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Search Results: 1 - 10 of 374243 matches for " J. Liu "
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Analytical Calculation of the Compton Single Scatter Component of Pencil Beam Scatter Kernel for Scatter Correction in kV Cone Beam CT (kV-CBCT)  [PDF]
Jie Liu, J. Daniel Bourland
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2018, DOI: 10.4236/ijmpcero.2018.72019
Abstract:

The accuracy of conventional superposition or convolution methods for scatter correction in kV-CBCT is usually compromised by the spatial variation of pencil-beam scatter kernel (PBSK) due to finite size, irregular external contour and heterogeneity of the imaged object. This study aims to propose an analytical method to quantify the Compton single scatter (CSS) component of the PBSK, which dominates the spatial distribution of total scatter assuming that multiple scatter can be estimated as a constant background and Rayleigh scatter is the secondary source of scatter. The CSS component of PBSK is the line integration of scatter production by incident primary photons along the beam line followed by the post-scattering attenuation as the scattered photons traverse the object. We propose to separate the object-specific attenuation term from the line integration and equivalently replace it with an average value such that the line integration of scatter production is object independent but only beam specific. We derived a quartic function formula as an approximate solution to the spatial distribution of the unattenuated CSS component of PBSK. The “effective scattering center” is introduced to calculate the average attenuation. The proposed analytical framework to calculate the CSS was evaluated using parameter settings of the On-Board Imager kV-CBCT system and was found to be in high agreement with the reference results. The proposed method shows highly increased computational efficiency compared to conventional analytical calculation methods based on point scattering model. It is also potentially useful for correcting the spatial variant PBSK in adaptive superposition method.

VLBI observation of giant radio galaxy J1313+696 at 2.3/8.4 GHz
X. Liu,J. Liu
Physics , 2010, DOI: 10.1007/s10509-008-9964-7
Abstract: We report the result of VLBI observation of the giant radio galaxy J1313+696 (4C +69.15) at 2.3/8.4 GHz, only the core component of the giant radio galaxy was detected in the VLBI observation at the dual frequencies. The result shows a steep spectrum core with $\alpha=-0.82$ ($S \propto \nu^{\alpha}$) between 2.3 GHz and 8.4 GHz. The steep spectrum core may be a sign of renewed activity. Considering also the upper limit flux density of 2.0 mJy at 0.6 GHz from Konar et al. 2004 the core has a GHz-peaked spectrum, implying that the core is compact and absorbed. Further high resolution VLBI observations are needed to identify if the steep spectrum core is consisting of a core and steep spectrum jet.
Financial Innovation and Aggregate Risk Sharing  [PDF]
Rodrigo J. Hernandez, Pu Liu, Yingying Shao
Theoretical Economics Letters (TEL) , 2018, DOI: 10.4236/tel.2018.811143
Abstract: In this paper we examine the impact of financial innovations on real economy. Based on data for US banks’ off-balance sheet activities from 1995 to 2013, we investigate aggregate risk sharing in two different channels: Personal consumption smoothening and personal income insurance. The results show that the use of financial innovations contributes to a reduction in the exposure of personal income and consumption to state-specific economic shocks, and the results suggest a positive role played by financial innovations in real economy.
High-order harmonic generation from diatomic molecules with large internuclear distance: The effect of two-center interference
Y. J. Chen,J. Liu
Physics , 2007, DOI: 10.1103/PhysRevA.77.013410
Abstract: In the present paper, we investigate the high-order harmonic generation (HHG) from diatomic molecules with large internuclear distance using a strong field approximation (SFA) model. We find that the hump and dip structure emerges in the plateau region of the harmonic spectrum, and the location of this striking structure is sensitive to the laser intensity. Our model analysis reveals that two-center interference as well as the interference between different recombination electron trajectories are responsible for the unusual enhanced or suppressed harmonic yield at a certain order, and these interference effects are greatly influenced by the laser parameters such as intensity.
