Search Our Scientific Publications & Authors

Magn Reson Med 2019 Apr 19. Epub 2019 Apr 19.

Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany.

Purpose: 4D flow MRI permits to quantify non-invasively time-dependent velocity vector fields, but it demands long acquisition times. 2D-selective excitation allows to accelerate the acquisition by reducing the FOV in both phase encoding directions. In this study, we investigate 2D-selective excitation with reduced FOV imaging for fast 4D flow imaging while obtaining correct velocity quantification. Read More

J Phys Chem C Nanomater Interfaces 2019 Apr 25;123(14):8892-8901. Epub 2019 Mar 25.

Debye Institute for Nanomaterials Science, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands.

On-surface synthesis has emerged in the last decade as a method to create graphene nanoribbons (GNRs) with atomic precision. The underlying premise of this bottom-up strategy is that precursor molecules undergo a well-defined sequence of inter- and intramolecular reactions, leading to the formation of a single product. As such, the structure of the GNR is encoded in the precursors. Read More

Nature 2019 Apr;568(7753):436

Proc Natl Acad Sci U S A 2019 Apr 18. Epub 2019 Apr 18.

Center for Theoretical Biological Physics, Rice University, Houston, TX 77030;

Refining predicted protein structures with all-atom molecular dynamics simulations is one route to producing, entirely by computational means, structural models of proteins that rival in quality those that are determined by X-ray diffraction experiments. Slow rearrangements within the compact folded state, however, make routine refinement of predicted structures by unrestrained simulations infeasible. In this work, we draw inspiration from the fields of metallurgy and blacksmithing, where practitioners have worked out practical means of controlling equilibration by mechanically deforming their samples. Read More

Science 2019 Apr 18. Epub 2019 Apr 18.

National Renewable Energy Laboratory, Golden, CO 80401, USA.

All-perovskite-based polycrystalline thin-film tandem solar cells have the potential to deliver efficiencies of > 30%. However, the performance of all-perovskite-based tandem devices have been limited by the lack of high-efficiency, low-band-gap Sn-Pb mixed-perovskite solar cells (PSCs). We report on using guanidinium thiocyanate (GuaSCN) to dramatically improve the structural and optoelectronic properties of Sn-Pb mixed, low-band-gap (~1. Read More

Nanomaterials (Basel) 2019 Apr 17;9(4). Epub 2019 Apr 17.

Department of Physics, School of Physics and Astronomy, Yunnan University, Kunming 650504, China.

One-dimensional (1D) vanadium oxide nanobelts (VO NBs) with variable V valence, which include VO·HO NBs, VO (B) NBs and VO NBs, were prepared by a simple hydrothermal treatment under a controllable reductive environment and a following calcination process. Electrochemical measurements showed that all these VO NBs can be adopted as promising cathode active materials for lithium ion batteries (LIBs). The Li storage mechanism, charge transfer property at the solid/electrolyte interface and Li diffusion characteristics for these as-synthesized 1D VO NBs were systematically analyzed and compared with each other. Read More

Phys Rev E 2019 Mar;99(3-1):032121

Theoretical Physics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom.

We study classical Markovian stochastic systems with discrete states, coupled to randomly switching external environments. For fast environmental processes we derive reduced dynamics for the system itself, focusing on corrections to the adiabatic limit of infinite timescale separation. We show that this can lead to master equations with bursting events. Read More

Phys Rev E 2019 Mar;99(3-1):032206

Department of Mathematics and Statistics, University of Massachusetts, Amherst, Massachusetts 01003, USA.

We observe dark and bright intrinsic localized modes (ILMs), also known as discrete breathers, experimentally and numerically in a diatomic-like electrical lattice. The experimental generation of dark ILMs by driving a dissipative lattice with spatially homogenous amplitude is, to our knowledge, unprecedented. In addition, the experimental manifestation of bright breathers within the band gap is also novel in this system. Read More

Phys Rev E 2019 Mar;99(3-1):032414

Department of Physics and Astronomy, and Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, USA.

The simplest model of DNA mechanics describes the double helix as a continuous rod with twist and bend elasticity. Recent work has discussed the relevance of a little-studied coupling G between twisting and bending, known to arise from the groove asymmetry of the DNA double helix. Here the effect of G on the statistical mechanics of long DNA molecules subject to applied forces and torques is investigated. Read More

Phys Rev E 2019 Mar;99(3-1):032902

Institute of Process Equipment, Zhejiang University, Hangzhou 310027, China.

