76 research outputs found
On Some Multi-Site Multi-Season Streamflow Generation Models
The relative performance of some multi-site multi-season models is compared with respect to their adequacy for simulating monthly streamflow sequences. The three models brought under examination are the extended version of the multi-variate model proposed by Matalas (1967), the model formulated by Young and Pisano (1968), and the disaggregation model of Valencia and Schaake (1972). Computer implementation of these models has been accomplished in the form of the Multi-site Multi-season Streamflow Generation Package (MMSGP). Evaluation and comparison of the models has been carried out in terms of statistical flow parameters only. Some of these parameters are not explicitly built into the model structure. At the end, some general comments concerning applicability of each model are presented.
[Since this phase of investigations was completed, Mejia and Roussele (1976) have proposed modification of the disaggregation model which will be taken into account in the further work on the MMSGP.
Interval identification of FMR parameters for spin reorientation transition in (Ga,Mn)As
In this work we report results of ferromagnetic resonance studies of a 6% 15
nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were
performed with in-plane oriented magnetic field, in the temperature range
between 5K and 120K. We observe a temperature induced reorientation of the
effective in-plane easy axis from [-110] to [110] direction close to the Curie
temperature. The behavior of magnetization is described by anisotropy fields,
H_{eff} (= 4\piM -H_{2\perp}), H_{2\parallel}, and H_{4\parallel}. In order to
precisely investigate this reorientation, numerical values of anisotropy fields
have been determined using powerful - but still largely unknown - interval
calculations. In simulation mode this approach makes possible to find all the
resonance fields for arbitrarily oriented sample, which is generally
intractable analytically. In 'fitting' mode we effectively utilize full
experimental information, not only those measurements performed in special,
distinguished directions, to reliably estimate the values of important physical
parameters as well as their uncertainties and correlations.Comment: 3 pages, 3 figures. Presented at The European Conference "Physics of
Magnetism 2011" (PM'11), June 27 - July 1, 2011, Poznan, Polan
Case Studies of Seismic Energy Release Ahead of Underground Coal Mining Before Strong Tremors
We would like to test the concept that induced
seismicity prior to relatively large mining tremor (ML[2.5,
E[106J) can be inferred from the cumulative Benioff strain
release (BSR) as power law time-to-failure before the strong event.
This study presents the application of accelerating BSR prior to a
large earthquake, widely used in natural seismicity, for analysis of
this phenomenon in induced seismicity. The Benioff strain release
is quantified as accelerated releases of cumulative (square root
sum) of seismic energy in the time series. During the study, five
sequences were extracted from the seismic catalogues from two
Polish hard coal mines: exhausted Bobrek Mine (data form the ISEPOS
Platform) and from a mine belonging to the Polish Mining
Group. Next, a search radius was used to select precursory events
and to indicate the type of processes occurring in the coal seam and
its vicinity. The fitted power law of cumulative Benioff strain
release showed changes of m-parameter. If the value of m was
lower than 1.0, the process was regarded as an accelerating-like and
if m was higher than 1.0—as a quiescence-like. The investigation
of m-parameter vs. the search radius showed the general behaviour
of the rock mass in the studied areas and allowed to evaluate the
relationship between the critical radius and magnitude of the target
event. The obtained scaling relation log(Rc) * 0.35 ML is similar
to these reported by other authors who analysed natural seismicity
which might suggest that the scaling relation works in a wide range
of magnitudes
Determination of Destress Blasting Effectiveness Using Seismic Source Parameters
Underground mining of coal seams in the Upper
Silesian Coal Basin is currently performed under difficult
geological and mining conditions. The mining depth, dislocations
(faults and folds) and mining remnants are
responsible for rockburst hazard in the highest degree. This
hazard can be minimized by using active rockburst prevention,
where destress blastings play an important role.
