170,429 research outputs found
Obituary: My Fond Remembrances of Dr M.K. Bhan
No full text13-14In the passing away of Dr Bhan, not only have we lost a great leader of modern science in India, passionate clinician-scientist par excellence but above all a great human being
Spatial rationalities and the possibilities for planing in the New Urban Agenda for Sustainable Development
No full textThis is the author accepted manuscript. The final version is available from [publisher] via the link in this record
Influence of first and second coordination environment on structural Fe(II) sites in MIL-101 for C−H bond activation in methane
No full textDivalent iron sites in tri-iron oxo-centered metal nodes in metal−organic frameworks (MOFs) catalyze light alkane oxidation. The first two steps of the reaction sequence, which are also the most energetically demanding ones, are the formation of the active species, Fe(IV)=O, by N2O decomposition and subsequent C−H bond cleavage. We have employed Kohn−Sham density functional methods to explore how modification of the microenvironment around the Fe(II) center can modulate its catalytic activity, akin to what noted in metalloenzymes. We have varied the substituents on the organic linker of the MIL-101(Fe) MOF, as a way to modulate the energy barriers associated with the first two steps of the methane to methanol reaction. The calculations show that varying substituents has a minimal electronic effect on the iron center and its first coordination shell. However, their proximity to the active site can modify the barriers by 20%. Hydrogen bond donors can lower both barriers, such that the resulting Fe(IV)=O species are simultaneously more stable and more reactive than those of the parent MOF. The screening of a large set of systems allowed us to establish rules for the selection of second coordination shell elements to improve the reactivity of oxoferryl-based catalysts: (i) functionality with a low pKa or large positive electrostatic potential, (ii) a distance around 1.5 Å between the oxoferryl and any atom of the ring substituent, and (iii) low conformational flexibility of the added substituent
Mechanism of Benzene Hydroxylation on Tri-Iron Oxo-Centered Cluster-Based Metal-Organic Frameworks
No full textHigh-valent Fe(IV)-oxo species derived upon reactions of N2O with Fe(II) centers & horbar;embedded in the framework of tri-iron oxo-centered-based metal-organic frameworks (MOFs)& horbar; selectively affect the conversion of benzene-to-phenol via electrophilic addition to arene C-H bonds akin to oxygen transfer mechanisms in the P450 enzyme. The Fe(II) species identified by M & ouml;ssbauer spectroscopy can be titrated in situ by the addition of NO to completely suppress benzene oxidation, verifying the relevance of Fe(II) centers. Observed inverse kinetic isotope effects in benzene hydroxylation preclude the involvement of H atom transfer steps from benzene to the Fe(IV)-oxo species and instead suggest that the electrophilic iron-oxo group adds to an sp(2) carbon of benzene, resulting in a change in the hybridization from sp(2)-to-sp(3). These mechanistic postulates are affirmed in Kohn-Sham density functional calculations, which predict lower barriers for additive mechanisms for arene oxidation than H atom abstraction steps. The calculations show that the reaction proceeds on the pentadectet spin surface and that a non-innocent ligand participates in the transfer of the H atom. Following precedent literature which demonstrates that these Fe(IV)-oxo species react with C-H bonds in alkanes via hydrogen atom abstraction to form alcohols, it appears that iron(IV)-oxo species in MOFs exhibit duality in their reactions with inert hydrocarbon substrates akin to enzymes & horbar;if the C-H bonds are in saturated aliphatic hydrocarbons, then activation occurs via hydrogen abstraction, while if the C-H bonds are aromatic, then activation occurs by addition rearrangement
Comparing the reaction profiles of single iron catalytic sites in enzymes and in reticular frameworks for methane-to-methanol oxidation
