Finnish CMS-TOB cosmic rack

Peer reviewe

Deformation, acoustic emission and ultrasound velocity during fatigue tests on paper

We study the evolution of mechanical properties of paper samples during cyclic experiments. The issue is to look at the sample-to-sample variation, and we try to predict the number of loading cycles to failure. We used two concurrent methods to obtain the deformation: the strain was calculated from vertical displacement measured by laser interferometer sensor, as well as, computed by digital image correlation technique from pictures taken each 2s by a camera. Acoustic emission of fracture was also recorded, and an active ultrasonic wave method using piezoelectric transducers is used to follow the viscoelastic behaviour of each sample. We found that a sharp final increase of different variables like deformation, strain rate and fluctuations, are signs of an imminent rupture of the paper. Moreover looking at the evolution of these quantities during the first cycle only is already an indicator about the lifetime of the sample.Peer reviewe

Optical position clamping with predictive control

The following article appeared in (Appl. Phys. Lett. 95, 181104 (2009)) and may be found at http://link.aip.org/link/?apl/95/181104We increase the effective stiffness of optical tweezers by position clamping a polystyrene bead with a predictive feedback control algorithm. This algorithm mitigates the effect of feedback loop delay. Hence, higher gain than with proportional control can be employed, which results in higher effective trap stiffness, without trap instability. In experiments (initial trap stiffness 0.056 pN/nm with a 1.78 μm diameter polystyrene bead) predictive control increased the effective trap stiffness by 55% relative to proportional control. We also derive theoretical expressions for the power spectra of the bead position controlled by our algorithm

Defect Localization By an Extended Laser Source on a Hemisphere

The primary goal of this study is to localize a defect (cavity) in a curved geometry. Curved topologies exhibit multiple resonances and the presence of hotspots for acoustic waves. Launching acoustic waves along a specific direction e.g. by means of an extended laser source reduces the complexity of the scattering problem. We performed experiments to demonstrate the use of a laser line source and verified the experimental results in FEM simulations. In both cases, we could locate and determine the size of a pit in a steel hemisphere which allowed us to visualize the defect on a 3D model of the sample. Such an approach could benefit patients by enabling contactless inspection of acetabular cups. © 2021, The Author(s).Open access funded by University of Helsinki Library

Calibration of RADMON radiation monitor onboard Aalto-1 CubeSat

RADMON is a small radiation monitor designed and assembled by students of University of Turku and University of Helsinki. It is flown on-board Aalto-1, a 3-unit CubeSat in low Earth orbit at about 500 km altitude. The detector unit of the instrument consists of two detectors, a Si solid-state detector and a CsI(Tl) scintillator, and utilizes the ΔE-E technique to determine the total energy and species of each particle hitting the detector. We present the results of the on-ground and in-flight calibration campaigns of the instrument, as well as the characterization of its response through extensive simulations within the Geant4 framework. The overall energy calibration margin achieved is about 5%. The full instrument response to protons and electrons is presented and the issue of proton contamination of the electron channels is quantified and discussed

Simulation of longitudinal string waves through a single polymer molecule

The capability of an individual polymer molecule to carry an acoustic wave along its length was investigated by a Brownian dynamics simulation using the algorithm of Ermak and McCammon and the discrete worm-like chain model. A 3 μm long DNA strand featuring 50 nm persistence length was subjected to longitudinal oscillations (2 kHz to 25 kHz) at one end, and the properties of the resulting propagating interaction were studied and shown to be wave-like. A proof of concept experiment is proposed, where an optical tweezers dumbbell experiment is conducted to induce and receive the wave, and the result is compared to that of a control experiment with the DNA strand absent. Simulations were conducted to show what one might expect to see in such an experiment

Calibration of Fourier domain short coherence interferometer for absolute distance measurements

We calibrated and determined the measurement uncertainty of a custom-made Fourier domain short coherence interferometer operated in laboratory conditions. We compared the optical thickness of two thickness standards and three coverslips determined with our interferometer to the geometric thickness determined by SEM. Using this calibration data, we derived a calibration function with a 95% confidence level system uncertainty of (5.9×10$^{-3}$+2.3)  μm, where r is the optical distance in μm, across the 240 μm optical measurement range. The confidence limit inclu3des contributions from uncertainties in the optical thickness, geometric thickness, and refractive index measurements as well as uncertainties arising from cosine errors and thermal expansion. The results show feasibility for noncontacting absolute distance characterization with micrometer-level accuracy. This instrument is intended for verifying the alignment of the discs of an accelerating structure in the possible future compact linear collider