Sudden Injection Research Articles

Competitive Impacts of Means-Tested Vouchers on Public School Performance: Evidence from Louisiana

Given the significant growth rate and geographic expansion of private school choice programs over the past two decades, it is important to examine how traditional public schools respond to the sudden injection of competition for students and resources. Although prior studies of this nature have been limited to Florida and Milwaukee, using multiple analytic strategies this paper examines the competitive impacts of the Louisiana Scholarship Program (LSP) to determine its achievement impacts on students in affected public schools. Serving 4,954 students in its first year of statewide expansion, this targeted school voucher program provides public funds for low-income students in low-performing public schools to enroll in participating private schools across the state of Louisiana. Using (1) a school fixed effects approach and (2) a regression discontinuity framework to examine the achievement impacts of the LSP on students in affected public schools, this competitive effects analysis reveals neutral to positive impacts that are small in magnitude. Policy implications are discussed.

Hydrodynamical simulations and similarity relations for eruptive mass-loss from massive stars

Motivated by the eruptive mass loss inferred from Luminous Blue Variable (LBV) stars, we present 1D hydrodynamical simulations of the response from sudden energy injection into the interior of a very massive ($100 \, M_\odot$) star. For a fiducial case with total energy addition set to a factor $f=0.5$ of the net stellar binding energy, and applied within the stellar envelope, we detail the dynamical response that leads to ejection of the outermost $7.2 \, M_\odot$. We find that the ejecta's variations in time $t$ and radius $r$ for the velocity $v$, density $\rho$, and temperature $T$ are quite well fit by similarity forms in the variable $r/t \approx v$. Specifically the scaled density follows a simple exponential decline $\rho t^{3} \sim \exp (-r/v_{\rm o} t)$. This `exponential similarity' leads to analytic scaling relations for total ejecta mass $\Delta M$ and kinetic energy $\Delta K$ that agree well with the hydrodynamical simulations, with the specific-energy-averaged speed related to the exponential scale speed $v_{\rm o}$ through ${\bar v} \equiv \sqrt{2 \Delta K/\Delta M} = \sqrt{12} \, v_{\rm o}$, and a value comparable to the star's surface escape speed, $v_{\rm esc}$. Models with energy added in the core develop a surface shock breakout that propels an initial, higher-speed ejecta ($>$5000km s$^{-1}$), but the bulk of the ejected material still follows the same exponential similarity scalings with ${\bar v} \approx v_{\rm esc}$. A broader parameter study examines how the ejected mass and energy depends on the energy-addition factor $f$, for three distinct model series that locate the added energy in either the core, envelope, or near-surface. We conclude by discussing the relevance of these results for understanding LBV outbursts and other eruptive phenomena, such as failed supernovae and pulsational pair instability events.

A Novel Experimental Technique to Simulate Shock Behaviour and Bursting Failure of Roadways

Rockburst is a sudden and dynamic failure of rock that can cause serious injury to miners and damage to the underground excavations. Stress path, dynamic disturbance, and support system play important and different roles in the generation processes of rockbursts, resulting rockbursts with variety of reasons and failure modes. A test facility that was capable of simulating such factors was developed to study shock behaviour and bursting failure of roadways. The results demonstrate that the modeled roadway was in good condition and retained a shock resistance capacity after three drop loads. Until the acceleration amplitude increased to a certain level at the time of the fourth dynamic loading, sudden bursting failure of modeled roadway occurred. Many large fragments ejected from the upper and middle regions of the roadway, accompanied with loud noise. A deep pit was observed after the bursting failure. The axial of the fan‐shaped pit had an angle above the vertical. In addition, shock behaviour of the modeled roadway had been changed by the anchor‐net support. Significant differences appeared between the acceleration signals measured in two roadway sections with and without the anchor‐net support. The acceleration magnitude of the supported roadway section was strongly reduced by the presence of the anchor‐net support. Even when the unsupported roadway section underwent a sudden injection failure, the roadway with anchor‐net support was in good condition. This study may eventually lead to a methodology for studying the rockbursting resistance capacity of underground roadways.

