Invertebrate Zooid Polymorphism: Hydractinia Polyclina And Pagurus Longicarpus Interactions Mediated Through Spiralzooids

Evaluating the net interaction between symbionts can be challenging when one participant is a colonial animal with polymorphic zooids, because each zooid type has unique functions. The colonial hydroid Hydractinia polyclina has three distinct zooid types, each of which contributes particular components to the interaction with host hermit crabs. Of these three zooid types, the function of spiralzooids is not well understood. Previously, spiralzooids have been proposed to contribute a strong negative interaction component by directly reducing their host hermit crab’s reproductive output. However, this hypothesis is not supported by past or current data. I propose that spiralzooids instead function to prevent hosts from foraging on the colonies in their own shells. I conducted a series of experiments and surveys that explored spiralzooid distribution, structure, and function. Spiralzooid distribution at the species level was quantified through an examination of the scientific literature, which documented that spiralzooids only form in colonies living on hermit crab occupied gastropod shells, regardless of crab species or geographic region. Within the local species H. polyclina, only colonies that were living on gastropod shells occupied by hermit crabs contained spiralzooids, regardless of collection site or colony gender. Next, I assessed spiralzooid structure. Spiralzooids had a mean length of 1.17 ± 0.62mm and occurred at a mean density of 1.91 ± 1.03 per mm2 along the aperture edge. Spiralzooids contain microbasic eurytele nematocysts, organized into nematocyst batteries, and battery abundance at zooid tips can be categorized into four levels. These nematocyst batteries adhered to hermit crab bodies and appendages, and adherence did not vary significantly among body parts. Spiralzooid function was studied through several experiments. Increased hermit crab contact and the presence of a host stimulated spiralzooid formation throughout a shell, in parts of the colony that are normally devoid of spiralzooids. Although hermit crabs are active scavengers, those that are symbiotic with H. polyclina have never been documented consuming their own epibiont colonies. Yet, hermit crabs are commonly observed feeding on polyps in colonies on other shells. If spiralzooids prevent crabs from foraging on the colonies on their own shells, then crabs should respond to contact with spiralzooids. The act of spiralzooid lashing, as tested by probing hydroid covered shells (with a bare shell control), significantly altered hermit crab behavior. Six crab behaviors were in turn analyzed to determine their effects on initiating spiralzooid lashing. Foraging on H. polyclina stimulating spiralzooid lashing significantly more frequently than other hermit crab behaviors. Lastly, hermit crab prey caloric values compiled from the literature were compared to the empirically determined caloric value for H. polyclina (4,011.55 ± 65.47 cal/g dry wt); hydroids ranked in the top 10% of potential hermit crab prey. In light of these findings I suggest the data support my guiding hypothesis that spiralzooids prevent hosts from foraging on their own colonies. Under this proposed function, I suggest that gonozooids actually contribute a weak positive interaction with the host crab by potentially providing caloric value, and spiralzooids in turn contribute a weak negative interaction. Therefore, the resulting net interaction between H. polyclina and Pagurus longicarpus should be considered commensal, or weakly mutualistic

