Channel Pixel Research Articles

TDICCD拼接相机的像元响应非均匀性校正方法

To improve the Pixel Response Non-uniformity(PRNU) in a TDICCD mosaic camera,an algorithm was proposed to correct the PRNU between the channels and among the pixels in channels at different gains,deviations and integrated time.Then,a design method was given to implement the algorithm on a Field Programmable Gate Array(FPGA) platform.The experimental results indicate that the problems of PRNU could be solved at different gains,deviations and integrated time in the TDICCD mosaic camera.The PRNU of a single TDICCD could be decreased from 4.72% to 0.27%.In bad circumstance,the PRNU of the single TDICCD could be decreased from 4.68% to 2.13%.The actual image also proves that the pixel correction algorithm has high real time performance,high reliability and stability,and a satisfied result to the requirements of space-projects.It solves the real-time pixel correction problem of the PRNU in TDICCD mosaic cameras.

Giga-Pixel Lensfree Holographic Microscopy and Tomography Using Color Image Sensors

We report Giga-pixel lensfree holographic microscopy and tomography using color sensor-arrays such as CMOS imagers that exhibit Bayer color filter patterns. Without physically removing these color filters coated on the sensor chip, we synthesize pixel super-resolved lensfree holograms, which are then reconstructed to achieve ∼350 nm lateral resolution, corresponding to a numerical aperture of ∼0.8, across a field-of-view of ∼20.5 mm2. This constitutes a digital image with ∼0.7 Billion effective pixels in both amplitude and phase channels (i.e., ∼1.4 Giga-pixels total). Furthermore, by changing the illumination angle (e.g., ±50°) and scanning a partially-coherent light source across two orthogonal axes, super-resolved images of the same specimen from different viewing angles are created, which are then digitally combined to synthesize tomographic images of the object. Using this dual-axis lensfree tomographic imager running on a color sensor-chip, we achieve a 3D spatial resolution of ∼0.35 µm×0.35 µm×∼2 µm, in x, y and z, respectively, creating an effective voxel size of ∼0.03 µm3 across a sample volume of ∼5 mm3, which is equivalent to >150 Billion voxels. We demonstrate the proof-of-concept of this lensfree optical tomographic microscopy platform on a color CMOS image sensor by creating tomograms of micro-particles as well as a wild-type C. elegans nematode.

Microlens performance limits in sub-2μm pixel CMOS image sensors

CMOS image sensors with smaller pixels are expected to enable digital imaging systems with better resolution. When pixel size scales below 2 mum, however, diffraction affects the optical performance of the pixel and its microlens, in particular. We present a first-principles electromagnetic analysis of microlens behavior during the lateral scaling of CMOS image sensor pixels. We establish for a three-metal-layer pixel that diffraction prevents the microlens from acting as a focusing element when pixels become smaller than 1.4 microm. This severely degrades performance for on and off-axis pixels in red, green and blue color channels. We predict that one-metal-layer or backside-illuminated pixels are required to extend the functionality of microlenses beyond the 1.4 microm pixel node.

Radiation hard diamond pixel detectors

Even though the LHC has not yet begun, already a high luminosity upgrade of the LHC is being planned. The sensors at radii of about 3 cm will have to withstand an expected fluence exceeding 10 16 particles/cm 2 in 5 years. At this fluence current silicon sensors cease to function. Due to its large bandgap and high displacement energy, diamond is an intrinsically very radiation hard material. Combined with its fast charge collection, its low dielectric constant and the absence of thermally generated leakage current, diamond is a very interesting detector material for the sensors close to the beam. A full size, 61×16.5 mm 2, ATLAS pixel module using chemical-vapor deposition (CVD) diamond was built and characterized in a beam test. The measured position resolution is consistent with the expected binary resolution. The efficiency was larger than 97%. Nowadays also large size single-crystal CVD diamonds are available. A single-crystal diamond was used to produce a 2880 channel pixel detector. This detector showed an 99.992±0.002% efficiency at an electric field as low as 0.25 V/μm.

