Subnanosecond spectral diffusion measurement using photon correlation

Spectral diffusion is a result of random spectral jumps of a narrow line as a result of a fluctuating environment. It is an important issue in spectroscopy, because the observed spectral broadening prevents access to the intrinsic line properties. However, its characteristic parameters provide local information on the environment of a light emitter embedded in a solid matrix, or moving within a fluid, leading to numerous applications in physics and biology. We present a new experimental technique for measuring spectral diffusion based on photon correlations within a spectral line. Autocorrelation on half of the line and cross-correlation between the two halves give a quantitative value of the spectral diffusion time, with a resolution only limited by the correlation set-up. We have measured spectral diffusion of the photoluminescence of a single light emitter with a time resolution of 90 ps, exceeding by four orders of magnitude the best resolution reported to date

Fourth order indirect integration method for black hole perturbations: even modes

On the basis of a recently proposed strategy of finite element integration in time domain for partial differential equations with a singular source term, we present a fourth order algorithm for non-rotating black hole perturbations in the Regge-Wheeler gauge. Herein, we address even perturbations induced by a particle plunging in. The forward time value at the upper node of the $(r^*,t)$ grid cell is obtained by an algebraic sum of i) the preceding node values of the same cell, ii) analytic expressions, related to the jump conditions on the wave function and its derivatives, iii) the values of the wave function at adjacent cells. In this approach, the numerical integration does not deal with the source and potential terms directly, for cells crossed by the particle world line. This scheme has also been applied to circular and eccentric orbits and it will be object of a forthcoming publication.Comment: This series of papers deals with EMRI for LISA. With the respect to the v1 version, the algorithm has been improved; convergence tests and references have been added; v2 is composed by 23 pages, and 6 figures. Paper accepted by Class. Quantum Gravity for the special issue on Theory Meets Data Analysis at Comparable and Extreme Mass Ratios (Capra and NRDA) at Perimeier Institute in June 201

Tips for implementing multigrid methods on domains containing holes

As part of our development of a computer code to perform 3D `constrained evolution' of Einstein's equations in 3+1 form, we discuss issues regarding the efficient solution of elliptic equations on domains containing holes (i.e., excised regions), via the multigrid method. We consider as a test case the Poisson equation with a nonlinear term added, as a means of illustrating the principles involved, and move to a "real world" 3-dimensional problem which is the solution of the conformally flat Hamiltonian constraint with Dirichlet and Robin boundary conditions. Using our vertex-centered multigrid code, we demonstrate globally second-order-accurate solutions of elliptic equations over domains containing holes, in two and three spatial dimensions. Keys to the success of this method are the choice of the restriction operator near the holes and definition of the location of the inner boundary. In some cases (e.g. two holes in two dimensions), more and more smoothing may be required as the mesh spacing decreases to zero; however for the resolutions currently of interest to many numerical relativists, it is feasible to maintain second order convergence by concentrating smoothing (spatially) where it is needed most. This paper, and our publicly available source code, are intended to serve as semi-pedagogical guides for those who may wish to implement similar schemes.Comment: 18 pages, 11 figures, LaTeX. Added clarifications and references re. scope of paper, mathematical foundations, relevance of work. Accepted for publication in Classical & Quantum Gravit

Recent Advances in Graph Partitioning

We survey recent trends in practical algorithms for balanced graph partitioning together with applications and future research directions

Label-free chemically specific imaging in planta with stimulated Raman scattering microscopy.

The growing world population puts ever-increasing demands on the agricultural and agrochemical industries to increase agricultural yields. This can only be achieved by investing in fundamental plant and agrochemical research and in the development of improved analytical tools to support research in these areas. There is currently a lack of analytical tools that provide noninvasive structural and chemical analysis of plant tissues at the cellular scale. Imaging techniques such as coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microscopy provide label-free chemically specific image contrast based on vibrational spectroscopy. Over the past decade, these techniques have been shown to offer clear advantages for a vast range of biomedical research applications. The intrinsic vibrational contrast provides label-free quantitative functional analysis, it does not suffer from photobleaching, and it allows near real-time imaging in 3D with submicrometer spatial resolution. However, due to the susceptibility of current detection schemes to optical absorption and fluorescence from pigments (such as chlorophyll), the plant science and agrochemical research communities have not been able to benefit from these techniques and their application in plant research has remained virtually unexplored. In this paper, we explore the effect of chlorophyll fluorescence and absorption in CARS and SRS microscopy. We show that with the latter it is possible to use phase-sensitive detection to separate the vibrational signal from the (electronic) absorption processes. Finally, we demonstrate the potential of SRS for a range of in planta applications by presenting in situ chemical analysis of plant cell wall components, epicuticular waxes, and the deposition of agrochemical formulations onto the leaf surface

