Design Of Lattice Research Articles

The transfer line design for the HEPS project

The high energy photon source (HEPS), a 6-GeV synchrotron radiation facility with ultralow emittance, is under construction in China. Three transfer lines are designed for HEPS. One low-energy transfer line is used to deliver the 500 MeV beam provided by the linac to the booster. Two high-energy transfer lines are used to connect the booster and the storage ring to realize beam accumulation in the booster at 6 GeV. The design of the transfer lines is closely related to the layout and optics design of the storage ring, booster and linac. Based on the physics design of the storage ring, booster and linac, the design of the transfer lines has been adjusted. In this paper, the considerations and design of the latest lattice of transfer lines are described. The design satisfies the requirements of the high efficiency transmission and injection.

A scalable two-dimensional moving electric lattice on a chip for polar molecules

Cold atoms and polar molecules have long been candidates for the implementation of quantum information processing. Although many schemes of two-dimensional (2D) moving optical or magnetic lattices have been proposed for atomic shift register, little work has been done on 2D electric lattice for molecular shift register, mainly due to the complexity of molecular energy level structures as well as the challenge to build micropotentials that are scalable, smoothly moving and accurately controlled. Here we present a design of chip-based 2D electric lattice for molecular shift register capable of scaling and controlling, which mainly consists of arrays of equidistant gold electrodes for generating a moving electric lattice. Our theoretical analysis and trajectory calculations, based on the polar molecules ammonia-D3 (ND3) and methylidyne radical (CH), show explicitly that the 2D lattice is able to directly slow down arrays of polar molecules from supersonic speeds to a standstill over a distance of a few centimeters, and then hold them for a certain time or shift them back in a smooth manner. Besides, it also enables decelerating and trapping of the two molecular species simultaneously, which contributes to the understanding towards new phenomena such as novel quantum mechanical collisions and cold chemistry.

Exact solution of the extended dimer Bose–Hubbard model with multi-body interactions

It is shown that the extended one-dimensional dimer Bose–Hubbard model with multi-body interactions can be solved exactly by using the algebraic Bethe ansatz mainly due to the site-permutation S2 symmetry. The solution for the model with up to three-particle hopping and three-body on-site interaction is explicitly shown. As an example of the application, lower part of the excitation energy levels and the ground-state entanglement measure of the standard Bose–Hubbard Hamiltonian with the attractive two-body on-site interaction plus the three-body on-site interaction for 100 bosons with variation of the control parameter are calculated by using the exact solution. It is shown that the attractive three-body on-site interaction reinforces the critical point entanglement of the system, which may be helpful for design of an optical lattice for ultracold atoms or a tuneable superconducting quantum interference device with maximal entanglement.

Topological design of square lattice structure for broad and multiple band gaps in low-frequency range

Several studies have demonstrated that the design of square lattice is an efficient approach to obtain band gap characteristics. However, there are still some challenges in the design of phononic crystals capable to prohibit the propagation of low-frequency waves. In the present paper, aiming to broaden and manipulate the low frequency band gaps, an innovative structure with filling materials in a square lattice is proposed, where the spatial distribution of the materials has been optimized using an improved genetic algorithm. By analyzing the band structure and vibration modes of the designed structure, it becomes evident that the low-frequency band gaps are obtained due to the local resonance of the constituent materials. The transmission spectrum of the finite designed structure confirms an efficient wave attenuation performance in the low-frequency range. Furthermore, the effect of ligament thickness on band gaps was also investigated. The designed phononic porous plate, featuring prominent band gap properties, can be used as an example to guide the topological design of phononic crystal structures for a wide range of engineering implementations.

Fault-tolerant elastic-plastic lattice material.

