An approximate mathematical model for solidification of a flowing liquid in a microchannel

A mathematical model is developed to analyse the combined flow and solidification of a liquid in a small pipe or two-dimensional channel. In either case, the problem reduces to solving a single equation for the position of the solidification front. Results show that for a large range of flow rates the closure time is approximately constant, and the value depends primarily on the wall temperature and channel width. However, the solid shape at closure will be very different for low and high fluxes. As the flow rate increases the closure time starts to depend on the flow rate until the closure time increases dramatically, subsequently the pipe will never close.     

上班时间，谁又在BT

利用BT下载时并不只对外进行一个连接．而是同是连接到多个用户的IP．所以对ADSL Modem这样低性能的NAT功能来说是很大的负载。用交接机连接多台PC上网．理论上每台PC的带宽是一样的，但实际上由于没有流量控制，有时会导致一台PC占去很多的带宽．比如在线BT就会这样．因此我们最好是通过一台服务器做代理上网，在服务器上把端口封锁掉。     

Rank Estimation in Missing Data Matrix Problems

A novel technique for missing data matrix rank estimation is presented. It is focused on matrices of trajectories, where every element of the matrix corresponds to an image coordinate from a feature point of a rigid moving object at a given frame; missing data are represented as empty entries. The objective of the proposed approach is to estimate the rank of a missing data matrix in order to fill in empty entries with some matrix completion method, without using or assuming neither the number of objects contained in the scene nor the kind of their motion. The key point of the proposed technique consists in studying the frequency behaviour of the individual trajectories, which are seen as 1D signals. The main assumption is that due to the rigidity of the moving objects, the frequency content of the trajectories will be similar after filling in their missing entries. The proposed rank estimation approach can be used in different computer vision problems, where the rank of a missing data matrix needs to be estimated. Experimental results with synthetic and real data are provided in order to empirically show the good performance of the proposed approach.     

Environmental metabolism of educational services. Case study of nursery schools in the city of Barcelona

The environmental analysis of public nursery schools is of great interest since they are crucial in the early education of children and are expected to show high environmental standards. This paper aims to analyse the environmental profile (energy, water and transport flows) of this sector. A sample of 12 public nursery schools belonging to the Scholar Agenda 21 (SA21) of the city of Barcelona were selected given their data quality (eight centres applied to all analysis) to determine their energy and water consumption, as well as the greenhouse gas emissions resulting from energy consumption and transport use. For each centre, energy and water consumption were obtained from bills and surveys were conducted to get data regarding the transport associated with the centre. Results show that, on average, a child consumes 966 kWh of energy (electricity and gas) and 12.9 m³ of potable water every year. Nursery schools with more energy-efficient devices hold lower energy consumption, a trend which could not be found in the case of water and water-efficient devices. Regarding transport, car usage was the flow with highest impact, since it accounts for 69 % of CO₂eq emissions, although only 19 % of the children commute by car.     

Influence of raw carbon nanotubes diameter for the optimization of the load composition ratio in epoxy amperometric composite sensors

In this work, it is reported the necessity to characterize the raw carbon materials before their application in composite electrodes based on multiwall carbon nanotubes (MWCNTs) dispersed in epoxy resin for the development of improved amperometric sensors. These sensors must contain an optimum MWCNT/epoxy ratio for their best electroanalytical response. The main drawback in MWCNTs composite materials resides in the lack of homogeneity of the different commercial nanotubes largely due to different impurities content, as well as dispersion in their diameter/length ratio and state of aggregation. The optimal composite electrode composition takes into account the high electrode sensitivity, low limit of detection, fast response, and electroanalytical reproducibility. These features depend on carbon nanotube physical properties as the diameter. Three different commercial carbon nanotubes with different diameters were characterized by transmission electron microscopy and the results were significantly different from the ones provided by the manufacturers. Then, the three MWCNTs were used for the MWCNT/epoxy sensors construction. After an accurate electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy, they were employed as working electrodes using ascorbic acid as a reference analyte. Percolation theory was applied in order to verify the electrochemical results. It is demonstrated that the optimum interval load of raw carbon material in the optimized-composite electrodes closely depends on the MWCNTs diameter, needing 5 % in carbon content for the narrowest MWCNTs containing composite electrodes versus 12 % for the widest MWCNTs.