63 research outputs found
Quantum corrections to the noncommutative kink
We calculate quantum corrections to the mass of noncommutative phi^4 kink in
(1+1) dimensions for intermediate and large values of the noncommutativity
parameter theta. All one-loop divergences are removed by a mass renormalization
(which is different from the one required in the topologically trivial sector).
For large theta quantum corrections to the mass grow linearly with theta
signaling about possible break down of the perturbative expansion.Comment: 18 pages, v2: minor change
Solitary Waves in Massive Nonlinear SN-Sigma Models
The solitary waves of massive (1+1)-dimensional nonlinear SN-sigma models are unveiled. It is shown that the solitary waves in these systems are in one-to-one correspondence with the separatrix trajectories in the repulsive N-dimensional Neumann mechanical problem. There are topological (heteroclinic trajectories) and non-topological (homoclinic trajectories) kinks. The stability of some embedded sine-Gordon kinks is discussed by means of the direct estimation of the spectra of the second-order fluctuation operators around them, whereas the instability of other topological and non-topological kinks is established applying the Morse index theorem
Supersymmetry and Integrability in Planar Mechanical Systems
We present an N=2-supersymmetric mechanical system whose bosonic sector, with
two degrees of freedom, stems from the reduction of an SU(2) Yang-Mills theory
with the assumption of spatially homogeneous field configurations and a
particular ansatz imposed on the gauge potentials in the dimensional reduction
procedure. The Painleve test is adopted to discuss integrability and we focus
on the role of supersymmetry and parity invariance in two space dimensions for
the attainment of integrable or chaotic models. Our conclusion is that the
relationships among the parameters imposed by supersymmetry seem to drastically
reduce the number of possibilities for integrable interaction potentials of the
mechanical system under consideration.Comment: 20 pages, 3 figure
Waves, boosted branes and BPS states in M-theory
Certain type II string non-threshold BPS bound states are shown to be related
to non-static backgrounds in 11-dimensional theory. The 11-d counterpart of the
bound state of NS-NS and R-R type IIB strings wound around a circle is a pure
gravitational wave propagating along a generic cycle of 2-torus. The extremal
(q_1,q_2) string with non-vanishing momentum along the circle (or infinitely
boosted black string) corresponds in D=11 to a 2-brane wrapped around 2-torus
with momentum flow along the (q_1,q_2) cycle. Applying duality transformations
to the string-string solution we find type IIA background representing a bound
state of 2-brane and 0-brane. Its lift to 11 dimensions is simply a 2-brane
finitely boosted in transverse direction. This 11-d solution interpolates
between a static 2-brane (zero boost) and a gravitational wave in 11-th
dimension (infinite boost). Similar interpretations are given for various bound
states involving 5-branes. Relations between transversely boosted M-branes and
1/2 supersymmetric non-threshold bound states 2+0 and 5+0 complement relations
between M-branes with momentum in longitudinal direction and 1/4 supersymmetric
threshold bound states 1+0 and 4+0. In the second part of the paper we
establish the correspondence between the BPS states of type IIB strings on a
circle and oscillating states of a fundamental supermembrane wrapped around a
2-torus. We show that the (q_1,q_2) string spectrum is reproduced by the
membrane BPS spectrum, determined using a certain limit. This supports the
picture suggested by Schwarz.Comment: 26 pages, harvmac (minor corrections; T-duality relation between IIB
string-string solution and boosted 0-brane made explicit
On BPS preons, generalized holonomies and D=11 supergravities
We develop the BPS preon conjecture to analyze the supersymmetric solutions
of D=11 supergravity. By relating the notions of Killing spinors and BPS
preons, we develop a moving G-frame method (G=GL(32,R), SL(32,R) or Sp(32,R))
to analyze their associated generalized holonomies. As a first application we
derive here the equations determining the generalized holonomies of k/32
supersymmetric solutions and, in particular, those solving the necessary
conditions for the existence of BPS preonic (31/32) solutions of the standard
D=11 supergravity. We also show that there exist elementary preonic solutions,
i.e. solutions preserving 31 out of 32 supersymmetries in a Chern--Simons type
supergravity. We present as well a family of worldvolume actions describing the
motion of pointlike and extended BPS preons in the background of a D'Auria-Fre
type OSp(1|32)-related supergravity model. We discuss the possible implications
for M-theory.Comment: 11 pages, RevTeX Typos corrected, a short note and references adde
Generalized Global Defect Solutions
We investigate the presence of defect structures in generalized models
described by real scalar field in space-time dimensions. We work with
two distinct generalizations, one in the form of a product of functions of the
field and its derivative, and the other as a sum. We search for static
solutions and study the corresponding linear stability on general grounds. We
