41

Physiology & Medicine / Re: How can cortisol be managed to keep levels OK for health and pain relief?

« on: 27/11/2018 18:19:34 »

Exogenous steroids (like prednisolone and dexamethasone) are best taken in the morning because this mirrors the natural steroid surge that accompanies waking. Regular use of an exogenous steroid will cause a reduction in the body's own steroid production, so topping up the morning surge is least disruptive to your circadian cycle. If you take the steroid later in the day then it provokes wakefulness and this can lead to disturbed sleep or insomnia.

42

Plant Sciences, Zoology & Evolution / Re: Why do most humans have traces of Neanderthal DNA?

« on: 27/11/2018 09:08:08 »

Both species definitely share ancestors, which is why our DNA is so similar in the first place, but Neanderthals and anatomically modern humans diverged from one another 200-300,000 years ago. Current thinking is that the last ancestor we both share is Homo erectus, which was spawned about 1.8 million years ago. Neanderthals disappeared about 30-40,000 years ago.

Because they are relatively recently extinct, Neanderthal remains are a good prospect for DNA recovery, and about 10 years ago scientists completed the Neanderthal genome project; this is the Neanderthal equivalent of the Human Genome Project that decoded all 3 billion letters of the human DNA code.

Armed with this sequence, and because we are so closely related, it's possible to align the Neanderthal DNA makeup with the modern human genome and to highlight areas that are shared and areas that are distinct.

Areas of the genome that are shared by both were inherited from an ancestor to both Neanderthals and us and will be universally present. Similarly, sequences that are specific to one species or the other - having evolved after the two species split - will be exclusively present in each species.

But there will also be regions of the genome that are variably shared in human and Neanderthal populations, indicating gene mixing. This is the example you highlight of some human populations carrying Neanderthal sequences but not others. It is also the evidence that tells palaeontologists and geneticists that the two species interbred, which is how these gene sequences came to be variably shared.

43

Physics, Astronomy & Cosmology / Re: What are gravitons and how do they explain gravity?

« on: 17/11/2018 08:31:19 »

Hi @miniguy

There are a number of theories for how gravity "works"; the most popular -  and evidence-based - is Einstein's theory of general relativity, which proposes that mass deforms the fabric of the universe - Spacetime.

People talk about a bowling ball sitting in the centre of a trampoline to make a dent that causes other bodes to roll down into the "gravity well" created by the bowling ball; this is why massive bodies, like stars, cause moving bodies like planets to deviate from a straight trajectory and instead adopt an orbital path.

Meanwhile, quantum mechanics (QM) has investigated how gravity can be fitted into what we call the "standard model", which is the collection of particles and force carriers that make up matter in the Universe around us. This QM theoretical model invokes a particle as the force carrier to convey gravitational attraction. This notional particle is the graviton. So the idea would be that objects are attracted to one another by constantly giving away and receiving a stream of gravitons between them. And like photons, these notional particles would travel at the speed of light.

The problem is that no one has ever seen a graviton, and all the theories that have so far tried to merge what we do know about gravity with QM yield nonsense results. So, for now, gravitons remain a theory among theories.

44

Geology, Palaeontology & Archaeology / Re: What is this ridged fossil found in Somerset?

« on: 05/11/2018 08:11:31 »

PS @Sandmidj - I modified your post to insert the image into the body text so it's immediately visible. To do this yourself, if you need to, you go to "attachments" below the text box (where you uploaded the image in the first place) and click on the "insert" link next to the image name. You can do this at the time of uploading, no need to modify later. I think it helps because the image is presented at full size and people have less work to do to review the picture. chris

45

Geology, Palaeontology & Archaeology / Re: What is this ridged fossil found in Somerset?

« on: 05/11/2018 08:09:27 »

Could be bits of fossilised marine algae. I found some nice fossilised wood pieces in Teignmouth, Devon, a few years back; the appearance is quite similar.

