405 research outputs found
Depletion interactions of non-spherical colloidal particles in polymer solutions
We consider anisotropic colloidal particles immersed in a solution of long,
flexible, and nonadsorbing polymers. For the dumbbell shapes of recently
synthesized particles consisting of two intersecting spheres and for
lens-shaped particles with spherical surfaces we calculate the isotropic and
anisotropic interaction parameters that determine the immersion free energy and
the orientation-dependent depletion interaction between particles that are
induced by the polymers. Exact results are obtained for random-walk like
(ideal) polymer chains
Security and Efficiency Analysis of the Hamming Distance Computation Protocol Based on Oblivious Transfer
open access articleBringer et al. proposed two cryptographic protocols for the computation of Hamming distance. Their first scheme uses Oblivious Transfer and provides security in the semi-honest model. The other scheme uses Committed Oblivious Transfer and is claimed to provide full security in the malicious case. The proposed protocols have direct implications to biometric authentication schemes between a prover and a verifier where the verifier has biometric data of the users in plain form.
In this paper, we show that their protocol is not actually fully secure against malicious adversaries. More precisely, our attack breaks the soundness property of their protocol where a malicious user can compute a Hamming distance which is different from the actual value. For biometric authentication systems, this attack allows a malicious adversary to pass the authentication without knowledge of the honest user's input with at most complexity instead of , where is the input length. We propose an enhanced version of their protocol where this attack is eliminated. The security of our modified protocol is proven using the simulation-based paradigm. Furthermore, as for efficiency concerns, the modified protocol utilizes Verifiable Oblivious Transfer which does not require the commitments to outputs which improves its efficiency significantly
Magnetic adatom induced skyrmion-like spin texture in surface electron waves
When a foreign atom is placed on a surface of a metal, the surrounding sea of
electrons responds screening the additional charge leading to oscillations or
ripples. On surfaces, those electrons are sometimes confined to two-dimensional
surface states, whose spin-degeneracy is lifted due to the Rashba effect
arising from the spin-orbit interaction of electrons and the inversion
asymmetric environment. It is believed that at least for a single adatom
scanning tunneling microscopy measurements are insensitive to the Rashba
splitting i.e. no signatures in the charge oscillations will be observed.
Resting on scattering theory, we demonstrate that, if magnetic, one single
adatom is enough to visualize the presence of the Rashba effect in terms of an
induced spin-magnetization of the surrounding electrons exhibiting a twisted
spin texture described as superposition of two skyrmionic waves of opposite
chirality.Comment: 11 pages, 5 figures, accepted in Phys. Rev. Letter
The Football Associationâs Child Protection in Football Research Project 2002-2006: Rationale, design and first year results
In common with most sport organisations, the English Football Association has come relatively recently to the issue of child protection. Abuses of various kinds have been known about in the sport for many years but, until the late 1990s, very little systematic work was undertaken to address this. The launch of a Child Protection Strategy by the Engalish FA in May 2000 reflected recognition by those in authority within the sport that child abuse and protection were properly the subject of football policy and should become embedded in all aspects of the affiliated game. In addition to adopting child protection, the then-Chief Executive Officer of the FA made a commitment to evidence-based policy in his strategic plan for the game. In line with this commitment, the FA commissioned a 5 year study of the impact of child protection on the game, the first year of which constituted an audit of the state of child protection in the affiliated game. Data were collected through 11 internet surveys, 32 club case studies, over 200 interviews with various stakeholders and an analysis of 132 case files for child abuse referrals. This paper sets out the context of child protection in sport more generally and the background to the FA's child protection reseach project in particular. It also presents selected first year results for key stakeholder groups
Measuring the impact of child protection through Activation States
Child protection (CP) has risen to the top of the UK sports policy agenda in the past four years and the Football Association has invested in this major strategy as part of its commitment to âuse the power of football to build a better futureâ (FA, 2000a). Evidencing the impact of child protection is, however, a complex task, exacerbated by the dearth of measurement tools that exist for this purpose in sport. This article presents a new model of âActivation Statesâ that has been designed and used to measure shifts in football culture as child protection has begun to impact upon the sport. The model is used to map changes over time related to the knowledge, feelings, actions and discourses of key stakeholders in football. The research for which the model was designed is a longitudinal study, commissioned by the English Football (soccer) Association, on the impact of the organisationâs child protection strategy on the culture of soccer. Sample data from the project are used to illustrate the model and to examine its potential and limitations as a tool for measuring impacts in child protection and other social inclusion themes
