Broadband Forward Light Scattering by Architectural Design of Core–Shell Silicon Particles

A goal in the field of nanoscale optics is the fabrication of nanostructures with strong directional light scattering at visible frequencies. Here, the synthesis of Mie-resonant core–shell particles with overlapping electric and magnetic dipole resonances in the visible spectrum is demonstrated. The core consists of silicon surrounded by a lower index silicon oxynitride (SiO_xN_y) shell of an adjustable thickness. Optical spectroscopies coupled to Mie theory calculations give the first experimental evidence that the relative position and intensity of the magnetic and electric dipole resonances are tuned by changing the core–shell architecture. Specifically, coating a high-index particle with a low-index shell coalesces the dipoles, while maintaining a high scattering efficiency, thus generating broadband forward scattering. This synthetic strategy opens a route toward metamaterial fabrication with unprecedented control over visible light manipulation.     

The relative positions of alanine residues in the hydrophobic core control the formation of two-stranded or four-stranded {alpha}-helical coiled-coils

The objective of this study was to investigate the positionaleffect of hydrophobic interactions in the -helical interfacein controlling the formation of two-stranded and four-strandedcoiled-coils. Two disulfide-bridged antiparallel coiled-coilswere designed which differ only in the position of a singleAla residue in the middle heptad: in peptide 2H the Ala residuesare in register (in the same rung), while in peptide 4H theyare not. Data from size-exclusion chromatography and sedimentationequilibrium experiments showed that under benign conditionspeptides 2H and 4H were two-stranded and four-stranded coiled-coilsrespectively. These results, in conjunction with molecular modelingstudies, suggest that when four Ala residues are in the sameplane of a potential four-stranded coiled-coil, the small sidechains of Ala would create a large cavity in the hydrophobicinterface of the potential four-stranded structure which isdestabilizing and favors the two-stranded, disulfide-bridgedcoiled-coil. In contrast, an alternating Leu-Ala hydrophobicpacking in the two planes distributes the potential cavity overa larger region, which may be partially filled by minor adjustmentsof the neighboring Leu side chains. As a result, there is stillsufficient hydrophobic contact to maintain the four-strandedstructure.     

Increasing the Efficiency of Organic Dye‐Sensitized Solar Cells over 10.3% Using Locally Ordered Inverse Opal Nanostructures in the Photoelectrode

3D inverse opal (3D‐IO) oxides are very appealing nanostructures to be integrated into the photoelectrodes of dye‐sensitized solar cells (DSSCs). Due to their periodic interconnected pore network with a high pore volume fraction, they facilitate electrolyte infiltration and enhance light scattering. Nonetheless, preparing 3D‐IO structures directly on nonflat DSSC electrodes is challenging. Herein, 3D‐IO TiO₂ structures are prepared by templating with self‐assembled polymethyl methacrylate spheres on glass substrates, impregnation with a mixed TiO₂:SiO₂ precursor and calcination. The specific surface increases from 20.9 to 30.7 m² g^?1 after SiO₂ removal via etching, which leads to the formation of mesopores. The obtained nanostructures are scraped from the substrate, processed as a paste, and deposited on photoelectrodes containing a mesoporous TiO₂ layer. This procedure maintains locally the 3D‐IO order. When sensitized with the novel benzothiadiazole dye YKP‐88, DSSCs containing the modified photoelectrodes exhibit an efficiency of 10.35% versus 9.26% for the same devices with conventional photoelectrodes. Similarly, using the ruthenium dye N719 as sensitizer an efficiency increase from 5.31% to 6.23% is obtained. These improvements originate mainly from an increase in the photocurrent density, which is attributed to an enhanced dye loading obtained with the mesoporous 3D‐IO structures due to SiO₂ removal.     

Atmospheric mercury depletion event study in Ny-Alesund (Svalbard) in spring 2005. Deposition and transformation of Hg in surface snow during springtime

A field campaign was conducted in Ny-Alesund (78 degrees 54'N, 11 degrees 53'E), Svalbard (Norway) during April and May 2005. An Atmospheric Mercury (Hg) Depletion Event (AMDE) was observed from the morning of April 24 until the evening of April 27. Transport of already Hg and ozone (O3) depleted air masses could explain this observed depletion. Due to a snowfall event during the AMDE, surface snow Hg concentrations increased two fold. Hg deposition took place over a short period of time corresponding to 3-4 days. More than 80% of the deposited Hg was estimated to be reemitted back to the atmosphere in the days following the event. During the campaign, we observed night and day variations in surface snow Hg concentrations, which may be the result of gaseous elemental mercury (GEM) oxidation to divalent Hg at the snow/air interface by daylight surface snow chemistry. Finally, a decrease in the reactive Hg (HgR) fraction of total Hg (HgT) in the surface snow was observed during spring. We postulate that the transformation of HgR to a more stable form may occur in Arctic snow during spring.     

A block diagram model of the thickness mode piezoelectric transducer containing dual oppositely polarized piezoelectric zones

A unidimensional, linear systems, block diagram model of a two-layer thickness mode piezoelectric transducer is presented. The layers are subject to opposing piezoelectric polarization and the device is assumed to be loaded by semi-infinite isotropic media at the two principal faces. Block diagram representations of the transducer acting as both a generator and a receiver of ultrasound are developed in conjunction with the equivalent model of the electrical admittance. When expressed in this manner, the underlying cause and effect relationships are identified, with the important contribution of the piezoelectric boundary highlighted. Comparisons with the conventional single-layer transducer are made throughout and the major physical differences in terms of transduction performance are discussed. The new model is compared with finite element analysis and good agreement is also demonstrated with experimental data. A key aspect of the methodology is the provision of a more intuitive understanding of such device behavior. Accordingly, emphasis has been placed on the physical relationships and this is considered a major contribution of the work.     

