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https://www.readbyqxmd.com/read/28817284/fabrication-of-mesoporous-polystyrene-films-with-controlled-porosity-and-pore-size-by-solvent-annealing-for-templated-syntheses
#1
Mohan Raj Krishnan, Yu-Cheng Chien, Chung-Fu Cheng, Rong-Ming Ho
Herein, we aim to develop a facile method for the fabrication of mesoporous polystyrene (PS) films with controlled porosity and pore size by solvent annealing. A PS polymer film is solvent-annealed using N,N-dimethyl formamide (DMF) vapor for the development of phase separation, followed by rapidly cooling to the preset cryogenic temperature. Subsequently, a nonsolvent (methanol) is introduced to extract the crystalline DMF from the DMF-swollen PS, giving mesoporous PS with a network structure after the removal of DMF...
August 17, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28814630/inverted-region-electron-transfer-as-a-mechanism-for-enhancing-photosynthetic-solar-energy-conversion-efficiency
#2
Hiroki Makita, Gary Hastings
In all photosynthetic organisms, light energy is used to drive electrons from a donor chlorophyll species via a series of acceptors across a biological membrane. These light-induced electron-transfer processes display a remarkably high quantum efficiency, indicating a near-complete inhibition of unproductive charge recombination reactions. It has been suggested that unproductive charge recombination could be inhibited if the reaction occurs in the so-called inverted region. However, inverted-region electron transfer has never been demonstrated in any native photosynthetic system...
August 16, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28811371/angular-reconstitution-based-3d-reconstructions-of-nanomolecular-structures-from-superresolution-light-microscopy-images
#3
Desirée Salas, Antoine Le Gall, Jean-Bernard Fiche, Alessandro Valeri, Yonggang Ke, Patrick Bron, Gaetan Bellot, Marcelo Nollmann
Superresolution light microscopy allows the imaging of labeled supramolecular assemblies at a resolution surpassing the classical diffraction limit. A serious limitation of the superresolution approach is sample heterogeneity and the stochastic character of the labeling procedure. To increase the reproducibility and the resolution of the superresolution results, we apply multivariate statistical analysis methods and 3D reconstruction approaches originally developed for cryogenic electron microscopy of single particles...
August 15, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28808333/noise-of-a-superconducting-magnetic-flux-sensor-based-on-a-proximity-josephson-junction
#4
R N Jabdaraghi, D S Golubev, J P Pekola, J T Peltonen
We demonstrate simultaneous measurements of DC transport properties and flux noise of a hybrid superconducting magnetometer based on the proximity effect (superconducting quantum interference proximity transistor, SQUIPT). The noise is probed by a cryogenic amplifier operating in the frequency range of a few MHz. In our non-optimized device, we achieve minimum flux noise ~4 μΦ0/Hz(1/2), set by the shot noise of the probe tunnel junction. The flux noise performance can be improved by further optimization of the SQUIPT parameters, primarily minimization of the proximity junction length and cross section...
August 14, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28805860/synthesis-of-n-doped-graphene-quantum-dots-by-pulsed-laser-ablation-with-diethylenetriamine-deta-and-their-photoluminescence
#5
S R M Santiago, T N Lin, C H Chang, Y A Wong, C A J Lin, C T Yuan, J L Shen
We report a facile, fast, and one-step approach to prepare N-doped graphene quantum dots (GQDs) using pulsed laser ablation with diethylenetriamine (DETA). The synthesized N-doped GQDs with an average size of about 3.4 nm and an N/C atomic ratio of 26% have been demonstrated. Compared to pristine GQDs, the N-doped GQDs emit enhanced photoluminescence (PL) with a factor as high as 66, originated from the enhanced densities of pyridinic and graphitic N. The temperature-dependent PL of the N-doped GQDs was studied from cryogenic to room temperature...
