On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications

Progress in the synthesis and engineering of advanced porous materials demands better pore structure characterization. The analysis of pore structure is complicated by (1) the wide range in pore sizes observed, from molecular ( 1 mm) dimensions, (2) complex pore shapes and connectivities, (3) chemical and physical heterogeneities, and (4) pore structure changes that can occur during characterization.The required pore structure information varies with application. Bulk density and the pore-size distribution are needed for thermal insulation. In this case, the dimension of interest is the so-called hydraulic radius since, for small pores, the gas-phase conductivity is proportional to the mean hydraulic radius to the mean free path. A few large but isolated pores will significantly affect conductivity but will go undetected in typical gas-absorption methods. In contrast, for separations, bottlenecks control performance. For transport, such as migration through geologic formations, both the pore-size distribution and pore connectivity are important. For adsorption, surface area and pore size are the relevant factors. Finally, the conventional concepts of pore structure lose meaning as the pore size approaches molecular dimensions, typical of adsorbents and gas-separation membranes.

Characterization of Porous Solids

Lithium metal has the highest volumetric and gravimetric energy density of all negative-electrode materials when used as an electrode material in a lithium rechargeable battery. However, the formation of lithium dendrites and/or ‘moss’ on the metal electrode surface can lead to short circuits following several electrochemical charge–discharge cycles, particularly at high rates, rendering this class of batteries potentially unsafe and unusable owing to the risk of fire and explosion. Many recent investigations have focused on the development of methods to prevent moss/dendrite formation. In parallel, it is important to quantify Li-moss formation, to identify the conditions under which it forms. Although optical and electron microscopy can visually monitor the morphology of the lithium-electrode surface and hence the moss formation, such methods are not well suited for quantitative studies. Here we report the use of in situ NMR spectroscopy, to provide time-resolved, quantitative information about the nature of the metallic lithium deposited on lithium-metal electrodes. The formation of lithium dendrites on the metal electrode surface of lithium batteries can lead to short circuits, making them potentially unsafe and unusable. The use of in situ NMR spectroscopy provides time-resolved and quantitative information about the nature of metallic lithium deposited on lithium-metal electrodes.

In situ NMR observation of the formation of metallic lithium microstructures in lithium batteries

Lithium-ion batteries (LIBs) containing silicon negative electrodes have been the subject of much recent investigation because of the extremely large gravimetric and volumetric capacity of silicon. The crystalline-to-amorphous phase transition that occurs on electrochemical Li insertion into crystalline Si, during the first discharge, hinders attempts to link structure in these systems with electrochemical performance. We apply a combination of static, in situ and magic angle sample spinning, ex situ 7Li nuclear magnetic resonance (NMR) studies to investigate the changes in local structure that occur in an actual working LIB. The first discharge occurs via the formation of isolated Si atoms and smaller Si−Si clusters embedded in a Li matrix; the latter are broken apart at the end of the discharge, forming isolated Si atoms. A spontaneous reaction of the lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge and potential capacity...

Real-Time NMR Investigations of Structural Changes in Silicon Electrodes for Lithium-Ion Batteries

7Li NMR study of intercalated lithium in curved carbon lattices

We have observed the equilibrium distribution of Xe atoms trapped in the alpha cages of zeolite NaA at 300 and at 360 K for low to high xenon loadings. The experimental distributions obtained by nuclear magnetic resonance (NMR) spectroscopy differ from two previously proposed statistical distributions. The experimental deviations from these statistical models can be explained by the attractive Xe–Xe interactions which favor clustering at low to medium loading, and the higher energies associated with the overcrowded cage disfavoring clusters of eight Xe atoms at high loadings. The temperature dependence of the 129Xe NMR chemical shift of each cluster has been measured in the range 188–421 K, except that for Xe8, which was determined only up to 300 K. The observed shifts and their temperature dependence are interpreted by using the results of ab initio calculations of the intermolecular shielding function in the 39Ar system as a model for the 129Xe system.

