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HbA1c is the gold standard test for monitoring medium/long term glycemia conditions in diabetes care, which is a critical factor in reducing the risk of chronic diabetes complications. Current technologies for measuring HbA1c concentration are invasive and adequate assays are still limited to laboratory-based methods that are not widely available worldwide. The development of a non-invasive diagnostic tool for HbA1c concentration can lead to the decrease of the rate of undiagnosed cases and facilitate early detection in diabetes care. We present a preliminary validation diagnostic study of W-band spectroscopy for detection and monitoring of sustained hyperglycemia, using the HbA1c concentration as reference. A group of 20 patients with type 1 diabetes mellitus and 10 healthy subjects were non-invasively assessed at three different visits over a period of 7 months by a millimeter-wave spectrometer (transmission mode) operating across the full W-band. The relationship between the W-band spectral profile and the HbA1c concentration is studied using longitudinal and non-longitudinal functional data analysis methods. A potential blind discrimination between patients with or without diabetes is obtained, and more importantly, an excellent relation (R-squared = 0.97) between the non-invasive assessment and the HbA1c measure is achieved. Such results support that W-band spectroscopy has great potential for developing a non-invasive diagnostic tool for in-vivo HbA1c concentration monitoring in humans.
In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1<Minv(GeV/c2)<1.4, the yield is found to be similar for π+p and π−p pairs, and to follow a power law 〈Apart〉α, where 〈Apart〉 is the mean number of participating nucleons. The exponent α depends strongly on the pair transverse momentum (pT) while its pT-integrated and charge-averaged value is α=1.5±0.08st±0.2sy.
For a long time, strong coupling expansions have not been applied systematically in lattice QCD thermodynamics, in view of the success of numerical Monte Carlo studies. The persistent sign problem at finite baryo-chemical potential, however, has motivated investigations using these methods, either by themselves or combined with numerical evaluations, as a route to finite density physics. This article reviews the strategies, by which a number of qualitative insights have been attained, notably the emergence of the hadron resonance gas or the identification of the onset transition to baryon matter in specific regions of the QCD parameter space. For the simpler case of Yang–Mills theory, the deconfinement transition can be determined quantitatively even in the scaling region, showing possible prospects for continuum physics.
We examine the thermodynamic behavior of a static neutral regular (non-singular) black hole enclosed in a finite isothermal cavity. The cavity enclosure helps us investigate black hole systems in a canonical or a grand canonical ensemble. Here we demonstrate the derivation of the reduced action for the general metric of a regular black hole in a cavity by considering a canonical ensemble. The new expression of the action contains quantum corrections at short distances and concludes to the action of a singular black hole in a cavity at large distances. We apply this formalism to the noncommutative Schwarzschild black hole, in order to study the phase structure of the system. We conclude to a possible small/large stable regular black hole transition inside the cavity that exists neither at the system of a classical Schwarzschild black hole in a cavity, nor at the asymptotically flat regular black hole without the cavity. This phase transition seems to be similar with the liquid/gas transition of a Van der Waals gas.
The present research in high energy physics as well as in the nuclear physics requires the use of more powerful and complex particle accelerators to provide high luminosity, high intensity, and high brightness beams to experiments. With the increased technological complexity of accelerators, meeting the demand of experimenters necessitates a blend of accelerator physics with technology. The problem becomes severe when optimization of beam quality has to be provided in accelerator systems with thousands of free parameters including strengths of quadrupoles, sextupoles, RF voltages, etc. Machine learning methods and concepts of artificial intelligence are considered in various industry and scientific branches, and recently, these methods are used in high energy physics mainly for experiments data analysis.
In Accelerator Physics the machine learning approach has not found a wide application yet, and in general the use of these methods is carried out without a deep understanding on their effectiveness with respect to more traditional schemes or other alternative approaches. The purpose of this PhD research is to investigate the methods of machine learning applied to accelerator optimization, accelerator control and in particular on optics measurements and corrections. Optics correction, maximization of acceptance, and simultaneous control of various accelerator components such as focusing magnets is a typical accelerator scenario. The effectiven- ess of machine learning methods in a complex system such as the Large Hadron Collider, which beam dynamics exhibits nonlinear response to machine settings is the core of the study. This work presents successful application of several machine learning techniques such as clustering, decision trees, linear multivariate models and neural networks to beam optics measurements and corrections at the LHC, providing the guidelines for incorporation of machine learning techniques into accelerator operation and discussing future opportunities and potential work in this field.
