Radīta sniega kristālu augšanas simulācija
Divi matemātiķi pirmo reizi radījuši datorsimulāciju, kas ģenerē reālistiskas 3D sniegpārslas, kaut arī
viņiem pašiem nav īsti skaidrs kā tas notiek.
Kalifornijas Tehnoloģiju institūta vadošais eksperts sniega kristālu fizikā saka, ka “šobrīd par kristālu
augšanu ir zināms pārsteidzoši maz. Simulācija dod iespēju fiziķiem uzzināt vairāk par sarežģīto
struktūru dabu, ko nanoinženieri pēdējo gadu laikā ir centušies izpētīt.”
Abi matemātiķi ir lietojuši jaunu metodi kā sasniegt vēlamo rezultātu. Iepriekšējā metodē sniega kristālu
virtuāli mēģināja uzbūvēt molekulu pa molekulai, taču jaunajā paņēmienā ūdens molekulas vietā tiek
ņemtas daudz lielākas 3D daļiņas. Domājams, ka šīs daļiņas, kristālu augšanas procesā, pakļaujas tai
pašai fizikai.
Datorsimulācijas autori šīs daļiņas ir nosaukuši par “cellular automāta” jeb “šūnveida automātiem”. Šo
daļiņu izmērs ir viens kubikmikrons. Modelis tika darbināts vairākas reizes, lai apzinātu izmaiņas, kas
rodas temperatūras un tvaika spiediena variācijas rezultātā. Rezultātā tika iegūti dažādi sniega kristāli,
gan vienkāršāki, gan ļoti komplicēti un pārsteidzoši. Viena sniega kristāla augšanas simulācija ilgst
apmēram 24 stundas.
Informācijas avoti:
www.abc.net.au/science
http://fizmati.lv/zinas/zinatne/radita_sniega_kristalu_augsanas_simulacija/
Tālāk – informācija angļu valodā.
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Snowflakes - sniegpārsliņas
Snowflakes and snow crystals are made of ice. A snow crystal is
a single crystal of ice. A snowflake can mean an individual
snow crystal, or a few snow crystals stuck together, or large
agglomerations of snow crystals that form "puff-balls" that float
down from the clouds.
A snowflake is an aggregate of typically hexagonally
symmetrical ice crystals. The most basic form of a
snow crystal is a hexagonal prism. When snow crystals
are very small, they are mostly in the form of simple
hexagonal prisms. But as they grow, branches sprout
from the corners to make more complex shapes. A
snowflake always has six symmetric arms (along three
symmetric axes), which arises from the hexagonal crystal structure.
By growing snow crystals in the laboratory under controlled conditions, one finds
that their shapes depend on the temperature and humidity. Thin plates and stars
grow around -2 C (28 F), while columns and slender needles appear near -5 C (23
F). Plates and stars again form near -15 C (5 F), and a combination of plates and
columns are made around -30 C (-22 F). Snow crystals tend to form simpler
shapes when the humidity is low, while more complex shapes appear at higher
humidities. The most extreme shapes form when the humidity is especially high.
Snowflakes are not frozen raindrops. Sometimes raindrops do freeze as they
fall, but this is called sleet. Sleet particles don't have any of the elaborate and
symmetrical patterning found in snow crystals. Snow crystals form when water
vapor condenses directly into ice, which happens in the clouds. The patterns
emerge as the crystals grow.
Types of Snowflakes
Simple Prisms A hexagonal prism is the most basic snow crystal. Depending on
how fast the different
facets grow, snow crystal
prisms can appear as thin
hexagonal plates, slender
hexagonal columns, or
anything in between.
Stellar Plate These
common snowflakes are thin, plate-like crystals with
six broad arms that form a star-like shape. Their
faces are often decorated with amazingly elaborate and symmetrical markings.
Sectored Plates Stellar plates often show distinctive ridges that point to the
corners between adjacent prism facets. When these ridges are especially
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prominent, the crystals are called sectored plates. The simplest sectored plates
are hexagonal crystals that are divided into six equal pieces, like the slices of a
h
e
x
a
g
o
n
a
l pie. More complex
specimens show
prominent ridges on broad, flat branches.
Stellar Dendrites Dendritic means "tree-like", so stellar dendrites are plate-like
snow crystals that have branches and sidebranches. These are fairly large
crystals, typically 2-4 mm in diameter, that are easily seen with the naked eye.
S
t
e
l
l
a
r
dendrites are clearly the
most popular snow crystal
type, seen in holiday decorations everywhere.
Fernlike Stellar Dendrites Sometimes the branches of stellar crystals have so
many sidebranches they look a bit like ferns, so we call them fernlike stellar
dendrites. These are the largest snow crystals, often falling to earth with
diameters of 5 mm or
more. In spite of their
large size, these are single crystals of ice.
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Hollow Columns Hexagonal columns often form with conical hollow regions in
their ends, the two hollow regions are symmetrical. These crystals are small, so
you
need a good magnifier to
see the hollow regions.
Sometimes the ends grow over and enclose a pair of bubbles in the ice.
Needles Needles are slender, columnar ice crystals that grow when the
temperature is around -5 C (23 F). These snowflakes look like small bits of white
hair.
Capped Columns These crystals first grow into stubby columns, and then they
the growth becomes plate-like. The result is two thin, plate-like crystals growing
on the ends of an ice column.
.
Double Plates / Dupla lapocskák
A double plate is basically a
capped column with an especially
short central column. The plates are so close together
that inevitably one grows out faster and shields the
other from its source of water vapor. The result is one large plate connected to
a much smaller one. These
crystals are common, many
snowflakes that look like
ordinary stellar plates are
actually double plates if
you look closely.
Split Plates and Stars /
These are forms of double plates, except that part of
one plate grows large along with part of the other
plate. The
all eight
a split star.
picture shows
ways to make
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Triangular Crystals Plates sometimes grow as truncated triangles when the
temperature is near -2 C (28 F). If the corners of the plates sprout arms, the
result is an odd version of a
stellar plate crystal. These
crystals are relatively rare.
12-Sided Snowflakes
Sometimes capped columns
form with a twist, a 30degree twist to be specific.
The two end-plates are both six-branched crystals, but
one is rotated 30 degrees relative to the other. This is
a form of crystal twinning, in which two crystals grow joined in a specific
orientation.
Bullet Rosettes The nucleation of an ice grain sometimes yields multiple crystals
all growing together at random orientations. When the different pieces grow
into columns, the result is called a bullet rosette. These polycrystals often break
up
to
leave isolated bulletshaped crystals.
Sometimes a bullet rosette can become a capped rosette.
When the pieces of a polycrystal grow out into dendrites, the result is called a
radiating dendrite or
spatial dendrite.
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Rimed Crystals Clouds are made of countless water droplets, and sometimes
these droplets collide with and stick to snow crystals. The frozen droplets are
called rime. All the different types of snow crystals can be found decorated
with rime. When the coverage is especially heavy, so that the assembly looks like
a tiny
snowball,
the result
is called
graupel.
Irregular
Crystals
The most common snow
crystals by far are the
irregular crystals. These are small, usually clumped together, and show little of
the symmetry seen in
stellar or columnar
crystals.
Artificial Snow
Artificial snow is
made of frozen water
droplets, with none of
the elaborate
structure found in real snow crystals.
Snowcrystals seen with electron microscope /
Avots: http://www.its.caltech.edu/~atomic/snowcrystals/
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