Nuclear magnetic resonance studies of xenon clusters in zeolite NaA

Solid-state NMR spectroscopy is well established as a method for describing molecular structure with resolution on the atomic scale. Many of the NMR observables result from anisotropic interactions between the nuclear spin and its environment. These observables can be described by second-rank tensors. For example, the eigenvalues of the traceless symmetric part of the hydrogen chemical shift (CS) tensor provide information about the strength of inter- or intramolecular hydrogen bonding. On the other hand, the eigenvectors of the deuterium electric field gradient (EFG) tensor give deuteron/proton bond directions with an accuracy rivalled only by neutron diffraction. In this paper the authors report structural information of this type for the amide and carboxyl hydrogen sites in a single crystal of the model peptide N-acetyl-D,L-valine (NAV). They use deuterium NMR to infer both the EFG and CS tensors at the amide and carboxyl hydrogen sites in NAV. Advantages of this technique over multiple-pulse proton NMR are that it works in the presence of {sup 14}N spins which are very hard to decouple from protons and that additional information in form of the EFG tensors can be derived. The change in the CS and EFG tensors upon exchange of a deuteron for amore » proton (the isotope effect) is anticipated to be very small; the effect on the CS tensors is certainly smaller than the experimental errors. NAV has served as a model peptide before in a variety of NMR studies, including those concerned with developing solid-state NMR spectroscopy as a method for determining the structure of proteins. NMR experiments on peptide or protein samples which are oriented in at least one dimension can provide important information about the three-dimensional structure of the peptide or the protein. In order to interpret the NMR data in terms of the structure of the polypeptide, the relationship of the CS and EFG tensors to the local symmetry elements of an amino acide, e.g., the peptide plane, is essential. The main purpose of this work is to investigate this relationship for the amide hydrogen CS tensor. The amide hydrogen CS tensor will also provide orientational information for peptide bonds in proteins complementary to that from the nitrogen CS and EFG tensors and the nitrogen-hydrogen heteronuclear dipole-dipole coupling which have been used previously to determine protein structures by solid-state NMR spectroscopy. This information will be particularly valuable because the amide hydrogen CS tensor is not axially symmetric. In addition, the use of the amide hydrogen CS interaction in high-field solid-state NMR experiments will increase the available resolution among peptide sites.« less

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Chemical shift and electric field gradient tensors for the amide and carboxyl hydrogens in the model peptide N-acetyl-D,L-valine. Single-crystal deuterium NMR study

The reversible electrochemical process (insertion/extraction) of lithium ions in graphitic carbon was monitored in situ for the first time by 7Li nuclear magnetic resonance (NMR) spectroscopy using a novel NMR apparatus. The compression coin cell battery imager is a simple device that combines the functions of an electrochemical cell and an NMR detector. A series of 7Li NMR spectra obtained for a blend of spherical and flaky disordered graphitic carbon particles revealed two distinct chemical shift signatures for the lithium ions that were inserted and extracted in the first electrochemical cycle. The lithium signal at ~50 ppm is consistent with the interplane sites for lithium ions on the sixfold axis between two stacked aromatic carbon rings aligned in registry. The second predominant lithium signal at ~12 ppm occurs in the chemical shift region reported for high-stage lithiated graphite and a dispersion of lithium-ion sites found in disordered carbon matrices. In addition, we observed chemical shift signatures similar to those assigned to Li-7 nuclei in lithium oxide, lithium carbonate, lithium alkyls, and lithium alkoxides that occur near 0 ppm and represent lithium nuclei that are irreversibly bound in the electrode/electrolyte interphase. An increase in intensity in the spectral region that is normally associated with irreversibly bound lithium was observed during the first discharge cycle, as anticipated. However, the same peaks in the spectrum unexpectedly diminished during the subsequent charge cycle, suggesting that the interphase between the carbon electrode and the electrolyte is built up over several cycles.

https://iopscience.iop.org/article/10.1088/0953-8984/13/36/304/pdf

In situ nuclear magnetic resonance investigations of lithium ions in carbon electrode materials using a novel detector

Using steady-shear rheometry in combination with high-pressure 11B nuclear magnetic resonance spectroscopy (11B NMR), we have found that gels formed from water-soluble polymers containing vicinal hydroxyl groups cross-linked with various boron-containing compounds undergo significant structural changes that result in a pronounced loss of viscosity when placed under pressure. Importantly, gels from other cross-linking agents tested, including Ti(IV) and Zr(IV), did not show this loss in viscosity. The experimental study probed pressure-induced changes to both galactomannan and polyvinyl alcohol (PVA) gels cross-linked with either aryl boronic acids or alkali metal boron-containing salts using pressure conditions that ranged from atmospheric to 680 bar and temperatures that ranged from 20 to 65 °C. Significantly, the pressure-induced losses in viscosity and, to a somewhat lesser extent, the concomitant pressure-induced 11B NMR spectral changes were found to be reversed upon lowering the pressure.

Rex E. Gerald

Papers

7Li NMR study of intercalated lithium in curved carbon lattices

Nuclear magnetic resonance studies of xenon clusters in zeolite NaA

Chemical shift and electric field gradient tensors for the amide and carboxyl hydrogens in the model peptide N-acetyl-D,L-valine. Single-crystal deuterium NMR study

In situ nuclear magnetic resonance investigations of lithium ions in carbon electrode materials using a novel detector

Influence of Pressure on Boron Cross-Linked Polymer Gels