arXiv subjects

V. Schmidt

Publications and source records attributed to V. Schmidt.

10 recordsLinked to original sources

arXiv2025

Penetration depth and effective sample size characterization of UV/Vis radiation into pharmaceutical tablets

The pharmaceutical industry is moving from off-line quality testing to real-time release testing (RTRT) to improve drug quality while reducing costs. The implementation of RTRT requires advanced in-line process analytics, where UV/Vis spectroscopy has proven its suitability. However, quantification of the sample size requires detailed knowledge of the penetration depth. In this study, bilayer tablets were produced using a hydraulic tablet press. The lower layer contained titanium dioxide and microcrystalline cellulose (MCC), while the upper layer consisted of MCC, lactose or a combination with theophylline. The thickness of the upper layer was stepwise increased. Spectra from 224 to 820 nm were recorded with an orthogonally aligned UV/Vis probe. Thereby, the experimental penetration depth reached up to 0.4 mm, while the Kubelka-Munk model yielded a theoretical maximum penetration depth of 1.38 mm. Based on these values, the effective sample sizes were determined. Considering a parabolic penetration profile, the maximum volume was 2.01 mm$^3$. The results indicated a wavelength and particle size dependency. Micro-CT analysis confirmed the even distribution of the API in the tablets proving the sufficiency of the UV/Vis sample size. Consequently, UV/Vis spectroscopy is a reliable alternative for RTRT in tableting.

physics.app-ph↗

arXiv2025

Quantifying local heterogeneities in the 3D morphology of X-PVMPT battery electrodes based on FIB-SEM measurements

Organic electrode-active materials (OAMs) not only enable a variety of charge and storage mechanisms, but are also safer for the environment and of lower cost compared to materials in commonly used lithium-ion batteries. Cross-linked Poly(3)-vinyl-N-methylphenothiazine (X-PVMPT) is a p-type OAM which shows high performance and enables fast and reversible energy storage in different battery configurations. The performance of an OAM does not only depend on its molecular or polymer structure, but also on the structure of the composite electrode. The porous nanostructure of an electrode composed of X-PVMPT, a conductive carbon additive and binder is investigated by statistical image analysis, based on 3D image data obtained by focused-ion beam scanning-electron microscopy (FIB-SEM) measurements. Univariate probability distributions of relevant morphological descriptors as well as bivariate distributions of pairs of such descriptors are parametrically modelled, among others, by utilization of copulas in the latter case. These models are then used for quantifying local heterogeneities of X-PVMPT considered in this paper. Furthermore, it is shown that the nanostructure changes when traversing from bottom to top face of the electrode, which influences its performance. While the observed short transportation paths trough the solid phase are beneficial in terms of electrical conductivity, the pathways through the pore phase influencing the effective ionic diffusivity are--in comparison--rather long.

cond-mat.mtrl-sci↗

arXiv2020

Measurement of deuteron carbon vector analyzing powers in the kinetic energy range 170-380 MeV

A measurement of vector analyzing powers in elastic deuteron-carbon scattering has been performed at the Cooler Synchrotron COSY of Forschungszentrum J\"ulich, Germany. Seven kinetic beam energies between 170 and 380 MeV have been used. A vector-polarized beam from a polarized deuteron source was injected, accelerated to the final desired energy and stored in COSY. A thin needle-shaped diamond strip was used as a carbon target, onto which the beam was slowly steered. Elastically scattered deuterons were identified in the forward direction using various layers of scintillators and straw tubes. Where data exist in the literature (at 200 and 270 MeV), excellent agreement of the angular shape was found. The beam polarization of the presented data was deduced by fitting the absolute scale of the analyzing power to these references. Our results extend the world data set and are necessary for polarimetry of future electric dipole moment searches at storage rings. They will as well serve as an input for theoretical description of polarized hadron-hadron scattering.

nucl-ex↗

arXiv2020

Proxima Centauri b: A Strong Case for including Cosmic-Ray-induced Chemistry in Atmospheric Biosignature Studies

Due to its Earth-like minimum mass of 1.27 M$_{\text{E}}$ and its close proximity to our Solar system, Proxima Centauri b is one of the most interesting exoplanets for habitability studies. Its host star, Proxima Centauri, is however a strongly flaring star, which is expected to provide a very hostile environment for potentially habitable planets. We perform a habitability study of Proxima Centauri b assuming an Earth-like atmosphere under high stellar particle bombardment, with a focus on spectral transmission features. We employ our extensive model suite calculating energy spectra of stellar particles, their journey through the planetary magnetosphere, ionosphere, and atmosphere, ultimately providing planetary climate and spectral characteristics, as outlined in Herbst et al. (2019). Our results suggest that together with the incident stellar energy flux, high particle influxes can lead to efficient heating of the planet well into temperate climates, by limiting CH$_4$ amounts, which would otherwise run into anti-greenhouse for such planets around M-stars. We identify some key spectral features relevant for future spectral observations: First, NO$_2$ becomes the major absorber in the visible, which greatly impacts the Rayleigh slope. Second, H$_2$O features can be masked by CH$_4$ (near infra-red) and CO$_2$ (mid to far infra-red), making them non-detectable in transmission. Third, O$_3$ is destroyed and instead HNO$_3$ features become clearly visible in the mid to far infra-red. Lastly, assuming a few percent of CO$_2$ in the atmosphere, CO$_2$ absorption at 5.3 $\mu$m becomes significant (for flare and non-flare cases), strongly overlapping with a flare related NO feature in Earth's atmosphere.

