Publications

We present extensive photometric and spectroscopic observations of the peculiar Type Ia supernova (SN Ia) 2022vqz. It shares many similarities with the SN 2002es-like SNe Ia, such as low luminosity ($M_{B,\rm max}=-18.11\pm0.16$ mag) and moderate post-peak decline rate ($Δm_{15,B}=1.33\pm0.11$ mag). The nickel mass synthesised in the explosion is estimated as $0.20\pm0.04~{\rm M}_\odot$ from the bolometric light curve, which is obviously lower than that of normal SNe Ia. SN 2022vqz is also characterised by slowly expanding ejecta, with Si II velocities persisting around 7000 km s$^{-1}$ since 16 days before peak brightness, unique among all known SNe Ia. While all of these properties imply a lower-energy thermonuclear explosion that should leave a considerable amount of unburnt materials, the absent signature of unburnt carbon in spectra of SN 2022vqz is puzzling. A prominent early peak is clearly detected in the ATLAS $c$- and $o$-band light curves and in the ZTF $gr$-band data within days after the explosion. Possible mechanisms for the early peak are discussed, including the sub-Chandrasekhar-mass double-detonation model and interaction of SN ejecta with circumstellar material. We find that both models face some difficulties in replicating all aspects of the observed data. As an alternative, we propose a hybrid C-O-Ne white dwarf as the progenitor of SN 2022vqz; it can simultaneously reconcile the tension between low ejecta velocity and the absence of carbon. We further discuss the diversity of SN 2002es-like objects and their origin in the context of different scenarios.

We are pleased to see that simulation results by Mukherjee et al. (1) and Nathamgari et al. (2) are accordant with our experimental results (3). We also very much appreciate the detailed simulation study by Mukherjee et al. (1), specifically, on the prediction of the existence of an intermediate optimum voltage for transporting macromolecules. Although we agree with Nathamgari et al. (2) on the simplicity of the nanopore-electroporation system in allowing for an easy … [↵][1]1To whom correspondence may be addressed. Email: p_yang{at}berkeley.edu. [1]: #xref-corresp-1-1

Doppelagent: Die enantioselektive Tandem-Oxyfluorierung von Enamiden mit einem doppelt axial-chiralen Phosphorsäurekatalysator wird beschrieben. Die chirale Phosphorsäure katalysiert sowohl den Fluorierungsschritt (in einem Phasentransferprozess) als auch die Addition an das entstehende Imin (in einer Brønsted-Säure-Katalyse).

An electronic oscillator circuit is designed by connecting an inductor in series with a locally-active PTC Memristor and a battery. The PTC Memristor is locally active on the negative resistance region of its DC [Formula: see text]–[Formula: see text] curve. A DC operating point [Formula: see text] is chosen on the locally-active region of the PTC Memristor and a small-signal equivalent circuit at [Formula: see text] is derived via Taylor series. The small-signal admittance [Formula: see text] of the composite one-port in Fig. 1 is derived using the small-signal equivalent circuit at [Formula: see text], in series with an inductor whose value is chosen such that [Formula: see text] at some [Formula: see text]. The sinusoidal oscillation computed numerically from this circuit is shown to emerge from a supercritical Hopf bifurcation.

The imine linkages of two layered, porous covalent organic frameworks (COFs), TPB-TP-COF ([C₆H₃(C₆H₄N)₃]₂[C₆H₄(CH)₂]₃, 1) and 4PE-1P-COF ([C₂(C₆H₄N)₄][C₆H₄(CH)₂]₂, 2), have been transformed into amide linkages to make the respective isostructural amide COFs 1' and 2' by direct oxidation with retention of crystallinity and permanent porosity. Remarkably, the oxidation of both imine COFs is complete, as assessed by FT-IR and ¹³C CP-MAS NMR spectroscopy and demonstrates (a) the first chemical conversion of a COF linkage and (b) how the usual "crystallization problem" encountered in COF chemistry can be bypassed to access COFs, such as these amides, that are typically thought to be difficult to obtain by the usual de novo methods. The amide COFs show improved chemical stability relative to their imine progenitors.

