RECERCAT - Física Fonamental
http://www.recercat.cat:80/handle/2072/48815
Wed, 30 Jul 2014 11:22:22 GMT2014-07-30T11:22:22ZThe Channel Imagehttp://www.recercat.cat:80/bitstream/id/34146/
http://www.recercat.cat:80/handle/2072/48815
Holographic isotropization linearized
http://www.recercat.cat:80/handle/2072/238353
Holographic isotropization linearized
Heller, Michal P.; Mateos, David (Mateos Solé); Van der Schee, Wilke; Triana, Miquel
The holographic isotropization of a highly anisotropic, homogeneous, strongly coupled, non-Abelian plasma was simplified in ref. [1] by linearizing Einstein"s equations around the final, equilibrium state. This approximation reproduces the expectation value of the boundary stress tensor with a 20% accuracy. Here we elaborate on these results and extend them to observables that are directly sensitive to the bulk interior, focusing for simplicity on the entropy production on the event horizon. We also consider next-to-leading-order corrections and show that the leading terms alone provide a better description of the isotropization process for the states that are furthest from equilibrium.
http://www.recercat.cat:80/handle/2072/238353Cherenkov mesons as in-medium quark energy loss
http://www.recercat.cat:80/handle/2072/238337
Cherenkov mesons as in-medium quark energy loss
Casalderrey-Solana, Jorge; Fernández, Daniel (Fernández Moreno); Mateos, David (Mateos Solé)
We recently showed that a heavy quark moving sufficiently fast through a quark-gluon plasma may lose energy by Cherenkov-radiating mesons [1]. Here we review our previous holographic calculation of the energy loss in N=4 Super Yang-Mills and extend it to longitudinal vector mesons and scalar mesons. We also discuss phenomenological implications for heavy-ion collision experiments. Although the Cherenkov energy loss is an O(1/Nc) effect, a ballpark estimate yields a value of dE/dx for Nc=3 which is comparable to that of other mechanisms.
http://www.recercat.cat:80/handle/2072/238337Shifted loops and coercivity from field imprinted high energy barriers in ferritin and ferrihydrite nanoparticles
http://www.recercat.cat:80/handle/2072/238226
Shifted loops and coercivity from field imprinted high energy barriers in ferritin and ferrihydrite nanoparticles
Silva, N. J. O.; Amaral, V. S.; Urtizberea, A.; Bustamante, R.; Millán, A.; Palacio, F.; Kampert, E.; Zeitler, U.; Brion, Sophie de; Iglesias, Òscar; Labarta, Amílcar
We show that the coercive field in ferritin and ferrihydrite depends on the maximum magnetic field in a hysteresis loop and that coercivity and loop shifts depend both on the maximum and cooling fields. In the case of ferritin, we show that the time dependence of the magnetization also depends on the maximum and previous cooling fields. This behavior is associated to changes in the intraparticle energy barriers imprinted by these fields. Accordingly, the dependence of the coercive and loop-shift fields with the maximum field in ferritin and ferrihydrite can be described within the frame of a uniform-rotation model considering a dependence of the energy barrier with the maximum and the cooling fields.
http://www.recercat.cat:80/handle/2072/238226Order-parameter fluctuations in Ising spin glasses at low temperatures
http://www.recercat.cat:80/handle/2072/233068
Order-parameter fluctuations in Ising spin glasses at low temperatures
Palassini, Matteo; Sales, M.; Ritort Farran, Fèlix
http://www.recercat.cat:80/handle/2072/233068'Making Science Understandable'. Divulgació científica i mediació editorial: el cas de The Wisdom of the Body de Walter B. Cannon (1871-1945)
http://www.recercat.cat:80/handle/2072/229172
'Making Science Understandable'. Divulgació científica i mediació editorial: el cas de The Wisdom of the Body de Walter B. Cannon (1871-1945)
Martínez Vidal, Àlvar; Sallent Del Colombo, Emma
The present paper aims at an historical reconstruction, in the framework of the publishing industry in the years between the two World Wars, of the role played by the publisher William W. Norton in the genesis, published in 1932, and new edition in 1938, of Walter B. Cannon"s book The Wisdom of the Body. With the analysis of this case study, we aimed at contributing to the current criticism of the «dominant view», which tries, in an uncritical manner, that scientific popularization follows an ineluctable, continuous and linear evolution.