Diffusion is an important particle behavior in granular flow. Although granular diffusion has been studied for decades, the diffusion of size bidisperse particles has not been well understood. In this paper, discrete element method simulations with the Lees-Edwards boundary condition are performed to quantify the relation between the diffusion coefficient (D) and flow parameters for size bidisperse spheres in dense granular flow. Read More

Phys Rev E 2019 Mar;99(3-1):031101

School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.

We propose an experiment combining fluid dynamics and strong magnetic field physics to simulate cosmological scenarios. Our proposed system consists of two immiscible, weakly magnetized fluids moved through a strong gradient magnetic field. The diamagnetic and paramagnetic forces thus generated amount to a time-dependent effective gravity, which allows us to precisely control the propagation speed of interface waves. Read More

Phys Rev E 2019 Mar;99(3-2):036103

School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.

We make three remarks in reply to the comment by Bryk, Duviryak, and Mryglod (BDM) [Bryk, Duviryak, and Mryglod, Phys. Rev. E 99, 036102 (2019)10. Read More

Phys Rev E 2019 Mar;99(3-1):032212

Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814, USA.

Homoclinic and heteroclinic orbits provide a skeleton of the full dynamics of a chaotic dynamical system and are the foundation of semiclassical sums for quantum wave packets, coherent states, and transport quantities. Here, the homoclinic orbits are organized according to the complexity of their phase-space excursions, and exact relations are derived expressing the relative classical actions of complicated orbits as linear combinations of those with simpler excursions plus phase-space cell areas bounded by stable and unstable manifolds. The total number of homoclinic orbits increases exponentially with excursion complexity, and the corresponding cell areas decrease exponentially in size as well. Read More

Phys Rev E 2019 Mar;99(3-1):032130

Department of Physics and Astronomy, California State University Northridge, 18111 Nordhoff Street, Northridge, California 91330, USA.

The Ornstein-Zernike (OZ) integral equation theory is a powerful approach to simple liquids due to its low computational cost and the fact that, when combined with an appropriate closure equation, the theory is thermodynamically complete. However, approximate closures proposed to date exhibit pressure or free energy inconsistencies that produce inaccurate or ambiguous results, limiting the usefulness of the Ornstein-Zernike approach. To address this problem, we combine methods to enforce both pressure and free energy consistency to create a new closure approximation and test it for a single-component Lennard-Jones fluid. Read More

Phys Rev E 2019 Mar;99(3-1):032131

CCSS, CTP and Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea.

We investigate a nonequilibrium phase transition in a dissipative and coherent quantum spin system using the quantum Langevin equation and mean-field theory. Recently, the quantum contact process (QCP) was theoretically investigated using the Rydberg antiblockade effect, in particular, when the Rydberg atoms were excited in s states so that their interactions were regarded as being between the nearest neighbors. However, when the atoms are excited to d states, the dipole-dipole interactions become effective, and long-range interactions must be considered. Read More

Phys Rev E 2019 Mar;99(3-1):033306

Information Sciences Institute, University of Southern California, Marina del Rey, California 90292, USA and Department of Physics and Astronomy, Center for Quantum Information Science & Technology, University of Southern California, Los Angeles, California 90089, USA.

We propose a mechanism for solving the "negative sign problem"-the inability to assign non-negative weights to quantum Monte Carlo configurations-for a toy model consisting of a frustrated triplet of spin-1/2 particles interacting antiferromagnetically. The introduced technique is based on the systematic grouping of the weights of the recently developed off-diagonal series expansion of the canonical partition function [Phys. Rev. Read More

Phys Rev E 2019 Mar;99(3-1):032203

Research Center for Astronomy, Academy of Athens Soranou Efesiou 4, GR-115 27 Athens, Greece.

We study and compare three characteristic times of the standard map: the Lyapunov time t_{L}, the Poincaré recurrence time t_{r}, and the stickiness (or escape) time t_{st}. The Lyapunov time is the inverse of the Lyapunov characteristic number (L) and in general is quite small. We find empirical relations for the L as a function of the nonlinearity parameter K and of the chaotic area A. Read More

Phys Rev E 2019 Mar;99(3-1):032122

Theoretical Physics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom.