A fully-implicit solution for the single-pressure two-fluid model with sharp discontinuities

Transient two-phase flow in pipes is a common phenomenon in nuclear and petroleum engineering. Due to complex interactions at phase interfaces and the large variation on fluid properties, multiphase flows are much more complex than single-phase flows. However, modeling pressure, temperature, phase velocities and volumetric fractions is essential for design, management, optimization and safety analysis. Two approaches are generally applied for modeling multiphase flow: (a) local instant formulation and (b) averaged formulation. In this paper, the averaged Single-Pressure Two-Fluid model (together with Bestion’s correlation for interfacial pressure) is studied and a fully-implicit numerical solution is proposed. The obtained numerical solutions were compared to reference solutions for benchmark problems (water faucet tests and phase segregation) available in the literature. Aiming to verify if the aforementioned averaged model and the proposed fully-implicit solutions can be applied to study problems with counter-current flow and sharp discontinuities in pressure, velocities and volumetric fractions, new reference solutions for a generalized transient frictionless segregation test are proposed. Comparison between the proposed reference and numerical solutions allowed for a detailed verification of the studied averaged model. Finally, sudden multiphase fluid injection with subsequent tube closure was studied and the numerical results were discussed. As expected, it was observed transient surge pressure and co-current/counter-current flow with phase appearance and disappearance.

From arteries to boreholes: transient response of a poroelastic cylinder to fluid injection.

The radially outward flow of fluid through a porous medium occurs in many practical problems, from transport across vascular walls to the pressurization of boreholes in the subsurface. When the driving pressure is non-negligible relative to the stiffness of the solid structure, the poromechanical coupling between the fluid and the solid can control both the steady state and the transient mechanics of the system. Very large pressures or very soft materials lead to large deformations of the solid skeleton, which introduce kinematic and constitutive nonlinearity that can have a non-trivial impact on these mechanics. Here, we study the transient response of a poroelastic cylinder to sudden fluid injection. We consider the impacts of kinematic and constitutive nonlinearity, both separately and in combination, and we highlight the central role of driving method in the evolution of the response. We show that the various facets of nonlinearity may either accelerate or decelerate the transient response relative to linear poroelasticity, depending on the boundary conditions and the initial geometry, and that an imposed fluid pressure leads to a much faster response than an imposed fluid flux.

Plasma Evolution within an Erupting Coronal Cavity

Abstract Coronal cavities have previously been observed to be associated with long-lived quiescent filaments and are thought to correspond to the associated magnetic flux rope. Although the standard flare model predicts a coronal cavity corresponding to the erupting flux rope, these have only been observed using broadband imaging data, restricting an analysis to the plane-of-sky. We present a unique set of spectroscopic observations of an active region filament seen erupting at the solar limb in the extreme ultraviolet. The cavity erupted and expanded rapidly, with the change in rise phase contemporaneous with an increase in nonthermal electron energy flux of the associated flare. Hot and cool filamentary material was observed to rise with the erupting flux rope, disappearing suddenly as the cavity appeared. Although strongly blueshifted plasma continued to be observed flowing from the apex of the erupting flux rope, this outflow soon ceased. These results indicate that the sudden injection of energy from the flare beneath forced the rapid eruption and expansion of the flux rope, driving strong plasma flows, which resulted in the eruption of an under-dense filamentary flux rope.

The Competitive Effects of the Louisiana Scholarship Program On Public School Performance

Given the significant growth rate and geographic expansion of private school choice programs over the past two decades, it is important to examine how traditional public schools respond to the sudden injection of competition for students and resources. This article uses 1) a school fixed effects approach, and 2) a regression discontinuity framework to examine the achievement impacts of the Louisiana Scholarship Program (LSP). This targeted school voucher program has provided public funds for low-income students in low-performing public schools to enroll in participating private schools since the 2012-13 school year. The main findings of the competitive effects analysis reveal neutral to positive impacts that are small in magnitude. Effects are largest for students attending those public schools most affected by the competitive threat. Policy implications are discussed.

Study of the effect of clay swelling on the oil recovery factor in porous media using a glass micromodel

Formation damage due to incompatibility between the formation and injected low-salinity water decreases the relative permeabilities of oil and brine, increases residual oil saturation, and decreases oil recovery. In the presence of swelling clays, the shock effect of sudden water injection results in an increase in formation damage. Clay minerals may cause formation damage due to swelling and migration during the production of oil and gas. Therefore a good understanding of the damage mechanisms of clays helps us to prevent and remedy possible damage in reservoirs.In this work, the effect of clay swelling behavior on the oil recovery factor at the pore scale by using a glass micromodel was studied. A clay-coated micromodel with sodium bentonite as the swelling clay was prepared. Using an image processing technique, the ultimate oil recovery factors after flooding with low-salinity water (LSW) and high-salinity water (HSW) were estimated and the effect of clay swelling phenomena on the oil recovery factor was studied.Final residual oil saturation was higher when LSW was used as the injection fluid compared to when HSW was used, and in fact it can be said that clay swelling somehow inhibits the film flow of injection fluid and causes more oil to be bypassed in the micromodel.

