Microscopic view on Landau level broadening mechanisms in graphene

Placing a two-dimensional sheet of graphene in an external magnetic field the continuous electronic band structure is discretized due to Landau quantization. The resulting optical transitions are subject to a broadening, which can lead to a significant overlap of Landau levels. We investigate the possible microscopic processes that could cause a broadening of the corresponding peaks in the absorption spectrum of Landau-quantized graphene: (i) radiative decay, (ii) Coulomb interaction, (iii) optical phonons, (iv) acoustic phonons, and (v) impurities. Since recent experiments have shown that independent of the magnetic field the resolvable number of Landau levels is constant, we put a special focus on the dependence of the broadening on the external magnetic field B and the Landau level index n. Our calculations reveal the impurities to be the crucial broadening mechanism, where different regimes of well separated and densely spaced Landau levels need to be taken into account. Furthermore, carrier-carrier and carrier-phonon scattering give rise to a very specific dependence on the Landau level index n that has not been observed yet

Energy transfer in porphyrin-functionalized graphene

We present a theoretical study on the molecule–substrate interaction within the porphyrin-functionalized graphene. Recent experiments on porphyrin-functionalized carbon nanotubes have revealed an extremely efficient energy transfer from the adsorbed molecules to the carbon substrate. To investigate the energy transfer mechanism, we have characterized the hybrid structure within the density functional theory including the calculation of the molecular transition dipole moment, which allows us to determine the Förster coupling rate. We find a strongly pronounced Förster-induced energy transfer in the range of fs−1 inline image confirming the experimental observations

Sustainable rural development in Serbia - relationship between population dynamicss and environment

In this paper the relationship between populatiOn and the environment, and their influence on rural sustainability in Serbia, using quantitative typology of rural areas will be examined. The typology is based on the net relative change of population in rural areas in Serbia, according to the difference between the number of inhabitants at the end of the studied period (2011) and a hypothetical population that each rural settlement would have if the population in base year (1961) was changed proportionally to the change of total rural population. Research results indicate types of population dynamics of rural areas with different scale and intensity of environmental degradation: progressive type with favorable human and economic potentials, strong urban influence and huge environmental transformation; stagnant type with advanced agricultural and demographic dimension which imposed pressures to the natural environment; regressive type with heterogeneous demographic, social and economic features, and different impacts on natural and social environment, and dominant regressive type of rural areas highly characterised by the deficient in human and economic potential and preserved natural resources. Based on analysed rural particularities it can be concluded that the different human, environmental and economic potentials and obstacles of determined types of rural areas should be the starting point in defining appropriate sustainable strategies and development directions

Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

Accurate and reliable analysis of polymers by GPC is vital in the field of controlled radical polymerisation. Often, water-soluble polymers are analysed by aqueous gel permeation chromatography (GPC) in a solvent containing dilute sodium azide as an anti-microbial agent. Previous reports have shown that sodium azide at high concentration is able to remove terminal CTA groups from polymer chains, producing thiol-terminated polymers. This study demonstrates that GPC sample preparation of RAFT polymers in aqueous solvents containing dilute (200 ppm) sodium azide can cause significant changes in the measured molecular weight distribution. These changes occur within hours of dissolving the polymer sample and are shown to be due to cleavage of the CTA in the polymer chain together with disulfide coupling of the resulting polymeric thiols. The extent to which this occurs is strongly dependent on the CTA attached to the polymer; an almost 10-fold difference in the rate of CTA removal is observed between different RAFT agents. The by-product of the reaction between sodium azide and RAFT polymers is also investigated and shown to be an unstable thiatriazole-functionalised Z group. The thiatriazole then degrades further to form a nitrile-functionalised Z group, N2 and elemental sulfur

Ultra-fast aqueous polymerisation of acrylamides by high power visible light direct photoactivation RAFT polymerisation

