Shell Dimensions Research Articles

A molecular phylogeny of the Calopiidae (Caenogastropoda: Truncatelloidea), with a taxonomic reassessment ofCalopia imitataPonder, 1999

The Calopiidae Ponder, 1999 (Caenogastropoda: Truncatelloidea) are a family of aquatic microgastropods endemic to Australia. Of its four known species, three—Calopia minutissima, C. laseroni and C. imitata (all Ponder, 1999)—are broadly distributed, whereas C. burni Ponder, 1999 is restricted to southeastern Victoria. We used a concatenated dataset (1,261 positions), containing fragments of the mitochondrial genes COI and 16S, to generate the first molecular phylogeny of the family. Bayesian inference and maximum likelihood analyses of the combined dataset elucidate evolutionary relationships within the Calopiidae. Furthermore, C. imitata and C. burni were recovered as a strongly supported clade of negligible sequence divergence, so we view these two taxa as conspecific. Consequently, C. burni is synonymized herein with C. imitata, and a taxonomic reassessment of C. imitata is provided. A discriminant function analysis of shell dimensions suggests some morphological differences between populations of C. imitata, possibly expressing ecophenotypic variability.

Cochlostoma mienisi of southwestern Turkey: Its distribution range and conchological characterization

A survey was carried out to determine the distribution range of Cochlostoma mienisi Schütt, 1978, a little studied land snail of southwestern Turkey. The species was found on the island of Kekova off the coast of Turkey and at an additional location on the mainland facing the island. The closest congeners of C. mienisi are on Crete and mainland Greece, more than 400 km away. As a possible explanation for its limited and disjunct range, it is proposed here that C. mienisi may have been introduced from another location by the shipping trade in the antiquity. No live snails were seen, but various conchological traits of C. mienisi provided clues to its biology and ecology. The presence of two overlapping size groups in the distribution of adult shell dimensions is interpreted as an indication of a sexual dimorphism: the larger shells (8.0 mm × 3.5 mm) are those of female snails and the smaller ones (7.4 mm × 3.3 mm) are of males. Also discussed are the structure of the operculum of C. mienisi, decollation observed in a few shells and the presence of small circular holes that were probably bored by an unknown predator or a parasite.

Formation of Polymeric Hollow Microcapsules and Microlenses Using Gas-in-Organic-in-Water Droplets

This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 μm. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.

Morphology-Controlled Synthesis of Au/Cu₂FeSnS₄ Core-Shell Nanostructures for Plasmon-Enhanced Photocatalytic Hydrogen Generation.

Copper-based chalcogenides of earth-abundant elements have recently arisen as an alternate material for solar energy conversion. Cu2FeSnS4 (CITS), a quaternary chalcogenide that has received relatively little attention, has the potential to be developed into a low-cost and environmentlly friendly material for photovoltaics and photocatalysis. Herein, we report, for the first time, the synthesis, characterization, and growth mechanism of novel Au/CITS core-shell nanostructures with controllable morphology. Precise manipulations in the core-shell dimensions are demonstrated to yield two distinct heterostructures with spherical and multipod gold nanoparticle (NP) cores (Au(sp)/CITS and Au(mp)/CITS). In photocatalytic hydrogen generation with as-synthesized Au/CITS NPs, the presence of Au cores inside the CITS shell resulted in higher hydrogen generation rates, which can be attributed to the surface plasmon resonance (SPR) effect. The Au(sp)/CITS and Au(mp)/CITS core-shell NPs enhanced the photocatalytic hydrogen generation by about 125% and 240%, respectively, compared to bare CITS NPs.

Sub-nanometer dimensions control of core/shell nanoparticles prepared by atomic layer deposition

Bimetallic core/shell nanoparticles (NPs) are the subject of intense research due to their unique electronic, optical and catalytic properties. Accurate and independent control over the dimensions of both core and shell would allow for unprecedented catalytic performance. Here, we demonstrate that both core and shell dimensions of Pd/Pt core/shell nanoparticles (NPs) supported on Al2O3 substrates can be controlled at the sub-nanometer level by using a novel strategy based on atomic layer deposition (ALD). From the results it is derived that the main conditions for accurate dimension control of these core/shell NPs are: (i) a difference in surface energy between the deposited core metal and the substrate to obtain island growth; (ii) a process yielding linear growth of the NP cores with ALD cycles to obtain monodispersed NPs with a narrow size distribution; (iii) a selective ALD process for the shell metal yielding a linearly increasing thickness to obtain controllable shell growth exclusively on the cores. For Pd/Pt core/shell NPs it is found that a minimum core diameter of 1 nm exists above which the NP cores are able to catalytically dissociate the precursor molecules for shell growth. In addition, initial studies on the stability of these core/shell NPs have been carried out, and it has been demonstrated that core/shell NPs can be deposited by ALD on high aspect ratio substrates such as nanowire arrays. These achievements show therefore that ALD has significant potential for the preparation of tuneable heterogeneous catalyst systems.

