Copper phosphoramidite-catalyzed enantioselective desymmetrization of meso-cyclic allylic bisdiethyl phosphates

A highly regio-, diastereo-, and enantioselective desymmetrization of five-, six-, and seven-membered meso-cyclic allylic bis-diethyl phosphates (2a, 2b, and 2c, respectively) was obtained with diethylzinc, using catalytic amounts of [Cu(OTf)](2).C6H6 and phosphoramidite ligands 5. Enantiomeric excesses of up to 87, 94, and >98% were obtained for the addition of diethylzinc to cyclopentene, cyclohexene, and cycloheptene bis-diethyl phosphates, respectively

Field evaluation of rigid and flexible scarifier shanks

Se llevaron a cabo ensayos en campo con el objeto de evaluar parámetros de prestación de arcos de escarificador rígidos y flexibles. Se empleó un tractor de diseño convencional de 73 kW de potencia y un bastidor de tracción libre, registrándose los esfuerzos traccionales mediante una celda de carga interpuesta entre ambos, determinándose el área removida mediante un perfilómetro y obteniéndose los valores de resistencia específica. Los arcos rígidos produjeron un frente de labor significativamente mayor que los arcos flexibles. Los arcos rígidos son energéticamente más eficientes que los arcos flexiblesField tests were carried out with the aim to evaluate both rigid and flexible scarifier shanks performance parameters. A 2WD, 73 kW tractor and a pull type implement were used. The draft force was measured with a force transducer with strain gauges. The loosening area was recorded through a profilometer and, from this data, the specific resistance was calculated. The rigid shanks produced a significantly greather working area than the flexible shanks. The rigid shanks shows higher efficiency than the flexible shanksFacultad de Ciencias Agrarias y Forestale

Field evaluation of rigid and flexible scarifier shanks

Se llevaron a cabo ensayos en campo con el objeto de evaluar parámetros de prestación de arcos de escarificador rígidos y flexibles. Se empleó un tractor de diseño convencional de 73 kW de potencia y un bastidor de tracción libre, registrándose los esfuerzos traccionales mediante una celda de carga interpuesta entre ambos, determinándose el área removida mediante un perfilómetro y obteniéndose los valores de resistencia específica. Los arcos rígidos produjeron un frente de labor significativamente mayor que los arcos flexibles. Los arcos rígidos son energéticamente más eficientes que los arcos flexiblesField tests were carried out with the aim to evaluate both rigid and flexible scarifier shanks performance parameters. A 2WD, 73 kW tractor and a pull type implement were used. The draft force was measured with a force transducer with strain gauges. The loosening area was recorded through a profilometer and, from this data, the specific resistance was calculated. The rigid shanks produced a significantly greather working area than the flexible shanks. The rigid shanks shows higher efficiency than the flexible shanksFacultad de Ciencias Agrarias y Forestale

A self-consistent perturbative evaluation of ground state energies: application to cohesive energies of spin lattices

The work presents a simple formalism which proposes an estimate of the ground state energy from a single reference function. It is based on a perturbative expansion but leads to non linear coupled equations. It can be viewed as well as a modified coupled cluster formulation. Applied to a series of spin lattices governed by model Hamiltonians the method leads to simple analytic solutions. The so-calculated cohesive energies are surprisingly accurate. Two examples illustrate its applicability to locate phase transition.Comment: Accepted by Phys. Rev.

Charge Transfer from Regularized Symmetry-Adapted Perturbation Theory

16 pages, 16 figure

Low energy measurement of the 7Be(p,gamma)8B cross section

We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm = 185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.Comment: Accepted for publication in Phys. Rev. Let

Isotopic control of the boron-vacancy spin defect in hexagonal boron nitride

We report on electron spin resonance (ESR) spectroscopy of boron-vacancy (V$_\text{B}^-$) centers hosted in isotopically-engineered hexagonal boron nitride (hBN) crystals. We first show that isotopic purification of hBN with $^{15}$N yields a simplified and well-resolved hyperfine structure of V$_\text{B}^-$ centers, while purification with $^{10}$B leads to narrower ESR linewidths. These results establish isotopically-purified h$^{10}$B$^{15}$N crystals as the optimal host material for future use of V$_\text{B}^-$ spin defects in quantum technologies. Capitalizing on these findings, we then demonstrate optically-induced polarization of $^{15}$N nuclei in h$^{10}$B$^{15}$N, whose mechanism relies on electron-nuclear spin mixing in the V$_\text{B}^-$ ground state. This work opens up new prospects for future developments of spin-based quantum sensors and simulators on a two-dimensional material platform.Comment: 6 pages, 3 figur

Stochastic optics: A local realistic analysis of optical tests of Bell inequalities

Stochastic optics may be considered as simply a local realistic interpretation of quantum optics and, in this sense, it is a first step in the reinterpretation of the whole of quantum theory. However, as it is not possible to interpret all the details of quantum theory in a local realistic manner, as shown by Bell’s theorem, minor changes are introduced in the formalism with the consequence that the new theory makes different predictions in some special cases. In stochastic optics, the quantum-operator formalism is simply considered a formal way of dealing with stochastic fields. In particular, the quantum zero point is taken as a real random electromagnetic radiation filling the whole of space. This radiation noise has the same nature as light signals, the only difference being the greater intensity of the latter. We assume that photon detectors have an intensity threshold just above the level of the noise, thus detecting only signals. Transmission of radiation through polarizers follows Malus’s law, but the interplay of signal and noise leads quite naturally to the prediction that the detection probability of some signals is enhanced, which is known to be a necessary condition for the violation of the empirically tested Bell inequalities. In our view, correlated photon pairs are pairs of light signals supercorrelated in polarization, in the sense that, as well as the signal, the accompanying noise is also correlated. Thus stochastic optics allows predictions for the empirical correlations very close, but not identical, to the quantum ones. The theory is applied to the analysis of all experiments designed to test the Bell inequalities by measuring polarization correlations of photon pairs. The predictions agree with quantum optics and experiments within statistical errors, except for the Holt-Pipkin experiment. In this case, the experimental results agree with stochastic optical predictions within two standard deviations while violating quantum optics by four

Very Active Neutral P,O-Chelated Nickel Catalysts for Ethylene Polymerization

ABSTRACT: A series of highly active nickel-based neutral catalysts for ethylene polymerization is presented. These catalysts are obtained by direct complexation of simple fluorinated ketoylides onto bis-(1,5-cyclooctadiene)nickel. Catalyst formation readily occurs in the presence of an olefin, but due to the electron deficiency of the ligand, it hardly happens in the absence of an olefin or another Lewis base. Activities greater than 2 × 10 6 (gPE/gNi)/h and productivities higher than 15 × 10 6 gPE/molNi are typically observed. These catalysts are also active for the polymerization of R-olefins such as 1-hexene and 1-propene. Polymer characterization indicates that highly linear, low molecular weight PEHD is formed by these complexes