Formations of dumbbell C118 and C119 inside clusters of C60 molecules by collision with α particles

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of C(60) fullerenes. Surprisingly, C(119)(+) and C(118)(+) are the dominant molecular fusion products. We use molecular dynamics simulations to show that C(59)(+) and C(58)(+) ions--effectively produced in prompt knockout processes with He(2+)--react rapidly with C(60) to form dumbbell C(119)(+) and C(118)(+). Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.

Fully differential single-photon double ionization of neon and argon

Triply differential cross sections are calculated for one-photon double ionization of neon and argon at various photon energies and electron energy sharings by using a frozen-core treatment to represent the remaining electrons of the residual ion. Angular distributions agree well with all existing experimental data, showing that in spite of its simplicity the method can treat the double ionization of complex targets reliably. A comparison of the cross sections for helium, neon, and argon into the same final state symmetry at the same relative excess energies reveals a distinctive signature of the role of electron correlation in each target.

Correlated electron and nuclear dynamics in strong field photoionization of H(2)(+)

We present a theoretical study of H(2)(+) ionization under strong IR femtosecond pulses by using a method designed to extract correlated (2D) photoelectron and proton kinetic energy spectra. The results show two distinct ionization mechanisms-tunnel and multiphoton ionization-in which electrons and nuclei do not share the energy from the field in the same way. Electrons produced in multiphoton ionization share part of their energy with the nuclei, an effect that shows up in the 2D spectra in the form of energy-conservation fringes similar to those observed in weak-field ionization of diatomic molecules. In contrast, tunneling electrons lead to fringes whose position does not depend on the proton kinetic energy. At high intensity, the two processes coexist and the 2D plots show a very rich behavior, suggesting that the correlation between electron and nuclear dynamics in strong field ionization is more complex than one would have anticipated.

Pump-probe scheme to study the autoionization decay of optically-forbidden H2 doubly excited states

A pump-probe scheme is proposed to investigate the autoionization dynamics of the optically forbidden Q(1)(1)Σ(g)(+) doubly excited states of the H(2) molecule. The scheme consists of a pump that contains an attosecond pulse train (APT) and an infrared (IR) pulse, which is phase-locked with the APT, and an IR probe identical to the former IR pulse. The dynamical information is obtained by analyzing the electron kinetic energy spectra (EKE) and proton kinetic energy spectra (PKE) as a function of the time delay between the pump and the probe. The essential requirement for an efficient population of the Q(1)(1)Σ(g)(+) states is that they are resonantly coupled to both the dipole-allowed Q(1)(1)Σ(u)(+) doubly excited states and the ground state of H(2) by the combined effect of the APT + IR fields.

Laser induced breakdown spectrometry of vanadium in titania supported silica catalysts

The capability of laser induced breakdown spectrometry (LIBS) for vanadium determination in a xV-2TiO(2)-SiO(2) catalyst is presented. The microplasma was generated onto the sample surface using a pulsed Nd:YAG laser operating in the second harmonic (532 nm). Laser produced plasmas were collected and detected using a charge-coupled device (CCD). In order to minimize the complex spectral interferences of emission lines and matrix effects a wide spectral range (210-660 nm) was studied. The focusing of the laser beam on the surface was optimized to improve the signal-to-background ratio, and consequently the limit of detection. The analytical lines selected were used to evaluate the calibration curve. The detection limit for V was estimated to be 38 mug g(-1) in 2TiO(2)-SiO(2). The method precision expressed as relative standard deviation (RSD) was better than 6% in the concentration range 200-1000 mug g(-1).

Helium, neon and argon diffraction from Ru(0001)

We present an experimental and theoretical study of He, Ne and Ar diffraction from the Ru(0001) surface. Close-coupling calculations were performed to estimate the corrugation function and the potential well depth in the atom-surface interaction in all three cases. DFT (density functional theory) calculations, including van der Waals dispersion forces, were used to validate the close-coupling results and to further analyze the experimental results. Our DFT calculations indicate that, in the incident energy range 20-150 meV, anticorrugating effects are present in the case of He and Ar diffraction, whereas normal corrugation is observed with Ne beams.

