Events Archive

Jul
09
2013
Nanoconfined DNA: From model system to tool in biological analysis
DNA coils undergo  striking conformational transitions when it is confined to volumes with dimensions smaller than one of the characteristic lengths of the molecule.  We are particularly interested in confinement to channels less than two persistence length wide, and hundreds of microns long.  In these channels, DNA extends to 50 % of its contour length and more, thus establishing a clear connection between location and the linear "genetic address" expressed in base pairs. We can fabricate nanochannel systems with arbitrary configurations in two dimensions using fused silica, and thus are...
Jun
25
2013
Development of novel magnetic tweezers technologies: Applications to biomaterials characterization
Characterization of the mechanical properties of cells, as well as the tissues and extracellular matrices (ECM) in which they reside, requires microscale manipulation platforms that allow precise measurement of their local rheology. To achieve this, my laboratory has developed a suite of NdFeB-based magnetic tweezers devices optimized for biomaterials characterization. In this talk, I will present the design and construction of three new microscope-mounted magnetic tweezers devices that allow controlled forces to be applied locally to networks, cells, and tissues while their deformation is...
May
24
2013
Adhesion at Heterogeneous Surfaces: From Fundamental Colloidal Interactions Manipulation of Proteins and Cells
Textbooks on colloidal phenomena teach us to describe the electrostatic and dispersion interactions at interfaces using single parameters (Hamaker constants, surface potentials or charge densities), an approach which treats surface as uniform. Real surfaces, be they mineral, polymeric, or biological, present heterogeneous surface chemistry that complicates their interactions.  It is recognized that clustered rather than uniform presentation of attractive chemistries, for instance peptide sequences, enhances biological interactions.  Likewise, heterogeneity in charge and acid-base...
May
07
2013
On the relation between Graphene and non-Abelian Quantization
We will present a simple non-relativistic model to describe the low energy excitations of graphene. Our model is based on a deformation of the Heisen-berg algebra in such a way that the commutator of momenta is proportional to the pseudo-spin. We solve the Landau problem for the resulting Hamil-tonian, which reduces in the large mass limit, while keeping constant the Fermi velocity, to the usual linear one employed to describe these excitationsas massless Dirac fermions. Extending this model to negative mass we re-produce the leading mass term in the low energy expansion of...
Apr
30
2013
Soft Matter Physics and Bacteria
One of the long term challenges in human health and disease is the control of pathogens, such as antibiotic-resistant forms of bacteria. In this talk, we will briefly describe two directions where soft condensed matter physics based approaches have been useful.
Apr
29
2013
Anomalous Electron Spin Decoherence in an Optically Pumped Quantum Dot
Recently, there is revived interest in non-equilibrium dynamics of the nuclear spins partially due to the decoherence issue of the electron spin qubit in semiconductor quantum dots for quantum computation. In this talk, I will first introduce a microscopic theory for the non-equilibrium nuclear spin dynamics controlled by a closed feedback loop mediated by the electron and/or the hole under continuous wave pumping in a quantum dot [W. Yang and L. J. Sham, Phy. Rev. B 85, 235319(2012)], and then present a study on the nuclear-spin-fluctuation induced spin decoherence of an electron (SDE) in an optically pumped quantum dot....
Apr
25
2013
Astrophysics and particle physics with cosmic-ray electrons and positrons
Cosmic rays are predominantly nuclei, in particular protons.  However, the less abundant cosmic-ray electrons and positrons are also important probes of open questions in astrophysics and particle physics.  The Fermi Gamma Ray Space Telescope, designed to study the high-energy universe with gamma rays, is also an excellent electron and positron detector.  Ground-based imaging atmospheric Cherenkov telescopes have also measured cosmic-ray electrons and positrons up to several TeV.  PAMELA, Fermi, and AMS have discovered a surprising excess of positrons between 10 GeV and 350 GeV.  I will describe these measurements and their...
Apr
25
2013
Experiments with Atoms in Optical Lattices
Atoms in optical lattices are very versatile experimental systems. They can be used to study many-body quantum physics, to aid precision measurements and tests of fundamental symmetries, and for quantum computation. I will describe ongoing efforts along these lines in my research group.
Apr
24
2013
Optimizing Undulatory Swimming
Most organisms live in aqueous environments and propel themselves by swimming. A large subclass is micro-organisms that have slender rod-like shapes, e.g. sperm. These organisms propel themselves using undulations that follow certain waveforms depending on the type of desired...
Apr
23
2013
Membranes, Interfaces, and the Interplay Between Curvature and Tension
Nature and technology abound with fluid interfaces such as the surfaces of oil droplets in water or the membrane surfaces of living cells.  These interfaces are typically crowded with adsorbed particles, proteins or other large molecules, which are effectively confined to a two-dimensional fluid.  This two-dimensional system, though, has a twist: it can spontaneously change its curvature and thereby substantially alter the interactions among the bound particles or proteins. ...

Pages