Towards Relativistic Skyrmions

We revisit baryons in the Skyrme model. Starting from static baryons in the helicity eigenstates, we generalize their wavefunctions to the non-static and relativistic regime. A new representation for gamma matrices in the soliton collective space is constructed and the corresponding Dirac equation is obtained. As an example, we draw consideration on how to apply this new representation on the calculus of vector current vacuum expectation values for baryon states of spin and isospin half and arbitrary momenta and we show how elastic form factors can be derived.Comment: 7 pages, 7th Conference Mathematical Methods in Physics - Londrina 2012, Rio de Janeiro, Brazi

Rotational energy transfer in hydrogen halide molecules at supersonic beam velocities

Rotational energy transfer cross sections are calculated for HCl–HCl and HCl–HF collisions using classical trajectories. The exponential model for the rotational results is compared with transitions j-->j[prime] in collisions of a supersonic HCl molecular beam with a thermal beam. Reasonable agreement with the functional form of that model is obtained. The trajectory results indicate that some modification is needed in the exponential formula, to account for microscopic reversibility in rotor–rotor collisions. Using a simple intermolecular potential without adjustable parameters, in which the only anisotropic terms are of the dipolar and dispersion type (i.e., long range), reasonable agreement is obtained with the experimental constant for HCl–HCl in the exponential. Calculations are also described for HCl–HI and HCl–HBr collisions. Microscopic reversibility for the averaged cross sections is discussed in connection with the exponential model

Evolution, Perfection, and Theories of Language

In this article it is argued that evolutionary plausibility must be made an important constraining factor when building theories of language. Recent suggestions that presume that language is necessarily a perfect or optimal system are at odds with this position, evolutionary theory showing us that evolution is a meliorizing agent often producing imperfect solutions. Perfection of the linguistic system is something that must be demonstrated, rather than presumed. Empirically, examples of imperfection are found not only in nature and in human cognition, but also in language — in the form of ambiguity, redundancy, irregularity, movement, locality conditions, and extra-grammatical idioms. Here it is argued that language is neither perfect nor optimal, and shown how theories of language which place these proper-ties at their core run into both conceptual and empirical problems

A microfluidic processor for gene expression profiling of single human embryonic stem cells

The gene expression of human embryonic stem cells (hESC) is a critical aspect for understanding the normal and pathological development of human cells and tissues. Current bulk gene expression assays rely on RNA extracted from cell and tissue samples with various degree of cellular heterogeneity. These cell population averaging data are difficult to interpret, especially for the purpose of understanding the regulatory relationship of genes in the earliest phases of development and differentiation of individual cells. Here, we report a microfluidic approach that can extract total mRNA from individual single-cells and synthesize cDNA on the same device with high mRNA-to-cDNA efficiency. This feature makes large-scale single-cell gene expression profiling possible. Using this microfluidic device, we measured the absolute numbers of mRNA molecules of three genes (B2M, Nodal and Fzd4) in a single hESC. Our results indicate that gene expression data measured from cDNA of a cell population is not a good representation of the expression levels in individual single cells. Within the G0/G1 phase pluripotent hESC population, some individual cells did not express all of the 3 interrogated genes in detectable levels. Consequently, the relative expression levels, which are broadly used in gene expression studies, are very different between measurements from population cDNA and single-cell cDNA. The results underscore the importance of discrete single-cell analysis, and the advantages of a microfluidic approach in stem cell gene expression studies

Production of negative parity baryons in the holographic Sakai-Sugimoto model

We extend our investigation of resonance production in the Sakai-Sugimoto model to the case of negative parity baryon resonances. Using holographic techniques we extract the generalized Dirac and Pauli baryon form factors as well as the helicity amplitudes for these baryonic states. Identifying the first negative parity resonance with the experimentally observed S_{11}(1535), we find reasonable agreement with experimental data from the JLab-CLAS collaboration. We also estimate the contribution of negative parity baryons to the proton structure functions.Comment: 1+30 pages, 8 figures. v3: typos corrected, references added, section 2 and 3 shortened, improved discussion of helicity amplitudes and comparison with experimental result