Hawking Radiation from an Acoustic Black Hole on an Ion Ring

In this article we propose to simulate acoustic black holes with ions in rings. If the ions are rotating with a stationary and inhomogeneous velocity profile, regions can appear where the ion velocity exceeds the group velocity of the phonons. In these regions phonons are trapped like light in black holes, even though we have a discrete field theory and a nonlinear dispersion relation. We study the appearance of Hawking radiation in this setup and propose a scheme to detect it.Comment: 4 pages, 3 figures, minor revisions, published versio

Wavelet Analysis for Wind Fields Estimation

Wind field analysis from synthetic aperture radar images allows the estimation of wind direction and speed based on image descriptors. In this paper, we propose a framework to automate wind direction retrieval based on wavelet decomposition associated with spectral processing. We extend existing undecimated wavelet transform approaches, by including à trous with B3 spline scaling function, in addition to other wavelet bases as Gabor and Mexican-hat. The purpose is to extract more reliable directional information, when wind speed values range from 5 to 10 ms−1. Using C-band empirical models, associated with the estimated directional information, we calculate local wind speed values and compare our results with QuikSCAT scatterometer data. The proposed approach has potential application in the evaluation of oil spills and wind farms

Structural dynamics of incommensurate charge-density waves tracked by ultrafast low-energy electron diffraction

We study the non-equilibrium structural dynamics of the incommensurate and nearly commensurate charge-density wave (CDW) phases in 1T-TaS2. Employing ultrafast low-energy electron diffraction with 1 ps temporal resolution, we investigate the ultrafast quench and recovery of the CDW-coupled periodic lattice distortion (PLD). Sequential structural relaxation processes are observed by tracking the intensities of main lattice as well as satellite diffraction peaks and the diffuse scattering background. Comparing distinct groups of diffraction peaks, we disentangle the ultrafast quench of the PLD amplitude from phonon-related reductions of the diffraction intensity. Fluence-dependent relaxation cycles reveal a long-lived partial suppression of the order parameter for up to 60 ps, far outlasting the initial amplitude recovery and electron-phonon scattering times. This delayed return to a quasi-thermal level is controlled by lattice thermalization and coincides with the population of zone-center acoustic modes, as evidenced by a structured diffuse background. The long-lived non-equilibrium order parameter suppression suggests hot populations of CDW-coupled lattice modes. Finally, a broadening of the superlattice peaks is observed at high fluences, pointing to a non-linear generation of phase fluctuation

2018 Beam-park observations of space debris with the EISCAT radars

Source at https://conference.sdo.esoc.esa.int/proceedings/neosst1/paper/480.Monitoring the evolution of the space debris environment requires regular radar observations of the space debris population. This study presents the results from 24 hours of beam-park observations of space objects conducted simultaneously with the EISCAT Svalbard and Tromsø radars on and between January 4th and 5th, 2018. The measurements are processed with a new matched filter bank analysis program, which doubles the coherent integration time, and hence sensitivity, compared with the previous program. We observe 2077 objects with the Tromsø radar and 2400 objects with the Svalbard radar. The detections are correlated with the NORAD catalog. We find that 68% of the Tromsø and 85% of the Svalbard radar detections are from objects in the NORAD catalog, with most of the catalog object detections being in the side lobes of the radar antenna. The beam-park data are compared with a simulated beam-park experiment for catalog objects. The simulation uses a radar detection model that includes the effects of coherent integration and an antenna beam shape with side lobes. We find that the simulation agrees well with the measurements, indicating that the radar sensor response is accurately modeled. Our results highlight the importance of modeling antenna side lobes when analyzing beam-park measurements. Not taking taking into account side lobe detections can lead to an underestimation of radar cross-sections and an overestimation of population density

IKZF1 Deletions with COBL Breakpoints Are Not Driven by RAG-Mediated Recombination Events in Acute Lymphoblastic Leukemia

IKZF1 deletion (ΔIKZF1) is an important predictor of relapse in both childhood and adult B-cell precursor acute lymphoblastic leukemia (B-ALL). Previously, we revealed that COBL is a hotspot for breakpoints in leukemia and could promote IKZF1 deletions. Through an international collaboration, we provide a detailed genetic and clinical picture of B-ALL with COBL rearrangements (COBL-r). Patients with B-ALL and IKZF1 deletion (n = 133) were included. IKZF1 ∆1-8 were associated with large alterations within chromosome 7: monosomy 7 (18%), isochromosome 7q (10%), 7p loss (19%), and interstitial deletions (53%). The latter included COBL-r, which were found in 12% of the IKZF1 ∆1-8 cohort. Patients with COBL-r are mostly classified as intermediate cytogenetic risk and frequently harbor ETV6, PAX5, CDKN2A/B deletions. Overall, 56% of breakpoints were located within COBL intron 5. Cryptic recombination signal sequence motifs were broadly distributed within the sequence of COBL, and no enrichment for the breakpoint cluster region was found. In summary, a diverse spectrum of alterations characterizes ΔIKZF1 and they also include deletion breakpoints within COBL. We confirmed that COBL is a hotspot associated with ΔIKZF1, but these rearrangements are not driven by RAG-mediated recombination

