Vacuum Background Research Articles

Gas chromatography‐mass spectrometry with supersonic molecular beams

Gas chromatography-mass spectrometry (GC-MS) with supersonic molecular beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.

Space–time filling branes in non-critical (super) string theories

We consider solutions of (super) gravities associated to non-critical (super) string theories in arbitrary space–time dimension D = p + 3 , that describe generically non-extremal black p-branes charged under NSNS or RR gauge fields, embedded in some non-critical vacuum. In the case of vacuum (uncharged) backgrounds, we solve completely the problem obtaining all the possible solutions, that consist of the ( p + 1 ) -dimensional Minkowski space–times a linear dilaton times an S 1 , and a three parameter family of solutions that includes ( p + 1 ) -dimensional Minkowski space–times the cigar, and its T-dual ( p + 1 ) -dimensional Minkowski space–times the trumpet. For NSNS charged solutions, we also solve in closed form the problem, obtaining several families of solutions, that include in particular the fundamental non-critical string solution embedded in the cigar vacuum, recently found in [A.R. Lugo, M.B. Sturla, Phys. Lett. B 637 (2006) 338, hep-th/0604202], a solution that we interpret as a fundamental non-critical string embedded in the linear dilaton vacuum, and a two-parameter family of regular curvature solutions asymptotic to AdS 1 , 2 × S 1 . In the case of RR charged D p-branes solutions, an ansatz allows us to find a non-conformal, constant curvature, asymptotically AdS 1 , p + 1 space, T-dual to AdS 1 , p + 2 , together with a two-parameter family of solutions that includes the non-conformal, AdS black hole like solution associated with the earlier space. The solutions obtained by T-duality are Einstein spaces consisting of a two-parameter family of conformal, constant dilaton solutions, that include, in particular, the AdS black hole of [S. Kuperstein, J. Sonnenschein, JHEP 0407 (2004) 049, hep-th/0403254]. We speculate about the possible applications of some of them in the framework of the gauge-gravity correspondence.

Nonperturbative equation of state of quark–gluon plasma

The paper is devoted to the systematic derivation of nonperturbative thermodynamics of quark–gluon plasma, on the basis of the background perturbation theory. Vacuum background fields enter only in the form of field correlators, which are known from lattice and analytic calculations. In the lowest order in αs the purely nonperturbative sQGP thermodynamics is expressed through single quark and gluon lines (single line approximation) which are interacting nonperturbatively with vacuum fields and with other lines. Nonperturbative EOS is obtained in terms (of the absolute value) of fundamental (adjoint) Polyakov loop Lfund(adj) and spatial string tension σs(T). In the lowest approximation the pressure for quarks (gluons) has a simple factorized form Pq(g)=PSBLfund(adj), where Li describe the action of vacuum colorelectric fields on particle trajectory.

A TOPOLOGICAL INTERPRETATION OF THE COLOR CHARGE

We develop a theory on a topologically nontrivial manifold which leads to different vacuum backgrounds at the field level. The different colors of the same quark flavor live in different backgrounds generated by the action of the torsion subgroup of H2(M, 2πℤ) on H2(M, 2πℤ) itself. This topological separation leads to a quark confinement mechanism which does not apply to the baryons as they turn out to live on the same vacuum state. The theory makes some topological assumptions on the spacetime manifold which are compared with the available data on the topology of the Universe.

Growth and small-polaron conduction of hole-dopedLaTiO3+δ∕2andNdTiO3+δ∕2thin films

$\mathrm{Re}\mathrm{Ti}{\mathrm{O}}_{3+\ensuremath{\delta}∕2}$ ($\mathrm{Re}=\mathrm{La}$ and Nd) thin films have been deposited on $(100)\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ substrates using the pulsed laser deposition technique. The oxygen content in the formula can be tuned to some extent by carefully adjusting the oxygen pressure during film deposition. When grown at higher oxygen pressures, the films tend to be in their fully oxidized insulating form ${\mathrm{Re}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ $(\ensuremath{\delta}=1,{\mathrm{Ti}}^{4+})$ with a twinned monoclinic structure of ${[01\overline{2}]}_{m}$ orientations. When grown in a background vacuum around $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}\mathrm{Pa}$, the films are lightly hole doped $(\ensuremath{\delta}\ensuremath{\sim}0,\ensuremath{\sim}{\mathrm{Ti}}^{3+})$ and retain the near-cubic perovskite structure with the ${[001]}_{c}$ axis perpendicular to the film surface, though high-density defects may exist. These two phases coexist in the films grown at intermediate oxygen pressures. For the vacuum-grown near-cubic films, the antiferromagnetic ordering dies in the lanthanum titanate due to oxygen doping but still survives in the neodymium titanate owing to the higher electron correlation strength in the latter. The transport behavior in the $\ensuremath{\sim}{\mathrm{Ti}}^{3+}$ Mott insulating films can be described well by the small-polaron hopping or variable range hopping model. In the hole-doped metallic films, a temperature-dependent carrier density and Hall mobility were observed, especially at low temperatures. The temperature dependence of the resistance can be almost perfectly fitted by a small-polaron coherent conduction model $[{R}_{s}(T)={R}_{s}(0)+C{\ensuremath{\omega}}_{\ensuremath{\alpha}}∕{\mathrm{sinh}}^{2}({T}_{\ensuremath{\omega}}∕T)]$.

Heun equation, Teukolsky equation, and type-D metrics

Starting with the whole class of type-D vacuum backgrounds with cosmological constant we show that the separated Teukolsky equation for zero rest-mass fields with spins s=±2 (gravitational waves), s=±1 (electromagnetic waves), and s=±1∕2 (neutrinos) is a Heun equation in disguise.

False vacuum bubble nucleation due to a nonminimally coupled scalar field

We study the possibility of forming the false vacuum bubble nucleated within the true vacuum background via the true-to-false vacuum phase transition in curved spacetime. We consider a semiclassical Euclidean bubble in the Einstein theory of gravity with a nonminimally coupled scalar field. In this paper we present the numerical computations as well as the approximate analytical computations. We mention the evolution of the false vacuum bubble after nucleation.

Method of vacuum correlation functions: Results and prospects

Basic results obtained within the QCD method of vacuum correlation functions over the past 20 years in the context of investigations into strong-interaction physics at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) are formulated Emphasis is placed primarily on the prospects of the general theory developed within QCD by employing both nonperturbative and perturbative methods. On the basis of ab initio arguments, it is shown that the lowest two field correlation functions play a dominant role in QCD dynamics. A quantitative theory of confinement and deconfinement, as well as of the spectra of light and heavy quarkonia, glueballs, and hybrids, is given in terms of these two correlation functions. Perturbation theory in a nonperturbative vacuum (background perturbation theory) plays a significant role, not possessing drawbacks of conventional perturbation theory and leading to the infrared freezing of the coupling constant α s.

Isotope abundance analysis methods and software for improved sample identification with supersonic gas chromatography/mass spectrometry

We present newly developed isotope abundance analysis (IAA) methods and software which are used to derive elemental formula information from experimental mass spectral data of molecular ion isotopomeric abundances. The software, using a novel method, can also be used to automatically confirm or reject NIST library search results, thereby significantly improving the confidence level in sample identifications. In the case of IAA confirmation of the NIST library results, sample identification is unambiguous, since the confirmation is achieved by two independent sets of data and analytical methods. In the case of a rejection, such as when the molecule is not included in the library's databases, the IAA software independently provides a list of elemental formulae with declining order of matching to the isotopomeric experimental data, in a similar way to accurate mass measurements with costly instruments. IAA is ideally applicable to gas chromatography/mass spectrometry (GC/MS) (and liquid chromatography/electron ionization mass spectrometry (LC/EI-MS)) with a supersonic molecular beam (SMB) since it requires a trustworthy and highly abundant true molecular ion that is unique to the SMB-MS systems, plus the absence of self chemical ionization and vacuum background noise, again unique features of GC/SMB-MS. The various features of the IAA methods and software are described, their performance is demonstrated with the analysis of experimental GC-SMB-MS data and the IAA concept is compared with accurate mass alternatives. The combination of IAA and GC/SMB-MS is believed to be superior to accurate mass GC/MS in view of the general availability of trustworthy molecular ions for an extended range of compounds.

Uniform MgB2 thin films grown on Si(111) and Al2O3(0001) substrates prepared by e-beam evaporation and in situ annealing methods

Mg B 2 superconducting thin films on Si(111) and Al2O3(0001) substrates were prepared by high vacuum e-beam evaporation and two-step in situ annealing techniques. The precursor films [B(100Å)∕Mg(151Å)]6∕Al2O3 (or Si) were deposited at room temperature and 1×10−7mbar of background vacuum, then annealed in situ at 630°C for 30min in an argon atmosphere of 150Pa. The atomic force microscopy image showed that the films were uniform with grain sizes of about 100nm. An extremely sharp superconducting transition with a width of 0.1K and a zero-resistance temperature of 30.3K was obtained, indicating a film of high uniformity and purity in its phase with perfect connection between the MgB2 grains.

Gas evolution during operation of a CsI-coated carbon fiber cathode in a closed vacuum system

In order to quantify the gases generated during operation of an explosive emission cathode, residual gas analysis was performed on a closed vacuum system. Two different anode materials were tested using an identical CsI-coated carbon fiber cathode. For both the nearly transparent molybdenum mesh and the carbon fiber anode, the largest pressure increases were observed in hydrogen and carbon dioxide. Use of the molybdenum mesh resulted in the generation of approximately 0.38 neutrals per electron compared to 0.73 neutrals per electron while using the carbon fiber anode. While the background vacuum pressure was typically in the low 10/sup -7/ torr scale, it was found that gas generation during these explosive emission pulses led to local diode pressures of 0.5 mtorr up to several tens of mtorr. Such pressures are consistent with the ability to generate ion densities that can drastically effect the space charge-limited current.

Quasilocal contribution to the gravitational self-force

The gravitational self-force on a point particle moving in a vacuum background space-time can be expressed as an integral over the past world line of the particle, the so-called tail term. In this paper, we consider that piece of the self-force obtained by integrating over a portion of the past world line that extends a proper time $\ensuremath{\Delta}\ensuremath{\tau}$ into the past, provided that $\ensuremath{\Delta}\ensuremath{\tau}$ does not extend beyond the normal neighborhood of the particle. We express this quasilocal piece as a power series in the proper time interval $\ensuremath{\Delta}\ensuremath{\tau}$. We argue from symmetries and dimensional considerations that the $O(\ensuremath{\Delta}{\ensuremath{\tau}}^{0})$ and $O(\ensuremath{\Delta}\ensuremath{\tau})$ terms in this power series must vanish, and compute the first two nonvanishing terms which occur at $O(\ensuremath{\Delta}{\ensuremath{\tau}}^{2})$ and $O(\ensuremath{\Delta}{\ensuremath{\tau}}^{3})$. The coefficients in the expansion depend only on the particle's four velocity and on the Weyl tensor and its derivatives at the particle's location. The result may be useful as a foundation for a practical computational method for gravitational self-forces in the Kerr space-time, in which the portion of the tail integral in the distant past is computed numerically from a mode-sum decomposition.

Secondary ion mass spectroscopic depth profile analysis of oxygen contamination in hydrogenated microcrystalline silicon

Oxygen contamination of samples fabricated by very high_frequency plasma_enhanced chemical vapor deposition with the variation of silane concentration and disc harge power was studied by secondary ion mass spectroscopy. The results showed t hat oxygen content in the samples depended strongly on the silane concentration and discharge power. Microcrystalline silicon thin films with higher crystallin e volume fraction has relatively higher oxygen content. Oxygen contamination of samples was also related with the background vacuum, especially for microcrystal line silicon thin films. Therefore, higher background vacuum is extremely necess ary in the fabrication of high-quality microcrystalline silicon thin films.

2,5-Dihydroxybenzoic acid: laser desorption/ionisation as a function of elevated temperature

The temperature dependence of laser desorption/ionization (LDI) ion yields has been measured for 2,5-dihydroxybenzoic acid (2,5-DHB) single crystals from room temperature to 160 °C using time-of-flight (TOF) mass spectrometry. A steep rise in ion production occurs at 90 °C, achieving a maximum at 120 °C, then decreases sharply to a minimum at 140 °C, and returns to a second maximum at 150 °C. Above 160 °C, useful information could not be obtained because of rapid volatilization of the sample into the vacuum. The overall trend in ion production, but not some of the details, is well described by a recent two-step theory of the laser desorption/ionization process, which takes into account the temperature-dependent effects of plume expansion. Measuring the background vacuum composition with a quadrupole mass spectrometer residual gas analyzer (RGA) showed an increase in thermal desorption of 2,5-DHB starting at 90 °C and maximizing at 130 °C. The increased neutral production by thermal desorption is believed to be the cause of the decrease in LDI ion production due to reduced pooling probabilities for laser-excited 2,5-DHB molecules. Thermal dehydration, condensation, and decarboxylation increase the volume of gas released at high temperatures which also serve to decrease LDI ion production at elevated temperatures. Lastly, to confirm the mass spectrometry results, the thermal desorption of 2,5-DHB single crystals under vacuum was measured using a quartz-crystal microbalance (QCM). The onset of desorption was found to occur at 90 °C and the maximum desorption rate was found at 135 °C.

Galactic systems against the background of the cosmic vacuum: Structure and evolution of the zero-acceleration surface

The structure and evolution of the zero-acceleration surface around wide triple systems of galaxies are studied in detail. (The zero-acceleration surface is the boundary separating regions in which (i) the Newtonian gravitational attraction of the galactic matter and (ii) the Einsteinian universal repulsion of the cosmic vacuum dominate.) For a typical system, this surface is spherical in shape and several megaparsecs in size, and remains nearly unchanged throughout the lifetime of the system. The concept of a boundary surface can also be extended to systems on the largest possible scales, and its general properties are discussed in relation to clusters, superclusters, and voids.

Elastic electron backscattering from Ti: grain size effect

AbstractMeasurements of elastic electron backscattering probabilities may provide the electron inelastic mean free paths (IMFP). This technique is known as elastic peak electron spectroscopy (EPES). The IMFPs in Ti can be determined from optical data by Tanuma et al., Gries or the TPP‐2M predictive formulae. Studies on Si and Ni show a weak influence of surface roughness, but a stronger influence of atomic composition, density, texture, average grain size and surface excitations on the IMFPs. In the present work, the elastic electron backscattering probability and IMFPs are determined for Ti exposed to sputtering and annealing. The atomic composition of Ti is determined by XPS and texture and grain size is determined by x‐ray diffraction (XRD). Ti samples exhibit no texture and grain size from 1 µm to 100 µm. For annealed samples the titanium hydride phase can be observed from the binding energy shift of Ti 2p XPS spectra. Scatter in the resulting IMFPs due to density and composition change (O and C contamination, and H from vacuum background) is negligible in comparison to scatter due to the grain size and standard used (Al and Cu). The IMFPs in Ti of grain size 1–10 µm are smaller than IMFPs in Ti of grain size 100 µm. These differences are explained by effects not accounted for in the calculations, i.e. the inelastic losses on the grain boundaries which are more pronounced in Ti of small grain size, and surface excitations which differ for Ti, Al and Cu. Copyright © 2004 John Wiley & Sons, Ltd.

A snapping cosmic string in a de Sitter or anti-de Sitter universe

We present and describe an exact solution of Einstein's equations which represents a snapping cosmic string in a vacuum background with a cosmological constant Λ. The snapping of the string generates an impulsive spherical gravitational wave which is a particular member of a known family of such waves. The global solution for all values of Λ is presented in various metric forms and interpreted geometrically. It is shown to represent the limit of a family of sandwich type N Robinson–Trautman waves. It is also derived as a limit of the C-metric with Λ, in which the acceleration of the pair of black holes becomes unbounded while their masses are scaled to zero.

COSMOLOGY WITH INTERACTING DARK ENERGY

The early cosmic inflation, when taken along with the recent observations that the universe is currently dominated by a low density vacuum energy, leads to at least two potential problems which modern cosmology must address. First, there is the old cosmological constant problem, with a new twist: the coincidence problem. Secondly, cosmology still lacks a model to predict the observed current cosmic acceleration and to determine whether or not there is a future exit out of this state (as previously in the inflationary case). This constitutes (what is called here) a dynamical problem. Here a framework is proposed to address these two problems, based on treating the cosmic background vacuum (dark) energy as both dynamical and interacting. The universe behaves as a vacuum-driven cosmic engine which, in search of equilibrium, always back-reacts to vacuum-induced accelerations by increasing its inertia (internal energy) through vacuum energy dissipation. The process couples cosmic vacuum (dark) energy to matter to produce future-directed increasingly comparable amplitudes in these fields by setting up oscillations in the decaying vacuum energy density and corresponding sympathetic ones in the matter fields. By putting bounds on the relative magnitudes of these coupled oscillations the model offers a natural and conceptually simple channel to discuss the coincidence problem, while also suggesting a way to deal with the dynamical problem. A result with important observational implications is an equation of state w(t) which specifically predicts a variable, quasi-periodic, acceleration for the current universe. This result can be directly tested by future observational techniques such as SNAP.

Free field dynamics in the generalized AdS (super)space

Pure gauge representation for general vacuum background fields (Cartan forms) in the generalized AdS superspace identified with OSp(L,M) is found. This allows us to formulate dynamics of free massless fields in the generalized AdS space–time and to find their (generalized) conformal and higher spin field transformation laws. Generic solution of the field equations is also constructed explicitly. The results are obtained with the aid of the star product realization of ortosymplectic superalgebras.

Very long time scales and black hole thermal equilibrium

We estimate the very long time behaviour of correlation functions in the presence of eternal black holes. It was pointed out by Maldacena (hep-th 0106112) that their vanishing would lead to a violation of a unitarity-based bound. The value of the bound is obtained from the holographic dual field theory. The correlators indeed vanish in a semiclassical bulk approximation. We trace the origin of their vanishing to the continuum energy spectrum in the presence of event horizons. We elaborate on the two very long time scales involved: one associated with the black hole and the other with a thermal gas in the vacuum background. We find that assigning a role to the thermal gas background, as suggested in the above work, does restore the compliance with a time-averaged unitarity bound. We also find that additional configurations are needed to explain the expected time dependence of the Poincar\'e recurrences and their magnitude. It is suggested that, while a semiclassical black hole does reproduce faithfully ``coarse grained'' properties of the system, additional dynamical features of the horizon may be necessary to resolve a finer grained information-loss problem. In particular, an effectively formed stretched horizon could yield the desired results.