Design optimisation of ring elements for broadband reflectarray antennas

Plane wave scattering from a flat surface consisting of two periodic arrays of ring elements printed on a grounded dielectric sheet is investigated. It is shown that the reflection phase variation as a function of ring diameter is controlled by the difference in the centre resonant frequency of the two arrays. Simulated and measured results at X-band demonstrate that this parameter can be used to reduce the gradient and improve the linearity of the reflection phase versus ring size slope. These are necessary conditions for the re-radiating elements to maximise the bandwidth of a microstrip reflectarray antenna. The scattering properties of a conventional dual resonant multilayer structure and an array of concentric rings printed on a metal backed dielectric substrate are compared and the trade-off in performance is discussed.

Accurate computational methods for two-electron atom-laser interactions

We discuss the application of quantitatively accurate computational methods to the study of laser-driven two-electron atoms in short intense laser pulses. The fundamental importance of such calculations to the subject area is emphasized. Calculations of single- and double-electron ionization rates at 390 nm are presented. (C) 2001 Optical Society of America.

Energetics reveals physiologically distinct castes in a eusocial mammal.

Eusociality, which occurs among mammals only in two species of African mole-rat, is characterized by division of labour between morphologically distinct 'castes'1. In Damaraland mole-rats (Cryptomys damarensis), colony labour is divided between 'infrequent worker' and 'frequent worker' castes2. Frequent workers are active year-round and together perform more than 95% of the total work of the colony, whereas infrequent workers typically perform less than 5% of the total work3. Anecdotal evidence suggests that infrequent workers may act as dispersers, with dispersal being limited to comparatively rare periods when the soil is softened by moisture4, 5. Here we show that infrequent workers and queens increase their daily energy expenditure after rainfall whereas frequent workers do not. Infrequent workers are also fatter than frequent workers. We suggest that infrequent workers constitute a physiologically distinct dispersing caste, the members of which, instead of contributing to the work of the colony and helping the queen to reproduce, build up their own body reserves in preparation for dispersal and reproduction when environmental conditions are suitable.

A Debriefing Session with a Nutritionist Can Improve Dietary Assessment Using Food Diaries.

The objective of the current study was to evaluate the effect of a debriefing call on nutrient intake estimates using two 3-d food diaries among women participating in the Women's Health and Interview Study (WISH) Diet Validation Study. Subjects were 207 women with complete data and six 24-h recalls (24-HR) by telephone over 8 mo followed by two 3-d food diaries during the next 4 mo. Nutrient intake was assessed using the food diaries before and after a debriefing session by telephone. The purpose of the debriefing call was to obtain more detailed information on the types and amounts of fat in the diet. However, due to the ubiquitous nature of fat in the diet, the debriefing involved providing more specific detail on many aspects of the diet. There was a significant difference in macronutrient and micronutrient intake estimates after the debriefing. Estimates of protein, carbohydrate, and fiber intake were significantly higher and total fat, monounsaturated fat, saturated fat, vitamin A, vitamin C, -tocopherol, folic acid, and calcium intake were significantly lower after the debriefing (P <0.05). The limits of agreement between the food diaries before and after the debriefing were especially large for total fat intake, which could be under- or overestimated by 15 g/d. The debriefing call improved attenuation coefficients associated with measurement error for vitamin C, folic acid, iron, tocopherol, vitamin A, and calcium estimates. A hypothetical relative risk (RR) = 2.0 could be attenuated to 1.16 for folic acid intake assessed without a debriefing but to only 1.61 with a debriefing. Depending on the nutrients of interest, the inclusion of a debriefing can reduce the potential attenuation of RR in studies evaluating diet disease associations.

Relationships between antioxidant activity, color, and flavor compounds of crystal malt extracts

Aqueous extracts were prepared from five barley crystal malts (color range 15-440 degrees EBC, European Brewing Convention units). Antioxidant activity was determined by using the 2,2'-azinobis(3-ethylbenothiazoline-6-sulfonic acid) (ABTS(.+)) radical cation scavenging method. Antioxidant activity increased with increasing color value although the rate of increase decreased with increasing color value. Color was measured in CIELAB space. Extracts of the 15, 23, and 72 degrees EBC malts followed the same dilution pathway as did the 148 degrees EBC sample at higher dilution levels, indicating that they could each be used to give the same color by appropriate dilution. The 440 degrees EBC sample followed a different dilution pathway, indicating that different compounds were responsible for color in this extract. Fifteen selected volatile compounds were monitored using gas chromatography/mass spectrometry (GC/MS). Levels of methylpropanal, 2-methylbutanal, and 3-methylbutanal were highest for the 72 degrees EBC sample. When odor threshold values of the selected compounds were taken into account, 3-methylbutanal was the most important contributor to flavor., Relationships between levels of the lipid oxidation products, hexanal and (E)-2-nonenal, and antioxidant activity were complex, and increasing antioxidant activity for samples in the range of 15-148 degrees EBC did-not result in reduced levels of these lipid-derived compounds. When different colored malt extracts were diluted to give the same a* and b* values, calculated antioxidant activity and amounts of 3-methylbutanal, hexanal, and (E)-2-nonenal decreased with increasing degrees EBC value.

Role of TGF-beta1 and nitric oxide in the bystander response of irradiated glioma cells.

The radiation-induced bystander effect (RIBE) increases the probability of cellular response and therefore has important implications for cancer risk assessment following low-dose irradiation and for the likelihood of secondary cancers after radiotherapy. However, our knowledge of bystander signaling factors, especially those having long half-lives, is still limited. The present study found that, when a fraction of cells within a glioblastoma population were individually irradiated with helium ions from a particle microbeam, the yield of micronuclei (MN) in the nontargeted cells was increased, but these bystander MN were eliminated by treating the cells with either aminoguanidine (an inhibitor of inducible nitric oxide (NO) synthase) or anti-transforming growth factor beta1 (anti-TGF-beta1), indicating that NO and TGF-beta1 are involved in the RIBE. Intracellular NO was detected in the bystander cells, and additional TGF-beta1 was detected in the medium from irradiated T98G cells, but it was diminished by aminoguanidine. Consistent with this, an NO donor, diethylamine nitric oxide (DEANO), induced TGF-beta1 generation in T98G cells. Conversely, treatment of cells with recombinant TGF-beta1 could also induce NO and MN in T98G cells. Treatment of T98G cells with anti-TGF-beta1 inhibited the NO production when only 1% of cells were targeted, but not when 100% of cells were targeted. Our results indicate that, downstream of radiation-induced NO, TGF-beta1 can be released from targeted T98G cells and plays a key role as a signaling factor in the RIBE by further inducing free radicals and DNA damage in the nontargeted bystander cells.