Specific Isotopic Labeling and Photooxidation-linked Structural Changes in the Manganese-stabilizing Subunit of Photosystem II

Photosystem II (PSII) oxidizes water to molecular oxygen; the catalytic site is a cluster of four manganese ions. The catalytic site undergoes four sequential light-driven oxidation steps to form oxygen; these sequentially oxidized states are referred to as the Sn states, where n refers to the number of oxidizing equivalents stored. The extrinsic manganese stabilizing protein (MSP) of PSII influences the efficiency and stability of the manganese cluster, as well as the rates of the S state transitions. To understand how MSP influences photosynthetic water oxidation, we have employed isotope editing and difference Fourier transform infrared spectroscopy. MSP was expressed in Escherichia coli under conditions in which MSP aspartic and glutamic acid residues label at yields of 65 and 41%, respectively. Asparagine and glutamine were also labeled by this approach. GC/MS analysis was consistent with minimal scrambling of label into other amino acid residues and with no significant scrambling into the peptide bond. Selectively labeled MSP was then reconstituted to PSII, which had been stripped of native MSP. Difference Fourier transform infrared spectroscopy was used to probe the S 1QA to S2QA- transition at 200 K, as well as the S1QB to S2Q B- transition at 277 K. These experiments show that aspargine, glutamine, and glutamate residues in MSP are perturbed by photooxidation of manganese during the S1 to S2 transition

Connecting Dualities and Machine Learning

Dualities are widely used in quantum field theories and string theory to obtain correlation functions at high accuracy. Here we present examples where dual data representations are useful in supervised classification, linking machine learning and typical tasks in theoretical physics. We then discuss how such beneficial representations can be enforced in the latent dimension of neural networks. We find that additional contributions to the loss based on feature separation, feature matching with respect to desired representations, and a good performance on a ‘simple’ correlation function can lead to known and unknown dual representations. This is the first proof of concept that computers can find dualities. We discuss how our examples, based on discrete Fourier transformation and Ising models, connect to other dualities in theoretical physics, for instance Seiberg duality

Anisotropy in the Cosmic Microwave Background at Degree Angular Scales: Python V Results

Observations of the microwave sky using the Python telescope in its fifth season of operation at the Amundsen-Scott South Pole Station in Antarctica are presented. The system consists of a 0.75 m off-axis telescope instrumented with a HEMT amplifier-based radiometer having continuum sensitivity from 37-45 GHz in two frequency bands. With a 0.91 deg x 1.02 deg beam the instrument fully sampled 598 deg^2 of sky, including fields measured during the previous four seasons of Python observations. Interpreting the observed fluctuations as anisotropy in the cosmic microwave background, we place constraints on the angular power spectrum of fluctuations in eight multipole bands up to l ~ 260. The observed spectrum is consistent with both the COBE experiment and previous Python results. There is no significant contamination from known foregrounds. The results show a discernible rise in the angular power spectrum from large (l ~ 40) to small (l ~ 200) angular scales. The shape of the observed power spectrum is not a simple linear rise but has a sharply increasing slope starting at l ~ 150.Comment: 5 page

Molecular Dynamics Simulation Study of Nonconcatenated Ring Polymers in a Melt: I. Statics

Molecular dynamics simulations were conducted to investigate the structural properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N=1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. For the rings, the radius of gyration squared was found to scale as N to the 4/5 power for an intermediate regime and N to the 2/3 power for the larger rings indicating an overall conformation of a crumpled globule. However, almost all beads of the rings are "surface beads" interacting with beads of other rings, a result also in agreement with a primitive path analysis performed in the following paper (DOI: 10.1063/1.3587138). Details of the internal conformational properties of the ring and linear polymers as well as their packing are analyzed and compared to current theoretical models.Comment: 15 pages, 14 figure

DASI First Results: A Measurement of the Cosmic Microwave Background Angular Power Spectrum

We present measurements of anisotropy in the Cosmic Microwave Background (CMB) from the first season of observations with the Degree Angular Scale Interferometer (DASI). The instrument was deployed at the South Pole in the austral summer 1999--2000, and made observations throughout the following austral winter. We have measured the angular power spectrum of the CMB in the range 100<l<900 with high signal-to-noise. In this paper we review the formalism used in the analysis, in particular the use of constraint matrices to project out contaminants such as ground and point source signals, and to test for correlations with diffuse foreground templates. We find no evidence of foregrounds other than point sources in the data, and find a maximum likelihood temperature spectral index beta = -0.1 +/- 0.2 (1 sigma), consistent with CMB. We detect a first peak in the power spectrum at l approx 200, in agreement with previous experiments. In addition, we detect a peak in the power spectrum at l approx 550 and power of similar magnitude at l approx 800 which are consistent with the second and third harmonic peaks predicted by adiabatic inflationary cosmological models.Comment: 8 pages, 1 figure, minor changes in response to referee comment

Overview of the spectrometer optical fiber feed for the Habitable-zone Planet Finder

The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed precision radial velocity (RV) spectrograph working in the Near Infrared (NIR): 810 - 1280 nm . In this paper we present an overview of the preparation of the optical fibers for HPF. The entire fiber train from the telescope focus down to the cryostat is detailed. We also discuss the fiber polishing, splicing and its integration into the instrument using a fused silica puck. HPF was designed to be able to operate in two modes, High Resolution (HR- the only mode mode currently commissioned) and High Efficiency (HE). We discuss these fiber heads and the procedure we adopted to attach the slit on to the HR fibers.Comment: Presented at 2018 SPIE Astronomical Telescopes + Instrumentation, Austin, Texas, USA. 18 pages, 25 figures, and 2 table

Bulk scalar field in brane-worlds with induced gravity inspired by the L(R){\cal L}(R) term

We obtain the effective field equations in a brane-world scenario within the framework of a DGP model where the action on the brane is an arbitrary function of the Ricci scalar, ${\cal L}(R)$, and the bulk action includes a scalar field in the matter Lagrangian. We obtain the Friedmann equations and acceleration conditions in the presence of the bulk scalar field for the $R^n$ term in four-dimensional gravity.Comment: 9 pages, to appear in JCA

Structure and dynamics of ring polymers: entanglement effects because of solution density and ring topology

The effects of entanglement in solutions and melts of unknotted ring polymers have been addressed by several theoretical and numerical studies. The system properties have been typically profiled as a function of ring contour length at fixed solution density. Here, we use a different approach to investigate numerically the equilibrium and kinetic properties of solutions of model ring polymers. Specifically, the ring contour length is maintained fixed, while the interplay of inter- and intra-chain entanglement is modulated by varying both solution density (from infinite dilution up to \approx 40 % volume occupancy) and ring topology (by considering unknotted and trefoil-knotted chains). The equilibrium metric properties of rings with either topology are found to be only weakly affected by the increase of solution density. Even at the highest density, the average ring size, shape anisotropy and length of the knotted region differ at most by 40% from those of isolated rings. Conversely, kinetics are strongly affected by the degree of inter-chain entanglement: for both unknots and trefoils the characteristic times of ring size relaxation, reorientation and diffusion change by one order of magnitude across the considered range of concentrations. Yet, significant topology-dependent differences in kinetics are observed only for very dilute solutions (much below the ring overlap threshold). For knotted rings, the slowest kinetic process is found to correspond to the diffusion of the knotted region along the ring backbone.Comment: 17 pages, 11 figure