Cationic liposome-DNA complexes: from liquid crystal science to gene delivery applications

At present, there is an unprecedented level of interest in the properties and structures of complexes consisting of DNA mixed with oppositely charged cationic liposomes (CLs). The interest arises because the complexes mimic natural viruses as chemical carriers of DNA into cells in worldwide human gene therapy clinical trials. However, since our understanding of the mechanisms of action of CL-DNA complexes interacting with cells remains poor, significant additional insights and discoveries will be required before the development of efficient chemical carriers suitable for long-term therapeutic applications. Recent studies describe synchrotron X-ray diffraction, which has revealed the liquid crystalline nature of CL-DNA complexes, and three-dimensional laser-scanning confocal microscopy, which reveals CL-DNA pathways and interactions with cells. The importance of the liquid crystalline structures in biological function is revealed in the application of these modern techniques in combination with functional transfection efficiency measurements, which shows that the mechanism of gene release from complexes in the cell cytoplasm is dependent on their precise liquid crystalline nature and the physical and chemical parameters (for example, the membrane charge density) of the complexes. In [section sign] 5, we describe some recent new results aimed at developing bionanotube vectors for gene delivery.     

In vitro synergistic effect of farnesol and human gingival cells against Candida albicans

Farnesol prevents the germination of yeast cells into mycelia, a fact that may be useful in eliminating C. albicans pathogenicity. Given the clinical potential of farnesol, its impact on C. albicans and host cells merited further investigation. We thus studied the effect of farnesol on C. albicans growth and filamentation and on gingival epithelial cells and fibroblasts and the synergistic effect of both gingival cells and farnesol on C. albicans filamentation. Repeated additions of farnesol reduced the growth of C. albicans. Farnesol was also effective at reducing C. albicans germ tube formation. While farnesol inhibited germ tube formation under the conditions tested, it was most effective at inhibiting C. albicans filamentation when added to the culture medium at the same time as the serum. Farnesol also had an effect on gingival cells. In a serum-free medium, farnesol reduced fibroblast adhesion and proliferation, promoted epithelial cell differentiation and reduced proliferation up to 48 h post-treatment. These effects were not seen in the presence of serum. When C. albicans, farnesol and gingival cells were present in the same culture, significantly greater inhibition of the yeast-to-hyphal transition was observed than germ tube inhibition in cultures containing only C. albicans and farnesol, suggesting a synergistic effect between the gingival cells and farnesol in inhibiting the transition. Overall, the data suggest that farnesol is effective against C. albicans and may have an effect on host cells at certain concentrations.     

Disposable immunochips for the detection of Legionella pneumophila using electrochemical impedance spectroscopy

The rapid diagnosis of Legionellosis is crucial for the effective treatment of this disease. Currently, most clinical laboratories utilize rapid immunoassays that are sufficient for the detection of Legionella serogroup 1, but not other clinically relevant serogroups. In this report, the development of a disposable immunochip system is described in connection with electrochemical impedance spectroscopy and fluorescence microscopy. The immunochips were prepared by covalently immobilizing fluorophore-conjugated L. pneumophilaantibodies on Au chips. The analytical performance of the immunochips was optimized as a prescreening tool for L. pneumophila. The versatile immunochips described here can be easily adapted for the monitoring of all Legionella serogroups in clinical and environmental samples.     

Theoretical study for safe and efficient energy transfer to deeply implanted devices using ultrasound

The goal of this paper is to prove that a safe and efficient energy transfer is possible between an external transducer located on the patient's skin and a device deeply implanted in the abdomen. An ultrasound propagation model based on the Rayleigh-Sommerfeld diffraction integral is coupled with the data from the Visible Human Project to account for the geometry of the organs in the body. The model is able to predict the amount of acoustic power received by the device for different acoustic paths. The acoustic model is validated by comparison with measurements in water and in heterogeneous liquid phantoms. Care is taken to minimize adverse bioeffects-mainly temperature rise and cavitation in tissues. Simulations based on the bio-heat transfer equation are performed to check that thermal effects are indeed small.     

Thermogravimetric analysis as a new method to determine the lignocellulosic composition of biomass

Biomass energy uses organic matter such as wood or plants - lignocellulosic biomass - for creating heat, generating electricity and producing green oil for cars. Modern biomass energy recycles organic leftovers from forestry and agriculture, like corn stovers, rice husks, wood waste and pressed sugar cane, or uses special, fast-growing “energy crops” like willow and switchgrass, as fuel. Biomass is composed of three major components: cellulose, hemicelluloses, and lignin. Their differences in chemical structures lead to different chemical reactivities, making the relative composition in cellulose, hemicelluloses and lignin in the biomass a crucial factor for process design. In this paper thermogravimetric analysis is investigated as a new method to obtain lignin, hemicellulose and ??-cellulose contents in biomass. It is shown that this alternative method lead to comparable results than common methods used for the determination of the ??-cellulose content, with an enhancement of the accuracy in the determination of the hemicellulose content. Unfortunately, this method cannot be adopted for the determination of the lignin amount.