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"Limiares auditivos tonais em altas freqüências e emissões otoacústicas em portadores da desordem pigmentar do tipo vitiligo" ; Auditory thresholds in high frequencies and otoacoustic emissions in pigmentary disorder type vitiligo

Carvalho, Mirley de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/09/2004 Português
Relevância na Pesquisa
55.76%
Para verificar a contribuição da audiometria em altas freqüências (9 a 20 kHz) e das emissões otoacústicas - produto de distorção para a identificação de alterações auditivas em indivíduos com desordem pigmentar do tipo vitiligo, 30 indivíduos portadores de vitiligo foram avaliados audiologicamente, e comparados a um grupo controle. Tanto para as altas freqüências (9 a 20 kHz) como para as emissões otoacústicas foram observadas diferenças significantes entre os grupos, que não foram evidenciadas na audiometria convencional (0,25 a 8 kHz). Os resultados sugerem prejuízo nas funções auditivas para o grupo com desordem pigmentar do tipo vitiligo. ; In order to verify the contribution of the high frequency audiometry (9 to 20 kHz) and distortion product- otoacoustic emissions for the identification of auditory impairments in individuals with pigmentary disorder type vitiligo, 30 individuals with vitiligo were evaluated, and compared with a control group. As much for the high frequencies (9 the 20 kHz) as for the otoacoustic emissions, significant differences were observed between the groups, that were not evidenced in the conventional audiometry (0,25 the 8 kHz). The results suggest damage in the auditory functions for the group with pigmentary disorder type vitiligo

Função coclear em frequências ultra-altas em pais de indivíduos com deficiência auditiva autossômica recessiva; Cochlear function in ultra-high frequencies in parents of individuals with autosomal recessive hearing loss

Mello, Jaqueline Medeiros de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 14/12/2012 Português
Relevância na Pesquisa
46.04%
INTRODUÇÃO: Na deficiência auditiva não sindrômica de herança autossômica recessiva, causada por alteração no gene GJB2 (Gap Junction Bet-2 Protein), os pais de indivíduos com deficiência auditiva são portadores em heterozigose de um alelo recessivo que causa a surdez, porém, são assintomáticos, mas podem apresentar alterações auditivas precoces e discretas. OBJETIVO: Avaliar a função coclear em pais de indivíduos com deficiência auditiva de herança autossômica recessiva por meio das Emissões Otoacústicas Evocadas Produto de Distorção (EOA-PD) em frequências convencionais e em frequências ultra-altas, comparando as respostas do grupo controle pareadas por gênero e idade. MÉTODO: Foram avaliados 56 indivíduos, entre 20 a 58 anos de idade, divididos em dois grupos, o Grupo Estudo (GE), constituído por 28 pais de deficientes auditivos decorrentes de herança autossômica recessiva, sendo 14 mulheres com idade entre 20 a 55 anos (média 32,8 anos) e 14 homens com idade entre 20 a 58 anos (média 35,2), e o Grupo Controle (GC). formado por indivíduos sem queixa auditiva, composto por 14 homens e 14 mulheres com idades pareadas ao GE. Os indivíduos foram submetidos aos exames de Audiometria Tonal Liminar (ATL)...

A new model for tubular fluorescent lamps operated at high frequencies for dimmable applications

Wakabayashi, F. T.; Canesin, C. A.; IEEE
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência Formato: 490-494
Português
Relevância na Pesquisa
65.82%
This paper presents a new static model for tubular fluorescent lamps (T12 bulb) operated at high frequencies. The main goal of this paper is to investigate the effects of ambient temperature and nominal switching frequency of operation in the static characteristics of tubular fluorescent lamps. The methodology for obtaining the model is based on several two-dimensional mathematical regressions, used to provide the behavior of the fluorescent lamp according to different independent variables, namely: power processed through the lamp and ambient temperature. In addition, the proposed model can be easily converted to a lamp equivalent resistance model, which can be useful for ballast designers. Finally, the curves obtained using the new model are compared to the correspondent experimental data, in order to verify the accuracy of the proposed methodology.

