bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of automated electric drives for limiting dynamic loads in shaft lines of roll mill stands
Authors: Radionov Andrey A. , Gasiyarov Vadim R. , Karandaev Alexander S. , Khramshin Vadim R.
Published: April 2019

This study introduces the results of scientific research and pilot testing of modernised automated electric drives of the plate mill stands. The experimental tests of electromechanical systems of the reversing stand of the mill 5000 showed the intolerable level of dynamic loads when biting. The problem of reducing dynamic loads and elastic vibrations in shaft lines was stated; it can be solved through enhancing the automated electric drive. The method for limiting loads through biting metal with accelerated rolls and compensating the dynamic component of speed was suggested. The functional diagram of the electric drive to implement the suggested method was designed. In order to study the suggested technical solution, the dynamic mathematic model of the mill stand electric drive with elastic coupling was developed. The results of modelling dynamic modes and experimental studies carried out on the mill 5000 were introduced. The operability and efficiency of the suggested solutions were substantiated.
Wide frequency range active damping of LCL‐filtered grid‐connected converters
Authors: Ghanem Abdelhady , Rashed Mohamed , Sumner Mark , El‐sayes Mohamed Adel , Mansy Ibrahim. I. I.
Published: April 2019

It can be challenging to guarantee the stability of grids with many converters with LCL filters connected due to the presence of multiple resonances within the system. This paper presents an active damping technique to mitigate multiple resonance effects and harmonics in power converters connected to weak grids. The proposed technique employs grid current and capacitor voltage feedback to achieve active damping for a wide range of multiple resonance frequencies. The effectiveness of the proposed wide frequency active damping and improved controller stability is demonstrated through frequency domain analysis and experimental results for single and parallel grid‐connected converters.
Efficient discrete firefly algorithm for Ctrie based caching of multiple sequence alignment on optimally scheduled parallel machines
Authors: Lalwani Soniya , Sharma Harish , Verma Abhay , Kumar Rajesh
Published: April 2019

This study introduces a two‐level strategy for efficient execution of multiple sequence alignment (MSA) of complex heterogeneous sequences. The two levels of the proposed technique are comprised of: designing the discrete firefly algorithm (DFFA) for the formation and implementation of makespan minimisation on parallel machines, followed by performing Ctrie‐based caching for pairwise alignment to reduce the load on the data servers for handling multiple queries. The proposed strategy addresses a multi‐client problem that aims to acquire the full advantage of the computational power of parallel connected machines. Further, it is shown that the inclusion of Ctrie as caching mechanism successively improves the performance of the system with accretion in several sequences. Performance of proposed DFFA is also compared with discrete versions of four swarm intelligence based algorithms at the criteria of makespan minimisation and the rate of convergence on two kinds of complex and diverse datasets. The work is unique in this sense: it is the first swarm‐intelligence‐based implementation for the addressed problem; it is so far the first approach for Ctrie based caching of the MSA on the scheduled parallel machines; hybridisation of DFFA with Ctrie for caching the MSA results is also a novel implementation.
Millijoule few-cycle 5 μm source at 1 kHz repetition rate for generating broadband pulses from the mid- to far-infrared
Authors: Folpini Giulia , Reimann Klaus , Woerner Michael , von Grafenstein Lorenz , Bock Martin , Griebner Uwe , Elsaesser Thomas
Published: April 2019

We present a novel few-cycle 5 um source delivering 75 fs pulses with 1.2 mJ energy at a 1 kHz repetition rate and its first applications for broadband pulse generation from the mid- to far-infrared.
Broadband extreme ultraviolet interferometry and imaging
Authors: Jansen Matthijs , de Beurs Anne , Liu Kevin , Eikema Kjeld , Witte Stefan
Published: April 2019

Using a pair of phase-locked high-harmonic generation sources, we demonstrate Fourier transform interferometry at extreme-ultraviolet (EUV) wavelengths between 17 and 55 nm. This is made possible by the adaptation of a birefringence-based ultrastable interferometer for infrared femtosecond pulses. Since we measure the interference with an EUV-sensitive CCD camera, this enables a wide range of spatially and spectrally resolved measurements at extreme ultraviolet wavelengths. We demonstrate the capabilities of this technique by performing wavelength-resolved high-resolution coherent diffractive imaging and by measuring the spatially resolved spectral absorption of a thin structured titanium film.
Generation of high-flux soft X-ray high harmonics driven by loosely focused TW-class infrared pulses
Authors: Nishimura Kotaro , Fu Yuxi , Suda Akira , Midorikawa Katsumi , Eiji J. Takahashi
Published: April 2019

We develop an experimental strategy for generating high-flux soft x-ray high-order harmonics (HH) driven by loosely focused high-energy infrared femtosecond pulses. Strong soft x-ray HHs are generated in a long Ne medium.
A beamline for attosecond UV pump - XUV probe experiments
Authors: Galli Mara , Wanie Vincent , Månsson Erik Peter , Trabattoni Andrea , Légaré Francois , Frassetto Fabio , Poletto Luca , Nisoli Mauro , Calegari Francesca
Published: April 2019

A time resolved setup combining sub-2fs UV pump pulses with attosecond XUV probe pulses is presented. This scheme will allow the UV photo-induced electron dynamics in bio-chemically relevant molecules to be investigated with unprecedented time resolution.
Direct observation of photo-mechanical stiffness in alkanethiol-capped gold nanoparticles supracrystals by ultrafast small-angle electron diffraction
Authors: Mancini Giulia F. , Pennacchio Francesco , Latychevskaia Tatiana , Reguera Javier , Stellacci Francesco , Carbone Fabrizio
Published: April 2019

