389 research outputs found
Discovery of pulsations, including possible pressure modes, in two new extremely low mass, He-core white dwarfs
We report the discovery of the second and third pulsating extremely low mass
white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS
J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 Msun and
effective temperatures below 10,000 K, establishing these putatively He-core
WDs as a cooler class of pulsating hydrogen-atmosphere WDs (DAVs, or ZZ Ceti
stars). The short-period pulsations evidenced in the light curve of J1112 may
also represent the first observation of acoustic (p-mode) pulsations in any WD,
which provide an exciting opportunity to probe this WD in a complimentary way
compared to the long-period g-modes also present. J1112 is a Teff = 9590 +/-
140 K and log(g) = 6.36 +/- 0.06 WD. The star displays sinusoidal variability
at five distinct periodicities between 1792-2855 s. In this star we also see
short-period variability, strongest at 134.3 s, well short of expected g-modes
for such a low-mass WD. The other new pulsating WD, J1518, is a Teff = 9900 +/-
140 K and log(g) = 6.80 +/- 0.05 WD. The light curve of J1518 is highly
non-sinusoidal, with at least seven significant periods between 1335-3848 s.
Consistent with the expectation that ELM WDs must be formed in binaries, these
two new pulsating He-core WDs, in addition to the prototype SDSS
J184037.78+642312.3, have close companions. However, the observed variability
is inconsistent with tidally induced pulsations and is so far best explained by
the same hydrogen partial-ionization driving mechanism at work in classic
C/O-core ZZ Ceti stars.Comment: 9 pages, 5 figures, accepted to The Astrophysical Journa
Radius constraints from high-speed photometry of 20 low-mass white dwarf binaries
We carry out high-speed photometry on 20 of the shortest-period, detached
white dwarf binaries known and discover systems with eclipses, ellipsoidal
variations (due to tidal deformations of the visible white dwarf), and Doppler
beaming. All of the binaries contain low-mass white dwarfs with orbital periods
less than 4 hr. Our observations identify the first eight tidally distorted
white dwarfs, four of which are reported for the first time here, which we use
to put empirical constraints on the mass-radius relationship for extremely
low-mass (<0.30 Msun) white dwarfs. We also detect Doppler beaming in several
of these binaries, which confirms the high-amplitude radial-velocity
variability. All of these systems are strong sources of gravitational
radiation, and long-term monitoring of those that display ellipsoidal
variations can be used to detect spin-up of the tidal bulge due to orbital
decay.Comment: 14 pages, 5 figures, accepted for publication in The Astrophysical
Journa
Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star
Using patterns in the oscillation frequencies of a white dwarf observed by
K2, we have measured the fastest rotation rate, 1.13(02) hr, of any isolated
pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy
from the SOAR telescope show that the star (SDSSJ0837+1856, EPIC 211914185) is
a 13,590(340) K, 0.87(03) solar-mass white dwarf. This is the highest mass
measured for any pulsating white dwarf with known rotation, suggesting a
possible link between high mass and fast rotation. If it is the product of
single-star evolution, its progenitor was a roughly 4.0 solar-mass
main-sequence B star; we know very little about the angular momentum evolution
of such intermediate-mass stars. We explore the possibility that this rapidly
rotating white dwarf is the byproduct of a binary merger, which we conclude is
unlikely given the pulsation periods observed.Comment: 5 pages, 4 figure, 1 table; accepted for publication in The
Astrophysical Journal Letter
TRANSMISSION DYNAMICS OF TOXOPLASMA GONDII IN ARCTIC FOXES (VULPES LAGOPUS): A LONG-TERM MARK-RECAPTURE SEROLOGIC STUDY AT KARRAK LAKE, NUNAVUT, CANADA
Transmission dynamics of Toxoplasma gondii, a parasite of importance for wildlife and human health, are enigmatic in the Arctic tundra, where free-ranging wild and domestic felid definitive hosts are absent and rarely observed, respectively. Through a multiyear mark-recapture study (2011– 17), serosurveillance was conducted to investigate transmission of T. gondii in Arctic foxes (Vulpes lagopus) in the Karrak Lake region, Nunavut, Canada. Sera from adult foxes and fox pups were tested for antibodies to T. gondii by using serologic methods, including the indirect fluorescent antibody test, direct agglutination test, and modified agglutination test. The overall seroprevalence was 39% in adults and 17% in pups. Mature foxes were more likely to be exposed (seroconvert) than young foxes (less than 1 yr old), with the highest level of seroprevalence in midaged foxes (2–4 yr old). Pups in two different litters were seropositive on emergence from the den, around 5 wk old, which could have been due to passive transfer of maternal antibody or vertical transmission of T. gondii from mother to offspring. The seropositive pups were born of seropositive mothers that were also seropositive the year before they gave birth, suggesting that vertical transmission might not be limited to litters from mothers exposed to T. gondii for the first time in pregnancy. All recaptured seropositive foxes remained seropositive on subsequent captures, suggesting that antibodies persist or foxes are constantly reexposed or a combination of both. The results of this study provided insights into how foxes were likely exposed to T. gondii, the dynamics of antibody persistence and immune response, and how the parasite was maintained in a terrestrial Arctic ecosystem in the absence of felid definitive hosts
PHarmacist Avoidance or Reductions in Medical Costs in CRITically Ill Adults: PHARM-CRIT Study
OBJECTIVES: To comprehensively classify interventions performed by ICU clinical pharmacists and quantify cost avoidance generated through their accepted interventions.
