escape_velocity

Maybe "make it lazy" is not the proper way to say it. I mean that by rushing to massacre the invader with outside help you're not allowing the body to develop the antibodies that will stop the next invasion, and so what you're developing is a dependency on outside help, which is not advisable. Forget about the names, then. I'm talking about the small red sores on the inner lining of the mouth that have a light yellowish spot in the middle. I heard them saying on television that they were caused by a herpes virus. It's always only one. Next time I'll put honey through the test because I always have some around, and I do know that it has antibacterial (and antiviral?) properties, but the only alcohol I have is methyl alcohol (industrial alcohol), which is toxic if ingested, because I stopped drinking ethyl alcohol a long time ago, and I'd never go buy vodka just to make an experiment, especially if there's plenty of salt in the cupboard. The quick way salt acts like an anesthetic for external application in this case is surprising, and I wonder whether or not you can expect the same thing if you use alcohol or honey. I'm not being deliberately misleading. I repeat that "in my case most episodes of influenza (or whatever gives you the said symptoms) now last for about half an hour or so". Six decades of frequent battles leave you with an impressive collection of antibodies, especially if you've kept away from antibiotics for one half of that period. Effective home remedies are important now that so many patients are being killed off by "superbugs" that stand up to everything you throw at them. These are superresistant strains and it's happening with diseases like TB that were easily dealt with, which is scary. Pharmacology has to do with chemistry but it now seems like it was a bad idea to bring up the case of the useless lemons. It derailed the discussion. I'd dropped the curtain, but since I was forced to raise it once again I might as well go back to the case of the useless list, and specifically the following two matters. 1) Number 10 on the list. The mistake there was relying on an elementary high-school textbook (not Sienko and Plane's, which is the old one and maybe on the junior-college level or higher). That kind of book is proving to be sketchy and simplistic. It says that "the oxidation number is, generally, a periodic property", which on a closer examination turned out to be false, as explained by "mississippichem". 2) The problem of n bodies. I wish I knew whether or not the method of the successive or consecutive approximations is ever used in chemistry, so maybe if I describe how it works in astronomy someone will recognize the procedure. The starting point (generally) is today. One calculates for this day all the positions of the planets and all the forces and one obtains the positions and forces for ten days from now, then one reckons them for ten days from that point, and so on. In that way, step by step, one builds the orbit. This requires a huge amount of memory space. That, then, is the numerical approach. With the analytic method one assumes that there's a predominant body, an overwhelming mass, which, in fact, there is --the Sun-- in order to obtain the orbit, then one inputs the forces exerted by the other planets as rectifications to that initial orbit, which is why it's called the method of the disturbances.

"A lot has happened since the 1960's." --hypervalent_iodine Yes, like chemist and Nobel-Prize winner Linus Pauling announcing to all of humankind that the common cold was avoidable by simply eating lemons daily and in large quantities, and then they told us this was nonsense. (Maybe he was ultimately responsible for the megavitamin trend.) I didn't need to have a Ph.D. to discover the solution: just stop using antibiotics, which weaken your immunological system and make it lazy. I replaced them with...table salt! Humble NaCl is a powerful bug killer, as they found out thousands of years ago. It will even destroy what no antibiotic can: viruses. Specifically, it will instantly desensitize the common, small and painful mouth ulcers called "aphthae" or "thrush", caused by a herpes type of virus. If you keep putting salt on the sore it will go away quickly. Why does nobody seem to know about this? I had to figure it out all by myself and it will work again and again. Not only that, but salt will make (external) ear infections and sore throats go away, too. I've been at it for the last three decades. In my case most episodes of influenza now last for about half an hour or so. They got shorter and shorter over the years. All of a sudden there's some sneezing, maybe mild pain in an eye socket and the temple on that same side and a runny nose, and then it's gone. In fact, the fleeting event is fun (especially the sneezing), as it breaks the routine. May I suggest that I be nominated for the Nobel Prize for medicine? These findings are earth-shaking and salt-shaking and maybe even life-saving. If doctors and drug companies won't preach the gospel then maybe chemists will. There's more to it, having to do with tropical ulcers (not mine!), but the subject here is old books. Another old textbook I saw at a used-book fair was Pauling's chemistry textbook. I almost rushed to buy it but then I saw that an entire chapter had been ripped out and I walked away. I should've bought it, in spite of iodine's suggestion to modernize. " (...) a list of chemistry exceptions is pointless in the sense that it's always a bit subjective, and not too useful." --mississippichem Both a fondness for old books and collecting exceptions can become an obstacle in the way and it can turn into compulsive behavior, like anorexia and bulimia…yet I've come up with at least one good use for the pointless list: a didactic one. Teachers can announce a contest where the winner will be the student who can find the most exceptions having to do with the Periodic Table. The winner won't have to take the final exam. Anyway, let these be my parting words: I hereby threaten to come back with more exceptions as soon as they go beyond the hundredth item, if ever, and I challenge those with enough spare time on their hands to beat me to it. I'm grateful to those who pointed out all the mistakes. It's back to the salt mines, then (i.e., the textbooks).

