


Forthcoming Seminars at F1
Tuesday 11 Dec 2018 11:15  Lucas Hackl (MPQ Garching)  Low energy spectra from variational tangent planes 

Variational methods are extensively used to study properties of ground states and low excited states. By focusing on a suitable submanifold of states, we can overcome the exponential growth of the Hilbert space with the system size. In this talk, I will introduce a geometric framework to approximate the low lying energy spectrum by studying the linearized Hamiltonian flow on the tangent plane at the ground state. The spectrum is then given by the eigenvalues of the covariant derivative on the variational manifold. Using the paradigmatic BoseHubbard model as an example, I will discuss advantages compared to methods based on directly diagonalizing the Hamiltonian restricted to the tangent plane.
Seminar room for physics (JSI main building) 
Seminars Archive
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 16 Dec 2008 15:00  Tilen Cadez  Vpliv sklopitve DzyaloshinskiiMoriya na kvantno
prepletenost dveh elektronov 

Seminarska soba odsekov za fiziko (106)
Predstavil bom kvantno prepletenost v sistemu dveh kubitov. Za
cista stanja je merilo prepletenosti podano kot von Neumannova
entropija poljubnega od obeh kubitov v paru, definicija
prepletenosti mesanih stanj pa vkljucuje
ekstremizacije. Analiticno resitev ponudi uporaba Woottersove formule.
Kot primer, bom predstavil sipanje in
prepletenost dveh letecih kubitov na linearni, homogeni verigi atomov. 
9 Dec 2008 15:00  Rudi Podgornik  Van der Waalsove interakcije med ogljikovimi nanocevkami 

Seminarska soba odsekov za fiziko (106)
V predavanju bom predstavil osnove Lifsiceve teorije van der Waalsovih interakcij
in pokazal, kako se jo da uporabiti v kontekstu ogljikovih nanocevk. Izpeljal bom
osnovne enacbe za interakcijsko energijo dveh nanocevk v vakuumu. Ker je dovisna
od dielektricnega odziva pri imaginarnih frekvencah, je tega potrebno najprej
izracunati z razlicnimi ab initio metodami. Predstavil bom
dielektricne spektre
za razlicne vrste nanocevk in pa lastnosti interakcije med nanocevkami, ki so
bistveno odvisne od lastnosti dielektricnega spektra. 
4 Dec 2008 12:00  Liliana Velasco Sevilla  Interplay between flavor symmetries and cosmology 

In the tea room of F1 department. more... 
26 Nov 2008 12:00  Gregor Bregar  Ekperimenti DAMA in CDMS 

In the tea room of F1 department. more... 
25 Nov 2008 15:00  dr. Daniel Harries  From molecular to granular selfassembly driven by crowding and depletion interactions 

In physics seminar room (106) 
20 Nov 2008 12:00  Jure Zupan  2komponentna temna snov in rezultati Pamele 

In the tea room of F1 department. more... 
13 Nov 2008 12:00  Mitja Rosina  Pogovor o WIMPih 

In the tea room of F1 department. more... 
11 Nov 2008 15:00  Elzbieta Zipper, Institute of Physics, Katowice, Pland  Entanglement of distant non interacting qubits by swapping 

Physics seminar room (106)
Scalable quantum networks require the capability to create, store and
distribute entanglement among distant nodes (atoms, trapped ions,
charge and spin qubits built on quantum dots, etc.) by means of
photonic channels. We show how the entanglement between qubits and
electromagnetic field modes allows generation of entangled states of
remotely located qubits. The presented scheme is able to drive an
initially separable state of two qubits into an highly entangled state
suitable for quantum information processing. 
10 Nov 2008 13:00  Jason de Rouchey, N. Institutes of Health, Bethesda, Maryland  Thermodynamic forces measurements to understand condensation and
specific ion effects on polycationDNA complexes 

