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Study Design: Case-control study. Purpose: Analyze association between imaging factors related to the failure of conservative treatment in isolated subaxial cervical facet fractures. Overview of Literature: Facet fracture (F1, F2, and F3 AOSpine) may be stable or unstable depending on clinical and imaging variables, which are not well established. As a result, differences in fracture management lead to differences in surgical or conservative indications, and there is no evidence to predict conservative treatment failure. Methods: Patients were categorized into two groups: six patients (16.2%) with conservative treatment failure (defined as the appearance of neurological symptoms, listhesis >3.5 mm, kyphotic deformation >11°, and/or non-union), and 31 patients (83.7%) with successful conservative management (defined as complete consolidation confirmed by computed tomography [CT] at the 6-month followup). All participants were fitted with rigid collars of the Miami type, and standardized follow-up was performed until consolidation or failure. CT and magnetic resonance imaging (MRI) was used to examine imaging characteristics. Sagittal balance parameters were assessed using CT, and signs of acute disc injury, prevertebral edema, facet synovitis, and interspinous hyperintense signal were assessed using MRI. Results: Thirty-seven patients were diagnosed with unilateral cervical facet fractures between 2009 and 2020. In this sample, acute disc injury had a significative association to failure of conservative treatment in F2 and F3 AOSpine facet fractures, 100% of the failure group presented with traumatic disc injury compared to 9.7% of the successful group, for the other variables: prevertebral edema, 83.7% vs. 41.9%; facet synovitis, 100% vs. 77.4%; and interspinous hyperintensity, 71.4% vs. 38.7%, respectively. With conservative management, all F1 fractures healed successfully. Conservative treatment failed in 20% of F2 fractures and 50% of F3 fractures, respectively. In terms of cervical sagittal balance parameters, there were no significant differences between groups. Conclusions: Conservative management was successful in all F1 fractures. In F2 and F3 types, there was a significant association between acute disc injury and conservative treatment failure. [ABSTRACT FROM AUTHOR]

We study the photodetachment of electrons from sodium anions in room temperature liquid tetrahydrofuran (THF) using a new type of three-pulse pump–probe spectroscopy. Our experiments use two variably-time-delayed pulses for excitation in what is essentially a resonant 1+1 two-photon ionization: By varying the arrival time of the second excitation pulse, we can directly observe how solvent motions stabilize and trap the excited electron prior to electron detachment. Moreover, by varying the arrival times of the ionization (excitation) and probe pulses, we also can determine the fate of the photoionized electrons and the distance they are ejected from their parent Na atoms. We find that as solvent reorganization proceeds, the second excitation pulse becomes less effective at achieving photoionization, and that the solvent motions that stabilize the excited electron following the first excitation pulse occur over a time of ∼450 fs. We also find that there is no spectroscopic evidence for significant solvent relaxation after detachment of the electron is complete. In combination with the results of previous experiments and molecular dynamics simulations, the data provide new insight into the role of the solvent in solution-phase electron detachment and charge-transfer-to-solvent reactions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In "outer sphere" electron transfer reactions, motions of the solvent molecules surrounding the donor and acceptor govern the dynamics of charge flow. Are the relevant solvent motions determined simply by bulk solvent properties such as dielectric constant or viscosity? Or are molecular details, such as the local solvent structure around the donor and acceptor, necessary to understand how solvent motions control charge transfer? In this paper, we address these questions by using ultrafast spectroscopy to study a photoinduced electron transfer reaction with only electronic degrees of freedom: the charge-transfer-to-solvent (CTTS) reaction of Na[sup -] (sodide). Photoexcitation of Na[sup -] places the excited CTTS electron into a solvent-bound excited state; motions of the surrounding solvent molecules in response to this excitation ultimately lead to detachment of the electron. The detached electron can then localize either in an "immediate" contact pair (in the same cavity as the Na atom), which undergoes back electron transfer to regenerate Na[sup -] in ∼ 1 ps, or in a "solvent-separated" contact pair (one solvent shell away from the Na atom), which undergoes back electron transfer in tens to hundreds of picoseconds. We present detailed results for the dynamics of each step of this reaction in several solvents: the ethers tetrahydrofuran, diethyl ether and tetrahydropyran and the amine solvent hexamethylphosphoramide (HMPA). The results are interpreted in terms of a kinetic model that both incorporates spectral shifting of the reaction intermediates due to solvation dynamics and accounts for anisotropic spectral diffusion in polarized transient hole-burning experiments. We find that the rate of CTTS detachment does not correlate simply with any bulk solvent properties, but instead appears to depend on the details of how the solvent packs around the solute. In contrast, the rate for back electron transfer of solvent-separated contact pairs varies inversely... [ABSTRACT FROM AUTHOR]

Investigates the mechanism of the ultrafast production and recombination of solvated electrons in weakly polar fluids. Relevance of solvated electrons on electron transfer reactions and radiation chemistry; Use of femtosecond spectroscopic techniques to explore the dynamics of solvated electrons; Production of delocalized electrons through multiphoton ionization.

