On the performance of improved quadrature spatial modulation

Quadrature spatial modulation (QSM) utilizes the in‐phase and quadrature spatial dimensions to transmit the real and imaginary parts of a single signal symbol, respectively. The improved QSM (IQSM) transmits two signal symbols per channel use through a combination of two antennas for each of the real and imaginary parts. The main contributions of this study can be summarized as follows. First, we derive an upper bound for the error performance of the IQSM. We then design constellation sets that minimize the error performance of the IQSM for several system configurations. Second, we propose a double QSM (DQSM) that transmits the real and imaginary parts of two signal symbols through any available transmit antennas. Finally, we propose a parallel IQSM (PIQSM) that splits the antenna set into equal subsets and performs IQSM within each subset using the same two signal symbols. Simulation results demonstrate that the proposed constellations significantly outperform conventional constellations. Additionally, DQSM and PIQSM provide a performance similar to that of IQSM while requiring a smaller number of transmit antennas and outperform IQSM with the same number of transmit antennas.     

A block diagram model of the thickness mode piezoelectric transducer containing dual oppositely polarized piezoelectric zones

A unidimensional, linear systems, block diagram model of a two-layer thickness mode piezoelectric transducer is presented. The layers are subject to opposing piezoelectric polarization and the device is assumed to be loaded by semi-infinite isotropic media at the two principal faces. Block diagram representations of the transducer acting as both a generator and a receiver of ultrasound are developed in conjunction with the equivalent model of the electrical admittance. When expressed in this manner, the underlying cause and effect relationships are identified, with the important contribution of the piezoelectric boundary highlighted. Comparisons with the conventional single-layer transducer are made throughout and the major physical differences in terms of transduction performance are discussed. The new model is compared with finite element analysis and good agreement is also demonstrated with experimental data. A key aspect of the methodology is the provision of a more intuitive understanding of such device behavior. Accordingly, emphasis has been placed on the physical relationships and this is considered a major contribution of the work.     

Complete mass spectral characterization of a synthetic ultralow-molecular-weight heparin using collision-induced dissociation

Glycosaminoglycans (GAGs) are a class of biologically important molecules, and their structural analysis is the target of considerable research effort. Advances in tandem mass spectrometry (MS/MS) have recently enabled the structural characterization of several classes of GAGs; however, the highly sulfated GAGs, such as heparins, have remained a relatively intractable class due their tendency to lose SO(3) during MS/MS, producing few sequence-informative fragment ions. The present work demonstrates for the first time the complete structural characterization of the highly sulfated heparin-based drug Arixtra. This was achieved by Na(+)/H(+) exchange to create a more ionized species that was stable against SO(3) loss, and that produced complete sets of both glycosidic and cross-ring fragment ions. MS/MS enables the complete structural determination of Arixtra, including the stereochemistry of its uronic acid residues, and suggests an approach for solving the structure of more complex, highly sulfated heparin-based drugs.     

Synthesis, Characterization, and Electroluminescent Characteristics of Mixed-Ligand Zinc(II) Complexes

Mixed-ligand zinc complexes, i.e., 2-(2-hydroxyphenyl)benzothiazolato-5,7- dichloro-8-hydroxyquinolinato zinc(II) [ZnBTZ(Cl₂q)], 2-(2-hydroxyphenyl) benzothiazolato-5,7-dimethyl-8-hydroxyquinolinato zinc(II) [ZnBTZ(Me₂q)], and 2-(2-hydroxyphenyl)benzothiazolato-2-carbonitril-8-hydroxyquinolinato zinc(II) [ZnBTZ(CNq)], were synthesized and characterized. The metal complexes have high thermal stability (>300°C) and high glass-transition temperature (>150°C) and are suitable for optoelectronic applications. Optical properties of the synthesized complexes were characterized by using ultraviolet–visible (UV–Vis) and photoluminescence spectroscopy. Color tuning by changing the ligand was observed in synthesized complexes. Multilayered organic electroluminescent devices were fabricated having structure indium–tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD)/zinc complex/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(quinolinolate)Al^III (Alq₃)/LiF/Al using the synthesized complexes as emissive material. The electroluminescence spectra show peak emission centered at 532 nm, 572 nm, and 541 nm, respectively, for these materials. The emitted light has chromaticity with Commission Internationale d’Éclairage coordinates x = 0.35 and y = 0.56 for ZnBTZ(Cl₂q), x = 0.49 and y = 0.47 for ZnBTZ(Me₂q), and x = 0.48 and y = 0.40 for ZnBTZ(CNq) complex.     

Towards a practical approach to fertilizer recommendations for food crop production in smallholder farms in Kenya

A comprehensive long-term fertilizer trial programme for annual crops was established in 1985 at 70 sites in the high and medium rainfall areas of Kenya testing N and P, farmyard manure and other critical nutrients. Sites were selected according to their representativeness regarding soils and climate in agro-ecological units. The fertilizer trial programme included all major food crops typical for the respective area, both monocropped and intercropped in the case of cereals. Economic optimum fertilizer rates were calculated taking into account input/output price ratios and value-cost ratios. The majority of sites showed responses to N or P, only at one site response to both N and P with a significant interaction was found. Price elasticity of crops such as potatoes and cabbages was higher than that of maize or sorghum. Critical soil P levels were determined for maize at 13 ppm P for modified Olsen extract and 32 ppm P for Mehlich I extract. Variability of rainfall was found to greatly influence viability of fertilizer recommendations. First attempts to extrapolate fertilizer recommendations from areas of representativeness to areas with similar conditions by means of GIS and modelling approaches are discussed.