http://www.recercat.cat:80/handle/2072/229172Ciència catalana a Madrid: el discurs de Jesús M. Bellido Golferichs a la Biblioteca Nacional (1927)
http://www.recercat.cat:80/handle/2072/229171
Ciència catalana a Madrid: el discurs de Jesús M. Bellido Golferichs a la Biblioteca Nacional (1927)
Sallent Del Colombo, Emma
We analyze Dr. Bellido"s discourse at the Spanish National Library in Madrid (1927) in the framework of what has been called Medical Catalanism. Further development of this case study will provide a better understanding of Catalan as a scientific language, the importance of the role played by Catalan publishing industry and the cultural and political relationship between Madrid and Barcelona.
http://www.recercat.cat:80/handle/2072/229171Understanding and modulating the competitive surface-adsorption of proteins through coarse-grained molecular dynamics simulations
http://www.recercat.cat:80/handle/2072/228155
Understanding and modulating the competitive surface-adsorption of proteins through coarse-grained molecular dynamics simulations
Vilaseca Mainar, Pol; Dawson, Kenneth A.; Franzese, Giancarlo
It is now well accepted that cellular responses to materials in a biological medium reflect greatly the adsorbed biomolecular layer, rather than the material itself. Here, we study by molecular dynamics simulations the competitive protein adsorption on a surface (Vroman effect), i.e. the non-monotonic behavior of the amount of protein adsorbed on a surface in contact with plasma as functions of contact time and plasma concentration. We find a complex behavior, with regimes during which small and large proteins are not necessarily competing between them, but are both competing with others in solution ("cooperative" adsorption). We show how the Vroman effect can be understood, controlled and inverted.
http://www.recercat.cat:80/handle/2072/228155Force Spectroscopy with Dual-Trap Optical Tweezers: Molecular Stiffness Measurements and Coupled Fluctuations Analysis
http://www.recercat.cat:80/handle/2072/227928
Force Spectroscopy with Dual-Trap Optical Tweezers: Molecular Stiffness Measurements and Coupled Fluctuations Analysis
Ribezzi-Crivellari, M.; Ritort Farran, Fèlix
ABSTRACT Dual-trap optical tweezers are often used in high-resolution measurements in single-molecule biophysics. Such measurements can be hindered by the presence of extraneous noise sources, the most prominent of which is the coupling of fluctuations along different spatial directions, which may affect any optical tweezers setup. In this article, we analyze, both from the theoretical and the experimental points of view, the most common source for these couplings in dual-trap optical-tweezers setups: the misalignment of traps and tether. We give criteria to distinguish different kinds of misalignment, to estimate their quantitative relevance and to include them in the data analysis. The experimental data is obtained in a, to our knowledge, novel dual-trap optical-tweezers setup that directly measures forces. In the case in which misalignment is negligible, we provide a method to measure the stiffness of traps and tether based on variance analysis. This method can be seen as a calibration technique valid beyond the linear trap region. Our analysis is then employed to measure the persistence length of dsDNA tethers of three different lengths spanning two orders of magnitude. The effective persistence length of such tethers is shown to decrease with the contour length, in accordance with previous studies.
