Atomic polarization in the photodissociation of diatomic molecules.

The angular momentum polarization of atomic photofragments provides a detailed insight into the dynamics of the photodissociation process. In this article, the origins of electronic angular momentum polarization are introduced and experimental and theoretical methods for the measurement or calculation of atomic orientation and alignment parameters described. Many diatomic photodissociation systems are surveyed, in order to provide an overview both of the historical development of the field and of the most state-of-the-art contemporary studies.

The photodissociation dynamics of O2 at 193 nm: an O3PJ angular momentum polarization study.

In the following paper we present translational anisotropy and angular momentum polarization data for O((3)P(1)) and O((3)P(2)) products of the photodissociation of molecular oxygen at 193 nm. The data were obtained using polarized laser photodissociation coupled with resonantly enhanced multiphoton ionization and velocity-map ion imaging. Under the jet-cooled conditions employed, absorption is believed to be dominated by excitation into the Herzberg continuum. The experimental data are compared with previous experiments and theoretical calculations at this and other wavelengths. Semi-classical calculations performed by Groenenboom and van Vroonhoven [J. Chem. Phys, 2002, 116, 1965] are used to estimate the alignment parameters arising from incoherent excitation and dissociation and these are shown to agree qualitatively well with the available experimental data. Following the work of Alexander et al. [J. Chem. Phys, 2003, 118, 10566], orientation and alignment parameters arising from coherent excitation and dissociation are modelled more approximately by estimating phase differences generated subsequent to dissociation via competing adiabatic pathways leading to the same asymptotic products. These calculations lend support to the view that large values of the coherent alignment moments, but small values of the corresponding orientation moments, could arise from coherent excitation of (and subsequent dissociation via) parallel and perpendicular components of the Herzberg I, II and III transitions.

The photodissociation dynamics of ozone at 193 nm: an O(1D2) angular momentum polarization study.

Polarized laser photolysis, coupled with resonantly enhanced multiphoton ionization detection of O(1D2) and velocity-map ion imaging, has been used to investigate the photodissociation dynamics of ozone at 193 nm. The use of multiple pump and probe laser polarization geometries and probe transitions has enabled a comprehensive characterization of the angular momentum polarization of the O(1D2) photofragments, in addition to providing high-resolution information about their speed and angular distributions. Images obtained at the probe laser wavelength of around 205 nm indicate dissociation primarily via the Hartley band, involving absorption to, and diabatic dissociation on, the B 1B2(3 1A1) potential energy surface. Rather different O(1D2) speed and electronic angular momentum spatial distributions are observed at 193 nm, suggesting that the dominant excitation at these photon energies is to a state of different symmetry from that giving rise to the Hartley band and also indicating the participation of at least one other state in the dissociation process. Evidence for a contribution from absorption into the tail of the Hartley band at 193 nm is also presented. A particularly surprising result is the observation of nonzero, albeit small values for all three rank K = 1 orientation moments of the angular momentum distribution. The polarization results obtained at 193 and 205 nm, together with those observed previously at longer wavelengths, are interpreted using an analysis of the long range quadrupole-quadrupole interaction between the O(1D2) and O2(1Deltag) species.

The photodissociation dynamics of NO2 at 308 nm and of NO2 and N2O4 at 226 nm.

Velocity-map ion imaging has been applied to the photodissociation of NO(2) via the first absorption band at 308 nm using (2 + 1) resonantly enhanced multiphoton ionization detection of the atomic O((3)P(J)) products. The resulting ion images have been analyzed to provide information about the speed distribution of the O((3)P(J)) products, the translational anisotropy, and the electronic angular momentum alignment. The atomic speed distributions were used to provide information about the internal quantum-state distribution in the NO coproducts. The data were found to be consistent with an inverted NO vibrational quantum-state distribution, and thereby point to a dynamical, as opposed to a statistical dissociation mechanism subsequent to photodissociation at 308 nm. Surprisingly, at this wavelength the O-atom electronic angular momentum alignment was found to be small. Probe-only ion images obtained under a variety of molecular-beam backing-pressure conditions, and corresponding to O atoms generated in the photodissociation of either the monomer, NO(2), or the dimer, N(2)O(4), at 226 nm, are also reported. For the monomer, where 226 nm corresponds to excitation into the second absorption band, the kinetic-energy release distributions are also found to indicate a strong population inversion in the NO cofragment, and are shown to be remarkably similar to those previously observed in the wavelength range of 193-248 nm. Mechanistic implications of this result are discussed. At 226 nm it has also been possible to observe directly O atoms from the photodissociation of the dimer. The O-atom velocity distribution has been analyzed to provide information about its production mechanism.

