Employing Plane Wave Research Articles

Super-Resolution Ultrasound Imaging for Analysis of Microbubbles Cluster by Acoustic Vortex Tweezers.

Using acoustic vortex tweezers (AVT) to spatially accumulate microbubbles (MBs) shows promise for enhancing drug delivery efficiency and reducing off-target effects. The strong echogenicity of accumulated MBs also improves diagnostics via conventional ultrasound (US) B-mode imaging. However, the annular high-pressure distribution of AVT inhibits MBs inflow at the inlet, reducing MBs collection. The spatial resolution of US B-mode imaging further limits theranostic applications of AVT-mediated MBs accumulation. To address these challenges, we integrated an AVT waveform with volumetric super-resolution imaging (VSRI) to monitor the dynamic growth of MBs cluster during accumulation. We used a 5-MHz 2D array transducer for VSRI, employing plane wave pulses interleaved with accumulating pulses to retain MBs at a flow rate of 0.023-0.047 mL/s in a 3-mm vessel phantom. An asymmetrical AVT waveform (AVT*) was produced by modulating the pressure at the MBs inlet compared to the outlet. The effectiveness was validated in rat cerebral vessels for real-time volumetric tracking of MBs clusters. Microscopy observations showed that AVT* could quickly gather flowing MBs into cluster without repelling them at a flow rate of 0.023 mL/s. Statistical results indicated that microscopic data correlated better with VSRI than with B-mode images, suggesting VSRI suffices to detect the dynamics of AVT*-actuated MBs accumulation in real-time. Additionally, VSRI detected a significant increase in MBs cluster size over time during AVT* in the superior sagittal sinus of the rat brain. These findings demonstrate that the proposed strategy can accumulate the flowing MBs at a desired location and simultaneously observe this phenomenon.

Chemisorption, diffusion and permeation of hydrogen isotopes in bcc bulk cr and cr(100) surface: First-principles dft simulations

Chromium, a transition metal, is one of the important constituents, used widely in steel. It is of paramount importance to study the behavior of hydrogen isotopes with Cr to design a suitable barrier materials for arresting the permeation of H isotopes. Here, the interaction and dynamical behaviours of hydrogen isotopes in bcc Cr lattice have been studied employing plane wave based density functional theory. Nudge elastic band methods have been used to determine the activation energy barrier whereas phonon calculations are performed to calculate the zero point energy in order to investigate the isotope effects. The dissociative surface adsorption of hydrogen is predicted to be exothermic, whereas surface to sub-surface and bulk absorption is found to be endothermic but the vacancy induced absorption energy for H atom in bulk Cr has been found to be exothermic. The diffusion of H atom from one tetrahedral hole to the adjacent tetrahedral hole has been established to be the most favoured pathway. The lighter H atom was shown to have higher diffusion coefficients, permeability coefficients, solubility and rate constants than heavier D and T atoms. The computed values of diffusion, permeability and solubility of H in Cr follow the experimental prediction. The computed results presented here might be of assistance in the future design of suitable materials to arrest the permeation of tritium.

Uranosphaerite: Crystal structure, hydrogen bonding, mechanics, infrared and Raman spectroscopy and thermodynamics

