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Ying Huang, Weihai Zhuo, Yiming Gao, Haikuan Liu
PURPOSE: To investigate lens dose reduction with organ based tube current modulation (TCM) using the Monte Carlo method. METHODS: To calculate lens dose with organ based TCM, 36 pairs of X-ray sources with bowtie filters were placed around the patient head using a projection angle interval of 10° for one rotation of Computed Tomography (CT). Each projection was simulated respectively. Both voxelized and stylized eye models and Chinese reference male phantoms were used in the simulation, and tube voltages 80, 100, 120 and 140 kVp were used...
April 2018: Physica Medica: PM
Shitao Luo, Fengming Zhang, Yingfei Ruan, Jie Li, Zheng Zhang, Yan Sun, Shixiong Deng, Rui Peng
Photomorphogenesis and heat shock are critical biological processes of plants. A recent research constructed the transcriptional regulatory networks (TRNs) of Arabidopsis thaliana during these processes using DNase-seq. In this study, by strong decomposition, we revealed that each of these TRNs can be represented as a similar bowtie structure with only one non-trivial and distinct strong component. We further identified distinct patterns of variation of a few light-related genes in these bowtie structures during photomorphogenesis...
April 28, 2018: Bio Systems
Prabhu K Venuthurumilli, Peide D Ye, Xianfan Xu
Black phosphorus, a recently intensely investigated two dimensional material, is promising for electronic and optoelectronic applications due to its higher mobility and thickness dependent direct band gap. With its low direct band gap and anisotropic properties in nature, black phosphorus is also suitable for near infrared polarization sensitive photodetection. To enhance photoresponsivity of black phosphorus based photodetector, we demonstrate two designs of plasmonic structures. In the first design, plasmonic bowtie antennas are used to increase the photocurrent, particularly in the armchair direction where the optical absorption is higher than that in the zigzag direction...
April 23, 2018: ACS Nano
Kaichen Dong, Yang Deng, Xi Wang, Kyle B Tom, Zheng You, Jie Yao
Dissipative loss in optical materials is considered one of the major challenges in nano-optics. Here we show that, counter-intuitively, a large imaginary part of material permittivity contributes positively to subwavelength light enhancement and confinement. The Purcell factor and the fluorescence enhancement of dissipative dielectric bowtie nanoantennas, such as Si in ultraviolet (UV), are demonstrated to be orders of magnitude higher than their lossless dielectric counterparts, which is particularly favorable in deep UV applications where metals are plasmonically inactive...
April 15, 2018: Optics Letters
Andrew Mao, William Shyr, Grace J Gang, J Webster Stayman
Purpose: Accurate centering of the patient within the bore of a CT scanner takes time and is often difficult to achieve precisely. Patient miscentering can result in significant dose and image noise penalties with the use of traditional bowtie filters. This work describes a system to dynamically position an x-ray beam filter during image acquisition to enable more consistent image performance and potentially lower dose needed for CT imaging. Methods: We propose a new approach in which two orthogonal low-dose scout images are used to estimate a parametric model of the object describing its shape, size, and location within the field of view (FOV)...
February 2018: Proceedings of SPIE
Kurtis H Dekker, Rubin Hazarika, Matheus A Silveira, Kevin J Jordan
Optical cone beam computed tomography (CT) scanning of radiochromic gel dosimeters, using a CCD camera and a low stray light convergent source, provides fast, truly 3D radiation dosimetry with high accuracy. However, a key limiting factor in radiochromic gel dosimetry at large (⩾10 cm diameter) volumes is the initial attenuation of the dosimeters. It is not unusual to observe a 5-10×  difference in signal intensity through the dosimeter center versus through the surrounding medium in pre-irradiation images...
March 16, 2018: Physics in Medicine and Biology
Adam Wang, Alexander Maslowski, Philippe Messmer, Mathias Lehmann, Adam Strzelecki, Elaine Yu, Pascal Paysan, Marcus Brehm, Peter Munro, Josh Star-Lack, Dieter Seghers
PURPOSE: To correct for scatter in kV cone-beam CT (CBCT) projection data on a clinical system using a new tool, Acuros® CTS, that estimates scatter images rapidly and accurately by deterministically solving the linear Boltzmann transport equation. METHODS: Phantom and patient CBCT scans were acquired on TrueBeam® radiotherapy machines. A first-pass reconstruction was used to create water and bone density maps of the imaged object, which was updated to include a more accurate representation of the patient couch...