Physics seminar room (106)
DNA in vivo is principally found in a highly condensed state within
chromosomes, viruses, and bacterial nucleoids often packaged via
multivalent cations. Despite the critical role that the condensed DNA
in chromosomes plays on gene expression and DNA replication within
eukaryotic cells, the dominant molecular forces which drive this
condensation are not fully understood. In recent years, new theories
have been proposed to explain DNADNA attractive forces which lead to
condensation but experimental data capable of distinguishing between
these theories has been sorely lacking. We have used osmotic stress
coupled with smallangle Xray scattering (SAXS) to probe the
magnitude and dependence of the thermodynamic forces between condensed
DNA helices.\\\\
This talk will be divided between two topics. In the first part, I
will discuss force measurements on condensed DNA arrays in the
presence of cations ranging from simple ions to complex real
proteins. Using homologous polycations, we have measured the effects
on the intermolecular DNADNA repulsions and attractions with length
(i.e. charge). For a given chemistry, we observe a common repulsion
and increasing attraction with length reaching a limiting value at
~610 repeats. Interestingly, this limit seems to be known in
naturally occurring peptides that interact with nucleic acids and
utilize similarly sized repeat motifs such as the arginine rich
repeats commonly found in protamines used for DNA packaging in
spermatids. Comparisons with force measurements of protamine shows
important differences from pure arginine polymers, however, and I will
discuss recent experiments utilizing short artificial peptides
designed to better understand the role of uncharged amino acids on
DNADNA forces. The second part of the talk will focus on specific ion
effects on protamineDNA condensates. The addition of simple mono or
divalent salt to polycationDNA complexes induces swelling of the
equilibrium spacing between DNA molecules. The sensitivity of
equilibrium spacings of protamineDNA complexes to the particular
anion species of the added salt, however, indicates that salt is not
operating through a simple screening or overcharging mechanism to
weaken attraction, but rather through anion binding to protamine to
lower the net protein charge. I will discuss several experiments
designed to quantify and better understand these specific ion
differences as well as quantitate anion binding within the
protamineDNA array. 
6 Nov 2008 12:00  Kerim Suruliz (ICTP)  Top Physics at ATLAS 

In the tea room of F1 department.
With millions of top quark pairs produced per year at nominal luminosity, the LHC will be a true \'top factory\'. In this talk I will review the prospects for top quark physics at the ATLAS experiment, focussing on the measurement of the top pair production crosssection. more... 
4 Nov 2008 15:00  Mojca Cepic  Diskretni model in banane


Seminarska soba odsekov za fiziko (106)
Diskretno fenomenolosko modeliranje, ki uposteva
plastovito strukturo smektikov, se je izkazalo za zelo uspesno pri
razlagi antiferoelektricnih tekocih kristalov in mnozice faz
ter faznih zaporedij v njih.
Ali je mogoce enak pristop uporabiti tudi za opisovanje bolj
kompleksnih molekul, kot so banane? Banane so akiralne polarne
molekule z upognjeno sredico. Njih oblika z mnogo domisljije
spominja na banano in to jim je dalo popularno ime. Izkaze se, da
je opis smekticnih faz z diskretnim pristopom v bananah prav tako
ucinkovit in lahko razlozi faze, fazne prehode med njimi in njih
makroskopske lastnosti, ter napoveduje nove pojave. Ker fenomenolosko modeliranje izhaja iz naivne slike intermolekularnih interakcij
med molekulami v plasti in med plastmi, ponuja tudi mnogo namigov za
sintezo novih materialov.

23 Oct 2008 12:00  Bojan Golli, Mitja Rosina, Simon Sirca  Problemi iz delavnice na Bledu septembra 2008 

In the tea room of F1 department. more... 
21 Oct 2008 15:00  prof. Janez Bonca  Optical and spectral properties of the tJ Holstein model 