We demonstrate that ultrastiff bonding between nanoparticles can be engineered by ad hoc assemblies of ligands, reaching strengths comparable to that of strong covalent bonds. Our observation relies on femtosecond small-angle electron diffraction.
Charge-density-wave in 1T-TiSe2: exciton-phonon separation by femtosecond valence band dynamics
Authors: Hedayat H. , Bugini D. , Karbassi S. , Friedmann S. , van Wezel J. , Clark S. R. , Sayers C. , Da Como E. , Cerullo G. , Dallera C. , Carpene E.
Published: April 2019

We investigate the driving mechanism leading to charge-density-wave transition in 1T-TiSe2 single crystals. Our results show that both exciton instability and phonons cooperate to develop the charge ordered phase below 202 K.
Ballistic excited state dynamics revealed by polarized fs-XANES
Authors: Sension Roseanne J. , Miller Nicholas A. , Deb Aniruddha , Alonso-Mori Roberto , Glownia James M. , Penner-Hahn James E.
Published: April 2019

Polarized time-resolved X-ray absorption near edge structure (XANES) is used to characterize the sequential ballistic excited state dynamics of two B12 vitamers: cyanocobalamin and adenosylcobalamin. Excitation at 550 nm and 365 nm is used to resolve axial and equatorial contributions to the excited state dynamics.
The femtochemistry of the ferrioxalate actinometer
Authors: Straub Steffen , Brünker Paul , Lindner Jörg , Vöhringer Peter
Published: April 2019

The ferrioxalate actinometer is widely used as an analytical standard to determine the photon flux of light sources in photochemical reactors. Yet, the underlying mechanistic functioning of the actinometer at the molecular level is entirely unknown. Here, we present results from femtosecond UV-pump/mid-infrared-probe spectroscopy to reveal the elementary events including the primary C–C and Fe–O-bond breakages that follow an initial photon absorption by the ferrioxalate complex.
Electron Dynamics in Anatase TiO2 Nanoparticles by Ultrafast Broadband Deep-Ultraviolet Spectroscopy
Authors: Baldini Edoardo , Palmieri Tania , Pomarico Enrico , Auböck Gerald , Chergui Majed
Published: April 2019

The optical bandgap of anatase TiO2 nanoparticles is dominated by bulk absorption bands in the deep-ultraviolet due to strongly bound excitons. These spectral features can be utilized as a sensitive probe of carrier and lattice dynamics inside the TiO2 nanoparticles. Here, we implement ultrafast broadband spectroscopy tuned to the exciton resonances in order to track the electron cooling in the conduction band of bare anatase nanoparticles and monitor the electron injection dynamics from an external dye in the case of sensitized anatase nanoparticles.
Single-Cycle Autocorrelation in Attosecond Coherent Nanotransport
Authors: M. Ludwig , T. Rybka , F. Ritzkowsky , D.-C. Marinica , A. Borissov , G. Aguirregabiria , J. Aizpurua , A. Leitenstorfer , D. Brida
Published: April 2019

We employ a pair of single-cycle near-infrared pulses to control coherent transfer of single electrons between the contacts of a plasmonic nanocircuit. As a result, attosecond and highly nonlinear phenomena occur at pJ pulse energies.
Robust sub-50 fs cavity-laser phase stabilization for ultra-fast electron diffraction instruments
Authors: Otto Martin R. , René de Cotret Laurent P. , Stern Mark J. , Siwick Bradley J.
Published: April 2019

A novel laser-RF cavity synchronization scheme was developed for ultrafast electron diffraction instruments. The approach directly generates a synchronized microwave tone by retrieving a phase-locked high-harmonic by photodetection. The radio-frequency cavity which performs electron pulse compression is detuning compensated using an active phase stabilization loop. Timing stability improved from 100 fs to 5 fs RMS and long-term time-zero stability improved to below our measurement resolution of 50 fs determined by pulse streaking.
Ultrafast proton transport in water-methanol mixtures
Authors: Ekimova Maria , Hoffmann Felix , Bekcioglu-Neff Gul , Rafferty Aidan , Nibbering Erik T. J. , Sebastiani Daniel
Published: April 2019

Femtosecond UV/IR pump-probe experiments and ab initio molecular dynamics simulations of 7-hydroxyquinoline in water-methanol mixtures demonstrate an unexpectedly dominant OH-/CH3O- transport pathway but consistent with a solvent-dependent photoacidity free energy-reactivity correlation behaviour.
Model-free decomposition of transient absorption spectra into components with time-dependent shape
Authors: B. Lang , A. Rosspeintner , G. Angulo , E. Vauthey
Published: April 2019

Disentangling overlapping spectral signatures with time-dependent shape is performed using additional information contained in ultrafast transient absorption data, without applying any assumption on the underlying kinetics.
Time-resolved high-harmonic spectroscopy of ultrafast ring-opening of 1,3-cyclohexadiene
Authors: Kaneshima Keisuke , Ninota Yuki , Sekikawa Taro
Published: April 2019

