packet, resulting in high energy dissipation due to the extended period of radio communication. In this paper, we design energy-efficient provenance encoding and construction schemes, which we refer to as Probabilistic Provenance Flow (PPF). Our work demonstrates the feasibility of adapting the Probabilistic Packet Marking (PPM) technique in IP traceback to wireless sensor networks. We design two bit-efficient provenance encoding schemes along with a complementary vanilla scheme. Depending on the network size and bit budget, we select the best method based on mathematical approximations and numerical analysis. We integrate PPF with provenance-based trust frameworks and investigate the trade-off between trustworthiness of data items and transmission overhead. We conduct TOSSIM simulations with realistic wireless links, and perform testbed experiments on 15–20TelosB motes to demonstrate the effectiveness of PPF. Our results show that the encoding schemes of PPF have identical performance with a low bit budget (∼32-bit), requiring 33% fewer packets and 30% less energy than PPM variants to construct provenance. With a twofold increase in bit budget, PPF with the selected encoding scheme reduces energy consumption by 46–60%. [Copyright &y& Elsevier]

Abstract: Due to the rising popularity of Wireless Sensor Networks (WSN), there has been an increasing demand for more challenging applications. Generally speaking, such applications demand the support of Quality of Service (QoS) constraints and often multiple conflicting objectives. To address these requirements, network management becomes a critical task. However, single layer and cross-layer techniques will probably not be sufficient. Fortunately, cognitive techniques have shown great potential in improving network performance and achieving the end-to-end goals. In this paper, cognitive solutions for resource management in WSN are proposed to address the needs of challenging applications. The solutions proposed include a reasoning machine designed for the first time using the mathematical tool known as Weighted Cognitive Maps (WCM), and a learning protocol designed using the Q-learning algorithm. The WCM has powerful inference properties and can model complex systems using their underlying causal relationships. Thus, it can consider multiple conflicting objectives with low complexity. On the other hand, the learning protocol uses Q-learning to build a knowledge base that is used to enhance the performance of the WCM reasoning machine and address the end-to-end goals of the applications directly. Extensive computer simulations are used to evaluate the performance of the cognitive framework. The results show that it can efficiently consider multiple conflicting goals and constraints, thus outperforming its state-of-the-art counterparts. [Copyright &y& Elsevier]

Abstract: This paper presents a novel, intelligent controller to support mobility in wireless sensor networks. In particular, the focus is on the deployment of such mobility solution to critical applications, like personnel safety in an industrial environment. A Fuzzy Logic-based mobility controller is proposed to aid sensor Mobile Nodes (MN) to decide whether they have to trigger the handoff procedure and perform the handoff to a new connection position or not. To do so, we use a combination of two locally available metrics, the RSSI and the Link Loss, in order to “predict” the End-to-End losses and support the handoff triggering procedure. As a performance evaluation environment, a real industrial setting (oil refinery) is used. Based on on-site experiments run in the oil refinery testbed area, the proposed mobility controller has shown significant benefits compared to other conventional solutions, in terms of packet loss, packet delivery delay, energy consumption, and ratio of successful handoff triggers. [Copyright &y& Elsevier]

Abstract: This paper proposes a novel data gathering method using Compressive Sensing (CS) and random projection to improve the lifetime of large Wireless Sensor Networks (WSNs). To increase the network lifetime, one needs to decrease the overall network energy consumption and distribute the energy load more evenly throughout the network. By using compressive sensing in data aggregation, referred to as Compressive Data Gathering (CDG), one can dramatically improve the energy efficiency, and this is particularly attributed to the benefits obtained from data compression. Random projection, together with compressive data gathering, helps further in balancing the energy consumption load throughout the network. In this paper, we propose a new compressive data gathering method called Minimum Spanning Tree Projection (MSTP). MSTP creates a number of Minimum-Spanning-Trees (MSTs), each rooted at a randomly selected projection node, which in turn aggregates sensed data from sensors using compressive sensing. We compare through simulations our method with the existing data gathering schemes. We further extend our method and introduce eMSTP, which joins the sink node to each MST and makes the sink node as the root for each tree. Our simulation results show that MSTP and eMSTP outperform the existing data gathering schemes in decreasing the communication cost and distributing the energy consumption loads and hence improving the overall lifetime of the network. [Copyright &y& Elsevier]

