Varifocal liquid lenses with integrated actuator, high focusing power and low operating voltage fabricated on 200 mm wafers

We developed an innovative type of varifocal liquid lens actuated by electrostatic parallel plates. The 3 mm diameter lens is made of a polymer membrane that encapsulates a high permittivity liquid in a cavity on top of a glass wafer. Annular electrodes situated below the membrane and on the glass wafer form the electrostatic parallel plates actuator. By applying a voltage between the electrodes, the electrostatic actuation generated reduces the gap and pushes the liquid towards the center of the lens changing the curvature of the membrane.Compared to previous liquid lenses, very compact devices (≤6 mm × 6 mm × 0.7 mm) working at a reduced supply voltage (<25 V) are demonstrated. Wave front measurements indicate an optical power change of 8 m⁻¹ at 22 V_RMS that can be further improved. The lenses were fabricated on 200 mm wafers using standard microelectronics processes that make our solution a promising small outline, low voltage and low cost candidate for auto-focus devices in camera phones.     

NUMERICAL ANALYSIS OF HEAT TRANSFER BY NATURAL CONVECTION AND RADIATION IN PARTICIPATING FLUIDS ENCLOSED IN SQUARE CAVITIES

The influence of thermal radiation on natural convection in a participating fluid contained in a square cavity is studied numerically. The radiative transfer process is solved from the PI approximation. The Navier-Stokes equations are solved by a finite difference scheme integrated over control volumes. A numerical study of the so-called window problem (thermally driven cavity) shows the influence of thermal radiation on this reference problem for Rayleigh numbers in the range of 10³-10⁷ and Planck numbers varying from 1 to 0.05. The isotherms, streamlines, and heat lines show an increase of the dynamical effects in the central part of the cavity and a significant modification of the boundary layers. Results obtained from the simulation of an isotropically scattering medium are given.     

Spectroscopic Evidences of Charge Transfer Phenomena and Stabilization of Unusual Phases at Iron Oxide Monolayers Grown on Pt(111)

Strong electrostatic coupling between the local structure of metal-supported oxide ultra-thin films and the charge state of adsorbed species (such as Au atoms and O₂ molecules) is at the origin of a co-existence of alternative adsorption configurations, with drastically different structural and electronic characteristics. This effect may contribute also to the stabilization of oxide phases of unusual stoichiometries, where the ion valences are compensated by an electron exchange with the metal substrate. We report an analysis of the spectroscopic signatures of such differently charged adsorbates and unusual oxide phases, including valence and core electrons spectroscopies and vibrational characteristics. We show that the adsorbate charge states can be identified by their signature in the electronic states around the Fermi level and by the modification of the vibrational frequencies of adsorbed probe molecules. Moreover, core level analysis may contribute to the identification of the oxygen-rich phase, formed at high oxygen exposure. The detailed theoretical investigation of the spectroscopic signatures of alternative adsorption configurations and adsorbate charge states supplies a set of data, which may help the experimental identification of such species.     

LaPO4 Mineral Liquid Crystalline Suspensions with Outstanding Colloidal Stability for Electro‐Optical Applications

Mineral liquid crystals are materials in which mineral's intrinsic properties are combined with the self‐organization behavior of colloids. However, the use of such a system for practical application, such as optical switching, has rarely been demonstrated due to the fundamental drawbacks of colloidal systems such as limited dispersion stability. Studying colloidal suspensions of LaPO₄ nanorods, it is found that drastic improvement of colloidal stability can be obtained through a transfer of particles from water towards ethylene glycol, thus enabling the investigation of liquid crystalline properties of these concentrated suspensions. Using polarization microscopy and small‐angle x‐ray scattering (SAXS), self‐organization into nematic and columnar mesophases is observed enabling the determination of the whole phase diagram as a function of ionic strength and rod volume fraction. When an external alternative electric field is applied, a very efficient orientation of the nanorods in the liquid‐crystalline suspension is obtained, which is associated with a significant optical birefringence. These properties, combined with the high colloidal stability, are promising for the use of such high transparent and athermal material in electro‐optical devices.     