We report, to the best of our knowledge, the first time-resolved high-harmonic spectroscopy (TR-HHS) study of a chemical bond rearrangement. We investigate the transient change of the high-harmonic signal from 1,3-cyclohexadiene (CHD), which undergoes ring-opening and isomerizes to 1,3,5-hexatriene (HT) upon photoexcitation. By associating the variation in the harmonic yield to the changes in the electronic state and vibrational frequencies of the molecule due to isomerization, we find that the CHD excited via two-photon absorption of 3.1 eV photons isomerizes to HT, i.e., ring-opening occurs, around 400 fs after the excitation. The present results demonstrate that TR-HHS, which can track both electronic and nuclear dynamics, is a powerful tool for studying ultrafast photochemical reactions.
Unveiling the concentration dependent direct triplet formation via singlet fission in a tetracene derivative
Authors: Wollscheid Nikolaus , Alagna Nicolo , Perez Lustres J. Luis , Buckup Tiago , Hahn Sebastian , Bunz Uwe H. F. , Motzkus Marcus
Published: April 2019

Singlet fission is slowed down on diffusional timescales in highly concentrated solutions compared to thin films for a tetracene-like molecule. The underlying mechanism suggests competing intersystem crossing and singlet fission, where in the latter singlets are converted directly to triplets without an intermediate excimer state.
Photoelectron Circular Dichroism at the Few-cycle Limit
Authors: Hanus Václav , Kangaparambil Sarayoo , Larimian Seyedreza , Tia Maurice , Xie Xinhua , Eckart Sebastian , Schöffler Markus , Baltuska Andrius , Kitzler Markus
Published: April 2019

Photoelectron circular dichroism (PECD) was investigated for methyloxirane with intense few-cycle pulses. The observed PECD shows a dependence on electron energy. This may signify an influence of the chiral potential on the outgoing electron’s trajectory.
Chromophore arrangement in light-harvesting complex II influenced by the protein dynamics on the microsecond time scale
Authors: Thallmair Sebastian , Marrink Siewert J.
Published: April 2019

Coarse-grained molecular dynamics simulations of light-harvesting complex II in thylakoid membrane reveal its microsecond dynamics. We analyze the fluctuations of the relative chromophore orientations which set the stage for the energy transfer.
Clinical Ultrasound in Inflammatory Bowel Disease
Authors: Kunze Georg , Seitz Karlheinz , Mauch Martin , Petersen Frauke
Published: April 2019

Ultrasound should be the first-line imaging method in the medical care of patients with inflammatory bowel disease. It can be used to differentiate between Crohn’s disease and ulcerative colitis and to detect numerous complications like stenoses, fistulas, and abscesses. As the method is also highly suitable for follow-up, stressful endoscopic procedures and examinations involving radiation are less necessary. Comparison studies with MRI and CT show that ultrasound is not an inferior method and it is therefore included in all guidelines. Intensifying physician training in this method will help to ensure its comprehensive use.
General and Greener Synthesis of Diverse Functional Organic Salts through Schiff Base Chemistry
Authors: Hu Baoping , Shi Qingrong , Lu Feipeng , Zhang Pengcheng , Peng Panpan , Zhao Chaofeng , Du Yao , Su Hui , Li Shenghua , Pang Siping , Nie Fudie
Published: April 2019

We report a greener and more-general organic method for the synthesis of functional organic salts containing organic anions through a Schiff base reaction between readily available aldehydes and simple aminoguanidinium salts. This reaction is operationally simple, free of metal salts, and forms water as the sole byproduct. The broad scope and good functional-group compatibility of this method permit its use to provide ready access to a library of more than 70 distinct organic salts, including those of heterocyclic anions, complex pharmaceutical anions, and polyanions, which are difficult to obtain through classical inorganic methods. Moreover, choosing different aldehydes and organic anions provides a convenient method for modulating or improving the functional properties of the designed organic salts, such as their melting points, fluorescence, and energetic properties. We therefore expect that this method will open new opportunities for the discovery and functionalization of a wide variety of organic salts and functional materials.
The Hudrlik–Peterson Reaction of Secondary cis-TMS-Epoxy Alcohols and its Application to the Synthesis of the Fatty Acid Intermediates
Authors: Saito Shun , Nanba Yutaro , Morita Masao , Kobayashi Yuichi
Published: April 2019

As an extension of the study on the Hudrlik–Peterson reaction of trans-TMS-epoxy alcohols with lithium acetylides, four cis-TMS-epoxy alcohols possessing different alkyl substituents were subjected to the reaction with TMS-acetylide. The reaction completed in 1 h at 0 °C to afford cis-enynyl alcohols in good yields. The results indicated that cis-TMS-epoxy alcohols had higher reactivity than the trans-isomers. Anions derived from 1-heptyne and phenylacetylene participated in the reaction as well. The reaction was applied to optically active cis-TMS-epoxy alcohols, and the resulting enynyl alcohols were transformed to the synthetic intermediates of protectin D1, maresin 1, resolvin E1, and leukotriene B4.
Brain Metastasis in Papillary Serous Adenocarcinoma of the Endometrium
Authors: Eulálio Filho Walberto Monteiro Neiva , Fé Taíla Sousa de Moura , Rodrigues Rodolfo Myronn de Melo , Lima Maria Simone Oliveira , Vieira Sabas Carlos
Published: April 2019

Background Most endometrial cancers (75%) are diagnosed in early stages (stages I and II), in which abnormal uterine bleeding is the most frequent clinical sign. When the diagnosis is performed in stage IV, the most common sites of metastasis are the lungs, liver and bones. Central nervous system (CNS) metastasis is a rare condition. The aim of this study is to describe a case of uterine papillary serous adenocarcinoma of the endometrium that progressed to brain and bone metastases.

