A mathematical expression for depth-light curves of therapeutic proton beams in a quenching scintillator

Purpose: Recently, there has been increasing interest in the development of scintillator-based detectors for the measurement of depth-dose curves of therapeutic proton beams1 . These detectors allow the measurement of single beam parameters such as the proton range or the reconstruction of the full three-dimensional dose distribution. Thus, scintillation detectors could play an important role in beam quality assurance, on-line beam monitoring, and proton imaging. However, the light output of the scintillator as a function of dose deposition is subject to quenching effects due to the high specific energy loss of incident protons, particularly in the Bragg peak. The aim of this work is to develop a model that describes the percent depth-light (PDL) curve in a quenching scintillator and allow the extraction of information about the beam range and the strength of the quenching. Methods: A mathematical expression of a depth-light curve, derived from a combination of Birks’ law2 and Bortfeld’s Bragg curve3 that is termed a “quenched Bragg” curve, is presented. The model is validated against simulation and measurement. Results: A fit of the quenched Bragg model to simulated depth-light curves in a polystyrenebased scintillator shows good agreement between the two, with a maximum deviation of 2.5% at the Bragg peak. The differences are larger behind the Bragg peak and in the dose build-up region. In the same simulation, the difference between the reconstructed range and the reference proton range is found to be always smaller than 0.16 mm. The comparison with measured data shows that the fitted beam range agrees with the reference range within their respective uncertainties. Conclusions: The quenched Bragg model is, therefore, an accurate tool for the range measurement from quenched depth-dose curves. Moreover, it allows the reconstruction of the beam energy spread, the particle fluence and the magnitude of the quenching effect from a measured depth-light curve

Techniques for quality pearl production

The success of pearl production adopting culture techniques depend on the quality of pearls rather than the quantity produced. It is quiet evident that the cost of production would go up in future and hence pearl quality alone can meet their challenges to make profits in this industry. There is long way to go to meet the challenges through application of advanced biotechnological tools for quality pearl production

Evidence Of Shark Predation And Scavenging On Fishes Equipped With Pop-Up Satellite Archival Tags

Over the past few years, pop-up satellite archival tags (PSATs) have been used to investigate the behavior, movements, thermal biology, and postrelease mortality of a wide range of large, highly migratory species including bluefin tuna (Block et al., 2001), swordfish (Sedberry and Loefer, 2001), blue marlin (Graves et al., 2002), striped marlin (Domeier and Dewar, 2003), and white sharks (Boustany et al., 2002). PSAT tag technology has improved rapidly, and current tag models are capable of collecting, processing, and storing large amounts of information on light level, temperature, and pressure (depth) for a predetermined length of time before the release of these tags from animals. After release, the tags float to the surface, and transmit the stored data to passing satellites of the Argos system

Untitled Narratives

Untitled Narratives is a photographic series about changing emotional states, and an evolving identity. The photographs represent a transformation between the confined and the free. The elements I use to portray the movement an individual makes between identities are a combination of a character and an environment. My photographs are driven by personal experiences and show recovery and openness. The character in the series is a representation of myself. The Character symbolizes emotional personas indicating past and present events, which shape the individual I am. I use the character as a representation of the hope and need for change. I describe the setting in the series as an enclosure; a space sealed off and separated from culture and other human presence. The enclosure functions first as a backdrop for the figureís emotive gestures, but it has also become a haven for the character. The scene is a safe space, designed for the figureís freed motions, making movement and performance possible

Timing and Potential Drivers of Symbiont Selection in the Early Life Stages of the Massive Starlet Coral Siderastrea siderea

The ability of corals to build reefs can be attributed to their relationship with single-celled algae of the familySymbiodiniaceae.Through the process of photosynthesis, these algae can provide their coral hosts with over 90% of their daily energy requirements. Most coral species acquire multiple species of symbionts from the surrounding water during their larval stage or immediately after settling. However, over time, the coral will select a dominant symbiont speciesthat can depend on the local environment. Until this study, the size or age of the coral at which this transition from multiple Symbiodiniaceaespecies to one dominant species occurs has remained uncertain. Likewise, it was unclear whether the selection of Symbiodiniaceaespeciesis influenced by the environment. The environmental conditions and symbiont composition of one hundred and eighteen juvenile Siderastrea siderea were assessed across four sites in Broward County, Florida. Presuming newly settled corals acquire multiple symbionts and then select just one dominant species, it was determined that the transition from multiple symbiont speciesto one dominant species in Siderastrea sidereaoccurs in the single polyp stage, between the time of settlement and approximately 4 to 6 months of age. The results also suggest that the selection of these dominant symbiont speciesis influenced by the environment, and that juveniles commonly select the same species as adults inhabiting similar environmental conditions. The selection of symbionts homologous to adult corals combined with environmental influences may be an early indicator of acclimatization in Siderastrea siderea

