5,7,7,12,14,14-Hexamethyl-4,11-diaza-1,8-diazo­niacyclo­tetra­decane bis­(perchlorate) monohydrate

In the title hydrated salt, C16H38N4 2+·2ClO4 −·H2O, the dication is protonated at the diagonally opposite N atoms proximate to the –C(CH3)2– groups. Within the cavity, there are two ammonium–amine N—H⋯N hydrogen bonds. Supra­molecular layers are formed in the crystal packing whereby the water mol­ecule links two perchlorate anions, and the resultant aggregates are connected to the dications via N—H⋯O hydrogen bonds. Layers, with an undulating topology, stack along the a axis being connected by C—H⋯O inter­actions

Airway management in cardiac arrest -- not a question of choice but of quality?

This study presented an innovative method in order to estimate training required for skilful and successful intubations during ED cardiac arrests. Video reviews were taken from a system that routinely records ED staff during cardiac arrests and as these recordings are already part of everyday clinical practice, it is likely that there is minimal Hawthorne effect. Cardiac arrest research often reiterates the fact that the basics should be done well. It is commendable that intubations by the residents in this observational study resulted in a modest mean delay in chest compressions of only 8.6 seconds for the intubation attempt. However, nearly a third of intubation attempts were unsuccessful at the first attempt, and there were 11 oesophageal intubations (albeit they were all recognised) in the 93 patients that were included

Synthesis and Characterization of Polymer-Based Complex Nanomaterials

The original research work in this dissertation is about the use of polymers in two significantly important areas. One involves creating mesoporous silica materials with various morphologies using a mixed Pluronic surfactant system made up of two poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) surfactants, one of which contains long hydrophilic (PEO) blocks and the other has a significantly higher proportion of hydrophobic PPO . In addition, a glucose responsive core-shell type microgel was also developed for shifting the glucose responsive volume phase transition by using polymeric nanomaterials. Chapter 1 of the dissertation discussed some historical background of synthesis and uses of mesoporous materials and a brief review of some related topics like the development of ordered mesoporous materials, such as MCM-41 and SBA-15, soft-templated synthesis of silica nanotubes, short silica nanotubes, and synthesis of asymmetric silica nanotubse. It also includes the theory and background of stimuli-responsive microgels. The second chapter of this dissertation discusses the effect of anionic surfactant sodium dodecyl sulfate (SDS) on controlling the length of the silica nanotubes templated by Pluronic F127 and P104 surfactant mixtures and using tetraethyl orthosilicate as a silica precursor. The anionic SDS surfactant can also significantly control the length of the silica and organosilica nanotubes templated by a wide range of surfactant mixtures, as is discussed in Chapter 3. Chapter 4 will discuss the synthesis of Janus-like asymmetric (single bulb) organosilica nanotubes and double-bulbs organosilica nanotubes using Pluronic F127 and P123 surfactant mixture and using bis(triethoxysilyl)ethane precursor. Synthesis of a new type of silica nanomaterials (nanotube-wrapped hollow silica spheres) templated by Pluronic F127 and P123 and using tetraethyl orthosilicate precursor is discussed in Chapter 5. In Chapter 6, the synthesis of a boronic acid containing glucose-responsive core-shell type microgel is discussed for on-site controllable smart insulin delivery. The original studies described herein is summarized in Chapter 7 at the end

Defect Chemistry and Doping of BiCuSeO

While p-type BiCuSeO is a well-known mid-temperature oxide thermoelectric (TE) material, computations predict that superior TE performance can be realized through n-type doping. In this study, we use first-principles defect calculations to show that Cu vacancies are responsible for the native p-type self doping; yet, we find that BiCuSeO is n-type dopable under Cu-rich growth conditions, where the formation of Cu vacancies is suppressed. We computationally survey a broad suite of 23 dopants and find that only Cl and Br are effective n-type dopants. Therefore, we recommend that future experimental doping efforts utilize phase boundary mapping to optimize the electron concentration and resolve the anomalous p-n-p transitions observed in halogen-doped BiCuSeO. The prospects of n-type doping, as revealed by our defect calculations, paves the path for rational design of BiCuSeO chemical analogues with similar doping behavior and even better TE performance

Material Descriptors to Predict Thermoelectric Performance of Narrow-gap Semiconductors and Semimetals

