195 research outputs found
Confinement-based direct design method for fibre reinforced polymer confined CFST short columns
The paper presents a detailed analysis of the behaviour of circular and square concrete filled steel tube (CFST) short columns strengthened externally with carbon or glass fibre reinforced polymer sheets (CFRP or GFRP, respectively). A thorough review of existing test information is presented and discussed, and the most salient parameters in terms of the overall strength are identified. There are a large number of influential and inter-related parameters which affect the load-carrying capacity, including the geometry, cross-sectional shape, type of steel, concrete strength, boundary and loading conditions, and type of FRP. It is shown that existing design approaches do not reliably predict the strength for the full range of possible parameters. Therefore, this paper proposes a new design model to calculate the axial compressive strength of FRP-confined concrete filled steel tubular (CFST) short columns with either a circular or square cross-section. The method accounts for the various complexities which affect the behaviour, yet presents a user-friendly, performance-based design expression. It is based on an evaluation of the lateral confining pressure provided by the both the FRP and the steel tube to the concrete core. This is employed in the confinement-based direct resistance calculations. The paper validates the approach by comparing its capacity predictions with a large database of experimental results and alternative design models available in the literature. The results show that the proposed model provides much accurate strength predictions with greater reliability for the full range of parameters examined, than existing methods
Topological Interactions in Warped Extra Dimensions
Topological interactions will be generated in theories with compact extra
dimensions where fermionic chiral zero modes have different localizations. This
is the case in many warped extra dimension models where the right-handed top
quark is typically localized away from the left-handed one. Using
deconstruction techniques, we study the topological interactions in these
models. These interactions appear as trilinear and quadrilinear gauge boson
couplings in low energy effective theories with three or more sites, as well as
in the continuum limit. We derive the form of these interactions for various
cases, including examples of Abelian, non-Abelian and product gauge groups of
phenomenological interest. The topological interactions provide a window into
the more fundamental aspects of these theories and could result in unique
signatures at the Large Hadron Collider, some of which we explore.Comment: 40 pages, 10 figures, 2 tables; modifications in the KK parity
discussion, final version at JHE
Differential equations for multi-loop integrals and two-dimensional kinematics
In this paper we consider multi-loop integrals appearing in MHV scattering
amplitudes of planar N=4 SYM. Through particular differential operators which
reduce the loop order by one, we present explicit equations for the two-loop
eight-point finite diagrams which relate them to massive hexagons. After the
reduction to two-dimensional kinematics, we solve them using symbol technology.
The terms invisible to the symbols are found through boundary conditions coming
from double soft limits. These equations are valid at all-loop order for double
pentaladders and allow to solve iteratively loop integrals given lower-loop
information. Comments are made about multi-leg and multi-loop integrals which
can appear in this special kinematics. The main motivation of this
investigation is to get a deeper understanding of these tools in this
configuration, as well as for their application in general four-dimensional
kinematics and to less supersymmetric theories.Comment: 25 pages, 7 figure
Mellin Amplitudes for Dual Conformal Integrals
Motivated by recent work on the utility of Mellin space for representing
conformal correlators in /CFT, we study its suitability for representing
dual conformal integrals of the type which appear in perturbative scattering
amplitudes in super-Yang-Mills theory. We discuss Feynman-like rules for
writing Mellin amplitudes for a large class of integrals in any dimension, and
find explicit representations for several familiar toy integrals. However we
show that the power of Mellin space is that it provides simple representations
even for fully massive integrals, which except for the single case of the
4-mass box have not yet been computed by any available technology. Mellin space
is also useful for exhibiting differential relations between various multi-loop
integrals, and we show that certain higher-loop integrals may be written as
integral operators acting on the fully massive scalar -gon in
dimensions, whose Mellin amplitude is exactly 1. Our chief example is a very
simple formula expressing the 6-mass double box as a single integral of the
6-mass scalar hexagon in 6 dimensions.Comment: 29+7 page
Sigma-1 receptors control neuropathic pain and macrophage infiltration into the dorsal root ganglion after peripheral nerve injury
Neuron-immune interaction in the dorsal root ganglia (DRG) plays a pivotal role in the neuropathic pain development after nerve injury. Sigma-1 receptor (Sig-1R) is expressed by DRG neurons but its role in neuropathic pain is not fully understood. We investigated the effect of peripheral Sig-1R on neuroinflammation in the DRG after spared (sciatic) nerve injury (SNI) in mice. Nerve injury induced a decrease in NeuN staining along with the nuclear eccentricity and ATF3 expression in the injured DRG. Sig-1R was present in all DRG neurons examined, and after SNI this receptor translocated to the periphery of the soma and the vicinity of the nucleus, especially in injured ATF3 + neurons. In WT mice, injured DRG produced the chemokine CCL2, and this was followed by massive infiltration of macrophages/monocytes, which clustered mainly around sensory neurons with translocated Sig-1R, accompanied by robust IL-6 increase and mechanical allodynia. In contrast, Sig-1R knockout (Sig-1R-KO) mice showed reduced levels of CCL2, decreased macrophage/monocyte infiltration into DRG, and less IL-6 and neuropathic mechanical allodynia after SNI. Our findings point to an important role of peripheral Sig-1R in sensory neuron-macrophage/monocyte communication in the DRG after peripheral nerve injury; thus, these receptors may contribute to the neuropathic pain phenotypeNeurofarmacologÃa del dolor de la Universidad de Granada (CTS-109)FPU grants from the Spanish Ministry of Education, Culture and Sports.Spanish Ministry of Economy and Competitiveness (MINECO, grant SAF2016-80540-R)the Junta de AndalucÃa (grant CTS 109)Esteve PharmaceuticalsEuropean Regional Development Fund (ERDF
No triangles on the moduli space of maximally supersymmetric gauge theory
Maximally supersymmetric gauge theory in four dimensions has a remarkably
simple S-matrix at the origin of its moduli space at both tree and loop level.
