Center-of-Mass Properties of the Exciton in Quantum Wells

We present high-quality numerical calculations of the exciton center-of-mass dispersion for GaAs/AlGaAs quantum wells of widths in the range 2-20 nm. The k.p-coupling of the heavy- and light-hole bands is fully taken into account. An optimized center-of-mass transformation enhances numerical convergence. We derive an easy-to-use semi-analytical expression for the exciton groundstate mass from an ansatz for the exciton wavefunction at finite momentum. It is checked against the numerical results and found to give very good results. We also show multiband calculations of the exciton groundstate dispersion using a finite-differences scheme in real space, which can be applied to rather general heterostructures.Comment: 19 pages, 12 figures included, to be published in Phys. Rev.

Paraneoplastic Limbic Encephalitis Resembling Acute Herpetic Encephalitis

Introduction. Paraneoplastic limbic encephalitis (PLE) is a rare disorder that typically follows a chronic or subacute course of personality changes, memory loss, seizures, and hallucinations. Early diagnosis is difficult and characteristic symptoms can be mimicked by a variety of conditions. We present a case of PLE, initially presenting as acute herpetic encephalitis. Case Presentation. A 56-year-old male was admitted for evaluation of acute onset headache, fever, and confusion. On neurological examination he was confused with MMSE score of 15/30. CSF analysis revealed marked lymphocytic pleocytosis. A possible diagnosis of acute herpetic encephalitis was rendered and patient was treated with acyclovir. CSF PCR was negative. Cranial MRI revealed bilateral hyperintense lesions in medial temporal lobes with contrast enhancement. Despite treatment with acyclovir patient was deteriorated; thus, a paraneoplastic syndrome was suspected. Chest CT showed a right paratracheal lymph node mass, while a biopsy revealed neuroendocrine lung cancer. Auto antibodies to Hu were also detected. The patient was treated with steroids and chemotherapy. Six months later, he had complete tumour remission and marked neurological improvement. Discussion. PLE can rarely invade acutely, being indistinguishable from herpetic encephalitis. Inclusion of PLE in the differential diagnosis of acute encephalitis is of great clinical significance

Acetyl Cholinesterase Inhibitors and Cell-Derived Peripheral Inflammatory Cytokines in Early Stages of Alzheimer's Disease

Clinical and preclinical studies firmly support the involvement of the inflammation in the pathogenesis of Alzheimer's disease (AD). Despite acetylcholinesterase inhibitors (AChEI) being widely used in AD patients, there is no conclusive evidence about their impact on the inflammatory response.Funding was received from a program co-financed by the European Social Fund and the Greek State (GSRT LS5-3808)info:eu-repo/semantics/publishedVersio

The potential of depressive symptoms to identify cognitive impairment in ageing

Depressive symptoms are common in mild cognitive impairment (MCI), dementia caused by Alzheimer’s disease (AD dementia) and in cognitively unimpaired older adults. However, it is unclear whether they could contribute to the identification of cognitive impairment in ageing. To assess the potential utility of depressive symptoms to distinguish between healthy cognitive ageing and MCI and AD dementia. The diagnostic workup of the cognitive function of 1737 older cognitively unimpaired individuals, 334 people with MCI and 142 individuals with AD dementia relied on a comprehensive neuropsychiatric assessment, including the Mini Mental State Examination (MMSE). Depressive symptoms were tapped with the 15-item Geriatric Depression Scale (GDS). Proportional odds logistic regression (POLR) models and the machine learning technique Adaptive Boosting algorithm (AdaBoost) were employed. Stratified repeated random subsampling (stratified bootstrap resampling) was used to recursive partitioning to training- and validation set (70/30 ratio). The average accuracy of the POLR models for the GDS total score in distinguishing between cognitive impairment and healthy cognitive ageing exceeded 78% and was inferior to that of MMSE. Of note, the sensitivity of GDS total score was very low. By employing the AdaBoost algorithm and considering GDS items separately, the average accuracy was higher than 0.72 and comparable to that of the MMSE, while sensitivity- and specificity values were more balanced. The findings of the study provide initial evidence that depressive symptoms may contribute to distinguishing between cognitive impairment and cognitively healthy ageing

Efficacy of antidepressants for depression in Alzheimer's disease: systematic review and meta-analysis