46

Geology, Palaeontology & Archaeology / Re: What is this ridged fossil found in Somerset?

« on: 03/11/2018 22:29:22 »

The first thing I thought about were fossilised ripples, but, as I pointed out, there are ridges on both sides, which made me question my original instinct. I've seen quite a lot of examples of ripple patterns, especially in the rocks in NW Australia where I spent a bit of time, but none had ripples on both sides.

47

Geology, Palaeontology & Archaeology / Re: What is this ridged fossil found in Somerset?

« on: 03/11/2018 15:59:03 »

Interesting how the ridged profile is symmetrical on both sides of the specimen.

This needs @Bass to make a diagnosis. It's above my paygrade.

48

Chemistry / Re: Why is there an asterisk next to an author's name in a journal paper?

« on: 28/10/2018 13:52:04 »

Usually this refers to the "corresponding author" (i.e. the person to write to about the paper), or can sometimes be used when applied to two first authors to indicate that both made a equal contribution to the work.

To find out what the asterisk means refer to the author details legend below the list of names. In electronic publications this is usually a clickable option next to the author list. In print copy journals they usually put the legend somewhere on page 1.

49

Chemistry / Re: How do you make a mirror?

« on: 19/10/2018 05:11:47 »

I've used a similar approach to silver-coat the inside-surface of a round-bottomed flask in order to make a scientifically-inspired Christmas baubal. The ammonia solution is very strong and you need good ventilation.

I'm not sure what the tin chloride solution does and why you need that - anyone know?

50

That CAN'T be true! / Re: Do photons, neutrinos and dark matter have a structure?

« on: 15/10/2018 10:46:25 »

Er either I'm really jetlagged or none of this makes any sense whatsoever...

51

Question of the Week / Re: QotW - 18.09.30 - Is second hand smoke more dangerous than smoking a cigarette?

« on: 07/10/2018 15:46:30 »

For many carcinogens and poisons (including cigarette smoke), risk increases with exposure.

Interesting choice of words, @evan_au , begging me to enquire what carcinogens and poisons do not follow a dosage-dependent relationship?

52

Physiology & Medicine / Re: What is the pathophysiology and histopathology of cataract?

« on: 07/10/2018 09:53:32 »

This is a very helpful article about the biochemistry and pathogenesis of cataract formation, which might help you.

53

Physiology & Medicine / Re: Is the shingles vaccine still useful if I've recently had shingles?

« on: 01/10/2018 09:51:17 »

Shingles, also called zoster, is a manifestation of varicella zoster virus (VZV), which is a member of the herpesvirus family. These viruses characteristically infect for life, establishing a latent state from which they can later reactivate multiple times, producing a range of symptoms.

In the case of VZV (chicken pox) the primary infection, which is acquired through the air, produces a rash all over the body; this leads to the infection of sensory nerves that subsequently harbour the viral DNA for the lifetime of the infected individual.

Reactivation occurs from these nerve cells; in response to as-yet undefined signals the viral DNA switches on and begins to assemble new virus particles inside the nerve cell. These are exported down the nerve fibre to the overlying skin where they bud out and infect skin cells, producing infectious blisters.

We don't know why, but unlike the primary disease, the reactivation of chicken pox / VZV remains confined to one patch of skin called a dermatome. This region is supplied by one spinal nerve segment, so it may be that the reactivating virus in some way sends signals to the nearby nerves that all supply one body region and in this way promotes all of them to reactivate together.

The result is a strip of painfully-blistered skin; this is the syndrome referred to as shingles. The lesions are loaded with virus and highly infectious.

The virus is normally held in check - and these manifestations prevented - by the immune system, specifically by white blood cells called T cells. These can recognise when an infected cell begins to express viral chemical signatures that herald a reactivation and can kill the relevant cells. As a result, attempts by the virus to reactivate periodically are stamped out without you even realising.

