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Impact of Charge-Transfer Excitons on Unidirectional Exciton Transport in Lateral TMD Heterostructures
Get PDFLateral heterostructures built of monolayers of transition-metal dichalcogenides host a thin one-dimensional interface exhibiting a large energy offset. Recently, the formation of spatially separated charge-transfer (CT) excitons at the interface has been demonstrated, but their impact on technologically important exciton propagation across the interface has remained in the dark. In this theoretical work, we microscopically investigate the spatiotemporal exciton dynamics in the exemplary hBN-encapsulated WSe₂–MoSe₂ lateral heterostructure. We reveal a highly interesting interplay of energy-offset-driven unidirectional exciton drift across the interface and efficient capture into energetically lower CT excitons at the interface. This interplay triggers a counterintuitive thermal control of exciton transport with less efficient propagation at lower temperatures, opposite to conventional semiconductors. We predict clear signatures of this intriguing exciton propagation in both far- and near-field photoluminescence experiments. Our results present an advance in the microscopic understanding of technologically relevant unidirectional exciton transport in lateral heterostructures
Peter Grünberg (1939 – 2018): von Darmstadt aus zum Physik-Nobelpreis
Get PDFVor 50 Jahren bestand der Physiker Peter Grünberg seine Promotion und legte in Darmstadt den Grundstein für seine beeindruckende wissenschaftliche Karriere, die ihm im Jahr 2007 den Physik-Nobelpreis einbrachte
Soil (microbial) disturbance affect the zinc isotope biogeochemistry but has little effect on plant zinc uptake
Get PDFZinc (Zn) is an important micronutrient but can be toxic at elevated concentrations. We conducted an experiment to test the effect of plant growth and soil microbial disturbance on Zn in soil and plants. Pots were prepared with and without maize and in an undisturbed soil, a soil that was disturbed by X-ray sterilization and a soil that was sterilized but reconditioned with the original microbiome. The Zn concentration and isotope fractionation between the soil and the soil pore water increased with time, which is probably due to physical disturbance and fertilization. The presence of maize increased the Zn concentration and isotope fractionation in pore water. This was likely related to the uptake of light isotopes by plants and root exudates that solubilized heavy Zn from the soil. The sterilization disturbance increased the concentration of Zn in the pore water, because of abiotic and biotic changes. Despite a threefold increase in Zn concentration and changes in the Zn isotope composition in the pore water, the Zn content and isotope fractionation in the plant did not change. These results have implications for Zn mobility and uptake in crop plants and are relevant in terms of Zn nutrition
Grafting and controlled release of antimicrobial peptides from mesoporous silica
Get PDFThe grafting of antimicrobial peptides onto mesoporous silica particles and their controlled release using a green light-responsive linker, which enables tunable release-concentration-time profiles, is presented. The mesoporous silica surface is functionalized with antimicrobial peptides employing sequential functionalization steps, including the grafting of 3-[(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS) as anchor, boron-dipyrromethene (BODIPY) as photosensitive linker, and C14R peptides as antimicrobial agents. Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), attenuated total reflectance infrared (ATR-IR) spectroscopy, and thermogravimetric analysis (TGA) validate the successful fabrication and functionalization of mesoporous silica. The ester-1,2,3-triazole-BODIPY demonstrates high sensitivity to green light and enables C14R antimicrobial peptide release with adjusted concentration-time profiles. Under the applied conditions up to 64 μg mL⁻¹ were released within 40 minutes. The antimicrobial activity of the released C14R on Escherichia coli. BL21(DE3) is demonstrated. Overall, the use of the photosensitive linker not only provides a promising avenue for controlling the release of biomolecules and therapeutics but also opens up opportunities for the development of materials for targeted release in wound dressings, for example
The Injectivity Radius of Souls of Alexandrov Spaces
Get PDFA sharp lower bound for the injectivity radius in noncompact nonnegatively curved Riemannian manifolds involving their soul goes back to Šarafutdinov. We generalize this bound to the setting of Alexandrov spaces. Our main theorem reads as follows. If the injectivity radius of an Alexandrov space of nonnegative curvature does not coincide with the one of its souls, then it is at least πK⁻¹/², where K is an upper curvature bound. We introduce the soul of Alexandrov spaces in some detail and compare two notions of injectivity radii
Automated Cephalometric Landmark Localization using a Coupled Shape Model
No full textCephalometric analysis is an important method in orthodontics for the diagnosis and treatment of patients. It is performed manually in clinical practice, therefore automation of this time consuming task would be of great assistance. In order to provide dentists with such tools, a robust and accurate identification of the necessary landmarks is required. However, poor image quality of lateral cephalograms like low contrast or noise make this task difficult. In this paper, an approach for automatic landmark localization is presented and used to find 19 landmarks in lateral cephalometric images. An initial predicting of the individual landmark locations is done by using a 2-D coupled shape model to utilize the spatial relation between landmarks and other anatomical structures. These predictions are refined with a Hough Forest to determine the final landmark location. The approach achieves competitive performance with a successful detection rate of 70.24% on 250 images for the clinically relevant 2mm accuracy range
Functional paper for paper-based microsampling and analysis techniques
Get PDFRecent advances in the sensitivity of chemical analytical instruments, as well as their miniaturization, have led to increasing interest in the use of micro samples, both for research purposes, as well as for sample collection at home or in medical facilities. Paper is by far the most commonly used substrates for micro collection of biofluids such as whole blood samples. MS is the preferred analytical method for analyzing DBS samples. With the development of novel paper-based ionization methods for MS, such as Paper-Spray MS, the evolution of these micro sampling devices into sophisticated sample preparation chips is becoming increasingly the subject of ongoing research.