Location: Physics seminar room (106)
We develop an efficient numerical method for the description of a singlehole
motion in the antiferromagnetic background. The method is free of finitesize
effects and allows calculation of physical properties at an arbitrary wavevector.
Methodical increase of the functional space leads to results that are valid in
the thermodynamic limit. In the case of the $t$$J$ model we found good agreement
with cumulant expansion, exact diagonalization approaches on finite lattices as
well as selfconsistent Born approximations. The method allows a straightforward
addition of other inelastic degrees of freedom, such as lattice effects. Our
results for spectral functions as well as quasiparticle weight of the
$t$$J$Holstein model are in agreement with diagrammatic Monte Carlo method.
Calculated spectral functions in the strong coupling limit reproduce
well the waterfall structure seen in ARPES spectra on
Ca$_{2x}$Na$_x$CuO$_2$Cl$_2$.
We also compute the charge stiffness and optical conductivity of the tJ Holstein
model. Coherent hole motion is most strongly influenced by the
electronphonon coupling within the physically relevant regime of the exchange
interaction. Optical conductivity in the crossover to the strong coupling regime
shows a twopeak structure. The lowfrequency peak represents the excitation of
the first string state, while the higherfrequency peak corresponds to the mid
infrared band, broadened and renormalized by phonon excitations. Results are in
agreement with recent optical measurements.
We furthermore extend the existing method to computation of the bipolaron. We
discuss the shape of the magnetic bipolaron and the condition for the formation of
the bound state. 
7 Oct 2008 15:00  P. Ziherl  A simple view of cell aggregates 

Location: Physics seminar room (106)
Many biological cells materialize the intertwinement of form and function
very transparently, and the shape of simplest cells is determined by their
lipid membrane. The morphology of these cells can be captured by membrane
elasticity and if this model is extended by intermembrane attraction, it
can be used for theoretical studies of cell aggregates. We show that it is
the elasticity that is responsible for the stability of anisotropic
aggregates present in amoebae and humans alike. We review recent results
related to sedimentation of blood, geometry of epithelial tissues,
embryogenesis, and structure of cell organelles. 
15 Jul 2008 12:00  Altug Ozpineci (Middle East Technical University, Ankara)  Magnetic Moments and Pion Couplings of Xi_Q Baryons in Light Cone QCD Sum Rules 

In the tea room of F1 department.
more... 
14 Jul 2008 15:00  Vladimir Hinkov, MaxPlanckInstitut, FKF, Stuttgart, Germany  Exotic magnetic phases as a reason for Fermisurface reconstruction in
underdoped cuprates 

After twenty years of intense experimental and
theoretical activity, the understanding of the physics of underdoped
cuprates remains one of the challenges of condensed matter
research. An important question arises, when antiferromagnetism (AF)
is destroyed by charge doping of the CuO$_2$ layers: Are concepts like a
Fermi surface (FS) and welldefined quasi particles applicable, and do
they form an adequate basis to deal with strong correlations imposing
competition effects between superconductivity (SC) and the various
proposed exotic phases?
In connection with the recently observed quantum oscillations, the
investigation of such phases has been revived. Some of these phases
break timereversal symmetry like the orbital currents, while others
break symmetries of the crystal lattice. Furthermore, incommensurate
spinmodulated phases such as spin spirals have been proposed.
YBa$_2$Cu$_3$O$_{6+x}$ is suited for the investigation of phases
breaking the C4 symmetry. Here we will report a systematic,
dopingdependent investigation of the spinexcitation spectrum and
show evidence for the occurrence of states which break the C4
symmetry, while keeping the translational symmetry of the lattice
preserved. Such states of matter have been previously postulated by
Kivelson, who termed them electronic liquid crystals.
Finally, we will discuss how our findings can be invoked to support
the occurrence of a Fermisurface reconstruction due to an additional
periodic structure superposed with the periodicity of the crystal
structure. A reconstructed Fermi surface, in turn, can explain the
occurrence of Fermi pockets in YBa$_2$Cu$_3$O$_{6.5}$.
Location: Seminarska soba odsekov za fiziko (106)

10 Jul 2008 14:00  Vikram Soni  Darwin, diversity and stability in an evolutionary network 

In the tea room of F1 department.
more... 
3 Jun 2008 15:00  Peter Horsch, MaxPlanckInstitut fur Festkorperforschung  Charge dynamics and magnetism of 1D Wigner lattices 

