Photoluminescence properties of CdS and CdMnS quantum dots prepared by a reverse-micelle method

We have investigated photoluminescence properties of CdS and CdMnS quantum dots (QDs) prepared by a reverse-micelle method. Before the surface modification, a broad luminescence band that originates from defects is dominant in CdS QDs. By the modification, the intensity of the band-edge luminescence is remarkably increased. The surface modification also causes drastic changes of decay profiles of the band-edge luminescence. The intensity of Mn2+ luminescence originating from the intra-3d shell transition of Mn2+ is also increased by the surface modification of CdMnS QDs. The decay time of the band-edge luminescence in surface-modified CdMnS QDs is faster than that in CdS QDs, which is due to the energy transfer from excitons to Mn2+.     

Numerical analysis of modal dispersion in graded-index plastic optical fibers

Modal dispersion properties of a fabricated plastic optical fiber are numerically calculated through a finite-element method. The modal index, group delay, impulse response, and output pulse shape are compared with those for the power-law profile plastic optical fiber; the influence of index profile deviations from the power-law profile is described. It is shown that index profile fluctuations in the actual index profile strongly affect the group delays, even though they are relatively small. On the other hand, they have little effect on the modal indices.     

Effects of follicle size and electrolytes and glucose in maturation medium on nuclear maturation and developmental competence of bovine oocytes

The concentrations of electrolytes (Na, K, Cl, Mg and Ca) and glucose in small follicle (SF) follicular fluid (SFF) and large follicle (LF) follicular fluid (LFF) from slaughterhouse-derived ovaries were studied. Oocytes were matured in medium based on synthetic oviductal fluid. The effects of various concentrations of electrolytes (Na, K, Ca and Mg) and glucose in the maturation medium on the progression of nuclear maturation and subsequent development were also studied. K in SFF was significantly greater than that in LFF. The Mg concentration in follicular fluid (FF) is 2.0-2.3 mM, which is greater than the concentration present in medium generally used for culture. The glucose concentration in FF is about 3.5-3.9 mM and rapidly decreases during the preservation of ovaries. LF oocytes resumed nuclear maturation and progressed to the M2 stage significantly faster than those collected from SF oocytes. In addition, more LF oocytes developed to blastocysts than did SF oocytes. Changing the Na/K ratio in the maturation medium from 16 to 24 did not affect either the progression of nuclear maturation or the rate of development. A low concentration of Mg (0.5 mM) combined with a low Ca concentration (0.5 mM) inhibited the rate of development, but did not affect the progression of nuclear maturation. On the other hand, increasing the Mg concentration to 2.0 mM from 0.5 mM hastened the progression of nuclear maturation and improved the rate of blastulation, irrespective of the Ca concentration. The progression of nuclear maturation was faster and the rate of development was greater with 5.56 mM glucose than with 1.5 mM glucose. The difference in time needed to progress to M2 among the experiment was about 2-3 h. Therefore, prolonging the maturation periods from 21 to 24 h did not change the rate of development. Our results show that the concentrations of Mg and glucose in the maturation medium and the follicle size enveloping the oocyte affect the progression of nuclear maturation and subsequent development. The time requirement for oocytes to reach M2 is strongly related to the developmental competence of the oocytes.     

Reducing agents induce microtubule extrusion in demembranated mammalian spermatozoa

To understand the mechanism regulating flagellar bending in spermatozoa, it is important to investigate the regulation of microtubule sliding in the flagellar axoneme. It has been shown that protease treatment following demembranation with Triton X-100 disrupts the connections between microtubules and induces extrusion of microtubules from the flagellar axoneme. This approach enables a direct investigation of the regulation of microtubule sliding; however, the percentage of spermatozoa with protease-induced extrusion was relatively low, probably due to protease digestion of some regulatory motility proteins, as well as proteins connecting the microtubules. In this study, we demonstrate microtubule extrusion in most hamster and mouse demembranated spermatozoa upon treatment with a high concentration of the reducing agents dithiothreitol or 2-mercaptoethanol, without the use of proteases. The extrusion of microtubules occurred when the spermatozoa were treated with concentrations of the reducing agents that were sufficient for the reduction of the disulfide bonds of IgG. These results suggest that the arrangement of the axonemal structures connecting doublet microtubules depends to an important degree on -S-S- bonds. Close observation of the extrusion process using the present method revealed that microtubules were extruded on the same side as that of the curve of the sperm head, and also on the opposite side. Furthermore, we noted that extrusion always started on one side, followed by the other side, but was never initiated on both sides simultaneously.     