The aim of the project presented in this thesis is the development and investigation of functional paper for the simplification of sample preparation steps targeting the analysis of micro samples
Redetermination of the crystal structure of tetrasodium tetrahedrotetrastannide, Na₄Sn₄ and tetrapotassium tetrahedro-tetrastannide, K₄Sn₄
No full textNa₄Sn₄, tetragonal, I4₁/acd (No. 142), a = 10.475(1) Å, c = 17.412(2) Å, V = 1910.5 ų, Ζ = 8, Rgt(F) = 0.058, wR(F) = 0.058, T = 295 K.
K₄Sn₄, tetragonal, I4₁/acd (No. 142), a = 11.409(1) Å, c = 18.649(2) Å, V = 2427.5 ų, Ζ = 8, Rgt(F) = 0.036, wR(F) = 0.036, T = 295 K
Arbitrary photonic wave plate operations on chip: Realizing Hadamard, Pauli-X and rotation gates for polarisation qubits
Get PDFChip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light
Low Gain Avalanche Diodes for Beam Monitoring and Reaction Time Determination at High Rates in HADES
Get PDFThe Low Gain Avalanche Diode (LGAD) technology enables high precision timing in the order of σₜ ≈ 30 ps for Minimum Ionizing Particles (MIPs), while simultaneously featuring high spatial resolution and excellent radiation hardness (operational up to fluences of Φₙₑ > 10¹⁵ nₑ/cm²). This technology sparked interest in the High Energy Physics (HEP) community for example for 4D-trackers (i.e. track reconstruction in coordinate space and time), beam monitoring and even medical applications. Due to those excellent properties of LGADs, the High Acceptance Di-Electron Spectrometer (HADES) collaboration employed LGADs as sensors for its in-beam Start detector, responsible for reaction time (T0) determination as well as beam spatial and time structure monitoring for the high rate p+p production beam time with a beam kinetic energy of 4.5 GeV in February 2022. Therefore, a dedicated HADES LGAD production was launched at Fondazione Bruno Kessler. This work will focus on the application of LGADs for the HADES Start detector and the fulfillment of the above mentioned tasks. After a presentation of the HADES LGAD production, the results of the full system test for the LGAD-based Start detector will be presented, indicating the viability of using LGADs for the purposes of the HADES Start detector. The performance as a beam time-structure monitoring tool at the p+p experiment will be shown, followed by a detailed discussion on the applied calibration and T0 reconstruction algorithms. The performance of the LGAD-based Start detector will be presented w.r.t. the reached T0 reconstruction efficiency and its precision as well as the sensor efficiency and radiation hardness over the entire p+p production beam time. After a full calibration of the sensor, T0s could be reconstructed with precisions of σ(T0) < 90 ps, when both sensors were used for the reconstruction, while single sensor T0 precisions up to σ(T0) ≈ 120 ps were achieved. The performance of the LGAD sensors deteriorated after the accumulation of radiation damage. Its effect will be presented for a selected single sensor. In order to demonstrate the excellent T0 reconstruction precision and accuracy, an analysis of the inclusive charged pion production was conducted employing only a particle identification via time of flight and momentum measurements. The resulting inclusive production cross section of σ(π⁺) ≈ (35.3 ± 4.6) mb and σ(π⁻) ≈ (9.7 ± 1.5) mb will be put into context with measurements of other experiments using p+p collisions