Revisiting Slotted ALOHA: Density Adaptation in FANETs

Unmanned aerial vehicles have been widely used in many areas of life. They communicate with each other or infrastructure to provide ubiquitous coverage or assist cellular and sensor networks. They construct flying ad hoc networks. One of the most significant problems in such networks is communication among them over a shared medium. Using random channel access techniques is a useful solution. Another important problem is that the variations in the density of these networks impact the quality of service and introduce many challenges. This paper presents a novel density-aware technique for flying ad hoc networks. We propose Density-aware Slotted ALOHA Protocol that utilizes slotted ALOHA with a dynamic random access probability determined using network density in a distributed fashion. Compared to the literature, this paper concentrates on proposing a three-dimensional, easily traceable model and stabilize the channel utilization performance of slotted ALOHA with an optimized channel access probability to its maximum theoretical level, 1/e, where e is the Euler’s number. Monte-Carlo simulation results validate the proposed approach leveraging aggregate interference density estimator under the simple path-loss model. We compare our protocol with two existing protocols, which are Slotted ALOHA and Stabilized Slotted ALOHA. Comparison results show that the proposed protocol has 36.78% channel utilization performance; on the other hand, the other protocols have 24.74% and 30.32% channel utilization performances, respectively. Considering the stable results and accuracy, this model is practicable in highly dynamic networks even if the network is sparse or dense under higher mobility and reasonable non-uniform deployments.

     

Thread vulnerability in parallel applications

Continuously reducing transistor sizes and aggressive low power operating modes employed by modern architectures tend to increase transient error rates. Concurrently, multicore machines are dominating the architectural spectrum today in various application domains. These two trends require a fresh look at resiliency of multithreaded applications against transient errors from a software perspective. In this paper, we propose and evaluate a new metric called the Thread Vulnerability Factor (TVF$TVF$). A distinguishing characteristic of TVF$TVF$ is that its calculation for a given thread (which is typically one of the threads of a multithreaded application) does not depend on its code alone, but also on the codes of the threads that share resources and data with that thread. As a result, we decompose TVF$TVF$ of a thread into two complementary parts: local and remote. While the former captures the TVF$TVF$ induced by the code of the target thread, the latter represents the vulnerability impact of the threads that interact with the target thread. We quantify the local and remote TVF$TVF$ values for three architectural components (register file, ALUs, and caches) using a set of ten multithreaded applications from the Parsec and Splash-2 benchmark suites. Our experimental evaluation shows that TVF$TVF$ values tend to increase as the number of cores increases, which means the system becomes more vulnerable as the core count rises. We further discuss how TVF$TVF$ metric can be employed to explore performance–reliability tradeoffs in multicores. Reliability-based analysis of compiler optimizations and redundancy-based fault tolerance are also mentioned as potential usages of our TVF$TVF$ metric.     

UV-visible technique for studying powder coatings and their dissolution

UV-Visible (UVV) technique used to monitor powder coating and its dissolution processes from hard latex particles. Three sets of latex coatings were prepared from poly(methyl methacrylate) (PMMA) particles. The first set of coatings was annealed at elevated temperatures in various time intervals during which reflected photon intensity, I_rf, was measured. The second set of coatings was annealed at various temperatures in 10 min time intervals during which transmitted intensity, I_tr, was measured. I_rf first decreased and then increased as the annealing temperature was increased. Decrease in I_rf was explained with the void closure mechanism due to viscous flow. Increase in I_tr and I_rf against time and temperature were attributed to an increase in crossing density at the junction surface. The activation energy of viscous flow, ΔH, was measured and found to be around 8 kcal/mol and the back and forth activation energies (ΔE_rf and ΔE_tr) were measured and found to be around 49 and 53 kcal/mol for a reptating polymer chain across the junction surface. Diffusion of solvent molecules (chloroform) into the annealed latex coatings was followed by desorption of PMMA chains for the third set of films. Desorption of pyrene, P, labeled PMMA chains was monitored in real-time by the absorbance change of pyrene in the polymer-solvent mixture. A diffusion model with a moving boundary was employed to quantify real-time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10⁻¹¹ cm² s⁻¹ in the 100 and 275°C temperature range. Presented at the 2000 Spring Meeting of the PMSE Div. of the American Chemical Society, March 26–30, 2000, San Francisco, CA. Dept. of Physics, Maslak 80626 Istanbul, Turkey. Dept. of Physics, 22030 Edirne, Turkey.     

