Quasiperiodic light.

Quasiperiodicity is a form of spatial order that has been observed in quasicrystalline matter but not light. We construct a quasicrystalline surface out of a light emitting diode. Using a nanoscale waveguide as a microscope (NSOM), we directly image the light field at the surface of the diode. Here we show, using reciprocal space representations of the images, that the light field is quasiperiodic. We explain the structure of the light field with wave superposition. Periodic ordering is limited to at most six-fold symmetry. The light field exhibits 12-fold quasisymmetry, showing order while disproving periodicity. This demonstrates that a new class, consisting of projections from hyperspace, exists in the taxonomy of light ordering.

The synthesis of recombinant membrane proteins in yeast for structural studies.

Historically, recombinant membrane protein production has been a major challenge meaning that many fewer membrane protein structures have been published than those of soluble proteins. However, there has been a recent, almost exponential increase in the number of membrane protein structures being deposited in the Protein Data Bank. This suggests that empirical methods are now available that can ensure the required protein supply for these difficult targets. This review focuses on methods that are available for protein production in yeast, which is an important source of recombinant eukaryotic membrane proteins. We provide an overview of approaches to optimize the expression plasmid, host cell and culture conditions, as well as the extraction and purification of functional protein for crystallization trials in preparation for structural studies.

Effect of non-conformal gold deposition on SERS related plasmonic effects.

Recently, a comprehensive three dimensional computational model based on rigorous coupled wave analysis (RCWA) has been developed to investigate the properties of surface plasmons resident on metal coated arrays of inverted pyramidal pits used for SERS sensing applications in the form of 'klarite'. This simulation tool allows the identification of a variety of dispersive features including propagating and localized surface plasmons as well as simple diffraction relating to the influence of geometrical features. In this paper, we investigate the influence of non-conformality of the gold coating over the internal surfaces of the inverted pyramidal pits on plasmon dispersion. Modeling reveals very strong changes in plasmon behavior as a function of gold layer conformality. Dependent upon conformality of the gold coating we find that the nano-textured metallic surface can behave either as an efficient broadband mirror-like reflector or as an efficient broadband, wide angle absorber at infrared wavelengths. Creation of a broadband wide angle absorbing surface such as this has important implications for photovoltaic cells. For sensing applications, understanding the effect of metal layer conformality on plasmon dispersion gives clear insight into how to further improve the SERS enhancement factor.

Design and fabrication of a 3D-structured gold film with nanopores for local electric field enhancement in the pore.

Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.

Reflectance properties of silicon moth-eyes in response to variations in angle of incidence, polarisation and azimuth orientation.

We report a study of the optical properties of silicon moth-eye structures using a custom-made fully automated broadband spectroscopic reflectometry system (goniometer). This measurement system is able to measure specular reflectance as a function of wavelength, polar incidence angle and azimuth orientation angle, from normal to near-parallel polar incidence angle. The system uses a linear polarized broadband super-continuum laser light source. It is shown that a moth-eye structure composed of a regular array of protruding silicon rods, with finite sidewall angle reduces reflectance and sensitivity to incident wavelength in comparison to truly cylindrical rods with perpendicular sidewalls. It is also shown that moth-eye structures have omnidirectional reflectance properties in response to azimuth orientation of the sample. The importance of applying the reflectometer setup to study the optical properties of solar cell antireflective structures is highlighted.

Broadband stimulated four-wave parametric conversion on a tantalum pentoxide photonic chip.

We exploit the large third order nonlinear susceptibility (χ(3) or "Chi 3") of tantalum pentoxide (Ta(2)O(5)) planar waveguides and realize broadband optical parametric conversion on-chip. We use a co-linear pump-probe configuration and observe stimulated four wave parametric conversion when seeding either in the visible or the infrared. Pumping at 800 nm we observe parametric conversion over a broad spectral range with the parametric idler output spanning from 1200 nm to 1600 nm in infrared wavelengths and from 555 nm to 600 nm in visible wavelengths. Our demonstration of on-chip stimulated four wave parametric conversion introduces Ta(2)O(5) as a novel material for broadband integrated nonlinear photonic circuit applications.

Emission characteristics of photonic crystal light-emitting diodes.

Experimentally measured optical properties of photonic crystal LEDs are reported here. Photonic crystal and photonic quasi-crystal structures were fabricated on GaN epilayer LED wafer material using both direct-write electron beam lithography and nanoimprint lithography. Some of these structures were processed to make finished LEDs. Both electroluminescence and photoluminescence measurements were performed on these structures. Devices were characterized for their current-voltage characteristics, emission spectra, far-field emission pattern, and angular emission pattern. These results are useful for fabricating photonic crystal LEDs and assessing their operational properties.

