Review of recent results in spin physics

Recent results in polarized DIS are reviewed. Particular emphasis is placed on new measurements of transverse and longitudinal asymmetries, on the tests of the spin sum rules and on the analysis of the spin structure function $g_1$ in perturbative QCD at NLO.Comment: 15 pages, LaTex, 15 eps figures included, to be published in Proceedings of 7th Int. Workshop on Deep Inelastic Scattering and QCD (DIS99

A Polarized HERA Collider

A brief review is given of the status of nucleon spin structure functions as determined from polarized deep inelastic lepton-nucleon scatttering, including current outstanding problems. The characteristics of a polarized HERA collider, some of the particle physics topics it could address, and the accelerator physics challenges it must meet are discussed.Comment: 5 Pages, 6 Figures, To be published in the Proceedings of the DIS99 Conference April 1999, DESY Zeuthen, German

Revealing the tidal scars of the Small Magellanic Cloud

Due to their close proximity, the Large and Small Magellanic Clouds (SMC/LMC) provide natural laboratories for understanding how galaxies form and evolve. With the goal of determining the structure and dynamical state of the SMC, we present new spectroscopic data for $\sim$ 3000 SMC red giant branch stars observed using the AAOmega spectrograph at the Anglo-Australian Telescope. We complement our data with further spectroscopic measurements from previous studies that used the same instrumental configuration and proper motions from the \textit{Gaia} Data Release 2 catalogue. Analysing the photometric and stellar kinematic data, we find that the SMC centre of mass presents a conspicuous offset from the velocity centre of its associated \mbox{H\,{\sc i}} gas, suggesting that the SMC gas is likely to be far from dynamical equilibrium. Furthermore, we find evidence that the SMC is currently undergoing tidal disruption by the LMC within 2\,kpc of the centre of the SMC, and possibly all the way in to the very core. This is evidenced by a net outward motion of stars from the SMC centre along the direction towards the LMC and apparent tangential anisotropy at all radii. The latter is expected if the SMC is undergoing significiant tidal stripping, as we demonstrate using a suite of $N$-body simulations of the SMC/LMC system disrupting around the Milky Way. These results suggest that dynamical models for the SMC that assume a steady state will need to be revisited.Comment: Revised version submitted to MNRAS after referee report, 18 pages, 18 figure

Transform-based particle filtering for elliptic Bayesian inverse problems

We introduce optimal transport based resampling in adaptive SMC. We consider elliptic inverse problems of inferring hydraulic conductivity from pressure measurements. We consider two parametrizations of hydraulic conductivity: by Gaussian random field, and by a set of scalar (non-)Gaussian distributed parameters and Gaussian random fields. We show that for scalar parameters optimal transport based SMC performs comparably to monomial based SMC but for Gaussian high-dimensional random fields optimal transport based SMC outperforms monomial based SMC. When comparing to ensemble Kalman inversion with mutation (EKI), we observe that for Gaussian random fields, optimal transport based SMC gives comparable or worse performance than EKI depending on the complexity of the parametrization. For non-Gaussian distributed parameters optimal transport based SMC outperforms EKI

Fetal-derived trophoblast use the apoptotic cytokine tumor necrosis factor-alpha-related apoptosis-inducing ligand to induce smooth muscle cell death.

Remodeling of the uterine spiral arteries during pregnancy transforms them from high to low resistance vessels that lack vasoconstrictive properties. This process is essential to meet the demand for increased blood flow imposed by the growing fetus. Loss of endothelial and smooth muscle cells (SMC) is evident in remodeled arteries but the mechanisms underlying this transformation remain unknown. This study investigated the hypothesis that fetal trophoblast invading from the placenta instigate remodeling by triggering cell death in vascular SMC. Specifically, a role for trophoblast-derived death inducing cytokine tumor necrosis factor-α–related apoptosis-inducing ligand (TRAIL) was investigated. Expression of the activating TRAIL receptors R1 and R2 was detected by flow cytometry on human aortic SMC and by immunohistochemistry on spiral artery SMC. Recombinant human TRAIL induced human aortic SMC apoptosis, which was inhibited by antibodies against TRAIL-R1 or -R2. Perfusion of denuded spiral artery segments with recombinant human TRAIL also induced SMC apoptosis. Trophoblasts isolated from first trimester placenta expressed membrane-associated TRAIL and induced apoptosis of human aortic SMC; apoptosis was significantly inhibited by a recombinant human TRAIL-R1:Fc construct. Trophoblast within the first trimester placental bed also expressed TRAIL. These data show that: 1) TRAIL causes SMC death; 2) trophoblast produce the apoptotic cytokine TRAIL; and 3) trophoblast induce SMC apoptosis via a TRAIL-dependent mechanism. We conclude that TRAIL produced by trophoblast causes apoptosis of SMC and thus may contribute to SMC loss during spiral artery remodeling in pregnancy

