905 research outputs found
Optimal operations and resilient investments in steam networks
Steam is a key energy vector for industrial sites, most commonly used for process heating and cooling, cogeneration of heat and mechanical power as a motive fluid or for stripping. Steam networks are used to carry steam from producers to consumers and between pressure levels through letdowns and steam turbines. The steam producers (boilers, heat and power cogeneration units, heat exchangers, chemical reactors) should be sized to supply the consumers at nominal operating conditions as well as peak demand. First, this paper proposes an Mixed Integer Linear Programing formulation to optimize the operations of steam networks in normal operating conditions and exceptional demand (when operating reserves fall to zero), through the introduction of load shedding. Optimization of investments based on operational and investment costs are included in the formulation. Though rare, boiler failures can have a heavy impact on steam network operations and costs, leading to undercapacity and unit shutdowns. A method is therefore proposed to simulate steam network operations when facing boiler failures. Key performance indicators are introduced to quantify the network’s resilience. The proposed methods are applied and demonstrated in an industrial case study using industrial data. The results indicate the importance of oversizing key steam producing equipments and the value of industrial symbiosis to increase industrial site resilience
Resilient decision making in steam network investments
Steam is a key energy vector for industrial sites, used for process heating, direct injection and stripping, tracing and cogeneration of mechanical power. Steam networks transport steam from producers to consumers and across different pressure levels. The steam production equipments (boilers, cogeneration units and heat exchangers) should be dimensioned to always supply key consumers as well as to deal with extreme demand caused by exceptional events such as unit startups or extreme weather. An important issue to be dealt with is that of unexpected boiler shutdowns, which can take significant amounts of time to bring back online. In cases where demand surpasses the available production of steam, load shedding is necessary in order to keep the network operable. A penalty cost can be associated to load shedding. A well dimensioned steam network is one which is resilient to such events, being able to overcome extreme demand and unexpected boiler shutdowns at minimum cost. This paper proposes a methodology for evaluating the operability of a steam network when facing unexpected boiler shutdowns. A Monte-Carlo simulation is carried out on a multi-period steam network problem, randomly shutting down boilers according to their failure properties (probability of failure and duration of failure). The aim of this method is to evaluate how resilient a steam network is to boiler shutdowns.
The Monte-Carlo simulation is applied to a steam network model built using a Mixed Integer Linear Programming (MILP) formulation, whose objective function is to minimise the operational costs of the steam network and therefore also to minimise the penalty costs associated to load shedding. A case study based on anonymised industrial data is used to demonstrate the method. Two investment propositions are evaluated and compared using the proposed method
Anisotropic excitation spectrum of a dipolar quantum Bose gas
We measure the excitation spectrum of a dipolar Chromium Bose Einstein
Condensate with Raman-Bragg spectroscopy. The energy spectrum depends on the
orientation of the dipoles with respect to the excitation momentum,
demonstrating an anisotropy which originates from the dipole-dipole
interactions between the atoms. We compare our results with the Bogoliubov
theory based on the local density approximation, and, at large excitation
wavelengths, with numerical simulations of the time dependent Gross-Pitaevskii
equation. Our results show an anisotropy of the speed of soundComment: 3 figure
Radial orbit instability as a dissipation-induced phenomenon
This paper is devoted to Radial Orbit Instability in the context of
self-gravitating dynamical systems. We present this instability in the new
frame of Dissipation-Induced Instability theory. This allows us to obtain a
rather simple proof based on energetics arguments and to clarify the associated
physical mechanism.Comment: 15 pages. Published in Monthly Notices of the RAS by the Royal
Astronomical Society and Blackwell Publishing. Corrected for page style,
typos, and added reference
Averaging out magnetic forces with fast rf-sweeps in an optical trap for metastable chromium atoms
We introduce a novel type of time-averaged trap, in which the internal state
of the atoms is rapidly modulated to modify magnetic trapping potentials. In
our experiment, fast radiofrequency (rf) linear sweeps flip the spin of atoms
at a fast rate, which averages out magnetic forces. We use this procedure to
optimize the accumulation of metastable chomium atoms into an optical dipole
trap from a magneto-optical trap. The potential experienced by the metastable
atoms is identical to the bare optical dipole potential, so that this procedure
allows for trapping all magnetic sublevels, hence increasing by up to 80
percent the final number of accumulated atoms.Comment: 4 pages, 4 figure
Control of dipolar relaxation in external fields
We study dipolar relaxation in both ultra-cold thermal and Bose-condensed
chromium atom gases. We show three different ways to control dipolar
relaxation, making use of either a static magnetic field, an oscillatory
magnetic field, or an optical lattice to reduce the dimensionality of the gas
from 3D to 2D. Although dipolar relaxation generally increases as a function of
a static magnetic field intensity, we find a range of non-zero magnetic field
intensities where dipolar relaxation is strongly reduced. We use this resonant
reduction to accurately determine the S=6 scattering length of chromium atoms:
. We compare this new measurement to another new
determination of , which we perform by analysing the precise spectroscopy
of a Feshbach resonance in d-wave collisions, yielding . These two measurements provide by far the most precise determination of
to date. We then show that, although dipolar interactions are long-range
interactions, dipolar relaxation only involves the incoming partial wave
for large enough magnetic field intensities, which has interesting consequences
on the stability of dipolar Fermi gases. We then study ultra-cold chromium
gases in a 1D optical lattice resulting in a collection of independent 2D
gases. We show that dipolar relaxation is modified when the atoms collide in
reduced dimensionality at low magnetic field intensities, and that the
corresponding dipolar relaxation rate parameter is reduced by a factor up to 7
compared to the 3D case. Finally, we study dipolar relaxation in presence of
radio-frequency (rf) oscillating magnetic fields, and we show that both the
output channel energy and the transition amplitude can be controlled by means
of rf frequency and Rabi frequency.Comment: 25 pages, 17 figure
O18O and C18O observations of rho Oph A
Observations of the (N_J=1_1-1_0) ground state transition of O_2 with the
Odin satellite resulted in a about 5 sigma detection toward the dense core rho
Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam
width of 10', larger than the size of the dense core, so that the precise
nature of the emitting source and its exact location and extent are unknown.
