Missing physics in stick-slip dynamics of a model for peeling of an adhesive tape

It is now known that the equations of motion for the contact point during peeling of an adhesive tape mounted on a roll introduced earlier are singular and do not support dynamical jumps across the two stable branches of the peel force function. By including the kinetic energy of the tape in the Lagrangian, we derive equations of motion that support stick-slip jumps as a natural consequence of the inherent dynamics. In the low mass limit, these equations reproduce solutions obtained using a differential-algebraic algorithm introduced for the earlier equations. Our analysis also shows that mass of the ribbon has a strong influence on the nature of the dynamics.Comment: Accepted for publication in Phys. Rev. E (Rapid Communication

Rat placentation: An experimental model for investigating the hemochorial maternal-fetal interface

The rat possesses hemochorial placentation with deep intrauterine trophoblast cell invasion and trophoblast-directed uterine spiral artery remodeling; features shared with human placentation. Recognition of these similarities spurred the establishment of in vitro and in vivo research methods using the rat as an animal model to address mechanistic questions regarding development of the hemochorial placenta. The purpose of this review is to provide the requisite background to help move the rat to the forefront in placentation research. © 2012 Elsevier Ltd. All rights reserved

Dynamics of stick-slip in peeling of an adhesive tape

We investigate the dynamics of peeling of an adhesive tape subjected to a constant pull speed. We derive the equations of motion for the angular speed of the roller tape, the peel angle and the pull force used in earlier investigations using a Lagrangian. Due to the constraint between the pull force, peel angle and the peel force, it falls into the category of differential-algebraic equations requiring an appropriate algorithm for its numerical solution. Using such a scheme, we show that stick-slip jumps emerge in a purely dynamical manner. Our detailed numerical study shows that these set of equations exhibit rich dynamics hitherto not reported. In particular, our analysis shows that inertia has considerable influence on the nature of the dynamics. Following studies in the Portevin-Le Chatelier effect, we suggest a phenomenological peel force function which includes the influence of the pull speed. This reproduces the decreasing nature of the rupture force with the pull speed observed in experiments. This rich dynamics is made transparent by using a set of approximations valid in different regimes of the parameter space. The approximate solutions capture major features of the exact numerical solutions and also produce reasonably accurate values for the various quantities of interest.Comment: 12 pages, 9 figures. Minor modifications as suggested by refere

Power Laws, Precursors and Predictability During Failure

We investigate the dynamics of a modified Burridge-Knopoff model by introducing a dissipative term to mimic the bursts of acoustic emission (AE) from rock samples. The model explains many features of the statistics of AE signals observed in experiments such as the crossover in the exponent value from relatively small amplitude AE signals to larger regime, and their dependence on the pulling speed. Significantly, we find that the cumulative energy dissipated identified with acoustic emission can be used to predict a major slip event. We also find a data collapse of the acoustic activity for several major slip events describable by a universal stretched exponential with corrections in terms of time-to-failure.Comment: 7 pages, 6 figures, Final version with minor change

Increases in plasma sheet temperature with solar wind driving during substorm growth phases

During the substorm growth phase, magnetic reconnection extracts ~10^15 J from the solar wind through magnetic reconnection at the magnetopause, which is then stored in the magnetotail lobes. Plasma sheet pressure then increases to balance magnetic flux density increases in the lobes. We examine plasma sheet pressure, density and temperature during substorm growth phases using nine years of Cluster data (>316,000 data points). We show that plasma sheet pressure and temperature are higher during growth phases with higher solar wind driving whereas the density is approximately constant. We also show a weak correlation between plasma sheet temperature before onset and the minimum SuperMAG SML auroral index in the subsequent substorm. We discuss how energization of the plasma sheet before onset may result from thermodynamically adiabatic processes; how hotter plasma sheets may result in magnetotail instabilities and how this relates to the onset and size of the subsequent substorm expansion phase

