684 research outputs found
Phase Angle Effects on 3-micron Absorption Band on Ceres: Implications for Dawn Mission
Phase angle-induced spectral effects are important to characterize since they
affect spectral band parameters such as band depth and band center, and
therefore skew mineralogical interpretations of planetary bodies via
reflectance spectroscopy. Dwarf planet (1) Ceres is the next target of NASA's
Dawn mission, which is expected to arrive in March 2015. The visible and
near-infrared mapping spectrometer (VIR) onboard Dawn has the spatial and
spectral range to characterize the surface between 0.25-5.0 microns. Ceres has
an absorption feature at 3.0 microns due to hydroxyl- and/or water-bearing
minerals (e.g. Lebofsky et al. 1981, Rivkin et al. 2003). We analyzed phase
angle-induced spectral effects on the 3-micron absorption band on Ceres using
spectra measured with the long-wavelength cross-dispersed (LXD: 1.9-4.2
microns) mode of the SpeX spectrograph/imager at the NASA Infrared Telescope
Facility (IRTF). Ceres LXD spectra were measured at different phase angles
ranging from 0.7o to 22o. We found that the band center slightly increases from
3.06 microns at lower phase angles (0.7o and 6o) to 3.07 microns at higher
phase angles (11 o and 22o), the band depth decreases by ~20% from lower phase
angles to higher phase angles, and the band area decreases by ~25% from lower
phase angles to higher phase angles. Our results will have implications for
constraining the abundance of OH on the surface of Ceres from VIR spectral
data, which will be acquired by Dawn starting spring 2015.Comment: 12 pages, 1 figure, 2 table
Indirect active and reactive powers control of doubly fed induction generator fed by three-level adaptive-network-based fuzzy inference system – pulse width modulation converter with a robust method based on super twisting algorithms
Aim. This paper presents the minimization of reactive and active power ripples of doubly fed induction generators using super twisting algorithms and pulse width modulation based on neuro-fuzzy algorithms. Method. The main role of the indirect active and reactive power control is to regulate and control the reactive and active powers of doubly fed induction generators for variable speed dual-rotor wind power systems. The indirect field-oriented control is a classical control scheme and simple structure. Pulse width modulation based on an adaptive-network-based fuzzy inference system is a new modulation technique; characterized by a simple algorithm, which gives a good harmonic distortion compared to other techniques. Novelty. adaptive-network-based fuzzy inference system-pulse width modulation is proposed. Proposed modulation technique construction is based on traditional pulse width modulation and adaptive-network-based fuzzy inference system to obtain a robust modulation technique and reduces the harmonic distortion of stator current. We use in our study a 1.5 MW doubly-fed induction generator integrated into a dual-rotor wind power system to reduce the torque, current, active power, and reactive power ripples. Results. As shown in the results figures using adaptive-network-based fuzzy inference system-pulse width modulation technique ameliorate effectiveness especially reduces the reactive power, torque, stator current, active power ripples, and minimizes harmonic distortion of current (0.08 %) compared to classical control.Мета У статті представлено мінімізацію пульсацій реактивної та активної потужності асинхронних генераторів подвійного живлення з використанням алгоритмів суперскрутки та широтно-імпульсної модуляції на основі нейро-нечітких алгоритмів. Метод. Основна роль непрямого управління активною та реактивною потужністю полягає у керуванні та регулюванні реактивної та активної потужностей асинхронних генераторів з подвійним живленням для вітроенергетичних систем з подвійним ротором змінної швидкості. Непряме керування, орієнтоване на поле, - це класична схема керування та проста структура. Широтно-імпульсна модуляція, заснована на системі нечітких висновків на основі адаптивної мережі, є новим методом модуляції; характеризується простим алгоритмом, який дає гарні гармонічні спотворення порівняно з іншими методами. Новизна. Пропонується адаптивна мережа на основі нечіткого висновку із широтно-імпульсною модуляцією. Запропонована побудова методу модуляції базується на традиційній широтно-імпульсній модуляції та системі нечітких висновків на основі адаптивних мереж для отримання