Peri-implant fracture: a rare complication after intramedullary fixation of trochanteric femoral fracture.

INTRODUCTION: Trochanteric femoral fractures are among the most common operatively treated fractures. Intramedullary fixation has become the treatment of choice in many centers around the world. Nevertheless, the knowledge of rare complications of these fractures is limited. In this study, the incidence and treatment strategies for peri-implant fractures (PIF) were assessed. MATERIALS AND METHODS: A single-center retrospective cohort study was done on 987 consecutive operatively treated trochanteric fractures. PFNA cephalomedullary nail was used as a fixation method. All patients were followed up from patient records for peri-implant fractures. Plain radiographs as well as different salvage methods were analyzed and compared. RESULTS: The total rate of peri-implant fractures was 1.4% (n = 14). The rate of PIF for patients treated with short (200 mm) nails, intermediate-length (240 mm) nails, and long nails was 2.7% (n = 2), 1.5% (n = 11), and 0.7% (n = 1), respectively (ns, p > 0.05 for difference). Treatment of choice for PIF was either ORIF with locking plate (57%, n = 8) or exchange nailing (43%, n = 6). None of the PIF patients needed additional surgeries for non-union, malunion, or delayed union. CONCLUSIONS: A PIF is a rare complication of intramedullary fixation of trochanteric fractures. It can be treated with either locking plates or exchange nailing with sufficient results. There are no grounds for favoring long nails to avoid PIFs.

Broadband Laser-Based Infrared Detector for Gas Chromatography.

Cantilever-enhanced photoacoustic spectroscopy coupled with gas chromatography is used to quantitatively analyze a mixture of alcohols in a quasi-online manner. A full identification and quantification of all analytes are achieved based on their spectral fingerprints using a widely tunable continuous-wave laser as a light source. This can be done even in the case of interfering column/septum bleed or simultaneously eluted peaks. The combination of photoacoustic spectroscopy and gas chromatography offers a viable solution for compact and portable instruments in applications that require straightforward analyses with no consumables.

An Ab Initio Molecular Dynamics Study of the Hydrolysis Reaction of Sulfur Trioxide Catalyzed by a Formic Acid or Water Molecule.

Ab initio molecular dynamics (AIMD) calculations have been performed to investigate the role of dynamical and steric effects in formic acid (FA) or H2O-catalyzed gas phase hydrolysis of SO3 to form sulfuric acid. This was done by colliding FA or H2O with the SO3-H2O complex and the water dimer with the SO3 molecule and analyzing the outcomes of 230 AIMD trajectories. Our calculations show that, within simulation times used, sulfuric acid is formed in 5% of FA collisions but is not produced when H2O collides with the SO3-H2O complex or when the water dimer collides with the SO3 molecule. We also find that FA collisions have about 2 times higher probability to form the prereactive complex than H2O collisions. Moreover, our simulations show that the SO3-H2O-FA prereactive complex is more stable in time than the SO3-H2O-H2O prereactive complex. These findings indicate that the FA-catalyzed mechanism is favored over the H2O one when looking from the steric and dynamic effect point of view. Additionally, AIMD simulations starting from the optimized structure of the SO3-H2O-FA prereactive complex have been computed to qualitatively estimate the rate of the sulfuric acid formation. Collisional energy has been observed to promote sulfuric acid formation more effectively than thermal excitation.

Broadband photoacoustic spectroscopy of CH414 with a high-power mid-infrared optical frequency comb.

We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Owing to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high-power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of CH414 is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane.

Cavity-enhanced cantilever-enhanced photo-acoustic spectroscopy.

We have improved the sensitivity of a state-of-the-art cantilever-enhanced photo-acoustic trace gas sensor by combining it with an optical power build-up cavity. The build-up cavity enhances the photo-acoustic signal by a factor of ∼100, resulting in an exceptionally good normalised noise equivalent absorption (NNEA) value of 1.75 × 10-12 W cm-1 Hz-1/2. We demonstrate the sensor platform in the 1530 nm wavelength range with a simple distributed feedback diode laser, achieving 75 ppt sensitivity for C2H2 with a 10 s integration time.

Step-modulated decay cavity ring-down detection for double resonance spectroscopy.

