Proceedings of the Twenty-Eighth AAAI Conference on Artificial Intelligence

Accurate Household Occupant Behavior
Modeling Based on Data Mining TechniquesMárcia Baptista, Anjie Fang, Helmut Prendinger
National Institute of Informatics
2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan
marcia.baptista@ist.utl.pt, af12331@my.bristol.ac.uk,helmut@nii.ac.jp

Rui Prada
INESC-ID and Instituto Superior Técnico, Universidade de Lisboa
Av. Prof. Cavaco Silva, Taguspark Porto Salvo, Portugal
rui.prada@ist.utl.pt

Yohei Yamaguchi
Sustainable Energy and Environmental Engineering
Graduate School of Engineering, Osaka University
2-1 Yamada-oka, Suita, Osaka 565-0871, Japanyohei@see.eng.osaka-u.ac.jp
Abstract

order of up to four times the mean annual energy consumption of buildings, based on the investigation of six residential districts in Japan that were clustered according to otherinfluencing factors such as city climate and building characteristics.
An increasing number of energy demand models (Kavgic
et al. 2010) simulate the influence of occupant behavior uponenergy consumption. In these models, households are simulated as multi-agent systems, where occupants are represented as social agents that behave according to the rules
prescribed by Markov chains. Here, Markov chain probability matrices are calculated from time-use (TU) data, i.e.,sequential high-resolution information of the real-life daily
routines of household occupants, such as sleeping or having
meals.
Traditional Markov chains show two important limitations as a technique to accurately encode occupant behavior. First, they do not accurately capture the coordinated behavior of household members, such as joint activities. By
joint activity we mean joint-in-purpose (having meal, having bath, etc.) rather than joint-in-time or joint-in-location,
following the distinction of Gliebe and Koppelman (2002).
Second, these models are prone to over fitting. Since theytend to accurately replicate the given, relatively sparse TU
data, they fail to generalize from the input trends.
To address these shortcomings, we propose an alternative
approach to the Markov chain approach, which is based on a
combination of data mining techniques. The core idea of ourapproach is that we predict agents’ behavior by searching the
TU database for past household states that resemble the current one. To select a past similar state we use nearest neighbor comparison based on a normal distribution. This mech-

An important requirement of household energy simulation models is their accuracy in estimating energy
demand and its fluctuations. Occupant behavior has amajor impact upon energy demand. However, Markov
chains, the traditional approach to model occupant behavior, (1) has limitations in accurately capturing thecoordinated behavior of occupants and (2) is prone toover-fitting. To address these issues, we propose a novel
approach that relies on a combination of data mining
techniques. The core idea of our model is to determine
the behavior of occupants based on nearest neighborcomparison over a database of sample data. Importantly,
the model takes into account features related to the coordination of occupants’ activities. We use a customized
distance function suited for mixed categorical and numerical data. Further, association rule learning allows us
to capture the coordination between occupants. Using
real data from four households in Japan we are able toshow that our model outperforms the traditional Markov
chain model with respect to occupant coordination andgeneralization of behavior patterns.

Introduction
Human behavior is a major determinant of energy consumption in buildings, particularly in the residential sector(Lopes, Antunes, and Martins 2012; Karatasou, Laskari, andSantamouris 2013). The way household members performtheir daily routines, share rooms or use electrical appliances,can greatly impact total energy use. Yu et al. (2011) foundthat occupant behavior was responsible for variations on the
Copyright c 2014, Association for the Advancement of Artificial
Intelligence (www.aaai.org). All rights reserved.

1164

Real-time prediction relies on sensor data and employs machine learning methods (Mamidi, Chang, and Maheswaran2012) or genetic algorithms (Yu 2010) to predict e.g. room
occupancy. In contrast, multi-agent systems rely on TU data
and typically use Markov chains to simulate the behavior of
occupants (Yamaguchi, Tanaka, and Shimoda 2012).
To date, most multi-agent systems aiming at energy demand simulation have modeled households as a set of
non-interacting individuals (Munkhammar and Widén 2012;
Baptista et al. 2014). This means that current systems are
based on the assumption that the probabilities of the activities of a household member are not dependent on the activities of other occupants. Accordingly, these systems often failto capture the coordination between occupants, such as theshared use of lighting and other electrical appliances. Thisin turn translates into inaccuracies in energy demand estimation.
Current energy demand simulations based on Markov
chains present additional limitations, such as the inaccurate modeling of the duration and temporal order of activities. Another constraint of current energy demand simulations relates to over-fitting of simulated activities to theoriginal TU data. This results in Markov chain based models being often unable to generalize beyond TU data to new
data. Some authors (Tanimoto, Hagishima, and Sagara 2008;
Richardson et al. 2010; Yamaguchi, Tanaka, and Shimoda2012) have attempted to address these points using alternative approaches to Markov chains, with some success.

