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MFA > Methodlogy lectures > Flashcards

Methodlogy lectures Flashcards

1
Q

Whar are the two main types of MFA?

A

Bulk-MFA (material flow accounting) and substance flow analysis (SFA)

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2
Q

What are th e 6 main terms used in SFA (Baccini and Brunner 1991)

A

1) substances
2) Goods
3) Flow/stock
4) Processes
5) systems
6) activities

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3
Q

What is the definition of a substance?

A

Any chemical element or compound composed of uniform units. All substances are characterized by a unique and identical constitution and area thus homogenours (eg. C, Ag, CO2 or NH3)

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4
Q

What is the definition of a Good?

A

Economic entities of matter with a positive or negative economic value. Goods are made up of several substance. (eg. drinking water, TV, cars, garbage)

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5
Q

What is the definition of a process?

A

Balance volume. Transformation, transport or storage of goods/substances. (eg. human body, households, manufacturing plant).

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6
Q

What is the definition of a Flow?

A

Amount of a good or substance per time (rate) (eg water consumption kg/a)

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7
Q

What is the definition of a flux?

A

Amount of good or substance per time (rate) per cross-section (eg. water consumption per cap in DK (kg/(cap*anno))

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8
Q

What is the definition of a stock?

A

The mass of a material residing in a process or system during the balancing period of the system. Likely to change overtime, especially with human activities. (eg. buildings, car fleet, mobile phones, waste in landfills)

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9
Q

What is the definition of a activity?

A

Basic human needs. Includes all relevant stocks and flows, processes, goods and substances to fulfill the need. (et. to nourish, to clean, to reside and work, to communicate)

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10
Q

What are the elements in the procedure of MFA/SFA

A
  • Problem formulation
  • Time frame
  • Indicator element selection
  • System definition
  • Quantification of goods
  • Quantification of substances
  • Mathematical model formulation
  • Scenario development
  • Interpretation
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11
Q

What is a system/ system boundary?

A

The system is the actual object of an MFA investigation. It is defined by a group of elements, interaction between these elements and the boundaries between these and other elements in space and time.
(Elements are processes. Interactions are flows of goods. A single process or a combination of several processes can represent a system.)

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12
Q

How should the system boundary be defined?

A

In time and space.

  • Temporal boundary: the time span over which the system is investigated and balanced.
  • Spacial boundary: Usually fixed by the geographical area in which the processes are located.
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13
Q

What is an indicator element?

A

An indicator element represents a group of substances. It shows the characteristic physical, biochemical and/or chemical behavior that is a specific property of all members of the group.
(eg: atmophile elements (Cd, Zn, Sb, Pb) have a lower boiling point.
In a combustion process, atmophile elements are transferred to off-gas. Cd may serve as an indicator for this group.)

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14
Q

What indicator elements has been presented to us in MFA?

A

Carbon (organic), Nitrogen, Fluorine, Phosphorous, Chlorine, Iron, Copper, Zinc, Cadmium, mercury, Lead.

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15
Q

What is a model?

A
  • A model is any goal satisfying representation or description of a given entity, such as an object, system, process or property.
  • A model is a real or abstract system which is the carrier of a function property of another pre-selected system or process with requested or sufficient accuracy.
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16
Q

What can models be used for in MFA?

A
  • Understanding a system
  • Predictions or forecasts
  • Data management and visualization
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17
Q

How can model help in understanding a MFA system?

A
  • System indentifcation: analyze interrelations between elements of the system. (what are the fundemental laws of the system)
  • Sensitivity analysis: analyze the impact of changes in model input and outputs. (what are key parameters determining the behavior of the system?)
  • Uncertainty propagation/calculus observation: analyze the role of errors (what is the impact of uncertainties in observations on the overall system? how can uncertainties be reduced?)
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18
Q

How can model be used in predictions or forecasts?

A
  • Simulation modelling: “if-then” calculations, scenarios (how is the system changing under given assumptions?)
  • Optimization modelling: minimize or maximize objective function (how is the system changing if it acts to maximize/minimize certain values without violation resource contraints?)
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19
Q

How is models used in Data managements and visualization of MFA systems?

A
  • Data structure: models help structuring data (orientation)
  • Visualization: allows for fast access and improved control.
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20
Q

What defines a first principle (ab initio) model?

A

It relies exclusively on basic and established laws of nature without additional assumptions or special models. (Eg. law of conversion of energy)

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21
Q

What defines a phenomenological model?

A

It combines basic laws with phenomenological approaches (phenomenological approaches are empirically tested relationships). (eg. process models, chemical engineering, MFA)

22
Q

What defines a data-based model?

A

It uses exclusively empirical data from measurements in combination with statistics to describe input and/or output characteristics of a system. (eg. dose-response relationships in toxicology, economic models)

23
Q

Give an example of a transfer coefficient

A

Recycling rate

multiple inputs, in output

24
Q

Give an example of a allocation coefficient

A

metal production using scrap (analyse one input fate in outputs)

25
Q

Give an example of a selective coefficient

A

Input requirement for a production (how much b is in q)

26
Q

What is a static model?

A

All system variables are invariant under time reversal

27
Q

What is a stationary model?

A

All system variables are invariable under time shift

28
Q

What is a Quasi-stationary model?

