Direct measurement of the group refractive index of air with interferometry between adjacent femtosecond pulses

The group refractive index of air in laboratory conditions is measured directly between adjacent femtosecond laser pulses by a new interferometry technique. Measurement of the repetition rate of the mode-locked pulse train that gives the maximum amplitude of the interference-signal envelope enables us to determine the group refractive index of air within a standard deviation of 2 x 10(-7). This simple method without vacuum reference is attractive for measuring the group refractive index needed for precise distance measurements in open fields.     

Variable reflectance vertical cavity surface emitting lasers

Singlemode operation in 850 nm vertical cavity surface emitting lasers is reported. The singlemode behaviour results from a radially-varying number of periods in the top distributed Bragg reflector mirror. At the centre of the device there are six additional quarter-wave layers (three periods) as compared to the edge. This provides higher mirror reflectivity to the fundamental mode without adding loss. Thus the top mirror geometry promotes singlemode operation of the laser from threshold to rollover     

Diamond Synthesis from Graphite in the Presence of MnCO3

In order to investigate the catalytic effect of MnCO₃, a typical transition-metal carbonate, a graphite and MnCO₃ (60:40 by weight) mixture was subjected to temperature and pressure ranges of 6.5–7.7 GPa and 1700°–2100°C, respectively. Diamonds were synthesized from graphite in the presence of MnCO₃, at 2000°C and 7.7 GPa, where MnCO₃ was confirmed to be in a molten state. Although MnO was found to be decomposed from the samples that were subjected to the aforementioned PT conditions, no diamond formation was detected from an MnO and graphite system for identical experimental conditions. Therefore, it was concluded that MnCO₃ solvent catalyzed diamond formation from graphite.     

Cell removal with supercritical carbon dioxide for acellular artificial tissue

BACKGROUND: The objective of this work was to decellularize artificial tissue without using surfactant solutions. For this purpose, supercritical carbon dioxide was used as the extraction medium. RESULTS: Supercritical carbon dioxide containing a small amount of entrainer was a suitable medium to extract both cell nuclei and cell membranes from artificial tissue. Under gentle extraction conditions (15 MPa, 37 °C), cell nuclei were satisfactorily extracted from tissue within 1 h. In contrast, the efficiency of phospholipid removal depended strongly on the transfer rate of carbon dioxide in the interior of the tissue. Mechanical strength of tissue was not decreased even with prolonged treatment. CONCLUSION: Acellular artificial tissues could be prepared quickly by treatment with a carbon dioxide/entrainer system. The prepared acellular tissue could be obtained in absolutely dry condition. This is advantageous from the viewpoint of long‐term preservation without putrefaction and contamination. Copyright © 2008 Society of Chemical Industry     

Telomerase activity in neuroblastoma: is it a prognostic indicator of clinical behaviour?

Neuroblastomas show remarkable biological heterogeneity, resulting in favourable prognosis or unfavourable prognosis due to aggressive growth despite multimodal therapy. Recently, we proposed that aggressive tumours express telomerase at a high level while the favourable tumours lack or have low telomerase expression. To evaluate the correlation between telomerase activity and other biological characteristics reported as prognostic markers (MYCN gene amplification, loss of heterogeneity (LOH) in the short arm of chromosome 1, trk-A expression, Ha-ras p21 expression, and DNA ploidy), we investigated these biological features in 105 untreated neuroblastomas. In these cases, 23 showed high telomerase activity, 78 showed low activity, and telomerase activity was undetectable in 4 cases. Most tumours with genetic alterations (MYCN amplification or 1p32 LOH) showed high telomerase activity. Most tumours with low or undetectable activity were aneuploid, and showed trk-A and Ha-ras expression. Three of the four tumours with undetectable telomerase activity regressed. In 2 of the tumours with low telomerase activity, the residual tumours maturated and showed repression of telomerase activity. Thus, the level of telomerase activity correlated with other genetic alterations and/or gene expression and may be a useful prognostic indicator in neuroblastoma.     

Charge-induced self-feedback optical bistable device: switchingtime and spatial resolution

We report extensive experimental and theoretical studies on the properties of an optical bistable device called the charge-induced self-feedback device (CSFD) which is a variation of a self electro-optic effect device (SEED). In the mechanism, a novelty: of the CSFD consists of the feedback due to field-screening, resulting in independent switchings of optical beams focused at different spots on the CSFD without the help of pixellated structures. We experimentally demonstrate independent switchings without pixellation. In addition, a spatial resolution of the CSFD on such a device operation is found to be limited by an in-plane spreading of photoexcited carriers enhanced by a lateral electric-field induced by photoexcitation. Also, it is experimentally demonstrated that shortening carrier escape times leads to an improvement on the spatial resolution in terms of the suppression of the in-plane carrier spreading. Furthermore, an investigation on dynamics of the photoexcited carriers in the device reveals that the switching time of the CSPD is on the order of nanosecond, limited mainly by the hole escape time     

Comparison of four serological tests to determine the CagA or VacA status of Helicobacter pylori strains

We compared four tests for antibodies to CagA or VacA, HelicoBlot 2. 0, RIDA Blot Helicobacter, CHIRON RIBA H. pylori SIA, and an enzyme-linked immunosorbent assay using recombinant CagA. Immunoblot assays were accurate for determining Helicobacter pylori status but poor for determining CagA or VacA status (accuracy, 66 to 80% for CagA status and 34 to 67% for VacA status). None can be recommended for determining CagA or VacA status.     

Ultraviolet B exposure and type of lens opacity in ophthalmic patients in Japan

Over the course of an individual's lifetime, lens fiber cells proliferate and differentiate to form various parts of the lens. The specific pathogenic effects of ultraviolet B radiation (UVB), one of the major causes of cataracts, may differ depending upon the particular part of the lens. In this study, the association of UVB exposure with specific types of lens opacity was investigated in relation to lifetime cumulative exposure, and was confirmed by subjects' ages at exposure. The severity of lens opacities was assessed by slit lamp examination after pupil dilatation. Information on UVB exposure based on place of residence and average hours spent outdoors per day was obtained by interview for several age ranges of exposure. The effects of UVB exposure on cortical and nuclear opacities for both sexes were evaluated using logistic regression analysis. The severity of opacities was found to increase with UVB exposure. In particular, lifetime cumulative UVB exposure and exposure after the teenage years correlated with the presence of nuclear opacities in females. The results indicate that the effect of UVB exposure is greater for nuclear than for cortical opacities. This is in agreement with the proposed type-specific mechanism for lens opacities caused by UVB exposure.     

Characteristics of germanium avalanche photodiodes in the wavelength region of 1-1.6 µm

Dark current, quantum efficiency, multiplication noise, and pulse response of germanium avalanche photodiodes with n+-p junction were studied to find an optimum structure. The dark current can be separated by graphical means into a leakage current component and a multiplied component which flows through the junction. The dark current components are also evaluated by using diodes with various diameters. The quantum efficiency and the multiplication noise are shown to be strongly affected by the n+ layer thickness. An n+ layer thickness optimized for signal-to-noise ratio is estimated from experimental and calculated results, using a figure of merit for avalanche photodiodes. The response waveform for mode-locked Nd:YAG laser shows a rise time of 100 ps and a half pulsewidth of less than 200 ps.