Mitochondrial fission regulates germ cell differentiation by suppressing ROS-mediated activation of Epidermal Growth Factor Signaling in the Drosophila larval testis.

Mitochondria are essential organelles that have recently emerged as hubs for several metabolic and signaling pathways in the cell. Mitochondrial morphology is regulated by constant fusion and fission events to maintain a functional mitochondrial network and to remodel the mitochondrial network in response to external stimuli. Although the role of mitochondria in later stages of spermatogenesis has been investigated in depth, the role of mitochondrial dynamics in regulating early germ cell behavior is relatively less-well understood. We previously demonstrated that mitochondrial fusion is required for germline stem cell (GSC) maintenance in the Drosophila testis. Here, we show that mitochondrial fission is also important for regulating the maintenance of early germ cells in larval testes. Inhibition of Drp1 in early germ cells resulted in the loss of GSCs and spermatogonia due to the accumulation of reactive oxygen species (ROS) and activation of the EGFR pathway in adjacent somatic cyst cells. EGFR activation contributed to premature germ cell differentiation. Our data provide insights into how mitochondrial dynamics can impact germ cell maintenance and differentiation via distinct mechanisms throughout development

A seed specific dose kernel method for low-energy brachytherapy dosimetry.

We describe a method for independently verifying the dose distributions from pre- and post-implant brachytherapy source distributions. Monte Carlo calculations have been performed to characterize the three-dimensional dose distribution in water phantom from a low-energy brachytherapy source. The calculations are performed in a voxelized, Cartesian coordinate geometry and normalized based upon a separate Monte Carlo calculation for the seed specific air-kerma strength to produce an absolute dose grid with units of cGy hr(-1) x U(-1). The seed-specific, three-dimensional dose grid is stored as a text file for processing using a separate visual basic program. This program requires the coordinate positions of each seed in the pre- or post-plan and sums the kernel file for a three-dimensional composite dose distribution. A kernel matrix size of 81x81x81 with a voxel size of 1.0x1.0x1.0 mm3 was chosen as a compromise between calculation time, kernel size, and truncation of the stored dose distribution as a function of radial distance from the midpoint of the seed. Good agreement is achieved for a representative pre- and post-plan comparison versus a commercial implementation of the TG-43 brachytherapy dosimetry protocol

Strongly interacting bosons in a disordered optical lattice

Disorder, prevalent in nature, is intimately involved in such spectacular effects as the fractional quantum Hall effect and vortex pinning in type-II superconductors. Understanding the role of disorder is therefore of fundamental interest to materials research and condensed matter physics. Universal behavior, such as Anderson localization, in disordered non-interacting systems is well understood. But, the effects of disorder combined with strong interactions remains an outstanding challenge to theory. Here, we experimentally probe a paradigm for disordered, strongly-correlated bosonic systems-the disordered Bose-Hubbard (DBH) model-using a Bose-Einstein condensate (BEC) of ultra-cold atoms trapped in a completely characterized disordered optical lattice. We determine that disorder suppresses condensate fraction for superfluid (SF) or coexisting SF and Mott insulator (MI) phases by independently varying the disorder strength and the ratio of tunneling to interaction energy. In the future, these results can constrain theories of the DBH model and be extended to study disorder for strongly-correlated fermionic particles.Comment: 15 pages, 4 figures updated to correct errors in referencing previous wor

A dynamic pressure generator for checking complete pressure sensing systems installed on an airplane

A portable dynamic pressure generator, how it operates, and a test setup on an airplane are described. The generator is capable of providing a sinusoidal pressure having a peak-to-peak amplitude of 3.5 N/sq cm (5 psi) at frequencies ranging from 100 hertz to 200 hertz. A typical power spectral density plot of data from actual dynamic pressure fluctuation tests within the air inlet of the YF-12 airplane is presented

Limits to Sympathetic Evaporative Cooling of a Two-Component Fermi Gas

We find a limit cycle in a quasi-equilibrium model of evaporative cooling of a two-component fermion gas. The existence of such a limit cycle represents an obstruction to reaching the quantum ground state evaporatively. We show that evaporatively the \beta\mu ~ 1. We speculate that one may be able to cool an atomic fermi gas further by photoassociating dimers near the bottom of the fermi sea.Comment: Submitted to Phys. Rev

Spin Excitations in a Fermi Gas of Atoms

We have experimentally investigated a spin excitation in a quantum degenerate Fermi gas of atoms. In the hydrodynamic regime the damping time of the collective excitation is used to probe the quantum behavior of the gas. At temperatures below the Fermi temperature we measure up to a factor of 2 reduction in the excitation damping time. In addition we observe a strong excitation energy dependence for this quantum statistical effect.Comment: 4 pages, 3 figure