1,445 research outputs found
Model Checking Probabilistic Pushdown Automata
We consider the model checking problem for probabilistic pushdown automata
(pPDA) and properties expressible in various probabilistic logics. We start
with properties that can be formulated as instances of a generalized random
walk problem. We prove that both qualitative and quantitative model checking
for this class of properties and pPDA is decidable. Then we show that model
checking for the qualitative fragment of the logic PCTL and pPDA is also
decidable. Moreover, we develop an error-tolerant model checking algorithm for
PCTL and the subclass of stateless pPDA. Finally, we consider the class of
omega-regular properties and show that both qualitative and quantitative model
checking for pPDA is decidable
Arithmetic complexity via effective names for random sequences
We investigate enumerability properties for classes of sets which permit
recursive, lexicographically increasing approximations, or left-r.e. sets. In
addition to pinpointing the complexity of left-r.e. Martin-L\"{o}f, computably,
Schnorr, and Kurtz random sets, weakly 1-generics and their complementary
classes, we find that there exist characterizations of the third and fourth
levels of the arithmetic hierarchy purely in terms of these notions.
More generally, there exists an equivalence between arithmetic complexity and
existence of numberings for classes of left-r.e. sets with shift-persistent
elements. While some classes (such as Martin-L\"{o}f randoms and Kurtz
non-randoms) have left-r.e. numberings, there is no canonical, or acceptable,
left-r.e. numbering for any class of left-r.e. randoms.
Finally, we note some fundamental differences between left-r.e. numberings
for sets and reals
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Upper ocean climate of the Eastern Mediterranean Sea during the Holocene Insolation Maximum – a model study
ine thousand years ago (9 ka BP), the Northern Hemisphere experienced enhanced seasonality caused by an orbital configuration close to the minimum of the precession index. To assess the impact of this "Holocene Insolation Maximum" (HIM) on the Mediterranean Sea, we use a regional ocean general circulation model forced by atmospheric input derived from global simulations. A stronger seasonal cycle is simulated by the model, which shows a relatively homogeneous winter cooling and a summer warming with well-defined spatial patterns, in particular, a subsurface warming in the Cretan and western Levantine areas.
The comparison between the SST simulated for the HIM and a reconstruction from planktonic foraminifera transfer functions shows a poor agreement, especially for summer, when the vertical temperature gradient is strong. As a novel approach, we propose a reinterpretation of the reconstruction, to consider the conditions throughout the upper water column rather than at a single depth. We claim that such a depth-integrated approach is more adequate for surface temperature comparison purposes in a situation where the upper ocean structure in the past was different from the present-day. In this case, the depth-integrated interpretation of the proxy data strongly improves the agreement between modelled and reconstructed temperature signal with the subsurface summer warming being recorded by both model and proxies, with a small shift to the south in the model results.
The mechanisms responsible for the peculiar subsurface pattern are found to be a combination of enhanced downwelling and wind mixing due to strengthened Etesian winds, and enhanced thermal forcing due to the stronger summer insolation in the Northern Hemisphere. Together, these processes induce a stronger heat transfer from the surface to the subsurface during late summer in the western Levantine; this leads to an enhanced heat piracy in this region, a process never identified before, but potentially characteristic of time slices with enhanced insolation
Tableaux for Policy Synthesis for MDPs with PCTL* Constraints
Markov decision processes (MDPs) are the standard formalism for modelling
sequential decision making in stochastic environments. Policy synthesis
addresses the problem of how to control or limit the decisions an agent makes
so that a given specification is met. In this paper we consider PCTL*, the
probabilistic counterpart of CTL*, as the specification language. Because in
general the policy synthesis problem for PCTL* is undecidable, we restrict to
policies whose execution history memory is finitely bounded a priori.
Surprisingly, no algorithm for policy synthesis for this natural and
expressive framework has been developed so far. We close this gap and describe
a tableau-based algorithm that, given an MDP and a PCTL* specification, derives
in a non-deterministic way a system of (possibly nonlinear) equalities and
inequalities. The solutions of this system, if any, describe the desired
(stochastic) policies.
Our main result in this paper is the correctness of our method, i.e.,
soundness, completeness and termination.Comment: This is a long version of a conference paper published at TABLEAUX
2017. It contains proofs of the main results and fixes a bug. See the
footnote on page 1 for detail
Flare-induced changes of the photospheric magnetic field in a -spot deduced from ground-based observations
Aims: Changes of the magnetic field and the line-of-sight velocities in the
photosphere are being reported for an M-class flare that originated at a
-spot belonging to active region NOAA 11865.