The main subject of this thesis is the study of hadron and photon production in relativistic heavy-ion collisions by means of hydrodynamics+transport approaches. Two different kinds of such hybrid approaches are employed in this work, the SMASH-vHLLE-hybrid and a MUSIC+SMASH hybrid. While the former is capable of simulating heavy-ion collisions covering a wide range of collision energies down to √s = 4.3 GeV, reproducing the correct baryon stopping powers, the latter provides a framework to consistently model photon production in the hadronic stage of high-energy heavy-ion collisions.
The SMASH-vHLLE-hybrid is a novel state-of-the-art hybrid approach whose development constitutes a major contribution to this thesis. It couples the hadronic transport SMASH to the 3+1D viscous hydrodynamics approach vHLLE. Therein, SMASH is employed to provide the fluctuating 3D initial conditions and to model the late hadronic rescattering stage, and vHLLE for the fluid dynamical evolution of the hot and dense fireball. The initial conditions are provided on a hypersurface of constant proper time, and the macroscopic evolution of the fireball is carried out down to an energy density of ecrit = 0.5 GeV/fm3, where particlization occurs. Consistency at the interfaces is verified in view of global, on-average quantum number conservation and the SMASH-vHLLE-hybrid is validated by comparison to SMASH+CLVisc as well as UrQMD+vHLLE hybrid approaches. The establishment of the SMASH-vHLLE-hybrid to theoretically describe heavy-ion collisions at intermediate and high collision energies forms a basis for a range of extensions and future research projects. It is further made available to the heavy-ion community by virtue of being published on Github.
The SMASH-vHLLE-hybrid is applied to simulate Au+Au/Pb+Pb collisions between √s = 4.3 GeV and √s = 200.0 GeV. A good agreement with the experimentally measured rapidity and transverse mass spectra is obtained. In particular the baryon stopping dynamics are well reproduced at low, intermediate, and high collision energies. Excitation functions for the mid-rapidity yield and mean transverse momentum of pions, protons and kaons are demonstrated to agree well with their experimentally measured counterpart. These results further validate the approach and provide a solid baseline for potential future studies. The importance of annihilations and regenerations of protons and anti-protons is additionally investigated in Au+Au/Pb+Pb collisions between √s = 17.3 GeV and √s = 5.02 TeV with the SMASH-vHLLE-hybrid. It is found that, regarding the p + p ̄ ↔ 5 π reaction, 20-50% (depending on the rapidity range) of the (anti-)proton yield lost to annihila- tions in the hadronic rescattering stage is restored owing to the back reaction. The back reaction thus constitutes a non-negligible contribution to the final (anti-)proton yield and should not be neglected when modelling the late rescattering stage of heavy-ion collisions.
The MUSIC+SMASH hybrid is a hybrid approach ideally suited to model the production of photons in relativistic heavy-ion collisions. Therein, the macroscopic production of photons in the hadronic stage in MUSIC relies on the identical effective field theories as the photon cross sections implemented in SMASH for the microscopic production. The MUSIC+SMASH hybrid thus provides the first consistent framework to the end of hadronic photon production. It accounts for 2 → 2 scattering processes of the kind π + ρ → π + γ and pion bremsstrahlung processes π + π → π + π + γ. The MUSIC+SMASH hybrid is employed in an ideal 2D setup to systematically assess the importance of non-equliibrium dynamics in the hadronic rescattering stage on mid-rapidity transverse momentum spectra and elliptic flow of photons at RHIC/LHC energies. This is achieved by comparing the outcome of the MUSIC+SMASH hybrid, involving an out-of-equilibrium late rescattering stage, to macroscopically approximating late stage photon production by means of MUSIC, employed down to temperatures well below the switching temperature. It is found that non-equilibrium dynamics have only minor implications for photon transverse momentum spectra, but significantly enhance the photon elliptic flow. At RHIC energies, an enhancement of up to 70%, and at LHC of up to 65% is observed in the non-equilibrium afterburner as compared to its hydrodynamical counterpart. In combination with the large amount of photons produced above the particlization temperature, these differences are modest regarding the transverse momentum spectra, but a significant enhancement of the elliptic flow is observed at low transverse momenta. Below pT ≈ 1.4 GeV, the combined v2 is enhanced by up to 30% at RHIC, and up to 20% at the LHC within the non-equilibrium setup as compared to its approximation via hydrodynamics. Non-equilibrium dynamics in the hadronic rescattering stage are hence important, especially in view of momentum anisotropies at low transverse momenta. These findings thus contribute to the understanding of low-pT photons produced in heavy-ion collisions at RHIC/LHC energies and the MUSIC+SMASH hybrid employed for this study provides a baseline for additional studies regarding photon production in the future.
