Trebuchet or Catapult?
Both a catapult and a trebuchet are military devices that hurl stuff at the enemy, but they work by different methods.
A catapult relies on some sort of stored energy—usually the tension in stretched or twisted ropes. Typically, a catapult is limited to loads of 30–40 kg.
A trebuchet relies on counterweights. It can easily hurl loads weighing 100 kg or more.
Further Spread
The Genoese inhabitants of Caffa fled back to their homes in southern Europe, taking the disease with them. Their arrival home was both bizarre and disastrous. The ships limped into ports or were washed up on the shores, most or all of the crew dead. Rescuers and visitors to the ships became infected.
Even without Caffa, the Black Death would have invaded Europe. The stream of infection from Caffa was just one of the many routes that the Black Death took into Europe.
It spread west via the other trading ports in the Black Sea, arriving in Constantinople in 1347.
Overland caravans also carried the disease into Europe. Several Italian merchant ships carried the disease to Sicily when they docked in October 1347. An eyewitness wrote: ‘…soon death was everywhere. Fathers abandoned their sick sons. Lawyers refused to come and make out wills for the dying. Friars and nuns were left to care for the sick, and monasteries and convents were soon deserted, as they were stricken too. Bodies were left in empty houses, and there was no one to give them a Christian burial.’
By January 1348, the Black Death had spread to Genoa and Venice. By June 1348, it had reached England, France, Spain and Portugal. It took two more years to reach Scandinavia and another year to get to northwestern Russia. The Black Death also devastated the Middle East, reaching Antioch in 1348–1349, Mecca and Mosul (then Mawsil) in 1349 and Yemen in 1351. It then kept returning, with major recurrences in 1361–1363, 1369–1371, 1374–1375, 1390 and 1400.
With each successive return of the plague, fewer people died, because the genetically susceptible people had already perished in earlier outbreaks. Even so, the population of Europe returned to pre-plague levels only in the early 1500s.
After this, there were a number of recurrences—the Italian Plague (1629–1631), the Great Plague of London (1665–1666), the Great Plague of Marseille (1720–1722) and the Plague Riot in Moscow (1771).
Results of Black Death
The Black Death was many things, but it was not unique to Europe, nor (as mentioned earlier) did it start there—it came from China.
In Europe, the successive revisitations of the Black Death caused, of course, massive depopulation. The population of Europe dropped from 75 million to 50 million. In Damascus, some 25–40% of the people died, with 1,000 dying horribly each day at the peak of the outbreak. The population of Florence dropped from 120,000 in 1338 to just 50,000 in 1351. In England, the population dropped from seven million before the arrival of the Black Death, to only two million in 1400.
Unsurprisingly, there were also major and long-reaching social effects of the Black Death.
The peasants who survived found themselves highly sought after as a source of labour. The landowners resented this because, for the first time, the peasants were not easy to replace and no longer a source of very cheap labour. By the end of the 1300s, there had been peasant uprisings in France (the Jacquerie Rebellion), Italy (the Ciompi Rebellion), Belgium and England (the English Peasant Revolt). Social barriers between the poor and the rich were torn asunder. Desperate laws (the Sumptuary Laws) were passed to stop peasants with newly acquired wealth from wearing the trappings of the rich.
It is also claimed that the sudden geographical movements of many English-speaking people led to the Great Vowel Shift, in which the pronunciation of the English language changed dramatically. The German, Icelandic and Dutch languages also experienced changes in pronunciation, similar to those in the English Great Vowel Shift.
The Roman Catholic Church was ineffectual against the plague and lost much of its influence.
It is even claimed that the Renaissance—the rise of classical scholarship and scientific and geographical discoveries in Europe—was a direct result of the Black Death.
They say that every cloud has a silver lining—although in this case, it was a really Big Black Cloud.
