Strong exciton-plasmon coupling in semiconducting carbon nanotubes

We study theoretically the interactions of excitonic states with surface electromagnetic modes of small-diameter (~1 nm) semiconducting single-walled carbon nanotubes. We show that these interactions can result in strong exciton-surface-plasmon coupling. The exciton absorption line shape exhibits Rabi splitting ~0.1 eV as the exciton energy is tuned to the nearest interband surface plasmon resonance of the nanotube. We also show that the quantum confined Stark effect may be used as a tool to control the exciton binding energy and the nanotube band gap in carbon nanotubes in order, e.g., to bring the exciton total energy in resonance with the nearest interband plasmon mode. The exciton-plasmon Rabi splitting we predict here for an individual carbon nanotube is close in its magnitude to that previously reported for hybrid plasmonic nanostructures artificially fabricated of organic semiconductors on metallic films. We expect this effect to open up paths to new tunable optoelectronic device applications of semiconducting carbon nanotubes.Comment: 22 pages, 8 figures, accepted for PR

Population structure of the spawning roach Rutilus rutilus in water bodies of the Dniprovs’ko-Orilsky nature reserve

Розглянуто стан популяції фонового виду іхтіофауни заповідника – Rutilus rutilus Linnaeus, 1758. Вивчено базові популяційні параметри виду. Надано оцінку сучасному стану та визначено перспективи подальшого існування плітки у водоймах заповідника.Розглянуто стан популяції фонового виду іхтіофауни заповідника – Rutilus rutilus Linnaeus, 1758. Вивчено базові популяційні параметри виду. Надано оцінку сучасному стану та визначено перспективи подальшого існування плітки у водоймах заповідника.The population state of Rutilus rutilus Linnaeus, 1758, which is a common species in the reserve, is under consideration. Basic population parameters of the species have been studied. Assessment of modern state and determination of further perspectives of the roach existence in the reserve’s basins have been done

Структура нерестової популяції ляща (Abramis brama) водойм Дніпровсько-Орільського природного заповідника

The population state of important food fish Abramis brama L. in the Dniprovsko-Orelsky Nature Reserve is under consideration . Basic population parameters of the species have been studied. Assessment of modern state and determination of perspectives of further existence of the roach in the Reserve’s basins have been done.Розглянуто стан популяції цінного промислового виду іхтіофауни Дніпровського водосховища – Abramis brama Linnaeus, 1758 на акваторії Дніпровсько-Орільського природного заповідника. Визначено основні популяційні характеристики виду у водоймах заповідника. Надано оцінку сучасному стану нерестової популяції та розглянуто перспективи подальшого існування ляща на акваторії заповідника. Розглянуто стан популяції цінного промислового виду іхтіофауни Дніпровського водосховища – Abramis brama Linnaeus, 1758 на акваторії Дніпровсько-Орільського природного заповідника. Визначено основні популяційні характеристики виду у водоймах заповідника. Надано оцінку сучасному стану нерестової популяції та розглянуто перспективи подальшого існування ляща на акваторії заповідника.

Фауна риб прибережної зони дншровсько-орільського заповідника на сучасному етапі розвитку Іхтюценозу

Status of groups of coastal fish in water bodies ofthenaturereserve, anddynamicsoftheirquantitativeandqualitativeparameters isconsidered. Responses of fish communities to changes occurring in floodplain lakes were recorded,with thedeterminationoftheirunderlyingfactors, andmeasuresonmaintaininghomeostasis of this group of aquatic organisms and optimizationoftheirrecoveryandreproductionarerecommended.Розглянуто стан угруповань риб прибережної зони водойм заповідника, динаміку їх кількі- сних та якісних параметрів. Відмічено реакції іхтіоценозів на зміни, які відбуваються в заплав- них озерах, та визначено вплив факторів, що їх обумовлюють. Рекомендовано заходи щодо під- тримки гомеостазу цієї групи водних організмів та оптимізаціїїх відновлення і відтворення.Розглянуто стан угруповань риб прибережної зони водойм заповідника, динаміку їх кількі- сних та якісних параметрів. Відмічено реакції іхтіоценозів на зміни, які відбуваються в заплав- них озерах, та визначено вплив факторів, що їх обумовлюють. Рекомендовано заходи щодо під- тримки гомеостазу цієї групи водних організмів та оптимізаціїїх відновлення і відтворення

Spontaneous decay of excited atomic states near a carbon nanotube

Spontaneous decay process of an excited atom placed inside or outside (near the surface) a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface has been demonstrated to dramatically increase the atomic spontaneous decay rate -- by 6 to 7 orders of magnitude compared with that of the same atom in vacuum. Such an increase is associated with the nonradiative decay via surface excitations in the nanotube.Comment: 8 pages, 3 figure

