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- A Bakk, J S Høye, A Hansen, K Sneppen, M H Jensen
- Biophysical journal
- 2000

Thermodynamic measurements of proteins indicate that the folding to the native state takes place either through stable intermediates or through a two-state process without intermediates. The rather short folding times of proteins indicate that folding is guided through some sequence of contact bindings. We discuss the possibility of reconciling a two-state… (More)

Technical details are given on how to use Fourier acceleration with iterative processes such as relaxation and conjugate gradient methods. These methods are often used to solve large linear systems of equations, but become hopelessly slow very rapidly as the size of the set of equations to be solved increases. Fourier acceleration is a method designed to… (More)

- Dirk Helbing, Anders Johansson, Joachim Mathiesen, Mogens H Jensen, Alex Hansen
- Physical review letters
- 2006

We propose a many-particle-inspired theory for granular outflows from a hopper and for the escape dynamics through a bottleneck based on a continuity equation in polar coordinates. If the inflow is below the maximum outflow, we find an asymptotic stationary solution. If the inflow is above this value, we observe queue formation, which can be described by a… (More)

- Srutarshi Pradhan, Alex Hansen, Bikas K. Chakrabarti, Bidhan Nagar
- 2008

The fiber bundle model describes a collection of elastic fibers under load. The fibers fail sucessively and for each failure, the load distribution among the surviving fibers changes. Even though very simple, this model captures the essentials of failure processes in a large number of materials and settings. We present here a review of the fiber bundle… (More)

- Srutarshi Pradhan, Alex Hansen, Per C Hemmer
- Physical review letters
- 2005

The statistics of damage avalanches during a failure process typically follows a power law. When these avalanches are recorded only near the point at which the system fails catastrophically, one finds that the power law has an exponent which is different from that one finds if the recording of events starts away from the vicinity of catastrophic failure. We… (More)

The folded conformation of globular proteins is a state of matter peculiar in more than one respect. The density is that of a condensed phase (solid or liquid), and the relative position of the atoms is, on average, fixed; these are the characteristics of the solid state. However, solids are either crystalline or amorphous, and proteins are neither: the… (More)

- Alex Hansen, Jean Schmittbuhl
- Physical review letters
- 2003

We suggest that the observed large-scale universal roughness of brittle fracture surfaces is due to the fracture propagation being a damage coalescence process described by a stress-weighted percolation phenomenon in a self-generated quadratic damage gradient. We use the quasistatic 2D fuse model as a paradigm of a mode I fracture model. We measure for this… (More)

- Christian André Andresen, Alex Hansen, Jean Schmittbuhl
- Physical review. E, Statistical, nonlinear, and…
- 2007

The network formed by ridges in a straightened sheet of crumpled paper is studied using a laser profilometer. Square sheets of paper were crumpled into balls, unfolded, and their height profile measured. From these profiles the imposed ridges were extracted as networks. Nodes were defined as intersections between ridges, and links as the various ridges… (More)

We study the size distribution of power blackouts for the Norwegian and North American power grids. We find that for both systems the size distribution follows power laws with exponents −1.65 ± 0.05 and −2.0 ± 0.1 respectively. We then present a model with global redistribution of the load when a link in the system fails which reproduces the power law from… (More)

- Stéphane Santucci, Knut Jørgen Måløy, +6 authors Purusattam Ray
- Physical review. E, Statistical, nonlinear, and…
- 2007

We analyze the statistical distribution function for the height fluctuations of brittle fracture surfaces using extensive experimental data sampled on widely different materials and geometries. We compare a direct measurement of the distribution to an analysis based on the structure functions. For length scales delta larger than a characteristic scale… (More)