620 research outputs found
Buckling and postbuckling of extensible, shear-deformable beams: Some exact solutions and new insights
No full textThis paper presents exact solutions for the buckling loads and postbuckling states of extensible, shear deformable beams. The governing equation for the large-amplitude lateral deformation of beams in compression is expanded in Taylor series up to the cubic nonlinearity. Closed-form solutions in terms of the axial and shear stiffnesses are developed for statically determinate and statically indeterminate beams. Namely, pinned–pinned, cantilevered, clamped–clamped, and clamped–pinned beams are considered with the loaded end is a roller that is able to slide. The postbuckling response under a given axial load is exactly derived. The dependence of the buckling load on the length-to-radius of gyration is discussed. It is shown that the extensibility and the shear deformation significantly affect the buckling loads and the postbuckling response. For conventional materials with positive Poisson's ratio, the inclusion of the axial and shear deformation results in a meaningful reduction of the buckling load. It is further shown that the buckling load can be enhanced by designing artificial metamaterials materials with an effective negative Poisson's ratio
A review on buckling and postbuckling of thin elastic beams
No full textThis paper provides a review of models and solutions for the buckling and postbuckling of beams available from the 50s of the last century to date. Beams with axially unrestrained (movable) ends and restrained (immovable) ends are covered. In each class, the formulation of the nonlinear buckling problem for the buckling loads and the postbuckling states is discussed and the underlying assumptions are highlighted. For relatively large-amplitude buckling of beams with movable ends, approximate analytical solutions up to the third order are presented and compared with the exact solutions expressed in terms of elliptic integrals. For beams with immovable ends, buckling involves midplane stretching that makes the nonlinear buckling problem takes the same form of the standard eigenvalue problem and, hence, exact solutions are affordable. This review combines the research outcomes on buckled beams from two scientific viewpoints: the structural dynamics and the nonlinear vibration viewpoints, respectively. Moreover, it presents in one place the formulation and the exact solutions for the buckling of beams to serve as an on-demand resource for researchers concerned with the buckling and postbuckling of beams
Estimation of groundwater recharge and its relation to land degradation: case study of a semi-arid river basin in Iran
No full textGroundwater extraction is one of the most important criteria of land degradation especially land subsidence in arid and semi-arid areas. Understanding the relationship between water extraction and recharge of groundwater can lead to better watershed management. For the estimation of groundwater recharge in Razan-Ghahavand watershed in Central Iran the Soil and Water Assessment Tools was used. Model calibration was done by using SUFI-2 based on monthly river discharge and annual crop yield, where crop yield was used to better estimate the evapotranspiration term, which consequently increased our knowledge on estimating aquifer recharge. The calibration results were satisfactory: The Nash-Sutcliffe model efficiency ranged from 0.53 to 0.63 for calibration and from 0.42 to 0.72 for validation. The results showed that, although the groundwater level was decreasing about 1 m per year, the groundwater recharge did not change significantly leading to a net withdrawal causing land subsidence over time
Economic Policy Uncertainty and Firm Value: Impact of Investment Sentiments in Energy and Petroleum
No full textThis study seeks to determine how economic policy uncertainty (EPU) influences investment decisions and the market value of the Pakistan Stock Exchange. This study examines investment and operational data from 249 energy and petroleum companies between 2015 and 2020 and macroeconomic variables such as EPU. This study investigates the moderating effects of EPU on investments in fixed and intangible assets and its effect on Tobin's Q and the market price per share. The outcomes demonstrate that EPU reduces the costs of both tangible and intangible assets for businesses. In addition, companies with a higher Tobin's Q and market price per share are more impacted by uncertain corporate investment policies. However, financial leverage is negatively correlated with share price and positively correlated with earnings per share and earnings per unit. Tobin's Q positively correlates with financial leverage, indicating that firms that raise capital through debt are more likely to create value for investors. The research indicates that market-dependent enterprises are more susceptible to the unpredictability of monetary policy. According to this study, consistent application and open communication of economic policies are likely to increase the efficacy of company investments, resulting in more effective resource allocation and business decision-making
