bluuebunny/crossref_metadata_2025 huggingface dataset:
DILUTED FERROMAGNETIC SEMICONDUCTORS — ORIGIN OF MAGNETIC ORDERING AND SPIN-TRANSPORT PROPERTIES
Authors: DIETL TOMASZ
Published: January 2008

In the first hour of the lecture the present understanding of the origin of exchange interaction and mechanisms leading to ferromagnetic order in diluted magnetic semiconductors will be presented.1 The lecture will start by discussing energy positions of relevant open magnetic shells, including the correlation energy and excitations within the magnetic ions. The origin and magnitude of sp–d exchange interactions will then be described. This will be followed by presenting the physics of indirect exchange interactions between localized spins contrasting magnetic characteristics in the absence and in the presence of free carriers. The Zener and RKKY models of ferromagnetism will be introduced and the role of confinement, dimensionality, and spin-orbit interaction in determining properties of the ferromagnetic phase will be outlined.

The second lecture will be devoted to theory of spin transport in layered structures of diluted ferromagnetic semiconductors, emphasizing the issues important for perspective spintronics devices. A recently developed theory,2 which combines a multi-orbital empirical tight-binding approach with a Landauer–Büttiker formalism will be presented. In contrast to the standard kp method, this theory describes properly the interfaces and inversion symmetry breaking as well as the band dispersion in the entire Brillouin zone, so that the essential for the spin-dependent transport Rashba and Dresselhaus terms as well as the tunneling via k points away from the zone center are taken into account. The applicability of this model for the description of tunneling magnetoresistance (TMR), resonant tunneling spectra, spin-current polarization in Esaki-Zener diodes, and domain-wall resistance will be presented.

Note from Publisher: This article contains the abstract only.
DEVICE CONCEPTS IN SEMICONDUCTOR SPINTRONICS
Authors: MOLENKAMP LAURENS W.
Published: January 2008

Semiconductor spintronics has now reached a stage where the basic physical mechanisms controlling spin injection and detection are understood. Moreover, some critical technological issues involved in the growth and lithography of the magnetic semiconductors have been solved. This has allowed us to explore the physics of meanwhile quite complex spintronic devices.

The lectures will start with an introduction to spin transport in metals and semiconductors. Building upon this, I will discuss various simple devices that demonstrate this basic physics in action. Subsequently, more advanced devices will be covered.

For example, I will discuss resonant tunneling diodes (RTDs) fabricated from paramagnetic II-VI semiconductors that can be operated as a voltage controlled spin-switch. A quantum dot version of these RTDs exhibits, unexpectedly, remanent magnetism at zero external field, which we interpret as resulting from tunneling through a single magnetic polaron.

In the ferromagnetic semiconductor ( Ga, Mn ) As we have observed a very large spin valve effect due to domain wall pinning at sub-10 nm sized constrictions.

Furthermore, we have found a novel magnetoresistance effect in this material, dubbed tunnel anisotropic magnetoresistance (TAMR), which is due to the strongly (magneto-)anisotropic density of states in a ferromagnetic semiconductor. The effect leads to the observation of a spin valve-like behavior in tunnel structures containg a single ferromagnetic layer and also dominates the spin-valve signal obtained from structures containing two ( Ga, Mn ) As layers, where the effect may cause resistance changes of five orders of magnitude.

Note from Publisher: This article contains the abstract only.
SPIN AND PSEUDOSPIN TRANSFER
Authors: MACDONALD ALLAN
Published: January 2008

Electrons in a Fermi liquid can be regarded as non-interacting particles (quasiparticles) in an effective potential that is a consequence of interactions between electrons. In many-body theory the effective potential is known as the electronic self-energy. When the electronic system has a broken symmetry, the effective potential can have different symmetries than the potential term that appears in the single particle Hamiltonian. For example, the effective potential of a superconductor includes terms that change the electron particle number and the effective potential of a ferromagnet includes terms that change the electron spin. When the electron system is not in equilibrium, the effective potential is altered. I will present a view of spin-transfer phenomena in ferromagnetic metals in which current-induced spin torques arise from changes in the ferromagnet's spin-dependent effective potential when the quasiparticle system is held out of equilibrium by applying a bias potential. In this view spin-transfer is an example of a more general set of phenomena and is not fundamentally associated with an approximate conservation law, for example the approximate conservation of total spin angular momentum. I will illustrate this point of view by discussing other examples of spin-transfer like phenomena, including transport anomalies that have been observed in bilayer quantum Hall systems, current-driven magnetization changes in antiferromagnetic metals, and current-drive bond-weakening in molecular electronics.

Note from Publisher: This article contains the abstract only.
TWO EQUATIONS OF STATE CONSIDERING THE THERMAL EFFECT FOR α, β AND ω PHASES OF ZIRCONIUM
Authors: TIAN RONGGANG , SUN JIUXUN , ZHANG CHAO , WANG FULONG
Published: January 2008

The Baonza and mGLJ equations of state (EOS) modified previously to consider the thermal effect are applied to study the thermodynamic properties of Zirconium (Zr) . It is proposed that the zero-point vibration term should be deleted in a thermal EOS, and the parameters cannot be directly taken as experimental data at a reference temperature, [Formula: see text] and [Formula: see text], but their values at absolute zero temperature, [Formula: see text] and [Formula: see text]. Based on the Einstein model, an approach is proposed to solve [Formula: see text] and [Formula: see text] from [Formula: see text] and [Formula: see text]. For the hcp (α phase), bcc (β phase) and hexagonal structure (ω phase) of Zr , the molar volume (V), isothermal bulk modulus (B) and thermal expansion coefficient (α) was calculated as a function of pressure and temperature. The predictive capabilities of the complete EOS are discussed and compared with experimental data.
PRESSURE PROFILES FOR BOSONS IN TRAPS
Authors: LUMB SHALINI , MUTHU S. K. , SINGH K. K.
Published: January 2008

