bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent Advances in Copper-Catalyzed Asymmetric Hydroboration of Electron-Deficient Alkenes: Methodologies and Mechanism
Authors: Whiting Andrew , Chen Jing-Biao
Published: July 2018

The efficient synthesis of enantioenriched organoboron compounds has been recognized as an important topic in recent years. As an update review, this article aims to select key achievements in copper-catalyzed, electron-deficient alkene enantioselective hydroboration methodologies since the beginning of 2017. In addition, it covers relevant mechanistic investigations developed over the last six years, as well as total synthesis applications for preparing 1,3-diols as important medicinal intermediates.

1 Introduction

2 Methodologies for Copper-Catalyzed Hydroboration

2.1 α,β-Unsaturated Ketones and Imines

2.2 α,β-Unsaturated Esters and Cyanides

2.3 Aryl Alkenes and Alkyl Alkenes

3 Mechanistic Investigations on the Copper-Catalyzed Hydroboration

3.1 A Cu–BX2 Intermediate

3.1.1 Experimental Analysis

3.1.2 Borylative Difunctionalization Methodologies

3.1.3 Density Functional Theory

3.2 A Cu–H Intermediate

3.3 Other Mechanistic Proposals

4 Synthetic Applications: Chiral 1,3-Diols

5 Conclusions and Outlook
Antiviral Bioactivity of Chiral β-Amino Acid Ester Derivatives Synthesized through a One-Pot, Solvent-Free Asymmetric Mannich Reaction
Authors: Bai Song , Liu Shan , Zhu Yunying , Zhao Kunhong , Wu Qin
Published: July 2018

A series of both enantiomers of chiral β-amino acid ester derivatives containing a 4-(piperidin-1-yl)pyrimidine moiety was prepared in high yield and excellent enantioselectivity excess (up to >99% enantiomeric excess) using a chiral cinchona alkaloid thiourea catalyst under one-pot solvent-free conditions. Antiviral bioassay experimental results showed that some of the chiral products exhibited higher antiviral activities against tobacco mosaic virus (TMV) in vivo than the commercial antiviral agent ningnanmycin.
Photoredox-Catalyzed Decarboxylative C–H Acylation of Heteroarenes
Authors: Yang Chao , Xia Wujiong , Jia Wei , Jian Yong , Huang Binbin
Published: July 2018

A mild, environmentally friendly, and regioselective acylation of heterocycles with inexpensive carboxylic acids is reported via photoredox catalysis. The strategy is highlighted with good functional group tolerance and substrate scope which could rapidly realize the acylation of various heterocyclic compounds.
One-Pot Conversion of Aldehydes and Ketones into 1-Substituted and 1,4-Disubstituted 1,3-Enynes
Authors: Cabezas Jorge , Poveda Rebeca , Brenes José
Published: July 2018

Sequential treatment of 2,3-dichloropropene with magnesium and n-BuLi generates the operational equivalent of 1,3-dilithiopropyne, which upon treatment with aldehydes or ketones, produces the corresponding alkoxy lithium acetylide intermediates. Reaction of this alkoxide with tosyl chloride, and t-BuLi produces 1-substituted, or 1,1-disubstituted 1,3-enynes in a one-pot reaction. When this lithium acetylide intermediates, obtained by this procedure, were used to perform palladium-catalyzed cross-coupling reactions, followed by addition of thionyl chloride and pyridine, 1,4-disubstituted or 1,1,4-trisubstituted 1,3-enynes were obtained in a one-pot protocol.
[3+2] Cycloaddition of N-Aminopyridines and Perfluoroalkynylphosphonates: Facile Synthesis of Perfluoroalkylated Pyrazolo[1,5-a]pyridines Containing a Phosphonate Moiety
Authors: Zhang Hui , Cao Weiguo , Huang Qi , He Dong , Han Jing , Chen Jie , He Weimin , Deng Hongmei , Shao Min
Published: July 2018

1,3-Zwitterions generated from N-aminopyridines in the presence of base are trapped by perfluoroalkynylphosphonates to yield a variety of perfluoroalkylated pyrazolo[1,5-a]pyridine derivatives bearing a phosphonate group. The salient features of these [3+2] cycloadditions include operational simplicity, good tolerance of functional groups, and good to excellent yields at room temperature.
Bone Recontouring by Guided Surgical Navigation Integrating “Mirroring” Computational Planning in the Management of Severe Fronto-orbital Asymmetry in Fibrous Dysplasia
Authors: Guatta Ramona , Scolozzi Paolo
Published: July 2018

We report the successful treatment of severe fronto-orbital asymmetry in a 20-year-old man with fibrous dysplasia by bone recontouring using a specific approach combining “mirroring” virtual computational planning with intraoperative guided surgical navigation.
Anterior Cervical Fusion with Stand-alone Trabecular Metal Cages to Treat Cervical Myelopathy Caused by Degenerative Disk Disease. Observations in 88 Cases with Minimum 12-month Follow-up
Authors: Roperto Raffaelino , Cacciotti Guglielmo , Calvosa Francesco , Mastronardi Luciano
Published: July 2018

Background Anterior cervical fusion (ACF) with autologous bone was reported > 50 years ago. The continuous development of materials with elastic properties close to that of the cortical bone improves induction of osteogenesis and simplifies the technique of interbody fusion. To determine the safety and efficiency of stand-alone trabecular metal (TM) (or porous tantalum) cages for ACF, we performed a retrospective analysis of 88 consecutive patients with one-level or two-level degenerative disk disease (DDD) causing cervical myelopathy treated by interbody fusion with stand-alone TM cages.

