Large Magnetoresistance over an Extended Temperature Regime in Monophosphides of Tantalum and Niobium

We report extremely large magnetoresistance (MR) in an extended temperature regime from 1.5 K to 300 K in non-magnetic binary compounds TaP and NbP. TaP exhibits linear MR around $1.8\times 10^4$ at 2 K in a magnetic field of 9 Tesla, which further follows its linearity up to $1.4\times 10^5$ in a magnetic field of 56 Tesla at 1.5 K. At room temperature the MR for TaP and NbP follows a power law of the exponent about $1.5$ with the values larger than $300\%$ in a magnetic field of 9 Tesla. Such large MR in a wide temperature regime is not likely only due to a resonance of the electron-hole balance, but indicates a complicated mechanism underneath.Comment: 13 pages, 4 figures; submitted in May 20, 2015; accepted for publicatio

Investigating behaviour of concrete at elevated temperatures

Concrete is one of the most widely used construction materials in the world and it provides superior fire resistance in comparison to other construction materials such as timber and steel. However, the outer walls of high-rise concrete buildings are often covered by foam insulation material and rooms are full of other flammable materials; these have resulted in damage and destruction of concrete structures due to fires in the past. Concrete behaviour at elevated temperatures changes drastically from that at ambient temperature and comprises of several complex thermomechanical responses. The primary aim of this study is to understand how concrete behaves under load and temperature. This study includes experimental work and computer simulation. The study evaluates mechanical behaviour of concrete due to heating and loading. Two series of tests are conducted: those in which heated samples are subjected to loading, load holding, unloading and recovery; and those in which loaded samples are subjected to heating, maintenance of constant temperature, unloading and recovery. Different strain components, free thermal strain, instantaneous stress-related strain, time-dependent creep strain and load induced thermal strain are evaluated and analysed. The experimental work uses digital image correlation to evaluate strains. By analysing the photos taken during the experiment, the value of strain is evaluated. The method of post-processing photos is found to be a simple and inexpensive way to evaluate strains at elevated temperatures. This study evaluates the transient temperature distribution under different heating rates and heating time. As the material with a low thermal conductivity, the thermal gradients increase within concrete at larger heating rates. The differential expansion with the thermal gradients can result in damage to concrete. The heat transfer analysis is conducted to find the most efficient and reasonable heating rates for experiments in order to prevent damage due to differential thermal expansion. Also, the heat transfer analysis shows the chamber temperature needs to be maintained constant for 2 hrs to achieve uniform temperature in the concrete for the size of samples considered. This study develops a method to simulate time-dependent creep using viscoelasticity with Prony series; this provides a simple way to model time-dependent creep. The parameters are evaluated through curve fitting in MATLAB. Then, the parameters are used in finite element analysis for defining viscoelastic material in ABAQUS. The simulation results fit the experimental data well. This study examines the components of load induced thermal strain (LITS). As one of the largest strain components at elevated temperatures, LITS is usually treated as plastic strain and irrecoverable during the first heating. The experiments show that LITS is only partly irrecoverable

Exotic Superconducting Properties in Topological Nodal Semimetal PbTaSe2_2

We report the electronic properties of superconductivity in the topological nodal-line semimetal PbTaSe$_2$. Angle-resolved photoemission measurements accompanied by band calculations confirmed the nodal-line band structure in the normal state of single crystalline PbTaSe$_2$. Resistivity, magnetic-susceptibility and specific heat measurements have also been performed on high-quality single crystals. We observed upward features and large anisotropy in upper critical field ($H_{c2}$) measured in-plane (H//\textbf{ab}) and out-plane (H//\textbf{c}), respectively. Especially, $H_{c2}$ measured in H//\textbf{ab} shows sudden upward features rather than a signal of saturation in ultralow temperatures. The specific heat measurements under magnetic field reveal a full superconducting gap with no gapless nodes. These behaviors in this clean noncentrosymmetric superconductor is possibly related to the underlying exotic physics, providing important clue for realization of topological superconductivity.Comment: 6 pages, 5 figures,1 table;Accepted for publication on PR

Divergence in function and expression of the NOD26-like intrinsic proteins in plants

<p>Abstract</p> <p>Background</p> <p>NOD26-like intrinsic proteins (NIPs) that belong to the aquaporin superfamily are plant-specific and exhibit a similar three-dimensional structure. Experimental evidences however revealed that functional divergence should have extensively occurred among NIP genes. It is therefore intriguing to further investigate the evolutionary mechanisms being responsible for the functional diversification of the NIP genes. To better understand this process, a comprehensive analysis including the phylogenetic, positive selection, functional divergence, and transcriptional analysis was carried out.</p> <p>Results</p> <p>The origination of NIPs could be dated back to the primitive land plants, and their diversification would be no younger than the emergence time of the moss <it>P. patens</it>. The rapid proliferation of NIPs in plants may be primarily attributed to the segmental chromosome duplication produced by polyploidy and tandem duplications. The maximum likelihood analysis revealed that <it>NIPs </it>should have experienced strong selective pressure for adaptive evolution after gene duplication and/or speciation, prompting the formation of distinct <it>NIP </it>groups. Functional divergence analysis at the amino acid level has provided strong statistical evidence for shifted evolutionary rate and/or radical change of the physiochemical properties of amino acids after gene duplication, and DIVERGE2 has identified the critical amino acid sites that are thought to be responsible for the divergence for further investigation. The expression of plant NIPs displays a distinct tissue-, cell-type-, and developmental specific pattern, and their responses to various stress treatments are quite different also. The differences in organization of <it>cis</it>-acting regulatory elements in the promoter regions may partially explain their distinction in expression.</p> <p>Conclusion</p> <p>A number of analyses both at the DNA and amino acid sequence levels have provided strong evidences that plant NIPs have suffered a high divergence in function and expression during evolution, which is primarily attributed to the strong positive selection or a rapid change of evolutionary rate and/or physiochemical properties of some critical amino acid sites.</p