5,738 research outputs found
Effective Action for Cosmological Scalar Fields at Finite Temperature
Scalar fields appear in many theories beyond the Standard Model of particle
physics. In the early universe, they are exposed to extreme conditions,
including high temperature and rapid cosmic expansion. Understanding their
behavior in this environment is crucial to understand the implications for
cosmology. We calculate the finite temperature effective action for the field
expectation value in two particularly important cases, for damped oscillations
near the ground state and for scalar fields with a flat potential. We find that
the behavior in both cases can in good approximation be described by a complex
valued effective potential that yields Markovian equations of motion. Near the
potential minimum, we recover the solution to the well-known Langevin equation.
For large field values we find a very different behavior, and our result for
the damping coefficient differs from the expressions frequently used in the
literature. We illustrate our results in a simple scalar model, for which we
give analytic approximations for the effective potential and damping
coefficient. We also provide various expressions for loop integrals at finite
temperature that are useful for future calculations in other models.Comment: 34 pages plus appendix, 17 figures: minor corrections, modifications
of discussions, added references, version published in JHE
Meteorin regulates mesendoderm development by enhancing nodal expression
During gastrulation, distinct lineage specification into three germ layers, the mesoderm, endoderm and ectoderm, occurs through an elaborate harmony between signaling molecules along the embryonic proximo-distal and anterior-posterior axes, and Nodal signaling plays a key role in the early embryonic development governing embryonic axis formation, mesoderm and endoderm specification, and left-right asymmetry determination. However, the mechanism by which Nodal expression is regulated is largely unknown. Here, we show that Meteorin regulates Nodal expression and is required for mesendoderm development. It is highly expressed in the inner cell mass of blastocysts and further in the epiblast and extra-embryonic ectoderm during gastrulation. Genetic ablation of the Meteorin gene resulted in early embryonic lethality, presumably due to impaired lineage allocation and subsequent cell accumulation. Embryoid body culture using Meteorin-null embryonic stem (ES) cells showed reduced Nodal expression and concomitant impairment of mesendoderm specification. Meteorin-null embryos displayed reduced levels of Nodal transcripts before the gastrulation stage, and impaired expression of Goosecoid, a definitive endoderm marker, during gastrulation, while the proximo-distal and anterior-posterior axes and primitive streak formation were preserved. Our results show that Meteorin is a novel regulator of Nodal transcription and is required to maintain sufficient Nodal levels for endoderm formation, thereby providing new insights in the regulation of mesendoderm allocation.open1113sciescopu
Controlled release of human growth hormone fused with a human hybrid Fc fragment through a nanoporous polymer membrane
Nanotechnology has been applied to the development of more effective and compatible drug delivery systems for therapeutic proteins. Human growth hormone (hGH) was fused with a hybrid Fc fragment containing partial Fc domains of human IgD and IgG(4) to produce a long-acting fusion protein. The fusion protein, hGH-hyFc, resulted in the increase of the hydrodynamic diameter (ca. 11 nm) compared with the diameter (ca. 5 nm) of the recombinant hGH. A diblock copolymer membrane with nanopores (average diameter of 14.3 nm) exhibited a constant release rate of hGH-hyFc. The hGH-hyFc protein released in a controlled manner for one month was found to trigger the phosphorylation of Janus kinase 2 (JAK2) in human B lymphocyte and to exhibit an almost identical circular dichroism spectrum to that of the original hGH-hyFc, suggesting that the released fusion protein should maintain the functional and structural integrity of hGH. Thus, the nanoporous release device could be a potential delivery system for the long-term controlled release of therapeutic proteins fused with the hybrid Fc fragment.X111313sciescopu
Palladium Catalysts for Dehydrogenation of Ammonia Borane with Preferential B−H Activation
Cationic Pd(II) complexes catalyzed the dehydrogenation of ammonia borane in the most efficient manner with the release of 2.0 equiv of H_2 in less than 60 s at 25 °C. Most of the hydrogen atoms were obtained from the boron atom of the ammonia borane. The first step of the dehydrogenation reaction was elaborated using density functional theory calculations
Derivation of the Classical Lagrangian for the Relativistic Spinning Particle
The `classical' model for a massive spinning particle, which was recently
proposed, is derived from the isotropic rotator model. Through this derivation,
we note that the spin can be understood as the relativistic extension of the
isotropic rotator. Furthermore, the variables t_\m corresponding to the
\p^* of the `pseudo-classical' model, are necessary for the covariant
formulation. The dynamical term for these extra variables is naturally obtained
and the meaning of the constraint term p^\s\L_{\s\n}+mt_\n =0, which was
recently shown to give `quasi-supersymmetry', is clarified.Comment: 8 pages, LaTe
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