Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants. All components of the cosmic rays show an ...intensity that decreases as a power law with increasing energy (for example as E-2.7). Electrons in particular lose energy rapidly through synchrotron and inverse Compton processes, resulting in a relatively short lifetime (about 105 years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away). Here we report an excess of galactic cosmic-ray electrons at energies of ∼300-800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar or micro-quasar) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza-Klein particle with a mass of about 620 GeV).
A CMOS-compatible ISFET with a Ta2O5 sensitive surface was developed. The structure was optimized for achieving high sensitivity using a subthreshold operation mode and by reducing the influence of ...the capacitances on the value of subthreshold swing. The developed ISFET was used as a basis for a biosensor for L-carnitine detection. To this end, carnitine acetyltransferase was immobilized on the ISFET sensitive surface. The immobilized enzyme was active (0.082 U/g model plate). The complete microsystem, consisting of a packaged chip, an immobilized enzyme and a microfluidic channel, detected L-carnitine at a range of 0.2–100 μM with a LOD of 0.2 μM. The biosensor response was linear in the range of 0.2–50 μM of L-carnitine with sensitivity 18.0 ± 1.7 mV/μM. An experiment with artificial urine containing 1.3 μM L-carnitine showed that the proposed biosensor could be used on a real sample. Therefore, a new sensor specially optimized for biosensing CMOS-compatible ISFET structures and direct determination of L-carnitine with immobilized carnitine acetyltransferase was developed.
•A novel CMOS-compatible ISFET was developed and specially optimized for use in subthreshold operation mode.•Carnitine acetyltransferase reaction was directly detected using an electrochemical method for the first time.•The fabricated biosensor allowed detection of L-carnitine in artificial urine.
A biosensor for the direct determination of organophosphorus pesticides (OPs) is described. It utilizes an ion‐selective field‐effect transistor and phosphotriesterase enzyme (PTE), which provides ...cleavage of OPs. The sensitivity of the biosensor was increased after PTE immobilization on the surface of the transistor. Packaging of the integrated circuit and creation of a microfluidic system for analyte delivery stabilized the signal. This system was able to detect 0.1 µM paraoxon and 0.5 µM parathion and methyl parathion and was stable for at least 1 month (PBS, 1°), and could thus provide the basis for a portable device for analyzing OPs in water.
This article is a brief review of the results of studying the collapse of sound waves in media with positive dispersion, which is described in terms of the three-dimensional Kadomtsev–Petviashvili ...(KP) equation. The KP instability of one-dimensional solitons in the long-wavelength limit is considered using the expansion for the corresponding spectral problem. It is shown that the KP instability also takes place for two-dimensional solitons in the framework of the three-dimensional KP equation with positive dispersion. According to Kadomtsev (see
Collective Effects in Plasma
by B.B. Kadomtsev) this instability belongs to the self-focusing type. The nonlinear stage of this instability is a collapse. One of the collapse criteria is the Hamiltonian unboundedness from below for a fixed momentum projection coinciding with the
L
2
-norm. This fact follows from scaling transformations, leaving this norm constant. For this reason, collapse can be represented as the process of falling a particle to the center in a self-consistent unbounded potential. It is shown that the radiation of waves from a region with a negative Hamiltonian, due to its unboundedness from below, promotes the collapse of the waves. This scenario was confirmed by numerical experiments. Two analytical approaches to the study of collapse are presented: using the variational method and the quasiclassical approximation. In contrast to the nonlinear Schrödinger equation (NLSE) with a focusing nonlinearity, a feature of the quasiclassical approach to describing acoustic collapse is that this method is proposed for the three-dimensional KP equation as a system with hydrodynamic nonlinearity. Within the framework of the quasiclassical description, a family of self-similar collapses is found. The upper bound of this family corresponds to a strong collapse, in which the energy captures into the singularity is finite. The existence of such a regime is also confirmed based on the variational approach. The other boundary of the collapsing hierarchy coincides with the self-similar solution of the three-dimensional KP equation, which describes the fastest weak collapse.
The current paper studies the influence of geometrical parameters of the fused deposition modeling (FDM)-fused filament fabrication (FFF) 3D printing process on printed part strength for open source ...desktop 3D printers and the most popular material used for that purpose-i.e., polylactic acid (PLA). The study was conducted using a set of different nozzles (0.4, 0.6, and 0.8 mm) and a range of layer heights from the minimum to maximum physical limits of the machine. To assess print strength, a novel assessment method is proposed. A tubular sample is loaded in the weakest direction (across layers) in a three-point bending fixture. Mesostructure evaluation through scanning electronic microscopy (SEM) scans of the samples was used to explain the obtained results. We detected a significant influence of geometric process parameters on sample mesostructure, and consequently, on sample strength.
Traditional homogeneous water oxidation catalysts are plagued by instability under the reaction conditions. We report that the complex Co₄(H₂O)₂(PW₉O₃₄)₂¹⁰⁻, comprising a Co₄O₄ core stabilized by ...oxidatively resistant polytungstate ligands, is a hydrolytically and oxidatively stable homogeneous water oxidation catalyst that self-assembles in water from salts of earth-abundant elements (Co, W, and P). With Ru(bpy)₃³⁺ (bpy is 2,2'-bipyridine) as the oxidant, we observe catalytic turnover frequencies for O₂ production ≥5 s⁻¹ at pH = 8. The rate's pH sensitivity reflects the pH dependence of the four-electron O₂-H₂O couple. Extensive spectroscopic, electrochemical, and inhibition studies firmly indicate that Co₄(H₂O)₂(PW₉O₃₄)₂¹⁰⁻ is stable under catalytic turnover conditions: Neither hydrated cobalt ions nor cobalt hydroxide/oxide particles form in situ.
