Linear stability of non-parallel flow in the entrance region of ducts

An investigation is made of the linear stability of the developing flow of an incompressible fluid in the entrance region of annular ducts, circular tubes, and parallel-plate channels. Small axisymmetric disturbances for annular duct and tube flows and small two-dimensional disturbances for channel flow are considered in the analysis. In formulating the stability problems, account is taken of the transverse velocity component of the mainflow. This results in the modified Orr-Sommerfeld equations, one for annular duct and tube flows and the other for channel flow. The mainflow velocity fields utilized in the stability analysis are those from the solutions of the linearized momentum equations. The governing equation for the disturbances and the boundary conditions for each of the flow configurations constitute an eigenvalue problem. The eigenvalue problems for the annular duct and circular tube flows are solved by a fourth order Runge-Kutta integration scheme along with a differential correction iteration technique. An orthonormalization process is used to remove the parasitic error inherent in the numerical integration of the disturbance equations. For flow in the parallel-plate channels, the eigenvalue problem is solved by a finite difference method and the differential correction iteration scheme is employed to obtain the eigenvalues. Neutral stability characteristics and critical Reynolds numbers at various axial locations are obtained for the developing flow in the annular ducts with radius ratios of 2.0 and 3.33, in the circular tubes, and in the parallel-plate channels, using the modified Orr-Sommerfeld equations. These stability results for the annular duct flow are also computed using the conventional Orr-Sommerfeld equation. Representative eigenfunctions are also presented for the annular duct flow. Comparisons of the results from the modified Orr-Sommerfeld equations are made with those from the conventional equations for all three flow configurations. The main findings of the present study are: (1) laminar flow in the entrance region of annular ducts, circular tubes, and parallel-plate channels is unstable to small axisymmetric or two-dimensional disturbances; (2) the critical Reynolds number for the developing flow in the annular ducts and parallel-plate channels decreases monotonically as the axial distance increases; (3) the flow in the annular ducts becomes more stable as the ratio of the outer to inner radius increases; (4) the minimum critical Reynolds numbers for annular duct flow occur in the fully developed flow region and have the values of 9720 and 40530, respectively, for radius ratios of 2.0 and 3.33; (5) the minimum critical Reynolds number for tube flow is about 19780 and occurs in the entrance region; (6) the modified Orr-Sommerfeld equation provides critical Reynolds numbers that differ somewhat from those obtained from the conventional equation; and (7) the effect of non-parallelism of the mainflow (that is, the effect of the mainflow transverse velocity) on the stability characteristics of the developing flow in ducts is of significance only in the range of small Reynolds numbers --Abstract, pages ii-iv

Optimization of ultrafine entanglement witnesses

The ultrafine entanglement witness, introduced in [F. Shahandeh, M. Ringbauer, J.C. Loredo, and T.C. Ralph, Phys. Rev. Lett. \textbf{118}, 110502 (2017)], can seamlessly and easily improve any standard entanglement witness. In this paper, by combining the constraint and the test operators, we rotate the hyperplane determined by the test operator and improve further the original ultrafine entanglement witness. In particular, we present a series of new ultrafine entanglement witnesses, which not only can detect entangled states that the original ultrafine entanglement witnesses cannot detect, but also have the merits that the original ultrafine entanglement witnesses have.Comment: 8 page

A 160-Gb/s OTDM demultiplexer based on parametric wavelength exchange

Parametric wavelength exchange (PWE) has been demonstrated as a versatile device in providing different functionalities. In this paper, we will concentrate, numerically and experimentally, on one of these functionalities, namely, all-optical time demultiplexing of 160-Gb/s return-to-zero (RZ) signals based on a pulsed-pump PWE in a 400 m highly nonlinear dispersion-shifted fiber. Experimental results show power penalties < 2.7 dB at bit-error rate of 10-9 for all demultiplexed 10-Gb/s RZ signals. We also derive theoretical expressions for the conversion/residual efficiencies and investigate the impact of pump pulse width and phase mismatch on these efficiencies. Furthermore, the impacts of pulsed-pump wavelength and power level on the characteristics of the switching window are investigated numerically. As a result, the demultiplexer can be easily upgraded to an add-drop multiplexer because of the complete exchange nature of PWE, which is justified by the surviving channels' waveform performance. © 2009 IEEE.published_or_final_versio

