Simulations of mass attenuation coefficients for shielding materials using the MCNP-X code

In this paper,mass attenuation coefficients of concrete,bricks and cement plaster,as shielding materials,are calculated at 59.5,356,662,1173,1274 and 1333 keV by using the MCNP-X (version 2.4.0) code.The numerical simulation results are compared with previous Monte Carlo studies,experimental results and XCOM data.The effects of barite on mass attenuation coefficients are investigated.The mass attenuation coefficients increase with the barite content.Thus,our results agree well with experimental studies on gamma ray shielding of barite.It is flexible for the MN method to change the barite rates in material by small increments,which is experimentally difficult.Also,modeled geometry can be used for future approaches such as new designs and new structures especially in investigating new barite-containing materials to build nuclear reactors or high-energy radiation therapy facilities.     

Influence of Powder Injection Parameters in High-Pressure Cold Spray

High-pressure cold spray systems are becoming widely accepted for use in the structural repair of surface defects of expensive machinery parts used in industrial and military equipment. The deposition quality of cold spray repairs is typically validated using coupon testing and through destructive analysis of mock-ups or first articles for a defined set of parameters. In order to provide a reliable repair, it is important to not only maintain the same processing parameters, but also to have optimum fixed parameters, such as the particle injection location. This study is intended to provide insight into the sensitivity of the way that the powder is injected upstream of supersonic nozzles in high-pressure cold spray systems and the effects of variations in injection parameters on the nature of the powder particle kinetics. Experimentally validated three-dimensional computational fluid dynamics (3D CFD) models are implemented to study the particle impact conditions for varying powder feeder tube size, powder feeder tube axial misalignment, and radial powder feeder injection location on the particle velocity and the deposition shape of aluminum alloy 6061. Outputs of the models are statistically analyzed to explore the shape of the spray plume distribution and resulting coating buildup.     

Decreased Serum Levels of Sphingomyelins and Ceramides in Sickle Cell Disease Patients

Limited data are available on the serum levels of different sphingomyelin (CerPCho) and ceramide (CER) species in sickle‐cell disease (SCD). This study was aimed at identifying the levels of C16–C24 CerPCho and C16–C24 CER in serum obtained from SCD patients and controls. Circulating levels of neutral sphingomyelinase (N‐SMase) activity, ceramide‐1‐phosphate (C1P), and sphingosine‐1‐phosphate (S1P) were also determined. Blood was collected from 35 hemoglobin (Hb)A volunteers and 45 homozygous HbSS patients. Serum levels of C16–C24 CerPCho and C16–C24 CER were determined by an optimized multiple reaction monitoring (MRM) method using ultrafast liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Serum activity of N‐SMase was assayed by standard kit methods, and C1P and S1P levels were determined by enzyme‐linked immunosorbent assay. A significant decrease was observed in the serum levels of C18–C24 CerPCho in patients with SCD compared to controls. No significant difference was found in C16 CerPCho levels between the two groups. Very‐long‐chain C22–C24 CER were significantly decreased in SCD, while long‐chain C16–C20 CER levels showed no significant difference between SCD patients and controls. Significant positive correlation was found between the serum total cholesterol levels and C18–C24 CerPCho and C22–C24 CER in SCD patients. Patients with SCD had significantly elevated serum activity of N‐SMase as well as increased circulating levels of C1P and S1P compared to controls. The decrease in serum levels of C18–C24 CerPCho in patients with SCD was accompanied by decreased levels of C22–C24 CER. Future studies are needed to understand the role of decreased CerPCho and CER in the pathophysiology of SCD.     