Molecular dynamics study on evaporation process of adherent molecules on surface by high temperature gas

Surface degreasing method with premixed flame is proposed as the removal method of adherent impurities on materials. Effects of adherent molecular thickness and surface potential energy on evaporation rate of adherent molecules and molecular evaporationmechanism were investigated and discussed in the present study. Evaporation processes of adherent molecules on surface molecules were simulated by the molecular dynamics method to understand thermal phenomena on evaporation processes of adherent molecules by using high temperature gas like burnt gas. The calculation system was composed of a high temperature gas region, an adherent molecular region and a surface molecular region. Both the thickness of adherent molecules and potential parameters affceted the evaporation rate of adherent molecules and evaporation mechanism in molecular scale.     

Finite-element modal analysis of large-core multimode optical fibers

Plastic optical fibers that are a typical large-core multimode optical fiber support a great number of modes compared with conventional silica-glass multimode optical fibers. So far the WKB method hasbeen used for most of the modal analyses of these fibers because of a great number of guided modes. We describe the accurate eigenmodal analysis of large-core multimode optical fibers with the finite-element method (FEM) and compute the propagation constants of all LP modes. In addition, the FEM has a strong advantage for arbitrary core profiles whereas the WKB method is not suitable fornonmonotonic profiles. To demonstrate the advantage, we apply the FEM to the fiber having sinusoidal fluctuations.     

Penetration of high-intensity Er:YAG laser light emitted by IR hollow optical fibers with sealing caps in water

The penetration depth in water was measured for Er:YAG laser light in a high density relevant to clinical applications. Various types of focusing elements were used to guide the light efficiently. We found that the transmission distance depended strongly on the beam shape in the water. When we used a plano-convex type of focusing cap, the penetration depth was larger than that when a dome- or ball-type cap were used.     

Superheated emulsions as high-energy neutron dosemeters

Superheated emulsions being inexpensive, easy to fabricate, and having tissue equivalent composition make them as one of the popular neutron dosemeters. One more advantage is that they can be made insensitive to gamma rays by the choice of the sensitive liquid. It is observed that the response of commercially available bubble detector to neutron decreases above 20 MeV while its response is roughly flat in the 0.1-15 MeV region. This restricts its application as a dosemeter to high-energy neutrons. The response of bubble detector from Bubble Technology Industries, has been observed by using Pb-breeder for high-energy neutrons from different facilities in Japan. It is observed that 2-3 cm Pb-breeder is effective in increasing the response of the detector to the nominal value. Theoretical calculation using MCNPX code indicates an increase in neutrons in the energy range of 0.1-10 MeV with Pb-breeder. The present work indicates the possibility of using the bubble detector as a dosemeter to high-energy neutron using a Pb-breeder of proper thickness.     

Bioimaging of nitric oxide with fluorescent indicators based on the rhodamine chromophore

Diaminofluoresceins are widely used for detection and imaging of nitric oxide (NO), but for biological applications, they have the disadvantages that the fluorescence of the fluorescein chromophore is pH-sensitive and overlaps the autofluorescence of cells. We have developed a membrane-permeable fluorescent indicator for NO based on the rhodamine chromophore, DAR-4M AM, which can be excited with 550-nm light. The fluorescence quantum yield of the product after reaction with NO is 840 times higher than that of DAR-4M. The detection limit of NO was 7 nM, and the fluorescence showed no pH dependency above pH 4. DAR-4M AM was successfully applied to practical bioimaging of NO produced in bovine aortic endothelial cells.     

Measurement of the Thermal Diffusivity of an Anisotropic Graphite Sheet Using a Laser-Heating AC Calorimetric Method

The thermal diffusivity of a graphite sheet having an extremely high anisotropy has been measured by a laser heating AC calorimetric method in the temperature range from 30 to 350 K. This graphite sheet has characteristics of high thermal diffusivity and high anisotropy, and it is only 100 m thick. Thus, it is difficult to apply the conventional AC technique. Therefore, we propose a simultaneous measurement method for the in-plane and out-of-plane thermal diffusivities, by analyzing the three-dimensional heat conduction process, which contains the effects of anisotropy and thermal wave reflections. This method was verified by checking with thermal diffusivity measurements of isotropic materials such as stainless steel and pure copper and was then applied to the anisotropic thermal diffusivity measurement of the graphite sheet.