Gray-scale skeletonization of small vessels in magnetic resonance angiography

Interpretation of magnetic resonance angiography (MRA) is problematic due to complexities of vascular shape and to artifacts such as the partial volume effect. We present new methods to assist in the interpretation of MRA. These include methods for detection of vessel paths and for determination of branching patterns of vascular trees. They are based on the ordered region growing (ORG) algorithm that represents the image as an acyclic graph, which can be reduced to a skeleton by specifying vessel endpoints or by a pruning process. Ambiguities in the vessel branching due to vessel overlap are effectively resolved by heuristic methods that incorporate a priori knowledge of bifurcation spacing. Vessel paths are detected at interactive speeds on a 500-MHz processor using vessel endpoints. These methods apply best to smaller vessels where the image intensity peaks at the center of the lumen which, for the abdominal MRA, includes vessels whose diameter is less than 1 cm.     

Global and Local Nonlinear System Responses under Narrowband Random Excitations. II: Prediction, Simulation, and Comparison

The response behavior of the single-degree-of-freedom (SDOF) nonlinear structural system subjected to narrowband stochastic excitations studied in Part I is investigated via simulations to verify the stochastic system characteristics assumed in the development of the semianalytical method. In addition, to demonstrate the accuracy of the method, predicted response–amplitude probability distributions are presented and compared to simulation results. Numerical simulations are conducted by directly integrating the SDOF system with the narrowband excitation modeled by the 1971 Shinozuka formulation. It is observed that the proposed semianalytical method is capable of accurately characterizing the stochastic response behavior of the nonlinear system by predicting the response–amplitude probability distribution and capturing the trends of variations in the response–amplitude statistical properties. In both the primary and the subharmonic resonance regions, good agreements between the response–amplitude probability distributions predicted by the semianalytical method and obtained from simulation results are observed both qualitatively and quantitatively. In addition, trends of the variations in the probability masses associated with the modes with variations in excitation parameters (bandwidth and variance) are captured.     

Wet-Style Superhydrophobic Antifogging Coatings for Optical Sensors

Transparent substrates are widely used for optical applications from lenses for personal and sports eyewear to transparent displays and sensors. While these substrates require excellent optical properties, they often suffer from a variety of environmental challenges such as excessive fogging and surface contamination. In this work, it is demonstrated that a wet-style superhydrophobic coating, which simultaneously exhibits antifogging, antireflective, and self-cleaning properties, can be prepared by pattern transferring low-surface-energy microstructures onto a heterostructured nanoscale thin film comprising polymers and silica nanoparticles. The polymer–silica nanocomposite base layer serves as a hydrophilic reservoir, guiding the water molecules to preferentially condense into this underlying region and suppress reflection, while the low-surface-energy microstructure enables contaminants adsorbed on the surface to be easily removed by rinsing with water.     

Generation, transport, and detection of linear accelerator based femtosecond-terahertz pulses

The generation and detection of intense terahertz (THz) radiation has drawn a great attention recently. The dramatically enhanced energy and peak electric field of the coherent THz radiation can be generated by coherent superposition of radiated fields emitted by ultrafast electron bunches. The femtosecond (fs)-THz beamline construction at the Pohang Accelerator Laboratory (PAL) was completed in the end of 2009. The fs-THz beamline at PAL can supply ultrafast and intense fs-THz radiation from a 75 MeV linear accelerator. The radiation is expected to have frequency up to 3 THz (～100 cm(-1)) and the pulse width of <200 fs with pulse energy up to 10 μJ. This intense THz source has great potential for applications in nonlinear optical phenomena and fields such as material science, biomedical science, chemistry, and physics, etc.     

Adaptive offloading with MPTCP for unmanned aerial vehicle surveillance system

Unmanned aerial vehicles (UAVs) are utilized in the surveillance and reconnaissance system of hazardous locations by utilizing the feature that they can freely move away from space constraints. Furthermore, the application scope of the UAVs expanded not only for simple image data collection but also for analysis of complex image data without human intervention. However, mobile UAV systems, such as drone, have limited computing resources and battery power which makes it a challenge to use these systems for long periods of time. In this paper, we propose an AOM, Adaptive Offloading with MPTCP (Multipath TCP), architecture for increasing drone operating time. We design not only the task offloading management module via the MPTCP to utilize heterogeneous network but also the response time prediction module for mission critical task offloading decision. Through the prototype drone implementation, we show the AOM reduces the task response time and increases drone operation time.     

