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Background: Liquid biopsy diagnostic methods are an emerging complementary tool to imaging and pathology techniques across various cancer types. However, there is still no established method for the detection of molecular alterations and disease monitoring in MB, the most common malignant CNS tumor in the pediatric population. In the presented study, we investigated droplet digital polymerase chain reaction (ddPCR) as a highly sensitive method for the detection of MYC amplification in bodily fluids of group 3 MB patients. Methods: We identified a cohort of five MYC-amplified MBs by methylation array and FISH. Predesigned and wet-lab validated probes for ddPCR were used to establish the detection method and were validated in two MYC-amplified MB cell lines as well as tumor tissue of the MYC-amplified cohort. Finally, a total of 49 longitudinal CSF samples were analyzed at multiple timepoints during the course of the disease. Results: Detection of MYC amplification by ddPCR in CSF showed a sensitivity and specificity of 90% and 100%, respectively. We observed a steep increase in amplification rate (AR) at disease progression in 3/5 cases. ddPCR was proven to be more sensitive than cytology for the detection of residual disease. In contrast to CSF, MYC amplification was not detectable by ddPCR in blood samples. Conclusions: ddPCR proves to be a sensitive and specific method for the detection of MYC amplification in the CSF of MB patients. These results warrant implementation of liquid biopsy in future prospective clinical trials to validate the potential for improved diagnosis, disease staging and monitoring.

We estimate fiscal multipliers for Austria in a framework of model uncertainty emanating from the choice of a particular econometric model. We present a comprehensive framework that allows to assess the effects of different multiplier definitions and choices related to the data, the model employed, and further technical choices associated with the specification of the model exert on fiscal multiplier estimates. The mean present-value government spending multiplier over all models entertained, based on around 3,000 estimates, is 0.68. Estimates of the peak spending multiplier for Austria tend to be larger than present-value spending multipliers, with a mean value of 0.85. The magnitude of the present-value tax multiplier is relatively high, with an average value across specifications of −1.12 and the mean peak tax multiplier is −0.54 for all specifications used.

Heterobilayers consisting of MoSe$_2$ and WSe$_2$ monolayers can host optically bright interlayer excitons with intriguing properties such as ultralong lifetimes and pronounced circular polarization of their photoluminescence due to valley polarization, which can be induced by circularly polarized excitation or applied magnetic fields. Here, we report on the observation of an intrinsic valley-magnetophonon resonance for localized interlayer excitons promoted by invervalley hole scattering. It leads to a resonant increase of the photoluminescence polarization degree at the same field of 24.2 Tesla for H-type and R-type stacking configurations despite their vastly different excitonic energy splittings. As a microscopic mechanism of the hole intervalley scattering we identify the scattering with chiral TA phonons of MoSe$_2$ between excitonic states mixed by the long-range electron hole exchange interaction., Comment: 7+5 pages, 2+0 figures

In van der Waals heterostructures (HS) consisting of stacked MoSe$_2$ and WSe$_2$ monolayers, optically bright interlayer excitons (ILE) can be observed when the constituent layers are crystallographically aligned. The symmetry of the monolayers allows for two different types of alignment, in which the momentum-direct interlayer transitions are either valley-conserving (R-type alignment) or changing the valley index (H-type anti-alignment). Here, we study the valley polarization dynamics of ILE in magnetic fields up to 30~Tesla by time-resolved photoluminescence (PL). For all ILE types, we find a finite initial PL circular degree of polarization ($DoP$) after unpolarized excitation in applied magnetic fields. For ILE in H-type HS, we observe a systematic increase of the PL $DoP$ with time in applied magnetic fields, which saturates at values close to unity for the largest fields. By contrast, for ILE in R-type HS, the PL $DoP$ shows a decrease and a zero crossing before saturating with opposite polarization. This unintuitive behavior can be explained by a model considering the different ILE states in H- and R-type HS and their selection rules coupling PL helicity and valley polarization.

We report about the investigation of twisted MoSe2 homo- and MoSe2–WSe2 heterobilayers by means of low-frequency Raman spectroscopy (LFRS) and low-temperature micro photoluminescence (µPL). In room-temperature LFRS experiments on both, twisted MoSe2 homobilayers and twisted MoSe2–WSe2 heterobilayers, we observe moiré phonons, i.e. folded acoustic phonon modes due to the moiré superlattice. In the heterobilayers, we can identify moiré phonons of both materials, MoSe2 and WSe2. While the twist angles for the homobilayers are relatively precisely known from the applied tear-and-stack preparation method, the twist angles of the heterobilayers have to be determined via second-harmonic-generation microscopy on monolayer regions of the samples, which has significant uncertainties. We show that by the moiré phonons of the heterobilayers, the relative twist angles can be determined on a local scale with much higher precision. We apply our technique for the investigation of a large area H-type (twist angle θ = 60∘ + δ) MoSe2–WSe2 heterobilayer. These investigations show that spatial regions, which can be identified to be atomically reconstructed (i.e. δ = 0∘) by the observation of an interlayer shear mode in LFRS experiments, exhibit a strong, momentum-allowed interlayer-exciton signal in low-temperature µPL. On the contrary, regions, where moiré phonons are observed, i.e. which can be identified to be rigidly twisted by a misalignment angle in the range of 5 ° ≲ | δ | ≲ 6 ° , exhibit no significant interlayer-exciton signals.

