617 research outputs found
Floating stocks in FMCG supply chains
In this paper we present a new distribution concept called ‘floating stocks’, which uses intermodal transport to deploy inventories in a supply chain in advance of retailer demand. Supplying part of the demand directly by road compensates the longer transit time of this transport. First an analytical comparison is made which shows that this concept has advantages in inventories over pure road and intermodal transport. Next a simulation study of a real case is made which quantifies the cost-differences in detail
Hysteresis and bi-stability by an interplay of calcium oscillations and action potential firing
Many cell types exhibit oscillatory activity, such as repetitive action
potential firing due to the Hodgkin-Huxley dynamics of ion channels in the cell
membrane or reveal intracellular inositol triphosphate (IP) mediated
calcium oscillations (CaOs) by calcium-induced calcium release channels
(IP-receptor) in the membrane of the endoplasmic reticulum (ER). The
dynamics of the excitable membrane and that of the IP-mediated CaOs have
been the subject of many studies. However, the interaction between the
excitable cell membrane and IP-mediated CaOs, which are coupled by
cytosolic calcium which affects the dynamics of both, has not been studied.
This study for the first time applied stability analysis to investigate the
dynamic behavior of a model, which includes both an excitable membrane and an
intracellular IP-mediated calcium oscillator. Taking the IP
concentration as a control parameter, the model exhibits a novel rich spectrum
of stable and unstable states with hysteresis. The four stable states of the
model correspond in detail to previously reported growth-state dependent states
of the membrane potential of normal rat kidney fibroblasts in cell culture. The
hysteresis is most pronounced for experimentally observed parameter values of
the model, suggesting a functional importance of hysteresis. This study shows
that the four growth-dependent cell states may not reflect the behavior of
cells that have differentiated into different cell types with different
properties, but simply reflect four different states of a single cell type,
that is characterized by a single model.Comment: 29 pages, 6 figure
A globally efficient means of distributing UTC time and frequency through GPS
Time and frequency outputs comparable in quality to the best laboratories have been demonstrated on an integrated system suitable for field application on a global basis. The system measures the time difference between 1 pulse-per-second (pps) signals derived from local primary frequency standards and from a multi-channel GPS C/A receiver. The measured data is processed through optimal SA Filter algorithms that enhance both the stability and accuracy of GPS timing signals. Experiments were run simultaneously at four different sites. Even with large distances between sites, the overall results show a high degree of cross-correlation of the SA noise. With sufficiently long simultaneous measurement sequences, the data shows that determination of the difference in local frequency from an accepted remote standard to better than 1 x 10(exp -14) is possible. This method yields frequency accuracy, stability, and timing stability comparable to that obtained with more conventional common-view experiments. In addition, this approach provides UTC(USNO MC) in real time to an accuracy better than 20 ns without the problems normally associated with conventional common-view techniques. An experimental tracking loop was also set up to demonstrate the use of enhanced GPS for dissemination of UTC(USNO MC) over a wide geographic area. Properly disciplining a cesium standard with a multi-channel GPS receiver, with additional input from USNO, has been found to permit maintaining a timing precision of better than 10 ns between Palo Alto, CA and Washington, DC
Double Exchange Alone Does Not Explain the Resistivity of
The system with has
traditionally been modelled with a ``double exchange'' Hamiltonian, in which it
is assumed that the only relevant physics is the tendency of carrier hopping to
line up neighboring spins. We present a solution of the double exchange model,
show it is incompatible with many aspects of the resistivity data, and propose
that a strong electron-phonon interaction arising from a Jahn-Teller splitting
of the outer Mn d-level plays a crucial role.Comment: Figure available via concentional mail. Contact
[email protected]
Impact of Charge Ordering on Magnetic Correlations in Perovskite (Bi,Ca)MnO_3
Single crystalline (Bi,Ca)MnO3 (74< %Ca <82) were studied with neutron
scattering, electron diffraction and bulk magnetic measurement. We discovered
dynamic ferromagnetic spin correlations at high temperatures, which are
replaced by antiferromagnetic spin fluctuations at a concomitant charge
ordering and structural transition. Our results indicate that thermal-activated
hopping of the Jahn-Teller active e_g electrons in these insulating materials,
nevertheless, induce ferromagnetic interaction through double-exchange
mechanism. It is the ordering of these charges competing with the
double-exchange ferromagnetic metallic state.Comment: 11 pages, 3 figures, Revte
Topological Phase Diagram of a Two-Subband Electron System
We present a phase diagram for a two-dimensional electron system with two
populated subbands. Using a gated GaAs/AlGaAs single quantum well, we have
mapped out the phases of various quantum Hall states in the density-magnetic
filed plane. The experimental phase diagram shows a very different topology
from the conventional Landau fan diagram. We find regions of negative
differential Hall resistance which are interpreted as preliminary evidence of
the long sought reentrant quantum Hall transitions. We discuss the origins of
the anomalous topology and the negative differential Hall resistance in terms
of the Landau level and subband mixing.Comment: 4 pages, 4 figure
Electron Correlation and Jahn-Teller Interaction in Manganese Oxides
The interplay between the electron repulsion and the Jahn-Teller
electron-phonon interation is studied with a large model for the
ferromagnetic state of the manganese oxides. These two interactions collaborate
to induce the local isospin (orbital) moments and reduce the bandwidth .
Especially the retardation effect of the Jahn-Teller phonon with the frequency
is effective to reduce , but the strong -dependence occurs
even when the Coulombic interaction is dominating () as long as
. The phonon spectrum consists of two components, i.e., the
temperature independent sharp peak at and that corresponding to the Kondo peak. These results
compared with the experiments suggest that in the metallic
manganese oxides.Comment: REVTE
Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges
A new traceability chain for the derivation of the farad from dc quantum Hall
effect has been implemented at INRIM. Main components of the chain are two new
coaxial transformer bridges: a resistance ratio bridge, and a quadrature
bridge, both operating at 1541 Hz. The bridges are energized and controlled
with a polyphase direct-digital-synthesizer, which permits to achieve both main
and auxiliary equilibria in an automated way; the bridges and do not include
any variable inductive divider or variable impedance box. The relative
uncertainty in the realization of the farad, at the level of 1000 pF, is
estimated to be 64E-9. A first verification of the realization is given by a
comparison with the maintained national capacitance standard, where an
agreement between measurements within their relative combined uncertainty of
420E-9 is obtained.Comment: 15 pages, 11 figures, 3 table
A simple view of linguistic complexity
Although a growing number of second language acquisition (SLA) studies take linguistic complexity as a dependent variable, the term is still poorly defined and often used with different meanings, thus posing serious problems for research synthesis and knowledge accumulation. This article proposes a simple, coherent view of the construct, which is defined in a purely structural way, i.e. the complexity directly arising from the number of linguistic elements and their interrelationships. Issues of cognitive cost (difficulty) or developmental dynamics (acquisition) are explicitly excluded from this theoretical definition and its operationalization. The article discusses how the complexity of an interlanguage system can be assessed based on the limited samples SLA researchers usually work with. For the areas of morphology, syntax and the lexicon, some measures are proposed which are coherent with the purely structural view advocated, and issues related to their operationalization are critically scrutinized
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