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Blomquist, N., Alimadadi, M., Hummelgård, M., Dahlström, C., Olsen, M. & Olin, H. (2019). Effects of Geometry on Large-scale Tube-shear Exfoliation of Multilayer Graphene and Nanographite in Water. Scientific Reports, 9(1), Article ID 8966.
Open this publication in new window or tab >>Effects of Geometry on Large-scale Tube-shear Exfoliation of Multilayer Graphene and Nanographite in Water
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 8966Article in journal (Refereed) Published
Abstract [en]

Industrially scalable methods for the production of graphene and other nanographites are needed to achieve cost-efficient commercial products. At present, there are several available routes for the production of these materials but few allow large-scale manufacturing and environmentally friendly low-cost solvents are rarely used. We have previously demonstrated a scalable and low-cost industrial route to produce nanographites by tube-shearing in water suspensions. However, for a deeper understanding of the exfoliation mechanism, how and where the actual exfoliation occurs must be known. This study investigates the effect of shear zone geometry, straight and helical coil tubes, on this system based on both numerical simulation and experimental data. The results show that the helical coil tube achieves a more efficient exfoliation with smaller and thinner flakes than the straight version. Furthermore, only the local wall shear stress in the turbulent flow is sufficient for exfoliation since the laminar flow contribution is well below the needed range, indicating that exfoliation occurs at the tube walls. This explains the exfoliation mechanism of water-based tube-shear exfoliation, which is needed to achieve scaling to industrial levels of few-layer graphene with known and consequent quality.

National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-36084 (URN)10.1038/s41598-019-45133-y (DOI)2-s2.0-85067662886 (Scopus ID)
Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-07-10Bibliographically approved
Olsen, M., Zhang, R., Örtegren, J., Andersson, H., Yang, Y. & Olin, H. (2019). Frequency and voltage response of a wind-driven fluttering triboelectric nanogenerator. Scientific Reports, 9(1), Article ID 5543.
Open this publication in new window or tab >>Frequency and voltage response of a wind-driven fluttering triboelectric nanogenerator
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 5543Article in journal (Refereed) Published
Abstract [en]

Triboelectric nanogenerators (TENG:s) are used as efficient energy transducers in energy harvesting converting mechanical energy into electrical energy. Wind is an abundant source of mechanical energy but how should a good triboelectric wind harvester be designed? We have built and studied a TENG driven by air flow in a table-top sized wind tunnel. Our TENG constitutes of a plastic film of size10 cm × 2 cm which is fluttering between two copper electrodes generating enough power to light up a battery of LED:s. We measured the voltage and frequency of fluttering at different wind speeds from zero up to 8 m/s for three electrode distances 6 mm, 10 mm and 14 mm. We found that the frequency increases linearly with the wind speed with a cutoff at some low speed. Power was generated already at 1.6 m/s. We seem to be able to explain the observed frequency dependence on wind speed by assuming excitation of the film into different harmonics in response to von Kármán vortices. We also find that the voltage increase linearly with frequency. We anticipate that TENG:s of this design could be useful both as generators and speed sensors because they work at low air speeds.

National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-35936 (URN)10.1038/s41598-019-42128-7 (DOI)000463178500004 ()30944397 (PubMedID)2-s2.0-85063884794 (Scopus ID)
Funder
J. Gust. Richert stiftelseSwedish Energy AgencyKnowledge FoundationEuropean Regional Development Fund (ERDF)
Note

Forskningsfinansiär: Länsstyrelsen Västernorrland

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-07-08Bibliographically approved
Zhang, R., Hummelgård, M., Örtegren, J., Olsen, M., Andersson, H. & Olin, H. (2019). Interaction of the human body with triboelectric nanogenerators. Nano Energy, 57, 279-292
Open this publication in new window or tab >>Interaction of the human body with triboelectric nanogenerators
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2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 57, p. 279-292Article in journal (Refereed) Published
Abstract [en]

The use of triboelectric nanogenerators (TENGs) is a new technique for energy harvesting at both small and large scales. Almost all types of mechanical energy can be harvested with TENGs by using four modes of operation that cover almost all mechanical motions. The interactions of the human body with TENGs range from energy harvesting, motion sensing, and biomedical applications to human-computer communications. Different types of TENGs have been developed to directly or indirectly involve the human body. This review will summarize the recent advances in the interaction of the human body with TENGs.