The paper describes a fault-tolerant design of a special two-dimensional beam lattice. The morphology of such lattices was suggested in the theoretical papers (Cherkaev and Ryvkin 2019 Arch. Appl. Mech. 89, 485-501; Cherkaev and Ryvkin 2019 Arch. Appl. Mech. 89, 503-519), where its superior properties were found numerically. The proposed design consists of beam elements with two different thicknesses; the lattice is macro-isotropic and stretch dominated. Here, we experimentally verify the fault-tolerant properties of these lattices. The specimens were three-dimensional-printed from the VeroWhite elastoplastic material. The lattice is subjected to uniaxial tensile loading. Due to its morphology, the failed beams are evenly distributed in the lattice at the initial stage of damage; at this stage, the material remains intact, preserves its bearing ability, and supports relatively high strains before the final failure. At the initial phase of damage, the thinner beams buckle; then another group of separated thin beams plastically yield and rupture. The fatal macro-crack propagates after the distributed damage reaches a critical level. This initial distributed damage stage allows for a better energy absorption rate before the catastrophic failure of the structure. The experimental results are supported by simulations which confirm that the proposed fault-tolerant material possesses excellent energy absorption properties thanks to the distributed damage stage phenomenon. This article is part of the theme issue 'Modelling of dynamic phenomena and localization in structured media (part 2)'.

Optimization of a Low-alpha Lattice for the HLS-II Storage ring

To generate terahertz radiation at HLS-II, a low-αc lattice scheme is proposed. The new lattice can reduce the bunch length in the storage ring, thus enhancing the coherent synchrotron radiation in the THz region. In this paper, the design and optimization of a low-αc lattice is reported. The new lattice preserves the symmetry of nominal lattice and reduces the first and second order momentum factor at the cost of increasing maximum β function and natural emittance. The bunch length is tracked and the result shows that the low-αc lattice can effectively compress bunches in the storage ring. The performance of this low-αc lattice can be further studied and improved.

Damage propagation in 2d beam lattices: 2. Design of an isotropic fault-tolerant lattice

The paper demonstrates a rational design of an isotropic heterogeneous beam lattice that is fault-tolerant and energy-absorbing. Combining triangular and hexagonal structures, we calculate elastic moduli of obtained hybrid heterogeneous structures; simulate the development of flaws in that composite lattice subjected to a uniform uniaxial deformation; investigate its damage evolution; measure various characteristics of damage that estimate fault tolerance; discuss the trade-off between stiffness and fault tolerance. A design is found that develops a cloud of small evenly spread flaws instead of a crack.

Refining Defect States in W18O49 by Mo Doping: A Strategy for Tuning N2 Activation towards Solar-Driven Nitrogen Fixation.

Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N2 chemisorption at active sites (e.g., surface defects), the N2 molecules have yet to receive energetic electrons toward efficient activation and dissociation, often forming a bottleneck. Herein, we report that the bottleneck can be well tackled by refining the defect states in photocatalysts via doping. As a proof of concept, W18O49 ultrathin nanowires are employed as a model material for subtle Mo doping, in which the coordinatively unsaturated (CUS) metal atoms with oxygen defects serve as the sites for N2 chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N2 activation and dissociation by refining the defect states of W18O49: (1) polarizing the chemisorbed N2 molecules and facilitating the electron transfer from CUS sites to N2 adsorbates, which enables the N≡N bond to be more feasible for dissociation through proton coupling; (2) elevating defect-band center toward the Fermi level, which preserves the energy of photoexcited electrons for N2 reduction. As a result, the 1 mol % Mo-doped W18O49 sample achieves an ammonia production rate of 195.5 μmol gcat-1 h-1, 7-fold higher than that of pristine W18O49. In pure water, the catalyst demonstrates an apparent quantum efficiency of 0.33% at 400 nm and a solar-to-ammonia efficiency of 0.028% under simulated AM 1.5 G light irradiation. This work provides fresh insights into the design of photocatalyst lattice for N2 fixation and reaffirms the versatility of subtle electronic structure modulation in tuning catalytic activity.