Housing co-operatives in Glasgow: The community ownership programme

Public sector housing is important. Its particular importance in Glasgow derives from the fact that over 57% of households in the City are Local Authority tenants. This thesis examines a new project being set up by Glasgow District Council in three high stress areas of its housing stock. The project, called the Community Ownership Programme, is the first of its kind in Scotland. It involves the formation of par-value housing co-operatives by the tenants, who will purchase their houses collectively from the Council and subsequently manage them along co-operative lines. The study begins with a brief chapter establishing the general context of the public sector in Britain, touching briefly on housing policies at a national level. Against this background. Chapter 2 examines the problems of difficult-to-let estates, their characterising factors and some fundamental causes. It then goes on to discuss some significant reports in this field and the remedial action they suggest. Finally some conclusions are drawn about future policies. Chapter 3 brings this discussion down to the local context. The twofold nature of Glasgow's housing problem is described, setting the scene for the next chapter. Against this framework. Chapter 4 examines the influences actually brought to bear in shaping the Community Ownership Programme, focussing particularly on the way in which the District Council have drawn on the resources and experience available to develop a new model to improve public sector housing. In Chapter 5, this model is discussed in detail. Par-value cooperatives are described, as are the three main factors involved - the tenants, the dwellings and finance. Finally the legal and financial procedures of establishing a co-operative are examined. Three detailed case studies are then presented in Chapter 6. In each of these, a preliminary sketch is given of the background, followed by a narrative account of the development of the co-operative and the proposed improvements. In Chapter 7 an attempt is made to tackle the difficult question of evaluation. Chapter 8 brings together and reviews some of the findings of the case studies in relation to the future development of the co-operatives. The analysis focusses particularly on two variables which are critical to the expansion of the project, namely community action capacity and continued political feasibility. This is followed by some concluding remarks

Symbolic Reachability Analysis of B through ProB and LTSmin

We present a symbolic reachability analysis approach for B that can provide a significant speedup over traditional explicit state model checking. The symbolic analysis is implemented by linking ProB to LTSmin, a high-performance language independent model checker. The link is achieved via LTSmin's PINS interface, allowing ProB to benefit from LTSmin's analysis algorithms, while only writing a few hundred lines of glue-code, along with a bridge between ProB and C using ZeroMQ. ProB supports model checking of several formal specification languages such as B, Event-B, Z and TLA. Our experiments are based on a wide variety of B-Method and Event-B models to demonstrate the efficiency of the new link. Among the tested categories are state space generation and deadlock detection; but action detection and invariant checking are also feasible in principle. In many cases we observe speedups of several orders of magnitude. We also compare the results with other approaches for improving model checking, such as partial order reduction or symmetry reduction. We thus provide a new scalable, symbolic analysis algorithm for the B-Method and Event-B, along with a platform to integrate other model checking improvements via LTSmin in the future

Risking Communications Security: Potential Hazards of the Protect America Act

A new US law allows warrantless wiretapping whenever one end of the communication is believed to be outside national borders. This creates serious security risks: danger of exploitation of the system by unauthorized users, danger of criminal misuse by trusted insiders, and danger of misuse by government agents

Observations of Particulates within the North Atlantic Flight Corridor: POLINAT 2, September-October 1997

This paper discusses particulate concentration and size distribution data gathered using the University of Missouri-Rolla Mobile Aerosol Sampling System (UMR-MASS), and used to investigate the southern extent of the eastern end of the North Atlantic Flight Corridor (NAFC) during project Pollution From Aircraft Emissions in the North Atlantic Flight Corridor/Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (POLINAT 2/SONEX) from September 19 to October 23, 1997. The analysis presented in this paper focuses on the corridor effect, or enhancement of pollutants by jet aircraft combustion events. To investigate the phenomena, both vertical and horizontal profiles of the corridor, and regions immediately adjacent to the corridor, were performed. The profiles showed a time-dependent enhancement of particulates within the corridor, and a nonvolatile (with respect to thermal volatilization at 300° C) aerosol enhancement at corridor altitudes by a factor of 3.6. The southern extent of the North Atlantic Flight Corridor was established from a four flight average of the particulate data and yielded a boundary near 42.5° N during the study period. A size distribution analysis of the nonvolatile particulates revealed an enhancement in the \u3c40 nm particulates for size distributions recorded within the flight corridor

Theory of Spin-Resolved Auger-Electron Spectroscopy from Ferromagnetic 3d-Transition Metals

