Monte Carlo simulation of a LSC based on stacked layers of fiber arrays with core-coating different absorbing properties.

In this work, a Monte Carlo ray-tracing model for the simulation and optimization of a fiber Luminescent Solar Concentrator (LSC) based on stacked layers of fiber arrays is developed and validated. The fiber LSC efficiency improvements are compared against a conventional planar LSC. We developed a new model to analyze the performance of different configurations of bulk-doped fibers and fibers constituted by a doped coating and a passive core. These configurations are analyzed also varying fiber packing geometry diameters, and length. Due to the exceptionally low absorption coefficient of the silica fibers (αwg ≈ 10-4 cm-1), concentration factors of up to 1.9 are predicted when dimensions are scaled over 1 m2, which improve more than twice the maximum concentration factor ever reported. These results serve as a preliminary theoretical study for the future development of a new LSC design based on flexible silica micro-fibers coated with Si-QDs doped poly(lauryl methacrylate) (PLMA) layers.

Three-dimensional Fourier transform evaluation of sequences of spatially and temporally modulated speckle interferograms.

Phase evaluation methods based on the 2D spatial Fourier transform of a speckle interferogram with spatial carrier usually assume that the Fourier spectrum of the interferogram has a trimodal distribution, i. e. that the side lobes corresponding to the interferential terms do not overlap the other two spectral terms, which are related to the intensity of the object and reference beams, respectively. Otherwise, part of the spectrum of the object beam is inside the inverse-transform window of the selected interference lobe and induces an error in the resultant phase map. We present a technique for the acquisition and processing of speckle interferogram sequences that separates the interference lobes from the other spectral terms when the aforementioned assumption does not apply and regardless of the temporal bandwidth of the phase signal. It requires the recording of a sequence of interferograms with spatial and temporal carriers, and their processing with a 3D Fourier transform. In the resultant 3D spectrum, the spatial and temporal carriers separate the conjugate interferential terms from each other and from the term related to the object beam. Experimental corroboration is provided through the measurement of the amplitude of surface acoustic waves in plates with a double-pulsed TV holography setup. The results obtained with the proposed method are compared to those obtained with the processing of individual interferograms with the regular spatial-carrier 2D Fourier transform method.

Does complexity relate to compensation? A comparison of relative value units in initial versus recurrent inguinal hernia repair.

PURPOSE: Work relative value units (wRVUs) can be used as a compensation model based on the effort required for providing a service and helps to determine adequate compensation for physicians. Thus, more complex surgical procedures that require greater technical skills and time should yield greater compensation. There are limited data comparing wRVUs and operative times within common general surgery procedures such as inguinal hernia repair. This study aims to compare mean operative times and wRVUs per minute between primary and recurrent inguinal hernia repairs, the latter being considered as a more difficult procedure to perform. METHODS: A retrospective analysis of the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database was performed to identify all patients undergoing primary inguinal hernia repair and recurrent inguinal hernia repair by general surgeons over a 6-year period (2012-2017). Calculation and comparison of mean operative times, wRVUs, and wRVU per minute were performed. RESULTS: A total of 134,391 patients were included in the analysis. 121,235 underwent primary inguinal repair and 13,156 patients underwent repair of recurrent inguinal hernia. Patients were distributed within open/reducible, open/incarcerated and laparoscopy groups. Mean operative time and RVUs were greater for recurrent inguinal procedures (p < 0.0001). Consistently, RVU per minute was also found to be higher for recurrent procedures within the different groups analyzed. CONCLUSION: Appropriately, general surgeons are reimbursed at a higher rate per minute in recurrent cases, regardless of the technique used.

Annulling parasitic fringes in real time holographic interferometry: a new method.

A method for annulling parasitic fringes in real time holographicin terferometrya nd its theoreticalj ustification is presented. The main advantage relates to cancellation of nondesired object motions or deformations with experimental simplicity.

Study of transient deformations with pulsed TV holography: application to crack detection.

