18 research outputs found
Radiation back-reaction in relativistically strong and QED-strong laser fields
The emission from an electron in the field of a relativistically strong laser
pulse is analyzed. At the pulse intensities of \ge 10^{22} W/cm^2 the emission
from counter-propagating electrons is modified by the effects of Quantum
ElectroDynamics (QED), as long as the electron energy is sufficiently high: E
\ge 1 GeV. The radiation force experienced by an electron is for the first time
derived from the QED principles and its applicability range is extended towards
the QED-strong fields.Comment: 4 pages, 4 figure
Emission and its back-reaction accompanying electron motion in relativistically strong and QED-strong pulsed laser fields
The emission from an electron in the field of a relativistically strong laser
pulse is analyzed. At pulse intensities of J > 2 10^22 W/cm2 the emission from
counter-propagating electrons is modified by the effects of Quantum
ElectroDynamics (QED), as long as the electron energy is sufficiently high: E >
1 GeV. The radiation force experienced by an electron is for the first time
derived from the QED principles and its applicability range is extended towards
the QED-strong fields.Comment: 14 pages, 5 figures. Submitted to Phys.Rev.
Generation of GeV protons from 1 PW laser interaction with near critical density targets
The propagation of ultra intense laser pulses through matter is connected
with the generation of strong moving magnetic fields in the propagation channel
as well as the formation of a thin ion filament along the axis of the channel.
Upon exiting the plasma the magnetic field displaces the electrons at the back
of the target, generating a quasistatic electric field that accelerates and
collimates ions from the filament. Two-dimensional Particle-in-Cell simulations
show that a 1 PW laser pulse tightly focused on a near-critical density target
is able to accelerate protons up to an energy of 1.3 GeV. Scaling laws and
optimal conditions for proton acceleration are established considering the
energy depletion of the laser pulse.Comment: 26 pages, 8 figure
X-ray phase contrast imaging of biological specimens with tabletop synchrotron radiation
Since their discovery in 1896, x-rays have had a profound impact on science, medicine and technology. Here we show that the x-rays from a novel tabletop source of bright coherent synchrotron radiation can be applied to phase contrast imaging of biological specimens, yielding superior image quality and avoiding the need for scarce or expensive conventional sources
Accelerating Protons to Therapeutic Energies with Ultra-Intense Ultra-Clean and Ultra-Short Laser Pulses
Proton acceleration by high-intensity laser pulses from ultra-thin foils for
hadron therapy is discussed. With the improvement of the laser intensity
contrast ratio to 10-11 achieved on Hercules laser at the University of
Michigan, it became possible to attain laser-solid interactions at intensities
up to 1022 W/cm2 that allows an efficient regime of laser-driven ion
acceleration from submicron foils. Particle-In-Cell (PIC) computer simulations
of proton acceleration in the Directed Coulomb explosion regime from ultra-thin
double-layer (heavy ions / light ions) foils of different thicknesses were
performed under the anticipated experimental conditions for Hercules laser with
pulse energies from 3 to 15 J, pulse duration of 30 fs at full width half
maximum (FWHM), focused to a spot size of 0.8 microns (FWHM). In this regime
heavy ions expand predominantly in the direction of laser pulse propagation
enhancing the longitudinal charge separation electric field that accelerates
light ions. The dependence of the maximum proton energy on the foil thickness
has been found and the laser pulse characteristics have been matched with the
thickness of the target to ensure the most efficient acceleration. Moreover the
proton spectrum demonstrates a peaked structure at high energies, which is
required for radiation therapy. 2D PIC simulations show that a 150-500 TW laser
pulse is able to accelerate protons up to 100-220 MeV energies.Comment: 26 pages, 6 figure
Dynamics of Emitting Electrons in Strong Electromagnetic Fields
We derive a modified non-perturbative Lorentz-Abraham-Dirac equation. It
satisfies the proper conservation laws, particularly, it conserves the
generalized momentum, the latter property eliminates the symmetry-breaking
runaway solution. The equation allows a consistent calculation of the electron
current, the radiation effect on the electron momentum, and the radiation
itself, for a single electron or plasma electrons in strong electromagnetic
fields. The equation is applied to a simulation of a strong laser pulse
interaction with a plasma target. Some analytical solutions are also provided.Comment: The original form of this paper was submitted to Phys. Rev. Lett. on
August 3, 2008. The current version of the paper is substantially extended
and includes modifications resulting from points raised during the review
proces
Consolidating the association of biallelic MAPKAPK5 pathogenic variants with a distinct syndromic neurodevelopmental disorder
[Background]: MAPK-activated protein kinase 5 (MAPKAPK5) is an essential enzyme for diverse cellular processes. Dysregulation of the pathways regulated by MAPKAPK enzymes can lead to the development of variable diseases. Recently, homozygous loss-of-function variants in MAPKAPK5 were reported in four patients from three families presenting with a recognisable neurodevelopmental disorder, so-called âneurocardiofaciodigitalâ syndrome.