Location: Physics seminar room (106)
Doped edgesharing CuO chains are ideal realizations of 1D Wigner
lattices (WL). Such chains are found in the recently synthesized
Na_3Cu_2O_4 and Na_8Cu_5O_10 systems. As a result of
the geometrical structure the kinetic energy is small compared to the
Coulomb interaction as required for WL formation. The optical
conductivity, the charge dynamics and the single particle spectral
function are studied by exact diagonalization and to some extent also
analytically. At quarterfilling these spectra show clear signatures
of charge fractionalization into pairs of domain walls. Finally
results for the magnetic phase diagram at quarterfilling are
presented, that are obtained by density matrix renormalization group
(DMRG) calculations and analytical considerations. 
27 May 2008 15:00  Anna Gorczyca, University of
Silesia, Katowice, Poland  Friedel oscillations in the presence of transport currents in nanowires 

Location: Physics seminar room (106)
Recent theoretical analysis of the Friedel oscillations in nanosystems has
been carried out for zero or vanishingly small bias voltage V. The most
of these investigations concerned the electron correlations which, as has
been shown, suppress the decay of oscillations.
In this paper we neglect the electronelectron interaction. Instead, we
focus on the nonequilibrium case that occurs for finite V.
We investigate a nanowire that is connected to two macroscopic particle
reservoirs with different Fermi energies.
Since this difference increases with V,
the meaning of the Fermi momentum, k_F, becomes ambiguous.
Therefore, the well known 2k_Fx spatial dependence of the density
oscillations (that holds also in the presence of correlations)
may be modified for V \\neq 0. We show that the
wavevector of the oscillations decreases monotonically with bias voltage
and vanishes when V is equal to the band width. In our analysis we
include also the influence of the asymmetry of the coupling between the
nanowire and the electrodes, as well as a linear potential drop in the
nanowire. 
13 May 2008 15:00  Igor Vilfan  Power and Limitations of the DensityFunctional Theory 

In physics seminar room (106)
The densityfunctional theory (DFT) is a powerful abinito method,
widely used in condensedmatter physics and also in chemistry.
I will discuss the results of DFT simulations of ultrathin Pb
layers, MoSI based nanowires, and novel superconductors based on, e.g.,
SmOFeP. In case of Pb layers quantumsize effects on the charge and Hall
conductivity were predicted and compared with experiments. In MoSI
the DFT helped us to determine the nanowire structure, mechanical and
electronic properties. In the case of recently observed superconductors
I will discuss their magnetic properties, as predicted by the DFT. 
12 May 2008 12:00  Veljko Dmitrasinovic (Vinca, Beograd)  Lowlying states in the Ystring threequark potential 

In the tea room of F1 department.
We study the masses of various threequark SU(6)
multiplets in the N=0,1,2 shells, confined by the
Ystring threequark potential. The exact Ystring
potential consists of one, socalled threestring
term, and three angledependent twostring terms. Due
to the technical complexity of the exact Ystring
potential we treat the problem at four levels of
increasingly accurate approximation: 1) the
areadependent part of the threestring potential in
the first order perturbation approximation; 2) the
(approximate) threestring potential expanded up to
the first power in hyperspherical angles; 3) the
(approximate) threestring potential to all orders in
power expansion in hyperspherical harmonics, without
taking into account the transition(s) to twostring
potentials; 4) the exact minimallength string
potential to all orders in power expansion in
hyperspherical harmonics, while taking into account
the transition(s) to twostring potentials. more... 
8 May 2008 12:00  Francesco Caravaglios  Universita` di Milano 

In the tea room of F1 department.
The hierarchy problem in grand unified theory suggests two possible extensions of ordinary quantum field theory. One extension is achieved adding non linear terms to the Schroedinger functional equation that describes ordinary quantum field theory. This extension violates the linear superimposition principle of quantum mechanics. We will make a comment on the safety of collider physics in the context of this theory. A more predictive and conservative extension of quantum field theory is achieved through third quantization. In this extension, the origin of fermion families is understood. We will discuss some interesting predictions in flavour physics and neutrino phenomenology.
more... 
24 Apr 2008 12:00  Stefan Antusch (MPI, Munich)  Leptogenesis and the Flavour Structure of the Seesaw 

In the tea room of F1 department. more... 
17 Apr 2008 16:00  George Giavaras Department of Physics, Lancaster University  Graphene Quantum Dots 

Location: Physics seminar room (106)
Monolayer graphene has attracted attention because its charge carriers behave as massless relativistic particles.
In this talk I will consider a cylindrically symmetric graphene quantum dot in a perpendicular magnetic field.
I will demonstrate that a confinementdeconfinement transition can take place depending on the form of
the vector and electrostatic potentials. In particular, the transition is related to the relativistic Klein effect
and can be probed in a realistic dot structure by varying the magnetic field. I will also discuss the transition
in bilayer graphene.

