bluuebunny/crossref_metadata_2025_split huggingface dataset:
Machine learned calibrations to high-throughput molecular excited state calculations
Authors: Verma Shomik , Rivera Miguel , Scanlon David O. , Walsh Aron 
Published: April 2022

Understanding the excited state properties of molecules provides insight into how they interact with light. These interactions can be exploited to design compounds for photochemical applications, including enhanced spectral conversion of light to increase the efficiency of photovoltaic cells. While chemical discovery is time- and resource-intensive experimentally, computational chemistry can be used to screen large-scale databases for molecules of interest in a procedure known as high-throughput virtual screening. The first step usually involves a high-speed but low-accuracy method to screen large numbers of molecules (potentially millions), so only the best candidates are evaluated with expensive methods. However, use of a coarse first-pass screening method can potentially result in high false positive or false negative rates. Therefore, this study uses machine learning to calibrate a high-throughput technique [eXtended Tight Binding based simplified Tamm-Dancoff approximation (xTB-sTDA)] against a higher accuracy one (time-dependent density functional theory). Testing the calibration model shows an approximately sixfold decrease in the error in-domain and an approximately threefold decrease in the out-of-domain. The resulting mean absolute error of ∼0.14 eV is in line with previous work in machine learning calibrations and out-performs previous work in linear calibration of xTB-sTDA. We then apply the calibration model to screen a 250k molecule database and map inaccuracies of xTB-sTDA in chemical space. We also show generalizability of the workflow by calibrating against a higher-level technique (CC2), yielding a similarly low error. Overall, this work demonstrates that machine learning can be used to develop a cost-effective and accurate method for large-scale excited state screening, enabling accelerated molecular discovery across a variety of disciplines.
Testing gravity with black hole shadow subrings
Authors: Ayzenberg Dimitry 
Published: April 2022

Abstract
The black hole shadow, first observed by the Event Horizon Telescope in 2017, is the newest method for studying black holes and understanding gravity. Much work has gone into understanding the shadow of a Kerr black hole, including all of the complex astrophysics of the accretion disk, and there are numerous studies of the ideal shadow in non-Kerr black holes and exotic compact objects. This paper presents one of the first studies of the black hole shadow of non-Kerr black holes when the illumination source is an accretion disk. In particular, the ability of current and future very long baseline interferometers to estimate the physical parameters of the black hole spacetime and accretion disk is investigated using two different parametrized black hole metrics that encode a number of possible deviations from Kerr. Both the full shadow image and the individual subrings of the shadow are analyzed as the higher order subrings are weakly dependent on the disk physics and may be a more viable observable for studying the spacetime. The results suggest that with current telescope capabilities and any future earth-based telescopes it will be quite difficult to place strong constraints on departures from the Kerr spacetime, primarily due to the low resolution and strong degeneracies between the spacetime parameters. More optimistically, space-based interferometers may be capable of testing the Kerr nature of black holes and general relativity to comparable or better precision than is currently possible with other observations.
Minimizing L
1 over L
2 norms on the gradient
Authors: Wang Chao , Tao Min , Chuah Chen-Nee , Nagy James , Lou Yifei 
Published: April 2022

Abstract
In this paper, we study the L
1/L
2 minimization on the gradient for imaging applications. Several recent works have demonstrated that L
1/L
2 is better than the L
1 norm when approximating the L
0 norm to promote sparsity. Consequently, we postulate that applying L
1/L
2 on the gradient is better than the classic total variation (the L
1 norm on the gradient) to enforce the sparsity of the image gradient. Numerically, we design a specific splitting scheme, under which we can prove subsequential and global convergence for the alternating direction method of multipliers (ADMM) under certain conditions. Experimentally, we demonstrate visible improvements of L
1/L
2 over L
1 and other nonconvex regularizations for image recovery from low-frequency measurements and two medical applications of magnetic resonance imaging and computed tomography reconstruction. Finally, we reveal some empirical evidence on the superiority of L
1/L
2 over L
1 when recovering piecewise constant signals from low-frequency measurements to shed light on future works.
Burr removal from high-aspect-ratio micro-pillars using ultrasonic-assisted abrasive micro-deburring
Authors: Kumar A Sravan , Deb Sankha , Paul S 
Published: April 2022