anism aims to generate a model that can generalize from the
input TU data. In addition, the nearest neighbor comparison
allows us to more accurately represent coordinated agent behavior.
The paper is structured as follows. The next section reviews major work in the fields of occupant behavior modeling and multi-agent systems that estimate energy demand.
Then we detail our proposed model. Next, we compare theperformance of traditional Markov chains to our model using real data of household occupant behavior. Finally, we
discuss and conclude the paper.

Related Work
Energy demand models can be classified in two broad categories: ‘top-down’ and ‘bottom-up’ models (Swan andUgursal 2009; Grandjean, Adnot, and Binet 2012). The two
approaches differ in the concepts and principles used forthe modeling of demand. The top-down approach follows
standard macroeconomic modeling techniques, whereas thebottom-up approach is based on the concept of disintegration. Top-down models describe behavioral relations at an
aggregated level. By contrast, bottom-up models calculateenergy demand at the level of the individual household, occupant or electrical appliance.
Several bottom-up models have recently been proposedin the energy field (Dounis and Caraiscos 2009; Widén andWäckelgård 2010; Shimoda et al. 2010), which are based on
the concepts of ‘agent’ and multi-agent system (as definedin Jennings, Sycara, and Wooldridge 1998). In those models,the occupant is modeled as a situated agent that can receive
sensory input from the household environment, such as information on electrical appliance usage. The agent can perform actions in that environment, such as moving between
rooms or using electrical appliances. Each agent decides its
actions autonomously, in each simulation step, showing responsive and pro-active behavior.
Bottom-up models based on multi-agent systems are used
for two distinct purposes: (i) real-time energy demand prediction and (ii) simulation. In the first case, models generate real-time predictions of occupant behavior. For instance, Mamidi, Chang, and Maheswaran (2012) proposed
an approach to improve the energy efficiency of commercial
buildings by controlling the HVAC (heating, ventilation, andair conditioning) systems according to an occupancy prediction model that estimates the presence or absence of persons
in a room.
In the second case, models aim at the simulation of energy
demand by generating probability densities of occupants’behavior. These models target the simulation the energy consumption of residential areas for extended periods of time.
They can be used to investigate how new energy policies or
smart grid technological advancements might impact energy
consumption of an urban area. For instance, Shimoda et al.
(2010) used an multi-agent approach to simulate the energy
consumption and CO2 emissions of the residential sector ofJapan by 2025. Several CO2 mitigation measures were evaluated using the simulation model as a test-bed.
The techniques used to model occupant behavior differ
greatly depending on the purpose of the multi-agent system.

Nearest Neighbor (NN) ModelIn this section, we introduce our approach to modeling occupant behavior in multi-agent systems. Our approach is basedon data mining techniques that allow us to model the behavior of occupants in a household as a set of coordinating
agents that learn from historical real-world data to decide
their daily routines.
Our model assumes the existence of n agents that represent the occupants of a household. It also assumes the existence of m simulation time-steps. In each time-step, eachagent in the household must decide its next behavior from a
set of possible alternatives such as sleeping or having bath.
The agents decide their behaviors taking into account the
behaviors of others, as in real life.
The reasoning of an agent for a time-step t involves
three stages. First, in the initialization stage, the agent collects all the necessary data about the current state of thehousehold (xt ). Second, in the prediction stage, the current
state is matched against a structured database of real-world
household states representing time-use data (TU data). The
database is classified according to the resemblance of statesto the current state, using a customized measure of similarity. A normal distribution (N (0, σ 2 )) determines the maximum allowed similarity distance i between the current state
and the states in the database. This forms the set of predictive states ({w0 , . . . , wk }). By predictive states we mean theset of states in the database that, due to their similarity to
the current state, are likely to predict what occupants will donext. We assume that if two household states are similar thenthere is a high probability that the next activity of one state1165