http://www.recercat.cat:80/handle/2072/227928Elastic properties and secondary structure formation of single-stranded DNA at monovalent and divalent salt conditions
http://www.recercat.cat:80/handle/2072/227927
Elastic properties and secondary structure formation of single-stranded DNA at monovalent and divalent salt conditions
Bosco, Alessandro; Camuñas Soler, Joan; Ritort Farran, Fèlix
Single-stranded DNA (ssDNA) plays a major role in several biological processes. It is therefore of fundamental interest to understand how the elastic response and the formation of secondary structures are modulated by the interplay between base pairing and electrostatic interactions. Here we measure force-extension curves (FECs) of ssDNA molecules in optical tweezers set up over two orders of magnitude of monovalent and divalent salt conditions, and obtain its elastic parameters by fitting the FECs to semiflexible models of polymers. For both monovalent and divalent salts, we find that the electrostatic contribution to the persistence length is proportional to the Debye screening length, varying as the inverse of the square root of cation concentration. The intrinsic persistence length is equal to 0.7 nm for both types of salts, and the effectivity of divalent cations in screening electrostatic interactions appears to be 100-fold as compared with monovalent salt, in line with what has been recently reported for single-stranded RNA. Finally, we propose an analysis of the FECs using a model that accounts for the effective thickness of the filament at low salt condition and a simple phenomenological description that quantifies the formation of non-specific secondary structure at low forces.
http://www.recercat.cat:80/handle/2072/227927Spectral properties of the Laplacian of multiplex networks.
http://www.recercat.cat:80/handle/2072/227861
Spectral properties of the Laplacian of multiplex networks.
Solé-Ribalta, A.; De Domenico, M.; Kouvaris, N. E.; Díaz Guilera, Albert; Gómez, S.; Arenas, Àlex
One of the more challenging tasks in the understanding of dynamical properties of models on top of complex networks is to capture the precise role of multiplex topologies. In a recent paper, Gómez et al. [ Phys. Rev. Lett. 110 028701 (2013)], some of the authors proposed a framework for the study of diffusion processes in such networks. Here, we extend the previous framework to deal with general configurations in several layers of networks and analyze the behavior of the spectrum of the Laplacian of the full multiplex. We derive an interesting decoupling of the problem that allow us to unravel the role played by the interconnections of the multiplex in the dynamical processes on top of them. Capitalizing on this decoupling we perform an asymptotic analysis that allow us to derive analytical expressions for the full spectrum of eigenvalues. This spectrum is used to gain insight into physical phenomena on top of multiplex, specifically, diffusion processes and synchronizability.
http://www.recercat.cat:80/handle/2072/227861Nonperturbative semiclassical stability of de Sitter spacetime for small metric deviations
http://www.recercat.cat:80/handle/2072/227862
Nonperturbative semiclassical stability of de Sitter spacetime for small metric deviations
Fröb, Markus B.; Papadopoulos, D. B.; Roura, Albert; Verdaguer Oms, Enric, 1950-
We consider the linearized semiclassical Einstein equations for small deviations around de Sitter spacetime including the vacuum polarization effects of conformal fields. Employing the method of order reduction, we find the exact solutions for general metric perturbations (of scalar, vector and tensor type). Our exact (nonperturbative) solutions show clearly that in this case de Sitter is stable with respect to small metric deviations and a late-time attractor. Furthermore, they also reveal a breakdown of perturbative solutions for a sufficiently long evolution inside the horizon. Our results are valid for any conformal theory, even self-interacting ones with arbitrarily strong coupling.
http://www.recercat.cat:80/handle/2072/227862Nature of the Epidemic Threshold for the Susceptible-Infected-Susceptible Dynamics in Networks
http://www.recercat.cat:80/handle/2072/227863
Nature of the Epidemic Threshold for the Susceptible-Infected-Susceptible Dynamics in Networks
Boguñá, Marián; Castellano, Claudio; Pastor-Satorras, R. (Romualdo), 1967-
We develop an analytical approach to the susceptible-infected-susceptible epidemic model that allows us to unravel the true origin of the absence of an epidemic threshold in heterogeneous networks. We find that a delicate balance between the number of high degree nodes in the network and the topological distance between them dictates the existence or absence of such a threshold. In particular, small-world random networks with a degree distribution decaying slower than an exponential have a vanishing epidemic threshold in the thermodynamic limit.
