Heterogeneity of Active Sites in the Polymer Chain Transfer Reactions at Olefin Polymerization over Multisite Supported Ziegler-Natta Catalysts.

In this review, we summarize and discuss our experimental data published in a number of papers on the transfer reactions of polymer chains in the polymerization of ethylene, propylene, and hexene-1, and the copolymerization of ethylene with α-olefins over multisite supported titanium-magnesium catalysts (TMC). Three groups of transfer reactions are discussed in the review: (1) transfer reactions with AlEt3 cocatalyst, (2) transfer reactions with hydrogen, and (3) transfer reactions with participation of α-olefins in the case of ethylene copolymerization with α-olefins. We have found polymerization conditions where it is possible to observe heterogeneity of active sites of TMC for all three groups of the indicated reactions. It is shown that (1) the transfer reaction with AlEt3 proceeds with higher reactivity on the active sites that produce polymers with low molecular weight; (2) the transfer reaction with hydrogen, in the case of α-olefin polymerization and copolymerization of ethylene with α-olefins, proceeds with higher reactivity on the active sites which produce polymers with high molecular weight; (3) the transfer reaction with α-olefins proceed with higher reactivity on the active sites that produce high molecular weight polymers.

Unusual Effect of α-olefins as Chain Transfer Agents in Ethylene Polymerization over the Catalyst with Nonsymmetrical Bis(imino)pyridine Complex of Fe(II) and Modified Methylalumoxane (MMAO) Cocatalyst.

Ethylene polymerization with bis(imino)pyridlyiron precatalysts generally produces linear polyethylene (PE) even with the presence of α-olefins because α-olefins are not incorporated into polymeric products. Interestingly, α-olefins, such as hexene-1 or butene-1, have been found to act as effective chain transfer agents in the ethylene polymerization promoted by nonsymmetrical bis(imino)pyridyliron complexes with modified methylalumoxane (MMAO), resulting in higher catalytic activities with higher amounts of polymers with lower molecular weights, and, more importantly, narrower molecular weight distributions of the resultant polyethylenes (PE). This phenomenon confirms the assistance of α-olefins in the chain-termination reaction of iron-initiated polymerization and regeneration of the active species for further polymerization. Besides higher activities of the catalytic system, the formation of linear PE with trans-vinylene terminal groups and lower molecular weights are explained. The observation will provide a new pathway for enhancing catalytic activity and improving the quality of polyethylenes obtained by regulation of molecular weights and molecular weight distribution.

Effect of Mono- and Multichlorinated Organic Compounds-Chlorocyclohexane and Hexachloro-p-xylene-On the Catalytic Properties of Titanium-Magnesium Catalysts in the Homo- and Copolymerization of Ethylene with 1-Hexene.

Ethylene polymerization and ethylene/1-hexene copolymerization over the titanium-magnesium catalytic system in the presence of chlorocyclohexane (CHC) and hexachloro-p-xylene (HCPX) has been studied. Modification of TMC with chlorocyclohexane and hexachloro-p-xylene increased catalyst activity severalfold for both ethylene polymerization and ethylene/1-hexene copolymerization. The key kinetic regularities of ethylene homopolymerization and ethylene/1-hexene copolymerization in the presence of CHC and HCPX were determined, and the copolymerization constants were measured. Molecular characteristics and the copolymer composition were determined for the synthesized samples of ethylene homopolymers and ethylene/hexene copolymers. Modification of the titanium-magnesium catalyst with chlorinated organic compounds reduced 1-hexene content in the copolymer; polymerization was sensitive to 1-hexene as a regulator of polymer molecular weight. The potential mode of action of chlorinated organic modifiers on catalytic properties of titanium-magnesium catalyst is discussed.

Fluctuating asymmetry as an indicator of stress.

Fluctuating asymmetry as a special kind of asymmetry can be defined as deviations from a known predetermined ratio of the parts of morphological structure under study. As a special type of phenotypic variability fluctuating asymmetry is a manifestation of ontogenetic noise or developmental variability. This type of variability is ubiquitous and plays a significant role in the observed phenotypic diversity. The level of fluctuating asymmetry turns out to be an indicator of optimal developmental conditions and genetic coadaptation. It is also considered as a parameter of fitness. Thus, fluctuating asymmetry acts as a measure of developmental stability in developmental biology and as a measure of population condition in population biology.

