Evidence against the Detectability of a Hippocampal Place Code Using Functional Magnetic Resonance Imaging

Individual hippocampal neurons selectively increase their firing rates in specific spatial locations. As a population, these neurons provide a decodable representation of space that is robust against changes to sensory- and path-related cues. This neural code is sparse and distributed, theoretically rendering it undetectable with population recording methods such as functional magnetic resonance imaging (fMRI). Existing studies nonetheless report decoding spatial codes in the human hippocampus using such techniques. Here we present results from a virtual navigation experiment in humans in which we eliminated visual- and path-related confounds and statistical limitations present in existing studies, ensuring that any positive decoding results would represent a voxel-place code. Consistent with theoretical arguments derived from electrophysiological data and contrary to existing fMRI studies, our results show that although participants were fully oriented during the navigation task, there was no statistical evidence for a place code

A rapid screening, “combinatorial-type” survey of the metalloligand chemistry of Pt₂(PPh₃)₄(μ-S)₂ using electrospray mass spectrometry

Electrospray mass spectrometry is a rapid and powerful technique for a combinatorial-like survey of the chemistry of the metalloligand Pt₂(PPh₃)₄(μ-S)₂, leading to the successful isolation and crystallographic characterisation of the novel protonated species Pt₂(PPh₃)₄(μ-S)(μ-SH) together with a range of metallated derivatives

The IRAS 1-Jy Survey of Ultraluminous Infrared Galaxies: I. The sample and Luminosity Function

A complete flux-limited sample of 118 ultraluminous infrared galaxies (ULIGs) has been identified from the IRAS Faint Source Catalog (FSC). The selection criteria were a 60 micron flux density greater than 1 Jy in a region of the sky delta > -40 deg, |b| > 30 deg. All sources were subsequently reprocessed using coadded IRAS maps in order to obtain the best available flux estimates in all four IRAS wavelength bands. The maximum observed infrared luminosity is L_ir = 10^{12.90} L_{sun}, and the maximum redshift is z = 0.268. The luminosity function for ULIGs over the decade luminosity range L_ir = 10^{12} - 10^{13} L_{sun} can be approximated by a power law Phi (L) ~= L^{-2.35} Mpc^{-3} mag^{-1}. In the local Universe z < 0.1, the space density of ULIGs appears to be comparable to or slightly larger than that of optically selected QSOs at comparable bolometric luminosities. A maximum likelihood test suggests strong evolution for our sample; assuming density evolution proportional to (1+z)^{alpha} we find alpha = 7.6+/-3.2. Examination of the two-point correlation function shows a barely significant level of clustering, xi (r) = 1.6 +/- 1.2, on size scales r ~= 22 h^{-1} Mpc.Comment: 18 pages of text, 10 pages of figures 1 to 6, 6 pages of tables 1 to 3, ApJS accepte

Synchrotron study of poly[[di-μ-aqua­(μ-2,2′-bipyridyl-5,5′-dicarboxyl­ato)di­potassium] dihydrate]

The title compound, {[K2(C12H6N2O4)(H2O)2]·2H2O}n, forms a three-dimensional coordination polymer in the solid state. The asymmetric unit consists of one K+ ion, half of a 2,2′-bipyridyl-5,5′-dicarboxyl­ate ligand, one coordinated water mol­ecule and one solvent water mol­ecule. The K+ ion is 7-coordinated by the oxygen atoms of two water mol­ecules and by five oxygen atoms of four carboxyl­ate groups, one of which is chelating. The extended structure can be described as a binodal network in which each K+ is a six-connected node, bonding to four carboxyl­ate groups and two bridging water mol­ecules, and the 2,2′-bipyridyl-5,5′-dicarboxyl­ate linkers are eight-connected nodes, with each carboxyl­ate group bridging four metal centers. Overall, this arrangement generates a complex network with point symbol {34.412.512}{34.44.54.63}2. Both of the bridging water mol­ecules participate as donors in hydrogen-bonding inter­actions; one to solvent water mol­ecules and a second to an oxygen atom of a carboxyl­ate group

Particle acceleration during merging-compression plasma start-up in the Mega Amp Spherical Tokamak

Magnetic reconnection occurred during merging-compression plasma start-up in the Mega Amp Spherical Tokamak (MAST), resulting in the prompt acceleration of substantial numbers of ions and electrons to highly suprathermal energies. Accelerated field-aligned ions (deuterons and protons) were detected using a neutral particle analyser at energies up to about 20 keV during merging in early MAST pulses, while nonthermal electrons have been detected indirectly in more recent pulses through microwave bursts. However no increase in soft X-ray emission was observed until later in the merging phase, by which time strong electron heating had been detected through Thomson scattering measurements. A test-particle code CUEBIT is used to model ion acceleration in the presence of an inductive toroidal electric field with a prescribed spatial profile and temporal evolution based on Hall-MHD simulations of the merging process. The simulations yield particle distributions with properties similar to those observed experimentally, including strong field alignment of the fast ions and the acceleration of protons to higher energies than deuterons. Particle-in-cell modelling of a plasma containing a dilute field-aligned suprathermal electron component suggests that at least some of the microwave bursts can be attributed to the anomalous Doppler instability driven by anisotropic fast electrons, which do not produce measurable enhancements in soft X-ray emission either because they are insufficiently energetic or because the nonthermal bremsstrahlung emissivity during this phase of the pulse is below the detection threshold. There is no evidence of runaway electron acceleration during merging, possibly due to the presence of three-dimensional field perturbations

catena-Poly[[penta-μ-benzoato-μ-chlorido-dioxanedineodymium(III)] dioxane 2.5-solvate]

