Domain Mode Research Articles

Effect of bias on dielectric properties of SmCA∗ and SmC∗ phases of a perfluorinated antiferroelectric liquid crystal

A laterally fluorinated antiferroelectric liquid crystal was studied using bias dependent dielectric spectroscopy. The domain mode appeared when Goldstone mode of SmC∗ phase suppressed under bias. Critical frequency of domain mode increases with bias. It also suppresses under bias. In SmCA∗, low frequency PL mode and high frequency PH mode were observed. Their ranges of critical frequencies are well separated. The weaker PL suppresses under bias, suggesting it arises from helical structure of antiferroelectric polarization. The critical field for suppression of PL increases with decrease of temperature. The stronger PH mode is almost bias independent, related to anti–phase fluctuation.

Design and simulation of normally open and normally closed all-optical switches based on photonic crystal triple-waveguide directional coupler

In this paper a novel photonic crystal all-optical switch is proposed. The proposed switch which can be made from Gallium arsenide, is based on a triple-waveguide directional coupler that exhibits Kerr effect nonlinearity. Two types of switches: normally open and normally closed, are derived from the proposed topology. One of the advantages of the suggested switch is the minimum input signal reflection. The chip area for the implementation of the switch is reduced in comparison with pervious works. All dimensions have been optimized for the fiber optic communications in the wavelength of 1550 nm. The employed simulation methods are Plane Wave Expansion, Finite Difference Time Domain and Coupled Mode Theory.

Heartbeat OCT: in vivo intravascular megahertz-optical coherence tomography.

Cardiac motion artifacts, non-uniform rotational distortion and undersampling affect the image quality and the diagnostic impact of intravascular optical coherence tomography (IV-OCT). In this study we demonstrate how these limitations of IV-OCT can be addressed by using an imaging system that we called "Heartbeat OCT", combining a fast Fourier Domain Mode Locked laser, fast pullback, and a micromotor actuated catheter, designed to examine a coronary vessel in less than one cardiac cycle. We acquired in vivo data sets of two coronary arteries in a porcine heart with both Heartbeat OCT, working at 2.88 MHz A-line rate, 4000 frames/s and 100 mm/s pullback speed, and with a commercial system. The in vivo results show that Heartbeat OCT provides faithfully rendered, motion-artifact free, fully sampled vessel wall architecture, unlike the conventional IV-OCT data. We present the Heartbeat OCT system in full technical detail and discuss the steps needed for clinical translation of the technology.

Ultra-widefield retinal MHz-OCT imaging with up to 100 degrees viewing angle.

We evaluate strategies to maximize the field of view (FOV) of in vivo retinal OCT imaging of human eyes. Three imaging modes are tested: Single volume imaging with 85° FOV as well as with 100° and stitching of five 60° images to a 100° mosaic (measured from the nodal point). We employ a MHz-OCT system based on a 1060nm Fourier domain mode locked (FDML) laser with a depth scan rate of 1.68MHz. The high speed is essential for dense isotropic sampling of the large areas. Challenges caused by the wide FOV are discussed and solutions to most issues are presented. Detailed information on the design and characterization of our sample arm optics is given. We investigate the origin of an angle dependent signal fall-off which we observe towards larger imaging angles. It is present in our 85° and 100° single volume images, but not in the mosaic. Our results suggest that 100° FOV OCT is possible with current swept source OCT technology.

Differentiated Doping Profile for Vertical Terahertz GaN Transferred-Electron Devices

The potential of vertical differentiated gallium nitride (GaN) transferred electron devices (TEDs) is compared with that of the base flat doping profile TED for the realization of RF power sources at 1 THz. The TED oscillator modeling is a time-domain continuous wave pure sine model. The semiconductor device model is a 1-D numerical physical macroscopic model based on the energy-momentum approach. Differentiated structures of notch, detached notch, and P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> spike (PS) types have been optimized. By contrast with millimeter-wave differentiated TEDs operating in the dipole domain mode, the terahertz TED RF operating mode remains the accumulation layer/transit time mode. Comparison point out that the differentiated doping profile TEDs slightly improve both the TED RF performance and electronic limitation but above all improve the thermal limitation resulting from the high dc bias conditions due to high threshold electric field in GaN. Thus, the PS TED distinguishes itself as the most promising structure.

Adaptive Topic Tracking Research Based on Title Semantic Domain and Double-state Mode

Aiming at problems of sparse training corpora and topic excursion existing in topic detection and tracking, this paper examines twenty one most recent references and patents, proposes an adaptive topic tracking strategy based on title semantic domain topic model and double-state model. Title semantic domain topic model can enhance the title-centric semantic domain cohesion of reports, and reduce dimensions of reports' feature space effectively. The double-state strat- egy is a tracking technology based on the combination of static model and dynamic model: static model uses a given number of training reports to construct topic model which is the basis of topic tracking; dynamic model uses the sliding text window mechanism to capture new contents of a topic, remove outdated ones and reflect the changes of topic's focus in a timely manner. Experimental results show that the combination of double-state model tracking strategy and title se- mantic domain topic model can improve the performance of adaptive topic tracking system.