надійного методу модуляції та зменшення гармонічних спотворень струму статора. У нашому дослідженні ми використовуємо асинхронний генератор з подвійним живленням потужністю 1,5 МВт, інтегрований у вітроенергетичну систему з подвійним ротором, щоб зменшити пульсації крутного моменту, струму, активної потужності та реактивної потужності. Результати. Як показано на рисунках з результатами, використання методу широтно-імпульсної модуляції на основі нечітких висновків системи адаптивних мереж покращує ефективність, особливо зменшує реактивну потужність, крутний момент, струм статора, пульсації активної потужності, та мінімізує гармонійне спотворення струму (0,08 %) порівняно з класичним керуванням
Detection of Rotational Spectral Variation on the M-type asteroid (16) Psyche
The asteroid (16) Psyche is of scientific interest because it contains ~ 1%
of the total mass of the asteroid belt and is thought to be the remnant
metallic core of a protoplanet. Radar observations have indicated the
significant presence of metal on the surface with a small percentage of
silicates. Prior ground-based observations showed rotational variations in the
near-infrared (NIR) spectra and radar albedo of this asteroid. However, no
comprehensive study that combines multi-wavelength data has been conducted so
far. Here we present rotationally resolved NIR spectra (0.7-2.5 microns) of
(16) Psyche obtained with the NASA Infrared Telescope Facility. These data have
been combined with shape models of the asteroid for each rotation phase.
Spectral band parameters extracted from the NIR spectra show that the pyroxene
band center varies from ~ 0.92 to 0.94 microns. Band center values were used to
calculate the pyroxene chemistry of the asteroid, whose average value was found
to be Fs30En65Wo5. Variations in the band depth were also observed, with values
ranging from 1.0 to 1.5%. Using a new laboratory spectral calibration we
estimated an average orthopyroxene content of 6+/-1%. The mass-deficit region
of Psyche, which exhibits the highest radar albedo, also shows the highest
value for spectral slope and the minimum band depth. The spectral
characteristics of Psyche suggest that its parent body did not have the typical
structure expected for a differentiated body or that the sequence of events
that led to its current state was more complex than previously thought.Comment: 21 pages, 8 figures, 2 tables, published in The Astronomical Journa
The Relationship between Music and Philosophy in the Light of Gestaltism: Case of Music of Ahmed Malek
Music is not only a field of knowledge or an art but is also life which is considered as a philosophy. The purpose of this research is to show the relationship between music and philosophy in the light of Gestalt theory. In doing so, some musical pieces of the Algerian musician Ahmed Malek who left his fingerprint in the Algerian artistic field were selected and analyzed as a case study. The result shows that his music is composed of part-whole, a quality, and a dependency and is not made haphazardly but after a deep research, where the musical note MI recurs in all the performances except for one performance that represents the film “Whiteand Black”
Bleeding Stomal Varices in Portal Hypertension
We report a case of a 50-year-old man with a history of liver cirrhosis and colon cancer post end colostomy presenting to the emergency department with stomal bleeding and passage of clots into the colostomy bag. The patient was treated with transjugular intrahepatic portosystemic shunt (TIPS) and concomitant embolization of the stomal varices via the TIPS shunt using N-butyl cyanoacrylate mixed with ethiodol. Although stomal variceal bleeding is uncommon, this entity can have up to 40% mortality upon initial presentation, given the challenges in diagnosis and management. Currently, there are no established standard treatments for stomal variceal bleeding. In addition, to the best of our knowledge, there are no cases in the current literature in which treatment of this entity is performed with a combination of TIPS shunt placement and N-butyl cyanoacrylate variceal embolization
Combined Transhepatic and Transjugular Approach for Mechanical Thrombectomy of Massive TIPS Thrombosis
