Semi-empirical MO calculations of nuclear spin coupling constants

The results obtained using different semi-empirical approaches, namely EHMO, IEHMO, CNDO/2 and INDO, in the calculation of spin–spin coupling constants within the framework of the one-electron MO approximation are systematically compared in the case of several classes of organic molecules. While, at a semi-empirical level SCF methods normally provide satisfactory wave function, the use of the simple EHMO seems better able to satisfy the problem connected with the calculation of spin–spin coupling constants, expecially when an appropriate set of AO's is chosen, in order to avoid parametrisation of Dirac monocentric integrals. Charge iteration (IEHMO) seems to improve the results slightly only when heteroatoms are present, but the complexity introduced into the calculations and the greatly increased computer time do not justify the slight improvement achieved, particularly as the method is applied to large molecules and organometallic compounds.     

One-pot synthesis of benzo[e]1,4-oxathiepin-5-ones under solvent-free condition via self-promoted thiolysis of 1,2-epoxides

Under solvent-free conditions, thiosalicylic acid (2) efficiently self-promotes the thiolysis of 1,2-epoxides 1, anti-stereoselectively and generally totally beta-regioselectively. The resulting beta-hydroxysulfide products 3 have been obtained in very good yields. Benzo[e]1,4-oxathiepin-5-ones 4 have been easily prepared in a regio- and diasteroselective manner and in satisfactory yields under SFC by a one-pot protocol including nucleophilic ring opening of 1,2-epoxides 1 by thiosalicylic acid (2) and thermally induced lactonization of beta-hydroxy arylsulfides 3. Solvent-free condition and the absence of any catalyst make this procedure atom-economical and environmentally friendly.     

Reconciling phase diffusion and Hartree–Fock approximation in condensate systems

Despite the weakly interacting regime, the physics of Bose–Einstein condensates is widely affected by particle–particle interactions. They determine quantum phase diffusion, which is known to be the main cause of loss of coherence. Studying a simple model of two interacting Bose systems, we show how to predict the appearance of phase diffusion beyond the Bogoliubov approximation, providing a self-consistent treatment in the framework of a generalized Hartree–Fock–Bogoliubov perturbation theory.     

A Protocol for Accessing the β-Azidation of α,β-Unsaturated Carboxylic Acids

This contribution reports the preparation and use of a new immobilized catalyst, PS-DABCOF (9), which has been specifically designed to access for the first time the efficient β-azidation of α,β-unsaturated carboxylic acids.     

Large bending behavior of creased paperboard. I. Experimental investigations

The large bending behavior of a creased paperboard is studied in the range of rotation θ ? [0°, 180°] – new results, apparently not reported previously in literature – with the aim to point out some crucial aspect involved in an adaptive robotic manipulation of the industrial cartons.The loading tests show a great variability of the mechanical behavior, depending dramatically on the crease indentation depth (also for the specimens obtained from the same carton): (a) when the damage induced during the crease formation is relatively small, the bending response is unusually complex: the moment constitutive function, m_L(θ), presents (up to) two peaks followed by unstable branches; (b) for greater indentation, the m_L(θ) is monotone.In the unloading case the response m_U(θ) is always monotone and is practically independent of the formation conditions of the crease. These behaviors can be easily described analytically using (piecewise) third degree splines.In a companion paper, the erection of a typical carton corner with unstable constitutive behavior is fully analyzed to detect the possible criticalities.     

A refined theory for laminated beams: Part I—A new high order approach

This paper presents a new displacement-based one-dimensional model for the analysis of multilayered composite beams. The kinematic restriction of cross sections rigid in their own planes is introduced. The axial displacements over the cross sections are represented in terms of explicitly defined piecewise polynomial warping functions with discontinuous derivatives at the interlaminae, whereas the amplitude of the displacements along the beam axis is established by means of a variational formulation. It is proved that the proposed representation of the axial displacements yields the exact solution of the interior domain problem for a beam subjected to a transverse load varying according to a polynomial law. It is shown that two or three coordinate functions are sufficient to yield continuous distributions of equilibrated stresses except for small neighborhoods of the constrained cross sections, where a higher number of warping functions could be used in order to obtain a better accuracy. The numerical results show excellent agreement with plane stress finite element and plane strain exact solutions.

