361 research outputs found
Institutional Teaching, Learning and Assessment Strategy July 2015 to July 2020
The Strategy was updated in 2016 and 2018. In 2020, a CCT Working Group on the Teaching, Learning and Assessment Strategy was formed to update the current iteration
Limits from BBN on Light Electromagnetic Decays
Injection of electromagnetic energy - photons, electrons, or positrons - into
the plasma of the early universe can destroy light elements created by
primordial Big Bang Nucleosynthesis (BBN). The success of BBN at predicting
primordial abundances has thus been used to impose stringent constraints on
decay or annihilation processes with primary energies near or above the
electroweak scale. In this work we investigate the constraints from BBN on
electromagnetic decays that inject lower energies, between 1-100 MeV. We
compute the electromagnetic cascade from such injections and we show that it
can deviate significantly from the universal spectrum commonly used in BBN
calculations. For electron injection below 100 MeV, we find that the final
state radiation of photons can have a significant impact on the resulting
spectrum relevant for BBN. We also apply our results on electromagnetic
cascades to investigate the limits from BBN on light electromagnetic decays
prior to recombination, and we compare them to other bounds on such decays.Comment: 31 pages, 9 figures, corrected note added, updated references, minor
code and plot fixes but nearly identical result
In vivo biological response to extracorporeal shockwave therapy in human tendinopathy:Response of tendinopathy to shockwave therapy
Extracorporeal shock wave therapy (ESWT) is a non-invasive treatment for chronic tendinopathies, however little is known about the in-vivo biological mechanisms of ESWT. Using microdialysis, we examined the real-time biological response of healthy and pathological tendons to ESWT. A single session of ESWT was administered to the mid-portion of the Achilles tendon in thirteen healthy individuals (aged 25.7Ā±7.0 years) and patellar or Achilles tendon of six patients with tendinopathies (aged 39.0Ā±14.9 years). Dialysate samples from the surrounding peri-tendon were collected before and immediately after ESWT. Interleukins (IL)-1Ī², IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-17A, vascular endothelial growth factor (VEGF) and interferon (IFN)-Ī³ were quantified using a cytometric bead array while gelatinase activity (MMP-2 and -9) was examined using zymography. There were no statistical differences between the biological tissue response to ESWT in healthy and pathological tendons. IL-1Ī², IL-2, IL-6 and IL-8 were the cytokines predominantly detected in the tendon dialysate. IL-1Ī² and IL-2 did not change significantly with ESWT. IL-6 and IL-8 concentrations were elevated immediately after ESWT and remained significantly elevated for four hours post-ESWT (p<0.001). Pro forms of MMP-2 and -9 activity also increased after ESWT (p<0.003), whereas there were no significant changes in active MMP forms. In addition, the biological response to ESWT treatment could be differentiated between possible responders and non-responders based on a minimum 5-fold increase in any inflammatory marker or MMP from pre- to post-ESWT. Our findings provide novel evidence of the biological mechanisms underpinning ESWT in humans in vivo. They suggest that the mechanical stimulus provided by ESWT might aid tendon remodelling in tendinopathy by promoting the inflammatory and catabolic processes that are associated with removing damaged matrix constituents. The non-response of some individuals may help to explain why ESWT does not improve symptoms in all patients and provides a potential focus for future research
An in vitro investigation into the effects of 10Hz cyclic loading on tenocyte metabolism
Tendinopathy is a prevalent, highly debilitating condition, with poorly defined aetiology. A wide range of clinical treatments have been proposed, with systematic reviews largely supporting shock wave therapy or eccentric exercise. Characterising these treatments has demonstrated both generate perturbations within tendon at a frequency of approximately 812Hz. Consequently, it is hypothesised that loading in this frequency range initiates increased anabolic tenocyte behaviour, promoting tendon repair. The primary aim of this study is to investigate the effects of 10Hz perturbations on tenocyte metabolism, comparing gene expression in response to a 10Hz and 1Hz loading profile. Tenocytes from healthy and tendinopathic human tendons were seeded into 3D collagen