Concentric Shells Research Articles

Capsules with Concentric Biopolymer-Nylon Shells Imaged by Cryo-FIB/SEM

Capsules with Concentric Biopolymer-Nylon Shells Imaged by Cryo-FIB/SEM

Consistency checks of results from a Monte Carlo code intercomparison for emitted electron spectra and energy deposition around a single gold nanoparticle irradiated by X-rays

Organized by the European Radiation Dosimetry Group (EURADOS), a Monte Carlo code intercomparison exercise was conducted where participants simulated the emitted electron spectra and energy deposition around a single gold nanoparticle (GNP) irradiated by X-rays. In the exercise, the participants scored energy imparted in concentric spherical shells around a spherical volume filled with gold or water as well as the spectral distribution of electrons leaving the GNP. Initially, only the ratio of energy deposition with and without GNP was to be reported. During the evaluation of the exercise, however, the data for energy deposition in the presence and absence of the GNP were also requested. A GNP size of 50 nm and 100 nm diameter was considered as well as two different X-ray spectra (50 kVp and 100 kVp). This introduced a redundancy that can be used to cross-validate the internal consistency of the simulation results. In this work, evaluation of the reported results is presented in terms of integral quantities that can be benchmarked against values obtained from physical properties of the radiation spectra and materials involved. The impact of different interaction cross-section datasets and their implementation in the different Monte Carlo codes is also discussed.

Microfossils from the Liuchapo Formation: Possible oldest radiolarians from deep-water chert and phylogenetic analysis

Radiolarian, as a group of siliceous skeleton-bearing heterotrophic protist, has a long history from modern ocean back to the Cambrian. The earliest stage in the evolution of radiolarians, although poorly understood, is important not only for itself but also with respect to the development of the global silica cycle and biogenetic siliceous sediments. It has been hypothesized that radiolarians evolved from an ancestral form constructed by spicules, although this is not without controversy since origin and their early morphology is still in dispute. However, the record of Cambrian radiolarians, especially the early Cambrian, is still sparse. Here we report a research in chert of the Liuchapo Formation from the latest Ediacaran to early Cambrian in South China that yielded the most probable oldest radiolarians from deep-water settings. Accompanied fossils and stratigraphic correlation indicate a Fortunian age. Judging by the prominent concentric multilayered shell and absence of spicules, the fossils were classified into the order Spumellaria according to the advance of radiolarian taxonomy and phylogeny. They can be compared with radiolarians from Series 2 to Furongian of the Cambrian. Molecular study conducted here also supports the existence of spumellarian during the Cambrian. Together with other reports of Cambrian radiolarians in recent years, the occurrence of non-spicule forms predates the ones constructed by spicules, which do not support the previous assumption about primitive radiolarian. The discovery not only added to the sparse fossils record of the Cambrian radiolarian, but also demonstrated their contribution to silica cycle and siliceous sediments. Evolution of early radiolarians still subjects to open discussion and awaits more evidence.

Investigating the impacts of intrafraction motion on dosimetric outcomes when treating small targets with virtual cones.

PurposeIntrafraction patient motion is a well‐documented phenomenon in radiation therapy. In stereotactic radiosurgery applications in which target sizes can be very small and dose gradients very steep, patient motion can significantly impact the magnitude and positional accuracy of the delivered dose. This work investigates the impact of intrafraction motion on dose metrics for small targets when treated with a virtual cone.Materials and MethodsMonte Carlo simulations were performed to calculate dose kernels for treatment apertures ranging from 1 × 2.5 mm2 to 10 × 10 mm2. The phantom was an 8.2‐cm diameter sphere and isotropic voxels had lengths of 0.25 mm. Simulated treatments consisted of 3 arcs: 1 axial arc (360° gantry rotation, couch angle 0°) and 2 oblique arcs (180° gantry rotation, couch angle ±45°). Dose distributions were calculated via superposition of the rotated kernels. Two different collimator orientations were considered to create a virtual cone: (a) each treatment arc was delivered twice, once each with a static collimator angle of ±45°, and (b) each treatment arc was delivered once, with dynamic collimator rotation throughout the arc. Two different intrafraction motion patterns were considered: (a) constant linear motion and (b) sudden, persistent motion. The impact of motion on dose distributions for target sizes ranging from 1 to 10 mm diameter spheres was quantified as a function of the aperture size used to treat the lesions.ResultsThe impact of motion on both the target and the surrounding tissue was a function of both aperture shape and target size. When a 0.5‐mm linear drift along each dimension occurred during treatment, targets ≥5 mm saw less than a 10% decrease in coverage by the prescription dose. Smaller apertures accrued larger penalties with respect to dosimetric hotspots seen in the tissues surrounding the target volume during intrafraction motion. For example, treating a 4‐mm‐sized target that undergoes 2.60 mm (3D vector) of continuous linear motion, the D5 in the concentric shells that extend 1, 2, and 3 mm from the surface of the target was 39%, 24%, and 14% smaller, respectively when comparing the delivery of a larger aperture (6 × 10 mm2) to a smaller aperture (2 × 5 mm2). Using a static collimator for shaping a virtual cone during treatment minimized the dosimetric impact of motion in the majority of cases. For example, the volume that is covered by 70% or more of the prescription dose is smaller in 60.4% of cases when using the static collimator. The volume covered by 50, and 30% or more of the prescription dose is also smaller when treating with a static collimator, but the clinical significance of this finding is unknown.ConclusionsIn this work, the dosimetric trade‐offs between aperture size and target size when irradiating with virtual cones has been demonstrated. These findings provide information about the tradeoffs between target coverage and normal tissue sparing that may help inform clinical decision making when treating smaller targets with virtual cones.

