A dichotomy in the enantioselective oxidation of aryl benzyl sulfides: A combined experimental and computational work

Pentafluorobenzyl pentafluorophenyl sulfide is oxidised with moderate e.e. value and a low yield by the usually highly successful oxidation protocol based upon tert-butyl hydroperoxide (TBHP) in the presence of a titanium/hydrobenzoin complex. This disappointing result resisted until the present work, in which the switch of the oxidation agent (from TBHP to cumene hydroperoxide), suggested by our previous computations, yielded the enantiopure sulfoxide. This valuable chiral compound was obtained in good yields (76%) without resorting to a chromatographic separation. DFT computations uncovered that this favourable reactivity was originated by a stabilizing π?π?stacking between the phenyl group of the oxidant and the pentafluorophenyl moiety of the substrate.     

A Note on Two-Weight Inequalities for Maximal Functions and Singular Integrals

We deal with weighted inequalities of the type [formula] where: T is either the Hardy–Littlewood maximal operator or asingular integral operator; G is any measurable subset of Rⁿ; f is any measurable function, vanishing outside G, such thatTf is well-defined; v and w are weights, that is, nonnegativelocally integrable functions on G; p, q(1, ). 1991 Mathematics Subject Classification 42B20, 42B25.     

A finiteness theorem for low-codimensional nonsingular subvarieties of quadrics

We prove that there are only finitely many families of codimension two nonsingular subvarieties of quadrics which are not of general type, for and . We prove a similar statement also for the case of higher codimension.

     

Poincaré-Invariant Markov Processes and Gaussian Random Fields on Relativistic Phase Space

We give a complete characterization, including a Lévy–Itô decomposition, of Poincaré-invariant Markov processes on , the relativistic phase space in 1+1 spacetime dimensions. Then, by means of such processes, we construct Poincaré-invariant Gaussian random fields, and we prove a no-go theorem for the random fields corresponding to Brownian motions on .     

LTE‐based satellite communications in LEO mega‐constellations

The integration of satellite and terrestrial networks is a promising solution for extending broadband coverage to areas not connected to a terrestrial infrastructure, as also demonstrated by recent commercial and standardisation endeavours. However, the large delays and Doppler shifts over the satellite channel pose severe technical challenges to traditional terrestrial systems, as long‐term evolution (LTE) or 5G. In this paper, 2 architectures are proposed for a low Earth orbit mega‐constellation realising a satellite‐enabled LTE system, in which the on‐ground LTE entity is either an eNB (Sat‐eNB) or a relay node (Sat‐RN). The impact of satellite channel impairments as large delays and Doppler shifts on LTE PHY/MAC procedures is discussed and assessed. The proposed analysis shows that, while carrier spacings, random access and RN attach procedures do not pose specific issues and hybrid automatic repeat request requires substantial modifications. Moreover, advanced handover procedures will be also required due to the satellites' movement.     

Long‐Term Electrical and Mechanical Function Monitoring of a Human‐on‐a‐Chip System

The goal of human‐on‐a‐chip systems is to capture multiorgan complexity and predict the human response to compounds within physiologically relevant platforms. The generation and characterization of such systems is currently a focal point of research given the long‐standing inadequacies of conventional techniques for predicting human outcome. Functional systems can measure and quantify key cellular mechanisms that correlate with the physiological status of a tissue, and can be used to evaluate therapeutic challenges utilizing many of the same endpoints used in animal experiments or clinical trials. Culturing multiple organ compartments in a platform creates a more physiologic environment (organ–organ communication). Here is reported a human 4‐organ system composed of heart, liver, skeletal muscle, and nervous system modules that maintains cellular viability and function over 28 days in serum‐free conditions using a pumpless system. The integration of noninvasive electrical evaluation of neurons and cardiac cells and mechanical determination of cardiac and skeletal muscle contraction allows the monitoring of cellular function, especially for chronic toxicity studies in vitro. The 28‐day period is the minimum timeframe for animal studies to evaluate repeat dose toxicity. This technology can be a relevant alternative to animal testing by monitoring multiorgan function upon long‐term chemical exposure.     

Evidence for the Band‐Edge Exciton of CuInS2 Nanocrystals Enables Record Efficient Large‐Area Luminescent Solar Concentrators

Ternary I‐III‐VI₂ nanocrystals (NCs), such as CuInS₂, are receiving attention as heavy‐metals‐free materials for solar cells, luminescent solar concentrators (LSCs), LEDs, and bio‐imaging. The origin of the optical properties of CuInS₂ NCs are however not fully understood. A recent theoretical model suggests that their characteristic Stokes‐shifted and long‐lived luminescence arises from the structure of the valence band (VB) and predicts distinctive optical behaviours in defect‐free NCs: the quadratic dependence of the radiative decay rate and the Stokes shift on the NC radius. If confirmed, this would have crucial implications for LSCs as the solar spectral coverage ensured by low‐bandgap NCs would be accompanied by increased re‐absorption losses. Here, by studying stoichiometric CuInS₂ NCs, it is revealed for the first time the spectroscopic signatures predicted for the free band‐edge exciton, thus supporting the VB‐structure model. At very low temperatures, the NCs also show dark‐state emission likely originating from enhanced electron‐hole spin interaction. The impact of the observed optical behaviours on LSCs is evaluated by Monte Carlo ray‐tracing simulations. Based on the emerging device design guidelines, optical‐grade large‐area (30×30 cm²) LSCs with optical power efficiency (OPE) as high as 6.8% are fabricated, corresponding to the highest value reported to date for large‐area devices.     

Extensions of thep-adic fields generated by the roots of a single polynomial in two variables

One of the generalizations of the Hilbert's Irreducibility Theorem states that if F(X, Y) is irreducible in Q _p [X, Y] then, for almost every n N, F(n, Y) is irreducible in Q _p [Y]. Let E{p, d} be the set of all the extensions of Q _p of degree d. We shall prove that for each subset S E{p, d}there exist polynomials F(X, Y) such that the set of extensions of Q _p generated by the roots of F (n, Y)is exactly S. Moreover we shall prove that all the functions f are induced by polynomials F(X) Z[X].M. S. C. N. 11S05, (11S15).The author would like to thank Prof. Roberto Dvornicich for several useful conversations and advices.     

Tunable,Grating-Gated,Graphene-On-Polyimide Terahertz Modulators

An electrically switchable graphene terahertz (THz) modulator with a tunable-by-design optical bandwidth is presented and it is exploited to compensate the cavity dispersion of a quantum cascade laser (QCL). Electrostatic gating is achieved by a metal grating used as a gate electrode, with an HfO₂/AlO_x gate dielectric on top. This is patterned on a polyimide layer, which acts as a quarter wave resonance cavity, coupled with an Au reflector underneath. The authors achieve 90% modulation depth of the intensity, combined with a 20 kHz electrical bandwidth in the 1.9–2.7 THz range. The modulator is then integrated with a multimode THz QCL. By adjusting the modulator operational bandwidth, the authors demonstrate that the graphene modulator can partially compensate the QCL cavity dispersion, resulting in an integrated laser behaving as a stable frequency comb over 35% of the operational range, with 98 equidistant optical modes and a spectral coverage ~1.2 THz. This paves the way for applications in the terahertz, such as tunable transformation-optics devices, active photonic components, adaptive and quantum optics, and metrological tools for spectroscopy at THz frequencies.