Non-Gaussianity after many-field reheating

International audienceWe numerically investigate reheating after quadratic inflation with up to 65 fields, focusing on the production of non-Gaussianity. We consider several sets of initial conditions, masses, and decay rates. As expected, we find that the reheating phase can have a significant effect on the non-Gaussian signal, but that for this number of fields a detectable level of non-Gaussianity requires the initial conditions, mass range, and decay rates to be ordered in a particular way. We speculate on whether this might change in the N-flation limit

An alternate proton acceptor for excited-state proton transfer in green fluorescent protein: Rewiring GFP

The neutral form of the chromophore in wild-type green fluorescent protein (wtGFP) undergoes excited-state proton transfer (ESPT) upon excitation, resulting in characteristic green (508 nm) fluorescence. This ESPT reaction involves a proton relay from the phenol hydroxyl of the chromophore to the ionized side chain of E222, and results in formation of the anionic chromophore in a protein environment optimized for the neutral species (the I* state). Reorientation or replacement of E222, as occurs in the S65T and E222Q GFP mutants, disables the ESPT reaction and results in loss of green emission following excitation of the neutral chromophore. Previously, it has been shown that the introduction of a second mutation (H148D) into S65T GFP allows the recovery of green emission, implying that ESPT is again possible. A similar recovery of green fluorescence is also observed for the E222Q/H148D mutant, suggesting that D148 is the proton acceptor for the ESPT reaction in both double mutants. The mechanism of fluorescence emission following excitation of the neutral chromophore in S65T/H148D and E222Q/H148D has been explored through the use of steady state and ultrafast time-resolved fluorescence and vibrational spectroscopy. The data are contrasted with those of the single mutant S65T GFP. Time-resolved fluorescence studies indicate very rapid (<1 ps) formation of I* in the double mutants, followed by vibrational cooling on the picosecond time scale. The time-resolved IR difference spectra are markedly different to those of wtGFP or its anionic mutants. In particular, no spectral signatures are apparent in the picosecond IR difference spectra that would correspond to alteration in the ionization state of D148, leading to the proposal that a low-barrier hydrogen bond (LBHB) is present between the phenol hydroxyl of the chromophore and the side chain of D148, with different potential energy surfaces for the ground and excited states. This model is consistent with recent high-resolution structural data in which the distance between the donor and acceptor oxygen atoms is =2.4 Å. Importantly, these studies indicate that the hydrogen-bond network in wtGFP can be replaced by a single residue, an observation which, when fully explored, will add to our understanding of the various requirements for proton-transfer reactions within proteins

Viewpoint consistency in Z and LOTOS: A case study

Specification by viewpoints is advocated as a suitable method of specifying complex systems. Each viewpoint describes the envisaged system from a particular perspective, using concepts and specification languages best suited for that perspective. Inherent in any viewpoint approach is the need to check or manage the consistency of viewpoints and to show that the different viewpoints do not impose contradictory requirements. In previous work we have described a range of techniques for consistency checking, refinement, and translation between viewpoint specifications, in particular for the languages LOTOS and Z. These two languages are advocated in a particular viewpoint model, viz. that of the Open Distributed Processing (ODP) reference model. In this paper we present a case study which demonstrates how all these techniques can be combined in order to show consistency between a viewpoint specified in LOTOS and one specified in Z. Keywords: Viewpoints; Consistency; Z; LOTOS; ODP

