Improved models for drop-on-demand ink-jet shortening

A previous 1-D model for the shortening of an unbroken drop-on-demand ink-jet ligament has been extended to the case of an arbitrary attached tail mass, and can also include extensional viscosity (which has ∼ 2% effect) as well as linear elasticity in the fluid. Predictions from the improved model are shown to be very similar to results from 2-D axisymmetric numerical simulations of DoD ink-jet ligaments and also to the results of recent experiments on Newtonian fluids jetted without satellite formation.

Imbibition dynamics of nano-particulate ink-jet drops on micro-porous media

Ink-jet printing of nano-metallic colloidal fluids on to porous media such as coated papers has become a viable method to produce conductive tracks for low-cost, disposable printed electronic devices. However, the formation of well-defined and functional tracks on an absorbing surface is controlled by the drop imbibition dynamics in addition to the well-studied post-impact drop spreading behavior. This study represents the first investigation of the real-time imbibition of ink-jet deposited nano-Cu colloid drops on to coated paper substrates. In addition, the same ink was deposited on to a non-porous polymer surface as a control substrate. By using high-speed video imaging to capture the deposition of ink-jet drops, the time-scales of drop spreading and imbibition were quantified and compared with model predictions. The influences of the coating pore size on the bulk absorption rate and nano-Cu particle distribution have also been studied.

Properties and applications of cold supersonic gas jet

By analyzing the formation mechanism of a supersonic gas jet, a set of equations which describe the atomic beam properties were established. The influence of initial temperature, initial pressure, background gas pressure and pumping speed was discussed in detail. A simulation program was developed based on the equations, and the results under different initial conditions were obtained. The results are in good agreement with the experimental data, and suggest that, in order to get much smaller transverse momentum in collision experiments, it is necessary to lower the initial temperature and the initial pressure of the supersonic gas jet, together with increasing the pumping speed. These results are very instructive for construction of a new generation of cold supersonic gas jets.

Droplet formation with electromagnetic pulse force

Methods for serial generation of droplets from a liquid jet are shortly reviewed. A method of liquid metal droplet generation based on AC high frequency magnetic field is considered in detail. Numerical model for direct simulation of the time dependent droplet generation process is presented. Computed examples demonstrate the liquid silicon droplet formation for the cases of 500-1500 μm diameter.

Cold atmospheric pressure plasma jet interactions with plasmid DNA

The effect of a cold (<40 °C) radio frequency-driven atmospheric pressure plasma jet on plasmid DNA has been investigated. Gel electrophoresis was used to analyze the DNA forms post-treatment. The experimental data are fitted to a rate equation model that allows for quantitative determination of the rates of single and double strand break formation. The formation of double strand breaks correlates well with the atomic oxygen density. Taken with other measurements, this indicates that neutral components in the jet are effective in inducing double strand breaks.

Relativistic High Harmonic Generation In Gas Jet Targets

We experimentally demonstrate a new regime of high-order harmonic generation by relativistic-irradiance lasers in gas jet targets. Bright harmonics with both odd and even orders, generated by linearly as well as circularly polarized pulses, are emitted in the forward direction, while the base harmonic frequency is downshifted. A 9 TW laser generates harmonics up to 360 eV, within the 'water window' spectral region. With a 120 TW laser producing 40 uJ/sr per harmonic at 120 eV, we demonstrate the photon number scalability. The observed harmonics cannot be explained by previously suggested scenarios. A novel high-order harmonics generation mechanism [T. Zh. Esirkepov et al., AIP Proceedings, this volume], which explains our experimental findings, is based on the phenomena inherent in the relativistic laser - underdense plasma interactions (self-focusing, cavity evacuation, and bow wave generation), mathematical catastrophe theory which explains formation of electron density singularities (cusps), and collective radiation due to nonlinear oscillations of a compact charge.

The role of deposition process on pressure dip formation underneath a granular pile

This paper describes an experimental investigation on the pressure dip phenomenon in a conical pile of granular solids. The roles of different deposition processes such as the pouring rate, pouring height and deposition jet size on the pressure dip formation were studied. Test results confirmed that the pressure dip is a robust phenomenon in a pile formed by top deposition. When the deposition jet radius is significantly smaller than the final pile radius (i.e. concentrated deposition), a dip developed in the centre as shown in previous studies. However, when the deposition jet radius is comparable to the final pile radius (i.e. diffuse deposition), the location of the dip moves towards the edge of deposition jet, with a local maximum pressure developed in the centre. For concentrated deposition, an increase in the pouring rate may enhance the depth of the dip and reduce its width, while an increase in the pouring height has only a negligible effect in the studied range. The results suggest the pressure dip is closely related to the initial location, intensity and form of downslope flows. © 2013 Elsevier Inc. All rights reserved.

