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• It is demonstrated that deep networks can generate multiple local optima during training process which can be combined to form a stronger model. • An efficient and easy-to-implement ensemble learning approach designed for deep networks is introduced. • The approach improves the performance of neural networks without additional training cost. • The approach can be directly applied to all kinds of neural networks without tuning the network architecture. • Comparison experiments with a range of ensemble strategies have shown that the simplest ensemble strategy performs best. The present work is motivated by the desire to find an efficient approach that can improve the performance of deep neural networks in a general sense. To this end, an easy-to-implement ensemble approach is proposed in this paper leveraging the 'local sub-optima' of deep networks, which is referred as to history-state ensemble (HSE) method. We demonstrated that neural networks can naturally generate multiple 'local sub-optima' with diversity during training process, and their combination can effectively improve the accuracy and stability of the single network. The merits of HSE are twofold: (1) It does not require additional training cost in order to acquire multiple base models, which is one of the main drawbacks limiting the generalization of ensemble techniques in deep learning. (2) It can be easily applied to any types of deep networks without tuning of network architectures. We proposed the simplest way to perform HSE and investigated more than 20 ensemble strategies for HSE as comparison. Experiments are conducted on six datasets and eight popular network architectures for the case of rotating machinery fault diagnosis. It is demonstrated that the stability and accuracy of neural networks can be generally improved through the simplest ensemble strategy proposed in this paper. [ABSTRACT FROM AUTHOR]

An original approach to α-olefin oligomerization as well as novel thermally stable zirconocene catalysts for use in such reactions has been elaborated. The method reported allows the achievement of fractions of lightweight α-olefin oligomers up to 90% yields without considerable formation of byproducts like internal alkenes, alkanes, and higher oligomers. Trimers, tetramers, and pentamers of 1-hexene, 1-octene, and 1-decene were isolated as individual compounds and were hydrogenated. Viscosity characteristics of the isolated saturated and unsaturated hydrocarbons have been studied at various temperatures. The isolated saturated oligomers of 1-octene and 1-decene outperform the traditional electrophilic oligomerization products in terms of viscosity indexes, pour points, and low-temperature viscosity. [ABSTRACT FROM AUTHOR]

In the present paper two types of load carrying shear welded joints are considered and analyzed numerically and experimentally. Fatigue tests have been carried out on two specific design solutions proposed and aimed to improve the fatigue strength of the joints. By employing three-dimensional models, the Strain Energy Density (SED) over a control volume surrounding the most critical point has been determined. All the experimental results have been summarized in terms of SED showing that all the data fall within the scatter band previously proposed in the literature for welded structural steel. [ABSTRACT FROM AUTHOR]

New mono- and bis-cyclopentadienyl neodymium ate -complexes, bearing phenyl-substituents in the cyclopentadienyl ring, have been synthesized: KNdCp′Cl 3 (thf) x (Cp′ = 1,3-Ph 2 C 5 H 3 ( 1 ), 1,2,4-Ph 3 C 5 H 2 ( 2 )) and KNdCp′ 2 Cl 2 (thf) x (Cp′ = 1,3-Ph 2 C 5 H 3 ( 3 ), 1,2,4-Ph 3 C 5 H 2 ( 4 ), 1,2-Me 2 -4-PhC 5 H 2 ( 5 ), 1,2-Ph 2 -4-(4-MeO-C 6 H 4 )C 5 H 2 ( 6 )). Their catalytic activity has been studied in ethylene oligomerization process in the presence of Bu 2 Mg as a chain transfer reagent with the Nd:Mg molar ratios being of 1:20, 1:40 or 1:80. Complex 4 exhibits catalytic activity close to the activity of the known complex [(C 5 Me 5 ) 2 NdCl 2 Li(OEt 2 ) 2 ] ( 7 ). The complex 6 has demonstrated the best catalytic activity among all studied complexes. Using selected complexes 2 , 4 and 6 as pre-catalysts, terminal iodo-functionalized oligoethylenes have been prepared. Obtained iodooligoethylenes have been studied by 1 H NMR technique and MALDI mass-spectrometry with preliminary derivatization, demonstrating 70–90% of functionalization. Crystal structures of ate -complexes [{(1,2,4-Ph 3 C 5 H 2 )Nd(thf)} 2 Cl 5 K] 2 (toluene) 4 ( 2a ), [(1,2,4-Ph 3 C 5 H 2 ) 2 NdCl 2 K(thf) 0.53 (1,4-dioxane) 1.47 ] 2 (dioxane) ( 4a ) and {[{1,2-Ph 2 -4-(4-MeO-C 6 H 4 )C 5 H 2 } 2 NdCl 2 K] 2 (1,4-dioxane)}(toluene) 4 have been studied by the single crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

The dimerization of 1-hexene was catalyzed by ten zirconocenes. High catalytic productivity was achieved via a two-step activation process, namely, the treatment of the zirconocene with triisobutylaluminum (TIBA) followed by methylaluminoxane (MAO). The zirconocene [(C 5 H 4 SiMe 2 ) 2 O]ZrCl 2 (10) exhibits a higher productivity and selectivity to dimer formation than the unsubstituted (C 5 H 5 ) 2 ZrCl 2 (1) complex. For the ansa -[Z(C 5 H 4 ) 2 ]ZrCl 2 complexes, the catalytic activity increases as the angle between the cyclopentadienyl rings decreases. The dimerization selectivity of 10 reaches 94% when the reaction is performed using Et 2 AlCl as the chlorine source needed to form the catalytic species. The possible mechanism of selective α-olefin dimerization is discussed. [ABSTRACT FROM AUTHOR]

It was experimentally found that, on the penetration of a flame through obstacles, gas dynamic factors such as flame turbulization can determine the kinetics of combustion, for instance, a transition of low-temperature hydrocarbon combustion to the high-temperature mode. [ABSTRACT FROM AUTHOR]

