Tag Archives: science

Diffraction grating of parallel electron beams

Diffraction gratings with narrow bars and bar spacing are useful for separating short-wavelength electromagnetic radiation (x-rays, gamma rays) into a spectrum, but the narrow bars and gaps are difficult to manufacture. The bars are also fragile and thus need a backing material, which may absorb some of the radiation, leaving less of it to be studied. Instead of manufacturing the grating out of a solid material composed of neutral atoms, an alternative may be to use many parallel electron beams. Electromagnetic waves do scatter off electrons, thus the grating of parallel electron beams should have a similar effect to a solid grating of molecules. My physics knowledge is limited, so this idea may not work for many reasons.

Electron beams can be made with a diameter a few nanometres across, and can be bent with magnets. Thus the grating could be made from a single beam if powerful enough magnets bend it back on itself. Or many parallel beams generated from multiple sources.

The negatively charged electrons repel each other, so the beams tend to bend away from each other. To compensate for this, the beam sources could target the beams to a common focus and let the repulsion forces bend the beams outward. There would exist a point at which the converging and then diverging beams are parallel. The region near that point could be used as the grating. The converging beams should start out sufficiently close to parallel that they would not collide before bending outward again.

Proton or ion beams are also a possibility, but protons and ions have larger diameter than electrons, which tends to create a coarser grating. Also, electron beam technology is more widespread and mature (cathode ray tubes were used in old televisions), thus easier to use off the shelf.

Training programs should be hands-on and use the scientific method

The current education and training programs (first aid, fire warden, online systems) in universities just take the form of people sitting in a room passively watching a video or listening to a talk. A better way would be to interactively involve the trainees, because active learning makes people understand faster and remember longer. Hands-on exercises in first aid or firefighting are also more interesting and useful.

At a minimum, the knowledge of the trainees should be tested, in as realistic a way as possible (using hands-on practical exercises). The test should use the scientific method to avoid bias: the examiner should be unconnected to the training provider. The trainer should not know the specific questions of the exam in advance (to prevent “teaching to the test”), only the general required knowledge. Such independent examination permits assessing the quality of the training in addition to the knowledge of the trainees. Double-blind testing is easiest if the goal of the training (the knowledge hoped for) is well defined (procedures, checklists, facts, mathematical solutions).

One problem is how to motivate the trainees to make an effort in the test. For example, in university lectures and tutorials, students do not try to solve the exercises, despite this being a requirement. Instead, they wait for the answers to be posted. One way to incentivise effort is to create competition by publicly revealing the test results.

Blind testing of bicycle fitting

Claims that getting a professional bike fit significantly improves riding comfort and speed and reduces overuse injuries seem suspicious – how can a centimetre here or there make such a large difference? A very wrong fit (e.g. an adult using a children’s bike) of course creates big problems, but most people can adjust their bike to a reasonable fit based on a few online suggestions.

To determine the actual benefit of a bike fit requires a randomised trial: have professionals determine the bike fit for a large enough sample of riders, measure and record the objective parameters of the fit (centimetres of seatpost out of the seat tube, handlebar height from the ground, pedal crank length, etc). Then randomly change the fit by a few centimetres or leave it unchanged, without the cyclist knowing, and let the rider test the bike. Record the speed, ask the rider to rate the comfort, fatigue, etc. Repeat for several random changes in fit. Statistically test whether the average speed, comfort rating and other outcome variables across the sample of riders are better with the actual fit or with small random changes. To eliminate the placebo effect, blind testing is important – the cyclists should not know whether and how the fit has been changed.

Another approach is to have each rider test a large sample of different bike fits, find the best one empirically, record its objective parameters and then have a sample of professional fitters (who should not know what empirical fit was found) choose the best fit. Test statistically whether the professionals choose the same fit as the cyclist.

A simpler trial that does not quite answer the question of interest checks the consistency of different bike fitters. The same person with the same bike in the same initial configuration goes to various fitters and asks them to choose a fit. After each fitting, the objective sizing of the bike is recorded and then the bike is returned to the initial configuration before the next fit. The test is whether all fitters choose approximately the same parameters. Inconsistency implies that most fitters cannot figure out the objectively best fit, but consistency does not imply that the consensus of the fitters is the optimal sizing. They could all be wrong the same way – consistency is insufficient to answer the question of interest.

Committing to an experimental design without revealing it

Pre-registering an experiment in a public registry of clinical trials keeps the experimenters honest (avoids ex post modifications of hypotheses to fit the data and “cherry-picking” the data by removing “outliers”), but unfortunately reveals information to competing research groups. This is an especially relevant concern in commercial R&D.

