FAST MODE SURFACE-PLASMON DAMPING ON TUNNEL JUNCTION STRUCTURES

Using a prism-air gap-sample (Otto) configuration we have optically excited surface plasmon polaritons at the Ag-air interface of passive Al-Al oxide-Ag tunnel junction structures at wavelength 632.8 nm. It is found that the internal damping of this excitation is more than a factor of 2 greater for samples with a very thin (approximately 15 nm) Ag electrode than for samples with a thicker (approximately 40 nm) Ag electrode. This observation is explained by the fact that the fields of the surface plasmon polariton penetrate more substantially into the lossy Al base electrode when the Ag top electrode is very thin.

Energy compensation in the real world: Good compensation for small portions of chocolate and biscuits over short time periods in complicit consumers using commercially available foods

While investigations using covert food manipulations tend to suggest that individuals are poor at adjusting for previous energy intake, in the real world adults rarely consume foods of which they are ill-informed. This study investigated the impact in fully complicit consumers of consuming commercially available dark chocolate, milk chocolate, sweet biscuits and fruit bars on subsequent appetite. Using a repeated measures design, participants received four small portions (4 × 10-11 g) of either dark chocolate, milk chocolate, sweet biscuits, fruit bars or no food throughout five separate study days (counterbalanced in order), and test meal intake, hunger, liking and acceptability were measured. Participants consumed significantly less at lunch following dark chocolate, milk chocolate and sweet biscuits compared to no food (smallest t(19) = 2.47, p = 0.02), demonstrating very good energy compensation (269-334%). No effects were found for fruit bars (t(19) = 1.76, p = 0.09), in evening meal intakes (F(4,72) = 0.62, p = 0.65) or in total intake (lunch + evening meal + food portions) (F(4,72) = 0.40, p = 0.69). No differences between conditions were found in measures of hunger (largest F(4,76) = 1.26, p = 0.29), but fruit bars were significantly less familiar than all other foods (smallest t(19) = 3.14, p = 0.01). These findings demonstrate good compensation over the short term for small portions of familiar foods in complicit consumers. Findings are most plausibly explained as a result of participant awareness and cognitions, although the nature of these cognitions cannot be discerned from this study. These findings however, also suggest that covert manipulations may have limited transfer to real world scenarios.

Fast Convergence of Regularised Region-based Mixture of Gaussians for Dynamic Background Modelling

The momentum term has long been used in machine learning algorithms, especially back-propagation, to improve their speed of convergence. In this paper, we derive an expression to prove the O(1/k2) convergence rate of the online gradient method, with momentum type updates, when the individual gradients are constrained by a growth condition. We then apply these type of updates to video background modelling by using it in the update equations of the Region-based Mixture of Gaussians algorithm. Extensive evaluations are performed on both simulated data, as well as challenging real world scenarios with dynamic backgrounds, to show that these regularised updates help the mixtures converge faster than the conventional approach and consequently improve the algorithm’s performance.

Effects of resistive magnetic field on fast electron divergence measured in experiments

Transport of fast electrons driven by an ultraintense laser through a tracer layer buried in solid targets is studied by particle-in-cell simulations. It is found that intense resistive magnetic fields, having a magnitude of several thousand Tesla, are generated at the interfaces of the materials due to the steep resistivity gradient between the target and tracer layer. Such magnetic fields can significantly inhibit the fast electron propagation. The electrons that can penetrate the first interface are mostly confined in the buried layer by the magnetic fields and cause heating of the tracer layer. The lateral extent of the heated region can be significantly larger than that of the relativistic electron beam. This finding suggests that the relativistic electron divergence inferred from Ká x-ray emission in experiments might be overestimated.

Fast-electron refluxing effects on anisotropic hard-x-ray emission from intense laser-plasma interactions

Fast-electron generation and dynamics, including electron refluxing, is at the core of understanding high-intensity laser-plasma interactions. This field is itself of strong relevance to fast ignition fusion and the development of new short-pulse, intense, x-ray, gamma-ray, and particle sources. In this paper, we describe experiments that explicitly link fast-electron refluxing and anisotropy in hard-x-ray emission. We find the anisotropy in x-ray emission to be strongly correlated to the suppression of refluxing. In contrast to some previous work, the peak of emission is directly along the rear normal to the target rather than along either the incident laser direction or the specular reflection direction.