set of predictive states {w0 , . . . , wk } from the database thatare within distance i of the feature vector. The search is optimized with a kd-tree approach. Prediction is complete whena random state w is chosen from the set of states returned by
the FRNN search.
Since the set of features that characterize a household
state include categorical attributes (such as activities, rooms,
appliances) and numerical attributes (such as length of ongoing activity), we use the method of Ahmad and Dey(2007) to compute the distance between two data elements.
Our distance function uses a weighted squared value of
the Euclidean distance. All numeric attributes are normalized to be on the same scale. This function is specially suited
to compute similarity between categorical data objects. For
instance, consider the categorical attribute of activity for thefollowing data objects: ‘Bathing’, ‘Showering’ and ‘Studying’. Our customized distance measure can recognize thatthe activities ‘Bathing’ and ‘Showering’ are more similar
than the activity of ‘Studying’ to either of them.
Our method works well in capturing similarity because
it considers the distribution of values in the dataset while
computing the distance between two attribute values. For
instance, consider the way the algorithm computes the distance (distance(A, B)) between two activities A, B. Let N
be the number of activities and act represent an activity,
1 ≤ act ≤ N . As shown in Algorithm 1, distance between
activities is computed as a function of activities distribution
in the overall dataset taking into account co-occurrence withother activities.

is also the next activity for the other state. We assume thatall predictive states have the same probability to accurately
determine the next behavior of the agent. Hence, we use arandom function to select the preferred predictive state (w)from the set of predictive states.
We introduce the notion of ‘maximum allowed similarity distance’ (i) to allow the agent to perform less restricted
matches of the sample database while predicting its next behavior. In turn, the normal distribution mechanism ensuressome degree of restriction in the selection of the set of predictive states. The effectiveness of the selection of this set
greatly determines how well our model can fit the sample
data and generalize from it. With this approach we aim toachieve a balance between over-fitting and under-fitting.
We assume that all predictive states have an equal probability of being selected and determine the agent’s next behavior accordingly. Note that the normal distribution mechanism already implements an approach that favors states withsimilarity distances close to zero.
The third stage of the reasoning process consists in the execution stage of the selected behavior. In the execution theagent mimics the occupant behavior predicted by the statechosen in the prediction stage. The agent’s reasoning cycle
continues until the simulation ends.

Initialization
At each time-step t the agent senses the household environment according to an array of characteristics (features):1. Activity, room and appliances used by agent at previous
time-step (t − 1);

Algorithm 1 Calculating distance of activities

2. Length in time-steps (duration) of the on-going activity(l);distance(A, B) ← 0
act ← 1for act ≤ N, act + + do
if P (act|A) ≤ P (act|B) thendistance(A, B) ← distance(A, B) + P (act|B)
else
distance(A, B) ← distance(A, B) + P (act|A)
end ifend fordistance(A, B) ← distance(A, B) − 1

3. Activities, rooms and appliances used by one other occupant at current time-step (t). This other (leader) occupantis selected as the agent whose behavior is more strongly
related to the current behavior of the agent. Relations between the behaviors of agents (two agents mainly) are
generated through association rules learning (Agrawal,
Imieliński, and Swami 1993) in the original TU data with
the Apriori algorithm (Agrawal et al. 1996). The Apriorialgorithm is applied to a collection of activities performedby pairs of occupants in each time-step. The algorithm
runs on this collection to find the most frequent relations.
Strong relations are required to satisfy a minimum confidence value and are prioritized according to their support value. Leader agents are identified with basis on thisstrong relations according to the actual context of the simulation.

Execution
After selecting a predictive state w from the TU data, thenext behavior of the agent is executed. This may involve theselection of the agent’s next activity such as sleeping or having meals and also its location in the household as well as theelectrical appliances used. This execution changes the stateof the agent and household.

Finally, the feature vector representing the household current state (xt ) is passed to a prediction system.

Experiment

Prediction
Having the feature vector as input (xt ), the agent must decide its next behavior based on a database of TU data using
a fixed-radius near neighbors (FRNN) comparison (Bentley1975). Given a feature vector and a distance i defined by anormal distribution N (0, σ 2 ), the FRNN search reports the

The aim of this section is to compare the accuracy of two
approaches to the modeling of occupant behavior in multiagent systems of energy demand estimation: the standard
Markov chain (MC) model and our Nearest Neighbor (NN)model.

