478 research outputs found
Sensitivity analysis of permeability parameters of bovine nucleus pulposus obtained through inverse fitting of the nonlinear biphasic equation : effect of sampling strategy
Permeability controls the fluid flow into and out of soft tissue, and plays an important role in maintaining the health status of such tissue. Accurate determination of the parameters that define permeability is important for the interpretation of models that incorporate such processes. This paper describes the determination of strain-dependent permeability parameters from the nonlinear biphasic equation from experimental data of different sampling frequencies using the NelderâMead simplex method. The ability of this method to determine the global optimum was assessed by constructing the whole manifold arising from possible parameter combinations. Many parameter combinations yielded similar fits with the NelderâMead algorithm able to identify the global maximum within the resolution of the manifold. Furthermore, the sampling strategy affected the optimum values of the permeability parameters. Therefore, permeability parameter estimations arising from inverse methods should be utilised with the knowledge that they come with large confidence intervals
Bond-order correlation energies for small Si-containing molecules compared with ab initio results from low-order Moller-Plesset perturbation theory
The present study of small molecules containing silicon has been motivated by
(a) the considerable interest being shown currently in the kinetics and
reactivity of such molecules, and (b) the biotechnological potential of
silicon-derivate surfaces as substrates in the adsorption of, for instance,
amino acids and proteins. Therefore, we have studied by (i) a semi-empirical
approach and (ii) an ab initio procedure employing low-order Moller-Plesset
perturbation theory, the molecular correlation energies of some neutral closed
and open shell silicon-containing molecules in the series SiXnYm. Procedure (i)
is shown to have particular merit for the correlation of the ionic members
studied in the above series, while the ab initio procedures employed come into
their own for neutral species.Comment: Mol. Phys., to be publishe
Vapor Pressure of Ionic Liquids
We argue that the extremely low vapor pressures of room temperature ionic
liquids near their triple points are due to the combination of strong ionic
characters and of low melting temperatures.Comment: Initially submitted manuscript of article M. Bier and S. Dietrich,
Mol. Phys. 108, 211 (2010) [Corrigendum: Mol. Phys. 108, 1413 (2010)
Finite size melting of spherical solid-liquid aluminium interfaces
We have investigated the melting of nano-sized cone shaped aluminium needles
coated with amorphous carbon using transmission electron microscopy. The
interface between solid and liquid aluminium was found to have spherical
topology. For needles with fixed apex angle, the depressed melting temperature
of this spherical interface, with radius , was found to scale linearly with
the inverse radius . However, by varying the apex angle of the needles we
show that the proportionality constant between the depressed melting
temperature and the inverse radius changes significantly. This lead us to the
conclusion that the depressed melting temperature is not controlled solely by
the inverse radius . Instead we found a direct relation between the
depressed melting temperature and the ratio between the solid-liquid interface
area and the molten volume.Comment: to appear in Philosophical Magazine (2009
Spectroscopy of free radicals and radical containing entrance-channel complexes in superfluid helium nano-droplets
The spectroscopy of free radicals and radical containing entrance-channel
complexes embedded in superfluid helium nano-droplets is reviewed. The
collection of dopants inside individual droplets in the beam represents a
micro-canonical ensemble, and as such each droplet may be considered an
isolated cryo-reactor. The unique properties of the droplets, namely their low
temperature (0.4 K) and fast cooling rates ( K s) provides
novel opportunities for the formation and high-resolution studies of molecular
complexes containing one or more free radicals. The production methods of
radicals are discussed in light of their applicability for embedding the
radicals in helium droplets. The spectroscopic studies performed to date on
molecular radicals and on entrance / exit-channel complexes of radicals with
stable molecules are detailed. The observed complexes provide new information
on the potential energy surfaces of several fundamental chemical reactions and
on the intermolecular interactions present in open-shell systems. Prospects of
further experiments of radicals embedded in helium droplets are discussed,
especially the possibilities to prepare and study high-energy structures and
their controlled manipulation, as well as the possibility of fundamental
physics experiments.Comment: 25 pages, 12 figures, 4 tables (RevTeX
Scanning-probe spectroscopy of semiconductor donor molecules
Semiconductor devices continue to press into the nanoscale regime, and new
applications have emerged for which the quantum properties of dopant atoms act
as the functional part of the device, underscoring the necessity to probe the
quantum structure of small numbers of dopant atoms in semiconductors[1-3].
Although dopant properties are well-understood with respect to bulk
semiconductors, new questions arise in nanosystems. For example, the quantum
energy levels of dopants will be affected by the proximity of nanometer-scale
electrodes. Moreover, because shallow donors and acceptors are analogous to
hydrogen atoms, experiments on small numbers of dopants have the potential to
be a testing ground for fundamental questions of atomic and molecular physics,
such as the maximum negative ionization of a molecule with a given number of
positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants
has been observed in transport studies[6,7]. In addition, Geim and coworkers
identified resonances due to two closely spaced donors, effectively forming
donor molecules[8]. Here we present capacitance spectroscopy measurements of
silicon donors in a gallium-arsenide heterostructure using a scanning probe
technique[9,10]. In contrast to the work of Geim et al., our data show
discernible peaks attributed to successive electrons entering the molecules.