Polymerization of Hexene-1 and Propylene over Supported Titanium-Magnesium Catalyst: Comparative Data on the Polymerization Kinetics and Molecular Weight Characteristics of Polymers.

Data are presented on the great differences of the kinetics of hexene-1 and propylene polymerization over the same supported titanium-magnesium catalyst, as well as molecular weight and molecular weight distribution of the polymers produced. It is found that the composition of cocatalysts (AlEt3 or Al(i-Bu)3 greatly affects the kinetics of hexene-1 polymerization and molecular weight distribution of polyhexene, contrary to data obtained at propylene polymerization. The presence of hydrogen at hexene-1 polymerization leads to a much higher increase of activity in comparison with propylene polymerization. Possible reasons for these differences are discussed on the basis of experimental results.

"Flora of Russia" on iNaturalist: a dataset.

BACKGROUND: The "Flora of Russia" project on iNaturalist brought together professional scientists and amateur naturalists from all over the country. Over 10,000 people were involved in the data collection. NEW INFORMATION: Within 20 months, the participants accumulated 750,143 photo observations of 6,857 species of the Russian flora. This constitutes the largest dataset of open spatial data on the country's biodiversity and a leading source of data on the current state of the national flora. About 87% of all project data, i.e. 652,285 observations, are available under free licences (CC0, CC-BY, CC-BY-NC) and can be freely used in scientific, educational and environmental activities.

Cometary Comae-Surface Links: The Physics of Gas and Dust from the Surface to a Spacecraft.

A comet is a highly dynamic object, undergoing a permanent state of change. These changes have to be carefully classified and considered according to their intrinsic temporal and spatial scales. The Rosetta mission has, through its contiguous in-situ and remote sensing coverage of comet 67P/Churyumov-Gerasimenko (hereafter 67P) over the time span of August 2014 to September 2016, monitored the emergence, culmination, and winding down of the gas and dust comae. This provided an unprecedented data set and has spurred a large effort to connect in-situ and remote sensing measurements to the surface. In this review, we address our current understanding of cometary activity and the challenges involved when linking comae data to the surface. We give the current state of research by describing what we know about the physical processes involved from the surface to a few tens of kilometres above it with respect to the gas and dust emission from cometary nuclei. Further, we describe how complex multidimensional cometary gas and dust models have developed from the Halley encounter of 1986 to today. This includes the study of inhomogeneous outgassing and determination of the gas and dust production rates. Additionally, the different approaches used and results obtained to link coma data to the surface will be discussed. We discuss forward and inversion models and we describe the limitations of the respective approaches. The current literature suggests that there does not seem to be a single uniform process behind cometary activity. Rather, activity seems to be the consequence of a variety of erosion processes, including the sublimation of both water ice and more volatile material, but possibly also more exotic processes such as fracture and cliff erosion under thermal and mechanical stress, sub-surface heat storage, and a complex interplay of these processes. Seasons and the nucleus shape are key factors for the distribution and temporal evolution of activity and imply that the heliocentric evolution of activity can be highly individual for every comet, and generalisations can be misleading.

Subjective cognitive decline as a predictor of future cognitive decline: a systematic review.

Over 44 million people suffer from dementia around the world. Researchers estimated that there will be 48.1 million people with dementia by 2020 and 90.3 million by 2040. In addition to dementia, mild cognitive impairment (MCI) and subjective cognitive decline (SCD) relate to cognitive impairment. It has been established that MCI precedes dementia, however the significance of SCD is still unclear. Recent studies suggest that SCD could be a risk factor for objective cognitive impairment. SCD is defined as а self-estimated decline in cognitive capacity in comparison to an individual's previous level of functioning, which cannot be determined by neuropsychological tests. OBJECTIVES: To perform a systematic review of prospective longitudinal cohort studies that assessed the risk of MCI and dementia among people with SCD. METHODS: A search was carried out for all available peer-reviewed articles in English related to SCD in PubMed and PsychINFO databases from database initiation through January 2020. The keywords used for the search were 'subjective cognitive (or memory) impairment (or decline or complaints)'. Three authors separately determined the inclusion or exclusion of all articles retrieved for full-text evaluation. RESULTS: The chance of progression to dementia in the SCD group was 2.17 (95% confidence interval [95%CI] 1.53‒3.07; p<0.05) compared to normal aging. Furthermore, the SCD group was 2.15 times more likely to progress to MCI than the group without SCD (95%CI 1.39‒3.30; p=0.005). CONCLUSIONS: SCD might precede cognitive impairment, however, more detailed longitudinal studies should be conducted.

