4,389 research outputs found
First-Principles Modeling of Pt/LaAlO3/SrTiO3 Capacitors Under an External Bias Potential
We study the electrical properties of Pt/LaAlO3/SrTiO3 capacitors under the
action of an external bias potential, using first-principles simulations
performed at constrained electric displacement field. A complete set of band
diagrams, together with the relevant electrical characteristics (capacitance
and built-in fields), are determined as a function of LaAlO3 thickness and the
applied potential.We find that the internal field in LaAlO3 monotonically
decreases with increasing thickness; hence, the occurrence of spontaneous Zener
tunneling is ruled out in this system.We discuss the implications of our
results in the light of recent experimental observations on biased
LaAlO3/SrTiO3 junctions involving metallic top electrodes.Comment: 5 pages, 4 figure
Laser-Accelerated proton beams as diagnostics for cultural heritage
This paper introduces the first use of laser-generated proton beams as diagnostic for materials of interest in the domain of Cultural Heritage. Using laser-accelerated protons, as generated by interaction of a high-power short-pulse laser with a solid target, we can produce proton-induced X-ray emission spectroscopies (PIXE). By correctly tuning the proton flux on the sample, we are able to perform the PIXE in a single shot without provoking more damage to the sample than conventional methodologies. We verify this by experimentally irradiating materials of interest in the Cultural Heritage with laser-accelerated protons and measuring the PIXE emission. The morphological and chemical analysis of the sample before and after irradiation are compared in order to assess the damage provoked to the artifact. Montecarlo simulations confirm that the temperature in the sample stays safely below the melting point. Compared to conventional diagnostic methodologies, laser-driven PIXE has the advantage of being potentially quicker and more efficien
A comparative assessment of different deviation strategies for dangerous NEO
In this paper a number of deviation strategies for dangerous Near Earth Objects (NEO) have been compared. For each strategy (i.e. Solar Collector, Nuclear Blast, Kinetic Impactor, Low-thrust Propulsion, Mass Driver) a multi criteria optimisation method has been used to reconstruct the set of Pareto optimal solutions minimising the mass of the spacecraft and the warning time, and maximising the deviation. Then, a dominance criterion has been defined and used to compare all the Pareto sets. The achievable deviation at the MOID, either for a low-thrust or for an impulsive variation of the orbit of the NEO, has been computed through a set of analytical formulas. The variation of the orbit of the NEO has been estimated through a deviation action model that takes into account the wet mass of the spacecraft at the Earth. Finally the technology readiness level of each strategy has been used to compute a more realistic value for the required warning time
Atomic-Scale Dynamics of the Formation and Dissolution of Carbon Clusters in SiO2
Oxidation of SiC produces SiO2 while CO is released. A `reoxidation' step at
lower temperatures is, however, necessary to produce high-quality SiO2. This
step is believed to cleanse the oxide of residual C without further oxidation
of the SiC substrate. We report first-principles calculations that describe the
nucleation and growth of O-deficient C clusters in SiO2 under oxidation
conditions, fed by the production of CO at the advancing interface, and their
gradual dissolution by the supply of O under reoxidation conditions. We predict
that both CO and CO2 are released during both steps.Comment: RevTex, 4 pages, 2 ps figures, to appear in Phys. Rev. Lett. (June
25, 2001
Universality of efficiency at maximum power
We investigate the efficiency of power generation by thermo-chemical engines.
For strong coupling between the particle and heat flows and in the presence of
a left-right symmetry in the system, we demonstrate that the efficiency at
maximum power displays universality up to quadratic order in the deviation from
equilibrium. A maser model is presented to illustrate our argument.Comment: 4 pages, 2 figure
ROSAT and BeppoSAX evidence of soft X-ray excess emission in the Shapley supercluster: A3571, A3558, A3560 and A3562
Excess soft X-ray emission in clusters of galaxies has so far been detected
for sources that lie along lines-of-sight to very low Galactic HI column
density (such as Coma, A1795, A2199 and Virgo, N_H 0.9-2.0 10^{20} cm-2). We
show that the cluster soft excess emission can be investigated even at higher
N_H, which provides an opportunity for investigating soft X-ray emission
characteristics among a large number of clusters.
The ROSAT PSPC analysis of some members of the Shapley concentration (A3571,
A3558, A3560 and A3562, at N_H 4-4.5 10^{20} cm-2) bears evidence for excess
emission in the 1/4 keV band. We were able to confirm the finding for the case
of A3571 by a pointed SAX observation. Within the current sample the soft X-ray
flux is again found to be consistently above the level expected from a hot
virialized plasma. The data quality is however insufficient to enable a
discrimination between alternative models of the excess low energy flux.Comment: ApJL in press, 5 figure
A momentum-space representation of Green's functions with modified dispersion on ultra-static space-time
We consider the Green's functions associated to a scalar field propagating on
a curved, ultra-static background, in the presence of modified dispersion
relations. The usual proper-time deWitt-Schwinger procedure to obtain a series
representation of the Green's functions is doomed to failure, because of higher
order spatial derivatives in the Klein-Gordon operator. We show how to overcome
this difficulty by considering a preferred frame, associated to a unit
time-like vector. With respect to this frame, we can express the Green's
functions as an integral over all frequencies of a space-dependent function.
The latter can be expanded in momentum space, as a series with geometric
coefficients similar to the deWitt-Schwinger's ones. By integrating over all
frequencies, we finally find the expansion of the Green's function up to four
derivatives of the metric tensor. The relation with the proper-time formalism
is also discussed.Comment: revtex, version accepted for publication in Phys. Rev.
Immunoscintigraphy for therapy decision making and follow-up of biological therapies
With the availability of new biological therapies there is the need of more accurate diagnostic tools to noninvasively
assess the presence of their targets. In this scenario nuclear medicine offers many radiopharmaceuticals for
SPECT or PET imaging of many pathological conditions. The availability of monoclonal antibodies provides tools to
target specific antigens involved in angiogenesis, cell cycle or modulation of the immune systems. The radiolabelling of
such therapeutic mAbs is a promising method to evaluate the antigenic status of each cancer lesion or inflamed sites
before starting the therapy. It may also allow to perform follow-up of such biological therapies. In the present review we
provide an overview of the most studied radiolabelled antibodies for therapy decision making and follow-up of patients
affected by cancer and other pathological conditions
A minimum-disturbing quantum state discriminator
We propose two experimental schemes for quantum state discrimination that
achieve the optimal tradeoff between the probability of correct identification
and the disturbance on the quantum state.Comment: 9 pages, 1 figure, OSID style. Submitted to the special issue of
"Open Systems and Information Dynamics", Proceedings of the "38th Symposium
on Mathematical Physics", Torun, Poland, June 200
Critical Behavior of the Two-Dimensional Randomly Driven Lattice Gas
We investigate the critical behavior of the two-dimensional randomly driven
lattice gas, in which particles are driven along one of the lattice axes by an
infinite external field with randomly changing sign. A finite-size scaling
(FSS) analysis provides novel evidences that this model is not in the same
universality class as the driven lattice gas with a constant drive (DLG),
contrarily to what has been recently reported in the literature. Indeed, the
FSS functions of transverse observables (i.e., related to order-parameter
fluctuations with wave vector perpendicular to the direction of the field)
differ from the mean-field behavior predicted and observed within the DLG
universality class. At variance with the DLG case, FSS is attained on lattices
with fixed aspect ratio and anisotropy exponent equal to 1 and the transverse
Binder cumulant does not vanish at the critical point.Comment: 4 pages, 4 figure
- âŠ