333 research outputs found
The effect of chemistry and thermal fluctuations on charge injection barriers at aluminum/polyolefin interfaces
Charge injection at metal/polymer interfaces is a critical process in many technological devices, including high voltage capacitors and cables in which polyolefin materials, such as polyethylene (PE) and polypropylene (PP), are often used as insulation materials. We use simulations based on density-functional theory to study charge injection at aluminum/PE and aluminum/PP interfaces. Specifically, we investigate the influence of incorporating a variety of polar chemical impurities at the PE and PP chain ends on electron and hole injection barriers. Crucially, we account for the effect of thermal disorder by considering ensembles of thousands of interface structures obtained from ab initio molecular dynamics trajectories at 373 K. We show that the mean injection barrier can change by up to 1.1 eV for Al/PE and 0.6 eV for Al/PP, as compared to the pristine case, depending on which chemical impurity is introduced. We also show that the spread of injection barriers from thermal fluctuations also depends strongly on the chemistry of the impurity. The observed trends can be understood with a simple model based on thermal fluctuations of the dipole moment density associated with the chemical impurity at the interface. We further verify this model by considering larger interface models with lower impurity densities. Our results demonstrate that small chemical modifications, which may arise from oxidation, for example, have a significant influence on charge injection barriers in metal/polyolefin interfaces
Survey of chemical manure on morphological traits in Iranian Aloe vera
This experiment was conducted at the Institute of National Genetic Engineering and Biotechnology in Iran to evaluate the effect of different amount of fertilizers on the leaf and plant characteristics, as well as the yield characteristics of Aloe vera. There were 6 different treatments viz., T1 = 100% soil (control), T2 = 100 PK (50% P + 50% K), T3 = 50% K + 50% soil, T4 = 50% N + 50% soil, T5 = 150% NPK (50% N + 50% P + 50% K), T6 = 50% P + 50% soil. It was observed that the plant produced the highest mature leaf length and number of tillers plant-1 and maximum leaf weight as well as maximum weight of largest leaves with the application of 50% P + 50% K (T2). Different plant characters such as mature leaf breadth and breadth of the largest leaf was also found to be high with T5 treatment when compared with the control (100% soil). The number of leaves was also significantly affected by different fertilizer treatments where the maximum effect was noticed at early stages with T4 (50% N). It was revealed that T3 had a little effect on the number of leaves of A. vera over chemical fertilizer.Key words: Aloe vera, fertilizer, morphological traits, leaf growth
The Antiquity of the Avesta
Paper read before the Bombay Branch of the Royal Asiatic Society, read 26th June 1896. Dr. Gerson Da Cunha in the Chair
First-principles study on the origin of large thermopower in hole-doped LaRhO3 and CuRhO2
Based on first-principles calculations, we study the origin of the large
thermopower in Ni-doped LaRhO3 and Mg-doped CuRhO2. We calculate the band
structure and construct the maximally localized Wannier functions from which a
tight binding Hamiltonian is obtained. The Seebeck coefficient is calculated
within the Boltzmann's equation approach using this effective Hamiltonian. For
LaRhO3, we find that the Seebeck coefficient remains nearly constant within a
large hole concentration range, which is consistent with the experimental
observation. For CuRhO2, the overall temperature dependence of the calculated
Seebeck coefficient is in excellent agreement with the experiment. The origin
of the large thermopower is discussed.Comment: 7 pages, to be published J. Phys.: Cond. Matt., Proc. QSD 200
Robotic Wireless Sensor Networks
In this chapter, we present a literature survey of an emerging, cutting-edge,
and multi-disciplinary field of research at the intersection of Robotics and
Wireless Sensor Networks (WSN) which we refer to as Robotic Wireless Sensor
Networks (RWSN). We define a RWSN as an autonomous networked multi-robot system
that aims to achieve certain sensing goals while meeting and maintaining
certain communication performance requirements, through cooperative control,
learning and adaptation. While both of the component areas, i.e., Robotics and
WSN, are very well-known and well-explored, there exist a whole set of new
opportunities and research directions at the intersection of these two fields
which are relatively or even completely unexplored. One such example would be
the use of a set of robotic routers to set up a temporary communication path
between a sender and a receiver that uses the controlled mobility to the
advantage of packet routing. We find that there exist only a limited number of
articles to be directly categorized as RWSN related works whereas there exist a
range of articles in the robotics and the WSN literature that are also relevant
to this new field of research. To connect the dots, we first identify the core
problems and research trends related to RWSN such as connectivity,
