Detecting Dissociation Dynamics of Phosphorus Molecular Ions by Atom Probe Tomography.

Dissociation processes involving phosphorus cations were investigated during laser-assisted atom probe tomography of crystalline indium phosphide (InP). This technique not only allows the formation of medium-sized phosphorus cations by means of femtosecond laser pulses under ultrahigh vacuum and high electric field conditions but also allows one to study the time-resolved dissociation dynamics. Data reveal the formation of cations up to P232+ and their subsequent dissociation into two smaller Pk+ cations (k > 2). The use of a time- and position-sensitive detector combined with numerical calculations provided information related to the molecule orientation, decay time, and kinetic energy release during dissociation phenomena. Results suggest that the dissociation processes are most likely due to the emission of Pk2+ cations in excited states and their subsequent decay in low field regions during their flight toward the detector. This study provides operative guidelines to obtain information on dissociation processes using a tomographic atom probe as a reaction microscope and indicates the current capabilities and limitations of such an approach.

Dissociation of GaN2+ and AlN2+ in APT: Analysis of experimental measurements.

The use of a tip-shaped sample for the atom probe tomography technique offers the unique opportunity to analyze the dynamics of molecular ions in strong DC fields. We investigate here the stability of AlN2+ and GaN2+ dications emitted from an Al0.25Ga0.75N sample in a joint theoretical and experimental study. Despite the strong chemical resemblance of these two molecules, we observe only stable AlN2+, while GaN2+ can only be observed as a transient species. We simulate the emission dynamics of these ions on field-perturbed potential energy surfaces obtained from quantum chemical calculations. We show that the dissociation is governed by two independent processes. For all bound states, a mechanical dissociation is induced by the distortion of the potential energy surface in the close vicinity of the emitting tip. In the specific case of GaN2+, the relatively small electric dipole of the dication in its ground 13Σ- and excited 11Δ states induces a weak coupling with the electric field so that the mechanical dissociation into Ga+ + N+ lasts for sufficient time to be observed. By contrast, the AlN2+ mechanical dissociation leads to Al2+ + N which cannot be observed as a correlated event. For some deeply bound singlet excited states, the spin-orbit coupling with lower energy triplet states gives another chance of dissociation by system inter-system crossing with specific patterns observed experimentally in a correlated time of flight map.

Electronic structure and stability of the SiO2+ dications produced in tomographic atom probe experiments.

The molecular electronic states of the SiO2+ dication have been investigated in a joint theoretical and experimental analysis. The use of a tip-shaped sample for tomographic atom probe analysis offers the unique opportunity to produce and to analyze the lifetime of some excited states of this dication. The perturbation brought by the large electric field of the polarized tip along the ion trajectory is analyzed by means of molecular dynamics simulation. For the typical electric fields used in the experiment, the lowest energy triplet states spontaneously dissociate, while the lowest energy singlet states do not. We show that the emission process leads to the formation of some excited singlet state, which dissociates by means of spin-orbit coupling with lower-energy triplet states to produce specific patterns associated with Si+ + O+ and Si2+ + O dissociation channels. These patterns are recorded and observed experimentally in a correlated time-of-flight map.

Bespoke video vignettes - an approach to enhancing reflective learning developed by dental undergraduates and their clinical teachers.

This study explores the selective use of video as a medium to support reflective processes as related to dental undergraduate learning. With the objective of developing and enhancing high-quality adult dental care, the use of compiled video materials created in an undergraduate clinical setting was investigated. Video cameras were used to capture elements of reflection-in-action and reflection-on-action typically found during everyday clinical practice. 'Gold standard' or 'textbook outcomes' are rarely, if ever, fully achieved in dental practice. Real-life clinical experiences offer challenges and opportunities for both teachers and students to engage with reflective learning processes. The materials generated allowed for an experience of individual reflective learning and the creation of a data bank or archive with potential use for the benefit of a wider student cohort. Various aspects of the students' views and comments on the process of reflection were reported and explored by means of a semi-structured focus group moderated by a linked educational advisor.

Ghrelin receptor-knockout mice display alterations in circadian rhythms of activity and feeding under constant lighting conditions.