Materials and Methods During a 65-month period, 88 consecutive patients had ACF at 105 levels between C3 and C7. All surgeries involved one- or two-segmental DDD producing mild or severe cervical spine myelopathy, in 31 patients (35.2%), associated with unilateral or bilateral radiculopathy. We implanted all disk spaces with unfilled TM trapezoidal cages (Zimmer Biomet Spine, Broomfield, Colorado, United States).

Results At a mean follow-up of 31 months (range: 12–65 months), 95.4% of patients had a good to excellent outcome, with subjective and objective improvement of myelopathy; the result was fair in two and poor in two other patients. Radicular pain and/or any deficits disappeared in 84 patients (95.4%) complaining of preoperative myeloradiculopathy. The fusion rate was 68.2% at 6 months and 100% at 1 year. Device fragmentation was never observed. In two cases, a second operation with removal of TM cages, corpectomy, expansion cages, and plating was necessary.

Conclusions TM cages appear to be safe and efficient for ACF in DDD patients with myelopathy. To confirm our preliminary impressions, larger studies with long-term follow-up are necessary.
Large Intratemporal Facial Nerve Schwannoma without Facial Palsy: Surgical Strategy of Tumor Removal and Functional Reconstruction
Authors: Yetiser Sertac
Published: July 2018

Background Three patients with large intratemporal facial schwannomas underwent tumor removal and facial nerve reconstruction with hypoglossal anastomosis. The surgical strategy for the cases was tailored to the location of the mass and its extension along the facial nerve.

Aim To provide data on the different clinical aspects of facial nerve schwannoma, the appropriate planning for management, and the predictive outcomes of facial function.

Patients Three patients with facial schwannomas (two men and one woman, ages 45, 36, and 52 years, respectively) who presented to the clinic between 2009 and 2015 were reviewed. They all had hearing loss but normal facial function. All patients were operated on with radical tumor removal via mastoidectomy and subtotal petrosectomy and simultaneous cranial nerve (CN) 7– CN 12 anastomosis.

Results Multiple segments of the facial nerve were involved ranging in size from 3 to 7 cm. In the follow-up period of 9 to 24 months, there was no tumor recurrence. Facial function was scored House-Brackmann grades II and III, but two patients are still in the process of functional recovery.

Conclusion Conservative treatment with sparing of the nerve is considered in patients with small tumors. Excision of a large facial schwannoma with immediate hypoglossal nerve grafting as a primary procedure can provide satisfactory facial nerve function. One of the disadvantages of performing anastomosis is that there is not enough neural tissue just before the bifurcation of the main stump to provide neural suturing without tension because middle fossa extension of the facial schwannoma frequently involves the main facial nerve at the stylomastoid foramen. Reanimation should be processed with extensive backward mobilization of the hypoglossal nerve.
Thrombin-Induced Platelet Factor Va Formation in Patients with a Gray Platelet Syndrome
Authors: Baruch Dominique , Lindhout Theo , Dupuy Evelyne , Caen Jacques P
Published: July 2018

The present study was initiated to establish the functional factor V concentration in platelets of patients with a mild bleeding disorder ascribed to a gray platelet syndrome. This inherited platelet disorder has been characterized by a specific deficiency of alpha-granules and subsequent deficiencies in the alpha-granule proteins. We found that the concentration of plasma factor V was slightly decreased (70% of normal values). In contrast, platelet factor Va formation was severely impaired. Besides a much lower factor V content than in control platelets (10-20% of normal), the dependency of platelet factor Va formation on tlnumbin concentration was altered. Increasing the thrombin concentration 4-lold compared to the concentration that results in maximal factor Va generation from normal platelets did not result in a maximal factor Va formation from gray platelets. When a suspension of washed gray platelets was incubated with a prostacyclin analogue prior to the stimulation with thrombin, a 10-fold lower factor VQ activity was measured. Thus, thrombin-induced factor Va formation in a suspension of gray platelets is the result of a release reaction, followed by the thrombin-catalyzed activation of released factor V. Whereas the kinetics of the former reaction are apparently impaired, the kinetics of the latter one were found to be identical to those observed for normal platelet and plasma factor V activation.
Prevention of Postoperative Venous Thrombosis: A Randomized Trial Comparing Unfractionated Heparin with Low Molecular Weight Heparin in Patients Undergoing Total Hip Replacement
Authors: Planes Andrè , Vochelle Nicole , Mazas Frçngois , Mansat Christian , Zucman Jean , Landais Alain , Pascariello Jean Claude , Weill Dan , Jean Butel
Published: July 2018

A double blind randomized trial comparing subcutaneous enoxaparin (40 mg once daily) with standard unfractionated calcium heparin administered at a dose of 5,000 units every 8 hours in patients undergoing elective hip replacement has been performed. Treatment regimens began 12 hours preoperatively with enoxaparin, 2 hours preoperatively with standard unfractionated calcium heparin, and were continued for 15 days or until discharge. Venography was performed in all patients. Two hundred thirty-seven patients were included in the study: 113 received unfractionated heparin and 124 received enoxaparin. The incidence of proximal deep vein thrombosis was reduced from 18.5% in the unfractionated heparin group to 7.5% in the enoxaparin group (p = 0.014), and the incidence of total deep vein thrombosis was similarly reduced from 25% to 12.5% (p = 0.03). There were two major bleeding episodes and one minor bleed in the enoxaparin group compared to two minor bleeds in the unfractionated heparin group. Patients who received enoxaparin required fewer red blood cell transfusions and had a significantly higher hemoglobin on postoperative days 3 and 4. Thus prophylaxis with enoxaparin, 40 mg once daily, is simple, safe and more effective than standard low dose unfractionated heparin in preventing deep vein thrombosis in patients undergoing elective hip replacement.
Zur Morphologie und Biochemie der Wundheilung: eine Übersicht
Authors: Huber P. , Lindner J.
Published: July 2018