Fundamental Study of the Dispersion of Carbon Nano-Onions

Since the discovery of the fullerene C60 in 1985 by Curl, Kroto and Smalley, carbon nanomaterials have been the focus of interdisciplinary chemical research. Multi-shell fullerenes, known as carbon nano-onions (CNOs) discovered by Ugarte in 1992, are structured by concentric shells of carbon atoms. Different methods for their synthesis have been developed and their properties have been widely studied. In addition, the chemical functionalization of CNOs has been investigated and several synthetic pathways were found to be applicable for the introduction of a variety of functional groups. The purpose of this project is to make the oxidized CNOs bear a relative centrifugal force at different time durations to analyzed how well the material disperses. This in turn, will provide a fundamental concept for the synthesis efficiency. According to preliminary results, there is a tendency on which the concentrated CNOs difference in weight gets narrow, as duration of the centrifugal force increases. Chemically modified CNOs were probed in different fields of application and have revealed to be a promising nanomaterial that attracts a growing interest among researchers and opens new avenues for investigation. Its development starts using nano-diamonds; a carbon nanomaterial of strong structure which undergoes through a temperature of approximately 1650°C inside a furnace to obtain the CNOs structure. The CNOs are then oxidize through synthesis that requires a constant temperature and stirring to attain oxygen based functional groups. Another way to obtain the oxygen based functional groups is through heating the sample at 400°C for two hours; these procedures are then analyzed to determine the efficiency of functionalization. The preliminary elemental detection of oxygen atoms was gathered by Energy-Dispersive Spectroscopy. To detect states in the CNO’s molecular system, Raman Spectroscopy was utilized to confirm the carbon structure of CNOs by the identification of the peaks D and G characteristic of this carbon material. An in-depth characterization analysis was done using X-Ray Diffraction, providing detailed information about chemical composition, and crystalline structure. The morphology and microstructure of CNOs were studied using a Transmission Electron Microscope and Scanning Electron Microscopy. Through Cyclic Voltammetry, CNO’s ink was prepared to characterize electrochemically comparing both functionalization processes. To study its catalytic properties, Oxygen Reduction Reaction (ORR) experiments was conducted utilizing Rotating Ring-Disk Electrode (RRDE). The ORR experiments were carried out by varying the rotation rates of the RRDE at 100, 400, 900, 1600 and 2500 rpm.

Late Eocene marginal marine deposits and paleoenvironment characterisation from the Maadi Formation (Northern Eastern Egypt)

Two beds containing relatively thick and highly concentrated oyster shell banks occurring in the densely fossiliferous Wadi Al Abraq outcrop (Upper Eocene Maadi Formation, Cairo-Sukhna Road, Egypt). Such shell beds are almost monospecific. The upper level consists mainly of Ostrea clotbeyi Bellardi, topped by a considerable concentration of Carolia placunoides Cantraine, while in the lower level occurs Ostrea multicostata Deshayes. In both beds, the upper contact with the overlying marl bed (about 2 m thick) is sharp and sometimes erosive. Similarly, the contact with the underlying shale (1.5 m thick) is sharp and erosional. The shell beds are composed mainly of loosely packed oyster shells and their fragments (usually with a high proportion of disarticulated specimens) set in the sandy limestone matrix. The collected oysters show bioerosion and skeletobiont assemblages. Bioerosion trace fossils comprise ten ichnospecies while skeletozoans comprise five taxa. In general, shells of O. clotbeyi show a higher incidence of bioerosion than O. multicostata. The shells' chaotic orientation and their moderate fragmentation indicate that the shell bed formation was associated with high energy events. On the other hand, the low frequency of articulated specimens suggests that the shell beds are parautochthonous oyster banks' remnants. The taphonomic features of the studied assemblage indicate deposition in a shallow-water, wave-dominated environment.

