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Permaculture

2006-12-13T20:52:21Z

169.229.215.15: New page: '''Permaculture Definitions''' -Permaculture is a design system for creating sustainable human environments. Defined From Bill Mollison: -Permaculture: the use of ecology as the basi...

'''Permaculture Definitions'''

-Permaculture is a design system for creating sustainable human environments.

Defined From Bill Mollison:

-Permaculture: the use of ecology as the basis for designing integrated systems of food production, housing, appropriate technology, and community development. Permaculture is built upon an ethic of caring for the earth and interacting with the environment in mutually beneficial ways.

From the Permaculture Drylands Institute, published in The Permaculture Activist (Autumn 1989):

-Permaculture (PERMAnent agriCULTURE or PERMAnent CULTURE) is a sustainable design system stressing the harmonious interrelationship of humans, plants, animals and the Earth.

From Lee Barnes (former editor of Katuah Journal and Permaculture Connections), Waynesville, North Carolina:

To paraphrase the founder of permaculture, designer Bill Mollison:

-Permaculture principles focus on thoughtful designs for small-scale intensive systems which are labor efficient and which use biological resources instead of fossil fuels. Designs stress ecological connections and closed energy and material loops. The core of permaculture is design and the working relationships and connections between all things. Each component in a system performs multiple functions, and each function is supported by many elements. Key to efficient design is observation and replication of natural ecosystems, where designers maximize diversity with polycultures, stress efficient energy planning for houses and settlement, using and accelerating natural plant succession, and increasing the highly productive "edge-zones" within the system.

-Permaculture is: the design of land use systems that are sustainable and environmentally sound; the design of culturally appropriate systems which lead to social stability; a design system characterized by an integrated application of ecological principles in land use; an international movement for land use planning and design; an ethical system stressing positivism and cooperation. In the broadest sense, permaculture refers to land use systems which promote stability in society, utilize resources in a sustainable way and preserve wildlife habitat and the genetic diversity of wild and domestic plants and animals. It is a synthesis of ecology and geography, of observation and design. Permaculture involves ethics of earth care because the sustainable use of land cannot be separated from life-styles and philosophical issues.

From Michael Pilarski, founder of Friends of the Trees, published in International Green Front Report (1988):

-Permaculture is a practical concept which can be applied in the city, on the farm, and in the wilderness. Its principles empower people to establish highly productive environments providing for food, energy, shelter, and other material and non-material needs, including economic. Carefully observing natural patterns characteristic of a particular site, the permaculture designer gradually discerns optimal methods for integrating water catchment, human shelter, and energy systems with tree crops, edible and useful perennial plants, domestic and wild animals and aquaculture.

From a Bay Area Permaculture Group brochure, published in West Coast Permaculture News & Gossip and Sustainable Living Newsletter (Fall 1995):

-Permaculture adopts techniques and principles from ecology, appropriate technology, sustainable agriculture, and the wisdom of indigenous peoples. The ethical basis of permaculture rests upon care of the earth-maintaining a system in which all life can thrive. This includes human access to resources and provisions, but not the accumulation of wealth, power, or land beyond their needs<>ATTRA - National Sustainable Agriculture Information Service http://attra.ncat.org/attra-pub/perma.html

Ethics

Care of the Earth
Care of the People
Return and sharing of Surplus

Principles

Work with nature, rather than against the natural elements, forces, pressures, processes, agencies, and evolutions, so that we assist rather than impede natural developments.
The problem is the solution; everything works both ways. It is only how we see things that makes them advantageous or not (if the wind blows cold, let us use its strength and its coolness to advantage). A corollary of this principle is that everything is a positive resource; it is just up to us to work out how we may use it as such.
Make the least change for the greatest possible effect.
The yield of a system is theoretically unlimited. The only limit on the number of uses of of a resources possible within a system is in the limit of the information and the imagination of the designer.
Everything gardens, or has an effect on its environment.
http://www.permaculture.biz/mollison.htm
Common Techniques and Strategies

By Julianne Skai Arbor

-Site Analysis and Inventory
-Mapping
-Designing with zones and sectors
-Sheet Mulching
-Swales
-Chickens Tractors
-Edible Food Forest
-Plant Guilds
-Native Plants
-Small Scale Intensive
-Herb Spirals
-Greywater systems

Benefits of well-developed permaculture projects include:

-Conserving and building healthy soils, the basis of food systems.