Peak of Evolution
We humans might think that because our Big Brains invented music, weapons of mass destruction and income tax, we must be at the top of the evolutionary chain. But bacteria, viruses and parasites don’t care about our fabulous achievements—they just want to survive and reproduce.
Today there is still much controversy over which infectious agent (bacteria, virus, etc.) caused which pandemic/epidemic. Certainly, epidemiologists all agree that the Third Pandemic was caused by the bacterium, Yersinia pestis. Most of them believe that this bacterium also caused the Black Death of the 1300s. However, there are a few odd details that cause disagreements among some epidemiologists. These include the speed at which the epidemic spreads, the different rates of death, and the effect of local temperatures.
References
Del Re, Gerard, The Whole Truth: A Compendium of Myths, Mistakes, and Misconceptions, New York: Random House, 2004, p 35.
Drancourt, M., Houhamdi, L. and Raoult, D., ‘Yersinia pestis as a telluric, human ectoparasite-borne organism’, Lancet Infectious Diseases, April 2006, Vol 6, Issue 4, pp 234–241.
Encyclopædia Britannica, Ultimate Reference Suite DVD, 2006—‘Black Death’.
Wheelis, Mark, ‘Biological warfare at the 1346 Siege of Caffa’, Emerging Infectious Diseases, September 2002, pp 971–975.
Fuelish Car Engine Idling
I’ve had a lot of fun teaching the junior members of my family how to drive the Family Chariot. But along the way, I realised that something I had done for a long time was actually wrong. Previously, I tried to be ‘kind’ to my car’s engine by allowing it to idle for quite a while before I pulled away from the kerb.
But when I began investigating the Science Behind It All, I found that a long idle was actually harming the engine, the environment—and my wallet.
Don’t Idle
The powertrain of a car refers to the mechanical components that make the car go. The power starts at the engine, goes through the gearbox and finishes at the driving wheels. Les Ryder, the chief powertrain engineer from Ford, USA, said in the January 2007 issue of Popular Mechanics, ‘Engines run best at their design temperature’. In other words, Mr Ryder is telling us that engines run most cleanly and efficiently somewhere between 85°C and 95°C. Idling is not the best or quickest way to warm up your engine—gentle driving is.
The Canadian Office of Energy Efficiency agrees that the best way to warm up your engine is to drive it. Even if the outside temperature is –20°C, they recommend that you idle the engine for only 15–30 seconds before pulling out onto the road. And you need even less idling time at the temperatures usually experienced in Australia.
Cold Idling Engines
Idling a cold engine to ‘warm it up’ is bad in so many ways.
In a cold engine, the fuel is not completely burnt, so it condenses into droplets on the cylinder walls. This leads to two kinds of damage inside the engine.
First, the droplets of raw unburnt fuel wash the lubricating oil off the cylinder walls. Without this protective coating of oil the cylinder walls wear very rapidly.
Second, the unburnt fuel flows down the walls and slips past the rings—diluting the oil in the sump. Diluted oil is not as good a lubricant as pure oil.
Idling also drops the temperature of the spark plugs. This can cause dirty plugs, which can worsen your fuel consumption by some 5%.
Idle thoughts
The Canadian Office of Energy Efficiency crunched the numbers for the hypothetical situation of each Canadian driver idling their car engine for 5 minutes fewer each day. Over a year, this reduced idling would save 680 million litres of fuel, and stop 1.6 million tonnes of greenhouse gases from escaping int
o the atmosphere.
A passenger-empty, idling car ‘warming up’ nothing more than the Earth’s atmosphere.
Glazing the Bore
If a brand-new or reconditioned engine is badly ‘run in’ by the owner, the engine can burn too much oil for its entire life.
The engine consumes extra oil through a phenomenon called ‘glazing’. You need just a tiny amount of ‘roughness’ to give good contact between the rings and the cylinder walls. The bore is manufactured with a deliberate diamond-like or crosshatching pattern on its walls to create a small, but definite, amount of friction. But when ‘glazing’ occurs, the rings ‘rub’ on the walls of the cylinder, making them too smooth, i.e. ‘glazed’ like glass. The oil blows past the rings and out the exhaust pipe.