Kirkendall pore evolution during interdiffusion and homogenization of titanium-coated nickel microwires

In-situ and ex-situ X-ray 3D-tomography is used to characterize the microstructure of Ni microwires, with wire diameters spanning 25–100 μm, (i) after vapor-phase deposition of Ti onto their surface and (ii) after subsequent homogenization to achieve the near-equiatomic NiTi composition desired for shape-memory or superelastic behavior. After Ti deposition at 925 °C, wires are partially homogenized, exhibiting a pure Ni core surrounded by concentric shells of Ni3Ti, NiTi and NiTi2 intermetallic phases. Because of the imbalanced Ni and Ti diffusive fluxes, Kirkendall porosity is formed near the center of the wire, which often merges into a single pore in cross-sections, due to spatial confinement of the wire geometry. During subsequent homogenization at 925 °C, these Kirkendall pores grow due to further Ni-Ti interdiffusion, and they coalesce into a single, hollow channel near the central axis of the wire, thus forming a NiTi microtube. In some cases, off-center pores form in addition to the central pore, but these off-center pores do not form continuous channels.

A constitutive model for glass–ceramic materials

Glass–ceramics have received recent attention for use in glass–ceramic to metal hermetic seals. Due to their heterogeneous microstructure, these materials exhibit a number of advantageous responses over conventional glass based seals. Key amongst them is the possibility of a controllable thermal strain response and apparent coefficient of thermal expansion which may be used to minimize thermally induced residual stresses for aforementioned seals. These behaviors result from an inorganic glass matrix and variety of crystalline ceramic phases including silica polymorph(s) that may undergo reversible solid-to-solid transformations with associated inelastic strain. Correspondingly, these materials exhibit complex thermomechanical responses associated with multiple inelastic mechanisms (viscoelasticity and phase transformation). While modeling these behaviors is essential for developing and analyzing the corresponding applications, no such model exists. Therefore, in this work a three-dimensional continuum constitutive model for glass–ceramic materials combining these various inelastic mechanisms is developed via an internal state variable approach. A corresponding fully implicit three dimensional numerical formulation is also proposed and implemented. The model is used to simulate existing experiments and validate the proposed formalism. As an example, the simple seal problem of a glass–ceramic seal inside a concentric metal shell is explored. Finally, the impact of the cooling rates, viscoelastic shift factors, and inelastic strain on final residual stress state are all investigated and the differing contributions highlighted.

Thermal performance investigation of concentric and eccentric shell and tube heat exchangers with different fin configurations containing phase change material

The aim of this study is to evaluate the combined effect of fin configuration and eccentricity of heat transfer tube on melting behavior of phase change material (PCM) inside the shell and tube heat exchanger (HX). Two unfinned HXs with concentric and eccentric heat transfer tubes and six other HXs with different arrangements of straight and bifurcated fins were fabricated while the total fin mass was kept constant. The shells of heat exchangers were made of transparent Plexiglas and the melting process was photographed to enable the analysis of the solid-liquid interface evolution. Experimental findings of the unfinned HXs showed that applying the eccentric tube HX leads to a 54% reduction in melting time compared to the concentric tube HX. Among all the cases considered, bifurcated fin configuration outperforms the straight fin configuration. The maximum melting time reduction compared to the HX with concentric unfinned tube was 85% obtained by eccentric tube HX with a long upper bifurcated fin and a short lower straight fin. Transient numerical simulations using a control volume approach were carried out for three tube wall temperatures of 75, 85 and 95 °C. Numerical results showed that the bifurcations increase the total heat transfer rate while the convective heat transfer coefficient decreases.

Emergence of rectangular shell shape in thermal energy storage applications: Fitting melted phase changing material in a fixed space

Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging.

