12,358 research outputs found
Statistical PT-symmetric lasing in an optical fiber network
PT-symmetry in optics is a condition whereby the real and imaginary parts of
the refractive index across a photonic structure are deliberately balanced.
This balance can lead to a host of novel optical phenomena, such as
unidirectional invisibility, loss-induced lasing, single-mode lasing from
multimode resonators, and non-reciprocal effects in conjunction with
nonlinearities. Because PT-symmetry has been thought of as fragile,
experimental realizations to date have been usually restricted to on-chip
micro-devices. Here, we demonstrate that certain features of PT-symmetry are
sufficiently robust to survive the statistical fluctuations associated with a
macroscopic optical cavity. We construct optical-fiber-based coupled-cavities
in excess of a kilometer in length (the free spectral range is less than 0.8
fm) with balanced gain and loss in two sub-cavities and examine the lasing
dynamics. In such a macroscopic system, fluctuations can lead to a
cavity-detuning exceeding the free spectral range. Nevertheless, by varying the
gain-loss contrast, we observe that both the lasing threshold and the growth of
the laser power follow the predicted behavior of a stable PT-symmetric
structure. Furthermore, a statistical symmetry-breaking point is observed upon
varying the cavity loss. These findings indicate that PT-symmetry is a more
robust optical phenomenon than previously expected, and points to potential
applications in optical fiber networks and fiber lasers.Comment: Submitted to Nature Communications, Pages 1-19: Main manuscript;
Pages 20-38: Supplementary material
Synthesis of Triazolo and Pyrazolo Derivatives of Quinoline Nucleus
New heterocyclic derivatives of quinoline are reported. Reaction of quinoline-2-thiol 4 with hydrazine hydrate gave 2-hydrazionoquinoline 5. Treatment of 5 with CS2 in pyridine afforded 1,2,4-triazolo-[4,3-a]-quinolin-1-2H-thione 6, whereas the reaction of 5 with carboxylic acids namely formic acid or acetic acid, yielded the 1,2,4-triazol-[4,3-a]-quinolin 7 or 5-methyl-1,2,4-triazolo [4,3-a]-quinoline 8 through ring closure. Diazotization of 5 under acidic conditions produced the fused tetrazole compound 9, tetrzolo-[1,5-a]-quinoline. Moreover, treatment of 5 with active methlyene compounds gave two pyrazole derivatives 10 and 11. Azomethines 12a-e were prepared through condensation of 5 with aromatic aldehydes or ketones. Keyword: triazoloquinoline, tetrazoloquinoline, pyrazoloquinolines, azomethines.
Effect of Interaction between Bridge Piers on Local Scouring in Cohesive Soils
Local scour at the piers is one of the main reasons of bridge foundation undermining. Earlier research studies focused mainly on the scour at a single bridge pier; nevertheless, modern designs of the bridges comprise wide-span and thus group of piers rather than a single pier are usually used to support the superstructure. The flow and scour pattern around group of piers is different from the case of a single pier due to the interaction effect. Reviewing the literature of local scour around bridge piers group revealed that the local scour around bridge piers group founded in cohesive soil bed was not investigated, and most of the scour studies were related to scour in cohesionless soils. The objective of the present study is to investigate the effect of the interaction between two in-line (tandem) circular bridge piers of variable spacings founded in cohesive soil on the local scour. A set of laboratory flume experiments were conducted under the clear-water scour condition to investigate this effect. This study is the first that investigates experimentally the scour around group of bridge piers in cohesive bed. It was found that the maximum scour depth at the upstream pier of the two in-line piers occurred at a spacing of two times the diameter of the pier, scour at the downstream pier was reduced due to a sheltering effect, the interference effect will be reduced for pier spacings larger than three times of the pier diameter. A recent pier scour equation was used to estimate the scour depths at the two in-line piers in cohesive soil and compare the estimated value with the measured scour depths in the laboratory. The comparison indicated that the proposed scour equation overestimates the scour depths at both the upstream and the downstream pier
Monte Carlo Performance Studies of Candidate Sites for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the next-generation gamma-ray
observatory with sensitivity in the energy range from 20 GeV to beyond 300 TeV.
CTA is proposed to consist of two arrays of 40-100 imaging atmospheric
Cherenkov telescopes, with one site located in each of the Northern and
Southern Hemispheres. The evaluation process for the candidate sites for CTA is
supported by detailed Monte Carlo simulations, which take different attributes
like site altitude and geomagnetic field configuration into account. In this
contribution we present the comparison of the sensitivity and performance of
the different CTA site candidates for the measurement of very-high energy gamma
rays.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
The Growth Of Highly Doped p-GaN On Sapphire By RF Plasma-Assisted Molecular Beam Epitaxy.