Destress blastings in coal seams aim to destress the local
stress concentrations. These blastings are usually performed
from the longwall face to decrease the stress level
ahead of the longwall. An accurate estimation of active
rockburst prevention effectiveness is important during
mining under disadvantageous geological and mining
conditions, which affect the risk of rockburst. Seismic
source parameters characterize the focus of tremor, which
may be useful in estimating the destress blasting effects.
Investigated destress blastings were performed in coal
seam no. 507 during its longwall mining in one of the coal
mines in the Upper Silesian Coal Basin under difficult
geological and mining conditions. The seismic source
parameters of the provoked tremors were calculated. The
presented preliminary investigations enable a rapid estimation
of the destress blasting effectiveness using seismic
source parameters, but further analysis in other geological
and mining conditions with other blasting parameters is
required
Application of seismic parameters for estimation of destress blasting effectiveness
Coal seams in the Upper Silesian Coal Basin are currently extracted under more and more disadvantageous geological and mining conditions. Mining depth, geological dislocations and mining remnants are factors which affect the rockburst hazard during underground mining to the greatest extent. This hazard can be minimized by employment of active rockburst prevention, where long-hole destress blasts in roof rocks (torpedo blasts) have an important role. The main goal of these blastings is to either destress local stress concentrations in rock mass and to fracture the thick layers of strong roof rocks to prevent or minimize the impact of high energy tremors on the excavations. Sometimes, these blastings are performed to make the roof rocks caving behind the longwall face easier. The efficiency of blasting is typically evaluated from the seismic effect, which is calculated based on seismic monitoring data (seismic energy) and the weight of the charged explosive. This method, as used previously in the Czech Republic, was adopted in a selected Polish hard coal mine in the Upper Silesian Coal Basin. This method enables rapid and easy estimation of destress blasting effectiveness, adjusted to conditions occurring in the designed colliery. Destress blasts effectiveness may be evaluated via the seismic source parameters analysis as well, as was carried out in the selected colliery in the Polish part of the Upper Silesian Coal Basin. These parameters provide information, for example, on its size, state of stress and occurrence of slip mechanism in the source of provoked tremors. Long-hole destress blasting effectiveness in selected colliery has been evaluated using the seismic effect method and seismic source parameters analysis. The results were compared with each other and conditions were observed in situ
An inversion of rayleigh waves dispersion curves as a tool to recognize the bedrock depth in Chorzów Stary, Poland
Identification of a bedrock beneath soft cover is one of the most important task in engineering geology. The
location of boundary-overburden information may be used by investors, builders and municipal authorities to design an infrastructure or land-use plans. In such issues the application of appropriate geophysical methods is useful. However, in urban zones and areas characterized by subsurface soft layer the usage of certain methods (eg.: seismic refraction) is not advisable. The passive method of Refraction Microtremor (ReMi) can fulfill its tasks in the relatively difficult urban environment. The vertical S-wave velocity profiles were carried out as a result of inversion of Rayleigh wave dispersion curves obtained from ReMi method. The change of S-wave velocities allowed to distinguish shallow geological layers in the area of Chorzów Stary. Preliminary measurements allowed to identify the Carboniferous bedrock at a depth of 14 -18 m what
has been confirmed by resistivity imaging. Furthermore, unconsolidated deposits are also recognized and the seismic results show a good correlation with the available geological information and resistivity imaging data
Wyznaczenie parametrów sprężystych płytkiego ośrodka geologicznego nad wykształcającą się niecką obniżeniową
Seismic and geodetic studies were carried out before, during, and after underground exploitation of
a coal bed in Katowice – Kleofas Coal Mine, located in the Upper Silesia Coal Basin, Poland. Development
of a subsidence trough was completed approximately 3 months after passage of a longwall exploitation
in the coal seam. This was the time required for the subsidence trough to appear on the surface, which
was confirmed by levelling measurements. Sharp changes in the elastic parameters were observed on
each profile during subsidence trough development. This observation can result from changing tension
and compression forces caused by increase and/or decrease of the elastic parameters of the rock mass.
