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Parton Distribution Functions of the Charged Pion Within The xFitter Framework
No full textUsing xFitter, we extract parton distribution functions of charged pions from currently available Drell-Yan and photon production data. While the valence distribution is well-constrained, we find that the considered data are not sensitive enough to unambiguously determine sea and gluon distributions. In the used approximation, we find the high-x behavior of the valence distribution to be linear in (1-x) at high x. Fractions of momentum carried by the valence, sea and gluon components are discussed
Acceleration of High Charge Ion Beams with Achromatic Divergence by Petawatt Laser Pulses
No full textWe present a study of laser-ion acceleration, where an increased laser spot size leads to sheath field geometries that accelerate ion beams of narrow and achromatic divergence at unprecedented charge densities, resulting from the high aspect ratio of the laser spot size to the acceleration distance. Matching the laser pulse length to the transverse laser spot size mitigated laser sweeping across the target front side and optimized the acceleration, with maximum energies deviating significantly from a linear intensity scaling
Promoting the Fe(VI) active species generation by structural and electronic modulation of efficient iron oxide based water oxidation catalyst without Ni or Co
No full textFe is considered as a promising alternative for OER catalysts owing to its high natural abundance and low cost. Due to the low conductivity and sluggish catalytic kinetics, the catalytic efficiency of Fe-rich catalysts is far from less abundant Ni, Co-rich alternatives and has been hardly improved without the involvement of Ni or Co. The lower activity of Fe-rich catalysts renders the real active center of state-of-the-art NiFe, CoFe catalyst in long-term scientific debate, despite of detection of Fe-based active intermediates in these catalysts during catalytic process. In the present work, we fabricated a series of sub-5 nm Fe1-yCryOx nanocatalysts via a simple solvothermal method, achieving systematically promoted high-valent Fe(VI) species generation by structural and electronic modulation, displaying highly active OER performance without involvement of Ni or Co. Detailed investigation revealed that the high OER activity is related to the ultrasmall nanoparticle size that promotes abundant edge- and corner-site exposure at catalyst surface, which involves in OER as highly reactive site; and the incorporated Cr ions that remarkably accelerate the charge transfer kinetics, providing an effective conduit as well as suitable host for high-valent active intermediate. This work reveals the structural prerequisites for efficient Fe-rich OER catalyst fabrication, inspiring deeper understanding of the structure-activity relationship as well as OER mechanism of Fe-based catalysts
Complex Geometric Structure of a Simple Solid-Liquid Interface: GaN(0001)-Ga
No full textThe equilibrium atomic interface structure between Ga and GaN(0001) is shown to contain substrate surface vacancies followed by substrate-induced layering and preferential lateral ordering in the liquid. The uncovered presence of point defects, in the form of vacancies at both sides of the solid-liquid interface, is an important structural feature which governs the local physical properties. Our x-ray diffraction study reveals that the layering is very stable and persists up to a temperature of 1123 K and a nitrogen pressure of 32 bar. The Ga layer spacing agrees remarkably well with the Friedel oscillation period for this system
Real-time observation of disintegration processes within argon clusters ionized by a hard-x-ray pulse of moderate fluence
No full textWe present a time-resolved study of disintegration within atomic clusters ionized by a hard-x-ray pulse of moderate fluence. It was performed with electron and ion spectroscopy, and complemented by theoretical simulations. The expanding clusters were probed with a near-infrared (NIR) laser pulse over a range of pump-probe delays from −4 to 10 ps. In addition to an increasing number of singly charged atomic ions, originating from the ionization of Rydberg atoms formed through electron-ion recombination, we observe a decrease of oligomer yields. The latter is due to the interaction of oligomers with the NIR probe pulse, leading to their dissociation. At time delays between −1 and 2 ps, efficient absorption of the NIR laser energy occurs, even though the NIR intensity is too low to trigger tuneling ionization of Ar atoms. Our observations are similar to earlier observations of the fragmentation behavior of clusters excited by soft-x-ray pulses. This indicates that the relaxation dynamics of x-ray-excited nano-objects are universal over a wide range of excitation photon energies
An effective approach to electroweak baryogenesis
No full textThe asymmetry between matter and antimatter is one of the big outstanding questions of particle physics and cosmology. In this talk, I will argue that electroweak baryogenesis is an interesting mechanism to generate the baryon asymmetry. The new physics needed for electroweak baryogenesis come into play at a relatively low scale and can thus be tested in experiment.I will address three issues related to Electroweak baryogenesis. First I will explain whether electroweak baryogenesis can be studied in the model-independent framework of the Standard Model Effective Field Theory. Second, I will compare the contributions to the value of the asymmetry resulting from CP-violating interactions of different Standard Model particles. Third, I will discuss the validity of the so-called vev-insertion approximation, that is used to compute the value of the baryon asymmetry
