Thermally evaporated Ag nanoparticle films for plasmonic enhancement in organic solar cells: effects of particle geometry

We report on the simple fabrication of Ag NP films via thermal evaporation and subsequent annealing. The NPs are formed on indium tin oxide electrodes, coated with PEDOT:PSS and implemented into PCPDTBT:PC70BM solar cells. Scanning electron microscopy and atomic force microscopy are used to determine the size distributions and surface coverage of the NP film. We apply finite‐difference time‐domain techniques to model the optical properties of different nanoparticle films and compare this with the absorption properties of the organic active layer. The simulations demonstrate that the absorption and scattering efficiency of the particles are very sensitive to particle geometry. Solar cells prepared with window electrodes containing NP layers with less surface coverage, show a 14.8% improvement in efficiency. We discuss variations in the external quantum efficiency of the devices in terms of forward scattering and parasitic absorption losses induced by the NP layer. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Improving performance of FxRLS algorithm for active noise control of impulsive noise

Active noise control (ANC) systems employing adaptive filters suffer from stability issues in the presence of impulsive noise. New impulsive noise control algorithms based on filtered-x recursive least square (FxRLS) algorithm are presented. The FxRLS algorithm gives better convergence than the filtered-x least mean square (FxLMS) algorithm and its variants but lacks robustness in the presence of high impulsive noise. In order to improve the robustness of FxRLS algorithm for ANC of impulsive noise, two modifications are suggested. First proposed modification clips the reference and error signals while, the second modification incorporates energy of the error signal in the gain of FxRLS (MGFxRLS) algorithm. The results demonstrate improved stability and robustness of proposed modifications in the FxRLS algorithm. However, another limitation associated with the FxRLS algorithm is its computationally complex nature. In order to reduce the computational load, a hybrid algorithm based on proposed MGFxRLS and normalized step size FxLMS (NSS-FXLMS) is also developed in this paper. The proposed hybrid algorithm combines the stability of NSS-FxLMS algorithm with the fast convergence speed of the proposed MGFxRLS algorithm. The results of the proposed hybrid algorithm prove that its convergence speed is faster than that of NSS-FxLMS algorithm with computational complexity lesser than that of FxRLS algorithm.     

Sequence limits in calculus: using design research and building on intuition to support instruction

This article is based on research completed within an ongoing project to develop a calculus course which serves as the foundation for the mathematical education of undergraduate students who are training to become elementary teachers. Several research-based activities have been developed, tested, and refined. In this paper we discuss how the design research approach was used to create and implement an instructional task that introduces the concept of limit of a sequence using popular characters from a children’s television show. We present the intuition that students brought to the instructional sequence, the development of the tasks based on the instructional design theory of Realistic Mathematics Education, and the evolution of the intuition that students displayed after instruction. Results include the instructional task developed and student work which reveals that students use context, informal notions of limit, and the notion of “arbitrarily close” to write about their limit understandings.     

Surface properties and electromagnetic excitation of a piezoelectric gallium phosphate biosensor

The surface properties of GaPO4 have been studied by secondary ion mass spectrometry, X-ray photoelectron spectroscopy and electromagnetic acoustic wave excitation in order to explore the potential of this relatively new piezoelectric material as a biosensor. The X-ray photoelectron spectrum of the substrate shows a Ga-rich surface (Ga:P = 1.4), while the negative secondary ion mass spectrum is similar to that of other phosphates, with PO3- and PO2- being the main fragments derived from the substrate. Surface analysis reveals that the linker protein for biotinylated moieties, neutravidin, is both readily chemisorbed to bare gallium phosphate at pH 7.5 and attached to p-hydroxy benzaldehyde-treated devices, establishing the possibility to exploit the surface chemistry of the phosphate for the fabrication of an electrode-free acoustic wave biosensor. Preliminary results regarding the detection of the adsorption of neutravidin with an electromagnetic field-excited GaPO4 device incorporated in a FIA configuration showed comparable results with those obtained with a quartz-sensor equivalent. The frequency shift for the adsorbed protein layer at the device fundamental frequency was 200 Hz and the noise was routinely around 13 Hz. The possibility to use the electrodeless acoustic GaPO4 device at higher harmonics in the liquid phase has also been confirmed.     