Die Wundheilung wird mit morphologischenund biochemischen Methoden untersuchL Die Ergebnissezeigen, daß die Wundsetzung zur Störungdes Gleichgewichtes zwischen physiologischen Auf- und Abbauvorgängen von Zellen, Grundsubstanzund Fasern (mit Erhöhung ihrer Umsatzraten) fiihrt, Die ä Zunahmedes Katabolismus ist ftir das AusmaB der sekundären kompensatorischen Steigerung des Anabolismus verantwortlich, speziell von Zellen, Proteoglykanen und Kollageno Art, Größe und Lokalisation der Wunde bestimmen den Heilungsablauf und damit das Ausmaß der Anpassung von Struktm, Funktion und Biomechanik an das umgebende, unverletzte Gewebeo Die Kapillarisierung und die Epithelisierung der Wunde start en ebenfalls rasch nach Wundsetzung und werden mit 3H-Thymidin-autoradiographischen Verfahren lokalisiert und quantifizierL Neben sogo reifen Narben können atrophische oder hypertrophe Narben entstehen, schlieBlich auch Keloideo In diesem Zusammenhang werden Regulationen und StOrungen der verschiedenen Wundheilungsphasen besprochen, insbesondere hinsichtlich sogo Zell- und Matrixhyperplasien und ihrer unzureichenden Riickbildung bei diesen pathologischen Wundheilungsverlaufeno Diese Ergebnisse der Bindegewebsforschung sind von praktischer und klinischer Bedeutung.
Mathematical Models for Tumor Growth and the Reduction of Overtreatment
Authors: Heesterman Berdine , Bokhorst John-Melle , de Pont Lisa , Verbist Berit , Bayley Jean-Pierre , van der Mey Andel , Corssmit Eleonora , Hes Frederik , van Benthem Peter , Jansen Jeroen
Published: July 2018

Background To improve our understanding of the natural course of head and neck paragangliomas (HNPGL) and ultimately differentiate between cases that benefit from early treatment and those that are best left untreated, we studied the growth dynamics of 77 HNPGL managed with primary observation.

Methods Using digitally available magnetic resonance images, tumor volume was estimated at three time points. Subsequently, nonlinear least squares regression was used to fit seven mathematical models to the observed growth data. Goodness of fit was assessed with the coefficient of determination (R
2) and root-mean-squared error. The models were compared with Kruskal–Wallis one-way analysis of variance and subsequent post-hoc tests. In addition, the credibility of predictions (age at onset of neoplastic growth and estimated volume at age 90) was evaluated.

Results Equations generating sigmoidal-shaped growth curves (Gompertz, logistic, Spratt and Bertalanffy) provided a good fit (median R
2: 0.996–1.00) and better described the observed data compared with the linear, exponential, and Mendelsohn equations (p < 0.001). Although there was no statistically significant difference between the sigmoidal-shaped growth curves regarding the goodness of fit, a realistic age at onset and estimated volume at age 90 were most often predicted by the Bertalanffy model.

Conclusions Growth of HNPGL is best described by decelerating tumor growth laws, with a preference for the Bertalanffy model. To the best of our knowledge, this is the first time that this often-neglected model has been successfully fitted to clinically obtained growth data.
Musik und Medizin
Authors: Evers S.
Published: July 2018

Beziehungen von Musik und Medizin sind in der Medizingeschichte schon immer von Interesse gewesen. In den letzten Jahrzehnten hat sich dieses interdisziplinäre Feld jedoch zu einem eigenständigen Forschungs- und Versorgungsgebiet entwickelt. In diesem Beitrag sollen die Überschneidungsgebiete von Musik und Medizin systematisch dargestellt werden. Nach propädeutischen Hinweisen wird Musik als Objekt der Medizin erläutert. Hierunter fallen die Bereiche der verschiedenen physiologischen und pathologischen Wirkungen von Musik, der Erkrankungen durch Musizieren und die Musiktherapie. Danach wird dann Medizin als Gegenstand der Musik(wissenschaft) diskutiert. Hierzu gehören Darstellungen von medizinischen Sachverhalten in der Musik, die Pathografien von berühmten Komponisten/Musikern und auch musikalische Aktivitäten von Medizinern. Insbesondere wird eine seriöse und nicht eine romantisierende Beschäftigung mit den Beziehungen zwischen Musik und Medizin gefordert.
Kongressnachlese Schmerzmedizin 4.0
Authors: Jäger-Becker Dagmar
Published: July 2018

Im März fand in Frankfurt der 29. Deutsche Schmerzund Palliativtag mit fast 2 000 Teilnehmern unter dem Motto “Schmerzmedizin 4.0 – Digitalisierung/Vernetzung/ Kommunikation” statt.
Neue Antibiotika für die Therapie von multiresistenten gramnegativen Bakterien
Authors: Probst-Kepper Michael , Geginat Gernot
Published: July 2018