After completion of subsidence trough development, the rock mass appeared to return to its isotropic state
and the observed changes ceased. Some minor fluctuations were noted, but they probably resulted from
changes in groundwater levels, which might have affected the measured parameters
Geophysical Evaluation of Effectiveness of Blasting for Roof Caving During Longwall Mining of Coal Seam
Deep longwall mining of coal seams is made in the
Upper Silesian Coal Basin (USCB) under complicated and mostly
unfavourable geological and mining conditions. Usually, it is correlated
with rockburst hazard mostly at a high level. One of the
geological factors affecting the state of rockburst hazard is the
presence of competent rocks in the roof of extracted coal seams, so
rock falling behind the longwall face does not occur, and hangingup
of roof rocks remains. The long-lasting absence of caving may
lead to an occurrence of high-energy tremor in the vicinity of the
longwall face. Roof caving behind the longwall face may be forced
by blasting. The column of explosives is then located in blastholes
drilled in layers of roof rocks, e.g. sandstones behind the longwall
face. In this article, a characterization of tremors initiated by blasts
for roof caving during underground extraction of coal seam no. 507
in one of the collieries in the USCB has been made using three
independent methods. By the basic seismic effect method, the
effectiveness of blasting is evaluated according to the seismic
energy of incited tremors and mass of explosives used. According
to this method, selected blasts gave extremely good or excellent
effect. An inversion of the seismic moment tensor enables determining
the processes happening in the source of tremors. In the foci
of provoked tremors the slip mechanism dominated or was clearly
distinguished. The expected explosion had lesser significance or
was not present. By the seismic source parameters analysis, among
other things, an estimation of the stress drop in the focus or its size
may be determined. The stress drop in the foci of provoked tremors
was in the order of 105 Pa and the source radius, according to the
Brune’s model, varied from 44.3 to 64.5 m. The results of the three
mentioned methods were compared with each other and observations
in situ. In all cases the roof falling was forced
Spatiotemporal analysis of elastic and inelastic deformations in roof-rocks from seismological observations
The spatiotemporal analysis of seismic zones characterised by the scattering and accumulation of strain energy in the roof-rocks of the excavated longwall panel where inelastic or elastic deformations occurred during hard coal seam mining is discussed. The studied longwall panel was designed to utilize the effect of partial stress relaxation caused by the earlier extraction of the coal seams located above. A full seismic moment tensor and spectral source parameter analyses were used to obtain information about the degree of inelastic and elastic coseismic deformations. This study also showed that these deformation changes correspond to variation in the Benioff strain release characteristics. Next, analyses of deformation zones were compared with the relationship between radiated energy and the excavated volume of rocks per month. The concept of balanced seismic energy release assumed the exponential increase of released seismic energy with the increase in the volume of excavated rock. Discrepancies between the observed and predicted radiated energies indicated that strain energy in selected zones in the rock mass was either scattered if the prediction was overestimated, or accumulated if underestimated. Moreover, the study showed that elastic deformation in one zone can lead to inelastic deformation in the same zone
Performance Analysis of Dataflow Architectures Using Timed Coloured Petri Nets
We present an approach to model dataflow architectures at a high level of abstraction using timed coloured Petri nets. We specifically examine the value of Petri nets for evaluating the performance of such architectures. For this purpose we assess the value of Petri nets both as a modelling technique for dataflow architectures and as an analysis tool
that yields valuable performance data for such architectures through the execution of Petri net models. Because our aim is to use the models for performance analysis, we focus on representing the timing and communication behaviour of the architecture rather than the functionality.
A modular approach is used to model architectures. We identify five basic hardware building blocks from which Petri net models of dataflow architectures can be constructed. In defining the building blocks we will identify strengths and weaknesses of Petri nets for modelling dataflow architectures. A technique called folding is applied to build generic models of dataflow architectures. A timed coloured Petri net model of the Prophid dataflow architecture, which is being developed at Philips Research Laboratories, is presented. This model has been designed in the tool ExSpect. The performance of the Prophid architecture has been analysed by simulation with this model
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