No imminent quantum supremacy by boson sampling

It is predicted that quantum computers will dramatically outperform their conventional counterparts. However, large-scale universal quantum computers are yet to be built. Boson sampling is a rudimentary quantum algorithm tailored to the platform of photons in linear optics, which has sparked interest as a rapid way to demonstrate this quantum supremacy. Photon statistics are governed by intractable matrix functions known as permanents, which suggests that sampling from the distribution obtained by injecting photons into a linear-optical network could be solved more quickly by a photonic experiment than by a classical computer. The contrast between the apparently awesome challenge faced by any classical sampling algorithm and the apparently near-term experimental resources required for a large boson sampling experiment has raised expectations that quantum supremacy by boson sampling is on the horizon. Here we present classical boson sampling algorithms and theoretical analyses of prospects for scaling boson sampling experiments, showing that near-term quantum supremacy via boson sampling is unlikely. While the largest boson sampling experiments reported so far are with 5 photons, our classical algorithm, based on Metropolised independence sampling (MIS), allowed the boson sampling problem to be solved for 30 photons with standard computing hardware. We argue that the impact of experimental photon losses means that demonstrating quantum supremacy by boson sampling would require a step change in technology.Comment: 25 pages, 9 figures. Comments welcom

The BARRIERS scale -- the barriers to research utilization scale: A systematic review

<p>Abstract</p> <p>Background</p> <p>A commonly recommended strategy for increasing research use in clinical practice is to identify barriers to change and then tailor interventions to overcome the identified barriers. In nursing, the BARRIERS scale has been used extensively to identify barriers to research utilization.</p> <p>Aim and objectives</p> <p>The aim of this systematic review was to examine the state of knowledge resulting from use of the BARRIERS scale and to make recommendations about future use of the scale. The following objectives were addressed: To examine how the scale has been modified, to examine its psychometric properties, to determine the main barriers (and whether they varied over time and geographic locations), and to identify associations between nurses' reported barriers and reported research use.</p> <p>Methods</p> <p>Medline (1991 to September 2009) and CINHAL (1991 to September 2009) were searched for published research, and ProQuest^®digital dissertations were searched for unpublished dissertations using the BARRIERS scale. Inclusion criteria were: studies using the BARRIERS scale in its entirety and where the sample was nurses. Two authors independently assessed the study quality and extracted the data. Descriptive and inferential statistics were used.</p> <p>Results</p> <p>Sixty-three studies were included, with most using a cross-sectional design. Not one study used the scale for tailoring interventions to overcome identified barriers. The main barriers reported were related to the setting, and the presentation of research findings. Overall, identified barriers were consistent over time and across geographic locations, despite varying sample size, response rate, study setting, and assessment of study quality. Few studies reported associations between reported research use and perceptions of barriers to research utilization.</p> <p>Conclusions</p> <p>The BARRIERS scale is a nonspecific tool for identifying general barriers to research utilization. The scale is reliable as reflected in assessments of internal consistency. The validity of the scale, however, is doubtful. There is no evidence that it is a useful tool for planning implementation interventions. We recommend that no further descriptive studies using the BARRIERS scale be undertaken. Barriers need to be measured specific to the particular context of implementation and the intended evidence to be implemented.</p

CCDC 881945: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.,Related Article: A.N.Carolan, A.E.Mroz, M.E.Ojaimi, D.G.VanDerveer, R.P.Thummel, R.D.Hancock|2012|Inorg.Chem.|51|3007|doi:10.1021/ic202337

CCDC 928436: Experimental Crystal Structure Determination

Related Article: A.N.Carolan,G.M.Cockrell,N.J.Williams,Gang Zhang,D.G.VanDerveer,Hee-Seung Lee,R.P.Thummel,R.D.Hancock|2013|Inorg.Chem.|52|15|doi:10.1021/ic3002509,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 928437: Experimental Crystal Structure Determination

Related Article: A.N.Carolan,G.M.Cockrell,N.J.Williams,Gang Zhang,D.G.VanDerveer,Hee-Seung Lee,R.P.Thummel,R.D.Hancock|2013|Inorg.Chem.|52|15|doi:10.1021/ic3002509,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

Metal-Ion-Complexing Properties of 2-(Pyrid-2′-yl)-1,10-phenanthroline, a More Preorganized Analogue of Terpyridyl. A Crystallographic, Fluorescence, and Thermodynamic Study

