Step-like Increase Research Articles

Electron emission from amorphous solid water after proton impact: Benchmarking PTra and Geant4 track structure Monte Carlo simulations

Track structure Monte Carlo simulations of ionising radiation in water are often used to estimate radiation damage to DNA. For this purpose, an accurate simulation of the transport of densely ionising low-energy secondary electrons is particularly important, but is impaired by a high uncertainty of the required physical interaction cross section data of liquid water.A possible tool for the verification of the secondary electron transport in a track structure simulation has been suggested by Toburen et al. (2010), who have measured the angle-dependent energy spectra of electrons, emitted from a thin layer of amorphous solid water (ASW) upon a passage of 6MeV protons.In this work, simulations were performed for the setup of their experiment, using the PTB Track structure code (PTra) and Geant4-DNA. To enable electron transport below the ionisation threshold, additional excitation and dissociative attachment anion states were included in PTra and activated in Geant4. Additionally, a surface potential was considered in both simulations, such that the escape probability for an electron is dependent on its energy and impact angle at the ASW/vacuum interface.For vanishing surface potential, the simulated spectra are in good agreement with the measured spectra for energies above 50eV. Below, the simulations overestimate the yield of electrons by a factor up to 4 (PTra) or 7 (Geant4-DNA), which is still a better agreement than obtained in previous simulations of this experimental situation. The agreement of the simulations with experimental data was significantly improved by using a step-like increase of the potential energy at the ASW surface.

Microdroplet Growth Mechanism during Water Condensation on Superhydrophobic Surfaces

By promoting dropwise condensation of water, nanostructured superhydrophobic coatings have the potential to dramatically increase the heat transfer rate during this phase change process. As a consequence, these coatings may be a facile method of enhancing the efficiency of power generation and water desalination systems. However, the microdroplet growth mechanism on surfaces which evince superhydrophobic characteristics during condensation is not well understood. In this work, the sub-10 μm dynamics of droplet formation on nanostructured superhydrophobic surfaces are studied experimentally and theoretically. A quantitative model for droplet growth in the constant base (CB) area mode is developed. The model is validated using optimized environmental scanning electron microscopy (ESEM) imaging of microdroplet growth on a superhydrophobic surface consisting of immobilized alumina nanoparticles modified with a hydrophobic promoter. The optimized ESEM imaging procedure increases the image acquisition rate by a factor of 10-50 as compared to previous research. With the improved imaging temporal resolution, it is demonstrated that nucleating nanodroplets coalesce to create a wetted flat spot with a diameter of a few micrometers from which the microdroplet emerges in purely CB mode. After the droplet reaches a contact angle of 130-150°, its base diameter increases in a discrete steplike fashion. The droplet height does not change appreciably during this steplike base diameter increase, leading to a small decrease of the contact angle. Subsequently, the drop grows in CB mode until it again reaches the maximum contact angle and increases its base diameter in a steplike fashion. This microscopic stick-and-slip motion can occur up to four times prior to the droplet coalescence with neighboring drops. Lastly, the constant contact angle (CCA) and the CB growth models are used to show that modeling formation of a droplet with a 150° contact angle in the CCA mode rather than in the CB mode severely underpredicts both the drop formation time and the average heat transfer rate through the drop.

Mesoscopic Stoner Instability in Metallic Nanoparticles Revealed by Shot Noise

We study sequential tunneling through a metallic nanoparticle close to the Stoner instability coupled to parallel magnetized electrodes. Increasing the bias voltage successively opens transport channels associated with excitations of the nanoparticle's total spin. For the current this leads just to a steplike increase. The Fano factor, in contrast, shows oscillations between large super-Poissonian and sub-Poissonian values as a function of bias voltage. We explain the enhanced Fano factor in terms of generalized random-telegraph noise and propose the shot noise as a convenient tool to probe the mesoscopic Stoner instability.

