5,654 research outputs found
Long-range Ni/Mn structural order in epitaxial double perovskite La2NiMnO6 thin films
We report and compare the structural, magnetic, and optical properties of
ordered La2NiMnO6 thin films and its disordered LaNi0.5Mn0.5O3 counterpart. An
x-ray diffraction study reveals that the B-site Ni/Mn ordering induces
additional XRD reflections as the crystal symmetry is transformed from a
pseudocubic perovskite unit cell in the disordered phase to a monoclinic form
with larger lattice parameters for the ordered phase. Polarized Raman
spectroscopy studies reveal that the ordered samples are characterized by
additional phonon excitations that are absent in the disordered phase. The
appearance of these additional phonon excitations is interpreted as the
clearest signature of Brillouin zone folding as a result of the long-range
Ni/Mn ordering in La2NiMnO6. Both ordered and disordered materials display a
single ferromagnetic-to-paramagnetic transition. The ordered films display also
a saturation magnetization close to 4.8 mB/f.u. and a transition temperature
(FM-TC) around 270 K, while the disordered ones have only a 3.7 mB/f.u.
saturation magnetization and a FM-TC around 138 K. The differences in their
magnetic behaviours are understood based on the distinct local electronic
configurations of their Ni/Mn cations.Comment: 15 pages, 5 fig
Phase formation, phonon behavior, and magnetic properties of novel ferromagnetic La3BAlMnO9 (B = Co or Ni) triple perovskites
In the quest for novel magnetoelectric materials, we have grown, stabilized
and explored the properties of La3BAlMnO9 (B = Co or Mn) thin films. In this
paper, we report the influence of the growth parameters that promote B/Al/Mn
ordering in the pseudo-cubic unit cell and their likely influence on the
magnetic and multiferroic properties. The temperature dependence of the
magnetization shows that La3CoAlMnO9 is ferromagnetic up to 190 K while
La3NiAlMnO9 shows a TC of 130 K. The behavior of these films are compared and
contrasted with related La2BMnO6 double perovskites. It is observed that the
insertion of AlO6 octahedra between CoO6 and MnO6 suppresses significantly the
strength of the superexchange interaction, spin-phonon and spin-polar coupling.Comment: 13 pages, 3 fig
Electrons on a sphere in disorder potential
We investigate, both analytically and numerically, the behavior of the
electron gas on a sphere in the presence of point-like impurities. We find a
criterion when the disorder can be regarded as small one and the main effect is
the broadening of rotational multiplets. In the latter regime the statistics of
one impurity-induced band is studied numerically. The energy level spacing
distribution function follows the law P(s) ~ s exp(-a s^b) with 1<b<2. The
number variance shows various possibilities, strongly dependent on the chosen
model of disorder.Comment: 11 pages, REVTEX, 9 eps figures; references added to Sec.
K_S\rightarrow \gamma\gamma , K_L\rightarrow\pi^0\gamma\gamma$ and Unitarity
Agreement between the experimental value and the number predicted via a one-loop chiral perturbation
theory calculation has been cited as a success for the latter. On the other
hand the one-loop prediction for the closely related process has been found to be a factor three below the experimental
value. Using the inputs of unitarity and dispersion relations, we demonstrate
the importance of higher order loop effects to both of these processes.Comment: 20 pages (4 figures available on request), UMHEP-39
Hybrid squeezing of solitonic resonant radiation in photonic crystal fibers
We report on the existence of a novel kind of squeezing in photonic crystal
fibers which is conceptually intermediate between the four-wave mixing induced
squeezing, in which all the participant waves are monochromatic waves, and the
self-phase modulation induced squeezing for a single pulse in a coherent state.
This hybrid squeezing occurs when an arbitrary short soliton emits
quasi-monochromatic resonant radiation near a zero group velocity dispersion
point of the fiber. Photons around the resonant frequency become strongly
correlated due to the presence of the classical soliton, and a reduction of the
quantum noise below the shot noise level is predicted.Comment: 5 pages, 2 figure
Optimizing ribavirin dose in HIV/hepatitis C (HCV) co-infected individuals treated for HCV
Hepatitis C (HCV) and HIV share common transmission pathways and the acquisition of both viruses are relatively common. Concurrent treatment for HCV with highly active anti-retroviral therapy (HAART) should be considered in HIV co-infected individuals to decrease the progression of liver damage. Adverse effects and less satisfactory treatment outcomes are often concerns when treating co-infected individuals. Although, direct acting antivirals (DAAs) may increase SVR, they may not be possible because of drug-drug interactions. he objective of this study is to investigate the difference in response rates of HCV treatment in HIV co-infected inmates with varying doses of ribavirin. Retrospective medical chart reviews of 52 HCV/HIV co-infected inmates who underwent HCV therapy between 2003 and 2010. All received standard doses of pegylated interferon alpha 2a or 2b and 800–1600 mg of ribavirin depending on weight. The recommended dosage for genotypes 2 and 3 is 800 mg/day. For other genotypes, if weight is<75 kg, the recommended ribavirin dose is 1000 mg/day or 1200 mg/day if>75 kg. Efficacy was defined as attaining sustained virological response (SVR) six months post treatment. Univariate analyses was performed using SPSS-18; Chi-square test with p-value<0.05 was defined significant. 52 co-infected (3 females & 49 males) were identified. Mean age was 40±7 years. Caucasians accounted for 84.6%; First Nations for 13.5% and Asians 1.9%. 36 were concurrently on HAART. The genotype distribution was: geno 1, 66.0%; geno 2, 7.5%; geno 3, 26.4%. SVR by ribavirin dosage ratio (actual dosage/recommended dosage):=1.0; 41.2% (14/34),>1.0; 58.8% (20/34). Doses greater than 1.5 times were associated with higher adverse events and lower SVR. Suboptimal doses of weight-based ribavirin may be contributing to a lower treatment response in HCV/HIV co-infectants. In our experience, the optimal dose of ribavirin is between 1 and 1.2 times the current recommended dose. We recommend that ribavirin dose be individualized in co-infected in order to enhance the likelihood of achieving SVR. Dual therapy is more practical in many of our population because of chaotic lifestyle. Therefore optimizing the ribavirin dose should be initially undertaken
Emergence of geometrical optical nonlinearities in photonic crystal fiber nanowires
We demonstrate analytically and numerically that a subwavelength-core
dielectric photonic nanowire embedded in a properly designed photonic crystal
fiber cladding shows evidence of a previously unknown kind of nonlinearity (the
magnitude of which is strongly dependent on the waveguide parameters) which
acts on solitons so as to considerably reduce their Raman self-frequency shift.
An explanation of the phenomenon in terms of indirect pulse negative chirping
and broadening is given by using the moment method. Our conclusions are
supported by detailed numerical simulations.Comment: 5 pages, 3 figure
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