A Mouse Model for Monitoring Calpain Activity under Physiological and Pathological Conditions

Calpains are Ca(2+)-dependent cysteine proteases known to be important for the regulation of cell functions and which aberrant activation causes cell death in a number of degenerative disorders. To provide a tool for monitoring the status of calpain activity in vivo under physiological and pathological conditions, we created a mouse model that expresses ubiquitously a fluorescent reporter consisting of eCFP and eYFP separated by a linker cleavable by the ubiquitous calpains. We named this mouse CAFI for calpain activity monitored by FRET imaging. Our validation studies demonstrated that the level of calpain activity correlates with a decrease in FRET (fluorescence resonance energy transfer) between the two fluorescent proteins. Using this model, we observed a small level of activity after denervation and fasting, a high level of activity during muscle regeneration and ischemia, and local activity in damaged myofibers after exercise. Finally, we crossed the CAFI mouse with the alpha-sarcoglycan-deficient model, demonstrating an increase of calpain activity at the steady state. Altogether, our results present evidence that CAFI mice could be a valuable tool in which to follow calpain activity at physiological levels and in disease states.

Rapid 4-Stokes parameter determination using a motorized rotating retarder

A motorized rotating retarder, a linear polarizer, and a digital camcorder are used to obtain polarization profiles of natural daylight scenes. A correlation technique synchronizes real-time video frames with respect to the rotating retarder's fast axis. Polarization parameters are calculated for each red-green-blue (RGB) channel and scene pixel. Extending the quasimonochromatic approximation to larger bandwidths is solved by expressing the Stokes parameters explicitly as functions of wavelength. A detailed numerical analysis examines errors due to ill-conditioning effects that are associated with specific relative angular orientations of the optical components. A comparison of the theoretical results with empirical data from the digital camcorder provides a validation process for the results in this paper. A RGB pseudocolor encoding algorithm provides a means to visualize the polarization imagery. An ellipticity study was conducted during the early morning hours when scene lighting conditions change rapidly. A comparison of the results from a digital still camera, using a 30-s data acquisition time period, was made with respect to a 0.6-s time period for the rotating retarder configuration. The results clearly show that errors due to temporal registration effects are dramatically reduced as the time interval between images goes to zero.

PTEN Deletion Leads to Up-regulation of a Secreted Growth Factor Pleiotrophin

Tumor suppressor gene PTEN is highly mutated in a wide variety of human tumors. To identify unknown targets or signal transduction pathways that are regulated by PTEN, microarray analysis was performed to compare the gene expression profiles of Pten null mouse embryonic fibroblasts (MEFs) cell lines and their isogenic counterparts. Expression of a heparin binding growth factor, pleiotrophin (Ptn), was found to be up-regulated in Pten-/- MEFs as well as Pten null mammary tumors. Further experiments revealed that Ptn expression is regulated by the PTEN-PI3K-AKT pathway. Knocking down the expression of Ptn by small interfering RNA resulted in the reduction of Akt and GSK-3beta phosphorylation and suppression of the growth and the tumorigenicity of Pten null MEFs. Our results suggest that PTN participates in tumorigenesis caused by PTEN loss and PTN may be a potential target for anticancer therapy, especially for those tumors with PTEN deficiencies.

Membrane-associated STAT3 and PY-STAT3 in the Cytoplasm

Signal transduction from the plasma membrane to the nucleus by STAT proteins is widely represented as exclusively a soluble cytosolic process. Using cell-fractionation methods, we observed that approximately 5% of cytoplasmic STAT3 was constitutively associated with the purified early endosome (EE) fraction in human Hep3B liver cells. By 15-30 min after interleukin-6 (IL-6) treatment, up to two-thirds of cytoplasmic Tyr-phosphorylated STAT3 can be associated with the purified early endosome fraction (Rab-5-, EEA1-, transferrin receptor-, and clathrin-positive fraction). Electron microscopy, immunofluorescence, and detergent dissection approaches confirmed the association of STAT3 and PY-STAT3 with early endosomes. STAT3 was constitutively associated with clathrin heavy chain in membrane and in the 1- to 2-MDa cytosolic complexes. The membrane association was dynamic in that, within 15 min of treatment with the vicinal-thiol cross-linker phenylarsine oxide, there was a dramatic increase in bulk STAT3 association with sedimentable membranes. The functional contribution of PY-STAT3 association with the endocytic pathway was evaluated in transient transfection assays using IL-6-inducible STAT3-reporter-luciferase constructs and selective regulators of this pathway. STAT3-transcriptional activation was inhibited by expression constructs for dominant negative dynamin K44A, epsin 2a, amphiphysin A1, and clathrin light chain but enhanced by that for the active dynamin species MxA. Taken together, these studies emphasize the contribution of the endocytic pathway to productive IL-6/STAT3 signaling.

