Curvature Computations of 2-Manifolds in $\mathbb{R}^k$

In this paper, we provide simple and explicit formulas for computing Riemannian curvatures, mean curvature vectors, principal curvatures and principal directions for a 2-dimensional Riemannian manifold embedded in IR^k with k ≥ 3.     

Shallow impurity centers in semiconductor quantum well structures

Interest in the study of the behavior of shallow impurity centers in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last few years. Several recent calculations of the energy levels of hydrogenic impurity states in quantum well structures, such as Ga_1?xAl_xAsGaAsGa_1?xAl_xAs, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. Recent experimental data concerning the variations of the binding energies of shallow donors and acceptors as a function of the GaAs quantum well size are reviewed. A comparison between these experimental measurements and the results of recent calculations is presented.     

A Case Study on the Use of Fractional Derivatives: The Low-Frequency Viscoelastic Uni-Directional Behavior of Polyurethane Foam

A fractional derivative model of dissipative effects is combined with a nonlinear elastic model to model the response of polyurethane foam in quasi-static compression tests. A system identification method is developed based on a separation of the elastic and viscoelastic parts of the response, which is possible because of symmetries in the imposed deformation time-history. Simulations are used to evaluate the proposed identification method when noise is present in the response. The system identification technique is also applied with some success to experimental data taken from several compression experiments on two types of polyurethane foam blocks.     

Two colour multiphoton ionization spectroscopy of uranium from a metastable state

Using two pulsed tunable dye lasers, a two colour multiphoton ionization process has been utilised to explore the higher energy levels of uranium. One hundred and thirty eight new UI levels have been observed in the 37540–38420 cm^–1 region. J assignments of these levels have been suggested on the basis of their excitation from intermediate levels with known and contiguous J values. In eight cases the J assignments are unique.     

Estimation of the dynamical properties of polyurethane foam through use of Prony series

A system identification procedure is formulated for estimation of parameters associated with a dynamic model of a single-degree-of-freedom foam-mass system. The foam is modelled as a linear viscoelastic material, whose constitutive law is expressed by an exponential hereditary relaxation kernel. The identification procedure is based on modelling the free response of the system as a Prony series (sum of exponentials terms) and fitting this Prony series to the data. This estimated response model is then utilized to estimate the parameters in the system model based on an explicit solution of the model. The procedure is analyzed for its reliability under different sources of error and uncertainties, such as the presence of weak components and experimental noise, and some modifications are evaluated to improve the robustness of the procedure. Finally, the procedure is applied to experimental data to obtain relevant stiffness, viscous and viscoelastic parameters associated with the system. Variations in values of these parameters as a function of static compression are also investigated.     

Promising anticancer drug thapsigargin: A perspective toward the total synthesis

The guaianolide ring containing sesquiterpene thapsigargin is found in the roots and fruits of Mediterranean plant Thapsia garganica L. It is known for its activity as a potent antagonist for Ca²⁺-ATPase (sarco–endoplasmic reticulum Ca²⁺-ATPase) inhibition. Recently, a prodrug mipsagargin is being investigated to target the blood vessel of the cancer cells for the treatment of tumors. The limited natural supply (low isolation and only localized growth (Mediterranean area)) from the natural sources strongly urges for the development of chemical synthetic strategies to access these natural products. This review pertain the various strategies used so far in the thapsigargin’s synthesis, focusing on major contributions in the total synthesis till date.     

Aromatic-aliphatic copolyesters—II. Various polycondensation processes

Aromatic aliphatic copolyesters, using hydroquinone, resorcinol, 4,4′-dihydroxybiphenyl (DHBP) 2,2 bis(4-hydroxyphenyl)propane and 4,4′-dihydroxydiphenyl sulphone (DHDPS) as bisphenols and ethylene glycol as diol, have been synthesized by interfacial, low temperature and high temperature solution condensation. Relative reactivities of these bisphenols and ethylene glycol have been evaluated by various polycondensation methods at a fixed ratio of bisphenol/glycol. Decrease in the extent of polymerization and viscosity was observed by incorporation of aliphatic diol. Viscosity was also influenced by the chemical structure of the bisphenol.     

Selective oxidation of cyclohexane by a Ru(III) analogue of the gif-system. RuIIIacetic acid-pyridine-KHSO5

Selective oxidation of cyclohexane to cyclohexanone was carried out in a RuCl₃-pyridine-acetic acid-KHSO₅ mixture. This system yields 2.8% of cyclohexanone (based on oxone concentration) under the conditions employed. Mechanistic postulate for the oxidation reaction involves the formation of a carbene intermediate (Ru=C) prior to the ketone formation.