University of Mainz

About: University of Mainz is a education organization based out in Mainz, Rheinland-Pfalz, Germany. It is known for research contribution in the topics: Population & Immune system. The organization has 37673 authors who have published 71163 publications receiving 2497880 citations. The organization is also known as: Johannes Gutenberg-Universität Mainz & Universität Mainz.

Direct observation of second-order atom tunnelling

Abstract: Tunnelling of material particles through a classically impenetrable barrier constitutes one of the hallmark effects of quantum physics. When interactions between the particles compete with their mobility through a tunnel junction, intriguing dynamical behaviour can arise because the particles do not tunnel independently. In single-electron or Bloch transistors, for example, the tunnelling of an electron or Cooper pair can be enabled or suppressed by the presence of a second charge carrier due to Coulomb blockade. Here we report direct, time-resolved observations of the correlated tunnelling of two interacting ultracold atoms through a barrier in a double-well potential. For the regime in which the interactions between the atoms are weak and tunnel coupling dominates, individual atoms can tunnel independently, similar to the case of a normal Josephson junction. However, when strong repulsive interactions are present, two atoms located on one side of the barrier cannot separate, but are observed to tunnel together as a pair in a second-order co-tunnelling process. By recording both the atom position and phase coherence over time, we fully characterize the tunnelling process for a single atom as well as the correlated dynamics of a pair of atoms for weak and strong interactions. In addition, we identify a conditional tunnelling regime in which a single atom can only tunnel in the presence of a second particle, acting as a single atom switch. Such second-order tunnelling events, which are the dominating dynamical effect in the strongly interacting regime, have not been previously observed with ultracold atoms. Similar second-order processes form the basis of superexchange interactions between atoms on neighbouring lattice sites of a periodic potential, a central component of proposals for realizing quantum magnetism.

Renormalization group improved black hole spacetimes

Abstract: We study the quantum gravitational effects in spherically symmetric black hole spacetimes. The effective quantum spacetime felt by a pointlike test mass is constructed by ``renormalization group improving'' the Schwarzschild metric. The key ingredient is the running Newton constant which is obtained from the exact evolution equation for the effective average action. The conformal structure of the quantum spacetime depends on its ADM mass $M$ and it is similar to that of the classical Reissner-Nordstr\"om black hole. For $M$ larger than, equal to, and smaller than a certain critical mass ${M}_{\mathrm{cr}}$ the spacetime has two, one, and no horizon(s), respectively. Its Hawking temperature, specific heat capacity, and entropy are computed as a function of $M.$ It is argued that the black hole evaporation stops when $M$ approaches ${M}_{\mathrm{cr}}$ which is of the order of the Planck mass. In this manner a ``cold'' soliton-like remnant with the near-horizon geometry of ${\mathrm{AdS}}_{2}\ifmmode\times\else\texttimes\fi{}{\mathrm{S}}^{2}$ is formed. As a consequence of the quantum effects, the classical singularity at $r=0$ is either removed completely or it is at least much milder than classically; in the first case the quantum spacetime has a smooth de Sitter core which would be in accord with the cosmic censorship hypothesis even if $Ml{M}_{\mathrm{cr}}.$

Treatment resistance of solid tumors: role of hypoxia and anemia.

Abstract: Hypoxia is a characteristic property of locally advanced solid tumors, resulting from an imbalance between the supply and consumption of oxygen. Major pathogenetic mechanisms for the development of hypoxia are (1) structural and functional abnormalities of the tumor microvasculature, (2) increased diffusion distances, and (3) tumor-associated and therapy-induced anemia. The oxygenation status is independent of clinical tumor size, stage, grade, and histopathological type, but is affected by the hemoglobin level. Hypoxia is intensified in anemic patients, especially in tumors with low perfusion rates. Hypoxia and anemia (most probably via worsening of tumor hypoxia) can lead to therapeutic problems, as they make solid tumors resistant to sparsely ionizing radiation and some forms of chemotherapy. In addition to more direct mechanisms involved in the development of therapeutic resistance, there are also indirect machineries that can cause barriers to therapies. These include hypoxia-driven proteome and genome changes and clonal selection. These, in turn, can drive subsequent events that are known to further increase resistance to therapy (in addition to critically affecting long-term prognosis). Treatment resistance in anemic patients can be, at least partially, prevented or overcome by anemia correction, resulting in better locoregional tumor control and overall survival of patients.