Low and high frequency tonal threshold audiometry: comparing hearing thresholds between smokers and non-smokers

Oliveira,Daniela Cecílio Capra Marques de; Lima,Marco Antonio de Melo Tavares de
Fonte: Associação Brasileira de Otorrinolaringologia e Cirurgia Cervicofacial Publicador: Associação Brasileira de Otorrinolaringologia e Cirurgia Cervicofacial
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2009 Português
Relevância na Pesquisa
45.87%
Cigarette smoking can cause many potentially fatal diseases and worsen others. Numerous studies have shown the relationship between smoking and hearing loss. However, the increase in auditory threshold in high frequency arising from smoking has been very little described. AIM: to compare low and high frequency auditory thresholds among a group of smoking and non-smoking male individuals between 18 and 40 years. STUDY DESIGN: Cross-sectional. MATERIALS AND METHODS: by means of low and high frequency tonal threshold audiometry we studied 30 male individuals between 18 and 40 years and 30 non-smokers of matching age and gender. RESULTS: auditory thresholds were different between smokers and non-smokers, being worse in the former. Although within normal ranges, auditory thresholds in low frequencies were higher among smokers. In high frequencies we noticed a marked increase in auditory thresholds among smokers. CONCLUSION: we found statistically significant difference in auditory thresholds in low and high frequencies, among young male individuals, smokers and non-smokers, being worse in the former.

Sustained High Frequencies of Specific CD4 T Cells Restricted to a Single Persistent Virus

Sester, Martina; Sester, Urban; Gärtner, Barbara; Kubuschok, Boris; Girndt, Matthias; Meyerhans, Andreas; Köhler, Hans
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /04/2002 Português
Relevância na Pesquisa
45.93%
Replication of cytomegalovirus (CMV) is largely controlled by the cellular arm of the immune response. In this study the CMV-specific CD4 T-cell response was characterized in a cohort of apparently healthy individuals. In 11% of all individuals, extremely high frequencies, between 10 and 40%, were found. High-level frequencies of CMV-specific CD4 T cells persisted over several months and were not the result of an acute infection. Specific T cells were oligoclonal and were phenotypically and functionally characterized as mature effector cells, with both cytokine-secreting and proliferative potential. These high-level frequencies do not seem to compromise the immune response towards heterologous infections, and no signs of immunopathology were observed. Whereas a large temporary expansion of virus-specific T cells is well known to occur during acute infection, we now show that extremely high frequencies of virus-specific T cells may continuously exist in chronic CMV infection without overtly compromising the remaining protective immunity.

Extremely high frequencies of alpha-globin gene deletion in Madang and on Kar Kar Island, Papua New Guinea.

Yenchitsomanus, P T; Summers, K M; Bhatia, K K; Cattani, J; Board, P G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1985 Português
Relevância na Pesquisa
45.86%
Extremely high frequencies of the deletion form of alpha(+)-thalassemia (-alpha/), as studied by the DNA mapping technique, were found in the population of Madang, a coastal province in the north of Papua New Guinea (PNG) and in the population of Kar Kar, an island situated near Madang. Ninety-seven percent of the population tested from Madang and 89% of that from Kar Kar Island were either alpha(+)-thalassemia heterozygotes or homozygotes. By contrast, no examples of the deletion form were detected in the Eastern Highlands of PNG. The haplotype frequencies of alpha(+)-thalassemia (-alpha/) in Madang and Kar Kar Island were found to be 81.33% and 66.67%, respectively. A more detailed analysis of the gene deletion revealed that in both populations 96% were of the 4.2 kilobase (kb) type and 4% were of the 3.7-kb type. Thus, this group is the only example in which the 4.2-kb deletion is predominant over 3.7-kb defect. The presence in high frequencies of alpha(+)-thalassemia in the coastal area of Madang and on the neighboring island, where malaria has long been holoendemic or hyperendemic, and its virtual absence from the nonmalarious highlands of PNG suggest the role of malaria as the selective factor in maintaining alpha(+)-thalassemia. If this selective pressure is still operating...