Pressure profiles P(R) for non-interacting bosons in an isotropic trap have been calculated exactly by applying the grand canonical method of quantum statistics to particles in a subsphere of the system. The results are compared with those of local Fermi–Thomas (semi-classical) theory both for non-interacting bosons as well as for bosons having weakly repulsive interactions between them. The essential conclusions are (i) that in the non-degenerate regions, both below as well as above the critical temperature, the pressure profiles remain essentially unaffected by weak interactions, and (ii) that near the center of the trap, the exact quantum mechanical profiles are appreciably lower than the semi-classical profiles.
NATIONAL SCIENCE FOUNDATION VISION IN PARTICLE AND NUCLEAR ASTROPHYSICS
Authors: BOYD RICHARD N.
Published: January 2008

The NSF has made investments in searches for dark matter, in ultrahigh energy cosmic rays and gamma rays, in neutrino physics and astrophysics, and in nuclear astrophysics. We expect the future to witness the expansion of these efforts, along with efforts to refine the measurements of the cosmic microwave background. In some of these efforts the Deep Underground Science and Engineering Laboratory is expected to play a major role.
PROPOSED OBSERVATIONS OF GRAVITATIONAL WAVES FROM THE EARLY UNIVERSE VIA "MILLIKAN OIL DROPS"
Authors: CHIAO RAYMOND Y.
Published: January 2008

Pairs of Planck-mass drops of superfluid helium coated by electrons (i.e. "Millikan oil drops"), when levitated in a superconducting magnetic trap, can be efficient quantum transducers between electromagnetic (EM) and gravitational (GR) radiation. This leads to the possibility of a Hertz-like experiment, in which EM waves are converted at the source into GR waves, and then back-converted at the receiver from GR waves into EM waves. Detection of the gravitational-wave analog of the cosmic microwave background using these drops can discriminate between various theories of the early Universe.
THEORY AND PHENOMENOLOGY OF DGP GRAVITY
Authors: DEFFAYET CÉDRIC
Published: January 2008

I review some aspects of the Dvali–Gabadadze–Porrati (also known as "brane-induced") model of gravity. This model provides a novel way to modify gravity at large distances and, as such, has potentially some interesting cosmological consequences, like the possibility of getting an accelerated expansion with a vanishing cosmological constant. In DGP gravity, the recovery of usual gravitational interaction at small (i.e. noncosmological) distances is rather nontrivial. This can lead to observable signature in observations made in the solar system. I discuss various aspects of the phenomenology of the model and briefly comment on the consistency of the whole approach.
OBSERVABLE CONSEQUENCES OF STRONG COUPLING IN THEORIES WITH LARGE DISTANCE MODIFIED GRAVITY
Authors: DVALI GIA
Published: January 2008

In this talk, we review theories that modify gravity at cosmological distances, and show that any such theory must exhibit a strong coupling phenomenon. We show that all consistent theories that modify the dynamics of the spin-2 graviton on asymptotically flat backgrounds, automatically have this property. Due to the strong coupling effect, modification of the gravitational force is source-dependent, and for lighter sources sets in at shorter distances. This universal feature makes modified gravity theories predictive and potentially testable by precision gravitational measurements at scales much shorter than the current cosmological horizon.
A ROBUST TEST OF GENERAL RELATIVITY IN SPACE
Authors: GRABER JAMES
Published: January 2008

LISA may make it possible to test the black-hole uniqueness theorems of general relativity, also called the no-hair theorems, by Ryan's method of detecting the quadrupole moment of a black hole using high-mass-ratio inspirals. This test can be performed more robustly by observing inspirals in earlier stages, where the simplifications used in making inspiral predictions by the perturbative and post-Newtonian methods are more nearly correct. Current concepts for future missions such as DECIGO and BBO would allow even more stringent tests by this same method. Recently discovered evidence supports the existence of intermediate-mass black holes (IMBHs). Inspirals of binary systems with one IMBH and one stellar-mass black hole would fall into the frequency band of proposed maximum sensitivity for DECIGO and BBO. This would enable us to perform the Ryan test more precisely and more robustly. We explain why tests based on observations earlier in the inspiral are more robust and provide preliminary estimates of possible optimal future observations.
SATELLITE TEST OF THE EQUIVALENCE PRINCIPLE: OVERVIEW AND PROGRESS
Authors: KOLODZIEJCZAK JEFFERY J. , MESTER JOHN
Published: January 2008

STEP, the Satellite Test of the Equivalence Principle, is reviewed and the current status of the project is discussed. This space-based experiment will test the universality of free fall and is designed to advance the present state of knowledge by over five orders of magnitude. The international STEP collaboration is pursuing a development plan to improve and verify the technology readiness of key systems. We discuss recent advances with an emphasis on accelerometer fabrication and tests. Critical technologies successfully demonstrated in flight by the Gravity Probe B mission also contribute to progress.
SPACE-BASED SCIENCE AND THE AMERICAN COMPETITIVENESS INITIATIVE
Authors: MARBURGER JOHN H.
Published: January 2008

