Stable Moduli Research Articles

Effect of Side Groups on the Hydrolytic Stability of Thiolated and Disulfide Cross-linked Polyaspartamides

Thiolated polyaspartamides either with N,N-dimethyl-2-aminoethyl (DME), N,N-dimethyl-3-aminopropyl (DMP) or 2-hydroxyethyl (HE) side groups were synthesized to study the effect of side groups on the hydrolytic stability of these polymers. The chemical structure of linear polymers was confirmed by 1H NMR spectroscopy, while thiol content was determined by Ellman's assay. Hydrolytic stability of thiolated polyaspartamides was studied by viscosity measurements and results suggested main-chain degradation in the presence of DME side groups. Polyaspartamides with DMP or HE side groups showed considerable stability. Thiolated polyaspartamides were converted to their disulfide cross-linked hydrogels and the gelation process was followed by oscillatory rheology. Time-dependence of dynamic moduli indicated the degradation of hydrogels containing DME side groups, while stable moduli were observed for hydrogels containing DMP or HE side groups. This structure-dependent aqueous degradation of polyaspartamides can be useful in different biomedical fields.

Operations on stable moduli spaces

We construct certain operations on stable moduli spaces and use them to compare cohomology of moduli spaces of closed manifolds with tangential structure. We obtain isomorphisms in a stable range provided the p-adic valuation of the Euler characteristics agree, for all primes p not invertible in the coefficients for cohomology.

Homological stability and stable moduli of flat manifold bundles

We prove that the group homology of the diffeomorphism group of #gSn×Sn\\int(D2n) as a discrete group is independent of g in a range, provided that n>2. This answers the high dimensional version of a question posed by Morita about surface diffeomorphism groups made discrete. The stable homology is isomorphic to the homology of a certain infinite loop space related to the Haefliger's classifying space of foliations. One geometric consequence of this description of the stable homology is a splitting theorem that implies certain classes called generalized Mumford–Morita–Miller classes lift to a secondary R/Z-invariants for flat (#gSn×Sn)-bundles provided g≫0.

The type IIB string axiverse and its low-energy phenomenology

Abstract We study closed string axions in type IIB orientifold compactifications. We show that for natural values of the background fluxes the moduli stabilisation mechanism of the LARGE Volume Scenario (LVS) gives rise to an axiverse characterised by the presence of a QCD axion plus many light axion-like particles whose masses are logarithmically hierarchical. We study the phenomenological features of the LVS axiverse, deriving the masses of the axions and their couplings to matter and gauge fields. We also determine when closed string axions can solve the strong CP problem, and analyse the first explicit examples of semi-realistic models with stable moduli and a QCD axion candidate which is not eaten by an anomalous Abelian gauge boson. We discuss the impact of the choice of inflationary scenario on the LVS axiverse, and summarise the astrophysical, cosmological and experimental constraints upon it. Moreover, we show how models can be constructed with additional light axion-like particles that could explain some intriguing astrophysical anomalies, and could be searched for in the next generation of axion helioscopes and light-shining-through-a-wall experiments.

On open membranes, cosmic strings and moduli stabilization

We discuss how cosmic strings can be created in heterotic M-theory compactifications with stable moduli. We conclude that the only appropriate candidates seem to be fundamental open membranes with a small length. In four dimensions they will appear as strings with a small tension. We make an observation that, in the presence of the vector bundle moduli, it might be possible to stabilize a five-brane very close to the visible sector so that a macroscopic open membrane connecting this five-brane and the visible brane will have a sufficiently small length. We also discuss how to embed such cosmic strings in heterotic models with stable moduli and whether they can be created after inflation.

Characterization of surgical suture materials using dynamic mechanical analysis

Dynamic mechanical analysis (DMA) has been used to characterize the viscoelastic properties of four suture materials, Prolene®, Maxon®, Vicryl® and silk. The technique identified the main transitions for the sutures and frequency multiplexing was used to define the variation of modulus with time. The monofilament Prolene has a β transition and the monofilament Maxon has an α transition close to room temperature, indicating that both materials exhibit a change in stiffness with time. The α transitions ( T g s) of silk and Vicryl occur at temperatures significantly above room temperature and frequency multiplexing data indicate that both materials exhibit stable moduli with respect to time at room temperature. Determination of the viscoelastic behaviour through DMS appears to be very useful in predicting the performance of suture materials.