1166

Markov Chain (MC) Model

Indicators

To compare the performance of our NN model with the stateof-the-art approach to modeling occupant behavior, we havedeveloped a model based on discrete non-homogeneous
Markov chains, following the implementation of Widén,
Nilsson, and Wäckelgård (2009). In our model, time-steptransition probabilities are estimated from TU data with thefollowing equation:

τij (n) =

I1
I2
I3
I4

Time performing an activity jointly with others# of different patterns of occupant behavior transitions
Probability distribution showing percentage of activity
at each time step
Number of activity transitions per day

Table 1: Indicator I1 is our original indicator; Indicators I2I4 are proposed in (Yamaguchi, Tanaka, and Shimoda 2012).


|S|
P



ηij (n) = 0
0, ifData

j=1

ηij (n), otherwise|S| P ηij (n)The data used in our experiment was collected from fourhouseholds in the region of Osaka, Japan, in late 2011and beginning of 2012. The surveyed household members
agreed to document their daily routines in diaries during
14 days, on a minute by minute basis. Behaviors are classified in thirty categories (see Table 2). Table 3 describes thehousehold composition, dwelling type and surveyed period
for each household in the data set.

j=1

where τij (n)[0, 1] defines the time-step transition probability that the system will evolve from state i to state j (assume
the existence of S states) from time n to n + 1 and ηij (n)stands for the number of occurrences of transitions between
states i and j from time n to n + 1.
Time-step transition probabilities define the likelihood ofan agent to change state in a given time-step. States in themodel correspond to the daily routines of the occupant, suchas ‘Sleeping’, ‘Being outside’, ‘Having meal’, and so on.

Activities
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Indicators and Hypotheses
We assess the accuracy of the MC and NN models according to some important indicators as presented in Table 1.
Three of the four indicators are taken from the literature,
the first indicator (I1) is our original indicator. This indicator measures if the models accurately reproduce how often
an occupant performs an activity as a joint activity, or sole
activity. This indicator is important since the simultaneous
performance of an activity, such as watching TV or cooking,
implies the sharing of electrical appliances. As a result, theaccurate estimation of the time that occupants perform anactivity simultaneously with others or individually may allow us to more accurately estimate the time when electricalappliances are shared.
Indicator I2 relates to variations in timing of performingsome activity. Such variation is important when peak demand of large residential areas is estimated (Tanimoto, Hagishima, and Sagara 2008). In the energy field, this indicator is often used to evaluate the diversity of agents’ behaviors (Tanimoto, Hagishima, and Sagara 2008; Yamaguchi,
Tanaka, and Shimoda 2012).
Based on the most prominent indicators from the literature (see Table 1), we formulate our hypotheses as follows:• Coordinated Behavior Hypothesis: our NN model is moreaccurate than the MC model in estimating the time an occupant performs an activity as a joint or sole activity (Indicator I1).
• Patterns of Behavior Hypothesis: our NN model can generate a higher number of different patterns of behavior
transitions than the MC model (Indicator I2).
The hypotheses have been tested with real TU data. Regarding the Indicators I3–I4, we do not claim that our NN
based approach outperforms the MC based approach.

Being outside
Sleeping
Having meal
Face washingBathingChanging clothes
No activity living room
Working at home
Studying
Cooking
Cleaning dishes
Cleaning living room
Cleaning other rooms
Clothes washing
Ironing

16
17
18
19
20
21
22
23
24
25
26
27
28
29
30

Other housework
Communication
Hobbies
TV in living room
TV in bedroom
Stereo living room
Reading living room
Reading bedroom
Stereo bedroomVideo
No activity bedroom
Showering
Having breakfast
Having lunch
Having dinner

Table 2: Available categories of activities in a household.

