Luminescence of a semiconductor quantum dot system

A microscopic theory is used to study photoluminescence of semiconductor quantum dots under the influence of Coulomb and carrier-photon correlation effects beyond the Hartree-Fock level. We investigate the emission spectrum and the decay properties of the time-resolved luminescence from initially excited quantum dots. The influence of the correlations is included within a cluster expansion scheme up to the singlet-doublet level.     

UVR emissions from solaria in Australia and implications for the regulation process

To assist in the development of the 2008 Australian/New Zealand standard on solaria and related regulations, Australian Radiation Protection and Nuclear Safety Agency scientists visited a number of tanning establishments during 2008 to measure the intensity and spectral distribution of the ultraviolet radiation (UVR) emissions from a range of solaria. The 2002 Australian/New Zealand Standard "Solaria for cosmetic purposes" (AS/NZS 2635) allowed a maximum UVR output from solaria of UV Index 60, a compromise between the solarium industry who wanted no upper limit and the health agencies who wanted to limit intensity. Of the 20 solaria examined in detail, only one had emissions of intensity less than UV Index 12, typical of mid-latitude summer sunlight, 15 units emitted more than UV Index 20, while three units emitted at intensities above UV Index 36, the maximum allowed by the new standard, AS/NZS 2635 (2008) and would thus not comply. UVA emissions ranged from 98W·m(-2) up to a maximum of 438W·m(-2) , more than six times the UVA content of mid-latitude summer sunshine. The results indicate that solaria users in Australia have access to solaria that are high intensity units with both significantly higher UVB and UVA emissions than sunlight, with implications for resultant adverse health effects.     

The quest for axions and other new light particles

Standard Model extensions often predict low‐mass and very weakly interacting particles, such as the axion. A number of small‐scale experiments at the intensity/precision frontier are actively searching for these elusive particles, complementing searches for physics beyond the Standard Model at colliders. Whilst a next generation of experiments will give access to a huge unexplored parameter space, a discovery would have a tremendous impact on our understanding of fundamental physics.     

Measurement of the UVR Exposures of Expeditioners on Antarctic Resupply Voyages†

A study to assess the potential exposure to solar UV radiation of expeditioners on Australian Antarctic resupply voyages was carried out over the Austral summers of 2004/2005 to 2006/2007. Subjects wore UVR‐sensitive polysulphone (PS) badges on the chest for the duration of their working day, which generally ranged from 5 to 10 h, but could be as long as 14 h. Measurements were carried out during unloading of two vessels while they were at the three Australian Antarctic stations. The subjects wore standard Australian Antarctic Division clothing assemblages, although the face and hands and in some cases more of the limbs were uncovered and subjected to exposure to UVR. The badges worn by the subjects received exposures ranging from 0.2 to 18 standard erythemal doses (SEDs), with a median of 3.2 SEDs. However, comparison with occupational exposure limits showed that more than 80% of the subjects’ PS badges received UVR exposures in excess of the limits while 31% received more than five times the limits. Despite sun protection being provided more than 70% of the workers reported mild erythema.     

Laser theory for semiconductor quantum dots in microcavities

Quantum dots (QDs) used as active material in microresonators are currently of strong topical interest due to breakthroughs in growth and device structuring. From the theory side, however, atomic models are still used to analyse the emission from these semiconductor systems, despite known differences between QDs and atoms. We introduce a semiconductor laser theory based on a microscopic approach with the goal of better describing the characteristic behaviour of QD-based laser devices and to show differences from predictions based on atomic models.     

Studies on clathrasils: VII. A new clathrate compound of silica: Synthesis,crystallographic, and thermal properties

Using l-aminoadamantane a new type of silica host framework has been stabilized. The clathrasil is rhombohedral with a=13.887 and c=40.989 for the hexagonal unit cell. Heating the compound on a thermal analyser shows that from 500°C on the guest molecule evaporates. The silica framework only very slowly breaks down when heated at 1100°C for several hours yielding cristobalite. Since l-aminoadamantane stabilizes, at higher temperatures of synthesis, dodecasil 1H the new clathrasil is regarded as low temperature form for this particular guest molecule.     

Renormalization flow of QED

We investigate textbook QED in the framework of the exact renormalization group. In the strong-coupling region, we study the influence of fluctuation-induced photonic and fermionic self-interactions on the nonperturbative running of the gauge coupling. Our findings confirm the triviality hypothesis of complete charge screening if the ultraviolet cutoff is sent to infinity. Though the Landau pole does not belong to the physical coupling domain owing to spontaneous chiral-symmetry-breaking (chiSB), the theory predicts a scale of maximal UV extension of the same order as the Landau pole scale. In addition, we verify that the chiSB phase of the theory which is characterized by a light fermion and a Goldstone boson also has a trivial Yukawa coupling.     

Electrospray mass spectrometry study of tiopronin monolayer-protected gold nanoclusters

Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) and gel permeation chromatography (GPC) were used to study the synthesis of a series of tiopronin monolayer-protected gold nanoclusters (MPCs) and to monitor their postsynthesis peptide ligand place-exchange reactions. All mass spectra identified the presence of cyclic gold(I)-thiolates with a strong preference for tetrameric species. During the synthesis of pre-monolayer-protected nanoclusters (pre-MPCs), esterified gold(I)-thiolate tetramers were initially observed in minor abundance (with respect to disulfide bridged tiopronin species) before dramatically increasing in abundance and precipitating from solution. After conversion of pre-MPCs to MPCs, ESI-TOF mass spectra demonstrated an overall predominance of tetrameric species with conversion from ester-terminated end groups to carboxyl-terminated end groups. Further modifications were performed through postsynthesis ligand place-exchange reactions to validate the existence of the tetramers. This work suggests that monolayer protection is accomplished by cyclized gold(I)-thiolate tetramers on the gold core surface, and/or that gold(I)-thiolates are a basic building block within the nanoparticles.