3,227 research outputs found
Distributed Optimization in Energy Harvesting Sensor Networks with Dynamic In-network Data Processing
Energy Harvesting Wireless Sensor Networks (EH- WSNs) have been attracting increasing interest in recent years. Most current EH-WSN approaches focus on sensing and net- working algorithm design, and therefore only consider the energy consumed by sensors and wireless transceivers for sensing and data transmissions respectively. In this paper, we incorporate CPU-intensive edge operations that constitute in-network data processing (e.g. data aggregation/fusion/compression) with sens- ing and networking; to jointly optimize their performance, while ensuring sustainable network operation (i.e. no sensor node runs out of energy). Based on realistic energy and network models, we formulate a stochastic optimization problem, and propose a lightweight on-line algorithm, namely Recycling Wasted Energy (RWE), to solve it. Through rigorous theoretical analysis, we prove that RWE achieves asymptotical optimality, bounded data queue size, and sustainable network operation. We implement RWE on a popular IoT operating system, Contiki OS, and eval- uate its performance using both real-world experiments based on the FIT IoT-LAB testbed, and extensive trace-driven simulations using Cooja. The evaluation results verify our theoretical analysis, and demonstrate that RWE can recycle more than 90% wasted energy caused by battery overflow, and achieve around 300% network utility gain in practical EH-WSNs
Origin of the Pseudogap in High-Temperature Cuprate Superconductors
Cuprate high-temperature superconductors exhibit a pseudogap in the normal
state that decreases monotonically with increasing hole doping and closes at x
\approx 0.19 holes per planar CuO2 while the superconducting doping range is
0.05 < x < 0.27 with optimal Tc at x \approx 0.16. Using ab initio quantum
calculations at the level that leads to accurate band gaps, we found that
four-Cu-site plaquettes are created in the vicinity of dopants. At x \approx
0.05 the plaquettes percolate, so that the Cu dx2y2/O p{\sigma} orbitals inside
the plaquettes now form a band of states along the percolating swath. This
leads to metallic conductivity and below Tc to superconductivity. Plaquettes
disconnected from the percolating swath are found to have degenerate states at
the Fermi level that split and lead to the pseudogap. The pseudogap can be
calculated by simply counting the spatial distribution of isolated plaquettes,
leading to an excellent fit to experiment. This provides strong evidence in
favor of inhomogeneous plaquettes in cuprates.Comment: 24 pages (4 pages main text plus 20 pages supplement
Electron Correlation and the c-axis Dispersion of Cu d_z^2: a New Band Structure for High Temperature Superconductors
Previously we showed the major effect of electron correlation in the cuprate
superconductors is to lower the energy of the Cu d_x^2-y^2/O p_sigma (x^2-y^2)
band with respect to the Cu d_z^2/O' p_z (z^2) band. In our 2D Hubbard model
for La_1.85Sr_0.15CuO_4 (LaSCO), the z^2 band is narrow and crosses the
standard x^2-y^2 band just below the Fermi level. In this work, we introduce
c-axis dispersion to the model and find the z^2 band to have considerable
anisotropic 3D character. An additional hole-like surface opens up in the z^2
band at (0,0,2pi/c) which expands with doping. At sufficient doping levels, a
symmetry allowed x^2-y^2/z^2 band crossing along the (0,0)-(pi,pi) direction of
the Brillouin zone appears at the Fermi level. At this point, Cooper pairs
between the two bands (e.g. (k uparrow x^2-y^2/k downarrow z^2)) can form,
providing the basis for the Interband Pairing Theory of superconductivity in
these materials.Comment: submitted to Phys. Rev. Lett. Related publications: Phys. Rev. B 58,
12303 (1998); Phys. Rev. B 58, 12323 (1998); cond-mat/9903088;
cond-mat/990310
The Antiferromagnetic Band Structure of La2CuO4 Revisited
Using the Becke-3-LYP functional, we have performed band structure
calculations on the high temperature superconductor parent compound, La2CuO4.
Under the restricted spin formalism (rho(alpha) equal to rho(beta)), the
R-B3LYP band structure agrees well with the standard LDA band structure. It is
metallic with a single Cu x2-y2/O p(sigma) band crossing the Fermi level. Under
the unrestricted spin formalism (rho(alpha) not equal to rho(beta)), the UB3LYP
band structure has a spin polarized antiferromagnetic solution with a band gap
of 2.0 eV, agreeing well with experiment. This state is 1.0 eV (per formula
unit) lower than that calculated from the R-B3LYP. The apparent high energy of
the spin restricted state is attributed to an overestimate of on-site Coulomb
repulsion which is corrected in the unrestricted spin calculations. The
stabilization of the total energy with spin polarization arises primarily from
the stabilization of the x2-y2 band, such that the character of the eigenstates
at the top of the valence band in the antiferromagnetic state becomes a strong
mixture of Cu x2-y2/O p(sigma) and Cu z2/O' p(z). Since the Hohenberg-Kohn
theorem requires the spin restricted and spin unrestricted calculations give
exactly the same ground state energy and total density for the exact
functionals, this large disparity in energy reflects the inadequacy of current
functionals for describing the cuprates. This calls into question the use of
band structures based on current restricted spin density functionals (including
LDA) as a basis for single band theories of superconductivity in these
materials.Comment: 13 pages, 8 figures, to appear in Phys. Rev. B, for more information
see http://www.firstprinciples.co
The Importance of Static Correlation in the Band Structure of High Temperature Superconductors
Recently we presented a new band structure for La(2-x)Sr(x)CuO(4) and other
high temperature superconductors in which a second narrow band was seen to
cross the primary band at the Fermi level. The existence of this second Fermi
level band is in complete disagreement with the commonly accepted LDA band
structure. Yet it provided a crucial piece of physics which led to an
explanation for superconductivity and other unusual phenomena in these
materials. In this work we present details as to the nature of the failure of
conventional methods in deriving the band structure of the cuprates. In
