Modification of Poly(5,6-epoxy-l-norleucine) Gives Functional Polypeptides with Alternative Side-Chain Linkages.

The preparation and characterization of a new epoxide containing polypeptide, poly(5,6-epoxy-l-norleucine), via postpolymerization modification of poly(l-homoallylglycine) is described. Addition of thiols to the epoxide groups in poly(5,6-epoxy-l-norleucine) was studied as a means to prepare side-chain functional polypeptides. The solution properties of the derivatized polypeptides were studied in water and compared to similar thioether containing functional polypeptides prepared via different routes. Subtle differences in side-chain linkage chemistry were found to influence polypeptide solubility, chain conformation in solution, and thermoresponsive behavior. Poly(5,6-epoxy-l-norleucine) was found to be useful as a readily prepared intermediate that can be reacted with thiols to give a variety of functional polypeptides

GOTCHA Password Hackers!

We introduce GOTCHAs (Generating panOptic Turing Tests to Tell Computers and Humans Apart) as a way of preventing automated offline dictionary attacks against user selected passwords. A GOTCHA is a randomized puzzle generation protocol, which involves interaction between a computer and a human. Informally, a GOTCHA should satisfy two key properties: (1) The puzzles are easy for the human to solve. (2) The puzzles are hard for a computer to solve even if it has the random bits used by the computer to generate the final puzzle --- unlike a CAPTCHA. Our main theorem demonstrates that GOTCHAs can be used to mitigate the threat of offline dictionary attacks against passwords by ensuring that a password cracker must receive constant feedback from a human being while mounting an attack. Finally, we provide a candidate construction of GOTCHAs based on Inkblot images. Our construction relies on the usability assumption that users can recognize the phrases that they originally used to describe each Inkblot image --- a much weaker usability assumption than previous password systems based on Inkblots which required users to recall their phrase exactly. We conduct a user study to evaluate the usability of our GOTCHA construction. We also generate a GOTCHA challenge where we encourage artificial intelligence and security researchers to try to crack several passwords protected with our scheme.Comment: 2013 ACM Workshop on Artificial Intelligence and Security (AISec

Effect of electron-phonon interaction on the shift and attenuation of optical phonons

Using the Boltzmann equation for electrons in metals, we show that the optical phonons soften and have a dispersion due to screening in agreement with the results reported recently [M. Reizer, Phys. Rev. B {\bf 61}, 40 (2000)]. Additional phonon damping and frequency shift arise when the electron--phonon interaction is properly included.Comment: 4 pages, late

Testing Autonomous Robot Control Software Using Procedural Content Generation

We present a novel approach for reducing manual effort when testing autonomous robot control algorithms. We use procedural content generation, as developed for the film and video game industries, to create a diverse range of test situations. We execute these in the Player/Stage robot simulator and automatically rate them for their safety significance using an event-based scoring system. Situations exhibiting dangerous behaviour will score highly, and are thus flagged for the attention of a safety engineer. This process removes the time-consuming tasks of hand-crafting and monitoring situations while testing an autonomous robot control algorithm. We present a case study of the proposed approach – we generated 500 randomised situations, and our prototype tool simulated and rated them. We have analysed the three highest rated situations in depth, and this analysis revealed weaknesses in the smoothed nearness-diagram control algorithm

AlGaInN laser diode technology for GHz high-speed visible light communication through plastic optical fiber and water

AlGaInN ridge waveguide laser diodes are fabricated to achieve single-mode operation with optical powers up to 100 mW at ∼420  nm∼420  nm for visible free-space, underwater, and plastic optical fiber communication. We report high-frequency operation of AlGaInN laser diodes with data transmission up to 2.5 GHz for free-space and underwater communication and up to 1.38 GHz through 10 m of plastic optical fiber

Engineering spin squeezing in a 3D optical lattice with interacting spin-orbit-coupled fermions

One of the most important tasks in modern quantum science is to coherently control and entangle many-body systems, and to subsequently use these systems to realize powerful quantum technologies such as quantum-enhanced sensors. However, many-body entangled states are difficult to prepare and preserve since internal dynamics and external noise rapidly degrade any useful entanglement. Here, we introduce a protocol that counterintuitively exploits inhomogeneities, a typical source of dephasing in a many-body system, in combination with interactions to generate metrologically useful and robust many-body entangled states. Motivated by current limitations in state-of-the-art three-dimensional (3D) optical lattice clocks (OLCs) operating at quantum degeneracy, we use local interactions in a Hubbard model with spin-orbit coupling to achieve a spin-locking effect. In addition to prolonging inter-particle spin coherence, spin-locking transforms the dephasing effect of spin-orbit coupling into a collective spin-squeezing process that can be further enhanced by applying a modulated drive. Our protocol is fully compatible with state-of-the-art 3D OLC interrogation schemes and may be used to improve their sensitivity, which is currently limited by the intrinsic quantum noise of independent atoms. We demonstrate that even with realistic experimental imperfections, our protocol may generate $\sim10$--$14$ dB of spin squeezing in $\sim1$ second with $\sim10^2$--$10^4$ atoms. This capability allows OLCs to enter a new era of quantum enhanced sensing using correlated quantum states of driven non-equilibrium systems.Comment: 20 pages, 12 figure