Polymerization of isoprene in n-heptane with triethylaluminum–titanium tetrachloride catalyst. I. Effect of Al/Ti ratio on stereoregularity,conversion, molecular weight,and molecular weight distribution

The influence of the Al/Ti ratio of the heterogeneous Ziegler–Natta catalyst system AlEt₃–TiCl₄ on the isoprene polymerization in n-heptane at 30°C in a bench scale reactor was investigated. Each batch run consisted of 50 mL isoprene, 200 mL n-heptane with 0.45 and 0.5g catalyst. Conversion of isoprene and molecular weights of polyisoprene increased with increasing Al/Ti ratio, reaching their maxima values at 1.0 and 1.2, respectively. Conversion and molecular weights decreased remarkably at a higher ratio of Al/Ti. As this ratio decreases from the value of 1.2 to 0.4, the cis1,4 content in polyisoprene decreased from 97 to 25%. When the ratio of Al/Ti increased from 1.2 to 2.2 the cis-1,4 structure of polyisoprene decreased from 97 to 85%.     

Deep Opacity Maps

We present a new method for rapidly computing shadows from semi‐transparent objects like hair. Our deep opacity maps method extends the concept of opacity shadow maps by using a depth map to obtain a per pixel distribution of opacity layers. This approach eliminates the layering artifacts of opacity shadow maps and requires far fewer layers to achieve high quality shadow computation. Furthermore, it is faster than the density clustering technique, and produces less noise with comparable shadow quality. We provide qualitative comparisons to these previous methods and give performance results. Our algorithm is easy to implement, faster, and more memory efficient, enabling us to generate high quality hair shadows in real‐time using graphics hardware on a standard PC.     

Prosthetic Hand Finger Control Using Fuzzy Sliding Modes

In order to improve the life quality of amputees, providing approximate manipulation ability of a human hand to that of a prosthetic hand is considered by many researchers. In this study, a biomechanical model of the index finger of the human hand is developed based on the human anatomy. Since the activation of finger bones are carried out by tendons, a tendon configuration of the index finger is introduced and used in the model to imitate the human hand characteristics and functionality. Then, fuzzy sliding mode control where the slope of the sliding surface is tuned by a fuzzy logic unit is proposed and applied to have the finger model to follow a certain trajectory. The trajectory of the finger model, which mimics the motion characteristics of the human hand, is pre-determined from the camera images of a real hand during closing and opening motion. Also, in order to check the robust behaviour of the controller, an unexpected joint friction is induced on the prosthetic finger on its way. Finally, the resultant prosthetic finger motion and the tendon forces produced are given and results are discussed.     

Limited Scale-Free Overlay Topologies for Unstructured Peer-to-Peer Networks

In unstructured peer-to-peer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of a search on such unstructured P2P networks, as well as other networks. A key limitation of scale-free (power-law) topologies is the high load (i.e., high degree) on a very few number of hub nodes. In a typical unstructured P2P network, peers are not willing to maintain high degrees/loads as they may not want to store a large number of entries for construction of the overlay topology. Therefore, to achieve fairness and practicality among all peers, hard cutoffs on the number of entries are imposed by the individual peers, which limits scale-freeness of the overall topology, hence limited scale-free networks. Thus, it is expected that the efficiency of the flooding search reduces as the size of the hard cutoff does. We investigate the construction of scale-free topologies with hard cutoffs (i.e., there are not any major hubs) and the effect of these hard cutoffs on the search efficiency. Interestingly, we observe that the efficiency of normalized flooding and random walk search algorithms increases as the hard cutoff decreases.     

Visualization of fibrous and thread-like data

Thread-like structures are becoming more common in modern volumetric data sets as our ability to image vascular and neural tissue at higher resolutions improves. The thread-like structures of neurons and micro-vessels pose a unique problem in visualization since they tend to be densely packed in small volumes of tissue. This makes it difficult for an observer to interpret useful patterns from the data or trace individual fibers. In this paper we describe several methods for dealing with large amounts of thread-like data, such as data sets collected using Knife-Edge Scanning Microscopy (KESM) and Serial Block-Face Scanning Electron Microscopy (SBF-SEM). These methods allow us to collect volumetric data from embedded samples of whole-brain tissue. The neuronal and microvascular data that we acquire consists of thin, branching structures extending over very large regions. Traditional visualization schemes are not sufficient to make sense of the large, dense, complex structures encountered. In this paper, we address three methods to allow a user to explore a fiber network effectively. We describe interactive techniques for rendering large sets of neurons using self-orienting surfaces implemented on the GPU. We also present techniques for rendering fiber networks in a way that provides useful information about flow and orientation. Third, a global illumination framework is used to create high-quality visualizations that emphasize the underlying fiber structure. Implementation details, performance, and advantages and disadvantages of each approach are discussed.     