August 14, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28804803/comparison-of-sample-preparation-procedures-on-metal-loid-fractionation-patterns-in-lichens
#6
E M Kroukamp, T W Godeto, P B C Forbes
The effects of different sample preparation strategies and storage on metal(loid) fractionation trends in plant material is largely underresearched. In this study, a bulk sample of lichen Parmotrema austrosinense (Zahlbr.) Hale was analysed for its total extractable metal(loid) content by ICP-MS, and was determined to be adequately homogenous (<5% RSD) for most elements. Several subsets of this sample were prepared utilising a range of sample preservation techniques and subjected to a modified sequential extraction procedure or to total metal extraction...
August 13, 2017: Environmental Monitoring and Assessment
https://www.readbyqxmd.com/read/28801884/identification-and-partial-structural-characterization-of-mass-isolated-valsartan-and-its-metabolite-with-messenger-tagging-vibrational-spectroscopy
#7
Olga Gorlova, Sean M Colvin, Antonio Brathwaite, Fabian S Menges, Stephanie M Craig, Scott J Miller, Mark A Johnson
Recent advances in the coupling of vibrational spectroscopy with mass spectrometry create new opportunities for the structural characterization of metabolites with great sensitivity. Previous studies have demonstrated this scheme on 300 K ions using very high power free electron lasers in the fingerprint region of the infrared. Here we extend the scope of this approach to a single investigator scale as well as extend the spectral range to include the OH stretching fundamentals. This is accomplished by detecting the IR absorptions in a linear action regime by photodissociation of weakly bound N2 molecules, which are attached to the target ions in a cryogenically cooled, rf ion trap...
August 11, 2017: Journal of the American Society for Mass Spectrometry
https://www.readbyqxmd.com/read/28795512/single-particle-cryo-em-improved-ab-initio-3d-reconstruction-with-simple-prime
#8
Cyril F Reboul, Michael Eager, Dominika Elmlund, Hans Elmlund
Cryogenic electron microscopy (cryo-EM) and single-particle analysis now enables the determination of high-resolution structures of macromolecular assemblies that have resisted X-ray crystallography and other approaches. We developed the SIMPLE open-source image-processing suite for analysing cryo-EM images of single-particles. A core component of SIMPLE is the probabilistic PRIME algorithm for identifying clusters of images in 2D and determine relative orientations of single-particle projections in 3D. Here we extend our previous work on PRIME and introduce new stochastic optimisation algorithms that improve the robustness of the approach...
August 10, 2017: Protein Science: a Publication of the Protein Society
https://www.readbyqxmd.com/read/28793764/continuous-arsine-detection-using-a-peltier-effect-cryogenic-trap-to-selectively-trap-methylated-arsines
#9
Guoying Chen, Bunhong Lai, Xuefei Mao, Tuanwei Chen, Miaomiao Chen
Hydride generation (HG) is an effective technique that eliminates interfering matrix species and enables hydride separation. Arsenic speciation analysis can be fulfilled by cryogenic trapping (CT) based on boiling points of resulting arsines using liquid nitrogen (LN2) as a coolant. In this work, LN2 was replaced by thermoelectric effect using a cryo-genic trap that consisted of a polytetrafluoroethylene (PTFE) body sandwiched by two Peltier modules. After the trap was precooled, the arsines flew along a zigzag channel in the body and reached a sorbent bed of 0...
August 10, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28783525/a-sub-kelvin-cryogen-free-epr-system
#10
Simon J Melhuish, Chloe Stott, Ana-Maria Ariciu, Lorenzo Martinis, Mark McCulloch, Lucio Piccirillo, David Collison, Floriana Tuna, Richard Winpenny
We present an EPR instrument built for operation at Q band below 1K. Our cryogen-free Dewar integrates with a commercial electro-magnet and bridge. A description of the cryogenic and RF systems is given, along with the adaptations to the standard EPR experiment for operation at sub-Kelvin temperatures. As a first experiment, the EPR spectra of powdered Cr12O9(OH)3 [Formula: see text] were measured. The sub-Kelvin EPR spectra agree well with predictions, and the performance of the sub-Kelvin system at 5K is compared to that of a commercial spectrometer...
