Рисуем космос 4 класс |
Тексты на английском | ||
<< World War II and the Collapse of Europe | A True American Tragedy The Indian Extermination >> |
Автор: Referee. Чтобы познакомиться с картинкой полного размера, нажмите на её эскиз. Чтобы можно было использовать все картинки для урока английского языка, скачайте бесплатно презентацию «Рисуем космос 4 класс.ppt» со всеми картинками в zip-архиве размером 1580 КБ.
Сл | Текст | Сл | Текст |
1 | Knowledge of space groups and the | 15 | that the identity operation is a trivial |
implications of space group symmetry on | operation of making no change, e.g., a | ||
the physical and chemical properties of | 360° rotation. 15. | ||
solids are pivotal factors in all areas of | 16 | The term "Special Position" | |
structural science. As we met to bring our | (not yet encountered...) is defined as | ||
ideas in teaching this subject to life, we | follows: A set of symmetrically equivalent | ||
both felt that teaching the concepts with | points...is said to be in 'special | ||
repetitive textual and visual | position' if each of its points is mapped | ||
reinforcement, “early and often”, will | onto itself by at least one further | ||
provide a sound basis for students in this | symmetry operation of the space group. | ||
subject. We chose PowerPoint as the | Later we'll see that a special position | ||
delivery vehicle for the tutorial, owing | always corresponds to the location of a | ||
to the facility of combining narrative | point group symmetry element (inversion ? | ||
pedagogy with animations of the buildup of | ), rotation (n = 2, 3, 4 or 6 ? rotations | ||
space groups, and the ease of making | of 360/n degrees), reflection (m)). A | ||
subtle changes and/or corrections. And, we | molecule located on a special position is | ||
realize that others may wish to alter the | expected to possess the point group | ||
approach, e.g., by rewriting the text in | symmetry of the special position. 16. | ||
another language, or altering the approach | 17 | Our first example is space group No. | |
(….hopefully, the desired changes will be | 1, P1 – the symbol informs us that we have | ||
small!). The student may also wish to | a primitive lattice, and only “1” | ||
consider M. E. Kastner's Crystallographic | symmetry. A number, n, as a symmetry | ||
Courseware, which provides an alternative | element in Hermann-Mauguin notation (used | ||
approach to the teaching of Space Group | throughout the tutorial) refers to a | ||
Symmetry. 1. | rotation by 360/n degrees. Thus 1 refers | ||
2 | We trust that the current and | to a 360° rotation. This element is also | |
subsequent versions of our tutorial will | called the identity in group theory, as it | ||
become ein lebendiges Buch (a living book) | represents a trivial operation of making | ||
to which all can contribute and enjoy, and | no change. We will consider the effect of | ||
from which all can learn. 2. | symmetry on a molecule or group located at | ||
3 | The tutorial is based in part upon an | a “general position” in the unit cell, | |
approach to teaching space groups | with coordinates (+x, +y, +z). Let’s try | ||
developed in a course in X-ray | it now. 17. | ||
Crystallography at Brandeis University. | 18 | a. c. 18. +. | |
However, through vigorous discussions, the | 19 | So, we’ve got one molecule per unit | |
ideas have been continuously reworked. 3. | cell (Z = 1). Let’s consider some | ||
4 | Acknowledgements We are particularly | properties of space groups that we’d like | |
grateful to the National Science | to track as we take this tour… Which two | ||
Foundation Summer Research Program in | phrases describe the properties of | ||
Solid State and Materials Chemistry, | handedness and centrosymmetry for P1? 19. | ||
directed by Prof. Shiou-Jyh Hwu, Clemson | 20 | Enantiomorphous. Non-centrosymmetric. | |
University. The Program provides an | 20. +. | ||
opportunity for a faculty member and | 21 | Now, let's review some of the jargon | |
student to carry out research in a host | introduced earlier: In this area we'll | ||
laboratory; Prof. Jasinski and student | list the set of equivalent points | ||
Lisa Bennett worked on solid-state | belonging to the general position. Number | ||
reactivity during Summer 2003 at Brandeis. | of equivalent positions contained within | ||
For the faculty member to return to the | one unit cell. 21. Reference atom. An | ||
program in subsequent years, a joint | equivalent position. Prefix. +. | ||
research program on educational aspects of | 22 | A final point or reminder regarding P | |
solid-state chemistry is required. With | (primitive lattices): The primitive | ||
