Cavity cooling of an optically trapped nanoparticle

We study the cooling of a dielectric nanoscale particle trapped in an optical cavity. We derive the frictional force for motion in the cavity field, and show that the cooling rate is proportional to the square of oscillation amplitude and frequency. Both the radial and axial centre-of-mass motion of the trapped particle, which are coupled by the cavity field, are cooled. This motion is analogous to two coupled but damped pendulums. Our simulations show that the nanosphere can be cooled to 1/e of its initial momentum over time scales of hundredths of milliseconds.Comment: 11 page

Kinetic modeling of evolution of 3 + 1:Resonance enhanced multiphoton ionization plasma in argon at low pressures

We present numerical kinetic modeling of generation and evolution of the plasma produced as a result of resonance enhanced multiphoton ionization (REMPI) in Argon gas. The particle-in-cell/Monte Carlo collision (PIC/MCC) simulations capture non-equilibrium effects in REMPI plasma expansion by considering the major collisional processes at the microscopic level: elastic scattering, electron impact ionization, ion charge exchange, and recombination and quenching for metastable excited atoms. The conditions in one-dimensional (1D) and two-dimensional (2D) formulations correspond to known experiments in Argon at a pressure of 5 Torr. The 1D PIC/MCC calculations are compared with the published results of local drift-diffusion model, obtained for the same conditions. It is shown that the PIC/MCC and diffusion-drift models are in qualitative and in reasonable quantitative agreement during the ambipolar expansion stage, whereas significant non-equilibrium exists during the first few 10 s of nanoseconds. 2D effects are important in the REMPI plasma expansion. The 2D PIC/MCC calculations produce significantly lower peak electron densities as compared to 1D and show a better agreement with experimentally measured microwave radiation scatterin

Gamma motor neurons express distinct genetic markers at birth and require muscle spindle-derived GDNF for postnatal survival

<p>Abstract</p> <p>Background</p> <p>Gamma motor neurons (γ-MNs) selectively innervate muscle spindle intrafusal fibers and regulate their sensitivity to stretch. They constitute a distinct subpopulation that differs in morphology, physiology and connectivity from α-MNs, which innervate extrafusal muscle fibers and exert force. The mechanisms that control the differentiation of functionally distinct fusimotor neurons are unknown. Progress on this question has been limited by the absence of molecular markers to specifically distinguish and manipulate γ-MNs. Recently, it was reported that early embryonic γ-MN precursors are dependent on GDNF. Using this knowledge we characterized genetic strategies to label developing γ-MNs based on GDNF receptor expression, showed their strict dependence for survival on muscle spindle-derived GDNF and generated an animal model in which γ-MNs are selectively lost.</p> <p>Results</p> <p>In mice heterozygous for both the <it>Hb9::GFP </it>transgene and a tau-lacZ-labeled (<it>TLZ</it>) allele of the GDNF receptor Gfrα1, we demonstrated that small motor neurons with high Gfrα1-TLZ expression and lacking Hb9::GFP display structural and synaptic features of γ-MNs and are selectively lost in mutants lacking target muscle spindles. Loss of muscle spindles also results in the downregulation of Gfrα1 expression in some large diameter MNs, suggesting that spindle-derived factors may also influence populations of α-MNs with β-skeletofusimotor collaterals. These molecular markers can be used to identify γ-MNs from birth to the adult and to distinguish γ- from β-motor axons in the periphery. We also found that postnatal γ-MNs are also distinguished by low expression of the neuronal nuclear protein (NeuN). With these markers of γ-MN identity, we show after conditional elimination of GDNF from muscle spindles that the survival of γ-MNs is selectively dependent on spindle-derived GDNF during the first 2 weeks of postnatal development.</p> <p>Conclusion</p> <p>Neonatal γ-MNs display a unique molecular profile characterized by the differential expression of a series of markers - Gfrα1, Hb9::GFP and NeuN - and the selective dependence on muscle spindle-derived GDNF. Deletion of GDNF expression from muscle spindles results in the selective elimination of γ-MNs with preservation of the spindle and its sensory innervation. This provides a mouse model with which to explore the specific role of γ-fusimotor activity in motor behaviors.</p

Atrial remodelling comparison after maze-3 and cryo-maze procedures in combined cardiac interventions: a retrospective study

