Depolarization current of novolac phenol-formaldehyde resins doped with 1,4-diazabicyclo [2.2.2] octane

Mixtures of novolac phenol-formaldehyde (NPF) resins and 1,4-diazabicyclo [2.2.2] octane (DABCO) were polarized at different temperatures applying different d. c. electric fields. Thermally stimulated depolarization current (TSDC) measurements performed from 298 to 373 K showed a dipolar α peak and a space charge α peak as in pure NPF. The addition of DABCO decreases the magnitude of the α peak and the activation energy of the dipolar relaxation but increases the background current and the magnitude of the α peak significantly. The maximum of the α peak is only slightly shifted towards higher temperatures. New aspects in the analysis of the background current by consecutive heating and cooling experiments are considered. The results obtained show an increase in concentration of trapping sites due to the heterogeneity of the mixed systems. The proposed interactions between nitrogen from DABCO and hydroxy groups from NPF are discussed.     

Why we believe the computer when it lies

A survey was conducted on the sample of 60 future engineers in order to determine whether inadequate computer feedback changes the supposed success in problem solving and whether personality traits are also in the function of this change. The research results showed that personality traits fail to influence the formation of beliefs on success. Results also showed that the situation of inadequate feedback results in the changes in beliefs, on the success in problem solving and that the change is in the function of personality traits and established experience-based behavior strategies. In this situation respondents do not form any strategy for attitude conservation, but inadequate computer feedback significantly reduces estimation of their success regardless to the fact that the objective achievement is not reduced.     

Thermal Lens Spectrometry: Still a Technique on the Horizon?

In this article, the historical development of thermal lens spectrometry (TLS) is briefly reviewed as an introduction. In continuation, the emphasis is on the recent progresses of TLS for measurements in ensembled sample cells and in microfluidic flow injection systems. Novel theories, instrumentation and their applications for high sample throughput for environmental, chemical and biomedical analysis, as well as thermal characterization and imaging, particularly in microspace, are presented. Discussion is given on the limitations of present TLS systems that open new horizons for future progress of this technique, which has already found place among routine techniques for chemical analysis. In the final section, proposals for the future development of TLS towards advanced applications in new research fields are presented.     

Numerically assisted analysis of flat and corrugated plate solar collectors thermal performances

The paper presents the results of experimentally supported numerical analysis performed in order to investigate the possibilities to improve the thermal efficiency of plate solar collectors. Different numerical models were developed in order to asses the influence of design and operating parameters such as bond conductance between absorber plate and tube, tube diameter, glass cover to absorber plate distance, optical properties of absorber and flow rate on thermal efficiency of collectors. Following the results, two designs of collector without tubes, with parallel flat and corrugated absorber plates of chevron type, is further considered and shown to be an effective way to increase the thermal efficiency of solar energy conversion beyond that of commercial glazed and unglazed solar water heaters. Based on the results, the guidelines for design of a new collector prototype consisting of chevron type corrugated plates normally used in plate heat exchangers are provided.     

The international publication productivity of Latin American countries in the economics and business administration fields

The present study compares the international publication productivityof Latin American countries in the fields of business administration and economicsfrom 1995 to 1999. Only four countries – Argentina, Brazil, Chile, andMexico – have a substantial research production in these areas. Amongthese countries, Chile showed the most favorable results according to variousindicators of publication productivity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ionic liquids as an attractive alternative solvent for thermal lens measurements

The use of ionic liquids (ILs) as a solvent for thermal lens measurements has been investigated. It was found that ILs provide a better medium for thermal lens measurements than water. Specifically, not only the ILs offer at least 20 times higher sensitivity than water but that the enhancement can be appropriately adjusted by changing either the cation or the anion of the ILs. For example, the sensitivity in [BMIm]+[Tf2N]- is approximately 26 times higher than in water. It can be increased up to 31 times by changing the anion to [PF6]- (i.e., [BMIm]+[PF6]-) or to 35 times by changing the cation to [OMIm]+ (i.e., [OMIm]+[Tf2N]-). In fact, the sensitivity of thermal lens measurements in ILs is comparable to those in volatile organic solvents such as benzene, carbon tetrachloride, and hexane. However, the ILs are more desirable as they have virtually no vapor pressure. Furthermore, additional sensitivity enhancement (up to 42 times higher than that in water) can be achieved by simply adding surfactants into the ILs. Based on the thermal conductivity (k) and dn/dT values, calculated from the measured thermal time constant tc and thermal lens strength theta, it is evident that the observed sensitivity enhancement by the ILs is due to their relatively better thermooptical properties. More specifically, the enhancement is due not to the relatively modest lowering of the thermal conductivity but rather to the substantial increase in their dn/dT values. Because of the relationship between dn/dT and drho/dT, it is expected that ILs can serve as an attractive and superior solvent not only for thermal lens measurements but also for other photothermal and photoacoustic techniques as well. Also equally important is the fact that the thermal lens technique in particular and photothermal techniques, in general, can offer a unique means to determine themooptical and thermal physical properties of the ILs (e.g., thermal conductivity, thermal diffusivity, and phase transition temperatures). This type of data is currently lacking but is of extreme importance for implementing ILs as a solvent in various industrial applications.     

Composite nanowire-based probes for magnetic resonance force microscopy

We present a nanowire-based methodology for the fabrication of ultrahigh sensitivity and resolution probes for atomic resolution magnetic resonance force microscopy (MRFM). The fabrication technique combines electrochemical deposition of multifunctional metals into nanoporous polycarbonate membranes and chemically selective electroless deposition of optical nanoreflector onto the nanowire. The completed composite nanowire structure contains all the required elements for an ultrahigh sensitivity and resolution MRFM sensor with (a) a magnetic nanowire segment providing atomic resolution magnetic field imaging gradients as well as large force gradients for high sensitivity, (b) a noble metal enhanced nanowire segment providing efficient scattering cross-section from a sub-wavelength source for optical readout of nanowire vibration, and (c) a nonmagnetic/nonplasmonic nanowire segment providing the cantilever structure for mechanical detection of magnetic resonance.