Die stetige Zunahme an bakteriellen Resistenzen und von multiresistenten Erregern (MRE) – vor allem im gramnegativen Bereich – ist ein weltweites Problem. Die Entwicklung neuer Wirkstoffe gegen Infektionen mit multiresistenten gramnegativen Erregern (MRGN) besitzt daher höchste Priorität. Im Folgenden werden kürzlich zugelassene oder in der fortgeschrittenen klinischen Prüfung befindliche Antibiotika mit Wirksamkeit gegen MRGN vorgestellt.
Dynamic features of China's photovoltaic listed companies in different periods: Based on partial Granger causality network
Authors: Li Xiuming , Sun Mei , Han Dun , Gao Cuixia , He Huizi , Mensah Issc Adjei
Published: July 2018

As an important kind of renewable energy, China's photovoltaic (PV) industry has experienced many challenges in different historical stages. Many PV enterprises emerge in the stock market, correlate with each other, and form China's PV stock market network. However, the mutual influence between any two companies in the stock market is impacted by other enterprises and some external factors, which is not considered in the previous studies. In order to study the direct interdependence among China's PV stock markets, we propose the partial Granger causality network (PGCN) model. It is a first practice in the model to apply partial Granger causality to quantify the direct interactions between stock returns. The daily closing prices of 79 China's PV enterprises are selected, and the whole research period 2007.10.2–2016.10.3 is divided into four sub-periods according to three important time nodes. The PGCN in the overall period and four sub-networks are also constructed. Combined with the dynamic behaviors of networks' topological properties, the distribution of enterprise's influence, the conductive force of enterprises, and the stability of the stock market are analyzed. Meanwhile, the regional agglomeration development pattern is revealed, and top 10 influential enterprises are identified.
Recombination defects at the 4H-SiC/SiO2 interface investigated with electrically detected magnetic resonance and ab initio calculations
Authors: Cottom J. , Gruber G. , Pobegen G. , Aichinger T. , Shluger A. L.
Published: July 2018

The selectivity of electrically detected magnetic resonance (EDMR) is utilized to probe the dominant recombination defect at the Si-face 4H-SiC/SiO2 interface. The nature of this defect has long been debated with the two main candidates being the Si vacancy (VSi) or the C-dangling bond (PbC). Through comparison between experimental EDMR measurements and ab initio calculations, an important performance limiting recombination defect observed with EDMR in the current generation of nMOSFETs is reasonably explained as a combination of the PbC and the dual-PbC defects. These defects match the symmetry, hyperfine interaction, and isotopic abundance observed in the experimental EDMR spectrum.
Identification and modulation of electronic band structures of single-phase β-(AlxGa1−x)2O3 alloys grown by laser molecular beam epitaxy
Authors: Li Jing , Chen Xuanhu , Ma Tongchuan , Cui Xiangyuan , Ren Fang-Fang , Gu Shulin , Zhang Rong , Zheng Youdou , Ringer Simon P. , Fu Lan , Tan Hark Hoe , Jagadish Chennupati , Ye Jiandong
Published: July 2018

Understanding the band structure evolution of (AlxGa1−x)2O3 alloys is of fundamental importance for developing Ga2O3-based power electronic devices and vacuum ultraviolet super-radiation hard detectors. Here, we report on the bandgap engineering of β-(AlxGa1−x)2O3 thin films and the identification of compositionally dependent electronic band structures by a combination of absorption spectra analyses and density functional theory calculations. Single-monoclinic β-phase (AlxGa1−x)2O3 (0 ≤ x ≤ 0.54) films with a preferred (−201) orientation were grown by laser molecular beam epitaxy with tunable bandgap ranging from 4.5 to 5.5 eV. The excellent fitting of absorption spectra by the relation of (αhν)1/2 ∝ (hν-E) unambiguously identifies that β-(AlxGa1−x)2O3 alloys are indirect bandgap semiconductors. Theoretical calculations predict that the indirect nature of β-(AlxGa1−x)2O3 becomes more pronounced with increased Al composition due to the increased eigenvalue energy gap between M and Г points in the valence band. The experimentally determined indirect bandgap exhibits almost a linear relationship with Al composition, which is consistent with the theoretical calculation and indicates a small bowing effect and a good miscibility. The identification and modulation of (AlxGa1−x)2O3 band structures allows rational design of ultra-wide bandgap oxide heterostructures for the applications in power electronics and solar-blind or X-ray detection.
High magnetic-field-induced solute interception among dendrite arms in the mushy zone of a Mn–Sb alloy
Authors: Liu Tie , Miao Ling , Wang Kai , Wang Li , Sun Jinmei , Wang Qiang
Published: July 2018

The effect of high magnetic fields on the solute diffusion behavior in the mushy zone of a Mn–Sb alloy has been investigated. A hypoeutectic Mn–Sb alloy was heated in high magnetic fields to yield a mixture of primary MnSb dendrites and Mn/Sb liquid to simulate the mushy state, annealed isothermally for various times, and quenched to room temperature. Without a magnetic field or with a 1-T field, the quenched alloy had a microstructure that was composed of MnSb particles that were dispersed in MnSb/Sb eutectics. At higher magnetic fields, a multiple-phase mixed microstructure that consisted of fine MnSb particles, bulk Sb, and MnSb dendrites and eutectic was observed at relatively short annealing times. The amounts of fine MnSb particles and bulk Sb decreased with an increase in annealing time but increased with an increase in magnetic-flux density. The appearance of the multiple-phase mixed microstructure can be attributed to solute interception in the mushy zone, which can change the solute distribution among the dendrite arms and which is caused by a high magnetic field that is based on the Lorentz force. The application of a high magnetic field to the mushy state of the alloys is proposed as an effective route for the in-situ control of solute diffusion in the mushy zone.
FORC+ analysis of perpendicular magnetic tunnel junctions
Authors: Abugri Joseph B. , Visscher P. B. , Gupta Subhadra , Chen P. J. , Shull R. D.
Published: July 2018