Pra WorldOfBiochemistry: obrigadissimo! (Your Evoluciencia website is now on my Favorites Bar so I won't miss any recent scientific news.) " (…) the whole thing is pointless, there are no exceptions to the actual rules." --insane_alien "Yeah (…)." --mississippichem Those two quotes deserve this counterquote: "Science admits no exceptions; otherwise there would be no determinism in science, or rather, there would be no science." (Leçons de Pathologie Expérimentale [1872], Claude Bernard [the French physiologist]) The nature of the list is being misunderstood. It wasn't presented as exceptions to any of the iron laws of Nature, which are etched in marble and are not supposed to have exceptions except when overruled by supernatural causes, but merely as a series of unusual or curious circumstances that disrupt a pattern --a pattern that may or may not be contrived and forced rather than one that obeys a natural decree. Such a list might be of some use or entirely useless, but what's certain is that some people are not amused. Some of the mistakes might be ascribed to the fact that the books I'm using are quite old. My chemistry textbook is from the early 60's. Moreover, item # 19 was found in the third edition (1948) of The Petroleum Handbook (Shell), so it's possible that other crudes that have carbon rings have been found. There has got to be at least one petroleum engineer amongst the nearly 40,000 members here who can help us out on this matter. Incidentally, I'm not supposed to have that book, which seems to be a FOR-YOUR-EYES-ONLY type of printed matter. On the other side of the title page it says "FOR PRIVATE CIRCULATION". I keep wondering how it ever got to the used-book market. I'm not in the industrial-espionage trade. Still, something else I keep wondering is what price it would fetch at an auction sale or a place like e-Bay. I bought it dirt-cheap, for the equivalent of about one U.S. dollar. Those who were selling it had no idea about what they had on their hands. It was as though they wanted to get rid of it after years of having it on the shelf. (By the way, that first quote up there is a run-on sentence.) "You can cross out # 3." --John Cuthber …but one new exception will compensate for that loss. It happens to be mentioned on the Wiki entry on the compound HOF you furnish the URL to: "It is the only hypohalic acid that can be isolated as a solid." Thank you for making a contribution to the list. " (…) number 10 is not an exception as the d and f blocks comprise most of the (…) table (…)." --mississippichem In that case then the exception would have to be the complete opposite: "cases where the oxidation number is a periodic property". Or not. It depends on how you handle the terms "most" and "exceptional". Transition elements (d- and f-blocks) make up 63 % of the table. Can a feature displayed by the remaining 37 % of anything be described as "exceptional"? Not if you agree with the statistic definition of "normal" in psychology and decide to apply it to chemistry (there are two other definitions of the word in that science): "whatever two thirds of people do". That makes 33 % the maximum of "abnormality", so that 37% would be beyond the realm of the abnormal and thus not strictly abnormal or exceptional. Alternately, you can embrace the transitionals as the paragon and treat all the rest as circus freaks, but would it be fair…. " (…) cross out 14, or at least redefine it to include only the 20 standard amino acids." --hypervalent_iodine So let's redefine. Also, while researching this I came across two other exceptional cases: - ONLY naturally occurring beta amino acid: beta-alanine - ONLY amino acid with the ability to easily cross the barrier between blood and brain tissue: glutamine " (…) QM and SM." --mississippichem Quantum mechanics? At least one can be sure that "SM" is not "sadomasochism" in the present context. " (…) no one knows how to solve an equation with that many variables (…)." --mississippichem Solve an equation??? What variables??? All one can say about this is that it recalls the "problem of n bodies" or "problem of multiple bodies". The mathematical difficulties are insurmountable. It pops up when wanting to describe the movement of a planet under the influence of all the others. Mechanics has no math tools for that yet, so you have to use a computer, a brute-force algorithm and a purely numerical method…but the memory requirements for one such program are gigantic. This is the method of the successive approximations. Discussing it goes beyond the scope of this forum unless you see any similarities to what you're talking about and it can be used for chemistry problems, too. (There's also the analytic approach --the method of the disturbances.)

