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Spatial visualization of mode distribution of light scattering from plasmonic nanostructures is of vital importance for understanding the scattering mechanism and applications based on these plasmonic nanostructures. A long unanswered question in how the spatial information of scattered light from a single plasmonic nanostructure can be recovered in the far-field, under the constraints of the diffraction limit of the detection or imaging optical system. In this paper, we reported a theoretical model on retrieving local spatial information of scattered light by plasmonic nanostructures in a far-field optical imaging system. In the far-field parametric sin δ images, singularity points corresponding to near-field hot spots of the edge mode and the gap mode were resolved for gold ring and split rings with subwavelength diameters and feature sizes. The experimental results were verified with Finite Difference Time Domain (FDTD) simulation in the near-field and far-field, for the edge mode and the gap mode at 566 nm and 534 nm, respectively. In sin δ image of split-ring, two singularity points associated with near-field hot spots were visualized and resolved with the characteristic size of 90 and 100 nm, which is far below the diffraction limit. The reported results indicate the feasibility of characterizing the spatial distribution of scattering light in the far-field and with sub-wavelength resolution for single plasmonic nanostructures with sub-wavelength feature sizes.

Quantitative detection of virus-like particles under a low concentration is of vital importance for early infection diagnosis and water pollution analysis. In this paper, a novel virus detection method is proposed using indirect polarization parametric imaging method combined with a plasmonic split-ring nanocavity array coated with an Au film and a quantitative algorithm is implemented based on the extended Laplace operator. The attachment of viruses to the split-ring cavity breaks the structural symmetry, and such asymmetry can be enhanced by depositing a thin gold film on the sample, which allows an asymmetrical plasmon mode with a large shift of resonance peak generated under transverse polarization. Correspondingly, the far-field scattering state distribution encoded by the attached virus exhibits a specific asymmetric pattern that is highly correlated to the structural feature of the virus. By utilizing the parametric image sinδ to collect information on the spatial photon state distribution and far-field asymmetry with a sub-wavelength resolution, the appearance of viruses can be detected. To further reduce the background noise and enhance the asymmetric signals, an extended Laplace operator method which divides the detection area into topological units and then calculates the asymmetric parameter is applied, enabling easier determination of virus appearance. Experimental results show that the developed method can provide a detection limit as low as 56 vp/150µL on a large scale, which has great potential in early virus screening and other applications.

We simulate and demonstrate experimentally an inner-wall grating double slot micro ring resonator (IG-DSMRR) with a center slot ring radius of only 6.72 µm based on the silicon-on-insulator platform. This novel photonic-integrated sensor for optical label-free biochemical analysis boosts the measured refractive index (RI) sensitivity in glucose solutions to 563 nm/RIU with the limit of detection value being 3.7 × 10−6 RIU (refractive index units). The concentration sensitivity for sodium chloride solutions can reach 981 pm/%, with a minimum concentration detection limit of 0.02%. Using the combination of DSMRR and IG, the detection range is enlarged significantly to 72.62 nm, three times the free spectral range of conventional slot micro ring resonators. The measured Q-factor is 1.6 × 104, and the straight strip and double slot waveguide transmission losses are 0.9 dB/cm and 20.2 dB/cm, respectively. This IG-DSMRR combines the advantages of a micro ring resonator, slot waveguide, and angular grating and is highly desirable for biochemical sensing in liquids and gases offering an ultra-high sensitivity and ultra-large measurement range. This is the first report of a fabricated and measured double-slot micro ring resonator with an inner sidewall grating structure.

