Cavity Axis Research Articles

Examining Hearts Containing Left Ventricular Assist Devices at Necropsy

There are no publications describing hearts at necropsy containing left ventricular assist devices (LVADs). The purpose was to study the relation of the LVAD cannula to the left ventricular (LV) cavity and wall. We studied the hearts at necropsy of 15 adults who had an LVAD inserted from 4 to 1,423 days (median 60) earlier. In 13 patients, the cannula had been inserted at an angle to the major longitudinal axis of the LV chamber, and in 11 patients, the orifice margin of the cannulas contacted the LV mural endocardium. In 3 patients, the LVAD cannula was inserted into the posterior wall, and, in another into the anterior wall. In the remaining 11 patients, the cannula had been inserted into the LV apex. Despite the insertion of the cannulas into the LV apex, the direction of the insertion was not into the longitudinal axis of the LV cavity in 9 patients. These unusual insertions in some patients may have altered flow into the orifice of the cannula; in others, based on their long postoperative survival, physiologic consequences were almost certainly absent. The presence of considerable quantities of subepicardial adipose tissue and pericardial adhesions from previous cardiac procedures (mainly coronary bypass) potentially interfered with achieving proper alignment of the LVAD cannula during its insertion. Misalignment of the cannulas of the LVAD in the LV cavity appears to be rather frequent.

Superradiant cooling, trapping, and lasing of dipole-interacting clock atoms.

A cold atomic gas with an inverted population on a transition coupled to a field mode of an optical resonator constitutes a generic model of a laser. For quasi-continuous operation, external pumping, trapping and cooling of the atoms is required to confine them in order to achieve enough gain inside the resonator. As inverted atoms are high-field seekers in blue detuned light fields, tuning the cavity mode to the blue side of the atomic gain transition allows for combining lasing with stimulated cavity cooling and dipole trapping of the atoms at the antinodes of the laser field. We study such a configuration using a semiclassical description of particle motion along the cavity axis. In extension of earlier work we include free space atomic and cavity decay as well as atomic dipole-dipole interactions and their corresponding forces. We show that for a proper choice of parameters even in the bad cavity limit the atoms can create a sufficiently strong field inside the resonator such that they are trapped and cooled via the superradiant lasing action with less than one photon on average inside the cavity.

Conditional nonclassical field generation in cavity QED

We introduce a method for the conditional generation of nonclassical states of light in a cavity. We consider two-level atoms traveling along the transverse direction to the cavity axis and show that by conditioning on one of the output measurements nonclassical field states are generated. The two-level atoms are prepared in the ground state and we conditioned on the events in which they are also detected in the ground state. Nonclassical properties of the cavity mode are identified and characterized. This includes: quadrature squeezing, sub-Poissonian photon-number distributions, and negative Wigner functions. We determine the optimal parameter regions where the corresponding nonclassical features are most distinct.

A 45° tilted 3D-printed scanner for compact side-view laser scanning endoscopy

Side viewing, miniaturized laser scanning endoscopes are powerful tools in providing sub-cellular level resolution and multi-layered imaging of the walls of body cavities. Yet, the level of miniaturization for such devices is significantly hampered by the necessity for 45° placement of the whole scanner unit with respect to the cavity axis. With its rapid and low-cost production capability, 3D printing can be employed in addressing the challenge of producing a laser scanner, whose scanning head makes 45°, or any desired angle, with the scanner unit. Producing a 10 × 10 mm2 scanner device with tilted scan head (as opposed to the conventional design with identical size) enabled size shrinkage of a near fully 3D-printed laser scanning imager by × 1.5 in diameter (from 17 to 11 mm). We also share the initial results on 5 × 5 mm2 total die size scanners, having literally identical die size with their MEMS counterparts, and discuss the road steps in producing < 8-mm diameter laser scanning devices with these scanners using 3D printing technology. The frame-rate improvement strategies are discussed in detail. Furthermore overall resolution and frame-rate values that can be achieved with the presented 3D printed scanners are tabulated and compared to MEMS counterparts. Overall with their low cost, easy and rapid fabrication, 3D printed actuators are great candidates for opto-medical imaging applications.