Thermal Fatigue Analysis in a High Pressure Cooling System (HPCS) Nozzle of a Boling Water Reactor

In this paper, the Cumulative Usage Factor (CUF) of a High Pressure Core Cooling System (HPCS) reactor nozzle of a Boiling Water Reactor was calculated. This fatigue damage has been caused by the sudden injection of cold water into the reactor vessel through such nozzle. For this purpose, a three-dimensional analysis was carried out. Accordingly, a transient heat transfer analysis was developed. The temperature distribution was determined. With this information, the stress analysis was carried out. The safe end was restricted to move along its axial direction and the forging end was free to expand axially and radially. The resultant stress field established the magnitude of the alternative stresses. In the last step, a fatigue analysis was developed. The most critical point is the junction of the nozzle with the thermal sleeve. The fatigue performance was evaluated during a period of sixty years. It was assumed that 1.5 cycles per year will take place. The fatigue curves of ASME code section III were used. The results showed that the Cumulative Usage Factor (CUF) vary with the temperature injection, being 0.4090 when the water injected was 4.44°C and 0.3797 when the water temperature was 37.77°C. Both of them were estimated for a period of 60 years of operation. Therefore, damage is reduced as the temperature of the injected water increases. Besides, it is advisable to at least follow the recommendations of the NUREG ́s 1800 and 1801 [1, 2]. In this way, the aging of the nozzle is adequately managed.

Pathways of volatile migration in the crust beneath Harrat Lunayyir (Saudi Arabia) during the unrest in 2009 revealed by attenuation tomography

Harrat Lunayyir is a relatively young basaltic field in Saudi Arabia located at the western margin of the Arabian Peninsula. In April–June 2009, strong seismic activity and ground deformations at this site marked the activation of the magma system beneath Harrat Lunayyir. In this study, we present new three-dimensional models of the attenuation of P and S waves during the unrest in 2009 based on the analysis of t*. We measured 1658 and 3170 values of t* for P and S waves, respectively, for the same earthquakes that were previously used for travel time tomography. The resulting anomalies of the P and S wave attenuation look very similar. In the center of the study area, we observe a prominent high-attenuation pattern, which coincides with the most active seismicity at shallow depths and maximum ground deformations. This high-attenuation zone may represent a zone of accumulation and ascending of gases, which originated at depths of 5–7km due to the decompression of ascending liquid volatiles. Based on these findings and previous tomography studies, we propose that the unrest at Harrat Lunayyir in 2009 was triggered by a sudden injection of unstable liquid volatiles from deeper magma sources. At some depths, they were transformed to gases, which caused the volume to increase, and this led to seismic activation in the areas of phase transformations. The overpressurized gases ultimately found the weakest point in the rigid basaltic cover at the junction of several tectonic faults and escaped to the surface.

Comparison of dust transport modelling codes in a tokamak plasma

Since the installation on the Joint European Torus of the ITER-like Wall (ILW), intense radiation spikes have been observed, especially in the discharges following a disruption, and have been associated with possible sudden injection of tungsten (W) impurities consequent to full ablation of W dust particles. The problem of dust production, mobilization, and interaction both with the plasma and the vessel tiles is therefore of great concern and requires the setting up of dedicated and validated numerical modeling tools. Among these, a useful role is played by the dust trajectory calculators, which can present in a relatively clear way the qualitative and quantitative description of the mobilization and fate of selected bunches of dust grains.

