Impurity Ion Complexation Enhances Carbon Dioxide Reduction Catalysis

Herein, we show that group 11 CO[subscript 2] reduction catalysts are rapidly poisoned by progressive deposition of trace metal ion impurities present in high purity electrolytes. Metal impurity deposition was characterized by XPS and in situ stripping voltammetry and is coincident with loss of catalytic activity and selectivity for CO[subscript 2] reduction, favoring hydrogen evolution on poisoned surfaces. Metal deposition can be suppressed by complexing trace metal ion impurities with ethylenediaminetetraacetic acid or solid-supported iminodiacetate resins. Metal ion complexation allows for reproducible, sustained catalytic activity and selectivity for CO[subscript 2] reduction on Au, Ag, and Cu electrodes. Together, this study establishes the principal mode by which group 11 CO[subscript 2] reduction catalysts are poisoned and lays out a general approach for extending the lifetime of electrocatalysts subject to impurity metal deposition.MIT Energy Initiative (Saudi Aramco, research agreement)United States. Air Force Office of Scientific Research (Award FA9550-15-1-0135)Massachusetts Institute of Technology. Department of Chemistry (Junior Faculty Funds)National Science Foundation (U.S.) (Predoctoral Fellowship)National Science Foundation (U.S.) (MIT MRSEC Program, award number DMR-0819762

Comparison of two experiments on radiative neutron decay

Over 10 years ago we proposed an experiment on measuring the characteristics of radiative neutron decay in papers [1, 2]. At the same time we had published the theoretical spectrum of radiative gamma quanta, calculated within the framework of the electroweak interactions, on the basis of which we proposed the methodology for the future experiment [3,4]. However, because we were denied beam time on the intensive cold neutron beam at ILL (Grenoble, France) for a number of years, we could only conduct the experiment in 2005 on the newly opened FRMII reactor of Technical University of Muenchen. The main result of this experiment was the discovery of radiative neutron decay and the measurement of its relative intensity B.R.= (3.2+-1.6)10-3 with C.L.=99.7% for radiative gamma quanta with energy over 35 kev [5,6]. Over a year after our first announcement about the results of the conducted experiment, "Nature" [7] published a letter asserting that its authors have also measured the branching ratio of radiative neutron decay B.R.= (3.13+-0.34)10-3 with C.L.=68% and gamma quanta energy from 15 to 340 kev. This article aims to compare these two experiments. It is shown that the use of strong magnetic fields in the NIST (Washington, USA) experiment methodology not only prevents any exact measurement of the branching ratio and identification of radiative neutron decay events, but also makes registration of ordinary neutron decay events impossible.Comment: contribution on conference ISINN-1

Is It Rational to Assume that Infants Imitate Rationally? A Theoretical Analysis and Critique

It has been suggested that preverbal infants evaluate the efficiency of others' actions (by applying a principle of rational action) and that they imitate others' actions rationally. The present contribution presents a conceptual analysis of the claim that preverbal infants imitate rationally. It shows that this ability rests on at least three assumptions: that infants are able to perceive others' action capabilities, that infants reason about and conceptually represent their own bodies, and that infants are able to think counterfactually. It is argued that none of these three abilities is in place during infancy. Furthermore, it is shown that the idea of a principle of rational action suffers from two fallacies. As a consequence, is it suggested that it is not rational to assume that infants imitate rationally. Copyright (C) 2012 S. Karger AG, Base

Plasticity induced by non-invasive transcranial brain stimulation: A position paper

Several techniques and protocols of non-invasive transcranial brain stimulation (NIBS), including transcranial magnetic and electrical stimuli, have been developed in the past decades. Non-invasive transcranial brain stimulation may modulate cortical excitability outlasting the period of non-invasive transcranial brain stimulation itself from several minutes to more than one hour. Quite a few lines of evidence, including pharmacological, physiological and behavioral studies in humans and animals, suggest that the effects of non-invasive transcranial brain stimulation are produced through effects on synaptic plasticity. However, there is still a need for more direct and conclusive evidence. The fragility and variability of the effects are the major challenges that non-invasive transcranial brain stimulation currently faces. A variety of factors, including biological variation, measurement reproducibility and the neuronal state of the stimulated area, which can be affected by factors such as past and present physical activity, may influence the response to non-invasive transcranial brain stimulation. Work is ongoing to test whether the reliability and consistency of non-invasive transcranial brain stimulation can be improved by controlling or monitoring neuronal state and by optimizing the protocol and timing of stimulation

