Probable Physical Mechanism Research Articles

Recent expansion of the Atlantic cownose ray (Rhinoptera bonasus) into Bermudian waters

Cownose rays (Family Rhinopteridae) are highly migratory pelagic rays that are generally restricted to continental shelves. Despite 100's of years of natural history records, cownose rays have never been reported in Bermuda, an atoll-like coral reef ecosystem that is separated from the continental mainland United States by ~1,000 km. Here we compile evidence that the Atlantic cownose ray (Rhinoptera bonasus) has recently established in Bermuda, supported by both morphological and genetic data. Potential ecological and inter-specific competition concerns are presented as well as probable physical mechanisms that facilitated this recent and presumed range expansion.

A clustering approach to determine biophysical provinces and physical drivers of productivity dynamics in a complex coastal sea

Abstract. The balance between ocean mixing and stratification influences primary productivity through light limitation and nutrient supply in the euphotic ocean. Here, we apply a hierarchical clustering algorithm (Ward's method) to four factors relating to stratification (wind energy, freshwater index, water-column-averaged vertical eddy diffusivity, and halocline depth), as well as to depth-integrated phytoplankton biomass, extracted from a biophysical ocean model of the Salish Sea. Running the clustering algorithm on 4 years of model output, we identify distinct regions of the model domain that exhibit contrasting wind and freshwater input dynamics, as well as regions of varying water-column-averaged vertical eddy diffusivity and halocline depth regimes. The spatial regionalizations in physical variables are similar in all 4 analyzed years. We also find distinct interannually consistent biological zones. In the northern Strait of Georgia and Juan de Fuca Strait, a deeper winter halocline and episodic summer mixing coincide with higher summer diatom abundance, while in the Fraser River stratified central Strait of Georgia, shallower haloclines and stronger summer stratification coincide with summer flagellate abundance. Cluster-based model results and evaluation suggest that the Juan de Fuca Strait supports more biomass than previously thought. Our approach elucidates probable physical mechanisms controlling phytoplankton abundance and composition. It also demonstrates a simple, powerful technique for finding structure in large datasets and determining boundaries of biophysical provinces.

Degradation of InGaN/GaN quantum well UV LEDs caused by short-term exposure to current

A comparative analysis of the initial stages of degradation of ultraviolet and blue LED structures with InGaN/GaN quantum wells is carried out. In the mode of accelerated aging, the structures were subjected to short-term, sequential exposure to currents of 80-190 mA at forward bias. The exposure time did not exceed three hours. There was an increase (up to 20%) in the external quantum efficiency. The most probable physical mechanisms explaining the changes in InGaN/GaN LEDs are presented and possible ways to slow down the aging of UV LEDs are outlined. Keywords: Degradation of ultraviolet light-emitting diodes, increase in quantum efficiency, slowing down the aging.

Деградация ультрафиолетовых светодиодов с квантовыми ямами InGaN/GaN, вызванная кратковременными воздействиями током

A comparative analysis of the initial stages of degradation of ultraviolet and blue LED structures with InGaN / GaN quantum wells is carried out. In the mode of accelerated aging, the structures were subjected to short-term, sequential exposure to currents of 80–190 mA at forward bias. The exposure time did not exceed three hours. There was an increase (up to 20%) in the external quantum efficiency. The most probable physical mechanisms explaining the changes in InGaN / GaN LEDs are presented and possible ways to slow down the aging of UV LEDs are outlined.

Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean

Atmospheric aerosols play an important role in the formation of warm clouds by acting as efficient cloud condensation nuclei (CCN) and their interactions are believed to cool the Earth-Atmosphere system (‘first indirect effect or Twomey effect’) in a highly uncertain manner compared to the other forcing agents. Here we demonstrate using long-term (2003–2016) satellite observations (NASA’s A-train satellite constellations) over the northern Indian Ocean, that enhanced aerosol loading (due to anthropogenic emissions) can reverse the first indirect effect significantly. In contrast to Twomey effect, a statistically significant increase in cloud effective radius (CER, µm) is observed with respect to an increase in aerosol loading for clouds having low liquid water path (LWP < 75 g m−2) and drier cloud tops. Probable physical mechanisms for this effect are the intense competition for available water vapour due to higher concentrations of anthropogenic aerosols and entrainment of dry air on cloud tops. For such clouds, cloud water content showed a negative response to cloud droplet number concentrations and the estimated intrinsic radiative effect suggest a warming at the Top of the Atmosphere. Although uncertainties exist in quantifying aerosol-cloud interactions (ACI) using satellite observations, present study indicates the physical existence of anti-Twomey effect over the northern Indian Ocean during south Asian outflow.

