493 research outputs found
The Otterbein Miscellany - September 1979
https://digitalcommons.otterbein.edu/miscellany/1019/thumbnail.jp
The Otterbein Miscellany - Fall 1979
https://digitalcommons.otterbein.edu/miscellany/1017/thumbnail.jp
The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658
We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658,
an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi
X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify
that the 401 Hz pulsation traces the spin frequency fundamental and not a
harmonic. Substantial pulse shape variability, both stochastic and systematic,
was observed during each outburst. Analysis of the systematic pulse shape
changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar
surface drifts longitudinally and a second hot spot may appear. The overall
pulse shape variability limits the ability to measure spin frequency evolution
within a given X-ray outburst (and calls previous nudot measurements of this
source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s
(2 sigma). However, combining data from all the outbursts shows with high (6
sigma) significance that the pulsar is undergoing long-term spin down at a rate
nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring
during X-ray quiescence. We discuss the possible contributions of magnetic
propeller torques, magnetic dipole radiation, and gravitational radiation to
the measured spin down, setting an upper limit of B < 1.5x10^8 G for the
pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the
fractional mass quadrupole moment. We also measured an orbital period
derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is
reminiscent of the large and quasi-cyclic orbital period variation observed in
the so-called "black widow" millisecond radio pulsars, supporting speculation
that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an
appendix we derive an improved (0.15 arcsec) source position from optical data.Comment: 22 pages, 10 figures; accepted for publication in Ap
Chartis Measurement of Collateral Ventilation:Conscious Sedation versus General Anesthesia
BACKGROUND: Absence of interlobar collateral ventilation using the Chartis measurement is the key predictor for successful endobronchial valve treatment in severe emphysema. Chartis was originally validated in spontaneous breathing patients under conscious sedation (CS); however, this can be challenging due to cough, mucus secretion, mucosal swelling, and bronchoconstriction. Performing Chartis under general anesthesia (GA) avoids these problems and may result in an easier procedure with a higher success rate. However, using Chartis under GA with positive pressure ventilation has not been validated. OBJECTIVES: In this study we investigated the impact of anesthesia technique, CS versus GA, on the feasibility and outcomes of Chartis measurement. METHODS: We retrospectively analyzed all Chartis measurements performed at our hospital from October 2010 until December 2017. RESULTS: We analyzed 250 emphysema patients (median forced expiratory volume in 1 s 26%, range 12-52% predicted). In 121 patients (48%) the measurement was performed using CS, in 124 (50%) using GA, and in 5 (2%) both anesthesia techniques were used. In total, 746 Chartis readings were analyzed (432 CS, 277 GA, and 37 combination). Testing under CS took significantly longer than GA (median 19 min [range 5-65] vs. 11 min [3-35], p < 0.001) and required more measurements (3 [1-13] vs. 2 [1-6], p < 0.001). There was no significant difference in target lobe volume reduction after treatment (-1,123 mL [-3,604 to 332] in CS vs. -1,251 mL [-3,333 to -1] in GA, p = 0.35). CONCLUSIONS: In conclusion, Chartis measurement under CS took significantly longer and required more measurements than under GA, without a difference in treatment outcome. We recommend a prospective trial comparing both techniques within the same patients to validate this approach
A New Oxygen Uptake Measurement Supporting Target Selection for Endobronchial Valve Treatment
BACKGROUND: Adequate target lobe selection for endobronchial valve (EBV) treatment in patients with severe emphysema is essential for treatment success and can be based on emphysema destruction, lobar perfusion, lobar volume, and collateral ventilation. As some patients have >1 target lobe for EBV treatment, we were interested whether we could identify the least functional lobe. OBJECTIVES: The objective of this study was to investigate the relationship between endoscopic lobar measurement of oxygen uptake, lobar destruction, and vascular volume, and whether this could help in identifying the least functional lobe and thus optimal target for EBV treatment. METHOD: We prospectively included patients who were scheduled for EBV treatment in our hospital. A customized gas analysis setup was used to measure lobar O2 uptake after lobar balloon occlusion. Quantitative CT analysis was performed to assess the degree of emphysematous destruction and lobar arterial and venous volumes. RESULTS: Twenty-one (5 male/16 female) patients with emphysema (median age 63 years, FEV1 25% of predicted, residual volume 234% of predicted) were included, and 49 endoscopic lobar measurements were performed. A lower O2 uptake significantly correlated with a higher degree of emphysematous lobar destruction (Spearman's Ï: 0.39, p < 0.01), and lower arterial and venous vascular volumes of the lobes (-0.46 and -0.47, respectively; both p < 0.001). CONCLUSIONS: Endoscopic measurement of lobar O2 uptake is feasible in patients with emphysema. Measurement of lobar O2 uptake helped to identify the least functional lobe and can be used as additional tool for EBV target lobe selection
The optical counterpart to gamma-ray burst GRB970228 observed using the Hubble Space Telescope
Although more than 2,000 astronomical gamma-ray bursts (GRBs) have been
detected, and numerous models proposed to explain their occurrence, they have
remained enigmatic owing to the lack of an obvious counterpart at other
wavelengths. The recent ground-based detection of a transient source in the
vicinity of GRB 970228 may therefore have provided a breakthrough. The optical
counterpart appears to be embedded in an extended source which, if a galaxy as
has been suggested, would lend weight to those models that place GRBs at
cosmological distances. Here we report the observations using the Hubble Space
Telescope of the transient counterpart and extended source 26 and 39 days after
the initial gamma-ray outburst. We find that the counterpart has faded since
the initial detection (and continues to fade), but the extended source exhibits
no significant change in brightness between the two dates of observations
reported here. The size and apparent constancy between the two epochs of HST
observations imply that it is extragalactic, but its faintness makes a
definitive statement about its nature difficult. Nevertheless, the decay
profile of the transient source is consistent with a popular impulsive-fireball
model, which assumes a merger between two neutron stars in a distant galaxy.Comment: 11 pages + 2 figures. To appear in Nature (29 May 1997 issue
A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus
The Trojan population consists of two swarms of asteroids following the same
orbit as Jupiter and located at the L4 and L5 Lagrange points of the
Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid
617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit
of this double system was hitherto unknown. Here we report that the components,
separated by 680 km, move around the system centre of mass, describing roughly
a circular orbit. Using the orbital parameters, combined with thermal
measurements to estimate the size of the components, we derive a very low
density of 0.8 g/cc. The components of Patroclus are therefore very porous or
composed mostly of water ice, suggesting that they could have been formed in
the outer part of the solar system.Comment: 10 pages, 3 figures, 1 tabl
TeV physics and the Planck scale
Supersymmetry is one of the best motivated possibilities for new physics at
the TeV scale. However, both concrete string constructions and phenomenological
considerations suggest the possibility that the physics at the TeV scale could
be more complicated than the Minimal Supersymmetric Standard Model (MSSM),
e.g., due to extended gauge symmetries, new vector-like supermultiplets with
non-standard SU(2)xU(1) assignments, and extended Higgs sectors. We briefly
comment on some of these possibilities, and discuss in more detail the class of
extensions of the MSSM involving an additional standard model singlet field.
The latter provides a solution to the problem, and allows significant
modifications of the MSSM in the Higgs and neutralino sectors, with important
consequences for collider physics, cold dark matter, and electroweak
baryogenesis.Comment: 17 pages, 5 figures. To appear in New Journal of Physic
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