July 20, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28777573/excited-state-dynamics-of-cold-protonated-cytosine-tautomers-characterization-of-charge-transfer-inter-system-crossing-and-internal-conversion-processes
#11
Michel Broquier, Satchin Soorkia, Gustavo A Pino, Claude Dedonder-Lardeux, Christophe Jouvet, Gilles Gregoire
Charge transfer reactions are ubiquitous in chemical reactivity and often viewed as ultrafast processes. For DNA, femtochemistry has undeniably revealed the primary stage of the deactivation dynamics of the locally excited state following electronic excitation. We here demonstrate that the full time scale excited state dynamics can be followed up to milliseconds through an original pump-probe photodissociation scheme applied to cryogenic ion spectroscopy. Protonated cytosine is chosen as a benchmark system in which the locally excited (1)ππ* state decays in the femtosecond range towards long-lived charge transfer state and triplet state with lifetimes ranging from microseconds to milliseconds, respectively...
August 4, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28776012/dna-s-chiral-spine-of-hydration
#12
M Luke McDermott, Heather Vanselous, Steven A Corcelli, Poul B Petersen
The iconic helical structure of DNA is stabilized by the solvation environment, where a change in the hydration state can lead to dramatic changes to the DNA structure. X-ray diffraction experiments at cryogenic temperatures have shown crystallographic water molecules in the minor groove of DNA, which has led to the notion of a spine of hydration of DNA. Here, chiral nonlinear vibrational spectroscopy of two DNA sequences shows that not only do such structural water molecules exist in solution at ambient conditions but that they form a chiral superstructure: a chiral spine of hydration...
July 26, 2017: ACS Central Science
https://www.readbyqxmd.com/read/28774102/vacuum-induced-surface-freezing-to-produce-monoliths-of-aligned-porous-alumina
#13
Sandra Großberger, Tobias Fey, Geoffrey Lee
Vacuum-induced surface freezing has been used to produce uni-directional freezing of colloidal aluminum oxide dispersions. It leads to zones of different structure within the resulting sintered monoliths that are highly similar to those known for freeze casting using a cryogen cold source. A more-or-less dense surface layer and a cellular sub-surface region are formed, beneath which is a middle region of aligned lamellae and pores that stretches through most of the depth of the monolith. This is the case even at a volume fraction of dispersed phase as low as 0...
December 5, 2016: Materials
https://www.readbyqxmd.com/read/28773179/effects-of-the-crack-tip-constraint-on-the-fracture-assessment-of-an-al-5083-o-weldment-for-low-temperature-applications
#14
Dong Hyun Moon, Jeong Yeol Park, Myung Hyun Kim
The constraint effect is the key issue in structural integrity assessments based on two parameter fracture mechanics (TPFM) to make a precise prediction of the load-bearing capacity of cracked structural components. In this study, a constraint-based failure assessment diagram (FAD) was used to assess the fracture behavior of an Al 5083-O weldment with various flaws at cryogenic temperature. The results were compared with those of BS 7910 Option 1 FAD, in terms of the maximum allowable stress. A series of fracture toughness tests were conducted with compact tension (CT) specimens at room and cryogenic temperatures...
July 18, 2017: Materials
https://www.readbyqxmd.com/read/28772648/effect-of-native-defects-on-transport-properties-in-non-stoichiometric-cosb%C3%A2
#15
Paula R Realyvázquez-Guevara, Francisco J Rivera-Gómez, Alejandro Faudoa-Arzate, María E Botello-Zubiate, Renee J Sáenz-Hernández, Carlos R Santillán-Rodríguez, José A Matutes-Aquino
The effect of native defects originated by a non-stoichiometric variation of composition in CoSb₃ on I-V curves and Hall effect was investigated. Hysteretic and a non-linear behavior of the  I-V curves at cryogenic temperatures were observed; the non-linear behavior originated from the Poole-Frenkel effect, a field-dependent ionization mechanism that lowers Coulomb barriers and increases emission of charge carriers, and the hysteresis was attributed to the drastic decrease of specific heat which produces Joule heating at cryogenic temperatures...