Unstable domains of tearing and Kelvin-Helmholtz instabilities in a rotating cylindrical plasma

Effects of poloidal rotation profile on tearing and Kelvin-Helmholtz (KH) instabilities in a cylindrical plasma are investigated by using a reduced magnetohydrodynamic model. Since the poloidal rotation has different effects on the tearing and KH modes in different rotation regimes, four unstable domains are numerically identified, i.e., the destabilized tearing mode domain, stabilized tearing mode domain, stable-window domain, and unstable KH mode domain. It is also found that when the rotation layer is in the outer region of the rational surface, the stabilizing role of the rotation can be enhanced so significantly that the stable window domain is enlarged. Moreover, Alfvén resonances can be induced by the tearing and KH modes in such rotating plasmas. Radially wide profiles of current and vorticity perturbations can be formed when multiple current sheets on different resonance positions are coupled together.

High definition live 3D-OCT in vivo: design and evaluation of a 4D OCT engine with 1 GVoxel/s.

We present a 1300 nm OCT system for volumetric real-time live OCT acquisition and visualization at 1 billion volume elements per second. All technological challenges and problems associated with such high scanning speed are discussed in detail as well as the solutions. In one configuration, the system acquires, processes and visualizes 26 volumes per second where each volume consists of 320 x 320 depth scans and each depth scan has 400 usable pixels. This is the fastest real-time OCT to date in terms of voxel rate. A 51 Hz volume rate is realized with half the frame number. In both configurations the speed can be sustained indefinitely. The OCT system uses a 1310 nm Fourier domain mode locked (FDML) laser operated at 3.2 MHz sweep rate. Data acquisition is performed with two dedicated digitizer cards, each running at 2.5 GS/s, hosted in a single desktop computer. Live real-time data processing and visualization are realized with custom developed software on an NVidia GTX 690 dual graphics processing unit (GPU) card. To evaluate potential future applications of such a system, we present volumetric videos captured at 26 and 51 Hz of planktonic crustaceans and skin.

Limited efficacy of specific HDAC6 inhibition in urothelial cancer cells

Epigenetic modifiers such as histone deacetylases (HDACs) have come into focus as novel drug targets for cancer therapy due to their functional role in tumor progression. Since common pan-HDAC inhibitors have adverse side effects and minor anti-cancer activity against solid tumors, enzyme-specific inhibitors were developed. HDAC6 is especially well-suited for specific inhibition due to its unique domain structure and mode of action and has been suggested to provide an exceptionally suitable target for cancer therapy. However, expression and function of HDACs have been insufficiently studied in urothelial cancers (UC), a disease urgently requiring new therapeutic approaches. The present study sought to evaluate HDAC6 as a target for treatment of urothelial cancers with enzyme-specific inhibitors. We observed moderate HDAC6 overexpression in urothelial cancer tissues and a broad range of expression in urothelial cancer cell lines. In the cell lines Tubacin was the most potent inhibitor, compared with Tubastatin and ST-80, but still active only at high micromolar concentrations. HDAC6 expression levels correlated poorly with sensitivity to enzyme inhibition. Combined treatments with heat shock, HSP90 inhibition by 17-AAG, proteasome inhibition by bortezomib, or DNA-damaging agents did not result in significant synergistic effects. Experiments with siRNA-mediated knockdown further underlined that urothelial cancer cells do not critically depend on HDAC6 expression for survival.

PseAAC-General: Fast Building Various Modes of General Form of Chou’s Pseudo-Amino Acid Composition for Large-Scale Protein Datasets

The general form pseudo-amino acid composition (PseAAC) has been widely used to represent protein sequences in predicting protein structural and functional attributes. We developed the program PseAAC-General to generate various different modes of Chou’s general PseAAC, such as the gene ontology mode, the functional domain mode, and the sequential evolution mode. This program allows the users to define their own desired modes. In every mode, 544 physicochemical properties of the amino acids are available for choosing. The computing efficiency is at least 100 times that of existing programs, which makes it able to facilitate the extensive studies on proteins and peptides. The PseAAC-General is freely available via SourceForge. It runs on both Linux and Windows.