Abstract
The demand for high-aspect-ratio microstructures is ever increasing in the fields of microelectromechanical systems, biomedicine, aerospace, telecommunication, and heat transfer. Mechanical micromachining processes have a distinct advantage over lithography-based processes for machining complex three-dimensional microstructures on a variety of materials with high accuracy and surface finish. But the tool-based micromachining operations face inherent issues in the form of excessive burr formation, which needs to be addressed by post-machining burr removal operations. In this study, an ultrasonic-assisted abrasive micro-deburring process employing a probe sonotrode and abrasive particles has been investigated for deburring high-aspect-ratio micro-pillars machined on aluminium 6061 and copper. Deburring of micromilled pillars of aspect ratio 5:1 has been achieved while maintaining pillar integrity. The mechanism of deburring has been observed to be mainly by the impact of the abrasive particles with a minor role played by liquid cavitation. Burr reduction as high as 88.75% for Al 6061 and 90.1% for copper has been achieved in a short processing time of 10 s. This is a significantly faster process than other ultrasonic cavitation-based deburring processes described in literature (deburring time ranging from 60 min to a few hours). With proper control of the process parameters like stand-off distance and power, burr removal has been achieved while maintaining the integrity of the micro-pillars. Pure water cavitation has also been studied for comparison, which has resulted in a burr removal by 51.5% and 53.1% for Al 6061 and copper, respectively. Upon proper selection of the process parameters, this process can be a viable alternative to existing deburring methods in terms of minimal processing time and structure damage.
Characteristics of the molecular above-threshold ionization by a bichromatic elliptically polarized field with co-rotating components
Authors: Habibović D , Gazibegović-Busuladžić A , Busuladžić M , Milošević D B 
Published: April 2022

Abstract
We address ionization of a diatomic molecule by a bichromatic elliptically polarized field with co-rotating components. Using the strong-field approximation we investigate symmetry properties of the photoelectron momentum distribution and explore the minima which appear in the photoelectron spectra. We distinguish two types of minima: (i) two-center interference minima which appear due to the destructive interference of the contributions of two electron wave packets emitted from the two centers of the diatomic molecule and (ii) the one-center minima which are caused by the interference of the parts of the wave packet emitted from the same atomic center at different times. The position of the two-center interference minima depends on the molecular orientation. When a molecular orbital is modelled using the atomic orbitals of a specific parity, the position of the two-center interference minima does not depend on the ellipticity of our driving field. However, when a molecular orbital consists of both odd and even atomic orbitals the interference of their contributions and the position of the minima depend on the ellipticity. The position of the interference minima in the photoelectron momentum plane is confirmed using the saddle-point method. The position and the number of the one-center minima do not depend on the molecular orientation, but they strongly depend on the ellipticity of the field components. Finally, comparing the photoelectron spectra of the CO molecule with the spectra of homonuclear molecules and the NO molecule we show that the electron probability density distribution plays a significant role for the high-energy rescattered electrons.
Spatio-temporal evolution of ion current extracted from pulsed dielectric barrier discharge
Authors: Khomich Vladislav Yu , Rebrov Igor E , Voevodin Vadim V , Yamshchikov Vladimir A , Zharkov Yaroslav E 
Published: April 2022

Abstract
In the present study, the influence of various factors on the shape of the ion cloud extracted from the specific discharge setup was investigated. The overall installment presented a surface dielectric barrier discharge plasma in the air fed by impulse high voltage. The effect of the amplitude, polarity, and duration for single and repetitive voltage pulses were examined. The patterns of ion current distribution depending on the gas gap length and the average field strength were obtained, and the effect of pulse duration and frequency on the amount of the extracted charge were examined. It was shown that the extracted charge was non-uniformly distributed in the gap volume during single and periodic voltage pulses. The effect of volume charge accumulation in the gap at high pulse repetition rate was shown. Computer simulations demonstrated that the main role in the ion cloud shape distortion was caused by the surface charge deposited on the dielectric barrier.
Exceptional points in an optically pumped magnetometer
Authors: Qin Haoye , Ding Ming 
Published: April 2022

