Matts Björck

GenX : an extensible X-ray reflectivity refinement program utilizing differential evolution

GenX is a versatile program using the differential evolution algorithm for fitting X-ray and neutron reflectivity data. It utilizes the Parratt recursion formula for simulating specular reflectivity. The program is easily extensible, allowing users to incorporate their own models into the program. This can be useful for fitting data from other scattering experiments, or for any other minimization problem which has a large number of input parameters and/or contains many local minima, where the differential evolution algorithm is suitable. In addition, GenX manages to fit an arbitrary number of data sets simultaneously. The program is released under the GNU General Public License.

Multicentre prospective study of fascial closure rate after open abdomen with vacuum and mesh-mediated fascial traction.

Damage control surgery and temporary open abdomen (OA) have been adopted widely, in both trauma and non‐trauma situations. Several techniques for temporary abdominal closure have been developed. The main objective of this study was to evaluate the fascial closure rate in patients after vacuum‐assisted wound closure and mesh‐mediated fascial traction (VAWCM) for long‐term OA treatment, and to describe complications.

Modern treatment of acute mesenteric ischaemia.

Diagnosis of acute mesenteric ischaemia in the early stages is now possible with modern computed tomography (CT), using intravenous contrast enhancement and imaging in the arterial and/or portal venous phase. The availability of CT around the clock means that more patients with acute mesenteric ischaemia may be treated with urgent intestinal revascularization.

Magnetic anisotropy of tetragonal FeCo/Pt (001) superlattices

The magnetic properties of tetragonally strained Fe0.36Co0.64 alloys in the form of FeCo/Pt(001) superlattices have been investigated experimentally. The strain was controlled by varying the indivi ...

Fitting with differential evolution: an introduction and evaluation

Differential evolution is a global optimization algorithm that has started to find widespread use in the scattering community because of its proven effectiveness. In this article the performance of the algorithm is evaluated by fitting an X-ray reflectivity data set and investigating its convergence behavior as a function of its tuning parameters. The results offer important insights for applying differential evolution algorithms to scattering problems and provide some rules of thumb on how to tune the parameters. It is shown that, by choosing optimal tuning parameter values, the speed of the fitting process can be increased by an order of magnitude.

Remote control of the Fe magnetic moment in magnetic heterostructures

In magnetic superlattices with interlayer exchange coupling, not only the coupling strength but also the magnetic moment of the ferromagnetic layer can be altered non-locally by modifying the electronic structure of the non-magnetic spacer layer. Specifically, changes of the electronic structure of the V spacer layers in Fe/V (001) superlattices are seen to affect the adjacent Fe layers. By reversibly loading the V layer with hydrogen, the magnetic moment of Fe increases, whereas the induced magnetic moment in V remains unchanged. The nature of this remote and non-local control of the magnetic moment is connected with a d-electron charge transfer and effective shift of the Fermi level relative to the d-bands of Fe and V, as elucidated on the basis of self-consistent electronic structure calculations.

Negative-pressure wound therapy for prevention and treatment of surgical-site infections after vascular surgery

Indications for negative‐pressure wound therapy (NPWT) in vascular surgical patients are expanding. The aim of this review was to outline the evidence for NPWT on open and closed wounds.

Structure of Fe-Co/Pt(001) superlattices : a realization of tetragonal Fe-Co alloys

The structural properties of a tetragonally distorted Fe1−xCox alloy, in the form of Fe1−xCox/Pt(001) superlattices with x = 0.64, have been investigated experimentally. The study follows recent theoretical predictions on the enhanced uniaxial magnetocrystalline anisotropy of such alloys with specific combinations of chemical composition and tetragonal distortion. The ratio between out-of-plane and in-plane lattice parameters in the Fe0.36Co0.64 layers, c/a, was found to vary between 1.18 and 1.31, depending on the thickness ratio between the alloy and the spacer. This covered the range of interest c/a = 1.20–1.25 in the previous calculations and should be compared to c/a = 1 in the original bcc alloy lattice. Simulations of x-ray diffraction patterns as well as density functional calculations support the derivation of the Fe0.36Co0.64 lattice parameters.

Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers

To address the amount of disorder and interface diffusion induced by annealing, all-Heusler multilayer structures, consisting of ferromagnetic Co2MnGe and nonmagnetic Rh2CuSn layers of varying thicknesses, have been investigated by means of hard x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. We find evidence for a 4 angstrom thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the unexpectedly small magnetoresistance found for current-perpendicular-to-plane giant magnetoresistance devices based on this all-Heusler system. We find that diffusion begins already at comparably low temperatures between 200 and 250 degrees C, where Mn appears to be most prone to diffusion.

Atomic imaging and direct phase retrieval using anomalous surface x-ray diffraction

The application of multi-wavelength anomalous diffraction to thin films, interfaces and surface structures is presented. The method directly determines the amplitudes and phases of the complex surface structure factors from surface x-ray diffraction data, measured at three different energies around the absorption edge of one of the elements present in the film. Thereby, one is able to directly Fourier transform the data, which immediately provides meaningful and unambiguous electron-density distributions. These serve as a starting point for subsequent structural refinement. The robustness of the algorithm was evaluated on simulated data as a proof of principle. The experimental limitations and their effect on the method will be discussed as well as stability tests for the algorithm, such as the positions of the anomalous scatterers and the interfacial roughness. It will be shown that the method can be applied to real structures. The algorithm was tested on real data from a thin film of SrTiO(3) grown on NdGaO(3)(110).