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Repetition rate control in continuous-wave-pumped, passively Q-switched solid-state lasers
No full textWe describe a technique for the adjustment and control of repetition rates in continuous-wave-pumped, passively Q-switched solid-state lasers. The method uses a movable intracavity lens to modify the mode matching and hence the gain of the laser beam per pass. The technique was applied to a diode-pumped Nd3+: YVO4 laser passively Q-switched with a Cr4+: YAG saturable absorber at 1064 nm. At a fixed pump power of 5.4 W, we were able to continuously adjust the repetition rate between 13.8 and 25 kHz by translating an intracavity converging lens. We also demonstrate that by adjusting the lens position, the repetition rate can be kept at a desired value as the pump power varies. In particular, as the pump power was increased from 3.95 to 5.9 W, the lens position was varied by 0.91 cm to keep the repetition rate constant at 13.8 kHz. Rate-equation formalism was used to investigate the variation of the repetition rate as a function of lens position, and very good agreement was obtained between experiment and theory. (c) 2007 Society of Photo-Optical Instrumentation Engineers
Cooling and quenching of (MgH+)-Mg-24(X-1 Sigma(+)) by He-4(S-1) in a Coulomb trap: A quantum study of the dynamics
No full textThe quantum dynamics of the rotational quenching of the (MgH+)-Mg-24(X-1 Sigma(+)) molecular cation interacting with He-4(S-1) as a buffer gas, at relative temperatures ranging from 1 K down to millikelvins, is described by accurate close coupling scattering calculations on an ab initio potential energy surface. The efficiency of the process is quantitatively analyzed by employing the ab initio quenching rates and cross sections and effective decay rate values are obtained from simple unimolecular kinetics over a broad range of trap conditions
Bose-Einstein condensate in a harmonic trap decorated with Dirac delta functions
No full textWe study Bose-Einstein condensation in a harmonic trap with a dimple potential. We specifically consider the case of a tight and deep dimple potential which is modeled by a Dirac delta function. This allows for simpler, explicit numerical and analytical investigations of noninteracting gases. Thus, the Schrodinger equation is used instead of the Gross-Pitaevski equation. Calculating the atomic density, chemical potential, critical temperature, and condensate fraction, the role of the relative depth of the dimple potential with respect to the harmonic trap in large condensate formation at enhanced temperatures is clearly revealed
Chaotic behavior of triatomic clusters
No full textThe dynamics of triatomic clusters is investigated employing two-body Lennard-Jones and three-body Axilrod-Teller potential functions. Lyapunov exponents are calculated for the total energy range of -2.70 epsilon <E< -0.72 epsilon. The effects of the initial geometry of the cluster, its angular momentum, and the magnitude of three-body interactions are analyzed. It has been found that the dominating factor for the extent of chaotic behavior is the energy assigned to vibrational modes. The introduction of the rotational motion regularizes the dynamics in spite of a higher degree of nonlinearity. The three-body terms in the potential function affect the extent of the chaos in different manners depending on the initial geometry of the cluster. Finally, the time evolution of heterogeneous clusters generated by varying the size, mass, and the interaction strength of a single atom is observed. Their Lyapunov exponent spectra show that the additional nonlinearity reduces the chaotic behavior of the system in most of the cases
Quenching of internal rotations versus collisional cooling at ultralow energies for weakly interacting partners: Cs-2((3)Sigma(+)(u)) with He-3,He-4
No full textQuantum-scattering calculations at ultralow (close to 10(-6) cm(-1)) collision energies are carried out for the Cs dimer in its spin-stretched triplet state, interacting with helium. An ab initio potential energy surface is computed and employed, while the target molecule is kept in its ground vibrational state and several excitated initial rotational states are considered in the quantum dynamics. The highly anisotropic interaction is seen to cause, in spite of its weakness, internal energy quenching rates comparable with the efficiency of the collisional cooling of relative kinetic energies. The rates of spin-flip processes are also analyzed and compared with pure rotational quenching events
Photonic crystal based amorphous silicon microcavity
No full textIn this research, properties of bulk and microcavity hydrogenated amorphous silicon nitride are studied. Microcavities were realized by embedding the active hydrogenated amorphous silicon layer between two dielectric mirrors. The dielectric mirrors were realized with two distributed Bragg reflectors (DBR's). The DBR's are one dimensional photonic bandgap (PBG) materials, i.e., photonic crystals, composed of alternating layers of silicon oxide and silicon nitride. All of the layers are grown by plasma enhanced chemical vapor deposition (PECVD) on silicon substrates. The temperature dependence of the amorphous silicon photoluminescence. is performed to fully characterize and optimize the material in the pursuit of obtaining novel photonic microdevices. Photonics device characterization was done by means of atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence, and reflectance measurements. The reflectance spectra calculations were performed using the transfer matrix method (TMM)