Transjugular intrahepatic portosystemic shunt (TIPS) is a well-validated decompressive therapy option to manage ascites and variceal bleeding secondary to portal hypertension. Complications following TIPS procedures include hepatic encephalopathy, liver failure, and TIPS dysfunction. TIPS dysfunction is due to occlusion or stenosis of the TIPS shunt and can be caused by acute or chronic thrombosis. TIPS thrombosis is often treated with mechanical thrombectomy or catheter-directed thrombolytic therapy. Most cases of in-stent occlusion can be treated via a transjugular approach with recanalization or placement of additional stents. We present a case of a 72-year-old female who presented with worsening ascites 17 months after initial TIPS procedure; she was found to have a large thrombus completely occluding the TIPS stent. In our case, a combined transhepatic and transjugular approach was required for TIPS revision given the extent of well-organized clot located near the hepatic venous end of the stent, resulting from prolonged stent occlusion. This was an extremely challenging scenario with two overlapping covered stents and a bare metal stent at the hepatic venous end in the setting of chronic thrombosis and a well-organized fibrous cap. The case highlights the need for optimal initial placement of the primary TIPS shunt to avoid the need for subsequent complex interventions to maintain TIPS shunt patency
Incremental Community Mining in Location-based Social Network
A social network can be defined as a set of social entities connected by a set of social relations. These relations often change and differ in time. Thus, the fundamental structure of these networks is dynamic and increasingly developing. Investigating how the structure of these networks evolves over the observation time affords visions into their evolution structure, elements that initiate the changes, and finally foresee the future structure of these networks. One of the most relevant properties of networks is their community structure – set of vertices highly connected between each other and loosely connected with the rest of the network. Subsequently networks are dynamic, their underlying community structure changes over time as well, i.e they have social entities that appear and disappear which make their communities shrinking and growing over time. The goal of this paper is to study community detection in dynamic social network in the context of location-based social network. In this respect, we extend the static Louvain method to incrementally detect communities in a dynamic scenario following the direct method and considering both overlapping and non-overlapping setting. Finally, extensive experiments on real datasets and comparison with two previous methods demonstrate the effectiveness and potential of our suggested method
Ground-based Characterization of Hayabusa2 Mission Target Asteroid 162173 Ryugu: Constraining Mineralogical Composition in Preparation for Spacecraft Operations
Asteroids that are targets of spacecraft missions are interesting because
they present us with an opportunity to validate ground-based spectral
observations. One such object is near-Earth asteroid (NEA) (162173) Ryugu,
which is the target of the Japanese Space Agency's (JAXA) Hayabusa2 sample
return mission. We observed Ryugu using the 3-m NASA Infrared Telescope
Facility (IRTF) on Mauna Kea, Hawaii, on July 13, 2016 to constrain the
object's surface composition, meteorite analogs, and link to other asteroids in
the main belt and NEA populations. We also modeled its photometric properties
using archival data. Using the Lommel-Seeliger model we computed the predicted
flux for Ryugu at a wide range of viewing geometries as well as albedo
quantities such as geometric albedo, phase integral, and spherical Bond albedo.
Our computed albedo quantities are consistent with results from Ishiguro et al.
(2014). Our spectral analysis has found a near-perfect match between our
spectrum of Ryugu and those of NEA (85275) 1994 LY and Mars-crossing asteroid
(316720) 1998 BE7, suggesting that their surface regoliths have similar
composition. We compared Ryugu's spectrum with that of main belt asteroid (302)
Clarissa, the largest asteroid in the Clarissa asteroid family, suggested as a
possible source of Ryugu by Campins et al. (2013). We found that the spectrum
of Clarissa shows significant differences with our spectrum of Ryugu, but it is
similar to the spectrum obtained by Moskovitz et al. (2013). The best possible
meteorite analogs for our spectrum of Ryugu are two CM2 carbonaceous
chondrites, Mighei and ALH83100.Comment: 23 pages, 7 figures, 4 tables, accepted in Monthly Notices of the
Royal Astronomical Society Main Journa
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