609 research outputs found
Elastic and magnetic effects on the infrared phonon spectra of MnF2
We measured the temperature dependent infrared reflectivity spectra of MnF2
between 4 K and room temperature. We show that the phonon spectrum undergoes a
strong renormalization at TN. The ab-initio calculation we performed on this
compound accurately predict the magnitude and the direction of the phonon
parameters changes across the antiferromagnetic transition, showing that they
are mainly induced by the magnetic order. In this material, we found that the
dielectric constant is mostly from phonon origin. The large change in the
lattice parameters with temperature seen by X-ray diffraction as well as the
A2u phonon softening below TN indicate that magnetic order induced distortions
in MnF2 are compatible with the ferroelectric instabilities observed in TiO2,
FeF2 and other rutile-type fluorides. This study also shows the anomalous
temperature evolution of the lower energy Eu mode in the paramagnetic phase,
which can be compared to that of the B1g one seen by Raman spectroscopy in many
isostructural materials. This was interpreted as being a precursor of a phase
transition from rutile to CaCl2 structure which was observed under pressure in
ZnF2.Comment: 8 pages, 8 figures, updated version accepted in PR
PENINGKATAN KECAKAPAN MASYARAKAT SONAF HONIS BONEN DALAM BUDIDAYA DAN PENGOLAHAN CABAI
Ketersediaan buah cabai di pasaran umumnya tidak stabil. Saat panen raya suplai cabai melimpah sehingga harganya rendah. Sebaliknya saat musim hujan, suplai cabai sangat terbatas sehingga harganya melonjak. Masyarakat desa Oeltua Kabupaten Kupang umumnya adalah petani dan peternak. Salah satu tanaman yang banyak diusahakan adalah cabai. Melalui kegiatan PKM ini dilakukan transfer ilmu pengetahuan dan keterampilan bagi Kelompok Tani Kaum Ibu Sonaf Honis Bonen dan masyarakat setempat untuk meningkatkan kecakapan dalam budidaya cabai serta pengolahan cabai, yaitu dengan pemanfaatan mulsa plastik hitam perak serta penggunaan food dehydrator dalam pengolahan buah cabai. Kegiatan dilakukan dengan metode penyuluhan dan diskusi serta demplot penggunaan mulsa plastik dalam budidaya cabai, serta praktek pengolahan buah cabai menggunakan food dehydrator. Mulsa plastik berguna untuk mencegah pertumbuhan gulma serta mengurangi evaporasi. Hal ini sesuai untuk Kabupaten Kupang yang termasuk daerah semi arid atau beriklim kering. Proses pengeringan buah cabai cukup sederhana sehingga mudah dipraktekkan oleh peserta kegiatan ini. Luaran kegiatan PKM ini berupa produk buah cabai kering, boncabai, serta serpihan cabai atau chilli-flake. Luaran akademik berupa publikasi ilmiah pada jurnal nasional terindeks Sinta-5, publikasi pada media lokal online serta visdeo kegiatan yang diunggah pada web-Fakultas Pertanian Undana
Gupta-Bleuler quantization for minimally coupled scalar fields in de Sitter space
We present in this paper a fully covariant quantization of the
minimally-coupled massless field on de Sitter space. We thus obtain a formalism
free of any infrared (e.g logarithmic) divergence. Our method is based on a
rigorous group theoretical approach combined with a suitable adaptation (Krein
spaces) of the Wightman-G\"{a}rding axiomatic for massless fields
(Gupta-Bleuler scheme). We make explicit the correspondence between unitary
irreducible representations of the de Sitter group and the field theory on de
Sitter space-time. The minimally-coupled massless field is associated with a
representation which is the lowest term of the discrete series of unitary
representations of the de Sitter group. In spite of the presence of negative
norm modes in the theory, no negative energy can be measured: expressions as
\le n_{k_1}n_{k_2}...|T_{00}|n_{k_1}n_{k_2}...\re are always positive.Comment: 20 pages, appear in class. quantum gra
Ferroelectric Solitons Crafted in Epitaxial Bismuth Ferrite Superlattices
In ferroelectrics, complex interactions among various degrees of freedom
enable the condensation of topologically protected polarization textures. Known
as ferroelectric solitons, these particle-like structures represent a new class
of materials with promise for beyond CMOS technologies due to their ultrafine
size and sensitivity to external stimuli. Such polarization textures have
scarcely been reported in multiferroics. Here, we report a range of soliton
topologies in bismuth ferrite strontium titanate superlattices. High-resolution
piezoresponse force microscopy and Cs-corrected high-angle annular dark-field
scanning transmission electron microscopy reveal a zoo of topologies, and
polarization displacement mapping of planar specimens reveals center-convergent
and divergent topological defects as small as 3 nm. Phase field simulations
verify that some of these topologies can be classed as bimerons, with a
topological charge of plus and minus one, and first-principles-based effective
Hamiltonian computations show that the co-existence of such structures can lead
to non-integer topological charges, a first observation in a BiFeO3-based
system. Our results open new opportunities in multiferroic topotronics
Graded Contractions of Affine Kac-Moody Algebras
The method of graded contractions, based on the preservation of the
automorphisms of finite order, is applied to the affine Kac-Moody algebras and
their representations, to yield a new class of infinite dimensional Lie
algebras and representations. After the introduction of the horizontal and
vertical gradings, and the algorithm to find the horizontal toroidal gradings,
I discuss some general properties of the graded contractions, and compare them
with the In\"on\"u-Wigner contractions. The example of is discussed
in detail.Comment: 23 pages, Ams-Te
Reprodutibilidade de uma escala para avaliar a percepção dos trabalhadores quanto ao ambiente e às condições de trabalho
The global tendency in the research of biological activity in endophytic fungi:a scientometric analysis
Expansions of algebras and superalgebras and some applications
After reviewing the three well-known methods to obtain Lie algebras and
superalgebras from given ones, namely, contractions, deformations and
extensions, we describe a fourth method recently introduced, the expansion of
Lie (super)algebras. Expanded (super)algebras have, in general, larger
dimensions than the original algebra, but also include the Inonu-Wigner and
generalized IW contractions as a particular case. As an example of a physical
application of expansions, we discuss the relation between the possible
underlying gauge symmetry of eleven-dimensional supergravity and the
superalgebra osp(1|32).Comment: Invited lecture delivered at the 'Deformations and Contractions in
Mathematics and Physics Workshop', 15-21 January 2006, Mathematisches
Forschungsinstitut Oberwolfach, German
Conformal linear gravity in de Sitter space II
From the group theoretical point of view, it is proved that the theory of
linear conformal gravity should be written in terms of a tensor field of rank-3
and mixed symmetry [Binegar, et al, Phys. Rev. D 27, (1983) 2249]. We obtained
such a field equation in de Sitter space [Takook, et al, J. Math. Phys. 51,
(2010) 032503]. In this paper, a proper solution to this equation is obtained
as a product of a generalized polarization tensor and a massless scalar field
and then the conformally invariant two-point function is calculated. This
two-point function is de Sitter invariant and free of any pathological
large-distance behavior.Comment: 16 pages, no figure, published versio
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