Weak intermolecular interactions in 11‐chloro‐2,3,4,5‐tetrahydro‐1H‐cyclohepta[b]quinoline

The title compound, C₁₄H₁₄ClN, is a chloro analogue of tacrine, an acetylcholinesterase inhibitor. The compound comprises a seven‐membered alicyclic ring whose CH donor groups are engaged in extensive intermolecular interactions. The important feature of this crystal structure is that, regardless of the presence of two typical hydrogen‐bonding acceptors, viz. chlorine and nitrogen, the corresponding C—H...Cl and C—H...N interactions take no significant role in crystal stabilization. The molecules form dimers through π–π interactions with an interplanar distance between interacting pyridine rings of 3.576 (1) Å. Within the dimers, the molecules are additionally interconnected by four C—H...π interactions. The dimers arrange into regular columns via further intermolecular C—H...π interactions.     

Robust optimization of contaminant sensor placement for community water systems

We present a series of related robust optimization models for placing sensors in municipal water networks to detect contaminants that are maliciously or accidentally injected. We formulate sensor placement problems as mixed-integer programs, for which the objective coefficients are not known with certainty. We consider a restricted absolute robustness criteria that is motivated by natural restrictions on the uncertain data, and we define three robust optimization models that differ in how the coefficients in the objective vary. Under one set of assumptions there exists a sensor placement that is optimal for all admissible realizations of the coefficients. Under other assumptions, we can apply sorting to solve each worst-case realization efficiently, or we can apply duality to integrate the worst-case outcome and have one integer program. The most difficult case is where the objective parameters are bilinear, and we prove its complexity is NP-hard even under simplifying assumptions. We consider a relaxation that provides an approximation, giving an overall guarantee of near-optimality when used with branch-and-bound search. We present preliminary computational experiments that illustrate the computational complexity of solving these robust formulations on sensor placement applications.     

Excitation of Electronic States of N<Subscript>2</Subscript> in Radio-Frequency Electric Field by Electron Impact

Excitation of electronic states of the N₂ molecule by electron impact is recognized as an essential process in nitrogen plasmas that strongly impacts their chemical reactivity and other properties. Many surface and coating technologies are based on radio-frequency plasma discharges in nitrogen. In this paper the electron impact excitation rate coefficients for singlet and triplet electronic states of the N₂ molecule have been calculated in non-equilibrium conditions in the presence of a radio-frequency electric field. A Monte Carlo simulation has been performed in order to determine non-equilibrium electron energy distribution functions within one period of the electric field. By using these distribution functions, the excitation rate coefficients have been obtained in the frequency range from 13.56 up to 500 MHz, at reduced electric field values from 200 to 700 Td.     

Magneto-intersubband zener tunneling in a wide GaAs quantum well at high filling factors

The dependence of the differential resistance r _xx on the dc current density J _dc in a wide GaAs quantum well with two occupied size quantization subbands has been investigated at the temperature T = 4.2 K in the magnetic fields B < 1 T. A peak, whose position is given by the relation 2R _c eE _H = ħω_c/2, where R _c is the cyclotron radius, E _H is the Hall electric field, and ω_c is the cyclotron frequency, has been observed in the r _xx (J _dc) curves at high filling factors. The experimental results are attributed to Zener tunneling of electrons between the Landau levels of different subbands.     

Shear stress analysis in engineering beams using deplanation field of special 2-D finite elements

This paper deals with the 2-D finite element shear stress analysis in beams, loaded by bending with shear and St. Venant’s torsion. The properties of these finite elements, like stiffness matrices as well as load vectors, are derived on the basis of their axial nodal displacements, e.g. by warping field. Proposed finite elements enable stress analysis independently of both cross-sectional member shape and material properties. Stiffness matrices and load vectors are derived for several finite element types. Material is assumed to be isotropic and linear elastic. For justification of the proposed stress analysis procedure, some examples are presented.     