Backscattering Properties of Gold Nanoshells: Quantitative Analysis and Optimization for Biological Imaging

In this article, we investigate the dependence of the backscattering properties of gold nanoshells on the core material, core radius, and shell thickness by using Mie theory of a coated sphere. The size-dependent and dispersive dielectric function of metal nanoparticles permits to consider the localized surface plasmon resonance of gold nanoshells with the classical Mie theory. Our results show that gold nanoshells exhibit resonant backscattering feature due to the resonance of the free electrons in gold shells at a specific incident wavelength. The resonance peak intensity depends on the core material and the dimensions of core and shell, and the resonance wavelength can be tuned to the near-infrared region where biological tissues possess high transmissivity. We obtain the maximum backscattering and the corresponding optimal core radii and shell thicknesses of gold nanoshells at four typical wavelengths (830, 840, 900, and 1310nm) frequently-used in biological imaging. It is found that silica core-gold nanoshells have maximum volume backscattering coefficient (7.01μm-1) at wavelength of 830nm when the core radius is 54.2nm and the shell thickness is 10.1nm. For longer wavelength, the optimal core radius is larger while the optimal shell thickness is thinner, and the maximum volume backscattering coefficient become small. If the core material is changed from silica to vacuum, the gold nanoshells have bigger maximum volume backscattering coefficient with larger core radius and thinner shell thickness. The optimized gold nanoshells can be used as the ideal contrast agents for biological imaging.

Shell morphological versus genetic identification of quagga mussel (Dreissena bugensis) and zebra mussel (Dreissena polymorpha)

Herein we provide first genetic evidence that Dreissena bugensis Andrusov, 1897 has reached the German Danube system. The occurrence of this species at several sampling sites along a 152 km river stretch of the upper Danube River thereby proved to be wrongly estimated by using solely shell morphology features for species identification. 17.5% of the dreissenid specimens (Dreissena bugensis, N=26, Dreissena polymorpha, N=34), identified according to exterior shell characteristics, were assigned to the wrong species. In contrast to RFLP identification, comparisons of shell dimension measurements by discriminant function analysis were not able to fully identify the two species, with correct classification rates between 61.1% and 94.4%, confirming their high morphological plasticity. The results of this study suggest that species records of dreissenid mussels should generally be genetically verified.

Growth of core-shell quantum dots/titanium dioxide hybrid films as photoanode for Graetzel cells

In this work, we illustrated a method for controlled growth of ZnSe/ZnS core/shell semiconductor and their insertion in a TiO2 anatase bulk. Core/shell quantum dots were grown by Laser Ablation in Solution followed by heating and sonication phases. Shape and dimensions of nanoparticles were controlled by measurements of optical absorption during laser irradiation. The obtained quantum dots, with a ZnS core and a ZnSe shell and radius dimensions of about 12nm, were spray-dried in film of anatase grains and characterized as photoanode for application on Graetzel cells. The efficiency of our hybrid photoanode is about 25% higher than classic organic dye/anatase.

Intrinsic variability in shell and soft tissue growth of the freshwater mussel Lampsilis siliquoidea.

