302 research outputs found

    Effective theories of phase transitions

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    In this thesis we study systems undergoing a superfluid phase transition at finite temperature and chemical potential. We construct an effective description valid at late times and long wavelengths, using both the holographic duality and the Schwinger-Keldysh formalism for non-equilibrium field theories. In particular, in chapter 2 we employ analytic techniques to find the leading dissipative corrections to the energy-momentum tensor and the electric current of a holographic superfluid, away from criticality. Our method is based on the symplectic current of Crnkovic and Witten [1] and extends on previous results [2, 3]. We assume a general black hole background in the bulk, with finite charge density and scalars fields turned on. We express one-point functions of the boundary field theory solely in terms of thermodynamic quantities and data related to the black hole horizon in the bulk spacetime. Matching our results with the expected constitutive relations of superfluid hydrodynamics, we obtain analytic expressions for the five transport coefficients characterising superfluids with small superfluid velocities. In chapter 3 we examine the hydrodynamics of holographic superfluids arbitrarily close to the critical point. The main difference in this case is that, close to the critical point, the amplitude of the order parameter is an additional hydrodynamic degree of freedom and we have to include it in our effective theory. For simplicity, we choose to work in the probe limit. Utilising the symplectic current once again, we find the equations that govern the critical dynamics of the order parameter and the charge density and show that our holographic results are in complete agreement with Model F of Hohenberg and Halperin [4]. Through this process, we find analytic expressions for all the parameters of Model F, including the dissipative kinetic coefficient, in terms of thermodynamics and horizon data. In addition, we perform various numerical checks of our analytic results. Finally, in chapter 4 we consider critical superfluid dynamics within the Schwinger-Keldysh formalism. As in chapter 3, we focus on the complex order parameter and the conserved current of the spontaneously broken global symmetry, ignoring temperature and normal fluid velocity fluctuations. We construct an effective action up to second order in the a-fields and compare the resulting stochastic system with Model F and our holographic results in chapter 3. A crucial role in this construction is played by a time independent gauge symmetry, called “chemical shift symmetry”. We also integrate out the amplitude mode and obtain the conventional equations of superfluid hydrodynamics, valid for energies well below the gap of the amplitude mode

    Rectifiers - Analysis and Optimization for Wireless Energy Transfer

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    IDTraffickers:An Authorship Attribution Dataset to link and connect Potential Human-Trafficking Operations on Text Escort Advertisements

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    Human trafficking (HT) is a pervasive global issue affecting vulnerable individuals, violating their fundamental human rights. Investigations reveal that a significant number of HT cases are associated with online advertisements (ads), particularly in escort markets. Consequently, identifying and connecting HT vendors has become increasingly challenging for Law Enforcement Agencies (LEAs). To address this issue, we introduce IDTraffickers, an extensive dataset consisting of 87,595 text ads and 5,244 vendor labels to enable the verification and identification of potential HT vendors on online escort markets. To establish a benchmark for authorship identification, we train a DeCLUTR-small model, achieving a macro-F1 score of 0.8656 in a closed-set classification environment. Next, we leverage the style representations extracted from the trained classifier to conduct authorship verification, resulting in a mean r-precision score of 0.8852 in an open-set ranking environment. Finally, to encourage further research and ensure responsible data sharing, we plan to release IDTraffickers for the authorship attribution task to researchers under specific conditions, considering the sensitive nature of the data. We believe that the availability of our dataset and benchmarks will empower future researchers to utilize our findings, thereby facilitating the effective linkage of escort ads and the development of more robust approaches for identifying HT indicators

    IDTraffickers:An Authorship Attribution Dataset to link and connect Potential Human-Trafficking Operations on Text Escort Advertisements

