לוח שנה משולב

Many membrane channels and receptors exhibit adaptive, or desensitized, response to a strong sustained input stimulus. A key mechanism that underlies this response is the slow, activity-dependent removal of responding molecules to a pool which is unavailable to respond immediately to the input. This mechanism is implemented in different ways in various biological systems and has traditionally been studied separately for each. Here we highlight the common aspects of this principle, shared by many biological systems, and suggest a unifying theoretical framework. We study theoretically a class of models which describes the general mechanism and allows to distinguish its universal from system-specific features. We show that under general conditions, regardless of the details of kinetics, molecule availability encodes an averaging over past activity, and feeds back multiplicatively on the system output. The kinetics of recovery from unavailability determines the effective memory kernel inside the feedback branch, giving rise to a variety of system-specific forms of adaptive response: precise or input-dependent, exponential or power-law, as special cases of the same model.

It is believed that the aqueous hydroxide ion possesses an anomalously fast diffusion constant because of its ability to accept a proton from a neighboring water molecule, leading to translocation of the ion. We use femtosecond 2D IR spectroscopy to investigate this process through the vibrational dynamics of the OH stretching vibration in aqueous NaOD solutions. Our experiments separate the dynamics of the hydroxide from those of its first solvation shell, characterize the kinetics for proton exchange, and show signatures of the intermolecular proton transfer dynamics. The interpretation of these experiments is assisted with spectroscopic modeling based on empirical valence bond simulations of this process. Our results indicate that proton transfer depends on a hierarchy of collective hydrogen bonding rearrangements with time scales >3 ps and proceeds through a fluctuating Zundel-like transition state that lives for 120 fs.

Following a brief introduction of basic background in Information Theory,
I will describe relationships and analogies between certain models
of spin glasses, in particular - the random energy model (REM), and
the behavior of certain ensembles of (randomly chosen) codes for
communication systems. Beyond the purely theoretical aspects of
these relations, I will also demonstrate how analysis techniques, rooted
in the statistical mechanics of the REM, can be harnessed to obtain
sharper and more accurate evaluations of the ensemble performance
of these codes. If time permits, I will also point out several extensions
of the basic model.

Brownian motors, or ratchets, are devices which "rectify" Brownian motion, i.e. they can generate a current of particles out of unbiased fluctuations. We experimentally implemented a Brownian motor using cold atoms in an optical lattice. This is quite an unusual system for a Brownian motor as there is no a real thermal bath, and both the periodic potential for the atoms and the fluctuations are determined by laser fields.

With the help of such a system, we investigated experimentally the relationship between symmetry and transport in a 1D rocking ratchet, both in the periodic and in the quasiperiodic case. We then went beyond 1D rocking ratchets, demonstrating 1D gating ratchets. We also realized 2D rocking ratchets and demonstrated a rectification mechanism unique to these high-dimensional ratchets. Stabilization mechanisms associated to ac transport are also discussed.

A new physical method for preparation of metal micro- and nanospheres is based on ultrasonic cavitation of low melting point metals (