Pracownia komputerowa

Dariusz Wardecki, wykład I

Kontakt

• dward@fuw.edu.pl

• http://www.fuw.edu.pl/~dward/pk

• ul. Hoża 69, pok. 114

• tel. 22 55 32 181

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Materiał na ćwiczenia• Linia poleceń w systemie Linux

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• Operacje na plikach i katalogach

• Prawa dostępu

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• Procesy

• Pakiet biurowy OpenOffice.org

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• Procesor tekstu (Write)

• Edytor równań

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• qtiplot (http://soft.proindependent.com/qtiplot.html)

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Plan wykładu• Zasada działania i budowa komputera

• Binarny zapis danych, reprezentacje liczb i znaków

• Struktura i budowa pamięci, rodzaje pamięci

• Masowe składowanie danych, systemy plikowe i drzewa katalogowe

• Przestrzeń dyskowa, pliki i katalogi

• Cyfrowy zapis dźwięku i obrazu

• Przesyłanie danych na odległość i sieci komputerowe

Cel wykładu i ćwiczeń

Teoria

Dane

7366

P. SONNTAG, P. BODEKER, T. THURSTON, AND H. ZABEL

52

33—

o+ 32-0'C~ 31-

30—

29

I500I

I

10001500

2000

Thickness [A]I2500

I3000

FIG. 3. The period of the out-of-plane CDW and SW as it

depends on the Cr layer thickness D. The dotted line designs

a relaxation curve 6tted to the data. The dashed line denotes

the bulk value of 29.5 A. .

50—Q 1000 A. Cr(001)/Nb

~ 3000 A Cr(001)/Nb

45X-Ray data bulk Cr

Q Neutron data bulk Cr

k~

35—

o0

030—

0I

50I100

I

I

150200T [K]

250300

350

FIG. 4. The temperature dependence of the CDW-SW pe-

riod of a 3000 A thick Cr film on Nb and a 1000 A thick Cr

film compared with the results of bulk Cr measurements. The

bulk data are taken from Refs. 9 and 11.1.2

+EN-

-C3

0.8—~WC. 0.6—

~ 04 — + 1000 A Cr(001)/Nb

~ 3000 A. Cr(001)/Nb

0 2Bulk Cr0

50100

I

I

150200T [K]

gil3.

El

4~+

bI

I

250300

350

FIG. 5. The temperaturedependence of the CDW-SW

satellite intensity of a 3000 A thick Cr film on Nb and a 1000

A. thick Cr film compared to the bulk behavior measuredby

means of x-ray difFraction (Ref. 27). The dotted line is a

guide to the eye designing the bulk behavior. The intensity

is normalized to 1 at T=100 K.

Figure 4 displays the CDW-SWperiod as a function

of the temperaturefor two Cr films with thicknesses of

1000 A and 3000 A compared with bulk measurements

done by means of neutron and x-ray scattering. 'The

deviation of the CDW/SWperiod observed in the Cr

films &om the bulk value increases with increasing tem-

perature.This effect appears to be much stronger in

the 1000 A. thick film. The temperaturedependence of

the satellite intensity is shown in Fig. 5 as compared with

bulk measurements.Over a wide temperature range be-

low T200 K the behavior of the thin film data is the

same as for bulk Cr. At 250 K a sudden drop of the

satellite intensity is observed in the thin films. The Neel

temperatureseems to be reduced compared to bulk Cr

and the Neel transition is smeared out. This could be

explained as an effect of epitaxial strains, as suggested

by Werner et al.Next we studied the satellite rejections around the

Cr[011] fundamental peak. This position in reciprocal

space is particularlyinteresting since here both in- and

out-of-plane components of the CDW's and SW's can be

investigated. In Fig. 1 the respective scans parallel to the

K direction (in-plane component) and L direction (out-

of-plane component) are reproduced. The experiments

show that no satellite refj.ections belonging to a q vector

pointing along an in-plane direction could be observed.

Therefore we have to conclude that the SDW is strongly

polarized along the [001] growth direction.

A comparison between out-of-plane and in-plane mea-

surements performed around a Cr[011] reflection is pro-

vided in Fig. 6.

V. DISCUSSION

From recent neutron and x-ray studies on the SDW's in

bulk Cr we know that there exists an orientational sur-

face pinning efFect which suppresses the in-plane SDW

modes.Hill et al. performed both x-ray and neutron

difFraction experiments on Cr bulk crystals with an (001)

oriented surface. Looking at the SDW's with neutron

scattering their samples seemed to be in a poly-q mode

in which all possible SDW modes were equally populated.

Using x-ray scattering around an off-axis Cr Bragg reHec-

tion and comparing the results with theoretical calcula-

tions for a poly-q state the out-of-planemode appears

to be stronger than those havingq vectors parallel to the

surface plane. This behavior could be explained by a sur-

face pinning efFect suppressing the in-plane SDW's and

leading to, a nearly singleq domain state when observed

with x rays, since x rays only provide information about

the surface of the bulk sample.

This observationsuggests that the behavior of our Cr

films could be a result of an orientational interface pin-

ning effect at both the Cr oxide surface and the Cr/Nb

interface. This pinning effect appears to be temperature

dependent, since the observed period of the out-of-plane

CDW and SW shows a strong temperature dependence.

The deviation of the period from the bulk values increases

with increasing temperature.As expected for an inter-

face effect this behavior is stronger in the thinner film.

Komputer

• Maszyna licząca, potrafiąca wykonywać obliczenia według zadanego programu.

Trochę historii• 1946 - ENIAC (Electronic Numierical

Integrator And Computer), waga 30t, 18 tyś. lamp elektronowych, wymiary 15x9m

Trochę historii

• 1946 - IAS (Institute for Advanced Study) według pomysłu Johna von Neumanna

• 1951 - EDVAC (Electronic Discrete Variable Automatic Computer), cząstość zegara 996,75 kHz, programowana za pomocą taśmy perforowanej i kart dziurkowanych

Trochę historii

1947 - TranzystorJohn Bardeen

Walter Brattain

Nobel 1956 r.

Trochę historii

1958 - Układ scalonyJack Kliby (Nobel 2000 r.)

Robert Noyce

Trochę historii

Trochę historii• 1976/77 - Apple oraz Apple II

Procesor: 1 MHzRAM: 4 kB

Trochę historii

• 1981 - IBM PC, 4,77 MHz, 16 - 256 kB

Trochę historii

• 1984 - Macintosh, 8 MHz, 128 kB, 2495 $

Współczesny komputer

Raspberry PI