We report the measurement of reproducible transient deformations with single-pulsed-subtraction and double-pulsed-addition TV holography with both in-plane and out-of-plane optical configurations. An original synchronization system (controlling mechanical excitation of the object, firing the laser pulses, and image acquisition) used to obtain the subtraction and the addition correlation fringes is described. Experimental results are presented for the propagation of mechanical shock waves in a cantilever specimen and their subsequent diffraction by a crack in the specimen. These preliminary results show that the technique may be used for crack detection.

Enhancing the sensitivity to small phase changes in double-exposure stroboscopic television holography.

We present a new technique for enhancing the sensitivity of double-exposure stroboscopic television holography (TVH) to detect and measure vibrations of small amplitude. The technique is based in the modulation of the phase of the reference beam in synchronism with the vibration of the measurand and derives from a former technique that we originally contrived for phase evaluation. We propose two variants, characterized by the demodulation process used to generate the secondary correlograms, with different behaviors in terms of the sensitivity to the sign of the measurand and of the ease in detecting the presence and shape of the vibration. We have implemented this new technique in an electronic speckle-pattern interferometer and compared its performance with standard TVH techniques; vibrations with amplitudes as small as 8 nm have been observed with this setup.

Fizeau phase-measuring interferometry using the moiré effect.

The automation of the fringe pattern analysis in Fizeau interferometry combining the moiré effect with the phase-stepping evaluation method is presented. In this case the phase modulator is a Ronchi grid placed at the interferometer image plane yielding a moiré image, and the necessary phase steps are obtained, simply translating the grid in its own plane, perpendicular to the optical axis. A detailed description of the moiré image formation as an incoherent superposition is developed. Measurements were carried out in a Fizeau interferometer built by the authors, and rms repeatabilities of less than 3 deg in the phase-difference values were attained.

Phase error calculation in a Fizeau interferometer by Fourier expansion of the intensity profile.

The spectrum of the intensity profile of multiple-beam Fizeau interferograms is presented. Knowledge of this spectrum provides valuable information about the characteristics of Fizeau interferograms, allowing one to calculate the phase error when the Fizeau profile is evaluated by means of two-beam phase-stepping algorithms, as is usual for low-reflectivity coefficients.

Multiplicative moiré two-beam phase-stepping and fourier-transform methods for the evaluation of multiple-beam fizeau patterns: a comparison.

A phase-evaluation method of multiple-beam Fizeau patterns that combines two-beam phase-stepping algorithms with the moiré effect was previously reported [Appl. Opt. 34, 3639-3643(1995)]. The method is based on a multiplicative moiréimage-formation process obtained by the direct superposition of high-frequency multiple-beam Fizeau carrier fringes upon a transmission grating (working as a phase modulator). We present a comparison between this multiplicative moiré two-beam phase-stepping method and the well-known Fourier-transform method for the topographic measurement of an undoped silicon wafer. The discrepancy between the two methods yields a rms phase-difference value of the order of(~2pi/90).

Transient Deformation Measurement by Double-Pulsed-Subtraction TV Holography and the Fourier Transform Method.

We report the measurement of transient bending waves with double-pulsed-subtraction TV holography. The correlation fringe patterns are automatically quantitatively analyzed by the application of Fourier methods. A novel optical setup with two different object-beam optical paths is demonstrated for the generation of carrier fringes. The proposed system is highly immune to environmental disturbances because the optical setup imposes no lower limit on the time separation between laser pulses. One removes the linear phase distribution due to the spatial carrier in the spatial domain by subtracting the phase of the undeformed carrier fringes from the phase of the modulated fringes. Experimental results obtained with an aluminum plate excited by the impact of a piezoelectric translator are presented.

Measurement range analysis in moiré evaluation Fizeau interferometry.

Fizeau interferograms are evaluated by two-beam phase-stepping algorithms. The sinusoidal intensity profile pattern needed for the application of these algorithms is obtained by low-pass filtering the moiré pattern provided by the superposition of the interferogram onto a Ronchi grid. The phase modulation is performed by the in-plane displacement of the grid by means of a motorized stage. In this research the measurement range of the evaluation method as a function of the maximum derivative of height surfaces is calculated. A spherical surface is measured in different configurations in order to verify the obtained results.