Increasing the usefulness of additive spline models by knot removal

Modern techniques for fitting generalized additive models mostly rely on basis expansions of covariates using a large number of basis functions and penalized estimation of parameters. For example, a mixed model approach is used to fit a model for children’s lung function that allows for non-linear influence of several covariates available in a substantial data set. While the resulting model is expected to have good prediction performance, its handling beyond simple visual presentation is problematic. It is shown how the number basis functions of the underlying B-spline representation can be reduced by knot removal techniques without refitting, while preserving the shape of the fitted functions. The condition for exact knot removal is extended towards approximate knot removal by incorporating the covariance matrix of the initial parameter estimates, resulting in considerable simplification of the model. Covariance matrices for the transformed parameter estimates are provided. It is demonstrated that enforcing the knot removal condition during estimation leads to the difference penalties employed in the P-spline approach for estimation of B-spline coefficients, and therefore provides a further justification for this type of penalty. A final transform to a truncated power basis provides a simple equation for the model. This increases transportability, while retaining properties of the initial fit such as good prediction performance.     

Correlation properties of combiners with memory in stream ciphers

For pseudo-random generators where one or several LFSRs are combined by a memoryless function, it is known that the output sequences are correlated to certain LFSR-sequences whose correlation coefficients c _t satisfy the equation _i c ₂ ⁱ = 1. In this paper it is proved that a corresponding result also holds for generators whose LFSRs are connected to a combiner with memory.If correlation probabilities are conditioned on side information, e.g., on known output digits, it is shown that new or stronger correlations may occur. This is exemplified for the summation cipher with only two LFSRs where such correlations can be exploited in a known plaintext attack. A cryptanalytic algorithm is given which is shown to be successful for LFSRs of considerable length and with arbitrary feedback connection.A preliminary version of this paper was presented at Eurocrypt '90, May 21–24, Århus, Denmark, and has appeared in the proceedings, pp. 204–213.     

Poisson’s ratio of porous and cellular materials with randomly distributed isometric pores or cells

The porosity dependence of Poisson's ratio of materials with random microstructure is investigated via analytical and numerical modeling. It is shown that all analytical models predict porosity independence if the solid Poisson ratio is 0.2 and for low porosities a converging trend toward this value with increasing porosity. From all theory-based relations, only power-law and exponential relations allow for auxetic behavior. Numerical calculations on computer-generated digital microstructures (overlapping and isolated spherical pores, pores between overlapping spherical grains, wall-based cellular materials/closed-cell foams, and strut-based cellular materials/open-cell foams) confirm the general qualitative trends of the analytical models, although a closer look reveals significant quantitative differences. Cellular materials and foams exhibit similar features as porous materials in general, but lack their converging trend toward values around 0.2. Comparison of our results with the classical Roberts-Garboczi results shows good agreement, with subtle differences due to the different microstructures generated.     

Orthoamide. L. Beiträge zur Chemie von Propiolaldehydaminalen – Synthesen und Umsetzungen zu Push–Pull-substituierten Buta-1,3-dienen,Cyclobutanen sowie vinylogen Amidiniumsalzen und 1,2,3-Triazolen

