Carnot, Stirling, Ericsson stochastic heat engines: Efficiency at maximum power

This work obtains the efficiency at maximum power for a stochastic heat engine performing Carnot-like, Stirling-like and Ericsson-like cycles. For the mesoscopic engine a Brownian particle trapped by an optical tweezers is considered. The dynamics of this stochastic engine is described as an overdamped Langevin equation with a harmonic potential, whereas is in contact with two thermal baths at different temperatures, namely, hot ($T_h$) and cold ($T_c$). The harmonic oscillator Langevin equation is transformed into a macroscopic equation associated with the mean value $\langle x^2(t)\rangle$ using the original Langevin approach. At equilibrium stationary state this quantity satisfies a state-like equation from which the thermodynamic properties are calculated. To obtained the efficiency at maximum power it is considered the finite-time cycle processes under the framework of low dissipation approach.Comment: 2 3pages, 5 figure

Efecto de la adición de antioxidantes en el diluyente de semen de macho cabrío antes de congelar y después de descongelar

El objetivo de este trabajo fue evaluar el efecto antioxidante de las vitaminas C y E en el se­men de macho cabrío antes y después de descongelar y su efecto sobre la condensación de la cromatina espermática y el grado de oxidación de los espermatozoides. Se utilizaron cuatro machos cabríos de la raza Alpino Francesa y se analizaron ocho eyaculados de cada semen­tal. Cada eyaculado fue dividido en cuatro grupos: control, con vitamina C, con vitamina E y combinación de C+E. La determinación de la condensación de la cromatina espermática se realizó mediante citometría de flujo, utilizando el fluorocromo yoduro de propidio. Los resultados no mostraron diferencia estadísticamente significativa en el semen antes de con­gelar y después de descongelar (p > 0,05), lo cual indica que con la adición de antioxidantes, la condensación de la cromatina espermática no registró variaciones. Para valorar el grado de oxidación de los espermatozoides se utilizó la reacción del ácido tiobarbitúrico, la cual puede detectar peroxidación de los lípidos de la membrana espermática. Se encontró que antes de congelar el semen no hubo diferencia estadísticamente significativa entre los gru­pos control, con vitamina C, con vitamina E y combinación de C+E (p > 0,05). Después de descongelar las muestras hubo diferencia significativa entre el grupo control y la mezcla de vitaminas C+E; se estimó que la combinación de antioxidantes redujo el estrés oxidativo (p < 0,05), siendo menor la cantidad de nanomoles de malondialdehido por miligramo de proteína. Se concluye que la adición de antioxidantes al diluyente, puede reducir el estrés oxidativo causado por la congelación y descongelación de los espermatozoides; sin embargo, no hubo efecto alguno sobre la condensación de la cromatina espermática.

Physical and Antimicrobial Properties of Compression-Molded Cassava Starch-Chitosan Films for Meat Preservation