gels and subjected to 15 mins cyclic strain at 10Hz or 1Hz. Tenocytes from healthy tendon showed increased expression of all analysed genes in response to loading, with significantly increased expression of inflammatory and degradative genes with 10Hz, relative to 1Hz loading. By contrast, whilst the response of tenocytes from tendinopathy tendon also increased with 10Hz loading, the overall response profile was more varied and less intense, possibly indicative of an altered healing response. Through inhibition of the pathway, IL1 was shown to be involved in the degradative and catabolic response of cells to high frequency loading, abrogating the loading response. This study has demonstrated for the first time that loading at a frequency of 10Hz may enhance the metabolic response of tenocytes by initiating an immediate degradatory and inflammatory cell response through the IL1 pathway, perhaps as an initial stage of tendon healing
Feasibility of isotope harvesting at a projectile fragmentation facility: ā¶ā·Cu
The work presented here describes a proof-of-principle experiment for the chemical extraction of (67)Cu from an aqueous beam stop at the National Superconducting Cyclotron Laboratory (NSCL). A 76 MeV/A (67)Cu beam was stopped in water, successfully isolated from the aqueous solution through a series of chemical separations involving a chelating disk and anion exchange chromatography, then bound to NOTA-conjugated Herceptin antibodies, and the bound activity was validated using instant thin-layer chromatography (ITLC). The chemical extraction efficiency was found to be 88 Ā± 3% and the radiochemical yield was ā„95%. These results show that extraction of radioisotopes from an aqueous projectile-fragment beam dump is a feasible method for obtaining radiochemically pure isotopes
CoGeNT Interpretations
Recently, the CoGeNT experiment has reported events in excess of expected
background. We analyze dark matter scenarios which can potentially explain this
signal. Under the standard case of spin independent scattering with equal
couplings to protons and neutrons, we find significant tensions with existing
constraints. Consistency with these limits is possible if a large fraction of
the putative signal events is coming from an additional source of experimental
background. In this case, dark matter recoils cannot be said to explain the
excess, but are consistent with it. We also investigate modifications to dark
matter scattering that can evade the null experiments. In particular, we
explore generalized spin independent couplings to protons and neutrons, spin
dependent couplings, momentum dependent scattering, and inelastic interactions.
We find that some of these generalizations can explain most of the CoGeNT
events without violation of other constraints. Generalized couplings with some
momentum dependence, allows further consistency with the DAMA modulation
signal, realizing a scenario where both CoGeNT and DAMA signals are coming from
dark matter. A model with dark matter interacting and annihilating into a new
light boson can realize most of the scenarios considered.Comment: 24 pages, 12 figs, v2: published version, some discussions clarifie
The Discovery of a Debris Disk Around the DAV White Dwarf PG 1541+651
To search for circumstellar disks around evolved stars, we targeted roughly
100 DA white dwarfs from the Palomar Green survey with the Peters Automated
Infrared Imaging Telescope (PAIRITEL). Here we report the discovery of a debris
disk around one of these targets, the pulsating white dwarf PG 1541+651 (KX
Draconis, hereafter PG1541). We detect a significant flux excess around PG1541
in the K-band. Follow-up near-infrared spectroscopic observations obtained at
the NASA Infrared Telescope Facility (IRTF) and photometric observations with
the warm Spitzer Space Telescope confirm the presence of a warm debris disk
within 0.13-0.36 Rsun (11-32x the stellar radius) at an inclination angle of
60deg. At Teff = 11880 K, PG1541 is almost a twin of the DAV white dwarf
G29-38, which also hosts a debris disk. All previously known dusty white dwarfs
are of the DAZ/DBZ spectral type due to accretion of metals from the disk.
High-resolution optical spectroscopy is needed to search for metal absorption
lines in PG1541 and to constrain the accretion rate from the disk. PG1541 is
only 55 pc away from the Sun and the discovery of its disk in our survey
demonstrates that our knowledge of the nearby dusty white dwarf population is
far from complete.Comment: MNRAS Letters, in pres
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