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Search Results: 1 - 10 of 325901 matches for " S. Ida "
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Evolution of the Velocity Dispersion of Self-Gravitating Particles in Disc Potentials
K. Shiidsuka,S. Ida
Physics , 1999, DOI: 10.1046/j.1365-8711.1999.02598.x
Abstract: The ratio of the vertical velocity dispersion to radial one (sigma_z / sigma_R) of self-gravitating bodies in various disc potentials is investigated through two different numerical methods (statistical compilation of two-body encounters and N-body simulations). The velocity dispersion generated by two-body relaxation is considered. The ratio is given as a function of a disc potential parameter, kappa/Omega, where kappa and Omega are the epicycle and circular frequencies (the parameters kappa/Omega=1 and 2 correspond to Kepler rotation and solid-body rotation). For 1 <= kappa/Omega <~ 1.5, the velocity dispersion increases keeping some anisotropy (sigma_z / sigma_R ~ 0.5-0.7) if the amplitude of radial excursion is larger than tidal radius, while sigma_z / sigma_R << 1 for smaller amplitude. On the other hand, for 1.5 <~ kappa/Omega <= 2.0, we found isotropic state (sigma_z / sigma_R ~ 1) in the intermediate velocity regime, while anisotropic state (sigma_z / sigma_R < 1) still exists for higher and lower velocity regimes. The range of the intermediate velocity regime expands with kappa/Omega. In the limit of solid-body rotation, the regime covers all over the velocity space. Thus, the velocity dispersion generally has two different anisotropic states for each disc potential (1 <= kappa/Omega < 2) and one isotropic state for 1.5 <~ kappa/Omega < 2 where the individual states correspond to different amplitude of velocity dispersion, while in the limit of solid-body rotation (kappa/Omega = 2.0), entire velocity space is covered by the isotropic state.
Spatial Structure and Coherent Motion in Dense Planetary Rings Induced by Self-Gravitational Instability
H. Daisaka,S. Ida
Physics , 1999, DOI: 10.1186/BF03351594
Abstract: We investigate the formation of spatial structure in dense, self-gravitating particle systems such as Saturn's B-ring through local $N$-body simulations to clarify the intrinsic physics based on individual particle motion. In such a system, Salo (1995) showed that the formation of spatial structure such as wake-like structure and particle grouping (clump) arises spontaneously due to gravitational instability and the radial velocity dispersion increases as the formation of the wake structure. However, intrinsic physics of the phenomena has not been clarified. We performed local $N$-body simulations including mutual gravitational forces between ring particles as well as direct (inelastic) collisions with identical (up to $N\sim40000$) particles. In the wake structure particles no longer move randomly but coherently. We found that particle motion was similar to Keplerian motion even in the wake structure and that the coherent motion was produced since the particles in a clump had similar eccentricity and longitude of perihelion. This coherent motion causes the increase and oscillation in the radial velocity dispersion. The mean velocity dispersion is rather larger in a more dissipative case with a smaller restitution coefficient and/or a larger surface density since the coherence is stronger in the more dissipative case. Our simulations showed that the wavelength of the wake structure was approximately given by the longest wavelength $\hs{\lambda}{cr} = 4\pi^2 G\Sigma/\kappa^2$ in the linear theory of axisymmetric gravitational instability in a thin disk, where $G$, $\Sigma$, and $\kappa$ are the gravitational constant, surface density, and a epicyclic frequency.
Avalia??o da motricidade orofacial em pacientes com mucopolissacaridose: um estudo transversal
Turra, Giovana S.;Schwartz, Ida Vanessa D.;
Jornal de Pediatria , 2009, DOI: 10.1590/S0021-75572009000300012
Abstract: objective: to characterize the stomatognathic system and stomatognathic functions in patients with mucopolysaccharidosis. methods: cross-sectional and observational study of patients with mucopolysaccharidosis seen at the outpatient clinic at the medical genetics service of hospital de clínicas de porto alegre. the inclusion criteria were the existence of a biochemical or molecular diagnosis of any type of mucopolysaccharidosis and the agreement to participate in the study by signing an informed consent form. seventy-eight patients were evaluated through phonoaudiological anamnesis and physical exam. results: alterations in at least one item of each structure of the stomatognathic system or stomatognathic function were found in all patients who allowed evaluation of both items on physical examination (n = 76/78). the most frequently compromised structures and functions were respectively the dental arch and the tongue, swallowing and mastication. the only statistically significant difference found between types of mucopolysaccharidosis involved the habitual position of the tongue between the teeth (most frequent in mucopolysaccharidosis vi). among patients with mucopolysaccharidosis i, ii or vi who underwent enzyme replacement therapy or not, there was statistically significant difference in oral breathing mode (more frequent in the group without enzyme replacement therapy). conclusions: alterations in stomatognathic systems and functions are prevalent among individuals with mucopolysaccharidosis, even if enzyme replacement therapy is administered. such finding suggests that speech therapy follow-up plays a major role in the treatment plan of this group of diseases; this hypothesis should be confirmed by additional studies.
