16,206 research outputs found
Noise from spatial heterogeneity changes signal amplification magnitude and increases the variability in dose responses
In most molecular level simulations, spatial heterogeneity is neglected by the well-mixed condition assumption. However, the signals of biomolecular
networks are affected from both time and space, which are responsible for diverse physiological responses. To account the spatial heterogeneity in the
kinetic model, we consider multiple subvolumes of a reaction, introduce parameters representing transfer of ligands between the volumes, and reduce
this to an error-term representing the difference between the well-mixed condition and the actual spatial factors. The error-term approach allows
modelling of varying spatial heterogeneity without increasing computational burden exponentially.
The effect of varying this term, d, between 0 (well-mixed) and 1 (no mixing) and of adding noise to the kinetic constants was then investigated and
correlated with knowledge of the behaviour of real systems and situations where network models are inadequate. The spatial distribution effects on the
epidermal growth factor receptor (EGFR) in human mammary epithelial tissue, which is involved in proliferation and tumorigenesis, are studied by
introducing noisy kinetic constants.
The steady-state of the dose response in the
EGFR is strongly affected by spatial
fluctuations. The ligand-bound receptor is
reduced up to 50% from the response
without spatial fluctuations and the variance
of the steady-state is increased at least 2-fold
from the one for no spatial fluctuations. On
the other hand, dynamic properties such as
the rising time and overshoot are less
sensitive to spatial noise
A comparison of observation-level random effect and Beta-Binomial models for modelling over dispersion in Binomial data in ecology and evolution
Overdispersion is a common feature of models of biological data, but researchers often fail to model the excess variation driving the overdispersion, resulting in biased parameter estimates and standard errors. Quantifying and modeling overdispersion when it is present is therefore critical for robust biological inference. One means to account for overdispersion is to add an observation-level random effect (OLRE) to a model, where each data point receives a unique level of a random effect that can absorb the extra-parametric variation in the data. Although some studies have investigated the utility of OLRE to model overdispersion in Poisson count data, studies doing so for Binomial proportion data are scarce. Here I use a simulation approach to investigate the ability of both OLRE models and Beta-Binomial models to recover unbiased parameter estimates in mixed effects models of Binomial data under various degrees of overdispersion. In addition, as ecologists often fit random intercept terms to models when the random effect sample size is low (<5 levels), I investigate the performance of both model types under a range of random effect sample sizes when overdispersion is present. Simulation results revealed that the efficacy of OLRE depends on the process that generated the overdispersion; OLRE failed to cope with overdispersion generated from a Beta-Binomial mixture model, leading to biased slope and intercept estimates, but performed well for overdispersion generated by adding random noise to the linear predictor. Comparison of parameter estimates from an OLRE model with those from its corresponding Beta-Binomial model readily identified when OLRE were performing poorly due to disagreement between effect sizes, and this strategy should be employed whenever OLRE are used for Binomial data to assess their reliability. Beta-Binomial models performed well across all contexts, but showed a tendency to underestimate effect sizes when modelling non-Beta-Binomial data. Finally, both OLRE and Beta-Binomial models performed poorly when models contained <5 levels of the random intercept term, especially for estimating variance components, and this effect appeared independent of total sample size. These results suggest that OLRE are a useful tool for modelling overdispersion in Binomial data, but that they do not perform well in all circumstances and researchers should take care to verify the robustness of parameter estimates of OLRE models
The future design direction of smart clothing development
Literature indicates that Smart Clothing applications, the next generation of clothing and
electronic products, have been struggling to enter the mass market because the consumers’
latent needs have not been recognised. Moreover, the design direction of Smart Clothes
remains unclear and unfocused. Nevertheless, a clear design direction is necessary for all
product development. Therefore, this research aims to identify the design directions of the
emerging Smart Clothes industry by conducting a questionnaire survey and focus groups
with its major design contributors. The results reveal that the current strategy of embedding
a wide range of electronic functions in a garment is not suitable. This is primarily because it
does not match the users’ requirements, purchasing criteria and lifestyle. The results
highlight the respondents’ preference for personal healthcare and sportswear applications
that suit their lifestyle, are aesthetically attractive, and provide a practical function
