Inversionless light amplification and optical switching controlled by state-dependent alignment of molecules

We propose a method to achieve amplification without population inversion by anisotropic molecules whose orientation by an external electric field is state-dependent. It is based on decoupling of the lower-state molecules from the resonant light while the excited ones remain emitting. The suitable class of molecules is discussed, the equation for the gain factor is derived, and the magnitude of the inversionless amplification is estimated for the typical experimental conditions. Such switching of the sample from absorbing to amplifying via transparent state is shown to be possible both with the aid of dc and ac control electric fields.Comment: AMS-LaTeX v1.2, 4 pages with 4 figure

A method for obtaining plastid pigments from the biomass of Chlorella microalgae

Microalgae are distinguished from land plants by the high content of plastid pigments and the biodiversity of carotenoids. The aim of this study is to develop a technology for extracting a pigment complex from the biomass of the microalgae of the genus Chlorella and to determine the extracted pigments’ composition. To obtain biomass, a crude cell suspension of microalgae was used, which was obtained under laboratory conditions for pre-culture cultivation of C. sorokiniana (strain 211-8k). The extraction of plastid pigments from air-dry biomass after disintegration of cell membrane was performed in the 40 kHz mode. It was found that the highest pigment content in ethanol extracts was observed after 30 min (870.0 ± 27.1 mg L -1 ) at 45−50 °C. The pigments’ composition in the resulting total extracts was determined by spectrophotometry and the Reverse Phase HPLC method. The established content of chlorophyll a in the obtained extracts was 537.5 ± 10.0 mg L -1 , the content of chlorophyll b was 182.5 ± 27.5 mg L -1 ; the maximum output of the amount of carotenoids in extracts was 150.0 ± 10.0 mg L -1 . Thus, the main identified forms of carotenoids in extracts from the biomass of microalgae C. sorokiniana were xanthophylls: lutein and fucoxanthin (18.6 and 4.7% of the amount of pigment in extract, respectively) and β-carotene (1.8% of the amount of pigment). It is planned to further fractionate the obtained total extracts of the pigment complex to obtain various forms of chlorophylls and carotenoids to study the spectrum of physiological activity of plastid pigments

Optical spectra, crystal-field parameters, and magnetic susceptibility of the new multiferroic NdFe3(BO3)4

We report high-resolution optical absorption spectra for NdFe3(BO3)4 trigonal single crystal which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering TN = 33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We perform crystal-field calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g-factors. In particular, the values g(perpendicular) = 2.385, g(parallel) = 1.376 were found for the Nd3+ ground-state doublet. We obtain Bloc=7.88 T and |JFN|= 0.48 K for the values of the local effective magnetic field at liquid helium temperatures at the Nd3+ site and the Nd - Fe exchange integral, respectively, using the experimentally measured Nd3+ ground-state splitting of 8.8 cm-1. To check reliability of our set of crystal field parameters we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe3+ ions Jnn = -6.25 K (intra-chain interactions) and Jnnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with the experimental data.Comment: 13 pages, 8 figures, 2 table

Mechanisms controlling primary and new production in a global ecosystem model ? Part I: The role of the large-scale upper mixed layer variability

International audienceA global general circulation model coupled to a simple six-compartment ecosystem model is used to study the extent to which global variability in primary and export production can be realistically predicted on the basis of advanced parameterizations of upper mixed layer physics, without recourse to introducing extra complexity in model biology. The ''K profile parameterization'' (KPP) scheme employed, combined with 6-hourly external forcing, is able to capture short-term periodic and episodic events such as diurnal cycling and storm-induced deepening. The model realistically reproduces various features of global ecosystem dynamics that have been problematic in previous global modelling studies, using a single generic parameter set. The realistic simulation of deep convection in the North Atlantic, and lack of it in the North Pacific and Southern Oceans, leads to good predictions of chlorophyll and primary production in these contrasting areas. Realistic levels of primary production are predicted in the oligotrophic gyres due to high frequency external forcing of the upper mixed layer (accompanying paper Popova et al., 2006) and novel parameterizations of zooplankton excretion. Good agreement is shown between model and observations at various JFOFS time series sites: BATS, KERFIX, Papa and station India. One exception is that the high zooplankton grazing rates required to maintain low chlorophyll in high-nutrient low-chlorophyll and oligotrophic systems lessened agreement between model and data in the northern North Atlantic, where mesozooplankton with lower grazing rates may be dominant. The model is therefore not globally robust in the sense that additional parameterizations were needed to realistically simulate ecosystem dynamics in the North Atlantic. Nevertheless, the work emphasises the need to pay particular attention to the parameterization of mixed layer physics in global ocean ecosystem modelling as a prerequisite to increasing the complexity of ecosystem models

Lattice vibrations of alpha'-NaV_2O_5 in the low-temperature phase. Magnetic bound states?