May 2018: Medical Physics
Alexander Maslowski, Adam Wang, Mingshan Sun, Todd Wareing, Ian Davis, Josh Star-Lack
PURPOSE: To describe Acuros® CTS, a new software tool for rapidly and accurately estimating scatter in x-ray projection images by deterministically solving the linear Boltzmann transport equation (LBTE). METHODS: The LBTE describes the behavior of particles as they interact with an object across spatial, energy, and directional (propagation) domains. Acuros CTS deterministically solves the LBTE by modeling photon transport associated with an x-ray projection in three main steps: (a) Ray tracing photons from the x-ray source into the object where they experience their first scattering event and form scattering sources...
May 2018: Medical Physics
C Yamauchi-Kawaura, S Yamamoto, K Fujii, M Komori, M Yamauchi, N Ohzawa, M Kozuka, N Suga, N Ito, A Fukuyama
This study proposes a new dosimetry method for the estimation of the internal radiation dose distribution of a subject undergoing computed tomography (CT) examinations. In this novel method, dose distribution of a subject by CT scans was estimated based on radiophotoluminance distribution with polyethylene terephthalate (PET) resin which was cut to the average head size of a Japanese 1-year-old child. The difference in dose distribution depending on the type of bowtie filter was visualized by imaging luminance distribution with the PET phantom using a charge-coupled device camera...
February 12, 2018: Radiation Protection Dosimetry
Ahmad Ibrahim Hassan, Martin Skalej, Helmut Schlattl, Christoph Hoeschen
The accuracy of Monte Carlo (MC) simulations in estimating the computed tomography radiation dose is highly dependent on the proprietary x-ray source information. To address this, this study develops a method to precisely estimate the x-ray spectrum and bowtie (BT) filter thickness of the x-ray source based on physical measurements and calculations. The static x-ray source of the CT localizer radiograph was assessed to measure the total filtration at the isocenter for the x-ray spectrum characterization and the BT profile (air-kerma values as a function of fan angle)...
January 2018: Journal of Medical Imaging
Boxuan Shen, Veikko Linko, Kosti Tapio, Siim Pikker, Tibebe Lemma, Ashwin Gopinath, Kurt V Gothelf, Mauri A Kostiainen, J Jussi Toppari
Programmable self-assembly of nucleic acids enables the fabrication of custom, precise objects with nanoscale dimensions. These structures can be further harnessed as templates to build novel materials such as metallic nanostructures, which are widely used and explored because of their unique optical properties and their potency to serve as components of novel metamaterials. However, approaches to transfer the spatial information of DNA constructions to metal nanostructures remain a challenge. We report a DNA-assisted lithography (DALI) method that combines the structural versatility of DNA origami with conventional lithography techniques to create discrete, well-defined, and entirely metallic nanostructures with designed plasmonic properties...
February 2018: Science Advances
George S Krasnov, Nataliya V Melnikova, Valentina A Lakunina, Anastasiya V Snezhkina, Anna V Kudryavtseva, Alexey A Dmitriev
We present MethyMer, a Python-based tool aimed at selecting primers for amplification of complete CpG islands. These regions are difficult in terms of selecting appropriate primers because of their low-complexity, high GC content. Moreover, bisulfite treatment, in fact, leads to the reduction of the 4-letter alphabet (ATGC) to 3-letter one (ATG, except for methylated cytosines), and this also reduces region complexity and increases mispriming potential. MethyMer has a flexible scoring system, which optimizes the balance between various characteristics such as nucleotide composition, thermodynamic features (melting temperature, dimers [Formula: see text]G, etc...
February 2018: Journal of Bioinformatics and Computational Biology
Pengfei Zhan, Te Wen, Zhen-Gang Wang, Yingbo He, Jia Shi, Ting Wang, Xinfeng Liu, Guowei Lu, Baoquan Ding
Metallic bowtie nanoarchitectures can produce dramatic electric field enhancement, which is advantageous in single-molecule analysis and optical information processing. Plasmonic bowtie nanostructures were successfully constructed using a DNA origami-based bottom-up assembly strategy, which enables precise control over the geometrical configuration of the bowtie with an approximate 5 nm gap. A single Raman probe was accurately positioned at the gap of the bowtie. Single-molecule surface-enhanced Raman scattering (SM-SERS) of individual nanostructures, including ones containing an alkyne group, was observed...