The distally based peroneus brevis flap: the 5-step technique
No full textThe peroneus brevis flap was first described as proximally based by Mathes et al (Surg Clin North Am. 1974;54:1337-1354) and later by Jackson and Scheker (Injury. 1982;13:324-330). A distally based version of this flap by Mathes and Nahai (Reconstructive Surgery: Principles, Anatomy and Technique. 1997:1437e46) was subsequently described in 1997. The first case series of distally based flaps was published by Eren et al (Plast Reconstr Surg. 2001;107:1443-1448).In our experience, the distally based flap is a useful muscle flap to reconstruct small defects in the lateral distal third of the leg. Initial interest and confidence in the use of this flap in our unit were hindered by lack of direct experience and descriptive detail in the literature. We have now developed a systematic approach to harvest the distally pedicled peroneus brevis muscle flap in 5 reproducible, safe steps. This has allowed the flap to become adopted as a standard technique of limb reconstruction in our unit with no cases of flap loss
Modelling potential habitats for Artemisia sieberi and Artemisia aucheri in Poshtkouh area, central Iran using the maximum entropy model and geostatistics
No full textPredicting potential habitats of endemic species is a suitable method for biodiversity conservation and rehabilitation of rangeland ecosystems. The present study was conducted to estimate the geographic distribution of Artemisia sieberi (A. sieberi) and Artemisia aucheri (A. aucheri), find the most important environmental predictor variables and seek for similarities and differences in habitat preferences between the two species for Poshtkouh rangelands in Central Iran. Maps of environmental variables were created by means of geographic information system (GIS) and geostatistics. Then predictive distribution maps of both species were produced using the maximum entropy modeling technique (Maxent) and presence-only data. Model accuracy is evaluated by using the area under the curve (AUC). Lime1, grave1, lime 2 and elevation most significantly affect habitat distribution of A. aucheri, while habitat distribution of A. sieberi is affected by elevation, lime1, am1, lime1 and om2. For both species, elevation has an influence on their potential distributions. However, A aucheri depends more on elevation, and consequently climate in comparison to A. sieberi. Finally, it is revealed that the potential distribution of A. aucheri is limited mostly to mountainous landscapes while A. sieberi is present in wide ranges of environmental conditions. (C) 2013 Elsevier B.V. All rights reserved
Evaluation of management practices in rice–wheat cropping system using multicriteria decision-making methods in conservation agriculture
No full text: In this study, we employed two multiple criteria decision-making (MCDM) methods, namely the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and the Analytic Hierarchic Process (AHP), to determine the best management choice for the cultivation of wheat with a regime of conservation agriculture (CA) practices. By combining alternative tillage approaches, such as reduced tillage and zero tillage, with the quantity of crop residues and fertilizer application, we were able to develop the regime of CA practices. The performance of the regimes compared to the conventional ones was then evaluated using conflicting parameters relating to energy use, economics, agronomy, plant protection, and soil science. TOPSIS assigned a grade to each alternative based on how close it was to the ideal solution and how far away it was from the negative ideal solution. However, employing AHP, we determined the weights of each of the main and sub-parameters used for this study using pairwise comparison. With TOPSIS, we found ZERO1 (0% residue + 100% NPK) followed by ZERO4 (50%residue + 100% NPK), and ZERO2 (100% residue + 50% NPK) were the best performing tillage-based alternatives. To best optimize the performance of wheat crops under various CA regimes, TOPSIS assisted the decision-makers in distinguishing the effects of the parameters on the outcome and identifying the potential for maneuvering the weak links. The outcomes of this investigation could be used to improve management techniques for wheat production with CA practices for upscaling among the farmers
Termitaria hexasporodochia Wilson, Emam, Davis, Barden, Hall, Ware. 2023, sp. nov.
