241

Technology / Re: Any experience with emergency vehicle starters?

« on: 06/01/2016 08:37:10 »

I have been quite sceptical of these gadgets prior to now, although admittedly I have never actually done the maths to work out what might or might not be achieveable with them.

My understanding is that they plug into the cigarette lighter / power socket in the car and top up the battery.

The max rated current through the power socket (roughly) is 10 amps. P=VI, so 12 x 10 = 120 J/s or 120W.

The starter motor of a car engine pulls 100-200 amps. Let's assume the engine needs a 5 second crank in the cold to make it start: that's 200 amps x 12 volts x 5 seconds = 12000 joules.

At 120W power delivery from the top-up charger, that's 12000 joules /120 joules/second = 100 seconds to return the energy from a single starting crank, which sounds reasonable.

But these products are usually marketed as rescue packs to get you going when you've left the lights on on and pancaked the battery. They often say they can "restore a flat battery in 15 minutes". So let's examine that:

A car battery is about 150 Ah (amp-hours). This means it can supply a current of 1 amp at about 12 volts for 150 hours; that's 1 x 12 x (150 x 3600) = 6,480,000 joules of energy.

To deliver this amount of energy back into the car battery via the cigarette lighter - at 120W - would therefore take 6,480,000 / 120 = 54,000 seconds or (divide by 3600 seconds per hour) = 15 hours!

After 15 minutes at 120W you could have transferred 120W x 15m x 60seconds per minute = 360,000 joules.

These are extreme case numbers that I have used, but all the same, you can see that one of these "get you started" rescue packs is not capable to restoring a car battery to the fully charged state from a fully discharged state.

Also, the current draw of 10A or higher from the recharge pack is quite high and likely to, ultimately, degrade the cells; so they are not going to survive too many discharge cycles like that.

I'd suggest, therefore, investing in a pair of jump leads, a mobile phone and an AA or RAC subscription as a more viable alternative.

[Can someone please check my reasoning / maths above, just in case my early-morning mental fog has caused me to make a mistake]

242

Physiology & Medicine / Re: Do Flu vaccines increase the risk of pandemic flu?

« on: 06/01/2016 00:07:57 »

The 2009 flu pandemic vaccines (H1N1) was a genetically-modified recombinant virus to generate monoclonal antibodies from low reactors (virus-like-particles).

No, that's not right.

No vaccine elicits monoclonal antibody production; that's something that happens in a test-tube under carefully managed conditions.

Vaccines elicit a polyclonal response; that is, they stimulate a broadly neutralising antibody response which, in the case of the split flu vaccine, recognises a range of epitopes.

Flu vaccine strains are, by definition, all man-made because they are manipulated to ensure that they replicate well in eggs, which is the culture vessel used to produce the (majority of) flu vaccines.

243

Physics, Astronomy & Cosmology / Re: What happens to light as universe expansion slows down?

« on: 02/01/2016 11:14:15 »

So the universe is expanding at an increasing rate. According to the law of conservation of energy this shouldn't be happening? The universe must be getting extra energy from somewhere hence Dark Energy?

That's right; the observations that we have suggest that the Universe is expanding, and that the rate of expansion is
increasing although this inflation is being powered by unknown physics. This is reconciled by invoking the as yet undefined, unknown and unmeasured theoretical entity dubbed "Dark Energy" as the driving force. We know that this must exist in one form or another, but no one has yet detected it or, for that matter, knows how to go about detecting it...

244

Just Chat! / Re: Jokes thread. :)

« on: 29/12/2015 08:52:10 »

Q: What kind of shoes do frogs prefer?

A: "Open-toad" sandals...

245

Physiology & Medicine / Re: Is psychiatry a pseudoscience?

« on: 22/12/2015 16:10:10 »

Psychiatry is a clinical disclipline which deals with the physical manifestations of underlying neurological disturbances, including genetic and biochemical disorders that cause depression and other behavioural abnormalities.

To say "psychiatry is a pseudoscience" is like calling cardiology quackery because you elicit a diagnosis by asking someone if they get chest pain when they exert themselves. It's not, and clinical diagnosis is the mainstay of medical practice. We identify the cause of a person's problems, in almost any sphere of medicine, more than 90% of the time just by talking to them. No stethoscope needed.

You want an example of something that is really pseudoscientific? Look no further than chiropractice, reflexology or, why not go for broke and consult a homeopath?

246

Physics, Astronomy & Cosmology / Re: Does a perfect blackbody exist?

« on: 02/12/2015 23:54:47 »

I think someone recently invented an even blacker black. This one uses gold nanoparticles and nanorods, which interfere with the incident radiation of different sizes and absorb the energy, meaning that even less radiation is reflected.

So, essentially, black just got blacker...

247

Physics, Astronomy & Cosmology / Re: By how much has the mass of the Earth changed over the planet's lifetime?

