A beginner’s guide to radiation damage

Radiation damage considerations affecting data collection by more than a factor of two are summarized and damage avoidance strategies are suggested

Towards the spatial resolution of metalloprotein charge states by detailed modeling of XFEL crystallographic diffraction.

Oxidation states of individual metal atoms within a metalloprotein can be assigned by examining X-ray absorption edges, which shift to higher energy for progressively more positive valence numbers. Indeed, X-ray crystallography is well suited for such a measurement, owing to its ability to spatially resolve the scattering contributions of individual metal atoms that have distinct electronic environments contributing to protein function. However, as the magnitude of the shift is quite small, about +2 eV per valence state for iron, it has only been possible to measure the effect when performed with monochromated X-ray sources at synchrotron facilities with energy resolutions in the range 2-3 × 10-4 (ΔE/E). This paper tests whether X-ray free-electron laser (XFEL) pulses, which have a broader bandpass (ΔE/E = 3 × 10-3) when used without a monochromator, might also be useful for such studies. The program nanoBragg is used to simulate serial femtosecond crystallography (SFX) diffraction images with sufficient granularity to model the XFEL spectrum, the crystal mosaicity and the wavelength-dependent anomalous scattering factors contributed by two differently charged iron centers in the 110-amino-acid protein, ferredoxin. Bayesian methods are then used to deduce, from the simulated data, the most likely X-ray absorption curves for each metal atom in the protein, which agree well with the curves chosen for the simulation. The data analysis relies critically on the ability to measure the incident spectrum for each pulse, and also on the nanoBragg simulator to predict the size, shape and intensity profile of Bragg spots based on an underlying physical model that includes the absorption curves, which are then modified to produce the best agreement with the simulated data. This inference methodology potentially enables the use of SFX diffraction for the study of metalloenzyme mechanisms and, in general, offers a more detailed approach to Bragg spot data reduction

A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves

A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO

Swimming with humans: biotelemetry reveals effects of “gold standard” regulated tourism on whale sharks

Wildlife tourism can benefit conservation of target species, however, it can have detrimental effects on animal behaviour and physiology. Whale shark Rhincodon typus tourism has seen recent rapid growth globally, but methods and regulations vary widely. Ningaloo Reef, Australia is considered “gold standard” whale shark tourism management due to legal regulation, strict enforcement, and high compliance. Rather than relying on observational data, we used biotelemetry to collect high-resolution data (20 Hz) on whale sharks’ movement behaviour in the presence or absence of tourists. Tourism encounters lasted an average of 62 min and swimming with tourists increased the activity levels of larger (> 7 m) but not smaller sharks. Given that activity levels positively correlate with energetic costs, it is likely the 18% increase seen in activity of large sharks would have incurred additional energetic costs. However, when considered as a proportion of daily energy requirements, these additional costs were only incurred for an average of 4% of a whale shark’s day. The tourism-induced impacts we found on the endangered whale sharks at this highly regulated tourism site would not have been apparent from purely observational studies, highlighting the utility of biotelemetry to quantify tourism-related impacts on wildlife

Bone marrow aspirate in the treatment of chondral injuries

The ability of mesenchymal stem cells (MSCs) to transdifferentiate into a desired cell lineage has captured the imagination of scientists and clinicians alike. The limited ability for chondrocytes to regenerate in chondral injuries has raised the concept of using MSCs to help regenerate and repair damaged tissue. The expansion of cells in a laboratory setting to be delivered back to the patient is too costly for clinical use in the present tough economic climate. This process is slow with due to the complexity of trying to imitate the natural environment and biological stimulation of chondral cell replication and proliferation. Bone marrow aspirate concentrate (BMAC) has the potential to provide an easily accessible and readily available source of MSCs with key growth factors that can be used in treating chondral injuries. This review summarizes the underlying basic science of MSCs and the therapeutic potential of BMAC

Wave Dynamics and Transport in the Stratosphere

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model

The basic science of bone marrow aspirate concentrate in chondral injuries

There has been great interest in bone marrow aspirate concentrate (BMAC) as a cost effective method in delivering mesenchymal stem cells (MSCs) to aid in the repair and regeneration of cartilage defects. Alongside MSCs, BMAC contains a range of growth factors and cytokines to support cell growth following injury. However, there is paucity of information relating to the basic science underlying BMAC and its exact biological role in supporting the growth and regeneration of chondrocytes. The focus of this review is the basic science underlying BMAC in relation to chondral damage and regeneration

The role of viscosity in stratified rotating fluids

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1964.Vita.Includes bibliographical references (leaf 109).by James Reed Holton.Ph.D

Producing performance collectively in austere times (UK 2008-2018)

This thesis examines collective and artist-run performance producing practices in the UK in the period of austerity from 2008-2018. This thesis examines collective practices in opposition to the rhetoric, logic, and impacts of neoliberal austerity, while examining how they are, at one and the same time, caught up within them, and frequently complicit with them. I argue that collectives can temporarily reverse and rework the negative material and affective impacts of austerity through gathering artists and producers with similar practices and concerns together in the same space, producing social and affective spaces that feel and operate differently to the rest of the artistic infrastructure, and sharing material and immaterial resources. As I go on to establish, austerity works by making people feel precarious, uncared for, alone, indebted, hopeless, and disentitled. At their best, collectives work by making people feel the opposite. In gathering together in their own space, these artists and producers feel and imagine the possibility of a different way of doing things. These spaces exist to present the performance of others, to support the organisers’ individual practices and administrative work, to run festivals and performance events, and to organise around particular issues. An analysis of these functions of collective practice structure the main body of this thesis, which begins by examining collective and artist-run models of performance venues, then studios, then festivals, and finally, networks. In each chapter I examine a specific negative affect of austerity which these groups seek to resist. These are: insecurity or precarity, neglect or a lack of care, isolation or disconnectedness, and hopelessness or a lack of access to futurity. I show, using Pierre Bourdieu’s concept of field, Henri Lefebvre’s production of space, and Sara Ahmed’s work on affect, how the practices of each structural model of collective and artist-run organisation responds to and reworks these conditions by producing affective spaces of security, care, communitas, and hope. These spaces, and the practices that create them, are embedded within the wider context of neoliberalism and austerity which they oppose, and are thus temporary and susceptible to reproducing exploitative and exclusive practices. The task of this thesis is to reveal the immediate positive affective and material impacts of these collectives in opposition to austerity, as well as the complexity of the problems that arise as these groups interact with a wider context over which they have no control. Despite the limitations of collective practice, this thesis argues that through providing relief from the negative affective impacts of austerity, it can provide vital support to artists, practices, and communities during difficult economic conditions, and allow them to survive, to organise, and to imagine and enact better and more liveable futures in the field of performance