We investigate WSe$_2$-MoSe$_2$ heterobilayers with different twist angles $\theta \pm \delta$ between the two layers, by low-frequency Raman scattering. In sufficiently aligned samples with $\theta=0^\circ$, or $\theta=60^\circ$, and $\delta \lesssim 3^\circ$, we observe an interlayer shear mode (ISM), which is a clear sign of a commensurate bilayer structure, i.e., the layers must undergo an atomic reconstruction to form R-type or H-type stacking orders. We find slightly different ISM energies of about 18~cm$^{-1}$ and 17~cm$^{-1}$ for H-type and R-type reconstructions, respectively, independent of the exact value of $\theta\pm \delta$. Our findings are corroborated by the fact that the ISM is not observed in samples with twist angles, which deviate by $\delta > 3^\circ$ from $0^\circ$ or $60^\circ$. This is expected, since in such incommensurate structures, with the possibility of Moir$\acute{\text{e}}$-lattice formation, there is no restoring force for an ISM. Furthermore, we observe the ISM even in sufficiently aligned heterobilayers, which are encapsulated in hexagonal Boron nitride. This is particularly relevant for the characterization of high-quality heterostructure devices., Comment: 5 pages, 4 figures

Moiré superlattices can induce correlated-electronic phases in twisted van der Waals materials: strongly correlated quantum phenomena emerge, such as superconductivity and the Mott-insulating state. However, moiré superlattices produced through artificial stacking can be quite inhomogeneous, which hampers the development of a clear correlation between the moiré period and the emerging electrical and optical properties. Here, it is demonstrated in twisted-bilayer transition-metal dichalcogenides that low-frequency Raman scattering can be utilized not only to detect atomic reconstruction, but also to map out the inhomogeneity of the moiré lattice over large areas. The method is established based on the finding that both the interlayer-breathing mode and moiré phonons are highly susceptible to the moiré period and provide characteristic fingerprints. Hyperspectral Raman imaging visualizes microscopic domains of a 5° twisted-bilayer sample with an effective twist-angle resolution of about 0.1°. This ambient methodology can be conveniently implemented to characterize and preselect high-quality areas of samples for subsequent device fabrication, and for transport and optical experiments.

Raman spectroscopy is a precious tool for the characterization of van der Waals materials, e.g. for the determination of the layer number in thin exfoliated flakes. For sensitive materials, however, this method can be dramatically invasive. In particular, the light intensity required to obtain a significant Raman signal is sufficient to immediately photo-oxidize few-layer thick metallic van der Waals materials. In this work we investigated the impact of the environment on Raman characterization of thin NbSe$_2$ crystals. We show that in ambient conditions the flake is locally oxidized even for very low illumination intensity. On the other hand, we observe no degradation if the Raman measurements are performed either in vacuum or on fully hBN-encapsulated samples. Interestingly, we find that covering samples deposited on the usual SiO$_2$ surface only from the top is not sufficient to prevent diffusion of oxygen underneath the layers., 7 pages, 4 figures. Johannes Holler and Lorenz Bauriedl contributed equally to this work

Heterostructures of atomically thin van der Waals bonded monolayers have opened a unique platform to engineer Coulomb correlations, shaping excitonic, Mott insulating, or superconducting phases. In transition metal dichalcogenide heterostructures, electrons and holes residing in different monolayers can bind into spatially indirect excitons with a strong potential for optoelectronics, valleytronics, Bose condensation, superfluidity, and moir\'e-induced nanodot lattices. Yet these ideas require a microscopic understanding of the formation, dissociation, and thermalization dynamics of correlations including ultrafast phase transitions. Here we introduce a direct ultrafast access to Coulomb correlations between monolayers; phase-locked mid-infrared pulses allow us to measure the binding energy of interlayer excitons in WSe2/WS2 hetero-bilayers by revealing a novel 1s-2p resonance, explained by a fully quantum mechanical model. Furthermore, we trace, with subcycle time resolution, the transformation of an exciton gas photogenerated in the WSe2 layer directly into interlayer excitons. Depending on the stacking angle, intra- and interlayer species coexist on picosecond scales and the 1s-2p resonance becomes renormalized. Our work provides a direct measurement of the binding energy of interlayer excitons and opens the possibility to trace and control correlations in novel artificial materials., Comment: This is a post-peer-review, pre-copyedit version of an article published in Nature Materials. The final authenticated version is available online at https://doi.org/10.1038/s41563-019-0337-0

We use a rich numerical OLG model of Auerbach-Kotlikoff type to simulate the long-run effects of refugee migration starting in 2015 for a country with an aging society and a generous welfare system, namely Austria. The respective refugee cohorts are on average younger, less educated, and less productive than both natives and the average migrant. The net fiscal contribution results from two opposing effects: a positive demographic effect which is counteracted by worse labor market outcomes. We robustly find that public debt is higher throughout the simulation horizon 2015-2060 than in the baseline. We further analyze the group-specific welfare consequences resulting from differentiated wage effects.

