Dual Material Rapid Prototyping Techniques for the Development of Biomedical Devices. Part 2: Secondary Powder Deposition

Polymeric drug delivery devices play an important role in drug administration. However, the current polymeric drug delivery device fabrication methods lack precision. This impairs the quality of the devices, resulting in a decrease in the efficiency and effectiveness of drug delivery. The concept of building parts layer by layer out of powdered raw materials makes selective laser sintering (SLS) a suitable process for fabricating polymeric matrix drug delivery devices. The current SLS process is not capable of processing two or more materials separately. This work explores the possibilities of using SLS to perform a dual material operation by developing two process models. The two processes can then be integrated to form a dual or multimaterial fabrication technique and act as a foundation for future work in multimaterial applications such as polymeric drug delivery device fabrication. Accordingly, two papers are presented. In this paper, Part 2, the emphasis is on a secondary powder deposition method, which is an electrostatic technique based on electrography. Developed toner on the photoconductor is scraped off using mechanical shearing and is deposited using an electrostatic force by electroplating. Results have shown that by reducing the distance between the photoconductor and surface of deposition, the resolution of the printout can be refined. Other important factors include the efficiency of powder removal from the photoconductor, printing speed, and the traversing speed during deposition.     

Which persistent organic pollutants can we map in soil using a large spacing systematic soil monitoring design? A case study in Northern France

Persistent organic pollutants (POPs) impact upon human and animal health and the wider environment. It is important to determine where POPs are found and the spatial pattern of POP variation. The concentrations of 90 molecules which are members of four families of POPs and two families of herbicides were measured within a region of Northern France as part of the French National Soil Monitoring Network (RMQS: Réseau de Mesures de la Qualité des Sols). We also gather information on five covariates (elevation, soil organic carbon content, road density, land cover and population density) which might influence POP concentrations. The study region contains 105 RMQS observation sites arranged on a regular square grid with spacing of 16 km. The observations include hot-spots at sites of POP application, smaller concentrations where POPs have been dispersed and observations less than the limit of quantification (LOQ) where the soil has not been impacted by POPs. Fifty nine of the molecules were detected at less than 50 sites and hence the data were unsuitable for spatial analyses. We represent the variation of the remaining 31 molecules by various linear mixed models which can include fixed effects (i.e. linear relationships between the molecule concentrations and covariates) and spatially correlated random effects. The best model for each molecule is selected by the Akaike Information Criterion. For nine of the molecules, spatial correlation is evident and hence they can potentially be mapped. For four of these molecules, the spatial correlation cannot be wholly explained by fixed effects. It appears that these molecules have been transported away from their application sites and are now dispersed across the study region with the largest concentrations found in a heavily populated depression. More complicated statistical models and sampling designs are required to explain the distribution of the less dispersed molecules.     

Dual Material Rapid Prototyping Techniques for the Development of Biomedical Devices. Part 1: Space Creation

Polymeric drug delivery devices play an important role in drug administration. However, the current polymeric drug delivery device fabrication methods lack precision. This impairs the quality of the devices, resulting in a decrease in the efficiency and effectiveness of drug delivery. The concept of building parts layer by layer out of powdered raw materials makes selective laser sintering (SLS) a suitable process for fabricating polymeric matrix drug delivery devices. The current SLS process is not capable of processing two or more materials separately. This work explores the possibilities of SLS per-forming a dual material operation by developing two process models. These two processes can then be integrated to form a dual or expanded multimaterial fabrication technique and act as a foundation for future work in multimaterial applications such as polymeric drug delivery device fabrication. Accord-ingly, two papers are presented. In this paper, Part 1, the focus is on the first process, which is a "space" creation technique in which a "space" is created by varying the density of a first representative material using heat during sintering. Three methods – one based on a vacuum and a place method, and the other two based on two variations of a laser compacting method – were tested. Results have shown that by varying the laser power during sintering, it is possible to create channels in which a second material can be deposited.     

一种有效的直接数据域地面动目标检测方法

直接数据域(Direct data domain, DDD)方法利用子孔径平滑来从单个距离门中获得足够样本,但空域、时域孔径损失严重,使得空时自适应处理的地面动目标检测性能下降严重.针对该问题提出了一种不需要协方差矩阵估计和求逆的DDD方法,该方法将多级维纳滤波器引入到DDD的最优权求解过程中,在低的空时孔径损失下仍然能够获得好的性能.某机载实测雷达数据的实验结果验证了该方法的有效性.     

