Open Webs Research Articles

Using mercury and lead stable isotopes to assess mercury, lead, and trace metal source contributions to Great Salt Lake, Utah, USA

Great Salt Lake is a critical habitat for migratory birds that is threatened by elevated metal concentrations, including mercury (Hg) and lead (Pb), and is subject to severe hydrologic changes, such as declining lake level. When assessing metal profiles recorded in Great Salt Lake sediment, a large data gap exists regarding the sources of metals within the system, which is complicated by various source inputs to the lake and complex biogeochemistry. Here, we leverage Hg and Pb stable isotopes to track relative changes in metal source contributions to Great Salt Lake over time. Mercury and Pb concentrations increase in sediments deposited after 1920 and peak between 1965 and 1995, following closure of several local smelters and the onset of increased emission controls. The nominal associations above are confirmed via Hg stable isotopes in pre-1920 background sediments, which reflect atmospheric inputs from regional and global origin, whereas Hg and Pb stable isotopes together indicate that elevated metal concentrations in mid-late 20th century sediments reflect increased mining/smelting inputs. The observed minimal rebound towards pre-1920 Pb isotope signatures in 21st century sediments indicates that mining/smelting inputs, though reduced, remain a primary source of Pb to Great Salt Lake. In contrast, the more pronounced rebound of Hg stable isotope signatures to pre-1920 values indicate a greater contribution of atmospheric inputs of regional/global origin to current Hg inputs, though Hg concentrations are ~10 times greater than pre-1920 background values due to global increases in atmospheric Hg concentrations or possibly slow recovery from local contamination. The importance of regional/global Hg sources to the system suggests that reductions in Hg bioaccumulation in the open water food webs of Great Salt Lake are more dependent on national and global reductions in Hg emissions and management strategies to limit methylmercury production within system. This work highlights the utility of using coupled Hg and Pb stable isotope values to assess trace metal pollution sources and pathways in aquatic systems.

On Some Classes of Cycles-Related Γ -Harmonious Graphs

A graph G(V, E) is Γ-harmonious when there is an injection f from V to an Abelian group Γ such that the induced edge labels defined as w(xy) = f(x) + f(y) form a bijection from E to Γ. We study Γ-harmonious labelings of several cycles-related classes of graphs, including Dutch windmills, generalized prisms, generalized closed and open webs, and superwheels.

Assessment of Vulnerabilities in Student Records Web-Based Systems for Public and Private Higher Learning Institutions in Tanzania

In spite that HLIs in Tanzania use web-based systems for managing, storing and processing of HLIs information and data such as website contents, academic results and financial records. The HLIs web-based system have been compromised by attackers due to presence of vulnerabilities. The main objective of this study is to assess the vulnerabilities of Students Records Web-based Systems (SRWBS) for private and public Higher Learning Institutions (HLIs) in Tanzania using black-box testing methodology by employing two automatic vulnerability scanners namely OWASP ZAP (Open Webs Application Security Project Zed Attack Proxy; open-source tool) and Acunetix (proprietary tool). This study assesses the vulnerability of SRWBS for 3 private HLIs and 5 public HLIs in Tanzania. The results reveal the total of 29 vulnerabilities which include but are not limited to Broken Authentication and Session Management, Broken Access Control, Security Misconfiguration, Sensitive Data Exposure, Vulnerable JS (Java Script) Libraries, CSRF (Cros Site Request Forgery), Using Components with Known Vulnerabilities, XSS (Cross Site Script), DOM (Document Object Model) based XSS and Reflected XSS. SRWBS of public HLIs were found more vulnerable by average 44.2% than the SRWBS of private HLIs which were vulnerable by average of 37%. Based on these results, this study provides some recommendations for mitigating vulnerabilities and improving the security of SRWBS for private and public HLIs in Tanzania.

