Complexity dichotomy on partial grid recognition

Deciding whether a graph can be embedded in a grid using only unit-length edges is NP-complete, even when restricted to binary trees. However, it is not difficult to devise a number of graph classes for which the problem is polynomial, even trivial. A natural step, outstanding thus far, was to provide a broad classification of graphs that make for polynomial or NP-complete instances. We provide such a classification based on the set of allowed vertex degrees in the input graphs, yielding a full dichotomy on the complexity of the problem. As byproducts, the previous NP-completeness result for binary trees was strengthened to strictly binary trees, and the three-dimensional version of the problem was for the first time proven to be NP-complete. Our results were made possible by introducing the concepts of consistent orientations and robust gadgets, and by showing how the former allows NP-completeness proofs by local replacement even in the absence of the latter

Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations

The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) experiment at the Antiproton Decelerator (AD) facility of CERN constructed segmented scintillators to detect and track the charged pions which emerge from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. A system of 541 cast and extruded scintillator bars were arranged in 11 detector modules which provided a spatial resolution of 17 mm. Green wavelength-shifting fibers were embedded in the scintillators, and read out by silicon photomultipliers which had a sensitive area of 1 x 1 mm^2. The photoelectron yields of various scintillator configurations were measured using a negative pion beam of momentum p ~ 1 GeV/c. Various fibers and silicon photomultipliers, fiber end terminations, and couplings between the fibers and scintillators were compared. The detectors were also tested using the antiproton beam of the AD. Nonlinear effects due to the saturation of the silicon photomultiplier were seen at high annihilation rates of the antiprotons.Comment: Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, Vol.85, Issue 2, 2014 and may be found at http://dx.doi.org/10.1063/1.486364

GW approximation with self-screening correction

The \emph{GW} approximation takes into account electrostatic self-interaction contained in the Hartree potential through the exchange potential. However, it has been known for a long time that the approximation contains self-screening error as evident in the case of the hydrogen atom. When applied to the hydrogen atom, the \emph{GW} approximation does not yield the exact result for the electron removal spectra because of the presence of self-screening: the hole left behind is erroneously screened by the only electron in the system which is no longer present. We present a scheme to take into account self-screening and show that the removal of self-screening is equivalent to including exchange diagrams, as far as self-screening is concerned. The scheme is tested on a model hydrogen dimer and it is shown that the scheme yields the exact result to second order in $(U_{0}-U_{1})/2t$ where $U_{0}$ and $U_{1}$ are respectively the onsite and offsite Hubbard interaction parameters and $t$ the hopping parameter.Comment: 9 pages, 2 figures; Submitted to Phys. Rev.

Beam Performance of Tracking Detectors with Industrially Produced GEM Foils

Three Gas-Electron-Multiplier tracking detectors with an active area of 10 cm x 10 cm and a two-dimensional, laser-etched orthogonal strip readout have been tested extensively in particle beams at the Meson Test Beam Facility at Fermilab. These detectors used GEM foils produced by Tech-Etch, Inc. They showed an efficiency in excess of 95% and spatial resolution better than 70 um. The influence of the angle of incidence of particles on efficiency and spatial resolution was studied in detail.Comment: 8 pages, 9 figures, accepted by Nuclear Instruments and Methods in Physics Research

On three-manifolds dominated by circle bundles

We determine which three-manifolds are dominated by products. The result is that a closed, oriented, connected three-manifold is dominated by a product if and only if it is finitely covered either by a product or by a connected sum of copies of the product of the two-sphere and the circle. This characterization can also be formulated in terms of Thurston geometries, or in terms of purely algebraic properties of the fundamental group. We also determine which three-manifolds are dominated by non-trivial circle bundles, and which three-manifold groups are presentable by products.Comment: 12 pages; to appear in Math. Zeitschrift; ISSN 1103-467

Microscopic Theory of Magnon-Drag Thermoelectric Transport in Ferromagnetic Metals

A theoretical study of the magnon-drag Peltier and Seebeck effects in ferromagnetic metals is presented. A magnon heat current is described perturbatively from the microscopic viewpoint with respect to electron--magnon interactions and the electric field. Then, the magnon-drag Peltier coefficient \Pi_\MAG is obtained as the ratio between the magnon heat current and the electric charge current. We show that \Pi_\MAG=C_\MAG T^{5/2} at a low temperature $T$; that the coefficient C_\MAG is proportional to the spin polarization $P$ of the electric conductivity; and that $P>0$ for C_\MAG<0, but $P0$. From experimental results for magnon-drag Peltier effects, we estimate that the strength of the electron--magnon interaction is about 0.3 eV$\cdot\AA^{3/2}$ for permalloy.Comment: 3 pages, 2 figures, accepted for publication in Journal of the Physical Society of Japa

