科研成果 by Year: 2014

For the real-time and low-delay video surveillance and teleconferencing applications, the newly video coding standard HEVC can achieve much higher coding efficiency over H.264/AVC. However, we still argue that the hierarchical prediction structure in the HEVC low-delay encoder still does not fully utilize the special characteristics of surveillance and conference videos that are usually captured by stationary cameras. In this case, the background picture (G-picture), which is modeled from the original input frames, can be used to further improve the HEVC low-delay coding efficiency meanwhile reducing the complexity. Therefore, we propose an optimization method for the hierarchical prediction and coding in HEVC for these videos with background modeling. First, several experimental and theoretical analyses are conducted on how to utilize the G-picture to optimize the hierarchical prediction structure and hierarchical quantization. Following these results, we propose to encode the G-picture as the long-term reference frame to improve the background prediction, and then present a G-picture-based bit-allocation algorithm to increase the coding efficiency. Meanwhile, according to the proportions of background and foreground pixels in coding units (CUs), an adaptive speed-up algorithm is developed to classify each CU into different categories and then adopt different speed-up strategies to reduce the encoding complexity. To evaluate the performance, extensive experiments are performed on the HEVC test model. Results show our method can averagely save 39.09% bits and reduce the encoding complexity by 43.63% on surveillance videos, whereas those are 5.27% and 43.68% on conference videos.

Organochlorine pesticides (OCPs) in placental tissue have been reported to be associated with an increased risk for fetal neural tube defects (NTDs). Our case-control study was performed to explore the association between maternal serum OCP concentration and NTD risk in offspring. Serum samples were collected from 117 mothers who delivered NTD infants (case group) and 121 mothers who delivered healthy infants (control group). Only three of the 25 OCPs were detected in more than half of the maternal serum samples. The median concentration of total OCPs in the case group was significantly higher than that of the control group. However, no dose-response relationships between higher levels of any individual OCPs or total OCPs and the risk of NTDs or subtypes were observed in either the unadjusted binary unconditional logistic regression model or the model adjusted by potential confounders. We conclude that no clear association between maternal serum OCP residues and NTD risk in offspring was observed in this population. Capsule: No clear association between maternal serum levels of organochlorine pesticides and risk of neural tube defects in offspring was observed for a Chinese population. (C) 2014 Elsevier B.V. All rights reserved.

Exposure to ultrafine particles poses a potential health risk to school children. While many studies have focused on measuring ultrafine particle (UFP) concentrations in environments where children are at risk of high exposure, few studies have examined the particle deposition in the respiratory tract of children. This study aims to examine the particle deposition in the respiratory tract of school children in different microenvironments. UFP size distribution data were collected in residential homes, school buses, school classrooms, and from school outdoor air in both rural and urban areas of South Texas. The size distribution data were input to the Multiple Path Particle Dosimetry model to calculate regional and total particle deposition fraction. A 24-hour-school-day exposure was simulated by adding the time children spend in each microenvironment. The maximum pulmonary deposition fraction occurs at a diameter ranging from 18 to 40 nm, depending on condition. Age mostly affected the pulmonary region and the total lung deposition with the highest deposition fraction observed for younger children. In addition, comparison of size-dependent regional deposition and particle concentration establishes an accurate depiction of children's exposure and dose profiles. While children only spend 4% of the day in the home source environment, that environment may account for up to 77% of total daily dose intake. Higher deposition fraction occurs at smaller particle size. Younger children show increased levels of particle deposition than older children. Exposure period does not correlate to daily percentage of dose intake. This research can be used to assess children's accumulative exposure to UFPs.

In this work, the performance of GaN-based MOS-Channel-HEMTs (MOSC-HEMTs) are shown to be greatly improved by a thin ALD-grown AlN interfacial layer inserted between the amorphous Al2O3 gate dielectric and GaN-channel. The single-crystalline AlN interfacial layer effectively blocks oxygen from the GaN surface and avoids the formation of detrimental Ga-O bonds. Frequency-dispersion in C-V characteristics has been effectively suppressed. The maximum drain current and field-effect mobility are boosted from 410 mA/mm and 98 cm(2)/V.s in a conventional Al2O3/GaN MOSC-HEMT to 660 mA/mm and 165 cm(2)/V.s in an Al2O3/AlN/GaN MOSC-HEMT, owing to improved interface quality. The devices also deliver a high ON/OFF current ratio of similar to 10(10), and significantly reduced dynamic on-resistance degradation.

Measurements of peroxyacetyl nitrate (PAN) were made at a Beijing urban site each August from 2005 to 2009. Over this 5-year period, the average PAN concentration for August in each year increased from 3 (2005) to 11.7 μg/m3 (2007); however, it decreased rapidly in 2008 (4.1 μg/m3). Generally, the variation over the 5 years showed a rise in the first part of the study period, followed by a decline. We considered two categories of local and regional air masses in this study, which revealed that the PAN concentration in Beijing was affected mainly by southeastern air masses. The August PAN variation was influenced predominantly by local air masses in 2005, but by 2009 regional air masses had become more important. This study showed the level and variation of PAN in the month of August in 5 consecutive years for the first time, and proved that control measures are useful in decreasing photochemical pollution; hence, these measures are probably feasible for other megacities too. Furthermore, this method of analyzing regional and local impacts might be useful for other studies as well.