Shape and cross-section optimization of plane trusses subjected to earthquake excitation using gradient and Hessian matrix calculations

This article describes a second-order shape and cross-section optimization method of plane truss subjected to earthquake excitation. The method is based on gradient and Hessian matrix calculation. First, the first and second derivatives of dynamic response with respect to design variables are calculated based on the Newmark method. Second, the inequality time-dependent constraint problem is converted into a sequence of appropriately formed unconstrained problems using the integral interior penalty function method. Then, the gradient and Hessian matrix of the integral interior penalty function are computed. Third, Marquardt's method is employed to solve the unconstrained problems. Finally, the new approach is validated through several case studies. The results show that the new optimization method is an efficient and effective approach for minimum weight design of truss structures.     

Observed and modelled effects of ice lens formation on passive microwave brightness temperatures over snow covered tundra

Immediately before an April 2007 snow survey and passive microwave radiometer field campaign in the Northwest Territories, Canada, a rain-on-snow event deposited a thin (~ 3 mm) continuous layer of ice on the surface of the snowpack. At eight sites the brightness temperature (T_b) of the undisturbed snow pack was measured with a multi-frequency dual polarization (6.9, 19, 37, and 89 GHz) ground based radiometer system. The ice lens was then carefully removed and the T_bs were measured again. The individual V-pol channels and the 37 V − 19 V difference were largely unaffected by the presence of the ice lens, exhibiting a systematic shift of about 3 K. In comparison, the ice lens had a considerable effect on the H-pol T_b at all frequencies, with a mean difference (ice lens present − ice lens removed) of − 9 K (± 5.3 K) at 6.9 GHz, − 40 K (± 11.3 K) at 19 GHz, − 33 K (± 7.6 K) at 37 GHz, and − 19 K (± 8.0 K) at 89 GHz. The effect of the ice lens on H-pol measurements was also observed with spaceborne data from the Advanced Microwave Scanning Radiometer (AMSR-E) satellite data.Simulations of T_b were produced for each site using a new two layer formulation of the Helsinki University of Technology (HUT) snow emission model. The ice lens was used as the top layer and the underlying snowpack considered as a homogenous second layer. The agreement between observations and simulations was variable, with agreement strongest at 19 GHz. A comparison with simulations produced using the Microwave Emission Model of Layered Snowpacks (MEMLS) suggests HUT model uncertainty is related not to the ice lens, but to difficulties in simulating emission from deep snow. Overall, the observations and simulations suggest H-pol measurements are capable of detecting new ice layers across the tundra snowpack, while V-pol measurements are more appropriate for snow water equivalent (SWE) retrievals due to their relative insensitivity to ice layers.     

Approximate cost-efficient sequential designs for binary response models with application to switching measurements

The efficiency of an experimental design is ultimately measured in terms of time and resources needed for the experiment. Optimal sequential (multi-stage) design is studied in the situation where each stage involves a fixed cost. The problem is motivated by switching measurements on superconducting Josephson junctions. In this quantum mechanical experiment, the sequences of current pulses are applied to the Josephson junction sample and a binary response indicating the presence or the absence of a voltage response is measured. The binary response can be modeled by a generalized linear model with the complementary log-log link function. The other models considered are the logit model and the probit model. For these three models, the approximately optimal sample size for the next stage as a function of the current Fisher information and the stage cost is determined. The cost-efficiency of the proposed design is demonstrated in simulations based on real data from switching measurements. The results can be directly applied to switching measurements and they may lead to substantial savings in the time needed for the experiment.     

Optimal designs to select individuals for genotyping conditional on observed binary or survival outcomes and non-genetic covariates

In gene-disease association studies, the cost of genotyping makes it economical to use a two-stage design where only a subset of the cohort is genotyped. At the first-stage, the follow-up data along with some risk factors or non-genetic covariates are collected for the cohort and a subset of the cohort is then selected for genotyping at the second-stage. Intuitively the selection of the subset for the second-stage could be carried out efficiently if the data collected at the first-stage are utilized. The information contained in the conditional probability of the genotype given the first-stage data and the initial estimates of the parameters of interest is being maximized for efficient selection of the subset. The proposed selection method is illustrated using the logistic regression and Cox’s proportional hazards model and algorithms that can find optimal or nearly optimal designs in discrete design space are presented. Simulation comparisons between D-optimal design, extreme selection and case-cohort design suggest that D-optimal design is the most efficient in terms of variance of estimated parameters, but extreme selection may be a good alternative for practical study design.     

Merge of motion analysis,multibody dynamics and finite element method for the subject-specific analysis of cartilage loading patterns during gait: differences between rotation and moment-driven models of human knee joint

Understanding joint loading is important when evaluating sports training methods, sports equipment design, preventive training regimens, post-op recovery procedures, or in osteoarthritis’ etiology research. A number of methods have been introduced to estimate joint loads but they have been limited by the lack of accuracy in the joint models, including primarily the lack of patient-specific motion inputs in the models with sophisticated, fibril-reinforced material models. The method reported here records and applies patient-specific human motion for in-depth cartilage stress estimation. First, the motion analysis of a subject was conducted. Due to skin motion, multibody simulation was used to correct motion capture. These data was used as an input in a finite element model. The model geometry was based on magnetic resonance imaging and cartilage was modeled as a fibril-reinforced poroviscoelastic material. Based on the experimental motion data (motion analysis and multibody simulation), two models were created: a rotation-controlled and a moment-controlled model. For comparison, a model with motion input from the literature was created. The rotation-controlled model showed the most even stress distribution between lateral and medial compartments and smallest stresses and strains in a depth-wise manner. The model based on the literature motion simulated very high stresses and uneven stress distribution between the joint compartments. Our new approach to determine dynamic knee cartilage loading enables estimations of stresses and strains for a specific subject over the entire motion cycle.     

