250 research outputs found
X-wave mediated instability of plane waves in Kerr media
Plane waves in Kerr media spontaneously generate paraxial X-waves (i.e.
non-dispersive and non-diffractive pulsed beams) that get amplified along
propagation. This effect can be considered a form of conical emission (i.e.
spatio-temporal modulational instability), and can be used as a key for the
interpretation of the out of axis energy emission in the splitting process of
focused pulses in normally dispersive materials. A new class of spatio-temporal
localized wave patterns is identified. X-waves instability, and nonlinear
X-waves, are also expected in periodical Bose condensed gases.Comment: 4 pages, 6 figure
Ultra-precise measurement of optical frequency ratios
We developed a novel technique for frequency measurement and synthesis, based
on the operation of a femtosecond comb generator as transfer oscillator. The
technique can be used to measure frequency ratios of any optical signals
throughout the visible and near-infrared part of the spectrum. Relative
uncertainties of for averaging times of 100 s are possible. Using a
Nd:YAG laser in combination with a nonlinear crystal we measured the frequency
ratio of the second harmonic at 532 nm to the fundamental at
1064 nm, .Comment: 4 pages, 4 figure
Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation
Numerical simulations of the onset phase of continuous wave supercontinuum
generation from modulation instability show that the structure of the field as
it develops can be interpreted in terms of the properties of Akhmediev
Breathers. Numerical and analytical results are compared with experimental
measurements of spectral broadening in photonic crystal fiber using nanosecond
pulsesComment: 22 pages, 6 figure
Mechanisms of Myocardial Injury in Coronavirus Disease 2019
Coronavirus disease 2019 (COVID-19) predominantly presents with symptoms of fever, fatigue, cough and respiratory failure. However, it appears to have a unique interplay with cardiovascular disease (CVD); patients with pre-existing CVD are at highest risk for mortality from COVID-19, along with the elderly. COVID-19 contributes to cardiovascular complications including arrhythmias, myocardial dysfunction and myocardial inflammation. Although the exact mechanism of myocardial inflammation in patients with COVID-19 is not known, several plausible mechanisms have been proposed based on early observational reports. In this article, the authors summarise the available literature on mechanisms of myocardial injury in COVID-19
Absolute Frequency Measurements of the Hg^+ and Ca Optical Clock Transitions with a Femtosecond Laser
The frequency comb created by a femtosecond mode-locked laser and a
microstructured fiber is used to phase coherently measure the frequencies of
both the Hg^+ and Ca optical standards with respect to the SI second as
realized at NIST. We find the transition frequencies to be f_Hg=1 064 721 609
899 143(10) Hz and f_Ca=455 986 240 494 158(26) Hz, respectively. In addition
to the unprecedented precision demonstrated here, this work is the precursor to
all-optical atomic clocks based on the Hg^+ and Ca standards. Furthermore, when
combined with previous measurements, we find no time variations of these atomic
frequencies within the uncertainties of |(df_Ca/dt)/f_Ca| < 8 x 10^{-14}
yr^{-1}, and |(df_Hg/dt)/f_Hg|< 30 x 10^{-14} yr^{-1}.Comment: 6 pages, including 4 figures. RevTex 4. Submitted to Phys. Rev. Let
Classification and feature selection algorithms for multi-class CGH data
Recurrent chromosomal alterations provide cytological and molecular positions for the diagnosis and prognosis of cancer. Comparative genomic hybridization (CGH) has been useful in understanding these alterations in cancerous cells. CGH datasets consist of samples that are represented by large dimensional arrays of intervals. Each sample consists of long runs of intervals with losses and gains
Policiklički aromatski ugljikovodici u zraku okolice plinskog polja Molve
