Double PN Research Articles

Optimizations of the Accelerated Axial Polynomial Method of Characteristics of the APOLLO3® Deterministic Neutron Transport Code

For some years now, the TDT (two- and three-dimensional transport) solver of the APOLLO3® deterministic neutron transport code has been able to perform lattice calculations on three-dimensional extruded and unstructured geometries. A polynomial expansion of the angular flux has been implemented to better describe the flux gradient axially to reduce the number of computational meshes required to reach a given accuracy. Then the polynomial approximation was extended to macroscopic cross sections to perform evolution calculations. Besides these transport schemes, synthetic acceleration has also been implemented, relying on double PN approximations of the angular flux on the boundaries of the spatial regions. The solver has already introduced several techniques to reduce the transport and memory footprint; for example, for the storage of the surfaces crossed by a trajectory or the classification of chords. In this paper, new optimizations are presented. One deals with how monomials of the polynomial basis are integrated along trajectories. Another one concerns the computation of the source term of the transmission equation in the case of polynomial cross sections. The last optimization exploits the fact that, along horizontal trajectories, the flux and the cross sections are constant to speed up the sweep algorithm. Calculations on 5 × 5 and 7 × 7 pressurized water reactor assemblies were performed to assess the gains of these recently developed strategies. The results show good improvements both in computing time and in memory footprint reductions.

Acceleration of an improved linear scheme for the neutron transport

This paper presents an accelerated version of an improved linear method of characteristics scheme that preserves first order spatial moments of the flux. This scheme has slow convergence rate and this is why an acceleration method has been investigated. This acceleration is obtained by using the double PN (DPN) method described in previous studies and used in other codes developed by the APOLLO3® team. While the improved linear MoC has a high memory cost and is difficult to implement, the DPN acceleration is shown to save a significant amount of time on a benchmark problem, even at the zeroth order treated in this paper.

Computational insight into pnictogen bonds in the self-assembly of caged pnictogen compounds

• PnBs in the self-assembly of caged pnictogen species were computationally studied. • Such interactions are primarily electrostatic. • Substituents can be used to tune self-assembly structures and processes. In current years, specific rigid caged structures have been designed to facilitate self-assembly via multiple pnictogen bonds (PnBs). On the basis of our survey of the Cambridge Structure Database and recent crystallographic reports, two sets of dimeric complexes of pnictogen alkoxide cages 1-Pn and pnictogen pyrrole crowns 2-Pn were selected to model PnB interactions in the self-assembly of caged pnictogen compounds. Electrostatic interactions play an important role in the formation of these complexes. The introduction of different substituents into the skeleton 1-Pn affects the properties of double Pn⋯O interactions slightly, because of the opposite influence of these substituents on the donor and acceptor abilities. However, the Pn⋯N interaction strength enhances to a large degree with the presence of strong electron-withdrawing substituents into 2-Pn , due to the markedly increased donor ability of pnictogens.

NanoCharacterization of Double PN Heterojunctions in Photoelectrochemical Devices

NanoCharacterization of Double PN Heterojunctions in Photoelectrochemical Devices

The Multi-PN approximation to neutron transport equation

The Multi-PN (MPN) approximation to the first-order neutron transport equation in one- and two-dimensional geometries is presented using a variational approach. The directional variations of the angular flux have been modeled by separate spherical harmonics expansions in M subdomains, while finite elements have been utilized to represent the spatial dependence. A straightforward procedure has been proposed to handle any order of discretized polynomial expansions in both isotropic and anisotropic scattering medium. A key problem with much of the literature regarding the full-range spherical harmonic method is that it cannot exactly describe the discontinuous nature of the angular flux. Thus, the use of customary expansions leads to substantial defect at boundary and interface of two distinct media (e.g. interface of fuel elements and moderators). The major contribution of the MPN discretization is a theory that overcomes these difficulties. The work represents the generalization of the Double-PN (DPN) approximation previously applied to the neutron transport equation. Numerical results in one- and two-dimensional problems compare MPN and customary PN calculations to the reference transport calculations.

A New Method for Fitting Current\u2013Voltage Curves of Planar Heterojunction Perovskite Solar Cells

Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current–voltage characteristic of P–I–N planar structure perovskite solar cells. This new method can theoretically solve the dilemma of the parameter diode ideal factor being larger than 2 from an ideal single heterojunction equivalent circuit, which usually is in the range from 1 to 2. The diode ideal factor reflects PN junction quality, which influences the recombination at electron transport layer/perovskite and perovskite/hole transport layer interface. Based on the double PN junction equivalent circuit, we can also simulate the dark current–voltage curve for analyzing recombination current (Shockley–Read–Hall recombination) and diffusion current (including direct recombination), and thus carrier recombination and transportation characteristics. This new model offers an efficacious and simple method to investigate interfaces condition, film quality of perovskite absorbing layer and performance of transport layer, helping us further improve the device efficiency and analyze the working mechanism.

