Continuum Transition Research Articles

Deep MUSE observations in the HDFS

(Abridged) We make use of the deepest VLT/MUSE observations performed so far on the Hubble Deep Field South (HDFS) to characterize the low-mass (< $10^{10}$M$_\odot$) galaxy population at intermediate redshift. We identify a sample of 28 spatially-resolved emission-line galaxies in the deep (27h integration time) MUSE data cube, spread over a redshift interval of 0.2 < z < 1.4. The public HST images and multi-band photometry over the HDFS are used to constrain the stellar mass and star formation rate (SFR) of the galaxies and to perform a morphological analysis. We derive the resolved ionized gas properties of these galaxies from the MUSE data and model the disk (both in 2D and with GalPaK$^{\rm 3D}$) to retrieve their intrinsic gas kinematics. We build a sample of resolved emission-line galaxies of much lower stellar mass and SFR (by $\sim$1-2 orders of magnitude) than previous 3D spectroscopic surveys. Most of the spatially-resolved MUSE-HDFS galaxies have gas kinematics consistent with disk-like rotation, but about 20% have velocity dispersions larger than the rotation velocities, and 30% are part of a close pair and/or show clear signs of recent gravitational interactions. In the high-mass regime, the MUSE-HDFS galaxies follow the Tully-Fisher relation defined from previous surveys in a similar redshift range. This scaling relation extends also to lower masses/velocities but with a higher dispersion. The MUSE-HDFS galaxies follow the scaling relations defined in the local universe between the specific angular momentum and the stellar mass. However, we find that intermediate-redshift star-forming galaxies fill a continuum transition from the spiral to elliptical local scaling relations, according to the dynamical state of the gas. This indicates that some galaxies may lose their angular momentum and become dispersion-dominated prior to becoming passive.

A model for multiple transport mechanisms through nanopores of shale gas reservoirs with real gas effect–adsorption-mechanic coupling

Multiple transport mechanisms coexist in nanopores of shale gas reservoirs with complex pore size distribution and different gas-storage processes, including continuum flow, slip flow and transition flow of bulk gas and surface diffusion for adsorbed gas. The force between gas molecules and the volume of the gas molecules themselves cannot be negligible in shale gas reservoirs with high pressure and nanoscale pores, influences gas transport and must be taken into account as a real gas effect. During depressurization development of shale gas reservoirs, the adsorbed gas desorption and a decrease in an adsorption layer influence gas transport. Meanwhile, due to the stress dependence, decreases in intrinsic permeability, porosity and a pore diameter also influence gas transport. In this work, a unified model for gas transport in organic nanopores of shale gas reservoirs is presented, accounting for the effects of coupling the real gas effect, stress dependence and an adsorption layer on gas transport. This unified model is developed by coupling a bulk gas transport model and an adsorbed gas surface diffusion model. The bulk gas transport model is validated with published molecular simulation data, and the adsorbed gas surface diffusion model is validated with published experimental data. The results show that (1) in comparison with the previous models, the bulk gas transport model developed on the basis of a weighted superposition of slip flow and Knudsen diffusion can more reasonably describe bulk gas transport, (2) surface diffusion is an important transport mechanism, and its contribution cannot be negligible and even dominates in nanopores with less than 2nm in diameter, and (3) the effect of stress dependence on fluid flow in shale gas reservoirs is significantly different from that in conventional gas reservoirs, and is related to not only the shale matrix mechanical properties and the effective stress but also the gas transport mechanisms.

An Analytical Model of Apparent Gas Permeability for Tight Porous Media

Simulation of fluid flow in tight rocks, such as shale gas reservoirs, has been a challenging task because of the coexistence of various flow regimes, including the continuum flow, slippage, transition flow, and Knudsen diffusion within the porous structure. Currently, both numerical and analytical methods have been applied to address this issue. In this paper, we have extended the application of most widely used analytical solution for single uniform capillary proposed by Beskok and Karniadakis (Microscale Thermophys Eng 3(1):43–77,1999) to the porous media. The porous structure is represented by a bundle of tortuous capillary tubes with different diameters. Fractal theory is applied to mathematically express the capillary diameter distribution and their tortuosity. For shale gas and coal seam gas formations where adsorption gas is present, the effect of surface diffusion is also included in the analytical solution. Thus, the presented analytical model has allowed us to study the effect of pore size distribution, fractal dimensions for pore size and tortuosity, porosity, surface diffusivity and Langmuir parameters on flow processes. Experimental data from 100 tight gas sand samples and one shale sample, with equivalent liquid permeability ranging from nanodarcy to millidarcy, are used to effectively evaluate the application of the analytical model in the study of flow behavior of gas in tight rocks. The results of this study also show that in tight formation, there has been an increase in apparent gas permeability through the life of production by a factor of 2.2.