A Modified Cable Formalism for Modeling Neuronal Membranes at High Frequencies

Bédard, Claude; Destexhe, Alain
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.93%
Intracellular recordings of cortical neurons in vivo display intense subthreshold membrane potential (Vm) activity. The power spectral density of the Vm displays a power-law structure at high frequencies (>50 Hz) with a slope of ∼−2.5. This type of frequency scaling cannot be accounted for by traditional models, as either single-compartment models or models based on reconstructed cell morphologies display a frequency scaling with a slope close to −4. This slope is due to the fact that the membrane resistance is short-circuited by the capacitance for high frequencies, a situation which may not be realistic. Here, we integrate nonideal capacitors in cable equations to reflect the fact that the capacitance cannot be charged instantaneously. We show that the resulting nonideal cable model can be solved analytically using Fourier transforms. Numerical simulations using a ball-and-stick model yield membrane potential activity with similar frequency scaling as in the experiments. We also discuss the consequences of using nonideal capacitors on other cellular properties such as the transmission of high frequencies, which is boosted in nonideal cables, or voltage attenuation in dendrites. These results suggest that cable equations based on nonideal capacitors should be used to capture the behavior of neuronal membranes at high frequencies.

High frequencies of polyfunctional HIV-specific T cells are associated with preservation of mucosal CD4 T cells in bronchoalveolar lavage

Brenchley, JM; Knox, KS; Asher, AI; Price, DA; Kohli, LM; Gostick, E; Hill, BJ; Hage, CA; Brahmi, Z; Khoruts, A; Twigg, HL; Schacker, TW; Douek, DC
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2008 Português
Relevância na Pesquisa
45.9%
The mechanisms underlying the massive gastrointestinal tract CD4 T-cell depletion in human immunodeficiency virus (HIV) infection are not well understood nor is it clear whether similar depletion is manifest at other mucosal surfaces. Studies of T-cell and virus dynamics in different anatomical sites have begun to illuminate the pathogenesis of HIV-associated disease. Here, we studied depletion and HIV infection frequencies of CD4 T cells from the gastrointestinal tract, bronchoalveolar lavage (BAL), and blood with the frequencies and functional profiles of HIV-specific T cells in these anatomically distinct sites in HIV-infected individuals. The major findings to emerge were as follows: (i) depletion of gastrointestinal CD4 T cells is associated with high frequencies of infected CD4 T cells; (ii) HIV-specific T cells are present at low frequencies in the gastrointestinal tract compared to blood; (iii) BAL CD4 T cells are not massively depleted during the chronic phase; (iv) infection frequencies of BAL CD4 T cells are similar to those in blood; (v) significantly higher frequencies and increased functionality of HIV-specific T cells were observed in BAL compared to blood. Taken together, these data suggest mechanisms for mucosal CD4 T-cell depletion and interventions that might circumvent global depletion of mucosal CD4 T cells.

Middle-Ear Function At High Frequencies Quantified With Advanced Bone Conduction Measures

Popelka, Gerald R.; Telukuntla, Goutham; Puria, Sunil
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.95%
Auditory thresholds with standardized clinical procedures are obtained over a much narrower frequency range by bone conduction than by air conduction. As a result, diagnostic information for both sensorineural and conductive-mechanism function is incomplete for high frequencies. A new magnetostrictive bone-conduction transducer that has the potential for improved output in the high-frequency range was evaluated in the laboratory and in a variety of subjects with normal hearing (N=11) or sensorineural hearing loss (N=9). Laboratory results indicated that harmonic distortion and acoustic radiation were both sufficiently low to allow accurate threshold measurements. Auditory thresholds obtained with this magnetostrictive bone-conduction transducer can be measured accurately under conventional clinical conditions for frequencies up to 16 kHz and levels up to 85 dB HL. These measures can be used to accurately characterize sensorineural hearing sensitivity for high frequencies and, when combined with standard air-conduction measures for high frequencies, to accurately characterize conductive-mechanism function for frequencies higher than possible with current diagnostic bone-conduction technology.