A search on "silicon-based life" might lead you somewhere since what you read about boron is also said about silicon. On one website they say, " On the surface, silicon seems like an ideal substitute for carbon in another living system. Theoretically, silicon has bonding chemistry identical to that of carbon, and like carbon, can combine with four other elements to construct an incredible range of different macromolecules. So why not silicon-based life?" The problem is that silicon has several disadvantages and it has now been discarded as a possible substitute for carbon. The most that can be said in its favor is that it might've helped to start life going.

Many years ago I started a list of zoological exceptions that's now hundreds of items long, so I was bound to notice the exceptional cases when I started to go over my long-forgotten knowledge of chemistry just four months ago. If so many have piled up in such a short period of time then surely there must be many others that only the advanced students or the pros are aware of. This is an invitation to add them to the following list. I doubt that it would ever grow to be as long as the other one, to which additional facts are frequently being added, or even as long as a much shorter one of botanical exceptions. I've been an amateur astronomer ever since 1985 and I have piles of notebooks but astronomy offers no notable amount of exceptional cases. Biology itself has turned out to be unique as far as exceptions are concerned. Not included are a set of exceptions having to do with metallurgy, which I suppose is in a somewhat different category, and two abstruse ones about the color phenomenon. 1) ONLY chemical element with no neutrons in the nucleus (or more exactly, "whose common isotope has no etc.", since both deuterium and tritium do): hydrogen 2) ONLY element in Group 18 (or Group 0), the "inert" gases, that doesn't have eight outer electrons: helium 3) ONLY halogen that doesn't combine to give oxyhydrogenated acid compounds: fluorine 4) "inert" elements (or how should this be worded, since they're not entirely so --maybe "largely inert"?) 5) nonmetallic elements with less than five outer electrons: ONLY hydrogen, helium and carbon 6) nonmetallic elements that don't make compounds by gaining or sharing electrons: ONLY the "inert" elements 7) elements on the upper right-hand corner of the table that are not among the most reactive: ONLY the ditto 8) elements on the far right that don't have a very high electronegativity: ONLY the ditto 9) elements whose atomic mass doesn't agree with the sequence of increasing atomic numbers: ONLY potassium, nickel and iodine 10) cases where the oxidation number is not a periodic property 11) compounds in which oxygen doesn't have -2 as the oxidation number 12) hydrogenated compounds in which the oxidation number of hydrogen is not +1 13) oscillating chemical reactions (see "Scientific American", 3/83) 14) amino acids (ONLY two) with atoms of elements other than carbon, hydrogen, oxygen and nitrogen 15) solids that dissolve exothermically 16) crystalline polymorphism 17) substances in whose phase diagram the S-L line leans towards the left as pressure increases 18) cases where the reticular energy and the hydration energy are approximately equal 19) crude oils (petroleums) with components having carbon rings: ONLY Caucasian crudes

"(…) it can be a ring (…) but it can also become linear. And it can go back too." ... a surprising supplement to the subject of the denaturation of proteins and the recent findings about partially or completely unstructured or unfolded proteins. Disarray can be catastrophic and irreversible in proteins, as in the classical example of the heated egg white, yet now it's known that many proteins are not rigidly folded and that this doesn't imply a loss of function, so one wonders whether or not they, too, can go back and forth between different shapes the way simpler molecules like glucose do. It also brings to mind the difference between normal chemical reactions, which eventually reach a state of equilibrium between reactives and products, and wildly oscillating reactions, which are exceptional. The latter seem to be similar to shape-shifting glucose, but since only 0.02 % of glucose molecules in solution are chained, according to the Virtual Chembook, stability would seem to be the usual thing. Otherwise, wouldn't one see far more chain molecules? "This happens already at room temperature." ...which seems to be saying that shape-shifting increases as temperature increases, and maybe at high temperatures no glucose molecules are ring-shaped….

