We have directly measured the energy threshold and efficiency for bubble nucleation from iodine recoils in a CF3I bubble chamber in the energy range of interest for a dark matter search. These interactions cannot be probed by standard neutron calibration methods, so we develop a new technique by observing the elastic scattering of 12 GeV/c negative pions. The pions are tracked with a silicon pixel telescope and the reconstructed scattering angle provides a measure of the nuclear recoil kinetic energy. The bubble chamber was operated with a nominal threshold of (13.6 ± 0.6) keV. Interpretation of the results depends on the response to fluorine and carbon recoils, but in general we find agreement with the predictions of the classical bubble nucleation theory. This measurement confirms the applicability of CF3I as a target for spin-independent dark matter interactions and represents a novel technique for calibration of superheated fluid detectors. PACS numbers: 29.40.-n, 95.35.+d, 95.30.Cq, FERMILAB-PUB-10-318-A-CD-ERecent years have seen a resurgence in the use of superheated liquids and bubble chambers as continuously sensitive nuclear recoil detectors searching for dark matter in the form of Weakly Interacting Massive Particles (WIMPs) [1][2][3]. At a low degree of superheat, bubble chambers are insensitive to minimum ionizing backgrounds that normally plague WIMP searches but retain sensitivity to the nuclear recoils that would be characteristic of WIMP scattering. In a superheated liquid the process of radiation-induced bubble nucleation is described by the classical "hot spike" model [4]. For the phase transition to occur, the energy deposited by the particle must create a critically sized bubble, requiring a minimum energy deposition in a volume smaller than the critical bubble. Under mildly superheated conditions, the latter requirement renders the bubble chamber insensitive to minimum ionizing particles.The radius of the critical bubble is given by the condition that the bubble be in (unstable) equilibrium with the surrounding superheated fluid [5]. This demands the pressure balancewhere P b is the pressure inside the bubble, P l is the pressure in the liquid, σ is the bubble surface tension, and r c is the critical bubble radius. The pressure P b is fixed by the condition that the chemical potential inside and outside the bubble be equal, givingwhere P sat is the pressure in a saturated system at the given temperature, and ρ l and ρ v are the liquid and vapor densities in the saturated system [6].In Seitz's "hot spike" model for bubble nucleation, the entire energy necessary to create the critical bubble must come from the particle interaction that nucleates the bubble. This is in contrast to earlier models that required only the work (free energy) to come from the particle interaction, with the remaining bubble-formation energy supplied by heat flowing in from the surrounding superheated fluid [7]. As the name "hot spike" implies, the nucleation site in Seitz's model begins as a hightemperature seed, so i...

We present a numerical method which exploits the biorthogonal interpolating wavelet family, and second-generation wavelets, to solve initial-boundary value problems on finite domains. Our predictor-corrector algorithm constructs a dynamically adaptive computational grid with significant data compression, and provides explicit error control. Error estimates are provided for the wavelet representation of functions, their derivatives, and the nonlinear product of functions. The method is verified on traditional nonlinear problems such as Burgers' equation and the Sod shock tube. Numerical analysis shows polynomial convergence with negligible global energy dissipation.

This paper proposes a novel method to accurately and efficiently reduce a microstructural mechanical model using a wavelet based discretisation. The model enriches a standard reduced order modelling (ROM) approach with a wavelet representation. Although the ROM approach reduces the dimensionality of the system of equations, the computational complexity of the integration of the weak form remains problematic. Using a sparse wavelet representation of the required integrands, the computational cost of the assembly of the system of equations is reduced significantly. This wavelet-reduced order model (W-ROM) is applied to the mechanical equilibrium of a microstructural volume as used in a computational homogenisation framework. The reduction technique however is not limited to micro-scale models and can also be applied to macroscopic problems to reduce the computational costs of the integration. For the sake of clarity, the W-ROM will be demonstrated using a one-dimensional example, providing full insight in the underlying steps taken.

Modeling and simulation have quickly become equivalent pillars of research along with traditional theory and experimentation. The growing realization that most complex phenomena of interest span many orders of spatial and temporal scales has led to an exponential rise in the development and application of multiscale modeling and simulation over the past two decades. In this perspective, the associate editors of the International Journal for Multiscale Computational Engineering and their co-workers illustrate current applications in their respective fields spanning biomolecular structure and dynamics, civil engineering and materials science, computational mechanics, aerospace and mechanical engineering, and more. Such applications are highly tailored, exploit the latest and ever-evolving advances in both computer hardware and software, and contribute significantly to science, technology, and medical challenges in the 21st century.

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