Deformation Behavior of Clay-Water Suspensions

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Performance Characteristics of Nano-Modified Asphalt Mixtures

The growing need for high quality paving materials has aroused an increasing interest in innovative reinforcing agents, such as those characterized by nanometric dimensions. The experimental study presented in this paper focused on the use in asphalt mixtures of nanoclays and multiwall carbon nanotubes as bitumen modifiers. The performance characteristics of asphalt mixtures containing these nano-sized additives and those of a reference neat mixture were compared in a wide array of temperature and loading conditions. The testing program included the assessment of linear viscoelastic characteristics, anti-rutting potential and crack propagation resistance, by means of stiffness modulus, flow number and semi-circular bending tests, respectively. Results highlighted that both types of nano-additives have the potential to improve the performance properties of neat asphalt mixtures, with nanoclays yielding a superior reinforcing actio

Singular potentials: Confinement and Riemann hypothesis

We analyze the role of singular potentials in quantum mechanics and field theory. In particular, we focus on the conformal invariant potential V (x) = 1/x2 which governs interesting physical phenomena like Efimov effect in atomic and nuclear compounds, quark confinement in QCD, scaling dimensions in the AdS/CFT correspondence, impurity effects in graphene and even models of the P´olya-Hilbert approach to the Riemann hypothesis

The Veneziano amplitude in AdS5×_5 \timesS3^3 from an 8-dimensional effective action

We study four-point functions of arbitrary half-BPS operators in a 4-dimensional $\mathcal{N}=2$ SCFT with flavour group $SO(8)$ at genus-zero and strong 't Hooft coupling, corresponding - via AdS/CFT - to the ($\alpha'$ expansion of the) Veneziano amplitude on an AdS$_5 \times$S$^3$ background. We adapt a procedure first proposed by Abl, Heslop and Lipstein in the context of AdS$_5 \times$S$^5$, and postulate the existence of an effective action in terms of an $8$-dimensional scalar field valued in the adjoint of the flavour group. The various Kaluza-Klein correlators can then be computed by uplifting the standard AdS/CFT prescription to the full product geometry with AdS bulk-to-boundary propagators and Witten diagrams replaced by suitable AdS$_5 \times$S$^3$ versions. After elucidating the main features of the procedure, valid at all orders in $\alpha'$, we show explicit results up to order $\alpha'^{5}$. The results provide further evidence of a novel relation between AdS$\times$S and flat amplitudes - which made its first appearance in $\mathcal{N}=4$ SYM - that is perhaps the most natural extension of the well known flat-space limit proposed by Penedones to cases where AdS and S have the same radius.Comment: 34 page

Bootstrapping string theory on AdS5×S5_5 \times S^5

We make an ansatz for the Mellin representation of the four-point amplitude of half-BPS operators of arbitrary charges at order $\lambda^{-\frac{5}{2}}$ in an expansion around the supergravity limit. Crossing symmetry and a set of constraints on the form of the spectrum uniquely fix the amplitude and double-trace anomalous dimensions at this order. The results exhibit a number of natural patterns which suggest that the bootstrap approach outlined here will extend to higher orders in a simple way.Comment: 6 page

BCJ relations in AdS5×S3{AdS}_5 \times S^3 and the double-trace spectrum of super gluons

We revisit the four-point function of super gluons in $AdS_5 \times S^3$ in the spirit of the large $p$ formalism and show how the integrand of a generalised Mellin transform satisfies various non-trivial properties such as $U(1)$ decoupling identity, BCJ relations and colour-kinematic duality, in a way that directly mirrors the analogous relations in flat space. We unmix the spectrum of double-trace operators at large $N$ and find all anomalous dimensions at leading order. The anomalous dimensions follow a very simple pattern, resembling those of other theories with hidden conformal symmetries.Comment: 9 page

Modification of electronic surface states by graphene islands on Cu(111)

We present a study of graphene/substrate interactions on UHV-grown graphene islands with minimal surface contamination using \emph{in situ} low-temperature scanning tunneling microscopy (STM). We compare the physical and electronic structure of the sample surface with atomic spatial resolution on graphene islands versus regions of bare Cu(111) substrate. We find that the Rydberg-like series of image potential states is shifted toward lower energy over the graphene islands relative to Cu(111), indicating a decrease in the local work function, and the resonances have a much smaller linewidth, indicating reduced coupling to the bulk. In addition, we show the dispersion of the occupied Cu(111) Shockley surface state is influenced by the graphene layer, and both the band edge and effective mass are shifted relative to bare Cu(111).Comment: 12 pages, 3 figure

Experimental investigation on the use of waste elastomeric polymers for bitumen modification

The study described in this paper focused on the possible use of waste products coming from the production of styrene-butadiene rubber (SBR) and polybutadiene rubber (PBR), as bitumen modifiers. Modified binders containing these products were prepared in the laboratory with different polymer dosages and were thereafter subjected to the evaluation of empirical and rheological properties. For comparative purposes, the study also considered SBR and PBR products of premium quality. Ageing effects were also taken into account by means of proper laboratory simulations. Obtained results indicated that the two types of polymer (SBR and PBR) have completely different effects on the rheology and expected performance of the resulting modified binders. In particular, while the two polymers showed similar effects in terms of resistance to permanent deformation, the SBR products proved to be superior from the viewpoint of fatigue resistance. However, only minor differences were found when comparing the effects produced by premium quality and waste polymers. As a result of the experimental findings, it was concluded that the use of waste SBR polymers can be an attractive solution for the production of affordable modified binders