The Curfew Bell

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Is the structure of 42Si understood?

A more detailed test of the implementation of nuclear forces that drive shell evolution in the pivotal nucleus \nuc{42}{Si} -- going beyond earlier comparisons of excited-state energies -- is important. The two leading shell-model effective interactions, SDPF-MU and SDPF-U-Si, both of which reproduce the low-lying \nuc{42}{Si}($2^+_1$) energy, but whose predictions for other observables differ significantly, are interrogated by the population of states in neutron-rich \nuc{42}{Si} with a one-proton removal reaction from \nuc{43}{P} projectiles at 81~MeV/nucleon. The measured cross sections to the individual \nuc{42}{Si} final states are compared to calculations that combine eikonal reaction dynamics with these shell-model nuclear structure overlaps. The differences in the two shell-model descriptions are examined and linked to predicted low-lying excited $0^+$ states and shape coexistence. Based on the present data, which are in better agreement with the SDPF-MU calculations, the state observed at 2150(13)~keV in \nuc{42}{Si} is proposed to be the ($0^+_2$) level.Comment: accepted in Physical Review Letter

Muscle Dysmorphia and the Effects of Emotion Regulation and Fitness Media

Research on Muscle Dysmorphia (MD) has identified various cognitive and behavioral variables related to other psychopathology (i.e., eating disorders, additive disorders) associated with increased levels of impulsivity, compulsivity, and difficulty regulating emotions. PURPOSE: The aim of the current study was to investigate the degree to which emotional dysregulation (EDys), through the mediating effects of compulsivity and impulsivity, influence one’s risk towards MD symptomatology. Due to recent findings relating social media and negative regulatory associations, exploratory analyses assessed the effect of ‘fitspiration’ content on the model. METHODS: Using MTurk with a Qualtrics survey, 129 adults (aged 23-69 years) completed a background questionnaire, the Muscle Dysmorphic Disorder Inventory, Difficulties in Emotion Regulation Scale, UPPS-P Impulsive Behavior Scale – Short English Version, and the Yale-Brown Obsessive-Compulsive Scale – Modified for Body Dysmorphic Disorder. For mediation analyses, PROCESS Model 4 was used in SPSS, and Model 59 was used to assess if ‘fitspiration’ exposure moderated any of the paths. RESULTS: Higher EDys was related to higher impulsivity (a1 = 0.21; 95% CI [0.15, 0.28]) and compulsivity (a2 = 0.39; 95% CI [0.31, 0.48]). Higher compulsivity was associated with increased MDDI scores (b2 = 0.32; 95% CI [0.12, 0.53]), while impulsivity was not (b1 = 0.01; 95% CI [-0.29, 0.29]). A direct effect was found for both models (c1’ = 0.68; 95% CI [-0.56, 0.81]; c2’ = 0.55; 95% CI [0.42, 0.69]); only compulsivity mediated this effect (a2 x b2 = 0.13; 95% CI [0.04, 0.23]). ‘Fitspiration’ exposure did not moderate this model (aint = -0.08; 95% CI [-0.22, 0.06]; bint = 0.50; 95% CI [-0.22, 1.23]; cint = -0.23; 95% CI [-0.64, 0.19]). CONCLUSION: Compulsivity significantly mediated the relationship between EDys and MD symptomatology, implying higher scores of EDys were associated with greater compulsivity, and increased compulsive scores were associated with more MD-related cognitions and behaviors. While related to EDys, impulsivity was not associated with dysmorphic symptoms. Exploratory analyses found ‘Fitspiration’ content exposure did not significantly moderate the model utilizing compulsivity as a mediating variable

Infrared multiphoton dissociation of two perfluorobutenes

Photofragment translational spectroscopy was used to examine the infrared multiphotondissociation of octafluoro-1-butene and octafluoro-2-butene. The predominant unimolecular reaction in octafluoro-1-butene at moderate laser fluences is cleavage of a carbon–carbon single bond to give the products CF3 and C3F5. The two other reactions that take place are CF2 elimination and the formation of equal weight fragments with the chemical compositionC2F4; both reactions take place via a diradical intermediate. Dissociation of octafluoro-1-butene to the resonance stabilized perfluoroallyl radical is suggested to account for the favoring of simple bond rupture. These three reaction pathways were also observed in octafluoro-2-butene dissociation, however, the branching fraction is different than from octafluoro-1-butene. In octafluoro-2-butene all three channels occur with roughly equal probability. The reactions involving CF2 loss and C2F4 formation in octafluoro-2-butene are thought to proceed through the same diradical intermediate as in octafluoro-1-butene, necessitating a 1,2-fluorine migration