Theoretical evaluation of tapered composite plate girders subjected to shear loads

The behavior of prismatic composite steel plate girders subjected to shear loads was thoroughly investigated, and different theories were evaluated. However, the behavior of tapered composite plate girders with and without openings has not yet been investigated. Therefore, this paper presents a new method for predicting the ultimate capacity of tapered composite plate girders subjected to shear loads. The shear capacities of tapered composite plate girders with and without web openings were developed based on the classical theory of tension-field action for prismatic composite plate girders. It is assumed that the shear capacity of such girders can be predicted from the steel plate girder and reinforced concrete slab anchored using shear studs. The effect of the composite action on the top flange owing to the shear studs was considered in the derivation of the equations to calculate the shear capacity of the steel plate girders. In addition, the shape and size of the opening were also considered. The proposed method was verified by comparing the results of the shear capacity with experimental results from previous studies. It can be concluded that the proposed method can predict the shear capacities of tapered composite plate girders with solid and open webs with acceptable accuracy.

Microplastic ingestion and plastic additive detection in pelagic squid and fish: Implications for bioindicators and plastic tracers in open oceanic food webs

The ubiquitous presence of microplastics (MPs) in the ocean represents a potential threat to marine organisms, with poorly understood long-term adverse effects, including exposure to plastic additives. The present study investigated the ingestion of MPs in two epipelagic fish species (Trachurus picturatus and Scomber colias) and three pelagic squid species (Loligo vulgaris, Ommastrephes caroli and Sthenoteuthis pteropus) from an open oceanic region of the Northeast Atlantic. Seven phthalate esters (PAEs) were also analysed in the organisms' tissue, and the potential correlation between PAEs concentrations and ingested MPs was investigated. Seventy-two fish and 20 squid specimens were collected and analysed. MPs were found in the digestive tract of all species and in the squid species' gills and ink sacs. The highest occurrence of MPs was in the stomach of S. colias (85 %) and the lowest in the stomach and ink sac of O. caroli and L. vulgaris (12 %). Most of the particles identified (>90 %) were fibres. Among all the ecological and biological factors considered (dietary preferences, season, body size, total weight, liver weight, hepatosomatic index and gastrosomatic index), only gastrosomatic index (GSI) and season were significant predictors of MPs ingestion in fish species, with a greater likelihood of ingestion in the cold season and in specimens with higher GSI values (i.e. higher feeding intensity). Four PAEs (DEP, DIBP, BBP, DEHP) were detected in all the species analysed, with average ∑PAEs concentrations ranging between 10.31 and 30.86 ng/g (wet weight). DIBP was positively correlated with ingested MPs, suggesting this compound might represent a “plastic tracer”. This study looks into the problem of MPs ingestion for pelagic species in an open oceanic region, highlighting the most suitable bioindicators and providing essential insights into the factors that may influence ingestion rates. Additionally, the detection of PAEs in all species indicates the need for further research on the contamination sources, the effects of these chemicals on marine organisms, and the potential risks to human health through seafood consumption.

Otolith-derived field metabolic rates of myctophids (Family Myctophidae) from the Scotia Sea (Southern Ocean)

Myctophids (Family Myctophidae, commonly known as the lanternfishes) are critical components of open ocean food webs and an important part of the ocean biological carbon pump, as many species actively transport carbon to the deep ocean through their diel vertical migrations. Estimating the magnitude of myctophids’ contribution to the biological carbon pump requires knowledge of their metabolic rate. Unfortunately, data on myctophid metabolic rates are sparse, as they rarely survive being captured and placed in a respirometer. Because of this limitation, many studies estimate myctophid metabolic rates indirectly from body mass and temperature scaling relationships, often extrapolating regressions from global data sets to regional scales. To test the validity of these estimates, we employed a newly developed proxy for mass-specific field metabolic rate (Cresp: the proportion of metabolically derived carbon in the otolith) based on the stable carbon isotope composition (δ13C) of otolith aragonite. We recovered estimates of Cresp for individuals of 6 species of myctophids from the Scotia Sea, giving a range in Cresp values from 0.123-0.248. We found that ecological and physiological differences among species are better predictors of variation in Cresp values than body mass and temperature. We compared our results to estimates of metabolic rates derived from scaling relationships and from measurements of electron transport system activity. When considering myctophids as a whole, we found that estimates of oxygen consumption from different methods are broadly similar; however, there are considerable discrepancies at the species level. Our study highlights the usefulness of metabolic proxies where respirometry is currently unavailable, and provides valuable information on field metabolic rates of myctophids.

