34,127 research outputs found
Evolution of complexity following a quantum quench in free field theory
Using a recent proposal of circuit complexity in quantum field theories
introduced by Jefferson and Myers, we compute the time evolution of the
complexity following a smooth mass quench characterized by a time scale in a free scalar field theory. We show that the dynamics has two distinct
phases, namely an early regime of approximately linear evolution followed by a
saturation phase characterized by oscillations around a mean value. The
behavior is similar to previous conjectures for the complexity growth in
chaotic and holographic systems, although here we have found that the
complexity may grow or decrease depending on whether the quench increases or
decreases the mass, and also that the time scale for saturation of the
complexity is of order (not parametrically larger).Comment: V2: added references, new plots, and improved discussion of results
on Section 5, V3: Few minor corrections. Published versio
Characterization of heterogeneity and spatial distribution of phases in complex solid dispersions by thermal analysis by structural characterization and X-ray micro computed tomography
Purpose: This study investigated the effect of drug-excipient miscibility on the heterogeneity and spatial distribution of phase separation in pharmaceutical solid dispersions at a micron-scale using two novel and complementary characterization techniques, thermal analysis by structural characterization (TASC) and X-ray micro-computed tomography (XCT) in conjunction with conventional characterization methods. Method: Complex dispersions containing felodipine, TPGS, PEG and PEO were prepared using hot melt extrusion-injection moulding. The phase separation behavior of the samples was characterized using TASC and XCT in conjunction with conventional thermal, microscopic and spectroscopic techniques. The in vitro drug release study was performed to demonstrate the impact of phase separation on dissolution of the dispersions. Results: The conventional characterization results indicated the phase separating nature of the carrier materials in the patches and the presence of crystalline drug in the patches with the highest drug loading (30% w/w). TASC and XCT where used to provide insight into the spatial configuration of the separate phases. TASC enabled assessment of the increased heterogeneity of the dispersions with increasing the drug loading. XCT allowed the visualization of the accumulation of phase separated (crystalline) drug clusters at the interface of air pockets in the patches with highest drug loading which led to poor dissolution performance. Semi-quantitative assessment of the phase separated drug clusters in the patches were attempted using XCT. Conclusion: TASC and XμCT can provide unique information regarding the phase separation behavior of solid dispersions which can be closely associated with important product quality indicators such as heterogeneity and microstructure
The Mixmaster Spacetime, Geroch's Transformation and Constants of Motion
We show that for -symmetric spacetimes on a constant of
motion associated with the well known Geroch transformation, a functional
, quadratic in gravitational momenta, is strictly positive
in an open subset of the set of all -symmetric initial data, and
therefore not weakly zero. The Mixmaster initial data appear to be on the
boundary of that set. We calculate the constant of motion perturbatively for
the Mixmaster spacetime and find it to be proportional to the minisuperspace
Hamiltonian to the first order in the Misner anisotropy variables, i.e. weakly
zero. Assuming that is exactly zero for the Mixmaster spacetime, we show
that Geroch's transformation, when applied to the Mixmaster spacetime, gives a
new \mbox{-symmetric} solution of the vacuum Einstein equations, globally
defined on \mbox{},which is non-homogeneous and
presumably exhibits Mixmaster-like complicated dynamical behavior.Comment: 25 pages, preprint YCTP-20-93, Revte
High-temperature constitutive modeling
Thermomechanical service conditions for high-temperature levels, thermal transients, and mechanical loads severe enough to cause measurable inelastic deformation are studied. Structural analysis in support of the design of high-temperature components depends strongly on accurate mathematical representations of the nonlinear, hereditary, inelastic behavior of structural alloys at high temperature, particularly in the relatively small strain range. Progress is discussed in the following areas: multiaxial experimentation to provide a basis for high-temperature multiaxial constitutive relationships; nonisothermal testing and theoretical development toward a complete thermomechanically path dependent formulation of viscoplasticity; and development of viscoplastic constitutive model accounting for initial anisotropy
Carbon Chemistry in Dense Molecular Clouds: Theory and Observational Constraints
For the most part, gas phase models of the chemistry of dense molecular clouds
predict the abundances of simple species rather well. However, for larger molecules and even
for small systems rich in carbon these models often fail spectacularly. We present a brief review
of the basic assumptions and results of large scale modeling of the carbon chemistry in dense
molecular clouds. Particular attention will be paid to the influence of the gas phase C/O ratio in
molecular clouds, and the likely role grains play in maintaining this ratio as clouds evolve from
initially diffuse objects to denser cores with associated stellar and planetary formation.
