排序方式: 共有33条查询结果,搜索用时 15 毫秒
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Distributions of the Two-Dimensional DCT Coefficients for Images 总被引:1,自引:0,他引:1
For a two-dimensional discrete cosine transform (DCT) image coding system, there have been different assumptions concerning the distributions of the transform coefficients. This paper presents results of distribution tests that indicate that for many images the statistics of the coefficients are best approximated by a Gaussian distribution for the DC coefficient and a Laplacian distribution for the other coefficients. Furthermore, from a simulation of the DCT coding System it is shown that the assumption that the coefficients are Laplacian yields a higher actual output signal-to-noise ratio and a much better agreement between theory and simulation than the Gaussian assumption. 相似文献
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Reininger R Hulbert SL Johnson PD Sadowski JT Starr DE Chubar O Valla T Vescovo E 《The Review of scientific instruments》2012,83(2):023102
A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-ray photon energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemission spectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances. 相似文献
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New knowledge about the deformation behaviour of Frankfurt clay und unloading conditions. Tishman and Speyer planed the construction of a new building complex “Opernturm” in the down town of Frankfurt, Germany. The construction of the new High‐Rise building required the demolishing of the old two high rise buildings of the Zurich insurance company. After demolishing the old high rise buildings, a time delay of about 6years has occurred. The deformations of the rest basement of the old buildings as well as the deformation of Neighbouring construction such as the underground tunnel were observed with time as a part of validating the serviceability requirements of the neighbouring constructions. The results of these measurements regarding the time effect on the behaviour of Frankfurt overconsolidated clay under unloading conditions will be presented. Furthermore, the results of cross hole tests that were carried out as a part of the design of the suggested piled raft foundation of the new high rise building to investigate the dynamic behaviour of Frankfurt subsoil will be demonstrated and discussed. 相似文献
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Hu YF Zuin L Wright G Igarashi R McKibben M Wilson T Chen SY Johnson T Maxwell D Yates BW Sham TK Reininger R 《The Review of scientific instruments》2007,78(8):083109
The variable line spacing plane grating monochromator beamline at the Canadian Light Source (CLS) employs three grazing incidence variable line spacing gratings to cover a photon energy range of 5-250 eV. It uses a 185 mm period length planar permanent magnet insertion device as the photon source, sharing a straight section with another soft x-ray beamline at the CLS. The commissioning and performance of the beamline is reported. The high resolution photoabsorption spectra of Ar and PF(5) gases are reported. A resolving power of over 40,000 for photons in the low energy region and >10,000 for a wider energy range (8-200 eV) can be achieved. A photon flux of up to 2 x 10(12) photons/s per 100 mA with slit settings of 50 microm has been measured. 相似文献
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Epidermal growth factor receptors (EGFR) were labeled with 10 nm immunogold and examined on uncoated specimens of A431 human epidermoid carcinoma cells. A field emission gun and a high-sensitivity YAG ring detector were used to demonstrate the affinity labeling simultaneously in the secondary-electron (SE) and backscattered-electron (BSE) modes with a low accelerating voltage (Vo). At Vo=2kV, the SE and BSE signals were too weak to identify all markers, while at Vo=3–7 kV labeling was observed unambiguously in both the SE and BSE modes with smaller and higher working distances. Increasing the Vo to above 7 kV sometimes provokes instability of the specimens. A Vo of ? 10 kV produces charging artifacts in the SE image, but permits a BSE image of the gold markers providing additional topographic information. In conclusion, immunogold labeling can be used with good results for uncoated specimens. 相似文献
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A joint rate control algorithm for variable bit rate (VBR) MPEG-compressed digital video on point-to-point permanent virtual
circuit (PVC) ATM links is proposed. The algorithm controls the encoding mode of a number of video encoders that operate either
on VBR or constant bit rate (CBR) mode. The algorithm selects the encoding mode based on the buffer occupancy of a multiplexer
co-located with the encoders that interfaces them to the PVC link. VBR encoding is the predominant encoding mode used during
congestion-free periods. CBR mode is used only during congested periods. When CBR is selected, new bit rates are jointly assigned
to the encoders based on their relative encoding complexities. The bit rate assigned to the encoders are enforced by a CBR
rate control local to each encoder. The performance of the joint rate control algorithm is evaluated through simulation of
a packet multiplexer, where a number of connections are multiplexed onto a fixed-capacity channel. The performance is compared
to that of multiplexing conventional CBR and open-loop VBR from the video quality and bandwidth efficiency points of view.
Simulation results show that the proposed algorithm improves performance over multiplexed conventional CBR or open-loop VBR
MPEG video, without significantly increasing implementation complexity. The application of the algorithm to video-on-demand
over ATM is discussed. 相似文献
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Reininger R Kriesel K Hulbert SL Sánchez-Hanke C Arena DA 《The Review of scientific instruments》2008,79(3):033108
We present an entrance slitless beamline design capable of maintaining its very high performance in terms of energy resolution (>10(4)) and spot size (4x4 microm2) at the sample position despite being exposed to more than 2.15 kW of undulator radiation and a maximum power density on the optics of more than 0.9 W/mm2. Ray tracing simulations of this beamline under the worst-case thermal deformations of the optical element surfaces verify that appropriate focusing corrections are able to cancel the deleterious effects of these deformations. One of the necessary conditions for this cancellation is to illuminate the optical elements with a larger solid angle than the undulator's central cone, which contains the usable photons but is considerably smaller than the angular power distribution. 相似文献