Nanomaterials enhance osteogenic differentiation of human mesenchymal stem cells similar to a short peptide of BMP-7
Lock J, Liu H
International Journal of Nanomedicine , 2011, DOI: http://dx.doi.org/10.2147/IJN.S24493
Abstract: nomaterials enhance osteogenic differentiation of human mesenchymal stem cells similar to a short peptide of BMP-7 Original Research (3974) Total Article Views Authors: Lock J, Liu H Published Date November 2011 Volume 2011:6 Pages 2769 - 2777 DOI: http://dx.doi.org/10.2147/IJN.S24493 Jaclyn Lock, Huinan Liu Department of Bioengineering, University of California, Riverside, CA, USA Background: Nanomaterials have unique advantages in controlling stem cell function due to their biomimetic characteristics and special biological and mechanical properties. Controlling adhesion and differentiation of stem cells is critical for tissue regeneration. Methods: This in vitro study investigated the effects of nano-hydroxyapatite, nano-hydroxyapatite-polylactide-co-glycolide (PLGA) composites, and a bone morphogenetic protein (BMP-7)-derived short peptide (DIF-7c) on osteogenic differentiation of human mesenchymal stem cells (MSC). The peptide was chemically functionalized onto nano-hydroxyapatite, incorporated into a nanophase hydroxyapatite-PLGA composite or PLGA control, or directly injected into culture media. Results: Unlike the PLGA control, the nano-hydroxyapatite-PLGA composites promoted adhesion of human MSC. Importantly, nano-hydroxyapatite and nano-hydroxyapatite-PLGA composites promoted osteogenic differentiation of human MSCs, comparable with direct injection of the DIF-7c peptide into culture media. Conclusion: Nano-hydroxyapatite and nano-hydroxyapatite-PLGA composites provide a promising alternative in directing the adhesion and differentiation of human MSC. These nanocomposites should be studied further to clarify their effects on MSC functions and bone remodeling in vivo, eventually translating to clinical applications.
On selection of the optimal data time interval for real-time hydrological forecasting
J. Liu,D. Han
Hydrology and Earth System Sciences Discussions , 2012, DOI: 10.5194/hessd-9-10829-2012
Abstract: With the advancement in modern telemetry and communication technologies, hydrological data can be collected with an increasingly higher sampling rate. An important issue deserving attention from the hydrological community is what suitable time interval of the model input data should be chosen in hydrological forecasting. Such a problem has long been recognised in the control engineering community but is a largely ignored topic in operational applications of hydrological forecasting. In this study, the intrinsic properties of rainfall-runoff data with different time intervals are first investigated from the perspectives of the sampling theorem and the information loss using the discrete wavelet decomposition tool. It is found that rainfall signals with very high sampling rates may not always improve the accuracy of rainfall-runoff modelling due to the catchment low-pass filtering effect. To further investigate the impact of data time interval in real-time forecasting, a real-time forecasting system is constructed by incorporating the Probability Distributed Model (PDM) with a real-time updating scheme, the autoregressive-moving average (ARMA) model. Case studies are then carried out on four UK catchments with different concentration times for real-time flow forecasting using data with different time intervals of 15 min, 30 min, 45 min, 60 min, 90 min and 120 min. A positive relation is found between the forecast lead time and the optimal choice of the data time interval, which is also highly dependent on the catchment concentration time. Finally, based on the conclusions from the case studies, a hypothetical pattern is proposed in three-dimensional coordinates to describe the general impact of the data time interval and to provide implications on the selection of the optimal time interval in real-time hydrological forecasting. Although nowadays most operational hydrological systems still have low data sampling rates (daily or hourly), the trend in the future is that higher sampling rates will become widespread and there is an urgent need for both academic and practising hydrologists to realise the significance of the data time interval issue. It is important that more case studies in different catchments with various hydrological forecasting models should be explored in the future to further verify and improve the proposed hypothetical pattern.
Nanomaterials enhance osteogenic differentiation of human mesenchymal stem cells similar to a short peptide of BMP-7
Lock J,Liu H
International Journal of Nanomedicine , 2011,
Abstract: Jaclyn Lock, Huinan Liu Department of Bioengineering, University of California, Riverside, CA, USA Background: Nanomaterials have unique advantages in controlling stem cell function due to their biomimetic characteristics and special biological and mechanical properties. Controlling adhesion and differentiation of stem cells is critical for tissue regeneration. Methods: This in vitro study investigated the effects of nano-hydroxyapatite, nano-hydroxyapatite-polylactide-co-glycolide (PLGA) composites, and a bone morphogenetic protein (BMP-7)-derived short peptide (DIF-7c) on osteogenic differentiation of human mesenchymal stem cells (MSC). The peptide was chemically functionalized onto nano-hydroxyapatite, incorporated into a nanophase hydroxyapatite-PLGA composite or PLGA control, or directly injected into culture media. Results: Unlike the PLGA control, the nano-hydroxyapatite-PLGA composites promoted adhesion of human MSC. Importantly, nano-hydroxyapatite and nano-hydroxyapatite-PLGA composites promoted osteogenic differentiation of human MSCs, comparable with direct injection of the DIF-7c peptide into culture media. Conclusion: Nano-hydroxyapatite and nano-hydroxyapatite-PLGA composites provide a promising alternative in directing the adhesion and differentiation of human MSC. These nanocomposites should be studied further to clarify their effects on MSC functions and bone remodeling in vivo, eventually translating to clinical applications. Keywords: human mesenchymal stem cells, osteogenesis, stem cell differentiation, bone morphogenetic protein, peptide delivery, nanocomposites
The Spirit Will Continue
K. J. Ray Liu
EURASIP Journal on Advances in Signal Processing , 2003, DOI: 10.1155/s1687617202001762
Abstract:
A novel phase shift technique in shearography for NDT
Liu Z.,Gao J.
