Bandwidth-Reconfigurable Coaxial Bandpass Filter With Multioctave Tuning Using a Single Element

A bandwidth (BW) tunable coaxial-loaded waveguide filter is presented in this letter based on a novel concept using a single tuning element. The operation principle relies on the rotation of coaxial resonators with respect to fixed irises in order to change the inter-resonator (IR) coupling strengths that control the BW. This mechanism features multioctave tuning while maintaining a fixed operating frequency and a stable unloaded quality factor with only one rotary post. Furthermore, the filter can be switched off by using the same tuning mechanism. A prototype is manufactured and measured to verify the proposed filter. The measured results demonstrate multioctave BW tunability from 12 to 83 MHz (tuning ratio > 6.9:1), promoting the technique for multistandard communication systems and applications

Converse Magnetoelectric Composite Resonator for Sensing Small Magnetic Fields

Magnetoelectric (ME) thin film composites consisting of sputtered piezoelectric (PE) and magnetostrictive (MS) layers enable for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities a magnetic bias field is necessary to operate at the maximum piezomagnetic coefficient of the MS phase, harnessing mechanical resonances further enhances this direct ME effect size. Despite being able to detect very small AC field amplitudes, exploiting mechanical resonances directly, implies a limitation to available signal bandwidth along with the inherent inability to detect DC or very low frequency magnetic fields. The presented work demonstrates converse ME modulation of thin film Si cantilever composites of mesoscopic dimensions (25 mm × 2.45 mm × 0.35 mm), employing piezoelectric AlN and magnetostrictive FeCoSiB films of 2 µm thickness each. A high frequency mechanical resonance at about 515 kHz leads to strong induced voltages in a surrounding pickup coil with matched self-resonance, leading to field sensitivities up to 64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as well as about 70 pT/Hz1/2 at 10 Hz, without the need for a magnetic bias field, pave the way towards biomagnetic applications

Ethnopharmacological survey of Samburu district, Kenya

<p>Abstract</p> <p>Background</p> <p>Ethnobotanical pharmacopoeia is confidently used in disease intervention and there is need for documentation and preservation of traditional medical knowledge to bolster the discovery of novel drugs. The objective of the present study was to document the indigenous medicinal plant utilization, management and their extinction threats in Samburu District, Kenya.</p> <p>Methods</p> <p>Field research was conducted in six divisions of Samburu District in Kenya. We randomly sampled 100 consented interviewees stratified by age, gender, occupation and level of education. We collected plant use data through semi-structured questionnaires; transect walks, oral interviews and focus groups discussions. Voucher specimens of all cited botanic species were collected and deposited at University of Nairobi's botany herbarium.</p> <p>Results</p> <p>Data on plant use from the informants yielded 990 citations on 56 medicinal plant species, which are used to treat 54 different animal and human diseases including; malaria, digestive disorders, respiratory syndromes and ectoparasites.</p> <p>Conclusion</p> <p>The ethnomedicinal use of plant species was documented in the study area for treatment of both human and veterinary diseases. The local population has high ethnobotanical knowledge and has adopted sound management conservation practices. The major threatening factors reported were anthropogenic and natural. Ethnomedical documentation and sustainable plant utilization can support drug discovery efforts in developing countries.</p

The effect of nutrients on pyrrolizidine alkaloids in Senecio plants and their interactions with herbivores and pathogens

The aim of this review is to combine the knowledge of studies on effects of nutrients on pyrrolizidine alkaloids (PAs) in Senecio with those studies of effects of PAs on herbivores and pathogens in order to predict the effects that nutrients may have on herbivores and pathogens via changes in PAs. We discuss whether these predictions match with the outcome of studies where the effect of nutrients on herbivores and insects were measured. PA concentrations in S. jacobaea, S. vulgaris and S. aquaticus were mostly reduced by NPK fertilization, with genotype-specific effects occurring. Plant organs varied in their response to increased fertilization; PA concentrations in flowers remained constant, while shoot and roots were mostly negatively affected. Biomass change is probably largely responsible for the change in concentrations. Nutrients affect both the variety and the levels of PAs in the plant. The reduced PA concentrations after NPK fertilization was expected to benefit herbivores, but no or negative responses from insect herbivores were observed. Apparently other changes in the plant after fertilization are overriding the effect of PAs. Pathogens do seem to benefit from the lower PA concentrations after fertilization; they were more detrimental to fertilized plants than to unfertilized control plants. Future studies should include the effect of each element of nutrients separately and in combinations in order to gain more insight in the effect of specific nutrients on PA content in Senecio plants