High content analysis: A sensitive tool to detect and quantify the cytotoxic, synergistic and antagonistic effects of chemical contaminants in foods

Aflatoxin B1 (AFB1), ochratoxin A (OTA) and fumonisin B1 (FB1) are important mycotoxins in terms of
human exposure via food, their toxicity and regulatory limits that exist worldwide. Mixtures of toxins can frequently be present in foods, however due to the complications of determining their combined toxicity,
legal limits of exposure are determined for single compounds, based on long standing toxicological
techniques. High content analysis (HCA) may be a useful tool to determine total toxicity of complex
mixtures of mycotoxins. Endpoints including cell number (CN), nuclear intensity (NI), nuclear area (NA),
plasma membrane permeability (PMP), mitochondrial membrane potential (MMP) and mitochondrial
mass (MM) were compared to the conventional 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium
bromide (MTT) and neutral red (NR) endpoints in MDBK cells. Individual concentrations of each
mycotoxin (OTA 3mg/ml, FB1 8mg/ml and AFB11.28mg/ml) revealed no cytotoxicity with MTTor NR but
HCA showed significant cytotoxic effects up to 41.6% (p0.001) and 10.1% (p0.05) for OTA and AFB1,
respectively. The tertiary mixture (OTA 3mg/ml, FB1 8mg/ml and AFB1 1.28mg/ml) detected up to 37.3%
and 49.8% more cytotoxicity using HCA over MTT and NR, respectively. Whilst binary combinations of
OTA (3mg/ml) and FB1 (8mg/ml) revealed synergistic interactions using HCA (MMP, MM, NI endpoints)
not detected using MTT or NR. HCA is a highly novel and sensitive tool that could substantially help
determine future regulatory limits, for single and combined toxins present in food, ensuring legislation is based on true risks to human health exposure.

Rapid quantification of microRNAs in plasma using a fast real time PCR system

The ability to rapidly detect circulating small RNAs, in particular microRNAs (miRNAs), would further increase their already established potential as biomarkers in a range of conditions. One rate-limiting factor is the time taken to perform quantitative real time PCR amplification. We therefore evaluated the ability of a novel thermal cycler to perform this step in less than 10 minutes. Quantitative PCR was performed on an xxpress® thermal cycler (BJS Biotechnologies, Perivale, UK), which employs a resistive heating system and forced air cooling to achieve thermal ramp rates of 10 °C/s, and a conventional peltier-controlled LightCycler 480 system (Roche, Basel, Switzerland) ramping at 4.8 °C/s. The threshold cycle (Ct) for detection of 18S rDNA from a standard genomic DNA sample was significantly more variable across the block (F-test, p=2.4x10-25) for the xxpress (20.01±0.47SD) than the LightCycler (19.87±0.04SD). RNA was extracted from human plasma, reverse transcribed and a panel of miRNAs amplified and detected using SYBR green (Kapa Biosystems, Wilmington, Ma, USA). The sensitivity of both systems was broadly comparable and both detected a panel of miRNAs reliably and indicated similar relative abundances. The xxpress thermal cycler facilitates rapid qPCR detection of small RNAs and brings point-of care diagnostics based upon circulating miRNAs a step closer to reality.

STARTEC: Novel processing technologies in the development of a decision support tool to ensure safe and nutritious Ready-To-Eat foods

Ready-to-eat (RTE) foods can be readily consumed with minimum or without any further preparation; their processing is complex—involving thorough decontamination processes— due to their composition of mixed ingredients. Compared with conventional preservation technologies, novel processing technologies can enhance the safety and quality of these complex products by reducing the risk of pathogens and/ or by preserving related health-promoting compounds. These novel technologies can be divided into two categories: thermal and non-thermal. As a non-thermal treatment, High Pressure Processing is a very promising novel methodology that can be used even in the already packaged RTE foods. A new “volumetric” microwave heating technology is an interesting cooking and decontamination method directly applied to foods. Cold Plasma technology is a potential substitute of chlorine washing in fresh vegetable decontamination. Ohmic heating is a heating method applicable to viscous products but also to meat products. Producers of RTE foods have to deal with challenging decisions starting from the ingredients suppliers to the distribution chain. They have to take into account not only the cost factor but also the benefits and food products’ safety and quality. Novel processing technologies can be a valuable yet large investment for several SME food manufacturers, but they need support data to be able to make adequate decisions. Within the FP7 Cooperation funded by the European Commission, the STARTEC project aims to develop an IT decision supporting tool to help food business operators in their risk assessment and future decision making when producing RTE foods with or without novel preservation technologies.

