A Class of Collisions of Plane Impulsive Light--Like Signals in General Relativity

We present a systematic study of collisions of homogeneous, plane--fronted, impulsive light--like signals which do not interact after head--on collision. For the head--on collision of two such signals, six real parameters are involved, three from each of the incoming signals. We find two necessary conditions to be satisfied by these six parameters for the signals to be non--interacting after collision. We then solve the collision problem in general when these necessary conditions hold. After collision the two signals focus each other at Weyl curvature singularities on each others signal front. Our family of solutions contains some known collision solutions as special cases.Comment: 14 pages, late

Scaling properties of step bunches induced by sublimation and related mechanisms: A unified perspective

This work provides a ground for a quantitative interpretation of experiments on step bunching during sublimation of crystals with a pronounced Ehrlich-Schwoebel (ES) barrier in the regime of weak desorption. A strong step bunching instability takes place when the kinetic length is larger than the average distance between the steps on the vicinal surface. In the opposite limit the instability is weak and step bunching can occur only when the magnitude of step-step repulsion is small. The central result are power law relations of the between the width, the height, and the minimum interstep distance of a bunch. These relations are obtained from a continuum evolution equation for the surface profile, which is derived from the discrete step dynamical equations for. The analysis of the continuum equation reveals the existence of two types of stationary bunch profiles with different scaling properties. Through a mathematical equivalence on the level of the discrete step equations as well as on the continuum level, our results carry over to the problems of step bunching induced by growth with a strong inverse ES effect, and by electromigration in the attachment/detachment limited regime. Thus our work provides support for the existence of universality classes of step bunching instabilities [A. Pimpinelli et al., Phys. Rev. Lett. 88, 206103 (2002)], but some aspects of the universality scenario need to be revised.Comment: 21 pages, 8 figure

Evaporation and growth of crystals - propagation of step density compression waves at vicinal surfaces

We studied the step dynamics during crystal sublimation and growth in the limit of fast surface diffusion and slow kinetics of atom attachment-detachment at the steps. For this limit we formulate a model free of the quasi-static approximation in the calculation of the adatom concentration on the terraces at the crystal surface. Such a model provides a relatively simple way to study the linear stability of a step train in a presence of step-step repulsion and an absence of destabilizing factors (as Schwoebel effect, surface electromigration etc.). The central result is that a critical velocity of the steps in the train exists which separates the stability and instability regimes. When the step velocity exceeds its critical value the plot of these trajectories manifests clear space and time periodicity (step density compression waves propagate on the vicinal surface). This ordered motion of the steps is preceded by a relatively short transition period of disordered step dynamics.Comment: 18 pages, 6 figure

Numerical analysis of droplet deposition in inkjet printed electronics assembly

In this paper, a computational approach for the analysis of microscale droplet impact dynamics is presented. The approach is intended to support a condition based monitoring system to enhance quality and reliability of inkjet printed electronics components. The Smoothed Particle Hydrodynamics (SPH) approach of Lucy and Gingold and Monaghan has been used as the basis for the model, with the δ-SPH terms of Marrone et al used to improve handling of the dynamic impact events and the gradient correction terms of Belytschko used to improve the accuracy of interface dynamics. Model validation has been performed through comparison against a macroscale dam break problem and through a microscale analysis designed to determine accurate surface tension-pressure behaviour based on the Young-Laplace relation. The model is used to assess impact of a single drop on a uniform surface and the three dimensional formation of multi-drop layers

Modelling methodologies for quality assessment of 3D inkjet printed electronic products

Purpose of the Fraunhofer Direct Digital Manufacturing Conference is an intellectual exchange between researchers, enterprises and users of Additive Manufacturing technologies in order to gather the latest information about trends, progress, importance and the future potential of these technologies for industrial applications. The range of topics covers Product Development (incl. simulation, co-design, mass customization), Technologies (incl. bio-printing, hybrid processes, novel developments/visionary concepts, process chains for industrial production), Materials (incl. ceramics, bio-materials, multi-material approaches), Quality (incl. process/ part quality management) as well as further innovative and visionary approaches not fitting the range of topics above. Renowned international keynote speakers give insight into the latest trends and challenges in additive manufacturing in a variety of industry sectors, including biomedical, aerospace and automotive

Modelling the impact of refinishing processes on COTS components for use in aerospace applications

Commercial off the shelf components (COTS) are being adopted by electronic equipment manufacturers for use in aerospace applications. To ensure that these components meet the quality and reliability standards, refinishing processes, such as hot solder dip and laser deballing/reballing, are used to replace component lead-free solder terminations with tin–lead solder. These processes provide a risk mitigation strategy against tin whiskers induced short circuit failures. Being an additional step to the subsequent PCB assembly process it is important that this additional process does not impose significant thermo-mechanical stress which can impact subsequent reliability. As part of a major study in collaboration with industry partners, process models have been developed to predict the thermo-mechanical behaviour of components when subjected to the refinishing process. This paper details the techniques used to provide model input data (e.g., process parameters and package geometric/materials data) as well as the development and application of these modelling techniques to the refinishing process

Autonomous pick-and-place using the dVRK.

PURPOSE: Robotic-assisted partial nephrectomy (RAPN) is a tissue-preserving approach to treating renal cancer, where ultrasound (US) imaging is used for intra-operative identification of tumour margins and localisation of blood vessels. With the da Vinci Surgical System (Sunnyvale, CA), the US probe is inserted through an auxiliary access port, grasped by the robotic tool and moved over the surface of the kidney. Images from US probe are displayed separately to the surgical site video within the surgical console leaving the surgeon to interpret and co-registers information which is challenging and complicates the procedural workflow. METHODS: We introduce a novel software architecture to support a hardware soft robotic rail designed to automate intra-operative US acquisition. As a preliminary step towards complete task automation, we automatically grasp the rail and position it on the tissue surface so that the surgeon is then able to manipulate manually the US probe along it. RESULTS: A preliminary clinical study, involving five surgeons, was carried out to evaluate the potential performance of the system. Results indicate that the proposed semi-autonomous approach reduced the time needed to complete a US scan compared to manual tele-operation. CONCLUSION: Procedural automation can be an important workflow enhancement functionality in future robotic surgery systems. We have shown a preliminary study on semi-autonomous US imaging, and this could support more efficient data acquisition

Differences in subjective well-being between individuals with distinct Joint Personality (temperament-character) Networks in a Bulgarian sample

Background: Personality is the major predictor of people\u27s subjective well-being ( Method: The sample consisted of 443 individuals from Bulgaria (68.70% females) with a mean age of 34 years ( Results: We found two Temperament Profiles and two Character Profiles that clustered into two distinctive Joint Personality Networks. All individuals in Joint Personality Network 1 had a Reliable (nhRP) Temperament Profile in combination with an Organized (SCt) Character Profile ( Conclusions: Although a stable temperament and a healthy character were separately important for well-being, it was clear that it was the interaction between such temperament and character configuration that yielded greater levels of subjective well-being. Nevertheless, future research needs to investigate this interaction further to evaluate other cultures with variable configurations of personality traits and values