Background: Depression is common in people with Alzheimer’s disease (AD) affecting overall outcomes and decreasing quality of life. Although depression in AD is primarily treated with antidepressants, there are few randomized controlled trials (RCTs) assessing efficacy and results have been conflicting. Objectives: To systematically review evidence on efficacy of antidepressant treatments for depression in AD. Methods: Systematic review and meta-analysis of double blind RCTs comparing antidepressants versus placebo for depression in AD. We searched MEDLINE, CINAHL, EMBASE, PsycINFO, the Cochrane Controlled Trials Register and on line national and international registers. Primary outcomes were treatment response and depressive symptoms. Secondary outcomes were cognition, acceptability, and tolerability. Risk of bias was also assessed. Results: Seven studies met inclusion criteria. Three compared sertraline with placebo; one compared both sertraline and mirtazapine to placebo; imipramine, fluoxetine, and clomipramine were evaluated in one study each. In terms of response to treatment (6 studies, 297 patients treated with antidepressants and 223 with placebo), no statistically significant difference between antidepressants and placebo was found (odds ratio (OR) 1.95, 95% CI 0.97–3.92). We found no significant drug-placebo difference for depressive symptoms (5 studies, 311 patients, SMD –0.13; 95% CI –0.49 to 0.24). Overall quality of the evidence was moderate because of methodological limitations in studies and the small number of trials. Conclusion: Despite the importance of depression in people with AD, few RCTs are available on efficacy of antidepressants, limiting clear conclusions of their potential role. There is a need for further high quality RCTs

Ultrafast terahertz probes of transient conducting and insulating phases in an electron–hole gas

Many-body systems in nature exhibit complexity and self-organization arising from seemingly simple laws. The long-range Coulomb interaction between electrical charges generates a plethora of bound states in matter, ranging from the hydrogen atom to complex biochemical structures. Semiconductors form an ideal laboratory for studying many-body interactions of quasi-particles among themselves and with lattice vibrations and light. Oppositely charged electron and hole quasi-particles can coexist in an ionized but correlated plasma, or form bound hydrogen-like pairs called excitons which strongly affect physical properties. The pathways between such states however remain elusive in near-visible optical experiments that detect a subset of excitons with vanishing center-of-mass momenta. In contrast, transitions between internal exciton levels which occur in the far-infrared at terahertz (10 s) frequencies are in dependent of this restriction suggesting their use as a novel pro be of pair dynamics. Here, we employ an ultrafast terahertz probe to directly investigate the dynamical interplay of optically-generated excitons and unbound electron-hole pairs in GaAs quantum wells. Our observations witness an unexpected quasi-instantaneous excitonic enhancement, reveal formation of insulating excitons on a hundred picosecond timescale and manifest conditions under which excitonic populations prevail

Exciton center-of-mass motion in quantum wells and quantum wires

Diese Arbeit stellt eine gründliche Analyse der Schwerpunktsbewegung von Exzitonen in Halbleiter-Quantengräben und -Quantendrähten dar. Dabei wurde die k.p-Kopplung der schweren und leichten Löcher im Valenzband sowie das Coulomb-Potential voll berücksichtigt. Die Optimierung der Schwerpunktstransformation auf der Basis eines Ansatzes für die Abhängigkeit des Grundzustands des Exzitons vom Schwerpunktsimpuls Q ermöglichte numerische Ergebnisse hoher Qualität. Es zeigt sich nämlich, daß in einer Subbandentwicklung die Enveloppe des Grundzustands des Exzitons in guter Näherung unabhängig vom Schwerpunktsimpuls ist. So konnten erstmalig Multiband-Exziton-Berechnungen in Quantendrähten mit voller Berücksichtigung der Coulomb-Wechselwirkung durchgeführt werden. Die in dieser Arbeit dargestellten Untersuchungen zeigen interessante physikalische Effekte auf, wie beispielsweise eine nichtmonotone Zunahme der Bindungsenergie des exzitonischen Grundzustands mit wachsendem Q und einen zur entsprechenden Kontinuumskante weitestgehend parallelen Verlauf der Dispersion des exzitonischen Grundzustands. Die Optimierung der Schwerpunktstransformation führt außerdem zu einem analytischen Ausdruck für eine mittlere Masse, die relevant für den exzitonischen Grundzustand ist.This thesis presents a thorough investigation of the center-of-mass dispersion properties of excitons in semiconductor quantum wells and quantum wires. The k.p coupling of heavy and light holes as well as the Coulomb coupling are taken fully into account. High-quality numerical calculations of the exciton center-of-mass dispersion are achieved by optimizing the center-of-mass transformation, making use of an Ansatz for the dependence of the groundstate exciton upon the center-of-mass momentum Q. Indeed, the envelope in the subband expansion of the groundstate exciton is to a good approximation independent of Q. This technique made possible for the first time multiband calculations in quantum wires that take the Coulomb coupling fully into account. Various physically interesting effects are found and investigated, like, e.g., the non-monotonous increase of the exciton groundstate binding energy with Q or the fact that the exciton groundstate energy follows the exciton continuum edge rather closely. The center-of-mass optimization leads also to an analytical expression for an estimate of the exciton groundstate center-of-mass mass