Gender and vocal production mode discrimination using the high frequencies for speech and singing

Monson, Brian B.; Lotto, Andrew J.; Story, Brad H.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 30/10/2014 Português
Relevância na Pesquisa
45.89%
Humans routinely produce acoustical energy at frequencies above 6 kHz during vocalization, but this frequency range is often not represented in communication devices and speech perception research. Recent advancements toward high-definition (HD) voice and extended bandwidth hearing aids have increased the interest in the high frequencies. The potential perceptual information provided by high-frequency energy (HFE) is not well characterized. We found that humans can accomplish tasks of gender discrimination and vocal production mode discrimination (speech vs. singing) when presented with acoustic stimuli containing only HFE at both amplified and normal levels. Performance in these tasks was robust in the presence of low-frequency masking noise. No substantial learning effect was observed. Listeners also were able to identify the sung and spoken text (excerpts from “The Star-Spangled Banner”) with very few exposures. These results add to the increasing evidence that the high frequencies provide at least redundant information about the vocal signal, suggesting that its representation in communication devices (e.g., cell phones, hearing aids, and cochlear implants) and speech/voice synthesizers could improve these devices and benefit normal-hearing and hearing-impaired listeners.

An Overrepresentation of High Frequencies in the Mouse Inferior Colliculus Supports the Processing of Ultrasonic Vocalizations

Garcia-Lazaro, Jose A.; Shepard, Kathryn N.; Miranda, Jason A.; Liu, Robert C.; Lesica, Nicholas A.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 05/08/2015 Português
Relevância na Pesquisa
45.9%
Mice are of paramount importance in biomedical research and their vocalizations are a subject of interest for researchers across a wide range of health-related disciplines due to their increasingly important value as a phenotyping tool in models of neural, speech and language disorders. However, the mechanisms underlying the auditory processing of vocalizations in mice are not well understood. The mouse audiogram shows a peak in sensitivity at frequencies between 15-25 kHz, but weaker sensitivity for the higher ultrasonic frequencies at which they typically vocalize. To investigate the auditory processing of vocalizations in mice, we measured evoked potential, single-unit, and multi-unit responses to tones and vocalizations at three different stages along the auditory pathway: the auditory nerve and the cochlear nucleus in the periphery, and the inferior colliculus in the midbrain. Auditory brainstem response measurements suggested stronger responses in the midbrain relative to the periphery for frequencies higher than 32 kHz. This result was confirmed by single- and multi-unit recordings showing that high ultrasonic frequency tones and vocalizations elicited responses from only a small fraction of cells in the periphery, while a much larger fraction of cells responded in the inferior colliculus. These results suggest that the processing of communication calls in mice is supported by a specialization of the auditory system for high frequencies that emerges at central stations of the auditory pathway.

Gender and vocal production mode discrimination using the high frequencies for speech and singing

Monson, Brian B.; Lotto, Andrew J.; Story, Brad H.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
55.9%
Humans routinely produce acoustical energy at frequencies above 6 kHz during vocalization, but this frequency range is often not represented in communication devices and speech perception research. Recent advancements toward high-definition (HD) voice and extended bandwidth hearing aids have increased the interest in the high frequencies. The potential perceptual information provided by high-frequency energy (HFE) is not well characterized. We found that humans can accomplish tasks of gender discrimination and vocal production mode discrimination (speech vs. singing) when presented with acoustic stimuli containing only HFE at both amplified and normal levels. Performance in these tasks was robust in the presence of low-frequency masking noise. No substantial learning effect was observed. Listeners also were able to identify the sung and spoken text (excerpts from “The Star-Spangled Banner”) with very few exposures. These results add to the increasing evidence that the high frequencies provide at least redundant information about the vocal signal, suggesting that its representation in communication devices (e.g., cell phones, hearing aids, and cochlear implants) and speech/voice synthesizers could improve these devices and benefit normal-hearing and hearing-impaired listeners.

