61,858 research outputs found
Quantitative analysis of the leakage of confidential data
Basic information theory is used to analyse the amount of confidential information which may be leaked by programs written in a very simple imperative language. In particular, a detailed analysis is given of the possible leakage due to equality tests and if statements. The analysis is presented as a set of syntax-directed inference rules and can readily be automated
A static analysis for quantifying information flow in a simple imperative language
We propose an approach to quantify interference in a simple imperative language that includes a looping construct. In this paper we focus on a particular case of this definition of interference: leakage of information from private variables to public ones via a Trojan Horse attack. We quantify leakage in terms of Shannon's information theory and we motivate our definition by proving a result relating this definition of leakage and the classical notion of programming language interference. The major contribution of the paper is a quantitative static analysis based on this definition for such a language. The analysis uses some non-trivial information theory results like Fano's inequality and L1 inequalities to provide reasonable bounds for conditional statements. While-loops are handled by integrating a qualitative flow-sensitive dependency analysis into the quantitative analysis
Formulation and evaluation of C-Ether fluids as lubricants useful to 260 C
Three base stocks were evaluated in bench and bearing tests to determine their suitability for use at bulk oil temperatures (BOT) from -40 C to +260 C. A polyol ester gave good bearing tests at a bulk temperature of 218 C, but only a partially successful run at 274 C. These results bracket the fluid's maximum operating temperature between these values. An extensive screening program selected lubrication additives for a C-ether (modified polyphenyl ether) base stock. One formulation lubricated a bearing for 111 hours at 274 C (BOT), but this fluid gave many deposit related problems. Other C-ether blends produced cage wear or fatigue failures. Studies of a third fluid, a C-ether/disiloxane blend, consisted of bench oxidation and lubrication tests. These showed that some additives react differently in the blend than in pure C-ethers
Efficient generation of graph states for quantum computation
We present an entanglement generation scheme which allows arbitrary graph
states to be efficiently created in a linear quantum register via an auxiliary
entangling bus. The dynamics of the entangling bus is described by an effective
non-interacting fermionic system undergoing mirror-inversion in which qubits,
encoded as local fermionic modes, become entangled purely by Fermi statistics.
We discuss a possible implementation using two species of neutral atoms stored
in an optical lattice and find that the scheme is realistic in its requirements
even in the presence of noise.Comment: 4 pages, 3 figures, RevTex 4; v2 - Major changes and new result
Bacterial Quality of Private Water Wells in Clark County, Arkansas
Most private water wells in Clark County appeared to be contaminated by bacteria, apparently entering the wells from surface water seepage. Eighteen to 24% of the wells investigated were positive for fecal contamination. Deeper wells were less often contaminated. More than one-half of the wells sampled exceeded recommended limits of inorganic chemicals for safe potable water. High concentrations of iron and manganese were most common, exceeding recommended limits in more than 40% of the well
Fast initialization of a high-fidelity quantum register using optical superlattices
We propose a method for the fast generation of a quantum register of
addressable qubits consisting of ultracold atoms stored in an optical lattice.
Starting with a half filled lattice we remove every second lattice barrier by
adiabatically switching on a superlattice potential which leads to a long
wavelength lattice in the Mott insulator state with unit filling. The larger
periodicity of the resulting lattice could make individual addressing of the
atoms via an external laser feasible. We develop a Bose-Hubbard-like model for
describing the dynamics of cold atoms in a lattice when doubling the lattice
periodicity via the addition of a superlattice potential. The dynamics of the
transition from a half filled to a commensurately filled lattice is analyzed
numerically with the help of the Time Evolving Block Decimation algorithm and
analytically using the Kibble-Zurek theory. We show that the time scale for the
whole process, i.e. creating the half filled lattice and subsequent doubling of
the lattice periodicity, is significantly faster than adiabatic direct quantum
freezing of a superfluid into a Mott insulator for large lattice periods. Our
method therefore provides a high fidelity quantum register of addressable
qubits on a fast time scale.Comment: 22 pages, 9 figures, IOP style. Revised version to appear in NJ
Proposed parametric cooling of bilayer cuprate superconductors by terahertz excitation
We propose and analyze a scheme for parametrically cooling bilayer cuprates
based on the selective driving of a -axis vibrational mode. The scheme
exploits the vibration as a transducer making the Josephson plasma frequencies
time-dependent. We show how modulation at the difference frequency between the
intra- and interbilayer plasmon substantially suppresses interbilayer phase
fluctuations, responsible for switching -axis transport from a
superconducting to resistive state. Our calculations indicate that this may
provide a viable mechanism for stabilizing non-equilibrium superconductivity
even above , provided a finite pair density survives between the bilayers
out of equilibrium.Comment: 4 pages + 7 page supplementa
Heat transport in the spin chain: from ballistic to diffusive regimes and dephasing enhancement
In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain
with homogeneous magnetic field, incoherently driven out of equilibrium by
reservoirs at the boundaries. We focus on the effect of bulk dephasing
(energy-dissipative) processes in different parameter regimes of the system.
The non-equilibrium steady state of the chain is obtained by simulating its
evolution under the corresponding Lindblad master equation, using the time
evolving block decimation method. In the absence of dephasing, the heat
transport is ballistic for weak interactions, while being diffusive in the
strongly-interacting regime, as evidenced by the heat-current scaling with the
system size. When bulk dephasing takes place in the system, diffusive transport
is induced in the weakly-interacting regime, with the heat current
monotonically decreasing with the dephasing rate. In contrast, in the
strongly-interacting regime, the heat current can be significantly enhanced by
dephasing for systems of small size
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