Long wavelength properties of phase field crystal models with second order dynamics

The phase field crystal (PFC) approach extends the notion of phase field models by describing the topology of the microscopic structure of a crystalline material. One of the consequences is that local variation of the interatomic distance creates an elastic excitation. The dynamics of these excitations poses a challenge: pure diffusive dynamics cannot describe relaxation of elastic stresses that happen through phonon emission. To this end, several different models with fast dynamics have been proposed. In this article we use the amplitude expansion of the PFC model to compare the recently proposed hydrodynamic PFC amplitude model with two simpler models with fast dynamics. We compare these different models analytically and numerically. The results suggest that in order to have proper relaxation of elastic excitations, the full hydrodynamical description of the PFC amplitudes is required.Comment: 10 pages, 7 figure

Mineraalikemiallisia todisteita erittäin magneisum-rikkaista kivisulista Karoon magmaprovinssissa

Peer reviewe

18O-rikastuminen Karoon suuren magmaprovinssin antarktisen osan vaippalähteissä

Karoo continental flood basalt (CFB) province is known for its highly variable trace element and isotopic composition, often attributed to the involvement of continental lithospheric sources. Here, we report oxygen isotopic compositions measured with secondary ion mass spectrometry for hand-picked olivine phenocrysts from similar to 190 to 180 Ma CFBs and intrusive rocks from Vestfjella, western Dronning Maud Land, that form an Antarctic extension of the Karoo province. The Vestfjella lavas exhibit heterogeneous trace element and radiogenic isotope compositions (e.g., epsilon(Nd) from -16 to +2 at 180 Ma) and the involvement of continental lithospheric mantle and/or crust in their petrogenesis has previously been suggested. Importantly, our sample set also includes rare primitive dikes that have been derived from depleted asthenospheric mantle sources (epsilon(Nd) up to + 8 at 180 Ma). The majority of the oxygen isotopic compositions of the olivines from these dike rocks (delta O-18 = 4.4-5.2%; Fo = 78-92 mol%) are also compatible with such sources. The olivine phenocrysts in the lavas, however, are characterized by notably higher delta O-18 (6.2-7.5%; Fo = 70-88 mol%); and one of the dike samples gives intermediate compositions (5.2-6.1%, Fo = 83-87 mol%) between the other dikes and the CFBs. The oxygen isotopic compositions do not correlate with radiogenic isotope compositions susceptible to crustal assimilation (Sr, Nd, and Pb) or with geochemical indicators of pyroxene-rich mantle sources. Instead, delta O-18 correlates positively with enrichments in large-ion lithophile elements (especially K) and Os-187. We suggest that the oxygen isotopic compositions of the Vestfjella CFB olivines primarily record large-scale subduction-related metasomatism of the sub-Gondwanan mantle (base of the lithosphere or deeper) prior to Karoo magmatism. The overall influence of such sources to Karoo magmatism is not known, but, in addition to continental lithosphere, they may be responsible for some of the geochemical heterogeneity observed in the CFBs.Peer reviewe

Lorentz shear modulus of fractional quantum Hall states

We show that the Lorentz shear modulus of macroscopically homogeneous electronic states in the lowest Landau level is proportional to the bulk modulus of an equivalent system of interacting classical particles in the thermodynamic limit. Making use of this correspondence we calculate the Lorentz shear modulus of Laughlin's fractional quantum Hall states at filling factor $\nu=1/m$ ($m$ an odd integer) and find that it is equal to $\pm \hbar mn/4$, where $n$ is the density of particles and the sign depends on the direction of magnetic field. This is in agreement with the recent result obtained by Read in arXiv:0805.2507 and corrects our previous result published in Phys. Rev. B {\bf 76}, 161305 (R) (2007).Comment: 8 pages, 3 figure

Phase-field-crystal models and mechanical equilibrium

Phase-field-crystal (PFC) models constitute a field theoretical approach to solidification, melting, and related phenomena at atomic length and diffusive time scales. One of the advantages of these models is that they naturally contain elastic excitations associated with strain in crystalline bodies. However, instabilities that are diffusively driven towards equilibrium are often orders of magnitude slower than the dynamics of the elastic excitations, and are thus not included in the standard PFC model dynamics. We derive a method to isolate the time evolution of the elastic excitations from the diffusive dynamics in the PFC approach and set up a two-stage process, in which elastic excitations are equilibrated separately. This ensures mechanical equilibrium at all times. We show concrete examples demonstrating the necessity of the separation of the elastic and diffusive time scales. In the small-deformation limit this approach is shown to agree with the theory of linear elasticity.Peer reviewe

End-of-life care pathway of head and neck cancer patients : single-institution experience

Studies on palliative care of head and neck cancer (HNC) patients are scarce although the affected patient population is quite large. To evaluate the role of a specialised palliative-care pathway of HNC patients. Data on all HNC patients who were treated at the Helsinki University Hospital Palliative Care Center during 1 year were retrospectively reviewed. The analysis comprised 60 patients (49 males; mean age 67 years; range 28-88). All patients had a minimum follow-up of 1 year or until death. Fifty-nine (98%) out of the 60 patients died during the follow-up period. Median survival after diagnosis was 11 months (range 3 weeks-11.9 years) and after withholding disease-specific therapies 3 months (range 0-16). Thirty-three (55%) patients received palliative radiotherapy, 27 (45%) had PEG tube and 17 (28%) tracheostomy. Thirty-seven (66%) patients visited an emergency department (ED) (median 1.3 visits; range 0-6) and 21 (35%) were hospitalised at the university hospital during the palliative period. The most common severe complications were infection (also the most common reason for ED visits and hospitalisation), bleeding (four massive airway bleedings with one death), delirium and airway obstruction (one emergency tracheostomy). Twelve (35%) out of the 34 patients who were referred to specialised home care died at home as compared with three (12%) out of the 26 patients not supported by a specialised home-care team. Severe complications leading to an emergency unit visit and hospitalisation are common among HNC patients in their relatively short palliative period reflecting the need for early-integrated palliative care. Collaboration with a specialised palliative home-care team seems to increase end-of-life care at home.Peer reviewe

Dynamics of magnetization coupled to a thermal bath of elastic modes

We study the dynamics of magnetization coupled to a thermal bath of elastic modes using a system plus reservoir approach with realistic magnetoelastic coupling. After integrating out the elastic modes we obtain a self-contained equation for the dynamics of the magnetization. We find explicit expressions for the memory friction kernel and hence, {\em via} the Fluctuation-Dissipation Theorem, for the spectral density of the magnetization thermal fluctuations. For magnetic samples in which the single domain approximation is valid, we derive an equation for the dynamics of the uniform mode. Finally we apply this equation to study the dynamics of the uniform magnetization mode in insulating ferromagnetic thin films. As experimental consequences we find that the fluctuation correlation time is of the order of the ratio between the film thickness, $h$, and the speed of sound in the magnet and that the line-width of the ferromagnetic resonance peak should scale as $B_1^2h$ where $B_1$ is the magnetoelastic coupling constant.Comment: Revised version as appeared in print. 12 pages 9 figure