-Diversifying and greatly increasing local food production (typically from a few sources to dozens, even hundreds), which increases the nutritional quality and pleasure of local diets and buffers against market fluctuations in food prices.

-Eliminating use of toxic chemicals that cause a variety of health problems from immediate toxic poisonings to longer-term chronic problems like cancer, birth defects and the destruction of healthy natural food source (i.e. toxic fish).

-Maximizing efficient beneficial use of local water sources, the critical lifeblood for people.

-Practically eliminating pollution of water by human wastes, thereby dramatically reducing water born diseases.

-Creating clean drinking water sources, further reducing disease.

-Increasing tree crops, which retain soils, slow water runoff, increase groundwater storage, and provide cooling shade.

-Increasing the beauty of the community though the creation of diverse life forms - flowers, insects, birds, frogs, and hundreds of others that create a pleasant and inspiring atmosphere for people, especially children.

-Harnessing natural renewable energies to create comfortable home living conditions.
http://www.essentiallivingfoods.com/permaculture.html

Combines Disciplines Examples

*Agriculture and Horticulture

Landcare
-Soil conservation
-Reafforestation
-Agroforestry
-Analog forestry
-Organic farming
-Biological pest control
-Kitchen gardens in cities and villages

Integrated farming systems:
-Aquaculture
-Aquaponics
-Intercropping
-Companion planting and polyculture
-Perennial and tree cropping systems.
-Trellising
-Worm composting

Gardening techniques:
-Utilizing crop rotations
-Cover crops
-Green manures
-Composts
-Mulches
-Medicinal plants
-Useful plants/edible landscaping
-Heritage plant varieties
-Seed saving

Bioregional planning
-citizen action
-cooperative organization
-micro-enterprise
-community credit schemes
-barter and LETS systems

*Appropriate Technology

Water collection
-Greywater reuse
-Rain & runoff catchment
-Swaling
-Constructed wetlands
-Fungal systems for wastewater treatment.

Energy
-Passive solar heating
-Solar and wind power
-Solar water pasteurizers

About fracture mechanics

2006-06-30T15:47:48Z

169.229.157.243:

{{cleanupdate|April 2006}}
{{references}}
{{wikify-date|April 2006}}

'''Fracture mechanics''' is a method for predicting failure of a structure containing a crack. It uses methods of analytical [[Solid Mechanics]] to calculate the driving force on a crack and those of experimental [[Solid Mechanics]] to characterize the material's resistance to fracture.

In modern [[Materials Science]], fracture mechanics is an important tool in improving the mechanical performance of materials and components. It applies the [[physics]] of [[stress (physics)|stress]] and [[strain]], in particular the theories of [[elasticity]] and [[plasticity (physics)|plasticity]], to the microscopic [[crystallographic defect]]s found in real materials in order to predict the macroscopic mechanical failure of bodies.

== The Need for Fracture Mechanics ==
[[Image:Tay1.jpg|left|thumb|Tay Bridge Disaster (1879)]]In many cases, failure of engineering structures through fracture can be fatal; one example is that of the [http://www.mcgonagall-online.org.uk/poems/pgdisaster.htm Tay Bridge Disaster] (left). Often disasters occur because engineering structures contain cracks - arising either during production or during service (e.g. from [[Fatigue (material)|fatigue]]). For instance, growth of cracks in pressure vessels due to crack propagation could cause a fatal explosion. If failure were ever to happen, we would rather it were by [[yield (engineering)|yield]] or by leak before break.

Since cracks can lower the strength of the structure beyond that due to loss of load-bearing area a material property, above and beyond conventional strength, is needed to describe the fracture resistance of engineering materials. This is the reason for the need for fracture mechanics - the evaluation of the strength of cracked structures.

