Studies of metals in soil,sediments, and selected food in Southwest Louisiana

Abstract

This review provides a background of Southwest Louisiana with a large petrochemical industry, potential for accidental spillage, and location in hurricane alley impacting on large seafood and recreational area with regard to potential metal pollution. Results with appropriate references on crawfish, oyster (both field and laboratory controlled), soil, sediments, and waters are shown. In general no lead, cadmium, or mercury was detected (limited by spectrochemical methods used). Results provided a baseline for current and future studies.     

Studies of Metals in Crocodilians by Spectrochemical Methods

Abstract: This review covers the results of metal determinations using various spectrochemical analytical techniques in crocodilians from various geographical regions. The most widely determined metal is mercury, both inorganic and organic. However, many other metals, including the known toxic metals of lead and cadmium, have been determined. In general, more elevated levels of metals have been determined in crocodilians from potentially contaminated as opposed to more pristine areas. Significant differences in concentrations for many metals have been demonstrated in captive versus wild alligators. The part of crocodilians most widely utilized for food, tail or tail meat, has attracted the most interest, but studies on kidney and liver as well as blood have been reported. Eggs and hatchings have also been examined for several metal concentrations.     

Use of Crustacean Shells for Uptake and Removal of Metal Ions in Solution

Abstract

The use of crustacean shells, in particular crab shells, for the removal of metal ions in solution is described. Research studies found in the literature on the ability of the shells, effect of particle size, pH, competitive studies in mixtures of metals, application to real samples such as acid mine drainage, and use of the shells in a column are presented. The major component of the shells that allows uptake to occur is chitin. Several mechanisms are proposed for uptake. There are conflicting accounts in the literature on such areas as the effect of pH, flow rate, and particle size.     

Structure of group cathode spots on the surfaces of hot-rolled steels

The results of investigations of cathode spots on steel surfaces are presented. Their behavior is found to have some distinctive features in comparison with the results obtained on clean metals. Zh. Tekh. Fiz. 68, 57–62 (November 1998)     

Mechanism for thermal conductivity in energetic displacement cascades

Abstract

Temperature relaxation inside and outside the energetic displacement cascade in fast neutron-irradiated metals is consistently described. The characteristic time of the energy transfer between phonons and electrons in the damaged area is calculated. The space–time temperature distribution in the cascade damaged area in Fe and Ni is presented. The electron–phonon coupling is shown to play an important role in the evolution of the damaged area due to non-equilibrium between the local phonon and electron systems at the beginning of the cooling phase of the displacement cascade.     

Assessment of LIBS for Spectrochemical Analysis: A Review

Abstract

This review assesses the applications of laser-induced breakdown spectroscopy (LIBS) for the analysis of a variety of samples, including biomaterials (teeth, nail, hair, gallstones, and kidney stones, etc.), food materials (fruits and vegetables, milk, salt, nutritional supplements, etc.), medicinal plants, industrial waste, liquid samples, etc. In addition, for the first time the identification of cholesterol and pigment stones was performed on the basis of atomic lines of different elements and molecular bands of C₂ molecules present in the LIBS spectra of gallstones. Chemometric techniques such as principal component analysis (PCA) was also applied to LIBS data for rapid identification/classification of different gallstone samples. LIBS analysis of toxic/heavy elements present in vegetables (spinach, tomato) and rice is also presented in this review. It was observed that vegetables grown near industrial areas are rich in several toxic metals like Pb and Cr. The wastewater samples from different industries were also analyzed by recording their spectra using a liquid jet. These results clearly demonstrate the ability of LIBS technique as an instant monitoring device to detect heavy metals present in liquid samples. Finally, this review shows that LIBS is a versatile analytical technique with unlimited applications.     

