I am pleased to announce that my PhD thesis, titled “Data Storage and Processing using Magnetic Nanowires” is now available online at the White Rose eTheses Online. In it I investigate the switching dynamics of Domain Wall Trap Magnetic Random Access Memory (DWT-MRAM). Later I take a thorough look into Spin Wave propagation along permalloy nanowires.
I’ve been using VBA to generate pivot tables in Excel for a few years now, and I’ve found it to be a very powerful tool. I can use VBA to quickly and easily create pivot tables that summarize large amounts of data. I can also use VBA to update pivot tables as my data changes. In this blog post, I’ll show you how I use VBA to generate pivot tables. I’ll start by explaining what pivot tables are and why they are useful. Then, I’ll show you how to create a pivot table using VBA. Finally, I’ll show you how to update a pivot table using VBA. ...
Many eInk devices now available Much has happened in the world of eReaders since my original blog posts highlighting the need for more 13.3" eReaders and it’s now more than 7 years since I bought my 9.7" Onyx Boox M96. There are now many 13.3" options available as well as 10.3" devices. I won’t go into details here or plug any particular manufacturers; a quick search on YouTube will present you with many up to date reviews and comparisons. ...
I recently had the honour of giving an invited talk on Heat-assisted Magnetic Recording (HAMR) at the Ex-Spring Industrial Conclave which was hosted by Exeter University. Apart from introducing the magnetic recording paradigms (LMR, PMR and HAMR) and emphasizing the need for energy-assisted magnetic recording in order to continue areal density growth, I shared details on the HAMR recording physics and highlighted challenges that have been overcome in the last few years in order to bring HAMR to product. ...
Recently I used balenaEtcher to create a bootable Linux drive. It is a nice Windows program that simplifies the process of creating Linux disks and is recommended by some Linux distro vendors. After the program successfully writes a bootable Linux USB drive, the drive no longer appears correctly in Windows. That’s because a bootable USB contains certain drive partitions with filesystem types that are not visible to the Windows operating system. ...
Zotero is a cross-platform literature manager that is able to sync to a remote server and across multiple user devices. There are many alternatives available, each with strengths and weaknesses, but I am currently using Zotero to manage my literature because it is free and works with WebDAV for additional free storage. In this article I will describe why optical character recognition (OCR) is important for Zotero and suggest a way to add OCR to existing items in a Zotero library. However, the method actually works for any collection of PDF files on your computer! ...
If you want to plot something on the terminal in ASCII you can use “eplot”. eplot itself is a Ruby script that acts as a frontend for gnuplot. eplot can be downloaded from the project’s GitHub page. It makes it easier to pipe numbers into gnuplot, which can otherwise be a bit of a hassle. It also has a dumb terminal mode which allows us to plot using ASCII. Plotting like this provides a way to quickly check data files without requiring any x windowing system, which might not be available when logging in remotely over the terminal. ...
Previously I showed how it was possible to obtain sunrise and sunset times for a whole year at any location on Earth, from a public source. This time I am going to explain how to fetch that data, clean it up and create graphical visualizations like the one below, all using Python. A Jupyter Notebook is available on GitHub. Such data might even be useful in, for example, simulation of solar power generation. ...
jinsngjung / Pixabay Today is 2nd January and the days are getting longer again. I was thinking about sunrise and sunset times and wondering if I should do some data analysis and plotting of these to visualize how they change over the course of a year. Of course, the first step is to get a suitable data set. You can get a data set of sunrise and sunset times from this page on the US Naval Observatory (USNO) website. Sunrise and sunset times depend on your specific location on the globe so you have to specify the location for your data set. Using the “Form B” Locations Worldwide" section on the page it is possible to enter precise coordinates for any location in terms of latitude and longitude. You can also do it for a timezone, but this is very broad and not precise enough for my liking. ...
UPDATE: These days it is recommended to use Python3 instead of Python2 Apparently it is tricky to get Python integration working in the KNIME Analytics Platform. If you read the official guide too quickly you can miss some critical information at the bottom of the page. I was getting an error complaining that the google.protobuf library was missing even though I thought that I had everything installed correctly: Library google.protobuf is missing, required minimum version is 2.5.0 ...
Figure: Building a geometry in the Salome graphical user interface (GUI). How Salome tracks ports When Salome is starting up, it checks for free ports on your system using a few built-in Python scripts. Then when you close Salome those ports should be freed up again for the next one. This has a number of uses, but one reason is to stop multiple instances of Salome trying to use the same port at once. ...