To summarize, the approaches and frameworks presented in this thesis provide a good baseline for further extensions and studies in order to improve the understanding of hadron and photon production in relativistic heavy-ion collisions across a wide range of collision energies. More broadly, such future studies of hadrons and photons may contribute to enhance the understandig of the properties of the fundamental building blocks of matter, of which everything that surrounds us is made of.
Stationarity of the constituents of the body and of its functionalities is a basic requirement for life, being equivalent to survival in first place. Assuming that the resting state activity of the brain serves essential functionalities, stationarity entails that the dynamics of the brain needs to be regulated on a time-averaged basis. The combination of recurrent and driving external inputs must therefore lead to a non-trivial stationary neural activity, a condition which is fulfiled for afferent signals of varying strengths only close to criticality. In this view, the benefits of working in the vicinity of a second-order phase transition, such as signal enhancements, are not the underlying evolutionary drivers, but side effects of the requirement to keep the brain functional in first place. It is hence more appropriate to use the term 'self-regulated' in this context, instead of 'self-organized'.
Liquid-jet photoelectron spectroscopy was applied to determine the first acid dissociation constant (pKa) of aqueous-phase glucose while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Valence spectra from solutions at pH values below and above the first pKa reveal a change in glucose’s lowest ionization energy upon the deprotonation of neutral glucose and the subsequent emergence of its anionic counterpart. Site-specific insights into the solution-pH-dependent molecular structure changes are also shown to be accessible via C 1s photoelectron spectroscopy. The spectra reveal a considerably lower C 1s binding energy of the carbon site associated with the deprotonated hydroxyl group. The occurrence of photoelectron spectral fingerprints of cyclic and linear glucose prior to and upon deprotonation are also discussed. The experimental data are interpreted with the aid of electronic structure calculations. Our findings highlight the potential of liquid-jet photoelectron spectroscopy to act as a site-selective probe of the molecular structures that underpin the acid–base chemistry of polyprotic systems with relevance to environmental chemistry and biochemistry.
Das Feld der Hochenergie-Schwerionenforschung hat sich der Untersuchung des Quark-Gluon-Plasmas (QGP) gewidmet. Ein QGP ist ein sehr heißer und dichter Materiezustand, der kurz nach dem Urknall für einige Mikrosekunden das Universum füllte. Unter diesen extremen Bedingungen sind die fundamentalen Bausteine der Materie, die Quarks und Gluonen, quasi frei, also nicht in Hadronen eingeschlossen, wie es unter normalen Bedingungen der Fall ist. Hadronen sind Teilchen, die aus Quarks und Gluonen bestehen. Die bekanntesten Hadronen sind Protonen und Neutronen, die Bestandteile von Atomkernen, aus denen, zusammen mit Elektronen, die gesamte bekannte Materie aufgebaut ist.
Um ein QGP im Labor zu erzeugen, lässt man ultrarelativistische schwere Ionen, wie zum Beispiel Pb-208-Kerne, aufeinander prallen. Dies geschieht am CERN, dem größten Kernforschungszentrum der Welt. Der Teilchenbeschleuniger, welcher Protonen und Pb-Kerne beschleunigt und zur Kollision bringt, heißt Large Hadron Collider (LHC) und ist mit 27 km Umfang der größte der Welt. Bei einer einzigen Pb-Pb Kollision am LHC werden mehrere Tausend Teilchen und Antiteilchen erzeugt. Das dedizierte Experiment zur Untersuchung von Schwerionenkollisionen am LHC ist ALICE. ALICE ist mit mehreren Teilchendetektoren ausgerüstet, die es ermöglichen, tausende Teilchen gleichzeitig zu messen und zu identifizieren.