    Get PDF
    Human trafficking (HT) is a pervasive global issue affecting vulnerable individuals, violating their fundamental human rights. Investigations reveal that a significant number of HT cases are associated with online advertisements (ads), particularly in escort markets. Consequently, identifying and connecting HT vendors has become increasingly challenging for Law Enforcement Agencies (LEAs). To address this issue, we introduce IDTraffickers, an extensive dataset consisting of 87,595 text ads and 5,244 vendor labels to enable the verification and identification of potential HT vendors on online escort markets. To establish a benchmark for authorship identification, we train a DeCLUTR-small model, achieving a macro-F1 score of 0.8656 in a closed-set classification environment. Next, we leverage the style representations extracted from the trained classifier to conduct authorship verification, resulting in a mean r-precision score of 0.8852 in an open-set ranking environment. Finally, to encourage further research and ensure responsible data sharing, we plan to release IDTraffickers for the authorship attribution task to researchers under specific conditions, considering the sensitive nature of the data. We believe that the availability of our dataset and benchmarks will empower future researchers to utilize our findings, thereby facilitating the effective linkage of escort ads and the development of more robust approaches for identifying HT indicators

    Towards exact holography in AdS3

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    Microservices-Based Autonomous Anomaly Detection for Mobile Network Observability

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    In modern telecommunication networks, network observability entails the use of diverse data sources to understand the state and behavior of the network, and its ability to provide the required service and user experience. Because of the vast amounts of data collection and transmission involved in this process, the network's performance is negatively impacted, and it can become difficult for network operators to identify the occurrence of problematic behavior before it is too late. To enable a more efficient form of data collection and aid in diagnostic operations, this thesis aims to develop an autonomous anomaly detection system for time series data. The system is to be developed as a microservices-based solution, to be integrated with a software-defined networking controller platform developed at \textit{Ericsson}. This thesis describes the extensive experimentation process conducted during the development of this system, including various methods of data processing, time series clustering, and anomaly detection. The resulting system is a highly customizable and scalable product, supported by modern and reliable anomaly detection models. The system is capable of detecting several different kinds of anomalies in an arbitrary number of mobile network monitoring metrics and can be easily configured to fit the specific needs of each customer

    Safe Halt as Fail-safe Concept for Automated Driving Systems

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    In order to guide a vehicle to the destination of a driving mission, various tasks shall be performed. These tasks include tactical and strategic planning of the driving mission and longitudinal and lateral vehicle motion control. Driver assistance systems support a human vehicle driver in performing these tasks. If faults occur in these systems, the vehicle driver is informed of the system limitations and shall take over the control of the vehicle. This fallback to a human driver is not an option in automated vehicles. If system limitations occur in these vehicles, a automated fallback level shall take over vehicle control. The automated driving system shall therefore be fail-safe. Fail-safe means that when faults occur, the automated driving system no longer has any function to perform a driving mission, but shall maintain the vehicle in a safe state and transition the vehicle into a Minimal Risk Condition (MRC). For this purpose, a situation-dependent MRC is selected. It is characterized by the global MRC concerning the length of the maneuver and the residual risk of the MRC itself. For the research project UNICARagil, the concept Safe Halt is proposed. This concept is intended to satisfy the requirements mentioned above. In the state of the art, an evaluation of this concept had not been included. This missing evaluation is performed in this thesis. The concept relies on pre-planned implicit emergency trajectories generated by a planning module. A unique concept feature is an independent environment perception system to ensure the Minimal Risk Maneuver (MRM) up to the MRC. Based on the pre-planned implicit emergency trajectory and the data of the independent environment perception system, Safe Halt plans trajectories up to the MRC. Thus, with this concept, even in the presence of failures to the environment perception system and to the strategic and tactical planning of an automated driving system, the safe state can be maintained, and the vehicle can be transitioned to a MRC. A methodology is presented to evaluate the concept of Safe Halt. For this purpose, the fault tolerance regimes of an automated vehicle are defined. Next, a reference implementation for Safe Halt is provided. For this, requirements for a Safe Halt in a generic automated driving system are identified first. These are supplemented by specific requirements from the application in the UNICARagil automated driving system. Finally, concepts and a synthesized reference solution are created for a Safe Halt in the UNICARagil ADS. The solution is verified with test criteria and test cases. A final evaluation of the Safe Halt concept shows a high effectiveness for the size of the subset of fault combinations of an automated driving system for which Safe Halt enables a fail-safe property. The requirements for Safe Halt are verified, and the specific requirements are met by the reference solution. The concept Safe Halt is thus suitable for an automated driving system to maintain a safe state. Validation of the concept in public road traffic is recommended

