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Mixed-criticality (MC) scheduling of sequential tasks (with no intra-task parallelism) has been well-explored by the real-time systems community. However, till date, there has been little progress on MC scheduling of parallel tasks. MC scheduling of parallel tasks is highly challenging due to the requirement of various assurances under different criticality levels. In this work, we address the MC scheduling of parallel tasks of gang model that allows workloads to execute on multiple cores simultaneously, as well as the change to degree of parallelism of a task upon a mode switch. It represents an efficient mode-based parallel processing scheme with many potential applications. To schedule such task sets, we propose a new technique GEDF-VD, which integrates Global Earliest Deadline First (GEDF) and Earliest Deadline First with Virtual Deadline (EDF-VD). We prove the correctness of GEDF-VD and provide a detailed quantitative evaluation in terms of speedup bound in both the MC and the non-MC cases. Specifically, we show that GEDF provides a speedup bound of 2 for non-MC gang tasks, while the speedup for GEDF-VD considering MC gang tasks is $$\sqrt{5}+1$$ . Experiments on randomly generated gang task sets are conducted to validate our theoretical findings and to demonstrate the effectiveness of the proposed approach.

The measurement of the volume scattering function (VSF) of suspended particles is an ongoing research topic since it has the potential to provide a rapid, nondestructive means of analyzing hydrosols. Despite the success of scattering theory, the measurement of multidirectional scattering intensity distributions over a wide, continuous range of scattering angles and multiple scattering planes, which is described by a three-dimensional VSF (3D VSF), has proven to be difficult. To measure the 3D VSF of submicron particles suspended in water, a measurement approach is proposed, built and tested with several standard submicron particles with diameters ranging from 60 nm to 1 μm. The experimental results indicate that the proposed setup can obtain an accurate 3D VSF for scattering angles from 21° to 160° and azimuthal angles from 1° to 179°. Comparisons between the experiment and theory show a high level of consistency for particles with diameters less than 200 nm. The variation in the VSF in response to the polarization direction of the incident light is also discussed. Both the experiment and theory show the potential of the device to detect the 3D VSF of marine submicron biological particles.

An optical liquid-level sensor based on a designed light guide plate (LGP) is proposed and experimentally demonstrated. Light transmits between the two surfaces of the LGP as in an optical waveguide. The front surface of the LGP is planar and contacts the liquid, and the back surface is designed with microstructures to uniform the light distribution by scattering. The uniform light intensity that escapes from the LGP abruptly decreases at the liquid level. A linear charge-coupled device (CCD) near the back surface is used to detect the liquid level by detecting the abrupt decrease in the light intensity. The feasibility of the proposed sensor is proved by a ray-tracing simulation and an experiment. The sensor shows high linearity and accuracy with a measurement error of 0.12 mm. The measurement range can be extended flexibly.

Water transportation plays an important role to maintain the sound and rapid economic development in the world. As the number of ships increases rapidly, every busy port need an efficient and intuitive navigation system to pilot the ship in and out of the harbor. A visual navigation system consists of three colors LEDs is proposed for sailing. By optimizing the collimation of high-power LED lamp with a rectangular concentrator and Fresnel lens, it outputs a rectangular light spot with a narrow navigation area. Furthermore, by adopting three color LEDs, the navigation area is divided into three areas in the horizontal direction, where the primary guiding path is the middle one. By navigating a motor boat on an inner lake, the feasibility of this system is demonstrated experimentally. The experimental results show that the colors of the three areas can be easily distinguished as far as 2 km, and the navigation system can assist sailors to adjust the sailing route efficiently even they sail along a complicated route.