DESIGN: A multicenter, prospective, observational study was performed between August 2018 and January 2019.
SETTING: Community hospitals and academic medical centers in the United States.
PARTICIPANTS: ICU clinical pharmacists.
INTERVENTIONS: Recommendations classified into one of 38 intervention categories (divided into six unique sections) associated with cost avoidance.
MEASUREMENTS AND MAIN RESULTS: Two-hundred fifteen ICU pharmacists at 85 centers performed 55,926 interventions during 3,148 shifts that were accepted on 27,681 adult patient days and generated 5,822,539 CA), resource utilization (12,630 interventions; 9,680,036 cost avoidance), prophylaxis (1,639 interventions; 1,339,621 cost avoidance), and administrative/supportive tasks (4,768 interventions; 418 per intervention, 7,435 per ICU pharmacist shift. The annualized cost avoidance from an ICU pharmacist is 3.3:1 and 3.3:1 and $9.6:1
Asteroseismology of PG 1541651 and BPM 31594 with TESS
We present the photometric data from TESS for two known ZZ Ceti stars, PG
1541+651 and BPM 31594. Before TESS, both objects only had observations from
short runs from ground-based facilities, with three and one period detected,
respectively. The TESS data allowed the detection of multiple periodicities, 12
for PG 1541651, and six for BPM 31594, which enables us to perform a
detailed asteroseismological study. For both objects we found a representative
asteroseismic model with canonical stellar mass ~ 0.61 Msun and thick hydrogen
envelopes, thicker than 10^(-5.3) M_*. The detection of triplets in the Fourier
transform also allowed us to estimate mean rotation periods, being ~22 h for PG
1541+651 and 11.6 h for BPM 31594, which is consistent with range of values
reported for other ZZ Ceti stars.Comment: 12 pages, 11 figures. Accepted for publication in MNRA
Coactivation index of children with congenital upper limb reduction deficiencies before and after using a wristdriven 3D printed partial hand prosthesis
Background: Co-contraction is the simultaneous activation of agonist and antagonist muscles that produces forces around a joint. It is unknown if the use of a wrist-driven 3D printed transitional prostheses has any influence on the neuromuscular motor control strategies of the affected hand of children with unilateral upper-limb reduction deficiencies. Thus, the purpose of the current investigation was to examine the coactivation index (CI) of children with congenital upper-limb reduction deficiencies before and after 6 months of using a wrist-driven 3D printed partial hand prosthesis.
Methods: Electromyographic activity of wrist flexors and extensors (flexor carpi ulnaris and extensor digitorum) was recorded during maximal voluntary contraction of the affected and non-affected wrists. Co-contraction was calculated using the coactivation index and was expressed as percent activation of antagonist over agonist. Nine children (two girls and seven boys, 6 to 16 years of age) with congenital upper-limb deficiencies participated in this study and were fitted with a wrist-driven 3D printed prosthetic hand. From the nine children, five (two girls and three boys, 7 to 10 years of age) completed a second visit after using the wrist-driven 3D printed partial hand prosthesis for 6 months.
Results: Separate two-way repeated measures ANOVAs were performed to analyze the coactivation index and strength data. There was a significant main effect for hand with the affected hand resulting in a higher coactivation index for flexion and extension than the non-affected hand. For wrist flexion there was a significant main effect for time indicating that the affected and non-affected hand had a significantly lower coactivation index after a period of 6 months.
Conclusion: The use of a wrist-driven 3D printed hand prosthesis lowered the coactivation index by 70% in children with congenital upper limb reduction deficiencies. This reduction in coactivation and possible improvement in motor control strategies can potentially improve prosthetic rehabilitation outcomes
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