Keywords
Energy harvesting, Healthcare, Human body, Human-robot interactions, Sensors, Triboelectric nanogenerators
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-35386 (URN)10.1016/j.nanoen.2018.12.059 (DOI)000458419000028 ()2-s2.0-85059038089 (Scopus ID)
Available from: 2019-01-06 Created: 2019-01-06 Last updated: 2019-03-18Bibliographically approved
Olsen, M. (2019). Nanomechanics – Quantum Size Effects, Contacts, and Triboelectricity. (Doctoral dissertation). Sundsvall: Mid Sweden University
Open this publication in new window or tab >>Nanomechanics – Quantum Size Effects, Contacts, and Triboelectricity
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanomechanics is different from the mechanics that we experience in everyday life. At the nano-scale, typically defined as 1 to 100 nanometers, some phenomena are of crucial importance, while the same phenomena can be completely neglected on a larger scale. For example, the feet of a gekko are covered by nanocontacts that yield such high adhesion forces that the animal can run up on walls and even on the ceiling. At small enough distances, matter and energy become discrete, and the description of the phenomena occurring at this scale requires quantum mechanics. However, at room temperature the transitions between quantized energy levels may be concealed by the thermal vibrations of the system. As two surfaces approach each other and come into contact, electrostatic forces and van der Waals forces may cause redistribution of matter at the nano level. One effect that may occur upon contact between two surfaces is the triboelectric effect, in which charge is transferred from one surface to the other.This effect can be used to generate electricity in triboelectric nanogenerators (TENGs), where two surfaces are repeatedly brought in and out of contact, and where the charge transfer is turned into electrical energy.

This thesis concerns nanomechanics addressing whether quantum mechanics play a role in elastic deformation, as well as various mechanical aspects of nanocontacts including electric charging. The objectives are to contribute to the understanding when quantum effects are of importance at the nanolevel, increase the fundamental understanding of the mechanisms responsible for triboelectric phenomena and apply the triboelectric effect to a wind harvesting device.

For more insight into whether quantum effects are of importance in nanomechanics, we use a one dimensional jellium model and the standard beam theory allowing the spring constant of an oscillating nanowire cantilever to be calculated. As the nanowire bends, more electron states fit in its cross section, giving rise to an amplitude dependent resonance frequency of the nanowire oscillations.

Furthermore, a model for electric field induced surface diffusion of adatoms was developed. The model takes electrostatic forces and van der Waals forces into account as a voltage is applied between a scanning tunneling microscope tip and a sample. The calculated force on the adatoms at the surface of the sample, which is stemming from the inhomogeneous electric field and the dipole moment of the adatoms, is relatively small, but due to thermal vibrations adatoms diffuse and form mounds at the sample.

When bringing two different materials into contact, the difference in triboelectric potentials between the materials results in electric charging. To increase the understanding of triboelectricity, a two-level Schottky model, assuming ion transfer, was developed to describe the temperature dependence of the triboelectric effect for a TENG. The two levels correspond to the binding energy for ions on the two surfaces that are brought into contact, where the difference in binding energy enters the Boltzmanndistribution. The model describes the decreasing triboelectric effect in TENG:s with increasing temperature as described in the literature, and results in a separation energy, which is of the right order of magnitude for physically adsorbed atoms.

It was recently demonstrated that TENGs can convert wind energy into electrical energy. Here, a TENG based on a plastic film fluttering between two copper electrodes was constructed. It was found that the frequency of the the fluttering film increases linearly with the wind speed. TENG:s designed in this way generate electricity already at low wind speed, and we therefore expect such TENG:s to be useful both as generators and speed sensors in the future.

While quantum mechanics is of importance in a limited number of nanomechanical systems, nanocontacts have a broader meaning, and are crucial for the understanding of triboelectric phenomena. We anticipate that the findings in this thesis will contribute to a better understanding of nanomechanics, in particular the mechanism of triboelectricity.

Abstract [sv]

Nanomekanik är annorlunda än den mekanik vi upplever i vardagen. I nanoskalan, som definieras som storleksområdet 1 -100 nanometer, är vissa fenomen viktiga medan dessa helt kan försummas i den större skalan i vardagslivet. Till exempel har evolutionen på nanoskalan designat en gekkoödlas fötter så att de har en så kraftigvidhäftning till omgivningen att gekkon kan gå omkring i taket. Tittar man på den lilla skalan finner man att materien är diskret och att beskrivning av fenomen i denna skala kräver kvantmekanik. Övergångar mellan kvantnivåer döljs dock ofta vid rumstemperatur av termiska vibrationer hos systemet. När två ytor närmar sig varandra och kommer i kontakt kan elektrostatiska krafter och van der Waalskrafter orsaka omfördelning av materia på nanonivå. En effekt som kan uppträda vid kontakt mellan två ytor är den triboelektriska effekten vid vilken det sker överföring av laddning från den ena ytan till den andra. Denna effekt kan användas för att generera elektrisk energi i triboelektriska nanogeneratorer (TENG:s) där två ytor omväxlande förs ihop och dras isär.