Reproducibility of observables and coherent control in molecular photoionization: from continuous wave to ultrashort pulsed radiation

One-photon single ionization of molecules has been at the focus of several discussions concerning the reconstruction of observables obtained with ultrashort pulses from those obtained from continuous wave radiation (and vice versa). A related controversy on the conditions and observables that allow for coherent control in one-photon processes has been recently revisited (Science 2006, 313, 1257; J. Chem. Phys. 2010, 133, 151101). Our benchmark to investigate these issues is photoionization of the hydrogen molecule, where the autoionization events are the time-dependent processes in field-free evolution that could serve as a target for coherent control. We show that the variation of one-photon ionization probabilities with pulse duration are solely due to spectral effects and thus cannot be coherently controlled. We then discuss for which observables and under which conditions phase control of autoionization dynamics is possible.

Observation of interference between two distinct autoionizing states in dissociative photoionization of H2

Dissociative photoionization (DPI) of randomly oriented H(2) molecules has been studied using linearly polarized synchrotron radiation at selected photon energies of 31, 33, and 35 eV. Large amplitude oscillations in the photoelectron asymmetry parameter β, as a function of electron energy, have been observed. The phase of these β oscillations are in excellent agreement with the results of recent close coupling calculations [Fernández and Martín, New J. Phys. 11, 043020 (2009)]. We show that the oscillations are the signature of interferences between the 1Q(1) (1)Σ(u)(+) and 1Q(2) (1)Π(u) doubly excited states decaying at different internuclear distances. The oscillations thus provide information about the classical paths followed by the nuclei. The presence of such oscillations is predicted to be a general phenomenon in DPI.

Protein kinase C phosphorylates the cAMP response element binding protein in the hypothalamic paraventricular nucleus during morphine withdrawal

BACKGROUND AND PURPOSE

Exposure to drugs of abuse or stress results in adaptation in the brain involving changes in gene expression and transcription factors. Morphine withdrawal modulates gene expression through various second-messenger signal transduction systems. Here, we investigated changes in activation of the transcription factor, cAMP-response element binding protein (CREB), in the hypothalamic paraventricular nucleus (PVN) and the kinases that may mediate the morphine withdrawal-triggered activation of CREB and the response of the hypothalamic-pituitary-adrenocortical (HPA) axis after naloxone-induced morphine withdrawal.

EXPERIMENTAL APPROACH

The effects of morphine dependence and withdrawal, phosphorylated CREB (pCREB), corticotrophin-releasing factor (CRF) expression in the PVN and HPA axis activity were measured using immunoblotting, immunohistochemistry and radioimmunoassay in controls and in morphine-dependent rats, withdrawn with naloxone and pretreated with vehicle, calphostin C, chelerythrine (inhibitors of protein kinase C (PKC) or SL-327 [inhibitor of extracellular signal regulated kinase (ERK) kinase]. In addition, changes in PKCα and PKCγ immunoreactivity were measured after 60 min of withdrawal.

KEY RESULTS

In morphine-withdrawn rats, pCREB immunoreactivity was increased within CRF immunoreactive neurons in the PVN and plasma corticosterone levels were raised. SL-327, at doses that reduced the augmented pERK levels in the PVN, did not attenuate the rise in pCREB immunoreactivity or plasma corticosterone secretion. In contrast, PKC inhibition reduced the withdrawal-triggered rise in pCREB, pERK1/2 and corticosterone secretion.

CONCLUSIONS AND IMPLICATIONS

PKC mediated, in part, both CREB activation and the HPA response to morphine withdrawal. The ERK kinase/ERK pathway might not be necessary for either activation of CREB or HPA axis hyperactivity.

Attosecond control in photoionization of hydrogen molecules

We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1sσ(g) and 2pσ(u) states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.

Ultrafast nonadiabatic fragmentation dynamics of doubly charged uracil in a gas phase

A combination of time-dependent density functional theory and Born-Oppenheimer molecular dynamics methods is used to investigate fragmentation of doubly charged gas-phase uracil in collisions with 100 keV protons. The results are in good agreement with ion-ion coincidence measurements. Orbitals of similar energy and/or localized in similar bonds lead to very different fragmentation patterns, thus showing the importance of intramolecular chemical environment. In general, the observed fragments do not correspond to the energetically most favorable dissociation path, which is due to dynamical effects occurring in the first few femtoseconds after electron removal.

Role of dispersion forces in the structure of graphene monolayers on Ru surfaces

Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% (∼0.4 Å) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level.

