Flavour quality of tomatoes

Tomato volatiles present in essential oils obtained by steam distillation–continuous extraction and by head-space condensation were identified and evaluated organoleptically. Flavour quality of different samples of fresh tomatoes, evaluated by a panel, could be related to the occurrence and concentration of n-hexanal, trans-2-hexenal, cis-3-hexen-1-ol, 2-isobutylthiazole and some unidentified compounds in the head space condensation essential oil.     

Scanning tunneling microscope spectroscopy of polymers

This paper presents theoretical results on the relationship between density of states (DOS) and scanning tunneling microscope current-voltage curves in polymers. We considered samples of linear hydrocarbons electrically grounded at one of their extremes. The other extreme is electrically connected to the microscope tip via electron tunneling through vacuum. When a voltage, V, is applied to the tip, electric current, I, flows in the tip-sample circuit. This current varies as the voltage varies and depends on the DOS to the extent that no current would flow if no electron states exist at a certain energy (or voltage). The detailed relationship between DOS and the current-voltage (I-V) curve is not known a priori. We solve the corresponding quantum problem in the context of tight binding and find that I-V reproduces accurately the resonant energy peaks of the DOS. We apply the results to 100 atom-long alkane and alkene chains and found that there is a significant voltage shift in the corresponding curves as to discriminate one structure from the other.     

Generalization of equivalent crystal theory to include angular dependence

The original equivalent crystal theory is a semi-empirical method for calculating the configurational energy of atomic systems. Each atomic site in the real crystal with defects is assigned an equivalent lattice constant, in general different from the ground state value. This parameter corresponds to a local compression or expansion of the perfect lattice. The basic method considers these volumetric transformations and, in addition, introduces the possibility that the reference lattice is anisotropically distorted. These distortions however, were introduced ad-hoc. In this work, we generalize the original Equivalent Crystal Theory by introducing site-dependent directional distortions of the lattice which account for the dependence of the energy on anisotropic local density variations. This is done in the spirit of the original framework of ECT, but includes a gradient in the density. This approach is introduced to ECT and may apply to other semi-empirical methods by making use of readily available first-principles results to fix parameters. We develop here the basic framework, and apply it to the calculation of Fe(1 1 0) and Fe(1 1 1) surface energy formation, and to the vacancy energy curve. The results, compared with first-principles calculations, show an improvement over previous semi-empirical approaches.     

Experimental evaluation of nonlinearities of small-sized insertable gradient coils

A phase imaging technique is proposed to map out and quantify gradient nonlinearities of small-sized insertable gradient coils, assuming the whole-body system gradients are highly linear in the domain of interest. The theory is developed and simple equations are derived to allow quantification. It is applied to a 4-loop 18-cm diameter cylindrical gradient coil of optimal design. Experimental gradient nonlinearity maps are obtained for different fields of view. Gradient non-linearities are quantified locally and in regions of interest, showing close agreement with model data.     

Low temperature heat source for power generation: Exhaustive analysis of a carbon dioxide transcritical power cycle

The main results of a theoretical work on the use of a low temperature heat source for power generation through a carbon dioxide transcritical power cycle are reported in this paper. The procedure for analyzing the behaviour of the proposed cycle consisted in modifying the input pressure to the turbine from 66 bar, maintained constant each evaluated temperature (60 °C, 90 °C, 120 °C and 150 °C) until the net work was approximately zero. As a result, the maximum exergy efficiency was 50%, while the energy efficiencies obtained were 9.8%, 7.3%, 4.9% and 2.4% and the net specific work was 18.2 kJ/kg, 12.8 kJ/kg, 7.8 kJ/kg and 3.5 kJ/kg, respectively. Furthermore, the effect of the addition of an internal heat exchanger, which obviously supposed an increase in the efficiency, was analyzed. The analysis of the proposed system shows the viability of implementing this type of process as an energy alternative and/or strengthener of non-conventional energy sources in non-provided zones, or for increasing the energy efficiency in the industry.     

Partitioning of Fatty Acids in Oil/Water Systems Analyzed by HPLC

Surfactant/oil/water systems in which the surface-active substance is a mixture of an undissociated fatty acid (FA) and its sodium salt soap, exhibit the typical phase behavior and the general emulsion phenomenology produced by a formulation scan. The phase behavior transition is induced by changing the FA concentration in the system at a fixed alkaline (NaOH) content in water, which results in a variable lipophilic acid/hydrophilic salt ratio. The partitioning is reported for different FA types (octanoic to myristic) and alcohol co-surfactants between excess oil and water phases of Winsor three-phase optimum formulation system. The concentrations are determined by using a method reported in a previous work to quantify the total acid fraction in each phase.

Modified solvent accessibility free energy prediction analysis of cyclic urea inhibitors binding to the HIV-1 protease

One of the most successful drug targets against AIDS in thelast decade has been the HIV-1 protease (HIV-1 PR), an enzymethat processes the polyprotein gene products into active replicativeviral proteins. In our quest for a wide-ranging, binding freeenergy function we have extended the solvent accessibility freeenergy predictor (SAFE_p) method, recently developed for peptidicHIV-1 PR inhibitors, to the study of the binding of cyclic urea(CU) HIV-1 PR inhibitors. Our results show that there is a needfor a specific term depicting polar contacts to be added tothe original SAFE_p analytical expression, an outcome not seenin our studies of HIV-1 PR peptidic inhibitors. Nevertheless,despite the higher profile of the electrostatic interactionsin the binding of the CU inhibitors, our analysis indicatesthat CU inhibitor binding is still driven by the hydrophobicentropic contribution, as much as for the peptidic inhibitors.