No full text<i>Species:</i> <i>Termitaria hexasporodochia</i> Wilson, Emam, Davis, Barden, Hall, Ware. <i>sp. nov.</i> <p>Mycobank ID: MB832822</p> <p>Newark Museum Herbarium, Newark, NJ (NEMU)</p> <p>American Museum of Natural History, NYC, NY (AMNH)</p> <p> <i>Type Specimens</i></p> <p> <i>Locality</i>: South America, Guyana: Rupununi River Region, Karanambu Ranch, Capuchin trail, elevation: 100km, 03°44.85’ N,059°19.13’ W, tropical rainforest surrounded by open savannah, on host termite in an arboreal soil mound, 11, January 2016, Collected by M. Wilson, J. Ware, P. Barden, S. George. L. Johnson, S.T. Mafla-Mills.</p> <p> On <i>Amitermes</i> sp., preserved in ethanol. Deposited at AMNH and registered at NEMU Herbarium (NEMU), labeled: South America, Guyana: Rupununi River Region, Karanambu Ranch, Capuchin trail, elevation: 100km, 03°44.85’ N, 059°19.13’ W, collected 11, January 2016, (holotype: T1-P1S7S3!, isotypes: T2-P1S7S3!, T2-P2S7S3!).</p> <p> <i>Diagnosis— Termitaria hexasporodochia sp. nov.</i> exhibits a unique phenotype, exclusively forming six moderately sized black rimmed, elliptical sporodochia on the ventral abdominal segments (4–6) of its host. <i>Termitaria hexasporodochia</i> <i>sp.nov</i>. exhibits8–9conidia per collarette,is 116–120μm thick,elliptical in shape, has a conidiogenesis zone location 20μm–25μm from the sporodochium base, and thick-walled, lobate haustoria. The dimensions of the sporodochia range from 256 μm–609μm to 102–218 μm, the phialides are 110–115 μm in length, and the expiculum is the only pigmented region noted.</p> <p> <i>Description of the holotype</i> —Entomogenous: Sporodochium thallus is 116 μm thick, 256 μm long, 102 μm wide, and ellipsoid in shape. At the basal layer, haustoria are initially formed from thick-walled haustorial mother cells at the base of the sporodochium and appear thick and lobular. Haustoria range from 19–23μm in length, and 1.7–2.4 μm in width. Superficial to this layer is the sporogenous hymenium layer composed of a mass of tight columnar phialides 110–115 μm thick. Each individual phialide ranges from 1.5–2.2 μm in diameter, terminating in two flat rounded tips. Endogenously-formed conidia originate from long rod-shaped conidiogenous cells at the conidiogenous locus, located 20–25 μm from the base of each phialide. Conidial spores are rectangular and catenate, 1–1.3 μm in width and 3–4 μm in length. 8–9 spores were found in each collarette and 11–13 in each phialide. Spores break off simultaneously as they reach the sporodochium surface. The surface of each sporodochial lesion appears perforated, bearing a hexagonal pattern referred to as “textura angularis”, with pores being larger in diameter along the rim preceding the sterile expiculum. The expiculum forms a smooth black crust with no apparent openings. The holotype selected for description was one of the six lesions found infesting the 4 th ventral abdominal segment of an <i>Amitermes</i> termite worker T1-S7S3!.</p> <p> <i>Etymology— Termitaria</i> is the established generic name, and <i>hexasporodochia</i> is an adjective referring to the hexad arrangement of sporodochia exhibited on the type-host, <i>Amitermes</i>.</p> <p> <i>Ecology and host species— Amitermes sp.</i> found to be infested with <i>Termitaria</i> were collected from large arboreal mounds constructed on sandpaper trees (<i>Curatella americana</i>) growing at the interface between open savannah and rainforest (Fig. 2). The mounds were found during the dry season (January) in regions surrounding the Rupununi River that flood during the annual wet season (May-August). It was found only on worker caste termite hosts, never on soldiers or reproductives.</p> <p> <i>Differential diagnoses— Termitaria hexasporodochia sp. nov.</i> exhibits a unique arrangement phenotype, forming six moderately-sized, black-rimmed, elliptical sporodochia on the ventral abdominal segments (4–6) of its host. This fungus belongs to the genus <i>Termitaria</i> and is readily distinguished from two described members of the genus <i>Mattirolella.</i> It lacks a major generic character shared amongst <i>Mattirolella</i>, the sterile hyphae separating fertile hyphae in the hymenium is not present in the new species. The maximum lengths of <i>T. hexasporodochia sp. nov.</i> sporodochia are less than half the size of those described for Australian species, <i>T. macrospora</i> and <i>T. rhombicarpa</i> (Table 1; Kimbrough & Lenz 1982). Additionally, <i>T. rhombicarpa</i> can be distinguished by the rhomboid shaped sporodochium it typically forms on the host as opposed to the elliptical/circular lesion formed on <i>T. hexasporodochia sp. nov.</i>, shorter phialide lengths (Table 1, 100–105 μm vs. 110–115μm), longer conidiogenous locus (Table 1. 30–35 μm vs. 20–15 μm from phialide base) and haustoria penetrating twice as deep into the host cuticle (TABLE 1. 50–55 μm vs. 20–23 μm). <i>T. hexasporodochia sp. nov.</i> spores are easily distinguished from those produced by <i>T. macrospora</i>.