98 research outputs found
Detecting Malicious Code by Model Checking
Abstract. The ease of compiling malicious code from source code in higher programming languages has increased the volatility of malicious programs: The first appearance of a new worm in the wild is usually followed by modified versions in quick succession. As demonstrated by Christodorescu and Jha, however, classical detection software relies on static patterns, and is easily outsmarted. In this paper, we present a flexible method to detect malicious code patterns in executables by model checking. While model checking was originally developed to verify the correctness of systems against specifications, we argue that it lends itself equally well to the specification of malicious code patterns. To this end, we introduce the specification language CTPL (Computation Tree Predicate Logic) which extends the well-known logic CTL, and describe an efficient model checking algorithm. Our practical experiments demonstrate that we are able to detect a large number of worm variants with a single specification. Key words: Model Checking, Malware Detection.
Effects of total solar eclipse of 29 March 2006 on surface radiation
International audienceSolar irradiance spectral measurements were performed during a total solar eclipse. The spectral effect of the limb darkening to the global, direct irradiance and actinic flux measurements was investigated. This effect leads to wavelength dependent changes in the measured solar spectra showing a much more pronounced decrease in the radiation at the lower wavelengths. Radiative transfer model results were used for the computation of a correction for the total ozone measurements due to the limb darkening. This correction was found too small to explain the large decrease in total ozone column derived from the standard Brewer measurements, which is an artifact in the measured irradiance due to the increasing contribution of diffuse radiation against the decreasing direct irradiance caused by the eclipse. Calculations of the Extraterrestrial spectrum and the effective sun's temperatures, as measured from ground based direct irradiance measurements, showed an artificial change in the calculations of both quantities due to the fact that radiation coming from the visible part of the sun during the eclipse phases differs from the back body radiation described by the Planck's law
Chemical transformations in monoterpene-derived organic aerosol enhanced by inorganic composition
Secondary organic aerosol (SOA) is known to impact both climate and air quality, yet molecular-level composition measurements remain challenging, hampering our understanding of SOA formation and evolution. Here, we reveal the importance of underestimated reaction pathways for the (trans) formation of SOA from monoterpenes, one of the largest SOA precursors globally. Utilizing mass spectrometric techniques to achieve a comprehensive characterization of molecular-level changes in the SOA, we were able to link the appearance of high-molecular weight (HMW) organic molecules to the concentration and level of neutralization of particulate sulfate. Interestingly, this oligomerization coincided with a decrease of highly oxygenated molecules (HOMs). Our findings highlight the role of particle-phase processing, and the underestimated importance of sulfate aerosol for monoterpene-SOA formation. The observations of these processes directly in the atmosphere reveal the need to account for the formation of HMW oligomers to fully understand the physicochemical properties of organic aerosol.Peer reviewe
Spectral actinic flux in the lower troposphere: measurement and 1-D simulations for cloudless, broken cloud and overcast situations
In September 2002, the first INSPECTRO campaign to study the influence of clouds on the spectral actinic flux in the lower troposphere was carried out in East Anglia, England. Measurements of the actinic flux, the irradiance and aerosol and cloud properties were made from four ground stations and by aircraft. The radiation measurements were modelled using the uvspec model and ancillary data. For cloudless conditions, the measurements of the actinic flux were reproduced by 1-D radiative transfer modelling within the measurement and model uncertainties of about ±10%. For overcast days, the ground-based and aircraft radiation measurements and the cloud microphysical property measurements are consistent within the framework of 1-D radiative transfer and within experimental uncertainties. Furthermore, the actinic flux is increased by between 60-100% above the cloud when compared to a cloudless sky, with the largest increase for the optically thickest cloud. Correspondingly, the below cloud actinic flux is decreased by about 55-65%. Just below the cloud top, the downwelling actinic flux has a maximum that is seen in both the measurements and the model results. For broken clouds the traditional cloud fraction approximation is not able to simultaneously reproduce the measured above-cloud enhancement and below-cloud reduction in the actinic flux
Spectral actinic flux in the lower troposphere: measurement and 1-D simulations for cloudless, broken cloud and overcast situations
In September 2002, the first INSPECTRO campaign to study the influence of clouds on the spectral actinic flux in the lower troposphere was carried out in East Anglia, England. Measurements of the actinic flux, the irradiance and aerosol and cloud properties were made from four ground stations and by aircraft. The radiation measurements were modelled using the uvspec model and ancillary data. For cloudless conditions, the measurements of the actinic flux were reproduced by 1-D radiative transfer modelling within the measurement and model uncertainties of about ±10%. For overcast days, the ground-based and aircraft radiation measurements and the cloud microphysical property measurements are consistent within the framework of 1-D radiative transfer and within experimental uncertainties. Furthermore, the actinic flux is increased by between 60-100% above the cloud when compared to a cloudless sky, with the largest increase for the optically thickest cloud. Correspondingly, the below cloud actinic flux is decreased by about 55-65%. Just below the cloud top, the downwelling actinic flux has a maximum that is seen in both the measurements and the model results. For broken clouds the traditional cloud fraction approximation is not able to simultaneously reproduce the measured above-cloud enhancement and below-cloud reduction in the actinic flux