Mais de 44 milhões de pessoas sofrem de demência em todo o mundo. Pesquisadores estimam que haverá 48,1 milhões de pessoas com demência até 2020 e 90,3 milhões até 2040. Além da demência, o comprometimento cognitivo leve (CCL) e o declínio cognitivo subjetivo (DCS) estão relacionados ao comprometimento cognitivo. Foi estabelecido que o CCL precede a demência, porém a significância do DCS ainda não é clara. Estudos recentes sugerem que o DCS pode ser um fator de risco para comprometimento cognitivo objetivo. DCS é definido como um declínio auto-estimado da capacidade cognitiva em comparação com o nível anterior de funcionamento do indivíduo, que não pode ser determinado por testes neuropsicológicos. OBJETIVOS: Realizar uma revisão sistemática de estudos prospectivos de coorte longitudinal que avaliaram o risco de CCL e demência entre pessoas com DCS. MÉTODOS: Foram pesquisados todos os artigos revisados por pares disponíveis em inglês relacionados com DCS nos bancos de dados PubMed e PsychINFO desde o início do banco de dados até janeiro de 2020. As palavras-chave utilizadas para a pesquisa foram "declínio cognitivo (ou de memória) subjetivo (ou comprometimento ou queixas)". Três autores determinaram separadamente a inclusão ou exclusão de todos os artigos que foram recuperados para avaliação em texto completo. RESULTADOS: A chance de progressão para demência no grupo com DCS foi de 2,17 (intervalo de confiança de 95% [IC95%] 1,53‒3,07; p<0,05) em comparação ao envelhecimento normal. Além disso, o grupo com DCS teve 2,15 vezes mais chances de progredir para CCL do que o grupo sem DCS (IC95% 1,39‒3,30; p=0,005). CONCLUSÕES: o DCS pode preceder o comprometimento cognitivo, no entanto, estudos longitudinais mais detalhados devem ser realizados.

Subjective cognitive decline as a predictor of future cognitive decline: a systematic review / Declínio cognitivo subjetivo como preditor de futuro declínio cognitivo: uma revisão sistemática

ABSTRACT. Over 44 million people suffer from dementia around the world. Researchers estimated that there will be 48.1 million people with dementia by 2020 and 90.3 million by 2040. In addition to dementia, mild cognitive impairment (MCI) and subjective cognitive decline (SCD) relate to cognitive impairment. It has been established that MCI precedes dementia, however the significance of SCD is still unclear. Recent studies suggest that SCD could be a risk factor for objective cognitive impairment. SCD is defined as а self-estimated decline in cognitive capacity in comparison to an individual's previous level of functioning, which cannot be determined by neuropsychological tests. Objectives: To perform a systematic review of prospective longitudinal cohort studies that assessed the risk of MCI and dementia among people with SCD. Methods: A search was carried out for all available peer-reviewed articles in English related to SCD in PubMed and PsychINFO databases from database initiation through January 2020. The keywords used for the search were 'subjective cognitive (or memory) impairment (or decline or complaints)'. Three authors separately determined the inclusion or exclusion of all articles retrieved for full-text evaluation. Results: The chance of progression to dementia in the SCD group was 2.17 (95% confidence interval [95%CI] 1.53‒3.07; p<0.05) compared to normal aging. Furthermore, the SCD group was 2.15 times more likely to progress to MCI than the group without SCD (95%CI 1.39‒3.30; p=0.005). Conclusions: SCD might precede cognitive impairment, however, more detailed longitudinal studies should be conducted.