Η "χρηματιστηριακή απάτη" και η σχέση της με την κοινή απάτη του Ποινικού Κώδικα

Η παρούσα εργασία έχει σκοπό να διερευνήσει την ποινική υπόσταση του αδικήματος της χειραγώγησης της κεφαλαιαγοράς, το οποίο συνίσταται σε συμπεριφορές "χρηματιστηριακής απάτης", όπως αυτό έχει διαμορφωθεί στην ελληνική έννομη τάξη, εστιάζοντας τόσο στο νόμο 3340/2005 όσο και στον ισχύοντα σήμερα 4443/2016. Στην συνέχεια, θα επιχειρηθεί η εξέταση της σχέσης μεταξύ της ειδικής υπόστασης της χειραγώγησης της κεφαλαιαγοράς και της κοινής απάτης του άρθρου 386 του ελληνικού Ποινικού Κώδικα προκειμένου να διαπιστωθεί αν η πρώτη αποτελεί ειδικότερη περίπτωση απάτης ή εάν περιγράφει εγκληματική συμπεριφορά ασύμβατη προς τα στοιχεία της ειδικής υπόστασης της διάταξης του Ποινικού Κώδικα.The aim of this paper is to examine the criminal substance of the stock exchange market manipulation which consists of "securities fraud" behaviors, as it has been formed in the Greek legal system, focusing on Law 4443 of 2016. Following that, it will be attempted to investigate the relation between the special substance of the stock exchange market manipulation and the common fraud described in article 386 of the criminal code, in order to determine if the former is a special case of fraud or if it describes an incompatible criminal behavior to the aspects of the special substance of the criminal code's provision

Developing a methodological framework using mathematical simulation models in order to investigate the operation of coastal aquifer systems: application in the aquifer of N. Moudania