Background. The maze procedure aims to eliminate atrial fibrillation (AF), restore sinus rhythm (SR) and atrial contractility. However, conflicting evidence exists regarding the extent of atrial remodelling in various techniques, which directed the focus of our study.Objectives. An atrial remodelling comparison after a cut-and-sew maze-3 surgery and its biatrial cryo-maze modification using 2D echocardiography.Methods. The study is a retrospective uncontrolled interrupted two-cohort time-series trial, with patients selected by pseudorandomisation according to a normal sinus rhythm-maintaining AF surgery method. A total of 217 maze-3 and 113 cryo-maze combined cardiac interventions have been performed within 2012–2021. The interventions included valve repair, coronary artery bypass grafting and their combination. Due to differences in long-term follow-up, the cohorts were pseudorandomised to select by 50 restored vs. maintained sinus rhythm patients using a nearest-neighbour classifier coupled with logistic regression. Mean follow-up period was 6 (1–17) months. The patients had paroxysmal, persistent and longstanding persistent AF. Echocardiography values prior to and long-term post-surgery were further analysed to determine the atrial remodelling dynamics. Results. A statistically significant atrial volume reduction is evident in a long-term within-cohort comparison. Meanwhile, a statistically more pronounced remodelling is observed between cohorts after maze-3 procedure. The cohort 1 vs. 2 estimates are: mean left atrial volume 120/125 mL3 (p = 0.011), left atrial size in apical view 52/53 mm (p = 0.023), right atrial size in apical view 58/62 mm (p = 0.004), right atrial size in parasternal short axis view 43/45 mm (p = 0.004), right atrial area in apical 4-chamber view 25/28 cm2 (p = 0.007). Maintained atrial pacing patients had positive systolic atrial function recovery rates (E/A ratio increased to average 1.5) in the long-term in both comparison cohorts.Conclusion. Remodelling is biatrial after all the maze procedures compared. A more pronounced atrial volume reduction occurs after maze-3 surgery. The presence of sinus rhythm is facilitated by cardiac conduction leading to mechanical and electrical remodelling of the atria

Capsule depolymerase activity of phages infecting the Acinetobacter baumannii-calcoaceticus complex

To be able to enter and replicate in exopolysaccharide (EPS) slime or capsule surrounded bacteria, bacteriophages (phages) have evolved the ability to overcome the EPS structure by producing virion-associated proteins with polysaccharide depolymerization activities. We have studied phages infecting the Acinetobacter baumannii-Acinetobacter calcoaceticus (ACB) complex, which groups A. baumannii, A. calcoaceticus, A. pittii, A. nosocomialis and A. seifertii species. It is known that about 100 different capsule polysaccharide (CPS) synthetic loci are found in A. baumannii genomes alone. This situation is even more complex, with some strains of A. baumannii having nearly identical CPS synthetic loci to strains of A. nosocomialis or A. pittii, and supposedly producing identical CPS. We have isolated and characterized 21 phages infecting the ACB complex and demonstrate that they have specialized depolymerases that degrade polymers (e.g. capsular and structural polysaccharides) to facilitate their access to the hosts. To further characterize the phage-host interactions, we have sequenced bacterial genomes and mutated the CPS synthetic loci to create CPS-deficient mutants, to prove that the ACB phages recognize the CPS as the primary receptor. We further demonstrate that recombinantly expressed depolymerases are active and key components in the tail specificity apparatus of Podoviridae viruses. We could conclude that phages infecting the ACB complex represent a source of enzymes that degrade a complex variety of polymeric substances that can be further exploited as a serotyping scheme currently inexistent for Acinetobacter species

Crystal structure and location of gp131 in the bacteriophage phiKZ virion

Pseudomonas phage phi KZ and its two close relatives phi PA3 and 201 phi 2-1 are very large bacteriophages that form a separate branch in phage classification because their genomes are very different from the rest of GenBank sequence data. The contractile tail of phi KZ is built from at least 32 different proteins, but a definitive structural function is assigned to only one of them-the tail sheath protein. Here, we report the crystal structure of the C-terminal domain of another phiKZ tail protein, gene product 131 (gp131C). We show that gp131 is located at the periphery of the baseplate and possibly associates with fibers that emanate from the baseplate. Gp131C is a seven-bladed beta-propeller that has a shape of a skewed toroid. A small but highly conserved and negatively charged patch on the surface of gp131C might be important for substrate binding or for interaction with a different tail protein. (C) 2012 Elsevier Inc. All rights reserved