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MAGNETIC RECONNECTION DURING THE TWO-PHASE EVOLUTION OF A SOLAR ERUPTIVE FLARE
Joshi, Bhuwan,Veronig, Astrid,Cho, K.-S.,Bong, S.-C.,Somov, B. V.,Moon, Y.-J.,Lee, Jeongwoo,Manoharan, P. K.,Kim, Y.-H. IOP Publishing 2009 The Astrophysical journal Vol.706 No.2
<P>We present a detailed multi-wavelength analysis and interpretation of the evolution of an M7.6 flare that occurred near the southeast limb on 2003 October 24. Pre-flare images at TRACE 195 angstrom show that the bright and complex system of coronal loops already existed at the flaring site. The X-ray observations of the flare taken from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft reveal two phases of the flare evolution. The first phase is characterized by the altitude decrease of the X-ray looptop (LT) source for similar to 11 minutes. Such a long duration of the descending LT source motion is reported for the first time. The EUV loops, located below the X-ray LT source, also undergo contraction with similar speed (similar to 15 km s(-1)) in this interval. During the second phase the two distinct hard X-ray footpoint (FP) sources are observed which correlate well with UV and Ha flare ribbons. The X-ray LT source now exhibits upward motion as anticipated from the standard flare model. The RHESSI spectra during the first phase are soft and indicative of hot thermal emission from flaring loops with temperatures T > 25 MK at the early stage. On the other hand, the spectra at high energies (epsilon greater than or similar to 25 keV) follow hard power laws during the second phase (gamma = 2.6-2.8). We show that the observed motion of the LT and FP sources can be understood as a consequence of three-dimensional magnetic reconnection at a separator in the corona. During the first phase of the flare, the reconnection releases an excess of magnetic energy related to the magnetic tensions generated before a flare by the shear flows in the photosphere. The relaxation of the associated magnetic shear in the corona by the reconnection process explains the descending motion of the LT source. During the second phase, the ordinary reconnection process dominates describing the energy release in terms of the standard model of large eruptive flares with increasing FP separation and upward motion of the LT source.</P>
Electrically Insulative Performances of Ceramic and Clay Films Deposited via Supersonic Spraying
Lee, J. G.,Kim, D. Y.,Joshi, B. N.,Lee, J. H.,Lee, T. K.,Kim, J. s.,Yang, D. h.,Kim, W. Y.,Al-Deyab, S. S.,Yoon, S. S. Springer Science + Business Media 2016 Journal of thermal spray technology Vol.25 No.4
<P>Supersonic spray coating techniques were applied to deposit ceramic and clay particles as films for use in electrical insulation. TiO2 and Al2O3 ceramics were aerosol-deposited under vacuum while kaolinite, montmorillonite, and bentonite clays were deposited by cold spraying in open air. The electrical resistivity of Al2O3 and TiO2 were similar to 10(9) and similar to 10(8) Omega cm, respectively. The resistivity of kaolinite and montmorillonite were similar to 10(12) Omega cm. Bentonite showed the lowest electrical resistivity of similar to 10(9) Omega cm among the clays because of the high cation exchange capacity of the material. The film surface morphologies and mechanical properties in the form of hardness and scratchability were also investigated.</P>
Nordstrom, U.,Beauvais, G.,Ghosh, A.,Pulikkaparambil Sasidharan, B.C.,Lundblad, M.,Fuchs, J.,Joshi, R.L.,Lipton, J.W.,Roholt, A.,Medicetty, S.,Feinstein, T.N.,Steiner, J.A.,Escobar Galvis, M.L.,Prochi Blackwell Science ; Academic Press 2015 Neurobiology of disease Vol.73 No.-
Current research on Parkinson's disease (PD) pathogenesis requires relevant animal models that mimic the gradual and progressive development of neuronal dysfunction and degeneration that characterizes the disease. Polymorphisms in engrailed 1 (En1), a homeobox transcription factor that is crucial for both the development and survival of mesencephalic dopaminergic neurons, are associated with sporadic PD. This suggests that En1 mutant mice might be a promising candidate PD model. Indeed, a mouse that lacks one En1 allele exhibits decreased mitochondrial complex I activity and progressive midbrain dopamine neuron degeneration in adulthood, both features associated with PD. We aimed to further characterize the disease-like phenotype of these En1<SUP>+/-</SUP> mice with a focus on early neurodegenerative changes that can be utilized to score efficacy of future disease modifying studies. We observed early