I discuss the process by which science contributes to the setting of government priorities, and how these priorities get translated into programs and budgets at the federal agencies that fund scientific research. New technologies are now opening exciting scientific opportunities across the biological and physical sciences. I review the motivations and goals of President Bush's American Competitiveness Initiative (ACI), the importance of societal relevance to federal investments in basic research, and the ACI's impacts on discovery-oriented disciplines within the physical sciences.
APOLLO: A NEW PUSH IN LUNAR LASER RANGING
Authors: MURPHY T. W. , MICHELSON E. L. , ORIN A. E. , ADELBERGER E. G. , HOYLE C. D. , SWANSON H. E. , STUBBS C. W. , BATTAT J. B.
Published: January 2008

APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is a new effort in lunar laser ranging that uses the Apollo-landed retroreflector arrays to perform tests of gravitational physics. It achieved its first range return in October 2005, and began its science campaign the following spring. The strong signal (> 2500 photons in a ten-minute period) translates to one-millimeter random range uncertainty, constituting at least an order-of-magnitude gain over previous stations. One-millimeter range precision will translate into order-of-magnitude gains in our ability to test the weak and strong equivalence principles, the time rate of change of Newton's gravitational constant, the phenomenon of gravitomagnetism, the inverse-square law, and the possible presence of extra dimensions. An outline of the APOLLO apparatus and its initial performance is presented, as well as a brief discussion on future space technologies that can extend our knowledge of gravity by orders of magnitude.
INVERSE-SQUARE LAW EXPERIMENT IN SPACE
Authors: PAIK HO JUNG , PRIETO VIOLETA A. , MOODY M. VOL
Published: January 2008

The objective of ISLES (Inverse-Square Law Experiment in Space) is to perform a null test of Newton's law in space with a resolution of 10 ppm or better at a 100 μm distance. ISLES will be sensitive enough to detect the axion, a dark matter candidate, with the strongest allowed coupling and probe large extra dimensions of string theory down to a few micrometers. The experiment will be cooled to < 2 K , which permits superconducting magnetic levitation of the test masses. This soft, low-loss suspension, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. To minimize Newtonian errors, ISLES employs a near-null source, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a nominal distance of 100 μm. The signal is detected by a superconducting differential accelerometer.
A LABORATORY TEST OF THE EQUIVALENCE PRINCIPLE AS PROLOG TO A SPACEBORNE EXPERIMENT
Authors: REASENBERG ROBERT D. , PHILLIPS JAMES D.
Published: January 2008

To test the equivalence principle (EP) to an accuracy of at least σ(Δ g)/g = 5 × 10-14, we are developing a modern Galilean experiment. In our principle-of-equivalence measurement (POEM), we directly examine the relative motion of two test mass assemblies (TMA) that are freely falling. Such an experiment tests both for a possible violation of the weak equivalence principle (WEP) and for new forces that might mimic a WEP violation. For the terrestrial version of the experiment, there are three key technologies. A laser gauge measures the separation of the TMA to picometer accuracy in a second as they fall freely in a comoving vacuum chamber. The motion system launches the TMA from their kinematic mounts inside the chamber and keeps the chamber on a trajectory that mimics free fall until the chamber nears the bottom of its motion. It then "bounces" the chamber back to upward motion in preparation for a new launch of the TMA. A capacitance gauge system measures an additional four degrees of freedom of the motion of each TMA. The resulting estimate of the rotation around and translation along the horizontal axes is used to correct systematic errors. We describe the status of POEM and discuss recent progress.
ADDRESSING THE CRISIS IN FUNDAMENTAL PHYSICS
Authors: STUBBS CHRISTOPHER W.
Published: January 2008

The observation that the expansion of the Universe is proceeding at an ever-increasing rate, i.e. the "dark energy" problem, constitutes a crisis in fundamental physics that is as profound as the one that preceded the advent of quantum mechanics. Cosmological observations currently favor a dark energy equation-of-state parameter w = P/ρ = -1. Awkwardly, this is the value that has the least ability to discriminate between alternatives for the physics that produces the observed accelerating expansion. If this result persists we therefore run a very real risk of stagnation in our attempt to better understand the nature of this new physics, unless we uncover another piece of the dark energy puzzle. I argue that precision fundamental measurements in space have an important role in addressing this crisis.
MEASUREMENT OF THE GRAVITATIONAL CONSTANT USING THE ATTRACTION BETWEEN TWO FREELY FALLING DISCS: A PROPOSAL
Authors: VITUSHKIN LEONID , WOLF PETER , VITUSHKIN ARTYOM
Published: January 2008

The constant of gravitation, G, is the least well-known of the physical constants. A new, independent method of measurement, estimated as having a potential uncertainty at least as small as that achieved by existing methods, would be useful for an improvement in G determination. This experiment is based on the measurement of the relative motion of two freely falling test bodies (discs), caused by their gravitational attraction. The uncertainties are analyzed for two parallel tungsten discs with masses of about 30 kg. The use of test bodies with an incorporated optical system of multipass two-beam interferometers, as well as of multibeam interferometers, is proposed to measure their relative displacement. The estimations were made for laboratory experiment with free fall duration of 0.714 s. In this case, the relative displacement to be measured is about 0.1 μm. These estimates show that relative uncertainties lower than 5 × 10-5 can be obtained in G measurement in a single drop of the test bodies. The proposed experiment can be made in outer space. In space a lower uncertainty can be achieved because the time interval of the measurement of relative motion of the test bodies can be increased.
VARIATIONAL INEQUALITIES IN COURNOT OLIGOPOLY
Authors: PENSAVALLE C. A. , PIERI G.
Published: January 2008