Prolonged magma emplacement as a mechanism for the origin of the marginal reversal of the Fongen–Hyllingen layered intrusion, Norway

AbstractThe ~100 m thick marginal zone of the Fongen–Hyllingen Intrusion (FHI) consists of non-layered, highly iron-enriched ferrodiorites that are overlain by a ~ 6 km thick layered sequence of gabbroic to dioritic rocks of the Layered Series. From the base upwards the marginal zone becomes more primitive as exemplified by a significant increase in whole-rock MgO, Mg-number and normative An. The reverse trends are also evident from an upward increase in An-content of plagioclase (from ~ 30 to ~ 43 at.%) and Mg-number of amphibole (from ~ 9 to ~ 23 at.%) and clinopyroxene (from ~ 23 to ~ 33 at.%). The marginal zone is abruptly terminated at the contact with the overlying Layered Series as is evident from a step-like increase in Mg-number of mafic minerals and An-content of plagioclase, as well as a sharp increase in whole-rock MgO and Mg-number in overlying olivine gabbronorites of the Layered Series. Based on these features the marginal zone of the FHI can be interpreted as an aborted marginal reversal. Reverse trends in whole-rock and mineral compositions, as well as a sharp break in these parameters are indicative of its formation in an open system with the involvement of the prolonged emplacement of magma that became increasingly more primitive. Such development of the marginal reversal was interrupted by the emplacement of a major influx of more primitive magma that produced the Layered Series. The open system evolution of a basaltic magma chamber may represent a general mechanism for the origin of marginal reversals in mafic sills and layered intrusions.

High-temperature dielectric properties of Gd2CuO4 ceramics

A sample of Gd2CuO4 (GCO) has been prepared through the solid state reaction technique. Dielectric properties of this material have been measured in detail as functions of temperature (between 285 and 450K) and frequency (20Hz–10MHz). A step-like increase below 330K and a broad peak around 360K were observed in the real part of the permittivity (ε′) which were found to be originated from the oxygen vacancy hopping motions that cause a dipolar relaxation, followed by a Maxwell–Wagner relaxation as the hopping carriers are blocked by the interfaces and surfaces of the sample.

The brain on art: intense aesthetic experience activates the default mode network.

Aesthetic responses to visual art comprise multiple types of experiences, from sensation and perception to emotion and self-reflection. Moreover, aesthetic experience is highly individual, with observers varying significantly in their responses to the same artwork. Combining fMRI and behavioral analysis of individual differences in aesthetic response, we identify two distinct patterns of neural activity exhibited by different sub-networks. Activity increased linearly with observers' ratings (4-level scale) in sensory (occipito-temporal) regions. Activity in the striatum (STR) also varied linearly with ratings, with below-baseline activations for low-rated artworks. In contrast, a network of frontal regions showed a step-like increase only for the most moving artworks (“4” ratings) and non-differential activity for all others. This included several regions belonging to the “default mode network” (DMN) previously associated with self-referential mentation. Our results suggest that aesthetic experience involves the integration of sensory and emotional reactions in a manner linked with their personal relevance.

Step-like enhancement of luminescence quantum yield of silicon nanocrystals

Carrier multiplication by generation of two or more electron-hole pairs following the absorption of a single photon may lead to improved photovoltaic efficiencies and has been observed in nanocrystals made from a variety of semiconductors, including silicon. However, with few exceptions, these reports have been based on indirect ultrafast techniques. Here, we present evidence of carrier multiplication in closely spaced silicon nanocrystals contained in a silicon dioxide matrix by measuring enhanced photoluminescence quantum yield. As the photon energy increases, the quantum yield is expected to remain constant, or to decrease as a result of new trapping and recombination channels being activated. Instead, we observe a step-like increase in quantum yield for larger photon energies that is characteristic of carrier multiplication. Modelling suggests that carrier multiplication is occurring with high efficiency and close to the energy conservation limit.

Lithospheric structure beneath the Zagros collision zone resolved by non-linear teleseismic tomography

The upper-mantle structure across the Zagros collision zone, in southwest Iran, is investigated using a non-linear weighted damped least-squares teleseismic tomography approach. The resolution of the structures/transitions in the upper mantle is enhanced significantly by correcting the teleseismic relative arrival time residuals for an a priori crustal velocity model and then performing the inversion with fixed crustal blocks. To investigate whether or not the lithospheric blocks and major transitions in the resulting model are required by the data or are artefacts of the inversion, the data were inverted using two different inverse methods (singular value decomposition and a quadratic programming method). New high-quality seismic velocity models show apparent correlation between surface geological features and seismic velocity structures at lithospheric depth across the Zagros collision zone. The image shows a sharp lithospheric boundary at the Main Zagros Thrust between 100 km and 250 km depth with P-wave velocity about 3 per cent faster within the Arabian Shield to the south. A step-like increase in lithospheric thickness across the Zagros collision zone is assumed to separate two different mantle structures namely the Arabian (to the south) and the Eurasian (to the north) domains. The most striking feature resolved is a north-dipping slab-like positive velocity anomaly.

