Dirac lattice

We study the emergence of Dirac fermionic field in the low energy description of non-relativistic dynamical models on graphs admitting continuum limit. The Dirac fermionic field appears as the effective field describing the excitations above point-like Fermi surface. Together with the Dirac fermionic field an effective space-time metric is also emerging. We analyze the conditions for such Fermi points to appear in general, paying special attention to the cases of two and three spacial dimensions.Comment: 26 pages, 4 figures; typo and grammatical corrections, new reference(s) added, version accepted for publicatio

A method for measuring the Neel relaxation time in a frozen ferrofluid

We report a novel method of determining the average Neel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm +/- 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H0 = 20 kA/m) driven at frequencies of 171 kHz, 232 kHz and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Neel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with previously published results

Adhesive force distributions for tungsten dust deposited on bulk tungsten and beryllium-coated tungsten surfaces

Comprehensive measurements of the adhesive force for tungsten dust adhered to tungsten surfaces have been performed with the electrostatic detachment method. Monodisperse spherical dust has been deposited with gas dynamics techniques or with gravity mimicking adhesion as it naturally occurs in tokamaks. The adhesive force is confirmed to follow the log-normal distribution and empirical correlations are proposed for the size-dependence of its mean and standard deviation. Systematic differences are observed between the two deposition methods and attributed to plastic deformation during sticking impacts. The presence of thin beryllium coatings on tungsten surfaces is demonstrated to barely affect adhesion

Thermal and magnetic properties of a low-temperature antiferromagnet Ce4_4Pt12_{12}Sn25_{25}

We report specific heat ($C$) and magnetization ($M$) of single crystalline Ce$_4$Pt$_{12}$Sn$_{25}$ at temperature down to $\sim$50mK and in fields up to 3T. $C/T$ exhibits a sharp anomaly at 180mK, with a large $\Delta C/T\sim$30J/molK$^2$-Ce, which, together with the corresponding cusp-like magnetization anomaly, indicates an antiferromagnetic (AFM) ground state with a N\'eel temperature $T_N$=180mK. Numerical calculations based on a Heisenberg model reproduce both zero-field $C$ and $M$ data, thus placing Ce$_4$Pt$_{12}$Sn$_{25}$ in the weak exchange coupling $J<J_c$ limit of the Doniach diagram, with a very small Kondo scale $T_K\ll T_N$. Magnetic field suppresses the AFM state at $H^*\approx$0.7T, much more effectively than expected from the Heisenberg model, indicating additional effects possibly due to frustration or residual Kondo screening.Comment: 8 pages, 7 figures, accepted for publication in Phys. Rev.

A note on the decay of noncommutative solitons

We propose an ansatz for the equations of motion of the noncommutative model of a tachyonic scalar field interacting with a gauge field, which allows one to find time-dependent solutions describing decaying solitons. These correspond to the collapse of lower dimensional branes obtained through tachyon condensation of unstable brane systems in string theory.Comment: 8 pages, no figures. Extended version, references adde

COVID-19 impact on EuroTravNet infectious diseases sentinel surveillance in Europe

BACKGROUND The COVID-19 pandemic resulted in a sharp decline of post-travel patient encounters at the European sentinel surveillance network (EuroTravNet) of travellers' health. We report on the impact of COVID-19 on travel-related infectious diseases as recorded by EuroTravNet clinics. METHODS Travelers who presented between January 1, 2019 and September 30, 2021 were included. Comparisons were made between the pre-pandemic period (14 months from January 1, 2019 to February 29, 2020); and the pandemic period (19 months from March 1, 2020 to September 30, 2021). RESULTS Of the 15,124 visits to the network during the 33-month observation period, 10,941 (72%) were during the pre-pandemic period, and 4183 (28%) during the pandemic period. Average monthly visits declined from 782/month (pre-COVID-19 era) to 220/month (COVID-19 pandemic era). Among non-migrants, the top-10 countries of exposure changed after onset of the COVID-19 pandemic; destinations such as Italy and Austria, where COVID-19 exposure peaked in the first months, replaced typical travel destinations in Asia (Thailand, Indonesia, India). There was a small decline in migrant patients reported, with little change in the top countries of exposure (Bolivia, Mali). The three top diagnoses with the largest overall decreases in relative frequency were acute gastroenteritis (-5.3%), rabies post-exposure prophylaxis (-2.8%), and dengue (-2.6%). Apart from COVID-19 (which rose from 0.1% to 12.7%), the three top diagnoses with the largest overall relative frequency increase were schistosomiasis (+4.9%), strongyloidiasis (+2.7%), and latent tuberculosis (+2.4%). CONCLUSIONS A marked COVID-19 pandemic-induced decline in global travel activities is reflected in reduced travel-related infectious diseases sentinel surveillance reporting