No full textThe design of synthetic inorganic catalysts mimicking the first coordination spheres of enzymatic cofactors often results in lower yields and selectivity than their biological counterparts. In this study, we exploit Kohn-Sham density functional methods to compare the reaction profiles of four single iron-based catalysts for the direct oxidation of methane to methanol: two biomimetic models based on two enzymes (cytochrome P450 and taurine dioxygenase [TauD]) and two synthetic reticular frameworks (iron-BEA zeolite and tri-iron oxo-center-based metal-organic framework). Both the biomimetic and inorganic catalysts show almost zero selectivity toward methanol for methane conversions >1% at ambient temperature. This study highlights that iron's first coordination shell can influence selectivity toward methanol but to a limited extent. In the absence of methanol protection strategies, high selectivity can be reached only by mimicking the reaction microenvironment of enzymes beyond the first coordination shell of iron
Replication Data for: Do neonates hear what we measure? Assessing neonatal ward soundscapes at the neonates' ears
No full text
This dataset contains the following data tables:
timeSeries1sec.csv: Computed acoustic metric scores across all microphones and measurement positions
The variables contained in the data table are detailed below:
location: [Factor w/ 2 levels: "NICU", "HD"] Variable for the location identifier of either the Neonatal Intensive Care Unit (NICU) and High Dependency (HD) wards measurement sites
microphone: [Factor w/ 5 levels: "146AEIn", "146AEOut", "binL", "binR", "146AE"] Variable describing the microphone type, where "146AEIn" and "146AEOut" refer to the measurement microphones located inside and outside the NICU ward incubator, respectively. "binL" and "binR" refer to the left and right channels of the binaural microphone attached to the neonate doll in both NICU and HD ward measurements, respectively. The "146AE" refers to the measurement microphone in above HD incubator only.
acoUnit: [Factor w/ 3 levels: "dBA", "dBC", "tuHMS"] Variable describing the acoustic metric computed, where "dBA" is the A-weighted slow time-weighted sound pressure level over 1 second, "dBC" is the C-weighted slow time-weighted sound pressure level over 1 second, and "tuHMS" is the tonality metric according to the Hearing Model of Sottek (HMS)
datetime: [POSIXct] Variable describing the timestamp.
score_1min: [numeric] Numerical score of the acoUnit</li
β-scission of olefins on acidic zeolites: A periodic PBE-D study in H-ZSM-5
No full textEight beta-scission modes involving C-6 and C-8 olefin isomers are investigated using dispersion-corrected density functional theory (i.e., PBE-D) calculations. Potential energy surfaces are evaluated within an acidic H-ZSM-5 supercell containing a single, isolated active site. Minimum energy pathways are localized using the nudged elastic band method. The relative enthalpic barriers of beta-scission steps can be described by the substitution order of the carbocationic carbon atom present in the reactant and transition states. Specifically, the total charge on the hydrocarbon fragment containing the beta C atom increases going from the physi- or chemisorbed reactant state to the beta-scission transition state; the magnitude of this change (+0.37e-0.97e) is found to correlate nearly monotonically with the activation energy (89-233 kJ mol(-1)). A comparison of 1 degrees to 3 degrees (E-1) and 3 degrees to 1 degrees (E-2) beta-scission modes as well as 2 degrees to 3 degrees (B-1) and 3 degrees to 2 degrees (B-2) beta-scission modes reveals that the barrier heights depend on the substitution order of the beta C, indicating that a subcategorization of beta-scission modes is required based on the substitution order of the beta C atom. Isomerization reactions, which are fast with respect to beta-scission, enable reactant hydrocarbons to explore and find low-barrier beta-scission pathways. Selectivities predicted on the basis of the relative barrier heights of beta-scission modes accessible to C-6 and C-8 species indicate agreement with experimental observations
The Forman Christian College Monthly
No full textEwing, J. C. R.-Speech-The Convocation Address: Delivered by the Rec. J. C. R. Ewing, D. D., Vice-Chancellor of the University of the Punjab. pp. 3-12; Luther, B. N.-Article-Education. pp. 13-18; Wir Bhan-Article-The Ideal Indian Student. pp. 19-23; A Trip to Nur Mahal. pp. 24-25; The Forman Christian College Dramatic Club. pp. 26; Newton Hall Activities. pp. 27; Sports: The Hockey Team Abroad. pp. 28-29; Annual Sports. pp. 29-30; The Surprising Cricket Eleven. pp. 30-3
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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