Accreting neutron stars as probes of dense matter physics

There are over 100 accreting neutron stars in our galaxy, in which matter (typically H/He) is tidally transferred from a secondary companion to the neutron star. Accretion of this matter perturbs the thermal structure of the interior away from that of an isolated cooling neutron star. In this paper. we review how this accretion induces reactions in the crust of the neutron star that keep the interior hot. If the accretion is intermittent, then the heated surface layers are directly observable when accretion stops. This heating also affects the unstable ignition of light elements in the neutron star envelope. Observations of the neutron star cooling following an accretion outburst can in principle constrain the thermal properties of the crust and core.     

Intramyocellular lipid quantification: comparison between 3.0- and 1.5-T (1)H-MRS

OBJECTIVE: This study aimed to prospectively compare measurement precision of calf intramyocellular lipid (IMCL) quantification at 3.0 and 1.5 T using (1)H magnetic resonance spectroscopy ((1)H-MRS). MATERIALS AND METHODS: We examined the soleus and tibialis anterior (TA) muscles of 15 male adults [21-48 years of age, body mass index (BMI)=21.9-38.0 kg/m(2)]. Each subject underwent 3.0- and 1.5-T single-voxel, short-echo-time, point-resolved (1)H-MRS both at baseline and at 31-day follow-up. The IMCL methylene peak (1.3 ppm) was scaled to unsuppressed water peak (4.7 ppm) using the LCModel routine. Full width at half maximum (FWHM) and signal-to-noise ratios (SNRs) of unsuppressed water peak were measured using jMRUI software. Measurement precision was tested by comparing interexamination coefficients of variation (CV) between different field strengths using Wilcoxon matched pairs signed rank test in all subjects. Overweight subjects (BMI>25 kg/m(2)) were analyzed separately to examine the benefits of 3.0-T acquisitions in subjects with increased adiposity. RESULTS: No significant difference between 3.0 and 1.5 T was noted in CVs for IMCL of soleus (P=.5). CVs of TA were significantly higher at 3.0 T (P=.02). SNR was significantly increased at 3.0 T for soleus (64%, P<.001) and TA (62%, P<.001) but was lower than the expected improvement of 100%. FWHM at 3.0 T was significantly increased for soleus (19%, P<.001) and TA (7%, P<.01). Separate analysis of overweight subjects showed no significant difference between 3.0- and 1.5-T CVs for IMCL of soleus (P=.8) and TA (P=.4). CONCLUSION: Using current technology, (1)H-MRS for IMCL at 3.0 T did not improve measurement precision, as compared with 1.5 T.     

Chemical exchange in novel spirobicyclic zwitterionic Janovsky complexes using dynamic 1H NMR spectroscopy

Highly coloured Janovsky complexes have been known for over 120 years, being used in many colourimetric analytical procedures. In this present study, two novel and stable nitrocyclohexadienyl spirobicyclic, zwitterionic Janovsky anionic hydantoin σ‐complexes, rac‐1,3‐diisopropyl‐6‐nitro‐2,4‐dioxo‐1,3‐diazaspiro[4.5]deca‐6,9‐dien‐8‐ylideneazinate, ammonium internal salt (1) and 1,3‐diisopropyl‐2,4‐dioxo‐1,3‐diazaspiro[4.5]deca‐6,9‐dien‐8‐ylideneazinate, ammonium internal salt (2) have been prepared and characterised by NMR, electrospray ionization mass spectrometry (ESI‐MS) and UV/visible methods. For the p‐mononitro‐substituted complex (2), we discovered chemical exchange behaviour using 1D saturation transfer and 2D exchange spectroscopy (EXSY) ¹H NMR techniques. The coalescence temperature was determined to be 62 °C in d₃‐acetonitrile. Analysis of these data provided a Gibbs free energy of activation, ΔG ?, of + 67 kJ mole^?1, a rate constant, k, coalescence of 220 Hz and an equilibrium constant, K_eqm, of 0.98 as estimates of the exchange process in this solvent. Of the two mechanisms proposed for this fluxional behaviour, ring opening to a substituted benzene or proton exchange, a further theoretical modelling study of 1D ¹H NMR spectra was able to confirm that simple proton exchange between the two nitrogen sites of the hydantoin ring provided an accurate simulation of the observed experimental evidence. Interestingly, the o,p‐dinitro‐substituted complex (1) did not show any chemical exchange behaviour up to 150 °C in d₃‐acetonitrile (to 75 °C) and d₆‐dimethyl sulfoxide (DMSO). Molecular modelling at the MM2 level suggests that steric collisions of an N‐acyl isopropyl substituent of the hydantoin ring with the ortho‐nitro group of the spirofused cyclohexadienyl ring prevents the proposed proton exchange mechanism occurring in this case. Copyright © 2008 Crown in the right of Canada. Published by John Wiley & Sons, Ltd     

