Experiment and numerical simulation of heat and mass transfer during a spray freeze-drying process of ovalbumin in a tray

Spray freeze-drying is a promising technology for producing high-quality porous particles primarily for pharmaceutical uses. The advantages of freeze-drying in the production of pharmaceuticals and biomedical products, such as minimization of thermal and chemical degradation, retention of volatile components, preservation of high porosity, and a very low content of residual water after drying, are mostly retained in spray freeze-drying. In this study, we performed spray freeze-drying of a 3% (w/w) chicken egg ovalbumin solution in a tray with a batch-type spray freeze-dryer that we developed. The physical characteristics of the spray freeze-dried particles were qualitatively evaluated by means of scanning electron microscopy. The freeze-drying behavior of spray-frozen particles was experimentally investigated by measuring the histories of product temperatures and numerically studied by developing an analysis model based on the finite volume method in a fixed grid system.     

New Colored Visual Secret Sharing Schemes

Visual secretsharing (VSS) schemes are used to protect the visual secret bysending n transparencies to different participantsso that k-1 or fewer of them have no informationabout the original image, but the image can be seen by stackingk or more transparencies. However, the revealedsecret image of a conventional VSS scheme is just black and white.The colored k out of n VSS scheme sharinga colored image is first introduced by Verheul and Van Tilborg[1]. In this paper, a new construction for the colored VSS schemeis proposed. This scheme can be easily implemented on basis ofa black & white VSS scheme and get much better block lengththan the Verheul-Van Tilborg scheme.     

Few-electron quantum dot fabricated with layered scanning force microscope lithography

Few-electron quantum dots with integrated charge read-out have been fabricated by layered local anodic oxidation of a Ga[Al]As heterostructure and a thin Titanium top gate. The additional set of gates provided by the metallic film is used to tune the quantum dots into the few-electron regime. Current through the quantum dots and the quantum dot charge have been simultaneously measured for electron numbers varying between zero and two. The singlet–triplet splitting varies in two different samples between 0.5 and 1.5 meV. The Zeeman splitting of the first conductance resonance is observed in parallel magnetic field. The high tunability and straightforward implementation of these structures are promising for future nanostructure design.     

Cotunneling-mediated transport through excited states in the Coulomb-blockade regime

We present finite-bias transport measurements on a few-electron quantum dot. In the Coulomb-blockade regime, strong signatures of inelastic cotunneling occur which can directly be assigned to excited states observed in the nonblockaded regime. In addition, we observe structures related to sequential tunneling through the dot, occurring after it has been excited by an inelastic cotunneling process. We explain our findings using transport calculations within the real-time Green's function approach, including diagrams up to fourth order in the tunneling matrix elements.     

Analysis of the metallic phase of two-dimensional holes in SiGe in terms of temperature dependent screening

We find that temperature dependent screening can quantitatively explain the metallic behavior of the resistivity on the metallic side of the so-called metal-insulator transition in p-SiGe. Interference and interaction effects exhibit the usual insulating behavior which is expected to overpower the metallic background at sufficiently low temperatures. We find empirically that the concept of a Fermi liquid describes our system with its large interaction parameter r(s) approximately 8.     

Spin effects in a quantum ring

Recent experiments that are reviewed explore the spin states of a ring-shaped many-electron quantum dot. Coulomb-blockade spectroscopy is used to access the spin degree of freedom. The Zeeman effect observed for states with successive electron number allows to select possible sequences of spin ground states of the ring. Spin-paired orbital levels can be identified by probing their response to magnetic fields normal to the plane of the ring and electric fields caused by suitable gate voltages. This narrows down the choice of ground-state spin sequences. A gate-controlled singlet–triplet transition is identified and the size of the exchange interaction matrix element is determined.