Efeitos da amplifica??o sonora sobre as modalidades comunicativas utilizadas pelos pais
Couto, Maria Inês Vieira;Lichtig, Ida;
Pró-Fono Revista de Atualiza??o Científica , 2007, DOI: 10.1590/S0104-56872007000100009
Abstract: background: auditory rehabilitation in deaf children users of sign language. aim: to verify the effects of sound amplification on parent's communicative modalities when interacting with their deaf children. method: participants were twelve deaf children, aged 50 to 80 months and their hearing parents. children had severe or profound hearing loss in their better ear and were fitted with hearing aids in both ears. children communicated preferably through sign language. the cause-effect relation between the children's auditory skills profile (insertion gain, functional gain and the meaningful auditory integration scale - mais) and the communicative modalities (auditive-oral, visuo-spacial, bimodal) used by parents was analyzed. communicative modalities were compared in two different experimental situations during a structured interaction between parents and children, i.e. when children were not fitted with their hearing aids (situation 1) and when children were fitted with them (situation 2). data was analyzed using descriptive statistics. results: the profile of the deaf children's auditory skills demonstrated to be lower than 53% (unsatisfactory). parents used predominately the bimodal modality to gain children's attention, to transmit and to end tasks. a slight positive effect of sound amplification on the communicative modalities was observed, once parents presented more turn-takings during communication when using the auditory-oral modality in situation 2. conclusion: hearing parents tend to use more turn-takings during communication in the auditory-oral modality to gain children's attention, to transmit and to end tasks, since they observe an improvement in the auditory skills of their children.
Valores positivos e desenvolvimento do adolescente: perfil de jovens paulistanos
Macedo, Rosa M. S. de;Kublikowski, Ida;
Psicologia em Estudo , 2009, DOI: 10.1590/S1413-73722009000400009
Abstract: this research is part of the project "the positive values and the adolescent development: from vulnerability to responsibility" that begun with the cultural adaptation of search institute profiles of student life: attitudes and behaviors, an instrument that aims to access the developmental assets present in adolescents of specific groups, proven to be very useful as a base from where to start planning actions to promote better lives to communities, families and their children. the adapted form of the instrument has been applied in a sample of 2725 adolescents from all regions of sp city, males and females, from 11 to 19 years, categorized by their social vulnerability (ipvs, seade, 2005) to design a map of positive values present in this population. the data showed that young people present a low number of positive values and that its variability is linked to sex and age, more than to social vulnerability. it also turns evident the necessity to review our health promotion strategies based in risk taking behaviors and grounded it in the promotion of positive values.
Computer-Aided Design in Electromagnetics - the Case for Surface Impedance Boundary Conditions
IDA, N.,Di RIENZO, L.,YUFEREV, S.
Advances in Electrical and Computer Engineering , 2012, DOI: 10.4316/aece.2012.03001
Abstract: Surface impedance boundary conditions (SIBCs) have been successfully used for over 70 years in both analytical and numerical computation. With the need to model increasingly complex geometries and smaller artifacts, its importance in computer-aided design of electromagnetic devices has become prominent. High frequency SIBCs have been particularly successful because of the minimal penetration of electromagnetic fields in conductors and lossy dielectrics. SIBCs based on the skin depth have also been used although these have been limited to the first order (Leontovich) condition and Leontovich-like conditions. Little has been done in incorporating second order SIBCs and higher. A general method of derivation of SIBCs of arbitrary order is presented here and shown to apply to low frequency power structures including electric machines, transmission lines and nondestructive testing of materials. The proposed SIBCs are universally applicable and the order of the SIBC allows control of errors in design. Whereas low order SIBCs apply to classical flat surfaces and perpendicular diffusion, higher order conditions take into account curvatures and lateral diffusion of fields as well. Results shown include transmission line parameters, eddy current testing and other power applications in which they contribute to speed and accuracy of the design. In some cases, the use of SIBCs is not only possible but rather is critical to the very ability to obtain an acceptable design.
Application of different signal analysis methods to the ULF data for the 1993 Guam earthquake
Y. Ida,M. Hayakawa,S. Timashev
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2007,
Abstract: Two different analysis methods; (1) mono-fractal analysis (based on Higuchi method) and (2) flicker noise spectroscopy, have been applied to the same ULF (frequency less than 10 Hz) electromagnetic data observed at Guam during 3 years including the 1993 August Guam earthquake. The results by these two methods are found to be very consistent with each other; that is, some precursory effects seem to start about 3 months before the earthquake. This gives us a strong support to the self-organizing critical process before the Guam earthquake.
