82 research outputs found
Open string models with Scherk-Schwarz SUSY breaking and localized anomalies
No full textWe study examples of chiral four-dimensional IIB orientifolds with Scherk-Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z_3 x Z_3' model, containing only D9-branes, and rederive from a more geometric perspective the known Z_6' x Z_2' model, containing D9, D5 and \bar D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green-Schwarz mechanism involving twisted Ramond-Ramond axions and four-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view.We study examples of chiral four-dimensional IIB orientifolds with Scherk–Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z 3 × Z ′ 3 model, containing only D9-branes, and rederive from a more geometric perspective the known Z ′ 6 × Z ′ 2 model, containing D9, D5 and D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green–Schwarz mechanism involving twisted Ramond–Ramond axions and 4-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view. We also point out that the number of spontaneously broken U (1) gauge fields is in general greater than what expected from a four-dimensional analysis of anomalies.We study examples of chiral four-dimensional IIB orientifolds with Scherk--Schwarz supersymmetry breaking, based on freely acting orbifolds. We construct a new Z3xZ3' model, containing only D9-branes, and rederive from a more geometric perspective the known Z6'xZ2' model, containing D9, D5 and \bar D 5 branes. The cancellation of anomalies in these models is then studied locally in the internal space. These are found to cancel through an interesting generalization of the Green--Schwarz mechanism involving twisted Ramond--Ramond axions and 4-forms. The effect of the latter amounts to local counterterms from a low-energy effective field theory point of view. We also point out that the number of spontaneously broken U(1) gauge fields is in general greater than what expected from a four-dimensional analysis of anomalies
String vacua with flux from freely-acting obifolds
No full textA precise correspondence between freely-acting orbifolds (Scherk-Schwarz compactifications) and string vacua with NSNS flux turned on is established using T-duality. We focus our attention to a certain non-compact Z(2) heterotic freely-acting orbifold with N = 2 supersymmetry (SUSY). The geometric properties of the T-dual background are studied. As expected, the space is non-Kahler with the most generic torsion compatible with SUSY. All equations of motion are satisfied, except the Bianchi identity for the NSNS field, that is satisfied only at leading order in derivatives, i.e. without the curvature term. We point out that this is due to unknown corrections to the standard heterotic T-duality rules
Supracondylar humerus fractures in children : a comparison of experiences
No full textThe most common elbow lesions found in pediatric practice are supracondylar fractures. We compared two groups of 34 patients each with a supracondylar humerus
fracture grade III (Gartland classification). The first group
was treated with percutaneous pinning with Kirschner wires, with patients in a supine position, sometimes preceded by transkeletal traction. The second group was treated with percutaneous pinning with Kirschner wires,
with patients in a prone position, within 6 h of the trauma. No statistically significant differences with regard to clinical outcomes and neurovascular complications were revealed in the comparison. Therefore, we can state that both
treatment techniques used are valid
Option hedging with risk averse reinforcement learning
No full textIn this paper we show how risk-averse reinforcement learning can be used to hedge options. We apply a state-of-the-art risk-averse algorithm: Trust Region Volatility Optimization (TRVO) to a vanilla option hedging environment, considering realistic factors such as discrete time and transaction costs. Realism makes the problem twofold: the agent must both minimize volatility and contain transaction costs, these tasks usually being in competition. We use the algorithm to train a sheaf of agents each characterized by a different risk aversion, so to be able to span an efficient frontier on the volatility-p&l space. The results show that the derived hedging strategy not only outperforms the Black & Scholes delta hedge, but is also extremely robust and flexible, as it can efficiently hedge options with different characteristics and work on markets with different behaviors than what was used in training
What do facial expressions of emotion express in young children? The relationship between facial display and EMG measures