자연하천 형상을 이용한 최적 흐름분배 알고리즘의 개발

수치고도모형을 이용한 흐름분배 알고리즘들은 지형을 따른 흐름의 분산특성을 잘 기술해 주는 방향으로 발달되어 왔지만, 수로격자의 연결성, 지형기복을 따른 다양한 분산특성, 수로격자크기 등과 관련한 한계성을 가지고 있다. 기존 흐름 알고리즘들이 흐름분배 결정에 사용한 지형 데이터들은 수치고도모형에서 산출가능한 흐름누적면적과 경사도로서 유역내 지배적인 흐름경로인 수로격자의 위치와 크기에 대한 고려를 하지 않는다. 따라서 본 연구에서는 기존 알고리즘들의 단점인 수로의 연결성과 복잡한 지형을 따른 다양한 흐름분산 특성을 기술할 수 있는 흐름 분배 알고리즘을 제안하고, 유전자 알고리즘을 이용하여 수로격자의 위치와 크기를 가장 잘 표현할 수 있도록 최적화하였으며, 기존의 방법에 비해 개선된 결과를 얻을 수 있었다. The flow apportioning algorithms with digital elevation models have been developed to reflect reasonable flow divergence properties but they showed several defects related to the connectivity of channel cells, various divergence features along to local topography and channel cells' size etc. Topographic data used by existing flow apportioning algorithms are flow accumulation area and local slope. However, the size and location of channel cells which play the dominant role in the flow pathway were not properly considered. Therefore, a new flow apportioning algorithm considering various flow divergence characteristics in the complicate terrain is proposed. The GA optimization scheme is used to represent the location and scale of the channel pixel. Improved result can be obtained by using both a new flow apportioning algorithm and optimization.

Digital elevation analysis for distributed hydrological modeling: Reducing scale dependence in effective hydraulic conductivity values

The recent widespread availability of digital terrain data has made automatic procedures for topographic analyses popular. Previous studies have shown that hydrological models and their effective parameter values are dependent on the resolution of the elevation grid. This paper examines the analysis of raster elevation data within the topography‐based model, TOPMODEL, framework. It is demonstrated that the algorithm used in processing channel pixels in calculating the topographic index k=ln(a/tanβ) can have a dramatic effect on the sensitivity of effective parameter values to the grid size. Suggestions are made for calculating the topographic index of channel pixels, consistent with the TOPMODEL assumptions, that strongly decrease the sensitivity of the calibrated effective hydraulic conductivity values to grid size.

Data pre‐processing: Stratospheric aerosol perturbing effect on the remote sensing of vegetation: Correction method for the composite NDVI after the Pinatubo eruption

Stratospheric aerosols produced by the eruption of Mount Pinatubo in the Philippines (6 June, 1991) had a detectable effect on NOAA AVHRR data. Following the eruption, a longitudinally homogeneous dust layer was observed between 20°N and 20°S. The largest optical thickness observed for the dust layer was 0.4–0.6 at 0.5 pm. The amount of aerosols produced by Mount Pinatubo was two to three times greater than that produced by El Chichon and the Stratospheric Aerosol and Gas Experiment (SAGE) on‐board the Earth Radiation Budget Experiment was not able to give quantitative estimate of aerosol optical thickness because of saturation problem. The monthly composite Normalized Difference Vegetation Index (NDVI) (generally bounded between ‐0.1 and 0.6) has systematically decreased by approximately 0.15 two months after the eruption. Such atmospheric effect has never been observed on composite product and is related to the persistence and spatial extent of the aerosol layer causing the composite technique to fail. Therefore, long term monitoring of vegetation using the NDVI necessitates correction of the effect of stratospheric aerosols. In this paper we present an operational stratospheric aerosol correction scheme adopted by the Laboratory for Terrestrial Physics, NASA/GSFC. The stratospheric aerosol distribution is assumed to be only variable with latitude. Each 9 days the latitudinal distribution of the optical thickness is computed by inverting radiances observed in AVHRR channel 1 (0.63 μm) and channel 2 (0.83 μm) over the Pacific Ocean. This radiance data set is used to check the validity of model used for inversion by checking consistency of the optical thickness deduced from each channel as well as optical thickness deduced from different scattering angles. Using the optical thickness profile previously computed and radiative transfer code assuming lambertian boundary condition, each pixel of channel 1 and 2 are corrected prior to computation of NDVI. Comparison between corrected, not corrected, and years prior to Pinatubo eruption (1989, 1990) NDVI composite, shows the necessity and the accuracy of the operational correction scheme.