Mechanical rupture explains a bacterium’s puzzling “pop”

Physics Today ◽  
2015 ◽  
Vol 68 (7) ◽  
pp. 12-14
Author(s):  
Ashley G. Smart
Keyword(s):  
Mechanical Rupture

Atomic structure and physical properties of fused porphyrin nanoclusters

2014 ◽  
Vol 18 (07) ◽  
pp. 552-568 ◽  
Author(s):  
Pavel V. Avramov ◽  
Alex A. Kuzubov ◽  
Seiji Sakai ◽  
Manabu Ohtomo ◽  
Shiro Entani ◽  
...  
Keyword(s):  
Self Assembly ◽  
Electronic Structures ◽  
Ligand Field ◽  
Spin States ◽  
Cubic Symmetry ◽  
Potential Barriers ◽  
High Spin States ◽  
Formation Energies ◽  
Homo Lumo ◽  
Mechanical Rupture

The atomic and electronic structures, mechanical properties and potential barriers of formation of a set of meso–meso β–β fused porphyrin/metalloporphyrin nanopages, nanotapes, nanotubes and 2D nanofabrics were studied by GGA LC-DFT technique using cluster and PBC models. The porphyrin pages of the nanoclusters are connected with each other by graphene fragments formed by meso–meso β–β links. Fusion of all the edges of six porphyrin/metalloporphyrin units produces a novel ~ 1 nm sized molecule of cubic symmetry with a hollow cage inside. It was found that all studied nanoclusters are metastable with formation energies 0.36–7.57 kcal/mol per atom. Under applied mechanical stress, the nanoclusters exhibit superelastic and ultrastrong properties with binding graphene fragments being the weakest links for mechanical rupture. Depending on the spin-dependent reaction pathways, the hollow caged nanoclusters exhibit almost zero or low potential energy barriers (1–10 kcal/mol) during the initial stages of self-assembly. All nanoclusters exibit the main features of the electronic structures of the parent porphyrins, in particular the nature of HOMO/LUMO states and the relative energetic positions of the metal d states. The induced curvature of the hollow cage nanoclusters leads to admixture of more than 2% of the dπ⊥ states to the dσ energy region and formation of vacant superatomic molecular orbitals of d character in cubic ligand field. The Fe -derived hollow-caged nanoclusters reveal extremely high spin states with small energy differences between ferromagnetic and antiferromagnetic configurations, which can be utilized for quantum holonomic computations.

Mechanical Fatigue Limit for Rubber

1966 ◽  
Vol 39 (2) ◽  
pp. 348-364 ◽  
Author(s):  
G. J. Lake ◽  
P. B. Lindley
Keyword(s):  
Fatigue Limit ◽  
Growth Behavior ◽  
Energy Characteristics ◽  
Mechanical Fatigue ◽  
Tearing Energy ◽  
Number Of Cycles ◽  
Cycles To Failure ◽  
Limiting Value ◽  
Mechanical Rupture

Abstract Investigations of the dynamic cut growth behavior of vulcanized rubbers indicate that there is a minimum tearing energy at which mechanical rupture of chains occurs. The limiting value is characteristic of each vulcanizate, but is in the region of 0.05 kg/cm. The mechanical fatigue limit, below which the number of cycles to failure increases rapidly, is accurately predicted from this critical tearing energy. Characteristics of cut growth at low tearing energies, and effects of polymer, vulcanizing system, oxygen, and fillers on the critical tearing energy and fatigue limit are discussed.

scholarly journals Embryonic nodal flow and the dynamics of nodal vesicular parcels

2006 ◽  
Vol 4 (12) ◽  
pp. 49-56 ◽  
Author(s):  
Julyan H.E Cartwright ◽  
Nicolas Piro ◽  
Oreste Piro ◽  
Idan Tuval
Keyword(s):  
Fluid Flow ◽  
Closed System ◽  
Biochemical Mechanism ◽  
Numerical Techniques ◽  
Biophysical Properties ◽  
Nodal Flow ◽  
Dynamical Simulations ◽  
Mechanical Rupture

We address with fluid-dynamical simulations using direct numerical techniques three important and fundamental questions with respect to fluid flow within the mouse node and left–right development. First, we consider the differences between what is experimentally observed when assessing cilium-induced fluid flow in the mouse node in vitro and what is to be expected in vivo . The distinction is that in vivo , the leftward fluid flow across the mouse node takes place within a closed system and is consequently confined, while this is no longer the case on removing the covering membrane and immersing the embryo in a fluid-filled volume to perform in vitro experiments. Although there is a central leftward flow in both instances, we elucidate some important distinctions about the closed in vivo situation. Second, we model the movement of the newly discovered nodal vesicular parcels (NVPs) across the node and demonstrate that the flow should indeed cause them to accumulate on the left side of the node, as required for symmetry breaking. Third, we discuss the rupture of NVPs. Based on the biophysical properties of these vesicles, we argue that the morphogens they contain are likely not delivered to the surrounding cells by their mechanical rupture either by the cilia or the flow, and rupture must instead be induced by an as yet undiscovered biochemical mechanism.

scholarly journals Tension-activated channels in the mechanism of osmotic fitness in Pseudomonas aeruginosa