http://www.recercat.cat:80/handle/2072/227863Local thermodynamics and the generalized Gibbs-Duhem equation in systems with long-range interactions
http://www.recercat.cat:80/handle/2072/227864
Local thermodynamics and the generalized Gibbs-Duhem equation in systems with long-range interactions
Latella, Iván; Pérez Madrid, Agustín
The local thermodynamics of a system with long-range interactions in d dimensions is studied using the mean-field approximation. Long-range interactions are introduced through pair interaction potentials that decay as a power law in the interparticle distance. We compute the local entropy, Helmholtz free energy, and grand potential per particle in the microcanonical, canonical, and grand canonical ensembles, respectively. From the local entropy per particle we obtain the local equation of state of the system by using the condition of local thermodynamic equilibrium. This local equation of state has the form of the ideal gas equation of state, but with the density depending on the potential characterizing long-range interactions. By volume integration of the relation between the different thermodynamic potentials at the local level, we find the corresponding equation satisfied by the potentials at the global level. It is shown that the potential energy enters as a thermodynamic variable that modifies the global thermodynamic potentials. As a result, we find a generalized Gibbs-Duhem equation that relates the potential energy to the temperature, pressure, and chemical potential. For the marginal case where the power of the decaying interaction potential is equal to the dimension of the space, the usual Gibbs-Duhem equation is recovered. As examples of the application of this equation, we consider spatially uniform interaction potentials and the self-gravitating gas. We also point out a close relationship with the thermodynamics of small systems.
http://www.recercat.cat:80/handle/2072/227864Substrate-selective repair and restart of replication forks by DNA translocases
http://www.recercat.cat:80/handle/2072/227860
Substrate-selective repair and restart of replication forks by DNA translocases
Bétous, Rémy; Couch, Frank B.; Mason, Aaron C.; Eichman, Brandt F.; Mañosas Castejón, María; Cortez, David
Stalled replication forks are sources of genetic instability. Multiple fork-remodeling enzymes are recruited to stalled forks, but how they work to promote fork restart is poorly understood. By combining ensemble biochemical assays and single-molecule studies with magnetic tweezers, we show that SMARCAL1 branch migration and DNA-annealing activities are directed by the single-stranded DNA-binding protein RPA to selectively regress stalled replication forks caused by blockage to the leading-strand polymerase and to restore normal replication forks with a lagging-strand gap. We unveil the molecular mechanisms by which RPA enforces SMARCAL1 substrate preference. E. coli RecG acts similarly to SMARCAL1 in the presence of E. coli SSB, whereas the highly related human protein ZRANB3 has different substrate preferences. Our findings identify the important substrates of SMARCAL1 in fork repair, suggest that RecG and SMARCAL1 are functional orthologs, and provide a comprehensive model of fork repair by these DNA translocases.
http://www.recercat.cat:80/handle/2072/227860Influence of the feeding mechanism on deposits of square particles
http://www.recercat.cat:80/handle/2072/227859
Influence of the feeding mechanism on deposits of square particles
Acevedo, M.; Hidalgo, R. C.; Zuriguel, I.; Maza, D.; Pagonabarraga Mora, Ignacio
In a previous paper [Hidalgo et al., Phys. Rev. Lett. 103, 118001 (2009)] it was shown that square particles deposited in a silo tend to align with a diagonal parallel to the gravity, giving rise to a deposit with very particular properties. Here we explore, both experimentally and numerically, the effect on these properties of the filling mechanism. In particular, we modify the volume fraction of the initial configuration from which the grains are deposited. Starting from a very dilute case, increasing the volume fraction results in an enhancement of the disorder in the final deposit characterized by a decrease of the final packing fraction and a reduction of the number of particles oriented with their diagonal in the direction of gravity. However, for very high initial volume fractions, the final packing fraction increases again. This result implies that two deposits with the same final packing fraction can be obtained from very different initial conditions. The structural properties of such deposits are analyzed, revealing that, although the final volume fraction is the same, their micromechanical properties notably differ.
http://www.recercat.cat:80/handle/2072/227859Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets
http://www.recercat.cat:80/handle/2072/227858
Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets
Sabsabi, Z.; Vernay, F.; Iglesias, Òscar; Kachkachi, H.
