Design of Diffractive Optical Elements by Direct and Indirect Construction of Diffraction Pattern: A Comparative Study

In this work, we present the design method of diffractive beam splitters via two comparative technical routes, the first referred as the direct scheme and the second referred as the indirect scheme. Comparative study is carried on the design procedures and results. The advantages of the direct design scheme include overcoming the limit on the number of phase pixels and being capable of realizing beam shaping and splitting simultaneously. Numerical simulation shows that the uniformity of spots array pattern in the direct design is close to that of the indirect design. These results are helpful for the design and application of diffractive optical elements (DOEs) in modern optical devices.

Scheduling of a Parcel Delivery System Consisting of an Aerial Drone Interacting with Public Transportation Vehicles

This paper proposes a novel parcel delivery system which consists of a drone and public transportation vehicles such as trains, trams, etc. This system involves two delivery schemes: drone-direct scheme referring to delivering to a customer by a drone directly and drone–vehicle collaborating scheme referring to delivering a customer based on the collaboration of a drone and public transportation vehicles. The fundamental characteristics including the delivery time, energy consumption and battery recharging are modelled, based on which a time-dependent scheduling problem for a single drone is formulated. It is shown to be NP-complete and a dynamic programming-based exact algorithm is presented. Since its computational complexity is exponential with respect to the number of customers, a sub-optimal algorithm is further developed. This algorithm accounts the time for delivery and recharging, and it first schedules the customer which leads to the earliest return. Its computational complexity is also discussed. Moreover, extensive computer simulations are conducted to demonstrate the scheduling performance of the proposed algorithms and the impacts of several key system parameters are investigated.

Efficient Modeling of the Interaction of Mesoscale Gravity Waves with Unbalanced Large-Scale Flows: Pseudomomentum-Flux Convergence versus Direct Approach

This paper compares two different approaches for the efficient modeling of subgrid-scale inertia–gravity waves in a rotating compressible atmosphere. The first approach, denoted as the pseudomomentum scheme, exploits the fact that in a Lagrangian-mean reference frame the response of a large-scale flow can only be due to forcing momentum. Present-day gravity wave parameterizations follow this route. They do so, however, in an Eulerian-mean formulation. Transformation to that reference frame leads, under certain assumptions, to pseudomomentum-flux convergence by which the momentum is to be forced. It can be shown that this approach is justified if the large-scale flow is in geostrophic and hydrostatic balance. Otherwise, elastic and thermal effects might be lost. In the second approach, called the direct scheme and not relying on such assumptions, the large-scale flow is forced both in the momentum equation, by anelastic momentum-flux convergence and an additional elastic term, and in the entropy equation, via entropy-flux convergence. A budget analysis based on one-dimensional wave packets suggests that the comparison between the abovementioned two schemes should be sensitive to the following two parameters: 1) the intrinsic frequency and 2) the wave packet scale. The smaller the intrinsic frequency is, the greater their differences are. More importantly, with high-resolution wave-resolving simulations as a reference, this study shows conclusive evidence that the direct scheme is more reliable than the pseudomomentum scheme, regardless of whether one-dimensional or two-dimensional wave packets are considered. In addition, sensitivity experiments are performed to further investigate the relative importance of each term in the direct scheme, as well as the wave–mean flow interactions during the wave propagation.

The Numerical Computation of the Time Fractional Schrödinger Equation on an Unbounded Domain

A fast and accurate numerical scheme is presented for the computation of the time fractional Schrödinger equation on an unbounded domain. The main idea consists of two parts. First, we use artificial boundary methods to equivalently reformulate the unbounded problem into an initial-boundary value (IBV) problem. Second, we present two numerical schemes for the IBV problem: a direct scheme and a fast scheme. The direct scheme stands for the direct discretization of the Caputo fractional derivative by using the L1-formula. The fast scheme means that the sum-of-exponentials approximation is used to speed up the evaluation of the Caputo fractional derivative. The resulting fast algorithm significantly reduces the storage requirement and the overall computational cost compared to the direct scheme. Furthermore, the corresponding stability analysis and error estimates of two schemes are established, and numerical examples are given to verify the performance of our approach.

Solution of the SEIR model of epidemics using HAM

In this paper, a new semi analytic technique namely the Homotopy Analysis Method (HAM) is applied for SEIR Epidemic model. HAM is different from already existing perturbation methods, and is most suitable for strongly non linear simultaneous differential equations arising in this model. The advantage of this method is that it provides a direct scheme for solving the problem, i.e. without the need for linearization, perturbation, massive computation and any transformation. MATHEMATICA 8.0 is used to carry out computations. Results were discussed graphically, for four childhood diseases.

Numerical Scheme for Fredholm Integral Equations Optimal Control Problems

This paper deals with a class of optimal control problems governed by linear Fredholm integral equations. A direct scheme based on the Taylor expansion and parametrization to calculate an approximate-analytical solution of the problem is proposed. This method produces an approximation with a controlled level of accuracy. Moreover, a hybrid algorithm to show the procedure of the scheme is given. The convergence of the proposed scheme is also discussed in detail. Some numerical examples illustrate the potential, efficiency and accuracy of the algorithm.