March 5, 2018: Angewandte Chemie
Claire Deeb, Zhi Guo, Ankun Yang, Libai Huang, Teri W Odom
Excited-state interactions between nanoscale cavities and photoactive molecules are critical in plasmonic nanolasing, although the underlying details are less-resolved. This paper reports direct visualization of the energy-transfer dynamics between two-dimensional arrays of plasmonic gold bowtie nanocavities and dye molecules. Transient absorption microscopy measurements of single bowties within the array surrounded by gain molecules showed fast excited-state quenching (2.6 ± 1 ps) characteristic of individual nanocavities...
February 14, 2018: Nano Letters
Xu Yang, Fei Liu, Yu Zhang, Lu Wang, Yu-Fu Cheng
BACKGROUND: Low temperature is an important abiotic stress in plant growth and development, especially for thermophilic plants. Eggplants are thermophilic vegetables, although the molecular mechanism of their response to cold stress remains to be elucidated. MicroRNAs (miRNAs) are a class of endogenous small non-coding RNAs that play an essential role during plant development and stress responses. Although the role of many plant miRNAs in facilitating chilling tolerance has been verified, little is known about the mechanisms of eggplant chilling tolerance...
December 29, 2017: BMC Genomics
Raman Sankar, G Peramaiyan, I Panneer Muthuselvam, Suyang Xu, M Zahid Hasan, F C Chou
We report the single crystal growth and transport properties of a Weyl semimetal TaAs. Unsaturated large magnetoresistance of about 22 100% at 2 K and 9 T is observed. From the Hall measurement, carrier concentrations n  =  4.608  ×  1024 m-3 and p  =  3.099  ×  1024 m-3 , and mobilities µp   =  2.502 m2 V-1 s-1 and µn   =  16.785 m2 V-1 s-1 at 2 K are extracted. The de Haas-van Alphen oscillations at 2 K and 9 T suggest the presence of a Fermi surface, and the quantum electronic parameters such as effective cyclotron mass and Dingle temperature were obtained using Lifshitz-Kosevich fitting...
January 10, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Priten B Savaliya, Arun Thomas, Rishi Dua, Anuj Dhawan
We propose the design of switchable plasmonic nanoantennas (SPNs) that can be employed for optical switching in the near-infrared regime. The proposed SPNs consist of nanoantenna structures made up of a plasmonic metal (gold) such that these nanoantennas are filled with a switchable material (vanadium dioxide). We compare the results of these SPNs with inverted SPN structures that consist of gold nanoantenna structures surrounded by a layer of vanadium dioxide (VO2 ) on their outer surface. These nanoantennas demonstrate switching of electric-field intensity enhancement (EFIE) between two states (On and Off states), which can be induced thermally, optically or electrically...
October 2, 2017: Optics Express
Punnag Padhy, Mohammad Asif Zaman, Paul Hansen, Lambertus Hesselink
Nanoparticles trapped on resonant near-field apertures/engravings carved in plasmonic films experience optical forces due to the steep intensity gradient field of the aperture/engraving as well as the image like interaction with the substrate. For non-resonant nanoparticles the contribution of the substrate interaction to the trapping force in the vicinity of the trap (aperture/engraving) mode is negligible. But, in the case of plasmonic nanoparticles, the contribution of the substrate interaction to the low frequency stable trapping mode of the coupled particle-trap system increases as their resonance is tuned to the trap resonance...
October 16, 2017: Optics Express
Chunrui Han, Edward P J Parrott, Georges Humbert, Aurelian Crunteanu, Emma Pickwell-MacPherson
Broadband modulation of terahertz (THz) light is experimentally realized through the electrically driven metal-insulator phase transition of vanadium dioxide (VO2) in hybrid metal antenna-VO2 devices. The devices consist of VO2 active layers and bowtie antenna arrays, such that the electrically driven phase transition can be realized by applying an external voltage between adjacent metal wires extended to a large area array. The modulation depth of the terahertz light can be initially enhanced by the metal wires on top of VO2 and then improved through the addition of specific bowties in between the wires...
October 5, 2017: Scientific Reports
Omran Ahmadi, Seyed Bagher Mortazavi, Ali Khavanin, Hamidreza Mokarami
BACKGROUND: Accident analysis is the main aspect of accident investigation. It includes the method of connecting different causes in a procedural way. Therefore, it is important to use valid and reliable methods for the investigation of different causal factors of accidents, especially the noteworthy ones. OBJECTIVE: This study aimed to prominently assess the accuracy (sensitivity index [SI]) and consistency of the six most commonly used accident analysis methods in the petroleum industry...
November 17, 2017: International Journal of Occupational Safety and Ergonomics: JOSE
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