The effect of visible LED power (λmax = 402 nm, 451 nm) on kinetics and control of direct photoactivation RAFT polymerisations of acrylamide and dimethylacrylamide are investigated. By increasing power supplied to the LEDs from 6 to 208 W, the polymerisation time required to reach >85% conversion is reduced from 12 hours to 11 minutes for acrylamide. Similar conversions are shown to be obtainable in 5 minutes for dimethylacrylamide, all without any exogenous photoinitiator or catalyst. This increase in polymerisation rate is attributed to an increase in both photon flux and a coincident increase in polymerisation temperature at higher light intensities. With both 402 nm and 451 nm LEDs exciting the same n → π* electronic transition, little difference in rate of polymerisation is seen between the two light sources. Minimal reduction in polymerisation control is observed at high irradiation intensity for acrylamide, while an increased production of low molecular weight dead chains is observed for dimethylacrylamide. This is shown to be mitigated by controlling the polymerisation temperature to 17 °C which caused both a reduction in low molecular weight tailing and an increased polymerisation time. Visible light direct photoactivation RAFT is also shown to have application in the synthesis of ultra-high molecular weight acrylamide polymers (Mn > 1 000 000 g mol−1)

Candida biofilms and oral candidosis : treatment and prevention

In recent years, there has been a significant increase in the incidence of human fungal infections (60). A number of factors have been implicated with this increase, but it is generally accepted that the main influences relate to the more widespread provision of new medical practices, such as immunosuppressive therapy and use of broad spectrum antibiotics, and invasive surgical procedures such as solid organ or bone marrow transplantation. Infections may either be superficial, affecting the skin, hair, nails and mucosal membranes, or systemic, involving major body organs (95). The risk of systemic infection appears to be enhanced in cases where the individual is already colonized by Candida (71). With regard to superficial mucosal infections, the continued spread of HIV infection (29) and the more extensive use of inhaled steroids (36) have also played significant roles

Efficient Auger scattering in Landau-quantized graphene

We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene

Carbon nanotubes as substrates for molecular spiropyran-based switches

We present a joint theory–experiment study investigating the excitonic absorption of spiropyran-functionalized carbon nanotubes. The functionalization is promising for engineering switches on a molecular level, since spiropyrans can be reversibly switched between two different conformations, inducing a distinguishable and measurable change of optical transition energies in the substrate nanotube. Here, we address the question of whether an optical read-out of such a molecular switch is possible. Combining density matrix and density functional theory, we first calculate the excitonic absorption of pristine and functionalized nanotubes. Depending on the switching state of the attached molecule, we observe a red-shift of transition energies by about 15 meV due to the coupling of excitons with the molecular dipole moment. Then we perform experiments measuring the absorption spectrum of functionalized carbon nanotubes for both conformations of the spiropyran molecule. We find good qualitative agreement between the theoretically predicted and experimentally measured red-shift, confirming the possibility for an optical read-out of the nanotube-based molecular switch

Sustainable rural development in Serbia - relationship between population dynamicss and environment

In this paper the relationship between populatiOn and the environment, and their influence on rural sustainability in Serbia, using quantitative typology of rural areas will be examined. The typology is based on the net relative change of population in rural areas in Serbia, according to the difference between the number of inhabitants at the end of the studied period (2011) and a hypothetical population that each rural settlement would have if the population in base year (1961) was changed proportionally to the change of total rural population. Research results indicate types of population dynamics of rural areas with different scale and intensity of environmental degradation: progressive type with favorable human and economic potentials, strong urban influence and huge environmental transformation; stagnant type with advanced agricultural and demographic dimension which imposed pressures to the natural environment; regressive type with heterogeneous demographic, social and economic features, and different impacts on natural and social environment, and dominant regressive type of rural areas highly characterised by the deficient in human and economic potential and preserved natural resources. Based on analysed rural particularities it can be concluded that the different human, environmental and economic potentials and obstacles of determined types of rural areas should be the starting point in defining appropriate sustainable strategies and development directions