Low wear partially fluorinated polyimides

Tribological studies were conducted on five different polyimide solid bodies formulated from the diamine 2,2-bis 4-(4-aminophenoxy)phenyl hexafluoropropane (4-BDAF) and the dianhydrides pyromellitic acid (PMDS) and benzophenonetetracarboxylic acid (BTDA). The following polyimides were evaluated 4-BDAF/PMDA, 4-BDAF/BTDA, 4-BDAF/80 mole percent PMDA, 20 mole percent BTDA, 4-BDAF/60 mole percent BTDA. Friction coefficients, polyimide wear rates, polyimide surface morphology and transfer films were evaluated at sliding speeds of 0.31 to 11.6 m/s and at temperatures of 25 C to 300 C. The results indicate that the tribological properties are highly dependent on the composition of the polyimide and on the experimental conditions. Two polyimides were found which produced very low wear rates but very high friction coefficients (greater than 0.85) under ambient conditions. They offer considerable potential for high traction types of application such as brakes

Tribological properties of graphite-fiber-reinforced, partially fluorinated polyimide composites

Graphite-fiber-reinforced polyimide (GFRPI) composites were formulated from three new partially fluorinated polyimides and three types of graphite fiber. Nine composites were molded into pins and evaluated in a pin-on-disk tribometer. Friction coefficients, wear rates, pin wear surface morphology, and transfer film formation were assessed at 25 and 300 C. Also assessed was the effect of sliding speed on friction. Wear was up to two orders of magnitude lower at 25 C and up to one order of magnitude lower at 300 C than with previously formulated NASA GFRPI composites

Full-scale metamaterial window for building application

The research on acoustic metamaterials (AMMs) has progressed rapidly over the last decades. One of the applications is for noise control and airflow in duct-like systems. These are useful features for natural ventilation window design; however, the visual impact between indoor and outdoor environment, as another key factor of windows, makes the existing AMMs not directly useable for this application due to their geometrical complexity and size limitations. In this research, an AMM previously developed by the authors is exploited for full-scale window design. The AMM is packed only in the window frame so that the window transparency is not compromised. A broadband attenuation performance is obtained by the resonant unit cells constituting the AMM. The effect of the geometric variation on the window performance in terms of both acoustics and the airflow is analysed numerically through Finite Element Method (FEM) models. The performances of different AMM windows are evaluated and compared with those of conventional window designs. The simulation results show that this new AMM-based window design can overcome the limitations of the conventional windows, with great potential in real applications

A metawindow with optimised acoustic and ventilation performance

Crucial factors in window performance, such as natural ventilation and noise control, are generally conceived separately, forcing users to choose one over the other. To solve this dualism, this study aimed to develop an acoustic metamaterial (AMM) ergonomic window design to allow noise control without dependence on the natural ventilation duration and vice versa. First, the finite element method (FEM) was used to investigate the noise control performance of the acoustic metawindow (AMW) unit, followed by anechoic chamber testing, which also served as the validation of the FEM models. Furthermore, FEM analysis was used to optimise the acoustic performance and assess the ventilation potential. The numerical and experimental results exhibited an overall mean sound reduction of 15 dB within a bandwidth of 380 to 5000 Hz. A good agreement between the measured and numerical results was obtained, with a mean variation of 30%. Therefore, the AMW unit optimised acoustic performance, resulting in a higher noise reduction, especially from 50 to 500 Hz. Finally, most of the AMW unit configurations are suitable for natural ventilation, and a dynamic tuned ventilation capacity can be achieved for particular ranges by adjusting the window’s ventilation opening. The proposed designs have potential applications in building acoustics and engineering where natural ventilation and noise mitigation are required to meet regulations simultaneously

End-to-end approach to flexible and sustainable commercial spaceflight initiatives: Evaluation of operational scenarios, safety aspects, spaceports and associated economic elements