Electron bistability and switching effects in Mo/p-CdTe/Mo structure

It has been experimentally shown that in a simple metal–semiconductor-metal structure with ohmic contacts, a reversible transition from a high-resistance state to a state with high electrical conductivity is possible under the influence of short current pulses of 80-ns duration with a peak voltage of more than 20 V. It was established that after the breakdown under static voltage, the structure irreversibly goes into a state with high electrical conductivity. At the same time, sections with negative differential resistance and negative differential conductivity appear on its low-frequency current–voltage characteristics at voltages less than 1 V. The most probable physical mechanisms that can provide such current–voltage characteristics are considered.

Electric field-assisted flash sintering of CaCu3Ti4O12: Microstructure characteristics and dielectric properties

The electric field-assisted flash sintering method recently introduced in the literature was here considered for producing high-quality CaCu3Ti4O12 electroceramics, from a powder originally synthesized by a Pechini-derived method and calcined at 800 °C for 2 h. The study included analyzing the dynamics of material shrinkage and densification. With increasing the electric field (E), three distinct regimes were observed: a conventional-like sintering behavior for E < 15 V/cm, followed by a region of accelerated (fast-dominated) sintering for 15 ≲ E < 30 V/cm, and then the flash-dominated regime, for E ≳ 30 V/cm, where sintering is not only accelerated but occurs suddenly. In consequence, sintering of the material under field input takes place at furnace temperatures sensibly lower, reaching a value as low as 750 °C for E = 60 V/cm versus 1050 °C in conventional processing. The probable physical mechanism behind each regime, including the role of the rise in sample temperature induced by the applied field (Joule heating), is also discussed. Finally, a correlation was found between the microstructure characteristics achieved during sintering and the dielectric response measured.

CSI 2264: CHARACTERIZING YOUNG STARS IN NGC 2264 WITH STOCHASTICALLY VARYING LIGHT CURVES*

ABSTRACT We provide CoRoT and Spitzer light curves and other supporting data for 17 classical T Tauri stars in NGC 2264 whose CoRoT light curves exemplify the “stochastic” light curve class as defined in 2014 by Cody et al. The most probable physical mechanism to explain the optical variability within this light curve class is time-dependent mass accretion onto the stellar photosphere, producing transient hot spots. Where we have appropriate spectral data, we show that the veiling variability in these stars is consistent in both amplitude and timescale with the optical light curve morphology. The veiling variability is also well-correlated with the strength of the He i 6678 Å emission line, predicted by models to arise in accretion shocks on or near the stellar photosphere. Stars with accretion burst light curve morphology also have variable mass accretion. The stochastic and accretion burst light curves can both be explained by a simple model of randomly occurring flux bursts, with the stochastic light curve class having a higher frequency of lower amplitude events. Members of the stochastic light curve class have only moderate mass accretion rates. Their Hα profiles usually have blueshifted absorption features, probably originating in a disk wind. The lack of periodic signatures in the light curves suggests that little of the variability is due to long-lived hot spots rotating into or out of our line of sight; instead, the primary driver of the observed photometric variability is likely to be instabilities in the inner disk that lead to variable mass accretion.

Experimental study of the mutual influence of fibre Faraday elements in a spun-fibre interferometer

An all-spun-fibre linear reflective interferometer with two linked Faraday fibre coils is studied. It is found experimentally that there is mutual influence of Faraday fibre coils in this interferometer. It manifests itself as an additional phase shift of the interferometer response, which depends on the circular birefringence induced by the Faraday effect in both coils. In addition, the interferometer contrast and magneto-optical sensitivity of one of the coils change. A probable physical mechanism of the discovered effect is the distributed coupling of orthogonal polarised waves in the fibre medium, which is caused by fibre bend in the coil.

Influence of an external magnetic field on the switching mode of a compact triggered vacuum gap

The possibility of excluding the binding of discharge cathode spots in a small-size pulse vacuum gap by placing the latter in a magnetic field is shown. The probable physical mechanism of this phenomenon is presented.