the encouragement provided by the program | translation operators, expressed in | ||
requirements and additional NSF support | fractional coordinates, are (1,0,0), | ||
through grants DMR-0089257 and DMR-0504000 | (0,1,0), (0,0,1). These operations apply | ||
to BMF, we designed and wrote this | to any and all lattice points and may be | ||
tutorial during Summer 2004 and 2005. 4. | applied once or many times. Thus, lattice | ||
5 | Finally, we wish to thank Dr. Eugene | points such as : (x,1+y,z) (x-1,y,z) | |
Cheung (Cardiff University) and Professors | (2+x,y-3,z+4) are all “symmetry-related” | ||
Jen Swift (Georgetown) and Mike Ward | to the point (x,y,z). A common error made | ||
(Minnesota) for reviewing the tutorial and | in the early stages of understanding is to | ||
providing oodles of helpful comments. | suppose that, e.g., (x,1-y,z) is “the same | ||
Local comments and stimulating discussions | as”, or is translation-related to | ||
at Brandeis University, from Professors | (x,y-1,z). Note the difference! In | ||
Dan Oprian, Chris Miller and undergraduate | general, adding or subtracting an integer | ||
students Jeremy Heyman and Stephen C. | to a fractional number is NOT the same as | ||
Wilson were of immeasurable help. We | first taking the negative of that number, | ||
invite your comment and constructive | and then adding or subtracting integers! | ||
criticism. The design of this tutorial | 22. | ||
will allow us to incorporate changes on a | 23 | Now, I’ll produce the point (x, 1-y, | |
regular basis. Bruce M. Foxman Brandeis | z) from my original “blue” point: (0.1, | ||
University foxman1@brandeis.edu | 0.8, 0.3). Ouch! This differs from the | ||
http://www.xray.chem.brandeis.edu Jerry P. | original by (0, 0.6, 0), and the brown | ||
Jasinski Keene State College | point by (0, 1.6, 0)….it isn’t related to | ||
jjasinski@keene.edu | either point by a primitive translation! I | ||
http://academics.keene.edu/chemistry/facul | see the key to it now: we can add positive | ||
y.htm September 2006. 5. | or negative integers to a point, but a | ||
6 | COLORS No doubt you have already | translation will NEVER change the sign of | |
noticed that we’re using underlined green | the coordinate. Hmmm…I don’t see what you | ||
text to indicate a hyperlinked page or | mean! Let me think about it. So…. I need | ||
pages. In order to minimize issues | to satisfy myself that (x, 1-y, z) and (x, | ||
involving broken links, all links are | y-1, z) are different, that is, they are | ||
included in the tutorial, and the exact | not related by a simple translation. OK. | ||
link references may be found in the | I’ll choose a point ….uh….(0.1, 0.2, 0.3). | ||
Credits section (Chapter 7) of this | I’ll calculate (x, y-1, z) = (0.1, -0.8, | ||
PowerPoint presentation. Blue is often | 0.3). This is clearly related to my “blue” | ||
used for emphasis. Red is usually employed | point by the translation (0, 1, 0). Sue N. | ||
when we are referring to symmetry elements | Smart. 23. | ||
or unit cell parameters a, b, c, ?, ?, ?. | 24 | OK! Now let’s take the same diagram, | |
Other colors, used less often, are | that is, the one we just finished, and add | ||
generally employed to emphasize particular | a center of symmetry at the origin. The | ||
points, or to improve the readability of a | symbol for this is a small circle. After | ||
particular presentation. 6. | we add the center, where is the next | ||
7 | Where should you be, in your knowledge | molecule? Will it be in front of the | |
of X-ray structure determination, or | screen (as for the (x, y, z) molecule), or | ||
crystallography before beginning this | behind? Think about its sign (the sign for | ||
tutorial? We’re starting with an assumed | the y-coordinate) before you push the | ||
knowledge of point groups, unit cells, | button. Yes, its coordinates are | ||
lattices and space group symmetry elements | (-x,-y,-z), and thus we place a “-” next | ||
(there will be some minor review of these | to it. If the new molecule that is | ||
topics). In the future we'll be adding a | generated has the opposite chirality to | ||
special section on unit cells and lattices | its symmetry-related mate, we’ll put a | ||
recently added to the tutorial. We | comma inside to indicate that. The other | ||
recommend reviewing or understanding the | thing to look for is the appearance of | ||
equivalent of Chapters 1-4 in Sands, | other centers of symmetry as you add | ||
Introduction to Crystallography (Dover, | molecules: these are the ones that are | ||
1975) or Sections 2.1 and 3.1-3.4 in Stout | generated by the interaction (i.e., the | ||