Due to the limit of the pixel size of the charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensor, the traditional differential algorithm has a limited measuring accuracy by determining the critical angle in integral pixel. In this paper, we present a practical algorithm based on the centroid value of the reflective ratio around the critical angle pixel to address the traditional differential algorithm problem of determining the critical angle under sub-pixel in a critical angle refractometer (CAR). When the change of refractive index (RI) of a liquid sample is beyond the sensitivity of the traditional differential algorithm, the RI of the liquid can be obtained by using the centroid value of reflectivity around the critical angle pixel. The centroid value is associated with the RI change of the liquid in sub-pixel. Demonstrated by both theoretical analyses and experimental results using saline solutions with RI that changes in sub-pixel tested through the reflective CAR, the algorithm is found to be computationally effective and robust to expand the measuring accuracy of the Abbe-type refractometer in sub-pixel.

A spectral-domain optical coherence tomography (SD-OCT) system with 1555nm center wavelength is tested for stability and accuracy from the micron level to the sub-micron level. The energy centrobaric correction method is used to extract the sub-axial-resolution information as the optical path difference, i.e., the topographic height. We compared the used algorithm with the widely applied phase slope method. The stability of a point scanning OCT system in Michelson style is experimentally compared with that of a system in Fizeau style. Several simple and complicated samples are measured and compared. Finally, we compare the topographic performance of the OCT system with a commercial confocal microscope and white-light interferometer (WLI).

We investigate a systematic improvement for 3D range-gated imaging in scattering environments. Drawbacks including absorption, ambient light, and scattering effect are studied. The former two are compensated through parameter estimation and preprocessing. With regard to the scattering effect, we propose a new 3D reconfiguration algorithm using a Bayesian approach that incorporates spatial constraints through a general Gaussian Markov random field. The model takes both scene depth and albedo into account, which provides a more informative and accurate restoration result. Hyper-parameters for the statistical mechanism are evaluated adaptively in the procedure and an iterated conditional mode optimization algorithm is employed to find an optimum solution. The performance of our method was assessed via conducting various experiments and the results also indicate that the proposed method is helpful for restoring the 2D image of a scene with improved visibility.

Accurate curved line shape object detection is important for assistant Autonomous Underwater Vehicles)AUVs( to complete underwater cable inspection tasks. In this article an algorithm based on adaptive canny's edge detection and an improved random sample consensus (RANSAC) algorithm, called Crossline Correction Non-linear RANSAC (CCNL-RANSAC), is proposed to detect curved line object. The algorithm is featured on adaptive threshold in the canny's operator to improve correctness of edge detection, preliminary check and cross line correction introduced in a nonlinear RANSAC method to locate cables with better success rate and less execution time. Comprehensive underwater cable detection experiments were carried out by a range-gated imaging system in a big water tank. With the proposed CCNL-RANSAC algorithm, we increased success rate to 96% ~99% in line detection for the images of curved cable taken as far as 21 m long in clear water. The average execution time is reduced from 202 ms (using standard RANSAC) to 88 ms on average using CCNL-RANSAC, with 80% time reduction at most. With the help of CCNL-RSNSAC algorithm proposed in the paper, vision based AUVs is able to make auto inspection of curved cables and pipeline underwater, which will make the periodical checking of those marine structures more efficiently.

We have investigated numerically a narrowband near unity mid-infrared absorber based on a periodic array of gold split cross antenna backed by a dielectric spacer and a gold backmirror. We systematically studied the spectral dependence on the antenna parameters and explored the optimized parameters for nanofabrication. The optimized structure has a linewidth of 39 nm at 3.17 µm and the peak absorption is 96.5%. This can be explained in terms of surface lattice resonance of the periodic structure. The investigated structure can be devised as a mid-infrared refractive index sensor. Due to the strong near field enhancement and spectral dependence on the surface dielectric conditions, the narrow linewidth arises from the coupled plasmonic-photonic modes in the structure and has potential applications in plasmonic biosensing.

