Layered -space-time architecture for MIMO block spread CDMA systems

In this paper, single-carrier block spread CDMA for multiple-input-multiple-output (MIMO) systems is proposed. With block spreading and despreading, multiple-user intererence free (MUI-free) transmission with reduced processing complexity is achieved. Layered space-time transmission (LST) is employed to enhance the data rak. of the proposed system. The proposed system is studied extensively under different channel conditions and its performance is compared against conventional single-carrier and multicarrier CDMA systems.     

Quantitative assessment of facial sensation in leprosy

Under ideal conditions, continuous arterial spin labeling (ASL) techniques are higher in SNR than pulsed ASL techniques by a factor of e. Presented here is a direct theoretical and experimental comparison of continuous ASL and pulsed ASL, using versions of both that are amenable to multislice imaging and insensitive to variations in transit times (continuous ASL with a delay before imaging, and QUIPSS II (Quantitative Imaging of Perfusion Using a Single Subtraction-second version)). Perfusion image quality for comparable imaging time was nearly identical for both single-slice and multislice imaging. The measured raw signal was approximately 25% higher with continuous ASL, but the SNR per unit time was identical.     

Carbon nanotubes in the liquid phase: addressing the issue of dispersion

The inherent size and hollow geometry with extraordinary electronic and optical properties make carbon nanotubes (CNTs) promising building blocks for molecular or nanoscale devices. Unfortunately, their hydrophobic nature and their existence in the form of agglomerated and parallel bundles make this interesting material inadequately soluble or dispersible in most of the common solvents, which is crucial to their processing. Therefore, various ingenious techniques have been reported to disperse the CNTs in various solvents with different experimental conditions. However, by analyzing the published scientific research articles, it is evident that there is an important issue or misunderstanding between the term "dispersion" and "solubilization". As a result many researchers use the terms interchangeably, particularly when stating the interaction of CNTs with liquids, which causes confusion among the readers, students, and researchers. In this article, this fundamental issue is addressed in order to give basic insight to the researchers who are working with CNTs, as well as to the scientists who deal with nano-related research domains.     

Spectroscopic evidence for atmospheric stabilization of aluminum borohydride in polydimethylsiloxane grease

Raman and infrared vibrational spectroscopy were used to confirm the presence of aluminum borohydride dissolved in a commercial polydimethylsiloxane vacuum grease at room temperature. Spectroscopic evidence for an adduct between the aluminum borohydride and polydimethylsiloxane is also presented. Once dissolved in the polydimethylsiloxane grease, the aluminum borohydride was stabilized with respect to its usual pyrophoric reactivity in wet or dry air.     

Natural protein engineering: a uniquely salt-tolerant, but not halophilic, alpha-type carbonic anhydrase from algae proliferating in low- to hyper-saline environments

Dunaliella salina is a unicellular green alga thriving in environments ranging from fresh water to hyper-saline lakes, such as the Dead Sea. An unusual, internally duplicated, 60 kDa alpha-type carbonic anhydrase (dCA I), located on the surface of this alga, is expected to function over a broad range of salinities. It would therefore differ from other carbonic anhydrases that already lose activity at low salinities and also from halophilic proteins that require high salinities for conformational stability. Enzymatic analyses indeed indicated that dCA I retained activity at salt concentrations ranging from low salt to at least 1.5 M NaCl or KCl for CO(2) hydration, 2.0 M NaCl for esterase activity and 0.5 M for bicarbonate dehydration. Although measurements at higher salinities were constrained by the interference of salt in the respective assayed reactions, activity was noticeable even at 4.0 M NaCl. Comparisons of the internally duplicated dCA I to single-domain derivatives indicated that inter-domain interactions played a decisive role in the stability, activity, salt tolerance and pH responses of dCA I. Hence dCA I is a uniquely salt- tolerant protein, retaining an active conformation over a large range of salinities and, as a Zn metalloenzyme, largely immune to the specific inhibitory effects of anions. Its unique features make dCA I a useful model to understand the physico-chemical basis of halotolerance and protein-salt interactions in general.     

Processing and microstructure of Powder Metallurgy Al-Fe-Ni Alloys

Prealloyed rapidly solidified Al-Fe-Ni alloy powder with dispersoid volume fractions of 0.19, 0.25, and 0.32 FeNiAl₉ was produced by air atomization. The powder was degassed, canned, and consolidated to full density by vacuum hot pressing and extrusion or by direct extrusion. Microstructures in the alloy powder and consolidated material were characterized by means of optical, scanning (SEM), and transmission electron microscopy (TEM) and constituent phases identified by X-ray diffraction. The coarsening kinetics of the FeNiAl₉ dispersoid were moni- tored by differential scanning calorimetry (DSC) and by quantitative metallography. Atomized powders exhibited two scales of microstructures: optically featureless regions and regions with a coarse dispersoid morphology. Within the featureless regions, there are three morphologies, namely, a fine uniform precipitate microstructure, a cellular microstructure, and an eutectic microstructure. The only dispersoid observed in the atomized powders and consolidated material was FeNiAl₉). The two scales of microstructure were retained after consolidation, and after hot extrusion, the typical microstructure consisted of a recovered matrix structure with a grain size of 0.2 to 0.3 μm and equiaxed intermetallics of average diameter 0.1 μm. The microstructure was resistant to coarsening up to approximately 370 °C. Coarsening kinetics in this alloy system were consistent with a grain boundary diffusion model (activation energy 146 kJ/mol) and were not appreciably affected by dispersoid volume fraction.     

MAC units for matched filters in DS-CDMA systems

High data rates in wireless radio environments are becoming common. Current system designs are inadequate to meet the speed requirements that are anticipated in newer services. The computational complexity in the subsystems of wireless radio increases in direct proportion to the data rate. In this correspondence, we propose alternative multiply accumulate (MAC) units for the pulse shaping filters that use a new representation for their coefficients. Consequently, these new structures are fast, efficient and dissipate less power. The filters proposed take into account constraints, such as, intersymbol interference, response characteristics etc. in their design methodology