# Upcoming Seminars

# Upcoming Seminars

__Fall 2015 Seminars__

__Fall 2015 Seminars__

All Physics Seminars are held in S-3-126 at 1pm on Thursday, unless otherwise noted.

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**Tuesday, Sep 8, 1:00pm**

**(UNUSUAL DAY)**

**Philip Fairman
CSIRO Manufacturing, Australia **

__TBA __

TBA

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**Thursday, Sep 17, 1:00pm**

**Alexey Tonyshkin
UMass Boston **

__Traveling-Wave MRI at Ultra-High Magnetic Fields __

In conventional magnetic resonance imaging (MRI) near-field RF coils are used as the only excitation method to obtain images of subjects in clinical and research environments. At high-field strength (exceeding 4Tesla), the propagation wave vector of the excitation field can no longer be ignored as the wavelength becomes comparable than the imaging volume, particularly if the medium dielectric constant is large. As ultra-high field MRI scanners are becoming widely available, it is essential to study the associated far-field effects and develop more efficient methods of spin excitation for MRI. In my talk, I show our latest developments in ultra-high field imaging based on a specially designed traveling-wave transmission system that allows RF wave propagation at ultra-high field NMR systems (7 T, 16.4 T, 21 T). The main implications of our research efforts include a gain in the size of the imaging field of view, as well as a possibility for the robust manipulation of the rf field profile.

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**Thursday, Sep 24, 1:00pm**

**Ilya Dodin
Princeton Plasma Physics Laboratory, Princeton University **

__Quantumlike physics in classical plasmas __

Dynamics of classical plasmas is essentially determined by collective oscillations, or waves, mediated by long-range electromagnetic (EM) interactions. The standard approach to studying these waves is to use Maxwell's equations for EM fields. But plasma waves are more than just EM fields; they can be viewed as dynamical objects with distinct properties that allow for an axiomatic variational theory. Using nothing but the definition of a classical wave, this theory leads to the identification of the wave most natural characteristic, the (classically normalized) "photon state function", and the corresponding quantumlike Lagrangian of a wave, or "photon", in a general dispersive medium.

Establishing the general quantitative analogy between the dynamics of classical dispersive waves and particles significantly simplifies calculations of many EM effects in plasmas and suggests new ways of manipulating plasma waves. Some examples will be presented, which include calculations of the wave canonical and kinetic energy-momenta, ponderomotive (dipole) forces on photons and their impact on the dispersion of the ambient medium, nonlinear autoresonant acceleration of classical waves, and extensions of geometrical optics. In particular, it will be shown that linear nondissipative EM waves can be viewed as generalized Dirac particles; hence they experience polarization-driven bending of ray trajectories and polarization dynamics that can be interpreted as the precession of the wave "spin". The same theory also yields, as a spinoff, a fully Lagrangian point-particle model of the actual Dirac electron. The well known Bargmann-Michel-Telegdi theory is hence naturally restated in a conservative variational form, and a relativistic ponderomotive Hamiltonian of the Dirac electron (with spin effects included) is derived.

http://www.princeton.edu/~idodin/

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**Thursday, Oct 1, 1:00pm**

**Peter Weichman
BAE Systems **

__TBA __

TBA

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**Thursday, Oct 8, 1:00pm**

**Rosemary Smith
U Maine **

__TBA __

TBA

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**Thursday, Oct 15, 1:00pm**

**Kabir Ramola
Brandeis U **

__Spatial Extent of Branching Brownian Motion __

One dimensional Branching Brownian Motion begins with a single particle at the origin and at each subsequent time step particles either diffuse, split into two (with a rate b), or die (with a rate d). Depending on the relative rates of birth and death, the process is either explosive (b > d), critical (b = d), or eventually dies (b < d). We investigate the joint statistics of the rightmost and leftmost visited sites by such a process (Xmax and -Xmin respectively) up to a time t. This is an interesting instance of extreme value statistics of correlated random variables. In the b > d regime Xmax and Xmin increase with a finite velocity and eventually become uncorrelated. In the b <= d regimes the individual and joint distributions of Xmax and Xmin become stationary at large times. We derive exact results for this stationary joint distribution and use it to construct the stationary distribution of the spatial extent s = Xmax - Xmin. This distribution has a non-trivial power law tail ~1/s^3 for large s in the critical case and is exponential for b < d. Our exact results demonstrate that the correlations between Xmax and Xmin persist even in the stationary state. These results have possible applications to the spread of epidemics in animal populations.

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**Thursday, Oct 22, 1:00pm**

**Andrzej Herczyński
Boston College **

__Pollockian Mechanics: Painting with Viscous Jets __

Beginning around 1945, American Abstract Expressionist painter Jackson Pollock invented and perfected a new artistic technique based on pouring and dripping liquid pigment onto a canvas stretched horizontally on the floor. Long recognized as important and influential by art historians, Pollock's works have also been studied as complex webs. But although the artist manipulated gravitational flows to achieve his aims, the fluid dynamical aspects of his process remained largely unexplored. I will discuss Pollockian Mechanics—the physics of lifting paint by viscous adhesion and dispensing it in free jets—focusing on the role of fluid instability. This technique will be contrasted with flows of pigment employed by other artists. I will conclude with comments on the scaling regularities of the poured patterns and their affinity to the "geometry of nature."

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**Thursday, Oct 29, 1:00pm**

**Udayan Mohanty
Boston College **

__Fluctuations of ions in ion atmosphere modulate RNA dynamics __

TBA

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**Thursday, Nov 5, 1:00pm**

**Ksenia Bravaya
Boston U **

__TBA __

TBA

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**Thursday, Nov 12, 1:00pm**

**TBA
TBA **

__TBA __

TBA

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**Thursday, Nov 19, 1:00pm**

**TBA
TBA **

__TBA __

TBA

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**Thursday, Nov 26, 1:00pm**

**N0 SEMINAR
THANKSGIVING **

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**Thursday, Dec 3, 1:00pm**

**TBA
TBA **

__TBA __

TBA

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**Thursday, Dec 10, 1:00pm**

**TBA
TBA **

__TBA __

TBA

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