Density functional theory studies of screw dislocation core structures in bcc metals

The core structures of d111 screw dislocations in bcc metals are studied using density functional theory in the local-density approximation. For Mo and Fe, direct calculations of the core structures show the cores to be symmetric with respect to 180 rotations around an axis perpendicular to the dislocation line. The magnetic moment in the Fe core is shown to be reduced relative to the bulk value. Calculations of nsurfaces and the elastic constants B , C ' and c 44 are reported for Fe and all group VB and VIB metals. Using a criterion suggested by Vitek and Duesbery the calculations point to symmetric core structures for all the studied metals.     

Solvothermal synthesis of nitrides

Abstract

III-V nitrides are large band-gap semiconductors. They are very promising materials for opto-electronic and microelectronic applications.

The present paper deals with a new process for preparing nitrides. Two nitrides, gallium nitride (GaN) and aluminium nitride (AlN), have been synthesiaed through a solvothermal route. This process uses ammonia in supercritical conditions as solvent and metals as source of gallium and aluminium. Moreover, an additive is used to improve the nitridation of the metals.

The resulting microcrystallites of nitrides have been charactensed by X-ray diffraction and the morphology has been observed by scanning Electron Microscopy.     

Properties of low-Dimensional metals at high pressure

Abstract

Low dimensional metals, in which the conduction electrons are confined to stacks or within layers, provide an important area of research into interactions in the electron gas and its coupling to the lattice. The metallic state is commonly unstable at low temperatures, and can be replaced by a wide variety of ground states, including the charge density wave (CDW) state, spin density wave (SDW) state, superconductivity etc. High pressure has always been an important experimental tool in this field, as many of the materials studied have high compressibilities, and it is often possible to switch from one ground state to another under pressure. We consider here the properties under pressure of a series of organo-metallic charge transfer salts in which the metallic behaviour is due to intermolecular delocalisation of the π electron systems of the ligand groups around the transition metal atom.     

Engineering of SERS Substrates Based on Noble Metal Nanomaterials for Chemical and Biomedical Applications

Abstract

Surface-enhanced Raman scattering (SERS) has attracted great interest due to its remarkable enhancement, excellent sensitivity, and the “fingerprinting” ability to produce distinct spectra for detecting various molecules. Noble metal nanomaterials have usually been employed as SERS-active substrates because of their strong SERS enhancement originated from their unique surface plasmon resonance (SPR) properties. Because the SPR property depends on metal material's size, shape, morphology, arrangement, and dielectric environment around metal nanostructures, the key to wider applications of SERS technique is to develop plasmon-resonant structures with novel geometries to enhance Raman signals and to control the periodic ordering of these structures over a large area to obtain reproducible Raman enhancement. This review presents a general view on the theory background of SERS effect and several basic concepts and focuses on recent progress in engineering metallic nanostructures with various morphologies using versatile methods for improving SERS properties. Their potential applications in the field of chemical detection and biological sensing are overviewed.     

Segregation of 57Co Atomic Probes in the Cores of Grain Boundaries in d-Transition Metals

A new method, which has been developed to examine the structure and physical properties of cores of grain boundaries (GB's) (S.M. Klotsman, Sov. Phys. Uspech. 33, 55 (1990); V.N. Kaigorodov and S.M. Klotsman, Phys. Rev. B 49 (1994)), was used to study segregats localized in two discrete regions of polycrystals: cores of GB's and two-dimensional regions of the lattice adjacent to the GB's. This paper reports and discusses results of investigations of segregation of ⁵⁷Co atomic probes in cores of GB's in the d-transition metals Cr, Ta and W. The interaction of ⁵⁷Co AP's with GB's cores in metals is similar to their interaction with vacancies, because GB's cores are characterized, as vacancies in metals, by an excess volume and a negative charge. GB's are enriched with ⁵⁷Co in chromium and tungsten. The activation enthalpy of the ⁵⁷Co atomic probes segregation at GB's in Cr and W is proportional tothe local magnetic moment of ⁵⁷Co atomic probes. GB's cores are found to be depleted of ⁵⁷Co atomic probes in Ta.     