DISCOVERY OF TRANSIENT INFRARED EMISSION FROM DUST HEATED BY STELLAR TIDAL DISRUPTION FLARES

ABSTRACT Stars that pass within the Roche radius of a supermassive black hole will be tidally disrupted, yielding a sudden injection of gas close to the black hole horizon which produces an electromagnetic flare. A few dozen of these flares have been discovered in recent years, but current observations provide poor constraints on the bolometric luminosity and total accreted mass of these events. Using images from the Wide-field Infrared Survey Explorer, we have discovered transient 3.4 μm emission from several previously known tidal disruption flares. The observations can be explained by dust heated to its sublimation temperature due to the intense radiation of the tidal flare. From the break in the infrared light curve we infer that this hot dust is located ∼0.1 pc from the supermassive black hole. Since the dust has been heated by absorbing UV and (potentially) soft X-ray photons of the flare, the reprocessing light curve yields an estimate of the bolometric flare luminosity. For the flare PTF-09ge, we infer that the most likely value of the luminosity integrated over frequencies at which dust can absorb photons is erg s−1, with a factor of 3 uncertainty due to the unknown temperature of the dust. This bolometric luminosity is a factor ∼10 larger than the observed blackbody luminosity. Our work is the first to probe dust in the nuclei of non-active galaxies on sub-parsec scales. The observed infrared luminosity implies a covering factor ∼1% for the nuclear dust in the host galaxies.

Black hole collapse in the 1/c expansion

We present a first-principles CFT calculation corresponding to the spherical collapse of a shell of matter in three dimensional quantum gravity. In field theory terms, we describe the equilibration process, from early times to thermalization, of a CFT following a sudden injection of energy at time t=0. By formulating a continuum version of Zamolodchikov's monodromy method to calculate conformal blocks at large central charge c, we give a framework to compute a general class of probe observables in the collapse state, incorporating the full backreaction of matter fields on the dual geometry. This is illustrated by calculating a scalar field two-point function at time-like separation and the time-dependent entanglement entropy of an interval, both showing thermalization at late times. The results are in perfect agreement with previous gravity calculations in the AdS$_3$-Vaidya geometry. Information loss appears in the CFT as an explicit violation of unitarity in the 1/c expansion, restored by nonperturbative corrections.

UNBOUND DEBRIS STREAMS AND REMNANTS RESULTING FROM THE TIDAL DISRUPTIONS OF STARS BY SUPERMASSIVE BLACK HOLES

ABSTRACT The kinetic energy of a star in orbit about a supermassive black hole is a significant fraction of its rest mass energy when its periapse is comparable to its tidal radius. Upon its destruction, a fraction of this energy is extracted and injected into the stellar debris, half of which becomes unbound from the black hole, with the fastest material moving at . In this paper, we present a formalism for determining the fate of these unbound debris streams (UDSs) as they depart from the black hole and interact with the surrounding gas. As the density and velocity varies along the length of a UDS, we find that hydrodynamical drag quickly shapes UDSs into loop-like structures, with the densest portions of the streams leading portions of lower density. As UDSs travel outwards, their drag against the ISM increases quadratically with distance, which causes UDSs to deposit their momentum and energy into the ambient medium before the surrounding shocked ISM has a chance to cool. This sudden injection of erg into the ambient medium generates a Sedov-like unbound debris remnant (UDR) that mimics supernova remnants (SNRs) in energetics and appearance, accelerates particles which will produce cosmic rays and synchrotron emission, and provides momentum feedback into the molecular clouds surrounding a black hole. We estimate that a few of these UDRs might be present within a couple degrees of the Galactic Center masquerading as SNRs, and that the UDR scenario is a plausible explanation for Sgr A east.

TimHarris. Rebellion: Britain's First Stuart Kings, 1567‐1642. Oxford: Oxford UP, 2014. 588pp. ISBN 13: 9780199209002. £30.00; $45.00 (cloth).

TimHarris. Rebellion: Britain's First Stuart Kings, 1567‐1642. Oxford: Oxford UP, 2014. 588pp. ISBN 13: 9780199209002. £30.00; $45.00 (cloth).

Observations of a large‐scale gravity wave propagating over an extremely large horizontal distance in the thermosphere

AbstractIn this paper we report the detection of a large‐scale gravity wave propagating over an extremely large horizontal distance in the thermosphere on 28 July 2006. Specifically, after being launched at the northern auroral region on the dayside, this wave propagated equatorward with phase speeds on the order of ∼720 m/s and finally almost traveled around the Earth once horizontally in the thermosphere prior to dissipation. The time taken to dissipate is about 15.5 h. It is the farthest‐traveling large‐scale gravity wave currently tracked by satellite measurements, made possible by a sudden injection of energy in an unusually clean propagation environment. This experiment of opportunity serves as an important step in furthering our theoretical understanding of gravity wave propagation and dissipation in the thermosphere.

