The best of the rest from the physics arXiv this week:
Archive for January, 2009
Muscle tissue is made of molecular engines called sarcomeres, which contract and expend when the muscle is flexed. In sarcomeres the business of contracting is carried out by molecular motors called myosins as they pull themselves along filaments of a protein called actin. When you flex your arm, it is these myosin molecular motors that are doing the work.
One curious phenomenon that can sometimes be observed in muscles is a wavelike oscillation of the tissue. What causes this infamous “rippling” of muscles has been somewhat of a mystery but today Stefan Gunther and Karsten Kruse from Saarland University in Germany throw some light on the matter.
They’ve modeled the rate at which molecular motors detach themselves from the actin filaments as the load they are under changes. It turns out that oscilllations occur naturally under certain loads, as the molecular motors attach and re-attach.
So when the next bodice ripper you read mentions rippling muscles, you’ll know exactly what this means.
Ref: arxiv.org/abs/0901.4517: Spontaneous Waves in Muscle Fibres
Let’s calm things down with some deep breaths: in…out…in…out. Relax. Feel your pulse rate slowing?
We’ve known for some time that there’s more to pulse rate than beats per minute. Heart rate variability–the change in intervals between beats–can be used to distinguish healthy hearts from diseased and damaged ones.
One sign of a healthy heart is slight, seemingly random variations in the intervals between beats. These variations seem to be governed by power laws which is somewhat of a puzzle in itself.
By contrast, a steady unchanging beat interval seems to be a sign of disease.
Now Nikitas Papasimakis and Fotini Pallikari at the University of Athens in Greece have studied the heart beat intervals in people who are meditating and found that the power law variations disappear.
That raises an interesting question: is meditating good for the heart or not? Papasimakis and Pallikari argue that the loss of power law correlations cannot be used as evidence of ill health because the correlations return as soon as the subject stops meditating. Fair enough.
But what does the ability to switch these correlations on and off mean for health? Nobody knows just yet but it’s a fascinating area in which it’ll be interesting to see where more data leads.
: Breakdown of Long-Range Correlations in Heart Rate Fluctuations During Meditation
It just gets worse for CERN and its attempts to reassure us that the Large Hadron Collider won’t make mincemeat of the planet.
It’s beginning to look as if a massive miscalculation in the safety reckonings means that CERN scientists cannot offer any assurances about the work they’re doing.
In a truly frightening study, Toby Ord and pals at the University of Oxford say that “while the arguments for the safety of the LHC are commendable for their thoroughness, they are not infallible.”
When physicists give a risk assessment, their figure is only correct if their argument is valid. So an important questions is then: what are the chances that the reasoning is flawed?
On Earth, wind blown dust storms generate powerful electric fields of up to 200 kV/m, with the ground becoming positively charged and the dust particles negatively charged.
The mechanism behind this is poorly understood but various scientists have assumed that a similar process takes place on Mars and that it leads to bizarre phenomenon.
One idea is that the excess electrons in dust break down methane in the atmosphere. Methane is a potential biological marker so estimating how much is produced is important.
The significance of this is that any methane we see in the martian atmosphere today must have survived both this and the ravages of sunlight.
Another idea is that the excess electrons catalyse the production of hydrogen peroxide in the atmosphere which then falls as a unique and rather nasty form of Martian snow.
But both these ideas are probably wrong, say Jasper Kok and Nilton Reno at the University of Michigan today. They’ve put together the most advanced model to date of how windblown dust on Mars becomes electrified and worked out how it affects the atmospheric chemistry.
“We find that the production of hydrogen peroxide and the dissociation of methane by electric fields are much less significant than previously thought,” they say.
Another thing that electrification leads to is lightning and there has been precious little evidence of that on Mars, which perhaps backs this team’s claims.
So it looks as if electric fields play a much smaller role in the Martian atmosphere than they do on Earth
Shame really, hydrogen peroxide snow sounds cool.
Ref: arxiv.org/abs/0901.3672: The Electrification of Wind-Blown Sand on Mars and its Implications for Atmospheric Chemistry
Rules are a good thing when it comes to road traffic: drive on the wrong side of the highway and you’ll cause chaos, if you live. If that seems forehead-smackingly obvious, then an analysis by Seung Ki Baek at Umea University in Sweden and pals my come as a surprise.
