Non existence of closed null geodesics in Kerr spacetimes

The Kerr-star spacetime is the extension over the horizons and in the negative radial region of the slowly rotating Kerr black hole. It is known that below the inner horizon, there exist both timelike and null (lightlike) closed curves. Nevertheless, we prove that the null geodesics cannot be closed in the Kerr-star spacetime.Comment: 26 pages, 17 figures. Corrections: typo at p. 14 and explicit non-vanishing Christoffel symbol in Prop. 5.

Somatosensory neurons integrate the geometry of skin deformation and mechanotransduction channels to shape touch sensing.

Touch sensation hinges on force transfer across the skin and activation of mechanosensitive ion channels along the somatosensory neurons that invade the skin. This skin-nerve sensory system demands a quantitative model that spans the application of mechanical loads to channel activation. Unlike prior models of the dynamic responses of touch receptor neurons in Caenorhabditis elegans (Eastwood et al., 2015), which substituted a single effective channel for the ensemble along the TRNs, this study integrates body mechanics and the spatial recruitment of the various channels. We demonstrate that this model captures mechanical properties of the worm's body and accurately reproduces neural responses to simple stimuli. It also captures responses to complex stimuli featuring non-trivial spatial patterns, like extended or multiple contacts that could not be addressed otherwise. We illustrate the importance of these effects with new experiments revealing that skin-neuron composites respond to pre-indentation with increased currents rather than adapting to persistent stimulation

Future Forecasting Wicked Problems: A New Framework For Design

Design can be characterized as ‘knowledge for future transformation’ and is a discipline concerned with developing new products, systems and services that change the future. However, the methods we use for generating foresight are underdeveloped and some gaps and issues remain. This is especially true between more speculative approaches to designing futures and applied industrial approaches. This paper explores these issues in relation to addressing wicked problems in design, specifically the emphasis on qualitative methods and how these lack measurable indicators of problem improvement. The use of mixed methods offers possibilities for combining the power of abductive thinking generating alternative visions of the future alongside quantifiable improvements. We review methods for future forecasting in other fields including economics and business management and explore how these can be transposed into design practice to address some of the issues raised. A proposal is made to achieve this via an interdisciplinary mixed method approach by instigating a process of gap analysis within a new design futures framework

Computational Neuroscience: Finding patterns in cortical responses

Simulations predict a paradoxical effect that should be revealed by patterned stimulation of the cortex

THEORETICAL PHYSICS MODELING OF NEUROLOGICAL PROBLEMS

In this thesis we approach different problems in neurobiology using methods from theoretical physics. The first topic that we studied is the mechanoelectrical transduction at the basis of touch sensation, i.e. the process by which a mechanical signal conveyed during touch is transformed into an electric signal. We investigate how the neural response is generated in the C. elegans and propose a channel gating mechanism to explain the activation of touch receptor neurons by mechanical stimuli. The second part of the thesis is related to our ability of orient ourself and navigate in space. The neural system underlying this ability has been extensively characterized in rats, where the activity of different types of neurons has been found to be correlated with the spatial position of the animal. Grid cells in the rat entorhinal cortex are part of this \u201cneural map\u201d of space; they form regular triangular lattices whose geometrical properties have a modular distribution among the population of neurons. We show that some of the features observed in the system may be explained by assuming that grid cells provide an efficient representation of space. We predict a scaling law connecting the number of neurons within a module and the spatial period of the associated grids. The last problem discussed in this thesis concerns the neurodegenerative Parkinson\u2019s disease. Limb tremor caused by the disease is currently treated by administering drugs and by fixed-frequency deep brain stimulation. The latter interferes directly with the brain dynamics by delivering electrical impulses to neurons in the subthalamic nucleus. We develop a theory to describe the onset of anomalous oscillations in the neural activity that are at the origin of the characteristic tremor. We propose a new feedback-controlled stimulation procedure and show that it could outperform the standard protocol

Behavior Prediction and Monitoring of a Deep Excavation in the Historic Center of Brescia

The construction of a new underground car park in the historic center of Brescia (Northern Italy) required the execution of a 130m long, 23m wide and 15-20m deep excavation which was supported by concrete multi-anchored diaphragm walls. The site is located between two facing ancient walls (15-16th century) that support 3-4 storey buildings in precarious conditions. The soil stratigraphy comprises a superficial layer of made ground over a clayey to sandy soil deposit supporting a perched water table. A comprehensive monitoring system was set up before construction that included inclinometers, precise leveling and automatic structural monitoring by means of a high-precision total station. A number of finite element numerical analyses were conducted using different constitutive laws for the soil to evaluate the behavior of the retaining structure and safety of adjacent buildings. The simple linear elastic-perfectly plastic constitutive law predicted unrealistic soil behavior and unreliable effects on adjacent structures. The result of numerical analyses performed with soil models that include isotropic hardening with stress and strain stiffness dependency compared well with measurements

Compression and Creep of Venice Lagoon Sands

A laboratory test program was conducted to evaluate the one-dimensional (1D) compression and creep properties of intact sand (and silty-sand) samples from a deep borehole at the Malamocco Inlet to the Venice Lagoon. The tests were performed with a constant rate of strain consolidometer and included special procedures for trimming the frozen samples and measuring strains during thawing and backpressure saturation. The specimens had variable fine fractions ranging from 6 to 21% and mica contents ranging from 1 to 10%. The results confirmed that there is a strong correlation between the creep rate coefficient and the compressibility index and between the swelling index and mica content. The compression behavior in all tests is well described by a nonlinear compression model with a unique limiting compression curve and a variable transition parameter that reflects the fines and mica content. Creep tests performed at different confining pressures are also well represented by a simple two-parameter model