We study stochastic population dynamics coupled to fast external environments and combine expansions in the inverse switching rate of the environment and a Kramers-Moyal expansion in the inverse size of the population. This leads to a series of approximation schemes, capturing both intrinsic and environmental noise. These methods provide a means of efficient simulation and we show how they can be used to obtain analytical results for the fluctuations of population dynamics in switching environments. Read More

Phys Rev E 2019 Mar;99(3-1):032142

C. N. Yang Institute for Theoretical Physics and Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3840, USA.

In this paper, we apply machine learning methods to study phase transitions in certain statistical mechanical models on the two-dimensional lattices, whose transitions involve nonlocal or topological properties, including site and bond percolations, the XY model, and the generalized XY model. We find that using just one hidden layer in a fully connected neural network, the percolation transition can be learned and the data collapse by using the average output layer gives correct estimate of the critical exponent ν. We also study the Berezinskii-Kosterlitz-Thouless transition, which involves binding and unbinding of topological defects, vortices and antivortices, in the classical XY model. Read More

Phys Rev A (Coll Park) 2018 Jan 16;97(1):013407. Epub 2018 Jan 16.

Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, College Park, Maryland 20742, USA.

Decoherence of quantum systems due to uncontrolled fluctuations of the environment presents fundamental obstacles in quantum science. Clock transitions which are insensitive to such fluctuations are used to improve coherence, however, they are not present in all systems or for arbitrary system parameters. Here we create a trio of synthetic clock transitions using continuous dynamical decoupling in a spin-1 Bose-Einstein condensate in which we observe a reduction of sensitivity to magnetic-field noise of up to four orders of magnitude; this work complements the parallel work by Anderson . Read More

EPJ Tech Instrum 2018 11;5(1). Epub 2018 Jul 11.

LaserLaB, Department of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, Amsterdam, The Netherlands.

We have recently demonstrated a general and sensitive method to study low energy collisions that exploits the unique properties of a molecular synchrotron (Van der Poel et al., Phys Rev Lett 120:033402, 2018). In that work, the total cross section for ND3 + Ar collisions was determined from the rate at which ammonia molecules were lost from the synchrotron due to collisions with argon atoms in supersonic beams. Read More

Eur Phys J C Part Fields 2018 29;78(5):428. Epub 2018 May 29.

CEA-Saclay, DSM/IRFU, 91191 Gif-sur-Yvette Cedex, France.

The CUPID-0 detector hosted at the Laboratori Nazionali del Gran Sasso, Italy, is the first large array of enriched scintillating cryogenic detectors for the investigation of Se neutrinoless double-beta decay ( ). CUPID-0 aims at measuring a background index in the region of interest (RoI) for at the level of 10  counts/(keV kg years), the lowest value ever measured using cryogenic detectors. CUPID-0 operates an array of Zn Se scintillating bolometers coupled with bolometric light detectors, with a state of the art technology for background suppression and thorough protocols and procedures for the detector preparation and construction. Read More

Eur Phys J C Part Fields 2018 28;78(5):425. Epub 2018 May 28.

7Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033 Japan.

Stop coannihilation may bring the relic density of heavy supersymmetric dark matter particles into the range allowed by cosmology. The efficiency of this process is enhanced by stop-antistop annihilations into the longitudinal (Goldstone) modes of the and bosons, as well as by Sommerfeld enhancement of stop annihilations and the effects of bound states. Since the couplings of the stops to the Goldstone modes are proportional to the trilinear soft supersymmetry-breaking -terms, these annihilations are enhanced when the -terms are large. Read More

Eur Phys J C Part Fields 2018 24;78(5):408. Epub 2018 May 24.

8DAMTP, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA UK.

We present a determination of the strong coupling constant based on the NNPDF3.1 determination of parton distributions, which for the first time includes constraints from jet production, top-quark pair differential distributions, and the distributions using exact NNLO theory. Our result is based on a novel extension of the NNPDF methodology - the correlated replica method - which allows for a simultaneous determination of and the PDFs with all correlations between them fully taken into account. Read More

Eur Phys J C Part Fields 2018 22;78(5):401. Epub 2018 May 22.

46CERN, Geneva, Switzerland.

The results of a search for new heavy bosons decaying to an electron or muon and a neutrino using proton-proton collision data at a centre-of-mass energy of  TeV are presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1  . Read More

Eur Phys J C Part Fields 2018 22;78(3):250. Epub 2018 Mar 22.

46CERN, Geneva, Switzerland.

A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb of = 13 TeV collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. Read More

Eur Phys J C Part Fields 2018 22;78(3):248. Epub 2018 Mar 22.

2Department of Physics and Astronomy, University College London, London, WC1E 6BT UK.

We investigate the impact of the high precision ATLAS and CMS 7 TeV measurements of inclusive jet production on the MMHT global PDF analysis at next-to-next-to-leading order (NNLO). This is made possible by the recent completion of the long-term project to calculate the NNLO corrections to the hard cross section. We find that a good description of the ATLAS data is not possible with the default treatment of experimental systematic errors, and propose a simplified solution that retains the dominant physical information of the data. Read More

New J Phys 2018 ;20

Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio 3, LT-10222 Vilnius, Lithuania.

