678 research outputs found
Vortex Solid-Liquid Transition in BiSrCaCuO with a High Density of Strong Pins
The introduction of a large density of columnar defects in %underdoped
BiSrCaCuO crystals does not, at sufficiently low
vortex densities, increase the irreversibility line beyond the first order
transition (FOT) field of pristine crystals. At such low fields, the flux line
wandering length behaves as in pristine
%BiSrCaCuO crystals. Next, vortex positional
correlations along the --axis in the vortex Bose glass at fields above the
FOT are smaller than in the low--field vortex solid. Third, the
Bose-glass-to-vortex liquid transition is signaled by a rapid decrease in
c-axis phase correlations. These observations are understood in terms of the
``discrete superconductor'' model.Comment: 4 pages, 4 figures Submitted to Phys. Rev. B Rapid Comm. 16-1-2004
Revised version 18-3-200
First order phase transition from the vortex liquid to an amorphous solid
We present a systematic study of the topology of the vortex solid phase in
superconducting BiSrCaCuO samples with low doses of
columnar defects. A new state of vortex matter imposed by the presence of
geometrical contours associated with the random distribution of columns is
found. The results show that the first order liquid-solid transition in this
vortex matter does not require a structural symmetry change.Comment: 4 pages, 5 figure
A mouse model of gestation-specific transient hyperglycemia for translational studies
The prevalence of gestational diabetes mellitus (GDM) is estimated at 14% globally, and in some countries, such as Singapore, exceeds 20%. Both women and children exposed to GDM have an increased risk of later metabolic diseases, cardiovascular disease and other health issues. Beyond lifestyle changes and pharmaceutical intervention using existing type 2 diabetes medications for expecting women, there are limited treatment options for women with GDM; targeting better outcomes of potentially affected infants is unexplored. Numerous animal models have been generated for understanding of pathological processes of GDM development and for development of treatment strategies. These models, however, suffer from limited windows of opportunity to examine risk factors and potential intervention options. By combining short-term high-fat diet (HFD) feeding and low-dose streptozotocin (STZ) treatments before pregnancy, we have established a mouse model with marked transient gestation-specific hyperglycemia, which allows testing of nutritional and pharmacological interventions before, during and beyond pregnancy
Support needs of Dutch young adult childhood cancer survivors
BACKGROUND: Studies about support needs of young adult childhood cancer survivors (YACCS) previously focused mainly on information needs. This study assessed support needs and associated factors (sociodemographic, medical, and psychosocial functioning) in Dutch YACCS. METHODS: YACCS (aged 18–30, diagnosed ≤ 18 years, time since diagnosis ≥ 5 years) cross-sectionally filled out a questionnaire regarding their need for various types of support (concrete information, personal counseling, and peer contact) in eight domains (physical consequences of childhood cancer, social-emotional consequences, relationships and sexuality, fertility, lifestyle, school and work, future perspective, insurance and mortgage), and questionnaires assessing health-related quality of life (PedsQL-YA), anxiety and depression (HADS), and fatigue (CIS-20R). Descriptive statistics were used to describe support needs. Linear regression was used to identify characteristics associated with support needs. RESULTS: One hundred fifty-one YACCS participated (response = 40%). Most YACCS reported a need for support in one or more domains (88.0%, N = 133). More than half of the participants reported a need for concrete information in the domains lifestyle, fertility, and physical consequences of childhood cancer and 25–50% in the domains insurance and mortgages, future perspective, and social-emotional consequences of childhood cancer. In the domains lifestyle and physical as well as emotional consequences of childhood cancer, 25–50% reported a need for counseling. Overall need for support was positively associated with middle (β = 0.26, p = 0.024) and high (β = 0.35, p = 0.014) compared to low educational attainment and (sub)clinical anxiety (β = 0.22, p = 0.017), and negatively associated with social functioning (β = − 0.37, p = 0.002) in multivariate analyses. CONCLUSION: YACCS report the strongest need for support, for concrete information, in the domains lifestyle, fertility, and physical consequences of childhood cancer. Associated factors were mostly socioeconomic and psychosocial in nature. Psychosocial care should be an integral part of survivorship care for YACCS, with screening for psychosocial problems, information provision including associated emotional consequences and support if necessary (psycho-education) and tailored interventions, and adequate referrals to more specialized care if necessary