Unter den produzierten Teilchen befinden sich auch leichte Atomkerne, wenngleich diese nur sehr selten erzeugt werden. Die Anzahl der produzierten Teilchen pro Teilchensorte hängt nämlich von deren Masse ab. In Pb-Pb Kollisionen am LHC sinkt die Anzahl der produzierten (Anti)kerne exponentiell um einen Faktor 1/330 bei Hinzufügen jedes weiteren Nukleons. Die Menge an produzierten Teilchen pro Spezies stellt Informationen über den Produktionsmechanismus beim Übergang vom QGP zum Hadrongas zur Verfügung. Hierbei sind leichte (Anti)kerne von besonderem Interesse, da sie vergleichsweise groß sind und ihre Bindungsenergie bis zu zwei Größenordnungen kleiner ist als die Temperaturen, die bei der Erzeugung der Hadronen vorherrschen. Es ist bis heute noch nicht verstanden, wie leichte (Anti)kerne bei diesen Bedingungen erzeugt werden und überleben können.
Für diese Arbeit wurden ca. 270 Millionen Pb-Pb Kollisionen bei einer Schwerpunktsenergie von 5,02 TeV, die von ALICE im November 2018 aufgezeichnet wurden, analysiert. Es wurde die Produktion von (Anti)triton und (Anti)alpha untersucht. Wegen ihrer großen Masse werden beide Kerne sehr selten produziert, bei weitem nicht bei jeder Kollision. Antialpha ist der schwerste Antikern, der jemals gemessen wurde. Aufgrund dieser Seltenheit ist die Größe des zur Verfügung stehenden Datensatzes entscheidend. Es war möglich, das erste jemals gemessene Antialpha-Transversalimpulsspektrum zu extrahieren. Auch für (Anti)triton und Alpha wurden Transversalimpulsspektren bestimmt.
Die Ergebnisse wurden mit theoretischen Modellen und anderen ALICE Messungen verglichen.
Am Ende wird in einem Ausblick auf das kürzlich durchgeführte Upgrade der ALICE Spurendriftkammer (TPC) eingegangen. In der nächsten, bald startenden Datennahmeperiode wird der LHC seine Kollisionsrate erheblich erhöhen, was es ermöglichen wird, mehr als 100 mal so viele Daten wie bisher aufzuzeichnen. Hiervon werden die in dieser Arbeit beschriebenen (Anti)triton- und (Anti)alpha-Analysen beachtlich profitieren. Um mit den erheblich höheren Kollisionsraten zurecht zu kommen, mussten einige Detektoren, unter anderem die TPC, maßgeblich erneuert werden. In den ersten beiden Datennahmeperioden wurde die TPC mit Vieldrahtproportionalkammern betrieben. Diese sind allerdings viel zu langsam für die geplanten Kollisionsraten. Deshalb wurden sie im Jahr 2019, während einer langen Betriebspause des LHC, durch Quadrupel-GEM (Gas Electron Multiplier) Folien basierte Auslesekammern ersetzt, welche eine kontinuierliche Auslese der TPC ermöglichen. Da es sich um die erste jemals gebaute GEM TPC im Großformat handelt, war ein umfangreiches Forschungs- und Entwicklungs- (F&E) Programm notwendig, um die GEM Auslesekammern zu charakterisieren und zu testen. Im Rahmen dieses F&E Programms wurden am Anfang dieser Promotion systematische Messungen an einer kleinen Test TPC mit Quadrupel-GEM Auslese, die extra zu diesem Zweck gebaut worden war, durchgeführt. Hierbei wurde der Rückfluss der bei der Gasverstärkung erzeugten Ionen in das Driftvolumen der TPC und die Energieauflösung mit verschiedenen GEM Folien Typen und unterschiedlicher Anordnung gemessen. Das Ziel war, möglichst kleine Ionenrückflüsse bei möglichst guter Energieauflösung zu erreichen. Hierbei musste ein Kompromiss gefunden werden, da die beiden Größen sich gegenläufig verhalten. Es war jedoch möglich, mit mehreren GEM Konfigurationen Spannungseinstellungen zu identifizieren, bei denen beide Größen den gewünschten Anforderungen entsprachen.
The QCD phase-diagram is studied, at finite magnetic field. Our calculations are based on the QCD effective model, the SU(3) Polyakov linear-sigma model (PLSM), in which the chiral symmetry is integrated in the hadron phase and in the parton phase, the up-, down- and strange-quark degrees of freedom are incorporated besides the inclusion of Polyakov loop potentials in the pure gauge limit, which are motivated by various underlying QCD symmetries. The Landau quantization and the magnetic catalysis are implemented. The response of the QCD matter to an external magnetic field such as magnetization, magnetic susceptibility and permeability has been estimated. We conclude that the parton phase has higher values of magnetization, magnetic susceptibility, and permeability relative to the hadron phase. Depending on the contributions to the Landau levels, we conclude that the chiral magnetic field enhances the chiral quark condensates and hence the chiral QCD phase-diagram, i.e. the hadron-parton phase-transition likely takes place, at lower critical temperatures and chemical potentials.