Фенологія нересту плоскирки (Blicca bjoerkna) у біотопах природного заповідника «Дніпровсько-Орільський» залежно від сезонної зміни температур

This paper examines the relationship between climatic conditions and the phenology of spawning of the white bream Blicca bjoerkna (Linnaeus, 1758) in natural habitats of the "Dnipro-Orylskiy" Nature Reserve. The characteristic of spawning distribution is symmetric, as the asymmetry coefficients do not significantly differ from zero. The distribution of the timing of spawning and its duration are also characterized by excesses, which do not significantly differ from zero alternatives. Analysis of meteorological data for the period of study allowed us to determine the trends in temperature variation, which correlate with the temperature of the water. Spawning events in any given year take place entirely within an upward temperature progression that can be accurately described by a linear equation in the form: Y = b + a · x, where Y – ten-day average temperature; x – the order of decades for I–VI months of the year, a and b – the parameters of the equation. The same equation can be used to describe downward movements in the temperature for decades during the VII–XII months of the year. Regression parameters and coefficients of determination have the following environmental sense. For the ascending temperature branch the regression coefficient b will decrease in proportion to the increase in the contrast between winter and summer temperatures. Due to the fact that linear approximation is a certain generalization of the sinusoid natural course of temperature, it should be borne in mind that the highest summer temperatures are close to the change in direction in the course of temperature from increase to decrease. Therefore, the coefficient b will largely depend on the minimum winter temperatures and should be interpreted as a marker of the coldness of the winter. This interpretation is all the more justified because we are concerned here with assessment of the impact on fish spawning, and the processes that precede spawning events clearly have importance for their explanation. Changes in the direction of the course of temperature which occur after spawning have no value in explaining spawning. If we consider coefficient b beyond the environmental context, then certainly this figure depends on the coldness of the winter and equally on the warmness of the summer. Similar considerations lead us to interpret the coefficient b of a descending branch as a marker of the warmness of the summer. Comparison of the ascending temperature branch of the current year and the descending branch of the previous year gives the coefficient of correlation between these parameters of linear regression r = –0.10, P = 0.39. This result confirms our assumption that the coefficient b of a descending branch is a marker of the warmness of summer, because if it were a marker of the coldness of a winter, then the coefficient of correlation parameters for the temperature course that are common for this winter would be statistically significant. In addition, the absence of connections indicates that these coefficients provide independent and additional information about the weather conditions. Coefficient a for the ascending branch characterizes the rate of warming during the spring, ie the rate of onset of summer, and for the descending branch – the rate of cooling in the fall, that is the speed of the onset of winter. The linear model reflects the general trend of warming in spring and cooling in autumn. In reality, the course of temperature change is by its nature a complex oscillatory process. Therefore the coefficient of determination of linear regression indicates the extent of correspondence of the real process to the linear model. Significant deviations from the general trend lead to a reduction in the coefficient of determination. These variations are the result of processes of sharp warming, alternating with periods of abrupt cooling. The more such events occur, the smaller the coefficient of determination. Thus, to describe the timing of spawning events we can examine the impact on them of such factors as regression model parameters for the current year for the ascending branch of temperature changes and parameters for the model of the previous year for the descending branch of temperature changes. As a result of our studies, we found that during the period 1997–2015 the typical course of temperature during the year is characterized by two branches: ascending and descending. The data obtained support the hypothesis that the onset of the various phases of spawning (the beginning of spawning, the end of spawning, spawning duration) is explained by temperature variation of the current year up to the spawning event and by temperature variation in the preceding year. The timing of the spawning of B. bjoerkna can be described at a statistically significant level by multidimensional factors reflecting the peculiarities of weather conditions and habitat type. The colder the previous summer and the winter of the current year and the fewer variables there are in the course of temperature, the later spawning occurs. The warmer the previous summer and the colder the winter of the current year, the later the spawning ends. Temperature variability in the course of temperature contributes to an earlier completion of spawning. There is a strong correlation between the beginning and the end of the spawning season so the impact of environmental factors at the beginning of spawning is also reflected in the timing of the end of spawning. The influence of conditions in the current year on the end of spawning is conditioned by the timing of the onset of spawning and the impact of weather conditions of the previous year on the end of spawning has independent significance. Установлено залежності фенології нересту плоскирки Bliccabjoerkna (Linnaeus, 1758) у біотопах природного заповідника «Дніпровсько-Орільський» від кліматичних умов. Протягом 1997–2015 рр. нерест плоскирки починався у діапазоні від 29 квітня до 23 травня (на 118–142-гу добу поточного року), а закінчувався в діапазоні від 20 травня до 12 червня (на 139–162-гу добу). Таким чином, нерест тривав 10–30 діб. Типовий хід температури протягом року характеризується наявністю двох гілок: висхідної та низхідної. Одержано дані, які підтверджують гіпотезу про те, що для пояснення часу настання етапів нересту значення має хід температури цього року до моменту настання події (початок нересту, кінець нересту, тривалість нересту) та хід температур минулого року. Терміни початку нересту плоскирки статистично вірогідно можуть бути описані за допомогою багатовимірних факторів, які відображають особливості метеорологічних умов та типів біотопу. Нерест настає тим пізніше, чим холодніші минуле літо та поточна зима, а також чим менш варіабельний хід температур. Кінець нересту настає тим пізніше, чим тепліше попереднє літо та чим холодніша зима. Варіабельність ходу температур сприяє ранньому завершенню нересту. Між термінами початку та кінця нересту існує сильний кореляційний зв’язок, тому вплив екологічних факторів на початок нересту віддзеркалюється також у термінах кінця нересту. Вплив умов поточного року на кінцевий термін нересту опосередковується терміном початку нересту, а вплив метеорологічних умов минулого року на термін закінчення нересту має самостійне значення