Our latest paper has just been published in the journal Acta Materialia. In it, we compare finite element micromagnetics simulations to experimental evidence in order to investigate the role of twin and anti-phase defects in the reduction of performance in MnAl permanent magnets. Figure: Room temperature (BH) max as a function of approximate raw material costs for the theoretical MnAl permanent magnet and experimental values for a selection of common commercial permanent magnets. The raw material costs are a good indication of the relative cost of the manufactured magnets. ...
It can be ridiculously easy to parallelize code in Python. Check out the following simple example: import time from joblib import Parallel, delayed # A function that can be called to do work: def work(arg): print "Function receives the arguments as a list:", arg # Split the list to individual variables: i, j = arg # All this work function does is wait 1 second... time.sleep(1) # ... and prints a string containing the inputs: print "%s_%s" % (i, j) return "%s_%s" % (i, j) # List of arguments to pass to work(): arg_instances = [(1, 1), (1, 2), (1, 3), (1, 4)] # Anything returned by work() can be stored: results = Parallel(n_jobs=4, verbose=1, backend="threading")(map(delayed(work), arg_instances)) print results Output: ...
If you have ever been stuck as a user on an out-of-date cluster without root access it can be frustrating to ask the admin guy to install packages for you. Even if they respond, by the time they get round to it you might have moved onto something else. The moment could be gone. Luckily, as far as Python is concerned, the pyenv project allows users to install their own local Python version or even assign different versions to different directories/projects. ...
The problem of how to visualize multivariate data sets is something I often face in my work. When using numerical optimization we might have a single objective function and multiple design variables that can be represented by columnar data in the form {x1, x2, x3, … xn, y} a.k.a. NXY. With design spaces of more than a few dimensions it is difficult to visualize them in order to estimate the relationship between each independent variable and the objective, or perform a sensitivity study. ...
As is known by anyone in the field of data visualization, the “jet” colormap has some flaws: Doesn’t work when printed black & white Doesn’t work well for colourblind people Not linear in colour space, so it’s hard to estimate numerical values from the resulting image The Matlab team recently developed a new colormap called “parula” but since Matlab is commercially-licensed software, it’s use is restricted. The Matplotlib team have therefore developed their own version, based on the principles of colour theory (covered in my own BSc lecture courses on Visualization). The new Matplotlib default colormap is named “viridis” and it will become the new default colour map starting with Matplotlib v2.0. Users of older versions v1.5.1 can still choose viridis manually using cmap=plt.cm.viridis. ...
New paper The reprint of our Journal of Applied Physics (JAP) paper “Grain-size dependent demagnetizing factors in permanent magnets” has been updated since the old version was not being discovered by the Google Scholar crawler. It is also available on arXiv.org. Full reference S. Bance, B. Seebacher, T. Schrefl, L. Exl, M. Winklhofer, G. Hrkac, G. Zimanyi, T. Shoji, M. Yano, N. Sakuma, M. Ito, A. Kato and A. Manabe, “Grain-size dependent demagnetizing factors in permanent magnets”, J. Appl. Phys. 116, 233903 (2014)
I recently bought a new notebook; the HP Spectre x360, a 13" convertible ultra-slim notebook PC. It is a really nice piece of hardware, chiselled from solid aluminium with great battery life, decent performance and a pretty usable keyboard. When the laptop is folded back it automatically converts to tablet mode, wherein the keyboard is automatically turned off so that the keys are not accidentally pressed while using the touchscreen interface. ...
Netronix and, purportedly also Onyx International, are developing 13.3 inch screen eReaders using eInk’s Mobius screen, as rivals to Sony’s expensive, PDF-only DPT-S1 Digital Paper. A new video shows the Netronix device prototype being displayed at a recent trade show: Unfortunately, it seems that without a major company to put up the money to manufacture, market, distribute and sell it the device won’t become available to consumers. That is a real shame! Many people, myself included, would love to have such a device for taking notes or reading scientific papers, magazines and textbooks that don’t display well on, say, a Kindle. ...
Salome is an open source software package used to create geometric models and finite element meshes for use in numerical simulations. It is also able to perform its own numerical simulations and has post-processing capabilities built in. Here are my 5 tips for anyone who is interested in using Salome for model and mesh creation. 1. Practice manually first This goes without saying. Although Salome has a powerful Python-based scripting capability, it is worth practicing with manual model generation. By that I mean, clicking with your mouse in the GUI. Manual practice lets you get familiar with the quirks of the Salome workflow, which has a different mentality to many other model generator programs. ...