</p> <p> As its name suggests <i>T. macrospora</i> produces 4–5 massive spores per collarette (app 3.8–9.1 μm) whereas <i>T. hexasporodochia sp. nov.</i> produces 8–9 spores per collarette (app 1–1.3 <i>×</i> 3–4 μm). Another Australian species, <i>T. longiphialidis</i>, is best identified by its small circular sporodochia and having the longest phialides of any <i>Termitaria</i> species (Table 1. 160–180 μm vs. 110–115 μm; Kimbrough & Lenz 1982). <i>T. hexasporodochia sp. nov.</i> is readily distinguished from the commonly described <i>T. snyderi</i>, by phialide length. <i>T. hexasporodochia sp. nov.</i> possesses a much thicker sporodochium, with phialides double the length of those found in <i>T. snyderi</i> (Table 1, 110–115 μm vs. 50–60 μm). <i>T. coronata</i> can be distinguished from all <i>Termitaria</i> species, <i>T. hexasporodochia</i> <i>sp. nov</i>. included, in the appearance of its sporodochium, with its echinulate surface and the high position of its conidiogenous locus (Table 1, 50–60 μm vs. 20–25 μm).</p> <p> <i>Ultrastructure of T. hexasporodochia sp. nov.</i> —The complete sporodochium (Fig.4) is composed of many tightly aligned vertical columns. We group the sporodochia layers into three major regions (Fig.5A); the basal region (Fig. 5) most closely appressed to the insect cuticle, the sporogenous hymenial region (Fig. 6), and the upper region (Fig.7) filled with conidia and phialides terminating into flaps.</p> <p> <i>The basal region</i> —This region of the sporodochium is approximately 4–5 rows and 8.5–12.5 μm thick. It is comprised of haustorial mother cells that give rise to a subcuticular layer of haustoria that penetrates the host (Fig. 5). The thin-walled cells composing the upper layer of the basal region have been referred to in previous studies as the “subhymenial layer” and gives rise apically to the hymenial phialides (Kimbrough and Thorne 1982). Haustoria aggregate towards and penetrate the host via tetra ocular channels in its cuticle. We observe 12+ major penetration points between the fungal body and its host (Fig.5 B), extending below the cuticle to thick-walled lobular haustoria ranging from 19–23 μm in length and 1.7–2.5 μm in width. We do not refer to this “haustorial region” as an internal region within the sporodochium because it lays below the cuticular layer of its host (Fig.6E–F). Additionally, its penetration into the host cuticle does not change the classification of this fungus as an ectoparasite, in that it does not invade the host cytoplasm. Each sporodochia appears to be formed from major infestation sites with cells growing upward from the basal layer, with approximately 160–240 openings per sporodochium (size dependent) that appear dark in photomicrographs (Fig.5C).</p> <p> <i>The sporogenous hymenium region</i> —This region consists of a thick hymenium of tightly appressed phialides (Fig.6A), comprised of long rod-shaped conidiogenous cells 14–22 μm in length, which differentiate into asexual conidia at a fixed conidiogenous locus (Fig 6B–C). The phialides are approximately 1.5–1.2 μm in diameter and the conidiogenous locus (Fig.6D), the initial point of asexual spore differentiation, occurs 20–25μm, from the base of each hymenial phialide. Each collarette contains 8–9 rectangular, catenate conidia (Fig.7B–C), and approximately 11–13 spores can be found in the phialide during this time. Under high-definition microscopy, the internal surface of the hymenial phialides are coated with a dense mat of minute filaments that appear to be restricted to the upper 3/4th of the secondary canals (Fig.7A).</p> <p> <i> The upper region <i>—</i> At the superficial level of the sporodochia, a dark, peripheral expiculum surrounds a region resembling a hexagonal honeycomb (Fig.7A,C). This pattern is formed by fields of terminating phialides (Fig.3B) of elongate tubes referred to as <i>textura angularis</i>, the apices of which are bivalved (Fig 7B–D). The apical valves are formed by two isosceles trapezoidal flaps that fit closely together to form a large circular pad of thousands of hexagons (Fig.7D). Visible from confocal stack images just below the pad surface, each sporodochia appears densely populated with hexagonal pores, with the conidial spores visible within each tubular hymenial channel leading to the apical pore valves (Fig.7B). On average, a sporodochia contains approximately 12,000 –14,000 phialides.</i></p> <p> Overall, the most striking feature of <i>Termitaria hexasporodochia sp. nov.</i> is apparent in the arrangement and ultrastructure of the six moderately-sized, black-rimmed, elliptical sporodochia it forms on its termite host. Of all members of the family Kathistaceae, the formation of sporodochia on termites is diagnostic for members of the genera <i>Termitaria</i> and <i>Mattirolella</i>, hence why we focus on those two genera in assessing the new species. <i>Termitariopsis</i> is the only remaining member of Kathistaceae which forms sporodochia, although it does not use termites as a host and exhibits sporodochial features absent in the other two genera (Table 2a). <i>Kathistes</i> genera do not form sporodochia and are described instead off of their sexual form, whereas <i>Termitaria hexasporodochia sp. nov.