Special Issue on Design, Analysis, and Construction of Segmental Bridges

Special Issue on Design, Analysis, and Construction of Segmental Bridges

Behavior of Concrete Segmental Box Girder Bridges with Open Webs

AbstractThe prestressed concrete (PC) box girder bridge with open webs, whose mechanical behavior is halfway between that of the traditional plain web and the lattice box girder bridges is a relatively new bridge form. The concept depends on new structural developments considering complex geometry that combines cast in situ and prefabricated elements. In this paper, the Abra Bridge (or Tavaro Viaduct) in France was measured and analyzed by using the so-called space frame lattice model. The paper discusses the advantages of this bridge type. The paper also presents the use of a space frame lattice computational method for structural analysis. Given the calculated results, to reduce the principal stresses in the webs, the shear stresses are reduced by the vertical preshear force provided by the external prestressed tendons along the whole bridge, which is proposed by the authors. At the same time, the vertical internal prestressed tendons in the webs can be designed to increase the vertical compressive stre...

Taxon-specific response of marine nitrogen fixers to elevated carbon dioxide concentrations

Marine cyanobacteria supply much of the nitrogen that supports open ocean food webs and biogeochemical cycles. An experimental study suggests that the relationship between nitrogen fixation and carbon dioxide concentration varies significantly between cyanobacterial strains.

Carles Lalueza-Fox

Carles Lalueza-Fox

Stability of columns with semi-rigid connections including shear effects using Engesser, Haringx and Euler approaches

A complete column classification and the corresponding stability equations that can be used to evaluate the elastic critical axial loads of prismatic columns with sidesway uninhibited, partially inhibited, and totally inhibited including the simultaneous effects of bending and shear deformations and semi-rigid connections are presented and derived using three different approaches. The first two approaches are those by Engesser and Haringx that include the shear component of the applied axial force proportional to the total slope ( d y / d x ) and to the angle of rotation of the cross-section ( ψ ) along the member, respectively. The third approach is a simplified formulation based on the classical Euler theory that includes the effects of shear deformations but neglects the shear component of the applied axial force along the member. Comparisons among the critical loads obtained using these three approaches and those using the classical Euler solutions for classical column cases are presented. Examples that demonstrate the effectiveness and accuracy of the proposed stability equations and the importance of shear deformations and shear component of the applied axial force are presented in detail. These effects must be taken into account particularly in structures made of columns with relatively low effective shear areas A s (like laced columns, columns with batten plates or with perforated cover plates, and columns with open webs) or with low shear stiffness GA s of the same order of magnitude as π 2 E I / h 2 (like short columns made of laminated composites with low shear modulus G when compared to their elastic modulus E ). These effects become even more significant when the external supports are not perfectly clamped. The effects of semi-rigid connections and those due to shear forces and deformations are condensed into the proposed characteristic equations.

Stability and non-linear second-order elastic analyses of beam and framed structures with semi-rigid connections using the cross method