Zirconocene obtained from 6,6-dimethylfulvene ‘dimer’, being activated subsequently with triisobutylaluminium and methylalumoxane, catalyzes transformation of α-olefins into a mixture of vinylidene oligomers with minimal losses to isomerization, which allows one to consider this catalyst perspective for the synthesis of branched hydrocarbons with uniform structure. [ABSTRACT FROM AUTHOR]

Cellular combustion regime of a 40% H 2 –air mixture in the presence of Pt wire at 270–350 °C was observed for the first time. The regime is caused by the catalytic action of Pt-containing particles formed by the decomposition of volatile platinum oxide in a gas phase. [ABSTRACT FROM AUTHOR]

Presents a study that developed a reflectivity discrepancy method used in distinguishing whether the losses in a material are due to either its dielectric or magnetic properties. Comparison of the standard procedure and the proposed method; Computer simulation of the measurement; Determination of the optimal experimental parameters; Comparison of the data obtained using the conventional open circuit-short circuit technique and the proposed method.

Features of combustion in flame cells caused by hydrodynamic instability were experimentally established. It was found that each flame cell represents a separate chemical reactor; the process of complete chemical transformation occurs in the cell. [ABSTRACT FROM AUTHOR]

Early fault detection (EFD) is a crucial component of proactive maintenance that can prevent expensive downtime, enhance safety, and optimize equipment performance and longevity. Existing limitations of the contemporary EFD approaches frequently include: (1) manually designed features relying on expert skills and knowledge, (2) the vaguely determined pre-set thresholds to distinguish between the faulty and healthy state of the testing object (however, the threshold value can vary notably from task to task), and (3) most methods, which have been originally designed for vibration data, cannot be generalised to other techniques, for example acoustic emission (AE) signals. To address these issues, a novel binary-classification generative adversarial network (BC-GAN) is designed for general EFD problems and applied to several specific datasets acquired from different run-to-failure tests of rotating components. Compared with conventional methods, unsupervised BC-GAN directly outputs the probability that an input belongs to either the "health" or "fault" state of the rotating machine without a priory threshold setting. Experimental results demonstrate the high versatility of the proposed network, which can be applied in various laboratory and industrial settings to both vibration and AE signals. [ABSTRACT FROM AUTHOR]

[Display omitted] Combination of the precision rheology and DSC helps to make an objective assessment of the effectiveness of modified copolymers of maleic anhydride with methylidenealkanes and best known commercial pour point depressants as cold flow improvers for corn oil based biodiesel. [ABSTRACT FROM AUTHOR]

[Display omitted] DFT simulations of ethylene polymerization with the participation of neutral Zr–Al3 hydride species revealed a fundamental difference in catalytic behaviour of triisobutylaluminium-activated heterocenes and conventional ansa- zirconocenes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Synthesis, X-ray study and catalytic behaviour in 1-octene polymerization of thiophene- or indole-fused Zr ansa -complexes. • Heterocenes demonstrate a full spectra of end-group formation mechanisms and hydrogen response depending the η5-ligand nature. • Preparation of hydrogenated oligo-α-olefins as promicing synthetic oil base stocks controlled by temperature and H 2 pressure. Abstract A series of SiMe 2 -bridged ansa -zirconocenes LZrCl 2 derived from heterocyclic ligands such as cyclopenta[1,2- b :4,3- b ']dithiophene, 5,6-dihydroindeno[2,1- b ]indole and 5,10-dihydroindeno[1,2- b ]indole, called "heterocenes", were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis. These complexes were activated by triisobutylaluminium (TIBA) at Al TIBA /Zr ratio ∼75 and then by MMАO-12 at Al MAO /Zr ratio ∼10, and were studied in the polymerization of 1-octene in the absence or presence of molecular hydrogen. In the absence of molecular hydrogen, derivatives of cyclopenta[1,2- b :4,3- b ']dithiophene and dihydroindeno[2,1- b ]indole demonstrated high catalytic activity, while dihydroindeno[1,2- b ]indole complexes catalyzed slow polymerization with the formation of ultrahigh molecular weight poly(1-octene)s. In the presence of molecular hydrogen, derivatives of dihydroindeno[1,2- b ]indole showed an order of magnitude increase in the catalytic activity. β-Hydride elimination, β-hexyl elimination and Zr-Al transfer were detected as the main chain release mechanisms depending on the nature of the ligand used. A novel chain termination with selective formation of –C(Me)=CHCH 2 – unsaturations was detected. It was found that heterocenes maintained a high catalytic activity up to 120 °C. Due to their high thermal stability and good hydrogen response, heterocenes are promising catalysts for the oligomerization and hydrooligomerization of α-olefins in the production of high-quality motor oil base stocks. [ABSTRACT FROM AUTHOR]

The title compounds, C9H12O6 and C10H14O6, were formed by careful hydrolysis of the corresponding diethyl esters. Their single crystals were grown from an ethyl acetate/hexane mixture. Crystals of both compounds have monoclinic (P21) symmetry with a single molecule in the asymmetric unit. Both crystal structures are very similar and display four -CO--OH...==O C(OH)-hydrogen bonds, forming a two-dimensional double-layered framework. [ABSTRACT FROM AUTHOR]

In-situ electrochemical nanoindentation (ECNI) experiment is performed to probe the nanomechanical properties of Inconel 625 alloy under a hydrogen environment. The hydrogen effect on various stages of the load-displacement (LD) plot is quantified. The pop-in load, which indicates the onset of a homogenous dislocation nucleation event, is reduced with hydrogen charging, which augers well with the 'Defactant' concept. The hydrogen solute hinders dislocation glide during pop-in (reduced pop-in width), and the resultant glide resistance force is found to be linearly dependent on dissolved hydrogen concentration. We have also quantified the hydrogen-reduced activation barrier for the secondary source by examining the secondary elastic hardening stage from LD data. Hydrogen charging-induced slip line formation and nanohardness variation at different polarizations are explained using a simple diffusion-desorption model. Furthermore, the electron channeling contrast imaging technique is used to study the dislocation patterns around the indents in air and in the hydrogen environment to shed light on the difference in plastic behavior. [ABSTRACT FROM AUTHOR]

