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1.
In this paper we discuss the different models proposed to explain the visible luminescence in porous silicon (PS). We review
our recent photoluminescence and Raman studies on PS as a function of different preparation conditions and isochronal thermal
annealing. Our results can be explained by a hybrid model which incorporates both nanostructures for quantum confinement and
silicon complexes (such as SiH
x
and siloxene) and defects at Si/SiO2 interfaces as luminescent centres. 相似文献
2.
Typically, brain MR images present significant intensity variation across patients and scanners. Consequently, training a classifier on a set of images and using it subsequently for brain segmentation may yield poor results. Adaptive iterative methods usually need to be employed to account for the variations of the particular scan. These methods are complicated, difficult to implement and often involve significant computational costs. In this paper, a simple, non-iterative method is proposed for brain MR image segmentation. Two preprocessing techniques, namely intensity-inhomogeneity-correction, and more importantly MR image intensity standardization, used prior to segmentation, play a vital role in making the MR image intensities have a tissue-specific numeric meaning, which leads us to a very simple brain tissue segmentation strategy.Vectorial scale-based fuzzy connectedness and certain morphological operations are utilized first to generate the brain intracranial mask. The fuzzy membership value of each voxel within the intracranial mask for each brain tissue is then estimated. Finally, a maximum likelihood criterion with spatial constraints taken into account is utilized in classifying all voxels in the intracranial mask into different brain tissue groups. A set of inhomogeneity corrected and intensity standardized images is utilized as a training data set. We introduce two methods to estimate fuzzy membership values. In the first method, called SMG (for simple membership based on a gaussian model), the fuzzy membership value is estimated by fitting a multivariate Gaussian model to the intensity distribution of each brain tissue whose mean intensity vector and covariance matrix are estimated and fixed from the training data sets. The second method, called SMH (for simple membership based on a histogram), estimates fuzzy membership value directly via the intensity distribution of each brain tissue obtained from the training data sets. We present several studies to evaluate the performance of these two methods based on 10 clinical MR images of normal subjects and 10 clinical MR images of Multiple Sclerosis (MS) patients. A quantitative comparison indicates that both methods have overall better accuracy than the k-nearest neighbors (kNN) method, and have much better efficiency than the Finite Mixture (FM) model-based Expectation-Maximization (EM) method. Accuracy is similar for our methods and EM method for the normal subject data sets, but much better for our methods for the patient data sets. 相似文献
3.
We introduce new inductive, generative semisupervised mixtures with more finely grained class label generation mechanisms than in previous work. Our models combine advantages of semisupervised mixtures, which achieve label extrapolation over a component, and nearest-neighbor (NN)/nearest-prototype (NP) classification, which achieve accurate classification in the vicinity of labeled samples or prototypes. For our NN-based method, we propose a novel two-stage stochastic data generation, with all samples first generated using a standard finite mixture and then all class labels generated, conditioned on the samples and their components of origin. This mechanism entails an underlying Markov random field, specific to each mixture component or cluster. We invoke the pseudo-likelihood formulation, which forms the basis for an approximate generalized expectation-maximization model learning algorithm. Our NP-based model overcomes a problem with the NN-based model that manifests at very low labeled fractions. Both models are advantageous when within-component class proportions are not constant over the feature space region "owned by" a component. The practicality of this scenario is borne out by experiments on UC Irvine data sets, which demonstrate significant gains in classification accuracy over previous semisupervised mixtures and also overall gains, over KNN classification. Moreover, for very small labeled fractions, our methods overall outperform supervised linear and nonlinear kernel support vector machines. 相似文献
4.
El-Hag A.H. Simon L.C. Jayaram S.H. Cherney E.A. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2006,13(1):122-128
The paper presents the experimental results obtained on the erosion resistance of silicone rubber (SIR) filled with 12 nm size fumed silica (nano filler) to those filled with 5 /spl mu/m size silica filler (micro filler). The ASTM 2303 inclined plane tracking and erosion test was used in the comparison as well as an infrared laser as the source of heat to erode the SIR samples. The erosion resistance of the SIR materials increased with increasing percentage of the fillers, and it was observed that 10% by weight of nano-filled SIR gives a performance that is similar to that obtained with 50% by weight of micro-filled SIR. The low frequency components of leakage current and the eroded mass are used to evaluate the relative erosion resistance of the composites and the third harmonic component of the leakage current shows good correlation to the measured eroded mass. The paper discusses the possible reasons for the improvement in the erosion resistance of nano-filled silicone composites. 相似文献
5.
