Atomic Processes in Planetary Nebulae and H II Regions

Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have driven much development in atomic physics. In the last few years the combination of a generation of powerful observatories, the development of ever more sophisticated spectral modeling codes, and large efforts on mass production of high quality atomic data have led to important progress in our understanding of the atomic spectra of such astronomical objects. In this paper I review such progress, including evaluations of atomic data by comparisons with nebular spectra, detection of spectral lines from most iron-peak elements and n-capture elements, observations of hyperfine emission lines and analysis of isotopic abundances, fluorescent processes, and new techniques for diagnosing physical conditions based on recombination spectra. The review is directed toward atomic physicists and spectroscopists trying to establish the current status of the atomic data and models and to know the main standing issues.Comment: 9 pages, 1 figur

Prevalence of HPV infection among Greek women attending a gynecological outpatient clinic

Background: Human papillomavirus (HPV) infection is a causative factor for cervical cancer. Early detection of high risk HPV types might help to identify women at high risk of cervical cancer. The aim of the present study was to examine the HPV prevalence and distribution in cervical smears in a sample of Greek women attending a gynecological outpatient clinic and to explore the determinants of the infection.Methods: A total of 225 women were studied. All women underwent a regular gynecological control. 35 HPV types were studied; 6, 11, 16, 18, 26, 31, 33, 35, 39, 40, 42, 43, 44, 45, 51, 52, 53, 54, 56, 58, 59, 61, 62, 66, 68, 70, 71, 72, 73, 81, 82, 83, 84, 85 and 89. Also, basic demographic information, sociodemographic characteristics and sexual behavior were recorded.Results: HPV was detected in 22.7% of the study population. The percentage of the newly diagnosed women with HPV infection was 17.3%. HPV-16 was the most common type detected (5.3%) followed by HPV-53 (4.9%). 66.2% of the study participants had a Pap test during the last year without any abnormalities. HPV infection was related positively with alcohol consumption (OR: 2.19, 95% CI: 1.04-4.63, P = 0.04) and number of sexual partners (OR: 2.16, 95% CI: 1.44-3.25, P < 0.001), and negatively with age (OR: 0.93, 95% CI: 0.87-0.99, P = 0.03), and monthly income (OR: 0.63, 95% CI: 0.44-0.89, P = 0.01).Conclusion: The prevalence of HPV in women attending an outpatient clinic is high. Number of sexual partners and alcohol consumption were the most significant risk factors for HPV infection, followed by young age and lower income

Neuroelectric Evidence for Cognitive Association Formation: An Event-Related Potential Investigation

Although many types of learning require associations to be formed, little is known about the brain mechanisms engaged in association formation. In the present study, we measured event-related potentials (ERPs) while participants studied pairs of semantically related words, with each word of a pair presented sequentially. To narrow in on the associative component of the signal, the ERP difference between the first and second words of a pair (Word2-Word1) was derived separately for subsequently recalled and subsequently not-recalled pairs. When the resulting difference waveforms were contrasted, a parietal positivity was observed for subsequently recalled pairs around 460 ms after the word presentation onset, followed by a positive slow wave that lasted until around 845 ms. Together these results suggest that associations formed between semantically related words are correlated with a specific neural signature that is reflected in scalp recordings over the parietal region

History-Dependent Excitability as a Single-Cell Substrate of Transient Memory for Information Discrimination

Neurons react differently to incoming stimuli depending upon their previous history of stimulation. This property can be considered as a single-cell substrate for transient memory, or context-dependent information processing: depending upon the current context that the neuron “sees” through the subset of the network impinging on it in the immediate past, the same synaptic event can evoke a postsynaptic spike or just a subthreshold depolarization. We propose a formal definition of History-Dependent Excitability (HDE) as a measure of the propensity to firing in any moment in time, linking the subthreshold history-dependent dynamics with spike generation. This definition allows the quantitative assessment of the intrinsic memory for different single-neuron dynamics and input statistics. We illustrate the concept of HDE by considering two general dynamical mechanisms: the passive behavior of an Integrate and Fire (IF) neuron, and the inductive behavior of a Generalized Integrate and Fire (GIF) neuron with subthreshold damped oscillations. This framework allows us to characterize the sensitivity of different model neurons to the detailed temporal structure of incoming stimuli. While a neuron with intrinsic oscillations discriminates equally well between input trains with the same or different frequency, a passive neuron discriminates better between inputs with different frequencies. This suggests that passive neurons are better suited to rate-based computation, while neurons with subthreshold oscillations are advantageous in a temporal coding scheme. We also address the influence of intrinsic properties in single-cell processing as a function of input statistics, and show that intrinsic oscillations enhance discrimination sensitivity at high input rates. Finally, we discuss how the recognition of these cell-specific discrimination properties might further our understanding of neuronal network computations and their relationships to the distribution and functional connectivity of different neuronal types

Noisy galvanic vestibular stimulation promotes GABA release in the substantia nigra and improves locomotion in hemiparkinsonian rats

Dopamine related disorders usually respond to dopaminergic drugs, but not all symptoms are equally responsive. In Parkinson’s disease (PD) in particular, axial symptoms resulting in impaired gait and postural control are difficult to treat. Stochastic vestibular stimulation (SVS) has been put forward as a method to improve CNS function in dopamine related disorders, but the mechanisms of action are not well understood. This thesis aimed to investigate the effects of SVS on neuronal brain activity and to evaluate the possible enhancing effect of SVS on motor control in PD and on cognitive functions and motor learning in Attention deficit hyperactivity disorder (ADHD). Behavioural tests were conducted in the 6-OHDA rat model of PD using the accelerating Rotarod and the Montoya skilled reach test to evaluate the effect of SVS on motor control. The effect of SVS on brain activity was assessed using in vivo microdialysis and immunohistochemistry. We evaluated the effect of SVS on postural control and Parkinsonism in patients with PD and the effect of SVS on cognitive function in people with ADHD. The behavioural animal studies indicate that SVS may have an enhancing effect on locomotion, but not skilled forepaw function. SVS increased GABA transmission in the ipsilesional substantia nigra (SN) and may have a rebalancing effect on dysfunctional brain activity. SVS increased c-Fos activity more than levodopa and saline in the vestibular nucleus of all animals. c-Fos expression was also higher in this region in the 6-OHDA lesioned than in shamlesioned animals, supporting the theory that SVS may have larger effects in the dopamine depleted brain. SVS increased c-Fos expression in the habenula nucleus substantially more than levodopa did. Furthermore, SVS and levodopa had similar effects on many brain regions, including the striatum, where saline had no effect. The clinical studies revealed improvement of postural control in PD during SVS. There was a trend towards reduced Parkinsonism during SVS when off levodopa. No substantial effects were found on cognitive performance in ADHD. In PD, SVS may improve motor control by inhibiting the overactive SN, possibly through a non-dopaminergic modulatory pathway involving increased neurotransmission in the habenula nucleus. SVS could be trialled in larger studies to evaluate long-term effects on treatment resistant axial symptoms associated with PD