Case Report We present the case of a 56-year-old woman with abnormal uterine bleeding and endometrial thickened echo (1.8 cm). A hysteroscopy with biopsy was performed, which identified poor differentiated serous adenocarcinoma of the endometrium. A total abdominal hysterectomy, with pelvic and para-aortic lymphadenectomy, was performed. Analysis of the surgical specimen revealed a grade III uterine papillary serous adenocarcinoma. Adjuvant radio/chemotherapy (carboplatin and paclitaxel—six cycles) was indicated. Sixteen months after the surgery, the patient began to complain of headaches. Brain magnetic resonance imaging demonstrated an expansile mass in the right parietal lobe, suggesting a secondary hematogenous implant subsequently confirmed by biopsy. She underwent surgery for treatment of brain metastasis, followed by radiotherapy. She died 12 months after the brain metastasis diagnosis due to disease progression.

Conclusion Uterine papillary serous adenocarcinoma of the endometrium has a low propensity to metastasize to the brain. To the best of our knowledge, this is the fifth documented case of uterine papillary serous adenocarcinoma of the endometrium with metastasis to the CNS.
Sex-Specific Differences in Late Preterm Neonatal Outcomes
Authors: Battarbee Ashley N. , Glover Angelica V. , Vladutiu Catherine J. , Gyamfi-Bannerman Cynthia , Aliaga Sofia , Manuck Tracy A. , Boggess Kim A.
Published: April 2019

Objective To estimate sex-specific differences in late preterm outcomes and evaluate whether betamethasone modifies this association.

Study Design We conducted a secondary analysis of a multicenter trial of women at risk for late preterm birth randomized to receive betamethasone or placebo. We included women who delivered at 34 to 37 weeks and excluded major fetal anomalies. The primary outcome was severe neonatal morbidity (mechanical ventilation, respiratory distress syndrome, bronchopulmonary dysplasia, sepsis, necrotizing enterocolitis, and intraventricular hemorrhage). Maternal characteristics were compared using chi-square test, t-test, or Mann–Whitney U-test. Multivariable logistic regression estimated the association between sex and morbidity, and likelihood ratio testing assessed for effect modification by betamethasone.

Results Of 2,831 women in the primary trial, 2,331 met the inclusion criteria: 1,236 delivered males and 1,095 delivered females. Betamethasone modified the association between sex and severe morbidity (p = 0.047). Among those who received betamethasone, male sex was associated with higher odds of severe morbidity (adjusted odds ratio: 1.95, 95% confidence interval: 1.25–3.05), compared with female sex. Among those who did not receive betamethasone, there was no significant association between sex and morbidity.

Conclusion Male sex is a risk factor for adverse late preterm outcomes, including severe neonatal morbidity after betamethasone receipt.
Epidemiological and Treatment Trends of Distal Radius Fractures across Multiple Age Groups
Authors: Azad Ali , Kang H. Paco , Alluri Ram K. , Vakhshori Venus , Kay Harrison F. , Ghiassi Alidad
Published: April 2019

Background The purpose of this study is to assess the epidemiology, population-specific treatment trends, and complications of distal radius fractures in the United States.

Methods The PearlDiver database (Humana [2007–2014], Medicare [2005–2014]) was used to access US inpatient and outpatient data for all patients who had undergone operative and nonoperative treatment for a distal radius fracture in the United States. Epidemiologic analysis was performed followed by age-based stratification, to assess prevalence, treatment trends, and rates of complications.

Results A total of 1,124,060 distal radius treatment claims were captured. The incidence of distal radius fractures follows a bimodal distribution with distinct peaks in the pediatric and elderly population. Fractures in the pediatric population occurred predominately in males, whereas fractures in the elderly population occurred more frequently in females. The most commonly used modality of treatment was nonoperative; however, the use of internal fixation increased significantly during the study period, from 8.75 to 20.02%, with a corresponding decrease in percutaneous fixation. The overall complication rate was 8.3%, with mechanical symptoms most frequently reported.

Conclusions The last decade has seen a significant increase in the use of internal fixation as treatment modality for distal radius fractures. The impetus for this change is likely multifactorial and partly related to recent innovations including volar locking plates and an increasingly active elderly population. The implicated financial cost must be weighed against the productivity cost of maintaining independent living to determine the true burden to the healthcare system.
The Accuracy and Cost-Effectiveness of Selective Fetal Echocardiography for the Diagnosis of Congenital Heart Disease in Patients with Pregestational Diabetes Stratified by Hemoglobin A1c
Authors: Finneran Matthew M. , Ware Courtney A. , Kiefer Miranda K. , Buschur Elizabeth O. , Foy Pamela M. , Thung Stephen F. , Landon Mark B. , Gabbe Steven G.
Published: April 2019

Objective To evaluate the accuracy of antenatal diagnosis of congenital heart disease (CHD) using screening methods including a combination of elevated hemoglobin A1c, detailed anatomy ultrasound, and fetal echocardiography.

Study Design This is a retrospective cohort study of all pregnancies complicated by pregestational diabetes from January 2012 to December 2016. The sensitivity, specificity, positive predictive value, and negative predictive value were calculated for each screening regimen. The incremental cost-effectiveness ratio (ICER) was calculated for each regimen with effectiveness defined as additional CHD diagnosed.

Results A total of 378 patients met inclusion criteria with an overall prevalence of CHD of 4.0% (n = 15). When compared with a detailed ultrasound, fetal echocardiography had a higher sensitivity (73.3 vs. 40.0%). However, all cases of major CHD were detected by detailed ultrasound (n = 6). Using an elevated early A1c > 7.7% and a detailed ultrasound resulted in a sensitivity and specificity of 60.0 and 99.4%, respectively. The use of selective fetal echocardiography for an A1c > 7.7% or abnormal detailed anatomy ultrasound would result in a 63.3% reduction in cost per each additional minor CHD diagnosed (ICER: $18,290.52 vs. $28,875.67).

