Fluxes of radiocaesium in selected rural study sites in Russia and Ukraine.

Food production and food harvesting systems common in the areas contaminated by the Chernobyl accident in Russia and Ukraine can be grouped into three major categories: collective farm produce, private farming produce and foods collected from natural ecosystems. The contribution of each of these sources to radiocaesium intake by people living in rural settlements in the mid 1990s has been estimated at two major study sites, one in each country. The collective farm system provided the smallest contribution (7-14%) to the intake of radiocaesium at both sites. Natural food was the major contributor to intake at the Russian site (83%). Whereas private farm produce was the major contributor (68%) at the Ukrainian study site. The difference between the two sites was mainly because private milk production was stopped at the Russian site due to the contamination in 1986. A retrospective assessment of the situation 1 year after the accident shows that collective farming could have been a minor contributor to radiocaesium intake (8%), whilst private farming would have been the major contributor wherever private milk production and consumption continued. The extent to which inhabitants consume natural foods from forests has a considerable effect on their radiocaesium intake. The comparative importance of food products from natural ecosystems increases with time due to the long effective ecological half-lives of radiocaesium in unimproved pastures and forests. Estimation of the fluxes of radiocaesium from the different production and harvesting systems showed that the contribution from private farming and food harvesting from natural ecosystems may be significant, contributing 14-30% to the total fluxes of radiocaesium from an area even if the quantity of food produced in these systems is small. However, the major contributor to the flux exported from an area was the collective farming system, accounting for about 70-86% of the total.     

A Distinctive Feature of the Surface Structure of Quasicrystals: Intrinsic and Extrinsic Heterogeneity

This paper reviews a feature of atomically-clean quasicrystal surfaces that distinguishes them from surfaces of crystalline materials. That feature is a high degree of heterogeneity among different terraces, and among structurally-identical adsorption sites. The heterogeneity can be both structural and chemical in origin. A large variability is expected even for a surface which is perfectly bulk-terminated, and we call this intrinsic heterogeneity. Additional variability can derive from the surface preparation process, which can yield metastable structures. We call this extrinsic heterogeneity. Experimental evidence is given for both cases. This heterogeneity can be an important factor in understanding and predicting surface phenomena such as chemisorption.     

Consumer characteristics and e-grocery services: the primacy of the primary shopper

Electronic Commerce Research - The literature does not agree on the precise role of socio-demographic characteristics in the adoption of online grocery shopping. This methodological note reviews...     

3-mm double-heterojunction microwave power HEMT fabricated byselective RIE

Current-voltage and initial RF measurements are presented on a double-heterojunction HEMT (high-electron-mobility transistor) structure designed for power MMIC applications. The device structure is grown by molecular-beam epitaxy and uses a spatially variant superlattice to improve the performance of the inverted AlGaAs/GaAs interface. Gate recessing is achieved using a hybrid wet-chemical selective dry etching process. For selective dry etching, reactive ion etching with a >600:1 selectivity for GaAs over AlGaAs is used to control the recess depth. The room temperature DC characteristics for a 3-mm power FET (0.7- μm gate) display an I_dss of 370 mA/mm, a peak transconductance of 180 mS/mm, and a maximum gate-to-drain breakdown of 22 V. Large-signal microwave measurements at 5.5 GHz yielded a saturated output power of 1.3 W (31.2 dBm), 8.3-dB large-signal gain, and a peak power-added efficiency of 55%     

Heat exchange in liquid helium by phonon tunneling through very thin plates

Thin plates with a thicknessd smaller than the phonon mean-free path can be used to increase the heat exchange in ³ He- ⁴ He refrigerators at very low temperatures. The resistanceR for the heat current density of these plates is theoretically investigated. For plates withd still larger than the dominant thermal-phonon wavelength _T in the plate,R is given by twice the Kapitza resistance. Ford _T the resistanceR decreases due to phonon tunneling. Ford _T there exists a region whereR varies asT ^–1, in contrast to theT ^–3 dependence for thicker plates. Numerical calculations are carried out for copper plates immersed in pure ⁴ He. The results show that one obtains a large increase of the heat exchange due to phonon tunneling for plates with a thickness of a few microns at temperatures in the millidegree range.     

Insulin secretion in lactating cows: responses to glucose infused intravenously in normal, ketonemic, and starved animals.

Changes in insulin concentrations of blood plasma were studied in lactating cows during and after a 1-h intravenous glucose infusion in 5 spontaneously ketonemic, 10 nonketonemic (normal), and 4 starved cows. A biphasic increase in insulin with a maximum 10 to 20 min after the start of the glucose infusion was followed by a sustained (1 to 2 h) elevation in the normal and ketonemic animals. In starved cows only the later phase was detectable. Insulin was higher in normal than in starved and ketonemic cows during both phases of the insulin secretion in spite of approximately identical glucose. Differences between starved and ketonemic cows were not major. Average rates of decline in sugar concentrations after the end of the infusion were higher in normal and ketonemic [half times 143 +/- 23 (standard deviation) and 166 +/- 22 min] than in starved cows (281 +/- 47 min). The low basal insulin of plasma and poor responses of insulin secretion following glucose infusions indicate sluggish beta-cell function in ketonemic cows.     

Long-term stability of cardiac function in normal and chronically failing mouse hearts in a vertical-bore MR system

We previously demonstrated stability of ventricular volumes and cardiac function in normal and in chronically failing mouse hearts in MR systems with a vertical-bore magnet for up to 1 h. However, in order to exploit the benefits of an increased magnetic field strength of these MR systems in more time-consuming studies required by, for example MR spectroscopy, we investigated whether cardiac function and ventricular volumes of healthy and infarcted mice would be affected in vertical position over a prolonged period. We applied high-resolution MR cine imaging on an 11.7 T vertical MR system to monitor cardiac functional parameters of normal and chronically failing mouse hearts over a period of 3 h in an upright position, with a temporal resolution of 15 min. We monitored left-ventricular volumes and cardiac functional parameters in both groups. In normal mice, we detected a decrease of left-ventricular end-systolic volumes by 8 l and an approximately 23% increase of ejection fraction over time indicating a small but detectable degree of orthostatic dysregulation. Observed changes were more pronounced in mice with heart failure. Despite significant changes in left-ventricular volumes and function, absolute values measured for all functional cardiac parameters are consistent with near-physiological conditions. Thus, mice can be studied in high-field MR systems positioned vertically for 3 h.     

S-parameter measurement based quasistatic large-signal cold HEMT model for resistive mixer design

The nonlinear cold HEMT model generation procedure is described. It starts with the determination of the corresponding small-signal model by adapting the cold FET extraction approach for HEMTs. Then, the small-signal model is transformed to obtain a straightforward implementable, consistent small-signal cold HEMT model, suitable for resistive mixer design. © 1996 John Wiley & Sons, Inc.