Imaging photon-initiated reactions: a study of the Cl(2P(3/2))+CH4-->HCl+CH3 reaction.

The hydrogen or deuterium atom abstraction reactions between Cl((2)P(3/2)) and methane, or its deuterated analogues CD(4) and CH(2)D(2), have been studied at mean collision energies around 0.34 eV. The experiments were performed in a coexpansion of molecular chlorine and methane in helium, with the atomic Cl reactants generated by polarized laser photodissociation of Cl(2) at 308 nm. The Cl-atom reactants and the methyl radical products were detected using (2+1) resonantly enhanced multiphoton ionization, coupled with velocity-map ion imaging. Analysis of the ion images reveals that in single-beam experiments of this type, careful consideration must be given to the spread of reagent velocities and collision energies. Using the reactions of Cl with CH(4), CD(4), and CH(2)D(2), as examples, it is shown that the data can be fitted well if the reagent motion is correctly described, and the angular scattering distributions can be obtained with confidence. New evidence is also provided that the CD(3) radicals from the Cl+CD(4) reaction possess significant rotational alignment under the conditions of the present study. The results are compared with previous experimental and theoretical works, where these are available.

Arabidopsis mutants resistant to S(+)-beta-methyl-alpha, beta-diaminopropionic acid, a cycad-derived glutamate receptor agonist.

Ionotropic glutamate receptors (iGluRs) are ligand-gated ion channels that are the predominant neuroreceptors in the mammalian brain. Genes with high sequence similarity to animal iGluRs have been identified in Arabidopsis. To understand the role of Arabidopsis glutamate receptor-like (AtGLR) genes in plants, we have taken a pharmacological approach by examining the effects of BMAA [S(+)-beta-methyl-alpha, beta-diaminopropionic acid], a cycad-derived iGluR agonist, on Arabidopsis morphogenesis. When applied to Arabidopsis seedlings, BMAA caused a 2- to 3-fold increase in hypocotyl elongation and inhibited cotyledon opening during early seedling development. The effect of BMAA on hypocotyl elongation is light specific. Furthermore, BMAA effects on early morphogenesis of Arabidopsis can be reversed by the simultaneous application of glutamate, the native iGluR agonist in animals. To determine the targets of BMAA action in Arabidopsis, a genetic screen was devised to isolate Arabidopsis mutants with a BMAA insensitive morphology (bim). When grown in the light on BMAA, bim mutants exhibited short hypocotyls compared with wild type. bim mutants were grouped into three classes based on their morphology when grown in the dark in the absence of BMAA. Class-I bim mutants have a normal, etiolated morphology, similar to wild-type plants. Class-II bim mutants have shorter hypocotyls and closed cotyledons when grown in the dark. Class-III bim mutants have short hypocotyls and open cotyledons when grown in the dark, resembling the previously characterized constitutively photomorphogenic mutants (cop, det, fus, and shy). Further analysis of the bim mutants should help define whether plant-derived iGluR agonists target glutamate receptor signaling pathways in plants.

Complications and management of diabetes: a review of current research.

Many complications are already present when the diagnosis of diabetes is made. This article reviews current research about the most common complications and describes innovative new research projects aimed at the future prevention of diabetes and its sequelae. Findings form the landmark DCCT study about the relationship of levels of blood glucose to some of the main complications are also discussed.

Targeted estrogen/progesterone replacement therapy for osteoporosis: calculation of health care cost savings.

