Microwave cavity perturbation studies on H-form and Cu ion-exchanged SCR catalyst materials: correlation of ammonia storage and dielectric properties

Ammonia-based selective catalytic reduction (SCR) has become the major control strategy for NOx emissions from light and heavy duty diesel engines. Before reducing NOx on the SCR active material, ammonia storage on the active sites of the catalyst is crucial. The in operando measurement of the dielectric properties of the catalyst material using microwave cavity perturbation is a promising indicator of ammonia loading. In this work, the influence of copper ion-exchange of the zeolite-based SCR material ZSM-5 on the NH3 storage and the dielectric properties is highlighted. The catalyst powder samples were monitored by microwave cavity perturbation as a function of the stored ammonia content at a frequency of approximately 1.2 GHz in a temperature range between 200 and 350 °C. Due to ion exchange, the NH3 storage behavior changes, what could be monitored in the sensitivity of the dielectric permittivity to NH3. The dependence of the complex dielectric permittivity on ammonia loading is decreased by ion exchange, hinting that mostly ammonia storage on Brønsted sites affects the dielectric permittivity. This finding adds new knowledge to the electrical conduction and polarization mechanisms occurring in these zeolite materials

Description of Baetao-Manteiga 41 and ‘Yunguilla’ superior Andean common beans for Tanzanian production environments

An international effort was initiated with the evaluation of a diverse set of largeseeded Andean common beans (Phaseolus vulgaris L.), the Andean Diversity Panel, in sub-Saharan Africa. Several entries in the panel have been selected for extensive characterization on the basis of high performance acrossmultiple location × year trials in Tanzania—conducted both on station and on farm. Baetao- Manteiga 41, tested asADP-190, has a commercialKablanketi (light purple speckled) seed type, and ‘Yunguilla’, tested as ADP-447, has a commercial Calima (red mottled) seed type. Both lines exhibited yield stability, vigorous growth under low fertility conditions, angular leaf spot resistance, andmoderate common bacterial blight resistance; Yunguilla also possessed rust resistance. These two lines were tested, selected, and characterized cooperatively by Sokoine University of Agriculture (SUA), the Tanzanian Agricultural Research Institute (TARI), the USDA-ARS, and the Agricultural Research Council (ARC) of South Africa, and in collaboration with local farmers in Tanzania

Unusual microwave response and bulk conductivity of very thin fese0.3te0.7 films as a function of temperature

Results of X-band microwave surface impedance measurements of FeSe1-xTex very thin film are reported. The effective surface resistance shows appearance of peak at T less and near Tc when plotted as function of temperature. The authors suggests that the most well-reasoned explanation can be based on the idea of the changing orientation of the microwave magnetic field at a SN phase transition near the surface of a very thin film. The magnetic penetration depth exhibits a power-law behavior of delta lambda proportional to T with an exponent n = 2.4 at low temperatures, which is noticeably higher than in the published results on FeSe1-xTexsingle crystal. However the temperature dependence of the superfluid conductivity remains very different from the behavior described by the BCS theory. Experimental results are fitted very well by a two-gap model with delta1/kTc=0.43 and delta2/kTc=1.22,thus supporting s(+-)- wave symmetry. The rapid increase of the quasiparticle scattering time is obtained from the microwave impedance measurements.Comment: 13 pages, 13 figure

Penetration Depth and Anisotropy in MgB2

The penetration depth lambda of MgB2 was deduced from both the ac susceptibility chi and the magnetization M(H) of sorted powders. The good agreement between the two sets of data without geometric correction for the grain orientation suggests that MgB2 is an isotropic superconductor.Comment: 9 pages, 5 figures; submitted to Physical Review B (February 28, 2001; revised June 28, 2001); reference list update

Unusual features in the nonlinear microwave surface impedance of Y-Ba-Cu-O thin films

Striking features have been found in the nonlinear microwave (8 GHz) surface impedance $Z_s=R_s + jX_s$ of high-quality YBaCuO thin films with comparable low power characteristics [$R_{res}\sim 35--60 \mu\Omega$ and $\lambda_L(15 K)\sim 130--260 nm$]. The surface resistance $R_s$ is found to increase, decrease, or remain independent of the microwave field $H_{rf}$ (up to 60 mT) at different temperatures and for different samples. However, the surface reactance $X_s$ always follows the same functional form. Mechanisms which may be responsible for the observed variations in $R_s$ and $X_s$ are briefly discussed.Comment: 4 pages, 4 figure

Penetration Depth Measurements in MgB_2: Evidence for Unconventional Superconductivity

We have measured the magnetic penetration depth of the recently discovered binary superconductor MgB_2 using muon spin rotation and low field $ac$-susceptibility. From the damping of the muon precession signal we find the penetration depth at zero temperature is about 85nm. The low temperature penetration depth shows a quadratic temperature dependence, indicating the presence of nodes in the superconducting energy gap.Comment: 4 pages 3 figure

Systematic behaviour of the in-plane penetration depth in d-wave cuprates

We report the temperature T and oxygen concentration dependences of the penetration depth of grain-aligned YBa_2Cu_3O_{7-\delta} with \delta= 0.0, 0.3 and 0.43. The values of the in-plane \lambda_{ab}(0) and out-of-plane \lambda_{c}(0) penetration depths, the low temperature linear term in \lambda_{ab}(T), and the ratio \lambda_{c}(0) /\lambda_{ab}(T) were found to increase with increasing $\delta$. The systematic changes of the linear term in \lambda_{ab}(T) with T_c found here and in recent work on HgBa_2Ca_{n-1} Cu_nO_{2n+2+\delta} (n = 1 and 3) are discussed.Comment: 4 pages, 4 figure

Pressure effect on the in-plane magnetic penetration depth in YBa_2Cu_4O_8

We report a study of the pressure effect (PE) on the in-plane magnetic field penetration depth lambda_{ab} in YBa_2Cu_4O_8 by means of Meissner fraction measurements. A pronounced PE on lambda_{ab}^{-2}(0) was observed with a maximum relative shift of \Delta\lambda^{-2}_{ab}/\lambda^{-2}_{ab}= 44(3)% at a pressure of 10.2 kbar. It arises from the pressure dependence of the effective in-plane charge carrier mass and pressure induced charge carrier transfer from the CuO chains to the superconducting CuO_2 planes. The present results imply that the charge carriers in YBa_2Cu_4O_8 are coupled to the lattice.Comment: 4pages 3 figure

A compact microwave applicator for the rapid detection of clostridium difficile

Clostridium difficile is a major cause of hospital acquired infection that poses significant diagnostic challenges. In this paper, a new type of resonant microwave applicator is proposed for the liberation of DNA from C. difficile spores via microwave disruption, followed by rapid detection using a sandwich hybridization assay. A split-ring resonator is designed to operate at 2.4 GHz with a 3 mm active gap region that contains an isolate volume of approximately 10 mm 3 , exposed to pulsed microwaves of 12 W rms power. The parallel electric field configuration maximizes the interaction between the microwaves and the sample. In a proof of principle study, in combination with pathogen specific DNA probes, we have used the system to correctly identify virulent strains of C. difficile using magnetic bead extraction of DNA suitable for point-of-care applicatio