and Jensen, X-Ray Structure Determination: | multiplication) of the operations of this | ||
A Practical Guide (Wiley, 1989). Finally, | group. 24. | ||
if you have around 3 minutes, listen to a | 25 | To reiterate, for each space group, as | |
humorous musical revue of Bravais lattices | we did for P1, we’ll derive the group from | ||
at : | the Hermann-Mauguin symbol. New figures | ||
http://www.haverford.edu/physics-astro/son | will "pop up", and you should | ||
s/bravais.htm. 7. | continually pause and consider the | ||
8 | This tutorial is divided into sections | figure's HCE : Height, Chirality, and | |
by crystal class. There are 32 | which new Elements have been generated. | ||
crystallographic point groups, or crystal | Carl Hermann. Charles-Victor Mauguin. 25. | ||
classes. The 32 crystal classes correspond | 26 | , Z=2; Is this space group | |
to the external shapes of crystals | enantiomorphous or non-enantiomorphous? | ||
actually observed. The crystal class may | Non-enantiomorphous. 26. -. | ||
be obtained from the space group symbol by | 27 | Z=2; Is this space group | |
“removing” the translations from the | centrosymmetric or non-centrosymmetric? | ||
symbol…more about that later! In this | Centrosymmetric. 27. | ||
section we consider the two triclinic | 28 | Note that there are two molecules per | |
space groups, P1 and P-1bar, which belong | unit cell, and that other centers of | ||
to crystal classes 1 and 1-bar, | symmetry (at a/2, b/2, c/2 and | ||
respectively. Paul von Groth. 8. | combinations thereof) were generated as we | ||
9 | In all of the tutorial presentations | added atoms or groups. It turns out that | |
which show a unit cell diagram, we have | there are eight centers of symmetry: where | ||
followed the style of the International | are they? (0, 0, 0) ; (?, 0, 0); (0, 0, | ||
Tables for Crystallography, Volume A, | ?); (?, 0, ?); (0, ?, 0); (?, ?, 0); (0, | ||
Space Group Symmetry, which contains | ?, ?); (?, ?, ?). 28. | ||
diagrams of the 230 space groups. We will | 29 | Above is a perspective view of a unit | |
use the Hermann-Mauguin symmetry notation1 | cell in P1bar, with all centers of | ||
throughout, and will be deriving each | symmetry shown. The eight independent | ||
space group from the Hermann-Mauguin | centers of symmetry (i. e., those NOT | ||
symbol. Our diagrams are “not exactly” | related by any symmetry operation) are | ||
identical to the diagrams in Volume A, but | shown in blue. 29. | ||
rather are a composite overlay of the unit | 30 | We say that the eight centers of | |
cell diagram, symmetry elements, and | symmetry are independent, since any single | ||
molecules which reside in the Equivalent | center of symmetry is unrelated to another | ||
General Positions. 9. 1There will be an | by the operations of the group : It’s easy | ||
opportunity to learn more of the history | to see that the centers of symmetry are | ||
of this notation on an upcoming slide. | unrelated; plug any value into the above | ||
10 | In the triclinic system, a ? b ? c; ? | set of equivalent positions, and we get | |
? ? ? ? ? 90?. Triclinic crystals either | the same value back: try (0,0,0) – this is | ||
have only 1 symmetry (a 360° rotation, | obvious. If we try (?,0,0) we generate | ||
crystal class 1) or possess a center of | (-?,0,0). Do these two points represent | ||
inversion (crystal class ). For | the same position? Yes, of course, since | ||
convenience, we’ll often write “1-bar” | we can always add a positive or negative | ||
instead of . | integer (unit cell translation) to any | ||
1http://phycomp.technion.ac.il/~sshaharr/i | point. Formally, the two have different | ||
tro.html. Primitive Triclinic (click to | locations, but they are identical upon | ||
rotate)1. 10. | unit translation along the a axis. 30. | ||
11 | On each slide you will see the ac | 31 | Each of the eight centers of symmetry |
projection of a triclinic or monoclinic | corresponds to a special position in . | ||
unit cell. The b axis, which points toward | Note that each point will be mapped onto | ||
the viewer, is either inclined to the a | itself by an operation of the group (cf. | ||
and c axes (triclinic) or perpendicular to | slides 16 & 30). Special positions | ||
the page (monoclinic). In the orthorhombic | always correspond to a point group | ||
case, we'll use an ab projection. Each | symmetry element, i. e. a rotation axis, | ||
slide opens with the ac (orthorhombic, ab) | reflection, inversion or rotary inversion | ||
projection and a reminder about the axial | axis. A special position always has | ||
directions. Upon tapping the advance | reduced multiplicity compared to the | ||