Shaped metal deposition of 300M steel

A component prepared by shaped metal deposition (SMD) using 300M steel wire is studied to reveal structure and material properties. The component exhibits a bainitic microstructure changing from distinct sheaves to homogenous from top to bottom. This change in microstructure is reflected by a step-like increase of the volume fraction of austenite towards the bottom of the component, and a step-like decrease of the microhardness. A certain deviation of the general change in the morphology of bainite from top to bottom appears at the very bottom of the component, caused by the influence of the base plate. Tensile tests show a very high ultimate tensile strength of about 1500 MPa and an elastic modulus of 200 GPa, which is comparable to that of material in cast condition.

Dynamical magnetotransport in Ln0.6Sr0.4MnO3 (Ln = La, Sm)

We compare radio frequency electrical transport in Ln0.6Sr0.4MnO3 (Ln = La and Sm). AC resistance (R) and reactance (X) were simultaneously measured as a function of temperature (T), magnetic field (H), and frequency (f). The R(T, H = 0 G) in La0.6Sr0.4MnO3 (LSMO) shows a broad insulator-metal transition around 247 K below the Curie temperature (TC) for f ≤ 2 MHz but a steplike increase at TC for f ≥ 3 MHz. Conversely, R(T, H = 0 G) in Sm0.6Sr0.4MnO3 exhibits a single peak at TC = 116±2 K for f = 0.1 MHz which splits into two peaks accompanied by a dip at TC for higher frequencies. While the low temperature peak shifts upward rapidly with the increasing H (μ0H > 1 T) for f = 5 MHz, the high temperature peak is insensitive to the magnetic field. A large ac magnetoresistance (ΔR/R= −32%) and magnetoreactance (ΔX/X = −21%) at a low magnetic field (H = 70 mT) is observed in LSMO around TC in contrast to a positive ΔR/R (=170%) and a negative ΔX/X (= −94%) at μ0H = 7 T. We discuss the possible origins of the observed effects.

Dielectric relaxation and magnetic behavior of bismuth-substituted yttrium iron garnet

Y3−xBixFe5O12 (x = 0–1.0) was prepared by solid state reaction. X-ray diffraction showed a gradual increase of lattice parameter with the Bi concentration, indicating that Bi had been incorporated into the lattice. Dielectric responses of the samples at room temperature increased initially at low Bi (x < 0.4) and then decreased rapidly at high Bi (x ≥ 0.6). Temperature dependence of dielectric constant showed a huge steplike increase at the temperatures between 20 and 200 °C, increasing with Bi. X-ray photoelectron spectroscopy revealed the presence of Fe2+ and Bi2+ in the samples, which might be responsible for the dielectric behaviors. An increase of coercivity and Curie temperature with Bi was observed. This was accompanied by a reduction of the saturation magnetization, whose variation with T follows a modified Bloch law.

Electric Field Gradient Fluctuations in Filled SkutteruditeReRu4Sb12(Re= La, Ce, and Pr) Probed by Sb-NQR

We have carried out 121,123 Sb nuclear quadrupole resonance (NQR) measurements on Re Ru 4 Sb 12 ( Re = La, Ce and Pr) to investigate an anomalous behavior of the nuclear spin–echo relaxation rate 1/ T 2 observed in Re Os 4 Sb 12 . The full width at half maximum of the NQR spectrum shows a step-like increase below 130 K with decreasing temperature. Temperature dependence of 1/ T 2 also shows a divergence at ∼115 K whereas the nuclear spin–lattice relaxation rate 1/ T 1 does not show any anomaly. These results are caused by a distribution of the electric field gradient (EFG) and its fluctuations, which might arise from a rattling motion of the rare earth ion centered in the cage which consists of twelve Sb and/or a small deformation of the cage. The EFG fluctuations observed in Re Os 4 Sb 12 and Re Ru 4 Sb 12 at T ∼120 K originates from an unique crystal structure of the filled skutterudite with oversized Sb-cage.