Search for a high frequency stochastic background of gravitational waves

Giampanis, Stefanos (1980 - ); Melissinos, Adrian C. (1929 - )
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xvii, 138 leaves
Português
Relevância na Pesquisa
45.87%
Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2008.; Over the past decades significant efforts have been made worldwide in the search for gravitational waves. Ground-based interferometry, primarily with the LIGO detectors, has reached a crucial point and it is believed that over the next few years a detection will take place. LIGO interferometers have recently completed collecting data from the longest science run that has been attempted so far. This thesis describes the search for a stochastic gravitational wave background radiation at high frequencies using data from the LIGO detectors located in Hanford, Washington USA. This is the first ever search for a stochastic signal at high frequencies by using data from two co-located interferometers. Chapter 1 provides a brief introduction to gravitational radiation as predicted by the general theory of relativity and the expected sources of gravitational waves with an emphasis on the stochastic background. Chapter 2 discusses the basic principles of laser interferometry and the experimental techniques used in modern ground-based interferometers such as the LIGO interferometers. Chapter 3 discusses in more detail the configuration, validation and characterization of the set of channels...

Distortion-product otoacoustic emissions at ultra-high frequencies in parents of individuals with autosomal recessive hearing loss

Mello,Jaqueline Medeiros de; Della-Rosa,Valter Augusto; Carvallo,Renata Mota Mamede
Fonte: Sociedade Brasileira de Fonoaudiologia Publicador: Sociedade Brasileira de Fonoaudiologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2014 Português
Relevância na Pesquisa
45.88%
Purpose: To evaluate the cochlear function of parents of individuals with autosomal recessive gene Gap Junction Protein Beta-2 hearing loss by ultra-high frequencies distortion-product otoacoustic emissions (DPOAEs), compared with responses of a control group matched for age and gender. Methods: We studied 56 subjects aged from 20 to 58 years, divided into two groups. The study group comprised 28 parents of hearing-impaired patients due to autosomal recessive inheritance, 14 females aged 20.0-55.0 years (mean 32.8 years) and 14 males aged 20.0-58.0 years (mean 35.2 years). Control group was composed of normal hearing individuals, 14 males and 14 females age-matched to the study group. The subjects underwent tests for audiometry, tympanometry, and DPOAE in the frequency range of 9.000-16.000 Hz. Results: We found 64.3% of normal results of DPOAE in the study group compared to 91.1% in the control. There were significant differences between groups in the ears and DPOAE responses, and the mean level of response was in 10 dBNPS in study group and 14 dBNPS in the control. The Pearson's correlation between age and DPOAE in ultra-high frequencies showed no statistical significance. Conclusion: DPOAE at ultra-high frequencies were able to identify individuals from both groups...

The AT20G view of Swift/BAT selected AGN: high-frequency radio waves meet hard X-rays

Burlon, D.; Ghirlanda, G.; Murphy, T.; Chhetri, R.; Sadler, E.; Ajello, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/04/2013 Português
Relevância na Pesquisa
45.9%
We cross-matched the 6-year Swift/Burst Alert Telescope (BAT) survey of active galactic nuclei (AGN) with the AT20G radio survey of the southern sky, which is one of the largest high-frequency radio surveys available. With these data we investigated the possible correlation between the radio and the X-ray emission at the highest radio and X-ray frequencies. We found 37 AGN with a high probability of association (>80 per cent), among which 19 are local Seyfert galaxies (with median redshift z = 0.03) and 18 blazars. We found that \approx 20 per cent of the AGN detected in hard X-rays are also bright radio sources at 20 GHz, but the apparent correlation between the radio and hard X-ray luminosity is completely driven by the different median redshifts of the two subgroups of AGN. When we consider only the local Seyfert sample we find no evidence of a correlation between their 20 GHz and 15-55 keV power. Therefore it appears that at high frequencies the radio-X connection, which had been previously observed at lower frequencies, disappears. The disappearance of the radio-X correlation at high radio and X-ray frequencies could be tested through Very Long Baseline Interferometry and the use of the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite.; Comment: MNRAS accepted (21 Feb 2013). 10 pages...