Diffraction techniques and vibrational spectroscopy opportunities to characterise bones

From a histological point of view, bones that allow body mobility and protection of internal organs consist not only of different organic and inorganic tissues but include vascular and nervous elements as well. Moreover, due to its ability to host different ions and cations, its mineral part represents an important reservoir, playing a key role in the metabolic activity of the organism. From a structural point of view, bones can be considered as a composite material displaying a hierarchical structure at different scales. At the nanometre scale, an organic part, i.e. collagen fibrils and an inorganic part, i.e. calcium phosphate nanocrystals are intimately mixed to assure particular mechanical properties

Genotoxic effect induced by hydrogen peroxide in human hepatoma cells using comet assay

Background: Hydrogen peroxide is a common reactive oxygen intermediate generated by variousforms of oxidative stress. Aims: The aim of this study was to investigate the DNA damage capacity ofH2O2 in HepG2 cells. Methods: Cells were treated with H2O2 at concentrations of 25 μM or 50 μM for5 min, 30 min, 40 min, 1 h or 24 h in parallel. The extent of DNA damage was assessed by the cometassay. Results: Compared to the control, DNA damage by 25 μM and 50 μM H2O2 increasedsignificantly with increasing incubation time up to 1 h, but it was not increased at 24 h. Conclusions:Our Findings confirm that H2O2 is a typical DNA damage inducing agent and thus is a good modelsystem to study the effects of oxidative stress. DNA damage in HepG2 cells increased significantlywith H2O2 concentration and time of incubation but later decreased likely due to DNA repairmechanisms and antioxidant enzyme

TMEM120A and B: Nuclear Envelope Transmembrane Proteins Important for Adipocyte Differentiation

<div><p>Recent work indicates that the nuclear envelope is a major signaling node for the cell that can influence tissue differentiation processes. Here we present two nuclear envelope trans-membrane proteins TMEM120A and TMEM120B that are paralogs encoded by the <i>Tmem120A</i> and <i>Tmem120B</i> genes. The TMEM120 proteins are expressed preferentially in fat and both are induced during 3T3-L1 adipocyte differentiation. Knockdown of one or the other protein altered expression of several genes required for adipocyte differentiation, <i>Gata3</i>, <i>Fasn</i>, <i>Glut4</i>, while knockdown of both together additionally affected <i>Pparg</i> and <i>Adipoq</i>. The double knockdown also increased the strength of effects, reducing for example <i>Glut4</i> levels by 95% compared to control 3T3-L1 cells upon pharmacologically induced differentiation. Accordingly, TMEM120A and B knockdown individually and together impacted on adipocyte differentiation/metabolism as measured by lipid accumulation through binding of Oil Red O and coherent anti-Stokes Raman scattering microscopy (CARS). The nuclear envelope is linked to several lipodystrophies through mutations in lamin A; however, lamin A is widely expressed. Thus it is possible that the TMEM120A and B fat-specific nuclear envelope transmembrane proteins may play a contributory role in the tissue-specific pathology of this disorder or in the wider problem of obesity.</p></div

Photo-crosslinkable, deformable PMMA colloids

Polymeric nano- and microparticles are finding widespread applications in materials and biological science. In all preparation methods pursued to date, the chemical stability of the particles is determined by the polymer system chosen. Usually, after particle synthesis, postprocessing with the aim of changing their stability is not possible. Therefore, one only has two choices: the synthesis of crosslinked polymer particles with high solvent and heat resistance and limited formability, or the synthesis of polymer particles consisting of linear polymer chains exhibiting low stability and high formability. In this contribution, we describe a new class of colloids which combine the advantages of both particle systems. The particles are composed of linear PMMA chains which are functionalized with photo-crosslinkable moieties. After preparation, the particles can be deformed before they are crosslinked by UV illumination. This offers unique possibilities for particle modification with a broad range of possible applications. Three examples are given. First, we show that the particles can be thermo-mechanically deformed into anisotropic shapes, in which they can be locked by subsequent crosslinking. Relaxation into the thermodynamically favorable spherical shape is thus suppressed, even in harsh environments. Second, we describe how the difference in solvent stability between illuminated and non-illuminated particles can be exploited for photolithography. Third, we demonstrate how photo-crosslinked anisotropic particles can be loaded with functional compounds, e.g. fluorophores