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Alligators v Crocodiles: What's the difference?

5/15/2016

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Alright, let's sort out once and for all the differences between alligators and crocodiles.  Many assume that the chief difference between the large reptiles is the shape of their heads; alligators having broader, more baguette shaped heads and crocodiles more narrow heads.  This is generally true, as per the illustration below.  However, head/snout shape is only part of the picture.
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Morphological differences in head/snout shape between alligators and crocodiles

​From the standpoint of biological classification, alligators and crocodiles are members of two distinct families.  They are both members of the order crocodilia.  Thus, all alligators and all crocodiles are crocodilians.  

Table 1 Biological classification of the crocodilian family

Classification Alligator | Crocodile
Kingdom Animalia
Phylum Chordata
Class Reptilia
Order Crocodilia
Family Alligatoridae Crocodylidae Gavialidae
Subfamily Alligatorinae Crocodylinae Gavialinae
Genus Alligator Crocodylus Gavialis


​Note an additional biological family in Table 1, the gavialidae.  The gavial, or gharial, is a fish eating (piscivorous) saltwater crocodile native to northern India.  The gharial is a highly endangered species, with a known number of extant individuals only a little over 200.  As can be seen in the photo below, the gharial has a very long, narrow snout specialized for catching and consuming fish.  Very different morphology than other crocodilians indeed.
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The piscivorous gavial, or gharial of northern India
Alligators and crocodiles.  Can you tell which is which?

​Other differences between alligators and crocodiles are the placement of teeth and jaw plan.  Alligators have a larger upper jaw than their lower jaw.  Thus, with jaws closed, an alligator's lower teeth are not visible (part A below).  Crocodile's upper and lower jaws are approximately the same width (part B), and when closed, the upper and lower teeth interlock.
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Tooth placement in alligators (A) and crocodiles (B)

Alligators and crocodiles both have integumentary (skin) sensory organs know as dermal pressure receptors. These highly sensitive receptors can detect the faintest of water perturbations, assisting them in locating and tracking prey.  These receptors are distributed differently in alligators and crocs.  Both have DPRs located in the skin of their upper and lower jaws.  However, crocs also have DPRs distributed about most of their body's surface area.
DPRs (Dermal Pressure Receptors), on the upper/lower jaws, and a close up

There are behavioral differences as well between the two families.  Crocodiles, in general, are more aggressive than alligators.  Alligators will often retreat from humans, where crocodiles may have a greater propensity to attack.  However, one has to be careful in overgeneralizing, as the speciation of crocodilians is very complex and vast.  Thus, depending upon the particular species, there will be many differences  in temperament, aggressiveness, as well as size.
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Maverick Supersonic!

5/10/2016

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Have you ever seen an internet video wherein a cone of condensation appears suddenly around the fuselage of a jet breaking the sound barrier, usually a fighter jet?  Or witnessed the phenomenon yourself from land or out at sea from a naval ship flyby?  This striking vapor cone is caused by a phenomenon referred to as Prandtl-Meyer expansion fans, named after their discoverers, the German engineer Ludwig Prandtl and his student, the mathematician Theodor Meyer. 
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An F/A-18 Hornet maneuvers in the transonic regime. Note the prominent supersonic expansion fan, technically known as the Prandtl–Meyer expansion fan, best visible in more humid weather

​Prandtl-Meyer expansion fans form when an object (in our case a supersonic capable jet) abruptly exceeds the speed of sound.  A low pressure region is formed in the vicinity of the expansion fans, which decreases the surrounding air pressure, density, and temperature below the dew point.  The result is a visible cone of water vapor.


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Illustration of Prandtl-Meyer expansion fans. They are more visible in weather with a small temperature-dewpoint difference

​First, a quick aside on the speed of sound.  The simplest explanation is as follows: the speed of sound depends almost entirely on the temperature of the air through which the sound waves propagate.  At sea level, at a temperature of about 59 degrees fahrenheit the speed of sound is 340.3 meters/second, or 761.2 MPH. Under normal meteorological conditions (absent temperature inversion) the speed of sound decreases as altitude increases, as temperature has an inverse relationship with altitude.

Prandtl-Meyer expansion fans form when abruptly induced supersonic flow bends around a convex corner (as in the illustration above). In this case, the apex formed between the jet's fuselage and the supersonic relative wind incident upon the jet. These fans consist of an infinite number of Mach waves (pressure waves propagating at or above the speed of sound). The physics underlying this phenomenon are rather complex, for more drill-down on the specifics please refer to this writeup by NASA.


