Prediction of the azimuth angle dependence of the quasimolecular anisotropy in heavy ion collisions

Within the quasimolecular (MO) kinematic dipole model we predict a strong dependence of the anisotropy of the MO radiation on the orientation of the heavy ion scattering plane relative to the direction of the photon detection plane.

Designing a Robust Pitch Angle Controller for a 2‐Motor‐Pitch‐System in a Large Wind Turbine

Für große Windenergieanlagen werden neue Pitchregler wie Einzelblattregler oder Turmdämpfungsregler entwickelt. Während diese neuen Pitchregler die Elemente der Windenergieanlagen entlasten, wird das Pitchantriebssystem stärker belastet. Die Pitchantriebe müssen weitaus häufiger bei höherer Amplitude arbeiten. Um die neuen Pitchregler nutzen zu können, muss zunächst das Problem der Materialermüdung der Pitchantriebssysteme gelöst werden. Das Getriebespiel in Getrieben und zwischen Ritzeln und dem Zahnkranz erhöht die Materialermüdung in den Pitchantriebssystemen. In dieser Studie werden als Lösung zwei Pitchantriebe pro Blatt vorgeschlagen. Die beiden Pitchantriebe erzeugen eine Spannung auf dem Pitchantriebssystem und kompensieren das Getriebespiel. Drehmomentspitzen, die eine Materialermüdung verursachen, treten bei diesem System mit zwei Pitchmotoren nicht mehr auf. Ein Reglerausgang wird via Drehmomentverteiler auf die beiden Pitchantriebe übertragen. Es werden mehrere Methoden verglichen und der leistungsfähigste Drehmomentverteiler ausgewählt. Während die Pitchantriebe in Bewegung sind, ändert sich die Spannung auf den Getrieben. Die neuen Pitchregler verstellen den Pitchwinkel in einer sinusförmigen Welle. Der Profilgenerator, der derzeit als Pitchwinkelregler verwendet wird, kann eine Phasenverzögerung im sinusförmigen Pitchwinkel verursachen. Zusätzlich erzeugen große Windenergieanlagen eine hohe Last, die sich störend auf die Pitchbewegung auswirkt. Änderungen der viskosen Reibung und Nichtlinearität der Gleitreibung bzw. Coulombsche Reibung des Pitchregelsystems erschweren zudem die Entwicklung eines Pitchwinkelreglers. Es werden zwei robuste Regler (H∞ und μ–synthesis ) vorgestellt und mit zwei herkömmlichen Reglern (PD und Kaskadenregler) verglichen. Zur Erprobung des Pitchantriebssystems und des Pitchwinkelreglers wird eine Prüfanordnung verwendet. Da der Kranz nicht mit einem Positionssensor ausgestattet ist, wird ein Überwachungselement entwickelt, das die Kranzposition meldet. Neben den beiden Pitchantrieben sind zwei Lastmotoren mit dem Kranz verbunden. Über die beiden Lastmotoren wird das Drehmoment um die Pitchachse einer Windenergieanlage simuliert. Das Drehmoment um die Pitchachse setzt sich zusammen aus Schwerkraft, aerodynamischer Kraft, zentrifugaler Belastung, Reibung aufgrund des Kippmoments und der Beschleunigung bzw. Verzögerung des Rotorblatts. Das Blatt wird als Zweimassenschwinger modelliert. Große Windenergieanlagen und neue Pitchregler für die Anlagen erfordern ein neues Pitchantriebssystem. Als Hardware-Lösung bieten sich zwei Pitchantriebe an mit einem robusten Regler als Software.

Oblique Angle Deposition of Germanium Film on Silicon Substrate

The effect of flux angle, substrate temperature and deposition rate on obliquely deposited germanium (Ge) films has been investigated. By carrying out deposition with the vapor flux inclined at 87° to the substrate normal at substrate temperatures of 250°C or 300°C, it may be possible to obtain isolated Ge nanowires. The Ge nanowires are crystalline as shown by Raman Spectroscopy.

Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon

A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si, Δθ, and the width of the transverse optical Raman peak, Γ, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for Δθ and Γ are used. This reduced dispersion in the predicted values of Δθ together with the broad agreement with the scarce direct determinations of Δθ is then used to analyze the strain energy in partially relaxed pure a-Si. It is concluded that defect annihilation does not contribute appreciably to the reduction of the a-Si energy during structural relaxation. In contrast, it can account for half of the crystallization energy, which can be as low as 7 kJ/mol in defect-free a-Si

Filter for Car Tracking Based on Acceleration and Steering Angle

The motion of a car is described using a stochastic model in which the driving processes are the steering angle and the tangential acceleration. The model incorporates exactly the kinematic constraint that the wheels do not slip sideways. Two filters based on this model have been implemented, namely the standard EKF, and a new filter (the CUF) in which the expectation and the covariance of the system state are propagated accurately. Experiments show that i) the CUF is better than the EKF at predicting future positions of the car; and ii) the filter outputs can be used to control the measurement process, leading to improved ability to recover from errors in predictive tracking.