The amount of copper affects the quality of herbal medicine greatly, it is necessary to develop some simple and sensitive methods to detect copper for the remote or resource-limited area. An electronic balance is one of the most familiar equipment that can be found nearly in all laboratories. The presence of Cu(i) can catalyze azide-alkyne cycloaddition reaction (called as click chemistry) with high efficiency. In this study, a simple method had been developed to detect copper ions in herbal medicine using an electronic balance as a readout device based on click chemistry. Cu(ii) is reduced to Cu(i) by sodium ascorbate in situ, which induces the "click" reaction between azido-DNA modified magnetic beads (MB-DNA) and alkynyl-DNA modified platinum nanoparticles (Pt NP-DNA) and results in the fixing of the platinum nanoparticles on the beads (called as MB-Pt NPs). MB-Pt NPs can be separated by a magnetic frame easily and transferred into a drainage reaction device containing hydrogen peroxide. Then, hydrogen peroxide can be decomposed by Pt NPs modified on MB to generate oxygen, which increases the pressure in the drainage reaction device and forces the water in the system to be discharged. The weight of the discharged water can be easily and accurately measured by an electronic balance. The weight of the water has a linear relationship with Cu(ii) in the range of 2.0-200 μM and a detection limit of 0.83 μM under 30 min of collected time. This method does not need complicated and expensive instruments, skilled technicians, and a complex data processing process. The proposed method had been applied to detect copper ions in herbal medicine with satisfactory results.

Polarization control is at the heart of high-capacity data optical communication systems, such as polarization-division multiplexers and Stokes vector modulation transmitters. Despite passive polarization control being mature, the realization of monolithically integrated polarization controllers and single longitudinal mode light sources, such as distributed-feedback (DFB) lasers, is of importance. In this research, we report an AlGaInAs multiple-quantum-well photonic integrated circuit device which can control the state of polarization of the output light source, consisting of a polarization mode converter (PMC), a differential phase shifter (DPS), and a sidewall grating DFB laser. We demonstrate an asymmetrical stepped-height ridge waveguide PMC to realize TE to TM polarization conversion and a symmetrical straight waveguide DPS to enable polarization rotation from approximately counterclockwise circular polarization to linear polarization. Based on the identical epitaxial layer scheme, all the PMC, DPS, and DFB lasers can be integrated monolithically using only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching. For the DFB-PMC device, a high TE to TM polarization conversion efficiency (98.4%) over a wide range of DFB injection currents is reported at 1555 nm wavelength. For the DFB-PMC-DPS device, a nearly 60° rotation of the Stokes vector on the Poincaré sphere was obtained with a range of bias voltage from 0 to −3.0 V at a laser drive current of 170 mA.

We report, to the best of our knowledge, the first demonstration of a 1555-nm stepped-height ridge waveguide polarization mode converter monolithically integrated with a sidewall grating distributed-feedback (DFB) laser using the identical epitaxial layer scheme. The device shows stable single longitudinal mode (SLM) operation with the output light converted from TE to TM polarization with an efficiency of >94% over a wide range of DFB injection currents (IDFB) from 140 mA to 190 mA. The highest TM mode purity of 98.2% was obtained at IDFB = 180 mA. A particular advantage of this device is that only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching are required for the whole integrated device fabrication, significantly reducing complexity and cost.

A four-laser array based on sampled Bragg grating distributed feedback (DFB) lasers in which each sampled period contains four phase-shift sections is proposed, fabricated, and experimentally demonstrated. The wavelength spacing between adjacent lasers is accurately controlled to 0.8 nm ± 0.026 nm and the lasers have single mode suppression ratios larger than 50 dB. Using an integrated semiconductor optical amplifier, the output power can reach 33 mW and the optical linewidth of the DFB lasers can be as narrow as 64 kHz. This laser array uses a ridge waveguide with sidewall gratings and needs only one metalorganic vapor-phase epitaxy (MOVPE) step and one III-V material etching process, simplifying the whole device fabrication process, and meeting the requirements of dense wavelength division multiplexing systems.

WebSocket is a TCP-based protocol, providing full-duplex communication channels over a single TCP connection. In recent years, more and more developers choose to use it to develop applications. This paper discusses the traditional real-time Web communication schemes, and analyzes the advantages of WebSocket. Based on the deep study of WebSocket, a real-time campus information push solution based on WebSocket and node.js is proposed. This paper expatiates the overall structure of the scheme, designs and realizes the functions of each module, and the functional testing results show that the scheme is feasible.

