Optimizing Dielectric Strips Over a Metallic Substrate for Subwavelength Light Confinement

In this letter, we develop an efficient method for optimizing the geometry of a dielectric strip over a metallic substrate for subwavelength waveguide applications. We investigate the effect of the design parameters on the light propagation and find the optimum design for both loss and light confinement. The proposed design technique generates optimal waveguide geometries that can support single-mode propagation while simultaneously achieving low loss and small modal sizes     

Analytical modeling methodology for ultrawideband low noise amplifiers with generalized filter-based impedance matching

In this paper, we present a modeling methodology for fully integrated inductively degenerated cascode ultrawideband low noise amplifiers (LNA) with generalized filter-based impedance matching networks. Our accurate analytical models capture the impact of device and passive component parasitics and transistor short channel effects to generate accurate designs. Utilizing our methodology, we are able to accurately generate an ultrawideband LNA in the 3.1–10.6 GHz frequency band using third and fifth order Chebyshev filters as input impedance matching networks. The speed and accuracy of the proposed analytical model will facilitate rapid design space exploration for ultrawideband LNAs.     

Study of the reaction of bulky aryllithium reagents with 3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine-2-borane derived from ephedrine

The ring opening of enantiomerically pure 3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine-2-borane (1) with a variety of bulky aryllithium reagents was studied. Our results are not in total agreement with those obtained by others. In fact, several 2,6-disubstituted aryl groups were successfully appended to the phosphorus atom, furnishing the corresponding (N-ephedrino)phosphine boranes 2a-g with dr>99:1. However, when the attack on the phosphorus atom is hindered, deprotonation on the benzylic position occurs, leading to the formation of enantiomerically pure trans-(N-methylamino)(phenyl)(1-phenyl-1-propenyloxy)phosphine-P-borane (3). While the attack of 2,2'-dilithio-1,1'-biarenes leads to the corresponding (P-phenyl)phosphole derivatives (4i,j) and to [bis(N-ephedrino)](phenyl)phosphine-P-borane (5), the attack of 1,1'-dilithiometallocenes (M=Fe, Ru) leads to a separable diastereomeric mixture of 1,1'-bis[(N-ephedrino)(phenyl)phosphino-P-borane]metallocenes (2k,l/2k',l') with dr approximately 80:20.     

Synthesis and structure of silver complexes with nicotinate-type ligands having antibacterial activities against clinically isolated antibiotic resistant pathogens

The synthesis and low-temperature X-ray crystal structures of five new silver complexes, [Ag(2)-mu-O,O'(2-aminonicotinium)(2)(NO(3))(2)](n) (7), [Ag(isonicotinamide)(2)-mu-O,O'(NO(3))](2) (8), [Ag(ethyl nicotinate)(2)](NO(3)) (9), [Ag(ethyl isonicotinate)(2)(NO(3))] (10), and [Ag(methyl isonicotinate)(2)(H(2)O)](NO(3)) (11), are presented and fully characterized by spectral and elemental analysis. The antimicrobial activities of these complexes were screened using 12 different clinical isolates belonging to four pathogenic bacteria, S. aureus, S. pyogenes, P. mirabilis, and Ps. Aeruginosa, all obtained from diabetic foot ulcers. These tested bacteria were resistant for at least 10 antibiotics commonly used for treatment of diabetic foot ulcers. Compounds 7 and 8 had considerable activity against Ps. Aeruginosa (MIC values 2-8 microg/mL), compound 9 against S. aureus (MIC 4-16 microg/mL) and S. pyogenes (MIC 2-4 microg/mL), and also 9 and 11 against P. mirabilis (MIC 1-16 microg/mL). All complexes were non-toxic for daphnia at concentrations above 512 microg/mL overnight.     

