Crystallization of model fat blends containing symmetric and asymmetric monounsaturated triacylglycerols

In this study, the crystallization and melting properties of four different fat blends with the same saturated fat content (30%) but with different ratios of symmetric and asymmetric monounsaturated triacylglycerols were investigated using pNMR, DSC and polarized light microscopy. Blends were either palmitic (P) or stearic (S) based, and were combinations of SatOSat‐rich (Sat = saturated, O = oleic) and SatSatO‐rich vegetable oils with high‐oleic sunflower oil. The DSC results demonstrate that there was almost no difference in crystallization mechanism and crystallization rate between the two P‐based blends. Both blends showed a two‐step crystallization, which can be explained by polymorphism. Stop‐and‐return DSC results suggested an initial crystallization into an unstable polymorph followed by polymorphic transition during the crystallization. For the S‐based blends there was a clear difference between the SOS‐rich and the SSO‐rich blend, with a slower crystallization for the SSO‐rich blend. Possibly, this can be explained by fractional crystallization. The microstructure did not differ greatly between the blends. Directly after crystallization, the crystals of the SSO‐rich blend were slightly larger than the crystals of the SOS‐rich blend.     

Students’ perceptions about the use of video games in the classroom

Video games are often regarded as promising teaching and learning tools for the 21st century. One of the main arguments is that video games are appealing to contemporary students. However, there are indications that video game acceptance cannot be taken for granted. In this study, a path model to examine and predict student acceptance of video games is proposed, and empirically tested by involving 858 secondary school students. The results show that students’ preference for using video games in the classroom is affected directly by a number of factors: the perceptions of students regarding the usefulness, ease of use, learning opportunities, and personal experience with video games in general. Gender effects are found as well, but appear to be mediated by experience and ease of use.     

Connect & Drive: design and evaluation of cooperative adaptive cruise control for congestion reduction

Road throughput can be increased by driving at small inter-vehicle time gaps. The amplification of velocity disturbances in upstream direction, however, poses limitations to the minimum feasible time gap. This effect is covered by the notion of string stability. String-stable behavior is thus considered an essential requirement for the design of automatic distance control systems, which are needed to allow for safe driving at time gaps well below 1 s. Using wireless inter-vehicle communications to provide real-time information of the preceding vehicle, in addition to the information obtained by common Adaptive Cruise Control (ACC) sensors, appears to significantly decrease the feasible time gap, which is shown by practical experiments with a test fleet consisting of six passenger vehicles. The large-scale deployment of this system, known as Cooperative ACC (CACC), however, poses challenges with respect to the reliability of the wireless communication system. A solution for this scalability problem can be found in decreasing the transmission power and/or beaconing rate, or adapting the communications protocol. Although the main CACC objective is to increase road throughput, the first commercial application of CACC is foreseen to be in truck platooning, since short distance following is expected to yield significant fuel savings in this case.

     

Physicochemical properties and amylopectin chain profiles of cowpea,chickpea and yellow pea starches

Starches from cowpea and chickpea seeds were isolated and their properties were compared with those of commercial yellow pea starch. Amylose contents were 25.8%, 27.2%, and 31.2%, and the volume mean diameter of granules, determined in the dry state, were 15.5, 17.9, and 33.8 μm for cowpea, chickpea and yellow pea starches, respectively. All three legume starches showed a C-type X-ray diffraction pattern and two-stage swelling pattern. Amylopectin populations were isolated and the unit chain profiles were analyzed by HPLC after debranching with pullulanase. The degree of polymerization (DP) of short chain populations was about 6–50 and the populations of long chain had a DP of 50–80. Cowpea showed a lower weight ratio of short:long chains than chickpea and yellow pea starches. The larger portion of long side chains in cowpea amylopectin can be correlated with a higher gelatinization temperature, greater pasting peak and a slight difference in crystalline structure found for cowpea starch. Chickpea and yellow pea starches exhibited similarity in unit chain profile of amylopectin as well as in gelatinization temperature and pasting profile, while they differed in amylose content, particle size and syneresis. It is assumed that the chain length distribution of amylopectin has a large influence on starch properties.     

Network markets and the structure of networks

Network markets are characterized by composite goods or services that can be obtained from alternative combinations of basic products. Examples are complex, multistage production and consumption systems, transport and communications. Efficiency in these markets depends on the net effect of the complementary and substitution relationships that exist between elementary products, which are determined by network topology and market structure. This paper examines factors that affect equilibria in network markets by considering a number of simple economic models of network markets. First it is shown how network topology influences profits and welfare under different market regimes. In particular, attention is given to price discrimination in monopolistic networks. Next evolution of networks is examined, which may occur via investment in new links by incumbent firms, or via entry of new firms in the network. It is shown that the number of competitors in equilibrium may not coincide with the socially optimal one, which in turn depends on the network structure. In order to show some concrete implications of the theoretical results two examples are presented, dealing with intermediate factors in an input-output production system, and with the trade-off between network externalities and economies of scale and density in hub-and-spoke transportation networks. Received: June 1997/Accepted: October 1999     

High throughput screening of Monophos instant ligand library leads to a ton-scale asymmetric hydrogenation process

The development of catalytic processes for pharmaceuticals intermediates is often under severe time-pressure. To cope with this constraint, high throughput experimentation (HTE) methods have been implemented for catalyst finding. In this article, we present the HTE protocols put in place at DSM in the area of enantioselective hydrogenation. They mostly rely on libraries of monodentate chiral phosphoramidites ligands. We applied our instant ligand library technology to solve a real-life case, i.e. the asymmetric hydrogenation of an α-substituted cinnamic acid derivative. This has led to a multi-ton scale process.     

Synthesis, characterization and aggregation behavior of block copolymers containing a polyisocyanopeptide segment

Following up on previous preliminary communications the synthesis of a series of block copolymers by applying amine end-capped polymers as initiators for the nickel(II) catalyzed polymerization of isocyanides is reported. Using a polystyrene derivative as the initiator, superamphiphiles containing a hydrophobic polystyrene tail and a charged helical polyisocyanide headgroup were prepared. Under proper conditions these superamphiphiles self-assembled in water to give a variety of aggregate morphologies, among which are superhelical architectures. Initiators derived from carbosilane dendritic wedges gave block copolymers with a unique combination of structural elements, i.e. a flexible dendritic block and a rigid polyisocyanide block. Block copolymers derived from the 3rd generation dendrimers form well-defined micellar aggregates in the presence of Ag⁺ ions. These aggregates have been used to construct nanoarrays of metallic silver.