Sandwich SiMe 2 -bridged ansa -complexes of zirconium, containing heterocycle-fused η5-cyclopentadienyls, derivatives of 2,5-dimethyl-7 H -cyclopenta[1,2- b :4,3- b ']dithiophene (2), 5,10-dihydroindeno[1,2- b ]indole (3) and 5,6-dihydroindeno[2,1- b ]indole (4) – 'heterocenes' – catalyzed ethylene homopolymerization and ethylene/oct-1-ene (E/O) copolymerization in the presence of triisobutylaluminum (TIBA) without MAO and perfluoroaryl borate activators, the benchmark bis(η5-fluorenyl) complex 1 was virtually inactive under these conditions. In the absence of MAO, E/O copolymerization resulted in a formation of copolymers not containing EOOE fragments even at E/O ratio of 2.4. Addition of 10 eq. of MMAO-12 resulted in increase of both catalytic activities of 2 – 4 and oct-1-ene incorporation. E/O copolymers POE-05 (obtained on TIBA activated precatalyst 2) and POE-17 (obtained on TIBA/MMAO-12 activated precatalyst 4) were not inferior to the best commercial E/O copolymers in physico-mechanical characteristics at −45 °C. Extrusion blends of POE-05 and POE-17 with high density polyethylene (HDPE) demonstrated high impact strength and frost resistance. [Display omitted] • TIBA-activated heterocenes catalyze ethylene/oct-1-ene (E/O) copolymerization. • Copolymers without EOOE fragments are formed up to E/O ratio of 2.4 • Random E/O copolymers have promising low-temperature mechanical characteristics. • Blends of E/O copolymers with HDPE have improved frost resistance. [ABSTRACT FROM AUTHOR]

Graphical abstract ansa -Complex O[SiMe 2 (η5-C 5 H 4)] 2 ZrCl 2 upon reduction with LiAlH 4 in contrast to zirconocene dichloride forms a dia-magnetic ZrIII complex with the dimeric molecular structure proved by X-ray analysis. This complex after activation by MeAlO initiates oligomerization of α-olefins. [ABSTRACT FROM AUTHOR]

• Synthesis and study of –CH 2 CH 2 – bridged indeno[2,1- b ]indole Zr (IV) ansa -complexes. • Study of dec-1-ene oligomerization using MMAO-12 and [PhNMe 2 H][B(C 6 F 5) 4 ] activators. • Formation and X-ray diffraction analysis of [ L6 -Zr(μ-Cl) 2 AliBu 2 ][B(C 6 F 5) 4 ]. • Oligomerization of dec-1-ene without double bond shift and skeletal rearrangements. • Hydrogenated lightweight oligomers of dec-1-ene are high-quality PAO base stocks. Hydrogenated oligomers of higher α-olefins (primarily, dec-1-ene) represent base stocks for high-quality polyolefin oils (PAOs), transmission fluids, lubricants and greases. Competitive advantages of zirconocene catalysts in oligomerization of α-olefins have been already demonstrated and industrially implemented for higher oligomers. However, the problem of the selective synthesis of α-olefin oligomers that have degree of polymerization (DP n) 3 and 4, remains unresolved. A series of –CH 2 CH 2 – bridged ansa -zirconocenes derived from 5,10-dihydroindeno[1,2- b ]indole, 'heterocenes' Zr4 – Zr6 , were synthesized and characterized by NMR spectroscopy and X-ray diffraction (XRD) analysis. New complexes Zr4 – Zr6 and known –SiMe 2 – bridged ansa -heterocenes Zr1 – Zr3 were investigated in oligomerization of dec-1-ene using MMAO-12 or [PhNMe 2 H][B(C 6 F 5) 4 ] activators. In the atmosphere of molecular hydrogen, at [dec-1-ene]/[Zr] ratios up to 4·105, rac -forms Zr4r – Zr6r provided more than 85% yields of dec-1-ene oligomers without skeletal rearrangements. In some experiments, at least 50% yields of lightweight oligomers (DP n =3–4) were achieved. After activation of Zr6r by TIBA and [PhNMe 2 H][B(C 6 F 5) 4 ] and completion of dec-1-ene oligomerization, we isolated new cationic complex Zr6r-Al containing Zr-(μ-Cl) 2 -Al fragment, as confirmed by XRD. Zr6r-Al alone was inactive against dec-1-ene, but after addition of TIBA oligomerization started. Due to uniform molecular structure of oligomers, complete catalytic hydrogenation of oligo(dec-1-ene)s was conducted using Ni/Al 2 O 3 catalyst under mild conditions (150°C, 3 h, 20 bar). Hydrogenated dec-1-ene oligomers turned out to be high-quality PAO base stocks far exceeding industrial dec-1-ene PAOs in terms of viscosity characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis and molecular structure of heterocycle-fused Ti (IV) CGCs. • Study of heterocycle-fused Ti (IV) CGCs in ethylene (co)polymerization. • Precision rheology studies of polyethylenes prepared on heterocycle-fused Ti (IV) CGCs. • Indeno[1,2- b ]indole based Ti complex Ti2 catalyzes LCB formation even at 80 °C. Long-chain branching is an efficient tool to design and produce polyolefins with enhanced mechanical characteristics, physical properties, and processability. In the synthesis of long-chain branched polyethylene (LCB PE), constrained geometry complexes (CGCs) of Ti (IV) [(η5-C 5 Me 4)SiMe 2 N t Bu]TiX 2 (X = Cl, Ti1 ; X = alkyl) are highly effective at elevated temperatures. However, further development of polyolefin technologies requires new catalytic approaches to provide LCB formation in broad temperature interval. In the present study, a series of CGCs of Ti (IV) of general formula [Cp#SiMe 2 N t Bu]TiCl 2 derived from heterocycle-fused cyclopentadienes Cp# (Ti2 – Ti5) were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis (XRD). New complexes Ti2 – Ti5 along with benchmark precatalysts (n -BuC 5 H 4) 2 ZrCl 2 (Zr1) and Ti1 were supported on MMAO-12/silica and investigated in ethylene homopolymerization and ethylene/hex-1-ene copolymerization. In contrast to benchmark complexes Ti1 and Zr1 , Ti2 – Ti5 catalyzed formation of LCB PEs even at 80 °C, as confirmed by precision rheology studies of ethylene/hex-1-ene copolymers. The complex Ti2 , derivative of 5-methyl-5,10-dihydroindeno[1,2- b ]indole, demonstrated the best set of properties. [ABSTRACT FROM AUTHOR]

