547 research outputs found
Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths
Using a hydrodynamic approach we examine bulk- and surface-induced second and
third harmonic generation from semiconductor nanowire gratings having a
resonant nonlinearity in the absorption region. We demonstrate resonant,
broadband and highly efficient optical frequency conversion: contrary to
conventional wisdom, we show that harmonic generation can take full advantage
of resonant nonlinearities in a spectral range where nonlinear optical
coefficients are boosted well beyond what is achievable in the transparent,
long-wavelength, non-resonant regime. Using femtosecond pulses with
approximately 500 MW/cm2 peak power density, we predict third harmonic
conversion efficiencies of approximately 1% in a silicon nanowire array, at
nearly any desired UV or visible wavelength, including the range of negative
dielectric constant. We also predict surface second harmonic conversion
efficiencies of order 0.01%, depending on the electronic effective mass,
bistable behavior of the signals as a result of a reshaped resonance, and the
onset fifth order nonlinear effects. These remarkable findings, arising from
the combined effects of nonlinear resonance dispersion, field localization, and
phase-locking, could significantly extend the operational spectral bandwidth of
silicon photonics, and strongly suggest that neither linear absorption nor skin
depth should be motivating factors to exclude either semiconductors or metals
from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure
Green's function of a finite chain and the discrete Fourier transform
A new expression for the Green's function of a finite one-dimensional lattice
with nearest neighbor interaction is derived via discrete Fourier transform.
Solution of the Heisenberg spin chain with periodic and open boundary
conditions is considered as an example. Comparison to Bethe ansatz clarifies
the relation between the two approaches.Comment: preprint of the paper published in Int. J. Modern Physics B Vol. 20,
No. 5 (2006) 593-60
Amicable pairs and aliquot cycles for elliptic curves
An amicable pair for an elliptic curve E/Q is a pair of primes (p,q) of good
reduction for E satisfying #E(F_p) = q and #E(F_q) = p. In this paper we study
elliptic amicable pairs and analogously defined longer elliptic aliquot cycles.
We show that there exist elliptic curves with arbitrarily long aliqout cycles,
but that CM elliptic curves (with j not 0) have no aliqout cycles of length
greater than two. We give conjectural formulas for the frequency of amicable
pairs. For CM curves, the derivation of precise conjectural formulas involves a
detailed analysis of the values of the Grossencharacter evaluated at a prime
ideal P in End(E) having the property that #E(F_P) is prime. This is especially
intricate for the family of curves with j = 0.Comment: 53 page
Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale
In the context of electromagnetism and nonlinear optical interactions damping
is generally introduced as a phenomenological, viscous term that dissipates
energy, proportional to the temporal derivative of the polarization. Here, we
follow the radiation reaction method presented in [G. W. Ford and R. F.
O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic
electrons of finite size, to introduce an explicit reaction force in the
Newtonian equation of motion, and derive a hydrodynamic equation that offers
new insight on the influence of damping in generic plasmas, metal-based and/or
dielectric structures. In these settings, we find new damping-dependent linear
and nonlinear source terms that suggest the damping coefficient is proportional
to the local charge density, and nonlocal contributions that stem from the
spatial derivative of the magnetic field and discuss the conditions that could
modify both linear and nonlinear electromagnetic responses.Comment: 11 pages, 1 figure, 19 reference
Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale
In the context of electromagnetism and nonlinear optical interactions damping
is generally introduced as a phenomenological, viscous term that dissipates
energy, proportional to the temporal derivative of the polarization. Here, we
follow the radiation reaction method presented in [G. W. Ford and R. F.