Sorry about the delay, and thank you for the prompt and juicy replies. I have not remained idle. It's that they had me thinking hard all these days, and maybe I finally reached a loftier level of understanding. So, the answer was NOT "simple and straightforward". There might be a "subjective" element involved, and controversies over basic matters, and "second opinions", just as with medical diagnoses. This is completely unexpected since we're dealing with one of the "exact sciences". Moreover, it's unquestionably the simplest: both advanced math and advanced physics are out of bounds for most people, including most scholars. Chemistry is reassuringly down-to-earth. I'm one third of the way through the textbook and by now it seems like most problems are to be solved by applying a "rule of three", or two or three (a matter of elementary proportionality). "(…) the whole point is an opinion that moles/liter are the relevant parameter instead of grams/liter, nothing more. "(…) I can argue that the solubility of glucose is greater [since the] dissolved mass per liter of water is greater (…)." --Capt. Panic The confusion seems to be caused by failing to make a distinction between dissolved and dissociated particles. The dissolved mass of sugar per liter of water is greater, but four out of the five ways of expressing concentration in a solution relate to the number of moles, and thus the number of particles, not to the mass, like the fifth way (normality) does. Also, the dissolved mass is greater but not the number of dissociated ions. Strong electrolytes such as table salt dissociate nearly 100 per centum. The solute in a 5.3 M salt solution weighs less (about four times less) than the solute in a 3.8 M sugar solution because the molecules are much, much lighter (6.5 times lighter), but the degree of dissociation is greater. Thus, molarity is the adequate measure for solubility, at least as regards four out of the five ditto, because one mole, of whatever substance, always has the same number of particles (the Avogadro number), so that a greater number of moles indicates a greater number of particles, and it's even greater in this case since salt dissociates almost entirely, which means that the initial number of particles (NaCl) is multiplied by two (Na+ and Cl-). Maybe the argument is fueled by not realizing that four of the methods are related to the number of particles and only one is mass-related? A question remains: does molarity always reveal the greater number of particles of a solute? In this case the number of grams does not because the sugar molecules are 6.5 times heavier than table salt molecules, so that less particles of the former can weigh much more than more particles of the latter. " (…) saccharose molecules are not non-polar [because they bear polar bonds]." --Capt. Panic …but the presence of polar bonds doesn't necessarily imply a polar molecule. It depends on the molecular structure. The book explains this with the following example (from the chapter on the chemical bond). "It is possible to predict the polar or nonpolar nature of a diatomic molecule: if both atoms are equal, their bond must be nonpolar, and so will the molecule; if they are different, both the bond and the molecule will be polar. (…) It is not that easy to predict the polar nature of a molecule having more than two atoms, since it can be nonpolar even if all of its bonds are individually polar. An example of this is carbon dioxide (CO2), in whose molecule the two oxygen atoms are linked to the carbon atom (Fig. 4-6). O.…C….O -..+…..+..- Fig. 4-6. Nonpolar molecule with polar bonds "Since the latter attracts the shared electrons with less strength than the oxygen atoms do, it is understandable that each one of the carbon-oxygen bonds must be polar. (…) Now, the molecule as a whole is linear, and the effect of one dipole is annulled by that of the other one. Thus, when the CO2 molecules are placed in an electric field, they do not align, because the momentum of each one of the dipoles is counteracted by the momentum (in the opposite sense) of the other one. This is why carbon dioxide has a very low dielectric constant." Then they point out that if the water molecule were linear, too… H….O….H …then it, too, would be nonpolar, but that a high dielectric constant argues in favor of a structure where the bonds are at an angle. "Confused yet?" --John Cuthber Maybe less so. I think the sand and steel ball simile finally managed to shake me out of my daze, because it reminded me of the tricky question meant for schoolchildren. Which weighs more: a pound of feathers or a pound of lead? Why this led to what seemed like a sudden insight is not clear. Anyway, what I then realized was the simple fact that fewer moles of sugar can weigh much more than more moles of salt, which is why the first pair of figures (number of grams) is misleading, apart from the fact that salt dissociates almost completely. This is all so intricate that it's starting to look like a complete chapter in a book or a paper sent to a journal, and I'm wondering whether or not I'm still unaware of something. To make a long story even longer, it might be helpful to say that the book is an old one, from the 60's, but the publishers are reliable (McGraw-Hill) and both coauthors were professors of chemistry at Cornell U. It's one of the books of my youth. I dropped out during my third semester of Biology in 1970 and never went back. You all will have to help me catch up at the virtual college here. One who did go back was the 99-year-old man who finally got his college degree just two weeks ago. In 1932 he, too, had to drop out, because he was offered a job as a professor during his very last semester, then he was offered twice as much at a lumber yard (not sawing logs, I guess). That was after the Crash of '29, when everyone was in a panic and no job opportunity was turned down, even barely months away from graduation, which shows how desperate people were, back in those days…just like right now once again! This piece of TV news on June 16 was quite encouraging for a (relatively youthful) nearly 60-year-old. …and going now somewhat off the topic, I recently came across another old textbook in the inexhaustible used-book market, Chemical Engineering Plant Design (Vilbrandt & Dryden, McGraw-Hill, too, 1959), which was exciting, like finding an Egyptian papyrus. Questions will come up while thumbing through it, and maybe our resident expert, the Captain, will have the patience to answer them? The very first phrase in the preface is just like the opening words of The Gallic Wars (Julius Caesar): "Chemical engineering design is divided into equipment design and plant design (…)." The Roman general starts out by saying: "The whole of Gaul is divided into four parts."

