237 research outputs found
Revealing the Compact Structure of Lactic Acid Bacterial Heteroexopolysaccharides by SAXS and DLS
Molecular structures
of exopolysaccharides are required to understand
their functions and the relationships between the structure and physical
and rheological properties. Small-angle X-ray scattering and dynamic
light scattering were used in conjunction with molecular modeling
to characterize solution structures of three lactic acid bacterial
heteroexopolysaccharides (HePS-1, HePS-2, and HePS-3). Values of radius
of gyration <i>R</i><sub>G</sub>, cross-sectional radius
of gyration <i>R</i><sub>XS</sub>, approximate length <i>L</i>, and hydrodynamic diameter were not directly proportional
to the molar mass and indicated the HePSs adopted a compact coil-like
rather than an extended conformation. Constrained molecular modeling
of 15000 randomized HePS-1 conformers resulted in five best-fit structures
with <i>R</i> factor of 3.9−4.6% revealing random
coil-like structure. Φ and Ψ angle analysis of glycosidic
linkages in HePS-1 structures suggests Gal<i>f</i> residues
significantly influence the conformation. Ab initio scattering modeling
of HePS-2 and HePS-3 gave excellent curve fittings with χ<sup>2</sup> of 0.43 and 0.34 for best-fit models, respectively, compatible
with coil-like conformation. The findings disclose solution behavior
of HePS relevant for their interactions with biomacromolecules, for
example, milk proteins
Order parameter model for unstable multilane traffic flow
We discuss a phenomenological approach to the description of unstable vehicle
motion on multilane highways that explains in a simple way the observed
sequence of the phase transitions "free flow -> synchronized motion -> jam" as
well as the hysteresis in the transition "free flow synchronized motion".
We introduce a new variable called order parameter that accounts for possible
correlations in the vehicle motion at different lanes. So, it is principally
due to the "many-body" effects in the car interaction, which enables us to
regard it as an additional independent state variable of traffic flow. Basing
on the latest experimental data (cond-mat/9905216) we assume that these
correlations are due to a small group of "fast" drivers. Taking into account
the general properties of the driver behavior we write the governing equation
for the order parameter. In this context we analyze the instability of
homogeneous traffic flow manifesting itself in both of the mentioned above
phase transitions where, in addition, the transition "synchronized motion ->
jam" also exhibits a similar hysteresis. Besides, the jam is characterized by
the vehicle flows at different lanes being independent of one another. We
specify a certain simplified model in order to study the general features of
the car cluster self-formation under the phase transition "free flow
synchronized motion". In particular, we show that the main local parameters of
the developed cluster are determined by the state characteristics of vehicle
motion only.Comment: REVTeX 3.1, 10 pages with 10 PostScript figure
First principles simulations of direct coexistence of solid and liquid aluminium
First principles calculations based on density functional theory, with
generalised gradient corrections and ultrasoft pseudopotentials, have been used
to simulate solid and liquid aluminium in direct coexistence at zero pressure.
Simulations have been carried out on systems containing up to 1000 atoms for 15
ps. The points on the melting curve extracted from these simulations are in
very good agreement with previous calculations, which employed the same
electronic structure method but used an approach based on the explicit
calculation of free energies [L. Vo\v{c}adlo and D. Alf\`e, Phys. Rev. B, {\bf
65}, 214105 (2002).]Comment: To appear in Phys. Rev.
Absence of lattice strain anomalies at the electronic topological transition in zinc at high pressure
High pressure structural distortions of the hexagonal close packed (hcp)
element zinc have been a subject of controversy. Earlier experimental results
and theory showed a large anomaly in lattice strain with compression in zinc at
about 10 GPa which was explained theoretically by a change in Fermi surface
topology. Later hydrostatic experiments showed no such anomaly, resulting in a
discrepancy between theory and experiment. We have computed the compression and
lattice strain of hcp zinc over a wide range of compressions using the
linearized augmented plane wave (LAPW) method paying special attention to
k-point convergence. We find that the behavior of the lattice strain is
strongly dependent on k-point sampling, and with large k-point sets the
previously computed anomaly in lattice parameters under compression disappears,
in agreement with recent experiments.Comment: 9 pages, 6 figures, Phys. Rev. B (in press
Interaction between structurally different heteroexopolysaccharides and β-lactoglobulin studied by solution scattering and analytical ultracentrifugation
Predmet ovog rada je Lean proizvodnja-korak ka uspjehu. Lean proizvodnje naglašava
minimiziranje količine resursa koji se koriste u raznim aktivnostima kompanije i uključuje
identificiranje i eliminiranje aktivnosti koje ne donosi vrijednost. Filozofija Lean proizvodnje
uključuje principe i praksu smanjivanja troškova kroz uklanjanje "otpada" i kroz
pojednostavljenje svih aktivnosti kompanije. Postoji sedam vrsta tradicionalnih otpada u
aktivnostima kompanije i više od desetak alata za njihovo uklanjanje. U postizanju filozofije
Lean proizvodnje pet je glavnih koraka koji označavaju životni ciklus racionalne proizvodnje.