Denna avhandling behandlar nanomekanik med fokus på om kvantmekaniken spelar en viktig roll vid elastisk deformation och även olika mekaniska aspekter hos nanokontakter inklusive elektrisk uppladdning. Målsättningen är att bidra till kunskap om när kvanteffekter är viktiga i nanoskalan och att öka den grundläggande förståelsen för triboelektriska fenomen samt att tillämpa den triboelektriska effekten för en vinddriven energiutvinnande apparat.

För att få bättre förståelse om kvanteffekter är betydelsefulla i nanomekanik har vi gjort en endimensionell fri elektronmodell och använder vanlig balkteori för att beräkna fjäderkonstanten för en nanotråd utgörande en svängande bladfjäder. När nanotråden böjs kommer fler elektrontillstånd att passa i trådens tvärsnittsyta vilket ger upphov till en amplitudberoende resonansfrekvens hos tråden.

Dessutom har vi utvecklat en modell för elektriskt fältinducerad ytdiffusion av adatomer. Modellen tar hänsyn till elektrostatiska krafter samt till van der Waalskrafter när en spänning påläggs mellan en spets i ett sveptunnelmikroskop och en provyta. Den beräknade kraften på adatomerna på provets yta - vilken kommer av det inhomogena elektriska fältet och adatomernas dipolmoment - är relativt liten, men på grund av de termiska vibrationerna kan adatomerna ändå diffundera och bilda en kulle under tippen.

När man sammanför två olika material kommer skillnaden i deras triboelektriska potentialer att orsaka uppladdning. För att öka förståelsen av triboelektriciteten har vi utvecklat en två-nivå Schottkymodell som antar joner som laddningsbärare för att beskriva den triboelektriska uppladdningens temperaturberoende för en TENG. De två nivåerna motsvarar de två kontaktande ytorna. Skillnaden i bindningsenergi mellan joner på ytorna kommer därför in i Boltzmannfaktorn. Modellen beskriver den minskande triboelektriska effekten vid ökande temperatur som rapporterats ilitteraturen, och stöds av att den separationsenergi man finner vid anpassning av modellen till data är av samma storleksordning som skillnaden i bindningsenergi för fysikaliskt ytadsorberade atomer (adatomer).

Nyligen visades det att TENG:s kan omvandla vindenergi till elektrisk energi.Vi har konstruerat en TENG baserad på ett flappande plastband löst inspänt mellan två kopparelektroder. Vi fann att frekvensen hos det flappande plastbandet ökar linjärt med vindhastigheten. TENG designade på detta sätt alstrar elektrisk energi redan vid låga vindhastigheter vilket gör att apparaten kan komma att användas både som generator och som vindhastighetsmätare i framtiden.

Medan kvantmekanik bara är betydelsefull i ett begränsat antal nanomekaniska system har nanokontakter en mer allmän tillämpning och är viktig för förståelsen av triboelektriska fenomen. Vi förutser att resultaten i denna avhandling kan komma att bidra till en bättre förståelse för nanomekanik i allmänhet och för mekanismen för triboelektricitet i synnerhet.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 50
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 299
Keywords
triboelectricity, adatom, ion, charge, mound, quantum size effect, triboelctric nanogenerator, TENG, wind driven, contact, nanomechanics, fri electron model, nanowire cantilever
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-36153 (URN)978-91-88947-02-4 (ISBN)
Public defence
2019-06-05, O102, Holmgatan 10, Sundsvall, 10:15 (English)
Opponent
Supervisors
Available from: 2019-05-20 Created: 2019-05-18 Last updated: 2019-05-20Bibliographically approved
Zhang, R., Hummelgård, M., Örtegren, J., Yang, Y., Andersson, H., Balliu, E., . . . Olin, H. (2019). Sensing body motions based on charges generated on the body. Nano Energy, 63, Article ID 103842.
Open this publication in new window or tab >>Sensing body motions based on charges generated on the body
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2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 63, article id 103842Article in journal (Refereed) Published
Abstract [en]

The sensing of body motions is of great importance in areas such as healthcare, rehabilitation, and human-computer interactions. Different methods have been developed based on visual or electrical signals. However, such signals are acquired by external devices and are not intrinsic signals that are created on the body. Here, we report a new universal body motion sensor (UBS) to detect motions based on the intrinsic contact electrification (CE) of the skin or electrical induction (EI) of the body. The CE or EI generates charges on the body, leading to potential differences between the body and ground that can be measured to identify different body motions, such as motions of the head, arms, fingers, waist, legs, feet and toes. Proof-of-concept experiments have demonstrated that the UBS can be used to monitor the conditions of people with Parkinson's disease (PD) and to quantitatively monitor the recovery of those with a leg injury, suggesting great potential for healthcare applications.