O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic
electrons of finite size, to introduce an explicit reaction force in the
Newtonian equation of motion, and derive a hydrodynamic equation that offers
new insight on the influence of damping in generic plasmas, metal-based and/or
dielectric structures. In these settings, we find new damping-dependent linear
and nonlinear source terms that suggest the damping coefficient is proportional
to the local charge density, and nonlocal contributions that stem from the
spatial derivative of the magnetic field and discuss the conditions that could
modify both linear and nonlinear electromagnetic responses.Comment: 11 pages, 1 figure, 19 reference
Acute respiratory distress syndrome in children with bilateral postviral pneumonia. Case report
USMF „Nicolae Testemițanu”, Catedra Anesteziologie și Reanimatologie, IMSP SCMC „V. Ignatenco”SDRA reprezintă cea mai severă manifestare
dintr-un spectru de răspunsuri apărute la
diverse leziuni pulmonare acute. Prezentăm
un caz clinic de tratament cu succes al
unui copil de 1 an si 6 luni, cu sindromul
de detresă respiratorie acută. Ca rezultat
pozitiv se conclude ca diagnosticarea cât
mai precoce a ARDS, urmată de instituirea
unui tratament eficace, măresc șansele de
recuperare a bolnavilor.ARDS represents the most rigorous
manifestation from large variety of acute
pulmonary lesions. We present a case
report of success treatment of a 1 year
and 6 months child with Acute respiratory
detress syndrome. As a positive
result we conclude that early diagnostic
and treatment in ARDS major the optimistic
chances in the recovering of the
patients
Респираторный дистресс-синдром взрослого со множеством пульмонарных и экстрапульмонарных осложнений в послеродовом периоде (Клинический случай)
USMF „Nicolae Testemiţanu” Catedra Anesteziologie şi Reanimatologie nr. 2, IMSP Institutul Mamei şi Copilului, IMSP
Institutul de Ftiziopneumologie „Chiril Draganiuc”, Clinica Otorinolaringologie, Spitalul Clinic RepublicanSummary. A case of a 36-year old woman with Adult Respiratory Distress Syndrome, which was complicated with pneumomediastinum and cardiogenic shock because of the extrapericardiac air tamponation of the heart. The pneumomediastinum was
resolved in 4 days. Cardiogenic shock provoked acute renal failure with oliguria and DIC syndrome, which caused acute
pulmonary embolism (on the 11th day of the treatment) and neurological aggravation up to coma I. Acute pulmonary embolism changed for the worse pre-existent acute respiratory failure, and the oxygen requirement increased to maximum. An exogenous pulmonary surfactant administration (on the 16-th day of the treatment) was the crucial decision in the management
of acute respiratory failure at the discussed patient because after that the oxygen requirement has considerably decreased.
On the 20-th day of treatment, oliguria has passed in polyuria, which lasted 9 days. In 7 days after the diuresis normalization,
paroxysmal sinus tachycardia with a heart rate of 200 was observed and successfully stopped. Neurological status was nearly
completely normalized, but swallowing infringement was observed till the 42 days of treatment. After 58 days of treatment, the
patient was sent home.Клинический случай респираторного дистресс-синдрома взрослого, осложненный пневмомедиастинумом и, как
следствие, кардиогенным шоком. Пневмомедиастинум разрешился через 4 дня. Кардиогенный шок спровоцировал
острую почечную недостаточность и ДВС-синдром, которые в свою очередь явились причиной тромбоэмболии
легочной артерии (на 11-й день лечения) и комы. Тромбоэмболия легочной артерии катастрофически ухудшила сердечную недостаточность, потребность в кислороде максимально возросла. Введение экзогенного сурфактанта (на
16-й день лечения) стало поворотным моментом в лечении острой дыхательной недостаточности, после которого потребность в кислороде значительно снизилась. На 20-й день лечения фаза олигурии острой почечной недостаточности сменилась фазой полиурии, которая продлилась 9 дней. На 7-ой день после восстановления адекватного диуреза был зарегистрирован пароксизм синусовой тахикардии (до 200 ударов/минуту), который был с успехом купирован. Неврологический статус пациентки почти полностью нормализовался. До 42 дня лечения наблюдались нарушения глотания вследствие ишемического инсульта. Через 52 лечения пациентка была выписана домой
Luminescence Properties of a Fibonacci Photonic Quasicrystal
We report the realization of an active one-dimensional Fibonacci photonic
quasi-crystal via spin coating. Manipulation of the luminescence properties of
an organic dye embedded in the quasi-crystal is presented and compared to
theoretical simulations. The luminescence occurs via the pseudo-bandedge mode
and follows the dispersion properties of the Fibonacci crystal. Time resolved
luminescence measurement of the active structure shows faster spontaneous
emission rate, indicating the effect of the large photon densities available at
the bandedge due to the presence of critically localized states. The
experimental results are in excellent agreement with the theoretical
calculations.Comment: PDF file, 14 pages 4 figure
Ordered arrays of multiferroic epitaxial nanostructures
Epitaxial heterostructures combining ferroelectric (FE) and ferromagnetic (FiM) oxides are a possible route to explore coupling mechanisms between the two independent order parameters, polarization and magnetization of the component phases. We report on the fabrication and properties of arrays of hybrid epitaxial nanostructures of FiM NiFe2O4 (NFO) and FE PbZr0.52Ti0.48O3 or PbZr0.2Ti0.8O3, with large range order and lateral dimensions from 200 nm to 1 micron
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