共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
Jin J.S. Wang Y. Hiller J. 《IEEE transactions on information technology in biomedicine》2000,4(4):298-305
The nonlinear anisotropic diffusive process has shown the good property of eliminating noise while preserving the accuracy of edges and has been widely used in image processing. However, filtering depends on the threshold of the diffusion process, i.e., the cut-off contrast of edges. The threshold varies from image to image and even from region to region within an image. The problem compounds with intensity distortion and contrast variation. We have developed an adaptive diffusion scheme by applying the central limit theorem to selecting the threshold. Gaussian distribution and Rayleigh distribution are used to estimate the distributions of visual objects in images. Regression under such distributions separates the distribution of the major object from other visual objects in a single-peak histogram. The separation helps to automatically determine the threshold. A fast algorithm is derived for the regression process. The method has been successfully used in filtering various medical images 相似文献
3.
In the last decades, researchers have tried to implement novel optoelectronic devices with new semiconductor material compounds. There are few competitors in the race for more reliable, more efficient, pump sources for solid-state lasers. These diodes should operate at high power, intense brightness, and with low threshold current. The strained AlInGaAs-GaAs quantum-well (QW) laser is a promising candidate. In this study we optimized the growth parameters of strained AlInGaAs quantum wells using a model for linewidth broadening of photoluminescence, which was extended for the first time to handle quaternary alloys. This model enables us to identify the dominant contributions to the broadening. As a result of our growth parameters optimization technique, low threshold current density of simple broad-area lasers has been obtained, indicating a superior material quality. Moreover, we have studied for the first time the effect of indium and aluminum content and QW width on the threshold current density of quaternary AlInGaAs QW lasers. As a result of these studies the lowest known threshold current density for AlInGaAs on GaAs single QW broad-area laser has been achieved. 相似文献
4.
5.
A. Baidullaeva V. P. Veleshchuk A. I. Vlasenko B. K. Dauletmuratov O. V. Lyashenko P. E. Mozol’ 《Semiconductors》2008,42(3):281-285
The effect of a threshold process of surface melting on the acoustic response in CdTe and GaAs subjected to pulsed laser radiation is considered and the mechanisms of excitation of sonic signals are analyzed. Melting thresholds of the surface of binary compounds CdTe and GaAs are established under irradiation by pulses of nanosecond duration of ruby and neodymium lasers from measurements of the amplitude of the acoustic response. 相似文献
6.
介绍了自主研制的质子转移反应飞行时间质谱的基本结构和性能。首先对数据采集卡甄别离子脉冲的阈值电压进行了优化,结果表明当阈值电压为0.33V时,H316O+(m/z 19)与H318O+(m/z 21)的离子计数比约500:1;然后考察了水团簇离子H3O+(H2O)n的分布与漂移管约化电场的关系,结果表明,当E/N为139 Td时,团簇离子得到很好地抑制,质谱观察到的离子主要是H3O+,其纯度可达99%以上;随后考察了质谱的分辨率,结果表明在m/z124处,分辨率最好,达到2653; 采用不同浓度的乙醇标样对仪器的线性范围和检测限性能进行了测试,结果表明该仪器的线性动态范围可达三个数量级,检测限可达3.8 ppb; 最后用该质谱仪检测了实验室空气,得到了实验室空气的质谱图。自主研制的质子转移反应飞行时间质谱可实现对痕量挥发性有机物的实时在线测量,在环境、食品、医学等领域具有重要应用价值。 相似文献
7.
Intercalation‐Induced Tunable Stimuli‐Responsive Color‐Change Properties of Crystalline Organic Layered Compound 下载免费PDF全文
Layered structures accommodate guest molecules and ions in the interlayer space through intercalation. Organic layered compounds, such as layered polymers, have both intercalation and dynamic properties. Here intercalation‐induced tunable temperature‐ and mechanical‐stress‐responsive color‐change properties of crystalline layered polydiacetylene (PDA) as an organic layered compound are reported. In general, organic materials with stimuli responsivity are developed by molecular design and synthesis. In the present work, intercalation of guest metal cations in the layered PDA directs tuning of the stimuli‐responsive color‐change properties, such as color, responsivity, and reversibility. Whereas PDA without intercalation of metal ions distinctly changes the color from blue to red at the threshold temperature, the PDA with intercalation of the divalent metal ions (PDA‐M2+) shows a variety of color‐change properties. The present study indicates that intercalation has versatile potentials for functionalization of organic layered compounds. 相似文献
8.