Ghrelin is an orexigenic hormone produced by the stomach. Ghrelin, however, may also be a modulator of the circadian system given that ghrelin receptors are expressed in the master clock, the suprachiasmatic nucleus (SCN) and several outputs of this region. To investigate this, we performed analyses of running wheel activity and neuronal activation in wild type (WT) and growth hormone secretagogue receptor-knockout (GHSR-KO) mice under various lighting conditions. GHSR-KO and WT mice were maintained under constant dark (DD) or constant light (LL) with ad libitum access to food before being placed on a schedule of temporally restricted access to food (4 h/day) for 2 weeks. There were no differences between KO and WT mice in free-running period under DD, but GHSR-KO mice required more days to develop a high level of food anticipatory activity, and this was lower than that observed in WT mice. Under LL, GHSR-KO mice showed greater activity overall, lengthening of their circadian period, and more resistance to the disorganisational effects of LL. Furthermore, GHSR-KO mice showed greater activity overall, and greater activity in anticipation of a scheduled meal under LL. These behavioral effects were not correlated with changes in the circadian expression of the Fos, Per1 or Per2 proteins under any lighting conditions. These results suggest that the ghrelin receptor plays a role in modulating the activity of the circadian system under normal conditions and under restricted feeding schedules, but does so through mechanisms that remain to be determined.

Morphology control of nanostructures: Na-doped PbTe-PbS system.

The morphology of crystalline precipitates in a solid-state matrix is governed by complex but tractable energetic considerations driven largely by volume strain energy minimization and anisotropy of interfacial energies. Spherical precipitate morphologies are favored by isotropic systems, while anisotropic interfacial energies give energetic preference to certain crystallographically oriented interfaces, resulting in a faceted precipitate morphology. In conventional solid-solution precipitation, a precipitate's morphological evolution is mediated by surface anchoring of capping molecules, which dramatically alter the surface energy in an anisotropic manner, thereby providing exquisite morphology control during crystal growth. Herein, we present experimental evidence and theoretical validation for the role of a ternary element (Na) in controlling the morphology of nanoscale PbS crystals nucleating in a PbTe matrix, an important bulk thermoelectric system. The PbS nanostructures formed by phase separation from a PbI(2)-doped or undoped PbTe matrix have irregular morphologies. However, replacing the iodine dopant with Na (1-2 mol %) alters dramatically the morphology of the PbS precipitates. Segregation of Na at PbTe/PbS interfaces result in cuboidal and truncated cuboidal morphologies for PbS. Using analytical scanning/transmission electron microscopy and atom-probe tomography, we demonstrate unambiguously that Na partitions to the precipitates and segregates at the matrix/precipitate interfaces, inducing morphological anisotropy of PbS precipitates. First-principles and semiclassical calculations reveal that Na as a solute in PbTe has a higher energy than in PbS and that Na segregation at a (100) PbTe/PbS interface decreases the total energy of matrix/precipitate system, resulting in faceting of PbS precipitates. These results provide an impetus for a new strategy for controlling morphological evolution in matrix/precipitate systems, mediated by solute partitioning of ternary additions.

Bright and ultrafast electron point source made of LaB6 nanotip.

The development of time-resolved transmission electron microscopy (TEM), ultrafast electron spectroscopy and pulsed X-ray sources relies on the realization of stable and high brightness sources of ultra-short electron bunches with a long service time. The flat photocathodes implanted in thermionic electron guns have been replaced by Schottky-type or cold-field emission sources driven by ultra-fast laser. Recently, lanthanum hexaboride (LaB6) nanoneedles have been reported to have high brightness and high emission stability when working in a continuous emission mode. Here, we prepare nano-field emitters from bulk LaB6 and we report on their use as ultra-fast electron sources. Using a high repetition rate laser in the infrared range, we present different field emission regimes as a function of the extraction voltage and laser intensity. The properties of the electron source (brightness, stability, energy spectrum and emission pattern) are determined for the different regimes. Our results show that LaB6 nanoneedles can be used as ultrafast and ultra-bright sources for time-resolved TEM, with better performances as compared to metallic ultra-fast field-emitters.

Teaching of the repair of defective composite restorations in Scandinavian dental schools.