Superconductivity at 1 K in Y-Au-Si quasicrystal approximants

We report the structural and physical properties of two Y-Au-Si (YAS) compounds, ${\mathrm{Y}}_{14.1}{\mathrm{Au}}_{69.2}{\mathrm{Si}}_{16.7}$ and ${\mathrm{Y}}_{15.4}{\mathrm{Au}}_{68.6}{\mathrm{Si}}_{16.1}$, which are 1/1 approximant crystals of a Tsai-type quasicrystal without intrinsic magnetic moments. The compounds differ by the presence of either a tetrahedron (Au,Si)${}_{4}$ or a single Y atom at the center of their characteristic structural building unit consisting of concentric polyhedral shells. Both compounds exhibit bulk superconductivity, which seems to be of a conventional type-II BCS type. The compound with Y atoms at the cluster center has a slightly higher transition temperature with a sharper step in the specific heat than the compound with tetrahedral units. We discuss the occurrence of this superconducting state in the light of the specific structural and physical properties of these quasicrystal approximants.

Ultra-Thin Solenoid and Cryostat Development for Novel Detector Magnets

In the scope of the Future Circular electron positron Collider study (FCC-ee), the IDEA detector is developed. It comprises a superconducting solenoid with free bore of 4 m, 6 m long and a central magnetic field of 2 T. The positioning of the magnet between the inner tracker and the electronic calorimeter heavily constrains the magnet design, as it is required to have the lowest possible radiation length, so minimum thickness and lowest density material. With respect to the classical solution of a solenoid enclosing the calorimeters, a cost reduction of about 50% is expected due to size reduction. An optimization of the different components of the magnet system has been carried out, resulting in the development of a new composite high-strength conductor that can be used to build a 30 mm thin solenoid. The quench analysis of the solenoid will be presented as it is of critical importance given the high energy density in the magnet of 21 kJ/kg. A cryostat made of concentric aluminium shells would account for about 50% of the radiation length of the magnet and most of this material is used in the outer vacuum shell of the cryostat to prevent buckling. In order to further reduce the radiation length, two fundamentally different approaches are being analysed. The first method focuses on reducing drastically the outer shell thickness. This leads to use honeycomb composites, reinforcing bars and corrugated shells for the outer shell of the cryostat. The second approach consists of supporting very thin cryostat shells directly on the solenoid cold mass using proper support. This can be achieved by replacing the thick walls and MLI insulation by a material that can sustain 1 atm while having low radiation length and low thermal conductivity. Cryogel Z has shown promising properties and its suitability for this project is being analysed. This novel approach has never been used so far for superconducting magnets.

Cosmological Parameter Estimation from the Two-dimensional Genus Topology—Measuring the Expansion History Using the Genus Amplitude as a Standard Ruler

Abstract We measure the genus of the galaxy distribution in two-dimensional slices of the SDSS-III BOSS catalog to constrain the cosmological parameters governing the expansion history of the universe. The BOSS catalogs are divided into 12 concentric shells over the redshift range 0.25 < z < 0.6, and we repeatedly measure the genus from the two-dimensional galaxy density fields, each time varying the cosmological parameters used to infer the distance–redshift relation to the shells. We also indirectly reconstruct the two-dimensional genus amplitude using the three-dimensional genus measured from SDSS Main Galaxy Sample with galaxies at low redshift z < 0.12. We combine the low- and high-redshift measurements, finding the cosmological model that minimizes the redshift evolution of the genus amplitude, using the fact that this quantity should be conserved. Being a distance measure, the test is sensitive to the matter density parameter (Ωm) and equation of state of dark energy (w de). We find a constraint of w de = − 1.05 − 0.12 + 0.13 , Ωm = 0.303 ± 0.036 after combining the high- and low-redshift measurements and combining with Planck CMB data. Higher-redshift data and combining data sets at low redshift will allow for stronger constraints.

Control of sound transmission into a hybrid double-wall sandwich cylindrical shell

A 3D analytical model is formulated for diffuse sound field transmission control through a smart hybrid double concentric sandwich circular cylindrical shell structure in presence of external and internal air gap mean flows. The multi-input multi-output sliding mode control is applied to enhance the sound transmission loss characteristics via direct control action of a uniform force piezoelectric actuator layer along with semi-active variation of the stiffness/damping characteristics of the electrorheological fluid core layer incorporated in a non-collocated configuration within the external or internal shell structure. Extensive numerical simulations examine the uncontrolled/controlled diffuse field sound transmission loss spectrums in a broad frequency range for single-wall and hybrid double-wall sandwich shells at selected external and air gap Mach numbers. The proposed smart hybrid active/semi-active double-wall configuration is demonstrated to provide satisfactory overall acoustic insulation control performance with much lower operative energy requirements. Limiting cases are considered, and validity of the formulation is verified against the available data.