Modulation of high-frequency seismic noise by tidal deformations: The features of the phenomenon before strong earthquakes and a probable physical mechanism

A probable physical mechanism of tidal modulation of intensity of the endogenous seismic noise is proposed. The mechanism associates this phenomenon with modulation of the size of the region over which the recorded noise is acquired due to nonhysteresis amplitude-dependent absorption in the Earth’s rocks. The two most important cases, namely dry and fluid-saturated rocks, are considered. In both cases, internal elongated strip-like contacts (even in minor quantities) are found to be of fundamental importance. The proposed mechanism provides an explanation for a variety of features of high-frequency seismic noise modulated by tides, which were revealed in the long-term observations on the Kamchatka Peninsula: (i) the modulation depth on the order of the first few percent; (ii) stabilization of the modulation phase before a strong earthquake; (iii) a frequently observed near jump-like change in the phase to the opposite-sign phase after the earthquake; (iv) the subsequent period of a relatively unstable phase; and (v) temporary predominance of the modulation component on the second harmonic of the fundamental tidal frequency in the vicinity of the time when the earthquake occurred.

Fiber polarizer based on W-lightguide Panda

Three kinds of fiber W-polarizer Panda are described: with lengths 200 m, 1 m, and 50 mm. In the first two cases dichroism is higher than 30 dB, in the third case it is higher than 15 dB. The feature of 50-mm polarizer is the scattering layer in quartz cladding. In each case a most probable physical dichroism mechanisms are described.

Femtosecond laser microstructuring of nickel foil

We observe the morphological change and grain structure of Ni foil when it is ablated with femtosecond laser pulses. Scanning electron microscopy and field emission transmission electron microscopy are used to study the nature of the morphology and grain structure of nickel foil and determine the essential features. The results indicate that there are many random nanostructures in the center of the ablated region composed of nanocrystalline grains as well as some core-shell structures. The observed morphologies seem to suggest that phase explosion and extremely high cooling rate are the most probable physical mechanisms responsible for the formation of surface nanostructures.

MOLECULAR HYDROGEN IN THE DISK OF THE HERBIG Ae STAR HD 97048

We present high-resolution spectroscopic mid-infrared observations of the circumstellar disk around the Herbig Ae star HD97048 obtained with the VLT Imager and Spectrometer for the mid-InfraRed (VISIR). We conducted observations of mid-infrared pure rotational lines of molecular hydrogen (H2) as a tracer of warm gas in the disk surface layers. In a previous paper, we reported the detection of the S(1) pure rotational line of H2 at 17.035 microns and argued it is arising from the inner regions of the disk around the star. We used VISIR on the VLT for a more comprehensive study based on complementary observations of the other mid-infrared molecular transitions, namely S(2) and S(4) at 12.278 microns and 8.025 microns respectively, to investigate the physical properties of the molecular gas in the circumstellar disk around HD97048. We do not detect neither the S(2) line nor the S(4) H2 line from the disk of HD97048, but we derive upper limits on the integrated line fluxes which allows us to estimate an upper limit on the gas excitation temperature, T_ex < 570 K. This limit on the temperature is consistent with the assumptions previously used in the analysis of the S(1) line, and allows us to set stronger contraints on the mass of warm gas in the inner regions of the disk. Indeed, we estimate the mass of warm gas to be lower than 0.1 M_Jup. We also discuss the probable physical mechanisms which could be responsible of the excitation of H2 in the disk of HD97048.

Origin of E+A galaxies - I. Physical properties of E+A galaxies formed from galaxy merging and interaction

We investigate the structural, kinematical, and spectrophotometric properties of ``E+A'' galaxies -- those with strong Balmer absorption lines but no significant [OII] emission -- using numerical simulations combined with stellar population synthesis codes. We particularly focus on the two-dimensional (2D) distributions of line-of-sight velocity, velocity dispersion, colors, line index in E+A galaxies formed via the interaction and merging of two gas-rich spirals. Our numerical simulations demonstrate that E+A elliptical galaxies formed by major galaxy merging have positive radial color gradients and negative radial H$\delta$ gradients by virtue of their central poststarburst populations. Furthermore, we show that the projected kinematical and spectroscopic properties of the simulated E+A galaxies can be remarkably different for different major merger models. For example, the simulated E+A ellipticals with kinematically decoupled cores clearly show regions of strong H$\delta$ absorption which are very flattened, with differences in rotation and velocity dispersion between the old and young stars. E+A ellipticals are highly likely to show more rapid rotation and a smaller central velocity dispersion in young stars than in old ones.We also provide specific predictions on the structural, kinematical, and spectrophotometric properties of young globular cluster systems in E+A's. Based on these results, we discuss the importance of spatially resolved, integral field unit spectroscopy on large (8-10m) ground-based telescopes in confirming the formation of kinematically distinct cores in elliptical galaxies produced via dissipative merging and determining the most probable physical mechanism(s) for E+A formation with disky and spheroidal morphologies.

