SubcriticalWater – a Perspective ReactionMedia for Biomass Processing to Chemicals: Study on Cellulose Conversion as aModel for Biomass

Biomass and water are recognized as a key renewable feedstock in sustainable production of chemicals, fuels and energy. Subcritical water (SubCW), or commonly referred as hot compressed water (HCW), is the water above boiling and below critical point (CP; 374 °C, 22.1 MPa). It has gained great attention in the last few decades as a green, cheap, and nontoxic reagent for conversion of biomass into valuable chemicals. In this paper, hydrothermal reactions of cellulose, as the model biomass substance, with subcritical water at mild temperature and pressure regimes have been studied. The experiments were done in a batch reactor in the temperature range of 220 ° – 300 °C. The main products distributed in liquid, gaseous and solid phase were separated and quantified. The conversions to each group of products were found strongly dependent on the temperature and residence time

Strain and band-mixing effects on the excitonic Aharonov-Bohm effect in In(Ga)As/GaAs ringlike quantum dots

Neutral excitons in strained axially symmetric In(Ga)As/GaAs quantum dots with ringlike shape are investigated. Similar to experimental self-assembled quantum rings, the analyzed quantum dots have volcano-like shapes. The continuum mechanical model is employed to determine the strain distribution, and the single-band envelope function approach is adopted to compute the electron states. The hole states are determined by the axially symmetric multiband Luttinger-Kohn Hamiltonian, and the exciton states are obtained from an exact diagonalization. We found that the presence of the inner layer covering the ring opening enhances the excitonic Aharonov-Bohm (AB) oscillations. The reason is that the hole becomes mainly localized in the inner part of the quantum dot due to strain, whereas the electron resides mainly inside the ring-shaped rim. Interestingly, larger AB oscillations are found in the analyzed quantum dot than in a fully opened quantum ring of the same width. Comparison with the unstrained ring-like quantum dot shows that the amplitude of the excitonic Aharonov-Bohm oscillations are almost doubled in the presence of strain. The computed oscillations of the exciton energy levels are comparable in magnitude to the oscillations measured in recent experiments.Comment: 16 pages, 9 figures, accepted for publication in Physical Review

Necessary and sufficient condition for L1L^1-convergence of cosine trigonometric series with δ-quasimonotone coefficients

For a cosine trigonometric series with coefficients in the class S_p(δ), 1 < p ≤ 2, the necessary and sufficient condition for L^1 -convergence is obtained

International mathematical olympiad

Today mathematical competitions are very popular with primary and secondary school students and there are many countries all around the world where they are regularly organised. There are several rounds and a lot of students are included, especially at the beginning rounds. The best students from the previous round have the right to continue on the higher level of competition. The final level for the secondary school student competitors is the International Mathematical Olympiad (IMO). The team for the IMO from Croatia is determined at the National Competition which is held in May. The first mathematical competitions were organised in Hungary in 1894, and in Romania in 1898. Mathematical competitions in Croatia for the secondary school students started in 1959 and next year the first Federal Competition was held, which was then organised every year until 1991. Romania was the initiator of the first international competition. The idea of organizing it came from the Romanian mathematician {it Tiberiu Roman in 1956, and mathematics is still his great love, although he is 83 years old. After detailed preparations the first International Mathematical Olympiad was held in Romania in 1959, as well as the second one in 1960. At the beginning only the following countries from the Eastern Europe participated: Bulgaria, East Germany, Czechoslovakia, Hungary, Poland, Romania and the USSR. In 1963 Yugoslavia participated for the first time, and after that new and new countries from Europe arrived. The first Olympiad in Yugoslavia took place in Cetinje, Montenegro, in 1967, and the second one in Belgrade in 1977. 21 countries took part at that 19th IMO. Cuba was the first non-European country which participated at the 13th IMO, in 1971, and it was the host country in 1987. Australia participated for the first time at the 22nd IMO in 1981, and was the host country in 1988, when the 200th anniversary of Europeans inhabiting that continent was. In 1980 the IMO was not organized, and only some local olympiads were held. In 1993 Croatia as well as Bosnia and Herzegovina, Macedonia and Slovenia became regular members of IMO. In 1999 the 40th IMO was organized in Romania, and it was the fifth one held in this country (the previous ones had been held in 1959, 1960, 1969, 1978). During the last few years there where about 80 countries and 450 contestants at the IMO

On a theorem of S.S.Bhatia and B.Ram

In this paper some inequalities for Dirichlet\u27s and Fejer\u27s kernels proved in [6] are refined and extended. Then we have obtained the conditions for L^1-convergence of the r-th derivatives of complex trigonometric series. These results are extensions of corresponding Bhatia\u27s and Ram\u27s results for complex trigonometric series (case r=0)

Orbital magnetic moments in insulating Dirac systems: Impact on magnetotransport in graphene van der Waals heterostructures

In honeycomb Dirac systems with broken inversion symmetry, orbital magnetic moments coupled to the valley degree of freedom arise due to the topology of the band structure, leading to valley-selective optical dichroism. On the other hand, in Dirac systems with prominent spin-orbit coupling, similar orbital magnetic moments emerge as well. These moments are coupled to spin, but otherwise have the same functional form as the moments stemming from spatial inversion breaking. After reviewing the basic properties of these moments, which are relevant for a whole set of newly discovered materials, such as silicene and germanene, we study the particular impact that these moments have on graphene nanoengineered barriers with artificially enhanced spin-orbit coupling. We examine transmission properties of such barriers in the presence of a magnetic field. The orbital moments are found to manifest in transport characteristics through spin-dependent transmission and conductance, making them directly accessible in experiments. Moreover, the Zeeman-type effects appear without explicitly incorporating the Zeeman term in the models, i.e., by using minimal coupling and Peierls substitution in continuum and the tight-binding methods, respectively. We find that a quasiclassical view is able to explain all the observed phenomena