1,846 research outputs found
GW Librae: Still Hot Eight Years Post-Outburst
We report continued Hubble Space Telescope (HST) ultraviolet spectra and
ground-based optical photometry and spectroscopy of GW Librae eight years after
its largest known dwarf nova outburst in 2007. This represents the longest
cooling timescale measured for any dwarf nova. The spectra reveal that the
white dwarf still remains about 3000 K hotter than its quiescent value. Both
ultraviolet and optical light curves show a short period of 364-373 s, similar
to one of the non-radial pulsation periods present for years prior to the
outburst, and with a similar large UV/optical amplitude ratio. A large
modulation at a period of 2 h (also similar to that observed prior to outburst)
is present in the optical data preceding and during the HST observations, but
the satellite observation intervals did not cover the peaks of the optical
modulation so it is not possible to determine its corresponding UV amplitude.
The similarity of the short and long periods to quiescent values implies the
pulsating, fast spinning white dwarf in GW Lib may finally be nearing its
quiescent configuration.Comment: 6 figures, accepted in A
Partnerships for child health: capitalising on links between the sustainable development goals
The Galactic Inner Halo: Searching for White Dwarfs and Measuring the Fundamental Galactic Constant, Vo/Ro
We establish an extragalactic, zero-motion frame of reference within the
deepest optical image of a globular star cluster, an HST 123-orbit exposure of
M4 (GO 8679, cycle 9). The line of sight beyond M4 (l,b (deg) = 351,16)
intersects the inner halo (spheroid) of our Galaxy at a tangent-point distance
of 7.6 kpc (for Ro = 8 kpc). We isolate these spheroid stars from the cluster
based on their proper motions over the 6-year baseline between these and
previous epoch HST data (GO 5461, cycle 4). Distant background galaxies are
also found on the same sight line using image-morphology techniques. This fixed
reference frame allows us to independently determine the fundamental Galactic
constant, Vo/Ro = 25.3 +/- 2.6 km/s/kpc, thus providing a velocity of the Local
Standard of Rest, v = 202.7 +/- 24.7 km/s for Ro = 8.0 +/- 0.5 kpc. Secondly,
the galaxies allow a direct measurement of M4's absolute proper motion,
mu_total = 22.57 +/- 0.76 mas/yr, in excellent agreement with recent studies.
The clear separation of galaxies from stars in these deep data also allow us to
search for inner-halo white dwarfs. We model the conventional Galactic
contributions of white dwarfs along our line of sight and predict 7.9 (thin
disk), 6.3 (thick disk) and 2.2 (spheroid) objects to the limiting magnitude at
which we can clearly delineate stars from galaxies (V = 29). An additional 2.5
objects are expected from a 20% white dwarf dark halo consisting of 0.5 Mo
objects, 70% of which are of the DA type. After considering the kinematics and
morphology of the objects in our data set, we find the number of white dwarfs
to be consistent with the predictions for each of the conventional populations.
However, we do not find any evidence for dark halo white dwarfs.Comment: 31 pages, including 6 diagrams and 2 tables. Accepted for publication
in Ap
Benefits associated with improving fatigue regulations for cargo pilots
This study investigated the potential business benefits of improving fatigue regulations for cargo pilots in Brazil. The research objectives were to compare fatigue levels between cargo and passenger operations, identify regulatory inefficiencies for cargo operators, simulate proposed changes, and analyze cost scenarios. The experimental design involved a review of fatigue regulations in Brazil and the USA, analyzing pilot scheduling data, and the creation of hypothetical flexible scheduling scenarios for 70 pilots flying 16,500 hours annually. We reviewed NTSB data on fatigue-related incidents in US cargo operations with flexible regulations and from the fatigue program of LATAM Cargo.
Comparisons between the USA and the rest of the world showed that the rate of accidents per number of cargo flights in the USA is below average, with most accidents not attributed to fatigue. The results indicated that aligning with the US CFR 117 could improve cargo pilot availability in Brazil by 34.28%, with a potential cost savings of up to $3.6 million for an airline of that size.
