Rayleigh-Taylor Instability of an Ultrathin Foil Accelerated by the Radiation Pressure of an Intense Laser

We report experimental evidence for a Rayleigh-Taylor-like instability driven by radiation pressure of an ultraintense (1021W/cm2) laser pulse. The instability is witnessed by the highly modulated profile of the accelerated proton beam produced when the laser irradiates a 5 nm diamondlike carbon (90% C, 10% H) target. Clear anticorrelation between bubblelike modulations of the proton beam and transmitted laser profile further demonstrate the role of the radiation pressure in modulating the foil. Measurements of the modulation wavelength, and of the acceleration from Doppler-broadening of back-reflected light, agree quantitatively with particle-in-cell simulations performed for our experimental parameters and which confirm the existence of this instability. © 2012 American Physical Society.

Monte Carlo radiation hydrodynamics:Methods, tests and application to Type Ia supernova ejecta

In astrophysical systems, radiation-matter interactions are important in transferring energy and momentum between the radiation field and the surrounding material. This coupling often makes it necessary to consider the role of radiation when modelling the dynamics of astrophysical fluids. During the last few years, there have been rapid developments in the use of Monte Carlo methods for numerical radiative transfer simulations. Here, we present an approach to radiation hydrodynamics that is based on coupling Monte Carlo radiative transfer techniques with finite-volume hydrodynamical methods in an operator-split manner. In particular, we adopt an indivisible packet formalism to discretize the radiation field into an ensemble of Monte Carlo packets and employ volume-based estimators to reconstruct the radiation field characteristics. In this paper the numerical tools of this method are presented and their accuracy is verified in a series of test calculations. Finally, as a practical example, we use our approach to study the influence of the radiation-matter coupling on the homologous expansion phase and the bolometric light curve of Type Ia supernova explosions. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

nero- a post-maximum supernova radiation transport code

The interpretation of supernova (SN) spectra is essential for deriving SN ejecta properties such as density and composition, which in turn can tell us about their progenitors and the explosion mechanism. A very large number of atomic processes are important for spectrum formation. Several tools for calculating SN spectra exist, but they mainly focus on the very early or late epochs. The intermediate phase, which requires a non-local thermodynamic equilibrium (NLTE) treatment of radiation transport has rarely been studied. In this paper, we present a new SN radiation transport code, nero, which can look at those epochs. All the atomic processes are treated in full NLTE, under a steady-state assumption. This is a valid approach between roughly 50 and 500days after the explosion depending on SN type. This covers the post-maximum photospheric and the early and the intermediate nebular phase. As a test, we compare nero to the radiation transport code of Jerkstrand, Fransson & Kozma and to the nebular code of Mazzali et al. All three codes have been developed independently and a comparison provides a valuable opportunity to investigate their reliability. Currently, nero is one-dimensional and can be used for predicting spectra of synthetic explosion models or for deriving SN properties by spectral modelling. To demonstrate this, we study the spectra of the 'normal' Type Ia supernova (SN Ia) 2005cf between 50 and 350 days after the explosion and identify most of the common SN Ia line features at post-maximum epochs. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Risk factors for falls and injuries in a long-term care facility in Ontario

Objective: To identify risk factors for falls and injuries among seniors living in a long-term care facility. Method: Case-control study of 335 residents living at St. Joseph's Villa, Dundas, Ontario. Cases were defined as residents who fell between July 1, 1996 and June 30, 1997; controls were those who did not fall. To identify risk factors for injury, cases were defined as those with completed incident injury forms and controls as those without. Results: The most important risk factors for falls included: having fallen in the past three months; residing in a secured unit; living in the facility for two or more years; having the potential to cause injury to others; and having an illness, disease or behaviour that may cause a fall. The most important risk factor for injury among those who fell was altered mental state. Conclusion: The risk factors identified may be helpful to those planning falls prevention initiatives within long-term care settings.

Surveillance of severe chemical corneal injuries in the UK

AIM: To estimate the incidence of severe chemical corneal injuries in the UK and describe presenting clinical features and initial management.

METHODS: All patients with severe chemical corneal injury in the UK from December 2005 to November 2006 inclusive were prospectively identified using the British Ophthalmological Surveillance Unit. Reporting ophthalmologists provided information regarding presentation and follow-up.

RESULTS: Twelve cases were identified, giving a minimum estimated incidence in the UK of severe chemical corneal injury of 0.02 per 100,000. 66.7% of injuries were in males of working age, 50% occurred at work, and alkali was causative in 66.7%. Only one patient was wearing eye protection at the time of injury, 75% received immediate irrigation. Six patients required one or more surgical procedures, most commonly amniotic membrane graft. At 6 months' follow-up, the best-corrected visual acuity was 6/12 or better in five patients, and worse than 6/60 in two.

CONCLUSION: The incidence of severe chemical corneal injury in the UK is low. The cases that occur can require extended hospital treatment, with substantial ocular morbidity and visual sequelae. Current enforcement of eye protection in the workplace in the UK has probably contributed to a reduced incidence of severe ocular burns.

