830 research outputs found
Effective Temperatures of a Driven System Near Jamming
Fluctuations in a model of a sheared, zero-temperature foam are studied
numerically. Five different quantities that reduce to the true temperature in
an equilibrium thermal system are calculated. All five have the same shear-rate
dependence, and three have the same value. Near the onset of jamming, the
relaxation time is the same function of these three temperatures in the sheared
system as of the true temperature in an unsheared system. These results imply
that statistical mechanics is useful for the system and provide strong support
for the concept of jamming.Comment: 4 pages, 4 postscript figure
Growth Kinetics in a Phase Field Model with Continuous Symmetry
We discuss the static and kinetic properties of a Ginzburg-Landau spherically
symmetric model recently introduced (Phys. Rev. Lett. {\bf 75}, 2176,
(1995)) in order to generalize the so called Phase field model of Langer. The
Hamiltonian contains two invariant fields and bilinearly
coupled. The order parameter field evolves according to a non conserved
dynamics, whereas the diffusive field follows a conserved dynamics. In the
limit we obtain an exact solution, which displays an interesting
kinetic behavior characterized by three different growth regimes. In the early
regime the system displays normal scaling and the average domain size grows as
, in the intermediate regime one observes a finite wavevector
instability, which is related to the Mullins-Sekerka instability; finally, in
the late stage the structure function has a multiscaling behavior, while the
domain size grows as .Comment: 9 pages RevTeX, 9 figures included, files packed with uufiles to
appear on Phy. Rev.
LAMP-2 is required for incorporating syntaxin-17 into autophagosomes and for their fusion with lysosomes
Autophagy is an evolutionarily conserved process used for removing surplus and damaged proteins and organelles from the cytoplasm. The unwanted material is incorporated into autophagosomes that eventually fuse with lysosomes leading to the degradation of their cargo. The fusion event is mediated by the interaction between the Qa-SNARE syntaxin-17 (STX17) on autophagosomes and the R-SNARE VAMP8 on lysosomes.
Cells deficient in lysosome membrane-associated protein-2 (LAMP-2) have increased numbers of autophagosomes but the underlying mechanism is poorly understood. By transfecting LAMP-2 deficient and LAMP-1/2 doubly deficient mouse embryonic fibroblast (MEF) with a tandem fluorescent-tagged LC3 we observed a failure of fusion between the autophagosomes and the lysosomes that could be rescued by complementation with LAMP-2A. Although we observed no change in expression and localization of VAMP8, its interacting partner STX17 was absent from autophagosomes of LAMP-2 deficient cells. Thus LAMP-2 is essential for STX17 expression by the autophagosomes and this absence is sufficient to explain their failure to fuse with lysosomes. The results have clear implications for situations associated with a reduction of LAMP-2 expression
Existence of immersed spheres minimizing curvature functionals in compact 3-manifolds
We study curvature functionals for immersed 2-spheres in a compact,
three-dimensional Riemannian manifold M. Under the assumption that the
sectional curvature of M is strictly positive, we prove the existence of a
smoothly immersed sphere minimizing the L^{2} integral of the second
fundamental form. Assuming instead that the sectional curvature is less than or
equal to 2, and that there exists a point in M with scalar curvature bigger
than 6, we obtain a smooth 2-sphere minimizing the integral of 1/4|H|^{2} +1,
where H is the mean curvature vector
THSD7A Positivity Predicts Poor Survival and Is Linked to High FAK Expression and FGFR1-Wildtype in Female Patients with Squamous Cell Carcinoma of the Lung
Lung cancer is the leading cause of cancer-related deaths in the western world, with
squamous cell carcinoma being one of the most common histological subtypes. Prognostic and
predictive markers are still largely missing for squamous cell carcinoma of the lung (LSCC). Several
studies indicate that THSD7A might at least play a role in the prognosis of different tumors. FAK
seems to play an important role in lung cancer and is discussed as a potential therapeutic target. In
addition, there is evidence that FAK-dependent signaling pathways might be affected by THSD7A.
For that reason, we investigated the role of THSD7A as a potential tumor marker in LSCC and
whether THSD7A expression has an impact on the expression level of FAK. A total of 101 LSCCs were
analyzed by immunohistochemistry using tissue microarrays. THSD7A positivity was associated
with poor overall survival in female patients and showed a relation to high FAK expression in this
subgroup. To our knowledge, we are the first to report these correlations in lung cancer. The results
might be proof of the assumed activation of FAK-dependent signaling pathways by THSD7A and that
as a membrane-associated protein, THSD7A might serve as a putative therapeutic target in LSCC
Validierung von Web-Usability-Heuristiken für eine ältere Zielgruppe
Dieser Beitrag stellt die Validierung von spezifischen Web-Usability-Heuristiken für die ältere Zielgruppe vor. Das Heuristiken-Set stammt aus einer Vorarbeit und wurde literarturbasiert abgeleitet. Zur Validierung werden ein Nutzertest mit zehn Probanden aus der Zielgruppe sowie eine heuristische Evaluation mit drei Experten durchgeführt. Die Ergebnisse beider Evaluationsmethoden werden quantitativ und qualitativ miteinander verglichen und etablierte Kennwerte zum Methodenvergleich berechnet. Beide Evaluationen liefern ähnliche Werte bezogen auf Validität und Effektivität. Aufgrund der hohen Anzahl an unique problems fällt die Gründlichkeit geringer aus, als bei anderen Methodenvergleichen
Loss of m-AAA protease in mitochondria causes complex I deficiency and increased sensitivity to oxidative stress in hereditary spastic paraplegia
Mmutations in paraplegin, a putative mitochondrial metallopeptidase of the AAA family, cause an autosomal recessive form of hereditary spastic paraplegia (HSP). Here, we analyze the function of paraplegin at the cellular level and characterize the phenotypic defects of HSP patients' cells lacking this protein. We demonstrate that paraplegin coassembles with a homologous protein, AFG3L2, in the mitochondrial inner membrane. These two proteins form a high molecular mass complex, which we show to be aberrant in HSP fibroblasts. The loss of this complex causes a reduced complex I activity in mitochondria and an increased sensitivity to oxidant stress, which can both be rescued by exogenous expression of wild-type paraplegin. Furthermore, complementation studies in yeast demonstrate functional conservation of the human paraplegin–AFG3L2 complex with the yeast m-AAA protease and assign proteolytic activity to this structure. These results shed new light on the molecular pathogenesis of HSP and functionally link AFG3L2 to this neurodegenerative disease
Statistics of Shear-Induced Rearrangements in a Two-Dimensional Model Foam
Under steady shear, a foam relaxes stress through intermittent rearrangements of bubbles accompanied by sudden drops in the stored elastic energy. We use a simple model of foam that incorporates both elasticity and dissipation to study the statistics of bubble rearrangements in terms of energy drops, the number of nearest neighbor changes, and the rate of neighbor-switching (T1) events. We do this for a two-dimensional system as a function of system size, shear rate, dissipation mechanism, and gas area fraction. We find that for dry foams, there is a well-defined quasistatic limit at low shear rates where localized rearrangements occur at a constant rate per unit strain, independent of both system size and dissipation mechanism. These results are in good qualitative agreement with experiments on two-dimensional and three-dimensional foams. In contrast, we find for progessively wetter foams that the event size distribution broadens into a power law that is cut off only by system size. This is consistent with criticality at the melting transition
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