The effect of damage accumulation behaviour on ablation thresholds and damage morphology in ultrafast laser micro-machining of common metals in air

Detailed studies on the ablation of metal targets in air with femtosecond laser pulses are reported. The laser pulses used for the study were 775 nm in wavelength, 150 fs in pulse duration, and the repetition rate used was 100 Hz. Ablation thresholds of copper, titanium, niobium, and stainless steel are measured. The ablation threshold fluence depends on the number of pulses applied to the same spot. The strength of this dependence is governed by the incubation coefficient, S, which has been determined along with the single-shot ablation threshold, φ th(1), for all the metals studied. The accumulation behaviour results from the build-up of plastic deformation induced by the laser pulses. Two distinct ablation phases have been identified from ablation rate curves and an SEM investigation of the ablated morphologies. Ripples were observed on the material surface during the gentle ablation phase, whereas much rougher structures occurred during the stronger ablation phase. Morphological changes of the ablated regions were studied as a function of fluence and incident laser shot number. The observed morphologies seem to suggest that normal vaporisation and phase explosion are the most probable physical mechanisms responsible for material removal during ablation.

Use of preliminary ultraviolet and infrared illumination for diagnostics of MOS and bipolar devices radiation response

The experimental results on the influence of UV and IR illumination and hydrogen ambient on the radiation response of metal-oxide-semiconductor (MOS) and bipolar transistors are presented and discussed. It is shown that preliminary UV treatment increases a radiation-induced degradation of MOS threshold voltage and effect of preliminary IR illumination on BJT radiation response depends on emitter–base bias during the illumination. The probable physical mechanism of the effects is discussed.

TRANSIENT STORAGE ASSESSMENTS OF DYE‐TRACER INJECTIONS IN RIVERS OF THE WILLAMETTE BASIN, OREGON1

ABSTRACT: Rhodamine WT dye‐tracer injections in rivers of the Willamette Basin yield concentration‐time curves with characteristically long recession times suggestive of active transient storage processes. The scale of drainage areas contributing to the stream reaches studied in the Willamette Basin ranges from 10 to 12,000 km2. A transient storage assessment of the tracer studies has been completed using the U.S. Geological Survey's One‐dimensional Transport with Inflow and Storage (OTIS) model, which incorporates storage exchange and decay functions along with the traditional dispersion and advection transport equation. The analysis estimates solute transport of the dye. It identifies first‐order decay coefficients to be on the order of 10−5/sec for the nonconservative Rhodamine W.T. On an individual subreach basis, the first‐order decay is slower (typically by an order of magnitude) than the transient storage process, indicating that nonconservative tracers may be used to evaluate transient storage in rivers. In the transient storage analysis, a dimensionless parameter (As/A) expresses the spatial extent of storage zone area relative to stream cross section. In certain reaches of Willamette Basin pool‐and‐riffle, gravel‐bed rivers, this parameter was as large as 0.5. A measure of the storage exchange flux was calculated for each stream subreach in the simulation analysis. This storage exchange is shown subjectively to be higher at higher stream discharges. Hyporheic linkage between streams and subsurface flows is the probable physical mechanism contributing to a significant part of this inferred active transient storage. Hyporheic linkages are further suggested by detailed measurements of river discharge with an Acoustic Doppler Current Profiler system delineating zones in two large rivers where water alternately enters and leaves the surface channels through gravel‐and‐cobble riverbeds. Measurements show patterns of hyporheic exchange that are highly variable in time and space.

Magnetopause position as an important index of the space weather

We studied long-term variability of the solar wind dynamic pressure (Psw) for the period of satellite observations from 1960 to 1996. The solar wind dynamic pressure is a crucial parameter determining the position of the magnetopause relative to the Earth. The latter parameter is thought to be an indicator of the amount of energy transferred from the solar wind to the near-Earth space. Therefore, we explored the connection between the solar wind dynamic pressure variations and some climatic characteristics such as the middle atmosphere thermal regime and the sea ice cover area. Unexpectedly high degree of correlation has been found between these parameters. We consider it as an evidence of the direct impact of the solar wind dynamics on the Earth's climate characteristics. Preliminary discussion of the probable physical mechanism responsible for these connections is made.

Observation of large-scale hydrodynamic structures in a vortex tube and the Ranque effect

The existence of large-scale structures in the form of a vortical double helix in a swirling Ranque flow is observed for the first time. The structure of the vortical double helix is visualized in real time by the method of Hilbert bichromatic filtering. The experimental result is interpreted on the basis that the most probable physical mechanism for the spatial energy separation in the gas flow (i.e., for the so-called Ranque effect) is viscous heating of the gas in a thin boundary layer at the walls of the vortex chamber and the adiabatic cooling at the center owing to the formation of an intense vortex braid near the axis.