Non-equilibrium agglomeration of helium-vacancy clusters in irradiated materials

Abstract

Time evolution of non-equilibrium systems, where the probability density is described by a continuum Fokker-Planck (F-P) equation, is a central area of interest in stochastic processes. In this paper, a numerical solution of a two-dimensional (2-D) F-P equation describing the growth of helium-vacancy clusters (HeVCs) in metals under irradiation is given. First, nucleation rates and regions of stability of HeVCs in the appropriate phase space for fission and fusion devices are established. This is accomplished by solving a detailed set of cluster kinetic rate equations. A nodal line analysis is used to map spontaneous and stochastic nucleation regimes in the helium-vacancy (h-v) phase space. Growth trajectories of HeVCs are then used to evaluate the average HeVC size and helium content during the growth phase of HeVCs in typical growth instability regions.

The growth phase of HeVCs is modeled by a continuum 2-D, time-dependent F-P equation. Growth trajectories are used to define a finite solution space in the h-v phase space. A highly efficient dynamic remeshing scheme is developed to solve the F-P equation. As a demonstration, typical HFIR irradiation conditions are chosen. Good agreement between the computed size distributions and those measured experimentally are obtained.     

New scientific opportunities for high pressure research by energy-dispersive XMCD

ABSTRACT

XMCD under pressure is used to study the magnetic properties of the transition metal (TM) systems for over 15 years. We present the technique and how it has been developed. The energy dispersive XAS spectrometer is particularly suited for these studies. The effect of pressure on TM magnetism is discussed. Recent studies performed at different edges illustrate the information that can be obtained through XMCD. Finally, some results obtained on TMs are presented, either at the L_II,III edges of 5d metals or at the K edge of 3d metals, which correspond to the energy ranges that can be probed when using diamond anvil cells for high pressure. Different cases are treated: pure 3d metals, alloys, magnetic insulator and inorganic compounds.     

Relationship between resistivity and specific heat in a canonical non-magnetic heavy fermion alloy system: UPt5-xAu x

A comprehensive study of the relationship between the electronic specific heat coefficient () and the temperature square coefficient (A) of the electrical resistivity for a single, cubic, heavy fermion alloy system, UPt_5-xAu_x is presented. In this alloy system, whose low temperature properties are consistent with the Fermi-liquid behavior, varies by more than a factor of 10 while the corresponding A coefficient changes by a factor larger than 200. A tracks changes in fairly well, but , postulated to have a universal value for heavy fermions, is not constant and varies from about 10^-6 (x = 0, 0.5) to 10^-5 cm (mol K/mJ)² (x > 1.1), thus from a value typical of transition metals to that characteristic of other heavy fermion compounds. We have found a correlation between and magnetic characteristics such as the paramagnetic Curie-Weiss temperature and the low temperature magnetic susceptibility divided by . Received 29 January 1999     

Helicon and Alfvén wave propagation in non-magnetic semiconductors and semi-metals: Active and passive waves

It was pointed out in 1960 that metals and semiconductors can support low frequency electromagnetic excitations in the presence of a magnetic field. We now feel that it is an appropriate time to discuss some of the progress made, over the last decade, in understanding and using this novel phenomenon. Naturally the field has grown quite rapidly and it would clearly be a Herculean task to review every aspect of it in other than a superficial manner. We have therefore chosen to discuss only semiconductors and semi-metals. This choice is dictated to us partly by the fact that magneto-plasma effects in metals have been reviewed from time to time but mainly by the fact that magneto-plasma effects in semiconductors have never been previously reviewed.

Of course the term ‘magneto-plasma’ covers a great deal of activity so we have decided to choose a theme which links the beginnings of the subject to the present day. This theme is that of helicon and Alfvén wave propagation.

We have produced a background of theory against which the nature of helicon and Alfvén waves can be readily understood. This background theory can also be used as a starting point for investigations of other plasma effects beyond the scope of this review.

Some considerable attention is paid to waves in active systems, i.e. systems possessing a pool of energy arising from the application of an external electric field. Such systems, while of basic physical interest, are also of technical interest from a solid-state device viewpoint. The possibility of transverse wave instabilities occurring in active systems is discussed and a review of the criteria for labelling the types of instability is presented. As an example of the use of these techniques we have attempted to correlate the high electric field microwave emission from indium antimonide with a helicon-based instability.

