Anisotropic ZnS:Cr2+ crystal: material for compact and efficient mid-IR tunable lasers.

A laser-quality anisotropic ZnS:Cr2+ element was obtained using prolonged hot isostatic pressing at high temperature. Lasing centered at a wavelength of 2.45 µm was obtained with longitudinal pumping at a wavelength of 1.94 µm. The short-cavity laser slope efficiency with respect to the absorbed power was about 78%. The lasing wavelength was continuously tuned in the range of 2.35-2.52 µm by rotating the Brewster active element around the normal to its surface.

Dynamics of the isotope exchange reaction of D with H3 +, H2D+, and D2H.

We have measured the merged-beams rate coefficient for the titular isotope exchange reactions as a function of the relative collision energy in the range of ∼3 meV-10 eV. The results appear to scale with the number of available sites for deuteration. We have performed extensive theoretical calculations to characterize the zero-point energy corrected reaction path. Vibrationally adiabatic minimum energy paths were obtained using a combination of unrestricted quadratic configuration interaction of single and double excitations and internally contracted multireference configuration interaction calculations. The resulting barrier height, ranging from 68 meV to 89 meV, together with the various asymptotes that may be reached in the collision, was used in a classical over-the-barrier model. All competing endoergic reaction channels were taken into account using a flux reduction factor. This model reproduces all three experimental sets quite satisfactorily. In order to generate thermal rate coefficients down to 10 K, the internal excitation energy distribution of each H3 + isotopologue is evaluated level by level using available line lists and accurate spectroscopic parameters. Tunneling is accounted for by a direct inclusion of the exact quantum tunneling probability in the evaluation of the cross section. We derive a thermal rate coefficient of <1×10-12 cm3 s-1 for temperatures below 44 K, 86 K, and 139 K for the reaction of D with H3 +, H2D+, and D2H+, respectively, with tunneling effects included. The derived thermal rate coefficients exceed the ring polymer molecular dynamics prediction of Bulut et al. [J. Phys. Chem. A 123, 8766 (2019)] at all temperatures.

Intraoperative Neurophysiological Monitoring during Surgical Correction of Scoliosis for Postoperative Recovery of the Patient's Motor Function.

The aim of the investigation was to study the effect of adverse intraoperative events on the subclinical decrease in the functional state of the sensorimotor system of patients with scoliosis and their early postoperative rehabilitation. Materials and Methods: The results of the examination of 30 adolescents of 13-16 years old with scoliosis before and after surgical correction were compared. Intraoperative neurophysiological monitoring was used by the method of transcranial evoked motor potentials. The patients were divided into two groups depending on the presence or absence of neurophysiological signs of damage to nerve structures during the operation. Results: The amplitude of the M-responses of the muscles of the lower limbs in the postoperative period remains at a level close to the initial one, with a noticeable decrease in the amplitude of voluntary electromyography, which is expressed unevenly and to a greater extent in patients with intraoperative signs of hazard for the motor pathways of the spinal cord. Conclusion: Adverse intraoperative events cause significant changes in the state of the motor system of patients with scoliosis and reduce the effectiveness of rehabilitation treatment in the postoperative period.

[Quantitative characterization of risk of iatrogenic damage to pyramidal tracts based on data of intraoperative neuromonitoring during surgical correction of spinal deformities]. / Kolichestvennaia kharakteristika riska iatrogennykh povrezhdenii piramidnykh putei po dannym intraoperatsionnogo neiromonitoringa pri khirurgicheskoi korrektsii deformatsii pozvonochnika.