Critical dynamics of self-gravitating Langevin particles and bacterial populations

We study the critical dynamics of the generalized Smoluchowski-Poisson system (for self-gravitating Langevin particles) or generalized Keller-Segel model (for the chemotaxis of bacterial populations). These models [Chavanis & Sire, PRE, 69, 016116 (2004)] are based on generalized stochastic processes leading to the Tsallis statistics. The equilibrium states correspond to polytropic configurations with index $n$ similar to polytropic stars in astrophysics. At the critical index $n_{3}=d/(d-2)$ (where $d\ge 2$ is the dimension of space), there exists a critical temperature $\Theta_{c}$ (for a given mass) or a critical mass $M_{c}$ (for a given temperature). For $\Theta>\Theta_{c}$ or $M<M_{c}$ the system tends to an incomplete polytrope confined by the box (in a bounded domain) or evaporates (in an unbounded domain). For $\Theta<\Theta_{c}$ or $M>M_{c}$ the system collapses and forms, in a finite time, a Dirac peak containing a finite fraction $M_c$ of the total mass surrounded by a halo. This study extends the critical dynamics of the ordinary Smoluchowski-Poisson system and Keller-Segel model in $d=2$ corresponding to isothermal configurations with $n_{3}\to +\infty$. We also stress the analogy between the limiting mass of white dwarf stars (Chandrasekhar's limit) and the critical mass of bacterial populations in the generalized Keller-Segel model of chemotaxis

Finite mass self-similar blowing-up solutions of a chemotaxis system with non-linear diffusion

For a specific choice of the diffusion, the parabolic-elliptic Patlak-Keller-Segel system with non-linear diffusion (also referred to as the quasi-linear Smoluchowski-Poisson equation) exhibits an interesting threshold phenomenon: there is a critical mass $M_c>0$ such that all the solutions with initial data of mass smaller or equal to $M_c$ exist globally while the solution blows up in finite time for a large class of initial data with mass greater than $M_c$. Unlike in space dimension 2, finite mass self-similar blowing-up solutions are shown to exist in space dimension $d?3$

Axon initial segment dysfunction in a mouse model of human genetic epilepsy with febrile seizures plus

Febrile seizures are a common childhood seizure disorder and a defining feature of genetic epilepsy with febrile seizures plus (GEFS+), a syndrome frequently associated with Na+ channel mutations. Here, we describe the creation of a knockin mouse heterozygous for the C121W mutation of the ß1 Na+ channel accessory subunit seen in patients with GEFS+. Heterozygous mice with increased core temperature displayed behavioral arrest and were more susceptible to thermal challenge than wild-type mice. Wild-type ß1 was most concentrated in the membrane of axon initial segments (AIS) of pyramidal neurons, while the ß1(C121W) mutant subunit was excluded from AIS membranes. In addition, AIS function, an indicator of neuronal excitability, was substantially enhanced in hippocampal pyramidal neurons of the heterozygous mouse specifically at higher temperatures. Computational modeling predicted that this enhanced excitability was caused by hyperpolarized voltage activation of AIS Na+ channels. This heat-sensitive increased neuronal excitability presumably contributed to the heightened thermal seizure susceptibility and epileptiform discharges seen in patients and mice with ß1(C121W) subunits. We therefore conclude that Na+ channel ß1 subunits modulate AIS excitability and that epilepsy can arise if this modulation is impaired

Customizable and scalable automated assessment of C/C++ programming assignments

The correction of exercises in programming courses is a laborious task that has traditionally been performed in a manual way. This situation, in turn, delays the access by students to feedback that can contribute significantly to their training as future professionals. Over the years, several approaches have been proposed to automate the assessment of students' programs. Static analysis is a known technique that can partially simulate the process of manual code review performed by lecturers. As such, it is a plausible option to assess whether students' solutions meet the requirements imposed on the assignments. However, implementing a personalized analysis beyond the rules included in existing tools may be a complex task for the lecturer without a mechanism that guides the work. In this paper, we present a method to provide automated and specific feedback to immediately inform students about their mistakes in programming courses. To that end, we developed the CAC++ library, which enables constructing tailored static analysis programs for C/C++ practices. The library allows for great flexibility and personalization of verifications to adjust them to each particular task, overcoming the limitations of most of the existing assessment tools. Our approach to providing specific feedback has been evaluated for a period of three academic years in a course related to object-oriented programming. The library allowed lecturers to reduce the size of the static analysis programs developed for this course. During this period, the academic results improved and undergraduates positively valued the aid offered when undertaking the implementation of assignments.Universidad de Cádiz, Grant/Award Numbers: sol-201500054192-tra, sol-201600064680-tra; Ministerio de Ciencia, Innovación y Universidades, Grant/Award Number: RTI2018-093608-B-C33; European Regional Development Fun