Dynamics of Low Anisotropy Morphologies in Directional Solidification

We report experimental results on quasi-two-dimensional diffusion limited growth in directionally solidified succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as a solute. Seaweed growth, or dense branching morphology, is selected by growing grains close to the $\{111\}$ plane, where the in-plane surface tension is nearly isotropic. The observed growth morphologies are very sensitive to small anisotropies in surface tension caused by misorientations from the $\{111\}$ plane. Different seaweed morphologies are found, including the degenerate, the stabilized, and the strongly tilted seaweeds. The degenerate seaweeds show a limited fractal scaling range and, with increased undercooling, suggests a transition from "fractal" to "compact" seaweed. Strongly tilted seaweeds demonstrate a significant twofold anisotropy. In addition, seaweed-dendrite transitions are observed in low anisotropy growth.Comment: 12 pages, 17 figures, submitted to Phys. Rev. E, reduced image quality for smaller file siz

Transients in sheared granular matter

As dense granular materials are sheared, a shear band and an anisotropic force network form. The approach to steady state behavior depends on the history of the packing and the existing force and contact network. We present experiments on shearing of dense granular matter in a 2D Couette geometry in which we probe the history and evolution of shear bands by measuring particle trajectories and stresses during transients. We find that when shearing is stopped and restarted in the same direction, steady state behavior is immediately reached, in agreement with the typical assumption that the system is quasistatic. Although some relaxation of the force network is observed when shearing is stopped, quasistatic behavior is maintained because the contact network remains essentially unchanged. When the direction of shear is reversed, a transient occurs in which stresses initially decrease, changes in the force network reach further into the bulk, and particles far from the wheel become more mobile. This occurs because the force network is fragile to changes transverse to the force network established under previous shear; particles must rearrange before becoming jammed again, thereby providing resistance to shear in the reversed direction. The strong force network is reestablished after displacing the shearing surface $\approx 3d$, where $d$ is the mean grain diameter. Steady state velocity profiles are reached after a shear of $\leq 30d$. Particles immediately outside of the shear band move on average less than 1 diameter before becoming jammed again. We also examine particle rotation during this transient and find that mean particle spin decreases during the transient, which is related to the fact that grains are not interlocked as strongly.Comment: 7 pages, 11 figures, accepted to Eur. Phys. J. E, revised version based on referee suggestion

Manual for starch gel electrophoresis: A method for the detection of genetic variation

The procedure to conduct horizontal starch gel electrophoresis on enzymes is described in detail. Areas covered are (I) collection and storage of specimens, (2) preparation of tissues, (3) preparation of a starch gel, (4) application of enzyme extracts to a gel, (5) setting up a gel for electrophoresis, (6) slicing a gel, and (7) staining a gel. Recipes are also included for 47 enzyme stains and 3 selected gel buffers. (PDF file contains 26 pages.

Mechanisms for Survival and Drug Resistance in Cancer Cells

PART I Prostate cells are hormonally driven to grow and divide. Typical treatments for prostate cancer involve blocking the hormone androgen from activating the androgen receptor (AR) and thus inhibit growth and proliferation of the cancer. Androgen deprivation therapy (ADT) can lead to the selection of cancer cells that grow and divide independently of androgen receptor activation. Prostate cancer cells that are insensitive to androgens commonly display metastatic phenotypes and reduced long-term survival of patients. In this study, we provide evidence that androgen-insensitive prostate cancer cells have elevated phospholipase D (PLD) activity relative to the androgen-sensitive prostate cancer cells. PLD activity has been linked with promoting survival in many human cancer cell lines; and consistent with the previous studies, suppression of PLD activity in the prostate cancer cells resulted in apoptotic cell death. Of significance, suppressing the elevated PLD activity in the androgen-insensitive prostate cancer lines also blocked the ability of these cells to migrate and invade MatrigelTM. Since survival signals are generally an early event in tumorigenesis, the apparent coupling of survival and metastatic phenotypes implies that metastasis could be an earlier event in malignant prostate cancer than generally thought. Resistance to ADT appears to involve an elevation in PLD activity providing a survival program that is coupled to migration and invasion. Interruption of this pathway could provide a therapeutic strategy for treating androgen-insensitive prostate cancer. PART II Inhibiting the mammalian Target of Rapamycin Complex 1 (mTORC1) with rapamycin while suppressing Transforming Growth Factor-β (TGF-β) signaling induces apoptosis in many cancer cells. Some cancer cells, though, are resistant to the apoptotic effects of rapamycin treatment in the absence of TGF-β signaling. Both mTORC1 and TGF-β are upstream effectors of Retinoblastoma protein (Rb), a key regulatory protein involved in cell cycle progression from G1 to S-phase. We found that rapamycin-resistant cell lines had a nonfunctional Rb protein and a deleted CDKN2A gene. When Rb function was restored in the rapamycin resistant cells, apoptosis was induced upon rapamycin treatment. When Rb was knocked down in cells with deleted CDKN2A, the cells gained the rapamycin resistant phenotype. The common downstream target of Rb and CDKN2A is E2F1 and inhibition of E2F1 sensitizes the cell to the apoptotic effects of rapamycin. The data suggest that Rb and CDKN2A may be part of compensatory pathways and that the interruption of both pathways is necessary to confer resistance to mTORC1 inhibition. Resistance to mTORC1 inhibition by rapamycin, a downstream target of PLD, appears to involve E2F1 and implicates the involvement of CDKN2A and Rb at the G1-S phase boundary of the cell cycle as a point of therapeutic intervention