Abstract
The exceptional points (EPs) in a system are the eigenvalue degeneracy that has been demonstrated in a wide range of optical arrangements. In this paper, EP is analyzed schematically in an optically pumped magnetometer, which is governed by the Bloch equation with a

3
×
3

matrix. We numerically illustrate EP enhanced sensing for magnetic field and EP encircling induced 2π phase shift by employing the sensing field along with transverse modulation field. These findings may contribute to the realization of EP magnetometers and atomic gyroscopes for improved field and rotation sensitivity.
Theoretical design of ultracompact three-dimensional isotropic two-photon 4Pi STED microscopy based on multifunctional metalenses focusing system
Authors: Li Yang , Zhao Shihu , Ju Dandan , Luo Mingyan , Xiu Dongming , Liu Shujing , Shen Hui 
Published: April 2022

Abstract
4Pi stimulated emission depletion (STED) microscopy shows outstanding three-dimensional (3D) isotropic super-resolution imaging performance. However, this technology is still difficult for achieving long-term studying of the synapses that are deeply embedded inside brain tissue. Metalens, which can realize arbitrary nanoscale amplitude, phase, and polarization modulations, is a very useful tool to solve this limitation. In this paper, an ultracompact two-photon 4Pi STED microscopy involved two multifunctional metalenses patterned on the two fiber facets respectively for focusing the excitation and depletion laser beams to the same position was proposed to realize the 3D isotropic super-resolution imaging. The designed complementary structure of two metalenses and the optimized pupil ratio β assured the symmetry of the STED spot. Furthermore, the isotropic super-resolution of 27 nm was theoretically implemented based on the two-photon STED theoretical model. Our approach will greatly increase the viability of the 3D super-resolution morphological imaging in the deep brain.
The development of new oral vaccines using porous silica
Authors: Oliveira C L P , Lopes J L S , Sant’Anna O A , Botosso V F , Bordallo H N , Fantini M C A 
Published: April 2022

Abstract
Ordered mesoporous silica (OMS) was proved to be an efficient oral adjuvant capable to deliver a wide in size variety of different antigens, promoting efficient immunogenicity. This material can be used in single or polivalent vaccines, which have been developed by a group of Brazilian scientists. The experiments performed with the model protein Bovine Serum Albumin (BSA) gave the first promissing results, that were also achieved by testing the virus like particle surface antigen of hepatitis B (HBsAg) and diphtheria anatoxin (dANA). Nanostructured OMS, SBA-15 type, with bi-dimensional hexagonal porous symmetry was used to encapsulate the antigens either in the mesoporous (pore diameter ∼ 10 nm) or macroporous (pore diameter > 50 nm) regions. This silica vehicle proved to be capable to create an inflammatory response, did not exhibit toxicity, being effective to induce immunity in high and low responder mice towards antibody production. The silica particles are in the range of micrometer size, leaving no trace in mice organs due to its easy expulsion by faeces. The methods of physics, usually employed to characterize the structure, composition and morphology of materials are of fundamental importance to develop proper oral vaccines in order to state the ideal antigen load to avoid clustering and to determine the rate of antigen release in different media mimicking body fluids.
Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi
Authors: Sk Shamim , Shahi Nisha , Pandey Sudhir K 
Published: April 2022

