Comparison of computational codes for direct numerical simulations of turbulent Rayleigh-B\'enard convection

Computational codes for direct numerical simulations of Rayleigh-B\'enard (RB) convection are compared in terms of computational cost and quality of the solution. As a benchmark case, RB convection at $Ra=10^8$ and $Pr=1$ in a periodic domain, in cubic and cylindrical containers is considered. A dedicated second-order finite-difference code (AFID/RBflow) and a specialized fourth-order finite-volume code (Goldfish) are compared with a general purpose finite-volume approach (OpenFOAM) and a general purpose spectral-element code (Nek5000). Reassuringly, all codes provide predictions of the average heat transfer that converge to the same values. The computational costs, however, are found to differ considerably. The specialized codes AFID/RBflow and Goldfish are found to excel in efficiency, outperforming the general purpose flow solvers Nek5000 and OpenFOAM by an order of magnitude with an error on the Nusselt number $Nu$ below $5\%$. However, we find that $Nu$ alone is not sufficient to assess the quality of the numerical results: in fact, instantaneous snapshots of the temperature field from a near wall region obtained for deliberately under-resolved simulations using Nek5000 clearly indicate inadequate flow resolution even when $Nu$ is converged. Overall, dedicated special purpose codes for RB convection are found to be more efficient than general purpose codes.Comment: 12 pages, 5 figure

Dynamic Behavior in Piezoresponse Force Microscopy

Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM) implemented on a beam-deflection atomic force microscope (AFM) is analyzed using a combination of modeling and experimental measurements. The PFM signal comprises contributions from local electrostatic forces acting on the tip, distributed forces acting on the cantilever, and three components of the electromechanical response vector. These interactions result in the bending and torsion of the cantilever, detected as vertical and lateral PFM signals. The relative magnitudes of these contributions depend on geometric parameters of the system, the stiffness and frictional forces of tip-surface junction, and operation frequencies. The dynamic signal formation mechanism in PFM is analyzed and conditions for optimal PFM imaging are formulated. The experimental approach for probing cantilever dynamics using frequency-bias spectroscopy and deconvolution of electromechanical and electrostatic contrast is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques

Standard Model Higgs boson production in association with a top anti-top pair at NLO with parton showering

We present predictions for the production cross section of a Standard Model Higgs boson in association with a top-antitop pair at next-to-leading order accuracy using matrix elements obtained from the HELAC-Oneloop package. The NLO prediction was interfaced to the PYTHIA and HERWIG shower Monte Carlo programs with the help of POWHEG-Box, allowing for decays of massive particles, showering and hadronization, thus leading to final results at the hadron level.Comment: 14 pages, 9 figure

Automation of one-loop QCD corrections

We present the complete automation of the computation of one-loop QCD corrections, including UV renormalization, to an arbitrary scattering process in the Standard Model. This is achieved by embedding the OPP integrand reduction technique, as implemented in CutTools, into the MadGraph framework. By interfacing the tool so constructed, which we dub MadLoop, with MadFKS, the fully automatic computation of any infrared-safe observable at the next-to-leading order in QCD is attained. We demonstrate the flexibility and the reach of our method by calculating the production rates for a variety of processes at the 7 TeV LHC.Comment: 64 pages, 12 figures. Corrected the value of m_Z in table 1. In table 2, corrected the values of cross sections in a.4 and a.5 (previously computed with mu=mtop/2 rather than mu=mtop/4). In table 2, corrected the values of NLO cross sections in b.3, b.6, c.3, and e.7 (the symmetry factor for a few virtual channels was incorrect). In sect. A.4.3, the labeling of the four-momenta was incorrec

MadGraph/MadEvent v4: The New Web Generation

We present the latest developments of the MadGraph/MadEvent Monte Carlo event generator and several applications to hadron collider physics. In the current version events at the parton, hadron and detector level can be generated directly from a web interface, for arbitrary processes in the Standard Model and in several physics scenarios beyond it (HEFT, MSSM, 2HDM). The most important additions are: a new framework for implementing user-defined new physics models; a standalone running mode for creating and testing matrix elements; generation of events corresponding to different processes, such as signal(s) and backgrounds, in the same run; two platforms for data analysis, where events are accessible at the parton, hadron and detector level; and the generation of inclusive multi-jet samples by combining parton-level events with parton showers. To illustrate the new capabilities of the package some applications to hadron collider physics are presented: 1) Higgs search in pp \to H \to W^+W^-: signal and backgrounds. 2) Higgs CP properties: pp \to H jj$in the HEFT. 3) Spin of a new resonance from lepton angular distributions. 4) Single-top and Higgs associated production in a generic 2HDM. 5) Comparison of strong SUSY pair production at the SPS points. 6) Inclusive W+jets matched samples: comparison with the Tevatron data.Comment: 38 pages, 15 figure

Micro- and nanosystems for biology and medicine

The development of new tools and instruments for biomedical applications based on nano- (NEMS) or microelectromechanical systems technology (MEMS) are bridging the gap between the macro- and the nano-world. The well mastered microtechnique allows controlling many parameters of these instruments, which is essential for conducting reproducible and repeatable experiments in the life sciences. Examples are multifunctional scanning probe sensors for cell biology, an arthroscopic scanning force microscope for minimally invasive medical interventions and a nanopore sensor for single molecule experiments in biochemistry. This paper reviews some of the activities conducted in a fruitful interdisciplinary collaboration between physicists, engineers, biologists and physicians

Polarizing the Dipoles

We extend the massless dipole formalism of Catani and Seymour, as well as its massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, to arbitrary helicity eigenstates of the external partons. We modify the real radiation subtraction terms only, the primary aim being an improved efficiency of the numerical Monte Carlo integration of this contribution as part of a complete next-to-leading order calculation. In consequence, our extension is only applicable to unpolarized scattering. Upon summation over the helicities of the emitter pairs, our formulae trivially reduce to their original form. We implement our extension within the framework of Helac-Phegas, and give some examples of results pertinent to recent studies of backgrounds for the LHC. The code is publicly available. Since the integrated dipole contributions do not require any modifications, we do not discuss them, but they are implemented in the software.Comment: 20 pages, 4 figures, Integrated dipoles implemented for massless and massive case

Silicon resonant microcantilevers for absolute pressure measurement

This work is focused on the developing of silicon resonant microcantilevers for the measurement of the absolute pressure. The microcantilevers have been fabricated with a two-mask bulk micromachining process. The variation in resonance response of microcantilevers was investigated as a function of pressure 10−1-105 Pa, both in terms of resonance frequency and quality factor. A theoretical description of the resonating microstructure is given according to different molecular and viscous regimes. Also a brief discussion on the different quality factors contributions is presented. Theoretical and experimental data show a very satisfying agreement. The microstructure behavior demonstrates a certain sensitivity over a six decade range and the potential evolution of an absolute pressure sensor working in the same rang

Les Houches 2015: Physics at TeV Colliders Standard Model Working Group Report

This Report summarizes the proceedings of the 2015 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) the new PDF4LHC parton distributions, (III) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (IV) a host of phenomenological studies essential for comparing LHC data from Run I with theoretical predictions and projections for future measurements in Run II, and (V) new developments in Monte Carlo event generators.Comment: Proceedings of the Standard Model Working Group of the 2015 Les Houches Workshop, Physics at TeV Colliders, Les Houches 1-19 June 2015. 227 page