139 research outputs found
Learning Assigned Secrets for Unlocking Mobile Devices
ABSTRACT Nearly all smartphones and tablets support unlocking with a short user-chosen secret: e.g., a numeric PIN or a pattern. To address users' tendency to choose guessable PINs and patterns, we compare two approaches for helping users learn assigned random secrets. In one approach, built on our prior work [16], we assign users a second numeric PIN and, during each login, we require them to enter it after their chosen PIN. In a new approach, we re-arrange the digits on the keypad so that the user's chosen PIN appears on an assigned random sequence of key positions. We performed experiments with over a thousand participants to compare these two repetition-learning approaches to simple user-chosen PINs and assigned PINs that users are required to learn immediately at account set-up time. Almost all of the participants using either repetition-learning approach learned their assigned secrets quickly and could recall them three days after the study. Those using the new mapping approach were less likely to write down their secret. Surprisingly, the learning process was less time consuming for those required to enter an extra PIN
Learning Assigned Secrets for Unlocking Mobile Devices
ABSTRACT Nearly all smartphones and tablets support unlocking with a short user-chosen secret: e.g., a numeric PIN or a pattern. To address users' tendency to choose guessable PINs and patterns, we compare two approaches for helping users learn assigned random secrets. In one approach, built on our prior work [16], we assign users a second numeric PIN and, during each login, we require them to enter it after their chosen PIN. In a new approach, we re-arrange the digits on the keypad so that the user's chosen PIN appears on an assigned random sequence of key positions. We performed experiments with over a thousand participants to compare these two repetition-learning approaches to simple user-chosen PINs and assigned PINs that users are required to learn immediately at account set-up time. Almost all of the participants using either repetition-learning approach learned their assigned secrets quickly and could recall them three days after the study. Those using the new mapping approach were less likely to write down their secret. Surprisingly, the learning process was less time consuming for those required to enter an extra PIN
The evolution of substructure II: linking dynamics to environment
We present results from a series of high-resolution N-body simulations that
focus on the formation and evolution of eight dark matter halos, each of order
a million particles within the virial radius. We follow the time evolution of
hundreds of satellite galaxies with unprecedented time resolution, relating
their physical properties to the differing halo environmental conditions. The
self-consistent cosmological framework in which our analysis was undertaken
allows us to explore satellite disruption within live host potentials, a
natural complement to earlier work conducted within static potentials. Our host
halos were chosen to sample a variety of formation histories, ages, and
triaxialities; despite their obvious differences, we find striking similarities
within the associated substructure populations. Namely, all satellite orbits
follow nearly the same eccentricity distribution with a correlation between
eccentricity and pericentre. We also find that the destruction rate of the
substructure population is nearly independent of the mass, age, and triaxiality
of the host halo. There are, however, subtle differences in the velocity
anisotropy of the satellite distribution. We find that the local velocity bias
at all radii is greater than unity for all halos and this increases as we move
closer to the halo centre, where it varies from 1.1 to 1.4. For the global
velocity bias we find a small but slightly positive bias, although when we
restrict the global velocity bias calculation to satellites that have had at
least one orbit, the bias is essentially removed.Comment: 14 pages, 14 figures, MNRAS in pres
Thermodynamic analysis of inverted bifurcation
We present a thermodynamic analysis of inverted bifurcation
in binary mixtures heated from below. From this analysis it
follows that an inverted bifurcation is caused by the competition
between a stabilizing effect with a long relaxation time and a
destabilizing effect with a short relaxation time. These
conditions are precisely the same as those that give rise to
overstability. This might explain why overstability and inverted
bifurcation occur in the same systems
Surface Gap Soliton Ground States for the Nonlinear Schr\"{o}dinger Equation
We consider the nonlinear Schr\"{o}dinger equation , with and and with periodic in each coordinate direction. This problem
describes the interface of two periodic media, e.g. photonic crystals. We study
the existence of ground state solutions (surface gap soliton ground
states) for . Using a concentration compactness
argument, we provide an abstract criterion for the existence based on ground
state energies of each periodic problem (with and ) as well as a more practical
criterion based on ground states themselves. Examples of interfaces satisfying