Freshwater mussels are ecologically and economically important members of many aquatic ecosystems, but are globally among the most imperiled taxa. Propagation techniques for mussels have been developed and used to boost declining and restore extirpated populations. Here we use a cohort of propagated mussels to estimate the intrinsic variability in size and growth rate of Lampsilis siliquoidea (a commonly propagated species). Understanding the magnitude and pattern of variation in data is critical to determining whether effects observed in nature or experimental treatments are likely to be important. The coefficient of variation (CV) of L. siliquoidea soft tissues (6.0%) was less than the CV of linear shell dimensions (25.1–66.9%). Size-weight relationships were best when mussel width (the maximum left-right dimension with both valves appressed) was used as a predictor, but 95% credible intervals on these predictions for soft tissues were ∼145 mg wide (about 50% of the mean soft tissue mass). Mussels in this study were treated identically, raised from a single cohort and yet variation in soft tissue mass at a particular size class (as determined by shell dimensions) was still high. High variability in mussel size is often acknowledged, but seldom discussed in the context of mussel conservation. High variability will influence the survival of stocked juvenile cohorts, may affect the ability to experimentally detect sublethal stressors and may lead to incongruities between the effects that mussels have on structure (via hard shells) and biogeochemical cycles (via soft tissue metabolism). Given their imperiled status and longevity, there is often reluctance to destructively sample unionid mussel soft tissues even in metabolic studies (e.g., studies of nutrient cycling). High intrinsic variability suggests that using shell dimensions (particularly shell length) as a response variable in studies of sublethal stressors or metabolic processes will make confident identifications of smaller effect sizes difficult.

MORFOMETRIK KIJING TAIWAN (Anodonta woodiana) DI BEBERAPA LOKASI DI KABUPATEN MINAHASA DAN MINAHASA UTARA

This study was conducted to determine morphometric kijing taiwan at several locations in Minahasa District and North Minahasa regency and its association with the abundance of plankton and water quality. Sampling gravestone taiwan and water quality obtained from the four (4 ) locations: Rap Rap Village, BBAT Tatelu North Minahasa Regency, Paleloan and Tataaran II Village, Minahasa regency. Morphometric measurements kijingg taiwan include dimensional measurements and weighing of the shell. Measurement of shell dimensions include length , width , and thickness. Include the weighing of the weighing of the total, shell weight and wet weight of meat. Water quality measurements carried out directly at the sites include measurement of temperature, pH, dissolved oxygen and water base texture, while the identification of plankton carried in Pathology and Clinical Laboratory of Fish Diseases, Faculty of Fisheries and Marine Sciences, University of Sam Ratulangi. Morphometric measurements will be taken in any of 50 individual kijing taiwan each location. The results of morphometric measurements in multiple locations showed uniform size Tataaran II contained in the Village, the Village and Village Paleloan Rap Rap while in BBAT Tatelu uniformity of size only in size from 7-18 to 9-74 cm was caused by Taiwan in the pool because kijing BBAT Tatelu regarded as pest extermination so regularly done. Relationships shell length and total weight kijing taiwan to change at any time is influenced by several factors such as the condition of gonadal maturation , water quality and availability of food in the waters.

Influence of complex structure on the shrinkage of part in investment casting process

Investment casting (IC) is traditionally used to produce high accuracy products, but the products gaining variable cross section, multidimensional, and unconstrained/constrained features make it hard to determine the tooling dimensions. Every individual stage in the investment casting process (ICP) also poses a potential and uncertain threat on the final part dimensions. In this article, a variable cross section, multidimensional and unconstrained/constrained part for IC, is designed and constructed. The dimensions of wax pattern and final casting part are measured by three-dimensional (3-D) laser scanning, and the inner cavity dimensions of the ceramic shell are measured by industrial computerized tomography (ICT). The dimensional changes and the change of shrinkage along with the dimensions in different processes are analyzed. Finally, the exponential relationship between shrinkage and dimension in the whole ICP is concluded, and the mechanisms of the dimensional changes are discussed. The conclusions can be used to guide the dimensional design of the die and the reworking of the wax pattern to reduce the trial-and-error procedures.

Plan-view transmission electron microscopy investigation of GaAs/(In,Ga)As core-shell nanowires

Plan-view transmission electron microscopy in combination with electron energy-loss spectroscopy have been used to analyze the strain and the chemical composition of GaAs/(In,Ga)As core-shell nanowires. The samples consist of an GaAs core and a radially arranged (In,Ga)As layer as quantum well and GaAs outer-shell. The nominal parameters of the quantum well in the two samples under investigation are: an indium concentration of 25% and a quantum well thickness of 22 nm and 11 nm, respectively, while the core and the external shell dimensions are fixed. Scanning transmission electron microscopy using high-angle annular dark field detector was performed to verify the actual dimensions of the layers. Geometric phase analysis was carried out in order to examine the local strain of the radial (In,Ga)As quantum well, while the local chemical composition was determined by means of spatially resolved electron energy-loss spectroscopy. Finite elements calculations were carried out in order to simulate the multi-shell structure and extract the actual strain distribution. The results indicate that there is a uniform strain distribution at the coherent interfaces. In addition, based on calculations, we show that there is no region in the considered core-shell structure absolutely free of strain.