THz wave emission from argon in two-color laser field**Project supported by the National Natural Science Foundation of China (Grant Nos. 11465016, 11374366, and 11164025).

Terahertz (THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional (1D) time-dependent Schrödinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime.

Critical cooperation range to improve spatial network robustness.

A robust worldwide air-transportation network (WAN) is one that minimizes the number of stranded passengers under a sequence of airport closures. Building on top of this realistic example, here we address how spatial network robustness can profit from cooperation between local actors. We swap a series of links within a certain distance, a cooperation range, while following typical constraints of spatially embedded networks. We find that the network robustness is only improved above a critical cooperation range. Such improvement can be described in the framework of a continuum transition, where the critical exponents depend on the spatial correlation of connected nodes. For the WAN we show that, except for Australia, all continental networks fall into the same universality class. Practical implications of this result are also discussed.

Pressure–temperature–deformation–time of the ductile Alpine shearing in Corsica: From orogenic construction to collapse

Definition of the Tertiary tectono-metamorphic history of Alpine Corsica is a key task to decipher the space–time linkage between the Alpine and Apennine subduction systems in the Mediterranean region. Alpine Corsica exposes a nappe stack of oceanic- and continental-derived units, structurally juxtaposed onto the former European continental margin (Hercynian Corsica). Still uncertain is the timing of involvement of the continental-derived units in orogenic construction and shift to regional extension. This paper focuses on reconstruction of the pressure–temperature–deformation–time evolution of selected ductile shear zones activated during transition from the tectonic underplating to the extensional reworking stages. New Rb–Sr mineral age data, integrated with structural and thermobarometric investigations constrain the waning stages of the high-pressure (from blueschist to greenschist facies metamorphic conditions) top-to-the-W thrusting of the HP, oceanic-derived realm (Schistes Lustrés Complex) onto the Hercynian Corsica along the East Tenda Shear Zone in the early Oligocene (from ~32 to ~27Ma). This early compressional evolution is overprinted by a major phase of retrogressive, syn-greenschist top-to-the-E extensional shearing in the Schistes Lustrés Complex with the last episode of deformation-related ductile recrystallization recorded during the early Miocene at ~20–21Ma, in a continuum transition from ductile to brittle shearing. The same early Miocene Rb–Sr deformation ages are recovered from the ductile-to-brittle top-to-the-E reactivation domains within the East Tenda Shear Zone, documenting that transition from compression to extension in Alpine Corsica occurred during the late Oligocene–early Miocene time lapse. Implications of these data are discussed in the broader context of the Tertiary geodynamic evolution of the Central Mediterranean region.

Nonlinear Seepage Model of Gas Transport in Multiscale Shale Gas Reservoirs and Productivity Analysis of Fractured Well

Shale is abundant in nanoscale pores, so gas flow in shales cannot be simply represented by Darcy formula anymore. It is crucial to figure out the influence of gas flow in nano/micro pores on actual productivity, which can provide basic theories for optimizing parameters and improving the gas production from engineering perspective. This paper considers the effects of slippage and diffusion in nanoscale based on Beskok-Karniadakis (BK) equation, which can be applicable for different flow regimes including continuum flow, slip flow, transition flow, and free-molecule flow. A new non-Darcy equation was developed based on the analysis of effects of high order terms of BK equation on permeability correction factor. By using the conformal transformation principle and pressure coupling method, we established the productivity formula of fractured well (infinite and limited conductivity) satisfying mass variable seepage flowing in fractures. The simulation results have been compared with field data and influencing parameters are analyzed thoroughly. It is concluded that slippage effect affects gas production of fractured well when wellbore pressure is less than 15 MPa, and the effects of slippage and diffusion have greater influence on gas production of fractured well for reservoir with smaller permeability, especially when permeability is at nano-Darcy scale.