We have studied magnetic tunnel junction (MTJ) thin-film stacks using the First Order Reversal Curve (FORC) method. The FORC distribution of these MTJs has very sharp features, unlike most particulate systems or patterned films. These features are hard to study using conventional FORC analysis programs that require smoothing because this washes out the features. We have used a new analysis program (FORC+) that is designed to distinguish fine-scale features from noise without the use of smoothing, to identify these features and gain information about the switching mechanism of the stack.
Phase transition in thermodynamically consistent biochemical oscillators
Authors: Nguyen Basile , Seifert Udo , Barato Andre C.
Published: July 2018

Biochemical oscillations are ubiquitous in living organisms. In an autonomous system, not influenced by an external signal, they can only occur out of equilibrium. We show that they emerge through a generic nonequilibrium phase transition, with a characteristic qualitative behavior at criticality. The control parameter is the thermodynamic force which must be above a certain threshold for the onset of biochemical oscillations. This critical behavior is characterized by the thermodynamic flux associated with the thermodynamic force, its diffusion coefficient, and the stationary distribution of the oscillating chemical species. We discuss metrics for the precision of biochemical oscillations by comparing two observables, the Fano factor associated with the thermodynamic flux and the number of coherent oscillations. Since the Fano factor can be small even when there are no biochemical oscillations, we argue that the number of coherent oscillations is more appropriate to quantify the precision of biochemical oscillations. Our results are obtained with three thermodynamically consistent versions of known models: the Brusselator, the activator-inhibitor model, and a model for KaiC oscillations.
Geometry optimisations with a nonlocal density-functional theory method based on a double Hirshfeld partitioning
Authors: Heßelmann Andreas
Published: July 2018

Energy gradients have been derived for the nonlocal density-functional theory (NLDFT) method from Heßelmann [J. Chem. Theory Comput. 9, 273 (2013)]. It is shown that the derivative of the NLDFT functional can easily be obtained analytically due to the fact that the inherent Hirshfeld weights are described in terms of analytic expressions of the atomic densities determined by Slater’s rules. The accuracy of the NLDFT gradient has been tested by performing geometry optimisations for a range of 76 tripeptide molecules and a number of small noncovalently bonded dimer systems for which high level coupled cluster reference structures are accessible. It was found that the resulting optimised structures are in good agreement with corresponding structures optimised using second-order Møller-Plesset or coupled cluster wave function electron correlation methods. Moreover, conformer energies as well as intermolecular interaction energies are shown to be in fair agreement with corresponding density-functional theory methods employing pairwise atom-atom dispersion models.
Phase diagram description of the CaCu3Fe4O12 double perovskite
Authors: Buitrago Ivon R. , Ventura C. I. , Allub R.
Published: July 2018

CaCu3Fe4O12 exhibits a temperature-induced transition from a ferrimagnetic-insulating phase, in which Fe appears charge disproportionated, as Fe3+ and Fe5+, to a paramagnetic-metallic phase at temperatures above 210 K, with Fe4+ present. To describe it, we propose a microscopic effective model with two interpenetrating sublattices of Fe(4−δ)++ and Fe(4+δ)++, respectively, δ being a measure of the Fe-charge disproportionation. We include all 3d-Fe orbitals: t2g localized orbitals, with spin 3/2 and magnetically coupled, plus two degenerate itinerant eg orbitals with local and nearest-neighbor (NN) electron correlations, and hopping between NN eg orbitals of the same symmetry. Allub and Alascio [J. Phys.: Condens. Matter 24(49), 495601 (2012)] previously proposed a model to describe the phase transition in LaCu3Fe4O12 from a paramagnetic-metal to an antiferromagnetic-insulator, induced by temperature or pressure, involving charge transfer between Fe and Cu ions, in contrast to Fe-charge disproportionation. With the model proposed for CaCu3Fe4O12, modified to account for this difference between the two compounds, the density of states of the itinerant Fe orbitals was obtained, using Green's function methods. The phase diagram of CaCu3Fe4O12 was calculated, including phases exhibiting Fe-charge disproportionation, where the two eg orbitals in each site are symmetrically occupied, as well as novel phases exhibiting local orbital selectivity/asymmetric occupation of eg orbitals. Both kinds of phases may exhibit paramagnetism and ferromagnetism. We determined the model parameters which best describe the phase transition observed in CaCu3Fe4O12 and found other phases in different parameter ranges, which might be relevant for other compounds of the ACu3Fe4O12 family, presenting Fe-charge disproportionation and intersite charge transfer Fe-Cu.
Plasma effects of the directional coupler for high-power microwave measurements
Authors: Cao Yibing , Sun Jun , Song Zhimin , Fan Zhiqiang , Zhang Guangshuai , Zhang Yuchuan , Teng Yan
Published: July 2018