The current investigation is intended to remedy this. Telluric absorption makes
ground based O_2 observations essentially impossible and observations had to be
done from space. mm-wave telescopes on space platforms were necessarily small,
which resulted in large, several arcminutes wide, beam patterns. Although the
Earth's atmosphere is entirely opaque to low-lying O_2 transitions, it allows
ground based observations of the much rarer O18O in favourable conditions and
at much higher angular resolution with larger telescopes. In addition, rho Oph
A exhibits both multiple radial velocity systems and considerable velocity
gradients. Extensive mapping of the region in the proxy C18O (J=3-2) line can
be expected to help identify the O_2 source on the basis of its line shape and
Doppler velocity. Line opacities were determined from observations of optically
thin 13C18O (J=3-2) at selected positions. During several observing periods,
two C18O intensity maxima in rho Oph A were searched for in the 16O18O
(2_1-0_1) line at 234 GHz with the 12m APEX telescope. Our observations
resulted in an upper limit on the integrated O18O intensity of < 0.01 K km/s (3
sigma) into the 26.5" beam. We conclude that the source of observed O_2
emission is most likely confined to the central regions of the rho Oph A cloud.
In this limited area, implied O_2 abundances could thus be higher than
previously reported, by up to two orders of magnitude.Comment: 7 pages, 6 figures (5 colour), Astronomy & Astrophysic
Systemic and central nervous system neuroinflammatory signatures of neuropsychiatric symptoms and related cognitive decline in older people.
Neuroinflammation may contribute to psychiatric symptoms in older people, in particular in the context of Alzheimer's disease (AD). We sought to identify systemic and central nervous system (CNS) inflammatory alterations associated with neuropsychiatric symptoms (NPS); and to investigate their relationships with AD pathology and clinical disease progression.
We quantified a panel of 38 neuroinflammation and vascular injury markers in paired serum and cerebrospinal fluid (CSF) samples in a cohort of cognitively normal and impaired older subjects. We performed neuropsychiatric and cognitive evaluations and measured CSF biomarkers of AD pathology. Multivariate analysis determined serum and CSF neuroinflammatory alterations associated with NPS, considering cognitive status, AD pathology, and cognitive decline at follow-up visits.
NPS were associated with distinct inflammatory profiles in serum, involving eotaxin-3, interleukin (IL)-6 and C-reactive protein (CRP); and in CSF, including soluble intracellular cell adhesion molecule-1 (sICAM-1), IL-8, 10-kDa interferon-γ-induced protein, and CRP. AD pathology interacted with CSF sICAM-1 in association with NPS. Presenting NPS was associated with subsequent cognitive decline which was mediated by CSF sICAM-1.
Distinct systemic and CNS inflammatory processes are involved in the pathophysiology of NPS in older people. Neuroinflammation may explain the link between NPS and more rapid clinical disease progression
Systemic and central nervous system neuroinflammatory signatures of neuropsychiatric symptoms and related cognitive decline in older people
BACKGROUND
Neuroinflammation may contribute to psychiatric symptoms in older people, in particular in the context of Alzheimer's disease (AD). We sought to identify systemic and central nervous system (CNS) inflammatory alterations associated with neuropsychiatric symptoms (NPS); and to investigate their relationships with AD pathology and clinical disease progression.
METHODS
We quantified a panel of 38 neuroinflammation and vascular injury markers in paired serum and cerebrospinal fluid (CSF) samples in a cohort of cognitively normal and impaired older subjects. We performed neuropsychiatric and cognitive evaluations and measured CSF biomarkers of AD pathology. Multivariate analysis determined serum and CSF neuroinflammatory alterations associated with NPS, considering cognitive status, AD pathology, and cognitive decline at follow-up visits.
RESULTS
NPS were associated with distinct inflammatory profiles in serum, involving eotaxin-3, interleukin (IL)-6 and C-reactive protein (CRP); and in CSF, including soluble intracellular cell adhesion molecule-1 (sICAM-1), IL-8, 10-kDa interferon-γ-induced protein, and CRP. AD pathology interacted with CSF sICAM-1 in association with NPS. Presenting NPS was associated with subsequent cognitive decline which was mediated by CSF sICAM-1.
CONCLUSIONS
Distinct systemic and CNS inflammatory processes are involved in the pathophysiology of NPS in older people. Neuroinflammation may explain the link between NPS and more rapid clinical disease progression
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