Granular jet impact: probing the ideal fluid description

AbstractWe investigate the impact of a granular jet on a finite target by means of particle simulations. The resulting hydrodynamic fields are compared with theoretical predictions for the corresponding flow of an incompressible and rotation-free fluid. The degree of coincidence between the field obtained from the discrete granular system and the idealized continuous fluid flow depends on the characteristics of the granular system, such as granularity, packing fraction, inelasticity of collisions, friction and target size. In certain limits we observe a granular–continuum transition under which the geometric and dynamic properties of the particle jet and the fluid jet become almost identical.

Ta L3-edge XANES study of perovskite oxynitrides ATaO2N (A=Ca, Sr, Ba)

Abstract X-ray absorption near edge structure (XANES) spectroscopy was performed at the Ta L3-edge to probe the bonding nature of tantalum and the conduction band minimum in d0 perovskites KTaO3, CaTaO2N, SrTaO2N, and BaTaO2N. The Ta L3 absorption edge energy (E0) varied from 9882.2 to 9883.6 eV in the manner, KTaO3 > BaTaO2N > SrTaO2N ⩾ CaTaO2N. These chemical shifts and the Ta−O/N bond covalency were discussed based on the bonding geometry, electronegativity of the anion, and the electronegativity of dodecahedral cation. Deconvolution of the XANES white line peak allowed for the determinations of Ta 2p → 5d and 2p → continuum transition energies, from which we infer that the band gap window gradually shifts to lower energy region, going from BaTaO2N to SrTaO2N to CaTaO2N.

Towards Predictions of Fission Probabilities for Astrophysics Applications

Abstract In almost all the evaluations of the neutron-induced fission cross section for nuclei involved in nuclear applications, a double- humped fission barrier described by two independent inverted parabolas is considered. In addition, the continuum transition states are described by a simple Fermi-gas type nuclear level density expression for which the formulation as well as the parametrization remain highly uncertain. For these reasons, these approaches can be considered as having a rather poor predictive power and are not recommended for applications requiring a proper description of fission for nuclei far from stability, such as nuclear astrophysics. Hartree-Fock-Bolgolyubov (HFB) calculation are now available and can provide all the nuclear ingredients required to describe the fission path from the equilibrium deformation up to the nuclear scission point. The aim of this contribution is to apply the basic features of the optical model for fission, using the full microscopic information obtained from HFB models to calculate neutron- induced fission cross sections on selected actinide nuclei. This approach includes not only the details of the energy surface along the fission path, but also the estimate of the nuclear level density derived within the combinatorial approach on the basis of the same HFB single-particle properties, in particular at the fission saddle points. The sensitivity of the calculated fission cross sections to different model approximations is illustrated and the predictive power of such a microscopic approach tested. It is also shown that the various inputs can be tuned to reproduce at best experimental data in one unique coherent framework, so that in a close future it should become possible to make, on the basis of such models, accurate fission cross-section calculations and the corresponding estimates for nuclei, energy ranges or reaction channels for which no data exist. Finally, the same model is applied to the calculation of the fission probabilities, including β-delayed fission, spontaneous fission and neutron-induced fission, for all nuclei potentially produced by the r-process nucleosynthesis. Nucleosynthesis calculations resulting from the decompression of neutron star matter are performed and the sensitivity of the abundance calculation with respect to nuclear fission uncertainties (including fission probabilities and fission fragment distributions) is studied.

Driving-frequency scaling of high-harmonic quantum paths

We have developed an analytical theory explaining how the single-atom efficiency of high-harmonic generation scales with laser frequency, and verified this by numerically solving the time-dependent Schrödinger equation in three spatial dimensions. According to our saddle-point analysis of quantum paths, the imaginary part of the action has a significant impact on the scaling law. Furthermore, we found that the scaling law depends on the analytical properties of the ground–continuum transition matrix element. Our analysis elucidates how the relative contributions of different quantum orbits and their relative phases vary with the driving laser frequency and how the resulting quantum-path interferences in high-harmonic spectra can be controlled with an attosecond accuracy.