2017 ◽  
Vol 149 (5) ◽  
pp. 595-609 ◽  
Author(s):  
Uğur Çetiner ◽  
Ian Rowe ◽  
Anthony Schams ◽  
Christina Mayhew ◽  
Deanna Rubin ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Opportunistic Pathogen ◽  
High Rate ◽  
Cloning And Expression ◽  
Osmotic Swelling ◽  
Excised Patches ◽  
Dilution Experiments ◽  
Kinetics Of ◽  
Flow Experiments ◽  
Mechanical Rupture

Pseudomonas aeruginosa (PA) is an opportunistic pathogen with an exceptional ability to adapt to a range of environments. Part of its adaptive potential is the ability to survive drastic osmolarity changes. Upon a sudden dilution of external medium, such as during exposure to rain, bacteria evade mechanical rupture by engaging tension-activated channels that act as osmolyte release valves. In this study, we compare fast osmotic permeability responses in suspensions of wild-type PA and Escherichia coli (EC) strains in stopped-flow experiments and provide electrophysiological descriptions of osmotic-release channels in PA. Using osmotic dilution experiments, we first show that PA tolerates a broader range of shocks than EC. We record the kinetics of cell equilibration reported by light scattering responses to osmotic up- and down-shocks. PA exhibits a lower water permeability and faster osmolyte release rates during large osmotic dilutions than EC, which correlates with better survival. To directly characterize the PA tension-activated channels, we generate giant spheroplasts from this microorganism and record current responses in excised patches. Unlike EC, which relies primarily on two types of channels, EcMscS and EcMscL, to generate a distinctive two-wave pressure ramp response, PA exhibits a more gradual response that is dominated by MscL-type channels. Genome analysis, cloning, and expression reveal that PA possesses one MscL-type (PaMscL) and two MscS-type (PaMscS-1 and 2) proteins. In EC spheroplasts, both PaMscS channels exhibit a slightly earlier activation by pressure compared with EcMscS. Unitary currents reveal that PaMscS-2 has a smaller conductance, higher anionic preference, stronger inactivation, and slower recovery compared with PaMscS-1. We conclude that PA relies on MscL as the major valve defining a high rate of osmolyte release sufficient to curb osmotic swelling under extreme shocks, but it still requires MscS-type channels with a strong propensity to inactivation to properly terminate massive permeability response.

scholarly journals Emphysema and Mechanical Stress-Induced Lung Remodeling

Physiology ◽  
2013 ◽  
Vol 28 (6) ◽  
pp. 404-413 ◽  
Author(s):  
Béla Suki ◽  
Susumu Sato ◽  
Harikrishnan Parameswaran ◽  
Margit V. Szabari ◽  
Ayuko Takahashi ◽  
...  
Keyword(s):  
Mechanical Stress ◽  
Transpulmonary Pressure ◽  
Mechanical Stresses ◽  
Lung Remodeling ◽  
Cell Functions ◽  
New Directions ◽  
Mechanical Factors ◽  
Mechanical Rupture

Transpulmonary pressure and the mechanical stresses of breathing modulate many essential cell functions in the lung via mechanotransduction. We review how mechanical factors could influence the pathogenesis of emphysema. Although the progression of emphysema has been linked to mechanical rupture, little is known about how these stresses alter lung remodeling. We present possible new directions and an integrated multiscale view that may prove useful in finding solutions for this disease.

scholarly journals Two different types of double-strand breaks in Saccharomyces cerevisiae are repaired by similar RAD52-independent, nonhomologous recombination events

1994 ◽  
Vol 14 (2) ◽  
pp. 1293-1301
Author(s):  
K M Kramer ◽  
J A Brock ◽  
K Bloom ◽  
J K Moore ◽  
J E Haber
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cleavage Site ◽  
Mammalian Cells ◽  
Strand Break ◽  
Double Strand Breaks ◽  
Strand Breaks ◽  
High Level ◽  
A Site ◽  
Mat Locus ◽  
Mechanical Rupture

In haploid rad52 Saccharomyces cerevisiae strains unable to undergo homologous recombination, a chromosomal double-strand break (DSB) can be repaired by imprecise rejoining of the broken chromosome ends. We have used two different strategies to generate broken chromosomes: (i) a site-specific DSB generated at the MAT locus by HO endonuclease cutting or (ii) a random DSB generated by mechanical rupture during mitotic segregation of a conditionally dicentric chromosome. Broken chromosomes were repaired by deletions that were highly variable in size, all of which removed more sequences than was required either to prevent subsequent HO cleavage or to eliminate a functional centromere, respectively. The junction of the deletions frequently occurred where complementary strands from the flanking DNA could anneal to form 1 to 5 bp, although 12% (4 of 34) of the events appear to have occurred by blunt-end ligation. These types of deletions are very similar to the junctions observed in the repair of DSBs by mammalian cells (D. B. Roth and J. H. Wilson, Mol. Cell. Biol. 6:4295-4304, 1986). When a high level of HO endonuclease, expressed in all phases of the cell cycle, was used to create DSBs, we also recovered a large class of very small (2- or 3-bp) insertions in the HO cleavage site. These insertions appear to represent still another mechanism of DSB repair, apparently by annealing and filling in the overhanging 3' ends of the cleavage site. These types of events have also been well documented for vertebrate cells.

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