Optical time-slot swapping based on parametric wavelength exchange

Proceedings of SPIE - The International Society for Optical Engineering (ISSN 0277786X), 2009, v. 7630, art. no. 763002We have experimentally demonstrated simultaneous 10-Gb/s optical time-slot swapping between return-to-zero (RZ) signal format and non-return-to-zero (NRZ) signal format based on the parametric wavelength exchange (PWE) in the highly-nonlinear dispersion shifted fiber (HNL-DSF). Original RZ and NRZ signals located at two different wavelengths are exchanged after the PWE process. After exchanging between RZ and NRZ signals, the swapping ability involving two different signal formats within particular time slot has been proved. Clear open eye diagrams of periodic mixed RZ and NRZ signals are recorded on both wavelengths. © 2009 SPIE-OSA-IEEE.published_or_final_versio

Byte-level parametric wavelength exchange for narrow pulsewidth return-to-zero signal

We investigate the feasibility of switching return-to-zero signals with 3-ps pulsewidth by byte-level parametric wavelength exchange (PWE) numerically and experimentally. Square-wave modulated pumps are used in PWE for pump gating. Simultaneous bit swapping for two signals at the same time slot is achieved. Error-free operation is achieved for both signal channels with ≈3.5-dB power penalty at 10-9 bit-error rate. © 2009 IEEE.published_or_final_versio

The impact of dispersion fluctuation on the optimization of parametric wavelength exchange

The optimized parameters of wavelength exchange vary from fiber to fiber due to zero-dispersion wavelength fluctuation. This problem can be solved by reducing wavelength separation between signal and idler at the expense of reduced tunability. © 2009 IEEE.published_or_final_versio

Performance of parametric wavelength exchange for narrow pulse width return-to-zero signal

Paper 1.1.6We demonstrate the parametric wavelength exchange for 10-Gb/s RZ and NRZ signals. The narrow pulse width of the exchanged RZ signal indicates that CW or quasi-CW pumps are capable of handling with ultrahigh-speed signal processing. © VDE VERLAG GMBH.published_or_final_versio

Automatic Video Self Modeling for Voice Disorder

Video self modeling (VSM) is a behavioral intervention technique in which a learner models a target behavior by watching a video of him- or herself. In the field of speech language pathology, the approach of VSM has been successfully used for treatment of language in children with Autism and in individuals with fluency disorder of stuttering. Technical challenges remain in creating VSM contents that depict previously unseen behaviors. In this paper, we propose a novel system that synthesizes new video sequences for VSM treatment of patients with voice disorders. Starting with a video recording of a voice-disorder patient, the proposed system replaces the coarse speech with a clean, healthier speech that bears resemblance to the patient’s original voice. The replacement speech is synthesized using either a text-to-speech engine or selecting from a database of clean speeches based on a voice similarity metric. To realign the replacement speech with the original video, a novel audiovisual algorithm that combines audio segmentation with lip-state detection is proposed to identify corresponding time markers in the audio and video tracks. Lip synchronization is then accomplished by using an adaptive video re-sampling scheme that minimizes the amount of motion jitter and preserves the spatial sharpness. Results of both objective measurements and subjective evaluations on a dataset with 31 subjects demonstrate the effectiveness of the proposed techniques

Fiber Optical Tweezers for Applying and Measuring Forces in a 3D Solid Compartment

We developed an inclined dual fiber optical tweezers (DFOTs) for simultaneous force application and measurements in a 3D hydrogel matrix. The inclined DFOTs provide a potential solution for cell mechanics study in a three-dimensional matrix