19 research outputs found
Recommended from our members
Automatic Detection of Anatomical Features on 3D Ear Impressions for Canonical Representation.
We propose a shape descriptor for 3D ear impressions, dederived from a comprehensive set of anatomical features. Motivated by hearing aid (HA) manufacturing, the selection of the anatomical features is carried out according to their uniqueness and importance in HA design. This leads to a canonical ear signature that is highly distinctive and potentially well suited for classification. First, the anatomical features are characterized into generic topological and geometric features, namely concavities, elbows, ridges, peaks, and bumps on the surface of the ear. Fast and robust algorithms are then developed for their detection. This indirect approach ensures the generality of the algorithms with potential applications in biomedicine, biometrics, and reverse engineering
Mid-infrared laser filaments in the atmosphere
Filamentation of ultrashort laser pulses in the atmosphere offers unique
opportunities for long-range transmission of high-power laser radiation and
standoff detection. With the critical power of self-focusing scaling as the
laser wavelength squared, the quest for longer-wavelength drivers, which would
radically increase the peak power and, hence, the laser energy in a single
filament, has been ongoing over two decades, during which time the available
laser sources limited filamentation experiments in the atmosphere to the
near-infrared and visible ranges. Here, we demonstrate filamentation of
ultrashort mid-infrared pulses in the atmosphere for the first time. We show
that, with the spectrum of a femtosecond laser driver centered at 3.9 um, right
at the edge of the atmospheric transmission window, radiation energies above 20
mJ and peak powers in excess of 200 GW can be transmitted through the
atmosphere in a single filament. Our studies reveal unique properties of
mid-infrared filaments, where the generation of powerful mid-infrared
supercontinuum is accompanied by unusual scenarios of optical harmonic
generation, giving rise to remarkably broad radiation spectra, stretching from
the visible to the mid-infrared
Recommended from our members
Excavation of a neolithic house at Yarnbury, near Grassington, North Yorkshire
YesLandscape geophysical survey around the small upland âhengeâ at Yarnbury, Grassington, North Yorkshire revealed few anthropogenic features around the enclosure but did identify a small rectangular structure in the same field. Sample trenching of this feature, radiocarbon and archaeomagnetic dating proved it to be an earlier Neolithic post and wattle structure of a type that is being increasingly recognised in Ireland and the west of Britain. It is the first to be recognised in the Yorkshire Dales and it is argued that the Dales may have been pivotal in the Neolithic for eastâwest trade as well as pastoral upland agriculture
A collaborative artefact reconstruction environment
A novel collaborative artefact reconstruction environment design is presented that is informed by experimental task observation and participatory design. The motivation for the design was to enable collaborative human and computer effort in the reconstruction of fragmented cuneiform tablets: millennia-old clay tablets used for written communication in early human civilisation. Thousands of joining cuneiform tablet fragments are distributed within and between worldwide collections. The reconstruction of the tablets poses a complex 3D jigsaw puzzle with no physically tractable solution. In reconstruction experiments, participants collaborated synchronously and asynchronously on virtual and physical reconstruction tasks. Results are presented that demonstrate the difficulties experienced by human reconstructors in virtual tasks compared to physical tasks. Unlike computer counterparts, humans have difficulty identifying joins in virtual environments but, unlike computers, humans are averse to making incorrect joins. A successful reconstruction environment would marry the opposing strengths and weaknesses of humans and computers, and provide tools to support the communications and interactions of successful physical performance, in the virtual setting. The paper presents a taxonomy of the communications and interactions observed in successful physical and synchronous collaborative reconstruction tasks. Tools for the support of these communications and interactions were successfully incorporated in the âi3Dâ virtual environment design presented
Ruled Surfaces for Rationalization and Design in Architecture
In this work, we address the challenges in the realization of free-form architecture and complex shapes in general with the technical advantages of ruled surfaces. We propose a geometry processing framework to approximate (rationalize) a given shape by one or multiple strips of ruled surfaces. We discuss techniques to achieve an overall smooth surface and develop a parametric model for the generation of curvature continuous surfaces composed of ruled surface strips. We illustrate the usability of the proposed process at hand of several projects, where the pipeline has been applied to compute NC data for mould production and to rationalize large parts of free-form facades.
High energy and average power femtosecond laser for driving mid-infrared optical parametric amplifiers
We have developed the first (to our knowledge) femtosecond Tm-fiber-laser-pumped Ho:YAG room-temperature chirped pulse amplifier system delivering scalable multimillijoule, multikilohertz pulses with a bandwidth exceeding 12 nm and average power of 15 W. The recompressed 530 fs pulses are suitable for broadband white light generation in transparent solids, which makes the developed source ideal for both pumping and seeding optical parametric amplifiers operating in the mid-IR spectral range.Published versio
Review of mid-infrared mode-locked laser sources in the 2.0 ÎŒ mâ3.5 ÎŒ m spectral region
Ultrafast laser sources operating in the mid-infrared (mid-IR) region, which contains the characteristic fingerprint spectra of many important molecules and transparent windows of atmosphere, are of significant importance in a variety of applications. Over the past decade, a significant progress has been made in the development of inexpensive, compact, high-efficiency mid-IR ultrafast mode-locked lasers in the picosecond and femtosecond domains that cover the 2.0âÎŒmâ3.5âÎŒm spectral region. These achievements open new opportunities for applications in areas such as molecular spectroscopy, frequency metrology, material processing, and medical diagnostics and treatment. In this review, starting with the introduction of mid-IR mode-locking techniques, we mainly summarize and review the recent progress of mid-IR mode-locked laser sources, including Tm3+-, Ho3+-, and Tm3+/Ho3+-doped all-solid-state and fiber lasers for the 2.0âÎŒm spectral region, Cr2+:ZnSe and Cr2+:ZnS lasers for the 2.4âÎŒm region, and Er3+-, Ho3+/Pr3+-, and Dy3+-doped fluoride fiber lasers for the 2.8âÎŒmâ3.5âÎŒm region. Then, some emerging and representative applications of mid-IR ultrafast mode-locked laser sources are presented and illustrated. Finally, outlooks and challenges for future development of ultrafast mid-IR laser sources are discussed and analyzed. The development of ultrafast mid-IR laser sources, together with the ongoing progress in related application technologies, will create new avenues of research and expand unexplored applications in scientific research, industry, and other fields.ASTAR (Agency for Sci., Tech. and Research, Sâpore)Published versio