5 Live Science Podcast — Artificial Pancreas

 

 

 

 

 

 

 

 

 

 

 

 

 

This week's program featured a segment about an "artificial pancreas" for Type 1 diabetes sufferers, which uses a closed loop control system to monitor blood glucose and administer a dose from an insulin pump.

What's a Closed Loop, Negative Feedback Control System?

Many systems use close loop control with negative feedback to control an output of interest. An example is the speed control on small engines, e.g. the one on your petrol lawn mower. If you run into longer grass, this slows down the blade and engine. To reduce the change in rotational speed (the output variable) and keep it at a setpoint (typically 3000 RPM for a mower), a governor is used. A vane, mounted adjacent to the engine's cooling fan that's integral to the flywheel, forms part of the governor mechanism. When the fan slows down, it blows less air onto the vane. The vane is connected via a linkage to a butterfly valve in the carburetor. This valve forms part of the throttle mechanism and as the valve opens up due to movement of the vane, more air/fuel mixture enters the engine. This generates more power which tends to compensate for the slowdown of the blade due to the long grass. Other systems use negative feedback and closed loop control, e.g. your phone charger which has electronics to keep the output at 5 V DC, irrespective of load. Without a voltage regulator, all power sources, including batteries, experience a voltage drop as they're loaded and more current drawn from them. Voltage stabilisation by a regulator is necessary so that the electronics in your phone for instance works in a predictable manner. Other examples of feedback control systems are servos on vehicles and aircraft and temperature and pressure control in industrial processes.

Why Negative Feedback and Not Positive Feedback?

The function of a feedback control system is to keep an output variable at a fixed or variable setpoint, irrespective of load. So in the lawn mower example the speed was the parameter that needed to be kept stable. In negative feedback, the actual speed is fed back and subtracted from the desired speed (the setpoint) to create an error signal. This error, via a controlled variable, drives the system in a direction to bring the output closer to the setpoint. In the lawnmower example, the controlled variable was the fuel. The term negative feedback comes from the subtraction that's involved. Positive feedback on the other hand causes the fed back signal to add to the set point, resulting in instability and the output diverging from a setpoint (e.g. positive feedback in a PA system, causing the squealing from loudspeakers). Many of the systems in our bodies are negative feedback control systems and like any control system if not tuned properly, there can be oscillations and instability. Hence the wobbling from side to side when we're learning to ride a bike!

 

Nova Due in a Binary Star System, 3000 Light Years Away

Image credit: Geralt, public domain via Pixabay

It won't be as spectacular as Tycho's Supernova of 1572 or Kepler's Supernova which occurred some decades later and was visible in daylight. However, a seemingly new star will appear in the constellation of Hercules and should be as bright as the North Star. The nova is predicted to happen before September 2024 in a binary system 3000 light years away, made up of a dead white dwarf and ageing red giant. The white dwarf, consisting of "star stuff" so dense that a teaspoon of it would weigh five tonnes, is sucking material off the "nearby" red giant. Every 80 years or so, the the material it accumulates reaches a critical mass and a thermonuclear fusion reaction is sparked off, the star lighting up so that it can be seen from Earth, 18 thousand trillion miles away. In reality, because the star system is 3000 light years away, the event really occurred 3000 years ago, the light taking this length of time to reach us.

This BBC article provides more details.

Move over, solar eclipse: Scientists predict a once-in-a-lifetime nova explosion in the coming months

Ordnance Survey of Ireland Discovery Maps on Scoilnet

This is more geography than science, but I just noticed that the OSI (now Tailte Éireann) Discovery Series, 1:50,000 scale maps are available online on the Scoilnet site. There's also a relief shading layer showing elevation levels. The Discovery Series layer was removed from the OSI's Geohive interactive maps website several years ago. The website is available at this link.

https://maps.scoilnet.ie/OSiMaps/EsriVer17/index.html

Image credit: Ordnance Survey Ireland (Tailte Éireann)

Recommended Books — Sticky

If you like science and physics, Sticky by Irish physicist and science writer Laurie Winkless is a fascinating read. In it, she delves into how glue and friction works, and explores dimples on golf balls, Speedo's shark-skin-inspired Fastskin swimsuits and why geckos can walk on walls! Available to order from Woodbine Books.