In vitro cytotoxic and antiviral activities of Ficus carica latex extracts

The latex of fig fruit (Ficus carica) is used in traditional medicine for the treatment of skin infections such as warts and also diseases of possible viral origin. Five extracts (methanolic, hexanic, ethyl acetate, hexane-ethyl acetate (v/v) and chloroformic) of this species were investigated in?vitro for their antiviral potential activity against herpes simplex type 1 (HSV-1), echovirus type 11 (ECV-11) and adenovirus (ADV). To evaluate the capacity of the extracts to inhibit the replication of viruses, the following assays were performed: adsorption and penetration, intracellular inhibition and virucidal activity. Observation of cytopathic effects was used to determine the antiviral action. The hexanic and hexane-ethyl acetate (v/v) extracts inhibited multiplication of viruses by tested techniques at concentrations of 78 μg mL(-1). These two extracts were possible candidates as herbal medicines for herpes virus, echovirus and adenovirus infectious diseases. All extracts had no cytotoxic effect on Vero cells at all tested concentrations.     

Harmonic functions on hypergroups

We initiate a study of harmonic functions on hypergroups. In particular, we introduce the concept of a nilpotent hypergroup and show such hypergroup admits an invariant measure as well as a Liouville theorem for bounded harmonic functions. Further, positive harmonic functions on nilpotent hypergroups are shown to be integrals of exponential functions. For arbitrary hypergroups, we derive a Harnack inequality for positive harmonic functions and prove a Liouville theorem for compact hypergroups. We discuss an application to harmonic spherical functions.     

X‐ray tomography of morphological changes after freeze/thaw in gas diffusion layers

Liquid water produced in a polymer electrolyte membrane fuel cell experiences a freeze/thaw cycle when the cell is switched off and on while operating at ambient temperatures below freezing. This freeze/thaw cycle permanently deforms the polymer electrolyte membrane fuel cell capillary structures and reduces both the cell life and its ability to generate electric power. The X‐ray tomography facility at the Pohang Accelerator Laboratory was used to observe the freeze/thaw effects on the gas diffusion layer (GDL), which is the thickest capillary layer in the cell. Morphological changes in the GDL under a water freeze/thaw cycle were observed. A scenario in which freeze/thaw cycles affect fuel cell performance is suggested based on images from X‐ray tomography.     

Biodistribution of ultra small superparamagnetic iron oxide nanoparticles in BALB mice

Recently ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles (NPs) have been widely used for medical applications. One of their important applications is using these particles as MRI contrast agent. While various research works have been done about MRI application of USPIOs, there is limited research about their uptakes in various organs. The aim of this study was to evaluate the biodistribution of dextran coated iron oxide NPs labelled with ^99mTc in various organs via intravenous injection in Balb/c mice. The magnetite NPs were dispersed in phosphate buffered saline and SnCl₂ which was used as a reduction reagent. Subsequently, the radioisotope ^99mTc was mixed directly into the reaction solution. The labeling efficiency of USPIOs labeled with ^99mTc, was above 99 %. Sixty mice were sacrificed at 12 different time points (From 1 min to 48 h post injections; five mice at each time). The percentage of injected dose per gram of each organ was measured by direct counting for 19 harvested organs of the mice. The biodistribution of ^99mTc-USPIO in Balb/c mice showed dramatic uptake in reticuloendothelial system. Accordingly, about 75 percent of injected dose was found in spleen and liver at 15 min post injection. More than 24 % of the NPs remain in liver after 48 h post-injection and their clearance is so fast in other organs. The results suggest that USPIOs as characterized in our study can be potentially used as contrast agent in MR Imaging, distributing reticuloendothelial system specially spleen and liver.     

Synthesis and characterization of Mn(II) and Zn(II) azido complexes with halo-substituted pyridine derivative ligands

The synthesis, IR spectra and single-crystal structures of two Mn(II) and one Zn(II) azido complexes with halo-substituted pyridine derivative ligands are reported: [Mn(N₃)-₂(3-Brpy)₂(H₂O)]₂(3-Brpy)₂ (1), [Mn(N₃)₂(3-Brpy)₂] _n (2) and [Zn(N₃)₂(3-amino,2-chloropyridine)] _n (3) with 3-Brpy = 3-bromopyridine. In the dinuclear Mn(II) complex 1 and polymeric 1D Zn(II) complex 3, di-EO only azido bridges exist, whereas in the polymeric Mn(II) 1D system of 2, a rather less common di-EO/di-EO/di-EE azido bridging sequence has been observed (EO = end-on, EE = end-to-end). The halo-substituted pyridine derivatives act in the three compounds as terminal ligands and in 1 also as solvent molecules.