17 Apr 2008 12:00  Umit Oktay Yilmaz  Model Independent Analysis of Rare Bc → Ds l+ l Decay Beyond the Standard Model 

In the tea room of F1 department.
The rare Bc → Ds l+ l decay is investigated by using the most general model independent effective Hamiltonian. The general expressions of longitudinal, normal and transversal polarization asymmetries for l and l+ and the combined asymmetries of them are found. The dependencies of the branching ratios and polarizations on the new Wilson coefficients are presented. The analysis shows that the branching ratios and the lepton polarization asymmetries are very sensitive to the scalar and tensor type interactions. These results will be very useful in searching new physics beyond the standard model.
more... 
15 Apr 2008 14:00  Damir Bećirević (LPT Universite ParisSud, Orsay)  Lifetimes of Beauty Hadrons : QCD corrections 

In the tea room of F1 department.
I discuss the current status of the theoretical control over the lifetime ratios of beauty mesons. I will explain how the OPE works in this case, review the perturbative QCD corrections and the nonperturbative ones. In particular I will show in what way the recent work with S.Fajfer and J.F.Kamenik [arXiv:0804.1750] is helpful in controlling the nonperturbative QCD effects. more... 
10 Apr 2008 15:00  Takami Tohyama, Yukawa Institute for Theoretical Physics, Japan  Effect of electronphonon interaction on optical properties
in onedimensional Mott insulators 

In physics seminar room (106) 
9 Apr 2008 11:00  Jelena Zivkovic, Radboud University, Nijmegen  Force Spectroscopy on PRERev Complex in HIV 

Force spectroscopy has become a powerful tool to characterize specific binding between species of molecules. Both binding partners are usually attached by flexible linkers, such as PEG to the probe and the surface, respectively. Force is then applied to unbind the two species and the events during unbinding are measured. These events, nevertheless depend on a number of not fully controllable parameters, such as precise geometry in the course of unbinding. This leads to the observation of different types of force curves and appropriate routines have to be implemented to categorize and analyze them.
Our research is focused on better understanding of RNAprotein complexes. As a model system for this interaction we use RRERev system of HIV.
TEA ROOM of F! Department

7 Apr 2008 12:00  Jernej Fesel Kamenik  Constraining minimal flavor violation 

In the tea room of F1 department. more... 
7 Apr 2008 11:00  Vyatcheslav Priezzhev  Comparison of two random sequences 

A classic alignment problem is the search
of the longest common subsequence (LCS) in two random sequences.
A simpler, yet nontrivial, variant of the LCS problem is the
Bernoulli matching model. Considering this model by the Bethe
ansatz method, we prove that the length of the LCS is asymptotically
identical to the TracyWidom distribution of the largest eigenvalue
of a random matrix with entries drawn from Gaussian unitary ensemble.
TEA ROOM of F1 Department 
3 Apr 2008 12:00  Yasaman Farzan (IPM Teheran, Iran)  Leptonic Unitarity Triangle and CPviolation 

In the tea room of F1 department.
Similarly to the CKM matrix in the quark sector, the mixing matrix in the lepton sector can contain a CPviolating phae that can show up in the neutrino oscillation. Measuring this CPviolating phase is one of the main challenges of the neutrino physics. Inspired by the unitarity triangle method in the quark sector, we introduce reconstrucing the unitarity triangle in the lepton sector as an alternative method to extract the CP violating phase of the neutrino mixing matrix. more... 
1 Apr 2008 15:00  Rasa Pirc  Physics of relaxor ferroelectrics 

Location: Seminar Room Physics (106)
Abstract: Relaxor ferroelectrics are compositionally disordered polar systems,
which are characterized by a broad temperature maximum in the static
dielectric constant and by strong frequency dispersion of the complex
dielectric permittivity; however, no spontaneous long range order is
present at any temperature. It has been suggested that the properties
of relaxors are closely related to the appearance of polar nanoregions
(PNRs) at temperatures well above the dielectric maximum. A
theoretical model of relaxors based on the interacting PNR picture
will be presented and its predictions will be discussed.

