12,093 research outputs found
Magnetization Measurements on Single Crystals of Superconducting Ba0.6K0.4BiO3
Extensive measurements of the magnetization of superconducting single crystal
samples of Ba0.6K0.4BiO3} have been made using SQUID and cantilever force
magnetometry at temperatures ranging between 1.3 and 350 K and in magnetic
fields from near zero to 27 T. Hysteresis curves of magnetization versus field
allow a determination of the thermodynamic critical field, the reversibility
field, and the upper critical field as a function of temperature. The lower
critical field is measured seperately and the Ginzburg-Landau parameter is
found to be temperature dependent. All critical fields have higher T = 0 limits
than have been previously noted and none of the temperature dependence of the
critical fields follow the expected power laws leading to possible alternate
interpretation of the thermodynamic nature of the superconducting transition.Comment: 33 pages, 11 figures, accepted for publication in Philosophical
Magazine B on 7 August 1999. This paper supplies the experimental details for
the argument presented in our PRL 82 (1999) p. 4532-4535 (also at
cond-mat/9904288
Young and middle age pulsar light-curve morphology: Comparison of Fermi observations with gamma-ray and radio emission geometries
Thanks to the huge amount of gamma-ray pulsar photons collected by the Fermi
Large Area Telescope since June 2008, it is now possible to constrain gamma-ray
geometrical models by comparing simulated and observed light-curve
morphological characteristics. We assumed vacuum-retarded dipole pulsar
magnetic field and tested simulated and observed morphological light-curve
characteristics in the framework of two pole emission geometries, Polar Cap
(PC), radio, and Slot Gap (SG), and Outer Gap (OG)/One Pole Caustic (OPC)
emission geometries. We compared simulated and observed/estimated light-curve
morphological parameters as a function of observable and non-observable pulsar
parameters. The PC model gives the poorest description of the LAT pulsar
light-curve morphology. The OPC best explains both the observed gamma-ray peak
multiplicity and shape classes. The OPC and SG models describe the observed
gamma-ray peak-separation distribution for low- and high-peak separations,
respectively. This suggests that the OPC geometry best explains the single-peak
structure but does not manage to describe the widely separated peaks predicted
in the framework of the SG model as the emission from the two magnetic
hemispheres. The OPC radio-lag distribution shows higher agreement with
observations suggesting that assuming polar radio emission, the gamma-ray
emission regions are likely to be located in the outer magnetosphere. The
larger agreement between simulated and LAT estimations in the framework of the
OPC suggests that the OPC model best predicts the observed variety of profile
shapes. The larger agreement between observations and the OPC model jointly
with the need to explain the abundant 0.5 separated peaks with two-pole
emission geometries, calls for thin OPC gaps to explain the single-peak
geometry but highlights the need of two-pole caustic emission geometry to
explain widely separated peaks.Comment: 28 pages, 20 figures, 8 tables; accepted for publication in Astronomy
and Astrophysic
Field-induced magnetic behavior in quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8: A single-crystal neutron diffraction study
BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system
that can be described in terms of Tomonaga-Luttinger liquid physics. This is
explored in the present study where the magnetic field-temperature phase
diagram is thoroughly established up to 12 T using single-crystal neutron
diffraction. The transition from the N\'eel phase to the incommensurate
longitudinal spin density wave (LSDW) phase through a first-order transition,
as well as the critical exponents associated with the paramagnetic to ordered
phase transitions, and the magnetic order both in the N\'eel and in the LSDW
phase are determined, thus providing a stringent test for the theory.Comment: 17 pages with 15 figure
Rotational velocities of A-type stars II. Measurement of vsini in the northern hemisphere
This work is the second part of the set of measurements of vsini for A-type
stars, begun by Royer et al. (2002). Spectra of 249 B8 to F2-type stars
brighter than V=7 have been collected at Observatoire de Haute-Provence (OHP).
Fourier transforms of several line profiles in the range 4200--4600 A are used
to derive vsini from the frequency of the first zero. Statistical analysis of
the sample indicates that measurement error mainly depends on vsini and this
relative error of the rotational velocity is found to be about 5% on average.
The systematic shift with respect to standard values from Slettebak et al.