Charge-transfer-to-solvent (CTTS) transitions have been the subject of a great deal of interest recently because they represent the simplest possible charge transfer reaction: The CTTS electron transfer from an atomic ion to a cavity in the surrounding solvent involves only electronic degrees of freedom. Most of the work in this area, both experimental and theoretical, has focused on aqueous halides. Experimentally, however, halides make a challenging choice for studying the CTTS phenomenon because the relevant spectroscopic transitions are deep in the UV and because the charge-transfer dynamics can be monitored only indirectly through the appearance of the solvated electron. In this paper, we show that these difficulties can be overcome by taking advantage of the CTTS transitions in solutions of alkali metal anions, in particular, the near-IR CTTS band of sodide (Na[sup -]) in tetrahydrofuran (THF). Using femtosecond pump-probe techniques, we have been able to spectroscopically separate and identify transient absorption contributions not only from the solvated electron, but also from the bleaching dynamics of the Na[sup -] ground state and from the absorption of the neutral sodium atom. Perhaps most importantly, we also have been able to directly observe the decay of the Na[sup -*] excited CTTS state, providing the first direct measure of the electron transfer rate for any CTTS system. Taken together, the data at a variety of pump and probe wavelengths provide a direct test for several kinetic models of the CTTS process. The model which best fits the data assumes a delayed ejection of the electron from the CTTS excited state in ∼700 fs. Once ejected, a fraction of the electrons, which remain localized in the vicinity of the neutral sodium parent atom, recombine on a ∼1.5-ps time scale. The fraction of electrons that recombine depends sensitively on the choice of excitation wavelength, suggesting multiple pathways for charge transfer. The spectrum ... [ABSTRACT FROM AUTHOR]

Observes quantum beats due to coherently prepared acoustic vibrational modes for 14 to 17 nanometer diameter gold particles. Production of quantum beats in transient absorption; Attribution of quantum beats to coherent acoustic vibrational motion in particles; Redistribution of energy from impulsively excited acoustic vibrations to phonon modes.

Studies the excited state dynamics of 9-anthracene-carboxylic acid adsorbed onto the surface of TiO[sub 2] semiconductor particles. Steady-state fluorescence spectra of solutions; Time-resolved measurements; Molecules' electron transfer to the TiO[sub 2] particles.

We control the chain conformation of a semiconducting polymer by encapsulating it within the aligned nanopores of a silica host. The confinement leads to polarized, low-threshold amplified spontaneous emission from the polymer chains. The polymer enters the porous silica film from only one face and the filling of the pores is therefore graded. As a result, the profile of the index of refraction in the film is also graded, in the direction normal to the pores, so that the composite film forms a low-loss, graded-index waveguide. The aligned polymer chains plus naturally formed waveguide are ideally configured for optical gain, with a threshold for amplified spontaneous emission that is twenty times lower than in comparable unoriented polymer films. Moreover, the optimal conditions for ASE are met in only one spatial orientation and with one polarization. The results show that nanometre-scale control of semiconducting polymer chain orientation and position leads to novel and desirable optical properties. [ABSTRACT FROM AUTHOR]

Utilizing the charge-transfer-to-solvent transition of Na−, we measure the excited-state lifetime of the solvated electron (es−) in tetrahydrofuran (THF) in each of three different well-defined local solvent environments: an isolated THF cavity, a THF cavity with a sodium atom located one solvent shell away, and a THF cavity with a sodium atom in the first solvent shell. We find that the excited-state lifetimes of the es− in each environment are the same, suggesting that the solvent-induced non-adiabatic coupling that determines the radiationless transition rate is insensitive to the details of the specific atoms or molecules in the first solvent shell. [Copyright &y& Elsevier]

Examines the femtosecond control of the dynamics of the sodium anion. Identification of the solvated electrons in tetrahydrofuran; Electronic states of the hydrated electrons; Characterization of the electron transfer dynamics of sodide.

Near-field two-photon optical lithography is demonstrated by using ∼120 fs laser pulses at 790 nm in an apertureless near-field optical microscope, which produces lithographic features with ∼70 nm resolution. The technique takes advantage of the field enhancement at the extremity of a metallic probe to induce nanoscale two-photon absorption and polymerization in a commercial photoresist, SU-8. Even without optimization of the resist or laser pulses, the spatial resolution of this technique is as high as λ/10, nearly a factor of 2 better than techniques based on far field two-photon lithography. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Study Design: Case-control study., Purpose: Analyze association between imaging factors related to the failure of conservative treatment in isolated subaxial cervical facet fractures., Overview of Literature: Facet fracture (F1, F2, and F3 AOSpine) may be stable or unstable depending on clinical and imaging variables, which are not well established. As a result, differences in fracture management lead to differences in surgical or conservative indications, and there is no evidence to predict conservative treatment failure., Methods: Patients were categorized into two groups: six patients (16.2%) with conservative treatment failure (defined as the appearance of neurological symptoms, listhesis >3.5 mm, kyphotic deformation >11°, and/or non-union), and 31 patients (83.7%) with successful conservative management (defined as complete consolidation confirmed by computed tomography [CT] at the 6-month followup). All participants were fitted with rigid collars of the Miami type, and standardized follow-up was performed until consolidation or failure. CT and magnetic resonance imaging (MRI) was used to examine imaging characteristics. Sagittal balance parameters were assessed using CT, and signs of acute disc injury, prevertebral edema, facet synovitis, and interspinous hyperintense signal were assessed using MRI., Results: Thirty-seven patients were diagnosed with unilateral cervical facet fractures between 2009 and 2020. In this sample, acute disc injury had a significative association to failure of conservative treatment in F2 and F3 AOSpine facet fractures, 100% of the failure group presented with traumatic disc injury compared to 9.7% of the successful group, for the other variables: prevertebral edema, 83.7% vs. 41.9%; facet synovitis, 100% vs. 77.4%; and interspinous hyperintensity, 71.4% vs. 38.7%, respectively. With conservative management, all F1 fractures healed successfully. Conservative treatment failed in 20% of F2 fractures and 50% of F3 fractures, respectively. In terms of cervical sagittal balance parameters, there were no significant differences between groups., Conclusions: Conservative management was successful in all F1 fractures. In F2 and F3 types, there was a significant association between acute disc injury and conservative treatment failure.