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

Similarities between Insect Swarms and Isothermal Globular Clusters

Previous work has suggested that disordered swarms of flying insects can be well modeled as selfgravitating systems, as long as the “gravitational” interaction is adaptive. Motivated by this work we compare the predictions of the classic, mean-field King model for isothermal globular clusters to observations of insect swarms. Detailed numerical simulations of regular and adaptive gravity allow us to expose the features of the swarms’ density and velocity profiles that are due to longrange interactions, and are captured by the King model phenomenology, and those that are due to adaptivity and short-range repulsion. Our results provide further support for adaptive gravity as a model for swarms

Two-dimensional Navier--Stokes simulation of deformation and break up of liquid patches

The large deformations and break up of circular 2D liquid patches in a high Reynolds number (Re=1000) gas flow are investigated numerically. The 2D, plane flow Navier--Stokes equations are directly solved with explicit tracking of the interface between the two phases and a new algorithm for surface tension. The numerical method is able to pursue the simulation beyond the breaking or coalescence of droplets. The simulations are able to unveil the intriguing details of the non-linear interplay between the deforming droplets and the vortical structures in the droplet's wake.Comment: 13 pages including 4 postscript figures; Revised version as resubmitted to PRL. Title has change

Microwave Assisted Synthesis of Py-Im Polyamides

Microwave synthesis was utilized to rapidly build Py-Im polyamides in high yields and purity using Boc-protection chemistry on Kaiser oxime resin. A representative polyamide targeting the 5′-WGWWCW-3′ (W = A or T) subset of the consensus Androgen and Glucocorticoid Response Elements was synthesized in 56% yield after 20 linear steps and HPLC purification. It was confirmed by Mosher amide derivatization of the polyamide that a chiral α-amino acid does not racemize after several additional coupling steps

Transverse Polarization of Σ+(1189)\Sigma^{+}(1189) in Photoproduction on a Hydrogen Target in CLAS

Experimental results on the $\Sigma^+(1189)$ hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson laboratory are presented. The $\Sigma^+(1189)$ was reconstructed in the exclusive reaction $\gamma+p\rightarrow K^{0}_{S} + \Sigma^+(1189)$ via the $\Sigma^{+} \to p \pi^{0}$ decay mode. The $K^{0}_S$ was reconstructed in the invariant mass of two oppositely charged pions with the $\pi^0$ identified in the missing mass of the detected $p\pi^+\pi^-$ final state. Experimental data were collected in the photon energy range $E_{\gamma}$ = 1.0-3.5 GeV ($\sqrt{s}$ range 1.66-2.73 GeV). We observe a large negative polarization of up to 95%. As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances.Comment: pages 1

On the progenitor of SN 2005gl and the nature of Type IIn supernovae

We present a study of the type IIn supernova (SN) 2005gl, in the relatively nearby (d~66 Mpc) galaxy NGC 266. Photometry and spectroscopy of the SN indicate it is a typical member of its class. Pre-explosion Hubble Space Telescope (HST) imaging of the location of the SN, along with a precise localization of this event using the Laser-Guide-Star assisted Adaptive Optics (LGS-AO) system at Keck Observatory, are combined to identify a luminous (M_V=-10.3) point source as the possible progenitor of SN 2005gl. If the source is indeed a single star, it was likely a member of the class of luminous blue variable stars (LBVs). This finding leads us to consider the possible general association of SNe IIn with LBV progenitors. We find this is indeed supported by observations of other SNe, and the known properties of LBV stars. For example, we argue that should the prototypical Galactic LBV eta Carina explode in a phase similar to its current state, it will likely produce a type IIn SN. We discuss our findings in the context of current ideas about the evolution of massive stars, and review the census of SNe with identified progenitors. We introduce the concept of the progenitor-SN map as a convenient means to discuss the present status and future prospects of direct searches for SN progenitors. We conclude that this field has matured considerably in recent years, and the transition from anecdotal information about rare single events to robust associations of progenitor classes with specific SN types has already begun.Comment: Submitted to ApJ. Comments welcom

Measurement of Exclusive π0\pi^0 Electroproduction Structure Functions and their Relationship to Transversity GPDs

Exclusive $\pi^0$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $x_B$, $t$, and $\phi_\pi$, in the $Q^2$ range from 1.0 to 4.6 GeV$^2$,\ $-t$ up to 2 GeV$^2$, and $x_B$ from 0.1 to 0.58. Structure functions $\sigma_T +\epsilon \sigma_L, \sigma_{TT}$ and $\sigma_{LT}$ were extracted as functions of $t$ for each of 17 combinations of $Q^2$ and $x_B$. The data were compared directly with two handbag-based calculations including both longitudinal and transversity GPDs. Inclusion of only longitudinal GPDs very strongly underestimates $\sigma_T +\epsilon \sigma_L$ and fails to account for $\sigma_{TT}$ and $\sigma_{LT}$, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity flip and helicity non-flip processes. The results confirm that exclusive $\pi^0$ electroproduction offers direct experimental access to the transversity GPDs.Comment: 6 pages, 2 figure

Early phase observations of extremely luminous Type Ia Supernova 2009dc

We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is $\Delta m_{15}(B)=0.65\pm 0.03$, which is one of the slowest among SNe Ia. The peak $V$-band absolute magnitude is $M_{V}=-19.90\pm 0.15$ mag even if the host extinction is $A_{V}=0$ mag. It reaches $M_{V}=-20.19\pm 0.19$ mag for the host extinction of $A_{V}=0.29$ mag as inferred from the observed Na {\sc i} D line absorption in the host. Our $JHK_{s}$-band photometry shows that the SN is one of the most luminous SNe Ia also in near-infrared wavelengths. These results indicate that SN 2009dc belongs to the most luminous class of SNe Ia, like SN 2003fg and SN 2006gz. We estimate the ejected $^{56}$Ni mass of $1.2\pm 0.3$ \Msun for no host extinction case (or 1.6$\pm$ 0.4 M$_{\odot}$ for the host extinction of $A_{V}=0.29$ mag). The C {\sc ii} $\lambda$6580 absorption line keeps visible until a week after maximum, which diminished in SN 2006gz before its maximum brightness. The line velocity of Si {\sc ii} $\lambda$6355 is about 8000 km s$^{-1}$ around the maximum, being considerably slower than that of SN 2006gz, while comparable to that of SN 2003fg. The velocity of the C {\sc ii} line is almost comparable to that of the Si {\sc ii}. The presence of the carbon line suggests that thick unburned C+O layers remain after the explosion. SN 2009dc is a plausible candidate of the super-Chandrasekhar mass SNe Ia

Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to Q^2 = 8.5 GeV^2

Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5 GeV2. By extending the range of Q2 for which GEp is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the non-perturbative regime