Consider G = (X1,…,XM,g1,…,gM) an M-player game in strategic form, where the set Xi is an interval of real numbers and the payoff functions gi are differentiable with respect to the related variable xi ∈ Xi. If they are also concave, with respect to the related variable, then it is possible to associate to the game G a variational inequality which characterizes its Nash equilibrium points. In this paper it is considered the variational inequality for two sets of Cournot oligopoly games. In the first case, for any i = 1,…,M, we have Xi = [0,+∞); the market price function is in C1 and convex; the cost production function of the player i is linear and the function xi → gi(…,xi,…) is strictly concave. We prove the existence and uniqueness of the Nash equilibrium point and illustrate, with an example, an algorithm which calculates its components. In the second case, for any i = 1,…,M, we have Xi = [0,+∞); the market price function is in C2 and concave and the cost production function of the i-player is in C2 and convex. In these circumstances, as a consequence of well known facts, the existence and uniqueness of the Nash equilibrium point are guaranteed and also the Tykhonov and Hadamard well-posedness of the game. We prove that the game G is well posed with respect to its variational inequality.
TARIFF RETALIATION AND THE FREE TRADE ARGUMENT
Authors: MÉNDEZ NAYA JOSÉ , MÉNDEZ NAYA LUCIANO
Published: January 2008

The effects of tariff wars on welfare are analysed for the case of trade between two countries with outputs of the traded good given exogenously. Assuming mild conditions, it is shown that if there are non-zero tariffs for which welfare-maximizing equilibrium holds, then free trade is not strictly preferable when the countries' outputs are equal, and if they are not equal is strictly disadvantageous to the country with the smaller output. Therefore, the main result of the paper is that free trade is not sustainable in an asymmetric context nor in a symmetric situation.
WELFARE LOSS IN LINEAR PRICE-PREFERENCE PROCUREMENT AUCTIONS
Authors: KOH WINSTON T. H.
Published: January 2008

In government procurement auctions, discrimination in favor of one group of participants (e.g. domestic firms, minority bidders) over another group is a common practice. The optimal discriminatory rules for these auctions are typically non-linear and could be administratively complex and costly to implement. In practice, procurement auctions are usually organized as sealed-bid first-price auction with a simple percentage price-preference policy. In this paper, we analyze a model with two bidders that draw their costs from a common uniform distribution, and derive an upper bound to the welfare loss resulting from the use of linear-price preference auctions.
QUANTUM TRANSPORT THROUGH SINGLE PHENALENYL MOLECULE: EFFECT OF INTERFACE STRUCTURE
Authors: MAITI SANTANU K.
Published: January 2008

The electronic transport characteristics through a single phenalenyl molecule sandwiched between two metallic electrodes are investigated by using Green's function technique. A parametric approach, based on the tight-binding model, is used to study the transport characteristics through such molecular bridge system. The electronic transport properties are significantly influenced by (a) the molecule-to-electrodes interface structure and (b) the molecule-to-electrodes coupling strength.
TOWARDS THE SINGLE-WALLED B- AND/OR N-DOPED CARBON NANOTUBES
Authors: WANG W. L. , BAI X. D. , WANG E. G.
Published: January 2008

Soon after the discovery of carbon nanotubes (CNTs) in the early 1990's, the B - and/or N -doped CNTs began to attract increasing interest owing to their modified structural, physical and chemical properties. In comparison with the multi-walled nanotubes and nanofibers, substitutional doping of the single-walled nanotubes (SWNTs) has proved to be much more difficult, and it is only in very recent years that some experimental studies concerning the B - and/or N -doped SWNTs are emerging. This paper intends to provide an up-to-date overview of current research on the doped SWNTs, with scopes covering both the binary system of CB x- and CN x-SWNTs and the ternary B x C y N z-SWNTs. A survey of the latest achievements in the syntheses of doped SWNTs through either the direct syntheses methods or the post-synthetic substitution reaction route is first presented; then the aspects concerning their structural features, elemental compositions, dopants bonding configuration and atomic distributions, as well as their physical and chemical properties are discussed.
THE EFFECT OF MIE-TYPE POTENTIAL RANGE ON THE COHESIVE ENERGY OF METALLIC NANOPARTICLES
Authors: BARAKAT T. , Al-DOSSARY O. M. , ALHARBI A. A.
Published: January 2008

We investigate the effect of Mie-type potential range on the cohesive energy of metallic nanoparticles using the size-dependent potential parameters method. The predicted cohesive energy for different cubic structures is observed to decrease with decreasing the particle size, and increase with decreasing the range of the interatomic potential, a result which is in the right direction at least to predict the experimental values of Molybdenum and Tungsten nanoparticles.
FORMATION OF Y- AND T-JUNCTION Ge NANOWIRES BY VAPOR–LIQUID–SOLID MECHANISM
Authors: DAS K. , CHAKRABORTY A. K. , GOSWAMI M. L. N. , SINGHA R. K. , DHAR A. , COLEMAN K. S. , RAY S. K.
Published: January 2008

