| 1. |
|
|
| 2. |
- Ahacic, Kozma, et al.
(författare)
-
Trends in smoking in Sweden from 1968 to 2002 : Age, period, and cohort patterns
- 2008
-
Ingår i: Preventive Medicine. - : Elsevier BV. - 0091-7435 .- 1096-0260. ; 46:6, s. 558-564
-
Tidskriftsartikel (refereegranskat)abstract
- Objective. Smoking is related to many later life health outcomes. We examined age, period, and cohort patterns in smoking between 1968 and 2002. Methods. A nationally representative panel study allowed repeated cross-sectional comparisons of ages 18-75 (5 waves n approximate to 5000), and ages 77+ at later waves (2 waves n approximate to 500). Cross-sectional 10-year age group differences in 5 waves, time-lag differences between waves for age groups, and within-cohort differences between waves for 10-year birth cohorts were evaluated using graphs and ordered logistic regressions. Results. Age-period-cohort models suggested that period and age effects dominated smoking patterns, showing decreases over time and age. The 1935-44 and 1945-54 cohorts, however, showed lesser period decline. Moreover, men showed a period reduction of smoking rates but no age related decrease, while women showed an age related decrease but no period effect. The genders' cohort patterns were similar, with higher smoking rates in the last waves for some cohorts, for men the 1945-54 cohort and women the 1935-44 cohort. Conclusions. Cross-sectional studies of cohorts must be aware of age effects. Due to the coming of age of the 1940s' cohorts smoking may increase among women in the oldest age groups.
|
|
| 3. |
|
|
| 4. |
- Nguyen, Hugo, et al.
(författare)
-
Structural Integrity of Flat Silicon Panels for Nanosatellites : Modeling and Testing
- 2006
-
Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics (AIAA). - 0022-4650 .- 1533-6794. ; 43:6, s. 1319-1327
-
Tidskriftsartikel (refereegranskat)abstract
- To utilize the high mass fraction of silicon material in a nanosatellite based on micro-electro-mechanical systems, part of the structural function has been assigned to the flat silicon stacks embracing these systems. Three modules for destructive testing in bending, warping and shearing cases were built with 68x68x1 mm silicon stacks bonded in aluminium frames by in-situ casting of silicone rubber. The rubber served as the deformation zone between the stiff and brittle silicon stacks and their weaker and ductile aluminium frames. A special test module of the same size was built with strain gauges of Nichrome (thin film deposited directly on the surface of the silicon stack). Elastic deformation tests on this as well as simulations using finite element analysis were performed for bending, warping and shearing loads of up to 80, 40 and 99 N, respectively. The test module was disassembled after the test series and examined. The actual thickness of the rubber was measured and entered into the model for simulation. The correlation between simulations and experimental measurements was good with deviation of about 30%. The results show that the rubber works well as a mechanical interface. Its thickness influences the stress in the silicon stack significantly. The silicon stack stiffens the module by a factor of 46 and lowers the stress in its frame 24 times in shearing mode, which is the most relevant loading case for the satellite framework. Thus, the concept of using flat silicon panels as structural elements is fully feasible.
|
|
| 5. |
- Williams, Kirk, et al.
(författare)
-
Electrothermal feasibility of carbon microcoil heaters for cold/hot gas microthrusters
- 2006
-
Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 16, s. 1154-1161
-
Tidskriftsartikel (refereegranskat)abstract
- With the miniaturization of spacecraft the need for efficient, accurate and low-weight attitude control systems is becoming evident. To this end, the cold/hot gas microthruster system of this paper incorporates carbon microcoils—deposited via laser-induced chemical vapor deposition—for heating the propellant gas (nitrogen) before the nozzle inlet. By increasing the temperature of the propellant gas for such a system, the specific impulse (Isp) of the microthruster will increase. The benefits of a higher Isp are lower propellant mass, higher thrust and shorter burning times. Therefore, the feasibility of achieving this increase with the carbon microcoils is investigated. The carbon microcoils have been characterized experimentally with respect to their electrothermal performance, i.e. resistance, temperature, parasitic heat losses and degradation in ambient. The resulting heat losses from the heater and the heated gas have been estimated through a combination of experiments, numerical simulation and approximate analytical expressions. At high powers, degradation of the carbon material leads to coil failure in ambient where trace oxygen was present. Thus, the next generation of carbon microcoils to be tested will have a protective coating to extend their lifetime. Theoretical modeling showed that an increase in the propellant gas temperature from 300 to 1200 K and a corresponding two-fold increase in the Isp can be achieved if 1.0 W of power is supplied to each coil in a three-coil thruster. These simulation results show that if the coils are capable of dissipating 1 W of heat at 1700 K coil temperature, the doubling of the Isp may be achieved. Comparing to the electrothermal characterization results we find that the carbon coils can survive at 1700 K if protected, and that they can be expected to reach 1700 K at power below 1 W.
|
|