Dual confinement of carbon/TiO2 hollow shells enables improved lithium storage of Si nanoparticles

Silicon is regarded as one of the most promising anode materials for next generation lithium-ion batteries (LIBs). However, the severe volume changes during lithiation/delithiation, leading to fast capacity decay and reduced cycling life, remains an obstacle to its practical application. In this work, we propose the design of a yolk-shell structure of carbon@TiO2@Si (CTS) by template process based on sol-gel chemistry. The Si nanoparticles are confined in the carbon/TiO2 double shells with abundant void space between the Si core and carbon/TiO2 shells. The yolk-shell architecture with concentric double shells substantially improves the structure stability of the electrodes. Consequently, the CTS delivers a high capacity of 747 mA h g−1 at a current density of 100 mA g−1, which is far superior to that (356 mA h g−1) of C@Si (CS) with only a single carbon shell. The double-shelled confinement strategy proposed in this work sheds some light on the development of improved Si-based anode for next-generation LIBs.

Neutron spectrometry with an 115In-based multi-shell neutron spectrometer in a medical linear accelerator facility

A new type of modified Bonner sphere spectrometer called In-MuNS (Indium-based MUltishell Neutron Spectrometer) was developed at the Philippine Nuclear Research Institute (PNRI). It consists of concentric high-density polyethylene spherical shells which can be combined to obtain Bonner Spheres with diameters from 5 to 30 cm. Indium activation foils are used as central detectors. The induced activity in the Indium foils is analyzed post-irradiation with a portable NaI(Tl) gamma spectrometer. The measured specific saturation activities are unfolded using the FRUIT code together with a previously validated In-MuNS response matrix. A measurement campaign was performed at three locations in the treatment room of a 15 MV medical LINAC: the isocenter, 70 cm from the isocenter, and the maze-room junction (5.4 m from the isocenter). Ambient dose equivalent values of 2.24 mSv/Gy, 0.72 mSv/Gy and 0.076 mSv/Gy, respectively, were derived from the measured spectra. These results are coherent with literature data. Relying on the In-MuNS spectrometer, neutron dosimetry studies in medical facilities are now possible also in the Philippines.

Recurrent relationships for reflection coefficients of electromagnetic wave potential representation modes in manylayered spherical environment excitation problem

In theoretical assessments of the electrodynamic characteristics of multilayer screens of electromagnetic waves, the concept of the input impedance of a wave on the surface of the screen is used [1]. In [2], an approach was proposed that is not based on this characteristic, and direct recurrence relations were obtained both for the reflection coefficient of a plane wave from a multilayer screen and for the coefficient of transmission of such a wave through this screen. In [3], this approach was applied to solving problems of excitation of a layered medium by localized sources. In this paper, we generalize the approach to the case of a multilayer medium with another simple layer geometry (with interface in the form of concentric spherical shells). The solution of excitation problems is based on the representation of the Hertz potentials of waves of electric (magnetic) types in the form of series in spherical harmonics. Each harmonic defines the angular distribution of radially converging and diverging modes of the representation of potentials in layers free from external sources. The recurrence relations for the reflection coefficients of convergent (diverging) modes of representation when sequentially adding interfaces are a consequence of the boundary conditions. One of the equivalent forms of these relations is derived from the condition for the existence of a nontrivial solution of a system of linear equations for the amplitudes of converging (diverging) modes in adjacent layers. The other is based on a simple physical model of the process of interaction of a converging (diverging) mode in a layer with a layered structure, which it covers (which covers it). For a field source inside one of the layers, one can determine the representation of potentials that this source would excite in an infinite medium with permeabilities similar to a layer. The amplitudes of the modes of representation of this «primary» field and the reflection coefficients of the modes of representation from structures at the internal and external boundaries of the layer, found from recurrence relations, determine the amplitudes of the modes of the total field of the layer incident on these boundaries. To determine the amplitudes of the modes of representation of the potentials of the fields in the remaining layers, recurrence relations can also be used, in a certain sense inverse to the recurrence relations for reflection coefficients. If a layered structure is excited by a plane wave (scattering problem), the total field potentials (of the electric and magnetic types) are the sum of radially converging modes in the potentials describing the incident plane wave and radially diverging modes formed by the reflection of these converging mod from structure. With the proposed approach, the complexity of solving the excitation problems of the considered layered structure remains almost unchanged with an increase in the number of layers. In essence, only the number of repetition cycles of the obtained recurrence relations increases. The proposed approach is conceptually simple, the final recurrence relations are physically transparent. The work does not represent the full facilities of the approach. Within the framework of this approach, recurrence relations for the permeability coefficients of multilayer spherical shells of the structure under consideration, recurrence relations during its layer-by-layer formation or formation from several multilayer shells can be found.