Bioactive-Tissue-Derived Nanocomposite Hydrogel for Permanent Arterial Embolization and Enhanced Vascular Healing

Transcatheter embolization is a minimally invasive procedure that uses embolic agents to intentionally block diseased or injured blood vessels for therapeutic purposes. Embolic agents in clinical practice are limited by recanalization, risk of non-target embolization, failure in coagulopathic patients, high cost, and toxicity. Here, a decellularized cardiac extracellular matrix (ECM)-based nanocomposite hydrogel is developed to provide superior mechanical stability, catheter injectability, retrievability, antibacterial properties, and biological activity to prevent recanalization. The embolic efficacy of the shear-thinning ECM-based hydrogel is shown in a porcine survival model of embolization in the iliac artery and the renal artery. The ECM-based hydrogel promotes arterial vessel wall remodeling and a fibroinflammatory response while undergoing significant biodegradation such that only 25% of the embolic material remains at 14 days. With its unprecedented proregenerative, antibacterial properties coupled with favorable mechanical properties, and its superior performance in anticoagulated blood, the ECM-based hydrogel has the potential to be a next-generation biofunctional embolic agent that can successfully treat a wide range of vascular diseases.     

Biogenic Amine Content of Beers Consumed in Turkey and Influence of Storage Conditions on Biogenic Amine Formation

The biogenic amine content of beers available in Turkey, both domestic production and imported products, was investigated. A total of 17 domestic and 13 imported beers were evaluated in terms of 8 different biogenic amines (histamine, tyramine, spermine, spermidine, 2‐phenylethylamine, putrescine, tryptamine and cadaverine). HPLC methodology with pre‐column derivatization and photodiode array detection after derivatization with dansyl chloride was used for quantification. In addition, the evolution of important amines such as histamine, tyramine, putrescine and cadaverine were investigated during different storage conditions by response surface methodology. The results indicated that both storage temperature and storage time were important factors affecting biogenic amine content. Histamine and putrescine increased during storage, but then decreased after reaching a maximum level after six weeks. With the biogenic amines tyramine and cadaverine, the amounts increased during the entire storage period. At higher storage temperatures, the formation of biogenic amines increased.     

Ibuprofen‐imprinted ultrathin poly[N‐(2‐hydroxypropyl) methacrylamide] films

Surface molecularly imprinted (MIP) poly[N‐(2‐hydroxypropyl) methacrylamide] [poly(HPMA)] films were prepared via interface‐mediated reversible addition‐fragmentation chain transfer (RAFT) polymerization from 4‐cyano‐4‐(propylsulfanylthiocarbonyl) sulfanyl pentanoic acid immobilized silicon substrate using N‐(2‐hydroxypropyl) methacrylamide as the functional monomer, N,N′‐methylene(bis)acrylamide as the crosslinking agent, and ibuprofen as the template molecule. The highly crosslinked MIP layer (～12 nm) was homogeneously grafted onto the silicon surface, which favors fast mass transfer and rapid binding kinetics. Binding capacities and adsorption parameters of the MIP poly(HPMA) films were calculated from the root‐mean‐square roughness data obtained by atomic force microscopy measurements using the Luzinov and Langmuir equations adopted for this study. The target binding assays demonstrate the desirable binding capacity and imprinting efficiency of the MIP poly(HPMA) films. Meanwhile, the computational optimization and energy calculations showed the formation of the self‐assembly of monomer and template molecule via noncovalent interactions that leads to a 1:4 molecular complex between ibuprofen and N‐(2‐hydroxypropyl) methacrylamide. This study provides a versatile approach to the quantitative determination of low‐molecular‐weight biomolecules on surface‐imprinted polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45707.     