A detailed structural, spectroscopic, mechanical and thermodynamic characterization of the bismuth uranyl-oxide hydroxy-hydrate mineral uranosphaerite, Bi(UO2)O2OH, is obtained using the X-ray diffraction and infrared and Raman spectroscopic techniques and first principles solid-state methods based on density functional theory employing plane wave basis sets and pseudopotentials. The full crystal structure of uranosphaerite, including the positions of the hydrogen atoms within the corresponding unit cell, is determined by the first time from X-ray diffraction data taken from a natural crystal sample from Menzenschwand uranium deposit (Germany). The crystal structure obtained from X-ray diffraction is confirmed by using the first principles methodology. The computed structural parameters and X-ray diffraction pattern are in excellent agreement with their experimental counterparts. From the energy-optimized crystal structure, the mechanical and dynamical stability of uranosphaerite is studied and a rich set of mechanical properties are determined. Uranosphaerite is shown to display the negative Poisson's ratio phenomenon. The experimental infrared spectrum is recorded from a natural sample from Schneeberg (Germany) and the Raman spectrum is collected from two crystal samples from Hagendorf and Schneeberg localities (Germany). Both spectra are also determined using density functional perturbation theory and compared with the observed spectra. Since the computed and experimental spectra have a very high degree of consistence, the infrared and Raman bands are completely assigned using a normal coordinate analysis of the theoretical vibrational results. The spectral zone from 1000 to 3000 cm−1 in the infrared and Raman spectra is shown to be plagued of low intensity combination bands. Eleven and eight combination bands are identified in the infrared and Raman spectra, respectively. The fundamental thermodynamic functions of uranosphaerite are computed as a function of temperature using phonon calculations. The computed specific heat and entropy at 298.15 K are 147.7 and 180.4 J·K−1·mol−1, respectively. The computed thermodynamic parameters are used to determine the corresponding thermodynamic properties of formation in terms of the elements as a function of temperature and the Gibbs free energies of reaction of a series of reactions involving uranosphaerite and a representative subset of the most important secondary phases of spent nuclear fuel. The relative stability of uranosphaerite with respect to these phases as a function of temperature and under different concentrations of hydrogen peroxide is reported.

Vibrational Response of Felodipine in the THz Domain: Optical and Neutron Spectroscopy Versus Plane-Wave DFT Modeling

We present a joint experimental and computational terahertz (THz) spectroscopy study of the most stable polymorph (form I) of an antihypertensive pharmaceutical solid, felodipine (FLD). The vibrational response has been analyzed at room temperature by combining optical (THz-TDS, FT-IR, THz-Raman) and neutron (INS) terahertz spectroscopy. With the challenging example of a large and flexible molecular solid, we illustrate the complementarity of the experimental techniques. We show how the results can be understood by employing ab initio modeling and discuss current progress in the field. To this end, we employ plane wave formulation of density functional theory (plane wave DFT) along with harmonic lattice dynamics calculations (HLD) and ab initio molecular dynamics (AIMD) simulations. Based on a comprehensive theoretical analysis, we discover an inconsistency in the commonly accepted structural model, which can be linked to a distinct librational dynamics of the side ester chains. As a result, only a moderate agreement with the experimental spectra can be achieved. We, therefore, propose an alternative structural model, effectively accounting for the influence of the large-amplitude librations and allowing for a comprehensive analysis of the vibrational resonances up to 4.5 THz. In that way, we illustrate the applicability of the computationally supported THz spectroscopy to detect subtle structural issues in molecular solids. While the provided structural model can be treated as a guess, the problem calls for further revision by means of high-resolution crystallography. The problem also draws a need of extending the THz experiments toward low-temperature conditions and single-crystal samples. On the other hand, the studied system emerges as a challenge for the DFT modeling, being extremely sensitive to the level of the theory used and the resulting description of the intermolecular forces. FLD form I can be, hence, considered as a testbed for the use of more sophisticated theoretical approaches, particularly relying on an advanced treatment of the van der Walls forces and going beyond zero-temperature conditions and harmonic approximation.

Negative linear compressibility in uranyl squarate monohydrate

The mechanical properties of the uranyl squarate monohydrate material, , were studied using theoretical solid-state methods based in density functional theory employing plane waves and pseudopotentials. Very demanding calculation parameters were utilized in order to obtain a realistic description of the mechanical behavior of this material. Since the determination of the positions of the hydrogen atoms in the unit cell of uranyl squarate monohydrate was not possible from x-ray diffraction data by structure refinement, they were fully optimized theoretically. The computed lattice parameters, bond distances, angles, and x-ray powder diffraction patterns of this material were in very good agreement with the experimental data. This material was found to be mechanically and dynamically stable since the corresponding stability conditions were satisfied. The values of the bulk modulus and its pressure derivatives, shear and Young moduli, Poisson ratio, ductility, hardness, and mechanical anisotropy indices of this material were reported. Furthermore, this study showed that this material exhibits the important negative Poisson ratio (NPR) and negative linear compressibility (NLC) phenomena. Uranyl squarate monohydrate is a very anisotropic brittle material characterized by a bulk modulus of ~33 GPa, which shows a minimum value of the NPR of the order of −0.5. Besides, this material displays NLC values for a limited range of positive pressures, from 0.025 GPa to 0.094 GPa, applied along the direction of minimum negative Poisson ratio. The analysis of the crystal structure as a function of pressure demonstrates that the mechanism of NLC of this material is associated to the change in shape of the uranyl pentagonal bipyramids and unrelated to the wine-rack structural mechanism commonly used to rationalize this phenomenon.