Trimethylamine emissions in animal husbandry
Degradation of plant material by animals is an important transformation pathway in the nitrogen (N) cycle. During the involved processes, volatile reduced alkaline nitrogen compounds, mainly ammonia (NH3) and aliphatic amines such as trimethylamine (TMA), are formed. Today, animal husbandry is estimated to constitute a main source of aliphatic amines in the atmosphere with TMA being the main emitted compound. Here, we show how the interaction between faeces and urine in animal production systems provides the primary source for agricultural TMA emissions. Excreted urine contains large quantities of urea and TMA-N-oxide, which are transformed into NH3 and TMA, respectively, via enzymatic processes provided by microbes present in faeces. TMA emissions from areas polluted with urine-faeces mixtures are on average of the order of 10 to 50 nmol m(-2) s(-1). Released amines promote secondary aerosol particle formation in the agricultural emission plume. The atmospheric lifetime of TMA, which was estimated to be of the order of 30 to 1000 s, is determined by the condensation onto aerosol particles.Peer reviewe
A two-parameter wind speed algorithm for Ku-band altimeters
Globally distributed crossovers of altimeter and scatterometer observations clearly demonstrate that ocean altimeter backscatter correlates with both the near-surface wind speed and the sea state. Satellite data from TOPEX/Poseidon and NSCAT are used to develop an empirical altimeter wind speed model that attenuates the sea-state signature and improves upon the present operational altimeter wind model. The inversion is defined using a multilayer perceptron neural network with altimeter-derived backscatter and significant wave height as inputs. Comparisons between this new model and past single input routines indicates that the rms wind error is reduced by 10%â15% in tandem with the lowering of wind error residuals dependent on the sea state. Both model intercomparison and validation of the new routine are detailed, including the use of large independent data compilations that include the SeaWinds and ERS scatterometers, ECMWF wind fields, and buoy measurements. The model provides consistent improvement against these varied sources with a wind-independent bias below 0.3 m s?1. The continuous form of the defined function, along with the global data used in its derivation, suggest an algorithm suitable for operational application to Ku-band altimeters. Further model improvement through wave height inclusion is limited due to an inherent multivaluedness between any single realization of the altimeter measurement pair [?o, HS] and observed near-surface winds. This ambiguity indicates that HS is a limited proxy for variable gravity wave properties that impact upon altimeter backscatter
High emission rates and strong temperature response make boreal wetlands a large source of isoprene and terpenes
Wetlands cover only 3â% of the global land surface
area, but boreal wetlands are experiencing an unprecedented warming of four
times the global average. These wetlands emit isoprene and terpenes
(including monoterpenes (MT), sesquiterpenes (SQT), and diterpenes (DT)),
which are climate-relevant highly reactive biogenic volatile organic
compounds (BVOCs) with an exponential dependence on temperature. In this
study, we present ecosystem-scale eddy covariance (EC) fluxes of isoprene,
MT, SQT, and DT (hereafter referred to together as terpenes) at Siikaneva, a
boreal fen in southern Finland, from the start to the peak of the growing
season of 2021 (19 May 2021 to 28 June 2021). These are the first EC fluxes
reported using the novel state-of-the-art Vocus proton transfer reaction
mass spectrometer (Vocus-PTR) and the first-ever fluxes reported for DTs
from a wetland. Isoprene was the dominant compound emitted by the wetland,
followed by MTs, SQTs, and DTs, and they all exhibited a strong exponential
temperature dependence. The Q10 values, the factor by which terpene
emissions increases for every 10ââC rise in temperature, were up
to five times higher than those used in most BVOC models. During the campaign,
the air temperature peaked above 31ââC on 21â22 June 2021, which
is abnormally high for boreal environments, and the maximum flux for all
terpenes coincided with this period. We observed that terpene emissions were
elevated after this abnormally âhigh-temperature stress periodâ,
indicating that past temperatures alter emissions significantly. The
standardized emission factor (EF) of the fen for isoprene (EFiso) was
11.1â±â 0.3ânmolâmâ2âsâ1, which is at least two times
higher than in previous studies and as high as the emission factors typical
for broadleaf and other forests in the lower latitudes. We observed
EFMT of 2.4â±â 0.1ânmolâmâ2âsâ1, EFSQT of 1.3â±â0.03ânmolâmâ2âsâ1, higher than typical for needle leaf
and broadleaf tree functional types, and EFDT of 0.011â±â0.001ânmolâmâ2âsâ1. We also compared the landscape average emissions
to the model of emissions of gases and aerosols from nature (MEGAN) v2.1
and found that the emissions were underestimated by over 9 times for
isoprene, over 300 times for MTs, and 800 times for SQTs. Our results show
that due to very high EFs and high sensitivity to increasing temperatures,
these high-latitude ecosystems can be a large source of terpenes to the
atmosphere, and anthropogenic global warming could induce much higher BVOC
emissions from wetlands in the future.</p
Intercomparison of solar UV direct irradiance spectral measurements at Izana in June 2005
Spectral measurements of direct solar ultraviolet irradiance are very important for many applications in the field of
atmospheric sciences. Despite its usefulness, few UV monitoring sites include such measurements in their regular
observational programs. Standardization of measurement methodologies and calibration techniques is required in order
to reach the quality standard of global irradiance measurements.
This study presents preliminary results from an intercomparison campaign of seven UV spectroradiometers of different
types that took place at the high altitude site of Izana (28.3°N, 16.5°W, 2367 m above sea level), in Tenerife, Canary
Islands in June 2005
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