436 research outputs found
Hopf-algebra description of noncommutative-spacetime symmetries
In the study of certain noncommutative versions of Minkowski spacetime there
is still a large ambiguity concerning the characterization of their symmetries.
Adopting as our case study the kappaMinkowski noncommutative space-time, on
which a large literature is already available, we propose a line of analysis of
noncommutative-spacetime symmetries that relies on the introduction of a Weyl
map (connecting a given function in the noncommutative Minkowski with a
corresponding function in commutative Minkowski) and of a compatible notion of
integration in the noncommutative spacetime. We confirm (and we establish more
robustly) previous suggestions that the commutative-spacetime notion of
Lie-algebra symmetries must be replaced, in the noncommutative-spacetime
context, by the one of Hopf-algebra symmetries. We prove that in kappaMinkowski
it is possible to construct an action which is invariant under a Poincare-like
Hopf algebra of symmetries with 10 generators, in which the noncommutativity
length scale has the role of relativistic invariant. The approach here adopted
does leave one residual ambiguity, which pertains to the description of the
translation generators, but our results, independently of this ambiguity, are
sufficient to clarify that some recent studies (gr-qc/0212128 and
hep-th/0301061), which argued for an operational indistiguishability between
theories with and without a length-scale relativistic invariant, implicitly
assumed that the underlying spacetime would be classical.Comment: 20 pages, no figures, LaTex. This version has exactly the same
technical content as version 1, but the observation reported in Section VII
is discussed more pedagogicall
Enabling RAN Slicing Through Carrier Aggregation in mmWave Cellular Networks
The ever increasing number of connected devices and of new and heterogeneous
mobile use cases implies that 5G cellular systems will face demanding technical
challenges. For example, Ultra-Reliable Low-Latency Communication (URLLC) and
enhanced Mobile Broadband (eMBB) scenarios present orthogonal Quality of
Service (QoS) requirements that 5G aims to satisfy with a unified Radio Access
Network (RAN) design. Network slicing and mmWave communications have been
identified as possible enablers for 5G. They provide, respectively, the
necessary scalability and flexibility to adapt the network to each specific use
case environment, and low latency and multi-gigabit-per-second wireless links,
which tap into a vast, currently unused portion of the spectrum. The
optimization and integration of these technologies is still an open research
challenge, which requires innovations at different layers of the protocol
stack. This paper proposes to combine them in a RAN slicing framework for
mmWaves, based on carrier aggregation. Notably, we introduce MilliSlice, a
cross-carrier scheduling policy that exploits the diversity of the carriers and
maximizes their utilization, thus simultaneously guaranteeing high throughput
for the eMBB slices and low latency and high reliability for the URLLC flows.Comment: 8 pages, 8 figures. Proc. of the 18th Mediterranean Communication and
Computer Networking Conference (MedComNet 2020), Arona, Italy, 202
A Multiscale Thermo-Fluid Computational Model for a Two-Phase Cooling System
In this paper, we describe a mathematical model and a numerical simulation
method for the condenser component of a novel two-phase thermosyphon cooling
system for power electronics applications. The condenser consists of a set of
roll-bonded vertically mounted fins among which air flows by either natural or
forced convection. In order to deepen the understanding of the mechanisms that
determine the performance of the condenser and to facilitate the further
optimization of its industrial design, a multiscale approach is developed to
reduce as much as possible the complexity of the simulation code while
maintaining reasonable predictive accuracy. To this end, heat diffusion in the
fins and its convective transport in air are modeled as 2D processes while the
flow of the two-phase coolant within the fins is modeled as a 1D network of
pipes. For the numerical solution of the resulting equations, a Dual
Mixed-Finite Volume scheme with Exponential Fitting stabilization is used for
2D heat diffusion and convection while a Primal Mixed Finite Element
discretization method with upwind stabilization is used for the 1D coolant
flow. The mathematical model and the numerical method are validated through
extensive simulations of realistic device structures which prove to be in
excellent agreement with available experimental data
Simulating the Impact on the Local Economy of Alternative Management Scenarios for Natural Areas
This working paper estimates the impact on the local economy of the High Garda Natural Park of alternative management scenarios for the West Garda Regional Forest. The local economy is specialized in tourist services and strongly linked to the tourist presence and their level of expenditure. We wish to investigate the effects of the participative management strategy, which takes into account users preferences and the non-participative strategy, using the SAM multiplier analysis. The local SAM has been constructed considering three sectors: agriculture, tourism and a third aggregate sector including all the other activities. The resident population has been divided into two categories: residents employed in the tourist sector and the remaining resident population. The SAM analysis shows that the accounting representation of the local economy is meaningful and that the participative program, if chosen by the central regional management, would be the most desirable program also at the local level.Tourism, SAM, Multiplier analysis
Linking ROS Levels to Autophagy: The Key Role of AMPK
