Category: Science

Mosquitoes

😱 Mosquitoes love Kim Zarins. The insects’ preference for Zarins, an English professor at Sacramento State University, is so extreme that her 18-year-old son likes her to come outside with him because she serves as a decoy and “he knows he’ll be safe,” Zarins says.

😱 From up to 200 feet away, they follow the carbon dioxide plumes we exhale with each breath.

😱 The work shows, for the first time, that mosquitoes can discriminate between multiple people in a large, spacious arena the size of an ice-skating rink.

😱 “This just drives home the point that even in complex situations with multiple sources of odor, mosquitoes do seem to prefer some people over others,” Giraldo says.

😱 The mosquitoes were especially beguiled by carboxylic acids, a class of fatty acids found in human sweat whose scent is sometimes compared to rancid butter or cheese.

😱 To the researchers’ surprise, in some cases, washing increased the number of mosquito landings—indicating that soap amplified that person’s attractiveness to mosquitoes.

😱 Because humans are so important to the lifecycle of some mosquitoes (females need a blood meal before they can produce eggs), the wily insects have evolved redundancies in their people-detection mechanism. “They can’t rely on just one signal—so they have a really robust system for detecting a range of odors, which is really hard to profile,” De Obaldia says.

😱 Some species of mosquitoes, for example, have begun to feed earlier in the day to thwart the use of bed nets.

https://www.nationalgeographic.com/premium/article/mosquito-magnet-smell-repell

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Osmosis

Osmosis is the diffusion of water (the solvent) through a semi-permeable membrane down its concentration gradient. If a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration).

For two different solutions concentrations separates by a semi-permeable membrane, osmosis equalizes the water concentration. OpenStax, CC 4.0, no changes
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Tupper’s self-referential formula

Tupper’s self-referential formula is a formula that visually represents itself when graphed in the plane. It is given by

\frac{1}{2} < \left\lfloor \mathrm{mod}\left(\left\lfloor \frac{y}{17} \right\rfloor 2^{-17 \lfloor x \rfloor - \mathrm{mod}\left(\lfloor y\rfloor, 17\right)},2\right)\right\rfloor.

Let k equal the following 543-digit integer:

960 939 379 918 958 884 971 672 962 \\ 
127 852 754 715 004 339 660 129 306 \\
651 505 519 271 702 802 395 266 424 \\ 
689 642 842 174 350 718 121 267 153 \\ 
782 770 623 355 993 237 280 874 144\\ 
307 891 325 963 941 337  723 487 857\\ 
735 749 823 926 629 715 517 173 716 \\ 
995 165 232 890 538 221 612 403 238 \\
855 866 184 013 235 585 136 048 828\\
 693 337 902 491 454 229 288 667 081 \\ 
096 184 496 091 705 183 454 067 827 \\ 
731 551 705 405  381 627 380 967 602 \\ 
565 625 016 981 482 083 418 783 163 \\ 
849 115 590 225 610 003 652 351 370 \\
 343 874 461 848 378 737 238 198 224\\ 
849 863 465 033 159 410 054 974 700 \\ 
593 138 339 226 497 249 461 751 545 \\ 
728 366 702 369 745 461 014 655 997 \\ 
933 798 537 483 143 786 841 806 593\\ 
422 227 898 388 722 980 000 748 404 \\
719

Then the formula reproduces itself in the range 0 ≤ x < 106 and k ≤ y < k+17:

In fact, Tupper’s formula can be used to draw any formula because for nonnegative values of y, the formula displays all possible combinations of 17-pixel tall bitmaps. So the above formula is just a special case. In fact, the formula can be used to decode any bitmap stored in the integer k.

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Generals’ Problems

Two Generals’ Problem

Two armies, each led by a different general, are preparing to attack a fortified city. The armies are encamped near the city, each in its own valley. A third valley separates the two hills, and the only way for the two generals to communicate is by sending messengers through the valley. Unfortunately, the valley is occupied by the city’s defenders and there’s a chance that any given messenger sent through the valley will be captured.

The first general may start by sending a message "Attack at 0900 on August 4." However, once dispatched, the first general has no idea whether or not the messenger got through. This uncertainty may lead the first general to hesitate to attack due to the risk of being the sole attacker.

To be sure, the second general may send a confirmation back to the first: "I received your message and will attack at 0900 on August 4." However, the messenger carrying the confirmation could face capture and the second general may hesitate, knowing that the first might hold back without the confirmation.

