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1.
Elife ; 92020 04 06.
Artigo em Inglês | MEDLINE | ID: mdl-32250243

RESUMO

Many animals collectively form complex patterns to tackle environmental difficulties. Several biological and physical factors, such as animal motility, population densities, and chemical cues, play significant roles in this process. However, very little is known about how sensory information interplays with these factors and controls the dynamics of pattern formation. Here, we study the direct relation between oxygen sensing, pattern formation, and emergence of swarming in active Caenorhabditis elegans aggregates. We find that when thousands of animals gather on food, bacteria-mediated decrease in oxygen level slows down the animals and triggers motility-induced phase separation. Three coupled factors-bacterial accumulation, aerotaxis, and population density-act together and control the entire dynamics. Furthermore, we find that biofilm-forming bacterial lawns including Bacillus subtilis and Pseudomonas aeruginosa strongly alter the collective dynamics due to the limited diffusibility of bacteria. Additionally, our theoretical model captures behavioral differences resulting from genetic variations and oxygen sensitivity.


Assuntos
Bacillus subtilis/crescimento & desenvolvimento , Quimiotaxia/fisiologia , Movimento/fisiologia , Pseudomonas aeruginosa/metabolismo , Animais , Bacillus subtilis/genética , Comportamento Animal , Biofilmes/crescimento & desenvolvimento , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Quimiotaxia/genética , Oxigênio/metabolismo , Pseudomonas aeruginosa/genética
2.
Nat Commun ; 10(1): 2285, 2019 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-31123251

RESUMO

Growing tissue and bacterial colonies are active matter systems where cell divisions and cellular motion generate active stress. Although they operate in the non-equilibrium regime, these biological systems can form large-scale ordered structures. How mechanical instabilities drive the dynamics of active matter systems and form ordered structures are not well understood. Here, we use chaining Bacillus subtilis, also known as a biofilm, to study the relation between mechanical instabilities and nematic ordering. We find that bacterial biofilms have intrinsic length scales above which a series of mechanical instabilities occur. Localized stress and friction drive buckling and edge instabilities which further create nematically aligned structures and topological defects. We also observe that topological defects control stress distribution and initiate the formation of sporulation sites by creating three-dimensional structures. In this study we propose an alternative active matter platform to study the essential roles of mechanics in growing biological tissue.


Assuntos
Bacillus subtilis/fisiologia , Biofilmes , Microscopia Intravital/métodos , Bacillus subtilis/ultraestrutura , Fenômenos Biomecânicos , Microscopia Eletrônica de Varredura/métodos , Microscopia de Fluorescência/métodos , Estresse Mecânico , Imagem com Lapso de Tempo/métodos
3.
Nat Methods ; 16(1): 126-133, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30573831

RESUMO

A fundamental question in neuroscience is how neural networks generate behavior. The lack of genetic tools and unique promoters to functionally manipulate specific neuronal subtypes makes it challenging to determine the roles of individual subtypes in behavior. We describe a compressed sensing-based framework in combination with non-specific genetic tools to infer candidate neurons controlling behaviors with fewer measurements than previously thought possible. We tested this framework by inferring interneuron subtypes regulating the speed of locomotion of the nematode Caenorhabditis elegans. We developed a real-time stabilization microscope for accurate long-term, high-magnification imaging and targeted perturbation of neural activity in freely moving animals to validate our inferences. We show that a circuit of three interconnected interneuron subtypes, RMG, AVB and SIA control different aspects of locomotion speed as the animal navigates its environment. Our work suggests that compressed sensing approaches can be used to identify key nodes in complex biological networks.


Assuntos
Caenorhabditis elegans/fisiologia , Rede Nervosa , Animais , Animais Geneticamente Modificados , Comportamento Animal , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Cálcio/metabolismo , Interneurônios/fisiologia , Locomoção , Microscopia/métodos
4.
Opt Lett ; 43(6): 1315-1318, 2018 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-29543280

RESUMO

We report, to the best of our knowledge, the shortest femtosecond pulses generated from a Kerr-lens mode-locked (KLM) Alexandrite laser operating near 750 nm. The Alexandrite gain medium was pumped with a continuous-wave (cw), 532 nm laser, and the performance of both the short and extended resonators was investigated. The use of an extended cavity eliminated the multi-wavelength spectral instabilities observed during the cw operation of the short cavity. Furthermore, since the repetition rate of the Alexandrite laser was reduced from 107 to 5.6 MHz, the resulting increase in the intracavity pulse energy provided enhanced Kerr nonlinearity and eliminated the Q-switching instabilities during mode-locked operation. The KLM MPC Alexandrite laser produced nearly transform-limited, 70 fs pulses at a pulse repetition rate of 5.6 MHz with only 1 W of pump power. The time-bandwidth product was further measured to be 0.331.

