908 research outputs found
Photographing the End of the World: Capitalist Temporality, Crisis, and the Performativity of Visual Objects
The Depression Era collective started as several photographers and video artists joined forces in March of 2011 to create an archive of photographic images about the Greek economic crisis, amidst the social and political upheaval provoked by ongoing austerity impositions of the EU on the Greek economy. In this essay, I examine selected images from Depression Era, including images from Marinos Tsagkarakisâs series Non-Places of Transition, Yannis Hadjiaslanisâs series After Dark, Pavlos Fisakisâs series Nea Elvetia, and Georges Salamehâs series Spleen. Bringing together Marxist philosophical approaches to aesthetics, via Walter Benjamin and Jean Luc-Nancy, I argue that these photographersâ work is a performative undoing of capitalist understandings of linear time that capture and foster desires for alternative radical temporalities, for non-capitalist senses of time. I discuss how these works disrupt linear notions of time as progress, and as measure of productivity and economic growth, which are intrinsic to modernity, and the creation of financial debt. Against capitalist linear temporality, these Depression Era photographs enable a performative encounter, a realm of visual experimentation in which the spectator is invited to feel time differently, to imagine different alternative temporalities that emerge from the collapse of capitalism
Regularity issues for the null-controllability of the linear 1-d heat equation
The fact that the heat equation is controllable to zero in any bounded domain of the Euclidean space, any time T>0 and from any open subset of the boundary is well known. On the other hand, numerical experiments show the ill-posedness of the problem. In this paper we develop a rigorous analysis of the 1-d problem which provides a sharp description of this ill-posedness. To be more precise, each initial data y0âL2(0,1) of the 1-d linear heat equation has a boundary control of the minimal L 2(0,T)-norm which drives the state to zero in time T>0. This control is given by a solution of the homogeneous adjoint equation with some initial data Ï0, minimizing a suitable quadratic cost. Our aim is to study the relationship between the regularity of y0 and that of Ï0. We show that there are regular data y0 for which the corresponding Ï0 are highly irregular, not belonging to any negative exponent Sobolev space. Moreover, the class of such initial data y 0 is dense in L2(0,1). This explains the severe ill-posedness of the numerical algorithms developed for the approximation of the minimal L2(0,T)-norm control of y0 based on the computation of Ï0. The lack of polynomial convergence rates for Tychonoff regularization processes is a consequence of this phenomenon too
Approximation of periodic solutions for a dissipative hyperbolic equation
This paper studies the numerical approximation of periodic solutions for an exponentially stable linear hyperbolic equation in the presence of a periodic external force f. These approximations are obtained by combining a fixed point algorithm with the Galerkin method. It is known that the energy of the usual discrete models does not decay uniformly with respect to the mesh size. Our aim is to analyze this phenomenon's consequences on the convergence of the approximation method and its error estimates. We prove that, under appropriate regularity assumptions on f, the approximation method is always convergent. However, our error estimates show that the convergence's properties are improved if a numerically vanishing viscosity is added to the system. The same is true if the nonhomogeneous term f is monochromatic. To illustrate our theoretical results we present several numerical simulations with finite element approximations of the wave equation in one or two dimensional domains and with different forcing terms
The Renormalization of Non-Commutative Field Theories in the Limit of Large Non-Commutativity
We show that renormalized non-commutative scalar field theories do not reduce
to their planar sector in the limit of large non-commutativity. This follows
from the fact that the RG equation of the Wilson-Polchinski type which
describes the genus zero sector of non-commutative field theories couples
generic planar amplitudes with non-planar amplitudes at exceptional values of
the external momenta. We prove that the renormalization problem can be
consistently restricted to this set of amplitudes. In the resulting
renormalized theory non-planar divergences are treated as UV divergences
requiring appropriate non-local counterterms. In 4 dimensions the model turns
out to have one more relevant (non-planar) coupling than its commutative
counterpart. This non-planar coupling is ``evanescent'': although in the
massive (but not in the massless) case its contribution to planar amplitudes
vanishes when the floating cut-off equals the renormalization scale, this
coupling is needed to make the Wilsonian effective action UV finite at all
values of the floating cut-off.Comment: 35 pages, 8 figures; typos correcte
The decay constants of pseudoscalar mesons in a relativistic quark model
The decay constants of pseudoscalar mesons are calculated in a relativistic
quark model which assumes that mesons are made of a valence quark antiquark
pair and of an effective vacuum like component. The results are given in terms
of quark masses and of some free parameters entering the expression of the
internal wave functions of the mesons. By using the pion and kaon decay
constants to fix the parameters of the
model one gets for the light quark masses
and the heavy quark masses in the
range: . In the case of
light neutral mesons one obtains with the same set of parameters
. The
values are in agreement with the experimental data and other theoretical
results.Comment: 11 pages, LaTe
Inter-observer reliability of ultrasound detection of tendon abnormalities at the wrist and ankle in patients with rheumatoid arthritis
OBJECTIVE: To assess inter-observer reliability in US detection of tendon inflammatory and structural changes at wrists and ankles in RA patients.