Polarization-dependent light-matter coupling and highly indistinguishable resonant fluorescence photons from quantum dot-micropillar cavities with elliptical cross section

We study the optical properties of coupled quantum dot-microcavity systems with elliptical cross section. First, we develop an analytic model that describes the spectrum of the cavity modes that are split due to the reduced symmetry of the resonator. By coupling the QD emission to the polarized fundamental cavity modes, we observe the vectorial nature of the Purcell enhancement, which depends on the intrinsic polarization of the quantum dot and its relative alignment with respect to the cavity axis. The variable interaction strength of the QD with the polarized cavity modes leads to the observation of strong and weak coupling. Finally, we demonstrate the capability of elliptical micropillars to emit single and highly indistinguishable photons (visibility over 93 \%).

Influence of the polarization anisotropy on the linewidth enhancement factor and reflection sensitivity of 1.55- μ m InP-based InAs quantum dash lasers

This work investigates the effect of the polarization anisotropy on the linewidth enhancement factor and the reflection sensitivity of InAs/InP quantum dash semiconductor lasers. The results show that the small linewidth enhancement factor and high stability against external optical feedback are obtained for nanostructures oriented perpendicular to the cavity axis as opposed to those oriented parallel to the cavity axis. Effective simulations on the critical feedback level of these two lasers are also in agreement with experimental results. Such anisotropy is attributed to the polarization dependence of the transition matrix element in these quantum nanostructures.

Free-running Fe:ZnSe laser pumped by an Er:YAG radiation along the cavity axis

A free-running Fe:ZnSe laser is demonstrated under the pump of a single-shot 2.94 μm Er:YAG laser along the cavity axis at liquid nitrogen temperature of 77 K. At the incident pump energy of 1.47 J, a maximum single pulse energy of 253.7 mJ is obtained with a minimum pulse duration of 92.4 μs, corresponding to a slope efficiency of 16.2%. The central wavelength and the full width at half maximum (FWHM) are 3944.7 and 68.4 nm, respectively.

Numerical simulation of longitudinal and transversal electron dynamics in classical microtron

Numerical simulation of 3D electron dynamics in classical Lebedev institute microtron with energy 6-10 MeV is carried out. Special attention is paid to particles transversal motion investigation. A comparison of physical electric field distribution along cavity axis with that obtained by means numerical calculation is done. The obtained results are discussed.

Development and Experimental Verification of an XY-Table for the Optimization of the Alignment of High-Power Gyrotrons

The proper alignment of the electron beam with the interaction cavity is essential in order to achieve efficient operation of modern high-power, high-frequency gyrotrons. However, tolerances, manufacturing, and magnetic field alignment errors may lead to the less optimal positioning of the electron beam in the gyrotron cavity. In this paper, we describe in detail the in-house design and development of a simple and low-cost prototype gyrotron-alignment XY-table, which can be used for the optimization of the alignment of the electron beam with the cavity axis. The efficient operation of the device is verified experimentally by operating the European ITER 170-GHz, 1-MW short-pulse prototype gyrotron in the Oxford Instruments superconducting magnet that is available at the Karlsruhe Institute of Technology gyrotron test-stand and is equipped with a set of dipole coils.

Cavity-Based 3D Cooling of a Levitated Nanoparticle via Coherent Scattering.

We experimentally realize cavity cooling of all three translational degrees of motion of a levitated nanoparticle in vacuum. The particle is trapped by a cavity-independent optical tweezer and coherently scatters tweezer light into the blue detuned cavity mode. For vacuum pressures around 10^{-5} mbar, minimal temperatures along the cavity axis in the millikelvin regime are observed. Simultaneously, the center-of-mass (c.m.) motion along the other two spatial directions is cooled to minimal temperatures of a few hundred millikelvin. Measuring temperatures and damping rates as the pressure is varied, we find that the cooling efficiencies depend on the particle position within the intracavity standing wave. This data and the behavior of the c.m. temperatures as functions of cavity detuning and tweezer power are consistent with a theoretical analysis of the experiment. Experimental limits and opportunities of our approach are outlined.

