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1.
Microdevices involving a stagnation-point flow, such as cross- and T-junctions, are useful for particle manipulation and characterization. In contrast to the wide use of cross-junctions, T-junctions have received limited attention as a medium for capsule deformation and characterization. In the present study, we investigate computationally the settling shape of an elastic capsule in a T-junction microchannel for a wide range of flow rates. Our work reveals that the capsules show a rich deformation behavior including (inverse) swallow-cap, sit-on and whitewater kayak shapes. We also propose a new methodology for the simultaneous and accurate determination of the shear and area-dilatation moduli of the membrane of artificial capsules via a single experimental technique by utilizing the dependence of the settling capsule’s dimensions on the capillary number and the membrane hardness identified in our investigation. Our moduli methodology utilizes high flow rates (i.e., large capsule deformations) where the effects of the membrane hardness become prominent and thus capsules with different area-dilatation modulus can be identified. Our procedure has the additional advantage of not being influenced by the fluids’ viscosity ratio or the membrane viscosity. 相似文献
2.
ABSTRACTThe life-of-mine optimization of open pit mine production scheduling under geological uncertainty is a computationally intensive process. Production scheduling determines the optimal extraction sequence by maximizing net present value (NPV). In this paper, an algorithm is proposed to schedule an open pit mine under geological uncertainty, where instead of solving the whole problem at once, the production schedule is generated by sequentially solving sub-problems. The sub-gradient method is used to generate the upper bound solution of a Lagrangian relaxed sub-problem. If the upper bound relaxed solution is infeasible, a mixed integer programming is applied to the latter solution. The algorithm is validated by solving six problems and is compared to the linear relaxation of the original production scheduling problem. The results show that the proposed algorithm generates a solution that is very close to optimal, with less than a 3% optimality gap. An application at a copper mine, where geological uncertainty is quantified with geostatistical simulations of the related orebody, shows that all constraints are satisfied and an 11% higher NPV is generated when compared to the corresponding deterministic equivalent of the proposed approach, while a 26% higher NPV is generated compared to a common conventional industry approach. 相似文献
3.
We propose an autoregressive conditional duration (ACD) model with periodic time-varying parameters and multiplicative error form. We name this model periodic autoregressive conditional duration (PACD). First, we study the stability properties and the moment structures of it. Second, we estimate the model parameters, using (profile and two-stage) Gamma quasi-maximum likelihood estimates (QMLEs), the asymptotic properties of which are examined under general regularity conditions. Our estimation method encompasses the exponential QMLE, as a particular case. The proposed methodology is illustrated with simulated data and two empirical applications on forecasting Bitcoin trading volume and realized volatility. We found that the PACD produces better in-sample and out-of-sample forecasts than the standard ACD. 相似文献
4.
Roussos Dimitrakopoulos 《国际露天开采、回填与环境杂志》2013,27(4):173-179
Abstract Conditional simulation is a class of Monte Carlo techniques that can be used to generate equally probable representations of in-situ orebody variability. Contrary to the traditional smooth orebody models, conditionally simulated orebodies provide the tools to quantify uncertainty in grade variability and the resulting effects on various aspects of open pit design and planning. This paper outlines a general framework for modelling uncertainty and assessing geological risk, presents currently used geostatistical simulation algorithms, and presents examples. 相似文献
5.
High-performance bottom electrode organic thin-film transistors 总被引:2,自引:0,他引:2
Kymissis I. Dimitrakopoulos C.D. Purushothaman S. 《Electron Devices, IEEE Transactions on》2001,48(6):1060-1064
Pentacene-based organic field effect transistors (FETs) exhibit enormous potential as active elements in a number of applications. One significant obstacle to commercial application remains: no completely lithographic process exists for forming high-performance devices. Processing constraints prevent electrodes from being lithographically patterned once the semiconductor is deposited, but depositing the electrodes before the semiconductor leads to low-performance transistors. By using self-assembled monolayers (SAMs) to change the surface energy of the metal electrodes and morphology of the pentacene subsequently grown on the electrodes, high-performance transistors may be formed using a process compatible with lithographic definition of the source and drain electrodes 相似文献
6.