A survey of the land snails of the Karaburun peninsula, Turkey

1. Bank R. A., Maassen W. J. M. 1998. Beiträge zur Mollusk­en­fauna der Präf­ektur Samos (Griechenland, östlichen Agä­is). De Kreukel 34: 45–80. Google Scholar

Multiexciton Generation in Seeded Nanorods.

The stochastic formulation of multiexciton generation (MEG) rates is extended to provide access to MEG efficiencies in nanostructures containing thousands of atoms. The formalism is applied to a series of CdSe/CdS seeded nanorod heterostructures with different core and shell dimensions. At energies above 3Eg (where Eg is the band gap), the MEG yield increases with decreasing core size, as expected for spherical nanocrystals. Surprisingly, this behavior is reversed for energies below this value, and is explained by the dependence of the density of states near the valence band edge, which increases with the core diameter. Our predictions indicate that the onset of MEG can be shifted to lower energies by manipulating the density of states in complex nanostructure geometries.

Size-dependent exchange bias in ferromagnetic (core)/antiferromagnetic (shell) nanoparticles

We report a numerical study of the dependence of exchange bias on ferromagnetic core/antiferromagnetic shell dimension in an isolated nanoparticle, on the basis of a modified Metropolis Monte Carlo simulation. A pronounced exchange bias field is obtained at a finite size of ferromagnetic core radius, while the value of exchange bias field decreases monotonously up to a lower stable value with further increasing core sizes. Due to the complex core/shell structure and the mode conversion of magnetization reversal for various core sizes, the dependence of exchange bias field on the ferromagnetic component size is different from that in planar systems. Moreover the exchange bias field can be stabilized above a certain antiferromagnetic shell thickness, where the effective anisotropy of the whole antiferromagnetic shell becomes strong enough. It has been demonstrated unambiguously how the core and shell dimensions optimize the exchange bias.

High-Temperature Photoluminescence of CdSe/CdS Core/Shell Nanoheterostructures

The steady-state and time-resolved photoluminescence properties of CdSe/CdS heterostructures are studied as a function of temperature from 300 to 600 K. The emission properties of samples are found to behave similarly to bulk CdSe, with the samples maintaining high color purity and a slightly contracting band gap at elevated temperature. Photoluminescence from CdSe/CdS samples is maintained with high stability over prolonged illumination and multiple heating and cooling cycles. Structures synthesized with variation in the core and the shell dimensions show that the preservation of emission intensity at high temperature depends strongly on the microscopic structure of the samples. For samples synthesized by seeded growth, the size of the CdSe core is highly correlated with the fraction of preserved sample photoluminescence intensity at high temperature. Temperature-dependent lifetime data suggest that the core structure predicts the stability of photoluminescence at elevated temperatures by controlling the radiative rate. The rate of electron capture, for which the volume fraction of the core is a structural proxy, underpins the ability for radiative processes to compete with thermally induced nonradiative decay pathways. Heterostructures synthesized below 200 °C using highly reactive organometallic precursors show markedly lower thermal stability than samples prepared by seeded growth at 360 °C, suggesting that the temperature of nanocrystal synthesis has direct consequences for the thermal stability of photoluminescence.

Controlled overgrowth of Pd on Au nanorods

In this paper, we present a detailed, systematic study of the controlled overgrowth of Pd on Au nanorods. Pd nanoshells with fine-controlled dimensions and architectures were overgrown on single-crystalline Au nanorods through seed-mediated growth using H2PdCl4 as the Pd precursor and ascorbic acid as the reducing agent in the presence of cetyltrimethylammonium chloride (CTAC) or cetyltrimethylammonium bromide (CTAB) as the surface capping agent. The effects of surface capping agent, ascorbic acid to H2PdCl4 ratio, reaction temperature, and structure-directing foreign ions, such as Ag+, on the dimensions and architectures of the resulting Au@Pd core–shell heteronanostructures were systematically studied. At 30 °C, Au nanorods coated with polycrystalline Pd shells were obtained using CTAC as the surface capping agent, while single-crystalline Au@Pd core–shell nanocuboids formed in the presence of CTAB. The thicknesses of the polycrystalline and single-crystalline Pd shells were fine-controlled by adjusting the molar ratio of ascorbic acid to H2PdCl4. At an elevated reaction temperature of 60 °C, irregularly shaped and cylindrical co-axial core–shell nanorods were obtained in CTAC and CTAB, respectively. By introducing Ag+ ions into the Pd growth solution, Au nanorods coated with segregated Pd nanoislands and dumbbell-like core–shell heteronanostructures were obtained as a consequence of the underpotential deposition of Ag and sustainable galvanic replacements that concurred during the Pd overgrowth processes. The effects of the Pd shell dimensions and morphologies on the plasmonic properties of the Au@Pd core–shell nanostructures were also investigated.

