A stereodivergent approach to substituted 4-hydroxypiperidines

A stereodivergent route toward both diastereomeric forms of functionalized 4-hydroxypiperidines has been successfully developed. This route involves biocatalytic generation of the enantiopure starting materials followed by functionalization via N-acyliminium ion-mediated CC-bond formation.     

Intra-organizational Networks and Performance: A Review

Intra-organizational network research had its first heyday during the empirical revolution in social sciences before World War II when it discovered the informal group within the formal organization. These studies comment on the classic sociological idea of bureaucracy being the optimal organization. Later relational interest within organizational studies gave way to comparative studies on the quantifiable formal features of organizations. There has been a resurgence in intra-organizational networks studies recently as the conviction grows that they are critical to organizational and individual performance. Along with methodological improvements, the theoretical emphasis has shifted from networks as a constraining force to a conceptualization that sees them as providing opportunities and finally, as social capital. Because of this shift it has become necessary not only to explain the differences between networks but also their outcomes, that is, their performance. It also implies that internal and external networks should no longer be treated separately.Research on differences between intra-organizational networks centers on the influence of the formal organization, organizational demography, technology and environment. Studies on outcomes deal with diffusion and adaptation of innovation; the utilization of human capital; recruitment, absenteeism and turnover; work stress and job satisfaction; equity; power; information efficiency; collective decision making; mobilization for and outcomes of conflicts; social control; profit and survival of firms and individual performance.Of all the difficulties that are associated with intra-organizational network research, problems of access to organizations and incomparability of research findings seem to be the most serious. Nevertheless, future research should concentrate on mechanisms that make networks productive, while taking into account the difficulties of measuring performance within organizations, such as the performance paradox and the halo-effect.     

Salt crystallization as damage mechanism in porous building materials--a nuclear magnetic resonance study

Salts can damage building materials by chemical reactions or crystallization, which is a serious threat to cultural heritage. In order to develop better conservation techniques, more knowledge of the crystallization processes is needed. In a porous material, the size of a salt crystal is limited by the sizes of the pores. It has been predicted that as a consequence, the solubility of a salt increases with decreasing pore size. This increase seems to be related to an increase of the stress generated by a crystal on the pore wall. It has been suggested that the resulting stress could become high enough to induce failure. We have studied the crystallization of salts in porous materials with well-defined pore sizes. Samples were saturated at 40 degrees C with saturated Na2SO4 and Na2CO3 solutions. Next we have cooled the samples to 0 degrees C and waited for nucleation. After nucleation occurred, the solubility in the porous material was measured with nuclear magnetic resonance (NMR) as a function of the temperature. The measurements on Na2CO3 indeed show an increase in solubility with a decrease in pore size. For Na2SO4, we did not observe a pore size-dependent solubility. However, we have to remark that these results show a metastable crystal phase. The results can be used to calculate the actual pressure exerted by the crystals onto the pore wall.     

Weakly dispersive band near the fermi level of GaMnAs due to Mn interstitials

The nature of the weakly dispersive electronic band near the Fermi level observed in photoemission experiments on the diluted magnetic semiconductor GaMnAs is investigated theoretically. The combination of experimental features appears puzzling. We show that the formation of the band is closely related to the presence of the Mn interstitial impurities. The states forming the band have predominantly minority-spin Mn-3d character. The low experimental Mn-3d intensity is explained by the low content of the interstitial Mn impurities. The features of the band are robust with respect to the calculational technique [local density approximation (LDA), LDA + U].     

Noise annoyance from stationary sources: relationships with exposure metric day-evening-night level (DENL) and their confidence intervals

Relationships between exposure to noise [metric: day-evening-night levels (DENL)] from stationary sources (shunting yards, a seasonal industry, and other industries) and annoyance are presented. Curves are presented for expected annoyance score, the percentage "highly annoyed" (%HA, cutoff at 72 on a scale from 0 to 100), the percentage "annoyed" (%A, cutoff at 50 on a scale from 0 to 100), and the percentage "(at least) a little annoyed" (%LA, cutoff at 28 on a scale from 0 to 100). The estimates of the parameters of the relations are based on the data from a field study (N=1875) at 11 locations (2 shunting yards, 1 seasonal industry, 8 other industries) in the Netherlands. With the same (yearly) DENL, the seasonal industry causes less annoyance than the other industries, while the other industries cause less annoyance than the shunting yards. It appears that annoyance caused by vibrations from shunting yards and annoyance caused by noise from through trains are (partly) responsible for the relatively high annoyance from shunting yards. The relatively low annoyance from the seasonal industry presumably is related to the presence of a relatively quiet period. Results for the two shunting yards and the seasonal industry are based on fewer data than the other industrial sources, and are indicative. The same patterns of influence of age and noise sensitivity that are generally found are also found in this study. For comparison, results regarding transportation sources are also given, including previously unpublished results for expected annoyance.     

Comparison of electron and neutron compton scattering from entangled protons in a solid polymer

We present, for the first time, a direct comparison between electron (ECS) and neutron (NCS) Compton scattering results from protons of a solid polymer. The momentum distributions of hydrogen obtained from ECS and NCS are in excellent agreement. In both experiments, a strong "anomalous" shortfall in the scattering intensity of protons [first detected in liquid water with NCS [Phys. Rev. Lett. 79, 2839 (1997)]]] is found ranging from about 20% up to 50%, depending on the momentum transfer applied. The characteristic times of electron- and neutron-proton collisions lie in the subfemtosecond range. The presented ECS and NCS results provide further direct evidence for this striking effect, which has been ascribed to attosecond quantum entanglement of the protons.     

Absence of zero-bias anomaly in spin-polarized vacuum tunneling in Co(0001)

In a joint experimental and theoretical study, we investigate the bias-voltage dependence of the tunnel magnetoresistance (TMR) through a vacuum barrier. The TMR observed by spin-polarized scanning tunneling microscopy between an amorphous magnetic tip and a Co(0001) sample is almost independent of the bias voltage at large tip-sample separations. Whereas qualitative understanding is achieved by means of the electronic surface structure of Co, the experimental findings are compared quantitatively with bias-voltage dependent first-principles calculations for ballistic tunneling. At small tip-sample separations, a pronounced minimum in the experimental TMR was found at +200 mV bias.     

Application of partial observability for analysis and design of synchronized systems

Synchronization in identical drive-response systems is a problem that can be cast in an observer design framework. In this paper we extend this approach by studying the analysis/design of partial synchronization by means of observer theory. In doing so, we introduce the concept of partial observer--an observer to reconstruct a part of the system state vector. It is also shown how the observability condition can be utilized to analyze the dynamics in an array of coupled identical systems.