Line Merging Research Articles

Equilibrium lines and barriers to phase transitions: the cubic diamond to beta-tin transition in Si from first principles

The phase transition between the cubic diamond (cd) and beta-tin (β-Sn) phases of Si under pressure and the region of interaction of the two phases are studied by first-principles total energy calculations. For a non-vibrating crystal we determine the pressure of the thermodynamic phase transition pt = 96 kbar, the Gibbs free energy barrier at pt of ΔG = 19.6 mRyd/atom that stabilizes the phases against a phase transition and the finite pressure range in which both phases are stable. We show that the phases in that pressure range are completely described by three equilibrium lines of states along which the structure, the total energy E, the hydrostatic pressure p that would stabilize the structure and the values of G all vary. Two equilibrium lines describe the two phases (denoted the ph-eq line, ph is cd or β-Sn phase); a third line is a line of saddle points of G with respect to structure (denoted the sp-eq line) that forms a barrier of larger G against instability of the metastable ranges of the phase lines. An important conclusion is that the sp-eq line merges with the two ph-eq lines: one end of the sp-eq line merges with the cd-eq line at high pressure, the other end merges with the β-Sn-eq line at low pressure. The mergers end the barrier protecting the metastable ranges of the two ph-eq lines, hence the lines go unstable beyond the mergers. The mergers thus simplify the phase diagram by providing a natural termination to the stable parts of all metastable ranges of the ph-eq lines. Although 96 kbar is lower than the experimental transition pressure, we note that phonon pressure raises the observed transition pressure.

Line Segment-Based Indoor Mapping with Salient Line Feature Extraction

We present a method of simultaneous localization and mapping (SLAM) in a large indoor environment using a Rao-Blackwellized particle filter (RBPF) along with a line segment as a landmark. To represent the environment in a compact form, we use only two end points of a line segment, thus reducing computational cost in modeling line segment uncertainty. With a modified scan point clustering method, the proposed adaptive iterative end point fitting contributes to the estimation of line parameters by considering noisy scan points near end points. Thus, by line segment matching the robot is localized well in a local frame. We also introduce an online and offline method of global line merging, which provides a more compact map by removing spurious lines and merging collinear lines. Each of our approaches is efficiently integrated into the proposed RBPF-SLAM framework. In experiments with well-known data sets, the proposed method provides reliable SLAM and compact map representation even in a cluttered environment.

Adaptive feature extraction and mapping for mobile robots in unknown environment

This paper proposes a new approach for feature and line extraction use in mobile robot mapping with high accuracy, efficient speed and low complexity to determine line boundaries. This algorithm called modified split and merge (MSAM) is robust against measurement noises and demonstrates satisfactory results on different surfaces. The method is based on the least square method to fit a line to a series of uncertain points. Different least square criterion is investigated to choose the best one for line extraction. A novel approach is proposed here to adopt threshold base split and merge method on different surfaces. The approach is applied to NAJI2 rescue robot for simultaneously localizing and mapping the observation of its performance. The results of this study proved that it has a good real-time capability to integrate the information of laser scanner into the navigation algorithm of the mobile robot; however, the extracted lines are suitable for object base mapping approaches. Key words: Line extraction, mapping, modified split and merge, feature extraction, fitting.

Adsorption of bovine serum albumin on amorphous carbon surfaces studied with dip pen nanolithography

This article reports the use of dip pen nanolithography (DPN) for the study of adsorption of bovine serum albumin (BSA) proteins on amorphous carbon surfaces; tetrahedral amorphous carbon (t-aC) and silicon doped hydrogenated amorphous carbon (a-C:H:Si). Contact angle study shows that the BSA proteins reduce the contact angle on both carbon materials. We also noticed that the drop volume dependence is consistent with a negative line tension, i.e. due to an attractive protein/surface interaction. The DPN technique was used to write short-spaced (100 nm) BSA line patterns on both samples. We found a line merging effect, stronger in the case of the a-C:H:Si material. We discuss possible contributions from tip blunting, scratching, cross-talk between lever torsion and bending and nano-shaving of the patterns. We conclude that the observed effect is caused in large measure by the diffusion of BSA proteins on the amorphous carbon surfaces. This interpretation of the result is consistent with the contact angle data and AFM force curve analysis indicating larger tip/surface adhesion and spreading for the a-C:H:Si material. We conclude by discussing the advantages and limitations of DPN lithography to study biomolecular adsorption in nanoscale wetting environments.