== The History of Fracture Mechanics ==
=== Griffith's Energy Relation ===
Fracture Mechanics was invented during World War I by English aeronautical engineer, [[Alan Arnold Griffith|A.A.Griffith]], to explain the failure of brittle materials. Griffith was faced with the problem that theoretical calculations showed that the stress at the tip of a sharp crack approaches infinity. Accordingly, any structure containing a crack should fail, no matter how small the crack or how light the load. To solve this dilemma, Griffith developed a thermodynamic approach. He assumed that growth of a crack requires creation of surface energy, which is supplied by the loss of strain energy accompanying the relaxation of local stresses as the crack advances. Failure occurs when the loss of strain energy is sufficient to provide the increase in surface energy, as shown in the Appendix to this article.

=== Irwin's Modification of Griffith's Energy Relation ===
[[Image:TankerSchenectady.jpg|left|thumb|The S.S.Schenectady Split Apart by Brittle Fracture while in Harbor (1944)]]Griffith’s work was ignored for over twenty years until a group under [[G.R. Irwin]] at the U.S. Naval Research Laboratory (NRL) took it up during World War II. Irwin and his colleagues developed a modified form of Griffith's approach; they reformulated it in terms of stress, rather than energy. Their work resulted in a new materials property, [[fracture toughness]], which is denoted KIc, and is now universally accepted as the defining property of fracture mechanics (see Appendix for equations).

But a problem arose for the NRL researchers because naval materials, e.g. ship-plate steel, are not perfectly elastic but undergo [[plastic deformation]] at the tip of a crack violating the underlying assumption of the theory. Linear-elastic fracture mechanics is of limited practical use for structural steels for two other reasons:

(1) Fracture toughness testing is very expensive and sufficient information for selection of steels can be obtained from the simpler and cheaper [[Charpy Impact Test]]

(2) If a part's response to load is sufficiently close to linear-elastic that KIc can be measured, there is little plastic relaxation at the crack tip and the steel will be [[brittle]]. Structural steels, in particular, can be prone to brittle fracture, which has led to a number of catastrophic failures.

== Elastic-Plastic Fracture Mechanics ==
[[Image:Aircraft_Crash.jpg|left|thumb|Vertical Stabilizer, which Separated from the Aircraft Leading to a Fatal Crash(2001)]]In the mid-1960s J.R. Rice (then at Brown University) developed a new toughness measure to describe the case where there is sufficient crack-tip deformation that the part no longer obeys the linear-elastic approximation. Rice's analysis, which assumes non-linear elastic deformation ahead of the crack tip, is designated the [[J integral]]. This analysis is limited to situations where plastic deformation at the crack tip does no extend to the furthest edge of the loaded part. It also demands that the assumed non-linear elastic behavior of the material is a reasonable approximation in shape and magnitude to the real material's load response. The elastic-plastic failure parameter is designated JIc and is conventionally converted to KIc using Equation (3.1) of the Appendix to this article. Also note that the J integral approach reduces to the Griffith theory for linear-elastic behavior.

== Fully Plastic Fracture Mechanics ==
If the alloy is so tough that the yielded region ahead of the crack extends to the far edge of the specimen before fracture, the crack is no longer an effective stress concentrator. Instead, the presence of the crack merely serves to reduce the load-bearing area. In this regime the failure stress is conventionally assumed to be the average of the yield and ultimate strengths of the alloy.

== Engineering Applications of Fracture Mechanics ==
The following information is needed for a fracture mechanics prediction of failure:
*Applied load
*Residual stress
*Size and shape of the part
*Size, shape, location, and orientation of the crack

Usually not all of this information is available and pessimistic assumptions have to be made.

Occasionally post-mortem fracture-mechanics analyses are carried out. In the absence of an extreme overload, the causes are either insufficient toughness (KIc) or an excessively large crack that was not detected during routine inspection.

