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# Date Archive: 2012 August

Computation & Analysis

## Analyzing Pedometer Data with Mathematica

In Stephen Wolfram's personal analytics blog post, he showed a number of interesting plots of the steps he's recorded on his pedometer over the past two years. Each plot highlighted a different feature of his activity. For example, this daily step distribution makes it clear that Stephen is typically most physically active around noon: In this blog post I'll show you how to analyze your own pedometer data and make cool plots like Stephen's. If you don't have any data, you can use the attached sample data that corresponds to my own physical activity. First we need to import the data and format it appropriately. The data is formatted as pairs of time stamps and step counts in five-minute intervals.
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## Model Your Own Medieval Catapult Design

Explore the contents of this article with a free Wolfram SystemModeler trial. Since my childhood, I have always been impressed by big mechanical structures, especially things that are used for demolition of some kind, like demolition machines (cranes with big metallic balls thrown hard at concrete buildings) or machines for warfare. All kids are by nature intrigued by demolishing, and I guess that some of us never lose that interest. When we grow up, our interest may shift toward understanding the physics behind the machines used for demolition more than the actual demolished result. Wouldn't it be nice to be able to study medieval warfare, and in particular, the mechanical system of a catapult? How should you design your catapult for maximal effect? How far can you hurl a projectile with a given design? What is required to throw a piano? The mechanics behind a catapult are rather simple to describe using ready-made components in Wolfram SystemModeler. The model could be used to fine-tune the design and calculate properties such as the maximum length of a hurl for a specific counterweight.
Announcements & Events

## Introducing the New Wolfram Screencast & Video Gallery

Did you know that we have more than 600 videos and screencasts that highlight (and help you get started with) different features of Mathematica and other Wolfram technologies? You've probably seen a number of them across our websites or on our YouTube channels. But now, it's easier than ever to explore the full collection—thanks to our newly redesigned Wolfram Screencast & Video Gallery.
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## Visualize a Satellite Path with Wolfram SystemModeler and Mathematica

Explore the contents of this article with a free Wolfram SystemModeler trial.Today we rely heavily on satellites orbiting Earth for a variety of purposes. Mapping satellites are used to collect satellite images used in maps. Communication satellites are used for both telecommunication and internet access or for navigation services like GPS and GLONASS. Other usage areas are weather study, scientific observation, and reconnaissance. The following model, created in Wolfram SystemModeler, is of a geocentric, inclined circular Low Earth Orbit (LEO) satellite. Geocentric means that it orbits around the Earth. An inclined circular orbit means that the orbit follows a circle, but is not aligned with the equator of the Earth. LEO is the name given to the altitude range below 2,000 kilometers (1,200 miles). Suppose you are considering using this geocentric LEO satellite to collect image data. To achieve this, you would want to know where it is at the moment, how high it is, and how fast it's going. If you want images of cities, you want to know over which cities it currently is. A SystemModeler model combined with data and computational resources in Mathematica can answer all of these questions. Creating such a model is straightforward in SystemModeler. Using drag-and-drop, create three subsystems. Model the Earth using a mass with constant rotation, the satellite using a mass with propulsion forces, and the control logic using two proportional derivative (PD) controllers. This blog post focuses on illustrating the orbit and flight of the satellite in the above model.
Announcements & Events

## Enter the Mathematica Experts Live: One-Liner Competition 2012

At the last two annual Wolfram Technology Conferences, attendees have enjoyed amazing, and being amazed by, each other in the One-Liner Competition, which challenges participants to show us the most astounding things they can do with 140 characters or less of Mathematica code. And each time we have been surprised, inspired, and gratified by their creativity. Now we've opened up the competition to you, and Mathematica users from around the world are sending us their submissions. In a Mathematica Experts Live broadcast on August 21, we'll reveal the winner and runners-up of the competition, show you what they did, and explain how they did it. You'll see applications you probably never thought possible, learn new Mathematica tricks and techniques, and have your socks blown off by elegant programming wizardry.
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## Battery Model and Analysis with Wolfram SystemModeler

Explore the contents of this article with a free Wolfram SystemModeler trial. How do different activities such as making phone calls, watching video, listening to music, or browsing the web affect cell phone battery life? What about the temperature—does it matter if the cell phone is in a warm pocket or out in the cold? In this blog post, we'll investigate how a model constructed with Wolfram SystemModeler can help in finding answers to such questions. An area where battery usage is taking off right now is cell phones. There are different kinds of battery types used in cell phones: nickel metal hydride, lithium-polymer, and Li-ion. The superior energy density, power density, low self-discharge, and long cycle life of the Li-ion batteries makes them interesting for cell phone applications. In this blog post, we'll look at Li-ion cells of the type LiFePO4, where lithium ions move from the negative electrode to the positive electrode during discharge and the other way around when charging. The are many types of battery models: analytical, electrical circuits, electrochemical, and combinations of these types. Our model of choice is the electrical circuit model, which provides sufficient accuracy for top-level performance analysis and is easy to connect to other systems. A typical schematic for an electrical circuit model of a battery cell might look something like this:
Announcements & Events

## Winners of Wolfram’s First Demonstrations School Coding Competition Announced

Wolfram Research today announced the winner of its first Demonstrations competition as Michael Lawson from Ermysted's Grammar School, North Yorkshire, with runners-up Patrick Stevens, Woodbridge School, Suffolk and David Harris, St. Dunstan's College, London. Michael's Demonstration, "Recursive Dungeon Generator," was a particularly good showcase for applications of programming---in this instance, for game design. "I was working on creating my own Rogue-like game, and I was experimenting with different ways to generate rooms. This was one of my own algorithm ideas," said Michael, who, although he has been programming for four years, only started using Mathematica recently. "I actually only learned how to use Mathematica for the purpose of the competition. I started creating my demo after having only watched a few of the videos recommended for entrants, and then finished about four days later!" All three of the winning entries are published on the Wolfram Demonstrations Project site alongside 8,000 other user-created programs. "Recursive Dungeon Generation” "Semitones In Pythagorean Tuning and 12 Tone Equal Temperament” "Sorting Algorithms” The idea of the competition was to promote the application of programming in schools and support the UK government initiative to bring programming into schools.
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## Building a Refrigerator Model in Wolfram SystemModeler

Explore the contents of this article with a free Wolfram SystemModeler trial. Refrigerators and freezers are common household appliances, present in almost every home. That means most people use one every day, but how do they actually work? And what happens to the temperature when you open the door? Or when the power goes out during a storm? Those are some of the questions this blog post seeks to answer by building a refrigerator model in Wolfram SystemModeler. A common way to construct a combined refrigerator and freezer is to keep the freezer compartment cool with a heat pump and to then transfer some of the air to the fridge compartment. That way only one heat pump is needed, and both compartments can be kept at different temperatures. The following diagram shows our goal: modeling a connected freezer and fridge complete with doors, casing, food contents, and a heat pump. At the top we see the freezer compartment together with the heat pump that cools the air, some frozen food in the freezer, and a door for the freezer. At the bottom we see a similar structure for the fridge. The two are connected with a component for air circulation at the middle right of the diagram, which will transfer cold air from the freezer to the fridge. Finally, to the left, we have components modeling the casing and insulation to the room temperature outside.