Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Efecto del alga marina Sargassum spp. sobre las variables productivas y la concentración de colesterol en el camarón café, Farfantepenaeus californiensis (Holmes, 1900)

La demanda de alimentos balanceados para camarón en cultivo tiene una tendencia creciente en el mundo, por lo que la búsqueda de nuevos ingredientes no convencionales como las algas marinas, para la elaboración de dichos alimentos cobra importancia, especialmente si éstos pueden reducir la concentración de colesterol en el camarón. El objetivo de este trabajo fue evaluar el efecto de una dieta que contiene 4% de harina de Sargassum spp. sobre los parámetros productivos y concentración de colesterol en el camarón café (Farfantepenaeus californiensis). Para ello se realizó un bioensayo con duración de 45 días, evaluando dos dietas: una comercial (tratamiento testigo) y otra que incluyó 4% de harina del alga Sargassum. Cuatro acuarios de 60 L fueron usados como réplicas para cada tratamiento. Al concluir el bioensayo se seleccionaron muestras de tejido muscular de camarones de los dos tratamientos, se liofilizaron y se les determinaron los lípidos totales, colesterol, triglicéridos y proteínas. No se encontraron diferencias significativas (P>0,05) en cuanto a ganancia de peso, talla, tasa de supervivencia y factor de conversión alimenticia entre los dos tratamientos. La concentración de colesterol en los camarones alimentados con la dieta que contenía Sargassum fue estadísticamente (P<0,05) menor (77 mg/100 g) que en los alimentados con la dieta testigo (110 mg/100 g). Los resultados obtenidos muestran que 4% de harina Sargassum puede ser incorporada a los alimentos balanceados para camarón café, sin causar efectos negativos en sus parámetros productivos y reduce la concentración de colesterol

Manteniendo una Producción Acuícola Sana: Todo lo que hay que saber - No.2

Participantes: Diego Montenegro Ernst, Representante del IICA en México. George Hernández López, Maestro en Ciencias Marinas. Guillermo Portillo Clark, Biólogo. Marco Antonio Ross Guerrero, Oceanologo. Graciela Peña Flores, moderadora. Daniel Coronado, Biólogo.Temas a tratar: Salinidad del agua. Mortalidad en producción de larvas de camarón. Cultivo del camarón

Detection of white spot syndrome virus in filtered shrimp-farm water fractions and experimental evaluation of its infectivity in Penaeus (Litopenaeus) vannamei

White spot syndrome virus (WSSV) may spread through water to neighbor ponds or farms. Routine water exchange and wastewater released during white spot disease (WSD)-emergency harvests may preserve WSSV in shrimp farming areas. To test this hypothesis, on-site experiments were performed in a WSSV-affected farm in Guasave, Sinaloa, Mexico. Plankton and shrimp hemolymph were collected from 12 ponds during a WSD outbreak. PCR analyses showed that 72% of the hemolymph pools (26 out of 36) were WSSV-positive. In contrast, only 14% (4 of 28) plankton samples (filtered through 10 and 0.45 µm) from three ponds (2, 7 and 10) were WSSV-positive. Plankton from pond 9 was WSSV-negative, but 14 days later, shrimp began to die. At this point, a differential filtration experiment was performed in pond 9. WSSV-positive samples were only found in three fractions [particulate fraction (PF) 1 µm and liquid fractions (LF) 0.65 µm) became WSSV-positive. Results indicate that water fractions between 100 and 0.65 µm induced WSSV infection to shrimp. Results showed that pond water and/or particulate fractions are vehicles for WSSV dispersion via virus suspended in water, attached to microalgae, or carried by zooplankton

Infection of WSSV-negative Shrimp, Litopenaeus vannamei, Cultivated under Fluctuating Temperature Conditions

To test whether effluents released from white spot syndrome virus (WSSV)-infected farm ponds are a pathway for spreading WSSV, WSSV-negative Pacific whiteleg shrimp, Litopenaeus vannamei, were exposed to WSSV-containing water under conditions of fluctuating water temperatures. White spot disease outbreaks occurred at the shrimp ponds before and during the experiment. Two cages were placed inside each test pond, and one was placed at the outlet canal. Each cage was stocked with 30 shrimp. Hemolymph from stocked shrimp was collected at intervals of 24, 48, 72, 120, 168, and 360 h after exposure and analyzed for presence of WSSV DNA by nested polymerase chain reaction. At diurnal variation of water temperature from 28.0 to 33.4 C, WSSV was detected as early as 120 h (ca. 11% of shrimp hemolymph pools) and 168 h (ca. 18% of shrimp hemolymph pools). WSSV was detected by 360 h (ca. 33% of shrimp hemolymph pools) in all cages, when water temperature varied from 24.9 to 28.5 C during a 48-h period. Cumulative mortality in cages inside ponds was ≤50.0 and 86.7% at the outlet canal. These data show that grow-out operations during the summer–autumn transition are at risk of WSSV outbreaks. The experiment demonstrated that WSSV can be spread by shrimp farm water drainage

Search for direct top squark pair production in final states with two leptons in s=13\sqrt{s} = 13 TeV pppp collisions with the ATLAS detector

International audienceThe results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using $36.1~\hbox {fb}^{-1}$ of integrated luminosity from proton–proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark $\tilde{t}$ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay $\tilde{t} \rightarrow b \tilde{\chi }_{1}^{\pm }$ into a b-quark and the lightest chargino with $\tilde{\chi }_{1}^{\pm } \rightarrow W \tilde{\chi }_{1}^{0}$ , the decay $\tilde{t} \rightarrow t \tilde{\chi }_{1}^{0}$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t} \rightarrow b W \tilde{\chi }_{1}^{0}$ and the four-body decay $\tilde{t} \rightarrow b \ell \nu \tilde{\chi }_{1}^{0}$ . No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the $\tilde{t}$ and $\tilde{\chi }_{1}^{0}$ masses. The results exclude at 95% confidence level $\tilde{t}$ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches

Measurements of ttˉt\bar{t} differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in pppp collisions at s=13 \sqrt{s}=13\, TeV using the ATLAS detector

Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and $t\bar{t}$ system kinematic observables using proton--proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV. The data set corresponds to an integrated luminosity of $36.1$ fb$^{-1}$, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum $p_{\rm T} > 500$ GeV and a second with $p_{\rm T}>350$ GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a $b$-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated $\chi^2$ values. The cross-section for $t\bar{t}$ production in the fiducial phase-space region is $292 \pm 7 \ \rm{(stat)} \pm 76 \rm{(syst)}$ fb, to be compared to the theoretical prediction of $384 \pm 36$ fb

Measurements of ttˉt\bar{t} differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in pppp collisions at s=13 \sqrt{s}=13\, TeV using the ATLAS detector

Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and $t\bar{t}$ system kinematic observables using proton--proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV. The data set corresponds to an integrated luminosity of $36.1$ fb$^{-1}$, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum $p_{\rm T} > 500$ GeV and a second with $p_{\rm T}>350$ GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a $b$-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated $\chi^2$ values. The cross-section for $t\bar{t}$ production in the fiducial phase-space region is $292 \pm 7 \ \rm{(stat)} \pm 76 \rm{(syst)}$ fb, to be compared to the theoretical prediction of $384 \pm 36$ fb