Hence this work represents the first addition spectrum measurement of dopant
molecules. More generally, to the best of our knowledge, this study is the
first example of single-electron capacitance spectroscopy performed directly
with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages,
3 figures, 5 supplementary figure
Enhanced doping effects of multiâelement on anisotropic thermal expansion in ZrO2 with new compositions
Coefficient of thermal expansion (CTE) of a solid material plays a critical role for a variety of high temperature applications such as thermal barrier coating (TBC) systems during the thermal cycling process. Ceramics contain ionic bonds; hence they tend to exhibit lower CTE values than alloys/metals. Developing new ceramic thermal barrier materials using promising dopants and compositions that have higher CTE values than the conventional 6â8 wt.% Y2O3 stabilized ZrO2 (8YSZ) will contribute to the decrease in thermal expansion mismatch between a typical ceramic 8YSZ (10~11Ă10â6 °Câ1) top coat and a metal alloy based bond coat such as NiCrAlY (14~17Ă10â6 °Câ1),1, 2 which is highly desirable. This work reports design, modelling, synthesis, and characterization of promising new compositions based on Dy3+, Al3+ and Ce4+ doped YSZ that consist of the tetragonal structure and have an enhanced thermal expansion than 8YSZ. The intrinsic CTE at the atomic level has been investigated via molecular dynamics (MD) simulation. The atomic scale analysis provides new insights into the enhanced doping effects of multiple trivalent and tetravalent cations on the lattice structure, lattice energy and thermal expansion in ZrO2. The calculated lattice energy becomes smaller with the incorporation of Dy3+, Al3+, and Ce4+ ions, which corresponds strongly to the increase in CTE. The crystalline size is reduced due to the incorporation of the Al3+ and Ce4+, whereas the sintering resistance is enhanced ascribed to the addition of Dy3+ and Al3+. Doping Dy3+, Al3+, and Ce4+ cations to YSZ increased the CTE value of YSZ and for Dy0.03Y0.075Zr0.895O1.948, the CTE is 12.494Ă10â6 °Câ1 at 900°C, which has an 11% increase, as compared with that of 8YSZ
A viscoelastic deadly fluid in carnivorous pitcher plants
Background : The carnivorous plants of the genus Nepenthes, widely
distributed in the Asian tropics, rely mostly on nutrients derived from
arthropods trapped in their pitcher-shaped leaves and digested by their
enzymatic fluid. The genus exhibits a great diversity of prey and pitcher forms
and its mechanism of trapping has long intrigued scientists. The slippery inner
surfaces of the pitchers, which can be waxy or highly wettable, have so far
been considered as the key trapping devices. However, the occurrence of species
lacking such epidermal specializations but still effective at trapping insects
suggests the possible implication of other mechanisms. Methodology/Principal
Findings : Using a combination of insect bioassays, high-speed video and
rheological measurements, we show that the digestive fluid of Nepenthes
rafflesiana is highly viscoelastic and that this physical property is crucial
for the retention of insects in its traps. Trapping efficiency is shown to
remain strong even when the fluid is highly diluted by water, as long as the
elastic relaxation time of the fluid is higher than the typical time scale of
insect movements. Conclusions/Significance : This finding challenges the common
classification of Nepenthes pitchers as simple passive traps and is of great
adaptive significance for these tropical plants, which are often submitted to
high rainfalls and variations in fluid concentration. The viscoelastic trap
constitutes a cryptic but potentially widespread adaptation of Nepenthes
species and could be a homologous trait shared through common ancestry with the
sundew (Drosera) flypaper plants. Such large production of a highly
viscoelastic biopolymer fluid in permanent pools is nevertheless unique in the
plant kingdom and suggests novel applications for pest control
Slow and fast diffusion in a lead sulphate gravity separation process
A model for the growth of lead sulphate particles in a gravity separation system
from the crystal glassware industry is presented. The lead sulphate particles are an undesirable
byproduct, and thus the model is used to ascertain the optimal system temperature configuration
such that particle extraction is maximised. The model describes the evolution of a single,
spherical particle due to the mass flux of lead particles from a surrounding acid solution. We
divide the concentration field into two separate regions. Specifically, a relatively small boundary
layer region around the particle is characterised by fast diffusion, and is thus considered quasistatic.
In contrast, diffusion in the far-field is slower, and hence assumed to be time-dependent.
The final system consisting of two nonlinear, coupled ordinary differential equations for the
particle radius and lead concentration, is integrated numerically
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