Conclusion Fetal echocardiography appears to have limited diagnostic value in women with pregestational diabetes. However, these results may not be generalizable outside of a high-volume academic setting.
Restenosis of a Polytetrafluoroethylene-Covered Stent Visualized by Coronary Angioscopy and Optical Coherence Tomography: A Case Report
Authors: Araki Makoto , Hikita Hiroyuki , Sudo Yuta , Hishikari Keiichi , Takahashi Atsushi
Published: April 2019

An expandable polytetrafluoroethylene (PTFE)-covered stent graft is beneficial for the treatment of coronary perforations. However, several reports have shown that restenosis and thrombotic occlusion occasionally occur in the stented segment after PTFE-covered stent implantation. A restenosis case after treatment with PTFE-covered stent against saphenous vein graft (SVG) perforation has never been evaluated with optical coherence tomography (OCT) or coronary angioscopy (CAS). This case report presents a 75-year-old man treated with a PTFE-covered stent after he suffered from SVG perforation 6 months ago. He was found to have a focal restenosis of the distal edge of the PTFE-covered stent and underwent percutaneous coronary intervention. OCT showed focal restenosis with homogeneous neointima and exposed struts in the middle and proximal part of the PTFE-covered stent. CAS showed white neointima with a smooth surface at the restenosis site and a sharp border against proximal exposed struts with characteristic links. This case study showed, for the first time in vivo and in a human, the neointimal characteristics of restenosis and uncovered stent struts in a PTFE-covered stent which had been implanted 6 months before. The delayed endothelialization was sustained until 12 months after implantation.
Trajectories of psychological stress among public servants after the Great East Japan Earthquake
Authors: Wakashima Koubun , Asai Keigo , Hiraizumi Taku , Noguchi Shuji
Published: April 2019

The Great East Japan Earthquake of 2011 had a serious psychological impact not only on residents, but also on public servants who worked for residents in prefectures and municipalities. Although public servants worked in highly stressful situations, disaster-related stress among them has not been studied, as has been the case for residents. We examine the stress trajectory of Ishinomaki public servants in Miyagi prefecture (N = 573; 317 men, 256 women), which was directly affected by the Great East Japan Earthquake, and analyse the effects of risk factors that included poor workplace communication, insufficient rest, having dead or missing family members, and living in a shelter. Six surveys were conducted (baseline approximately three months after the earthquake, and follow-up in approximately six-month intervals over a four-year period) using the Japanese version of the Kessler six-item Psychological Distress Scale. The analysis was conducted using five models, which included one for each risk factor and all four risk factors. Latent growth curve analysis indicated that stress response follows a cubic trajectory over four years. Psychological distress sharply reduced from 2011 to 2012 before stabilising and then slowly declining from 2014 to 2015. In the results of the analysis for each model, all risk factors affected stress response in the baseline. Individuals with poor levels of workplace communication experienced higher stress than those who had good levels of workplace communication. Our findings show that public servants’ stress responses decrease with time, regardless of whether or not there are risk factors involved. These results suggest that workplace communication in daily life can prevent the deterioration of mental health since risk factors affect the baseline of stress response.
First principles study of graphene on metals with the SCAN and SCAN+rVV10 functionals
Authors: Shepard Stuart , Smeu Manuel
Published: April 2019

Integrating graphene into electronic devices requires support by a substrate and contact with metal electrodes. Ab initio calculations at the level of density functional theory are performed on graphene-fcc-metal(111) [Gr/M(111)] (M = Ni, Cu, Au) systems. The strongly constrained and appropriately normed (SCAN) and SCAN with the revised Vydrov-van Voorhis (SCAN+rVV10) functionals are relatively new approximations to the exchange-correlation (xc) energy shown to account for van der Waals (vdW) interactions which many non-empirical semi-local functionals fail to include. Binding energies and distances as well as electronic band structures are calculated with SCAN, SCAN+rVV10, Perdew-Burke-Ernzerhof (PBE), and PBE-D3 with and without Becke-Johnson damping, Bayesian error estimation functional with van der Waals correlation (BEEF-vdW), and optB86b-vdW. SCAN and SCAN+rVV10 succeed in describing chemisorption and physisorption in the Gr/Ni(111) system and physisorption in the Gr/Cu(111) and Gr/Au(111) systems. Incorrectly, the physisorption is found to be more favorable than chemisorption in the Gr/Ni(111) system with SCAN, but the result is reversed when the experimental bulk Ni lattice parameter is used as opposed to the SCAN calculated lattice parameter. The SCAN+rVV10 functional produces binding energies and distances comparable to those calculated using the random phase approximation as well as the experiment. The SCAN based functionals produce the highest spin magnetic moments in the bulk Ni and Gr/Ni(111) systems compared to the rest of the functionals investigated, overestimating the experiment by at least ∼0.18 μB. Also, in contrast to the rest of the functionals, the induced spin magnetic moment in graphene is found to be larger in magnitude in the physisorption region than the chemisorption region. The pristine graphene band structure is preserved in the physisorbed systems but with a shift in the Dirac point away from the Fermi energy causing graphene to become n-doped in the Gr/Cu(111) system and p-doped in the Gr/Au(111) system. Chemisorption occurs in the Gr/Ni(111) system where carbon pz states mix with the nickel d states causing a gap to form at the K point, destroying the Dirac point and conical dispersion.
Combined photo- and electroreflectance of multijunction solar cells enabled by subcell electric coupling
Authors: Fuertes Marrón D. , Barrigón E. , Ochoa M. , Artacho I.
Published: April 2019