In situ photobiology of corals over large depth ranges: A multivariate analysis on the roles of environment, host, and algal symbiont

We applied a multivariate analysis to investigate the roles of host and symbiont on the in situ physiological response of genus Madracis holobionts towards light. Across a large depth gradient (5–40 m) and for four Madracis species and three symbiont genotypes, we assessed several variables by measuring chlorophyll a fluorescence, photosynthetic pigment composition, or symbiont population descriptors. Most of the variation is explained by two major photobiological components: light-use efficiency and symbiont cell densities. Two other minor components emphasize photoprotective pathways and light-harvesting properties such as secondary pigments. Statistics highlight the role of irradiance on coral physiology and reveal mechanisms that are either genetically constrained, such as symbiont cell sizes, or environmentally dependent, such as photochemical efficiencies. Other parameters, such as cellular light-harvesting and photoprotective pigment concentrations, are regulated by host, symbiont, and environment. The interaction between host and environment stresses the role of host properties in adjusting the internal environment available for the endosymbionts. Different holobiont strategies, relating to symbiont cell density, vary in their physiological optimization of light-harvesting or photoprotective mechanisms and link to host-species distribution and dominance over the reef slope. Symbiont functional diversity appears to have a significant role but does not explain host vertical distribution patterns per se, highlighting the importance of species-specific morphological and physiological properties of the coral host

Fluid Ontologies in the Search for MH370

This paper gives an account of the disappearance of Malaysian Airways Flight MH370 into the southern Indian Ocean in March 2014 and analyses the rare glimpses into remote ocean space this incident opened up. It follows the tenuous clues as to where the aeroplane might have come to rest after it disappeared from radar screens – seven satellite pings, hundreds of pieces of floating debris and six underwater sonic recordings – as ways of entering into and thinking about ocean space. The paper pays attention to and analyses this space on three registers – first, as a fluid, more-than-human materiality with particular properties and agencies; second, as a synthetic situation, a composite of informational bits and pieces scopically articulated and augmented; and third, as geopolitics, delineated by the protocols of international search and rescue. On all three registers – as matter, as data and as law – the ocean is shown to be ontologically fluid, a world defined by movement, flow and flux, posing intractable difficulties for human interactions with it

The Rise and Fall of Plankton: Long-Term Changes in the Vertical Distribution of Algae and Grazers in Lake Baikal, Siberia

Both surface water temperatures and the intensity of thermal stratification have increased recently in large lakes throughout the world. Such physical changes can be accompanied by shifts in plankton community structure, including changes in relative abundances and depth distributions. Here we analyzed 45 years of data from Lake Baikal, the world’s oldest, deepest, and most voluminous lake, to assess long-term trends in the depth distribution of pelagic phytoplankton and zooplankton. Surface water temperatures in Lake Baikal increased steadily between 1955 and 2000, resulting in a stronger thermal gradient within the top 50 m of the water column. In conjunction with these physical changes our analyses reveal significant shifts in the daytime depth distribution of important phytoplankton and zooplankton groups. The relatively heavy diatoms, which often rely on mixing to remain suspended in the photic zone, shifted downward in the water column by 1.90 m y-1, while the depths of other phytoplankton groups did not change significantly. Over the same time span the density-weighted average depth of most major zooplankton groups, including cladocerans, rotifers, and immature copepods, exhibited rapid shifts toward shallower positions (0.57–0.75 m y21). As a result of these depth changes the vertical overlap between herbivorous copepods (Epischura baikalensis) and their algal food appears to have increased through time while that for cladocerans decreased. We hypothesize that warming surface waters and reduced mixing caused these ecological changes. Future studies should examine how changes in the vertical distribution of plankton might impact energy flow in this lake and others