Ryan D. Murphy

Variation in the femoral bow: a novel high-throughput analysis of 3922 femurs on cross-sectional imaging.

Objectives: To evaluate femoral radius of curvature in a large sample of computed tomography scans to definitively determine the relationship between radius of curvature and femoral length, age, gender, ethnicity, body mass index and cortical thickness. Methods: A retrospective review was conducted of the electronic medical records and advanced imaging of 1961 patients who underwent pulmonary embolism protocol computed tomography scans between December 1999 and March 2010. The computed tomography scans were imported from the clinical picture archiving and communication system archive into a research image archive and analysis system. Each scan was processed by an automated system that algorithmically determined bony landmarks, adjusted for body position within the scanner and measured the radius of curvature. Results: The mean medullary radius of curvature of 3922 femurs was 112 cm (SD = 26 cm). The mean anterior radius of curvature of the femurs was 145 cm (SD = 55 cm). There was a moderately strong positive correlation (0.36–0.39) between femoral length and radius of curvature (P < 0.0001) that was not affected by age, body mass index, cortical thickness, gender, or ethnicity. No significant relationship was found between either gender or ethnicity and radius of curvature independent of femoral length. Conclusions: Differences in radius of curvature based on ethnicity and gender exist primarily because of the variation in average height, and therefore femur length, that exists between ethnic groups and genders. These data may prove useful in the design of safer intramedullary implants that accommodate a greater spectrum of anatomic variation.

Polarization dependent formation of femtosecond laser-induced periodic surface structures near stepped features

Laser-induced periodic surface structures (LIPSS) are formed near 110 nm-tall Au microstructured edges on Si substrates after single-pulse femtosecond irradiation with a 150 fs pulse centered near a 780 nm wavelength. We investigate the contributions of Fresnel diffraction from step-edges and surface plasmon polariton (SPP) excitation to LIPSS formation on Au and Si surfaces. For certain laser polarization vector orientations, LIPSS formation is dominated by SPP excitation; however, when SPP excitation is minimized, Fresnel diffraction dominates. The LIPSS orientation and period distributions are shown to depend on which mechanism is activated. These results support previous observations of the laser polarization vector influencing LIPSS formation on bulk surfaces.

The role of an interface on Ni film removal and surface roughness after irradiation by femtosecond laser pulses

We have observed thin film removal from glass substrates after the irradiation of Ni films with femtosecond laser pulses in air. It was found that the material removal threshold and laser-induced morphology are dependent on film thickness. With decreasing thickness, material removal transitions from intra-film separation to removal at the Ni-glass interface. The Gaussian energy distribution of the laser pulse allows for intra-film separation in the annular region of the crater and interface separation in the center. We propose a model to explain these data as well as the observed increased surface roughness in the interfacial removal regions.

Laser-induced periodic surface structure formation resulting from single-pulse ultrafast irradiation of Au microstructures on a Si substrate

We have observed laser-induced periodic surface structure (LIPSS) formation with sub-micron periodicities after single-pulse ultrafast irradiation of isolated, 110 nm-tall Au microstructures on Si substrates. Fresnel diffraction patterns are established on both the structure surface and surrounding Si substrate when light is scattered by feature edges, and the resultant intensity distribution is partially responsible for LIPSS formation. LIPSS form for any in-plane, laser polarization orientation with respect to surface feature edges, although the LIPSS amplitude varies with the orientation. This explains the formation of LIPSS patterns having different wavevectors and amplitudes after multi-pulse irradiation of initially smooth surfaces.

Pump-probe imaging of laser-induced periodic surface structures after ultrafast irradiation of Si

Ultrafast pump-probe microscopy has been used to investigate laser-induced periodic surface structure (LIPSS) formation on polished Si surfaces. A crater forms on the surface after irradiation by a 150 fs laser pulse, and a second, subsequent pulse forms LIPSS within the crater. Sequentially delayed images show that LIPSS with a periodicity slightly less than the fundamental laser wavelength of 780 nm appear on Si surfaces ∼50 ps after arrival of the second pump laser pulse, well after the onset of melting. LIPSS are observed on the same timescale as material removal, suggesting that their formation involves material ejection.

The dynamics of Al/Pt reactive multilayer ignition via pulsed-laser irradiation

Reactive multilayers consisting of alternating layers of Al and Pt were irradiated by single laser pulses ranging from 100 μs to 100 ms in duration, resulting in the initiation of rapid, self-propagating reactions. The threshold intensities for ignition vary with the focused laser beam diameter, bilayer thickness, and pulse length and are affected by solid state reactions and conduction of heat away from the irradiated regions. High-speed photography was used to observe ignition dynamics during irradiation and elucidate the effects of heat transfer into a multilayer foil. For an increasing laser pulse length, the ignition process transitioned from a more uniform to a less uniform temperature profile within the laser-heated zone. A more uniform temperature profile is attributed to rapid heating rates and heat localization for shorter laser pulses, and a less uniform temperature profile is due to slower heating of reactants and conduction during irradiation by longer laser pulses. Finite element simulations of laser heating using measured threshold intensities indicate that micron-scale ignition of Al/Pt occurs at low temperatures, below the melting point of both reactants.

Nanoparticle size and morphology control using ultrafast laser induced forward transfer of Ni thin films

We have developed a nanoparticle (NP) printing technique using Ni thin film lift-off from glass substrates after ultrafast irradiation in air. Unique interactions of ultrafast laser pulses with thin films allow for control over NP faceting and size distributions. Control is achieved by changing the laser fluence, film thickness, and film-substrate distance. We demonstrate 20 nm Ni film removal from substrates and rapid NP printing, with size distributions centered at a 6 nm diameter. When the Ni film thickness is lowered to 10 nm, NPs are printed with distributions peaked at a 2 nm diameter.

Ultrafast laser orthogonal alignment and patterning of carbon nanotube-polymer composite films

Dual orthogonal alignment of carbon nanotubes (CNTs) within the plane and perpendicular to a substrate is essential for many applications but difficult to obtain. Here, we demonstrate that it is possible using a combination of layer-by-layer deposition and ultrafast laser irradiation. Single-wall CNT-polymer composites preferentially aligned within the plane are irradiated with ultrafast laser pulses. After irradiation with distinct fluences at ambient conditions, morphology is seen where CNTs are formed into bundled CNTs with some orthogonal alignment. A model is presented to account for thermal expansion of the polymer and the formation of CNT bundles.

The role of surface plasmon polariton excitation in Laser Induced Periodic Structure formation after single-shot ultrafast irradiation of Au microstructures

Single-shot ultrafast irradiation of Au microstructures on Si substrates forms Laser Induced Periodic Structures (LIPS) on Si surfaces near features. Surface plasmon polariton excitation influences LIPS formation for certain polarization vector orientations with edges.