terminal defects in the dopaminergic nigrostriatal pathway in En1<SUP>+/-</SUP> mice. Several weeks before a significant loss of dopaminergic neurons in the substantia nigra could be detected, we found that striatal terminals expressing high levels of dopaminergic neuron markers TH, VMAT2, and DAT were dystrophic and swollen. Using transmission electron microscopy, we identified electron dense bodies consistent with abnormal autophagic vacuoles in these terminal swellings. In line with these findings, we detected an up-regulation of the mTOR pathway, concurrent with a downregulation of the autophagic marker LC3B, in ventral midbrain and nigral dopaminergic neurons of the En1<SUP>+/-</SUP> mice. This supports the notion that autophagic protein degradation is reduced in the absence of one En1 allele. We imaged the nigrostriatal pathway using the CLARITY technique and observed many fragmented axons in the medial forebrain bundle of the En1<SUP>+/-</SUP> mice, consistent with axonal maintenance failure. Using in vivo electrochemistry, we found that nigrostriatal terminals in the dorsal striatum were severely deficient in dopamine release and reuptake. Our findings support a progressive retrograde degeneration of En1<SUP>+/-</SUP> nigrostriatal neurons, akin to what is suggested to occur in PD. We suggest that using the En1<SUP>+/-</SUP> mice as a model will provide further key insights into PD pathogenesis, and propose that axon terminal integrity and function can be utilized to estimate dopaminergic neuron health and efficacy of experimental PD therapies.
Supersonically sprayed thermal barrier layers using clay micro-particles
Kim, D.Y.,Lee, J.G.,Joshi, B.,Lee, J.H.,Al-Deyab, S.S.,Yoon, H.G.,Yang, D.R.,Yarin, A.,Yoon, S.S. Elsevier 2016 Applied clay science Vol.120 No.-
<P>Several clay minerals were supersonically sprayed onto flexible substrates to form highly thermally and electrically insulating materials which could be wrapped onto protected surfaces. Among these clay minerals, montmorillonite (Mt) revealed the best thermal insulating properties. (C) 2015 Elsevier B.V. All rights reserved.</P>
Kaur, P.,Shin, M.S.,Sharma, N.,Kaur, N.,Joshi, A.,Chae, S.R.,Park, J.S.,Kang, M.S.,Sekhon, S.S. Pergamon Press ; Elsevier Science Ltd 2015 International journal of hydrogen energy Vol.40 No.3
Carbon based nanomaterials (carbon nanotubes, graphene etc) containing various hetero atoms are promising metal free catalysts for oxygen reduction reaction in fuel cells. We report the non-covalent functionalization of graphene with poly(diallyl dimethylammonium) chloride (PDDA), a polyelectrolyte containing nitrogen, using a very simple method. The addition of a non-ionic surfactant (Triton X-100) during functionalization has been observed to improve the interactions between graphene and PDDA. An up-shift in the position of G-peak in the Raman spectra, down-shift in the binding energy (B.E.) of N1s peak and an up-shift in the B.E. of C1s peak in XPS spectra have been observed due to an inter-molecular charge-transfer from carbon in graphene to nitrogen in PDDA, which get enhanced in the presence of Triton X-100. Graphene functionalized with PDDA also show good thermal stability. The addition of a non-ionic surfactant enhances the non-covalent functionalization of graphene with PDDA, which is desirable from applications point of view.
Yoon, H.,Kim, M.w.,Kim, H.,Kim, D.Y.,An, S.,Lee, J.G.,Joshi, B.N.,Jo, H.S.,Choi, J.,Al-Deyab, S.S.,Yarin, A.L.,Yoon, S.S. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.101 No.-
Several types of nano-textured surfaces were studied with the goal to enhance heat removal rate in a cooling device (a heat sink) with water flow-through. The nano-textured surfaces where heat removal to flowing water took place included: (i) electrospun copper-plated thorny-devil nanofibers deposited on the copper substrate, (ii) graphene oxide flakes sprayed on the copper substrate, and (iii) silver nanowires spin-coated on a separate copper substrate. Their cooling performance was monitored by measuring the difference between the outlet and inlet temperature of water flowing through the heat sink and the temperature of the nano-textured copper substrate in the heat sink. The effect of the macroscopic vortex generator (wires) on cooling of the heat sink surface was less than that of the nano-textured surfaces, which revealed that the latter provide a much larger interfacial area, rather than an extra flow mixing, to enhance heat transfer rate. Of the nano-textured surfaces the most significant cooling enhancement was achieved with silver nanowires.