Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both 'soft' and solid thin films. 'Soft' polymer thin films of polystyrene and poly(styrene-ethylene/butylene-styrene) block copolymer were prepared by spin-coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two-layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80-130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright (c) 2007 John Wiley & Sons, Ltd.

Cu-II acetate complexes involving N,N,O donor Schiff base ligands: Mono-atomic oxygen bridged dimers and alternating chains of the dimers and Cu-2(OAc)(4)

Two tridentate N,N,O donor Schiff bases, HL1 (4-(2-ethylamino-ethylimino)-pentan-2-one) and HL2 (3-(2-amino-propylimino)-1-phenyl-butan-1-one) on reaction with Cu-II acetate in presence of triethyl amine yielded two basal-apical, mono-atomic acetate oxygen-bridging dimeric copper(II) complexes, [Cu2L21(OAc)(2)] (1), [Cu2L22(OAc)(2)] (2). Whereas two other similar tridentate ligands HL3 (4-(2-amino-propylimino)-pentane-2-one) and HL3 (3-(2-amino-ethylimino)-1-phenyl-butan-1-one) under the same conditions produced a mixture of the corresponding dinners and a one-dimensional alternating chain of the dimer and copper acetate moiety, [Cu4L23(OAc)(6)](n) (3) and [Cu4L24(OAc)(6)](n) (4), formed by a very rare mu(3) bridging mode of the acetate ion. All four complexes (1-4) have been characterized by X-ray crystallography. The isotropic Hamiltonian, H = -JS(1)S(2) has been used to interpret the magnetic data. Magnetic measurements of 1 and 2 in the temperature range 2-300 K reveal a very weak antiferromagnetic coupling for both complexes U = -0.56 and -1.19 cm(-1) for 1 and 2, respectively). (C) 2008 Elsevier Ltd. All rights reserved.

Crystal structure of the complementary quadruplex formed by d(GCATGCT) at atomic resolution

Here we report the crystal structure of the DNA heptanucleotide sequence d(GCATGCT) determined to a resolution of 1.1 Angstrom. The sequence folds into a complementary loop structure generating several unusual base pairings and is stabilised through cobalt hexammine and highly defined water sites. The single stranded loop is bound together through the G(N2)-C(O2) intra-strand H-bonds for the available G/C residues, which form further Watson-Crick pairings to a complementary sequence, through 2-fold symmetry, generating a pair of non-planar quadruplexes at the heart of the structure. Further, four adenine residues stack in pairs at one end, H-bonding through their N7-N6 positions, and are additionally stabilised through two highly conserved water positions at the structural terminus. This conformation is achieved through the rotation of the central thymine base at the pinnacle of the loop structure, where it stacks with an adjacent thymine residue within the lattice. The crystal packing yields two halved biological units, each related across a 2-fold symmetry axis spanning a cobalt hexammine residue between them, which stabilises the quadruplex structure through H-bonds to the phosphate oxygens and localised hydration.

Learning and memory in holocaust survivors with posttraumatic stress disorder

Background: Impairments in explicit memory have been observed in Holocaust survivors with posttraumatic stress disorder. Methods: To evaluate which memory components are preferentially affected, the California Verbal Learning Test was administered to Holocaust survivors with (n = 36) and without (n = 26) posttraumatic stress disorder, and subjects not exposed to the Holocaust (n = 40). Results: Posttraumatic stress disorder subjects showed impairments in learning and short-term and delayed retention compared to nonexposed subjects; survivors without posttraumatic stress disorder did not. Impairments in learning, but not retention, were retained after controlling fir intelligence quotient. Older age was associated with poorer learning and memory performance in the posttraumatic stress disorder group only. Conclusions: The most robust impairment observed in posttraumatic stress disorder was in verbal learning, which may be a risk factor for or consequence of chronic posttraumatic stress disorder. The negative association between performance and age may reflect accelerated cognitive decline in posttraumatic stress disorder.