Developing of dual junction GaInP/GaAs solar cell devices: effects of different metal contacts

DJ GaInP/GaAs SC structure was designed by using analytical solar cell model. The electrical parameters (Jsc, Voc, FF and η) were calculated by determining optimum conditions for improving the performance of the SCs. Considering the optimization conditions in design of SC, lattice and current matched DJ GaInP/GaAs SC structure was grown using MBE technique. Alloy composition and lattice constants of each layers in the structure were estimated from measured XRD data. To evaluate of effects on conversion efficiency of different metal contact materials, SC devices were fabricated by photolithographic technique. Two types of front-side electrodes, which included Au and Au/Ti metals, were separately fabricated on devices and denoted as S1 and S2, respectively. Performance of the S1 and S2 were determined using I–V measurements under the AM1.5 illuminations. S2 possesses 4.16% enhancement in conversion efficiency compared to that of S1. The better performance of the S2 can be attributed to having higher Isc and Voc due to higher conductivity of titanium as well as good adhesion on GaAs. In addition, Al2O3/TiO2 anti-reflective coating effect on performance of the S1 and S2 was also investigated. Sputtered anti-reflective layer increased the efficiencies from 14.65 to 15.72% and 15.26 to 16.90% for S1 and S2, respectively.

Noninterleaved round beam lattice for light sources

A conceptual design and performance of a round beam lattice for synchrotron light sources based on the phase space exchange principle and the noninterleaved sextupole distribution is presented. Optics design is performed for an approximately 30 pm emittance 6 GeV machine of 2300 m circumference which combines cells with and without straight sections for the insertion devices.7 MoreReceived 16 March 2018DOI:https://doi.org/10.1103/PhysRevAccelBeams.21.051601Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeam opticsLattices in beam opticsAccelerators & Beams

Lattice design and start-to-end simulations for the ARES linac

The SINBAD (Short INnovative Bunches and Accelerators at DESY) project is a dedicated, long-term accelerator research and development facility currently under construction at the DESY Hamburg campus, aiming to provide an infrastructure for developing ultrafast science and several types of novel high-gradient accelerators. We present the design of the magnetic lattice as well as the start-to-end simulation results for ultrashort electron bunch generation at the ARES (Accelerator Research Experiment at SINBAD) linac, which is one of the two experiments at the SINBAD facility. In order to meet the requirements for external injection into high-gradient accelerators, the ARES linac was optimized to provide ∼100 MeV, low charge (0.5 to 30 picocoulombs) and ultrashort electron bunches (sub-femtosecond to dozens of femtoseconds) with ultrasmall spot sizes (less than a few micrometers) and excellent timing stability (rms bunch arrival-time jitter <10 femtoseconds).

Design and control of large-detuned optical lattice based on 87Rb atoms

An innovative and practical scheme of building far-detuned optical lattice for 87Rb atoms is proposed.The disposals of aligning the lattice beams,tuning the lattice frequency and controlling the tapered amplifier for output are described in detail.Alignment of optical lattices is quite difficult in principle,for several beams are required to hit the same atomic cloud.For the relatively near-detuned one-and two-dimensional lattices,the coarse alignment is accomplished by tuning the lattice laser onto resonance with the magnetic-optic trap(MOT) frequency,and then blowing away the MOT in real time.A more precision alignment is implemented at the end of the MOT loading,the atoms are first pumped into the lower hyperfine level by turning off the repumping for some time;then,the pulsed lattice beams are turned on for a short time at some reasonably large detuning.Finally,a fluorescent image of the MOT is taken without repumping,in order to detect only those atoms which are repumped by the lattice laser.For the purpose of controlling the detuning of the lattice easily and accurately,a home-made grating wavemeter with a resolution better than 1 GHz is used.This way allows the laser to be locked at any frequency by using a software PID and is experimentally simple to implement.The intensity of the lattice is controlled directly by pulsing the current through the tapered amplifier using a function generator and a laser diode driver.This technique has already been demonstrated before by Prof.M.Kasevich's group at Stanford. Our experiment starts with a MOT capturing approximately 4107 atoms in 200 ms.The lattice loading is overlap with the end of polarization gradient cooling(PGC),after that,the molasses laser beams are extinguished, and the adiabatic expansion is accomplished in the same time by a decrease in the lattice light intensity according to release function.On the basis of MOT and PGC,the dependences of atomic loading on such parameters as the intensity and frequency detuning of optical lattice are investigated experimentally.The vibration frequency is measured by intentionally modulating the trap intensity.Experimental results show that the lattice structure facilitates the cooling with the temperature of atoms cloud being reduced to 1/3 compared with free space polarization gradient cooling.The system design,experimental results and conclusions are of definite significance and can serve as a fine reference for other kinds of lattices designs or alkali atomic plans.