Percolation and Electrical Conductivity Modeling of Novel Microstructured Insulator-Conductor Nanocomposites Fabricated from PMMA and ATO

ABSTRACTThe electrical conductivity of insulating polymer matrix composites undergoes radical increase at a certain concentration of conductive filler, which is known as the percolation threshold. Polymer matrix conductive nanocomposites were fabricated by compression molding the mechanically mixed poly (methyl methacrylate) (PMMA) and antimony tin oxide (ATO) nanoparticles, as has been done with other polymer composites before. The electrical conductivity of PMMA/ATO nanocomposites increased by several orders of magnitude at a small concentration of ATO (∼ 0.27 vol %). The continuous 3D network like distribution of ATO nanoparticles contributed to this percolation at subcritical filler concentrations. The effects of processing parameters on these unique microstructures and electrical properties were investigated. The tetrakaidecahedron-like microstructure was observed by scanning electron microscopy (SEM) and was found to be affected by the molding pressure, temperature and amount of nanoparticles. The viscoelastic flow of matrix under the optimum processing conditions allowed the shape transformation of PMMA into space filling polyhedra and an ordered distribution of ATO nanoparticles along the sharp edges of the PMMA. Parametric finite element analysis was performed to model this unique microstructure-driven percolation. The 2D simplified model was generated in AC/DC frequency domain mode in COMSOL Multiphysics®to solve the effects of ordered distribution of conductive nanoparticles on the electrical properties of the composite. There was excellent agreement between experimental and simulated values of electrical conductivity and percolation concentration. This model can be used to predict percolation threshold and electrical properties for any types of composite systems containing insulating matrix and conductive fillers that can form this unique microstructure.

Frequency synchronization of Fourier domain harmonically mode locked fiber laser by monitoring the supermode noise peaks

In a harmonically mode locked laser, the supermode noise peaks in the RF spectrum can be observed directly because they are separated from the driving frequency and its harmonics of the active mode locker. Using a simple theoretical model, we showed that the intensities of the supermode noise peaks will decrease if the coherence of the laser output decreases. We harmonically mode locked a Fourier domain mode locked (FDML) fiber laser to the third order. We observed that the supermode noise peak intensities decrease significantly when the detune between the sweeping frequency of the tunable filter and the cavity resonant frequency increases. It is therefore possible to use the supermode noise peaks to monitor the frequency detune of the tunable filter for auto-calibration of FDML fiber lasers.

Effect of dye dispersion on the relaxation modes of smectic C* phase

We study how the dye dispersion influences the properties of ferroelectric liquid crystal (FLC). The polarisation measurement shows the decreasing linear behaviour with the increasing concentration of dye, indicating the orientation of dye in a direction opposite to FLC molecules. Accordingly, the response time increases with increasing concentration of dye. Dielectric data clearly show the existence of two relaxation phenomena in FLC and dye–dispersed systems. The relaxation strength of the Goldstone mode, which is observed around 200 Hz, has decreased with the dispersion of dye, and the relaxation frequency of this mode shifts towards the lower frequency side, due to increase in the rotational viscosity. The second relaxation mode, observed at ∼30 KHz, arises due to the formation of domains at the surface interface. This domain mode got suppressed with the dispersion of dye into FLC.

Towards common basis for 3D Cadastres from legal perspective

Legal aspects play an increasingly important role in establishing a functional 3D Cadastre, especially in urban areas with multiple strata, crossing networks and overlapping legal spaces in the form of apartments and utility infrastructures. A wide range of national laws and regulations govern the way these real world objects and associated rights, restrictions and responsibilities (RRRs) are defined and represented in the two- or three-dimensional (2D/3D) space. In fact, despite all research and latest technological advances, no country has so far developed a real 3D Cadastre, while in all legal systems, basic terminology and key concepts need to be clarified first in order to meet the harmonisation of the different Land Administration Systems (LASs) in the near future. This paper aims to contribute to reach towards this harmonisation, by identifying similarities, differences and constraints imposed by jurisdictions that need to be addressed, to ensure 3D cadastral registration and representation of the real world objects, as well as determination of RRRs complying with the different national land law. This paper also engages in worldwide trends of modelling legal relations between spatial units and RRRs on the basis of existing standards that ensure harmonisation and interoperability. Thoughts and proposals for the integration of legally defined spaces into a 3D Cadastres system are offered, including the clarification of RRRs and related source documents, within the context of the Land Administration Domain Mode, recently approved as official International ISO Standard.

Dynamics of Fourier domain mode-locked lasers

An analysis of the dynamical features in the output of a Fourier Domain Mode Locked laser is presented. An experimental study of the wavelength sweep-direction asymmetry in the output of such devices is undertaken. A mathematical model based on a set of delay differential equations is developed and shown to agree well with experiment.