20 Mar 2008 12:00  Matej Pavšič  Izjemno preprosta teorija vsega (Članek Garretta Lisija o poenotenju na osnovi E8) 

In the tea room of F1 department. more... 
18 Mar 2008 15:00  Matej Kanduc  Electrostatic interactions in highly charged soft matter 

Location: Seminar Room Physics (106)
Abstract: Soft matter materials, such as membranes, proteins, polymers and DNA, are often electrically charged. This makes them water soluble, which is of great importance in technological applications and a prerequisite for biological functions.
In all these systems salt plays a crucial role, and some of the important features can already be obtained on the PoissonBoltzmann level. But this traditional meanfield approach fails as soon as materials are highly charged or surrounding ions are multivalent. In recent years mounting evidence from experiments and numerical simulations showed that likecharged bodies can attract each other. Such counterintuitive effects indicate strong electrostatic coupling between likecharged particles, which essentially results from electrostatic correlations among ions residing near surfaces.
In this seminar, I will present attraction mechanism and the structure of counterionic correlations in the cases of charged membranes and DNA molecules. 
11 Mar 2008 15:00  Osor S. Barisic (Institute of Physics, Zagreb)  Lowfrequency properties of Holstein polarons 

Location: seminarska soba odsekov za fiziko (106)
Recent years have witnessed a constant growth of attention for
polaronrelated physics. In particular, the polaronic effects have been
reported in a number of experiments on systems ranging from colossal
magnetoresistive manganites to highTc superconductors. In this context, a
better understanding of the polaron states is of particular importance.
The interpretation of lowfrequency polaronic correlations is given in
terms of three dichotomies in the polaron dynamics: adiabatic vs.
nonadiabatic, local vs. translational, and continuous vs. discrete.
According to these distinctions, a complete phase diagram for the 1D
Holstein polaron is proposed. A suitable description of the crossovers
between wellknown regimes; from classical to quantum, from weak coupling
to strong coupling, from adiabatic to nonadiabatic, from itinerant to
selftrapped, and from large to small polarons, is obtained in this way.
In addition to the phase diagram, the diagrammatic content of the DMFT for
the Holstein polaron problem is analyzed. It is shown that the vertex
corrections neglected by the DMFT are important in low dimensions for the
description of the adiabatic polaronic correlations spreading over
multiple lattice sites. By investigating the phonon spectra, qualitatively
different behaviors of the deformation field on the lattice are obtained
in the lowfrequency range. 
6 Mar 2008 12:00  Jan O. Eeg  Short and long distance strong interaction effects in B → D π decays 

In the tea room of F1 department. more... 
4 Mar 2008 15:00  prof. Tomaz Prosen  Third quantization: a general method to solve master equations for quadratic open Fermi systems 

Location: Seminar Room Physics (106)
Abstract: The Lindblad master equation for an arbitrary quadratic system of n
fermions is solved explicitly in terms of diagonalization of a 4n times
4n matrix, provided that all Lindblad bath operators are linear in the
fermionic variables. The method is applied to the explicit construction
of nonequilibrium steady states and the calculation of asymptotic
relaxation rates in the far from equilibrium problem of heat and spin
transport in a nearest neighbor Heisenberg XY spin 1/2 chain in a
transverse magnetic field. 
28 Feb 2008 12:00  Miha Nemevšek  Lepton flavour violation in a SU(5) inspired model 

In the tea room of F1 department. more... 
26 Feb 2008 15:00  Franziska Matthaeus  Noiseinduced powerlaw behaviour in chemotactic motion of E.coli 

Location: Seminar Room Physics (106)
Abstract:
We study with numerical simulations the motion of bacteria E.coli in an
environment with food gradients. The bacteria move towards positive food
gradients by means of several flagellar motors whose direction of rotation
is determined by the outcome of a set of chemical reactions inside the
cell. We show that the efficiency of swimming towards food depends on the
protein concentrations inside the cells, more precisely, the classical
diffusion with exponential runlength distribution turns into motion with
powerlaw distribution of the runlengths, usually called Levy flights in
the literature, upon adding noise to one of the protein concentrations. We
discuss under which conditions Levy flights are observed and in what kind
of environment this is advantageous for the bacterial population.