Abstract: Duty cycling is a fundamental mechanism for battery-operated ad hoc networks, such as Wireless Sensor Networks, Delay Tolerant Networks, and solar-powered Wireless Mesh Networks. Because of its utter importance, it has been proposed in a wide variety of flavors, one of the most prominent being that of the asynchronous mechanisms. In particular, schedule-based duty cycling has earned attention due to its low requirements and simplicity of implementation. Despite its potential, a comprehensive and realistic study on the neighbor discovery latency that results from schedule-based asynchronous duty cycling is still missing. This paper fills in this gap, by providing accurate models for major schedule-based mechanisms: Block Designs, Quorum systems and Disco. The provided models consider message loss probability and yield more precise estimations than traditional models. Based on this improved accuracy, the relative latency, a new metric for studying the trade off between latency and power, is proposed as a substitute to the power-latency product. Finally, a practical mapping of which schedule is more adequate for given requirements of latency, energy savings and link reliability is presented. [Copyright &y& Elsevier]

Abstract: Among the IEEE 802.11 models proposed in the literature most concentrate solely on homogeneous traffic sources (i.e., with the same arrival rate) and there are only a few which concentrate on heterogeneous nonsaturated traffic sources. This paper proposes a comprehensive analysis of heterogeneous traffic sources (saturated or nonsaturated) with M/M/1/K queues. The mathematical model proposed in this paper allows the calculation of the following parameters: per-station and network throughput, delay (including service time and queuing delay), and frame loss probability (including probability of dropping a frame at the MAC layer and in a transmission queue). Simulation results show the impact of the presence of different traffic source types on each other and validate the correctness of the proposal for a variable number of stations and under different network loads. Importantly, the new model is kept reasonably simple to attract network designers. We provide examples of its practical applicability by performing an estimation of the maximum number of voice calls which can be accepted by a particular network and the optimal buffer size. [Copyright &y& Elsevier]

Abstract: Vehicular ad hoc networks can play an important role in enhancing transportation efficiency and improving road safety. Therefore, direct vehicle-to-vehicle communications are considered as one of the main building blocks of a future Intelligent Transportation System. The success and availability of IEEE 802.11 radios made this technology the most probable choice for the medium access control layer in vehicular networks. However, IEEE 802.11 was originally designed in a wireless local area network context and it is not optimised for a dynamic, ad hoc vehicular scenario. In this paper, we investigate the compatibility of the IEEE 802.11 medium access control protocol with the requirements of safety vehicular applications. As the protocols in this family are well-known for their scalability problems, we are especially interested in high density scenarios, quite frequent on today’s roads. Using an analytical framework, we study the performance of the back-off mechanism and the role of the contention window on the control channel of a vehicular network. Based on these findings, we propose a reverse back-off mechanism, specifically designed with road safety applications in mind. Extensive simulations are carried out to prove the efficiency of the proposed enhancement scheme and to better understand the characteristics of vehicular communications. [Copyright &y& Elsevier]

Abstract: Many sensor networks suffer from the energy hole problem which is a special case of load imbalance caused by the funnelling effect of many sensor nodes transmitting their data to a single, central sink. In order to mitigate the problem, a balanced routing tree is often required and this can be constructed with either a centralised or distributed algorithm. Distributed solutions are typically less effective but are significantly cheaper than centralised solutions in terms of communication overhead and they scale better for the same reason. In this paper we propose a novel distributed algorithm for the construction of a load balanced routing tree. Our proposed solution, Degree Constrained Routing, is unique in that it aims to maximise global balance during construction rather that relying on rebalancing an arbitrary tree or only maximising local balance. The underlying principle is that if all nodes adopt the same number of children as each other while the routing tree grows, then the final tree will be globally balanced. Simulation results show that our algorithm can produce trees with improved balance which results in lifetimes increased by up to 80% compared to the next best distributed algorithm. [Copyright &y& Elsevier]