The Cloud and Data Clutter

Public domain image by 200 degreess on Pixabay

The "Cloud" conjures up an image of a futuristic, esoteric, floating entity, high above our heads (I see the clouds in The Simpsons opening sequence!), but in reality, information from our smartphones and other devices stored in the cloud actually resides in data centres. These are big industrial buildings, with large numbers of racks or cabinets of servers, effectively hard drives or solid-state drives and their auxiliary networking and telecommunications hardware. To make data bulletproof, multiple redundancy is built into cloud storage so that any piece of data is duplicated over multiple systems, possibly in different geographical locations. In this clip from Today With Claire Byrne, Colm Ó Mongáin talks to technology journalist Adam Maguire about data clutter, old and hoarded files and the ever-increasing demand for more storage.

Electromagnetic Induction and the Force on a Conductor in a Magnetic Field

A varying electrical current in the coil on the left produces a fluctuating magnetic field. This loops through the coil on the right, inducing an electrical current. Image by Ponor, CC BY-SA 4.0 via Wikimedia Commons.

 

Two principles, discovered in the early 19th century on which motors, generators and transformers work.

Electromagnetic Induction

Move a conductor (e.g. a piece of wire) in a magnetic field (produced by a magnet), or move the field and keep the conductor stationary or thirdly, vary the strength of the field. The result is that a current is induced in the conductor. This is how all electrical generators and transformers work, electricity being induced or generated in coils of wire as a magnetic field varies in strength. It's the main reason too why we use AC electricity for distribution.

Force on a Conductor in a Magnetic Field

Pass a current through a conductor placed in a magnetic field. The conductor experiences a force which tends to push it. This is the principle on which electric motors work.

Several scientists in the early 19th century made fundamental discoveries about the nature of electric currents and magnetic fields. Two of these were the Danish physicist Hans Christian Ørsted and the English scientist Michael Faraday. Faraday's apparatus including a transformer and motor can be seen in the Faraday Museum at the home of the Royal Institution in London.

150 MWh of Battery Storage

Public domain image by Sandia National Laboratories via Wikimedia Commons.

A new energy storage facility opened at the Poolbeg Power Station which according to The Irish Times has the ability to source 75 MW of power for two hours. Hopefully it'll act as a stop gap in times of energy need. For comparison, the pumped storage hydroelectric station at Turlough Hill in Wicklow can provide 292 MW of electricity from its four alternators (AC generators) for 6 hours (so the energy storage capacity is 292 MW x 6 = 1752 MWh)

More details are available in this Irish Times article.

 

What is the Relationship Between Power and Energy?

 

Power is measured in watts and is defined as the rate of use of energy or rate of doing work.

 

So

 

Power = energy/time (dividing something by time gives a rate)

 

Therefore, rearranging the equation

 

Energy = power x time. 

 

In the SI system, energy or work done is measured in joules (or calories in imperial units)

One joule is equivalent to 1 watt for 1 second.

 

A one kilowatt (1000 watts) heater uses 1000 W x 3600 seconds = 3.6 million joules in one hour

 

However in the context of electricity, the watt-hour (Wh), kilowatt-hour (kWh) and megawatt-hour (MWh) are more commonly used as units of energy.

 

One kWh (or a unit on your electricity bill) is the amount of energy used by a 1000 W or 1 kW appliance in one hour (or 100 W in 10 hours etc)

 

An example of doing work and using power to do it is lifting an object off the ground. To lift an object a certain distance requires work to be done to give the object potential energy by way of its height above the ground. If you lift the object faster, your arm produces more power, but the object takes less time to be lifted. Similarly if the object is lifted less forcefully, i.e less power is used, the time is greater. In both cases although the power is different, energy = power x time is the same.