Modified gravity without dark matter

On an empirical level, the most successful alternative to dark matter in bound gravitational systems is the modified Newtonian dynamics, or MOND, proposed by Milgrom. Here I discuss the attempts to formulate MOND as a modification of General Relativity. I begin with a summary of the phenomenological successes of MOND and then discuss the various covariant theories that have been proposed as a basis for the idea. I show why these proposals have led inevitably to a multi-field theory. I describe in some detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and discuss its successes and shortcomings. This lecture is primarily pedagogical and directed to those with some, but not a deep, background in General RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School, The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected, references update

EpCAM as multi-tumour target for near-infrared fluorescence guided surgery

Background: Evaluation of resection margins during cancer surgery can be challenging, often resulting in incomplete tumour removal. Fluorescence-guided surgery (FGS) aims to aid the surgeon to visualize tumours and resection margins during surgery. FGS relies on a clinically applicable imaging system in combination with a specific tumour-targeting contrast agent. In this study EpCAM (epithelial cell adhesion molecule) is evaluated as target for FGS in combination with the novel Artemis imaging system. Methods: The NIR fluorophore IRDye800CW was conjugated to the well-established EpCAM specific monoclonal antibody 323/A3 and an isotype IgG1 as control. The anti-EpCAM/800CW conjugate was stable in serum and showed preserved binding capacity as evaluated on EpCAM positive and negative cell lines, using flow cytometry and cell-based plate assays. Four clinically relevant orthotopic tumour models, i.e. colorectal cancer, breast cancer, head and neck cancer, and peritonitis carcinomatosa, were used to evaluate the performance of the anti-EpCAM agent with the clinically validated Artemis imaging system. The Pearl Impulse small animal imaging system was used as reference. The specificity of the NIRF signal was confirmed using bioluminescence imaging and green-fluorescent protein. Results: All tumour types could clearly be delineated and resected 72 h after injection of the imaging agent. Using NIRF imaging millimetre sized tumour nodules were detected that were invisible for the naked eye. Fluorescence microscopy demonstrated the distribution and tumour specificity of the anti-EpCAM agent. Conclusions: This study shows the potential of an EpCAM specific NIR-fluorescent agent in combination with a clinically validated intraoperative imaging system to visualize various tumours during surgery

Multiscale formulation for material failure accounting for cohesive cracks at the macro and micro scales

This contribution presents a two-scale formulation devised to simulate failure in materials with het- erogeneous micro-structure. The mechanical model accounts for the activation of cohesive cracks in the micro-scale domain. The evolution/propagation of cohesive micro-cracks can induce material instability at the macro-scale level. Then, a cohesive crack is activated in the macro-scale model which considers, in a homogenized sense, the constitutive response of the intricate failure mode taking place in the smaller length scale.The two-scale model is based on the concept of Representative Volume Element (RVE). It is designed following an axiomatic variational structure. Two hypotheses are introduced in order to build the foundations of the entire two-scale theory, namely: (i) a mechanism for transferring kinematical information from macro- to-micro scale along with the concept of “Kinematical Admissibility”, relating both primal descriptions, and (ii) a Multiscale Variational Principle of internal virtual power equivalence between the involved scales of analysis. The homogenization formulae for the generalized stresses, as well as the equilibrium equations at the micro-scale, are consequences of the variational statement of the problem.The present multiscale technique is a generalization of a previous model proposed by the authors and could be viewed as an application of a general framework recently proposed by the authors. The main novelty in this article lies on the fact that failure modes in the micro-structure now involve a set of multiple cohesive cracks, connected or disconnected, with arbitrary orientation, conforming a complex tortuous failure path. Tortuosity is a topic of decisive importance in the modelling of material degradation due to crack propagation. Following the present multiscale modelling approach, the tortuosity effect is introduced in order to satisfy the “Kinematical Admissibility” concept, when the macro-scale kinematics is transferred into the micro-scale domain. There- fore, it has a direct consequence in the homogenized mechanical response, in the sense that the proposed scale transition method (including the tortuosity effect) retrieves the correct post-critical response.Coupled (macro-micro) numerical examples are presented showing the potentialities of the model to sim- ulate complex and realistic fracture problems in heterogeneous materials. In order to validate the multiscale technique in a rigorous manner, comparisons with the so-called DNS (Direct Numerical Solution) approach are also presented

Two Types of Planning in Neighborhoods

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68338/2/10.1177_0739456X8400300209.pd