[Objective and methods]: In order to improve characterisation of the clinical features associated with biallelic MAPKAPK5 variants, we employed a genotype-first approach combined with reverse deep-phenotyping of three affected individuals.
[Results]: In the present study, we identified biallelic loss-of-function and missense MAPKAPK5 variants in three unrelated individuals from consanguineous families. All affected individuals exhibited a syndromic neurodevelopmental disorder characterised by severe global developmental delay, intellectual disability, characteristic facial morphology, brachycephaly, digital anomalies, hair and nail defects and neuroradiological findings, including cerebellar hypoplasia and hypomyelination, as well as variable vision and hearing impairment. Additional features include failure to thrive, hypotonia, microcephaly and genitourinary anomalies without any reported congenital heart disease.
[Conclusion]: In this study, we consolidate the causality of loss of MAPKAPK5 function and further delineate the molecular and phenotypic spectrum associated with this new ultra-rare neurodevelopmental syndrome.HH is funded by the MRC (MR/S01165X/1, MR/S005021/1, G0601943), the National Institute for Health Research University College London Hospitals Biomedical Research Centre, Rosetree Trust, Ataxia UK, MSA Trust, Brain Research UK, Sparks GOSH Charity, Muscular Dystrophy UK (MDUK), Muscular Dystrophy
Association (MDA USA). SE is supported by an MRC strategic award to establish an International Centre for Genomic Medicine in Neuromuscular Diseases (ICGNMD) MR/S005021/1â
Consolidating the association of biallelic MAPKAPK5 pathogenic variants with a distinct syndromic neurodevelopmental disorder
BACKGROUND: MAPK-activated protein kinase 5 (MAPKAPK5) is an essential enzyme for diverse cellular processes. Dysregulation of the pathways regulated by MAPKAPK enzymes can lead to the development of variable diseases. Recently, homozygous loss-of-function variants in MAPKAPK5 were reported in four patients from three families presenting with a recognisable neurodevelopmental disorder, so-called 'neurocardiofaciodigital' syndrome. OBJECTIVE AND METHODS: In order to improve characterisation of the clinical features associated with biallelic MAPKAPK5 variants, we employed a genotype-first approach combined with reverse deep-phenotyping of three affected individuals. RESULTS: In the present study, we identified biallelic loss-of-function and missense MAPKAPK5 variants in three unrelated individuals from consanguineous families. All affected individuals exhibited a syndromic neurodevelopmental disorder characterised by severe global developmental delay, intellectual disability, characteristic facial morphology, brachycephaly, digital anomalies, hair and nail defects and neuroradiological findings, including cerebellar hypoplasia and hypomyelination, as well as variable vision and hearing impairment. Additional features include failure to thrive, hypotonia, microcephaly and genitourinary anomalies without any reported congenital heart disease. CONCLUSION: In this study, we consolidate the causality of loss of MAPKAPK5 function and further delineate the molecular and phenotypic spectrum associated with this new ultra-rare neurodevelopmental syndrome
Femtosecond Diode-Pumped Cr : Lisgaf Lasers
The design and performance of diode-pumped Cr : LiSGAF lasers mode-locked by Kerr-Iens mode-locking and a solid-state saturable absorber are described. The different regimes of operation of the laser mode-locked by the saturable absorber are discussed. Both lasers generate 100-fs pulses with average powers of 40 mW and low fluctuations
Narrow Energy Spread Protons and Ions from High-Intensity, High-Contrast Laser Solid Target Interactions
Recent simulations show that an idealized, high intensity, short pulse laser can generate quasi-monoenergetic proton beams with energies over 100 MeV in an interaction with a thin film [1]. However, most short pulse laser facilities with sufficient intensity have difficulty controlling the nanosecond and picosecond contrast necessary to realize such a regime. Experiments were performed to investigate proton and ion acceleration from a high contrast, short pulse laser by employing dual plasma mirrors along with a deformable mirror at the HERCULES laser facility at the Center for Ultrafast Optical Sciences, University of Michigan. Plasma mirrors were characterized, allowing a 50% throughput with an intensity contrast increase of 10(5). The focal spot quality was also exceptional, showing a 1.1 micron full width at half maximum (FWHM) focal diameter. Experiments were done using temporally cleaned 30 TW, 32 fs pulses to achieve an intensity of up to 10(21)Wcm(-2) on Si(3)N(4) and Mylar targets with thicknesses ranging 50 nm to 13 microns. Proton beams with energy spreads below 2 MeV were observed from all thicknesses, peaking with energies up to 10.3 MeV and an energy spread of 0.8 MeV. Similar narrow energy spreads were observed for oxygen, nitrogen, and carbon at the silicon nitride thickness of 50 nm with energies up to 24 MeV with an energy spread of 3 MeV, whereas the energy spread is greatly increased at a larger thickness. Maximum energies were confirmed with CR39 track detectors, while a Thomson ion spectrometer was used to gauge the monoenergetic nature of the beam