The IUPAC-IUGS joint Task Group “Isotopes in Gesciences”, TGIG, has evaluated the published measurement results for the decay constant (i.e. half life) of 87Rb and updated those of 235U and 234U relative to that of 238U. A significant part of our evaluation was the effort to follow strict metrological criteria (VIM, 2012) in our assessment of the measurement uncertainties according to GUM (2008). The 87Rb half life was estimated by two groups using totally independent approaches. Nebel et al. (2011) compared Rb-Sr and U-Pb ages of different minerals, whose geological context suggests contemporaneity. This approach, which also applies to the comparison between 238U-206Pb and 235U-207Pb ages mentioned below, assumes that certain natural samples behave “ideally”, i.e. all the relevant ages are expected a priori to be equal. This assumption is only as good as the independent control on the samples’ petrology, and it is possible to underestimate systematic bias. Rotenberg et al. (2012) measured the radiogenic 87Sr accumulated in a batch of Sr-free Rb salt after 35 years. This approach relies on having performed precise and accurate measurements of the concentration and isotopic composition of the Sr present in the RbClO4 at the time of crystallisation. The two sets of experiments yield indistin¬guishable results, which is a good indication that systematic biases were either coincidentally of the same magnitude and direction in two radically different experimental designs, or negligible altogether. The resulting best estimates are λ87 = (1.395 ± 0.002) x 10-11 a-1 (1s uncertainty), t1/2 = 49.7 ± 0.1 Ga. The half life of 235U, which we had presented last year at the INCC congress (Villa et al., 2011, and references therein), has been slightly revised. It was brought to the attention of the Task Group that some workers reported a mass-independent fractionation of incompletely understood origin that affects odd- and even-mass isotopes in a different way (e.g. Amelin et al., 2005). Moreover, recent reports on N(238U)/N(235U) number ratio measurements in the same zircon samples used for geochronology (Hiess et al., 2012) indicate an individually variable number ratio, on average lower by (0.031 ± 0.011) % relative to the previously assumed value of 137.88. Including both effects into the 235U half life re-evaluation gives t1/2 = 703.41 ± 0.19) Ma (1s uncertainty), λ235 = 0.98540 ± 0.00027 Ga-1. These two effects do not modify the 234U half life relative to our 2011 assessment: t1/2 = 245.44 ± 0.16 ka (1s uncertainty), corresponding to λ234 = 2.8241 ± 0.0018 Ma-1. Amelin Y., Davis D.W., Davis W.J. (2005) Decoupled fractionation of even- and odd-mass isotopes of Pb in TIMS. Geochim. Cosmochim. Acta 69, Abstract Supplement, A215. GUM (2008) Guide to the expression of uncertainty in measurement. www.bipm.org/en/publications/guides/gum.html Hiess J., Condon D.J., McLean N., Noble S.R. (2012) 238U/235U systematics in terrestrial U-bearing minerals. Science 335, 1610-1614. Nebel O., Scherer E.E., Mezger K. (2011) Evaluation of the 87Rb decay constant by age comparison against the U-Pb system. Earth Planet. Sci. Lett. 301, 1-8. Rotenberg E., Davis D.W., Amelin Y., Ghosh S., Bergquist B.A. (2012) Determination of the decay-constant of 87Rb by laboratory accumulation of 87Sr. Geochim. Cosmochim. Acta, 85, 41-57. Villa I.M., Bonardi M.L., De Bièvre P., Holden N.E., Renne P.R., 2011. Half-lives of nuclides for geological use: 2011 evaluations for 235U and 234U. Abstract, 3rd International Nuclear Chemistry Congress, Palermo. VIM (2012) The International Vocabulary of metrology – Basic and general concepts and associated terms, 3rd edition, JCGM 200:2012, http://www.bipm.org/vim