This research highlights the importance of flexibility and adaptation in fatigue management and mental health programs for pilots in the aviation industry, particularly cargo operations. Introducing more flexible fatigue regulations for cargo pilots could lead to operational efficiencies and potential cost savings without compromising safety. Further research needs to explore the impacts of these changes on passenger operations and to gather feedback from pilots and unions regarding extended pilot schedules. The proposed regulatory changes focused on maximum duty time, flight hours, rest periods, and monthly/annual limits
Effect of a Single Amino Acid Change in MHC Class I Molecules on the Rate of Progression to AIDS
Background From studies of genetic polymorphisms and the rate of progression from human immunodeficiency virus type 1 (HIV-1) infection to the acquired immunodeficiency syndrome (AIDS), it appears that the strongest susceptibility is conferred by the major-histocompatibility-complex (MHC) class I type HLA-B*35,Cw*04 allele. However, cytotoxic T-lymphocyte responses have been observed against HIV-1 epitopes presented by HLA-B*3501, the most common HLA-B*35 subtype. We examined subtypes of HLA-B*35 in five cohorts and analyzed the relation of structural differences between HLA-B*35 subtypes to the risk of progression to AIDS. Methods Genotyping of HLA class I loci was performed for 850 patients who seroconverted and had known dates of HIV-1 infection. Survival analyses with respect to the rate of progression to AIDS were performed to identify the effects of closely related HLAB* 35 subtypes with different peptide-binding specificities.
Results HLA-B*35 subtypes were divided into two groups according to peptide-binding specificity: the HLA-B*35-PY group, which consists primarily of HLAB* 3501 and binds epitopes with proline in position 2 and tyrosine in position 9; and the more broadly reactive HLA-B*35-Px group, which also binds epitopes with proline in position 2 but can bind several different amino acids (not including tyrosine) in position 9. The influence of HLA-B*35 in accelerating progression to AIDS was completely attributable to HLAB* 35-Px alleles, some of which differ from HLA-B*35- PY alleles by only one amino acid residue.
Conclusions This analysis shows that, in patients with HIV-1 infection, a single amino acid change in HLA molecules has a substantial effect on the rate of progression to AIDS. The different consequences of HLA-B*35-PY and HLA-B*35-Px in terms of disease progression highlight the importance of the epitope specificities of closely related class I molecules in the immune defense against HIV-1
A Rydberg Quantum Simulator
Following Feynman and as elaborated on by Lloyd, a universal quantum
simulator (QS) is a controlled quantum device which reproduces the dynamics of
any other many particle quantum system with short range interactions. This
dynamics can refer to both coherent Hamiltonian and dissipative open system
evolution. We investigate how laser excited Rydberg atoms in large spacing
optical or magnetic lattices can provide an efficient implementation of a
universal QS for spin models involving (high order) n-body interactions. This
includes the simulation of Hamiltonians of exotic spin models involving
n-particle constraints such as the Kitaev toric code, color code, and lattice
gauge theories with spin liquid phases. In addition, it provides the
ingredients for dissipative preparation of entangled states based on
engineering n-particle reservoir couplings. The key basic building blocks of
our architecture are efficient and high-fidelity n-qubit entangling gates via
auxiliary Rydberg atoms, including a possible dissipative time step via optical
pumping. This allows to mimic the time evolution of the system by a sequence of
fast, parallel and high-fidelity n-particle coherent and dissipative Rydberg
gates.Comment: 8 pages, 4 figure
An argument for the use of Aristotelian method in bioethics
The main claim of this paper is that the method outlined and used in Aristotle's Ethics is an appropriate and credible one to use in bioethics. Here “appropriate” means that the method is capable of establishing claims and developing concepts in bioethics and “credible” that the method has some plausibility, it is not open to obvious and immediate objection. It begins by suggesting why this claim matters and then gives a brief outline of Aristotle's method. The main argument is made in three stages. First, it is argued that Aristotelian method is credible because it compares favourably with alternatives. In this section it is shown that Aristotelian method is not vulnerable to criticisms that are made both of methods that give a primary place to moral theory (such as utilitarianism) and those that eschew moral theory (such as casuistry and social science approaches). As such, it compares favourably with these other approaches that are vulnerable to at least some of these criticisms. Second, the appropriateness of Aristotelian method is indicated through outlining how it would deal with a particular case. Finally, it is argued that the success of Aristotle's philosophy is suggestive of both the credibility and appropriateness of his method.</p
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