Influence of the substrate type on CVD grown homoepitaxial diamond layer quality by cross sectional TEM and CL analysis

To assess diamond-based semiconducting devices, a reduction of point defect levels and an accurate control of doping are required as well as the control of layer thickness. Among the analyses required to improve such parameters, cross sectional studies should take importance in the near future. The present contribution shows how FIB (focused ion beam) preparations followed by electron microscopy related techniques as TEM or CL allowed to performanalysis versus depth in the layer, doping and point defect levels. Three samples grown along the sameweek in the same machinewith identical growth conditions but on different substrates (CVD-IIIa (110) oriented, CVD-optical grade (100) oriented and a HPHT-Ib (100) oriented) are studied. Even though A-band is observed by CL, no dislocation is observed by CTEM. Point defect type and level are shown to substantially change with respect to the substrate type as well as the boron doping levels that vary within an order of magnitude. H3 present in the epilayer grown on HPHT type of substrate is replaced by T1 and NE3 point defects for epilayers grown on the CVD type one. An increase of excitonic transitions through LO phonons is also shown to take place near the surface while only TO ones are detected deeper in the epilayer. Such results highlight the importance of choosing the correct substrate.5 page

Cellular mechanisms underlying Pax3-related neural tube defects and their prevention by folic acid

Neural tube defects (NTDs), including spina bifida and anencephaly, are among the most common birth defects worldwide, but their underlying genetic and cellular causes are not well understood. Some NTDs are preventable by supplemental folic acid. However, despite widespread use of folic acid supplements and implementation of food fortification in many countries, the protective mechanism is unclear. Pax3 mutant (splotch; Sp2H) mice provide a model in which NTDs are preventable by folic acid and exacerbated by maternal folate deficiency. Here, we found that cell proliferation was diminished in the dorsal neuroepithelium of mutant embryos, corresponding to the region of abolished Pax3 function. This was accompanied by premature neuronal differentiation in the prospective midbrain. Contrary to previous reports, we did not find evidence that increased apoptosis could underlie failed neural tube closure in Pax3 mutant embryos, nor that inhibition of apoptosis could prevent NTDs. These findings suggest that Pax3 functions to maintain the neuroepithelium in a proliferative, undifferentiated state, allowing neurulation to proceed. NTDs in Pax3 mutants were not associated with abnormal abundance of specific folates and were not prevented by formate, a one-carbon donor to folate metabolism. Supplemental folic acid restored proliferation in the cranial neuroepithelium. This effect was mediated by enhanced progression of the cell cycle from S to G2 phase, specifically in the Pax3 mutant dorsal neuroepithelium. We propose that the cell-cycle-promoting effect of folic acid compensates for the loss of Pax3 and thereby prevents cranial NTDs

Quantum field theory approach to the optical conductivity of strained and deformed graphene

The computation of the optical conductivity of strained and deformed graphene is discussed within the framework of quantum field theory in curved spaces. The analytical solutions of the Dirac equation in an arbitrary static background geometry for one dimensional periodic deformations are computed, together with the corresponding Dirac propagator. Analytical expressions are given for the optical conductivity of strained and deformed graphene associated with both intra and interbrand transitions. The special case of small deformations is discussed and the result compared to the prediction of the tight-binding model.The authors acknowledge financial supportfrom the Brazilian agencies FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico)

Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment

In this paper, we review theoretical and experimental research on rare region effects at quantum phase transitions in disordered itinerant electron systems. After summarizing a few basic concepts about phase transitions in the presence of quenched randomness, we introduce the idea of rare regions and discuss their importance. We then analyze in detail the different phenomena that can arise at magnetic quantum phase transitions in disordered metals, including quantum Griffiths singularities, smeared phase transitions, and cluster-glass formation. For each scenario, we discuss the resulting phase diagram and summarize the behavior of various observables. We then review several recent experiments that provide examples of these rare region phenomena. We conclude by discussing limitations of current approaches and open questions.Comment: 31 pages, 7 eps figures included, v2: discussion of the dissipative Ising chain fixed, references added, v3: final version as publishe

Dynamic acetylation profile during mammalian neurulation

Neural tube defects (NTDs) result from failure of neural tube closure during embryogenesis. These severe birth defects of the central nervous system include anencephaly and spina bifida, and affect 0.5-2 per 1,000 pregnancies worldwide in humans. It has been demonstrated that acetylation plays a pivotal role during neural tube closure, as animal models for defective histone acetyltransferase proteins display NTDs. Acetylation represents an important component of the complex network of posttranslational regulatory interactions, suggesting a possible fundamental role during primary neurulation events. This study aimed to assess protein acetylation contribution to early patterning of the central nervous system both in human and murine specimens

Soil organisms in organic and conventional cropping systems.