== Short Summary ==
Arising from the manufacturing process, interior and surface flaws are found in all metal structures. Not all such flaws are unstable under service conditions. Fracture mechanics is the analysis of flaws to discover those that are safe (that is, do not grow) and those that are liable to propagate as cracks and so cause [[structural failure|failure]] of the flawed structure. Fracture mechanics as a subject for critical study has barely been around for a century and thus is relatively new. There is a high demand for engineers with fracture mechanics expertise - particularly in this day and age where engineering failure is considered 'shocking' amongst the general public.

== Appendix: Mathematical Relations ==
=== Griffith's Crack Theory: Strain Energy Release Rate ===
For the simple case of a thin rectangular plate with a crack perpendicular to the load Griffith’s theory becomes:

:<math>G = \frac{\pi \sigma^2 a}{E}\,</math>                 (1.1)

where G is the strain energy release rate, σ is the applied stress, a is half the crack length, and E is the [[Elastic modulus|Young’s modulus]]. The strain energy release rate can otherwise be understood as: the rate at which energy is absorbed by growth of the crack.

However, we also have that:

:<math>G_c = \frac{\pi \sigma_f^2 a}{E}\,</math>                 (1.2)

where Gc the critical strain energy release rate (also [[fracture energy]]), σf is the [[brittle fracture stress]], a is half the crack length, and E is the [[Elastic modulus|Young’s modulus]]. This [[fracture energy]] can otherwise be understood as: the rate of strain energy release by growth of the crack.

If G ≥ Gc, this is the criterion for which the crack will begin to propagate.

=== Irwin's Modified Griffith Crack Theory: Fracture Toughness ===
Eventually a modification of Griffith’s theory emerged from this work; a term called [[stress intensity]] replaced strain energy release rate and a term called [[fracture toughness]] replaced surface energy. Both of these terms are simply related to the energy terms that Griffith used:

:<math>K_I = \sigma \sqrt{\pi a}\,</math>                 (2.1)

and

:<math>K_c = \sqrt{E G_c}\,</math> (for [[plane stress]])                 (2.2)

:<math>K_c = \sqrt{\frac{E G_c}{1 - \nu^2}}\,</math> (for [[plane strain]])                 (2.3)

where KI is the [[stress intensity]], Kc the [[fracture toughness]], and ν is [[Poisson ratio|Poisson’s ratio]]. It is important to recognise the fact that fracture parameter Kc has different values when measured under plane stress and plane strain

Fracture occurs when KI ≥ Kc. For the special case of plane strain deformation, Kc becomes KIc and is considered a material property. The subscript I arises because of the different ways of loading a material to enable a crack to propagate. It refers to loading via Mode I - the most common form of loading:

There are three ways of applying a force to enable a crack to propagate: 
Mode I - Opening mode (a [[tensile stress]] normal to the plane of the crack) 
Mode II - Sliding mode (a [[shear stress]] acting parallel to the plane of the crack and perpendicular to the crack front) 
Mode III - Tearing mode (a [[shear stress]] acting parallel to the plane of the crack and parallel to the crack front)

We must note that the expression for KI in Eq (2.1) will be different for geometries other than the center cracked plate, as discussed in the article on [[stress intensity]]. Consequently, it is necessary to introduce a [[dimensionless number|dimensionless correction factor]], Y, in order to characterise the geometry. We thus have:

:<math>K_I = Y \sigma \sqrt{\pi a}\,</math>                 (2.4)

where Y is a function of the crack length and width of sheet given by:

:<math>Y \left ( \frac{a}{W} \right ) = \sqrt{\sec\left ( \frac{\pi a}{W} \right )}\,</math>                 (2.5)

for a sheet of finite width W containing a through-thickness crack of length 2a, or

:<math>Y \left ( \frac{a}{W} \right ) = 1.12 - \frac{0.41}{\sqrt \pi} \frac{a}{W} + \frac{18.7}{\sqrt \pi} \left ( \frac{a}{W} \right )^2 - ...\,</math>                 (2.6)

for a sheet of finite width W containing a through-thickness edge crack of length a

=== Elastic-Plastic Fracture Mechanics Theory ===
Since engineers became accustomed to using KIc to characterise fracture toughness, a relation has been used to reduce JIc to it:

:<math>K_{Ic} = \sqrt{\frac{E J_{Ic}}{1 - \nu^2}}\,</math>                 (3.1)

The remainder of the mathematics employed in this approach is interesting, but is probably better summarised in external pages due to its complex nature (refer to the Useful Websites section).