localization, routing, and robust flow of information. Next, we classify the
existing research on RWSN as well as the relevant state-of-the-arts from
robotics and WSN community according to the problems and trends identified in
the first step. Lastly, we analyze what is missing in the existing literature,
and identify topics that require more research attention in the future
Half-metallic Antiferromagnet BaCrFeAs2
First-principles calculations and a tight-binding analysis predict that the
iron-pnictide BaCrFeAs2 is a promising candidate for half-metallic material
with fully-compensated magnetization. The transition-metal ions Cr and Fe
prefer the three-dimensional intervening lattice, which yields the
antiferromagnetic order of spin orientations. Due to the difference between Cr
and Fe in the electronegativity, a band gap is opened at the Fermi level in the
spin channel in which Fe provides the majority carriers. The selective
hybridization between 3d orbitals of Cr and As:4p states due to the peculiar
lattice structure of the iron-pnictide is shown to be crucial for the novel
properties.Comment: added reference
Emergence of non-centrosymmetric topological insulating phase in BiTeI under pressure
The spin-orbit interaction affects the electronic structure of solids in
various ways. Topological insulators are one example where the spin-orbit
interaction leads the bulk bands to have a non-trivial topology, observable as
gapless surface or edge states. Another example is the Rashba effect, which
lifts the electron-spin degeneracy as a consequence of spin-orbit interaction
under broken inversion symmetry. It is of particular importance to know how
these two effects, i.e. the non-trivial topology of electronic states and
Rashba spin splitting, interplay with each other. Here we show, through
sophisticated first-principles calculations, that BiTeI, a giant bulk Rashba
semiconductor, turns into a topological insulator under a reasonable pressure.
This material is shown to exhibit several unique features such as, a highly
pressure-tunable giant Rashba spin splitting, an unusual pressure-induced
quantum phase transition, and more importantly the formation of strikingly
different Dirac surface states at opposite sides of the material.Comment: 5 figures are include
wannier90: A tool for obtaining maximally-localised Wannier functions
We present Wannier90, a program for calculating maximally-localised Wannier
functions (MLWF) from a set of Bloch energy bands that may or may not be
attached to or mixed with other bands. The formalism works by minimising the
total spread of the MLWF in real space. This done in the space of unitary
matrices that describe rotations of the Bloch bands at each k-point. As a
result, Wannier90 is independent of the basis set used in the underlying
calculation to obtain the Bloch states. Therefore, it may be interfaced
straightforwardly to any electronic structure code. The locality of MLWF can be
exploited to compute band-structure, density of states and Fermi surfaces at
modest computational cost. Furthermore, Wannier90 is able to output MLWF for
visualisation and other post-processing purposes. Wannier functions are already
used in a wide variety of applications. These include analysis of chemical
bonding in real space; calculation of dielectric properties via the modern
theory of polarisation; and as an accurate and minimal basis set in the
construction of model Hamiltonians for large-scale systems, in linear-scaling
quantum Monte Carlo calculations, and for efficient computation of material
properties, such as the anomalous Hall coefficient. Wannier90 is freely
available under the GNU General Public License from http://www.wannier.org/Comment: Submitted to Computer Physics Communication
Emergent quantum confinement at topological insulator surfaces
Bismuth-chalchogenides are model examples of three-dimensional topological
insulators. Their ideal bulk-truncated surface hosts a single spin-helical
surface state, which is the simplest possible surface electronic structure
allowed by their non-trivial topology. They are therefore widely
regarded ideal templates to realize the predicted exotic phenomena and
applications of this topological surface state. However, real surfaces of such
compounds, even if kept in ultra-high vacuum, rapidly develop a much more
complex electronic structure whose origin and properties have proved
controversial. Here, we demonstrate that a conceptually simple model,
implementing a semiconductor-like band bending in a parameter-free
tight-binding supercell calculation, can quantitatively explain the entire
measured hierarchy of electronic states. In combination with circular dichroism
in angle-resolved photoemission (ARPES) experiments, we further uncover a rich
three-dimensional spin texture of this surface electronic system, resulting
from the non-trivial topology of the bulk band structure. Moreover, our study
reveals how the full surface-bulk connectivity in topological insulators is
modified by quantum confinement.Comment: 9 pages, including supplementary information, 4+4 figures. A high
resolution version is available at
http://www.st-andrews.ac.uk/~pdk6/pub_files/TI_quant_conf_high_res.pd
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