button, various events will occur, | general position. 31. | ||
depending upon the space group under | 32 | x. y. z. Why is the multiplicity for | |
consideration. We’ll describe these | the special positions in equal to 1? | ||
precisely as we approach each example. | Recall that the equivalent positions for | ||
Each atom or group of atoms will be | are: If we "run" any of the | ||
displayed by an open circle. An open | special position coordinates through these | ||
circle with a large comma inside will be | general positions, we only get one value | ||
used to indicate opposite chirality to the | in return: (0, 0, 0) gives identically (0, | ||
reference molecule. 11. | 0, 0), and, (?, ?, ?) gives (-?, -?, -?). | ||
12 | We need to define the coordinate | Placing these two points within the same | |
system we'll be working in. Of course, | unit cell by unit translations along a, b | ||
we'll need to specify the positions of | and c renders them identical. 32. | ||
atoms or molecules within the unit cells | 33 | So. It is easy to see that P1-bar must | |
under consideration. Let's imagine that a | contain racemic molecules….but could P1 | ||
particular atom is located (in ?) at (X, | contain a racemate? Of course. In P1, the | ||
Y, Z). A preferred method to specify the | left- and right-handed molecules are | ||
location of this atom would be to use a | simply unrelated by any symmetry | ||
formalism that is independent of the size | operation, while in P1-bar, they are | ||
of the unit cell. To do this we use | related by the crystallographic inversion | ||
fractional coordinates (x, y, z), where x | center. 33. | ||
= X/a y = Y/b and z = Z/c Within the unit | 34 | We've completed the triclinic space | |
cell, values of x, y and z are thus | groups, but there are a few final relevant | ||
constrained to decimal values between 0 | points worth making from both experimental | ||
and 1. And, for example, a location in a | and pedagogic points of view. It is very | ||
unit cell adjacent to the reference cell | useful for us to know something about the | ||
but displaced along a would thus be (1 + | density of a crystal. If the measured and | ||
x, y, z). 12. | calculated densities agree, we may be | ||
13 | What is our reference molecule or atom | confident that we know the stoichiometry | |
? This is the first atom or group that | of the crystal contents well. | ||
appears on the screen as an open circle. | Alternatively, if the two values do not | ||
It will always have the coordinates (x, y, | match, we can calculate the unit cell's | ||
z), and we'll draw an ac projection of the | molecular weight from the measured | ||
unit cell, with axis b coming out of the | density, and often deduce the | ||
page. Finally, we must specify the | stoichiometry. 34. | ||
location of the atom or group along the | 35 | Can we actually define the density of | |
third dimension (its "height" | a crystal in terms of the language & | ||
in/out of the screen). We’ll do this by | ideas we have used thus far? The mass, m, | ||
placing the “prefix” of the y-coordinate | of one unit cell is just nM/N0 , where n = | ||
next to the open circle. For the reference | the number of molecules per unit cell, M = | ||
molecule, this will simply be a “+”, as it | formula weight in grams, and N0 = | ||
is located at (x, y, z) ? +y. An indicator | Avogadro's number. V is the unit cell | ||
such as “?+” signifies “?+y”; “-” is just | volume. Normally we will use formula | ||
“-y”. Remember that x, y and z are | weight in grams and volume in cm3. 35. | ||
fractional coordinates, and for molecules | 36 | Crystal density is conveniently | |
within the unit cell, each has a value | measured by the neutral buoyancy | ||
between 0 and 1. As you push the advance | technique. Imagine what would happen if we | ||
button, the operations of the group are | placed crystals of density 1.30 g-cm-3 in | ||
applied …. in the following case, space | a solution of heptane, ? = 0.68 g-cm-3: | ||
group P1, we have only unit translations | Now imagine what would happen if we used | ||
to apply, in sequence. 13. | CCl4, ? = 1.59 : 36. | ||
14 | We’ll start by adding the | 37 | Often, it is most useful to measure |
translations, and recording the unique set | the density by the neutral buoyancy | ||
of symmetry position(s) generated for a | technique, and then calculate n, the | ||
single atom. As the atoms are added, think | number of molecules in the unit cell. | ||
about how many are actually within the | Thus, a compound C12H12N2O2 crystallizes | ||
unit cell; we’ll call this number Z. | in the triclinic system, and has formula | ||