A vapor–liquid–solid method has been used to grow Ge nanowires on Au -coated Si (100) substrates with diameters ranging from 30–80 nm. The nanowires have been found to form Y- and T-junctions along with the growth of straight nanowires of length up to 10 μm. X-ray diffraction and Raman analyses support the formation of a core-sheath Ge – GeO 2 structure in consistent with the observation made by transmission electron microscopy.
AN INVESTIGATION INTO THE ORIGIN OF SMALL ENERGY CHANGES (~ 10-7eV) OF ULTRACOLD NEUTRONS IN TRAPS
Authors: KARTASHOV D. G. , LYCHAGIN E. V. , MUZYCHKA A. Yu. , NESVIZHEVSKY V. V. , NEKHAEV G. V. , STRELKOV A. V.
Published: January 2008

We studied the phenomenon of relatively small changes in the energy of ultracold neutrons (UCN) (when compared to thermal motion energy) when these are reflected on a surface. The changes observed involved both increases in UCN energy (their heating) and decreases (cooling) of the order of ~ 10-7eV. The probability values of this process on various surfaces ranged between 10-8and 10-5per one collision; the probability of such a small heating was many times larger than that of such a small cooling. We measured the spectra of such heated neutrons and the dependence of small heating probability on the temperature of sample out-gazing. We found that out-gazing of samples in vacuum at a temperature of 500–600 K could increase the small heating probability on stainless steel surface by a factor of ~ 100; and on copper surface by a factor of ~ 10. We observed, for the first time, extremely intensive small heating of UCN on powder of diamond nanoparticles. Neither small heating of UCN, nor nanoparticles could be found on a sapphire single crystal surface. This set of experimental data indicates that the inelastic scattering of UCN on weakly bound nanoparticles at a surface in a state of thermal motion is responsible for the process investigated.
ANISOTROPIC ASSEMBLY OF COLLOIDAL NANOPARTICLES: EXPLOITING SUBSTRATE CRYSTALLINITY
Authors: HAYTON JAMES A. , PAULIAC-VAUJOUR EMMANUELLE , MORIARTY PHILIP J.
Published: January 2008

We show that the crystal structure of a substrate can be exploited to drive the anisotropic assembly of colloidal nanoparticles. Pentanethiol-passivated Au particles of ~ 2 nm diameter deposited from toluene onto hydrogen-passivated Si (111) surfaces form linear assemblies (rods) with a narrow width distribution. The rod orientations mirror the substrate symmetry, with a high degree of alignment along principal crystallographic axes of the Si (111) surface. There is a strong preference for anisotropic growth with rod widths substantially more tightly distributed than lengths. Entropic trapping of nanoparticles provides a plausible explanation for the formation of the anisotropic assemblies we observe.
A SANDWICH-INJECTION METHOD FOR MICROCHIP ELECTROPHORESIS
Authors: LI GANG , ZHUANG GUI-SHENG , ZHOU HONG-BO , ZHAO JIAN-LONG , XU YUAN-SEN
Published: January 2008

In microchip electrophoresis (μ-CE), sample injection is generally achieved through cross, double-T, or T-form injector structures. In these reported approaches, the separation efficiency and detection sensitivity of μ-CE is significantly influenced by the shape and size of the sample plug introduced into the separation channel or sample leakage in separation phase. Here, we present a sandwich-injection method for controlling discrete sample injection in μ-CE. This method involves four accessory arm channels in which symmetrical potentials are loaded to form a unique parallel electric field distribution at the intersection of sample and separation channels. The parallel electric field effectuate a virtual wall to confine the shape of a sample plug and depress the spreading of the sample plug at the junction of sample and separation channels, and also prevent sample leakage during separation step. The key features of this method are the ability to inject well-defined sample plugs at the original sample concentration and the ability to control the sample plug size. The virtues of the novel injection technique were demonstrated with numerical models and validated with fluorescence visualizations of electrophoretic experiments.
SYNTHESIS AND PROPERTIES OF ONE-DIMENSIONAL ALUMINUM NITRIDE NANOSTRUCTURES
Authors: TANG YONG-BING , CONG HONG-TAO , CHENG HUI-MING
Published: January 2008

This article presents a brief review of the recent research progresses achieved in the field of one-dimensional (1D) aluminum nitride ( AlN ) nanostructures. It mainly covers three aspects: The first one is to introduce the synthetic strategies for several classic 1D AlN nanostructures (such as nanofibers, nanobelts, nanorods, nanowires, nanotips, etc.) including template-confined reaction, arc discharge, catalyst-assisted growth, and vapor transport and related growth methods. The second is to elaborate some special physical properties, such as field emission and photoluminescence, which associate with the uniqueness of 1D AlN nanostructures. It is revealed that aligned AlN 1D nanostructures have low turn-on and threshold voltages, high emission current and small current fluctuation, and that the photoluminescence of AlN nanobelts are different from those of conventional AlN material. The third is to briefly illustrate the potential application of these 1D AlN nanostructures in composite materials. It is found that AlN nanowire is a good reinforcement for improving the mechanical and thermal properties of metal matrix composites, which can be expected to be utilized as packaging material with high strength and low thermal expansion. Finally, we summarize the major challenges in this field. Among them, a thorough understanding of the growth mechanism of 1D AlN nanostructures is the most important issue, and more precisely controlled growth is required to obtain tailored AlN nanostructures according to device applications.
Sedimentary provenance and palaeoenvironment of the Baixo Araguaia Supergroup: constraints on the palaeogeographical evolution of the Araguaia Belt and assembly of West Gondwana
Authors: Moura C. A. V. , Pinheiro B. L. S. , Nogueira A. C. R. , Gorayeb P. S. S. , Galarza M. A.
Published: January 2008

