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NMR relaxation studies and spectroscopic measurements of zeolitic imidazolate framework-8 (ZIF-8) are reported. The dominant nuclear spin–lattice relaxation (T1) mechanism for ZIF-8 in air arises from atmospheric paramagnetic molecular oxygen. The 13C T1 measurements indicate that the oxygen interacts primarily with the imidazolate ring rather than the methyl substituent. Similar relaxation behavior was also observed in a ZIF with an unsubstituted ring, ZIF-4. Single-crystal X-ray diffraction was used to provide data for the study of the thermal ellipsoids of ZIF-8 at variable temperatures from 100 to 298 K, which further confirmed the rigid nature of this ZIF framework. These results highlight a rigid ZIF framework and are in contrast with dynamic metal–organic frameworks based on benzenedicarboxylate linking groups, for which the relaxation reflects the dynamics of the benzenedicarboxylate moiety.

Aims. The association of Type Ic supernovae (SNe) with long-duration gamma-ray bursts (GRBs) is well established. We endeavor, through\naccurate ground-based observational campaigns, to characterize these SNe at increasingly high redshifts.\nMethods. We obtained a series of optical photometric and spectroscopic observations of the Type Ic SN 2012bz associated with the Swift long-\nduration GRB 120422A (redshift z = 0.283) using the 3.6-m TNG and the 8.2-m VLT telescopes during the time interval between 4 and 36 days\nafter the burst.\nResults. The peak times of the light curves of SN 2012bz in various optical filters differ, with the B-band and i'-band light curves reaching\nmaximum at 9 ± 4 and 23 ± 3 rest-frame days, respectively. The bolometric light curve has been derived from individual bands photometric\nmeasurements, but no correction for the unknown contribution in the near-infrared (probably around 10­-15%) has been applied. Therefore, the\npresent light curve should be considered as a lower limit to the actual UV-optical-IR bolometric light curve. This pseudo-bolometric curve reaches\nits maximum (Mbol = -18.56 ± 0.06) at 13 ± 1 rest-frame days; it is similar in shape and luminosity to the bolometric light curves of the SNe\nassociated with z < 0.2 GRBs and more luminous than those of SNe associated with X-ray flashes (XRFs). A comparison with the model generated\nfor the bolometric light curve of SN 2003dh suggests that SN 2012bz produced only about 15% less 56 Ni than SN 2003dh, about 0.35 M . Similarly\nthe VLT spectra of SN 2012bz, after correction for Galactic extinction and for the contribution of the host galaxy, suggest comparable explosion\nparameters with those observed in SN 2003dh (EK 3.5 × 1052 erg, Mej 7 M ) and a similar progenitor mass (25­40 M ). GRB 120422A is\nconsistent with the Epeak - Eiso and the EX,iso - E,iso - Epeak relations. GRB 120422A / SN 2012bz shows the GRB-SN connection at the highest\nredshift so far accurately monitored both photometrically and spectroscopically.

MOFs with Guest Rooms Metal organic framework (MOF) solids typically boast large pores in their crystal lattices that can accommodate molecular guests and are useful as compact media for gas storage. However, guest binding has generally relied upon nonspecific interactions with the framework components. Li et al. (p. 855 ) have now prepared MOFs that incorporate macrocyclic ethers into the structural ligands comprising the framework walls within which certain cationic guests can bind quantitatively and site-specifically, akin to the molecular docking of drug molecules within protein receptors.

We introduce a novel sequential modeling approach which enables learning a Large Vision Model (LVM) without making use of any linguistic data. To do this, we define a common format, "visual sentences", in which we can represent raw images and videos as well as annotated data sources such as semantic segmentations and depth reconstructions without needing any meta-knowledge beyond the pixels. Once this wide variety of visual data (comprising 420 billion tokens) is represented as sequences, the model can be trained to minimize a cross-entropy loss for next token prediction. By training across various scales of model architecture and data diversity, we provide empirical evidence that our models scale effectively. Many different vision tasks can be solved by designing suitable visual prompts at test time.

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International audience

We present mid-infrared (5.2-15.2 μm) spectra of the Type Ia supernovae (SNe Ia) 2003hv and 2005df observed with the Spitzer Space Telescope. These are the first observed mid-infrared spectra of thermonuclear supernovae, and show strong emission from fine-structure lines of Ni, Co, S, and Ar. The detection of Ni emission in SN 2005df 135 days after the explosion provides direct observational evidence of high-density nuclear burning forming a significant amount of stable Ni in a SN Ia. The SN 2005df Ar lines also exhibit a two-pronged emission profile, implying that the Ar emission deviates significantly from spherical symmetry. The spectrum of SN 2003hv also shows signs of asymmetry, exhibiting blueshifted [Co III], which matches the blueshift of [Fe II ] lines in nearly coeval near-infrared spectra. Finally, local thermodynamic equilibrium abundance estimates for the yield of radioactive ^(56)Ni give M^(56)Ni ≈ 0.5 M⊙, for SN 2003hv, but only M^(56)Ni ≈ 0.13-0.22 M⊙ for the apparently subluminous SN 2005df, supporting the notion that the luminosity of SNe Ia is primarily a function of the radioactive ^(56)Ni yield. The observed emission-line profiles in the SN 2005df spectrum indicate a chemically stratified ejecta structure, which matches the predictions of delayed detonation (DD) models, but is entirely incompatible with current three-dimensional deflagration models. Furthermore, the degree that this layering persists to the innermost regions of the supernova is difficult to explain even in a DD scenario, where the innermost ejecta are still the product of deflagration burning. Thus, while these results are roughly consistent with a delayed detonation, it is clear that a key piece of physics is still missing from our understanding of the earliest phases of SN Ia explosions.

The authors develop a plane-wave-based transfer matrix method in curvilinear coordinates to study the guided modes in curved nanoribbon waveguides. The problem of a curved structure is transformed into an equivalent one of a straight structure with spatially dependent tensors of dielectric constant and magnetic permeability. The authors investigate the coupling between the eigenmodes of the straight part and those of the curved part when the waveguide is bent. The authors show that curved sections can result in strong oscillations in the transmission spectrum similar to the recent experimental results of Lawet al. [Science 305, 1269 (2004)].