Sintesis dan Karakterisasi Struktur Kristal, Sifat Termal dan Konduktivitas Ionik Gelas Komposit (Agi)0,7(napo3)0,3

SINTESIS DAN KARAKTERISASI STRUKTUR KRISTAL, SIFAT TERMAL DAN KONDUKTIVITAS IONIK GELAS KOMPOSIT (AgI)0,7(NaPO3)0,3. Telah disintesis bahan elektrolit padat baru berbasis gelas NaPO3 dan gelas komposit (AgI)0,7(NaPO3)0,3. Berbagai karakterisasi telah dilakukan pada kedua elektrolit padat ini seperti pengukuran struktur kristal menggunakan X-ray Diffractometer, sifat termal dengan Differential Scanning Calorimetry (DSC) dan pengukuran konduktivitas ionik menggunakan Impedance Spectroscopy (LCR meter). Pola difraksi sinar-x pada suhu ruang menunjukkan bahwa gelas NaPO3 terdiri dari dua puncak lebar yang menandakan gelas ini benar-benar masih amorf dan kualitasnya baik. Pada gelas komposit (AgI)0,7(NaPO3)0,3 ditunjukkan bahwa sebagian cuplikan telah terkristalisasi. Analisis struktur kristal pada suhu ruang menunjukkan bahwa presipitat tersebut berasal dari campuran fasa γ-AgI dan β-AgI, sedangkan pada suhu 250 oC telah terjadi Perubahan fasa menjadi α-AgI. Hal ini didukung dengan pengamatan sifat termal bahwa telah terjadi transisi fasa pada suhu sekitar 148,43 oC dengan enthalpy sebesar 21,43 J/g. Hasil pengukuran sifat listrik pada tegangan dan frekuensi yang berbeda menunjukkan bahwa telah terjadi kenaikan konduktivitas ionik yang signifikan pada gelas komposit (AgI)0,7(NaPO3)0,3 yaitu α(0,1volt) = 6,918 x 10–6 S/cm, α(1 volt) = 3,09 x 10-5 S/cm, α(2 volt) = 4,36 x 10-5 S/cm, dibandingkan dengan gelas tanpa dopan NaPO3 yaitu α(0,1volt) = 1,62 x 10–8 S/cm, α(1 volt) = 2,39 x 10-7 S/cm, α(2 volt) = 2,51 x 10-7 S/cm. Kenaikan konduktivitas ini bukan disebabkan karena α-AgI sebagaimana yang diperkirakan sebelumnya, melainkan karena mekanisme konduksi Ag+ and I- pada matriks gelas NaPO3

Free energy and molecular dynamics calculations for the cubic-tetragonal phase transition in zirconia

The high-temperature cubic-tetragonal phase transition of pure stoichiometric zirconia is studied by molecular dynamics (MD) simulations and within the framework of the Landau theory of phase transformations. The interatomic forces are calculated using an empirical, self-consistent, orthogonal tight-binding (SC-TB) model, which includes atomic polarizabilities up to the quadrupolar level. A first set of standard MD calculations shows that, on increasing temperature, one particular vibrational frequency softens. The temperature evolution of the free energy surfaces around the phase transition is then studied with a second set of calculations. These combine the thermodynamic integration technique with constrained MD simulations. The results seem to support the thesis of a second-order phase transition but with unusual, very anharmonic behaviour above the transition temperature

A facile quantitative assay for viral particle genesis reveals cooperativity in virion assembly and saturation of an antiviral protein

Conventional assays of viral particle assembly and release are time consuming and laborious. We have developed an enzymatic virus-like particle (VLP) genesis assay that rapid and quantitative and is also versatile and applicable to diverse viruses including HIV-1 and Ebola virus. Using this assay, which has a dynamic range of several orders of magnitude, we show that the efficiency of VLP assembly and release, i.e., the fraction of the expressed protein that is assembled into extracellular particles, is dependent on the absolute level of expression of either HIV-1 Gag or Ebola virus VP40. We also demonstrate that the activity of the antiviral factor tetherin is dependent on the level of HIV-1 Gag expression and the numbers of VLPs generated, and appears to become saturated as these parameters are increased