Electric coupling between subcells of a monolithically grown multijunction solar cell in short circuit allows their simultaneous and independent characterization by means of photo- and electro-reflectance. The photovoltage generated by selective absorption of the pump beam in a given subcell during photoreflectance measurements results in reverse biasing the complementary subunits at the modulation frequency set on the pump illumination. Such voltage bias modulation then acts as external perturbation on the complementary subcells. The spectral separation of different subcell absorption ranges permits the probe beam to record in a single spectrum the response of the complete device as a combination of photo- and electro-reflectance, thereby providing access for the diagnosis of subcells on an individual basis. This form of modulation spectroscopy is demonstrated on a GaInP/GaAs tandem solar cell.
Initiation and detonation growth characteristics of polymer bonded explosives under ramp-wave loadings
Authors: Bai Zhiling , Duan Zhuoping , Liu Haiqing , Cai Jintao , Ou Zhuocheng , Wang Guiji , Huang Fenglei
Published: April 2019

An experimental research approach is proposed to investigate the initiation and detonation growth characteristics of polymer bonded explosives (PBXs) under ramp-wave loadings, in which a magnetic compression device and a multichannel photonic Doppler velocimetry are taken as the ramp-wave loading and the measurement systems, respectively. The ramp loadings have a rise time of 530 ns, and the peak pressure P0 varies from 5.4 GPa to 12.4 GPa with the range of the peak ramp loading rate being from 11.6 GPa/μs to 31.3 GPa/μs. Five PBX specimens in different thicknesses were compressed simultaneously until detonation occurs in some of the specimens. All the particle-velocity histories on the reverse side of each sample were measured, which characterizes both the ignition and the detonation growth processes. It is found, under the ramp-wave loadings, that no significant chemical reaction inside the explosive occurs before a strong precursory shock-wave is formed, and the ignition and detonation growth processes are still dominated by the shock-wave induced hot-spots mechanism. Moreover, the experimental data are also found to be basically in good agreement with the numerical results simulated by using the DZK (named Duan-Zhang-Kim) reaction rate model with a pressure threshold, which implies that the ramp-wave loading experimental technique is also practicable for investigating the ramp-induced shock initiation and detonation growth characteristics of PBXs.
Low-energy/pulse response and high-resolution-CMOS camera for spatiotemporal femtosecond laser pulses characterization @ 1.55 μm
Authors: Zapata-Farfan Jennyfer , Contreras-Martínez Ramiro , Rosete-Aguilar Martha , Garduño-Mejía Jesús , Castro-Marín Pablo , Rodríguez-Herrera Oscar G. , Bruce Neil C. , Ordóñez-Pérez Mitzi , Qureshi Naser , Ascanio Gabriel
Published: April 2019

In this work, we present a commercial CMOS (Complementary Metal Oxide Semiconductor) Raspberry Pi camera implemented as a Near-Infrared detector for both spatial and temporal characterization of femtosecond pulses delivered from a femtosecond Erbium Doped Fiber laser (fs-EDFL) @ 1.55 µm, based on the Two Photon Absorption (TPA) process. The capacity of the device was assessed by measuring the spatial beam profile of the fs-EDFL and comparing the experimental results with the theoretical Fresnel diffraction pattern. We also demonstrate the potential of the CMOS Raspberry Pi camera as a wavefront sensor through its a nonlinear response in a Shack-Hartmann array and for the temporal characterization of the femtosecond pulses delivered from the fs-EDFL through TPA Intensity autocorrelation measurements. The direct pulse detection and measurement, through the nonlinear response with a CMOS, is proposed as a novel and affordable high-resolution and high-sensitivity alternative to costly detectors such as CCDs, wavefront sensors and beam profilers @ 1.55 µm. The measured fluence threshold, down to 17.5 µJ/cm2, and pJ/pulse energy response represents the lowest reported values applied as a beam profiler and a TPA Shack-Hartmann wavefront sensor, to our knowledge.
Optimal basis sets for CBS extrapolation of the correlation energy: oV
x
Z and oV(x+d)Z
Authors: Varandas A. J. C. , Pansini F. N. N.
Published: April 2019

We seek correlation consistent double- and triple-zeta basis sets that perform optimally for extrapolating the correlation energy to the one-electron complete basis set limit. Since the methods used are approximate, the novel basis sets become method specific in the sense of performing best for the chosen level of theory. Such basis sets are also shown to perform accurately for tensorial properties and do not significantly alter the Hartree-Fock energy. Quantitatively, the extrapolated correlation energies from (oVdZ, oVtZ) outperform typically by three- to fivefold those obtained from traditional ansatzes with similar flexibility, thus being (VtZ, VqZ) type or even better. They may even outperform explicitly correlated ones. Not surprisingly, the outperformance in relative energies (e.g., atomization and dissociation energies, and ionization potential) is somewhat downscaled, albeit consistently better than with traditional basis sets. As a case study, we also consider the polarizability of p-nitroaniline, a sizeable system for which complete basis set (CBS)(oVdZ, oVtZ) calculations are shown to outperform equally expensive CBS(VdZ, VtZ) results.
Influence of voltage rise time on operation frequency in magnetically insulated transmission line oscillator
Authors: Fan Yuwei , Li Sirui , Wang Xiaoyu , Li Ankun , Yu Yuanqiang , Liu Zeyang
Published: April 2019

