BCC vs. HCP—The Effect of Crystal Symmetry on the High Temperature Mobility of Solid 4He

We report results of torsional oscillator (TO) experiments on solid ⁴He at temperatures above 1?K. We have previously found that single crystals, once disordered, show some mobility (decoupled mass) even at these rather high temperatures. The decoupled mass fraction with single crystals is typically 20–30%. In the present work we performed similar measurements on polycrystalline solid samples. The decoupled mass with polycrystals is much smaller, ～1%, similar to what is observed by other groups. In particular, we compared the properties of samples grown with the TO’s rotation axis at different orientations with respect to gravity. We found that the decoupled mass fraction of bcc samples is independent of the angle between the rotation axis and gravity. In contrast, hcp samples showed a significant difference in the fraction of decoupled mass as the angle between the rotation axis and gravity was varied between zero and 85 degrees. Dislocation dynamics in the solid offers one possible explanation of this anisotropy.     

Airborne video thermal radiometry as a tool for monitoring microscale structures of the urban heat island

An advance thermal video radiometer (TVR) was mounted onboard a helicopter and used to collect data over Tel-Aviv, Israel, from an altitude of 7000 feet. The sensor, sensitive to the 3-12 mu m spectral region, consisted of an onboard calibration device and a 1.8 mRad instantaneous field of view (IFOV), which enabled direct assessment of surface radiometric temperature patterns in very high spatial and thermal resolutions. The TVR capability was examined by studying the microscale structures of the urban heat island (UHI) of Tel-Aviv, Israel, during a stable calm night on 28 February 1995. The TVR data were found to be of high quality in terms of signal to noise ratio, reproducibility, stability, thermal sensitivity and spatial resolution capabilities. The radiometric data were analysed against air temperature acquired during the flight time by four mobile traverses that crossed the city from north to south. A significant heat island was identified over the inner city areas, which was found to be 5 C warmer than the rural areas located 4 km to the south-east. Throughout the city, asphalt was found to be the major heat source whereas vegetation was found to be the most cooling element. A linear regression analysis between the air and radiometric temperatures showed that in general, good agreement exists between the two temperatures. Along the western routes (A and B) the correlation was relatively higher than that along the eastern routes (C and D) and was significantly different in the linear regression slope a . We assume that differences in atmospheric conditions, especially in the water vapour variation throughout the city, caused these inconsistencies. We concluded that the examined TVR is a very promising, low-cost remote sensing sensor, which can rapidly and quantitatively monitor the UHI in very high spatial and thermal resolutions from a high altitude. Based on these results we strongly recommend that the TVR be further examined in other remote sensing applications.     

Location-Based Services

Today, location information is in the hands of the masses. The success of location in pervasive computing has exposed new challenges and opportunities for researchers including making location sensing more robust, accurate, deployable, secure, and developer-friendly. This special issue showcases papers that describe recent research that addresses these challenges.     

Microencapsulation of Lactobacillus paracasei by spray freeze drying

This study evaluates the implementation of a new process: spray freeze drying (SFD), to produce dry micro-capsules of Lactobacillus paracasei with high viability. The study concentrated on determining the survival of the cells, encapsulated in a matrix of maltodextrin and trehalose. SFD was compared with the conventional bulk freeze drying (BFD). Overall it was shown that SFD is a successful method to generate dry micro-capsules of probiotic cells with high viability (>60%). The spraying stage did not affect the viability of the bacteria. In the freezing stage, high osmotic pressures originated by elevated trehalose concentrations, helped preserving the cells viability. It was also found that the lower the maltodextrin molecular weight, the larger the beads volume and solids concentration, the higher is the bacteria survival during the freezing and drying stages. In the drying stage, trehalose concentration was also the critical factor that increased final probiotic viability.     

Optimization of Light Weight Armor Using Experimental Data

It is shown how the experimental data on ballistic limit velocity (BLV) of two-component ceramic target may be directly used for the analysis and optimization of the armor. The suggested approach is applied for two sets of data available in the literature.     

Estimation of perforation thickness for concrete shield against high-speed impact

We extended the existing engineering two-stage models for high-speed penetration of projectiles into concrete shields and suggested a semi-empirical model that is applicable for truncated bodies of revolution penetrating into shields having a finite thickness. In this model at the first stage of penetration (cratering), the resistance force is a linear function of the distance between the nose of the impactor and the front surface of the shield, while at the second stage (tunneling), the resistance force is proportional to a squared instantaneous velocity of the impactor and the linear term vanishes. The proposed model allows determining the minimal thickness of the plate which prevents from the perforation. The obtained theoretical predictions are compared with available experimental data.     

Effect of layering on ballistic properties of metallic shields against sharp-nosed rigid projectiles

On the basis of general assumptions that are pertinent to penetration modeling, we investigated the effect of layering of metallic shields on their protective characteristics against sharp-nosed rigid impactors and established/explained a number of general features of the penetration phenomenon. The main results can be formulated as follows: (i) any layering has an adverse effect on protective properties of the shield against perforation, (ii) increasing the number of layers with the same thicknesses impairs protective properties of the shield. These assertions are validated by analyzing results of experiments and numerical calculations available in the literature that allow comparing protective properties of monolithic and layered shields.     

Elaboration of Ultra‐High Molecular Weight Polyethylene/Carbon Nanotubes Electrospun Composite Fibers

Micron‐sized fibers of UHMWPE reinforced with CNT were fabricated by the electrospinning process. Conditions for a metastable mutual solution of UHMWPE and CNTs were found at elevated temperature. These solutions were used for electrospining using a device having controlled temperature and gaseous environment around the electrospun liquid jet. The fabricated micron‐sized fibers exhibited the reinforcing CNTs as self‐organized nano‐ropes embedded within them. A post‐spinning drawing process enhanced the mechanical properties of the composite fibers to the level of 6.6 GPa strength and elongation at break of 6%. The CNT nano‐ropes form spontaneously in the liquid jet during electrospinning, and provide the reinforcement framework which is amenable for post‐drawing of the fibers for subsequent utilization as composite nanofibers. The experimental results exhibit the highest strength value reported to date for electrospun fibers.

     

Exciton-plasmon interactions in quantum dot-gold nanoparticle structures

We present a self-assembly method to construct CdSe/ZnS quantum dot-gold nanoparticle complexes. This method allows us to form complexes with relatively good control of the composition and structure that can be used for detailed study of the exciton-plasmon interactions. We determine the contribution of the polarization-dependent near-field enhancement, which may enhance the absorption by nearly two orders of magnitude and that of the exciton coupling to plasmon modes, which modifies the exciton decay rate.     

Structural characterization of amylose-long chain fatty acid complexes produced via the acidification method

Amylose molecular inclusion complexes, or V-amylose, have been studied as a possible nano-sized delivery system for unsaturated fatty acids. This study aimed to study three different structural levels of V-amylose produced via an acidification method. Molecular attributes were studied using XRD, DSC and ¹³C CP/MAS NMR, nanostructures using SAXS and AFM, and the microscopic level by SEM and AFM. ¹³C labeled fatty acids revealed head groups were entrapped in both COO- and COOH forms. SAXS data, showed that conjugated linoleic acid yield particles with the highest values for parameters like average crystalline lamellar thickness (φ = 0.46) and characteristic particle dimension (R_g = 1011). AFM revealed surface roughness increases from 7.72 ± 4.34 nm to 11.54 ± 6.05 nm during the formation of V-amylose. The insights described contribute to the understanding of V-amylose structure and help establish a model for V-amylose structure which may prospectively be used in the fabrication of a novel delivery system.