2,253 research outputs found
Do Concentration Cells Store Charge in Water? Comment on Can Water Store Charge?
In a recent article, Ovchinnikova and Pollack (O&P)(1) reported that the persistent pH gradients (>100 min after electrolysis) generated upon charging a simple electrolytic cell (Pt electrodes in dilute aqueous NaCl solutions) imply that “water can store charge”, in apparent violation of the principle of electroneutrality in bulk macroscopic fluid phases
Monitoring Winter Flow Conditions on the Ivishak River, Alaska
The Sagavanirktok River, a braided river on the Alaska North Slope, flows adjacent to the trans-Alaska pipeline for approximately 100 miles south of Prudhoe Bay. During an unprecedented flooding event in mid-May 2015, the pipeline was exposed in an area located approximately 20 miles south of Prudhoe Bay. The Ivishak River is a main tributary of the Sagavanirktok River, but little is known about its water flow characteristics and contribution to the Sagavanirktok River, especially in winter and during spring breakup. To gather this information, we installed water level sensors on two main tributaries of the Ivishak River (Upper Ivishak and Saviukviayak rivers), early in winter season 2016–2017, in open-water channels that showed promise as locations for long-term gauging stations. Our ultimate goal was to find a location for permanent deployment of water level sensors. By February, the first sites chosen were ice covered, so two additional sensors, one on each river, were deployed in different locations. Some of the sensors were lost (i.e., carried away by the current or buried under a thick layer of sediments). Water level data gathered from the sensors showed a maximum change of 1.07 m. Winter discharge measurements indicate a 44% reduction between February and April 2017. A summer discharge measurement shows a 430% increase from winter to summer
Is J 133658.3-295105 a Radio Source at z >= 1.0 or at the Distance of M 83?
We present Gemini optical imaging and spectroscopy of the radio source J
133658.3-295105. This source has been suggested to be the core of an FR II
radio source with two detected lobes. J 133658.3-295105 and its lobes are
aligned with the optical nucleus of M 83 and with three other radio sources at
the M 83 bulge outer region. These radio sources are neither supernova remnants
nor H II regions. This curious configuration prompted us to try to determine
the distance to J 133658.3-295105. We detected H_alpha emission redshifted by ~
130 km s^-1 with respect to an M 83 H II region 2.5" east-southeast of the
radio source. We do not detect other redshifted emission lines of an optical
counterpart down to m_i = 22.2 +/- 0.8. Two different scenarios are proposed:
the radio source is at z >= 2.5, a much larger distance than the previously
proposed lower limit z >= 1.0, or the object was ejected by a gravitational
recoil event from the M 83 nucleus. This nucleus is undergoing a strong
dynamical evolution, judging from previous three-dimensional spectroscopy.Comment: 6 pages, 4 figure
Decoherent time-dependent transport beyond the Landauer-B\"uttiker formulation: a quantum-drift alternative to quantum jumps
We present a model for decoherence in time-dependent transport. It boils down
into a form of wave function that undergoes a smooth stochastic drift of the
phase in a local basis, the Quantum Drift (QD) model. This drift is nothing
else but a local energy fluctuation. Unlike Quantum Jumps (QJ) models, no jumps
are present in the density as the evolution is unitary. As a first application,
we address the transport through a resonant state
that undergoes decoherence. We show the equivalence with the decoherent steady
state transport in presence of a B\"{u}ttiker's voltage probe. In order to test
the dynamics, we consider two many-spin systems whith a local energy
fluctuation. A two-spin system is reduced to a two level system (TLS) that
oscillates among and . We show that QD model recovers not only
the exponential damping of the oscillations in the low perturbation regime, but
also the non-trivial bifurcation of the damping rates at a critical point, i.e.
the quantum dynamical phase transition. We also address the spin-wave like
dynamics of local polarization in a spin chain. The QD average solution has
about half the dispersion respect to the mean dynamics than QJ. By evaluating
the Loschmidt Echo (LE), we find that the pure states and are quite robust against the
local decoherence. In contrast, the LE, and hence coherence, decays faster when
the system is in a superposition state. Because its simple implementation, the
method is well suited to assess decoherent transport problems as well as to
include decoherence in both one-body and many-body dynamics.Comment: 10 pages, 5 figure
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