Beside the number of symmetry related | weight 216.24, a density of 1.341 g-cm-3 | ||
atoms, we’ll list their positions. See if | and a unit cell volume of 535.59 ?3. Let's | ||
you can assign coordinates to each | calculate n = ?VNo/M = 1.341(535.59 ? | ||
molecule added; some answers are given as | 10-24)(6.02 ? 1023)/(216.24) = 2.002! So, | ||
you proceed. At a time after all the | there's 2 molecules per unit cell…..can we | ||
unique atoms within the cell have been | tell, in general, whether the space group | ||
generated we’ll draw a box around the | is P1 or P-1bar from such data? More | ||
“General Position”, the set within the | pertinently: can we ever determine the | ||
unit cell equivalent by symmetry. The | space group from density information? 37. | ||
General Position thus contains a certain | 38 | Bonjour, Professeur! I have a | |
number of equivalent points per cell; the | crystal…I have measured the density and | ||
number is referred to as Z. We will also | determined the crystal system. It’s | ||
say that the multiplicity (the number) of | triclinic, and Z = 1. Therefore, it MUST | ||
the General Position is Z. 14. | belong to space group P1 !!!!!!!!!! Silly | ||
15 | In the International tables for X-ray | boy! No. You may be correct, but it just | |
Crystallography, Volume A. section 2.11, | as well could be in P1-bar, with a | ||
the term "General Position" is | molecule simply occupying a special | ||
defined as follows: A set of symmetrically | position (the center of symmetry). You | ||
equivalent points...is said to be in | CANNOT obtain the space group from a | ||
'general position' if each of its points | density measurement! 38. | ||
is left invariant only by the identity | 39 | Ah, Professeur! I beg to differ! Now I | |
operation but by no other symmetry | have a different crystal. Again I have | ||
operation of the space group. Each space | measured its density and determined the | ||
group has only one general position. We'll | crystal system. It’s triclinic, and this | ||
see, time and time again, that, in the | time Z = 2. It is very clear that the | ||
general position, no symmetry requirements | space group is P1-bar !!! No. No. No. | ||
are imposed upon the molecule. Thus, | Again, you may be correct, but it just as | ||
general positions always have | well could be in P1, with two molecules | ||
'site-symmetry' 1 (Hermann-Mauguin | each occupying a general position; the two | ||
notation) or alternatively C1 (Schoenflies | are unrelated by symmetry. As I said, you | ||
notation). More info about Hermann-Mauguin | CANNOT obtain the space group from a | ||
notation appears on slides 17, 25 and | density measurement! 39. | ||
throughout the tutorial. We hope you will | 40 | End of Section 1, Introduction & | |
recall from your knowledge of point groups | Pointgroups 1 and 1-bar. 40. | ||
Рисуем космос 4 класс.ppt |
«The animals» - SEAL. DOLPHIN. The animals which live in the desert. KOALA. EMU. SQUIRREL. PARROT. BISON. HIPPO. GORILLA. BEAR. ZEBRA. The ANIMALS of our planet. GIRAFFE. POLAR BEAR. GRIFFIN. WOMBAT. LION. LIZARD. KANGAROO. FLAMINGO. WHALE. The animals which live in the OCEAN. The animals which live in the polar regions.
«The green movement» - The countries in which there are offices Greenpeace. National offices Green Peace are opened in 43 countries of the world as the independent units working over achievement of the purposes of the national projects. Their features. Green color which is used by participants of movement as the general emblem, serves as a symbol of the nature, hope and updating.
«The english-speaking countries» - USA. Great Britain. The English-speaking countries. Scotland. Disneyland. Australia.
«Женщина the woman» - A woman’s tongue wags like a lamb’s tail. Женский интеллект. « Der mann»- нем. 9 семантических подгрупп, характеризующих женщин по: Муж - голова, жена- шея; куда хочу- туда верчу. Бабий язык, куда ни завались, достанет. Chicken’s mind- Куриные мозги. От нашего ребра нам не ждать добра; Пути пополнения лексической группы «женщина» в английском языке.
«Kaleidoscope» - Industry. Another cube. Kaleidoscope. Sometimes the object cell is filled. Kaleidoscope operates. Modern kaleidoscopes. A tetrahedron. Initially intended as a scientific tool, the kaleidoscope was later. History. Part containing. Kinds of kaleidoscopes. Craft galleries.
«Teddy bear» - The grizzly has 30 years an average life. Black bear. Bear. Kodiak Bear (Ursus arctos middendorffi) is the largest terrestrial carnivore. Panda Bear. The bears maintained the talents of some early miacids for tree-climbing. The size of the large males Kodiak Bear exceeds 3 m and their weight can reach a ton.