Multiple initiatives are going on today, aimed at developing new technologies for commercial exploitation of space. The potential benefits of widening up the access to space to a broader users community affect different applications ranging from space tourism to microgravity experimentation to astronauts and pilots training; moreover, in the new space economy users communities may include parties that do not traditionally operate in the space business but can take advantage of microgravity exploitation as an opportunity to carry out experimental activities with potential more significant outcome. The present paper initially approaches commercial access to space by evaluating different mission concepts, technologies and platforms such as suborbital spaceflight, orbital spaceflight, air launch and deployment of small satellites. In order to select the most promising alternative, trade off methodologies, making use of safety, cost and complexity as figures of merit are suggested for the specific case of the suborbital flight. Moreover, the paper describes the outcome of simplified mission simulations, encompassing both suborbital vehicle as well as satellite air launch trajectories predictions. The trajectories simulations can also provide useful inputs to the vehicle design and performance analysis and are instrumental to planning air space operations after lift off from the launch site, as well as to assess logistics and operational aspects. Thus, simulations of really operating environment provide the link to the Spaceport selection process aiming at defining an adequate operating base and a set of proper ground infrastructures that efficiently support in integrated fashion the execution of the planned activities with the selected platforms. An integrated end-to-end approach is also described, that basing upon the specific users' needs identifies the appropriate platform and delivers the associated service matching the relevant goals. The paper finally discusses some economic and organizational aspects for developing a sustainable commercial spaceflight initiative. Ideas for next activities are drawn too, mainly focusing on trajectory validation simulation with real data coming from the initial test campaigns

Résultats de l'expérimentation italienne sur les principales provenances de pins de la section halepensis dix ans après la plantation

Comparaison du comportement des principales provenances de ces 3 espèces, en utilisant des graines récoltées dans les peuplements les plus intéressants des différentes régions

Polyhedral Oligomeric Silsesquioxane Based Catalyst for the Efficient Synthesis of Cyclic Carbonates

In this work, the synthesis of a novel imidazolium-based polyhedral oligomeric silsesquioxane (POSS-mim-Cl) material is presented. The new nanometer-size organosilica based compound was employed for chemical fixation of CO2 into epoxide under homogeneous conditions. The target reaction was represented by the obtention of cyclic carbonates starting from epoxides and CO2. Particularly, styrene oxide was chosen as reference substrate. In addition, different parameters (solvent, temperature, pressure of CO2, and mass of the catalyst) were modified to find the best condition for CO2 conversion. The catalyst POSS-mim-Cl displayed good catalytic performances, the best results being obtained at 40 bar of CO2, 150\ub0C, with 110 mg of catalyst and using isopropanol as co-solvent. It is worth to mention that POSS-mim-Cl displayed better catalytic performance than the corresponding 1-butyl-3-methyl imidazolium chloride. As far as we know this study represents the first use of imidazolium-based POSS as catalysts for the chemical fixation of CO2

Cost-Effective Cloud Computing: A Case Study Using the Comparative Genomics Tool, Roundup

Background Comparative genomics resources, such as ortholog detection tools and repositories are rapidly increasing in scale and complexity. Cloud computing is an emerging technological paradigm that enables researchers to dynamically build a dedicated virtual cluster and may represent a valuable alternative for large computational tools in bioinformatics. In the present manuscript, we optimize the computation of a large-scale comparative genomics resource—Roundup—using cloud computing, describe the proper operating principles required to achieve computational efficiency on the cloud, and detail important procedures for improving cost-effectiveness to ensure maximal computation at minimal costs. Methods Utilizing the comparative genomics tool, Roundup, as a case study, we computed orthologs among 902 fully sequenced genomes on Amazon's Elastic Compute Cloud. For managing the ortholog processes, we designed a strategy to deploy the web service, Elastic MapReduce, and maximize the use of the cloud while simultaneously minimizing costs. Specifically, we created a model to estimate cloud runtime based on the size and complexity of the genomes being compared that determines in advance the optimal order of the jobs to be submitted. Results We computed orthologous relationships for 245,323 genome-to-genome comparisons on Amazon's computing cloud, a computation that required just over 200 hours and cost $8,000 USD, at least 40% less than expected under a strategy in which genome comparisons were submitted to the cloud randomly with respect to runtime. Our cost savings projections were based on a model that not only demonstrates the optimal strategy for deploying RSD to the cloud, but also finds the optimal cluster size to minimize waste and maximize usage. Our cost-reduction model is readily adaptable for other comparative genomics tools and potentially of significant benefit to labs seeking to take advantage of the cloud as an alternative to local computing infrastructure