RESUMO. Mais de 44 milhões de pessoas sofrem de demência em todo o mundo. Pesquisadores estimam que haverá 48,1 milhões de pessoas com demência até 2020 e 90,3 milhões até 2040. Além da demência, o comprometimento cognitivo leve (CCL) e o declínio cognitivo subjetivo (DCS) estão relacionados ao comprometimento cognitivo. Foi estabelecido que o CCL precede a demência, porém a significância do DCS ainda não é clara. Estudos recentes sugerem que o DCS pode ser um fator de risco para comprometimento cognitivo objetivo. DCS é definido como um declínio auto-estimado da capacidade cognitiva em comparação com o nível anterior de funcionamento do indivíduo, que não pode ser determinado por testes neuropsicológicos. Objetivos: Realizar uma revisão sistemática de estudos prospectivos de coorte longitudinal que avaliaram o risco de CCL e demência entre pessoas com DCS. Métodos: Foram pesquisados todos os artigos revisados por pares disponíveis em inglês relacionados com DCS nos bancos de dados PubMed e PsychINFO desde o início do banco de dados até janeiro de 2020. As palavras-chave utilizadas para a pesquisa foram "declínio cognitivo (ou de memória) subjetivo (ou comprometimento ou queixas)". Três autores determinaram separadamente a inclusão ou exclusão de todos os artigos que foram recuperados para avaliação em texto completo. Resultados: A chance de progressão para demência no grupo com DCS foi de 2,17 (intervalo de confiança de 95% [IC95%] 1,53‒3,07; p<0,05) em comparação ao envelhecimento normal. Além disso, o grupo com DCS teve 2,15 vezes mais chances de progredir para CCL do que o grupo sem DCS (IC95% 1,39‒3,30; p=0,005). Conclusões: o DCS pode preceder o comprometimento cognitivo, no entanto, estudos longitudinais mais detalhados devem ser realizados.

Bound State Soliton Gas Dynamics Underlying the Spontaneous Modulational Instability.

We investigate the fundamental phenomenon of the spontaneous, noise-induced modulational instability (MI) of a plane wave. The statistical properties of the noise-induced MI, observed previously in numerical simulations and in experiments, have not been explained theoretically. In this Letter, using the inverse scattering transform (IST) formalism, we propose a theoretical model of the asymptotic stage of the noise-induced MI based on N-soliton solutions of the focusing one-dimensional nonlinear Schrödinger equation. Specifically, we use ensembles of N-soliton bound states having a special semiclassical distribution of the IST eigenvalues, together with random phases for norming constants. To verify our model, we employ a recently developed numerical approach to construct an ensemble of N-soliton solutions with a large number of solitons, N∼100. Our investigation reveals a remarkable agreement between spectral (Fourier) and statistical properties of the long-term evolution of the MI and those of the constructed multisoliton, random-phase bound states. Our results can be generalized to a broad class of strongly nonlinear integrable turbulence problems.

Breather Wave Molecules.

We present both a theoretical description and experimental observation of the nonlinear mutual interactions between a pair of copropagative breathers in the framework of the focusing one-dimensional nonlinear Schrödinger equation. As a general case, we show that the resulting bound state of breathers exhibits moleculelike behavior with quasiperiodic oscillatory dynamics (i.e., internal coherent interactions and pulsations), while for commensurate conditions the molecule oscillations become exactly periodic. Our theoretical model is confirmed by an experimental observation of shaped moleculelike breather light waves propagating in a nearly conservative optical fiber system. Our work sheds new light on the existence of localized wave structures and recurrence dynamics beyond the multisoliton complexes.

NMR spectroscopic identification of Ni(ii) species formed upon activation of (α-diimine)NiBr2 polymerization catalysts with MAO and MMAO.

The nature of Ni(ii) species formed upon the activation of the Brookhart's α-diimine polymerization pre-catalyst LNiBr2 with MAO and MMAO (L = 1,4-bis-2,4,6-dimethylphenyl-2,3-dimethyl-1,4-diazabuta-1,3-diene) has been established using 1H and 13C NMR spectroscopy. The heterobinuclear ion pair [LNiII(µ-Me)2AlMe2]+[MeMAO]- is observed at the initial stage of the reaction of LNiBr2 with MAO at -40 °C, whereas the ion pair [LNiII-tBu]+[MeMMAO]- predominates at the initial stage of the reaction of LNiBr2 with MMAO under the same conditions. At higher temperatures, both ion pairs transform into a Ni(i) species displaying an axially anisotropic EPR spectrum (g‖ = 2.21, g⊥ = 2.06, A⊥ = 1.06 mT).

