571 research outputs found
Bringing Statistical Learning Machines Together for Hydro-Climatological Predictions - Case Study for Sacramento San Joaquin River Basin, California
Study region: Sacramento San Joaquin River Basin, California Study focus: The study forecasts the streamflow at a regional scale within SSJ river basin with largescale climate variables. The proposed approach eliminates the bias resulting from predefined indices at regional scale. The study was performed for eight unimpaired streamflow stations from 1962–2016. First, the Singular Valued Decomposition (SVD) teleconnections of the streamflow corresponding to 500 mbar geopotential height, sea surface temperature, 500 mbar specific humidity (SHUM500), and 500 mbar U-wind (U500) were obtained. Second, the skillful SVD teleconnections were screened non-parametrically. Finally, the screened teleconnections were used as the streamflow predictors in the non-linear regression models (K-nearest neighbor regression and data-driven support vector machine). New hydrological insights: The SVD results identified new spatial regions that have not been included in existing predefined indices. The nonparametric model indicated the teleconnections of SHUM500 and U500 being better streamflow predictors compared to other climate variables. The regression models were capable to apprehend most of the sustained low flows, proving the model to be effective for drought-affected regions. It was also observed that the proposed approach showed better forecasting skills with preprocessed large scale climate variables rather than using the predefined indices. The proposed study is simple, yet robust in providing qualitative streamflow forecasts that may assist water managers in making policy-related decisions when planning and managing watersheds
Structural characteristics of various types of helically wound cables in bending
The primary aim of this research was to investigate the bending behaviour of helically
wound steel cables of various types (i.e. normal spiral strands, sheathed spiral strands
and locked coil cables) in the presence of friction and to propose more efficient
computational models for their analysis under combined tension and bending.
The proposed model fully takes into account interwire contact forces both in the
radial direction (point contact between wires in different layers) and hoop direction
(line contact within the wires in the same layer). Extensive theoretical parametric
studies have been undertaken on a variety of cable constructions covering a wide
range of geometrical and material parameters. Explicit formulations have been
developed for the smooth transition of the bending stiffness from no-slip to full slip
regimes, as a function of cable curvature. Based on these formulations, it is now
possible to calculate the relative displacements of the wires, as well as the tensile,
bending and hoop stresses in the individual wires of the cable. Furthermore, bending
stiffness of the cable is shown to decrease by a factor of 2 to 16, depending upon the
friction coefficient between wires and the type of cable construction. Wherever
possible, the theoretical results have been compared with experimental results from
the available literature and are found in very good agreement with them.
A simple method for the determination of the bending stiffness of large diameter
multi-layered cable has been developed. The simplified method is further shown to
provide estimates of the bending stiffness which are very close to those calculated by
the original theory, allowing hand calculations for an easier use in industry.
The proposed formulations have been extended to cater for the effects of external
hydrostatic pressure on sheathed spiral strands in deep water applications. These
forces are shown to have a great influence on the pattern of interwire contact forces
and hence the interlayer slippage between the wires in the strand. Numerical results
have been obtained and analysed for three different 127 mm diameter strands with
lay angles of 12°, 18° and 24° respectively, experiencing a wide range of external
hydrostatic pressures of 0 to 2,000 metres. The significant increase in normal contact
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force between wires is shown to suppress the slippage of wires in the cable. However,
the no-slip and full slip values of the effective bending stiffness of the cable is shown
to be independent of the level of hydrostatic pressure.
A theoretical model is also proposed for estimating wire kinematics, pattern of
interwire slippage, contact forces as well as the flexural rigidity of locked coil cables
with outer layers made of shaped wires. In order to validate this model, numerical
results are reported for two different locked coil cables. It is shown that the shaped
wires in the outer layers of locked coil cables play an important role in the
distribution of contact forces, slip initiation and cable unwinding
High-Speed Molecular Communication in Vacuum
Existing molecular communication systems, both theoretical and experimental,
are characterized by low information rates. In this paper, inspired by
time-of-flight mass spectrometry (TOFMS), we consider the design of a molecular
communication system in which the channel is a vacuum and demonstrate that this
method has the potential to increase achievable information rates by many
orders of magnitude. We use modelling results from TOFMS to obtain arrival time
distributions for accelerated ions and use them to analyze several species of
ions, including hydrogen, nitrogen, argon, and benzene. We show that the
achievable information rates can be increased using a velocity (Wien) filter,
which reduces uncertainty in the velocity of the ions. Using a simplified
communication model, we show that data rates well above 1 Gbit/s/molecule are
achievable.Comment: Accepted for publication in IEEE Transactions on Molecular,
Biological, and Multi-Scale Communication
Quantum transport at the Dirac point: Mapping out the minimum conductivity from pristine to disordered graphene
The phase space for graphene's minimum conductivity is
mapped out using Landauer theory modified for scattering using Fermi's Golden
Rule, as well as the Non-Equilibrium Green's Function (NEGF) simulation with a
Monte Carlo sampling over impurity distributions. The resulting `fan diagram'
spans the range from ballistic to diffusive over varying aspect ratios (),
and bears several surprises. {The device aspect ratio determines how much
tunneling (between contacts) is allowed and becomes the dominant factor for the
evolution of from ballistic to diffusive regime. We find an
increasing (for ) or decreasing () trend in vs.
impurity density, all converging around at the dirty
limit}. In the diffusive limit, the {conductivity} quasi-saturates due to the
precise cancellation between the increase in conducting modes from charge
puddles vs the reduction in average transmission from scattering at the Dirac
Point. In the clean ballistic limit, the calculated conductivity of the lowest
mode shows a surprising absence of Fabry-P\'{e}rot oscillations, unlike other
materials including bilayer graphene. We argue that the lack of oscillations
even at low temperature is a signature of Klein tunneling
Security-as-a-Service in Multi-cloud and Federated Cloud Environments: 9th IFIP WG 11.11 International Conference, IFIPTM 2015, Hamburg, Germany, May 26-28, 2015, Proceedings
The economic benefits of cloud computing are encouraging customers to bring complex applications and data into the cloud. However security remains the biggest barrier in the adoption of cloud, and with the advent of multi-cloud and federated clouds in practice security concerns are for applications and data in the cloud. This paper proposes security as a value added service, provisioned dynamically during deployment and operation management of an application in multi-cloud and federated clouds. This paper specifically considers a data protection and a host & application protection solution that are offered as a SaaS appli- cation, to validate the security services in a multi-cloud and federated cloud environment. This paper shares our experiences of validating these security services over a geographically distributed, large scale, multi-cloud and federated cloud infrastructure
Security-as-a-Service in Multi-cloud and Federated Cloud Environments
The economic benefits of cloud computing are encouraging customers to bring complex applications and data into the cloud. However security remains the biggest barrier in the adoption of cloud, and with the advent of multi-cloud and federated clouds in practice security concerns are for applications and data in the cloud. This paper proposes security as a value added service, provisioned dynamically during deployment and operation management of an application in multi-cloud and federated clouds. This paper specifically considers a data protection and a host & application protection solution that are offered as a SaaS application, to validate the security services in a multi-cloud and federated cloud environment. This paper shares our experiences of validating these security services over a geographically distributed, large scale, multi-cloud and federated cloud infrastructure
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