A modified cable formalism for modeling neuronal membranes at high frequencies

Bedard, Claude; Destexhe, Alain
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.93%
Intracellular recordings of cortical neurons in vivo display intense subthreshold membrane potential (Vm) activity. The power spectral density (PSD) of the Vm displays a power-law structure at high frequencies (>50 Hz) with a slope of about -2.5. This type of frequency scaling cannot be accounted for by traditional models, as either single-compartment models or models based on reconstructed cell morphologies display a frequency scaling with a slope close to -4. This slope is due to the fact that the membrane resistance is "short-circuited" by the capacitance for high frequencies, a situation which may not be realistic. Here, we integrate non-ideal capacitors in cable equations to reflect the fact that the capacitance cannot be charged instantaneously. We show that the resulting "non-ideal" cable model can be solved analytically using Fourier transforms. Numerical simulations using a ball-and-stick model yield membrane potential activity with similar frequency scaling as in the experiments. We also discuss the consequences of using non-ideal capacitors on other cellular properties such as the transmission of high frequencies, which is boosted in non-ideal cables, or voltage attenuation in dendrites. These results suggest that cable equations based on non-ideal capacitors should be used to capture the behavior of neuronal membranes at high frequencies.; Comment: To appear in Biophysical Journal; Submitted on May 25...

High-resolution radio observations of SNR 1987A at high frequencies

Zanardo, Giovanna; Staveley-Smith, L.; Ng, C. -Y.; Gaensler, B. M.; Potter, T. M.; Manchester, R. N.; Tzioumis, A. K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
55.9%
We present new imaging observations of the remnant of Supernova (SN) 1987A at 44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA). The $0\farcs35\times0\farcs23$ resolution of the diffraction-limited image is the highest achieved to date in high-dynamic range. We also present a new ATCA image at 18 GHz derived from 2011 observations, which is super-resolved to $0\farcs25$. The flux density is 40$\pm$2 mJy at 44 GHz and 81$\pm$6 mJy at 18 GHz. At both frequencies, the remnant exhibits a ring-like emission with two prominent lobes, and an east-west brightness asymmetry that peaks on the eastern lobe. A central feature of fainter emission appears at 44 GHz. A comparison with previous ATCA observations at 18 and 36 GHz highlights higher expansion velocities of the remnant eastern side. The 18-44 GHz spectral index is $\alpha=-0.80$ ($S_{\nu}\propto\nu^{\alpha}$). The spectral index map suggests slightly steeper values at the brightest sites on the eastern lobe, whereas flatter values are associated with the inner regions. The remnant morphology at 44 GHz generally matches the structure seen with contemporaneous X-ray and H$\alpha$ observations. Unlike the H$\alpha$ emission, both the radio and X-ray emission peaks on the eastern lobe. The regions of flatter spectral index align and partially overlap with the optically-visible ejecta. Simple free-free absorption models suggest that emission from a pulsar wind nebula or a compact source inside the remnant may now be detectable at high frequencies...

The radio remnant of Supernova 1987A at high frequencies and high resolution

Zanardo, G.; Staveley-Smith, L.; Ng, C. -Y.; Gaensler, B. M.; Potter, T. M.; Manchester, R. N.; Tzioumis, A. K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/10/2013 Português
Relevância na Pesquisa
55.79%
As the remnant of Supernova (SN) 1987A has been getting brighter over time, new observations at high frequencies have allowed imaging of the radio emission at unprecedented detail. We present a new radio image at 44 GHz of the supernova remnant (SNR), derived from observations performed with the Australia Telescope Compact Array (ATCA) in 2011. The diffraction-limited image has a resolution of $349\times225$ mas, which is the highest achieved to date in high-dynamic range images of the SNR. We also present a new image at 18 GHz, also derived from ATCA observations performed in 2011, which is super-resolved to $0./!/!^{\prime\prime}25$. The new 44 and 18 GHz images yield the first high-resolution spectral index map of the remnant. The comparison of the 44 GHz image with contemporaneous X-ray and H$\alpha$ observations allows further investigations of the nature of the remnant asymmetry and sheds more light into the progenitor hypotheses and SN explosion. In light of simple free-free absorption models, we discuss the likelihood of detecting at 44 GHz the possible emission originating from a pulsar wind nebula (PWN) or a compact source in the centre of the remnant.; Comment: 4 pages, to appear in the proceedings of IAU Symposium 296, "Supernova Environmental Impacts" (eds Ray and McCray)