Some metal-ion-complexing properties of the ligand 2-(pyrid-2′-yl)-1,10-phenanthroline (MPP) are reported. MPP is of interest in that it is a more preorganized version of 2,2′;6,2″-terpyridine (tpy). Protonation constants (p<i>K</i>₁ = 4.60; p<i>K</i>₂ = 3.35) for MPP were determined by monitoring the intense π–π* transitions of 2 × 10^–5 M solutions of the ligand as a function of the pH at an ionic strength of 0 and 25 °C. Formation constants (log <i>K</i>₁) at an ionic strength of 0 and 25 °C were obtained by monitoring the π–π* transitions of MPP titrated with solutions of the metal ion, or 1:1 solutions of MPP and the metal ion were titrated with acid. Large metal ions such as Ca^II or La^III showed increases of log <i>K</i>₁ of about 1.5 log units compared to that of tpy. Small metal ions such as Zn^II and Ni^II showed little increase in log <i>K</i>₁ for MPP compared to the tpy complexes, which is attributed to the presence of five-membered chelate rings in the MPP complexes, which favor large metal ions. The structure of [Cd­(MPP)­(H₂O)­(NO₃)₂] (<b>1</b>) is reported: monoclinic, <i>P</i>2₁/<i>c</i>, <i>a</i> = 7.4940(13) Å, <i>b</i> = 12.165(2) Å, <i>c</i> = 20.557(4) Å, β = 96.271(7)°, <i>V</i> = 1864.67(9) ų, <i>Z</i> = 4, and final <i>R</i> = 0.0786. The Cd in <b>1</b> is seven-coordinate, comprising the three donor atoms of MPP, a coordinated water, a monodentate, and a bidentate NO₃^–. Cd^II is a fairly large metal ion, with <i>r</i>⁺ = 0.96 Å, slightly too small for coordination with MPP. The effect of this size matching in terms of the structure is discussed. Fluorescence spectra of 2 × 10^–7 M MPP in aqueous solution are reported. The nonprotonated MPP ligand fluoresces only weakly, which is attributed to a photoinduced-electron-transfer effect. The chelation-enhanced-fluorescence (CHEF) effect induced by some metal ions is presented, and the trend of the CHEF effect, which is Ca^II > Zn^II > Cd^II ∼ La^III > Hg^II, is discussed in terms of factors that control the CHEF effect, such as the heavy-atom effect

Selectivity of the Highly Preorganized Tetradentate Ligand 2,9-Di(pyrid-2-yl)-1,10-phenanthroline for Metal Ions in Aqueous Solution, Including Lanthanide(III) Ions and the Uranyl(VI) Cation

