Upconversion assisted self-pulsing in a high-concentration erbium doped fiber laser

We report results on experimental and theoretical characterisation of self-pulsing in high concentration erbium doped fibre laser which is free from erbium clusters. Unlike previous models of self-pulsing accounting for pair-induced quenching (PIQ) on the clustered erbium ions, new model has been developed with accounting for statistical nature of the excitation migration and upconversion and resonance-like pumpto-signal intensity noise transfer. The obtained results are in a good agreement with the experimental data

Spiral attractor created by vector solitons

Mode-locked lasers emitting a train of femtosecond pulses called dissipative solitons are an enabling technology for metrology, high-resolution spectroscopy, fibre optic communications, nano-optics and many other fields of science and applications. Recently, the vector nature of dissipative solitons has been exploited to demonstrate mode locked lasing with both locked and rapidly evolving states of polarisation. Here, for an erbium-doped fibre laser mode locked with carbon nanotubes, we demonstrate the first experimental and theoretical evidence of a new class of slowly evolving vector solitons characterized by a double-scroll chaotic polarisation attractor substantially different from Lorenz, Rössler and Ikeda strange attractors. The underlying physics comprises a long time scale coherent coupling of two polarisation modes. The observed phenomena, apart from the fundamental interest, provide a base for advances in secure communications, trapping and manipulation of atoms and nanoparticles, control of magnetisation in data storage devices and many other areas

Rigorous modeling and physical interpretation of terahertz near-field imaging

Apertureless scanning near-field optical microscopy (SNOM) operating with terahertz (THz) laser pulses is a subject of great research interest. The Mie scattering theory is commonly used to explain the features of the optical waves produced by field interactions with SNOM tips and microstructures. However, since Mie scattering fails with SNOMs at submillimeter wavelengths, a rigorous model and analysis are desirable to assess the feasibility of the THz tip-enhanced scanning near-field techniques. In this paper, we present a numerical simulation of an apertureless SNOM imaging system in the THz band. A 2-dimensional model based on the finite element method (FEM) is investigated and discussed. The modeling results are in good agreement with the experimental data obtained for this system at 2 THz radiation [H.-T. Chen at al., Phys. Rev. Lett. 93, 267401 (2004)]. Additionally, a physical interpretation using the antenna theory is successfully confirmed by the simulation results

Objective and violation upper bounds on a DIRECT-filter method for global optimization

This paper addresses the problem of solving a constrained global optimization problem using a modification of the DIRECT method that incorporates the filter methodology to simultaneously minimize the objective function and the constraints violation. Thus, in the “Selection” step of the herein proposed DIRECT-filter algorithm, the hyperrectangles are classified in four categories and subsequently handled separately. The new algorithm also imposes upper bounds on the objective function and constraints violation aiming to discard some hyperrectangles from the process of identifying the potentially optimal ones. A heuristic to avoid the exploration of the hyperrectangles that have been mostly divided is also implemented. Preliminary numerical experiments are carried out to show the effectiveness of the imposed upper bounds on the objective and violation as well as the goodness of the heuristic.The authors wish to thank two anonymous referees for theircomments and suggestions to improve the paper. This work has been supported by FCT{ Fundação para a Ciência e Tecnologia within the Projects Scope: UID/CEC/00319/2019 and UID/MAT/00013/2013

Polarisation dynamics of vector soliton molecules in mode locked fibre laser

Two fundamental laser physics phenomena - dissipative soliton and polarisation of light are recently merged to the concept of vector dissipative soliton (VDS), viz. train of short pulses with specific state of polarisation (SOP) and shape defined by an interplay between anisotropy, gain/loss, dispersion, and nonlinearity. Emergence of VDSs is both of the fundamental scientific interest and is also a promising technique for control of dynamic SOPs important for numerous applications from nano-optics to high capacity fibre optic communications. Using specially designed and developed fast polarimeter, we present here the first experimental results on SOP evolution of vector soliton molecules with periodic polarisation switching between two and three SOPs and superposition of polarisation switching with SOP precessing. The underlying physics presents an interplay between linear and circular birefringence of a laser cavity along with light induced anisotropy caused by polarisation hole burning

The CRESST Experiment: Recent Results and Prospects

The CRESST experiment seeks hypothetical WIMP particles that could account for the bulk of dark matter in the Universe. The detectors are cryogenic calorimeters in which WIMPs would scatter elastically on nuclei, releasing phonons. The first phase of the experiment has successfully deployed several 262 g sapphire devices in the Gran Sasso underground laboratories. A main source of background has been identified as microscopic mechanical fracturing of the crystals, and has been eliminated, improving the background rate by up to three orders of magnitude at low energies, leaving a rate close to one count per day per kg and per keV above 10 keV recoil energy. This background now appears to be dominated by radioactivity, and future CRESST scintillating calorimeters which simultaneously measure light and phonons will allow rejection of a great part of it.Comment: To appear in the proceedings of the CAPP2000 Conference, Verbier, Switzerland, July, 2000 (eds J. Garcia-Bellido, R. Durrer, and M. Shaposhnikov