The directional coupler is an important online power measurement device based on coupling principles. It is widely used for real-time monitoring of the performance of high-power microwave devices. However, insufficient power handling capacity limits further applications of the coupler in higher-pulsed energy measurements. From a theoretical and numerical analysis, the plasma effects of breakdown on the coupler are investigated. The plasma is found to break the fixed phase relationship between the coupling holes and eventually the directivity of the coupler. As the plasma density increases, the isolation of the coupler decreases rapidly, and thus, a negative power flux in the secondary rectangular waveguide increases gradually. Simultaneously, the positive power flux fluctuates and even terminates ahead of the microwave pulse in the main circular waveguide. The conclusions provide a good interpretation of the experimental phenomena.
Effects of external magnetic field and hydrostatic pressure on magnetic and structural phase transitions in Pr0.6Sr0.4MnO3
Authors: Chanda Amit , Mahendiran R.
Published: July 2018

We investigate the effect of hydrostatic pressure on the temperature dependence of magnetization and also the influence of magnetic field on the linear thermal expansion in polycrystalline Pr0.6Sr0.4MnO3, which is ferromagnetic at room temperature (TC = 305 K) but its magnetization undergoes an abrupt decrease at TS = 89 K within the ferromagnetic state. Normal and inverse magnetocaloric effects around TC and TS, respectively, were reported earlier in this single phase compound [Repaka et al., J. Appl. Phys. 112, 123915 (2012)]. The thermal expansion shows an abrupt decrease at TS in zero magnetic field but transforms into an abrupt increase at the same temperature under 7 T, which we interpret as a consequence of magnetic field-induced structural transition from the low-temperature monoclinic (I2/a symmetry) to high-temperature orthorhombic (Pnma symmetry) phase in corroboration with a published neutron diffraction study in zero magnetic field. While the external magnetic field does not change TS, the application of a hydrostatic pressure of P = 1.16 GPa shifts the magnetic anomaly at TS towards high temperature. The pressure induced shift of the low-temperature magneto-structural anomaly (ΔTS = 27 K) is nine-times higher than that of the ferromagnetic Curie temperature (ΔTC = 3 K). Our results suggest that while the hydrostatic pressure stabilizes the low temperature monoclinic phase at the expense of the orthorhombic phase, the applied magnetic field does not affect the structural transition temperature.
Local normal modes and lattice dynamics
Authors: Nasrollahi Seyed H. , Vvedensky Dimitri D.
Published: July 2018

The calculation of phonon dispersion for crystalline solids with r atoms in a unit cell requires solving a 3r-dimensional eigenvalue problem. We propose a simplified approach to lattice dynamics which yields approximate analytical expressions and accurate numerical solutions to phonon dispersion without explicitly solving this eigenvalue problem. This is accomplished by a coordinate transformation to the normal modes of the isolated primitive unit cell, which is extended over the entire crystal by Fourier transformation, so each phonon branch is labelled by the irreducible representations of the symmetry group of the unit cell from which the atomic displacements can be readily identified from standard group theoretic methods. The resulting dynamical matrix is analyzed perturbatively, with the diagonal elements as the zeroth-order matrix and the off-diagonal elements as the perturbation. The zeroth-order matrix provides approximate analytical expressions for the phonon dispersions, the first-order terms vanish, with the higher-order terms converging to the exact solutions. We describe the application of this method to a one-dimensional diatomic chain, graphene, and hexagonal close-packed zirconium. In all cases, the zeroth-order solution provides reasonable approximations, while the second-order solutions already show the rapid convergence to the exact dispersion curves. This methodology provides insight into the lattice dynamics of crystals, molecular solids, and Jahn–Teller systems, while significantly reducing the computational cost. Similarities between our method and other techniques that use local basis sets for calculating electronic and vibrational properties of materials are discussed. We conclude by exploring extensions that widen the scope of our approach.
Operating characteristics of a clamp klystron oscillator at E-band
Authors: Liu M. , Schamiloglu E. , Fuks M. , Liu C.
Published: July 2018

We describe a klystron-like oscillator operating at a frequency of 77.2 GHz (E-band) using particle-in-cell (PIC) simulations with the code MAGIC. It is shown that the klystron oscillator with one “buncher” cavity and one “catcher cavity” shaped like a “clamp” driven with an applied voltage U=20 kV−100 kV can operate with an electronic efficiency of above 11% with MW output power. To increase the electronic efficiency, we combined two clamp klystrons along the z-axis in a hybrid configuration between a klystron and the slow wave structure of a coupled-cavity TWT. PIC simulations demonstrate that when this hybrid design operates in the TE30 mode, its electronic efficiency can be as high as 28% with an output power as high as 1.35 MW. This article describes in detail this approach to the high power millimeter-wave source design.
The occurrence of staircases in ITG turbulence with kinetic electrons and the zonal flow drive through self-interaction
Authors: Weikl A. , Peeters A. G. , Rath F. , Seiferling F. , Buchholz R. , Grosshauser S. R. , Strintzi D.
Published: July 2018

Large scale structures in the E × B shearing rate, known as staircases, are shown to form in nonlinear gyro-kinetic turbulence simulations with kinetic electrons. However, in many cases, a small scale structure in the shearing rate is observed that appears to prevent the formation of staircases. The small scale structures are interpreted to be linked to the self-interaction of turbulent modes connected with the double periodic boundary conditions on the torus. The self-interaction is a newly discovered mechanism for zonal flow generation and is shown to scale proportional to the normalized Larmor radius. The mechanism is also affected by magnetic shear, being weaker at larger values.
A third and fourth order perturbation theory for dipolar hard spheres
Authors: Theiss Marc , Gross Joachim
Published: July 2018