Discrete to continuum transition in multifractal spacetimes

We outline a field theory on a multifractal spacetime. The measure in the action is characterized by a varying Hausdorff dimension and logarithmic oscillations governed by a fundamental physical length. A fine hierarchy of length scales identifies different regimes, from a microscopic structure with discrete symmetries to an effectively continuum spacetime. Thanks to general arguments from fractal geometry, this scenario explicitly realizes two indirect or conjectured features of most quantum gravity models: a change of effective spacetime dimensionality with the probed scale, and the transition from a fundamentally discrete quantum spacetime to the continuum. It also allows us to probe ultramicroscopic scales where spectral methods based on ordinary geometry typically fail. Consequences for noncommutative field theories are discussed.

Buckled nano rod – a two state system and quantum effects on its dynamics using system plus reservoir model

We consider a suspended elastic rod under longitudinal compression. The compression can be used to adjust potential energy for transverse displacements from harmonic to double well regime. As compressional strain is increased to the buckling instability, the frequency of the fundamental vibrational mode drops continuously to zero (first buckling instability). As one tunes the separation between the ends of a rod, the system remains stable beyond the instability and develops a double-well potential for transverse motion. The two minima in the potential energy curve describe two possible buckled states at a particular strain. From one buckled state it can go over to the other by thermal fluctuations or quantum tunnelling. Using a continuum approach and transition state theory (TST) one can calculate the rate of conversion from one state to the other. The saddle point for the change from one state to the other is the straight rod configuration. The rate, however, diverges at the second buckling instability. At this point, the straight rod configuration, which was a saddle until then, becomes a hill top and two new saddles are generated. The new saddles have bent configurations and as the rod goes through further instabilities, they remain stable and the rate calculated according to harmonic approximation around a saddle point remains finite. In our earlier paper, a classical rate calculation including friction was carried out [J. Comput. Theor. Nanosci. 4, 1 (2007)], by assuming that each segment of the rod is coupled to its own collection of harmonic oscillators – our rate expression is well behaved through the second buckling instability. In this paper we have extended our method to calculate quantum rate using the same system plus reservoir model. We find that friction lowers the rate of conversion.

High Knudsen number fluid flow at near-standard temperature and pressure conditions using precision nanochannels

Gas flows over a wide range of Knudsen numbers (~0.5–10) are studied using silicon nanochannel arrays with slit-shaped pores. The pore sizes of the silicon nanochannel arrays range from micrometer to sub-10-nm scales. The flows are generated under conditions of room temperature and near-atmospheric pressure (~22°C and ~101–115 kPa) and span the continuum flow, continuum-slip flow, transition flow and free-molecular flow regimes. The measured flow rates of helium, argon and carbon dioxide are in good agreement with a theoretical model (Unified Slip Model) proposed by Beskok and Karniadakis (Nanoscale Microscale Thermophys Eng 3:43–77, 1999).

KINETIC ENERGY DISTRIBUTION OF H(1s) FROM H2X1Σ+g-a3Σ+gEXCITATION AND LIFETIMES AND TRANSITION PROBABILITIES OFa3Σ+g(v,J)

Dissociative excitation of molecular hydrogen plays an important role in the heating of outer planet upper thermospheres. This paper addresses the role of one of the triplet states involved in the process. H2 excited to the a3Σ+g state, or higher triplet-ungerade states, is dissociated via the a3Σ+g−b3Σ+u continuum. The kinetic energy distribution of H(1s) produced from direct X1Σ+g–a3Σ+g(v, J) excitation by electrons is investigated by an accurate theoretical evaluation of spontaneous transition probabilities of the a3Σ+g(v, J)−b3Σ+u continuum transition. It is shown that the X1Σ+g(0)–a3Σ+g(v, J) excitation primarily produces H(1s) atoms with kinetic energies lower than 2 eV. In addition to the continuum a3Σ+g(v, J)−b3Σ+u transition probabilities, spontaneous emission lifetimes of the a3Σ+g(v, J) (v = 0–20, J ⩽ 14) levels have been calculated by considering both the a3Σ+g−b3Σ+u and a3Σ+g–c3Πu transitions. The calculated lifetimes show a moderately strong rotational dependence, and the lifetimes for the J = 0 rotational level of the low v levels agree well with previous calculations and experimental measurements. Calculations of the a3Σ+g−b3Σ+u continuum emission spectra from electron impact X1Σ+g–a3Σ+g excitation are included.