The same verifiability of honesty could be achieved without revealing scientific details by initially publicly distributing an encrypted description of the experiment, and after finishing the research, publishing the encryption key. Ex post, everyone can check that the specified experimental design was followed and all variables reported (no p-hacking). Ex ante, competitors do not know the trial details, so cannot copy it or infer the research direction.

Blind testing of clothes

Inspired by blind taste testing, manufacturers’ claims about clothes could be tested by subjects blinded to what they are wearing. The test would work as follows. People put clothes on by feel with their eyes closed or in a pitch dark room and wear other clothes on top of the item to be tested. Thus the subjects cannot see what they are wearing. They then rate the comfort, warmth, weight, softness and other physical aspects of the garment. This would help consumers select the most practical clothing and keep advertising somewhat more honest than heretofore. For example, many socks are advertised as warm, but based on my experience, many of them do not live up to the hype. I would be willing to pay a small amount for data about past wearers’ experience. Online reviews are notoriously emotional and biased.

Some aspects of clothes can also be measured objectively – warmth is one of these, measured by heat flow through the garment per unit of area. Such data is unfortunately rarely reported. The physical measurements to conduct on clothes require some thought, to make these correspond to the wearing experience. For example, if clothes are thicker in some parts, then their insulation should be measured in multiple places. Some parts of the garment may usually be worn with more layers under or over it than others, which may affect the required warmth of different areas of the clothing item differently. Sweat may change the insulation properties dramatically, e.g. for cotton. Windproofness matters for whether windchill can be felt. All this needs taking into account when converting physical measurements to how the clothes feel.

Keeping an open mind and intellectual honesty

„Keep an open mind” is often used as an argument against science, or to justify ignoring evidence more broadly. Let’s distinguish two cases of keeping an open mind: before vs after the evidence comes in. It is good to keep an open mind before data is obtained – no hypothesis is ruled out. In reality, all possibilities have positive probability, no matter how great the amount and quality of information, so one should not dogmatically rule out anything even given the best evidence. However, for practical purposes a small enough probability is the same as zero. Decisions have to be made constantly (choosing not to decide is also a decision), so after enough scientific information is available, it is optimal to make up one’s mind, instead of keeping it open.
Intellectually honest people who want to keep an open mind after obtaining evidence would commit to it from the start: publicly say that no matter what the data shows in the future, they will ignore it and keep an open mind. Similarly, the intellectually honest who plan to make up their mind would also commit, in this case to a policy along the lines of „if the evidence says A, then do this, but if the evidence says B, then that”. The latter policy resembles (parts of) the scientific method.
The anti-science or just intellectually dishonest way of “keeping an open mind” is to do this if and only if the evidence disagrees with one’s prior views. In other words, favourable data is accepted, but unfavourable ignored, justifying the ignoring with the open mind excuse. In debates, the side that runs out of arguments and is about to lose is usually the one who recommends an open mind, and only at that late stage of the debate and conditional on own weak position. Similarly, “agreeing to disagree” is mostly recommended intellectually dishonestly by the losing side of an argument, to attempt to leave the outcome uncertain. This is an almost logically contradictory use of “agreeing to disagree”, because it is mathematically proven that rational agents putting positive probability on the same events cannot agree to disagree – if their posterior beliefs are common knowledge, then these must coincide.

Seasonings may reduce the variety of diet

Animals may evolve a preference for a varied diet in order to get the many nutrients they need. A test of this on mice would be whether their preference for different grains is negatively autocorrelated, i.e. they are less likely to choose a food if they have eaten more of it recently.

Variety is perceived mainly through taste, so the mechanism via which the preference for a varied diet probably operates is that consuming a substance repeatedly makes its taste less pleasant for the next meal. Spices and other flavourings can make the same food seem different, so may interfere with variety-seeking, essentially by deceiving the taste. A test of this on mice would flavour the same grain differently and check whether this attenuates the negative autocorrelation of consumption, both when other grains are available and when not.

If seasonings reduce variety-seeking, then access to spices may lead people to consume a more monotonous diet, which may be less healthy. A test of this hypothesis is whether increased access to flavourings leads to more obesity, especially among those constrained to eat similar foods over time. The constraint may be poverty (only a few cheap foods are affordable) or physical access (living in a remote, unpopulated area).

A preference for variety explains why monotonous diets, such as Atkins, may help lose weight: eating similar food repeatedly gets boring, so the dieter eats less.

