On the accuracy of analysed low temperatures in the stratosphere

International audienceThe accuracy of ECMWF (European Centre for Medium-Range Weather Forecasts) temperatures has been investigated by comparison to radiosonde temperatures. Particularly, the extent of temperatures below which Polar Stratospheric Clouds (PSCs) consisting of nitric acid trihydrate can exist (TNAT) has been studied. In the 1999/2000 winter analyses and in the 40 year reanalyses (ERA40) from the winter 1996/1997 the analysed extent agrees quite well with the radiosondes extent, whereas the 2002/2003 winter analyses considerably overestimate the extent from 40-11 hPa due to a general cold bias. Close to the frost point small-scale temperature variations, which ECMWF does not catch, substantially increase the extent of these low temperatures. Some of these small-scale variations are caused by lee-waves

The influence of polar vortex ozone depletion on NH mid-latitude ozone trends in spring

International audienceReverse domain-filling trajectory calculations have been performed for the years 1993, 1995, 1996, 1997, and 2000 to calculate the spreading of ozone depleted air from the polar vortex to midlatitudes in spring. We find that for these years with massive Arctic ozone depletion the zonal mean total ozone column at midlatitudes is reduced with between 7 and 12 DU in the April-May period. The polar vortex and remnants have preferred locations which leads to longitudinal differences in the midlatitude ozone trends. Together with decadal variations in circulation the dilution of ozone depleted air may explain the major fraction of longitudinal differences in midlatitude ozone trends. For the period 1979?1997 the dilution may explain 50% of the longitudinal differences in ozone trends and for the period 1979?2002 it may explain 45%. The dilution also has a significant impact on the zonal mean ozone trends in the April-May period. Although uncertainties are large due to uncertainties in the ozone depletion values and neglect of ozone depletion in other years than 1993, 1995, 1996, 1997, and 2000 we have tried to calculate the size of this effect. We estimate that dilution may explain 29% of the trend in the period 1979?1997 and 33% of the trend in the period 1979?2002 as a lower limit

Development of Spatial Preferences for Counting and Picture Naming

The direction of object enumeration reflects children’s enculturation but previous work on the development of such spatial preferences has been inconsistent. Therefore, we documented directional preferences in finger counting, object counting, and picture naming for children (4 groups from 3 to 6 years, N = 104) and adults (N = 56). We found a right-side preference for finger counting in 3- to 6-year-olds and a left-side preference for counting objects and naming pictures by 6 years of age. Children were consistent in their special preferences when comparing object counting and picture naming, but not in other task pairings. Finally, spatial preferences were not related to cardinality comprehension. These results, together with other recent work, suggest a gradual development of spatial-numerical associations from early non-directional mappings into culturally constrained directional mappings

Surveying the solar system by measuring angles and times: from the solar density to the gravitational constant

A surprisingly large amount of information on our solar system can be gained from simple measurements of the apparent angular diameters of the sun and the moon. This information includes the average density of the sun, the distance between earth and moon, the radius of the moon, and the gravitational constant. In this note it is described how these and other quantities can be obtained by simple earthbound measurements of angles and times only, without using any explicit information on distances between celestial bodies. The pedagogical and historical aspects of these results are also discussed briefly.Comment: 12 pges, one figur

Provably Secure Double-Block-Length Hash Functions in a Black-Box Model

In CRYPTO’89, Merkle presented three double-block-length hash functions based on DES. They are optimally collision resistant in a black-box model, that is, the time complexity of any collision-finding algorithm for them is Ω(2^<l/2>) if DES is a random block cipher, where l is the output length. Their drawback is that their rates are low. In this article, new double-block-length hash functions with higher rates are presented which are also optimally collision resistant in the blackbox model. They are composed of block ciphers whose key length is twice larger than their block length

Fluctuation theorem for the effusion of an ideal gas

The probability distribution of the entropy production for the effusion of an ideal gas between two compartments is calculated explicitly. The fluctuation theorem is verified. The analytic results are in good agreement with numerical data from hard disk molecular dynamics simulations.Comment: 11 pages, 10 figures, 2 table