Methods: High-resolution ground-based near-infrared spectropolarimetric
observations were acquired simultaneously in two photospheric spectral lines,
Fe I 10783 \AA\ and Si I 10786 \AA, with the Tenerife Infrared Polarimeter at
the Vacuum Tower Telescope (VTT) in Tenerife on 2013 October 15. The
observations covered several stages of the M-class flare. Inversions of the
full-Stokes vector of both lines were carried out and the results were put into
context using (extreme)-ultraviolet filtergrams from the Solar Dynamics
Observatory (SDO).
Results: The active region showed high flaring activity during the whole
observing period. After the M-class flare, the longitudinal magnetic field did
not show significant changes along the polarity inversion line (PIL). However,
an enhancement of the transverse magnetic field of approximately 550 G was
found that bridges the PIL and connects umbrae of opposite polarities in the
-spot. At the same time, a newly formed system of loops appeared
co-spatially in the corona as seen in 171 \AA\ filtergrams of the Atmospheric
Imaging Assembly (AIA) on board SDO. However, we cannot exclude that the
magnetic connection between the umbrae already existed in the upper atmosphere
before the M-class flare and became visible only later when it was filled with
hot plasma. The photospheric Doppler velocities show a persistent upflow
pattern along the PIL without significant changes due to the flare.
Conclusions: The increase of the transverse component of the magnetic field
after the flare together with the newly formed loop system in the corona
support recent predictions of flare models and flare observations.Comment: 8 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysic
Study of the Regeneration Cleaning of Used Mineral Oils – Ecotoxicological Properties and Biodegradation
The aim of the study was to establish and compare the model of the biodegradability and ecotoxicological properties of oil samples in aqueous environment.The unused new mineral oil Turbinol and used (after 1 year of usage) recovered oil Turbinol purified by the electrostatical method were the tested samples. For the determination of the ecotoxicological properties, the test organisms used were seeds of Sinapis alba L. and the small aquatic crustaceans Daphnia magna. Preliminary tests were positive and determined the acute toxicity with the values of IC50 and EC50. Biodegradability was determined
by the manometric method, in tests which lasted 28 days. Tests of toxicity were positive, and the samples were found to be hard to biodegrade. Determination of the oil composition by gas chromatography with mass detection (GC – MS); found that the
composition of the electrostatically cleaned oil is comparable to the new oil, which is confirmed by the results obtained with the response inhibition in selected tests. Regeneration extends the oil life, reducing the cost of disposal of waste oils, saving fossil raw materials, thus belonging to the environmentally friendly techniques.
This work is licensed under a Creative Commons Attribution 4.0 International License
Global analysis of seasonality in the shell flux of extant planktonic foraminifera
Shell fluxes of planktonic Foraminifera species vary intra-annually in a
pattern that appears to follow the seasonal cycle. However, the variation in
the timing and prominence of seasonal flux maxima in space and among species
remains poorly constrained. Thus, although changing seasonality may result in
a flux-weighted temperature offset of more than 5° C within a
species, this effect is often ignored in the interpretation of
Foraminifera-based paleoceanographic records. To address this issue we present an analysis of
the intra-annual pattern of shell flux variability in 37 globally distributed
time series. The existence of a seasonal component in flux variability was
objectively characterised using periodic regression. This analysis yielded
estimates of the number, timing and prominence of seasonal flux maxima. Over
80% of the flux series across all species showed a statistically
significant periodic component, indicating that a considerable part of the
intra-annual flux variability is predictable. Temperature appears to be a
powerful predictor of flux seasonality, but its effect differs among species.
Three different modes of seasonality are distinguishable. Tropical and
subtropical species (Globigerinoides ruber (white and pink varieties),
Neogloboquadrina dutertrei, Globigerinoides sacculifer, Orbulina universa,
Globigerinella siphonifera, Pulleniatina obliquiloculata, Globorotalia menardii, Globoturborotalita rubescens, Globoturborotalita tenella and Globigerinoides conglobatus) appear to have a less predictable flux
pattern, with random peak timing in warm waters. In colder waters,
seasonality is more prevalent: peak fluxes occur shortly after summer
temperature maxima and peak prominence increases. This tendency is stronger
in species with a narrower temperature range, implying that warm-adapted
species find it increasingly difficult to reproduce outside their optimum
temperature range and that, with decreasing mean temperature, their flux is
progressively more focussed in the warm season. The second group includes the
temperate to cold-water species Globigerina bulloides,
Globigerinita glutinata, Turborotalita quinqueloba, Neogloboquadrina incompta, Neogloboquadrina pachyderma,
Globorotalia scitula, Globigerinella calida, Globigerina falconensis, Globorotalia theyeri
and Globigerinita uvula. These species show a highly predictable seasonal
pattern, with one to two peaks a year, which occur earlier in warmer waters.