We experimentally study the radii of excitons in hBN-encapsulated WS2 monolayers by means of magneto-optical reflectance spectroscopy at cryogenic temperatures in magnetic fields up to 29 T. We observe field-induced energy shifts of the exciton ground and excited states due to valley Zeeman and diamagnetic effects. We find the g factor of the first excited state of $-4.2(+/-0.1) to be essentially equal to that of the ground state of -4.35(+/-0.1). From diamagnetic shifts we determine the root mean square radii of the excitons. The radius of the first excited state is found to be 5-8 nm and that of the ground state around 2 nm. Our results further confirm the Wannier-Mott nature of the exciton quasiparticles in monolayer semiconductors and the assignment of the optical resonances in absorption-type measurements. They also provide additional support for the applicability of the effective mass hydrogenlike models in these systems., accepted for publication in Phys. Rev. B

Most sovereign debt management agencies operate on a narrow definition of risk which does not reflect the potential of sovereign debt portfolios to insure the budget against macroeconomic shocks. This paper analyzes the different forms of risk implied by the composition of the sovereign debt portfolio and discusses methods for their evaluation. By determining the risk properties of existing debt management instruments we underline the potential of certain debt management instruments to insure the budget against stylized demand and supply shocks producing strong incentives for debt management agencies to operate on a broader definition of risk. The identified risk properties further highlight that the establishment of Economic and Monetary Union reduced market, rollover and liquidity risk in the aggregate euro area debt portfolio, whereas the loss of the risk free status for euro area sovereign assets and the steepening of the yield curve, both triggered by the sovereign debt crisis, led to a shift towards more short-term debt resulting in an increase in rollover risk and market risk.

Before the crisis hit, many euro area countries had failed to create sufficient fiscal room for times of economic difficulty, which made a new reform of the Stability and Growth Pact inevitable. Above all, this most recent reform introduces an expenditure rule in the preventive arm of the pact, operationalizes the debt criteron in the dissuasive arm and imposes stricter sanctions in case of noncompliance. The reform strengthens the preventive arm by making it easier to measure compliance and launch procedures as well as by introducing symbolic sanctions. While the introduction of the debt rule certainly tightened the conditions of the dissuasive arm for highly indebted countries, it remains to be seen by how much, given the large number of exceptions. Notwithstanding the new voting procedure (which is designed to make it more likely that sanctions are in fact applied), we doubt that economically significant penalties will be imposed in the foreseeable future.

In this paper we examine whether di¤erent pension systems a¤ect the set of initial human capital conditions capturing an economy in a low steady state equilibrium income. To analyze this problem, we employ a three period over- lapping generations model where fertility and investments into the children?s education are chosen endogenously. We show that education investments are higher and start at lower income levels for a pay-as-you-go pension system econ- omy compared to an informal, fertility related one. The income threshold needed to escape the ?poverty trap? is therefore lower if a pay-as-you-go pension sys- tem is employed. Moreover, unless the economy is caught in the low income steady state, a pay-as-you-go pension system supports higher equilibrium in- come. We further highlight that pension systems in?uence the timing of de- mographic transition through their di¤erent valuation of fertility, contributing to the explanation for observed di¤erences between developed and developing countries.

This paper studies the implications of di¤erent public pension systems on fertility and economic growth. Employing a three period overlapping gener- ations endogenous growth model we compare the di¤erent impacts of pay-as- you-go-, fully funded- and informal pension systems. The novelty of our work lies in the formulation of altruism that is assumed to be one sided (descending) for economies represented by a public pension system and two sided (descend- ing and ascending) for economies with informal pension systems. Through the incorporation of a mixed procreation motive we can study the case of fully crowded out intrafamilial transfers inside a public pension system model while still capturing fertility endogenously. We show that the introduction of public pension systems to a developing economy reduce fertility and stimulate economic growth. Through a comparison of the di¤erent public pension systems we highlight that a fully funded pension system results in higher economic growth compared to a pay-as-you-go one despite higher fertility because the growth enhancing e¤ect of the higher capital stock is dominant. This suggests that observed fertility and growth di¤erences between the US and Europe can partly be explained by the di¤erent types of pension systems.