Electron-optical system for a high-current Ka-band relativistic gyrotron

An electron-optical system for a high-current relativistic Ka-band gyrotron was developed and experimentally tested. The system consists of a coaxial magnetically insulated diode forming a rectilinear hollow beam and an additional short coil (kicker) pumping the transverse electron velocities. An electron beam with a particle energy of 500 keV, a current of 1.5–2 kA, and a pitch-ratio of up to 1 has been produced. The beam is intended for a gyrotron with the output power of 200 MW. The measured beam characteristics are in good agreement with the results of calculations. The influence of the beam and gyrotron cavity axis misalignment on gyrotron operation is analyzed using PIC simulations.

Field emission studies in vertical test and during cryomodule operation using precise x-ray mapping system

Field emission is one of the most serious issues in the degradation of superconducting cavity performance. However, surveying field emission sources during the cavity performance test (called the ``vertical test'') and cryomodule operation is difficult. Therefore, to precisely investigate electron emissions from the field emission source, we developed a diagnostic system for the energy recovery linac 1.3 GHz nine-cell superconducting cavity for both vertical tests and the cryomodule operation. The developed system is comprised of two types of sensors: a carbon sensor and a Si $p$-$i$-$n$ diode, that measure the temperature rise and the radiation produced by electron emissions, respectively. Rotating the sensor array around the cavity axis in the vertical test provides detailed information on the entire cavity surface. The precise x-ray mapping profile measured by the system in the vertical test enables identification of the local emission source. This paper describes how the field emission source is identified in the vertical test from the standpoint of not only experimental results obtained with the newly developed rotating mapping system but also the detailed approach based on precise simulations. In addition, field emission studies with the optimized instrumentation have been extended to cryomodule tests, both standalone and in the beam line. These developments allow us to monitor changes in the cavity field emission signatures introduced by cryomodule assembly and beam operation.

Single-mode scannable nanosecond Ti:sapphire laser for high-resolution two-photon absorption laser-induced fluorescence (TALIF)

A pulsed Ti:sapphire laser has been developed so as to operate over a wide range of frequencies, even far from the optimum wavelength (790 nm), as a narrow-band light source for TALIF experiments on O, Cl, N and H. The coupling of the optical cavity, both to its injection seeder and to the laser output beam, relies on a reflecting plate, which makes it fundamentally easier to control the coupling coefficient over a wider spectral range than with an ordinary transmission coupler. Two intra-cavity prisms are used to bring the green pumping light longitudinally coincident with the cavity axis, inside the Ti:sapphire crystal. Seeding by a CW Ti:sapphire laser has made it possible to obtain single-mode emission over the whole range of tunability, thanks to the spectral selection of the prisms and to a specifically developed digital/analog controller. Experiments carried out with the system on oxygen atoms inside an oxygen plasma show that the experimental bandwidth is limited essentially by the collisional dephasing rate and the finite pulse duration.

Структуры течений во вращающемся цилиндре с жидкостью и свободным цилиндрическим ядром при вибрациях

In the present work, the modes of steady time-average flows are studied experimentally, which are realized in a quasi-coaxial layer at circular inertial oscillations of a free cylindrical core and its simultaneous differential rotation. The outer cylinder is formed by the wall of a hermetically sealed rotating container. The inner cylinder (core) is hollow and made of polyester film. The volume between the cylinders is filled with a low-viscosity incompressible fluid (water), into which small heavy particles are added, which serve for visualization. The container is installed horizontally and rotates rapidly, so that the core occupies a stable position on the cavity axis. To measure the rotation rate of the core, synchronization with the flicker frequency of a stroboscope is used; to study the flow structure by the distribution of visualizer particles, photo-recording is used. To excite the core oscillations, translational vibrations are applied to the container directed perpendicular to the axis of rotation. In this case, an intensive leading rotation of the core is generated. Depending on the mode of the core motion, various distribution structures of the visualizers are observed. At relatively low rates of the core rotation, structures with a spatial period characteristic of inertial waves are observed. In the case of moderate rates, one observes a regular system of toroidal vortices. At high rates, the flow becomes irregular. The system of toroidal vortices is associated with the centrifugal instability. The threshold of its occurrence is noticeably lower than in the case of the classical Couette–Taylor flow. Analysis of the results shows that the system under study has essential prerequisites for the lowering of the onset threshold of Taylor vortex flow.