Heat transfer enhancement by X-type lattice in ventilated brake disc

We introduce an improved design of the X-type lattice cored ventilated brake disc proposed in a previous study. Several annular sector X-type lattice components are integrated into the ventilated channel. Detailed thermo-fluidic characteristics of this new brake disc are explored by experiments and numerical simulations. Experimental results reveal that the new brake disc exhibits better thermal uniformity than the preliminary X-type brake disc, leading to approximately uniform reduction of rubbing surface temperature relative to a prevalent radial vane brake disc. Within the typical operating range of a passenger vehicle (i.e., 200–1000 RPM), the new brake disc provides 18–21% and 7–17% higher steady-state overall cooling capacity than the radial vane and preliminary X-type brake discs, respectively. Numerical results reveal that replacement of radial vanes by the X-type lattice reduces pumping capacity by approximately 40%, deteriorating therefore local heat transfer on the inner surface, the outer rim surface, the inner rim surface and the rubbing surface of the rubbing discs. However, the unique topology of the X-type lattice results in successive interruption and redevelopment of flow and thermal boundary layers, flow impingement on upstream surface of each ligament, and stronger flow mixing in conjunction with an enlarged core surface area. Hence, heat transfer on core surface is substantially improved, which acts as the dominant mechanism for enhanced overall cooling performance of the new brake disc.

Direct comparison of shot-to-shot noise performance of all normal dispersion and anomalous dispersion supercontinuum pumped with sub-picosecond pulse fiber-based laser.

Coherence of supercontinuum sources is critical for applications involving characterization of ultrafast or rarely occurring phenomena. With the demonstrated spectral coverage of supercontinuum extending from near-infrared to over 10 μm in a single nonlinear fiber, there has been a clear push for the bandwidth rather than for attempting to optimize the dynamic properties of the generated spectrum. In this work we provide an experimental assessment of the shot-to-shot noise performance of supercontinuum generation in two types of soft glass photonic crystal fibers. Phase coherence and intensity fluctuations are compared for the cases of an anomalous dispersion-pumped fiber and an all-normal dispersion fiber. With the use of the dispersive Fourier transformation method, we demonstrate that a factor of 100 improvement in signal-to-noise ratio is achieved in the normal-dispersion over anomalous dispersion-pumped fiber for 390 fs long pump pulses. A double-clad design of the photonic lattice of the fiber is further postulated to enable a pump-related seeding mechanism of normal-dispersion supercontinuum broadening under sub-picosecond pumping, which is otherwise known for similar noise characteristics as modulation instability driven, soliton-based spectra.

New Anti-Fluorite Transition Metal Nitrides As High Capacity Li-Ion Intercalation Anodes