Band Offsets at the Si/SiO Interface from Many-Body Perturbation Theory
We use many-body perturbation theory, the state-of-the-art method for band
gap calculations, to compute the band offsets at the Si/SiO interface. We
examine the adequacy of the usual approximations in this context. We show that
(i) the separate treatment of band-structure and potential lineup
contributions, the latter being evaluated within density-functional theory, is
justified, (ii) most plasmon-pole models lead to inaccuracies in the absolute
quasiparticle corrections, (iii) vertex corrections can be neglected, (iv)
eigenenergy self-consistency is adequate. Our theoretical offsets agree with
the experimental ones within 0.3 eV
Recent high-magnetic-field studies of unusual groundstates in quasi-two-dimensional crystalline organic metals and superconductors
After a brief introduction to crystalline organic superconductors and metals,
we shall describe two recently-observed exotic phases that occur only in high
magnetic fields. The first involves measurements of the non-linear electrical
resistance of single crystals of the charge-density-wave (CDW) system
(Per)Au(mnt) in static magnetic fields of up to 45 T and temperatures
as low as 25 mK. The presence of a fully gapped CDW state with typical CDW
electrodynamics at fields higher that the Pauli paramagnetic limit of 34 T
suggests the existence of a modulated CDW phase analogous to the
Fulde-Ferrell-Larkin-Ovchinnikov state. Secondly, measurements of the Hall
potential of single crystals of -(BEDT-TTF)KHg(SCN), made using
a variant of the Corbino geometry in quasistatic magnetic fields, show
persistent current effects that are similar to those observed in conventional
superconductors. The longevity of the currents, large Hall angle, flux
quantization and confinement of the reactive component of the Hall potential to
the edge of the sample are all consistent with the realization of a new state
of matter in CDW systems with significant orbital quantization effects in
strong magnetic fields.Comment: SNS 2004 Conference presentatio
Electronic structure reconstruction: the driving force behind the magnetic and structural transitions in NaFeAs
The electronic structure of NaFeAs is studied with angle resolved
photoemission spectroscopy on high quality single crystals. Large portions of
the band structure start to shift around the structural transition temperature,
and smoothly evolve as the temperature lowers through the spin density wave
transition. Moreover, band folding due to magnetic order emerges around
structural transition. Our observation provides direct evidence that the
structural and magnetic transitions share the same origin, and are both driven
by the electronic structure reconstruction in Fe-based superconductors, instead
of Fermi surface nesting.Comment: 5 pages, 5 figure
Electronic structure and Jahn-Teller effect in GaN:Mn and ZnS:Cr
We present an ab-initio and analytical study of the Jahn-Teller effect in two
diluted magnetic semiconductors (DMS) with d4 impurities, namely Mn-doped GaN
and Cr-doped ZnS. We show that only the combined treatment of Jahn-Teller
distortion and strong electron correlation in the 3d shell may lead to the
correct insulating electronic structure. Using the LSDA+U approach we obtain
the Jahn-Teller energy gain in reasonable agreement with the available
experimental data. The ab-initio results are completed by a more
phenomenological ligand field theory.Comment: 15 pages, 5 figure
Spontaneous order in the highly frustrated spin-1/2 Ising-Heisenberg model on the triangulated Kagome lattice due to the Dzyaloshinskii-Moriya anisotropy
The spin-1/2 Ising-Heisenberg model on the triangulated Kagome
(triangles-in-triangles) lattice is exactly solved by establishing a precise
mapping correspondence to the simple spin-1/2 Ising model on Kagome lattice. It
is shown that the disordered spin liquid state, which otherwise occurs in the
ground state of this frustrated spin system on assumption that there is a
sufficiently strong antiferromagnetic intra-trimer interaction, is eliminated
from the ground state by arbitrary but non-zero Dzyaloshinskii-Moriya
anisotropy.Comment: 4 pages, 3 figures, to be presented at conference Highly Frustrated
Magnetism, 7-12 September 2008, Braunschweig, German
Landau quantization effects in the charge-density-wave system (Per)(mnt) (where Au and Pt)
A finite transfer integral orthogonal to the conducting chains of a
highly one-dimensional metal gives rise to empty and filled bands that simulate
an indirect-gap semiconductor upon formation of a commensurate
charge-density-wave (CDW). In contrast to semiconductors such as Ge and Si with
bandgaps eV, the CDW system possesses an indirect gap with a greatly
reduced energy scale, enabling moderate laboratory magnetic fields to have a
major effect. The consequent variation of the thermodynamic gap with magnetic
field due to Zeeman splitting and Landau quantization enables the electronic
bandstructure parameters (transfer integrals, Fermi velocity) to be determined
accurately. These parameters reveal the orbital quantization limit to be
reached at T in (Per)(mnt) salts, making them highly
unlikely candidates for a recently-proposed cascade of field-induced
charge-density wave states
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