Small-volume air samples (~7 m3 per 24 h) of airborne PM10 particle fraction were collected on quartz fibre filters at two measuring sites in the vicinity of the gas field Molve in April and July 2006. It took five to seven days for each sample to collect and one month to collect five to seven samples. Mass concentrations of PM10 fractions were determined by gravimetry while PAHs were analysed using a HPLC with a fluorescent detector. The analysis included fluoranthene (Flu), pyrene (Pyr), benzo(a)anthracene (BaA), chrysene (Cry), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), benzo(ghi)perylene (BghiP) and indene(1,2,3-cd)pyrene (Ind). Average concentrations of all PAHs in April at site A were slightly higher than at site B while in July they were lower and similar on both sites. Average BaP concentration measured at site A in April was 0.156 ng m-3 and at site B 0.129 ng m-3, while July BaP averages were 0.022 ng m-3 at both sites. In both months, the mass concentration of BaP was lower than the limit value (1 ng m-3) and well below the tolerant value (2 ng m-3) set by a Croatian regulation of 2005. This suggests that the air near gas field Molve was of acceptable quality in respect to BaP at the time of the measurement.Uzorci PM10 frakcije lebdećih čestica skupljani su prosisavanjem malog volumena zraka (~7 m3 za 24 h) kroz filtre od kvarcnih vlakana. Svaki je uzorak skupljan tijekom pet do sedam dana na dva mjerna mjesta u okolici plinskog polja Molve. Uzorkovanje je provedeno tijekom travnja i srpnja 2006. godine. Masene koncentracije PM10 frakcije određene su gravimetrijski, dok je analiza policikličkih aromatskih ugljikovodika (PAU) rađena tekućinskom kromatografijom visoke djelotvornosti (HPLC) s fluorescentnim detektorom. Mjereni su sljedeći PAU: fluoranten, piren, benzo(a)antracen, krizen, benzo(b)fluoranten, benzo(k)fluoranten, benzo(a)piren, benzo(ghi)perilen i indeno(1,2,3-cd)piren. Srednje vrijednosti masenih koncentracija svih PAU u travnju na mjernome mjestu A bile su neznatno više od onih na mjernome mjestu B, dok su u srpnju na oba mjerna mjesta bile vrlo slične. Srednja vrijednost koncentracije BaP izmjerenog u travnju na mjernome mjestu A bila je viša od vrijednosti izmjerene na mjernome mjestu B. U srpnju su srednje vrijednosti bile znatno niže i na oba mjerna mjesta iznosile su 0.022 ng m-3. Iz rezultata dobivenih mjerenjem vidljivo je da je koncentracija benzo(a)pirena bila znatno niža od granične vrijednosti (1 ng m-3) i tolerantne vrijednosti (1 ng m-3, Uredba iz 2005.), pa možemo zaključiti da je zrak u okolici plinskog polja Molve tijekom istraživanog razdoblja bio prve kategorije kakvoće
On the Properties of Two Pulses Propagating Simultaneously in Different Dispersion Regimes in a Nonlinear Planar Waveguide
Properties of two pulses propagating simultaneously in different dispersion
regimes, anomalous and normal, in a Kerr-type planar waveguide are studied in
the framework of the nonlinear Schroedinger equation. Catastrophic
self-focusing and spatio-temporal splitting of the pulses is investigated. For
the limiting case when the dispersive term of the pulse propagating in the
normal dispersion regime can be neglected an indication of a possibility of a
stable self-trapped propagation of both pulses is obtained.Comment: 18 pages (including 15 eps figures
Modulational instability of bright solitary waves in incoherently coupled nonlinear Schr\"odinger equations
We present a detailed analysis of the modulational instability (MI) of
ground-state bright solitary solutions of two incoherently coupled nonlinear
Schr\"odinger equations. Varying the relative strength of cross-phase and
self-phase effects we show existence and origin of four branches of MI of the
two-wave solitary solutions. We give a physical interpretation of our results
in terms of the group velocity dispersion (GVD) induced polarization dynamics
of spatial solitary waves. In particular, we show that in media with normal GVD
spatial symmetry breaking changes to polarization symmetry breaking when the
relative strength of the cross-phase modulation exceeds a certain threshold
value. The analytical and numerical stability analyses are fully supported by
an extensive series of numerical simulations of the full model.Comment: Physical Review E, July, 199
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