More than 20 years after the commercialization of Li-ion batteries, graphite (372 mAh g-1) [1] remains the most widespread negative electrode material for commercial applications. Whilst graphite is typically the “best” anode material for standard battery applications, certain device requirements of a battery make it a less obvious choice and as a result efforts are currently underway to find alternatives that show either higher capacity, such as silicon (3572 mAh g-1) [2], or higher rate capability, such as Li4Ti5O12 (175 mAh g-1) [3]. The latter offers the additional benefit of enhanced safety derived from its activity at potentials ~ 1.5 V vs. Li+/Li. This feature removes the danger of lithium plating at high current densities, known to be a significant problem with current battery technology. Metal oxides have been heavily investigated over the past 10 years and no stand-out candidate has appeared in the search for materials which can reversibly react with lithium at sufficiently low voltages to be used as anodes. In more recent years, the search was extended to the study of less well known transition metal pnictides, with most research efforts directed toward phosphides and nitrides. Lithium transition metal nitrides and oxynitrides have been reported to show interesting performance, making them candidates for the negative electrode [4–9]. Among them, anti-fluorite-type Li7MnN4 and Li7.9MnN3.2O1.6 show specific gravimetric capacities in excess of 300 mAh g-1 with excellent retention, most likely due to the small volume changes undergone during lithium extraction/insertion [4, 9, 10]. As might be expected in the fluorite type crystal structure, significant lithium mobility through their frameworks was proven to exist, even at room temperature, and was enhanced as lithium was removed from the structure [9,10]. This effect is presumably due to the formation of Li vacancies, which can be easily introduced with appropriate compositional design of the crystal lattice. Following on from these results, here we will discuss recent investigations into defect engineered varieties of Li7MnN4and demonstrate the resultant properties of such defects on the anode performance. [1] J.R. Dahn, T. Zheng, Y.H. Liu, J.S. Xue, Science 270 (1995) 590. [2] D. Larcher, S. Beattie, M. Morcrette, K. Edström, J.C. Jumas, J.M. Tarascon, J. Mater. Chem. 17 (2007) 3759. [3] A. Du Pasquier, C.C. Huang, T. Spitler, J. Power Sources 186 (2009) 508. [4] M. Nishijima, N. Takodoro, Y. Takeda, N. Imanishi, O. Yamamoto, J. Electrochem. Soc. 141 (1994) 2966. [5] T. Shodai, S. Okada, S. Tobishima, J. Yamaki, Solid State Ionics 86–88 (1996) 785. [6] Y. Liu, K. Horikawa, M. Fujiyosi, N. Imanishi, A. Hirano, Y. Takeda, J. Electrochem. Soc. 151 (2004) A1450. [7] J. Cabana, Z. Stoeva, J.J. Titman, D.H. Gregory, M.R. Palacín, Chem. Mater. 20 (2008) 1676. [8] J. Cabana, G. Rousse, A. Fuertes, M.R. Palacín, J. Mater. Chem. 13 (2003) 2402. [9] J. Cabana, N. Dupré, C.P. Grey, G. Subias, M.T. Caldés, A.M. Marie, M.R. Palacín, J. Electrochem. Soc. 152 (2005) A2246. [10] J. Cabana, N. Dupré, G. Rousse, C.P. Grey, M.R. Palacín, Solid State Ionics 176 (2005) 2205.

A dihydrogen phosphate anionic network as a host lattice for cations in 1-methylpiperazine-1,4-diium bis(dihydrogen phosphate) and 2-(pyridin-2-yl)pyridinium dihydrogen phosphate-orthophosphoric acid (1/1).

In the salt 1-methylpiperazine-1,4-diium bis(dihydrogen phosphate), C5H13N2(2+)·2H2PO4(-), (I), and the solvated salt 2-(pyridin-2-yl)pyridinium dihydrogen phosphate-orthophosphoric acid (1/1), C10H9N2(+)·H2PO4(-)·H3PO4, (II), the formation of O-H...O and N-H...O hydrogen bonds between the dihydrogen phosphate (H2PO4(-)) anions and the cations constructs a three- and two-dimensional anionic-cationic network, respectively. In (I), the self-assembly of H2PO4(-) anions forms a two-dimensional pseudo-honeycomb-like supramolecular architecture along the (010) plane. 1-Methylpiperazine-1,4-diium cations are trapped between the (010) anionic layers through three N-H...O hydrogen bonds. In solvated salt (II), the self-assembly of H2PO4(-) anions forms a two-dimensional supramolecular architecture with open channels projecting along the [001] direction. The 2-(pyridin-2-yl)pyridinium cations are trapped between the open channels by N-H...O and C-H...O hydrogen bonds. From a study of previously reported structures, dihydrogen phosphate anions show a supramolecular flexibility depending on the nature of the cations. The dihydrogen phosphate anion may be suitable for the design of the host lattice for host-guest supramolecular systems.