Some metal ion complexing properties of DPP (2,9-Di­(pyrid-2-yl)-1,10-phenanthroline) are reported with a variety of Ln­(III) (Lanthanide­(III)) ions and alkali earth metal ions, as well as the uranyl­(VI) cation. The intense π–π* transitions in the absorption spectra of aqueous solutions of 10^–5 M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln­(III) (Ln = lanthanide) ions. It was found that log <i>K</i>₁(DPP) for the Ln­(III) ions has a peak at Ln­(III) = Sm­(III) in a plot of log <i>K</i>₁ versus 1/<i>r</i>⁺ (<i>r</i>⁺ = ionic radius for 8-coordination). For Ln­(III) ions larger than Sm­(III), there is a steady rise in log <i>K</i>₁ from La­(III) to Sm­(III), while for Ln­(III) ions smaller than Sm­(III), log <i>K</i>₁ decreases slightly to the smallest Ln­(III) ion, Lu­(III). This pattern of variation of log <i>K</i>₁ with varying size of Ln­(III) ion was analyzed using MM (molecular mechanics) and DFT (density functional theory) calculations. Values of strain energy (∑U) were calculated for the [Ln­(DPP)­(H₂O)₅]³⁺ and [Ln­(qpy)­(H₂O)₅]³⁺ (qpy = quaterpyrdine) complexes of all the Ln­(III) ions. The ideal M–N bond lengths used for the Ln­(III) ions were the average of those found in the CSD (Cambridge Structural Database) for the complexes of each of the Ln­(III) ions with polypyridyl ligands. Similarly, the ideal M–O bond lengths were those for complexes of the Ln­(III) ions with coordinated aqua ligands in the CSD. The MM calculations suggested that in a plot of ∑U versus ideal M–N length, a minimum in ∑U occurred at Pm­(III), adjacent in the series to Sm­(III). The significance of this result is that (1) MM calculations suggest that a similar metal ion size preference will occur for all polypyridyl-type ligands, including those containing triazine groups, that are being developed as solvent extractants in the separation of Am­(III) and Ln­(III) ions in the treatment of nuclear waste, and (2) Am­(III) is very close in M–N bond lengths to Pm­(III), so that an important aspect of the selectivity of polypyridyl type ligands for Am­(III) will depend on the above metal ion size-based selectivity. The selectivity patterns of DPP with the alkali-earth metal ions shows a similar preference for Ca­(II), which has the most appropriate M–N lengths. The structures of DPP complexes of Zn­(II) and Bi­(III), as representative of a small and of a large metal ion respectively, are reported. [Zn­(DPP)₂]­(ClO₄)₂ (triclinic, <i>P</i>1, <i>R</i> = 0.0507) has a six-coordinate Zn­(II), with each of the two DPP ligands having one noncoordinated pyridyl group appearing to be π-stacked on the central aromatic ring of the other DPP ligand. [Bi­(DPP)­(H₂O)₂(ClO₄)₂]­(ClO₄) (triclinic, <i>P</i>1, <i>R</i> = 0.0709) has an eight-coordinate Bi, with the coordination sphere composed of the four N donors of the DPP ligand, two coordinated water molecules, and the O donors of two unidentate perchlorates. As is usually the case with Bi­(III), there is a gap in the coordination sphere that appears to be the position of a lone pair of electrons on the other side of the Bi from the DPP ligand. The Bi-L bonds become relatively longer as one moves from the side of the Bi containg the DPP to the side where the lone pair is thought to be situated. A DFT analysis of [Ln­(tpy)­(H₂O)_<i>n</i>]³⁺ and [Ln­(DPP)­(H₂O)₅]³⁺ complexes is reported. The structures predicted by DFT are shown to match very well with the literature crystal structures for the [Ln­(tpy)­(H₂O)_<i>n</i>]³⁺ with Ln = La and <i>n</i> = 6, and Ln = Lu with <i>n</i> = 5. This then gives one confidence that the structures for the DPP complexes generated by DFT are accurate. The structures generated by DFT for the [Ln­(DPP)­(H₂O)₅]³⁺ complexes are shown to agree very well with those generated by MM, giving one confidence in the accuracy of the latter. An analysis of the DFT and MM structures shows the decreasing O--O nonbonded distances as one progresses from La to Lu, with these distances being much less than the sum of the van der Waals radii for the smaller Ln­(III) ions. The effect that such short O--O nonbonded distances has on thermodynamic complex stability and coordination number is then discussed

Housekeeping genes for phylogenetic analysis of eutherian relationships

The molecular relationship of placental mammals has attracted great interest in recent years. However, 2 crucial and conflicting hypotheses remain, one with respect to the position of the root of the eutherian tree and the other the relationship between the orders Rodentia, Lagomorpha (rabbits, hares), and Primates. Although most mitochondrial (mt) analyses have suggested that rodents have a basal position in the eutherian tree, some nuclear data in combination with mt-rRNA genes have placed the root on the so-called African clade or on a branch that includes this clade and the Xenarthra (e.g., anteater and armadillo). In order to generate a new and independent set of molecular data for phylogenetic analysis, we have established cDNA sequences from different tissues of various mammalian species. With this in mind, we have identified and sequenced 8 housekeeping genes with moderately fast rate of evolution from 22 placental mammals, representing I I orders. In order to determine the root of the eutherian tree, the same genes were also sequenced for 3 marsupial species, which were used as outgroup. Inconsistent with the analyses of nuclear + mt-rRNA gene data, the current data set did not favor a basal position of the African clade or Xenarthra in the eutherian tree. Similarly, by joining rodents and lagomorphs on the same basal branch (Glires hypothesis), the data set is also inconsistent with the tree commonly favored in mtDNA analyses. The analyses of the currently established sequences have helped examination of problematic parts in the eutherian tree at the same time as they caution against suggestions that have claimed that basal eutherian relationships have been conclusively settled