Ways in which an eater can get negative calories from food

There are at least four ways in which an eater may have less energy and nutrients after consuming a food: mechanical, chemical, physical and biological. The mechanical way is that chewing and other parts of digestion take energy, so if a food requires serious mastication and contains few calories, then more energy may be spent than absorbed. This has been claimed for raw celery.
Chemically, one food may react with another in a way that makes one or both of them less digestible. The less effective absorption reduces the nutrients obtained compared to not eating the second reactant. The chemical pathway to inefficient digestion may have multiple steps. For example, ascorbic acid leaches calcium from the body, and calcium is required for the absorption of vitamin D, so eating more citrus fruits may indirectly reduce one’s vitamin D levels.
When calculating the calorie content of food, indigestible fibre is subtracted from carbohydrates before adding up the energy obtained from carbohydrates, fats and proteins. However, if fibre reduces the absorption of calories (in addition to its known reduction of the absorption iron, zinc, magnesium, calcium and phosphorus), then the food’s bioavailable calorie content is less than that obtained by simply subtracting the fibre. To derive the correct calorie content, the fibre should then have negative weight in the calculation, not zero. This difference may explain why in Western countries, a high-fibre diet predicts better health in multiple dimensions in large prospective studies (Nurses’ Health Study, Framingham Heart Study), controlling for calorie intake, lifestyle and many other factors. If the calorie absorption is overestimated for people eating lots of fibre (because the calorie intake is larger than the absorption), then their predicted health based on the too high calorie estimate is worse than their actual health. This is because most people in Western countries overeat, so eating less improves health outcomes. If the predicted health is underestimated, then the high-fibre group looks unusually healthy, which is attributed to the beneficial effects of fibre, but may actually be due to absorbing fewer calories.
A food may chemically break down tissues, e.g. bromelain and papain, from fresh pineapple and papaya respectively, denature meat proteins, so cause mouth sores. Rebuilding the damaged tissue requires the energy and nutrients, the quantity of which may exceed that absorbed from the food.
Chemically causing diarrhea reduces the time that foods (including the laxative agent) spend in the gut, thus reduces nutrient absorption.
Stimulants like caffeine speed up metabolism and cause greater energy expenditure, but may give zero calories themselves, resulting in a net negative caloric balance.
Just like chemical damage, physical injury to the body necessitates spending calories and nutrients for tissue repair. For example, scratchy food (phytoliths, bran) may cause many microscopic wounds to the digestive tract.
Cold food requires the body to spend energy on heating, so if the calorie content is small, then the net energy obtained is is negative. Examples are ice cubes and cold water.
A food substance may physically partially block the absorption of another, for example a gelling agent (methylcellulose, psyllium husks) may turn a juice into a gel in the gut and thereby reduce its absorption. Based on my personal experience, psyllium husks gel liquid feces, thus effectively reducing diarrhea. Mixing psyllium husks with carrot juice and with asparagus powder dissolved in water before consuming them during the same meal results in the excretion of separated faint orange and green gels somewhat distinct from the rest of the feces (photos available upon request, not posted to keep the blog family-friendly). This is suggestive evidence that the gelling agent both kept the juices from mixing in the gut and reduced the absorption of the colourful compounds by keeping the juice in the centre of the gel away from the intestinal wall.
Biologically, a food may reduce the nutrients available to the organism by causing infection, the immune response to which requires energy and depletes the body’s reserves of various substances. Infection may lead to diarrhea, although the mechanism is chemical, namely the toxins excreted by the microbes. Infection with helminths (intestinal worms) that suck blood through the wall of the gut requires the replenishment of blood cells, which uses up calories, protein and iron.
If the food takes a long time to chew or is bulky, then chemical and electrical signals of satiation are sent from the gastrointestinal tract to the the appetite centre of the brain. These signals reduce the desire to eat, thus decrease calorie intake.

Bad popular science books

There is a class of books that is marketed as popular science, but have the profit from sales as their only goal, disregarding truth. Easily visible signs of these are titles that include clickbait keywords (sex, seduction, death, fear, apocalypse, diet), controversial or emotional topics (evolution, health, psychology theories, war, terrorism), radical statements about these topics (statements opposite to mainstream thinking, common sense or previous research), and big claims about the authors’ qualifications that are actually hollow (PhD from an obscure institution or not in the field of the book). The authors typically include a journalist (or writer, or some other professional marketer of narratives) and a person that seems to be qualified in the field of the book. Of course these signs are an imperfect signal, but their usefulness is that they are visible from the covers.
Inside such a book, the authors cherry-pick pieces of science and non-science that support the claim that the book makes, and ignore contradicting evidence, even if that evidence is present in the same research articles that the book cites as supporting it. Most pages promise that soon the book will prove the claims that are made on that page, but somehow the book never gets to the proof. It just presents more unfounded claims.
A book of this class does not define its central concepts or claims precisely, so it can flexibly interpret previous research as supporting its claims. The book does not make precise what would constitute evidence refuting its claim, but sets up “straw-man” counterarguments to its claim and refutes them (mischaracterising the actual counterarguments to make them look ridiculous).
Examples of these books that I have read to some extent before becoming exasperated by their demagoguery: Sex at dawn, Games people play.