Observational constraints on the afterglow of GRB 020531
We present the data acquired by the TAROT automated observatory on the
afterglow of GRB 020531. Up to now, no convincing afterglow emission has been
reported for this short/hard GRB at any wavelength, including X-ray and
optical. The combination of our early limits, with other published data allows
us to put severe constraints on the afterglow magnitude and light curve. The
limiting magnitude is 18.5 in R band, 88 minutes after the GRB, and the decay
slope power law index could be larger than 2.2.Comment: 4 pages, submitted to A&A (letter
Maximising transparency in a doctoral thesis: The complexities of writing about the use of QSR*NVIVO within a grounded theory study
This paper discusses the challenges of how to provide a transparent account of the use of the software programme QSR*NVIVO (QSR 2000) within a Grounded Theory framework (Glaser and Strauss 1967; Strauss and Corbin 1998). Psychology students are increasingly pursuing qualitative research projects such to the extent that the UK Economic and Social Research Council (ESRC) advise that students should have skill in the use of computer assisted qualitative data analysis software (CAQDAS) (Economic and Social Research Council 2001). Unlike quantitative studies, rigid formulae do not exist for writing-up qualitative projects for doctoral theses. Most authors, however, agree that transparency is essential when communicating the findings of qualitative research. Sparkes (2001) recommends that evaluative criteria for qualitative research should be commensurable with the aims, objectives, and epistemological assumptions of the research project. Likewise, the use of CAQDAS should vary according to the research methodology followed, and thus researchers should include a discussion of how CAQDAS was used. This paper describes how the evolving process of coding data, writing memos, categorising, and theorising were integrated into the written thesis. The structure of the written document is described including considerations about restructuring and the difficulties of writing about an iterative process within a linear document
A Formal Study of the Privacy Concerns in Biometric-Based Remote Authentication Schemes
With their increasing popularity in cryptosystems, biometrics have attracted more and more attention from the information security community. However, how to handle the relevant privacy concerns remains to be troublesome. In this paper, we propose a novel security model to formalize the privacy concerns in biometric-based remote authentication schemes. Our security model covers a number of practical privacy concerns such as identity privacy and transaction anonymity, which have not been formally considered in the literature. In addition, we propose a general biometric-based remote authentication scheme and prove its security in our security model
Early re-brightening of the afterglow of GRB 050525a
We present time resolved optical data acquired by the TAROT automated
observatory on the afterglow of GRB 050525a from 6 to 136 minutes after the
GRB. We evidence a rapid re-brightening of 0.65 magnitude of the afterglow at
33 min after the GRB. The decay slope is in the
first part and is after the re-brightening event. The afterglow
of GRB 050525a is the third known afterglow that exhibits a re-brightening
event begining at 0.01--0.02 day in the rest time frame.Comment: 4 pages, 2 figures, submitted to A&
Stellar evolution through the ages: period variations in galactic RRab stars as derived from the GEOS database and TAROT telescopes
The theory of stellar evolution can be more closely tested if we have the
opportunity to measure new quantities. Nowadays, observations of galactic RR
Lyr stars are available on a time baseline exceeding 100 years. Therefore, we
can exploit the possibility of investigating period changes, continuing the
pioneering work started by V. P. Tsesevich in 1969. We collected the available
times of maximum brightness of the galactic RR Lyr stars in the GEOS RR Lyr
database. Moreover, we also started new observational projects, including
surveys with automated telescopes, to characterise the O-C diagrams better. The
database we built has proved to be a very powerful tool for tracing the period
variations through the ages. We analyzed 123 stars showing a clear O-C pattern
(constant, parabolic or erratic) by means of different least-squares methods.
Clear evidence of period increases or decreases at constant rates has been
found, suggesting evolutionary effects. The median values are beta=+0.14
day/Myr for the 27 stars showing a period increase and beta=-0.20 day/Myr for
the 21 stars showing a period decrease. The large number of RR Lyr stars
showing a period decrease (i.e., blueward evolution) is a new and intriguing
result. There is an excess of RR Lyr stars showing large, positive
values. Moreover, the observed beta values are slightly larger than those
predicted by theoretical models.Comment: 15 pages, 9 figures; to be published in Astronomy and Astrophysics;
full resolution version available at
http://dbrr.ast.obs-mip.fr/tarot/publis/publis.htm
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