We study the interplay between the effects of surface anisotropy and dipolar interactions in monodisperse assemblies of nanomagnets with oriented anisotropy. We derive asymptotic formulas for the assembly magnetization, taking into account temperature, applied field, core and surface anisotropy, and dipolar interparticle interactions. We find that the interplay between surface anisotropy and dipolar interactions is well described by the analytical expression of the assembly magnetization derived here: the overall sign of the product of the two parameters governing the surface and the dipolar contributions determines whether intrinsic and collective terms compete or have synergistic effects on the magnetization. This is illustrated by the magnetization curves of γ-Fe2O3 nanoparticle assemblies in the low concentration limit.
http://www.recercat.cat:80/handle/2072/227858Large D gravity and low D strings
http://www.recercat.cat:80/handle/2072/227857
Large D gravity and low D strings
Emparan García de Salazar, Roberto A.; Grumiller, Daniel; Tanabe, Kentaro
We show that in the limit of a large number of dimensions a wide class of nonextremal neutral black holes has a universal near-horizon limit. The limiting geometry is the two-dimensional black hole of string theory with a two-dimensional target space. Its conformal symmetry explains the properties of massless scalars found recently in the large-D limit. For black branes with string charges, the near-horizon geometry is that of the three-dimensional black strings of Horne and Horowitz. The analogies between the α′ expansion in string theory and the large-D expansion in gravity suggest a possible effective string description of the large-D limit of black holes. We comment on applications to several subjects, in particular to the problem of critical collapse.
http://www.recercat.cat:80/handle/2072/227857Self-similar community structure in a network of human interactions
http://www.recercat.cat:80/handle/2072/227856
Self-similar community structure in a network of human interactions
Guimerà Manrique, Roger; Danon, L.; Díaz Guilera, Albert; Giralt, Francesc; Arenas, Àlex
We propose a procedure for analyzing and characterizing complex networks. We apply this to the social network as constructed from email communications within a medium sized university with about 1700 employees. Email networks provide an accurate and nonintrusive description of the flow of information within human organizations. Our results reveal the self-organization of the network into a state where the distribution of community sizes is self-similar. This suggests that a universal mechanism, responsible for emergence of scaling in other self-organized complex systems, as, for instance, river networks, could also be the underlying driving force in the formation and evolution of social networks.
http://www.recercat.cat:80/handle/2072/227856Effective squark/chargino/neutralino couplings: MadGraph implementation
http://www.recercat.cat:80/handle/2072/227795
Effective squark/chargino/neutralino couplings: MadGraph implementation
Abrahantes, Arian; Guasch Inglada, Jaume; Peñaranda Rivas, Siannah; Sánchez-Florit, Raül
We have included the effective description of squark interactions with charginos/neutralinos in the MadGraph MSSM model. This effective description includes the effective Yukawa couplings, and another logarithmic term which encodes the supersymmetry-breaking. We have performed an extensive test of our implementation analyzing the results of the partial decay widths of squarks into charginos and neutralinos obtained by using FeynArts/FormCalc programs and the new model file in MadGraph. We present results for the cross-section of top-squark production decaying into charginos and neutralinos.
