The incredible ULKs

Macroautophagy (commonly abbreviated as autophagy) is an evolutionary conserved lysosome-directed vesicular trafficking pathway in eukaryotic cells that mediates the lysosomal degradation of intracellular components. The cytoplasmic cargo is initially enclosed by a specific double membrane vesicle, termed the autophagosome. By this means, autophagy either helps to remove damaged organelles, long-lived proteins and protein aggregates, or serves as a recycling mechanism for molecular building blocks. Autophagy was once invented by unicellular organisms to compensate the fluctuating external supply of nutrients. In higher eukaryotes, it is strongly enhanced under various stress conditions, such as nutrient and growth factor deprivation or DNA damage. The serine/threonine kinase Atg1 was the first identified autophagy-related gene (ATG) product in yeast. The corresponding nematode homolog UNC-51, however, has additional neuronal functions. Vertebrate genomes finally encode five closely related kinases, of which UNC-51-like kinase 1 (Ulk1) and Ulk2 are both involved in the regulation of autophagy and further neuron-specific vesicular trafficking processes. This review will mainly focus on the vertebrate Ulk1/2-Atg13-FIP200 protein complex, its function in autophagy initiation, its evolutionary descent from the yeast Atg1-Atg13-Atg17 complex, as well as the additional non-autophagic functions of its components. Since the rapid nutrient- and stress-dependent cellular responses are mainly mediated by serine/threonine phosphorylation, it will summarize our current knowledge about the relevant upstream signaling pathways and the altering phosphorylation status within this complex during autophagy induction

Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains

By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)$_2$P$_2$O$_7$, the effects of two energy scales of the weakly dimerized antiferromagnetic $S$ = 1/2 Heisenberg chain are explored. The low energy scale, given by the spin gap $\Delta$, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing T-DMRG calculations, shows that this feature originates from changes in the magnetic entropy with respect to $\Delta$, $\partial S^{m}/ \partial \Delta$. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in $\Delta$.Comment: 4 pages, 4 figures now identical with finally published versio

Floffy: Designing an Outdoor Robot for Children

In our research we utilized the domain of entertainment robotics to educate children on the principles of environmental awareness by playful means outdoors. Our research revolved around the iterative design of Floffy: the environmental robot, which was essentially a playful toy robot that would respond positively to interaction that was beneficial for the environment and the child’s own well being and negatively to interaction or behaviour that was detrimental to the surroundings. We conducted an explorative, informal evaluation of Floffy with two small groups of children and they rated their experience with it positively. Our results show that there is potential in utilizing entertainment robots to educate children on serious and critical issues such as saving our environment and being sustainable

The Ultrasonic Measurement of Stress on Ferrous Plate

It has recently been shown that one can measure stress, in the presence of texture, or other metallurgical variables, by comparing the velocities of horizontally polarized (SH) ultrasonic waves propagating in orthogonal directions [1,2].</p

Solitonic-exchange mechanism of surface~diffusion

We study surface diffusion in the framework of a generalized Frenkel-Kontorova model with a nonconvex transverse degree of freedom. The model describes a lattice of atoms with a given concentration interacting by Morse-type forces, the lattice being subjected to a two-dimensional substrate potential which is periodic in one direction and nonconvex (Morse) in the transverse direction. The results are used to describe the complicated exchange-mediated diffusion mechanism recently observed in MD simulations [J.E. Black and Zeng-Ju Tian, Phys. Rev. Lett. {\bf 71}, 2445-2448(1993)].Comment: 22 Revtex pages, 9 figures to appear in Phys. Rev.

Sliding charge density wave in manganites

The so-called stripe phase of the manganites is an important example of the complex behaviour of metal oxides, and has long been interpreted as the localisation of charge at atomic sites. Here, we demonstrate via resistance measurements on La_{0.50}Ca_{0.50}MnO_3 that this state is in fact a prototypical charge density wave (CDW) which undergoes collective transport. Dramatic resistance hysteresis effects and broadband noise properties are observed, both of which are typical of sliding CDW systems. Moreover, the high levels of disorder typical of manganites result in behaviour similar to that of well-known disordered CDW materials. Our discovery that the manganite superstructure is a CDW shows that unusual transport and structural properties do not require exotic physics, but can emerge when a well-understood phase (the CDW) coexists with disorder.Comment: 13 pages; 4 figure

Conductance of Mesoscopic Systems with Magnetic Impurities

We investigate the combined effects of magnetic impurities and applied magnetic field on the interference contribution to the conductance of disordered metals. We show that in a metal with weak spin-orbit interaction, the polarization of impurity spins reduces the rate of electron phase relaxation, thus enhancing the weak localization correction to conductivity. Magnetic field also suppresses thermal fluctuations of magnetic impurities, leading to a recovery of the conductance fluctuations. This recovery occurs regardless the strength of the spin-orbit interaction. We calculate the magnitudes of the weak localization correction and of the mesoscopic conductance fluctuations at an arbitrary level of the spin polarization induced by a magnetic field. Our analytical results for the ``$h/e$'' Aharonov-Bohm conductance oscillations in metal rings can be used to extract spin and gyromagnetic factor of magnetic impurities from existing experimental data.Comment: 18 pages, 8 figure