They say that a small proportion of lunatics driving on the wrong side of the road actually reduces the chances of a jam rather than increasing it and they have an interesting model to prove it.
Their model is a 100 lane highway in which cars can drive in either direction in any lane. When two cars collide, that lane becomes blocked and other vehicles have to move to one side or the other to get round them.
In theory, it’s easy to imagine that the best strategy is for everyone to agree to move to their left (or right, the model is symmetrical) when they meet.
The question is what happens when there are two kinds of drivers: rule-followers and rule-breakers who move either way.
Ki Baek and co considered the two obvious extremes. When everybody is a rule-breaker, the result is chaos and the road jams up quickly as collisions ensue. Equally, when everybody is a rule-follower, the likelihood of jam is much lower and road users travelling in the same direction tend to end up driving on the left (or right), just as they do on real roads.
But here’s the strange thing: the probability of a jam reaches a minimum somewhere in between, when the number of rule-breakers is between 10 and 40 per cent.
That’s kinda counterintuitive but Ki Baek and co say several factors explain what is going on.
First, a small number of collisions disperses the rule-followers to their respective side of the roads more quickly, making jamming less likely.
And second, rule-followers tend to form convoys which can lead to pile ups that jam the road. A few collisions here and there helps to break up these convoys into smaller groups, making large pile ups and the jams they cause, less likely .
“Our result suggests that there are situations when abiding too strictly by a traffic rule could lead to a jamming disaster which would be avoided if some people just ignored the traffic rule altogether,” say the team.
Might be fun to try it on the San Diego Freeway one of these days. Dare ya!
Ref: arxiv.org/abs/0901.3513: Flow Improvement Caused by Traffic-Rule Ignorers
There is absolutely, positively, definitely no chance of the LHC destroying the planet when it eventually switches on some time later this year. Right?
Err, yep. And yet a few niggling doubts are persuading some scientists to run through their figures again. And the new calculations are throwing up some surprises.
One potential method of destruction is that the LHC will create tiny black holes that could swallow everything in their path including the planet. In 2002, Roberto Casadio at the Universita di Bologna in Italy and a few pals reassured the world that this was not possible because the black holes would decay before they got the chance to do any damage.
Now they’re not so sure. The question is not simply how quickly a mini-black hole decays but whether this decay always outpaces any growth.
Casadio have reworked the figures and now say that: ” the growth of black holes to catastrophic size does not seem possible.”
Does not seem possible? That’s not the unequivocal reassurance that particle physicists have been giving us up till now.
What’s more, the new calculations throw up a tricky new prediction. In the past, it had always been assumed that black holes would decay in the blink of an eye.
Not any more. Casadio and co say: “the expected decay times are much longer (and possibly ≫ 1 sec) than is typically predicted by other models”
Whoa, let’s have that again: these mini black holes will be hanging around for seconds, possibly minutes?
That doesn’t sound good. Anybody at CERN care to clarify?
Ref: arxiv.org/abs/0901.2948: On the Possibility of Catastrophic Black Hole Growth in the Warped Brane-World Scenario at the LHC
In the last ten years or so electronic noses have become commercially available, based on a detection device known as a Taguchi sensor. These are heated semiconductor oxide films that change their resistance when they absorb gases. The gases break down inside the film and the various molecular species gather at grain boundaries within the film changing its resistance.
Electronic noses consist of an array of Taguchi sensors designed to spot different molecular species. These are connected to a computer that analyses the pattern of signals they produce to identify the gases present in a mixture. These can work with fairly complex volatiles and some electronic noses are capable of evaluating various foods .
Now Hung-Chih Chang at Texas A&M University and a few pals say it is possible to use the tools to identify bacteria by their smell alone. (more…)
Ranking scientists by their citations–the number of times they are mentioned in other scientists’ papers– is a miserable business. Everybody can point to ways in which this system is flawed:
- not all citations are equal. The importance of the citing paper is a significant factor
- scientists in different fields of study use citations in different ways. An average paper in the life sciences is cited about six times, three times in physics, and about once in mathematics.
- ground-breaking papers may be cited less often because a field is necessarily smaller in its early days.
- important papers often stop being cited when they are incorporated into textbooks
The pattern of citations between papers forms a complex network, not unlike the one the internet forms. Might that be a clue that point us towards a better way of assessing the merits of the papers that it consists of?