A method of measuring double resonant two-photon signal and background from a single cavity ring-down decay is introduced. This is achieved by modulating the double resonance loss via one of the light sources exciting the transition. The noise performance of the method is characterized theoretically and experimentally. The addition of a new parameter to the fitting function introduces a minor noise increase due to parameter correlation. However, the concurrent recording of the background can extend the stable measurement time. Alternatively, the method allows a faster measurement speed, while still recording the background, which is often advantageous in double resonance measurements. Finally, the method is insensitive to changes in the cavity decay rate at short timescales and can lead to improved performance if they have significant contribution to the final noise level compared to the detector noise.

Ab initio molecular dynamics studies of formic acid dimer colliding with liquid water.

Ab initio molecular dynamics simulations of formic acid (FA) dimer colliding with liquid water at 300 K have been performed using density functional theory. The two energetically lowest FA dimer isomers were collided with a water slab at thermal and high kinetic energies up to 68kBT. Our simulations agree with recent experimental observations of nearly a complete uptake of gas-phase FA dimer: the calculated average kinetic energy of the dimers immediately after collision is 5 ± 4% of the incoming kinetic energy, which compares well with the experimental value of 10%. Simulations support the experimental observation of no delayed desorption of FA dimers following initial adsorption. Our analysis shows that the FA dimer forms hydrogen bonds with surface water molecules, where the hydrogen bond order depends on the dimer structure, such that the most stable isomer possesses fewer FA-water hydrogen bonds than the higher energy isomer. Nevertheless, even the most stable isomer can attach to the surface through one hydrogen bond despite its reduced hydrophilicity. Our simulations further show that the probability of FA dimer dissociation is increased by high collision energies, the dimer undergoes isomerization from the higher energy to the lowest energy isomer, and concerted double-proton transfer occurs between the FA monomers. Interestingly, proton transfer appears to be driven by the release of energy arising from such isomerization, which stimulates those internal vibrational degrees of freedom that overcome the barrier of a proton transfer.

Reduction of FENO by tap water and carbonated water mouthwashes: magnitude and time course.

Fractional exhaled nitric oxide (FENO) assesses eosinophilic inflammation of the airways, but FENO values are also influenced by oral nitric oxide (NO). The aim of this pilot study was to measure FENO and compare the effect of two different mouthwashes on FENO and analyse the duration of the effect. FENO was measured in 12 randomized volunteers (healthy or asthmatic subjects) with a NIOX VERO® analyser at an expiratory flow rate of 50 mL/s. After a baseline measurement, a mouthwash was performed either with tap water or carbonated water and was measured during 20 min in 2 min intervals. The procedure was repeated with the other mouthwash. We found that both mouthwashes reduced FENO immediately at the beginning compared to the baseline (p < .001). The carbonated water mouthwash effect lasted 12 min (p ranging from <0.001 to <0.05). The tap water mouthwash reduced FENO statistically significantly only for 2 min compared with the baseline. We conclude that a single carbonated water mouthwash can significantly reduce the oropharyngeal NO contribution during a 12 min time interval.

Frequency comb assisted two-photon vibrational spectroscopy.

We report a setup for high-resolution two-photon spectroscopy using a mid-infrared continuous wave optical parametric oscillator (CW-OPO) and a near-infrared diode laser as the excitation sources, both of which are locked to fully stabilized optical frequency combs. The diode laser is directly locked to a commercial near-infrared optical frequency comb using an optical phase-locked loop. The near-infrared frequency comb is also used to synchronously pump a degenerate femtosecond optical parametric oscillator to produce a fully stabilized mid-infrared frequency comb. The beat frequency between the mid-infrared comb and the CW-OPO is then stabilized through frequency locking. We used the setup to measure a double resonant two-photon transition to a symmetric vibrational state of acetylene with a sub-Doppler resolution and high signal-to-noise ratio.

Stabilization of femtosecond optical parametric oscillators for infrared frequency comb generation.

A synchronously pumped optical parametric oscillator (SP-OPO) is one of the most common techniques to generate femtosecond frequency combs in the mid-infrared region. Stable long-term operation of an SP-OPO requires active locking of the OPO resonator round-trip time to the pump pulse interval. A simple modulation-free locking method based on stabilization of narrow-band frequency-doubled power of the SP-OPO output comb is demonstrated in this Letter. The method relies on the strong dependency of frequency-doubled power on spectral shape of the comb, leading to better stability of the comb envelope spectrum than the commonly used dither-and-lock method.

Temperature and collision energy effects on dissociation of hydrochloric acid on water surfaces.

