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

All Things Retarded: Radiation-Reaction in Worldline Quantum Field Theory

We exhibit an initial-value formulation of the worldline quantum field theory (WQFT) approach to the classical two-body problem in general relativity. We show that the Schwinger-Keldysh (in-in) formalism leads to purely retarded propagators in the evaluation of observables in the WQFT. Integration technology for retarded master integrals is introduced at third post-Minkowskian (3PM) order. As an application we compute the complete radiation-reacted impulse and radiated four momentum for the scattering of two non-spinning neutron stars including tidal effects at 3PM order, as well as the leading (2PM) far-field gravitational waveform. <br

Single-nucleotide polymorphisms: analysis by mass spectrometry

Matrix-assisted laser desorption-ionization (MALDI) mass spectrometry has evolved as a powerful method for analyzing nucleic acids. Here we provide protocols for genotyping single-nucleotide polymorphisms (SNPs) by MALDI based on PCR and primer extension to generate allele-specific products. Furthermore, we present three different approaches for sample preparation of primer-extension products before MALDI analysis and discuss their potential areas of application. The first approach, the 'GOOD' assay, is a purification-free procedure that uses DNA-modification chemistry, including alkylation of phosphorothioate linkages in the extension primers. The other two approaches use either solid-phase extraction or microarray purification for the purification of primer-extension products. Depending on the reaction steps of the various approaches, the protocols take about 6–8 hours

Solar sail formation flying for deep-space remote sensing

In this paper we consider how 'near' term solar sails can be used in formation above the ecliptic plane to provide platforms for accurate and continuous remote sensing of the polar regions of the Earth. The dynamics of the solar sail elliptical restricted three-body problem (ERTBP) are exploited for formation flying by identifying a family of periodic orbits above the ecliptic plane. Moreover, we find a family of 1 year periodic orbits where each orbit corresponds to a unique solar sail orientation using a numerical continuation method. It is found through a number of example numerical simulations that this family of orbits can be used for solar sail formation flying. Furthermore, it is illustrated numerically that Solar Sails can provide stable formation keeping platforms that are robust to injection errors. In addition practical trajectories that pass close to the Earth and wind onto these periodic orbits above the ecliptic are identified

Unraveling the molecular basis of subunit specificity in P pilus assembly by mass spectrometry

P pili are multisubunit fibers essential for the attachment of uropathogenic Escherichia coli to the kidney. These fibers are formed by the noncovalent assembly of six different homologous subunit types in an array that is strictly defined in terms of both the number and order of each subunit type. Assembly occurs through a mechanism termed “donor-strand exchange (DSE)” in which an N-terminal extension (Nte) of one subunit donates a β-strand to an adjacent subunit, completing its Ig fold. Despite structural determination of the different subunits, the mechanism determining specificity of subunit ordering in pilus assembly remained unclear. Here, we have used noncovalent mass spectrometry to monitor DSE between all 30 possible pairs of P pilus subunits and their Ntes. We demonstrate a striking correlation between the natural order of subunits in pili and their ability to undergo DSE in vitro. The results reveal insights into the molecular mechanism by which subunit ordering during the assembly of this complex is achieved

Developing collaborative partnerships with culturally and linguistically diverse families during the IEP process

Family participation in the special education process has been federally mandated for 40 years, and educators recognize that effective collaboration with their students’ families leads to improved academic and social outcomes for students. However, while some family-school relationships are positive and collaborative, many are not, particularly for culturally and linguistically diverse (CLD) families. This article provides practice guidelines based in research for teachers who seek to improve their practices when working with CLD families who have children served by special education

Entanglement in bipartite quantum systems: Euclidean volume ratios and detectability by Bell inequalities

Euclidean volume ratios between quantum states with positive partial transpose and all quantum states in bipartite systems are investigated. These ratios allow a quantitative exploration of the typicality of entanglement and of its detectability by Bell inequalities. For this purpose a new numerical approach is developed. It is based on the Peres-Horodecki criterion, on a characterization of the convex set of quantum states by inequalities resulting from Newton identities and from Descartes' rule of signs, and on a numerical approach involving the multiphase Monte Carlo method and the hit-and-run algorithm. This approach confirms not only recent analytical and numerical results on two-qubit, qubit--qutrit, and qubit--four-level qudit states but also allows for a numerically reliable numerical treatment of so far unexplored qutrit--qutrit states. Based on this numerical approach with the help of the Clauser-Horne-Shimony-Holt inequality and the Collins-Gisin inequality the degree of detectability of entanglement is investigated for two-qubit quantum states. It is investigated quantitatively to which extent a combined test of both Bell inequalities can increase the detectability of entanglement beyond what is achievable by each of these inequalities separately.Comment: 29 pages, 4 figure

Measurement of the electron electric dipole moment using YbF molecules

The most sensitive measurements of the electron electric dipole moment d_e have previously been made using heavy atoms. Heavy polar molecules offer a greater sensitivity to d_e because the interaction energy to be measured is typically 10^3 times larger than in a heavy atom. We report the first measurement of this kind, for which we have used the molecule YbF. Together, the large interaction energy and the strong tensor polarizability of the molecule make our experiment essentially free of the systematic errors that currently limit d_e measurements in atoms. Our first result d_e = (- 0.2 \pm 3.2) x 10^-26 e.cm is less sensitive than the best atom measurement, but is limited only by counting statistics and demonstrates the power of the method.Comment: 4 pages, 4 figures. v2. Minor corrections and clarifications made in response to referee comment