Time-of-flight mass spectrometer for diagnostics of continuous plasma flow

This paper describes a version of the time-of-flight mass spectrometer based on a modified two-field acceleration approach of Wiley and McLaren. The aim of the device is a diagnostic of continuous plasma flow. The acceleration scheme idea, the construction of the spectrometer, and results of testing in plasma flow of Gd and CeO₂ generated by vacuum arc discharge are described. The instrument function of the spectrometer was measured, and its mass resolution was evaluated as ∼20. With the use of the instrument function, how to interpret the registered signal in the case of intersection of mass peaks was suggested. The presented device has a simple construction and relatively low values of applied acceleration voltages, so it has fewer requirements in manufacturability and cost.

A repeating fast radio burst source in a globular cluster

Fast radio bursts (FRBs) are flashes of unknown physical origin¹. The majority of FRBs have been seen only once, although some are known to generate multiple flashes^2,3. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission^4,5. Recently, the discovery⁶ of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths⁶. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system⁷. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.

A synchrotron computed tomography dataset for validation of longitudinal tensile failure models based on fibre break and cluster development

We performed in-situ tensile tests on two carbon fibre/epoxy composites with continuous scanning using synchrotron computed tomography (CT). Both composites were cross-ply laminates, and two specimens were tested for each composite. The voxel size was sufficiently small to recognize individual fibres and fibre breaks. For each test, 16-19 volumes were reconstructed, cropped down to the 0° plies and analysed to track fibre break and cluster development. This dataset provides the last CT volume before failure for each of the four specimens as well as the individual fibre break locations in all reconstructed volumes. These data are then plotted against predictions from six state-of-the-art strength models. The target is that these data become a benchmark for the development of new models, inspiring researchers to set up refined experiments and develop improved models.

Structure of the bacteriophage PhiKZ non-virion RNA polymerase

Bacteriophage ΦKZ (PhiKZ) is the archetype of a family of massive bacterial viruses. It is considered to have therapeutic potential as its host, Pseudomonas aeruginosa, is an opportunistic, intrinsically antibiotic resistant, pathogen that kills tens of thousands worldwide each year. ΦKZ is an incredibly interesting virus, expressing many systems that the host already possesses. On infection, it forms a ‘nucleus’, erecting a barrier around its genome to exclude host endonucleases and CRISPR-Cas systems. ΦKZ infection is independent of the host transcriptional apparatus. It expresses two different multi-subunit RNA polymerases (RNAPs): the virion RNAP (vRNAP) is injected with the viral DNA during infection to transcribe early genes, including those encoding the non-virion RNAP (nvRNAP), which transcribes all further genes. ΦKZ nvRNAP is formed by four polypeptides thought to represent homologues of the eubacterial β/β′ subunits, and a fifth with unclear homology, but essential for transcription. We have resolved the structure of ΦKZ nvRNAP to better than 3.0 Å, shedding light on its assembly, homology, and the biological role of the fifth subunit: it is an embedded, integral member of the complex, the position, structural homology and biochemical role of which imply that it has evolved from an ancestral homologue to σ-factor.

On Krylov’s estimates for optional semimartingales

The estimates of N. V. Krylov for distributions of stochastic integrals by means of the L d {L_{d}} -norm of a measurable function are well-known and are widely used in the theory of stochastic differential equations and controlled diffusion processes. We generalize estimates of this type for optional semimartingales, then apply these estimates to prove the change of variables formula for a general class of functions from the Sobolev space W d 2 {W^{2}_{d}} . We also show how to use these estimates for the investigation of L 2 {L^{2}} -convergence of solutions of optional SDE’s.

Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(0 0 1) interfaces

We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(0 0 1) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs^-1 (close to the Fermi velocity) and the decay length on the order of 100 nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.

