Uniform Index Research Articles

Femtosecond laser line-by-line inscription of apodized fiber Bragg gratings.

The reflection spectra of conventional fiber Bragg gratings (FBGs) with uniform index modulation profiles typically have strong sidelobes, which hamper the performance of FBG-based optical filters, fiber lasers, and sensors. Here, we propose and demonstrate a femtosecond laser line-by-line (LbL) scanning technique for fabricating apodized FBGs with suppressed sidelobes. This approach can flexibly achieve various apodized modulation profiles via precise control over the length and/or transverse position of each laser-inscribed index modification track. We theoretically and experimentally studied the influences of the apodization function on the side-mode suppression ratio (SMSR) in the fabricated apodized FBG, and the results show that a maximum SMSR of 20.6 dB was achieved in a Gaussian-apodized FBG. Subsequently, we used this method to fabricate various apodized FBGs, and the SMSRs in these FBGs were reduced effectively. Specifically, a dense-wavelength-division-multiplexed Gaussian-apodized FBG array with a wavelength interval of 1.50 nm was successfully fabricated, and the SMSR in such an array is 14 dB. Moreover, a Gaussian-apodized phase-shifted FBG and chirped FBG were also demonstrated with a high SMSR of 14 and 16 dB, respectively. Therefore, such an apodization method based on a modified femtosecond laser LbL scanning technique is an effective and flexible way to fabricate various FBGs with high SMSRs, which is promising to improve the performance of optical filters, fiber lasers, and sensors.

Clarifying the factors affecting Larix gmelinii forest regeneration based on structural equation model

Based on data from 49 plots of natural Larix gmelinii forests in Cuigang Forest Farm of Xinlin Forestry Bureau, Daxing'anling Mountains, China, we used 37 measurable variables that mainly focused on stand non-spatial structure, stand spatial structure, species diversity, soil condition, and site condition to construct the structural equation model of natural regeneration densities and size diversities (i.e., height and ground-diameter). The direct, indirect, and total influence coefficients of each path were quantified to extract the critical and controllable factors that influence regeneration density and diversity of natural L. gmelinii forests, which would help implement sustainable forest management. The results showed that the effects of various latent variables on rege-neration density were following an order as: stand non-spatial structure (-0.410) > species diversity (0.380) > soil condition (0.250) > site condition (0.249) > stand spatial structure (0.197), while the order were changed as: soil condition (0.778) > site condition (0.748) > stand spatial structure (0.684) > stand non-spatial structure (0.287) > forest diversity (0.105), when evaluated on the regeneration diversity. Generally, the critical and controllable factors affecting rege-neration quantity and diversity were soil pH, total potassium concentration, species diversity, tree height diversity, uniform angle index and stand volume per hectare. In the management, suitable thinning treatments or replanting broadleaved trees were recommended for optimizing and adjusting species composition, species diversity, soil pH and nutrition, which would promote natural regene-ration.

Effects of Randomized Management on the Forest Distribution Patterns of Larix kaempferi Plantation in Xiaolongshan, Gansu Province, China

Patterns of tree distribution are an important attribute of forest structure and directly affect the health and stability of forest ecosystems. This paper studied the effects of forest management on the forest distribution pattern of Larix kaempferi plantations with an aim to improve the quality of the spatial structure of plantations by providing scientific grounds for near-nature distribution pattern adjustment. We set up 15 long-term positioning and monitoring plots of 20 m × 20 m of L. kaempferi plantations in Xiaolongshan, Gansu Province, China, based on the Clark and Evans index, and applied the structure analysis method of the neighboring tree relationship to determine the standard angle of the uniform angle index of regularly distributed plantation forests. The changes in forest distribution patterns were compared before and after randomized management (R1 (dumbbell-shaped random unit), R2 (torch-shaped random unit) and R1:R2 = 1:2 models) and underlayer tending and unmanaged control (CK). The results showed that (1) Under different management modes, the distribution patterns obtained by the Clark and Evans index and the mean values of the uniform angle index were entirely the same; all stand patterns were evenly distributed. (2) Regardless of randomized management or underlayer tending, the number of trees in the even distribution was the largest, accounting for more than 40%. (3) The mean values of the uniform angle index of most stands increased obviously after randomized management, among which the R1 and R2 stands showed an upward trend, while the R1:R2 = 1:2 stands showed a slight decrease. However, the mean values of the uniform angle index of the stands with underlayer management showed a decreasing trend. (4) The proportion of random trees in most stands increased significantly after randomized management, increasing by 1%~19% compared with that before adjustment, while the proportion of random trees in the underlayer tending treatment decreased by 2%~10%. Our results suggest that (1) The method based on the modified uniform angle index standard angle could effectively improve the accuracy of the distribution pattern of individual trees in plantation forests and further improve the accuracy of the overall stand pattern quantitatively. (2) Randomized management significantly increased the proportion of random trees in the stands, which accelerated the evolution of the forest distribution pattern of the L. kaempferi plantation to a random distribution.

