Weak-localization corrections to the conductivity of double quantum wells

The weak-localization contribution \delta\sigma(B) to the conductivity of a tunnel-coupled double-layer electron system is evaluated and its behavior in weak magnetic fields B perpendicular or parallel to the layers is examined. In a perpendicular field B, \delta \sigma(B) increases and remains dependent on tunneling as long as the magnetic field is smaller than \hbar/e D \tau_t, where D is the in-plane diffusion coefficient and \tau_t the interlayer tunneling time. If \tau_t is smaller than the inelastic scattering time, a parallel magnetic field also leads to a considerable increase of the concuctivity starting with a B**2 law and saturating at fields higher than \hbar/e Z (D \tau_t)**(1/2), where Z is the interlayer distance. In the limit of coherent tunneling, when \tau_t is comparable to elastic scattering time, \delta \sigma(B) differs from that of a single-layer system due to ensuing modifications of the diffusion coefficient. A possibility to probe the weak-localization effect in double-layer systems by the dependence of the conductivity on the gate-controlled level splitting is discussed.Comment: Text 18 pages in Latex/Revtex format, 4 Postscript figures. J. Phys.: CM,in pres

Effect and process evaluation of a kindergarten-based, family-involved cluster randomised controlled trial in six European countries on four- to six-year-old children's steps per day: The ToyBox-study

Background: The ToyBox-intervention is a theory- and evidence-based intervention delivered in kindergartens to improve four- to six-year-old children''s energy balance-related behaviours and prevent obesity. The current study aimed to (1) examine the effect of the ToyBox-intervention on increasing European four- to six-year-old children'' steps per day, and (2) examine if a higher process evaluation score from teachers and parents was related to a more favourable effect on steps per day. Methods: A sample of 2438 four- to six-year-old children (51.9% boys, mean age 4.75±0.43years) from 6 European countries (Belgium, Bulgaria, Germany, Greece, Poland and Spain) wore a motion sensor (pedometer or accelerometer) for a minimum of two weekdays and one weekend day both at baseline and follow-up to objectively measure their steps per day. Kindergarten teachers implemented the physical activity component of the ToyBox-intervention for 6 weeks in total, with a focus on (1) environmental changes in the classroom, (2) the child performing the actual behaviour and (3) classroom activities. Children''s parents received newsletters, tip cards and posters. To assess intervention effects, multilevel repeated measures analyses were conducted for the total sample and the six intervention countries separately. In addition, process evaluation questionnaires were used to calculate a total process evaluation score (with implementation and satisfaction as a part of the overall score) for teachers and parents which was then linked with the physical activity outcomes. Results: No significant intervention effects on four- to six-year-old children'' steps per weekday, steps per weekend day and steps per average day were found, both in the total sample and in the country-specific samples (all p>0.05). In general, the intervention effects on steps per day were least favourable in four- to six-year-old children with a low teachers process evaluation score and most favourable in four- to six-year-old children with a high teachers process evaluation score. No differences in intervention effects were found for a low, medium or high parents'' process evaluation score. Conclusion: The physical activity component of the ToyBox-intervention had no overall effect on four- to six-year-old children'' steps per day. However, the process evaluation scores showed that kindergarten teachers that implemented the physical activity component of the ToyBox-intervention as planned and were satisfied with the physical activity component led to favourable effects on children''s steps per day. Strategies to motivate, actively involve and engage the kindergarten teachers and parents/caregivers are needed to induce larger effects

Differences in energy balance-related behaviours in European preschool children: The ToyBox-study

