arXiv subjects

H. Ballhausen

Publications and source records attributed to H. Ballhausen.

7 recordsLinked to original sources

arXiv2006

Imaging with Scattered Neutrons

We describe a novel experimental technique for neutron imaging with scattered neutrons. These scattered neutrons are of interest for condensed matter physics, because they permit to reveal the local distribution of incoherent and coherent scattering within a sample. In contrast to standard attenuation based imaging, scattered neutron imaging distinguishes between the scattering cross section and the total attenuation cross section including absorption. First successful low-noise millimeter-resolution images by scattered neutron radiography and tomography are presented.

nucl-ex↗

arXiv2006

Neutron Radiography Analysis of a Transient Liquid Phase Joint

Neutron radiography in many cases is the only non-destructive technique available for the analysis of a wide range of samples from metallurgy, materials engineering and materials testing. In this paper the potential of the technique is illustrated for a transient liquid phase (TLP) joint. TLP bonding produces interface free and stress free joints. The quality and properties of the joint depend on the diffusion of an interlayer into the base material. A TLP joint is visualised and the diffusion profile of the boron contained in the bonding additives is determined. Parameters of the bonding process are determined quantitatively from this profile, and flaws in the joint are detected.

cond-mat.mtrl-sci↗

arXiv2004

Critical Phenomena in Continuous Dimension

We present a calculation of critical phenomena directly in continuous dimension d employing an exact renormalization group equation for the effective average action. For an Ising-type scalar field theory we calculate the critical exponents nu(d) and eta(d) both from a lowest--order and a complete first--order derivative expansion of the effective average action. In particular, this can be used to study critical behavior as a function of dimensionality at fixed temperature.

hep-th↗

arXiv2004

The Effective Average Action Beyond First Order

A derivative expansion of the effective average action beyond first order yields renormalization group functional flow equations which are used for the computation of critical exponents of the Ising universality class. The critical exponent nu in D=3 is consistent with high-precision methods.

hep-th↗

arXiv2003

Critical Exponents from Dimensional Variation

Recent work on exact renormalization group flow equations has pointed out the possibility to study critical phenomena in continuous dimension D of space. In an investigation of the O(N) model the dimension N of the fields may be seen as a continuous parameter as well. One may conjecture that a variation of D or N in the vicinity of a second order phase transition yields the same critical exponents as a variation of the temperature. A numerical computation confirms this.

hep-th↗

arXiv2003

Direct Calculation of the Critical Effective Potential

The critical effective potential is the nonperturbative part of the effective action at a phase transition. It equals the scale invariant effective average potential and can be calculated from the renormalization group flow of the effective average action. In some cases this requires only the solution of an ordinary differential equation without actually simulating the renormalization group flow. Here the Ising model is examined beyond leading order and with full field dependent effective potential.

hep-th↗

arXiv2003

Fair Solution to the Reader-Writer-Problem with Semaphores only

The reader-writer-problem is a standard problem in concurrent programming. A resource is shared by several processes which need either inclusive reading or exclusive writing access. The known solutions to this problem typically involve a number of global counters and queues. Here a very simple algorithm is presented which needs only two semaphores for synchronisation and no other global objects. The approach yields a fair solution without starving.

cs.DC↗