Comparison of two headspace sampling techniques for the analysis of off-flavour volatiles from oat based products

Two different headspace sampling techniques were compared for analysis of aroma volatiles from freshly produced and aged plain oatcakes. Solid phase microextraction (SPME) using a Carboxen–Polydimethylsiloxane (PDMS) fibre and entrainment on Tenax TA within an adsorbent tube were used for collection of volatiles. The effects of variation in the sampling method were also considered using SPME. The data obtained using both techniques were processed by multivariate statistical analysis (PCA). Both techniques showed similar capacities to discriminate between the samples at different ages. Discrimination between fresh and rancid samples could be made on the basis of changes in the relative abundances of 14–15 of the constituents in the volatile profiles. A significant effect on the detection level of volatile compounds was observed when samples were crushed and analysed by SPME–GC–MS, in comparison to undisturbed product. The applicability and cost effectiveness of both methods were considered.     

Air Drying Behaviour of Fresh and Osmotically Dehydrated Onion Slices (Allium cepa) and Tomato Fruits (Lycopersicon esculentum)

Onion slices (0.5 cm thick) and tomato fruits, fresh and osmotically dehydrated in sugar (600 g/l), salt (300 g/l) or mixed salt and sugar (45/15, w/w) solutions, were air dried at 60°C and drying constants determined. The air drying occurred in two falling rate periods, characterised each by a drying constant. The drying rate and the moisture diffusivity of osmosed samples were higher than that of fresh samples. The overall drying behaviour of osmosed onion slices was not influenced by osmotic conditions (solution and time), while the drying behaviour of osmosed tomato samples depended on osmotic solution and pre-treatment time. 15 minutes and 20 hours of pre osmosis seemed more convenient before drying of onion slices and tomato respectively. In this respect, the structural modification of cells of tomato membrane during extended pre treatment seemed to explain the variation in the drying behaviour.     

Instant coffee with high chlorogenic acid levels protects humans against oxidative damage of macromolecules

Scope: Coffee is among the most frequently consumed beverages. Its consumption is inversely associated to the incidence of diseases related to reactive oxygen species; the phenomenon may be due to its antioxidant properties. Our primary objective was to investigate the impact of consumption of a coffee containing high levels of chlorogenic acids on the oxidation of proteins, DNA and membrane lipids; additionally, other redox biomarkers were monitored in an intervention trial. Methods and results: The treatment group (n=36) consumed instant coffee co‐extracted from green and roasted beans, whereas the control consumed water (800 mL/P/day, 5 days). A global statistical analysis of four main biomarkers selected as primary outcomes showed that the overall changes are significant. 8‐Isoprostaglandin F2α in urine declined by 15.3%, 3‐nitrotyrosine was decreased by 16.1%, DNA migration due to oxidized purines and pyrimidines was (not significantly) reduced in lymphocytes by 12.5 and 14.1%. Other markers such as the total antioxidant capacity were moderately increased; e.g. LDL and malondialdehyde were shifted towards a non‐significant reduction. Conclusion: The oxidation of DNA, lipids and proteins associated with the incidence of various diseases and the protection against their oxidative damage may be indicative for beneficial health effects of coffee.     

Cirality induction in liquid crystalline side-chain polyethers prepared by copolymerization of oxiranes with mesogenic and non mesogenic groups

Copolymers prepared by anionic initiation from racemic or optically active styrene oxide and a racemic oxirane bearing cyanobiphenyl mesogenic group in the side chain are liquid crystalline when the content of the mesogenic monomer exceeds 60 mole %. Copolymers prepared from a mesogenic oxirane with a short spacer and racemic styrene oxide exhibit a nematic phase, while those prepared with optically active styrene oxide exhibit a cholesteric phase, thus indicating a transfer of chirality from the main chain towards the mesophase. Such a transfer of chirality is no more observed in the case of a copolymer prepared from a mesogenic oxirane with a long spacer. Received: 18 October 1996/Revised: 18 November 1996/Accepted: 20 November 1996     

Ceria Nanocrystals Exposing Wide (100) Facets: Structure and Polarity Compensation

Compact CeO₂(111) films grown on Ru(0001) can be transformed into well‐shaped nanoparticles by annealing them in an oxygen‐poor environment. With increasing temperature, the particles undergo a distinct shape evolution that finally leads to crystallites exposing wide (100) facets. The atomic structure of the (100) termination is determined with a combination of high‐resolution scanning tunneling microscopy and density functional theory. Two surface reconstructions are identified that are compatible with the need to compensate for the intrinsic dipole of the (100) plane and with a substantial reduction of the oxide material. Our study provides insights into the rarely explored (100) surface of ceria, which can be considered as model system for studying chemical processes on the polar termination of reducible oxides.