Dode bijen geven hun geheimen prijs

Al jaren sturen bijenhouders ons monsters van dode bijen en bijenbroed. We kijken deze monsters na op ziekten om de doodsoorzaak na te gaan. De laatste twee jaar hebben we actief bekendheid gegeven aan deze (gratis) service, waardoor het aantal ingezonden monsters gigantisch is toegenomen. Dat levert wel meer werk, maar vooral meer gegevens op. Een overzicht van de resultaten van september 2008 tot september 200

Concurrentie tussen honingbijen en wilde bijen (1)

Eerste deel van een reeks over de concurrentie tussen honingbijen en wilde bijen. In 2010 was er veel te doen over concurrentie tussen honingbijen en wilde bijen. Erik van der Spek (2010) stelde dat het plaatsen van grote aantallen bijenkasten een bedreiging vormt voor de wilde bijen in natuurgebieden. Niet vee later schreef Arie Koster (2010) hij op de Elspeter heide rond bijenvolken net zoveel heidezijdebijen waarnam als op andere delen van de heide. Een dergelijke discussie is zeker niet nieuw. In 1998 schreef Koster er al over in bijenteelt en in 1998 verscheen er een rapport over dit onderwerp met aanbevelingen vooer aantallen bijenvolken in natuurgebieden (Smeekens e.a., 1998). Sindsdien is echter nog veel meer onderzoek gedaan. Tijd voor een updat

Met gezonde bijen naar de heide

Op 22 maart 2010 kwam een bont gezelschap van bijenhouders van ABTB, ANI en NBV bijeen in Hoenderloo. Het onderwerp die avond was de vraag: “Hoe combineer ik varroabestrijding met de heidedracht?” Hieronder het antwoord en wel in de vorm van de basisprincipes van varroa bestrijding plus een concrete methode om deze te combineren met de heidedracht

Analysis of yarn bending behaviour

This paper adresses the bending behaviour of individual multi-filament yarns for use in textile forming analyses. Yarn specimens deform nonlinearly under their own weight in a cantilever configuration. a relation between the applied moment and the resulting curvature is established. Numerical simulations are performed to establish the contribution of shear rigidity to the deflectio

Magnon Planar Hall Effect and Anisotropic Magnetoresistance in a Magnetic Insulator

Electrical resistivities can be different for charge currents travelling parallel or perpendicular to the magnetization in magnetically ordered conductors or semiconductors, resulting in the well-known planar Hall effect and anisotropic magnetoresistance. Here, we study the analogous anisotropic magnetotransport behavior for magnons in a magnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$. Electrical and thermal magnon injection, and electrical detection methods are used at room temperature with transverse and longitudinal geometries to measure the magnon planar Hall effect and anisotropic magnetoresistance, respectively. We observe that the relative difference between magnon current conductivities parallel and perpendicular to the magnetization, with respect to the average magnon conductivity, i.e. $|(\sigma_{\parallel}^{\textrm{m}}-\sigma_{\perp}^{\textrm{m}})/\sigma_{0}^{\textrm{m}}|$ , is approximately 5% with the majority of the measured devices showing $\sigma_{\perp}^{\textrm{m}}>\sigma_{\parallel}^{\textrm{m}}$.Comment: 18 pages, 16 figure

Friction measurements on carbon fibre tows

Friction plays an important role in the production of fibre reinforced\ud composite products. The fibrous tows deform during the forming phase. Friction is\ud regarded as a dominant phenomenon in tow deformation mechanisms. The coefficient\ud of friction is a material-interface characteristic which gives a relation between applied\ud deformation loads and frictional forces. A capstan experiment has been performed with\ud carbon fibre tows on a steel cylinder. This work aims to clarify friction related mechanisms\ud and identify dominant parameters. The applicability of the capstan experiment is\ud investigated with respect to the frictional behaviour of fibrous tows

Criteria for accurate determination of the magnon relaxation length from the nonlocal spin Seebeck effect

The nonlocal transport of thermally generated magnons not only unveils the underlying mechanism of the spin Seebeck effect, but also allows for the extraction of the magnon relaxation length ($\lambda_m$) in a magnetic material, the average distance over which thermal magnons can propagate. In this study, we experimentally explore in yttrium iron garnet (YIG)/platinum systems much further ranges compared with previous investigations. We observe that the nonlocal SSE signals at long distances ($d$) clearly deviate from a typical exponential decay. Instead, they can be dominated by the nonlocal generation of magnon accumulation as a result of the temperature gradient present away from the heater, and decay geometrically as $1/d^2$. We emphasize the importance of looking only into the exponential regime (i.e., the intermediate distance regime) to extract $\lambda_m$. With this principle, we study $\lambda_m$ as a function of temperature in two YIG films which are 2.7 and 50 $\mu$m in thickness, respectively. We find $\lambda_m$ to be around 15 $\mu$m at room temperature and it increases to 40 $\mu$m at $T=$ 3.5 K. Finite element modeling results agree with experimental studies qualitatively, showing also a geometrical decay beyond the exponential regime. Based on both experimental and modeling results we put forward a general guideline for extracting $\lambda_m$ from the nonlocal spin Seebeck effect.Comment: 9 pages, 7 figure

Cosine Contours: a Multipurpose Representation for Melodies

Melodic contour is central to our ability to perceive and produce music. We propose to represent melodic contours as a combination of cosine functions, using the discrete cosine transform. The motivation for this approach is twofold: (1) it approximates a maximally informative contour representation (capturing most of the variation in as few dimensions as possible), but (2) it is nevertheless independent of the specifics of the data sets for which it is used. We consider the relation with principal component analysis, which only meets the first of these requirements. Theoretically, the principal components of a repertoire of random walks are known to be cosines. We find, empirically, that the principal components of melodies also closely approximate cosines in multiple musical traditions. We demonstrate the usefulness of the proposed representation by analyzing contours at three levels (complete songs, melodic phrases and melodic motifs) across multiple traditions in three small case studies