« on: 29/11/2015 09:53:41 »

The Earth is losing between 50,000 and 60,000 tonnes of mass each year.

How do we arrive at this figure?

We need to consider the "mass balance"; that is, how much material is arriving here that wasn't here to start with, and how much material is leaving the planet.

First, let's consider how the Earth is gaining mass:

Earth is continuously gaining mass in the form of dust particles, and sometimes larger bodies, that fall in from space. Scientists estimate that this adds up to about 40,000 tonnes of material each year.

At the same time, using planet-wide temperature readings from NASA and other sources, one can see that the planet is warming up, or gaining thermal energy. This is coming from the Sun, and if energy is added to a system, then since E=mc^2, there is a corresponding increase in mass. Based on present data, this is probably adding a small amount of mass to the planet each year, of the order of 200 tonnes or so.

So the total mass gained by the planet each year is about 40,000 tonnes.

At the same time, the Earth is losing heat energy from its core as radioactive elements decay. Based on estimates of how much energy exits in this way, the mass loss is trivial though at about 16 tonnes per year.

More significant is what happens in the outer reaches of our atmosphere where the gravity field is weaker and lighter elements, like helium and hydrogen are hard to hold on to.

Earth loses about 1600 tonnes of helium to space each year like this. More dramatically, physicists estimate that we're losing about 3 kilograms per second of hydrogen in the same way. This adds up to 95,000 tonnes of hydrogen over a year.

So the net change in mass each year is 40,000 tonnes coming in, minus 96,000 tonnes going out. So the Earth loses about 56,000 tonnes of mass every year.

That sounds like a lot, but actually, as a proportion of the mass of the planet, which is 6 x10^21 tonnes, it's about 0.000000000000001% per year, so probably not worth losing any sleep over!

248

New Theories / Re: What is the time?

« on: 12/11/2015 07:29:52 »

The items you are posting are just collections of graphics from another site.

The material isn't properly explained or discussed. As a result, no one is engaging with the material, because it's poorly presented.

Please consider making actual text-based posts to set out your arguments; the odd image is helpful, but this is a discussion forum, not a podium for presentations of pet theories lifted from other websites.

Chris

249

Just Chat! / Re: What do we think of the medals next to your name?

« on: 05/11/2015 23:10:43 »

Nice comments everyone; thanks for the feedback. I' think, on balance, it will be best to decommission the medals for now and then replace them once we have a better, less cluttered solution, which I'll work on.

Chris

250

Just Chat! / Re: Found this codes...

« on: 29/10/2015 23:34:08 »

Extraordinarily strong smell of SPAM here...

And how funny, the youtube channel is run by someone with the same name as the person who has registered here.

Whoops. Sorry pal, but lying to us in your first post is not a good way to start the relationship.

Chris

251

Just Chat! / Re: Seen the promo for Consciousness3D Science documentary-in-progress?

« on: 29/10/2015 09:20:35 »

Very thought provoking.

252

Geology, Palaeontology & Archaeology / Re: Can you please help me identify these?

« on: 27/10/2015 18:21:48 »

RD is correct on the holes; there are a range of petrophagic (stone-eating) marine organisms capable of drilling through things in this way.

253

Plant Sciences, Zoology & Evolution / Re: What is the Benefit of Biofluorescence in Animals?

« on: 16/10/2015 18:51:33 »

I'm speaking strictly of "biofluorescence" here, not bioluminescence.

Perhaps you could explain the distinction between these two terms, and to what sorts of animals each applies?

254

Physiology & Medicine / Re: Why Is It so painful When Ewe almost Sneeze Then don't ?

« on: 18/09/2015 13:05:09 »

I don't find it painful, merely desperately frustrating; it feels like someone has dangled a delicious treat in front of me, like a cool beer on a hot day when I'm really thirsty... but then snatched it away just at the instant I had lifted it to my lips...

PS - nice to see you Neil.

255

Physiology & Medicine / Do antibiotics accelerate wound healing?

« on: 01/10/2011 09:23:04 »

Antibiotics will certainly speed up wound healing if infection was formerly present, because bacteria cause inflammation and secrete tissue-degrading enzymes that prevent the wound knitting together.

However, there is one exception where having an infection in a wound is actually a blessing rather than a curse:

http://www.thenakedscientists.com/HTML/articles/article/angel-glow/

Chris

256

General Science / Why should adding salt to a humidifier increase steam production?

« on: 18/06/2010 22:38:23 »

I was asked on the radio the other day why adding salt to the water fed to a humidifier should cause a significant boost in steam production.

Apart from raising the boiling point of water, I couldn't think of any specific reason why this should be the case.

Can anyone help?

Chris

257

General Science / Is it true that most women are attracted to bad guys?

« on: 22/06/2008 15:28:28 »

The brain is not being logical and hasn't caught up with the fact that todays good provider is intelligent and has a good job in the city. They don't need any fishing our hunting skills any more.