CVV Auger electron spectra are calculated for a multi-band Hubbard model including correlations among the valence electrons as well as correlations between core and valence electrons. The interest is focused on the ferromagnetic 3d-transition metals. The Auger line shape is calculated from a three-particle Green function. A realistic one-particle input is taken from tight-binding band-structure calculations. Within a diagrammatic approach we can distinguish between the \textit{direct} correlations among those electrons participating in the Auger process and the \textit{indirect} correlations in the rest system. The indirect correlations are treated within second-order perturbation theory for the self-energy. The direct correlations are treated using the valence-valence ladder approximation and the first-order perturbation theory with respect to valence-valence and core-valence interactions. The theory is evaluated numerically for ferromagnetic Ni. We discuss the spin-resolved quasi-particle band structure and the Auger spectra and investigate the influence of the core hole.Comment: LaTeX, 12 pages, 8 eps figures included, Phys. Rev. B (in press

Heterochromatin-Driven Nuclear Softening Protects the Genome against Mechanical Stress-Induced Damage

Summary Tissue homeostasis requires maintenance of functional integrity under stress. A central source of stress is mechanical force that acts on cells, their nuclei, and chromatin, but how the genome is protected against mechanical stress is unclear. We show that mechanical stretch deforms the nucleus, which cells initially counteract via a calcium-dependent nuclear softening driven by loss of H3K9me3-marked heterochromatin. The resulting changes in chromatin rheology and architecture are required to insulate genetic material from mechanical force. Failure to mount this nuclear mechanoresponse results in DNA damage. Persistent, high-amplitude stretch induces supracellular alignment of tissue to redistribute mechanical energy before it reaches the nucleus. This tissue-scale mechanoadaptation functions through a separate pathway mediated by cell-cell contacts and allows cells/tissues to switch off nuclear mechanotransduction to restore initial chromatin state. Our work identifies an unconventional role of chromatin in altering its own mechanical state to maintain genome integrity in response to deformation.Peer reviewe

Observation of Stratospheric Ozone Depletion associated with Delta II Rocket Emissions

Ozone, chlorine monoxide, methane, and submicron particulate concentrations were measured in the stratospheric plume wake of a Delta II rocket powered by a combination of solid (NH4ClO4/Al) and liquid (LOX/kerosene) propulsion systems. We apply a simple kinetics model describing the main features of gas-phase chlorine reactions in solid propellant exhaust plumes to derive the abundance of total reactive chlorine in the plume and estimate the associated cumulative ozone loss. Measured ozone loss during two plume encounters (12 and 39 minutes after launch) exceeded the estimate by about a factor of about two. Insofar as only the most significant gas-phase chlorine reactions are included in the calculation, these results suggest that additional plume wake chemical processes or emissions other than reactive chlorine from the Delta II propulsion system affect ozone levels in the plume

Application of a hygroscopicity tandem differential mobility analyzer for characterizing PM emissions in exhaust plumes from an aircraft engine burning conventional and alternative fuels

In the last several decades, significant efforts have been directed toward better understanding the gaseous and particulate matter (PM) emissions from aircraft gas turbine engines. However, limited information is available on the hygroscopic properties of aircraft engine PM emissions which play an important role in the water absorption, airborne lifetime, obscuring effect, and detrimental health effects of these particles. This paper reports the description and detailed lab-based performance evaluation of a robust hygroscopicity tandem differential mobility analyzer (HTDMA) in terms of hygroscopic properties such as growth factor (GF) and the hygroscopicity parameter (κ). The HTDMA system was subsequently deployed during the Alternative Aviation Fuel EXperiment (AAFEX) II field campaign to measure the hygroscopic properties of aircraft engine PM emissions in the exhaust plumes from a CFM56-2C1 engine burning several types of fuels. The fuels used were conventional JP-8, tallow-based hydroprocessed esters and fatty acids (HEFA), Fischer–Tropsch, a blend of HEFA and JP-8, and Fischer–Tropsch doped with tetrahydrothiophene (an organosulfur compound). It was observed that GF and κ increased with fuel sulfur content and engine thrust condition, and decreased with increasing dry particle diameter. The highest GF and κ values were found in the smallest particles, typically those with diameters of 10&thinsp;nm.</p