Formation of Low-Density and Free-Flowing Hollow Microparticles from Butter and Fractionated Palm Oil Mixture

The use of solid fats is challenging due to difficulty in incorporating into foods, handling during industrial food production, and relatively high-calorie contributions. The objective of this study was to form free-flowing and low-density hollow microparticles from nonhydrogenated fats, namely, butter and fractionated palm oil, using a novel method based on atomization of a carbon dioxide (CO₂)-expanded lipid mixture. The melting point of the fractionated palm oil decreased from 66.2 to 47.3°C above 120 bar in the presence of pressurized CO₂. The density of the particles decreased fivefolds compared to that of the original oils. The average particle size D [4,3] decreased from 67.0 to 27.1 μm when the concentration of fractionated palm oil was increased from 50% to 100%. The hollow structure was more pronounced for the particles obtained from higher melting oils/oil blends, as well as with more spherical uniformity. Ten percent (d_10%) and 50% (d_50%) of the palm oil particles were smaller than 4.5 and 23.0 μm, respectively, whereas they were 14.5 and 58.3 μm when mixed with butter at 50% butter concentration, respectively. Polymorphic form of α was more pronounced in the solid lipid particles, indicating that they had a less-ordered crystalline structure than the original oil. This new method forms low-density and free-flowing lipid powders that make the handling and storage of solid lipids feasible and convenient, and may provide reduced fat usage and calorie intake, and more rapid oil melting in mouth.     

MoOx/Ag/MoOx multilayers as hole transport transparent conductive electrodes for n-type crystalline silicon solar cells

Substitution of highly doped layers with conventional transparent conductive electrodes as carrier collecting and selective contacts in conventional crystalline silicon (c-Si) solar cell configurations is crucial in increasing affordability of solar cells by lowering material costs. In this study, oxide/metal/oxide (OMO) multilayers featuring molybdenum oxide (MoO_x) and silver (Ag) thin films are developed by thermal evaporation technique, as dopant-free hole transport transparent conductive electrodes (HTTCEs) for n-type c-Si solar cells. Semidopant-free asymmetric heterocontact (semi-DASH) solar cells on n-type c-Si utilizing OMO multilayers are fabricated. The effect of outer MoO_x layer thickness and Ag deposition rate on the photovoltaic characteristics of the fabricated semi-DASH solar cells are investigated. A comparison of front side pyramid textured and flat surface solar cells is performed to optimize the optical and electrical properties. Highest efficiency of 9.3% ± 0.2% is achieved in a pyramid textured semi-DASH c-Si solar cell with 15/10/30 nm of HTTCE structure.     

A graph structure approach to improving message dissemination in vehicular networks

Efficient message dissemination in vehicular ad-hoc networks (VANETs) is crucial for supporting communication among vehicles and also between users and the Internet, with minimal delay and overhead but maximum reachability. To improve the message dissemination in these networks, we show the need to study the graph-theoretic properties of VANETs, since they neither follow the small-world nor the scale-free network characteristics often found in large self-organized networks. We consider three fundamental properties: connectivity, node degree, and clustering coefficient. For each property, we develop and validate analytical models for both the urban and highway scenarios, building an extensive graph structure perspective on VANETs. With this, we see how connectivity changes with network density, that VANETs exhibit truncated Gaussian node degree distributions, and that network clustering coefficients do not depend on the network’s size or density. We then show how these results can be used to generate individual behavior favorable to the whole network using local information. The usefulness of this new approach is demonstrated by proposing new mechanisms to enhance the urban vehicular broadcasting protocol UV-CAST. Our results show that these new mechanisms lead to excellent performance while reducing the overhead in the UV-CAST protocol.     

Hand-Off Performance of the Integrated Cellular and Ad Hoc Relaying (iCAR) System

In this paper, we study the hand-off performance of a wireless system with heterogeneous technologies called iCAR (Integrated Cellular and Ad hoc Relaying). In iCAR, hand-offs can occur not only from a Base Transceiver Station (BTS) to another BTS, but also from a BTS to a so-called Ad hoc Relaying Station (ARS) in the form of relaying, as well as from an ARS back to a BTS. The latter two types of hand-offs effectively increase the hand-off buffer time and thus reduce the call dropping probability. We develop an analytical model for the hand-off performance in iCAR. In addition, we verify the analytical model via simulations and quantify the hand-off performance benefits of the iCAR system over conventional cellular systems. It is anticipated that the analytical and simulation models reported in this paper will serve as a guideline to other researches on the inter-system hand-off involving heterogenous wireless technologies.