Download ppt2 - professor paul dowling department of culture communication

EDUCATIONAL RESEARCH
quality and quantity
Paul Dowling
Institute of Education
University of London
Photometric redshifts can be routinely obtained to accuracies of better than 0.1 in
Deltaz/(1 +z). The issue of dust extinction, however, is one that has still not been
well quantified. In this paper the success of two template-fitting photometric
redshift codes (IMPZ and HYPERZ) at reliably returning AV in addition to redshift is
explored. New data on the 2nd Canadian Network for Observational Cosmology
(CNOC2) spectroscopic sample of 0.2 < z < 0.7 galaxies are presented. These data
allow us to estimate AV values from the observed Balmer decrements. We also
investigate whether the empirical value of gamma= 0.44, the ratio between gasand star- derived extinction, as determined by Calzetti, is necessarily the best value
for this sample.
When comparing the two codes with the Balmer-derived AV (Balmer [AV]), a
correlation between the photometrically derived AV (Phot [AV]) and the Balmer
[AV] is found. The correlation is improved when the empirical value of gamma=
0.44 is allowed to vary. From least-squares fitting, the minimum in the reduced
chi2 distribution is found for gamma~ 0.25 +/- 0.2. For the sample of galaxies here,
the factor of 2 difference in covering factor implied by the Calzetti ratio is found to
be plausible. The CNOC2 galaxies with detected Balmer lines have some preference
for an increased covering-factor difference, which perhaps implies that they are
undergoing more rapid, `bursty' star formation than the galaxies Calzetti used in
her derivation. (Babbedge et al, 2005)
Can a photometric redshift code reliably determine
dust extinction?
1. Stellar evolutionary history can be inferred from spectral
energy distribution (SED)
2. Galactic dust absorbs and reflects some of the light = dust
extinction
3. Physicists need to correct for dust extinction
4. Researchers compared results of using 2 photometric
codes with another method
5. Found strong correlation between the 2 photometric
codes
6. Quite good correlation with third method when poor
accuracy of all 3 considered
7. So measurement of dust extinction reliable but not
accurate
Galaxy
A
PC1
a1
PC2
a2
Method 3
a3
B
C
D
b1
c1
d1
b2
c2
d2
b3
c3
d3
• 3 methods reliable but not accurate
• The context needs to have been fully theorised
in advance
• New theory is called for only to explain
anomalies
Alexander Luria
• societies move/develop between different
patterns of social relations, specifically, from
individualised to collective production
• cultural practices, and specifically language,
develop in line with social development
• sociocultural development causes
development in individual human cognition
Variable
Primitive Society
Advanced Society
Social relations
Individualised labour
Collective labour
Cultural practices
Non-literate
Literate
Cognitive development
Graphic functional
Theoretical
[The subject is shown pictures of a a log, a saw, an axe and a hammer and asked to select
the one that does not go with the other three]
'They're all alike. I think all of them have to be here. See, if you're going to saw, you need a
saw, and if you have to split something you need a hatchet. So they're all needed here.
''Which of these things could you call by one word?'’
How's that? If you call all three of them a 'hammer', that won't be right either.
''But one fellow picked three things—the hammer, saw, and hatchet—and said they were
alike.
''A saw, a hammer, and a hatchet all have to work together. But the log has to be here too.
''Why do you think he picked these three things and not the log?
''Probably he's got a lot of firewood, but if we'll be left without firewood, we won't be able
to do anything.
''True, but a hammer, a saw, and a hatchet are all tools.
''Yes, but even if we have tools, we still need wood—otherwise, we can't build anything.’
(Luria, 1976)
Group
No. of subjects
Graphic
method
Graphic &
Categorical
Categorical
Illiterate
peasants from
remote villages
26
21 (80%)
4 (16%)
1 (4%)
Collective farm
activists (barely
literate
10
0
3 (30%)
7 (70%)
Young people
with 1-2 years
schooling
12
0
0
12 (100%)
Importance of Theory
• Luria (cognitive development or familiarity
with school problems?)
• Piaget
– Watson
– Dowling’s sociological interpretation
• Lawler
• Two open bottles, one filled with vinegar and
the other with olive oil, were left on a window
sill in the Sun. Several days later it was
observed that the bottles were no longer full.
What can be concluded from this
observation?
– Vinegar evaporates faster than olive oil.
– Olive oil evaporates faster than vinegar.
– Both vinegar and olive oil evaporate.
– Only liquids containing water evaporate.
– Direct sunlight is needed for evaporation.
• Four children can feel and smell an object
inside a bag, but they cannot see it. Which of
the following is NOT an observation about the
object?
– “It is flat at one end and round at the other”.
– “It smells like peppermint”.
– “It has a bump on it”.
– “I hope it is candy”.
Importance of Theory
• Luria (cognitive development or familiarity
with school problems?)
• Piaget
– Watson
– Dowling’s sociological interpretation
• Lawler
Importance of Theory
• Luria (cognitive development or familiarity
with school problems?)
• Piaget
– Watson
– Dowling’s sociological interpretation
• Lawler
• What is 76 + 25?
• What is ¢76 + ¢25?
South African Research
(Dowling & Brown)
South African Research
(Dowling & Brown)
… there are two Ps if and only if there are x, y such
that x is P and y is P and x is not the same thing as
y and for all z, if z is P then z is the same thing as x
or z is the same thing as y.
A4 What is the bill for each of these shopping lists?
Work out each bill in your head.
(a) 1 kg potatoes (b) 2 oranges (c) 2kg spuds (d) 1kg
bananas (e) grapefruit 1 cauli 100g mushrooms 1
orange1kg bananas
(SMP 11-16 Book G1, p. 14; original shopping lists drawn as fragments of paper)
+
=