Microwavephysics and Atmospheric Physics
Biomedizinische Photonik
Ultrafast Science and Technology
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Last update: 18.10.2017
HS 2011: Seminare über Ultrafast Science and Technology
Thursday 11:15am
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Donnerstag, 22.09.2011

Coherent Discrimination of Biomolecules in the Deep UV

Zeit: 10:15 Uhr
Hörsaal: B77
 
Dr. Ariana Rondi
GAP-Biophotonics
University of Geneva

The high sensitivity of fluorescence spectroscopy and the broad range of promising applications enabled by this technique are severely limited by its lack of molecular selectivity. This drawback becomes particularly evident when the identification of cellular endogenous fluorophores is of interest.

To overcome this limitation, our group demonstrated in 2009 that the fluorescence-based identification of two almost identical and highly relevant biomolecules (FMN, RBF) is possible by using the Optimal Dynamic Discrimination (ODD) technique, a two-step photo-excitation scheme implying a phase-tailored UV femtosecond pulse.

During the talk, I will present the work that I have done during my thesis. I will start by providing some general information about femtosecond pulse shaping and closed-loop optimization of molecular photo-dynamics. In particular, I will concentrate on two innovative features we have brought to this field in terms of shaping technology (reflective MEMS shaper) and optimization algorithm (multi-objective approach). I will then show how we extended the ODD technique to the deep UV. We demonstrated discrimination of two amino-acids, opening interesting perspectives for future experiments involving biomolecules of increasing complexity, namely polypeptides and proteins, eventually in a cellular environment.

 
Donnerstag, 27.10.2011

Making Research Open Access: Current situation and trends

Zeit: 10:15 Uhr
Hörsaal: B77
 
Dr. Eva Maurer
Universitätsbibliothek Bern, Zentralbibliothek
Koordination Open Access
Universität Bern

I will start the presentation with definitions, problems, and a description of the historical evolution of Open Access. Specifically, I will discuss the two viable routes, i.e. the so-called green and the golden routes, and show trends in Journal Publishing. Towards the end, I will give guidelines on what one should observe if one wants to publish scientific results to a broader community through Open Access.

 
Donnerstag, 03.11.2011

Dissecting the mechanistic bases of allosteric transduction in proteins: a coarse-grained approach

Zeit: 10:15 Uhr
Hörsaal: B77
 
Prof. Francesco Piazza
Université d'Orléans
Département de Physique
Centre de Biophysique Moléculaire
Orléans, France

Control at the molecular level is essential for the functioning of biological processes, both within molecules and between molecules. Intramolecular control often implies the effect of one ligand on the binding or catalysis of another with no direct interaction between the two effectors. To describe such interaction at a distance, often referred to also as intramolecular signaling, the adjective allosteric (from the greek "allos", other and , "stereos", hard, stiff) was coined in 1961 by Jacques Monod and Francois Jacob [1].

Although their importance is now widely recognized, the mechanistic bases of allosteric mechanisms remain rather elusive. Recent findings seem to confirm that in all proteins allosteric signals propagate through multiple, pre-existing fold-rooted pathways. Which pathways dominate depend on protein topologies, specific nature of the binding events, covalent modifications, and cellular (environmental) conditions, such as crowding effects [2]. Such picture is also confirmed by sequence-based statistical methods, suggesting that evolutionarily conserved sparse networks of amino acid interactions represent structural motifs for allosteric transduction [3,4].

In this talk I will illustrate how nonlinear effects in a coarse-grained network model of protein dynamics prove highly effectively in dissecting the relevant "hot-spot" sites and energy transduction pathways [5-9]. After reviewing the methods and the main techniques, I will survey different recent applications as well as the future challenges. Finally, I will show how our techniques allow to shed light on the result of recent NMR measurements reporting previously unknown collective motions spanning four beta-strands separated by up to 15 Angstroem in ubiquitin [10].

REFERENCES

[1] J. Monod and F. Jacob. Teleonomic mechanisms in cellular metabolism, growth, and differentiation. Cold Spring Harb. Symp. Quant. Biol., 26, 389–401 (1961).
[2] A. del Sol, C. J. Tsai, B. Y. Ma, and R. Nussinov. The origin of allosteric functional modulation: Multiple pre- existing pathways. Structure, 17(8), 1042–1050 (2009).
[3] S. W. Lockless and R. Ranganathan. Evolutionarily conserved pathways of energetic connectivity in protein families. Science, 286(5438), 295–299, 10 (1999).
[4] Gurol M. Suel, Steve W. Lockless, Mark A. Wall, and Rama Ranganathan. Evolutionarily conserved networks of residues mediate allosteric communication in proteins. Nat Struct Mol Biol, 10(1), 59–69, 01 (2003).
[5] B. Juanico, Y.-H. Sanejouand, F. Piazza, and P. De Los Rios. Discrete breathers in nonlinear network models of proteins. Phys. Rev. Lett., 99, 238104 (2007).
[6] F. Piazza and Y.-H. Sanejouand. Discrete breathers in protein structures. Phys. Biol, 5,026001 (2008).
[7] F. Piazza and Y.-H. Sanejouand. Long-range energy transfer in proteins. Physical Biology, 6, 046014 (2009).
[8] F. Piazza and Y.-H. Sanejouand. Energy transfer in nonlinear network models of proteins. Europhysics Letters, 88, 68001 (2009).
[9] F. Piazza and Y.-H. Sanejouand. Breather-mediated energy transfer in proteins, Discrete and Continuous Dynamical Systems, Series S 4, 1247–1266 (2010).
[10] R. B. Fenwick, S. Esteban-Martin, B. Richter, D. Lee, K. F. A. Walter, D. Milovanovic, S. Becker, N. A. Lakomek, C. Griesinger and X. Salvatella, Journal of the American Chemical Society 133, 10336–10339 (2011).

