GGRA03H3 Lecture : Landscape

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pearsardine837

1 Feb 2012

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Key concepts in the study of urban environments and urban geography: Examines how pristine nature (trees, wildlife, water, soil, grasslands, etc. ) is produced through social decisions and practices. Nature is constantly re-produced through the evolution of social decisions and practices. The relationship between social decisions and practices and changing natural landscapes makes it impossible to separate society" from. Socio-nature: intertwining of social and natural processes in the transformation of nature. Cyborg urbanization: mechanical insertions into natural urban spaces. The production of nature is highly apparent in cities due to population concentration, industrial activity and infrastructure (under and above the ground). The urban natural landscape is always changing due to political decisions, economic interests, and public needs and uses: social production of nature. Every day on st patrick"s day: engineers pour green food colouring into the river, Toronto waterfront: landfill used to create new land. Three gorges dam: (start of construction: 1994)

A right triangle has legs ofknown lengths 2L and h. Find thelength of the line segment x whichis parallel to side h. Explainyour reasoning. Image in weblinkbelow:

http://paer.rutgers.edu/194/Downloads/194LAB07.pdfRY4bB71082bfFuqzISDrWGDOWfNgGl208qJNQTAhpzWjb_ahDlhGHPLz19S1Eq95&q=cache%3AnpyQu9LlzykJ%3Apaer.rutgers.edu%2F194%2FDownloads%2F194LAB07.pdf%20this%20geometry%20task%20may%20be%20helpful%20for%20devising%20a%20mathematical%20procedure%20for%20the%20next%20lab.%20A%20right%20triangle&docid=5c8a26db354186a31ce6383

POSTSCRIPT: EFFECTS OFASSUMPTIONS

The marbled murrelet is asmall bird that lives in the PacificNorthwest where old-growthforests are close to the sea. It nests inthe forests and feedsoffshore. It is now highly endangeredthroughout its range, whichextends from Northern California toAlaska.

These birds are extremelyvulnerable to loss of their habitat,because they nest exclusivelyin the same old-growth coniferoustrees that are prime targets forlogging. Considerable efforts havebeen made to protect the speciesby restricting timber operations inthe areas in which they areknown to nest. Scientists predicted thatthe population should growback. However until recently naturalistswere puzzledand

dismayed because thepopulation of marbled murrelets did notseem to be recovering oreven stabilizing.

A recent study suggests thereason why this testing experimentin conservation did not confirmthe prediction. The scientistsoverlooked an important assumption:murrelets can also be threatenedby man's activity at sea.Overfishing has severely reduced thepopulation of small,energy-rich fish that murrelets rely upon formost of theircalories.

Climate change of uncertainorigin may have also disrupted thefood chain, and El Nino currentsmay have changed the distributionof the phytoplankton that formsthe base of all marine life.

Further efforts to preservethe marbled murrelet must be basedon accurate assumptions aboutthe origin of their difficulties.

Could naturalists have betterconsidered their originalassumptions years ago? What would yousay?

3. 3 Stratosphere-troposphere exchange

The rate of exchange of air between the troposphere and thestratosphere is critical for determining the potential of variouspollutants emitted from the surface to reach the stratosphere andaffect the stratospheric ozone layer. One of the first estimates ofthis rate was made in the 1960s using measurements of strontium-90(90Sr) in the stratosphere. Strontium-90 is a radioactive isotope(half-life 28 years) produced in nuclear explosions. It has nonatural sources. Large amounts of 90Sr were injected into thestratosphere in the 1950s by above-ground nuclear tests. Thesetests were banned by international treaty in 1962. Following thetest ban the stratospheric concentrations of 90Sr began to decreaseas 90Sr was transferred to the troposphere. In the troposphere,90Sr is removed by wet deposition with a lifetime of 10 days (bycontrast there is no rain, and hence no wet deposition, in thestratosphere). An intensive stratospheric measurement network wasoperated in the 1960s to monitor the decay of 90Sr in thestratosphere. We interpret these observations here using a 2-boxmodel for stratosphere-troposphere exchange with transfer rateconstants kTS and kST (yr-1) between the tropospheric andstratospheric reservoirs. The reservoirs are assumed to beindividually well-mixed.