No full textThe present paper explored the relationship between emotional facial response and electromyographic modulation in children when they observe facial expression of emotions. Facial responsiveness (evaluated by arousal and valence ratings) and psychophysiological correlates (facial electromyography, EMG) were analyzed when children looked at six facial expressions of emotions (happiness, anger, fear, sadness, surprise and disgust). About EMG measure, corrugator and zygomatic muscle activity was monitored in response to different emotional types. ANOVAs showed differences for both EMG and facial response across the subjects, as a function of different emotions. Specifically, some emotions were well expressed by all the subjects (such as happiness, anger and fear) in terms of high arousal, whereas some others were less level arousal (such as sadness). Zygomatic activity was increased mainly for happiness, from one hand, corrugator activity was increased mainly for anger, fear and surprise, from the other hand. More generally, EMG and facial behavior were highly correlated each other, showing a “mirror” effect with respect of the observed faces
Addressing Non-Stationarity in FX Trading with Online Model Selection of Offline RL Experts
No full textReinforcement learning has proven to be successful in obtaining profitable trading policies; however, the effectiveness of such strategies is strongly conditioned to market stationarity. This hypothesis is challenged by the regime switches frequently experienced by practitioners; thus, when many models are available, validation may become a difficult task. We propose to overcome the issue by explicitly modeling the trading task as a non-stationary reinforcement learning problem. Nevertheless, state-of-the-art RL algorithms for this setting usually require task distribution or dynamics to be predictable, an assumption that can hardly be true in the financial framework. In this work, we propose, instead, a method for the dynamic selection of the best RL agent which is only driven by profit performance. Our modular two-layer approach allows choosing the best strategy among a set of RL models through an online-learning algorithm. While we could select any combination of algorithms in principle, our solution employs two state-of-the-art algorithms: Fitted Q-Iteration (FQI) for the RL layer and Optimistic Adapt ML-Prod (OAMP) for the online learning one. The proposed approach is tested on two simulated FX trading tasks, using actual historical data for the AUS/USD and GBP/USD currency pairs
Atypical varicella-zoster virus reactivation: a case report
No full textVaricella-zoster virus (VZV) commonly causes benign skin manifestations in children; it then establishes a latent infection and may reactivate, causing herpes zoster. The most common zoster complication is postherpetic neuralgia, but complications can also occur without a rash. VZV infection may cause neurological manifestations and even vasculopathy may occur, in both primary and reactivated VZV infection. Thrombotic complications are mainly described in children, while a few case reports have described cerebral venous sinus thrombosis (CVST), deep-vein thrombosis of the lower limbs and pulmonary embolism in adults. In this article we report the case of a young woman who developed systemic thromboembolic sequelae due to a hypercoagulable state following VZV reactivation. She had deep venous lower-limb thrombosis extended to the inferior vena cava (IVC), massive pulmonary embolism and CVST. Moreover, VZV reactivation caused an acute hepatitis and clinical manifestations suggesting viral encephalitis
Expression of αv Integrin in Feline Injection-Site Sarcoma (FISS): Preliminary Investigations
No full textFeline injection-site sarcomas (FISSs) are malignant skin tumors of mesenchymal origin arising at local post-vaccination (or injection) sites. In recent years, a fluorescence imaging technique based on probes targeting αvβ3 integrin has been effectively applied for the surgical complete resection of the tumor. In our study, we investigated the utility of a commercially available anti-αv integrin polyclonal antibody for the histopathological evaluation of FISS’s surgical excision margins. We collected 10 formalin-fixed paraffin-embedded (FFPE) feline excisional biopsies with a histopathological diagnosis of FISS (7 fibrosarcomas and 3 pleomorphic sarcomas) and wide margin tissue, along with one subcutaneous injection-site granuloma and 6 osteosarcomas. Samples were processed for histology, and slides were stained for IHC with the anti-αv integrin antibody. Immunostained slides were evaluated for the cellular localization and intensity of the staining in different neoplastic and non-neoplastic cell populations. Neoplastic and non-neoplastic spindle cells had cytoplasmic positivity in all fibrosarcomas. Inflammatory cells, including macrophages of the injection-site granuloma, were negative. Multinucleated giant cells in the pleomorphic sarcomas had an intense membranous positivity. Although the anti-αv integrin antibody was ineffective for the histopathological evaluation of surgical excision margins, the membranous localization of αv integrin in multinucleated giant cells of pleomorphic sarcomas suggests that it plays a role in the oncogenesis of this FISS variant
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