1,548 research outputs found
WAMDII observation of an auroral atmosphere wave event
Field tests of WAMDII (Wide Angle Michelson Doppler Imaging Interferometer) on February 23 to 24, 1984 in Saskatoon produced wind images of the aurora that show well defined wave structures in lambda 5577. Wavelengths and velocities of these structures suggest an acoustic-gravity wave interpretation, but their short duration warrants their being termed an event. The Dopplergrams are presented with emphasis on the interpretation of the waves and a discussion of possible sources
Relating two standard notions of secrecy
Two styles of definitions are usually considered to express that a security
protocol preserves the confidentiality of a data s. Reachability-based secrecy
means that s should never be disclosed while equivalence-based secrecy states
that two executions of a protocol with distinct instances for s should be
indistinguishable to an attacker. Although the second formulation ensures a
higher level of security and is closer to cryptographic notions of secrecy,
decidability results and automatic tools have mainly focused on the first
definition so far.
This paper initiates a systematic investigation of the situations where
syntactic secrecy entails strong secrecy. We show that in the passive case,
reachability-based secrecy actually implies equivalence-based secrecy for
digital signatures, symmetric and asymmetric encryption provided that the
primitives are probabilistic. For active adversaries, we provide sufficient
(and rather tight) conditions on the protocol for this implication to hold.Comment: 29 pages, published in LMC
Deduction with XOR Constraints in Security API Modelling
We introduce XOR constraints, and show how they enable a theorem prover to reason effectively about security critical subsystems which employ bitwise XOR. Our primary case study is the API of the IBM 4758 hardware security module. We also show how our technique can be applied to standard security protocols
Ubiquitination directly enhances activity of the deubiquitinating enzyme ataxinâ3
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102210/1/emboj2008289-sup-0001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102210/2/emboj2008289.pd
Chemical genetic analysis of the regulatory role of Cdc2p in the S. pombe septation initiation network
The protein kinase Cdc2p is the master regulator of cell cycle progression in the fission yeast Schizosaccharomyces pombe. It is required both for entry into mitosis and for onset of DNA replication. Cdc2p must be inactivated to permit exit from mitosis, licensing of replication origins and cytokinesis. To study the role of Cdc2p in greater detail, we generated a cdc2 allele that is sensitive to an inhibitory ATP analogue. We show that the inhibitor-induced cell cycle arrest is reversible and examine the effect of inhibiting Cdc2p on the regulation of the septation initiation network (SIN), which controls the initiation of cytokinesis in S. pombe. We found that specific inactivation of Cdc2p in a mitotically arrested cell promotes the asymmetrical recruitment of SIN proteins to the spindle poles and the recruitment of the most downstream SIN components and beta-(1,3) glucan synthase to the contractile ring. Thus, we conclude that inactivation of Cdc2p is sufficient to activate the SIN and promote cytokinesis
Quantum Decay of Domain Walls in Cosmology II: Hamiltonian Approach
This paper studies the decay of a large, closed domain wall in a closed
universe. Such walls can form in the presence of a broken, discrete symmetry.
