Light-sheet microscopy: a tutorial

This paper is intended to give a comprehensive review of light-sheet (LS) microscopy from an optics perspective. As such, emphasis is placed on the advantages that LS microscope configurations present, given the degree of freedom gained by uncoupling the excitation and detection arms. The new imaging properties are first highlighted in terms of optical parameters and how these have enabled several biomedical applications. Then, the basics are presented for understanding how a LS microscope works. This is followed by a presentation of a tutorial for LS microscope designs, each working at different resolutions and for different applications. Then, based on a numerical Fourier analysis and given the multiple possibilities for generating the LS in the microscope (using Gaussian, Bessel, and Airy beams in the linear and nonlinear regimes), a systematic comparison of their optical performance is presented. Finally, based on advances in optics and photonics, the novel optical implementations possible in a LS microscope are highlighted.Peer ReviewedPostprint (published version

Estimation of the mechanical properties of the eye through the study of its vibrational modes

Measuring the eye's mechanical properties in vivo and with minimally invasive techniques can be the key for individualized solutions to a number of eye pathologies. The development of such techniques largely relies on a computational modelling of the eyeball and, it optimally requires the synergic interplay between experimentation and numerical simulation. In Astrophysics and Geophysics the remote measurement of structural properties of the systems of their realm is performed on the basis of (helio-)seismic techniques. As a biomechanical system, the eyeball possesses normal vibrational modes encompassing rich information about its structure and mechanical properties. However, the integral analysis of the eyeball vibrational modes has not been performed yet. Here we develop a new finite difference method to compute both the spheroidal and, specially, the toroidal eigenfrequencies of the human eye. Using this numerical model, we show that the vibrational eigenfrequencies of the human eye fall in the interval 100 Hz - 10 MHz. We find that compressible vibrational modes may release a trace on high frequency changes of the intraocular pressure, while incompressible normal modes could be registered analyzing the scattering pattern that the motions of the vitreous humour leave on the retina. Existing contact lenses with embebed devices operating at high sampling frequency could be used to register the microfluctuations of the eyeball shape we obtain. We advance that an inverse problem to obtain the mechanical properties of a given eye (e.g., Young's modulus, Poisson ratio) measuring its normal frequencies is doable. These measurements can be done using non-invasive techniques, opening very interesting perspectives to estimate the mechanical properties of eyes in vivo. Future research might relate various ocular pathologies with anomalies in measured vibrational frequencies of the eye.Comment: Published in PLoS ONE as Open Access Research Article. 17 pages, 5 color figure

Fast tomographic inspection of cylindrical objects

This paper presents a method for improved analysis of objects with an axial symmetry using X-ray Computed Tomography (CT). Cylindrical coordinates about an axis fixed to the object form the most natural base to check certain characteristics of objects that contain such symmetry, as often occurs with industrial parts. The sampling grid corresponds with the object, allowing for down-sampling hence reducing the reconstruction time. This is necessary for in-line applications and fast quality inspection. With algebraic reconstruction it permits the use of a pre-computed initial volume perfectly suited to fit a series of scans where same-type objects can have different positions and orientations, as often encountered in an industrial setting. Weighted back-projection can also be included when some regions are more likely subject to change, to improve stability. Building on a Cartesian grid reconstruction code, the feasibility of reusing the existing ray-tracers is checked against other researches in the same field.Comment: 13 pages, 13 figures. submitted to Journal Of Nondestructive Evaluation (https://www.springer.com/journal/10921

On higher rank coisotropic A-branes

This article is devoted to a world sheet analysis of A-type D-branes in N=(2,2) supersymmetric non-linear sigma models. In addition to the familiar Lagrangian submanifolds with flat connection we reproduce the rank one A-branes of Kapustin and Orlov, which are supported on coisotropic submanifolds. The main focus is however on gauge fields of higher rank and on tachyon profiles on brane-antibrane pairs. This will lead to the notion of a complex of coisotropic A-branes. A particular role is played by the noncommutative geometry on the brane world volume. It ensures that brane-antibrane pairs localize again on coisotropic submanifolds.Comment: 24 pages; v2: three references adde

