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Electron beam modification of melt-spun polylactide fibers at elevated temperature
No full textElectron beam (EB) modification was carried out on the polylactide (PLA) fibers at the temperature both below and above the glass transition temperature (Tg) under nitrogen atmosphere. The irradiation at elevated temperature was performed by using a novel fiber stretching frame setup to protect fibers from shrinking, in which a permanent constant tension was loaded along fiber bundles to maintain their straightness throughout the irradiation. In contrast to irradiation at room temperature, where PLA predominantly undergoes chain scission, irradiation above Tg can introduce long chain branching (LCB) into the PLA matrix without the need of branching additives. The polymer chain orientation in the amorphous regions of drawn fibers is beneficial for achieving a higher yield of LCB. This improvement is attributed to the shortened intermolecular distance and the disentanglement in the amorphous domains which are caused by melt spinning and post-drawing. This is counteracted by the typically high crystallinity degrees in PLA fibers (measured by differential scanning calorimetry, 31.0 % – 41.2 % for neat fibers), due to the chain scission is mainly induced by EB in the rigid crystalline domains. The chain scission effect in the crystalline regions mitigates the branching effect in the amorphous regions on the material properties, such as tensile strength, even in irradiation above Tg. However, by reducing the PLA fiber crystallinity while applying temperatures above Tg, the amount of EB-induced LCB molecules was significantly increased. Moreover, the branched unit per PLA chain increases when a dose of 50 kGy is applied, as determined by analyzing the branching ratio g’ using multi-detector size exclusion chromatography. In addition, the amount of branched unit also increases with the increasing irradiation dose. The tensile properties of fibers with varying drawing ratios were analyzed before and after irradiation. The resulting tensile properties are primarily determined by the draw ratio and appear to be barely affected by crystal orientation (examined using synchrotron X-ray scattering). However, the crystal orientation increases with higher irradiation doses (above Tg) and is likely driven by the interplay between chain scission and cold crystallization
Revealing the role of Fe and Ti in the quest for different magnetic ordering in double perovskite SrFeTiO
No full textB/B′-sites ordering and disordering play a decisive role in determining the magnetic characteristics of the ABB'O-types of double perovskites (DPs). Generally, B/Bʹ-site ordered structures promote the B–O–B′ bond (interaction). In contrast, a disordered state of the B/B′-site induces additional B–O–B, B–O–B′, and B′-O-B′ bonds (interactions) and facilitates multiple magnetic interactions within the ceramic. We interpolate this phenomenon to understand the mechanism of the magnetic behavior of double perovskite SrFeTiO (SFTO). This report reveals the role of multivalent states of Fe and Ti in ferromagnetic (FM), ferrimagnetic (FiM), and antiferromagnetic (AFM) ordering in SFTO. Structural and geometrical analysis revealed a combination of orthorhombic and cubic crystal symmetry of SFTO. The electronic structural analysis confirmed the 3+ and 4+ charge states of both Fe/Ti-cations. Temperature and field-dependent magnetic analysis revealed complex magnetic behavior attributed to the exchange interaction between partially vacant Fe:te and partially filled Ti:te states. In contrast, this system showed non-collinearity in AFM behavior at low temperatures due to the available weak ferromagnetic interaction between Fe-O-Ti, Fe-O-Ti, etc
Transient quasiperiodic oscillations of Fermi-LAT blazars under the curved jet model
No full textContext. This study explores transient quasiperiodic oscillations (QPOs) in the γ-ray emission of two blazars, PMN J0531−4827 and PKS 1502+106, using over a decade of Fermi Large Area Telescope observations.Aims. The analysis focuses on identifying QPO signatures in their long-term light curves and interpreting the variability through a curved jet model, which predicts multiplicative oscillations with exponentially decaying amplitudes.Methods. We developed an analysis methodology to characterize the QPOs and the specific properties of the amplitudes of such QPOs.Results. The findings offer insights into the dynamic processes driving relativistic jet evolution and their potential connections to underlying mechanisms, such as binary systems or other phenomena influencing the observed characteristics of these blazars.Key words: methods: statistical / techniques: photometric / astronomical databases: miscellaneous / galaxies: active / BL Lacertae objects: genera
Search for charged-lepton flavour violation in top quark interactions with an up-type quark, a muon, and a τ lepton in proton-proton collisions at TeV