Ferroelectric orthorhombic ZrO2 thin films achieved through nanosecond laser annealing

A new approach for the stabilization of the ferroelectric orthorhombic ZrO2 films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiOx/W(14 nm)/ZrO2(8 nm)/W(22 nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8 mu C cm(-2), remnant polarization of 12.7 mu C cm(-2) and coercive field of 1.2 MV cm(-1). The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0 x 10(5) cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.A.P.S.C. and M.C.I. contributed equally to this work. This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020. This work has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 958174 (M-ERA-NET3/0003/2021-NanOx4EStor). M. C. I. and C. G. acknowledge the financial support by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI - UEFISCDI, project number COFUND-M-ERANET-3-NanOx4Estor, within PNCDI III and POC 332/390008/29.12.2020-SMIS 109522. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposals 20202037, 20202038, and 20192055. The authors would also like to thank Jose Santos for technical support in the Thin Film Laboratory at CF-UM-UP. J.L.M-D. thanks the ERC grant, EU-H2020-ERC-ADG #882929, EROS. And the Royal Academy of Engineering, grant CIET1819_24. MOH thanks the Herchel Smith foundation of Cambridge for a research fellowship. This work made use of the University of Cambridge Wolfson Electron Microscopy Suite

HBM4EU chromates study - Reflection and lessons learnt from designing and undertaking a collaborative European biomonitoring study on occupational exposure to hexavalent chromium

Multicenter StudyThe EU human biomonitoring initiative, HBM4EU, aims to co-ordinate and advance human biomonitoring (HBM) across Europe. As part of HBM4EU, we presented a protocol for a multicentre study to characterize occupational exposure to hexavalent chromium (Cr(VI)) in nine European countries (HBM4EU chromates study). This study intended to collect data on current occupational exposure and to test new indicators for chromium (Cr) biomonitoring (Cr(VI) in exhaled breath condensate and Cr in red blood cells), in addition to traditional urinary total Cr analyses. Also, data from occupational hygiene samples and biomarkers of early biological effects, including genetic and epigenetic effects, was obtained, complementing the biomonitoring information. Data collection and analysis was completed, with the project findings being made separately available. As HBM4EU prepares to embark on further European wide biomonitoring studies, we considered it important to reflect on the experiences gained through our harmonised approach. Several practical aspects are highlighted for improvement in future studies, e.g., more thorough/earlier training on the implementation of standard operating procedures for field researchers, training on the use of the data entry template, as well as improved company communications. The HBM4EU chromates study team considered that the study had successfully demonstrated the feasibility of conducting a harmonised multicentre investigation able to achieve the research aims and objectives. This was largely attributable to the engaged multidisciplinary network, committed to deliver clearly understood goals. Such networks take time and investment to develop, but are priceless in terms of their ability to deliver and facilitate knowledge sharing and collaboration.Highlights: Feasibility of conducting harmonised Pan-European biomonitoring study on occupational exposure demonstrated; Developing a successful network and implementation of systematic methodology takes significant dedication from all involved; Methodological improvements were identified which will benefit future large-scale occupational biomonitoring campaigns; Developed multicentre network allows and promotes further opportunities for future research, knowledge sharing and collaboration; Data produced supports science to policy interface in the scope of REACH and occupational safety and health regulations.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 733032 and received co-funding from the author’s organizations and/or Ministries.info:eu-repo/semantics/publishedVersio