Abstract: This paper explores Fibonacci Multipath Load Balancing protocol (FMLB) for Mobile Ad Hoc Networks (MANETs). The FMLB protocol distributes transmitted packets over multiple paths through the mobile nodes using Fibonacci sequence. Such distribution can increase the delivery ratio since it reduces the congestion. The FMLB protocol’s responsibility is balancing the packets transmission over the selected paths and ordering them according to hops count. The shortest path is used more frequently than the other ones. The simulation results show that the FMLB protocol has achieved an enhancement on packet delivery ratio, up to 21%, as compared to the Ad Hoc On-demand Distance Vector routing protocol (AODV) protocol, and up to 11% over the linear Multiple-path routing protocol. Also the results show the effect of nodes pause time and speed on each of the data delivery ratio and End-to-End (E2E) delay transmission time. Finally, the simulation results are obtained by the well-known Glomosim Simulator, version 2.03, without any distance or location measurements devices. [Copyright &y& Elsevier]

Abstract: We analyze the problem of buffer sizing for backlogged TCP flows in 802.11-based wireless mesh networks. Our objective is to maintain high network utilization while providing low queueing delays. Unlike wired networks where a single link buffer feeds a bottleneck link, the radio spectral resource in a mesh network is shared among a set of contending mesh routers. We account for this by formulating the buffer size problem as sizing a collective buffer distributed over a set of interfering nodes. In this paper we propose mechanisms for sizing and distributing this collective buffer among the mesh nodes constituting the network bottleneck. Our mechanism factors in the network topology and wireless link rates, improving on pre-set buffer allocations that cannot optimally work across the range of configurations achievable with 802.11 radios. We evaluate our mechanisms using simulations as well as experiments on a testbed. Our results show that we can reduce the RTT of a flow by or more, at the cost of less than 10% drop in end-to-end flow throughput. [Copyright &y& Elsevier]

Despite the increased social acceptance and widespread use of pornography over the past few decades, reliable and valid instruments assessing problematic use of pornography are lacking. This paper reports the findings of three studies aimed at developing and validating a new scale measuring problematic pornography use. The Problematic Pornography Use Scale (PPUS) items showed high internal consistency, convergent validity, and construct validity. Exploratory and confirmatory factor analyses revealed four core factors relating to proposed domains of problematic pornography use. High PPUS scores were positively correlated with measures of psychopathology, low self-esteem and poor attachment. Although PPUS scores were related to other behavioral addictions, problematic pornography use as operationalized in the current paper appears to be uniquely distinguished from features of behavioral addictions relating to gambling and Internet use. Findings highlight the potential use of the PPUS for future research and possible clinical applications by defining problematic pornography use as a behavioral addiction.

Positive parenting behaviors and parental modeling of alcohol use are consistent predictors of offspring&apos;s alcohol use. Recent research extends these findings to emerging adult children and confirms continued parental influence beyond adolescence. This paper examines how maternal warmth and supervision moderate the effects of mother&apos;s heavy alcohol use on their offspring&apos;s alcohol use among a sample of non-college-attending emerging adults. Three-way interactions were used to examine if these moderating effects differed between emerging adults who lived at home and those with other living arrangements. Separate analyses within gender were used to further examine these associations. Participants were 245 emerging adults between ages 18 and 22years with no post-secondary education (59% female) who were selected from a national probability-based internet panel. Path analyses indicated that, regardless of living arrangements, male emerging adults who were more likely to witness their mother getting drunk were themselves more likely to engage in risky drinking. However, among female emerging adults, similarity between mothers&apos; and daughters&apos; drunkenness was strongest among participants who resided with their family and also reported low levels of maternal warmth. This study extends previous research by indicating that the effects of maternal modeling of heavy alcohol use on emerging adults&apos; heavy alcohol use depend upon several factors, including the gender of the child and the family context. Implications of the study findings are discussed in terms of expanding the scope of a parent-based intervention (PBI) to all emerging adults, including those who do not attend colleges or universities.