We study a novel process of quantum decay for such a wall, in which the vacuum
fluctuates from one discrete state to another throughout one half of the
universe, so that the wall decays into pure field energy. Equivalently, the
fluctuation can be thought of as the nucleation of a second closed domain wall
of zero size, followed by its growth by quantum tunnelling and its collision
with the first wall, annihilating both. We therefore study the 2-wall system
coupled to a spherically symmetric gravitational field. We derive a simple form
of the 2-wall action, use Dirac quantization, obtain the 2-wall wave function
for annihilation, find from it the barrier factor for this quantum tunneling,
and thereby get the decay probability. This is the second paper of a series.Comment: 27 pages LaTeX, using revtex and psfig. 3 figure
A Machine-Checked Formalization of the Generic Model and the Random Oracle Model
Most approaches to the formal analyses of cryptographic protocols make the perfect cryptography assumption, i.e. the hypothese that there is no way to obtain knowledge about the plaintext pertaining to a ciphertext without knowing the key. Ideally, one would prefer to rely on a weaker hypothesis on the computational cost of gaining information about the plaintext pertaining to a ciphertext without knowing the key. Such a view is permitted by the Generic Model and the Random Oracle Model which provide non-standard computational models in which one may reason about the computational cost of breaking a cryptographic scheme. Using the proof assistant Coq, we provide a machine-checked account of the Generic Model and the Random Oracle Mode
Watching a superfluid untwist itself: Recurrence of Rabi oscillations in a Bose-Einstein condensate
The order parameter of a condensate with two internal states can continuously
distort in such a way as to remove twists that have been imposed along its
length. We observe this effect experimentally in the collapse and recurrence of
Rabi oscillations in a magnetically trapped, two-component Bose-Einstein
condensate of ^87Rb
Metallicity of low-mass stars in Orion
Determining the metal content of low-mass members of young associations
provides a tool that addresses different issues, such as triggered star
formation or the link between the metal-rich nature of planet-host stars and
the early phases of planet formation. The Orion complex is a well known example
of possible triggered star formation and is known to host a rich variety of
proto-planetary disks around its low-mass stars. Available metallicity
measurements yield discrepant results. We analyzed FLAMES/UVES and Giraffe
spectra of low-mass members of three groups/clusters belonging to the Orion
association. Our goal is the homogeneous determination of the metallicity of
the sample stars, which allows us to look for [Fe/H] differences between the
three regions and for the possible presence of metal-rich stars. Nine members
of the ONC and one star each in the Ori cluster and OB1b subgroup
were analyzed. After the veiling determination, we retrieved the metallicity by
means of equivalent widths and/or spectral synthesis using MOOG. We obtain an
average metallicity for the ONC [Fe/H]=-0.01\pm 0.04. No metal-rich stars were
detected and the dispersion within our sample is consistent with measurement
uncertainties. The metallicity of the Ori member is also solar, while
the OB1b star has an [Fe/H] significantly below the ONC average. If confirmed
by additional [Fe/H] determinations in the OB1b subgroup, this result would
support the triggered star formation and the self-enrichment scenario for the
Orion complex.Comment: 13 pages, accepted for publication in A&
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Efficacy of oocytes donated by older women in an oocyte donation programme
Population and insemination studies indicate that women experience declining fertility with ageing. The question therefore arises whether older women are suitable oocyte donors. This study addresses this issue by examining the relationship between oocyte donor age and clinical outcome in a large oocyte donation programme. We retrospectively reviewed data from 458 consecutive oocyte donation cycles completed by 164 different designated oocyte donors. Data were divided into two groups: group A, cycles with donors aged 21â30 years at the time of follicular aspiration (193 cycles, 88 donors); and group B, cycles with donors aged 31â40 years at the time of follicular aspiration (265 cycles, 86 donors). Five donors, because of ageing during repetitive donations, contributed data to groups A and B. In a given cycle, all oocytes for a recipient came from only one designated donor. Comparing the two donor groups, there was no difference in the amount of gonadotrophin used to achieve optimal stimulation; however, more oocytes were obtained from group A than group B donors (16.8 ± 6.9 and 15.1 ± 8.1 respectively, P < 0.05). Similar percentages of oocytes were fertilized in each group, resulting in the transfer of comparable numbers of embryos (4.5 ± 1.1 and 4.4 ± 13 respectively). Comparable clinical pregnancy rates were achieved (group A, 36%; group B, 37%). The spontaneous abortion rates were also similar (group A, 20%; group B, 12%), resulting in comparable ongoing and delivered pregnancy rates per cycle (group A, 29%; group B, 32%) and per embryo transferred (group A, 6.4%; group B, 7.3%). In conclusion, women of proven fertility should not be excluded from donating oocytes simply because of their age. There exists a cohort of fertile women who resist the decreasing fecundity and increasing spontaneous abortion rates associated with ageing. With careful screening, many women of proven fertility can donate oocytes until the age of 40 years with an efficacy equal to that of younger women. Given the relative shortage of suitable oocyte donors, and increasing requests from recipients with previous donor oocyte babies to obtain oocytes from the same, now older, donor, the findings of this study are of practical clinical importance
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