A simple method for the determination of the structure of ultrashort relativistic electron bunches

In this paper we propose a new method for measurements of the longitudinal profile of 100 femtosecond electron bunches for X-ray Free Electron Lasers (XFELs). The method is simply the combination of two well-known techniques, which where not previously combined to our knowledge. We use seed 10-ps 1047 nm quantum laser to produce exact optical replica of ultrafast electron bunches. The replica is generated in apparatus which consists of an input undulator (energy modulator), and the short output undulator (radiator) separated by a dispersion section. The radiation in the output undulator is excited by the electron bunch modulated at the optical wavelength and rapidly reaches 100 MW-level peak power. We then use the now-standard method of ultrashort laser pulse-shape measurement, a tandem combination of autocorrelator and spectrum (FROG -- frequency resolved optical gating). The FROG trace of the optical replica of electron bunch gives accurate and rapid electron bunch shape measurements in a way similar to a femtosecond oscilloscope. Real-time single-shot measurements of the electron bunch structure could provide significant information about physical mechanisms responsible for generation ultrashort electron bunches in bunch compressors. The big advantage of proposed technique is that it can be used to determine the slice energy spread and emittance in multishot measurements. It is possible to measure bunch structure completely, that is to measure peak current, energy spread and transverse emittance as a function of time. We illustrate with numerical examples the potential of the proposed method for electron beam diagnostics at the European X-ray FEL.Comment: 41 pages, 18 figure

Surface and bulk stresses drive morphological changes in fibrous microtissues

Engineered fibrous tissues consisting of cells encapsulated within collagen gels are widely used three-dimensional in vitro models of morphogenesis and wound healing. Although cell-mediated matrix remodeling that occurs within these scaffolds has been extensively studied, less is known about the mesoscale physical principles governing the dynamics of tissue shape. Here, we show both experimentally and by using computer simulations how surface contraction through the development of surface stresses (analogous to surface tension in fluids) coordinates with bulk contraction to drive shape evolution in constrained three-dimensional microtissues. We used microelectromechanical systems technology to generate arrays of fibrous microtissues and robot-assisted microsurgery to perform local incisions and implantation. We introduce a technique based on phototoxic activation of a small molecule to selectively kill cells in a spatially controlled manner. The model simulations, which reproduced the experimentally observed shape changes after surgical and photochemical operations, indicate that fitting of only bulk and surface contractile moduli is sufficient for the prediction of the equilibrium shape of the microtissues. The computational and experimental methods we have developed provide a general framework to study and predict the morphogenic states of contractile fibrous tissues under external loading at multiple length scales.Published versio

Slow relaxation due to optimization and restructuring: Solution on a hierarchical lattice

Motivated by the large strain shear of loose granular materials we introduced a model which consists of consecutive optimization and restructuring steps leading to a self organization of a density field. The extensive connections to other models of statistical phyics are discussed. We investigate our model on a hierarchical lattice which allows an exact asymptotic renormalization treatment. A surprisingly close analogy is observed between the simulation results on the regular and the hierarchical lattices. The dynamics is characterized by the breakdown of ergodicity, by unusual system size effects in the development of the average density as well as by the age distribution, the latter showing multifractal properties.Comment: 11 pages, 7 figures revtex, submitted to PRE see also: cond-mat/020920

CTX: A Clock-Gating-Based Test Relaxation and X-Filling Scheme for Reducing Yield Loss Risk in At-Speed Scan Testing

At-speed scan testing is susceptible to yield loss risk due to power supply noise caused by excessive launch switching activity. This paper proposes a novel two-stage scheme, namely CTX (Clock-Gating-Based Test Relaxation and X-Filling), for reducing switching activity when test stimulus is launched. Test relaxation and X-filling are conducted (1) to make as many FFs inactive as possible by disabling corresponding clock-control signals of clock-gating circuitry in Stage-1 (Clock-Disabling), and (2) to make as many remaining active FFs as possible to have equal input and output values in Stage-2 (FF-Silencing). CTX effectively reduces launch switching activity, thus yield loss risk, even with a small number of donpsilat care (X) bits as in test compression, without any impact on test data volume, fault coverage, performance, and circuit design.2008 17th Asian Test Symposium (ATS 2008), 24-27 November 2008, Sapporo, Japa

