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1.
2.
Adaptive methods of signal analysis have proved a very useful tool for analysis of non-stationary signals. This is due to the ability of these methods to adapt to the local structures of the signals being analysed, as these methods are not constrained by a fixed basis. Empirical mode decomposition (EMD) is among the more recent data-adaptive signal decomposition methods, which decomposes a given signal into modes which are hierarchically arranged based on their frequency content. In this paper, we will present a novel adaptive hierarchical decomposition scheme based on a novel modification of EMD, namely empirical mode decomposition-modified peak selection (EMD-MPS). EMD-MPS allows a time-scale-based signal decomposition, thereby allowing control over the decomposition process, not possible in the original EMD algorithm. Using time-scale-based decomposition and the properties of EMD-MPS, a given signal can be decomposed into octave frequency bands, with the centre frequency of the separated modes given by the frequency separation criterion of EMD-MPS. The spectral limits of the separated bands are established, and their relation with the centre frequency derived empirically. The method is validated by its application to simulated and real signals.  相似文献   

3.
The discrete wavelet decomposition of second-order harmonizable random processes is considered. The deterministic wavelet decomposition of a complex exponential function is examined, where its pointwise and bounded convergence to the function is proved. This result is then used for establishing the stochastic wavelet decomposition of harmonizable processes. The similarities and differences between the wavelet decompositions of general harmonizable processes and a subclass of processes having no spectral mass at zero frequency, e.g., those that are wide-sense stationary and have continuous power spectral densities, are also investigated. The relationships between the harmonization of a process and that of its wavelet decomposition are examined. Finally, certain linear operations such as addition, differentiation, and linear filtering on stochastic wavelet decompositions are considered. It is shown that certain linear operations can be performed term by term with the decomposition  相似文献   

4.
Recent advances in statistics have spawned powerful methods for regression and data decomposition that promote sparsity, a property that facilitates interpretation of the results. Sparse models use a small subset of the available variables and may perform as well or better than their full counterparts if constructed carefully. In most medical applications, models are required to have both good statistical performance and a relevant clinical interpretation to be of value. Morphometry of the corpus callosum is one illustrative example. This paper presents a method for relating spatial features to clinical outcome data. A set of parsimonious variables is extracted using sparse principal component analysis, producing simple yet characteristic features. The relation of these variables with clinical data is then established using a regression model. The result may be visualized as patterns of anatomical variation related to clinical outcome. In the present application, landmark-based shape data of the corpus callosum is analyzed in relation to age, gender, and clinical tests of walking speed and verbal fluency. To put the data-driven sparse principal component method into perspective, we consider two alternative techniques, one where features are derived using a model-based wavelet approach, and one where the original variables are regressed directly on the outcome.  相似文献   

5.
《Organic Electronics》2008,9(5):873-877
In organic memory devices, we introduce non-interacting “write” and “read” processes so that the state of a device is not perturbed during the “read” process. We have used heterojunction devices based on suitable materials in such a way that they can generate photovoltage and photocurrent upon illumination. Both open-circuit voltage or short-circuit current of the device have responded to conductance switching. We have showed that the device can be switched to a high-conducting state by applying a suitable voltage pulse and its state can be probed or “read” by measuring open-circuit voltage or short-circuit current. The results show newer parameters to probe organic memory devices.  相似文献   

6.
A thermal treatment for healing voids in the aluminum metallization of integrated circuit (IC) chips has been discovered. The aluminum metallization is alloyed with nominally 1 wt.% of silicon. This discovery arose from efforts to cause further growth of preexisting voids in IC RAMs intended for long-term unattended spacecraft applications. The experimental effort was intended to cause further void propagation for the purpose of establishing a time/temperature propagation relationship, but it resulted instead in a healing of the voids. The thermal treatment consisted of heating IC chips with voids in the aluminum/silicon metallization to temperatures in excess of 200°C, followed by quick immersion into liquid nitrogen. The thermal treatment is described, and a theory based on silicon solubility and migration in aluminum is advanced to explain both the formation and the healing of voids in the aluminum metallization of IC chips  相似文献   

7.
A generalised block-matching motion estimation with variable-size blocks is proposed. The location and size of each block are determined from a quad-tree spatial decomposition algorithm. Experimental results with head-and-shoulders test image sequences show that motion-compensated errors with this method have lower entropy than the conventional fixed or variable-size block-matching techniques. The quality of the coded pictures under the proposed method with an H.261 codec, both subjectively and in terms of PSNR, outperforms the conventional use of fixed and variable block-size motion estimators  相似文献   

8.
This paper proposes a new model for image decomposition which separates an image into a cartoon, consisting only of geometric objects, and an oscillatory component, consisting of textures or noise. The proposed model is given in a variational formulation with adaptive second-order total generalized variation (TGV). The adaptive behavior preserves the key features such as object boundaries and textures while avoiding staircasing effect. To speed up the computation, the split Bregman method is used to solve the proposed model. Experimental results and comparisons demonstrate the proposed model is more effective for image decomposition than the methods of the state-of-the-art image decomposition models.  相似文献   

