149 research outputs found
Multiferroic behavior in the new double-perovskite LuMnCoO
We present a new member of the multiferroic oxides, LuMnCoO, which we
have investigated using X-ray diffraction, neutron diffraction, specific heat,
magnetization, electric polarization, and dielectric constant measurements.
This material possesses an electric polarization strongly coupled to a net
magnetization below 35 K, despite the antiferromagnetic ordering of the Mn and Co spins in an configuration along the c-direction. We discuss the magnetic order
in terms of a condensation of domain boundaries between and
ferromagnetic domains, with each domain boundary
producing a net electric polarization due to spatial inversion symmetry
breaking. In an applied magnetic field the domain boundaries slide, controlling
the size of the net magnetization, electric polarization, and magnetoelectric
coupling
Genetic evidence of two sibling species within the Contracoecum ogmorhini Johnson & Mawson 1941 complex (Nematoda; Anisakidae) from otariid seals in boreal and austral regions
Genetic variation of Contracaecum ogmorhini (sensu lato) populations from different otariid seals of the northern
and southern hemisphere was studied on the basis of 18 enzyme loci as well as preliminary sequence analysis of
the mitochondrial cyt b gene (260 bp). Samples were collected from Zalophus californianus in the boreal region
and from Arctocephalus pusillus pusillus, A. pusillus doriferus and A. australis from the austral region. Marked
genetic heterogeneity was found between C. ogmorhini (sensu lato) samples from the boreal and austral region,
respectively. Two loci (Mdh-2 and NADHdh) showed fixed differences and a further three loci (Iddh, Mdh-1 and
6Pgdh) were highly differentiated between boreal and austral samples. Their average genetic distance was DNei =
0.36 at isozyme level. At mitochondrial DNA level, an average proportion of nucleotide substitution of 3.7% was
observed. These findings support the existence of two distinct sibling species, for which the names C. ogmorhini
(sensu stricto) and C. margolisi n. sp., respectively, for the austral and boreal taxon, are proposed. A description
for C. margolisi n. sp. is provided. No diagnostic morphological characters have so far been detected; on the other hand, two enzyme loci, Mdh-2 and NADHdh, fully diagnostic between the two species, can be used for the routine identification of males, females and larval stages. Mirounga leonina was found to host C. ogmorhini (s.s.) inmixed infections with C. osculatum (s.l.) (of which C. ogmorhini (s.l.) was in the past considered to be a synonym)
and C. miroungae; no hybrid genotypes were found,confirming the reproductive isolation of these three anisakid species. The hosts and geographical range so far recorded for C. margolisi n. sp. and C. ogmorhini (s.s.) are given
Dpes massless QCD have vacuum energy?
It is widely thought that this question has a positive answer, but we argue
that the support for this belief from both experiment and theory is weak or
nonexistent. We then list some of the ramifications of a negative answer.Comment: 8 pages, no figures, version to appear in NJ
Spiral spin-liquid and the emergence of a vortex-like state in MnScS
Spirals and helices are common motifs of long-range order in magnetic solids,
and they may also be organized into more complex emergent structures such as
magnetic skyrmions and vortices. A new type of spiral state, the spiral
spin-liquid, in which spins fluctuate collectively as spirals, has recently
been predicted to exist. Here, using neutron scattering techniques, we
experimentally prove the existence of a spiral spin-liquid in MnScS by
directly observing the 'spiral surface' - a continuous surface of spiral
propagation vectors in reciprocal space. We elucidate the multi-step ordering
behavior of the spiral spin-liquid, and discover a vortex-like triple-q phase
on application of a magnetic field. Our results prove the effectiveness of the
- Hamiltonian on the diamond lattice as a model for the spiral
spin-liquid state in MnScS, and also demonstrate a new way to realize a
magnetic vortex lattice.Comment: 10 pages, 11 figure
The discovery of an evolving dust scattered X-ray halo around GRB 031203
We report the first detection of a time-dependent, dust-scattered X-ray halo
around a gamma-ray burst. GRB 031203 was observed by XMM-Newton starting six
hours after the burst. The halo appeared as concentric ring-like structures
centered on the GRB location. The radii of these structures increased with time
as t^{1/2}, consistent with small-angle X-ray scattering caused by a large
column of dust along the line of sight to a cosmologically distant GRB. The
rings are due to dust concentrated in two distinct slabs in the Galaxy located
at distances of 880 and 1390 pc, consistent with known Galactic features. The
halo brightness implies an initial soft X-ray pulse consistent with the
observed GRB.Comment: 4 pages. 4 figures. Accepted for publication in ApJ Letter
