1,497 research outputs found
Time walkers and spatial dynamics of ageing information
The distribution of information is essential for living system's ability to
coordinate and adapt. Random walkers are often used to model this distribution
process and, in doing so, one effectively assumes that information maintains
its relevance over time. But the value of information in social and biological
systems often decay and must continuously be updated. To capture the spatial
dynamics of ageing information, we introduce time walkers. A time walker moves
like a random walker, but interacts with traces left by other walkers, some
representing older information, some newer. The traces forms a navigable
information landscape. We quantify the dynamical properties of time walkers
moving on a two-dimensional lattice and the quality of the information
landscape generated by their movements. We visualise the self-similar landscape
as a river network, and show that searching in this landscape is superior to
random searching and scales as the length of loop-erased random walks
Cell line-specific efficacy of thermoradiotherapy in human and canine cancer cells in vitro
Objective
Aims were to investigate sensitivity of various human and canine cancer cell lines to hyperthermia and the influence of particular treatment conditions, and to analyze the DNA-damage response and mode of cell death in cell line radiosensitized by hyperthermia. Additionally, we were interested in the involvement of HSP70 in radiosensitization.
Methods
Radiosensitization by hyperthermia was determined in a panel of human and canine cancer cell lines using clonogenic cell survival assay, as well as levels of heat shock proteins (HSPs) using immunoblotting. The influence of the hyperthermia-radiotherapy time gap, different temperatures and the order of treatments on clonogenicity of hyperthermia-sensitive A549 cells was investigated. Additionally, DNA damage and cell death were assessed by Comet assay and an apoptosis/necrosis assay. Further we induced transient knockdown in A549 cells to test HSP70’s involvement in radiosensitization.
Results
Out of eight cell lines tested, only two (A549 and Abrams) showed significant decrease in clonogenic cell survival when pre-treated with hyperthermia at 42ËšC. Strong induction of HSP70 upon thermoradiotherapy (HT-RT) treatment was found in all cell lines. Transient knockdown of HSP70 in A549 cells did not result in decrease of clonogenic cell survival in response to HT-RT.
Conclusion
Tumor cell-type, temperature and order of treatment play an important role in radiosensitization by hyperthermia. However, hyperthermia has limited potency to radiosensitize canine cancer cells grown in a 2D cell culture setting presented here. DNA damage and apoptosis/necrosis did not increase upon combined treatment and cytosolic levels of HSP70 appear not to play critical role in the radiosensitization of A549 cells
Coupled modelling of permafrost and groundwater : a case study approach
This report investigates the sensitivity of simulated permafrost thickness and dynamics to a
variety of climatic, geological and hydrogeological conditions for two geological environments,
basement under sedimentary cover and a low permeability succession of Mesozoic shales and
siltstones (Case 1 and Case 2 respectively). A combination of one dimensional heat conduction
modelling, including the effects of freeze-thaw, and two dimensional heat conduction-advection
modelling, including freeze thaw, has been undertaken to simulate permafrost development in
these two contrasting geological environments. This enables an assessment of the sensitivities to
a range of possible geological parameters, advective heat flow, and the effect of glaciation with
and without the influence of glacial loading.
In this report, permafrost is defined as the sub-surface in which ice is present even in very small
amounts, i.e. ice content is greater than 0%, and in the model, this is at the zero degree isotherm.
The maximum permafrost thickness is strongly dependent on the mean annual surface
temperature, the presence of ice that will insulate the system and the duration of the cold phase.
By scaling the minimum temperature of 57 Pliocene-Pleistocene globally distributed benthic
δ18O records to temperatures of 14°C, 18°C and 25 °C below the present day mean annual
temperature, the maximum permafrost thickness for Case 1 is simulated to reach 171 m, 248 m,
and 475 m, and for Case 2 80 m, 138 m, and 238 m respectively. The difference in permafrost
thickness between the two Cases is attributed to the variation in subsurface rock properties.
Deeper permafrost depths than for Case 1 and 2 can be expected where the thermal conductivity
is higher than for Case 1 and 2.
A sensitivity study of the geological parameters has shown that there is a strong, non-linear,
relationship between thermal conductivity, latent heat and geothermal heat flow for a series of
temperatures representative of the glacial cycles of the past one million years. This is in contrast
to a steady state temperature profile, where permafrost thickness relates linearly to thermal
conductivity, heat flow and ground surface temperature. Thickest permafrost under unchanged
climatic conditions is to be expected where there is a low heat flow, a high thermal conductivity
and a low porosity, such as for example in the north of Scotland.
The results of the modelling show that when the temperature regime is dominated by heat
conduction, such as for the low permeability Case 2, a heat conduction only model is sufficient
to estimate the thickness and distribution of permafrost. However, when heat advection is likely
to be important, such as in Case 1, the coupling of permafrost and groundwater flow is necessary
to simulate the permafrost distribution during freeze and thaw, or during shallow permafrost
events. This particularly holds true when permafrost is modelled to be relatively permeable,
where modelling suggests that heat advection of cold water at recharge points (interfluves)
results in cooling and thicker permafrost compared to discharge points where discharge of
warmer water results in thinner permafrost. However, these variabilities in local permafrost
thickness are of minor importance for the question of freezing of the repository. However, when
assessing the broader influences of permafrost on a geological environment, local variations in
permafrost extent of thickness can have consequences on the biosphere.
