Efficient single-photon frequency conversion using a Sagnac interferometer

We propose a scheme for efficient optical frequency conversion at the single-photon power level. The scheme exploits the quantum interference of single-photon states at a three-level quantum emitter coupled to a Sagnac interferometer. We show that this device can achieve single-photon frequency up- or down-conversion with near unity efficiency.     

Correction of Nonuniform Response in the Reconstruction for Single Photon Emission Computed Tomography with a Spatially Varying Focal Length Collimator

SPECT (single photon emission computed tomography) images can visualize physiological functions directly and are diagnostically useful. The reconstruction methods based on the Continuous-Discrete (C-D) mapping model have an immediate effect on SPECT imaging because they employ photon detection kernels describing the photon transport from the body to the detector. However, in a spatially varying focal length geometry, the concentration of the sensitivity around the center of rotation of the detector causes a change in the response from the original image to the reconstructed image. As a result, a false hot spot often appears around the center of rotation. This paper presents a convenient method to repress the change by correcting the resolving kernels. Numerical simulations show that the method can reduce the false hot spots.     

1-Acyl-5-methoxy-8-nitro-1,2-dihydroquinoline: a biologically useful photolabile precursor of carboxylic acids

The synthesis, photochemistry, and biological application of 1-acyl-5-methoxy-8-nitro-1,2-dihydroquinoline (MNDQ-caged carboxylic acid) are described. Optimization experiments were carried out on three acetyl derivatives (3a-c), and the most appropriate analogue for application to the caging of glutamate was determined to be 3c. Thus, a MNDQ-caged glutamate (MNDQ-Glu) was synthesized, and the photochemical release of glutamate by uncaging of MNDQ-Glu was confirmed by NMR, MS, and HPLC analysis. When MNDQ-Glu was tested with pyramidal neurons in hippocampal slices, whole-field UV illumination resulted in a large inward current due to the release of l-glutamate. A short two-photon uncaging of MNDQ-Glu at single dendritic spines induced a transient current that exhibited similar kinetic properties to miniature excitatory postsynaptic currents (mEPSC).     

Rate coefficients for the gas‐phase reactions of OH radicals with methylbutenols at 298 K

The relative‐rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C₅ biogenic alcohols, 2‐methyl‐3‐buten‐2‐ol (k₁), 3‐methyl‐3‐buten‐1‐ol (k₂), and 3‐methyl‐2‐buten‐1‐ol (k₃), in the gas phase. OH radicals were produced by the photolysis of CH₃ONO in the presence of NO. Di‐n‐butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O₃ and O‐atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH₃ONO and NO₂ photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k₁ = (6.6 ± 0.5) × 10^?11, k₂ = (9.7 ± 0.7) × 10^?11, and k₃ = (1.5 ± 0.1) × 10^?10 cm³ molecule^?1 s^?1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004     

The magnetic anisotropy of cold-rolled and as-quenched amorphous (Fe1−x Ni x )78Si10B12 alloy systems

In order to make clear the origin of magnetic anisotropy of amorphous alloys produced by a single roller quenching method, the composition dependence of the in-plane magnetic anisotropy of cold-rolled and as-quenched amorphous (Fe₁− _x Ni _x )₇₈Si₁₀B₁₂ alloy systems was studied at room temperature. The twofold in-plane magnetic anisotropy constantK _u of cold rolled and as-quenched specimen decreases with increase inx at the Fe-rich side, and increases drastically at aboutx=0.2. Beyondx=0.25,K _u decreases gradually with further increase inx. From this study, it is emphasized that there is a clear correspondence between the atomic ratio of Fe to Ni at which the anomaly in magnetic anisotropy of the amorphous alloy occurs and the position of the fcc/bcc phase boundary in the Fe−Ni metal alloy system.     

Monte Carlo Simulations of Reflected Spectra Derived from Tissue Phantom with Double-Peak Particle Size Distribution

We made a tissue phantom with double-peak particle size distribution, which has polystyrene particles of cell nuclear size and mitochondrial size, and measured the spectrum from the tissue phantom using a single optical fiber. In this paper we investigate the characterization method for the tissue phantom with double-peak particle size distribution by comparing the measured spectra with the calculated ones using the Monte Carlo (MC) method. It is first shown that the Mie phase function characterizes better than the Henyey-Greenstein (H-G) phase function in MC calculation. Next, we compare the measurement spectra with those obtained by modeling as single-peak, conventional modeling for particle size distribution, and for double-peak particle size distribution. The single-peak modeling is found to cause considerable error for the tissue phantom with double-peak particle size distribution, which seems to simulate a biological tissue. We suggest that if one simulates the particle size distribution of a biological tissue by conventional modeling, the accuracy of estimation will be lower.     

Multiple-discriminant analysis for light-scattering spectroscopy and imaging of two-layered tissue phantoms

We propose a new method for enhancing the sensitivity of the reflectance spectrum to the scattering feature of the superficial tissue layer. This method is based on multiple-discriminant analysis in the eigensubspace of the spectrum. Considering the application of scattering imaging, we evaluated this method by performing multispectral imaging of two-layered tissue phantoms. A color map converted from the spectral reflectance corresponds well to variations in the size of the scattering in the first layer.     

Preparation and Properties of Cellulose/Waste Leather Buff Biocomposites

The aim of the present work was to utilize waste leather buff (WLB) as filler in cellulose and make biocomposites for packaging applications such as wrappers. Cellulose was dissolved in the environmentally friendly ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). To this solution, WLB was added in amounts of 5 to 25 wt.% of cellulose. The cellulose and cellulose/WLB composite films were prepared by regenerating the corresponding cast solutions in a water coagulation bath followed by washing and drying. These films were tested for their tensile properties, thermal stability, and morphology. The tensile modulus and strength of the composite films were lower than those of the matrix. The lowering of the tensile modulus and strength with increasing WLB loading was attributed to the random orientation of the leather fibers of WLB in the composites. However, the % elongation at break of the composite films was found to be higher than that of the matrix and increased with increasing WLB content. The possible interaction between the matrix and WLB filler was probed using FT-IR analysis. The thermal stability of the composite films was higher than that of the matrix. The increase in thermal stability of the composite films was attributed to cross-linked collagen protein leather fibers in WLB. The fractographs of the composite films indicated good interfacial bonding between cellulose and leather fibers of WLB. These composite films may be considered for packaging and wrapping applications.     

Effect of Chemical Treatment and Fiber Loading on Mechanical Properties of Borassus (Toddy Palm) Fiber/Epoxy Composites

The aim of the present study was to investigate and compare the mechanical properties of untreated and chemically modified Borassus fiber–reinforced epoxy composites. Composites were prepared by the hand lay-up process by reinforcing Borassus fibers with epoxy matrix. To improve the fiber-matrix adhesion properties, alkali (NaOH) and alkali combined with silane (3-aminopropyltriethoxysilane) treatment of the fiber surface was carried out. Examinations through Fourier transform-infrared spectroscopy and scanning electron microscopy (SEM) were conducted to investigate the structural and physical properties of the Borassus fibers. Tensile properties such as modulus and strength of the composites made with chemically modified and untreated Borassus fibers were studied using a universal testing machine. Based on the experimental results, it was found that the tensile properties of the Borassus-reinforced epoxy composites were significantly improved as compared with the neat epoxy. It was also found that the fiber treated with a combination of alkali and silane exhibited superior mechanical properties to alkali-treated and untreated fiber composites. The nature of the fiber/matrix interface was examined through SEM of cryo-fractured samples. Chemical resistance of composites was also found to be improved with chemically modified fiber composites.