9.
Luminance, conduction current and threshold voltage of ZnS:Mn ac thin film electroluminescent display devices were measured as functions of device temperature (10 K-300 K) and risetime of the excitation voltage pulse (2 /spl mu/s-50 /spl mu/s). Results provided insight into the electron ejection mechanism at the insulator-phosphor interfaces. It was found that the distribution of interface state electrons at the beginning of the excitation voltage pulse varied substantially with device temperature. Pure tunneling is thought to be the dominant electron ejection mechanism at the beginning of the voltage pulse while phonon-assisted tunneling is responsible for altering the interface electron distribution during the interval between the pulses. A delay of several microseconds was observed in the build up of the transferred charge. It is attributed to the relatively small population of electrons available at the insulator-phosphor interface.<>  相似文献   

10.
Switching times of power MOSFET devices are investigated as function of temperature and high-field stress. Measurements show that important variations are obtained on the devices turn-on time. The threshold voltage is decreasing with temperature and varies with stress, especially at low temperatures. The oxide leakage current is found to be having safe values even at high temperatures, stressing the devices does not increase the leakage current to unsafe values except for very high temperatures.  相似文献   

11.
Most of the modern epitaxial structures for semiconductor lasers serving the needs of optical storage and fiber pumping are grown on misoriented GaAs(0 0 1) substrates. It has been found in metal-organic vapor-phase epitaxy that surface misorientation helps to achieve better epitaxial quality of the alloy layers. On the other hand, these misoriented or, in other definition, high-index surfaces are known to undergo phase transformations, depending on the misorientation angle, from nanofaceting (like (3 1 1)A, (3 1 1)B, (3 3 1), (2 1 1)B GaAs surfaces) to arrays of step bunches (like (7 7 5) GaAs, etc.). In the present paper, we consider growth-related effects during growth of both standard and advanced laser structures on GaAs substrates which are typically used for growth of 650 nm GaAlInP devices. We show that the active region of the laser structures represents a corrugated superlattice with a 25 nm in-plane periodicity, while the surrounding layers are natural superlattices with a 5 nm vertical periodicity. Corrugated superlattice used as an active region manifests itself through a strong modification of optical properties. Strong in-plane polarization evidences the formation of arrays of quantum wires. Both standard and advanced red laser have been grown and processed. The advanced lasers have demonstrated a vertical beam divergence of only 7–8° full-width at half-maximum (FWHM). The advanced lasers with 10 μm-wide stripes demonstrate continuous wave (CW) power up to 200 mW and the lateral beam divergence of 4°, and those with 4 μm-wide stripes show CW power up to 120 mW and the lateral beam divergence of 6.5°. No facet passivation has been applied and the power is limited by the catastrophic optical mirror damage (COMD). 20 W pulsed power has been achieved in 100 μm-wide stripes for the advanced design and 6 W has been obtained for the standard design. The advantage comes from the design optimization of the laser waveguide using the concept of the longitudinal photonic bandgap crystal. We believe that also the optimization of the active region with better utilization of the nanofaceting effects may enable, in addition, a dramatic extension of the emission wavelength towards bright red (620–630 nm) and, probably, yellow (580 nm) spectral ranges.  相似文献   

12.
Spatial uniformity, or the uniformity of product output characteristics at different locations in a batch of product is modeled, optimized, and controlled using a methodology called multiple response surfaces, which may be used to characterize the results of an experimental design. Multiple, low-order polynomial models are used to model the output characteristics at each of several sites within a batch of product. The uniformity model is then obtained by manipulating these multiple models. The approach is compared to the traditional method of fitting a single high-order polynomial to the calculated uniformity. Experimental results confirm that similar or improved modeling accuracy is obtained with fewer data points using the new method due to the use of low-order models. Characteristics of the approach are examined both analytically and in application to plasma etching, silicon epitaxy, tungsten chemical vapor deposition (CVD) and the simulation of polysilicon low-pressure CVD (LPCVD)  相似文献   

13.
Approximate analytical solutions are obtained for symmetrical p-n junctions which provide the range of bias for constant quasi-Fermi potentials across the transition region under forward bias and small reverse bias. The solutions also show that the variations of the quasi-Fermi potentials are essentially complete in the transition region for large reverse bias. The actual spatial dependences are computed numerically for the step junction case, using the parabolic potential as first approximation and applied junction voltage as the parameter, and are graphed. Numerical calculations and curves are also made in this case for the total change of the quasi-Fermi potentials across the transition region as a function of bias voltage, with the barrier height as a parameter. These confirm the commonly adopted assumption that the quasi-Fermi potentials are essentially constant across the transition region for small bias.  相似文献   

14.
Decreasing pixel size, perfection of isolation, and improved dynamic range of advanced imaging devices requires an adequate optical arrangement to check crosstalk behavior within the pixel matrix. The Fraunhofer diffraction pattern; an inherent feature of any focused circular beam, leads to unintended direct illumination of the neighbors even if accurately centered. A Simple setup has been applied to determine the beam profile focused down to the subwavelength range. We propose to characterize the beam focusing for spatial resolution tests by the first zero to-zero width independent of peak intensity. We provide an estimate of minimum requirements to be fulfilled in order to test for a given crosstalk and demonstrate their importance on filled trench-isolated pixels.  相似文献   