We describe anoveltechniqueforcreatinganartificialmagneticfieldforultracoldatomsusinga periodicallypulsedpairofcounterpropagatingRamanlasersthatdrivetransitionsbetween a pair of internal atomic spin states: a multi-frequency coupling term. In conjunction with a magnetic field gradient, this dynamically generates a rectangular lattice with a non-staggered magnetic flux. For a wide range of parameters, the resulting Bloch bands have non-trivial topology, reminiscent of Landau levels, as quantified by their Chern numbers. Read More

Earth Planets Space 2018 5;70(1):93. Epub 2018 Jun 5.

Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond St. North, London, ON N6A 3K7 Canada.

With the recent increase in numbers of small and versatile low-power meteor radars, the opportunity exists to benefit from simultaneous application of multiple systems spaced by only a few hundred km and less. Transmissions from one site can be recorded at adjacent receiving sites using various degrees of forward scatter, potentially allowing atmospheric conditions in the mesopause regions between stations to be diagnosed. This can allow a better spatial overview of the atmospheric conditions at any time. Read More

Sol Phys 2018 28;293(6):86. Epub 2018 May 28.

1Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Hounsfield Road, Hicks Building, Sheffield, S3 7RH UK.

Recent observations have shown that bulk flow motions in structured solar plasmas, most evidently in coronal mass ejections (CMEs), may lead to the formation of Kelvin-Helmholtz instabilities (KHIs). Analytical models are thus essential in understanding both how the flows affect the propagation of magnetohydrodynamic (MHD) waves, and what the critical flow speed is for the formation of the KHI. We investigate both these aspects in a novel way: in a steady magnetic slab embedded in an asymmetric environment. Read More

J Hazard Mater 2019 Apr 9;374:177-185. Epub 2019 Apr 9.

Hӧganäs Environmental Solutions LLC, Cary, NC, 27513, USA.

Technetium-99 (Tc) is a major contaminant at nuclear power plants and several US Department of Energy sites. Its most common aqueous species, pertechnetate (TcO), is very mobile in the environment, and currently there are no effective technologies for its sequestration. In this work, a porous iron (pFe) material was investigated for TcO and perrhenate (ReO) sequestration from artificial groundwater. Read More

Biol Reprod 2019 Feb 19. Epub 2019 Feb 19.

Department of Genetics and Evolution, Institute of Zoology and Biomedical Research, Jagiellonian University, Kraków, Poland.

Progressive functional maturation of spermatozoa is completed during the transit of these cells through the epididymis, a tubule structure connecting a testicle to a vas deferens. Epididymal epithelial cells by means of their secretory and absorptive functions determine a highly specialized luminal microenvironment containing multiple organic and inorganic components. The latter include copper ions, which due to their redox properties are indispensable for critical homeostatic processes occurring in spermatozoa floating in different part of epididymis but can be potentially toxic. Read More

Phys Chem Chem Phys 2019 Apr 18. Epub 2019 Apr 18.

Department of Chemistry, University College London, WC1H 0AJ, London, UK. and School of Chemistry, Cardiff University, Main Building, Park Place, CF10 3AT, Cardiff, UK.

SmCoO3 is a promising perovskite material for the next generation of intermediate temperature solid oxide fuel cells (SOFC), but its potential application is directly linked to, and dependent on, the presence of dopant ions. Doping on the Co-site is suggested to improve the catalytic and electronic properties of this cathode material. Fe, Mn, Ni, and Cu have been proposed as possible dopants and experimental studies have investigated and confirmed the potential of these materials. Read More

Sci Rep 2019 Apr 17;9(1):6233. Epub 2019 Apr 17.

Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, PL-02668, Warsaw, Poland.

Experimental evidence of tremendous magnetic moment dynamical inversion, from metastable trapping state to the state with essentially the same moment oriented in the opposite direction, appearing during giant flux jump connected to thermomagnetic avalanche process in superconducting YBaCuO single crystal, is presented. Magnetization inversion takes place in the system, without thermal contact between sample and sample holder, with a tremendous stored energy once the avalanche process is completed in quasi-adiabatic conditions. A model of magnetic moment inversion, caused by the jump between two metastable states of superconductor with the same energy storage, is presented and discussed in terms of the critical state with peculiar evolution of the critical-current spatial distribution. Read More

Nature 2019 Apr;568(7752):311-312

Nature 2019 Apr 17;568(7752):360-363. Epub 2019 Apr 17.

ASTRON, Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands.