We report high resolution polarized infrared studies of the quarter-filled spin ladder compound alpha'-NaV_2O_5 as a function of temperature (5K <= T <= 300K). Numerous new modes were detected below the temperature T_c=34K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at T_c and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2, 1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.Comment: 15 pages, 13 Postscript figure

The future of the subsurface chlorophyll-a maximum in the Canada Basin-A model intercomparison

Six Earth system models and three ocean-ice-ecosystem models are analyzed to evaluate magnitude and depth of the subsurface Chl-a maximum (SCM) in the Canada Basin and ratio of surface to subsurface Chl-a in a future climate scenario. Differences in simulated Chl-a are caused by large intermodel differences in available nitrate in the Arctic Ocean and to some extent by ecosystem complexity. Most models reproduce the observed SCM and nitracline deepening and indicate a continued deepening in the future until the models reach a new state with seasonal ice-free waters. Models not representing a SCM show either too much nitrate and hence no surface limitation or too little nitrate with limited surface growth only. The models suggest that suppression of the nitracline and deepening of the SCM are caused by enhanced stratification, likely driven by enhanced Ekman convergence and freshwater contributions with primarily large-scale atmospheric driving mechanisms. The simulated ratio of near-surface Chl-a to depth-integrated Chl-a is slightly decreasing in most areas of the Arctic Ocean due to enhanced contributions of subsurface Chl-a. Exceptions are some shelf areas and regions where the continued ice thinning leaves winter ice too thin to provide a barrier to momentum fluxes, allowing winter mixing to break up the strong stratification. Results confirm that algorithms determining vertically integrated Chl-a from surface Chl-a need to be tuned to Arctic conditions, but likely require little or no adjustments in the future

Optical spectra, crystal-field parameters, and magnetic susceptibility of multiferroic Nd Fe3 (B O3) 4

We report high-resolution optical absorption spectra for Nd Fe3 (B O3) 4 trigonal single crystal, which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering TN =33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We perform crystal-field calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g factors. In particular, the values g =2.385 and g =1.376 were found for the Nd3+ ground-state doublet. We obtain Bloc =7.88 T and JFN =0.48 K for the values of the local effective magnetic field at liquid-helium temperatures at the Nd3+ site and the Nd-Fe exchange integral, respectively, using the experimentally measured Nd3+ ground-state splitting of 8.8 cm-1. To check the reliability of our set of crystal-field parameters, we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe3+ ions Jnn =-6.25 K (intrachain interactions) and Jnnn =-1.92 K (interchain interactions) obtained from fitting agree well with the experimental data. © 2007 The American Physical Society

Three Aspects of the Phenomenon of Science: In Search for Unity among Sociologists

Introduction. In today’s globalising world, science acquires a crucial importance: integrating humanity within the framework of solving global problems, it becomes one of the leading factors in social development, facilitating work and diversifying leisure time, as well as serving as an instrument of transformations in the political sphere. Undoubtedly, the social aspects of contemporary science are capturing the attention of a huge number of researchers. However, it is not clear that all areas of the sociology of science treat the object of their study in the same way. Aim. A lack of reflection on the unity or otherwise in the understanding of the essence of science in the various fields of sociological research makes it difficult to compare different theories of the institutional, cultural, social and communicative contexts of scientific development. An urgent methodological task therefore consists in developing an understanding of the various definitions of the concept of “science” used in the framework of contemporary sociological analysis of this phenomenon. Results and scientific novelty. In this paper, two dominant sociological views on science – as an experimental-mathematical approach to cognising the world and as a system of representations in general – are compared. We conclude that while researchers studying institutional aspects of science tend to interpret it in terms of the “heritage” of post-Enlightenment European rationalism, constructionist and communicatively-oriented researchers tend to approach science as the system of knowledge and cognition that is formed in any human society, having its own specific sociocultural features in each respective case. While each of these two approaches undoubtedly has its own methodological potential, in order to provide such a diverse field of studies with a common ground, it would be necessary to balance them with a third aspect. We argue that this balancing role, since both common for all mankind and unique for every culture, could be played by Heidegger’s conceptualisation of science as “the theory of the real”. Practical significance. In order to avoid a pluralism of incompatible theories, it is important to continually pose the question “what is the object of study when conducting a sociological study of various scientific phenomena?” – as well as to understand the “limits of applicability” of the particular interpretation of science on which basis sociological analysis proceeds.Введение. В современном глобализующемся мире научные знания приобретают все большую значимость: они интегрируют усилия человечества для решения общих проблем, становятся одними из ведущих факторов развития общества, облегчают труд и разнообразят досуг людей. Кроме того, они используются и в качестве инструмента социально-политических трансформаций. Не случайно сегодня внимание огромного количества исследователей приковано к социальным аспектам науки, а также образования как важнейшего взаимосвязанного с ней социального института. Однако вопрос о том, все ли направления социологии науки трактуют объект своего изучения одинаково, остается открытым. Между тем практически полное отсутствие рефлексии по поводу единства в понимании существа науки в поле социологических исследований затрудняет сопоставление различных теорий развития научного знания в институциональном, культурном, социально-коммуникативном контекстах. Такое положение дел актуализирует поиск решения одной из центральных методологических задач по осмыслению вариантов определения понятия «наука», используемых в рамках современного социологического анализа данного феномена. Цель публикации заключается в попытке сопоставить основные трактовки науки – как экспериментально-математического способа познания мира и как системы представлений о существующих реалиях. Результаты и научная новизна. В ходе обсуждения проблемы авторы приходят к выводу о том, что исследования, посвященные изучению институциональных аспектов, тяготеют к пониманию науки как рационалистического «наследия» Европы Нового времени, а конструкционистски и коммуникативистски ориентированные течения склонны рассматривать ее как систему знания и познания, которая формируется в любом человеческом сообществе, имея, однако, в каждом случае свои специфические социокультурные черты. Каждое из двух указанных направлений, несомненно, обладает своим методологическим потенциалом. Тем не менее в целях выведения таких разноплановых исследований на единую почву предлагается уравновесить их третьей точкой зрения, согласно которой наука есть «теория действительного», имеющая черты универсально-общечеловеческого и уникально-культурного феномена. Практическая значимость. Ответ на вопрос: «Что мы изучаем, когда проводим социологическое исследование науки?» позволит избежать плюрализма несопоставимых теорий и понять «границы применимости» той трактовки науки, от которой мы отталкиваемся в социологическом анализе