Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework

Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the strongest isotropic negative thermal expansion (NTE) effect yet reported for a metal-organic framework (MOF). Incorporation of correlated vacancy defects within the framework affects both the extent of thermal densification and the magnitude of NTE observed in the densified product. We thus demonstrate that defect inclusion can be used to tune systematically the physical behaviour of a MOF.Comment: 8 pages, 4 figures, revise

Rotation-Induced Breakdown of Torsional Quantum Control

Control of the torsional angles of nonrigid molecules is key for the development of emerging areas like molecular electronics and nanotechnology. Based on a rigorous calculation of the rotation-torsion-Stark energy levels of nonrigid biphenyl-like molecules, we show that, unlike previously believed, instantaneous rotation-torsion-Stark eigenstates of such molecules, interacting with a strong laser field, present a large degree of delocalization in the torsional coordinate even for the lowest energy states. This is due to a strong coupling between overall rotation and torsion leading to a breakdown of the torsional alignment. Thus, adiabatic control of changes on the planarity of this kind of molecule is essentially impossible unless the temperature is on the order of a few Kelvin

Bio-logging science: sensing beyond the boundaries

Bio-logging has emerged as a tool in animal biology much as genomics has emerged as a tool in the study of cellular and organ function. Bio-logging is certain to increase in its importance and to influence the way we study events and processes that are beyond the usual boundaries of perception and that are remote from the observer. It is providing insights into the behaviour and function of organisms in environments that are hostile to the observer and in natural situations. In terms of the way that data are collected it has much in common with remote sensing and Earth observation. This includes post hoc analysis and interpretation of extensive data sets involving a low diversity of measured variables. Owing to the sparseness of data sets, practitioners need to develop better methods of applying the data to models of the organisms being studied. Although increasing technological sophistication is leading to collection of a greater diversity of variables, this also brings complications of interpreting multi-dimension data sets. Although it appears that technology currently constrains the type of biological questions that can be addressed, there is a danger that technological advancement could result in a loss of focus on hypothesis testing. There is evidence that the discipline of bio-logging is developing a substructure within which specialist teams of modellers, theoretical and field biologists, and engineers collaborate to address complex biological questions

Defects and disorder in metal organic frameworks.

The wide-ranging properties of metal organic frameworks (MOFs) rely in many cases on the presence of defects within their structures and the disorder that is inevitably associated with such defects. In the present work we review several aspects of defects in MOFs, ranging from simple substitutional defects at metal cation or ligand positions, to correlated defects on a larger length scale and the extreme case of disorder associated with amorphous MOFs. We consider both porous and dense MOFs, and focus particularly on the way in which defects and disorder can be used to tune physical properties such as gas adsorption, catalysis, photoluminescence, and electronic and mechanical properties.The authors would like to thank Ras Al Khaimah Center for Advanced Materials (AKC, TDB), Trinity Hall (TDB), and the ERC (ALG, Grant 279705).This is the author accepted manuscript. The final version is available from RSC via http://dx.doi.org/10.1039/C5DT04392

Two-photon double ionization of neon using an intense attosecond pulse train

We present the first demonstration of two-photon double ionization of neon using an intense extreme ultraviolet (XUV) attosecond pulse train (APT) in a photon energy regime where both direct and sequential mechanisms are allowed. For an APT generated through high-order harmonic generation (HHG) in argon we achieve a total pulse energy close to 1 $\mu$J, a central energy of 35 eV and a total bandwidth of $\sim30$ eV. The APT is focused by broadband optics in a neon gas target to an intensity of $3\cdot10^{12}$W$\cdot$cm$^{-2}$. By tuning the photon energy across the threshold for the sequential process the double ionization signal can be turned on and off, indicating that the two-photon double ionization predominantly occurs through a sequential process. The demonstrated performance opens up possibilities for future XUV-XUV pump-probe experiments with attosecond temporal resolution in a photon energy range where it is possible to unravel the dynamics behind direct vs. sequential double ionization and the associated electron correlation effects

Notions of Connectivity in Overlay Networks

International audience" How well connected is the network? " This is one of the most fundamental questions one would ask when facing the challenge of designing a communication network. Three major notions of connectivity have been considered in the literature, but in the context of traditional (single-layer) networks, they turn out to be equivalent. This paper introduces a model for studying the three notions of connectivity in multi-layer networks. Using this model, it is easy to demonstrate that in multi-layer networks the three notions may differ dramatically. Unfortunately, in contrast to the single-layer case, where the values of the three connectivity notions can be computed efficiently, it has been recently shown in the context of WDM networks (results that can be easily translated to our model) that the values of two of these notions of connectivity are hard to compute or even approximate in multi-layer networks. The current paper shed some positive light into the multi-layer connectivity topic: we show that the value of the third connectivity notion can be computed in polynomial time and develop an approximation for the construction of well connected overlay networks

