移动终端软件的成功要素

随着手机市场的成熟,移动电话制造商正面临着如何在试图赶上移动终端下一波发展潮流的同时,以更短的开发时间为其产品增添日益丰富的功能这一挑战。移动终端是一种采用先进通信协议栈的复杂系统,它需要具有与许多网络设备互操作、支持先进而丰富的多媒体的应用程序。而且,所有这些都必需在一个资源有限的嵌入式系统的约束条件下实现。此外,由于运营商已经或将要开始推广部署GPRS和3G网络相关的服务。因此,目前的手机市场对于最新推出的功能和应用程序有着迫切的需要。这反过来又使产品的生命周期变短。于是,开发一个具有最新功能和应用程…     

Co3O4 Nanostructures with Different Morphologies and their Field‐Emission Properties

We report an efficient method to synthesize vertically aligned Co₃O₄ nanostructures on the surface of cobalt foils. This synthesis is accomplished by simply heating the cobalt foils in the presence of oxygen gas. The resultant morphologies of the nanostructures can be tailored to be either one‐dimensional nanowires or two‐dimensional nanowalls by controlling the reactivity and the diffusion rate of the oxygen species during the growth process. A possible growth mechanism governing the formation of such nanostructures is discussed. The field‐emission properties of the as‐synthesized nanostructures are investigated in detail. The turn‐on field was determined to be 6.4 and 7.7 V μm^–1 for nanowires and nanowalls, respectively. The nanowire samples show superior field‐emission characteristics with a lower turn‐on field and higher current density because of their sharp tip geometry and high aspect ratio.     

Three‐dimensional hydrogel encapsulated embryonic stem and carcinoma cells as culture platforms for cytotoxicity studies

The utility of alginate hydrogels for three‐dimensional (3‐D) culture of mouse embryonic stem cells (mESCs) and future development of 3‐D stem cell culture‐based in vitro screens of toxicity is described. Using alginate hydrogels of various stiffness, we first evaluated the impact of substrate modulus on mESC viability, proliferation, as well as expression of pluripotency and germ‐layer markers and observed that low concentration alginate hydrogels (0.5% and 1% alginate) were most suitable for long‐term culture of mESCs. These results were not unique to mESCs; long‐term viability and proliferation of mouse embryonic carcinoma cells (mECCs) was also best supported by similar conditions. Finally, we determined cytotoxic responses of alginate encapsulated cells to commercially available chemicals and interestingly observed similar responses for mESCs and mECCs, thereby suggesting that mECCs can predict stem cell responses to chemicals. These studies will facilitate future design of optimal stem cell‐based platforms of organ‐specific and developmental toxicity. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3180–3184, 2015     

Biocatalytic Polymer Coatings: On‐Demand Drug Synthesis and Localized Therapeutic Effect under Dynamic Cell Culture Conditions

Biocatalytic surface coatings are prepared herein for localized synthesis of drugs and their on‐demand, site‐specific delivery to adhering cells. This novel approach is based on the incorporation of an enzyme into multilayered polymer coatings to accomplish enzyme‐prodrug therapy (EPT). The build‐up of enzyme‐containing multilayered coatings is characterized and correlations are drawn between the multilayer film assembly conditions and the enzymatic activity of the resulting coatings. Therapeutic effect elicited by the substrate mediated EPT (SMEPT) strategy is investigated using a prodrug for an anticancer agent, SN‐38. The performance of biocatalytic coatings under flow conditions is investigated and it is demonstrated that EPT allows synthesizing the drugs on‐demand, at the time desired and in a controllable amount to suit particular applications. Finally, using cells cultured in sequentially connected flow chambers, it is demonstrated that SMEPT affords a site‐specific drug delivery, that is, exerts a higher therapeutic effect in cells adhering directly to the biocatalytic coatings than in the cells cultured “downstream”. Taken together, these data illustrate biomedical opportunities made possible by engineering tools of EPT into multilayered polymer coatings and present a novel, highly versatile tool for surface mediated drug delivery.     