• Synthesis and study of –CH 2 CH 2 – bridged indeno[2,1- b ]indole Zr (IV) ansa -complexes. • Study of dec-1-ene oligomerization using MMAO-12 and [PhNMe 2 H][B(C 6 F 5) 4 ] activators. • Formation and X-ray diffraction analysis of [ L6 -Zr(μ-Cl) 2 AliBu 2 ][B(C 6 F 5) 4 ]. • Oligomerization of dec-1-ene without double bond shift and skeletal rearrangements. • Hydrogenated lightweight oligomers of dec-1-ene are high-quality PAO base stocks. Hydrogenated oligomers of higher α-olefins (primarily, dec-1-ene) represent base stocks for high-quality polyolefin oils (PAOs), transmission fluids, lubricants and greases. Competitive advantages of zirconocene catalysts in oligomerization of α-olefins have been already demonstrated and industrially implemented for higher oligomers. However, the problem of the selective synthesis of α-olefin oligomers that have degree of polymerization (DP n) 3 and 4, remains unresolved. A series of –CH 2 CH 2 – bridged ansa -zirconocenes derived from 5,10-dihydroindeno[1,2- b ]indole, 'heterocenes' Zr4 – Zr6 , were synthesized and characterized by NMR spectroscopy and X-ray diffraction (XRD) analysis. New complexes Zr4 – Zr6 and known –SiMe 2 – bridged ansa -heterocenes Zr1 – Zr3 were investigated in oligomerization of dec-1-ene using MMAO-12 or [PhNMe 2 H][B(C 6 F 5) 4 ] activators. In the atmosphere of molecular hydrogen, at [dec-1-ene]/[Zr] ratios up to 4·105, rac -forms Zr4r – Zr6r provided more than 85% yields of dec-1-ene oligomers without skeletal rearrangements. In some experiments, at least 50% yields of lightweight oligomers (DP n =3–4) were achieved. After activation of Zr6r by TIBA and [PhNMe 2 H][B(C 6 F 5) 4 ] and completion of dec-1-ene oligomerization, we isolated new cationic complex Zr6r-Al containing Zr-(μ-Cl) 2 -Al fragment, as confirmed by XRD. Zr6r-Al alone was inactive against dec-1-ene, but after addition of TIBA oligomerization started. Due to uniform molecular structure of oligomers, complete catalytic hydrogenation of oligo(dec-1-ene)s was conducted using Ni/Al 2 O 3 catalyst under mild conditions (150°C, 3 h, 20 bar). Hydrogenated dec-1-ene oligomers turned out to be high-quality PAO base stocks far exceeding industrial dec-1-ene PAOs in terms of viscosity characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

Being activated by methylalumoxane ([Al]/[Zr] = 10), (η5-C 5 H 5) 2 ZrCl 2 (Zr1) and [(η5-C 5 H 4 SiMe 2) 2 O]ZrCl 2 (Zr2) catalyze selective dimerization of α-olefins with low productivity (turnover number TON ∼2000). Our previous research of heterocycle-fused ansa -zirconocenes revealed that SiMe 2 -bridged complexes catalyze polymerization of α-olefins, whereas CH 2 CH 2 -bridged complexes are high-performance oligomerization catalysts (TON ∼ 4∙105). We proposed that further elongation of the bridge will allow obtaining dimerization catalysts. New –SiMe 2 OSiMe 2 – bridged ansa -zirconocenes Zr3 – Zr11 were synthesized and studied in oct-1-ene dimerization at 100 °C and [oct-1-ene]/[Zr] ratio of 3∙104. In the absence of H 2 bis(5,6-dihydroindeno[2,1- b ]indole) derivatives Zr8 and Zr9 demonstrated high activity and dimerization selectivity up to 94%. In the presence of H 2 symmetrical indenoindole complexes Zr5 – Zr9 appeared to be even more active, but up to 24% of hydrogenated oct-1-ene dimer HC16 was formed. Mixed-ligand complexes Zr10 and Zr11 catalyzed oct-1-ene dimerization with up to 99% selectivity without the formation of HC16 even in trace amounts. [Display omitted] • Synthesis and structure of new –SiMe 2 OSiMe 2 – bridged Zr(IV) ansa -complexes. • Derivatives of fluorene, cyclopentadithiophene and isomeric indenoindoles. • Study of oct-1-ene dimerization using MMAO-12 and [PhNMe 2 H][B(C 6 F 5) 4 ] activators. • 5,6-Dihydroindeno[2,1- b ]indole-based heterocenes are efficient in the absence of H 2 • In H 2 mixed-ligand fluorenyl complexes catalyze dimerization without hydrogenolysis. [ABSTRACT FROM AUTHOR]