Wideband generalized admittance matrix representation for the analysis and design of waveguide filters with coaxial excitation

A very efficient technique for the full-wave analysis and design of complex passive waveguide filters, including rectangular cavities with metallic cylindrical posts and coaxial excitation, is presented. This novel technique provides the wideband generalized admittance matrix representation of the whole structure in the form of pole expansions, thus extracting the most expensive computations from the frequency loop. For this purpose, the structure is properly segmented into its key building blocks, all of them characterized in terms of wideband admittance matrices. Then, an efficient iterative algorithm for combining these matrices, and finally providing the wideband generalized admittance matrix of the complete structure, is followed. In order to validate the accuracy and efficiency of this full-wave modal technique, four different waveguide filters have been considered. In particular, the design of a compact four-pole in-line filter with tuning screws and of an evanescent-mode filter, both operating in the X-band and including a standard (vertical) coaxial excitation, are first presented. Finally, two C-band six-resonator comb-line filters, one of them with a cross-coupling configuration, and both excited with a collinear end-launcher transition based on a disc-ended coaxial, are also designed. Numerical data from a commercial software, as well as measurements of a manufactured prototype, are included for verification purposes.Mira Pérez, FE.; San Blas Oltra, ÁA.; Boria Esbert, VE.; Rogla Madrid, LJ.; Gimeno Martinez, B. (2013). Wideband generalized admittance matrix representation for the analysis and design of waveguide filters with coaxial excitation. Radio Science. 48:1-11. doi:10.1002/rds.20013S11148Alessandri, F., Bartolucci, G., & Sorrentino, R. (1988). Admittance matrix formulation of waveguide discontinuity problems: computer-aided design of branch guide directional couplers. IEEE Transactions on Microwave Theory and Techniques, 36(2), 394-403. doi:10.1109/22.3528Alessandri, F., Mongiardo, M., & Sorrentino, R. (1992). Computer-aided design of beam forming networks for modern satellite antennas. IEEE Transactions on Microwave Theory and Techniques, 40(6), 1117-1127. doi:10.1109/22.141343Arcioni, P., & Conciauro, G. (1999). Combination of generalized admittance matrices in the form of pole expansions. IEEE Transactions on Microwave Theory and Techniques, 47(10), 1990-1996. doi:10.1109/22.795073Arcioni, P., Bozzi, M., Bressan, M., Conciauro, G., & Perregrini, L. (2002). Frequency/time-domain modelling of 3D waveguide structures by a BI-RME approach. International Journal of Numerical Modelling: Electronic Networks, Devices and Fields, 15(1), 3-21. doi:10.1002/jnm.429Boria, V. E., Guglielmi, M., & Arcioni, P. (1998). Computer-aided design of inductively coupled rectangular waveguide filters including tuning elements. International Journal of RF and Microwave Computer-Aided Engineering, 8(3), 226-235. doi:10.1002/(sici)1099-047x(199805)8:33.0.co;2-hBozzi, M., Perregrini, L., & Wu, K. (2009). A novel technique for the direct determination of multimode equivalent circuit models for substrate integrated waveguide discontinuities. International Journal of RF and Microwave Computer-Aided Engineering, 19(4), 423-433. doi:10.1002/mmce.20360Chang, H.-C., & Zaki, K. A. (1991). Evanescent-mode coupling of dual-mode rectangular waveguide filters. IEEE Transactions on Microwave Theory and Techniques, 39(8), 1307-1312. doi:10.1109/22.85405Gentili, G. G. (2001). Multiport analysis of arbitrary circular-rod insets in rectangular waveguide by the generalized admittance matrix. IEEE Transactions on Microwave Theory and Techniques, 49(8), 1438-1442. doi:10.1109/22.939924Gimeno, B., & Guglielmi, M. (1997). Multimode equivalent network representation for junctions between coaxial and circular waveguides. International Journal of Microwave and Millimeter-Wave Computer-Aided Engineering, 7(2), 180-194. doi:10.1002/(sici)1522-6301(199703)7:23.0.co;2-wGuglielmi, M. (1994). Simple CAD procedure for microwave filters and multiplexers. IEEE Transactions on Microwave Theory and Techniques, 42(7), 1347-1352. doi:10.1109/22.299728Hoft, M., & Yousif, F. (2011). Orthogonal Coaxial Cavity Filters With Distributed Cross-Coupling. IEEE Microwave and Wireless Components Letters, 21(10), 519-521. doi:10.1109/lmwc.2011.2165533Ihmels , R. F. Arndt 1993 Field theory CAD of L-shaped iris coupled mode launchers and dual-mode filters IEEE MTT-S Int. Microw. Symp. DigLevy, R., Hui-Wen Yao, & Zaki, K. A. (1997). Transitional combline/evanescent-mode microwave filters. IEEE Transactions on Microwave Theory and Techniques, 45(12), 2094-2099. doi:10.1109/22.643743Liang, J.-F., Chang, H.-C., & Zaki, K. A. (1992). Coaxial probe modeling in waveguides and cavities. IEEE Transactions on Microwave Theory and Techniques, 40(12), 2172-2180. doi:10.1109/22.179878Mansour, R. R., & Macphie, R. H. (1986). An Improved Transmission Matrix Formulation of Cascaded Discontinuities and its Application to E-Plane Circuits. IEEE Transactions on Microwave Theory and Techniques, 34(12), 1490-1498. doi:10.1109/tmtt.1986.1133568Marcuvitz, N. (1986). Waveguide Handbook. doi:10.1049/pbew021eMira, F., Bressan, M., Conciauro, G., Martinez, B. G., & Esbert, V. E. B. (2005). Fast S-domain modeling of rectangular waveguides with radially symmetric metal insets. IEEE Transactions on Microwave Theory and Techniques, 53(4), 1294-1303. doi:10.1109/tmtt.2005.845762Mira , F. A. A. San Blas V. E. Boria B. Gimeno G. Conciauro 2005b Fast and accurate CAD tool of passive rectangular waveguide devices including cylindrical conducting posts Proc. 35th Eur. Microw. ConfMira , F. A. A. San Blas V. E. Boria B. 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Gimeno A. Álvarez 2010 Broad band analysis of arbitrarily shaped microwave filters using a novel singular value decomposition technique Proc. 4th Eur Conf. Ant. Prop. (EuCAP)San Blas , A. A. F. Mira V. E. Boria B. Gimeno G. Conciauro M. Bressan P. Arcioni 2006 Efficient CAD of generalized coaxial probes in rectangular waveguide using the 3D BI-RME method Proc. 36th Eur. Microw. ConfHui-Wen Yao, Zaki, K. A., Atia, A. E., & Hershtig, R. (1995). Full wave modeling of conducting posts in rectangular waveguides and its applications to slot coupled combline filters. IEEE Transactions on Microwave Theory and Techniques, 43(12), 2824-2830. doi:10.1109/22.47564

