Finding the Center of Mass of a Soft Spring

This article shows how to use calculus to find the center of mass position of a soft cylindrical helical spring that is suspended vertically. The spring is non-uniformly stretched by the action of gravity. A general expression for the vertical position of the center of mass is obtained.Comment: LaTeX, 7 pages, 2 figures. Minor changes to agree with published versio

Electronic properties of mono-substituted tetraferrocenyl porphyrins in solution and on a gold surface: Assessment of the influencing factors for photoelectrochemical applications

Two unsymmetric meso-tetraferrocenyl-containing porphyrins of general formula Fc3(FcCOR)Por (Fc=ferrocenyl, R=CH3 or (CH2)5Br, Por=porphyrin) were prepared and characterized by a variety of spectroscopic methods, whereas their redox properties were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches. The mixed-valence [Fc3(FcCOR)Por]n+ (n=1,3) were investigated using spectroelectrochemical as well as chemical oxidation methods and corroborated with density functional theory (DFT) calculations. Inter-valence charge-transfer (IVCT) transitions in [Fc3(FcCOR)Por]+ were analyzed, and the resulting data matched closely previously reported complexes and were assigned as Robin–Day class II mixed-valence compounds. Self-assembled monolayers (SAMs) of a thioacetyl derivative (Fc3(FcCO(CH2)5SCOCH3)Por) were also prepared and characterized. Photoelectrochemical properties of SAMs in different electrolyte systems were investigated by electrochemical techniques and photocurrent generation experiments, showing that the choice of electrolyte is critical for efficiency of redox-active SAMs

A neutral-pH aqueous redox flow battery based on sustainable organic electrolytes

Aqueous organic redox flow batteries (AORFBs) have gained increasing attention for large-scale storage due to the advantages of decoupled energy and power, safe and sustainable chemistry, and tunability of the redox-active species. Here, we report the development of a neutral-pH AORFB assembled with a highly water-soluble ferrocene 1,1-disulfonic disodium salt (DS−Fc) and two viologen derivatives, 1,1’-bis(3-sulfonatopropyl)-viologen (BSP−Vi) and Bis(3-trimethylammonium)propyl viologen tetrachloride (BTMAP−Vi). Synthesized electrolytes showed excellent redox potential, good diffusion coefficient, and a good transfer rate constant. In particular, BSP−Vi has a more negative redox potential (-0.4 V) than BTMAP−Vi (−0.3 V) and faster kinetics; therefore, it was selected to be assembled in an AORFB as anolyte, coupled with DS−Fc as catholyte.The resulting AORFB based on BTMAP−Vi/DS−Fc and BSP−Vi/DS−Fc redox couple had a high cell voltage (1.2 V and 1.3 V, respectively) and theoretical energy density (13 WhL−1 and 14 WhL−1 respectively) and was able to sustain 70 charge-discharge cycles with energy efficiency as high as 97 %

21 de setiembre: día de la ciencia y la técnica

Con motivo del 3O aniversario de la instauración del 21 de setiembre como día de la Ciencia y la Técnica en la Provincia de Buenos Aires, la CIC le ha solicitado a un grupo selecto de científicos, su opinión sobre aspectos esenciales del quehacer científico y tecnológico. El presente texto contiene los siguientes trabajos: - Consideraciones acerca de la investigacion técnico-científica sobre materiales, por Eduardo R. Abril. - Ciencia y tecnología de alimentos, por Pedro Cattáneo - Ciencia y tecnología en química orgánica por Venancio Deulofeu. - Ciencia y tecnología - recursos humanos por Ernesto E. Galloni. - Discurso de apertura de la reunion sobre ciencia y tecnologia realizada en Mar del Plata del 6 al 8 de julio de 1978 por Luis F. Leloir. - Incidencia de la investigación en el desarrollo de la metalurgia por Roberto F. Recoder. - Importancia de la investigación matemática en la sociedad contemporánea por Luis A. Santaló. - La investigación en fisicoquímica y su proyección en el desarrollo científico y tecnológico por Hans J. Schumacher

Search for a pseudoscalar boson decaying into a ZZ boson and the 125 GeV Higgs boson in ℓ+ℓ−bbˉb\bar{b} final states

Results are reported on a search for decays of a pseudoscalar A boson into a $Z$ boson and a light scalar h boson, where the Z boson decays into a pair of oppositely-charged electrons or muons, and the h boson decays into $b\bar{b}$. The search is based on data from proton–proton collisions at a center-of-mass energy $\sqrt{s}$=8 TeV collected with the CMS detector, corresponding to an integrated luminosity of 19.7 $fb^{−1}$ . The h boson is assumed to be the standard model-like Higgs boson with a mass of 125 GeV. With no evidence for signal, upper limits are obtained on the product of the production cross section and the branching fraction of the A boson in the Zh channel. Results are also interpreted in the context of two Higgs doublet models