Given increased tooth retention into later years of life, dentists face increasing challenges in maintaining teeth with extensive composite restorations. Accompanying the increase in placement of composite restorations in general practice, there has also been increased evidence that repair, rather than replacement, of composite restorations is being increasingly considered as a treatment option. Previous work has demonstrated that such techniques are often underutilised in practice. The aim of this study was to examine contemporary teaching of composite repair techniques in Scandinavian dental schools. A questionnaire was distributed by email to each of the 12 Scandinavian dental schools in late 2010/early 2011. This questionnaire sought information on the undergraduate teaching of composite repair techniques as well as indications and materials utilised for this technique. A 100% response rate was achieved (12 schools). Eleven of the 12 respondent schools indicated that they included the teaching of composite repair techniques within their dental school programme. The most commonly reported indications for the teaching of the repair of direct composite restorations were tooth substance preservation (11 schools) and reduced risk of harmful effects on the pulp (10 schools). The most commonly taught surface treatment was mechanical roughening of the existing composite restoration, including the removal of the surface layer of material, prior to application of fresh composite (11 schools). Overall, the results of this study showed that the teaching of composite repair techniques is established within Scandinavian dental schools. This may influence the practising habits of dentists graduating from these schools when considering treatment options for defective composite restorations.

Teaching of direct composite restoration repair in undergraduate dental schools in the United Kingdom and Ireland.

AIM: To investigate aspects of the teaching of restoration repair as a minimally invasive alternative to the replacement of defective direct composite restorations in teaching programmes in undergraduate curricula in dental schools in the United Kingdom and Ireland. METHODS: An online questionnaire which sought information in relation to the current teaching of composite restoration repair was developed and distributed to the 17 established UK and Irish dental schools with undergraduate teaching programmes in Spring 2010. RESULTS: Completed responses were received from all 17 schools (response rate= 100%). Fifteen schools reported that they included teaching of repair techniques for defective direct composite restorations in their programme. Of the two remaining schools, one indicated that it would introduce teaching of repair techniques during the next five years. The most common indication for a composite repair was that of 'tooth substance preservation' (15 schools). The defects in restorations considered appropriate for repair rather than replacement by the largest number of schools included partial loss of restoration (13 schools) and marginal defects (12 schools). The most commonly taught surface treatment when performing a repair was mechanical roughening of the existing composite with removal of the surface layer (14 schools). Thirteen schools taught etching and the application of an adhesive bonding agent to the prepared surfaces, while the most commonly taught material for completing the repair was a hybrid composite resin (12 schools). Popular finishing implements included diamond finishing instruments (13 schools) and finishing discs (11 schools). CONCLUSION: Not withstanding reluctance amongst general dental practitioners, the teaching of repair of a defective composite restoration, rather than total restoration replacement, is firmly established within UK and Irish dental school programmes. Repair techniques have clear advantages for patients, not least including a minimally invasive approach to treatment and avoidance of unnecessary loss of tooth tissue and pulpal damage. Dental practitioners should look more to repair techniques when managing defective composite restorations and clinical dental teachers should continue to research and refine composite repair techniques.

Defective dental restorations: to repair or not to repair? Part 1: direct composite restorations.

The presentation of patients with failing dental restorations that exhibit minor defects is a common clinical situation in everyday dental practice. The repair of such restorations, rather than replacement, is increasingly considered to be a viable alternative to the replacement of the defective restoration. This first of two papers considers indications and techniques for the repair of defective direct composite restorations. It is possible that some dental practitioners are unaware of the option of repair rather than replacement of composite restorations. This article provides an overview of contemporary knowledge and understanding of restoration repair in the clinical management of defective composite restorations.

Defective dental restorations: to repair or not to repair? Part 2: all-ceramics and porcelain fused to metal systems.

With the increasing use of ceramics in restorative dentistry, and trends to extend restoration longevity through the use of minimal interventive techniques, dental practitioners should be familiar with the factors that may influence the decision either to repair or replace fractured metal-ceramic and all-ceramic restorations and, also, the materials and techniques available to repair these restorations. This second of two papers addresses the possible modes of failure of ceramic restorations and outlines indications and techniques in this developing aspect of restoration repair in clinical practice.

Photoassisted and multiphoton emission from single-crystal diamond needles.

Practical realization of stable and high brightness sources of ultra-short electron pulses is an important issue in the development of time-resolved electron microscopy for the study of ultra-fast dynamics in materials. Here, we report on the experimental investigation of static (in the dark) and pulsed (under illumination by sub-picosecond laser pulses at 1040 nm) electron emission from single-crystal diamond needles. A significant increase of electron emission current was detected under laser illumination. The nonlinear dependence of the emission current on the laser intensity and on the angle between the needle and the laser beam polarization axis suggests multi-photon emission processes. This interpretation is in agreement with electron spectroscopy measurements performed for electrons emitted at different bias voltages and different laser power levels and repetition rates. The remarkable feature of the diamond emitters is their stability under high average power of laser radiation. This provides a new highly efficient source of photoemitted electrons based on single-crystal diamond.