About copying a free-space electromagnetic field by an invisible object

The structure of a monochromatic electromagnetic field inside a spherical object that does not distort the wave field of external sources outside its surface has been studied using transformation optics methods. It is assumed that the object is made of isotropic materials with equal values of permittivity and permeability and consists of a spherical volume of material with a positive spatially uniform refractive index and an adjacent spherical layer of material with a negative inhomogeneous refractive index (i.e., it is a spherical superlens made of isotropic materials). It is shown that the field inside a sphere with a positive refractive index is the reduced-size copy of the field in which the object was located. This copy contains information about the radiation field of external sources in a spherical free-space volume whose radius depends on the object parameters and can be significantly larger than the radius of the object. It is shown that the copying properties of the object with given dimensions can be fully preserved if its outer layer is made of anisotropic materials.

Modeling of a sampled apodized fiber Bragg grating moisture sensor

This study presents a theoretical model that enables a fast and precise calculation of a sampled apodized fiber Bragg grating and the related sensor. Transfer matrix method was used since there is no analytical solution due to the complex refractive index profile. Errors brought by the uniform refractive index profile approximation were compensated, which allows a smaller number of divided segments and therefore a fast and memory efficient simulation. This compensation method realizes a high speed and high precision simulation. The theoretical spectra of both the grating and the sensor agrees well with those given by the experiments. According to the experiment, the sensitivity of the moisture sensor is −0.6165 pm/ppm in mineral oil. This theoretical model provides a new choice for the researchers and developers to design and optimize the sensing structure instead of a blind try and error process.

Influence of M-EMS on Fluid Flow and Initial Solidification in Slab Continuous Casting.

A mathematical model coupled with electromagnetic field has been developed to simulate the transient turbulence flow and initial solidification in a slab continuous casting mold under different electromagnetic stirring (EMS) currents and casting speeds. Through comparing the magnetic flux density, flow field with measured results, the reliability of the mathematical model is proved. The uniform index of solidified shell thickness has been introduced to judge the uniformity of the solidified shell. The results show that a horizonal recirculation flow has been generated when EMS is applied, and either accelerated or decelerated regions of flow field are formed in the liquid pool. Large EMS current and low casting speed may cause the plug flow near the mold narrow face and a suitable EMS current can benefit to the uniform growth of solidified shell. Meanwhile, an industrial test exhibits that EMS can weaken the level fluctuation and number density of inclusion. Overall, a rational EMS current range is gained, when the casting speed is 1.2 m/min, the rational EMS current is 500–600 A.