Osteoporosis is a crippling affliction in which bone mass decreases, making it more susceptible to fracture. In postmenopausal women it presents most often as a hip, spinal, or forearm fracture. Adult women face a 15% lifetime risk of a hip fracture, and the annual costs of hip fractures alone are estimated at $7.3 billion in the United States. Since the 1970s, estrogen/progestogen therapy has been recognized as an effective intervention that reduces the risk of fractures. Recently, the development of methods for accurately determining bone mass and thus helping to predict bone fracture risk has made this intervention attractive for use in a targeted population. This report analyzes the health care costs and calculates the cost savings of coupling bone mineral density screening at the time of menopause with long-term estrogen/progestogen therapy for those most at risk for developing fractures. The model assumes that a cohort of 100,000 American white women, aged 50, are screened for bone mineral density and that 90% of the high-risk group (density less than 0.85 g/cm3) and 70% of the mid-risk group (density between 0.85 and 1.00 g/cm3) elect to take hormone replacement therapy for 15 years. Based on calculations of the costs of screening and hormone replacement therapy, and the savings in cost of treatment and lost productivity from reduced fractures, it is estimated that the present value of savings in cost of illness for this cohort over a 40-year period is $5.1 million.(ABSTRACT TRUNCATED AT 250 WORDS)

Developing a standard for endotracheal tube cuff care.

Potential complications from the use of cuffed endotracheal tubes are well documented and have generated a large body of research focusing on cuff design and interventions to decrease tracheal damage caused by the cuffs. The authors conducted a state-wide survey to determine the extent to which these procedures were incorporated into practice and to develop a current standard of care for patients with cuffed endotracheal tubes.

Legal implications of standards of care.

Many legal implications related to standards of care exist for the critical care nurse. This article tells how care standards are derived and used in the legal system, describes important legal concepts, and gives samples of actual court testimony by nurses about endotracheal tube cuff care.

The physiologic basis for continuous mixed venous oxygen saturation monitoring.

Critically ill patients often have conditions that reduce oxygen delivery and increase oxygen demand. Routine nursing care, such as suctioning, positioning, and bathing, also increases the patient's oxygen demand. If the patient's oxygen demand exceeds the supply, dysrhythmias, hypotension, altered level of consciousness, and other adverse responses can occur. We describe use of continuous monitoring of mixed venous oxygen saturation (SvO2) as a tool to assess the patient's supply/demand balance during nursing care. The physiology of oxygen transport is reviewed, and oxygen delivery, reserve, and consumption are defined. Conditions that decrease oxygen delivery and increase oxygen demand are discussed, and the effects on SvO2 are illustrated. With continuous SvO2 monitoring, critical care nurses can see the effect of their nursing care on the patient's oxygenation and can adjust their care according to the patient's tolerance.

Effects of endotracheal suctioning on mixed venous oxygen saturation and heart rate in critically ill adults.

The purpose of this multisite study was to determine the effects of endotracheal suctioning on mixed venous oxygen saturation (SvO2) and heart rate in 189 critically ill adults. One-pass, intermittent suction was applied for 10 or fewer seconds, with three prehyperoxygenation and three posthyperoxygenation breaths of 100% oxygen. Subjects at three hospitals (n = 127) underwent suctioning using hyperoxygenation with anesthesia bags and traditional suction catheters (open suction method). Subjects at one hospital (n = 62) underwent suctioning with hyperoxygenation by ventilator and in-line suction catheters (closed suction method). For subjects from all hospital sites combined, the SvO2 decreased from 67% to 64% (p = 0.001), a 4% change from baseline, and returned to baseline within 2 minutes. However, in subjects receiving the open method of suction, SvO2 dropped from 66% to 62% immediately after suctioning and returned to baseline within 4 minutes. In contrast, when the closed suction method was used, SvO2 rose from 67.7% to 67.86% immediately after suctioning, drifting upward to 71% for the next 2 minutes before dropping toward the baseline after 4 minutes. Mean heart rate increased from a baseline of 99 beats/min to 104 beats/min immediately after suctioning (p = 0.001), a 5% change from baseline, and gradually returned to baseline over the next 4 minutes. No significant differences were seen in heart rate between subjects having the open versus closed suction method. In conclusion, the closed suction method showed a higher SvO2 after endotracheal suctioning compared with the open suction method (p = 0.0001). Some form of hyperoxygenation before and after endotracheal suctioning is recommended.