[EN] Cassava starch-chitosan films were obtained by melt bending and compression molding, using glycerol and polyethylene glycol as plasticizers. Both the starch/chitosan and the polymer/plasticizer ratios were varied in order to analyze their effect on the physical properties of the films. Additionally, the antimicrobial activity of 70:30 polymer:plasticizer films was tested in cold-stored pork meat slices as affected by chitosan content. All film components were thermally stable up to 200 A degrees C, which guaranteed their thermostability during film processing. Starch and chitosan had limited miscibility by melt blending, which resulted in heterogeneous film microstructure. Polyethylene glycol partially crystallized in the films, to a greater extent as the chitosan ratio increased, which limited its plasticizing effect. The films with the highest plasticizer ratio were more permeable to water vapor, less rigid, and less resistant to break. The variation in the chitosan content did not have a significant effect on water vapor permeability. As the chitosan proportion increased, the films became less stretchable, more rigid, and more resistant to break, with a more saturated yellowish color. The incorporation of the highest amount of chitosan in the films led to the reduction in coliforms and total aerobic counts of cold-stored pork meat slices, thus extending their shelf-life.The authors acknowledge the financial support provided by the Spanish Ministerio de Economia y Competividad (Projects AGL2013-42989-R and AGL2016-76699-R). Author Cristina Valencia-Sullca thanks the Peruvian Grant National Program (PRONABEC Grant).Valencia-Sullca, CE.; Atarés Huerta, LM.; Vargas, M.; Chiralt, A. (2018). Physical and Antimicrobial Properties of Compression-Molded Cassava Starch-Chitosan Films for Meat Preservation. Food and Bioprocess Technology. 11(7):1339-1349. https://doi.org/10.1007/s11947-018-2094-5S13391349117Alves, V. 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Gandini (Eds.), Monomers, polymers and composites from renewable resources. Amsterdam: Elsevier.Chillo, S., Flores, S., Mastromatteo, M., Conte, A., Gerschenson, L., & Del Nobile, M. A. (2008). Influence of glycerol and chitosan on tapioca starch-based edible film properties. Journal of Food Engineering, 88(2), 159–168.Commission Regulation, 2005 (EC) No 2073/2005 of 15 November 2005 on microbiological criteria for foodstuffs. In Official Journal of the European Union pp 338/1–338/26.Da Róz, A., Carvalho, A., Gandini, A., & Curvelo, A. (2006). The effect of plasticizers on thermoplastic starch compositions obtained by melt processing. Carbohydrate Polymers, 63(3), 417–424.Dang, K., & Yoksan, R. (2015). Development of thermoplastic starch blown film by incorporating plasticized chitosan. Carbohydrate Polymers, 115, 575–581.Dou, B., Dupont, V., Williams, P. T., Chen, H., & Ding, Y. (2009). Thermogravimetric kinetics of crude glycerol. 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Antioxidant and antidiabetic activity and phytoconstituents of lichen extracts with temperate and polar distribution

The objective of this research was to characterize the chemical composition of ethanolic extracts of the lichen species Placopsis contortuplicata, Ochrolechia frigida, and Umbilicaria antarctica, their antioxidant activity, and enzymatic inhibition through in vitro and molecular docking analysis. In total phenol content, FRAP, ORAC, and DPPH assays, the extracts showed significant antioxidant activity, and in in vitro assays for the inhibition of pancreatic lipase, α-glucosidase, and α-amylase enzymes, together with in silico studies for the prediction of pharmacokinetic properties, toxicity risks, and intermolecular interactions of compounds, the extracts evidenced inhibitory potential. A total of 13 compounds were identified by UHPLC-ESI-QTOF-MS in P. contortuplicata, 18 compounds in O. frigida, and 12 compounds in U. antarctica. This study contributes to the knowledge of the pool of bioactive compounds present in lichens of temperate and polar distribution and biological characteristics that increase interest in the discovery of natural products that offer alternatives for treatment studies of diseases related to oxidative stress and metabolic syndrome

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version includes a minor typo correction that will be submitted as an erratu

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV

The t t-bar production cross section (sigma[t t-bar]) is measured in proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS experiment, corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurement is performed in events with two leptons (electrons or muons) in the final state, at least two jets identified as jets originating from b quarks, and the presence of an imbalance in transverse momentum. The measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/- 2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction of the standard model.Comment: Replaced with published version. Included journal reference and DO

Measurement of the Z/gamma* + b-jet cross section in pp collisions at 7 TeV

The production of b jets in association with a Z/gamma* boson is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV and recorded by the CMS detector. The inclusive cross section for Z/gamma* + b-jet production is measured in a sample corresponding to an integrated luminosity of 2.2 inverse femtobarns. The Z/gamma* + b-jet cross section with Z/gamma* to ll (where ll = ee or mu mu) for events with the invariant mass 60 < M(ll) < 120 GeV, at least one b jet at the hadron level with pT > 25 GeV and abs(eta) < 2.1, and a separation between the leptons and the jets of Delta R > 0.5 is found to be 5.84 +/- 0.08 (stat.) +/- 0.72 (syst.) +(0.25)/-(0.55) (theory) pb. The kinematic properties of the events are also studied and found to be in agreement with the predictions made by the MadGraph event generator with the parton shower and the hadronisation performed by PYTHIA.Comment: Submitted to the Journal of High Energy Physic