Push it to the limit: comparing periodic and local approaches to density functional theory for intermolecular interactions

ABSTRACTWith the aim of systematically comparing two popular approaches to density functional theory – all-electron calculations with local basis sets, and periodic calculations employing plane wave basis sets and norm-conserving pseudopotentials – we have computed complete-basis binding energies across the S22 set of intermolecular interactions, a dataset consisting of noncovalent interactions of small- and medium-sized molecules containing first- and second-row atoms, using the Troullier-Martins norm-conserving pseudopotentials with SPW92, a local spin-density approximation; and PBE, a generalised gradient approximation. We have found that it is challenging to reach the basis set limit with these periodic calculations; for the methods and systems examined, a minimum vacuum distance of 30 Å between a system and its nearest images is necessary – unless some form of dipole correction is employed – as is a kinetic energy cutoff of at least 80 Ry. The trends in convergence with respect to vacuum size and kinetic energy cutoff are largely independent of the level of density functional approximation employed. A sense of the impact of each hyperparameter on basis set error provides a foundation for ensuring quality calculations in future studies and allows us to quantify the basis set errors incurred in existing studies on similar systems.

Graphene based effectual photodetector for photonic integrated circuit

Graphene based p-i-n photodetector circuit is thoroughly addressed in the present research at signal of 650 nm, where intrinsic layer is wrapped with graphene material and it plays vital role to realise effectual detector. To accomplish the same, various parameters of intrinsic layer such as reflectance, transmittance, absorbance, and photocurrent and quantum efficiency are lucidly included to compute the overall transmitted efficiency of the proposed photodetector. Reflectance as well as transmittance is examined by employing plane wave expansion (PWE) method whereas numerical equations are used to find other aforementioned parameters of the intrinsic graphene layer. Simulation results affirm that there is negligible reflectance of 0.0000002 and transmittance of 0.05 from the graphene layer whereas 94% of light get absorbed in the intrinsic layer, pertaining to the proposed structure, and as a result of which intrinsic graphene layer generates massive photocurrent with respect to apposite potential difference in the photodetector circuit. Moreover, photocurrent and quantum efficiency of the said photodetector is analysed with the variation of potential across the photodetector. Finally, it is divulged that photocurrent increases from 3.01 mA to 3.10 mA and quantum efficiency increases from 38.33% to 39.44% with the variation of applied voltage from 0.34 V to 0.43 V respectively. The above piece of work asserts that graphene material is a suitable candidate for photodetector as well as photonic integrated circuits.

The fast multi-pole indirect BEM for solving high-frequency seismic wave scattering by three-dimensional superficial irregularities

Taking full advantage of the indirect boundary element method (IBEM) and fast multi-pole expansion algorithm, this paper proposes a fast multi-pole indirect boundary element method (FM-IBEM) to solve the scattering of high-frequency seismic waves by three-dimensional (3-D) superficial irregularities or heterogeneity in a solid half-space. First, IBEM utilizes an exact dynamic Green's function for a full-space to construct the scattered wave field. Subsequently, by employing plane waves expansion of 3-D potential functions of compressional and shear waves, the multi-pole expansion and local expansion coefficients were derived. Implementation of FM-IBEM is presented in detail for wave-scattering problems. Numerical examples illustrate that the proposed FM-IBEM can reduce the memory required by more than an order of magnitude and also greatly improve the computing efficiency, retaining excellent accuracy as well. Ultimately, several high-frequency plane wave scattering problems of 3-D superficial irregularities in a solid half-space are illustrated, and several important scattering characteristics are described based on the high-precision numerical results.

