Directly writing with nanoparticles at the nanoscale using dip-pen nanolithography

Well-defined nanostructures were written with quantum dots and magnetic nanoparticles on gold and mica surfaces using dip-pen nanolithography at room temperature. The structures with both the nanoparticles were characterised by in situ topography measurements, and the quantum dot structures were mapped by fluorescence mapping. It is demonstrated that structures of various kinds such as dots and lines can be prepared using such nanoparticles on suitably prepared surfaces.     

Motion of micrometer sized spherical particles exposed to a transient radial flow: attraction, repulsion, and rotation

It is now accepted that the physical forces in ultrasonic cleaning are due to strongly pulsating bubbles driven by the sound field. Here we have a detailed look at bubble induced cleaning flow by analyzing the transport of an individual particle near an expanding and collapsing bubble. The induced particulate transport is compared with a force balance model. We find two important properties of the flow which explain why bubbles are effectively cleaning: During bubble expansion a strong shear layer loosens the particle from the surface through particle spinning and secondly an unsteady boundary layer generates an attractive force, thus collecting the contamination in the bubble's close proximity.     

Approximate solution of the Riemann problem for the Burgers equation by the transversal method of lines

The transversal method of lines is applied to Riemann problems for the Burgers equation whose solution contains Shockwaves. Existence, uniqueness and convergence of the approximate solution is shown and a numerical example is calculated.

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Zusammenfassung Die transversale Linienmethode wird auf Riemannprobleme für die Burgers-Gleichung angewandt, deren Lösungen Stoßwellen enthalten. Die Existenz, Eindeutigkeit und die Konvergenz der Näherungslösungen wird gezeigt, numerische Ergebnisse werden für ein Beispiel angegeben.

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Supported by DFG.     

A tracking method for gas flow into vacuum based on the vacuum Riemann problem

In this paper, a tracking method is proposed for the expansion of gas flow into vacuum which may be combined with numerical methods for the equations of gas dynamics, the Euler equations. This tracking prevents the difficulties of the numerical approximation introduced by the vacuum as a region where the Euler equations are not valid due to the failure of the continuum assumption. The tracking algorithm is based on the exact or an approximate solution of the vacuum Riemann problem. This is the initial value problem with two constant states, one being the gas and the other the vacuum state, and a limit case of the usual Riemann problem. In this approach, the gas–vacuum boundary is sharply resolved within one mesh interval. For a test problem, the numerical results of gas flow into vacuum are presented which indicate that the gas vacuum boundary is captured very well.     

ESPI solution for non-contacting MEMS-on-wafer testing

Rapid progress in the field of micro-electro-mechanical systems (MEMS) makes the development of appropriate measuring and testing means timely. Characterizing the mechanical properties of MEMS structures at a very early stage of manufacturing is a challenging task for quality assurance in this field. The paper describes a new solution that is based upon the vibration analysis of the microparts. The nanometer amplitudes are detected by advanced electronic speckle pattern interferometry (ESPI). A specific signal processing technique has been applied to make the solution robust. Comprehensive numerical simulations provide the theoretical base for the HNDT concept. A laboratory system for 4″ wafer has been built, and extensive tests show that such key properties as e.g. the thickness of springs or membranes can be determined exactly. Automated frequency scanning and corresponding digital image processing open the way to reliable and fast industrial systems for MEMS testing on wafer level.     

The Peculiar Dynamics of Cavitation Bubbles

Details from cavitation bubble dynamics are reported: jet formation, counterjet formation, shock wave radiation and light emission. Multiple shock wave radiation from single bubble collapse with jet formation could be time resolved by high speed photography with 20 million frames per second. An explanation of counterjet formation is given. Pictures of the light emission (sonoluminescence) in acoustic cavitation are presented.     

Influence of narrow starter notches on the initial crack growth resistance curve of ceramics

In experimental R-curve investigations crack development usually starts from notches. The validity of R-curves depends on the size of the notch root radius. This influence is completely ignored in most cases. In this theoretical study it is shown how the notch radius affects the formally computed crack resistance curve. First, the influence of the notch radius on the starting point of the R-curve, the so-called crack-tip toughness K _I0, will be addressed. Then, the effect of the notch on the shielding stress intensity factor will be discussed, and, finally, the influence on T-stress and the consequences on local path stability will be shown.     

Multiple pressure variables methods for fluid flow at all Mach numbers

In this paper we present a method for the simulation of incompressible as well as compressible unsteady flows. At first we discuss three different forms, i.e. a primitive‐, conservative‐ and a semi‐conservative form of the governing equations. We use a semi‐implicit time integration in such a fashion that the stability is guaranteed independently of the speed of sound and the resulting method is independent of the Mach number range. Moreover, with the application of the so‐called multiple pressure variables (MPV) approach the difficulties with the pressure term can be circumvented as in the incompressible limit the hydrodynamic pressure decouples from the equation of state. Increasing approximation errors in the low Mach number regime are avoided. As a result, the proposed algorithm can also simulate incompressible flows as limit for zero Mach number. Copyright © 2005 John Wiley & Sons, Ltd.     

Singlet Fission in Carbene-Derived Diradicaloids

Herein, we present a new class of singlet fission (SF) materials based on diradicaloids of carbene scaffolds, namely cyclic (alkyl)(amino)carbenes (CAACs). Our modular approach allows the tuning of two key SF criteria: the steric factor and the diradical character. In turn, we modified the energy landscapes of excited states in a systematic manner to accommodate the needs for SF. We report the first example of intermolecular SF in solution by dimer self-assembly at cryogenic temperatures.     

Determination of sulfur forms in wine including free and total sulfur dioxide based on molecular absorption of carbon monosulfide in the air–acetylene flame

A new method for the determination of sulfur forms in wine, i.e., free SO₂, total SO₂, bound SO₂, total S, and sulfate, is presented. The method is based on the measurement of the carbon monosulfide (CS) molecular absorption produced in a conventional air–acetylene flame using high-resolution continuum source absorption spectrometry. Individual sulfur forms can be distinguished because of the different sensitivities of the corresponding CS molecular absorption. The sensitivity of free SO₂ is about three times higher than the value for bound SO₂ and sulfate. The method makes use of procedures similar to those used in classic reference methods. Its performance is verified by analyzing six wine samples. Relative standard deviations are between 5 and 13% for free SO₂ and between 1 and 3% for total SO₂. For the validation of the accuracy of the new method, the results are compared with those of reference methods. The agreement of the values for total SO₂ with values of the classic method is satisfactory: five out of six samples show deviations less than 16%. Due to the instability of free SO₂ in wine and the known problems of the used reference method, serious deviations of the free SO₂ results are found for three samples. The evaluation of the limits of detection focuses on the value for free SO₂, which is the sulfur form having by far the lowest concentration in wine. Here, the achievable limit of detection is 1.8 mg L⁻¹. Figure Detection of non-metal elements using continuum source flame absorption spectrometry