Nmag micromagnetic simulation tool - software engineering lessons learned

We review design and development decisions and their impact for the open source code Nmag from a software engineering in computational science point of view. We summarise lessons learned and recommendations for future computational science projects. Key lessons include that encapsulating the simulation functionality in a library of a general purpose language, here Python, provides great flexibility in using the software. The choice of Python for the top-level user interface was very well received by users from the science and engineering community. The from-source installation in which required external libraries and dependencies are compiled from a tarball was remarkably robust. In places, the code is a lot more ambitious than necessary, which introduces unnecessary complexity and reduces main- tainability. Tests distributed with the package are useful, although more unit tests and continuous integration would have been desirable. The detailed documentation, together with a tutorial for the usage of the system, was perceived as one of its main strengths by the community.Comment: 7 pages, 5 figures, Software Engineering for Science, ICSE201

Multiphysics simulations of magnetic nanostructures

Multiphysics simulations of magnetic nanostructures by Matteo Franchin.In recent years the research on magnetism has seen a new trend emerging, characterised by considerable effort in developing new nanostructures and finding new ways to control and manipulate their magnetisation, such as using spin polarised currents or light pulses. The field of magnetism is thus moving towards the multiphysics direction, since it is increasingly studied in conjunction with other types of physics, such as electric and spin transport, electromagnetic waves generation and absorption, heat generation and diffusion. Understanding these new phenomena is intriguing and may lead to major technological advances. Computer simulations are often invaluable to such research, since they offer a way to predict and understand the physics of magnetic nanostructures and help in the design and optimisation of new devices.For the preparation of this thesis the Nmag multiphysics micromagnetic simulation package has been further developed and improved by the author. The software has also been extended in order to model exchange spring systems. Using Nmag, we carried out micromagnetic simulations in order to characterise the magnetisation dynamics in exchange spring systems and derived analytical models to validate and gain further insight into the numerical results. We found that the average magnetisation moves in spiral trajectories near equilibrium and becomes particularly soft (low oscillation frequency and damping, high amplitude) when the applied field is close to a particular value, called the bending field.We studied spin transport in exchange spring systems and investigated new geometries and setups in order to maximise the interaction between spin polarised current and magnetisation. We found that by engineering a trilayer exchange spring system in the form of a cylindrical nanopillar, it is possible to obtain microwave emission with frequencies of 5-35 GHz for applied current densities between 0.5-2.0 x 1011 A/m2 and without the need for an externally applied magnetic field. We proposed a one dimensional analytical model and found a formula which relates the emission frequency to the geometrical parameters and the current density

Nephrology@Point of Care: A New Journal for Hands-On Clinicians

Stenosis and thrombosis are common causes of prosthetic vascular access (pVA) failure. The role of arteriovenous fistula (AVF) surveillance is widely debated. The aim of this paper is to present a new real-time application designed for AVF surveillance called SPIDER. Surgical staff and hemodialysis nurses are responsible for data entry. SPIDER automatically analyses data and generates alerts in case of abnormal trends. Surgical evaluation and duplex Doppler ultrasonography are then immediately performed to confirm presence of stenosis or other possible pVA defects. Surgery can be performed if required. A preliminary analysis of results will be completed at 12 months after the program begins and subsequently after 24 months. Primary assisted patency will be compared with historical using multivariate analysis. Expected results are an improvement in primary assisted pVA patency and reduction of hospitalizations. Simultaneous management of a high number of patients can become difficult due to the large amount of data required for surveillance. We want to demonstrate whether a real-time automated system could help to prevent thrombosis and graft loss

Effect of rounded corners on the magnetic properties of pyramidal-shaped shell structures

In recent years, the advance of novel chemical growth techniques has led to the fabrication of complex, three-dimensional magnetic nanostructures. The corners and edges of such realistic geometries are generally not sharp but rounded. In a previous article we have argued that high demagnetization fields in the vicinity of sharp edges lead to the formation of an asymmetric vortex state in pyramidal-shaped magnetic shell structures. The asymmetric vortex state is potentially interesting with respect to future magnetic memory devices. In this work a micromagnetic model is used to investigate the effect of rounded corners and edges on the magnetic reversal process within these pyramidal-shaped magnetic shell structures. In particular, we explore the degree of rounding, which has to be introduced in order to suppress the asymmetric vortex state. Another emphasis is placed on the magnetic reversal of (quasi-)homogeneous states within these structures. We demonstrate that the rounding of corners significantly reduces the coercivity. This complies with former studies on cuboidal structures, which suggest the important effect of corners on the magnetic reversal of homogeneous magnetic states. The present study uses a finite-element discretization for the numerical solution of the micromagnetic equations, which provides flexibility with respect to the modeling of complex shapes. In particular, this method is very accurate with respect to structures with a smooth surface

A new approach to (quasi) periodic boundary conditions in micromagnetics: the macrogeometry

