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Zhengcai Zhang, Guang-Jun Guo
Although ice powders are widely used in gas hydrate formation experiments, the effects of ice on hydrate nucleation and what happens in the quasi-liquid layer of ice are still not well understood. Here, we used high-precision constant energy molecular dynamics simulations to study methane hydrate nucleation from vapor-liquid mixtures exposed to the basal, prismatic, and secondary prismatic planes of hexagonal ice (ice Ih). Although no significant difference is observed in hydrate nucleation processes for these different crystal planes, it is found, more interestingly, that methane hydrate can nucleate either on the ice surface heterogeneously or in the bulk solution phase homogeneously...
July 18, 2017: Physical Chemistry Chemical Physics: PCCP
Xiaoliang Zeng, Yucheng Xiong, Qiang Fu, Rong Sun, Jianbin Xu, Dongyan Xu, Ching-Ping Wong
The ability to control thermal conductivity is important in a wide variety of applications, especially in heat removal, heat insulation, and thermoelectric energy conversion. Herein, we reveal that the thermal conductivity of epoxy resin fibers increases on decreasing the fiber diameter and surpasses the bulk value (0.25 W m(-1) K(-1) at 300 K) for the fiber with a diameter of 211 nm. The variation of thermal conductivity in epoxy resin fibers can likely be attributed to their microstructure change-enhanced interface phonon scattering between amorphous and crystalline regions and the enhanced alignment of the molecular chain orientation...
July 17, 2017: Nanoscale
Jian-Qiang Zhong, Mengen Wang, Nusnin Akter, John D Kestell, Alejandro M Boscoboinik, Taejin Kim, Dario J Stacchiola, Deyu Lu, J Anibal Boscoboinik
The confinement of noble gases on nanostructured surfaces, in contrast to bulk materials, at non-cryogenic temperatures represents a formidable challenge. In this work, individual Ar atoms are trapped at 300 K in nano-cages consisting of (alumino)silicate hexagonal prisms forming a two-dimensional array on a planar surface. The trapping of Ar atoms is detected in situ using synchrotron-based ambient pressure X-ray photoelectron spectroscopy. The atoms remain in the cages upon heating to 400 K. The trapping and release of Ar is studied combining surface science methods and density functional theory calculations...
July 17, 2017: Nature Communications
Sanjay Kumar Upadhyay, Kartik K Iyer, E V Sampathkumaran
We report the magnetic behavior of two intermetallic-based kagome lattices, Tb3Ru4Al12 and Er3Ru4Al12, crystallizing in the Gd3Ru4Al2-type hexagonal crystal structure, by measurements in the range 1.8-300 K with bulk experimental techniques (ac and dc magnetization, heat capacity, and magnetoresistance). The main finding is that the Tb compound, known to order antiferromagnetically below (T N =) 22 K, shows glassy characteristics at lower temperatures ([Formula: see text]15 K), thus characterizing this compound as a re-entrant spin-glass...
July 17, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Daolun Feng, Ying Liu, Yi Gao, Jinxing Zhou, Lirong Zheng, Gang Qiao, Liming Ma, Zhifen Lin, Peter Grathwohl
Atmospheric deposition leads to accumulation of atmospheric polycyclic aromatic hydrocarbons (PAHs) on urban surfaces and topsoils. To capture the inherent variability of atmospheric deposition of PAHs in Shanghai's urban agglomeration, 85 atmospheric bulk deposition samples and 7 surface soil samples were collected from seven sampling locations during 2012-2014. Total fluxes of 17 PAHs were 587-32,300 ng m(-2) day(-1), with a geometric mean of 2600 ng m(-2) day(-1). The deposition fluxes were categorized as moderate to high on a global scale...
July 13, 2017: Environmental Pollution
Saumyak Mukherjee, Sayantan Mondal, Biman Bagchi
Since the pioneering works of Pethig, Grant, and Wüthrich on a protein hydration layer, many studies have been devoted to find out if there are any "general and universal" characteristic features that can distinguish water molecules inside the protein hydration layer from bulk. Given that the surface itself varies from protein to protein, and that each surface facing the water is heterogeneous, search for universal features has been elusive. Here, we perform an atomistic molecular dynamics simulation in order to propose and demonstrate that such defining characteristics can emerge if we look not at average properties but the distribution of relaxation times...