 
Donnerstag, 10.11.2011

Advanced Nonlinear Optics with Lithium Niobate Crystals

Zeit: 10:15 Uhr
Hörsaal: B77
 
Prof. Dr. Karsten Buse
Fraunhofer Institute of Physical Measurement Techniques, Freiburg,
and
Institute of Microsystem Technology (IMTEK), University Freiburg, Germany

Lithium niobate is a wide-band-gap crystalline dielectric material with large second-order nonlinear-optical coefficients. The ability to structure lithium niobate on the micro- and nanometer scale has led to a boost of the interest in this material. The talk will review novel developments where lithium niobate gratings, waveguides, and resonators are employed. This involves, e.g., holographic gratings, ridge waveguides, and whispering-gallery-mode cavities. Linear and nonlinear diffraction, slowing down of light, sum-frequency mixing for making quantum detectors in the infrared, generation of terahertz waves and very-high-efficiency second-harmonic generation became possible because of the remarkable properties of lithium niobate crystals.

 
Donnerstag, 24.11.2011

Carbon nanotubes: Synthesis, Characterization and Integration

Zeit: 10:15 Uhr
Hörsaal: B77
 
Dr. Salvatore Bagiante
Laboratory for Micro- and Nanotechnology
PSI, Villigen

Since the 1950s, the semiconductor industry has been able to improve the performance of electronic systems for more than four decades by making ever smaller devices. However, this approach will soon encounter both scientific and technical limits, which is why the industry is exploring a number of alternative device technologies. In this context, particular emphasis has been placed on research of carbon materials. Carbon nanotubes (CNTs) and graphene have been among the most promising candidate for the next generation electronics.

The first part of this work is focused on the study of CNTs synthesis by one of the techniques that allow high yield/cost ratio: arc discharge in liquid nitrogen. This method still needs to be fully understood in order to achieve a good control of the produced nanomaterials and their properties by the use of suitable experimental parameters. We report a morphological study of the Carbon deposit produced and study the effect of the size of electrodes, applied voltage and discharge current on the formation of Multi Wall CNTs and hybrid structure (linear carbon chains (LCCs) and CNTs).

The second aspect that has been considered in this work is the use of Single Wall CNTs for the fabrication of new and innovative devices. The unconventional approach considered here is the use of ultra-clean nanotubes, grown by chemical vapor deposition in the very last fabrication step, after all the device structure has already been completed. We report a description of the fabrication process of an optoelectronic device based on ultra-clean carbon nanotubes. After that, we present the preliminary results obtained by electrical and optical characterization. Optical measurements, realized by means of the Scanning photocurrent microscopy (SPCM) technique, permit to investigate the spatial variations of the potential along the suspended nanotubes for different gates voltages under laser excitation without altering its characteristics. In our case, SPCM allow us to observe how a precise doping spatial control in the nanotube can be achieved in this kind of device.

-G. Buchs, S. Bagiante et al., Journal of Applied Physics in press (2011).
-Scuderi, S. Bagiante et al., CARBON 47, 2112–2142 (2009).
-S. Scalese, S. Bagiante et al., Journal of applied physics, 107, 014304 (2010)
-S. Bagiante, S. Scalese et al., Physics Status Solid B 247, No. 4, 884–887 (2010).

 
Donnerstag, 01.12.2011

Entwicklung einer Steuer- und Messsoftware für Nahfeld-THz-Mikroskopie (Präsentation der Bachelorarbeit)

Zeit: 10:15 Uhr
Hörsaal: B77
 
Michael Hostettler
Institute of Applied Physics
University of Bern

 
Donnerstag, 08.12.2011

Ultrafast Photonic Quantum Technologies: Photon Sources and Detectors

Zeit: 10:15 Uhr
Hörsaal: B77
 
Dr. Brian J. Smith
University Lecturer and Tutorial Fellow
Department of Physics and Keble College
University of Oxford

Quantum physics holds promise to enhance the performance of certain tasks beyond what is possible with only classical resources. These quantum-enhanced technologies, such as quantum computing, cryptography, and metrology, utilize nonclassical behavior of quantum systems to surpass the performance of their classical analogues. In both the classical and quantum domains, light is central to communications and sensing applications. Here I will discuss recent progress in the preparation of broadband quantum states of light, e.g. heralded single photons and squeezed states, as well as approaches to detecting such nonclassical states using photon-counting and homodyne detection.

 
Donnerstag, 15.12.2011

DNA as a framework for the assembly of aromatic chromophores: on the application for light harvesting systems

Zeit: 10:15 Uhr
Hörsaal: B77
 
Florian Garo
Häner group
Department of Chemistry and Biochemistry
University of Bern

DNA is increasingly used as a scaffold for the construction of multi-chromophore arrays since ordered ensembles possess different properties than the monomeric units. During the last few years the use of non-nucleosidic polyaromatic building blocks was shown to form extended interstrand-stacked arrays in DNA double strands. This approach allowed the construction of stable and well-defined Pi-stacks with intrinsic properties. These specific properties rendered the Pi-stacks an interesting and versatile tool for the use in different fields. Recently the combination of phenanthrene and pyrene building blocks showed a potential application as light harvesting antennas.

 
Dienstag, 20.12.2011

Automated two-dimensional pulse shaping and spectroscopy (Promotionsvortrag)

Zeit: 10:15 Uhr
Hörsaal: B5
 
Franziska Frei
Institute of Applied Physics
University of Bern