No full textA search for charged-lepton flavour violation (CLFV) in top quark (t) production and decay is presented. The search uses proton-proton collision data corresponding to 138 fb collected with the CMS experiment at TeV. The signal consists of the production of a single top quark via a CLFV interaction or top quark pair production followed by a CLFV decay. The analysis selects events containing a hadronically decaying τ lepton and a muon of opposite electric charge, as well as at least three jets, one of which is identified as originating from the fragmentation of a bottom quark. Machine learning classification techniques are used to distinguish signal from standard model background events. The results of this search are consistent with the standard model expectations. The upper limits at 95% confidence level on the branching fraction for CLFV top quark decays to a muon, a τ lepton, and an up or a charm quark are set at < (0.04, 0.08, and 0.12) × 10, and < (0.81, 1.71, and 2.05) × 10 for scalar, vector, and tensor-like operators, respectively.[graphic not available: see fulltext
Microstructure formation during gas flow-assisted additive manufacturing of a metallic glass powder on ground and in microgravity
No full textWe studied bulk metallic glasses produced from gas flow-assisted laser-based powder bed fusion process, which is capable of additive manufacturing metallic parts in microgravity. A Zr-based bulk metallic glass composition ZrCuAlNb has been processed on ground and in microgravity in a compact sounding rocket payload MARS-M. Microstructure characterization was performed using electron microscopy and X-ray diffraction computed tomography, which cope with small amounts of sample materials, especially for those fabricated under microgravity conditions. Very similar microstructures and crystalline fractions are observed in sample manufactured on ground and in microgravity, which shows that process parameters of conventional laser powder bed fusion for manufacturing metallic glasses can be transferred to the processes in microgravity. Two different origins of crystallization have been identified in the ZrCuAlNb sample. The preferred occurrence of CuZr at the interlayer boundaries is likely a result of recrystallization from the undercooled melt and hence associated with laser scanning strategy. In contrast, the more uniformly distributed AlZr phase is considered to be triggered by the formation of CuZrO. Thus, for the fabrication of fully amorphous builds both on ground and in space, our findings point to higher scanning speeds and lower oxygen contents, while the latter can also be used to tune the crystalline fractions in the sample
Evolution and Broadening of the National Analysis Facility at DESY
No full textThe National analysis Facility (NAF) at DESY has constantly been evolving since its inception in 2007. Starting as a distributed computing platform between the DESY sites in Hamburg and Zeuthen, it has been serving the German HEP users as well as international collaborators since as a experimentagnostic compute and data infrastructure. The technical implementations NAF have changed in a number of evolutionary steps over time to adapt to the changing requirements by its users as well as to the always changing technological landscape. While technological details have changed, central points to the NAF have been constant like data rather than plain compute being pivotal or like user support as a cornerstone. Followingly, we will describe the recent developments and updates in the NAF ecosystem. On the user side, further experiments have chosen the NAF as their computing platform and have build up their analyses pipelines ontop the NAF. On the operational side, effort has been made to further harden the security and increase monitoring and integration between compute and storage systems as complementary components of the NAF
Ultrabroad Near Infrared Emitting Perovskites
No full textPhosphor converted light emitting diodes (pc-LEDs) have revolutionized solid-state white lighting by replacing energy-inefficient filament-based incandescent lamps. However, such a pc-LED emitting ultrabroad near-infrared (NIR) radiations still remains a challenge, primarily because of the lack of ultrabroad NIR emitting phosphors. To address this issue, we have prepared 2.5% W-doped and 2.8% Mo-doped CsNaAgBiCl perovskites emitting ultrabroad NIR radiation with unprecedented spectral widths of 434 and 468 nm, respectively. Upon band-edge excitation, the soft lattice of the host exhibits broad self-trapped exciton (STE) emission covering NIR-I (700 nm), which then nonradiatively excites the dopants. The p–donor ligand Cl- reduces the energy of dopant d–d transitions emitting NIR-II with a peak at ~950 nm. Vibronic coupling broadens the dopant emission. The large spin-orbit coupling and local structural distortion might possibly enhance the dopant emission intensity, leading to an overall NIR photoluminescence quantum yield ~40%. The composite of our ultrabroad NIR phosphors with biodegradable polymer polylactic acid could be processed into free-standing films and 3D printed structures. Large (170 x170 mm), robust, and thermally stable 3D printed pc-LED panels emit ultrabroad NIR radiation, demonstrating NIR imaging applications
Measurement of the time-integrated CP asymmetry in decays using Belle and Belle II data
No full textWe measure the time-integrated CP asymmetry in decays reconstructed in events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 fb and 428 fb, respectively. The decays are required to originate from the decay, which determines the charm flavor at production time. A control sample of decays is used to correct for production and detection asymmetries. The result, , is consistent with previous determinations and with CP symmetry