Thermoelectric (TE) cooling is an environment-friendly alternative to vapor compression cooling. Narrow-gap semiconductors and semimetals have garnered interest for Peltier cooling, especially following the discovery of Mg3Bi2-based materials. New TE materials with high coefficients of performance are needed to further advance this technology. Computations have enabled the discovery and design of new TE materials. Large-scale computational searches often rely on material descriptors, which are based on the single-band model that does not account for bipolar conduction effects. In this work, we derive three material descriptors to assess the TE performance of narrow-gap semiconductors and semimetals -- band gap, n- and p-type TE quality factors, and an asymmetry parameter. These computationally-accessible descriptors are derived from Boltzmann transport theory applied to a two-band model. We show that a large asymmetry parameter is critical to achieving high TE performance through suppression of bipolar conduction. We validate the predictive power of the descriptors by correctly identifying Mg3Bi2 as a high-performing room-temperature TE material. By applying these descriptors to a broader set of 650 Zintl phases, we identify four candidate materials for room-temperature TEs, namely, SrSb2, Zn3As2, NaZnSb, and NaCdSb. The proposed material descriptors will enable fast targeted search of narrow-gap semiconductors and semimetals for low-temperature TEs

Defect Chemistry and Doping of Lead Phosphate Oxo Apatite Pb10(PO4)6O

Lead phosphate oxo apatite Pb10(PO4)6O is claimed to host room-temperature superconductivity when doped with copper. However, unsuccessful attempts to reproduce this claim has raised many questions about the composition, off-stoichiometry, and copper doping itself, among others. These questions are related to the native defect chemistry and thermodynamic phase stability. We perform first-principles defect calculations to provide much needed insights into the defect chemistry and doping of Pb10(PO4)6O. We find that the dominant Pb and O vacancies pin the Fermi energy in the mid-gap region. Our calculations suggest the plausible existence of closely related off-stoichiometric phase(s); we predict one such phase. We predict moderate levels of Cu doping, which still results in insulating behavior that is consistent with single-crystal measurements. We also rule out interstitial Cu doping, but find that unintentional S incorporation is highly possible. Our findings emphasize the need for careful characterization of the parent composition and the identification of synthesis conditions that will maximize (minimize) intentional (unintentional) doping

Y2Te3: A New n-type Thermoelectric Material

Rare-earth chalcogenides Re3-xCh4 (Re = La, Pr, Nd, Ch = S, Se, Te) have been extensively studied as high-temperature thermoelectric (TE) materials owing to their low lattice thermal conductivity (kL) and tunable electron carrier concentration via cation vacancies. In this work, we introduce Y2Te3, a rare-earth chalcogenide with a rocksalt-like vacancy-ordered structure, as a promising n-type TE material. We computationally evaluate the intrinsic transport properties, optimized TE performance, and doping characteristics of Y2Te3. Combined with a low kL, multiple low-lying conduction band valleys yield a high n-type TE quality factor. We find that a maximum figure-of-merit zT > 1.0 can be achieved when Y2Te3 is optimally doped with electron concentrations 1-2 x 10^20 cm-3. We use defect calculations to show that Y2Te3 is n-type dopable under Y-rich growth conditions, which suppresses the formation of acceptor-like cation vacancies. Furthermore, we propose that optimal n-type doping can be achieved with halogens (Cl, Br, I), with I being the most effective dopant. Our computational results as well as experimental results reported elsewhere motivate further optimization of Y2Te3 as an n-type TE material

Defect Chemistry and Doping of Lead Phosphate Oxo Apatite Pb₁₀(PO₄)₆O

Lead phosphate oxo apatite Pb10(PO4)6O is claimed to host room-temperature superconductivity when doped with copper. However, unsuccessful attempts to reproduce this claim have raised many questions about the composition, off-stoichiometry, and copper doping itself, which are related to native defect chemistry. We perform first-principles defect calculations to provide much needed insights into the defect chemistry and doping of Pb10(PO4)6O. We find that Fermi energy pinning in the midgap region occurs due to Pb and O vacancies. Our calculations also suggest the plausible existence of closely related off-stoichiometric phase(s); we predict one such phase. We predict only moderate levels of Cu doping, which calls into question the experimental claim of 10% incorporation on the Pb sites. Cu substitution on the Pb(1) and Pb(2) Wyckoff sites is possible, resulting in Cu d9 and d10 electronic configurations, respectively. We predict unintentional S incorporation is highly possible. Our findings emphasize the need for careful characterization of the parent composition and the identification of synthesis conditions that will maximize (minimize) intentional (unintentional) doping