Effects of a solar wind dynamic pressure increase in the magnetosphere and in the ionosphere

Abstract. On 17 July 2005, an earthward bound north-south oriented magnetic cloud and its sheath were observed by the ACE, SoHO, and Wind solar wind monitors. A steplike increase of the solar wind dynamic pressure during northward interplanetary magnetic field conditions was related to the leading edge of the sheath. A timing analysis between the three spacecraft revealed that this front was not aligned with the GSE y-axis, but had a normal (−0.58,0.82,0). Hence, the first contact with the magnetosphere occurred on the dawnside rather than at the subsolar point. Fortunately, Cluster, Double Star 1, and Geotail happened to be distributed close to the magnetopause in this region, which made it possible to closely monitor the motion of the magnetopause. After the pressure front had impacted the magnetosphere, the magnetopause was perceived first to move inward and then immediately to correct the overshoot by slightly expanding again such that it ended up between the Cluster constellation with Double Star 1 inside the magnetosphere and Geotail in the magnetosheath. Coinciding with the inward and subsequent outward motion, the ground-based magnetic field at low latitudes was observed to first strengthen and then weaken. As the magnetopause position stabilised, so did the ground-based magnetic field intensity, settling at a level slightly higher than before the pressure increase. Altogether the magnetopause was moving for about 15 min after its first contact with the front. The high latitude ionospheric signature consisted of two parts: a shorter (few minutes) and less intense preliminary part comprised a decrease of AL and a negative variation of PC. A longer (about ten minutes) and more intense main part of the signature comprised an increase of AU and a positive variation of PC. Measurements from several ground-based magnetometer networks (210 MM CPMN, CANMOS, CARISMA, GIMA, IMAGE, MACCS, SuperMAG, THEMIS, TGO) were used to obtain information on the ionospheric E×B drift. Before the pressure increase, a configuration typical for the prevailing northward IMF conditions was observed at high latitudes. The preliminary signature coincided with a pair of reverse convection vortices, whereas during the main signature, mainly westward convection was observed at all local time sectors. Afterwards, the configuration preceding the pressure increase was recovered, but with slightly enhanced convection. Based on the timing analysis, the existence of the preliminary signature coincided with the passage of the oblique pressure front, whereas during the main signature the front was already well past Earth. The main signature existed during the time the magnetopause was observed to move. As the position stabilised, also the signature disappeared.

ChemInform Abstract: Orbital Magnetization and Iron Contribution to the Magnetic Anisotropy of Er2Fe17Cx.

Abstract A detailed 57 Fe Mossbauer spectroscopy study of the spin reorientation phenomenon in the Er 2 Fe 17 C x series is presented. From the step-like increase of the effective magnetic field at the spin reorientation temperature the sign and magnitude of the anisotropy of the orbital contribution to the iron hyperfine field are estimated. The spin-orbit contribution to the anisotropy energy is compared with the value of the macroscopic magnetocrystalline anisotropy.

The case for recurring outbreaks of a new type of infectious disease across all parts of the United Kingdom

The higher than expected increase in medical emergency hospital admissions has been a matter of debate for many years. While regular growth of around 1.0-1.5% per annum may be expected due to demography recent evidence has emerged from England and Scotland that the increase over time appears to occur in concentrated spurts of growth at an interval of 3 to 6 years resulting in an approximate 10% step-like increase in certain medical and mental health related diagnoses. A characteristic time-related pattern in admissions then follows each step-increase. Outbreaks of a previously uncharacterised infectious disease have been proposed to account for this behaviour. Evidence is presented to show that simultaneous outbreak(s) across the remainder of the UK (Wales and Northern Ireland) are occurring with step-like increases in a similar range of diagnoses. The infectious agent is proposed to be a member of the group of persistent viruses and appears to show some form of collective switch to a dormant state around 3½ years after the initial outbreak. This behaviour accounts for the unique pattern of hospital admissions seen over time and is so strong that any underlying demographic trends are overwhelmed. This particular pattern of admissions will have uniquely profound financial effects upon the cost pressures experienced within the health services.

