Click a publication’s row for more information

### Abstract

The role of petal spurs and specialized pollinator interactions has been studied since Darwin. Aquilegia petal spurs exhibit striking size and shape diversity, correlated with specialized pollinators ranging from bees to hawkmoths in a textbook example of adaptive radiation. Despite the evolutionary significance of spur length, remarkably little is known about Aquilegia spur morphogenesis and its evolution. Using experimental measurements, both at tissue and cellular levels, combined with numerical modelling, we have investigated the relative roles of cell divisions and cell shape in determining the morphology of the Aquilegia petal spur. Contrary to decades-old hypotheses implicating a discrete meristematic zone as the driver of spur growth, we find that Aquilegia petal spurs develop via anisotropic cell expansion. Furthermore, changes in cell anisotropy account for 99 per cent of the spur-length variation in the genus, suggesting that the true evolutionary innovation underlying the rapid radiation of Aquilegia was the mechanism of tuning cell shape.

### Abstract

When matter falls past the horizon of a large black hole, the expectation from string theory is that the configuration thermalizes and the information in the probe is rather quickly scrambled away. The traditional view of a classical unique spacetime near a black hole horizon conflicts with this picture. The question then arises as to what spacetime does the probe actually see as it crosses a horizon, and how does the background geometry imprint its signature onto the thermal properties of the probe. In this work, we explore these questions through an extensive series of numerical simulations of D0 branes. We determine that the D0 branes quickly settle into an incompressible symmetric state—thermalized within a few oscillations through a process driven entirely by internal nonlinear dynamics. Surprisingly, thermal background fluctuations play no role in this mechanism. Signatures of the background fields in this thermal state arise either through fluxes, i.e. black hole hair; or if the probe expands to the size of the horizon—which we see evidence of. We determine simple scaling relations for the D0 branes’ equilibrium size, time to thermalize, lifetime, and temperature in terms of their number, initial energy, and the background fields. Our results are consistent with the conjecture that black holes are the fastest scramblers as seen by matrix theory.

#### From the Cover…

“Townsend is the best book I know for advanced undergraduate quantum mechanics. It is clear, contemporary, and compact. My students used it as a wonderful springboard to graduate school.”

—Ralph D. Amado, University of Pennsylvania

“With this second edition, Townsend has succeeded in making a clear and pedagogical textbook on undergraduate quantum mechanics even better.”

—Charles Gale, McGill University

### Abstract

The helical coiling of plant tendrils has fascinated scientists for centuries, yet the underlying mechanism remains elusive. Moreover, despite Darwin’s widely accepted interpretation of coiled tendrils as soft springs, their mechanical behavior remains unknown. Our experiments on cucumber tendrils demonstrate that tendril coiling occurs via asymmetric contraction of an internal fiber ribbon of specialized cells. Under tension, both extracted fiber ribbons and old tendrils exhibit twistless overwinding rather than unwinding, with an initially soft response followed by strong strain-stiffening at large extensions. We explain this behavior using physical models of prestrained rubber strips, geometric arguments, and mathematical models of elastic filaments. Collectively, our study illuminates the origin of tendril coiling, quantifies Darwin’s original proposal, and suggests designs for biomimetic twistless springs with tunable mechanical responses.

### Abstract

We study the primary root growth of wild-type Medicago truncatula plants in heterogeneous environments using 3D time-lapse imaging. The growth medium is a transparent hydrogel consisting of a stiff lower layer and a compliant upper layer. We find that the roots deform into a helical shape just above the gel layer interface before penetrating into the lower layer. This geometry is interpreted as a combination of growth-induced mechanical buckling modulated by the growth medium and a simultaneous twisting near the root tip. We study the helical morphology as the modulus of the upper gel layer is varied and demonstrate that the size of the deformation varies with gel stiffness as expected by a mathematical model based on the theory of buckled rods. Moreover, we show that plant-to-plant variations can be accounted for by biomechanically plausible values of the model parameters.

### Abstract

Measuring an entangled state of two particles is crucial to many quantum communication protocols. Yet Bell- state distinguishability using a finite apparatus obeying linear evolution and local measurement is theoretically limited. We extend known bounds for Bell-state distinguishability in one and two variables to the general case of entanglement in n two-state variables. We show that at most $$2^{n+1} - 1$$ classes out of $$4^{n}$$ hyper-Bell states can be distinguished with one copy of the input state. With two copies, complete distinguishability is possible. We present optimal schemes in each case.