A

Flows are invariant under timeshift. Stocks may change under time shift

29
Q

Dynamic models

A

Flows may change under time shift . Stocks may change under time shift.

30
Q

What are the 5 steps in approach for quasi-stationary MFA models?

A
  1. Define system
  2. List system vaiables, count unknowns.
    x unknowns = x equations
  3. Mass balance equations
    (First principle part of MFA)
  4. Model approach equations (empirical part of MFA)
  5. Solve equations system for all system variables. ( a) algebraic or b) matrix inversion)
31
Q

Which have standardization Bulk-MFA or SFA?

A

Bulk-MFA (economy-wide MFA)

32
Q

What are the limitations of these domestic material extraction and consumption numbers (bulk-MFA) in unveilling resource use patterns?

A
  • Aggregated, low resolution in types of materials
  • Only raw materials (and semi-products), no final products (indirect trade of raw materials embodied on final products excluded)
  • Only flows no stock information
33
Q

What are precision and accuracy in data uncertainty?

A

Accuracy: correctness, deviation from “true” value.
Precision: Number of significant digits

34
Q

What 3 ways did we deal with uncertainty?

A
  1. Sensitivity analysis (how sensitive are variables to change in parameters)
  2. Error propagation (how reliable are results? what are the impact of uncertainties of parameters on variables? (analytical approach, numerical monte carlo approach simulation)
  3. Data reconciliation/flow adjustment (How can flows and their uncertainties be adjusted by making use of the mass balance principle? )
35
Q

What are the three proposed uses of sensitivity analysis?

A
  1. improve model (validate a model, warn of unrealistic model behaviour.)
  2. Improve data: Identify key parameters/assumptions, Suggest necessary levels of accuracy for parameters (if model i sensitive to parameter change => high accuracy required), Suggest improved measurements (guide data collection efforts), adjust numerical values of parameters.
  3. Improve system understanding: Identify most effective ways to control system, test the behavior of the model in extreme situations.
36
Q

What are absolute and relative sensitivity used for?

A
  • Absolute sensitivity: calculate change in output due to change in input. Analyse when a parameter has its greatest effect.
  • Relative sensitivity: compare parameters. analyse which parameter has the greatest effect.
37
Q

What are the 5 steps in the procedure of monte carlo simulation?

A
  1. Specify probability distributions for all input parameters.
  2. Draw a randome sample of all input parameters
  3. compute the result for the selected set of randome samples.
  4. Repeat 2 and 3 for many trials (hurdreds or thousands of iterations (law of large numbers says convergence).
  5. Analyze the resulting model outputs using statistics (histogram, mean, std. deviation.)
38
Q

What are the benefits of data reconciliation?

A
  1. Adjusted flows are consistent with mass balance principle.
  2. reconciliation provides information about: Possible systematic errors (eg missing flows), accuracy of results, propagation of uncertainty (measurement errors) and how to optimize measurement strategy.
39
Q

Does data reconciliation provide true values or best estimates?

A

only best estimates!

40
Q

Does data reconciliation only work for random erros?

A

yes, if the system is not understood correctly (systematic errors) data reconciliation may even worsen the flow values!

41
Q

When is a stationary model used?

A
  • The system behaves linearly (eg. no stock changes)

- we are interested only in a short time period (e.g. one year)

42
Q

When is a dynamic model used?

A
  • when we want to analyze change

- When we want to understand when the effects of actions may occur.

43
Q

What are the three types of time-dependent (dynamic models)?

A
  1. Discrete, given time series (of quasi-stationary models)
  2. Discrete model approach (difference equations)
  3. continuous model approach (differential equations)
44
Q

Material stocks can be determined in two ways, which?

A

1) “bottom-up”: from building and vehicle statistics and product-specific material content data.
2) “top-down”: from aggregated consumption data and a lifetime model.

45
Q

What are the 4 steps of an inflow-driven model?

A

1) Determine apparent consumption
2) apply the convolution: differential equation (with lifetimes).
3) Determine stock change
4) Determine stock

46
Q

Is the stock-driven model the inverse of the inflow driven?

A

yes.

47
Q

What is the definition of service lifetime?

A

The timespan a product is either in use or hibernating (time from input to waste management)

48
Q

Three main points of lifetime determination

A
  1. Product lifetimes are often very critical for estimating waste flows and projecting demand.
  2. Product lifetimes are poorly understood (lifetime distributions can change over time, very few quantitative studies)
  3. Be critical about “expert judgements”
49
Q

There are 4 categories of obsolescence, which?

A
  1. Technical obsolescence (new products or technologies supersede old ones)
  2. Systemic or functional obsolescence (system changes causes malfunction of products in new environment)
  3. Style obsolescence (change in style makes products lose their appeal, independent of functionality)
  4. Notification obsolescence (Obsolescence is predetermined in product design and customers are advised to replace product parts to avoid health risk or maintain optimal performance. )
50
Q

What are the 3 scenario typologies?

A
  1. forecasting (predict most likely future)
  2. Explorative (explore alternative futures)
  3. Backcasting (asses feasibility of desirable future)
51
Q

Are scenarios the same as forecasting?

A

No! the scenarios are not predictions but a “storyline” supported by models.

MFA (2 decks)

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