Routing Trains Through Railway Junctions

The problem of routing trains through railway junctions is an integral part of railway operations. Large junctions are highly interconnected networks of track where multiple railway lines merge, in...

Routing Trains Through Railway Junctions: A New Set-Packing Approach

The problem of routing trains through railway junctions is an integral part of railway operations. Large junctions are highly interconnected networks of track where multiple railway lines merge, intersect, and split. The number of possible routings makes this a very complicated problem. We show how the problem can be formulated as a set-packing model with a resource-based constraint system. We prove that this formulation is tighter than the conventional node-packing model, and develop a branch-and-price algorithm that exploits the structure of the set-packing model. A discussion of the variable generation phase, as well as a pricing routine in which these variables are represented by tree structures, is also described. Computational experiments on 25 random timetables show this to be an efficient approach.

Periodic variations of geomagnetic activity indices

Geomagnetic activity is generated by the interaction of the solar wind with the magnetosphere in connection with energy and mass transfer. Most observations suggest that the solar wind energy is transferred to the magnetosphere by the reconnection process at the dayside magnetopause, where oppositely directed southward IMF and northward magnetospheric magnetic field lines merge. Yearly averages of geomagnetic activity indices Ap for the years 1965 to 2009 are compared to the respective averages of v and Bx, By, Bz, where v is the solar wind velocity and Bx, By, Bz are the southward, northward and north-south component of inter- planetary magnetic field (IMF). The correlation of these quantities is known to be rather good. Comparing the averages of Ap with v and Bx, By, Bz separately we find that, during the declining phase of the solar cycle, v and during the ascending phase Bx have more influence on Ap. Analysing the daily variation of ap in an analogue manner suggesting that during phases of the solar cycle, when ap depends more on the IMF- Bx, By, Bz, components, whereas during phases when ap increases as v increases.

A Three-Dimensional Transmission Line Management System Based on TerraExplorer Pro

Aiming to the features and demands of transmission line information management and merging the remote sensing images, digital elevation model and GIS layers, this paper creates a three-dimensional scene of transmission line, which takes TerraExplorer Pro as basic platform and combines the attribute information of transmission line, and develops an interactive and visualized management system which is oriented to power system. The system realizes the 3D display, query and analysis of transmission line and provides the integrated supports to the design, construction, operation and maintenance at a certain extent

Evolution of the magnetic field–temperature phase diagram inUAs1−xSex

The evolution of the magnetic field--temperature phase diagram of ${\text{UAs}}_{1\ensuremath{-}x}{\text{Se}}_{x}$ with $x$ in the range of 0--0.1 is studied by means of magnetocaloric and specific-heat measurements. Our interest is focused on the high-temperature phase transitions and especially on the point, where the paramagnetic (P) and two ordered phases meet. For undoped UAs these two ordered states are the ferrimagnetic (Fi) and the type-I antiferromagnetic phases. According to Sinha et al. [Phys. Rev. Lett. 45, 1028 (1980)] the antiferromagnetic phase transition is in the vicinity of a Lifshitz point. Furthermore, Kuznietz et al. [J. Magn. Magn. Mater. 61, 246 (1986)] showed that an incommensurate phase (IC) emerges between the type-I (or type-IA) antiferromagnetic and paramagnetic phases in the case of ${\text{UAs}}_{1\ensuremath{-}x}{\text{Se}}_{x}$ with $0<x<0.15$ in zero magnetic field. The results reported in this paper show the existence of a ${T}_{\text{Fi}/\text{IC}}(B)$ line that separates the ferrimagnetic region from a phase, which cannot be identified on the basis of our thermodynamic measurements. However, one may assume it is the IC phase, consistent with the above mentioned zero field results. The ${T}_{\text{Fi}/\text{IC}}(B)$ line merges with the order-disorder line at point $({B}_{p},{T}_{p})$, where the critical line (IC/P) meets with two first order transitions lines: Fi/P and Fi/IC. This point can be considered as an analog of a Lifshitz point. A simple phenomenological description of the phase transitions near this special point is provided.