Lightning is a dangerous yet poorly understood natural phenomenon. Lightning forms a network of plasma channels propagating away from the initiation point with both positively and negatively charged ends-called positive and negative leaders. Negative leaders propagate in discrete steps, emitting copious radio pulses in the 30-300-megahertz frequency band that can be remotely sensed and imaged with high spatial and temporal resolution. Read More

J Phys Condens Matter 2019 Apr 17. Epub 2019 Apr 17.

Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska- Lincoln, Jorgensen Hall, 855 North 16th Str., NE 68588-0299, Lincoln, 68588-0299, UNITED STATES.

The spin crossover (SCO) transitions at both the surface and over the entire volume of the [Fe{H₂B(pz)₂}₂(bipy)] polycrystalline films on Al2O3 substrates have been studied, where pz = pyrazol-1-yl and bipy = 2,2'-bipyridine. For [Fe{H₂B(pz)₂}₂(bipy)] films of hundreds of nm thick, magnetometry and x-ray absorption spectroscopy measurements show thermal hysteresis in the SCO transition with temperature, although the transition in bulk [Fe{H2B(pz)2}2(bipy)] occurs in a non-hysteretic fashion at 157 K. While the size of the crystallites in those films are similar, the hysteresis becomes more prominent in thinner films, indicating a significant effect of the [Fe{H₂B(pz)₂}₂(bipy)]/Al₂O₃ interface. Read More

Langmuir 2019 Apr 17. Epub 2019 Apr 17.

Department of Physics and Astronomy , The University of Sheffield , Hounsfield Road , Sheffield S3 7RH , U.K.

Force spectroscopy was used to show that extracellular DNA (eDNA) has a pre-eminent structural role in a biofilm. The adhesive behavior of extracellular polymeric substances to poly(ethylene terephthalate), a model hydrophobic surface, was measured in response to their degradation by hydrolytic enzymes known for their biofilm dispersion potential: DNaseI, protease, cellulase, and mannanase. Only treatment with DNaseI significantly decreased the adhesive force of the model bacterium Micrococcus luteus with the surface, and furthermore this treatment almost completely eliminated any components of the biofilm maintaining the adhesion, establishing a key structural role for eDNA. Read More

Astrobiology 2019 Apr 17. Epub 2019 Apr 17.

2 Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Carbon-enriched rocky exoplanets have been proposed to occur around dwarf stars as well as binary stars, white dwarfs, and pulsars. However, the mineralogical make up of such planets is poorly constrained. We performed high-pressure high-temperature laboratory experiments ( = 1-2 GPa,  = 1523-1823 K) on chemical mixtures representative of C-enriched rocky exoplanets based on calculations of protoplanetary disk compositions. Read More

Phys Chem Chem Phys 2019 Apr 17. Epub 2019 Apr 17.

Department of Physics, Michigan Technological University, Houghton, MI 49931, USA.

Titania (TiO2) is a material of choice for energy-related applications, such as photovoltaics and photocatalysis. The presence of a large band gap and fast electron-hole recombination occurring in the lattice significantly reduce the material's quantum efficiency, and therefore limit industrial-scale applications. In this article, we investigate whether silicene can be a viable substrate for TiO2 nanostructures in photocatalytic applications. Read More

Contrast Media Mol Imaging 2019 12;2019:3728563. Epub 2019 Mar 12.

Department of Chemistry, University of Helsinki, FI-00014 Helsinki, Finland.

Mesoporous silicon (PSi) is biocompatible and tailorable material with high potential in drug delivery applications. Here, we report of an evaluation of PSi as a carrier platform for theranostics by delivering a radioactive ion beam- (RIB-) based radioactive lanthanoid into tumors in a mouse model of prostate carcinoma. Thermally hydrocarbonized porous silicon (THCPSi) wafers were implanted with Dy at the facility for radioactive ion beams ISOLDE located at CERN, and the resulting [Dy]THCPSi was postprocessed into particles. Read More

Nature 2019 Apr;568(7752):284-285

Nat Commun 2019 Apr 16;10(1):1778. Epub 2019 Apr 16.

Department of Physical Electronics, School of Electrical Engineering, Tel-Aviv University, 6997801, Tel Aviv, Israel.

The past two decades have witnessed an ever-growing number of emerging applications that utilize terahertz (THz) waves, ranging from advanced biomedical imaging, through novel security applications, fast wireless communications, and new abilities to study and control matter in all of its phases. The development and deployment of these emerging technologies is however held back, due to a substantial lack of simple methods for efficient generation, detection and manipulation of THz waves. Recently it was shown that uniform nonlinear metasurfaces can efficiently generate broadband single-cycle THz pulses. Read More