New MnZn Ferrite with Low Losses at 500 kHz Over a Broad Temperature Range

In this article the development of a medium frequency MnZn ferrite with low losses over a broad temperature range is described. This has been realized through optimization in the design of the unit cell lattice with the addition of the appropriate dopants. The addition of Tin (Sn) ions results to an increase of the specific resistivity. Consequently the power losses at medium frequencies, 500kHz, are decreased. Cobalt (Co) ions possess opposite sign anisotropy constant of the host lattice. Their introduction compensates the already existing lattice anisotropy. As a result, the temperature dependence of the anisotropy constant of the host lattice decreases and this leads to an increase of the permeability and decrease of the power losses. The newly developed MnZn ferrite exhibits initial permeability of 1656 at 10kHz, 0.1 mT, 25°C, power losses 783 mW cm-3 at 25°C and 656 mW cm-3 at 80°C, 500kHz, 100 mT and is therefore ideal for applications where low losses with small dependency on the working temperature are demanded.

Incorporating fabrication cost into topology optimization of discrete structures and lattices

In this article, we propose a method to incorporate fabrication cost in the topology optimization of light and stiff truss structures and periodic lattices. The fabrication cost of a design is estimated by assigning a unit cost to each truss element, meant to approximate the cost of element placement and associated connections. A regularized Heaviside step function is utilized to estimate the number of elements existing in the design domain. This makes the cost function smooth and differentiable, thus enabling the application of gradient-based optimization schemes. We demonstrate the proposed method with classic examples in structural engineering and in the design of a material lattice, illustrating the effect of the fabrication unit cost on the optimal topologies. We also show that the proposed method can be efficiently used to impose an upper bound on the allowed number of elements in the optimal design of a truss system. Importantly, compared to traditional approaches in structural topology optimization, the proposed algorithm reduces the computational time and reduces the dependency on the threshold used for element removal.

Design of a photonic lattice using shortcuts to adiabaticity

In this article we use the method of shortcuts to adiabaticity to design a photonic lattice (array of waveguides) which can drive the input light to a controlled location at the output. The output position in the array is determined by functions of the propagation distance along the waveguides, which modulate the lattice characteristics (index of refraction, first and second neighbor couplings). The proposed coupler is expected to posses the robustness properties of the design method, coming from its adiabatic nature, and also to have a smaller footprint than purely adiabatic couplers. The present work provides a very interesting example where methods from quantum control can be exploited to design lattices with desired input-output properties.

Adaptive k-space sampling design for edge-enhanced DCE-MRI using compressed sensing

The critical challenge in dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is the trade-off between spatial and temporal resolution due to the limited availability of acquisition time. To address this, it is imperative to under-sample k-space and to develop specific reconstruction techniques. Our proposed method reconstructs high-quality images from under-sampled dynamic k-space data by proposing two main improvements; i) design of an adaptive k-space sampling lattice and ii) edge-enhanced reconstruction technique. A high-resolution data set obtained before the start of the dynamic phase is utilized. The sampling pattern is designed to adapt to the nature of k-space energy distribution obtained from the static high-resolution data. For image reconstruction, the well-known compressed sensing-based total variation (TV) minimization constrained reconstruction scheme is utilized by incorporating the gradient information obtained from the static high-resolution data. The proposed method is tested on seven real dynamic time series consisting of 2 breast data sets and 5 abdomen data sets spanning 1196 images in all. For data availability of only 10%, performance improvement is seen across various quality metrics. Average improvements in Universal Image Quality Index and Structural Similarity Index Metric of up to 28% and 24% on breast data and about 17% and 9% on abdomen data, respectively, are obtained for the proposed method as against the baseline TV reconstruction with variable density random sampling pattern.