Disconnected Glass-Glass Transitions and Diffusion Anomalies in a Model with Two Repulsive Length Scales

Building on mode-coupling-theory calculations, we report a novel scenario for multiple glass transitions in a purely repulsive spherical potential: the square shoulder. The liquid-glass transition lines exhibit both melting by cooling and melting by compression as well as associated diffusion anomalies, similar to the ones observed in water. Differently from all previously investigated models, we find for small shoulder widths a glass-glass line that is disconnected from the liquid phase. Upon increasing the shoulder width such a glass-glass line merges with the liquid-glass transition lines, featuring two distinct end point singularities that give rise to logarithmic decays in the dynamics. We analytically explain these findings by considering the interplay of different repulsive length scales.

Growth and properties of tin oxide nanowires and the effect of annealing conditions

Luminescence data obtained in the visible region from the SnO2 nanowires are used to determine the defect levels within the bandgap responsible for the strong orange emission, and a shift in the orange luminescence is seen at low temperatures. Temperature-dependent photoluminescence (PL) in the UV region shows the merging of the various emission lines at low temperature into a single broad UV peak with increasing temperatures. Investigations of PL and transmission electron microscope-energy dispersive x-ray spectroscopy (TEM-XEDS) from wires of different diameters show that the luminescence in the gap originates from surface states and thinner wires have more oxygen vacancies compared to thicker ones. Nanowires post rapid thermal annealing in two different ambients viz. oxygen and nitrogen are compared, using Raman, photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS) as characterization tools. Our data demonstrate that annealing in oxygen improves the crystalline quality of the nanowires due to the decrease in the oxygen vacancies.

True and quasi-long-range order in the generalizedq-state clock model

From consideration of the order-parameter distribution, we propose an observable which makes a clear distinction between true and quasi-long-range orders in the two-dimensional generalized q-state clock model. Measuring this quantity by Monte Carlo simulations for q=8, we construct a phase diagram and identify critical properties across the phase-separation lines among the true long-range order, quasi-long-range order, and disorder. Our result supports the theoretical prediction that there appears a discontinuous order-disorder transition as soon as the two phase-separation lines merge.

Opacity and radiative power losses calculations

In this contribution we present results on opacity and radiative power losses in laser-produced plasmas. We focus our attention on the inner shell transition array 1 s–2 p in an aluminum plasma. At high densities, electron, Doppler and ion Stark broadening play a role in line merging. This is why the PPP line-shape code developed at Université de Provence was adapted to calculate opacity and radiative power losses in Al and Ge ions. Atomic physics data required in PPP calculations is provided by an MCDF code. Comparison with experiments is discussed.

Knot solitons in the AFZ model

This paper studies the topological properties of knotted solitons in the (3 + 1)-dimensional Aratyn–Ferreira–Zimerman (AFZ) model. Topologically, these solitons are characterized by the Hopf invariant I, which is an integral class in the homotopy group π3(S3) = Z. By making use of the decomposition of U(1) gauge potential theory and Duan's topological current theory, it is shown that the invariant is just the total sum of all the self-linking and linking numbers of the knot family while only linking numbers are considered in other papers. Furthermore, it is pointed out that this invariant is preserved in the branch processes (splitting, merging and intersection) of these knot vortex lines.