Analysis of the time-resolved magneto-optical Kerr effect for ultrafast magnetization dynamics in ferromagnetic thin films

We discuss fundamental aspects of laser-induced ultrafast demagnetization probed by the time-resolved magneto-optical Kerr effect (MOKE). Studying thin Fe films on MgO substrate in the absence of electronic transport, we demonstrate how to disentangle pump-induced variations of magnetization and magneto-optical coefficients. We provide a mathematical formalism for retrieving genuine laser-induced magnetization dynamics and discuss its applicability in real experimental situations. We further stress the importance of temporal resolution achieved in the experiments and argue that measurements of both time-resolved MOKE rotation and ellipticity are needed for the correct assessment of magnetization dynamics on sub-picosecond timescales. The framework developed here sheds light onto the details of the time-resolved MOKE technique and contributes to the understanding of the interplay between ultrafast laser-induced optical and magnetic effects.

Optoelectronic transport properties in amorphous/crystalline silicon solar cell heterojunctions measured by frequency-domain photocarrier radiometry: multi-parameter measurement reliability and precision studies

A theoretical one-dimensional two-layer linear photocarrier radiometry (PCR) model including the presence of effective interface carrier traps was used to evaluate the transport parameters of p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) passivated by an intrinsic hydrogenated amorphous silicon (i-layer) nanolayer. Several crystalline Si heterojunction structures were examined to investigate the influence of the i-layer thickness and the doping concentration of the a-Si:H layer. The experimental data of a series of heterojunction structures with intrinsic thin layers were fitted to PCR theory to gain insight into the transport properties of these devices. The quantitative multi-parameter results were studied with regard to measurement reliability (uniqueness) and precision using two independent computational best-fit programs. The considerable influence on the transport properties of the entire structure of two key parameters that can limit the performance of amorphous thin film solar cells, namely, the doping concentration of the a-Si:H layer and the i-layer thickness was demonstrated. It was shown that PCR can be applied to the non-destructive characterization of a-Si:H/c-Si heterojunction solar cells yielding reliable measurements of the key parameters.

Laser-induced magnetization dynamics of lanthanide-doped permalloy thin films

We investigate the effect of Ho, Dy, Tb, and Gd impurities on the femtosecond laser-induced magnetization dynamics of thin Permalloy films using the time-resolved magneto-optical Kerr effect. Varying the amount of Ho, Dy, Tb content from 0% to 8%, we observe a gradual change of the characteristic demagnetization time constant from approximately 60 to approximately 150 fs. In contrast, Gd concentrations up to 15% do not influence the time scale of the initial photoinduced magnetization loss. We propose a demagnetization mechanism that relies on strong magnetic inertia of the rare-earth dopant which stabilizes the ferrimagnetic ordering and thereby delays the demagnetization.

Magnon-enhanced phonon damping at Gd(0001) and Tb(0001) surfaces using femtosecond time-resolved optical second-harmonic generation

Damping of coherent optical phonons is investigated by femtosecond time-resolved second-harmonic generation at Gd(0001) and Tb(0001) surfaces. At low temperature the damping rate increases monotonically with temperature, but close to the Curie point the damping rate is strongly reduced. We explain this behavior by phonon-magnon scattering originating from spin-orbit coupling proven by a larger effect for Tb than for Gd. Consideration of phonon-electron and phonon-phonon scattering shows that magnon-mediated damping is dominant almost up to the Curie temperature.

Nonequilibrium magnetization dynamics of gadolinium studied by magnetic linear dichroism in time-resolved 4f core-level photoemission

The magnetic linear dichroism of the gadolinium 4f core level is studied in a time-resolved photoemission experiment employing laser pump- and synchrotron-radiation probe pulses. Upon optical excitation of the 5d6s valence electrons with femtosecond laser pulses, the magnetic order in the 4f spin system is reduced. Remarkably, the linear dichroism remains at 80% of the equilibrium contrast while the lattice temperature reaches the Curie temperature due to electron-phonon scattering. Contrasting itinerant ferromagnets, this shows that equilibration between the lattice and spin subsystems takes in Gd about 80 ps and is established in parallel with heat diffusion.

Complex electrooptic research of nano-particle parameters in colloids

A research of some colloids has been carried out by means of dynamic light scattering, electrooptical and magnetooptical techniques. Intensity autocorrelation functions of scattered light have been compared to the relaxation curves of electrooptical effect for colloid particles of different shapes. The results of complex research confirm that the complicated character of light scattering by particles allows us to use the methods of birefringence and dichroism only formally when studying most colloid systems. Very thin nano-disperse structures are an exception to this rule. The investigation of polydispersity of some colloids was carried out by magnetooptical and two electrooptical techniques. Size distribution functions resulted from the different techniques agree. This justifies the suppositions about particle light scattering that are required for the use of the methods.