Curvature fields, topology, and the dynamics of spatiotemporal chaos

The curvature field is measured from tracer-particle trajectories in a two-dimensional fluid flow that exhibits spatiotemporal chaos and is used to extract the hyperbolic and elliptic points of the flow. These special points are pinned to the forcing when the driving is weak, but wander over the domain and interact in pairs at stronger driving, changing the local topology of the flow. Their behavior reveals a two-stage transition to spatiotemporal chaos: a gradual loss of spatial and temporal order followed by an abrupt onset of topological changes.     

Noncovalent interactions in paired DNA nucleobases investigated by terahertz spectroscopy and solid-state density functional theory

Cocrystallized adenine and thymine derivatives, along with the pure monomeric crystals, were investigated by terahertz spectroscopy and solid-state density functional theory (DFT). The methylated nucleobase derivatives crystallize in planar hydrogen-bonded adenine-thymine pairs similar to the manner found in DNA. The spectra obtained for 1-methylthymine, 9-methyladenine, and the 1:1 cocrystal in the range of 10-100 cm(-1) clearly demonstrate that absorptions in this spectral range originate from the uniquely ordered assembly and the intermolecular interactions found in each individual crystal system. The quality of spectral reproduction for the DFT simulations of each system was clearly improved by the inclusion of an empirical correction term for London-type dispersion forces to the calculations. Notably, it was found that these weak dispersion forces in the adenine-thymine cocrystal were necessary to produce a properly converged crystal structure and meaningful simulation of the terahertz vibrational spectrum.     

Malmquist indexes with quasi-fixed inputs: an application to school districts in Québec

We present a space and time allocation problem that arises in assembly halls producing large building blocks (namely, a shipyard which assembles prefabricated keel elements). The building blocks are very large, and, once a block is placed in the hall, it cannot be moved until all assembly operations on this block are complete. Each block must be processed during a predetermined time window. The objective is to maximize the number of building blocks produced in the hall.     

Transport of finite-sized particles in chaotic flow

By extending traditional particle tracking techniques, we study the dynamics of neutrally buoyant finite-sized particles in a spatiotemporally chaotic flow. We simultaneously measure the flow field and the trajectories of millimeter-scale particles so that the two can be directly compared. While the single-point statistics of the particles are indistinguishable from the flow statistics, the particles often move in directions that are systematically different from the underlying flow. These differences are especially evident when Lagrangian statistics are considered.     

一种新的测定微粒的电化学技术

设计了一种由2个石墨电极短路相连组成工作电极的新的电化学池装置.操作时首先通过外力按压使极少量固体微粒粘附在其中一个石墨电极表面上,然后在溶液存在下将微粒夹紧并固定在2个石墨电极表面之间进行电化学测定.电化学转化过程中生成的可溶性物质被封闭在2个石墨电极表面之间而得到测定.用该技术对钯沉积在氧化铝上而组成的催化剂的电化学行为以及黄铁矿的电化学行为进行了研究.结果表明,其兼具可电解粘合剂碳糊电极和固体微粒伏安法(voltammetry of microparticles)技术的优点而避免了各自的缺点:即不使用粘合剂,从而消除了粘合剂中杂质产生的氧化或还原电流的影响;可测定电化学转化过程中生成的可溶性物质;分辨率好、易于操作.