Numerical calculation and experimental measurement of temperatures and welding residual stresses in a thick-walled T-joint structure

Journal of Thermal Analysis and Calorimetry - In this investigation, a T-joint numerical welding simulation of thick steel plates is performed to estimate transient temperature distributions,...     

Some globally determined classes of graphs

For a class of graphs we say that it is globally determined if any two nonisomorphic graphs from that class have nonisomorphic globals. We will prove that the class of so called CCB graphs and the class of finite forests are globally determined.     

An “Ingredients” Approach to Functional Self‐Synthesizing Materials: A Metal‐Ion‐Selective,Multi‐Responsive,Self‐Assembled Hydrogel

New methodology for making novel materials is highly desirable. Here, an “ingredients” approach to functional self‐assembled hydrogels was developed. By designing a building block to contain the right ingredients, a multi‐responsive, self‐assembled hydrogel was obtained through a process of template‐induced self‐synthesis in a dynamic combinatorial library. The system can be switched between gel and solution by light, redox reactions, pH, temperature, mechanical energy and sequestration or addition of Mg^II salt.     

Solvolysis of 1,1-dimethyl-4-alkenyl chlorides: evidence for pi-participation

Tertiary 1,1-dimethyl-4-alkenyl chloride (1) solvolyzes with significantly reduced secondary beta-deuterium kinetic isotope effect (substrate with two trideuteromethyl groups) and has a lower entropy and enthalpy of activation than the referent saturated analogue 4 (k(H)/k(D) = 1.30 +/- 0.03 vs k(H)/k(D) = 1.79 +/- 0.01; Delta Delta H(++) = -9 kJ mol(-1), Delta Delta S(++) = -36 J mol(-1) K(-1), in 80% v/v aqueous ethanol), indicating participation of the double bond in the rate-determining step. Transition structure 1-TS computed at the MP2(fc)/6-31G(d) level of theory revealed that the reaction proceeds through a late transition state with considerably pronounced double bond participation and a substantially cleaved C-Cl bond. The doubly unsaturated compound 3 (1,1-dimethyl-4,8-alkadienyl chloride) solvolyzes with further reduction of the isotope effect, and a drastically lower entropy of activation (k(H)/k(D) = 1.14 +/- 0.01; DeltaS(++) = -152 +/- 12 J mol(-1) K(-1), in 80% v/v aqueous ethanol), suggesting that the solvolysis of 3 proceeds by way of extended pi-participation, i.e., the assistance of both double bonds in the rate-determining step.     

HPLC Separation of Fluorescent Products of Lipid Peroxidation in Erythrocytes and Mitochondria

Polyunsaturated fatty acids found in membrane phospholipids are readily oxidized by free radicals producing highly reactive aldehydes such as malondialdehyde. These aldehydes react with biological material to form fluorescent lipid peroxidation end products known as lipofuscin-like pigments. We studied fluorescent pigments from beef heart mitochondria incubated with malondialdehyde in vitro and from erythrocytes of patients with Alzheimer’s disease to evaluate their potential as markers of oxidative stress and to develop HPLC methods for their qualitative analysis. We used tridimensional fluorescence spectral arrays and synchronous fluorescence spectra in connection with HPLC separation with fluorescence detection. Stable fluorophores were found in both models and were successfully resolved into several distinctive fractions. This creates the basis for further characterization of this relatively less studied group of products of oxidative damage.     

Extraction of multiple pure component H and C NMR spectra from two mixtures: Novel solution obtained by sparse component analysis-based blind decomposition

Sparse component analysis (SCA) is demonstrated for blind extraction of three pure component spectra from only two measured mixed spectra in ¹³C and ¹H nuclear magnetic resonance (NMR) spectroscopy. This appears to be the first time to report such results and that is the first novelty of the paper. Presented concept is general and directly applicable to experimental scenarios that possibly would require use of more than two mixtures. However, it is important to emphasize that number of required mixtures is always less than number of components present in these mixtures. The second novelty is formulation of blind NMR spectra decomposition exploiting sparseness of the pure components in the wavelet basis defined by either Morlet or Mexican hat wavelet. This enabled accurate estimation of the concentration matrix and number of pure components by means of data clustering algorithm and pure components spectra by means of linear programming with constraints from both ¹H and ¹³C NMR experimental data. The third novelty is capability of proposed method to estimate number of pure components in demanding underdetermined blind source separation (uBSS) scenario. This is in contrast to majority of the BSS algorithms that assume this information to be known in advance. Presented results are important for the NMR spectroscopy-associated data analysis in pharmaceutical industry, medicine diagnostics and natural products research.     

Temperature effect on optical properties of the cuticle of Lucilia sericata

Optical properties of the spinal cuticle taken from the species of Lucilia sericata are studied by the reflectance measurements and their structural properties by scanning electron microscopy. The multilayer structure of the cuticle has been confirmed from the scanning electron micrographs. The temperature sensitivity of the multilayer structure is documented by the modification of optical properties in a heating process. The heating process and the local heating using the focused laser beam causes the local changes of the optical properties what is finally demonstrated by the structural color shift of the reflected spectra.     

Stabilization of the Oxidation State +IV in Siloxide‐Supported Terbium Compounds

The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of Tb^IV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six‐coordinate complex [Tb^IV(OSiPh₃)₄(MeCN)₂], 2 ‐Tb^Ph, shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong π(O?Tb) interaction which is stronger than in the previously reported Tb^IV complexes. Cyclic‐voltammetry experiments demonstrate that non‐binding counterions contribute to the stability of Tb^IV in solution by destabilizing the +III oxidation state, while alkali ions promote Tb^IV/Tb^III electron transfer.     

Ultrafast Photophysics of Regioisomeric Triphenylamine Dyes Having Dipolar D-π-A-A and Octupolar D-(π-A-A)3 Character with a Benzothiazole Unit in Matched or Mismatched Orientation

Benzothiazole is among prominent electron-withdrawing heteroarene moieties used in a variety of π-conjugated molecules. Its relative orientation with respect to the principal dipole vector(s) of chromophores derived thereof is crucial, affecting photophysical and nonlinear optical properties. Here we compare the photophysics and ultrafast dynamics of dipolar and octupolar molecules comprising a triphenylamine electron-donating core, ethynylene π-conjugated linker(s) and benzothiazole acceptor(s) having the matched or mismatched orientation (with respect to the direction of intramolecular charge transfer), while a carbaldehyde group is attached as an auxiliary acceptor. Among chromophores without the auxiliary acceptor, stronger fluorescence solvatochromism and faster excited state dynamics are exhibited for the derivatives with the mismatched geometry. On the contrary, introduction of the auxiliary acceptor to the benzothiazole unit enhances the intramolecular charge transfer ICT (featuring ultrafast dynamics of the excited state) for the matched geometry. The data confirm the crucial role of the relative orientation of asymmetric heteroaromatic unit (regioisomeric effect) in dipolar as well as in multipolar molecules in tuning linear and nonlinear optical properties as well as excited state dynamics.