为了研究液晶材料结构与性能的关系,本文以含乙炔桥键的四环异硫氰酸酯化合物为研究对象,芳基硼酸和3-氟-4-溴碘苯为起始原料,经6步反应合成了12种目标化合物,LC纯度大于99%,采用核磁共振、红外光谱对其结构进行了表征。采用DSC和POM对目标化合物的介晶性进行了研究,采用外推法对其双折射率和介电各向异性值进行了测试。结果表明:目标化合物具有300℃以上高清亮点、150℃以上向列相温度区间、0.40~0.51的双折射率以及大于17的介电各向异性值。对于同一系列化合物,随着末端烷基链的增长,化合物熔点降低,但呈现近晶相的趋势增加。在Y、Z位引入侧向氟取代基,熔点和清亮点均降低;X位再引入侧向氟取代基,熔点上升、清亮点下降。用环己烷替代左边第一个苯环,化合物熔点降低、向列相温度区间变宽。引入侧向氟取代基使双折射率下降0.008~0.036。目标化合物有利于提高混合液晶配方的双折射率、清亮点和降低阈值电压。 相似文献
9.
Optimum conditions are reported for the growth of high-quality AlxGa1_xAs by means of vapor phase epitaxy from organometallic compounds (OMVPE). Typical values of mobili-ty and radiative recombination efficiency are reported, showing that OMVPE material quality is the same as that grown by liquid phase epitaxy (LPE). OMVPE-grown DH narrow-stripe lasers with Al.06Ga.94As active layers show minimum threshold currents of85 mÅ, comparable to the best lasers with similar structures produced by LPE. 相似文献
10.
A. P. Astakhova N. D. Il’inskaya A. N. Imenkov S. S. Kizhaev S. S. Molchanov Yu. P. Yakovlev 《Semiconductors》2005,39(4):472-476
Sources of coherent radiation are fabricated on the basis of a double InAs/InAsSbP heterostructure, grown by vapor-phase epitaxy from metal-organic compounds, that includes a thick (3.3μm) active region. The spectral characteristics of diodes with various cavity lengths are studied, and light polarization is measured. It is established that the modes that compose the spectrum of radiation are controlled by radiative recombination at the heteroboundary and in the bulk of the active region. A new mode with a wavelength of intermediate value, lying between the wavelengths of the aforementioned kinds of radiation, is observed if the current exceeds the threshold value by 30%. This intermediate mode presumably results from an interaction between the modes related to the interfacial and interband radiative recombination, which are present in the cavity at the same time. 相似文献
11.
Garbuzov D.Z. Lee H. Khalfin V. Martinelli R. Connolly J.C. Belenky G.L. 《Photonics Technology Letters, IEEE》1999,11(7):794-796
A new approach in the design of (Al)InGaAsSb-GaSb quantum-well separate confinement heterostructure (QW-SCH) diode lasers has led to continuous-wave (CW) room-temperature lasing up to 2.7 μm. This has been achieved by using quasiternary heavily strained InGaSb(As) QW's inside a broad-waveguide SCH laser structure. The QW compositions are chosen in the region outside the miscibility gap and, as a consequence, do not suffer from clustering and composition inhomogeneity normally found with quaternary InGaAsSb compounds of 2.3-2.7-μm spectral range. Very low threshold current density (~300 A/cm2) and high CW output powers (>100 mW) were obtained from devices operating in the 2.3-2.6-μm wavelength range 相似文献
12.
13.
M. V. Maksimov N. Yu. Gordeev S. V. Zaitsev P. S. Kop’ev I. V. Kochnev N. N. Ledentsov A. V. Lunev S. S. Ruvimov A. V. Sakharov A. F. Tsatsul’nikov Yu. M. Shernyakov Zh. I. Alferov D. Bimberg 《Semiconductors》1997,31(2):124-126
Gaseous phase epitaxy from metal organic compounds is used to obtain a low-temperature injection laser with an active region
based on In0.5Ga0.5As/GaAs quantum dots. Optimizing the growth conditions and geometric parameters of the structure has made it possible to increase
the range of ultrahigh thermal stability in the threshold current (the characteristic temperature is T
0=385 K) up to 50 °C.