The paper presents a brief review of the quasiclassical wave dynamics for the nonlinear Schrödinger equation (NLSE) as applied to focusing and defocusing media. The NLSE depends significantly on the ...space dimension d. The two-dimensional NLSE has an additional symmetry of the conformal type with respect to the Talanov transformations (Talanov in JETP Lett. 11:199–201, 1970), which were initially found for the stationary self-focusing in a medium with the Kerr nonlinearity. A consequence of this symmetry is the Vlasov–Petrishchev–Talanov theorem (Vlasov et al. in Radiophys. Quantum Electron. 14:1062–1070, 1971) that relates the mean of the squared distribution and the Hamiltonian of the system. This theorem is valid for both focusing and defocusing media. In the quasiclassical limit, this makes it possible to construct anisotropic solutions which describe beam compression during self-focusing and quantum-gas expansion into vacuum within the so-called critical nonlinear Schrödinger equations, in particular, for the Gross–Pitaevskii equation with a chemical potential having a power-law dependence on density with the exponent ν = 2/d. For the Gross–Pitaevskii equation, the case d = 2 corresponds to a condensate of a weakly nonideal Bose gas, and the case d = 3 describe condensate of a Fermi gas in the unitary limit. For d = 3, the Gross–Pitaevskii equation in the quasiclassical limit transforms into equations of the gas dynamics with the adiabatic exponent γ = 5/3. The self-similar solutions in this approximation describe the angular deformations of a gas cloud against the background of an expanding gas. Angular deformations of such type are observed in both the expansion of quantum gases and the action of high-power laser radiation on matter. For three-dimensional supercritical focusing NLSE, the quasiclassical solutions of the collapsing type are presented, including the exact semiclassical solution described by the strong collapse regime. It is found that all such quasiclassical collapses are found to be unstable, except for the collapse that is simultaneously the weakest and the fastest collapse corresponding to the self-similar NLSE solution. The problem of post-collapse is also considered as the continuation of a weak collapse, which results in the formation of a quasistationary singularity in the form of a black hole into which energy is drawn from the surrounding collapsing region. For the NLSE with d ≥ 4, the formation of a black hole can be described in the quasiclassical approximation. It is shown that the anisotropy caused by the magnetic field significantly alters the structure of the Langmuir collapse, in particular, leads to the formation of strongly anisotropic black holes described quasiclassically.
We give a qualitative conceptual explanation of the Fermi–Pasta–Ulam (FPU) like recurrence in the onedimensional focusing nonlinear Schrodinger equation (NLSE). The recurrence can be considered as a ...result of the nonlinear development of the modulation instability. All known exact localized solitary wave solutions describing propagation on the background of the modulationally unstable condensate show the recurrence to the condensate state after its interaction with solitons. The condensate state locally recovers its original form with the same amplitude but a different phase after soliton leave its initial region. Based on the integrability of the NLSE, we demonstrate that the FPU recurrence takes place not only for condensate, but also for a more general solution in the form of the cnoidal wave. This solution is periodic in space and can be represented as a solitonic lattice. That lattice reduces to isolated soliton solution in the limit of large distance between solitons. The lattice transforms into the condensate in the opposite limit of dense soliton packing. The cnoidal wave is also modulationally unstable due to soliton overlapping. The recurrence happens at the nonlinear stage of the modulation instability. Due to generic nature of the underlying mathematical model, the proposed concept can be applied across disciplines and nonlinear systems, ranging from optical communications to hydrodynamics.
Purpose
This paper aims to investigate how the user-controlled parameters of the fused filament fabrication three-dimensional printing process define temperature conditions on the boundary between ...layers of the part being fabricated and how these conditions influence the structure and strength of the polylactic acid part.
Design/methodology/approach
Fracture load in a three-point bending test and calculated related stress were used as a measure. The samples were printed with the long side along the z-axis, thus, in the bend tests, the maximum stress occurred orthogonally to the layers. Temperature distribution on the sample surface during printing was monitored with a thermal imager. Sample mesostructure was analyzed using scanning electron microscopy. The influence of the extrusion temperature, the intensity of part cooling, the printing speed and the time between printing individual layers were considered.
Findings
It is shown that the optimization of the process parameters responsible for temperature conditions makes it possible to approximate the strength of the interlayer cohesion to the bulk material strength.
Originality/value
The novelty of the study consists in the generalization of the outcomes. All the parameters varied can be expressed through two factors, namely, the temperature of the previous layer and the extrusion efficiency, determining the ratio of the amount of extruded plastic to the calculated. A regression model was proposed that describes the effect of the two factors on the printed part strength. Along with interlayer bonding strength, these two factors determine the formation of the part mesostructure (the geometry of the boundaries between individual threads).
Recently, carbon allotropes were shown to play a key role in energy harvesting and as hydrophobic coatings on metal alloys. We have designed octylamine-functionalized graphene oxide materials for ...energy harvesting and as an anti-corrosion coating for metal alloy protection in a 3.5% NaCl medium. The material has been characterized by different techniques to confirm the structure and composition of the modified graphene oxide sheet: FTIR spectroscopy, XRD, Raman spectroscopy, FESEM and TEM. The electrochemical stability and corrosion inhibition efficiency were studied by electrochemical methods. The electrochemical stability increased with an increase in the applied voltage up to 500 mV, and the corrosion inhibition efficiency was shown to be 73%. The coating stability studies showed a long stability time in the corrosion medium.
Octylamine-functionalized graphene oxide chemisorbed onto a Mg alloy surface by non-bonding electron.
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