The theoretical work is set in perspective by the inclusion of discussions of the experimental work in the appropriate areas. We have also included a brief review of experimental observations of microwave emission from indium antimonide and the proposed mechanisms, other than helicon instability, which may account for it.     

On the 240 K anomaly in the magnetic properties of LiNiO2

In this work, results of X-band ESR spectroscopy, ac-magnetic susceptibility and X-ray powder diffraction measurements on Li_1-xNi _1+x O₂ (x = 0.02 and x = 0.07) are presented and discussed. While the susceptibility of the compound with x = 0.02 is shown to follow a Curie-Weiss law, with a Weiss temperature of the order of 30 K, the compound with x = 0.07 is found to order ferromagnetically below K. However, an additional anomaly is observed in the magnetic properties of this latter compound at around 240 K. We attribute this anomaly to the presence of macroscopic Ni-rich regions which order ferrimagnetically below this temperature. This phenomenon is different from the bulk ferromagnetism that occurs at much lower temperatures, and allows us to discard earlier suggestions proposed in the literature in which the 240 K anomaly has been considered as denoting an intrinsic phenomenon. Received 14 May 1999 and Received in final form 5 August 1999     

Bulk diamond formation from graphite in the presence of C-O-H fluid under high pressure

Abstract

C-O-H fluids have been successfully applied as catalysts for bulk diamond formation under high pressure. New insight into C-O-H fluids extends the understanding of the origin of natural diamond, which is presently of interest in materials and geological sciences. This review presents current literature data concerning the synthesis and characterization of bulk diamond formation assisted by C-O-H fluids at high pressure and high temperature. Based on a general survey of this subject, the pressure-temperature regime for diamonds formed in these fluids was established and the mechanism of conversion from graphite to diamond is discussed. Finally, a few questions are put forward that may be useful for the continued development of this research area.     

The de Haas-van Alphen effect in quasi-two-dimensional materials

We calculate the amplitude of magnetization oscillations for a quasi-two-dimensional electron system. In the two-dimensional case the behavior of this amplitude as a function of magnetic field and temperature differ completely from the conventional Lifshitz-Kosevich formula valid for three-dimensional metals. Previously only the ideal two-dimensional case has been considered, and the difference of the shape of the Fermi surface from cylindrical has not been taken into account. We obtain the general formula for the envelope of magnetization oscillations as a function of magnetic field, temperature, and the strength of the warping of the Fermi surface. This problem is important because of the great amount of interest in heterostructures and quasi-two-dimensional organic metals which has arisen in recent years. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 2, 139–144 (25 January 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Resilience of public transport networks against attacks

The behavior of complex networks under failure or attack depends strongly on the specific scenario. Of special interest are scale-free networks, which are usually seen as robust under random failure but appear to be especially vulnerable to targeted attacks. In recent studies of public transport networks of fourteen major cities of the world it was shown that these systems when represented by appropriate graphs may exhibit scale-free behavior [Physica A 380, 585 (2007); Eur. Phys. J. B 68, 261 (2009)]. Our present analysis focuses on the effects that defunct or removed nodes have on the properties of public transport networks. Simulating different directed attack strategies, we derive vulnerability criteria that result in minimal strategies with high impact on these systems.     

Advances in nitrogen-15 use for environmental studies in the soil-plant system

Abstract

A review is being presented of the latest results in the use of nitrogen-15 in the soil-plant system. The literature covers the period from 1991 to early April 1993. The increase in environmentally related experiments shows that the stable nitrogen isotope technique, applied either as tracer or as the natural isotope tracing approach, is well suited particularly to ecosystem studies. This trend is supported by convenient analytical systems. An important challenge to scientists in the field of environmental research is to contrive ways and means of permitting the plants to utilize the available nitrogen in the soil more efficiently. Examples of research areas needing more attention are pointed out.