22 Feb 2008 11:00  Dejan Stokic (COSY, Medical University of Vienna)  Reverse engineering of gene networks 

Location: Tea room F1
Abstract:
Reverse engineering of gene regulatory networks presents one of the
greatest challenges in system biology today. Gene regulatory networks
are most usually inferred with a set of single gene overexpressions
and/or knockout experiments. The functional relationships between genes
are being retrieved either out of the steady state gene expressions or
out of the time series. We present a novel algorithm for gene network
reconstructing and we compare its performance with the NIR algorithm
(Gardner,T.S. et.al, Science, 301, 102 (2003) ), both on E.Coli
experimental data and in silico experiments. We show improvements in the
number of correctly reconstructed links, computational time and
robustness on both noise and experimental errors. We further improve the
applicability of reverse engineering, by enlarging the number of genes
and links which can simultaneously be reconstructed. more... 
21 Feb 2008 12:00  Saša Prelovšek  Uspehi in težave pri simulacijah lahkih skalarnih mezonov na mreži 

V čajni sobi F1.
Narava lahkih skalarnih mezonov še danes ni povsem znana. Povzela bom rezultate različnih simulacij skalarnih mezonov na mreži. Poudarila bom tudi težave zaradi katerih simulacije še danes niso dale dokončnega odgovora za mase skalarnih mezonov. more... 
21 Feb 2008 11:30  Peter F. Stadler, Institut für Bioinformatik Universität Leipzig  Structure of Discrete Energy Landscapes and Folding of Biopolymers 

Research of Peter Stadler more... 
14 Feb 2008 12:00  Emile Grgin (New York)  An approach to the structural unification of quantum mechanics and relativity 

In the tea room of F1 department.
The unification of quantum mechanics and relativity into a single mathematical structure has been a
vexing problem for the last eighty years. By its nature, the unification problem is a problem in physics,
but a less ambitious attitude consists in viewing it as a purely mathematical problem. This is the subject
of the present talk.
The idea consists in finding the simplest generalization of nonrelativistic quantum mechanics (in
Schrodinger’s picture) without asking whether this generalization is physically justified or not. If a
structural unification of relativity and quantum mechanics does exist at an experimentally accessible
scale (meaning down to 10‐18 m) the hope is that it might be compatible with the simplest possible
generalization of nonrelativistic quantum mechanics. The problem thus reduces to finding the simplest
generalization in question.
Work on this project began in the late sixties in collaboration with Aage Petersen at Yeshiva University in
New York. After some initial results, our work had to be interrupted. A new breakthrough was needed to
continue. This happened some ten years ago.
The idea consists in generalizing Schrodinger’s quantum mechanics by extending the field of complex
numbers over which Hilbert space is built to a much richer algebra – named the algebra of quantions.
The mathematical unification takes place without effort because the new number system (the
quantions) is inherently relativistic.
The main results obtained so far are the fundamental differential equations of physics: Schrodinger’s
and Dirac’s equations. Thus, while these equations are postulated in standard physics, they are
theorems in the quantionic approach.
The objective of the lecture is to indicate the mathematical steps that lead to these results. Clearly, the
proofs must be omitted, as they are far from trivial. They are however available in great detail in two
books on the subject.
more... 
12 Feb 2008 15:00  Marija Mitrovic (SCL, Institute of Physics, Belgrade)  Network of networks: modeling modularity of realworld 

