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Ch Renner

Publications and source records attributed to Ch Renner.

5 recordsLinked to original sources
PubMed2006

Polarons and confinement of electronic motion to two dimensions in a layered manganite.

A remarkable feature of layered transition--metal oxides-most famously, the high-temperature superconductors--is that they can display hugely anisotropic electrical and optical properties (for example, seeming to be insulating perpendicular to the layers and metallic within them), even when prepared as bulk three-dimensional single crystals. This is the phenomenon of 'confinement', a concept at odds with the conventional theory of solids, and recognized as due to magnetic and electron-lattice interactions within the layers that must be overcome at a substantial energy cost if electrons are to be transferred between layers. The associated energy gap, or 'pseudogap', is particularly obvious in experiments where charge is moved perpendicular to the planes, most notably scanning tunnelling microscopy and polarized infrared spectroscopy. Here, using the same experimental tools, we show that there is a second family of transition-metal oxides--the layered manganites La(2-2x)Sr(1+2x)Mn2O7--with even more extreme confinement and pseudogap effects. The data demonstrate quantitatively that because the charge carriers are attached to polarons (lattice- and spin-textures within the planes), it is as difficult to remove them from the planes through vacuum-tunnelling into a conventional metallic tip, as it is for them to move between Mn-rich layers within the material itself.

Journal Article↗
PubMed2006

[Cancer immunotherapy--current status].

Cancer immunotherapy includes passive and active strategies. Passive immunotherapy such as the use of therapeutic monoclonal antibodies, and in a broader sense also of other immunological effector molecules, such as interferon-alpha is clinically established. The efficacy of passive immunotherapy attests to the fact that the immune system can successfully fight cancer. The logical next step is therefore to develop strategies for active immunotherapy, i.e. "vaccines against cancer". This review focuses on the current status of active immunotherapy with respect to clinical application. Although active immunotherapy is still in the experimental stage, the data are highly encouraging and it is expected that vaccination will soon become part of cancer management.

Antibodies, Monoclonal↗
PubMed2002

Universality of small scale turbulence.

The proposed universality of small scale turbulence is investigated for a set of measurements in a cryogenic free jet with a variation of the Reynolds number (Re) from 8500 to 10(6) (max(R(lambda) approximately 1200). The traditional analysis of the statistics of velocity increments by means of structure functions or probability density functions is replaced by a new method which is based on the theory of Markov processes. It gives access to a more complete characterization by means of joint probabilities of finding velocity increments at several scales. Based on this more comprehensive method, our results are very far from a possible universal state, even for R(lambda) above 1000.

Journal Article↗
PubMed2002

Atomic-scale images of charge ordering in a mixed-valence manganite.

Transition-metal perovskite oxides exhibit a wide range of extraordinary but imperfectly understood phenomena. The best known examples are high-temperature superconductivity in copper oxides, and colossal magnetoresistance in manganese oxides ('manganites'). All of these materials undergo a range of order-disorder transitions associated with changes in charge, spin, orbital and lattice degrees of freedom. Measurements of such order are usually made by diffraction techniques, which detect the ionic cores and the spins of the conduction electrons. Unfortunately, because such techniques are only weakly sensitive to valence electrons and yield superpositions of signals from distinct submicrometre-scale phases, they cannot directly image phase coexistence and charge ordering, two key features of the manganites. Here we present scanning tunnelling microscope measurements of the manganite Bi1-xCaxMnO3. We show that charge ordering and phase separation can be resolved in real space with atomic-scale resolution. By taking together images and current-voltage spectroscopy data we find that charge order correlates with both structural order and the local conductive state (either metallic or insulating). These experiments provide an atomic-scale basis for descriptions of manganites as mixtures of electronically and structurally distinct phases.

Journal Article↗