In-beam γ\gamma-ray spectroscopy at the proton dripline: 40^{40}Sc

We report on the first in-beam $\gamma$-ray spectroscopy of the proton-dripline nucleus $^{40}$Sc using two-nucleon pickup onto an intermediate-energy rare-isotope beam of $^{38}$Ca. The $^{9}$Be($^{38}$Ca,$^{40}$Sc$+\gamma$)X reaction at 60.9 MeV/nucleon mid-target energy selectively populates states in $^{40}$Sc for which the transferred proton and neutron couple to high orbital angular momentum. In turn, due to angular-momentum selection rules in proton emission and the nuclear structure and energetics of $^{39}$Ca, such states in $^{40}$Sc then exhibit $\gamma$-decay branches although they are well above the proton separation energy. This work uniquely complements results from particle spectroscopy following charge-exchange reactions on $^{40}$Ca as well as $^{40}$Ti EC/$\beta^+$ decay which both display very different selectivities. The population and $\gamma$-ray decay of the previously known first $(5^-)$ state at 892 keV and the observation of a new level at 2744 keV are discussed in comparison to the mirror nucleus and shell-model calculations. On the experimental side, this work shows that high-resolution in-beam $\gamma$-ray spectroscopy is possible with new generation Ge arrays for reactions induced by rare-isotope beams on the level of a few $\mu$b of cross section.Comment: Accepted for publication in Phys. Lett.

Two-neutron knockout as a probe of the composition of states in 22^{22}Mg, 23^{23}Al, and 24^{24}Si

Simpson and Tostevin proposed that the width and shape of exclusive parallel momentum distributions of the A-2 residue in direct two-nucleon knockout reactions carry a measurable sensitivity to the nucleon single-particle configurations and their couplings within the wave functions of exotic nuclei. We report here on the first benchmarks and use of this new spectroscopic tool. Exclusive parallel momentum distributions for states in the neutron-deficient nuclei $^{22}$Mg, $^{23}$Al, and $^{24}$Si populated in such direct two-neutron removal reactions were extracted and compared to predictions combining eikonal reaction theory and shell-model calculations. For the well-known $^{22}$Mg and $^{23}$Al nuclei, measurements and calculations were found to agree, supporting the dependence of the parallel momentum distribution width on the angular momentum composition of the shell-model two-neutron amplitudes. In $^{24}$Si, a level at 3439(9) keV, of relevance for the important $^{23}$Al(p,$\gamma$)$^{24}$Si astrophysical reaction rate, was confirmed to be the $2^+_2$ state, while the $4^+_1$ state, expected to be strongly populated in two-neutron knockout, was not observed. This puzzle is resolved by theoretical considerations of the Thomas-Ehrman shift, which also suggest that a previously reported 3471-keV state in $^{24}$Si is in fact the ($0^+_2$) level with one of the largest experimental mirror-energy shifts ever observed.Comment: Accepted for publication in Phys. Rev. C as a Rapid Communicatio

Experimental identification of the T=1T = 1, Jπ=6+J^{\pi} = 6^+ state of 54^{54}Co and isospin symmetry in A=54A = 54 studied via one-nucleon knockout reactions

New experimental data obtained from $\gamma$-ray tagged one-neutron and one-proton knockout from $^{55}$Co is presented. A candidate for the sought-after $T=1, T_z = 0, J^{\pi} = 6^+$ state in $^{54}$Co is proposed based on a comparison to the new data on $^{54}$Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full $fp$-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the $A=54$, $T=1$ triplet is studied by calculating the experimental $c$ coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin $J=6$ expected for the $(1f_{7/2})^{-2}$ two-hole configuration relative to the doubly-magic nucleus $^{56}$Ni. The experimental quantities are compared to the theoretically predicted $c$ coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to-leading order (N$^3$LO).Comment: 6 pages, 5 figures. Work has been publishe