13,837 research outputs found
Polymorphism of the glass former ethanol confined in mesoporous silicon
X-ray diffraction patterns of ethanol confined in parallel-aligned channels
of approx. 10 nm diameter and 50 micrometer length in mesoporous silicon have
been recorded as a function of filling fraction, temperature and for varying
cooling and heating rates. A sorption isotherm, recorded in the liquid state,
indicates a three monolayer thick, strongly adsorbed wall layer and a capillary
condensed fraction of molecules in the pore center. Though the strongly
adsorbed film remains in an amorphous state for the entire temperature range
investigated, the capillary condensed molecules reproduce the polymorphism of
bulk solid ethanol, that is the formation of either crystalline or glass-like
states as a function of cooling rate. The critical rate necessary to achieve a
vitrification in the mesopores is, however, at least two orders of magnitude
smaller than in the bulk state. This finding can be traced both to pure
geometrical constraints and quenched disorder effects, characteristic of
confinement in mesoporous silicon.Comment: 6 pages, 4 figure
Lorentz symmetry is relevant
We set up a covariant renormalisation group equation on a foliated spacetime
which preserves background diffeomorphism symmetry. As a first application of
the new formalism, we study the effect of quantum fluctuations in Lorentz
symmetry breaking theories of quantum gravity. It is found that once a small
breaking is introduced e.g. at the Planck scale, quantum fluctuations enhance
this breaking at low energies. A numerical analysis shows that the
magnification is of order unity for trajectories compatible with a small
cosmological constant. The immediate consequence is that the stringent
observational constraints on Lorentz symmetry breaking are essentially
scale-independent and must be met even at the Planck scale.Comment: 10 pages, 1 figur
Critical (Chiral) Heisenberg Model with the Functional Renormalisation Group
We discuss the Heisenberg model and its chiral extension in an extended
truncation with the help of functional methods. Employing computer algebra to
derive the beta functions, and pseudo-spectral methods to solve them, we are
able to go significantly beyond earlier approximations, and provide new
estimates on the critical quantities of both models. The fixed point of the
Heisenberg model is mostly understood, and our results are in agreement with
estimates from various other approaches, including Monte Carlo and conformal
bootstrap studies. By contrast, in the chiral case, the formerly known
disagreement with lattice studies persists, raising the question whether
actually the same universality class is described.Comment: 10 pages, 5 figures; v2: matches journal versio
Crystallization of medium length 1-alcohols in mesoporous silicon: An X-ray diffraction study
The linear 1-alcohols n-C16H33OH, n-C17H35OH, n-C19H37OH have been imbibed
and solidified in lined up, tubular mesopores of silicon with 10 nm and 15 nm
mean diameters, respectively. X-ray diffraction measurements reveal a set of
six discrete orientation states (''domains'') characterized by a perpendicular
alignment of the molecules with respect to the long axis of the pores and by a
four-fold symmetry about this direction, which coincides with the crystalline
symmetry of the Si host. A Bragg peak series characteristic of the formation of
bilayers indicates a lamellar structure of the spatially confined alcohol
crystals in 15 nm pores. By contrast, no layering reflections could be detected
for 10 nm pores. The growth mechanism responsible for the peculiar orientation
states is attributed to a nano-scale version of the Bridgman technique of
single-crystal growth, where the dominant growth direction is aligned
parallelly to the long pore axes. Our observations are analogous to the growth
phenomenology encountered for medium length n-alkanes confined in mesoporous
silicon (Phys. Rev. E 75, 021607 (2007)) and may further elucidate why porous
silicon matrices act as an effective nucleation-inducing material for protein
solution crystallization.Comment: 4 pages, 4 figures, to appear as a Brief Report in Physical Review
Bayesian Modelling of Inseparable Space-Time Variation in Disease Risk
This paper proposes a unified framework for a Bayesian analysis of incidence or mortality data in space and time. We introduce four different types of prior distributions for space time interaction in extension of a model with only main effects. Each type implies a certain degree of prior dependence for the interaction parameters, and corresponds to the product of one of the two spatial with one of the two temporal main effects. The methodology is illustrated by an analysis of Ohio lung cancer data 1968-88 via Markov chain Monte Carlo simulation. We compare the fit and the complexity of several models with different types of interaction by means of quantities related to the posterior deviance. Our results confirm an epidemiological hypothesis about the temporal development of the association between urbanization and risk factors for cancer
The excitation of ion bursts from grids
Step function excitation of ion bursts from gri
Towards reconstructing the quantum effective action of gravity
Starting from a parameterisation of the quantum effective action for gravity
we calculate correlation functions for observable quantities. The resulting
templates allow to reverse-engineer the couplings describing the effective
dynamics from the correlation functions. Applying this new formalism to the
autocorrelation function of spatial volume fluctuations measured within the
Causal Dynamical Triangulations program suggests that the corresponding quantum
effective action consists of the Einstein-Hilbert action supplemented by a
non-local interaction term. We expect that our matching-template formalism can
be adapted to a wide range of quantum gravity programs allowing to bridge the
gap between the fundamental formulation and observable low-energy physics.Comment: 6 pages, 1 figure; v2: reference update+clarification; v3: matches
published versio
- …