LIII. On the atmospherical refraction

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Investigation of the mechanism of electron capture and electron transfer dissociation of peptides with a covalently attached free radical hydrogen atom scavenger

The mechanisms of electron capture and electron transfer dissociation (ECD and ETD) are investigated by covalently attaching a free-radical hydrogen atom scavenger to a peptide. The 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) radical was chosen as the scavenger due to its high hydrogen atom affinity (ca. 280 kJ/mol) and low electron affinity (ca. 0.45 eV), and was derivatized to the model peptide, FQX^(TEMPO)EEQQQTEDELQDK. The X^(TEMPO) residue represents a cysteinyl residue derivatized with an acetamido-TEMPO group. The acetamide group without TEMPO was also examined as a control. The gas phase proton affinity (882 kJ/mol) of TEMPO is similar to backbone amide carbonyls (889 kJ/mol), minimizing perturbation to internal solvation and sites of protonation of the derivatized peptides. Collision-induced dissociation (CID) of the TEMPO-tagged peptide dication generated stable odd-electron b and y type ions without indication of any TEMPO radical induced fragmentation initiated by hydrogen abstraction. The type and abundance of fragment ions observed in the CID spectra of the TEMPO and acetamide tagged peptides are very similar. However, ECD of the TEMPO-labeled peptide dication yielded no backbone cleavage. We propose that a labile hydrogen atom in the charge reduced radical ions is scavenged by the TEMPO radical moiety, resulting in inhibition of N-Cα backbone cleavage processes. Supplemental activation after electron attachment (ETcaD) and CID of the charge-reduced precursor ion generated by electron transfer of the TEMPO-tagged peptide dication produced a series of b + H (b^H) and y + H (y^H) ions along with some c ions having suppressed intensities, consistent with stable O-H bond formation at the TEMPO group. In summary, the results indicate that ECD and ETD backbone cleavage processes are inhibited by scavenging of a labile hydrogen atom by the localized TEMPO radical moiety. This observation supports the conjecture that ECD and ETD processes involve long-lived intermediates formed by electron capture/transfer in which a labile hydrogen atom is present and plays a key role with low energy processes leading to c and z ion formation. Ab initio and density functional calculations are performed to support our conclusion, which depends most importantly on the proton affinity, electron affinity and hydrogen atom affinity of the TEMPO moiety

Manufacturing consensus in a diverse field of scholarly opinions: A comment on Bushman, Gollwitzer, and Cruz (2015).

We appreciate the efforts of Bushman and Cruz to provide new data describing parents’ and professionals’ opinions regarding effects of media violence. Unfortunately, we feel it is necessary to call attention to apparent errors and inaccuracies in the way those data are interpreted and represented in their article. The article overstates the extent to which there is agreement that media violence has meaningful negative societal effects and misrepresents the relevance of the study to an understanding of the effects of media violence on societal violence. In contrast, we call for a climate of research on media violence that better recognizes the diversity of findings and conclusions in an active and growing research agenda and eschews unwarranted insinuations about effects on criminal violence from research focused on aggression-related measures not assessing violent crime

Response to Kamath et al 'A syncretic approach can yield dividends'

We welcome the response from Kamath et al. and their insight into the issues and culture within medicine in India, and their thoughts about how to address these issues. We also agree that a drama-based approach is not sufficient on its own to deal with entrenched power issues which affect students adversely. As we have indicated, we believe “a multipronged approach is needed to generate systemic change.” These authors similarly advocate that student mistreatment be dealt with “in a comprehensive manner” including a ‘grievance redressal system’ and other measures to withhold accreditation where there are issues of abuse of power. Nevertheless, we note that Kamath et al. have responded positively to our approach—as a part of that mix—and it would be of great interest to see whether drama-based workshops could support medical students developing embodied acting skills in their institution and whether they may have similar transformative effects. We’d like to refer the authors to an excellent Medical Humanities paper we referenced that outlined drama-based activities in medical education in India: Gupta S, Singh S. Confluence: understanding medical humanities through street theatre. Medical Humanities. 2011;37(2):127-128. Despite the above article, the authors note that medical education in India has not embraced the medical humanities. We would draw a distinction within the medical humanities between activities which are primarily studious (reading literature, studying medical history) and workshops that are based on participative and embodied activity. Our experience has indicated the effectiveness of drama-based workshops in addressing both the cognitive and emotive aspects of harmful practices and we believe that it is the embodied nature of acting skills workshops that is transformative

Ballistic Atom Pumps

We examine a classically chaotic system consisting of two reservoirs of particles connected by a channel containing oscillating potential-energy barriers. We investigate whether such a system can preferentially pump particles from one reservoir to the other, a process often called “quantum pumping.” We show how to make a “particle diode” which under specified conditions permits net particle pumping in only one direction. Then we examine systems having symmetric barriers. We find that if all initial particle energies are considered, a system with symmetric barriers cannot preferentially pump particles. However, if only finite initial energy bands are considered, the system can create net particle transport in either direction. We study the system classically, semiclassically, and quantum mechanically, and find that the quantum description cannot be fully understood without the insight gained from classical and semiclassical analysis

Vegetation Controls on Weathering Intensity During the Last Deglacial Transition in Southeast Africa

Tropical climate is rapidly changing, but the effects of these changes on the geosphere are unknown, despite a likelihood of climatically-induced changes on weathering and erosion. The lack of long, continuous paleo-records prevents an examination of terrestrial responses to climate change with sufficient detail to answer questions about how systems behaved in the past and may alter in the future. We use high-resolution records of pollen, clay mineralogy, and particle size from a drill core from Lake Malawi, southeast Africa, to examine atmosphere-biosphere-geosphere interactions during the last deglaciation (~ 18-9 ka), a period of dramatic temperature and hydrologic changes. The results demonstrate that climatic controls on Lake Malawi vegetation are critically important to weathering processes and erosion patterns during the deglaciation. At 18 ka, afromontane forests dominated but were progressively replaced by tropical seasonal forest, as summer rainfall increased. Despite indication of decreased rainfall, drought-intolerant forest persisted through the Younger Dryas (YD) resulting from a shorter dry season. Following the YD, an intensified summer monsoon and increased rainfall seasonality were coeval with forest decline and expansion of drought-tolerant miombo woodland. Clay minerals closely track the vegetation record, with high ratios of kaolinite to smectite (K/S) indicating heavy leaching when forest predominates, despite variable rainfall. In the early Holocene, when rainfall and temperature increased (effective moisture remained low), open woodlands expansion resulted in decreased K/S, suggesting a reduction in chemical weathering intensity. Terrigenous sediment mass accumulation rates also increased, suggesting critical linkages among open vegetation and erosion during intervals of enhanced summer rainfall. This study shows a strong, direct influence of vegetation composition on weathering intensity in the tropics. As climate change will likely impact this interplay between the biosphere and geosphere, tropical landscape change could lead to deleterious effects on soil and water quality in regions with little infrastructure for mitigation