A characterization of the Raman modes in a J-aggregate-forming dye: a comparison between theory and experiment.

J-Aggregates are a class of organic molecules that possess several interesting characteristics that make them attractive for a range of organic-based optoelectronic devices. We present experimental and computer-simulation studies of the Raman-active vibrational modes in the J-aggregate-forming dye 5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulfobutyl)benzimidazol-2-ylidene]propenyl]-1-ethyl-3-(4-sulfobutyl)benzimidazolium hydroxide, sodium salt, inner salt. The molecular monomer and dimer are analyzed computationally and the Raman mode energies extracted. There is a good agreement between the energies of the theoretical and experimental Raman modes. Experimentally, an enhancement is seen in the intensity of two low frequency modes upon aggregation of the dye. This is attributed to aggregation-enhanced Raman scattering. An enhancement is also observed in certain modes of the calculated spectra upon changing from a monomer to dimeric arrangement. A link is suggested between the Raman-active vibrational modes of the molecule, and a time-dependent electronic coupling present over several molecules.

From genomics to proteomics: techniques and applications in cancer research.

New technologies designed to facilitate the comprehensive analyses of genomes, transcriptomes and proteomes in health and disease are poised to exert a dramatic change on the pace of cancer research and to impact significantly on the care of cancer patients. These approaches have already demonstrated the power of molecular medicine in discriminating among disease subtypes that are not recognizable using traditional pathological criteria and in identifying specific genetic events involved in cancer progression. This review outlines the current status of these technologies and highlights recent studies in which they have been applied in the context of carcinogenesis.

Insulin-stimulated glucose uptake by subcellular particles from adipose tissue cells.

Microsomal particles prepared from isolated rat adipose cells take up D-glucose more rapidly than L-glucose. The rate of D-glucose uptake, but not that of L-glucose, is stimulated by incubation of the intact cells with insulin at concentrations as low as 10 microunits per milliliter before disruption and preparation of the microsomes.

Significance of tissue myo-inositol concentrations in metabolic regulation in nerve.

Approximately 25 percent of resting energy utilization in isolated nerve endoneurium is inhibited by medium containing defatted albumin and selectively restored by arachidonic acid but is unaffected by indomethacin or nordihydroguaiaretic acid. The same component of energy utilization is inhibited by small decreases in endoneurial myo-inositol, which decrease incorporation of carbon-14-labeled arachidonic acid into phosphatidylinositol. The fraction of the resting oxygen uptake inhibited by ouabain is decreased 40 to 50 percent by a reduced tissue myo-inositol concentration or by defatted albumin. Metabolic regulation by rapid, basal phosphatidylinositol turnover is dependent on the maintenance of normal tissue myoinositol concentrations.

Efficient light harvesting in hybrid quantum dot-interdigitated back contact solar cells via resonant energy transfer and luminescent downshifting.

In this paper, we propose a hybrid quantum dot (QD)/solar cell configuration to improve performance of interdigitated back contact (IBC) silicon solar cells, resulting in 39.5% relative boost in the short-circuit current (JSC) through efficient utilisation of resonant energy transfer (RET) and luminescent downshifting (LDS). A uniform layer of CdSe1-xSx/ZnS quantum dots is deposited onto the AlOx surface passivation layer of the IBC solar cell. QD hybridization is found to cause a broadband improvement in the solar cell external quantum efficiency. Enhancement over the QD absorption wavelength range is shown to result from LDS. This is confirmed by significant boosts in the solar cell internal quantum efficiency (IQE) due to the presence of QDs. Enhancement over the red and near-infrared spectral range is shown to result from the anti-reflection properties of the QD layer coating. A study on the effect of QD layer thickness on solar cell performance was performed and an optimised QD layer thickness was determined. Time-resolved photoluminescence (TRPL) spectroscopy was used to investigate the photoluminescence dynamics of the QD layer as a function of AlOx spacer layer thickness. RET can be evoked between the QD and Si layers for very thin AlOx spacer layers, with RET efficiencies of up to 15%. In the conventional LDS architecture, down-converters are deposited on the surface of an optimised anti-reflection layer, providing relatively narrowband enhancement, whereas the QDs in our hybrid architecture provide optical enhancement over the broadband wavelength range, by simultaneously utilising LDS, RET-mediated carrier injection, and antireflection effects, resulting in up to 40% improvement in the power conversion efficiency (PCE). Low-cost synthesis of QDs and simple device integration provide a cost-effective solution for boosting solar cell performance.