Low Level Jet stream of Asian Summer Monsoon and its Variability

The main objective of the of present study are to study the intraseasonal variability of LLJ and its relation with convective heating of the atmosphere, to establish whether LLJ splits into two branches over the Arabian sea as widely believed, the role of horizonatal wind shear of LLJ in the episodes of intense rainfall events observed over the west coast of India, to perform atmospheric modeling work to test whether small (meso) scale vortices form during intense rainfall events along the west coast; and to study the relation between LLJ and monsoon depression genesis. The results of a study on the evolution of Low Level Jetstream (LLJ) prior to the formation of monsoon depressions are presented. A synoptic model of the temporal evolution of monsoon depression has been produced. There is a systematic temporal evolution of the field of deep convection strength and position of the LLJ axis leading to the genesis of monsoon depression. One of the significant outcomes of the present thesis is that the LLJ plays an important role in the intraseasonal and the interannual variability of Indian monsoon activity. Convection and rainfall are dependent mainly on the cyclonic vorticity in the boundary layer associated with LLJ. Monsoon depression genesis and the episodes of very heavy rainfall along the west coast of India are closely related to the cyclonic shear of the LLJ in the boundary layer and the associated deep convection. Case studies by a mesoscale numerical model (MM5) have shown that the heavy rainfall episodes along the west coast of India are associated with generation of mesoscale cyclonic vortices in the boundary layer.

Meteorological aspects of mud bank formation along south west coast of India

The study mainly intends to investigate the meteorological aspects associated with the formation of mud banks along southwest coast of India. During the formation of mud bank, the prominent monsoon organized convection is located in the equatorial region and relatively low clouding over Indian mainland. The wind core of the low level jet stream passes through the monsoon organized convection. When the monsoon organized convection is in the equatorial region, the low level wind over the southwest coast of India is parallel to the coastline and toward south. This wind along the coast gives rise to Ekman mass transport away from the coastline and subsequently formation of mud bank, if the high wind stress persists continuously for three or more days. As a result of the increased alongshore wind stress, the coastal upwelling increases. An increase in chlorophyll-a concentration and total chlorophyll can also be seen associated with mudbank formation

The formation mechanism of the Bonin high in August

The Bonin high is a subtropical anticyclone that is predominant near Japan in the summer. This anticyclone is associated with an equivalent-barotropic structure, often extending throughout the entire troposphere. Although the equivalent-barotropic structure of the Bonin high has been known for years among synopticians because of its importance to the summer climate in east Asia, there are few dynamical explanations for such a structure. The present paper attempts to provide a formation mechanism for the deep ridge near Japan. We propose a new hypothesis that this equivalent-barotropic ridge near Japan is formed as a result of the propagation of stationary Rossby waves along the Asian jet in the upper troposphere (‘the Silk Road pattern’). First, the monthly mean climatology is examined in order to demonstrate this hypothesis. It is shown that the enhanced Asian jet in August is favourable for the propagation of stationary Rossby waves and that the regions of descent over the eastern Mediterranean Sea and the Aral Sea act as two major wave sources. Second, a primitive-equation model is used to simulate the climatology of August. The model successfully simulates the Bonin high with an equivalent-barotropic structure. The upper-tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hPa, when a wave packet arrives. Sensitivity experiments are conducted to show that the removal of the diabatic cooling over the Asian jet suppresses the Silk Road pattern and formation of an equivalent-barotropic ridge near Japan, while the removal of the diabatic heating in the western Pacific does not. Copyright © 2003 Royal Meteorological Society

Exploring the applications of a pulsating jet hydrodynamic modulated voltammetric (HMV) system - electrochemistry of nanostructured Pt electrodes and trace analysis

The electrochemistry of nanostructured electrodes is investigated using hydrodynamic modulated voltammetry (HMV). Here a liquid crystal templating process is used to produce a platinum modified electrode with a relatively high surface area (Roughness factor, Rf = 42.4). The electroreduction of molecular oxygen at a nanostructured platinum surface is used to demonstrate the ability of HMV to discriminate between Faradaic and non-Faradaic electrode reactions. The HMV approach shows that the reduction of molecular oxygen shows considerable hysteresis correlating with the formation and stripping of oxide species at the platinum surface. Without the HMV analysis it is difficult to discern the same detail under the conditions employed. In addition the detection limit of the apparatus is explored and shown, under ideal conditions, to be of the order of 45 nmol dm(-3) employing [Fe(CN)(6)](4-) as a test species. (C) 2009 Elsevier B.V. All rights reserved.