== Useful Websites ==
*[http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_intro.cfm eFunda - Fracture Mechanics]
*[http://www2.umist.ac.uk/material/research/intmic/features/charpy/notes.htm UMIST - Charpy Impact Test]
*[http://www.engin.brown.edu/courses/EN175/Notes/Failure_Plasfrac/Failure_Plasfrac.htm Brown University Engineering - Mathematical Relations]
*[http://hdl.handle.net/1813/3075 - Lecture Notes on Fracture Mechanics]

== References ==
*C. P. Buckley, "Material Failure", Lecture Notes (2005), [[University of Oxford]]

== See also ==
*[[fatigue (material)|Fatigue fracture]]

[[Category:Engineering]]
[[Category:Materials science]]
[[Category:Continuum mechanics]]
[[de:Bruchmechanik]]
[[zh:断裂力学]]

Transculturation

2006-03-22T09:50:13Z

169.229.98.97: /* Homogenization versus ethnoconvergence */

'''Transculturation''' is a term coined by [[Fernando Ortiz]] in [[1947]] to describe the phenomenon of merging and converging cultures. In simple terms, it reflects the natural tendency of people (in general) to resolve conflicts over time, rather than exacerbating them. In the modern context, both conflicts and resolutions are amplified by communication and transportation technology —the ancient tendency of cultures drifting or remaining apart has been replaced by stronger forces for bringing societies together. Where tranculturation impacts ethnicity and ethnic issues the term "ethnoconvergence" is sometimes used.

In one general sense, transculturation covers [[war]], [[ethnic conflict]], [[racism]], [[multiculturalism]], [[interracial marriage]], and any other of a number of contexts that deal with more than one culture. In the other general sense, tranculturation is the ''positive'' aspect of global phenomena and human events, where resolutions to conflicts are inevitable.

The general processes of transculturation are extremely complex -- steered by powerful forces at the macrosocial level, yet ultimately resolved at the interpersonal level. The driving force for conflict is simple [[proximity]] -- boundaries, once separating people (providing for a measure of isolation) become the issue of a conflict when societies encroach upon one another territorially. If a means to co-exist cannot be immediately found, then conflicts can be hostile, leading to a process by which contact between individuals leads to some resolution. Often, history shows us, the processes of co-existence begins with hostilities, and with the natural passing of polarist individuals, comes the passing of their polarist sentiments, and soon some resolution is achieved. Degrees of hostile conflict vary from outright genocidal [[conquest]], to lukewarm infighting between differing poitical views within the same ethnic community.

==Concepts==
Where attempts are made to keep a cultural identity "pure," the realities of social change, via natural and artificial means, dictate that cultures do not remain "pure" and never were "pure" in the first place, but are destined to change. It is the perception of individuals within cultures that their cultures do not in fact change fundamentally over time.

Human [[mortality]] and [[reproduction]] provides for social [[regeneration]] as well, and by this process of regeneration, which naturally includes sexual union, other cultures are often integrated. The inability of societies to maintain divisions over generations, despite attempts to engrain divisive elements, is reflective of this. As parents die, their children have the opportunity to reflect upon the nature and validity of established non-convergent precepts, and change them if they like.

These changes often represent differences between homeland populations, and their [[diasporic]] communities abroad. Nevertheless, obstacles to '''ethnoconvergence''' are not great. The primary issue; [[language]], (''hence, communication and education'') can, be overcome within a single generation - as is evident in the easy acclimation of children of foreign parents. English, for example, is spoken by more non-Anglo-American people than Anglo-Americans, making it the current [[lingua-franca]], the worldwide de facto standard international language.