Keywords
Body motions, Sensors, Charges, Contact electrification, Electrical induction, Healthcare
Identifiers
urn:nbn:se:miun:diva-36826 (URN)10.1016/j.nanoen.2019.06.038 (DOI)000480422400034 ()
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-09-02Bibliographically approved
Zhang, R., Örtegren, J., Hummelgård, M., Olsen, M., Andersson, H. & Olin, H. (2018). Harvesting triboelectricity from the human body using non-electrode triboelectric nanogenerators. Nano Energy, 45, 298-303
Open this publication in new window or tab >>Harvesting triboelectricity from the human body using non-electrode triboelectric nanogenerators
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2018 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 45, p. 298-303Article in journal (Refereed) Published
Abstract [en]

Triboelectrification has been known and discussed since antiquity. Triboelectrification occurs in the human body due to friction between human skin and other materials such as clothing. However, charges on the body have not been harvested to power small electronics. Here, we report for the first time that the electricity generated on the human body due to triboelectrification can be measured and harvested using human body-based non-electrode triboelectric nanogenerators (H-TENGs). The H-TENGs can have an output of up to 3.3 W/m(2) and can spontaneously harvest energy from several people. The functions of the human body in the H-TENGs are analyzed and experimentally proven to be those of a triboelectric material, conductor and capacitor. Our results demonstrate that the triboelectricity generated on a human body can be harvested using H-TENGs and provide scientific insights into body functions that will promote further studies of TENGs.

Keywords
Human body, Non-electrode TENG, Mechanisms, Charges
National Category
Medical Biotechnology
Identifiers
urn:nbn:se:miun:diva-33301 (URN)10.1016/j.nanoen.2017.12.053 (DOI)000425396400033 ()2-s2.0-85043782783 (Scopus ID)
Available from: 2018-03-19 Created: 2018-03-19 Last updated: 2018-03-28Bibliographically approved
Zhang, R., Hummelgård, M., Örtegren, J., Olsen, M., Andersson, H., Yang, Y. & Olin, H. (2018). Human body constituted triboelectric nanogenerators as energy harvesters, code transmitters and motion sensors. ACS Applied Energy Materials, 1(6), 2955-2960
Open this publication in new window or tab >>Human body constituted triboelectric nanogenerators as energy harvesters, code transmitters and motion sensors
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2018 (English)In: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 1, no 6, p. 2955-2960Article in journal (Refereed) Published
Abstract [en]

Human skin is a dielectric material that can be used as a triboelectric material for harvesting energy from body motions. The output power of such a human skin-based triboelectric nanogenerator (TENG) is relatively low. Here, we assembled high-output human body constituted TENGs (H-TENGs) by taking advantage of the unique electrical properties of the human body, such as high skin impedance, low tissue resistance, body capacitance, and conductivity. The output of a H-TENG can reach 30 W/m2, which is enough to drive small electronic devices, such as a timer or a calculator. The unique feature of the H-TENG is that it can perform the four fundamental modes of TENGs, which has not been reported elsewhere. Such a feature allows the H-TENG to act as a code transmitter to send light and electrical signals, such as Morse code. H-TENGs also benefit the development of high-performance, self-powered body motion sensors. Our findings suggest new strategies for harvesting energy from human body motions, as well as new types of motion sensors and signal senders.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
Keywords
code transmitters; energy harvesting; human body; motion sensors; triboelectric nanogenerators
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-34433 (URN)10.1021/acsaem.8b00667 (DOI)000458705800070 ()
Available from: 2018-09-18 Created: 2018-09-18 Last updated: 2019-03-15Bibliographically approved
Zhang, R., Hummelgård, M., Forsberg, V., Andersson, H., Engholm, M., Öhlund, T., . . . Olin, H. (2018). Photoconductivity of acid exfoliated and flash-light-processed MoS2 films. Scientific Reports, 8, Article ID 3296.
Open this publication in new window or tab >>Photoconductivity of acid exfoliated and flash-light-processed MoS2 films
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 3296Article in journal (Refereed) Published
Abstract [en]