Transcriptome analysis of a respiratory Saccharomyces cerevisiae strain suggests the expression of its phenotype is glucose insensitive and predominantly controlled by Hap4, Cat8 and Mig1.

BACKGROUND: We previously described the first respiratory Saccharomyces cerevisiae strain, KOY.TM6*P, by integrating the gene encoding a chimeric hexose transporter, Tm6*, into the genome of an hxt null yeast. Subsequently we transferred this respiratory phenotype in the presence of up to 50 g/L glucose to a yeast strain, V5 hxt1-7Delta, in which only HXT1-7 had been deleted. In this study, we compared the transcriptome of the resultant strain, V5.TM6*P, with that of its wild-type parent, V5, at different glucose concentrations. RESULTS: cDNA array analyses revealed that alterations in gene expression that occur when transitioning from a respiro-fermentative (V5) to a respiratory (V5.TM6*P) strain, are very similar to those in cells undergoing a diauxic shift. We also undertook an analysis of transcription factor binding sites in our dataset by examining previously-published biological data for Hap4 (in complex with Hap2, 3, 5), Cat8 and Mig1, and used this in combination with verified binding consensus sequences to identify genes likely to be regulated by one or more of these. Of the induced genes in our dataset, 77% had binding sites for the Hap complex, with 72% having at least two. In addition, 13% were found to have a binding site for Cat8 and 21% had a binding site for Mig1. Unexpectedly, both the up- and down-regulation of many of the genes in our dataset had a clear glucose dependence in the parent V5 strain that was not present in V5.TM6*P. This indicates that the relief of glucose repression is already operable at much higher glucose concentrations than is widely accepted and suggests that glucose sensing might occur inside the cell. CONCLUSION: Our dataset gives a remarkably complete view of the involvement of genes in the TCA cycle, glyoxylate cycle and respiratory chain in the expression of the phenotype of V5.TM6*P. Furthermore, 88% of the transcriptional response of the induced genes in our dataset can be related to the potential activities of just three proteins: Hap4, Cat8 and Mig1. Overall, our data support genetic remodelling in V5.TM6*P consistent with a respiratory metabolism which is insensitive to external glucose concentrations.

Colloidal Synthesis of CsX Nanocrystals (X = Cl, Br, I).

A facile colloidal synthesis of highly ionic cesium halide nanocrystals is reported. Colloidal nanocrystals of CsI, CsCl and CsBr with unprecedentedly small dimensions are obtained using oleylammonium halides and cesium oleate as precursors. The ease and adaptability of our method enables its universalization for the formation of other highly ionic nanocrystals.

Glucagon secretion from the perfused rat pancreas. Studies with glucose and catecholamines.

The isolated in situ perfused rat pancreas was used to study glucose and catecholamine control of glucagon secretion, and to investigate the possible role of endogenous cyclic AMP as a mediator of this secretory process. When perfusate glucose was acutely dropped from 100 to 25 mg/100 ml, glucagon was released in a biphasic pattern with an early spike and a later plateau-like response. 300 mg/100 ml glucose suppressed glucagon secretion to near the detection limit of the radioimmunoassay (15 pg/ml). When perfusate glucose was dropped from 300 to 25 mg/100 ml, a delayed, relatively small peak occurred suggesting persisting alpha cell suppression by prior high glucose exposure. 2-Deoxy d-glucose stimulated glucagon secretion and inhibited insulin secretion. Glucagon was secreted in a biphasic pattern in response to both 2.7 x 10(-7) M epinephrine and norepinephrine. The glucagon response to epinephrine was markedly suppressed by glucose at 300 mg/100 ml, and the biphasic response pattern was obliterated. Glucose evoked a two-phase insulin secretory pattern, and the second phase was markedly and rapidly inhibited by epinephrine. Pancreases were perfused with glucose at 300 mg/100 ml which was then lowered to 80 mg/100 ml. 5 min later, epinephrine was infused and definite blunting of the first-phase spike occurred. 10 mM theophylline produced modest rapid uniphasic stimulation of glucagon release, and, in addition, caused enhancement of epinephrine-stimulated glucagon release. An inhibitory influence upon epinephrine-stimulated glucagon was observed as well. Insulin secretion was stimulated by 10 mM theophylline, and this stimulation was inhibited by epinephrine.

Basal phosphatidylinositol turnover controls aortic Na+/K+ ATPase activity.