Analysis of HLB pass filter using silicon photonics structure

High, low and band (HLB) pass filter using silicon waveguide structure is presented in this research. Silicon structure is realised by the combination of nine layers of silicon and air material in an alternative arrangement. Reflection characteristics of above proposed structure is a salient feature to envisage the filtering application where reflection properties are investigated by employing plane wave expansion technique. Finally simulation studies divulges that all three type of filters (High, Low and Band pass) can be designed by changing structure parameter including the thickness of odd and even layer of silicon waveguide structure.

Band analysis of polymer photonic structure for MUX/DEMUX application

In this research, polymer structure is used to realize MUX/DEMUX application via photonic bandgap analysis. The bandgap analysis of proposed structure is carried out at wavelength 1310 and 1550nm by employing plane wave expansion technique. Simulation result reveals that lattice spacing and thickness of odd and even layer of photonic structure controls the bandgap, which leads to allow or disallow the desired wavelengths.

Kinetics and Coverage Dependent Reaction Mechanisms of the Copper Atomic Layer Deposition from Copper Dimethylamino-2-propoxide and Diethylzinc

Atomic layer deposition (ALD) has been recognized as a promising method to deposit conformal and uniform thin film of copper for future electronic devices. However, many aspects of the reaction mechanism and the surface chemistry of copper ALD remain unclear. In this paper, we employ plane wave density functional theory (DFT) to study the transmetalation ALD reaction of copper dimethylamino-2-propoxide [Cu(dmap)2] and diethylzinc [Et2Zn] that was realized experimentally by Lee et al. [Angew. Chem., Int. Ed. 2009, 48, 4536−4539]. We find that the Cu(dmap)2 molecule adsorbs and dissociates through the scission of one or two Cu–O bonds into surface-bound dmap and Cu(dmap) fragments during the copper pulse. As Et2Zn adsorbs on the surface covered with Cu(dmap) and dmap fragments, butane formation and desorption was found to be facilitated by the surrounding ligands, which leads to one reaction mechanism, while the migration of ethyl groups to the surface leads to another reaction mechanism. During both reacti...

PWE approach to optical thyristor for investigation of doping concentration

Computation of doping concentration in optical thyristor using plane wave expansion (PWE) method is reported in this paper. In this research, two types of optical thyristors such as InSb and GaSb are cogitated for investigation of doping concentration. Here concentration of InSb is studied at wavelength of 6.89μm and concentration of GaSb is investigated at wavelength of 1.7μm. Both absorption and reflection losses are considered to find out the doping concentration of InSb and GaSb optical thyristor. The absorption loss is computed using Maxwell's curl equation where reflection loss is investigated by employing plane wave expansion method. An interestingly, it is found that extinction coefficient of all optical thyristors are found zero at aforementioned wavelengths. Simulation results revealed that reflectance from such optical structures gradually decreases with respect to doping concentration. It is also revealed that the output intensity through same structures increases linearly with increasing doping concentration. Aside this, it is also observed that the variation of output intensity is an excellently fitted with linearship (R2=0.999 for InSb and R2=0.9914 for Gasb), which leads to an accurate investigation of doping concentration in both (InSb and GaSb) thyristors.

Numerical simulation for photonic bandgap of cuboid structure

Abstract Detailed numerical simulations are carried out to envisage the band structure of silicon cuboid (3D) photonic crystal structure is presented in this paper. Photonic bandgap of above cuboid structure are simulated by employing plane wave expansion method. Simulation result revealed that both radius of air holes and lattice spacing of crystal play vital role to realize the photonic bandgap of the cuboid structure. Also present simulation result showed that photonic bandgaps of silicon cuboid structure exist for certain values of lattice spacing; for an example bandgap is observed, if lattice spacing along x -axis varies from 0.7 μm to 1.4 μm and lattice spacing along y and z axis is 1 μm each. Similarly photonic bandgap is found if lattice spacing along y -axis varies from 0.7 μm to 1.1 μm and lattice spacing along x and z axis is 1 μm each. Also, the photonic bandgap is found if the lattice spacing along z -axis varies from 0.8 μm to 2.1 μm and the lattice spacing of x and y axis are taken of 1 μm. Apart from this it is also seen that variation of lower and upper edges of the photonic bandgap is non-linear with respect to aforementioned lattice spacing of cuboid crystal structure.