Minimizing the earliness/tardiness costs on parallel machine with learning effects and deteriorating jobs: a mixed nonlinear integer programming approach

In this study, we introduce a mixed nonlinear integer programming formulation for parallel machine earliness/tardiness (ET) scheduling with simultaneous effects of learning and linear deterioration, sequence-dependent setups, and a common due-date for all jobs. By the effects of learning and linear deterioration, we propose that the processing time of a job is defined by increasing function of its execution start time and position in the sequence. The developed model allows sequence-dependent setups and sequence-dependent early/tardy penalties. The model can easily provide the optimal solution to problems involving about eleven jobs and two machines.     

Wall-to-particle heat transfer in steam reformer tubes: CFD comparison of catalyst particles

Computational fluid dynamics (CFD) was used to simulate non-reacting heat transfer in a steam reforming packed reactor tube of tube-to-particle diameter ratio (N) equal to 4, with cylindrical multi-hole catalyst particles. These simulations extend those of our previous study [Nijemeisland, M., Dixon, A.G., Stitt, E.H., 2004. Catalyst design by CFD for heat transfer and reaction in steam reforming. Chemical Engineering Science 59, 5185-5191] to provide accurate tube wall temperatures, runs at constant pressure drop in addition to those at constant mass flow rate and simulations of particles with different sizes of holes. At constant pressure drop, particles with higher void fractions allowed higher mass flow rates, resulting in tube wall temperatures and radial temperature profiles in order: solid cylinders>one-hole particles>multi-hole particles. Little difference was seen between three-hole and four-hole particles. The particles with multiple holes gave a substantial reduction in tube wall temperature, with only a small decrease in core tube heat transfer. The effect of hole size was small, for the cases investigated in this study.     

Application of Solid‐Phase Micro‐Extraction (SPME) for Determining Residues of Chlorpyrifos and Chlorpyrifos‐Methyl in Wine with Gas Chromatography (GC)

The incorrect use of insecticides in many countries' vineyards may result in some toxicological risks for the consumers by their presence on the grapes. In this research, a rapid gas chromatographic method was used for the determination of the residue levels of two organophosphorus pesticides (chlorpyrifos and chlorpyrifos‐methyl) in wine. Pesticides are described and compared with each other. Ten red wines from two different regions of Turkey were analyzed for their chlorpyrifos and chlorpyrifos‐methyl content. The samples were diluted with water and extracted by solid‐phase micro extraction. Nitrogen‐Phosphorus Detection (NDP) and Electron‐Capture Detection (ECD) were used to identify and quantify the pesticides, the findings being confirmed using Mass Spectrometric Detection. Individual detection limits were in the range of (chlorpyrifos) 0.02‐(chlor‐pyrifos‐methyl) 0.1 ng. Limits of quantification varied from (chlorpyrifos) 0.01‐(chlorpyrifos‐methyl) 0.05 mg kg^?1. The maximum residues limits of the two pesticides in the Turkish wines examined were much lower than the Turkish and European Union limits.     

Real time monitoring of latex film dissolution by UVV technique

UV–visible (UVV) technique is used for monitoring of polymer film dissolution. These films are formed from pyrene (P)‐labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by poly isobutylene (PIB, Annealing of films was performed above T_g at various temperatures for 30‐min time intervals. Diffusion of solvent molecules (chloroform) into the annealed latex film was followed by desorption of PMMA chains. Desorption of P‐labeled PMMA chains was monitored in real time by the absorbance change of P in the polymer–solvent mixture. A diffusion model with a moving boundary was used to quantify real time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10⁻¹¹ cm² s⁻¹ in the 100 and 275°C temperature range. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1075–1082, 2000