In the present dissertation the investigation of the operation of coastal aquifer systems, which are characterized by overexploitation conditions as well as by seawater intrusion and intense nitrate contamination, is attempted through the application of mathematical simulation models and in light of the absence of sufficient data relating both to the conceptual model of the aquifers and the variables of the problem under study. The methodological framework which is developed consists of the formation of a series of mathematical models through the use of the widely applied codes MODFLOW (groundwater flow simulation), MT3DMS (solute mass transport simulation) and SEAWAT (variable density flow simulation). The sequence and the connection between these models constitute an integral and fundamental part of the whole procedure. The development of these models aims to the proper adjustment of various aquifer parameters, particularly those with high uncertainty and a significant lack of data and measurements (e.g. hydraulic-hydrodynamic aquifer parameters), as well as to the most representative determination of the initial conditions regarding the seawater intrusion problem, a procedure which by its nature involves considerable difficulties and is hindered greatly due to the absence of data. The successful implementation of the proposed methodology has as direct results the satisfactory simulation of the physical processes of groundwater flow, seawater intrusion and nitrate transport, the accurate projection in time of both hydraulic head and nitrate concentrations distribution, as well as the expansion of seawater front, and finally the successful assessment of different management scenarios aimed at increasing the quantity and improving the quality of the available water resources. The pilot implementation of the proposed methodology is performed in the aquifer of N. Moudania in Chalkidiki peninsula (Northern Greece), which is characterized by intense quantitative and qualitative problems that are directly linked to the intensification of agricultural activities in the region, something which is translated into intensive exploitation of groundwater resources and excessive usage of artificial fertilizers. In the former case, both increased drawdown and seawater intrusion are produced, while the later one results to the appearance of elevated nitrate concentrations.Με την εκπόνηση της παρούσας διδακτορικής διατριβής επιχειρείται η διερεύνηση της λειτουργίας παράκτιων υδροφόρων συστημάτων που υπόκεινται σε καθεστώς υπερεκμετάλλευσης και στα οποία παρατηρείται αφενός διείσδυση θαλασσινού νερού και αφετέρου έντονη ρύπανση από νιτρικά, μέσω της εφαρμογής μαθηματικών μοντέλων προσομοίωσης και υπό το πρίσμα της έλλειψης επαρκών δεδομένων, που σχετίζονται τόσο με το εννοιολογικό μοντέλο των υδροφορέων όσο και με τις μεταβλητές του υπό μελέτη προβλήματος. Η μεθοδολογία που αναπτύσσεται συνίσταται στη διαμόρφωση μιας σειράς μαθηματικών μοντέλων μέσω της χρήσης των ευρέως χρησιμοποιούμενων κωδίκων MODFLOW (προσομοίωση υπόγειας ροής), MT3DMS (προσομοίωση μεταφοράς διαλυμένης μάζας) και SEAWAT (προσομοίωση ροής μεταβλητής πυκνότητας), η αλληλουχία καθώς και η σύνδεση μεταξύ των οποίων αποτελούν αναπόσπαστο τμήμα της όλης διαδικασίας. Η κατάρτιση των συγκεκριμένων μοντέλων αποβλέπει αφενός στην προσαρμογή των επιμέρους παραμέτρων των υδροφόρων συστημάτων και ειδικότερα εκείνων που χαρακτηρίζονται από υψηλό βαθμό αβεβαιότητας καθώς και από σημαντική έλλειψη δεδομένων και μετρήσεων (π.χ. υδραυλικές-υδροδυναμικές παράμετροι υδροφορέων) και αφετέρου στον όσο το δυνατόν πιο αντιπροσωπευτικό καθορισμό των αρχικών συνθηκών του προβλήματος της θαλάσσιας διείσδυσης, μία διαδικασία που από τη φύση της ενέχει σημαντικές δυσκολίες και η οποία δυσχεραίνεται σε μεγάλο βαθμό ελλείψει δεδομένων. Άμεση απόρροια της επιτυχούς εφαρμογής της προτεινόμενης μεθοδολογίας αποτελούν η ικανοποιητική προσομοίωση των φυσικών διεργασιών της υπόγειας ροής, της θαλάσσιας διείσδυσης και της μεταφοράς των νιτρικών, η εύστοχη πρόβλεψη αφενός της κατανομής του υδραυλικού φορτίου και της συγκέντρωσης των νιτρικών και αφετέρου της επέκτασης του θαλάσσιου μετώπου, καθώς και η επιτυχημένη αξιολόγηση διαφόρων διαχειριστικών σεναρίων που αποβλέπουν στην αύξηση της ποσότητας και στη βελτίωση της ποιότητας των διαθέσιμων υδατικών αποθεμάτων. Τέλος, αναφέρεται ότι η πιλοτική εφαρμογή της προτεινόμενης μεθοδολογίας πραγματοποιείται στον παράκτιο υδροφορέα των Ν. Μουδανιών Χαλκιδικής, μία περίπτωση υδροφορέα που χαρακτηρίζεται από έντονα ποσοτικά και ποιοτικά προβλήματα, τα οποία είναι άμεσα συνυφασμένα με την εντατικοποίηση των αγροτικών δραστηριοτήτων στην περιοχή, η οποία με τη σειρά της οδηγεί στην εντατική εκμετάλλευση των υπόγειων υδατικών αποθεμάτων και στην αλόγιστη χρήση των τεχνητών λιπασμάτων. Στην πρώτη περίπτωση, άμεση απόρροια αποτελεί τόσο η πτώση του υδραυλικού φορτίου όσο και η διείσδυση θαλασσινού νερού στο εσωτερικό της ενδοχώρας, ενώ στη δεύτερη η εμφάνιση αυξημένων συγκεντρώσεων νιτρικών ιόντων