This sub-clinically recurrent reactivation most probably has the effect of re-priming your immune response, encouraging the T cells to up their game and remain vigilant. It's called the Hope-Simpson model after the man who poposed it.

But as we age, or suffer intercurrent immune suppression or other chronic illnesses, the T cell population and the T cell response can dwindle. This can create a chink in the immunological armour, offering the virus an opportunity to break through and produce a shingles manifestation. Some people seem to be more susceptible to this than others.

Off the back of a reactivation, you will develop a much more profound immunity afterwards, but this will extinguish again over time and your vulnerability will return.

The vaccine contains a heavily-attenuated live VZV strain; injected into the muscle it undergoes limited replication but as it does so it displays the full genetic repertoire of the virus to the immune system, helping to re-kindle a comprehensive immune response. This increases the potency of your surveillance, reducing the likelihood of shingles.

Therefore, having the vaccine will reduce the risk of shingles in the near future; but having shingles will also reduce the risk of another attack of shingles in the near future, but probably not for as long as the vaccine because this will be given when you are well and able to make a more resilient immune response. By definition, when you have a shingles attack you are suffering an immune decrement, so this is not the best time to be making a long-lasting immune response.

I hope that answers the question for you.

54

Physiology & Medicine / Re: Why do people punish themselves sometimes?

« on: 25/09/2018 22:13:20 »

What do you mean by "punish themselves"?

Are you referring to "punishment" in the Max Moseley sense (https://www.dailymail.co.uk/news/article-1033319/Our-kinky-games-Max-Mosley-Girls-tell-sex-session-Grand-Prix-boss--deny-Nazi-orgy.html) or do you mean people self-harming as a means of psychological release, or people who inflict self-deprivation to atone for a perceived failure or expunge feelings of regret?

55

Physics, Astronomy & Cosmology / Re: How do you steer a rocket following take-off?

« on: 08/09/2018 10:55:32 »

Thanks both.

the atmosphere is a real drag, so you want to go vertically to get above it as quickly as possible.

That's a really good point and I should have said that in passing. I'll commit that to memory.

attaining a stable orbit means that you need to be traveling horizontally at about 11km/second.

That sounds a bit fast, @evan_au - I had in my head that orbital velocity is about 7km/s and escape velocity is about 11km/s?

Turning east gives you a useful 1000 mph contribution to speed in that direction

Thanks for that @alancalverd - I did say this on the radio and I was relieved that you agreed with me!

56

General Science / Re: What do nerves do in a human?

« on: 02/09/2018 09:58:15 »

This video we made about how nerves work might be helpful:

57

Physiology & Medicine / Re: How does peritoneal dialysis work?

« on: 02/09/2018 09:54:07 »

Dialysis is indicated when a person's own kidneys fail; in an acute setting, and in chronic kidney conditions where other options may not be suitable, this is usually acheived by placing a tube into a large blood vessel and pumping blood through a partially permeable filter system that uses osmotic and concentration gradients to equilibrate and correct the blood biochemistry.

This sort of process is very invasive, takes a long time and is therefore inconvenient for the patient. Therefore, where the process needs to be carried out in the long term, doctors often elect to do continuous ambulatory peritoneal dialysis (CAPD) as an alternative, at least for a while.

In simple terms, a catheter with a tap on the end is implanted into the abdominal cavity to provide a route between the outside world and the space around the internal organs.

The patient connects this catheter to a large bag of dialysis fluid with the correct biochemical composition to correct their blood chemistry. The fluid runs into the peritoneal cavity and sits there. The patient disconnects the tap and then goes about their business. Meanwhile, the body exchanges ions and water across the membranes of the internal abdominal organs over a period of hours with the infused dialysis fluid.

After a set period of time, the patient re-opens the tap, drains out the spent fluid and then replaces it with fresh. With regular biochemical monitoring, and checks and care to avoid infection, this can be a safe and convenient mode of dialysis for many patients. Yes, the patient walks around with some extra fluid inside them, and they have a tube running into their abdomen so they need to be careful what they do to avoid trauma or infection, but on the whole this is a safe and well-tolerated procedure.