Ultra-high molecular weight poly-α-olefins are widely used as drag reducing agents (DRAs) for pipeline transportation of oil and refined petroleum products. The synthesis of polyolefin DRAs is based on low-temperature Ziegler–Natta (ZN) polymerization of higher α-olefins. 1-Hexene based DRAs, the most effective at room temperature, typically lose DR activity at low temperatures. The use of 1-hexene copolymers with C8–C12 linear α-olefins appears to offer a solution to the problem of low-temperature drag reducing. The present work aims to develop two-stage synthesis of polyolefin DRAs that is based on selective oligomerization of ethylene in the presence of efficient chromium/aminodiphosphine catalysts (Cr-PNP), followed by polymerization of the olefin mixtures, formed at oligomerization stage, using efficient titanium–magnesium ZN catalyst. We have shown that oligomerization of ethylene in α-olefin reaction media proceeds faster than in saturated hydrocarbons, providing the formation of 1-hexene, 1-octene, and branched C10 and C12 olefins; the composition and the ratio of the reaction products depended on the nature of PNP ligand. Oligomerizates were used in ZN polymerization 'as is', without additional treatment. Due to branched character of C10+ hydrocarbons, formed during oligomerization of ethylene, resulting polyolefins demonstrate higher low-temperature DR efficiency at low polymer concentrations (~1 ppm) in comparison with benchmark polymers prepared from the mixtures of linear α-olefins and from pure 1-hexene. We assume that faster solubility and more efficient solvation of the polyolefins, prepared using 'tandem' ethylene-based process, represent an advantage of these type polymers over conventional poly(1-hexene) and linear α-olefin-based polymers when used as 'winter' DRAs. [ABSTRACT FROM AUTHOR]

The genesis of lasing, as an evolution of the laser hybrid eigenstates comprised of electromagnetic modes and atomic polarization, is considered. It is shown that the start of coherent generation at the laser threshold is preceded by the formation of a special hybrid state at the lasing prethreshold. This special state is characterized by an enhanced coupling among excited atoms and electromagnetic modes. This leads to an increase in the rate of stimulated emission in the special state and, ultimately, to lasing. At the lasing prethreshold, the transformation of hybrid eigenstates has the features of an exceptional point (EP) observed in non‐Hermitian systems. The special state is formed when eigenfrequencies of two hybrid states coalesce or come close to each other. Below the prethreshold, lifetimes of all hybrid states grow with increasing pump rate. When the pump rate crosses the prethreshold, resonance trapping occurs with the lifetime of the special state continuing to increase while the lifetimes of all other eigenstates begin to decrease. Consequently, the latter eigenstates do not participate in the lasing. Thus, above the prethreshold, a laser transitions into the single‐mode regime. [ABSTRACT FROM AUTHOR]

• Heterocenes are defined as heterocycle-fused cyclopentadienyl metal complexes. • Synthetic strategies for η1-η5 and η5-η5 ansa -ligand precursors are discussed. • The fused heterocycles affect a heterocene's molecular structure and reactivity. • Heterocenes are efficient catalysts for the polymerization of α-olefins. Metallocenes of the group 4 metals have attracted great attention as precursors of single-site catalysts for the production of advanced polyolefins. The annelation of a cyclopentadienyl ring with a heterocyclic fragment fundamentally changes the electronic and structural characteristics of η 5-coordinated ligands and provides new dimensions for the design of novel and effective catalysts. Heterocycle-fused half-sandwich and sandwich metal complexes, called heterocenes, have been extensively studied since the early 2000s. This review describes the different synthetic strategies employed in the preparation of heterocycle-fused η1-η5 and η5-η5 ansa -ligand precursors, and further, discusses the synthesis, molecular structure, and catalytic applications of heterocenes. [ABSTRACT FROM AUTHOR]

Usually, the cavity is considered an intrinsic part of laser design to enable coherent emission. For different types of cavities, it is assumed that the light coherence is achieved by different ways. We show that regardless of the type of cavity, the lasing condition is universal and is determined by the ratio of the width of the atomic spectrum to the product of the number of atoms and the spontaneous radiation rate in the laser structure. We demonstrate that cavity does not play a crucial role in lasing since it merely decreases the threshold by increasing the photon emission rate thanks to the Purcell effect. A threshold reduction can be achieved in a cavity-free structure by tuning the local density of states of the electromagnetic field. This paves the way for the design of laser devices based on cavity-free systems. [ABSTRACT FROM AUTHOR]

Zirconocene-catalyzed coordination oligomerization of higher α-olefins is of theoretical and practical interest. In this paper, we present the results of experimental and theoretical study of α-olefin oligomerization, catalyzed by (η5-C5H5)]2ZrX21/1′ and O[SiMe2(η5-C5H4)]2ZrX22/2′ (X = Cl, Me) with the activation by modified methylalymoxane MMAO-12 or by perfluoroalkyl borate [PhNMe2H][B(C6F5)4] (NBF) in the presence and in the absence of organoaluminium compounds, Al(CH2CHMe2)3 (TIBA) and/or Et2AlCl. Under the conditions providing a conventional mononuclear reaction mechanism, 1′ catalyzed dimerization with low selectivity, while 2′ initiated the formation of oligomers in equal mass ratio. The presence of TIBA and especially Et2AlCl resulted in an increase of the selectivity of dimerization. Quantum chemical simulations of the main and side processes performed at the M-06x/ DGDZVP level of the density functional theory (DFT) allowed to explain experimental results involving traditional mononuclear and novel Zr-Al1 and Zr-Al2 mechanistic concepts. [ABSTRACT FROM AUTHOR]

The free radical copolymerization of electron-acceptor and electron-donor vinyl monomers represents a particular case of sequence-controlled polymerization. The reactions of maleic anhydride (MA) or related compounds (acceptor comonomers) with α-olefins (donor comonomers) result in the formation of the alternating copolymers that have clear prospects for petrochemical and biomedical applications. However, in contrast to the well-established polymerization of acrylate monomers, these processes have not been studied theoretically using the density functional theory (DFT) calculations. In our research, we performed a comprehensive theoretical analysis of the free radical copolymerization of MA and closely related maleimide with different structural types of olefins at mpw1pw91/6-311g(d) level of the DFT. The results of our calculations clearly indicated the preference of the alternating reaction mode for the copolymerization of MA with α-olefins, isobutylene and prospective unsaturated monomers, as well as methylenealkanes. The DFT modeling of the thermally induced Alder-ene reaction between MA and olefins allowed to exclude this reaction from the scope of possible side processes at moderately high temperatures. Comparative analysis of MA and N-methylmaleimide (MMI) reactivity shown that the use of MMI instead of MA makes no sense in terms of the reaction rate and selectivity. [ABSTRACT FROM AUTHOR]