Measuring laser carrier-envelope-phase effects in the noble gases with an atomic hydrogen calibration standard

We present accurate measurements of carrier-envelope-phase effects on ionization of the noble gases with few-cycle laser pulses. The experimental apparatus is calibrated by using atomic hydrogen data to remove any systematic offsets and thereby obtain accurate CEP data on other generally used noble gases such as Ar, Kr, and Xe. Experimental results for H are well supported by exact time-dependent Schrödinger equation theoretical simulations; however, significant differences are observed in the case of the noble gases.Griffith Sciences, School of Natural SciencesFull Tex

Strong-field control of the dissociative ionization of N2O with near-single-cycle pulses

The dissociative ionization of N2O by near-single-cycle laser pulses is studied using phase-tagged ion-ion coincidence momentum imaging. Carrier-envelope phase (CEP) dependences are observed in the absolute ion yields and the emission direction of nearly all ionization and dissociation pathways of the triatomic molecule. We find that laser-field-driven electron recollision has a significant impact on the dissociative ionization dynamics and results in pronounced CEP modulations in the dication yields, which are observed in the product ion yields after dissociation. The results indicate that the directional emission of coincident N+ and NO+ ions in the denitrogenation of the dication can be explained by selective ionization of oriented molecules. The deoxygenation of the dication with the formation of coincident N-2(+) + O+ ions exhibits an additional shift in its CEP dependence, suggesting that this channel is further influenced by laser interaction with the dissociating dication. The experimental results demonstrate how few-femtosecond dynamics can drive and steer molecular reactions taking place on (much) longer time scales

Simply longer is not better: reversal of theta burst after-effect with prolonged stimulation

From all rTMS protocols at present, the theta burst stimulation (TBS) is considered the most efficient in terms of number of impulses and intensity required during a given stimulation. The aim of this study was to investigate the effects of inhibitory and excitatory TBS protocols on motor cortex excitability when the duration of stimulation was doubled. Fourteen healthy volunteers were tested under four conditions: intermittent theta bust stimulation (iTBS), continuous theta burst stimulation (cTBS), prolonged intermittent theta bust stimulation (ProiTBS) and prolonged continuous theta burst stimulation (ProcTBS). The prolonged paradigms were twice as long as the conventional TBS protocols. Conventional facilitatory iTBS converted into inhibitory when it was applied for twice as long, while the normally inhibitory cTBS became facilitatory when the stimulation duration was doubled. Our results show that TBS-induced plasticity cannot be deliberately enhanced simply by prolonging TBS protocols. Instead, when stimulating too long, after-effects will be reversed. This finding supplements findings at the short end of the stimulation duration range, where it was shown that conventional cTBS is excitatory in the first half and switches to inhibition only after the full length protocol. It is relevant for clinical applications for which an ongoing need for further protocol improvement is imminent

Electron correlations for ground state properties of group IV semiconductors

Valence energies for crystalline C, Si, Ge, and Sn with diamond structure have been determined using an ab-initio approach based on information from cluster calculations. Correlation contributions, in particular, have been evaluated in the coupled electron pair approximation (CEPA), by means of increments obtained for localized bond orbitals and for pairs and triples of such bonds. Combining these results with corresponding Hartree-Fock (HF) data, we recover about 95 % of the experimental cohesive energies. Lattice constants are overestimated at the HF level by about 1.5 %; correlation effects reduce these deviations to values which are within the error bounds of this method. A similar behavior is found for the bulk modulus: the HF values which are significantly too high are reduced by correlation effects to about 97 % of the experimental values.Comment: 22 pages, latex, 2 figure