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Contact resistance is a severe performance bottleneck for electronic devices based on two-dimensional (2D) layered semiconductors, whose contacts are Schottky rather than Ohmic. Although there is a general consensus that the injec...
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Contact resistance is a severe performance bottleneck for electronic devices based on two-dimensional (2D) layered semiconductors, whose contacts are Schottky rather than Ohmic. Although there is a general consensus that the injection mechanism changes from thermionic to tunneling with gate biasing, existing models tend to oversimplify the transport problem, by neglecting the 2D transport nature and the modulation of the Schottky barrier height, the latter being of particular importance in back-gated devices. In this paper, we develop a semianalytical model based on Bardeen's transfer Hamiltonian approach to describe both effects. Remarkably, our model is able to reproduce several experimental observations of a metallic behavior in the contact resistance, i.e., a decreasing resistance with decreasing temperature, occurring at high gate voltages.
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Semiconducting two-dimensional (2D) crystals such as MoS_2 and WSe_2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-op...
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Semiconducting two-dimensional (2D) crystals such as MoS_2 and WSe_2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light-matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.
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The Two-Dimensional (2-D)/One-Dimensional (1-D) method allows pin-resolved computational transport solutions for large, full-core light water reactor simulations at relatively low computational cost compared to a true three-dimens...
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The Two-Dimensional (2-D)/One-Dimensional (1-D) method allows pin-resolved computational transport solutions for large, full-core light water reactor simulations at relatively low computational cost compared to a true three-dimensional (3-D) transport method. The 2-D/1-D method constructs an approximation to the 3-D transport equation with (1) a 2-D transport equation in the radial variables and , discretized on a fine radial spatial grid, and (2) a 1-D transport (or approximate P_(N)) equation in the axial variable , discretized on a radially coarse spatial grid. The 2-D and 1-D equations are coupled through transverse leakage (TL) terms. In this paper, a new 2-D/1-D P_(3) method with anisotropic transverse leakages and anisotropic homogenized 1-D cross sections (XSs) is proposed to improve the accuracy of conventional 2-D/1-D with pin homogenization. It is shown that only the polar component of the anisotropic homogenized XS has a significant effect on the solution; the azimuthal component is negligible. However, the polar and azimuthal components of the leakage terms are both important. The new method is implemented in the 2-D/1-D code Michigan PArallel Characteristics Transport (MPACT). The method in this paper is shown to achieve nearly 3-D transport accuracy with sufficient refinement in space and angle. The improvement of this new method compared to the previous 2-D/1-D method in MPACT is most notable in problems with strong axial leakage and sharp axial discontinuities, such as control rod tips or part-length rods. The method is computationally more expensive than the existing 2-D/1-D method with isotropic TL and XSs, but this additional cost may be justified when the axial flux shape does not vary smoothly due to axial heterogeneity and needs to be resolved well.
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This paper discusses the convenience of using two-dimensional (2-D) coding techniques for the compression of electrocardiogram (ECG) signals. These signals present a very clear periodicity that can be exploited by the use of a 2-D...
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This paper discusses the convenience of using two-dimensional (2-D) coding techniques for the compression of electrocardiogram (ECG) signals. These signals present a very clear periodicity that can be exploited by the use of a 2-D time/frequency transform to decorrelate it as much as possible. A brief theoretical approach is given to justify the use of this technique, and a comparison is made between a 2-D and a one-dimensional (1-D) uniform quantization scenarios. The influence of the error as well as the frame size on the estimation of the fundamental period is studied.
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With a model for two-dimensional (2D) Brownian rotary ratchets being capable of producing a net torque under athermal random forces, its optimization for mean angular momentum (L), mean angular velocity (ω), and efficiency (η) i...
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With a model for two-dimensional (2D) Brownian rotary ratchets being capable of producing a net torque under athermal random forces, its optimization for mean angular momentum (L), mean angular velocity (ω), and efficiency (η) is considered. In the model, supposing that such a small ratchet system is placed in a thermal bath, the motion of the rotor in the stator is described by the Langevin dynamics of a particle in a 2D ratchet potential, which consists of a static and a time-dependent interaction between rotor and stator; for the latter, we examine a force [randomly directed dc field (RDDF)] for which only the direction is instantaneously updated in a sequence of events in a Poisson process. Because of the chirality of the static part of the potential, it is found that the RDDF causes net rotation while coupling with the thermal fluctuations. Then, to maximize the efficiency of the power consumption of the net rotation, we consider optimizing the static part of the ratchet potential. A crucial point is that the proposed form of ratchet potential enables us to capture the essential feature of 2D ratchet potentials with two closed curves and allows us to systematically construct an optimization strategy. In this paper, we show a method for maximizing L, ω, and η, its outcome in 2D two-tooth ratchet systems, and a direction of optimization for a three-tooth ratchet system.
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In recent years, attempts to improve the mechanical properties of composites have increased remarkably owing to the inadequate utilization of matrices in demanding technological systems where efficiency, durability, and environmen...