There is a growing body of research supporting the use of buprenorphine and other medication assisted treatments (MATs) for the rapidly accelerating opioid epidemic in the United States. Despite numerous advantages of buprenorphine (accessible in primary care, no daily dosing required, minimal stigma), implementation has been slow. As the field progresses, there is a need to understand the impact of participation in practitioner-scientist research networks on acceptance and uptake of buprenorphine. This paper examines the impact of research network participation on counselor attitudes toward buprenorphine addressing both counselor-level characteristics and program-level variables using hierarchical linear modeling (HLM) to account for nesting of counselors within treatment programs. Using data from the National Treatment Center Study, this project compares privately funded treatment programs (N=345) versus programs affiliated with the National Institute on Drug Abuse Clinical Trials Network (CTN) (N=198). Models included 922 counselors in 172 CTN programs and 1203 counselors in 251 private programs. Results of two-level HLM logistic (Bernoulli) models revealed that counselors with higher levels of education, larger caseloads, more buprenorphine-specific training, and less preference for 12-step treatment models were more likely to perceive buprenorphine as acceptable and effective. Furthermore, buprenorphine was 50% more likely to be perceived as effective among counselors working in CTN-affiliated programs as compared to private programs. This study suggests that research network affiliation positively impacts counselors&apos; acceptance and perceptions of buprenorphine. Thus, research network participation can be utilized as a means to promote positive attitudes toward the implementation of innovations including medication assisted treatment.

Although many studies have estimated the influence of peers on risky health behaviors, few have estimated the gains that adolescents receive from such behaviors, particularly in terms of social payoffs for complying with peer behavior. In this paper, we explore the extent to which alcohol consumption increases popularity of adolescents. Using data from a nationally-representative sample of adolescents, we estimate endogeneity-corrected models with school-level fixed effects to identify the effect of alcohol consumption on social network ties. We find that alcohol consumption leads to an increase in popularity, with the largest gains experienced by white males and females. Our results provide new evidence on the motivation behind adolescent drinking and have important implications for substance abuse interventions.

This paper examines how an adolescent&apos;s position relative to cohesive friendship groups in the school-wide social network is associated with alcohol, tobacco, and marijuana use. We extend prior research in this area by refining the categories of group positions, using more extensive friendship information, applying newer analytic methods to identify friendship groups, and making strategic use of control variables to clarify the meaning of differences among group positions. We report secondary analyses of 6th through 9th grade data from the PROSPER study, which include approximately 9500 adolescents each year from 27 school districts and 368 school grade cohort friendship networks. We find that core members of friendship groups were more likely to drink than isolates and liaisons, especially in light of their positive social integration in school, family, and religious contexts. Isolates were more likely to use cigarettes than core members, even controlling for all other factors. Finally, liaisons were more likely to use marijuana than core members.

Abstract: The development of a highly controllable drug delivery system (DDS) for capsule endoscopy has become an important field of research due to its promising applications in therapeutic treatment of diseases in the gastrointestinal (GI) tract and drug absorption studies. Several factors need to be considered to establish the minimum requirements for a functional DDS. Environmental factors of the GI tract and also pharmaceutical factors can help determine the requirements to be met by a DDS in an endoscopic capsule. In order to minimize the influence of such factors on the performance of an effective DDS, at least two mechanisms should be incorporated into a capsule endoscope: an anchoring mechanism to control the capsule position and a drug release mechanism to control variables such as the drug release rate, number of doses and amount of drug released. The implementation of such remotely actuated mechanisms is challenging due to several constraints, including the limited space available in a swallowable capsule endoscope and the delicate and complex environment within the GI tract. This paper presents a comprehensive overview of existing DDS. A comparison of such DDS for capsule endoscopy based on the minimum DDS requirements is presented and future work is also discussed. [Copyright &y& Elsevier]

Highlights: [•] Investigated influence of process shear on nanosmearing and its subsequent powder and tablet properties. [•] Experimental techniques were developed to interpret % nanosmearing. [•] Applied process shear on powder particles had a significant effect on powder and tablet properties. [•] Nanosmeared structures influenced the powder hydrophobicity and drug release rate. [•] Drug release rate dropped with an increase in the amount of nanosmear on particle surface. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between lipid bilayers in water has been intensively studied over the last decades. Osmotic stress was applied to evaluate the forces between two approaching lipid bilayers in aqueous solution. The force–distance relation between lipid mono- or bilayers deposited on mica sheets using a surface force apparatus (SFA) was also measured. Lipid stabilised foam films offer another possibility to study the interactions between lipid monolayers. These films can be prepared comparatively easy with very good reproducibility. Foam films consist usually of two adsorbed surfactant monolayers separated by a layer of the aqueous solution from which the film is created. Their thickness can be conveniently measured using microinterferometric techniques. Studies with foam films deliver valuable information on the interactions between lipid membranes and especially their stability and permeability. Presenting inverse black lipid membrane (BLM) foam films supply information about the properties of the lipid self-organisation in bilayers. The present paper summarises results on microscopic lipid stabilised foam films by measuring their thickness and contact angle. Most of the presented results concern foam films prepared from dispersions of the zwitterionic lipid 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC) and some of its mixtures with the anionic lipid — 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DMPG). The strength of the long range and short range forces between the lipid layers is discussed. The van der Waals attractive force is calculated. The electrostatic repulsive force is estimated from experiments at different electrolyte concentrations (NaCl, CaCl2) or by modification of the electrostatic double layer surface potential by incorporating charged lipids in the lipid monolayers. The short range interactions are studied and modified by using small carbohydrates (fructose and sucrose), ethanol (EtOH) or dimethylsulfoxide (DMSO). Some results are compared with the structure of lipid monolayers deposited at the liquid/air interface (monolayers spread in Langmuir trough), which are one of most studied biomembrane model system. The comparison between the film thickness and the free energy of film formation is used to estimate the contribution of the different components of the disjoining pressure to the total interaction in the film and their dependence on the composition of the film forming solution. [Copyright &y& Elsevier]

