3,684 research outputs found
Simulating infiltration processes into fractured and swelling soils as triggering factors of landslides
The influence of rainfall in triggering landslides is a widely discussed topic in scientific literature. The slope stability of fractured surface soils is often influenced by the soil suction. Rainfall, infiltrating into soil fractures, causes the decrease in soil suction and shear strength, which can trigger the collapse of surface soil horizons. Water flow through fractured soils can also be affected by soil swelling and by capillary barrier effects in the case of low permeable soil overlying a more permeable one. These conditions are rarely investigated by the existing models, especially from the point of view of rainfall triggering surface landslides. For this purpose, we have developed a dual-porosity model that simulates water flow through fractured swelling soils overlying a more permeable soil. The model has been applied to a soil profile consisting of a thin layer of fractured loamy soil above a coarse sand layer, in order to investigate the influence of different rainfall intensities on the infiltration process, and on the distribution of the pore pressure that affects slope stability. © Springer-Verlag Berlin Heidelberg 2013
Interactive Joint Transfer of Energy and Information
In some communication networks, such as passive RFID systems, the energy used
to transfer information between a sender and a recipient can be reused for
successive communication tasks. In fact, from known results in physics, any
system that exchanges information via the transfer of given physical resources,
such as radio waves, particles and qubits, can conceivably reuse, at least
part, of the received resources. This paper aims at illustrating some of the
new challenges that arise in the design of communication networks in which the
signals exchanged by the nodes carry both information and energy. To this end,
a baseline two-way communication system is considered in which two nodes
communicate in an interactive fashion. In the system, a node can either send an
"on" symbol (or "1"), which costs one unit of energy, or an "off" signal (or
"0"), which does not require any energy expenditure. Upon reception of a "1"
signal, the recipient node "harvests", with some probability, the energy
contained in the signal and stores it for future communication tasks. Inner and
outer bounds on the achievable rates are derived. Numerical results demonstrate
the effectiveness of the proposed strategies and illustrate some key design
insights.Comment: 29 pages, 11 figures, Submitted in IEEE Transactions on
Communications. arXiv admin note: substantial text overlap with
arXiv:1204.192
Linear Precoding and Equalization for Network MIMO with Partial Cooperation
A cellular multiple-input multiple-output (MIMO) downlink system is studied
in which each base station (BS) transmits to some of the users, so that each
user receives its intended signal from a subset of the BSs. This scenario is
referred to as network MIMO with partial cooperation, since only a subset of
the BSs are able to coordinate their transmission towards any user. The focus
of this paper is on the optimization of linear beamforming strategies at the
BSs and at the users for network MIMO with partial cooperation. Individual
power constraints at the BSs are enforced, along with constraints on the number
of streams per user. It is first shown that the system is equivalent to a MIMO
interference channel with generalized linear constraints (MIMO-IFC-GC). The
problems of maximizing the sum-rate(SR) and minimizing the weighted sum mean
square error (WSMSE) of the data estimates are non-convex, and suboptimal
solutions with reasonable complexity need to be devised. Based on this,
suboptimal techniques that aim at maximizing the sum-rate for the MIMO-IFC-GC
are reviewed from recent literature and extended to the MIMO-IFC-GC where
necessary. Novel designs that aim at minimizing the WSMSE are then proposed.
Extensive numerical simulations are provided to compare the performance of the
considered schemes for realistic cellular systems.Comment: 13 pages, 5 figures, published in IEEE Transactions on Vehicular
Technology, June 201
Wiggly Strings in Linearized Brans-Dicke Gravity
The metric around a wiggly cosmic string is calculated in the linear
approximation of Brans-Dicke theory of gravitation. The equations of motion for
relativistic and non-relativistic particles in this metric are obtained.