Topological phases set themselves apart from other phases since they cannot be understood in terms of the usual Landau theory of phase transitions. This fact, which is a consequence of the property that topological phase transitions can occur without breaking symmetries, is reflected in the complicated form of topological order parameters. While the mathematical classification of phases through homotopy theory is known, an intuition for the relation between phase transitions and changes to the physical system is largely inhibited by the general complexity.
In this thesis we aim to get back some of this intuition by studying the properties of the Chern number (a topological order parameter) in two scenarios. First, we investigate the effect of electronic correlations on topological phases in the Green's function formalism. By developing a statistical method that averages over all possible solutions of the manybody problem, we extract general statements about the shape of the phase diagram and investigate the stability of topological phases with respect to interactions. In addition, we find that in many topological models the local approximation, which is part of many standard methods for solving the manybody lattice model, is able to produce qualitatively correct phase transitions at low to intermediate correlations.
We then extend the statistical method to study the effect of the lattice, where we evaluate possible applications of standard machine learning techniques against our information theoretical approach. We define a measure for the information about particular topological phases encoded in individual lattice parameters, which allows us to construct a qualitative phase diagram that gives a more intuitive understanding of the topological phase.
Finally, we discuss possible applications of our method that could facilitate the discovery of new materials with topological properties.
The COLTRIMS Reaction Microscope C-REMI can image the momentum vectors of all emitted charged fragments in an atomic or molecular reactions similar to the bubble chamber in high energy particle physics. C-REMI can detect fragments with “zero” kinetic energy in an ultrahigh vacuum environment by projecting them with weak electromagnetic fields onto position-sensitive detectors. Geometrically a nearly 4π collection solid angle and a nearly 50% efficiency for a fivefold multi-coincidence can be achieved. Measuring time-of-flight and detector position the momenta of the fragments can be measured with excellent resolution (<0.01 a.u.; see A1 in the Appendix). Thus, multivector correlations in momentum space are measured, which provide insight into the entangled dynamics of atomic and molecular quantum systems. From these vector-correlations phases and energies can be deduced which allow for relative time measurements even in the zeptosecond range. C-REMI provides a “spyhole” into the secrets of ultrafast dynamics of atomic and molecular processes. It is applied today around the globe in numerous research projects in physics and chemistry. The purpose for writing this article is to demonstrate the universal application possibilities of C-REMI, and its high multi-coincidence efficiency and high momentum resolution. This paper will not give a review on all milestone experiments performed with C-REMI.
The recent discovery of binary neutron star mergers has opened a new and exciting venue of research into hot and dense strongly interacting matter. For the first time, this elusive state of matter, described by the theory of quantum chromo dynamics, can be studied in two very different environments. On the macroscopic scale, in the collisions of neutron stars; and on the microscopic scale, in collisions of heavy ions at particle collider facilities. We will discuss the conditions that are created in these mergers and the corresponding high energy nuclear collisions. This includes the properties of quantum chromo dynamics matter, that is, the expected equation of state as well as expected chemical and thermodynamic properties of this exotic matter. To explore this matter in the laboratory, a new research prospect is available at the Facility for Antiproton and Ion Research, FAIR. The new facility is being constructed adjacent to the existing accelerator complex of the GSI Helmholtz Centre for Heavy Ion Research at Darmstadt/Germany, expanding the research goals and technical possibilities substantially. The worldwide unique accelerator and experimental facilities of FAIR will open the way for a broad spectrum of unprecedented research supplying a variety of experiments in hadron, nuclear, atomic, and plasma physics as well as biomedical and material science, which will be briefly described.
This work aims at radar sensors in the frequency band from 57 to 64 GHz that can be embedded in wind turbine blades during manufacturing, enabling non-destructive quality inspection directly after production and structural health monitoring (SHM) during the complete service life of the blade. In this paper, we show the fundamental damage detection capability of this sensor technology during fatigue testing of typical rotor blade materials. Therefore, a frequency modulated continuous wave (FMCW) radar sensor is used for damage diagnostics, and the results are validated by simultaneous camera recordings. Here, we focus on the failure modes delamination, fiber waviness (ondulation), and inter-fiber failure. For each failure mode, three samples have been designed and experimentally investigated during fatigue testing. A damage index has been proposed based on residual, that is, differential, signals exploiting measurements from pristine structural conditions. This study shows that the proposed innovative radar approach is able to detect continuous structural degradation for all failure modes by means of gradual signal changes.
