7,967 research outputs found
Model Checking Tap Withdrawal in C. Elegans
We present what we believe to be the first formal verification of a
biologically realistic (nonlinear ODE) model of a neural circuit in a
multicellular organism: Tap Withdrawal (TW) in \emph{C. Elegans}, the common
roundworm. TW is a reflexive behavior exhibited by \emph{C. Elegans} in
response to vibrating the surface on which it is moving; the neural circuit
underlying this response is the subject of this investigation. Specifically, we
perform reachability analysis on the TW circuit model of Wicks et al. (1996),
which enables us to estimate key circuit parameters. Underlying our approach is
the use of Fan and Mitra's recently developed technique for automatically
computing local discrepancy (convergence and divergence rates) of general
nonlinear systems. We show that the results we obtain are in agreement with the
experimental results of Wicks et al. (1995). As opposed to the fixed parameters
found in most biological models, which can only produce the predominant
behavior, our techniques characterize ranges of parameters that produce (and do
not produce) all three observed behaviors: reversal of movement, acceleration,
and lack of response
Electron emission of Au nanoparticles embedded in ZnO for highly conductive oxide
We investigated the effect of embedded Au nanoparticles (Au NPs) on electrical properties of zinc oxide (ZnO) for highly conductive oxide semiconductor. Au NPs in ZnO films influenced both the structural and electrical properties of the mixture films. The electrical resistivity decreases by as much as five orders of magnitude. This is explained by the electron emission from Au NPs to the ZnO matrix. Temperature-dependent Hall effect measurements show that an electron emission mechanism changes from tunneling to thermionic emission at T = 180 K. The electron mobility in the mixture film is mainly limited by the grain boundaries at lower temperature (80-180 K), and the Au/ZnO heterogeneous interface at higher temperature (180-340 K). In addition to the electron emission, embedded Au NPs alter the ZnO matrix microstructure and improve the electron mobility. Compared to the undoped ZnO film, the carrier concentration of the Au NP-embedded ZnO film can be increased by as much as six orders of magnitude with a small change in the carrier mobility. This result suggests a way to circumvent the inherent tradeoff between the carrier concentration and the carrier mobility in transparent conductive oxide (TCO) materials. © 2014 AIP Publishing LLC
Bounded Verification with On-the-Fly Discrepancy Computation
Simulation-based verification algorithms can provide formal safety guarantees
for nonlinear and hybrid systems. The previous algorithms rely on user provided
model annotations called discrepancy function, which are crucial for computing
reachtubes from simulations. In this paper, we eliminate this requirement by
presenting an algorithm for computing piece-wise exponential discrepancy
functions. The algorithm relies on computing local convergence or divergence
rates of trajectories along a simulation using a coarse over-approximation of
the reach set and bounding the maximal eigenvalue of the Jacobian over this
over-approximation. The resulting discrepancy function preserves the soundness
and the relative completeness of the verification algorithm. We also provide a
coordinate transformation method to improve the local estimates for the
convergence or divergence rates in practical examples. We extend the method to
get the input-to-state discrepancy of nonlinear dynamical systems which can be
used for compositional analysis. Our experiments show that the approach is
effective in terms of running time for several benchmark problems, scales
reasonably to larger dimensional systems, and compares favorably with respect
to available tools for nonlinear models.Comment: 24 page
A Solid-State Battery Cathode with a Polymer Composite Electrolyte and Low Tortuosity Microstructure by Directional Freezing and Polymerization
Solidâstate Li metal batteries (SSLMBs) combine improved safety and high specific energy that can surpass current Li ion batteries. However, the Li^{+} ion diffusivity in a composite cathodeâa combination of active material and solidâstate electrolyte (SSE)âis at least an order of magnitude lower than that of the SSE alone because of the highly tortuous ion transport pathways in the cathode. This lowers the realizable capacity and mandates relatively thin (30â300 ÎŒm) cathodes, and hence low overall energy storage. Here, a thick (600 ÎŒm) hybrid cathode comprising vertically aligned LiNi_{0.8}Mn_{0.1}Co_{0.1}O_{2} (NMC811)ârich channels filled with a [LiTFSI+PEGMA+MePrPyl TFSI] polymer composite electrolyte is fabricated by an innovative directional freezing and polymerization method. Xâray microâcomputed tomography, ion mobility simulations, and DC depolarization show that the cathode structure improves Li^{+} ion diffusivity in the cathode from 4.4 Ă 10^{-9} to 1.4 Ă 10^{-7} cm^{2} s^{â1}. In a SSLMB full cell at 25 oC, the cathode provides gravimetric capacities of 199 and 120 mAh g^{â1}, and ultraâhigh areal capacities of 16.7 and 10.1 mAh cm^{â2} at 0.05 and 1 C, respectively. The work demonstrates a scalable approach to realizing composite cathode structures with kinetically favorable ion transport characteristics in SSLMBs
Evidence for the classical integrability of the complete AdS(4) x CP(3) superstring
We construct a zero-curvature Lax connection in a sub-sector of the
superstring theory on AdS(4) x CP(3) which is not described by the
OSp(6|4)/U(3) x SO(1,3) supercoset sigma-model. In this sub-sector worldsheet
fermions associated to eight broken supersymmetries of the type IIA background
are physical fields. As such, the prescription for the construction of the Lax
connection based on the Z_4-automorphism of the isometry superalgebra OSp(6|4)
