| Dr. Hypothesis |
| Sunday, 13 January 2008 | |
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Please email your queries to drhypothesis@bluesci.org for your chance to win a £10 book voucher Dear Dr Hypothesis, Why do I feel tired after a meal - and work less efficiently? Why does my supervisor experience a post-lunch dip? Could it be due to stomach distension, an increased blood supply for the digestive system compromising brain circulation, hypoglycaemia as a result of overreacting to the initial rise in blood sugar levels, release of hormones such as cholecystokinin (CCK), or perhaps there are other reasons? Kipping Kristjan DR HYPOTHESIS SAYS: Well, Kristjan, you’ve certainly given me food for thought with all of these possibilities! Actually, there are a number of reasons that act together to cause the ‘post-prandial lull’: it costs energy (an increase in metabolism of 25-50%) to digest the food; and, due to digestion, the hormone CCK is released to tell the brain that you’re full while simultaneously activating the areas of the brain involved in sleep. Finally, when you eat a lot of carbohydrates the level of tryptophan (an amino acid) in your blood increases, which is converted into serotonin in the brain, and this also makes you sleepy. My only advice to you is to avoid eating a particularly large meal before that important meeting with your supervisor. Dear Dr Hypothesis, I spent most of the summer holidays trekking through the Andes hoping to discover a lost civilization – but that’s another story. What I was really intrigued by was the variety of different methods that my travelling companions used to purify their water while we were away. From simply drinking only from clean-looking streams, to carefully measuring out iodine drops, I saw the lot! Which method is the best? Thirsty Thelma DR HYPOTHESIS SAYS: I definitely would not recommend drinking out of streams just because they look clean, as it is impossible to judge how many micro-organisms may be growing there. Boiling is the best way to sterilise water as it has been estimated that most pathogens will be killed by only a few minutes at 85˚C, so should die in the time it takes water to boil. I realise that this may be impractical at times, and so iodine tablets would be my second choice, although it is important to store it in a dark bottle as it is light-sensitive. An alternative chemical method for purification is chlorine, which is recommended for those allergic to either iodine or shellfish (many people who are allergic to shellfish are also allergic to iodine). I hope that hasn’t muddied the waters even more for you, Helen. Dear Dr Hypothesis, I'm a keen meat-eater, but I'm worried about the global impact of my diet. How much of a carbon footprint do I leave?
Ravenous Ron DR HYPOTHESIS SAYS: Dear Ron, it's an important question that you ask. Quite aside from the ethical questions about eating meat, there is a real environmental impact associated with being carnivorous. The carbon costs include the production and transportation of feed, the process of calf rearing, and getting the meat from the farm to the shops. A recent study suggested that one kilogram of beef on the table has the equivalent footprint of travelling 250 kilometers by car, as a conservative estimate. Cows also produce a large amount of methane (an important greenhouse gas), but carnivores like to remind us that the personal emissions of vegetarians exceeds that of their meat-eating friends! Dear Dr Hypothesis, I'm a keen climber, and yet I watch with green envy videos of gecko lizards scurrying about on smooth surfaces. How do they do it? Agile Annie DR HYPOTHESIS SAYS: Dear Annie, the effect you're seeing is the result of a high degree of adaptation in the gecko. Each of the gecko’s toes is covered with millions of tiny hairs called satea, each of which is further split into hundreds of bristles called spatulae. As the gecko places a toe on a surface each of the tiny spatulae forms a bond at the molecular level with the surface, using tiny forces called Van der Waals interactions. Although weak individually, together, billions of these interactions are so strong that all four feet of a gecko could hold the equivalent of 90 lbs. Now that would be a large gecko! These interactions are of great interest to nanoscientists, who have recently come up with a version that works underwater, called geckel. Hang on in there, Annie - you may yet get some use from this technology yet! Dear Dr Hypothesis, my friend recently lost a hand in a potting shed-related accident. What are the recent advances in bionic hands so that he may continue his gardening in the future? Friendly Fred DR HYPOTHESIS SAYS: Dear Fred, your friend is indeed most fortunate - a Scottish firm has just created a new bionic hand. It features fully articulated joints, as well as myoelectrical sensors, allowing the motors to be controlled by thought alone. The artificial joints allow a dexterity of movement never seen before, which gives the patient the ability to grip gently. One soldier fitted with the hand commented that he was now able to hold polystyrene cups again - so a pair of gardening shears should ‘posie’ no problem! Dear Dr Hypothesis, I think I may have a slight problem, as I am unable to leave the house without my trusty personal stereo. I just don’t seem to be able to face my daily commute without blocking out the hectic world around me and I often get panicky if my batteries die before I reach the office. However, sometimes, I am able to turn my stereo back on as I leave work and the batteries seem to have recovered. Do you have any idea why this could be happening? Musical Muriel DR HYPOTHESIS SAYS: Muriel, this recovery is due to a fairly simple chemical process. In a common zinc/carbon battery, the zinc and carbon rods are immersed in sulphuric acid and connected by a wire so that electrons can flow from the zinc to the carbon and create an electrical circuit, thereby powering your personal stereo. During this reaction, hydrogen gas is produced as a by-product at the carbon rod and this can completely coat the rod, preventing the further flow of electrons. If this battery is allowed to rest for a few hours (while you’re at work), the gas will dissipate and the connection between the carbon rod and the wire will be restored. In larger batteries, such a those in a car in which the drain on the battery is quite high, the hydrogen gas builds up more quickly and so, once given time to rest, the battery will show a more pronounced recovery as there will still be a greater charge stored within it. |
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