Studying chiral molecules with broadband microwave spectroscopy
No full textNatural essential oils are complex mixtures containing several compounds of structural similarity.They are well known for their wide range of applications in different areas, frommedicine to cosmetics. One of the conventional methods for their quantitative analysis is gaschromatography (GC). Despite the numerous advantages of GC as an analytical tool, someaspects such as structure determination cannot be addressed with it. Another techniquewhich is applicable to the volatile essential oil components is rotational spectroscopy. It is apowerful method for the structure determination not only of the respective compounds, butalso of their different isomers and conformers. Rotational spectroscopy thus complements theinformation obtained with GC, which is necessary for a comprehensive study on the molecularsystems of interest.In the first part of this thesis, some of the main constituents of peppermint and thyme oils wereanalyzed with rotational spectroscopy. Structure determination of several oil componentsincluding menthol, thymol, linalool, and pulegone was performed. The internal dynamics oftrans-thymol-B, linalool, pulegone, and menthyl acetate, resulting from the internal rotationof their methyl groups were studied. The conformational landscape of menthyl acetate wascharacterized both experimentally and computationally. All these key points help to betterunderstand the functionality of the chemical substances discussed here, and their mode ofinteraction in our body. Additionally, a semi-quantitative analysis of thyme oil was performed.The results were compared to the GC study for benchmarking purposes, showing a goodagreement.Many of the essential oil constituents are chiral. Chirality is of utmost importance in the biologicalcontext. There is a high demand for reliable methods for a detailed characterizationof chiral molecules. Recent developments in rotational spectroscopy have enabled the explorationof molecules in a chirality-sensitive way by applying the microwave three-wave mixing(M3WM) technique. The M3WM makes use of the advantages of rotational spectroscopysuch as conformer selectivity and mixture compatibility. It was successfully applied in thescope of this thesis to differentiate between the enantiomers of some essential oil constituents.The M3WM was recently extended to allow coherent population transfer (CPT) of the enantiomersto rotational states of choice. This approach is discussed in the second part of thepresent work. It may pave the way for enantioseparation in future experiments. Finally,M3WM and CPT were combined in the experiment to manipulate the chiral conformers ofa molecule, which has no stereogenic center (cyclohexylmethanol). Such a procedure significantlywidens the range of molecular systems available for chiral analysis with rotationalspectroscopy
Microscopic pathways for stress relaxation in repulsive colloidal glasses
No full textResidual stresses are well-known companions of all glassy materials. They affect and, in many cases, even strongly modify important material properties like the mechanical response and the optical transparency. The mechanisms through which stresses affect such properties are, in many cases, still under study, and their full understanding can pave the way to a full exploitation of stress as a primary control parameter. It is, for example, known that stresses promote particle mobility at small length scales, e.g., in colloidal glasses, gels, and metallic glasses, but this connection still remains essentially qualitative. Exploiting a preparation protocol that leads to colloidal glasses with an exceptionally directional built-in stress field, we characterize the stress-induced dynamics and show that it can be visualized as a collection of “flickering,” mobile regions with linear sizes of the order of ≈20 particle diameters (≈2 μm here) that move cooperatively, displaying an overall stationary but locally ballistic dynamics
Discovery of Ternary Silicon Titanium Nitride with Spinel-Type Structure
No full textHere we report on the discovery of a ternary silicon titanium nitride with the general composition (Si1−x,Tix)3N4 with x = 0 < x < 1 and spinel-type crystal structure. The novel nitride is formed from an amorphous silicon titanium nitride (SiTiN) precursor under high-pressure/high-temperature conditions in a large volume high-pressure device. Under the conditions of 15–20 GPa and 1800–2000 °C, spinel-type γ-Si3N4 and rock salt-type c-TiN are formed. In addition, crystals of the discovered nano-sized ternary phase (Si1−x,Tix)3N4 embedded in γ-Si3N4 are identified. The ternary compound is formed due to kinetically-controlled synthesis conditions and is analyzed to exhibit the spinel-type structure with ca. 8 atom% of Ti. The Ti atoms occur in both Ti3+ and Ti4+ oxidation states and are located on the Si sites. The ternary nano-crystals have to be described as (Si,Ti)3N4 with N-vacancies resulting in the general composition (Si4+1−x Ti4+x-δTi3+δ)3N4-δ