Reduced heart rate responding to trauma reliving in trauma survivors with PTSD: correlates and consequences

The authors investigated whether heart rate (HR) responses to voluntary recall of trauma memories (a) are related to posttraumatic stress disorder (PTSD), and (b) predict recovery 6 months later. Sixty-two assault survivors completed a recall task modeled on imaginal reliving in the initial weeks postassault. Possible cognitive modulators of HR responsivity were assessed; dissociation, rumination, trauma memory disorganization. Individuals with PTSD showed a reduced HR response to reliving compared to those without PTSD, but reported greater distress. Notably, higher HR response but not self-reported distress during reliving predicted greater symptom reduction at follow-up in participants with PTSD. Engagement in rumination was the only cognitive factor that predicted lower HR response. The data are in contrast to studies using trauma reminders to trigger memories, which have found greater physiological reactivity in PTSD. The authors' observations are consistent with models of PTSD that highlight differences between cued or stimulus-driven retrieval and intentional trauma recall, and with E B. Foa and M.J. Kozak (1986) hypothesis that full activation of trauma memories facilitates emotional processing.

Surface structure of thin asymmetric PS-b-PMMA diblock copolymers investigated by atomic force microscopy

Asymmetric poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers of molecular weight M-n = 29,700g mol(-1) (M-PS = 9300 g mol(-1) M-PMMA = 20,100 g mol(-1), PD = 1.15, chi(PS) = 0.323, chi(PMMA) = 0.677) and M-n = 63,900 g mol(-1) (M-PS = 50,500 g mol(-1), M-PMMA = 13,400 g mol(-1), PD = 1.18, chi(PS) = 0.790, chi(PMMA) = 0.210) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Atomic force microscopy (AFM) was used to investigate the surface structure of thin films, prepared by spin-coating the diblock copolymers on a silicon substrate. We show that the nanostructure of the diblock copolymer depends on the molecular weight and volume fraction of the diblock copolymers. We observed a perpendicular lamellar structure for the high molar mass sample and a hexagonal-packed cylindrical patterning for the lower molar mass one. Small-angle X-ray scattering investigation of these samples without annealing did not reveal any ordered structure. Annealing of PS-b-PMMA samples at 160 degrees C for 24 h led to a change in surface structure.

Direct visualisation of lipid bilayer cubic phases using Atomic Force Microscopy

Inverse bicontinuous cubic (Q(II)) phases are nanostructured materials formed by lipid self-assembly. We have successfully imaged thin films of hydrated Q(II) phases from two different systems using AFM. The images show periodic arrays of water channels with spacing and symmetry consistent with published SAXS data on the bulk materials.

Post-traumatic stress symptoms in childhood brain tumour survivors and their parents

Objectives This study aimed to investigate post-traumatic stress symptoms (PTSS) in childhood brain tumour survivors and their parents. A further aim was to explore the relationship between objective illness parameters, parent–child interactions, coping styles and PTSS. Methods A cross-sectional correlational design was employed. Fifty-two childhood brain tumour survivors, aged 8–16, and 52 parents completed a battery of questionnaires designed to assess quality of parent–child interactions, monitoring and blunting attentional coping styles and PTSS. Results Over one-third (35%) of survivors and 29% of their parents reported severe levels of PTSS (suggestive of post-traumatic stress disorder ‘caseness’). Increased parent–child conflict resolution for survivors and number of tumour recurrences for parents independently predicted the variance in PTSS. Conclusions For a substantial proportion of brain tumour survivors and their parents the process of survivorship is a considerably distressing experience.

