Efficient Spatial Redistribution of Quantum Dot Spontaneous Emission from 2D Photonic Crystals

We investigate the modification of the spontaneous emission dynamics and external quantum efficiency for self-assembled InGaAs quantum dots coupled to extended and localised photonic states in GaAs 2D-photonic crystals. The 2D-photonic bandgap is shown to give rise to a 5-10 times enhancement of the external quantum efficiency whilst the spontaneous emission rate is simultaneously reduced by a comparable factor. Our findings are quantitatively explained by a modal redistribution of spontaneous emission due to the modified local density of photonic states. The results suggest that quantum dots embedded within 2D-photonic crystals are suitable for practical single photon sources with high external efficiency

The inverse electromagnetic scattering problem in a piecewise homogeneous medium

This paper is concerned with the problem of scattering of time-harmonic electromagnetic waves from an impenetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is established, employing the integral equation method. Inspired by a novel idea developed by Hahner [11], we prove that the penetrable interface between layers can be uniquely determined from a knowledge of the electric far field pattern for incident plane waves. Then, using the idea developed by Liu and Zhang [21], a new mixed reciprocity relation is obtained and used to show that the impenetrable obstacle with its physical property can also be recovered. Note that the wave numbers in the corresponding medium may be different and therefore this work can be considered as a generalization of the uniqueness result of [20].Comment: 19 pages, 2 figures, submitted for publicatio

A versatile dual spot laser scanning confocal microscopy system for advanced fluorescence correlation spectroscopy analysis in living cell

A fluorescence correlation spectroscopy (FCS) system based on two independent measurement volumes is presented. The optical setup and data acquisition hardware are detailed, as well as a complete protocol to control the location, size and shape of the measurement volumes. A method that allows to monitor independently the excitation and collection efficiency distribution is proposed. Finally, a few examples of measurements that exploit the two spots in static and/or scanning schemes, are reported.Comment: Accepted for publication in Review of Scientific Instrumen

Hydration and mobility of HO-(aq)

The hydroxide anion plays an essential role in many chemical and biochemical reactions. But a molecular-scale description of its hydration state, and hence also its transport, in water is currently controversial. The statistical mechanical quasi-chemical theory of solutions suggests that HO[H2O]3- is the predominant species in the aqueous phase under standard conditions. This result is in close agreement with recent spectroscopic studies on hydroxide water clusters, and with the available thermodynamic hydration free energies. In contrast, a recent ab initio molecular dynamics simulation has suggested that HO[H_2O]4- is the only dominant aqueous solution species. We apply adiabatic ab initio molecular dynamics simulations, and find good agreement with both the quasi-chemical theoretical predictions and experimental results. The present results suggest a picture that is simpler, more traditional, but with additional subtlety. These coordination structures are labile but the tri-coordinate species is the prominent case. This conclusion is unaltered with changes in the electronic density functional. No evidence is found for rate-determining activated inter-conversion of a HO[H2O]4- trap structure to HO[H2O]3-, mediating hydroxide transport. The view of HO- diffusion as the hopping of a proton hole has substantial validity, the rate depending largely on the dynamic disorder of the water hydrogen-bond network.Comment: 7 pages, 5 figures, additional results include

Impact Biomechanics of the Human Body

The research reported on in this dissertation has been systematically developed through a series of interrelated studies and experiments. The purpose has been to understand and characterize the effects of sever impact loading on the human body that results from accidents involving automobiles, motorcycles, boats, other vehicles, pedestrians, swimmer, et cetera. Previous work in this arena had relied strongly on simulations of human body anatomy, has focused on the microscopic mechanical properties of bone and soft tissue, or has resorted to analytical modeling. Literature regarding mechanical properties of human tissue is plentiful. The experimental results in comparison among researchers are often quite variable, probably due to the complexity and diversity of the hard and soft materials that compose the human body. The majority of the research involves mechanical properties of human and animal bones and rarely is a full intact bone or specimen used for testing purposes. Instead, small cube samples are usually tested under static conditions. One reason for the widespread use of small cubes is their ease of use in material testing. The mechanical properties, however, of a full intact bone and/or intact specimen are much different than those found in a small cube section of bone or a dissected soft tissue part. This is due to the anisotropic and viscoelastic nature of these materials. When bone is combined with the various soft tissue components (muscles, tendons, ligaments, vessels, nerves, fascia, fat, skin, et cetera), a black box complex composite structure is created that needs to be characterized as a material of its own. Hence, more realistic data is needed about impact trauma effect on the human body. This research helps bridge-the-gap to this previous research through the use of various intact cadaveric specimens. The approach has been to develop a unique impact biomechanics laboratory, an air bad research laboratory, and various other testing apparatuses. In addition, existing facilities such as a drop tower, standard structural mechanical test equipment, and, in one instance, a specialized marine research facility were used when appropriate. This research focuses on macroscopic effects of impact loading and includes: comparison of embalmed versus unembalmed specimens, fracture patterns of long bones, impact response of the frontal bone and face, and response of the spine. The study also includes evaluation of the air bad as a protective device and evaluation of a particular cage guard design for boat propellers as a safety device. Reduction or prevention of impact injury through design of protective devices/safer environments requires certain biomechanical information. This includes a characterization of how the body region of interest responds to impact forces in terms of mechanical parameters such as force-time histories of impact, accelerations/decelerations, and deformations in the tissue structures. Also, mechanisms by which the tissues fail, mechanical parameters by which they respond, and the values of the injury criteria are important results in impact biomechanics research. These biomechanical behaviors and injury characterizations are the essence of the different parts of this dissertation

A Nonpolymorphic Class I Gene in the Murine Major Histocompatibility Complex

DNA sequence analysis of a class I gene (QlO), which maps to the Qa2,3 locus in the C57BL/lO (H- 2b haplotype) mouse, reveals that it is almost identical to a cDNA clone (pH16) isolated from a SWR/J (H-2q haplotype) mouse liver cDNA library. Exon 5, in particular, has an unusual structure such that a polypeptide product is unlikely to be anchored in the cell membrane. Our findings suggest that the two sequences are derived from allelic class I genes, which are nonpolymorphic, in contrast to H-2K allelic sequences from the same mice, and they may encode liver-specific polypeptides of unknown function. Our previous studies indicate that the QlO gene is a potential donor gene for the generation of mutations at the H-2K locus by inter-gene transfer of genetic information. Thus the lack of polymorphism in class I genes at the QlO locus implies either that they are not recipients for such exchanges or that selective pressure prevents the accumulation of mutations in genes at this locus