Poincaré-invariant gravitational field and equations of motion of two pointlike objects: The postlinear approximation of general relativity

Using a fast-motion approximation method we obtain the second-order gravitational field and equations of motion for two pointlike objects in algebraically closed form. A regularization procedure is used which is shown to guarantee the consistency of the approximation scheme. The equations of motion are then transformed within the framework of relativistic predictive mechanics into a system of ordinary differential equations.     

Partial breakdown of the evaporation model and possible preequilibrium α-particle emission in heavy-ion fusion reactions

Relative cross sections for residual nuclei following fusion reactions were measured by γ-ray spectroscopy in the reactions ⁵²Cr+ ¹²C at 56.00 MeV and ⁴⁸Ti+ ¹⁶O at 57.74 MeV, in which the common “compound nucleus” ⁶⁴Zn was excited at the same energies and the relative distributions of the entrance spins were nearly identical. It is shown that ratios of the measured cross sections in both entrance channels can be precisely determined experimentally and are insensitive to small changes of the parameters in calculations based on the evaporation model. Using these particular quantities, we have shown that the evaporation process is not the sole mechanism producing the observed residues, especially those resulting from α-particle emission. The assumption of preequilibrium α-particle emission at high channel spins is shown to reproduce the present data fairly well.     

‘All‐supramolecular’ Nanocapsules from Low‐Molecular Weight Ureas Through Interfacial Addition Reaction in Miniemulsion

This contribution presents a new strategy for preparing nanocapsules with a shell made of a supramolecular polymer which repeating units are held together by reversible interactions rather than covalent bonds. These nanocapsules were prepared in classical miniemulsion through interfacial addition reaction of a diisocyanate (IPDI) and a monoamine (iBA), forming low‐molecular weight bis‐ureas moieties which are strong self‐complementary interacting molecules through hydrogen‐bonding. The nanocapsules present a diameter around 100 nm, and MALDI‐TOF MS and ¹H NMR analyses confirm the expected molecular characteristics for the shell. This strategy opens the scope of a new type of nanomaterials exhibiting stimuli‐responsiveness due to the reversible interaction linking the repeating units.

     

Exchange and correlation effects in electronic excitations of Cu(2)O

State-of-the-art theoretical methods fail in describing the optical absorption spectrum, band gap, and optical onset of Cu(2)O. We have extended a recently proposed self-consistent quasiparticle approach, based on the GW approximation, to the calculation of optical spectra, including excitonic effects. The band structure compares favorably with our present angle-resolved photoemission measurements. The excitonic effects based on these realistic band structure and screening provide a reliable optical absorption spectrum, which allows for a revised interpretation of its main structures.     

Lithium environment in dilute poly(ethylene oxide)/lithium triflate polymer electrolyte from REDOR NMR spectroscopy

The role of the lithium ion environment is of fundamental interest regarding transport and conductivity in lithium polymer electrolytes. X-ray crystallography has been used to characterize the lithium environment in completely crystalline poly(ethylene oxide) (PEO) electrolytes, but this approach cannot be used with dilute PEO electrolytes. Here, using solid-state NMR data collected with the rotational-echo double-resonance 13C[7Li] (REDOR) pulse sequence, we have been able to characterize the crystalline microdomains of a PEO-lithium triflate sample with an oxygen/lithium ratio of 20:1. Our data clearly demonstrates that the lithium crystalline microdomains are nearly identical to those of a completely crystalline 3:1 sample, for which the crystal structure is known.     

UV photolysis of C4N2 in water ices: new possible route of synthesis of ammonium bicarbonate and ammonium formate

Laboratory experiments involving ultraviolet (UV) irradiation of dicyanoacetylene (C(4)N(2)) trapped in water ice at 10 K have been conducted and monitored by infrared spectroscopy (FTIR). By the support of isotopic experiments and theoretical calculations, the irradiation of a DCA/H(2)O ice mixture at lambda > 230 nm has been found to be a possible source of NH(4)(+)HCO(3)(-) (ammonium bicarbonate) and NH(4)(+)HCOO(-) (ammonium formate). These latter compounds can arise from a proton-transfer reaction between H(2)O and the CN radical, which is issued from photolyzed C(4)N(2).     

BOLD responses to trigeminal nerve stimulation

The current study investigates a new model of barrel cortex activation using stimulation of the infraorbital branch of the trigeminal nerve. A robust and reproducible activation of the rat barrel cortex was obtained following trigeminal nerve stimulation. Blood oxygen level-dependent (BOLD) effects were obtained in the primary somatosensory barrel cortex (S1BF), the secondary somatosensory cortex (S2) and the motor cortex. These cortical areas were reached from afferent pathways from the trigeminal ganglion, the trigeminal nuclei and thalamic nuclei from which neurons project their axons upon whisker stimulation. The maximum BOLD responses were obtained for a stimulus frequency of 1 Hz, a stimulus pulse width of 100 μs and for current intensities between 1.5 and 3 mA. The BOLD response was nonlinear as a function of frequency and current intensity. Additionally, modeling BOLD responses in the rat barrel cortex from separate cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO₂) measurements showed good agreement with the shape and amplitude of measured BOLD responses as a function of stimulus frequency and will potentially allow to identify the sources of BOLD nonlinearities. Activation of the rat barrel cortex using trigeminal nerve stimulation will contribute to the interpretation of the BOLD signals from functional magnetic resonance imaging studies.