The main objective of this publication is to present an extended version of the Moment Distribution Method (MDM) for the stability and non-linear second-order analysis of indeterminate beams and framed structures made of beam-columns of symmetrical cross-section including the combined effects of shear and bending deformations, axial loads, and semi-rigid connections. The proposed method along each member has the following advantages: (1) it can be utilized in the first- and second-order analyses (including buckling analysis) of indeterminate beams and framed structures made of beam-columns with rigid, semi-rigid, and simple end connections; (2) the effects of semi-rigid connections are condensed into the bending stiffness and fixed-end moments without introducing additional degrees of freedom and equations of equilibrium; and (3) it is accurate, powerful, practical, versatile, and an excellent teaching tool. Analytical studies indicate that shear deformations, semi-rigid connections, and axial loads increase the lateral deflections and affect the internal moments and reactions of continuous beams and framed structures. These effects must be taken into account particularly in slender structures and when they are made of beam or columns with relatively low effective shear areas (like laced columns, columns with batten plates or with perforated cover plates, and columns with open webs) or with low shear stiffness (like short columns made of laminated composites with low shear modulus G when compared to their elastic modulus E) making the shear stiffness GAs of the same order of magnitude as EI/L2. These effects become even more significant when the external supports are not perfectly clamped. Three comprehensive examples are included that show the effectiveness of the proposed method.

Slope-deflection equations for stability and second-order analysis of Timoshenho beam–column structures with semi-rigid connections

A new set of slope-deflection equations for Timoshenko beam–columns of symmetrical cross section with semi-rigid connections that include the combined effects of shear and bending deformations, and second-order axial load effects are developed in a classical manner. The proposed method that also includes the effects of the shear component of the applied axial force as the member deflects laterally (Haringx Model) has the following advantages: (1) it can be utilized in the stability and second-order analyses of framed structures made up of Timoshenko beam–columns with rigid, semi-rigid, and simple end connections; (2) the effects of semi-rigid connections are condensed into the slope-deflection equations for tension or compression axial loads without introducing additional degrees of freedom and equations; (3) it is more accurate than any other method available and capable of capturing the phenomena of buckling under axial tension forces; and (4) it is powerful, practical, versatile and easy to teach. Analytical studies indicate that shear deformations increase the lateral deflections and reduce the critical axial loads of framed structures made of members with low shear stiffness. The effects of shear deformations must be considered in the analysis of beam–columns with relatively low effective shear areas (like laced columns, columns with batten plates or with perforated cover plates, and columns with open webs) or with low shear stiffness (like elastomeric bearing and short columns made of laminated composites with low shear modulus G when compared to their elastic modulus E ) making the shear stiffness GA s of the same order of magnitude as EI / L 2 . The shear effects are also of great importance in the static, stability and dynamic behavior of laminated elastomeric bearings used for seismic isolation of buildings. Four comprehensive examples are included that show the effectiveness of the proposed method and equations.

Large deflection and postbuckling behavior of Timoshenko beam–columns with semi-rigid connections including shear and axial effects

The nonlinear large deflection-small strain analysis and postbuckling behavior of Timoshenko beam–columns of symmetrical cross section with semi-rigid connections subjected to conservative and non-conservative end loads (forces and moments) including the combined effects of shear, axial and bending deformations, axial load eccentricities, lateral bracing and out-of-plumbness are developed in a simplified manner. A new set of stability functions based on the “modified shear equation” that includes the effects of shear deformations and the shear component of the applied axial forces is derived. Also, an expression for the axial displacement δ b caused by the “bowing” of the beam–column subjected to end forces and moments with generalized end conditions is derived in a classic manner. The proposed method and corresponding nonlinear equations, although approximate, can be used in the tension and compression stability and nonlinear large deflection-small strain elastic analyses of Timoshenko beam–columns with rigid, semi-rigid, and simple connections. Analytical studies indicate that shear deformations increase the longitudinal and transverse deflections and reduce the buckling axial load capacities of beam–columns. The effects of shear deformations must be considered in the analysis of beam–columns with relatively low effective shear areas (like in short laced columns, columns with batten plates and with open webs) or low shear stiffness (like elastomeric bearings and short columns made of laminated composites with low shear modulus G when compared to their elastic modulus E making the shear stiffness G A s of the same order of magnitude as E I / h 2 ). The shear effects are also of great importance in the tension and compression stability and dynamic behavior of laminated elastomeric bearings used for seismic isolation of buildings. Four comprehensive examples are included that show the effectiveness of the proposed method and equations.