Provenance studies on metasedimentary rocks of the Baixo Araguaia Supergroup of the Brasiliano Araguaia Belt, central Brazil, yield
207
Pb/
206
Pb zircon evaporation ages for detrital zircons from quartzites concentrated around 1000–1200 Ma and 2800–2900 Ma; Sm–Nd
T
DM
model ages of schists and phyllites scatter around 1600–1700 Ma. Facies analysis of low-grade metasedimentary rocks from drill cores suggests a sedimentary environment of basin floor and lower- to upper-slope turbidites. Nearby sources are indicated by the textural and mineralogical immaturity; together with structural geological data indicating tectonic transport of the supracrustal pile towards the NW, this suggests probable provenance from the southeastern portion of the Araguaia Belt and not from the Amazonian Craton as usually believed. The Goiás Massif, Goiás Magmatic Arc, São Francisco Craton and Paranapanema block are considered to be the best candidates. They may have formed a larger continental mass during West Gondwana amalgamation, prior to their collision with the Amazonian Craton to form the Araguaia Belt. Final timing of this collision is constrained by
c
. 550 Ma syntectonic granites. Similar ages for high-grade gneisses in the Rokelide Belt suggest coeval collision and coetaneous metamorphism of the Araguaia and Rokelide belts, but more geological and geophysical data are required for a decisive correlation between these belts.
Tectonic evolution of the Brasília Belt, Central Brazil, and early assembly of Gondwana
Authors: Valeriano C. M. , Pimentel M. M. , Heilbron M. , Almeida J. C. H. , Trouw R. A. J.
Published: January 2008

The Brasília Belt comprises terranes and thrust-sheets that were tectonically transported towards the western passive margin of the São Francisco–Congo palaeocontinent during an orogenic episode resulting from collision of the Paranapanema and Goiás blocks and the Goiás magmatic arc against São Francisco–Congo at 0.64–0.61 Ga. The tectonic zones of the belt are, from east to west: a foreland zone with Archaean–Palaeoproterozoic granite–greenstone basement covered by Neoproterozoic anchimetamorphic sedimentary rocks (Bambuí Group); a low metamorphic grade thrust-fold belt of proximal shelf successions, mostly siliciclastic, containing rare basement slivers; metamorphic nappes in upper greenschist to granulite facies of distal shelf and slope metasediments and subordinate tholeiitic metabasalts; the Goiás massif, possibly a microcontinent; and the Goiás magmatic arc. The accretion of these terranes against the western margin of the São Francisco–Congo palaeocontinent took place during an early phase of Gondwana supercontinent amalgamation, when terranes accreted around São Francisco–Congo to create a proto-West Gondwana landmass, around which subsequent collisional and accretionary events followed, such as those in the Borborema–Trans-Saharan province (
c.
0.62–0.60 Ga); in the Ribeira–Araçuaí belt (
c.
0.58 Ga); along the Araguaia and Paraguay belts (collision of Amazonia,
c.
0.54–0.52 Ga); and the accretion of Cabo Frio terrane in the Ribeira Belt (
c.
0.53–0.50 Ga).
Correlation of Neoproterozoic terranes between the Ribeira Belt, SE Brazil and its African counterpart: comparative tectonic evolution and open questions
Authors: Heilbron M. , Valeriano C. M. , Tassinari C. C. G. , Almeida J. , Tupinambá M. , Siga O. , Trouw R.
Published: January 2008

Four main classes of tectonic entities may be considered for the Ribeira Belt and southwest African counterparts: (1) cratonic fragments older than 1.8 Ga and their passive margin successions, (2) reworked basement terranes with Mesoproterozoic and/or Neoproterozoic deformed cover, (3) magmatic arc associations, (4) terranes with Palaeoproterozoic basement and deformed Neoproterozoic back-arc successions. Based on comparative investigation, a tectonic model of polyphase amalgamation is proposed with
c
. 790 and 630–610 Ma major episodes of intra-oceanic and cordilleran arc magmatism along both sides of the Adamastor Ocean. Subsequent diachronous collision of the arc terranes and small plates followed at
c
. 630, 600, 580 and 530 Ma. The tectonic complexity reflects an accretionary evolution from Cryogenian to Cambrian times. The São Francisco–Congo and Angola palaeo-continents did probably not behave as one consolidated block, but rather may have accommodated considerable convergence during the Brasiliano/Pan-African episodes. The final docking of Cabo Frio and Kalahari in the Cambrian was coeval with the arrival of Amazonia on the opposite side, resulting in lateral reactivation and displacement between the previously amalgamated pieces. The transition between the Cambrian and the Ordovician is marked by the extensional collapse of the metamorphic core zones of the orogens.
West Gondwana amalgamation based on detrital zircon ages from Neoproterozoic Ribeira and Dom Feliciano belts of South America and comparison with coeval sequences from SW Africa
Authors: Basei M. A. S. , Frimmel H. E. , Nutman A. P. , Preciozzi F.
Published: January 2008

