Magnetic equilibrium and transport modeling of divertors for solutions to exhaust problems in tokamaks

Problems of intense exhaust heat and particle fluxes incident on material surfaces are obstacles for magnetic confinement fusion in tokamaks. Advanced divertors offer magnetic solutions to the problems by (a) increasing the plasma-wetted area via flux expansion at the targets, (b) increasing the connection length and (c) in the case of X-divertors opening regimes of stable, detached operation via poloidal flaring. By magnetic equilibrium modeling using CORSICA code, X-divertors appear feasible on NSTX-U tokamak, requiring no hardware change and respecting coil current limits. Transport simulations using SOLPS code on NSTX-U have demonstrated the advantages of the X-divertor over the standard divertor: reducing target heat and particle fluxes, achieving detachment with a lower upstream density and stabilizing the detachment front near the target.Physic

Load Balancing Dynamic Source Routing Protocol Based on Multi-Path Routing

A HWMP improved routing protocol (HWMMRP) is proposed in this paper. The protocol adopts the integrated link state routing criterion algorithm LCCM providing small overhead, with factors such as bandwidth, queue length and noise interference fully considered. In order to solve the problem of the tree routing mechanism being easily congested at the root node, a multi-path multi-gateway shunting mechanism is applied. A multipath routing mechanism is also incorporated in the reactive routing mode. Both the new criteria and the protocol are simulated in the NS-2 environment, and are compared with comparable protocols. The experimental results show that our protocol can effectively avoid node congestion, and provides a better dynamic load balancing capability as well as a better performance than the standard HWMP and AODV protocols

Multimodal photoacoustic imaging: systems, applications, and agents

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Multimodality endoscopic imaging technology for visualization of layered architecture and vasculature

Endoscopic imaging technologies, such as endoscopic optical coherence tomography (OCT), near infrared (NIR) fluorescence, photoacoustic (PA), and ultrasound (US) have been used to investigate vascular and morphological changes as hallmarks of early cancer in the gastrointestinal (GI) tract. Here, we developed two multimodality imaging systems which are integrated PA/US and integrated OCT/NIR fluorescence which can obtain layered architecture and vasculature simultaneously. In vivo imaging of rectum wall from Sprague Dawley (SD) rats with these two imaging systems were demonstrated. Both imaging systems enable the use of one imaging probe for performing two different imaging, thereby improving prognosis by early detection and reducing costs. For integrated PA/US, the architectural morphology and vasculature of the rectum wall were visualized without the usage of contrast agent, but slow imaging speed and usage of match medium are the main limitations for clinical translation. With regard to the integrated OCT/NIR fluorescence, it is able to perform high speed imaging, however the addition of contrast agent and limited imaging depth are the main concern for clinical application

Second harmonic optical coherence tomography

Second harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical response of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second harmonic waves from collagen harvested from rat tail tendon and a reference nonlinear crystal. Second harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of second harmonic generation on molecular and tissue structures, this technique offers contrast and resolution enhancement to conventional optical coherence tomography.Comment: 3 pages, 5 figures. Submitted on November 8, 2003, this paper has recently been accepted by Optics Letter