I know of two driver behaviours that can glaze the bore. The first is idling the engine for too long while it’s new. The second is driving for too long on cruise control with a new engine on flat countryside. In this case, the engine sits on the same engine revs for extended periods of time, thus smoothing out the diamond-like pattern.
New Idling Engines
Excessive idling can also damage new engines.
Inside a new engine, the piston rings need a reasonable load in order to ‘settle’ into the grooves (known as ‘lands’) on the walls of the piston. Too much idling means that the rings won’t settle in properly. The rings can rattle, cause strange wear patterns on the cylinder wall and may even crack.
Therefore, with a new or reconditioned engine, you should accelerate away within a few seconds of starting—but not with a ‘lead foot’—to keep a steady load on the rings. This is easy to do from a cold start, providing you keep the engine revs fairly low for the first 3–5 minutes. This gives the oil a chance to warm up and get thinner, so that it can flow easily into all the small clearances inside the engine.
Exhausted Idling Engines
You might have noticed a vapour trailing out of the exhaust of some cars in the early morning. This is not the oil vapour of a worn engine but the normal water vapour from a cold engine. So the longer you idle the engine, the longer it will take to warm up. And more water droplets will be deposited inside your exhaust system—making it rust sooner.
With a long idle time the engine will produce many more unwanted pollutants. For example, modern cars have catalytic converters. When they reach their normal operating temperature (400–800°C), they convert nasty pollutants into fewer nasty chemicals. And you guessed it, the quickest way for catalytic converters to reach their normal operating temperature is by driving, not idling. The longer you idle your engine, the longer your catalytic converter will remain too cold to do its job.
Problem and Cure
On an average day in the middle of winter, Canadians will idle their car engines for a total of 75 million minutes. This works out to be one car idling for over 142 years! For this reason, Canada has started a national campaign to reduce the unnecessary idling of engines. There are similar regional campaigns in Japan and the UK. In the USA, 13 states have now passed laws regulating the idling of engines. And the ski resort town of Aspen, in Colorado, has actually passed laws making it illegal for car engines to idle for more than five minutes.
Automotive engineers are now talking about the benefits of switching off your engine in traffic, if you are going to be stopped for more than ten seconds.
However, this is contrary to the philosophy behind the Remote Start Function. Available in some US cars, it lets you start the engine from about 60 m away. The advantage is that you can walk out of your house into a nice warm car. The disadvantage is that in ten minutes of idling, you burn about half a litre of fuel.
City of Aspen Municipal Code
13.08.110 Engine Idling.
(a) Except as hereinafter provided, it shall be unlawful for any person to idle or permit the idling of the motor of any stationary motor vehicle for a prolonged or unreasonable period of time determined herein to be five (5) minutes or more within any one (1) hour period of time.
(b) This section shall not apply when an engine must be operated in the idle mode for safety reasons including, but not limited to, the operation of cranes and fork lifts used in the construction industry.
The Canadian Office of Energy Efficiency crunched the numbers for the hypothetical situation of each Canadian driver idling their car engine for five minutes fewer each day. Over a year, this reduced idling would save 680 million litres of fuel and stop 1.6 million tonnes of greenhouse gases from escaping into the atmosphere.
The best way to warm an engine is to drive it gently. When you idle a car, you get zero kilometres per litre, lots of pollution—and a hole in your wallet.
Idling in Traffic
Yes, it does take a little extra fuel to start a cold engine in the morning. But it takes very little extra fuel to start an engine that is already warm. So if you have to stop in traffic for more than 5–10 seconds, switch off the engine.
References
Allen, Mike, ‘Warm the engine first? Debunking more of dad’s myths’, Popular Mechanics, March 2007.