Dependence of Photochemical Reactivity of the All-trans Retinal Protonated Schiff Base on the Solvent and the Excitation Wavelength

An all-optical experimental technique aimed at measuring photoisomerization quantum yield (ϕ) of the all-trans protonated Schiff base of retinal in solution has been implemented. Upon the increase in the excitation wavelength from 400 to 540 nm a slight increase in ϕ from 0.16 ± 0.03 to 0.20 ± 0.02 is observed in the chromophore dissolved in methanol, whereas the ϕ value of the one dissolved in acetonitrile varies only from 0.22 ± 0.03 (400 nm) to 0.23 ± 0.04 (540 nm). The results suggest that dissipation of the excited-state vibrational energy excess, along with environment-induced modifications of the potential energy surfaces are necessary for an efficient retinal photoisomerization in both solvent and protein environment.     

Synthesis,characterization and biological studies of alkenyl‐substituted titanocene(IV) carboxylate complexes

The carboxylate compounds [Ti(η⁵‐C₅H₅)(η⁵‐C₅H₄{CMe₂(CH₂CH₂CH?CH₂)})(O₂CCH₂SXyl)₂] (2; Xyl = 3,5‐Me₂C₆H₃) and [Ti(η⁵‐C₅H₅)(η⁵‐C₅H₄{CMe₂(CH₂CH₂CH?CH₂)})(O₂CCH₂SMesl)₂] (3; Mes 1 = 2,4,6‐Me₃C₆H₂) were synthesized by the reaction of [Ti(η⁵‐C₅H₅)(η⁵‐C₅H₄{CMe₂(CH₂CH₂CH?CH₂)})Cl₂] (1) with 2 equivalents of xylylthioacetic acid or mesitylthioacetic acid, respectively. Compounds 2 and 3 were characterized by spectroscopic methods. The cytotoxic activity of 1–3 was tested against human tumor cell lines from four different histogenic origins—8505C (anaplastic thyroid cancer), DLD‐1 (colon cancer) and the cisplatin sensitive A253 (head and neck cancer) and A549 (lung carcinoma)—and compared with those of the reference complex [Ti(η⁵‐C₅H₅)₂Cl₂] (R1) and cisplatin. Surprisingly, the cytotoxic activities of the carboxylate derivatives were lower than those of their corresponding dichloride analogue (1). However, complexes 1–3 were more active than titanocene dichloride against all the studied cells with the exception of complex 2 against A253 and A549 cell lines. DNA‐interaction tests were also carried out. Solutions of all the studied complexes were treated with different concentrations of fish sperm DNA, observing modifications of the UV spectra with intrinsic binding constants of 2.99 × 10⁵, 2.45 × 10⁵, and 2.35 × 10⁵ M ^?1 for 1–3. Structural studies based on density functional theory calculations of 2 and 3 were also carried out. Copyright © 2010 John Wiley & Sons, Ltd.     

Isothermal crystallization kinetics and spherulitic morphology of poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

Isothermal crystallization behavior of a new regular polyester constituted by glycolic acid and 4‐hydroxybutyric acid units is studied by means of differential scanning calorimetry and hot‐stage optical microscopy. A wide range of crystallization conditions were experimentally accessible, allowing various morphological features to be observed and accurate estimates made of characteristic growth parameters, including radial growth and nucleation rates. Three‐dimensional spherulitic growth from heterogeneous nuclei is deduced from the Avrami analysis, whereas optical micrographs reveal two different spherulitic textures that agree with the existence of two crystallization regimes. These can be well distinguished from the breaks observed in the Lauritzen and Hoffman plots when the linear crystal growth rate or the overall crystallization rate is considered. Ringed and nonringed spherulites with negative and positive birefringence, respectively, can be obtained depending on crystallization conditions and regimes. The studied polyester shows rather complex melting behavior which is interpreted in terms of a recrystallization process involving the two different kinds of spherulites. This study allows polymorphism to be discounted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2640–2653, 2007     

A simple chemical method for visualization of sebaceous fingerprints on unfired cartridge cases by Prussian blue deposition

Russian Journal of Applied Chemistry - This paper presents a new method for chemical development of latent fingerprints on unfired cartridge cases and some metal surfaces. It is based on chemical...