In this paper, we present the study of the electrical, structural and optical properties of p-type GaN grown on sapphire by RF plasma-assisted molecular beam epitaxy
(RF-MBE)
A UK-Wide Survey of Life-Threatening Thyroidectomy Complications
Background and Aims. Complications following thyroidectomy can prolong hospital stay and cause significant morbidity particularly for patients treated for benign thyroid conditions. Our aim was to administer a UK-wide survey of thyroid surgery units on frequency and timing of the onset of life-threatening airway complications & correlate to factors that might be associated with them. Methods. A questionnaire including the number of and timing of the onset of life-threatening airway complications, number of thyroidectomy procedures performed per year, surgeon years of experience, the use of difficult airway management protocol, post-operative patient destination, and patient deaths, was sent to 80 UK surgical units. Results. 23/41 hospitals responded reported no postthyroidectomy airway complications. Life-threatening airways complications all occurred within the first 12 hours postoperatively, with 9 cases occurring in the recovery room and in less than 2 hours, 3 cases occurring 2–6 hours, and 3 cases occurring 6 to 12 hours after surgery. Conclusion. The results may support recent publications that advocate thyroidectomy as a less-than-24-hour surgery procedure in selected patients. Further a larger study and standardised protocol are required to establish patients' selection criteria to determine who are likely to develop serious postoperative complication and may require HDU bed
Effects Of Thermal Annealing Of Pt Schottky Contacts On n-GaN.
In this paper, the Schottky behavior of Pt contact on n- GaN grown by RF-plasma assisted molecular beam epitaxy was investigated under different annealing temperatures
Analysis of generalized negative binomial distributions attached to hyperbolic Landau levels
To each hyperbolic Landau level of the Poincar\'e disc is attached a
generalized negative binomial distribution. In this paper, we compute the
moment generating function of this distribution and supply its decomposition as
a perturbation of the negative binomial distribution by a finitely-supported
measure. Using the Mandel parameter, we also discuss the nonclassical nature of
the associated coherent states. Next, we determine the L\'evy-Kintchine
decomposition its characteristic function when the latter does not vanish and
deduce that it is quasi-infinitely divisible except for the lowest hyperbolic
Landau level corresponding to the negative binomial distribution. By
considering the total variation of the obtained quasi-L\'evy measure, we
introduce a new infinitely-divisible distribution for which we derive the
characteristic function
Collective character of spin excitations in a system of Mn spins coupled to a two-dimensional electron gas
We have studied the low energy spin excitations in n-type CdMnTe based dilute
magnetic semiconductor quantum wells. For magnetic fields for which the
energies for the excitation of free carriers and Mn spins are almost identical
an anomalously large Knight shift is observed. Our findings suggests the
existence of a magnetic field induced ferromagnetic order in these structures,
which is in agreement with recent theoretical predictions [J. K{\"o}nig and A.
H. MacDonald, submitted Phys. Rev. Lett. (2002)]Comment: 4 figure
Microbial biomass, nutrient availability and nutrient uptake by wheat in two soils with organic amendments
A 72-day greenhouse pot experiment was conducted with a sandy loam or a silt loam soil to examine the effects of farmyard manure (FYM), poultry litter (PL) and biogenic waste compost (BWC) at 10 g dw kg-1 soil on microbial biomass and activity and growth and nutrient uptake by wheat. Soil samples were collected at days 0, 14, 28, 42, 56 and 72 after planting. Growth and nutrient uptake by wheat were determined on day 72. All three amendments increased microbial biomass C, N and P, dehydrogenase activity, plant growth and nutrient uptake with a greater effect by FYM and PL than by BWC. All amendments increased microbial biomass C, N and P and enzyme activity particularly on day 0. These microbial parameters decreased after day 0 indicating microbial biomass turnover. All amendments increased plant growth and nutrient uptake. It is concluded that organicamendments can stimulate microbial growth and nutrient uptake as well as plant growth and nutrient uptake. Microbes can increase plant nutrient availability by nutrient mobilisation but also because nutrients taken up by the microbial biomass initially could become available to plants when the microbial biomass turns over as the easily available C is depleted.M.A. Malik, K.S. Khan, P. Marschner, Fayyaz-ul-Hassa
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