976 research outputs found
Early Globus Pallidus Internus Stimulation in Pediatric Patients With Generalized Primary Dystonia: Long-Term Efficacy and Safety
Primary generalized dystonia presents mainly at a young age and commonly is severely disabling. The authors report the long-term follow-up (mean, 73 months; range, 50-101 months) of 5 pediatric patients (mean age at surgery 13 years; range, 8-16 years) undergoing globus pallidus internus deep brain stimulation. Mean improvement in the Burke-Fahn-Marsden movement score was 67.4% (range, 47.0%-87.5%), 75.4% (range, 61.5%-91.7%), and 83.5% (range, 72.0%-93.3%) at 3 months, 12 months, and long-term follow-up (>36 months), respectively. Hardware problems (electrode dislocation/breakage of extension cable, and imminent perforation of extension cable) were observed in 2 patients (operative revision without sequelae). Except for mild dysarthria in 2 patients, no other therapy-related morbidity was observed. The authors found globus pallidus internus stimulation to offer a very effective and safe therapy in pediatric patients with primary dystonia. Early neurosurgical intervention seems to be crucial to prevent irreversible impairment of motor function
The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves is the Oosterhoff/Arp/Preston Period Ratio Effect in Disguise
The correlation of particular Fourier components of the light curves of RR
Lyrae variables with metallicity, discovered by Simon and later by Kovacs and
his coworkers, is shown to have the same explanation as the period ratios
(period shifts in log P) between RRab Lyrae variables that have the same
colors, amplitudes, and light-curve shapes but different metallicities. A
purpose of this paper is to demonstrate that the model which predicts the
period-metallicity relations is the mediating parameters of colors, amplitudes,
and light-curve shapes also explains the Simon/Kovacs et al. correlation
between period, Phi_31, and metallicity. The proof is made by demonstrating
that the combination of the first and third phase terms in a Fourier
decomposition of RRab light curves, called Phi_31 by Simon and Lee, varies
monotonically across the RR Lyrae instability strip in the same way that
amplitude, color, and rise time vary with period within the strip. The premise
of the model is that if horizontal branches at the RR Lyrae strip are stacked
in luminosity according to the metallicity, then there necessarily must be a
log period shift between RR Lyraes with different metallicities at the same
Phi_31 values. However, there are exceptions to the model. (...)Comment: 17 pages, 8 figures, 1 table. Accepted for publication in The A
Period-colour and amplitude-colour relations in classical Cepheid variables IV: The multi-phase relations
The superb phase resolution and quality of the OGLE data on LMC and SMC
Cepheids, together with existing data on Galactic Cepheids, are combined to
study the period-colour (PC) and amplitude-colour (AC) relations as a function
of pulsation phase. Our results confirm earlier work that the LMC PC relation
(at mean light) is more consistent with two lines of differing slopes,
separated at a period of 10 days. However, our multi-phase PC relations reveal
much new structure which can potentially increase our understanding of Cepheid
variables. These multi-phase PC relations provide insight into why the Galactic
PC relation is linear but the LMC PC relation is non-linear. This is because
the LMC PC relation is shallower for short (log P < 1) and steeper for long
(log P > 1) period Cepheids than the corresponding Galactic PC relation. Both
of the short and long period Cepheids in all three galaxies exhibit the
steepest and shallowest slopes at phases around 0.75-0.85, respectively. A
consequence is that the PC relation at phase ~0.8 is highly non-linear.
Further, the Galactic and LMC Cepheids with log P > 1 display a flat slope in
the PC plane at phases close to the maximum light. When the LMC
period-luminosity (PL) relation is studied as a function of phase, we confirm
that it changes with the PC relation. The LMC PL relation in V- and I-band near
the phase of 0.8 provides compelling evidence that this relation is also
consistent with two lines of differing slopes joined at a period close to 10
days.Comment: 12 pages, 1 table and 13 figures, MNRAS accepte
Intracranial hypotension following traumatic brain injury: a diagnostic and therapeutic challenge.
