1,674 research outputs found
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
Examining the Connections within the Startup Ecosystem: A Case Study of St. Louis
This paper documents the resurgence of entrepreneurial activity in St. Louis by reporting on the collaboration and local learning within the startup community. This activity is happening both between entrepreneurs and between organizations that provide support, such as mentoring and funding, to entrepreneurs. As these connections deepen, the strength of the entrepreneurial ecosystem grows. Another finding from the research is that activity-based events, where entrepreneurs have the chance to use and practice the skills needed to grow their businesses, are most useful. St. Louis provides a multitude of these activities, such as Startup Weekend, 1 Million Cups, Code Until Dawn, StartLouis, and GlobalHack. Some of these are St. Louis specific, but others have nationwide or global operations, providing important implications for other cities
Manifestation of spin-charge separation in the dynamic dielectric response of one--dimensional Sr2CuO3
We have determined the dynamical dielectric response of a one-dimensional,
correlated insulator by carrying out electron energy-loss spectroscopy on
Sr2CuO3 single crystals. The observed momentum and energy dependence of the
low-energy features, which correspond to collective transitions across the gap,
are well described by an extended one-band Hubbard model with moderate nearest
neighbor Coulomb interaction strength. An exciton-like peak appears with
increasing momentum transfer. These observations provide experimental evidence
for spin-charge separation in the relevant excitations of this compound, as
theoretically expected for the one-dimensional Hubbard model.Comment: RevTex, 4 pages+2 figures, to appear in PRL (July 13
Bias in child maltreatment self-reports using Interactive Voice Response
Few methods estimate the prevalence of child maltreatment in the general population due to concerns about socially desirable responding and mandated reporting laws. Innovative methods, such as Interactive Voice Response (IVR), may obtain better estimates that address these concerns. This study examined the utility of Interactive Voice Response (IVR) for child maltreatment behaviors by assessing differences between respondents who completed and did not complete a survey using IVR technology. A mixed-mode telephone survey was conducted in English and Spanish in 50 cities in California during 2009. Caregivers (n = 3,023) self-reported abusive and neglectful parenting behaviors for a focal child under the age of 13 using Computer-Assisted Telephone Interviewing and IVR. We used Hierarchical Generalized Linear Models to compare survey completion by caregivers nested within cities for the full sample and age-specific ranges. For demographic characteristics, caregivers born in the United States were more likely to complete the survey when controlling for covariates. Parenting stress, provision of physical needs, and provision of supervisory needs were not associated with survey completion in the full multivariate model. For caregivers of children 0 to 4 years (n = 838), those reporting they could often or always hear their child from another room had a higher likelihood of survey completion. The findings suggest IVR could prove to be useful for future surveys that aim to estimate abusive and/or neglectful parenting behaviors given the limited bias observed for demographic characteristics and problematic parenting behaviors. Further research should expand upon its utility to advance estimation rates
Possible manifestation of spin fluctuations in the temperature behavior of resistivity in Sm_{1.85}Ce_{0.15}CuO_4 thin films
A pronounced step-like (kink) behavior in the temperature dependence of
resistivity is observed in the optimally-doped
thin films around and attributed to
manifestation of strong spin fluctuations induced by moments with the
energy . In addition to fluctuation
induced contribution due to thermal broadening effects (of the
width ), the experimental data are found to be well fitted
accounting for residual (zero-temperature) , electron-phonon and electron-electron contributions. The
best fits produced , ,
, and for estimates of the plasmon frequency, the
impurity scattering rate, electron-phonon coupling constant, and the Fermi
energy, respectively.Comment: 6 pages (REVTEX4), 2 EPS figures; accepted for publication in JETP
Letter
High Accretion Rate during Class 0 Phase due to External Trigger
Recent observations indicate that some class 0 sources have orders of
magnitude higher accretion rates than those of class I. We investigated the
conditions for the high accretion rates of some class 0 sources by numerical
calculations, modelling an external trigger. For no external trigger, we find
that the maximum value of the accretion rate is determined by the ratio
of the gravitational energy to the thermal one within a flat inner
region of the cloud core. The accretion rate reaches \sim 10^{-4} M_{\sun}
yr^{-1} if the cloud core has . For an external trigger we find
that the maximum value of the accretion rate is proportional to the momentum
given to the cloud core. The accretion rate reaches > 10^{-4} M_{\sun}
yr^{-1} with a momentum of \sim 0.1 M_{\sun} km s^{-1} when the initial
central density of the cloud core is . A comparison
between recent observational results for prestellar cores and our no triggered
collapse model indicates that the flat inner regions of typical prestellar
cores are not large enough to cause accretion rates of \sim 10^{-4} M_{\sun}
yr^{-1}. Our results show that the triggered collapse of the cloud core is
more preferable for the origin of the high accretion rates of class 0 sources
than no triggered collapse.Comment: 7 pages, 8 figures, accepted for publication in MNRA
Nonequilibrium orientational patterns in two-component Langmuir monolayers
A model of a phase-separating two-component Langmuir monolayer in the
presence of a photo-induced reaction interconvering two components is
formulated. An interplay between phase separation, orientational ordering and
treaction is found to lead to a variety of nonequilibrium self-organized
patterns, both stationary and traveling. Examples of the patterns, observed in
numerical simulations, include flowing droplets, traveling stripes, wave
sources and vortex defects.Comment: Submitted to the Physical Review
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