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Micro Electrokinetic Flow Meter for Measuring Flow Rates of Buffer Solutions
Dong-Kwon Kim(김동권),Arun Majumdar,Sung Jin Kim(김성진) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Recently, microfluidic systems have received enormous attention for biological analysis such as micro chromatography, biochemical detection. The flow control and monitoring of the buffer solutions are crucial in these microfluidic systems. In the present study, a new concept of a micro flow meter has been developed for measuring the flow rates of buffer solutions. The liquid flow rate through a glass rectangular micro channel was obtained by measuring electrokinetically generated electric signals. A model is presented for which allows for flow rate measurements independent of the cation concentration. Experimental investigations were performed in order to demonstrate the proposed concept. The flow meter was able to measure the flow rate of phosphate buffered saline solutions, which have various concentrations, with error of less than 10%. The electrokinetic flow meter has a linear range that is several orders of magnitude wider than conventional thermal flow meters. This flow meter may be used to monitor and control the liquid flow in micro fluidic systems.
나노구조물 첨가를 이용한 고온에서의 고체 열전도도 감소
김우철(Woochul Kim),김강민(Kangmin Kim),박준영(Junyoung Park),Suzanne L. Singer,Arun Majumdar,Dmitri Klenov,Arthur C. Gossard,Susanne Stemmer,Joshua M. O. Zide 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Thermal conductivity of a crystalline solid at high temperature is dominated by the Umklapp process because the number of high frequency phonons increases as with temperature. It is challenging to reduce the thermal conductivity of crystalline solids at high temperature although it is widely known that by increasing the atomic defect concentration, thermal conductivity of crystalline solids can be reduced at low temperature. By increasing the concentration of ErAs nanoparticles in In0.53Ga0.47 As up to 6 atomic percent, we demonstrate a thermal conductivity reduction by almost a factor of three below that of In0.53Ga0.47 As at high temperature. A theoretical model suggests that the mean free path of the low frequency phonons is suppressed by increasing the ErAs nanoparticle concentration.
임시형(Si-Hyung Lim),임홍재(Hong Jae Yim),아룬 마줌다(Arun Majumdar) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Understanding the interactions between aromatic gas molecules and various simple aromatic receptor molecules is important in developing selective receptors for volatile organic compounds (VOCs). Here, five benzene thiols with different functional end groups were used to investigate the weak binding of aromatic vapors like dinitrotolouene (DNT) and toluene. A multiplexed microcantilever array in conjunction with a very low concentration vapor generation system was developed to study multiple receptor-target interactions simultaneously. Differential nanomechanical responses of such devices provided insight about the influence of various chemical and structural features of such molecules.
Nanowires for enhanced boiling heat transfer.
Chen, Renkun,Lu, Ming-Chang,Srinivasan, Vinod,Wang, Zhijie,Cho, Hyung Hee,Majumdar, Arun American Chemical Society 2009 NANO LETTERS Vol.9 No.2
<P>Boiling is a common mechanism for liquid-vapor phase transition and is widely exploited in power generation and refrigeration devices and systems. The efficacy of boiling heat transfer is characterized by two parameters: (a) heat transfer coefficient (HTC) or the thermal conductance; (b) the critical heat flux (CHF) limit that demarcates the transition from high HTC to very low HTC. While increasing the CHF and the HTC has significant impact on system-level energy efficiency, safety, and cost, their values for water and other heat transfer fluids have essentially remained unchanged for many decades. Here we report that the high surface tension forces offered by liquids in nanowire arrays made of Si and Cu can be exploited to increase both the CHF and the HTC by more than 100%.</P>
The use of poly-cation oxides to lower the temperature of two-step thermochemical water splitting
Zhai, Shang,Rojas, Jimmy,Ahlborg, Nadia,Lim, Kipil,Toney, Michael F.,Jin, Hyungyu,Chueh, William C.,Majumdar, Arun The Royal Society of Chemistry 2018 ENERGY AND ENVIRONMENTAL SCIENCE Vol.11 No.8
<P>We report the discovery of a new class of oxides - poly-cation oxides (PCOs) - that consist of multiple cations and can thermochemically split water in a two-step cycle to produce hydrogen (H2) and oxygen (O2). Specifically, we demonstrate H2 yields of 10.1 ± 0.5 mL-H2 per g and 1.4 ± 0.5 mL-H2 per g from (FeMgCoNi)Ox (<I>x</I> ≈ 1.2) with thermal reduction temperatures of 1300 °C and 1100 °C, respectively, and also with background H2 during the water splitting step. Remarkably, these capacities are mostly higher than those from measurements and thermodynamic analysis of state-of-the-art materials such as (substituted) ceria and spinel ferrites. Such high-performance two-step cycles ≤1100 °C are practically relevant for today's chemical infrastructure at large scale, which relies almost exclusively on thermochemical transformations in this temperature regime. It is likely that PCOs with complex cation compositions will offer new opportunities for both fundamental investigations of redox thermochemistry as well as scalable H2 production using infrastructure-compatible chemical systems.</P>
Selective and Sensitive TNT Sensors Using Biomimetic Polydiacetylene-Coated CNT-FETs
Kim, Tae Hyun,Lee, Byung Yang,Jaworski, Justyn,Yokoyama, Keisuke,Chung, Woo-Jae,Wang, Eddie,Hong, Seunghun,Majumdar, Arun,Lee, Seung-Wuk American Chemical Society 2011 ACS NANO Vol.5 No.4
<P>Miniaturized smart sensors that can perform sensitive and selective real-time monitoring of target analytes are tremendously valuable for various sensing applications. We developed selective nanocoatings by combining trinitrotoluene (TNT) receptors bound to conjugated polydiacetylene (PDA) polymers with single-walled carbon nanotube field-effect transistors (SWNT-FET). Selective binding events between the TNT molecules and phage display derived TNT receptors were effectively transduced to sensitive SWNT-FET conductance sensors through the PDA coating layers. The resulting sensors exhibited an unprecedented 1 fM sensitivity toward TNT in real time, with excellent selectivity over various similar aromatic compounds. Our biomimetic receptor coating approach may be useful for the development of sensitive and selective micro- and nanoelectronic sensor devices for various other target analytes.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-4/nn103324p/production/images/medium/nn-2010-03324p_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn103324p'>ACS Electronic Supporting Info</A></P>
Observation of Anisotropy in Thermal Conductivity of Individual Single-Crystalline Bismuth Nanowires
Roh, Jong Wook,Hippalgaonkar, Kedar,Ham, Jin Hee,Chen, Renkun,Li, Ming Zhi,Ercius, Peter,Majumdar, Arun,Kim, Woochul,Lee, Wooyoung American Chemical Society 2011 ACS NANO Vol.5 No.5
<P>The thermal conductivity of individual single-crystalline Bi nanowires grown by the on-film formation of nanowires (ON–OFF) has been investigated. We observed that the thermal conductivity of single-crystalline Bi nanowires is highly anisotropic. Thermal conductivity of nanowires (diameter ∼100 nm) in the off-axis [1̅02] and [110] directions exhibits a difference of ∼7.0 W/m·K. The thermal conductivity in both growth directions is diameter-dependent, which indicates that thermal transport through the individual Bi nanowires is limited by boundary scattering of both electrons and phonons. This huge anisotropy in thermal conductivities of Bi nanowires suggests the importance of direction-dependent characterization of charge, thermal transport, and thermoelectric properties of Bi nanowires.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-5/nn200474d/production/images/medium/nn-2011-00474d_0006.gif'></P>