Photon helicity driven electric currents in graphene

We report on the observation of photon helicity driven currents in graphene. The directed net electric current is generated in single layer graphene by circularly polarized terahertz laser radiation at normal as well as at oblique incidence and changes its sign upon reversing the radiation helicity. The phenomenological and microscopic theories of the observed photocurrents are developed. We demonstrate that under oblique incidence the current is caused by the circular photon drag effect in the interior of graphene sheet. By contrast, the effect at normal incidence stems from the sample edges, which reduce the symmetry and result in an asymmetric scattering of carriers driven by the radiation field. Besides a photon helicity dependent current we also observe photocurrents in response to linearly polarized radiation. The microscopic mechanisms governing this effect are discussed.Comment: 13 pages, 7 figure

Anisotropic photoconductivity in graphene

We investigate the photoconductivity of graphene within the relaxation time approximation. In presence of the inter-band transitions induced by the linearly polarized light the photoconductivity turns out to be highly anisotropic due to the pseudospin selection rule for Dirac-like carriers. The effect can be observed in clean undoped graphene samples and be utilized for light polarization detection.Comment: 4 pages, 2 figure

Cadmium Telluride Quantum Dots as a Fluorescence Marker for Adipose Tissue Grafts

Plastic and reconstructive surgeons increasingly apply adipose tissue grafting in a clinical setting, although the anticipation of graft survival is insecure. There are only few tools for tracking transplanted fat grafts in vivo. Murine adipose tissue clusters were incubated with negatively charged, mercaptoproprionic acid-coated cadmium telluride quantumdots (QDs) emitting in the dark red or near infrared. The intracellular localization of QDs was studied by confocal laser scanning microscopy. As a result, the adipose tissue clusters showed a proportional increase in fluorescence with increasing concentrations (1, 10, 16, 30, 50 nM) of cadmium telluride QDs. Laser scanning microscopy demonstrated a membrane bound localization of QDs. Vacuoles and cell nuclei of adipocytes were spared by QDs. We conclude that QDs were for the first time proven intracellular in adult adipocytes and demonstrate a strong fluorescence signal. Therefore, they may play an essential role for in vivo tracking of fat grafts

The Impact of Socio-Demographic and Religious Factors upon Sexual Behavior among Ugandan University Students

INTRODUCTION: More knowledge is needed about structural factors in society that affect risky sexual behaviors. Educational institutions such as universities provide an opportune arena for interventions among young people. The aim of this study was to investigate the relationship between sociodemographic and religious factors and their impact on sexual behavior among university students in Uganda. METHODS: In 2005, 980 university students (response rate 80%) were assessed by a self-administered questionnaire. Validated instruments were used to assess socio-demographic and religious factors and sexual behavior. Logistic regression analyses were applied. RESULTS: Our findings indicated that 37% of the male and 49% of the female students had not previously had sex. Of those with sexual experience, 46% of the males and 23% of the females had had three or more sexual partners, and 32% of the males and 38% of the females did not consistently use condoms. For those who rated religion as less important in their family, the probability of early sexual activity and having had a high number of lifetime partners increased by a statistically significant amount (OR = 1.7; 95% CI: 1.2-2.4 and OR = 1.6; 95% CI: 1.1-2.3, respectively). However, the role of religion seemed to have no impact on condom use. Being of Protestant faith interacted with gender: among those who had debuted sexually, Protestant female students were more likely to have had three or more lifetime partners; the opposite was true for Protestant male students. CONCLUSION: Religion emerged as an important determinant of sexual behavior among Ugandan university students. Our findings correlate with the increasing number of conservative religious injunctions against premarital sex directed at young people in many countries with a high burden. of HIV/AIDS. Such influence of religion must be taken into account in order to gain a deeper understanding of the forces that shape sexual behavior in Uganda

Redox-Neutral Photocatalytic C−H Carboxylation of Arenes and Styrenes with CO2

Carbon dioxide (CO2) is an attractive one-carbon (C1) building block in terms of sustainability and abundance. However, its low reactivity limits applications in organic synthesis as typically high-energy reagents are required to drive transformations. Here, we present a redox-neutral C-H carboxylation of arenes and styrenes using a photocatalytic approach. Upon blue-light excitation, the anthrolate anion photocatalyst is able to reduce many aromatic compounds to their corresponding radical anions, which react with CO2 to afford carboxylic acids. High-throughput screening and computational analysis suggest that a correct balance between electron affinity and nucleophilicity of substrates is essential. This novel methodology enables the carboxylation of numerous aromatic compounds, including many that are not tolerated in classical carboxylation chemistry. Over 50 examples of C-H functionalizations using CO2 or ketones illustrate a broad applicability. The method opens new opportunities for the valorization of common arenes and may find application in late-stage C-H carboxylation