A general Bayesian framework for foreground modelling and chromaticity correction for global 21 cm experiments

ABSTRACTThe H i 21 cm absorption line is masked by bright foregrounds and systematic distortions that arise due to the chromaticity of the antenna used to make the observation coupling to the spectral inhomogeneity of these foregrounds. We demonstrate that these distortions are sufficient to conceal the 21 cm signal when the antenna is not perfectly achromatic and that simple corrections assuming a constant spatial distribution of foreground power are insufficient to overcome them. We then propose a new physics-motivated method of modelling the foregrounds of 21 cm experiments in order to fit the chromatic distortions as part of the foregrounds. This is done by generating a simulated sky model across the observing band by dividing the sky into N regions and scaling a base map assuming a distinct uniform spectral index in each region. The resulting sky map can then be convolved with a model of the antenna beam to give a model of foregrounds and chromaticity parametrized by the spectral indices of the N regions. We demonstrate that fitting this model for varying N using a Bayesian nested sampling algorithm and comparing the results using the evidence allows the 21 cm signal to be reliably detected in data of a relatively smooth conical log spiral antenna. We also test a much more chromatic conical sinuous antenna and find this model will not produce a reliable signal detection, but in a manner that is easily distinguishable from a true detection.

Margulis lemma and Hurewicz fibration theorem on Alexandrov spaces

We prove the generalized Margulis lemma with a uniform index bound on an Alexandrov [Formula: see text]-space [Formula: see text] with curvature bounded below, i.e. small loops at [Formula: see text] generate a subgroup of the fundamental group of the unit ball [Formula: see text] that contains a nilpotent subgroup of index [Formula: see text], where [Formula: see text] is a constant depending only on the dimension [Formula: see text]. The proof is based on the main ideas of V. Kapovitch, A. Petrunin and W. Tuschmann, and the following results: (1) We prove that any regular almost Lipschitz submersion constructed by Yamaguchi on a collapsed Alexandrov space with curvature bounded below is a Hurewicz fibration. We also prove that such fibration is uniquely determined up to a homotopy equivalence. (2) We give a detailed proof on the gradient push, improving the universal pushing time bound given by V. Kapovitch, A. Petrunin and W. Tuschmann, and justifying in a specific way that the gradient push between regular points can always keep away from extremal subsets.

Design and Analysis of Ultra-Wideband Highly-Birefringent Bragg Layered Photonic Bandgap Fiber With Concave-Index Cladding

A ultra-wideband highly-birefringent Bragg layered photonic bandgap fiber (BL-PBGF) with concave-index cladding is proposed and demonstrated, by incorporating PBG effect with Bragg multilayers for the first time to the best of our knowledge. The proposed BL-PBGF contains honeycomb capillary cladding and elliptical core with horizontal asymmetry for birefringence. By innovatively introducing three modified silica capillary layers with different refractive indices, the cladding with concave-convex refractive index distribution is combined, providing superior characteristics for optical polarization implementation, such as confinement loss, bending loss and birefringence. Results show that the confinement loss stays around 2 dB/km level within ultrawide 180 nm wavelength range, basically 3 times wider than conventional PBGF. The birefringence maintains at the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> across the entire bandwidth and the maximum value reaches 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The bending loss at 1550 nm is significantly reduced to below one third of the conventional uniform index PBGF when the bending radius is less than 3.5 mm, and maintains below 1 dB/km level when the bending radius is beyond 10 mm. The proposed universal BL-PBGF has great potential in minimized freestanding fiber coil and small footprint fiber optical gyroscope applications.

On the transmission of data packets through fiber-optic cables of uniform index

Abstract The treatment of Maxwell equations show that propagating wave of packets in fiber-optic cables is dispersive, propagating in groups, such that group velocity along certain curves in the frequency-phase velocity diagrams vanishes. It is suggested that stalling of wave groups is responsible, for bursting propagation observed in experimental measurements, causing some delay in transmission. The dispersion equations developed here, are different from those given in texts that are based on “weakly guiding approximation”. The queue of such data packets arriving at a router station is found to have a “raised tail” distribution unlike that of Poisson arrivals. For accounting the property, a Mittag–Leffler function distribution (MLFD) of probability is used following a modification of that for a Poisson process, the tail raising is shown to cause delay in transmission, and its estimate is analysed based on the theory.

A robust scheme for unidirectional emission from a hybrid whispering gallery cavity system based on transformation optics.