In this work, we develop and analyze a third order and a fourth order perturbation theory for non-polarizable dipolar hard spheres. The electrostatic potential is split into a short-ranged and a long-ranged part. A perturbation expansion is applied for the short-ranged potential where the contribution of higher order terms is approximated through a [2,1]-Padé approximation for the third order theory and by a [2,2]-Padé approximation for the fourth order theory. Rodgers and Weeks [J. Chem. Phys. 131, 244108 (2010)] developed the Local Molecular Field (LMF) theory for the long-ranged contribution of the electrostatic energy. The LMF theory requires the relative permittivity of the considered fluid. We apply a perturbation theory for the relative permittivity and show that the LMF is then in very good agreement with the results for the long-ranged energy from molecular simulations. The short-ranged contribution to the Helmholtz energy from the third order and from the fourth order perturbation theory is, for densities ρ* ≤ 1 and for dipole moments of μ*2 ≤ 1, in very good agreement with the data from molecular simulations. For larger dipole densities (up to μ*2 ≤ 4 for ρ* ≲ 1), we observe significantly improved results for the fourth order perturbation theory compared to the third order perturbation theory.
A study of the stability properties of Sagdeev solutions in the ion-acoustic regime using kinetic simulations
Authors: Hosseini Jenab S. M. , Spanier F. , Brodin G.
Published: July 2018

The Sagdeev pseudo-potential approach has been employed extensively in theoretical studies to determine large-amplitude (fully) nonlinear solutions in a variety of multi-species plasmas. Although these solutions are repeatedly considered as solitary waves (and even solitons), their temporal stability has never been proven. In this paper, a numerical study of the Vlasov-Poisson system is made to follow their temporal evolution in the presence of numerical noise and thereby test their long-time propagation stability. Considering the ion-acoustic regime, both constituents of the plasma, i.e., electrons and ions are treated following their distribution functions in these sets of fully-kinetic simulations. The findings reveal that the stability of the Sagdeev solution depends on a combination of two parameters, i.e., velocity and trapping parameter. It is shown that there exists a critical value of trapping parameter for both fast and slow solutions which separates stable from unstable solutions. In the case of stable solutions, it is shown that these nonlinear structures can propagate for long periods, which confirms their status as solitary waves. Stable solutions are reported for both Maxwellian and Kappa distribution functions. For unstable solutions, it is demonstrated that the instability causes the Sagdeev solution to decay by emitting ion-acoustic wave-packets on its propagation trail. The instability is shown to take place in a large range of velocities and even for Sagdeev solutions with a velocity much higher than the ion-sound speed. Besides, in order to validate our simulation code, two precautionary measures are taken. First, the well-known effect of the ion dynamics on a stationary electron hole solution is presented as a benchmarking test of the approach. Second, In order to verify the numerical accuracy of the simulations, the conservation of energy and entropy is presented.
Note: Parallel processing algorithm of temperature and noise error for micro-electro-mechanical system gyroscope based on variational mode decomposition and augmented nonlinear differentiator
Authors: Shen Chong , Yang Jiangtao , Tang Jun , Liu Jun , Cao Huiliang
Published: July 2018

The traditional processing model of the temperature error for a gyroscope is serial, meaning that de-noising and temperature drift compensation are implemented in a two-step procedure. Hence, the result of the latter depends on the performance of the former; in particular, negative de-noising produces a negative compensation result. To reduce this dependence, we propose a parallel processing algorithm of the temperature error based on variational mode decomposition (VMD) and an augmented nonlinear differentiator (AND). An application to a micro-electro-mechanical system gyroscope is described to demonstrate the effectiveness and applicability of the proposed algorithm. Its major advantages are (i) a combination of VMD, extreme learning machines, and AND is proposed, and an adaptive accelerometer factor determination method for AND is given based on the VMD, both of which improve the effectiveness of the de-noising process; (ii) temperature drift and noise in the temperature error can be extracted and processed synchronously, thereby reducing the dependency of drift compensation on the de-noising result and making the temperature error process more efficient.
Toward interactive scanning tunneling microscopy simulations of large-scale molecular systems in real time
Authors: Dubois Marc-André , Bouju Xavier , Rochefort Alain
Published: July 2018

We have developed a simulation tool in which structural or chemical modifications of an adsorbed molecular layer can be interactively performed, and where structural relaxation and nearly real-time evaluation of a scanning tunneling microscopy (STM) image are considered. This approach is built from an optimized integration of the atomic superposition and electron delocalization molecular orbital theory (ASED-MO) to which a van der Waals correction term is added in conjunction with a non-linear optimization algorithm based on the Broyden-Fletcher-Goldfarb-Shanno method. This integrated approach provides reliable optimized geometries for adsorbed species on metallic surfaces in a reasonable time. Although we performed a major revision of the ASED-MO parameters, the proposed computational approach can accurately reproduce the geometries of a various amount of covalent molecules and weakly bonded complexes contained in two well-defined datasets. More importantly, the relaxation of adsorbed species on a metal surface leads to molecular geometries in good agreement with experimental and Density Functional Theory results. From this, the electronic structure obtained from ASED-MO is used to compute the STM image of the system nearly in real-time using the Tersoff-Hamann formalism. We developed a parallelization strategy that uses Graphics Processing Units to reduce the computing time of STM simulation by a factor of 30. Such improvements allow one to simulate STM images of large supramolecular arrangements and to investigate the influence of realistic local chemical or structural defects on metal surfaces.
Long range ordering of 71° domain walls in epitaxial BiFeO3 thin films
Authors: Yun Yeseul , Ramakrishnegowda Niranjan , Park Dae-Sung , Bhatnagar Akash
Published: July 2018

