An Approximate Method of Images for Finite and Non-Linear Boundaries

The method of images is used in many different modeling scenarios such as electrostatics, fluid mechanics, and groundwater flow modeling to create infinitely long linear boundaries, such as a no-flow boundary across which flux is zero. We are using the groundwater flow arena to experiment with creating an adapted method of images to model a finite length no-flow boundaries. This is applicable to real world scenarios such as groundwater flow near impermeable bedrock. Using MATLAB, as well as our own work by hand, we are attempting to create a process that allows us to model flow near finite straight and curved boundaries. The programming is still in preliminary stages so there are not yet conclusive results, but we anticipate being able to construct both straight and curved finite no-flow boundaries

TRPV4 is the temperature-sensitive ion channel of human sperm.

Ion channels control the ability of human sperm to fertilize the egg by triggering hyperactivated motility, which is regulated by membrane potential, intracellular pH, and cytosolic calcium. Previous studies unraveled three essential ion channels that regulate these parameters: (1) the Ca2+ channel CatSper, (2) the K+ channel KSper, and (3) the H+ channel Hv1. However, the molecular identity of the sperm Na+ conductance that mediates initial membrane depolarization and, thus, triggers downstream signaling events is yet to be defined. Here, we functionally characterize DSper, the Depolarizing Channel of Sperm, as the temperature-activated channel TRPV4. It is functionally expressed at both mRNA and protein levels, while other temperature-sensitive TRPV channels are not functional in human sperm. DSper currents are activated by warm temperatures and mediate cation conductance, that shares a pharmacological profile reminiscent of TRPV4. Together, these results suggest that TRPV4 activation triggers initial membrane depolarization, facilitating both CatSper and Hv1 gating and, consequently, sperm hyperactivation

Deletion mutants in COP9/Signalosome subunits in fission yeast Schizosaccharomyces pombe display distinct phenotypes

The COP9/signalosome complex is highly conserved in evolution and possesses significant structural similarity to the 19S regulatory lid complex of the proteasome. It also shares limited similarity to the translation initiation factor eIF3. The signalosome interacts with multiple cullins in mammalian cells. In the fission yeast Schizosaccharomyces pombe, the Csn1 subunit is required for the removal of covalently attached Nedd8 from Pcu1, one of three S. pombe cullins. It remains unclear whether this activity is required for all the functions ascribed to the signalosome. We previously identified Csn1 and Csn2 as signalosome subunits in S. pombe. csn1 and csn2 null mutants are DNA damage sensitive and exhibit slow DNA replication. Two further putative subunits, Csn4 and Csn5, were identified from the S. pombe genome database. Herein, we characterize null mutations of csn4 and csn5 and demonstrate that both genes are required for removal of Nedd8 from the S. pombe cullin Pcu1 and that their protein products associate with Csn1 and Csn2. However, neither csn4 nor csn5 null mutants share the csn1 and csn2 mutant phenotypes. Our data suggest that the subunits of the signalosome cannot be considered as a distinct functional unit and imply that different subunits of the signalosome mediate distinct functions

The Rotation of Young Low-Mass Stars and Brown Dwarfs

We review the current state of our knowledge concerning the rotation and angular momentum evolution of young stellar objects and brown dwarfs from a primarily observational view point. Periods are typically accurate to 1% and available for about 1700 stars and 30 brown dwarfs in young clusters. Discussion of angular momentum evolution also requires knowledge of stellar radii, which are poorly known for pre-main sequence stars. It is clear that rotation rates at a given age depend strongly on mass; higher mass stars (0.4-1.2 M$_\odot$) have longer periods than lower mass stars and brown dwarfs. On the other hand, specific angular momentum is approximately independent of mass for low mass pre-main sequence stars and young brown dwarfs. A spread of about a factor of 30 is seen at any given mass and age. The evolution of rotation of solar-like stars during the first 100 Myr is discussed. A broad, bimodal distribution exists at the earliest observable phases ($\sim$1 Myr) for stars more massive than 0.4 M$_\odot$. The rapid rotators (50-60% of the sample) evolve to the ZAMS with little or no angular momentum loss. The slow rotators continue to lose substantial amounts of angular momentum for up to 5 Myr, creating the even broader bimodal distribution characteristic of 30-120 Myr old clusters. Accretion disk signatures are more prevalent among slowly rotating PMS stars, indicating a connection between accretion and rotation. Disks appear to influence rotation for, at most, $\sim$5 Myr, and considerably less than that for the majority of stars. If the dense clusters studied so far are an accurate guide, then the typical solar-like star may have only $\sim$1 Myr for this task. It appears that both disk interactions and stellar winds are less efficient at braking these objects.Comment: Review chapter for Protostars and Planets V. 15 page and 8 figure

[Rezension zu:] Torsten Grumbach, Kurmainzer Medicinalpolicey 1650 – 1803. Eine Darstellung entlang der landesherrlichen Verordnungen, Frankfurt a.M. (Klostermann) 2006, XVIII – 326 S. (Studien zu Policey und Policeywissenschaft), ISBN 3-465-04010-4, EUR 49,00.

Rezension der Dissertation an der Goethe-Universität Frankfurt am Main: Torsten Grumbach, Kurmainzer Medicinalpolicey 1650–1803 : Eine Darstellung entlang der landesherrlichen Verordnungen, Frankfurt a.M. (Klostermann) 2006, XVIII–326 S. (Studien zu Policey und Policeywissenschaft), ISBN 3-465-04010-4, EUR 49,00