EPJ Web of Conferences , 2010, DOI: 10.1051/epjconf/20100633003
Abstract: Digital shearography (DS) is a whole-field non-contacting optical method for nondestructive testing (NDT) of subsurface flaws and strain measurement. In this paper, we describe a novel phaseshifting technique in DS for nondestructive evaluation (NDE) and NDT of quasi dynamic behaviour of objects subject to varying loads. A Wollaston lens, a precise wave plate device and a polariser are employed to introduce constant phase differences between two shearing wavefronts. The wave plate device is in front of the polariser, which has a transmissive wavefront distortion of less than 1/8 wavelength. Phase difference can be adjusted by rotating the polariser. The rotation for angle adjusting can be easily carried out according to the requirement of the phase shifting. In this technique, the phase shifting is performed only on the static images of the object before deformation or loading. By setting the angle of the polariser to 0o, -60o and 60o, three speckle patterns with the defined phase differences are captured, and are referred to as initial speckle patterns I1,0, I1,-60 and I1,60. Afterwards, the polariser is reset to 0o before loading. The speckle pattern I0 is treated as a base pattern, and will be subtracted from the subsequent speckle patterns which are captured in the quasi dynamic deformation process. During the quasi dynamic deformation process, the optical path and the entire optical set-up will be kept unchanged, and a series of speckle patterns (Im,0, m=2,3,…..) which carry the deformation information will be quickly captured. In the meantime, fast image subtractions will be performed. The speckle fringes (Im,0 -I1,0) will be displayed in real-time. In detailed post-processing, phase of differences method (PDM) [1] is used to extract phase information from the speckle images Im,0 -I1,0, I1,0, I1,-60 and I1,60. Specifically, when a three phase step technique is employed, the phase of the fringe pattern (Im,0-I1,0) can be calculated from (Im,0 -I1,0)+ I1,0 -I1,-60, (Im,0 -I1,0), and (Im,0 -I1,0)+ I1,0 -I1,60. Because this temporal phase shifting is not performed in the deformation process, the technique is suitable for NDT and NDE of quasi dynamic deformation behaviour of an object. The technique only requires three speckle patterns with phase differences prior to the object deformation. When a varying or quasi dynamic load is applied on the object, no physical phase shifting is needed to be conducted when sequential speckle patterns are recorded by a digital camera during the deformation process. Compared with the (5, n) temporal phase shifting tech
Status of Marine Biodiversity of the China Seas
J. Y. Liu
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0050719
Abstract: China's seas cover nearly 5 million square kilometers extending from the tropical to the temperate climate zones and bordering on 32,000 km of coastline, including islands. Comprehensive systematic study of the marine biodiversity within this region began in the early 1950s with the establishment of the Qingdao Marine Biological Laboratory of the Chinese Academy of Sciences. Since that time scientists have carried out intensive multidisciplinary research on marine life in the China seas and have recorded 22,629 species belonging to 46 phyla. The marine flora and fauna of the China seas are characterized by high biodiversity, including tropical and subtropical elements of the Indo-West Pacific warm-water fauna in the South and East China seas, and temperate elements of North Pacific temperate fauna mainly in the Yellow Sea. The southern South China Sea fauna is characterized by typical tropical elements paralleled with the Philippine-New Guinea-Indonesia Coral triangle typical tropical faunal center. This paper summarizes advances in studies of marine biodiversity in China's seas and discusses current research mainly on characteristics and changes in marine biodiversity, including the monitoring, assessment, and conservation of endangered species and particularly the strengthening of effective management. Studies of (1) a tidal flat in a semi-enclosed embayment, (2) the impact of global climate change on a cold-water ecosystem, (3) coral reefs of Hainan Island and Xisha-Nansha atolls, (4) mangrove forests of the South China Sea, (5) a threatened seagrass field, and (6) an example of stock enhancement practices of the Chinese shrimp fishery are briefly introduced. Besides the overexploitation of living resources (more than 12.4 million tons yielded in 2007), the major threat to the biodiversity of the China seas is environmental deterioration (pollution, coastal construction), particularly in the brackish waters of estuarine environments, which are characterized by high productivity and represent spawning and nursery areas for several economically important species. In the long term, climate change is also a major threat. Finally, challenges in marine biodiversity studies are briefly discussed along with suggestions to strengthen the field. Since 2004, China has participated in the Census of Marine Life, through which advances in the study of zooplankton and zoobenthos biodiversity were finally summarized.
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