Crystal Nucleation in a Supercooled Liquid with Glassy Dynamics

In simulations of supercooled, high-density liquid silica we study a range of temperature T in which we find both crystal nucleation, as well as the characteristic dynamics of a glass forming liquid, including a breakdown of the Stokes-Einstein relation. We find that the liquid cannot be observed below a homogeneous nucleation limit (HNL) at which the liquid crystallizes faster than it can equilibrate. We show that the HNL would occur at lower T, and perhaps not at all, if the Stokes-Einstein relation were obeyed, and hence that glassy dynamics plays a central role in setting a crystallization limit on the liquid state in this case. We also explore the relation of the HNL to the Kauzmann temperature, and test for spinodal-like effects near the HNL.Comment: 4 pages, 4 figure

Cavity-assisted spontaneous emission as a single-photon source: Pulse shape and efficiency of one-photon Fock state preparation

Within the framework of exact quantum electrodynamics in dispersing and absorbing media, we have studied the quantum state of the radiation emitted from an initially in the upper state prepared two-level atom in a high-$Q$ cavity, including the regime where the emitted photon belongs to a wave packet that simultaneously covers the areas inside and outside the cavity. For both continuing atom--field interaction and short-term atom--field interaction, we have determined the spatio-temporal shape of the excited outgoing wave packet and calculated the efficiency of the wave packet to carry a one-photon Fock state. Furthermore, we have made contact with quantum noise theories where the intracavity field and the field outside the cavity are regarded as approximately representing independent degrees of freedom such that two separate Hilbert spaces can be introduced.Comment: 16 pages, 7 eps figures; improved version as submitted to Phys. Rev.

Determination of quantum-noise parameters of realistic cavities

A procedure is developed which allows one to measure all the parameters occurring in a complete model [A.A. Semenov et al., Phys. Rev. A 74, 033803 (2006); quant-ph/0603043] of realistic leaky cavities with unwanted noise. The method is based on the reflection of properly chosen test pulses by the cavity.Comment: 5 pages, 2 figure

Universal measurement of quantum correlations of radiation

A measurement technique is proposed which, in principle, allows one to observe the general space-time correlation properties of a quantized radiation field. Our method, called balanced homodyne correlation measurement, unifies the advantages of balanced homodyne detection with those of homodyne correlation measurements.Comment: 4 pages, 4 figures, small misprints were corrected, accepted to Phys. Rev. Let

INFLUENCE OF LIGNIN ON DIGESTIBILITY OF FORAGE CELL WALL MATERIAL

One-hundred-ninety-four grass samples, representing eight species, were used to determine the relationships of in vitro forage dry matter, cell wall, hemicellulose and cellulose digestibilities with lignin concentration. Linear regressions indicated that dry matter digestion was inhibited to a lesser degree (P\u3c.05) by lignin concentration than was cell wall digestion. Results for linear regressions of hemicellulose and cellulose digestibilities as functions of lignin concentration showed a greater (P\u3c.05) effect of lignin on cellulose digestion. Smooth bromegrass and switchgrass were collected at both Clay Center and Mead, NE; for all digestibility measures, the Clay Center samples gave stronger (P\u3c.05) negative correlations with lignin. A comparison of linear and curvilinear models indicated that, for all digestion measurements, the curvilinear model was a better (P\u3c.05) description of relationships with lignin concentration. For all digestibility measures, lignin\u27s inhibiting effect declined at higher lignin concentrations. The curvilinear models did not show significant differences among the digestibility measures for effect of lignin. The demonstration that the forage digestibility response to lignin\u27s inhibitory effect is curvilinear in nature suggests that the mechanism of hgnin\u27s inhibition is complex

De novo sequencing of the Hypericum perforatum L. flower transcriptome to identify potential genes that are related to plant reproduction sensu lato

BACKGROUND: St. John’s wort (Hypericum perforatum L.) is a medicinal plant that produces important metabolites with antidepressant and anticancer activities. Recently gained biological information has shown that this species is also an attractive model system for the study of a naturally occurring form of asexual reproduction called apomixis, which allows cloning plants through seeds. In aposporic gametogenesis, one or multiple somatic cells belonging to the ovule nucellus change their fate by dividing mitotically and developing functionally unreduced embryo sacs by mimicking sexual gametogenesis. Although the introduction of apomixis into agronomically important crops could have revolutionary implications for plant breeding, the genetic control of this mechanism of seed formation is still not well understood for most of the model species investigated so far. We used Roche 454 technology to sequence the entire H. perforatum flower transcriptome of whole flower buds and single flower verticils collected from obligately sexual and unrelated highly or facultatively apomictic genotypes, which enabled us to identify RNAs that are likely exclusive to flower organs (i.e., sepals, petals, stamens and carpels) or reproductive strategies (i.e., sexual vs. apomictic). RESULTS: Here we sequenced and annotated the flower transcriptome of H. perforatum with particular reference to reproductive organs and processes. In particular, in our study we characterized approximately 37,000 transcripts found expressed in male and/or female reproductive organs, including tissues or cells of sexual and apomictic flower buds. Ontological annotation was applied to identify major biological processes and molecular functions involved in flower development and plant reproduction. Starting from this dataset, we were able to recover and annotate a large number of transcripts related to meiosis, gametophyte/gamete formation, and embryogenesis, as well as genes that are exclusively or preferentially expressed in sexual or apomictic libraries. Real-Time RT-qPCR assays on pistils and anthers collected at different developmental stages from accessions showing alternative modes of reproduction were used to identify potential genes that are related to plant reproduction sensu lato in H. perforatum. CONCLUSIONS: Our approach of sequencing flowers from two fully obligate sexual genotypes and two unrelated highly apomictic genotypes, in addition to different flower parts dissected from a facultatively apomictic accession, enabled us to analyze the complexity of the flower transcriptome according to its main reproductive organs as well as for alternative reproductive behaviors. Both annotation and expression data provided original results supporting the hypothesis that apomixis in H. perforatum relies upon spatial or temporal mis-expression of genes acting during female sexual reproduction. The present analyses aim to pave the way toward a better understanding of the molecular basis of flower development and plant reproduction, by identifying genes or RNAs that may differentiate or regulate the sexual and apomictic reproductive pathways in H. perforatum. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12864-015-1439-y) contains supplementary material, which is available to authorized users

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

The recently discovered scaling law for the relaxation times, tau=f(T,V^g), where T is temperature and V the specific volume, is derived by a revision of the entropy model of the glass transition dynamics originally proposed by Avramov [I. Avramov, J. Non-Cryst. Solids 262, 258 (2000).]. In this modification the entropy is calculated by an alternative route, while retaining the approximation that the heat capacity is constant with T and P. The resulting expression for the variation of the relaxation time with T and V is shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover. From this analysis, which is valid for any model in which the relaxation time is a function of the entropy. we find that the scaling exponent g can be identified with the Gruneisen constant.Comment: 24 pages, 7 figure

Origin of non-exponential relaxation in a crystalline ionic conductor: a multi-dimensional 109Ag NMR study

The origin of the non-exponential relaxation of silver ions in the crystalline ion conductor Ag7P3S11 is analyzed by comparing appropriate two-time and three-time 109Ag NMR correlation functions. The non-exponentiality is due to a rate distribution, i.e., dynamic heterogeneities, rather than to an intrinsic non-exponentiality. Thus, the data give no evidence for the relevance of correlated back-and-forth jumps on the timescale of the silver relaxation.Comment: 4 pages, 3 figure