ARF-OCE for mapping mechanical properties of ocular and vascular tissues

Elastography is an imaging modality for clinical diagnosis based on the tissue stiffness. Benefiting from the high resolution, three-dimensional, and noninvasive nature of optical coherence tomography (OCT), optical coherence elastography (OCE) has the ability to determine elastic properties with a resolution of ~10 μm in 3D. Typical OCE imaging includes excitation for inducing mechanical vibrations, measurement of the sample response using OCT, and estimation of elastic parameters. Acoustic radiation force (ARF) generated by an ultrasonic transducer can noninvasively excite internal tissues without contact; thus, ARF-OCE is suitable for measuring the mechanical properties in deeper tissues. For assessment of the elastic properties of tissues using ARF-OCE, the shear wave velocity, resonant frequency, and vibrational displacement can be measured. Shear wave velocity measurements can be conveniently used for quantitative calculation of the elastic modulus.1-3 The resonant frequency of a tissue has a squared relationship with the Young\u27s modulus, and thus can quantify the elasticity.4 Vibrational displacement can be compared directly when the same pressure is applied to different samples.5 Several diseases are accompanied by and result in the changes in composition and local geometry of tissues. Keratoconus, which causes vision distortions and blurriness, will change the geometry of the cornea. The development of presbyopia is generally caused by the loss of elasticity in the lens. The composition and biomechanical properties of vessels will usually be altered when atherosclerosis occurs. The ARF-OCE technology provides a new opportunity for the early diagnosis of ocular and vascular diseases. Based on the shear wave measurements, our system can be used to quantify the elastic modulus of the cornea and the crystalline lens. By comparing the vibrational displacement, we have detected the differences between normal and cross-linked cornea.6 Recently we developed a miniature probe for mapping the mechanical properties of vascular lesions using ARF-OCE. It has the ability to detect the a vulnerable plaque due to its higher stiffness.7 Because of the noninvasive nature, ARF-OCE has the potential to perform in vivo imaging of deep tissues for the early diagnosis of ocular and vascular diseases. 1. Zhu, J., Qu, Y., Ma, T., Li, R., Du, Y., Huang, S., Shung, K.K., Zhou, Q. and Chen, Z., 2015. Imaging and characterizing shear wave and shear modulus under orthogonal acoustic radiation force excitation using OCT Doppler variance method. Optics letters, 40(9): 2099-2102. 2. Zhu, J., Qi, L., Miao, Y., Ma, T., Dai, C., Qu, Y., He, Y., Gao, Y., Zhou, Q. and Chen, Z., 2016. 3D mapping of elastic modulus using shear wave optical micro-elastography. Scientific reports, 6: 35499. 3. Xu, X., Zhu, J. and Chen, Z., 2016. Dynamic and quantitative assessment of blood coagulation using optical coherence elastography. Scientific reports, 6: 24294. 4. Qi, W., Li, R., Ma, T., Li, J., Kirk Shung, K., Zhou, Q. and Chen, Z., 2013. Resonant acoustic radiation force optical coherence elastography. Applied physics letters, 103(10): 103704. 5. Qi, W., Li, R., Ma, T., Kirk Shung, K., Zhou, Q. and Chen, Z., 2014. Confocal acoustic radiation force optical coherence elastography using a ring ultrasonic transducer. Applied physics letters, 104(12): 123702. 6. Qu, Y., Ma, T., He, Y., Zhu, J., Dai, C., Yu, M., Huang, S., Lu, F., Shung, K.K., Zhou, Q. and Chen, Z., 2016. Acoustic radiation force optical coherence elastography of corneal tissue. IEEE Journal of Selected Topics in Quantum Electronics, 22(3): 288-294. Qu, Y., Ma, T., He, Y., Yu, M., Zhu, J., Miao, Y., Dai, C., Patel, P., Shung, K.K., Zhou, Q. and Chen, Z., 2017. Miniature probe for mapping mechanical properties of vascular lesions using acoustic radiation force optical coherence elastography. Scientific Reports, 7: 473

Multimodality endoscopic imaging technology for visualization of layered architecture and vasculature

Endoscopic imaging technologies, such as endoscopic optical coherence tomography (OCT), near infrared (NIR) fluorescence, photoacoustic (PA), and ultrasound (US) have been used to investigate vascular and morphological changes as hallmarks of early cancer in the gastrointestinal (GI) tract. Here, we developed two multimodality imaging systems which are integrated PA/US and integrated OCT/NIR fluorescence which can obtain layered architecture and vasculature simultaneously. In vivo imaging of rectum wall from Sprague Dawley (SD) rats with these two imaging systems were demonstrated. Both imaging systems enable the use of one imaging probe for performing two different imaging, thereby improving prognosis by early detection and reducing costs. For integrated PA/US, the architectural morphology and vasculature of the rectum wall were visualized without the usage of contrast agent, but slow imaging speed and usage of match medium are the main limitations for clinical translation. With regard to the integrated OCT/NIR fluorescence, it is able to perform high speed imaging, however the addition of contrast agent and limited imaging depth are the main concern for clinical application