Apesar do crescente interesse pela agricultura orgânica, são poucas as informações de pesquisa disponíveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrófico foram comparados os efeitos de sistemas de cultivo orgânico e convencional, para as culturas do tomate (Lycopersicum esculentum) e do milho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populações de fungos,bactérias e actinomicetos, determinadas pela contagem de colônias em meio de cultura, foram semelhantes para os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO2, manteve-se superior no sistema orgânico, sendo que em determinadas avaliações foi o dobro da evolução verificada no sistema convencional. O número de espécimes de minhoca foi praticamente dez vezes maior no sistema orgânico. Não foi observada diferença na taxa de decomposição de matéria orgânica entre os dois sistemas. De modo geral, o número de indivíduos de microartrópodos foi superior no sistema orgânico do que no sistema convencional, refletindo no maior índice de diversidade de Shannon. As maiores populações de insetos foram as da ordem Collembola, enquanto para os ácaros a maior população foi a da superfamília Oribatuloidea. Indivíduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foram ocasionalmente coletados e de forma similar entre os sistemas

The impact of nature of onset of pain and posttraumatic stress on adjustment to chronic pain and treatment outcome

Despite the demonstrated efficacy of cognitive-behavioural therapy for chronic pain, recent research has attempted to identify predictors of treatment outcome in order to improve the effectiveness of such treatments. This research has indicated that variables such as the nature of the onset of the pain and psychopathology are associated with poor adjustment to chronic pain. Accordingly, these variables might also be predictive of poor response to treatment. Individuals who experience a sudden onset of pain following an injury or accident, particularly when the instigating event is experienced as psychologically traumatic, may present for treatment with high levels of distress, including symptoms consistent with a posttraumatic stress response. The impact of this type of onset of pain and posttraumatic stress symptoms on adjustment to chronic pain and treatment outcome is the focus of this thesis. Three studies were conducted to clarify and extend earlier research findings in this area. Using 536 patients referred for treatment in a tertiary referral pain management centre, the first study examined the psychometric properties of a widely used self-report measure of posttraumatic stress symptoms (the PTSD Checklist, or PCL), modified for use in a chronic pain sample. This study provided preliminary support for the suitability of the PCL as a self-report measure of Posttraumatic Stress Disorder (PTSD) symptoms in chronic pain patients. However, the study also highlighted a number of issues with the use of self-report measures of posttraumatic stress symptoms in chronic pain patient samples. In particular, PCL items enquiring about symptoms which are a common aspect of the chronic pain experience (e.g. irritability, sleep problems) appeared to contribute to high mean scores on the PCL Avoidance and Arousal subscales. Furthermore, application of diagnostic cut-off scores and an algorithm recommended for the PCL in other trauma groups suggested that a much larger proportion of the sample was identified as potentially meeting diagnostic criteria for PTSD than would have been expected from previous research. The second study utilised the modified PCL to investigate the impact of different types of onset of pain (e.g. traumatic onset) and posttraumatic stress symptoms on adjustment to chronic pain in a sample of 196 chronic pain patients referred to the same centre. For patients who experienced the onset of pain related to a specific event, two independent experts in the field of PTSD determined whether these events satisfied the definition of a traumatic event according to DSM-IV diagnostic criteria. Adjustment was assessed through a number of validated measures of mood, disability, pain experience, and pain-related cognitions. Contrary to expectations, comparisons between patients who had experienced different types of onset of pain revealed few significant differences between them. That is, analyses comparing patients presenting with accident-related pain, or pain related to other specific events, to patients who had experienced spontaneous or insidious onset of pain revealed no significant differences between the groups on measures of pain severity, pain-related disability, and symptoms of affective distress after adjustment for age, pain duration, and compensation status. Similarly, comparisons between patients who had experienced a potentially traumatic onset of pain with those who had experienced a non-traumatic or spontaneous or insidious onset of pain also revealed no significant differences on the aforementioned variables. In contrast, compensation status, age, and a number of cognitive variables were significant predictors of pain severity, pain-related disability, and depression. The final study investigated the impact of type of pain onset and posttraumatic stress symptoms on response to a multidisciplinary cognitive-behavioural pain management program. Unlike the previous study, this treatment outcome study revealed a number of differences between onset groups. Most notably, patients who had experienced an insidious or spontaneous onset of pain reported greater improvements in pain severity and maintained these improvements more effectively over a one month period than patients who had experienced pain in the context of an accident or other specific incident. There was also limited evidence that improvements in depression favoured patients who had experienced an insidious or spontaneous and non-traumatic onset of pain. Consistent with this, posttraumatic stress symptoms were a significant predictor of treatment outcome, with higher levels of symptoms being associated with smaller improvements in pain-related disability and distress. Notably, this study also revealed that certain cognitive variables (i.e. catastrophising, self-efficacy, and fear-avoidance beliefs) were also significant predictors of treatment outcome, consistent with previous findings in the pain literature. This provided some perspective on the relative roles of both PTSD symptoms and cognitive variables in adjustment to persisting pain and treatment response. These findings were all consistent with expectations and with previous research. Implications for future research and for the assessment and treatment of chronic pain patients who present with posttraumatic stress symptoms are discussed

A Coulomb gas approach to the anisotropic one-dimensional Kondo lattice model at arbitrary filling

We establish a mapping of a general spin-fermion system in one dimension into a classical generalized Coulomb gas. This mapping allows a renormalization group treatment of the anisotropic Kondo chain both at and away from half-filling. We find that the phase diagram contains regions of paramagnetism, partial and full ferromagnetic order. We also use the method to analyze the phases of the Ising-Kondo chain.Comment: 19 pages, 9 figure