Quantitative Mapping of Strains and Young Modulus Based on Phase-Sensitive OCT

In this chapter we consider mapping of local strains and tissue elasticity in optical coherence tomography (OCT) based on analysis of phase-sensitive OCT scans. Conventional structural OCT scans correspond to spatially resolved mapping of the backscattering intensity of the probing optical beam. Deeper analysis of such sequentially acquired multiple OCT scans can be used to extract additional information about motion of scatterers in the examined region. Such detailed analysis of OCT scans has already resulted in creation of OCT-based visualization of blood microcirculation, which has been implemented in several commercially available devices, especially for ophthalmic applications. Another functional extension of OCT emerging in recent years is the OCT-based elastography, i.e., mapping of local strains and elastic properties in the imaged region. Here, we describe the main principles of local strain mapping in phase-sensitive OCT with a special focus on the recently proposed efficient vector method of estimation of interframe phase-variation gradients. The initially performed mapping of local strains is then used for realization of quantitative compressional elastography, i.e., mapping of the Young modulus and obtaining stress-strain dependences for the studied samples. The discussed principles are illustrated by simulated and experimental examples of elastographic OCT-based visualization. The presented elastographic principles are rather general and can be used in a wide area of biomedical and technical applications

Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens

The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e–e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from −20 to −1100 V/mm for Ekin = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 μm above the sample surface for Ekin = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at Ekin = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm2 (retarding field −21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm2, it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at Ekin = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments

Application of MW delay lines in combined SAR calibration

This paper gives a description of the facilities for the combined calibration of the L- and VHF-band radars (λ ≈ 23 cm, SAR-23 and λ ≈ 180 cm, SAR-180, respectively) installed in the air-borne "MARS" system [1] where the MW delay lines are employed. The technique for the combined SAR calibration involves a periodic external calibration of point calibrated reflectors (transponders) being mounted close to the surfaces under study or on special testing sites as well as continuous internal calibration with indispensable recording of real carrier flight parameters [2]

Share the happiness

Due to the technological developments over the past year´s payment methods have advanced significantly. This thesis aims to investigate how different payment methods affect consumers' behaviour. Today, consumers can choose to pay with several different payment methods, where many of these payment methods have been proven to make the consumers increasingly psychologically detached from the event of spending money (Shah, Eisenkraft, Bettman & Chartrand, 2015). The society is moving towards a “cashless economy”, and it is therefore of high relevance to understand how different payment methods influence how much we value and feel psychologically connected to what we spend our money on (Shah et al., 2015). In addition to affecting our willingness to share, different forms of payments also impact our prosocial behaviour (e.g., donation amounts). Being prosocial is a personal characteristic in which a person wants to do things for others without expecting something in return (Bradley, Laurence & Ferguson, 2018). Since mobile payments have become an increasingly common way of paying, our research will contribute to understanding how the use of smart technology impacts individuals’ prosociality. In this paper we investigated if prosociality is affected by different payment methods, and if this connection is strengthened by the mediating effect of pain of paying and the perceived value of receiving a gift from e.g., a friend or family. This effect is measured by looking at the amount we are willing to share with others, in the form of a gift. In order to check for other variables that enhance prosociality, we looked at several moderators such as observability of the act, the attitudes towards mobile payments and attitudes towards prosociality. Two studies were conducted to explore if mobile payments make people more generous when treating their friends, distinguishing between mobile payments and gift cards or credit cards. Previous studies have found a clear difference between the use of cash and credit card, while the distinction between credit card and mobile payment has not yet been studied as extensively. In conclusion, our studies find no statistical difference in the levels of prosocial gifting between individuals that use mobile payments relative to gift card and credit card. In addition, the paper gives thorough insights about which mechanisms affect our prosociality