The critical angle method for refractive index measurement has attracted considerable attention. Precisely obtaining the critical angle is vital to the measurement process. Two advanced algorithms capable of improving the resolution of critical angle refractive index measurement systems are demonstrated. It is experimentally verified that the two algorithms improve the measurement resolution and retain linearity in the entire measurement range. The algorithm analyzes the data near the critical angle to achieve high precision, and this approach provides a notable improvement over the traditional algorithm. We perform verification experiments using liquid samples with low concentration differences, and the RI changes of these samples cannot be identified by traditional algorithms. The proposed algorithm is superior to the traditional method, which yields a resolution of less than 10-5 refractive index unit (RIU). The repeatability test shows that the uncertainty is 10-5 RIU (99.7% confidence).

A novel critical angle refractometer with self-referenced performance (SRCAR) under mechanical vibration and temperature fluctuation is presented. In a traditional CAR, mechanical vibrations and temperature fluctuations always exist and cause errors. To reduce these errors, a CAR is redesigned by introducing a reference glass with a known refractive index so that an exact calibration curve can always be determined, even though intense mechanical vibrations exist. To verify the insensitivity to these vibrations, the refractive index is monitored while the peak acceleration of the vibration is approximately 14 m/s2. The SRCAR is also used to measure a sample under different temperatures to verify the insensitivity to temperature fluctuations. Experimental measurements show that the SRCAR has the ability to lower the influences of vibrations as well as temperature fluctuations and retain a high precision of 2.5×10−4 refractive index units (RIU).

Fixed-priority multiprocessor schedulers are often preferable to dynamic-priority ones because they entail less overhead, are easier to implement, and enable certain tasks to be favored over others. Under global fixed-priority (G-FP) scheduling, as applied to the standard sporadic task model, response times for low-priority tasks may be unbounded, even if the total task system utilization is low. In this paper, it is shown that this negative result can be circumvented if different jobs of the same task are allowed to execute in parallel. In particular, a response-time bound is presented for task systems that allow intra-task parallelism. This bound merely requires that the total utilization does not exceed the overall processing capacity—individual task utilizations need not be further restricted. This result implies that G-FP is optimal for scheduling soft real-time tasks that require bounded tardiness, if intra-task parallelism is allowed.

In order to improve the visual quality to a best possible level for target recognition in turbid water such as river and lake, based on previous works, Maximum a posteriori (MAP) regularization based super-resolution restoration techniques using suitable point spread function (PSF) as prior knowledge are applied for a laser diode (LD) based imaging system operating in turbid water. Objective image quality metrics are used to evaluate the effectiveness of image enhancement and determine the iteration time of the proposed algorithm. Experimental results prove that the proposed method can effectively improve the resolution and quality for LD based imaging in turbid lake water, which shows potential of LD based imaging for detecting objects embedded in turbid media, such as murky water, lake water, river water, and sea water in various applications.

This paper presents a method to focus azimuthally polarized vortex light beam by the combination of a vortex phase plate, a binary-phase optical element (BOE) and a high-numerical aperture (NA) objective lens. Our proposed method achieves a smaller spot size than other polarized beams under the same condition. Compared to the system with the annular aperture, the minimum of full width at half-maximum is improved to 0.259λ and the energy conversion efficiency is higher in the proposed method when FWHM

Digital correlators play a significant role in dynamic light scattering (DLS) technology, which characterizes particle size distribution. We present a field programmable gate array (FPGA)-based digital correlator that can be applied to process DLS data. To satisfy the DLS requirements in the FPGA logic with limited resources, a multiple lag time period (multi-{\tau} ) method is employed that does not require storing the full data set in memory. Moreover, the device directly accepts the transistor-transistor logic (TTL) signal from the photon counting detector by measuring the time intervals between photon events and calculates the autocorrelation functions in real time. Furthermore, we derive estimates for the error arising from the use of the multi-{\tau} correlator. We implement all the necessary operations in a single Xilinx FPGA chip with a lag time from 10 ns to 45 min, including a highly optimized photon counter.