In the chapter on solutions of Sienko & Plane's Chemistry the authors say that the amount of grams per liter of solution is not a reliable indicator of solubility, but the molarity --moles per liter of solution-- is, without explaining why. The following example is given. "At room temperature the solubility of saccharose [sugar] in water is 1311 g. per liter of solution, more than four times that of sodium chloride [table salt]. These figures are, however, misleading, and it is necessary to compare the molar solubilities if one wants to infer some consequence relating to the number of [dissolved] particles. The saturated solution of sodium chloride is 5.3 M, whereas that of saccharose is 3.8 M, that is to say, in that sense the solubility of the former compound is greater than that of the latter, which is logical, since between the ions Na+ and Cl- and the dipolar water molecules there is a greater attraction than between these and the nonpolar saccharose molecules." So, the question is why "grams per liter of solution" and "moles per liter of solution" can indicate opposite circumstances. This is puzzling since grams and moles (meaning "gram-molecules", of course, as usual) are akin (a gram-molecule being the amount in grams of a substance numerically equal to its molecular weight) and one would expect them to show the same situation. I suspect the explanation is elementary, which is a disturbing idea, so I'm in urgent need of it so I can get on with the task of going back to my high-school knowledge base.

Nobody's mentioned the old classics I read in my youth: --Hans Zinsser's Rats, Lice & History, which I think Guns, Germs & Steel is trying to imitate without giving due credit, unless I'm mistaking it for some other one, --biologist René Dubos's The Mirage of Health, --Watson's The Double Helix (a funny history of the discovery of the structure of DNA by its co-discoverer), --1965 Nobel Prize winner Jacques Monod's Chance & Necessity, --playwright Rob't. Ardrey's The Territorial Imperative, --pioneering ethologist Konrad Lorenz's On Aggression, --paleontologist G.G. Simpson's The Meaning of Evolution (and I'd like to read his sci-fi novel The Dechronization of Sam Magruder), ...and another classic is How To Lie With Statistics, which I'd like to read before I die and become a part of the statistics. As I said elsewhere, I'm younger than "owl" but not terribly younger, but at least I'm still not as forgetful (that bane of ripe old age) as venerable "owl". Harlow Shapley's collection of essays titled Beyond the Observatory (1967) has been important for me because one of the essays inspired an int'l. space mission I've very recently suggested to the space agencies, but I don't think it deserves a discussion unless I get at least one reply, even if it's from the space agency of, for instance, humble Bangladesh, Malaysia, Vietnam, Peru or Algeria. The message was sent to 39 nat'l. space agencies or research organizations and seven int'l. organizations, including the U.N., in the course of a few days (Jan. 15-20).

So what if they're being respectful of our free will by abstaining from showing up and saying "take me to your leader or suffer the consequences", and they're showing their hardware here and there so people will investigate, and they communicate individually with those who do that, either physically or mentally (telepathy), and are waiting for a "critical mass" of welcoming humans to be reached, a majority of two-thirds, for example….