Imaging the atomic structure of activated carbon

The precise atomic structure of activated carbon is unknown, despite its huge commercial importance in the purification of air and water. Diffraction methods have been extensively applied to the study of microporous carbons, but cannot provide an unequivocal identification of their structure. Here we show that the structure of a commercial activated carbon can be imaged directly using aberration-corrected transmission electron microscopy. Images are presented both of the as-produced carbon and of the carbon following heat treatment at 2000 degrees C. In the 2000 degrees C carbon clear evidence is found for the presence of pentagonal rings, suggesting that the carbons have a fullerene-related structure. Such a structure would help to explain the properties of activated carbon, and would also have important implications for the modelling of adsorption on microporous carbons.

The Bomb: Nuclear Weapons in their Historical, Strategic and Ethical Context

This book examines to what extent the invention and first use of nuclear weapons was a turning point in the history of warfare and strategy(to what extent was it a mere continuation or perfection of air power strategy? Were the casualty numbers really unprecedented?), the ethics of war (was this form of war against civilians unprecedented?), and it asks whether it was an expression of total war or did it create total war

On the difficulties of present theoretical models to predict the oxidation state of atomic Au adsorbed on regular sites of CeO2(111)

The electronic structure and oxidation state of atomic Au adsorbed on a perfect CeO2(111) surface have been investigated in detail by means of periodic density functional theory-based calculations, using the LDA+U and GGA+U potentials for a broad range of U values, complemented with calculations employing the HSE06 hybrid functional. In addition, the effects of the lattice parameter a0 and of the starting point for the geometry optimization have also been analyzed. From the present results we suggest that the oxidation state of single Au atoms on CeO2(111) predicted by LDA+U, GGA+U, and HSE06 density functional calculations is not conclusive and that the final picture strongly depends on the method chosen and on the construction of the surface model. In some cases we have been able to locate two well-defined states which are close in energy but with very different electronic structure and local geometries, one with Au fully oxidized and one with neutral Au. The energy difference between the two states is typically within the limits of the accuracy of the present exchange-correlation potentials, and therefore, a clear lowest-energy state cannot be identified. These results suggest the possibility of a dynamic distribution of Au0 and Au+ atomic species at the regular sites of the CeO2(111) surface.

Inverse modeling of the 14C bomb pulse in stalagmites to constrain the dynamics of soil carbon cycling at selected European cave sites

The decomposition of soil organic matter (SOM) is temperature dependent, but its response to a future warmer climate remains equivocal. Enhanced rates of decomposition of SOM under increased global temperatures might cause higher CO2 emissions to the atmosphere, and could therefore constitute a strong positive feedback. The magnitude of this feedback however remains poorly understood, primarily because of the difficulty in quantifying the temperature sensitivity of stored, recalcitrant carbon that comprises the bulk (>90%) of SOM in most soils. In this study we investigated the effects of climatic conditions on soil carbon dynamics using the attenuation of the 14C ‘bomb’ pulse as recorded in selected modern European speleothems. These new data were combined with published results to further examine soil carbon dynamics, and to explore the sensitivity of labile and recalcitrant organic matter decomposition to different climatic conditions. Temporal changes in 14C activity inferred from each speleothem was modelled using a three pool soil carbon inverse model (applying a Monte Carlo method) to constrain soil carbon turnover rates at each site. Speleothems from sites that are characterised by semi-arid conditions, sparse vegetation, thin soil cover and high mean annual air temperatures (MAATs), exhibit weak attenuation of atmospheric 14C ‘bomb’ peak (a low damping effect, D in the range: 55–77%) and low modelled mean respired carbon ages (MRCA), indicating that decomposition is dominated by young, recently fixed soil carbon. By contrast, humid and high MAAT sites that are characterised by a thick soil cover and dense, well developed vegetation, display the highest damping effect (D = c. 90%), and the highest MRCA values (in the range from 350 ± 126 years to 571 ± 128 years). This suggests that carbon incorporated into these stalagmites originates predominantly from decomposition of old, recalcitrant organic matter. SOM turnover rates cannot be ascribed to a single climate variable, e.g. (MAAT) but instead reflect a complex interplay of climate (e.g. MAAT and moisture budget) and vegetation development.