3D loop models and the CP(n-1) sigma model

Many statistical mechanics problems can be framed in terms of random curves; we consider a class of three-dimensional loop models that are prototypes for such ensembles. The models show transitions between phases with infinite loops and short-loop phases. We map them to CP(n-1) sigma models, where n is the loop fugacity. Using Monte Carlo simulations, we find continuous transitions for n=1, 2, 3, and first order transitions for n≥5. The results are relevant to line defects in random media, as well as to Anderson localization and (2+1)-dimensional quantum magnets.     

The Window of Opportunity: Logic and Chance in Becquerel's Discovery of Radioactivity

The discovery of radioactivity by Henri Becquerel is frequently called serendipitous, because on March 1, 1896, he developed "unexposed" photographic plates, which he had kept near a uranium salt, and found dark images on them. I show that Becquerel's discovery was a process in which, even in its early stage in 1896, chance entered in a number of episodes, and that his discovery resulted from a complex interaction of logic and chance.     

Removal of fluoride from aqueous solution using acid and thermally treated bone char

In this work, bone char (BC) was synthesized at different calcination temperatures and modified by using HNO₃ solutions having distinct concentrations. Furthermore, the relationship between the crystalline structure and physicochemical properties of BC on the adsorption capacity of BC towards fluoride from aqueous solution was analyzed. It was noted that the calcination temperature and the acid modification of BC significantly influenced the crystalline phases, crystallite size, and contents of hydroxyapatite, monetite, and other calcium phosphates, which are the main constituents of the BC. Additionally, the surface area diminished by raising both the calcination temperature and acid concentration used in the modification. The adsorption capacity of BC linearly declined as the calcination temperature was increased from 400 to 800 °C. On the other hand, BC modified with HNO₃ solutions showed that the adsorption capacity of BC was enhanced when monetite and hydroxyapatite with low crystallinity were present in these materials. Hence, the adsorption capacity of BC treated with acid was independent of textural properties. The adsorption capacity of BC was enhanced by increasing the solution pH due to the electrostatic interactions between the fluoride in the solution and the surface charge of BC. Finally, DRX, FTIR spectroscopy, and XPS studies corroborated that the fluoride adsorption mechanism on BC modified with acid solutions was influenced by electrostatic interactions and chemisorption between fluoride ions in solution and calcium phosphates from hydroxyapatite and monetite.     

Protein–ligand interaction of T. cruzi trans-sialidase inhibitors: a docking and QM/MM MD study

The trans-Sialidase from Trypanosoma cruzi (TcTS) might be a key enzyme in search of new and more effective anti-Trypanosoma cruzi agents. In this report, molecular docking and quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations were employed to determine the binding mode of the three TcTS inhibitors, two quinolinones derivatives (DHQ and THQ) and DANA. The results show that the sulfone group from THQ plays an important role in the protein-inhibitor interactions. In addition, a detailed analysis of the interactions of these inhibitors with key residues inside the binding pocket of TcTS has been carried out using AM1/MM. The residues Asp59, Asp247, Arg35, Arg245, and Arg314 are appointed as key residues to affinity energy of the complexes studied. Finally, the B3LYP/MM and AM1/MM methods were used to calculate global interaction energy, in order to understand the potential of these inhibitors. Among the inhibitors studied, THQ is confirmed as the most efficient one for inhibiting TcTS.     

Hiporfin‐Mediated Photodynamic Therapy in Preclinical Treatment of Osteosarcoma

This study was carried out to investigate the anti‐tumor effect and mechanism of hiporfin‐mediated photodynamic therapy (hiporfin‐PDT) in osteosarcoma. We found that hiporfin accumulated mainly in the cytoplasm of osteosarcoma cells in a time and concentration‐dependent manner. Hiporfin‐PDT inhibited the proliferation, induced apoptosis and produced cell cycle arrest at G2M in osteosarcoma cell lines. Hiporfin‐PDT increased the expression of cleaved‐caspase‐3, cleaved PARP‐1, Bax and RIP1 while it decreased the expression of Bcl‐2; in addition, low concentration of hiporfin increased LC3 conversion. Furthermore, cell death caused by hiporfin‐PDT could be rescued by Nec‐1 but not by Z‐VAD‐FMK. Production of reactive oxygen species was increased after hiporfin‐PDT. In vivo studies showed a significant decrease in tumor volume and weight after hiporfin‐PDT in all three tumor mouse models investigated (subcutaneous and orthotopic). Histological analysis showed widespread cell apoptosis and necrosis after treatment. Immunohistochemistry also showed upregulation of cleaved‐caspase‐3 and downregulation of Bcl‐2 after hiporfin‐PDT. These results indicate that hiporfin‐PDT exhibits a killing effect in osteosarcoma both in vitro and in vivo, which is associated with apoptosis and necroptosis, while autophagy plays a protective role. All these findings shed light on a potential future clinical use for hiporfin in the treatment of osteosarcoma.     

Rational Abandonment from Tele-Queues: Nonlinear Waiting Costs with Heterogeneous Preferences

We consider the modelling of abandonment from a queueing system by impatient customers. Within the proposed model, customers act rationally to maximise a utility function that weights service utility against expected waiting cost. Customers are heterogeneous, in the sense that their utility function parameters may vary across the customer population. The queue is assumed invisible to waiting customers, who do not obtain any information regarding their standing in the queue during their waiting period. Such circumstances apply, for example, in telephone centers or other remote service facilities, to which we refer as tele-queues. We analyse this decision model within a multi-server queue with impatient customers, and seek to characterise the Nash equilibria of this system. These equilibria may be viewed as stable operating points of the system, and determine the customer abandonment profile along with other system-wide performance measures. We provide conditions for the existence and uniqueness of the equilibrium, and suggest procedures for its computation. We also suggest a notion of an equilibrium based on sub-optimal decisions, the myopic equilibrium, which enjoys favourable analytical properties. Some concrete examples are provided to illustrate the modelling approach and analysis. The present paper supplements previous ones which were restricted to linear waiting costs or homogeneous customer population.     

Basis Function Adaptation in Temporal Difference Reinforcement Learning

Reinforcement Learning (RL) is an approach for solving complex multi-stage decision problems that fall under the general framework of Markov Decision Problems (MDPs), with possibly unknown parameters. Function approximation is essential for problems with a large state space, as it facilitates compact representation and enables generalization. Linear approximation architectures (where the adjustable parameters are the weights of pre-fixed basis functions) have recently gained prominence due to efficient algorithms and convergence guarantees. Nonetheless, an appropriate choice of basis function is important for the success of the algorithm. In the present paper we examine methods for adapting the basis function during the learning process in the context of evaluating the value function under a fixed control policy. Using the Bellman approximation error as an optimization criterion, we optimize the weights of the basis function while simultaneously adapting the (non-linear) basis function parameters. We present two algorithms for this problem. The first uses a gradient-based approach and the second applies the Cross Entropy method. The performance of the proposed algorithms is evaluated and compared in simulations. This research was partially supported by the Fund for Promotion of Research at the Technion. The work of S.M. was partially supported by the National Science Foundation under grant ECS-0312921.