illustrate the results with several examples, where we find stable defect
structures of modified profile. In particular, we show how the new defect
solutions may give rise to evolutions not present in the standard scenario in
higher spatial dimensions.Comment: RevTex, 10 pages, 2 figures; version to appear in EPJ
Comprehensive Comparison of Various Techniques for the Analysis of Elemental Distributions in Thin Films
The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limit
Thermodynamics of phantom energy in the presence of a Reissner-Nordstrom black hole
In this paper, we study the validity of the generalized second law (GSL) in
phantom dominated universe in the presence of a Reissner-Nordstr\"{o}m (RN)
black hole. Our study is independent of the origin of the phantom like behavior
of the considered universe. We also discuss the GSL in the neighborhood of
transition from quintessence to phantom regime. We show that for a constant
equation of state parameter, the GSL may be satisfied provided that the
temperature is proportional to de Sitter temperature. It is shown that in
models with (only) a transition from quintessence to phantom regime the
generalized second law does not hold in the transition epoch. Next we show that
if the phantom energy has a chemical potential, then the GSL will hold if the
mass of black hole is above from a critical value.Comment: 5 pages, Accepted for publication in Astrophysics & Space Scienc
Active fixturing: literature review and future research directions
Fixtures are used to fixate, position and support workpieces and represent a crucial tool in manufacturing. Their performance determines the result of the whole manufacturing process of a product. There is a vast amount of research done on automatic fixture layout synthesis and optimisation and fixture design verification. Most of this work considers fixture mechanics to be static and the fixture elements to be passive. However, a new generation of fixtures has emerged that has actuated fixture elements for active control of the part–fixture system during manufacturing operations to increase the end product quality. This paper analyses the latest studies in the field of active fixture design and its relationship with flexible and reconfigurable fixturing systems. First, a brief introduction is given on the importance of research of fixturing systems. Secondly, the basics of workholding and fixture design are visited, after which the state-of-the-art in active fixturing and related concepts is presented. Fourthly, part–fixture dynamics and design strategies which take these into account are discussed. Fifthly, the control strategies used in active fixturing systems are examined. Finally, some final conclusions and prospective future research directions are presented
J-PLUS: The javalambre photometric local universe survey
ABSTRACT: TheJavalambrePhotometric Local UniverseSurvey (J-PLUS )isanongoing 12-band photometricopticalsurvey, observingthousands of squaredegrees of theNorthernHemispherefromthededicated JAST/T80 telescope at the Observatorio Astrofísico de Javalambre (OAJ). The T80Cam is a camera with a field of view of 2 deg2 mountedon a telescopewith a diameter of 83 cm, and isequippedwith a uniquesystem of filtersspanningtheentireopticalrange (3500–10 000 Å). Thisfiltersystemis a combination of broad-, medium-, and narrow-band filters, optimallydesigned to extracttherest-framespectralfeatures (the 3700–4000 Å Balmer break region, Hδ, Ca H+K, the G band, and the Mg b and Ca triplets) that are key to characterizingstellartypes and delivering a low-resolutionphotospectrumforeach pixel of theobservedsky. With a typicaldepth of AB ∼21.25 mag per band, thisfilter set thusallowsforanunbiased and accuratecharacterization of thestellarpopulation in our Galaxy, itprovidesanunprecedented 2D photospectralinformationforall resolved galaxies in the local Universe, as well as accuratephoto-z estimates (at the δ z/(1 + z)∼0.005–0.03 precisionlevel) formoderatelybright (up to r ∼ 20 mag) extragalacticsources. Whilesomenarrow-band filters are designedforthestudy of particular emissionfeatures ([O II]/λ3727, Hα/λ6563) up to z < 0.017, theyalsoprovidewell-definedwindowsfortheanalysis of otheremissionlines at higherredshifts. As a result, J-PLUS has thepotential to contribute to a widerange of fields in Astrophysics, both in thenearbyUniverse (MilkyWaystructure, globular clusters, 2D IFU-likestudies, stellarpopulations of nearby and moderate-redshiftgalaxies, clusters of galaxies) and at highredshifts (emission-line galaxies at z ≈ 0.77, 2.2, and 4.4, quasi-stellarobjects, etc.). Withthispaper, wereleasethefirst∼1000 deg2 of J-PLUS data, containingabout 4.3 millionstars and 3.0 milliongalaxies at r < 21mag. With a goal of 8500 deg2 forthe total J-PLUS footprint, thesenumbers are expected to rise to about 35 millionstars and 24 milliongalaxiesbytheend of thesurvey.Funding for the J-PLUS Project has been provided by the Governments of Spain and Aragón through the Fondo de Inversiones de Teruel, the Spanish Ministry of Economy and Competitiveness (MINECO; under grants AYA2017-86274-P, AYA2016-77846-P, AYA2016-77237-C3-1-P, AYA2015-66211-C2-1-P, AYA2015-66211-C2-2, AYA2012-30789, AGAUR grant SGR-661/2017, and ICTS-2009-14), and European FEDER funding (FCDD10-4E-867, FCDD13-4E-2685
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