A Dynamic 6,000-Year Genetic History of Eurasia's Eastern Steppe

The Eastern Eurasian Steppe was home to historic empires of nomadic pastoralists, including the Xiongnu and the Mongols. However, little is known about the region's population history. Here, we reveal its dynamic genetic history by analyzing new genome-wide data for 214 ancient individuals spanning 6,000 years. We identify a pastoralist expansion into Mongolia ca. 3000 BCE, and by the Late Bronze Age, Mongolian populations were biogeographically structured into three distinct groups, all practicing dairy pastoralism regardless of ancestry. The Xiongnu emerged from the mixing of these populations and those from surrounding regions. By comparison, the Mongols exhibit much higher eastern Eurasian ancestry, resembling present-day Mongolic-speaking populations. Our results illuminate the complex interplay between genetic, sociopolitical, and cultural changes on the Eastern Steppe

Effect of the collision medium size on thermal performance of silver nanoparticles based aqueous nanofluids

The present paper describes an influence of different ball sizes (1 mm, 3 mm and 5 mm) of the planetary ball milling machine on the thermal conductivity characteristics of silver-based aqueous nanofluids. Nano-metric silver dispersed water based nanofluids with various loadings (1 wt%, 2 wt% and 3 wt%) have been prepared by a single-step approach. It has been observed that the ground silver nanoparticles suspended in conventional fluids have superior thermal conductivity performance mainly due to flattened particles and/or increased aspect ratio. The silver particles present in colloidal phase have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy, particle sizing system (PSS) and zeta potential measurements. The stability as well as thermal conductivity of these nanofluids have been measured at wavelength ranging from 300 to 800 nm and at temperature ranging 20-40 C, respectively. As a result, the silver nanoparticles ground by 1 mm ball size that dispersed in aqueous solution (1 wt%) is showed highest thermal conductivity (621 W/mk) which was greater than that of the nanofluids prepared by other conditions, at a temperature of 40 C. A significant trends in the thermal conductivity of nanofluids are attributed to several specific reasons which have been discussed in this article

Effect of functionalized MWCNTs/water nanofluids on thermal resistance and pressure fluctuation characteristics in oscillating heat pipe

An influence of multi-walled carbon nanotube (MWCNT) based aqueous nanofluids with different concentrations on the heat transport and the relevant pressure distribution in oscillating heat pipe (OHP) has been investigated. The present paper describes the heat transfer phenomena in terms of thermal resistance, pressure and frequency of pressure fluctuation in multi-loop oscillating heat pipe (OHP) charged by aqueous nanofluids with MWCNT loadings of 0.05 wt.%, 0.1 wt.%, 0.2 wt.% and 0.3 wt.%. The multi-loop OHP with 3 mm inner diameter has been conducted in the experiment at 60% filling ratio. Experimental results show that thermal characteristics are significantly inter-related with pressure distribution and strongly depend upon the number of pressure fluctuations with time. The investigation shows that the 0.2 wt.% MWCNTs based aqueous nanofluids obtain maximum number of the fluctuation frequency and low thermal resistance at any evaporator power input. Based on the experimental results, we discuss the reasons for enhancement and decrement of thermal characteristics of the nanofluids.Md. Riyad Tanshen, B. Munkhbayar, Md. J. Nine, Hanshik Chung, Hyomin Jeon

Effect of N719–dye adsorption into composition of different sized TiO<SUB>2</SUB> films for photovoltaic performance of the dye-sensitized solar cells

Effect of N719-dye adsorption into TiO films prepared via incorporating small (~15 nm) and large (~300 nm) TiO nanoparticles at several ratios were investigated to improve the photovoltaic efficiency of dye-sensitized solar cell. The photovoltaic efficiency is significantly improved after incorporation of large and small TiO nanoparticles. From experimental result, the composition with 70% small: 30% large TiO is found as an optimum mixing ratio for the best performance (5.57%) of a dye-sensitized solar cell. This high photovoltaic performance is attributed to an effect of following factors. Besides an increase in dye molecules adsorption, the light scattering of over layer large TiO enhances harvesting light of the solar cells and the under layer small TiO ensures good electronic contact between film electrode and the fluorine-doped tin oxide glass substrate. However, we found that the composition with 50% small: 50% large TiO was adsorbed much more N719-dye molecule than that of the other mixtures of TiO and hence resulting in a decrease photovoltaic performance. This decrement of performance may be attributed to the decreased surface area and dye aggregation

Effects of macro and micro roughness in forced convective heat transfer

The article reports a comparative study of macro and micro type artificial roughness in convective heat transfer performance under laminar and low turbulent regime. Circular ribs with different rib height to channel height ratios (e/H = 0.05, 0.1, 0.15) fabricated on copper substrate are introduced as macro type roughness whereas copper (Cu) nano-porous layer (avg. thickness about 5 μm) is considered as micro roughness. Surface heat transfer and friction characteristics are investigated under different scale roughnesses on one principle wall of a rectangular channel having an aspect ratio (AR) of 7.5. Result shows that the average turbulence intensity between two ribs decreases with decreasing roughness height. On the other hand, nano-porous layer provides significant heat transfer efficiency (about maximum 42% more than bare copper plate) under laminar and lowturbulent region without inducing significant turbulence into the channel. Nano-porous layer less than 5 μm is found to increase heat transfer surface area significantly that influences the dynamic behaviors of working fluids in the vicinity of heat transfer wall

Highly productive synthesis process of well dispersed Cu(2)O and Cu/Cu(2)O nanoparticles and its thermal characterization