July 14, 2017: Journal of Chemical Physics
Christoph Schick, R Androsch, Juern W P Schmelzer
The pathway of crystal nucleation significantly influences the structure and properties of semi-crystalline polymers. Crystal nucleation is normally heterogeneous at low supercooling, and homogeneous at high supercooling, of the polymer melt. Homogeneous nucleation in bulk polymers has been, so far, hardly accessible experimentally, and was even doubted to occur at all. This topical review summarizes experimental findings on homogeneous crystal nucleation in polymers. Recently developed fast scanning calorimetry, with cooling and heating rates up to 106 K s-1, allows for detailed investigations of nucleation near and even below the glass transition temperature, including analysis of nuclei stability...
July 14, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Mahdi Shirazi, Annemie Bogaerts, Erik C Neyts
In this study, we investigated the diffusion of H-atoms to the subsurface and their further diffusion into the bulk of a Ni(111) crystal by means of density functional theory calculations in the context of thermal and plasma-assisted catalysis. The H-atoms at the surface can originate from the dissociative adsorption of H2 or CH4 molecules, determining the surface H-coverage. When a threshold H-coverage is passed, corresponding to 1.00 ML for the crystalline Ni(111) surface, the surface-bound H-atoms start to diffuse to the subsurface...
July 12, 2017: Physical Chemistry Chemical Physics: PCCP
Hyunsoo Lee, Jae-Hyeon Ko, Jin Sik Choi, Jin Heui Hwang, Yong-Hyun Kim, Miquel B Salmeron, Jeong Young Park
Common experience shows that friction converts mechanical energy into heat. The first part of this process is the vibrational excitation of the atoms at the interface between the rubbing bodies. The second and necessary part is the effective removal of this vibration energy by transfer from the contact region to the bulk substrate. A fundamental understanding of these phenomena is important for the design of improved tribological contact; however, this is difficult because excitation and dissipation are usually intimately entangled processes...
July 11, 2017: Journal of Physical Chemistry Letters
Paula Kayser, Sean Injac, Ben Ranjbar, Brendan J Kennedy, Maxim Avdeev, Kazunari Yamaura
Ruthenium-containing double perovskites A2ScRuO6 have been synthesized as polycrystalline powders and structurally characterized using a combination of synchrotron X-ray and neutron powder diffraction methods. When A = Ba, a hexagonal 6L perovskite structure is obtained if the synthesis is conducted at ambient pressure and a rock-salt ordered cubic structure is obtained if the sample is quenched from high pressures. The Sr oxide Sr2ScRuO6 is obtained with a rock-salt ordered corner sharing topology. Heat capacity and bulk magnetic susceptibility measurements show that the three oxides are antiferromagnets...
July 10, 2017: Inorganic Chemistry
Lixin Wang, Thomas Barclay, Yunmei Song, Paul Joyce, Isaac G Sakala, Nikolai Petrovsky, Sanjay Garg
Insoluble, nanostructured delta inulin particles enhance the immunogenicity of co-administered protein antigens and consequently are used as a vaccine adjuvant (Advax™). To better understand their immunomodulatory properties, the in vitro hydrolysis and in vivo distribution of delta inulin particles were investigated. Delta inulin particle hydrolysis under bio-relevant acidic conditions resulted in no observable change to the bulk morphology using SEM, and HPLC results showed that only 6.1% of the inulin was hydrolysed over 21days...
July 1, 2017: Vaccine
Zahra Besharat, Joakim Halldin Stenlid, Markus Soldemo, Kess Marks, Anneli Önsten, Magnus Johnson, Henrik Öström, Jonas Weissenrieder, Tore Brinck, Mats Göthelid
Adsorption and desorption of methanol on the (111) and (100) surfaces of Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120-620 K, in combination with density functional theory calculations and sum frequency generation spectroscopy. The bare (100) surface exhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface...
June 28, 2017: Journal of Chemical Physics
N Tao, X L Li, J G Sun
Thermal properties are important for material applications involved with temperature. Although many measurement methods are available, they may not be convenient to use or have not been demonstrated suitable for testing of a wide range of materials. To address this issue, we developed a new method for the nondestructive measurement of the thermal effusivity of bulk materials with uniform property. This method is based on the pulsed thermal imaging-multilayer analysis (PTI-MLA) method that has been commonly used for testing of coating materials...