Abstract
Here, we study the thermoelectric properties of topological semimetal CoSi in the temperature range 300–800 K by using combined experimental and density functional theory (DFT) based methods. CoSi is synthesized using arc melting technique and the Rietveld refinement gives the lattice parameters of a = b = c = 4.445 Å. The measured values of Seebeck coefficient (S) shows the non-monotonic behaviour in the studied temperature range with the value of ∼−81 μV K−1 at room temperature. The |S| first increases till 560 K (∼−93 μV K−1) and then decreases up to 800 K (∼−84 μV K−1) indicating the dominating n-type behaviour in the full temperature range. The electrical conductivity, σ (thermal conductivity, κ) shows the monotonic decreasing (increasing) behaviour with the values of

∼
5.2
×
1

0

5

(12.1 W m−1 K−1) and

∼
3.6
×
1

0

5

(14.2 W m−1 K−1) Ω−1 m−1 at 300 K and 800 K, respectively. The κ exhibits the temperature dependency as, κ ∝ T
0.16. The DFT based Boltzmann transport theory is used to understand these behaviour. The multi-band electron and hole pockets appear to be mainly responsible for deciding the temperature dependent transport behaviour. Specifically, the decrease in the |S| above 560 K and change in the slope of σ around 450 K are due to the contribution of thermally generated charge carriers from the hole pockets. The temperature dependent relaxation time (τ) is computed by comparing the experimental σ with calculated σ/τ and it shows temperature dependency of 1/T
0.35. Further this value of τ is used to calculate the temperature dependent electronic part of thermal conductivity (κ
e) and it gives a fairly good match with the experiment. Present study suggests that electronic band-structure obtained from DFT provides a reasonably good estimate of the transport coefficients of CoSi in the high temperature region of 300–800 K.
High precision measurement of blade profile curve using iterative normal vector approximation
Authors: Liu Junfeng , He Xiaomei , Zhang Li , Huang Xiang , Wang Yizhang 
Published: April 2022

Abstract
The precision measurement of blades has always been a complex problem in free-form surface inspection. For contact inspection of blades by coordinate measuring machine (CMM), the probe radius compensation has a critical influence on the measurement accuracy. In this study, an iterative approach based on the normal vector approximation is proposed to measure the blade profile curve, which aims to reduce the measurement error caused by the conventional method relying on a computer aided design model for compensation. The proposed method combines the local reconstruction of blade surface and CMM measurement software. It first takes the measured results of conventional method as a base, then the resulting corrected points of several sectional profiles are fitted to a B-spline surface to provide an alternative nominal model for CMM software, leading to the next same measurement task. Thus, the measurement-fitting process iterates, in which the current nominal model in CMM software is updated by the reconstructed model of foregoing iteration, until a preset condition is reached. Consequently, the proposed method is implemented on a four-axis CMM, and two blade samples are designed to verify the approach’s effectiveness. Experiments show that our approach is superior to the conventional one in blade profile measurement accuracy.
Measurement of laser powder bed fusion surfaces with light scattering and unsupervised machine learning
Authors: Liu Mingyu , Senin Nicola , Su Rong , Leach Richard 
Published: April 2022

Abstract
Quality monitoring for laser powder bed fusion (L-PBF), particularly in-process and real-time monitoring, is of importance for part quality assurance and manufacturing cost reduction. Measurement of layer surface topography is critical for quality monitoring, as any anomaly on layer surfaces can result in defects in the final part. In this paper, we propose a surface measurement method, based on the use of scattered light patterns and a convolutional autoencoder-based unsupervised machine learning method, designed and trained using a large set of scattering patterns simulated from reference surfaces using a scattering model. The advantage of using an autoencoder is that the monitoring model can be trained using solely data from acceptable surfaces, without the need to ensure the presence of representative observations for all the types of possible surface defects. The advantage of using simulated data for training is that we can obtain an effective monitoring solution without the need for a large collection of experimental observations. Here we report the results of a preliminary investigation on the performance of the proposed solution, where the trained autoencoder is tested on experimental data obtained off-process, using a dedicated experimental apparatus for generating and collecting light scattering patterns from manufactured L-PBF surfaces. Our results indicate that the proposed monitoring solution is capable of detecting both acceptable and anomalous surfaces. Although further validation is required to fully assess performance within an on-machine and in-process setup, our preliminary results are encouraging and provide a glimpse of the potential benefits of using our surface measurement solution for L-PBF in-process monitoring.
A new laser-based monitoring method for the cryomodule components alignment
Authors: He Zhenqiang , Wang Tong , Wang Xiaolong , Lu Shang , Liu Huachang , Li Xiao , Men Lingling , Ma Na , Ke Zhiyong , Liang Jing , Dong Lan , Li Bo 
Published: April 2022

