Massive, Topologically Massive, Models

In three dimensions, there are two distinct mass-generating mechanisms for gauge fields: adding the usual Proca/Pauli-Fierz, or the more esoteric Chern-Simons (CS), terms. Here we analyze the three-term models where both types are present, and their various limits. Surprisingly, in the tensor case, these seemingly innocuous systems are physically unacceptable. If the sign of the Einstein term is ``wrong'' as is in fact required in the CS case, then the excitation masses are always complex; with the usual sign, there is a (known) region of the two mass parameters where reality is restored, but instead we show that a ghost problem arises, while, for the ``pure mass'' two-term system without an Einstein action, complex masses are unavoidable. This contrasts with the smooth behavior of the corresponding vector models. Separately, we show that the ``partial masslessness'' exhibited by (plain) massive spin-2 models in de Sitter backgrounds is formally shared by the three-term system: it also enjoys a reduced local gauge invariance when this mass parameter is tuned to the cosmological constant.Comment: 7 pages, typos corrected, reference adde

Topologically massive gravity as a Pais-Uhlenbeck oscillator

We give a detailed account of the free field spectrum and the Newtonian limit of the linearized "massive" (Pauli-Fierz), "topologically massive" (Einstein-Hilbert-Chern-Simons) gravity in 2+1 dimensions about a Minkowski spacetime. For a certain ratio of the parameters, the linearized free theory is Jordan-diagonalizable and reduces to a degenerate "Pais-Uhlenbeck" oscillator which, despite being a higher derivative theory, is ghost-free.Comment: 9 pages, no figures, RevTEX4; version 2: a new paragraph and a reference added to the Introduction, a new appendix added to review Pais-Uhlenbeck oscillators; accepted for publication in Class. Quant. Gra

Compromising system and user interests in shelter location and evacuation planning

Cataloged from PDF version of article.Traffic management during an evacuation and the decision of where to locate the shelters are of critical importance to the performance of an evacuation plan. From the evacuation management authority’s point of view, the desirable goal is to minimize the total evacuation time by computing a system optimum (SO). However, evacuees may not be willing to take long routes enforced on them by a SO solution; but they may consent to taking routes with lengths not longer than the shortest path to the nearest shelter site by more than a tolerable factor. We develop a model that optimally locates shelters and assigns evacuees to the nearest shelter sites by assigning them to shortest paths, shortest and nearest with a given degree of tolerance, so that the total evacuation time is minimized. As the travel time on a road segment is often modeled as a nonlinear function of the flow on the segment, the resulting model is a nonlinear mixed integer programming model. We develop a solution method that can handle practical size problems using second order cone programming techniques. Using our model, we investigate the importance of the number and locations of shelter sites and the trade-off between efficiency and fairness. 2014 Elsevier Ltd. All rights reserved

Assembly of a heptameric STRIPAK complex is required for coordination of light-dependent multicellular fungal development with secondary metabolism in Aspergillus nidulans

This work is licensed under a Creative Commons Attribution 4.0 International License.Eukaryotic striatin forms striatin-interacting phosphatase and kinase (STRIPAK) complexes that control many cellular processes including development, cellular transport, signal transduction, stem cell differentiation and cardiac functions. However, detailed knowledge of complex assembly and its roles in stress responses are currently poorly understood. Here, we discovered six striatin (StrA) interacting proteins (Sips), which form a heptameric complex in the filamentous fungus Aspergillus nidulans. The complex consists of the striatin scaffold StrA, the Mob3-type kinase coactivator SipA, the SIKE-like protein SipB, the STRIP1/2 homolog SipC, the SLMAP-related protein SipD and the catalytic and regulatory phosphatase 2A subunits SipE (PpgA), and SipF, respectively. Single and double deletions of the complex components result in loss of multicellular light-dependent fungal development, secondary metabolite production (e.g. mycotoxin Sterigmatocystin) and reduced stress responses. sipA (Mob3) deletion is epistatic to strA deletion by supressing all the defects caused by the lack of striatin. The STRIPAK complex, which is established during vegetative growth and maintained during the early hours of light and dark development, is mainly formed on the nuclear envelope in the presence of the scaffold StrA. The loss of the scaffold revealed three STRIPAK subcomplexes: (I) SipA only interacts with StrA, (II) SipB-SipD is found as a heterodimer, (III) SipC, SipE and SipF exist as a heterotrimeric complex. The STRIPAK complex is required for proper expression of the heterotrimeric VeA-VelB-LaeA complex which coordinates fungal development and secondary metabolism. Furthermore, the STRIPAK complex modulates two important MAPK pathways by promoting phosphorylation of MpkB and restricting nuclear shuttling of MpkC in the absence of stress conditions. SipB in A. nidulans is similar to human suppressor of IKK-ε(SIKE) protein which supresses antiviral responses in mammals, while velvet family proteins show strong similarity to mammalian proinflammatory NF-KB proteins. The presence of these proteins in A. nidulans further strengthens the hypothesis that mammals and fungi use similar proteins for their immune response and secondary metabolite production, respectively