In the experiments of a magnetically insulated transmission line oscillator (MILO), the initiatory microwave frequency is slightly higher than the stable microwave frequency. This paper investigates the influence of the front edge of the voltage on microwave frequency. The theoretical analysis shows that the MILO operates at the 2π mode in the initiatory stage; therefore, the microwave frequency is determined by the single slow wave structure (SWS) cavity. During the stable operation, the MILO works at the π mode and the microwave frequency is decided by the structure parameters of the resonant cavity chain. It is a fact that the resonant frequency of a single SWS cavity is higher than that of the resonant cavity chain, so the reason why the initiatory microwave frequency is slightly higher than the stable microwave frequency can be explained. The simulation results agree with the theoretical results.
Numerical study of species separation in rarefied gas mixture flow through micronozzles using DSMC
Authors: Sabouri Moslem , Darbandi Masoud
Published: April 2019

This work investigates the species separation in the rarefied flow of the argon-helium mixture through convergent-divergent micronozzles. Imposing a molecular mass ratio in the order of 10, the flow of this mixture can lead to the formation of serious nonhomogeneous phenomena such as the species separation. This study is performed in the ranges of 2.0–4.0 for the geometrical expansion ratio, 200–400 K for the wall temperature, and 0.003–1.454 for the inlet Knudsen number. The effects of these parameters are examined on the separative performances of micronozzle. The direct simulation Monte Carlo method is selected as the solution method because it can provide reliable solutions in the current rarefied flow regime study. The current study reveals two important separative effects in the mixture flow through micronozzles. The first effect is the lateral species separation, which results in the enrichment of heavier species near the centerline. The second effect is the streamwise separation, which leads to the enrichment of one species, mostly the lighter one, as the mixture passes through the micronozzle. The current results show that increasing the expansion ratio will enhance the lateral separation monotonically. However, there are specific wall temperature and Knudsen values, which can result in optimum lateral separative effects. In addition, it is observed that the expansion ratio has little effect on the streamwise separation. However, increasing either the wall temperature or the Knudsen number will enhance the streamwise separation, albeit with a limiting value at very high Knudsen numbers.
Charge injection and trapping at perovskite interfaces with organic hole transporting materials of different ionization energies
Authors: Droseros Nikolaos , Dänekamp Benedikt , Tsokkou Demetra , Boix Pablo P. , Banerji Natalie
Published: April 2019

The extraction of photogenerated holes from CH3NH3PbI3 is crucial in perovskite solar cells. Understanding the main parameters that influence this process is essential to design materials and devices with improved efficiency. A series of vacuum deposited hole transporting materials (HTMs) of different ionization energies, used in efficient photovoltaic devices, are studied here by means of femtosecond transient absorption spectroscopy. We find that ultrafast charge injection from the perovskite into the different HTMs (<100 fs) competes with carrier thermalization and occurs independently of their ionization energy. Our results prove that injection takes place from hot states in the valence band making this efficient even for HTMs with higher ionization energy than that of the perovskite. Moreover, a new trapping mechanism is observed after the addition of HTMs, which is attributed to interfacial electron traps formed between the CH3NH3PbI3 and the HTMs, in addition to traps in the neat perovskite. Interfacial electron trapping is slower compared to the ultrafast hole injection, which contributes to the high efficiency obtained when these HTMs are employed in solar cells.
Photoconductive detection of a hydrogen-related donor in SnO2
Authors: Herklotz F. , Chaplygin I. , Lavrov E. V. , Agekyan V. F.
Published: April 2019

Hydrogen defects in single-crystalline SnO2 are studied by combined photoconductivity and IR absorption spectroscopy. Our results indicate that a defect with an O–H local vibrational mode at 3272 cm−1 (10 K) is a donor with a level less than 300 meV below the conduction band. Annealing experiments demonstrate that the defect is stable up to approximately 450 °C and therefore may contribute to persistent n-type conductivity of SnO2.
ZnO1−xTex highly mismatched alloys beyond the dilute alloy limit: Synthesis and electronic band structure
Authors: Ting M. , Yu K. M. , Jaquez M. , Sharp I. D. , Ye Yifan , Segercrantz N. , Greif R. , Mao S. S. , Liu Chao Ping , Walukiewicz W.
Published: April 2019

We have synthesized ZnO1−xTex highly mismatched alloys (HMAs) with high, up to x = 0.34, Te content using pulsed laser deposition. We have found that the film composition is strongly dependent on the growth temperature and background pressure during growth. Lowering the growth temperature and/or increasing the background Ar or N2 pressure increases the Te content in the film. When grown in O2 atmosphere, however, oxidation of the Te species occurred, resulting in much less Te incorporation in the O sublattice. While a lower substrate temperature is needed for the incorporation of more Te in the ZnO1−xTex film, the crystallinity of the film degrades at low growth temperature. X-ray photoemission, soft x-ray absorption, and x-ray emission measurements reveal that the observed drastic narrowing of the optical bandgap with increasing Te content is primarily due to the modification of the valence band. The experimentally observed evolution of the optical properties of ZnO1−xTex HMAs from dilute to mid-composition range (x > 0.3) is analyzed within the framework of a modified band anticrossing model with composition dependent coupling parameters describing the anticrossing interaction between the valence band of the matrix and Te localized states. Electrically, we found that adding Te in ZnO increases the film resistivity. When doped with N, a drastic drop in n from mid-1019 to 1015 cm−3 is observed for ZnO1−xTex with ∼2%–4% of Te. These electrical behaviors can be understood as the effect of the upward shift of the valence band, which favors the formation of native as well as N acceptors.
Low-frequency sound absorption of hybrid absorber based on micro-perforated panel and coiled-up channels
Authors: Wu Fei , Xiao Yong , Yu Dianlong , Zhao Honggang , Wang Yang , Wen Jihong
Published: April 2019

