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We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here, we report on characteristics of these three unusual CR events, which develop nearly horizontally, 20-30 km above the surface of Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible τ-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the standard model τ-neutrino cross section.
RESUMO
We report the observation of 16 cosmic ray events with a mean energy of 1.5 × 10¹9 eV via radio pulses originating from the interaction of the cosmic ray air shower with the Antarctic geomagnetic field, a process known as geosynchrotron emission. We present measurements in the 300-900 MHz range, which are the first self-triggered, first ultrawide band, first far-field, and the highest energy sample of cosmic ray events collected with the radio technique. Their properties are inconsistent with current ground-based geosynchrotron models. The emission is 100% polarized in the plane perpendicular to the projected geomagnetic field. Fourteen events are seen to have a phase inversion due to reflection of the radio beam off the ice surface, and two additional events are seen directly from above the horizon. Based on a likelihood analysis, we estimate angular pointing precision of order 2° for the event arrival directions.
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We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmic neutrinos above energies of E(nu) approximately 3 x 10(18) eV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. We report here on our initial analysis, which was performed as a blind search of the data. No neutrino candidates are seen, with no detected physics background. We set model-independent limits based on this result. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In a background horizontal-polarization channel, we also detect six events consistent with radio impulses from ultrahigh energy extensive air showers.
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We report on observations of coherent, impulsive radio Cherenkov radiation from electromagnetic showers in solid ice. This is the first observation of the Askaryan effect in ice. As part of the complete validation process for the ANITA experiment, we performed an experiment at the Stanford Linear Accelerator Center in June 2006 using a 7.5 metric ton ice target. We measure for the first time the large-scale angular dependence of the radiation pattern, a major factor in determining the solid-angle acceptance of ultrahigh-energy neutrino detectors.
Assuntos
Síndrome de Wolff-Parkinson-White/etiologia , Adolescente , Criança , Pré-Escolar , Eletrocardiografia/métodos , Eletrofisiologia , Feminino , Seguimentos , Cardiopatias Congênitas/complicações , Humanos , Lactente , Masculino , Síndromes de Pré-Excitação/etiologia , Síndromes de Pré-Excitação/fisiopatologia , Fatores de Risco , Taquicardia Supraventricular/etiologia , Taquicardia Supraventricular/fisiopatologia , Síndrome de Wolff-Parkinson-White/diagnóstico , Síndrome de Wolff-Parkinson-White/fisiopatologiaRESUMO
The aim of the study was to evaluate by Doppler tissue imaging (DTI) the combined effects of atrio-ventricular (AV) delay and heart rate (HR) changes on global and segmental right (RV) and left (LV) ventricular diastolic function in 15 patients with dual-chamber pacemakers paced in the DDD mode. RV and LV inflow velocities and regional systolic and diastolic pulsed-wave (PW) DTI parameters were analyzed at four different pacing modes: (1) HR 70 beats/min, AV delay 125 ms; (2) HR 70 beats/min, AV delay 188 ms; (3) HR 89 beats/min, AV delay 125 ms; (4) HR 89 beats/min, AV delay 188 ms. For each pacing mode selected, RV diastolic filling velocities always prevailed over LV ones. As for RV and LV adaptation to the four different stimulation protocols, a higher paced rate and a prolonged AV delay caused across both the AV valves a decrease of E wave and of E/A ratios. The intersegmental comparison of PW-DTI parameters outlined that RV free wall exhibited significantly higher peak systolic (Sm) and early-diastolic (Em) wall velocities, and longer systolic ejection time. Considering separately RV and LV segmental physiology at the four programmed pacing modes, an increase in HR determined a progressive shortening of systolic ejection times in all the segments analyzed. Moreover, in each region the Em/Am ratio decreased with higher HR and longer AV delay. Conversely, Em encountered a progressive reduction in RV free wall, while remaining quite unchanged in all the LV regions. Both ventricles shared a similar pattern of global and regional adaptation to programmed HR and AV delay modifications, consisting in a progressive greater contribution of late diastole to ventricular filling at higher HR and more prolonged AV delay. However, at a regional level the right ventricle exhibited higher systolic and diastolic wall velocities than all left ventricular regions.
Assuntos
Arritmias Cardíacas/diagnóstico por imagem , Arritmias Cardíacas/terapia , Estimulação Cardíaca Artificial , Ecocardiografia Doppler , Função Ventricular Esquerda/fisiologia , Função Ventricular Direita/fisiologia , Idoso , Análise de Variância , Arritmias Cardíacas/fisiopatologia , Nó Atrioventricular/diagnóstico por imagem , Nó Atrioventricular/fisiopatologia , Velocidade do Fluxo Sanguíneo/fisiologia , Diástole/fisiologia , Feminino , Frequência Cardíaca/fisiologia , Ventrículos do Coração/diagnóstico por imagem , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
BACKGROUND: Atrial fibrillation (AF) is the most frequently encountered arrhythmic complication associated with cardiac surgery. The aim of this paper was to identify the clinical predictors of AF occurrence following aortic valve replacement. METHODS: Three hundred and two patients were included in this study and divided into two groups according to the absence (SR group, 243 patients, mean age 55.6 +/- 15 years) or the evidence (AF group, 59 patients, mean age 63.8 +/- 11 years) of post-aortic valve replacement AF. Sixty-five perioperative variables (37 preoperative, 8 intraoperative and 20 postoperative) were considered. RESULTS: Post-aortic valve replacement paroxysmal AF occurred in 59 out of 302 patients (19%). At univariate analysis, post-aortic valve replacement AF was associated with advanced age, left atrial enlargement, preoperative episodes of paroxysmal AF, the use of a warm blood cardioplegic solution and normothermia, administration of inotropic agents, prolonged assisted ventilation but also with postoperative acidosis, electrolyte imbalance and atrioventricular and intraventricular conduction disorders. Stepwise forward multivariate logistic regression analysis identified age (p = 0.002, odds ratio--OR 1.04), left atrial enlargement (p = 0.004, OR 2.6), a prior history of paroxysmal AF (p = 0.0003, OR 10.9), and postoperative electrolyte imbalance (p = 0.01, OR 2.3) as independent correlates of AF, whereas the use of hypothermia appeared to be a protective factor (p = 0.0004, OR 0.26). CONCLUSIONS: According to our findings, post-aortic valve replacement AF seems to be associated with well-defined anatomical and electrical substrates generated by advanced age, increased left atrial dimensions, and a possible electrical remodeling consequent to prior repetitive episodes of paroxysmal AF. On these grounds, external factors such as postoperative electrolyte imbalance might enhance atrial ectopic activity and trigger postoperative sustained tachyarrhythmias, while the use of hypothermia might allow for better protection of the atrial myocardium against intraoperative ischemia.
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Valva Aórtica/cirurgia , Fibrilação Atrial/etiologia , Doenças das Valvas Cardíacas/cirurgia , Complicações Pós-Operatórias , Análise de Variância , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Fatores de RiscoRESUMO
Idiopathic left ventricular tachycardia is a rare arrhythmia whose electrophysiological basis is not yet well-defined. We report a case of idiopathic left ventricular tachycardia caused by a reentrant circuit limited exclusively to the two fascicles of the left bundle branch.