[Takotsubo syndrome. Usefulness of nuclear medicine studies]

Takotsubo syndrome can mimic an acute myocardial infarction. It is characterized by anginal chest pain with ST elevation in precordial leads, no coronary obstruction on angiography, and typical and reversible deformation of the left ventricular due to antero-apical ballooning with basal hyperkinesis. The pathophysiology of this syndrome is uncertain. It is probably multifactorial, cardiac adrenergic nervous dysfunction standing out in the acute phase. We report two cases performed within the diagnostic context of Takotsubo syndrome. Cardiac SPECT was performed using (123)I Metaiodobenzylguanidine (MIBG) and (99m)Tc-Tetrofosmin and the results of two cases were adrenergic denervation in the anterior wall without alterations in myocardial perfusion study. Identification of Takotsubo syndrome is of clinical importance because its management and prognosis differ significantly from that of acute myocardial infarction.

An epidemiological survey of hymenoptera venom allergy in the Spanish paediatric population

Hypersensitivity reactions to hymenoptera venom are infrequent in paediatric patients. A study was made to determine the incidence of this pathology in children, based on an epidemiological survey targeted to all members of the SEICAP (Sociedad Española de Inmunología Clínica y Alergia Pediátrica/Spanish Society of Paediatric Clinical Immunology and Allergy), and designed to collect the data on patients under 17 years of age diagnosed with hymenoptera venom allergy.

RESULTS

The data corresponding to 175 patients (135 males) were collected. The mean age was 9.9 ± 3.6 years. Seventeen percent (32 patients) were the offspring of beekeepers, and 68.9% had experienced previous stings. The causal insect was Apis melifera, implicated in 55 cases, followed by Polistes dominulus (33 cases). In 151 patients (83.9%) the condition consisted of a local reaction. The most frequent systemic response was urticaria and angio-oedema. Fourteen patients suffered anaphylactic shock. The diagnosis was based on skin test (intradermal and prick) and/or specific IgE testing. Three treatment categories were established: (a) prevention and educational measures; (b) symptomatic treatment with oral antihistamines as well as self-injectable adrenalin; and (c) immunotherapy. In this context, 135 patients underwent immunotherapy with a mean duration of 3.5 ± 1.7 years (range 2-5 years) - with excellent tolerance. The starting regimen was predominantly conventional (92 patients).

CONCLUSIONS

The results of this survey show hypersensitivity reactions to hymenoptera venom to be infrequent in paediatrics, though with a strong impact upon patient quality of life.

Use of liming in the remediation of soils polluted by sulphide oxidation: a leaching-column study

Pure CaCO(3) in ascending quantities was added to a soil to study the effect of liming after contamination by an acidic solution from the oxidation of pyrite tailings. The samples were placed in percolation columns, and soils and leachates were monitored. In the soil samples, the mineralogy, pH, CaCO(3), iron, and total content in Cu, Zn, As, Cd, and Pb were determined. The presence of CaCO(3) in the soils considerably limited their acidification, favouring the precipitation of Cu, Zn, and Cd, and promoting precipitation of iron and SO(4)(2-) ions in the form of iron hydroxysulphates and gypsum. The iron hydroxysulphates tended to retain the less mobile elements (As, and Pb) near the top of the soil. The more mobile elements (Zn, Cd and Cu) precipitated in deeper layers, directly related mainly to the CaCO(3) added and to pH. The CaCO(3) clearly did not reduce Zn and Cd toxicity effectively enough, given that the concentrations of both elements were above the toxic level in all leachates. The amounts of liming needs to be properly controlled, as excessively high pH limits As fixing, at the same time as the effectiveness of CaCO(3) is limited by coating precipitation, reducing its capacity to react with the acidic solution.

Circular dichroism in photoionization of H2

Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit it when the measurement itself introduces chirality, e.g., when measuring molecular-frame photoelectron angular distributions. The few such experiments performed on homonuclear diatomic molecules show that, as expected, circular dichroism vanishes when the molecular-frame photoelectron angular distributions are integrated over the polar electron emission angle. Here we show that this is not the case in resonant dissociative ionization of H2 for photons of 30-35 eV, which is the consequence of the delayed ionization from molecular doubly excited states into ionic states of different inversion symmetry.