particular, we use a number of chemical analogues to describe the problem of
static correlation in the band structure calculations and show how this can be
corrected with the predictable outcome of a Fermi level band crossing.Comment: The Journal of Physical Chemistry, in press. References and figures
updated. See www.firstprinciples.com for more information related to this
wor
Investigating processing window of Affinisolâ„¢ and Plasdoneâ„¢ - S630 polymers during hot-melt extrusion (for 3D printing by fused deposition modelling)
There are numerous polymers that have been used commercially to produce pharmaceutical solid dispersions and solutions from hot melt extrusion. Affinisolâ„¢ (HPMC) and Plasdoneâ„¢ S630 (PVP based co-povidone copolymer) have been used in the present work to determine the viable processing space with regards thermal and work input on a twin screw extruder. Processing viability has been determined by monitoring degradation, initially assessed by physical appearance and colour of the extrudates across the full operating range of a twin screw extruder. It has been found that the Affinisolâ„¢ had a relatively narrow viable operating window compared with the Plasdoneâ„¢
Gap opening in the zeroth Landau level in gapped graphene: Pseudo-Zeeman splitting in an angular magnetic field
We present a theoretical study of gap opening in the zeroth Landau level in
gapped graphene as a result of pseudo-Zeeman interaction. The applied magnetic
field couples with the valley pseudospin degree of freedom of the charge
carriers leading to the pseudo-Zeeman interaction. To investigate its role in
transport at the Charge Neutrality Point (CNP), we study the integer quantum
Hall effect (QHE) in gapped graphene in an angular magnetic field in the
presence of pseudo-Zeeman interaction. Analytical expressions are derived for
the Hall conductivity using Kubo-Greenwood formula. We also determine the
longitudinal conductivity for elastic impurity scattering in the first Born
approximation. We show that pseudo-Zeeman splitting leads to a minimum in the
collisional conductivity at high magnetic fields and a zero plateau in the Hall
conductivity. Evidence for activated transport at CNP is found from the
temperature dependence of the collisional conductivity.Comment: 20 pages, 4 figures, Accepted in J. Phys. Condensed matte
Parallel processing for fault tolerant aircraft control.
This thesis addresses the problem of real-time optimal control of aircraft systems
using parallel processing techniques. It is shown that transputer hardware can
be used in designing a suitable optimal controller for general nonlinear time-varying
aircraft. In the first part of the thesis, nonlinearties and time varying aspects of the
aircraft system, together with the current available solutions are investigated and
suitable designs presented. Here the linear regulator approach for linear time-varying
aircraft is investigated first but it is shown that real-time performance is difficult to
achieve. The problem is then approached differently in that the aircraft is considered
as a linear time-invariant system for short time intervals and it is then found possible
to implement an optimal control solution in real-time, and suitable multi-transputer
architectures are presented. The receding/moving horizon approach is applied to
the aircraft system and is shown to be adequate for achieving satisfactory results.
The problem of selection of the weights in the performance index of the optimal
control problem is then studied and a design procedure is presented. The modeling
of the aircraft as decoupled longitudinal and lateral dynamics is investigated and approached
in such a way as to reduce the cross-coupling effects. Another important aspect of this research involves the consideration of failure detection and diagnosis
in the aircraft hardware. Problems including actuator failure are studied and some
remedial methods for handling the failures by enabling system reconfiguration after
the occurrence of the failure are presented.
The multi-processor based control system design is shown to offer a viable
solution to solving complicated optimisation problems without the need for the simplification
of the system dynamical equations and thereby loosing accuracy. Such
simplification is usually a prerequisite for enabling practical designs. However with
the use of parallel processing techniques such designs can be achieved for the more
complicated (and more computationally demanding) cases as well
Nuclear expression of Lyn, a Src family kinase member, is associated with poor prognosis in renal cancer patients
Background: 8000 cases of renal cancer are diagnosed each year in the UK, with a five-year survival rate of 50 %.
Treatment options are limited; a potential therapeutic target is the Src family kinases (SFKs). SFKs have roles in
multiple oncogenic processes and promote metastases in solid tumours. The aim of this study was to investigate
SFKs as potential therapeutic targets for clear cell renal cell carcinoma (ccRCC).
Methods: SFKs expression was assessed in a tissue microarray consisting of 192 ccRCC patients with full clinical
follow-up. SFK inhibitors, dasatinib and saracatinib, were assessed in early ccRCC cell lines, 786-O and 769-P and a
metastatic ccRCC cell line, ACHN (± Src) for effects on protein expression, apoptosis, proliferation and wound
healing.
Results: High nuclear expression of Lyn and the downstream marker of activation, paxillin, were associated with
decreased patient survival. Conversely, high cytoplasmic expression of other SFK members and downstream marker
of activation, focal adhesion kinase (FAK) were associated with increased patient survival. Treatment of non-metastatic
786-O and 769-P cells with dasatinib, dose dependently reduced SFK activation, shown via SFK (Y419) and FAK (Y861)
phosphorylation, with no effect in metastatic ACHN cells. Dasatinib also increased apoptosis, while decreasing
proliferation and migration in 786-O and 769-P cell lines, both in the presence and absence of Src protein.
Conclusions: Our data suggests that nuclear Lyn is a potential therapeutic target for ccRCC and dasatinib
affects cellular functions associated with cancer progression via a Src kinase independent mechanism
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