10,796 research outputs found
Nitrification-denitrification in WSP: a mechanism for permanent nitrogen removal in maturation ponds
A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N labelled nitrite (Na15NO2), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of δ15N showed that
nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity
Single-shot measurement of quantum optical phase
Although the canonical phase of light, which is defined as the complement of
photon number, has been described theoretically by a variety of distinct
approaches, there have been no methods proposed for its measurement. Indeed
doubts have been expressed about whether or not it is measurable. Here we show
how it is possible, at least in principle, to perform a single-shot measurement
of canonical phase using beam splitters, mirrors, phase shifters and
photodetectors.Comment: This paper was published in PRL in 2002 but, at the time, was not
placed on the archive. It is included now to make accessing this paper easie
The Response to a Perturbation in the Reflection Amplitude
We apply inverse scattering theory to calculate the functional derivative of
the potential and wave function of a one-dimensional
Schr\"odinger operator with respect to the reflection amplitude .Comment: 16 pages, no figure
Recreation carrying capacity estimations to support beach management at Praia de Faro, Portugal
The purpose of this research paper is to outline the theory and practice of tourism carrying capacity
assessment and its relevance as a management tool for coastal management. Based on the Tourism
Carrying Capacity Assessment for Protected Areas Framework and the Image Capture Technique associated
with the PAOT (people at one time) approach, this paper explores Praia de Faro as the study area
and attempts to assess the optimum number of people that should be allowed without jeopardizing the
surrounding ecological, social and cultural environments. Results showed that the physico-ecological
carrying capacity should be between 1385 and 2628 visitors/day with maximum impact acceptability
curves being 305 and 608 tourists (for local people and tourists respectively). Although there was
a significant difference between the physico-ecological and socio-cultural carrying capacity, this study
suggests that the physico-ecological carrying may be applied for ecosystem management, whilst the
socio-cultural carrying capacity may be addressed when management objectives are tourists and beach
users
Vortex ring refraction at large Froude numbers
We have experimentally studied the impact of an initially planar axisymmetric
vortex ring, incident at an oblique angle, upon a gravity-induced interface
separating two fluids of differing densities. After impact, the vortex ring was
found to exhibit a variety of subsequent trajectories, which we organize
according to both the incidence angle, , and the interface strength,
defined as the ratio of the Atwood and Froude numbers, . For grazing
incidence angles ( deg.) vortices either penetrate or
reflect from the interface, depending on whether the interface is weak or
strong. In some cases, reflected vortices execute damped oscillations before
finally disintegrating. For smaller incidence angles (
deg.) vortices penetrate the interface. When there is a strong interface, these
vortices are observed to curve back up toward the interface. When there is a
weak interface, these vortices are observed to refract downward, away from the
interface. The critical interface strength below which vortex ring refraction
is observed is given by .Comment: 26 pages, 11 figures; Submitted to Physical Review
Causality, delocalization and positivity of energy
In a series of interesting papers G. C. Hegerfeldt has shown that quantum
systems with positive energy initially localized in a finite region,
immediately develop infinite tails. In our paper Hegerfeldt's theorem is
analysed using quantum and classical wave packets. We show that Hegerfeldt's
conclusion remains valid in classical physics. No violation of Einstein's
causality is ever involved. Using only positive frequencies, complex wave
packets are constructed which at are real and finitely localized and
which, furthemore, are superpositions of two nonlocal wave packets. The
nonlocality is initially cancelled by destructive interference. However this
cancellation becomes incomplete at arbitrary times immediately afterwards. In
agreement with relativity the two nonlocal wave packets move with the velocity
of light, in opposite directions.Comment: 14 pages, 5 figure
Dissociative electron attachment to the H2O molecule. I. Complex-valued potential-energy surfaces for the 2B1, 2A1, and 2B2 metastable states of the water anion
We present the results of calculations defining global, three-dimensional
representations of the complex-valued potential-energy surfaces of the doublet
B1, doublet A1, and doublet B2 metastable states of the water anion that
underlie the physical process of dissociative electron attachment to water. The
real part of the resonance energies is obtained from configuration-interaction
calculations performed in a restricted Hilbert space, while the imaginary part
of the energies (the widths) is derived from complex Kohn scattering
calculations. A diabatization is performed on the 2A1 and 2B2 surfaces, due to
the presence of a conical intersection between them. We discuss the
implications that the shapes of the constructed potential-energy surfaces will
have upon the nuclear dynamics of dissociative electron attachment to H2O.
This work originally appeared as Phys Rev A 75, 012710 (2007). Typesetting
errors in the published version have been corrected here.Comment: Corrected version of PRA 75, 012710 (2007
- …