Exact local fermionic zero modes

We introduce a simple method to find localized exact fermionic zero modes for any local fermionic action. The zero modes are attached to specific local gauge configurations. Examples are provided for staggered and Wilson fermion actions in 2-6 dimensions, at finite and infinite lattice volumes, and for abelian and non-abelian gauge groups. One of our concrete results is that a finite density of almost zero modes must occur in quenched four dimensional lattice gauge theory simulations that use traditional methods. This density is exponentially suppressed in the gauge coupling constant.Comment: Revtex Latex, 10 pages, 1 figure, minor correction

The effects of irradiation on the biological and biomechanical properties of an acellular porcine superflexor tendon graft for cruciate ligament repair

Acellular xenogeneic tissues have the potential to provide ‘off‐the‐shelf’ grafts for anterior cruciate ligament (ACL) repair. To ensure that such grafts are sterile following packaging, it is desirable to use terminal sterilization methods. Here, the effects of gamma and electron beam irradiation on the biological and biomechanical properties of a previously developed acellular porcine superflexor tendon (pSFT) were investigated. Irradiation following treatment with peracetic acid was compared to peracetic acid treatment alone and the stability of grafts following long‐term storage assessed. Irradiation did not affect total collagen content or biocompatibility (determined using a contact cytotoxicity assay) of the grafts, but slightly increased the amount of denatured collagen in and decreased the thermal denaturation temperature of the tissue in a dose dependant fashion. Biomechanical properties of the grafts were altered by irradiation (reduced ultimate tensile strength and Young's modulus, increased failure strain), but remained superior to reported properties of the native human ACL. Long term storage at 4°C had no negative effects on the grafts. Of all the conditions tested, a dose of minimum 25 kGy of gamma irradiation had least effect on the grafts, suggesting that this dose produces a biocompatible pSFT graft with adequate mechanical properties for ACL repair

Decellularization and Characterization of Porcine Superflexor Tendon: A Potential Anterior Cruciate Ligament Replacement

The porcine superflexor tendon (SFT) was identified as having appropriate structure and properties for development of a decellularised device for use in ACL reconstruction. SFTs were decellularised using a combination of freeze thaw and washes in hypotonic buffer and 0.1% (w/v) SDS in hypotonic buffer plus proteinase inhibitors followed by nuclease treatment and sterilisation using peracetic acid. The decellularised biological scaffold was devoid of cells and cell remnants and contained only 13 ng.mg-1 (dry weight) residual total DNA. Immunohistochemistry showed retention of collagens type I and III and tenascin-C. Quantitative analysis of sulphated sugar and hydroxyproline content revealed a loss of glycosaminoglycans compared to native tissue but no loss of collagen. The decellularised SFT was biocompatible in vitro and in vivo following implantation in a mouse subcutaneous model for 12 weeks. Uniaxial tensile testing to failure indicated that the gross material properties of decellularised SFT were not significantly different to native tissue. Decellularised SFTs had an ultimate tensile strength of 61.8 ± 10.3 MPa (± 95 % confidence limits), a failure strain of 0.29 ± 0.04 and a Young’s modulus of the collagen phase of 294.1 ± 61.9 MPa. Analysis of the presence of the alpha-Gal (galactose-α-1,3-galactose) epitope by immunohistochemistry, lectin binding and antibody absorption assay indicated that the epitope was reduced but still present post decellularisation. This is discussed in light of the potential role of non-cellular alpha-Gal in the acceleration of wound healing and tissue regeneration in the presence of antibodies to alpha-Gal

An alternative to domain wall fermions

We define a sparse hermitian lattice Dirac matrix, $H$, coupling $2n+1$ Dirac fermions. When $2n$ fermions are integrated out the induced action for the last fermion is a rational approximation to the hermitian overlap Dirac operator. We provide rigorous bounds on the condition number of $H$ and compare them to bounds for the higher dimensional Dirac operator of domain wall fermions. Our main conclusion is that overlap fermions should be taken seriously as a practical alternative to domain wall fermions in the context of numerical QCD.Comment: Revtex Latex, 26 pages, 1 figure, a few minor change

High rate of lymphoma among a UK cohort of adolescents with vertically acquired HIV-1 infection transitioning to adult care in the era of antiretroviral therapy