The CRESST Dark Matter Search

The current status of CRESST (Cryogenic Rare Event Search using Superconducting Thermometers) and new results concerning the detector development are presented. The basic technique of CRESST is to search for particle Dark Matter (WIMPS, Weakly Interacting Massive particles) by the measurement of non-thermal phonons as created by WIMP-induced nuclear recoils. Combined with the newly developed method of simultaneous measurement of scintillation light, strong background discrimination is possible, resulting in a substantial increase in WIMP detection sensitivity. The short and long term perspectives of CRESST are discussed.Comment: 12 pages, 6 figure

Ятрогенные повреждения лучевого нерва при остеосинтезе плечевой кости. Профилактика, диагностика и лечение

THE RELEVANCE is determined by the significant frequency of iatrogenic injuries of the radial nerve during internal osteosynthesis of the humerus, long-lasting functional disorders, a large number of unsatisfactory results, as well as the lack of a unified approach to diagnosis and treatment.MATERIAL AND METHODS. The causes of iatrogenic damage to the radial nerve were studied in 22 patients who underwent internal fixation during fractures of the humeral diaphysis. The ultrasound examination was used to visualize the radial nerve. In 13 patients (59.1%), a pathogenetic treatment was used, including medication, physical and mechanical therapy.RESULTS AND DISCUSSION. In plate osteosynthesis, a greater number of iatrogenic damage to the radial nerve was observed than during osteosynthesis with screws. The ultrasound method had high diagnostic values to determine the continuity of the nerve trunk and identify conflicts with solid structures. The use of pathogenetic therapy of neuropathy led to a more rapid clinical recovery of limb function.CONCLUSION. To prevent iatrogenic injuries and avoid gross manipulations, the access with sufficient visualization of the radial nerve is necessary in plate osteosynthesis and distal blocking outside the projection of the radial nerve is necessary in intramedullary osteosynthesis. Indications for early revision after iatrogenic damage are neurotmesis and a nerve conflict with bone fragments or an implant.АКТУАЛЬНОСТЬ. Определяется значительной частотой ятрогенных повреждений лучевого нерва при внутреннем остеосинтезе плечевой кости, длительно сохраняющимися функциональными расстройствами, большим количеством неудовлетворительных результатов, а также отсутствием единого подхода к диагностике и лечению.МАТЕРИАЛ И МЕТОДЫ. Изучены причины ятрогенных повреждений лучевого нерва у 22 пациентов, которым при переломах диафиза плечевой кости был выполнен погружной остеосинтез. Для визуализации лучевого нерва использовали ультразвуковое исследование (УЗИ). У 13 пациентов (59,1%) применили патогенетическую схему лечения, включающую медикаментозную, физио- и механотерапию.РЕЗУЛЬТАТЫ И ОБСУЖДЕНИЕ. При остеосинтезе плечевой кости пластинами наблюдали большее число ятрогенных повреждений лучевого нерва, чем при остеосинтезе штифтами. Метод УЗИ имеет высокие показатели диагностической ценности для определения непрерывности нервного ствола и выявления конфликта с твердыми структурами. Применение патогенетической терапии нейропатии приводило к более быстрому клиническому восстановлению функции конечности.ЗАКЛЮЧЕНИЕ. Для профилактики ятрогенных повреждений, кроме избегания грубых манипуляций при накостном остеосинтезе, необходим доступ с достаточной визуализацией лучевого нерва, а при интрамедуллярном остеосинтезе — выполнение дистального блокирования вне проекции лучевого нерва. Показаниями к ранней ревизии после ятрогенного повреждения являются нейротмезис и конфликт нерва с костными отломками или имплантом

The astrometric Gaia-FUN-SSO observation campaign of 99 942 Apophis

Astrometric observations performed by the Gaia Follow-Up Network for Solar System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects first detected by ESA's Gaia mission remain recoverable after their discovery. An observation campaign on the potentially hazardous asteroid (99 942) Apophis was conducted during the asteroid's latest period of visibility, from 12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall performance of the Gaia-FUN-SSO . The 2732 high quality astrometric observations acquired during the Gaia-FUN-SSO campaign were reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric reduction process and the precision of the newly obtained measurements are discussed. We compare the residuals of astrometric observations that we obtained using this reduction process to data sets that were individually reduced by observers and accepted by the Minor Planet Center. We obtained 2103 previously unpublished astrometric positions and provide these to the scientific community. Using these data we show that our reduction of this astrometric campaign with a reliable stellar catalog substantially improves the quality of the astrometric results. We present evidence that the new data will help to reduce the orbit uncertainty of Apophis during its close approach in 2029. We show that uncertainties due to geolocations of observing stations, as well as rounding of astrometric data can introduce an unnecessary degradation in the quality of the resulting astrometric positions. Finally, we discuss the impact of our campaign reduction on the recovery process of newly discovered asteroids.Comment: Accepted for publication in A&