astro-ph.EP↗

arXiv2019

Exploration of Gibbs-Laguerre tessellations for three-dimensional stochastic modeling

Random tessellations are well suited for probabilistic modeling of three-dimensional (3D) grain microstructures of polycrystalline materials. The present paper is focused on so-called Gibbs-Laguerre tessellations, in which the generators of the Laguerre tessellation form a Gibbs point process. The goal is to construct an energy function of the Gibbs point process such that the resulting tessellation matches some desired geometrical properties. Since the model is analytically intractable, our main tool of analysis is stochastic simulation based on Markov chain Monte Carlo. Such simulations enable us to investigate the properties of the models, and, in the next step, to apply the knowledge gained to the statistical reconstruction of the 3D microstructure of an aluminum alloy extracted from 3D tomographic image data.

eess.IV↗

arXiv2018

Phase Measurement for Driven Spin Oscillations in a Storage Ring

This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Jülich using a vector polarized, bunched $0.97\,\textrm{GeV/c}$ deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.

physics.acc-ph↗

arXiv2017

Phase locking the spin precession in a storage ring

This letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV/$c$ bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate ($\approx 121$ kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a one standard deviation range of $σ= 0.21$ rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.

physics.acc-ph↗

arXiv2017

Spin tune mapping as a novel tool to probe the spin dynamics in storage rings

Precision experiments, such as the search for electric dipole moments of charged particles using storage rings, demand for an understanding of the spin dynamics with unprecedented accuracy. The ultimate aim is to measure the electric dipole moments with a sensitivity up to 15 orders in magnitude better than the magnetic dipole moment of the stored particles. This formidable task requires an understanding of the background to the signal of the electric dipole from rotations of the spins in the spurious magnetic fields of a storage ring. One of the observables, especially sensitive to the imperfection magnetic fields in the ring is the angular orientation of stable spin axis. Up to now, the stable spin axis has never been determined experimentally, and in addition, the JEDI collaboration for the first time succeeded to quantify the background signals that stem from false rotations of the magnetic dipole moments in the horizontal and longitudinal imperfection magnetic fields of the storage ring. To this end, we developed a new method based on the spin tune response of a machine to artificially applied longitudinal magnetic fields. This novel technique, called \textit{spin tune mapping}, emerges as a very powerful tool to probe the spin dynamics in storage rings. The technique was experimentally tested in 2014 at the cooler synchrotron COSY, and for the first time, the angular orientation of the stable spin axis at two different locations in the ring has been determined to an unprecedented accuracy of better than $2.8μ$rad.

physics.acc-ph↗

arXiv2015

Impact of micro-alloying on the plasticity of Pd-based Bulk Metallic Glasses

Micro-alloying was performed using additions of Co and Fe to monolithic Pd40Ni40P20 bulk metallic glass to study selectively the influence on the plastic behavior in uniaxial compression and three-point bending tests. The corresponding Poisson's ratios were determined by ultrasonic measurements. The microstructure of the individual bulk metallic glasses was characterized by electron microscopy, X-ray diffraction and calorimetry. A plastic strain of 13% was found for the Co addition (1 at.%), whereas the Fe addition (0.6 at.%) led to immediate failure after reaching the elastic limit. Surprisingly, the plasticity is not reflected by the high Poisson's ratio of 0.4 since it remained unaffected by the minor alloying.

cond-mat.mtrl-sci↗

arXiv2011

Spatial modeling of the 3D morphology of hybrid polymer-ZnO solar cells, based on electron tomography data

A spatial stochastic model is developed which describes the 3D nanomorphology of composite materials, being blends of two different (organic and inorganic) solid phases. Such materials are used, for example, in photoactive layers of hybrid polymer zinc oxide solar cells. The model is based on ideas from stochastic geometry and spatial statistics. Its parameters are fitted to image data gained by electron tomography (ET), where adaptive thresholding and stochastic segmentation have been used to represent morphological features of the considered ET data by unions of overlapping spheres. Their midpoints are modeled by a stack of 2D point processes with a suitably chosen correlation structure, whereas a moving-average procedure is used to add the radii of spheres. The model is validated by comparing physically relevant characteristics of real and simulated data, like the efficiency of exciton quenching, which is important for the generation of charges and their transport toward the electrodes.

stat.AP↗