Using the transformation cavity, a gradient index cavity designed by transformation optics, we propose a hybrid resonator system to extract unidirectional narrow-beam emission from high-Q whispering gallery modes by embedding a transformation cavity inside a deformed uniform index cavity that exhibits unidirectional narrow-beam emission. For effective mode coupling between the transformation cavity and enclosing cavity, the embedded transformation cavity is designed to have bidirectional evanescent emission, which enables most of the emission from the transformation cavity to be laterally incident on the rim of the enclosing deformed cavity. Consequently, ultrahigh-Q resonances of this system can provide a sharp free-space light output, which is difficult to achieve by embedding a homogeneous disk cavity instead of the transformation cavity.

Application of Green Building Materials and Multi-objective Energy-Saving Optimization Design

Green building materials have brought fundamental changes to the traditional construction methods, enabling better environmental protection and energy-saving performance of the buildings. However, due to the various material types and the large property differences, until now there isn’t a uniform evaluation index system (EIS) for green building materials, the existing studies on the green-level evaluation of green building materials during production and use are insufficient, and the research on energy-saving design is just getting started. For this reason, this paper attempted to launch a research on the multi-objective energy-saving optimization design of buildings based on the application of green building materials. First, the quantification method for the environmental impact factors of green building materials was elaborated, and the intervals and standards of the quantification evaluation were given; then, a green building material optimization selection model was constructed, and a multi-objective energy-saving optimization algorithm was proposed; at last, experimental results gave the green levels of a few candidate green building materials and the scores of the environmental impact factors, which had verified the effectiveness of the proposed algorithm.

Comparison of conventional and new cascaded multilevel inverter topologies based on novel indices

This paper proposes new indices of cascaded multilevel inverters (MLIs) in order to compare the conventional topology with 10-existed new topologies. Reduction in the number of power switches is the main target of these new topologies. This aim is to reduce the total cost of designed inverters, though the mentioned aim is not enough to design new inverters. Thus, in this study, four comparative indices including sources power uniform distribution index (SPUDI), switches current uniform distribution index (SCUDI), switches loss uniform distribution index (SLUDI), and switches voltage uniform distribution index (SVUDI), are proposed. In addition, it is shown that in most of the new topologies, reducing the number of switches can lead to lowered values of the proposed indices, after which non-uniform power, current, loss, and voltage pattern are obtained. The results prove that mere emphasis on the number of switches, along with the exclusion of either of the proposed indices will cause significant problems, where cost reduction may be underachieved. Based on new indices, the advantages of conventional topology over new ones are presented in this study.

Numerical investigation of swirl effects on a short natural draft dry cooling tower under windless and crosswind conditions

Swirling motions have been proven to improve the thermal performance of short natural draft dry cooling towers by reducing the cold air inflow and increasing the draft speed. However, crosswind influences on the favourable swirl effects have not been investigated. To fill this gap, 3-Dimensional simulations of a short natural draft dry cooling tower are carried out. Three different locations of the swirl generator, with solid body rotation, are compared under windless and crosswind conditions. The results show that, with no wind present, introducing swirling motions right above the heat exchangers is found to be the optimal location for improving around 40% of the reduced thermal performance, which is casued by cold air inflow penetration. On the other hand, as the swirl intensity further increases after the cold air inflow is eliminated, locating it at the tower outlet performs the best on the air draft speed enhancement, and thus further increases approximately 17% of the heat transfer rate at the angular frequency input of 2s-1. In the presence of crosswind and windbreak walls, air flows through the heat exchangers and tower non-uniformly. By mounting the swirl generator right above the heat exchangers, the uniform index of the heat flux can be improved by 5% with 1s-1 angular frequency input. More importantly, inducing swirls at the tower outlet is still the optimal choice for increasing the air draft speed through the tower. With 2s-1 angular frequency input, the thermal performance of the tower can be enhanced by 11~17% in accordance with the crosswind speed.