虚拟信源直接数据域高分辨算法

目标高分辨算法的性能优劣直接影响声纳、雷达的目标感知能力。考虑基于空间平滑思想的直接数据域算法,在干扰方向产生稳定的零陷。虚拟出期望信号并加入到接收数据中,将实际目标当作干扰,通过直接数据域自适应的方法在实际目标方向产生零陷：在波束图的左半部分适当位置虚拟一个期望信号,得到0°~90°的零陷分布图,在右半部分适当位置虚拟一个期望信号,得到90°~0°的零陷分布图,将这两部分零陷图组合后,取倒数得到实际功率谱图。该方法可以在单快拍、未知目标信号先验信息的情况下得到稳定、高分辨力的目标方位估计,并能够处理相干信号。仿真分析验证了算法的正确性和良好性能。     

Complete dechlorination of DDT and its metabolites in an alcohol mixture using NaOH and Pd/C catalyst

DDT (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane) was dechlorinated in 2-propanol/methanol (99:1v/v) by means of stoichiometric reaction with NaOH and subsequent catalytic dechlorination over Pd/C catalyst. When DDT was treated with a molar excess of NaOH ([NaOH]/[DDT]=9) in the alcohol mixture at room temperature, DDT disappeared within 15min. The reaction of DDT produced an equimolar amount of HCl to yield DDE (1,1-bis(4-chlorophenyl)-2,2-dichloroethylene). The produced DDE was successfully dechlorinated to a chlorine-free product (1,1-diphenylethane, 97% yield) by addition of Pd/C to the alkaline solution and heating at 40 degrees C for 4h. DDD (1,1-bis(4-chlorophenyl)-2,2-dichloroethane) was also dechlorinated to 1,1-diphenylethane in a similar manner. Possible dechlorination pathways for DDT, DDE, and DDD were investigated by observation of the partially dechlorinated intermediates by means of gas chromatography/mass spectrometry (GC/MS).     

基于领域驱动设计的应用系统模型

领域驱动设计（Domain-Driven Design,DDD）是Evans提出来的用来处理软件系统核心复杂性的方法。该方法的有效性在实践中得到证明,但是方法在细节上存在不够清晰、对设计人员素质要求高等问题。在对大量业务系统进行分析和实践的基础上,对业务对象的公共操作进行了抽象,提出了基于DDD的应用系统模型来指导系统设计和开发。研发了开发框架对业务系统中通用的属性和操作进行了封装。实际项目中的应用证明了该框架能够辅助进行系统设计开发,提高软件开发效率和减少缺陷。     

基于DDD离心加载法的黑山铁矿西帮边坡稳定性研究

非连续变形与位移分析方法（DDD）是一种新的岩石破坏全过程分析方法,该方法有效的结合了RFPA有限元方法及非连续变形分析（DDA）方法的优势,解决了有限元不能很好地进行大位移动态分析及DDA不能模拟岩石中新破裂的萌生、扩展过程的问题,真实再现了边坡由细观裂纹的演化直至宏观破坏的全过程。在原有的DDD方法的基础上,结合了传统的离心加载试验机理,形成了全新的DDD离心加载法。该方法不仅保存了DDD方法原有的计算特点,且实现了不用预先假定滑移面而是通过计算得出其滑移失稳面,更加符合工程实际。基于改进的DDD离心加载法,结合黑山铁矿西帮边坡给出的剖面及要进行崩落开采的实际工况,建立了二维的含有采空区的边坡稳定性分析模型。模拟了在有无锚索作用下的含有采空区边坡的滑移机理并进行了对比分析,分别分析了有无锚索作用下的含有采空区边坡由细观裂纹的演化直至宏观破坏的剪应力变化过程、安全系数、竖向及水平位移矢量的变化。结果表明：采空区外凸棱角区是边坡应力集中的关键点,边坡的失稳破坏过程有明显的张拉作用,与实际提供的工况现场取得了较好的一致性。锚索虽将断层以上坡体应力集中形态有效分散提高了边坡的安全系数、使得各向位移矢量的变化明显减小,但黑山西帮边坡仍然存在潜在滑移的可能,仍需后续的继续观测。