Circular External Fixation as a New Offloading Standard of Treatment in Charcot Neuro-Osteoarthropathy Complicated by Midfoot Osteomyelitis: A Pilot, Prospective Case-Control Study.

After surgical treatment of Charcot neuro-osteoarthropathy (CNO) complicated by plantar ulcer and midtarsal osteomyelitis, offloading is mandatory to protect the surgical site. Total contact casting is, to date, the standard-of-care to offload the foot during the postoperative period. We have compared the application of external circular fixator, to the standard of care, with regard to surgical wound healing and time to healing. During the time period from January 2020 to December 2021, 71 consecutive patients admitted to our unit with diabetes and CNO complicated by plantar ulceration and midtarsal osteomyelitis were enrolled in our study. All patients were classified as stage 2, according to the Frykberg & Sanders classification. Wifi wound stage was W2 I0 FI2 in 43 of 71 patients (60.6%) and W2 I2 FI2 in 28 of 71 patients (39.4%). In cases where critical limb ischemia occurred, we performed an endovascular procedure to obtain patency in at least one of the tibial arteries. Localization of osteomyelitis was carried out with magnetic resonance imaging studies, and the degree of deformity was assessed using plain X-ray or computed tomography. A localized ostectomy through the ulceration was carried out with a fasciocutaneous flap to cover the surgical site. In 36 patients, an external circular fixator was applied intraoperatively (exfix+ group); the remaining 35 patients received fiberglass cast in the postoperative period (exfix- group). Complete healing of the surgical site was achieved in 36 of 36 patients in the exfix+ arm and in 22 of 35 in the exfix- arm (P < .02). Time to healing was 68 ± 28 days in exfix+ and 102 ± 88 days in exfix- (P = .05). Circular external frames should be considered as an effective offloading device that enhances the healing rate and reduces time to healing after surgical treatment of midfoot osteomyelitis in subjects affected by CNO.

Calculation of high-order harmonic generation in laser-produced lithium plasma.

We report on detailed calculations of high-order harmonic generation (HHG) spectra from Li, Li+, and He using the Lewenstein model. Our model well describes the HHG experiment in Li plasma [J. Phys. B45, 065601 (2012)JPAPEH0953-407510.1088/0953-4075/45/6/065601]. The cutoff position, in the case of neutral lithium atoms (43th harmonic of 800 nm radiation), corresponds to 3.5×1014 W/cm2 laser intensity, as numerically-simulated in the current work. The difference from the experimental value can be well explained by the measurement errors and uncertainty in determining the laser intensity, which is usually around 25%. We found that Li+ ions do not contribute to HHG plateau region of the spectra and that those ions start to contribute only at very high intensities. Our calculations show that the application of materials possessing higher ionization potential does not necessarily leads to the extension of HHG cutoff.

Time-resolved nuclear dynamics in bound and dissociating acetylene.

We have investigated nuclear dynamics in bound and dissociating acetylene molecular ions in a time-resolved reaction microscopy experiment with a pair of few-cycle pulses. Vibrating bound acetylene cations or dissociating dications are produced by the first pulse. The second pulse probes the nuclear dynamics by ionization to higher charge states and Coulomb explosion of the molecule. For the bound cations, we observed vibrations in acetylene (HCCH) and its isomer vinylidene (CCHH) along the CC-bond with a periodicity of around 26 fs. For dissociating dication molecules, a clear indication of enhanced ionization is found to occur along the CH- and CC-bonds after 10 fs to 40 fs. The time-dependent ionization processes are simulated using semi-classical on-the-fly dynamics revealing the underling mechanisms.

Steering Proton Migration in Hydrocarbons Using Intense Few-Cycle Laser Fields.

Proton migration is a ubiquitous process in chemical reactions related to biology, combustion, and catalysis. Thus, the ability to manipulate the movement of nuclei with tailored light within a hydrocarbon molecule holds promise for far-reaching applications. Here, we demonstrate the steering of hydrogen migration in simple hydrocarbons, namely, acetylene and allene, using waveform-controlled, few-cycle laser pulses. The rearrangement dynamics is monitored using coincident 3D momentum imaging spectroscopy and described with a widely applicable quantum-dynamical model. Our observations reveal that the underlying control mechanism is due to the manipulation of the phases in a vibrational wave packet by the intense off-resonant laser field.

Subfemtosecond steering of hydrocarbon deprotonation through superposition of vibrational modes.