15.
The large-scale application of semiconducting polymers in organic electronics is hindered significantly by catastrophic device failure. Some of these processes are associated with coupled phenomena of electro-migration and thermal localization, which are poorly understood till date. In this paper we identify structural instability and its sources in a simple device configuration consisting of a semiconducting polymer sandwiched between two metal electrodes and subjected to various DC operating voltages. The coupled effect of temperature and electric fields leads to fracture of the polymer layer and the metal electrode layer, interestingly, in mutually exclusive regions. This failure is significantly observable beyond a certain applied voltage. It is observed that defects nucleate in a chain-like pattern with alternating fracture sites of polymer and metal electrode respectively. We subsequently propose a coupled electro-thermal mechanism which explains the observed phenomena. The mechanism is further validated by an analytical model of stress due to thermal and electric field distributions. The model predicts criteria of failure, which are interestingly complementary for the polymer and the electrode films, and hence explains the observation of the chain-like nucleation pattern. The failure criteria are functions of device geometry, operating voltage and temperature. This study will be useful toward reliability-based design of organic electronic devices including important factors such as coupled electro-thermal response and length-scale. The study also opens up important fundamental questions relating to the spatio-temporal evolution of electro-thermally induced minuscule electrical shorts in thin-film electronic devices.  相似文献   

16.
Some integrated circuit manufacturing processes produce variation which is strongly correlated between devices physically near each other but not correlated between devices which are widely separated. Devices separated by intermediate distances are partial correlated. In this paper we describe a method to characterize and model variation which shows this type of spatial correlations.  相似文献   

17.
One- and two-dimensional photonic crystal slabs have numerous applications in integrated optics. Unfortunately, due to their finite height, their in-plane guided modes can suffer outcoupling losses. Although considered as detrimental in the context of the development of photonic integrated circuits, it turns that the coupling of waveguided modes to radiative modes can be usefully exploited for the manipulation of photons in free space. It is shown in this paper that interaction of radiative and guided modes through a photonic crystal, especially under conditions where the latter correspond to extrema of the dispersion characteristics of the photonic crystal, results in resonance phenomena, which can be used practically for the development of new classes of devices, e.g., combining photonic crystal and microoptoelectromechanical systems structures.  相似文献   

18.
Key assumptions are made, with justification, to simplify the three-dimensional, nonlinear boundary-value problem that defines minority-carrier transport, including recombination, in polysilicon devices. These assumptions enable the separation of the grain-boundary recombination analysis, which is based on quasi-equilibrium in the space-charge region, from the intragrain transport analysis, which is done by partitioning the grain into subregions in which the minority-carrier flow is predominantly one-dimensional. The analyses are coupled through the effective minority-carrier recombination velocity at the grain boundary, which generally is dependent on the minority-carrier density in the quasi-neutral grain. Limitations of the model implied by the quasi-equilibrium assumption are effectively removed by recognizing that when conditions obtain that negate quasi-equilibrium, the effective recombination velocity is fixed at the minority-carrier kinetic-limit velocity. The model development is facilitated by computer-aided numerical analysis of the grain-boundary recombination and is supported by qualitative discussion of the underlying physics.  相似文献   

19.
Apparent computational difficulties with the direct integral equation and method of moments have prompted an alternative numerical solution procedure based on the spatial decomposition technique. Using rigorous electromagnetic equivalence, the spatial decomposition technique virtually divides an electrically large object into a multiplicity of subzones. It permits the maximum size of the method of moments system matrix that needs to be inverted to be strictly limited, regardless of the electrical size of the large scattering object being modeled. The requirement on the computer resources is O(N ), where N is the number of spatial subzones and each subzone is electrically small, spanning on the order of a few wavelengths. Numerical examples are reported along with comparative data and relative error estimation to expose the applicability and limitations of the spatial decomposition technique for the two-dimensional scattering study of electrically large conducting and dielectric objects  相似文献   

20.
The spatial variations of the three charged gold states in the transition region of silicon p+n and n+p step junctions are calculated. The exact solution is obtained at thermal equilibrium. Under reverse applied bias, exact solution is not possible and approximate solutions using staircased charge distributions are obtained. Under reverse bias, most of the gold atoms in the transition region are in the negative or acceptor charge state for both p+n and n+p junctions. This is due to the dominance of the hole emission process at the neutral gold centers over all other electron and hole emission processes of the three charge states at 300°K. Since the shallow-level impurities in these two types of junctions are of opposite charge and the deep-level gold impurity is mainly in the negative charge state, quite different electrical behaviors are expected from these two junction types. In work to be described elsewhere, some of these differences have been demonstrated experimentally, such as the breakdown voltage and the impedance, and quantitatively correlated with theory using the spatial variations obtained in this paper.  相似文献   

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