Finite entanglement entropy from the zero-point-area of spacetime

The calculation of entanglement entropy S of quantum fields in spacetimes with horizon shows that, quite generically, S (a) is proportional to the area A of the horizon and (b) is divergent. I argue that this divergence, which arises even in the case of Rindler horizon in flat spacetime, is yet another indication of a deep connection between horizon thermodynamics and gravitational dynamics. In an emergent perspective of gravity, which accommodates this connection, the fluctuations around the equipartition value in the area elements will lead to a minimal quantum of area, of the order of L_P^2, which will act as a regulator for this divergence. In a particular prescription for incorporating L_P^2 as zero-point-area of spacetime, this does happen and the divergence in entanglement entropy is regularized, leading to S proportional to (A/L_P^2) in Einstein gravity. In more general models of gravity, the surface density of microscopic degrees of freedom is different which leads to a modified regularisation procedure and the possibility that the entanglement entropy - when appropriately regularised - matches the Wald entropy.Comment: ver 2: minor clarifications added; reformatted with Sections; 11 page

Forms and functions of intertextuality in academic tweets composed by research groups

This paper explores the forms and functions of intertextuality in academic tweets composed by research groups. Academic tweets are dialogic and intertextual texts, usually composed by incorporating other voices and taking up text-visual elements from other contexts. Based on the analysis of 300 tweets taken from the Twitter accounts of four research groups in two different disciplines (Chemistry and Medicine), this study investigates the ways in which intertextual practices contribute to the communicative purposes of the genre. The analysis shows that the affordances of Twitter (e.g. hyperlinking, modularity, multimodality) and the purpose of academic tweets shape the forms and functions of intertextuality in these tweets. When composing these tweets academics both reconfigure well-established forms of intertextuality and display novel forms which help them to promote their research, negotiate their relationships with their readers, and share content with diverse audiences

Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field

We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. Application of a magnetic field perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular interactions turn this equilibrium state into a ferromagnetically ordered phase. However, long range ferromagnetic correlations nearly disappear for fields larger 5.5 T, possibly suggesting the existence of a quantum critical point.Comment: 4 pages, 4 figure

Coupling far and near tectonic signals in syn-orogenic sediments : the Olvena growth strata (Sierras Marginales, southern Pyrenees)

The Olvena area (Sierras Marginales, southern Pyrenees) provides an outstanding example for studying the relationships between tectonics and sedimentation related to fold-and-thrust systems having shallow décollements. Stratigraphic and sedimentological features allow infer i) the relationship between Oligocene-Miocene locallysourced alluvial fans and a far-sourced wider fluvial system, and ii) the control exerted by tectonics on the stratigraphic architecture. Initially, uplift resulting from folding and thrusting in the Sierras Marginales precluded the entrance through this area into the Ebro basin of a wide fluvial system sourced in internal zones of the Pyrenean chain (including the Axial Zone). A subsiding area was created in the southern front of the Sierras where west-flowing alluvial fans generated, having their source areas in the rejuvenated reliefs. The subsequent cessation of movement of the tectonic structures permitted these reliefs to be subdued and the overpassing of the north-coming fluvial system that progressively covered a wider area. Sequential evolution and stratigraphic architecture evidence thrust emplacement geometry and chronology, including out-of-sequence reactivation of structures and the influence of evaporite flow along the décollement. Although these syn-tectonic deposits belong to the Ebro basin succession, its megasequential evolution differs from the general sequence established for the basin fill, highlighting the importance of differentiating the influence of near-coming sedimentary systems when interpreting basin-scale sequence stratigraphy

Can we infer the presence of Differential Privacy in Deep Learning models' weights? Towards more secure Deep Learning

Differential Privacy (DP) is a key property to protect data and models from integrity attacks. In the Deep Learning (DL) field, it is commonly implemented through the Differentially Private Stochastic Gradient Descent (DP-SGD). However, when a model is shared or released, there is no way to check whether it is differentially private, that is, it required to trust the model provider. This situation poses a problem when data privacy is mandatory, specially with current data regulations, as the presence of DP can not be certificated consistently by any third party. Thus, we face the challenge of determining whether a DL model has been trained with DP, according to the title question: Can we infer the presence of Differential Privacy in Deep Learning models' weights? Since the DP-SGD significantly changes the training process of a DL model, we hypothesize that DP leaves an imprint in the weights of a DL model, which can be used to predict whether a model has been trained with DP regardless of its architecture and the training dataset. In this paper, we propose to employ the imprint in model weights of using DP to infer the presence of DP training in a DL model. To substantiate our hypothesis, we developed an experimental methodology based on two datasets of weights of DL models, each with models with and without DP training and a meta-classifier to infer whether DP was used in the training process of a DL model, by accessing its weights. We accomplish both, the removal of the requirement of a trusted model provider and a strong foundation for this interesting line of research. Thus, our contribution is an additional layer of security on top of the strict private requirements of DP training in DL models, towards to DL models

The CAST Time Projection Chamber

One of the three X-ray detectors of the CAST experiment searching for solar axions is a Time Projection Chamber (TPC) with a multi-wire proportional counter (MWPC) as a readout structure. Its design has been optimized to provide high sensitivity to the detection of the low intensity X-ray signal expected in the CAST experiment. A low hardware threshold of 0.8 keV is safely set during normal data taking periods, and the overall efficiency for the detection of photons coming from conversion of solar axions is 62 %. Shielding has been installed around the detector, lowering the background level to 4.10 x 10^-5 counts/cm^2/s/keV between 1 and 10 keV. During phase I of the CAST experiment the TPC has provided robust and stable operation, thus contributing with a competitive result to the overall CAST limit on axion-photon coupling and mass.Comment: 19 pages, 11 figures and images, submitted to New Journal of Physic

Renormalization Ambiguities in Chern-Simons Theory

We introduce a new family of gauge invariant regularizations of Chern-Simons theories which generate one-loop renormalizations of the coupling constant of the form $k\to k+2 s c_v$ where $s$ can take any arbitrary integer value. In the particular case $s=0$ we get an explicit example of a gauge invariant regularization which does not generate radiative corrections to the bare coupling constant. This ambiguity in the radiative corrections to $k$ is reminiscent of the Coste-L\"uscher results for the parity anomaly in (2+1) fermionic effective actions.Comment: 10 pages, harvmac, no changes, 1 Postscript figure (now included