Seasonality and interannual variability of the westerly jet in the Tibetan Plateau region

In this study, 40-yr ECMWF Re-Analysis (ERA-40) data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the Tibetan Plateau region. To complement results based on the analysis of monthly mean horizontal wind speeds, an occurrence-based jet climatology is constructed by identifying the locations of the jet axes at 6-hourly intervals throughout 1958–2001. Thus, a dataset describing the highly transient and localized features of jet variability is obtained. During winter and summer the westerly jet is located, respectively, to the south and north of the Tibetan Plateau. During the spring and autumn seasons there are jet transitions from south to north and vice versa. The median dates for these transitions are 28 April and 12 October. The spring transition is associated with large interannual variations, while the fall transition occurs more reliably within a 3-week period. The strength of the jet exhibits a peculiar seasonal cycle. During northward migration in April/May, the jet intensity weakens and its latitudinal position varies largely. In some springs, there are several transitions and split configurations occur before the jet settles in its northern summer position. In June, a well-defined and unusually strong jet reappears at the northern flanks of the Tibetan Plateau. In autumn, the jet gradually but reliably recedes to the south and is typically more intense than in spring. The jet transitions between the two preferred locations follow the seasonal latitudinal migration of the jet in the Northern Hemisphere. An analysis of interannual variations shows the statistical relationship between the strength of the summer jet, the tropospheric meridional temperature gradient, and the all-India rainfall series. Both this analysis and results from previous studies point to the particular dynamical relevance of the onsetting Indian summer monsoon precipitation and the associated diabatic heating for the formation of the strong summer jet. Finally, an example is provided that illustrates the climatological significance of the jet in terms of the covariation between the jet location and the spatial precipitation distribution in central Asia.

The dependence of contrail formation on the weather pattern and altitude in the North Atlantic

Aircraft flying through cold ice-supersaturated air produce persistent contrails which contribute to the climate impact of aviation. Here, we demonstrate the importance of the weather situation, together with the route and altitude of the aircraft through this, on estimating contrail coverage. The results have implications for determining the climate impact of contrails as well as potential mitigation strategies. Twenty-one years of re-analysis data are used to produce a climatological assessment of conditions favorable for persistent contrail formation between 200 and 300 hPa over the north Atlantic in winter. The seasonal-mean frequency of cold ice-supersaturated regions is highest near 300 hPa, and decreases with altitude. The frequency of occurrence of ice-supersaturated regions varies with large-scale weather pattern; the most common locations are over Greenland, on the southern side of the jet stream and around the northern edge of high pressure ridges. Assuming aircraft take a great circle route, as opposed to a more realistic time-optimal route, is likely to lead to an error in the estimated contrail coverage, which can exceed 50% for westbound north Atlantic flights. The probability of contrail formation can increase or decrease with height, depending on the weather pattern, indicating that the generic suggestion that flying higher leads to fewer contrails is not robust.

Shock wave formation in hot nuclear matter

Assuming that nuclear matter can be treated as a perfect fluid, we study the propagation of perturbations in the baryon density at high temperature. The equation of state is derived from the non-linear Walecka model. The expansion of the Euler and continuity equations of relativistic hydrodynamics around equilibrium configurations lead to the breaking wave equation for the density perturbation. We solve it numerically for this perturbation and follow the propagation of the initial pulses.

3C 273 variability at 7 mm: evidence of shocks and precession in the jet

We report on four years of observations of 3C 273 at 7mm obtained with the Itapetinga radio telescope, in Brazil, between 2009 and 2013. We detected a flare in 2010 March, when the flux density increased by 50 per cent and reached 35 Jy. After the flare, the flux density started to decrease and reached values lower than 10 Jy. We suggest that the 7-mm flare is the radio counterpart of the γ -ray flare observed by the Fermi Large Area Telescope in 2009 September, in which the flux density at high energies reached a factor of 50 of its average value. A delay of 170 d between the radio and γ -ray flares was revealed using the discrete correlation function (DCF) that can be interpreted in the context of a shock model, in which each flare corresponds to the formation of a compact superluminal component that expands and becomes optically thin at radio frequencies at latter epochs. The differences in flare intensity between frequencies and at different times are explained as a consequence of an increase in the Doppler factor δ, as predicted by the 16-yr precession model proposed by Abraham & Romero. This increase has a large effect on boosting at high frequencies while it does not affect the observed optically thick radio emission too much. We discuss other observable effects of the variation in δ, such as the increase in the formation rate of superluminal components, the variations in the time delay between flares and the periodic behaviour of the radio light curve that we have found to be compatible with changes in the Doppler factor.