OBJECTIVE: Development of a quantitative indicator for the risk level of intraoperative iatrogenic motor disorders in the process of surgical correction of spinal deformity based on current neurophysiological monitoring data. MATERIAL AND METHODS: 288 patients 12.6±0.35 y.o. underwent surgical correction of spinal deformities under the control of intraoperative neuromonitoring. The nature of changes in motor evoked potentials was assessed according to the earlier proposed ranking scale. The incidence of different variants of changes in the rank values of the state of the pyramidal system during the operation and the resulting postoperative motor disturbances was calculated. RESULTS: By comparing probabilities of various changes in the conduction properties of pyramidal tracts during surgery with the incidence of the observed motor deficiencies we quantitatively assessed the possible correlation between these phenomena. We propose a method for calculating the risk index for postoperative motor disorders depending on the maximum rank of the pyramidal system's response to surgical aggression. CONCLUSION: The developed system of ranking evaluation of changes in motor evoked potentials during surgical correction of spinal deformity makes it possible to quantify the risk of postoperative motor disorders and, accordingly, to monitor the level of anxiety for a neurosurgeon during individual stages of surgical intervention.

Measurements of the effective electron density in an electron beam ion trap using extreme ultraviolet spectra and optical imaging.

In an electron beam ion trap (EBIT), the ions are not confined to the electron beam, but rather oscillate in and out of the beam. As a result, the ions do not continuously experience the full density of the electron beam. To determine the effective electron density, n e,eff, experienced by the ions, the electron beam size, the nominal electron density n e, and the ion distribution around the beam, i.e., the so-called ion cloud, must be measured. We use imaging techniques in the extreme ultraviolet (EUV) and optical to determine these. The electron beam width is measured using 3d → 3p emission from Fe xii and xiii between 185 and 205 Å. These transitions are fast and the EUV emission occurs only within the electron beam. The measured spatial emission profile and variable electron current yield a nominal electron density range of n e ∼ 1011-1013 cm-3. We determine the size of the ion cloud using optical emission from metastable levels of ions with radiative lifetimes longer than the ion orbital periods. The resulting emission maps out the spatial distribution of the ion cloud. We find a typical electron beam radius of ∼60 µm and an ion cloud radius of ∼300 µm. These yield a spatially averaged effective electron density, n e,eff, experienced by the ions in EBIT spanning ∼ 5 × 109-5 × 1011 cm-3.

Generation of neutral atomic beams utilizing photodetachment by high power diode laser stacks.

We demonstrate the use of high power diode laser stacks to photodetach fast hydrogen and carbon anions and produce ground term neutral atomic beams. We achieve photodetachment efficiencies of ∼7.4% for H(-) at a beam energy of 10 keV and ∼3.7% for C(-) at 28 keV. The diode laser systems used here operate at 975 nm and 808 nm, respectively, and provide high continuous power levels of up to 2 kW, without the need of additional enhancements like optical cavities. The alignment of the beams is straightforward and operation at constant power levels is very stable, while maintenance is minimal. We present a dedicated photodetachment setup that is suitable to efficiently neutralize the majority of stable negative ions in the periodic table.

Experimental Width Shift Distribution: A Test of Nonorthogonality for Local and Global Perturbations.

The change of resonance widths in an open system under a perturbation of its interior has been recently introduced by Fyodorov and Savin [Phys. Rev. Lett. 108, 184101 (2012)] as a sensitive indicator of the nonorthogonality of resonance states. We experimentally study universal statistics of this quantity in weakly open two-dimensional microwave cavities and reverberation chambers realizing scalar and electromagnetic vector fields, respectively. We consider global as well as local perturbations, and also extend the theory to treat the latter case. The influence of the perturbation type on the width shift distribution is more pronounced for many-channel systems. We compare the theory to experimental results for one and two attached antennas and to numerical simulations with higher channel numbers, observing a good agreement in all cases.

The impact of recent advances in laboratory astrophysics on our understanding of the cosmos.