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In recent years, attempts to improve the mechanical properties of composites have increased remarkably owing to the inadequate utilization of matrices in demanding technological systems where efficiency, durability, and environmental compatibility are the key requirements. The search for novel materials that can potentially have enhanced mechanical properties continues. Recent studies have demonstrated that two-dimensional (2D) nanomaterials can act as excellent reinforcements because they possess high modulus of elasticity, high strength, and ultralow friction. By incorporating 2D nanomaterials in a composite, 2D nanomaterial-based composites (2DNBCs) have been developed. In view of this, a critical review of recent mechanical and tribological studies based on 2DNBCs has been undertaken. Matrices such as polymers, ceramics, and metals, as well as most of the representative 2D nanomaterial reinforcements such as graphene, boron nitride (BN), molybdenum disulfide (MoS2), and transition metal carbides and nitrides (MXenes) have been included in this review. Their preparation strategies, intrinsic mechanical properties, friction and lubrication performances, strengthening mechanisms, influencing factors, and potential applications have been comprehensively discussed. A brief summary and prospects are given in the final part, which would be useful in designing and fabricating advanced 2D nanocomposites in the future.
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Filter banks over finite fields have found applications in digital signal processing and error-control coding. One method to design a filter bank is to factor its polyphase matrix into the product of elementary building blocks tha...
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Filter banks over finite fields have found applications in digital signal processing and error-control coding. One method to design a filter bank is to factor its polyphase matrix into the product of elementary building blocks that are fully parameterized. It has been shown that this factorization is always possible for one-dimensional (1-D) paraunitary filter banks. In this paper, we focus on two-channel two-dimensional (2-D) paraunitary filter banks that are defined over fields of characteristic two. We generalize the 1-D factorization method to this case. Our approach is based on representing a bivariate finite-impulse-response paraunitary matrix as a polynomial in one variable whose coefficients are matrices over the ring of polynomials in the other variable. To perform the factorization, we extend the definition of paraunitariness to the ring of polynomials. We also define two new building blocks in the ring setting. Using these elementary building blocks, we can construct FIR two-channel 2-D paraunitary filter banks over fields of characteristic two. We also present the connection between these 2-D filter banks and 2-D error-correcting codes. We use the synthesis bank of a 2-D filter bank over the finite field to design 2-D lattice-cyclic codes that are able to correct rectangular erasure bursts. The analysis bank of the corresponding 2-D filter bank is used to construct the parity check matrix. The lattice-cyclic property of these codes provides very efficient decoding of erasure bursts for these codes.
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Background: One of the largest challenges in endoscopic surgical training is adapting to a two-dimensional (2D) view. The glasses-free three-dimensional (GF-3D) display system was designed to integrate the merits of both 2D and co...
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Background: One of the largest challenges in endoscopic surgical training is adapting to a two-dimensional (2D) view. The glasses-free three-dimensional (GF-3D) display system was designed to integrate the merits of both 2D and conventional 3D (C-3D) displays, allowing surgeons to perform video-assisted endoscopic surgery under a stereoscopic view without heavy and cumbersome 3D glasses. Methods: In this study, 15 junior thoracic surgeons were divided to test one routine and one complex task three times each via traditional high-definition 2D (HD-2D) and GF-3D to determine whether there was any advantage when using the GF-3D system to acquire endoscopic skills. The duration, numbers of stitches, and distance between every two stitches were recorded for every procedure. Results: Seven participants were enrolled in the HD-2D group and eight participants were enrolled in the GF-3D group. All 15 participants successfully completed porcine skin continuous suture and tracheal continuous anastomosis procedures three times each. For skin continuous suture, there was no significant difference between the two groups in terms of the learning curve for speed (P=0.683) and accuracy (P=0.556). For tracheal continuous anastomosis, there was a significant difference between the two groups in terms of the learning curve for speed (P=0.001), but no significant difference was observed between the two groups in terms of the learning curve for accuracy (P=0.211). Conclusions: In summary, both HD-2D and GF-3D display systems are efficient for routine and complex endoscopic surgery. With the help of GF-3D, surgeons can acquire new complex endoscopic skills faster than HD-2D and be free from burdensome polarized glasses. More comparative studies in a clinical setting are needed to further explore the feasibility, necessity, and economic aspects of the GF-3D display system.
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In this note, we show that the mathematical formulation of the two-dimensional discriminant locality preserving projections (2D-DLPP) proposed in the paper [R. Zhi, Q. Ruan, Facial expression recognition based on two-dimensional d...
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In this note, we show that the mathematical formulation of the two-dimensional discriminant locality preserving projections (2D-DLPP) proposed in the paper [R. Zhi, Q. Ruan, Facial expression recognition based on two-dimensional discriminant locality preserving projections, Neurocomputing 71 (2008) 1730-1734] is not very sound. The rigorous version is thus given. We also point out that 2D-DLPP can be viewed from the perspective of the discriminant locality preserving projections (DLPP).
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In this study, an efficient semi-discrete method based on the twodimensional Legendre wavelets (2D LWs) is developed to provide approximate solutions for nonlinear variable-order time fractional two-dimensional (2D) Schrodinger e...
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In this study, an efficient semi-discrete method based on the twodimensional Legendre wavelets (2D LWs) is developed to provide approximate solutions for nonlinear variable-order time fractional two-dimensional (2D) Schrodinger equation. First, the variable-order time fractional derivative involved in the considered problem is approximated via the finite difference technique. Then, by help of the finite difference scheme and the theta-weighted method, a recursive algorithm is derived for the problem under examination. After that, the real functions available in the real and imaginary parts of the unknown solution of the problem are expanded via the 2D LWs. Finally, by applying the operational matrices of derivative, the solution of the problem is transformed to the solution of a linear system of algebraic equations in each time step which can simply be solved. In the proposed method, acceptable approximate solutions are achieved by employing only a small number of the basis functions. To illustrate the applicability, validity and accuracy of the wavelet method, some numerical test examples are solved using the suggested method. The achieved numerical results reveal that the method established based on the 2D LWs is very easy to implement, appropriate and accurate in solving the proposed model.
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