The Analysis of Light Intensity Transmission Coefficient Through Plastic Fibers for the Design of Closed Room Lighting without Electricity

The phenomenon of total internal reflection can be used to guide the light to be transmitted from one place to another, it is applied to the guiding principle of light in fiber optics. A fiber rope made of clear plastic material with a uniform refractive index, when one end fired a beam of light then the light will be forwarded along the strap so that out at the other end. This principle can be applied as a lighting source in a closed room by passing light from the outdoors by using plastic fiber, so it doesn’t need the electricity. In this study, theoretical analysis of the percentage of the intensity of light transmitted by the fiber plastic succeed as a function of the refractive index and determine the transmission coefficient for some plastic seeds are eligible to be used as a plastic fiber light successor. From the results of deriving the equation, the light transmission coefficient of plastic is and the terms of plastic seeds that can be used as a plastic fiber are having a refractive index . Based on refractive index data from profesionalplastics, the maximum transmission coefficient value for Ethylene Tetrafluoro Ethylene Copolymer is 82.23% and the minimum transmission value of Fluorinated Ethylene Propylene Copolymer is 55.99%.

Refractive index distribution of the ice-layer in ICF target from the interference method

In the inertial confinement fusion (ICF) system, the uniformity of the target is important to the successful ignition. A method based on the phase-shifting interferometry and ray tracing is proposed to obtain the 2D (two-dimensional) refractive index distributions of the ice-layer at three wavelengths (532 nm, 785 nm, 1064 nm), from which the 2D density distribution of the ice-layer is got. A differential method is utilized to get the reference refractive index, based on which the refractive index distribution of the layer is retrieved. For targets with uniform refractive index in the ice-layer, simulations show that the relative retrieval accuracies are better than 10 ppb. Experiments show that the refractive index distributions have good consistency at different wavelengths for the same target. The detectable normalized RMS (root mean square) of the refractive index distributions is at least 2.9E-4. The relative accuracies of the average refractive indexes of the shells are better than 1.5% for all three wavelengths. The optimal selection of the two rings on the wavefront map that yields minimal uncertainty to the reference refractive index is discussed. It is concluded that the proposed method and system poses great potential in the in-situ measurement of the refractive index and density distribution of the ICF target layers.

A simple and effective approach to quantitatively characterize structural complexity

This study brings insight into interpreting forest structural diversity and explore the classification of individuals according to the distribution of the neighbours in natural forests. Natural forest communities with different latitudes and distribution patterns in China were used. Each tree and its nearest neighbours form a structural unit. Random structural units (or random trees) in natural forests were divided into different sub-types based on the uniform angle index (W). The proportions of different random structural units were analysed. (1) There are only two types of random structural units: type R1 looks similar to a dumbbell, and type R2 looks similar to a torch. These two random structural units coexist in natural forests simultaneously. (2) The proportion of type R1 is far less than that of R2, is only approximately 1/3 of all random structural units or random trees; R2 accounts for approximately 2/3. Furthermore, the proportion of basal area presents the same trend for both random structural units and random trees. R2 has approximately twice the basal area of R1. Random trees (structural units) occupy the largest part of natural forest communities in terms of quantity and basal area. Meanwhile, type R2 is the largest part of random trees (structural units). This study finds that the spatial formation mechanism of natural forest communities which is of great significance to the cultivation of planted forests.

Assessment of facial landmarks for bone asymmetry in geometric morphometric studies: A review

