88,476 research outputs found
A flexible mandatory access control policy for XML databases
A flexible mandatory access control policy (MAC) for XML
databases is presented in this paper. The label type and label
access policy can be defined according to the requirements of
applications. In order to preserve the integrity of data in XML
databases, a constraint between a read access rule and a write
access rule in label access policy is introduced. Rules for label
assignment and propagation are proposed to alleviate the
workload of label assignment. Also, a solution for resolving
conflicts of label assignments is proposed. At last, operations for
implementation of the MAC policy in a XML database are
illustrated
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A practical mandatory access control model for XML databases
A practical mandatory access control (MAC) model for XML databases is presented in this paper. The
label type and label access policy can be defined according to the requirements of different applications. In order to
preserve the integrity of data in XML databases, a constraint between a read-access rule and a write-access rule in
label access policy is introduced. Rules for label assignment and propagation are presented to alleviate the workload
of label assignments. Furthermore, a solution for resolving conflicts in label assignments is proposed. Rules for
update-related operations, rules for exceptional privileges of ordinary users and the administrator are also proposed
to preserve the security of operations in XML databases. The MAC model, we proposed in this study, has been
implemented in an XML database. Test results demonstrated that our approach provides rational and scalable
performance
Pairing of 1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol
Molecular dynamics simulations are obtained and analyzed to study pairing of
1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol, in
particular by evaluating the potential-of-mean-force between counter ions. The
present molecular model and simulation accurately predicts the dissociation
constant Kd in comparison to experiment, and thus the behavior and magnitudes
for the ion-pair pmf at molecular distances, even though the dielectric
constant of the simulated solvent differs from the experimental value by about
30%. A naive dielectric model does not capture molecule structural effects such
as multiple conformations and binding geometries of the Hmim+ and BF4-
ion-pairs. Mobilities identify multiple time-scale effects in the
autocorrelation of the random forces on the ions, and specifically a slow,
exponential time-decay of those long-ranged forces associated here with
dielectric friction effects.Comment: 5 pages, 7 figures. V2: Figs. 4 & 7 redrawn for better visual clarity
with log-scales. No change in results. In press J. Chem. Phys. 201
Dynamic microscopic structures and dielectric response in the cubic-to-tetragonal phase transition for BaTiO3 studied by first-principles molecular dynamics simulation
The dynamic structures of the cubic and tetragonal phase in BaTiO3 and its
dielectric response above the cubic-to-tetragonal phase transition temperature
(Tp) are studied by first-principles molecular dynamics (MD) simulation. It's
shown that the phase transition is due to the condensation of one of the
transverse correlations. Calculation of the phonon properties for both the
cubic and tetragonal phase shows a saturation of the soft mode frequency near
60 cm-1 near Tp and advocates its order-disorder nature. Our first-principles
calculation leads directly to a two modes feature of the dielectric function
above Tp [Phys. Rev. B 28, 6097 (1983)], which well explains the long time
controversies between experiments and theories
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