Static verification of dynamically detected program invariants: Integrating Daikon and ESC/Java

This paper shows how to integrate two complementary techniques for manipulating program invariants: dynamic detection and static verification. Dynamic detection proposes likely invariants based on program executions, but the resulting properties are not guaranteed to be true over all possible executions. Static verification checks that properties are always true, but it can be difficult and tedious to select a goal and to annotate programs for input to a static checker. Combining these techniques overcomes the weaknesses of each: dynamically detected invariants can annotate a program or provide goals for static verification, and static verification can confirm properties proposed by a dynamic tool.We have integrated a tool for dynamically detecting likely program invariants, Daikon, with a tool for statically verifying program properties, ESC/Java. Daikon examines run-time values of program variables; it looks for patterns and relationships in those values, and it reports properties that are never falsified during test runs and that satisfy certain other conditions, such as being statistically justified. ESC/Java takes as input a Java program annotated with preconditions, postconditions, and other assertions, and it reports which annotations cannot be statically verified and also warns of potential runtime errors, such as null dereferences and out-of-bounds array indices.Our prototype system runs Daikon, inserts its output into code as ESC/Java annotations, and then runs ESC/Java, which reports unverifiable annotations. The entire process is completely automatic, though users may provide guidance in order to improve results if desired. In preliminary experiments, ESC/Java verified all or most of the invariants proposed by Daikon.     

Statistics of twin-related domains and the grain boundary network

The twin-related domain, or a collection of contiguous grains related by twinning operations, is proposed as the basis for the analysis of grain boundary network connectivity in materials prone to annealing twinning. The distribution of the number of grains in a twin-related domain was measured for materials with a variety of compositions and processing histories. The Weibull distribution is found to accurately reflect many features of the twin-related domain populations, and the parameters of the Weibull distribution vary systematically with the number fraction of resistant boundaries in the microstructure. An alternative model based on the microstructural effects of sequential thermomechanical processing is proposed. This provides an overall fit to the experimental data of comparable quality to the Weibull distribution, while allowing an interpretation of the model parameters that suggests a refinement of the usual thermomechanical processing schedule.     

An emergent approach to analogical inference

In recent years, a growing number of researchers have proposed that analogy is a core component of human cognition. According to the dominant theoretical viewpoint, analogical reasoning requires a specific suite of cognitive machinery, including explicitly coded symbolic representations and a mapping or binding mechanism that operates over these representations. Here we offer an alternative approach: we find that analogical inference can emerge naturally and spontaneously from a relatively simple, error-driven learning mechanism without the need to posit any additional analogy-specific machinery. The results also parallel findings from the developmental literature on analogy, demonstrating a shift from an initial reliance on surface feature similarity to the use of relational similarity later in training. Variants of the model allow us to consider and rule out alternative accounts of its performance. We conclude by discussing how these findings can potentially refine our understanding of the processes that are required to perform analogical inference.     

Mechanical properties of borothermally synthesized zirconium diboride at elevated temperatures

The mechanical properties of a nominally phase pure ZrB₂ ceramic were measured up to 2300°C in an argon atmosphere. ZrB₂ was hot pressed at 2000°C utilizing borothermally synthesized powder from high purity ZrO₂ and B raw materials. The relative density of the ceramics was about 95% with an average ZrB₂ grain size of 8.8 µm. The room temperature flexural strength was 447 MPa, with strength decreasing to 196 MPa at 1800°C, and then increasing to 360 MPa at 2300°C. The strength up to 1800°C was likely controlled by a combination of effects: surface damage from oxidation of the specimens, stress relaxation, and decreases in the elastic modulus. The strength above 1800°C was controlled by flaws in the range consistent with sizes of the maximum ZrB₂ grain size and the largest pores. Fracture toughness was 2.3 MPa·m^1/2 at room temperature, increasing to 3.1 MPa·m^1/2 at 2200°C. The use of higher purity starting materials improved the mechanical behavior in the ultra-high temperature regime compared to previous studies.     

Evolution of polyacrylonitrile precursor fibers and the effect of stretch profile in wet spinning

Wet spinning of polyacrylonitrile-based polymers is a common technique to manufacture carbon fiber precursors. Understanding the role of stretch profile on structural evolution will support efforts to reduce cost and improve process robustness. Fiber stretch generally occurs in three sequential stages: jet stretch, wet stretch (first draw), and hot draw (second draw). In this study, total fiber stretch was kept constant, but distributed differently across the stretch stages yielding three different fiber variants. Samples were collected and analyzed after each stretch stage in order to correlate process parameters to structural information. For all variants, orientation of the ordered phase increases gradually for each stage of stretch while activation energy for the structural relaxation decreases. Alternatively, crystallite size increases substantially during hot draw, which is shown to have the most pronounced effect on cyclization behavior. Given the process conditions, the variant with the lowest jet stretch and highest hot draw demonstrates the highest tenacity and modulus along with the greatest orientation, crystallite size, and highest peak exotherm temperature.