Estimation Vehicular Waiting Time at Traffic Build-Up Queues

Due to the high growth of social economic activities and the increased need for mobility in recent days, transportation problems like congestion, accidents, and pollution have been increased. However, improving the reliability of delay estimates and real-time dissemination of information remains a challenge. An advanced border-crossing system corresponding to the changes of cross-border circumstances becomes an urgent matter. An automated system for queue end monitoring has been proposed using image processing based transformed domain and empirical mode decomposition (EMD) feature extraction systems. The performance of feedforward backpropagation algorithm artificial neural networks (ANNs) was evaluated and tested, based on a selected set of features. The experimental results showed that the use of discrete wavelet transform (DWT) based Daubechies with decomposition of level 2 has accomplished the target with a processing time 2 sec and 3 epochs of training network only with best validation performance of (2.1053e-007) for vehicle recognition. Also the use of EMD as a feature extractor has accomplished the target of vehicle recognition with a best validation performance of (about 3.42e-09) and a processing time of 1 sec at epoch 3 of training network only with a minimal percentage of error for the recognition of each vehicle in the appropriate queue with the aid of the new concept of road side unit (RSU).

Swept-Source OCT System Based on a Polarization-Dependent Semiconductor Optical Amplifier-Enabled Fourier Domain Mode Locked Laser

We demonstrate a swept-source OCT system based on a polorization-dependent semiconductor optical amplifier (SOA)-enabled Fourier Domain Mode Locked laser (FDML). The broad bandwidth and high saturation power of the semiconductor optical amplifier enables single semiconductor optical amplifier operation with enough bandwidth and output power. The FDML generates ~32mW output power at 45kHz sweep rates, with a tuning range of 115 nm centered at 1326 nm. Using the SOA-enabled FDML laser, ~12.9μm axial resolution,9μm transverse spot size and 105dB sensitivity are achieved. OCT imaging of biological sample is also demonstrated.

Intravascular optical coherence tomography imaging at 3200 frames per second

We demonstrate intravascular optical coherence tomography (OCT) imaging with frame rate up to 3.2 kHz (192,000 rpm scanning). This was achieved by using a custom-built catheter in which the circumferential scanning was actuated by a 1.0 mm diameter synchronous motor. The OCT system, with an imaging depth of 3.7 mm (in air), is based on a Fourier domain mode locked laser operating at an A-line rate of 1.6 MHz. The diameter of the catheter is 1.1 mm at the tip. Ex vivo images of human coronary artery (78.4 mm length) were acquired at a pullback speed of 100 mm/s. True 3D volumetric imaging of the entire artery, with dense and isotropic sampling in all dimensions, was performed in <1 second acquisition time.

Functional Dissection of Toxoplasma gondii Perforin-like Protein 1 Reveals a Dual Domain Mode of Membrane Binding for Cytolysis and Parasite Egress

The recently discovered role of a perforin-like protein (PLP1) for rapid host cell egress by the protozoan parasite Toxoplasma gondii expanded the functional diversity of pore-forming proteins. Whereas PLP1 was found to be necessary for rapid egress and pathogenesis, the sufficiency for and mechanism of membrane attack were yet unknown. Here we further dissected the PLP1 knock-out phenotype, the mechanism of PLP1 pore formation, and the role of each domain by genetic complementation. We found that PLP1 is sufficient for membrane disruption and has a conserved mechanism of pore formation through target membrane binding and oligomerization to form large, multimeric membrane-embedded complexes. The highly conserved, central MACPF domain and the β-sheet-rich C-terminal domain were required for activity. Loss of the unique N-terminal extension reduced lytic activity and led to a delay in rapid egress, but did not significantly decrease virulence, suggesting that small amounts of lytic activity are sufficient for pathogenesis. We found that both N- and C-terminal domains have membrane binding activity, with the C-terminal domain being critical for function. This dual mode of membrane association may promote PLP1 activity and parasite egress in the diverse cell types in which this parasite replicates.

Retinal polarization-sensitive optical coherence tomography at 1060 nm with 350 kHz A-scan rate using an Fourier domain mode locked laser

We present a novel, high-speed, polarization-sensitive, optical coherence tomography set-up for retinal imaging operating at a central wavelength of 1060 nm which was tested for in vivo imaging in healthy human volunteers. We use the system in combination with a Fourier domain mode locked laser with active spectral shaping which enables the use of forward and backward sweep in order to double the imaging speed without a buffering stage. With this approach and with a custom designed data acquisition system, we show polarization-sensitive imaging with an A-scan rate of 350 kHz. The acquired three-dimensional data sets of healthy human volunteers show different polarization characteristics in the eye, such as depolarization in the retinal pigment epithelium and birefringence in retinal nerve fiber layer and sclera. The increased speed allows imaging of large volumes with reduced motion artifacts. Moreover, averaging several two-dimensional frames allows the generation of high-definition B-scans without the use of an eye-tracking system. The increased penetration depth of the system, which is caused by the longer probing beam wavelength, is beneficial for imaging choroidal and scleral structures and allows automated segmentation of these layers based on their polarization characteristics.