Photoelastic force measurements in granular materials

Photoelastic techniques are used to make both qualitative and quantitative measurements of the forces within idealized granular materials. The method is based on placing a birefringent granular material between a pair of polarizing filters, so that each region of the material rotates the polarization of light according to the amount of local of stress. In this review paper, we summarize past work using the technique, describe the optics underlying the technique, and illustrate how it can be used to quantitatively determine the vector contact forces between particles in a 2D granular system. We provide a description of software resources available to perform this task, as well as key techniques and resources for building an experimental apparatus

Receipt for Paid Advertisement, G. B. & J. H. Utter, Steam Job Printers, to Peleg Clarke Jr., August 3, 1868

This receipt, dated August 3, 1868, is for an advertisement with the Narragansett Weekly and The Sabbath recorder through the G.B. and J. H. Utter Steam Job Printers, purchased by Peleg Clarke, advertising as Executor for the estate of Benjamin Reynolds. The payment of $1.75 for a 1 inch 6 week advertisement was received by G. B. and J. H. Utter.https://scholarsjunction.msstate.edu/fvw-manuscripts-clarke/1068/thumbnail.jp

The Behavior of Granular Materials under Cyclic Shear

The design and development of a parallel plate shear cell for the study of large scale shear flows in granular materials is presented. The parallel plate geometry allows for shear studies without the effects of curvature found in the more common Couette experiments. A system of independently movable slats creates a well with side walls that deform in response to the motions of grains within the pack. This allows for true parallel plate shear with minimal interference from the containing geometry. The motions of the side walls also allow for a direct measurement of the velocity profile across the granular pack. Results are presented for applying this system to the study of transients in granular shear and for shear-induced crystallization. Initial shear profiles are found to vary from packing to packing, ranging from a linear profile across the entire system to an exponential decay with a width of approximately 6 bead diameters. As the system is sheared, the velocity profile becomes much sharper, resembling an exponential decay with a width of roughly 3 bead diameters. Further shearing produces velocity profiles which can no longer be fit to an exponential decay, but are better represented as a Gaussian decay or error function profile. Cyclic shear is found to produce large scale ordering of the granular pack, which has a profound impact on the shear profile. There exist periods of time in which there is slipping between layers as well as periods of time in which the layered particles lock together resulting in very little relative motion.Comment: 10 pages including 12 figure

Evolution of displacements and strains in sheared amorphous solids

The local deformation of two-dimensional Lennard-Jones glasses under imposed shear strain is studied via computer simulations. Both the mean squared displacement and mean squared strain rise linearly with the length of the strain interval $\Delta \gamma$ over which they are measured. However, the increase in displacement does not represent single-particle diffusion. There are long-range spatial correlations in displacement associated with slip lines with an amplitude of order the particle size. Strong dependence on system size is also observed. The probability distributions of displacement and strain are very different. For small $\Delta \gamma$ the distribution of displacement has a plateau followed by an exponential tail. The distribution becomes Gaussian as $\Delta \gamma$ increases to about .03. The strain distributions consist of sharp central peaks associated with elastic regions, and long exponential tails associated with plastic regions. The latter persist to the largest $\Delta \gamma$ studied.Comment: Submitted to J. Phys. Cond. Mat. special volume for PITP Conference on Mechanical Behavior of Glassy Materials. 16 Pages, 8 figure

Spectral catalogue of the intermediate ionization states of iron in the extreme ultraviolet

Using precisely controlled laboratory conditions we have begun to establish a spectral catalogue of the intermediate ionization states of iron, Fe IX - Fe XXIV, in the extreme ultraviolet. The measurements are being performed in support of the development of reliable modeling codes for the analysis of data from the Extreme Ultraviolet Explorer and future space astrophysics missions sensitive to extreme ultraviolet radiation. They aim to resolve the controversies surrounding the short-wavelength spectra of stellar coronae. Preliminary measurements showing the wealth of iron lines in the 50-120 {Angstrom} region are presented

Force distributions in a triangular lattice of rigid bars

We study the uniformly weighted ensemble of force balanced configurations on a triangular network of nontensile contact forces. For periodic boundary conditions corresponding to isotropic compressive stress, we find that the probability distribution for single-contact forces decays faster than exponentially. This super-exponential decay persists in lattices diluted to the rigidity percolation threshold. On the other hand, for anisotropic imposed stresses, a broader tail emerges in the force distribution, becoming a pure exponential in the limit of infinite lattice size and infinitely strong anisotropy.Comment: 11 pages, 17 figures Minor text revisions; added references and acknowledgmen