Energy in Topologically Massive Gravity

We define conserved gravitational charges in -cosmologically extended- topologically massive gravity, exhibit them in surface integral form about their de-Sitter or flat vacua and verify their correctness in terms of two basic types of solution.Comment: 6 page

Biofabrication of Gelatin Tissue Scaffolds with Uniform Pore Size via Microbubble Assembly

The control of pore size and uniform porosity remains as an important challenge in gelatin scaffolds. The precise control in building blocks of tissue scaffolds without any additional porogen is possible with costly equipment and techniques, though some pre‐requirements for polymeric material, such as photo‐polymerizability or sintering ability, may be needed prior to construction. Herein, a method for the fabrication of gelatin scaffolds with homogenous porosity using simple T‐junction microfluidics is described. The size of the microbubbles is precisely controlled with 5% deviation from the average. Porous gelatin scaffolds are obtained by building‐up the monodispersed microbubbles in dilute cross‐linker solutions. The effect of cross‐linker density on pore diameter is also investigated. After cross‐linking, pore size of the resultant five scaffold groups are precisely controlled as 135 ± 11, 193 ± 11, 216 ± 9, 231 ± 5, and 250 ± 12 µm. Porosity ratios above 65% are achieved in every sample group. According to the cell culture experiments, structures support high cell adhesion, viability, and migration through the porous network via interconnectivity. This study offers a practical and economical approach for the preparation of porous gelatin scaffolds with homogenous porosity which can be utilized in diverse tissue engineering applications

Self-assembled micro-stripe patterning of sessile polymeric nanofluid droplets

When sessile nanofluid droplets evaporate, solid nanoparticles can be organized in a wide variety of patterns on the substrate. The composition of the nanofluid, internal flow type of droplet and the rate of drying affect drop geometry, and the final pattern. Using poly(lactic-co-glycolic acid)-block-poly(ethylene glycol)(PLGA-b-PEG) as the example, we produced micro-stripe patterning from nanoparticles by drying of sessile fluid droplets. We investigated the nanoparticle properties and flow dynamics to clarify their effects on the patterning. Nanoparticles were prepared by hydrodynamic flow focusing using a T-junction microfluidic device with high production efficiency and the ability to generate an extremely narrow size distribution. PLGA-b-PEG was prepared as oil phase in acetonitrile and water/oil flow rate was changed from 1 to 3 at constant oil phase flow rate (50 μL/min). Then, nanofluid was collected on the surface as sessile droplets within acetonitrile/water binary dispersed phase. Depending on size, charge and size-distribution, the nanoparticles deposited on the surface exhibited various patterns. Dynamic Light and X-ray Scattering measurements showed that, approximately 100 nm particles with relatively low PDI (0.04) were produced for the first time in surfactant free conditions in a microfluidic device and they generated self-assembled ordered patterns, which are regulated by the type of internal flow in the sessile nanofluid droplet during sequential evaporation of acetonitrile and water

Co-Axial Gyro-Spinning of PCL/PVA/HA Core-Sheath Fibrous Scaffolds for Bone Tissue Engineering

The present study aspires towards fabricating core-sheath fibrous scaffolds by state-of-the-art pressurized gyration for bone tissue engineering applications. The core-sheath fibers comprising dual-phase poly-ε-caprolactone (PCL) core and polyvinyl alcohol (PVA) sheath are fabricated using a novel "co-axial" pressurized gyration method. Hydroxyapatite (HA) nanocrystals are embedded in the sheath of the fabricated scaffolds to improve the performance for application as a bone tissue regeneration material. The diameter of the fabricated fiber is 3.97 ± 1.31 µm for PCL-PVA/3%HA while pure PCL-PVA with no HA loading gives 3.03 ± 0.45 µm. Bead-free fiber morphology is ascertained for all sample groups. The chemistry, water contact angle and swelling behavior measurements of the fabricated core-sheath fibrous scaffolds indicate the suitability of the structures in cellular activities. Saos-2 bone osteosarcoma cells are employed to determine the biocompatibility of the scaffolds, wherein none of the scaffolds possess any cytotoxicity effect, while cell proliferation of 94% is obtained for PCL-PVA/5%HA fibers. The alkaline phosphatase activity results suggest the osteogenic activities on the scaffolds begin earlier than day 7. Overall, adaptations of co-axial pressurized gyration provides the flexibility to embed or encapsulate bioactive substances in core-sheath fiber assemblies and is a promising strategy for bone healing

All unitary cubic curvature gravities in D dimensions

We construct all the unitary cubic curvature gravity theories built on the contractions of the Riemann tensor in D -dimensional (anti)-de Sitter spacetimes. Our construction is based on finding the equivalent quadratic action for the general cubic curvature theory and imposing ghost and tachyon freedom, which greatly simplifies the highly complicated problem of finding the propagator of cubic curvature theories in constant curvature backgrounds. To carry out the procedure we have also classified all the unitary quadratic models. We use our general results to study the recently found cubic curvature theories using different techniques and the string generated cubic curvature gravity model. We also study the scattering in critical gravity and give its cubic curvature extensions.Comment: 24 pages, 1 figure, v2: A subsection on cubic curvature extensions of critical gravity is added, v3: The part regarding critical gravity is revised. Version to appear in Class. Quant. Gra