Supercooling of the disordered vortex lattice in Bi_2Sr_2CaCu_2O_8+d
Time-resolved local induction measurements near to the vortex lattice
order-disorder transition in optimally doped
BiSrCaCuO single crystals shows that the
high-field, disordered phase can be quenched to fields as low as half the
transition field. Over an important range of fields, the electrodynamical
behavior of the vortex system is governed by the co-existence of the two phases
in the sample. We interpret the results in terms of supercooling of the
high-field phase and the possible first order nature of the order-disorder
transition at the ``second peak''.Comment: 4 pages, 3 figures. Submitted to Nature, July 10th, 1999; Rejected
August 8th for lack of broad interest Submitted to Physical Review Letters
September 10th, 199
Flux pinning in (1111) iron-pnictide superconducting crystals
Local magnetic measurements are used to quantitatively characterize
heterogeneity and flux line pinning in PrFeAsO_1-y and NdFeAs(O,F)
superconducting single crystals. In spite of spatial fluctuations of the
critical current density on the macroscopic scale, it is shown that the major
contribution comes from collective pinning of vortex lines by microscopic
defects by the mean-free path fluctuation mechanism. The defect density
extracted from experiment corresponds to the dopant atom density, which means
that dopant atoms play an important role both in vortex pinning and in
quasiparticle scattering. In the studied underdoped PrFeAsO_1-y and NdFeAs(O,F)
crystals, there is a background of strong pinning, which we attribute to
spatial variations of the dopant atom density on the scale of a few dozen to
one hundred nm. These variations do not go beyond 5% - we therefore do not find
any evidence for coexistence of the superconducting and the antiferromagnetic
phase. The critical current density in sub-T fields is characterized by the
presence of a peak effect, the location of which in the (B,T)-plane is
consistent with an order-disorder transition of the vortex lattice.Comment: 12 pages, submitted to Phys Rev.
Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals
Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K)
are studied using Josephson plasma resonance (JPR). From the data in zero
magnetic field, we obtain the penetration depth along the c-axis,
lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The
low plasma frequency allows us to study phase correlations over the whole
vortex solid (Bragg-glass) state. The JPR results yield a wandering length
r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its
increase with applied dc magnetic field can only be explained by the
renormalization of the tilt modulus by thermal fluctuations, and suggest the
latter is responsible for the dissociation of the vortices at the first order
transition.Comment: 4 pages, 5 figures. Submitted to Phys. Rev. Let
Collective pinning of a frozen vortex liquid in ultrathin superconducting YBa_2Cu_3O_7 films
The linear dynamic response of the two-dimensional (2D) vortex medium in
ultrathin YBa_2Cu_3O_7 films was studied by measuring their ac sheet impedance
Z over a broad range of frequencies \omega. With decreasing temperature the
dissipative component of Z exhibits, at a temperature T*(\omega) well above the
melting temperature of a 2D vortex crystal, a crossover from a thermally
activated regime involving single vortices to a regime where the response has
features consistent with a description in terms of a collectively pinned vortex
manifold. This suggests the idea of a vortex liquid which, below T*(\omega),
appears to be frozen at the time scales 1/\omega of the experiments.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Depinning transition in type-II superconductors
The surface impedance Z(f) of conventional isotropic materials has been
carefully measured for frequencies f ranging from 1 kHz to 3 MHz, allowing a
detailed investigation of the depinning transition. Our results exhibit the
irrelevance of classical ideas to the dynamics of vortex pinning. We propose a
new picture, where the linear ac response is entirely governed by disordered
boundary conditions of a rough surface, whereas in the bulk vortices respond
freely. The universal law for Z(f) thus predicted is in remarkable agreement
with experiment, and tentatively applies to microwave data in YBaCuO films.Comment: 4 pages, 4 figures, 14 reference
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