GGRC33H3 Study Guide - Final Guide: Sustainable City, Ville Radieuse, Brownfield Land

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7 Jul 2011

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urban form directly affects habitat, ecosystems, endangered species, and water quality through land consumption, habitat fragmentation, and replacement of natural cover with impervious surfaces. In addition, urban form affects travel behaviour, which, in turn, affects air quality; premature loss of farmland, wetlands, and open space; soil pollution and contamination; global climate; and noise. the concept of sustainable development has given a major stimulus to the question of the contribution that certain urban forms might make to lower energy consumption and lower pollution levels. this challenge has induced scholars, planners, local and international ngos, civil societies, and governments to propose supposedly new frameworks for the redesigning and restructuring of urban places to achieve sustainability. these approaches have been addressed on different spatial levels: (1) the regional and metropolitan levels, (2) the city level, (3) the community and (4) the building level.

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.

Vapor cycles
5EM - Thermodynamics
September 2010
1 The T-S diagram
The temperature-entropy diagram is an alternative to the well knownpressure-
volume diagram. Before using it to analyze different vapor cycles,we need
to understand it properly.
1. Plot the following transformations for ideal gases in a T-Sdiagram
(a) Isothermal expansion
(b) Isobaric expansion
(c) Isometric heating
(d) Reversible adiabatic expansion
(e) Irreversible adiabatic expansion
2. Repeat the last question, but this time do it for a realsubstance,
starting in the compressed liquid1 region and ending in thesuperheated
region, when possible. Indicate the boundaries of eachregion.
3. We know that under certain circumstances the area under theplot
in a P-V diagram represents the work performed during theprocess.
What does it represent in this case? Under what assumptions isyour
answer true? Compare examples 6.1 and 6.2.
2 Thermal machines
We understand by thermal machine a device capable of transformingther-
mal energy (heat) into mechanical energy (work). We already knowthat
these machines have a limited efficiency which, in the two-sourcesmodel, is
obtained by Carnotâs cycle.
(Compressed liquid is sometimes also called subcooled liquid)
2.1 Carnot cycle
This cycle, although efficient, is impractical. To begin with, theextreme
temperatures of the cycle should be within the sources temperaturesfor a
finite heat flow to exist.
1. Given the temperature of the sources, draw the cycle accordingto the
named limitation.
2. Show that this leads to lower efficiency than the theoreticallimit.
3. Assume that heat flow from/to the sources is proportional to thetem-
perature difference between them and the working fluid, anddemon-
strate that a higher power output is related to a decreasedefficiency.
2.2 Rankine cycle
Out of the several practical possibilities, Rankine cycle and itsvariations is
widely used, especially for electric power generation.
1. Draw the basic cycle in a T-S diagram and explain it.
2. What does the efficiency of the cycle depend on? Comparewith
Carnotâs.
3. What are the differences between the ideal cycle and the realone?
4. Describe how it is modified by superheating and/or reheating.Explain
te benefits.
2.3 Problems
After answering the previous questions solve the followingexercises from the
book: 8.2, 8.4, 8.5, 8.13, 8.19, 8.20
3 Frigorific machines
3.1 Reverse Carnot cycle
We have already studied Carnot cycle in detail as the ideal thermalmachine.
Now we will take is as the starting point to understand thecharacteristics
of frigorific machines.
1. Draw the ideal cycle in a T-S diagram and explain it.
2. Show that this cycle has a theoretical efficiency Ã =Tcold/Thot-Tcold
3. What are the difficulties in implementing such cycle in actualdevices?
3.2 Actual refrigerators
1. Why is the turbine replaced by an expansion valve in mostcases?
2. Plot the actual cycle and explain the differences with the idealcase.
3. How do cascade and multistage systems improve the performanceof
the refrigerator?
4. What aspects are important in the choice of a refrigerant fluid?Justify
3.3 Problems
After answering the previous questions solve the followingexercises from the
book: 10.2 10.7, 10.8, 10.9, 10.22, 10.23 10.1D

GGRC33H3 Study Guide - Final Guide: Sustainable City, Ville Radieuse, Brownfield Land

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