Subfemtosecond control of the breaking and making of chemical bonds in polyatomic molecules is poised to open new pathways for the laser-driven synthesis of chemical products. The break-up of the C-H bond in hydrocarbons is an ubiquitous process during laser-induced dissociation. While the yield of the deprotonation of hydrocarbons has been successfully manipulated in recent studies, full control of the reaction would also require a directional control (that is, which C-H bond is broken). Here, we demonstrate steering of deprotonation from symmetric acetylene molecules on subfemtosecond timescales before the break-up of the molecular dication. On the basis of quantum mechanical calculations, the experimental results are interpreted in terms of a novel subfemtosecond control mechanism involving non-resonant excitation and superposition of vibrational degrees of freedom. This mechanism permits control over the directionality of chemical reactions via vibrational excitation on timescales defined by the subcycle evolution of the laser waveform.

Electron correlation in the formation of hollow states along the Li-like isoelectronic sequence.

Hollow-state (double K-shell vacancy) production in Li-like Be+, B2+, C3+, and F6+ ions colliding with He has been investigated using high-resolution Auger-electron spectroscopy. The formation of discrete states and their relative intensities show striking dependences on the nuclear charge Z of the ion. From the projectile velocity dependences of these states the contribution of the electron-electron interaction is determined, showing that the hollow states are formed largely by electron correlation with a strength that diminishes for increasing Z.

Routes to control of H2 Coulomb explosion in few-cycle laser pulses.

We have measured coincident ion pairs produced in the Coulomb explosion of H2 by 8-30 fs laser pulses at different laser intensities. We show how the Coulomb explosion of H2 can be experimentally controlled by tuning the appropriate pulse duration and laser intensity. For laser pulses less than 15 fs, we found that the rescattering-induced Coulomb explosion is dominated by first-return recollisions, while for longer pulses and at the proper laser intensity, the third return can be made to be the major one. Additionally, by choosing suitable pulse duration and laser intensity, we show H2 Coulomb explosion proceeding through three distinct processes that are simultaneously observable, each exhibiting different characteristics and revealing distinctive time information about the H2 evolution in the laser pulse.

Vibrationally resolved K-shell photoionization of CO with circularly polarized light.

Diffraction of a low energy (<4 eV) carbon-K-photoelectron wave that is created inside a CO molecule by absorption of a circularly polarized photon is investigated. The measurements resolve the vibrational states of the K-shell ionized CO+ molecule and display the photoelectron diffraction patterns in the molecular frame. These show significant variation for the different vibrational states. This effect is stronger than predicted by state-of-the-art theory. As this study is performed close to C-K-threshold and, therefore, far below the molecule's sigma-shape resonance, this surprisingly strong effect is not related to that resonance phenomenon.

Effects of molecular structure on ion disintegration patterns in ionization of O2 and N2 by short laser pulses.

We demonstrate that the structure of the outermost orbitals of oxygen and nitrogen can be observed in the angular distribution of coincident ion pairs generated by the double ionization of these molecules by 8 fs laser pulses. We do this by establishing that these ions emerge from well defined excited electronic states of O2+2 and N2+2 respectively and that they are produced dominantly through a process which involves electron rescattering. The angular distributions of the ions from the two targets are very different, reflecting the different structures of the outermost orbitals of the two molecules.

Evidence for Pauli exchange leading to excited-state enhancement in electron transfer.

Single- and double-electron transfer to autoionizing 1s2l2l(') configurations in fluorine ions have been investigated for 1.1 MeV/u collisions of F7+ and F8+ with He and Ne. The resulting Auger electron emission spectra show anomolously large intensities for the formation of the metastable 1s(2s2p 3P) 4P state compared to the similarly configured 1s(2s2p 3P) 2P- and 1s(2s2p 1P) 2P+ states. The large 4P intensity, which cannot be explained on the basis of spin statistics, is attributed instead to the Pauli exchange of similarly aligned electrons.

Rescattering double ionization of D2 and H2 by intense laser pulses.

We have measured momentum spectra and branching ratios of charged ionic fragments emitted in the double ionization of D2 (and H2) molecules by short intense laser pulses. We find high-energy coincident D+ (and H+) ion pairs with kinetic energy releases between 8 and 19 eV which appear for linearly polarized light but are absent for circularly polarized light. The dependence on the polarization, the energy distributions of the ions, and the dependence on laser intensity of yield ratios lead us to interpret these ion pairs as due to a rescattering mechanism for the double ionization. A quantitative model is presented which accounts for the major features of the data.