A survey of undergraduate education in dental implantology in UK dental schools.

The aim of this study was to ascertain knowledge on current teaching of implant dentistry in the undergraduate curriculum of Dental Schools in the UK. Information on the teaching modalities, including year of introduction of implant dentistry into undergraduate curriculum, departments involved in teaching, format of teaching, use of adjunctive teaching aids, and types of implant systems used in undergraduate teaching was collected by means of a questionnaire, which was sent to all undergraduate dental schools in the UK. Based on a 100% response rate, the findings indicate that all dental schools in the UK reported that they included dental implantology in their undergraduate curriculum; however there were marked variations in the content and delivery of the teaching.

Compositional accuracy of atom probe tomography measurements in GaN: Impact of experimental parameters and multiple evaporation events.

A systematic study of the biases occurring in the measurement of the composition of GaN by Atom Probe Tomography was carried out, in which the role of surface electric field and laser pulse intensity has been investigated. Our data confirm that the electric field is the main factor influencing the measured composition, which exhibits a deficiency of N at low field and a deficiency of Ga at high field. The deficiency of Ga at high field is interpreted in terms of preferential evaporation of Ga. The detailed analysis of multiple evaporation events reveals that the measured composition is not affected by pile-up phenomena occurring in detection system. The analysis of correlation histograms yields the signature of the production of neutral N2 due to the dissociation of GaN32+ ions. However, the amount of N2 neutral molecules that can be detected cannot account for the N deficiency found at low field. Therefore, we propose that further mechanisms of neutral N evaporation could be represented by dissociation reactions such as GaN+→ Ga++ N and GaN2+→ Ga2++ N.

Prevention of hypoglycemic attacks by propranolol in a patient suffering from insulinoma.

An insulinoma was diagnosed in a fifty-seven-year-old woman suffering from frequent hypoglycemic attacks. Propranolol--a beta-adrenergic blocker--in a dose of 80 mg. per day effectively prevented recurrent hypoglycemic attacks. It also corrected the basal hyperinsulinemia as well as the increased insulin secretion which results from stimulation with glucose or arginine.

A cohort investigation of the changes in vocational dental practitioners' views on repairing defective direct composite restorations.

OBJECTIVE: To investigate changes in vocational dental practitioners (VDPs) views on repairing direct composite restorations (DCRs) during the vocational training (VT) year 2002-2003. DESIGN: A questionnaire-based cohort study. METHOD: Data on the repair of DCRs, including indications and details of operative techniques were collected by a questionnaire sent at the beginning of the VT year (September 2002) to all 12 Postgraduate Dental Deans in England. A follow-up questionnaire was sent to the Deans near the end of the VT year (May 2003). They were asked, on both occasions, to distribute the questionnaires among their VDPs and to return the completed questionnaires. RESULTS: Ten deaneries participated in the study. The September 2002 and May 2003 findings (306 respondents [66%] and 313 respondents [67%] respectively) were analysed using Chi-square statistic and t-test to identify any significant differences (P<0.05). Significant changes in the attitudes of the VDPs during the VT year included a shift to viewing reduction in treatment time (30% to 48%), cost to patient (12% to 20%) and the management of the partial loss of a restoration (57% to 70%) as indications for repairs. In contrast, there was a significant change in viewing secondary caries as an indication for repair (46% to 29%). In addition, there was a significant, worrisome shift in relation to the use of bonding systems and finishing instruments, together with a reduction in the anticipated longevity of composite repairs. CONCLUSION: Aspects of VDPs' attitudes to the repair of DCRs were found to change significantly during the VT year. Not all aspects of the changes observed were considered to be positive. Knowledge and understanding of repairs to DCRs need to be strengthened.

Role of the resistivity of insulating field emitters on the energy of field-ionised and field-evaporated atoms.

