Coherent spin-current oscillations in transverse magnetic fields

We address the coherence of the dynamics of spin-currents with components transverse to an external magnetic field for the spin-1/2 Heisenberg chain. We study current autocorrelations at finite temperatures and the real-time dynamics of currents at zero temperature. Besides a coherent Larmor oscillation, we find an additional collective oscillation at higher frequencies, emerging as a coherent many-magnon effect at low temperatures. Using numerical and analytical methods, we analyze the oscillation frequency and decay time of this coherent current-mode versus temperature and magnetic field.     

Two classes of finite groups whose Chermak-Delgado lattice is a chain of length zero

It is an open question in the study of Chermak-Delgado lattices precisely which finite groups G have the property that 𝒞𝒟(G) is a chain of length 0. In this note, we determine two classes of groups with this property. We prove that if G = AB is a finite group, where A and B are abelian subgroups of relatively prime orders with A normal in G, then the Chermak-Delgado lattice of G equals {AC_B(A)}, a strengthening of earlier known results.     

Non-chromate deoxidation of AA2024-T3: Sodium bromate-nitric acid (20-60 °C)

The effect of a non-chromate deoxidiser (bromate-nitric acid) on AA2024-T3 has been examined by SEM, TEM/EELS and XPS. At low temperatures (20 °C) the deoxidiser removed all intermetallics but had little effect on the surface oxide. At 40 °C, attack on the intermetallics was again extensive but there was also evidence of attack on the surface oxide covering the matrix after 10 min of immersion, leaving a roughened porous oxide. At 60 °C, removal of intermetallics was complete and longer immersion times resulted in a characteristic scalloped structure across the surface which became more pronounced with increasing immersion time.     

Abrupt stress induced transformation in amorphous carbon films with a highly conductive transition phase

We demonstrate that when, and only when, the biaxial stress is increased above a critical value of 6+/-1 GPa during the growth of a carbon film at room temperature, tetrahedral amorphous carbon is formed. This confirms that the stress present during the formation of an amorphous carbon film determines its sp;{3} bonding fraction. In the vicinity of the critical stress, a highly oriented graphitelike material is formed which exhibits low electrical resistance and provides Ohmic contacts to silicon. Atomistic simulations reveal that the structural transitions are thermodynamically driven and not the result of dynamical effects.     

New determination of the upper limit for the muon neutrino mass

We have measured the muon momentum in pion decay at rest using a magnetic spectrometer. From the result, p_μ⁺ = (29.787±0.005) MeV/c, we deduce a squared muon neutrino mass of (0.23±0.54) MeV²/c⁴.     

Synthesis of an end-capped sexithiophene bearing fused tetrathiafulvalene (TTF) units

[structure: see text] We report the synthesis of a novel end-capped sexithiophene derivative bearing two pendent, fused tetrathiafulvalene (TTF) units linked to the main chain through 1,4-dithiin heterocycles. Cyclic voltammetry and absorption spectroscopy are used to investigate the electronic properties of this hybrid electroactive material. The oligomer has a band gap of 2.1 eV, and the material can be oxidized through the sexithiophene and TTF units simultaneously.     

Ventricular interaction quantified with a novel multi-scale cardiovascular model

Ventricular interaction (VI) in the heart is the influence of function of one ventricle on the other. To investigate VI, a novel multi-scale model of the canine cardiovascular system was developed. Multiple beats of a normal heart were simulated, followed by pulmonary artery constriction (PAC). VI was quantified by computing ventricular co-compliances, i.e. the volumic changes in each ventricle due to a pressure change in the other ventricle (CRL = dV_R/dP_L and CLR = dV_L/dP_R). CLR and CRL varied throughout the cardiac cycles. After PAC, diastolic values changed acutely from –5.7 to –6.5 ml/mmHg, due to an abrupt change in VI. The model is likely to be useful in investigating VI, among others, in many clinical settings. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

CFC and Halon replacements in the environment

Substitute fluorocarbons may have direct environmental impact, for example as greenhouse gases, or indirect impacts through the products of their decomposition in the environment. The mechanisms of that atmospheric decomposition are reviewed here and shown to be well established now. The end products are halogen acids and trifluoroacetic acid, all of which pre-exist in the environment in quantities greater than are expected to arise from fluorocarbon use and emissions. Furthermore, the growth in use of fluorocarbon replacements has been shown to be far less than the fall in CFC and Halon production. Hydrochlorofluorocarbons (HCFCs) have replaced less than one third of CFCs and are, themselves, ozone depleting substances that will be phased out under the Montreal Protocol. The growth in hydrofluorocarbons (HFCs) amounts to about 10% of the fall in CFCs. It is likely that the impact of new fluorocarbons on climate change will be a very small fraction of the total impact, which comes mainly from the accumulation of carbon dioxide in the atmosphere.