Effect of optical purity on phase sequence in antiferroelectric liquid crystals

We use the discrete phenomenological model to study theoretically the phase diagrams in antiferroelectric liquid crystals (AFLCs) as a function of optical purity and temperature. Recent experiments have shown that in some systems the number of phases is reduced if the optical purity is extremely high. In some materials the SmC$_{A}^{\star}$ phase is the only stable tilted smectic phase in the pure sample. In the scope of the presented model this high sensitivity of the phase sequence in the AFLCs to optical purity is attributed to the piezoelectric coupling which is reduced if optical purity is reduced. We limit our study to three topologically equal phases - SmC$^{*}$, SmC$_{\alpha}^{*}$ and SmC$_{A}^{*}$ and show that the reduction of optical purity forces the system from the antiferroelectric to the ferroelectric phase with a possible SmC$_{\alpha}^{\star}$ between them. The effect of the flexoelectric and quadrupolar coupling is considered as well. If the phase diagram includes only two phases, SmC$^{\star}$ and SmC$$, the flexoelectric coupling is very small. The materials which exhibit the SmC$_{\alpha}^{\star}$ in a certain range of optical purity and temperature, can be expected to have a significant flexoelectric coupling that is comparable with the piezoelectric coupling. And finally, when temperature is lowered the phase sequence SmA $\to$ SmC$$ $\to$ SmC$^{\star}$ $\to$ SmC$$ is possible only in materials in which quadrupolar coupling is very strong.Comment: 17 pages including 6 figures, submitted to PR

Molecular basis for SMC rod formation and its dissolution upon DNA binding.

SMC condensin complexes are central modulators of chromosome superstructure in all branches of life. Their SMC subunits form a long intramolecular coiled coil, which connects a constitutive "hinge" dimerization domain with an ATP-regulated "head" dimerization module. Here, we address the structural arrangement of the long coiled coils in SMC complexes. We unequivocally show that prokaryotic Smc-ScpAB, eukaryotic condensin, and possibly also cohesin form rod-like structures, with their coiled coils being closely juxtaposed and accurately anchored to the hinge. Upon ATP-induced binding of DNA to the hinge, however, Smc switches to a more open configuration. Our data suggest that a long-distance structural transition is transmitted from the Smc head domains to regulate Smc-ScpAB's association with DNA. These findings uncover a conserved architectural theme in SMC complexes, provide a mechanistic basis for Smc's dynamic engagement with chromosomes, and offer a molecular explanation for defects in Cornelia de Lange syndrome

The Temperature Structure of Be Star Disks in the Small Magellanic Cloud

The temperature structure of Be star circumstellar disks at the sub-solar metallicity appropriate to the Small Magellanic Cloud (SMC) is investigated. It is found that for central stars of the same spectral type, Be star disks in the SMC are systematically hotter by several thousand degrees compared to Milky Way (MW) disks with the same density structure. For early spectral types (B0e - B3e), this results in systematically smaller H{\alpha} equivalent widths for Be stars in the SMC. The implication of this result on Be star frequency comparisons between MW and SMC clusters is shown to be a 5 - 10% lowering of the detection efficiency of Be stars in SMC clusters. These calculations are also compared to the known H{\alpha} equivalent width distributions in the MW and SMC. For the MW, reasonable agreement is found; however, for the SMC, the match is not as good and systematically larger Be star disks may be required.Comment: 31 pages, 10 figures, Accepted for publication in the astrophysical Journa