Rimertown / an atlas by Laura Walker

173 Book Notes Rimertown / an atlas, by Laura Walker University of California Press, 2008 reviewed by Sharon Lynn Osmond Walking this morning in the shaggy plenitude of my garden, I thought about Laura Walker’s poems. As on previous days during the past few months, phrases from her second collection, Rimertown / an atlas, filled my head. The poems in this book have become as palpable to me as the plants that lean into this path and in many ways as and troubling and unruly. Today, on my left I noticed a thickened clot of foliage and bent to examine it. Under a buoyant green spill of Geranium sylvaticum were layers of brittle, brown decay—an accrual of several seasons. Under these layers, on a jagged rock, was a forgotten pair of high-heeled sandals. Their green insoles were curled now and their green leather rotting. Perched there, the shoes seemed to punctuate a rift between disparities: an upright, rusty cylinder and a sprawling patch of wild pink geraniums. Seeing them, I remembered the staccato click of my mother’s high heels as she walked back and forth across our kitchen’s blue linoleum, slender and red-lipped, unaware that she had come to the edge of a landscape that would soon thicken with personal sorrow. Green Shoes. Memory. Decay. Resurrection. The “dark ground of cognition.” Buried layers of memory inform Laura Walker’s work of inquiry in Rimertown / an atlas. In poems titled “map” or “story ” and in untitled prose paragraphs, she excavates the site of her childhood in rural North Carolina, disturbing and finally destroying boundaries between geography and psyche. Her probing is intrusive and risky, pushing her again and again into a breach where consciousness is vertiginous and the retrieval of knowledge is dangerous. In “Map 42,” for example, Walker explores falling into what might be seen as an afterworld: . . . in falling off the edge sinewy and stiff, lines merging we come back to idea parchment CRSP09 nonfiction.indd 173 1/30/2009 12:55:49 PM colorado review 174 “Edge” marks a wilderness where landscape, thought, and written word bleed into each other. Falling is prelude to entering perplexity, necessary preparation for learning to live darkly underground among roots where plotted site-lines and the waking logic of narrative purpose have blurred and disappeared (“come down, oh come down”). Walker’s investigative poetics is careful, deliberate, lyrical. It is also ragged and paratactic, housing fragments of remembered conversations and shards of half-understood stories. The poems become an archive of vernacular echoes where the singularities of an inscribed landscape reside. This landscape, mapped and given, has sunk under layers of history and human experience. It is a place where sentences veer away from their teleological goal and wander instead off course and into a syntactic realm of illogic and uncertainty (“carried stairwise, back pasture / collated . collected, its leaves and thistles”). Like Thomas Hardy’s Egdon Heath, Rimertown broods and seems quasi-conscious. It is an entelechy that casts its dark presence over the lives of its inhabitants (“we are in its shadows”). Its world is field, and field is contained, not within boundaries mapped on parchment merely, but within lines of ephemeral , blue inflorescence as well: “bachelor buttons lining the field”; “cornflowers towing the field”; “morning glory buttons the fields”; “morning glories choke the field.” Place guards its own stasis (“fences radiating inertia”), and yet it is endemically haunted and disordered—a surreal tenement for the random and disorganized: “there were hundreds of brown dresses floating among crows”; “thrift spilling its banks, a chimney where nevermore.” And it preserves a troubling kind of “oneness” (atonement?) with its denizens (“we sat down and fed ourselves dirt”). Body ingests landscape; body inscribes upon itself the map of place (“added line to line, increments of flesh”). Within such oneness, fracture is violent. Dreaming gives way to waking , to “seeing,” painfully: hands held fervently against the face that in knotting. in knowing red sorrows and awake Tension between desire and act, rising and falling, death and CRSP09 nonfiction.indd 174 1/30/2009 12:55:49 PM 175 Book Notes resurrection articulates an informing duality, and associated with this duality is...

Linear colloidal crystal arrays by electrohydrodynamic printing

We use electrohydrodynamic jets of colloidal suspensions to produce arrays of colloidal crystalline stripes on surfaces. A critical factor in maintaining a stable jet is the distance of separation between the nozzle and the surface. Colloidal crystalline stripes are produced as two wetting lines of the deployed suspension merge during drying. To ensure that the two wetting lines merge, the “deployed-line-width” to “particle size” ratio is kept below a critical value so that the capillary forces overcome the frictional forces between the particles and the substrate.

