Thermoelectric Properties of (Pb,Sn,Ge)Te-Based Alloys

The search for alternative energy sources is presently at the forefront of␣applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This␣paper is␣concerned with the development of highly efficient p-type [(PbTe)(SnTe)(Bi₂Te₃)] _x (GeTe)_1−x alloys for thermoelectric applications using spark plasma sintering (SPS). Varying the carrier concentration of GeTe was achieved by alloying of PbTe, SnTe, and/or Bi₂Te₃. The rhombohedral to cubic phase transition temperature, T _c, was found to be sensitive to the degree of alloying. Highest power factor values (P ≤ 33 μW/cm K²) were obtained for (GeTe)_0.95(Bi₂Te₃)_0.05 composition.     

Graphene: Materials to devices (invited)

Despite recent progress in understanding geometric structure, electronic structure, and transport properties in a graphene device (GD), role of point defects, edges, traps in a GD or a gate insulator has been poorly defined. We have studied electronic and geometric structures of these defects using scanning probe microscopy and try to link those with the transport properties of the GD. We perform scanning gate microscopy study to understand the local carrier scattering. It was found that geometric corrugations, defects and edges directly influence the local transport current. This observation is linked directly with a proposed scattering model based on macroscopic transport measurements. We suggest that dangling bonds in insulator-material SiO₂ mainly used in GDs produce charge puddles and they work as scattering centers.     

More on Security of Public-Key Cryptosystems Based on Chebyshev Polynomials

Recently, a public-key cryptosystem based on Chebyshev polynomials has been proposed, but it has been later analyzed and shown insecure. This paper addresses some unanswered questions about the cryptosystem. We deal with the issue of computational precision. This is important for two reasons. Firstly, the cryptosystem is defined on real numbers, but any practical data communication channel can only transmit a limited number of digits. Any real number can only be specified to some precision level, and we study the effect of that. Secondly, we show that the precision issue is related to its security. In particular, the algorithm previously proposed to break the cryptosystem may not work in some situations. Moreover, we introduce another method to break the cryptosystem with general precision settings. We extend the method to show that a certain class of cryptosystems is insecure. Our method is based on the known techniques on the shortest vector problem in lattice and linear congruences.     

Multiple-valued decoder using MOS-HBT-NDR circuit

The design of a four-valued decoder based on the negative-differential- resistance (NDR) circuit is demonstrated. The presented NDR circuit is composed of a Si-based metal-oxide-semiconductor field-effect- transistor (MOS) and a SiGe-based heterojunction bipolar transistor (HBT). The fabrication of the four-valued decoder using this MOS- HBT-NDR circuit is based on the standard 0.35 mum SiGe-based BiCMOS process.     

Optimal low-complexity detection for space division multiple access wireless systems

A symbol detector for wireless systems using space division multiple access (SDMA) and orthogonal frequency division multiplexing (OFDM) is derived. The detector uses a sphere decoder (SD) and has much less computational complexity than the naive maximum likelihood (ML) detector. We also show how to detect non-constant modulus signals with constrained least squares (CLS) receiver, which is designed for constant modulus (unitary) signals. The new detector outperforms existing suboptimal detectors for both uncoded and coded systems.     

Phenanthrene and pyrene uptake by arbuscular mycorrhizal maize and their dissipation in soil

Polycyclic aromatic hydrocarbons (PAHs) commonly found in soils can be degraded in rhizosphere, but may also be taken up by plants. The effects of arbuscular mycorrhizal (AM) fungi on uptake of phenanthrene (PHE) and pyrene (PYR) in maize and on their dissipation in soil were investigated using the three-compartmentalized rhizoboxes. Inoculation of Glomus mosseae significantly (p<0.01) increased PHE and PYR concentrations in maize roots and significantly (p<0.05) enhanced PYR translocation from roots to stems in the soil treatments of the PHE+PYR spiked-soils added into the central compartment of the rhizoboxes. There was a significant (p<0.05) dissipation gradient of PHE and PYR observed away from the maize roots, with the highest dissipation rates recorded in rhizosphere zone in the central compartments of the rhizoboxes, followed by near rhizosphere zone and bulk soil zone in the outer compartments. However, G. mosseae only exerted minimal impacts on dissipation of PHE and PYR in the rhizosphere. The present study suggested that the hyphae and extraradical mycelium of AM fungi could play important roles in the uptake and translocation of PHE and PYR in plants. The present results indicated that there is a potential for the use of AM fungi and plant for remediating PAHs contaminated soils.     

One-dimensional ZnO nanostructures

The wide-gap semiconductor ZnO with nanostructures such as nanoparticle, nanorod, nanowire, nanobelt, nanotube has high potential for a variety of applications. This article reviews the fundamentals of one-dimensional ZnO nanostructures, including processing, structure, property, application and their processing-microstructure-property correlation. Various fabrication methods of the ZnO nanostructures including vapor-liquid-solid process, vapor-solid growth, solution growth, solvothermal growth, template-assisted growth and self-assembly are introduced. The characterization and properties of the ZnO nanostructures are described. The possible applications of these nanostructures are also discussed.     

Recent progress in hydrothermal synthesis of zinc oxide nanomaterials

Hydrothermal synthesis is of considerable interest due to its low cost, simplicity and relatively low growth temperature (typically below 200 °C). Since the synthesis is performed in aqueous solutions (no organic solvents), it can also be safe and environmentally friendly (depending on precursor chemicals). Consequently, it has been a subject of intense research in recent years. In this article, we review recent progress in hydrothermal synthesis of zinc oxide nanomaterials, with focus on practical relevance for a variety of applications.     

GENERALIZED CENTER METHOD FOR MULTIOBJECTIVE ENGINEERING OPTIMIZATION

This paper presents a new approach to multiobjective engineering optimization: the generalized center method (GCM). A multiobjective problem is solved by calculating the centers of a sequence of level sets. These sets comprise intersections of the original constraints and level constraints imposed on objective functions. In view of the different dimensions and conflicting nature of multiple objectives, some scaling and trade-off procedures are implemented. Several engineering optimization examples are given to demonstrate the effectiveness of the proposed method.     

Characterization and Physical Explanation of Energetic Particles on Planck HFI Instrument

The Planck High Frequency Instrument (HFI) has been surveying the sky continuously from the second Lagrangian point (L2) between August 2009 and January 2012. It operates with 52 high impedance bolometers cooled at 100 mK in a range of frequency between 100 GHz and 1 THz with unprecedented sensitivity, but strong coupling with cosmic radiation. At L2, the particle flux is about 5 \(\hbox {cm}^{-2}\,\hbox {s}^{-1}\) and is dominated by protons incident on the spacecraft. Protons with an energy above 40 MeV can penetrate the focal plane unit box causing two different effects: glitches in the raw data from direct interaction of cosmic rays with detectors (producing a data loss of about 15 % at the end of the mission) and thermal drifts in the bolometer plate at 100 mK adding non-Gaussian noise at frequencies below 0.1 Hz. The HFI consortium has made strong efforts in order to correct for this effect on the time ordered data and final Planck maps. This work intends to give a view of the physical explanation of the glitches observed in the HFI instrument in-flight. To reach this goal, we performed several ground-based experiments using protons and \(\alpha \) particles to test the impact of particles on the HFI spare bolometers with a better control of the environmental conditions with respect to the in-flight data. We have shown that the dominant part of glitches observed in the data comes from the impact of cosmic rays in the silicon die frame supporting the micro-machined bolometric detectors propagating energy mainly by ballistic phonons and by thermal diffusion. The implications of these results for future satellite missions will be discussed.