BackgroundMedulloblastoma is the most common malignant brain tumor in children and can be divided in different molecular subgroups. Patients whose tumor is classified as a Group 3 tumor have a dismal prognosis. However only very few tumor models are available for this subgroup.MethodsWe established a robust orthotopic xenograft model with a cell line derived from the malignant pleural effusions of a child suffering from a Group 3 medulloblastoma.ResultsBesides classical characteristics of this tumor subgroup, the cells display cancer stem cell characteristics including neurosphere formation, multilineage differentiation, CD133/CD15 expression, high ALDH-activity and high tumorigenicity in immunocompromised mice with xenografts exactly recapitulating the original tumor architecture.ConclusionsThis model using unmanipulated, human medulloblastoma cells will enable translational research, specifically focused on Group 3 medulloblastoma.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2170-z) contains supplementary material, which is available to authorized users.
Photogenerated excitonic ensembles confined in coupled GaAs quantum wells are probed by a complementary approach of emission spectroscopy and resonant inelastic light scattering.Lateral electrostatic trap geometries are used to create dense systems of spatially indirect excitons and excess holes with similar densities in the order of 10 11 cm -2. Inelastic light scattering spectra reveal a very sharp low-lying collective mode that is identified at an energy of 0.44 meV and a FWHM of only ~50 µeV. This mode is interpreted as a plasmon excitation of the excess hole system coupled to the photogenerated indirect excitons. The emission energy of the indirect excitons shifts under the application of a perpendicular applied electric field with the quantum-confined Stark effect unperturbed from the presence of free charge carriers. Our results illustrate the potential of studying low-lying collective excitations in photogenerated exciton systems to explore the many-body phase diagram, related phase transitions, and interaction physics. [1] . BEC has been observed for the first time in atomic systems [2,3] and later also in more exotic solid-state systems like exciton-polaritons [4][5][6] . Already more than 50 years ago, BEC has been predicted for excitons in semiconductors [7] . Most of such experiments are based on two tunnelcoupled semiconductor quantum wells (CQWs) hosting the excitons. These are electron-hole pairs coupled by the attractive Coulomb interaction. The bosonic quasiparticles exhibit a rich quantum phase diagram including a free exciton gas at elevated temperatures and low densities, which is expected to condense into a BEC with a macroscopic coherence at low temperatures.At high densities, an electron-hole plasma is predicted at higher temperatures that undergoes a Bardeen-Cooper-Schrieffer (BCS) transition to an excitonic insulator at low temperatures [1] .Also, signatures for a (classical) exciton liquid formed by repulsive exciton interactions have been reported [8] . The phase transition between the different phases might be gradual, and the coexistence of different (classical and quantum) phases is possible. Each phase inherently holds a characteristic spectrum of low energy collective excitations of strongly or weakly coupled electron-hole pairs including phenomena such as roton instabilities in their wave vector dispersion [9,10] . In this context, it has been shown for electron bilayers at a total filling factor of one, where exciton condensation occurs [11][12][13][14] , that deep and soft magnetorotons as well as collective spin excitations exist [15,16] . These excitations are linked to quantum phase transitions [15,16] .In general, there are two types of CQW systems hosting excitons. In one case, both CQWs are doped with electrons, and a strong perpendicular magnetic field is applied such that in each quantum well, the lowest Landau level is exactly half filled with electrons and consequently also half filled with holes. If the Coulomb interaction is strong enough in such CQWs, the...
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