March 14, 2017: Materials
https://www.readbyqxmd.com/read/28764534/assessing-infrared-intensity-using-the-evaporation-rate-of-liquid-hydrogen-inside-a-cryogenic-integrating-sphere-for-laser-fusion-targets
#16
K Iwano, A Iwamoto, T Asahina, K Yamanoi, Y Arikawa, H Nagatomo, M Nakai, T Norimatsu, H Azechi
Infrared (IR) heating processes have been studied to form a deuterium layer in an inertial confinement fusion target. To understand the relationship between the IR intensity and the fuel layering time constant, we have developed a new method to assess the IR intensity during irradiation. In our method, a glass flask acting as a dummy target is filled with liquid hydrogen (LH2) and is then irradiated with 2-μm light. The IR intensity is subsequently calculated from the time constant of the LH2 evaporation rate...
July 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28762419/efficient-3-he-4-he-separation-in-a-nanoporous-graphenylene-membrane
#17
Yuanyuan Qu, Feng Li, Mingwen Zhao
Helium-3 is a precious noble gas, which is essential in many advanced technologies such as cryogenics, isotope labeling and nuclear weapons. The current imbalance of (3)He demand and supply shortage leads to the search for an efficient membrane with high performance for (3)He separation. In this study, based on first-principles calculations, we demonstrated that highly efficient (3)He harvesting can be achieved in a nanoporous graphenylene membrane with industrially-acceptable selectivity and permeance. The quantum tunneling effect leads to (3)He harvesting with high efficiency via kinetic sieving...
August 16, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28760605/advanced-fingerprinting-of-high-quality-cocoa-challenges-in-transferring-methods-from-thermal-to-differential-flow-modulated-comprehensive-two-dimensional-gas-chromatography
#18
Federico Magagna, Erica Liberto, Stephen E Reichenbach, Qingping Tao, Andrea Carretta, Luigi Cobelli, Matthew Giardina, Carlo Bicchi, Chiara Cordero
The possibility to transfer methods from thermal to differential-flow modulated comprehensive two-dimensional gas chromatographic (GC×GC) platforms opens interesting perspectives for routine analysis of complex samples. Flow modulated platforms avoid the use of cryogenics, thereby simplifying laboratory operations and analyst supervision during intensive analytical sessions. This study evaluates the feasibility of transferring a fingerprinting method capable of classifying and discriminating cocoa samples based on the volatiles fraction composition according to their origin and processing steps...
July 8, 2017: Journal of Chromatography. A
https://www.readbyqxmd.com/read/28759216/allosteric-inhibitors-crystallography-and-comparative-analysis-reveal-network-of-coordinated-movement-across-human-herpesvirus-proteases
#19
Timothy M Acker, Jonathan E Gable, Markus-Frederik Bohn, Priyadarshini Jaishankar, Michael C Thompson, James S Fraser, Adam R Renslo, Charles S Craik
Targeting of cryptic binding sites represents an attractive but underexplored approach to modulating protein function with small molecules. Using the dimeric protease (Pr) from Kaposi's sarcoma-associated herpesvirus (KSHV) as a model system, we sought to dissect a putative allosteric network linking a cryptic site at the dimerization interface to enzyme function. Five cryogenic x-ray structures were solved of the monomeric protease with allosteric inhibitors bound to the dimer interface site. Distinct coordinated movements captured by the allosteric inhibitors were also revealed as alternative states in room temperature X-ray data and comparative analyses of other dimeric herpesvirus proteases...
July 31, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28759197/cryogenic-fab-on-a-chip-sticks-the-landing
#20
Matthias Imboden, Han Han, Thomas Stark, David Bishop
Using a microelectromechanical systems (MEMS)-based Fab-on-a-Chip, we quench-condense lead thin-films. Suppressing the formation of lead islands makes it possible to grow a homogeneous and continuous film as thin as 2 nm, without the use of an adhesion layer. Thermal cycling from 3 K to as low as 10 K reveals irreversible annealing of the thin-film characteristic of a metastable state. The transition to the stable state is smooth and is completed by cycling the temperature above ∼42 K, where a distinctive resistance minimum is observed...
July 31, 2017: ACS Nano
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