Making the invisible visible

Whilst some disabilities are easily identifiable to others because they are visible – such as use of a wheelchair or loss of limbs – others may be more difficult to ascertain as they are hidden

Asymptotic properties of DVCS

We compute the deeply virtual Compton scattering (DVCS) amplitude for forward and backward scattering in the asymptotic limit. We make use of the Regge calculus to resum important logarithmic contributions that are beyond those included by the DGLAP evolution. We find a power-like behavior for the forward DVCS amplitude.Comment: 3 pages, LaTeX, 3 figures. To be published in the proceedings of 7th International Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19-23 Apr 199

QCD running coupling effects for the non-singlet structure function at small x

A generalization of the leading-order DGLAP evolution at small x is performed for the non-singlet structure function by resumming the leading-order DGLAP anomalous dimension to all orders in the QCD coupling. Explicit expressions are obtained for the non-singlet structure function of the deep inelastic scattering, taking into account both the double-logarithmic and the single-logarithmic contributions, including the running alpha_s effects. It is shown that when these contributions are included, the asymptotic small-x behaviour is power-like, with an exponent of about 0.4.Comment: Latex, 20 pages, 7 figure

Soft-gluon resummation for pseudoscalar Higgs boson production at hadron colliders

We compute the threshold-resummed cross section for pseudo-scalar MSSM Higgs boson production by gluon fusion at hadron colliders. The calculation is performed at next-to-next-to leading logarithmic accuracy. We present results for both the LHC and Tevatron Run II. We analyze the factorization and renormalization scale dependence of the results, finding that after performing the resummation the corresponding cross section can be computed with an accuracy better than 10%.Comment: 10 pages, 7 figures, accepted by Physics Letters

The Self-Organisation of Biological Soft matter Systems at Different Length-scales

Spontaneous self-organisation occurs in physical, chemical and biological systems throughout the natural world when the components of an initially unstructured system arrange to form ordered structures. Research into the mechanisms underlying these systems has led to exciting developments in materials chemistry where a bottom-up approach based on directed self-organisation has the potential to yield novel materials with a wide range of technological and scientific applications. Owing to their high specificity and potency, biopharmaceutical therapeutics are often favoured over small molecule drugs. However, protein based biopharmaceuticals are prone to degradation as a result of physical and chemical instability, a process leading to devastating financial and safety outcomes. Accordingly, understanding and quantifying the adverse effects of protein degradation is imperative. One such form of degradation is protein self-organisation in the form of aggregation. For certain solution conditions, aggregated unfolded protein leads to the formation of gels. Hydrogels are a class of gel formed from hydrophilic polymer chains capable of holding large amounts of water in their three dimensional network and have numerous medical and pharmaceutical uses. Self-organisation drives gel formation. Therefore, understanding the principles of self-organisation is a prerequisite in the development of novel hydrogels with increased functionality. At longer length-scales cells self-associate to form tissues. Spheroids are self-organised entities comprised of a single-cell type. They are the archetypal model for tumours and are an ideal system to study the biophysical phenomena associated with self-organisation. Unlike tissues, when a single cell type is used to form the spheroid, compositionally identical replicates can easily be grown. Furthermore, unlike with explants, other factors including age and the biochemical environment, which have been shown to alter the mechanical characteristics of cells and tissues can be rigorously controlled. Here, the experimental techniques of the wider soft matter field are used to investigate the biophysical properties of systems that span the biologically relevant spectrum of length-scales in which soft matter contributions are important. Differential scanning calorimetry analysis was used to quantify the reversibility of unfolding following thermal denaturation of lysozyme. Solution conditions (pH, ionic strength and the presence/absence of disaccharides) were varied to systematically alter the temperature at which the protein unfolds, Tm. The enthalpies of unfolding during successive heating and cooling cycles were compared to quantify the degree of reversible unfolding that occurs following thermal denaturation. The sugars were used to evaluate whether a disaccharide induced increase in Tm affects the reversibility of thermally induced denaturation. It was shown that there was considerable overlap between the Tm values where reversible and non-reversible thermal denaturation occurred. Indeed, at the highest and lowest Tm no refolding was observed whereas at intermediate values refolding occurred. Furthermore, similar Tm values had different proportions of refolded protein. Using this novel analysis, it was possible to quantify the degree to which protein is lost to irreversible aggregation and show that an increase in the melt transition temperature does not necessarily confer an increase in reversibility. This type of analysis may be a useful tool for the biopharmaceutical and food industries to assess the stability of protein solutions. Bigels are an emerging class of tuneable soft materials composed of two discrete but interpenetrating networks, both of which contribute to the physical and mechanical properties of the material. A bigel network was formed from two proteins, BSA and gelatin. Thorough control of the solution conditions and kinetics ensured that the inter-species attraction between the two protein systems were weak compared to the intra-protein attraction, leading to bigel formation. The protein bigel was shown to have an elastic modulus four times greater than the combined elastic moduli of the parent gels. Furthermore, the elastic response was maintained over several deformation cycles and the gel is both thermo- and chemo-responsive. These gels have the potential to be used in drug delivery, for biomedical applications such as wound healing or as a biomimetic in tissue culture. Cavitation rheology was used to show that for spheroids formed from HEK293 cells the interfacial tension was dominated by cortical tension at length-scales < 30 μm. It was found that the elastic modulus could be related quantitatively to the disruption of cell-cell adhesion molecules which facilitates the formation of the cavity. A cascade of cadherin-cadherin dissociation events, totalling a disrupted surface are equivalent to 3, 8 and 117 cells was calculated for 5, 10 and 30 μm needles, respectively, was calculate. Furthermore, the process involved was shown to be largely elastic and a mechanism involving a rapid cycle of “unzipping” and “re-zipping” the cadherin bonds was proposed to account for this elasticity. Since changes in cortical tension and cell-cell adhesion are associated with the transition from healthy to malignant cells, CR may prove a useful addition to the oncologists’ toolbox

