3,990 research outputs found
ΔNp63α a key factor of epithelial differentiation controls the activity of YB-1 oncoprotein: potential implications in carcinogenesis
No full textMy thesis unveils a novel protein-protein association involving ΔNp63αand YB-1 and a mechanism through which a factor essential for epithelial development and differentiation can control the activity of an oncoprotein
Revascularization of turnover sternum: A definitive treatment for intractable funnel chest.
No full textErbium:ytterbium co-doped large-core fiber laser with 297W continuous-wave output power
No full textWe have demonstrated a high-power and high-efficiency erbium:ytterbium (Er:Yb) co-doped fiber laser that produces 297 W of continuous-wave output at 1567 nm. The slope efficiency with respect to the launched pump power changed from 40% to 19% at higher output power due to the onset of Yb co-lasing at 1067 nm. However, the Yb co-lasing was essential for the suppression of catastrophic pulsation at high pump powers that otherwise results if the Yb band gain is allowed to build up. Spectroscopic characteristics of the fiber and the impact of the Yb co-lasing on the 1567 nm slope efficiency are also discussed
High power pulsed ytterbium doped fibre lasers and their applications
No full textThe aim of my project is to develop pulsed Ytterbium (Yb) doped fibre master oscillator power amplifier (MOPA) systems seeded by semiconductor lasers. I was principally focused on two specific projects aligned to sponsored programs of research within the ORC pulsed fibre laser group: the first project, TSB funded project LAMPS, aimed to develop an important class of next generation laser system capable of average output powers of more than 100 W when operating in both the nanosecond and picosecond regimes. The goal was to develop a fully fiberized, polarisation maintaining, single transverse mode system. The full project included the development of the necessary diode & micro-optic systems, fibre beam delivery technology and with application focused evaluations in collaboration with our industrial partners. The main project partners were BAE Systems, Selex, Ceram, Intense Photonics, ORC, Herriot Watt University, Power Photonics, OptoCap and Rofin Sinar. I contributed to the development of the single transverse mode Ytterbium (Yb)-doped fibre system and achieved the full target specifications of 100 W of output power with single mode and single polarisation operation in both the nanosecond and picosecond regimes. In addition, second harmonic generation pumped by the fundamental beam at 1.06 µm was also achieved. In order to transfer from picosecond pulses to nanosecond pulses it is only necessary to switch the seed laser, the power amplifier system remaining unchanged making for a highly flexible system. Both fundamental and second harmonic beam were successfully used to do material processing and various high power frequency conversion experiments (visible, broadband supercontinuum and mid-IR). The second project, called HEGAC (also funded by the TSB), was a collaboration with the University of Cambridge and SPI Lasers Ltd. The aim of the HEGAC project was to develop a high power nanosecond fibre laser with an active pulse shaping capability suitable for cutting metals. This project targeted mJ pulses with more than 100 W average power at the final output – with a 200 W stretch objective. We first achieved more than 310 W using a free space seeding and pumping configuration in our laboratories proving power scaling of our proposed approach. I subsequently rebuilt and improved this system and developed a fully- fiberized version (including all pump launches). The laser was capable of generating >100 W of output power and pulse energies up to 2.5 mJ. This project also involved spatial mode as well as temporal pulse shaping. Using a pair of axicon lenses the normal Gaussian beam profile was converted to a ring shaped profile as required and the system tested up to average powers of 100 W. In addition to the normal temporal pulse shapes required using our pulse shaping system (square, triangle and step), I also achieved high average power pulses with smooth shaped pulses (Parabolic and Gaussian) using an adaptive pulse shaping technique. The laser was transported and successfully used in materials processing experiments at Cambridge, proving the robustness of the design and implementation. I also did some novel experiments on high efficiency Raman conversion exploiting the square shaped pulses possible using this laser
Ytterbium doped nano-crystalline optical fiber for reduced photodarkening
No full textWe report suppression of photodarkening in Yb-doped nano-crystalline fibers in silica host. The photodarkening induced loss reduced by 20 times compared to Yb-doped aluminosilicate fibers. The laser efficiency of the nano-crystalline fiber was 79%
A new technique for substernal colon transposition with a breast dissector: report of 39 cases
No full textThis paper investigates the effectiveness of the breast dissector to
create a substernal space for oesophageal reconstruction. The surgeon must be
extremely careful while dissecting the tissue below the sternum in order to avoid
pneumothorax. The endoscopically assisted preparation of the substernal route is
safe but it requires appropriate training.
A retrospective study on 68 patients who underwent oesophageal reconstruction
was done analysing the patients’ records. In 39 cases, the breast dissector was used.
In 29 cases, the substernal tunnel was created with hand dissection only.
All 68 colon segments were successfully transferred in the two groups of patients.