Merging Criteria for Giant Impacts of Protoplanets
H. Genda,E. Kokubo,S. Ida
Physics , 2011, DOI: 10.1088/0004-637X/744/2/137
Abstract: At the final stage of terrestrial planet formation, known as the giant impact stage, a few tens of Mars-sized protoplanets collide with one another to form terrestrial planets. Almost all previous studies on the orbital and accretional evolution of protoplanets in this stage have been based on the assumption of perfect accretion, where two colliding protoplanets always merge. However, recent impact simulations have shown that collisions among protoplanets are not always merging events, that is, two colliding protoplanets sometimes move apart after the collision (hit-and-run collision). As a first step towards studying the effects of such imperfect accretion of protoplanets on terrestrial planet formation, we investigated the merging criteria for collisions of rocky protoplanets. Using the smoothed particle hydrodynamic (SPH) method, we performed more than 1000 simulations of giant impacts with various parameter sets, such as the mass ratio of protoplanets, $\gamma$, the total mass of two protoplanets, $M_{\rm T}$, the impact angle, $\theta$, and the impact velocity, $v_{\rm imp}$. We investigated the critical impact velocity, $v_{\rm cr}$, at the transition between merging and hit-and-run collisions. We found that the normalized critical impact velocity, $v_{\rm cr}/v_{\rm esc}$, depends on $\gamma$ and $\theta$, but does not depend on $M_{\rm T}$, where $v_{\rm esc}$ is the two-body escape velocity. We derived a simple formula for $v_{\rm cr}/v_{\rm esc}$ as a function of $\gamma$ and $\theta$, and applied it to the giant impact events obtained by \textit{N}-body calculations in the previous studies. We found that 40% of these events should not be merging events.
Orbital Circularization of a Planet Accreting Disk Gas: Formation of Distant Jupiters in Circular Orbits based on Core Accretion Model
A. Kikuchi,A. Higuchi,S. Ida
Physics , 2014, DOI: 10.1088/0004-637X/797/1/1
Abstract: Recently, gas giant planets in nearly circular orbits with large semimajor axes ($a \sim$ 30--1000AU) have been detected by direct imaging. We have investigated orbital evolution in a formation scenario for such planets, based on core accretion model: i) Icy cores accrete from planetesimals at $\lesssim$ 30AU, ii) they are scattered outward by an emerging nearby gas giant to acquire highly eccentric orbits, and iii) their orbits are circularized through accretion of disk gas in outer regions, where they spend most of time. We analytically derived equations to describe the orbital circularization through the gas accretion. Numerical integrations of these equations show that the eccentricity decreases by a factor of more than 5 during the planetary mass increases by a factor of 10. Because runaway gas accretion increases planetary mass by $\sim$ 10--300, the orbits are sufficiently circularized. On the other hand, $a$ is reduced at most only by a factor of 2, leaving the planets in outer regions. If the relative velocity damping by shock is considered, the circularization is slowed down, but still efficient enough. Therefore, this scenario potentially accounts for the formation of observed distant jupiters in nearly circular orbits. If the apocenter distances of the scattered cores are larger than the disk sizes, their $a$ shrink to a quarter of the disk sizes; the $a$-distribution of distant giants could reflect outer edges of the disks in a similar way that those of hot jupiters may reflect inner edges.
Evidence for early stellar encounters in the orbital distribution of Edgeworth-Kuiper Belt objects
S. Ida,J. D. Larwood,A. Burkert
Physics , 1999, DOI: 10.1086/308179
Abstract: We have investigated effects of early stellar encounters on a protoplanetary disk (planetesimal disk) and found that they can explain the high eccentricities and inclinations observed in the outer part ($>42$AU) of the Edgeworth-Kuiper Belt (EKB). The proto-sun is considered as a member of a stellar aggregation that undergoes dissolution on a timescale $\sim 10^8$yrs, such that a planetesimal disk experiences a flyby encounter at pericenter distance ($q$) on the order of 100AU. We simulated dynamical evolution of a planetesimal (test particle) disk perturbed by a passing star. We show that the stellar encounter pumps the velocity dispersion in the disk in the outer parts ($> 0.25q$). Planet formation is forestalled in that region. We also find that a stellar encounter with pericenter distance $q \sim 100-200$AU could have pumped up the velocity dispersion of EKB objects outside 42AU to the observed magnitude while preserving that inside Neptune's 3:2 mean-motion resonance (located at 39.5AU), which allows for the efficient capture of objects by the sweeping of the 3:2 resonance during orbital migration by proto-Neptune.
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