    Breaking rotations without violating the KSS viscosity bound

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    We revisit the computation of the shear viscosity to entropy ratio in a holographic p-wave superfluid model, focusing on the role of rotational symmetry breaking. We study the interplay between explicit and spontaneous symmetry breaking and derive a simple horizon formula for η/s\eta/s, which is valid also in the presence of explicit breaking of rotations and is in perfect agreement with the numerical data. We observe that a source which explicitly breaks rotational invariance suppresses the value of η/s\eta/s in the broken phase, competing against the effects of spontaneous symmetry breaking. However, η/s\eta/s always reaches a constant value in the limit of zero temperature, which is never smaller than the Kovtun-Son-Starinets (KSS) bound, 1/4π1/4\pi. This behavior appears to be in contrast with previous holographic anisotropic models which found a power-law vanishing of η/s\eta/s at small temperature. This difference is shown to arise from the properties of the near-horizon geometry in the extremal limit. Thus, our construction shows that the breaking of rotations itself does not necessarily imply a violation of the KSS bound.Comment: 20 pages, 7 figure

    HARMONI: advancing science with the next-generation integral field spectrograph

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    We start by investigating the noise behaviour of Teledyne HxRG infrared detectors. We look at data from KMOS H2RG darks, along with data from a MOONS engineering grade H4RG detector. From these we determine read noise distributions for the HxRG detectors, and identify a number of other non-uniform noise contributions. We then incorporate this information, along with a pre-existing HxRG noise generation tool, into HSIM. We then use this new advanced detector systematics (ADS) mode to produce simulations investigating the point source sensitivities, spatial variation of noise, reproducibility of recovered point source flux, and signal-to-noise ratio (SNR) for a number of different noise components. We determine from this that these additional detector noise effects provide non-trivial contributions to the noise profile of the detectors. In particular we find pink noise to be problematic, as it is a spatially-varying noise component that has a large impact on the overall SNR. We recommend careful use of the detector reference pixels to correct this, accounting for the potential for bad pixels within these. We also look at the impact of an under-illuminated spectrograph entrance slit on telluric correction. We model the SINFONI 250x125 mas H-band line spread function (LSF) and vary the level of the input illumination. From this we determine an expected reduction in LSF width of 14%. We then use observations of CD-23 13701 and Callisto taken with SINFONI with adaptive optics (AO) correction to confirm a result of 14.0+/-2.1% when fitted using molecfit. We attempt four methods of telluric correction; directly using CD-23 13701 as a telluric standard star, a synthetic spectrum created from molecfit run on CD-23 13701, this synthetic spectrum convolved with the appropriate LSF, and a synthetic spectrum created from molecfit run on the Callisto data. We perform this analysis on multiple spaxels within the Callisto data, and determine average residual sum of squares of 0.43, 0.34, 0.30, and 0.29 for the four methods. We determine from this that inadequate knowledge of the LSF leads to systematically worse telluric correction. Provided the LSF is known, the level of correction is similar between using a telluric standard star or the science target itself, with the remaining differences partly explained by variations in the atmospheric profile between the observations. We end with testing a science case of HARMONI; recovering spatially resolved kinematics from high redshift galaxies. We use the NUTFB simulation to create a galaxy at an effective redshift of 1.44. We then produce a number of simulations using HSIM to determine how well we can recover the rotation curve and star formation rate (SFR), varying the simulated observation time and spectral resolution. We determine that 1 hour of HARMONI observation is sufficient to recover the kinematics to the point at which we become limited by effects within the galaxy. We also investigate the impact of the AO point spread function (PSF), particularly showing the effects of the PSF wings smearing out the rotation curve, as well as differences in the kinematics as a result of PSF elongation
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