Nonlinear analytical flame models with amplitude-dependent time-lag distributions

In the present work, we formulate a new method to represent a given Flame Describing Function by analytical expressions. The underlying idea is motivated by the observation that different types of perturbations in a burner travel with different speeds and that the arrival of a perturbation at the flame is spread out over time. We develop an analytical model for the Flame Describing Function, which consists of a superposition of several Gaussians, each characterised by three amplitude-dependent quantities: central time-lag, peak value and standard deviation. These quantities are treated as fitting parameters, and they are deduced from the original Flame Describing Function by using error minimisation and nonlinear optimisation techniques. The amplitude-dependence of the fitting parameters is also represented analytically (by linear or quadratic functions). We test our method by using it to make stability predictions for a burner with well-documented stability behaviour (Noiray's matrix burner). This is done in the time-domain with a tailored Green's function approach

La protección frente al ruido de los forjados proyectados por Eduardo Torroja en la E.T.S. de Arquitectura de la Ciudad Universitaria de Madrid.

En este trabajo se exponen y se analizan los resultados de las mediciones acústicas del aislamiento acústico a ruido aéreo y a ruido de impactos de los forjados de hormigón armado macizo, proyectados por D. Eduardo Torroja Miret y fabricados en la primera mitad de los años 1930 en la Escuela Técnica Superior de Arquitectura de la UPM, situada en la Ciudad Universitaria de Madrid. Los valores experimentales obtenidos de los parámetros acústicos: índice ponderado de reducción acústica aparente R’w y nivel de presión acústica ponderado de impactos normalizado L’n,w están bien relacionados con los previstos por las estimaciones en los modelos de cálculo de las normas europeas EN 12354 partes 1, 2:2000. Se ha obtenido una relación experimental de reciprocidad para la suma de los valores del índice de reducción acústica aparente y el nivel de presión sonora de impactos normalizado

Transmission-dominated mid-infrared supermirrors with finesse exceeding 200 000

We fabricate and characterize substrate-transferred single-crystal mirror coatings with 9.33 $\pm$ 0.17 ppm of transmittance and 4.27 $\pm$ 0.52 ppm of excess optical loss, corresponding to a transmission-loss dominated reflectance of 99.9986% at 4.45 $\mu$m. For the first time, a cavity finesse > 200 000 is achieved in the mid-infrared.Comment: Sept 21: Minor revisions to conform to 2-page length requirement including abbr. refs.; Figure font sizes increase

Simultaneously-Measured Mid-Infrared Refractive Indices of GaAs/AlGaAs

We present our results for a simultaneous measurement of the refractive indices of Gallium Arsenide (GaAs) and Aluminum Gallium Arsenide (Al$_\mathrm{x}$Ga$_\mathrm{1-x}$As) in the spectral region from $2.0$ to $7.1\,\mathrm{\mu}\mathrm{m}$ ($5000$ to $1400\,\mathrm{cm^{-1}}$). These values are obtained from a monocrystalline thin-film multilayer Bragg mirror of excellent purity (background doping $\leq 1 \times 10^{-14}\,\mathrm{cm^{-3}}$), grown via molecular beam epitaxy. To recover the refractive indices over such a broad wavelength range, we fit a dispersion model for each material. For that, we measure both a photometrically accurate transmittance spectrum of the Bragg mirror via Fourier-transform infrared spectrometry and the individual physical layer thicknesses of the structure via scanning electron microscopy. To infer the uncertainty of the refractive index values, we estimate relevant measurement uncertainties and propagate them via a Monte-Carlo-type method. This method conclusively yields propagated relative uncertainties on the order of $10^{-4}$ over the measured spectral range for both GaAs and Al$_{0.929}$Ga$_{0.071}$As. The fitted model can also approximate the refractive index for MBE-grown Al$_\mathrm{x}$Ga$_\mathrm{1-x}$As for $0 \leq x \leq 1$. These updated values will be essential in the design and fabrication of next-generation active and passive optical devices in a spectral region which is of high interest in many fields, e.g., laser design and cavity-enhanced spectroscopy.Comment: 20 pages, 5 figures, submitted to PR