The effect of flow field & geometry on the dynamic contact angle

A number of recent experiments suggest that, at a given wetting speed, the dynamic contact angle formed by an advancing liquid-gas interface with a solid substrate depends on the flow field and geometry near the moving contact line. In the present work, this effect is investigated in the framework of an earlier developed theory that was based on the fact that dynamic wetting is, by its very name, a process of formation of a new liquid-solid interface (newly “wetted” solid surface) and hence should be considered not as a singular problem but as a particular case from a general class of flows with forming or/and disappearing interfaces. The results demonstrate that, in the flow configuration of curtain coating, where a liquid sheet (“curtain”) impinges onto a moving solid substrate, the actual dynamic contact angle indeed depends not only on the wetting speed and material constants of the contacting media, as in the so-called slip models, but also on the inlet velocity of the curtain, its height, and the angle between the falling curtain and the solid surface. In other words, for the same wetting speed the dynamic contact angle can be varied by manipulating the flow field and geometry near the moving contact line. The obtained results have important experimental implications: given that the dynamic contact angle is determined by the values of the surface tensions at the contact line and hence depends on the distributions of the surface parameters along the interfaces, which can be influenced by the flow field, one can use the overall flow conditions and the contact angle as a macroscopic multiparametric signal-response pair that probes the dynamics of the liquid-solid interface. This approach would allow one to investigate experimentally such properties of the interface as, for example, its equation of state and the rheological properties involved in the interface’s response to an external torque, and would help to measure its parameters, such as the coefficient of sliding friction, the surface-tension relaxation time, and so on.

Cellulose microfibril angle in the cell wall of wood fibres

The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described. Differences in MFA have a profound effect on the properties of wood, in particular its stiffness. The large MFA in juvenile wood confers low stiffness and gives the sapling the flexibility it needs to survive high winds without breaking. It also means, however, that timber containing a high proportion of juvenile wood is unsuitable for use as high-grade structural timber. This fact has taken on increasing importance in view of the trend in forestry towards short rotation cropping of fast grown species. These trees at harvest may contain 50% or more of timber with low stiffness and therefore, low economic value. Although they are presently grown mainly for pulp, pressure for increased timber production means that ways will be sought to improve the quality of their timber by reducing juvenile wood MFA. The mechanism by which the orientation of microfibril deposition is controlled is still a matter of debate. However, the application of molecular techniques is likely to enable modification of this process. The extent to which these techniques should be used to improve timber quality by reducing MFA in juvenile wood is, however, uncertain, since care must be taken to avoid compromising the safety of the tree.

Capillary flow behavior of worm-like micelles studied by small-angle X-ray scattering and small angle light scattering

A novel capillary flow device has been developed and applied to study the orientation of worm-like micelles, among other systems. Small-angle X-ray scattering (SAXS) data from micelles formed by a Pluronic block copolymer in aqueous salt solution provides evidence for the formation of worm-like micelles, which align under flow. A transition from a rod-like form factor to a less persistent conformation is observed under flow. Flow alignment of worm-like micelles formed by the low molar mass amphiphile system cetyl pyridinium chloride+sodium salicylate is studied for comparative purposes. Here, inhomogenous flow at the micron scale is revealed by streaks in the small-angle light scattering pattern perpendicular to the flow direction. Copyright (c) 2006 John Wiley & Sons, Ltd.

Pressure effects revealed by small angle neutron scattering on block copolymer gels

We study the effects of hydrostatic pressure (P) on aqueous solutions and gels of the block copolymer B20E610 (E, oxyethylene; B, oxybutylene; subscripts, number of repeats), by performing simultaneous small angle neutron scattering/pressure experiments. Micellar cubic gels were studied for 9.5 and 4.5 wt% B20E610 at T = 20-80 and 35-55 degrees C, respectively, while micellar isotropic solutions where Studied for 4.5 wt% B20E610 at T > 55 degrees C. We observed that the interplanar distance d(110) (cubic unit cell parameter a = root 2d(110)) decreases while the correlation length of the Cubic order (delta) increases, upon increasing P at a fixed T for 9.5 wt% B20E610. The construction of master Curves for d(110) and delta corresponding to 9.5 wt% B20E610 proved the correlation between changes in T and P. Neither d(110) and delta nor the cubic-isotropic phase transition temperature was affected by the applied pressure for 4.5 wt% B20E610. The dramatic contrast between the pressure-induced behavior observed for 9.5 and 4.5 wt% B20E610 suggests that pressure induced effects might be more effectively transmitted through samples that present wider domains of cubic structure order (9.5 wt% compared to 4.5 wt% B20E610).

Cellulose microfibril angle in the cell wall of wood fibres

The term microfibril angle (MFA) in wood science refers to the angle between the direction of the helical windings of cellulose microfibrils in the secondary cell wall of fibres and tracheids and the long axis of cell. Technologically, it is usually applied to the orientation of cellulose microfibrils in the S2 layer that makes up the greatest proportion of the wall thickness, since it is this which most affects the physical properties of wood. This review describes the organisation of the cellulose component of the secondary wall of fibres and tracheids and the various methods that have been used for the measurement of MFA. It considers the variation of MFA within the tree and the biological reason for the large differences found between juvenile (or core) wood and mature (or outer) wood. The ability of the tree to vary MFA in response to environmental stress, particularly in reaction wood, is also described. Differences in MFA have a profound effect on the properties of wood, in particular its stiffness. The large MFA in juvenile wood confers low stiffness and gives the sapling the flexibility it needs to survive high winds without breaking. It also means, however, that timber containing a high proportion of juvenile wood is unsuitable for use as high-grade structural timber. This fact has taken on increasing importance in view of the trend in forestry towards short rotation cropping of fast grown species. These trees at harvest may contain 50% or more of timber with low stiffness and therefore, low economic value. Although they are presently grown mainly for pulp, pressure for increased timber production means that ways will be sought to improve the quality of their timber by reducing juvenile wood MFA. The mechanism by which the orientation of microfibril deposition is controlled is still a matter of debate. However, the application of molecular techniques is likely to enable modification of this process. The extent to which these techniques should be used to improve timber quality by reducing MFA in juvenile wood is, however, uncertain, since care must be taken to avoid compromising the safety of the tree.