Genetically Programmable Thermoresponsive Plasmonic Gold/Silk-Elastin Protein Core/Shell Nanoparticles

The design and development of future molecular photonic/electronic systems pose the challenge of integrating functional molecular building blocks in a controlled, tunable, and reproducible manner. The modular nature and fidelity of the biosynthesis method provides a unique chemistry approach to one-pot synthesis of environmental factor-responsive chimeric proteins capable of energy conversion between the desired forms. In this work, facile tuning of dynamic thermal response in plasmonic nanoparticles was facilitated by genetic engineering of the structure, size, and self-assembly of the shell silk-elastin-like protein polymers (SELPs). Recombinant DNA techniques were implemented to synthesize a new family of SELPs, S4E8Gs, with amino acid repeats of [(GVGVP)4(GGGVP)(GVGVP)3(GAGAGS)4] and tunable molecular weight. The temperature-reversible conformational switching between the hydrophilic random coils and the hydrophobic β-turns in the elastin blocks were programmed to between 50 and 60 °C by site-specific glycine mutation, as confirmed by variable-temperature proton NMR and circular dichroism (CD) spectroscopy, to trigger the nanoparticle aggregation. The dynamic self-aggregation/disaggregation of the Au-SELPs nanoparticles was regulated in size and pattern by the β-sheet-forming, thermally stable silk blocks, as revealed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The thermally reversible, shell dimension dependent, interparticle plasmon coupling was investigated by both variable-temperature UV–vis spectroscopy and finite-difference time-domain (FDTD)-based simulations. Good agreement between the calculated and measured spectra sheds light on design and synthesis of responsive plasmonic nanostructures by independently tuning the refractive index and size of the SELPs through genetic engineering.

Dependence of exchange bias on core/shell relative dimension in ferromagnetic/antiferromagnetic nanoparticles

Abstract We employ a modified Metropolis Monte Carlo simulation to study the effect of bimagnetic core/shell relative dimension on exchange bias in ferromagnetic/antiferromagnetic nanoparticles. The exchange bias field is inversely proportional to the ferromagnetic shell thickness in the antiferromagnetic (core)/ferromagnetic (shell) nanoparticles, while in the nanoparticles with an opposite core/shell structure the exchange bias behavior is complex and distinguished in different ranges of the ferromagnetic core radius. The work elucidates unambiguously how the core and shell dimensions optimize the exchange bias in nanoparticles.

Visible Mie Scattering from Hollow Silica Particles with Particulate Shells

A series of colloidal nanocomposite dispersions are synthesized by alcoholic dispersion polymerization of styrene in the presence of an ultrafine silica sol. The original core/shell polystyrene/silica nanocomposite particles have mean diameters ranging from 321 to 471 nm, as determined by dynamic light scattering. Upon calcination of the polystyrene cores, some shrinkage occurs but intact hollow silica shells are observed by transmission electron microscopy. On visual inspection, these silica residues display remarkable colors that vary depending on the particle diameter. When examined in transmittance mode (i.e., with an illuminated background) the silica powders appear yellow to red in color, but when viewed in reflectance (i.e., with a dark background) relatively intense blue/green colors are observed. The latter phenomenon has been analyzed by visible reflectance spectroscopy and the reflectance maximum depends on the dimensions of the silica shell, which are in turn dictated by the initial nanocomposite particle diameter. Small-angle X-ray scattering is used to determine the packing density of the silica nanoparticles, both in the original polystyrene/silica nanocomposite particles and in the calcined silica shells. Combined with geometrical considerations, this allows the equivalent uniform silica shell thickness to be calculated for a particulate silica shell and this parameter is then related to the theoretical predictions made by Retsch et al. for hollow particles comprising uniform silica shells (see Retsch, M.; Schmelzeisen, M.; Butt, H. J.; Thomas, E. L. Nano Lett., 2011, 11, 1389).