Ab initio investigations of dioctahedral interlayer-deficient mica: modelling 1 M polymorphs of illite found within gas shale

In this investigation we create a variety of dioctahedral, interlayer (cation)-deficient mica clay mineral models of the 1 M -illite series, using the ab initio method of density functional theory (DFT), employing plane waves, pseudo potentials, and super cells. The structures we create are modelled on an average formula of illite such as (Ca 0.059 , K 0.655 )(Si 3.597 , Al 0.403 )(Fe 0.628 , Al 0.969 ,Mg 0.428 )O 10 (OH) 2 , as well as existing crystal structures and experimental data. This study investigates the relative positions of both octahedral and tetrahedral cation substitutions ( e.g . Fe 3+ for Al 3+ and Al 3+ for Si 4+ ) in both trans- and cis-vacant structures. The purpose of this work is to create robust, representative models of single layers (I) and double layers (I-I) of illite found within gas shale, that can be used in future investigations. We examine lattice parameters, interatomic distances of tetrahedral and octahedral sheets, K–O distances, and K positions, and find reasonable agreement with experimental data, and excellent agreement with simulated data of similar structures. Finally, to enable experimental characterization of samples of illite with different compositions, we provide simulated X-ray powder diffraction (XRPD) patterns including up to the first ten ( h k l ) reflections, and find characteristic identifiers of trans- and cis-vacant micas in agreement with previous theoretical and experimental studies. We conclude that the models we create are feasible models of I and I-I layers of illite found within shale and are ready for use in future work.

Near-field to far-field transformation utilising multilevel plane wave representation for planar and quasi-planar measurement contours

A fully probe-corrected near-field far-field transformation employing plane wave expansion and diagonal translation operators has recently been presented, which is able to efficiently carry out transformations for arbitrary measurement point locations. Here, the algorithm is discussed in its multilevel version for the application to planar and quasi-planar measurement contours. The measurement points are grouped in a multilevel box structure and translations of the plane waves, representing the antenna under test, are only carried out to the box centres on the highest level. The plane waves are further processed through the different levels towards the measurement points with a decreasing sampling rate using a disaggregation and anterpolation procedure. This reduces the overall complexity to O(N q log N), N being the total number of measurement points, which is comparable to the classical fast Fourier transform-based algorithms for planar measurements. The proposed algorithm includes a full correction of arbitrary near-field probes and is able to cope with irregular measurement grids and is further optimised for highly directive antennas within this contribution.

Hybrid multilevel plane wave based near-field far-field transformation utilising combined near- and far-field translations

Abstract. The radiation of large antennas and those operating at low frequencies can be determined efficiently by near-field measurement techniques and a subsequent near-field far-field transformation. Various approaches and algorithms have been researched but for electrically large antennas and irregular measurement contours advanced algorithms with low computation complexity are required. In this paper an algorithm employing plane waves as equivalent sources and utilising efficient diagonal translation operators is presented. The efficiency is further enhanced using simple far-field translations in combination with the expensive near-field translations. In this way a low complexity near-field transformation is achieved, which works for arbitrary sample point distributions and incorporates a full probe correction without increasing the complexity.

Multilevel Plane Wave Based Near-Field Far-Field Transformation for Electrically Large Antennas in Free-Space or Above Material Halfspace

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A recently presented fully probe-corrected near-field far-field transformation employing plane wave expansion and diagonal translation operators enables near-field far-field transformation for arbitrary measurement contours and arbitrary antennas. A multilevel extension, inspired by the multilevel fast multipole method, is presented that is suitable for the efficient transformation of electrically large antennas with a size of tens or even hundreds of wavelengths. The measurement points are grouped in a multilevel fashion and translations are carried out to the box centers on the highest level only. The plane waves are processed through the different levels to the measurement points using a disaggregation and anterpolation procedure resulting in a reduced overall complexity. In the second part of this paper, the influence of perfectly conducting ground planes and dielectric halfspaces, as an approximation for ground effects in a real measurement setup, is investigated. As such ground reflected waves are assumed, which propagate from the investigated antenna to the field probe and add to the direct wave contributions. The far-field conditions required for these assumptions are achieved by a source box grouping scheme. By this extension ground effects are directly considered within the near-field far-field transformation. Transformation results using simulated and measured near-field data are shown. </para>

