GEOG 1220 Lecture 5: Modern Agriculture

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ochreherring44

15 Feb 2012

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Week 5 review: modern agriculture: the agricultural and environmental viewpoints regarding our ability to feed 11 billion people: Agricultural viewpoint: the view that we have enough resources and food for the entire world population; it is just a question of equal distribution. Environmental viewpoint: describes agriculture as ecologically dysfunctional farming. This viewpoint does not support the idea that we can feed the entire world: the greatest population is found in areas that are favorable to agriculture. 1. 2 billion people those are over-nourished, compared to 1. 2 billion who are undernourished, (15% of the population in developed countries are over-nourished) List of shortcomings: limited participation by small subsistence farmers: in developing countries farmers cannot afford the materials necessary to produce the hybrid varieties. Increased mechanization and farm size: displaces many tenant farmers so less farm labor needed = unemployment/underemployment and therefore poverty in the countryside. Increased commercialization: harvests from mechanized farms are sold at prices that local poor cannot afford.

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Tiny solid and liquid particles suspended in the atmosphere are called aerosols. Windblown dust, sea salts, volcanic ash, smoke from wildfires, and pollution from factories are all examples of aerosols. Depending upon their size, type, and location, aerosols can either cool the surface, or warm it. They can help clouds to form, or they can inhibit cloud formation. And if inhaled, some aerosols can be harmful to people's health.

These maps show average monthly aerosol amounts around the world based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. Satellite measurements of aerosols, called aerosol optical thickness, are based on the fact that the particles change the way the atmosphere reflects and absorbs visible and infrared light. An optical thickness of less than 0.1 (palest yellow) indicates a crystal clear sky with maximum visibility, whereas a value of 1 (reddish brown) indicates very hazy conditions.

High aerosol amounts are linked to different process in different places and times of year. High aerosol amounts occur over South America from July through September. This pattern is due to land clearing and agricultural fires that are widespread across the Amazon Basin and Cerrado regions during the dry season. Aerosols have a similar seasonal pattern in Central America (March-May), central and southern Africa (June-September, and Southeast Asia (January-April).

In other cases, however, aerosol concentrations are not related to fires. For example, from May through August each year, aerosol amounts rise dramatically around the Arabian Peninsula and nearby oceans due to dust storms. Elevated aerosol amounts nestle at the foothills of the Himalaya Mountains in northern India in some months, and linger over eastern China for much of the year. These elevated aerosol amounts are due to human-produced air pollution.

What is the most likely source of the high concentration of particulates that appear off the coast of northwestern Africa?

What is the most likely source of the high concentrations of particulates over central Africa and central South America?

What is the most likely source of the high concentrations of particulates over eastern China?

apricottermite85

It is currently popular for automobiles to use 10% ethanol / 90%gasoline mixtures (âgasoholâ) as fuel. According to popularconsensus the main benefit of gasohol use is that it âreduces ourdependence upon foreign oil.â We test this assertion by making someelementary calculations. Our analysis will unrealistically ignoreengine maintenance issues associated with older automobiles (suchas gasket and seal hardening), added fuel consumption necessary toproduce grain used as a feedstock in ethanol production,incremental food price increases associated with a reduction ingrain stocks, and many other effects. Gasohol use typically reducesaverage fuel economy by approximately 15% and effectively leavesfuel prices unchanged. This article further debates the wisdom ofethanol use and may be of interest outside the problems:
http://harvardmagazine.com/2006/11/the-ethanol-illusion.html
These concerns and problems have been strongly influenced byconversations with Dr. H.J. Harmon, of the OSU physicsdepartment.

2. Consider a 14.2 mpg 1991 Ford F150 driven 761 miles. Calculatethe pure gasoline consumption of this truck when: a) usinggasoline, and b) when using gasohol (with its attendant economyreduction). Determine the total CO2 emissions for each fuelassuming all fuels produce 20 lbs of CO2 per gallon. Comment uponthe wisdom of using gasohol versus pure gasoline in this vehicle.

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

GEOG 1220 Lecture 5: Modern Agriculture

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