does not do the job. So, to construct the Lax connection we have used an
alternative method which nevertheless relies on the isometry of the target
superspace and kappa-symmetry of the Green-Schwarz superstring.Comment: 1+26 pages; v2: minor typos corrected, acknowledgements adde
Global Properties of Topological String Amplitudes and Orbifold Invariants
We derive topological string amplitudes on local Calabi-Yau manifolds in
terms of polynomials in finitely many generators of special functions. These
objects are defined globally in the moduli space and lead to a description of
mirror symmetry at any point in the moduli space. Holomorphic ambiguities of
the anomaly equations are fixed by global information obtained from boundary
conditions at few special divisors in the moduli space. As an illustration we
compute higher genus orbifold Gromov-Witten invariants for C^3/Z_3 and C^3/Z_4.Comment: 34 pages, 3 figure
Seasonal pattern of Echinococcus re-infection in owned dogs in Tibetan communities of Sichuan, China and its implications for control
Background
Human cystic echinococcosis (CE) and alveolar echinococcosis (AE) are highly endemic in Tibetan communities of Sichuan Province. Previous research in the region indicated that domestic dog was the major source of human infection, and observations indicated that domestic dog could have more access to intermediate hosts of Echinococcus spp.: both domestic livestock (CE) viscera and small mammals (AE), in early winter and again in spring. We hypothesized that there would therefore be a significant increase in the risk of canine infection with Echinococcus spp. in these two seasons and conducted a reinfection study to investigate this further.
Methods
Faecal samples were collected from owned dogs in seven townships in Ganze Tibetan Autonomous Prefecture (Sichuan Province, China), and Echinococcus spp. infection status was determined using copro-antigen ELISA. Dogs were sampled in April (spring), July (early summer), September/October (autumn/early winter) and December (winter) in 2009; and in April (spring) 2010. Dogs were treated with praziquantel following each of the five sample collections to eliminate any tapeworms. Information on dog sex, age and body weight was also collected. The t-test, Fisherâs exact test, Poisson regression and logistic regression were used to compare means and prevalences, and to identify factors associated with infection status.
Results
The proportion of female dogs was significantly lower than that of male dogs; female dogs had significantly higher (22.78 %) baseline copro-ELISA prevalence than males (11.88 %). Dog body weight, sex, age, county and previous infection status at any sampling point had no influence on the re-infection prevalence in general. Poisson regression did not found a significant influence on the re-infection prevalence due to different deworming/sampling time spans. Dogs exhibited significantly higher re-infection prevalences in spring and early summer of 2009 and in early winter between September/October and December of 2009, suggesting a higher infection pressure in these seasons comparing with other seasons.
Conclusion
Following praziquantel treatment, dog body weight, sex, age, county, deworming time span and previous infection status at any sampling point had no influence on the re-infection prevalence in the region in general. The differences between re-infection prevalences were probably due to the seasonality in Echinoccocus spp. infection pressure in the region. Early winter, spring and early summer should be important seasons for optimal dog deworming intervention in these Tibetan communities
4D Bragg Edge Tomography of Directional Ice Templated Graphite Electrodes
Bragg edge tomography was carried out on novel, ultra-thick, directional ice templated graphite electrodes for Li-ion battery cells to visualise the distribution of graphite and stable lithiation phases, namely LiC12 and LiC6. The four-dimensional Bragg edge, wavelength-resolved neutron tomography technique allowed the investigation of the crystallographic lithiation states and comparison with the electrode state of charge. The tomographic imaging technique provided insight into the crystallographic changes during de-/lithiation over the electrode thickness by mapping the attenuation curves and Bragg edge parameters with a spatial resolution of approximately 300 ”m. This feasibility study was performed on the IMAT beamline at the ISIS pulsed neutron spallation source, UK, and was the first time the 4D Bragg edge tomography method was applied to Li-ion battery electrodes. The utility of the technique was further enhanced by correlation with corresponding X-ray tomography data obtained at the Diamond Light Source, UK
A Non-Abelian Self-Dual Gauge Theory in 5+1 Dimensions
We construct a non-Abelian gauge theory of chiral 2-forms (self-dual gauge
fields) in 6 dimensions with a spatial direction compactified on a circle of
radius R. It has the following two properties. (1) It reduces to the Yang-Mills
theory in 5 dimensions for small R. (2) It is equivalent to the
Lorentz-invariant theory of Abelian chiral 2-forms when the gauge group is
Abelian. Previous no-go theorems prohibiting non-Abelian deformations of the
chiral 2-form gauge theory are circumvented by introducing nonlocality along
the compactified dimension.Comment: 23 pages, reference adde
Synthesis of novel thieno[3,2-b]thienobis(silolothiophene) based low bandgap polymers for organic photovoltaics
Thieno[3,2-b]thienobis(silolothiophene), a new electron rich hexacyclic monomer has been synthesized and incorporated into three novel donorâacceptor low-bandgap polymers. By carefully choosing the acceptor co-monomer, the energy levels of the polymers could be modulated and high power conversion efficiencies of 5.52% were reached in OPV devices
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