Abstract not availableMd.J. Nine, B. Munkhbayar, M.Sq. Rahman, Hanshik Chung, Hyomin Jeon

Surfactant-free dispersion of silver nanoparticles into MWCNT-aqueous nanofluids prepared by one-step technique and their thermal characteristics

This paper reports a significant enhancement in the thermal conductivity of silver-nanoparticle-based aqueous nanofluids with the addition of negligible amounts of multi-walled carbon nanotubes (MWCNTs). The present work was conducted using purified MWCNTs/water nanofluids prepared by a wet grinding method. Silver nanoparticles were dispersed into the MWCNT/water nanofluids via a one-step method using pulse power evaporation, which was observed to improve the dispersibility and thermal conductivity of the nanofluids. A particle sizing system (PSS) and transmission electron microscopy (TEM) were used to confirm the size of silver nanoparticles in base fluids. The PSS measurement results reveal that the size of the silver nanoparticles was approximately 100 nm, which is in good agreement with the results obtained from TEM and SEM. The maximum absorbance (2.506 abs at a wavelength of 264 nm) and highest thermal conductivity enhancement (14.5% at 40 °C) were achieved by a fluid containing '0.05 wt% MWCNTs-3 wt% Ag' composite

An experimental study of the planetary ball milling effect on dispersibility and thermal conductivity of MWCNTs-based aqueous nanofluids

The present study conducted two different structures, namely raw and acid oxidized multi-walled carbon nanotubes (MWCNTs) were ground under wet condition at various rotation speeds (300-600 rpm). The ground MWCNTs were dispersed in aqueous solution by ultrasonication was investigated. The particle size analyzer reveals the agglomerated size of raw MWCNTs ground at a rotation speed of 300 rpm was 69.2 μm. Nevertheless, the agglomerated size of particle significantly decreased to 13.2 μm after grinding at a rotation speed of 600 rpm. The maximum absorbance (4.0 abs at a wavelength of 300 nm) and highest thermal conductivity enhancement (18.12% at 40°C) of suspensions correspond to the grinding speed of 600 rpm assisted by ultrasonication dispersion of the purified and raw structures, respectively. It is found that the grinding method with high rotation speed plays can be significantly increased both the dispersibility and thermal conductivity of raw and purified MWCNTs nanofluids

Experimental investigation of the mechanical grinding effect on graphene structure

Graphene has been proven to be a promising material for various applications due to its outstanding chemical, physical, optical as well as mechanical properties. To further improve these properties of graphene, here we apply a grinding method with various speeds (100–600 rpm) of a planetary ball mill under wet conditions in graphene based aqueous solution. Therefore, the improvements in dispersion and thermal characteristics of the graphene–water solution were investigated based on the morphological and structural changes. The best dispersibility and highest thermal conductivity of graphene–water solution were observed for a grinding speed of 500 rpm. As a result, the grinding speed of 500 rpm is found as the optimum condition of planetary ball milling in the case study. The reason for the grinding speed of 500 rpm revealing the best condition is attributed to the reduced ratio (/D//G=0.221)of the D band and the G band in Raman spectroscopy. We believe that structurally upgraded graphene in this study would greatly improve the performance of the graphene based devices.Munkhshur Myekhlai, B. Munkhbayar, Taejin Lee, Md. Riyad Tanshen, Hanshik Chung and Hyomin Jeon

Gas-Phase Rate Coefficients for the OH + <i>n</i>‑, <i>i</i>‑, <i>s</i>‑, and <i>t</i>‑Butanol Reactions Measured Between 220 and 380 K: Non-Arrhenius Behavior and Site-Specific Reactivity

Butanol (C₄H₉OH) is a potential biofuel alternative in fossil fuel gasoline and diesel formulations. The usage of butanol would necessarily lead to direct emissions into the atmosphere; thus, an understanding of its atmospheric processing and environmental impact is desired. Reaction with the OH radical is expected to be the predominant atmospheric removal process for the four aliphatic isomers of butanol. In this work, rate coefficients, <i>k</i>, for the gas-phase reaction of the <i>n-</i>, <i>i</i>-, <i>s</i>-, and <i>t</i>-butanol isomers with the OH radical were measured under pseudo-first-order conditions in OH using pulsed laser photolysis to produce OH radicals and laser induced fluorescence to monitor its temporal profile. Rate coefficients were measured over the temperature range 221–381 K at total pressures between 50 and 200 Torr (He). The reactions exhibited non-Arrhenius behavior over this temperature range and no dependence on total pressure with <i>k</i>(296 K) values of (9.68 ± 0.75), (9.72 ± 0.72), (8.88 ± 0.69), and (1.04 ± 0.08) (in units of 10^–12 cm³ molecule^–1 s^–1) for <i>n-</i>, <i>i</i>-, <i>s</i>-, and <i>t</i>-butanol, respectively. The quoted uncertainties are at the 2σ level and include estimated systematic errors. The observed non-Arrhenius behavior is interpreted here to result from a competition between the available H-atom abstraction reactive sites, which have different activation energies and pre-exponential factors. The present results are compared with results from previous kinetic studies, structure–activity relationships (SARs), and theoretical calculations and the discrepancies are discussed. Results from this work were combined with available high temperature (1200–1800 K) rate coefficient data and room temperature reaction end-product yields, where available, to derive a self-consistent site-specific set of reaction rate coefficients of the form <i>AT</i>^<i>n</i> exp­(−<i>E</i>/<i>RT</i>) for use in atmospheric and combustion chemistry modeling