Abstract: The knowledge of surface shear rheology is important to understand and model flow in systems where interfaces are present: multiphase flow, wetting, foaming and others. The topic has been investigated for more than 100years, but the knowledge accumulated is still partial. The experimental devices used for the measurement of the viscoelastic parameters are delicate to operate and the response of the monolayers is complex, usually non-linear and time dependent. Furthermore, it is difficult to decouple from the response of the bulk liquid. Important discrepancies between microscopic and macroscopic methods were reported and remain to be clarified. The knowledge of shear properties does not suffice in general to achieve proper descriptions of the flow behavior and measurements of compression properties are needed as well. This paper presents examples taken from the literature and discusses the current level of understanding. [Copyright &y& Elsevier]

Abstract: In the past decade, mesoporous silica nanoparticles (MSNs) as nanocarriers have showed much potential in advanced nanomaterials due to their large surface area and pore volume. Especially, more and more MSNs based nanodevices have been designed as efficient drug delivery systems (DDSs) or biosensors. In this paper, lipid, protein and poly(NIPAM) coated MSNs are reviewed from the preparation, properties and their potential application. We also introduce the preparative methods including physical adsorption, covalent binding and self-assembly on the MSNs' surfaces. Furthermore, the interaction between the aimed cells and these molecular modified MSNs is discussed. We also demonstrate their typical applications, such as photodynamic therapy, bioimaging, controlled release and selective recognition in biomedical field. [Copyright &y& Elsevier]

Abstract: The use of highly brilliant synchrotron light sources in the middle of the 1980s for X-ray diffraction has revolutionized the research of condensed monolayers. Since then, monolayers gained popularity as convenient quasi two-dimensional model systems widely used in biophysics and material science. This review focuses on structures observed in one-component phospholipid monolayers used as simplified two-dimensional models of biological membranes. In a monolayer system the phase transitions can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction. Competing interactions between the different parts of the molecule are responsible for the different monolayer structures. These forces can be modified by chemical variations of the hydrophobic chain region, of the hydrophilic head group region or of the interfacial region between chains and head groups. Modifications of monolayer structures triggered by changes of the chemical structure of double-chain phospholipids are highlighted in this paper. [Copyright &y& Elsevier]

Abstract: The responses of the ionospheric F region using GPS–TEC measurements during two moderate geomagnetic storms at equatorial, low-, and mid-latitude regions over the South American and African sectors in May 2010, during the ascending phase of solar cycle 24, are investigated. The first moderate geomagnetic storm studied reached a minimum Dst value of −64nT at 1500UT on 02 May 2010 and the second moderate geomagnetic storm reached a minimum Dst value of −85nT at 1400UT on 29 May 2010. In this paper, we present vertical total electron content (VTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations from the equatorial to mid-latitude regions in the South American and African sectors. Our results obtained during these two moderate geomagnetic storms from both sectors show significant positive ionospheric storms during daytime hours at the equatorial, low-, and mid-latitude regions during the main and recovery phases of the storms. The thermospheric wind circulation change towards the equator is a strong indicator that suggests an important mechanism is responsible for these positive phases at these regions. A pre-storm event that was observed in the African sector from low- to the mid-latitude regions on 01 May 2010 was absent in the South American sector. This study also showed that there was no generation or suppression of ionospheric irregularities by storm events. Therefore, knowledge about the suppression and generation of ionospheric irregularities during moderate geomagnetic storms is still unclear. [Copyright &y& Elsevier]