Glaciation influences the thermal regime of the ground surface. If the glacier bed is undergoing
pressure melting, as found in the ablation zone, a reduction in permafrost depth can be expected.
If the glacier bed is cold based, as often found in the accumulation zone or at ice divides where
strong vertical advection of cold ice has a cooling effect, then the maximum permafrost thickness
can be expected to be similar to the scenario without glaciation. It may even increase if the
temperatures at the glacier bed are colder than the ground surface temperatures, which may occur.
when the temperature in the area where the ice is forming is colder than that prevailing
downstream.
Recharge and discharge decrease considerably during periods when permafrost is present. In the
case of a model with an open model boundary to one side, representing the coast for example,
and a high topographic gradient (Case 1), a large drop in hydraulic heads is observed beneath the
permafrost. This results in lower groundwater flows at depth compared to unfrozen conditions.
Where a modelled area is closed on all sides (Case 2), a decrease in flow at depth is also
observed, however the hydraulic heads do not decrease to the same extent as the hydraulic
gradient is less than for Case 1. During permafrost thaw, hydraulic heads rise, resulting in an
uptake of groundwater into elastic storage from recharge over the top boundary of the model
domain.
When taliks underneath surface water bodies develop, the groundwater flow system remains
more active than during continuous permafrost. Recharge and discharge are focused on the lakes
and a regional groundwater flow system connecting the lakes can develop. Heat advection
remains more important during thick permafrost when through taliks remain open.
In the model, during periods of glaciation, hydraulic heads increase by ~1500 m at depth for
Case 1 and Case 2 when ice loading is applied. When ice-sheet loading is not accounted for, the
hydraulic head signal in low permeability layers is dampened. During glacial advance,
groundwater recharge increases by up to two orders of magnitude, and during glacial retreat
discharge increases. During ice advance, groundwater flow is in a downward direction but during
ice retreat it is in an upward direction. Depending on the flow direction of the glacier,
groundwater flow directions can be reversed during a glaciation. Modelling the Anglian
Glaciation (middle Pleistocene glaciation, equivalent to the Elsterian or Mindel glaciation in
Europe and the Alps, most extensive glaciation in the British Isles, MIS 12), the hydraulic head
and groundwater flow magnitude are affected by the glaciation for tens of thousands of years,
whereas after the Devensian glaciation (late Pleistocene glaciation, equivalent to the
Weichselian/Vistulian or Würm glaciation in Europe and the Alps, MIS 5d to 2), the signal
remains for thousands of years.
High hydraulic heads that may be present during glaciation are likely to modify the groundwater
flow around a GDF. The modelling presented here based on two settings and typical thermal and
hydraulic properties for the rocks present, demonstrates that the depth of permafrost could
extend up to a depth of 300m below the surface and, depending on specific characteristics (large
thermal conductivity and low porosity) and an exceptionally long cold period, could extend to
greater depths. Permafrost to these depths may affect the engineering properties of some rock
types and could lead to the development of new fracture pathways in more brittle formations.
Permafrost could also affect some of the engineered components of a GDF in similar ways, such
as the properties of clay materials
Distributed Learning with Biogeography-Based Optimization
We present hardware testing of an evolutionary algorithm known as biogeography-based optimization (BBO) and extend it to distributed learning. BBO is an evolutionary algorithm based on the theory of biogeography, which describes how nature geographically distributes organisms. We introduce a new BBO algorithm that does not use a centralized computer, and which we call distributed BBO. BBO and distributed BBO have been developed by mimicking nature to obtain an algorithm that optimizes solutions for different situations and problems. We use fourteen common benchmark functions to obtain results from BBO and distributed BBO, and we also use both algorithms to optimize robot control algorithms. We present not only simulation results, but also experimental results using BBO to optimize the control algorithms of mobile robots. The results show that centralized BBO generally gives better optimization results and would generally be a better choice than any of the newly proposed forms of distributed BBO. However, distributed BBO allows the user to find a less optimal solution to a problem while avoiding the need for centralized, coordinated control
Connectivity strategies to enhance the capacity of weight-bearing networks
The connectivity properties of a weight-bearing network are exploited to
enhance it's capacity. We study a 2-d network of sites where the weight-bearing
capacity of a given site depends on the capacities of the sites connected to it
in the layers above. The network consists of clusters viz. a set of sites
connected with each other with the largest such collection of sites being
denoted as the maximal cluster. New connections are made between sites in
successive layers using two distinct strategies. The key element of our
strategies consists of adding as many disjoint clusters as possible to the
sites on the trunk of the maximal cluster. The new networks can bear much
higher weights than the original networks and have much lower failure rates.