5.
Nature ; 490(7419): 273-7, 2012 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-23000898

RESUMO

Animals locate and track chemoattractive gradients in the environment to find food. With its small nervous system, Caenorhabditis elegans is a good model system in which to understand how the dynamics of neural activity control this search behaviour. Extensive work on the nematode has identified the neurons that are necessary for the different locomotory behaviours underlying chemotaxis through the use of laser ablation, activity recording in immobilized animals and the study of mutants. However, we do not know the neural activity patterns in C. elegans that are sufficient to control its complex chemotactic behaviour. To understand how the activity in its interneurons coordinate different motor programs to lead the animal to food, here we used optogenetics and new optical tools to manipulate neural activity directly in freely moving animals to evoke chemotactic behaviour. By deducing the classes of activity patterns triggered during chemotaxis and exciting individual neurons with these patterns, we identified interneurons that control the essential locomotory programs for this behaviour. Notably, we discovered that controlling the dynamics of activity in just one interneuron pair (AIY) was sufficient to force the animal to locate, turn towards and track virtual light gradients. Two distinct activity patterns triggered in AIY as the animal moved through the gradient controlled reversals and gradual turns to drive chemotactic behaviour. Because AIY neurons are post-synaptic to most chemosensory and thermosensory neurons, it is probable that these activity patterns in AIY have an important role in controlling and coordinating different taxis behaviours of the animal.


Assuntos
Caenorhabditis elegans/fisiologia , Quimiotaxia/fisiologia , Animais , Comportamento Animal/fisiologia , Estimulação Elétrica , Interneurônios/fisiologia , Neurônios/fisiologia
6.
Opt Express ; 17(18): 15541-9, 2009 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-19724552

RESUMO

We report on a comparative study of grating based plasmonic band gap cavities. Numerically, we calculate the quality factors of the cavities based on three types of grating surfaces; uniform, biharmonic and Moiré surfaces. We show that for biharmonic band gap cavities, the radiation loss can be suppressed by removing the additional grating component in the cavity region. Due to the gradual change of the surface profile in the cavity region, Moiré type surfaces support cavity modes with higher quality factors. Experimentally, we demonstrate the existence of plasmonic cavities based on uniform gratings. Effective index perturbation and cavity geometries are obtained by additional dielectric loading. Quality factor of 85 is obtained from the measured band structure of the cavity.

7.
Opt Express ; 17(10): 8542-7, 2009 May 11.
Artigo em Inglês | MEDLINE | ID: mdl-19434187

RESUMO

In this study, we demonstrate that periods of metallic gratings on elastomeric substrates can be tuned with external strain and hence are found to control the resonance condition of surface plasmon polaritons. We have excited the plasmon resonance on the elastomeric grating coated with gold and silver. The grating period is increased up to 25% by applying an external mechanical strain. The tunability of the elastomeric substrate provides the opportunity to use such gratings as efficient surface enhanced Raman spectroscopy substrates. It's been demonstrated that the Raman signal can be maximized by applying an external mechanical strain to the elastomeric grating.

8.
Phys Rev Lett ; 102(6): 063901, 2009 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-19257590

RESUMO

We have demonstrated slow propagation of surface plasmons on metallic Moiré surfaces. The phase shift at the node of the Moiré surface localizes the propagating surface plasmons and adjacent nodes form weakly coupled plasmonic cavities. Group velocities around v_{g}=0.44c at the center of the coupled cavity band and almost a zero group velocity at the band edges are observed. A tight binding model is used to understand the coupling behavior. Furthermore, the sinusoidally modified amplitude about the node suppresses the radiation losses and reveals a relatively high quality factor (Q=103).

9.
Opt Express ; 16(17): 12469-77, 2008 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-18711483

RESUMO

Surface-enhanced Raman Scattering (SERS) of rhodamine 6G (R6G) adsorbed on biharmonic metallic grating structures was studied. Biharmonic metallic gratings include two different grating components, one acting as a coupler to excite surface plasmon polaritons (SPP), and the other forming a plasmonic band gap for the propagating SPPs. In the vicinity of the band edges, localized surface plasmons are formed. These localized plasmons strongly enhance the scattering efficiency of the Raman signal emitted on the metallic grating surfaces. It was shown that reproducible Raman scattering enhancement factors of over 10(5) can be achieved by fabricating biharmonic SERS templates using soft nano-imprint technique. We have shown that the SERS activities from these templates are tunable as a function of plasmonic resonance conditions. Similar enhancement factors were also measured for directional emission of photoluminescence. At the wavelengths of the plasmonic absorption peak, directional enhancement by a factor of 30 was deduced for photoluminescence measurements.


Assuntos
Refratometria/instrumentação , Rodaminas/química , Análise Espectral Raman/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Espalhamento de Radiação
10.
Opt Express ; 14(22): 10228-32, 2006 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-19529418

RESUMO

We use the soft lithography technique to fabricate a polymeric waveguide Bragg grating filter. Master grating structure is patterned by e-beam lithography. Using an elastomeric stamp and capillary action, uniform grating structures with very thin residual layers are transferred to the UV curable polymer without the use of an imprint machine. The waveguide layer based on BCB optical polymer is fabricated by conventional optical lithography. This approach provides processing simplicity to fabricate Bragg grating filters.

11.
Opt Lett ; 30(23): 3150-2, 2005 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-16342705

RESUMO

An elastomeric grating coupler fabricated by the replica molding technique is used to measure the modal indices of a silicon-on-insulator (SOI) planar waveguide structure. Because of the van der Waals interaction between the grating mold and the waveguide, the elastomeric stamp makes conformal contact with the waveguide surface, inducing a periodic index perturbation at the contact region. The phase of the incident light is changed to match the guided modes of the waveguide. The modal and bulk indices are obtained by measuring the coupling angles. This technique serves to measure the high refractive index with a precision better than 10(-3) and allows the elastomeric stamp to be removed without damaging the surface of the waveguide.


Assuntos
Elastômeros , Aumento da Imagem/instrumentação , Refratometria/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Aumento da Imagem/métodos , Refratometria/métodos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
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