The only African wild tobacco, Nicotiana africana: Alkaloid content and the effect of herbivory

Herbivory in some Nicotiana species is known to induce alkaloid production. This study examined herbivore-induced defenses in the nornicotine-rich African tobacco N. africana, the only Nicotiana species indigenous to Africa. We tested the predictions that: 1) N. africana will have high constitutive levels of leaf, flower and nectar alkaloids; 2) leaf herbivory by the African bollworm Helicoverpa armigera will induce increased alkaloid levels in leaves, flowers and nectar; and 3) increased alkaloid concentrations in herbivore-damaged plants will negatively affect larval growth. We grew N. africana in large pots in a greenhouse and exposed flowering plants to densities of one, three and six fourth-instar larvae of H. armigera, for four days. Leaves, flowers and nectar were analyzed for nicotine, nornicotine and anabasine. The principal leaf alkaloid was nornicotine (mean: 28 µg/g dry mass) followed by anabasine (4.9 µg/g) and nicotine (0.6 µg/g). Nornicotine was found in low quantities in the flowers, but no nicotine or anabasine were recorded. The nectar contained none of the alkaloids measured. Larval growth was reduced when leaves of flowering plants were exposed to six larvae. As predicted by the optimal defense theory, herbivory had a localized effect and caused an increase in nornicotine concentrations in both undamaged top leaves of herbivore damaged plants and herbivore damaged leaves exposed to one and three larvae. The nicotine concentration increased in damaged compared to undamaged middle leaves. The nornicotine concentration was lower in damaged leaves of plants exposed to six compared to three larvae, suggesting that N. africana rather invests in new growth as opposed to protecting older leaves under severe attack. The results indicate that the nornicotine-rich N. africana will be unattractive to herbivores and more so when damaged, but that potential pollinators will be unaffected because the nectar remains alkaloid-free even after herbivory