Attractor behaviour in multifield inflation

We study multifield inflation in scenarios where the fields are coupled non-minimally to gravity via $\xi_I(\phi^I)^n g^{\mu\nu}R_{\mu\nu}$, where $\xi_I$ are coupling constants, $\phi^I$ the fields driving inflation, $g_{\mu\nu}$ the space-time metric, $R_{\mu\nu}$ the Ricci tensor, and $n>0$. We consider the so-called $\alpha$-attractor models in two formulations of gravity: in the usual metric case where $R_{\mu\nu}=R_{\mu\nu}(g_{\mu\nu})$, and in the Palatini formulation where $R_{\mu\nu}$ is an independent variable. As the main result, we show that, regardless of the underlying theory of gravity, the field-space curvature in the Einstein frame has no influence on the inflationary dynamics at the limit of large $\xi_I$, and one effectively retains the single-field case. However, the gravity formulation does play an important role: in the metric case the result means that multifield models approach the single-field $\alpha$-attractor limit, whereas in the Palatini case the attractor behaviour is lost also in the case of multifield inflation. We discuss what this means for distinguishing between different models of inflation.Comment: 20 pages, 6 figures. Typos corrected and references added. This is an author-created, un-copyedited version of an article published in JCAP. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://iopscience.iop.org/article/10.1088/1475-7516/2018/06/032/pd

Examining the dynamics of decision making when designing curriculum in partnership with students: How should we proceed?

[This paper is part of the Focused Collection on Curriculum Development: Theory into Design.] Common models of curricular development in physics education research (PER) have typically involved a hierarchical relationship between researchers and students, where researchers lead the design and testing of curriculum for students. We draw from work in students as partners and related fields in order to codesign curriculum in partnership with students. Such work has the potential to disrupt typical hierarchical relationships and interactions between students and faculty by involving students in the process of making curricular decisions. We invited undergraduate students to participate in a partnership to codesign a set of curricular materials for topics in quantum mechanics that students often struggle with. Four undergraduate students, one PER graduate student, and one PER faculty member met for a series of codesign meetings. We collected videotapes of the meetings, written artifacts, and meeting reflections. This paper presents a fine-grained analysis of one interaction in which researchers attempted to create space for students to contribute to decision making about how the collaboration should proceed. Through analyzing the complex dynamics of how participants negotiated decision-making space, including characterizing the types of decisions that were made, we describe how access to those decisions were opened up or cut off, and how those decisions contested or reaffirmed participants\u27 roles. Working towards partnership is a complex and messy process: attempts to open up space for some forms of decision making closed off access to other forms of decision making. In some ways, the interactions between the participants also reified the traditional student and faculty roles that the partnership had intended to disrupt. Through closely analyzing these dynamics, we aim to self-critically reflect on the challenges and tensions that emerge in codesign partnerships. We discuss our own areas for growth and speak to implications for more responsible partnerships

Relaxation Dynamics of Pseudomonas aeruginosa Re^I(C)O_3(α-diimine)(HisX)^+ (X=83, 107, 109, 124, 126)Cu-^(II) Azurins

Photoinduced relaxation processes of five structurally characterized Pseudomonas aeruginosa Re^I(CO)_3(α-diimine)(HisX) (X = 83, 107, 109, 124, 126)Cu^(II) azurins have been investigated by time-resolved (ps−ns) IR spectroscopy and emission spectroscopy. Crystal structures reveal the presence of Re-azurin dimers and trimers that in two cases (X = 107, 124) involve van der Waals interactions between interdigitated diimine aromatic rings. Time-dependent emission anisotropy measurements confirm that the proteins aggregate in mM solutions (D2O, KPi buffer, pD = 7.1). Excited-state DFT calculations show that extensive charge redistribution in the ReI(CO)_3 → diimine ^3MLCT state occurs: excitation of this ^3MLCT state triggers several relaxation processes in Re-azurins whose kinetics strongly depend on the location of the metallolabel on the protein surface. Relaxation is manifested by dynamic blue shifts of excited-state ν(CO) IR bands that occur with triexponential kinetics: intramolecular vibrational redistribution together with vibrational and solvent relaxation give rise to subps, 2, and 8−20 ps components, while the ~10^2 ps kinetics are attributed to displacement (reorientation) of the Re^I(CO)_3(phen)(im) unit relative to the peptide chain, which optimizes Coulombic interactions of the Re^I excited-state electron density with solvated peptide groups. Evidence also suggests that additional segmental movements of Re-bearing β-strands occur without perturbing the reaction field or interactions with the peptide. Our work demonstrates that time-resolved IR spectroscopy and emission anisotropy of Re^I carbonyl−diimine complexes are powerful probes of molecular dynamics at or around the surfaces of proteins and protein−protein interfacial regions

