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At least 55 records · Page 3Linked to original sources
PubMed2005

Spiral patterns, spiral breakup, and zigzag spirals in an optical device.

Above the first lasing threshold the degenerate optical parametric oscillator with saturable absorber displays successive Hopf and Turing instabilities. Various spiral patterns and defect turbulent patterns are numerically observed on the light intensity profiles. Close to the Hopf threshold, a normal form is derived which leads to a complex Ginzburg-Landau equation where a bi-Laplacian instead of a Laplacian drives the formation of spirals. At resonance the predictions of the normal form are compared with the numerical observations of the full equations. Above the Hopf threshold, the spirals destabilize, breaking into slowly evolving patterns with small spirals and filaments. Further above the threshold, when both the Turing and Hopf bifurcations interplay, a new spiral pattern emerges, with large notched arms.

Journal Article↗
PubMedDate not supplied

New method for the detection of thrombus formation in cardiovascular devices: optical sensor evaluation in a flow chamber model.

We proposed a new method of detecting the onset of thrombus formation based upon the backscattered light intensity changes caused by the alteration of blood flow behavior in the cardiopulmonary devices. In an optical senor based upon the First Order Scattering theory, the relationship between the backscattered light intensity and hematocrit exhibited a monotonically decaying curve for the hematocrit level greater than 45%. To distinguish the effect either by thrombus formation or erythrocyte aggregation on the back-scattered light intensity with a flow chamber connected to a rabbit arterial-venous bypass model, we generated an oscillatory flow using a roller pump and analyzed the results using a Fast Fourier Transform (FFT) method. Our hypothesis was that the nonclotting blood flow would yield an unchanged fundamental spectral power density of the oscillation frequency generated by a roller pump, whereas the thrombus formation would attenuate its power. We measured the back-scattered light intensity in the flow chamber of high shear region and low shear region (n = 5). The blood flow rate was 40 ml/min with the roller pump. The activated clotting time and the hematocrit level were adjusted to 170 +/- 10 s with heparin and 35 +/- 5% with a phosphate buffered sulfate solution, respectively. As a result, the backscattered light intensity from the low shear rate region gradually diminished with time (p < 0.05; 0-5 minutes vs. more than 10-15 minutes), whereas that from the high shear rate region remained fairly constant. The experimental finding supported the hypothesis that the decrease of the backscattered light intensity and diminished spectral power density were caused by the aggregation or clotting erythrocytes. In conclusion, we found that the measurement of the average backscattered light intensity level together with FFT analysis of the backscattered light from the flowing blood is a valuable approach in detecting the onset of thrombus formation.

Animals↗
PubMed2000

A ten channel fibre-optic device for distributed sensing of underground hydrocarbon leakage.

With millions of fuel storage tanks and oil pipelines installed around the world, there is inevitably frequent leakage of potentially hazardous hydrocarbons. As many of these installations are below ground, it can often be many years before the extent of the leak is discovered. We have previously reported the development of a sensor for the detection of such subterranean leaks, using infrared reflectometry to interrogate a hydrocarbon sensitive membrane. However, a single sensor cannot provide any information about the flow rate or direction of the leak. This paper describes the extension of the technology to a multi-channel distributed sensing system, using optical fibres capable of distributing the sensors over large subterranean areas. Results are reported from the evaluation of the device, which consisted of monitoring the movement of different hydrocarbons (gasoline, diesel and insulating oil) through a vertical sand-filled vessel.

Environmental Monitoring↗
PubMed2003

Medical devices; exemption from premarket notification; Class II devices; optical impression systems for computer assisted design and manufacturing. Final rule.

The Food and Drug Administration (FDA) is publishing an order granting a petition requesting exemption from the premarket notification requirements for data acquisition units for ceramic dental restoration systems. This rule exempts from premarket notification data acquisition units for ceramic dental restoration systems and establishes a guidance document as a special control for this device. FDA is publishing this order in accordance with the Food and Drug Administration Modernization Act of 1997 (FDAMA).

Computer-Aided Design↗
PubMed2003

Optimized staircase profiles for diffractive optical devices made from absorbing materials.

We report on the optimization of staircase grating profiles for the case of absorbing grating materials. Using a simple numerical algorithm, we determined the grating parameters, maximizing the first-order diffraction efficiency for different numbers of staircase steps. The results show that there is a significant difference between the staircase profiles for nonnegligible and negligible absorption. The obtained solutions are of importance for diffractive optics in the soft-x-ray and extreme-ultraviolet ranges.

Journal Article↗
PubMed2006

Enhanced anisotropy in Paratellurite for inhomogeneous waves and its possible importance in the future development of acousto-optic devices.

The anisotropic feature of most crystals, involves a direction dependent wave velocity for each of the possible modes. Paratellurite (Tellurium dioxide) is extraordinary because, for one of the propagation modes, i.e. the quasi shear horizontal (QSH) mode, the anisotropy is exceptional. This results, on the one hand in a very strong directional dependent sound velocity and on the other hand, in a low wave velocity in certain directions, resulting in a high figure of merit for the acousto-optical interaction. In the case of inhomogeneous waves, the slowness surfaces change their shape and magnitude, for all crystals. However, for paratellurite, this effect is again extraordinary. As soon as a relatively small inhomogeneity is considered, the sound velocity for the QSH mode becomes really exceptionally anisotropic, resulting in a slowness surface that is almost spherical, covered by pins. The velocity corresponding to those 'pins', is much lower than in the case of homogeneous plane waves, which is very promising for the future development of acousto-optic cells involving an even higher figure of merit.

Journal Article↗
PubMed2002

A new non-contact optical device for ocular biometry.