A note about the Prandtl-Meyer fan in the preceding illustration:  the arrow pointing towards the aircraft may at first seem counter intuitive, as the arrow is pointing towards the jet, not in the jet's direction of travel.  Yes, the aircraft is exceeding the speed of sound, but the relative wind is also incident upon the jet at or above the speed of sound.  Subsequently as the jet quickly passes the sound barrier, the Mach waves encounter a convex corner, resulting in the Prandt-Meyer fans.
More examples of vapor cones formed from different perspectives, and one from a rocket.

​Real world examples of vapor cones formed as a result of Prandtl-Meyer expansion fans, both from the point of view of naval vessels:
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Join me on the Flying Trapeze!

5/8/2016

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Let's take a detour this time from the sciences and humanities and delve into a truly obscure subject:  that of the flying trapeze!  The flying trapeze was invented in Toulouse, France by Jules Leotard in 1859.  In so doing he concurrently invented a form fitting suit used in his trapeze acts called none other than... the leotard!
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Jules Léotard, the inventor of the flying trapeze

​Somehow Mr. Leotard became inspired to affix two pieces of ventilator chord to either side of a crossbar, and test out the aerial acrobatics capability of his new device over his father's gymnasium swimming pool as a safety net.  In the early years of flying trapeze practice and performance mattresses were often used until the invention of the safety net.
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​Various flying trapeze maneuvers

Although the flying trapeze may seem like a very simple device, it turns out that there are a rather large range of maneuvers that can be performed, both solo and with multiple performers.  Here are some of the most commonly used flying trapeze tricks:


  • Half Turn
  • Heels Off
  • Hocks Off
  • Splits (Front End/Back End)
  • Straddle Whip (Front End/Back End)
  • Feet Across 
  • Whip 
  • Bird's Nest
  • Shooting Star
  • Straight Jump
  • Double Over
  • Uprise Shoot
  • Forward Over
  • Forward Under
  • Cut Catch

A pretty extensive list indeed!   Please refer to the video examples below to see some of these aerial maneuvers in action:

Half Turn


​Heels off


​Hocks off


​Straddle Whip


​Bird's Nest


​Uprise Shoot

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Why is Latin so difficult?

5/1/2016

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It's a common conception that Latin is a difficult language to learn.  I believe this notion is altogether correct.  The question is, why?  What is it about this important and highly influential classical language that makes learning it such a formidable endeavor?  Arguably one of the principal reasons is thus:  Latin is an inflected language.
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​In a nutshell, inflection is a way of changing grammatical function via affixing.  Affixing is the addition of a prefix or suffix to nouns, adjectives, and pronouns. To make matters even more confusing, this process is formally referred to as declension. Latin never uses prefixing, but strictly suffixing to decline words.

Thus the newcomer to Latin from an uninflected language such as English is confronted by a dense thicket of grammatical rules that can seem arbitrary and labyrinthine, and that have no equivalents in their own language. This description of inflection may sound confusing, so let's dive straightaway into some concrete examples.

Lingua Latina - Latin Language

but:

Puella linguam Latinam discit - The girl is learning Latin

So we can see that the object of the sentence, the Latin language, has changed via the addition of the declension "-m."   But why?  Why go through all this trouble?  In other words, why not simply say:

Puella lingua Latina discit

The immediate explanation is that Latin makes use of seven different grammatical cases.  In our example, the suffixing, or declension of lingua Latina, Linguam Latinam, is referred to as the Accusative case.  That is, the noun (in this case the Latin language) is the direct object of the subject (the girl).  In other words, lingua Latina is the receiver of the action (learning) and so is assigned the accusative case per the strictures of Latin grammar.

As a stark reminder of the difference between Latin and, say English, compare the previous example with the simplicity of an equivalent in English:

"She is learning Spanish."
"They are learning Spanish."
"I am learning Spanish."
"We are learning Spanish."

Much simpler indeed without have to deal with noun declension!  Are there any inflected words in the English lexicon at all?  Well, yes, but vanishingly few.  Take, for example, the difference between who and whom, both pronouns:

"Who is that person over there?"

vs.

"To whom can we turn to in order to address this question?"

Whom in this case being the objective pronoun, that is, the object of the sentence.  This is the exception, though, not the rule in English.

Whether an unintended consequence or via design, this inflection actually serves to make the word ordering of Latin highly flexible.  For example:

​Agricola - farmer
Taurus - bull
Fugare - to chase
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​Agricola taurum fugat - The farmer chases the bull

Taurus agricolam fugat - The bull chases the farmer

Here we can see how inflection via declension of nouns allows for highly flexible word ordering in Latin:

Taurum agricola fugat - The farmer chases the bull

​Agricolam fugat Taurus - The bull chases the farmer

So, the accusative suffix "-m" informs us as to who is the direct object, negating the need for a strict word ordering.  This is a different way of thinking indeed for speakers of languages that follow fixed word orderings.


