Scaling Theory and Numerical Simulations of Aerogel Sintering

A simple scaling theory for the sintering of fractal aerogels is presented. The densification at small scales is described by an increase of the lower cut-off length $a$ accompanied by a decrease of the upper cut-off length $\xi$, in order to conserve the total mass of the system. Scaling laws are derived which predict how $a$, $\xi$ and the specific pore surface area $\Sigma$ should depend on the density $\rho$. Following the general ideas of the theory, numerical simulations of sintering are proposed starting from computer simulations of aerogel structure based on a diffusion-limited cluster-cluster aggregation gelling process. The numerical results for $a$, $\xi$ and $\Sigma$ as a function of $\rho$ are discussed according to the initial aerogel density. The scaling theory is only fully recovered in the limit of very low density where the original values of $a$ and $\xi$ are well separated. These numerical results are compared with experiments on partially densified aerogels.Comment: RevTex, 17 pages + 6 postscript figures appended using "uufiles". To appear in J. of Non-Cryst. Solid

Statistical inference in matched case-control studies of recurrent events.

BACKGROUND: The concurrent sampling design was developed for case-control studies of recurrent events. It involves matching for time. Standard conditional logistic-regression (CLR) analysis ignores the dependence among recurrent events. Existing methods for clustered observations for CLR do not fit the complex data structure arising from the concurrent sampling design. METHODS: We propose to break the matches, apply unconditional logistic regression with adjustment for time in quintiles and residual time within each quintile, and use a robust standard error for observations clustered within persons. We conducted extensive simulation to evaluate this approach and compared it with methods based on CLR. We analysed data from a study of childhood pneumonia to illustrate the methods. RESULTS: The proposed method and CLR methods gave very similar point estimates of association and showed little bias. The proposed method produced confidence intervals that achieved the target level of coverage probability, whereas the CLR methods did not, except when disease incidence was low. CONCLUSIONS: The proposed method is suitable for the analysis of case-control studies with recurrent events

Initial cardiovascular treatment patterns during the first 90 days following an incident cardiovascular event

Aims: The aim of this study was to investigate the initial cardiovascular prescription patterns in patients after their first cardiovascular events, and to identify factors associated with cardiovascular polypharmacy. Methods: This was a cross‐sectional study including patients aged ≥ 45 years with the first record of coronary heart disease (CHD) or stroke between 2007 and 2016 using The Health Improvement Network database. This study investigated the patterns of cardiovascular drugs prescribed during the first 90 days after the first cardiovascular events. Logistic regression was used to examine the association between patients' baseline characteristics and cardiovascular polypharmacy (≥5 cardiovascular drugs). Results: A total of 121,600 (59,843 CHD and 61,757 stroke) patients were included in the study. The mean age was 69.5 ± 11.9 years. The proportion of patients who were prescribed 0–1, 2–3, 4–5 drugs and ≥6 drugs were 11.0%, 29.8%, 38.6% and 20.5%, respectively. Factors associated with cardiovascular polypharmacy were sex (female: OR 0.74, 95% CI 0.72–0.76 vs male), age (75–84 years old: OR 0.50, 0.47–0.53 vs 45–54 years old), smoking status (current smoking: OR 1.29, 1.15–1.24 vs never), body mass index (obesity: OR 1.38, 1.34–1.43 vs normal), deprivation status (most deprived: OR 1.09, 1.04–1.14 vs least deprived) and Charlson comorbidity index (index ≥5: OR 1.25, 1.16–1.35 vs index 0). Conclusion: Multiple cardiovascular drugs treatment was common in patients with CVD in the UK. High‐risk factors of CVD were also associated with cardiovascular polypharmacy. Further studies are warranted to assess the impact of cardiovascular polypharmacy and its interaction on CVD recurrence and mortality

Polyelectrolyte interlayers with a broad processing window for high efficiency inverted organic solar cells towards mass production

