Signatures of electronic polarons in La1−x_{1-x}Sr1+x_{1+x}MnO4_4 observed by electron energy-loss spectroscopy

The dielectric properties of La$_{1-x}$Sr$_{1+x}$MnO$_4$ single crystals with x = 0, 0.125, 0.25, and 0.5 were studied by means of electron energy-loss spectroscopy as a function of temperature and momentum transfer. A clear signature of the doped holes is observed around 1.65 eV energy loss, where spectral weight emerges with increasing x. For all $x \neq 0$, this doping-induced excitation can propagate within the ab-plane, as revealed by a clear upward dispersion of the corresponding loss peak with increasing momentum transfer. The hole-induced excitation also shifts to higher energies with the onset of magnetic correlations for x = 0.5, implying a strong coupling of charge and spin dynamics. We conclude that (i) the loss feature at 1.65 eV is a signature of electronic polarons, which are created around doped holes, and that (ii) this low-energy excitation involves the charge transfer between manganese and oxygen. The finite dispersion of these excitations further indicates significant polaron-polaron interactions.Comment: 7 pages, 4 figure

Conditional expression of retrovirally delivered anti-MYCN shRNA as an in vitro model system to study neuronal differentiation in MYCN-amplified neuroblastoma

Background: Neuroblastoma is a childhood cancer derived from immature cells of the sympathetic nervous system. The disease is clinically heterogeneous, ranging from neuronal differentiated benign ganglioneuromas to aggressive metastatic tumours with poor prognosis. Amplification of the MYCN oncogene is a well established poor prognostic factor found in up to 40% of high risk neuroblastomas. Using neuroblastoma cell lines to study neuronal differentiation in vitro is now well established. Several protocols, including exposure to various agents and growth factors, will differentiate neuroblastoma cell lines into neuron-like cells. These cells are characterized by a neuronal morphology with long extensively branched neurites and expression of several neurospecific markers. Results: In this study we use retrovirally delivered inducible short-hairpin RNA (shRNA) modules to knock down MYCN expression in MYCN-amplified (MNA) neuroblastoma cell lines. By addition of the inducer doxycycline, we show that the Kelly and SK-N-BE(2) neuroblastoma cell lines efficiently differentiate into neuron-like cells with an extensive network of neurites. These cells are further characterized by increased expression of the neuronal differentiation markers NFL and GAP43. In addition, we show that induced expression of retrovirally delivered anti- MYCN shRNA inhibits cell proliferation by increasing the fraction of MNA neuroblastoma cells in the G1 phase of the cell cycle and that the clonogenic growth potential of these cells was also dramatically reduced. Conclusion: We have developed an efficient MYCN-knockdown in vitro model system to study neuronal differentiation in MNA neuroblastomas

Synthesis and physical properties of LaO1−xFxFeAs\rm\bf LaO_{1-x}F_xFeAs

We have prepared the newly discovered Fe-based superconducting material $\rm LaO_{1-x}F_xFeAs$ ($0\leq x\leq 0.2$) in polycrystalline form and have investigated the samples by means of structural, thermodynamic and transport measurements. Our investigations reveal a non superconducting phase at $0\leq x\lesssim0.04$ which for $x=0$ is characterized by a structural transition towards an orthorhombic distortion at $T_s\approx 160$ K and antiferromagnetic spin order at $T_N\approx138$ K. Both transitions lead to strong anomalies in various transport properties as well as in magnetization and in specific heat. Remarkably, the transition temperatures are only weakly doping dependent up $x\lesssim 0.04$. However, the transitions are abruptly suppressed at $x\geq0.05$ in favour of a superconducting phase with a critical temperature $T_c\gtrsim 20$ K. Upon further increasing the F-doping $T_c$ increases up to a maximum of $T_c=26.8$ K at $x=0.1$ which is followed by a decrease down to $T_c\approx10$ K at $x\geq0.15$

