Results 1 - 10 of 605
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[en] One of the most serious problems in the field of perfecting of InGaAs P/In P - hetero lasers is the problem of improvement of their temperature characteristics, namely, attenuation of temperature dependence of threshold current and differential effectiveness. Rapid temperature growth of threshold current is an obstacle for receiving oscillation at high temperature. In this work we specified the solutions of this problem. (author)
[en] In this paper, entropy and between-class variance based thresholding methods for color images segmentation are studied. The maximization of the between-class variance (MVI) and the entropy (ME) have been used as a criterion functions to determine an optimal threshold to segment images into nearly homogenous regions. Segmentation results from the two methods are validated and the segmentation sensitivity for the test data available is evaluated, and a comparative study between these methods in different color spaces is presented. The experimental results demonstrate the superiority of the MVI method for color image segmentation.
[en] We investigate a perpendicular electric current passing through a 'ferromagnetic nanojunction', that is through some layered nanosized structure of spin-valve type, containing two ferromagnetic metallic layers. Spacer may be used between the metallic layers to prevent the rotation of the moving spin phases. Such an arrangement is typical for spin valves: one of the metallic layers has strongly pinned magnetic lattice and the other one has free magnetic lattice and free mobile spins. Further the conditions are derived to provide a very high nonequilibrium spin injection level. It appears that the so-called spin resistances of the constitutive layers should be in definite relations to each other. These relations lead to the situation where the spin injection becomes dominant and significantly suppresses the 'ordinary' spin-transfer torque. As a result, the threshold current becomes lowered down to 2-3 and even more orders of magnitude
[en] A complex-coupled DFB laser with sampled grating has been designed and fabricated. The method uses the +1st order reflection of the sampled grating for laser single-mode operation. The typical threshold current of the sampled grating based DFB laser is 25 mA, and the optical output is about 10 mW at the injected current of 100 mA. The lasing wavelength of the device is 1.5385 μm, which is the +1st order wavelength of the sampled grating.
[en] The lasing wavelength of a complex-coupled DFB laser is controlled by a sampled grating. The key concepts of the approach are to utilize the −1st order (negative first order) reflection of a sampled grating for laser single mode operation, and use conventional holographic exposure combined with the usual photolithography to fabricate the sampled grating. The typical threshold current of the sampled grating based DFB laser is 32 mA, and the optical output is about 10 mW at an injected current of 100 mA. The lasing wavelength of the device is 1.5356 µm, which is the −1st order wavelength of the sampled grating
[en] A 16-channel monolithically integrated index-coupled distributed-feedback laser array has been fabricated using nanoimprint technology. Selective lasing wavelengths with 300 and 100 GHz frequency space are obtained. The fine tenability for an individual laser in the array is achieved with a Ti–Au thin-film resistor integrated on the chip. The typical threshold current is between 10 and 15 mA without current in the thin-film resistor. The optical output power of each channel is about 6 mW at an injection current of 70 mA. (paper)
[en] We investigate multipass beam breakup (BBU) in a recirculating linear accelerator in the framework of a single cavity model. We present expressions for the beam breakup threshold current for various situations derived from a perturbative solution of BBU equations. These formulae should serve as a guide to understand the BBU phenomenon for a particular system and also as a tool to estimate the BBU threshold current quickly. Many of the results presented are more general than previous considerations because they include the effects of coupling between the two transverse polarizations in each dipole higher order mode
[en] This paper presents a new, physical threshold voltage model to solve the ambiguity in determining the threshold voltage of double-gate (DG) MOSFETs. To avoid the difficulties of the conventional 2ψB model in nearly undoped DG MOSFETs, this study proposes to define the on–off switching based on the actual roles of the drift and diffusion components in the total drain current. The drift current strongly enhances beyond the threshold voltage, while the diffusion current plays a major role in the subthreshold. The threshold voltage is defined as the drift component that exceeds the diffusion counterpart. From the solutions of Poisson's equation, the drift and diffusion currents of DG MOSFETs are separately formulated to derive the analytical expressions of the threshold voltage and associated threshold current. This model provides a comprehensive description of the switching behavior of DG MOSFET devices, and offers a physical onset threshold current to determine the threshold voltage in practical extraction
[en] The effect of turbulent fluctuations on the threshold criteria for incipient grain motion over a wide range of sediment size is investigated. In this work, attention is paid to the comparison of the critical Shields parameter θ_c profile obtained when the near-bed fluid forces induced sediment motion are oscillating-grid turbulence and a single idealised eddy of vortex ring. For experimental work, near-spherical monodisperse sediments were used throughout with relative densities of 1.2 and 2.5 and mean diameters d ranging between 80 and 1087 μm. The measured values of θ_c on a horizontal bed α = 0 (hence denoted as θ_c_0), were compared to the θ_c_0 profiles obtained by grid turbulence and vortex ring experiments. Although different in magnitude, the θ_c_0 profiles were comparable, that is the θ_c_0 were seen to increase monotonically for hydraulically smooth bed forms and to be approximately constant for hydraulically rough bed forms. However the limit of hydraulically smooth region was found to vary between the oscillating-grid turbulence experiments, where wider smooth region was found when the turbulent fluctuations used to calculate θ_c_0 is not the near-bed velocity. (author)
[en] We extend analysis of Ref.  of the closed orbit instability driven by the resistive wall impedance for the case of strong focusing lattice. A numerical estimate for the Low Energy Ring of PEP-II shows that the threshold current is three times higher than the nominal one