Higher Winding Strings and Confined Monopoles in N=2 SQCD

We consider composite string solutions in N=2 SQCD with the gauge group U(N), the Fayet--Iliopoulos term \xi \neq 0 and N (s)quark flavors. These bulk theories support non-Abelian strings and confined monopoles identified with kinks in the two-dimensional world-sheet theory. Similar and more complicated kinks (corresponding to composite confined monopoles) must exist in the world-sheet theories on composite strings. In a bid to detect them we analyze the Hanany--Tong (HT) model, focusing on a particular example of N=2. Unequal quark mass terms in the bulk theory result in the twisted masses in the N=(2,2) HT model. For spatially coinciding 2-strings, we find three distinct minima of potential energy, corresponding to three different 2-strings. Then we find BPS-saturated kinks interpolating between each pair of vacua. Two kinks can be called elementary. They emanate one unit of the magnetic flux and have the same mass as the conventional 't Hooft--Polyakov monopole on the Coulomb branch of the bulk theory (\xi =0). The third kink represents a composite bimonopole, with twice the minimal magnetic flux. Its mass is twice the mass of the elementary confined monopole. We find instantons in the HT model, and discuss quantum effects in composite strings at strong coupling. In addition, we study the renormalization group flow in this model.Comment: 41 pages, 11 figure

The Cosmological Constant and Domain Walls in Orientifold Field Theories and N=1 Gluodynamics

We discuss domain walls and vacuum energy density (cosmological constant) in N=1 gluodynamics and in non-supersymmetric large N orientifold field theories which have been recently shown to be planar equivalent (in the boson sector) to N=1 gluodynamics. A relation between the vanishing force between two parallel walls and vanishing cosmological constant is pointed out. This relation may explain why the cosmological constant vanishes in the orientifold field theory at leading order although the hadronic spectrum of this theory does not contain fermions in the limit N-->infinity. The cancellation is among even and odd parity bosonic contributions, due to NS-NS and R-R cancellations in the annulus amplitude of the underlying string theory. We use the open-closed string channel duality to describe interaction between the domain walls which is interpreted as the exchange of composite ``dilatons'' and ``axions'' coupled to the walls. Finally, we study some planar equivalent pairs in which both theories in the parent-daughter pair are non-supersymmetric.Comment: 20 pages, Latex. 1 figure. v2: Final version to appear in Nucl.Phys.B. Section 4 expanded to include an expression for the cosmological constant in terms of glueball correlator

Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to Published Work, see https://pubs.acs.org/doi/10.1021/acs.jpcc.8b04676."[EN] Optical trapping of individual particles is believed to be only effective under highly focused beams because these conditions strengthen the gradient forces. This is especially critical in the beam propagating direction, where the scattering and absorption forces must be counterbalanced. Here, we demonstrate that optical trapping of nanostructures is also possible in a weakly focused beam. We study the theoretical conditions for effective three-dimensional optical confinement and verify them experimentally on iron-oxide-based nanoparticles with and without a silica coating, for which scattering, absorption, and gradient forces exist. This chemical approach to their all-optical control is, in turn, convenient for making magnetic nanostructures biocompatible. Weakly focused beams reduce the irradiance in the focal region and therefore the photon damage to the samples, which is further important to delay quantum dot quenching in the trap or to prevent artifacts in the study of biomolecular motor dynamics.We are grateful to Dr. Maria Acebron and Dr. Beatriz H. Juarez for their support in the silica encapsulation of the nano particles. This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO, Grant MAT2015-71806-R). IMDEA Nanociencia acknowledges support from the "Severo Ochoa" Programme for Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). H.R.-R. is supported by an FPI-UAM fellowship.Rodríguez-Rodríguez, H.; De Lorenzo, S.; De La Cueva, L.; Salas, G.; Arias-Gonzalez, JR. (2018). Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles. The Journal of Physical Chemistry C. 122(31):18094-18101. https://doi.org/10.1021/acs.jpcc.8b04676S18094181011223

Quantum Chromodynamics and Other Field Theories on the Light Cone

We discuss the light-cone quantization of gauge theories as a calculational tool for representing hadrons as QCD bound-states of relativistic quarks and gluons, and also as a novel method for simulating quantum field theory on a computer. The light-cone Fock state expansion of wavefunctions provides a precise definition of the parton model and a general calculus for hadronic matrix elements. We present several new applications of light-cone Fock methods, including calculations of exclusive weak decays of heavy hadrons, and intrinsic heavy-quark contributions to structure functions. Discretized light-cone quantization, is outlined and applied to several gauge theories. We also discuss the construction of the light-cone Fock basis, the structure of the light-cone vacuum, and outline the renormalization techniques required for solving gauge theories within the Hamiltonian formalism on the light cone.Comment: 206 pages Latex, figures included, Submitted to Physics Report