http://www.recercat.cat:80/handle/2072/227795Microwave spectrometry for the Evaluation of the structural integrity of metallic stents
http://www.recercat.cat:80/handle/2072/227732
Microwave spectrometry for the Evaluation of the structural integrity of metallic stents
Arauz-Garofalo, Gianluca; López-Domínguez, V.; Hernández Ferràs, Joan Manel; Rodríguez-Leor, Oriol; Bayés Genís, Antoni; O'Callaghan Castellà, Joan; García Santiago, Antoni; Tejada Palacios, Javier
Purpose: To assess the feasibility of a method based on microwave spectrometry to detect structural distortions of metallic stents in open air conditions and envisage the prospects of this approach toward possible medical applicability for the evaluation of implanted stents. Methods: Microwave absorbance spectra between 2.0 and 18.0 GHz were acquired in open air for the characterization of a set of commercial stents using a specifically design setup. Rotating each sample over 360º, 2D absorbance diagrams were generated as a function of frequency and rotation angle. To check our approach for detecting changes in stent length (fracture) and diameter (recoil), two specific tests were performed in open air. Finally, with a few adjustments, this same system provides 2D absorbance diagrams of stents immersed in a water-based phantom, this time over a bandwidth ranging from 0.2 to 1.8 GHz. Results: The authors show that metallic stents exhibit characteristic resonant frequencies in their microwave absorbance spectra in open air which depend on their length and, as a result, may reﬂect the occurrence of structural distortions. These resonances can be understood considering that such devices behave like dipole antennas in terms of microwave scattering. From fracture tests, the authors infer that microwave spectrometry provides signs of presence of Type I to Type IV stent fractures and allows in particular a quantitative evaluation of Type III and Type IV fractures. Recoil tests show that microwave spectrometry seems able to provide some quantitative assessment of diametrical shrinkage, but only if it involves longitudinal shortening. Finally, the authors observe that the resonant frequencies of stents placed inside the phantom shift down with respect to the corresponding open air frequencies, as it should be expected considering the increase of dielectric permittivity from air to water. Conclusions: The evaluation of stent resonant frequencies provided by microwave spectrometry allows detection and some quantitative assessment of stent fracture and recoil in open air conditions. Resonances of stents immersed in water can be also detected and their characteristic frequencies are in good agreement with theoretical estimates. Although these are promising results, further verifica tion in a more relevant phantom is required in order to foresee the real potential of this approach.
http://www.recercat.cat:80/handle/2072/227732Goya's artwork imaging with Terahertz waves
http://www.recercat.cat:80/handle/2072/227731
Goya's artwork imaging with Terahertz waves
Seco-Martorell, C.; López-Domínguez, V.; Arauz-Garofalo, Gianluca; Redo-Sanchez, A.; Tejada Palacios, Javier
In this paper we use a Terahertz (THz) time-domain system to image and analyze the structure of an artwork attributed to the Spanish artist Goya painted in 1771. The THz images show features that cannot be seen with optical inspection and complement data obtained with X-ray imaging that provide evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya"s known signatures is seen in the THz images. In particular, this paper demonstrates the potential of THz imaging as a complementary technique along with X-ray for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection.
http://www.recercat.cat:80/handle/2072/227731Microwave spectrometry for the Evaluation of the structural integrity of metallic stents
http://www.recercat.cat:80/handle/2072/227668
Microwave spectrometry for the Evaluation of the structural integrity of metallic stents
Arauz-Garofalo, G.; López-Domínguez, V.; Hernández Ferràs, Joan Manel; Rodríguez-Leor, Oriol; Bayés Genís, Antoni; O'Callaghan Castellà, Joan; García Santiago, Antoni; Tejada Palacios, Javier
Purpose: To assess the feasibility of a method based on microwave spectrometry to detect structural distortions of metallic stents in open air conditions and envisage the prospects of this approach toward possible medical applicability for the evaluation of implanted stents. Methods: Microwave absorbance spectra between 2.0 and 18.0 GHz were acquired in open air for the characterization of a set of commercial stents using a specifically design setup. Rotating each sample over 360º, 2D absorbance diagrams were generated as a function of frequency and rotation angle. To check our approach for detecting changes in stent length (fracture) and diameter (recoil), two specific tests were performed in open air. Finally, with a few adjustments, this same system provides 2D absorbance diagrams of stents immersed in a water-based phantom, this time over a bandwidth ranging from 0.2 to 1.8 GHz. Results: The authors show that metallic stents exhibit characteristic resonant frequencies in their microwave absorbance spectra in open air which depend on their length and, as a result, may reﬂect the occurrence of structural distortions. These resonances can be understood considering that such devices behave like dipole antennas in terms of microwave scattering. From fracture tests, the authors infer that microwave spectrometry provides signs of presence of Type I to Type IV stent fractures and allows in particular a quantitative evaluation of Type III and Type IV fractures. Recoil tests show that microwave spectrometry seems able to provide some quantitative assessment of diametrical shrinkage, but only if it involves longitudinal shortening. Finally, the authors observe that the resonant frequencies of stents placed inside the phantom shift down with respect to the corresponding open air frequencies, as it should be expected considering the increase of dielectric permittivity from air to water. Conclusions: The evaluation of stent resonant frequencies provided by microwave spectrometry allows detection and some quantitative assessment of stent fracture and recoil in open air conditions. Resonances of stents immersed in water can be also detected and their characteristic frequencies are in good agreement with theoretical estimates. Although these are promising results, further verifica tion in a more relevant phantom is required in order to foresee the real potential of this approach.