Are you saying that womens' brains are defective...?!! You'll be saying that mens' brains are in their trousers next...oops, so they are; my mistake!!

258

Chemistry / Re: What is "Laughing gas"? Why does laughing gas make you laugh?

« on: 19/05/2007 11:19:26 »

Nitrous oxide (formula N₂0) is a volatile gas discovered by the English clergyman and scientist Joseph Priestley in 1793 (Priestley was certainly a bit of a gas man because he also discovered oxygen, carbon monoxide, carbon dioxide, ammonia, and sulphur dioxide).

Priestley made his nitrous oxide by heating ammonium nitrate in the presence of iron filings, and then passing the nitric oxide (NO) that came off through water:

2NO + H₂O + Fe → N₂O + Fe(OH)₂

Humphry Davy, from the Pneumatic Institute in Bristol, England, then began to experiment with the physiological properties of the gas, and visitors to the institute were given nitrous oxide to breathe. Their reactions and his own experiments led Davy to coin the term 'laughing gas', and he also noticed that the gas had anaesthetic properties. "As nitrous oxide in its extensive operation appears capable of destroying physical pain, it may probably be used with advantage during surgical operations in which no great effusion of blood takes place".

However, for 40 years or so after Davy made this observation, most N₂O was used for recreational purposes, including at public shows and carnivals; members of the public would pay a small price to inhale a minute's worth of the gas. It wasn't until the mid 1800's that doctors and dentists began to re-explore the pain-killing potential of nitrous oxide.

As is usually the case with a medical breakthrough, it took an accident to help a local dentist to make the intellectual leap that was to catapult nitrous oxide into the domain of medicine. Horace Wells watched as one of the volunteers breathing the gas, a man named Samuel Cooley, staggered into some nearby benches and injured his leg.

But what intrigued Wells was that Cooley remained unaware of his injury until the effects of the gas wore off. Realising that N₂O might possess painkilling qualities Wells approached the demonstrator, a medical school dropout called Gardner Quincy Colton, and invited him to participate in an experiment the next day.

Colton agreed and subsequently administered nitrous oxide to Dr. Wells whilst another dentist extracted one of Wells' teeth! Wells experienced no pain during the procedure, and the birth of N₂O as a dental and medical painkiller had arrived.

That's the history of nitrous oxide. Since that time it's been embraced as a safe agent that can be used for pain relief (such as during childbirth and dental procedures) and in general anaesthesia.

On its own it's not a sufficiently potent anaesthetic to induce (i.e. cause) anaesthesia, but once a patient is "under", it's a very good gaseous agent for anaesthetic "maintenance".

In this respect, N₂O isn't that unusual since most volatile gases can behave as anaesthetics with intoxicating effects; they differ only in their potency (i.e. how much of them is needed to have an effect). Volatiles with this propery includes the butane you squirt into your cigarette lighter, and even petrol vapours. In fact this latter example has been a serious problem in parts of Australia where members of some Aboriginal communities have been sniffing petrol. This has resulted in BP (British Petroleum) recently producing a blend of unleaded for the Australian market that is less good for sniffing.

No one knows exactly how general anaesthetics work, but the fact that they are usually organic, lipid-loving chemicals suggests that they probably alter nerve cell function by dissolving in the oily cell membrane and affecting the behaviour of membrane pores or channels which control the excitability of the cell.

Alcohol probably works similarly (as someone has already suggested) and there is now evidence that alcohol specifically renders cells more sensitive to one of the brain's inhibitory nerve transmitters called GABA. This means that cells become less responsive in the presence of alcohol, which is why booze is a CNS depressant.

As an aside, it's not just animals that can benefit from the effects of N₂O. Cars receive a boost in performance when a burst of "nitro" is injected into the cylinder during combustion. The heat of the burning fuel causes the nitrous oxide to decompose to nitrogen and oxygen: 2N₂O → 2N₂ + O₂

So 2 molecules of gas turn into 3 molecules of gas, which increases the volume of products inside the cylinder, boosting performance. So a bit like Viagra really, although that relies initially on the effects of nitric oxide (NO), rather than nitrous!

259

NAKED SCIENCE - THE OFFICIAL BOOK / Re: NAKED SCIENCE

« on: 10/10/2006 00:05:36 »

quote:Originally posted by Roy P

Cracking little book! A perfect accompaniment to a trip to the loo :-)

___________________________________________________
Roy P

That's so funny - everyone's saying that!

And I suppose the real bonus is that even if you hate it (which you won't) you can always wipe your ar$e on it, which is nice!

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

260

Complementary Medicine / A new Forum for alternative remedies ?

« on: 23/07/2003 10:54:44 »

I'm just looking at the degree of interest that there seems to be in alternative and complementary therapies. It struck me that maybe we should set up an additional forum, like the medicine one, just devoted to complementary medicine. Or is it better to keep everything together ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx