Simple Reference System Research Articles

Self-energy functional theory with symmetry breaking for disordered lattice bosons

We extend the self-energy functional theory to the case of interacting lattice bosons in the presence of symmetry breaking and quenched disorder. The self-energy functional we derive depends only on the self-energies of the disorder-averaged propagators, allowing for the construction of general non-perturbative approximations. Using a simple single-site reference system with only three variational parameters, we are able to reproduce numerically exact quantum Monte Carlo (QMC) results on local observables of the Bose–Hubbard model with box disorder with high accuracy. At strong interactions, the phase boundaries are reproduced qualitatively but shifted with respect to the ones observed with QMC due to the extremely low condensate fraction in the superfluid phase. Deep in the strongly-disordered weakly-interacting regime, the simple reference system employed is insufficient and no stationary solutions can be found within its restricted variational subspace. By systematically analyzing thermodynamical observables and the spectral function, we find that the strongly interacting Bose glass is characterized by different regimes, depending on which local occupations are activated as a function of the disorder strength. We find that the particles delocalize into isolated superfluid lakes over a strongly localized background around maximally-occupied sites whenever these sites are particularly rare. Our results indicate that the transition from the Bose glass to the superfluid phase around unit filling at strong interactions is driven by the percolation of superfluid lakes which form around doubly occupied sites.

Hyperfine interaction in the Autler-Townes effect: The formation of bright, dark, and chameleon states

This paper is devoted to clarifying the implications of hyperfine (HF) interaction in the formation of adiabatic (i.e., ``laser-dressed'') states and their expression in the Autler-Townes (AT) spectra. We first use the Morris-Shore model [J. R. Morris and B. W. Shore, Phys. Rev. A 27, 906 (1983)] to illustrate how bright and dark states are formed in a simple reference system where closely spaced energy levels are coupled to a single state with a strong laser field with the respective Rabi frequency ${\mathrm{\ensuremath{\Omega}}}_{S}$. We then expand the simulations to realistic hyperfine level systems in Na atoms for a more general case when non-negligible HF interaction can be treated as a perturbation in the total system Hamiltonian. A numerical analysis of the adiabatic states that are formed by coupling of the $3{p}_{3/2}$ and $4{d}_{5/2}$ states by the strong laser field and probed by a weak laser field on the $3{s}_{1/2}\ensuremath{-}3{p}_{3/2}$ transition yielded two important conclusions. Firstly, the perturbation introduced by the HF interaction leads to the observation of what we term ``chameleon'' states---states that change their appearance in the AT spectrum, behaving as bright states at small to moderate ${\mathrm{\ensuremath{\Omega}}}_{S}$, and fading from the spectrum similarly to dark states when ${\mathrm{\ensuremath{\Omega}}}_{S}$ is much larger than the HF splitting of the $3{p}_{3/2}$ state. Secondly, excitation by the probe field from two different HF levels of the ground state allows one to address orthogonal sets of adiabatic states; this enables, with appropriate choice of ${\mathrm{\ensuremath{\Omega}}}_{S}$ and the involved quantum states, a selective excitation of otherwise unresolved hyperfine levels in excited electronic states.

Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays

The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime ( fs) at moderate intensities W cm−2 and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as W cm−2, such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales.

Nonequilibrium variational-cluster approach to real-time dynamics in the Fermi-Hubbard model

The nonequilibrium variational-cluster approach is applied to study the real-time dynamics of the double occupancy in the one-dimensional Fermi-Hubbard model after different fast changes of hopping parameters. A simple reference system, consisting of isolated Hubbard dimers, is used to discuss different aspects of the numerical implementation of the approach in the general framework of nonequilibrium self-energy functional theory. Opposed to a direct solution of the Euler equation, its time derivative is found to serve as numerically tractable and stable conditional equation to fix the time-dependent variational parameters.

Field-Cycling Relaxometry as a Molecular Rheology Technique: Common Analysis of NMR, Shear Modulus and Dielectric Loss Data of Polymers vs Dendrimers

Linear poly(propylene glycol) (PPG) as well as a poly(propyleneimine) (PPI) dendrimer with different molar masses (M) are investigated by field-cycling (FC) 1H NMR, shear rheology (G) and dielectric spectroscopy (DS). The results are compared in a reduced spectral density representation: the quantity R1(ωτα)/R1α(0), where R1(ωτα) is the master curve of the frequency dependent spin–lattice relaxation rate with τα denoting the local correlation time, is compared to the rescaled dynamic viscosity η′(ωτα)/η′α(0). The quantities R1α(0) and η′α(0), respectively, are the zero-frequency limits of a simple liquid reference system. Analogously, the dielectric loss data can be included in the methodological comparison. This representation allows quantifying the sensitivity of each method with respect to the polymer-specific relaxation contribution. Introducing a “cumulative mode ratio” Fi(M) for each technique i, which measures the zero-frequency plateau of the rescaled spectral density, characteristic power-law beh...

Structure determination of liquid carbon tetrabromide via a combination of x-ray and neutron diffraction data and Reverse Monte Carlo modelling

In order to reveal the atomic level structure of liquid carbon tetrabromide, a new synchrotron x-ray diffraction measurement, over a wide momentum transfer (Q-)range, has been performed. These x-ray data have been interpreted together with a neutron diffraction dataset, measured earlier, using the Reverse Monte Carlo method. The structure is analysed on the basis of partial radial distribution functions and distance dependent orientational correlation functions. Orientational correlations behave similarly to other carbon tetrahalides. Moreover, the information content of the new x-ray diffraction dataset, and in particular, of the varying Q-range, is also discussed.Only very small differences have been found between the results of calculations that apply one single experimental structure factor and the ones that use both x-ray and neutron diffraction data: the latter showed slightly more ordered carbon–carbon radial distribution function, which resulted in seemingly more ordered orientational correlations between pairs of molecules. Neither the extended Q-range, nor the application of local invariance constraints yielded significant new information. For providing a simple reference system, a hard sphere model has also been created that can describe most of the partial radial distribution functions and orientational correlations of the real system at a semi-quantitative level.

Kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB): the influence of interfacial transport and bulk diffusion on the oxidation of oleic acid by ozone

Abstract. We present a novel kinetic multi-layer model that explicitly resolves mass transport and chemical reaction at the surface and in the bulk of aerosol particles (KM-SUB). The model is based on the PRA framework of gas-particle interactions (Pöschl-Rudich-Ammann, 2007), and it includes reversible adsorption, surface reactions and surface-bulk exchange as well as bulk diffusion and reaction. Unlike earlier models, KM-SUB does not require simplifying assumptions about steady-state conditions and radial mixing. The temporal evolution and concentration profiles of volatile and non-volatile species at the gas-particle interface and in the particle bulk can be modeled along with surface concentrations and gas uptake coefficients. In this study we explore and exemplify the effects of bulk diffusion on the rate of reactive gas uptake for a simple reference system, the ozonolysis of oleic acid particles, in comparison to experimental data and earlier model studies. We demonstrate how KM-SUB can be used to interpret and analyze experimental data from laboratory studies, and how the results can be extrapolated to atmospheric conditions. In particular, we show how interfacial and bulk transport, i.e., surface accommodation, bulk accommodation and bulk diffusion, influence the kinetics of the chemical reaction. Sensitivity studies suggest that in fine air particulate matter oleic acid and compounds with similar reactivity against ozone (carbon-carbon double bonds) can reach chemical lifetimes of many hours only if they are embedded in a (semi-)solid matrix with very low diffusion coefficients (≤10−10 cm2 s−1). Depending on the complexity of the investigated system, unlimited numbers of volatile and non-volatile species and chemical reactions can be flexibly added and treated with KM-SUB. We propose and intend to pursue the application of KM-SUB as a basis for the development of a detailed master mechanism of aerosol chemistry as well as for the derivation of simplified but realistic parameterizations for large-scale atmospheric and climate models.

Development of a Peptide Probe for the Occurrence of Hydrogen (1H/2H) Scrambling upon Gas-Phase Fragmentation

Hydrogen (1H/2H) exchange combined with mass spectrometry (HX-MS) has become a valuable method for the analysis of protein structural dynamics. Currently, localization of the incorporated deuterons is made by enzymatic cleavage of the labeled proteins, and single-residue resolution is typically only achieved for a few residues. Determination of site-specific deuterium levels by gas-phase fragmentation would greatly increase the applicability of the HX-MS method. It is, however, mandatory for this gas-phase approach that hydrogen (1H/2H) scrambling in the gaseous peptide is negligible. Thus, it is important to have a simple reference system where the onset of scrambling processes is readily detected. Here we describe a simple well-characterized set of peptides with a unique regioselective labeling that ensures an inherent high sensitivity for the detection of scrambling. This selective labeling is achieved by utilizing differences in the intrinsic exchange rates between various amino acid residues. We demonstrate that our peptides can be infused directly into an electrospray ion source by means of a cooled glass syringe, while maintaining their selective labeling in solution. We further show that the selective labeling is completely erased upon low-energy collisional activation in a tandem mass spectrometry experiment as a result of extensive hydrogen (1H/2H) scrambling.

Iron under Earth’s core conditions: Liquid-state thermodynamics and high-pressure melting curve fromab initiocalculations

{\em Ab initio} techniques based on density functional theory in the projector-augmented-wave implementation are used to calculate the free energy and a range of other thermodynamic properties of liquid iron at high pressures and temperatures relevant to the Earth's core. The {\em ab initio} free energy is obtained by using thermodynamic integration to calculate the change of free energy on going from a simple reference system to the {\em ab initio} system, with thermal averages computed by {\em ab initio} molecular dynamics simulation. The reference system consists of the inverse-power pair-potential model used in previous work. The liquid-state free energy is combined with the free energy of hexagonal close packed Fe calculated earlier using identical {\em ab initio} techniques to obtain the melting curve and volume and entropy of melting. Comparisons of the calculated melting properties with experimental measurement and with other recent {\em ab initio} predictions are presented. Experiment-theory comparisons are also presented for the pressures at which the solid and liquid Hugoniot curves cross the melting line, and the sound speed and Gr\"{u}neisen parameter along the Hugoniot. Additional comparisons are made with a commonly used equation of state for high-pressure/high-temperature Fe based on experimental data.

A very simple structure for neural network control of distillation

This paper presents a novel approach for process control that uses neural networks to model the steady-state inverse of a process which is then coupled with a simple reference system synthesis to generate a multivariable controller. The control strategy is applied to dynamic simulations of two methanol-water distillation columns that express distinctly different behaviour from each other (one simulates a lab column, while the second simulates an industrial-scale high-purity column). A steady-state process simulation package was used to generate all the neural network training data. An efficient training algorithm based on a nonlinear least-squares technique was used to train the networks. The neural network model-based controllers show robust performance for both setpoints and disturbances, and performed better than conventional feedback proportional-integral (PI) controllers with feedforward features.

Resummations in Hot Scalar Electrodynamics

The gauge-boson sector of perturbative scalar electrodynamics is investigated in detail as a testing ground for resummation methods in hot gauge theories. It also serves as a simple non-trivial reference system for the non-Abelian gluon plasma. The complete next-to-leading order contributions to the polarization tensor are obtained within the resummation scheme of Braaten and Pisarski. The simpler scheme proposed recently by Arnold and Espinosa is shown to apply to static quantities only, whereas Braaten-Pisarski resummation turns out to need modification for collective phenomena close to the light-cone. Finally, a recently proposed resummation of quasi-particle damping contributions is assessed critically.

Dependence of peripheral and central parameters describing handwriting generation on movement direction

This paper studies the dependence of parameters of the trajectory formation process in goal-directed line drawing movement on the orientation of such lines in a planar surface. Based on a handwriting generation model developed earlier, movement parameters are extracted directly from on-line recordings of velocity profiles. These parameters, which either reflect peripheral or central processes, are found to be highly dependent upon the direction of movement. Further, it is shown that asymmetries as found do not suggest a simple reference system of two bipolar principal motor axes, contrary to claims by many model developers to be characteristic for writing movements. The strategy used by the subjects to compensate for the anisotropy of their biomechanical system is comparable to other studies on aimed movement. These results support the idea that a generation model with anistropic properties reflecting the global interaction among the various muscles and nerves involved in the process seems to be more appropriate to study handwriting.

Now where did I put that paper?: A simple reference system for accident and emergency medicine related papers and publications.

Now where did I put that paper?: A simple reference system for accident and emergency medicine related papers and publications.

Processing of auditory information by the blind in spatial localization tasks.

Spatial localization of sonorous targets in the near space, by blindfolded sighted subjects and by early- or late-blind subjects, was investigated using a two-dimensional coordinate system (direction and distance) in various experimental conditions: The head was free or restrained, and the subject’s response was either a finger pointing on a coordinate grid in open loop or a verbal assessment based on a simple reference system. The results for each group of subjects were processed by dealing separately with distance and direction parameters. They show that with early blinds, only the distance evaluation was particularly impaired. Performance did not seem to depend much on whether the head was restrained or free. Finally, direction was best evaluated by motor responses, whereas distance was more accurately judged verbally.

Representation of quantum mechanical wavefunctions by transformation generators. III. Canonical transformations in an extended phase space

For pt.II see ibid., vol.16, no.7, p.1397-408 (1983). It is shown how quantum mechanical wavefunctions can be obtained from a sequence of simple canonical transformations, which map the given system onto a simple reference system. The resulting wavefunctions are at least uniformly valid up to order h(cross). Under some more restrictive conditions for the individual transformation steps the authors even find the exact wavefunctions. The essential point of the paper is to enlarge the conventional coordinate-momentum phase space by taking time and energy as an additional conjugate pair. In this extended space they exploit the possibility of using transformations which intermix energy and time with position coordinates and momenta. Compared with transformations in the conventional position-momentum phase space, they gain the advantage that scattering states and bound states can be treated in a unified way. Therefore this method is appropriate for systems with mixed spectra. In addition it allows for more flexibility in choosing the individual transformation steps. The practicability of the method is demonstrated by several examples.

A numericlature of the yeasts.

A numericlature, based on a descriptive numerical code has been compiled for the yeasts. A total of 429 yeast species are represented by 389 unique four-, six- or seven-digit numbers and of these 364 correspond to single species. It is suggested that the coding method is a valid alternative to binomial nomenclature based on a conventional hierarchical classification. It can serve as a simple reference system and can be used practically as a means of differentiating between large numbers of new isolates of yeasts.

Pseudopotential band structure calculation for a linear chain

A method is proposed for calculating the energy spectrum for a rather general type of well, of which the potentials encountered in molecules and thin films may be considered representative. The procedure is to introduce a simple reference system and corresponding perturbation series. The parameters defining the reference potential are chosen by optimizing the perturbed energy, to first order, which is of standard variational form. Then higher terms in the series provide systematic corrections. Tests on simple cases, where exact solutions are known, suggest that second-order energies should be nowhere in error by greater than 4%. The procedure is then applied to a linear chain of pseudoatoms and the band structure for sodium is considered. The result is a very free-electron-like picture for the occupied states but with (m*/m)-1 strongly influenced by virtual transverse excitations.

A standard reference system for spatial vectorcardiography. Comparison of the equilateral tetrahedron and the Frank systems

The sVCG was recorded with both the equilateral tetrahedral and Frank reference systems and carefully studied in 450 patients and normal subjects, the hearts of 30 of these patients being studied carefully at autopsy. Ninety of the patients were geriatric, and all of the other patients had organic heart disease. The sVCG recorded with the two systems were remarkably similar in most instances. However, in many patients with heart disease the tetrahedron produced recordings which were more abnormal than those produced with the Frank system. In only one of the group of sVCG studied with wire models did the Frank system provide more clinical assistance than the tetrahedron, but the tetrahedron was more helpful clinically in detecting cardiac disease in many instances. The latter was especially true in the geriatric patients whose electrocardiograms appeared to be even normal in some instances. The study of these 450 people indicates that for practical clinical purposes the equilateral tetrahedral reference system is definitely superior to the Frank system. The technicians found the tetrahedron to be easier to employ. The back electrode was the only other electrode needed when recording the sVCG with the ECG. This back electrode was easy to place reliably and reproducibly. The Frank system was difficult and at times impossible to employ accurately in newborn infants, obese patients with small or large hearts, patients with deformed chests, very ill people, and in postoperative patients with dressings on the chest. The sVCG recorded with the equilateral tetrahedral system in general revealed abnormalities of the heart earlier and with greater disturbance in contour, direction of rotation, and spatial orientation than the sVCG recorded with the Frank system. The Frank system tended to make the contour of the complexes smooth, thus erasing early and definite irregularities and distortions in configuration which were often related to myocardial disease. We strongly advise the use of the equilateral tetrahedron as the standard system for clinical vectorcardiography the world over. Until a simple, easy, reliable, and reproducible reference system such as the equilateral tetrahedron is accepted for general clinical use, vectorcardiography is unlikely to become a useful routine procedure in clinical practice in hospitals, clinics, and physicians' offices.

LETTERS OF FATHER THOMAS INNES ABOUT THE ARCHIVES OF THE CHURCH OF GLASGOW

It is unnecessary in the pages of this Review to say much by way of introduction to the letters which follow. Several descriptions already exist of the work of Father Thomas Innes in looking after the documents taken in 1560 by Archbishop Beaton from Glasgow to Paris.1 But these letters are valuable for the details which they add to the story. They give, for example, a description of the documents as found by fnnes including (in Letter 2, paragraph 1) an indication that they were originally preserved in series under the respective lands concerned. This arrangement would be the natural one for the medieval custodians of the Glasgow archives, but it presented difficulties for Innes in his work of arrangement. The letters also reveal Innes' approach to problems of document preservation and charter study. He paid much attention to the physical safety of the documents, and especially of their seals. He outlines a simple but effective reference system, which enables one document to be consulted without touching, tossing or casting the next. He tackles the problems of transcription and adopts a rule about spelling based on contemporary authorities