Collisions of HCl at the air-water interface modelled by a 72 molecule water slab are studied for a range of various impact energies and temperatures using ab initio molecular dynamics with density functional theory. A range of short-timescale events can follow the collision, from direct scattering to nondissociative trapping on the surface. In most cases, HCl dissociation occurs within a few picoseconds, followed by the formation of a solvent-separated ion pair, or rarely, the reformation of HCl. With increasing impact energy and/or system temperature, dissociation occurs more rapidly, with Cl(-) tending to diffuse deeper into the slab. At temperatures corresponding to the frozen water regime, dissociation is seen only once out of the five thermal collisions, but with the addition of a total of 4kT or more of kinetic energy to HCl, it occurs in all our trajectories within a few ps.

Deprotonation of formic acid in collisions with a liquid water surface studied by molecular dynamics and metadynamics simulations.

Deprotonation of organic acids at aqueous surfaces has important implications in atmospheric chemistry and other disciplines, yet it is not well-characterized or understood. This article explores the interactions of formic acid (FA), including ionization, in collisions at the air-water interface. Ab initio molecular dynamics simulations with dispersion-corrected density functional theory were used. The 8-50 picosecond duration trajectories all resulted in the adsorption of FA within the interfacial region, with no scattering, absorption into the bulk or desorption into the vapor. Despite the known weak acidity of FA, spontaneous deprotonation of the acid was observed at the interface on a broad picosecond timescale, ranging from a few picoseconds typical for stronger acids to tens of picoseconds. Deprotonation occurred in 4% of the trajectories, and was followed by Grotthuss proton transfer through adjacent water molecules. Both sequential and ultrafast concerted proton transfer were observed. The formation of contact ion pairs and solvent-separated ion pairs, and finally the reformation of neutral FA, both trans and cis conformers, occurred in different stages of the dynamics. To better understand the deprotonation mechanisms at the interface compared with the process in bulk water, we used well-tempered metadynamics to obtain deprotonation free energy profiles. While in bulk water FA deprotonation has a free energy barrier of 14.8 kJ mol-1, in fair agreement with the earlier work, the barrier at the interface is only 7.5 kJ mol-1. Thus, at the air-water interface, FA may dissociate more rapidly than in the bulk. This finding can be rationalized with reference to the dissimilar aqueous solvation and hydrogen-bonding environments in the interface compared to those in bulk liquid water.

Generalized Intermolecular Interaction Tensor Applied to Long-Range Interactions in Hydrogen and Coinage Metal (Cu, Ag, and Au) Clusters.

We present a novel formulation for the intermolecular interaction tensor, which is used to describe the long-range electrostatic, induction, and dispersion interactions. Our formulation is based on concepts drawn from combinatorial analysis and Clifford calculus and enables us to present the interaction tensor in a form that is simple to use and suitable for both numerical and symbolic analyses. We apply the derived formulas to calculate the long-range interaction coefficients in hydrogen and coinage metal (Cu, Ag, and Au) clusters. The electronic structure calculations are performed at the CCSD(T) level, with triple-ζ and quadruple-ζ basis sets. The multipole moments and dispersion coefficients are obtained as fits to the derived interaction formulas. The most important interaction parameters are obtained accurately and are in good agreement with other results.

The effect of large amplitude motions on the vibrational intensities in hydrogen bonded complexes.

We have developed a model to calculate accurately the intensity of the hydrogen bonded XH-stretching vibrational transition in hydrogen bonded complexes. In the Local Mode Perturbation Theory (LMPT) model, the unperturbed system is described by a local mode (LM) model, which is perturbed by the intermolecular modes of the hydrogen bonded system that couple with the intramolecular vibrations of the donor unit through the potential energy surface. We have applied the model to three complexes containing water as the donor unit and different acceptor units, providing a series of increasing complex binding energy: H2O⋯N2, H2O⋯H2O, and H2O⋯NH3. Results obtained by the LMPT model are presented and compared with calculated results obtained by other vibrational models and with previous results from gas-phase and helium-droplet experiments. We find that the LMPT model reduces the oscillator strengths of the fundamental hydrogen bonded OH-stretching transition relative to the simpler LM model.

High-power mid-infrared frequency comb from a continuous-wave-pumped bulk optical parametric oscillator.