With the development of Internet, new applications are emerging in an endless stream, and traditional applications are constantly changing. Over the past decade, Internet applications develop rapidly, and great changes have taken place in application traffic characteristics of ordinary hosts and servers. Analyzing Internet application traffic characteristics is meaningful to understanding today's network applications, traffic classification, application optimization, network planning and so on. This paper first studies the current composition of Web traffic on the Internet based on analyzing HTTP (Hypertext Transfer Protocol) messages. Instead of page response time, it analyzes types of Web servers and measures Web server response time to speculate the development of Web servers.

Enabling machines to read like human beings has been a hot issue for more than fifty years. A novel offline degraded numeral recognition method (DNRBM) based on the measure of medium truth degree (MMTD) is proposed in this paper to identify segmented degraded numeral characters in gray images. It consists of distinguishing foreground from background, rotating an image, wiping off mottles, cutting margins, calculating both statistic and structural features, and recognizing numerals by the fuzzy classifiers constructed based on MMTD using features selected by logistic regression. The experimental results show that in comparison with the template matching method and the k-NN method, the proposed method performs well on recognizing degraded numeral characters with better scalability and better recognition performance.

A fundamental problem in machine learning is to discriminate a representative set of features on which to construct a classification model for a particular task. This paper presents a feature selection algorithm RF-MI for multiple classes based on ReliefF algorithm and Mutual Information (MI) measure. RF-MI algorithm gets a feature subset by excluding irrelevant and redundant features from original features based on ReliefF algorithm and MI measure respectively, adjusting the feature weight threshold δ and the correlation threshold θ respectively by the classification performance of a specific classifier when using newly generated feature subsets on training data sets, and repeating above procedures until the best classification performance is achieved. Experiments conducted on UCI data sets showed that the presented RF-MI algorithm is better than both ReliefF and GR algorithms in minishing the feature set on the premise that better classification accuracy is maintained. That means classification models based on the feature subset derived from the algorithm can have lower time and space complexity.

Current Web services composition proposals, such as Web Service Choreography Interface (WSCI), provide no mechanisms or tool support for the verification of service composition in the design, when describing the control and message flows in service collaboration. For solving this problem, this paper presents an approach for transforming the composition language WSCI into colored Petri nets (CPNs) so as to effectively verify the model with existing CPNs-specialized tools. The colored Petri nets model of a typical use case "Plan and Book Trip" is then constructed, analyzed, verified and simulated as prototypes of WSCI models with the CPNs tools.

The Web service choreography interface (WSCI) describes the observable behavior of a Web service and the collective message exchange among interacting Web Services. However, WSCI does not address the definition and the implementation of the internal processes that actually drive the message exchange. In order to describe and compose a global view of the dynamic of the message exchange by understanding the interactions with the Web service, this paper presents the process and result of modeling Web service choreography and orchestration with colored Petri nets (CPNs) on the basis of analysis, simplicity and composition of WSCI. The colored Petri nets model of a typical use case 'plan and book trip" is constructed, whose correctness is validated by the simulation analysis of message sequence chart (MSC).

Internet banking fraud can be performed internally by genuine staff or externally by customers or suppliers. This paper presents a security analysis of the proposed Internet banking model compared with that of the current existing models used in fraudulent Internet payments detection and prevention. Several modern models in preventing and detecting fraud are evolving and being applied to many banking systems. However, they have no effective detection mechanism to identify legitimate users and trace their unlawful activities. Also they are not secure enough to prevent fraudulent users from performing fraudulent transactions over the Internet. The proposed model facilitates Internet banking fraud detection and prevention (FDP) by applying two new secure mechanisms, dynamic key generation (DKG) and group key (GK).