Regions Of High Energy Density Research Articles

Experimental study on thrust pulsation characteristics of water jet propulsion pump units

Due to the influence of the rotating impeller in the water jet propulsion pump, the thrust generated by the water jet propulsion pump unit has a time-series pulsation characteristic. Firstly, through theoretical derivation, it is found that the thrust of a water jet propulsion pump unit is related to the outlet flow rate of the nozzle, and there is a pulsating characteristic of the thrust. Secondly, a direct thrust measurement system for the water jet propulsion pump unit was designed to achieve direct thrust measurement, further verifying the pulsating characteristics of thrust. The experimental results show that the transient thrust of the water jet propulsion pump unit fluctuates with time in a distinctly periodic manner, with low-frequency pulsations dominating. As the rotating speed increases, the amplitude of the subdominant frequency of the pump unit thrust pulsation tends to increase, while the influence of the impeller and guide vane on the transient thrust pulsation decreases with increasing speed, and the high energy density region in the wavelet transform time-frequency data gradually concentrates to the low-frequency. The experimental results and the related analysis can provide an empirical basis for studying the hydrodynamic aspects of the water jet pump unit.

Generating high-energy densities by sidelobe suppression in the far-field of phase-locked lasers

Laser beams with high-energy densities are desired for both fundamental research and applied applications. We present a numerical study on the generation of high-energy densities by sidelobe suppression in the far-field intensity distribution of phase-locked lasers. The method relies on modifying the combined field distribution of phase-locked lasers to obtain uniform amplitude and phase distributions in a near-field plane, which enables the formation of a high-energy density main central lobe (zeroth order) in the far field. The method is applied to various one-dimensional (1D) and two-dimensional (2D) array geometries, such as square, triangular, Kagome, random, and 1D ring. The results show that for in-phase-locked lasers in 2D array geometries, the diffraction efficiency of the high-energy density region (zeroth-order lobe) can be increased in the range of 90%–95%. For in-phase-locked lasers in a 1D ring array, the maximum diffraction is found to be ∼ 75 % . Further, the effects of the range of phase locking, system size, as well as topological defects are examined on diffraction efficiency. The method is also applied to an out-of-phase-locked laser in the square array, and a high-energy density output beam is obtained.

N-Graphene-Metal-Oxide(Sulfide) hybrid Nanostructures: Single-step plasma-enabled approach for energy storage applications

• Novel plasma-based approach to design hybrid N-Graphene-metal-based nanostructures is created. • The synthesis method is controllable, single-step and at atmospheric conditions. • Metal oxide/sulfide anchored N-graphene at large scale (~19 mg/min) are produced. • Electrode for supercapacitor with metal oxide/sulfide-N-graphene was developed. • The electrode demonstrated promising specific capacitances ∼ 273 F.g −1 at 0.5 A.g −1 . Hybrid graphene-based nanostructures are considered promising materials for energy storage applications. However, the synthesis of high-quality hybrid graphene nanostructures at high yields is challenging. In the present work we propose a novel, single-step microwave plasma-enabled approach to synthetize customizable hybrid graphene-based nanostructures at high-yield while preserving their quality. Hybrid N-graphene (nitrogen-doped graphene) metal-based nanostructures, for instance, can be produced at a rate of ∼ 19 mg/min. The high energy density region of a microwave plasma provides sufficient energy and “building particles” fluxes towards the low-energy density plasma afterglow for the processes of assembly and growth of N-graphene sheets. Simultaneously, a controlled jet of metal-oxide(-sulfide) microparticles is sprayed into the plasma afterglow region where they bind to N-graphene sheets. Methane/methylamine are used as carbon and nitrogen precursors, combined with micron-sized MnO 2 and oxy-MnS particles to synthesize the hybrid structures. As a result, nano-sized (∼10–30 nm) MnO x particles decorated N-graphene (4.6 at. N%) and oxidized metal sulfide anchored N-graphene sheets (3.1 at. N%) are produced at atmospheric conditions. High structural quality and distribution of metal-based nanostructures on N-graphene sheets are revealed using transmission and scanning electron microscopes and other advanced spectroscopic techniques. Finally, an electrode for supercapacitor based on the N-graphene-metal-oxide(sulfide) hybrid nanostructures is developed with promising specific capacitances (∼273 F.g −1 at 0.5 A.g −1 ). The described chemically engineered process is one of the fastest approaches reported for designing the high-quality hybrid nanostructures produced at a high-yield, and as such, is expected to provide a high impact on the design of electrode materials for sustainable energy storage systems.