Heating my apartment with a gas stove

There is no built-in heating system in my Australian-standard un-insulated apartment, and the plug-in electric radiators do not have enough power to raise the temperature by a degree. In the past two winters, I used the gas stove as a heater. It is generally unwise to heat an enclosed space without purpose-built ventilation (such as a chimney) by burning something, because of the risk of CO poisoning. Even before CO becomes a problem, suffocation may occur because the CO2 concentration rises and oxygen concentration falls. Therefore, before deciding to heat with a gas stove, I looked up the research, made thorough calculations and checked them several times. I also bought a CO detector, tested it and placed it next to the gas stove. The ceiling has a smoke alarm permanently attached, but this only detects soot in the air, not gases like CO.
For the calculations, I looked up how much heat is produced by burning a cubic metre or kilogram of CH4 (natural gas), how much the temperature of the air in the apartment should rise as a result, how much CO2 the burning produces, and what the safe limits of long-term CO2 exposure are.
The energy content of CH4 is 37.2 MJ/m3, equivalently 50-55.5 MJ/kg. A pilot light of a water heater is estimated to produce 5.3 kWh/day = 20 MJ/day of heat, but a gas stove’s biggest burner turned fully on is estimated to produce 5-15 MJ/h, depending on the stove and the data source.
The chemical reaction of burning natural gas when oxygen is not a limiting factor is CH4 +2*O2 =CO2 +2*H2O. The molar masses of these gases are CH4=16 g/mol, O2=32 g/mol, CO2=44 g/mol, H2O=18 g/mol, air 29 g/mol. One stove burner on full for 1 hour uses about 0.182 kg =0.255 m3 of CH4 and 0.364 kg of O2, which depletes 1.82 kg = 1.52 m3 of air. The burning produces 2.75*0.182 = 0.5 kg = 0.41 m3 of CO2. The CO2 is denser than air, which is why it may remain in the apartment and displace air when the cracks around the windows are relatively high up. On the other hand, the CO2 also mixes with the air, so may escape at the same rate. Or alternatively, the CO2 is hot, so may rise and escape faster than air. For safety calculations, I want to use a conservative estimate, so assume that the CO2 remains in the apartment.
The volume of the apartment is 6x5x2.5 m =75 m^3. The density of air at room temperature is 1.2 kg/m^3, thus the mass of air in the apartment is 90 kg. The specific heat of air is 1005 kJ/(kg*K) at 20C. The walls and ceiling leak heat, thus more energy is actually needed to heat the apartment by a given amount than the calculation using only air shows. It takes 900 kJ of heat to raise the temperature of the air, not the walls, by 10C (from 12C to 22C). This requires 9/555 kg = 9/(16*555) kmol of CH4 with estimated energy density 55500 kJ/kg. Burning that CH4 also takes 9/(8*555) kmol of O2 and produces 9*11/(4*555) kmol = 9/200 kg of CO2.
The normal concentration of CO2 in outside air is 350-450 ppm. Estimate the baseline concentration in inside air to be 1/2000 ppm because of breathing and poor ventilation. Adding 1/2000 ppm from heating, the CO2 concentration reaches 1/1000 ppm. This is below the legal limit for long-term exposure.
CO is produced in low-oxygen burning. As long as the CO2 concentration in the air is low and the oxygen concentration high, the risk of CO poisoning is small.
For the actual heating, I first tested running the smallest burner all day while I was at home, and paid attention to whether I felt sleepy and whether the air in the apartment smelled more stale than outside or in the corridor. There seemed to be no problems. For nighttime heating, I started with the smallest burner in the lowest setting, similarly paying attention to whether the air in the morning smelled staler than usual and whether I felt any different. Because there were no problems, I gradually increased the heating from week to week. The maximum I reached was to turn on the largest burner to less than half power, and one or two smaller burners fully. Together, these burners produced much less heat than the largest burner on full, as could be easily checked by feel when standing next to the stove. At night, the stove prevented the temperature in the apartment from dropping by the usual 2C, but did not increase it. The CO2 produced was probably far less than the bound I calculated above by assuming a 10C increase in temperature. Empirically, I’m still alive after two winters of letting the gas stove run overnight.