The Neural Network Pushdown Automaton: Model, Stack and Learning Simulations

In order for neural networks to learn complex languages or grammars, they must have sufficient computational power or resources to recognize or generate such languages. Though many approaches have been discussed, one obvious approach to enhancing the processing power of a recurrent neural network is to couple it with an external stack memory - in effect creating a neural network pushdown automata (NNPDA). This paper discusses in detail this NNPDA - its construction, how it can be trained and how useful symbolic information can be extracted from the trained network. In order to couple the external stack to the neural network, an optimization method is developed which uses an error function that connects the learning of the state automaton of the neural network to the learning of the operation of the external stack. To minimize the error function using gradient descent learning, an analog stack is designed such that the action and storage of information in the stack are continuous. One interpretation of a continuous stack is the probabilistic storage of and action on data. After training on sample strings of an unknown source grammar, a quantization procedure extracts from the analog stack and neural network a discrete pushdown automata (PDA). Simulations show that in learning deterministic context-free grammars - the balanced parenthesis language, 1n0n, and the deterministic Palindrome - the extracted PDA is correct in the sense that it can correctly recognize unseen strings of arbitrary length. In addition, the extracted PDAs can be shown to be identical or equivalent to the PDAs of the source grammars which were used to generate the training strings. (Also cross-referenced as UMIACS-TR-93-77.

Numerical Simulation-Based Optimization of Contact Stress Distribution and Lubrication Conditions in the Straight Worm Drive

Tooth contact area optimization/meshing of the straight worm pair is vital for improving its operation efficiency. Geometric parameters of a worm helicoid were derived via the gear meshing theory using the equations of the instantaneous contact line. The visualization function and powerful computing capability of MATLAB are used for the numerical analysis where the instantaneous contact line distribution is simulated for particular worm drive parameters, which yields the induced curvature and slip angle in the direction of the line. The above results are used for further optimization of the meshing performance of the straight worm gear and identification of its influencing factors. A case study of the particular cylindrical worm gear in compliance with the GB 10085-1988 Standard of China demonstrate that a reasonable selection of worm gear parameters can extend the contact line and the working range of the tooth surface of the worm gear and/or make the contact line distribution along the worm wheel more uniform, thus improving the local meshing performanceОптимизация зубчатой контактной поверхности/зацепление прямолинейной червячной пары определяют повышение эффективности ее эксплуатации. Геометрические параметры червячного геликоида получены с использованием теории зацепления зубчатых колес и уравнения линии мгновенного контакта. Численный анализ основан на функции визуализации и вычислительных возможностях программы MATLAB, что позволяет моделировать распределение на линии мгновенного контакта для специфических параметров червячного привода, создавая вынужденную кривизну и угол скольжения в направлении этой линии. Полученные результаты обеспечивают последующую оптимизацию параметров зацепления прямолинейной червячной передачи и установление определяющих факторов. Пример использования специфической цилиндрической червячной передачи в соответствии со стандартом Китая (GB 10085-1988) показывает, что рациональный выбор параметров этой передачи может увеличить линию контакта, а также расширить рабочий диапазон ее зубчатой поверхности и/или обеспечить более равномерный контакт по червячному колесу, повышая тем самым эффективность локального зацепления

Self-trapping of strong electromagnetic beams in relativistic plasmas

Interaction of an intense electromagnetic (EM) beam with hot relativistic plasma is investigated. It is shown that the thermal pressure brings about a fundamental change in the dynamics - localized, high amplitude, EM field structures, not accessible to a cold (but relativisic) plasma, can now be formed under well- defined conditions. Examples of the trapping of EM beams in self-guiding regimes to form stable 2D solitonic structures in a pure e-p plasma are worked out.Comment: 9 pages, 6 figure

Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe

The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ~15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ~6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.UTokyo Research掲載「鉄系超伝導物質の転移温度が圧力下で4倍以上に上昇する謎を解明」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/mysterious-increased-transition-temperature-of-iron-selenide-superconductor-under-high-pressure.htmlUTokyo Research "Mysterious increased transition temperature of iron selenide superconductor under high pressure" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/mysterious-increased-transition-temperature-of-iron-selenide-superconductor-under-high-pressure.htm

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362