14,907 research outputs found
P/Q-type calcium-channel blockade in the periaqueductal gray facilitates trigeminal nociception: a functional genetic link for migraine?
No full textThe discovery of mis-sense mutations in the alpha1A subunit of the P/Q-type calcium channel in patients with familial hemiplegic migraine indicates the potential involvement of dysfunctional ion channels in migraine. The periaqueductal gray (PAG) region of the brainstem modulates craniovascular nociception and, through its role in the descending pain modulation system, may contribute to migraine pathophysiology. In this study we sought to investigate the possible link between the genetic mutations found in migraineurs and the PAG as a modulator of craniovascular nociception. We microinjected the P/Q-type calcium-channel blocker omega-agatoxin IVA into the rat ventrolateral PAG (vlPAG). We examined its effect on the nociceptive transmission of second-order neurons recorded in the trigeminal nucleus caudalis and activated by stimulation of the parietal dura mater. After injection of agatoxin into the vlPAG (n = 20) responses to dural stimulation were facilitated by 143% (p < 0.0001) for Adelta-fiber activity and 180% for C-fiber activity (p < 0.05). Similarly, spontaneous background activity increased by 163% (p < 0.0001). These results demonstrate that P/Q-type calcium channels in the PAG play a role in modulating trigeminal nociception and suggest a role for dysfunctional P/Q-type calcium channels in migraine pathophysiology.<br/
Ultrahigh–Q Microtoroid On-Chip Resonators for Low Threshold Microlasers
No full textRecently demonstrated silica toroidal microcavities, as on-chip resonant cavities, become one of the most promising laser resonators due to their exceptional ability to confine optical energy temporarily and spatially (high Q-factor and small mode volume) while being integrated on a silicon substrate.
In the first part of this thesis, semianalytic theory is presented for an in-depth understanding of the high-Q toroidal microcavity coupled to a tapered fiber waveguide. Basic properties of toroidal microcavities such as cavity mode field, resonance wavelength, cavity mode volume, radiative Q-factor, and phase-matching condition are described within the limit of an iterative perturbation expansion method. With this theoretical background, various laser systems with different gain media, utilizing the high-Q toroidal microcavity as a laser resonator, are demonstrated in the latter parts.
As a first example, II-VI semiconductor nanocrystal, CdSe/ZnS (core/shell), quantum dots are coated on the surface of ultrahigh-Q toroidal microcavities. By pulsed excitation of quantum dots on the surface, either through tapered fiber waveguides or free-space, lasing is observed at both room and liquid nitrogen temperature. Use of a tapered fiber coupling substantially lowered the threshold energy when compared to the case of free-space excitation. Further threshold reduction down to 9.9 fJ was made possible by quantum dot density control.
Lasing from an erbium-implanted high-Q silica toroidal microcavity is demonstrated and analyzed in the next chapter. A minimum threshold power as low as 4.5 uW and a maximum output lasing power as high as 39.4 uW are obtained. Control of lasing wavelength is demonstrated by changing the cavity loading. Analytic formulas predicting threshold power, differential slope efficiency are derived and their dependence on cavity loading, erbium ion concentration and Q-factor is found and compared with the experimental results.
The nonlinear oscillation in an ultrahigh-Q silica toroidal microcavity is investigated in the last chapter. A controllable and reversible transition between parametric and Raman oscillation is experimentally demonstrated and theoretically analyzed. By direct change of cavity loading and indirect adjustment of frequency detuning, parametric and/or Raman oscillation can be accessed selectively without modification of cavity geometry in a toroidal microcavity with large enough aspect ratio. Based on an effective cavity gain theory, this transition is analyzed in terms of cavity loading and frequency detuning leading to a better understanding of the combined effects of parametric and Raman processes in silica microcavities.</p
Towards Crowd-based Customer Service: A Mixed-Initiative Tool for Managing Q&A Sites
No full textIn this paper, we propose a mixed-initiative approach to integrate a Q&A site based on a crowd of volunteers with a standard operator-based help desk, ensuring quality of customer service. Q&A sites have emerged as an efficient way to address questions in various domains by leveraging crowd knowledge. However, they lack sufficient reliability to be the sole basis of customer service applications. We built a proof-of-concept mixed-initiative tool that helps a crowd-manager to decide if a question will get a satisfactory and timely answer by the crowd or if it should be redirected to a dedicated operator. A user experiment found that our tool reduced the participants’ cognitive load and improved their performance, in terms of their precision and recall. In particular, those with higher performance benefited more than those with lower performance
Cladding-pumped Raman fibre laser sources
