AR Versus MA Disturbance Terms

We show how several models with moving average errors can be easily rewritten as models with autoregressive errors, thereby simplifying inference.

Experimental assessment of exposure to gaseous pollutants from mattresses and pillows while asleep

Every human spends 30% of his or her lifetime and about 70% of the time he or she is at home in their bed. Mattresses, pillows and bedlinnen are heavily treated with flame-retardants, detergents etc, substances that are known to have, next to a useful effect, an impact on human health. While asleep, the nose and mouth are in the direct proximity of these sources for a long period of time. Although these circumstances seem worrying at the least, virtually no research has been published on the exposure to and intake emissions from bedding. This paper presents the results form climate chamber tests with a breathing thermal mannequin that assess the intake fraction for nose breathing for gaseous emissions from mattresses and pillows under steady state conditions, using a continuous SF6 source. The intake fractions for supine, lateral and prone sleep positions as well as different bedding arrangements are reported. The results demonstrate that the human metabolism is a dominant factor in the dilution of emissions in close proximity of the nose, reducing exposure by 40% compared to a case without metabolic heat output. This effect is more important than the sleep position. Additionally, covering the head with the bedding is shown to increase exposure with magnifying factor of 25 and is therefore to be avoided

Mixed finite element methods for linear elasticity with weakly imposed symmetry

In this paper, we construct new finite element methods for the approximation of the equations of linear elasticity in three space dimensions that produce direct approximations to both stresses and displacements. The methods are based on a modified form of the Hellinger--Reissner variational principle that only weakly imposes the symmetry condition on the stresses. Although this approach has been previously used by a number of authors, a key new ingredient here is a constructive derivation of the elasticity complex starting from the de Rham complex. By mimicking this construction in the discrete case, we derive new mixed finite elements for elasticity in a systematic manner from known discretizations of the de Rham complex. These elements appear to be simpler than the ones previously derived. For example, we construct stable discretizations which use only piecewise linear elements to approximate the stress field and piecewise constant functions to approximate the displacement field.Comment: to appear in Mathematics of Computatio

The Stakes Could Not Be Higher: The Allied Response in Ukraine

Why are the United States and other western NATO allies so invested in the war in Ukraine?  Why have NATO partners provided such enormous military assistance?  This short essay argues that Russia’s attempt to override the sovereignty of its neighbour poses a threat not just to Ukraine (although it is, of course, principally that) but also a threat to the modern world order which is built on fundamentally liberal institutions.  Nor is it just the fact of Russia’s invasion (второжение) but also how the war is being prosecuted.  The essay then examines President Volodymyr Zelensky’s attempts to cultivate his image in line with Western heroes like Washington and Churchill before turning to rebutting potential criticisms.  In all, the essay concludes that the stakes for the world could not be higher