Bioaccumulation of PCBs and chlorinated pesticides in seals, fishes and invertebrates from the White Sea, Russia

Persistent organochlorines (OC) contaminants, including polychlorinated biphenyl (PCB) congeners, Dichlorophenyltrichloroethane (DDT)- and chlordane (CHL) related compounds, hexachlorocyclohexanes (HCH) isomers and chlorobenzenes (CBz) were determined in blubber of harp seals ( Phoca groenlandica), ringed seals ( Phoca hispida) and bearded seals ( Eringnathus barbatus) as well as in fishes and invertebrates from the White Sea, in northwest Russia. Highest ∑PCB and ∑DDT concentrations were found in samples from two male bearded seals (means of 4150 ng/g lw and 3950 ng/g lw, respectively). Female harp seals had mean ∑PCB and ∑DDT concentrations of 1070±504 ng/g lw and 619±328 ng/g lw, respectively. Male and female adult ringed seals had similar mean ∑PCB concentrations as harp seals (955±385 ng/g lw and 999±304 ng/g lw, respectively). ∑CHL concentrations ranged from 63±29 ng/g lw in blubber of female adult ringed seals, to 322±156 ng/g lw in adult harp seals and averaged 465 ng/g lw in bearded seals. HCH isomers, mirex and chlorobenzenes were detected in all seal samples but were present at lower levels than ∑CHL, ∑DDT and ∑PCB. Concentrations of ∑CHL, ∑DDT and ∑PCB in ringed seals from the White Sea were within the range reported for the Barents Sea but lower than in ringed seals from the Kara Sea. Temporal trends were investigated by comparing concentrations of OCs in blubber of harp seal pups collected in 1992 with pups of the same age collected in 1998. The declines over the 6 year period ranged from approximately 33% for ∑DDT to 60% for ∑PCB. These declines are consistent with reports of declining concentrations ∑DDT in seawater from the White Sea and inflowing rivers in the 1980's and early 1990s. The major OC contaminants in fishes from the White Sea were DDT-related compounds and PCBs. Navaga ( Eleginus navaga) had the highest concentrations of the 5 fish species studied with mean ∑PCB of 41±6 ng/g wet wt. while lowest mean concentrations were present in cod muscle (16±8 ng/g ww). Concentrations of hexachlorobenzene (HCB), DDT, CHL—related compounds and PCB congeners were strongly correlated with trophic level of the organisms assigned using δ 15N values, while β-HCH, γ-HCH and cis-chlordane showed no relationship with trophic level. Food web magnification factors (FWMFs) for p,p′-DDE, α-HCH, oxychlordane and trans-nonachlor the White Sea were similar to those from marine food webs in the Barents Sea and the Canadian arctic, while FWMFs for HCB and PCBs were generally lower. Overall the results suggest that the White Sea marine food differs in terms of the availability of contaminants in comparison to studies of open ocean arctic food webs due to proximity to urban/industrial areas and greater importance of benthic food sources.

Automatic construction and management of large open webs

Many researchers have noted the problems associated with manually created or maintained hyperdocument links, and the consequent need for automated methods. A number of techniques have been applied to the problem, including pattern-matching, information retrieval, and natural language processing. This paper describes a system for the automatic detection and management of structural and referential links. The paper also addresses the issues of link-set soundness and completeness, open link management, and the particular problems engendered by large volatile hyperbases.

Co-adapted foraging traits in a guild of orb-weaving spiders.

From a previous two-species comparison, specific suites of morphological and web design traits are predicted to characterize foraging specializations in old-field orb-weaving spiders. Species with stout legs, large fangs, open mesh webs, high webs, and retreats should specialize on innocuous, rapidly escaping prey types. Species with long legs, small fangs, dense mesh webs, and low webs that rest in the hub should specialize on dangerous, clumsy prey that escape from webs slowly. Factor and discriminant analyses are used to test for these association patterns in eight co-occurring species of old-field orb-weavers. The association between most of the characters is supported, but the appearance of a new combination suggests that another dimension needs to be added to the model. Habitat use and diet predicted by the model are tested for species where data are available.