Suitability of III-V[XH4][YH4]materials for hydrogen storage: A density functional study

In the search for novel hydrogen storage media, the III-V hydridic material $[{\text{NH}}_{4}][{\text{BH}}_{4}]$ is a natural candidate. It can store a high $\text{wt}\text{ }%$ of hydrogen and has a favorable volumetric density. Unfortunately it was found to decompose slowly at room temperature. It is of interest to consider chemically related materials, such as the series of $[X{\text{H}}_{4}][Y{\text{H}}_{4}]$ ionic solids ($X=\text{B}$,Al,Ga and $Y=\text{N}$,P,As). Even if the $\text{wt}\text{ }%$ of hydrogen in the heavier congeners is necessarily lower, they might offer superior material properties, notably higher (but not too high) stability. We have therefore performed a first-principles investigation of the cohesive energies of the $X{\text{H}}_{4}Y{\text{H}}_{4}$ solid-state materials. In addition we have analyzed the bond character and energy within the building blocks of these materials, the $X{\text{H}}_{4}^{\ensuremath{-}}$ and $Y{\text{H}}_{4}^{+}$ molecular ions, including a comparison to the $A{\text{H}}_{4}$ molecules $(A=\text{C},\text{Si},\text{Ge})$. The calculations have been performed within the density functional framework employing plane waves for the bulk materials and Slater-type functions for the molecules. A detailed study of the electronic structure reveals that the hydrides of the light (second period) elements, ${\text{BH}}_{4}^{\ensuremath{-}}$, ${\text{CH}}_{4}$, and ${\text{NH}}_{4}^{+}$, exhibit the strongest and shortest $X\ensuremath{-}\text{H}$ bonds. This is caused by Pauli repulsion effects of the hydrogen substituents with the larger cores of the heavier (third and fourth period) elements. The important consequence is that in the crystals, where the ionic hydrides retain their identity and charge, the distance between the negative and positive ions is larger in the heavier systems, hence less Madelung stabilization and a smaller cohesive energy. Moving from $[{\text{NH}}_{4}][{\text{BH}}_{4}]$ to heavier congeners thus does not seem to be a promising route to obtain more suitable materials for hydrogen storage. Other types of chemical variation (different substituents) on the $[{\text{NH}}_{4}][{\text{BH}}_{4}]$ building blocks may prove more advantageous.

Fully Probe-Corrected Near-Field Far-Field Transformation Employing Plane Wave Expansion and Diagonal Translation Operators

Near-field antenna measurements combined with a near-field far-field transformation are an established antenna characterization technique. The approach avoids far-field measurements and offers a wide area of post-processing possibilities including radiation pattern determination and diagnostic methods. In this paper, a near-field far-field transformation algorithm employing plane wave expansion is presented and applied to the case of spherical near-field measurements. Compared to existing algorithms, this approach exploits the benefits of diagonalized translation operators, known from fast multipole methods. Due to the plane wave based field representation, a probe correction, using directly the probe's far-field pattern can easily be integrated into the transformation. Hence, it is possible to perform a full probe correction for arbitrary field probes with almost no additional effort. In contrast to other plane wave techniques, like holographic projections, which are suitable for highly directive antennas, the presented approach is applicable for arbitrary radiating structures. Major advantages are low computational effort with respect to the coupling matrix elements owing to the use of diagonalized translation operators and the efficient correction of arbitrary field probes. Also, irregular measurement grids can be handled with little additional effort.

In-plane Littrow lasing of broad photonic crystal waveguides

Broad photonic crystal waveguides forming open resonators are shown to support an hitherto unnoticed lasing pattern. The feedback for lasing originates in Littrow-type reflections of higher-order modes from the waveguide boundaries. The authors employ plane wave and finite-difference time-domain simulations of bulk crystal and waveguide to substantiate the concept of a distributed Littrow reflector. Experimental results are reported for a 10-μm-wide photonic crystal waveguide deeply etched into InP substrate. In-plane lasing and low modal threshold gain due to longer path lengths are the key features of this resonator.