Methods for comparative evaluation of propulsion system designs for supersonic aircraft

The propulsion system comparative evaluation study was conducted to define a rapid, approximate method for evaluating the effects of propulsion system changes for an advanced supersonic cruise airplane, and to verify the approximate method by comparing its mission performance results with those from a more detailed analysis. A table look up computer program was developed to determine nacelle drag increments for a range of parametric nacelle shapes and sizes. Aircraft sensitivities to propulsion parameters were defined. Nacelle shapes, installed weights, and installed performance was determined for four study engines selected from the NASA supersonic cruise aircraft research (SCAR) engine studies program. Both rapid evaluation method (using sensitivities) and traditional preliminary design methods were then used to assess the four engines. The method was found to compare well with the more detailed analyses

The end-state comfort effect in 3- to 8-year-old children in two object manipulation tasks

The aim of the study was to compare 3- to 8-year-old children’s propensity to antici- pate a comfortable hand posture at the end of a grasping movement ( end-state comfort effect ) between two different object manipulation tasks, the bar-transport task, and the overturned-glass task. In the bar-transport task, participants were asked to insert a verti- cally positioned bar into a small opening of a box. In the overturned-glass task, participants were asked to put an overturned-glass right-side-up on a coaster. Half of the participants experienced action effects (lights) as a consequence of their movements (AE groups), while the other half of the participants did not (No-AE groups). While there was no differ- ence between the AE and No-AE groups, end-state comfort performance differed across age as well as between tasks. Results revealed a significant increase in end-state comfort performance in the bar-transport task from 13% in the 3-year-olds to 94% in the 8-year- olds. Interestingly, the number of children grasping the bar according to end-state comfort doubled from 3 to 4 years and from 4 to 5 years of age. In the overturned-glass task an increase in end-state comfort performance from already 63% in the 3-year-olds to 100% in the 8-year-olds was significant as well. When comparing end-state comfort performance across tasks, results showed that 3- and 4-year-old children were better at manipulating the glass as compared to manipulating the bar, most probably, because children are more familiar with manipulating glasses. Together, these results suggest that preschool years are an important period for the development of motor planning in which the familiarity with the object involved in the task plays a significant role in children’s ability to plan their movements according to end-state comfort

Relative validity of a web-based food frequency questionnaire for patients with type 1 and type 2 diabetes in Denmark

BACKGROUND: Diet has an important role in the management of diabetes. However, little is known about dietary intake in Danish diabetes patients. A food frequency questionnaire (FFQ) focusing on most relevant nutrients in diabetes including carbohydrates, dietary fibres and simple sugars was developed and validated. OBJECTIVES: To examine the relative validity of nutrients calculated by a web-based food frequency questionnaire for patients with diabetes. DESIGN: The FFQ was validated against a 4-day pre-coded food diary (FD). Intakes of nutrients were calculated. Means of intake were compared and cross-classifications of individuals according to intake were performed. To assess the agreement between the two methods, Pearson and Spearman's correlation coefficients and weighted kappa coefficients were calculated. SUBJECTS: Ninety patients (64 with type 1 diabetes and 26 with type 2 diabetes) accepted to participate in the study. Twenty-six were excluded from the final study population. SETTING: 64 volunteer diabetes patients at the Steno Diabetes Center. RESULTS: Intakes of carbohydrates, simple sugars, dietary fibres and total energy were higher according to the FFQ compared with the FD. However, intakes of nutrients were grossly classified in the same or adjacent quartiles with an average of 82% of the selected nutrients when comparing the two methods. In general, moderate agreement between the two methods was found. CONCLUSION: The FFQ was validated for assessment of a range of nutrients. Comparing the intakes of selected nutrients (carbohydrates, dietary fibres and simple sugars), patients were classified correctly according to low and high intakes. The FFQ is a reliable dietary assessment tool to use in research and evaluation of patient education for patients with diabetes