Content Validity of the LIMB-Q: A Patient-Reported Outcome Instrument for Lower Extremity Trauma Patients.

BACKGROUND: Limb-threatening lower extremity traumatic injuries can be devastating events with a multifaceted impact on patients. Therefore, evaluating patient-reported outcomes (PROs) in addition to traditional surgical outcomes is important. However, currently available instruments are limited as they were not developed specific to lower extremity trauma patients and lack content validity. The LIMB-Q is being developed as a novel PRO instrument to meet this need, with the goal to measure all relevant concepts and issues impacting amputation and limb-salvage patients after limb-threatening lower extremity trauma. METHODS: This is a qualitative interview-based study evaluating content validity for the LIMB-Q. Patients aged 18 years and older who underwent amputation, reconstruction, or amputation after failed reconstruction were recruited using purposeful sampling to maximize variability of participant experiences. Expert opinion was solicited from a variety of clinical providers and qualitative researchers internationally. Preliminary items and scales were modified, added, or removed based on participant and expert feedback after each round of participant interviews and expert opinion. RESULTS: Twelve patients and 43 experts provided feedback in a total of three rounds, with changes to the preliminary instrument made between each round. One scale was dropped after round one, one scale was added after round two, and only minor changes were needed after round three. Modifications, additions and removal of items, instructions, and response options were made after each round using feedback gathered. CONCLUSION: The LIMB-Q was refined and modified to reflect feedback from patients and experts in the field. Content validity for the LIMB-Q was established. Following a large-scale field test, the LIMB-Q will be ready for use in research and clinical care.

Multi-spectral terahertz sensing: proposal for a coupled-cavity quantum cascade laser based optical feedback interferometer.

We propose a laser feedback interferometer operating at multiple terahertz (THz) frequency bands by using a pulsed coupled-cavity THz quantum cascade laser (QCL) under optical feedback. A theoretical model that contains multi-mode reduced rate equations and thermal equations is presented, which captures the interplay between electro-optical, thermal, and feedback effects. By using the self-heating effect in both active and passive cavities, self-mixing signal responses at three different THz frequency bands are predicted. A multi-spectral laser feedback interferometry system based on such a coupled-cavity THz QCL will permit ultra-high-speed sensing and spectroscopic applications including material identification.

Origin of terminal voltage variations due to self-mixing in terahertz frequency quantum cascade lasers.

We explain the origin of voltage variations due to self-mixing in a terahertz (THz) frequency quantum cascade laser (QCL) using an extended density matrix (DM) approach. Our DM model allows calculation of both the current-voltage (I-V) and optical power characteristics of the QCL under optical feedback by changing the cavity loss, to which the gain of the active region is clamped. The variation of intra-cavity field strength necessary to achieve gain clamping, and the corresponding change in bias required to maintain a constant current density through the heterostructure is then calculated. Strong enhancement of the self-mixing voltage signal due to non-linearity of the (I-V) characteristics is predicted and confirmed experimentally in an exemplar 2.6 THz bound-to-continuum QCL.

Model for a pulsed terahertz quantum cascade laser under optical feedback.

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

Micromotion-induced limit to atom-ion sympathetic cooling in Paul traps.

We present, and derive analytic expressions for, a fundamental limit to the sympathetic cooling of ions in radio-frequency traps using cold atoms. The limit arises from the work done by the trap electric field during a long-range ion-atom collision and applies even to cooling by a zero-temperature atomic gas in a perfectly compensated trap. We conclude that in current experimental implementations, this collisional heating prevents access to the regimes of single-partial-wave atom-ion interaction or quantized ion motion. We determine conditions on the atom-ion mass ratio and on the trap parameters for reaching the s-wave collision regime and the trap ground state.

Starfish Procedure.

For those patients with partial hand level amputation who would benefit from myoelectric prosthetic digits for enhanced prehensile function, the Starfish Procedure provides muscle transfers, which allow for the generation of intuitively controlled electromyographic signals for individual digital control with minimal myoelectric cross-talk. Thoughtful preoperative planning allows for creation of multiple sources of high-quality myoelectric signal in a single operation, which does not require microsurgery, providing for wide applicability to hand surgeons of all backgrounds.

Author Correction: Ultrafast switch-on dynamics of frequency-tuneable semiconductor lasers.

The original version of this Article contained an error in the Acknowledgements, which incorrectly omitted the following: 'We also acknowledge support from the Australian Research Council's Discovery Projects Funding Scheme (Grant DP 160 103910).' This has been corrected in both the PDF and HTML versions of the Article.

Ultrafast switch-on dynamics of frequency-tuneable semiconductor lasers.

Single-mode frequency-tuneable semiconductor lasers based on monolithic integration of multiple cavity sections are important components, widely used in optical communications, photonic integrated circuits and other optical technologies. To date, investigations of the ultrafast switching processes in such lasers, essential to reduce frequency cross-talk, have been restricted to the observation of intensity switching over nanosecond-timescales. Here, we report coherent measurements of the ultrafast switch-on dynamics, mode competition and frequency selection in a monolithic frequency-tuneable laser using coherent time-domain sampling of the laser emission. This approach allows us to observe hopping between lasing modes on picosecond-timescales and the temporal evolution of transient multi-mode emission into steady-state single mode emission. The underlying physics is explained through a full multi-mode, temperature-dependent carrier and photon transport model. Our results show that the fundamental limit on the timescales of frequency-switching between competing modes varies with the underlying Vernier alignment of the laser cavity.

Observation of cold collisions between trapped ions and trapped atoms.

We study cold collisions between trapped ions and trapped atoms in the semiclassical (Langevin) regime. Using Yb+ ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes over three decades of collision energies down to 3 mueV (k_{B}x35 mK). The minimum measured rate coefficient of 6x10;{-10} cm;{3} s;{-1} is in good agreement with that derived from a Langevin model for an atomic polarizability of 143 a.u.