Ultrafast Momentum Imaging of Pseudospin-Flip Excitations in Graphene

The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photo-excited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization, and are maximum perpendicular to it. Here, we use time- and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy and in-plane momentum. We first show that the rapidly-established quasi-thermal electron distribution initially exhibits an azimuth-dependent temperature, consistent with relaxation through collinear electron-electron scattering. Azimuthal thermalization is found to occur only at longer time delays, at a rate that depends on the substrate and the static doping level. Further, we observe pronounced differences in the electron and hole dynamics in n-doped samples. By simulating the Coulomb- and phonon-mediated carrier dynamics we are able to disentangle the influence of excitation fluence, screening, and doping, and develop a microscopic picture of the carrier dynamics in photo-excited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photo-control experiments and optoelectronic device applications.Comment: 23 pages, 12 figure

Assessment of the Patient\u27s Education and Motivation in the Maintaince of Oral Hygiene

Zadovoljavajuća oralna higijena je conditio sine qua non u prevenciji karijesa i parodontnih bolesti. Prihvaćanje informacija za održavanje oralne higijene ovisi o više čimbenika među kojima su: pacijentova dob, stupanj naobrazbe, inteligencija, druπtveno-ekonomski status itd. Prijašnje studije su utvrdile da se gotovo 50% ljudi u održavanju oralne higijene služi samo četkicom (Karihovski B et al., 2001). Malendijk B et al 1995. Koivusilt A et al. 2003, pokazali su da ljudi s nižim stupnjem naobrazbe rijetko ili nikako ne čiste svoje zube. Ukupno 117 slučajno odabranih pacijenata koji su liječeni na klinikama Stomatološkog fakulteta uključeno je u ovu studiju. Svi pacijenti su uredno ispunili upitnik koji je posebno pripremljen za tu prigodu. Najveći dio pacijenata u našoj studiji imali su visoku i srednju školsku naobrazbu (33,3%, odnosno 43,6%). Visok postotak ispitanika već je prije dobio upute kako održavati oralnu higijenu i to od: stomatologa i medija 63,8%, stomatologa i laika 54,6%, dok je stomatolog sa stomatološkom sestrom bio zastupljen u 47 % slučajeva. Više od 61% ispitanika smatra da je dobilo dovoljno uputa u održavanju oralne higijene i da ih nije potrebno ponavljati. Ispitanici su upotrebljavali samo četkicu za zube u održavanju higijene usta u 50% slučajeva. Najveći broj pacijenata koristio se je četkicom dva puta na dan (79,5%), a četkicu pacijenti najčešće mijenjaju unutar tri mjeseca. U slučaju kada nastane neki stomatološki problem jedna četvrtina pacijenata odgađa intervenciju. Dobiveni su rezultati pokazali da je održavanje oralne higijene u naših pacijenata bilo na zadovoljavajućem stupnju. Ovakav rezultat mogao bi proizlaziti iz visoke opće razine naobrazbe naših ispitanika i iz već prije dobivenih naputaka kako održavati oralnu higijenu.Good oral hygiene is conditio sine qua non in prevention of dental caries and periodontal diseases. The acceptance of obtained information related to maintain good oral hygiene depends on several factors such as: age, educational level, personal skill, socioeconomic level etc. Previous studies revealed that almost 50 % of the general population use a toothbrush only to maintain their oral hygiene (Karihovski B et al., 2001). Malendijk B et al 1995, Koivulsit A et al., 2003, showed that people with a lower level of general education very rarely, or not at all, brush their teeth. A total of 117 randomly selected patients who attend the Clinics at our Faculty was enrolled in our study. All of them agreed to fulfill the questionaire designed by the investigators. The majority of our patients were highly educated (high school and university degree; 33.3 % and 43.6% respectively). A high percentage of the investigated patients were already educated in oral hygiene through their dentist and media (63.8%), dentist and non-preofessionals (54.6%) and dentist and dental nursing stuff in 47% of cases. A relatively high percentage (61.5%) of the investigated patients consider that there is no need for additional instructions related to oral hygiene. More than 50% of our cases only use toothbrush in their oral hygiene. The frequency of brushing the teeth was twice daily in the majority of the investigated patients, while replacements of an old toothbrush with a new one within a period of 3 months was in 79.5% of cases. One quater of the investigated patients who suffer from some kind of dental problem do not ask immediately for dental intervention. Our results have shown that the level of maintenanace of oral hygiene is rather high. Such results could be related to the high level of general education of the subjects enrolled in the study, and previously obtained education in oral hygiene

Characteristics and drivers of forest cover change in the post-socialist era in Croatia: evidence from a mixed-methods approach

© 2016, Springer-Verlag Berlin Heidelberg.Extensive forests in Croatia represent an important biological and economic resource in Europe. They are characterised by heterogeneity in forest management practices dating back to the socialist planned economy of the pre-1991 era. In this study we investigated the difference in rates of deforestation and reforestation in private- and state-owned forests during the post-socialist period and the causal drivers of change. The selected region of Northern Croatia is characterised by a high percentage of privately owned forests with minimal national monitoring and control. We used a mixed-methods approach which combines remote sensing, statistical modelling and a household-based questionnaire survey to assess the rates of forest cover change and factors influencing those changes. The results show that predominantly privately owned forests in Northern Croatia have recorded a net forest loss of 1.8 % during the 1991–2011 period, while Croatia overall is characterised by a 10 % forest cover increase in predominantly state-owned forests. Main factors influencing forest cover changes in private forests are slope, altitude, education structure, population age and population density. The results also show that the deforestation in private forests is weakening overall, mostly due to the continuation of the de-agrarisation and de-ruralisation processes which began during socialism

Multi-dimensional modeling and simulation of semiconductor nanophotonic devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources

Ultrafast nonequilibrium carrier dynamics in a single graphene layer

Nonequilibrium carrier dynamics in single exfoliated graphene layers on muscovite substrates are studied by ultrafast optical pump-probe spectroscopy and compared with microscopic theory. The very high 10-fs-time resolution allows for mapping the ultrafast carrier equilibration into a quasi-Fermi distribution and the subsequent slower relaxation stages. Coulomb-mediated carrier-carrier and carrier-optical phonon scattering are essential for forming hot separate Fermi distributions of electrons and holes which cool by intraband optical phonon emission. Carrier cooling and recombination are influenced by hot phonon effects

Activation of innate and adaptive immunity by a recombinant human cytomegalovirus strain expressing an NKG2D ligand

Development of an effective vaccine against human cytomegalovirus (HCMV) is a need of utmost medical importance. Generally, it is believed that a live attenuated vaccine would best provide protective immunity against this tenacious pathogen. Here, we propose a strategy for an HCMV vaccine that aims at the simultaneous activation of innate and adaptive immune responses. An HCMV strain expressing the host ligand ULBP2 for the NKG2D receptor was found to be susceptible to control by natural killer (NK) cells, and preserved the ability to stimulate HCMV-specific T cells. Infection with the ULBP2-expressing HCMV strain caused diminished cell surface levels of MHC class I molecules. While expression of the NKG2D ligand increased the cytolytic activity of NK cells, NKG2D engagement in CD8+ T cells provided co-stimulation and compensated for lower MHC class I expression. Altogether, our data indicate that triggering of both arms of the immune system is a promising approach applicable to the generation of a live attenuated HCMV vaccine