311 research outputs found
Dirac-Born-Infeld Action on the Tachyon Kink and Vortex
The tachyon effective field theory describing the dynamics of a non-BPS
D-brane in superstring theory has an infinitely thin but finite tension kink
solution describing a codimension one BPS D-brane. We study the world-volume
theory of massless modes on the kink, and show that the world volume action has
precisely the Dirac-Born-Infeld (DBI) form without any higher derivative
corrections. We generalize this to a vortex solution in the effective field
theory on a brane-antibrane pair. As in the case of the kink, the vortex is
infinitely thin, has finite energy density, and the world-volume action on the
vortex is again given exactly by the DBI action on a BPS D-brane. We also
discuss the coupling of fermions and restoration of supersymmetry and
-symmetry on the world-volume of the kink. Absence of higher derivative
corrections to the DBI action on the soliton implies that all such corrections
are related to higher derivative corrections to the original effective action
on the world-volume of a non-BPS D-brane or brane-antibrane pair.Comment: LaTeX file, 34 pages; references and other minor comments adde
Nonequilibrium fluid-dynamics in the early stage of ultrarelativistic heavy-ion collisions
To describe ultrarelativistic heavy-ion collisions we construct a three-fluid
hydrodynamical model. In contrast to one-fluid hydrodynamics, it accounts for
the finite stopping power of nuclear matter, i.e. for nonequilibrium effects in
the early stage of the reaction. Within this model, we study baryon dynamics in
the BNL-AGS energy range. For the system Au+Au we find that kinetic equilibrium
between projectile and target nucleons is established only after a time
. Observables which are
sensitive to the early stage of the collision (like e.g. nucleon flow)
therefore differ considerably from those calculated in the one-fluid model.Comment: 36 pages, Late
Hamiltonian structure and noncommutativity in -brane models with exotic supersymmetry
The Hamiltonian of the simplest super -brane model preserving 3/4 of the
D=4 N=1 supersymmetry in the centrally extended symplectic superspace is
derived and its symmetries are described. The constraints of the model are
covariantly separated into the first- and the second-class sets and the Dirac
brackets (D.B.) are constructed. We show the D.B. noncommutativity of the super
-brane coordinates and find the D.B. realization of the
superalgebra. Established is the coincidence of the D.B. and Poisson bracket
realizations of the superalgebra on the constraint surface and the
absence there of anomaly terms in the commutation relations for the quantized
generators of the superalgebra.Comment: Latex, 27 pages, no figures. Latex packages amsfonts and euscript are
use
Kinky D-branes and straight strings of open string tachyon effective theory
In this letter we construct the kink D1-brane super D-helix solution and its
T-dual the D2-brane supertube using the effective action of non-BPS tachyonic
D-branes . In the limit of zero angular momentum, both types of solutions
collapse to zero radius, giving rise respectively to a degenerate string
configuration corresponding to a particle travelling with the speed of light
and to a static straight string configuration. These solutions share all the
properties of fundamental strings and do not have the pathological behavior of
other solutions previously found in this context. A short discussion on the
``generalized gauge transformations'' suggested by Sen is used to justify the
validity of our approach.Comment: 10 pages, latex, typos corrected and references adde
Quantitative considerations in medium energy ion scattering depth profiling analysis of nanolayers
The high depth resolution capability of medium energy ion scattering (MEIS) is becoming increasingly relevant to the characterisation of nanolayers in e.g. microelectronics. In this paper we examine the attainable quantitative accuracy of MEIS depth profiling. Transparent but reliable analytical calculations are used to illustrate what can ultimately be achieved for dilute impurities in a silicon matrix and the significant element-dependence of the depth scale, for instance, is illustrated this way. Furthermore, the signal intensity-to-concentration conversion and its dependence on the depth of scattering is addressed. Notably, deviations from the Rutherford scattering cross section due to screening effects resulting in a non-coulombic interaction potential and the reduction of the yield owing to neutralization of the exiting, backscattered H+ and He+ projectiles are evaluated. The former mainly affects the scattering off heavy target atoms while the latter is most severe for scattering off light target atoms and can be less accurately predicted. However, a pragmatic approach employing an extensive data set of measured ion fractions for both H+ and He+ ions scattered off a range of surfaces, allows its parameterization. This has enabled the combination of both effects, which provides essential information regarding the yield dependence both on the projectile energy and the mass of the scattering atom. Although, absolute quantification, especially when using He+, may not always be achievable, relative quantification in which the sum of all species in a layer add up to 100%, is generally possible. This conclusion is supported by the provision of some examples of MEIS derived depth profiles of nanolayers. Finally, the relative benefits of either using H+ or He+ ions are briefly considered
Seismology of the Sun : Inference of Thermal, Dynamic and Magnetic Field Structures of the Interior
Recent overwhelming evidences show that the sun strongly influences the
Earth's climate and environment. Moreover existence of life on this Earth
mainly depends upon the sun's energy. Hence, understanding of physics of the
sun, especially the thermal, dynamic and magnetic field structures of its
interior, is very important. Recently, from the ground and space based
observations, it is discovered that sun oscillates near 5 min periodicity in
millions of modes. This discovery heralded a new era in solar physics and a
separate branch called helioseismology or seismology of the sun has started.