New paper Our latest paper has been published in JOM (Springer). It is a summary of the achievements (so far) of the ROMEO fp7 project. ROMEO is a project that aims to research and develop novel microstructural-engineering strategies that will dramatically improve the properties of magnets based purely on light rare earth elements, especially the coercivity, which will enable them to be used for applications above 100 degrees C. ...
This week our new paper titled “Thermal Activation in Permanent Magnets” has been published in JOM (Springer). The invited paper is under a special topic, “Permanent Magnets beyond Nd-Dy-Fe-B”. An author manuscript (reprint) is available here. Fig 1: Explanation of method for calculating the thermally activated coercivity of using micromagnetics. In the paper we provide a more detailed overview of the micromagnetic methods we have developed to model the thermal activation of permanent magnets. These methods allow us to simulate and understand the behaviour of permanent magnets at finite temperatures, which is important since the generators in wind turbines and electric motors in green cars operate at higher temperatures. For example, in electric cars the typical operation temperature of the motors can be around 450ºK (177º C). ...
Our EU-funded FP7 project “Replacement and Original Magnet Engineering Options” (ROMEO) has recently been covered in the news in Slovenia, to promote the participation of our Slovenian collaborators. Video »Video file« Newsletter There is also now a project newsletter highlighting the aims and progress of the project. Please click here to download it.
Introduction Last July (nearly a year ago) I bought a larger format eReader that is manufactured by a chinese company named Onyx under the branding “Onyx Boox”. The model, the M96, was an upgrade to their previous one, the M92, and I had been waiting patiently for a while, desperate to have a larger eReader for textbooks. The screen is 9.7 inches diagonally. This doesn’t sound much of an increase on a 6 inch screen, but consider that this gives 2.56 times the surface area (see comparison below). ...
The problem If you are visiting/living abroad but still want the Firefox search bar to default to your home version of Google, it is possible to fix it! In the following solution I assume that you are from the UK and want to use the UK/GB version of Google Search: The solution Access the Firefox settings: type about:config in the address bar, then click I'll be careful, I promise. For each setting you want to modify, use the search bar to find it more quickly. Set both browser.search.countryCode and browser.search.region to “GB” by double-clicking it and typing the new value. Make sure browser.search.isUS is set to False. For both distribution.searchplugins.defaultLocale and general.useragent.locale use “en-GB”. Restart Firefox. Visit http://www.google.com/ncr, to activate a no country redirect cookie that stops the browser from looking for country-specific search results. Searching from the search bar should now give results at Google.com, but notice that at the very end of the search results URL there is a flag for UK regional content. ...
Our new paper “Thermally activated coercivity in core-shell permanent magnets” has been published today as J. Appl. Phys. 117, 17A733 (2015); http://dx.doi.org/10.1063/1.4916542 . In the paper we use numerical miromagnetics to calculate the performance of nanostructured core-shell-like permanent magnets, like the type that can now be produced by grain boundary diffusion of granular hot-deformed or sintered rare earth permanent magnets. FIG. 3. Reversal processes in the sin- gle grain models with (i) a pure NdFeB grain, (ii) a NdFeB grain with a soft outer defect, and (iii) NdFeB core, (Dy, Nd)FeB shell and an outer soft defect. Thermally activated coercive field values are indicated with the field direction (red arrows). The saddle point image is the configuration with the highest total energy, forming the peak of the energy barrier. ...
Our paper titled “Micromagnetics for the coercivity of nanocomposite permanent magnets” has been published in the proceedings of the 23rd International Workshop on Rare Earth and Future Permanent Magnets and Their Applications (REPM2014). The proceedings were not made available to the public but we are providing a PDF reprint here. Fig. 1. Switching field of Nd 2 Fe 14 B cubes and spheres with volume V The work was presented by Johann Fischbacher on 19th August 2014 in Annapolis, Maryland. ...
Our paper titled “Enhanced Nucleation Fields due to Dipolar Interactions in Nanocomposite Magnets” was presented by first author, Johann Fischbacher, at the JEMS 2012 conference and subsequently published in the The European Physical Journal B. Figure: Magnetic reversal process: The pictures show the magnetic flux lines. The color denotes the magnetization direction (red: magnetization up, blue magnetization down). The gap between the soft magnetic spheres (d incl = 8 nm) is 1 nm in the first two columns and 4 nm in the third column. The external field is applied in z-direction and its value is written next to each picture. In the first column the soft magnetic inclusions are aligned perpendicular to the applied external field. The interaction with the outside inclusions is weakening the central sphere and forces it to switch first. In the second and third column the soft magnetic spheres are aligned in a parallel manner to the applied external field. The two outside spheres reinforce the central one and therefore nucleation should not start in the center. But for gaps smaller than 4 nm a strong demagnetizing field in the location of the central sphere caused by the shell diminishes the strengthening effect due to dipolar interaction. ...