This leads to the question what, if any, of this structure survives at the
complement of this one point. Here this question is studied in detail at one
loop for the branch of the moduli space parameterized by a vacuum expectation
value for one complex scalar. Motivated by the parallel D-brane picture of
spontaneous symmetry breaking a simple relation is demonstrated between the
Lagrangian of broken super Yang-Mills theory and that of its higher dimensional
unbroken cousin. Using this relation it is proven both through an on- as well
as an off-shell method there are no so-called triangle coefficients in the
natural basis of one-loop functions at any finite point of the moduli space for
the theory under study. The off-shell method yields in addition absence of
rational terms in a class of theories on the Coulomb branch which includes the
special case of maximal supersymmetry. The results in this article provide
direct field theory evidence for a recently proposed exact dual conformal
symmetry motivated by the AdS/CFT correspondence.Comment: 39 pages, 4 figure
Analyticity and the Holographic S-Matrix
We derive a simple relation between the Mellin amplitude for AdS/CFT
correlation functions and the bulk S-Matrix in the flat spacetime limit,
proving a conjecture of Penedones. As a consequence of the Operator Product
Expansion, the Mellin amplitude for any unitary CFT must be a meromorphic
function with simple poles on the real axis. This provides a powerful and
suggestive handle on the locality vis-a-vis analyticity properties of the
S-Matrix. We begin to explore analyticity by showing how the familiar poles and
branch cuts of scattering amplitudes arise from the holographic description.
For this purpose we compute examples of Mellin amplitudes corresponding to
1-loop and 2-loop Witten diagrams in AdS. We also examine the flat spacetime
limit of conformal blocks, implicitly relating the S-Matrix program to the
Bootstrap program for CFTs. We use this connection to show how the existence of
small black holes in AdS leads to a universal prediction for the conformal
block decomposition of the dual CFT.Comment: 28+15 pages, 7 figures; v2: typos correcte
Unitarity and the Holographic S-Matrix
The bulk S-Matrix can be given a non-perturbative definition in terms of the
flat space limit of AdS/CFT. We show that the unitarity of the S-Matrix, ie the
optical theorem, can be derived by studying the behavior of the OPE and the
conformal block decomposition in the flat space limit. When applied to
perturbation theory in AdS, this gives a holographic derivation of the cutting
rules for Feynman diagrams.
To demonstrate these facts we introduce some new techniques for the analysis
of conformal field theories. Chief among these is a method for conglomerating
local primary operators to extract the contribution of an individual primary in
their OPE. This provides a method for isolating the contribution of specific
conformal blocks which we use to prove an important relation between certain
conformal block coefficients and anomalous dimensions. These techniques make
essential use of the simplifications that occur when CFT correlators are
expressed in terms of a Mellin amplitude.Comment: 33+12 pages, 6 figures; v2: typos corrected, some clarifications
adde
Large N and Bosonization in Three Dimensions
Bosonization is normally thought of as a purely two-dimensional phenomenon,
and generic field theories with fermions in D>2 are not expected be describable
by local bosonic actions, except in some special cases. We point out that 3D
SU(N) gauge theories on R^{1,1} x S^{1}_{L} with adjoint fermions can be
bosonized in the large N limit. The key feature of such theories is that they
enjoy large N volume independence for arbitrary circle size L. A consequence of
this is a large N equivalence between these 3D gauge theories and certain 2D
gauge theories, which matches a set of correlation functions in the 3D theories
to corresponding observables in the 2D theories. As an example, we focus on a
3D SU(N) gauge theory with one flavor of adjoint Majorana fermions and derive
the large-N equivalent 2D gauge theory. The extra dimension is encoded in the
color degrees of freedom of the 2D theory. We then apply the technique of
non-Abelian bosonization to the 2D theory to obtain an equivalent local theory
written purely in terms of bosonic variables. Hence the bosonized version of
the large N three-dimensional theory turns out to live in two dimensions.Comment: 30 pages, 2 tables. v2 minor revisions, references adde
Prospective Acid Reflux Study of Iran (PARSI): Methodology and study design
<p>Abstract</p> <p>Background</p> <p>Gastroesophageal reflux disease is a common and chronic disorder but long term, prospective studies of the fate of patients seeking medical advice are scarce. This is especially prominent when looking at non-erosive reflux disease (NERD) patients.</p> <p>Methods</p> <p>We designed a prospective cohort to assess the long term outcome of GERD patients referring to gastroenterologists. Consecutive consenting patients, 15 years of age and older, presenting with symptoms suggestive of GERD referring to our outpatient clinics undergo a 30 minute interview. Upper gastrointestinal endoscopy is performed for them with protocol biopsies and blood samples are drawn. Patients are then treated according to a set protocol and followed regularly either in person or by telephone for at least 10 years.</p> <p>Discussion</p> <p>Our data show that such a study is feasible and follow-ups, which are the main concern, can be done in a fairly reliable way to collect data. The results of this study will help to clarify the course of various subgroups of GERD patients after coming to medical attention and their response to treatment considering different variables. In addition, the basic symptoms and biological database will fuel further molecular epidemiologic studies.</p
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