439 research outputs found
Epoxy-cross-linked Polyamine CO2 Sorbents Enhanced via Hydrophobic Functionalization
Optimizing sorption capacity and amine efficiency are among the major challenges in developing solid carbon dioxide sorbents. Such materials frequently feature polyamines impregnated onto supports adding weight to the sorbents. This work presents the cross-linking of polyethyleneimine (PEI) by the industrially available epoxy resin, bisphenol-A diglycidyl ether (DER) to form support-free sorbent materials. Prior to cross-linking, the polyamine chain is functionalized with hydrophobic additives; one material modified with the branched chain hydrocarbon 2-ethylhexyl glycidyl ether displays CO2 uptake of 0.195 g/g, 4.43 mmol CO2/g (1 atm single component CO2, 90 °C). The additive loading affects the cross-linking, with the lesser cross-linked materials showing more favorable sorption capacities and higher amine efficiencies. The type of additive also influences sorption, with the larger, longer and bulkier additives better able to free the amine from their hydrogen bonding network, generally promoting better sorption. As well as increasing CO2 uptake, the additives also reduce the optimum sorption temperature, offering a handle to tune sorbents for specific working conditions. The best performing material shows high selectivity for CO2 sorption, and under sorption cycles in a 10% CO2/90% N2 mixture, utilizing temperature swing desorption, demonstrates a good working capacity of 9.5% CO2 uptake over the course of 29 cycles. Furthermore, humidity has been found to promote CO2 sorption at lower temperatures with a CO2 uptake of 0.235 g/g, 5.34 mmol/g (1 atm single component CO2, 25 °C) using a pre-hydrated sample. Overall, these findings confirm the value of our approach where cross-linking emerges as a valid and practical alternative to loading polyamines onto solid supports. This work demonstrates the versatility of these types of materials and their potential for use in large scale carbon capture systems
Competing magnetic orders in the superconducting state of Nd-doped CeRhIn under pressure
Applied pressure drives the heavy-fermion antiferromagnet CeRhIn
towards a quantum critical point that becomes hidden by a dome of
unconventional superconductivity. Magnetic fields suppress this superconducting
dome, unveiling the quantum phase transition of local character. Here, we show
that magnetic substitution at the Ce site in CeRhIn, either by Nd
or Gd, induces a zero-field magnetic instability inside the superconducting
state. This magnetic state not only should have a different ordering vector
than the high-field local-moment magnetic state, but it also competes with the
latter, suggesting that a spin-density-wave phase is stabilized in zero field
by Nd and Gd impurities - similarly to the case of
CeNdCoIn. Supported by model calculations, we attribute
this spin-density wave instability to a magnetic-impurity driven condensation
of the spin excitons that form inside the unconventional superconducting state
Carotid artery wall mechanics in young males with high cardiorespiratory fitness
The influence of cardiorespiratory fitness (CRF) on arterial stiffness in young adults remains equivocal. Beyond conventional measures of arterial stiffness, 2D strain imaging of the common carotid artery (CCA) provides novel information related to the intrinsic properties of the arterial wall. Therefore, this study aimed to assess the effect of CRF on both conventional indices of CCA stiffness and 2D strain parameters, at rest and following a bout of aerobic exercise in young healthy males. Shortâaxis ultrasound images of the CCA were recorded in 34 healthy men [22 years (95%CI, 19â22)] before, and immediately after 5âminutes of aerobic exercise (40% VO2max). Images were analysed for arterial diameter, peak circumferential strain (PCS), and peak systolic and diastolic strain rates (SâSR, DâSR). Heart rate (HR), systolic and diastolic blood pressure (SBP, DBP) were simultaneously assessed and Petersons' elastic modulus (Ep) and Beta stiffness (ÎČ1) were calculated. Participants were separated post hoc into moderate and high fitness groups [VO2max: 48.9 ml.kgâ1 minâ1 (95%CI, 44.7â53.2) vs. 65.6 ml.kgâ1 minâ1 (95%CI, 63.1â68.1); P 0.13) but were elevated in the moderateâfitness group postâexercise (P 0.05). Highâfit individuals exhibit elevated CCA PCS and SâSR, which may reflect trainingâinduced adaptations that help to buffer the rise in pulseâpressure and stroke volume during exercise
Post-Synthetic Ligand Exchange in Zirconium-Based Metal-Organic Frameworks: Beware of The Defects!