Observation of MeV-energy ions from the interaction of over picosecond laser pulses with near-critical density foam targets

In order to enhance the conversion efficiency of ultra-intense laser energy into plasma leading to ion acceleration, we have performed an experiment with over-picosecond laser pulses having a relativistic intensity interacting with foam targets. We adjust the prepulse of the laser to control the plasma density near the critical density. The combination of hydrodynamic and particle-in-cell simulations suggest that the region of high energy density is induced in the near-critical plasma, leading to enhance the proton energy up to 23 MeV with the laser intensity of 6 × 1018 W/cm2.

Relativistic polytropic spheres with electric charge: Compact stars, compactness and mass bounds, and quasiblack hole configurations

We study the static stellar equilibrium configurations ofuncharged and charged spheres composed by a relativistic polytropic fluid, and compare with those of spheres composed by a non-relativistic polytropic fluid, the later case already being studied in a previous work [J. D. Arba\~nil, P. S. Lemos, V. T. Zanchin, Phys. Rev. D \textbf{88}, 084023 (2013)]. In the relativistic fluid case, a relativistic polytropic equation of state, $p=\omega\delta^{\gamma}$, is assumedd. Here, $\delta=\rho-p/(\gamma-1)$, with $\delta$ and $\rho$ being the rest mass density and the energy density, respectively, and $\omega$ and $\gamma$ are respectively the polytropic constant and the polytropic exponent. We assume that the charge density $\rho_e$ is proportional to the energy density $\rho$, $\rho_e = \alpha\, \rho$, with $\alpha$ being a constant such that $0\leq |\alpha|\leq 1$. Some properties of the charged spheres such as mass, total electric charge, radius, redshift, and the speed of sound are analyzed. The dependence of such properties with the polytropic exponent is also investigated. In addition, some limits that arise in general relativity, such as the Chandrasekhar limit, the Oppenheimer-Volkoff limit, the Buchdahl bound and the Buchdahl-Andr\'easson bound, i.e., the Buchdahl bound for the electric case, are studied. As in a charged non-relativistic polytropic sphere, the charged relativistic polytropic sphere with $\gamma\to\infty$ and $\alpha \to 1$ saturates the Buchdahl-Andr\'easson bound, thus indicating that it reaches the quasiblack hole configuration. We show by means of numerical analysis that, as expected, the major differences between the two cases appear in the high energy density region.

Effective dynamical coupling of hydrodynamics and transport for heavy-ion collisions

Present hydrodynamics-based simulations of heavy-ion collisions neglect the feedback from the frozen-out particles flying back into the hydrodynamical region. This causes an artefact called “negative Cooper-Frye contributions”, which is negligible for high collision energies, but becomes significant for lower RHIC BES energies and for event-by-event simulations. To avoid negative Cooper-Frye contributions, while still preserving hydrodynamical behavior, we propose a pure hadronic transport approach with forced thermalization in the regions of high energy density. It is demonstrated that this approach exhibits enhancement of strangeness and mean transverse momenta compared to conventional transport – an effect typical for hydrodynamical approaches.

Wireless power transfer to deep-tissue microimplants.