A simple approach to expand the measurement range of a critical angle refractometer (CAR) is demonstrated. Our method is based on measuring the centroid point of the angular reflective ratio of the CAR. According to the Snell׳s reflective law, the CAR with a divergent beam source has a limited measurement range. When the refractive index (RI) is higher than the upper limit, the reflective ratio curve is gradual changing without cutoff edge between the total internal reflection (TIR) and non-TIR. We find that the centroid point of the gradual changing curve is associated with the RI value of a liquid. Theorectical analysis and experimental results on sugar solutions with RI that varying from 1.359 to 1.3766 show that this method is effective and accurate to expand the measurement range.

Discerning the geometry of spheroidal scatterers of micron order is an important topic in identifying marine microbes. Optical diffraction tomography theory indicates that under the first-order Born approximation for weak scattering, scattering amplitude in the far zone and scattering potential of the scatterer have a Fourier relationship. In this paper, we describe a method based on diffraction tomography theory and determine the size and the shape of spheroidal scatterers by reconstructing the distribution of scattering potential from angular resolved scattered field. As a demonstration of this method, the scattering from spheroidal particles with equal-volume-sphere radii of 0.5429, 1.00, and 2.00 μm and an aspect ratio that varies from 0.4 to 1.5 was modeled by using T-matrix theory and used as test data. Simulation results show that in the case of low contrast, size and shape determination can be achieved with sub-wavelength precision.

A procedure for automated bullet identification is described based on striation measurement using the bullet 3D digital representations obtained by a laser color scanner. When we do bullet identification by eye, we try to best match the striations according to the order of the striations and the distance between them. Based on this principle, individual characteristics which describe the unique striation pattern on the bullet are extracted. Experimental results prove that our algorithm can find the bullets with high trace similarity correctly and do bullet identification successfully.

The all-optical orthogonal frequency division multiplexing has a better spectral efficiency and a lower response requirement of modulators for high capacity transmission. In the system, the optical filter will degrade the performance of subcarriers which are far away from the center carrier. We proposed an improvement method of all-optical OFDM scheme using Nyquist pulse shape in the pulse source generator. Comparing a Nyquist shape pulse with a Gauss pulse in a 4 × 100 Gb/s DP-QPSK all-optical sampling OFDM system, the side lobe of transmitted spectrum can be effective suppressed, and the optical power will be more focused on the effective frequency band. By coherent receiver, the results show that the Nyquist pulse shaping can improve the OSNR and transmission performance of subcarriers which deviate mostly from the center frequency of optical filter. This improvement is of great benefit for multi-users system.

Localization of underwater objects is essential for exploring the vast ocean resources, and circular features are the most common quadratic-curved features that have been addressed for localization. This paper presents a monocular-vision-based method for localization of underwater circular features (UCFs). Using a single camera image, this method can immediately extract the UCFs from the image, compensate the image distortion caused by the underwater environment, and estimate both orientation and position of the UCFs. Laboratory experiments demonstrate that the method is capable of estimating the 3-D location of a cylindrical object in clean water, and the accuracy and stability of the method are also analyzed by moving and relocating the object.

In order to enhance the visual quality of underwater images, applications such as enhancement and restoration can be applied, but the resolution is still limited. Super-resolution reconstruction is a widely used technique for improving resolution beyond the limit of imaging system. With knowledge of the point spread function and techniques of regularization, the performance of reconstruction can be further enhanced. The presented effort proposed a robust image super-resolution reconstruction method under maximum a posteriori framework with regularization by the point spread function for underwater imaging detection. Objective image quality metrics are used to quantify the effectiveness of the reconstruction. Experimental results showed that the proposed method can effectively improve the resolution and quality of underwater imaging detection.