GAMMA-RAY BURST SPECTRA AND SPECTRAL CORRELATIONS FROM SUB-PHOTOSPHERIC COMPTONIZATION

One of the most important unresolved issues in gamma-ray burst physics is the origin of the prompt gamma-ray spectrum. Its general non-thermal character and the softness in the X-ray band remain unexplained. We tackle these issues by performing Monte Carlo simulations of radiation-matter interactions in a scattering dominated photon-lepton plasma. The plasma -- initially in equilibrium -- is driven to non-equilibrium conditions by a sudden energy injection in the lepton population, mimicking the effect of a shock wave or the dissipation of magnetic energy. Equilibrium restoration occurs due to energy exchange between the photons and leptons. While the initial and final equilibrium spectra are thermal, the transitional photon spectra are characterized by non-thermal features such as power-law tails, high energy bumps, and multiple components. Such non-thermal features are observed at infinity if the dissipation occurs at small to moderate optical depths, and the spectrum is released before thermalization is complete. We model the synthetic spectra with a Band function and show that the resulting spectral parameters are similar to observations for a frequency range of 2-3 orders of magnitude around the peak. In addition, our model predicts correlations between the low-frequency photon index and the peak frequency as well as between the low- and high-frequency indices. We explore baryon and pair dominated fireballs and reach the conclusion that baryonic fireballs are a better model for explaining the observed features of gamma-ray burst spectra.

Removal of isopropyl alcohol (IPA) in UPW by synergistic photocatalytic oxidation and adsorption

Earlier work showed that the commercial granular activated carbon (GAC) could effectively remove large non‐polar molecules, but showed poor removal efficiency for small polar compounds such as isopropyl alcohol (IPA) [Schmotzer et al. Clean Technol. Environ. Policy 2002;4:125; Cong et al. J. Phys. Chem. C 2007;111:6976]. To achieve the goal of increasing the lifetime and removal efficiency of GAC bed for small polar organic compounds in ultrapure water (UPW), the synergistic partial photocatalytic oxidation and adsorption system using commercial GAC coated with nitrogen doped titanium dioxide as an adsorbate was proposed in this work. The influence of operating factors such as UV intensity, flow rate, feed concentration, and the sudden injection of air or inorganic acid on IPA removal efficiency was systematically investigated. Compared to the traditional GAC adsorption bed, at feed total organic carbon (TOC) concentration of 800 ppb, the lifetime of GAC bed in this synergistic photocatalytic oxidation and adsorption system was extended from 348 to 600 min and the outlet TOC concentration was decreased from 793 to 499 ppb. The difference of the TOC outlet concentration in those two configurations was attributed to the photocatalytic effect by GAC coated with nitrogen doped titanium dioxide. The reactions between oxidation radicals and organic contaminants caused the majority of IPA to be decomposed into secondary organic compounds such as acetone and acetone had already been shown a higher affinity to GAC than that of IPA. Experiments also demonstrated the injection of air or inorganic acid in the stream would facilitate the removal of IPA in UPW.

Inhomogeneous holographic thermalization

Abstract The sudden injection of energy in a strongly coupled conformal field theory and its subsequent thermalization can be holographically modeled by a shell falling into anti-de Sitter space and forming a black brane. For a homogeneous shell, Bhattacharyya and Minwalla were able to study this process analytically using a weak field approximation. Motivated by event-by-event fluctuations in heavy ion collisions, we include inhomogeneities in this model, obtaining analytic results in a long wavelength expansion. In the early-time window in which our approximations can be trusted, the resulting evolution matches well with that of a simple free streaming model. Near the end of this time window, we find that the stress tensor approaches that of second-order viscous hydrodynamics. We comment on possible lessons for heavy ion phenomenology.

The Formation of Debris Flow Dams: Geomorphic Setting and Influential Factors

Temporary dams can be formed by the sudden injection of debris flow into main stream for some favorable geomorphologic and hydraulic conditions, which would result in extensive inundations upstream and catastrophic floods downstream due to dam breach and consequently dramatic changes of channel and valley. Expeditious means of assessing potential of dam-forming are necessary, particularly in geological active regions. The complete blockages or dam-forming significantly relate to the discharge ratio and velocity ratio between tributary and main stream, bulk density of debris flow, confluent angles and evenness degree of grain sizes.