Methodology
Our NN model was compared with the traditional MC modelusing the following methodology:• Simulation: Each of the four households is simulated using the MC model and the NN model (σ 2 = 0.002). In
each simulation of a household, the daily activities of theoccupants are reproduced for a period of 500 days.
• Validation: The accuracy of the models is assessed bycomparing their output with the original TU data.
This validation method is the standard approach to validating occupant behavior models in the energy field (Widén,
Nilsson, and Wäckelgård 2009; Widén and Wäckelgård
2010; Tanimoto, Hagishima, and Sagara 2008; Yamaguchi,
Tanaka, and Shimoda 2012). It is important to note that
this approach is different from a method like 10-fold crossvalidation, which is used to validate models generated by1167

Dwelling

PeriodOccupant

Abbr

HA

Detached
house 3LDK

30 Oct 12 11
Nov 11

Working male
Working female
High-school
Junior high-school

M(A)
F(A)
H(A)
J(A)

HB

Appartment
4LDK

16 Jan 12 29
Jan 12Working male
Working female
Primary school
Junior high-school

M(B)
F(B)
P(B)
J(B)

HC

Appartment
4LDK

7 Dec 11 21
Dec 11

Working maleHousewife
Primary school

M(C)
F(C)
P(C)

8 Dec 11 22
Dec 11

Working maleHousewife
Primary school

M(D)
F(D)
P(D)

HD

Appartment
4LDK

Occupant

Table 3: Household composition of the TU dataset with 3 or
4 rooms and LDK (Living, Dining, Kitchen).

M(A)
F(A)
H(A)
J(A)

Estimation Error
MC
NN
7.55
7.2
9.05
8
9.3
8.3
7.8
7.35

p
0.18
<0.05
<0.05
0.12

M(B)
F(B)
P(B)
J(B)

11.1
8.35
10.35
10.75

11.15
7.75
7.15
9.3

0.43
0.06
<0.05
<0.05

M(C)
F(C)
P(C)

6.3
6
5.95

6.5
6
6.4

0.25
0.45
0.09

M(D)
F(D)
P(D)

7
6.65
8.7

7.7
8.55
8.8

0.09
<0.05
0.37

Table 4: Average daily estimation error (in minutes) of time
performing an activity jointly with others (I1) for NN and
MC models.

machine learning techniques (Mamidi, Chang, and Maheswaran 2012). Please note that the models we study output
probability densities rather than specific predictions.

MC for 3 cases. The average difference of error was of 1%(35.6 to 36.1min). For remaining activities, difference was
the double: 2% (1.2 to 1.19min) and t-tests proved difference between models for six cases. These differences can be
explained by NN overcoming the limitations of MC in modeling the coordination of agents in short joint time activities(Yamaguchi, Tanaka, and Shimoda 2012).
It is important to note that the NN model not only replicates but also generalizes from the coordination behavior
patterns found in TU data. The MC model tries to predict
the future based on samples of TU data that exactly matchthe current state in the dimensions of time and activity (Baptista et al. 2014). By contrast, our NN model is not limited
to perfect matching with TU data, and thus is less prone toover-fitting. The NN model occasionally picks a state fromthe past TU data that is slightly dissimilar to the current statewith regard to some dimension (time or activity). Simply
put, the NN model trades accuracy for generality.

Results
We first present results regarding the Coordinated Behavior Hypothesis (Indicator I1) and the Patterns of Behavior
Hypothesis (Indicator I2). Then we present results for Indicators I3 and I4.

Coordinated Behavior Hypothesis
Table 4 reports the average error (in minutes) in estimating
the time each occupant spent performing an activity jointlywith others (I1) for both MC and NN models. It also shows
the results of Student t-tests. We note that these estimation
errors were calculated only from activities that were performed jointly by the occupants.
Interestingly, we obtain different results for 3- and 4person households. In 4-person households (A and B), we
found that our NN model is better than the MC model,
mostly with statistical significance (or near-significance),
except for one case. In 3-person households (C and D), theMC model is better in the majority of cases. Hence, our results only partially support the Coordinated Behavior Hypothesis.
With a larger number of household members it is more
likely that an occupant performs some activity jointly withanother occupant. Since our NN model explicitly models
joint activity, it performs better in 4-person households thanin 3-person households.
We found differences in the performance of NN model
related to the joint duration of activities. Here, joint duration is time of activity performing together with others. In
activities with large joint duration such as ‘Sleeping’, ‘Being outside’, ‘TV in living room’ and ‘Hobbies’, the better
performance of NN is not as pronounced as for remaining
activities. For these four activities, Student t-tests could only
reveal a statistically significant difference between NN and

