Search

We investigated negative photoconductivity in graphene using ultrafast terahertz techniques. Infrared transmission was used to determine the Fermi energy, carrier density, and mobility of p-type chemical vapor deposition graphene samples. Time-resolved terahertz photoconductivity measurements using a tunable mid-infrared pump probed these samples at photon energies between 0.35 eV and 1.55 eV, approximately one-half to three times the Fermi energy of the samples. Although interband optical transitions in graphene are blocked for pump photon energies less than twice the Fermi energy, we observe negative photoconductivity at all pump photon energies investigated, indicating that interband excitation is not required to observe this effect. Our results are consistent with a thermalized free-carrier population that cools by electron-phonon scattering, but are inconsistent with models of negative photoconductivity based on population inversion. [ABSTRACT FROM AUTHOR]

We report terahertz and infrared transmission measurements of a high-performance thermoelectric material containing tellurium nanowires in a conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) matrix. The DC electrical conductivity of the hybrid material (41 S/cm) is approximately one hundred times that of pure PEDOT:PSS and more than 400 times that of a film of pure tellurium nanowires, while the terahertz-frequency (THz) conductivity of PEDOT:PSS and the hybrid material are comparable at f~2THz. A frequency-dependent conductivity model indicates that the increased DC conductivity of the hybrid material results from an increase in the DC charge mobility rather than in the free charge density. We suggest that the increased DC conductivity of the hybrid material results from an increase in linkage between PEDOT domains by the tellurium nanowires. [ABSTRACT FROM AUTHOR]

A long term follow up (mean 7.2 years) of 30 children with anorexia nervosa (mean age at onset 11.7 years) was carried out. The outcome was good in only 18 (60%), 10 children remaining moderately to severely impaired and two died. Poor prognostic factors included early age at onset (less than 11 years), depression during the illness, disturbed family life and one parent families, and those in which one or both parents had been married before. [ABSTRACT FROM AUTHOR]

The first documented case of algal meningitis due to Prototheca wickerhamii is reported in a patient with AIDS. The initial CSF culture yielded only Cryptococcus neoformans. P. wickerhamii was isolated on four subsequent lumbar punctures. The patient died, and at autopsy the alga was isolated from leptomeninges over the brain and about the spinal cord. Histologic sections from numerous locations of the brain revealed masses of cryptococci and protothecae. [ABSTRACT FROM PUBLISHER]