The ability to implant electronic systems in the human body has led to many medical advances. Progress in semiconductor technology paved the way for devices at the scale of a millimeter or less ("microimplants"), but the miniaturization of the power source remains challenging. Although wireless powering has been demonstrated, energy transfer beyond superficial depths in tissue has so far been limited by large coils (at least a centimeter in diameter) unsuitable for a microimplant. Here, we show that this limitation can be overcome by a method, termed midfield powering, to create a high-energy density region deep in tissue inside of which the power-harvesting structure can be made extremely small. Unlike conventional near-field (inductively coupled) coils, for which coupling is limited by exponential field decay, a patterned metal plate is used to induce spatially confined and adaptive energy transport through propagating modes in tissue. We use this method to power a microimplant (2 mm, 70 mg) capable of closed-chest wireless control of the heart that is orders of magnitude smaller than conventional pacemakers. With exposure levels below human safety thresholds, milliwatt levels of power can be transferred to a deep-tissue (>5 cm) microimplant for both complex electronic function and physiological stimulation. The approach developed here should enable new generations of implantable systems that can be integrated into the body at minimal cost and risk.

Use specification of multiscale materials for life spanned over macro-, micro-, nano-, and pico-scale

Multiscale material intends to enhance the strength and life of mechanical systems by matching the transmitted spatiotemporal energy distribution to the constituents at the different scale, say—macro, micro, nano, and pico,—, depending on the needs. Lower scale entities are, particularly, critical to small size systems. Large structures are less sensitive to microscopic effects. Scale shifting laws will be developed for relating test data from nano-, micro-, and macro-specimens. The benefit of reinforcement at the lower scale constituents needs to be justified at the macroscopic scale. Filling the void and space in regions of high energy density is considered. Material inhomogeneity interacts with specimen size. Their combined effect is non-equilibrium. Energy exchange between the environment and specimen becomes increasingly more significant as the specimen size is reduced. Perturbation of the operational conditions can further aggravate the situation. Scale transitional functions f j j + 1 and/or f j / j + 1 are introduced to quantify these characteristics. They are represented, respectively, by ( f mi ma , f na mi , f pi na ) , and f mi / ma , f na / mi , f pi / na . The abbreviations pi, na, mi, and ma refer to pico, nano, micro and macro. Local damage is assumed to initiate at a small scale, grows to a larger scale, and terminate at an even larger scale. The mechanism of energy absorption and dissipation will be introduced to develop a consistent book keeping system. Compaction of mass density for constituents of size 10 −12, 10 −9, 10 −6, 10 −3 m, will be considered. Energy dissipation at all scales must be accounted for. Dissipations at the smaller scale must not only be included but they must abide by the same physical and mathematical interpretation, in order to avoid inconsistencies when making connections with those at the larger scale where dissipations are eminent. Three fundamental Problems I, II, and III are stated. They correspond to the commonly used service conditions. Reference is made to a Representative Tip (RT), the location where energy absorption and dissipation takes place. The RT can be a crack tip or a particle. At the larger size scales, RT can refer to a region. Scale shifting of results from the very small to the very large is needed to identify the benefit of using multiscale materials.

Si nanopillar array optimization on Si thin films for solar energy harvesting

In this letter, Si thin film (800 nm thick) with nanopillar array decorated surface is studied via simulation for its solar energy absorption characteristics. It is found that the light absorption is significantly enhanced due to the adding of the Si nanopillar (SiNP) array to the Si thin film. The absorption characteristics of the SiNP structure would be approximately optimum (especially at ∼2.5 eV, the high energy density region in the solar spectrum) when the periodicity of SiNP array is set as ∼500 nm, which can be explained when comparing the incident light wavelength with the periodicity of SiNP array.