Among an inner London UK cohort of 147 adolescents transitioning from paediatric into adult care between 2007 and 2015, a new diagnosis of lymphoma was made in five patients; incidence rate = 0.425/100 person-years (95% confidence interval = 0.424–0.426). Previously described risk factors, including low nadir CD4+ cell count and ongoing HIV-1 viraemia, appeared to be important. These data suggest that careful surveillance and a low threshold for investigating relevant symptoms continue to be essential for such patients

Decellularisation affects the strain rate dependent and dynamic mechanical properties of a xenogeneic tendon intended for anterior cruciate ligament replacement

Development of new replacement grafts for anterior cruciate ligament (ACL) repair requires mechanical testing to ensure they can provide joint stability following implantation. A decellularised porcine superflexor tendon (pSFT) has been developed previously as an alternative to current reconstruction methods and subjected to biomechanical analysis. The application of varied strain rates to biological tissues is known to alter their biomechanical properties, however the effects of decellularisation on strain rate dependent and dynamic mechanical behaviour of tissues have not been explored. This study utilised tensile testing to investigate the material properties of native and decellularised pSFTs at three different strain rates (1%.s−1, 10%.s−1 and 100%.s−1). In addition, dynamic mechanical analysis (DMA) was used to ascertain the relative contributions of the solid and fluid phase components of the tissues. Ultimate tensile strength was significantly reduced in decellularised compared with native untreated pSFTs but was unaffected by strain rate. In contrast, toe region moduli increased with increasing strain rate for native tissues, but this effect was not observed in decellularised pSFTs. Linear region moduli were unaffected by strain rate, but were significantly reduced in decellularised pSFT compared with native tissue. Following DMA, significant reductions in dynamic modulus, storage modulus and loss modulus were seen in decellularised compared with native pSFT. Interestingly, the damping ability of the tendons was unaffected by decellularisation, suggesting that solid and fluid phases of the tissue were affected equally. These results, alongside previous studies, suggest that decellularisation affects collagen crimp, tissue swelling and collagen fibre sliding. However, despite these findings, the biomechanical properties of decellularised pSFT remain sufficient to act as an off-the-shelf solution for ACL reconstruction

Understanding the exercise of agency within structural inequality: the case of personal debt

This article contributes to debates about agency (meaning the behaviour of individuals) and structure, by drawing on empirical research into personal debt. Consideration of debt allows for debate about agency and structure beyond the narrow confines of welfare, and for the examination of agency in relation to citizens at different points in the broader socio-economic structure, not solely poor people. Based on the research findings, themselves grounded in interviewees' experience, the question of why two people in the same material circumstances will have different experiences becomes reframed as why two people whose exercise of agency is the same, face very different outcomes? It is argued that while the research supports a ‘both-and’ rather than ‘either-or’ approach to understanding agency and structure, a ‘both-and’ approach still does not fully capture the experience of interviewees. The key point is that the exercise of agency is overlaid onto structural inequality, and it is understanding the exercise of ‘agency within structure’ that is critical

Waterproofed Photomultiplier Tube Assemblies for the Daya Bay Reactor Neutrino Experiment

In the Daya Bay Reactor Neutrino Experiment 960 20-cm-diameter waterproof photomultiplier tubes are used to instrument three water pools as Cherenkov detectors for detecting cosmic-ray muons. Of these 960 photomultiplier tubes, 341 are recycled from the MACRO experiment. A systematic program was undertaken to refurbish them as waterproof assemblies. In the context of passing the water leakage check, a success rate better than 97% was achieved. Details of the design, fabrication, testing, operation, and performance of these waterproofed photomultiplier-tube assemblies are presented.Comment: 16 pages, 11 figures. Submitted to Nucl. Instr. Met

The overlap lattice Dirac operator and dynamical fermions

I show how to avoid a two level nested conjugate gradient procedure in the context of Hybrid Monte Carlo with the overlap fermionic action. The resulting procedure is quite similar to Hybrid Monte Carlo with domain wall fermions, but is more flexible and therefore has some potential worth exploring.Comment: Further expanded version. 12 pages, plain Te

Bounds on the Wilson Dirac Operator

New exact upper and lower bounds are derived on the spectrum of the square of the hermitian Wilson Dirac operator. It is hoped that the derivations and the results will be of help in the search for ways to reduce the cost of simulations using the overlap Dirac operator. The bounds also apply to the Wilson Dirac operator in odd dimensions and are therefore relevant to domain wall fermions as well.Comment: 16 pages, TeX, 3 eps figures, small corrections and improvement