Background: The aim of the current study was to compare levels of energy balance-related behaviours (physical activity, sedentary behaviour, and dietary behaviours (more specifically water consumption, sugar-sweetened beverage consumption and unhealthy snacking)) in four- to six-year-old preschoolers from six European countries (Belgium, Bulgaria, Germany, Greece, Poland, and Spain) within the ToyBox cross-sectional study. Methods: A sample of 4,045 preschoolers (4.77 ± 0.43 years; 52.2% boys) had valid physical activity data (steps per day), parents of 8,117 preschoolers (4.78 ± 0.46 years; 53.0% boys) completed a parental questionnaire with questions on sedentary behaviours (television viewing, computer use, and quiet play), and parents of 7,244 preschoolers (4.77 ± 0.44 years; 52.0% boys) completed a food frequency questionnaire with questions on water consumption, sugar-sweetened beverage consumption and unhealthy snacking. Results: The highest levels of physical activity were found in Spain (12,669 steps/day on weekdays), while the lowest levels were found in Bulgaria and Greece (9,777 and 9,656 steps/day on weekdays, respectively). German preschoolers spent the least amount of time in television viewing (43.3 min/day on weekdays), while Greek preschoolers spent the most time in television viewing (88.5 min/day on weekdays). A considerable amount of time was spent in quiet play in all countries, with the highest levels in Poland (104.9 min/day on weekdays), and the lowest levels in Spain (60.4 min/day on weekdays). Belgian, German, and Polish preschoolers had the lowest intakes of water and the highest intakes of sugar-sweetened beverages. The intake of snacks was the highest in Belgian preschoolers (73.1 g/day) and the lowest in Greek preschoolers (53.3 g/day). Conclusions: Across six European countries, differences in preschoolers'' energy balance-related behaviours were found. Future interventions should target European preschoolers '' energy balance- related behaviours simultaneously, but should apply country-specific adaptations

Possibility of enhanced oil recovery from the Nosówka oil reservoir by CO2 injection

W artykule przeanalizowano problem wspomaganego wydobycia ropy naftowej ze złoża Nosówka przy pomocy zatłaczania do złoża dwutlenku węgla. W tym celu skonstruowano kompozycyjny model symulacyjny złoża. Model ten wykorzystano do przeprowadzenia wielowariantowych symulacji prognostycznych. Porównano efekty różnych scenariuszy zatłaczania CO2 i wydobycia ropy ze złoża oraz wskazano najbardziej skuteczny program sczerpania ropy ze złoża Nosówka. Określono również pojemność sekwestracyjną struktury do magazynowania CO2.The paper addresses the problem of enhanced oil recovery (EOR) in the Nosówka oil field by the injection of CO2. It was analysed with the use of a compositional simulation model of the reservoir. Multi-scenario forecasts of the process were performed by simulation modeling. Their results were discussed and compared with respect to the final recovery factor. A most effective scenario was found and characterized. The CO2 storage capacity of the structure was also determined

Analiza procesu wspomaganego wydobycia ropy odwiertem bilateralnym z wykorzystaniem WAG-CO2 w oparciu o symulacje złożowe. Część II – model złoża rzeczywistego

