לוח שנה משולב

Nanoscale or colloidal particles are exceptionally important in many realms of science and technology. They can dramatically change the properties of materials, imparting solid-like behavior to a wide variety of complex fluids, from yoghurt to cast ceramics. This behavior arises when particles aggregate to form mesoscopic clusters and networks.
Systems with weak attractions, where gel formation requires high colloid densities, are of particular importance. Despite its ubiquity and significance, gelation is far from understood; even the location of the gelation phase boundary is not agreed upon. I will show that gelation of spherical particles with isotropic short-ranged attractions is initiated by spinodal decomposition; this thermodynamic instability triggers the formation of density fluctuations, leading to spanning clusters that dynamically arrest to create a gel. This simple picture of gelation does not depend on microscopic system-specific details, and should thus apply broadly to any short-ranged attractive particle system. Our results suggest that gelation, often previously considered a purely kinetic phenomenon, is in fact a direct consequence of equilibrium liquid-gas phase separation."

Experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein (MOG) in brown Norway rats mimicks neurodegenerative aspects of multiple sclerosis (MS). In this model, optic neuritis leads to acute axonal lesions and consecutive apoptotic cell death of RGCs, whose axons form the optic nerve. The intracellular mechanisms of RGC apoptosis resemble those described after surgical transection of the optic nerve. These mechanisms involve shifts in the expression of Bcl-2 family members, mitogen-activated protein kinases , and the phosphatidylinositol-3-kinase/Akt pathway.
Current research on neurodegenerative aspects in EAE or MS is focused on developing treatment strategies that inhibit degeneration of axons as well as protection of the neuronal cell body from apoptotic cell death. The concept of achieving neuroprotective effects by successful treatment of inflammation and autoimmunity was supported by studies showing a close association of axonal damage and inflammation. However, trials evaluating anti-inflammatory therapies in MS patients have shown that elimination of the inflammatory component of the disease does not necessarily stop progression of brain and spinal cord atrophy. Methylprednisolone, the standard treatment of autoimmune optic neuritis, accelerates visual recovery, but it does not influence the final visual outcome. In MOG-induced optic neuritis, even detrimental effects of anti-inflammatory treatment with methylprednisolone on the survival of RGCs were observed. On the other hand, blocking apoptosis signals in neurons without simultaneously treating inflammation-induced axon degeneration does not lead to functionally relevant results: Although application of Epo as well as CNTF increases survival rates of RGCs during MOG-induced optic neuritis, visual acuity in these animals remains poor due to severe and ongoing degeneration of optic nerve axon fibers. These observations led to a hypothesis that can easily be transferred to the situation in MS: Due to the much larger proportion of white matter in the human brain, preventing apoptosis of neuronal cell bodies alone might not find its expression in clinical scores and neurological function. Therefore, neuroprotective approaches in combination with the established disease-modifying therapies might be more promising. Simultaneous application of methylprednisolone and Epo or Minocycline in MOG-induced optic neuritis resulted in a functional, electrophysiological improvement of optic nerves and RGCs as well as in increased neuronal and axonal survival The lecture will outline the transfer of these experimental approaches into a clinical trial and discuss other new neuroprotective and regenerative strategies.

We report the first detection of asymmetry in a supernova (SN) photosphere based on SN light echo (LE) spectra of Cas A from the different perspectives of dust concentrations on its LE ellipsoid. New LEs are reported based on difference images, and optical spectra of these LEs are analyzed and compared. After properly accounting for the effects of finite dust filament extent and inclination, we find one field where the He I and H alpha features are blueshifted by an additional ~4000 km/s relative to other spectra and to the spectra of the Type IIb SN 1993J. That same direction does not show any shift relative to other Cas A LE spectra in the Ca II near-infrared triplet feature. We compare the perspectives of the Cas A LE dust concentrations with recent three-dimensional modeling of the SN remnant and note that the location having the blueshifted He I and H alpha features is roughly in the direction of an Fe-rich outflow and in the opposite direction of the motion of the compact object at the center of the SN remnant. We conclude that Cas A was an intrinsically asymmetric SN, and that future LE spectroscopy of this object, and other historical SNe, will provide additional insight into the connection of explosion mechanism to SN to SN remnant, as well as give crucial observational evidence of how stars explode.