BACKGROUND: Intracranial hypotension (IH) is a recognised cause of coma, however, the diagnosis is often challenging, especially in patients with superimposed traumatic brain injury (TBI). CASE REPORT: We report a case of a 67-year-old patient who became comatose following evacuation of bilateral acute subdural haematomas with concurrent respiratory failure. Imaging and intraparenchymal intracranial pressure (ICP) monitoring confirmed secondary IH. She was managed with an epidural blood patch, and a 72 hours period in the trendelenberg position guided by ICP monitoring and clinical assessment. She subsequently made an excellent neurological recovery from an initial Glasgow coma scale (GCS) of 3 to a GCS of 15. CONCLUSION: A diagnosis of secondary IH can easily be missed in patients who have suffered a primary brain injury. In patients with a poor neurological recovery, clinicians should rule out secondary IH as a potential cause as immediate treatment can lead to a profound clinical improvement
Period-color and amplitude-color relations in classical Cepheid variables III: The Large Magellanic Cloud Cepheid models
Period-colour (PC) and amplitude-colour (AC) relations are studied for the
Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the
hydrogen ionization front (HIF) - photosphere interaction. LMC models are
constructed with pulsation codes that include turbulent convection, and the
properties of these models are studied at maximum, mean and minimum light. As
with Galactic models, at maximum light the photosphere is located next to the
HIF for the LMC models. However very different behavior is found at minimum
light. The long period (P>10days) LMC models imply that the photosphere is
disengaged from the HIF at minimum light, similar to the Galactic models, but
there are some indications that the photosphere is located near the HIF for the
short period (P<10 days) LMC models. We also use the updated LMC data to derive
empirical PC and AC relations at these phases. Our numerical models are broadly
consistent with our theory and the observed data, though we discuss some
caveats in the paper. We apply the idea of the HIF-photosphere interaction to
explain recent suggestions that the LMC period-luminosity (PL) and PC relations
are non-linear with a break at a period close to 10 days. Our empirical PC and
PL relations are also found to be non-linear with the F-test. Our explanation
relies on the properties of the Saha ionization equation, the HIF-photosphere
interaction and the way this interaction changes with the phase of pulsation
and metallicity to produce the observed changes in the Cepheid PC and PL
relations.Comment: 19 pages, 6 tables and 18 figures, MNRAS accepte
The Cepheid Period-Luminosity Relation at Mid-Infrared Wavelengths: II. Second-Epoch LMC Data
We present revised and improved mid-infrared Period-Luminosity (PL) relations
for Large Magellanic Cloud (LMC) Cepheids based on double-epoch data of 70
Cepheids observed by Spitzer at 3.6, 4.5, 5.8 and 8.0um. The observed scatter
at all wavelengths is found to decrease from +/-0.17 mag to +/-0.14 mag, which
is fully consistent with the prediction that the total scatter is made up of
roughly equal contributions from random sampling of the light curve and
nearly-uniform samplings of stars across the instability strip. It is
calculated that the Cepheids in this sample have a full amplitude of about 0.4
mag and that their fully-sampled, time-averaged magnitudes should eventually
reveal mid-infrared PL relations that each have intrinsic scatter at most at
the +/-0.12 mag level, and as low as +/-0.08 mag after correcting for the tilt
of the LMC.Comment: 7 pages, 6 figures, 1 data tabl
On the use of Principal Component Analysis in analysing Cepheid light curves
We show how Principal Component Analysis can be used to analyse the structure
of Cepheid light curves. This method is more efficient than Fourier analysis at
bringing out changes in light curve shape as a function of period. Using this
technique, we study the shape of fundamental and first overtone mode Cepheid
light curves in the Galaxy, LMC and SMC over a wide period range. For
fundamentals, we find evidence for structural changes at . It is suggested that the feature at is associated
with a resonance in the Cepheid normal mode spectrum. For overtones, we recover
the Z shape in the period plane and reproduce the metallicity
dependence of this Z shape.Comment: Accepted for publication in MNRA
The Period Changes of the Cepheid RT Aurigae
Observations of the light curve for the 3.7-day Cepheid RT Aur both before
and since 1980 indicate that the variable is undergoing an overall period
increase, amounting to +0.082 +-0.012 s/yr, rather than a period decrease, as
implied by all observations prior to 1980. Superposed on the star's O-C
variations is a sinusoidal trend that cannot be attributed to random
fluctuations in pulsation period. Rather, it appears to arise from light travel
time effects in a binary system. The derived orbital period for the system is P
= 26,429 +-89 days (72.36 +-0.24 years). The inferred orbital parameters from
the O-C residuals differ from those indicated by existing radial velocity data.
The latter imply the most reasonable results, namely a1 sin i = 9.09 (+-1.81) x
10^8 km and a minimum secondary mass of M2 = 1.15 +-0.25 Msun. Continued
monitoring of the brightness and radial velocity changes in the Cepheid are
necessary to confirm the long-term trend and to provide data for a proper
spectroscopic solution to the orbit.Comment: Accepted for publication in PASP (November 2007
Period-color and amplitude-color relations in classical Cepheid variables
In this paper we analyze the behavior of Galactic, LMC and SMC Cepheids in
terms of period-color (PC) and amplitude-color (AC) diagrams at the phases of
maximum, mean and minimum light. We find very different behavior between
Galactic and Magellanic Cloud Cepheids. Motivated by the recent report of a
break in LMC PC relations at 10 days (Tammann et al. 2002), we use the
F-statistical test to examine the PC relations at mean light in these three
galaxies. The results of the F-test support the existence of the a break in the
LMC PC(mean) relation, but not in the Galactic or SMC PC(mean) relations.
Furthermore, the LMC Cepheids also show a break at minimum light, which is not
seen in the Galactic and SMC Cepheids. We further discuss the effect on the
period-luminosity relations in the LMC due to the break in the PC(mean)
relation.Comment: 10 pages, 5 figures and 5 tables. MNRAS accepte
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