We propose a hybrid acoustic metamaterial as a super absorber for a relatively broadband low-frequency sound based on a simple construction with deep-subwavelength thickness (5 cm). The hybrid metamaterial absorber is carefully designed and constructed based on a microperforated panel (MPP) and coiled-up Fabry–Pérot channels. It is demonstrated analytically, numerically, and experimentally that over 99% of acoustic absorption could be achieved at a resonance frequency (<500 Hz) with the working wavelength about 30 times larger than its total thickness. It is revealed that the superior absorption is mainly caused by the friction losses of acoustic wave energy in the MPP. The frequency of the absorption peak could be tuned by adjusting the geometry parameters of the MPP and the channel folding numbers. The relative absorption bandwidth could also be tuned flexibly (up to 82%) with a fixed deep-subwavelength thickness (5 cm). The absorber has wide potential applications in noise control engineering due to its deep-subwavelength thickness, relatively broad bandwidth, and easy fabrication.
Evolution of a shock wave generated by underwater electrical explosion of a single wire
Authors: Rososhek A. , Efimov S. , Gurovich V. , Virozub A. , Tewari S. V. , Krasik Ya. E.
Published: April 2019

The results of an experimental, analytical, and numerical study of the cylindrical shock wave generated by the underwater electrical explosion of copper and aluminum wires are reported. Experiments were conducted using a microsecond timescale generator delivering ∼180 kA pulses with a 1.2 μs rise time. Shadow streak images were used to study the radial expansion of the exploding wire and the generated shock wave. It was found that the shock wave expansion velocity decreases to the velocity of sound in two stages: a fast stage and then a gradual stage. The fast stage occurs during ∼1.5 μs after the maximum of the resistive voltage is reached, and then, a gradual decrease occurs during several tens of microseconds. It was shown that the duration of the fast stage corresponds to the period of time when the main energy deposition into the wire occurs. Hydrodynamic simulations show that the fast decrease in the shock velocity is related to the evolution of the exploded wire's subsonic expansion, which leads to time/spatial compression of the adjacent water layer. For the gradual decrease stage of the shock wave velocity, we developed a simplified model, which considers uniform water density between the wire boundary and the shock wave front. The results of this model agree satisfactorily with the experimentally obtained shock wave trajectory and radial expansion of the wire.
Electronic structure properties of CuZn2InTe4 and AgZn2InTe4 quaternary chalcogenides
Authors: Shi Wencong , Khabibullin Artem R. , Hobbis Dean , Nolas George S. , Woods Lilia M.
Published: April 2019

Quaternary chalcogenides composed of earth-abundant and primarily nontoxic constituents are currently being explored for thermoelectric applications. The representatives of this class, CuZn2InTe4 and AgZn2InTe4, have been synthesized, and here, we present a comparative study of their structure–property relations using first principles simulations. Our calculations show that the lattice structure for both materials is very similar in terms of characteristic atomic distances and lattice structures, which compare well with experimental data. The electronic structure results indicate that both materials are direct gap semiconductors whose electron localization and charge transfer properties reveal polar covalent bonding in the lattice. The calculated phonon structure shows dynamic stability with unique vibrational properties for each material.
Isospin-phonon coupling and Fano-interference in spin-orbit Mott insulator Sr2IrO4
Authors: Samanta K. , Rigitano D. , Pagliuso P. G. , Granado E.
Published: April 2019

The “isospin-phonon” coupling in Sr2IrO4 is investigated by temperature dependent phonon Raman scattering. Anomalous behavior in the frequency of all studied optical phonons is observed below the magnetic transition temperature TN ∼ 240 K. The strongest effect is detected for the A1g mode at 272 cm−1 associated with the modulation of the Ir–O–Ir bond angle. Additionally, the A1g mode at 560 cm−1 shows a Fano asymmetric lineshape sensitive to TN, supporting the existence of low energy (∼70 meV) electronic excitations that are renormalized by the magnetic order. These results reveal the characteristics of the interaction between the crystal lattice and electronic degrees of freedom in this “spin-orbit” entangled Mott insulator.
Lifting of parallelohedra
Authors: Grishukhin V. P. , Danilov V. I.
Published: April 2019

A parallelohedron is a polyhedron that can tessellate the space via translations without gaps and overlaps. Voronoi conjectured that any parallelohedron is affinely equivalent to a Dirichlet-Voronoi cell of some lattice. Delaunay used the term displacement parallelohedron in his paper “Sur la tiling régulière de l’espace à 4 dimensions. Première partie”, where the four-dimensional parallelohedra are listed. In our work, such a parallelohedron is called a lifted parallelohedron, since it is obtained as an extension of a parallelohedron to a parallelohedron of dimension larger by one.

It is shown that the operation of lifting yields precisely parallelohedra whose Minkowski sum with some nontrivial segment is again a parallelohedron. It is proved that Voronoi’s conjecture holds for parallelohedra admitting lifts and lifted in general position.

Bibliography: 20 titles.