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Sommario In questo lavoro viene presentato un nuovo modello monodimensionale per l'analisi di travi composite multistrato. Viene introdotta l'ipotesi di indeformabilita delle sezioni nel proprio piano mentre gli spostamenti assiali nella sezione sono rappresentati facendo uso di funzioni ingobbamento definite sull'intera altezza e con derivata discontinua all'in erlamina. Infine, l'ampiezza degli spostamenti lungo l'asse della trave è determinata facendo uso di una formulazione variazionale. Si mostra come la rappresentazione degli spostamenti assiali proposta sia in grado di fornire la soluzione esatta, all'interno del dominio, per una trave soggetta ad un carico trasversale variabile con legge nolinomiale. Due o tre funzioni coordinate sono sufficienti a fornire distribuzioni di sforzi che verificano l'equilibrio anche all'interlamina, a meno di zone rislrette in vicinanza di sezioni vincolate. I risultati numerici mostrano un eccellente accordo con soluzioni agli elementi finiti in stato piano di tensione e con soluzioni esatte in stato piano di deformazione.

     

De formae,in quam geometra britannicus Hamilton integralia mechanices analyticae redegit,origine genuina

Den Wiederabdruck dieser Abhandlung rechtfertigt der bedeutsame Inhalt, der zu den für die moderne analytische Mechanik fundamentalen Untersuchungen von Lipschitz und Beltrami in nächster Beziehung steht. S. Schlömilch's Ztschr. Bd. 45 hist.-litter. Abth. S. 118. Die Abhandlung ist als Gratulationsschrift der Universität Dorpat für die Sternwarte Pulkowa erschienen, aber wie es scheint bis jetzt unbekannt geblieben. Sie trägt den Titel: Imperiali speculae astronomicae Pulcoviensi a. d. VII id. Aug. a. MDCCCLXIV quintum lustrum exactum celebranti gratulatur Universitas literarum Caesarea Dorpatensis. Inest Ferdinandi Mindingii disquisitio de formae, in quam geometra britannicus Hamilton integralia mechanices analyticae redegit, origine genuina. Dorpati Livonorum. Typis C. Mattiesenii. MDCCCLXIV. Sodann folgt eine Widmung: Speculae in Rossia primariae quinque lustra feliciter peracta congratulantes et Deum Optimum Maximum sospitet eam ac prosperet in perpetuum promovendae ut scientiae naviter pergat inservire maxima huius imperii generisque humani cum utilitate comprecantes studii oservantiaeque documentum hasce pagellas misimus Universitatis Literarum Dorpatensis Rector et Senatus.     

Overlaps help: Improved bounds for group testing with interval queries

Given a finite ordered set of items and an unknown distinguished subset P of up to p positive elements, identify the items in P by asking the least number of queries of the type ‘‘does the subset Q intersect P?”, where Q is a subset of consecutive elements of {1,2,…,n}. This problem arises, e.g., in computational biology, in a particular method for determining splice sites in genes. We consider time-efficient algorithms where queries are arranged in a fixed number s of stages: In each stage, queries are performed in parallel. In a recent bioinformatics paper, we proved optimality (subject to lower-order terms) with respect to the number of queries, of some strategies for the special cases p=1 or s=2. Exploiting new ideas, we are now able to provide improved lower bounds for any p?2 and s?3 and improved upper bounds for larger s. Most notably, our new bounds converge as s grows. Our new query scheme uses overlapping query intervals within a stage, which is effective for large enough s. This contrasts with our previous results for s?2 where optimal strategies were implemented by disjoint queries. The main open problem is whether overlaps help already in the case of small s?3. Anyway, the remaining gaps between the current upper and lower bounds for any fixed s?3 amount to small constant factors in the main term. The paper ends with a discussion of practical implications in the case that the positive elements are well separated.     

X-Ray Structural Analysis of Ethyl [2,2-dimethyl-6-(Δ2-thiazolin-2-yl)-4H-1,4-benzoxazin-3-one-4-yl]butyrate

With the aim of discovering new molecules with K⁺ channel modulating properties, we have synthesized analogues of cromakalim, an important molecule which shows specific affinity toward the K⁺ channels, by replacing the benzopyrane ring with a benzoxazine moiety. As a part of this study, we have synthesized and characterized, in solution and in the solid state as well, the compound ethyl [2,2-dimethyl-6-(²-thiazolin-2-yl)-4H-l,4-benzoxazin-3-one-4-yl]butyrate (V). This compound exhibits in the solid state the following parameters: molecular formula C₁₉H₂₄N₂O₄S, triclinic, space group , M_w = 376.5, a = 12.581(3) Å, b = 5.485(4) Å, c = 14.612(2) Å, = 91.85(2), = 108.9(3), = 82.04(4), V = 944.7 ų, Z = 2, d = 1.323 g·cm^–3. We describe here the synthesis and discuss the solid-state conformation of this new molecule; when tested on rat aorta ring precontracted with phenylephrine, the compound showed a concentration-dependent relaxation comparable to that measured for cromakalin taken as reference drug.