On the numerical implementation of variational arbitrary Lagrangian–Eulerian (VALE) formulations

This paper is concerned with the implementation of variational arbitrary Lagrangian–Eulerian formulations, also known as variational r-adaption methods. These methods seek to minimize the energy function with respect to the finite-element mesh over the reference configuration of the body. We propose a solution strategy based on a viscous regularization of the configurational forces. This procedure eliminates the ill-posedness of the problem without changing its solutions, i.e. the minimizers of the regularized problems are also minimizers of the original functional. We also develop strategies for optimizing the triangulation, or mesh connectivity, and for allowing nodes to migrate in and out of the boundary of the domain. Selected numerical examples demonstrate the robustness of the solution procedures and their ability to produce highly anisotropic mesh refinement in regions of high energy density. Copyright © 2006 John Wiley & Sons, Ltd.

Evolution of a pulse of noninteracting quasiparticles with dispersion and initial angular width

The evolution of a pulse of noninteracting quasiparticles, caused by their different velocities and angular distribution of momenta, is studied theoretically. Equations are found that describe the shape of the pulse surface at any time. The times of the beginning and end and the duration of the quasiparticle energy flux density is determined at a general spatial point. The quasiparticle energy density is considered at all times and positions, and it is shown that in the region of high energy density, in the middle of the pulse, it is equal to the initial energy density under certain conditions. These theoretical results are discussed in relation to experimental data on the evolution of a pulse of noninteracting phonons in superfluid helium.

Strongly coupled plasma physics and high energy-density matter

High energy–density matter—matter with pressures in excess of a megabar—covers a wide range of parameter space. Many laboratory experiments span a large portion of this parameter space as they evolve from a liquid or solid phase through the strongly coupled plasma phase to a hot plasma phase. This tutorial will introduce the basic physics of the intermediate, strongly coupled plasma phase from a very general point of view, including a discussion of experiments, such as laser-cooled ions, dusty plasmas, and white dwarfs. Basic definitions and results will be given for simple strongly coupled plasmas in the context of concepts familiar from weakly coupled plasma physics, to the extent possible. Definitions relevant to high energy–density physics are then introduced before focusing on dense plasmas, which form the overlap between the strongly coupled and high energy–density regions.

A new approach to deal with non-linearities in Si detector response

A model is proposed to understand the non-linear response of Si detectors to high Z particles, which are responsible for the pulse height defect (PHD). In this phenomenon, inefficient charge collection due to charge carrier recombination is related to high energy density regions in the vicinity of the particle track, while contributions from non-ionizing atomic collisions are also estimated from the radial distribution of scattered lattice ions. These model calculations successfully reproduce published PHD data, while predicting unexpected effects in silicon-based semiconductor detection of high (relativistic) energy heavy ions. This is used to explain what seemed as intriguing features of silicon-tracker data from the Alpha Magnetic Spectrometer space project. The present model is proposed to obtain reliable ion energy measurements using silicon detectors.

Relativistic hydrodynamic scaling from the dynamics of quantum field theory.

Relativistic hydrodynamic scaling or boost invariance is a particularly important hydrodynamic regime, describing collective flows of relativistic many body systems and is used in the interpretation of experiments from high-energy cosmic rays to relativistic heavy-ion collisions. We show evidence for the emergence of hydrodynamic scaling from the dynamics of relativistic quantum field theory. We consider a scalar lambdaphi(4) model in 1+1 dimensions in the Hartree approximation and study the relativistic collisions of two kinks and the decay of a localized high-energy density region. We find that thermodynamic scalar isosurfaces show approximate boost invariance at high-energy densities.

Partonic effects on the elliptic flow at relativistic heavy ion collisions

The elliptic flow in heavy ion collisions at RHIC is studied in a multiphase transport model. By converting the strings in the high energy density regions into partons, we find that the final elliptic flow is sensitive to the parton scattering cross section. To reproduce the large elliptic flow observed in Au+Au collisions at $\sqrt s=130A$ GeV requires a parton scattering cross section of about 6 mb. We also study the dependence of the elliptic flow on the particle multiplicity, transverse momentum, and particle mass.

