2,716 research outputs found
Comment on "Conductance fluctuations in mesoscopic normal-metal/superconductor samples"
Recently, Hecker et al. [Phys. Rev. Lett. 79, 1547 (1997)] experimentally
studied magnetoconductance fluctuations in a mesoscopic Au wire connected to a
superconducting Nb contact. They claimed to have observed an enhancement of the
rms magnitude of these conductance fluctuations in the superconducting state
(rms(Gns)) relative to that in the normal state (rms(Gn)) by a factor of 2.8.
In this comment, we argue that the measured rms(Gns) is NOT significantly
enhanced compared to rms(Gn) when we correct for the presence of an incoherent
series resistance from the contacts, which is different when Nb is in the
superconducting or normal state.Comment: 1 pag
Two-point motional Stark effect diagnostic for Madison Symmetric Torus
A high-precision spectral motional Stark effect (MSE) diagnostic provides internal magnetic field measurements for Madison Symmetric Torus (MST) plasmas. Currently, MST uses two spatial views-on the magnetic axis and on the midminor (off-axis) radius, the latter added recently. A new analysis scheme has been developed to infer both the pitch angle and the magnitude of the magnetic field from MSE spectra. Systematic errors are reduced by using atomic data from atomic data and analysis structure in the fit. Reconstructed current density and safety factor profiles are more strongly and globally constrained with the addition of the off-axis radius measurement than with the on-axis one only
Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
Recent radiative lifetime measurements accurate to +/- 5% using laser-induced
fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have
been combined with new branching fractions measured using a Fourier transform
spectrometer (FTS) to determine transition probabilities for 921 lines of Ce
II. This improved laboratory data set has been used to determine a new solar
photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45
lines), a value in excellent agreement with the recommended meteoritic
abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been
derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052,
CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for
determining the Ce abundance in these five stars, yielding a small statistical
uncertainty of 0.01 dex similar to the Solar result. The relative abundances in
the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun,
matches r-process only model predictions for Solar System material. This
consistent match with small scatter over a wide range of stellar metallicities
lends support to these predictions of elemental fractions. A companion paper
includes an interpretation of these new precision abundance results for Ce as
well as new abundance results and interpretations for Pr, Dy and Tm.Comment: 84 pages, 8 Figures, 14 Tables; To appear in the Astrophysical
Journal Supplemen
Nonmonotonic Trust Management for P2P Applications
Community decisions about access control in virtual communities are
non-monotonic in nature. This means that they cannot be expressed in current,
monotonic trust management languages such as the family of Role Based Trust
Management languages (RT). To solve this problem we propose RT-, which adds a
restricted form of negation to the standard RT language, thus admitting a
controlled form of non-monotonicity. The semantics of RT- is discussed and
presented in terms of the well-founded semantics for Logic Programs. Finally we
discuss how chain discovery can be accomplished for RT-.Comment: This paper appears in the proceedings of the 1st International
Workshop on Security and Trust Management (STM 2005). To appear in ENTC
Improved V II log() Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
New experimental absolute atomic transition probabilities are reported for
203 lines of V II. Branching fractions are measured from spectra recorded using
a Fourier transform spectrometer and an echelle spectrometer. The branching
fractions are normalized with radiative lifetime measurements to determine the
new transition probabilities. Generally good agreement is found between this
work and previously reported V II transition probabilities. Use of two
spectrometers, independent radiometric calibration methods, and independent
data analysis routines enables a reduction in systematic uncertainties, in
particular those due to optical depth errors. In addition, new hyperfine
structure constants are measured for selected levels by least squares fitting
line profiles in the FTS spectra. The new V II data are applied to high
resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to
determine new, more accurate V abundances. Lines covering a range of wavelength
and excitation potential are used to search for non-LTE effects. Very good
agreement is found between our new solar photospheric V abundance, log
{\epsilon}(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value.
In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of
[V/Fe] = 0.24.Comment: 32 pages, 7 tables (3 machine-readable), 8 figures; accepted for
publication in ApJ
You cannot hide behind the mask : power analysis on a provably secure S-box implementation
Power analysis has shown to be successful in breaking symmetric cryptographic algorithms implemented on low resource devices. Prompted by the breaking of many protected implementations in practice, researchers saw the need of validating security of implementations with formal methods. Three generic S-box implementation methods have been proposed by Prouff el al., together with formal proofs of their security against 1st or 2nd-order side-channel analysis. These methods use a similar combination of masking and hiding countermeasures. In this paper, we show that although proven resistant to standard power analysis, these implementation methods are vulnerable to a more sophisticated form of power analysis that combines Differential Power Analysis (DPA) and pattern matching techniques. This new form of power analysis is possible under the same assumptions about power leakage as standard DPA attacks and the added complexity is limited: our experiments show that 900 traces are sufficient to break these algorithms on a device where 150 traces are typically needed for standard DPA. We conclude that the defense strategies—hiding by repeating operations for each possible value, and masking and hiding using the same random number—can create new vulnerabilities
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