Photon localization barrier can be overcome

In contradistinction to a widespread belief that the spatial localization of photons is restricted by a power-law falloff of the photon energy density, I.Bialynicki-Birula [Phys. Rev. Lett. 80, 5247 (1998)] has proved that any stronger -- up to an almost exponential -- falloff is allowed. We are showing that for certain specifically designed cylindrical one-photon states the localization is even better in lateral directions. If the photon state is built from the so-called focus wave mode, the falloff in the waist cross-section plane turns out to be quadratically exponential (Gaussian) and such strong localization persists in the course of propagation.Comment: Short communication -- 4 pages, 2 figure

Population Pharmacokinetics and Pharmacodynamics of Dobutamine in Neonates on the First Days of Life

Aims: To describe the pharmacokinetics (PK) and concentration‐related effects of dobutamine in critically ill neonates in the first days of life, using nonlinear mixed effects modelling. Methods: Dosing, plasma concentration and haemodynamic monitoring data from a dose‐escalation study were analysed with a simultaneous population PK and pharmacodynamic model. Neonates receiving continuous infusion of dobutamine 5–20 μg kg−1 min−1 were included. Left ventricular ejection fraction (LVEF) and cardiac output of right and left ventricle (RVO, LVO) were measured on echocardiography; heart rate (HR), mean arterial pressure (MAP), peripheral arterial oxygen saturation and cerebral regional oxygen saturation were recorded from patient monitors. Results: Twenty‐eight neonates with median (range) gestational age of 30.4 (22.7–41.0) weeks and birth weight (BW) of 1618 (465–4380) g were included. PK data were adequately described by 1‐compartmental linear structural model. Dobutamine clearance (CL) was described by allometric scaling on BW with sigmoidal maturation function of postmenstrual age (PMA). The final population PK model parameter mean typical value (standard error) estimates, standardised to median BW of 1618 g, were 41.2 (44.5) L h−1 for CL and 5.29 (0.821) L for volume of distribution, which shared a common between subject variability of 29% (17.2%). The relationship between dobutamine concentration and RVO/LVEF was described by linear model, between concentration and LVO/HR/MAP/cerebral fractional tissue oxygen extraction by sigmoidal Emax model. Conclusion: In the postnatal transitional period, PK of dobutamine was described by a 1‐compartmental linear model, CL related to BW and PMA. A concentration–response relationship with haemodynamic variables has been established

Population pharmacokinetics and pharmacodynamics of dobutamine in neonates on the first days of life

Aims: To describe the pharmacokinetics (PK) and concentration‐related effects of dobutamine in critically ill neonates in the first days of life, using nonlinear mixed effects modelling. Methods: Dosing, plasma concentration and haemodynamic monitoring data from a dose‐escalation study were analysed with a simultaneous population PK and pharmacodynamic model. Neonates receiving continuous infusion of dobutamine 5–20 μg kg−1 min−1 were included. Left ventricular ejection fraction (LVEF) and cardiac output of right and left ventricle (RVO, LVO) were measured on echocardiography; heart rate (HR), mean arterial pressure (MAP), peripheral arterial oxygen saturation and cerebral regional oxygen saturation were recorded from patient monitors. Results: Twenty‐eight neonates with median (range) gestational age of 30.4 (22.7–41.0) weeks and birth weight (BW) of 1618 (465–4380) g were included. PK data were adequately described by 1‐compartmental linear structural model. Dobutamine clearance (CL) was described by allometric scaling on BW with sigmoidal maturation function of postmenstrual age (PMA). The final population PK model parameter mean typical value (standard error) estimates, standardised to median BW of 1618 g, were 41.2 (44.5) L h−1 for CL and 5.29 (0.821) L for volume of distribution, which shared a common between subject variability of 29% (17.2%). The relationship between dobutamine concentration and RVO/LVEF was described by linear model, between concentration and LVO/HR/MAP/cerebral fractional tissue oxygen extraction by sigmoidal Emax model. Conclusion: In the postnatal transitional period, PK of dobutamine was described by a 1‐compartmental linear model, CL related to BW and PMA. A concentration–response relationship with haemodynamic variables has been established

Airy–Bessel wave packets as versatile linear light bullets

The generation of spatiotemporal optical wave packets that are impervious to both dispersion and diffraction has been a fascinating challenge. Despite intense research activity, such localized waves, referred to as light bullets, have remained elusive. In nonlinear propagation, three-dimensional light bullets tend to disintegrate as a result of inherent instabilities. Three-dimensional wave packets that propagate linearly have been reported, but their utility is severely limited by the need to tailor the wave packet precisely to material properties. To overcome these limitations, we explore a new approach based on the one-dimensional Airy wave packet. Here, we report the first observation of a class of versatile three-dimensional linear light bullets, which combine Bessel beams in the transverse plane with temporal Airy pulses. Their evolution does not depend critically on the material in which they propagate, and the consequent versatility will facilitate their study and applications ranging from bioimaging to plasma physics. © 2010 Macmillan Publishers Limited. All rights reserved

Diffraction-free pulsed optical beams via space-time correlations

Diffraction places a fundamental limitation on the distance an optical beam propagates before its size increases and spatial details blur. We show here that imposing a judicious correlation between spatial and spectral degrees of freedom of a pulsed beam can render its transverse spatial profile independent of location along the propagation axis, thereby arresting the spread of the time-averaged beam. Such correlation introduced into a beam with arbitrary spatial profile enables spatio-temporal dispersion to compensate for purely spatial dispersion that underlies diffraction. As a result, the spatio-temporal profile in the local time-frame of the pulsed beam remains invariant at all positions along the propagation axis. One-dimensional diffraction-free space-time beams are described - including non-accelerating Airy beams, despite the well-known fact that cosine waves and accelerating Airy beams are the only one-dimensional diffraction-free solutions to the monochromatic Helmholtz equation