Convection of a heat-generating fluid in a rotating cylindrical cavity subject to transverse vibrations

abstract The goal of this research is to study experimentally and theoretically the influence of transversal vibrations on the average convection of a non-isothermal fluid in a rotating cavity when the rotational frequency and vibration frequency approach each other. The research involves experimental studies of the convection of a heat-generating fluid in a rotating horizontal cylinder with isothermal boundaries subject to translational vibrations, perpendicular to the rotation axis. In the absence of vibrations, at fast cavity rotation the fluid is in an equilibrium state in the centrifugal force field with the temperature maximum at the cavity axis. The excitation of average convection and increase of heat transport is discovered when the vibration frequency is near to the rotation frequency. At some discrepancy between the frequencies, the resonance excitation of azimuthal two-dimensional inertial oscillations of the non-isothermal fluid column takes place. This results in significant decrease of the temperature at the cavity axis. When the frequencies coincide, the vibrations break the axial symmetry of the centrifugal force field. The resulting force field is stationary in the cavity frame and results in an intensive thermal convection; the theoretical analysis of this phenomenon is presented. The dependence of heat transport on the parameters of vibrations is determined both in the case of resonance liquid oscillations and in the case of equal frequencies. The vibrational and the centrifugal mechanisms play the key role in the convection. The transverse vibrations are demonstrated to be an efficient tool for the control of thermal convection in rotating systems.

Kinetic simulations of laser-induced plume expansion into a background gas under conditions of spatial confinement

Expansion of vapor plume induced by short-pulse laser irradiation of a bottom of a cylindrical cavity or planar trench in a copper target into helium, argon, and xenon background gases at pressure varying from zero to 1 bar is studied numerically. The simulations are performed based on a hybrid computational model that includes an unsteady heat conduction equation, Hertz-Knudsen model of evaporation, and a kinetic model of two-component gas flow implemented in the form of the Direct Simulation Monte Carlo method. It is found that increasing background pressure results in the formation of a complex structure of shock waves, which drastically changes the flow compared to the case of expansion into a vacuum. The moving shocks strongly affect the deposition of the ablated material inside the cavity. In particular, they induce the formation of a near-surface layer with a reduced fraction of vapor, which protects the cavity wall from vapor redeposition. The overall effect of the increasing background gas pressure on the flow structure and redeposition of vapor inside the cavity can be described as a trade-off between the confinement effect, i.e. a reduction in the propagation speed of the primary shock and overall rate of the plume expansion, and the focusing effect of moving shock waves that induce the radial flow towards the cavity axis, increase vapor density around the axis of symmetry, and reduce vapor density at the cavity wall. The efficiency of vapor removal out of the cavity can increase or decrease with increasing molar mass of the background gas depending on whether the flow is dominated by the focusing or confinement effect. These findings suggest that tuning the background gas parameters and geometrical parameters of spatial confinement can be used to effectively control the laser-induced plume expansion process in applications of laser ablation.

Directional Bistability and Nonreciprocal Lasing with Cold Atoms in a Ring Cavity.

We demonstrate lasing into counterpropagating modes of a ring cavity using a gas of cold atoms as a gain medium. The laser operates under the usual conditions of magneto-optical trapping with no additional fields. We characterize the threshold behavior of the laser and measure the second-order optical coherence. The laser emission exhibits directional bistability, switching randomly between clockwise and counterclockwise modes, and a tunable nonreciprocity is observed as the atoms are displaced along the cavity axis.

Computer-aided design-based guided endodontic: A novel approach for root canal access cavity preparation.