DNA double strand break repair: a radiation perspective

SIGNIFICANCE:
Ionizing radiation (IR) can induce a wide range of unique deoxyribonucleic acid (DNA) lesions due to the spatiotemporal correlation of the ionization produced. Of these, DNA double strand breaks (DSBs) play a key role. Complex mechanisms and sophisticated pathways are available within cells to restore the integrity and sequence of the damaged DNA molecules.
RECENT ADVANCES:
Here we review the main aspects of the DNA DSB repair mechanisms with emphasis on the molecular pathways, radiation-induced lesions, and their significance for cellular processes.
CRITICAL ISSUES:
Although the main characteristics and proteins involved in the two DNA DSB repair processes present in eukaryotic cells (homologous recombination and nonhomologous end-joining) are reasonably well established, there are still uncertainties regarding the primary sensing event and their dependency on the complexity, location, and time of the damage. Interactions and overlaps between the different pathways play a critical role in defining the repair efficiency and determining the cellular functional behavior due to unrepaired/miss-repaired DNA lesions. The repair pathways involved in repairing lesions induced by soluble factors released from directly irradiated cells may also differ from the established response mechanisms.
FUTURE DIRECTIONS:
An improved understanding of the molecular pathways involved in sensing and repairing damaged DNA molecules and the role of DSBs is crucial for the development of novel classes of drugs to treat human diseases and to exploit characteristics of IR and alterations in tumor cells for successful radiotherapy applications.

Radiation retinopathy--clinical, histopathological, ultrastructural and experimental correlations

Clinical, pathological and experimental studies of radiation retinopathy confirm that the primary vascular event is endothelial cell loss and capillary closure. Pericytes are less susceptible, but typically atrophy as the capillaries become non-functional. The immediate effects of radiation reflect interphase and early mitotic death of injured endothelial cells, whereas later changes may be attributed to delayed mitotic death of compromised endothelial cells as they attempt division in the ordinary course of repair and replacement. Capillary occlusion leads to the formation of dilated capillary collaterals which may remain serviceable and competent for years. Microaneurysms develop in acellular and poorly supported capillaries, predominantly on the arterial side of the circulation and adjacent to regions of poorly perfused retina. Alterations in haemodynamics produce large telangiectatic-like channels which, typically develop a thick collagenous adventitia and may become fenestrated. Limited capillary regeneration occurs, usually evident as recanalisation of arterioles or venules by new capillaries. Vitreo-retinal neovascularisation may occur where retinal ischaemia is widespread. Radiation produces an exaggerated vasculopathy in patients with diabetes mellitus, and five month streptozotocin-induced diabetic rats develop a severe ischaemic retinopathy with vitreoretinal neovascularisation when exposed to 1500 cGy of radiation. Later photocoagulation is useful in containing or reversing microvascular incompetence and vasoproliferation in some patients with advanced radiation retinopathy.

A light microscopic and autoradiographic study of non-irradiated and irradiated ocular wounds

Focal gamma irradiation was used to limit the intraocular extension of scar tissue which typically occurs after posterior perforating injury to the eye. Standard posterior perforating injuries were created in the right eye of forty-eight rabbits, half of which had the site of perforation focally irradiated using a Cobalt 60 ophthalmic plaque. Non-irradiated wounds healed with profuse formation of highly cellular and vascularised granulation tissue which invaded the vitreous to form contractile vitreo-retinal membranes. In irradiated eyes vitreo-retinal membrane formation was infrequent; the wounds showing only sparse granulation tissue with little or no extension into the vitreous cavity. Autoradiographic studies carried out in a second group of 40 animals showed that the episclera was the main source of the proliferating fibroblasts, and cell counts confirmed that the inflammatory and repair responses in irradiated wounds were both delayed and attenuated.

Localised gamma irradiation and experimental intraocular proliferation

A controlled study was undertaken to assess the effect of gamma irradiation on post-traumatic intraocular cellular proliferation. A standard perforating injury in the posterior segment of the rabbit eye was used to induce intraocular cellular proliferation and vitreo-retinal membrane formation. The site of injury was irradiated with an ophthalmic Cobalt60 applicator which provided a continuous source of gamma rays. Non-irradiated eyes developed traction retinal detachments associated with post-traumatic vitreo-retinal membranes. Irradiated eyes developed attenuated membranes or atrophic retinal scars, with the retina remaining attached. The membranes in non-irradiated eyes were highly cellular with abundant collagen, while irradiated membranes had fewer cells within a sparse collagen matrix. The episcleral fibroblasts, on autoradiographic studies appeared to be the main source of the cells that formed the proliferating tissue in both non-irradiated and irradiated eyes. In irradiated eyes both the inflammatory response and division of fibroblasts were delayed and reduced.

Evaluation of Microcollimated Pars Plana External Beam Radiation in the Porcine Eye

Purpose: To evaluate the clinical and histological side effects of a prototype stereotactic radiotherapy system delivering microcollimated external beam radiation through pars plana in porcine eyes.

Methods: Five Yucatan mini-swine (10 eyes) were randomized to five treatment groups. Eight eyes were dosed with X-ray radiation on Day 1, and two eyes served as untreated controls. Treated eyes received doses up to 60 Gy to the retina and up to 130 Gy to the sclera using single or overlapping beams. The treatment beams were highly collimated such that the diameter was approximately 2.5 mm on the sclera and 3 mm on the retinal surface. Fundus photography, fluorescein angiography (FA), and spectral domain optical coherence tomography (SD-OCT) were obtained on days 7, 30, 60, and 110. Images were examined by a masked grader and evaluated for abnormalities. Animals were sacrificed on day 111 and gross and histopathological analysis was conducted.

Results: Histological and gross changes to eye structures including conjunctiva and lens were minimal at all doses. Fundus, FA, and SD-OCT of the targeted region failed to disclose any abnormality in the control or 21 Gy treated animals. In the 42 and 60 Gy animals, hypopigmented spots were noted after treatment on clinical exam, and corresponding hyperfluorescent staining was seen in late frames. No evidence of choroidal hypoperfusion was seen. The histological specimens from the 60 Gy animals showed photoreceptor loss and displacement of cone nuclei.

Conclusion: Transcleral stereotactic radiation dosing in porcine eyes can be accomplished with no significant adverse events as doses less than 42 Gy.