Analog E1 transitions and isospin mixing

We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2--->5/2+ transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we obtain a lifetime for the relevant 7/2- state in 31S using the Doppler-shift attenuation method. We then collate the available information on matrix elements to examine the level of isospin mixing for both A=31 and A=35 mirror pairs

Emergence of Anti-Cancer Drug Resistance: Exploring the Importance of the Microenvironmental Niche via a Spatial Model

Practically, all chemotherapeutic agents lead to drug resistance. Clinically, it is a challenge to determine whether resistance arises prior to, or as a result of, cancer therapy. Further, a number of different intracellular and microenvironmental factors have been correlated with the emergence of drug resistance. With the goal of better understanding drug resistance and its connection with the tumor microenvironment, we have developed a hybrid discrete-continuous mathematical model. In this model, cancer cells described through a particle-spring approach respond to dynamically changing oxygen and DNA damaging drug concentrations described through partial differential equations. We thoroughly explored the behavior of our self-calibrated model under the following common conditions: a fixed layout of the vasculature, an identical initial configuration of cancer cells, the same mechanism of drug action, and one mechanism of cellular response to the drug. We considered one set of simulations in which drug resistance existed prior to the start of treatment, and another set in which drug resistance is acquired in response to treatment. This allows us to compare how both kinds of resistance influence the spatial and temporal dynamics of the developing tumor, and its clonal diversity. We show that both pre-existing and acquired resistance can give rise to three biologically distinct parameter regimes: successful tumor eradication, reduced effectiveness of drug during the course of treatment (resistance), and complete treatment failure

A novel system to map protein interactions reveals evolutionarily conserved immune evasion pathways on transmissible cancers

Around 40% of humans and Tasmanian devils (Sarcophilus harrisii) develop cancer in their lifetime, compared to less than 10% for most species. In addition, devils are affected by two of the three known transmissible cancers in mammals. Immune checkpoint immunotherapy has transformed human medicine, but a lack of species-specific reagents has limited checkpoint immunology in most species. We developed a cut-and-paste reagent development system and used the fluorescent fusion protein system to show that immune checkpoint interactions are conserved across 160,000,000 years of evolution, CD200 is highly expressed on transmissible tumor cells, and coexpression of CD200R1 can block CD200 surface expression. The system’s versatility across species was demonstrated by fusing a fluorescent reporter to a camelid-derived nanobody that binds human programmed death ligand 1. The evolutionarily conserved pathways suggest that naturally occurring cancers in devils and other species can be used to advance our understanding of cancer and immunological tolerance.</p

Mirror energy differences in the A=31 mirror nuclei, S31 and P31, and their significance in electromagnetic spin-orbit splitting

Excited states in S31 and P31 were populated in the C12(Ne20,n) and C12(Ne20,p) reactions, respectively, at a beam energy of 32 MeV. High spin states of positive and negative parity have been observed in S31 for the first time, and the yrast scheme of P31 has been extended. Large mirror energy differences between the first 9/2- and 13/2- states were observed, but only small differences for the first 7/2- and 11/2- levels. The significance of these observations is discussed in relation to the electromagnetic spin-orbit effect and the relative binding energy of the levels

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

Candidate superdeformed band in 28Si

Recent antisymmetrized molecular dynamics (AMD) calculations for 28Si suggest the presence of a superdeformed (SD) band with a dominant 24Mg+α clustering for its configuration, with firm predictions for its location and associated moment of inertia. This motivates a review of the experimental results reported in the literature with a particular focus on 24Mg(α,γ) studies, as well as on α-like heavy-ion transfer reactions such as 12C(20Ne,α)28Si. Combining this information for the first time leads to a set of candidate SD states whose properties point to their α-cluster structure and strong associated deformation. Analysis of data from Gammasphere allows the electromagnetic decay of these candidate states to be probed and reveals further supporting evidence for such a structure. This paper appraises this body of information and finds the evidence for an SD band is strong

Single-neutron states in Sn101

The first data on the relative single-particle energies outside the doubly magic Sn100 nucleus were obtained. A prompt 171.7(6)keV γ-ray transition was correlated with protons emitted following the β decay of Sn101 and is interpreted as the transition between the single-neutron g7/2 and d5/2 orbitals in Sn101. This observation provides a stringent test of current nuclear structure models. The measured νg7/2-νd5/2 energy splitting is compared with values calculated using mean-field nuclear potentials and is used to calculate low-energy excited states in light Sn isotopes in the framework of the shell model. The correlation technique used in this work offers possibilities for future, more extensive spectroscopy near Sn100

New results near 100Sn: Observation of single-neutron states in 101Sn

A search for in-beam γ-ray transitions in 101Sn, which contains only one neutron outside the 100Sn core, using a novel approach was carried out at the Argonne Tandem-Linac System. 101Sn nuclei were produced using the 46Ti(58Ni, 3n) 101Sn fusion-evaporation reaction. Beta-delayed protons with energies and decay times consistent with previous 101Sn decay studies were observed at the focal plane of the Fragment Mass Analyzer. In-beam γ rays were detected in the Gammasphere Ge-detector array and were correlated with the 101Sn β-delayed protons using the Recoil-Decay Tagging method. As a result, a γ-ray transition between the single-neutron vg7/2 and vd5/2 states situated at the Fermi surface was identified. The measured vg7/2-vd5/2 energy splitting was compared with predictions corresponding to various mean-field potentials and was used to calculate multi-neutron configurations in light Sn isotopes. Similar approach can be used to study core excitations in 101Sn and other exotic nuclei near 100Sn

Reevaluation of the P30(p,γ)S31 astrophysical reaction rate from a study of the T=1/2 mirror nuclei, S31 and P31

The P30(p,γ)S31 reaction rate is expected to be the principal determinant for the endpoint of nucleosynthesis in classical novae. To date, the reaction rate has only been estimated through Hauser-Feschbach calculations and is unmeasured experimentally. This paper aims to remedy this situation. Excited states in S31 and P31 were populated in the C12(Ne20,n) and C12(Ne20,p) reactions, respectively, at a beam energy of 32 MeV, and their resulting γdecay was detected with the Gammasphere array. Around half the relevant proton unbound states in S31 corresponding to the Gamow window for the P30(p,γ)S31 reaction were identified. The properties of the unobserved states were inferred from mirror symmetry using our extended data on P31. The implications of this new spectroscopic information for the P30(p,γ)S31 reaction rate are considered and recommendations for future work with radioactive beams are discussed