Transmission phase lapses at zero energy in graphene quantum dots

We address theoretically the electronic transport through graphene quantum dots with the emphasis on the transmission phase. Analytical and numerical results are presented regarding the existence – or not – of a π lapse of the transmittance phase (and, consequentially, a Fano zero in the transmittance) at the charge neutrality point. A simple universal criterium is found, the phase lapses being always present if the contact sites belong to the same sub‐lattice. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Vibrating Portable Machine-Tools Acting on Human Operator

This paper will be a short presentation of the specialized literature and international standards about the importance of vibration action of portable machine tools on human body and particularly on the hand-arm system. Exposure to harmful vibrations can lead to health problems and disorders, especially in the upper joints and dorsal region of the human body. A detailed understanding of the undesirable effects of vibration on the human body is essential to achieve administrative and technical prevention. In modern times, vibration studies become more frequent, decisive for the many machines, vehicles and construction. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Market efficiency of the Post Communist East European stock markets

The stock markets from Post Communist East-European Countries are still considered highly speculative. For this reason, the previously performed tests often infirmed the efficient market hypothesis. However, especially in the past years, different studies revealed an improvement in the level of efficiency. In this context, our paper has tested the predictability of returns based on past records (as a proxy for the weak-form efficiency) for the market index and the most important stocks of 20 East European former communist countries: Bosnia-Herzegovina, Bulgaria, Croatia, Czech Republic, Estonia, Georgia, Hungary, Kazakhstan, Latvia, Lithuania, Former Yugoslav Republic of Macedonia, Moldova, Montenegro, Poland, Romania, Russia, Serbia, Slovakia, Slovenia, and Ukraine, for the period January 2008–December 2010, a period of financial crisis for most of these countries. Various methods for testing were used (unit root tests, runs test, variance ratio test, filter rules test and the January Effect). The tests have revealed that for some assets the efficient market hypothesis cannot be rejected. However, the results have shown that there are serious doubts concerning the stock market efficiency for all the countries in the analyzed period. Moreover, heterogeneity between the results for different countries was revealed. A higher level of market efficiency can suggest to decision-makers the use of passive portfolio management techniques while a lower level of efficiency implies the use of active portfolio management instruments.     

Multitime Dynamic Programming for Curvilinear Integral Actions

This paper justifies dynamic programming PDEs for optimal control problems with performance criteria involving curvilinear integrals. The main novel feature, relative to the known theory, is that the multitime dynamic programming PDEs are now connected to the multitime maximum principle. For the first time, an interesting and useful connection between the multitime maximum principle and the multitime dynamic programming is given, characterizing the optimal control by means of a PDE system that may be viewed as a multitime feedback law.     

On the Electrical and Optical Properties of Some Poly(Azomethine Sulfone)s in Thin Films

Poly(azomethine sulfone)s were synthesized by reacting 4,4′-sulfonyl bis(4-chlorophenyl) with 2,2-bis(4-hydroxyphenyl)propane and azomethine bisphenol in different molar ratios. Thin films were deposited from solution onto glass substrates. Study of the temperature dependences of the electrical conductivity, σ, and Seebeck coefficient, S, were performed in the temperature range 300 K–500 K. Thermal activation energies of electrical conduction, E_a , calculated from these dependences, ranged between 1.50 eV and 1.85 eV. The values of E_a were smaller for polymers with extended conjugation systems. The possibility to use the polymers in thermistor technology is discussed. The aspect of the temperature dependences of σ and S shows that a model based on the energy band-gap representation can be successfully used for explaining the electronic transport mechanism in the higher temperature range. In the lower temperature range, the mechanism of the electrical conduction is discussed in terms of the Mott variable range hopping conduction. The values of some optical parameters (absorption coefficient, optical band gap, etc.) were determined from transmission spectra.     

Extrema Constrained by a Family of Curves and Local Extrema

This paper considers the connections between the local extrema of a function f:DR and the local extrema of the restrictions of f to specific subsets of D. In particular, such subsets may be parametrized curves, integral manifolds of a Pfaff system, Pfaff inequations. The paper shows the existence of C ¹ or C ²-curves containing a given sequence of points. Such curves are then exploited to establish the connections between the local extrema of f and the local extrema of f constrained by the family of C ¹ or C ²-curves. Surprisingly, what is true for C ¹-curves fails to be true in part for C ²-curves. Sufficient conditions are given for a point to be a global minimum point of a convex function with respect to a family of curves.