It looks like most people think that so-called social networks are exclusively for socializing and losing one's precious time when one ought to be learning new things. This is a BIG mistake. I log in at Facebook just to visit the Walls of the Radio Netherlands Worldwide programs that I listen to weekly and make comments about their subject matters. "Earth Beat", an environmentalist program, is especially useful, but so are "The State We're In", "South Asia Wired" and "Bridges With Africa". Then there's the Walls of so many scientific journals, etc. For instance, one of the most recent reports from "Earth Beat", titled "Waiting in the wings", is about inventions that are amazing but haven't been adopted widely yet, or not at all, like "food tubes", a science-fictiony network of underground rails for the distribution of food supplies that would replace trucks and save a lot of fuel (they already have the blueprint for one that would be built in Croydon, U.K. and would have a total extension of 80 km.), or "bio-couture" (lab-grown cloth), or the Philips universal wireless mobile phone charger. That last matter would be a good excuse for starting a thread about the conspiracy theory involving Tesla and the wireless transmission of electricity through electromagnetic waves. If it's true then power networks are unnecessary and all that's needed is a central radio transmitter, maybe on a satellite, and a receiver in every household or business, a system of free energy for everyone. I hereby threaten to go discuss this on the Speculations Forum. The interviewee explains that it's a very inefficient way to transmit energy. The two artifacts --the phone and the charger-- have to be in close contact, and if they're so much as 1 mt. apart then the efficiency drops drastically, to less than one percent: the percentage that reaches the phone is less than one percent of the emitted energy, but that's as far as mainstream science and tech are concerned. The programs can be found online. I have nothing to do with either RNW or the Philips company, though. It's just that I appreciate the former's usefulness. So, you see, there's more to social networking than meets the mind.

Mr. Skeptic said: Our universe could be cyclic, in which case our own time dimension might be infinite. Closed time loops might be possible but I don't know whether that would even be considered infinite or not." Coincidentally, I used the phrase "time loop" some weeks ago at some other website in a comment elicited by this question: " (...) is every universe always the same as the one that came before it? (Is it like rewinding the same tape over and over (...)?" My comment: ------------------------------------------ That's exactly what the Stoics believed. See, for example, Nemesius, "De nat. hom.", 38: "When the heavenly bodies, in the course of their movement, have returned to the same sign and to the latitude and longitude that each one occupied in the beginning, there takes place, in the cycle of the times, an utter conflagration and destruction; then there is a going back, from the start, to the same cosmic order and once again, as the heavenly bodies move just as before, every event in the preceding cycle repeats itself without any difference whatsoever. In fact, Socrates and Plato will exist again, and every individual with the same friends and fellow citizens, the same beliefs and the same arguments in discussions, every city and village, will come back. This universal return will happen, not just once, but many times, to infinity." In our days some would call this a "time loop", and they'd say we're trapped in one. ------------------------------------------ ...and as for Zeno's Paradox, mentioned by "michel123456", it's only apparent. His reasoning was that, since one can divide any distance into an infinite number of segments, movement is impossible because anything would have to spend an infinite amount of time traveling over all those numberless segments. His mistake was confusing the physical realm with the mental realm. In the latter the mind can divide a distance an infinite amount of times, but in the former space is not divided but is continuous, so that movement implies no impossibility whatsoever.

I dutifully read the automatic welcoming message that arrives at one's e-inbox and I see that everybody's expected to introduce him/herself, so I'll say that I'm a Seventies college dropout who dropped out in his third semester of Biology and that's all the higher education I ever got, but I never lost my scientific curiosity. I've been an amateur astronomer for a quarter of a century now, ever since taking an introductory course imparted by an engineer who studied astronomy at the University of Paris. That was in 1985, when everybody was excited about the imminent arrival of the Halley Comet, which was a complete failure this time. Now we have to wait for another 76 years and I can't wait that long, unless the longevity pill is invented soon (some people actually believe this). I'm not as old as "owl", with whom I share this page 98, but I'm just six years younger. On page 1 someone makes some demeaning comments about this thread. He thinks it's all rubbish. As far as I'm concerned it's the other way around. There are many amusing remarks. People should say how they got here, too. I discovered the site yesterday when I did a search on the Branly effect, which is discussed here. This was because I was reading an article about it in the "Scientific American" mag. (enviado el 21/1/11 al tema de las presentaciones personales en Science Forums, p. 98)