Our new paper “Grain-size dependent demagnetizing factors in permanent magnets” has been published in Journal of Applied Physics (JAP). Abstract: The coercive field of permanent magnets decreases with increasing grain size. The grain size dependence of coercivity is explained by a size dependent demagnetizing factor. In Dy free Nd2Fe14B magnets, the size dependent demagnetizing factor ranges from 0.2 for a grain size of 55 nm to 1.22 for a grain size of 8300 nm. The comparison of experimental data with micromagnetic simulations suggests that the grain size dependence of the coercive field in hard magnets is due to the non-uniform magnetostatic field in polyhedral grains. ...
This August Prof. Dominique Givord of Institut Néel CNRS presented our paper titled “Hard Magnet Coercivity” during the 23rd International Workshop on Rare earth and Future Permanent Magnets and Their Applications (REPM2014) in Annapolis, Maryland. The manuscript was included in the conference proceedings and we would now like to make the reprint available to the wider public: Please click here for the PDF file. Abstract: Based on a critical analysis of the experimental coercive properties, general considerations on the reversal mechanisms in RFeB magnets are recalled. By plotting together the experimental parameters obtained in various magnets, common features of the reversal processes are demonstrated. Modeling provides an almost quantitative description of coercivity in these materials and permits connecting the defect characteristic properties to reversal mechanisms. ...
Grace a.k.a. xmgrace is a really useful tool for plotting histograms from tabular data files. Its power comes from the command line control and being scriptable. Yes, there are other options which are sometimes more suitable for specific situations (e.g. GNUplot, Matplotlib/PyLab), but for quick, basic plotting I usually find myself relying on xmgrace. Here is an example of a single line command to plot two columns from each of a large number of data files: ...
Our new, cake-themed paper on nanostructured permanent magnets has now been published in Applied Physics Letters. In the paper we present results from micromagnetic simulations that assess the performance of multi-phase nanostructured permanent magnets, whose cross-section resemble that of a Battenberg cake. By including a super-hard outer shell we are able to counteract the effects of thermal fluctuations and surface defects, both of which are detrimental to the performance of such permanent magnets. Such magnets are important for the motors in electric vehicles and for the generators in wind turbines, and these machines usually operate at elevated temperatures. ...
Our new paper titled “Thermally-activated coercivity in core-shell permanent magnets” has been accepted for publication in Journal of Applied Physics. Click here to download the paper as a PDF file. In the paper we describe recent micromagnetics simulations on NdFeB grains that have undergone a dysprosium (Dy) grain boundary diffusion process (GBDP). The super hard (Dy,Nd)FeB shell that is formed during this process stabilizes the grains against thermal fluctuations that can be detrimental to the coercivity of the magnet in high-temperature situations. NdFeB permanent magnets are usually doped with Dy to increase their performance at high temperatures but the GBDP allows us to target the Dy at the most important locations i.e. the grain surface, thus reducing the overall required amount of Dy, which is expensive and in short supply. ...
qhost is a UNIX command line tool to print the status of nodes on a Grid Engine system. The output is normally quite readable and is sorted by columns to give information on the hostname (“HOSTNAME”), architecture (“ARCH”), no. of CPUs (“NCPU”), processor load (“LOAD”), total available memory (“MEMTOT”), current memory usage (“MEMUSE”), swap memory size (“SWAPTO”) and current swap usage (“SWAPUS”) of each node on the cluster. Unfortunately, when the hostnames are too long, instead of truncating them to keep the columns aligned the row gets shunted along, making the output messy and much harder to read quickly. ...
Congratulations to our Industrial Simulation bachelor students who graduated today. Sponsion 2014
I use Zotero to manage my literature collection, including all the associated PDF attachments. It really made my life easier when I set up the WebDAV file sync on Box. However, until now the only way to sync files to my Onyx Boox M96 eReader (image) was by connecting a USB cable and copying them manually to the device. Since Zotero stores the files in cryptically-named individual folders it is hard to do this manually in an organised manner and involves lots of clicking. Today I am going to find a better way. ...
