231 research outputs found
Spectrophotometric high-precision seawater pH determination for use in underway measuring systems
Autonomous sensors are required for a comprehensive documentation of the changes in the marine carbon system and thus to differentiate between its natural variability and anthropogenic impacts. Spectrophotometric determination of pH – a key variable of the seawater carbon system – is particularly suited to achieve precise and drift-free measurements. However, available spectrophotometric instruments are not suitable for integration into automated measurement systems (e.g. FerryBox) since they do not meet the major requirements of reliability, stability, robustness and moderate cost. Here we report on the development and testing of a~new indicator-based pH sensor that meets all of these requirements. This sensor can withstand the rough conditions during long-term deployments on ships of opportunity and is applicable to the open ocean as well as to coastal waters with a complex matrix and highly variable conditions. The sensor uses a high resolution CCD spectrometer as detector connected via optical fibers to a custom-made cuvette designed to reduce the impact of air bubbles. The sample temperature can be precisely adjusted (25 °C ± 0.006 °C) using computer-controlled power supplies and Peltier elements thus avoiding the widely used water bath. The overall setup achieves a measurement frequency of 1 min−1 with a precision of ±0.0007 pH units, an average offset of +0.0005 pH units to a reference system, and an offset of +0.0081 pH units to a certified standard buffer. Application of this sensor allows monitoring of seawater pH in autonomous underway systems, providing a key variable for characterization and understanding of the marine carbon system
Deciding Robust Feasibility and Infeasibility Using a Set Containment Approach: An Application to Stationary Passive Gas Network Operations
In this paper we study feasibility and infeasibility of nonlinear two-stage
fully adjustable robust feasibility problems with an empty first stage. This is
equivalent to deciding whether the uncertainty set is contained within the
projection of the feasible region onto the uncertainty-space. Moreover, the
considered sets are assumed to be described by polynomials. For answering this
question, two very general approaches using methods from polynomial
optimization are presented - one for showing feasibility and one for showing
infeasibility. The developed methods are approximated through sum of squares
polynomials and solved using semidefinite programs. Deciding robust feasibility
and infeasibility is important for gas network operations, which is a nonconvex
feasibility problem where the feasible set is described by a composition of
polynomials with the absolute value function. Concerning the gas network
problem, different topologies are considered. It is shown that a tree
structured network can be decided exactly using linear programming.
Furthermore, a method is presented to reduce a tree network with one additional
arc to a single cycle network. In this case, the problem can be decided by
eliminating the absolute value functions and solving the resulting linearly
many polynomial optimization problems. Lastly, the effectivity of the methods
is tested on a variety of small cyclic networks. It turns out that for
instances where robust feasibility or infeasibility can be decided
successfully, level 2 or level 3 of the Lasserre relaxation hierarchy typically
is sufficient
Microservice Transition and its Granularity Problem: A Systematic Mapping Study
Microservices have gained wide recognition and acceptance in software
industries as an emerging architectural style for autonomic, scalable, and more
reliable computing. The transition to microservices has been highly motivated
by the need for better alignment of technical design decisions with improving
value potentials of architectures. Despite microservices' popularity, research
still lacks disciplined understanding of transition and consensus on the
principles and activities underlying "micro-ing" architectures. In this paper,
we report on a systematic mapping study that consolidates various views,
approaches and activities that commonly assist in the transition to
microservices. The study aims to provide a better understanding of the
transition; it also contributes a working definition of the transition and
technical activities underlying it. We term the transition and technical
activities leading to microservice architectures as microservitization. We then
shed light on a fundamental problem of microservitization: microservice
granularity and reasoning about its adaptation as first-class entities. This
study reviews state-of-the-art and -practice related to reasoning about
microservice granularity; it reviews modelling approaches, aspects considered,
guidelines and processes used to reason about microservice granularity. This
study identifies opportunities for future research and development related to
reasoning about microservice granularity.Comment: 36 pages including references, 6 figures, and 3 table
Tracking dark excitons with exciton polaritons in semiconductor microcavities