Fiz. Tekh. Poluprovodn. 31, 226–229 (February 1997) 相似文献
14.
The experimental results on the influence of non-stoichiometry on defect structure, band structure and physical properties of the IV–VI and I–III–VI2 semiconductor compounds with wide homogeneity regions were analyzed. It was shown that compositions at which peculiarities in the concentration dependences of properties in the homogeneity region are observed, correspond to the maximum in the melting curves. Using the approach of percolation theory, the transition from weak to heavy self-doping within the homogeneity region was considered, and the percolation threshold under the introduction of non-stoichiometric defects was estimated. Compositions optimal for long-range ordering were determined. 相似文献
15.
David D. Thornburg 《Journal of Electronic Materials》1973,2(1):3-15
Amorphous chalcogenides may be divided among three classes based upon the changes in local order and bond type on transition
from the amorphous to the crystalline phases. These types include: (I) Stoichiometric compounds which do not undergo significant
changes in local order on crystallization (e.g., As2Se3). (II) Stoichiometric compounds which undergo significant changes in local order on crystallization (e.g., GeTe). (III) Non-stoichiometric
alloys which phase separate on crystallization.
Previous work on memory switching has been performed primarily on type II and type III chalcogenides. The memory switching
process in thin film specimens of a type I chalcogenide, amorphous As2Se3, is examined in this paper. Measurements of the threshold voltage distribution for devices of a given thickness display a
sharp peak at some value VO . A plot of VO as a function of film thickness shows the initiation of switching to be field controlled, suggesting a non-thermal initiation
mechanism. Microscopic examination of switched devices yields evidence for Joule heating, which is enchanced by self-capacitive
energy released during switching subsequent to formation of the low resistance path.
From the thickness dependence of VO and measurements of the failure time of devices biased below threshold, a switching mechanism for this material is deduced
which incorporates spinodal decomposition of metallic As clusters in an insulating matrix. These clusters then chain under
the influence of an applied field and form a low resistance filamentary path. 相似文献
16.
动态阈值nMOSFET阈值电压随温度退化特性 总被引:1,自引:0,他引:1
对动态阈值nMOSFET阈值电压随温度退化特性进行了一阶近似推导和分析。动态阈值nMOSFET较之普通nMOSFET,降低了阈值电压温度特性对温度、沟道掺杂浓度及栅氧厚度等因素的敏感程度。讨论了动态阈值nMOSFET优秀阈值电压温度特性的内在机理。动态阈值nMOSFET优秀的阈值电压随温度退化特性使之非常适合工作于高温恶劣环境。 相似文献
17.
18.
An Sang Hou 《Circuits, Systems, and Signal Processing》2005,24(1):83-101
In this paper, analog multiplexers, a threshold voltage measurement block, 16-bit analog-to-digital converter, and a computer
are employed to achieve a new scheme of threshold voltage measurement for a floating-gate MOS transistor (FGT). Feedback technology
is applied so that the threshold voltage can be measured with good accuracy. A threshold voltage measurement with a maximum
error equal to 1% can be achieved. The proposed scheme does not require any matched components, and thus it can be applied
effectively to threshold voltage measurement for multiple FGTs. The sampling time of the threshold voltage measurement is
3 ms. Dynamic responses and static characteristics are demonstrated with experimental results. 相似文献
19.
20.
A performance optimization based on the optimal switching threshold(s) for a multi-branch switched diversity system is discussed in this paper. For the conventional multi-branch switched diversity system with a single switching threshold, the optimal switching threshold is a function of both the average channel SNR and the number of diversity branches, where computing the optimal switching threshold is not a simple task when the number of diversity branches is high. The newly proposed multi-branch switched diversity system is based on a sequence of switching thresholds, instead of a single switching threshold, where a different diversity branch uses a different switching threshold for signal comparison. Thanks to the fact that each switching threshold in the sequence can be optimized only based on the number of the remaining diversity branches, the proposed system makes it easy to find these switching thresholds. Furthermore, some selected numerical and simulation results show that the proposed switched diversity system with the sequence of optimal switching thresholds outperforms the conventional system with the single optimal switching threshold. 相似文献