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We report the use of a terahertz (THz) receiver fabricated using a photoconductive antenna mounted upon a distributed Bragg reflector (DBR). It is shown that the relative performance of the device is in accordance with the reflectivity curves of the DBR. At maximum reflectivity the device improved upon the reference THz signal by up to 30%. In addition, we characterize the saturation of the device with laser pump power and it is shown that the device exhibits an improved optical efficiency when compared to the reference receiver.

Notes that of 600 carotenoids found in nature, only 40 are regularly consumed by humans. Looks at the biological functions of carotenoids. Reports on studies with regard to the effects on health carotenoid‐rich diets.

Despite interest in the health-beneficial role of carotenoids little is known about the specific storage metabolism and mechanisms involved in various target tissues. The aim of the study was to search for a relatively simple non-invasive method to detect and determine the cellular effects of supplemented dosage of beta-carotene and lycopene to peripheral tissues such as the buccal mucosa in relation to the plasma concentrations. Subjects (30) were allocated into five different subgroups of 6 volunteers. The change in concentration of all-trans-beta-carotene and lycopene in plasma and in buccal mucosal cells was measured in groups of volunteers supplemented with either 15 mg, 30 mg or placebo capsules in a randomised double blind study for a period of 7 days. With the exception of supervised high fat (40 g carotenoid free sunflower oil) breakfasts and capsule ingestion the volunteers ate their habitual diets. Plasma lycopene and beta-carotene concentrations were determined at baseline and following one week of capsule ingestion. In all the supplemented groups the plasma carotenoid levels were significantly higher than in the placebo group indicating absorption of the supplement. Carotenoid concentrations, expressed per unit protein, assayed in buccal mucosal cells before (at baseline) and at the end of the study were found to be significantly higher in the groups supplemented at 30 mg/d, of either carotenoid as compared to the 15 mg/d or placebo supplemented groups. We conclude that buccal mucosal cells respond readily to changes in plasma beta-carotene and lycopene concentration. These observations suggest that dietary carotenoids are quickly incorporated into rapidly turning over mucosal tissues. It is not clear if the change in carotenoid content of the plasma is reflected in existing cells or only in those concurrently produced during the elevated plasma concentration. If desquamated buccal mucosal cells reflect habitual plasma carotenoid concentration then it is not an appropriate tissue for the measurement of acute changes.

We report the use of a multilayered structure comprising of alternating layers of low temperature grown GaAs and high temperature grown AlAs, as a terahertz (THz) photoconductive antenna emitter and receiver. Devices based on 10×10 μm2 mesa defined photoconductive gaps were fabricated on the multilayered structure, and a comparison made to conventional planar devices. The mesa defined photoconductive antennas allowed successive contact through the multilayered structure, which resulted in an increase in THz emission power and detection responsivity with increasing number of layers in contact with the antenna electrodes. A comparison with a conventional single layered device, processed in an identical mesa geometry, confirmed that the enhancement in THz emission is solely due to the multilayered nature of the device, whereas the improved receiver performance can be partially attributed to the mesa geometry.

We present a terahertz (THz) photoconductive emitter structure, which employs a n-doped layer underneath a low-temperature-grown GaAs region to enable the THz transient to couple vertically through a defined mesa. A nonlinear bias dependence is observed, yielding an order in magnitude improvement in power for a mesa device with a 100 μm2 area over a conventional planar control reference device at 32 V and 5 mW illumination power. We relate the bias dependence of the THz signal to the breakdown voltage observed in the current-voltage characteristic. Reducing the antenna gap size through reducing the thickness of the low temperature-GaAs region below 1 μm shows a large improvement in the bandwidth of the device, with an enhancement of the normalized intensity between 0.2 to 2 THz for a bow-tie antenna geometry.

We present a study into the properties of terahertz (THz) emission and detection using low temperature grown GaAs photoconductive switches over a range of ex situ anneal temperatures. Our analysis focuses on the effect of defect saturation, which has been confirmed in many experiments. However its effect on the THz emission and detection has so far not been fully investigated. In this letter, we examine the dependence of the radiated THz pulse width (full width at half maximum) upon optical power, and show that the differences in the characteristics with annealing can be theoretically accounted for when defect saturation is taken into account. Defect saturation was found to substantially increase the trapping time of photoexcited electrons, which in turn can cause THz pulse broadening at high optical powers. This effect was found to increase with anneal temperature due to the decrease in defect density. The radiated peak THz amplitude from emitters increases monotonically with increasing optical power acr...

When the potato gained popular acceptance as a food item in the UK about 200 years ago it quickly became, and has remained, a major component of the diet. The reasons for its popularity are both agronomic and culinary. The potato is easily cultivated in our temperate climate and gives good yields even if harvested immature in summer, as often happened, to fill the gap between cereal harvests. The potato has a natural dormant period which allows it to be stored through the winter months when other fresh vegetables are in short supply. It lends itself readily to a wide range of cooking methods of which the most common are chipped, boiled, mashed, roast and baked, although it can also be made into flour and used to replace or extend wheat flour in certain baked foods. So well established has the potato become that it is now difficult to envisage a hot cooked meal without potatoes — despite the popularity and convenience of pastas and rice.

The texture of cooked potato is an amalgam of those physical characteristics perceived during preparation and consumption. They may range from a visual assessment of disintegration and flouriness, hardness or crispness, physical work needed to mash, cut, or penetrate with a fork, through to the more subtle sensations of bite, smoothness or graininess sensed in the mouth. Different criteria for the assessment of textural quality will be applied to different cooked potato products, such as boiled, mashed, chipped, roast or baked potatoes, and it is therefore important to understand the underlying physical, compositional and chemical properties of the tuber and how they contribute to the production of textural attributes.