Algorithms for network analysis in systems-ADME/Tox using the MetaCore and MetaDrug platforms

The authors have previously applied two integrated platforms, MetaCore and MetaDrug, for the assembly and analysis of human biological networks as a useful method for the integration and functional interpretation of high-throughput experimental data. The present study demonstrates in detail the specific algorithms that are used in both software platforms. Using a standard set of genes as input, namely CYP3A4 (an enzyme), PXR (a nuclear hormone receptor), MDR1 (a transporter) and hERG (an ion channel) related to the absorption, distribution, metabolism, excretion and toxicity (ADME/Tox) of xenobiotics, we have now generated networks with each algorithm. The relative advantages and disadvantages of these algorithms are explained using these examples as well as appropriate instances of utility to illustrate further the particular circumstances for their use. In addition, the benefits of the different network algorithms are identified when compared with algorithms available in other products, where this information is available.

Scaling of the low-temperature dephasing rate in Kondo systems

We present phase coherence time measurements in quasi-one-dimensional Ag wires doped with Fe Kondo impurities of different concentrations n_{s}. Because of the relatively high Kondo temperature T_{K} approximately 4.3 K of this system, we are able to explore a temperature range from above T_{K} down to below 0.01T_{K}. We show that the magnetic contribution to the dephasing rate gamma_{m} per impurity is described by a single, universal curve when plotted as a function of T/T_{K}. For T>0.1T_{K}, the dephasing rate is remarkably well described by recent numerical results for spin S=1/2 impurities. At lower temperature, we observe deviations from this theory. Based on a comparison with theoretical calculations for S>1/2, we discuss possible explanations for the observed deviations.

Femtosecond electron and spin dynamics in Gd(0001) studied by time-resolved photoemission and magneto-optics

Femtosecond electron and spin dynamics of the Gd(0001) surface are investigated by time-resolved photoemission and second harmonic generation. Upon optical excitation the spin polarization of the surface state is reduced by half while its exchange splitting remains nearly unchanged. Electron-magnon interaction is proposed to facilitate electron-spin-flip scattering among spin-mixed surface and bulk states, which provides a mechanism for ultrafast demagnetization.

Coherent optical phonons and parametrically coupled magnons induced by femtosecond laser excitation of the Gd(0001) surface

Coherent spin dynamics in the THz domain coupled to a coherent phonon is observed in the time-resolved second harmonic response of the Gd(0001) ferromagnetic metal surface. An LO phonon of 2.9 THz is excited by a transient charge displacement at the surface caused by resonant absorption of a fs laser pulse in the exchange-split surface state. This lattice vibration modulates the interlayer distance inducing a coherent variation of the exchange interaction between spins in adjacent layers. The resulting magnetization dynamics is considered as optical magnon wave packets coupled to the phonon.

Clinical and environmental isolates of Burkholderia cepacia exhibit differential cytotoxicity towards macrophages and mast cells

Burkholderia cepacia is an emerging opportunistic pathogen that causes fatal infections in patients suffering from cystic fibrosis (CF) and chronic granulomatous disease. Various environmental isolates of B. cepacia are, however, capable of degrading environmental pollutants, such as trichloroethylene, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), etc., and are also highly effective in controlling plant diseases caused by nematodes and fungi. Such strains have therefore been proposed for environmental release to clean up toxic dump sites or as biopesticides. Various efforts to distinguish between clinical and environmental isolates of B. cepacia with regard to their virulence characteristics have produced ambiguous results, suggesting that newer methods are needed to test for the presence or absence of pathogenic potential in B. cepacia strains proposed for environmental release. We now report that several clinical strains of B. cepacia secrete cytotoxic factors that allow macrophage and mast cell death in the presence of external ATP. Several environmental strains had reduced activity in this regard. We also demonstrate that, while all the strains secrete enzymes that have nucleoside diphosphate kinase (Ndk), adenylate kinase (Ak) and 5'-nucleotidase activity, the level of secretion of the 5'-nucleotidase (and/or ATPase/phosphatase) appears to be lower in the environmental strains than in the clinical strains. The secretion of these enzymes is specifically activated in the presence of eukaryotic proteins such as alpha2-macroglobulin. As macrophage-or mast cell surface-associated P2Z receptors promote their cell death in the presence of mM concentrations of ATP, and as the secreted ATP-using enzymes generate various phosphorylated or non-phosphorylated adenine nucleotides that may even be better agonists than ATP in activating the P2Z receptors or may act through the activation of additional purinergic receptors, such enzymes may play an important role in allowing B. cepacia to evade host defence.

