2,372 research outputs found
Detailed Balance Condition and Effective Free Energy in the Primitive Chain Network Model
We consider statistical mechanical properties of the primitive chain network
(PCN) model for entangled polymers from its dynamic equations. We show that the
dynamic equation for the segment number of the PCN model does not reduce to the
standard Langevin equation which satisfies the detailed balance condition. We
propose heuristic modifications for the PCN dynamic equation for the segment
number, to make it reduce to the standard Langevin equation. We analyse some
equilibrium statistical properties of the modified PCN model, by using the
effective free energy obtained from the modified PCN dynamic equations. The PCN
effective free energy can be interpreted as the sum of the ideal Gaussian chain
free energy and the repulsive interaction energy between slip-links. By using
the single chain approximation, we calculate several distribution functions of
the PCN model. The obtained distribution functions are qualitatively different
from ones for the simple slip-link model without any direct interactions
between slip-links.Comment: 29 pages, 7 figures, to appeare in J. Chem. Phy
Plateau Moduli of Several Single-Chain Slip-Link and Slip-Spring Models
We calculate the plateau moduli of several single-chain slip-link and
slip-spring models for entangled polymers. In these models, the entanglement
effects are phenomenologically modeled by introducing topological constraints
such as slip-links and slip-springs. The average number of segments between two
neighboring slip-links or slip-springs, , is an input parameter in these
models. To analyze experimental data, the characteristic number of segments in
entangled polymers estimated from the plateau modulus is used instead.
Both and characterize the topological constraints in entangled
polymers, and naively is considered to be the same as . However,
earlier studies showed that and (or the plateau modulus) should
be considered as independent parameters. In this work, we show that due to the
fluctuations at the short time scale, deviates from . This means
that the relation between and the plateau modulus is not simple as
naively expected. The plateau modulus (or ) depends on the
subchain-scale details of the employed model, as well as the average number of
segments . This is due to the fact that the subchain-scale fluctuation
mechanisms depend on the model rather strongly. We theoretically calculate the
plateau moduli for several single-chain slip-link and slip-spring models. Our
results explicitly show that the relation between and is
model-dependent. We compare theoretical results with various simulation data in
the literature, and show that our theoretical expressions reasonably explain
the simulation results.Comment: 26 pages, 3 figures, to appear in Macromolecule
FGF23 and Hypophosphatemic Rickets/Osteomalacia
Purpose of review
X-linked hypophosphatemia and tumor-induced osteomalacia are diseases characterized by hypophosphatemia with impaired proximal tubular phosphate reabsorption. Complete resection of responsible tumors is the first line therapy for patients with tumor-induced osteomalacia. In contrast, phosphate and active vitamin D have been used for patients with X-linked hypophosphatemia and inoperable ones with tumor-induced osteomalacia. The purpose of this review is to summarize the pathogenesis of these diseases and discuss about the new treatment.
Recent findings
Excessive FGF23 production has been shown to underline several kinds of hypophosphatemic rickets/osteomalacia including X-linked hypophosphatemia and tumor-induced osteomalacia. Burosumab, an anti-FGF23 monoclonal antibody, was approved for clinical use while the indications of burosumab are different depending on countries.
Summary
The inhibition of excessive FGF23 activity has been approved as a new therapy for several kinds of hypophosphatemic diseases. Further studies are necessary to clarify the long-term effects and safety of burosumab
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