Meyer L.H. Jayaram S.H. Cherney E.A. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2004,11(3):424-432
Silicone rubber samples, filled with 30% alumina trihydrate, subjected to the ASTM inclined plane test, show good correlation between the measured harmonic power components of dry band arcing and the surface temperature recorded with a thermovision camera. The simultaneous study of the low frequency fast Fourier transform and variations in temperature shows that when the temperature rises above 100/spl deg/C there is a well defined increase in the low frequency harmonic components of the measured power; however, this trend is not verified by the fundamental component. The eroded mass of the samples is measured independently by a laser approach and a model to rank the tested samples using the inclined plane test is developed. The model is validated by applying it to both the recorded harmonic power components and temperature, resulting in the correct ranking of damage on the samples tested in the inclined plane test. 相似文献
6.
The academic literature on manufacturing technology was reviewed to identify key contingency variables that can moderate the influence of advanced manufacturing technologies on manufacturing performance. Using this literature as a basis, this research proposes an ordering of relative importance of individual contingency variables among a set of contingency variables that influence the advanced manufacturing technologies–manufacturing performance relationship. Plant level data from a large multi-industry sample of firms are analysed, using regression and Chow tests, to confirm the hypothesized ordering among the contingency variables. The findings indicate that lean manufacturing and work organization practices are the primary contingency variables that affect the advanced manufacturing technologies–manufacturing performance relationship. The implications of the results are discussed in the light of past findings and their impact on practice. 相似文献
7.
Cadambi Sumanth Govindarajan Jayaram Vikram 《Metallurgical and Materials Transactions A》2018,49(12):6084-6092
Metallurgical and Materials Transactions A - Coated ball-on-disk wear configuration was used to study the effect of relative humidity, water vapor pressure, and water on wear of TiN coatings in the... 相似文献
8.
Medical image segmentation by combining graph cuts and oriented active appearance models 总被引:1,自引:0,他引:1
In this paper, we propose a novel method based on a strategic combination of the active appearance model (AAM), live wire (LW), and graph cuts (GCs) for abdominal 3-D organ segmentation. The proposed method consists of three main parts: model building, object recognition, and delineation. In the model building part, we construct the AAM and train the LW cost function and GC parameters. In the recognition part, a novel algorithm is proposed for improving the conventional AAM matching method, which effectively combines the AAM and LW methods, resulting in the oriented AAM (OAAM). A multiobject strategy is utilized to help in object initialization. We employ a pseudo-3-D initialization strategy and segment the organs slice by slice via a multiobject OAAM method. For the object delineation part, a 3-D shape-constrained GC method is proposed. The object shape generated from the initialization step is integrated into the GC cost computation, and an iterative GC-OAAM method is used for object delineation. The proposed method was tested in segmenting the liver, kidneys, and spleen on a clinical CT data set and also on the MICCAI 2007 Grand Challenge liver data set. The results show the following: 1) The overall segmentation accuracy of true positive volume fraction TPVF > 94.3% and false positive volume fraction can be achieved; 2) the initialization performance can be improved by combining the AAM and LW; 3) the multiobject strategy greatly facilitates initialization; 4) compared with the traditional 3-D AAM method, the pseudo-3-D OAAM method achieves comparable performance while running 12 times faster; and 5) the performance of the proposed method is comparable to state-of-the-art liver segmentation algorithm. The executable version of the 3-D shape-constrained GC method with a user interface can be downloaded from http://xinjianchen.wordpress.com/research/. 相似文献
9.
10.
Assessment of the performance of different compost models to manage urban household organic solid wastes 总被引:2,自引:1,他引:1
P. Ravi Kumar Ambika Jayaram R. K. Somashekar 《Clean Technologies and Environmental Policy》2009,11(4):473-484
The environmental, cultural, socio-economic and political conditions of each community greatly affect the municipality’s effort
and decision-making in managing household wastes. Composting at home can be used as a sound method of SWM, can manage the
waste at source itself thereby can increase their recycling. And vermicomposting is a viable and completely feasible option
at household level, provided it is acceptable to family members to handle the worms and to remove worm-casts subsequently.
In this regard, the present paper gives a methodological framework for assessing the management of urban household organic
wastes using different compost models to influence the actual efficiency and effectiveness of a municipality’s collection
and management services. The current study also deals with the challenges of solid waste management with a focus on the segregation
of compostable wastes from the non-compostable ones and their composting, recycling or disposal. The non-compostable wastes
can be left for recycling and re-use by the concerned authorities. The composting behavior and the efficiency of different
compost models have been dealt with, and it is concluded that vermicomposting model is the best option. Urban residents can
be educated to vermicompost not only their entire kitchen wastes but also garden wastes to reduce the burden on the municipal
councils. 相似文献