Peak prominence in this group is independent of temperature. The
earlier-when-warmer pattern in this group is related to the timing of
productivity maxima. Finally, the deep-dwelling Globorotalia truncatulinoides
and Globorotalia inflata show a regular and pronounced peak in winter and
spring. The remarkably low flux outside the main pulse may indicate a long
reproductive cycle of these species. Overall, our analysis indicates that the
seasonality of planktonic Foraminifera shell flux is predictable and reveals
the existence of distinct modes of phenology among species. We evaluate the
effect of changing seasonality on paleoceanographic reconstructions and find
that, irrespective of the seasonality mode, the actual magnitude of
environmental change will be underestimated. The observed constraints on flux
seasonality can serve as the basis for predictive modelling of flux pattern.
As long as the diversity of species seasonality is accounted for in such
models, the results can be used to improve reconstructions of the magnitude
of environmental change in paleoceanographic records
Sensitivity to species selection indicates the effect of nuisance variables on marine microfossil transfer functions
The species composition of many groups of marine plankton appears well
predicted by sea surface temperature (SST). Consequently, fossil plankton
assemblages have been widely used to reconstruct past SST. Most applications
of this approach make use of the highest possible taxonomic resolution.
However, not all species are sensitive to temperature, and their distribution
may be governed by other parameters. There are thus reasons to question the
merit of including information about all species, both for transfer function
performance and for its effect on reconstructions.
Here we investigate the effect of species selection on planktonic
foraminifera transfer functions. We assess species importance for transfer
function models using a random forest technique and evaluate the performance
of models with an increasing number of species. Irrespective of using models
that use the entire training set (weighted averaging) or models that use
only a subset of the training set (modern analogue technique), we find that
the majority of foraminifera species does not carry useful information for
temperature reconstruction. Less than one-third of the species in the
training set is required to provide a temperature estimate with a prediction
error comparable to a transfer function that uses all species in the
training set. However, species selection matters for paleotemperature
estimates. We find that transfer function models with a different number of
species but with the same error may yield different reconstructions of sea
surface temperature when applied to the same fossil assemblages. This
ambiguity in the reconstructions implies that fossil assemblage change
reflects a combination of temperature and other environmental factors. The
contribution of the additional factors is site and time specific, indicating
ecological and geological complexity in the formation of the sedimentary
assemblages. The possibility of obtaining multiple different reconstructions
from a single sediment record presents a previously unrecognized source of
uncertainty for sea surface temperature estimates based on planktonic
foraminifera assemblages. This uncertainty can be evaluated by determining
the sensitivity of the reconstructions to species pruning.</p
Noise of the Air-to-Water Heat Pump Compressor
Článek se zaměřuje na hluk a vibrace šířené od nejčastěji instalovaného typu tepelných čerpadel vzduch-
-voda do okolí a do stavebních konstrukcí. Z funkčního hlediska je téma omezeno na tepelná čerpadla
s elektricky poháněnými a hermeticky uzavřenými scroll kompresory, protože se jedná o nejčastěji instalovaný
typ tepelných čerpadel menších výkonů (do 50 kW). Příspěvek pokrývá jak téma ON/OFF regulace, tak
i problematiku invertorových tepelných čerpadel. Řešena jsou pouze tepelná čerpadla instalovaná v exteriéru
rodinných nebo bytových domů. Vzhledem k rozsahu bude téma tu věnováno několik samosta tných článků.The article focuses on the noise and vibration propagated from air-to-water heat pump, the most commonly
installed type of heat pumps, to its surroundings and to the building structures. From a technical point of
view, the topic is limited to heat pumps with electrically driven and hermetically sealed scroll compressors,
as these are the most commonly installed type of heat pumps of smaller capacities (up to 50 kW).
The paper covers the issue of ON/OFF control as well as the issue of inverter heat pumps. Only the heat
pumps installed in the exterior of houses or apartment buildings are addressed. Several separate articles
will be devoted to the topic due to its wide scope.
Keywords: heat pump, scroll compressor, axial fan, heating
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