</i> is described by its asexual sporodochia form. The genus <i>Ectomyces calotermi</i>, described on termites to form sporodochial lesions, has been synonymized with <i>Termitaria snyderi</i> (Tate 1928), a species described in this article. No further examination is needed on this genus as its synonym <i>T. snyderi</i> is examined here. We place the new species in <i>Termitaria</i> because it lacks the defining features of <i>Mattirolella</i>: sterile hyphae interspersed with fertile hyphae and an epihymenium (Table 2a). The new species can be differentiated from other <i>Termitaria</i> species by sporodochial length (<i>T. macrospora</i> and <i>T. rhombicarpa),</i> sporodochial shape (<i>T. rhombicarpa),</i> phialide lengths (<i>T. longiphialidis, T. snyderi</i>), location of conidiogenous locus, spore size, and haustorial depth (Table 2a).</p>Published as part of <i>Wilson, Megan M., Emam, Amany, Davis, Steven R., Hall, Gene, Barden, Phillip & Ware, Jessica L., 2023, Description of a novel termite ectoparasite, Termitaria hexasporodochia sp. nov. (Kathistaceae), presenting an unusual six-sectioned infestation, and a key to the fungal family Kathistaceae, pp. 106-124 in Phytotaxa 591 (2)</i> on pages 111-113, DOI: 10.11646/phytotaxa.591.2.3, <a href="http://zenodo.org/record/7797494">http://zenodo.org/record/7797494</a>
Choroidal volume variations with age, axial length, and sex in healthy subjects: a three-dimensional analysis
No full textPurpose: To demonstrate the 3-dimensional choroidal volume distribution in healthy subjects using enhanced depth imaging (EDI) spectral-domain optical coherence tomography (SD-OCT) and to evaluate its association with age, sex, and axial length. Design: Retrospective case series. Participants: A total of 176 eyes from 114 subjects with no retinal or choroidal disease. Methods: The EDI SD-OCT imaging studies of healthy patients who had undergone a 31-raster scanning protocol on a commercial SD-OCT device were reviewed. Manual segmentation of the choroid was performed by 2 retinal specialists. A macular choroidal volume map and 3-dimensional topography were automatically created by the built-in software of the device. Mean choroidal volume was calculated for each Early Treatment Diabetic Retinopathy Study (ETDRS) subfield. Regression analyses were used to evaluate the correlation between macular choroidal volume and age, sex, and axial length. Main Outcome Measures: Three-dimensional topography and ETDRS-style volume map of the choroid. Results: Three-dimensional topography of the choroid and volume map was obtained in all cases. The mean choroidal volume was 0.228±0.077 mm3 for the center ring and 7.374±2.181 mm3 for the total ETDRS grid. The nasal quadrant showed the lowest choroidal volume, and the superior quadrant showed the highest choroidal volume. The temporal and inferior quadrants did not show different choroidal volume values. Choroidal volume in all the EDTRS rings was significantly correlated with axial length after adjustment for age (P < 0.0001), age after adjustment for axial length (P < 0.0001), and sex after adjustment for axial length (P < 0.05). Choroidal volume decreases by 0.54 mm3 (7.32%) for every decade and by 0.56 mm3 (7.59%) for every millimeter of axial length. Male subjects have a 7.37% greater choroidal volume compared with that of female subjects. Conclusions: Enhanced depth imaging SD-OCT is a noninvasive and well-tolerated procedure with an excellent ability to visualize 3-dimensional topography of the choroid and to measure choroidal volume at the posterior pole using manual segmentation. Age and axial length are inversely correlated with choroidal volume, most likely leading to changes in retinal metabolic support in elderly, highly myopic patients. Sexual differences should be considered when interpreting an EDI SD-OCT scan of the choroid. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article
Energy and exergy analyses of an integrated SOFC and coal gasification system
No full textThis paper examines an integrated gasification and solid oxide fuel cell (SOFC) system with a gas turbine and steam cycle that uses heat recovery of the gas turbine exhaust. Energy and exergy analyses are performed with two different types of coal. For the two different cases, the energy efficiency of the overall system is 38.1% and 36.7%, while the exergy efficiency is 27% and 23.2%, respectively. The effects of changing the reference temperature on the exergy destruction and exergy efficiency of different components are also reported. A parametric study on the effects of changing the pressure ratio on the component performance is presented.Natural Sciences and Engineering Research Council of Canad
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