Orthoamides. L. Contribution to the Chemistry of Propiolaldehydaminales – Synthesis and Transformations to Push–Pull-substituted Buta-1,3-dienes, Cyclobutanes, Vinylogous Amidinium Salts and 1,2,3-Triazoles Tert-butylaminalester 5 reacts with terminal alkynes to give aminals of substituted propiolaldehydes 3c, d . The aminal 3a is accessible from N,N,N′,N′-tetramethylformamidinium chloride (7b) and sodium acetylide. The aminals 3b,c can also be prepared from bis(dimethylamino)acetonitrile 8 and terminal alkynes in the presence of sodium hydride. The nitrile 8 is also useful for the preparation of the bis-aminal of acetylenedialdehyde 6 . The aminal 3e can be transaminated by heating with secondary amines to give the aminals 3f–i . The aminals 3a–i react with strong CH₂-acidic compounds (pK_a between 9 and 14) to give the 1-dialkylamino-1,3-butadienes 10 . The isomeric 1-dialkylamino-butadienes 18 can be obtained from the condensation of the CH-acidic cinnamic acid derivatives 19 with dimethylformamidedimethylacetal. CH and NH-acidic compounds as cyanacetamide react with the aminals 3c,e exclusively with the acidic methylene group to produce the enamines 10h,t . The acylformamidine 21 can be obtained from 10t and tert-butylaminalester 5 . The pyridone 22 is accessible from the condensation product 10h by thermal cyclization. The pyrido[2,3-d]pyrimidine 26 is formed in the reaction of the 6-amino-uracile 23 with the aminal 3a . In an unexpected reaction the 1,2-bis(cyano-dialkylaminomethylene)-cyclobutanes 28a–d result from the action of trimethylsilylcyanide on the aminals 3e–h . The corresponding reaction with trimethylsilylisothiocyanate affords the vinylogous amidinium thiocyanates 34a, b . In the reaction of trimethylsilylazide and the aminals 3 are produced the 4-(dialkylaminomethylene)-4H-1,2,3-triazoles 38 .     

Graphene decoration with metal nanoparticles: towards easy integration for sensing applications

A simple and versatile method for the decoration of CVD grown graphene with metal nanoparticles is presented. The mechanism of nanoparticle formation is galvanic displacement resulting in physically adsorbed clusters. The single layer graphene obtained by this method can be easily transferred. Integration onto a gas sensing transducer is presented as proof of concept.     

Starch Consolidation Casting of Cordierite Precursor Mixtures—Rheological Behavior and Green Body Properties

The rheology of suspensions and mechanical properties of green bodies with cordierite composition (raw materials 37 wt% kaolin, 41 wt% talc, 22 wt% alumina, resulting in 46.6 wt% SiO₂, 38.1 wt% Al₂O₃, 13.6 wt% MgO) and two types of starch (corn or potato) are investigated. Rotational viscometry of suspensions with solids loading 50, 60, and 70 wt% without starch showed that all tend to be shear‐thinning with a small degree of thixotropy. Suspensions with a total solids loading of 60 wt% with 25 wt% replaced by starch exhibited higher viscosity and thixotropy, but the viscometric behavior is almost identical for the two starch types (apparent viscosities 130–50 mPa ·s). Oscillatory rheometry shows that for suspensions with potato starch the onset temperature for gelatinization is 61°C–63°C, that is, lower than for corn starch (72°C–73°C). Maximum storage moduli and phase shift values after gelatinization are similar for both systems. The mechanical properties of green disks, measured via diametral compression tests, reveal clear differences between materials prepared with corn and potato starch, with the latter showing higher elastic modulus, higher strength, and higher deformation at fracture, obviously because of incompletely gelatinized starch granules in the green bodies prepared with corn starch .     

Elastic properties of porous oxide ceramics prepared using starch as a pore-forming agent

The elastic properties, in particular the tensile modulus (Young's modulus) and Poisson ratio, of porous alumina, zirconia, and alumina–zirconia composite ceramics are studied using the resonance frequency method and the results compared with theoretical predictions. Starch is used as a pore-forming agent, so that the resulting microstructure is essentially of the matrix-inclusion type (with large bulk pores, connected by small throats when a percolation threshold is exceeded). It is found that for this type of microstructure the porosity dependence of the Young's modulus is significantly below the upper Hashin–Shtrikman bound and the power-law prediction; it corresponds well, however, to a recently proposed exponential relation and to an empirical volume-weighted average of the upper and lower Hashin–Shtrikman bounds. Results for all three types of ceramics indicate that – in the porosity range considered, i.e. up to approximately 50% – the Poisson ratio depends only slightly on porosity.