We present a new method to simulate repetitive ferromagnetic structures. This macro geometry approach combines treatment of short-range interactions (i.e. the exchange field) as for periodic boundary conditions with a specification of the arrangement of copies of the primary simulation cell in order to correctly include effects of the demagnetizing field. This method (i) solves a consistency problem that prevents the naive application of 3d periodic boundary conditions in micromagnetism and (ii) is well suited for the efficient simulation of repetitive systems of any size

Spin-polarized currents in exchange spring systems

We present a computational study of the magnetization dynamics of a trilayer exchange spring system in the form of a cylindrical nanopillar in the presence of an electric current. A three-dimensional micromagnetic model is used, where the interaction between the current and the local magnetization is taken into account following a recent model by Zhang and Li [Phys. Rev. Lett. 93, 127204 (2004)] We obtain a stationary rotation of the magnetization of the system around its axis, accompanied by a compression of the artificial domain wall in the direction of the electron flow

Magnetic switching modes for exchange spring systems ErFe2/YFe2/DyFe2/YFe2 with competing anisotropies

The magnetization reversal processes of ½10nm ErFe2=nYFe2=4nm DyFe2=nYFe2" multilayer films with a (110) growth axis and a variable YFe2 layer thickness n are investigated. The magnetically soft YFe2 compound acts as a separator between the hard rare earth (RE) ErFe2 and DyFe2 compounds, each of them bearing different temperature dependent magnetic anisotropy properties. Magnetic measurements of a system with n ¼ 20nm reveal the existence of three switching modes: an independent switching mode at low temperatures, an ErFe2 spin flop switching mode at medium high temperatures, and an YFe2 dominated switching mode at high temperatures. The measurements are in qualitative agreement with the findings of micromagnetic simulations which are used to illustrate the switching modes. Further simulations for a varied YFe2 layer thickness n ranging from 2 to 40nm are carried out. Quantitative criteria are defined to classify the reversal behavior, and the resultant switching modes are laid out in a map with regard to n and the temperature T. A new coupled switching mode emerges above a threshold temperature for samples with thin YFe2 separation layers as a consequence of the exchange coupling between the magnetically hard ErFe2 and DyFe2 layers. It reflects the increasing competition of the two conflicting anisotropies to dominate the magnetic switching states of both RE compounds under decreasing n

what does early mean remarks on immediate prosthetic vascular access cannulation for urgent hemodialysis

Management of complicated vascular access. A step-by-step description of a case of hyperkalemia and vascular access failure in a patient receiving maintenance hemodialysis treated for numerous prev..

Total endovascular treatment for extent type 1 and 5 thoracoabdominal aortic aneurysms

OBJECTIVE: The study objective was to describe the results of thoracic endovascular aortic repair with the intentional coverage of the celiac artery and distal supramesenteric landing zone for extent type 1 and type 5 thoracoabdominal aortic aneurysms. METHODS: Inclusion criteria were thoracic endovascular aortic repair with celiac artery coverage to treat elective or urgent extent type 1 and 5 thoracoabdominal aortic aneurysms. Primary end points were in-hospital and follow-up survival, freedom from aortic-related mortality, and freedom from reintervention. RESULTS: Thoracoabdominal disease extent was type 1 in 12 patients (71%) and type 5 in 5 patients (29%). Urgent repair was performed in 4 patients (23.5%). Primary technical success was 100%. Early mortality and visceral ischemia did not occur. Permanent spinal cord ischemia rate was 6% (n = 1). Follow-up ranged from 3 to 120 months (interquartile range, 12-36.5). Survival estimate was 85% \ub1 9% (95% confidence interval, 67-94) at 1 year and 49% \ub1 17% (95% confidence interval, 21-78) at 5 years. Cumulative freedom from aortic-related mortality was 94%, and estimated freedom from reintervention at 1 and 5 years was 93% \ub1 7% (95% confidence interval, 68-99). Neither type 1 endoleaks nor distal stent-graft migration causing superior mesenteric artery occlusion was detected. CONCLUSIONS: Thoracic endovascular aortic repair with intentional coverage of celiac artery for extent 1 and 5 thoracoabdominal aortic aneurysms had satisfactory results in selected patients at high risk for open repair. Visceral ischemia did not occur, but spinal cord ischemia is still high at 6%. At midterm follow-up, neither endoleak development nor aortic reintervention was related to the inadequate distal landing zone. Follow-up survival is satisfactory and comparable to open repair

Reliability analysis of GEM® Premier™ technology: a multicenter study

This paper describes how specific blood gas analyzer characteristics can support the emerging clinical and organizational user's needs while ensuring patient safety. A oneyear data set from two Italian hospitals was analyzed from 10 different blood gas analyzers. Performance measurements in terms of mean down time (MDT) were calculated to show how technical characteristics declared by the manufacturer compare to the analyzer availability in real clinical settings. Results show a high level of reliability for the analyzed technology, associated with very low MDT of each sensor integrated in the cartridge. Moreover, results show a high level of efficiency in cartridge usage. Such results are consistent with the specification of the GEM® Premier™ maintenance- free technology and are particularly relevant in the point-of-care testing setting.</p