Proximal Isovelocity Surface Area Method for Assessment of Mitral Regurgitation Severity

Quantification of mitral regurgitation (MR) is important in clinical practice. As fluid approaches a finite circular orifice, concentric hemispherical shells are formed with gradually decreasing surface area and increasing velocity. Severity of MR by the proximal isovelocity surface area (PISA) can be quantified using this principle. Careful attention to detail needs to be paid in the acquisition and measurement to ensure accuracy and reproducibility of the PISA method. The pitfalls of this method are related to geometric assumptions, the limitations of ultrasound, and the shape of the orifice. Some of these can be overcome with a good understanding of the principles and limitations of PISA and also newer three-dimensional techniques for quantification.

Obtained Carbon Nano-onions from Underwater Arc Discharge Without the Complex Purification Procedures

Carbon nano-onions (CNOs), which consist of concentric graphitic shells, currently attract much attention because of their unique structural and physical properties, which are different from the properties of the other carbon nanomaterials such as fullerenes, graphene, and carbon nanotubes (CNTs). Due to their small size, the large external surface area and high conductivity, CNOs are used for supercapacitor applications. The arc discharge underwater is an effective and simple method for the synthesis of larger CNOs in reasonable quantities. In this research, we have been obtained carbon nanomaterials using arc discharge in water between two high purity graphite electrodes. The main experimental techniques used to characterize carbon nanostructures have been Transmission Electron Microscopy (TEM) and Raman Spectroscopy. Among them, Raman spectroscopy is the most useful non-destructive technique capable of differentiating between these various structures. Our TEM images showed that the samples collected from the material floating on the water surface consist CNOs with other carbon nanomaterials such as CNTs. We observed for the first time the formation of solid agglomerate on the cathode surface. Raman and TEM results revealed that the agglomerate is made exclusively of CNOs. The defragmentation of such agglomerate allows to obtain CNOs free of other carbon nanomaterials without the complex purification procedures needed for floating nanomaterials.

Phenotypic and Genetic Identification of Mercenaria mercenaria, Mercenaria campechiensis, and Their Hybrids

The goal of this study was to evaluate the efficacy of phenotypic traits and two genetic assays to distinguish between Mercenaria mercenaria, an important aquaculture species, and Mercenaria campechiensis, a conspecific species that is partially sympatric, but that has not been successfully farmed. The objectives were to evaluate (1) four established diagnostic phenotypic traits (lunule shape, thickness of concentric shell ridges, prominence of anterior side of the concentric ridges, and presence of purple nacre inside of the shells) to distinguish between species, (2) size polymorphism of PCR fragments from four genes [16S rRNA, 18S rRNA, Internal Transcribed Spacer genes (ITS1 and ITS2)], and (3) PCR-restriction fragment length polymorphism (RFLP) on three of these genes (16S, ITS1, and ITS2). Phenotypic traits correctly distinguished two geographically distant conspecific populations (two locations in Maine for M. mercenaria and in Bradenton, FL, for M. campechiensis); however, among all other locations, both species had overlapping phenotypic trait values. Although PCR fragments were obtained for all genes tested, size polymorphism was not identified between the two species. Restriction enzyme digestion of PCR fragments resulted in diagnostic fragments distinguishing the two species for 16S, ITS1, and ITS2. Although phenotypic scores failed to delineate between the two species in most locations, PCR-RFLP results failed to identify hybrids in wild or hatchery samples. Further investigation is needed to apply the PCR-RFLP assays on known hybrid offspring from crosses of M. mercenaria and M. campechiensis. Results have elucidated the difficulties in confidently detecting hybridization in quahogs; however, determining effective methods for species identification and hybrid detection will be important to address issues such as the prevalence and distribution of hybridization in aquaculture and in wild populations, and to determin the presence of M. campechiensis which are currently difficult to find.