Alexandros Askounis
Kyushu University
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Publication
Featured researches published by Alexandros Askounis.
Applied Physics Letters | 2016
Yutaku Kita; Alexandros Askounis; Masamichi Kohno; Yasuyuki Takata; Jungho Kim; Khellil Sefiane
We report on experimental observations/visualization of thermocapillary or Marangoni flows in a pure water drop via infrared thermography. The Marangoni flows were induced by imposing a temperature gradient on the drop by locally heating the substrate directly below the center with a laser. Evidently, a temperature gradient along the liquid-air interface of ca. 2.5 °C was required for the Marangoni flows to be initiated as twin vortices and a subsequent gradient of ca. 1.5 °C to maintain them. The vortices exhibited an oscillatory behavior where they merged and split in order for the drop to compensate for the non-uniform heating and cooling. The origin of these patterns was identified by comparing the dimensionless Marangoni and Rayleigh numbers, which showed the dominance of the Marangoni convection. This fact was further supported by a second set of experiments where the same flow patterns were observed when the drop was inverted (pendant drop).
AIP Advances | 2016
Alexandros Askounis; Yutaka Yamada; Tatsuya Ikuta; Koji Takahashi; Yasuyuki Takata; Khellil Sefiane
Thermal transport in carbon nanofibers (CNFs) was thoroughly investigated. In particular, individual CNFs were suspended on T-type heat nanosensors and their thermal conductivity was measured over a range of temperatures. Unexpectedly, thermal conductivity was found to be dependent on CNF wall thickness and ranging between ca. 28 and 43 W/(m⋅K). Further investigation of the CNF walls with high resolution electron microscopy allowed us to propose a tentative description of how wall structure affects phonon heat transport inside CNFs. The lower thermal conductivities, compared to other CNTs, was attributed to unique CNF wall structure. Additionally, wall thickness is related to the conducting lattice length of each constituent graphene cone and comparable to the Umklapp length. Hence, as the wall thickness and thus lattice length increases there is a higher probability for phonon scattering to the next layer.
Journal of Applied Physics | 2017
Yutaka Yamada; Alexandros Askounis; Tatsuya Ikuta; Koji Takahashi; Yasuyuki Takata; Khellil Sefiane
Hollow carbon nanotubes (CNTs) were impregnated with an ionic liquid, resulting in a composite core-shell nanostructure. Liquid infusion was verified by transmission electron microscopy and rigorous observations unveiled that the nanocomposite is stable, i.e., liquid did not evaporate owing to its low vapor pressure. A series of individual nanostructures were attached on T-type heat sensors and their thermal behavior was evaluated. The liquid core was found to reduce the thermal conductivity of the base structure, CNT, from ca. 28 W/mK to ca. 15 W/mK. These findings could contribute to a better understanding of nanoscale thermal science and potentially to applications such as nanodevice thermal management and thermoelectric devices.
Nanotoxicology | 2014
Anja Schinwald; Fiona Murphy; Alexandros Askounis; Vasileios Koutsos; Khellil Sefiane; Ken Donaldson; Colin J. Campbell
Colloids and Surfaces A: Physicochemical and Engineering Aspects | 2014
Alexandros Askounis; Khellil Sefiane; Vasileios Koutsos; Martin E.R. Shanahan
Soft Matter | 2011
Alexandros Askounis; Daniel Orejon; Vasileios Koutsos; Khellil Sefiane; Martin E. R. Shanahan
Physical Review E | 2013
Alexandros Askounis; Khellil Sefiane; Vasileios Koutsos; Martin E. R. Shanahan
Chemical Engineering Science | 2013
Xingxun Li; Xianfeng Fan; Alexandros Askounis; Kejian Wu; Khellil Sefiane; Vasileios Koutsos
Advances in Colloid and Interface Science | 2015
Alexandros Askounis; Khellil Sefiane; Vasileios Koutsos; Martin E.R. Shanahan
Langmuir | 2016
Alexandros Askounis; Yasuyuki Takata; Khellil Sefiane; Vasileios Koutsos; Martin E.R. Shanahan