In this paper, the response of the equatorial and low latitude ionosphere to three intense geomagnetic storms occurred in 2002 and 2003 is reported. For that, critical frequency of F2-layer foF2 and the peak height hmF2 hmF2 for the stations Jicamarca (11.9°S), Ascension Is (7.92°S) and Tucuman (26.9°S) are used. The results show a “smoothing” of the Equatorial Anomaly structure during the development of the storms. Noticeable features are the increases in foF2 before the storm sudden commencement (SC) at equatorial latitudes and the southern crest of the Equatorial Anomaly. In some cases nearly simultaneous increases in foF2 are observed in response to the storm, which are attributed to the prompt electric field. Also, positive effects observed at equatorial and low latitudes during the development of the storm seem to be caused by the disturbance dynamo electric field due to the storm-time circulation. Increases in foF2 above the equator and simultaneous decreases in foF2 at the south crest near to the end of a long-duration main phase are attributed to equatorward-directed meridional winds. Decreases in foF2 observed during the recovery phase of storms are believed to be caused by composition changes. The results indicate that the prompt penetration electric field on the EA is important but their effect is of short lived. More significant ionospheric effects are the produced by the disturbance dynamo electric field. The role of storm-time winds is important because they modify the “fountain effect” and transport the composition changes toward low latitudes. [ABSTRACT FROM AUTHOR]

Highlights: [•] The paper presents an analytical model for tape-tethers probability of survival against debris in LEO orbit. [•] The model quite accurately follows full numerical results using NASA and ESA debris flux data. [•] It keeps the complex dependency on tape cross-section dimensions and orbit altitude/inclination. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers a formation control problem for a multiple-UAV (unmanned aerial vehicle) system where each UAV is able to exchange information with other UAVs according to a fixed information graph. In this paper, each UAV tries to minimize its own performance index which is chosen independently based on its local information. Because of the UAVs' different objectives, the formation control problem is formulated and solved as a differential game problem. Realizing the incapability of the classical Nash strategy approach in dealing with the distributed information, we propose a novel open-loop Nash strategy design approach for each UAV to implement in a fully distributed manner through estimating its terminal state. An illustrative example of a five-UAV formation control problem is solved under different scenarios. [Copyright &y& Elsevier]

Abstract: Liquid sloshing in partially filled spacecraft tanks during the powered-flight phase of rocket influences greatly the sensitive elements onboard by means of the sloshing frequencies and total sloshing forces. However, little research on the nonlinear parametric sloshing for this case can be found in the literature. In this paper, the equivalent pendulum model was incorporated into the spacecraft system to represent the liquid propellant sloshing motion. Besides, the dynamic model of liquid sloshing under both lateral and longitudinal excitations was developed by Lagrangian method. The nonlinear effect and the damping effect of liquid sloshing were accommodated in this model. Then, parametric resonance analysis of small amplitude sloshing was studied by the Floquet theory to plot the stability diagrams for different sloshing damping. The research emphasis of this paper was parametric resonance analyses on the nonlinear characteristics of relatively large amplitude sloshing under soft and hard excitations, which were carried out respectively by multiple scales method. The analytical and numerical results were presented in the forms of phase diagrams, frequency-response curves as well as time histories of sloshing motion and sloshing force to illustrate the effects of principal parametric resonance, sub-resonance and non-resonance conditions on the sloshing motion separately. The investigations in this paper provided an effective way to reveal the nonlinear parametric resonance of liquid sloshing in partially filled spacecraft. [Copyright &y& Elsevier]

Abstract: In this paper, we studied the influence of different inflow conditions on the MVG controlled supersonic ramp flow. In front of the MVG, the inflow of three turbulent inflow profiles with different boundary layer thickness is generated. It is found that the generation of ring-like vortical structure is not dominated by the inflow conditions. However, the inflow conditions give significant influences to the ring-like vortex shapes, vorticity origins, momentum deficit zones, streamwise velocity profiles after MVG and vortex organizations. Further, it is seen that the interaction between ring-like vortices and shock waves at the ramp corner is also affected. [Copyright &y& Elsevier]