Ground vs. excited state interaction in ruthenium-thienyl dyads:implications for through bond interactions in multicomponent systems

The vibrational and photophysical properties of mononuclear ruthenium(II) and ruthenium(III) polypyridyl complexes based on the ligands 2-(5'-(pyridin-2"-yl)-1'H-1',2',4'-triaz-3'-yl)-thiophene, 2-(5'-(pyrazin-2"-yl)-1'H-1',2',4'-triaz-3'-yl)-thiophene, are reported. The effect of the introduction of the non-innocent thiophene group on the properties of the triazole based ruthenium(II) complex is examined. The pH sensitive 1,2,4-triazole group, although influenced by the electron withdrawing nature of the thiophene group, does not facilitate excited state interaction of the thiophene and Ru(II) centre. Deuteriation and DFT calculations are employed to enable a deeper understanding of the interaction between the two redox-active centres and rationalise the difference between the extent of ground and excited state interaction in this simple dyad. The results obtained provide considerable evidence in support of earlier studies examining differences in ground and excited state interaction in multinuclear thiophene-bridged systems, in particular with respect to HOMO- and LUMO- mediated superexchange interaction processes.

Snowpack Relative Permittivity and Density Derived from Near-Coincident Lidar and Ground-Penetrating Radar

Depth-based and radar-based remote sensing methods (e.g., lidar, synthetic aperture radar) are promising approaches for remotely measuring snow water equivalent (SWE) at high spatial resolution. These approaches require snow density estimates, obtained from in-situ measurements or density models, to calculate SWE. However, in-situ measurements are operationally limited, and few density models have seen extensive evaluation. Here, we combine near-coincident, lidar-measured snow depths with ground-penetrating radar (GPR) two-way travel times (twt) of snowpack thickness to derive \u3e20 km of relative permittivity estimates from nine dry and two wet snow surveys at Grand Mesa, Cameron Pass, and Ranch Creek, Colorado. We tested three equations for converting dry snow relative permittivity to snow density and found the Kovacs et al. (1995) equation to yield the best comparison with in-situ measurements (RMSE = 54 kg m−3). Variogram analyses revealed a 19 m median correlation length for relative permittivity and snow density in dry snow, which increased to \u3e 30 m in wet conditions. We compared derived densities with estimated densities from several empirical models, the Snow Data Assimilation System (SNODAS), and the physically based iSnobal model. Estimated and derived densities were combined with snow depths and twt to evaluate density model performance within SWE remote sensing methods. The Jonas et al. (2009) empirical model yielded the most accurate SWE from lidar snow depths (RMSE = 51 mm), whereas SNODAS yielded the most accurate SWE from GPR twt (RMSE = 41 mm). Densities from both models generated SWE estimates within ±10% of derived SWE when SWE averaged \u3e 400 mm, however, model uncertainty increased to \u3e 20% when SWE averaged \u3c 300 mm. The development and refinement of density models, particularly in lower SWE conditions, is a high priority to fully realize the potential of SWE remote sensing methods

No Humanitarian Intervention in Asian Genocides: How Possible and Legitimate?

This paper addresses an important empirical puzzle: why has the United States, without exception, chosen not to intervene in the six humanitarian catastrophes in post-war Asia, namely in Indonesia, East Pakistan/Bangladesh, Cambodia, East Timor, Sri Lanka and Myanmar? We use an eclectic approach that blends arguments about the international normative structure and geostrategic interests to examine what has made the absence of humanitarian intervention in Asia by the US possible and legitimate. Specifically, we focus on the paradox between calls for humanitarian intervention and the historically and geographically contingent social construction of the norms of humanity, national sovereignty and UN-backed multilateralism in conjunction with US and Chinese concerns over their regional geostrategic interests. The normative narratives about race, ‘communists’, ‘terrorists’, international order and inclusive multilateral process, and geostrategic interests of the US and China combine to make non-intervention possible and legitimate