The crystal structures of three unusual chromium organophosphate complexes have been determined, namely, bis(μ‐butyl 2,6‐di‐tert‐butyl‐4‐methylphenyl hydrogen phosphato‐κO:κO′)di‐μ‐hydroxido‐bis[(butyl 2,6‐di‐tert‐butyl‐4‐methylphenyl hydrogen phosphato‐κO)(butyl 2,6‐di‐tert‐butyl‐4‐methylphenyl phosphato‐κO)chromium](Cr—Cr) heptane disolvate or {Cr2(μ2‐OH)2[μ2‐PO2(OBu)(O‐2,6‐tBu2‐4‐MeC6H2)‐κO:κO′]2[PO2(OBu)(O‐2,6‐tBu2‐4‐MeC6H2)‐κO]2[HOPO(OBu)(O‐2,6‐tBu2‐4‐MeC6H2)‐κO]2}·2C7H16, [Cr2(C19H32O4P)4(C19H33O4P)2(OH)2]·2C7H16, denoted (1)·2(heptane), [μ‐bis(2,6‐diisopropylphenyl) phosphato‐1κO:2κO′]bis[bis(2,6‐diisopropylphenyl) phosphato]‐1κO,2κO‐chlorido‐2κCl‐triethanol‐1κ2O,2κO‐di‐μ‐ethanolato‐1κ2O:2κ2O‐dichromium(Cr—Cr) ethanol monosolvate or {Cr2(μ2‐OEt)2[μ2‐PO2(O‐2,6‐iPr2‐C6H3)2‐κO:κO′][PO2(O‐2,6‐iPr2‐C6H3)2‐κO]2Cl(EtOH)3}·EtOH, [Cr2(C2H5O)2(C24H34O4P)3Cl(C2H6O)3]·C2H6O, denoted (2)·EtOH, and di‐μ‐ethanolato‐1κ2O:2κ2O‐bis{[bis(2,6‐diisopropylphenyl) hydrogen phosphato‐κO][bis(2,6‐diisopropylphenyl) phosphato‐κO]chlorido(ethanol‐κO)chromium}(Cr—Cr) benzene disolvate or {Cr2(μ2‐OEt)2[PO2(O‐2,6‐iPr2‐C6H3)2‐κO]2[HOPO(O‐2,6‐iPr2‐C6H3)2‐κO]2Cl2(EtOH)2}·2C6H6, [Cr2(C2H5O)2(C24H34O4P)2(C24H35O4P)2Cl2(C2H6O)2]·2C6H6, denoted (3)·2C6H6. Complexes (1)–(3) have been synthesized by an exchange reaction between the in‐situ‐generated corresponding lithium or potassium disubstituted phosphates with CrCl3(H2O)6 in ethanol. The subsequent crystallization of (1) from heptane, (2) from ethanol and (3) from an ethanol/benzene mixture allowed us to obtain crystals of (1)·2(heptane), (2)·EtOH and (3)·2C6H6, whose structures have the monoclinic P21, orthorhombic P212121 and triclinic P space groups, respectively. All three complexes have binuclear cores with a single Cr—Cr bond, i.e. Cr2O6P2 in (1), Cr2PO4 in (2) and Cr2O2 in (3), where the Cr atoms are in distorted octahedral environments, formally having 16 ē per Cr atom. The complexes have bridging ligands μ2‐OH in (1) or μ2‐OEt in (2) and (3). The organophosphate ligands demonstrate terminal κO coordination modes in (1)–(3) and bridging μ2‐κO:κO′ coordination modes in (1) and (2). All the complexes exhibit hydrogen bonding: two intramolecular Ophos...H—Ophos interactions in (1) and (3) form two {H[PO2(OR)2]2} associates; two intramolecular Cl...H—OEt hydrogen bonds additionally stabilize the Cr2O2 core in (3); two intramolecular Ophos...H—OEt interactions and two O...H—O intermolecular hydrogen bonds with a noncoordinating ethanol molecule are observed in (2)·EtOH. The presence of both basic ligands (OH− or OEt−) and acidic [H(phosphate)2]− associates at the same metal centres in (1) and (3) is rather unusual. Complexes may serve as precatalysts for ethylene polymerization under mild conditions, providing polyethylene with a small amount of short‐chain branching. The formation of a small amount of α‐olefins has been detected in this reaction. [ABSTRACT FROM AUTHOR]

Zirconocene-mediated selective dimerization of α-olefins usually occurs when precatalyst (η5-C5H5)2ZrCl2 is activated by minimal excess of methylalumoxane (MAO). In this paper, we present the results of density functional theory (DFT) simulation of the initiation, propagation, and termination stages of dimerization and oligomerization of propylene within the framework of Zr-Al binuclear mechanism at M-06x/DGDZVP level of theory. The results of the analysis of the reaction profiles allow to explain experimental facts such as oligomerization of α-olefins at high MAO/(η5-C5H5)2ZrCl2 ratios and increase of the selectivity of dimerization in the presence of R2AlCl. The results of DFT simulations confirm the crucial role of the presence of chloride in the selectivity of dimerization. The molecular hydrogen was found in silico and proven experimentally as an effective agent that increases the rate and selectivity of dimerization. [ABSTRACT FROM AUTHOR]