===Homogenization versus ethnoconvergence===
It is observed that even in monolingual, industrial societies like urban North America, some individuals do cling to a "modernized" primordial identity, apart from others. Some intellectuals, such as [[Michael Ignatieff]], argue that convergence of a general culture does not directly entail a similar convergence in [[ethnic]] identities. This can become evident in social situations, where people divide into separate groups, despite being of an identical ''"super-ethnicity"'', such as [[nationality]].

Within each smaller ethnicity, individuals may tend to see it perfectly justified to assimilate with other cultures, and some others view assimilation as wrong and incorrect for their culture. This common theme, representing dualist opinions of ethnoconvergence itself, within a single ethnic group is often manifested in issues of [[sexual partners and matrimony]], employment preferences, etc. These varied opinions of ethnoconvergence represent themselves in a spectrum; [[cultural assimilation|assimilation]], [[homogenization]], [[acculturation]], and [[cultural compromise]] are commonly used terms for ethnoconvegence which flavor the issues to a bias.

Often it's in a secular, multi-ethnic environment that cultural concerns are both minimalised and exaccerbated; Ethnic prides are boasted, hierarchy is created ("center" culture versus "periphery") but on the other hand, they will still share a common "culture", and common language and behaviours. Often the elderly, more conservative-in-association of a clan, tend to reject cross-cultural associations, and participate in ethnically similar community-oriented activities. [[Xenophobia|Xenophobes]] tend to think of cross-cultural contact as a component of [[cultural assimilation|assimilation]], and see this as harmful.

===Obstacles to ethnoconvergence===
The obstacle to ethnoconvergence is [[ethnocentrism]], which is the view that one's culture is of greater importance than anothers.' Ethnocentrism often takes different forms, as it is a highly personal bias, and manifests itself in countless aspects of culture. [[Religion]], or belief, is the prime ethnocentric divider. Second is [[custom]], which may overlap religion. With the adherence to each distinct component, comes the repulsion of the other. In most regions, ethnic divides are binary, meaning only two distinct cultures are present, each seeing the other as foreign. Many, however make the point that the binary example is the exception, and the norm is far more dynamic.

We can divide ethnicity into two distinct areas, as they relate to ethnoconvergence: Utilitarian traits, and traditional customs. Language usually falls into the first category, as people often do not attach to language a highly ethnic value. Learning a [[foreign language]] does not, in the eyes of most people, constitute a forfeiting of one's cultural heritage.

Religion, on the other hand, is a highly personal and attached part of culture. However, religion does not neatly correspond with ethnic identity. In many [[cosmopolitan]] societies, religion is everything - social, utilitarian, intellectual, political; from the point of view of people of immersed cultures; The very concept of ethnicity and its distinctions is incongruous to their immersed concepts.

In many societies, such as in those in Europe, languages are considered a significant component of ethnic values. This does not mean that most Europeans reject learning other languages. Quite the contrary, Europeans are often polyglots, and may label other individuals by their ethnicities; practical means of distinguishing cultures may resemble tendencies similar to ethnocentrism.

However, the political and cultural significance of regional or national languages are retained due to the fact that these polyglots conform to the linguistic norms of the place they visit - doing "as the Romans do". Thus, conforming to the "ethnic integrity" of the region.

It has even become a cliche that "to learn a new language is to adopt a new soul". There are many other examples of the essential significance of language. In pre-[[Russia|Russian]] [[Siberia]], [[Tatar-Mongol]] colonists in the [[Taiga]] often recognized indigenous speakers of [[Turkic languages]] as their "own people" and non-Turkic groups as "foreigners". This is in spite of the fact that these indigenous groups had a similar level of material culture, and shared much of a primitive culture with tribes foreign to the Muslim-Buddhist Tatar-Mongols.

==See also==
* [[Intercultural relations]]
* [[Multiculturalism]]

[[category:Culture]]
[[category:Human migration]]

[[pl:Transkulturacja]]