The next example illustrates Latin's subject-object-verb order flexibility.  All three statements below are equivalent to: "Carthage must be destroyed."
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​Carthago delenda est!

Delenda est Carthago!

Delenda Carthago est!

These are just a couple of  simple examples; there are in total seven Latin grammatical cases.  If you're still not convinced about the grammatical complexity of Latin, consider the following:

Latin possesses six general tenses: present, imperfect, future, pluperfect, and future perfect, three moods: indicative, imperative and subjunctive, three persons: first, second, and third, two numbers: singular and plural, two voices: active and passive, and three aspects: perfective, imperfective, and stative.   Complicated indeed!  from Wikipedia

​As for Latin numbers, cardinal numbering is slightly more complicated than, for example, the numbering in the English language.  Also, as can be seen below, some of these numbers are quite long!  For example, the numbers 40 to 50:  

40 - quadraginta

41 - quadraginta unum
42 - quadraginta duo
43 - quadraginta tres
44 - quadraginta quattuor
45 - quadraginta quinque
46 - quadraginta sex
47 - quadraginta septem

but:

48 - duodequinquaginta  (2 less than fifty, fifty = quinquaginta)
49 - undequinquaginta (1 less than fifty)
50 - quinquaginta



So with all these complications and rules, why would one want to undertake such a formidable task as learning Latin?  The rewards for this toil are great.  One develops, in the course of learning Latin, a greater appreciation for and understanding of word origins and etymology, both in English, and in the romance languages.  Studying Latin is an intellectually rigorous exercise that provides both tangible and intangible benefits.

And, lest we forget, classical Latin is an ancient language, and opens the door to another time. A working knowledge of Latin allows us access to classical texts from the Aeneid to Pliny the Elder!  Yes, we can read the transliterations of these tomes in our native language, but Latin also possesses several different grammatical moods, so there is a risk of losing the precise shades of meaning contained in the original texts.

It goes without saying that Latin words undergird a vast amount of scientific nomenclature and taxonomy, along with it's classical fellow ancient Greek. The same is true for many common words, in this case in English. Here are just a few examples of Latin words that formed the origin of their English cognates:

Ego - personal pronoun "I."  As in,  "Ego sitio sum" - I am thirsty. e.g., egotistical, egomaniac

Equus - horse.  e.g., equestrian


Urbs - city.  e.g., urban

Canis - dog.  e.g., canine

Albus - the color white.  e.g., albino

Feles - cat.  e.g., feline, felid

Terra - country.  e.g., terrestrial

​Scribit - he/she writes.  e.g., scribe, script

​Ambulat - he/she walks.  e.g., an ambulatory hospital patient

Loquitur - he/she speaks. e.g., loquacious. As in: Robert becomes very loquacious (talkative) when drinking wine.


In the midst of all the complexity of Latin, there is one "saving grace" that makes speaking straightforward:  there are no silent consonants in Latin, that is, what you see is what you get.  Pronunciation is very straightforward.  Some things to note are that "c" is always pronounced as a hard "k" sound, and "v" is pronounced as one would pronounce "w."

Other inflected languages include Hungarian, Lithuanian, Greek, Sanskrit, Pashto, Russian, Irish, Latvian, Faroese, Icelandic, Albanian, Punjabi, as well as many others.

In fact, Hungarian has no less than 18 general cases!  For a child whose native language is Hungarian, language acquisition at a young age is likely relatively straightforward.  However, for someone learning such a highly inflected language for academic or traveling purposes, the endeavor would appear to be daunting, to say the least.  Ultimately I defer to native Hungarian speakers as to what extent all 18 cases are used in common everyday speech.

Hungarian grammatical cases for nouns:


  • Nominative   - subject
  • Accusative     - direct object
  • Dative               - indirect object
  • Illative               - into
  • Inessive            - in
  • Elative               - out of
  • Allative             - to
  • Adessive          - by, at
  • Ablative           - from, away from
  • Sublative         - onto
  • Superessive   - on
  • Delative           - off, about, concerning 
  • Instrumental - with
  • Causal               - or, for the purpose of
  • Terminative   - as far as, up to
  • Temporal         - at (for time related words)
  • Translative     - into
  • Modal               - by way of​
  • ​
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    I am a lifelong "fact geek" and enjoy writing about obscure yet interesting topics from the sciences to the humanities, and everything in between.

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