Морфофункциональная характеристика отека-набухания коры головного мозга белых крыс после тяжелой черепно-мозговой травмы без и на фоне применения L-лизина эсцината

Aim of study The study is devoted to a morphometric assessment of the manifestations of edema-swelling of the somatosensory cortex (SSC) of the brain of white rats after severe traumatic brain injury (TBI) without using L-lysine escinate and when using it as a therapeutic effect.Material and methods We stained sections with hematoxylin-eosin and performed morphometric methods. On thin (4 μm) serial frontal sections of SSC, neurons and microvessels in the control (intact animals, n=5) were examined in 1 (n= 5), 3 (n=5), 5 (n=5), 7 (n=5) and 14 (n=5) days after injury without treatment (n=25, comparison group) and with treatment (n=25, main group). In color raster images (lens x100), using the plug-in filter “Find Maxima”, maximum brightness areas (MBA) were determined , which were then analyzed using the “Analyze Particles” program from ImageJ 1.52 s. MBA corresponded to SSC sites with a high degree of hydration of nerve tissue - edema-swelling. Statistical hypotheses were tested using nonparametric criteria.Results and discussion In control animals, a low degree of hydration of SSC tissue was noted (relative area 3-8%). In the comparison group, 1 and 3 days after STBI, foci of edema-swelling covered up to 30% of SSC, in 5 days - up to 15%, in 7 days - up to 20%, in 15 - up to 18%. Significant heteromorphism and heterogeneity of changes in the neuropil around neurons and blood vessels was noted. In the dynamics of the post-traumatic period, the proportion of large foci of edema-swelling (intra- and perineuronal, perivascular) decreased. In the main group, one day after STBI, there was a statistically significantly smaller number of foci of edema-swelling and their total relative area. The values range of these variables significantly decreased. L-lysine escinat affected the water balance most effectively in the acute post-traumatic period (day 1 and 3). The drug “smoothed out” the manifestation peaks (number, focal area) of edema-swelling: the values of the studied morphometric indicators were statistically significantly different. Consequently, morphometric signs of hydropic dystrophy after STBI were detected in both studied groups during the 15 days of observation.Conclusion The degree of SSC nervous tissue hydration increased after STBI. L-lysine escinate statistically significantly reduced manifestations of hydropic dystrophy. The drug significantly affected the degree of hydration of neural tissue observed in the early post-traumatic period.Цель Исследование посвящено морфометрической оценке проявлений отека-набухания соматосенсорной коры (ССК) головного мозга белых крыс после тяжелой черепно-мозговой травмы (ТЧМТ) на фоне использования в качестве лечебного воздействия L-лизина эсцината.Методы исследования Использована окраска срезов гематоксилином-иозином и методы морфометрии. На тонких (4 мкм) серийных фронтальных срезах ССК изучены нейроны и микрососуды в контроле (интактные животные, n=5), через 1 (n=5), 3 (n=5), 5 (n=5), 7 (n=5) и 14 (n=5) суток после травмы без лечения (n=25, группа сравнения) и с лечением (n=25, основная группа). На цветных растровых изображениях (объектив х100) с помощью плагин-фильтра “Find Maxima” определяли зоны максимальной яркости, которые затем анализировали с помощью “Analyze Particles” из программы ImageJ 1.52s. Зоны соответствовали участкам ССК с высокой степенью гидратации нервной ткани - отек-набухание. Статистические гипотезы проверяли с помощью непараметрических критериев.Результаты и обсуждение У контрольных животных отмечена низкая степень гидратации нервной ткани ССК (относительная площадь 3−8%). В группе сравнения через 1 и 3 суток после ТЧМТ очаги отека-набухания охватывали до 30% ССК, через 5 суток - до 15%, через 7 суток - до 20%, через 15 - до 18%. Отмечалась значительная гетероморфность и гетерогенность изменений в нейропиле, вокруг нейронов и сосудов. В динамике посттравматического периода доля крупных очагов отека-набухания (интра- и перинейрональных, периваскулярных) снижалась. В основной группе через одни сутки после ТЧМТ было статистически значимо меньшее количество очагов отека-набухания и их общая относительная площадь была меньше, чем в группе сравнения. Значительно уменьшался разброс значений данных переменных. Наиболее эффективно L-лизина эсцинат действовал на водный баланс в остром посттравматическом периоде (1-е и 3-и сутки). Препарат «сглаживал»  пики проявлений (количество, площадь очагов) отека-набухания: значения изученных морфометрических показателей статистически значимо отличались. Следовательно, морфометрическиепризнаки гидропической дистрофии после ТЧМТ выявлялись в обеих изученных группах на протяжении 15 суток наблюдения.Заключение После ТЧМТ увеличивалась степень гидратации нервной ткани ССК. L-лизин эсцинат статистически значимо уменьшал проявления гидропической дистрофии. Особенно выраженное влияние препарата на степень гидратации нервной ткани отмечено в раннем посттравматическом периоде