Portfolios of buyer–supplier exchange relationships in an online marketplace for IT services

Most studies on the role of IT for economic exchange predicted that under a given set of exchange attributes buyers would choose a certain mode of relationship with suppliers. Our study of an online IT services marketplace revealed that buyers do not have a single, uniformly preferred type of relationship, but rather maintain a portfolio of relationships. Furthermore, different buyers arrange their portfolios of exchange relationships in different ways. We found four clusters of buyers' portfolios of relationships labeled Transactional buyers, Recurrent buyers, Small diversifiers and Large diversifiers, that differ in their usage of auction or negotiation mechanism, their supplier relations as well as their usage of preferred suppliers. Our results thus paint a richer picture of how buyers organize their supplier networks online.     

Flexible large area polymer solar cells based on poly(3-hexylthiophene)/fullerene

Photovoltaic devices based on regioregular poly(3-hexylthiophene) (P3HT) and ([6,6]-phenyl-C61-butyric acid methyl ester) (PCBM) were fabricated and characterized using 5×5 cm ITO polyester foils with an active cell area of 0.5×0.5 cm². The HOMO/LUMO of P3HT and PCBM were estimated from cyclic voltammetry data. The complete quenching of photoluminescence of P3HT after mixing with PCBM indicates an effective charge transfer from P3HT to PCBM. The absorption spectrum of a blend (1:3 wt%) of both components shows that there is no ground state doping. Following device parameters without any special postproduction treatment were determined: V_OC=600 mV, I_SC=6.61 mA/cm², FF=0.39 and η_AM1.5 (P_IN:100 mW/cm²)=1.54%.     

Effect of annealing of poly(3-hexylthiophene)/fullerene bulk heterojunction composites on structural and optical properties

Composite films of P3HT/PCBM-(poly[3-2,5-diyl]/[6,6]-phenyl C₆₁ butyric acid methyl ester) are widely used as an active layer in plastic solar cells. We have studied the influence of thermal annealing on nano-structural and optical properties of thin spin-coated P3HT/PCBM-films. Their structural properties were studied by X-ray diffraction in grazing incidence geometry. It was found that the crystallinity of the investigated films is drastically increased upon annealing. Furthermore, the anisotropic dielectric function of such films was determined by spectroscopic ellipsometry. Significant changes were observed both in parallel and perpendicular components of the dielectric function after annealing. These changes were attributed to the formation of crystalline domains upon annealing.     

半导体激光热输入对渗氮层结构和性能的影响

目的 提高Ti-6Al-4V钛合金的表面硬度和耐磨性,解决失效问题。方法 利用半导体激光器在纯氮气氛下对Ti-6Al-4V钛合金表面进行激光渗氮处理,研究激光功率和扫描速度耦合作用下不同热输入对渗氮层质量的影响。分别采用X射线衍射仪、扫描电子显微镜、X射线能谱仪,对渗氮层的物相组成、截面微观组织以及元素分布进行表征,采用显微维氏硬度仪测量渗氮层截面硬度分布。结果 不同热输入下Ti-6Al-4V钛合金氮化区域均生成TiN相,且含量随热输入的增大而增加,渗氮层厚度随热输入的增大呈近似直线增长。渗氮层组织由表及里依次由连续的TiN薄层、柱状晶、树枝晶和针状晶组成,使渗氮层内硬度随层厚的增加呈下降趋势,随热输入的增大,树枝晶中粗枝晶的数量增加,渗氮层硬度也随之增加。然而当热输入较高（320 J/mm）时,渗氮层内产生大量的裂纹。结论 利用激光气体氮化技术,控制热输入为210~275 J/mm时,在Ti-6Al-4V钛合金表面制备渗氮层,其表面成形良好、无裂纹,厚度约为413~517 μm,近表层硬度较基材提高2.5倍以上。     

Structural and optical properties of both pure poly(3-octylthiophene) (P3OT) and P3OT/fullerene films

We have investigated the structural and optical properties of P3OT and P3OT/fullerene thin films in view of their application as active layer in plastic solar cells. Films of these materials were prepared by spin coating from toluene solutions onto silicon substrates. Their optical properties were studied by spectroscopic ellipsometry, which provides the anisotropic dielectric function of the films. Moreover, structural properties were studied using X-ray diffraction. A close correlation between the results obtained by both methods could be found. Especially, the strong optical anisotropy of the films can be explained in terms of a preferable orientation of the polymer chains parallel to the substrate. The effect of the optical anisotropy on the performance of optoelectronic devices is discussed.     

Alignment materials with controllable anchoring energy

New polymers with photo‐controllable anchoring energy and tunable pretilt angle within 90°–0° range for nematic liquid crystals alignment were developed. The functional properties of polymers are provided by the effect of photoinduced planar alignment and the presence of side hydrocarbon chains in macromolecules that create a homeotropic alignment effect. Applying photosensitive alignment layers based on polymers with side benzaldehyde and hydrocarbon groups, fabrication of optical devices with refractive index gradient, uniform cell gap, and low operation voltage is possible. The developed materials are suitable for simple fabrication of tunable liquid crystal lenses.     

Semantic flooding

Classifications are trees where links between nodes codify the fact that a node lower in the hierarchy describes a topic (and contains documents about this topic) which is more specific than the topic of the node one level above. In turn, multiple classifications can be connected by semantic links which represent mappings among them and which can be computed, e.g. by ontology matching. In this paper, we describe how these two types of links can be used to define a semantic overlay network which can cover any number of peers and which can be flooded to perform a semantic search on documents, i.e. to perform semantic flooding. We have evaluated our approach by simulating networks of 10, 100, 1,000 and 10,000 peers containing classifications which are fragments of the DMoz web directory. The results are promising and show that, in our approach, only a relatively small number of peers needs to be queried in order to achieve high accuracy.     

厚度主导铝合金表面304不锈钢涂层组织结构及性能的演变行为

目的 评价不同沉积厚度对铝合金基体上304不锈钢涂层综合性能的影响。方法 采用超音速火焰喷涂在铝合金表面制备3种不同厚度（200、600、1 000μm）的304不锈钢涂层。利用附带能谱的扫描电镜（SEM）、X射线衍射仪（XRD）、维氏显微硬度计、纳米压痕仪、液压式万能试验机以及摩擦磨损试验机，研究涂层的微观结构、物相组成、残余应力、硬度分布、弹性模量、结合强度、弯曲性能和摩擦学行为。结果 304不锈钢涂层组织均匀、无裂纹，与基体结合良好。涂层主要由奥氏体相组成，其余为少量铁素体相和氧化物，且涂层中奥氏体晶粒相比粉末中发生晶粒细化。随着涂层厚度的增加，涂层孔隙率（C200≈0.5%、C600≈2.5%、C1000≈4.3%）、氧含量（C200≈2.4%、C600≈3.1%、C1000≈4.2%）增加，涂层残余压应力减小，显微硬度、弹性模量和结合强度均呈下降趋势；但涂层断裂刚度与其厚度成正比，断裂时裂纹主要沿未熔颗粒边界和氧化物聚集区域萌生和扩展。在干摩擦条件下，304不锈钢涂层的摩擦系数约为0.6，与铝合金相比，摩擦过程更加稳定，耐磨性提高3倍。随着涂层厚度的增加，涂层摩擦系数稳定性降...