(1975), previously found in the first paper, is here confirmed. Comparisons
with data from the literature agree with our findings: vsini values from
Slettebak et al. are underestimated and the relation between both scales
follows a linear law: vsini(new) = 1.03 vsini(old) + 7.7. Finally, these data
are combined with those from the previous paper (Royer et al. 2002), together
with the catalogue of Abt & Morrell (1995). The resulting sample includes some
2150 stars with homogenized rotational velocities.Comment: 16 pages, includes 13 figures, accepted in A&
Neutron diffraction investigation of the H-T phase diagram above the longitudinal incommensurate phase of BaCo2V2O8
The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has
been shown to be describable by the Tomonaga-Luttinger liquid theory in its
gapless phase induced by a magnetic field applied along the Ising axis. Above
3.9 T, this leads to an exotic field-induced low-temperature magnetic order,
made of a longitudinal incommensurate spin-density wave, stabilized by weak
interchain interactions. By single-crystal neutron diffraction we explore the
destabilization of this phase at a higher magnetic field. We evidence a
transition at around 8.5 T towards a more conventional magnetic structure with
antiferromagnetic components in the plane perpendicular to the magnetic field.
The phase diagram boundaries and the nature of this second field-induced phase
are discussed with respect to previous results obtained by means of nuclear
magnetic resonance and electron spin resonance, and in the framework of the
simple model based on the Tomonaga-Luttinger liquid theory, which obviously has
to be refined in this complex system.Comment: 7 pages, 5 figure
Cosmic-ray propagation properties for an origin in SNRs
We have studied the impact of cosmic-ray acceleration in SNR on the spectra
of cosmic-ray nuclei in the Galaxy using a series expansion of the propagation
equation, which allows us to use analytical solutions for part of the problem
and an efficient numerical treatment of the remaining equations and thus
accurately describes the cosmic-ray propagation on small scales around their
sources in three spatial dimensions and time. We found strong variations of the
cosmic-ray nuclei flux by typically 20% with occasional spikes of much higher
amplitude, but only minor changes in the spectral distribution. The locally
measured spectra of primary cosmic rays fit well into the obtained range of
possible spectra. We further showed that the spectra of the secondary element
Boron show almost no variations, so that the above findings also imply
significant fluctuations of the Boron-to-Carbon ratio. Therefore the commonly
used method of determining CR propagation parameters by fitting
secondary-to-primary ratios appears flawed on account of the variations that
these ratios would show throughout the Galaxy.Comment: Accepted for publication in Ap
Study protocol: addressing evidence and context to facilitate transfer and uptake of consultation recording use in oncology: a knowledge translation implementation study
Background:
The time period from diagnosis to the end of treatment is challenging for newly diagnosed cancer patients. Patients have a substantial need for information, decision aids, and psychosocial support. Recordings of initial oncology consultations improve information recall, reduce anxiety, enhance patient satisfaction with communication, and increase patients' perceptions that the essential aspects of their disease and treatment have been addressed during the consultation. Despite the research evidence supporting the provision of consultation recordings, uptake of this intervention into oncology practice has been slow. The primary aim of this project is to conduct an implementation study to explicate the contextual factors, including use of evidence, that facilitate and impede the transfer and uptake of consultation-recording use in a sample of patients newly diagnosed with breast or prostate cancer.
Methods:
Sixteen oncologists from cancer centres in three Canadian cities will participate in this three-phase study. The preimplementation phase will be used to identify and address those factors that are fundamental to facilitating the smooth adoption and delivery of the intervention during the implementation phase. During the implementation phase, breast and prostate cancer patients will receive a recording of their initial oncology consultation to take home. Patient interviews will be conducted in the days following the consultation to gather feedback on the benefits of the intervention. Patients will complete the Digital Recording Use Semi-Structured Interview (DRUSSI) and be invited to participate in focus groups in which their experiences with the consultation recording will be explored. Oncologists will receive a summary letter detailing the benefits voiced by their patients. The postimplementation phase includes a conceptual framework development meeting and a seven-point dissemination strategy.
Discussion:
Consultation recording has been used in oncology, family medicine, and other medicine specialties, and despite affirming evidence and probable applications to a large number of diseases and a variety of clinical contexts, clinical adoption of this intervention has been slow. The proposed study findings will advance our conceptual knowledge of the ways to enhance uptake of consultation recordings in oncology
Investigação sobre a capacidade de sobrevivência durante o inverno na ilha Terceira, Açores, de Istocheta aldrichi (Mesnil) (Diptera: Tachinidae) um parasitóide de Popillia japonica Newman (Coleoptera: Scarabaeidae).
A study of diapause in the parasitic fly Istocheta aldrichi (Diptera: Tachinidae) was
undertaken to help investigate the possibility of its establishment in Terceira as a biological control agent of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae). It was
concluded that pupae should be imported from the USA only when they are almost ready to
emerge, and to optimise rearing conditions there to increase emergence percentages. Conditions are not ideal for its development in Terceira, as this univoltine parasitoid has a high pupal mortality both in laboratory cultures and outdoors during the overwintering period. These studies should continue until I. aldrichi has become established in the Azores
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