A használatalapú biztosítás múltja, jelene és jövője

[Cp*RuCl]₄ (1) has previously been shown to be the precatalyst of choice for stereochemically unorthodox trans-hydrometalations of internal alkynes. Experimental and computational data now prove that the alkyne primarily acts as a four-electron donor ligand to the catalytically active metal fragment [Cp*RuCl] but switches to adopt a two-electron donor character once the reagent R₃MH (M = Si, Ge, Sn) enters the ligand sphere. In the stereodetermining step the resulting loaded complex evolves via an inner-sphere mechanism into a ruthenacyclopropene which swiftly transforms into the product. In accord with the low computed barriers, spectral and preparative data show that the reaction is not only possible but sometimes even favored at low temperatures. Importantly, such trans-hydrometalations are distinguished by excellent levels of regioselectivity when unsymmetrical alkynes are used that carry an −OH or −NHR group in vicinity of the triple bond. A nascent hydrogen bridge between the protic substituent and the polarized [Ru–Cl] unit imposes directionality onto the ligand sphere of the relevant intermediates, which ultimately accounts for the selective delivery of the R₃M– group to the acetylene C-atom proximal to the steering substituent. The interligand hydrogen bonding also allows site-selectivity to be harnessed in reactions of polyunsaturated compounds, since propargylic substrates bind more tightly than ordinary alkynes; even the electronically coupled triple bonds of conjugated 1,3-diynes can be faithfully discriminated as long as one of them is propargylic. Finally, properly positioned protic sites lead to a substantially increased substrate scope in that they render even 1,3-enynes, arylalkynes, and electron-rich alkynylated heterocycles amenable to trans-hydrometalation which are otherwise catalyst poisons

Reactivity of Gold Hydrides: O2 Insertion into the Au–H Bond

Dioxygen reacts with the gold(I) hydride (IPr)AuH under insertion to give the hydroperoxide, (IPr)AuOOH, a long-postulated reaction in gold catalysis and the first demonstration of O2 activation by Au-H in a well-defined system. Subsequent condensation gave the peroxide (IPr)Au-OO-Au(IPr) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The reaction kinetics are reported, as well as the reactivity of Au(I) hydrides with radical scavengers

Relating different Polynomial-LWE problems

In this paper we focus on Polynomial Learning with Errors (PLWE). This problem is parametrized by a polynomial and we are interested in relating the hardness of the $\text{PLWE}^f$ and $\text{PLWE}^h$ problems for different polynomials $f$ and $h$. More precisely, our main result shows that for a fixed monic polynomial $f$, $\text{PLWE}^{f\circ g}$ is at least as hard as $\text{PLWE}^f$, in both search and decision variants, for any monic polynomial $g$. As a consequence, $\text{PLWE}^{\phi_n}$ is harder than $\text{PLWE}^{f},$ for a minimal polynomial $f$ of an algebraic integer from the cyclotomic field $\mathbb{Q}(\zeta_n)$ with specific properties. Moreover, we prove in decision variant that in the case of power-of-2 polynomials, $\text{PLWE}^{\phi_n}$ is at least as hard as $\text{PLWE}^f,$ for a minimal polynomial $f$ of algebraic integers from the $n$th cyclotomic field with weaker specifications than those from the previous result

Structure from motion photogrammetry in forestry : a review

AbstractPurpose of ReviewThe adoption of Structure from Motion photogrammetry (SfM) is transforming the acquisition of three-dimensional (3D) remote sensing (RS) data in forestry. SfM photogrammetry enables surveys with little cost and technical expertise. We present the theoretical principles and practical considerations of this technology and show opportunities that SfM photogrammetry offers for forest practitioners and researchers.Recent FindingsOur examples of key research indicate the successful application of SfM photogrammetry in forestry, in an operational context and in research, delivering results that are comparable to LiDAR surveys. Reviewed studies have identified possibilities for the extraction of biophysical forest parameters from airborne and terrestrial SfM point clouds and derived 2D data in area-based approaches (ABA) and individual tree approaches. Additionally, increases in the spatial and spectral resolution of sensors available for SfM photogrammetry enable forest health assessment and monitoring. The presented research reveals that coherent 3D data and spectral information, as provided by the SfM workflow, promote opportunities to derive both structural and physiological attributes at the individual tree crown (ITC) as well as stand levels.SummaryWe highlight the potential of using unmanned aerial vehicles (UAVs) and consumer-grade cameras for terrestrial SfM-based surveys in forestry. Offering several spatial products from a single sensor, the SfM workflow enables foresters to collect their own fit-for-purpose RS data. With the broad availability of non-expert SfM software, we provide important practical considerations for the collection of quality input image data to enable successful photogrammetric surveys

Boson stars in massless and massive scalar-tensor gravity

We study phenomenological features and stability of boson stars in massless and massive scalar-tensor theory of gravity with Damour-Esposito-Farèse coupling. This coupling between the tensor and scalar sectors of the theory leads to a phenomenon called spontaneous scalarization, the onset of which we investigate by numerically computing families of boson-star models using shooting and relaxation algorithms. We systematically explore the effects of the theory's coupling, the mass of the gravitational scalar and the choice of the bosonic potential on the structure of weakly and strongly scalarized solutions. Scalarized boson-star models share many common features with neutron stars in the same scalar-tensor theory of gravity. In particular, scalarization can result in boson stars with significantly larger radii and masses, which tend to be energetically favored over their weakly or nonscalarized counterparts. Overall, we find that boson stars are not quite as susceptible to scalarization as neutron stars

Feeding ecology of two newt species (

The aim of this study was to provide an in-depth survey of feeding ecology and trophic interactions of two syntopic newt species (Triturus cristatus and Lissotriton vulgaris) inhabiting aquatic breeding habitats from the eastern Romanian Carpathian Mountains. We sampled 736 individuals from both species. The trophic spectrum was based mostly on Asselidae (>30%). Our results show that both species may be considered generalists because their niche breadth is higher than 0.5, with largely overlapping trophic niches (>70%), which may indicate food competition

The blocking of an inhomogeneous Bingham fluid. Applications to landslides

This work is concerned with the flow of a viscous plastic fluid. We choose a model of Bingham type taking into account inhomogeneous yield limit of the fluid, which is well-adapted in the description of landslides. After setting the general threedimensional problem, the blocking property is introduced. We then focus on necessary and sufficient conditions such that blocking of the fluid occurs. The anti-plane flow in twodimensional and onedimensional cases is considered. A variational formulation in terms of stresses is deduced. More fine properties dealing with local stagnant regions as well as local regions where the fluid behaves like a rigid body are obtained in dimension one