Neoproterozoic–Cambrian amalgamation of West Gondwana involved the collision of several terranes of older crust that are now in eastern South America and western Africa. U–Pb (SHRIMP) detrital zircon ages from representative metasedimentary units of the Ribeira and Dom Feliciano belts (South America) and Gariep and Damara belts (Africa) provide constraints on the possible sediment source areas across probable suture zones. Ribeira detrital zircons are Palaeoproterozoic and Archaean. For the Dom Feliciano Belt, a contribution of Meso- and Neoproterozoic zircons is present, which definitely indicate Neoproterozoic sedimentation. It is proposed that the inflow of material to the Ribeira basin was essentially derived from the Paranapanema and Rio de la Plata cratons, whereas for the Damara and Gariep–Rocha belts source areas were from the Namaqua Belt. The Dom Feliciano Belt received sediments from the South American side and to a lesser degree from African sources. These results highlight the differences in the detrital zircon signatures across a proposed West Gondwanan suture, with those in the west being derived from distinctive South American basement sources and those in the east from distinctive African sources.
A Damara orogen perspective on the assembly of southwestern Gondwana
Authors: Gray D. R. , Foster D. A. , Meert J. G. , Goscombe B. D. , Armstrong R. , Trouw R. A. J. , Passchier C. W.
Published: January 2008

The Pan-African Damara orogenic system records Gondwana amalgamation involving serial suturing of the Congo–São Francisco and Río de la Plata cratons (North Gondwana) from 580 to 550 Ma, before amalgamation with the Kalahari–Antarctic cratons (South Gondwana) as part of the 530 Ma Kuunga–Damara orogeny. Closure of the Adamastor Ocean was diachronous from the Araçuaí Belt southwards, with peak sinistral transpressional deformation followed by craton overthrusting and foreland basin development at 580–550 Ma in the Kaoko Belt and at 545–530 Ma in the Gariep Belt. Peak deformation/metamorphism in the Damara Belt was at 530–500 Ma, with thrusting onto the Kalahari Craton from 495 Ma through to 480 Ma. Coupling of the Congo and Río de la Plata cratons occurred before final closure of the Mozambique and Khomas (Damara Belt) oceans with the consequence that the Kuunga suture extends into Africa as the Damara Belt, and the Lufilian Arc and Zambezi Belt of Zambia. Palaeomagnetic data indicate that the Gondwana cratonic components were in close proximity by
c.
550 Ma, so the last stages of the Damara–Kuunga orogeny were intracratonic, and led to eventual out-stepping of deformation/metamorphism to the Ross–Delamerian orogen (
c.
520–500 Ma) along the leading edge of the Gondwana supercontinental margin.
The Neoproterozoic glacial record in the Río de la Plata Craton: a critical reappraisal
Authors: Pazos P. J. , Bettucci L. S. , Loureiro J.
Published: January 2008

Neoproterozoic glacial successions have been described in South America, but the glacial deposits of the Río de la Plata Craton have been neglected in previous studies addressing the global distribution of glacially influenced successions. The Río de la Plata Craton contains Neoproterozoic glacial deposits in the Sierra del Volcán Formation (Tandilia System, Argentina), glacial influenced deposits in the Playa Hermosa and Zanja del Tigre formations (Dom Feliciano Belt, Uruguay) and suspected glacially influenced deposits in Passo da Areia (São Gabriel block, Brazil). The Tandilia System glacial record includes diamictites, dropstones and rhythmites deposited in glaciomarine conditions in a tectonically stable depositional setting. The Dom Feliciano Belt includes a thin section with ice-rafted clasts in carbonates and a thicker section containing diamictites, rhythmites, outsized clasts and deformed beds in a volcano-sedimentary succession. The São Gabriel block occurrence deserves more attention to confirm any glacial influence in the fine-grained part of the succession. Glaciation is considered to be contemporaneous with the Gaskiers glaciation (580 Ma), with the exception of the carbonates with dropstones that may represent a previous event correlative with one of the glaciations described in the Kalahari Craton, prior to Kalahari–Río de la Plata assembly in the proto-western Gondwana margin.
South Atlantic divergent margin evolution: rift-border uplift and salt tectonics in the basins of SE Brazil
Authors: Mohriak W. , Nemčok M. , Enciso G.
Published: January 2008

The South Atlantic Ocean evolved after rupture of the São Francisco–Congo–Rio de la Plata–Kalahari cratonic landmass and the Late Proterozoic fold belts. Break-up in the South Atlantic realm developed diachronously: rifting started in the south (Argentina) during the Jurassic and progressed towards the equatorial segment. The central portion was controlled by a rift-resistant cratonic nucleus (the São Francisco–Congo craton) and as a result underwent development of narrow basins; parts controlled by Neoproterozoic fold belts developed wide basins. The final break-up of western Gondwana and the onset of plate divergence were marked by thick wedges of seaward-dipping reflectors, located near the incipient ocean-ridge spreading centre that had already been formed by the time Aptian evaporites were deposited. Subsequently, a few episodes of intraplate tectonic and magmatic activity affected the Santos, Campos and Espírito Santo basins.

Post-break up development of the offshore basins was affected by gravity gliding over the Aptian evaporites. Continental uplift may be invoked as the main cause of salt mobilization, generating prograding clastic wedges that thickened basin-wards and produced a loading effect on the salt basin. Coupled with onshore erosional unloading and the effects of the gravity gliding, this probably resulted in further flexural uplift of the continental margin.
Restoring Pan-African-Brasiliano connections: more Gondwana control, less Trans-Atlantic corruption
Authors: de Wit M. J. , Stankiewicz J. , Reeves C.
Published: January 2008

