Preface to Focused Section on Efficient High-Order Time Discretization Methods for Partial Differential Equations

During May 8-10,2019,the International Workshop on Efficient High-Order Time Discretization Methods for Partial Differential Equations took place in Villa Orlandi,Anacapri,Italy,a Congress Center of the University of Naples Federico II.About 40 senior researchers,young scholars,and Ph.D.students attended this workshop.The purpose of this event was to explore recent trends and directions in the area of time discretization for the numerical solution of evolutionary partial differential equations with particular application to high-order methods for hyperbolic systems with source and advection-diffusion-reaction equations,and with special emphasis on efficient time-stepping methods such as implicit-explicit(IMEX),semi-implicit and strong stability preserving(SSP)time discretization.The present focused section entitled“Efficient High-Order Time Discretization Methods for Partial Differential Equations”in Communications on Applied Mathematics and Computation(CAMC)consists of five regularly reviewed manuscripts,which were selected from submissions of works presented during the workshop.We thank all the authors of these contributions,and hope that the readers are interested in the topics,techniques and methods,and results of these papers.We also want to thank the CAMC journal editorial staff as well as all the referees for their contributions during the review and publication processes of this focused section.

Minimal Free Resolutions of Zero-dimensional Schemes in P1 ×P1

Let X be a zero-dimensional scheme in p1 × p1. Then X has a minimal free resolution of length 2 if and only if X is ACM. In this paper we determine a class of reduced schemes whose resolutions, similarly to the ACM case, can be obtained by their Hilbert functions and depend only on their distributions of points in a grid of lines. Moreover, a minimal set of generators of the ideal of these schemes is given by curves split into the union of lines.

Direct Simulation of Charge Transport in Graphene Nanoribbons

Graphene nanoribbons are considered as one of the most promising ways to design electron devices where the active area is made of graphene.In fact,graphene nanoribbons present a gap between the valence and the conduction bands as in standard semiconductors such as Si or GaAs,at variancewith large area graphenewhich is gapless,a feature that hampers a good performance of graphene field effect transistors.To use graphene nanoribbons as a semiconductor,an accurate analysis of their electron properties is needed.Here,electron transport in graphene nanoribbons is investigated by solving the semiclassical Boltzmann equation with a discontinuous Galerkin method.All the electron-phonon scattering mechanisms are included.The adopted energy band structure is that devised in[1]while according to[2]the edge effects are described as an additional scattering stemming from the Berry-Mondragon model which is valid in presence of edge disorder.With this approach a spacial 1D transport problem has been solved,even if it remains two dimensional in the wavevector space.A degradation of charge velocities,and consequently of the mobilities,is found by reducing the nanoribbon width due mainly to the edge scattering.

Simulation of Bipolar Charge Transport in Graphene by Using a Discontinuous Galerkin Method

Charge transport in suspended monolayer graphene is simulated by a numerical deterministic approach,based on a discontinuous Galerkin(DG)method,for solving the semiclassical Boltzmann equation for electrons.Both the conduction and valence bands are included and the interband scatterings are taken into account.The use of a Direct Simulation Monte Carlo(DSMC)approach,which properly describes the interband scatterings,is computationally very expensive because the va-lence band is very populated and a huge number of particles is needed.Also the choice of simulating holes instead of electrons does not overcome the problem because there is a certain degree of ambiguity in the generation and recombination terms of electron-hole pairs.Often,direct solutions of the Boltzmann equations with a DSMC neglect the interband scatterings on the basis of physical arguments.The DG approach does not suffer from the previous drawbacks and requires a reasonable computing effort.In the present paper the importance of the interband scatterings is accurately evaluated for several values of the Fermi energy,addressing the issue related to the validity of neglecting the generation-recombination terms.It is found out that the inclusion of the interband scatterings produces huge variations in the average values,as the current,with zero Fermi energy while,as expected,the effect of the interband scattering becomes negligible by increasing the absolute value of the Fermi energy.

Embedded fuzzing:a review of challenges,tools,and solutions

Fuzzing has become one of the best-established methods to uncover software bugs.Meanwhile,the market of embedded systems,which binds the software execution tightly to the very hardware architecture,has grown at a steady pace,and that pace is anticipated to become yet more sustained in the near future.Embedded systems also beneft from fuzzing,but the innumerable existing architectures and hardware peripherals complicate the development of general and usable approaches,hence a plethora of tools have recently appeared.Here comes a stringent need for a systematic review in the area of fuzzing approaches for embedded systems,which we term'embedded fuzzing"for brevity.The inclusion criteria chosen in this article are semi-objective in their coverage of the most relevant publication venues as well as of our personal judgement.The review rests on a formal definition we develop to represent the realm of embedded fuzzing.It continues by discussing the approaches that satisfy the inclusion criteria,then defines the relevant elements of comparison and groups the approaches according to how the execution environment is served to the system under test.The resulting review produces a table with 42 entries,which in turn supports discussion suggesting vast room for future research due to the limitations noted.

The cold chain and the COVID-19 pandemic:an unusual increase in histamine content in fish samples collected in Southern Italy during lockdown

Objectives:We analysed 900 samples of fresh(250)and processed(650)fish products collected in Sicily(Southern Italy)in 2020 during the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pandemic(hereafter:COVID-19).Materials and methods:The samples were divided temporally based on four phases relating to the various restrictions imposed by the Italian government in this period.The validated method of ultrahigh-performance liquid chromatography combined with a diode array detector was then employed for the analysis.Results:The samples collected during the Phase I lockdown period and after it had ended(Phase II)revealed significant increases in the mean histamine levels:(41.89±87.58)mg/kg and(24.91±76.76)mg/kg,respectively.The 11(1.3%of the total)fresh fish samples that were identified as being non-compliant with Regulation(EC)No.2073/2005 were only found during these two periods.All the processed samples were always compliant.The histamine values decreased as the restrictions eased,achieving a mean value of(11.16±9.3)mg/kg(Phase III).Conclusions:There was an increase in the incidence offish samples that were non-compliant with Regulation(EC)No.2073/2005 compared to previous surveillance data.These results provide a first report on the effect of lockdown measures on food safety and the cold chain.Our findings must cause food safety operators to intensify their controls over fresh fish products in such periods to safeguard consumer health.Further studies are required to evaluate whether the same trend would be observed with other food contaminants.