Verifying and Monitoring IoTs Network Behavior using MUD Profiles

IoT devices are increasingly being implicated in cyber-attacks, raising community concern about the risks they pose to critical infrastructure, corporations, and citizens. In order to reduce this risk, the IETF is pushing IoT vendors to develop formal specifications of the intended purpose of their IoT devices, in the form of a Manufacturer Usage Description (MUD), so that their network behavior in any operating environment can be locked down and verified rigorously. This paper aims to assist IoT manufacturers in developing and verifying MUD profiles, while also helping adopters of these devices to ensure they are compatible with their organizational policies and track devices network behavior based on their MUD profile. Our first contribution is to develop a tool that takes the traffic trace of an arbitrary IoT device as input and automatically generates the MUD profile for it. We contribute our tool as open source, apply it to 28 consumer IoT devices, and highlight insights and challenges encountered in the process. Our second contribution is to apply a formal semantic framework that not only validates a given MUD profile for consistency, but also checks its compatibility with a given organizational policy. We apply our framework to representative organizations and selected devices, to demonstrate how MUD can reduce the effort needed for IoT acceptance testing. Finally, we show how operators can dynamically identify IoT devices using known MUD profiles and monitor their behavioral changes on their network.Comment: 17 pages, 17 figures. arXiv admin note: text overlap with arXiv:1804.0435

The mechanisms underlying mechanical cell competition and leader cell migration in mammalian epithelia

Cell competition is a form of cell-cell signalling that results in the elimination of less fit cells from a tissue by their fitter counterparts. I take advantage of an established in vitro model of cell competition using Madin-Darby canine kidney (MDCK) cells to shed insight into the molecular basis of cell competition in epithelial cells. In this system, silencing of the tumour suppressor scribble (scribKD) results in a ‘loser’ phenotype whereby scribKD cells are specifically eliminated from the monolayer by surrounding wild-type cells. More specifically, scribKD cells are compacted into tight clones through activation of a directed, collective migration in the wild-type population: scribKD are ‘mechanical losers’ and delaminate and die due to an intrinsic hypersensitivity to high cell density. Remarkably, p53 activation is both necessary and sufficient for this mechanical loser cell status. I first investigate the role of E-, N-, and P-cadherin in the directed migration between scribKD and wild-type cells and in scribKD cell loser status. I show that differential expression of E-cadherin between scribKD losers and wild-type winners is required but not sufficient for directed migration and has no impact on loser cell status. I also show that elevation of neither E-cadherin nor N-cadherin is sufficient to induce directed migration or loser status, but that P-cadherin may play a role in both. I next focus on translating findings about the molecular details of competition from the scribKD set-up into a system where p53 differences alone drive the formation and elimination of mechanical losers. I show that the ROCK – P-p38 – p53 pathway activated in response to mechanical compaction in scribKD cells is conserved in p53-driven losers. In the latter part of my thesis, I characterise the directed migration observed during MDCK competition by drawing parallels to canonical leader-follower migration. Canonical leader cells emerge when epithelial sheets are wounded and, by becoming migratory, drive collective cell migration of follower cells, which results in wound closure. It was not known what confers the leader cell fate. I show that p53 and its effector p21 (and potentially other cyclin-dependent kinase inhibitors) are the key drivers of leader cell migration. I demonstrate that p53-induced leaders use the same molecular pathways that have been shown to drive leader cell migration during wound healing and, in fact, p53 and p21 are also elevated in leaders generated by wounding. Importantly, I establish that p53 activity drives efficient wound closure. Lastly, I show that leader cells are often eliminated by cell competition in the final stages of wound closure, as their elevated p53 mediates their hypersensitivity to density. The model incorporating these data proposes that cellular damage during wounding generates cells with elevated p53, which become leaders and drive wound healing, but these are then cleared once the wound is closed because their high p53 levels cause them to become mechanical losers

Status of Muon Collider Research and Development and Future Plans

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides continued work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (CoM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ($\pi \to \mu \nu_{\mu}$) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. We also present theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics, Accelerators and Beam