Patterns of Behavior Hypothesis
Fig. 1 compares the number of different patterns of occupant
behavior transitions per day (I2) found in TU data, MC andNN model. We calculate this indicator by first counting, foreach time-step, the number of distinct transitions registeredin all the simulated days. Here, transition means a change
from an activity to a different activity. Then, we sum thedistinct transitions of each time-step for all time-steps.
As illustrated in Fig. 1, the number of different daily behavior transition patterns registered in all simulations runs isvery different in MC and NN. The MC model generated asmuch distinct patterns as the ones found in TU data. By contrast, the NN model was able to generate up to 394 new patterns averaging 228 new patterns per occupant. Hence, ourresults strongly support the Patterns of Behavior Hypothesis.
Fig. 2 shows, for each time step, the number of distinct1168

Nr patterns

TU Data

MC

NN
I3
I4

600

Nr patterns

STD

Avg

NN
Max

STD

0.001
3.55

0.003
5.17

0.0005
0.88

0.003
3.52

0.004
4.87

0.00080.87

Table 5: Estimation errors of indicators I3 and I4.

200

Student t-tests were used to compare the MC and NN
models with respect to indicator I3 and I4. For Indicator I3,
Student’s t-test did not show a statistically significant difference for 13 of the 14 occupants. In the case of Indicator I4,
Student’s t-tests could reveal a statistically significant difference (p < 0.05) for 8 out of 14 occupants.
The results on Indicators I3 and I4 are important as theyshow that the NN model is comparable to the MC model inmodeling (1) the way agents perform activities at each timestep (I3) and (2) how often agents change their activities ina day (I4). The second finding is noteworthy: even though
NN generates more patterns of transitions (I2), this does not
influence the accuracy of the number of transitions per day(I3). In other words, NN agents change activities during a
day as often as MC agents despite the fact that changes ofactivities are being delayed or advanced in time. We notethat we calibrated NN to delay and advance activities to a
maximum of one time-step (5 minutes).

M(A)F(A) H(A) J(A) M(B) F(B) P(B) J(B)
600
400
200
0
M(C) F(C)P(C) M(D) F(D)P(D)

Figure 1: Comparison of number of different patterns of occupant behavior transitions (I2) per day.
transitions (transition patterns) registered during the 500
simulations runs of the MC model (top chart) and NN model(bottom chart) for occupant M(A). The figure illustrates that
the NN model generates far more patterns than TU data andMC model. Additionally, the NN model generates transition
patterns in time ranges near the ones of the original patterns.
In other words, NN agents are able to delay and advance, thetransitions found in the TU data.

Nr patterns

MC
Max

400

0

Nr patterns

Avg

10
8
6
4
2
0
0:00
10
8
6
4
2
0
0:00

Conclusions
Energy demand simulations play an important role in implementing the smart grid and in reducing CO2 emissions.
Human behavior is at the core of these simulations; the way
household occupants behave and interact with each other cangreatly determine the accuracy of demand estimation. Our
work attempts to present a new perspective on occupant behavior modeling by accommodating three factors: individual
behavior, coordination of behavior among occupants, and diversity of behavior patterns.
We present a Nearest Neighbor (NN) occupant behavior
model that (1) aims to replicate coordinated behavior moreaccurately than a Markov Chain (MC) model, the state-ofthe-art approach, while at the same time (2) generalizes newpatterns of behavior. Our results suggest that our solution isa good compromise between agreement of simulated data to
TU data and generalization of patterns.
There are two main research directions for future work.
The first line of research will focus on validating the quality of the new generalized patterns of data. As our model
outputs density probabilities, we can investigate density estimation cross validation techniques (Marron 1987).
The second direction relates to further exploring coordination of agents. For instance, we may consider more than
one leader in the household or coordinate all agents at thesame time. The influence of these strategies upon variabilityof coordinated behavior is an important future topic.

MC

24:00
NN

24:00

Figure 2: Comparison of average number of different behavior transitions (I2) generated by MC and NN models foroccupant M(A).

Other Indicators

Acknowledgments
This work was partially supported partly by the ‘Global
Lab’ Grand Challenge grant from the National Insti-

Table 5 presents the average, maximum and standard deviation of Indicators I3 and I4.

1169

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tute of Informatics (NII), the NII Int’l Internship Program, and Fundação para a Ciência e a Tecnologia, under
project PEst-OE/EEI/LA0021/2013 and scholarship reference SFRH/BD/52347/2013.

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