Photon emission under MeV carbon cluster impact for probing cluster–solid interactions

First experimental results on the luminescence induced in thin molecular samples by the impact of single cluster ions Cn+ (n=2–10) at 1 MeV/atom have been reported. The cluster ions were produced and accelerated at the Erlangen tandem accelerator. The samples were a 1 μm CsI layer deposited onto a 2 μm aluminized polyester foil and a 100 nm POPOP layer prepared onto a 20 nm formvar film. The bombarding ions could traverse the samples but the cluster constituents did not remain in proximity in all cases. The luminescence was registrated by time-correlated single photon counting using either secondary electrons or transmitted clusters for starting the measurement. The relative photon yield obtained with clusters of various size increases linearly with the number of cluster constituents. The increase is less pronounced in case of the thin sample. This experimental result can be explained by the fact that the cluster ions leave the exit side of the sample as intact entities and that the photon emission is reduced in regions of high energy density.

Dynamics of laser induced phase transformations in amorphous silicon

The kinetics of the crystallization process in amorphous hydrogenated Si (a-Si:H) thin films induced by XeCl and ArF excimer laser pulses has been studied both experimentally and theoretically. Time-resolved reflectivity spectroscopy (TRR) has been used to monitor phase changes as a function of pulse energy density. The time of the recrystallization process, tr, has been determined experimentally. Independently of the wavelength of applied laser radiation, a strong minimum has been found in the tr versus energy density (E) curves. The theoretical simulations have been done with the non-equilibrium thermal model which includes a nucleation process. The results clearly demonstrate that the crystallization from the phase interface dominates for energy densities close to the melting threshold in contrast to the high energy density region where the nucleation and solidification in the subsurface region prevails.

Linking dynamical and thermal models of ultrarelativistic nuclear scattering.

To analyze ultrarelativistic nuclear interactions, usually either dynamical models like the string model are employed, or a thermal treatment based on hadrons or quarks is applied. String models encounter problems due to high string densities; thermal approaches are too simplistic, considering only average distributions and ignoring fluctuations. We propose a completely new approach, providing a link between the two treatments, and avoiding their main shortcomings: based on the string model, connected regions of high energy density are identified for single events, such regions being referred to as quark matter droplets. Each individual droplet hadronizes instantaneously according to the available $n$-body phase space, making use of special Monte Carlo techniques.

Disoriented chiral condensates in the (2+1)-dimensional Gross-Neveu model: a dynamical simulation

We study the dynamics of the formation of disoriented chiral condensate (DCC) regions which follow the expansion of a high energy density region into the “cold” vacuum. We numerically solve the classical equations of motions for an effective Hamiltonian based on the one-loop effective potential for the massive 2+1-dimensional Gross-Neveu model. We pay attention to the setting of the initial conditions and to determining which parameters are relevant for a strong amplification of the pion field. We find that the size of the “hot” source plays a significant role. For large enough source radii, we observe strong correlation phenomena, corresponding to the growth of large regions where the pion field oscillates along a given direction. We give our results in terms of the θ angle which defines the DCC disorientation, of the local ratios R a = π a 2 π 2 ( a = 1,2,3), and of the energies associated with the fields at representative times.

Radiation transfer in gamma-ray bursts

We have calculated gamma-ray radiative transport in regions of high energy density, such as gamma-ray burst source regions, using a discrete ordinate, discrete energy group method. The calculations include two-photon pair production and annihilation, as well as three-photon pair annihilation. The radiation field itself acts as an absorbing medium, and the optical depth depends on its intensity, so the problem is intrinsically nonlinear. Spherical divergence produces effective collimation of the flux. At high optical depth the high energy ($E > 1$ MeV) portion of the emergent spectrum assumes a nearly universal form. An approximate limit is derived for the high energy flux from a gamma-ray burst source region of given size, and the implications of this limit for the distance to the March 5, 1979 event are briefly discussed. We discuss more generally the problem of very luminous bursts, and implications of Galactic halo distances for flare models.