Nonequilibrium phonon mean free paths in anharmonic chains

Harnessing the power of low-dimensional materials in thermal applications calls for a solid understanding of the anomalous thermal properties of such systems. We analyze thermal conduction in one-dimensional systems by determining the frequency-dependent phonon mean free paths (MFPs) for an anharmonic chain, delivering insight into the diverging thermal conductivity observed in computer simulations. In our approach, the MFPs are extracted from the length-dependence of the spectral heat current obtained from nonequilibrium molecular dynamics simulations. At low frequencies, the results reveal a power-law dependence of the MFPs on frequency, in agreement with the diverging conductivity and the recently determined equilibrium MFPs. At higher frequencies, however, the nonequilibrium MFPs consistently exceed the equilibrium MFPs, highlighting the differences between the two quantities. Exerting pressure on the chain is shown to suppress the mean free paths and to generate a weaker divergence of MFPs at low frequencies. The results deliver important insight into anomalous thermal conduction in low-dimensional systems and also reveal differences between the MFPs obtained from equilibrium and nonequilibrium simulations.Comment: 8 pages, 7 figures, minor changes to v

Role of anharmonic phonon scattering in the spectrally decomposed thermal conductance at planar interfaces

Detailed understanding of vibrational heat transfer mechanisms between solids is essential for the efficient thermal engineering and control of nanomaterials. We investigate the frequency dependence of anharmonic scattering and interfacial thermal conduction between two acoustically mismatched solids in planar contact by calculating the spectral decomposition of the heat current flowing through an interface between two materials. The calculations are based on analyzing the correlations of atomic vibrations using the data extracted from non-equilibrium molecular dynamics simulations. Inelastic effects arising from anharmonic interactions are shown to significantly facilitate heat transfer between two mass-mismatched face-centered cubic lattices even at frequencies exceeding the cut-off frequency of the heavier material due to (i) enhanced dissipation of evanescent vibrational modes and (ii) frequency-doubling and frequency-halving three-phonon energy transfer processes at the interface. The results provide substantial insight into interfacial energy transfer mechanisms especially at high temperatures, where inelastic effects become important and other computational methods are ineffective.Comment: minor changes to v

Magnetic nanocomposites at microwave frequencies

Most conventional magnetic materials used in the electronic devices are ferrites, which are composed of micrometer-size grains. But ferrites have small saturation magnetization, therefore the performance at GHz frequencies is rather poor. That is why functionalized nanocomposites comprising magnetic nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm, and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have a significant potential for the electronics industry. When the size of the nanoparticles is smaller than the critical size for multidomain formation, these nanocomposites can be regarded as an ensemble of particles in single-domain states and the losses (due for example to eddy currents) are expected to be relatively small. Here we review the theory of magnetism in such materials, and we present a novel measurement method used for the characterization of the electromagnetic properties of composites with nanomagnetic insertions. We also present a few experimental results obtained on composites consisting of iron nanoparticles in a dielectric matrix.Comment: 20 pages, 10 figures, 5 table

Static friction measurements on steel against uncoated and coated cast iron

Static friction is a phenomenon we may mainly consider as related to frictional joints within staticmechanics. The step from static friction to tribological phenomena is, however, rather short, since at theonset of sliding in a mechanical contact, the static friction determines the initial resistance against motion.Static friction furthermore plays a role in contacts subjected to traction and fretting. Although being aphenomenon of short duration, the tribological phenomena during the transition from static friction to slidingfriction may be of great importance for the operational life of the contact surfaces, particularly if theprocedure is repeated for a sufficient number of times.The present paper describes the principles of static friction measurements, details of the employed staticfriction tribometer and the results of measurements with unlubricated and lubricated sliding couplesconsisting of steel against uncoated and coated cast iron

Milloin epäillä skitsofreniaa?

Skitsofrenia ilmenee laaja-alaisena tunteiden, havaitsemisen, motivaation ja käyttäytymisen säätelyn häiriönä. Skitsofrenian kehittymisen ajatellaan liittyvän keskushermoston kehittymis- ja kypsymisprosessiin, johon liittyy usein häiriöitä kognitiivisissa toiminnoissa. Potilaat ovat myös herkkiä erilaisille ympäristön ­kuormitustekijöille. Varhainen psykoosioireiston tunnistaminen ja hoidon aloittaminen parantavat ennustetta. Suuressa psykoosiriskissä olevien nuorten tunnistaminen ja hoito voivat estää skitsofrenian puhkeamisen. Diagnostinen selvittely ja hoidon aloitus on usein perusteltua toteuttaa erikoissairaanhoidossa, kun kyseessä on uusi skitsofreniapotilas.Peer reviewe

Maallikkohypnoosiin liittynyt akuutti skitsofreenistyyppinen psykoosi

Vaik­ka hyp­noosia pi­detään var­sin haitat­to­mana hoito­muo­tona, kirjal­li­suu­dessa on ku­vattu sen varo­mat­tomaan käyt­töön liitty­neitä kompli­kaa­tioita, ku­ten disso­sia­tii­visia ja lyhyt­kes­toisia psy­koot­tisia ti­loja. Yli 50-vuotiaan aiem­min ter­veen ja työelä­mässä menes­tyneen nai­sen akuutti skit­sof­ree­nis­tyyp­pinen ­psy­koot­tinen häi­riö al­koi varo­mat­to­masti käy­tetyn maallik­ko­hyp­noosin yhtey­dessä. Po­tilas ko­keili sel­laista ensim­mäistä ker­taa, ja hä­nen koke­mansa hallu­si­naatiot ja harha­luulot liit­tyivät yksi­nomaan hyp­noosiin. Po­tilaan oi­reistoon liit­tyi vaaral­lisia piir­teitä, ku­ten har­haääniä, jot­ka kehot­tivat hän­tä riski­käyt­täy­ty­miseen liiken­teessä. Ly­hyen sairaa­la­hoidon jäl­keen po­tilas voi seuran­nassa hy­vin. Hyp­noosia tu­lisi käyt­tää vain valvo­tusti tervey­den­huol­lossa.Peer reviewe