MoS2 has been studied intensively during recent years as a semiconducting material in several fields, including optoelectronics, for applications such as solar cells and phototransistors. The photoresponse mechanisms of MoS2 have been discussed but are not fully understood, especially the phenomenon in which the photocurrent slowly increases. Here, we report on a study of the photoresponse flash-light-processed MoS2 films of different thicknesses and areas. The photoresponse of such films under different light intensities and bias voltages was measured, showing significant current changes with a quick response followed by a slow one upon exposure to pulsed light. Our in-depth study suggested that the slow response was due to the photothermal effect that heats the MoS2; this hypothesis was supported by the resistivity change at different temperatures. The results obtained from MoS2 films with various thicknesses indicated that the minority-carrier diffusion length was 1.36 mu m. This study explained the mechanism of the slow response of the MoS2 film and determined the effective thickness of MoS2 for a photoresponse to occur. The method used here for fabricating MoS2 films could be used for fabricating optoelectronic devices due to its simplicity.

National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-33302 (URN)10.1038/s41598-018-21688-0 (DOI)000425380900079 ()29459668 (PubMedID)2-s2.0-85061713034 (Scopus ID)
Available from: 2018-03-19 Created: 2018-03-19 Last updated: 2019-03-20Bibliographically approved
Olsen, M., Örtegren, J., Zhang, R., Reza, S., Andersson, H. & Olin, H. (2018). Schottky model for triboelectric temperature dependence. Scientific Reports, 8(1), Article ID 5293.
Open this publication in new window or tab >>Schottky model for triboelectric temperature dependence
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 5293Article in journal (Refereed) Published
Abstract [en]

The triboelectric effect, charging by contact, is the working principle in a device called a triboelectric nanogenerator. They are used as efficient energy transducers in energy harvesting. In such generators the charging of surfaces at contact is followed by a separation of the surfaces increasing the electrical energy which can subsequently be used. Different materials have different triboelectric potentials leading to charging at contact. The temperature dependence of the charging has just recently been studied: the triboelectric effect is decreasing with temperature for a generator of Al-PTFE-Cu. Here, we suggest a mechanism to explain this effect assuming ion transfer using a two-level Schottky model where the two levels corresponds to the two surfaces. The difference in binding energy for ions on the two surfaces then enters the formula for charging. We fit the triboelectric power density as a function of temperature obtained from a two-level Schottky model to measured data for nanogenerators made of Al-PTFE-Cu found in three references. We obtain an average separation energy corresponding to a temperature of 365 K which is of the right magnitude for physically adsorbed atoms. We anticipate that this model could be used for many types of triboelectric nanogenerators.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-33379 (URN)10.1038/s41598-018-23666-y (DOI)000428518500004 ()2-s2.0-85044510140 (Scopus ID)
Available from: 2018-03-28 Created: 2018-03-28 Last updated: 2019-05-18Bibliographically approved
Zhang, R., Hummelgård, M., Olsen, M., Örtegren, J. & Olin, H. (2017). Nanogenerator made of ZnO nanosheet networks. Semiconductor Science and Technology, 32(5), Article ID 054002.
Open this publication in new window or tab >>Nanogenerator made of ZnO nanosheet networks
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2017 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 32, no 5, article id 054002Article in journal (Refereed) Published
Abstract [en]

The piezoelectricity of nanomaterials attracts a great deal of attention due to its broad application, including the harvesting of ambient mechanical energy to power small electronics devices. We report here a simple method to fabricate piezoelectric nanogenerators consisting of networks of ZnO nanosheets grown on aluminum (Al) foils, where the Al acts as both a substrate for growth and as an electrode contacting the ZnO network. A second, top electrode was tapped, rolled, or rubbed against the ZnO to generate piezoelectricity. This second electrode was either a copper foil or fluorine doped tin oxide (FTO) glass. A piezo voltage of up to 0.924 V was detected during rolling and 6 μA was the highest current observed when rubbing the ZnO film with a FTO glass. Due to its simplicity, this nanogenerator fabrication method has the potential to be scaled up for the industrial production of piezoelectric energy harvesting devices.

Keywords
nano networks, nanogenerator, piezoelectric, ZnO nanosheet
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-30672 (URN)10.1088/1361-6641/aa660c (DOI)000413490800001 ()2-s2.0-85018449243 (Scopus ID)
Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2018-09-20Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4376-2676

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