• Pd-diphosphine catalyzed methoxycarbonylation of methylenealkanes. • Trans -2,3-bis(diphenylphosphinomethyl)norbornane is the best diphosphine screened. • At least 99% regioselectivity in formation of RCH 2 CH 2 C(R)CH 2 COOMe with 62–81% isolated yields. • Fully catalytic method for the preparation of branched carboxylic esters. A series of methylenealkanes RCH 2 CH 2 (R)C = CH 2 (R = n- butyl, n -hexyl, isopropyl and isobutyl), which are products of selective zirconocene-catalyzed dimerization of α-olefins, were introduced into Pd-catalyzed methoxycarbonylation. With the use of 5-methyleneundecane (1-hexene dimer) as a substrate, the roles of protic acid, Lewis acid and molecular hydrogen were established for model Pd(II)/PPh 3 and Pd(II)/diphosphine catalysts. A series of bridged diphosphines were studied as catalyst components L in PdCl 2 /L-catalyzed methoxycarbonylation in the presence of H 2. One of the nine diphosphines studied, trans -2,3-bis(diphenylphosphinomethyl)norbornane, demonstrated the best catalytic results in terms of catalytic activity, selectivity and isolated yields of the products. Under the optimized conditions during 24 h experiments, dimers RCH 2 CH 2 (R)C = CH 2 were transformed to methyl carboxylates RCH 2 CH 2 (R)CHCH 2 COOMe with 99+% regioselectivity; isolated yields were 62–81%. In that way, the catalytic methoxycarbonylation of synthetically available methylenealkanes is an effective approach to branched carboxylic acids, with high prospects for practical application. [ABSTRACT FROM AUTHOR]

An effective method of 1-hexene polymerization in fluorous reaction media has been developed. When using perfluorinated compounds (FCs) as a solvent, the process, catalyzed by highly active titanium-magnesium catalysts modified with 3,3-bis(methoxymethyl)pentane (BMMP) as an electron-donor, proceeds as a precipitation polymerization, and the reaction products represent highly stereo- and regioregular poly(1-hexene)s in the form of microparticles. In freons, polymerization can be carried out at sub-zero temperatures with monomer conversion up to 50% within 1 h and the formation of UHMW poly(1-hexene)s with M n ∼2·10 6  Da. The polymers prepared in FCs demonstrate a high drag reducing effect (up to 40% in n -heptane for 0.25 ppm concentration), exceeding the previously described UHMW poly(1-hexene)s. Polymerization products after mixing with rapeseed oil form stable dispersions of ready-to-use drag reducing agents (DRAs) for pipeline oil transportation. [ABSTRACT FROM AUTHOR]

Luminescent composite materials based on linear polyethylene doped by a well dispersed tetrakis dibenzoylmethanate europium complex have been developed. The anion of the latter serves as an efficient light harvesting antenna and possesses the desired photophysical properties. The targeted modification of the Eu complex, namely introduction of a long hydrocarbon chain into the tetraalkylammonium cation [RNEt3]+, has ensured the compatibility of the complex with the polyethylene matrix. The [RNEt3]+ cation has been obtained by using long-chained 1-iodoalkanes synthesized via the Nd-catalyzed ethylene oligomerization process. The photophysical properties and the homogeneity of the obtained composites have been controlled by optical spectroscopy, luminescence intensity mapping as well as scanning electron microscopy. [ABSTRACT FROM AUTHOR]

This paper describes our recent results in the field of zirconocene-catalyzed α-oltfin transformations, and focuses on questions regarding the reaction mechanism, rational design of zirconocene pre-catalysts, as well as prospective uses of α-olefin products. It has been determined that a wide range of α-olefin-based products, namely vinylidene dimers, oligomers and polymers, can be prepared via catalysis by zirconocene dichlorides, activated by a minimal (10-20 eq.) amount of MAO. We assumed that in the presence of minimal quantities of MAO, various types of zirconocene catalysts form different types of catalytic particles. In the case of bis-cyclopentadienyl complexes, the reactive center is formed under the influence of R2AlCl, which makes the chain termination via β-hydride elimination significantly easier, with α-olefin dimers being formed as the primary product. Bis -indenyl complexes and their heteroanalogues, form stable cationic catalytic particles and effectively catalyze the polymerization. Mono-indenyl and mono-substituted bis-cyclopentadienyl- ansa complexes catalyze α-olefin oligomerization. Effective catalysts of dimerization, oligomerization and polymerization of α-olefins in the presence of minimal MAO quantities are proposed. Prospects of using α-olefin dimers, oligomers and polymers in the synthesis of branched hydrocarbon functional derivatives (dimers), high quality, low viscosity motor oils (oligomers), and thickeners and absorbents (polymers) are examined. [ABSTRACT FROM AUTHOR]

Branched alkylphosphinic acids obtained from synthetically available α-olefin dimers demonstrate promising anti-wear properties and represent a prospective group of ogranic friction modifiers due to high thermal stability. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement susceptibility of nickel alloy (Inconel 625) is examined by a conventional strain rate tensile test (10−3 s−1) equipped with an acoustic emission (AE) setup. From the spectral analysis of AE signals coupled with the clustering procedure followed by the electron microscopic characterization, we have demonstrated the capability of the AE technique in identifying the hydrogen-dislocation interactions, crack initiation and propagation in various hydrogen-charged samples. The enhanced hardening behavior of hydrogen-charged samples is investigated from the viewpoint on the elementary dislocation theory, using a phenomenological relationship between the acoustic emission power and the experimentally measurable strain hardening parameters derived from the monotonic tensile test. In this way, we have shown that the mobile dislocation density increases with hydrogen content. In addition, the average velocity of dislocations is assessed from the AE data, and it is found to be reduced with the hydrogen concentration. The statistical crack analysis reveals the crack transition from the transgranular to intergranular mode in the samples failed under the hydrogen environment. The competition between these two fracture modes is explained by relating the hydrogen concentration profile with loading conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