Further confirmations may seem like a solution—let the first general send a second confirmation: "I received your confirmation of the planned attack at 0900 on August 4." However, this new messenger from the first general is liable to be captured, too. Thus it quickly becomes evident that no matter how many rounds of confirmation are made, there is no way to guarantee the second requirement that each general be sure the other has agreed to the attack plan. Both generals will always be left wondering whether their last messenger got through.

Byzantine Generals Problem

When besieging a city, several Byzantine generals have a communication problem. It is necessary for the generals to attack the city with their troops simultaneously from different directions. The generals can communicate with each other via messengers. However, some of the generals plot against others. Their goal is to discredit their rivals — for example, by trying to drive the others to an early attack by cleverly scattering misinformation. None of the generals now knows what information is authentic and whom they can trust.

Thus, the problem is one of agreement, which is that the army commanders must unanimously decide whether or not to attack. The problem is complicated by the physical separation of the commanders; thus, they must send messengers back and forth. In addition, there is the possibility that there may be traitors among the generals, who may intentionally send misleading information to the other generals.

One solution considers scenarios in which messages may be forged, but which will be Byzantine-fault-tolerant as long as the number of disloyal generals is less than one third of the generals. The impossibility of dealing with one-third or more traitors ultimately reduces to proving that the one Commander and two Lieutenants problem cannot be solved, if the Commander is traitorous. To see this, suppose we have a traitorous Commander A, and two Lieutenants, B and C: when A tells B to attack and C to retreat, and B and C send messages to each other, forwarding A’s message, neither B nor C can figure out who is the traitor, since it is not necessarily A — another Lieutenant could have forged the message purportedly from A. It can be shown that if n is the number of generals in total, and t is the number of traitors in that n, then there are solutions to the problem only when n > 3t and the communication is synchronous (bounded delay).

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Bubble boy

David Phillip Vetter (September 21, 1971 – February 22, 1984) was an American who was a prominent sufferer of severe combined immunodeficiency (SCID), a hereditary disease which dramatically weakens the immune system. Individuals born with SCID are abnormally susceptible to infections, and exposure to typically innocuous pathogens can be fatal. Vetter was referred to as “David, the bubble boy” by the media, as a reference to the complex containment system used as part of the management of his SCID.

Water, air, food, diapers and clothes were sterilized before entering the sterile chamber. Items were placed in a chamber filled with ethylene oxide gas for four hours at 60˚C, and then aerated for a period of one to seven days before being placed in the sterile chamber.

When Vetter was four years old, he discovered that he could poke holes in his bubble using a butterfly syringe that was left inside the chamber by mistake. At this point, the treatment team explained to him what germs were and how they affected his condition. As he grew older, he became aware of the world outside his chamber, and expressed an interest in participating in what he could see outside the windows of the hospital and via television.

In 1977, researchers from NASA used their experience with the fabrication of space suits to develop a special suit that would allow Vetter to get out of his bubble and walk in the outside world. The suit was connected to his bubble via a 2.5 m long cloth tube and although cumbersome, it allowed him to venture outside without serious risk of contamination. Vetter was initially resistant to the suit, and although he later became more comfortable wearing it, he used it only seven times. He outgrew the suit and never used the replacement one provided for him by NASA.

In his first years of life he lived mostly at Texas Children’s Hospital in Houston, Texas. As he grew older, he lived increasingly at home with his parents and older sister Katherine in Dobbin, Texas. He died in 1984, at the age of 12 from complications of a bone marrow transplant provided by his sister. His mother touched his skin for the first time only several hours before his death.

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Fangschreckenkrebse

Die Fangschreckenkrebse (Stomatopoda) sind eine Ordnung der Höheren Krebse (Malacostraca). Ihren Namen verdanken sie ihren Fangwerkzeugen, die äußerlich denen von Fangschrecken (Gottesanbeterinnen) ähneln.

Oft lebt sie in lockeren Gruppen dicht mit Artgenossen zusammen. Die Tiere sind promisk, und Männchen paaren sich mit mehreren Weibchen. Manche leben paarweise monogam. Weibchen der Pseudosquilla ciliata sind sexuell aggressiv und erbetteln oft oder erzwingen sogar Kopulationen von Männchen. 

Fangschreckenkrebse besitzen ein hoch entwickeltes Sehvermögen mit ungewöhnlich leistungsfähigen Komplexaugen. Einige Arten sind Dodekachromaten, das heißt sie besitzen zwölf Farbrezeptoren (Zapfen).