Feasibility of pulse combustion in micro gas turbines

In gas turbines, a fast decrease of efficiency appears when the output decreases; the efficiency of a large gas turbine (20…30 MW) is in the order of 40 %, the efficiency of a 30 kW gas turbine with a recuperator is in the order of 25 %, but the efficiency of a very small gas turbine (2…6 kW) in the order of 4…6 % (or 8…12 % with an optimal recuperator). This is mainly a result of the efficiency decrease in kinetic compressors, due to the Reynolds number effect. Losses in decelerating flow in a flow passage are sensitive to the Reynolds number effects. In contrary to the compression, the efficiency of expansion in turbines is not so sensitive to the Reynolds number; very small turbines are made with rather good efficiency because the flow acceleration stabilizes the boundary layer. This study presents a system where the kinetic compressor of a gas turbine is replaced with a pulse combustor. The combustor is filled with a combustible gas mixture, ignited, and the generated high pressure gas is expanded in the turbine. The process is repeated frequently, thus producing a pulsating flow to the turbine; or almost a uniform flow, if several parallel combustors are used and triggered alternately in a proper way. Almost all the compression work is made by the temperature increase from the combustion. This gas turbine type is investigated theoretically and its combustor also experimentally with the conclusion that in a 2 kW power size, the pulse flow gas turbine is not as attractive as expected due to the big size and weight of parallel combustors and due to the efficiency being in the order of 8 % to 10 %. However, in special applications having a very low power demand, below 1000 W, this solution has better properties when compared to the conventional gas turbine and it could be worth of a more detailed investigation.     

World-wide university rankings: A Scandinavian approach

Although universities’ world rankings are popular, their design and methods still request considerable elaborations. The paper demonstrates some shortcomings in the Academic World Ranking of Universities (ARWU, Shanghai Jiao Tong University) ranking methods. One deficiency is that universities’ scale differences are neglected due to omitting the whole input side. By resampling and reanalyzing the ARWU data, the paper proposes an input-output analysis for measuring universities’ scientific productivity with special emphasis on those universities which meet the productivity threshold (i.e. share of output exceeds share of input) in a certain group of universities. The productivity analysis on Scandinavian universities evaluates multidisciplinary and specialized universities on their own terms; consequently the ranking based on scientific productivity deviates significantly from the ARWU.     

Screening for the Drug–Phospholipid Interaction: Correlation to Phospholipidosis

Phospholipid bilayers represent a complex, anisotropic environment fundamentally different from bulk oil or octanol, for instance. Even “simple” drug association to phospholipid bilayers can only be fully understood if the slab‐of‐hydrocarbon approach is abandoned and the complex, anisotropic properties of lipid bilayers reflecting the chemical structures and organization of the constituent phospholipids are considered. The interactions of drugs with phospholipids are important in various processes, such as drug absorption, tissue distribution, and subcellular distribution. In addition, drug–lipid interactions may lead to changes in lipid‐dependent protein activities, and further, to functional and morphological changes in cells, a prominent example being the phospholipidosis (PLD) induced by cationic amphiphilic drugs. Herein we briefly review drug–lipid interactions in general and the significance of these interactions in PLD in particular. We also focus on a potential causal connection between drug‐induced PLD and steatohepatitis, which is induced by some cationic amphiphilic drugs.     

Acoustic emission of rolling bearings lubricated with contaminated grease

In elastohydrodynamic lubrication (EHL), an extreme smoothness of the contacting surfaces is essential for the formation of a thin lubricant film, which separates the moving surfaces from each other. Sharp asperities, in particular, are very detrimental for the sliding surfaces. Because of the limited thickness of the lubricating film, the contact zone is very vulnerable if the lubricant contains contaminants, especially if hard particles are present in the lubricant.The present paper focuses on the acoustic emission (AE) measurement method for the monitoring of the lubrication situation in a grease lubricated rolling bearing. The aim of the investigation was to clarify how the contaminants in the grease influence the acoustic emission of the rolling bearing. In the paper, the results of tests with clean greases and with deliberately contaminated greases, and the influence of the cleaning and re-greasing of the bearing are discussed. The results showed that the AE measurement indicated very clearly the lowest contaminant concentration included in the study that was as low as 0.02 weight-%. Small size contaminant particles generated a higher AE pulse count level than large size particles. The AE time signal analysis method proved to be a suitable method to indicate the hardness of the contaminant particles. Cleaning the bearing of contaminants and re-greasing with a clean grease reduced the AE level of the bearing.     

The dependence on temperature of gas-phase photocatalytic oxidation of methyl tert-butyl ether and tert-butyl alcohol

The influence of temperature on the mechanism and kinetics of gas-phase photocatalytic oxidation (PCO) and thermal oxidation (TO) of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA) over TiO₂ was studied in a continuous flow annular reactor. The reaction products of PCO of both substances included acetone, water, carbon dioxide and carbon monoxide. Volatile TO products of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Thermal oxidation of MTBE became noticeable at 388 K, TBA started to decompose thermally at 393 K. Both PCO and TO fit well to the Langmuir–Hinshelwood (L–H) model for monomolecular reactions. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation. The TiO₂ catalyst showed no deactivation at temperatures above 373 K but gradually lost its activity below 373 K.