ARTEMIDA Trial (A Randomized Trial of Efficacy, 12 Months International Double-Blind Actovegin): A Randomized Controlled Trial to Assess the Efficacy of Actovegin in Poststroke Cognitive Impairment.

BACKGROUND AND PURPOSE: Poststroke cognitive impairment is a debilitating consequence of stroke. The aim of this study was to assess whether Actovegin confers cognitive benefit in patients who have had an ischemic stroke. METHODS: This was a 12-month, parallel-group, randomized, multicenter, double-blind, placebo-controlled study. Eligible patients were ≥60 years of age with a Montreal Cognitive Assessment test score of ≤25 points. Patients were randomized into 2 groups within 1 week of acute supratentorial ischemic stroke in a 1:1 ratio: Actovegin (a deproteinized hemoderivative of calf blood, 2000 mg/d for ≤20 intravenous infusions followed by 1200 mg/d orally) or placebo for 6 months. Patients were treated in accordance with standard clinical practice for a further 6 months. The primary end point was the change from baseline in Alzheimer's Disease Assessment Scale, cognitive subscale, extended version at 6 months. RESULTS: Two-hundred forty-eight patients were randomized to Actovegin and 255 patients to placebo. At month 6, the least squares mean change from baseline in Alzheimer's Disease Assessment Scale, cognitive subscale, extended version was -6.8 for Actovegin and -4.6 for placebo; the estimated treatment difference was -2.3 (95% confidence interval, -3.9, -0.7; P=0.005). Recurrent ischemic stroke was the most frequently reported serious adverse event, with a nonsignificantly higher number for Actovegin versus placebo. CONCLUSIONS: Actovegin had a beneficial effect on cognitive outcomes in patients with poststroke cognitive impairment. The safety experience was consistent with the known safety and tolerability profile of the drug. These results warrant confirmation in additional robustly designed studies. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01582854.

Localized sources of water vapour on the dwarf planet (1) Ceres.

The 'snowline' conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt. Recent observations indicate the presence of water ice on the surface of some asteroids, with sublimation a potential reason for the dust activity observed on others. Hydrated minerals have been found on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle. The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl (ref. 12), but could not be confirmed by later, more sensitive observations. Here we report the detection of water vapour around Ceres, with at least 10(26) molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.

Formation and evolution of chain-propagating species upon ethylene polymerization with neutral salicylaldiminato nickel(II) catalysts.

Formation of Ni-polymeryl propagating species upon the interaction of three salicylaldiminato nickel(II) complexes of the type [(N,O)Ni(CH3 )(Py)] (where (N,O)=salicylaldimine ligands, Py=pyridine) with ethylene (C2 H4 /Ni=10:30) has been studied by (1) H and (13) C NMR spectroscopy. Typically, the ethylene/catalyst mixtures in [D8 ]toluene were stored for short periods of time at +60 °C to generate the [(N,O)Ni(polymeryl)] species, then quickly cooled, and the NMR measurements were conducted at -20 °C. At that temperature, the [(N,O)Ni(polymeryl)] species are stable for days; diffusion (1) H NMR measurements provide an estimate of the average length of polymeryl chain (polymeryl=(C2 H4 )n H, n=6-18). At high ethylene consumptions, the [(N,O)Ni(polymeryl)] intermediates decline, releasing free polymer chains and yielding [(N,O)Ni(Et)(Py)] species, which also further decompose to form the ultimate catalyst degradation product, a paramagnetic [(N,O)2 Ni(Py)] complex. In [(N,O)2 Ni(Py)], the pyridine ligand is labile (with activation energy for its dissociation of (12.3±0.5) kcal mol(-1) , ΔH(≠) 298 =(11.7±0.5) kcal mol(-1) , ΔS(≠) 298 =(-7±1) cal K(-1) mol(-1) ). Upon the addition of nonpolar solvent (pentane), the pyridine ligand is lost completely to yield the crystals of diamagnetic [(N,O)2 Ni] complex. NMR spectroscopic analysis of the polyethylenes formed suggests that the evolution of chain-propagating species ends up with formation of polyethylene with predominately internal and terminal vinylene groups rather than vinyl groups.