The asymmetric unit of the title compound, [Nd2(C6H5COO)5Cl(C4H8O2)]·2.5C4H8O2, consists of two NdIII ions bridged by one Cl− ion, five benzoate ions and one coordinating 1,4-dioxane mol­ecule. One NdIII ion is nine-coordinate, with a very distorted monocapped square-anti­prismatic geometry. It is coordinated by two chelating carboxyl­ate groups, three monodentate carboxyl­ate groups, one chloride ion and one dioxane mol­ecule. A second independent NdIII ion is eight-coordinated in a distorted square-anti­prismatic geometry by one chelating carboxyl­ate group, five monodentate carboxyl­ate groups and one chloride ion. The chains of the extended structure are parallel to the crystallographic b axis. There is a small amount of void space which is filled with five disordered dioxane solvent mol­ecules per unit cell. The intensity contribution of the disordered solvent molecules was removed by applying the SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65, 148–155]

A cationic rhodium(I) N-heterocyclic carbene complex isolated as an aqua adduct

The title complex, aqua­[1,3-bis­(2,6-diiso­propyl­phen­yl)imid­az­ol-2-yl­idene](η4-cyclo­octa-1,5-diene)rhodium(I) tetra­fluor­ido­borate, [Rh(C8H12)(C27H36N2)(H2O)]BF4, exihibits a square-planar geometry around the Rh(I) atom, formed by a bidentate cyclo­octa-1,5-diene (cod) ligand, an N-heterocylcic carbene and an aqua ligand. The complex is cationic and a BF4 − anion balances the charge. The structure exists as a hydrogen-bonded dimer in the solid state, formed via inter­actions between the aqua ligand H atoms and the BF4 − F atoms

1,3,5-Triaza­adamantan-7-amine

The title compound, C7H14N4, represents the first structurally characterized, isolated triaza­adamantane. In the crystal structure, weak inter­molecular N—H⋯N hydrogen bonds link the mol­ecules into columns about the crystallographic fourfold axis

Design of the Synthetic Aperture Microwave Imager Upgrade for measurement of the edge current density on MAST-U

The Synthetic Aperture Microwave Imager (SAMI) has demonstrated the feasibility of 2D Doppler backscattering for measurement of the edge magnetic pitch angle on MAST and NSTX-U. The aim of SAMI-Upgrade (SAMI-U) is to build on this methodology to produce higher quality pitch angle data simultaneously in multiple spatial locations, enabling calculation of the edge current density. This movement from proof of principle to production quality necessitates several alterations to the design. There will be a fourfold increase in the number of antennas, as minimising the sidelobe level is key to ensuring maximum resolution in the reconstructed Doppler backscattered power map. SAMI-U will actively probe the plasma with two frequencies at the same time. These correspond to two different backscattering locations in the edge plasma which allows the edge current density to be calculated from the measured magnetic field vector. Dual-polarised sinuous antennas will be used in the array as they are planar and broadband. Polarisation separation is necessary for differentiation between the O-and X-mode cut off surfaces, as their locations can be separated by up to a few centimetres. Due to spatial constraints many of the components will be placed on a PCB behind each antenna. FPGAs will be used to stream the high data throughput, over 16 GB s−1, into PC memory

Direct Measurement of the System-Environment Coupling as a Tool For Understanding Decoherence and Dynamical Decoupling

Decoherence is a major obstacle to any practical implementation of quantum information processing. One of the leading strategies to reduce decoherence is dynamical decoupling --- the use of an external field to average out the effect of the environment. The decoherence rate under any control field can be calculated if the spectrum of the coupling to the environment is known. We present a direct measurement of the bath coupling spectrum in an ensemble of optically trapped ultracold atoms, by applying a spectrally narrow-band control field. The measured spectrum follows a Lorentzian shape at low frequencies, but exhibits non-monotonic features at higher frequencies due to the oscillatory motion of the atoms in the trap. These features agree with our analytical models and numerical Monte-Carlo simulations of the collisional bath. From the inferred bath-coupling spectrum, we predict the performance of well-known dynamical decoupling sequences: CPMG, UDD and CDD. We then apply these sequences in experiment and compare the results to predictions, finding good agreement in the weak-coupling limit. Thus, our work establishes experimentally the validity of the overlap integral formalism, and is an important step towards the implementation of an optimal dynamical decoupling sequence for a given measured bath spectrum.Comment: 9 pages, 6 figure