Let mS and mT represent the masses of 90Sr in the stratosphere andin the troposphere respectively. Observations of the decrease inthe stratospheric inventory for the period 1963-1967 can be fittedto an exponential mS(t) = mS(0)exp(-kt) where k = 0.77 yr-1.

1. Write mass balance equations for mS and mT in the 1963-1967period.

2. Assuming that transfer of 90Sr from the troposphere to thestratosphere is negligible (we will verify this assumption later),show that the residence time of air in the stratosphere is tS =1/kST = 1.3 years.

3. Let m'T and m'S represent the total masses of air in thetroposphere and the stratosphere, respectively. Show that theresidence time of air in the troposphere is tT = tS (m'T/m'S) = 7.4years. Conclude as to the validity of your assumption in question2.

4. Hydrochlorofluorocarbons (HCFCs) have been adopted asreplacement products for the chlorofluorocarbons (CFCs), which werebanned by the Montreal protocol because of their harmful effect onthe ozone layer. In contrast to the CFCs, the HCFCs can be oxidizedin the troposphere, and the oxidation products washed out byprecipitation, so that most of the HCFCs do not penetrate into thestratosphere to destroy ozone. Two common HCFCs have trade namesHCFC-123 and HCFC-124; their lifetimes against oxidation in thetroposphere are 1.4 years and 5.9 years, respectively. There are noother sinks for these species in the troposphere. Using our 2-boxmodel, determine what fractions of the emitted HCFC-123 andHCFC-124 penetrate the stratosphere.

19. The interstellar medium has a cool component measuredvia_________ observations and a hot component revealed by________observations.
AX-ray; optical
BX-ray; infrared
CX-ray;gamma-ray
Doptical; X-ray
Einfrared; X-ray

20. Which of the following processes will NOT cause a gas cloudtocollapse?
Aionization from youngstars
Bsupernovaexplosions
Cgalacticrotation
Dthe expansion of theUniverse

21. What is responsible for emitting photons in anemissionnebula?
Aexcitedprotons
Bexcitedneutrons
Cexcitedelectrons
Dexcitedneutrinos
Eexcitedastronomers

22. White dwarf stars are supported from collapse by
Anuclear fusionreactions in a shell around the core.
Belectron degeneracypressure.
Cnuclear fusion reactionsin their cores.
Dcentrifugal force due torapid rotation.

23. The "star" that is seen at the center of a planetarynebulais
Aa planet in theprocess of formation.
Ba small, hot, and verydense, white dwarf star.
Cthe accretion disk arounda black hole.
Dcomposed almost entirelyof neutrons, and is spinning rapidly.

24. A white dwarf star, the surviving core of a low-massstartowards the end of its life, can be found ontheHertzsprung-Russell diagram
Aat the bottom end ofthe main sequence, along which it has evolvedthroughout itslife.
Babove and to the right ofthe main sequence, since it evolved thereafter itshydrogen-burning phase.
Cbelow and to the left ofthe main sequence.
Dat the upper left end ofthe main sequence, since its surfacetemperature is extremelyhigh.

25. The mechanism which gives rise to the phenomenon of thenovais
Amaterial fallinginto a black hole and being condensed to the pointwhere athermonuclear explosion is produced.
Bthe impact and subsequentexplosion of a large comet nucleus upon astar's surface.
Cthe completedisintegration of a massive star because ofthermonuclear runawayin the star's interior.
Dmatter from a companionstar falling onto a white dwarf in a closebinary system,eventually causing a nuclear explosion on thedwarf'ssurface.

GGRA03H3 Lecture : Landscape

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