CDP

The observed support for the idea of an expanding universe grew gradually through the first decades of last century through Slipher, Lundmark, Hubble and others. But the way towards the discovery also included a very important and to a great extent independent theoretical development through Einstein, de Sitter, Freidmann and Lemaitre. The history of the discovery with its interaction, and lack of interaction, between theoretical and empirical work, is fascinating, illustrating the sometimes capricious development of exact sciences.

Professor Nussbaumer is a well known astrophysicist, who has also written the book "Discovering the Expanding Universe", Cambridge University Press 2009, with Lydia Bieri as co-author.

Self-assembly at the nanoscale is one of the unifying features of nanoscience and nanotechnology, with numerous examples being provided by recent advances in the synthesis of self-assembled quantum dots, nanowires, and nanotubes. Although varying widely in their specific nature, a common feature of these different nanoscale structures is that their synthesis favors the formation of stable configurations not realizable for their bulk counterparts. In my talk, however, I discuss evidence of a very different kind of “naturally-formed” nanostructure, namely a localized electronic spin that may be realized in conventional semiconductor nanostructures fabricated by standard, top-down, microfabrication. The devices of interest are “quantum point contacts”, which are nanoscale constrictions formed by depositing split Schottky gates on a semiconductor substrate. Near their threshold for conduction, I discuss the formation of a self-consistent bound state in these structures, which may be occupied by just a single spin. I demonstrate an approach for electrical detection of such bound spins, and discuss the possibility that this system may ultimately be used to construct ensembles of coherently interacting spins with possible application to spintronics.

The way how proteins fold into their native three-dimensional shape, is one of the great mysteries in biology. An understanding of the laws of protein folding enables us to predict the phenotypes of living organisms, and develop cures for illnesses that are caused by misfolded proteins including Alzheimer's and Parkinson's diseases and various forms of cancer.

In this talk we describe how concepts of fundamental physics can be employed to develop a theoretical model that folds proteins into their native states in seconds with an ordinary PC. Our model provides a simple explanation for homochirality, describes all major secondary protein structures, predicts the emergence of a molten globule, and correctly computes the radius of gyration of biologically active proteins.

There are things we know, things we know we don't know, and then there are things we don't know we don't know. The later two issues can be consistently addressed in a Bayesian model comparison framework, which considerably expands the scope and power of our statistical tools.

In this talk I will first present some ideas stemming from a Bayesian approach to cosmological model building, which in the post-WMAP era of precision cosmology provides the means for answering questions such as: is dark energy evolving with time? What can we say about the primordial spectrum of density fluctuations? Is the Universe flat? Have we detected hints of new physics in the sky? I will then introduce the notion of "doubt" to quantify the degree of (dis)belief in a model given observational data in the absence of explicit alternative models. I will illustrate how a properly calibrated doubt can lead to model discovery in the absence of explicit alternatives. The outlook for the application to the current cosmological concordance model will also be discussed.

Where geometry gives us quantitative measurements: how much? how far? how large?, topology deals with geometrical properties that ignore any metric present. Thus, as it turns out, topological techniques excel at qualitative measurement: how many? how is it connected? is it homogenous? does it cover?

In recent years, this difference has been leveraged in the approach of persistent algebraic topology: algebraic topological invariants are used to measure qualitative properties of data sets with a view to how stable the invariants occur under change of granularity of measurements. We can count components, holes, tunnels and bubbles in data set with a means of measuring how relevant and noise resistant these features are.

Lately, [Morozov/de Silva/Vejdemo-Johansson] have been working on cohomology in a persistent context, and on how to generate topologically motivated circle-valued coordinate maps for data sets with cohomology. Based on this, [de Silva/Skraba/Vejdemo-Johansson] are working on applications to signals processing and to periodic dynamical systems.

In this talk, I shall sketch the general philosophy of the persistent algebraic topology approach as well as some of the results and methods we have been able to generate using our approach.

In this seminar, after an introduction on spin glasses and a brief summary of our theoretical understanding I will briefly discuss some open problems in the field. I will concentrate the attention on computer simulations. In recent years (also using specialized computers) the ability of simulating Ising spin glasses has dramatically increased and at the present moment there are large scale simulations of spin glass systems up to a 1011 Montecarlo sweep, i.e. about 0.1 second in physical time. This time scale nearly overlaps with the one accessible to experiments (1-105 seconds) and it allows to us to observe with the same methodology the system on times that differs up to 11 orders of magnitude.

Prof. Krider is known worldwide for his work on lightning and thunderstorm electricity. He lead the group that developed the first gated, wideband magnetic direction-finders that are now the basis of the U.S. National Lightning Detection Network. Prof. Krider is also a Fellow of the American Meteorological Society and a former Co-Chief Editor and Editor of the Journal of the Atmospheric Sciences. He is also past President of the International Commission on Atmospheric Electricity. Currently he teaches courses on physical meteorology at the University of Arizona.

The water oxidising enzyme of photosynthesis is largely responsible for converting solar energy into the high energy chemicals that sustian life on the planet. It is also the only known catalyst able to oxidise water at close to its thermodynamic optimum. As such it is the focus of much attention with a view to producing bio-inspired catalysts for use in energy conversion processes, such as H2 production from electrolysis or photolysis, and electricity production in fuel cells.