An emerging theme in modern astrophysics is the connection between astronomical observations and the underlying physical phenomena that drive our cosmos. Both the mechanisms responsible for the observed astrophysical phenomena and the tools used to probe such phenomena-the radiation and particle spectra we observe-have their roots in atomic, molecular, condensed matter, plasma, nuclear and particle physics. Chemistry is implicitly included in both molecular and condensed matter physics. This connection is the theme of the present report, which provides a broad, though non-exhaustive, overview of progress in our understanding of the cosmos resulting from recent theoretical and experimental advances in what is commonly called laboratory astrophysics. This work, carried out by a diverse community of laboratory astrophysicists, is increasingly important as astrophysics transitions into an era of precise measurement and high fidelity modeling.

Experimental results for H2 formation from H- and H and implications for first star formation.

During the epoch of first star formation, molecular hydrogen (H2) generated via associative detachment (AD) of H- and H is believed to have been the main coolant of primordial gas for temperatures below 10(4) kelvin. The uncertainty in the cross section for this reaction has limited our understanding of protogalaxy formation during this epoch and of the characteristic masses and cooling times for the first stars. We report precise energy-resolved measurements of the AD reaction, made with the use of a specially constructed merged-beams apparatus. Our results agreed well with the most recent theoretically calculated cross section, which we then used in cosmological simulations to demonstrate how the reduced AD uncertainty improves constraints of the predicted masses for Population III stars.

A simple double-focusing electrostatic ion beam deflector.

We have developed an electrostatic, double-focusing 90 degrees deflector for fast ion beams consisting of concentric cylindrical plates of differing heights. In contrast to standard cylindrical deflectors, our design allows for focusing of an incoming parallel beam not only in the plane of deflection but also in the orthogonal direction. The optical properties of our design resemble those of a spherical capacitor deflector while it is much easier and more cost effective to manufacture.

A novel merged beams apparatus to study anion-neutral reactions.

We have developed a novel laboratory instrument for studying gas phase, anion-neutral chemistry. To the best of our knowledge, this is the first such apparatus which uses fast merged beams to investigate anion-neutral chemical reactions. As proof-of-principle we have detected the associative detachment reaction H(-)+H-->H(2)+e(-). Here we describe the apparatus in detail and discuss related technical and experimental issues.

Microwave fidelity studies by varying antenna coupling.

The fidelity decay in a microwave billiard is considered, where the coupling to an attached antenna is varied. The resulting quantity, coupling fidelity, is experimentally studied for three different terminators of the varied antenna: a hard-wall reflection, an open wall reflection, and a 50 Ω load, corresponding to a totally open channel. The model description in terms of an effective Hamiltonian with a complex coupling constant is given. Quantitative agreement is found with the theory obtained from a modified VWZ approach [J. J. M. Verbaarschot, Phys. Rep. 129, 367 (1985)].

Distribution of proper delay times in quantum chaotic scattering: a crossover from ideal to weak coupling.

The probability distribution of the proper delay times during scattering on a chaotic system is derived in the framework of the random matrix approach and the supersymmetry method. The result obtained is valid for an arbitrary number of scattering channels as well as arbitrary coupling to the energy continuum. The case of statistically equivalent channels is studied in detail. In particular, the semiclassical limit of an infinite number of weak channels is paid appreciable attention.

Reducing nonideal to ideal coupling in random matrix description of chaotic scattering: application to the time-delay problem.

We write explicitly a transformation of the scattering phases reducing the problem of quantum chaotic scattering for systems with M statistically equivalent channels at nonideal coupling to that for ideal coupling. Unfolding the phases by their local density leads to universality of their local fluctuations for large M. A relation between the partial time delays and diagonal matrix elements of the Wigner-Smith matrix is revealed for ideal coupling. This helped us in deriving the joint probability distribution of partial time delays and the distribution of the Wigner time delay.

Dilatation of deep medullary veins in cortical venous occlusion due to focal tuberculous leptomeningitis.

We report a case of surgically proven, focal left parietal tuberculous leptomeningitis. Occlusion of superficial cerebral veins in the affected area led to dilatation of medullary veins to drain the left parietal lobe. Deep medullary veins were clearly demonstrated on MRI and angiography.