Clinical significance of genetic aberrations in secondary acute myeloid leukemia

The study aimed to identify genetic lesions associated with secondary acute myeloid leukemia (sAML) in comparison with AML arising de novo (dnAML) and assess their impact on patients' overall survival (OS). High-resolution genotyping and loss of heterozygosity mapping was performed on DNA samples from 86 sAML and 117 dnAML patients, using Affymetrix Genome-Wide Human SNP 6.0 arrays. Genes TP53, RUNX1, CBL, IDH1/2, NRAS, NPM1, and FLT3 were analyzed for mutations in all patients. We identified 36 recurrent cytogenetic aberrations (more than five events). Mutations in TP53, 9pUPD, and del7q (targeting CUX1 locus) were significantly associated with sAML, while NPM1 and FLT3 mutations associated with dnAML. Patients with sAML carrying TP53 mutations demonstrated lower 1-year OS rate than those with wild-type TP53 (14.3% +/- 9.4% vs. 35.4% +/- 7.2%; P = 0.002), while complex karyotype, del7q (CUX1) and del7p (IKZF1) showed no significant effect on OS. Multivariate analysis confirmed that mutant TP53 was the only independent adverse prognostic factor for OS in sAML (hazard ratio 2.67; 95% CI: 1.335.37; P = 0.006). Patients with dnAML and complex karyotype carried sAML-associated defects (TP53 defects in 54.5%, deletions targeting FOXP1 and ETV6 loci in 45.4% of the cases). We identified several co-occurring lesions associated with either sAML or dnAML diagnosis. Our data suggest that distinct genetic lesions drive leukemogenesis in sAML. High karyotype complexity of sAML patients does not influence OS. Somatic mutations in TP53 are the only independent adverse prognostic factor in sAML. Patients with dnAML and complex karyotype show genetic features associated with sAML and myeloproliferative neoplasms. Am. J. Hematol., 2012

One- and Two-Photon Spectroscopy of Donor−Acceptor−Donor Distyrylbenzene Derivatives: Effect of Cyano Substitution and Distortion from Planarity

The one- and two-photon spectroscopic properties of four symmetrically substituted donor−acceptor−donor distyrylbenzenes with either di-n-butyl- or diphenylamino donor groups and cyano acceptor groups are reported. It has been found that the position of the substitution of the electron-withdrawing cyano groups on the central phenylene ring as compared to the vinylene bond strongly affects the observed properties. In particular, the molecules with cyano substitution on the α-carbon of the vinylene linkage are characterized by weak fluorescence, short fluorescence lifetimes, and two-photon cross sections (δ) that are comparable to analogous molecules with no acceptor groups. In contrast, the molecules with acceptor substitution on the central phenylene ring are strongly fluorescent and have δ values roughly twice those of the vinyl-substituted molecules. These results are discussed in terms of the larger deviation of the conjugated backbone from planarity and the smaller distance between the donors and acceptors when the cyano groups are substituted on the vinylene carbon rather than the central phenylene ring

One- and Two-Photon Spectroscopy of Donor−Acceptor−Donor Distyrylbenzene Derivatives: Effect of Cyano Substitution and Distortion from Planarity

The one- and two-photon spectroscopic properties of four symmetrically substituted donor−acceptor−donor distyrylbenzenes with either di-n-butyl- or diphenylamino donor groups and cyano acceptor groups are reported. It has been found that the position of the substitution of the electron-withdrawing cyano groups on the central phenylene ring as compared to the vinylene bond strongly affects the observed properties. In particular, the molecules with cyano substitution on the α-carbon of the vinylene linkage are characterized by weak fluorescence, short fluorescence lifetimes, and two-photon cross sections (δ) that are comparable to analogous molecules with no acceptor groups. In contrast, the molecules with acceptor substitution on the central phenylene ring are strongly fluorescent and have δ values roughly twice those of the vinyl-substituted molecules. These results are discussed in terms of the larger deviation of the conjugated backbone from planarity and the smaller distance between the donors and acceptors when the cyano groups are substituted on the vinylene carbon rather than the central phenylene ring

Three-dimensional microfabrication using two-photon-activated chemistry

Photochemical reactions which can be activated by the simultaneous absorption of two photons provide a means for single-step fabrication of complex 3D microstructures. These types of structures are needed for a wide range of applications, including microfluidics, electrooptics, and micro-electromechanical systems. We have shown that chromophores can be engineered to have both large two-photon absorptivities as well as an efficient means for activating chemical processes, such as radical polymerization, subsequent to the photoexcitation. Chromophores designed following this strategy two-photon-activate the radical polymerization of acrylates at lower incident laser powers than conventional UV initiators. Efficient two-photon photopolymer resins based on these chromophores were used in the fabrication of complex microarchitectures, such as photonic bandgap structures and tapered waveguides. We have devised a strategy which allows this approach to be extended to other chemical systems

Development and Function of Invariant Natural Killer T Cells Producing TH2- and TH17-Cytokines

Four distinct subsets of invariant natural killer T (NKT) cells are shown to differentiate in the thymus, then migrate to peripheral tissues where they retain their phenotypic and functional characteristics