Spectral Properties of Bacteriochlorophyll c in Organisms and in Model Systems

Polarized absorption and fluorescence spectra of bacteriochlorophyll c and green photosynthetic bacterium Prostheecochloris aestuarii cells and cell fragments embedded in stretched polymer film were measured. In pigment samples the artificial oligomers of bacteriochlorophyll c (with absorption about 750 nm) and other forms of this pigment and bacteriopheophytin (with absorption at 670 nm) were present. In bacteria samples, embedded in polymer, oligomers were in high degree disaggregated and as a result the absorption about 670 nm was observed. Previously for similar sets of samples the decay of fluorescence excited only at one wavelength was analyzed on three exponential components, but exact lifetime values of these components for various samples were different. The aim of present paper was to check if these differences occur because of various contributions to decay from three well defined forms or if they were related to the existence of several pigment forms with slightly different lifetimes. The global analysis of data obtained for various excitation and observation wavelengths of fluorescence were done. From this analysis it follows that the second situation occurs. For a model system containing artificial oligomers the largest component of decay has a ⁴ of about 0.183 ns or 0.136 ns depending on observation wavelength. For the bacteria sample, in which the emission at 680 nm is the superposition from various pigments, global analysis done for various excitation wavelengths shows also that the values differ depending on the regions of fluorescence observation. From polarized spectra, it follows that in the model system the pigments absorbing at 670 nm are randomly distributed whereas oligomers are highly oriented. In bacteria fragments absorbing at 670 nm pigment molecules can be divided into two groups: one oriented along the axis of film stretching and the second practically randomly distributed. In living organisms, under some conditions, small amount of 670 nm pigments can be present and can work as excitation energy traps or as antenna transferring the excitation. Present results show that the role of various pools of 670 nm absorbing pigments can be different because of their differing orientation.     

New Coordination Compounds Based on a Pyrazine Derivative: Design,Characterization, and Biological Study

New coordination compounds of Mn(II), Fe(III), Co(II), and Ni(II) and the biologically active ligand L (N′-benzylidenepyrazine-2-carbohydrazonamide) were synthesized and characterized by appropriate analytical techniques: elemental analysis (EA), thermogravimetric analysis (TG–DTG), infrared spectroscopy (FTIR), and flame-atomic absorption spectrometry (F-AAS). The biological activity of the obtained compounds was then comprehensively investigated. Rational use of these compounds as potential drugs was proven by ADME analysis. All obtained compounds were screened in vitro for antibacterial, antifungal, and anticancer activities. Some of the studied complexes exhibited significantly higher activity than the ligand alone.     

Radioactivity levels in peloids used in main Cuban spas

In this work, an approach for determining both the outer dead layer thickness of the p-type coaxial HPGe detector and the inner dead layer thickness of the n-type coaxial HPGe detector was proposed by using two full energy peak area count ratios of a X-ray and a gamma ray emitted from the same radioisotope of ¹³⁷Cs. Monte Carlo calculations and experimental measurements were conducted to determine these dead layer thicknesses. The results showed that the outer dead layer thickness reached 0.57 ± 0.03 mm on 06 Jan 2017 after nearly 3 years of use for the p-type detector. The inner dead layer thickness reached 1.21 ± 0.24 mm on 01 Aug 2016 after more than 3 years of operation for the n-type detector. Simulation model with the modified dead layer thicknesses was used to estimate full energy peak efficiencies and gamma spectra from seven radioactive sources. The results were in good agreement with the corresponding experimental values in the gamma energy region of interest.     

Comparison of HPLC and CE methods for the determination of cetirizine dihydrochloride in human plasma samples

Two methods, capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC), for analysis of cetirizine dihydrochloride in small sample volumes of human plasma were compared. The CE and HPLC assays were developed and validated by analyzing a series of plasma samples containing cetirizine dihydrochloride in different concentrations using these two methods. The extraction procedure is simple and no complicated purification steps or derivatization are required. The analysis time in the HPLC method was shorter than that in the CE method, but solvent consumption was considerably lower in the CE method. The calibration curve was linear to at least 10-1000 ng/mL both for CE and HPLC with r(2) = 0.9993 and r(2) = 0.9994, respectively. The detection limits for cetirizine dihydrochloride were 3 and 5 ng/mL with CE and HPLC (a UV detector was applied in the both cases), respectively. Both methods were selective, robust and specific, allowing reliable quantification of cetirizine dihydrochloride, and could be useful for clinical and biomedical investigations.     

Magnetism and crystal structures of CuMn and CuNi ordered bimetallic chains

The syntheses, crystal structures and magnetic properties of the new bimetallic compounds {CuL_α[Ni(NCS)₄(H₂O)₂]} (1) and {CuL_α[Mn(NCS)₄(H₂O)₂]} (2), where L = N-dl-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene, are reported. Both structures consist of well-separated and magnetically equivalent layers which are composed of thiocyanate-bridged Cu(II)–Mn(II) or Cu(II)–Ni(II) binuclear units and create infinite polymeric zig-zag-like chains in the crystal lattices. The [Ni(NCS)₄(H₂O)₂] and [Mn(NCS)₄(H₂O)₂] molecular fragments have a distorted octahedral symmetry. The geometry of the Cu(II) unit is octahedral with the apical positions occupied by bridging thiocyanate ligands and the basal ones by four nitrogen atoms from the macrocyclic ring. The shortest intramolecular M–M distances are: 6.342 Å (Cu–Ni) and 6.421 Å (Cu–Mn). Magnetic susceptibility and magnetization measurements for the examined compounds have been carried out over the range 1.8–300 K. The data suggest antiferromagnetic interactions through the thiocyanate bridge. Finally, the magnitudes of the Cu(II)–M(II) interactions (M = Ni and Mn) have been compared and qualitatively rationalised.