Surface Plasmon Dispersion Relations in Chains of Metallic Nanoparticles: Exact Quasistatic Calculation

We calculate the surface plasmon dispersion relations for a periodic chain of spherical metallic nanoparticles in an isotropic host, including all multipole modes in a generalized tight-binding approach. For sufficiently small particles ($kd \ll 1$, where $k$ is the wave vector and $d$ is the interparticle separation), the calculation is exact. The lowest bands differ only slightly from previous point-dipole calculations provided the particle radius $a \lesssim d/3$, but differ substantially at smaller separation. We also calculate the dispersion relations for many higher bands, and estimate the group velocity $v_g$ and the exponential decay length $\xi_D$ for energy propagation for the lowest two bands due to single-grain damping. For $a/d=0.33$, the result for $\xi_D$ is in qualitative agreement with experiments on gold nanoparticle chains, while for larger $a/d$, such as $a/d=0.45$, $v_g$ and $\xi_D$ are expected to be strongly $k$-dependent because of the multipole corrections. When $a/d \sim 1/2$, we predict novel percolation effects in the spectrum, and find surprising symmetry in the plasmon band structure. Finally, we reformulate the band structure equations for a Drude metal in the time domain, and suggest how to include localized driving electric fields in the equations of motion.Comment: 19 pages 3 figures To be published in Phy. Rev.

Theory and simulation of two-dimensional nematic and tetratic phases

Recent experiments and simulations have shown that two-dimensional systems can form tetratic phases with four-fold rotational symmetry, even if they are composed of particles with only two-fold symmetry. To understand this effect, we propose a model for the statistical mechanics of particles with almost four-fold symmetry, which is weakly broken down to two-fold. We introduce a coefficient $\kappa$ to characterize the symmetry breaking, and find that the tetratic phase can still exist even up to a substantial value of $\kappa$. Through a Landau expansion of the free energy, we calculate the mean-field phase diagram, which is similar to the result of a previous hard-particle excluded-volume model. To verify our mean-field calculation, we develop a Monte Carlo simulation of spins on a triangular lattice. The results of the simulation agree very well with the Landau theory.Comment: 7 pages, including 12 postscript figures, uses REVTeX

Effect of Faecalibacterium prausnitzii on intestinal barrier function and immune homeostasis : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science, Massey University, Manawatū, New Zealand

Various gastrointestinal (GI) diseases, for example inflammatory bowel disease, are linked to impaired barrier function, chronic inflammation and dysbiosis of the resident microbiota. Faecalibacterium prausnitzii, an abundant obligate anaerobe of the healthy human microbiota, has reduced abundance in the GI tract of people with these diseases, and has been suggested to exert beneficial effects. Only a few studies have investigated its mechanisms of action, partly due to the difficulty of co-culturing live obligate anaerobes with oxygen-requiring human cells. The novel apical anaerobic co-culture model used in this study allows this co-culture through the separation of anaerobic and aerobic compartments. This model was used to investigate the effects of live F. prausnitzii (strains A2-165, ATCC 27768 and HTF-F) on intestinal barrier integrity, measured by transepithelial electrical resistance (TEER) of the intestinal epithelial cell line Caco-2, and on immune homeostasis, specifically on Toll-like receptor (TLR) activation. Method development was required to adapt these assays to the novel model and to optimise the growth of F. prausnitzii co-cultured with Caco-2 cells and TLR-expressing cell lines while maintaining their viabilities. Firstly, the optimised co-culture conditions were used to determine the effect of the three F. prausnitzii strains on barrier integrity of healthy and tumour necrosis factor alpha (TNF-α) treated Caco-2 cells. Live and growing F. prausnitzii did not alter the TEER across healthy Caco-2 cells. However, under TNF-α mediated inflammatory conditions, dead F. prausnitzii decreased TEER, whereas live bacteria maintained TEER. Secondly, the TLR activation assay was adapted to be carried out in the novel model. Using the adapted assay conditions it was determined that live F. prausnitzii induced greater TLR2 and TLR2/6 activation than dead F. prausnitzii. Collectively, these results indicate greater immuno-stimulatory effects of live F. prausnitzii, via TLR2 activation, and this effect is potentially linked to its barrier maintaining properties, because previous research showed enhancement of barrier integrity induced by TLR2 signalling. This new knowledge contributes to the understanding of how F. prausnitzii may maintain immune homeostasis in the GI tract. Unravelling the biological mechanisms used by prevalent species of the human microbiota, such as F. prausnitzii, will ultimately allow better comprehension of microbial regulation of GI function

Parameterized Differential Equations over k((t))(x)

In this article, we consider the inverse Galois problem for parameterized differential equations over k((t))(x) with k any field of characteristic zero and use the method of patching over fields due to Harbater and Hartmann. As an application, we prove that every connected semisimple k((t))-split linear algebraic group is a parameterized Galois group over k((t))(x).Comment: 13 page

Magnetization transfer effect on T1 relaxometry on 1.5T vs. 3T

PURPOSE: To assess the variability of incidental magnetization transfer effect (MT) by the number of slices and the magnetic field strength. METHODS: Various magnetic resonance images (MRI) were obtained with a phantom containing a series of solutions of gadolinium (Gd) and sucrose in distilled water, agarose gel and two vials with olive oil and distilled water. A diffusion weighted image (DWI) sequence was acquired to determine diffusion coefficient for each component of the phantom. Several inversion recovery (IR) sequences having different TI values were run for single-slice and used to calculate T1 relaxation time with maximum precision and minimizing magnetization transfer effect. The T1 relaxation value resulting from processing IR sequences was used as reference value. The mixed-TSE sequences were used to calculate T1, T2 and PD values and to assess MT effect for single-slice as for multi-slice acquisition. All the DICOM MR images were processed using various algorithms programmed in Mathcad (version 2001i, PTC Needham, MA) by Dr. Hernan Jara. According with the potential of each sequences the programs generated the qMRI maps and values of T1, T2, PD were obtained for all the components of the phantom. Values resulted from Mathcad calculation were used for analysis. All the acquisitions, calculations and measurements were performed for 1.5T and 3T field strength

Picturing words: The semantics of speech balloons

Semantics traditionally focuses on linguistic meaning. In recent years, the Super Linguistics movement has tried to broaden the scope of inquiry in various directions, including an extension of semantics to talk about the meaning of pictures. There are close similarities between the interpretation of language and of pictures. Most fundamentally, pictures, like utterances, can be either true or false of a given state of affairs, and hence both express propositions (Zimmermann, 2016; Greenberg, 2013; Abusch, 2015). Moreover, sequences of pictures, like sequences of utterances, can be used to tell stories. Wordless picture books, comics, and film are cases in point. In this paper I pick up the project of providing a dynamic semantic account of pictorial story-telling, started by Abusch (2012) and continued by Abusch & Rooth (2017); Maier & Bimpikou (2019); Fernando (2020). More specifically, I propose here a semantics of speech and thought bubbles by adding event reference to PicDRT. To get there I first review the projection-based semantics for pictures (section 1), noting the fundamental distinction between symbolic and iconic meaning that makes speech bubbles especially interesting (section 2). I then review the dynamic PicDRT framework for pictorial narratives (section 3), add events (section 4), and propose an account of speech bubbles as quotational event modification (section 5). I end with a brief look at other conventional, symbolic enrichments in comics (section 6)

Old Worlds, New Travels: Jack London’s People of the Abyss, Ernest Hemingway’s The Sun Also Rises, and the Cultural Politics of Travel

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