Buckled Nano Rod—A Two State System and Its Dynamics

We consider a suspended elastic rod under longitudinal compression. The compression can be used to adjust potential energy for transverse displacements from harmonic to double well regime. As compressional strain is increased to the buckling instability, the frequency of fundamental vibrational mode drops continuously to zero (first buckling instability). As one tunes the separation between ends of a rod, the system remains stable beyond the instability by developing a double well potential for transverse motion. The two minima in the potential energy curve describe two possible buckled states at a particular strain. From one buckled state it can go over to the other by thermal fluctuations. Using a continuum approach and transition state theory (TST) we have calculated the rate of conversion from one state to other. If the strain is between $\epsilon_c$ and $4\epsilon_c$, the saddle point is the straight rod. Using TST we find exact expressions for the rate under the harmonic approximation. The expression, however, diverges at the second buckling instability $(\epsilon_c = 4\epsilon_c)$. At this point, the straight rod configuration, which was a saddle till then, becomes hill top, and two new saddles are generated. The new saddles have bent configurations (S-shaped) and as rod goes through further instabilities, they remain stable and the rate calculated under the harmonic approximation around saddle point remains finite. However, the rate diverges near the second buckling instability. We suggest methods to correct this divergence. Using these expressions, we calculate rate of passage from one buckled state to the other, for Si rods of nano dimensions. A calculation including friction has been carried out, by assuming that each segment of the rod is coupled to its own collection of harmonic oscillators. We find that friction lowers the rate of conversion.

A critical transition state in liquid metals

Temperature dependence of viscosities of liquid Sn, Cu, Pb 38.1Sn 61.9, Pb 44.8Bi 55.2, and Cu 0.7Sn 99.3 has been studied by a torsional oscillation viscometer. During the measurement process, a deviation from the Arrhenius behavior is found when the temperature is lowered to about 60 K higher than the melting point. The abnormal increasing of the viscosity and the activation energy indicates the changes of the elementary melt structure during cooling towards the melting point. The deviation region from Arrhenius viscosity is defined as the transition state. The differential scanning calorimeter experiments also show the existence of the critical transition state in liquid metals near the melting point. The drastic increase of the viscosity in the transition state can be regarded as continuum transition and be presented well by the amended Arrhenius equation which is based on the critical phenomenon.

Theoretical study of the dissociation process by multiphoton absorption in the diatomic molecule

AbstractWe investigate multiphoton absorption, including the dissociation process in the OH molecule by means of wavepacket dynamics. The time‐development scheme is the so‐called split‐operator method, which conserves the norm of the state vector. The resultant wavepacket involves the information of all discrete vibrational states and the dissociative continuum state substantially, so we are able to treat all the bound–bound, the bound–continuum and the continuum–continuum transitions. The energy spectra of the system under the strong laser pulse can also be obtained by the spectrum method, where the autocorrelation function of the wavepacket under consideration is Fourier transformed. First, we discuss the field intensity dependence of the population and the competition between dissociation and absorption processes in multiphoton processes of above‐threshold dissociation (ATD). Then, we analyze the above‐threshold dissociation due to the continuum–continuum transition in detail. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Broadband staircase quantum well infrared photodetector with low dark current

We present a theoretical investigation of a novel staircase-like quantum well infrared photodetector (QWIP). It detects wavelengths between 8.8 μm and 12.3 μm at an applied electric field of F = 6 × 10 4 V/cm at room temperature. Device operation is based on inter-subband bound to continuum transition. We also calculated the responsivity at room temperature and dark current density at 77 K. The dark current density was found to be around 10 −8 A/cm 2 at operating bias, which is lower than the conventional QWIPs in the literature.

Matrix elements for the Morse potential under an external field

Explicit analytical formulae for the matrix elements of a spatially periodic potential in a Morse basis are obtained. The finite component of the continuum–continuum transition is expressed by a hypergeometric function while the singular part is a Schwartz distribution. The deviation from the usual dipole approximation is investigated and shows a rich structure of maxima and minima in the region of intermediate energy.