Oxygen reactive species (ROS) are a group of molecules generated from the incomplete reduction of oxygen. Due to their high reactivity, ROS can interact with and influence the function of multiple targets, which include DNA, lipids, and proteins. Among the proteins affected by ROS, AMP-activated protein kinase (AMPK) is considered a major sensor of the intracellular energetic status and a crucial hub involved in the regulation of key cellular processes, like autophagy and lysosomal function. Thanks to these features, AMPK has been recently demonstrated to be able to perceive signals related to the variation of mitochondrial dynamics and to transduce them to the lysosomes, influencing the autophagic flux. Since ROS production is largely dependent on mitochondrial activity, through the modulation of AMPK these molecules may represent important signaling agents which participate in the crosstalk between mitochondria and lysosomes, allowing the coordination of these organelles' functions. In this review, we will describe the mechanisms through which ROS activate AMPK and the signaling pathways that allow this protein to affect the autophagic process. The picture that emerges from the literature is that AMPK regulation is highly tissue-specific and that different pools of AMPK can be localized at specific intracellular compartments, thus differentially responding to altered ROS levels. For this reason, future studies will be highly advisable to discriminate the specific contribution of the activation of different AMPK subpopulations to the autophagic pathway
Boiling on a tube bundle:heat transfer, pressure drop and flow patterns
The complexity of the two-phase flow in a tube bundle presents important problems in the design and understanding of the physical phenomena taking place. The working conditions of an evaporator depend largely on the dynamics of the two-phase flow that in turn influence the heat exchange and the pressure drop of the system. A characterization of the flow dynamics, and possibly the identification of the flow pattern in the tube bundle, in thus expected to lead to a better understanding of the phenomena and to reveal on the mechanisms governing the tube bundle. Therefore, the present study aims at providing further insights into two-phase bundle flow through a new visualization system able to provide for the first time a view of the flow in the core of a tube bundle. In addition, the measurement of the light attenuation of a laser beam through the two-phase flow and measurement of the high frequency pressure fluctuations with a piezo-electric pressure transducer are used to characterize the flow. The design and the validation of this new instrumentation also provided a method for the detection of dry-out in tube bundles. This was achieved by a laser attenuation technique, flow visualization, and estimation of the power spectrum of the pressure fluctuation. The current investigation includes results for two different refrigerants, R134a and R236fa, three saturations temperatures Tsat = 5, 10 and 15 °C, mass velocities ranging from 4 to 40 kg/sm2 in adiabatic and diabatic conditions (several heat fluxes). Measurement of the local heat transfer coefficient and two-phase frictional pressure drop were obtained and utilized to improve the current prediction methods. The heat transfer and pressure drop data were supported by extensive characterization of the two-phase flow, which was to improve the understanding of the two-phase flow occurring in tube bundles
The broad spectrum of lung diseases in primary antibody deficiencies
Human primary immunodeficiency diseases (PIDs) represent a heterogeneous group of more than 350 disorders. They are rare diseases, but their global incidence is more relevant than generally thought. The underlying defect may involve different branches of the innate and/or adaptive immune response. Thus, the clinical picture may range from severe phenotypes characterised by a broad spectrum of infections to milder infectious phenotypes due to more selective (and frequent) immune defects. Moreover, infections may not be the main clinical features in some PIDs that might present with autoimmunity, auto-inflammation and/or cancer. Primary antibody deficiencies (PADs) represent a small percentage of the known PIDs but they are the most frequently diagnosed, particularly in adulthood. Common variable immunodeficiency (CVID) is the most prevalent symptomatic PAD.PAD patients share a significant susceptibility to respiratory diseases that represent a relevant cause of morbidity and mortality. Pulmonary complications include acute and chronic infection-related diseases, such as pneumonia and bronchiectasis. They also include immune-mediated interstitial lung diseases, such as granulomatous-lymphocytic interstitial lung disease (GLILD) and cancer. Herein we will discuss the main pulmonary manifestations of PADs, the associated functional and imaging findings, and the relevant role of pulmonologists and chest radiologists in diagnosis and surveillance
Does texting while walking really affect gait in young adults?
Abstract
Background: Texting on a smartphone while walking has become a customary task among young adults. In recent
literature many safety concerns on distracted walking have been raised. It is often hypothesized that the allocation
of attentional resources toward a secondary task can influence dynamic stability. In the double task of walking and
texting it was found that gait speed is reduced, but there is scarce evidence of a modified motor control strategy
compromising stability. The aim of this study is twofold: 1) to comprehensively examine the gait modifications
occurring when texting while walking, including the study of the lower limb muscle activation patterns, 2) to
specifically assess the co-contraction of ankle antagonist muscles. We hypothesized that texting while walking
increases co-contractions of ankle antagonist muscles when the body weight is transferred from one lower limb to
the other, to improve the distal motor control and joint stabilization.
Methods: From the gait data collected during an instrumented walk lasting 3 min, we calculated the spatio-temporal
parameters, the ankle and knee kinematics, the muscle activation patterns of tibialis anterior, gastrocnemius
lateralis, peroneus longus, rectus femoris, and lateral hamstrings, and the co-contraction (occurrence and
duration) of the ankle antagonist muscles (tibialis anterior and gastrocnemius lateralis), bilaterally.
Results: Young adults showed, overall, small gait modifications that could be mainly ascribable to gait speed
reduction and a modified body posture due to phone handling. We found no significant alterations of ankle
and knee kinematics and a slightly delayed activation onset of the left gastrocnemius lateralis. However, we
found an increased co-contraction of tibialis anterior and gastrocnemius lateralis, especially during mid-stance.
Conversely, we found a reduced co-contraction during terminal stance.
Conclusions: Our results suggest that, in young adults, there is an adjustment of the motor control strategy
aimed at increasing ankle joint stability in a specific and âcriticalâ phase of the gait cycle, when the body
weight is transferred from one leg to the other
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