The attention to hydrogen embrittlement (HE) has been intensified recently in the light of hydrogen as a carbon-free energy carrier. Despite worldwide research, the multifaceted HE mechanism remains a matter of debate. Here we report an atomistic study of the coupled effect of hydrogen and deformation temperature on the pathway to intergranular fracture of nickel. Uniaxial straining is applied to nickel Σ5(210)[001] and Σ9(1-10)[22-1] grain boundaries with or without pre-charged hydrogen at various temperatures. Without hydrogen, vacancy generation at grain boundary is limited and transgranular fracture mode dominates. When charged, hydrogen as a booster can enhance strain-induced vacancy generation by up to ten times. This leads to the superabundant vacancy stockpiling at the grain boundary, which agglomerates and nucleates intergranular nanovoids eventually causing intergranular fracture. While hydrogen tends to persistently enhance vacancy concentration, temperature plays an intriguing dual role as either an enhancer or an inhibitor for vacancy stockpiling. These results show good agreement with recent positron annihilation spectroscopy experiments. An S -shaped quantitative correlation between the proportion of intergranular fracture and vacancy concentration was for the first time derived, highlighting the existence of a critical vacancy concentration, beyond which fracture mode will be completely intergranular. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The light transmission through metallic films with different types of nano-structures was studied both theoretically and experimentally. It is shown that the positions of the surface plasmon resonances depend on nano-structural details. Those can be changed from sample to sample or in given sample by applying an external dc electric or magnetic field. The dependence of transmission spectrum on the shape of holes (inclusions) and external fields can be used for manipulation of the light transmission, as well as the polarization of the transmitted light and other optical properties, by external field. Two complementary situations are considered: a metal film with dielectric holes and a dielectric film with metallic islands. A new analytical asymptotic approach for calculation of the optical properties of such plasmonic systems is developed. [Copyright &y& Elsevier]

• Fatigue crack growth properties of carbon steels was investigated in hydrogen gas. • Materials with distinctly different carbon content were chosen for investigation. • The roles of pearlite phase on hydrogen-assisted fracture was elucidated. • Net impact of pearlite was to mitigate hydrogen-assisted crack growth acceleration. • Pearlite exhibited dual failure modes that inhibits/enhances H-related fracture. Fatigue crack growth of two carbon steels with different pearlite volume fractions were studied in pressurized gaseous hydrogen environment. Notably, pearlite was found to mitigate hydrogen-assisted fatigue crack acceleration. This positive impact of pearlite was ascribed to ferrite/cementite lamellar aligned perpendicularly to the cracking direction, which functioned as barriers to intermittently arrest the crack propagation. Meanwhile, brittle delamination fracture ensued in the pearlite lamellar lying parallel to the crack-plane increased the crack growth rate and compromised the above positive effect to some extent. The material behavior is rationalized in light of fractographical observations and microstructural analyses of the crack-wake. [ABSTRACT FROM AUTHOR]

• The analysis of possibilities of development of hypervelocity accelerators on the basis of shaped charges with two-layer metal/ceramic liners is carried out. • The peculiarities of the processes of explosion collapse of such liners, consisting in explosive evaporation of the inner layer material, are studied. • The use of materials with high boiling point, such as niobium and tantalum, is proposed. The analysis of material flow fields under the explosive collapse of two-layer metal/ceramics tubes is carried out. It is shown that the main reason for the absence of condensed jet is the explosion evaporation of the inner metal layer due to ultra-high temperatures in the compression area. For the case of the copper inner layer, very interesting and extraordinary features of the flows are observed. The non-stationarity of the process during the entire tube compression period attracts attention. The copper density at the point of contact decreases to 6.06 g/cm3 to the moment of time of 13 µs. This can only mean that copper is already partially vaporized before the collision point. To produce condensed hypervelocity jets, it is proposed to use a material of the inner layer with a high evaporation temperature. The analysis of properties of existing materials shows the perspective of using such refractory and plastic metals as niobium and tantalum as an inner layer of the tube. [ABSTRACT FROM AUTHOR]

Aiming at obtaining the enhanced mechanical properties profile for lightweight applications, bulk billets of the commercial 1570C aluminium alloy (Al–5Mg-0.18Mn-0.20Sc-0.08Zr, wt. %) with nanosized aluminides of transition metals (TM) were subjected to various thermomechanical treatments comprising severe plastic deformation for grain refinement and favourable distribution of disperse phases. The potential of multiaxial isothermal forging (MIF) for the fabrication of ultrafine-grain advanced aluminium alloys is unveiled via a multistep pathway involving two primary routes – the one under constant processing temperature and the other with the inter-step temperature reduction from 325 to 175 °C - combined with conventional cold rolling or high-pressure torsion. Processing-dependent microstructural factors controlling the alloy's behaviour under monotonic and cyclic loading at ambient temperature are discussed with the account of the role of the grain size, grain boundary distribution, precipitates of Mg-rich β-phase and TM-aluminides. In particular, it is shown that after MIF followed by cold rolling, the outstanding combination of the tensile strength and ductility was observed concomitantly with the fatigue resistance superior to that in the contemporary alloys of the same class and/or of many currently available commercial high-strength alloys. [ABSTRACT FROM AUTHOR]

The expansion of the range of physico-chemical methods in the study of industrially significant α-olefin oligomers and polymers is of particular interest. In our article, we present a comparative Raman study of structurally uniform hydrogenated dimers, trimers, tetramers, and pentamers of 1-hexene and 1-octene, that are attractive as bases for freeze-resistant engine oils and lubricants. We found out that the joint monitoring of the disorder longitudinal acoustic mode (D-LAM) and symmetric C–C stretching modes allows the quantitative characterization of the number and length of alkyl chains (i.e., two structural characteristics), upon which the pour point and viscosity of the hydrocarbons depend, and to distinguish these compounds from both each other and linear alkanes. We demonstrated that the ratio of the contents of CH2 and CH3 groups in these hydrocarbons can be determined by using the intensities of the bands in the spectra, related to the asymmetric stretching vibrations of these groups. The density functional theory (DFT) calculations were applied to reveal the relations between the wavenumber and bandshape of the symmetric C–C stretching mode and a conformation arrangement of the 1-hexene and 1-octene dimers. We found that the branched double-chain conformation results in the splitting of the C–C mode into two components with the wavenumbers, which can be used as a measure of the length of branches. This conformation is preferable to the extended-chain conformation for hydrogenated 1-hexene and 1-octene dimers. [ABSTRACT FROM AUTHOR]