Based on the general conclusions in part I of the study, this part II presents the analysis of the selected EOR methods with particular attention paid to the WAG (Water-Alternating-Gas) method and its SWAG (Simultaneous Water-Alternating-Gas) version, involving the simultaneous and selective injecting of water and CO2 (water through the upper section of the injection well, CO2 through the lower section of the well) for a real reservoir model. Forecasts of oil production have been performed with the use of the primary method, waterflooding method as well as the WAG and SWAG methods. For each of the above production methods, additional options were considered to increase the number of injection wells from 6 to 8. In order to perform the above described forecasts, a number of general assumptions were made concerning the amount of injected and produced liquids as well as limitations associated with them. The paper presents a detailed analysis of the reservoir operation for each case. Results of total amounts of the injected and produced fluids are presented in detail. Qualitative assessment of the analyzed methods is presented based on the main simulation results including distribution of oil saturation in the reservoir model at the end of production forecasts.Bazując na wnioskach ogólnych w części I pracy w niniejszej II części przedstawiono analizę wybranych metod EOR ze szczególnym uwzględnieniem metody WAG (Water-Alternating-Gas) i jej odmiany SWAG (Simultaneous Water-Alternating-Gas) polegającej na równoczesnym i selektywnym tłoczeniu wody i CO2 (górną sekcją wody, dolną sekcją CO2) dla modelu rzeczywistego złoża. Przeprowadzono prognozy wydobycia ropy przy użyciu metody pierwszej, metody nawadniania i metod WAG i SWAG. Dla każdej z powyższych metod wspomagania wydobycia rozpatrzono dodatkowe warianty zakładające zwiększenie liczby odwiertów tłoczących z 6 do 8. W celu przeprowadzenia powyżej opisanych prognoz przyjęto szereg założeń ogólnych dotyczących ilości zatłaczanych i wydobywanych płynów oraz ograniczeń z tym związanych. W pracy przedstawiono szczegółową analizę pracy złoża dla każdego wariantu. Podano szczegółowe wyniki dla sumarycznych wielkości zatłaczanych i wydobytych płynów. Ocenę jakościową przedstawiono w oparciu o podstawowe wyniki eksploatacji, w tym rozkłady nasycenia ropą w złożu na koniec jej eksploatacji złoża

liza procesu wspomaganego wydobycia ropy odwiertem bilateralnym z wykorzystaniem WAG-CO2w oparciu o symulacje złożowe. Część I – model złoża syntetycznego

The paper presents analysis of the selected EOR methods based on the results of reservoir simulations with particular attention paid to WAG method and its SWAG variation consisting in simultaneous and selective injecting of water and CO2 (water through the upper section, CO2 through the lower section of the injector). Reservoir simulations have been performed on two models of synthetic reservoir: one with standard permeability equal to the average permeability of the largest Polish reservoir and the second one with reduced permeability. Forecasts of oil production with the use of the primary method, waterflooding method as well as WAG and SWAG methods have been performed for each of these models. For each of these methods, the cases of oil production by a vertical, standard horizontal and by bilateral well with two sections situated one above the other were considered. In order to perform the above described forecasts, a number of general assumptions were made concerning the amount of injected and produced liquids as well as limitations associated with it. The paper presents a detailed analysis of the reservoir exploitation for each of the cases. Results for total amounts are presented in the table, and the qualitative assessment is presented based on simulation results including distribution of oil saturation in the reservoir at the end of exploitation process.W pracy w oparciu o wyniki symulacji złożowych przedstawiono wybrane metody EOR ze szczególnym uwzględnieniem metody WAG i jej odmiany SWAG polegającej na równoczesnym i selektywnym tłoczeniu wody i CO2 (wody górną sekcją odwiertu zatłaczającego, CO2 dolną jego sekcją). Symulacje złożowe przeprowadzono na dwóch modelach syntetycznego złoża: jednego o standardowej przepuszczalności, tj. równej średniej przepuszczalności dla jednego z największych polskich złóż i drugiego o przepuszczalności zredukowanej. Dla każdego z tych modeli przeprowadzono prognozy wydobycia ropy przy użyciu metody pierwszej, metody nawadniania oraz metod WAG i SWAG. Dla każdej z powyższych metod rozpatrzono przypadki wydobycia ropy przez odwiert pionowy, standardowy horyzontalny oraz bilateralny o dwóch sekcjach znajdujących się jedna nad drugą. W celu przeprowadzenia powyżej opisanych prognoz przyjęto szereg założeń ogólnych dotyczących ilości zatłaczanych i wydobywanych płynów oraz ograniczeń z tym związanych. W pracy przedstawiono szczegółową analizę eksploatacji złoża dla każdego wariantu. Wyniki dla sumarycznych wielkości zestawiono w tabeli, a ocenę jakościową przedstawiono w oparciu o podstawowe wyniki symulacji, w tym rozkłady nasycenia ropą w złożu na koniec eksploatacji złoża