Dunne, Jim, ‘Your dad was wrong: A lot of traditional automotive wisdom just doesn’t hold up’, Popular Mechanics, January 2007.
‘Fuelish Myths’, Time, Vol 114, No 2, 17 September 1979.
Magliozzi, Tom, Magliozzi, Ray and Berman, Doug, ‘Click & clack: Hot air on AC’, Washington Post, 8 April 2007.
Office of Transportation and Air Quality, US Environmental Protection Agency, ‘Compilation of State, County, and Local Anti-Idling Regulations’, EPA420-B-06–004, April 2006, p 26.
Cranberry Juice and Urinary Tract Infections
Urinary Tract Infections (UTIs) are very common in women. And cranberry juice does have a place in preventing recurring UTIs, but it can’t get rid of an established infection.
UTI—Stats and Micropathology
Most men will never have a UTI. However, about half of all women will have a UTI at some stage in their life.
Unfortunately, about one-third of women who have a UTI will have a recurrence in the following year. The major risk groups are women aged 25–29 years (sexual activity is a risk factor) and over 55 years (caused by lower levels of protective oestrogen).
In the USA, approximately 7–11 million women are prescribed antibacterials for their UTIs. Each year UTIs cost the American community US$1.6 billion in direct and indirect costs. Each year UTIs in female university students result in 6.1 days of suffering the symptoms before the treatment begins to work, 2.4 days during which their daily activities are restricted and 0.4 days of bed rest.
The symptoms are unpleasant—and include frequency (a desire to urinate far too frequently, and usually producing only a small volume), urgency (the sudden desire to urinate), dysuria (pain on passing urine), haematuria (blood in the urine), nocturia (having to get up at night to pass urine, which had not occurred previously), fever, and pain in the back or flanks. The later symptoms in this list are more uncommon—and more serious.
A microbiologist diagnoses a UTI by getting a ‘clean catch of midstream urine’, placing some on a ‘culture plate’, and seeing if any bacteria has grown. A diagnosis depends on having more than 100,000 bacteria per millilitre of urine—a millilitre is roughly the volume of the tip of your little finger, including the fingernail.
Causes of UTIs
There are many factors that can increase your risk of getting a UTI.
Sexual intercourse is a risk factor in both young and post-menopausal women. Low oestrogen levels is an additional risk factor for older women.
Diseases such as diabetes mellitus increase both the incidence of UTIs and the chance of complications. Kidney stones and other abnormalities, as well as spinal cord injury are also risk factors—as is pregnancy (which is definitely not a disease).
Genetics are also involved—if one person in a family has a history of UTIs, related women in the family then have an increased risk. Individuals who are ‘non-secretors for ABO blood-group
antigens’ are also at greater risk for recurrent UTIs.
UTI—Pathology and Treatment
In a simple UTI, the bacteria live in the urethra (the pipe to the outside world) and the urinary bladder. In a more complicated situation, the bacteria can migrate upwards, even to the kidneys, which can sometimes become damaged.
The bacteria involved, which usually come from the bowel, are most often faecal bacteria, the well-known E. coli being the culprit about 80–95% of the time. Women are about 30–50 times more likely to suffer UTIs than men for a couple of reasons. In women there is a very short distance between the rectum and the opening of the urethra, and a very short length of urethra from its opening at the skin to the bladder.
Treating an acute UTI is relatively straightforward—simply take the appropriate antibiotics. However, it’s more of a problem for a woman who gets recurrent UTIs. If she does nothing, she will probably get yet another UTI in the next year or so. But if she takes the antibiotics for an extended period of time, the bacteria are likely to evolve resistance to those antibiotics—and we already have enough problems with antibiotic-resistant bacteria.
Enter the Cranberry
This is where the cranberry—along with simple hygiene measures—can play a role. Indeed, the first report about the benefits of cranberry juice for bladder infections in a peer-reviewed medical journal dates back to 1914.
Science is Golden Page 13