Before the advent of helioseismology, sun's thermal structure of the interior
was understood from the evolutionary solution of stellar structure equations
that mimicked the present age, mass and radius of the sun. Whereas solution of
MHD equations yielded internal dynamics and magnetic field structure of the
sun's interior. In this presentation, I review the thermal, dynamic and
magnetic field structures of the sun's interior as inferred by the
helioseismology.Comment: To be published in the proceedings of the meeting "3rd International
Conference on Current Developments in Atomic, Molecular, Optical and Nano
Physics with Applications", December 14-16, 2011, New Delhi, Indi
Observational diagnostics of gas in protoplanetary disks
Protoplanetary disks are composed primarily of gas (99% of the mass).
Nevertheless, relatively few observational constraints exist for the gas in
disks. In this review, I discuss several observational diagnostics in the UV,
optical, near-IR, mid-IR, and (sub)-mm wavelengths that have been employed to
study the gas in the disks of young stellar objects. I concentrate in
diagnostics that probe the inner 20 AU of the disk, the region where planets
are expected to form. I discuss the potential and limitations of each gas
tracer and present prospects for future research.Comment: Review written for the proceedings of the conference "Origin and
Evolution of Planets 2008", Ascona, Switzerland, June 29 - July 4, 2008. Date
manuscript: October 2008. 17 Pages, 6 graphics, 134 reference
Highly strained III-V-V coaxial nanowire quantum wells with strong carrier confinement
Coaxial quantum wells (QWs) are ideal candidates for nanowire (NW) lasers, providing strong carrier confinement and allowing close matching of the cavity mode and gain medium. We report a detailed structural and optical study and the observation of lasing for a mixed group-V GaAsP NW with GaAs QWs. This system offers a number of potential advantages in comparison to previously studied common group-V structures (e.g., AlGaAs/GaAs) including highly strained binary GaAs QWs, the absence of a lower band gap core region, and deep carrier potential wells. Despite the large lattice mismatch (âŒ1.7%), it is possible to grow defect-free GaAs coaxial QWs with high optical quality. The large band gap difference results in strong carrier confinement, and the ability to apply a high degree of compressive strain to the GaAs QWs is also expected to be beneficial for laser performance. For a non-fully optimized structure containing three QWs, we achieve low-temperature lasing with a low external (internal) threshold of 20 (0.9) ÎŒJ/cm2/pulse. In addition, a very narrow lasing line width of âŒ0.15 nm is observed. These results extend the NW laser structure to coaxial IIIâVâV QWs, which are highly suitable as the platform for NW emitters
Amelioration of systemic inflammation via the display of two different decoy protein receptors on extracellular vesicles
Extracellular vesicles (EVs) can be functionalized to display specific protein receptors on their surface. However, surface-display technology typically labels only a small fraction of the EV population. Here, we show that the joint display of two different therapeutically relevant protein receptors on EVs can be optimized by systematically screening EV-loading protein moieties. We used cytokine-binding domains derived from tumour necrosis factor receptor 1 (TNFR1) and interleukin-6 signal transducer (IL-6ST), which can act as decoy receptors for the pro-inflammatory cytokines tumour necrosis factor alpha (TNF-α) and IL-6, respectively. We found that the genetic engineering of EV-producing cells to express oligomerized exosomal sorting domains and the N-terminal fragment of syntenin (a cytosolic adaptor of the single transmembrane domain protein syndecan) increased the display efficiency and inhibitory activity of TNFR1 and IL-6ST and facilitated their joint display on EVs. In mouse models of systemic inflammation, neuroinflammation and intestinal inflammation, EVs displaying the cytokine decoys ameliorated the disease phenotypes with higher efficacy as compared with clinically approved biopharmaceutical agents targeting the TNF-α and IL-6 pathways.International Society for Advancement of Cytometry Marylou Ingram Scholar 2019-2023H2020 EXPERTSwedish foundation of Strategic Research (SSF-IRC; FormulaEx)ERC CoG (DELIVER)Swedish Medical Research CouncilAccepte
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