METHODS: Fourteen consecutive RA patients underwent bilateral US assessment of the extensor carpi ulnaris (ECUT) and tibialis posterior tendons (TPTs) by two blinded rheumatologists, with different level of experience in musculoskeletal (MS) US. Grey scale and power Doppler (PD) US assessment was focused on detection of tenosynovitis, tenosynovial and intra-tendon PD signal and structural lesions (i.e. tendinosis, tendon erosion, partial or total rupture).
RESULTS: The frequency of US findings detected by Investigator 1 was 28.6% for inflammatory changes and 51.8% for structural damage changes while Investigator 2 detected 34 and 53.6% for the corresponding abnormalities. A high overall agreement (82.7%) was found for inflammatory pathology and 89.7% for structural lesions in all tendons. Mean kappa (Îș) values for all tendons and pathology was moderate (Îș = 0.42), with fair level of agreement for the wrist region (0.27-0.34) and moderate to good values for the ankle region (Îș = 0.47-0.62). Subclinical abnormalities were detected in 37.5% of the tendons by Investigator 1 and 28.6% of the tendons by Investigator 2.
CONCLUSIONS: MSUS showed high overall agreement and fair to moderate inter-observer Îș-values between investigators with different levels of experience in detection of tendon pathology at the wrist and ankle in RA patients. Further standardization of scanning method and pathology definitions may improve MSUS reproducibility
Cornwall-Jackiw-Tomboulis effective potential for canonical noncommutative field theories
We apply the Cornwall-Jackiw-Tomboulis (CJT) formalism to the scalar theory in canonical-noncommutative spacetime. We construct the CJT
effective potential and the gap equation for general values of the
noncommutative parameter . We observe that under the
hypothesis of translational invariance, which is assumed in the effective
potential construction, differently from the commutative case
(), the renormalizability of the gap equation is
incompatible with the renormalizability of the effective potential. We argue
that our result, is consistent with previous studies suggesting that a uniform
ordered phase would be inconsistent with the infrared structure of canonical
noncommutative theories.Comment: 15 pages, LaTe
One-loop renormalization of general noncommutative Yang-Mills field model coupled to scalar and spinor fields
We study the theory of noncommutative U(N) Yang-Mills field interacting with
scalar and spinor fields in the fundamental and the adjoint representations. We
include in the action both the terms describing interaction between the gauge
and the matter fields and the terms which describe interaction among the matter
fields only. Some of these interaction terms have not been considered
previously in the context of noncommutative field theory. We find all
counterterms for the theory to be finite in the one-loop approximation. It is
shown that these counterterms allow to absorb all the divergencies by
renormalization of the fields and the coupling constants, so the theory turns
out to be multiplicatively renormalizable. In case of 1PI gauge field functions
the result may easily be generalized on an arbitrary number of the matter
fields. To generalize the results for the other 1PI functions it is necessary
for the matter coupling constants to be adapted in the proper way. In some
simple cases this generalization for a part of these 1PI functions is
considered.Comment: 1+26 pages, figures using axodraw, clarifications adde
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