From Au-Thiolate Chains to Thioether Sierpiński Triangles: The Versatile Surface Chemistry of 1,3,5-Tris(4-Mercaptophenyl)Benzene on Au(111)

Self-assembly of 1,3,5-tris(4-mercaptophenyl)benzene (TMB) – a three-fold symmetric, thiol functionalized aromatic molecule – was studied on Au(111) with the aim to realize extended Au-thiolate linked molecular architectures. The focus lay on resolving thermally activated structural and chemical changes by a combination of microscopy and spectroscopy. Thereby Scanning Tunneling Microscopy provided submolecularly resolved structural information, while the chemical state of sulfur was assessed by X-ray Photoelectron Spectroscopy. Directly after room temperature deposition only less well ordered structures were observed. Mild annealing promoted the first structural transition into ordered molecular chains, partly organized in homochiral molecular braids. Further annealing led to self-similar Sierpiński triangles, while annealing at even higher temperatures again resulted in mostly disordered structures. Both the irregular aggregates observed at room temperature and the chains were identified as metal-organic assemblies, whereby two out of the three intermolecular binding motifs are energetically equivalent according to Density Functional Theory simulations. The emergence of Sierpiński triangles is driven by a chemical transformation, i.e. the conversion of coordinative Au-thiolate to covalent thioether linkages, and can be further understood by Monte Carlo simulations. The great structural variance of TMB on Au(111) can on one hand be explained by the energetic equivalence of two binding motifs. On the other hand, the unexpected chemical transition even enhances the structural variance and results in thiol-derived covalent molecular architectures

Genome-Scale CRISPR-Cas9 Knockout Screening in Human Cells

The simplicity of programming the CRISPR (clustered regularly interspaced short palindromic repeats)–associated nuclease Cas9 to modify specific genomic loci suggests a new way to interrogate gene function on a genome-wide scale. We show that lentiviral delivery of a genome-scale CRISPR-Cas9 knockout (GeCKO) library targeting 18,080 genes with 64,751 unique guide sequences enables both negative and positive selection screening in human cells. First, we used the GeCKO library to identify genes essential for cell viability in cancer and pluripotent stem cells. Next, in a melanoma model, we screened for genes whose loss is involved in resistance to vemurafenib, a therapeutic RAF inhibitor. Our highest-ranking candidates include previously validated genes NF1 and MED12, as well as novel hits NF2, CUL3, TADA2B, and TADA1. We observe a high level of consistency between independent guide RNAs targeting the same gene and a high rate of hit confirmation, demonstrating the promise of genome-scale screening with Cas9.National Institutes of Health (U.S.) (Award 1DP1-MH100706)National Institutes of Health (U.S.) (1R01-DK097768

Direct frequency comb measurement of OD + CO → DOCO kinetics

The kinetics of the hydroxyl radical (OH) + carbon monoxide (CO) reaction, which is fundamental to both atmospheric and combustion chemistry, are complex because of the formation of the hydrocarboxyl radical (HOCO) intermediate. Despite extensive studies of this reaction, HOCO has not been observed under thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observed deuteroxyl radical (OD) + CO reaction kinetics and detected stabilized trans-DOCO, the deuterated analog of trans-HOCO. By simultaneously measuring the time-dependent concentrations of the trans-DOCO and OD species, we observed unambiguous low-pressure termolecular dependence of the reaction rate coefficients for N_2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield

Rigid Chiral Membranes

Statistical ensembles of flexible two-dimensional fluid membranes arise naturally in the description of many physical systems. Typically one encounters such systems in a regime of low tension but high stiffness against bending, which is just the opposite of the regime described by the Polyakov string. We study a class of couplings between membrane shape and in-plane order which break 3-space parity invariance. Remarkably there is only {\it one} such allowed coupling (up to boundary terms); this term will be present for any lipid bilayer composed of tilted chiral molecules. We calculate the renormalization-group behavior of this relevant coupling in a simplified model and show how thermal fluctuations effectively reduce it in the infrared.Comment: 11 pages, UPR-518T (This replaced version has fonts not used removed.