Alterations of erythrocyte rheology and cellular susceptibility in end stage renal disease: effects of peritoneal dialysis
No full textIn this study, we investigated the effects of peritoneal dialysis on hemorheological and hematological parameters and their relations with oxidant and antioxidant status of uremic patients. Hemorheological parameters (erythrocyte deformability, erythrocyte aggregation, osmotic deformability, blood and plasma viscosity) were measured in patients with renal insufficiency undergoing peritoneal dialysis (PD) and volunteers. Erythrocyte deformability, osmotic deformability and aggregation in both autologous plasma and 3% dextran 70 were measured by laser diffraction ektacytometry. Enzyme activities of glutathione peroxidase, superoxide dismutase and catalase were studied in erythrocytes; lipid peroxidation was studied by measuring the amount of malondialdehyde in both erythrocytes and plasma samples. Blood viscosity at native hematocrit was significantly lower in PD patients at all measured shear rates compared to controls, but it was high in PD patients at corrected (45%) hematocrit. Erythrocyte deformability did not show any difference between the two groups. Osmotic deformability was significantly lower in PD patients compared to controls. Aggregation index values were significantly high in PD patients in plasma Catalase and glutathione peroxidase activities in erythrocytes were decreased in PD patients whereas superoxide dismutase activity was increased compared to controls. Malondialdehyde was significantly increased in erythrocytes and plasma samples of PD patients which also shows correlations with aggregation parameters. It has been concluded that erythrocytes in PD patients are more prone to aggregation and this tendency could be influenced by lipid peroxidation activity in patient's plasma. These results imply that uremic conditions, loss of plasma proteins and an increased risk of oxidative stress because of decreasing levels of antioxidant enzymes affect erythrocyte rheology during peritoneal dialysis. This level of distortion may have crucial effects, impairing the blood flow dynamics and causing inadequate microcirculatory perfusion. © 2017 Ertan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Peer-to-Peer epidemic algorithms for reliable multicasting in Ad Hoc networks
No full textCharacteristics of ad hoc networks and even their existence depend on the nodes forming them. Thus, services and applications designed for ad hoc networks should adapt to this dynamic and distributed environment. In particular, multicast algorithms having reliability and scalability requirements should abstain from centralized approaches. We aspire to define a reliable and scalable multicast protocol for ad hoc networks. Our target is to utilize epidemic techniques for this purpose. In this paper, we present a brief survey of epidemic algorithms for reliable multicasting in ad hoc networks, and describe formulations and analytical results for simple epidemics. Then, P2P anti-entropy algorithm for content distribution and our prototype simulation model are described together with our initial results demonstrating the behavior of the algorithm
Symplectic and lagrangian surfaces in 4-Manifolds
No full textThis is a brief summary of recent examples of isotopically different symplectic and Lagrangian surfaces representing a fixed homology class in a simply-connected symplectic 4-manifold
From liquid to thin film: colloidal suspensions for tungsten oxide as an electrode material for Li-ion batteries
No full textUsing a colloidal suspension, tungsten oxide thin films (150 nm) have been prepared via ultrasonic spray deposition using two different current collectors, namely TiN and Pt. First, the precursor chemistry was studied, revealing that the tungsten present is reduced due to the formation of chlorine gas. Due to a dehydrogenation 1,1-diethoxyethane (DEE) and hydrogen chloride (HCl) evolve from the precursor, reducing the chloride content of the precursor. The thin films were annealed at 400 and 500 degrees C, yielding tetragonal tungsten oxide without the presence of chlorides. Electrochemical analysis indicated that the TiN current collector has a pronounced positive effect on cycling behavior of the WO3 thin film. A higher annealing temperature yields an improved performance, but annealing at temperatures as low as 400 degrees C also yielded electrochemically active WO3. The current study presents a versatile method to produce electrochemically active tungsten oxide thin films with a high volumetric capacity (640 mA h cm(-3)) at relatively low temperature to be applied in all-solid-state Li-ion batteries