לוח שנה משולב

We present a model, that while simple to define, shows rich behavior
that accounts for a variety of physical phenomena, such as
localization of phonons, anomalous diffusion, and slow relaxations in
glassy systems. The 'crux of the matter' lies in the fact that the
rate of many processes in nature is exponential in the relevant
distance: quantum tunneling is a common example. If we think about a
particle diffusing in a random environment, its dynamics will be
described by a matrix A where the i,j'th element is
exponential in the distance between points i and j. This leads us
naturally to the model of exponential random matrices, which is a
novel ensemble of random matrices, with interesting properties. We
solve the model exactly, and discuss the implications on the various
physical problems.

We compute N=4 Super Yang Mills planar amplitudes at strong coupling by considering minimal surfaces in AdS5 space. The surfaces end on a null polygonal contour at the boundary of AdS. We show how to compute the area of the surfaces as a function of the conformal cross ratios characterizing the polygon at the boundary. We reduce the problem to a simple set of functional equations for the cross ratios as functions of the spectral parameter. These equations have the form of Thermodynamic Bethe Ansatz equations. The area is the free energy of the TBA system. We consider any number of gluons and in any kinematic configuration.

Technicolor is a mechanism for electroweak symmetry breaking,
> alternative to the elementary Higgs field. A gauge theory
> (technicolor sector) is coupled to the electroweak sector, and
> electroweak symmetry breaking is induced by techni-chiral
> symmetry breaking. While a rescaled version of QCD was excluded
> as technicolor model several years ago, theoretical developments
> in the last years have shown that gauge theories close to the
> conformal window are possible good candidates.
> SU(2) with two Dirac fermions in the adjoint representation is
> one of these candidates. Understanding whether this theory is
> confining or IR-conformal is a challenging problem, which can
> be addressed by means of numerical simulations. I will present
> the most recent spectrum measurements, both in the mesonic and
> gluonic sectors close to the chiral limit. I will discuss what
> are the signatures of conformality we are looking for, and how
> the available data are consistent with those signatures.

Although much work in the field of reinforcement learning has been devoted to understanding how animals and humans learn to perform the best action in each state of affairs, strikingly scant work targets the question of what constitutes such a state. In initial phases of learning, an animal or a person cannot know which facets of its rich experience should be attended to in order to identify their ‘state’. In a number of projects, we use tasks in which several different attributes can potentially be important for procuring rewards (odors, spatial location, previous actions), and specifically investigate the behavioral and neural processes underlying learning of which is the relevant state. This talk will focus on parameter coding by hippocampal primary neurons.
The hippocampus serves an important role in learning and memory. In humans, it is associated with declarative episodic memory. Single unit recordings of hippocampal neurons in freely behaving rats have shown that many of them act as place-cells, confining their firing to well-defined locations in space. We recorded the activity of hippocampal primary neurons in a specially devised olfactory space, in which rats foraged for reward based solely on olfactory cues and studied the dependence of the activity of these neurons on their availability. We show that place cells shifted their firing fields from room coordinates to olfactory coordinates as animals learned to rely on them in order to obtain reward.
The use of olfactory cues provides the additional benefit of careful control over the sensory inputs provided to the animals. Classical studies on hippocampal place-cells show that when the environment is visually altered, these hippocampal neurons 'remap', in a seemingly random manner. Although studies have been conducted to investigate the contribution of various visual aspects to the activity of place cells, the exact correlation of hippocampal cell firing to the visual input to the rats cannot be studied in freely behaving rats, because their field of view is unknown. By repeating the sequence of olfactory stimuli provided in the maze in a new environment, we study the relation between the neuronal responses of single neurons to given sensory stimuli in distinct spatial contexts. Preliminary results suggesting that the mapping of hippocampal neurons is not random, but critically depends on the sequence in which the different items are encountered, in support of the relational representation theory of hippocampal function.

Physical behavior of grain boundaries (i.e., interfaces between crystallites in polycrystalline
ceramics) differs from that of the bulk due to their structural deviation from the crystal interior. In
the past decade, the electrical nature of grain boundaries relative to the bulk has attracted
considerable attention as “size effects” on the conductivity have become one of the main foci of
research interest, particularly in the field of “nanoionics”. Reducing the size of the crystallites
enhances the geometric contribution of the grain boundaries to the total volume of the
polycrystalline ceramic such that the overall electrical properties may be governed by the
property associated with the grain boundaries when the grain size is sufficiently small. Solid
electrolytes (SEs) are virtually pure ionic conductors that serve as a key component in
electrochemical devices such as solid oxide fuel cells (SOFCs). The SEs currently being
employed present sufficiently high ionic conductivity only at very high temperatures, leading to
the high operating temperature (>800 °C) of the SOFCs. It is desirable to lower the operating
temperature down to the intermediate temperature (IT) range (500–700 °C or even less) to
ameliorate the problems associated with high-temperature operation, such as long-term durability
of the cells and cost. Lower-temperature operation, on the other hand, requires enhanced
conductance in the SEs. Nanocrystalline SEs have been the centre of attention for over a decade
owing to their potential for use in the IT-SOFCs. Such expectation stems from a hypothesis that
the grain boundaries may serve as highly conductive paths (short-circuit), leading to enhanced
overall conductivity of a material with a higher density of grain boundaries. However, it has been
realized that the grain boundaries in the SEs often impede the ion transport inherently, serving as
electrically blocking layers (open-circuit). In this presentation, electrical nature of the grain
boundaries in the SEs will be discussed at a fundamental level. Based upon such a understanding
of the electrical property of the grain boundaries, the concept of grain-boundary engineering in
nanoionics will also be discussed.