The group in Saclay use enzyme isolated from a themophilic species of cyanobacteria. The focus of attention is the cluster of metal ions made up of four high valence Mn ions and a Ca ion. We also design, synthetize and study chemical models that are aimed at mimicking certain features of the water oxidising enzyme. These artificial systems could be useful in solar fuel production and in fuel cells.

Transition-metal based compounds with first order magnetic phase transitions near room temperature have attracted great attention as potential magnetic refridgerants. Fe2P based compounds, such as FeMnP1-xAsx, are attractive due to low cost, good magnetocaloric properties and tunability, but their eventual application has been questioned due to presence of As.

We were able to substitute the As by Si and Ge while retaining the good magnetocaloric properties and tunability. The wide range of working temperatures (150-450K) makes these materials feasible to employ for power coversion of waste heat.

If there is sufficiently strong, attractive interaction between the electrons of a metal they will form bound pairs below a temperature To proportional to the binding energy. Such bound states will then undergo Bose-Einstein Condensation into a superconducting state at Tc < To. I will argue that, in the light of recent experiments (Doiron-Leyrad et al., Nature, 2007), this scenario provides a natural explanation for the mysterious ‘pseudo-gap’ state observed between Tc and T* in the so-called High Temperature Superconductors.

Recently optical properties of biased molecular junctions started to attract attention of researchers. Optical response (in particular Raman scattering) measurements together with the conductance of single molecule junctions promise to become a superior diagnostic tool. Theoretical understanding of optical response of biased junctions is of major importance for development of molecular optoelectronic devices. We discuss optical response of current- carrying molecular junction within a simple 2-level (HOMO-LUMO) model. Besides coupling to the contacts and molecular vibration, the model takes into account interaction with external (radiation) field and electron-hole excitations in the contacts. We use the approach to study absorption, fluorescence, and Raman spectroscopy of such junctions, as well as possibility of light and excitation induced currents.

In this talk, I will discuss Pauli spin blockade in carbon nanotube double quantum dots. Spin blockade is observed in double quantum dots when electron transitions between the dots are forbidden by spin conservation. As such, it is of considerable importance in spin-based quantum information processing schemes as a way to convert the spin degree of freedom to a much easier detectable charge state or current. We have investigated this phenomenon in carbon nanotubes in which the double dot is either formed by a defect in the nanotube or by top gates. Because of the absence of nuclear spin in the dominant carbon-12 isotope, our work opens the possibility of single-spin manipulation and read-out in a system that is not limited by hyperfine interaction. The large energy scales observed in our devices also show that basic operations, such as single-spin rotations, should be possible at a much faster rate than in other semiconductor systems.

The presentation begins with an introductory overview of climate change issues. I will concentrate on the physical principles of the greenhouse effect and touch only briefly on other issues, such as the global carbon cycle and climatic feedback effects. After the lengthy introduction, I present selected highlights from the SVECSE 2008 conference. Topics include: - Can the 11-year solar cycle be found from climate data? - What is the true value of TSI, total solar irradiance (aka solar constant)? - How well can historical variations of TSI be reconstructed, and have they affected the climate? - Do spectral irradiance variations or cosmic ray modulation affect climate? The level of the presentation is semi-popular: no expertise of solar or climate science is needed, but I expect the audience to be "scientifically literate" and have some university-level education in physics.

I will discuss how robot simulations can show how a stable semantics emerges from scratch. General principles are also presented for mathematical modelling of conceptual systems.

Interstellar beacons (radio signals designed to attract the attention of another civilization) need good detection sensitivity, strong embedded statistical evidence of technological origin, robustness to interference at the receiver, consistency with stellar scanning strategies at both transmitter and receiver, and immunity to interstellar propagation impairments, all without the possibility of explicit transmitter-receiver coordination.

We address this challenge from a modern communication theory perspective, focusing on signal acquisition and taking the perspective of a transmit signal design that presumes a specific receiver structure known to give the highest post-detection SNR and emphasizing simplicity of design consistent with compelling design criteria. This line of reasoning leads us to favor transmit signals that superficially resemble broadband white Gaussian noise, but rather than being random are based on deterministic mathematical algorithms that are presumably universally appreciated, such as number theory or finite field algebra.

In several important ways this conclusion is diametrically opposed to assumptions in past and current efforts in the radio search for extraterrestrial intelligence (SETI). In this talk, we outline the line of reasoning that leads to this conclusion, and discuss some of the strategies and resultant challenges in receiver search and acquisition. It is hoped that this talk might lead to new collaboration, particularly in the area of interstellar medium modeling. This research is being conducted in cooperation with the SETI Institute of Mountain View, California, and is supported in part by a grant from the U.S. National Aeronautics and Space Administration.

Beams have now been put into the Large Hadron Collider (LHC), and the first proton collisions are expected soon. What can be expected from the LHC in the coming months and years? The LHC is the most powerful microscope ever built to probe the inner structure of matter and the nature of the fundamental interactions, and it may also cast light on many cosmological parameters. Within the Standard Model of particle physics, the LHC's primary objective is the Higgs boson, which is thought to be responsible for the masses of the elementary particles. Beyond the Standard Model, the LHC may reveal the nature of dark matter.