Substrate-related aspects are often utilized to tune domain architectures in ferroelectric thin films. In this work, however, we report on the role of background pressure during film growth in stabilizing certain domain states. The growth of BiFeO3 films in high-background pressure conditions results in c-oriented films in conjunction with a long-range ordering of 71° domain walls. The importance of high-pressure is highlighted by replacing half of the oxygen background gas with argon. The proposed mechanism takes into account the enhanced surface diffusivity and screening of depolarization fields during high-pressure growth.
The symmetrical quasi-classical approach to electronically nonadiabatic dynamics applied to ultrafast exciton migration processes in semiconducting polymers
Authors: Liang Ruibin , Cotton Stephen J. , Binder Robert , Hegger Rainer , Burghardt Irene , Miller William H.
Published: July 2018

In the last several years, a symmetrical quasi-classical (SQC) windowing model applied to the classical Meyer-Miller (MM) vibronic Hamiltonian has been shown to be a simple, efficient, general, and quite-accurate method for treating electronically nonadiabatic processes at the totally classical level. Here, the SQC/MM methodology is applied to ultrafast exciton dynamics in a Frenkel/site-exciton model of oligothiophene (OT) as a model of organic semiconductor polymers. In order to keep the electronic representation as compact and efficient as possible, the adiabatic version of the MM Hamiltonian was employed, with dynamical calculations carried out in the recently developed “kinematic momentum” representation, from which site/monomer-specific (diabatic) excitation probabilities were extracted using a new procedure developed in this work. The SQC/MM simulation results are seen to describe coherent exciton transport driven by planarization of a central torsion defect in the OT oligomer as well as to capture exciton self-trapping effects in good agreement with benchmark quantum calculations using the multi-layer multiconfiguration time-dependent Hartree approach. The SQC/MM calculations are also seen to significantly outperform the standard Ehrenfest approach, which shows serious discrepancies. These results are encouraging, not only because they illustrate a significant further application of the SQC/MM approach and its utility, but because they strongly suggest that classical mechanical simulations (with the potential for linear scaling efficiency) can be used to capture, quantitatively, important dynamical features of electronic excitation energy transfer in semiconducting polymers.
All-carbon diamond/graphite metasurface: Experiment and modeling
Authors: Komlenok M. S. , Tikhodeev S. G. , Weiss T. , Lebedev S. P. , Komandin G. A. , Konov V. I.
Published: July 2018

We model theoretically the electromagnetic response of a diamond/graphite metasurface, acting as a THz beam polarizer. The response appears to be quite sensitive to the thickness and burial depth of laser-induced graphitized structure, and its simulation is validated by our experiments. Our simulations create a theoretical basis for designing optical elements based on all-carbon metamaterials, fabricated by laser direct-write technique.
Perspective: Current advances in solid-state NMR spectroscopy
Authors: Ashbrook Sharon E. , Hodgkinson Paul
Published: July 2018

In contrast to the rapid and revolutionary impact of solution-state Nuclear Magnetic Resonance (NMR) on modern chemistry, the field of solid-state NMR has matured more slowly. This reflects the major technical challenges of much reduced spectral resolution and sensitivity in solid-state as compared to solution-state spectra, as well as the relative complexity of the solid state. In this perspective, we outline the technique developments that have pushed resolution to intrinsic limits and the approaches, including ongoing major developments in the field of Dynamic Nuclear Polarisation, that have enhanced spectral sensitivity. The information on local structure and dynamics that can be obtained using these gains in sensitivity and resolution is illustrated with a diverse range of examples from large biomolecules to energy materials and pharmaceuticals and from both ordered and highly disordered materials. We discuss how parallel developments in quantum chemical calculation, particularly density functional theory, have enabled experimental data to be translated directly into information on local structure and dynamics, giving rise to the developing field of “NMR crystallography.”
The influence of hydrophilicity on the orientational dynamics and structures of imidazolium-based ionic liquid/water binary mixtures
Authors: Bailey Heather E. , Wang Yong-Lei , Fayer Michael D.
Published: July 2018

The orientational dynamics and microscopic structures of imidazolium-based ionic liquids of varying hydrophilicity were investigated using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy and atomistic simulations. Hydrophilicity was tuned via anion selection, cation alkyl chain length, and the addition of a strong hydrogen bond donor on the cation (protic ionic liquid). In the hydrophobic samples, which saturate at relatively low water concentration, OHD-OKE data display Debye Stokes Einstein (DSE) behavior as a function of water concentration. The DSE behavior indicates that the microstructures of the hydrophobic ionic liquid/water mixtures do not fundamentally change as a function of water concentration. The hydrophilic samples have two regimes of different DSE behaviors demonstrating the presence of two structural regimes depending on water concentration. These experimental results indicate that in hydrophilic ionic liquid/water samples, significant structural changes occur to accommodate high water concentrations, while hydrophobic samples become water saturated because the restructuring of local ionic structures is unfavorable. Atomistic simulations show that the local ionic microstructures experience distinct changes in these hydrophilic ionic liquid/water binary samples because of the delicate interplay of intermolecular interactions among imidazolium cations, hydrophilic anions, and water molecules.