Geomagnetic disturbances on ground associated with particle precipitation during SC

Abstract. We have examined several cases of magnetosphere compression by solar wind pressure pulses using a set of instruments located in the noon sector of auroral zone. We have found that the increase in riometric absorption (sudden commencement absorption, SCA) occurred simultaneously with the beginning of negative or positive magnetic variations and broadband enhancement of magnetic activity in the frequency range above 0.1 Hz. Since magnetic variations were observed before the step-like increase of magnetic field at equatorial station (main impulse, MI), the negative declinations resembled the so-called preliminary impulse, PI. In this paper a mechanism for the generation of PI is introduced whereby PI's generation is linked to SCA – associated precipitation and the local enhancement of ionospheric conductivity leading to the reconstruction of the ionospheric current system prior to MI. Calculation showed that PI polarity depends on orientation of the background electric field and location of the observation point relative to ionospheric irregularity. For one case of direct measurements of electric field in the place where the ionospheric irregularity was present, the sign of calculated disturbance corresponded to the observed one. High-resolution measurements on IRIS facility and meridional chain of the induction magnetometers are utilized for the accurate timing of the impact of solar wind irregularity on the magnetopause.

Transport in armchair graphene nanoribbons modulated by magnetic barriers

In this study, we investigated the one-dimensional transport in armchair graphene nanoribbons (AGNRs) modulated by a magnetic barrier structure. The conductance as a function of Fermi energy shows a step-like increase by the height of 4 e 2 / h with characteristic oscillations associated with tunneling resonances. The results turn out to be sensitive to the boundary conditions. In addition, we discussed bound states which exist in the region of the magnetic structure.

State-Dependent Performance of Optic-Flow Processing Interneurons

Active locomotive states are metabolically expensive and require efficient sensory processing both to avoid wasteful movements and to cope with an extended bandwidth of sensory stimuli. This is particularly true for flying animals because flight, as opposed to walking or resting, imposes a steplike increase in metabolism for the precise execution and control of movements. Sensory processing itself carries a significant metabolic cost, but the principles governing the adjustment of sensory processing to different locomotor states are not well understood. We use the blowfly as a model system to study the impact on visual processing of a neuromodulator, octopamine, which is known to be involved in the regulation of flight physiology. We applied an octopamine agonist and recorded the directional motion responses of identified visual interneurons known to process self-motion-induced optic flow to directional motion stimuli. The neural response range of these neurons is increased and the response latency is reduced. We also found that, due to an elevated spontaneous spike rate, the cells' negative signaling range is increased. Meanwhile, the preferred self-motion parameters the cells encode were state independent. Our results indicate that in the blowfly energetically expensive sensory coding strategies, such as rapid, large responses, and high spontaneous spike activity could be adjusted by the neuromodulator octopamine, likely to save energy during quiet locomotor states.

Electron field emission from transparent multiwalled carbon nanotube sheets for inverted field emission displays

Strong, conducting, transparent carbon nanotube sheets were prepared by solid-state draw from well-ordered, aligned multiwalled carbon nanotube (MWCNT) forests [Zhang et al., 2005] [1]. Study of electron field emission from such transparent MWCNT sheets shows threshold fields of less than 0.5 V/μm with current densities high enough for display applications. Step-like field emission current increase and hysteresis behavior in I– V curves has been observed. The origin of such behavior is discussed in terms of mechanical rearrangement of the nanotube network in high electric field. Studied MWCNT transparent sheet field emission cathodes have several advantages when used as multi-functional electrodes. They are high current, high stability, transparent, and flexible field emission sources and can be used in an inverted geometry, with cathode being in front of the light emitting plate. At the same time transparent CNT sheets may serve as a transparent conducting electrode for electrical connection and pixel addressing in field emission displays (FEDs). Also, these sheets can be used as an optical polarizer in FEDs.

Sodium diffusion in cryolite at elevated temperatures studied by quasielastic neutron scattering

Quasielastic neutron scattering (QENS) has been applied to study the sodium mobility on nanosecond time scales in the perovskite fluoride cryolite, Na 3AlF 6, at high temperatures. Up to T = 1153 K the diffusion of Na ions is well described by a diffusion process of jumps between six and eight-fold coordinated sites. Above this temperature, where a step-like increase in the electrical conductivity occurs, the jump length increases, which indicates additional jumps over larger distances. The electrical conductivity derived from the self-diffusion coefficient via the Nernst–Einstein relation and the corresponding activation energy are in excellent agreement with the previous conductivity measurements. We conclude that the jump diffusion of sodium ions is the dominant mechanism for the electrical conductivity in cryolite at high temperatures up to T = 1153 K.