Abstract
Alignment of superconducting cavities is one of the important issues for the China Spallation Neutron Source Phase II (CSNS II) linac. In order to obtain the cavity displacement in the process of cooling down to the liquid helium temperature, a laser-based Poisson Spot Monitor (PSM) system was newly proposed and a verification system in the laboratory was built. The PSM system uses the diffraction spot formed on the CMOS camera after a beam of parallel laser passes through a spherical target to monitor the position of the measured object, where the spherical target is fixed on the monitored object. The displacement during the cooling process of the cryomodule is replaced by the movement of the high-precision two-axis motorized translation stage. A spherical target is fixed on the translation stage as the monitoring object. A beam of parallel laser passes through the spherical monitoring target to form a Poisson spot image on a CMOS camera. The coordinates of the Poisson spot center are obtained through image processing. Through experiments, the PSM system obtained a high accuracy within 5 μm, which meets the displacement monitoring requirement of the CSNS II cryomodule components. The system is fairly simple and able to be constructed without highly specialized parts and can also be used in other high-precision alignment and monitoring fields.
Synthesis of silver nanoparticles by atmospheric pressure plasma jet
Authors: Habib Tatiana , Caiut José Mauricio A , Caillier Bruno 
Published: April 2022

Abstract
Silver nanoparticles are one of the most extensively used metallic nanomaterials due to their unusual physical and chemical properties as well as their promising applications in a wide range of different fields. In this study, a non-thermal atmospheric pressure helium plasma jet was used to successfully synthesize silver nanoparticles with silver nitrate as a precursor and trisodium citrate as a capping agent. The browning of the solution after only 5 min of plasma irradiation is a result of the surface plasmon resonance (SPR) from the obtained silver nanoparticles. The SPR was confirmed by the presence of an absorption band in the visible range between 400 and 450 nm demonstrated in the UV–vis spectra. The effect of different chemical parameters such as the concentration of silver nitrate and the concentration of citrate on the silver nanoparticles have been studied. These nanoparticles were further characterized using transmission electron microscopy and dynamic light scattering. Therefore, the plasma jet was advantageous to fast produce silver nanoparticles in friendly conditions. In addition, the used experimental setup allows further studies in different solvents conditions and with different capping agents. So, this methodology could be useful for the preparation of silver nanoparticles required for numerous applications such as bioactivity, catalysis, surface enhanced Raman scattering, and photonic.
Electronic properties and behavior of carbon network based on graphene and single-walled carbon nanotubes in strong electrical fields: quantum molecular dynamics study
Authors: Slepchenkov Michael M , Glukhova Olga E 
Published: April 2022

Abstract
Using the self-consistent-charge density-functional tight-binding method (SCC-DFTB) and extended lagrangian DFTB-based molecular dynamics, we performed in silico studies of the behavior of graphene–nanotube hybrid structures that are part of a branched 3D carbon network in strong electrical fields. It has been established that strong fields with strength ranging from 5 to 10 V nm−1 cause oscillating deformations of the atomic framework with a frequency in the range from 1.22 to 1.38 THz. It has been revealed that the oscillation frequency is determined primarily by the topology of the atomic framework of graphene–nanotube hybrid, while the electric field strength has an effect within 1%–2%. A further increase in electric field strength reduces the oscillation frequency to 0.7 THz, which accompanies the partial destruction of the atomic framework. The critical value of the electric field strength when the graphene is detached from the nanotube is ∼20 V nm−1.