Spectroscopic parameters for silacyclopropynylidene, SiC2_2, from extensive astronomical observations toward CW Leo (IRC +10216) with the Herschel satellite

A molecular line survey has been carried out toward the carbon-rich asymptotic giant branch star CW Leo employing the HIFI instrument on board of the Herschel satellite. Numerous features from 480 GHz to beyond 1100 GHz could be assigned unambiguously to the fairly floppy SiC$_2$ molecule. However, predictions from laboratory data exhibited large deviations from the observed frequencies even after some lower frequency data from this survey were incorporated into a fit. Therefore, we present a combined fit of all available laboratory data together with data from radio-astronomical observations.Comment: 7 pages, 1 figure, J. Mol. Spectrosc., appeared; CDMS links corrected (version 2; current version: 3; may be updated later this year

THE THRESHOLD PHOTOELECTRON SPECTRUM OF SiH₂ AS MODELED WITH MCTDH

Although the ground X̃¹A₁ electronic state of silylene SiH₂ is fairly well characterized, fewer results are available about its first excited triplet a˜³B₁ electronic state and about its cationic species SiH−2⁺. The ground electronic state of the latter is split into bent X̃+²A₁ and linear Ã⁺²B₁ doublet electronic states by the Renner-Teller coupling. Threshold photoelectron (TPE) spectroscopy has been used to obtain spectroscopic information about the cationic species SiH⁺ of silylene and about the first excited triplet electronic state of neutral SiH₂. The TPE spectrum, recorded at Synchrotron SOLEIL from 7.5 to 11.5 eV using VUV synchrotron radiation, displays several sharp features and was modeled using wavepacket propagation. ωB97XD ab initio calculations were carried out using cc-PVTZ correlation-consistent basis set functions to retrieve 3-D potential energy surfaces for the four electronic states involved in the TPE spectrum. The MCTDH method was first used to obtain the 3-D vibrational wavefunctions of the neutral species X̃¹A₁ and a˜³B₁ electronic states using propagation in negative imaginary time. The wavefunctions thus obtained were then time- propagated in the potential energy surfaces of the coupled electronic states of the cationic species using also MCTDH. The photoionisation cross-section was at last computed as the Fourier transform of the auto-correlation function. In the talk, the results of the rovibronic energies calculation will be reported and the experimental TPE spectrum will be compared to the theoretical one. The importance of the Renner-Teller coupling will be assessed and the vibrational reproduces the experimental spectrum will be evaluated

Line Position And Line Intensity Analyses Of H218o Up To The First Triad And J=20a

We present a line position analysis of a large body of data pertaining to H$_2^{18}$O and involving all 5 vibrational states up to the First Triad, namely, the lowest lying states (000), (010), (020), (100), and (001).\footnotetext[1]{Financial support from the French Programme National de Physique et Chimie du Milieu Interstellaire is acknowledged} The data set contains infrared lines retrieved in this work, from FTS and from high-temperature emission spectra, and already published high-resolution measurements including microwave and THz transitions, and kHz accuracy transitions.$^b$\footnotetext[2]{Kyr\"o, {\em J.\ Mol.\ Spec.}~{\bf 88} (1981) 167; Matsushima {\em et al.,} {\em J.\ Mol.\ Spec.}~{\bf 193} (1999) 217; and Diouf {\em et al.,} {\em J.\ Phys.\ Chem.\ Ref.\ Data}~{\bf 50} (2021) 023106} The analysis, carried out with the Bending-Rotation fitting Hamiltonian,$^c$\footnotetext[3]{Coudert and Ch\'elin, {\em J.\ Mol.\ Spec.}~{\bf 326} (2015) 130} allows us to reproduce more than 11700 data with a unitless standard deviation of 1.6 up to $J=20$ and $K_a=16$. The highly accurate THz transitions$^b$ are reproduced with an RMS of 0.2~MHz and the kHz accuracy transitions$^b$ with an RMS better than 0.3~MHz. A line intensity analysis of absorption transitions involving the same vibrational states will also be presented. FIR line intensities measured in this work using FTS were fitted in addition to previously measured line intensities. 3890 line intensities are accounted for with a unitless standard deviation of 1.4. The absorption line list calculated using these results will be compared to that recently obtained from theoretical calculations.$^d$\footnotetext[4]{Conway {\em et al.,} {\em J.\ Quant.\ Spec.\ Rad.\ Trans.}~{\bf 241} (2020) 106711} With the present set of spectroscopic parameters, discrepancies up to 0.09~cm$^{-1}$ are noted for the line positions