http://www.recercat.cat:80/handle/2072/227668Exact results for Wilson loops in arbitrary representations
http://www.recercat.cat:80/handle/2072/227411
Exact results for Wilson loops in arbitrary representations
Fiol Núñez, Bartomeu; Torrents, Genís
We compute the exact vacuum expectation value of 1/2 BPS circular Wilson loops of TeX = 4 U(N) super Yang-Mills in arbitrary irreducible representations. By localization arguments, the computation reduces to evaluating certain integrals in a Gaussian matrix model, which we do using the method of orthogonal polynomials. Our results are particularly simple for Wilson loops in antisymmetric representations; in this case, we observe that the final answers admit an expansion where the coefficients are positive integers, and can be written in terms of sums over skew Young diagrams. As an application of our results, we use them to discuss the exact Bremsstrahlung functions associated to the corresponding heavy probes.
http://www.recercat.cat:80/handle/2072/227411New horizons for black holes and branes
http://www.recercat.cat:80/handle/2072/227410
New horizons for black holes and branes
Emparan García de Salazar, Roberto A.; Harmark, Troels; Niarchos, Vasilis; Obers, Niels A.
We initiate a systematic scan of the landscape of black holes in any spacetime dimension using the recently proposed blackfold effective worldvolume theory. We focus primarily on asymptotically flat stationary vacuum solutions, where we uncover large classes of new black holes. These include helical black strings and black rings, black odd-spheres, for which the horizon is a product of a large and a small sphere, and non-uniform black cylinders. More exotic possibilities are also outlined. The blackfold description recovers correctly the ultraspinning Myers-Perry black holes as ellipsoidal even-ball configurations where the velocity field approaches the speed of light at the boundary of the ball. Helical black ring solutions provide the first instance of asymptotically flat black holes in more than four dimensions with a single spatial U(1) isometry. They also imply infinite rational non-uniqueness in ultraspinning regimes, where they maximize the entropy among all stationary single-horizon solutions. Moreover, static blackfolds are possible with the geometry of minimal surfaces. The absence of compact embedded minimal surfaces in Euclidean space is consistent with the uniqueness theorem of static black holes
http://www.recercat.cat:80/handle/2072/227410Direct Observation of Magnetic Metastability in Individual Iron Nanoparticles
http://www.recercat.cat:80/handle/2072/227175
Direct Observation of Magnetic Metastability in Individual Iron Nanoparticles
Balan, Ana; Derlet, Peter M.; Fraile Rodríguez, Arantxa; Bansmann, Joachim; Yanes, Rocio; Nowak, Ulrik; Kleibert, Armin; Nolting, Frithjof
X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times
http://www.recercat.cat:80/handle/2072/227175Coarse-graining and thermodynamics in far-from-equilibrium systems
http://www.recercat.cat:80/handle/2072/226990
Coarse-graining and thermodynamics in far-from-equilibrium systems
Rubí Capaceti, José Miguel; Pérez Madrid, Agustín
Lying at the core of statistical physics is the need to reduce the number of degrees of freedom in a system. Coarse-graining is a frequently-used procedure to bridge molecular modeling with experiments. In equilibrium systems, this task can be readily performed; however in systems outside equilibrium, a possible lack of equilibration of the eliminated degrees of freedom may lead to incomplete or even misleading descriptions. Here, we present some examples showing how an improper coarse-graining procedure may result in linear approaches to nonlinear processes, miscalculations of activation rates and violations of the fluctuation-dissipation theorem.