Zeros of regular functions of quaternionic and octonionic variable: a division lemma and the camshaft effect
We study in detail the zero set of a regular function of a quaternionic or
octonionic variable. By means of a division lemma for convergent power series,
we find the exact relation existing between the zeros of two octonionic regular
functions and those of their product. In the case of octonionic polynomials, we
get a strong form of the fundamental theorem of algebra. We prove that the sum
of the multiplicities of zeros equals the degree of the polynomial and obtain a
factorization in linear polynomials.Comment: Proof of Lemma 7 rewritten (thanks to an anonymous reviewer
pygwb: Python-based library for gravitational-wave background searches
The collection of gravitational waves (GWs) that are either too weak or too
numerous to be individually resolved is commonly referred to as the
gravitational-wave background (GWB). A confident detection and model-driven
characterization of such a signal will provide invaluable information about the
evolution of the Universe and the population of GW sources within it. We
present a new, user-friendly Python--based package for gravitational-wave data
analysis to search for an isotropic GWB in ground--based interferometer data.
We employ cross-correlation spectra of GW detector pairs to construct an
optimal estimator of the Gaussian and isotropic GWB, and Bayesian parameter
estimation to constrain GWB models. The modularity and clarity of the code
allow for both a shallow learning curve and flexibility in adjusting the
analysis to one's own needs. We describe the individual modules which make up
{\tt pygwb}, following the traditional steps of stochastic analyses carried out
within the LIGO, Virgo, and KAGRA Collaboration. We then describe the built-in
pipeline which combines the different modules and validate it with both mock
data and real GW data from the O3 Advanced LIGO and Virgo observing run. We
successfully recover all mock data injections and reproduce published results.Comment: 32 pages, 14 figure
Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4
Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV2O4, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration
Dissipative and Non-dissipative Single-Qubit Channels: Dynamics and Geometry
Single-qubit channels are studied under two broad classes: amplitude damping
channels and generalized depolarizing channels. A canonical derivation of the
Kraus representation of the former, via the Choi isomorphism is presented for
the general case of a system's interaction with a squeezed thermal bath. This
isomorphism is also used to characterize the difference in the geometry and
rank of these channel classes. Under the isomorphism, the degree of decoherence
is quantified according to the mixedness or separability of the Choi matrix.
Whereas the latter channels form a 3-simplex, the former channels do not form a
convex set as seen from an ab initio perspective. Further, where the rank of
generalized depolarizing channels can be any positive integer upto 4, that of
amplitude damping ones is either 2 or 4. Various channel performance parameters
are used to bring out the different influences of temperature and squeezing in
dissipative channels. In particular, a noise range is identified where the
distinguishability of states improves inspite of increasing decoherence due to
environmental squeezing.Comment: 12 pages, 4 figure
Tumor Angiogenesis and Vascular Patterning: A Mathematical Model
Understanding tumor induced angiogenesis is a challenging problem with important consequences for diagnosis and treatment of cancer. Recently, strong evidences suggest the dual role of endothelial cells on the migrating tips and on the proliferating body of blood vessels, in consonance with further events behind lumen formation and vascular patterning. In this paper we present a multi-scale phase-field model that combines the benefits of continuum physics description and the capability of tracking individual cells. The model allows us to discuss the role of the endothelial cells' chemotactic response and proliferation rate as key factors that tailor the neovascular network. Importantly, we also test the predictions of our theoretical model against relevant experimental approaches in mice that displayed distinctive vascular patterns. The model reproduces the in vivo patterns of newly formed vascular networks, providing quantitative and qualitative results for branch density and vessel diameter on the order of the ones measured experimentally in mouse retinas. Our results highlight the ability of mathematical models to suggest relevant hypotheses with respect to the role of different parameters in this process, hence underlining the necessary collaboration between mathematical modeling, in vivo imaging and molecular biology techniques to improve current diagnostic and therapeutic tools
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