Networks with a modular (or community) structure arise in social and biological sciences. The respective subgraph structure of complex networks is strongly connected with dynamical processes in network. Search for subgraphs
is of great importance in understanding dynamics of complex networks. Here we represent model of multiscale networks and demonstrate how maximum likelihood method works on networks with well defined modular structure. We then
implement the generalization of algorithm to multigraphs and show its efficiency in finding weighted subgraphs. We also analyze spectral density of adjacency matrix which can be tightly connected to multiscale structure of the network. 
5 Feb 2008 15:00  Jelena Grujic (SCL, Institute of Physics, Belgrade)  Esocial networks: Movies recommendations 

Seminarska soba odsekov za fiziko (106)
Rapidly evolving electronic technology has fundamentally changed the world that we live in. Email, chats, web portals, etc. gave us huge amount of informations needed for investigating social structures, but also gave new dimension to social interactions we are investigating. Here we explore social structures through movies watching habits, from data collected on the Internet movie data base (IMDb). We studied the customers recommendation networks based on two type of inputs, generated directly from recommendation lists on the web site and second generated through users habits. From users comments we constructed naturally emerging bipartite graph in which movies are connected through common users. Detailed analysis will be presented. more... 
4 Feb 2008 12:00  Alejandro Ibarra (DESY, Hamburg)  Gravitino Dark Matter: Signatures From Colliders and Gamma Ray Observatories 

In the tea room of F1 department.
Scenarios with gravitino dark matter face potential cosmological
problems induced by the presence of the NexttoLightest Supersymmetric
Particle (NLSP) at the time of Big Bang Nucleosynthesis (BBN). A very
simple solution to avoid all these problems consists on assuming that
Rparity is slightly violated, since in this case the NLSP decays well
before the onset of BBN. Remarkably, even if the gravitino is no longer
stable in this scenario, it still constitutes a very promising dark matter
candidate. In this talk we review the motivations for this scenario and we
present a model that naturally generates Rparity breaking parameters of
the right size to produce a consistent thermal history of the Universe,
while satisfying at the same time all the laboratory and cosmological
bounds on Rparity breaking. We also discuss possible signatures of this
scenario at gamma ray observatories and at colliders. more... 
1 Feb 2008 12:00  P. Q. Hung (University of Virginia)  Mirror fermions, electroweak scale righthanded neutrinos and experimental implications 

In the tea room of F1 department.
Abstract:
The particle content of the Standard Model is extended to include mirror fermions resulting in a model in which righthanded neutrinos obtain electroweak scale masses. It has a number of experimental implications such as a direct production of righthanded neutrinos at colliders with likesign dileptons being characteristic signatures, Lepton Flavour Violating processes mediated by mirror fermions such as mu > e gamma, tau > mu gamma, etc. more... 
24 Jan 2008 12:00  Borut Bajc  Spontana zlomitev globalne supersimetrije brez umeritvenih singletov 

In the tea room of F1 department. more... 
17 Jan 2008 12:00  Mitja Rosina  Nekaj vtisov s konference 2nd Workshop on Flavour Dynamics, Albufeira, Portugalska, 3.10. november, 2007 

In the tea room of F1 department. more... 
15 Jan 2008 15:00  Anton Ramsak  Can advances in computer performace lead to new results of old problems? 

Forty years after the publication of his law, which states that transistor density on integrated circuits doubles about every two years, Gordon Moore said recently: It can not continue forever. The nature of exponentials is that you push them out and eventually disaster happen. As an example of numerical developments in last two decades some properties of mobile holes in planar quantum antiferomagnets will be reviewed. Unexpected new findings regarding quasiparticle properties will be discussed. However, because the Moore s law is dead, it seems that for a really complete understanding entirely new approaches will be required.
V seminarski sobi odsekov za fiziko (106). VABLJENI! 
8 Jan 2008 15:00  Andrej Kosmrlj  Model of T cell development in thymus 

T cell precursors, thymocytes, develop in the thymus where they are trained by many endogenous (self) peptides. Developed T cells are very specific to antigenic (nonself) peptides  only small fraction react to particular antigenic peptide. On the other hand experiments show that T cells trained by only one type of peptides are very promiscuous  a lot of T cells react to every antigenic peptide. I will propose simple sequence based model of thymic selection and compare properties of developed T cells with experimental results.
V seminarski sobi odsekov za fiziko (106).
Vabljeni! 




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