these criteria are provided. In 1D it is shown that, surprisingly, the criteria
can be reduced to conditions on the linear Bloch waves of the operators
and .Comment: definition of ground and bound states added, assumption (H2) weakened
(sign changing nonlinearity is now allowed); 33 pages, 4 figure
Constructing a bivariate distribution function with given marginals and correlation: application to the galaxy luminosity function
We show an analytic method to construct a bivariate distribution function
(DF) with given marginal distributions and correlation coefficient. We
introduce a convenient mathematical tool, called a copula, to connect two DFs
with any prescribed dependence structure. If the correlation of two variables
is weak (Pearson's correlation coefficient ), the
Farlie-Gumbel-Morgenstern (FGM) copula provides an intuitive and natural way
for constructing such a bivariate DF. When the linear correlation is stronger,
the FGM copula cannot work anymore. In this case, we propose to use a Gaussian
copula, which connects two given marginals and directly related to the linear
correlation coefficient between two variables. Using the copulas, we
constructed the BLFs and discuss its statistical properties. Especially, we
focused on the FUV--FIR BLF, since these two luminosities are related to the
star formation (SF) activity. Though both the FUV and FIR are related to the SF
activity, the univariate LFs have a very different functional form: former is
well described by the Schechter function whilst the latter has a much more
extended power-law like luminous end. We constructed the FUV-FIR BLFs by the
FGM and Gaussian copulas with different strength of correlation, and examined
their statistical properties. Then, we discuss some further possible
applications of the BLF: the problem of a multiband flux-limited sample
selection, the construction of the SF rate (SFR) function, and the construction
of the stellar mass of galaxies ()--specific SFR () relation. The
copulas turned out to be a very useful tool to investigate all these issues,
especially for including the complicated selection effects.Comment: 14 pages, 5 figures, accepted for publication in MNRAS
Vector meson dominance and the rho meson
We discuss the properties of vector mesons, in particular the rho^0, in the
context of the Hidden Local Symmetry (HLS) model. This provides a unified
framework to study several aspects of the low energy QCD sector. Firstly, we
show that in the HLS model the physical photon is massless, without requiring
off field diagonalization. We then demonstrate the equivalence of HLS and the
two existing representations of vector meson dominance, VMD1 and VMD2, at both
tree level and one loop order. Finally the S matrix pole position is shown to
provide a model and process independent means of specifying the rho mass and
width, in contrast to the real axis prescription currently used in the Particle
Data Group tables.Comment: 18 pages, REVTE
The Toroid Moment of Majorana Neutrino
If neutrino is the Majorana particle it can possess only one electromagnetic
characteristic, the toroid dipole moment (anapole) in the static limit and
nothing else. We have calculated the diagonal toroid moment (form factor) of
the Majorana neutrino by the dispersion method in the one-loop approximation of
the Standard Model and found it to be different from zero in the case of
massive as well as massless neutrinos. All external particles are on the mass
shells and there are no problems with the physical interpretation of the final
result. Some manifestations of the toroid interactions of Majorana neutrinos,
induced by their toroid moments, are also remarked.Comment: 22 pages, 1 table and 3 EPS-figures included, uses prd.sty,
preprint.sty, aps.sty and epsfig.sty (RevTeX is used), major conceptual
changes of E2-96-53 are include
A distortion of very--high--redshift galaxy number counts by gravitational lensing
The observed number counts of high-redshift galaxy candidates have been used
to build up a statistical description of star-forming activity at redshift z >~
7, when galaxies reionized the Universe. Standard models predict that a high
incidence of gravitational lensing will probably distort measurements of flux
and number of these earliest galaxies. The raw probability of this happening
has been estimated to be ~ 0.5 percent, but can be larger owing to
observational biases. Here we report that gravitational lensing is likely to
dominate the observed properties of galaxies with redshifts of z >~ 12, when
the instrumental limiting magnitude is expected to be brighter than the
characteristic magnitude of the galaxy sample. The number counts could be
modified by an order of magnitude, with most galaxies being part of multiply
imaged systems, located less than 1 arcsec from brighter foreground galaxies at
z ~ 2. This lens-induced association of high-redshift and foreground galaxies
has perhaps already been observed among a sample of galaxy candidates
identified at z ~ 10.6. Future surveys will need to be designed to account for
a significant gravitational lensing bias in high-redshift galaxy samples.Comment: Nature, Jan. 13, 2011 issue (in press
- …