### Abstract

In single-qubit quantum secret sharing, a secret is shared between N parties via manipulation and measurement of one qubit at a time. Each qubit is sent to all N parties in sequence; the secret is encoded in the first participant’s preparation of the qubit state and the subsequent participants’ choices of state rotation or measurement basis. We present a protocol for single-qubit quantum secret sharing using polarization entanglement of photon pairs produced in type-I spontaneous parametric downconversion. We investigate the protocol’s security against eavesdropping attack under common experimental conditions: a lossy channel for photon transmission, and imperfect preparation of the initial qubit state. A protocol which exploits entanglement between photons, rather than simply polarization correlation, is more robustly secure. We implement the entanglement-based secret-sharing protocol with 87% secret-sharing fidelity, limited by the purity of the entangled state produced by our present apparatus. We demonstrate a photon-number splitting eavesdropping attack, which achieves no success against the entanglement-based protocol while showing the predicted rate of success against a correlation-based protocol.

### Abstract

A new method of direct, rapid nano- to micro-scale patterning of high purity cobalt is presented. The method utilizes a combination of electron beam induced deposition (EBID) and seeded growth at elevated temperatures below the temperature of spontaneous thermal decomposition. Dicobalt octacarbonyl $$\mathrm{Co_{2}(CO)_{8}}$$ is used as the precursor and carbon as a seed layer. Seeded deposition is carried out in the substrate temperature range from 55 to 75°C. Deposition yield is significantly higher than conventional EBID and magnetotransport measurements indicate that resistivity, $$22~\mu\Omega~\mathrm{cm}$$, and saturation magnetization, 1.55 T, are much closer to the corresponding values for bulk Co than those for standard EBID.

### Abstract

A popular method for generating micron-sized aerosols is to submerge ultrasonic ( ω ~ MHz) piezoelectric oscillators in a water bath. The submerged oscillator atomizes the fluid, creating droplets with radii proportional to the wavelength of the standing wave at the fluid surface. Classical theory for the Faraday instability predicts a parametric instability driving a capillary wave at the subharmonic (ω/2) frequency. For many applications it is desirable to reduce the size of the droplets; however, using higher frequency oscillators becomes impractical beyond a few MHz. Observations are presented that demonstrate that smaller droplets may also be created by increasing the driving amplitude of the oscillator, and that this effect becomes more pronounced for large driving frequencies. It is shown that these observations are consistent with a transition from droplets associated with subharmonic ( ω/2) capillary waves to harmonic (ω) capillary waves induced by larger driving frequencies and amplitudes, as predicted by a stability analysis of the capillary waves.

#### From the Cover…

“Townsend has written an excellent book that someone needed to write for the modern physics textbook market. He has given it the same care that he gave to his excellent quantum mechanics book.”

—Jeff Dunham, Middlebury College

“When I read this book I immediately adopted it for my sophomore modern physics class. This is the best introduction to quantum mechanics available.”

—B. Paul Padley, Rice University

# Recent Publications

Student authorFaculty author

1. L. Mahadevan, Sharon J. Gerbode, E. M. Kramer, S. A. Hodges, and J. R. Puzey, “Evolution of spur-length diversity in Aquilegia petals is achieved solely through cell-shape anisotropy”, Proc. R. Soc. B 273:1733 (2012) 1640. Paul Riggins and Vatche Sahakian, “Black hole thermalization, D0 brane dynamics, and emergent spacetime”, Phys. Rev. D 86 (2012) 046005. John S. Townsend, A Modern Approach to Quantum Mechanics, Second Edition, University Science Books, Sausalito (2012). L. Mahadevan, J. R. Puzey, Sharon J. Gerbode, and A. G. McCormick, “How the cucumber tendril coils and overwinds”, Sci 337 (2012) 1087. J. L. Silverberg, R. N. Noar, M. Packer, M. Harrison, I. Cohen, C. Henley, and Sharon J. Gerbode, “3D Imaging and mechanical modeling of helical buckling in Medicago truncatula plant roots”, PNAS 109 (2012) 16794. N. Pisenti, Carl Philipp Emanuel Gaebler, and Theresa W. Lynn, “Distinguishability of hyperentangled Bell states by linear evolution and local projective measurement”, Phys. Rev. A 84 (2011) 022340. David Berryrieser, Peter Scherpelz, R. Resch, and Theresa W. Lynn, “Entanglement-secured single-qubit quantum secret sharing”, Phys. Rev. A 84 (2011) 032303. L. M. Belova, James C. Eckert, J. J. L. Mulders, C. Christophersen, E. D. Dahlberg, and A. Riazanova, “Rapid electron beam assisted patterning of pure cobalt at elevated temperatures via seeded growth”, Nanotechnology 22 (2011) 145305. Andrew Higginbotham, Andrew J. Bernoff, Aaron Guillen, Thomas D. Donnelly, and Nathan Jones, “Evidence of the harmonic Faraday instability in ultrasonic atomization experiments with a deep, inviscid fluid”, J. Acoust. Soc. Am. 130 (2011) 2694-2699. John S. Townsend, Quantum Physics: a Fundamental Approach to Modern Physics, University Science Books, Sausalito (2010).