The first strategy leads to a greater enhancement of stability whereas the
second leads to a greater enhancement of capacity compared to the original
networks. The original network used here is a typical example of the branching
hierarchical class. However the application of strategies similar to ours can
yield useful results in other types of networks as well.Comment: 17 pages, 3 EPS files, 5 PS files, Phys. Rev. E (to appear
Fellhanera gyrophorica, a new European species with conspicuous pycnidia
Fellhanera gyrophorica Sérus., Coppins, Diederich & Scheidegger is described as new from Europe Austria, Lithuania, Luxembourg, Poland, Switzerland and Ukraine. It is a sterile corticolous species with conspicuous and sometimes shortly stalked pycnidia whose outer walls produce gyrophoric acid. Its position in the genus Fellhanera (Pilocarpaceae) is tentative and further studies may necessitate its transfer to another genu
Bayesian uncertainty assessment of flood predictions in ungauged urban basins for conceptual rainfall-runoff models
Urbanization and the resulting land-use change strongly affect the water cycle and runoff-processes in watersheds. Unfortunately, small urban watersheds, which are most affected by urban sprawl, are mostly ungauged. This makes it intrinsically difficult to assess the consequences of urbanization. Most of all, it is unclear how to reliably assess the predictive uncertainty given the structural deficits of the applied models. In this study, we therefore investigate the uncertainty of flood predictions in ungauged urban basins from structurally uncertain rainfall-runoff models. To this end, we suggest a procedure to explicitly account for input uncertainty and model structure deficits using Bayesian statistics with a continuous-time autoregressive error model. In addition, we propose a concise procedure to derive prior parameter distributions from base data and successfully apply the methodology to an urban catchment in Warsaw, Poland. Based on our results, we are able to demonstrate that the autoregressive error model greatly helps to meet the statistical assumptions and to compute reliable prediction intervals. In our study, we found that predicted peak flows were up to 7 times higher than observations. This was reduced to 5 times with Bayesian updating, using only few discharge measurements. In addition, our analysis suggests that imprecise rainfall information and model structure deficits contribute mostly to the total prediction uncertainty. In the future, flood predictions in ungauged basins will become more important due to ongoing urbanization as well as anthropogenic and climatic changes. Thus, providing reliable measures of uncertainty is crucial to support decision making
Breakdown of Kolmogorov scaling in models of cluster aggregation with deposition
The steady state of the model of cluster aggregation with deposition is
characterized by a constant flux of mass directed from small masses towards
large masses. It can therefore be studied using phenomenological theories of
turbulence, such as Kolmogorov's 1941 theory. On the other hand, the large
scale behavior of the aggregation model in dimensions lower than or equal to
two is governed by a perturbative fixed point of the renormalization group
flow, which enables an analytic study of the scaling properties of correlation
functions in the steady state. In this paper, we show that the correlation
functions have multifractal scaling, which violates linear Kolmogorov scaling.
The analytical results are verified by Monte Carlo simulations.Comment: 5 pages 4 figure
Modeling temperature-dependent population dynamics in the excited state of the nitrogen-vacancy center in diamond
The nitrogen-vacancy (NV) center in diamond is well known in quantum
metrology and quantum information for its favorable spin and optical
properties, which span a wide temperature range from near zero to over 600 K.
Despite its prominence, the NV center's photo-physics is incompletely
understood, especially at intermediate temperatures between 10-100 K where
phonons become activated. In this work, we present a rate model able to
describe the cross-over from the low-temperature to the high-temperature
regime. Key to the model is a phonon-driven hopping between the two orbital
branches in the excited state (ES), which accelerates spin relaxation via an
interplay with the ES spin precession. We extend our model to include magnetic
and electric fields as well as crystal strain, allowing us to simulate the
population dynamics over a wide range of experimental conditions. Our model
recovers existing descriptions for the low- and high-temperature limits, and
successfully explains various sets of literature data. Further, the model
allows us to predict experimental observables, in particular the
photoluminescence (PL) emission rate, spin contrast, and spin initialization
fidelity relevant for quantum applications. Lastly, our model allows probing
the electron-phonon interaction of the NV center and reveals a gap between the
current understanding and recent experimental findings
Review of saturated groundwater model codes for Hydro-JULES
This report reviews saturated groundwater model codes, one to be implemented into the Hydro-JULES modelling framework. First, the criteria for the code evaluation is described, and then commercial groundwater modelling codes, codes for thermo-hydro-chemical modelling and finally open source groundwater modelling codes are evaluated using the aforementioned criteria. Considering a groundwater code for the simulation of groundwater flooding or drought, we recommend either MODFLOW-2005, or the newly developed MODFLOW 6, the latter will need to be tested. Alternatively, BGS could develop a custom code that can solve the groundwater flow equation using moving grids, allowing a dynamic representation of the model grid for a moving water table. If also thermo and chemical processes are of interest, then codes such as OpenGeoSys, Dumux, and PFLOTRAN could be good choices, however they will need benchmarking to evaluate their ease of use
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