April 1st, 2014

лошадь, диаграмма, Фейнман

Нобелевка Намбу, сигма-мезон и масса видимой материи

Nambu's Nobel Prize, the $σ$ meson and the mass of visible matter: http://arxiv.org/abs/1403.7804

The electroweak Higgs boson has been discovered in ongoing experiments at the LHC, leading to a mass of this particle of 126 GeV. This Higgs boson mediates the generation of mass for elementary particles, including the mass of elementary (current) quarks. These current-quark masses leave 98% of the mass of the atom unexplained. This large fraction is mediated by strong interaction, where instead of the Higgs boson the $\sigma$ meson is the mediating particle. Though already discovered in 1957 by Schwinger, the $\sigma$ meson has been eliminated from many theories of hadron properties because it had not been observed and was doubted to exist. With the observation of the $\sigma$ meson in recent experiments on Compton scattering by the nucleon at MAMI (Mainz) it has become timely to review the status of experimental and theoretical researches on this topic.
Comments:19 pages, 2 figures, topical review
лошадь, диаграмма, Фейнман

Что мы знаем о лоренц-инвариантности?

What Do We Know About Lorentz Invariance? http://arxiv.org/abs/1403.7785

The realization that Planck-scale physics can be tested with existing technology through the search for spacetime-symmetry violation brought about the development of a comprehensive framework, known as the gravitational Standard-Model Extension (SME), for studying deviations from exact Lorentz and CPT symmetry in nature. The development of this framework and its motivation led to an explosion of new tests of Lorentz symmetry over the past decade and to considerable theoretical interest in the subject. This work reviews the key concepts associated with Lorentz and CPT symmetry, the structure of the SME framework, and some recent experimental and theoretical results.
27 pages, 1 figure, review article to appear in Rep. Prog. Phys.
лошадь, диаграмма, Фейнман

Эксперименты с липидным бислоем и самодельный усилитель

Каждый, кто когда-либо увлекался биофизикой, знает, что такое липидный бислой. Возьмем молекулы, у которых одна сторона (голова) гидрофильная, а другая (хвост) - гидрофобная. Нальем такой вещество в воду, хорошенько встряхнем - и случится чудо: гидрофобные (несмачивающиеся) хвосты выстроятся друг к дружке, а гидрофильные (смачивающиеся) головы будут смотреть наружу. Получится такой вот достаточно устойчивый двойной слой молекул, скорее всего, замкнувшийся в виде пузырька. Это хорошая модель клеточной мембраны (собственно, настоящая, живая мембрана отличается тем, что в нее тут и там встроены молекулы различных белков и тому подобными вещами). [Если я в чем-то неправ, химики, поправьте!]

Вот в этой статье: The OpenPicoAmp : an open-source planar lipid bilayer amplifier for hands-on learning of neuroscience: http://arxiv.org/abs/1403.7439
рассказывается, как сделать чувствительный усилитель для учебных экспериментов с такими искусственными мембранами и описываются сами эксперименты. Для первого семестра биофизики и нейрофизиологии.

Neuroscience education can be promoted by the availability of low cost and engaging teaching materials. To address this, we developed an open-source lipid bilayer amplifier, the OpenPicoAmp, which is appropriate for use in introductory courses in biophysics or neurosciences concerning the electrical properties of the cell membrane. The amplifier is designed using the common lithographic printed circuit board fabrication process and off-the-shelf electronic components. In addition, we propose a specific design for experimental chambers allowing the insertion of a commercially available polytetrafluoroethylene film. This experimental setup can be used in simple experiments in which students monitor the bilayer formation by capacitance measurement and record unitary currents produced by ionophores like gramicidin A. Used in combination with a low-cost data acquisition board this system provides a complete solution for hands-on lessons, therefore improving the effectiveness in teaching basic neurosciences or biophysics.
Comments:10 pages, 4 figures and supplementary information (9 files including one movie)