Dark excitons are of fundamental importance for a wide variety of processes in semiconductors but are difficult to investigate using optical techniques due to their weak interaction with light fields. We reveal and characterize dark excitons nonresonantly injected into a semiconductor microcavity structure containing InGaAs/GaAs quantum wells by a gated train of eight 100 fs pulses separated by 13 ns by monitoring their interactions with the bright lower polariton mode. We find a surprisingly long dark exciton lifetime of more than 20 ns, which is longer than the time delay between two consecutive pulses. This creates a memory effect that we clearly observe through the variation of the time-resolved transmission signal. We propose a rate equation model that provides a quantitative agreement with the experimental data.PostprintPeer reviewe
Theoretical study of peculiarities of unstable longitudinal shear crack growth in sub-Rayleigh and supershear regimes
In the paper we present the results of the theoretical study of some fundamental aspects of mode II crack propagation in conventional sub-Rayleigh regime and transition to intersonic regime. It is shown that development of a sub-Rayleigh shear crack is determined in many respects by elastic vortex traveling ahead of the crack tip at a shear wave velocity. Formation of such a vortex helps to better understand the well-known phenomenon of acceleration of a shear crack towards the longitudinal wave velocity. Simulation results have shown that due to self-similarity of shear crack propagation the conditions of sub-Rayleigh to intersonic transition depend on dimensionless material and crack parameters. Two key dimensionless parameters are proposed
SARS-CoV-2 Wastewater Genomic Surveillance: Approaches, Challenges, and Opportunities
During the SARS-CoV-2 pandemic, wastewater-based genomic surveillance (WWGS)
emerged as an efficient viral surveillance tool that takes into account
asymptomatic cases and can identify known and novel mutations and offers the
opportunity to assign known virus lineages based on the detected mutations
profiles. WWGS can also hint towards novel or cryptic lineages, but it is
difficult to clearly identify and define novel lineages from wastewater (WW)
alone. While WWGS has significant advantages in monitoring SARS-CoV-2 viral
spread, technical challenges remain, including poor sequencing coverage and
quality due to viral RNA degradation. As a result, the viral RNAs in wastewater
have low concentrations and are often fragmented, making sequencing difficult.
WWGS analysis requires advanced computational tools that are yet to be
developed and benchmarked. The existing bioinformatics tools used to analyze
wastewater sequencing data are often based on previously developed methods for
quantifying the expression of transcripts or viral diversity. Those methods
were not developed for wastewater sequencing data specifically, and are not
optimized to address unique challenges associated with wastewater. While
specialized tools for analysis of wastewater sequencing data have also been
developed recently, it remains to be seen how they will perform given the
ongoing evolution of SARS-CoV-2 and the decline in testing and patient-based
genomic surveillance. Here, we discuss opportunities and challenges associated
with WWGS, including sample preparation, sequencing technology, and
bioinformatics methods.Comment: V Munteanu and M Saldana contributed equally to this work A Smith and
S Mangul jointly supervised this work For correspondence:
[email protected]
Extreme variations of pCO2 and pH in a macrophyte meadow of the Baltic Sea in summer: evidence of the effect of photosynthesis and local upwelling
The impact of ocean acidification on benthic habitats is a major preoccupation of the scientific community. However, the natural variability of pCO2 and pH in those habitats remains understudied, especially in temperate areas. In this study we investigated temporal variations of the carbonate system in nearshore macrophyte meadows of the western Baltic Sea. These are key benthic ecosystems, providing spawning and nursery areas as well as food to numerous commercially important species. In situ pCO2, pH (total scale), salinity and PAR irradiance were measured with a continuous recording sensor package dropped in a shallow macrophyte meadow (Eckernförde bay, western Baltic Sea) during three different weeks in July (pCO2 and PAR only), August and September 2011.The mean (± SD) pCO2 in July was 383±117 µatm. The mean (± SD) pCO2 and pHtot in August were 239±20 µatm and 8.22±0.1, respectively. The mean (± SD) pCO2 and pHtot in September were 1082±711 µatm and 7.83±0.40, respectively. Daily variations of pCO2 due to photosynthesis and respiration (difference between daily maximum and minimum) were of the same order of magnitude: 281±88 µatm, 219±89 μatm and 1488±574 µatm in July, August and September respectively. The observed variations of pCO2 were explained through a statistical model considering wind direction and speed together with PAR irradiance. At a time scale of days to weeks, local upwelling of elevated pCO2 water masses with offshore winds drives the variation. Within days, primary production is responsible. The results demonstrate the high variability of the carbonate system in nearshore macrophyte meadows depending on meteorology and biological activities. We highlight the need to incorporate these variations in future pCO2 scenarios and experimental designs for nearshore habitats
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