Its hard to stay organized when you work on multiple computers, with multiple operating systems. My main notebook is a dual boot Ubuntu/Win7 machine where I have a shared partition for work files. I sync my work folder with my Ubuntu tower PC via BitTorrent Sync. This has now been working well for some time (the syncing happens under Ubuntu only, which is a drawback, but if BTSync under Windows also tries to sync the same shared folder it causes problems, thus I avoided doing so) although if you start with two identical copies of the folder on the two PCs it still wants to sync all of the files one way over the network. Not good when the folder is 100 GB large! (Update: this may have been solved in the latest version of the software). ...
Our new paper titled “Influence of defect thickness on the angular dependence of coercivity in rare-earth permanent magnets” has just been published in the journal Applied Physics Letters. It was a long time coming and the result of much collaborative effort but I am really proud that this work is finally out there. Thank you to all of my co-authors for their input, support and advice. The work shows using micromagnetics simulations and experimental data that there is a direct connection between the coercivity in rare earth permanent magnets and the thickness of the surface defect with reduced anisotropy. The applicability of the two main theoretical models for reversal in such magnets is related to the role of such soft defects and their sizes. ...
Our new paper titled “Micromagnetics of shape anisotropy based permanent magnets” has been accepted for publication in Journal of Magnetism and Magnetic Materials (JMMM). Short description Visualizations of the computed magnetization data during reversal of soft prolate spheroids for aspect ratios (a) 1.95 and (b) 15.6, showing the different reversal modes. ...
New paper I am pleased to announce our new paper, which can be downloaded from http://arxiv.org/abs/1312.3791 Abstract In the search for rare-earth free permanent magnets, various ideas related to shape anisotropy are being pursued. In this work we assess the limits of shape contributions to the reversal stability using micromagnetic simulations. In a first series of tests we altered the aspect ratio of single phase prolate spheroids, ranging from 1 (sphere) to 20. We start with a sphere with a radius of 4.3 Lex and kept the total magnetic volume constant as the shape is transformed. For a ferromagnet with zero magnetocrystalline anisotropy the maximum coercive field reached up to 0.5 Ms. Therefore, in materials with moderate uniaxial magnetocrystalline anisotropy, the addition of shape anisotropy could even double the coercive field. Interestingly due to non-uniform magnetization reversal there is no significant increase of the coercive field for an aspect ratio greater than 5. A similar limit of the maximum aspect ratio was observed in cylinders. The coercive field depends on the wire diameter. By decreasing the wire diameter from 8.7 Lex to 2.2 Lex the coercive field increases by 40 percent. In the cylinders nucleation of a reversed domain starts at the corners at the end. Smoothing the edges can improve the coercive field by about 10 percent. In further simulation tests we compacted soft magnetic cylinders into a bulk like arrangement. There are various effects that reduce the coercivity in assemblies of rods: Misalignment, magnetostatic interactions, and direct coupling through exchange interactions. These cause a spread of 0.1 Ms in the switching field of the rods. Comparing the volume averaged hysteresis loops computed for isolated rods and the hysteresis loop computed for interaction rods, we conclude that magnetostatic interactions reduce the coercive field by up to 30 percent.
Photos from our European Researcher’s Night can now be found at http://www.destinationfuture.eu/fotos
When writing Salome scripts that include a step to explode objects to their sub-shapes (using “ExtractShapes”) it is worth paying attention to the isSorted parameter, which is True by default. In my experience this parameter is best set to False in order to avoid Salome unpredictably changing the order of the objects in the resulting list. For example, here I have a Compound of two objects A and B, which has the faces glued resulting in Glue_1. I want to extract the two solids and use them in the script. ...
In July our paper “System Dynamics models for improved power plant operation” was presented at ICOSC 2013 (The Fourth International Conference on Optimization, Simulation and Control) in Ulaanbaatar by our colleague and friend Bayasgalan Zagdkhorol of Mongolian University of Science & Technology (MUST). The abstract, which shows some of our early results, can be found here. Thank you, Zagdaa, for representing us and our work! Model of power generation grid including naive load model, coal, solar, wind and hydroelectric power sources. Various scenarios can be tested. ...
Our tumour cell filter project was judged the Innovation Of The Year by futurezone magazine. You can read our paper here and a press release here. For more information about the awards ceremony please visit futurezone.at **Figure: Markus Gusenbauer accepting the award. **
A project that I am involved with has been shortlisted for the 2012 Futurezone Innovation Award. The project aims to develop microfluidic chips for circulating tumour cell (CTC) filtering, which could one day lead to better cancer diagnosis. Futurezone is a technology news website and formerly a printed supplement in the Austrian Kurier newspaper. For more information please visit (http://futurezone.at/innovationaward)[http://futurezone.at/innovationaward]