Postâsynthetic ligand exchange in the prototypical zirconiumâbased metalâorganic framework UiOâ66 was investigated by in situ solution 1H nuclear magnetic resonance. Samples of UiOâ66 having different degrees of defectivity were exchanged using solutions of several terephthalic acid analogues in a range of conditions. Linker exchange only occurred in defectâfree UiOâ66, whereas monocarboxylates grafted at defective sites were found to be preferentially exchanged with respect to terephthalic acid over the whole range of conditions investigated. A 1:1 exchange ratio between the terephthalic acid analogue and modulator was observed, providing evidence that the defects had missingâcluster nature. Ex situ characterisation of the MOF powders after exchange corroborated these findings and evidenced that the physicalâchemical properties of the MOF depend on whether the functionalisation occurs at defective sites or on the framework. N2 sorption analysis showed that, upon exchange, defective samples underwent significant decrease of surface area and disappearance of large pores, associated with the presence of missingâcluster defects in the starting material. CO2 sorption studies displayed the different impact of pure defect functionalisation and pure framework functionalisation on isosteric heat of adsorption and CO2/N2 selectivity
Multiabsorber Transition-Edge Sensors for X-Ray Astronomy
We are developing arrays of position-sensitive microcalorimeters for future x-ray astronomy applications. These position-sensitive devices commonly referred to as hydras consist of multiple x-ray absorbers, each with a different thermal coupling to a single-transition-edge sensor microcalorimeter. Their development is motivated by a desire to achieve very large pixel arrays with some modest compromise in performance. We report on the design, optimization, and first results from devices with small pitch pixels (<75 m) being developed for a high-angular and energy resolution imaging spectrometer for Lynx. The Lynx x-ray space telescope is a flagship mission concept under study for the National Academy of Science 2020 decadal survey. Broadband full-width-half-maximum (FWHM) resolution measurements on a 9-pixel hydra have demonstrated E(FWHM) = 2.23 0.14 eV at Al-K, E(FWHM) = 2.44 0.29 eV at Mn-K, and E(FWHM) = 3.39 0.23 eV at Cu-K. Position discrimination is demonstrated to energies below <1 keV and the device performance is well-described by a finite-element model. Results from a prototype 20-pixel hydra with absorbers on a 50-m pitch have shown E(FWHM) = 3.38 0.20 eV at Cr-K1. We are now optimizing designs specifically for Lynx and extending the number of absorbers up to 25/hydra. Numerical simulation suggests optimized designs could achieve 3 eV while being compatible with the bandwidth requirements of the state-of-the art multiplexed readout schemes, thus making a 100,000 pixel microcalorimeter instrument a realistic goal
An industrial reference fluid for moderately high viscosity
In industrial practice, there is a demand for a reference standard for viscosity that is established for a readily available fluid to simplify the calibration of industrial viscometers for moderately high viscosities [(50 to 125) mPa · s]. Diisodecyl phthalate (DIDP) has been suggested as that reference fluid, and a number of studies of its properties have been carried out in several laboratories throughout the world, within the auspices of a project coordinated by the International Association for Transport Properties. That project has now progressed to the point where it is possible to collate the results of studies of the viscosity of the fluid by
a number of different techniques, so as to lead to a proposed standard reference value which will be included in the paper. To support this recommended value, the various measurements conducted have been critically
reviewed, and the sample purity and other factors affecting the viscosity have been studied. Density and surface tension measurements have also been performed. This paper does not describe the individual viscosity determinations carried out in independent laboratories because these are the subject of individual publications,
but it does describe the ancillary studies conducted and their relevance to the viscosity standard. In addition, the paper contains recommended values for the viscosity of liquid DIDP. The samples of DIDP to which the recommended values refer are isomeric mixtures available commercially from certain suppliers, with a minimum purity by gas chromatography of 99.8 %. The recommended values result from a critical examination of all the measurements conducted to date and are supported by careful arguments dealing with the likely
effects of the isomeric content of the sample as well as of other impurities. The proposed reference standard is intended particularly to serve an industrial need for a readily available calibration material with a viscosity close to that required in practical situations. To that end, the recommended value has an overall relative
uncertainty of approximately 1 %. It is therefore not intended to supersede for the reference value for the viscosity of water at 20 °C, which is known much more accurately, but rather to complement it
Thermal Fluctuation Noise in Mo/Au Superconducting Transition-Edge Sensor Microcalorimeters
In many superconducting transition-edge sensor (TES) microcalorimeters, the measured electrical noise exceeds theoretical estimates based on a thermal model of a single body thermally connected to a heat bath. Here, we report on noise and complex impedance measurements of a range of designs of TESs made with a Mo/Au bilayer. We have fitted the measured data using a two-body model, where the x-ray absorber and the TES are connected by an internal thermal conductance Gae. We find that the so-called excess noise measured in these devices is consistent with the noise generated from the internal thermal fluctuations between the x-ray absorber and the TES. Our fitted parameters are consistent with the origin of Gae being from the finite thermal conductance of the TES itself. These results suggest that even in these relatively low resistance Mo/Au TESs, the internal thermal conductance of the TES may add significant additional noise and could account for all the measured excess noise. Furthermore, we find that around regions of the superconducting transition with rapidly changing derivative of resistance with respect to temperature, an additional noise mechanism may dominate. These observations may lead to a greater understanding of TES devices and allow the design of TES microcalorimeters with improved performance
Arte convenzionale â ovvero â perchĂ© non possono esistere artisti realmente anticonformisti
The representation of the artist is generally that of a nonconformist, a lonely Bohemian eager to revolutionise the world from his studio. From this perspective, the traditional interpretation of art history is one of linear progress, spurred on by moments of innovation aiming at new states of conventionalism. This article shows how such a perspective has much to do with the philosophy of modern times, even though it doesnât provide a satisfactory explanation of the meaning and development of art throughout the centuries, bound as they are instead to the necessity of convention with the values of society (or of its Ă©lite) rather than on wild individualism
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