This study presents an ultra-wideband, elliptical slot, planar monopole antenna for early breast cancer microwave imaging. The on-body antenna's operation is optimised by direct contact with the patient's skin. With a compact size of 9 × 7 mm, the antenna covers a wide bandwidth from 16 to 24 GHz for reflection coefficients lower than –10 dB. Besides, it also features an electrode for electrical impedance tomography applications. Verification on a volunteer's breast gives an excellent agreement with the simulation for the defined bandwidth. Furthermore, as the first stage of the system's characterisation, pork fat is also used to demonstrate the possibility to enhance the transmission between the antennas within the high loss environment. Those results propose the feasibility of implementing a high-frequency radar system for breast cancer detection.
The cosmological implications of the Covariant Canonical Gauge Theory of Gravity (CCGG) are investigated. CCGG is a Palatini theory derived from first principles using the canonical transformation formalism in the covariant Hamiltonian formulation. The Einstein-Hilbert theory is thereby extended by a quadratic Riemann-Cartan term in the Lagrangian. Moreover, the requirement of covariant conservation of the stress-energy tensor leads to necessary presence of torsion. In the Friedman universe that promotes the cosmological constant to a time-dependent function, and gives rise to a geometrical correction with the EOS of dark radiation. The resulting cosmology, compatible with the ΛCDM parameter set, encompasses bounce and bang scenarios with graceful exits into the late dark energy era. Testing those scenarios against low-z observations shows that CCGG is a viable theory.
Consequences of minimal length discretization on line element, metric tensor, and geodesic equation
(2021)
When minimal length uncertainty emerging from a generalized uncertainty principle (GUP) is thoughtfully implemented, it is of great interest to consider its impacts on gravitational Einstein field equations (gEFEs) and to try to assess consequential modifications in metric manifesting properties of quantum geometry due to quantum gravity. GUP takes into account the gravitational impacts on the noncommutation relations of length (distance) and momentum operators or time and energy operators and so on. On the other hand, gEFE relates classical geometry or general relativity gravity to the energy–momentum tensors, that is, proposing quantum equations of state. Despite the technical difficulties, we intend to insert GUP into the metric tensor so that the line element and the geodesic equation in flat and curved space are accordingly modified. The latter apparently encompasses acceleration, jerk, and snap (jounce) of a particle in the quasi-quantized gravitational field. Finite higher orders of acceleration apparently manifest phenomena such as accelerating expansion and transitions between different radii of curvature and so on.
One of the most challenging problems in solid state systems is the microscopic analysis of electronic correlations. A paramount minimal model that encodes correlation effects is the Hubbard Hamiltonian, which—regardless of its simplicity—is exactly solvable only in a few limiting cases and approximate many-body methods are required for its solution. In this review, an overview on the non-perturbative two-particle self-consistent method (TPSC), which was originally introduced to describe the electronic properties of the single-band Hubbard model, is presented. A detailed derivation of the multi-orbital generalization of TPSC is introduced here and particular features of the method on exemplary interacting models in comparison to dynamical mean-field theory results are discussed.
An investigation of photoelectron angular distributions and circular dichroism of chiral molecules
(2021)
The present work demonstrates the capability of several type of molecular frame photoelectron angular distributions (MFPADs) and their linked chiroptical phenomenon the photoelectron circular dichroism (PECD) to map in great detail the molecular geometry of polyatomic chiral molecules as a function of photoelectron energy. To investigate the influence of the molecular potential on the MFPADs, two chiral molecules were selected, namely 2-(methyl)oxirane (C3H6O, MOx, m = 58,08 uma) and 2-(trifluoromethyl)oxirane (C3H3F3O, TFMOx, m = 112,03 uma). The two molecules differs in one substitutional group and share an oxirane group where the O(1s) electron was directly photoionized with the use of synchrotron radiation in the soft X-ray regime. The direct photoionization of the K-shell electron is well localized in the molecule and it induces the ejection of two or more electrons; the excited system separates into several charged (and eventually neutral) fragments which undergo Coulomb explosion due to their charges. The electrons and the fragments were detected using the COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) and the momentum vectors calculated for each fragment belonging from a single ionization. The former method gives the possibility to post-orient molecules in space, giving access to the molecular frame, thus the MFPAD and its related PECD for multiple light propagation direction.