Light propagation is also studied and it is shown that photon trajectories
can be bounded.Comment: 10 pages, LaTeX, added reference
Compound Multiple Access Channels with Partial Cooperation
A two-user discrete memoryless compound multiple access channel with a common
message and conferencing decoders is considered. The capacity region is
characterized in the special cases of physically degraded channels and
unidirectional cooperation, and achievable rate regions are provided for the
general case. The results are then extended to the corresponding Gaussian
model. In the Gaussian setup, the provided achievable rates are shown to lie
within some constant number of bits from the boundary of the capacity region in
several special cases. An alternative model, in which the encoders are
connected by conferencing links rather than having a common message, is studied
as well, and the capacity region for this model is also determined for the
cases of physically degraded channels and unidirectional cooperation. Numerical
results are also provided to obtain insights about the potential gains of
conferencing at the decoders and encoders.Comment: Submitted to IEEE Transactions on Information Theor
Relaying Simultaneous Multicast Messages
The problem of multicasting multiple messages with the help of a relay, which
may also have an independent message of its own to multicast, is considered. As
a first step to address this general model, referred to as the compound
multiple access channel with a relay (cMACr), the capacity region of the
multiple access channel with a "cognitive" relay is characterized, including
the cases of partial and rate-limited cognition. Achievable rate regions for
the cMACr model are then presented based on decode-and-forward (DF) and
compress-and-forward (CF) relaying strategies. Moreover, an outer bound is
derived for the special case in which each transmitter has a direct link to one
of the receivers while the connection to the other receiver is enabled only
through the relay terminal. Numerical results for the Gaussian channel are also
provided.Comment: This paper was presented at the IEEE Information Theory Workshop,
Volos, Greece, June 200
Joint Interference Alignment and Bi-Directional Scheduling for MIMO Two-Way Multi-Link Networks
By means of the emerging technique of dynamic Time Division Duplex (TDD), the
switching point between uplink and downlink transmissions can be optimized
across a multi-cell system in order to reduce the impact of inter-cell
interference. It has been recently recognized that optimizing also the order in
which uplink and downlink transmissions, or more generally the two directions
of a two-way link, are scheduled can lead to significant benefits in terms of
interference reduction. In this work, the optimization of bi-directional
scheduling is investigated in conjunction with the design of linear precoding
and equalization for a general multi-link MIMO two-way system. A simple
algorithm is proposed that performs the joint optimization of the ordering of
the transmissions in the two directions of the two-way links and of the linear
transceivers, with the aim of minimizing the interference leakage power.
Numerical results demonstrate the effectiveness of the proposed strategy.Comment: To be presented at ICC 2015, 6 pages, 7 figure
Brans-Dicke cylindrical wormholes
Static axisymmetric thin-shell wormholes are constructed within the framework
of the Brans-Dicke scalar-tensor theory of gravity. Examples of wormholes
associated with vacuum and electromagnetic fields are studied. All
constructions must be threaded by exotic matter, except in the case of
geometries with a singularity of finite radius, associated with an electric
field, which can have a throat supported by ordinary matter. These results are
achieved with any of the two definitions of the flare-out condition considered.Comment: 11 pages, 3 figures; v3: corrected version, conclusions unchange
Hydraulic stream network conditioning by a tectonically induced, giant, deep-seated landslide along the front of the Apennine chain (south Italy)
Abstract. The tectonic stresses that produced the uplift of Apennine chain ridge in southern Italy generated advanced buried thrusts of allochthonous deposits that induced deformations of foredeep deposits. This thrust may cause giant, deep-seated landslides at the front of the chain. Starting from a specific case history in low Biferno Valley, this work presents how giant, deep-seated landslides along the front of the chain may be generated by the thrust of allochthonous nappe of the chain. In addition, the influence that these huge phenomena may have on landslide and flood susceptibility and on natural hazards of the involved area is analysed. The work presents an interpretation of local morphology and stream network paths of low Biferno Valley as a consequence of a giant, deep-seated landslide affecting the right side of the valley. The proposed interpretation is supported by numerical geomorphological analyses of the area at stake. It is shown how both the morphologies of the catchments of the river Biferno and its tributary Cigno and stream paths are strongly conditioned by this large, deep-seated landslide. This landslide deviates the stream paths affecting both the flooding susceptibility of low Biferno Valley and landslide susceptibility on the left side of Biferno Valley
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