Next week's seminars

[Cond.Matt. & Stat.Mech.Section]

INFORMAL SEMINAR on   Statistical Physics
 

 Monday, 14 March    -    11:00 a.m.

 

SISSA, Santorio Building, Room 129 (1st Floor)

 

Alexei M. TSVELIK    ( Brookhaven National Laboratory, Upton )

  

"A field theory for fermionic ladder   with generic intrachain interactions"



Abstract

An effective low energy field theory is developed for a system of two chains.  The main novelty of the approach is that it allows to treat generic intrachain repulsive interactions of arbitrary strength.   The chains are coupled by a direct tunneling and four-fermion  interactions.  At low energies the individual chains are described as   Luttinger liquids with an arbitrary ratio of spin $v_s$ and charge $v_c$ velocities.  A judicious choice of the basis for the decoupled chains greatly  simplifies the description and allows one to separate high and low energy degrees of freedom.  In a direct analogy to the bulk cuprates the resulting effective field theory distinguishes  between three qualitatively different regimes: (i) small doping ($v_c << v_s$), (ii) optimal doping ($v_s \approx v_c$) and (iii) large doping ($v_s << v_c$). I discuss the excitation spectrum and derive expressions for the electron spectral function which turns out to be highly incoherent. The degree of incoherence increases when one considers an array of ladders (stripe phase).


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JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR

 

Tuesday, 15 March   -   11:30 hrs.

 

Luigi Stasi Seminar Room, ICTP Leonardo Building - 1st floor



 Michele CASELLE    ( Universita' di Torino )



"Statistical methods in gene regulation"

 

Abstract



Gene regulation is one of the most interesting open problems in modern molecular biology.  In this talk I will discuss in particular a class of regulatory motifs known as "mixed feed forward loops (mFFLs)".  These motifs seem to be under positive selection in the human regulatory network, thus suggesting that they should play some important functional role.  Moreover, in human, several of the genes involved in these mFFLs are known to be oncogenes (i.e. genes related to cancer progression).  Our proposal is that these mFFLs are used by the cell to keep under  control the stochastic fluctuations in the amount of proteins expressed by the target genes and that for this reason their disregulation plays such an important role in cancer progression.  The talk will be divided in two parts.  The first will be devoted to a short pedagogical introduction to the organization of Eukaryotic genomes and to the mechanisms of gene regulation.  Then in the second part I will discuss, using both stochastic equations and bioinformatic tools the role played by mFFLs in the regulatory network.