http://www.recercat.cat:80/handle/2072/226990Direct Observation of Magnetic Metastability in Individual Iron Nanoparticles
http://www.recercat.cat:80/handle/2072/226991
Direct Observation of Magnetic Metastability in Individual Iron Nanoparticles
Balan, Ana; Derlet, Peter M.; Fraile Rodríguez, Arantxa; Bansmann, Joachim; Yanes, Rocio; Nowak, Ulrik; Kleibert, Armin; Nolting, Frithjof
X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times
http://www.recercat.cat:80/handle/2072/226991Holographic collisions in confining theories
http://www.recercat.cat:80/handle/2072/226989
Holographic collisions in confining theories
Cardoso, Vitor; Emparan García de Salazar, Roberto A.; Mateos, David (Mateos Solé); Pani, Paolo; Rocha, Jorge V.
We study the gravitational dual of a high-energy collision in a confining gauge theory. We consider a linearized approach in which two point particles traveling in an AdS-soliton background suddenly collide to form an object at rest (presumably a black hole for large enough center-of-mass energies). The resulting radiation exhibits the features expected in a theory with a mass gap: late-time power law tails of the form t −3/2, the failure of Huygens" principle and distortion of the wave pattern as it propagates. The energy spectrum is exponentially suppressed for frequencies smaller than the gauge theory mass gap. Consequently, we observe no memory effect in the gravitational waveforms. At larger frequencies the spectrum has an upward-stairway structure, which corresponds to the excitation of the tower of massive states in the confining gauge theory. We discuss the importance of phenomenological cutoffs to regularize the divergent spectrum, and the aspects of the full non-linear collision that are expected to be captured by our approach.
http://www.recercat.cat:80/handle/2072/226989From Full stopping to transparency in a holographic model of heavy ion collisions
http://www.recercat.cat:80/handle/2072/226988
From Full stopping to transparency in a holographic model of heavy ion collisions
Casalderrey-Solana, Jorge; Heller, Michal P.; Mateos, David (Mateos Solé); Van der Schee, Wilke
We numerically simulate planar shock wave collisions in anti<br>de Sitter space as a model for heavy ion collisions of large nuclei. We uncover a crossover between two different dynamical regimes as a function of the collision energy. At low energies the shocks first stop and then explode in a manner approximately described by hydrodynamics, in close similarity with the Landau model. At high energies the receding fragments move outwards at the speed of light, with a region of negative energy density and negative longitudinal pressure trailing behind them. The rapidity distribution of the energy density at late times around midrapidity is not approximately boost invariant but Gaussian, albeit with a width that increases with the collision energy.
http://www.recercat.cat:80/handle/2072/226988Friedman's Excess energy and the McMillan-Mayer theory of solutions:Thermodynamics
http://www.recercat.cat:80/handle/2072/226987
Friedman's Excess energy and the McMillan-Mayer theory of solutions:Thermodynamics
Gómez Estévez, Juan Luis
In his version of the theory of multicomponent systems, Friedman used the analogy which exists between the virial expansion for the osmotic pressure obtained from the McMillan<br>Mayer (MM) theory of solutions in the grand canonical ensemble and the virial expansion for the pressure of a real gas. For the calculation of the thermodynamic properties of the solution, Friedman proposed a definition for the"excess free energy" that is a reminder of the ancient idea for the"osmotic work". However, the precise meaning to be attached to his free energy is, within other reasons, not well defined because in osmotic equilibrium the solution is not a closed system and for a given process the total amount of solvent in the solution varies. In this paper, an analysis based on thermodynamics is presented in order to obtain the exact and precise definition for Friedman"s excess free energy and its use in the comparison with the experimental data.
http://www.recercat.cat:80/handle/2072/226987