The concept of South America and Africa as rigid continents during the formation, growth and motion of their respective plates has frustrated reconstruction of a tight, geologically economic fit between these two fragments in their Gondwana framework. We recognize that (1) internal strains released during and following Gondwana break-up have distorted their actual shapes within Gondwana and (2) these two continents comprise mosaics of smaller microblocks, or platelets, of relatively undistorted Precambrian terrains that experienced modest, episodic relative motions along rift zones that separate them. This permits a fresh approach to quantitative reconstructions of palaeo-continents. Former geological ties forged at the time of Gondwana amalgamation, now exposed at the continental margins of the South Atlantic as piercing points, provide robust anchors for new paleo-cartographic experiments. We present two new tectonic maps of the Brasiliano and Pan-African structures of West Gondwana on which we identify ten piercing points that, if re-joined simultaneously, could facilitate quantification of a well-substantiated Gondwana fit and help retrace the evolution of its continental margins with greater accuracy than has been achieved until now. This has significant bearing on understanding the origin and evolution of passive continental margins, and the geodynamics of Gondwana break-up.
Geology of the northern Borborema Province, NE Brazil and its correlation with Nigeria, NW Africa
Authors: Arthaud M. H. , Caby R. , Fuck R. A. , Dantas E. L. , Parente C. V.
Published: January 2008

The Borborema and Benin–Nigeria provinces of NE Brazil and NW Africa, respectively, are key areas in the amalgamation of West Gondwana by continental collision during the Brasiliano/Pan-African orogenies. Both are underlain by complex basement: Nigeria has
c.
3.05 Ga Archaean crust but no known Palaeoproterozoic rocks >2.0 Ga; in NE Brazil, 2.6–3.5 Ga Archaean rocks form small cores within Palaeoproterozoic gneiss terrains affected by plutonism at
c.
2.17 Ga. Both regions exhibit Late Palaeoproterozoic (
c.
1.8 Ga) rift-related magmatism and metasedimentary sequences overlying the basement. The Seridó Group of NE Brazil (<0.65 Ga) is similar to the Igarra Sequence in SW Nigeria. The Ceará Group, which may date back to
c.
0.85 Ga, is a passive margin deposit on crust thinned during initiation of an oceanic domain. In both provinces, basement and sedimentary cover were involved in tangential tectonics that resulted in crust-thickening by nappe-stacking associated with closure of this ocean. Frontal collision between
c.
0.66 and 0.60 Ga later evolved to an oblique collision, generating north–south continental strike-slip shear zones at
c.
0.59 Ga. In NE Brazil, the main Pan-African suture is probably buried beneath the Parnaíba Basin. The Transbrasiliano Lineament, interpreted as the prolongation of the Kandi–4°50 Lineament in Hoggar, may represent a cryptic suture.
Proterozoic links between the Borborema Province, NE Brazil, and the Central African Fold Belt
Authors: van Schmus W. R. , Oliveira E. P. , da Silva Filho A. F. , Toteu S. F. , Penaye J. , Guimarães I. P.
Published: January 2008

The Congo (CC) and the São Francisco (SFC) cratons were joined at about 2.05 Ga; northern parts of Palaeoproterozoic basement subsequently underwent extension at about 1 Ga, forming intracratonic basins. Neoproterozoic metasedimentary rocks in these basins yield detrital zircons as young as 630 Ma. The Brasiliano and Pan-African (
c.
620–580 Ma) assembly of West Gondwana extensively altered this system. The Sergipano domain occurs north of the SFC, and the comparable Yaoundé domain occurs north of the CC. Crust north of the Sergipano domain comprises the Pernambuco–Alagoas (PEAL) domain. The NE–SW-striking Tcholliré–Banyo fault in Cameroon may extend southwestwards between the PEAL and Sergipano domains, defining northern limits of abundant SFC/CC basement. The Adamawa–Yadé domain in Africa does not appear to extend into Brazil. The Transverse domain of Brazil is a collage of Palaeoproterozoic crustal blocks, the 1.0 Ga Cariris Velhos orogen (CVO), late Neoproterozoic basins, and Brasiliano granites. The CVO extends ENE for more than 700 km in Brazil, but eastern continuation into Africa has not been identified. North of the Transverse domain contiguous
c.
2.15 Ga gneisses comprise basement of Rio Grande do Norte and Ceará domains, which continue eastwards into western Nigeria and western Sahara.
São Luís Craton and Gurupi Belt (Brazil): possible links with the West African Craton and surrounding Pan-African belts
Authors: Klein E. L. , Moura C. A. V.
Published: January 2008

The São Luís Craton and the Palaeoproterozoic basement rocks of the Neoproterozoic Gurupi Belt in northern Brazil are part of an orogen having an early accretionary phase at 2240–2150 Ma and a late collisional phase at 2080±20 Ma. Geological, geochronological and isotopic evidence, along with palaeogeographic reconstructions, strongly suggest that these Brazilian terrains were contiguous with the West African Craton in Palaeoproterozoic times, and that this landmass apparently survived subsequent continental break-up until its incorporation in Rodinia.

The Gurupi Belt is an orogen developed in the southern margin of the West African–São Luís Craton at
c
. 750–550 Ma, after the break up of Rodinia. Factors such as present-day and possible past geographical positions, the timing of a few well-characterized events, the structural polarity and internal structure of the belt, in addition to other indirect evidence, all favour correlation between the Gurupi Belt and other Brasiliano/Pan-African belts, especially the Médio Coreaú domain of the Borborema Province and the Trans-Saharan Belt of Africa, despite the lack of proven physical links between them. These Neoproterozoic belts are part of the branched system of orogens associated with amalgamation of the Amazonian, West Africa–São Luís, São Francisco and other cratons and minor continental blocks into the West Gondwana supercontinent.