Characterization of the Quasi-Stationary State of an Impurity Driven by Monochromatic Light I: The Effective Theory

We consider an impurity (N-level atom) driven by monochromatic light in a host environment which is a fermionic thermal reservoir. The external light source is a time-periodic perturbation of the atomic Hamiltonian stimulating transitions between two atomic energy levels E ₁ and E _N and thus acts as an optical pump. The purpose of the present work is the analysis of the effective atomic dynamics resulting from the full microscopic time-evolution of the compound system. We prove, in particular, that the atomic dynamics of population relaxes for large times to a quasi-stationary state, that is, a stationary state up to small oscillations driven by the external light source. This state turns out to be uniquely determined by a balance condition. The latter is related to “generalized Einstein relations” of spontaneous/stimulated emission/absorption rates, which are conceptually similar to the phenomenological relations derived by Einstein in 1916. As an application we show from quantum mechanical first principles how an inversion of population of energy levels of an impurity in a crystal can appear. Our results are based on the spectral analysis of the generator of the evolution semigroup related to a non-autonomous Cauchy problem effectively describing the atomic dynamics.     

Lefschetz periodic point free self-maps of compact manifolds

Let f be a self-map of a compact connected manifold M. We characterize Lefschetz periodic point free continuous self-maps of M for several classes of manifolds and generalize the results of Guirao and Llibre [J.L.G. Guirao, J. Llibre, On the Lefschetz periodic point free continuous self-maps on connected compact manifolds, Topology Appl. 158 (16) (2011) 2165–2169].     

The BCC to FCC/HCP phase transformation of the Co70Fe30 alloy produced by ion irradiation of Co70Fe30/Cu discontinuous multilayers

We report on the BCC to FCC/HCP structural transformation of Co₇₀Fe₃₀ alloy produced by room temperature ion irradiation of Co₇₀Fe₃₀/Cu discontinuous multilayers. The structural changes were analyzed by X-ray diffraction and X-ray absorption spectroscopy. For this study, two different samples were examined, one irradiated with 50 keV He⁺ and another with 600 keV Kr⁺ with doses of 1×10¹⁷ and 3×10¹⁵ ions/cm², respectively. No substantial change is observed after He⁺ irradiation, while after Kr⁺ irradiation an unexpected structural transition from BCC to FCC/HCP closed packed of the Co₇₀Fe₃₀ alloy was found.     

Struktur- und Absorptionspotentiale von KCl und NaCl aus Beugungsaufnahmen im konvergenten Elektronenbündel

By improvement of an earlier published preparation method for producing thin single crystals soluble in water, it is possible to determine structure and absorption potentials of some reflections of KCl and NaCl crystals by a convergent beam diffraction technique. The structure potentials evaluated on the basis of the two-beam dynamical theory are found to depend on the thickness of the crystals used. The structure potentials corrected for relativistic, thermal and many-beam effects are compared with theoretical values. The measured (220)- and (420)-absorption potentials of NaCl are in good agreement with theoretical values. Radiation damage in KCl and NaCl crystals by electron beams is observed.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Organic synthesis with sulfones XXXII. A convenient route to α,β -unsaturated sulfones from saturated sulfones.

α-sulfonyl litiated anions are oxidized by cupric carboxylates into β, β-unsaturated sulfones. Primary sulfones lead to pure trans-vinylic sulfones.     

In vivo TESTS OF THE CONCEPT OF PHOTODYNAMIC THRESHOLD DOSE IN NORMAL RAT LIVER PHOTOSENSITIZED BY ALUMINUM CHLOROSULPHONATED PHTHALOCYANINE

In its simplest form, the photodynamic therapy (PDT) threshold dose model states that tissue necrosis due to PDT will occur if the number of photons absorbed by the photosensitizer per unit volume of tissue exceeds a critical value. This threshold is given by the product of photon fluence, photosensitizer concentration and specific absorption coefficient. To test the validity of this concept for PDT of normal rat liver sensitized with aluminum chlorosulphonated phthalocyanine (AISPC), all three of these parameters were varied by changing the injected AISPC dose, the wavelength of excitation and the irradiation geometry. The extent of necrosis caused by the treatment was consistent with the threshold model, except when the concentration of AISPC in the liver exceeded 20 micrograms g-1. For this animal model, we estimate the threshold to be (3.8 +/- 0.2) x 10(19) photons cm-3.     

Synthesis and Complexation Properties of a New Class of Receptors based on a cone-configurated tetra-p-(tert-butyl)calix[4]arene and bipyridyl subunits

0The bipyridyl-armed tetra-p-(tert-butyl)calix[4]arenes 1 – 5 were synthesized from tetra-p-(tert-butyl)-calix[4]arene A and 6-(bromomethyl)-6′-methyl-2,2′-bipyridine ( B ) by direct base-strength-driven regioselective O-alkylation or by stepwise procedures. Preliminary complexation studies of the ligands 1 – 3 with Cu^I affording the complexes 6 – 8 are described.     

Utilisation d'ylides du phosphore en chimie des sucres. XVIII Synthèse de furannoses à insaturation conjuguée. Communication préliminaire

Several sugars with conjugated unsaturation (dienes or α, β-unsaturated carbonyl compounds) have been synthesised by use of Wittig reactions. Keto-sugars bearing a carbonyl group α to a furanose ring are prone to undergo an elimination leading to conjugated unsaturated systems. This constitutes a novel kind of side-reaction in the application of Wittig reactions to carbonyl sugars. The synthesis of a new kind of acetylenic sugar is also described.     

Accelerating high-throughput virtual screening through molecular pool-based active learning

Structure-based virtual screening is an important tool in early stage drug discovery that scores the interactions between a target protein and candidate ligands. As virtual libraries continue to grow (in excess of 10⁸ molecules), so too do the resources necessary to conduct exhaustive virtual screening campaigns on these libraries. However, Bayesian optimization techniques, previously employed in other scientific discovery problems, can aid in their exploration: a surrogate structure–property relationship model trained on the predicted affinities of a subset of the library can be applied to the remaining library members, allowing the least promising compounds to be excluded from evaluation. In this study, we explore the application of these techniques to computational docking datasets and assess the impact of surrogate model architecture, acquisition function, and acquisition batch size on optimization performance. We observe significant reductions in computational costs; for example, using a directed-message passing neural network we can identify 94.8% or 89.3% of the top-50 000 ligands in a 100M member library after testing only 2.4% of candidate ligands using an upper confidence bound or greedy acquisition strategy, respectively. Such model-guided searches mitigate the increasing computational costs of screening increasingly large virtual libraries and can accelerate high-throughput virtual screening campaigns with applications beyond docking.

Bayesian optimization can accelerate structure-based virtual screening campaigns by minimizing the total number of simulations performed while still identifying the vast majority of computational hits.