Forthcoming Seminars at F-1

Seminars Archive

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16 Dec 2008
15:00
Tilen CadezVpliv sklopitve Dzyaloshinskii-Moriya 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 SevillaInterplay between flavor symmetries and cosmology
In the tea room of F1 department. more...

26 Nov 2008
12:00
Gregor BregarEkperimenti DAMA in CDMS
In the tea room of F-1 department. more...

25 Nov 2008
15:00
dr. Daniel HarriesFrom molecular to granular self-assembly driven by crowding and depletion interactions
In physics seminar room (106)

20 Nov 2008
12:00
Jure Zupan2-komponentna temna snov in rezultati Pamele
In the tea room of F1 department. more...

13 Nov 2008
12:00
Mitja RosinaPogovor o WIMP-ih
In the tea room of F-1 department. more...

11 Nov 2008
15:00
Elzbieta Zipper, Institute of Physics, Katowice, PlandEntanglement 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, MarylandThermodynamic forces measurements to understand condensation and specific ion effects on polycation-DNA 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 DNA-DNA 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 small-angle X-ray 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 DNA-DNA 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 ~6-10 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 DNA-DNA forces. The second part of the talk will focus on specific ion effects on protamine-DNA condensates. The addition of simple mono- or divalent salt to polycation-DNA complexes induces swelling of the equilibrium spacing between DNA molecules. The sensitivity of equilibrium spacings of protamine-DNA complexes to the particular anion species of the added salt, however, indicates that salt is not operating through a simple screening or over-charging 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 protamine-DNA array.

6 Nov 2008
12:00
Kerim Suruliz (ICTP)Top Physics at ATLAS
In the tea room of F-1 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 cross-section. more...

4 Nov 2008
15:00
Mojca CepicDiskretni 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 SircaProblemi iz delavnice na Bledu septembra 2008
In the tea room of F-1 department. more...

21 Oct 2008
15:00
prof. Janez BoncaOptical and spectral properties of the t-J Holstein model
Location: Physics seminar room (106)
We develop an efficient numerical method for the description of a single-hole motion in the antiferromagnetic background. The method is free of finite-size 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 self-consistent 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$_{2-x}$Na$_x$CuO$_2$Cl$_2$. We also compute the charge stiffness and optical conductivity of the t-J Holstein model. Coherent hole motion is most strongly influenced by the electron-phonon coupling within the physically relevant regime of the exchange interaction. Optical conductivity in the crossover to the strong coupling regime shows a two-peak structure. The low-frequency peak represents the excitation of the first string state, while the higher-frequency 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. ZiherlA 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 F-1 department. more...

14 Jul 2008
15:00
Vladimir Hinkov, Max-Planck-Institut, FKF, Stuttgart, GermanyExotic magnetic phases as a reason for Fermi-surface 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 well-defined 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 time-reversal symmetry like the orbital currents, while others break symmetries of the crystal lattice. Furthermore, incommensurate spin-modulated 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, doping-dependent investigation of the spin-excitation 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 Fermi-surface 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 SoniDarwin, diversity and stability in an evolutionary network
In the tea room of F-1 department.

more...

3 Jun 2008
15:00
Peter Horsch, Max-Planck-Institut fur FestkorperforschungCharge dynamics and magnetism of 1D Wigner lattices
Location: Physics seminar room (106)
Doped edge-sharing Cu-O 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 quarter-filling these spectra show clear signatures of charge fractionalization into pairs of domain walls. Finally results for the magnetic phase diagram at quarter-filling 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, PolandFriedel 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 electron--electron 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 wave--vector 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 VilfanPower and Limitations of the Density-Functional Theory
In physics seminar room (106)

The density-functional theory (DFT) is a powerful ab-inito method, widely used in condensed-matter physics and also in chemistry.
I will discuss the results of DFT simulations of ultrathin Pb layers, Mo-S-I based nanowires, and novel superconductors based on, e.g., SmOFeP. In case of Pb layers quantum-size effects on the charge and Hall conductivity were predicted and compared with experiments. In Mo-S-I 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)Low-lying states in the Y-string three-quark potential
In the tea room of F-1 department.

We study the masses of various three-quark SU(6) multiplets in the N=0,1,2 shells, confined by the Y-string three-quark potential. The exact Y-string potential consists of one, so-called three-string term, and three angle-dependent two-string terms. Due to the technical complexity of the exact Y-string potential we treat the problem at four levels of increasingly accurate approximation: 1) the area-dependent part of the three-string potential in the first order perturbation approximation; 2) the (approximate) three-string potential expanded up to the first power in hyper-spherical angles; 3) the (approximate) three-string potential to all orders in power expansion in hyper-spherical harmonics, without taking into account the transition(s) to two-string potentials; 4) the exact minimal-length string potential to all orders in power expansion in hyper-spherical harmonics, while taking into account the transition(s) to two-string potentials. more...