Random mutagenesis by recombinational capture of PCR products in Bacillus subtilis and Acinetobacter calcoaceticus

We describe a general method for random mutagenesis of cloned genes by error-prone PCR or DNA shuffling that eliminates the need for post-amplification subcloning following each cycle of mutagenesis. This method exploits the highly efficient and recombinogenic nature of DNA uptake during natural transformation in the Gram-positive bacterium Bacillus subtilis and the Gram-negative bacterium Acinetobacter calcoaceticus. Plasmid systems were designed that allow capture of PCR-amplified DNA fragments by marker-replacement recombination with a structurally similar helper plasmid resident in the transformation recipient. This recombination event simultaneously transfers the amplified sequences into the helper plasmid and restores the integrity of a drug resistance gene, thereby affording a direct selection for fragment capture. Although this strategy was sufficiently effective to permit recovery in B. subtilis of up to 10(3) transformants/microgram of PCR product, equivalent plasmid systems were approximately 100 times more efficient in A.calcoaceticus. Acinetobacter calcoaceticus also offers the advantage of essentially constitutive transformation competence in ordinary complex broth, such as LB, in contrast to two-step growth in semi-synthetic media required for optimal transformation of B.subtilis.

The Bacillus SpoIIGA protein is targeted to sites of spore septum formation in a SpoIIE-independent manner

The process of bacterial cell division involves the assembly of a complex of proteins at the site of septation that probably provides both the structural and the cytokinetic functions required for elaboration and closure of the septal annulus. During sporulation in Bacillus subtilis, this complex of proteins is modified by the inclusion of a sporulation-specific protein, SpoIIE, which plays a direct role in gene regulation and also has a genetically separable role in determining the gross structural properties of the specialized sporulation septum. We demonstrate by both green fluorescent protein (GFP) fusions and indirect immunofluorescence microscopy that SpoIIGA, a protein required for proteolytic cleavage of pro-sigmaE, is also targeted to the sporulation septum. Septal localization of SpoIIGA-GFP occurred even in the structurally abnormal septum formed by a SpoIIE null mutant. We also report the isolation of a spoIIGA homologue from Bacillus megaterium, a species in which the cells are significantly larger than those of B. subtilis. We have exploited the physical dimensions of the B. megaterium sporangium, in conjunction with wide-field deconvolution microscopy, to construct three-dimensional projections of sporulating cells. These projections indicate that SpoIIGA-GFP is initially localized in an annulus at the septal periphery and is only later localized uniformly throughout the septa. Localization was also detected in a B. subtilis spo0H null strain that fails to construct a spore septum. We propose that SpoIIGA is sequestered in the septum by an interaction with components of the septation machinery and that this interaction begins before the construction of the asymmetric septum.

Voltage-sensitive dye recordings of electrophysiological activation in a Langendorff-perfused mouse heart

The pattern of electrophysiological activation of adult mouse ventricles was measured with the use of voltage-sensitive dye methods. Di-4-ANEPPS was used to monitor membrane potential as small changes in fluorescence, which were detected by a state of the art, cooled, charged coupled device camera/image intensifier system. The extremely rapid conduction velocity, coupled with the small size of this preparation, necessitated taking these measurements at room temperature (22 to 23 degrees C). Initial experiments demonstrate that ventricular activation can be identified and its conduction pattern can be monitored reproducibly and with high resolution for extended time periods (10 to 20 mins) during spontaneous activity.