Lean proizvodnja i filozofija racionalnog poslovanja omogućava kompanijama da budu bolje,
brže, njihovi proizvodi i/ili usluge jeftinije, a one same privlačnije kupcima.The subject of this paper is Lean production-step to success. Lean Production highlights the minimization of the amount of resources used in the company's various activities and involves identifying and eliminating activities that do not bring value. The Lean manufacturing philosophy includes the principles and practice of reducing costs through the removal of
"waste" and simplifying all company activities. There are seven types of traditional waste in the company's activities and more than a dozen tools for their removal. In achieving the Lean production philosophy, five major steps are to be found that indicate the life cycle of rational production. Lean manufacturing and the philosophy of rational business enable companies to be better, faster, their products and/or services cheaper, and those more attractive to customers
Iron under Earth's core conditions: Liquid-state thermodynamics and high-pressure melting curve
{\em Ab initio} techniques based on density functional theory in the
projector-augmented-wave implementation are used to calculate the free energy
and a range of other thermodynamic properties of liquid iron at high pressures
and temperatures relevant to the Earth's core. The {\em ab initio} free energy
is obtained by using thermodynamic integration to calculate the change of free
energy on going from a simple reference system to the {\em ab initio} system,
with thermal averages computed by {\em ab initio} molecular dynamics
simulation. The reference system consists of the inverse-power pair-potential
model used in previous work. The liquid-state free energy is combined with the
free energy of hexagonal close packed Fe calculated earlier using identical
{\em ab initio} techniques to obtain the melting curve and volume and entropy
of melting. Comparisons of the calculated melting properties with experimental
measurement and with other recent {\em ab initio} predictions are presented.
Experiment-theory comparisons are also presented for the pressures at which the
solid and liquid Hugoniot curves cross the melting line, and the sound speed
and Gr\"{u}neisen parameter along the Hugoniot. Additional comparisons are made
with a commonly used equation of state for high-pressure/high-temperature Fe
based on experimental data.Comment: 16 pages including 6 figures and 5 table
Equation of state and phonon frequency calculations of diamond at high pressures
The pressure-volume relationship and the zone-center optical phonon frequency
of cubic diamond at pressures up to 600 GPa have been calculated based on
Density Functional Theory within the Local Density Approximation and the
Generalized Gradient Approximation. Three different approaches, viz. a
pseudopotential method applied in the basis of plane waves, an all-electron
method relying on Augmented Plane Waves plus Local Orbitals, and an
intermediate approach implemented in the basis of Projector Augmented Waves
have been used. All these methods and approximations yield consistent results
for the pressure derivative of the bulk modulus and the volume dependence of
the mode Grueneisen parameter of diamond. The results are at variance with
recent precise measurements up to 140 GPa. Possible implications for the
experimental pressure determination based on the ruby luminescence method are
discussed.Comment: 10 pages, 6 figure
Structure and Dynamics of Liquid Iron under Earth's Core Conditions
First-principles molecular dynamics simulations based on density-functional
theory and the projector augmented wave (PAW) technique have been used to study
the structural and dynamical properties of liquid iron under Earth's core
conditions. As evidence for the accuracy of the techniques, we present PAW
results for a range of solid-state properties of low- and high-pressure iron,
and compare them with experimental values and the results of other
first-principles calculations. In the liquid-state simulations, we address
particular effort to the study of finite-size effects, Brillouin-zone sampling
and other sources of technical error. Results for the radial distribution
function, the diffusion coefficient and the shear viscosity are presented for a
wide range of thermodynamic states relevant to the Earth's core. Throughout
this range, liquid iron is a close-packed simple liquid with a diffusion
coefficient and viscosity similar to those of typical simple liquids under
ambient conditions.Comment: 13 pages, 8 figure
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