June 2017: Review of Scientific Instruments
Yunshan Zhao, Dan Liu, Jie Chen, Liyan Zhu, Alex Belianinov, Olga S Ovchinnikova, Raymond R Unocic, Matthew J Burch, Songkil Kim, Hanfang Hao, Daniel S Pickard, Baowen Li, John T L Thong
The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking. While this could be achieved by making use of composites and metamaterials at bulk length-scales, engineering the thermal conductivity at micro- and nano-scale dimensions is considerably more challenging. In this work, we show that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose...
June 27, 2017: Nature Communications
Camelia V Stan, Rajkrishna Dutta, Robert J Cava, Vitali B Prakapenka, Thomas S Duffy
The effect of incorporation of Fe(2+) on the perovskite (Pbnm) and postperovskite (Cmcm) structures was investigated in the (Mg,Fe)GeO3 system at high pressures and temperatures using laser-heated diamond anvil cell and synchrotron X-ray diffraction. Samples with compositions of Mg# ≥ 48 were shown to transform to the perovskite (∼30 GPa and ∼1500 K) and postperovskite (>55 GPa, ∼1600-1800 K) structures. Compositions with Mg# ≥ 78 formed single-phase perovskite and postperovskite, whereas those with Mg# < 78 showed evidence for partial decomposition...
July 17, 2017: Inorganic Chemistry
Lijun Wang, Siyi Chang, Shuqi Zheng, Teng Fang, Wenlin Cui, Peng-Peng Bai, Luo Yue, Zhi-Gang Chen
Extensive attention has been focused on thermoelectric performance optimization of SnTe because of its potential in waste heat recovery. Here, we fabricate high thermoelectric performance Se/Cd codoped SnTe octahedral particles by microwave-stimulated solvothermal method. The SnTe-based octahedral particles have sizes ranging from several micrometers to hundreds of nanometers, forming dense bulks after spark plasma sintering. Combined with the strong point defect scattering by Se and Cd dopants, a low thermal conductivity of 1...
July 12, 2017: ACS Applied Materials & Interfaces
Samira Shiri, James C Bird
The ability to enhance or limit heat transfer between a surface and impacting drops is important in applications ranging from industrial spray cooling to the thermal regulation of animals in cold rain. When these surfaces are micro/nanotextured and hydrophobic, or superhydrophobic, an impacting drop can spread and recoil over trapped air pockets so quickly that it can completely bounce off the surface. It is expected that this short contact time limits heat transfer; however, the amount of heat exchanged and precise role of various parameters, such as the drop size, are unknown...
June 19, 2017: Proceedings of the National Academy of Sciences of the United States of America
U Stockert, R D Dos Reis, M O Ajeesh, S J Watzman, M Schmidt, C Shekhar, J P Heremans, C Felser, M Baenitz, M Nicklas
The Weyl semimetal NbP exhibits an extremely large magnetoresistance and an ultra-high mobility. The large magnetoresistance originates from a combination of the nearly perfect compensation between electron- and hole-type charge carriers and the high mobility, which is relevant to the topological band structure. In this work we report on temperature- and field-dependent thermopower and thermal conductivity experiments on NbP. Additionally, we carried out complementary heat capacity, magnetization, and electrical resistivity measurements...
June 19, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Margarita Albertí, Anna Amat, Antonio Aguilar, Fernando Pirani
The present paper focuses on the characterization of the properties of methanol and water molecules in gas and liquid environments. A force field for methanol-methanol and methanol-water interactions, useful to be applied in Molecular Dynamics (MD) simulations, is proposed. The electrostatic interaction contributions, arising from permanent charge and/or from anisotropic charge distributions originating from permanent electric multipoles (Vel), different in gas and in liquid phases, are combined with the non electrostatic ones (Vnel), defined by means of Improved Lennard-Jones (ILJ) functions [F...
June 28, 2017: Physical Chemistry Chemical Physics: PCCP
Cheng-Hua Lee, Dmitriy V Soldatov, Chung-Hao Tzeng, Long-Li Lai, Kuang-Lieh Lu
Three dendrimers, (t-Bu-G 2 N) 2 , CC(t-Bu-G 1 N) 3 and (t-Bu-G 1 N) 2 , with 3,5-di-tert-butyl amidobenzene as a common peripheral moiety were prepared in 64-83% yields and characterized. The bulk solids had high BET surface areas of 136-138 m(2)/g, which were similar for the three dendrimers in spite of their different molecular weight (ranging from 1791 to 2890). It was concluded that the peripheral amide groups do not imbed in the interstitial space of neighbouring dendrimer molecules but rather build a supramolecular architecture through strong intermolecular H-bonds...
June 16, 2017: Scientific Reports
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