A simple optical fiber structure with a section of no-core fiber for measuring pH is presented. Precursor TEOS and pH-sensitive indicators are used to form the pH coating on the no-core fiber by dip-coating method. The pH induced refractive index changes on the outside coating of no-core fiber will lead to the variations of the optical output power. The results show that a high pH sensitivity of 0.6 dBm/pH at 1550 nm and a good linear response with a wide pH operation range, from 1 to 13, are obtained. Through monitoring the optical output powers, the responses demonstrate the good stability and repeatability of our proposed structure. At last, the measured data can be obtained with a rapid response time of less than 40 s.

Light scattering characteristics of a spheroidal bubble are researched for turbulent bubbly flow in which bubbles are not exactly spheral. Aiming at the influence of shape of the bubble, the angular distributions of light scattered by prolate and oblate spheroidal bubbles with incident beam parallel to the rotating axis are calculated based on ray tracing method, neglecting the diffraction and interference. The width of incident beam is presented as a influencing factor for the light scattering. Furthermore, effects on the scattering properties are analyzed in terms of the shape parameter, refractive index of water and times of internal reflections and refractions. The results that the nonsphericity of bubbles has a considerable effect on their scattering profiles, can be used to optimize the bubbly flow measurements.

It is known that absorption and scattering properties of water are the main causes of blur in underwater images. With the knowledge of point spread function (PSF), the performance of underwater image restoration can be effectively enhanced, which will also extend the imaging range as well. The presented effort reviews several empirical PSF models and an imagery-derived approach based on image formation. Varied models are applied for blind deconvolution restoration, performance of which are compared and discussed. Models under comparison include the empirical models by Duntley, Voss, Wells, as well as the imagery-derived approach which can also provide adequate accuracy and flexibility for image restoration, as shown by experimental results.

Light emitting diode (LED) is one of the most important light sources in the 21st century and has broad prospects in the illumination. Currently, the white LED is used not only for illumination, but also for transmission data. A new technique referred as visible light communication (VLC) is rapidly growing in optical communication. In order to enhance the performance of the communication link, we present optical multiple input and multiple output (MIMO) communication system to achieve high data rate, which can mitigate the shadow effect of indoor communication. Moreover, the MIMO will bring about multi-path effect, which causes inter-symbol interference (ISI) to degrade the performance of the link. Hence, an adaptive equalization technique has been used in the receiver system, which can reduce the ISI when the system is determined to receive symbol. Finally, we have simulated the MIMO system with adaptive equalization. The simulation results show significant improvement in the transmission rate using on off keying (OOK) and the average signal to noise ratio (SNR) in this channel has increased 13.5 dB after equalization.

In order to process underwater imaging to the best possible level, an imaging model based on beam propagation was established. The presented model included not only the laser beam propagation affected by absorption and scattering, but also the effects of underwater turbulence and the diffraction limit of sensors. By this model approximately quantified optical transfer functions (OTFs) were studied. Thus, under this framework, the approaches of image enhancement, restoration and super-resolution reconstruction (SRR) can be extended by incorporating underwater optical properties based on OTF or point spread function (PSF) of the imaging system. Experimental results proved that the imaging range and the image quality can be effectively enhanced, which are critical in underwater imaging or detecting.

Edge information is important for measurement based on structured light. The presented effort puts forward an image restoration method with edge regularization for structured light measurement, which detects the edge of image, then updates the parameters of image degradation model and restores results in iteration. The diffraction limit of optics and nonlinear distortion of sensors are calculated as prior knowledge for semi-blind deconvolution. Blur metric is introduced for constraints of deconvolution iterations. Images before and after restoration are sent to shape recognition and automatic calibration modules for comparison. From experimental results we can conclude that the proposed approach can effectively enhance image quality and edge details, so that greater precision can be achieved.