Structure, mechanical characteristics and high-temperature stability of sintered under high and by hot pressing ZrB2- and HfB2–based composites

Program and book of abstracts / 2nd International Conference on Innovative Materials in Extreme Conditions i. e. (IMEC2024), 20-22 March 2024 Belgrade, Serbia

A Formação na Maturidade como Apropriação da Própria História de Vida

No presente artigo, a disposição e a competência para a apropriação da própria história de vida são consideradas como modos de formação1 na maturidade. Estas se relacionam com fatores históricos e sócio-políticos e estão inscritas em contextos multigeracionais de formação e processos de desenvolvimento ao longo da vida. Nesta perspectiva, conceitos como geração, geracionalidade, geratividade e transmissão transgeracional ganham destaque e serão aprofundados no texto. A linha argumentativa que sustenta este ponto de vista baseia-se em estudos de países de língua alemã sobre crianças da Segunda Guerra Mundial que envelheceram. Apesar de se tratar de uma situação específica, nos parece possível a extensão das reflexões também para o contexto brasileiro

Scenario set-up and forcing data for impact model evaluation and impact attribution within the third round of the Inter-Sectoral Model Intercomparison Project (ISIMIP3a)

This paper describes the rationale and the protocol of the first component of the third simulation round of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a, www.isimip.org) and the associated set of climate-related and direct human forcing data (CRF and DHF, respectively). The observation-based climate-related forcings for the first time include high-resolution observational climate forcings derived by orographic downscaling, monthly to hourly coastal water levels, and wind fields associated with historical tropical cyclones. The DHFs include land use patterns, population densities, information about water and agricultural management, and fishing intensities. The ISIMIP3a impact model simulations driven by these observation-based climate-related and direct human forcings are designed to test to what degree the impact models can explain observed changes in natural and human systems. In a second set of ISIMIP3a experiments the participating impact models are forced by the same DHFs but a counterfactual set of atmospheric forcings and coastal water levels where observed trends have been removed. These experiments are designed to allow for the attribution of observed changes in natural, human and managed systems to climate change, rising CH4 and CO2 concentrations, and sea level rise according to the definition of the Working Group II contribution to the IPCC AR6

MYCN and microRNAs in neuroblastoma

Neuroblastoma is the most common extra-cranial solid tumor in childhood. Tumors with amplification of the MYCN proto-oncogene are characterized by aggressive biology and poor survival of the patients. To improve future treatment options, it is of fundamental interest to understand MYCN’s role in tumorigenesis and determine factors regulating MYCN expression. In this thesis focuses on the interactions between MYCN and miRNAs, a group of endogenous small regulatory RNA molecules that can act as both tumor suppressors and oncogenes. In paper I, we knocked-down MYCN in a neuroblastoma cell lines with MYCN amplification by short hairpin RNA (shRNA) (method described in the appendix paper) and performed a miRNA expression profiling study to elucidate miRNAs that are correlated to MYCN expression. This approach is different from other studies used to investigate the role of N-myc on miRNAs, as MYCN knockdown in addition induces significant neuronal differentiation of the cells. We observed both up- and down-regulation of miRNAs. MiRNAs with positive correlation to MYCN included members of the oncogenic mir-17-92 cluster. One of the most prominently up-regulated miRNAs upon MYCN knockdown was mir-21. However, we were not able to establish a functional role for this miRNA during differentiation. Mir-92a and mir-92b were both positively correlated to MYCN expression. In paper III, we demonstrated that both miRNAs target the tumor suppressor DKK3 in neuroblastoma and repress secretion of the DKK3 protein. Finally, we demonstrated in paper II that the interaction between MYCN and miRNAs is mutual, as the MYCN mRNA itself is targeted by several miRNAs. Some of these miRNAs showed anti-proliferative properties. Re-establishment of these miRNAs in MYCN-amplified neuroblastoma may prove to be of therapeutic value