Neutral polyelectrolyte interfacial layers in organic solar cells are well-known for their ability to tailor the work function of electrodes, improve charge carrier extraction and maximize open circuit voltage. However, they also suffer from low charge carrier conductivity, and therefore the interlayer must be kept thin, which in turn requires very precise deposition. This prerequisite significantly reduces the robustness of the fabrication process and makes such structures difficult to up-scale for roll-to-roll mass production. Herein, we find that by washing the polyelectrolyte layer with N,N-dimethylformamide (DMF) after deposition, solar cell efficiency jumps to near optimum levels, no matter what the original thickness of the polyelectrolyte layer. Subsequent characterization of the DMF-washed ZnO/PEI interlayer reveals a changed surface structure, passivated surface trap states, and thus improved transport properties and lower recombination losses. We demonstrate the general applicability of the method to other state-of-the-art material systems, namely P3HT:ICBA, PTB7:PC71BM and PTB7-Th:PC71BM. We find that the more efficient the material system, the larger the improvement in efficiency after DMF washing. Thus, this method represents a general way to relax the fabrication criteria for high efficiency organic solar cells. We anticipate that this method could be of use in other classes of devices such as OTFTs and OLEDs

Quantized reduction as a tensor product

Symplectic reduction is reinterpreted as the composition of arrows in the category of integrable Poisson manifolds, whose arrows are isomorphism classes of dual pairs, with symplectic groupoids as units. Morita equivalence of Poisson manifolds amounts to isomorphism of objects in this category. This description paves the way for the quantization of the classical reduction procedure, which is based on the formal analogy between dual pairs of Poisson manifolds and Hilbert bimodules over C*-algebras, as well as with correspondences between von Neumann algebras. Further analogies are drawn with categories of groupoids (of algebraic, measured, Lie, and symplectic type). In all cases, the arrows are isomorphism classes of appropriate bimodules, and their composition may be seen as a tensor product. Hence in suitable categories reduction is simply composition of arrows, and Morita equivalence is isomorphism of objects.Comment: 44 pages, categorical interpretation adde

Incoherent non-Fermi liquid scattering in a Kondo lattice

One of the most notorious non-Fermi liquid properties of both archetypal heavy-fermion systems [1-4] and the high-Tc copper oxide superconductors [5] is an electrical resistivity that evolves linearly with temperature, T. In the heavy-fermion superconductor CeCoIn5 [5], this linear behaviour was one of the first indications of the presence of a zero-temperature instability, or quantum critical point. Here, we report the observation of a unique control parameter of T-linear scattering in CeCoIn5, found through systematic chemical substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce sub-lattice. We find that the evolution of inelastic scattering in Ce1-xRxCoIn5 is strongly dependent on the f-electron configuration of the R ion, whereas two other key properties -- Cooper-pair breaking and Kondo-lattice coherence -- are not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature of incoherent scattering centers in the Kondo lattice, which provides insight into the anomalous scattering rate synonymous with quantum criticality [7].Comment: 4 pages, 3 figures (published version

Extended X-ray Emission in Compton Thick AGN with Deep Chandra Observations

We present the spatial analysis of five Compton thick (CT) active galactic nuclei (AGNs), including MKN 573, NGC 1386, NGC 3393, NGC 5643, and NGC 7212, for which high resolution Chandra observations are available. For each source, we find hard X-ray emission (>3 keV) extending to ~kpc scales along the ionization cone, and for some sources, in the cross-cone region. This collection represents the first, high-signal sample of CT AGN with extended hard X-ray emission for which we can begin to build a more complete picture of this new population of AGN. We investigate the energy dependence of the extended X-ray emission, including possible dependencies on host galaxy and AGN properties, and find a correlation between the excess emission and obscuration, suggesting a connection between the nuclear obscuring material and the galactic molecular clouds. Furthermore, we find that the soft X-ray emission extends farther than the hard X-rays along the ionization cone, which may be explained by a galactocentric radial dependence on the density of molecular clouds due to the orientation of the ionization cone with respect to the galactic disk. These results are consistent with other CT AGN with observed extended hard X-ray emission (e.g., ESO 428-G014 and the Ma et al. 2020 CT AGN sample), further demonstrating the ubiquity of extended hard X-ray emission in CT AGN.Comment: 29 pages, 22 figures, 7 tables, Accepted for publication in Ap