Asymptotic exchange coupling of quasi-1D excitons in carbon nanotubes

An analytical expression is obtained for the biexciton binding energy as a function of the inter-exciton distance and binding energy of constituent quasi-one-dimensional excitons in carbon nanotubes. This allows one to trace biexciton energy variation and relevant non-linear absorption under external conditions whereby the exciton binding energy varies. The non-linear absorption lineshapes calculated exhibit characteristic asymmetric (Rabi) splitting as the exciton energy is tuned to the nearest interband plasmon resonance. These results are useful for tunable optoelectronic device applications of optically excited semiconducting carbon nanotubes, including the strong excitation regime with optical non-linearities.Comment: 4 pages, 3 figures. Text and figures updated. References adde

van der Waals coupling in atomically doped carbon nanotubes

We have investigated atom-nanotube van der Waals (vdW) coupling in atomically doped carbon nanotubes (CNs). Our approach is based on the perturbation theory for degenerated atomic levels, thus accounting for both weak and strong atom-vacuum-field coupling. The vdW energy is described by an integral equation represented in terms of the local photonic density of states (DOS). By solving it numerically, we demonstrate the inapplicability of standard weak-coupling-based vdW interaction models in a close vicinity of the CN surface where the local photonic DOS effectively increases, giving rise to an atom-field coupling enhancement. An inside encapsulation of atoms into the CN has been shown to be energetically more favorable than their outside adsorption by the CN surface. If the atom is fixed outside the CN, the modulus of the vdW energy increases with the CN radius provided that the weak atom-field coupling regime is realized (i.e., far enough from the CN). For inside atomic position, the modulus of the vdW energy decreases with the CN radius, representing a general effect of the effective interaction area reduction with lowering the CN curvature.Comment: 15 pages, 5 figure

Spontaneous decay dynamics in atomically doped carbon nanotubes

We report a strictly non-exponential spontaneous decay dynamics of an excited two-level atom placed inside or at different distances outside a carbon nanotube (CN). This is the result of strong non-Markovian memory effects arising from the rapid variation of the photonic density of states with frequency near the CN. The system exhibits vacuum-field Rabi oscillations, a principal signature of strong atom-vacuum-field coupling, when the atom is close enough to the nanotube surface and the atomic transition frequency is in the vicinity of the resonance of the photonic density of states. Caused by decreasing the atom-field coupling strength, the non-exponential decay dynamics gives place to the exponential one if the atom moves away from the CN surface. Thus, atom-field coupling and the character of the spontaneous decay dynamics, respectively, may be controlled by changing the distance between the atom and CN surface by means of a proper preparation of atomically doped CNs. This opens routes for new challenging nanophotonics applications of atomically doped CN systems as various sources of coherent light emitted by dopant atoms.Comment: 10 pages, 4 figure

Nonpolar optical scattering of positronium in magnesium fluoride

We report the results of the analysis of the temperature broadening of the momentum distribution of delocalized Positronium (Ps) in Magnesium Fluoride in terms of optical deformation-potential scattering model (long-wavelength optical phonons). The Ps optical deformation-potential coupling constant $D_{o}$ in MgF$_{2}$ has been determined to be $(1.8\pm0.3)\times10^{9}$ eV/cm. We also show that the Ps momentum distribution is sensitive to second-order phase transitions in those crystals where optical deformation-potential scattering is allowed in one and forbidden in another crystalline phase