Orebody modelling, support effects and the estimation of recoverable reserves are key parts of open pit optimization studies. A case study is presented on the estimation of recoverable reserves using an implementation of indicator kriging where metal quantity is used to select cutoffs, and support corrections founded on a conditional simulation approach. Mining selectivity is explored in the subsequent optimization study to compare results from indicator kriging of grade estimates on a regular size blocks and indicator kriging estimates on small size blocks. The use of indictor kriging models adjusted for a given selectivity and the use of grade proportions in each block for the optimization study, provide a presentation of the expected ore recovery for a predefined level of selectivity. The case study shows that indicator kriging estimation with full accounting of block grade distributions generates substantially better results in the pit optimization study. In addition, the adverse effects of small blocks and over-smoothing on optimization results are illustrated. 相似文献
7.
R. Dimitrakopoulos 《Journal of Mining Science》2011,47(2):138-150
Conventional approaches to estimating reserves, optimizing mine planning, and production forecasting result in single, and
often biased, forecasts. This is largely due to the non-linear propagation of errors in understanding orebodies throughout
the chain of mining. A new mine planning paradigm is considered herein, integrating two elements: stochastic simulation and
stochastic optimization. These elements provide an extended mathematical framework that allows modeling and direct integration
of orebody uncertainty to mine design, production planning, and valuation of mining projects and operations. This stochastic
framework increases the value of production schedules by 25%. Case studies also show that stochastic optimal pit limits (i)
can be about 15% larger in terms of total tonnage when compared to the conventional optimal pit limits, while (ii) adding
about 10% of net present value to that reported above for stochastic production scheduling within the conventionally optimal
pit limits. Results suggest a potential new contribution to the sustainable utilization of natural resources. 相似文献
8.
A maximum upside / minimum downside approach to the traditional optimization of open pit mine design 总被引:1,自引:0,他引:1
The management of cash flows and risk during production is a critical part of a surface mining venture as well as an integral
part of a strategy in developing new and existing operating mines. Orebody uncertainty is a critical factor in strategic mine
planning, the optimization of mine designs and long-term sequencing. Traditional optimization approaches do not account for
in situ grade variability or deal with geological risk. This paper presents a new approach to mine design based on risk quantification
and alternative strategic decision-making criteria.
__________
Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 81–90, January–February, 2007. 相似文献
9.
Elias G. Dimitrakopoulos 《Engineering Structures》2011,33(3):813-826
In this paper the seismic response of short skew bridges with deck-abutment pounding joints is revisited. The permanent deck rotations and transverse displacements of such bridges after the recent earthquake in Chile created an incentive to revisit their non-conventional behaviour. A novel non-smooth rigid body approach is proposed to analyze the seismic response of pounding skew bridges which involves oblique frictional multi-contact phenomena. The coupling of the response, due to contact, is analysed in depth. It is shown that the tendency of skew bridges to exhibit transverse displacements and/or rotate (and hence unseat) after deck-abutment collisions is not a factor of the skew angle alone, but rather of the plan geometry plus friction. This is expressed with proposed dimensionless criteria. The study also unveils that the coupling is more pronounced in the low range of the frequency spectrum (short-period excitations/flexible structures) and presents novel dimensionless response spectra for the transverse displacements and rotations, triggered by oblique contact in a skew bridge subsystem. Despite the complexity of the response, the proposed spectra highlight a clear pattern. The dimensionless rotations, arising from contact, decline as the ratio of the structural versus excitation frequency increases and become practically negligible in the upper range of the frequency spectrum. Finally, a pilot application to a typical skew bridge is presented. 相似文献
10.
G. A. Dimitrakopoulos C. N. Capsalis 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(6):1335-1351
A new statistical model for rms delay spread is presented. The model has been developed under the assumption of the existence of two paths (two-path model). It is assumed that the amplitude of each path follows the so-called log-Student distribution with one degree of freedom, while the differential propagation delay of the two paths follows the uniform distribution. The parameters involved with the model are mz and sz the mean and standard deviation of the ratio of the two paths’ amplitudes. Theoretical curves for τrms as well as for the mean and standard deviation of τrms are plotted for different values of mz and sz. These curves are extremely useful for the choice of the parameters of the model for different cases. In order to examine the validity of the new model, measurements from the literature have been collected and compared with the theoretical results. In all cases a very good agreement, according to the X-square criterion, between theoretical and experimental curves has been observed. As a result, the new model can be used by system engineers for the development of wireless high bit-rate digital systems that will not suffer from intersymbol interference. 相似文献