Time- and spatially-resolved characterization of electrical discharge machining plasma

Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and with time- and spatially-resolved optical emission spectroscopy. After the breakdown, the plasma develops very fast (<50 ns) and then remains stable. The plasma excites a broad volume around the electrode gap. Light is still emitted after the discharge by incandescent liquid metallic particles coming from the erosion of the workpiece. Typical plasma spectra show a strong Hα and continuum radiation, with many lines emitted by impurities coming from electrodes materials. The plasma is thus composed of species coming from the cracking of the dielectric molecules, mainly hydrogen, with contamination from the electrodes. This contamination is mostly concentrated in the vicinity of the electrodes. The electron density reaches 2 × 1018 cm−3 at the beginning of the discharge. This extreme density causes merging of lines, strong Stark broadening and shift of the Hα line. The density decreases afterwards rapidly with time, remaining nevertheless above 1016 cm−3 after 50 µs. The electron temperature remains roughly constant around 0.7 eV in the whole plasma. The low temperature, the high density measured and other spectroscopic evidence prove that the EDM plasma is weakly non-ideal (Γ ≃ 0.33).

X-ray absorption spectroscopy for the study of spatial Mn ion distribution in diluted magnetic semiconductors and discrete heterostructures

The X-ray K spectra of Mn absorption were used for Mn ion distribution in (Ga, Mn)N. According to the performed calculations, two threshold lines were observed in the K spectra of (Ga, Mn)N crystals with uniform Mn ion distribution. If Mn ions form chains, these two threshold lines merge into one broad line.

Ionospheric signatures of internal reconnection for northward interplanetary magnetic field: Observation of “reciprocal cells” and magnetosheath ion precipitation

Magnetic reconnection that involves overdraped lobe field lines is called internal reconnection since it occurs inside the magnetopause. When the interplanetary magnetic field (IMF) is due northward and the Earth's dipole is tilted significantly, internal reconnection occurs in the winter hemisphere, not only between a summer lobe field line and a winter lobe field line but also between a summer lobe field line and a closed field line. The latter internal reconnection drives “reciprocal cells” in the winter ionosphere that circulate exclusively in the closed field line region. The reciprocal cells are intimately related to the lobe cells in the summer ionosphere in that in the steady state, the reconnection voltage associated with merging of IMF and open field lines is equal to the sum of the lobe cell potential and the reciprocal cell potential. In this paper we present observations of convection patterns consistent with those expected for reciprocal cells, using ionospheric radar and low‐altitude satellite data. We also show the concurrence of lobe cells and reciprocal cells. The observations of reciprocal cells provide support for the internal reconnection between a summer lobe field line and a closed field line. In addition, we show that equatorward of the polar cap boundary, magnetosheath‐like ions are drifting from noon toward the flankside in both hemispheres. We suggest that these ions are of magnetosheath origin and that they entered the closed region of the magnetosphere through the rotational discontinuity associated with internal reconnection. These magnetosheath‐like ion observations strongly support the occurrence of internal reconnection.

Theoretical calculation of saturated absorption spectra for multi-level atoms

We have developed a model for calculating saturated absorption spectra for dipole transitions in multi-level atoms. Using a semiclassical density matrix formalism, we derive a set of coupled differential equations for the internal state of the atom in a standing wave light field. The equations are solved using standard integration techniques. The absorption at each laser detuning is found from an average of the absorption for a number of velocities along the laser field, thermally weighted. The method is relatively efficient computationally yet quantitatively predicts important details of saturated absorption spectra including saturation, crossover resonances, merging of absorption lines at high intensity and optical pumping between hyperfine levels. We have measured saturated absorption and fluorescence spectra of 85Rb, and compare to our computational results for a 36-level model.