Optimum performance and potential flow field of hovering rotors

Rotor and propeller performance and induced potential flowfields were studied on the basis of a rotating actuator disk concept, with special emphasis on rotors hovering out of ground effect. A new theory for the optimum performance of rotors hovering OGE is developed and presented. An extended theory for the optimum performance of rotors and propellers in axial motion is also presented. Numerical results are presented for the optimum distributions of blade-bound circulation together with axial inflow and ultimate wake velocities for the hovering rotor over the range of thrust coefficient of interest in rotorcraft applications. Shapes of the stream tubes and of the velocities in the slipstream are obtained, using available methods, for optimum and off-optimum circulation distributions for rotors hovering in and out of ground effect. A number of explicit formulae useful in computing rotor and propeller induced flows are presented for stream functions and velocities due to distributions of circular vortices over axi-symmetric surfaces

Application of finite element techniques in predicting the acoustic properties of turbofan inlets

An analytical technique was developed for predicting the acoustic performance of turbofan inlets carrying a subsonic axisymmetric steady flow. The finite element method combined with the method of weighted residuals is used in predicting the acoustic properties of variable area, annular ducts with or without acoustic treatments along their walls. An approximate solution for the steady inviscid flow field is obtained using an integral method for calculating the incompressible potential flow field in the inlet with a correction to account for compressibility effects. The accuracy of the finite element technique was assessed by comparison with available analytical solutions for the problems of plane and spinning wave propagation through a hard walled annular cylinder with a constant mean flow

Acoustic properties of turbofan inlets

The acoustic field within a duct containing a nonuniform steady flow was predicted. This analysis used the finite element method to calculate the velocity potential within the duct

Inducing Language Networks from Continuous Space Word Representations

Recent advancements in unsupervised feature learning have developed powerful latent representations of words. However, it is still not clear what makes one representation better than another and how we can learn the ideal representation. Understanding the structure of latent spaces attained is key to any future advancement in unsupervised learning. In this work, we introduce a new view of continuous space word representations as language networks. We explore two techniques to create language networks from learned features by inducing them for two popular word representation methods and examining the properties of their resulting networks. We find that the induced networks differ from other methods of creating language networks, and that they contain meaningful community structure.Comment: 14 page

Acoustic properties of turbofan inlets

The finite element codes were improved using Hermitian elements and numerical integration of element relations. The question of real variable versus complex variable formulation was resolved and an integrated civil engineering system was implemented on the Georgia Tech Cyber 70/74. Efforts are underway to restructure the program to obtain the most efficient use of array storage

Enzyme-level interconversion of nitrate and nitrite in the fall mixed layer of the Antarctic Ocean

In the Southern Ocean, the nitrogen (N) isotopes of organic matter and the N and oxygen (O) isotopes of nitrate (NO_3^−) have been used to investigate NO_3^− assimilation and N cycling in the summertime period of phytoplankton growth, both today and in the past. However, recent studies indicate the significance of processes in other seasons for producing the annual cycle of N isotope changes. This study explores the impact of fall conditions on the ^(15)N/^(14)N (δ^(15)N) and ^(18)O/^(16)O (δ^(18)O) of NO_3^− and nitrite (NO_2^−) in the Pacific Antarctic Zone using depth profiles from late summer/fall of 2014. In the mixed layer, the δ^(15)N and δ^(18)O of NO_3^− + NO_2^− increase roughly equally, as expected for NO_3^− assimilation; however, the δ^(15)N of NO_3^−-only (measured after NO_2− removal) increases more than does NO_3^− -only δ^(18)O. Differencing indicates that NO_2^− has an extremely low δ^(15)N, often < −70‰ versus air. These observations are consistent with the expression of an equilibrium N isotope effect between NO_3^− and NO_2^−, likely due to enzymatic NO_3^- - NO_2^− interconversion. Specifically, we propose reversibility of the nitrite oxidoreductase (NXR) enzyme of nitrite oxidizers that, having been entrained from the subsurface during late summer mixed layer deepening, are inhibited by light. Our interpretation suggests a role for NO_3^- - NO_2^− interconversion where nitrifiers are transported into environments that discourage NO_2^− oxidation. This may apply to surface regions with upwelling, such as the summertime Antarctic. It may also apply to oxygen-deficient zones, where NXR-catalyzed interconversion may explain previously reported evidence of NO_2^− oxidation

Threshold and non-linear behavior of lasers of Λ\Lambda and V - configurations

Dynamic properties of closed three level laser systems are investigated. Two schemes of pumping - $\Lambda$ and V - are considered. It is shown that the non-linear behavior of the photon number as a function of pump both near and far above threshold is crucially different for these two configurations. In particular, it is found that in the high pump regime laser can turn off in a phase-transition-like manner in both $\Lambda$ and V schemes.Comment: 9 pages, 5 figure

Hierarchical Organization in Complex Networks

Many real networks in nature and society share two generic properties: they are scale-free and they display a high degree of clustering. We show that these two features are the consequence of a hierarchical organization, implying that small groups of nodes organize in a hierarchical manner into increasingly large groups, while maintaining a scale-free topology. In hierarchical networks the degree of clustering characterizing the different groups follows a strict scaling law, which can be used to identify the presence of a hierarchical organization in real networks. We find that several real networks, such as the World Wide Web, actor network, the Internet at the domain level and the semantic web obey this scaling law, indicating that hierarchy is a fundamental characteristic of many complex systems

Good practices for a literature survey are not followed by authors while preparing scientific manuscripts

The number of citations received by authors in scientific journals has become a major parameter to assess individual researchers and the journals themselves through the impact factor. A fair assessment therefore requires that the criteria for selecting references in a given manuscript should be unbiased with respect to the authors or the journals cited. In this paper, we advocate that authors should follow two mandatory principles to select papers (later reflected in the list of references) while studying the literature for a given research: i) consider similarity of content with the topics investigated, lest very related work should be reproduced or ignored; ii) perform a systematic search over the network of citations including seminal or very related papers. We use formalisms of complex networks for two datasets of papers from the arXiv repository to show that neither of these two criteria is fulfilled in practice