Au/Porous silicon‐based sodium borohydride fuel cells

The Au/Porous silicon structure (Au/PS) was developed as hydrogen fuel cell. The use of a porous silicon filled with hydrochloric acid as a proton‐conducting membrane and thin gold film as a catalyst in Au/PS/Si fuel cell is demonstrated. The devices were fabricated by first creating 10–20 µm thick porous silicon layer by anodization etching in a standard silicon wafer and then depositing the gold catalyst film onto the porous silicon. Using sodium borohydride (NaBH₄) solution as the fuel, generation of the open‐circuit voltage of 0.55 V and the fuel cell peak power density of 13 mW cm⁻² at room temperature was achieved. Moreover production of hydrogen by evolution (out‐diffusion) of hydrogen from solid sodium borohydride during thermal annealing at 30–120°C was investigated. Data on the effective diffusion coefficient of the hydrogen in NaBH₄ were determined from intensity changes of infrared vibration peaks of B–H bond (2280 and 3280 cm⁻¹), as a result of thermal annealing of NaBH₄ samples. The relatively high values of the diffusion coefficient of hydrogen, increasing from 1×10⁻⁶ cm² s⁻¹ to 2×10⁻⁴ cm² s⁻¹ suggest that a thermo‐stimulated evolution process can be used for producing hydrogen from NaBH₄. Copyright © 2010 John Wiley & Sons, Ltd.     

Copper activated LiF nanorods as TLD material for high exposures of gamma-rays

Lithium fluoride (LiF) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanorods of this material activated with Cu, Mg and P as single dopants are synthesized in our laboratory and exposed to gamma-rays for their thermoluminescence (TL) properties. The induced TL glow curves of the Cu, Mg and P doped samples are similar with a single peak at 410 K. Copper doped sample is found to be the most sensitive sample with TL intensity around 65, 7 and 8 times of those of LiF:Mg, LiF:P and LiF:Mg,Cu,P, respectively, indicating that Cu is the luminescence center in the host of LiF nanorods, while Mg and P act as TL quencher particularly when used as codopants. These observations on the nanostructured form of LiF doped with these activators are entirely different from those of the widely studied LiF:Mg,Cu,P and LiF:Mg,Ti single crystals. The nanorods of LiF:Cu might be used for heavy doses measurement as they are sensitive to gamma-rays and have a linear TL response curve in a long span of exposures.     

Using augmented reality technology in storytelling activities: examining elementary students’ narrative skill and creativity

The aim of the study was to examine the effects of augmented reality technology on stories in terms of narrative skill, story length and creativity and also to examine correlations between these variables. Posttest-only design with a nonequivalent group model was used. In this study, the sample consisted of 100 fifth-grade elementary students, comprising 46 boys and 54 girls. Purposive and convenience sampling methods were applied. For purposive sampling, the group’s ages, education levels, and experiences in storytelling activities were gathered, and for convenience sampling, easy access to schools was considered. As data collection tools, a suitable narrative scale was used which was found in the literature and creative story form was developed by the researcher. According to the findings, mean scores for all variables for the experimental group were higher than those for the control group. Also, a statistically significant mean difference was found between the experimental and control groups with regard to narrative skill, length of stories, and creativity in stories. In fact, a positive correlation was found between all variables. It is important to recognize when a technology is found to contribute positively to narrative skill and creativity in telling stories, and to ensure this technology is used. Determining correlation between these variables may provide a contribution to studies about evaluating the effect of the new technologies.     

Effects of B2O3 addition on structural and dielectric properties of PVDF

α‐Crystalline form of PVDF doped with Boron oxide (B₂O₃₎ composite films were produced between 0.2 and 1% weight ratio via the casting procedure. This low‐level doping rate did not change the crystalline structure of PVDF; however, they increased the lower and upper glass transition temperatures, which are associated with the amorphous ratio of polymer. This increment was found to be the highest for the sample 0.8% B₂O₃‐doped PVDF as 25 and 9.7%, respectively. Because of the low specific volume occurred in the 0.8% doped sample, B₂O₃ molecules are closer to the side groups of PVDF and, therefore, the coordination bonds also occurred according to the interaction between them and as a result of this interaction a geometric deformation occurred on the morphology of B₂O₃. In consequence of this deformation, morphology of B₂O₃ gained net dipole moment and provided a contribution to the dipole moment density of the structure. Hence, higher dielectric constant values obtained than that of pure PVDF. At 1 kHz and 300 K, the real dielectric constant increased by 236% compared to that of pure PVDF. It was shown experimentally by the 0.8% doping level of B₂O₃ that decreasing porous and gap structure resulted a high dielectric constant. POLYM. ENG. SCI., 54:2536–2543, 2014. © 2013 Society of Plastics Engineers