In order to improve the accuracy of laser atom probe analyses, it is important to understand all the physical processes induced by the combination of the high electrical field and the femtosecond laser beam during field evaporation. New information can be accessed from the energy of evaporated surface atoms or field-ionised atoms of an imaging gas. In order to study the ions energy, we combine La-APT and FIM analyses in a new experimental setup equipped with electrostatic lenses. We report measurements for semiconductors and oxides and we study the influence of the illumination conditions (laser power and wavelength), the evaporation rate, the sample geometry and the tip preparation processes. The results are discussed taking into account the resistive properties of non-metallic samples and the photo-stimulated conductivity. This work clarifies the role of the laser and DC field in the energy deficit of field evaporated ions.

Primary hyperparathyroidism: possible cause of primary hyperaldosteronism in a 60-year-old woman.

Hypertension and hypokalemia were found in a 60-yr-old woman suffering from primary hyperparathyroidism. Laboratory investigations in this patient disclosed 1) elevated levels of plasma aldosterone (PA) which could not be suppressed by a high sodium diet alone or in combination with fludrocortisone (Florinef); 2) a decline of the elevated PA levels after 4 h of ambulation; and 3) low PRA which was unresponsive to stimulation by a low sodium diet coupled with diuretic-induced volume depletion and 4 h of ambulation. These findings were consistent with the diagnosis of primary hyperaldosteronism. Extirpation of a parathyroid adenoma reduced the patient's serum calcium level to normal, and subsequently, a normalization of her blood pressure, serum electrolytes, PA, and PRA were observed. On the basis of these data is is suggested that in this case hyperaldosteronism may have been caused directly or indirectly by primary hyperparathyroidism.

Plasma neurotransmitter profile during different phases of the ovulatory cycle.

The influence of the different phases of the menstrual cycle on platelet-poor plasma norepinephrine (NE) and serotonin (5HT) was examined in 17 normal volunteers. The examinations were performed consecutively during 3 phases of the ovulatory cycle: 1) follicular phase, 2) ovulation, and 3) luteal phase. This investigation was initiated after a preliminary study in 51 volunteers showed wide and consistent variations of plasma NE and 5HT during the different phases of the cycle. Since in this first group the determinations had not been performed consecutively in the same subjects, and the changes observed in the different phases of the cycle could reflect interpersonal variations, the determinations were performed consecutively in a second group, concomitantly with serum estradiol (E2) and LH measurements. The results showed a decrease in plasma 5HT from the follicular phase [144.3 +/- 69.3 nmol/L (+/- SD)] to ovulation (55.7 +/- 41.4; P less than 0.001) and a subsequent increase in the luteal phase (141.3 +/- 96.4; P less than 0.01). The nadir in plasma 5HT showed an inverse correlation with serum LH (r = -0.07). Plasma NE increased from the follicular phase (1226.5 +/- 475.1 pmol/L) to ovulation (1694.0 +/- 564.4; P = 0.027) and reached a maximum in the luteal phase (2335.0 +/- 728.2; P = 0.0034). This rise correlated positively with serum E2. In conclusion, plasma 5HT and NE vary with the different phases of the menstrual cycle. Plasma NE rises during ovulation and seems to to correlate positively with serum E2 levels. Plasma 5HT reaches a nadir during ovulation and correlates inversely with serum LH.

Low platelet-poor plasma concentrations of serotonin in patients with combat-related posttraumatic stress disorder.

BACKGROUND: Combat-related posttraumatic stress disorder (CR-PTSD) is associated with a dysregulation of various neurotransmitter systems. METHODS: We assessed levels of platelet-poor plasma (PPP) norepinephrine (NE), and serotonin (5-HT), and 24-hour urinary excretion of NE, dopamine (DA), and homovanillic acid (HVA) in 17 male outpatients with untreated chronic CR-PTSD (age, 33.1 +/- 7.4 years) and 10 normal control subjects (age, 35.8 +/- 2.7 years). RESULTS: Compared with the control subjects, the PTSD patients showed significantly lower PPP 5-HT levels, elevated PPP NE levels, and significantly higher mean 24-hour urinary excretion of all three catecholamines (NE, DA, and HVA). The 24-hour urinary HVA values of the CR-PTSD patients correlated significantly and positively with the total Impact of Event Scale scores and the avoidance symptoms cluster scores, and the PPP 5-HT levels correlated negatively with the Hamilton Anxiety Rating Scale scores. The PPP NE/5-HT ratio was significantly higher in the study group than in the control subjects. CONCLUSIONS: We believe this combined enhanced noradrenergic activity and diminished 5-HT activity may be relevant to the neurobiology of CR-PTSD.