Phototransistors with Negative or Ambipolar Photoresponse Based on As‐Grown Heterostructures of Single‐Walled Carbon Nanotube and MoS2

A facile synthesis method for the heterostructures of single‐walled carbon nanotubes (SWCNTs) and few‐layer MoS₂ is reported. The heterostructures are realized by in situ chemical vapor deposition of MoS₂ on individual SWCNTs. Field effect transistors based on the heterostructures display different transfer characteristics depending on the formation of MoS₂ conduction channels along SWCNTs. Under light illumination, negative photoresponse originating from charge transfer from MoS₂ to SWCNT is observed while positive photoresponse is observed in MoS₂ conduction channels, leading to ambipolar photoresponse in devices with both SWCNT and MoS₂ channels. The heterostructure phototransistor, for negative photoresponse, exhibits high responsivity (100–1000 AW^?1) at low bias voltages (0.1 V) in the visible spectrum (500–700 nm) by combining high mobility conduction channel (SWCNT) with efficient light absorber (MoS₂).     

Comparative Study on Infrared Irradiance Emitted from Standard and Real Rocket Motor Plumes

The infrared irradiance signature from exhaust plume is essential for the design of solid rocket motors. To overcome the difficulty of conducting experiments using real rocket motors, experimental studies were carried out to compare standard rocket motors and real rocket motors of the same propellant. The static firing tests on standard and real rocket motors of NEPE and HTPB propellants were conducted. Despite different rocket motor size and methodology of spectro‐radiometric measurement, the spectral characteristics of the infrared irradiance signature for both rocket motors were quite similar. The standard and real rocket motors of HTPB propellant showed similar tendency of steady infrared irradiance emission throughout the combustion, whereas both rocket motors of NEPE propellant showed a rapid emission in the midstream of combustion. The total infrared irradiance of NEPE was about 55 % less than that of HTPB propellant for both standard and real rocket motor experiments. Additionally, the relative amounts of chemical products produced during propellant combustion came out to be similar for both rocket motors. The experimental results indicated that the spectral characteristics of infrared irradiance and combustion products were quite similar for different sized rocket motors of same propellant and that a correlation of infrared irradiance signature exists between small‐sized standard rocket motors and real rocket motors. Thus, the spectral characteristics of real rocket motors could be reasonably estimated from the results of standard rocket motors.     

Evaluation of temporal variation of video quality in packet loss networks

We examine the effect that variations in the temporal quality of videos have on global video quality. We also propose a general framework for constructing temporal video quality assessment (QA) algorithms that seek to assess transient temporal errors, such as packet losses. The proposed framework modifies simple frame-based quality assessment algorithms by incorporating a temporal quality variance factor. We use packet loss from channel errors as a specific study of practical significance. Using the PSNR and the SSIM index as exemplars, we are able to show that the new video QA algorithms are highly responsive to packet loss errors.     

Two-dimensional photonic crystal arrays for polymer:fullerene solar cells

We report the application of two-dimensional (2D) photonic crystal (PC) array substrates for polymer:fullerene solar cells of which the active layer is made with blended films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The 2D PC array substrates were fabricated by employing a nanosphere lithography technique. Two different hole depths (200 and 300 nm) were introduced for the 2D PC arrays to examine the hole depth effect on the light harvesting (trapping). The optical effect by the 2D PC arrays was investigated by the measurement of optical transmittance either in the direction normal to the substrate (direct transmittance) or in all directions (integrated transmittance). The results showed that the integrated transmittance was higher for the 2D PC array substrates than the conventional planar substrate at the wavelengths of ca. 400 nm, even though the direct transmittance of 2D PC array substrates was much lower over the entire visible light range. The short circuit current density (J(SC)) was higher for the device with the 2D PC array (200 nm hole depth) than the reference device. However, the device with the 2D PC array (300 nm hole depth) showed a slightly lower J(SC) value at a high light intensity in spite of its light harvesting effect proven at a lower light intensity.     

Controlling spatial density and size of nanocrystals by two-step atomic layer deposition

Two-step atomic layer deposition (ALD) is proposed in order to control both the spatial density and size of nanocrystals (NCs) via modulation of the nucleation rate during deposition. In this process, two different deposition conditions are sequentially used: a high nucleation rate condition for the formation of high density NCs and a low nucleation rate condition with a slow growth rate for the subsequent growth of pre-formed NCs. To control the nucleation rate of Ru during ALD, pulsing time and carrier flow rate of the Ru precursor are varied. By controlling those factors, both the film growth rate and a nucleation rate of Ru are decreased considerably. Two-step ALD of Ru NCs using the surface-saturated condition followed by the reduced condition allows for variation of the spatial density from 7.9 × 10(11) to 3.2 × 10(12) cm(-2) and variation of the average diameter from 1.9 to 3.3 nm.