No full textIn this thesis, I investigate cladding-pumped Raman fibre lasers and amplifiers. Such devices, offering a novel way to generate Raman gain, combine the advantages of the hugely successful cladding-pumped rare-earth doped fibre lasers with those of stimulated Raman scattering. They not only inherit most advantages of conventional fibre devices, such as flexibility, high efficiency, compactness, and robustness, but also provide their own advantages and distinct properties relative to conventional fibre sources, i.e., wavelength flexibility and nearly instantaneous gain without energy storage.Cladding-pumped Raman fibre laser sources utilise double-clad Raman fibres as the gain medium. These are similar to a rare-earth doped double-clad fibre except that there is no laserion doping of the core. With double-clad fibres, the high-power output from low-cost multimode pump sources can be converted into diffraction-limited signal beams, e.g., through stimulated Raman scattering. Thus, cladding-pumped Raman fibre laser sources are a kind of brightness enhancers. In the beginning of this thesis, I theoretically analyse various factors that limit the brightness enhancement of such devices. One of the limits is unwanted 2nd-Stokes generation, which restricts the area ratio between the inner cladding and core. By designing a new DCRF with a W-type core, I successfully relax this restriction by nearly five times. Combined with other factors, i.e., core damage threshold, walk-off, numerical aperture, and background loss, a brightness enhancement of more than 3500 for the designed fibre could be achieved in such devices shown by a model with right pump sources and parameters.Secondly, I focus on the conversion efficiency of such devices. A well-designed fibre with inner-cladding-to-core area ratio around six was used as a double-clad Raman fibre, pumped by a source with nearly rectangular pulse shapes. The nearly rectangular pulses were obtained from an erbium and ytterbium co-doped master optical power oscillator through prepulse shaping. A sufficiently short piece was chosen to reduce the background loss and walk-off. The highest peak power conversion into the 1st Stokes was 75% and the energy conversion efficiency was over 60% in a pulsed cladding-pumped Raman fibre amplifier.Thirdly, I study the power scalability. Theoretically, I analyse the achievable power of such devices. The core size turns out to be a critical factor in most cases. The ultimately output power is limited to around 24 kW by thermal lensing if the core is large enough and enough pump power available. Experimentally, in collaboration with co-workers, a 100 W claddingpumped Raman fibre laser was demonstrated at 1116 nm. The output beam was nearly diffraction-limited. It shows the potential of power scalability of such devices and the ability of generating high power diffraction-limited sources at wavelengths outside the conventional range that rare-earth doped fibres offer.Since a large core size is a critical factor for power scaling, new double-clad Raman fibres with large-mode areas were introduced. They were experimentally demonstrated to work as efficiently as the previous fibre. An Nd:YAG laser was used to pump one of these fibres, and a 1 mJ Raman fibre source with good beam quality was thus demonstrated. This shows that double-clad Raman fibres offer another approach to obtaining high-brightness high-energy sources. In addition, based on a cladding-pumped Raman fibre converter, a simple and efficient method was proposed to generate supercontinuum sources
Prediction of Retained Austenite Fraction in Quenching-and-Partitioning (Q&P) Steels Using the Gibbs Energy Balance Approach
No full textPrediction of retained austenite fraction is quite important in designing advanced high strength steels since retained austenite is the source of transformation-induced plasticity. The present study investigates the phase constitution of a medium-carbon Q&P steel by comparing various approaches to the transformation stasis of bainitic ferrite and applying them to the partitioning process. Among them, the modified GEB approach gave the best agreement with the experimental observation, including the effects of heat-treatment condition and chemical composition on phase constitution. This indicates phase transformation during partitioning can be effectively described by the physics of Gibbs energy balance approach.11Nsciescopuskc
Some extensions of the Prabhu-Srivastava theorem involving the (p,q)-gamma function
No full textIn this paper, we obtain some limit formulas for derivatives of (p,q)-gamma
function and (p,q)- digamma function at their poles. These limit formulas
extend the Prabhu-Srivastava theorem involving gamma function and digamma
function.</jats:p
Exclusive [Rho] 0 and [Phi] muoproduction at large Q 2
No full textArneodo M, Arvidson A, Badelek B, et al. Exclusive [Rho] 0 and [Phi] muoproduction at large Q 2. Nucl.Phys. B. 1994;429(3):503-529
Charge density waves and the Coulomb correlation effects in Na2Ti2P2O (P=Sb, As)
No full textTo explore the origin of the phase transitions in Na2Ti2P2O (P = Sb, As), we have investigated their band structures and phonon dispersions based on the ab initio density functional theory. We have found that the phonon softening instabilities occur for both compounds at q(X) and q(M), which lead to charge density wave (CDW) instabilities through the electron-phonon coupling. When the Coulomb correlation effect of Ti d electrons is taken into account, the CDW transition to a 2 x 1 x 1 supercell driven by the normal mode at q(X) produces the most stable state for both compounds. In the CDW ground states, Na2Ti2Sb2O and Na2Ti2As2O have the partial and full gap openings in the band structures, respectively, which are in good agreement with the observed transport and angle-resolved photoemission spectroscopy results. Our paper reveals that the Coulomb correlation effects of Ti d electrons are essential to properly describe the CDW transitions in Na2Ti2P2O.111Nsciescopu
sj-docx-1-npx-10.1177_1934578X211038792 - Supplemental material for Q-marker Prediction Analysis of Rhubarb in <i>Fengyin</i> Decoction Based on Fingerprint and Network Pharmacology
No full textSupplemental material, sj-docx-1-npx-10.1177_1934578X211038792 for Q-marker Prediction Analysis of Rhubarb in Fengyin Decoction Based on Fingerprint and Network Pharmacology by Ji-le Lan, Ye-ping Ruan, Zhu-jun Mao, Li-yan You and Zhong Chen in Natural Product Communications</p
- …