We demonstrate that it is possible to obtain a mid-infrared optical frequency comb (OFC) experimentally by using a continuous-wave-pumped optical parametric oscillator (OPO). The comb is generated without any active modulation. It is based on cascading quadratic nonlinearities that arise from intra-cavity phase mismatched second harmonic generation of the signal wave that resonates in the OPO. The generated OFC is transferred from the signal wavelength (near-infrared) to the idler wavelength (mid-infrared) by intracavity difference frequency generation between the OPO pump wave and the signal comb. We have produced a mid-infrared frequency comb which is tunable from 3.0 to 3.4 µm with an average output power of up to 3.1 W.

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy.

We report on a tunable continuous-wave mid-infrared optical parametric oscillator (OPO), which is locked to a fully stabilized near-infrared optical frequency comb using a frequency doubling scheme. The OPO is used for 40 GHz mode-hop-free, frequency-comb-locked scans in the wavelength region between 2.7 and 3.4 µm. We demonstrate the applicability of the method to high-precision cavity-ring-down spectroscopy of nitrous oxide (N2O) and water (H2O) at 2.85 µm and of methane (CH4) at 3.2 µm.

First and second deprotonation of H2SO4 on wet hydroxylated (0001) α-quartz.

We present an ab initio molecular dynamics study of deprotonation of sulfuric acid on wet quartz, a topic of atmospheric interest. The process is preferred, with 65% of our trajectories at 250 K showing deprotonation. The time distribution of the deprotonation events shows an exponential behavior and predicts an average deprotonation time of a few picoseconds. The process is exoergic, with most of the temperature increase being due to formation of hydrogen bonds prior to deprotonation. In agreement with existing studies of H2SO4 in water clusters, in liquid water, and at the air-water interface, the main determinant of deprotonation is the degree of solvation of H2SO4 by neighboring water molecules. However, we find that if both hydrogens of H2SO4 are simultaneously donated to water oxygens, deprotonation is disfavored. Predicted spectroscopic signatures showing the presence of solvated hydronium and bisulfate are presented. Increasing the temperature up to 330 K accelerates the process but does not change the main features of the deprotonation mechanisms or the spectroscopic signatures. The second deprotonation of H2SO4, studied only at 250 K, occurs provided there is sufficient solvation of the bisulfate by additional water molecules. In comparison to HCl deprotonation on the identical surface examined in our previous work, the first deprotonation of H2SO4 occurs more readily and releases more energy.

Pair-potential approach to accurate dispersion energies between group 12 (Zn, Cd, Hg) clusters.

Dispersion interactions between group 12 (Zn, Cd, Hg) metal clusters are studied at the CCSD(T) level with triple-ζ basis sets. We use atomic orientation dependent C6 dispersion coefficients derived from simple model systems to calculate the intermolecular dispersion energy between larger metal clusters. By using an atomic pair-potential model, we are able to obtain highly accurate results comparable to the CCSD(T) level of theory. For all the systems studied, our method results in a robust description of the dispersion energy at long distances, and it is able to outperform the examined dispersion corrected DFT calculations.

Dispersion interactions in small zinc, cadmium, and mercury clusters.

Dispersion interactions in small clusters of group XII (Zn, Cd, Hg) metal atoms are studied at the CCSD(T) level with triple-ζ basis sets. A pair potential model together with a least-squares fit to the interaction potential energy surface is used to calculate interatomic dispersion coefficients, which are found to be in good agreement with atomistic calculations. The angular dependence of the dispersion interaction, extracted by explicitly accounting for the leading order electrostatic and induction terms, is determined with the aid of a coupled spherical harmonic expansion. The distance dependence of the orientation averaged dispersion energy is modeled by an integral average of our potential model, which is able to robustly account for the average dispersion energy to a remarkable degree.

The effect of large amplitude motions on the transition frequency redshift in hydrogen bonded complexes: a physical picture.

We describe the vibrational transitions of the donor unit in water dimer with an approach that is based on a three-dimensional local mode model. We perform a perturbative treatment of the intermolecular vibrational modes to improve the transition wavenumber of the hydrogen bonded OH-stretching transition. The model accurately predicts the transition wavenumbers of the vibrations in water dimer compared to experimental values and provides a physical picture that explains the redshift of the hydrogen bonded OH-oscillator. We find that it is unnecessary to include all six intermolecular modes in the vibrational model and that their effect can, to a good approximation, be computed using a potential energy surface calculated at a lower level electronic structure method than that used for the unperturbed model.