Special functions, transcendentals and their numerics

Cyclotomic polylogarithms are reviewed and new results concerning the special constants that occur are presented. This also allows some comments on previous literature results using PSLQ

The NNLO non-singlet QCD analysis of parton distributions based on Bernstein polynomials

A non-singlet QCD analysis of the structure function $xF_3$ up to NNLO is performed based on the Bernstein polynomials approach. We use recently calculated NNLO anomalous dimension coefficients for the moments of the $xF_3$ structure function in $\nu N$ scattering. In the fitting procedure, Bernstein polynomial method is used to construct experimental moments from the $xF_3$ data of the CCFR collaboration in the region of $x$ which is inaccessible experimentally. We also consider Bernstein averages to obtain some unknown parameters which exist in the valence quark densities in a wide range of $x$ and $Q^2$. The results of valence quark distributions up to NNLO are in good agreement with the available theoretical models. In the analysis we determined the QCD-scale $\Lambda^ {\bar{MS}}_{QCD, N_{f}=4}=211$ MeV (LO), 259 MeV (NLO) and 230 MeV (NNLO), corresponding to $\alpha_s(M_Z^2)=0.1291$ LO, $\alpha_s(M_Z^2)=0.1150$ NLO and $\alpha_s(M_Z^2)=0.1142$ NNLO. We compare our results for the QCD scale and the $\alpha_s(M_Z^2)$ with those obtained from deep inelastic scattering processes.Comment: 20 pages, 7 figures, published in JHE

Light-Ray Evolution Equations and Leading-Twist Parton Helicity-Dependent Nonforward Distributions

We discuss the calculation of the evolution kernels \Delta W_{\zeta}(X,Z) for the leading-twist nonforward parton distributions G_\zeta(X,t) sensitive to parton helicities. We present our results for the kernels governing evolution of the relevant light-ray operators and describe a simple method allowing to obtain from them the components of the nonforward kernels \Delta W_{\zeta}(X,Z).Comment: 8 pages; final version, to appear in Physics Letters

On Sudakov and Soft resummations in QCD

In this article we extract soft distribution functions for Drell-Yan and Higgs production processes using mass factorisation theorem and the perturbative results that are known upto three loop level. We find that they are maximally non-abelien. We show that these functions satisfy Sudakov type integro differential equations. The formal solutions to such equations and also to the mass factorisation kernel upto four loop level are presented. Using the soft distribution function extracted from Drell-Yan production, we show how the soft plus virtual cross section for the Higgs production can be obtained. We determine the threshold resummation exponents upto three loop using the soft distribution function.Comment: 22 pages, no figures. Discussion on soft plus virtual part of Higgs production and DIS adde

The 16th moment of the three loop anomalous dimension of the non-singlet transversity operator in QCD

We present the result of the three loop anomalous dimension of non-singlet transversity operator in QCD for the Mellin moment N=16. The obtained result coincides with the prediction from arXiv:1203.1022 and can serve as a confirmation of the correctness of the general expression for three loop anomalous dimension of non-singlet transversity operator in QCD for the arbitrary Mellin moment.Comment: 7 pages, 1 figure, minor changes in the tex