In cases of teeth with unusual morphology like calcified pulp canal, guided endodontic treatment is suggested. An endodontic guide which navigates burs according to a preplanned path is used. Existing approaches of endodontic guide design are based on visual observation and analysis of tomographic scan of teeth. Hence, they are time-consuming and expert-dependent. Computer-aided design-based methodology was employed to design and fabricate a customized endodontic guide. A cone beam computed tomographic scan with MIMICS software was used to create a solid model of the teeth. The solid model generated was sliced through the developed program in MATLAB. The geometric centers of consecutive slices were joined to plot the root canals central axis. To gauge the optimum bur angulation for guide design, a straight line fitted in the data set of the geometric center helped create minimally invasive access. Methodology involved simulated verification of the drill path to judge the accuracy and feasibility of root canal access cavity preparation. Next, endodontic guides for extracted teeth were designed and fabricated using a three-dimensional printer, followed by guided root canal access cavity preparation for extracted teeth. To validate the proposed methodology, using a MATLAB image processing tool box, the deviation between the prepared root canal access cavity axis and root canal axis was analyzed in radiographs of post-treated teeth. The deviation between the tool path axis and root canal axis in simulated root canals was found to be not more than 0.210 ± 0.04 mm. The deviation between the axis of the planned root canal access cavity and the prepared root canal access cavity was 0.07 ± 0.02 mm. The proposed method reveals encouraging results for endodontic guide design.

Driven-Dissipative Supersolid in a Ring Cavity.

Supersolids are characterized by the counterintuitive coexistence of superfluid and crystalline order. Here we study a supersolid phase emerging in the steady state of a driven-dissipative system. We consider a transversely pumped Bose-Einstein condensate trapped along the axis of a ring cavity and coherently coupled to a pair of degenerate counterpropagating cavity modes. Above a threshold pump strength the interference of photons scattered into the two cavity modes results in an emergent superradiant lattice, which spontaneously breaks the continuous translational symmetry towards a periodic atomic pattern. The crystalline steady state inherits the superfluidity of the Bose-Einstein condensate, thus exhibiting genuine properties of a supersolid. A gapless collective Goldstone mode correspondingly appears in the superradiant phase, which can be nondestructively monitored via the relative phase of the two cavity modes on the cavity output. Despite cavity-photon losses the Goldstone mode remains undamped, indicating the robustness of the supersolid phase.

Underdosing of the maxillary sinus for small fields used in newer radiotherapy techniques: Comparison of thermoluminescent dosimeter and Monte Carlo data.

To evaluate the underdosing of the maxillary sinus at its distal end produced by air cavity in the path of the 6 MV photon beam. A cubic solid water slab phantom of dimensions 18 cm × 18 cm × 18 cm with 4 cm × 4 cm × 4 cm air cavity 3 cm away from its anterior surface was used in this study. The percentage depth dose (PDD) for 6 MV X-rays along the central axis of the cubical air cavity was measured using thermoluminescent dosimeter-100 chips. The EGSnrc/DOSXYZnrc Monte Carlo (MC) code was used to estimate the PDD values in both homogeneous and inhomogeneous conditions. The dose data were generated for 1 cm × 1 cm, 2 cm × 2 cm, 3 cm × 3 cm, and 5 cm × 5 cm field sizes. Average percentage dose reductions at 1 mm beyond the distal surface of the maxillary sinus for the field sizes 1 × 1, 2 × 2, and 3 × 3 cm2 are 42.4%, 39.5%, and 29.4%, respectively. However, for 5 cm × 5 cm field size, there is a dose enhancement (i.e., overdosing) at 1 mm from the distal surface of the maxillary sinus and the average percentage dose enhancement is 5.9%. Also, beyond 1 cm from the air-water interface, there is dose enhancement for all the field sizes. This study showed that the significant dose reduction occurs near the air-water interface for the treatment techniques using small photon fields such as intensity-modulated radiotherapy or other newer techniques. MC-based treatment planning calculation predicts realistic dose distribution while using small photon fields in the treatment of maxillary sinus.