Formation of trivalent zirconocene complexes from ansa-zirconocene-based olefin-polymerization precatalysts: an EPR- and NMR-spectroscopic study.

Reduction of Zr(IV) metallocenium cations with sodium amalgam (NaHg) produces EPR signals assignable to Zr(III) metallocene complexes. The chloro-bridged heterodinuclear ansa-zirconocenium cation [(SBI)Zr(µ-Cl)2AlMe2](+) (SBI = rac-dimethylsilylbis(1-indenyl)), present in toluene solution as its B(C6F5)4(-) salt, thus gives rise to an EPR signal assignable to the complex (SBI)Zr(III)(µ-Cl)2AlMe2, while (SBI)Zr(III)-Me and (SBI)Zr(III)(µ-H)2Al(i)Bu2 are formed by reduction of [(SBI)Zr(µ-Me)2AlMe2](+) B(C6F5)4(-) and [(SBI)Zr(µ-H)3(Al(i)Bu2)2](+) B(C6F5)4(-), respectively. These products can also be accessed, along with (SBI)Zr(III)-(i)Bu and [(SBI)Zr(III)](+) AlR4(-), when (SBI)ZrMe2 is allowed to react with HAl(i)Bu2, eliminating isobutane en route to the Zr(III) complex. Further studies concern interconversion reactions between these and other (SBI)Zr(III) complexes and reaction mechanisms involved in their formation.

A Randomised, Double-Blind, Placebo-Controlled Trial of Actovegin in Patients with Post-Stroke Cognitive Impairment: ARTEMIDA Study Design.

BACKGROUND: No drug treatment to date has shown convincing clinical evidence of restoring cognitive function or preventing further decline after stroke. The ongoing ARTEMIDA study will evaluate the efficacy and safety of Actovegin for the symptomatic treatment of post-stroke cognitive impairment (PSCI) and will explore whether Actovegin has any disease-modifying effect by assessing whether any changes are sustained after treatment. DESIGN: ARTEMIDA is a 12-month, multicentre trial in patients (planned a total of 500, now recruited) with cognitive impairment following ischaemic stroke. The study consists of a baseline screening (≤7 days after stroke), after which eligible patients are randomised to Actovegin (2,000 mg/day for up to 20 intravenous infusions followed by 1,200 mg/day orally) or placebo for a 6-month double-blind treatment period. Patients will be followed up for a further 6 months, during which time they will be treated in accordance with standard clinical practice. The primary study endpoint is change from baseline in the Alzheimer's Disease Assessment Scale, cognitive subscale, extended version. Secondary outcomes include: Montreal Cognitive Assessment; dementia diagnosis (ICD-10); National Institutes of Health Stroke Scale; Barthel Index; EQ-5D; Beck Depression Inventory, version II, and safety. CONCLUSION: There is a clear need for effective treatments for PSCI. ARTEMIDA should provide important insights into the use of a novel drug therapy for PSCI.

Spontaneous breaking of the spatial homogeneity symmetry in wave turbulence.

We report a surprising new result for wave turbulence which may have broader ramifications for general turbulence theories. Spatial homogeneity, the symmetry property that all statistical moments are functions only of the relative geometry of any configuration of points, can be spontaneously broken by the instability of the finite flux Kolmogorov-Zakharov spectrum in certain (usually one dimensional) situations. As a result, the nature of the statistical attractor changes dramatically, from a sea of resonantly interacting dispersive waves to an ensemble of coherent radiating pulses.

Turbulent transfer of energy by radiating pulses.

We propose a new mechanism for turbulent transport in systems which support radiating nonlinear solitary wave packets or pulses. The direct energy cascade is provided by adiabatically evolving pulses, whose widths and carrier wavelengths decrease. The inverse cascade is due to the excitation of radiation. The spectrum is steeper than the Kolmogorov-Zakharov spectrum of wave turbulence.