Stereochemistry (from the Greek στερεο- stereo- meaning solid) refers to chemistry in three dimensions. Since most molecules show a three-dimensional structure (3D), stereochemistry pervades all fields of chemistry and biology, and it is an essential point of view for the understanding of chemical structure, molecular dynamics and molecular reactions. The understanding of the chemistry of life is tightly bounded with major discoveries in stereochemistry, which triggered tremendous technical advancements, making it a flourishing field of research since its revolutionary introduction in late 18th century. In chemistry, chirality is a brunch of stereochemistry which focuses on objects with the peculiar geometrical property of not being superimposable to their mirror-images. The word chirality is derived from the Greek χειρ for “hand”, and the first use of this term in chemistry is usually attributed to Lord Kelvin who called during a lecture at the Oxford University Junior Scientific Club in 1893 “any geometrical figure, or group of points, “chiral”, and say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.”. Although the latter is usually considered as the birth of the word chirality, the concept underlying it was already present in several fields of science (above all mathematics), already proving the already multidisciplinary relevance of chirality across many field of science and beyond. Nature shows great examples of chiral symmetry on all scales. Empirically, it is possible to observe it at macroscopic scale (e.g. distribution of rotations of galaxies), down to the microscopic scale (e.g. structure of some plankton species), but it is at the molecular level where the number gets remarkable: most of the pharmaceutical drugs, food fragrances, pheromones, enzymes, amino acids and DNA molecules, in fact, are chiral. Moreover, the concept of chirality goes far beyond the mere spatial symmetry of objects being crucially entangled with the fundamental properties of physical forces in nature. The symmetry breaking, namely the different physical behaviour of a two chiral systems upon the same stimuli, is considered to be one of the best explanation for the long standing questions of homochirality in biological life, and ultimately to the chemical origin of life on Earth as we know it. Our organism shows high enantio-selectivity towards specific compounds ranging from drugs, to fragrances. Over 800 odour molecules commonly used in food and fragrance industries have been identified as chiral and their enantiomeric forms are perceived to have very different smells, as the well-know example of D- and L- limonene. Similarly, responses to pharmaceuticals drugs can be enantiomer specific, and in fact about 60 % the drugs currently on the market are chiral compounds, and nearly 90 % of them are sold as racemates. The same degree of enantio-selectivity is observed in the communications systems of plants and insects. Plants produce lipophilic liquids with high vapour pressure called plant volatiles (PVs) which are synthesized via different enzymes called tarpene synthases that are usually chiral. Chiral molecules and chiral effects have a strong impact on all the fields of science with exciting developments ranging from stereo-selective synthesis based on heterogeneous enantioselective catalysis, to optoelctronics, to photochemical asymmetric synthesis, and chiral surface science, just to cite a few.
Chiral molecules come in two forms called enantiomers. Their almost identical chemical and physical properties continue to pose technical challenges concerning the resolution of racemic mixtures, the determination of the enantiomeric excess, and the direct determination of the absolute configuration of an enantiomer. ...
Nano-granular metals are materials that fall into the general class of granular electronic systems in which the interplay of electronic correlations, disorder and finite size effects can be studied. The charge transport in nano-granular metals is dominated by thermally-assisted, sequential and correlated tunneling over a temperature-dependent number of metallic grains. Here we study the frequency-dependent conductivity (AC conductivity) of nano-granular Platinum with Pt nano-grains embedded into amorphous carbon (C). We focus on the transport regime on the insulating side of the insulator metal transition reflected by a set of samples covering a range of tunnel-coupling strengths. In this transport regime polarization contributions to the AC conductivity are small and correlation effects in the transport of free charges are expected to be particularly pronounced. We find a universal behavior in the frequency dependence that can be traced back to the temperature-dependent zero-frequency conductivity (DC conductivity) of Pt/C within a simple lumped-circuit analysis. Our results are in contradistinction to previous work on nano-granular Pd/ZrO2ZrO2 in the very weak coupling regime where polarization contributions to the AC conductivity dominated. We describe possible future applications of nano-granular metals in proximity impedance spectroscopy of dielectric materials.