Regrettably, it is not, however, an indefinite option. With time, the peritoneal membranes thicken and develop adhesions in response to the low-grade irritation imparted by the presence of the dialysis fluid. This impairs the effectiveness of the dialysis process, eventually rendering it inadequate. It also carries a risk of other complications such as intestinal obstruction and infection.

At this point, patients normally need to move onto haemodialysis, where blood is piped to a machine for filtering. To facilitate this, a fistula is normally fashioned between an artery and a vein in one arm to provide a high-flow system so that large volumes of blood can be obtained and returned to the body rapidly to minimise the time spent on dialysis.

All of these processes take a heavy toll on a person's health and their well-being. It's also extremely expensive. As such, and where possible, patients are transplanted with a healthy kidney to free them from the burden.

58

General Science / Re: Does using 93 octane petrol rather than 95 octane make a difference?

« on: 31/08/2018 13:48:50 »

The octane rating - known as the RON (research octane number) is a measure of the tendency of a fuel to ignite / detonate under compression. A lower octane fuel, such as 93 RON, will ignite more readily than an 95 RON rated fuel.

This distinction is important because fuels used in petrol engines are mixed with air and added to the cylinder before the piston begins its up-stroke. This means that the fuel and air mixture must be able to withstand being compressed until the spark plug electrically ignites the mix at the desired time.

More powerful engines have a higher compression ratio (because the more air you can pack into the cylinder the more gas there is to do thermal work and the more fuel you can burn from which to extract energy). The downside is that the higher compression produces more adiabatic heating within the cylinder, increasing the chances that the fuel will pre-ignite or begin to burn before it should.

If this does happen, then rather than the fuel burning smoothly and with a "flame-front" originating at the point of ignition (where the spark triggers the burn) and spreading through the fuel air mix, the fuel can begin to burn in a disorganised distribution in multiple places at one; this "pre-ignition" creates pressure waves and resonances within the cylinder that affect the efficiency and speed of the overall burning process, reducing the power development of the engine and also resulting in potentially damaging pressure changes within the cylinder. When this happens it produces a characteristic grating, rattling or banging sound called, appropriately enough, "knocking" or "pinking".

To combat this effect, performance engines use 95 RON fuels that are harder to detonate.

If you put 93 RON fuel into a 95 RON-recommended engine, it will probably pre-ignite and performance will be lower. It might also damage the engine in the long-term.

Most modern engines do have knock / preignition detection built into the engine management system, so the engine can detect when pinking is happening and it will attempt to adjust the timing and mixture to compensate. While this can abolish the knock, it will come at the cost of reduced power, so it amounts to the same thing - poorer output.

59

Chemistry / Re: How is sodium chloride - NaCl - and electrically neutral compound?

« on: 30/08/2018 03:02:11 »

You've already have the correct answer from @Ophiolite above, but to add a further perspective: in a sodium chloride crystal there are equal numbers of sodium ions and chloride ions, because when the sodium and chlorine reacted together, each sodium atom donated one electron to each chlorine atom; as such, no charge has actually been added or taken away, so there is no reason for the constituents to be electrically charged.

Now if we dissolve that sodium chloride crystal in water, although the particles will spread out in solution, there will still be the same number of positively- and negatively-charged ions; hence the solution is also electrically neutral.

60

Chemistry / Re: What is the difference between 'molecule ' and 'compound'?

« on: 22/08/2018 19:19:37 »

Compounds are chemicals formed from mixtures of different elements that are either covalently or ionically bonded. Molecule is a word used to describe a group of atoms, which may be the same or different, chemically bound together.

To be clear, the difference between the two is that a molecule can consist of two or more different or the same atoms joined together - e.g. hydrogen H₂ - whereas a compound is the species formed by the mixing of two or more different atomic species. e.g. magnesium oxide - MgO.