Background&#x0D; Anthropometrical points or landmarks are key for facial shape analysis using geometric morphometrics. In the early 1990s Fred Bookstein created a classification system with landmarks type 1., type 2., type 3. based on anatomical landmark homology. However, thirty years later, a uniform referece index of landmarks that can be used for assessing facial asymmetry still does not exist. The criteria for selecting landmark points are not fully defined, which makes classification of homology and and landmarks prone to arbitrary interpretations. A systematic review of literature indicates that authors of studies do not provide explanation for choosing exact points. Most of them also do not provide a clear definition of landmarks and landmarks classification according to homology.&#x0D; Objective&#x0D; The objective of this systematic review was to assess, in an evidence based manner, which landmarks inside the Bookstein groups of on facial hard tissues can be reccomended for facial asymmetry assessment using geometric mophometrics.&#x0D; Search methods&#x0D; An electronic search of 9 databases up to March 2020 by two reviewers was conducted to identify relevant articles.&#x0D; Selection criteria&#x0D; Prospective randomized, non-randomized controlled trials and cross sectional studies reporting on facial asymmetry using three-dimensional images and geometric morphometric methods. The reasons for assessing facial asymmetry were not considered.&#x0D; Data collection and analysis&#x0D; The 23 selected studies were categorized according to the number and specification of the research subjects, types of three-dimensional images, number of landmarks, and the craniofacial region of interest. All landmarks were extracted with the following data: name, abbreviation, and the author’s definition of the location.&#x0D; Results&#x0D; The craniofacial region is divided into neurobasic cranial part, ethmomaxillar part and the mandible. Assessment of neurobasic cranial asymmetry was conducted in 6 studies and 45 different landmarks were recorded, of which 11 were medial and 34 bilateral. Bregma and Lambda occur most frequently and according to homology both belong to type 1 landmarks.&#x0D; Assessment of ethmomaxillary asymmetry was conducted in 21 studies and 68 different landmarks were recorded, of which 16 were medial and 52 bilateral. Nasion and Jugale occur most frequently and according to homology Nasion belongs to type 1 landmarks and Jugale to type 2 landmarks.&#x0D; Conclusion &#x0D; The selection and definition of craniofacial hard tissue landmarks is one of the most important tasks in the design of morphometric studies, and thus for the purpose of assessing facial asymmetry. The review provides an extensive cross-section of possible landmarks with the definition of the location as well as the possible location variation. The list of these landmarks should be observed through the classification of landmarks according to their homology, as well as possible variations of the classification.

Introducing tree neighbouring relationship factors in forest pattern spatial analysis: weighted Delaunay triangulation method

It is important to quantify and analyze forest spatial patterns for studying biological characteristics, population interaction and the relationship between the population and environment. In this study, the forest spatial structure unit was generated based on the Delaunay triangulation model (DTM), and the weights were generated using the comprehensive values of the tree diameter at breast height, total height and crown width. The distance between neighbors determined by the DTM was weighted to transform the original coordinates of trees into logical coordinates. Then, a weighted spatial pattern (WSP) was developed. After weighting, the neighboring trees were replaced, the replacement ratio was 38.3%, and there was 57.4% of the central tree. Correlation analysis showed that the uniform angle index of the WSP was significantly correlated with the tree size standard deviation under uniformity (r = 0.932) and randomness (r = 0.711). The DTM method not only considers the spatial distance between trees, but also considers the non-spatial attributes of trees. By changing the spatial topological relation between trees, this method further improves the spatial structure measurement of forest.

In vitro multiplication of Cedrela fissilis Vell.: A threatened brazilian hardwood forest tree

Cedrela fissilis Vell. is a valuable wood species from Atlantic Forest and is at risk of extinction. Therefore, a protocol for plant regeneration was developed for C. fissilis using different explants from in vitro germinated plant. The seeds were germinated in total or half- strength MS and B5 basal. The half-strength MS medium was chosen because of its uniform morphological aspect, highgermination rate (82) and germination speed index (1.218). The shoot tips, nodal segments and cotyledonary nodes explants were extracted from the germinated in vitro plants and cultivated for shoot induction in MS medium supplemented with KIN or BAP (0, 0.5, 2, 4 μM). Among the different explants, cytokinins and concentrations, the highest number (2.2) and length (3.84 cm) of shoots were induced in cotyledonary nodes without cytokinin. For rooting of shoot regenerated from explants, the MS medium was supplemented with IBA or NAA (0, 1, 3 μM). Rooting was induced in all auxins type and concentrations, with higher number of roots per explant with 3μM IBA (2.54). In conclusion, the present study provides in vitro shoot and root regeneration system in C. fissilis without plant growth regulators and great potential in micropropagation, germplasm preservation and genetic transformation. Index terms: Cedro-rosa; vulnerable; cotyledonary nodes; plant growth regulator; micropropagation.