Recent spectral line surveys at centimeter and millimeter wavelengths along with selected
observations in the submillimeter have now produced an accurate "inventory" of the gas phase
carbon budget in several different types of molecular clouds, though gaps in our knowledge clearly
remain. The constraints these observations place on theoretical models of interstellar chemistry
can be used to gain insights into why the models fail, and show also which neglected processes
must be included in more complete analyses. Looking toward the future, larger molecules are
especially difficult to study both experimentally and theoretically in such dense, cold regions, and
some new methods are therefore outlined which may ultimately push the detectability of small
carbon chains and rings to much heavier species
Predictability: a way to characterize Complexity
Different aspects of the predictability problem in dynamical systems are
reviewed. The deep relation among Lyapunov exponents, Kolmogorov-Sinai entropy,
Shannon entropy and algorithmic complexity is discussed. In particular, we
emphasize how a characterization of the unpredictability of a system gives a
measure of its complexity. Adopting this point of view, we review some
developments in the characterization of the predictability of systems showing
different kind of complexity: from low-dimensional systems to high-dimensional
ones with spatio-temporal chaos and to fully developed turbulence. A special
attention is devoted to finite-time and finite-resolution effects on
predictability, which can be accounted with suitable generalization of the
standard indicators. The problems involved in systems with intrinsic randomness
is discussed, with emphasis on the important problems of distinguishing chaos
from noise and of modeling the system. The characterization of irregular
behavior in systems with discrete phase space is also considered.Comment: 142 Latex pgs. 41 included eps figures, submitted to Physics Reports.
Related information at this http://axtnt2.phys.uniroma1.i
Evolution of Complexity in Out-of-Equilibrium Systems by Time-Resolved or Space-Resolved Synchrotron Radiation Techniques
Out-of-equilibrium phenomena are attracting high interest in physics,
materials science, chemistry and life sciences. In this state, the study of
structural fluctuations at different length scales in time and space are
necessary to achieve significant advances in the understanding of
structure-functionality relationship. The visualization of patterns arising
from spatiotemporal fluctuations is nowadays possible thanks to new advances in
X-ray instrumentation development that combine high resolution both in space
and in time. We present novel experimental approaches using high brilliance
synchrotron radiation sources, fast detectors and focusing optics, joint with
advanced data analysis based on automated statistical, mathematical and imaging
processing tools. This approach has been used to investigate structural
fluctuations in out-of-equilibrium systems in the novel field of inhomogeneous
quantum complex matter at the crossing point of technology, physics and
biology. In particular, we discuss how nanoscale complexity controls the
emergence of high temperature superconductivity (HTS), myelin functionality and
formation of hybrid organic-inorganic nanostructures. The emergent complex
geometries, opening novel venues to quantum technology and to development of
quantum physics of living systems, are discussedComment: 18 pages, 7 figure
Interdisciplinary research on the nature and properties of ceramic materials
Several investigations concerning the properties and processing of brittle ceramic materials as related to design considerations are briefly described. Surface characterization techniques, fractography, high purity materials, creep properties, impact and thermal shock resistance, and reaction bonding are discussed
Chemistry in Dense Molecular Clouds: Theory and Observational Constraints
For the most part, gas phase models of the chemistry of dense molecular clouds
predict the abundances of simple species rather well. However, for larger molecules and even for
small systems rich in carbon these models often fail spectacularly. We present a brief review of the
basic assumptions and results of large scale modeling of the chemistry in dense molecular clouds.
Particular attention will be paid to the influence of the gas phase ratios of the major elements
in molecular clouds, and the likely role grains play in maintaining these ratios as clouds evolve
from initially diffuse objects to denser cores with associated stellar and planetary formation.
Recent spectral line surveys at centimeter and millimeter wavelengths along with selected
observations in the submillimeter have now produced an accurate "inventory" of the gas phase
elemental budgets in different types of molecular clouds, though gaps in our knowledge clearly
remain. The constraints these observations place on theoretical models of interstellar chemistry
can be used to gain insights into why the models fail, and show also which neglected processes
must be included in more complete analyses. Looking toward the future, truly protostellar regions
are only now becoming available for both experimental and theoretical study, and some of the
expected modifications of molecular cloud chemistry in these sources are therefore outlined
Detection of a branched alkyl molecule in the interstellar medium: iso-propyl cyanide
The largest non-cyclic molecules detected in the interstellar medium (ISM)
are organic with a straight-chain carbon backbone. We report an interstellar
detection of a branched alkyl molecule, iso-propyl cyanide (i-C3H7CN), with an
abundance 0.4 times that of its straight-chain structural isomer. This
detection suggests that branched carbon-chain molecules may be generally
abundant in the ISM. Our astrochemical model indicates that both isomers are
produced within or upon dust grain ice mantles through the addition of
molecular radicals, albeit via differing reaction pathways. The production of
iso-propyl cyanide appears to require the addition of a functional group to a
non-terminal carbon in the chain. Its detection therefore bodes well for the
presence in the ISM of amino acids, for which such side-chain structure is a
key characteristic.Comment: This is the author's version of the work. It is posted here by
permission of the AAAS for non-commercial use. The definitive version was
published in Science 345, 1584 (2014), doi:10.1126/science.125667
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