In all 39 the cases where the breast dissector was used no pneumothorax followed. In
10 (34%) patients of the control group pneumothorax occurred.
Concluding, no more pneumothorax has occurred during the substernal oesophageal
reconstruction since we started using the breast dissector
Yb-doped femtosecond lasers and their frequency doubling
No full textUltralow threshold, compact and highly efficient femtosecond lasers based on Yb³⁺-doped
potassium yttrium tungstate (Yb:KYW) and Yb³⁺-doped vanadium yttrium oxide
(Yb:YVO 4 ) have been demonstrated within this PhD-research project. For a continuous
wave unmode-locked Yb:KYW laser a threshold as low as 101 mW was obtained with a
slope efficiency of 74%. By employing a single prism for dispersion control, the laser was
tunable between 1012 nm to 1069 nm. When operated in the mode-locked regime, this
laser produced transform-limited pulses having durations of 210 fs at a central wavelength
of 1044 nm. Stable mode locking was observed for an optimised incident pulse fluence on
the SESAM between 140 μJ/cm²
to 160 μJ/cm²
which was 2-3 times higher than the
designed energy pulse fluence of the SESAM (70 μJ/cm²).
The employment of several combinations of chirped mirror designs for control of
intracavity group velocity dispersion led to excellent results. The threshold for mode
locking was satisfied for a pump power of 255 mW where the slope efficiency was
measured to be 62%. This is the most efficient SESAM-assisted femtosecond laser yet
reported and the highest optical-to-optical efficiency of 37% is exceptional. Transform-limited pulses with durations as short as 90 fs were produced in a spectral region centred
on 1052 nm. The success of this research thus represents a good foundation on which to
design and build more compact configurations that will incorporate just one chirped mirror
for dispersion compensation.
A relatively high nonlinear refractive index, n₂ , of 15 x 10⁻¹⁶ cm²/W was measured
in Yb:YVO₄ and this affords particular potential for this candidate material in Kerr-lens
mode locking. In fact, for operation in the femtosecond domain, the threshold power was
190 mW with a slope efficiency of 26% and near-transform-limited pulses as short as 61fs were generated at a centre wavelength of 1050 nm. The main objectives in developing
this type of laser relate to a demonstration of high peak power operation in thin disc laser
configurations.
The deployment of a diode-pumped Yb:KYW femtosecond laser as a pump source
for frequency doubling in a periodically-poled LiTaO₃ crystal was realised. The maximum
realized output power of 150 mW corresponded to an impressive second harmonic
conversion efficiency of 43%. 225-fs duration green pulses (centred at 525 nm) were
generated under the condition of strong focusing in the nonlinear crystal
Topological states of thermoelectric Yb-filled skutterudites
No full textThe effects of topological states on the thermoelectric performance of a highly efficient thermoelectric Yb-filled CoSb3 skutterudite are investigated through combined ab initio calculations and electrical transport measurements. The nontrivial topological states are revealed by ab initio calculations and inferred from anoma-lous Hall conductivity and magnetoresistance. The linear bands associated with the topological states lead to low single-band effective mass and high carrier mobility, and consequently high power factor. Furthermore, the additional band minima due to filling the voids with Yb atoms raise the valley degeneracy, which favors the density-of-states effective mass and thus the Seebeck coefficient but scarcely changing the carrier mobility. These effects together contribute to the high power factor of Yb-filled CoSb3 skutterudite. Our results show that topological states play a crucial role in improving the performance of thermoelectric materials
Fiber type and myosin heavy chain compositions of adult pretarsal orbicularis oculi muscle.
No full textTowards the tumble resistant microlight
No full textThe tumble mode is a pitching departure from controlled flight which leads to a pitch autorotation that is generally unrecoverable – resulting in vertical ground impact, usually preceded by in-flight breakup (the mechanism for which, surprisingly, can sometimes prevent loss of life). This was identified in work led by the British Microlight Aircraft Association beginning in 1997 as a response to a number of fatal accidents in Rogallo winged microlight aeroplanes, although the tumble is also known to occur to hang-gliders. This paper explains how this class of aeroplane is controlled, and how it has been found that they can enter the tumble mode. The mechanism by which the tumble can be entered is described. This has led to work showing how flight testing can be used to establish and demonstrate resistance to tumble entry – particularly important with increasing number of very high performance flexwings. These flight tests will be explained, together with the significance of the results. Recent accident investigation work has also shown a new mechanism of tumble entry, through partial failure of the A-frame structure and the pitch-trimmer mechanism. Also described is a possible relevance to well known historical accidents to flying wing aeroplanes– specifically the YB-49 and dH-108, and discovered data on the characteristics of the BKB-1flying wing glider; are also described
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