A structured light-based system for human heads

The 3-D modeling of heads by using optical triangulation techniques is of great interest in the context of virtual reality, telecommunication and computer animation. This paper presents a structured light-based system mainly for human heads. It is named “3-D Laser Color Scanner” (3DLCS). A 3-D model is obtained with a cylindrical scan. The laser beam is switched on and off using a “light valve” and two successive CCD frames are captured, one with the laser line showing and one without. We can simplify the laser line extracting by subtracting these two images.In this system, two CCD cameras are used to avoid occlusion problems. Color information is read from the CCD when the laser light is absent. Since traditional laser scanner will miss the range data in the low-reflectance areas such as the hair area of human head, a shape from silhouette algorithm is presented to overcome this problem. Finally, we give some results using our system. The resulting model is suitable for many applications.     

Does the beam width affect the generalized M factor of hard-edged diffracted beams?

A detailed study of the generalized M² factor of hard-edged diffracted beams based on the truncated second-order moments method, asymptotic analysis and self-convergent beam width approach is performed. The dependence of the generalized M² factor on the parameters characterizing the spatial profile, and beam truncation, etc. is analyzed.     

Strongly confined quantum wire states in strained T-shaped GaAs/InAlAs structures

The confinement energy of T-shaped quantum wires (QWRs), which were fabricated by the cleaved edge overgrowth technique in a way that the QWRs form at the intersection of In_0.2Al_0.8As stressor layers and the overgrown (1 1 0) GaAs quantum well (QW), is examined using micro-photoluminescence spectroscopy. Photoluminescence (PL) signals from individual QWRs can be spatially resolved, since the strained films are separated by 1 μm wide Al_0.3Ga_0.7As layers. We find that due to the tensile strain being transmitted to the QW, the confinement energy of the QWRs rises systematically up to 40 meV with increasing thickness of the stressor layers. By reducing the excitation power to 0.1 μW the QWR PL emission occurs 48 meV redshifted with respect to the QW. All QWR peaks exhibit smooth lineshapes, indicating the absence of pronounced exciton localization.     

Investigations of backscattering peaks and of the nature of the confining potential in open quantum dots

The properties of open quantum dots are examined in magneto-transport. The quantum dots are prepared from a two-dimensional electron system (2DES) in AlGaAs/GaAs by lateral gate structures. These quantum dots are open, i.e. they are still connected to the surrounding 2DES regions. The low magnetic field magnetoresistance shows peak structures. These structures can be related to semi-classical ballistic trajectories in the confining potential of a dot. The calculations of different confining potentials (abrupt “hard-wall” and parabolic “soft-wall”) are compared with the experimental results. The experiments are better described by a soft-wall potential.     

Long-wavelength light emission from InAs quantum dots covered by GaAsSb grown on GaAs substrates

We fabricated InAs quantum dots (QDs) with a GaAsSb strain-reducing layer (SRL) on a GaAs(0 0 1) substrate. The wavelength of emission from InAs QD is shown to be controllable by changing the composition and thickness of the SRL. An increase in photoluminescence intensity with increasing compositions of Sb and thickness of the GaAsSb SRL is also seen. The efficiency of radiative recombination was improved under both conditions because the InAs/GaAsSb/GaAs hetero-interface band structure more effectively suppressed carrier escape from the InAs QDs.     

Optical spectroscopy of single InAs/InP quantum dots around λ=1.55 μm

We discuss the preparation and spectroscopic characterisation of a single InAs/InP quantum dot suitable for long-distance quantum key distribution applications around λ=1.55 μm. The dot is prepared using a site-selective growth technique which allows a single dot to be deposited in isolation at a controlled spatial location. Micro-photoluminescence measurements as a function of exciton occupation are used to determine the electronic structure of the dot. Biexciton emission, shell filling and many-body re-normalization effects are observed for the first time in single InAs/InP quantum dots.     

Coulomb blockade in triangular lateral small-size quantum dots

An AlGaAs/GaAs lateral quantum dot of triangular shape with a characteristic size L<100 nm containing less than ten electrons was studied. Single-electron oscillations of the conductance G of this dot were measured at G<e²/h. When going from Ge²/h to G≈0.5e²/h, a decrease was found not only in the amplitude but also in the period of the oscillations. A calculation of the 3D-electrostatics demonstrated that this effect is due to a change in the dot size produced by control voltages.     

Phase diagram of aqueous solution at high pressure and low temperature

Abstract

This paper presents a constant mass high pressure isothermal calorimeter and describes the range of applications that this type of equipment can deal with. As an example, the thermophysical properties of an aqueous solution of MgSO₄ at low temperature and at high pressure have been investigated. The main results showed that the phase change heat of the solution decreased with increasing pressure and the phase change temperature of the eutectic concentration was depressed under high pressure. Those changes could be related to the MgSO₄ solubility and to water latent heat changes.     

Colorimetric and Spectrofluorimetric Methods for the Determination of Melatonin in Tablets and Serum

Abstract

Two sensitive and accurate colorimetric and spectrofluonmetric methods, are presented for the determination of melatonin in tablets and serum. The first method utilizes the reactions of p-dimethylaminobenzaldehyde in hydrochloric acid (van Urk reagent)-ferric chloride in sulphuric acid (Salkowski reagent) mixture. The blue color of the resulting reaction product is measured at 630 nm. The second method is based on the reaction of melatonin with o-phthalaldehyde in acid medium which yields highly fluorescent condensation product that is measured at 465 nm as emission wavelength, using excitation wavelength at 355 nm. No interference was observed from tableting additives, and the applicability of the methods was examined by analysing tablets containing melatonin (single and combined with pyridoxine). Mean percentage recoveries from tablets were found to be 99.9+0.31 for single and 100.5+0.15 for combined tablets using colorimetric method, while by applying spectrofluorimetric method the recoveries were found to be 100.610.41 for single and 100.2+0.39 for combined tablets. Furthermore, the proposed methods were extended to the in-vitro determination of melatonin in serum. The detection limits are 0.27 ug ml^?1 for colorimetric method and 0.00035 ug ml^?1 for spectrofluorimetric method.