To determine whether basal phosphoinositide turnover plays a role in metabolic regulation in resting rabbit aortic intima-media incubated under steady state conditions, we used deprivation of extracellular myo-inositol as a potential means of inhibiting basal phosphatidylinositol (PI) synthesis at restricted sites and of depleting small phosphoinositide pools with a rapid basal turnover. Medium myo-inositol in a normal plasma level was required to prevent inhibition of a specific component of basal de novo PI synthesis that is necessary to demonstrate a discrete rapidly turning-over [1,3-14C]glycerol-labeled PI pool. Medium myo-inositol was also required to label the discrete PI pool with [1-14C]arachidonic acid (AA). The rapid basal turnover of this PI pool, when labeled with glycerol or AA, was not attributable to its utilization for polyphosphoinositide formation, and it seems to reflect basal PI hydrolysis. Depleting endogenous free AA with medium defatted albumin selectively inhibits the component of basal de novo PI synthesis that replenishes the rapidly turning-over PI pool. A component of normal resting energy utilization in aortic intima-media also specifically requires medium myo-inositol in a normal plasma level and a free AA pool; its magnitude is unaltered by indomethacin, nordihydroguaiaretic acid, or Ca2+-free medium. This energy utilization results primarily from Na+/K+ ATPase activity (ouabain-inhibitable O2 consumption), and in Ca2+-free medium deprivation of medium myo-inositol or of free AA inhibits resting Na+/K+ ATPase activity to a similar degree (60%, 52%). In aortic intima-media basal PI turnover controls a major fraction of resting Na+/K+ ATPase activity.

Compliance-Free ZrO2/ZrO2 - x /ZrO2 Resistive Memory with Controllable Interfacial Multistate Switching Behaviour.

A controllable transformation from interfacial to filamentary switching mode is presented on a ZrO2/ZrO2 - x /ZrO2 tri-layer resistive memory. The two switching modes are investigated with possible switching and transformation mechanisms proposed. Resistivity modulation of the ZrO2 - x layer is proposed to be responsible for the switching in the interfacial switching mode through injecting/retracting of oxygen ions. The switching is compliance-free due to the intrinsic series resistor by the filaments formed in the ZrO2 layers. By tuning the RESET voltages, controllable and stable multistate memory can be achieved which clearly points towards the capability of developing the next-generation multistate high-performance memory.

Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition.

Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin films with the thickness of a few nanometers on rough surfaces. We present a new "paradigm shift" non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In,Ga)Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase.

Tuning localized plasmons in nanostructured substrates for surface-enhanced Raman scattering.

Comprehensive reflectivity mapping of the angular dispersion of nanostructured arrays comprising of inverted pyramidal pits is demonstrated. By comparing equivalently structured dielectric and metallic arrays, diffraction and plasmonic features are readily distinguished. While the diffraction features match expected theory, localised plasmons are also observed with severely flattened energy dispersions. Using pit arrays with identical pitch, but graded pit dimensions, energy scaling of the localized plasmon is observed. These localised plasmons are found to match a simple model which confines surface plasmons onto the pit sidewalls thus allowing an intuitive picture of the plasmons to be developed. This model agrees well with a 2D finite-difference time-domain simulation which shows the same dependence on pit dimensions. We believe these tuneable plasmons are responsible for the surface-enhancement of the Raman scattering (SERS) of an attached layer of benzenethiol molecules. Such SERS substrates have a wide range of applications both in security, chemical identification, environmental monitoring and healthcare.

Bridging the "green gap" of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals.

Green LEDs do not show the same level of performance as their blue and red cousins, greatly hindering the solid-state lighting development, which is the so-called "green gap". In this work, nano-void photonic crystals (NVPCs) were fabricated to embed within the GaN/InGaN green LEDs by using epitaxial lateral overgrowth (ELO) and nano-sphere lithography techniques. The NVPCs act as an efficient scattering back-reflector to outcouple the guided and downward photons, which not only boost the light extraction efficiency of LEDs with an enhancement of 78% but also collimate the view angle of LEDs from 131.5° to 114.0°. This could be because of the highly scattering nature of NVPCs which reduce the interference giving rise to Fabry-Perot resonance. Moreover, due to the threading dislocation suppression and strain relief by the NVPCs, the internal quantum efficiency was increased by 25% and droop behavior was reduced from 37.4% to 25.9%. The enhancement of light output power can be achieved as high as 151% at a driving current of 350 mA. Giant light output enhancement and directional control via NVPCs point the way towards a promising avenue of solid-state lighting.