57 research outputs found
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
On the quantum stability of IIB orbifolds and orientifolds with Scherk-Schwarz SUSY breaking
No full textOpen 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
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
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
Essential role of weekly high-frequency plyometric training to enhance physical performance 2 and manage muscle soreness in male adolescent soccer players
No full textPurpose: this study aims to investigate the effects of volume-matched plyometric training (PT) with different frequency distributions on physical performance and muscle soreness in adolescent soccer players. Methods: Thirty-four sub-elite players were allocated into two groups: PLYO-1 (n = 17, age 1=16.02±0.26 years) underwent one PT session per week, while PLYO-3 (n = 17, age = 15.81±0.37 years) underwent three volume-matched PT sessions per week. The PT program lasted 9 -weeks with an initial weekly volume of ~55 -foot contacts, increasing by 10% per week. The 7-point Likert scale was employed to assess the perceived muscle soreness before and after each PT session. All players were tested for countermovement horizontal (CMHJ) and vertical (CMVJ) jumps, 10-m sprint and change of direction (COD) performance using the modified 505 test (505mod). Results: After the 9- week experimental period, both groups exhibited significant improvements in CMHJ distance (p 0.911, d = −0.12). The changes in perceived muscle soreness were significantly lower for PLYO-3 compared with PLYO-1 (p < 0.001, d = 1.04) throughout the experimental period. Conclusions: Employing weekly volume-matched PT conducted at different frequencies can help to maintain, or even enhance, jump and COD performance, while differently impacting muscle soreness
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
Rispecchiamento non verbale delle emozioni in età prescolare
No full textLa capacità di rispecchiare la mimica facciale degli attori sociali durante l’interazione sembra facilitare la comprensione dei loro stati mentali. Numerosi studi riportano come i soggetti ch e osservano volti emotivi tendono a produrre una risposta muscolare facciale coerente on quella dei volti loro proposti.Il presente studio indaga la capacità di rispecchiamento mimico di pattern facciali di 6 emozioni (gioia, rabbia, paura, tristezza, sorpresa, disgusto) in bambini di età prescolare. La capacità di rispecchiamento emotivo è intesa in senso quantitativo (quantità di produzione) e qualitativo (coerenza con la configurazione facciale proposta e con la risposta verbale). Inoltre, è stata veicolata la modalità di presentazione degli stimoli facciali emotivi (contestualizzati/non contestualizzati). I dati evidenziano che la modalità di presentazione influenza la capacità di produzione del rispecchiamento mimico nel suo complesso, mentre la coerenza con lo stimolo target e con la produzione verbale sembra essere modulata dal tipo di emozione
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