4,805 research outputs found
Effect of hydrofracking fluid on colloid transport in the unsaturated zone
Hydraulic fracturing is expanding rapidly in the US to meet increasing energy demand and requires high volumes of hydrofracking fluid to displace natural gas from shale. Accidental spills and deliberate land application of hydrofracking fluids, which return to the surface during hydrofracking, are common causes of environmental contamination. Since the chemistry of hydrofracking fluids favors transport of colloids and mineral particles through rock cracks, it may also facilitate transport of in situ colloids and associated pollutants in unsaturated soils. We investigated this by subsequently injecting deionized water and flowback fluid at increasing flow rates into unsaturated sand columns containing colloids. Colloid retention and mobilization was measured in the column effluent and visualized in situ with bright field microscopy. While <5% of initial colloids were released by flushing with deionized water, 32–36% were released by flushing with flowback fluid in two distinct breakthrough peaks. These peaks resulted from 1) surface tension reduction and steric repulsion and 2) slow kinetic disaggregation of colloid flocs. Increasing the flow rate of the flowback fluid mobilized an additional 36% of colloids, due to the expansion of water filled pore space. This study suggests that hydrofracking fluid may also indirectly contaminate groundwater by remobilizing existing colloidal pollutants
A Multi-Phase Transport Model for Relativistic Heavy Ion Collisions
We describe in detail how the different components of a multi-phase transport
(AMPT) model, that uses the Heavy Ion Jet Interaction Generator (HIJING) for
generating the initial conditions, Zhang's Parton Cascade (ZPC) for modeling
partonic scatterings, the Lund string fragmentation model or a quark
coalescence model for hadronization, and A Relativistic Transport (ART) model
for treating hadronic scatterings, are improved and combined to give a coherent
description of the dynamics of relativistic heavy ion collisions. We also
explain the way parameters in the model are determined, and discuss the
sensitivity of predicted results to physical input in the model. Comparisons of
these results to experimental data, mainly from heavy ion collisions at the
Relativistic Heavy Ion Collider (RHIC), are then made in order to extract
information on the properties of the hot dense matter formed in these
collisions.Comment: 33 pages, 38 figures, revtex. Added 9 figures, version published in
Phys. Rev. C. The full source code of the AMPT model in the Fortran 77
language and instructions for users are available from the EPAPS ftp site
(ftp://ftp.aip.org/epaps/phys_rev_c/E-PRVCAN-72-781512/) and the OSCAR
website (http://www-cunuke.phys.columbia.edu/OSCAR/
STRENGTH AND CONDITIONING PROGRAMMES FOR IMPROVING BACK MUSCLE FATIGABILITY IN FIREFIGHTERS
Back pain and back-related injuries are common in firefighters. The purpose of this study was to compare the effectiveness of two different types of strength and conditioning programmes in improving back muscle fatigability in firefighters. A total of 12 male firefighters completed 16 weeks on supervised exercise intervention programme. The Functional Group was prescribed unilateral movements that mimicked the asymmetrical nature of firefighting tasks. The Conventional Group performed more bilaterally loaded, symmetrical exercise training. The lumbar extensor muscles’ resistance to fatigue was assessed using the Modified Sorensen test with electromyography (EMG). The EMG median frequency slope was less steep (p = 0.023, η²p =0.420) after training, indicating improvement in fatigability. There was no difference between the groups (p = .605, η²p = 0.028) and no interaction effect (p = 0.245, η²p =0.132). In conclusion, a well-rounded strength and conditioning programme is promising in improving back muscle fatigability in firefighters
Control the entanglement of two atoms in an optical cavity via white noise
Two two-level atoms within a leaky optical cavity is driven by two
independent external optical white noise fields. We investigate how
entanglement between two atoms arises in such a situation. The steady state
entanglement of two atoms is also investigated. A stochastic-resonance-like
behavior of entanglement is revealed. Finally, the Bell violation between atoms
is discussed.Comment: 10 pages, 9 figure
Prototype Design and Feasibility Analysis for Self-Levitated Conveying
In order to avoid friction and scratching when conveying object, an acoustic levitation prototype was designed to verify the feasibility. The modal shapes and the forced harmonic shapes of the prototype are obtained by an ANSYS coupled field computation with a one-quarter symmetry model and the levitation capacity was assessed by the use of groups of simulation and physical testing. The simulation results showed that the pure flexural and mixed flexural wave shapes with different wave numbers existed at some specific frequency. The amplitude in the central point of an aluminum plate having four piezo-electric discs glued to the bottom surface was simulated for a frequency spectrum. The experimental results confirmed the theoretical results and the feasibility of the prototype and confirm that objects can be floated at several resonant frequencies under forced vibrating condition. The system can provide largest bearing capacity when both the piezoelectric disc and the plate resonances coincide
A proposed reaction channel for the synthesis of the superheavy nucleus Z = 109
We apply a statistical-evaporation model (HIVAP) to calculate the cross
sections of superheavy elements, mainly about actinide targets and compare with
some available experimental data. A reaction channel Si + Am is
proposed for the synthesis of the element Z = 109 and the cross section is
estimated.Comment: 4 pages, 2 figures, 2 tables; two typos are corrected in Ref. [12]
and [19
Total Reaction Cross Section in an Isospin-Dependent Quantum Molecular Dynamics (IDQMD) Model
The isospin-dependent quantum molecular dynamics (IDQMD) model is used to
study the total reaction cross section . The energy-dependent Pauli
volumes of neutrons and protons have been discussed and introduced into the
IDQMD calculation to replace the widely used energy-independent Pauli volumes.
The modified IDQMD calculation can reproduce the experimental well
for both stable and exotic nuclei induced reactions. Comparisons of the
calculated induced by with different initial density
distributions have been performed. It is shown that the calculation by using
the experimentally deduced density distribution with a long tail can fit the
experimental excitation function better than that by using the
Skyrme-Hartree-Fock calculated density without long tails. It is also found
that at high energy is sensitive to the long tail of density
distribution.Comment: 4 page, 4 fig
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