An extended half-range spherical harmonics method for first-order neutron transport equation based on variational treatment

A new variational approach with anisotropic scattering kernel for first order neutron transport equation based on Finite Element Method (FEM) and Double-PN (DPN) approximation has been introduced. In presented variational principle, the angular dependence of the neutron flux has been separated into two sub-ranges of the forward and backward moving particles. The applied boundary conditions for the DPN method are straightforward in comparison to the conditions for the PN method. The method has also been extended for 2D plane geometry by using extended half-range spherical harmonics method. By defining a new variational principle, the discontinuity of angular flux on the boundary surface has been treated. A new computing program has been developed, to calculate the angular flux by this method which has the capability to solve neutron transport equation by arbitrary DPN approximation in 1D anisotropic scattering media. Moreover, by investigating extended half-range spherical harmonics method, the program has been developed for 2D geometry. The efficacy of the method is assessed by comparing the required order of angular expansion which is necessary to achieve fine results in several benchmarks. The results demonstrate the superiority of the method against traditional PN method.

Broad spectra receivers for wavelength-encoded electrical current measurement based on light-emitting diode transducer

We report on novel optical receivers for demodulation of wavelength-encoded signals, from ultra-bright green light-emitting diodes (LEDs), used as high-voltage electrical current optical transducers, operating at stable environmental temperature. The intensity/wavelength-modulated light is transmitted to the receiver on the ground potential, by means of a plastic optical fibre (POF) link. Wavelength demodulation of the broad spectra is achieved by means of passive or active filtering based receiver, to overcome the known drawbacks of intensity-modulated sensors. Passive filtering receiver uses OG 530 coloured (orange) glass edge filter, with 12 nm spectral range. It has shown 23 times more slope sensitivity than the (brown) polymer edge filter, but the latter has shown a larger spectral range of 40 nm. An immunity of at least 23 dB under light attenuation was achieved. Measurements with and without modal scrambling are qualitatively described, aiming at sensor stability. Active receivers are built from a commercial double PN junction colour sensor, but could work for dc current sensing only.

The identification of color difference of polychromatic light by silicon color sensor with double PN junction

An investigation on the relation between the spectral distribution of polychromatic light and output signal of silicon color sensor with double PN junction is carried out. It shows that silicon color sensor has considerable capability to discriminate the color difference resulted from the variation in the wavelength corresponding to the peak value of power in the spectral distribution. An experimental set-up is designed for the identification of color difference by the silicon color sensor. The experimental observation confirms the theoretical analysis.

Embryo characteristics and the outcome of day 3 embryo transfer related to pronuclear morphology (PNM) in ejaculate ICSI cycles.

Embryo characteristics and the outcome of day 3 embryo transfer related to pronuclear morphology (PNM) in ejaculate ICSI cycles.

Molecular dynamics simulations of polyphosphazenes: poly[bis(chloro)phosphazene][NPCl2] n

Suitable parameter sets for the CHARMm force field were derived for the structural units in polychlorophosphazene [P=N, P N, P Cl] using the Dinur Hagler energy second derivative procedure based on quantum mechanical SCI calculations using the 6–31G* basis set. To validate the reliability of the parameter set, structural results obtained with CHARMm for the adopted model compounds (OP2NCl5 and OP3N2Cl5) were compared with those derived fromab initio quantum mechanics using the 6–31G* basis set. Application of molecular dynamics (MD) simulations in combinatioin with the available X-ray diffraction data provided structural and conformational information on the polymer. The calculation made using the periodic boundary conditions (PBC) agree well with the polychlorophosphazene ordered in a monoclinic unit cell (a=5.98,b=12.99,c=4.92 A; β=111.7). This model was stabilized mainly by the image atoms contribution to the electrostatic energy term and had aquasi-planar conformation of the backbone chain (glide symmetry). The MD calculations also provided evidence that the difference between single and double PN bonds is less marked than that measured experimentally. This result is, however, in agreement with more recent and accurate X-ray studies on poly(methylphosphazene). Validation of the polymer model provided a complete picture, otherwise experimentally inaccessible, of the internal fluctuations of the polymeric chains.

TheDPNSurface Flux Integral Neutron Transport Method for Slab Geometry

The transport equation in slab geometry is solved by means of the DPN “surface flux” method, based on a Pn polynomial expansion in both angle and space and a double Pn approximation of the angular distribution at interval surfaces. The method, which has been incorporated into the multigroup transport code SURCU, is compared to a number of different codes such as ANISN, DIT, etc. For a given accuracy in the flux SURCU turns out to be faster than other codes since it needs fewer spatial flux moments than other programs need regions or space points. In addition, the required DPN surface flux approximation is much lower than the corresponding Sn approximation. A number of similarities between the present method and both Sn theory and collision probabilities are discussed.

Asymptotic PN and double PN approximations

The P N and double P N approximations to the monoenergetic transport equation are modified to improve their asymptotic behaviour. Free parameters are introduced into the P N and double P N equations through the use of a pseudo-scattering kernel. The parameters are evaluated by stipulating that the resulting scalar flux approximations to the infinite-medium Green's function yield exact asymptotic solutions while conserving specified spatial moments. Asymptotic P 3 and double P 1 solutions are presented for the infinite-medium and half-space Green's functions and for the source-free and constant-source Milne problems.