Physiological Characterization of Stolon Regression in a Colonial Hydroid

As with many colonial animals, hydractiniid hydroids display a range of morphological variation. Sheet-like forms exhibit feeding polyps close together with short connecting stolons, whereas runner-like forms have more distant polyps and longer connecting stolons. These morphological patterns are thought to derive from rates of stolon growth and polyp formation. Here, stolon regression is identified and characterized as a potential process underlying this variation. Typically, regression can be observed in a few stolons of a normally growing colony. For detailed studies, many stolons of a colony can be induced to regress by pharmacological manipulations of reactive oxygen species (e.g. hydrogen peroxide) or reactive nitrogen species (e.g. nitric oxide). The regression process begins with a cessation of gastrovascular flow to the distal part of the stolon. High levels of endogenous H2O2 and NO then accumulate in the regressing stolon. Remarkably, exogenous treatments with either H2O2 or an NO donor equivalently trigger endogenous formation of both H2O2 and NO. Cell death during regression is suggested by both morphological features, detected by transmission electron microscopy, and DNA fragmentation, detected by TUNEL. Stolon regression may occur when colonies detect environmental signals that favor continued growth in the same location rather than outward growth

Advanced Radiation Panel design for applications in National Security and Food Safety

We describe a new concept for a basic radiation detection panel based on conventional scintillator technology and commercially available solid-state photo-detectors. The panels are simple in construction, robust, very efficient and cost-effective and are easily scalable in size, from tens of cm$^2$ to tens of m$^2$. We describe two possible applications: flagging radioactive food coontamination and detection of illicit radio nucleides, such as those potentially used in a terrorist attack with a dirty bomb.Comment: 10 pages, 11 figure

A model of rf breakdown arcs

This paper presents a rst iteration of a model that attempts to describe all aspects of breakdown in rf cavities and provides some estimates of the parameters and parameter ranges involved, as an aid to producing more precise models and more useful experiments. The model describes how breakdown events can be triggered, how they grow, it identi es the power source for their rapid growth, mechanisms that limit their growth, how they are extinguished and how they can be mitigated. We also discuss applications to superconducting rf and high pressure gas structures. The model relies heavily on previous experiments with 805 and 201 MHz warm copper cavities, and pre-liminary plasma modeling using the code OOPIC Pro. We compare estimates from the model with experimental data where this is possible. Because of the geometrical dependence of all parameters, the wide range of experiments being performed, the wide range of experimental parameters in a given breakdown event and the lack of extensive systematic parameter searches at this stage in our studies, it is diffcult to present precise results. We are constrained to showing what mechanisms are involved, the strength of these mechanisms and how they interact to produce the experimental data. We are primarily interested in the development and dynamics of the arc, magnetic and gas effects and insights on how to avoid arcing in all environments

Differential Transfer Ionization Cross Sections for 50175-keV Proton-Helium Collisions

We have measured coincidences between neutralized projectiles and He recoil ions for 50175-keV proton-helium collisions. From the data we obtained transfer ionization (TI) cross sections differential in the projectile scattering angle. Laboratory scattering angles range from 0 to 2.0 mrad. The experimental method allowed separation of the postcollision charge states of the target atoms. The ratio of the cross sections for TI to the sum of TI and single capture, F, is presented as a function of projectile scattering angle. Comparison is made to previous measurements of this ratio where data is available. The differential cross sections are compared to dynamical classical trajectory Monte Carlo (dCTMC) calculations. Agreement in the shape of the differential cross sections is good between the theory and measurement over the entire energy range

Valence band photoemission from the GaN(0001) surface

A detailed investigation by one-step photoemission calculations of the GaN(0001)-(1x1) surface in comparison with recent experiments is presented in order to clarify its structural properties and electronic structure. The discussion of normal and off-normal spectra reveals through the identified surface states clear fingerprints for the applicability of a surface model proposed by Smith et al. Especially the predicted metallic bonds are confirmed. In the context of direct transitions the calculated spectra allow to determine the valence band width and to argue in favor of one of two theoretical bulk band structures. Furthermore a commonly used experimental method to fix the valence band maximum is critically tested.Comment: 8 pages, 11 eps files, submitted to PR

Partial return yoke for MICE - General concept and performance

N/

Partial return yoke for MICE - Engineering design

N/