Effect of polyethylenimine, a cell permeabilizer, on the photosensitized destruction of algae by methylene blue and nuclear fast red

The present study reports the effect a cell permeabilizer, polyethylenimine (PEI) has on the photodynamic effect of methylene blue (MB) and nuclear fast red (NFR) in the presence of hydrogen peroxide (H₂O₂). The photosensitized destruction of the algae Chlorella vulgaris under irradiation with visible light is examined. The photodynamic effect was investigated under aerobic and anaerobic conditions. The presence of a permeabilizer during the photosensitized destruction of C. vulgaris does not enhance the activity of the MB, MB/H₂O₂ system or the NFR, NFR/H₂O ₂ system under aerobic conditions. However under anaerobic conditions we have determined that when a cell permeabilizer was added to the MB/H ₂O₂ system, the photosensitized destruction of C. vulgaris proceeded via a combination of Type I and Type II mechanisms. The presence of PEI enforces MB/H₂O₂ to be active toward the destruction of C. vulgaris whether oxygen is present or absent. Under aerobic and anaerobic conditions the activity of NFR was suppressed in the presence of PEI as a result of electrostatic interactions between the photosensitizer and the cell permeabilizer. The decrease in fluorescence recorded is indicative of destruction of the chlorophyll a pigment. 

Photosensitized destruction of Chlorella vulgaris by methylene blue or nuclear fast red combined with hydrogen peroxide under visible light irradiation

A considerable number of investigations have started to elucidate the essential roles biological agents play in the biodeterioration of stone. Chemical biocides are becoming increasingly banned because of the environmental and health hazards associated with these toxic substances. The present study reports the photodynamic effect of Methylene Blue (MB) and Nuclear Fast Red (NFR) in the presence of hydrogen peroxide (H₂O₂) on the destruction of the algae Chlorella vulgaris (C. vulgaris) under irradiation with visible light. Illumination of C. vulgaris in the presence of MB or NFR combined with H₂O₂ results in the decomposition of both the algal species and the photosensitizer. The photodynamic effect was investigated under aerobic and anaerobic conditions. Differences in mechanism type are reported and are dependent on both the presence and the absence of oxygen. The behavior of each photosensitizer leads to a Type II mechanism and a Type I/Type II combination for MB and NFR, respectively, being concluded. This novel combination could be effective for the remediation of biofilm-colonized stone surfaces.

Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

The high-current fast electron beams generated in high-intensity laser-solid interactions require the onset of a balancing return current in order to propagate in the target material. Such a system of counter-streaming electron currents is unstable to a variety of instabilities such as the current-filamentation instability and the two-stream instability. An experimental study aimed at investigating the role of instabilities in a system of symmetrical counter-propagating fast electron beams is presented here for the first time. The fast electron beams are generated by double-sided laser-irradiation of a layered target foil at laser intensities above 10(19) W/cm(2). High-resolution X-ray spectroscopy of the emission from the central Ti layer shows that locally enhanced energy deposition is indeed achieved in the case of counter-propagating fast electron beams

High resolution X-ray spectroscopy in fast electron transport studies

A detailed knowledge of the physical phenomena underlying the generation and the transport of fast electrons generated in high-intensity laser-matter interactions is of fundamental importance for the fast ignition scheme for inertial confinement fusion.

Here we report on an experiment carried out with the VULCAN Petawatt beam and aimed at investigating the role of collisional return currents in the dynamics of the fast electron beam. To that scope, in the experiment counter-propagating electron beams were generated by double-sided irradiation of layered target foils containing a Ti layer. The experimental results were obtained for different time delays between the two laser beams as well as for single-sided irradiation of the target foils. The main diagnostics consisted of two bent mica crystal spectrometers placed at either side of the target foil. High-resolution X-ray spectra of the Ti emission lines in the range from the Ly alpha to the K alpha line were recorded. In addition, 2D X-ray images with spectral resolution were obtained by means of a novel diagnostic technique, the energy-encoded pin-hole camera, based on the use of a pin-hole array equipped with a CCD detector working in single-photon regime. The spectroscopic measurements suggest a higher target temperature for well-aligned laser beams and a precise timing between the two beams. The experimental results are presented and compared to simulation results.

X-ray Polarization Measurements of Dense Plasmas Heated by Fast Electrons

The detailed knowledge of fast electron energy transport following interaction with high-intensity, ultra-short laser pulses is a key area for secondary source generation for ELI. We demonstrate polarization spectroscopy at laser intensities up to 10(21) Wcm(-2). This is significant as it suggests that in situ emission spectroscopy may be used as an effective probe of fast electron velocity distributions in regimes relevant to electron transport in solid targets. Ly-alpha doublet emission of nickel (Z = 28) and sulphur (Z = 16) is observed to measure the degree of polarization from the Ly-alpha(1) emission. Ly-alpha(2) emission is unpolarized, and as such acts as a calibration source between spectrometers. The measured ratio of the X-ray sigma- and pi-polarization allows the possibility to infer the velocity distribution function of the fast electron beam.