Relationship between low and high frequencies in Delta Scuti stars: Photometric Kepler and spectroscopic analyses of the rapid rotator KIC 8054146

Breger, M.; Fossati, L.; Balona, L.; Kurtz, D. W.; Robertson, P.; Bohlender, D.; Lenz, P.; Mueller, I.; Lueftinger, Th.; Clarke, Bruce D.; Hall, Jennifer R.; Ibrahim, Khadeejah A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/09/2012 Português
Relevância na Pesquisa
46.01%
Two years of Kepler data of KIC 8054146 (delta Sct/gamma Dor hybrid) revealed 349 statistically significant frequencies between 0.54 and 191.36 c/d (6.3 microHz to 2.21 mHz). The 117 low frequencies cluster in specific frequency bands, but do not show the equidistant period spacings predicted for gravity modes of successive radial order, n, and reported for at least one other hybrid pulsator. The four dominant low frequencies in the 2.8 to 3.0 c/d (32 to 35 microHz) range show strong amplitude variability with timescales of months and years. These four low frequencies also determine the spacing of the higher frequencies in and beyond the delta Sct pressure-mode frequency domain. In fact, most of the higher frequencies belong to one of three families with spacings linked to a specific dominant low frequency. In the Fourier spectrum, these family regularities show up as triplets, high-frequency sequences with absolutely equidistant frequency spacings, side lobes (amplitude modulations) and other regularities in frequency spacings. Furthermore, within two families the amplitude variations between the low and high frequencies are related. We conclude that the low frequencies (gravity modes, rotation) and observed high frequencies (mostly pressure modes) are physically connected. This unusual behavior may be related to the very rapid rotation of the star: from a combination of high and low-resolution spectroscopy we determined that KIC 8054146 is a very fast rotator (v sin i = 300 +/- 20 km/s) with an effective temperature of 7600 +/- 200 K and a surface gravity log g of 3.9 +/- 0.3. Several astrophysical ideas explaining the origin of the relationship between the low and high frequencies are explored.; Comment: to be published in "The Astrophysical Journal"...

Re-visiting Bolt's criterion for homogeneous distribution of normal frequencies in rectangular enclosures

Moreno, Antonio; Ruiz, Joaquín; Colina, Carlos de la
Fonte: Sociedad Española de Acústica Publicador: Sociedad Española de Acústica
Tipo: Comunicación de congreso Formato: 311254 bytes; application/pdf
Português
Relevância na Pesquisa
45.89%
6 pp.-- PACS nrs: 43.55.Gx, 43.55.Hy, 43.55.Nd.-- Comunicación presentada en los siguientes congresos: II Congreso Iberoamericano de Acústica. XXXI Congreso Nacional de Acústica – TecniAcústica 2000. II Jornadas Iberoamericanas de Ultrasonidos. II Congreso Ibérico de Acústica. EAA Symposium on Architectural Acoustics (Madrid, 16-20 Octubre 2000).; Publicado también en número especial de la Revista de Acústica, Vol. XXXI, año 2000.; [EN] The classical criterion of Bolt for homogeneous distribution of normal frequencies in rectangular enclosures is revisited. Coincidence of normal frequencies is considered a detrimental factor concerning frequency and spatial regularity in sound response of enclosures. New fundamental facts influencing normal frequency distribution are analyzed and a metric is proposed as an efficient criterion. Merit figures are compared to Bolt's results. New areas of p,q ratios leading to homogeneous distributions in the low frequency range are found. At high frequencies a generally better situation is observed but some values of p and/or q and some ratios p/q lead to clusters and "holes" of normal frequencies causing high scores of transmission irregularity.; [ES] Se presenta un nuevo enfoque del criterio de Bolt sobre distribución homogénea de frecuencias propias en recintos prismáticos. La coincidencia de frecuencias propias se considera un factor clave de deterioro de la regularidad de la transmisión sonora en recintos. Se analizan las causas del espaciado homogéneo de frecuencias propias proponiendo una nueva métrica cuyos resultados se comparan con los de Bolt...