Phase-dispersion optical tomography

We report on phase-dispersion optical tomography, a new imaging technique based on phase measurements using low-coherence interferometry. The technique simultaneously probes the target with fundamental and second-harmonic light and interferometrically measures the relative phase shift of the backscattered light fields. This phase change can arise either from reflection at an interface within a sample or from bulk refraction. We show that this highly sensitive 5 phase technique can complement optical coherence tomography, which measures electric field amplitude, by revealing otherwise undetectable dispersive variations in the sample

Measurement of angular distributions by use of low-coherence interferometry for light-scattering spectroscopy

We present a novel interferometer for measuring angular distributions of backscattered light. The new system exploits a low-coherence source in a modified Michelson interferometer to provide depth resolution, as in optical coherence tomography, but includes an imaging system that permits the angle of the reference field to be varied in the detector plane by simple translation of an optical element. We employ this system to examine the angular distribution of light scattered by polystyrene microspheres. The measured data indicate that size information can be recovered from angular-scattering distributions and that the coherence length of the source influences the applicability of Mie theory

Cavity ring-down technique and its application to the measurement of ultraslow velocities

We have developed a new ring-down technique that does not require a shutter to turn a probe laser on and off. With a rapid cavity scan we can measure a simple exponential cavity decay from which a cavity finesse can be found. When the cavity is scanned slowly, the cavity decay exhibits an amplitude modulation, and an analytic expression is derived for this modulation. With this new technique we measured the ultraslow relative velocity of the mirrors (of the order of micrometers per second) as well as the linewidth (~100 kHz) of the probe laser

Efficient dynamical downscaling of general circulation models using continuous data assimilation

Continuous data assimilation (CDA) is successfully implemented for the first time for efficient dynamical downscaling of a global atmospheric reanalysis. A comparison of the performance of CDA with the standard grid and spectral nudging techniques for representing long- and short-scale features in the downscaled fields using the Weather Research and Forecast (WRF) model is further presented and analyzed. The WRF model is configured at 25km horizontal resolution and is driven by 250km initial and boundary conditions from NCEP/NCAR reanalysis fields. Downscaling experiments are performed over a one-month period in January, 2016. The similarity metric is used to evaluate the performance of the downscaling methods for large and small scales. Similarity results are compared for the outputs of the WRF model with different downscaling techniques, NCEP reanalysis, and Final Analysis. Both spectral nudging and CDA describe better the small-scale features compared to grid nudging. The choice of the wave number is critical in spectral nudging; increasing the number of retained frequencies generally produced better small-scale features, but only up to a certain threshold after which its solution gradually became closer to grid nudging. CDA maintains the balance of the large- and small-scale features similar to that of the best simulation achieved by the best spectral nudging configuration, without the need of a spectral decomposition. The different downscaled atmospheric variables, including rainfall distribution, with CDA is most consistent with the observations. The Brier skill score values further indicate that the added value of CDA is distributed over the entire model domain. The overall results clearly suggest that CDA provides an efficient new approach for dynamical downscaling by maintaining better balance between the global model and the downscaled fields

Spatial coherence of forward-scattered light in a turbid medium

We study spatially coherent forward-scattered light propagating in a turbid medium of moderate optical depth (0-9 mean free paths). Coherent detection was achieved by using a tilted heterodyne geometry, which desensitizes coherent detection of the attenuated incident light. We show that the degree of spatial coherence is significantly higher for light scattered only once in comparison with that for multiply scattered light and that it approaches a small constant value for large numbers of scattering events

EFFECT OF TOCOTRIENOL PRETREATMENT ON EX VIVO SUPEROXIDE AND PEROXIDE HANDLING CAPACITIES (SPHC) OF RAT SERUM AND BRAIN

Objective: Tocotrienol (TT), a constituent of vitamin E, present only in selected seed oil. Because of the isoprenoid side chain, antioxidant property of tocotrienol is recently highlighted. Application of tocotrienol is also proven to be neuroprotective. The current study was aimed to evaluate the effect of tocotrienol pretreatment on the serum and brain oxidative stress parameters and oxidant handling capacities.Methods: Male albino Wistar rats were treated with tocotrienol (10 mg/day) for two weeks and maintained for the next four weeks. Levels of reduced glutathione and lipid peroxidation and activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase were estimated fortnightly in serum. After sacrifice, oxidative stress parameters were measured in the frontal cortex, temporal cortex, thalamic area, hippocampus and cerebellum. Glutathione-dependent and glutathione-independent superoxide and peroxide handling capacities (SPHC) were calculated for serum and brain regions. Data collected from both the groups are statistically processed with Kruskal-Wallis test and Mann-Whitney pairwise comparisons.Results: Significant impacts of TT treatment have been observed in terms of growth and water intake. Serum SPHC (Glutathione-independent) has been found to be reduced significantly immediately after the TT treatment. Region-specific alterations in oxidative stress parameters have also been observed after 4 w of supplementation. Global reductions in reduced glutathione and lipid peroxidation have been observed in the brain without any alteration in the SPHC.Conclusion: From the results, it can be suggested that the tocotrienol pretreatment possibly be used as neuroprotective measure particularly against oxidative stress. In addition, the antioxidant impacts of TT were found to be maintained for a longer period in brain regions, even though it was not so in the case of serum