8 May 2008
12:00
Francesco CaravagliosUniversita` di Milano
In the tea room of F-1 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 F-1 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 confinement-deconfinement 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 YilmazModel Independent Analysis of Rare Bc → Ds l+ l- Decay Beyond the Standard Model
In the tea room of F-1 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 Paris-Sud, Orsay)Lifetimes of Beauty Hadrons : QCD corrections
In the tea room of F-1 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 non-perturbative 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 non-perturbative QCD effects. more...

10 Apr 2008
15:00
Takami Tohyama, Yukawa Institute for Theoretical Physics, JapanEffect of electron-phonon interaction on optical properties in one-dimensional Mott insulators
In physics seminar room (106)

9 Apr 2008
11:00
Jelena Zivkovic, Radboud University, NijmegenForce Spectroscopy on PRE-Rev 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 RNA-protein complexes. As a model system for this interaction we use RRE-Rev system of HIV.
TEA ROOM of F! Department

7 Apr 2008
12:00
Jernej Fesel KamenikConstraining minimal flavor violation
In the tea room of F-1 department. more...

7 Apr 2008
11:00
Vyatcheslav PriezzhevComparison 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 Tracy-Widom 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 CP-violation
In the tea room of F-1 department.

Similarly to the CKM matrix in the quark sector, the mixing matrix in the lepton sector can contain a CP-violating phae that can show up in the neutrino oscillation. Measuring this CP-violating 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 PircPhysics 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 PavšičIzjemno preprosta teorija vsega (Članek Garretta Lisija o poenotenju na osnovi E8)
In the tea room of F-1 department. more...

18 Mar 2008
15:00
Matej KanducElectrostatic 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 Poisson-Boltzmann level. But this traditional mean-field 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 like-charged bodies can attract each other. Such counter-intuitive effects indicate strong electrostatic coupling between like-charged 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)Low-frequency properties of Holstein polarons
Location: seminarska soba odsekov za fiziko (106)
Recent years have witnessed a constant growth of attention for polaron-related physics. In particular, the polaronic effects have been reported in a number of experiments on systems ranging from colossal magnetoresistive manganites to high-Tc superconductors. In this context, a better understanding of the polaron states is of particular importance. The interpretation of low-frequency 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 well-known regimes; from classical to quantum, from weak coupling to strong coupling, from adiabatic to nonadiabatic, from itinerant to self-trapped, 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 low-frequency range.

6 Mar 2008
12:00
Jan O. EegShort and long distance strong interaction effects in B → D π decays
In the tea room of F-1 department. more...

4 Mar 2008
15:00
prof. Tomaz ProsenThird 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 non-equilibrium 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 NemevšekLepton flavour violation in a SU(5) inspired model
In the tea room of F-1 department. more...

26 Feb 2008
15:00
Franziska MatthaeusNoise-induced power-law 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 run-length distribution turns into motion with power-law distribution of the run-lengths, 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 PrelovšekUspehi in težave pri simulacijah lahkih skalarnih mezonov na mreži
V čajni sobi F-1.

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 LeipzigStructure 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 F-1 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 real-world
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 multi-scale networks and demonstrate how maximum likelihood method works on networks with well defined modular structure. We then implement the generalization of algorithm to multi-graphs and show its efficiency in finding weighted subgraphs. We also analyze spectral density of adjacency matrix which can be tightly connected to multi-scale structure of the network.

5 Feb 2008
15:00
Jelena Grujic (SCL, Institute of Physics, Belgrade)E-social networks: Movies recommendations
Seminarska soba odsekov za fiziko (106)
Rapidly evolving electronic technology has fundamentally changed the world that we live in. E-mail, 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 F-1 department.

Scenarios with gravitino dark matter face potential cosmological problems induced by the presence of the Next-to-Lightest Supersymmetric Particle (NLSP) at the time of Big Bang Nucleosynthesis (BBN). A very simple solution to avoid all these problems consists on assuming that R-parity 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 R-parity 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 R-parity 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 right-handed neutrinos and experimental implications
In the tea room of F-1 department. Abstract: The particle content of the Standard Model is extended to include mirror fermions resulting in a model in which right-handed neutrinos obtain electroweak scale masses. It has a number of experimental implications such as a direct production of right-handed neutrinos at colliders with like-sign 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 BajcSpontana zlomitev globalne supersimetrije brez umeritvenih singletov
In the tea room of F-1 department. more...

17 Jan 2008
12:00
Mitja RosinaNekaj vtisov s konference 2nd Workshop on Flavour Dynamics, Albufeira, Portugalska, 3.-10. november, 2007
In the tea room of F-1 department. more...

15 Jan 2008
15:00
Anton RamsakCan 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 KosmrljModel 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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12 Dec, 2017 Abroad:
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12 Dec, 2017 Abroad:
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