BACKGROUND: A new commercially available device (IOLMaster, Zeiss Instruments) provides high resolution non-contact measurements of axial length (using partial coherent interferometry), anterior chamber depth, and corneal radius (using image analysis). The study evaluates the validity and repeatability of these measurements and compares the findings with those obtained from instrumentation currently used in clinical practice. METHOD: Measurements were taken on 52 subjects (104 eyes) aged 18-40 years with a range of mean spherical refractive error from +7.0 D to -9.50 D. IOLMaster measurements of anterior chamber depth and axial length were compared with A-scan applanation ultrasonography (Storz Omega) and those for corneal radius with a Javal-Schiötz keratometer (Topcon) and an EyeSys corneal videokeratoscope. RESULTS: Axial length: the difference between IOLMaster and ultrasound measures was insignificant (0.02 (SD 0.32) mm, p = 0.47) with no bias across the range sampled (22.40-27.99 mm). Anterior chamber depth: significantly shorter depths than ultrasound were found with the IOLMaster (-0.06 (0.25) mm, p <0.02) with no bias across the range sampled (2.85-4.40 mm). Corneal radius: IOLMaster measurements matched more closely those of the keratometer than those of the videokeratoscope (mean difference -0.03 v -0.06 mm respectively), but were more variable (95% confidence 0.13 v 0.07 mm). The repeatability of all the above IOLMaster biometric measures was found to be of a high order with no significant bias across the measurement ranges sampled. CONCLUSIONS: The validity and repeatability of measurements provided by the IOLMaster will augment future studies in ocular biometry.

Adult↗
PubMed2003

Polarization state fixer composed of passive optical devices.

We investigate a polarization state fixer that produces light with an arbitrary desired polarization state and constant power from an arbitrary elliptically polarized input light whose principal polarization axis fluctuates randomly. An example of such a device composed of a quarter-wave plate and a polarizer is proposed, and its characteristics at wavelengths of 633 nm and 1550 nm are demonstrated. We conclude that we cannot obtain a passive device that produces fixed-axis, linearly polarized light with a constant power level from an elliptically polarized light with a varying elliptical parameter.

Journal Article↗
PubMed2006

Dichroic mirror embedded in a submicrometer waveguide for enhanced resonant nonlinear optical devices.

We report the design, fabrication and characterization of novel dichroic mirrors embedded in a tightly confining AlGaAs/Al(x)O(y) waveguide. Reflection at the first-harmonic wavelength as high as 93% is achieved, while high transmission is maintained at the second-harmonic wavelength. The measured cavity spectrum is in excellent agreement with finite-difference time-domain simulations. Such a mirror is essential for achieving resonant enhancement of second-harmonic generation.

Journal Article↗
PubMed2005

Validity of optical device lipometer and bioelectric impedance analysis for body fat assessment in men and women.

The aims of this study were to validate different subcutaneous adipose tissue layers (SAT-layers) measured by lipometer for body fat percentage (BF%) assessment with dual-energy X-ray absorptiometry (DXA) and to compare the validity of lipometer and bioelectrical impedance analysis (BIA). The subjects were 21 male (18-60 years) and 19 female (23-54 years) healthy Estonian volunteers. SAT-layers were measured by lipometer using 15 standardized SAT-layers. Sum of arms, legs and trunk SAT-layers were calculated and compared with arms, legs and trunk fat percentage measured by DXA. BF% was calculated by BIA using the equations of Lukaski et al. and Chumlea et al. for both genders and the equations of Segal et al. for males and Van Loan and Mayclin for females. BF% measured by DXA was significantly higher than calculated by Lukaski et al. and Chumlea et al. in both genders. The correlation was highest between the BF% measured by DXA and using Segal et al. equation in males (r = 0.94) and Van Loan and Mayclin equation in females (r = 0.84). High relationship was observed between BF% measured by DXA and sum of 15 SAT-layers (r = 0.88 in males and r = 0.91 in females). Stepwise multiple regression analysis indicated that two selected SAT-layers explained 85.9% and 86.7% (R2 x 100) of the total variance in BF% measured by DXA in males and females, respectively: [BF% = 1.308 neck + 0.638 hip + 6.971 (males; SEE = 2.59) and BF% = 1.152 hip + 1.797 calf + 12.347 (females; SEE = 3.46)]. In conclusion, lipometer and BIA give a similar mean estimation of BF% when compared with DXA. However, there is a wide range of variance for the upper and lower limits of agreement between the methods, and the methods are not interchangeable. Lipometer seems to be superior to BIA.

Absorptiometry, Photon↗
PubMed1987

[Devic's optic neuromyelitis. 4 cases].

We report 4 cases of neuromyelitis optic (Devic's disease), with 3 to 7 year-follow-up for 3 of them. Most of the data agreed with the previously reported cases: subacute onset, association of optic neuritis and myelitis within several weeks or months, absence of relapse, good prognosis for paraplegia but poor prognosis for visual loss, and effectiveness of corticosteroids on spinal cord involvement in 4 cases. Moreover these 4 cases have revealed the following rare features: unilateral visual disturbance (1 case), total recovery of visual signs (1 case) with only a short period of follow-up, onset during childhood (1 case), onset following an acute lymphocytic meningitis (1 case), and dependency from corticosteroid therapy (2 cases). None of the patients had obvious immunological disturbance. N.M.R. imaging revealed in 2 cases, disseminated demyelinated areas which confirmed neuropathological data from the literature, showing that anatomical lesions could be wider than expected on clinical signs. The poor visual prognosis, the serum inflammatory signs, the epidemiologic data, the high cell and protein levels in C.S.F., and the absence of relapse suggested, in our cases and in most of the previously reported ones, that neuromyelitis optic must be differentiated from multiple sclerosis.

Adrenal Cortex Hormones↗