392 research outputs found
Formal Specifications and Analysis of the Computer Assisted Resuscitation Algorithm (CARA) Infusion Pump Control System
Reliability of medical devices such as the CARA Infusion Pump Control System is of extreme importance given that these devices are being used on patients in critical condition. The Infusion Pump Control System includes embedded processors and accompanying embedded software for monitoring as well as controlling sensors and actuators that allow the embedded systems to interact with their environments. This nature of the Infusion Pump Control System adds to the complexity of assuring the reliability of the total system. The traditional methods of developing embedded systems are inadequate for such safety-critical devices. In this paper, we study the application of formal methods to the requirements capture and analysis for the Infusion Pump Control System. Our approach consists of two phases. The first phase is to convert the informal design requirements into a set of reference specifications using a formal system, in this case EFSMs (Extended Finite State Machines). The second phase is to translate the reference specifications to the tools supporting formal analysis, such as SCR and Hermes. This allows us to conclude properties of the reference specifications. Our research goal is to develop a framework and methodology for the integrated use of formal methods in the development of embedded medical systems that require high assurance and confidence
Sensitive Probing of Exoplanetary Oxygen via Mid Infrared Collisional Absorption
The collision-induced fundamental vibration-rotation band at 6.4 um is the
most significant absorption feature from O2 in the infrared (Timofeyev and
Tonkov, 1978; Rinslandet al., 1982, 1989), yet it has not been previously
incorporated into exoplanet spectral analyses for several reasons. Either CIAs
were not included or incomplete/obsolete CIA databases were used. Also, the
current version of HITRAN does not include CIAs at 6.4 um with other collision
partners (O2-X). We include O2-X CIA features in our transmission spectroscopy
simulations by parameterizing the 6.4 um O2-N2 CIA based on Rinsland et
al.(1989) and the O2-CO2 CIA based on Baranov et al. (2004). Here we report
that the O2-X CIA may be the most detectable O2 feature for transit
observations. For a potentialTRAPPIST-1e analogue system within 5 pc of the
Sun, it could be the only O2 detectable signature with JWST (using MIRI LRS)
for a modern Earth-like cloudy atmosphere with biological quantities of O2.
Also, we show that the 6.4 um O2-X CIA would be prominent for O2-rich
desiccated atmospheres (Luger and Barnes, 2015) and could be detectable with
JWST in just a few transits. For systems beyond 5 pc, this feature could
therefore be a powerful discriminator of uninhabited planets with
non-biological "false positive" O2 in their atmospheres - as they would only be
detectable at those higher O2 pressures.Comment: Published in Nature Astronom
Habitable Moist Atmospheres on Terrestrial Planets near the Inner Edge of the Habitable Zone around M Dwarfs
Terrestrial planets in the habitable zones (HZs) of low-mass stars and cool
dwarfs have received significant scrutiny recently because their shorter
orbital periods increase their chances of detection and characterization
compared to planets around G-dwarfs. As these planets are likely tidal-locked,
improved 3D numerical simulations of such planetary atmospheres are needed to
guide target selection. Here we use a 3-D climate system model, updated with
new water-vapor absorption coefficients derived from the HITRAN 2012 database,
to study ocean covered planets at the inner edge of the HZ around late-M to
mid-K stars ( K <= Teff <= 4500K). Our results indicate that these
updated water-vapor coefficients result in significant warming compared to
previous studies, so the inner HZ around M-dwarfs is not as close as suggested
by earlier work. Assuming synchronously rotating planets with background 1 bar
N2 atmospheres, we find that planets at the inner HZ of stars with Teff > 3000K
undergo the classical "moist-greenhouse" (H2O mixing ratio > 10-3 in the
stratosphere) at significantly lower surface temperature (~ 280K) in our 3-D
model compared with 1-D climate models (~ 340K). This implies that some planets
around low mass stars can simultaneously undergo water-loss and remain
habitable. However, for star with Teff <= 3000K, planets at the inner HZ may
directly transition to a runaway state, while bypassing the moist greenhouse
water-loss entirely. We analyze transmission spectra of planets in a moist
green-house regime, and find that there are several prominent H2O features
within JWST instruments range. Thus, relying only upon standard Earth-analog
spectra with 24-hour rotation period around M-dwarfs for habitability studies
will miss the strong H2O features that one would expect to see on synchronously
rotating planets around M-dwarf stars, with JWST.Comment: Accepted to Astrophysical Journa
Designing sequential transcription logic: a simple genetic circuit for conditional memory
The ability to learn and respond to recurrent events depends on the capacity
to remember transient biological signals received in the past. Moreover, it may
be desirable to remember or ignore these transient signals conditioned upon
other signals that are active at specific points in time or in unique
environments. Here, we propose a simple genetic circuit in bacteria that is
capable of conditionally memorizing a signal in the form of a transcription
factor concentration. The circuit behaves similarly to a "data latch" in an
electronic circuit, i.e. it reads and stores an input signal only when
conditioned to do so by a "read command". Our circuit is of the same size as
the well-known genetic toggle switch (an unconditional latch) which consists of
two mutually repressing genes, but is complemented with a "regulatory front
end" involving protein heterodimerization as a simple way to implement
conditional control. Deterministic and stochastic analysis of the circuit
dynamics indicate that an experimental implementation is feasible based on
well-characterized genes and proteins. It is not known, to which extent
molecular networks are able to conditionally store information in natural
contexts for bacteria. However, our results suggest that such sequential logic
elements may be readily implemented by cells through the combination of
existing protein-protein interactions and simple transcriptional regulation.Comment: 20 pages, 5 figures; supplementary material available upon request
from the author
Introducing the “analogs for Venus’ geologically recent surfaces” initiative: an opportunity for identifying and analyzing recently active volcano-tectonic areas of Venus trough a comparative study with terrestrial analogs
Several missions to Venus have been recently selected for launch [1–6], opening a new era for the exploration of the planet. One of the key questions that the future missions need to address is whether Venus is presently volcanically active [7–15]. Studying areas of active volcanism and tectonism on Venus is crucial to reveal clues about the geologic past of the planet, as well as provide information about the volatile content of its interior and the formation of its dense atmosphere. The “Analogsfor VENus’ GEologically Recent Surfaces” (AVENGERS) initiative aims to build a comprehensive database of terrestrial analog sites for the comparative study of recent and possibly on- going volcanic activity on Venus. Besides its scientific relevance, the AVENG- ERS initiative also acts as a bridge for international scientific collaboration, including the leadership and/or team members from the currently selected missions to Venus
- …