A real time all-optical orthogonal frequency division multiplexing (OOFDM) system based on two time lenses is experimentally demonstrated. At the transmitter, groups of initial optical pulses are transformed into OOFDM symbols by a continuous inverse Fourier transform (IFT) device, which consists of the first a quadratic phase modulator and two high dispersive elements. After transmission, a continuous Fourier transform (FT) device, consisting of another quadratic phase modulator and two high dispersive elements, rebuilds the initial optical pulses at the receiver. The electrical sinusoidal waveform employed in the FT module at the receiver is obtained directly from the transmitter with certain phase shift. In the system, the guard interval is necessary for each OOFDM symbol to ensure the initial pulses are operated FT/IFT under a parabolic waveform driving and to have more Fourier transformation time window. Experiment results show that 8 × 2.5 Gb/s signals successfully transmit through 200-km-G.655 fibers without any dispersion compensation, with the BER being 10 − 12 .

The influence of IP bursty traffic on combined nonlinear effects of XPM (cross phase modulation) and FWM (four-wave mixing) in IP over WDM networks are investigated and calculated by solving the nonlinear Schrodinger equation (NLSE) using a novel method under two conditions: on---off Poisson distributed IP traffic and self-similar traffic. Different eye diagrams are obtained under various IP traffic types and input optical powers. When the input power of a single channel is larger than 3 dBm, the effect of IP bursty traffic will deteriorate eye diagrams dramatically in a 40-channel WDM network. We also calculate the FWM powers and interchannel power distribution under different IP traffic loads. Based on the interchannel power distribution, we could find out which channels affect the probe channel seriously by the FWM effect. All these numerical results are useful for the Quality-of-Service (QoS) design, traffic grooming, lightpath routing, and wavelength assignment of IP over WDM networks.

Although the use of blind deconvolution of image restoration is a widely known concept, little literatures have discussed in detail its application in the problem of restoration of underwater range-gated laser images. With the knowledge of the point spread function (PSF) and modulation transfer function (MTF) of water, underwater images can be better restored or enhanced. We first review image degradation process and Wells’ small angle approximation theory, and then provide an image enhancement method for our underwater laser imaging system by blind deconvolution method based on small angle approximation. We also introduce a modified normalized mean square error (NMSE) method to validate the convergence of the blind deconvolution algorithm which is applied in our approach. The results of different initial guess of blind deconvolution are compared and discussed. Moreover, restoration results are obtained and discussed by intentionally changing the MTF parameters and using non-model-based PSF as the initial guess.

How to guarantee high image quality is the key point when converting standard-definition television (SDTV) images to high-definition television (HDTV) images. The change of pixel shape from rectangular to square makes traditional interpolation methods inappropriate because traditional methods are based on integer coordinates. In this paper, we propose a novel interpolation algorithm using center coordinates of pixels (IAUCCP). This method revises the color value of each pixel on HDTV images by correcting the pixels’ xy coordinates. After that, considering the huge enlarging multiples, sharpening treatment is done to the HDTV images. Experiments show that our method greatly improves the HDTV image quality comparing with traditional interpolation algorithms.

Early signs of diseases can be revealed from cell detection in biofluids, such as detection of white blood cells (WBCs) in the peritoneal fluid for peritonitis. A lab-on-a-chip microfluidic device offers an attractive platform for such applications because of its small size, low cost, and ease of use provided the device can meet the performance requirements which many existing LoC devices fail to satisfy. We report an integrated microfluidic device capable of accurately counting low concentration of white blood cells in peritoneal fluid at 150 μl min−1 to offer an accurate (

We propose a novel and simple all-optical 160-Gb/s orthogonal frequency division multiplexing (OFDM) symbol generator which is based on discrete triangle waveform driving-LiNbO3 modulators to realize largerange linear optical shift. The entire system needs 64 discrete modulators: at the transmitter, a 2.5-Gb/s optical duobinary (ODB) modulator for data modulation and a 2.5-Gb/s triangle waveform driving-LiNbO3 phase modulator for phase shift to generate each subcarrier; and at the receiver, a 2.5-GHz optical band pass filter (OBPF) using Faraday anomalous dispersion optical effect to separate them. Excellent bit error rate (BER) is observed after 1060 km of transmission without any dispersion compensation.