Bei ihrer Jagdweise unterscheidet man im Wesentlichen Speerer und Schmetterer. Einige Schmetterer können besonders heftige Schläge ausführen. Gelegentlich sollen Treffer beim unvorsichtigen Ergreifen von Schmetterern die spätere Amputation eines Fingers notwendig gemacht haben.[*]

A female Odontodactylus Scyllarus mantis shrimp.
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Tetrachromasie

Ein Tetrachromat (τετρα- tetra- „vier“ und χρῶμα chrōma „Farbe“) ist ein Lebewesen, welches vier Arten von Farbrezeptoren zum Sehen benutzt. Dazu zählen zum Beispiele Wellensittiche.

Es gibt Wirbeltiere mit einem, zwei, drei, vier oder fünf Zapfentypen. Zapfen sind farbempfindliche Fotorezeptoren. Der Mensch hat meistens in der lichtempfindlichen Netzhaut des Auges drei verschiedene Arten von Zapfen, und wird deshalb als Trichromat bezeichnet.

Die Absorptionsmaxima der Zapfen liegen bei etwa 455 nm, 535 nm und 563 nm liegen und entsprechen den Farben Blauviolett, Smaragdgrün und Gelbgrün. Ungefähr 12% aller Frauen besitzen einen weiteren Zapfen. Allerdings können nur wenige dies zur genaueren Farbunterscheidung nutzen. 

Das für den Menschen sichtbare Licht liegt zwischen 380 und 780 nm.
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Daniell-Element

Daniell-Element

Wenn man Zink in Kupfer-Sulfat auflöst, erhält man Kupfer und Zink-Sulfat:

Zn_{(s)} + {Cu^{2+}SO_4^{2-}}_{(aq)} \rightharpoonup Cu_{(s)} + {Zn^{2+}SO_4^{2-}}_{(aq)}

Das heißt das unedlere Zink gibt seine Elektronen an das edlere Kupfer ab. Man kann diese Redox-Reaktion (Reduktion-Oxidations) entsprechend aufteilen:

\begin{aligned} &Zn_{(s)}& &\rightharpoonup& &Zn^{2+}_{(aq)}+ 2 \ e^{-}& &\text{(Ox.)}\\ &Cu^{2+}_{(aq)}+ 2 \ e^{-}& &\rightharpoonup& &Cu_{(s)}& &\text{(Red.)} \end{aligned}

Die Idee des Daniell-Elements ist es beide Prozesse räumlich zu trennen und mit der Elektronen-Abgabe gezielt Strom zu erzeugen.

Daniell-Element

In der linken Halb-Zelle (der Anode) befindet sich ein Zink-Stab in Zink-Sulfat. Das Zink-Sulfat ist in Wasser gelöst (aq), das heißt die positiven Zink-Ionen und die negativen Sulfat-Ionen bewegen sich frei im Wasser. Aus dem Zink lösen sich nun Zink-Ionen und Elektronen werden frei gesetzt. An der nun negativ geladenen Anode bildet sich eine Grenzschicht von Elektronen und Zink-Ionen.

In der rechten Halb-Zelle (der Kathode) befindet sich Kupfer in Kupfer-Sulfat. Auch hier lösen sich einige Kupfer-Ionen aus dem Kupfer-Stab. Jedoch wesentlich langsamer als dies beim Zink der Fall ist. Verbindet man nun beide Halb-Zellen mit einem elektrischen Leiter so können wie bei der eingangs beschriebenen Reaktion die aus dem Zink gelösten Elektronen zur Kathode wandern, da die positiven Kupfer-Ionen stärker an den Elektronen zerren als die ebenfalls positiven Zink-Ionen. In der Kathode verbinden sich die Elektronen mit den Kupfer-Ionen zu reinem/soliden Kupfer (s).

Theoretisch würde sich nun ein neues Gleichgewicht einstellen. Irgendwann sind links so viele Zink-Ionen frei gesetzt, dass sie gleichermaßen stark an den Elektronen zerren wie die Kupfer-Ionen rechts. Dadurch dass sich nun festes Kupfer in der Kathode bildet, erhöht sich die Konzentration der negativen Sulfat-Ionen. Durch ein semi-permeables Diaphragma diffundieren diese nun jedoch von der rechten Halbzelle zur linken und neutralisieren dort einige Zink-Ionen, so dass das Kupfer weiter neue Elektronen durch den elektrischen Leiter zieht. 

Somit ist der elektrische Stromkreislauf geschlossen. Chemische Energie wird in elektrische umgewandelt. Zink wird verbraucht und Kupfer erzeugt.

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