544 research outputs found
Two-component radiation model of the sonoluminescing bubble
Based on the experimental data from Weninger, Putterman & Barber, Phys. Rev.
(E), 54, R2205 (1996), we offer an alternative interpretation of their
experimetal results. A model of sonoluminescing bubble which proposes that the
electromagnetic radiation originates from two sources: the isotropic black body
or bramsstrahlung emitting core and dipole radiation-emitting shell of
accelerated electrons driven by the liquid-bubble interface is outlined.Comment: 5 pages Revtex, submitted to Phys. Rev.
Non-ergodicity of a globular protein extending beyond its functional timescale
Internal motions of folded proteins have been assumed to be ergodic, i.e., that the dynamics of a single protein molecule averaged over a very long time resembles that of an ensemble. Here, by performing single-molecule fluorescence resonance energy transfer (smFRET) experiments and molecular dynamics (MD) simulations of a multi-domain globular protein, cytoplasmic protein-tyrosine phosphatase (SHP2), we demonstrate that the functional inter-domain motion is observationally non-ergodic over the time spans 1012 to 107 s and 101 to 102 s. The difference between observational non-ergodicity and simple non-convergence is discussed. In comparison, a single-strand DNA of similar size behaves ergodically with an energy landscape resembling a one-dimensional linear chain. The observed non-ergodicity results from the hierarchical connectivity of the high-dimensional energy landscape of the protein molecule. As the characteristic time for the protein to conduct its dephosphorylation function is 10 s, our findings suggest that, due to the non-ergodicity, individual, seemingly identical protein molecules can be dynamically and functionally different
Visualizing leukocyte trafficking in the living brain with 2-photon intravital microscopy
Intravital imaging of the superficial brain tissue in mice represents a powerful tool for the dissection of the cellular and molecular cues underlying inflammatory and infectious central nervous system (CNS) diseases. We present here a step-by-step protocol that will enable a non-specialist to set up a two-photon brain-imaging model. The protocol offers a two-part approach that is specifically optimized for imaging leukocytes but can be easily adapted to answer varied CNS-related biological questions. The protocol enables simultaneous visualization of fluorescently labeled immune cells, the pial microvasculature and extracellular structures such as collagen fibers at high spatial and temporal resolution. Intracranial structures are exposed through a cranial window, and physiologic conditions are maintained during extended imaging sessions via continuous superfusion of the brain surface with artificial cerebrospinal fluid (aCSF). Experiments typically require 1–2 h of preparation, which is followed by variable periods of immune cell tracking. Our methodology converges the experience of two laboratories over the past 10 years in diseased animal models such as cerebral ischemia, lupus, cerebral malaria, and toxoplasmosis. We exemplify the utility of this protocol by tracking leukocytes in transgenic mice in the pial vessels under steady-state conditions
Mechanisms for Stable Sonoluminescence
A gas bubble trapped in water by an oscillating acoustic field is expected to
either shrink or grow on a diffusive timescale, depending on the forcing
strength and the bubble size. At high ambient gas concentration this has long
been observed in experiments. However, recent sonoluminescence experiments show
that in certain circumstances when the ambient gas concentration is low the
bubble can be stable for days. This paper presents mechanisms leading to
stability which predict parameter dependences in agreement with the
sonoluminescence experiments.Comment: 4 pages, 3 figures on request (2 as .ps files
Differential criterion of a bubble collapse in viscous liquids
The present work is devoted to a model of bubble collapse in a Newtonian
viscous liquid caused by an initial bubble wall motion. The obtained bubble
dynamics described by an analytic solution significantly depends on the liquid
and bubble parameters. The theory gives two types of bubble behavior: collapse
and viscous damping. This results in a general collapse condition proposed as
the sufficient differential criterion. The suggested criterion is discussed and
successfully applied to the analysis of the void and gas bubble collapses.Comment: 5 pages, 3 figure
Modelling mutational landscapes of human cancers in vitro
Experimental models that recapitulate mutational landscapes of human cancers are needed to decipher the
rapidly expanding data on human somatic mutations. We demonstrate that mutation patterns in
immortalised cell lines derived from primary murine embryonic fibroblasts (MEFs) exposed in vitro to
carcinogens recapitulate key features of mutational signatures observed in human cancers. In experiments
with several cancer-causing agents we obtained high genome-wide concordance between human tumour
mutation data and in vitro data with respect to predominant substitution types, strand bias and sequence
context. Moreover, we found signature mutations in well-studied human cancer driver genes. To explore
endogenous mutagenesis, we used MEFs ectopically expressing activation-induced cytidine deaminase
(AID) and observed an excess of AID signature mutations in immortalised cell lines compared to their
non-transgenic counterparts. MEF immortalisation is thus a simple and powerful strategy for modelling
cancer mutation landscapes that facilitates the interpretation of human tumour genome-wide sequencing
data
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